The Chemistry and Manufacture of Hydrogen

THE IHEMISTRY

A N D

M A N U F A C T U R E

OF H

T

D

R

O

G

E

N

BY P. L l T H E R L A N D T E E D \R is MjMlNINC* AND METALLURGY), A I M M MAJOR, KAI-,

LONDQ. E D W A R D

1 1919

DEDICATECBTO M ^ I T L A N D . J L M . G , D.S.O., R.A.F ANI> . A-F.C, R . A F .

DEFACE. aiH&nal requirements a r e p e r h a p s

the

greatest, it i3 t&sJUfrortl^ that our contribution to the technology o$%vMfe"en •& probably the least of any of the Qreat* F f l w W ; work

in

so, should it h a p p e n t h a t this

a n y way stimulates

interest,

resulting

in

further i m p r o v e m e n t in the technology of t h e subject, the author will feel himself more than amply rewarded T h e author would like to express his t h a n k s

to

the Director of Airship Production for permission to publish this book, and to Major L. R u t t y , for m a n y helpful

R.A.F.,

suggestions in the compilation of

t h e text and assistance in correcting the proofs. P. L. EYNSKORD, KENT

T

CONTENTS. CHAP.

PAGE

I. HYDROGEN—ITS USES—DISCOVERY, AND OCCURRENCE IN NATURE II

I

THE CHEMICAL PROPERTIES OF HYDROGEN

III

THE

MANUFACTURE

OF

IV

THE MANUFACTURE OF HYDROGEN.

METHODS METHODS V

HYDROGEN

CHEMICAL

. .

.

39 CHEMICO-PHYSICAL

.

THE MANUFACTURE OF HYDROGEN. APPENDIX,

9

PHYSICAL CONSTANTS

113 PHYSICAL METHODS .

126 145

CHAPTER HYDROGEN—ITS

I.

USES—DISCOVERY, RENCE IN NATURE.

AND

OCCUR-

T h e U s e s of H y d r o g e n . — T h e commercial production of h y d r o g e n has received a great stimulus during the last few years owing to its being required for industrial a n d war purposes in quantities never previously anticipated. T h e discoveries of M. Sabatier with regard to t h e conversion of olein and other unsaturated fats and their corresponding acids into stearin or stearic acid have created a n enormous demand for hydrogen in every industrial c o u n t r y ; 1 the synthetic production of ammonia by t h e H a b e r process has produced another industry with great hydrogen requirements, while the Great W a r has, t h r o u g h the development of the kite balloon and airship, m a d e requirements for hydrogen in excess of t h e two previously mentioned industries combined. T h e increase in hydrogen production has modified t h e older processes by which it was made, and has also led to t h e invention of new processes, with the result t h a t t h e cost of production has decreased and will probably continue to decrease, thus allowing of its employment in yet new industries. 1

The weight of oil hardened by mean&xSBk*.fliQKenin Europe in 1914 probably exceeded 250,000 tons. I

2

HYDROGEN

T h e Discovery of H y d r o g e n . — T h e discovery of hydrogen should b e attributed to T u r q u e t d e Mayerne, 1 who in 1650 obtained, b y the action of dilute sulphuric acid on iron, a gas, or " inflammable air,", which we now know to have been hydrogen. T u r q u e t de M a y e r n e recognised thergpf he obtained as a distinct substance. Robert B o y l e 9 made some experiments with it, b u t many of its m o r e important properties were not discovered until Cavendish's investigations, 8 beginning in 1 7 6 6 ; while the actual name " H y d r o g e n , " m e a n i n g " w a t e r former," was given to t h e g a s by Lavoisier, w h o may be r e g a r d e d as the first philosopher to recognise its elemental n a t u r e . Occurrence in N a t u r e , H y d r o g e n occurs in small quantities in Nature in the uncombined state. It is found in a state of condensation in many rocks and in s o m e specimens of meteoric iron. It is present in t h e gaseous discharges from oil and g a s wells a n d volcanoes, a n d is also a constituent to a very m i n u t e extent of t h e atmosphere. Hydrogen in the uncombined s t a t e exists in enormous masses upon t h e sun, a n d is p r e s e n t in the " p r o m i n e n c e s " observed in solar eclipses, while by optical means it may also be detected in m a n y stars and nebulae. 1

Paracelsus, in a similar experiment in the sixteenth century, obtained the same gas, but failed to recognise it as a distinct substance. 2 " New Experiments touching the Relation between Flame and Air," by the Hon. Robert Boyle, 1672. 8 James Wat^^discoverer of the steam engine, did many similar experirffl^^^^^^^game time, but his interpretation of his results

Was r ^ j j f f i ^ ^ y ^ ^ ^ f e l

OCCURRENCE IN N A T U R E

3

In. the combined state hydrogen is extremely a b u n dant. It is present t o the extent of one part in nine (by weight) in water, and is a constituent of all acids a n d most organic compounds. In R o c k s . — I n a state of "occlusion," or molecular condensation, hydrogen is to be found in most igneous rocks in association with other gases, the total volume of occluded gases being on the average about 4*5 times the volume of the rock. T h e following analyses of Sir William T i l d e n 1 give the composition of the occluded gases in several rocks from different parts of the world :—

Granite. Gabbro Pyroxene gneiss. Gneiss . Basalt .

Skye . Lizard Ceylon

. . .

23-6 55 7 72

6-45 2-16 8*o6

303 2-03 56

5-13 1-90 ri6

6r68 88*42 12*49

Senngpatam Antrim .

31*62 32*08

5-36 2008

51 10*00

-56 I*6I

6193 36*15

In Meteoric Iron # —An examination of certain meteoric irons, made by Sir William Ramsay and D r . Travers, 3 showed that these contained occluded gas, a n d that this gas was hydrogen :— D

MetSrite.°f

Toluca . . Charca . . Rancho de la Pila 1(

Weight Taken. Hydrogen Evolved. 1 grm. ,, „

'Proc. Roy. Soc," 1897.

2*8 c.c "28 „ *57 „

4

HYDROGEN

Observing that meteoric iron contains occluded hydrogen, it is interesting to note that the examination of steel shows that it also possesses this property of condensing gases. Steel of the following composition— Per Cent Combined carbon . . . . *8io Silicon . . . . . . "o8o Manganese . 050 Sulphur '028 Phosphorus . . . . -019 Iron (by difference) . 9 9 "013 IOO'OOO in pieces 6 x i x i cm. was heated (ultimate temperature 979 0 C.) for ten days in vacuo and the gases evolved analysed, with the result that they were found to have the following composition :— Per Cent by Volume. Hydrogen . . . . 52*00 Carbon monoxide . 45'52 „ dioxide . . 1 68 Methane . . . 72 Nitrogen . 08 IOO'OO T h e total weight of steel was 69*31 grammes, while the total volume of gas evolved was 19*86 c c . 1 A n examination of a defective Admiralty b r o n z e casting showed that there was an appreciable quantity of occluded gas in it, containing J'6 per cent, of hydrogen by v o l u m e 2 1

" GasesOccluded in Steel," by T. Baker, Iron and Steel Institute, "Carnegie Scholarship Memoirs," vol. 1., 1909. 2 " Ast4gyf|»|ff1aon on Unsound Castings of Admiralty Bronze, by H^&LiimfflHIfcej: and C. F. Elam, Inst. of Metals, 1918.

OCCURRENCE IN N A T U R E

5

In Discharge from Oil and Gas W e l l s , — T h e gas discharged from g a s and oil wells contains small quantities of hydrogen, as will be seen from the following analyses of natural g a s discharges in Pennsylvania, W e s t Virginia, Ohio, Indiana, and Kansas. AVERAGE COMPOSITION By VOLUME 1

Pa. & W. Va. Ohio & Ind. Hydrogen Carbon dioxide Sulphuretted hydrogen Oxygen Carbon monoxide Methane Other hydrocarbons Nitrogen

.

'10 <0 5 oo trace 40 80-85 14 00 4 60

1-50 •20 •15 •15 "5° 93 60 .30 3'60

Kansas •00 3° •00 •00 1'00 93'65 •25 480

In Gases from V o l c a n o e s . 2 — T h e nature of the gases discharged from volcanoes has been most carefully studied from about the middle of the last century, with the result that the chemical composition of the gas discharged has been determined at many different volcanoes, and a t different times at the same volcano. F r o m these investigations it would appear that in the more violent discharges there are very considerable amounts of hydrogen, while in the more placid eruptions there is little gas of a n y description, except steam, generally accompanied b y water containing mineral salts. ^ S A . Geological Survey, "Mineral Resources of U S.A.," 1909, 2, 297. 2 For further information on this subject-^see F. W. Clarke's " The Data of Geochemistry," U.S G.S.. Bull, tufi

6

HYDROGEN

Below are given analyses of volcanic gas from different parts of the world by different authorities :— From a group of fumaroles at Reykjalidh, Ice1 land :— Hydrogen . 25*14 Oxygen — Nitrogen • o"72 Carbon dioxide . . . • 5°'°° Sulphur dioxide . . . . — Sulphuretted hydrogen . . .24*12

From afumarole on Mont Pelee, Hydrogen Oxygen Nitrogen . . . . Carbon dioxide . . Sulphur dioxide. . Carbon monoxide . . . . Sulphuretted hydrogen Methane . . . Argon . .

Martinique*:— 8fi2 13 67 . 54"94 . 15 "38 . . — i"6o . . — 5'46 -71 99-88

%

From Kilattea :— Hydrogen Oxygen

.

10*2 —

Nitrogen

II*8

Carbon dioxide „ monoxide Sulphur dioxide.

73 9 4-0 —

.

.

.

.

.

99'9 1

R. W Bunsen, " Annales Chim. Phys.," 3rd ser., vol. 38, 1853 H . Moissan^^Comptes Rend.," vol. 135, 1902. 8 A. L. Day*andE. S Shepherd, "Bull. Geol. Soc. America," vol. 24, 2

OCCURRENCE IN N A T U R E From

7

Santonn1:—

Hydrogen . Oxygen . Nitrogen Carbon dioxide . Carbon monoxide . Methane . Sulphuretted hydrogen

.

. .

.

.

.

.

. . .

.

29 43 -32 32*97 . 36 43 — -86 — 100 00

In C l a y s . — N o t only is hydrogen present in most igneous rocks, but it is to be found to a small extent in some clays. Sir William Crooks, O.M., F . R . S . , was kind enough to investigate for the author the gases occluded in the celebrated " Blue G r o u n d " — a clay in which the Kimberley diamonds are found. T h i s clay was found to contain gas composed of 82 per cent, of carbon dioxide, the bulk of the residue being oxygen and nitrogen, with detectable traces of hydrogen. I n Air*—As is not surprising, hydrogen is present in the atmosphere to a very small extent, as will be seen from the following analysis of air under average conditions. It is doubtless derived from the sources already mentioned, and also from the decay of organic matter containing hydrogen T h e following represents the average composition of normal a i r : — Volumes per 1000. Nitrogen . . . . . 769 500 Oxygen . . . . 206*594 Aqueous vapour . . . . i4"ooo 1

F Fouque, " Santonn et ses eruptions," Pans, 1879.

HYDROGEN Argon Carbon dioxide Hydrogen Ammonia . Ozone Nitric acid . Neon Helium Krypton Xenon . .

.

.

.

.

.

.

. .

.

.

Volumes per iooo. 9"358 "336 '19 *oo8 "0015 . -0005 "oi "ooi *ooi 00005

THE CHEMICAL PROPERTIES OF HYDROGEN. HYDROGEN in the free state h a s a capability of entering into combination with a large variety of substances, forming chemical compounds, while h y d r o g e n in t h e combined state reacts with m a n y other chemical compounds, forming new c o m p o u n d s . Reaction of H y d r o g e n w i t h O x y g e n i n the Free State* By far the most important chemical reaction of hydrogen is undoubtedly t h a t which it e n t e r s into with oxygen. W h e n h y d r o g e n is mixed with oxygen a n d the temperature of t h e mixed g a s e s raised, they combine with explosive violence, p r o d u c i n g steam. T h i s reaction may be expressed by t h e following equation :— 2H2 + O2 =» 2H 2 O. If a stream of h y d r o g e n issues into air and a light is applied to it, it burns (in a c c o r d a n c e with the above equation) with an almost non-luminous flame. (This reaction is, of course, reversible, i.e. a stream of air would burn in the s a m e w a y in an a t m o s p h e r e of hydrogen.) It was discovered b y F r a n k l a n d 1 that while at atmospheric pressure t h e flame of h y d r o g e n burning in oxygen is almost non-luminous if t h e pressure is 1

" Proc. Royal Soc ," vol. xvi, p. 419. (9)

io

HYDROGEN

increased to two atmospheres the flame is strongly luminous. T h e combination of oxygen and h y d r o g e n is most violent if the t w o gases are present in t h e relative quantities given in t h e equation, viz. two volumes of hydrogen a n d one of oxygen. If one or other of the gases is in excess of these quantities the violence of the reaction is reduced a n d the quantity of the gas in excess of that required by the equation remains as a residue. W h e n one gas is enormously in excess of the other a condition may arise in which the dilution is so great that on sparking the mixture n o reaction takes place. 1 Mixtures of air a n d hydrogen in which the air is under 20 per cent. (i.e. u n d e r 4 per cent, of oxygen) of the total volume b e h a v e in this way. T h i s point is of importance in airships, as, providing the purity of t h e h y d r o g e n in the envelope is above 80 per c e n t by volume, a n internal spark in the envelope will not cause a n explosion, b u t if t h e quantity of hydrogen by volume falls below this a m o u n t there is a risk of explosion ; h e n c e the procedure of deflating airships when t h e purity has dropped to 80 p e r cent, hydrogen by volume. T h e Temperature of Ignition of H y d r o g e n and O x y g e n , — W h e n the two gases are mixed in the proportion of two volumes of hydrogen a n d one volume of oxygen it has been found t h a t t h e temperature of the mixed gases m u s t b e raised to about 580 0 C. 2 1

Schoop states that when either gas contains 6 to 8 per cent, of the other it is explosive. a Victor Meyer, "Berichte," No. 16, 1893, gives the temperature of violent reaction as 612-15° C. Gautier and Helier, "Comptes Rend.," 125, 271, 1897, gwe about 5500 C

CHEMICAL PROPERTIES

n

before explosion t a k e s place. H o w e v e r , Professor a B a k e r has shown that, if t h e t w o g a s e s a r e n o t only perfectly pure b u t also perfectly d r y (dried b y b e i n g kept in contact for as long as t h r e e w e e k s with a n h y d r o u s phosphoric acid) a t t h e t e m p e r a t u r e of i o o o 0 C , t h e y do not combine, but even in this d r y condition t h e y will explode with an electric spark. 2 T h i s p h e n o m e n o n is of great interest, a n d opens a wide field of philosophic speculation, but t h e conditions of purity a n d d r y n e s s a r e such that this h i g h t e m p e r a t u r e of ignition can n e v e r be attained under commercial conditions. Professor B a k e r has also s h o w n that, w h e n a mixture of ordinary h y d r o g e n a n d o x y g e n is exposed t o t h e influence of strong sunlight, t h e t w o g a s e s v e r y slowly react, with the production of w a t e r in m i n u t e q u a n tities. In the experiment b y which Professor B a k e r m a d e this discovery h e placed a m i x t u r e of these two gases in a state of great purity b u t not of absolute d r y n e s s (in the ratio of two volumes of h y d r o g e n a n d one of oxygen) in a h a r d glass t u b e closed a t o n e end a n d sealed at the other b y mercury. T h i s t u b e w a s exposed outside a south window for four m o n t h s , from S e p t e m b e r to December, at t h e e n d of which time it w a s found, after due correction for t e m p e r a t u r e a n d pressure, t h a t the mixture of t h e two gases h a d contracted b y ^ of its original v o l u m e 3 b y t h e formation of water. A similar experiment with the g a s e s in a n exceptionally d r y state, lf

'Jour. Chem Soc.," April, 1902. Dixon, "Jour. Chem. Soc," vols. 97 and 98. 3 The volume of the resulting water is almost negligible, as one volume of hydrogen and oxygen in the ratio stated produces only "006 volume (approximately) of water. 2

12

HYDROGEN

but otherwise under exactly similar conditions, showed n o such contraction. W h e t h e r the union of h y d r o g e n with the infiltrating oxygen of the atmosphere takes place in airship envelopes, which are comparatively transparent, h a s not b e e n determined, b u t since in airship practice there is n e v e r more t h a n 4 per cent, of o x y g e n in the envelope, it is 1

!>530 I :525

520 " r s i

60

100

160

200

Z5O

300

350

400

Volumes jofOjg to 100 Volumes offy FIG. I.

t o b e a n t i c i p a t e d t h a t s u c h a c t i o n , if it t o o k p l a c e , w o u l d of necessity be relatively slower. T h e temperature of ignition hydrogen and oxygen has been by Professor H .

B. D i x o n ,

1

of v a r y i n g m i x t u r e s o f most

carefully

studied

who, besides much very

in-

g e n i o u s a p p a r a t u s , e m p l o y e d t h e c i n e m a t o g r a p h for

ob-

taining c o n c l u s i v e e v i d e n c e of t h e conditions p r e v a i l i n g during explosion. 1(

'Jour. Chem S o c , " vols. 97 and 98, and vols 99 and 100

CHEMICAL PROPERTIES

13

B y means of adiabatic compression, the temperature of ignition of different mixtures of hydrogen a n d oxygen was determined, with results which may b e seen in Fig. 1. F r o m a s t u d y of this curve it will b e noticed that t h e most easily ignited mixture is not o n e in which the proportion of h y d r o g e n to oxygen is as t w o to one, as might perhaps b e expected, b u t when t h e ratio is one volume of h y d r o g e n t o four of oxygen. IGNITION TEMPERATURES OF HYDROGEN AND OXYGEN MIXTURES.

(As determined by Prof. H B Dixon, M.A., F R.S.) [Ignition by Adiabatic Compression) Composition of Mixture. By Volume.

Ignition Temperature

Oxygen.

Hydrogen.

° Centigrade.

33"33

100

557

40

5o

542

536

100

53°

150

525

200

520

250 300

5i6

350

509 507

400

512

T h e temperature of ignition of a mixture fired by adiabatic compression is lower than when the same mixture is fired by b e i n g h e a t e d in a glass or silica tube at atmospheric pressure. Professor H B. Dixon in a private communication to t h e author states that h e found the ignition t e m p e r a t u r e of electrolytic gas under the latter conditions t o be 580" C.

i4

HYDROGEN

Besides studying the temperature of ignition of various gaseous mixtures Professor H . B. Dixon investigated t h e nature of explosions 1 and found that Berthelot's conception of an explosion as being an advancing locus of high pressure and of rapid chemical change, which he described as " l ' o n d e explosive," was fundamentally correct. Without going into detail with regard to this very interesting subject, it may b e stated that " the velocity of the explosion wave in a gaseous mixture is nearly equal to the velocity of sound in the burning gases ". While this statement does not satisfy all cases of gaseous explosion, it may be regarded as fundamentally correct, exceptions to the rule being capable of explanation on the basis of undoubted secondary reactions. O n the basis of this relationship between the velocity of sound in t h e burning gases and the velocity of explosion, Professor H . B. Dixon calculated the velocity of the explosion wave in certain gaseous mixtures and also determined it experimentally, with the results given below:— Velocity of Explosion Wave in Metres per sec Gas Mixture. Calculated

Found

8H2 + Oa

3554

3535

H 2 + 3O2

1740

1712

While it has been said that the temperature of igni1

"The Rate of Explosion in Gases," by H. B. Dixon, Bakenan Lecture, Phil. Trans. Royal Society, 1893

CHEMICAL PROPERTIES

15

tion of hydrogen a n d o x y g e n in their m o s t readily ignited proportions m u s t b e at s o m e point a t least 500° C. in t h e mixture of t h e gases, this s t a t e m e n t requires modification in that, t h o u g h it is perfectly t r u e in the case of a mixture of t h e g a s e s contained in glass or nonporous vessels, in t h e presence of certain substances of a porous nature this t e m p e r a t u r e of ignition is greatly reduced. T h i s is particularly so in t h e case of platinum in a spongy condition. If a piece of spongy platinum is introduced at o r d i n a r y atmospheric t e m p e r a t u r e into an explosive mixture of h y d r o g e n a n d oxygen, t h e platinum is observed to glow and, a n explosion almost immediately takes place. T h i s p r o p e r t y is m o r e m a r k e d if the platinum is in t h e s p o n g y condition, b u t it is equally true if it is in t h e form of wire or foil. T h e r e is no complete explanation of this phenomenon, but it h a s been observed that certain substances possess the property of a b s o r b i n g m a n y t i m e s their own volume of different gases, a n d t h a t these a b s o r b e d gases possess a greatly increased chemical activity over their normal activity a t the same temperature. N e u m a n a n d Strientz 1 found that one volume of various metals in a fine state of division is capable of a b s o r b i n g t h e following amounts of hydrogen :— Palladium black Platinum sponge Gold Iron . . Nickel Copper . Aluminium Lead. . 1

. .

. .

. . .

. .

.

502*35 volumes. 49*3 . 46-3 19*17 i7'57 4-5 . 2*72 -15

"Zeitschrift fur analytiscbe cheraie," vol. 32.

16

HYDROGEN

T h i s p r o p e r t y of certain s u b s t a n c e s , without themselves u n d e r g o i n g chemical c h a n g e , 1 of b e i n g able to i m p a r t increased chemical activity to t h e gases they a b s o r b is not confined to t h e metals, b u t is possessed by charcoal (particularly a n i m a l charcoal), m a g n e s i t e brick, a n d p r o b a b l y to s o m e e x t e n t b y all p o r o u s substances. I t is a subject of v e r y g r e a t interest, a n d in m a n y cases of practical i m p o r t a n c e 2 which is n o w b e c o m i n g a subdivision of Physical Chemistry, u n d e r t h e n a m e of " Surface E n e r g y ". T h e T e m p e r a t u r e Produced b y the Ignition of H y d r o g e n and O x y g e n . — I n the p r e v i o u s p a r a g r a p h t h e t e m p e r a t u r e a t w h i c h the ignition of h y d r o g e n and o x y g e n begins h a s b e e n given, a n d n o w t h e t e m p e r a t u r e which t h e flame r e a c h e s will be considered. B u n s e n d e t e r m i n e d t h e t e m p e r a t u r e of the flame p r o d u c e d t o b e :— Flame of hydrogen burning in air „ „ oxygen

.

. .

20240 C. 28440 C.

A later d e t e r m i n a t i o n by Fe"ry ( " C o m p t e s R e n d , " 1902, 134, 1201) g i v e s t h e values 1900° C. a n d 2420° C. respectively, while B a u e r (ibid., 1909, 148, 1756) obt a i n e d figures for h y d r o g e n b u r n i n g in o x y g e n varying from 2200 0 C. to 2300 0 C , according to t h e proportion of o x y g e n present. T h e reason that t h e flame of h y d r o g e n burning in o x y g e n is h o t t e r t h a n t h e flame p r o d u c e d in air is due 1

It is contended by Troost and Hautefeuille that in the case of palladium the absorption of the hydrogen is chemical and not physical, palladium hydride (Pd2H) being formed. 2 The Bonecourt flameless boiler depends on the surface energy of magnesite brick.

CHEMICAL PROPERTIES

17

to the fact t h a t the speed of burning in oxygen is g r e a t e r t h a n in air, because of the absence of a n y dilution, a n d also because the nitrogen a n d other inert constituents in the air a r e themselves heated at the expense of the flame t e m p e r a t u r e . 1 T h e calculated value for the flame t e m p e r a t u r e of h y d r o g e n b u r n i n g in air, assuming that the heat of reaction is distributed a m o n g t h e inert constituents of the air, is 1970 0 C. ( L e Chatelier), a n d this agrees a p proximately with t h e a b o v e figures of 202 4 0 C. and 1900 0 C. A comparison between the flame temperature of h y d r o g e n a n d other gases burning in air is given in the following table :— Hydrogen 2 . Acetylene3 Alcohol2 Carbon Monoxide 4

. . . .

.

. .

. .

. .

i9oo°C. 2548°C 1705° C 2ioo°C

T h e Q u a n t i t y of Heat Produced by B u r n i n g H y d r o g e n . — T h e t e m p e r a t u r e of ignition a n d the flame temperature of h y d r o g e n h a v e already been considered. It now o n l y remains for the quantity of h e a t produced by a g i v e n weight of hydrogen to be considered in comparison with s o m e other gases combustible in air. 1

In the case of Zeppelin airships brought down in flames, it is not surprising that considerable amounts of molten metal have been found in the locality, observing that the melting point of aluminium is 6570 C, copper 10870 C. 2 Fery, le 3 Fery, / c. The temperature of acetylene burning in oxygen is about 40000 C , but this arises from circumstances not present in the case of hydrogen flames 4 Le Chatelier. 2

18

HYDROGEN i lb of hydrogen on combustion gives „ marsh gas „ „ „ ,, benzene „ ,, ,, „ carbon monoxide „ „

62,100 B.T U x 24,020 „ 18,090 ,, 4,380 „

Reactions of H y d r o g e n w i t h O x y g e n in the Com* bined State* S o far the reaction of h y d r o g e n and oxygen has only been considered when b o t h are in the gaseous form. However, such is the attraction of hydrogen for oxygen that w h e n the latter is in combination with some other element the h y d r o g e n will generally combine with the oxygen, forming water and leaving the substance formerly in combination with the oxygen in a partially or wholly reduced state. Thus, oxides of such metals as iron, nickel, cobalt, tin, and lead are reduced to the metallic state by heating in an atmosphere of hydrogen. Thus:— (1) FeaOa + 3H2 - 2Fe + 3H2O (2) NiO + H2 - Ni + H a O (3) CoO + H2 = Co + H3O (4) SnOa + 2H2 - Sn + 2HaO (5) PbO + Ha - Pb + H 2 O T h e temperature at which the reduction by the hydrogen takes place varies with t h e different oxides and also with the same oxide, depending on its physical condition. " Crystalline haematite," as t h e natural ferric oxide is called, requires to be at a r e d heat (about 500° C.) before reduction begins to t a k e place, while if iron is precipitated from one of its salts (as ferric hydrate by 1

The latent heat of the steam produced is included in the heat units of fuels containing hydrogen.

CHEMICAL PROPERTIES

19

a m m o n i a ) t h e resulting ferric h y d r a t e can b e reduced to the metallic state at t h e t e m p e r a t u r e of boiling water. W i t h nickel t h e s a m e variation oi t h e t e m p e r a t u r e of reduction is noted, d e p e n d i n g on t h e physical condition. T h u s Moisson states that t h e sub-oxide of nickel ( N i O ) which h a s not been calcined, is r e d u c e d by hydrogen a t 23O°-24O° C. ; Muller, on t h e o t h e r hand, states that t h e reduction of t h e oxide at this t e m p e r a t u r e is not complete b u t only partial, but that if t h e t e m p e r a t u r e is raised to 270° C. a complete reduction t a k e s place. If the oxide of nickel h a s b e e n strongly h e a t e d its temperature of reduction to t h e metallic state is a t least 420° C , in which case it is q u i t e unsuitable for use as t h e catalytic a g e n t in t h e hydrogenation of organic oils. S u c h is t h e affinity of h y d r o g e n for o x y g e n that hydrogen will u n d e r certain circumstances r e d u c e hydrogen peroxide. If a n acid solution of h y d r o g e n peroxide is electrolysed, o x y g e n will be liberated a t t h e positive pole (or anode), but n o g a s will be liberated at the negative (or cathode), for the h y d r o g e n which is set free there immediately reduces t h e h y d r o g e n p e r o x i d e in the solution to water, as s h o w n in the following equation:— H2Od + H 2 - 2 H 2 O. It h a s been m e n t i o n e d that t h e t e m p e r a t u r e of reduction of t h e metallic oxides by h y d r o g e n varies with the different oxides a n d with the physical condition of the s a m e oxide. It m i g h t further b e a d d e d t h a t t h e physical condition of t h e h y d r o g e n also modifies t h e temperature of reduction. T h i s can b e well s h o w n by taking s o m e artificial binoxide of tin ( S n O 3 ) a n d placing it in a m e t a l tray in a solution of slightly acidulated water. T h e metal tray is then c o n n e c t e d to t h e

20

HYDROGEN

negative pole of a n electric supply, and another conductor placed in the liquid c o n n e c t e d to the positive of the supply. O n the current b e i n g switched on electrolysis takes place, that is to say, t h e w a t e r is decomposed into hydrogen and oxygen, t h e hydrfigen being liberated on the surface of t h e metal t r a y containing the binoxide of tin, and the oxygen a t t h e other pole. T h e nascent hydrogen liberated in the neighbourhood of the white tin oxide reduces it on t h e surface of the particle to metallic tin, in accordance w i t h t h e following equation :— SnOa + 2H2 = Sn + 2H2O, a fact which can easily b e p r o v e d by chemical means, but which is also detectable b y the c h a n g e of the oxide from white to the-dark g r e y of metallic tin. Chemical Combination o f H y d r o g e n w i t h Carbon. It has been shown t h a t if hydrogen is passed over pure carbon heated to 1150° C , direct chemical union takes place, 1 m e t h a n e or m a r s h g a s being formed :— C + 2H S - CH 4 . This reaction is of s o m e i m p o r t a n c e , as formerly in the production of blue water g a s t h e presence of m e t h a n e was entirely accounted for b y t h e presence of hydrocarbons in the fuel. H o w e v e r , t h e experiments of B o n e and Jerdan show t h a t e v e n if no hydrogen whatever were present in t h e fuel, m e t h a n e would b e formed if the temperature of t h e fuel b e sufficient. If the temperature of t h e carbon is somewhat hotter than 1150° C , direct u n i o n continues to take place, but the product of the reaction is n o t methane b u t acetylene. 1

Bone and Jerdan, "Chem Soc Trans.," 71, 41, 1897

CHEMICAL PROPERTIES

21

T h u s if a small p u r e carbon electric a r c is m a d e in a n a t m o s p h e r e of hydrogen, small quantities of acetylene are produced, b u t no m e t h a n e . Chemical C o m b i n a t i o n of H y d r o g e n w i t h Chlorine, B r o m i n e , and Iodine. W i t h C h l o r i n e . — H y d r o g e n will c o m b i n e with chlorine, in accordance with t h e following chemical equation, to m a k e hydrochloric acid :— H a + Cl2 = 2HCI. If the two g a s e s are mixed in equal proportions in a diffused light a n d are subjected to a n electric spark, the above reaction takes p l a c e with explosive violence. If a glass t u b e containing a m i x t u r e of t h e g a s e s is heated, the s a m e reaction takes place with violence. If a mixture of h y d r o g e n a n d chlorine at atmospheric t e m p e r a t u r e is exposed t o s t r o n g sunlight, hydrochloric acid is immediately formed, with t h e characteristic explosion. Investigation of this increase in t h e chemical activity of h y d r o g e n a n d chlorine in t h e presence of sunlight h a s shown t h a t it is t h e actinic rays which produce the p h e n o m e n o n ; t h u s if t h e r a y s which are p r e s e n t at the blue a n d violet e n d of t h e s p e c t r u m a r e p r e v e n t e d from r e a c h i n g t h e m i x t u r e of t h e gases b y protecting this b y a red glass screen, n o reaction b e t w e e n t h e m takes place. W h e n sunlight is n o t available, t h e explosive combination of these t w o g a s e s can be s h o w n by exposing a mixture of t h e m in a glass vessel to the light of b u r n i n g m a g n e s i u m , such a s is frequently used by photographers. T h e r e m a r k s which h a v e a l r e a d y b e e n m a d e with regard t o t h e reduction in chemical activity of h y d r o g e n

22

HYDROGEN

and-oxygen w h e n perfectly dry apply also in the case of h y d r o g e n and chlorine. W h i l e referring to t h e production of chemical union between h y d r o g e n a n d chlorine b r o u g h t a b o u t by the influence of light, attention may be drawn to what is known a s t h e " D r a p e r Effect," which is best demonstrated in the following apparatus :—

FIG

2.

Insolation Vessel T h e mixed gases, in the ratio of o n e volume of hydrogen to one of chlorine, are contained in a flat glass bulb A, called t h e insolation vessel. T h e lower part of the insolation vessel usually contains some water saturated with the t w o gases. T h e capillary t u b e B C contains a thread of liquid ac, to serve as an index. Under the influence of a flash of light the t h r e a d of liquid ac is pushed outwards, to r e t u r n immediately to its original position. T h u s , a travels to b, a n d immediately returns to a. W i t h every flash of light t h e same p h e n o m e n o n takes place. A t the time of its discovery (1843, " Ph^Mag.," 1843, "*•> 23» 4°3» 4*5) t n e reason for this sudden rise in pressure was not understood, b u t careful investigation by J. W . Mellor a n d W . R. A n d e r s o n 1 has shown that a t each flash m i n u t e quantities of hydrochloric acid are formed, with the production of a little heat, thus causing a rise in pressure until it is dispersed 1

"Jour. Chera. Soc," April, 1902.

CHEMICAL PROPERTIES

23

—in fact, t h e D r a p e r effect m a y b e likened to a very small explosion without sufficient e n e r g y to propagate itself t h r o u g h o u t t h e gas. Such is t h e attraction of chlorine for hydrogen that even w h e n t h e latter is in combination with some other element the chlorine often will combine with the hydrogen, liberating t h a t element. T h u s , if chlorine is passed through turpentine, t h e carbon is liberated, in accordance with t h e following equation :— C10H10 + 8Cla = 10C + 16HCI. Again, at ordinary temperatures a n d in ordinary diffused light, but m o r e rapidly in sunlight or other light of ictinic value, chlorine will decompose water, liberating Dxygen, in accordance with the following equation :— 2H2O + 2CI2 = 4HCI + Oa. T h e combination of hydrogen with chlorine is attended with the evolution of heat. A c c o r d i n g to Thornsen, the combination of 1 g r a m m e of h y d r o g e n with 35'5 g r a m m e s of chlorine is a t t e n d e d with the evolution 3f 22,000 gramme-calories of heat. W i t h B r o m i n e . — T h e element bromine will combine with h y d r o g e n to form hydrobromic acid, in accordance with t h e following equation :— H a + Br2 - aHBr. This reaction between h y d r o g e n a n d bromine is in many 'espects comparable with the combination of hydrogen with chlorine, b u t unlike the latter, t h e reaction cannot be brought a b o u t b y sunlight. H o w e v e r , if the two ^ases are heated, they will combine, b u t their combination is a t t e n d e d with t h e evolution of less heat t h a n

24

HYDROGEN

in the case of chlorine. T h o m s e n states that the combination of i g r a m m e of hydrogen with 80 grammes of bromine (liquid) is a t t e n d e d with the evolution of 8440 gramme-calories of heat. W i t h I o d i n e , — H y d r o g e n will combine with iodine, in accordance with the following equation, providing the iodine is in the form of vapour a n d t h e mixture of the two gases is strongly heated in the presence of spongy platinum :— H 2 + I2 - 2HI. T h o m s e n h a s s h o w n that this combination, unlike t h e two previous ones, is n o t attended with evolution of heat, but by the absorption of it. T h u s when 1 gramme of hydrogen combines with 127 g r a m m e s of iodine (solid), 6040 gramme-calories of heat are absorbed. Chemical Combination of H y d r o g e n w i t h

Sulphur,

S e l e n i u m , and T e l l u r i u m . W i t h Sulphur.—If a mixture of sulphur vapour and hydrogen is passed t h r o u g h a tube h e a t e d to at least 250° C , a chemical union of t h e two elements takes place, in accordance with the equation— H2 + S «= H<jS. T h e resulting gas, which is known as " sulphuretted hydrogen," h a s a characteristic and extremely unpleasant odour, a n d is poisonous when inhaled. According to The"nard, respiration in an atmosphere containing shs part of its volume of sulphuretted h y d r o g e n is fatal to a dog, and smaller animals die when half that quantity is present.

CHEMICAL PROPERTIES

25

S u l p h u r e t t e d h y d r o g e n is an inflammable gas, and b u r n in air, in a c c o r d a n c e with t h e following equaion:— aH a S + 3O2 - 2SO2 + 2H2O, >roducing sulphur dioxide a n d water. If the g a s is mixed with oxygen in t h e proportions equired b y t h e equation, a n d subjected to a n electric park, it explodes with violence, g i v i n g t h e s a m e prolucts as w h e n b u r n t in air. S u l p h u r e t t e d h y d r o g e n is soluble in water at o° C. 0 the e x t e n t of 4*3706 p a r t s b y volume p e r unit v o l u m e >f water. T h e density of sulphuretted h y d r o g e n is 17 times hat of h y d r o g e n . W i t h S e l e n i u m . — W h e n selenium is h e a t e d to 250° I. with h y d r o g e n , chemical union results, with t h e prouction of selenuretted h y d r o g e n .— H 2 + Se - H2Se T h e resulting g a s is colourless, r e s e m b l i n g sulhuretted h y d r o g e n in smell a n d in its chemical properes. It is, however, m u c h m o r e poisonous t h a n the )rmer g a s . S e l e n u r e t t e d h y d r o g e n is inflammable a n d b u r n s in le same w a y a s s u l p h u r e t t e d h y d r o g e n . If the g a s is :rongly h e a t e d it b r e a k s u p into its t w o constituents, le selenium b e i n g deposited in the crystalline form. Selenuretted h y d r o g e n is soluble in water at 13*2° C. ) the extent of 3 31 p a r t s b y volume p e r unit volume of ater. T h e density of s e l e n u r e t t e d h y d r o g e n is 40*5 times lat of h y d r o g e n .

26

HYDROGEN

W i t h T e l l u r i u m * — W h e n tellurium is heated to 400° C. in hydrogen, the elements combine, forming hydrogen telluride :— H 2 + Te - H2Te. T h i s gas, like sulphuretted a n d selenuretted hydrogen, is both offensive smelling and poisonous. Like selenuretted hydrogen, on strongly heating it is decomposed into its components, t h e tellurium b e i n g deposited in the crystalline form. T e l l u r e t t e d h y d r o g e n is soluble in water to some extent, b u t in course of time t h e telluretted hydrogen is decomposed a n d tellurium deposited. T h e density of telluretted h y d r o g e n is 63*5 times that of h y d r o g e n . Chemical Combination of H y d r o g e n w i t h Nitrogen, P h o s p h o r u s , and A r s e n i c . W i t h N i t r o g e n * — D o n k i n has shown that when a mixture of h y d r o g e n a n d nitrogen is subjected to the silent electric discharge, a partial union of the two gases takes place, with the formation of a m m o n i a :— N2 + 3 H 2 - 2 NH 3 . H o w e v e r , this reaction could in no w a y b e regarded as commercial, as the quantity of ammonia produced after the gases have long been subjected to the silent electric discharge is only j u s t sufficient to b e identified by the most delicate means. R e c e n t investigations have, however, shown that if t h e two gases are mixed and subjected to very great pressure (1800 lb. per sq. inch) in the presence of a catalytic agent, union to an appreciable extent takes place. T h i s process, which is now being used on a

CHEMICAL PROPERTIES

27

commercial scale in G e r m a n y , is k n o w n as t h e H a b e r process, b u t few details as to t h e m e t h o d of operation are available. I n t h e earlier s t a g e s of t h e working of this process the catalytic a g e n t w a s probably osmium, but it is considered doubtful if this is still being employed. THE

U S E S OF AMMONIA.

S u c h is the importance of a m m o n i a in the existence of a modern country t h a t it is desirable t h a t some account of its use should b e given, o b s e r v i n g that it is not improbable that t h e H a b e r process m a y be p u t into operation in this country in the near future, consequently enormously increasing t h e d e m a n d for t h e commercial production of hydrogen. A m m o n i a or its salts are employed in a variety of ways in m a n y trades. F r o m it nitric acid, the vital necessity for t h e manufacture of all h i g h explosives, can b e m a d e ; it is a n essential for t h e B r u n n e r M o n d or Solvay a m m o n i a soda process for t h e production of alkali; in t h e liquid form it is employed all over the world in refrigerating machinery, b u t its e n o r m o u s and increasing use is in agriculture, where, in the form of sulphate of ammonia, it constitutes o n e of, if not t h e most important chemical m a n u r e s known to m a n . During the year 1916 350,000 tons of a m m o n i u m sulphate were produced in this country, the larger proportion of which was consumed in agriculture—a proportion likely to increase a n d not diminish if t h e d e m a n d for home production of food continues. PROPERTIES

OF A M M O N I A .

A m m o n i a is a strongly smelling gas, possessing a most characteristic odour. It is lighter t h a n a i r ; taking

28

HYDROGEN

the density of hydrogen as i, air is 14 39, and ammonia 8'5. A m m o n i a is not in the ordinary sense combustible in air, but if the air is heated or oxygen is supplied it will burn with a feeble, almost non-luminous flame, in accordance with the following equation :— 4 NH 3

+ 3O2 - 2N2 + 6H2O.

A m m o n i a is strongly basic, i.e. it possesses the property of combining with acids to make neutral salts. T h u s with the common acids—sulphuric acid, hydrochloric acid and nitric acid—it forms salts, in accordance with the following equations :— 2 NH 3

+ H2SO4 = (NH4)2SO4, NH 8 + HC1 - (NHJCl, NH 3 + HNOa = (NH4)NO3 A m o n g the physical properties of ammonia the outstanding features are its solubility in water, its absorption by charcoal, and its liquefaction. Solubility of Ammonia in Water. — A m m o n i a is very soluble in water. Its solubility decreases with increase of temperature, and, as is of course natural, increases with increase of pressure. T h e following table for the solubility of ammonia in water is interesting :—

Temperature.

o°C. 8 16 3o 5°

Grammes of NH3 Dissolved in 1 c.c of Water. •875 •713 •582 •4O3 •229

0

C c of Nl \J and 7c 1148 923 764 S29 306

CHEMICAL PROPERTIES

29

A feature of t h e absorption of a m m o n i a by water, is the reduction of t h e specific gravity of the solution. T h u s at 15° C. a s a t u r a t e d solution containing 34*95 per cent, of t h e g a s b y w e i g h t h a s a density of 882, while pure water at t h e s a m e t e m p e r a t u r e has a density of •99909. Absorption of Ammonia by Charcoal—Reference to the surface e n e r g y of charcoal h a s already been made. Its absorption of a m m o n i a is very considerable, b u t varies with the physical condition of t h e charcoal, as well as with the m a t e r i a l from which it h a s b e e n made. Saussure found t h a t freshly ignited boxwood absorbs about 90 times its own v o l u m e of ammonia, while H u n t e r has shown t h a t freshly p r e p a r e d charcoal m a d e from cocoanut shell absorbs about 171 times its own volume of ammonia. Liquefaction of Ammonia.—Ammonia is an easily liquefiable g a s , a n d consequently it is o w i n g to this property t h a t it is employed in refrigerating plants on land and in ships, for b y t h e rapid evaporation of the liquid g a s a h i g h d e g r e e of cold m a y be obtained. The critical t e m p e r a t u r e of ammonia, i.e. that temperature i b o v e which b y m e r e pressure it cannot b e liquefied, is 131 ° C. A t this t e m p e r a t u r e a p r e s s u r e of approximately 1700 lb. p e r sq. inch must b e applied to produce liquefaction ; if, h o w e v e r , t h e t e m p e r a t u r e is below the zxitical o n e for t h e gas, t h e pressure required for liqueaction is greatly reduced. T h u s , if the ammonia is :ooled to 15*5° C , a pressure of 101 lb. per sq. inch is -equired, while if t h e g a s is cooled to o° C , a pressure }f only 61 "8 lb. p e r sq. inch will effect liquefaction. Liquid a m m o n i a is a colourless, mobile liquid. It boils lt ~ 3 3 7 ° C-i a n d a * o° C. h a s a specific gravity of 0*6234.

30

HYDROGEN

A t - 75 0 C. liquid a m m o n i a solidifies into a white crystal* line solid. W i t h P h o s p h o r u s . — I f red phosphorus is gently heated in a stream of hydrogen, direct chemical union takes place to a small extent, with t h e production of a gas termed " Phosphoretted H y d r o g e n " or " Phosphine " : — 2P

+ 3 H 2 - 2PH8,

Phosphine is a n offensive smelling, poisonous gas which in the p u r e state is not spontaneously inflammable. However, its t e m p e r a t u r e of ignition is v e r y low ; thus, if a stream of phosphine is allowed to impinge in air on a glass vessel containing boiling water, it will immediately burst into flame, b u r n i n g with considerable luminosity, in accordance with t h e equation :— PH 3 + 2O2 = HPO3 + H 2 O. Phosphine possesses a n exceedingly interesting reaction with oxygen. T h u s , if a mixture of phosphine and oxygen is subjected to a sudden reduction in pressure at ordinary atmospheric temperature, chemical combination immediately t a k e s place with explosive violence, in accordance with t h e equation already given. Phosphine, which is produced in small quantities in the Silicol process for m a k i n g hydrogen, 1 h a s under certain conditions a deteriorating effect on cotton fabrics, not as a n immediate action but as a secondary reaction. T h e examination of a balloon envelope which burst at M i l a n 2 in 1906 showed that a t some spots t h e material could b e easily torn, while over the g r e a t e r portion it 1

The total volume of phosphine and arsme does not exceed •025 per cent, and is usually about "oi per cent 2 Namias, "L'Ind. Chim," 1907, 7, 257-258; "Chem. Cent.," 1907, 2, 1460-1461.

CHEMICAL PROPERTIES

31

showed a g r e a t resistance t o t e a r i n g . T h e d a m a g e d spots w e r e found to b e i m p r e g n a t e d with phosphoric acid and a r s e n i c acid, p r o d u c e d b y t h e oxidation of the phosphine a n d arsine contained in t h e h y d r o g e n with which the balloon h a d b e e n inflated. Phosphine in small quantities in h y d r o g e n containing over 1 p e r cent, of o x y g e n a t t a c k s copper, producing an acid liquid which h a s a m o s t corrosive action on fabric. H o w e v e r , it does not a p p e a r u n d e r these circumstances t o h a v e a n y action o n aluminium or zinc ; consequently a n y m e t a l p a r t s inside t h e envelope of a n airship should b e of aluminium. P h o s p h i n e under the above conditions a t t a c k s h e m p a n d o t h e r textiles which h a v e b e e n t r e a t e d with copper compounds, b u t it does not a p p e a r to h a v e a n y action on fabrics free from copper c o m p o u n d s or copper or brass fastenings. T h o u g h it has b e e n stated t h a t phosphine, is not spontaneously inflammable, with quite small admixtures of liquid h y d r o g e n p h o s p h i d e it immediately bursts into flame on c o m i n g into contact with air. Phosphine p r o d u c e d b y t h e reaction of water on calcium phosphide always contains a q u a n t i t y of the liquid h y d r o g e n p h o s p h i d e sufficient t o m a k e the g a s spontaneously inflammable. U s e of this property is m a d e in t h e H o l m e s ' L i g h t used a t s e a a s a distress signal, a n d also as a m a r k e r a t t o r p e d o practice. Phosphine is soluble in water to a slight extent. T h e solution of phosphine in w a t e r is not very stable, particularly in s t r o n g light, w h e n it b r e a k s up, depositi n g red p h o s p h o r u s . T h e d e n s i t y of p h o s p h i n e is 17*5 times that of hydrogen.

32

HYDROGEN

W i t h A r s e n i c , — H y d r o g e n does not directly combine with arsenic, but if an arsenic compound is in solution in a liquid in which hydrogen is being generated, i.e. hydrogen in the nascent state, chemical union takes place. T h u s , if arsenious oxide is dissolved in dilute hydrochloric acid and a piece of metallic zinc is added, t h e hydrogen produced by the action of the acid on the zinc will combine with the arsenic, in accordance with t h e following equation :— AS4O6 + I2H a = 4ASH3 + 6H2O. T h e g a s produced, which is called " A r s i n e " or " Arsenuretted H y d r o g e n , " is unpleasant smelling and poisonous. It burns in air with a lilac-coloured but not very luminous flame, thus :— 4ASH3 + 6O2 - As4Ofl + 6H2O. If the g a s is strongly heated it is decomposed and elemental arsenic deposited. Arsine is produced to a small extent in the Silicol process of making hydrogen, and has a deteriorating effect on fabric (see phosphine), while with many metals it is decomposed, arsenic being deposited and hydrogen liberated. It can be liquefied easily (the liquid g a s boiling at - 54*8° C), and it solidifies at - H 3 ' 5 ° C. Arsine is soluble in water, one volume of water at o° C. dissolving 5 volumes of arsine. T h e density of arsine is 39 times that of hydrogen. Chemical Combination of Hydrogen w i t h Lithium, Sodium, P o t a s s i u m , M a g n e s i u m , Calcium, and Cerium, T h e chemical combination of hydrogen has so far only been considered with regard to a few non-metallic

CHEMICAL PROPERTIES

33

elements, b u t n o w a n e w series of reactions will be considered in which h y d r o g e n combines chemically with a metal. T h e s e metals a r e those of the alkaline and alkaline earth g r o u p . W i t h Lithium.—If h y d r o g e n is passed over metallic lithium a t about 200° C , the h y d r o g e n is absorbed, not as h y d r o g e n is absorbed by platinum, etc., but chemically absorbed, in accordance with t h e following equation :— 4L1 + H 2 - LI^HJJ

If the resulting lithium hydride is allowed to cool a n d is placed in water it becomes a source of h y d r o g e n , not only giving up w h a t it h a s already received, b u t also a volume twice as much as this, which it has derived from the water, as may be seen in the following equation :— Li4H2 + 4H a O = 4L1OH + 3H3 W i t h S o d i u m . — U n d e r similar circumstances the n e t a l sodium absorbs h y d r o g e n with the production of 1 hydride :— 4Na + H 2 = Na4H3. This hydride, like t h a t of lithium, behaves in a similar nanner with water. It, however, has a n o t h e r interesting )roperty in t h a t if sodium hydride is h e a t e d in vacuo to -bout 300° C , the whole of t h e h y d r o g e n is given off ,nd metallic sodium again remains. W i t h P o t a s s i u m . — I f the metal potassium is heated a the presence of hydrogen, a hydride is formed .— 4K. + H 2 = K4H2. "his hydride has the s a m e characteristic reaction with 3

34

HYDROGEN

water, b u t it has a distinctive reaction, in that on exposure to air it catches fire:— 2K4Ha + 9O3 - 4 K A +

2H

a0.

W i t h M a g n e s i u m . — I f hydrogen is passed over hot metallic magnesium t h e hydrogen is absorbed :— Mg + H 2 = MgHjj. T h i s hydride is decomposed with water, with the production of magnesium hydrate a n d hydrogen :— MgH2 + 2H2O = Mg(OH)2 + zH 2 . W i t h Calcium.—If h y d r o g e n is passed over hot metallic calcium the hydrogen is absorbed :— Ca + H 2 = CaH2 T h e hydride is decomposed by water, according to the equation— CaH2 + 2H2O = Ca(OH)a + 2 H 2 . Calcium hydride, unlike the metallic hydrides already mentioned, is a commercial possibility, and under t h e n a m e of " H y d r o l i t h " has been used by the F r e n c h A r m y in the field for the inflation of observation balloons. Its use for this purpose is g o v e r n e d by F r e n c h p a t e n t No. 327878, 1902, in the name of Jaubert. W i t h Cerium.—If hydrogen is passed over hot metallic cerium the hydrogen is absorbed :— Ce + H2 = CeH2. T h i s hydride is decomposed with water in the same m a n n e r as calcium hydride, but as a source of hydrogen it is far too rare to be employed. However, if an alloy of cerium with magnesium and

CHEMICAL PROPERTIES

35

iluminium is h e a t e d below its m e l t i n g p o i n t in a stream )f h y d r o g e n , t h e latter is a b s o r b e d , with t h e formation )f cerium h y d r i d e within t h e alloy, which, after cooling, Dossesses to a r e m a r k a b l e d e g r e e t h e p r o p e r t y of emiting sparks w h e n r u b b e d with a n y r o u g h surface. These s p a r k s a r e sufficiently h o t to ignite coal g a s and )etrol vapour, h e n c e t h e e m p l o y m e n t of this h y d r o g e n ited alloy in t h e p a t e n t lighters which h a v e of recent r ears b e c o m e so c o m m o n in this country. Zhemical C o m b i n a t i o n of H y d r o g e n w i t h a n d V e g e t a b l e Oil.

Animal

O w i n g to the discoveries of M . S a b a t i e r a new se h a s b e e n found for h y d r o g e n , a n d a v a s t a n d everrowing industry created, k n o w n as " fat h a r d e n i n g ". T h e chief uses for animal a n d v e g e t a b l e fats are for be m a k i n g of candles, soap, a n d edible fats s u c h as are icorporated in b u t t e r substitutes, sold generically under i e n a m e of " M a r g a r i n e ". A n i m a l a n d v e g e t a b l e fats are g e n e r a l l y m i x t u r e s of certain n u m b e r of complicated o r g a n i c chemical comounds, a m o n g s t t h e chief of which m a y b e mentioned nolein, olein, stearin, a n d palmitin. T h e physical roperties of these c o m p o u n d s a r e s o m e w h a t different. 'hus, those containing considerable p r o p o r t i o n s of earin a n d palmitin are usually solid at atmospheric imperature, while t h o s e in which t h e chief constituent either linolein or olein a r e liquids at such t e m p e r a t u r e . T h e s e chemical c o m p o u n d s — l i n o l e i n , olein, stearin, i d palmitin—are w h a t a r e k n o w n a s " glycerides," 1. they a r e c o m p o u n d s of glycerine with a n organic

36

HYDROGEN

N o w since glycerine is of great value in a variety of ways, chiefly for the production of nitro-glycerine, it is customary to split these glycerides up into glycerine and their organic acid before indulging in a n y other process T h i s may be accomplished by t h e use of superheated steam. T h u s , when such steam is blown through palmitin t h e following reaction takes place :— ( W C U H J A ) . + 3H2O Falmitin Steam

3H(C16H31O2)

Palmitic acid

+ C8H6(HO)8 Glycerine

Or through olein :— C3HB(C1BH33Oa)3 + 3HaO = aHCQsHsA) + C8H6(HO)3. Olein Steam Oleic acid Glycerine T h e physical properties of these organic acids are very interesting and important. T h e i r melting points are:— Palmitic acid Stearic acid . Oleic acid

. .

.

.

Melting point, 62 6° C ,, „ 69 30 C. „ „ 14*0° C.

N o w this oleic acid, owing to its low melting point, is not of great value, as it cannot b e used for candles However, the discoveries of M. Sabatier have shown that u n d e r certain conditions of temperature and in the presence of nickel or cobalt (which themselves undergo n o p e r m a n e n t change), the low melting linoleic a n d oleic acids m a y be converted into stearic acid by the introduction of hydrogen into t h e liquid organic acid. T h u s : — C17H38COOH + H 2 = CnH Oleic acid Stearic acid T h e nickel in this process m a y be introduced into the liquid organic acid by merely a d d i n g spongy nickel to the molten oleic acid ; or as a volatile compound

CHEMICAL PROPERTIES

3;

k n o w n a s " Nickel C a r b o n y l " it may b e blown in tog e t h e r with t h e h y d r o g e n . I n either case, for t h e conversion of t h e linoleic and oleic acids into stearic acid, the t e m p e r a t u r e of t h e acids should b e b e t w e e n 200° and 220° C. W h e n t h e nickel is introduced, in the form of carbonyl, at t h e s a m e time as t h e h y d r o g e n , t h e carbonyl is decomposed into metallic nickel a n d carbon m o n o x i d e — t h e latter t a k i n g no p a r t whatever in t h e reaction a n d being available for t h e production of further nickel carbonyl. T h e nickel which is used in this process performs merely a catalytic function a n d does not of itself underg o p e r m a n e n t change. H o w e v e r , its catalytic property m a y be d e s t r o y e d either by the m e t h o d b y which it is prepared or b y certain impurities in the h y d r o g e n with which the h y d r o g e n a t i o n is carried out. W h i l e it is not important t h a t t h e h y d r o g e n should be v e r y pure—in fact, it may contain carbon monoxide, nitrogen, carbon dioxide, a n d m e t h a n e — i t is absolutely essential that it should be entirely free from sulphur dioxide, sulphuretted hydrogen, a n d o t h e r sulphur compounds, bromine, chlorine, iodine, hydrochloric acid, a r s e n u r e t t e d h y d r o gen, selenuretted h y d r o g e n , a n d teluretted h y d r o g e n . If the nickel is introduced into t h e fatty acid in the solid form it is important t h a t it should b e absolutely free from sulphur, selenium, tellurium, arsenic, chlorine, iodine, bromine. F u r t h e r , it is important t h a t t h e nickel should h a v e b e e n p r e p a r e d by the reduction of t h e oxide at a t e m p e r a t u r e not e x c e e d i n g 300° C , a n d should not h a v e been long exposed to the air prior to its use. T h e w e i g h t of nickel used is about o ' l part to 100 parts of oil or fatty acid ; however, larger quantities do no harm. After t h e hydrogenation of t h e fatty acid or

38

HYDROGEN

oil, practically the whole of the nickel is recovered by merely filtering the hot oil or fatty acid. In this note the use of hydrogen in the fat hardening industry has been described with particular reference to t h e conversion of the unsaturated oleic and linoleic fatty acids into stearic acid. However, what has been said in regard to this matter is equally applicable to the conversion of olein and linolein into stearin, cotton-seed and most fish oils being quite easily converted into solid fats.

CHAPTER

III.

T H E MANUFACTURE OF HYDROGEN. CHEMICAL METHODS. THE

PRODUCTION OF

HYDROGEN.

W H I L E all t h e processes d e s c r i b e d yield h y d r o g e n , some are of merely laboratory use, o t h e r s of commercial use, and yet others of u s e for t h e g e n e r a t i o n of h y d r o g e n for w a r purposes, u n d e r conditions w h e r e rapidity of production a n d low weight of r e a g e n t s a r e m o r e important t h a n t h e cost of t h e final product. W h e r e h y d r o g e n is w a n t e d for commercial purposes, two types of process will generally b e found m o s t useful . the electrolytic, w h e r e not m o r e t h a n i o o o cubic feet of h y d r o g e n a r e required p e r h o u r a n d conditions are such t h a t t h e o x y g e n p r o d u c e d c a n b e e i t h e r advantageously used or sold locally ; t h e I r o n C o n t a c t process, t h e L i n d e - F r a n k - C a r o process, or t h e B a d i s c h e Anihn Catalytic process, w h e r e yields of 3000 a n d m o r e cubic feet a r e required per hour. H o w e v e r , local conditions a n d t h e r e q u i r e m e n t s of a particular t r a d e m a y m a k e s o m e of t h e other processes t h e m o r e desirable. F o r w a r h y d r o g e n m a y b e economically p r o d u c e d a t a base, a n d used t h e r e for the inflation of airships, or the filling of high-pressure bottles for transport t o t h e K i t e Balloon Sections in t h e field. W h e r e transport conditions a r e difficult it m a y b e a d v a n t a g e o u s to g e n e r a t e (39)

40

M A N U F A C T U R E OF H Y D R O G E N

t h e hydrogen on the field at t h e place where it will b e u s e d ; then, probably, the Silicol, H y d r o g e n i t e or Hydrolith processes will have t h e a d v a n t a g e , b u t here again it is not possible to speak with a n y great precision, as local conditions, even in war, must h a v e g r e a t influence on the selection of the most suitable process. T h e production of h y d r o g e n can b e accomplished by a large variety of methods, which m a y b e divided into two main classes, viz. chemical a n d physical, while there is a n intermediate class in which the production of hydrogen is accomplished in two stages, one being chemical a n d t h e other physical. CHEMICAL M E T H O D S O F PRODUCING

HYDROGEN.

T h e chemical m e t h o d s of producing h y d r o g e n may be divided into four classes :— 1. Methods using a n acid. 2. Methods using an alkali. 3. Methods in which the hydrogen is derived from water. 4. Methods in which the hydrogen is produced b y methods other than the a b o v e (1) M e t h o d s U s i n g an Acid, W i t h Iron.—If dilute sulphuric acid is b r o u g h t into contact with iron, chemical action takes place, with t h e production of h y d r o g e n a n d ferrous sulphate, in accordance with the following equation :— Fe + H2SO4 « H2 + FeSO4. Theoretically, to produce 1000 cubic feet of hydrogen at 30 inches barometric pressure a n d 40° F . b y this process, 155 Ib. of iron a n d 272 lb. of pure sulphuric acid a r e

CHEMICAL METHODS

41

equired, or a total weight of p u r e r e a g e n t s equal to 27 1b. per 1000 cubic feet of h y d r o g e n p r o d u c e d . F r o m be figures g i v e n a b o v e , t h e a p p r o x i m a t e cost of material >er 1000 cubic feet of h y d r o g e n can b e calculated if the revaihng prices of iron a n d sulphuric acid a r e known. )f course, p u r e sulphuric acid is n o t a n essential for t h e rocess, b u t allowance for t h e impurity of t h e sulphuric cid and iron m u s t be m a d e in a n y calculation for cost r weight. T h e h y d r o g e n p r o d u c e d by this m e t h o d varies conderably in purity. It is liable to contain m e t h a n e to n extent which d e p e n d s on the carbon c o n t e n t of t h e on ; it m a y also contain phosphine, d e p e n d i n g o n t h e hosphorus c o n t e n t of t h e iron, sulphuretted h y d r o g e n , epending on t h e sulphur c o n t e n t of the iron, a n d traces f silicon hydride, d e p e n d i n g on t h e silicon c o n t e n t of le iron. It is also liable to contain arsine or a r s e n u itted h y d r o g e n , d e p e n d i n g on t h e arsenic content of le sulphuric acid, t h e commercial acid frequently conLining considerable a m o u n t s of this impurity. Unless Decially treated, t h e h y d r o g e n p r o d u c e d is a l w a y s acid, id therefore unsuitable for balloon a n d airship purDses. T h e i m p u r e g a s p r o d u c e d by this m e t h o d m a y b e jrined b y b e i n g passed t h r o u g h or s c r u b b e d b y w a t e r ; lis will r e m o v e m u c h of t h e acid carried by t h e gas, jst, and some of t h e m e t h a n e , p h o s p h i n e , arsine, a n d ilphuretted h y d r o g e n . If after this t r e a t m e n t t h e g a s passed t h r o u g h a solution of a lead salt, t h e r e m a i n g acidity a n d sulphuretted h y d r o g e n can b e r e m o v e d , his m e t h o d of t h e t r e a t m e n t of the impure g a s is »vered b y E n g l i s h p a t e n t 16277, 1896, in t h e n a m e s of ratis a n d M a r e n g o . F u r t h e r p a t e n t s in connection

42

MANUFACTURE OF HYDROGEN

with this method of producing h y d r o g e n have been taken out by Williams (English p a t e n t 8895, I 8 8 6 ) » H a w k i n s (English p a t e n t 15379, 1891), Pratis and Marengo (English p a t e n t 15509, 1897), H a w k i n s (English patent 25084, 1897), a n d Fielding (English patent 17516, 1898). W i t h Zinc*—If dilute sulphuric acid is brought into contact with zinc, chemical action t a k e s place, with t h e production of zinc sulphate~and h y d r o g e n , in accordance with t h e following equation :— Zn + H2SO4 - H a + ZnSO*. Theoretically, to produce 1000 cubic feet of hydrogen at 30 inches barometric pressure and 40° F . by this process, 180 lb. of zinc a n d 27? lb. of p u r e sulphuric acid are required, or a total weight of p u r e reagents equal to 452 lb. per 1000 cubic feet of h y d r o g e n produced. T h e h y d r o g e n produced by this process is liable to fewer impurities t h a n -frhen iron is used, but it is always acid a n d liable to contain arsine if commercial sulphuric acid is used. T h e zinc sulphate produced in this process can be turned more easily t o commercial account than iron sulphate. If to t h e solution of the zinc sulphate resulti n g from the process sodium carbonate or sodium h y d r o g e n carbonate is added, a precipitate of hydrated zinc basic carbonate or zinc carbonate is obtained, which on ignition in a furnace yields zinc oxide (commercially known a s " z i n c w h i t e " ) , water, a n d carbon dioxide. Zinc white has a commercial value as a basis or body *n paints ; it h a s one g r e a t a d v a n t a g e over white lead, which is used for t h e same purpose, in t h a t it is far less poisonous. T h i s m e t h o d of t r e a t m e n t of the residual

CHEMICAL METHODS

43

zinc sulphate is t h e subject of a p a t e n t by B a r t o n ( E n g l i s h p a t e n t 28534, 1910). T h e previous list of p a t e n t s for t h e reaction of iron and sulphuric acid also c o v e r t h e use of zinc a n d sulphuric acid for the production of hydrogen. T h e r e a r e other metals which will yield h y d r o g e n with sulphuric acid, such as cadmium a n d nickel, while m a n y metals will yield h y d r o g e n with hydrochloric acid, such as tin, nickel, a n d aluminium. However, these reactions c a n n o t b e r e g a r d e d as commercial m e a n s of producing h y d r o g e n . (2) M e t h o d s U s i n g an Alkali, W i t h Zinc*—If a solution of caustic soda in water is b r o u g h t into contact with metallic zinc, chemical reaction t a k e s place, with t h e production of sodium zincate a n d h y d r o g e n . T h e reaction is expressed in the following equation :— Zn + 2NaOH => H 2 + Na2ZnC>2. Theoretically, to produce 1000 cubic feet of h y d r o gen at 30 inches barometric pressure a n d 40° F . , 180 lb. of zinc a n d 224 lb. of p u r e caustic s o d a a r e required, or a total weight of p u r e r e a g e n t s equal t o 404 lb. p e r 1000 cubic feet of h y d r o g e n produced. T h e h y d r o g e n p r o d u c e d b y this process is generally very pure, but, d e p e n d i n g on the purity of the zinc, it is liable to contain arsine. A s t h e g a s is alkaline, owing to the caustic s o d a carried in suspension, it requires to b e scrubbed to m a k e it suitable for balloons a n d airships. A modification of this process h a s been the subject of a patent. Zinc as a fine powder is mixed with dry

44

MANUFACTURE OF HYDROGEN

slaked l i m e ; then when hydrogen is required, t h e mixture is h e a t e d in a retort a n d hydrogen is evolved, the reaction being expressed :— Zn + Ca(OH)3 = H 2 + CaZnO3. In this modification of t h e process to produce i o o o cubic feet of hydrogen at 30 inches barometric pressure and 40° F . , 180 lb. of zinc and 207 lb of slaked lime are required, or a total weight of pure r e a g e n t s equal to 387 lb. per 1000 cubic feet of hydrogen produced. By t h e substitution of magnesium hydroxide instead of slaked lime a similar reaction takes place, b u t t h e total weight per 1000 cubic feet of h y d r o g e n produced is reduced t o 341 lb. T h i s process, with its modification, is covered by a patent by Majert a n d Richter ( E n g l i s h patent 4881, 1887), and is primarily intended as a process for the generation of h y d r o g e n in t h e field for t h e inflation of observation balloons. THE

HYDRIK

OR A L U M I N A L

PROCESS.

W i t h A l u m i n i u m . — I f a solution of caustic soda is brought into contact with metallic aluminium, chemical reaction takes place,' with t h e production of sodium aluminate a n d hydrogen, in accordance with t h e following equation :— 2AI + 6NaOH = 3 H 2 + 2Al(ONa)3. Theoretically, to p r o d u c e 1000 cubic feet of hydrogen at 30 inches barometric pressure a n d 40° F . , 50 lb. of aluminium and 225 lb. of p u r e caustic soda are required, or a total weight of pure reagents equal to 275 lb. per 1000 cubic feet of h y d r o g e n . T h e h y d r o g e n produced by this process is generally

CHEMICAL METHODS

45

sry pure, b u t t h e g a s is frequently alkaline from m i n u t e a c e s of caustic s o d a carried in suspension, which m u s t s r e m o v e d b y s c r u b b i n g with w a t e r before t h e h y d r o g e n suitable for balloons a n d airships. THE

SILICOL

PROCESS.

W i t h S i l i c o n , — I f a solution of caustic soda is b r o u g h t to contact with elemental silicon, chemical reaction ikes place, with t h e production of sodium silicate a n d y d r o g e n . T h e following equation was supposed to ipresent t h e reaction •— Si + 2NaOH + H 2 O - NajjSiOa + 2H 2 . Theoretically, to p r o d u c e 1000 cubic feet of h y d r o g e n : 3 0 inches barometric pressure a n d 40 0 F . , 38*8 lb. of licon a n d 111 lb. of p u r e caustic soda a r e required, or t o t a l weight of p u r e r e a g e n t s equal to 149*8 lb. p e r DOO cubic feet of h y d r o g e n . T h e g a s p r o d u c e d b y this process is singularly pure, enerally containing 99'9 p e r cent, h y d r o g e n b y v o l u m e f t h e w a t e r vapour is r e m o v e d before analysis), "oi per snt. of arsine a n d phosphine, "005 p e r cent, a c e t y l e n e , l e r e m a i n i n g impurity b e i n g air, which is introduced 1 t h e p o w d e r e d silicon a n d also in solution in t h e r ater. I n w o r k i n g this process practically, p u r e silicon is ot used, h i g h - g r a d e ferro-silicon, c o n t a i n i n g 82-92 p e r snt. silicon, b e i n g employed. A s will b e seen from t h e b o v e equation, theoretically 2 '86 parts of a n h y d r o u s austic s o d a by weight should b e used for o n e p a r t of licon: H o w e v e r , in w o r k i n g in practice, o n e p a r t of u r e silicon a n d 1 7 p a r t s of p u r e caustic s o d a a r e emloyed. T h i s discrepancy b e t w e e n t h e theoretical

46

MANUFACTURE OF HYDROGEN

quantity of soda a n d that actually used has b e e n investigated by the author, who originally considered t h a t the following reaction might b e taking place :— Si + 2HaO = SiO2 + 2H2. T h a t is to say, the silicon was being oxidised by the oxygen of the water, and hydrogen liberated. T h e first experiment performed was t h e h e a t i n g of the ferro-silicon* (92 per cent Si) in a flask with boiling w a t e r ; the resulting steam was condensed, b u t t h e r e was no residual gas. Therefore it was concluded that at the temperature of boiling water no reaction b e t w e e n ferro-silicon a n d water took place. R e m e m b e r i n g t h a t t h e temperature of t h e caustic soda solution used in the silicol process is a b o v e iocf C , frequently rising to 120 0 C , it was thought t h a t a higher temperature might perhaps produce t h e suspected rea c t i o n ; ferro-silicon was accordingly heated in an atmosphere of steam in a n electric resistance furnace to a temperature of 300° C , but still n o h y d r o g e n was produced. Consequently it was concluded t h a t t h e explanation of the smaller consumption of caustic soda t h a n would b e anticipated from theoretical considerations must b e explained on some basis other t h a n t h e reaction of silicon with water. T h e next experiment attempted was the h e a t i n g of ferro-silicon with sodium silicate, i.e. with a p u r e form of t h e product of the usual equation. W h e n ferro-silicon was h e a t e d with a n aqueous solution of p u r e sodium mono-silicate, considerable quantities of h y d r o g e n w e r e 1

The ferro-silicon employed was of French manufacture. I have since found that some high-grade Canadian ferro-sihcons give traces of hydrogen with water under the conditions cited in the experiments

CHEMICAL METHODS

47

evolved, thus w a r r a n t i n g t h e conclusion t h a t the o r d i n a r y equation— Si + 2NaOH + H2O - Na 2 Si0 3 + 2H 2 s not entirely correct, a n d t h a t a silicate richer in silica Jian that indicated in the equation was formed, a n d t h a t Drobably t h e following reaction p r o c e e d s to s o m e exent:— Si + Na 2 Si0 3 + 2H,0 « Na2Si20B + 2H,. A s s u m i n g this second reaction t o t a k e place a t t h e same time as the first, the reaction can b e e x p r e s s e d : — 2S1 + 2NaOH + 3H2O = Na«SijO« + 4H2, which is e q u i v a l e n t to 1000 cubic feet of h y d r o g e n a t 30 inches b a r o m e t r i c p r e s s u r e a n d 40° F . b e i n g p r o d u c e d Dy 38*8 lb. of silicon a n d 55*5 lb. of caustic soda, t h e •atio of p u r e caustic soda to pure silicon b e i n g a s 1 "43 s to 1. U s i n g a plant p r o d u c i n g about 30,000 cubic feet of l y d r o g e n p e r hour, it was found that 1 "9 p a r t s of caustic soda (j6 per cent. N a O H ) to 1 part of C a n a d i a n ferrojilicon (84 p e r cent. Si) g a v e very satisfactory results, ;he ratio of t h e p u r e r e a g e n t s being as 1 7 2 p a r t s of ;austic soda b y weight to 1 p a r t of silicon. Theoretically, 22*5 cubic feet of h y d r o g e n should h a v e seen produced p e r lb. of the commercial ferro-silicon ised, but in practice it was found that 2 0 7 cubic feet w e r e obtained, t h e discrepancy of 1 *8 cubic feet b e i n g t o s o m e extent accounted for b y t h e protective action of impurities, oss through leaks a n d also b y hydrogen b e i n g m e c h a n i ;ally carried a w a y b y t h e w a t e r used for cooling t h e ssuing h y d r o g e n . Description of Silicol P l a n t . — T h e essentials of a iilicol plant a r e shown in the diagram (Fig. 3). The

48

MANUFACTURE OF

HYDROGEN

r e q u i s i t e q u a n t i t y of c a u s t i c s o d a is p l a c e d in t h e t a n k o n t h e r i g h t a n d t h e n e c e s s a r y w a t e r a d d e d t o it t o m a k e a 25 p e r cent, s o l u t i o n .

T o a s s i s t s o l u t i o n t h e r e is a

o

s t i r r e r i n this t a n k , w h i c h , in s m a l l p l a n t s , is h a n d - o p e r a t e d a n d in l a r g e o n e s p o w e r - o p e r a t e d .

W h e n the whole

of t h e c a u s t i c s o d a h a s g o n e i n t o s o l u t i o n , w h i c h it r e a d i l y

CHEMICAL METHODS

49

does a s a result of the heat of solution a n d the stirring, the valve D is opened, allowing t h e whole of t h e soda solution to r u n via the pipe E into the generator. W h e n t h e solution has run from t h e caustic soda t a n k into t h e g e n e r a t o r t h e valve D is closed, t h e n the necessary quantity of ferro-silicon is placed in the h o p p e r on t h e top of t h e g e n e r a t o r a n d t h e lid of the h o p p e r closed, m a k i n g a gas-tight joint. In small plants a little mineral grease is a d d e d to the generator, via the g r e a s e box. T h e p l a n t is then ready for operation, a n d silicol is cautiously fed into the g e n e r a t o r b y means of t h e h a n d operated feed worked from F . D u r i n g the generation the fluid charge in t h e g e n e rator is k e p t stirred b y m e a n s of t h e stirring mechanism worked from G. T h e h y d r o g e n produced passes t h r o u g h the t u b e condenser (where it is cooled a n d t h u s freed from s t e a m ) a n d then on to t h e g a s holder. A n excessive pressure, d u e to rapid g e n e r a t i o n of hydrogen, is g u a r d e d against b y means of a water seal as shown. W h e n generation is complete, t h e resulting sodium silicate solution is rapidly run out via the t r a p p e d discharge pipe a n d the interior of the g e n e r a t o r washed with cold water supplied from the tap B. Thermometers at T i , T 2 , T 3 , a n d T 4 enable the t e m p e r a t u r e at different parts of the a p p a r a t u s to be observed and, if necessary, controlled. T h e description of the apparatus has, of necessity, to be s o m e w h a t general, as these plants a r e m a d e in sizes v a r y i n g from 1500 to 60,000 cubic feet per h o u r production a n d consequently differ in d e t a i l ; thus, in large plants, t h e t u b e condenser is not employed a n d t h e hot h y d r o g e n passes u p a tower packed with coke, down 4

50

M A N U F A C T U R E OF H Y D R O G E N

which water is falling. F u r t h e r , in large plants, the generator itself is water-jacketed, as t h e heat of chemical reaction would otherwise be excessive. T h e silicol process has t h e a d v a n t a g e of giving a very g r e a t h y d r o g e n production per hour from a plant of small cost—its d i s a d v a n t a g e is that at the prevailing cost of t h e r e a g e n t s employed the hydrogen is expensive. T o sum up, this process is exceedingly useful where large quantities of h y d r o g e n a r e from time to time required, but it is not t h e best process to use where there is a constant hour-to-hour d e m a n d for hydrogen. T h e Silicon Content of the FerrO'Silicon.—The g r a d e of ferro-silicon used in this process is very important, as low-grade material does not yield anything like t h e theoretical quantity of h y d r o g e n which should be obtained from t h e silicol present. T h i s arises to a slight extent from t h e protective action of t h e impurities, which enclose particles of silicon and therefore prevent the caustic soda from attacking it. T h e curve ( F i g . 4), obtained experimentally, shows that to g e t even m o d e r a t e efficiency ferro-silicon of over 8 0 per cent, silicon c o n t e n t should b e used. T h e Degree of F i n e n e s s of the Ferro'Silicon.— T h e degree of subdivision of t h e ferro-silicon is also important, not so m u c h because of its effect on the total yield of hydrogen, b u t because of its influence on the rapidity of generation. F i g . 5 indicates t h e speed of evolution of hydrogen from t w o samples of t h e same material, under identical conditions, except t h a t o n e sample was much coarser than t h e other

CHEMICAL

METHODS

"$18 Relation of Sihco! Content to Hydrogen Yield.

0

ID

20

30

40

50

60

70

80

90

100%

Silicon in Ferrosilicon

FIG. 4

I

JU-!

i

I

i

^ >

1/

J

f / Evolution of Hydrogen from 88% Fenrosf I icon, 20-30 Mesh and same Material ground to pass 100 Mesh.

6& D I

12 14- 16 18 Time in Minutes FIG.

5.

20

22

Z4- 26

28

30

52

MANUFACTURE OF HYDROGEN

T h e Strength of the Caustic S o d a . — T h e strength of the caustic soda is v e r y important in this process. If t h e solution is too dilute, a very poor yield of hydrogen is obtained, a n d also another difficulty is introduced.' W h e n t h e caustic s o d a solution is very weak, on the introduction of t h e ferro-silicon or " silicol" reaction takes place, but the whole solution froths violently, the froth being carried along t h e pipes from t h e generator, causing trouble to be experienced in t h e valves, a n d tending to ultimately block t h e pipes themselves. O n t h e other hand, the caustic soda solution m a y b e too strong. In this case, before t h e whole of t h e caustic soda has reacted with t h e requisite a m o u n t of silicol, t h e solution b e c o m e s either v e r y viscous or actually solid, so a poor yield is obtained a n d t h e sludge cannot b e got out of t h e generator without allowing it to cool down and then digging it out b y manual labour. T h e following laboratory e x p e r i m e n t s with ferrosilicon containing 92 per cent silicon a n d caustic soda containing 98 per cent, of sodium hydroxide illustrate the effect of soda solutions of v a r y i n g strength, a n d also the effect of varying ratios of p u r e silicon t o pure sodium hydroxide. F r o m these it will b e seen t h a t the most economical results a r e obtained w h e n a 40 per cent, solution of caustic soda is employed a n d the ratio of silicon to sodium h y d r o x i d e is approximately 1 to 1 "6. In practice such s t r o n g solutions a r e not used, as, owing to t h e e v a p o r a t i o n of a g o o d deal of the water during t h e process, t o w a r d s the e n d a d e g r e e of concentration would be reached which would prevent the sludge from being r u n out of the plant. A solution containing about 25 p e r cent, of caustic s o d a is found to give in practice v e r y satisfactory results. Such a solu-

CHEMICAL

METHODS

53

tion of commercial caustic soda, c o n t a i n i n g a b o u t 25 p e r cent, of p u r e sodium hydrate, h a s at i o o ° F . a specific gravity of a p p r o x i m a t e l y 1-32—a figure which is very useful to r e m e m b e r , a s by m e a n s of a h y d r o m e t e r a rapid check can b e m a d e of t h e caustic soda solution being p r e p a r e d for use in the process. T h e ratio of silicol to caustic soda should be such that t h e ratio of p u r e silicon to p u r e sodium h y d r a t e is as 1 t o 1 7 2 , b u t this figure is capable of modification to a slight extent, d e p e n d i n g on t h e t e m p e r a t u r e of t h e mixture, which is naturally higher in large p l a n t s than in small ones. of Silicon Yield in Cubic Feet per lb of Soda Ratio of Silicol. to pure Caustic 1 Experiment. Strength Solution. (At 30" Bar. and 6o° F.). Soda. 10 per cent. 10 10 10 30 30

3°

—The

23-90 23 5 3 2 4 10 2450

U s e of S l a k e d L i m e instead of C a u s t i c experiments

obtain h y d r o g e n to react

i5 3 6 16-80

3 9 158 3 19

40 40

The

13 62

r to o 745 1 „ 1 065 1*480 3 200 o 852 2 13

with

it.

already

described

indicate

that

from ferro-silicon a b a s e m u s t b e It therefore

occurred

to t h e

t h a t t h e c o s t of t h e o p e r a t i o n of t h e p r o c e s s reduced

Soda,

by the substitution

of

slaked

lime

author

might for

to

used

be

caustic

soda. 1

Theoretically t h e m a x i m u m possible yield u n d e r t h e s e condi-

tions of t e m p e r a t u r e a n d p r e s s u r e would b e 2 5 4 c u b i c feet p e r lb of sihcol of this purity

54

MANUFACTURE OF HYDROGEN

Laboratory experiments, using ferro-silicon containing 92 per cent, silicon a n d p u r e slaked lime, w e r e m a d e to see if the following reaction took place :— Si + Ca(OH)2 + H3O = CaSiO3 + 2H2. T h e results of these experiments indicated t h a t w h e n 1 part of ferro-silicon, 2*5 parts of slaked lime, a n d 10 parts of water w e r e used, a yield of 1*53 cubic feet of hydrogen was obtained per lb. of ferro-silicon used. Theoretically, u n d e r t h e conditions of t h e experiment, 25*4 cubic feet should h a v e been produced p e r lb. of ferro-silicon; consequently it can b e safely concluded t h a t without a n external supply of heat t h e suspected reaction only takes place to a v e r y limited extent. R e m e m b e r i n g t h a t slaked lime will decompose sodium silicate, p r o d u c i n g caustic soda a n d calcium silicate, in accordance with the following equation :— Ca(OH)2 = 2NaOH + CaSiO3, it was thought that t h e following reactions might t a k e place if both caustic soda a n d slaked lime w e r e employed at the same time :— (1) 2S1 + 2NaOH + 3H2O = NagSiaOa + 4H 2 . (2) Na2Sia06 + Ca(OH)2 = 2Na0H + CaSi3OB. Since the caustic soda in t h e solution would be r e g e n e r a t e d after it h a d reacted with t h e silicol, it would b e available for reacting with yet more silicol, a n d would consequently reduce t h e quantity of caustic soda used in t h e process. T h e following experiments, using a mixture of slaked lime a n d caustic soda, appear to indicate that the surmise was partly or wholly correct, for with approximately only half as much caustic soda as ferro-silicon a yield of almost 16 cubic feet of hydrogen per lb. of ferro-

C H E M I C A L METHODS

55

silicon was obtained. By contrasting these experiments with those already given, using caustic soda alone, it will b e seen t h a t the yield obtained from the caustic soda is much g r e a t e r t h a n t h a t which would have been obtained were no lime present. W h e t h e r in operating on a large scale equally g o o d results would b e obtained has not y e t b e e n determined. 1 Expenment. ^ o , o f Silicon to fetao of Sihcon pure Caustic Soda. to Lime. 1 2 3

i to 0426 1 „ 0426 1 „ 0-426

1 to 1*52 1 „ 272 1 „ 3 04

^ ^ S S S ^ t *« Bar and §5 F. I

4'9S 15-95 15-23

T h e Chemical Composition of the S l u d g e . — T h e equations which h a v e already been given indicate that the p r o d u c t s of this process are h y d r o g e n a n d sodium disilicate in solution in water. Since, however, neither t h e ferro-silicon nor caustic soda employed are pure, in the practical production of h y d r o g e n b y this method, products o t h e r than those shown in the equations are found. T h e commercial caustic soda employed always contains a certain a m o u n t of carbonate of soda, which takes no p a r t in the reaction and is found unaltered in the sludge. T h e s a m e r e m a r k applies to the iron contained in the ferro-silicon. T h e following analysis gives t h e chemical composition of t h e sludge produced w h e n 1414 1b. of ferrosilicon, containing 84 per cent, of silicon, and 2688 1b. 1

Since the above experiments the author has found that there is a patent for the use of lime in conjunction with caustic soda and silicon, which, under the name of " Hydrogenite," has been employed by the French Army for inflating observation balloons in the field

56

MANUFACTURE O F

HYDROGEN

of caustic soda, containing 76 per cent, of sodium hydrate, was employed. Besides the sludge 29,300 cubic feet of hydrogen was produced, measured at a temperature of 6o° F . a n d a barometer of 30 inches. CHEMICAL COMPOSITION OF SLUDGE.

Moisture . Silica . . . . Sodium carbonate . . . Soda (NaaO, other than carbonate) Insoluble and undetermined

. .

Per Cent by Weight • 27 74 3 6 79 6 04 20 08 9"35 IOO'OO

CHEMICAL COMPOSITION OF SODA SOLUTION USED.

Caustic soda . Sodium carbonate Specific gravity at ioo° F

. .

. 24 5 3"o 1 324

.

CHEMICAL COMPOSITION OF FERRO-SILICON USED.

Silicon Iron . Aluminium . Carbon Undetermined

. .

. . .

. .

.

84 o 6*9 c7 f 2 3-6 100 o

. .

SCREEN l ANALYSIS OF FERRO-SILICON.

Through 20, on 30 ii 3° » 4O 31 40 1 50 II So , , 60 II 60 , • 7O >> 70 , , 80 80 , , 9O >) )> 90 ,, TOO )} TOO , , I2O 91 120 , 150 >> 150 , 200 3 200 assing 1

Standard I M.M. screens,

Grms Per Cent. 141-5 = 10 28 85 "o = 617

CHEMICAL METHODS

57

T h e U s e of Mineral Grease*—To reduce t h e frothing a n d p r i m i n g in this process it is customary to introduce a little mineral g r e a s e , which floats on t h e surface of the caustic soda solution and p r e v e n t s the formation of the froth to a considerable e x t e n t A b o u t 32 lb. of mineral g r e a s e a r e advocated per 1000 l b . of silicol used. H o w e v e r , if t h e caustic soda solution is strong, i.e. a b o u t 25 p e r c e n t , sodium hydrate, and t h e g e n e r a t o r is wide, giving a large surface and a shallow d e p t h t o t h e caustic s o d a solution, n o grease need b e used at all. Precautions to be O b s e r v e d . — I n this process very great care m u s t b e t a k e n in the introduction of t h e ferrosilicon. W h e n t h e ferro-silicon is a t t a c k e d by the caustic s o d a l a r g e quantities of h e a t a r e g i v e n out, raising t h e t e m p e r a t u r e of t h e caustic soda solution. If the caustic soda solution is cold, ferro-silicon can be introduced into the solution far m o r e rapidly t h a n it is attacked b y t h e s o d a ; consequently t h e r e is likely to exist an accumulation of ferro-silicon in t h e solution, the temperature of which is gradually rising. A certain critical t e m p e r a t u r e is ultimately reached w h e n t h e whole of the accumulated ferro-silicon is a l m o s t instantly attacked, with large yield of h y d r o g e n a n d consequently the production of high pressure in t h e generator. Several explosions h a v e been caused in this country from this reason. W h i l e it is impossible to g i v e any definite figures, in t h e ordinary commercial plant for the Droduction of h y d r o g e n b y this process the ferro-silicon ihould b e a d d e d in small quantities, with a period of vaiting b e t w e e n each addition, until t h e caustic soda olution r e a c h e s a t e m p e r a t u r e of a b o u t 180° F At

58

MANUFACTURE OF

HYDROGEN

this temperature, with a 25 per cent, solution of caustic soda, high-grade ferro-silicon is almost instantly attacked, so it can then be a d d e d continuously at a rate which does n o t produce a p r e s s u r e above the w o r k i n g pressure of the plant. In plants for t h e operation of this process no red or white lead w h a t e v e r should b e used for making joints, as both these substances at a comparatively low temperature are reduced to metallic lead by ferro-silicon, with the evolution of large quantities of h e a t a n d the production of incandescence, t h e reaction t a k i n g place with such rapidity as to constitute almost a n explosion. T h i s can b e easily illustrated by m a k i n g a mixture of finely divided ferro-silicon a n d dry red lead, in which the ratio of the two is 1 part of pure silicon t o 12*2 parts of red lead. If a match or t h e end of a cigarette is put to this mixture it goes off violently, with t h e production of great heat, in accordance with the following equation :— Pb8O4 + 2S1 = 3Pb + 2SiO3. T h a t the t e m p e r a t u r e produced is exceedingly high can b e well illustrated b y p u t t i n g , say, half a n ounce of an intimate dry m i x t u r e of ferro-silicon a n d red lead, in which t h e proportions of the active principals are as indicated in the a b o v e equation, on a sheet of thin aluminium, say -ik of a n inch thick. O n putting a match to this mixture it will be found a hole is melted in the aluminium sheet. 1 All air must, if possible, be excluded from t h e plant prior to the introduction of t h e caustic soda, as otherwise in the early stages of generation of hydrogen an explosive mixture m i g h t arise which on ignition would 1

The melting point of aluminium is 658° C

CHEMICAL METHODS

59

produce a d a n g e r o u s explosion. Such ignition m i g h t arise from a spark produced from t h e mechanism inside the generator, b y ferro-silicon coming in contact with red lead which m i g h t h a v e been used in m a k i n g the joints in t h e plant, by incandescence produced b y t h e reaction of ferro-silicon with caustic soda itself. If a n intimate mixture of p o w d e r e d caustic soda is m a d e with ferro-silicon in t h e ratio indicated in the equations on the silicol process, and this mixture is just m o i s t e n e d with water, h y d r o g e n is rapidly evolved a n d the r e a c t i n g mass frequently becomes incandescent. Such conditions might arise in a plant for operation of this process, by the caustic soda b e i n g splashed o n to s o m e r e c e s s in the generator, t h e r e b e c o m i n g concentrated, a n d ferrosilicon coming into contact with this concentrated solution. I t is for this reason t h a t caustic soda a n d ferro-silicon should never b e stored in close proximity to each other, as this dangerous reaction m a y arise from the b r e a k i n g of d r u m s containing t h e two reagents. Since this process is generally operated in conjunction with a gas-holder, the m o s t e a s y way to exclude air is to allow h y d r o g e n from t h e gas-holder t o blow b a c k through t h e p l a n t prior to p u t t i n g this in operation. H y d r o g e n equal to about four times the v o l u m e of the plant is required to thoroughly exclude t h e air. T h e following patents with r e g a r d to this process are in existence :— Consort. Elektrochem. I n d . — E n g l i s h patent 21032, September 14th, 1909 F r e n c h p a t e n t 418946, July 18th, 1910. English p a t e n t 11640, M a y 13th, 1911. J a u b e r t — F r e n c h patent 430302, A u g u s t 6th, 1910

60

MANUFACTURE OF HYDROGEN THE

HYDROGENITE

PROCESS.

T h e r e is a modification of this m e t h o d k n o w n as the hydrogenite process whereby t h e use of an aqueous solution of caustic soda is avoided. A n intimate m i x t u r e of ferro-silicon a n d powdered caustic soda or lime is packed in s t r o n g cylinders communicating with a high pressure storage. B y means of a fuse t h e t e m p e r a t u r e is locally raised so t h a t chemical reaction takes place, with the production of h y d r o g e n and sodium and calcium silicates. T h i s modification is covered by Jaubert, English patent 422296, 1910; English p a t e n t 153, 1911. W i t h Carbon,—If caustic soda is h e a t e d to dull redness with .charcoal or anthracite or some o t h e r form of pure carbon, h y d r o g e n is evolved a n d sodium carbonate a n d sodium oxide produced, in accordance with the following equation :— 4NaOH + C = Na2CO8 + Na2O + 2H2. Theoretically, t o produce 1000 cubic feet of hydrog e n at 30 inches barometric pressure a n d 40° F . by this process, 222 lb. of caustic soda and I 6 ' 6 I lb of carbon are required, or a total weight of pure r e a g e n t s equal to 238*61 per 1000 cubic feet of hydrogen produced. T h e hydrogen produced by this process would be liable t o contain traces of methane, arsine, a n d sulphuretted hydrogen, t h e a m o u n t d e p e n d i n g on t h e purity of the coal used. A modification of this process, w h e r e b y t h e caustic soda is replaced by slaked lime, is covered b y a patent taken out in U . S . A . b y Bailey in 1887. W i t h a Formate or Oxalate.—If sodium formate is

CHEMICAL METHODS

61

heated with caustic soda in t h e form of soda lime, t h e following reaction takes place :— H COONa + NaOH =» NasCOg + H a T h i s m e t h o d h a s b e e n used for t h e p r o d u c t i o n of hydrogen in t h e laboratory ; however, it c a n n o t b e regarded a s singularly convenient. If t h e sodium formate is replaced b y sodium or potassium oxalate a similar reaction takes place :— Na2C2O4 + 2NaOH = 2Na2CO8 + H 2 . This last method, it is interesting to note, w a s e m ployed b y A m a g a t for t h e p r e p a r a t i o n of t h e h y d r o g e n for his classic experiments on t h e relationship of pressure to volume. (3) M e t h o d s in w h i c h H y d r o g e n i s Derived Water.

from

H y d r o g e n can b e derived from w a t e r b y m e a n s of the alkali a n d alkali e a r t h s groups of metals, b u t since all these a r e expensive, t h e production of h y d r o g e n from these sources is limited to t h e r e q u i r e m e n t s of t h e chemical laboratory. W i t h L i t h i u m . — I f metallic lithium is placed in water it is a t t a c k e d b y it, in a c c o r d a n c e with t h e following equation, with the production of h y d r o g e n and lithium h y d r a t e :— 2L1 + 2HaO - 2L1OH + H 2 . It is i n t e r e s t i n g to n o t e that since metallic lithium has a density of "59 (the smallest density of a n y solid), it floats on t h e surface of t h e w a t e r while it is b e i n g attacked.

62

M A N U F A C T U R E OF HYDROGEN

W i t h S o d i u m . — I f metallic sodium is placed in w a t e r it is attacked b y it, in accordance with t h e followi n g equation, with t h e production of hydrogen and sodium h y d r a t e : — 2Na + 2 H 2 O = 2NaOH + H 3 Since considerable quantities of heat a r e given out when the sodium is attacked by the water, much of which h e a t is communicated to t h e metal, it frequently melts while being attacked, the melting point of the metal being 95 6° C. W h i l e t h e a b o v e equation expresses t h e principal reaction which takes place, a second reaction also occurs, leading to the production of sodium hydride, which is s o m e w h a t unstable under these conditions and occasionally explodes with violence, to avoid which a piece of apparatus has been designed by J. Rosenfeld. 1 W i t h P o t a s s i u m , — I f metallic potassium is placed in water it is attacked, in accordance with the following equation, with t h e production of h y d r o g e n a n d potassium hydrate:— 2K + 2H2O = 2KOH + H 2 . Such is the heat which is liberated during the reaction that if a piece of potassium is placed in a bucket of water, the metal is carried to t h e surface b y the vigorous stream of h y d r o g e n produced, a n d t h e r e b e comes so hot as to ignite the hydrogen evolved. T h e s a m e r e m a r k s which h a v e been m a d e as to a secondary reaction with regard to sodium, apply with like force to potassium. 1

"Prakt Chem.," 48, 599-601.

CHEMICAL METHODS

63

With the A l k a l i n e Earths, W i t h M a g n e s i u m . — I f metallic m a g n e s i u m is placed n water which is h e a t e d to its boiling point, h y d r o g e n is slowly evolved, in accordance with t h e following equa:ion, producing h y d r o g e n a n d m a g n e s i u m h y d r a t e :— Mg + 2 H 2 O = Mg(OH)3 + H 2 T o accelerate t h e reaction, the m a g n e s i u m heated in a t u b e a n d steam passed over it

is gently

W i t h Calcium.—If metallic calcium is placed in water at ordinary atmospheric t e m p e r a t u r e it decomposes it in accordance with the following equation, p r o d u c i n g a. vigorous s t r e a m of h y d r o g e n a n d calcium hydrate :— Ca + 2 H a O = Ca(OH)2 + H 2 W i t h S t r o n t i u m . — A similar reaction t o that already given for calcium takes place, but s o m e w h a t more vigorously W i t h B a r i u m . — A similar reaction t o that a l r e a d y given for calcium takes place, b u t much m o r e vigorously. THE

BERGIUS

PROCESS.

W i t h Iron.—If metallic iron is heated in t h e presence of water u n d e r v e r y high pressure, h y d r o g e n is evolved a n d magnetic oxide formed, in accordance with the following equation :— 3Fe + 4H2O = Fe8O4 + 4H2. T h i s method, which is k n o w n as t h e Bergius process, was put into commercial operation in 1913 at H a n o v e r . It has t w o great a d v a n t a g e s — a v e r y p u r e h y d r o g e n is produced, a n d since it is u n d e r g r e a t pressure, it can b e

64

MANUFACTURE OF H Y D R O G E N

used to fill bottles without the use of a compressor. T h e chemical composition of the hydrogen p r o d u c e d is given as follows :— Hydrogen . . Carbon monoxide . Saturated hydrocarbons. Unsaturated hydrocarbons

. 99-95 per cent 'ooi „ „ '042 „ „ . "008 „ „

b u t a m o u n t of the carbon compounds must be greatly influenced by purity of the iron e m p l o y e d ; however, it appears to be a 'fact that little or no sulphuretted hydrogen is produced even if the iron contains appreciable quantities of sulphur. W h i l e it has been stated that the hydrogen is produced by the action of water at high t e m p e r a t u r e and pressure upon metallic iron, this does not entirely describe the chemistry of the process, for the inventor has found t h a t the presence of certain metallic salts in the solution, and also other metals, greatly increase the speed of production of hydrogen. T h e following comparative table of productions of hydrogen from equal weights of iron clearly illustrates this p o i n t : — Temperature Volume of Hydrogen rf C. per Hour. Iron and pure water . Iron, water, and ferrous chloride Iron, water, ferrous chloride, and metallic copper . . . Iron, water, ferrous chloride, and metallic copper . .

300 300

230 c.c. 1390 „

300

1930 „

340

345° ,,

In t h e commercial employment of this process it is believed that the working pressure is about 3000 lb. per sq. inch and the temperature 350° C.

CHEMICAL

METHODS

65

I n t h e d i s c h a r g e from t h e vessel in which t h e h y d r o g e n is p r o d u c e d t h e r e is a reflux c o n d e n s e r which effectively p r e v e n t s a n y s t e a m from escaping from t h e p l a n t w h e n t h e h y d r o g e n is d r a w n off. O n e of t h e r e m a r k a b l e features of this process is t h e fact t h a t since the water pressure is so high, it p e n e t r a t e s right into the iron p a r t i c l e s ; consequently they a r e entirely e m p l o y e d , a n d a yield closely a p p r o a c h i n g t h e theoretical is obtained. Theoretically, 1000 cubic feet of h y d r o g e n (at 30 inches b a r o m e t e r a n d 40° F . ) would b e p r o d u c e d with a n e x p e n d i t u r e of 116*5 ^D- of metallic iron. T h e size of t h e p l a n t is v e r y small for t h e yields obtained, it b e i n g stated t h a t a g e n e r a t o r of 10 g a l l o n s ' capacity gives 1000 cubic feet of h y d r o g e n a t a t m o s p h e r i c t e m p e r a t u r e a n d p r e s s u r e per h o u r After t h e completion of the reaction the pressure can b e let off from t h e g e n e r a t o r a n d t h e magnetic oxide of iron p r o d u c e d r e m o v e d a n d reduced by w a t e r g a s to t h e metallic state, when it can again be employed in t h e process I t is claimed that t h e cost of h y d r o g e n b y this p r o c e s s is exceedingly low ; consequently, if this is corr e c t a n d the mechanical difficulties of manufacturing g e n e r a t o r s t o w i t h s t a n d t h e v e r y high pressures a n d c h e m i c a l action a r e satisfactorily overcome, this process would a p p e a r to be o n e of t h e highest value for t h e commercial production of h y d r o g e n . A certain a m o u n t of information with r e g a r d t o this process can b e found in t h e following p a p e r : " P r o d u c tion of H y d r o g e n from W a t e r a n d Coal from Cellulose a t H i g h T e m p e r a t u r e s a n d Pressures," b y F . Bergius, 5

66

MANUFACTURE O F HYDROGEN

t h e " Journal of the Society of Chemical Industry," vol xxxii., 1913. T h e process is protected by t h e following patents :— G e r m a n Patent, 254593, 1911. F r e n c h Patent, 447080, 1912. English Patents, 19002 and 19003, 1912. U n i t e d States P a t e n t s , 1059817, 1059818, 1913, all in t h e n a m e of F . Bergius. W h i l e the previous method is of commercial importance, t h e following method is of i n t e r e s t : — W h e n the ordinary process of rusting of iron takes place, hydrogen is evolved. It is generally considered t h a t iron does not rust w h e n it is in contact with perfectly p u r e water, free from carbon dioxide or any other mild acid. In the following method iron filings are placed in a steel bottle partly filled with water saturated with carbon dioxide, t h e bottle is then closed a n d sealed. It is then agitated, t h e following reaction taking p l a c e : — Fe + H2O + COa = FeCO3 + H 2 . T h i s method is o n e of interest a n d is described by B r u n o in the " B u l l . Soc. Chim.," 1907, [iv.], 1661. It cannot, however, be regarded as h a v i n g a commercial use. W i t h Hydrides.—As has already been stated, the hydrides of the metals of t h e alkali and alkaline earth groups produce hydrogen on being placed in water. H o w e v e r , in only two cases are these reactions worth consideration. W i t h Lithium Hydride.—If lithium hydride is brought into contact with water, hydrogen is evolved

CHEMICAL METHODS

67

i lithium h y d r a t e formed, in accordance with t h e folding equation :— Li4H2 + 4 H 2 O = 4L1OH + 3H2. Such is t h e rarity of lithium at t h e present time t h a t • above is neither a commercial nor a laboratory m e t h o d Droducing hydrogen. It is, however, of t h e g r e a t e s t srest, owing to the large yield of h y d r o g e n obtained m a small weight of lithium h y d r i d e Theoretically, 30 cubic feet of h y d r o g e n at 30 inches b a r o m e t e r 1 40° F . a r e produced from 2 7 7 6 lb. of p u r e lithium Iride a n d 66 6 lb. of water. M a n y ingenious ideas re been p u t forward for t h e e m p l o y m e n t of lithium iride in airships so that in the e v e n t of a n airship sing g a s from some cause, this m a y b e replaced by Irogen manufactured in t h e airship. A s has b e e n seen, oretically, 94*36 lb. of reagents a r e required t o pro:e 1000 cubic feet of h y d r o g e n at 30 inches b a r o m e t e r I 40° F . N o w this a m o u n t of h y d r o g e n would h a v e ft of 74*06 lb., so if t h e products of the manufacture hydrogen were d r o p p e d the b u o y a n c y of t h e ship aid be increased by 94*36 + 74*06 lb., or 168*42 lb. every 94*36 lb. of material d r o p p e d from t h e ship, •wever, interesting as these suggestions are, such ihe rarity a n d cost of lithium t h a t at t h e p r e s e n t e they a r e not capable of realisation, t h o u g h future -overies of lithium minerals and cheaper m e t h o d s for production of lithium hydride m a y possibly r e n d e r se ideas of practical value. THE

HYDROLITH

PROCESS.

W i t h C a l c i u m H y d r i d e , — I f calcium h y d n d e is j g h t into contact with water, h y d r o g e n is evolved

68

M A N U F A C T U R E OF HYDROGEN

a n d calcium h y d r a t e formed, in accordance with the following equation :— CaH2 + 2H2O =* Ca(OH)2 + 2 H 2 . Theoretically, to p r o d u c e i o o o cubic feet of hydrogen at 30 inches barometric pressure and 40° F . , 58*4 lb. of p u r e calcium hydride a n d 49 Mg5 lb. of water are required, or a total weight of 108*4 lb. of pure reagents per 1000 cubic feet of hydrogen. Since, however, water does not h a v e to b e carried in most parts of Europe, the theoretical weight to b e carried per 1000 cubic feet of hydrogen required is 58*4 lb. T h i s method, k n o w n as the Hydrolith process, has been satisfactorily employed by the F r e n c h A r m y in t h e field for t h e inflation of observation balloons, the calcium hydride being packed in air- and water-tight boxes for transportation. In the commercial production of calcium hydride small quantities of calcium nitride a r e produced, which, when the hydride is attacked with water gives rise to ammonia, in accordance with t h e following equation :— Ca3Na + 6H2O = 3Ca(OH)2 + 2 NH 3 . H o w e v e r , as a m m o n i a is very readily soluble in water, if t h e h y d r o g e n produced in t h e process is scrubbed with w a t e r the a m m o n i a is almost entirely removed a n d an exceedingly p u r e h y d r o g e n results. T h i s process is protected by a F r e n c h patent, No. 327878, 1902, in t h e n a m e of Jaubert. W i t h Metallic S o d i u m and A l u m i n i u m Silicide.— If a mixture of metallic sodium a n d aluminium silicide is placed in water, h y d r o g e n is evolved, with the production of sodium silicate and aluminium hydrate, in accordance with the following equation .— Al2Si4 + 8Na + i8H 2 O = Al2(OH)fl + 4Na2Si0J + 15H2

CHEMICAL M E T H O D S

69

Theoretically, 1000 cubic feet of h y d r o g e n a t 30 •hes barometer a n d 40° F . are produced from 64*8 lb. this m i x t u r e It is, however, believed t h a t t h e ictical yield is a b o u t 80 per cent of this figure. T h i s process is essentially one for the p r o d u c t i o n of drogen for w a r purposes, t h o u g h the a u t h o r does not ow of any actual use of it. T h e m i x t u r e can b e m a d e 0 briquettes, which must b e packed into air- a n d w a t e r ht boxes. T h e method, which is sometimes k n o w n the " S i c a l process," is protected by a U n i t e d S t a t e s :ent—977442, 1910—in the n a m e of F o e r s t e r l i n g a n d ilipps. W i t h A l u m i n i u m . — I f ordinary metallic aluminium placed in even boiling water, little or n o chemical ion takes place. H o w e v e r , if the aluminium is first algamated with mercury it is rapidly a t t a c k e d b y h o t ter, with t h e formation of aluminium h y d r a t e a n d irogen, in accordance with the following equation :— 2AI + 61-LjO = A12(OH)0 + 3H0. Theoretically, to produce 1000 cubic feet of h y d r o 1 at 30 inches barometric pressure a n d 40° F . , 5 0 lb. aluminium a r e required. In the commercial application of this m e t h o d it is necessary to a m a l g a m a t e the metallic aluminium h mercury by h a n d , as a d v a n t a g e is taken of t h e t that aluminium will reduce aqueous solutions of s of mercury to t h e metallic state, in a c c o r d a n c e with following equation — 2AI + 3HgCl2 = 2AICI3 + 3Hg nsequently, if there is an excess of aluminium over t required by the equation, this excess will be

70

MANUFACTURE OF HYDROGEN

automatically a m a l g a m a t e d by the metallic mercury as it is produced. In a practical application of this method by Mauricheau Baupre, 1 fine aluminium filings a r e mixed with a small proportion of mercuric chloride (HgCla) a n d potassium cyanide ( K C N ) , which causes a slight rise in t e m p e r a t u r e and produces a coarse powder, which is quite stable if kept free from moisture. T h i s mixture can be kept in air- a n d water-tight boxes until it is required, w h e n it can be gradually added to water kept at about 70° C. A brisk evolution of h y d r o g e n then takes place which closely approximates to the theoretical yield A n o t h e r very interesting application of this increased chemical activity of aluminium when amalgamated with mercury is incorporated in a toy which is sometimes seen on sale under t h e n a m e of " D a d d y T i n W h i s k e r s ". T h i s toy consists of an aluminium stamping of a face a n d a pencil, the core of which is filled with a preparation chiefly composed of a mercury salt. It is operated by rubbing t h e eyebrows and chin with this special pencil. Shortly afterwards white hairs of aluminium oxide (A1 2 O 3 ) gather w h e r e v e r t h e pencil h a s touched the aluminium. T o operate the a b o v e process for the manufacture of h y d r o g e n it is necessary that the aluminium should be as p u r e as possible a n d should not contain copper. T h e commercial light alloy k n o w n as " d u r a l u m i n , " which contains about 9 4 per cent, of aluminium and 4 p e r cent, of copper, is entirely unsuitable for generating hydrogen in the method above described, as it is almost unattacked by even boiling water containing a small quantity of a mercury salt. 1

"Comptes Rend.," 1908, 147, 310-1.

CHEMICAL M E T H O D S T h e following p a t e n t s deal with this process F r e n c h p a t e n t 392725, 1908, in t h e n a m e of cheau Baupre. E n g l i s h p a t e n t 3188, 1909, in t h e n a m e of heim G e r m a n p a t e n t 229162, 1909, in t h e n a m e of heim.

y\ :— MauriGriesGries-

W i t h A l u m i n i u m A l l o y * — T h e following a l l o y — Aluminium Zinc Tin

.

. . .

.

78-98 parts 15-15 » .7-05 »

is m a d e a n d cast into a p l a t e ; after cooling it is a m a l g a mated with mercury. After a m a l g a m a t i o n t h e p l a t e is heated a s strongly as possible without volatilising t h e mercury. W h e n it has become thoroughly a m a l g a m a t e d it is allowed to cool a n d is then ready for use. If this alloy is put into hot water it readily yields hydrogen ; the h y d r o g e n yield is proportionate t o t h e aluminium a n d zinc content. T h e g a s produced is very pure. T h i s process is protected by the following p a t e n t U y e n o , ' B r i t i s h patent, 11838, 1912. W i t h Steam. In considering the production of h y d r o g e n from steam, a considerable n u m b e r of processes must b e considered in which t h e first s t a g e (which is c o m m o n to all the processes) consists in the manufacture of blue water g a s ; consequently, prior to t h e description of these processes, a m o n g s t the most important of which are:—

72

MANUFACTURE OF HYDROGEN

T h e Iron Contact process, T h e Badische process, T h e L i n d e - F r a n k - C a r o process, t h e manufacture of water gas will b e described. T H E MANUFACTURE

OF W A T E R

GAS.

W h e n steam is passed over red-hot carbon, t h e two following chemical reactions take place .— (1) C + H2O = CO + Ho. (2) C + 2H2O = CO2 + 2 H2 T h e question a s to which equation represents the predominant reaction t a k i n g place, d e p e n d s on the temperature of t h e c a r b o n ; roughly speaking, the higher t h e temperature the more closely does the reaction coincide with the first chemical equation. T h e following experimental results ( H . Bunte, " J . fur Gasbeleuchtung," vol. $y, 81) clearly illustrate the effect of temperature on t h e chemical composition of the p r o ducts of the reaction —

Temperature *C.

674 758 838 954 IOIO 1125

Per Cent, of Steam Decomposed Q.Q 0 25 30 41-0 70*2 94 'o 99 4

Composition, by Volume of Gas rroaucea. Ha.

CO.

COa

65-2 65 2 61 9 53 3 488 509

49 7*8 15 1 39 3 49 7 48-5

298 27 0 22 9 6-8 15 06

In the first of t h e chemical equations given, it will b e seen that the products are composed of 50 per cent.

CHEMICAL METHODS

73

ydrogen a n d 50 per cent, c a r b o n monoxide, while in ie second, t h e composition is 66"66 per cent, h y d r o g e n n d 33'33 per cent carbon dioxide ; in D r . B u n t e ' s tperiments, figures closely approximating to t h e first luation were obtained w h e n t h e t e m p e r a t u r e of t h e irbon was IOOO°-IIOO C C , while figures similar t o t h e -oducts indicated in the second equation w e r e found hen the t e m p e r a t u r e was 674 0 C. Now, w h a t e v e r purpose w a t e r g a s may b e required r, its use for this purpose d e p e n d s on the fact t h a t t h e is will combine with oxygen with t h e evolution of iat, consequently t h e plant should be worked to m a k e e product with the highest calorific power for t h e west fuel consumption. T h i s requirement is r e a c h e d ore closely if t h e plant is operated so t h a t the first uation represents the chemical reaction which t a k e s ice; consequently, in the practical manufacture of w a t e r s the coke or other fuel in the g a s p r o d u c e r should at a t e m p e r a t u r e of a b o u t iooo° C. T h e chemical reaction producing the d e c o m p o s i 11 of the steam is endothermic, t h a t is to say, a s t h e iction proceeds, t h e t e m p e r a t u r e of t h e coke falls, so it in order t o obtain a g a s approximating t o the p r o cts in the first equation, heat must b e supplied t o t h e ce, to counteract t h e fall in temperature, d u e t o its LCtion with the steam. In the oldest type of plant, the c o k e which was used the manufacture of the water gas was in a cylinder, ich was externally h e a t e d by a coke or coal fire ; vever, this p r o c e d u r e was not very efficient, a n d t h e ctice is not in use at all a t t h e p r e s e n t time. In practice to-day there a r e two m e t h o d s of m a k i n g :er gas, one the E n g l i s h or H u m p h r e y a n d G l a s g o w

74

M A N U F A C T U R E OF

method, a n d t h e Fleischer method.

other

HYDROGEN

t h e Swedish

or

Dellwick-

E n g l i s h M e t h o d . — I t has already been pointed out t h a t from t h e r m a l chemical reasons, t h e c o k e t h r o u g h which t h e steam is passing in the manufacture of w a t e r g a s should b e a t a b o u t iooo° C. in order to obtain g o o d results, a n d that as a result of t h e reaction b e t w e e n t h e c o k e a n d steam, t h e t e m p e r a t u r e of t h e former falls, necessitating t h e addition of heat to t h e coke mass, in order to k e e p up the efficiency of the process. It is in the m e t h o d of maintaining the coke t e m p e r a t u r e t h a t t h e E n g l i s h a n d Swedish systems differ. In b o t h systems t h e coke is kept at t h e proper t e m p e r a t u r e by shutting off the steam supply from time to time, a n d blowing air through the coke, t h e products of t h e air blast passing out of t h e generator t h r o u g h a different passage to those of t h e steam blast. T h e effect of blowing air t h r o u g h t h e coke is of course to produce heat, for the following reactions t o a lesser or greater e x t e n t take place .— (i) C + O2 - CO2j (a) CO2 + C = 2CO, a n d the heat, which is produced by the combustion of some of the coke, h e a t s the remainder, thus raising its temperature, so that the air blast can b e shut off, a n d t h e steam blast again turned on. In t h e English s y s t e m the depth of t h e coke in t h e g e n e r a t o r is considerable, consequently t h e carbon d i oxide formed at the base of the fire tends to be r e d u c e d in the u p p e r p a r t of t h e fire by t h e h o t coke, in accordance with equation (2), therefore in t h e English s y s t e m during t h e air blast a combustible g a s is produced.

CHEMICAL METHODS

75

owever, while at first sight this m i g h t appear to b e a n Ivantage, there a r e several d i s a d v a n t a g e s -associated ith this m e t h o d of working. In t h e first place, t h e is which is produced d u r i n g the air blast, t h o u g h c o m lstible, is not a gas of high calorific power, a s it contains ich a l a r g e a m o u n t of atmospheric n i t r o g e n ; in fact, ider the m o s t favourable circumstances, t h e g a s p r o iced d u r i n g the air blast will not contain over 30 per •nt. of carbon monoxide, while t h e rest of it will b e in>mbustible, b e i n g chiefly nitrogen t o g e t h e r with s o m e rbon dioxide A n o t h e r d i s a d v a n t a g e of this s y s t e m that since t h e c o k e is p e r m a n e n t l y b u r n t only t o -rbon monoxide, t h e a m o u n t of h e a t actually g e n e r a t e d the coke mass is comparatively small, consequently e rate of temperature rise in the coke m a s s is slow. In t h e Swedish or Dellwick-Fleiscker method, the >ke t e m p e r a t u r e is from time to t i m e raised by m e a n s an air blast, b u t in this case t h e d e p t h of fuel is latively shallow, so t h a t t h e carbon b u r n t remains irmanently in the form of carbon dioxide ; and since in irning equal weights of carbon to carbon m o n o x i d e id carbon dioxide over t h r e e times as much h e a t is merated in situ w h e n the carbon is b u r n t to c a r b o n oxide t h a n w h e n b u r n t to carbon monoxide, t h e rate rise of t e m p e r a t u r e of t h e coke m a s s in t h e g e n e r a t o r much m o r e rapid t h a n is the case in the E n g l i s h -stem, a n d consequently t h e period occupied b y t h e r blast is very much reduced. Fig. 6 shows a diagram from Dellwick's E n g l i s h itent 29863, 1896, illustrating his plant for the p r o d u c Dn of blue w a t e r g a s . A is the g e n e r a t o r provided with a c o k e receptacle , which passes t h r o u g h a stuffing-box D placed o n

76

MANUFACTURE O F H Y D R O G E N

t h e cover or top of the generator. T h e object o f this receptacle is to keep the fuel height constant i n t h e generator , if B is kept filled with fuel, as t h a t which is on the grate burns away, fresh fuel will run in f r o m B and will keep the depth of fuel on the g r a t e c o n s t a n t

L is the main air inlet, while a secondary s u p p l y of air takes place t h r o u g h the vertical pipe G , the purpose of this latter air inlet being to ensure a t h o r o u g h supply of air to all parts of the fuel bed. S and S ' are steam inlets, I a n d I ' are g a s o u t l e t s , a n d E is an outlet for t h e products m a d e during t h e air blast.

CHEMICAL METHODS

77

T h e m e t h o d of w o r k i n g this g e n e r a t o r would b e as follows :— W h e n a c o k e o r o t h e r fire of suitable d e p t h h a s b e e n obtained o n t h e g r a t e , t h e receptacle B is c h a r g e d with fuel, a n d t h e lid C firmly closed ; v a l v e s I a n d I ' a r e closed a n d v a l v e F opened, t h e n air u n d e r suitable p r e s s u r e is a d m i t t e d t h r o u g h L a n d G ; this causes t h e fuel to b u r n with rise in t e m p e r a t u r e of t h e u n b u r n t portion, while the p r o d u c t s of combustion, containing a b o u t 20 p e r cent, of carbon dioxide a n d 70 per cent, of nitrogen, escape by t h e p a s s a g e E . W h e n t h e t e m p e r a t u r e of the coke on the hearth has b e e n raised to a b o u t i o o o 0 C. the air blast is stopped, v a l v e F closed, v a l v e I ' opened, a n d s t e a m a d m i t t e d t h r o u g h S ' with t h e c o n s e q u e n t production of blue g a s , which passes out t o a scrubber a n d holder, via the valve I'. W h e n a s a result of t h e decomposition of t h e steam by the fuel mass, the t e m p e r a t u r e of the latter h a s fallen below the economic limit, t h e steam supply is s h u t off, a n d the air blast started again to raise t h e fuel t e m p e r a ture. W h e n t h e t e m p e r a t u r e is a g a i n suitable, t h e air is shut off a n d steam a g a i n passed t h r o u g h t h e fuel, b u t o n this occasion d o w n w a r d s from t h e s t e a m supply S, t h e w a t e r g a s p a s s i n g o u t by t h e outlet I. T h e object of this alternation of t h e direction of the s t e a m blast is to k e e p t h e t e m p e r a t u r e as uniform as possible t h r o u g h o u t t h e fuel mass. F i g . 7 shows a m o d e r n water g a s producer, which is self-explanatory, t h e fuel c h a r g i n g is d o n e after every third s t e a m blast, a n d t h e d e p t h of t h e fuel k e p t correct by m e a n s of a g a u g e rod, d r o p p e d t h r o u g h t h e lid at t h e t o p of t h e g e n e r a t o r . T h e s a m e alternation

78

MANUFACTURE OF HYDROGEN

in the direction of t h e steam blast is maintained, while during the air blast the products of combustion escape through the lid at t h e top of the generator, which is open d u r i n g this stage.

Steam Inlet \ Gas Outlet

\~Ash Outlet FIG

7

T h e sequence of operation with a s t a n d a r d g e n e r ator, having a circular hearth about 5 feet 6 inches in diameter, would be :— 1. Air blast 2 Steam up 3. Air blast

. . ,

.

.

,

,

,

2 minutes 6 „ j minute

CHEMICAL METHODS 4. Steam down 5. Air blast 6. Steam up

.

.

79 . 6 minutes 1 minute . 6 minutes.

Lt the end of the last operation, additional fuel would e added a n d the sequence again started. T h e air jpply main would b e a t a pressure of a b o u t 15 inches f water a b o v e the atmospheric, while t h e s t e a m main p ould be at about 120 lb. per sq. inch, t h e rate of flow F the steam being about 45 lb per m i n u t e , d u r i n g the earning periods. W o r k i n g under t h e conditions described, using coke f the following composition as a fuel:— Moisture . Ash . Volatile sulphur . Nitrogen . Carbon, etc. (by difference)

Per Cent. 6'o by 9o 1-35 .0*6 . 83x5

weight. ,, „ „ „

100 00 water g a s of a b o u t t h e following composition would e obtained :— Per Cent. Hydrogen . 52*0 by volume Carbon monoxide 39*6 „ Methane . . . . 0 4 , , Carbon dioxide . . . -3*5 » Sulphuretted hydrogen 0*5 „ Nitrogen . . . 4 0 ,, 100 o >r a consumption in t h e g e n e r a t o r of a b o u t 35-40 lb. of Dke per 1000 cubic feet of blue water gas m e a s u r e d at tmospheric temperature a n d pressure. A consideration of this coke consumption is instruc-

80

MANUFACTURE OF HYDROGEN

t i v e ; from the analysis of the water gas, it will be seen in i o o o cubic feet of the gas there a r e — 396 cubic feet of carbon monoxide. 35 » 11 .. .. dioxide. If the barometer is 30 inches and the temperature 6o° F , 1000 cubic feet of carbon monoxide weighs 74*6 lb. 74-6 x 396 •' 39° •> . .1 » » IOOO = 29*6 lb But carbon monoxide contains i | of its total weight of carbon. 28 20 6 X 12 .•. 396 cubic feet of carbon monoxide contains „ lb. carbon = 1 2 7 lb. Similarly, 1000 cubic feet of carbon dioxide weighs 117 3 lb 35 x " 7 3 • •35 •! » » » » Iooo = 4 1 lb. But carbon dioxide contains — of its total weight of carbon. 44 .. 35 cubic feet of carbon monoxide contains lb. of 44 carbon = 1 1 lb A d d i n g these two results together, it is seen that while 35-40 lb. of coke, equivalent to 29-33 lb. of carbon, a r e consumed in the generator per 1000 cubic feet of water gas, only 13 8 lb. of this carbon, or 42-46 per cent., are present in the g a s produced, the bulk of t h e remainder of the carbon consumed in the generator b e i n g burnt during the air blast period, and the remainder lost in the ash pit, and during clinkering; however, while these figures are instructive, as indicating the m a g n i t u d e of air blast consumption of fuel, to gain comparative figures it is necessary to obtain the calorific power of the coke

CHEMICAL METHODS

81

consumed, a n d of t h a t of t h e w a t e r g a s p r o d u c e d from a given w e i g h t of coke. If 35 lb. of t h e coke, t h e analysis of which h a s been already given, a r e c o n s u m e d in t h e production of 1000 cubic feet of water g a s at 30 inches b a r o m e t e r a n d 6o° F. f of t h e composition which h a s also been given, it will b e found t h a t t h e calorific power of t h e coke consumed, c o m p a r e d w i t h t h a t of the g a s produced, is as 516:342, t h a t is to say, j u d g e d o n a t h e r m a l efficiency basis, t h e efficiency of t h e p r o d u c e r w o r k i n g u n d e r these conditions is 342 x 100 _ 516 which is a figure such as is obtained in ordinary commercial w a t e r g a s manufacture. T h e analysis of t h e water g a s so far g i v e n e n u m e r ates t h e chief constituents, but in reality t h e r e are traces of other products, such as carbon bisulphide, carbonyl sulphide, a n d thiophene, derived from t h e sulphur in t h e "uel, which, m i n u t e in quantity, m a y nevertheless in the :ertain chemical processes p r o d u c e appreciable a n d uniesirable r e s u l t s : from t h e iron contained in t h e fuel, n i n u t e a m o u n t s of iron carbonyl a r e formed, which in n o s t processes in which water g a s is used is a m a t t e r >f n o importance, b u t if the g a s is to b e used for i g h t i n g with incandescent mantles, its removal is de•irable. T h e producer, which has been described, is not in >ractice absolutely continuous in operation, as from ime t o t i m e t h e process has to b e interrupted in order o r e m o v e t h e clinker from t h e fire. 6

82

MANUFACTURE OF

HYDROGEN

T h e process of " clinkering," besides requiring labour, is wasteful, as h o t fuel as well as clinker is d r a w n from the fire, consequently various devices h a v e b e e n d e s i g n e d to m a k e self-clinkering producers. T h e majority of these designs consist essentially of a rotating conical hearth. F i g . 8 s h o w s a device described in E n g l i s h patent 2461 n , 1909, which is almost self-explanatory. T h e clinker p a n h a n d t h e blast nozzle i are connected a n d free to rotate o n t h e ball r a c e shown in the vertical section. T h e end of t h e blast nozzle i is fitted with helical excrescences w i t h holes k for steam and air in their trailing edge. During the working of the producer, the nozzle and clinker p a n a r e rotated, a n y clinker forming being b r o k e n u p b e t w e e n the helical vanes on the fixed water j a c k e t e d b o d y of the producer a n d those on the rotating b l a s t nozzle. T h e clinker on b e i n g broken up falls into t h e clinker hearth, which is filled with water to such a d e p t h a s t o make a water seal b e t w e e n t h e producer b o d y a n d t h e moving hearth. T h e bottom of the clinker h e a r t h h a s fixed ribs, which t e n d to hold t h e crushed clinker, w h i c h d u r i n g the rotation of t h e hearth is carried r o u n d until it is brought against the fixed v a n e 0 , this lifts it out of t h e water. Producer h e a r t h s of t h e type described d o n o t a p pear to effect a n y appreciable saving in fuel, b u t since they eliminate clinkering, they h a v e a decided a d v a n t a g e , as the g a s yield is g r e a t e r in a given t i m e t h a n w o u l d otherwise be t h e case. Purification of W a t e r G a s , — F o r m o s t industrial purposes, it is necessary t h a t the crude w a t e r g a s should

CHEMICAL

METHODS

TV

71/ S e c t i o n CD. FIG 8.

84

M A N U F A C T U R E OF H Y D R O G E N

b e purified before its ultimate use. F o r practically every process in which water g a s is used it is necessary t h a t it should b e freed from t h e impurities which it mechanically contains, a n d which are composed of ash a n d dust, carried b y the g a s from t h e producer. T h e mechanically retained impurities in water g a s a r e r e m o v e d b y s c r u b b i n g the g a s with water, t h a t is to say, b y passing it up a tower, down which water is falling. N o t only does this water scrubbing r e m o v e t h e mechanically retained impurities, b u t it also, by reducing t h e t e m p e r a t u r e of t h e gas, causes the condensation and r e m o v a l of the m i n u t e quantity of iron carbonyl contained in the gas. R e m o v a l of Sulphuretted H y d r o g e n . — F o r most purposes for which water gas is required it is desirable t h a t it should b e free from sulphuretted h y d r o g e n , this is usually accomplished b y passing t h e g a s a t about 55°-65° F . over h y d r a t e d oxide of iron, when the following reaction takes place :— Fe3(OH)6 + 3H2S = 2FeS + 6HaO + S. After lapse of time, t h e hydrated ferric oxide ceases to h a v e a n y sulphuretted hydrogen-absorbing power, so t h e g a s is diverted t h r o u g h other h y d r a t e d oxide, and t h e spent oxide r e m o v e d and placed in the open air, when, after moistening with water a n d exposure, the following reaction takes place .— 4FeS + 6HSO + 3O2 - 2Fea(OH)<j + 4S T h u s it is seen the original oxide can b e reproduced, a n d on reproduction can b e used for t h e absorption of fresh sulphuretted hydrogen. In practice each revivification increases t h e free sulphur content of t h e oxide

CHEMICAL METHODS

85

>out 7 per cent., a n d as time goes o n t h e free s u l p h u r t h e iron oxide increases to 50-60 per cent, sulphur, hen it c o m m a n d s a ready sale to manufacturers of sulmric acid ; r o u g h l y speaking, 1 ton of oxide will purify 000,000 cubic feet of g a s before it is finally spent. I n this country, it is n o t generally necessary t o h e a t e hydrated oxide of iron t h r o u g h which the crude ater gas is passed, as t h e h e a t evolved by t h e chemical action is sufficient to k e e p t h e oxide at a suitable t e m Tature. H o w e v e r , in m a n y parts of t h e world, w h e r e e winter t e m p e r a t u r e is exceedingly low, it is n e c e s ry to pass steam coils through t h e oxide, a s otherwise ) absorption of sulphuretted h y d r o g e n t a k e s place. T h e reason for this failure to absorb the s u l p h u r e t t e d 'drogen is d u e to t h e fact, already given in t h e e q u a m, that with t h e absorption of t h e s u l p h u r e t t e d r drogen, water is produced, which freezes on t h e sur:e of the h y d r a t e d iron oxide, and thus p r e v e n t s further lphuretted h y d r o g e n coming in contact with i t In the practical removal of sulphuretted h y d r o g e n , is desirable to h a v e quite a considerable a m o u n t of iter in t h e h y d r a t e d oxide (about 15 per cent, b y sight), as this tends to k e e p it open a n d t h u s k e e p t h e essure necessary to g e t the water g a s t h r o u g h t h e .ide quite l o w ; it is also desirable to k e e p t h e oxide kaline, consequently a b o u t 1 per c e n t of lime is m i x e d th it to accomplish this. W h e n new h y d r a t e d oxide is p u t in w a t e r g a s irifiers, e v e n t h o u g h it m a y contain a sufficiency of iter, it tends to cake t o g e t h e r a n d create b a c k essure. T h i s can b e p r e v e n t e d , either b y mixing s a w d u s t th the n e w oxide before p u t t i n g it in t h e purifiers

86

M A N U F A C T U R E OF

HYDROGEN

(about i part to 5 of oxide by volume) or by mixing s o m e already used oxide containing a considerable a m o u n t of free sulphur with the n e w oxide ; this also tends to p r e v e n t caking. In ordinary commercial purification of water g a s , 100 tons of h y d r a t e d ferric oxide will effectively purify 200,000 cubic feet of crude water g a s per 24 h o u r s ; this allows of k e e p i n g 20-30 tons of " r e v i v i f i e d " oxide in reserve, available to replace t h e working oxide a s it becomes " s p e n t " . T h i s d e g r e e of purification of crude water gas to b e used in t h e manufacture of h y d r o g e n is common t o all t h e processes using i t ; in some of t h e processes special m e t h o d s of purification a r e employed, a n d these will b e g i v e n in the description of t h e process which r e n d e r s such m e t h o d s necessary. T h e Iron Contact P r o c e s s . Of all the processes for the production of h y d r o g e n in which water g a s represents one of the active r e a g e n t s , t h e Iron Contact process is the most important, as it is b y this process t h a t t h e greater a m o u n t of t h e w o r l d production of h y d r o g e n for use in industry a n d w a r is at present m a d e ; b u t important as this process is, it is doubtful if it will maintain its p r e s e n t pre-eminent position d u r i n g the next few years, as other processes, m o r e economical, but at p r e s e n t n o t so reliable, are a l r e a d y in existence, and with lapse of time g r e a t e r reliability will p r o b a b l y b e obtained in these later processes, which will result in the I r o n Contact process occupying a less imp o r t a n t position in h y d r o g e n production than it d o e s to-day. When

steam is passed over h e a t e d metallic

iron,

CHEMICAL METHODS

87

drogen is produced in accordance with t h e following uation;— 3Fe + 4 H / ) - Fe3O4 + 4H2 Theoretically, to produce 1000 cubic feet of h y d r o g e n 30 inches barometric p r e s s u r e a n d 40° F . , 116*5 lb. iron and 49*95 lb of s t e a m are required : h o w e v e r , in actice these figures a r e not closely a p p r o a c h e d b e c a u s e e magnetic oxide of iron formed t e n d s to shield t h e stallic iron from the action of t h e s t e a m ; indeed, t h e action m a y b e r e g a r d e d as merely a surface one. W h e n the protective action of t h e m a g n e t i c o x i d e s reached such a d e g r e e that t h e yield of h y d r o g e n s become negligible, t h e supply of steam is stopped, Ld the water g a s is passed over the m a g n e t i c oxide, ducing it to metallic iron, in accordance with t h e folwing equations .— Fe3O4 + 4H2 = 3Fe + 4H2O F e A + 4CO - 3Fe + 4CO*. hen further steam can b e passed over t h e iron, with e production of further h y d r o g e n . T h u s , it is seen t h a t t h e same iron is u s e d continuisly, and steam a n d blue water g a s are t h e t w o rerents consumed. S u c h is t h e chemical outline of t h e on Contact process ; however, in practice, t h e process somewhat more complex and v e r y much less efficient tan either t h e Electrolytic process or t h e B a d i s c h e -ocess, b o t h of which a r e described at a later stage, nor in the hydrogen produced b e r e g a r d e d as so satisfactory >r some industrial purposes, such as fat h a r d e n i n g , as lat m a d e by t h e other two processes. In the practical w o r k i n g of the Iron Contact process, le process is not b e g u n b y passing s t e a m over h o t

88

MANUFACTURE O F H Y D R O G E N

metallic iron, b u t by manufacturing t h e iron in situ, by reducing iron ore, such as hematite, with the water gas, which can be expressed by the following equations :— 2Fe2O8 + 3H2 = 2Fe + 3H2O Fe2O8 + 3CO - 2Fe + 3CO2. T h e a d v a n t a g e of this procedure is t h a t a s p o n g y coating of metallic iron is obtained on the refractory iron oxide, with the result that the iron and the resulting magnetic oxide tend to be held together, a n d so keep t h e material open, and therefore free from back pressure t o the passage of t h e steam and water gas. In practice, to obtain a yield of 3500 cubic feet of hydrogen per hour, a b o u t 6 tons of iron ore are required. T h i s ore, both in its original form and its subsequently surface altered state, is kept at a temperature of 650 0 900° C . ; if lower than 650 0 C. the reactions b e c o m e very slow, a n d if higher t h a n 900° C. t h e material tends to frit, and become less open, thus creating resistance to t h e flow of gas a n d steam. In t h e practical working of t h e Iron Contact process, t h e process consists of three s t a g e s : — 1. Reducing. 2. Purging. 3. Oxidising. Reducing*—The reducing stage consists in passing water g a s over t h e heated oxide, thus producing a coati n g of metallic iron on the oxide. D u r i n g t h e first moment of reducing the reaction is comparatively effective, but with fewer opportunities for the gas to come into contact with unacted-upon oxide, the water g a s is less and less effectively used, a n d consequently the gas on leaving the retorts contains m o r e and more

CHEMICAL METHODS

89

jrdrogen a n d carbon monoxide as the reaction connues. T h i s variation in t h e efficiency of reduction, with pse of time, is clearly illustrated in the g r a p h , F i g . 9, hich shows the carbon monoxide a n d carbon dioxide Dntent of t h e water g a s after passing at the r a t e of DOO cubic feet p e r hour over 4*2 tons of iron oxide, sated to 750 0 C. In practice, it is found t h a t the speed of reduction is 60 56

^

^

'60

^

:«

^

i>40

i 1

Weight of Oxide =4-2 tons _ Volume of Water Gae -9000 cu ft per hour " | i i i I l I l I 1S 0 1 2 3 4 5 6 7 8 9 3D 11 1Z 13 14 15 16 17 38 Minutes FIG 9 Luch slower than the speed of oxidation, consequently, L practice, t h e duration of the various stages is :— Reducing . . . . 2 0 minutes. Purging . . 35 seconds. Oxidising . . . 9 minutes, 25 seconds. 20

„...*-

.--"""

P u r g i n g , — W h e n the reducing s t a g e is stopped, t h e itort or retorts, containing the surface reduced oxide, , or are, rilled with an atmosphere of partly altered p ater g a s ; consequently w h e n steam is t u r n e d on ydrogen is produced contaminated with the residual ater g a s ; thus impure h y d r o g e n is allowed to flow

9o

MANUFACTURE O F HYDROGEN

into some receptacle, where it is subsequently used for heating, or some other process, which will be described later. A t the end of 35 seconds the outflow of the g a s is altered, and the now comparatively pure h y d r o g e n is directed into a g a s holder, or wherever it may be r e quired. O x i d i s i n g . — T h e oxidising stage is exactly the s a m e as the purging stage, except as to the direction of o u t flow of the resulting hydrogen. In normal working the gas produced has approximately the following composition :— Per Cent, by Volume Hydrogen 97 5 Carbon dioxide 15 „ monoxide 5 Sulphuretted hydrogen '03 Nitrogen (by difference) 47 100 00 Purification of Crude H y d r o g e n . — T h e crude h y drogen is first scrubbed with water, which besides r e moving mechanically contained impurities also reduces t h e amount of carbon dioxide, as this gas is soluble in water. T h e hydrogen is then passed through boxes containing slaked lime, where both the carbon dioxide a n d sulphuretted hydrogen are absorbed in accordance w i t h the following equations :— Ca(0H)2 + C0 2 = CaCO8 + H 2 0, Ca(OH), + H2S = CaS + 2 H 2 O. However, since there is no simple process of revivi-

CHEMICAL METHODS

91

ring the lime after use, it is probably better practice to ass the crude hydrogen first t h r o u g h an iron oxide box, lentical with that used in purifying water g a s ; h e r e the jlphuretted hydrogen would be absorbed, a n d t h e n t h e as would pass on to a lime box, where t h e carbon dixide would b e absorbed, as already s t a t e d ; h o w e v e r , r hichever procedure is adopted as to the purification, gas of t h e following a p p r o x i m a t e composition is btained:— Hydrogen Carbon dioxide „ monoxide Sulphuretted hydrogen Nitrogen (by difference)

. . . . .

.

. .

.99-0 ml . -5 trace "5 IOO'O

Secondary Chemical R e a c t i o n s . — T h e fundamental lemical reactions, whereby h y d r o g e n is p r o d u c e d b y le use of water g a s a n d steam alternately, in t h e resence of iron oxide, h a v e now been g i v e n in conderable detail, and so far there does not a p p e a r a n y iason w h y t h e same iron ore should not b e used inefinitely ; however, there are two reasons which necestate the replacement of the ore from time to time, 'he first reason for the deterioration of the ore is purely hysical, while the second is partly chemical and partly hysical. T h e physical reason for the g r a d u a l failure f the material is d u e to t h e fact that with constant use le ore tends to b r e a k up into smaller a n d smaller pieces, IUS creating back pressure to the flow of water g a s a n d earn , consequently a condition arises from this disitegration of the ore which necessitates its replacelent.

92

M A N U F A C T U R E OF H Y D R O G E N W h e n carbon monoxide is in contact with hot metal-

lic iron, t h e following reaction slowly takes place :— Fe + 6CO - FeC8 + 3COa Such a condition arises in the I r o n Contact process towards the end of t h e reducing stage, while during the oxidising stage the following reaction slowly takes place:— 3FeC3 + 13H2O = 9CO + F e A + i3H 2 T h u s , by the continued operation of the process, there tends to b e an increasing amount of carbon monoxide in the resulting hydrogen. T h e r e are t w o methods whereby this difficulty can be dealt with : one is anticipatory, a n d consists in adding a volume of s t e a m x to t h e water gas, prior to its passage over the iron oxide, equal to a b o u t one-half t h e carbon monoxide content of the gas. This, while slightly retarding t h e speed of reduction of the oxide, prevents the absorption of carbon b y the metallic iron, formed during the reduction, a n d consequently allows of hydrogen of high purity being produced. T h e o t h e r method is intermittently employed a n d consists in occasionally passing air over the carboncontaminated iron oxide, when the following reaction takes p l a c e : — 4FeQ, + i5O a = zFeaOs + 12CO2, thus allowing after reduction a purer hydrogen to be made. H o w e v e r , this process, k n o w n as " b u r n i n g off," while undoubtedly improving the purity of t h e hydrogen subsequently produced, appears to hasten the disintegration of t h e oxide, contributing to t h e necessity for its ultimate replacement, owing to the high back pressure this physical condition produces. French patent 395132, i9o8,Dellwick-Fleischer Wassergas Ges

CHEMICAL M E T H O D S

93

T h e minute quantities of sulphuretted h y d r o g e n present in t h e crude h y d r o g e n arise from two causes, t h e first of which is sulphur in the original ore, which, during t h e oxidising stage, produces sulphuretted h y d r o gen, while the other is due to t h e small quantities of sulphuretted h y d r o g e n present in the purified w a t e r gas, which during t h e reducing stage are absorbed b y t h e iron in t h e retorts as ferrous sulphide, which is subsequently decomposed d u r i n g the oxidising stage, t h u s :— FeS + H2O = FeO + H2S, 3FeO + HaO - Fe3O4 + H 2 W i t h r e g a r d to t h e sulphuretted h y d r o g e n , which is produced merely from t h e sulphur originally contained in the ore, this decreases with t i m e ; ore which w h e n put in the retorts contained 7 5 per c e n t of sulphur, after a year in continuous use contained only 0*03 per cent. I r o n C o n t a c t P l a n t * — T h e fundamental a n d secondary chemical reactions involved in this process h a v i n g been considered, t h e r e remains only t h e plant, a n d t h e actual fuel consumption per 1000 cubic feet of h y d r o g e n to b e described. T h e Iron Contact plant is commercially manufactured in two distinct types :— 1. T h e Multi-Retort t y p e . 2. T h e Single R e t o r t type. Fig. 10 shows a purely diagrammatic a r r a n g e ment of a multi-retort generator. T h e retorts a r e externally h e a t e d b y means of a g a s producer incorporated in the retort bench. T h e even h e a t i n g of the retorts is secured by t h e use of refractory baffles (not s h o w n ) a n d by the admission of air for the proper combustion of t h e producer g a s a t different points.

94

M A N U F A C T U R E OF HYDROGEN

T h e retorts are a r r a n g e d so that either blue w a t e r g a s or steam can b e passed through them by t h e operation of t h e valves A a n d B. D u r i n g the reducing stage t h e valves A a n d D are open, and B and C s h u t ; thus t h e reducing g a s passes through the oxide, a n d since in practice t h e whole of the carbon monoxide and hydrogen in t h e water g a s is not used up in its passage through t h e retorts, it is passed ^Blue Water Gas Inlet

Steamlnlet

FIG

IO.

back outside of them, giving up its remaining heat, and consequently contributing to the external heating. On t h e reducing stage being complete, the valves A and D are closed, and B and C opened ; steam passes through t h e retorts, a n d hydrogen issues past t h e valve C to the water seal, a n d thence to scrubbers and purifiers, a n d finally to t h e gasholder. W h e n high purity hydrogen is required, on the reducing stage being complete, the valve A is first closed, a n d then t h e valve B t u r n e d on, allowing the hydrogen

CHEMICAL

METHODS

95

•st m a d e to pass, t o g e t h e r with t h e residual g a s , in e retorts via the valve D . W h e n this p u r g i n g h a s mtinued for a b o u t half a minute, C is o p e n e d a n d D Dsed, t h e h y d r o g e n p r o d u c e d p a s s i n g via t h e w a t e r al ultimately to the gasholder. Fig. I I s h o w s a d i a g r a m of a single r e t o r t plant

FIG

II.

ten from Messerschmitt's specification, c o n t a i n e d in lghsh p a t e n t N o . 18942, 1913. T h i s p l a n t is circular in plan, a n d consists essentially two cast-iron cylinders (19) a n d (20), t h e first of lich is supported on its b a s e a n d free t o e x p a n d uptrds, while the other is h u n g from a flange at its top, d is free to e x p a n d d o w n w a r d s T h e a n n u l a r space

96

MANUFACTURE OF H Y D R O G E N

(3) between the two cylinders is filled with suitable iron ore, while t h e circular space inside t h e smaller cylinder (19) is filled with a checker w o r k of refractory brick (8). T h e plant is operated b y first h e a t i n g t h e refractory bricks (8) b y means of water g a s a n d air, admitted through pipes (15) a n d (16), t h e products of combustion g o i n g out to a chimney by the pipe (18). T h e heating of the checker work is communicated by conduction to t h e ore mass (3) ; w h e n this is at a suitable temperature (about 750° C.) the gas supply (15) is shut a n d water g a s enters by the pipe (10), passing up through the ore and reducing it in accordance with t h e equations already given. W h e n t h e reducing g a s reaches the top of the annular space (3) it mixes with air entering by the pipe (16) and t h e unoxidised portion (the amount of which varies, as has been shown in t h e graph, Fig. 9) burns, heating u p t h e brick work, and finally passing away to t h e chimney by the pipe

(18). W h e n reduction is complete (after about twenty minutes) pipes (16) and (10) are closed, and steam is admitted through t h e pipe (17), which passes upwards through the checker work (8) becoming superheated, a n d then down through t h e contact mass (3), where it is decomposed in accordance with t h e equations already given, producing hydrogen, which passes out b y t h e pipe (12), through a water seal, a n d t h e n c e to a g a s holder. W h e r e very pure hydrogen is required, a p u r g i n g period can be introduced b y a d o p t i n g the following procedure :— W h e n reduction is complete, pipes (18) a n d (16) are closed, but pipe (10) is left open, a n d (12) still remains closed.

CHEMICAL METHODS

97

O n the admission of steam by t h e p i p e (17) hydrogen generated in the reaction space (3), which, together h the residual water gas, is forced back into t h e ter gas m a i n ( i o ) , thus t e n d i n g to increase t h e irogen content of t h e w a t e r g a s in t h e gasholder. After t h e lapse of sufficient t i m e (about half a nute) pipe (12) is opened a n d (10) shut, t h e hydrogen >sequently produced p a s s i n g via t h e water seal to • hydrogen holder. After t h e ore h a s originally been ited by m e a n s of water g a s a n d air, admitted b y ies (15) a n d (16), the h e a t can b e maintained entirely the combustion of t h e unoxidised water gas, d u r i n g • reducing stage, by the admission of air by the pipe " Burning off" can b e accomplished by the admisn. of air by the pipe (11), the products passing out b y pipe (18). T h e top of the plant is fitted with four ighted valves, o n e of which is s h o w n at (14). The :sserschmitt plant is not in commercial employment this country, b u t it is considerably used b o t h in rmany a n d in the U n i t e d States, w h e r e the standard t contains about 5 t o n s of iron ore, with a production Dver 3000 cubic feet per hour. Fuel C o n s u m p t i o n * — I n the multi-retort type of nt, the consumption of w a t e r g a s is about 2*5 cubic t per cubic foot of h y d r o g e n produced, while in t h e gle retort type, where t h e water g a s is employed h for reduction and heating, t h e consumption is >ut 3'5 per cubic foot of h y d r o g e n produced In h type of plant, if t h e s a m e kind of coke is used, h for t h e production of water g a s a n d for all heating, luding steam raising, b o t h for t h e process and for its 7

98

M A N U F A C T U R E OF HYDROGEN

auxiliary machinery, such as blowers, feed pumps, e t c , t h e hydrogen yield from each is a b o u t : — 6500-7000 cubic feet of h y d r o g e n per ton of average soft coke. Relative A d v a n t a g e s of the Multi* and Single Retort Plants*—While in fuel consumption there is little to choose between the two plants, there is undoubtedly less complication in t h e single retort p l a n t than in the multi, owing to the fewer joints, etc., which are at high temperature. A n o t h e r a d v a n t a g e in the single retort type lies in the fact that fuel is consumed at two points only :— 1. F o r the production of steam, for t h e process and auxiliary machinery. 2. F o r the production of the necessary water gas. In the multi-retort type, there is also fuel required for the supply of t h e producer, which heats the retort b e n c h ; however, this additional complication can be eliminated by h e a t i n g the retorts externally by means of water gas, a procedure which is a d o p t e d in at least one commercial h y d r o g e n plant. W i t h the gradual failure of the retorts themselves from their oxidation by t h e steam, the advantage again lies with the single r e t o r t type, as it is a simpler job to draw the cast-iron liners, and replace them, than it is to replace the individual retorts a n d m a k e the various pipe joints. T o sum up, while in chemical efficiency there is little to choose b e t w e e n the two types, the advantage on t h e whole appears to lie with t h e single retort type, on account of its greater simplicity of repair. T h e following patents with regard to this process are in existence :—

CHEMICAL M E T H O D S Oettli. Betou. Lewes. Hills & L a n e . Elworthy. Vignon. L a n e & Monteux. Dellwick & Fleischer. Lane. Caro. Strache. Messerschmitt. a

Lane.

English

jj U.S. French

16759. 75i8. 20752. 10356. 778182. 373*7*' 386991

M English

395132 I759I11878.

German

249269 2537O5971206. 12117. 263390 263391. 268062. 1028366. 1040218.

US. English German

US

II

Badische Anilin und S o d a Fabrik. French Messerschmitt.

Badische Anilin und S o d a Fabrik. Badische Anilin und S o d a Fabrik.

99 1885. 1887. 1890. 1903. 1904. 1907. 1908. 1908. 1909. 1910. 1910. 1910. 191c. 1912. 1912 1912. 1912. 1912. 1912.

1912.

English

440780. 461480. 461623. 461624. 18942.

19131913 19131913.

French

453077-

1913

459918.

1913.

ioo

MANUFACTURE OF HYDROGEN

Lane. U.S. patent Berlin A n h a l t i s c h e Maschinenbau. E n g l i s h ,, Pintoch. French „ Berlin Anhaltische Maschinenbau English „

1078686.

1913.

28390 466739.

1913. 1913.

6155

1914

W i t h B a r i u m S u l p h i d e . — I n t h e previous process which was considered, steam was decomposed by means of spongy i r o n ; in t h e present process, instead of iron, barium sulphide is used. If s t e a m is passed over barium sulphide h e a t e d to a bright red heat, the following reaction takes place :— BaS + 4H 2 O - BaSO4 + 4H 2 . T h e barium sulphate p r o d u c e d m a y b e reduced by heating with coke t o barium sulphide in accordance with the following equation :— BaSO4 + C = BaS + 4CO. T h e barium sulphide can b e e m p l o y e d for the g e n e r a t i o n of fresh h y d r o g e n a n d t h e carbon monoxide can be used for s u p p l y i n g a portion of t h e heat which is required for the process. T h e process is protected b y F r e n c h p a t e n t 361866, 1905, in t h e n a m e of Lahousse. A s o m e w h a t similar process to t h e L a h o u s s e has been protected by F r e n c h p a t e n t 447688, 1912, in the names of Teissier a n d Chaillaux. In this process barium sulphate is h e a t e d with m a n g a n o u s oxide, when the following reaction t a k e s place .— BaSO4 + 4M11O = BaS + 4MnO2. T h e resulting m i x t u r e of b a r i u m sulphide a n d m a n -

CHEMICAL METHODS

101

ganese dioxide is t h e n raised to a w h i t e heat, w h e n the following reaction takes place •-— BaS + 4MnO2 = BaS + 4MnO + 2O2 W h e n the is passed over ganous oxide, cordance with

reaction is complete, s t e a m u n d e r p r e s s u r e t h e mixture of b a r i u m sulphide a n d m a n with t h e production of h y d r o g e n , in acthe following equation :—

BaS + MnO + 4H 2 O = BaSO4 + MnO + 4H 2 . T h e process is t h e n ready to b e s t a r t e d again. W h e t h e r it will h a v e a considerable commercial application remains y e t to b e proved. THE

BADISCHE CATALYTIC

PROCESS

U s i n g a Catalytic A g e n t . — I n t h e processes so far described for t h e production of h y d r o g e n from s t e a m , the steam has b e e n decomposed b y t h e action of s o m e solid which itself u n d e r g o e s a distinct chemical c h a n g e requiring t r e a t m e n t to b r i n g it back into a form in which it can be a g a i n used for t h e production of h y d r o g e n . In the process a b o u t to b e described t h e s t e a m is d e composed by virtue of a catalytic a g e n t which itself undergoes n o p e r m a n e n t c h a n g e . T h i s process, which is protected b y p a t e n t s ( e n u m e r ated at t h e e n d of this n o t e ) by t h e Badische Anilin und Soda F a b r i k Gesellschaft, consists of t h e following stages:— First, Blue W a t e r G a s is p r e p a r e d in a n ordinary producer a n d purified from suspended m a t t e r b y m e a n s Df a scrubber ; t h e n into this clean w a t e r g a s steam is introduced a n d t h e mixture p a s s e d o v e r a catalytic naterial, w h e r e t h e following reaction t a k e s place :— Water gas H a + CO + H 2 O - 2H2 + CO2.

102

MANUFACTURE OF HYDROGEN

Thus it is seen that the carbon monoxide contained in the blue gas is oxidised by the steam, which itself is decomposed with the production of hydrogen. Now carbon dioxide is readily soluble in water, consequently the product of the reaction is passed under pressure through water, where it is absorbed, leaving a comparatively pure hydrogen. Starting with blue water gas, which may be roughly taken as being composed of 50 per cent, hydrogen and 50 per cent, carbon monoxide, the composition of the gas, after the introduction of the steam and passage over the catalyst, is approximately as follows :— Per Cent, by Volume. Hydrogen . 65 Carbon dioxide . 30 „ monoxide . . 1*2-1 "8 Nitrogen . . . . . 2*5-4 The bulk of the carbon dioxide is absorbed by means of water, but if the hydrogen is required for aeronautical purposes, the gas is finally passed through either a caustic soda solution or over lime. Traces of carbon monoxide are removed by passing the gas under pressure through ammoniacal cuprous chloride solution. As a result of these final purifications a gas is obtained of approximately the following composition :— Per Cent, by Volume Hydrogen 97 Nitrogen . . .2*7 Carbon dioxide . . — ,, monoxide . . '3 In practice it was stated that in commercial ironcontact plants the consumption of blue gas was from

CHEMICAL M E T H O D S

103

'3 t 0 3"5 cubic feet per cubic foot of h y d r o g e n ultimately produced. In t h e method which has just been described t h e Dnsumption of blue g a s is about i"i to 1*3 cubic feet er cubic foot of h y d r o g e n , or assuming a consumption 35 lb. of coke per 1000 cubic feet of water g a s proiiced, t h e h y d r o g e n yield is 49,000 to 58,000 cubic feetj er ton of soft coke. In the operation of this process, the blue water gas, )gether with a requisite a m o u n t of steam, is passed over le catalytic material at a temperature of 400° to 500° C. ince t h e oxidation of t h e carbon m o n o x i d e is exotherlic, after the reaction chamber is heated to t h e temerature of 400° to 500° C , no more heat n e e d be applied from external sources. T h e chemical composition of the catalyst a p p e a r s to e somewhat variable, but, as in the case of the catalyst sed in the fat-hardening industry, its physical condition Efects t h e efficiency of the process. I n the p a t e n t s pro:cting this process a variety of methods a r e described >r the preparation of t h e catalyst, but t h e following lay be given as r e p r e s e n t a t i v e . — " Dissolve a mixture of 40 parts by weight of ferric itrate, 5 parts of nickel nitrate, a n d 5 parts of chromium itrate, all free from chlorine Precipitate with potasum carbonate, filter, wash, form into masses a n d dry." T h e quantity of nickel can be varied, for example, etween t h e limits of 10 parts and three parts of nickel itrate T h i s contact mass is used at a t e m p e r a t u r e of 400° 5 5OO C. A s is t r u e of all catalysers, the above a p p e a r s to e subject to " poisoning," the chief poisoners being

104

MANUFACTURE OF HYDROGEN

chlorine, bromine, iodine, phosphorus, arsenic, boron, and silicon in some forms ; hence in the preparation of the catalyser, as well as in the manufacture of the water gas, precautions must be taken to prevent the presence of these " poisons ". The mixture of blue water gas and steam is passed over the catalyst at approximately atmospheric pressure. On leaving the reaction chamber after passage through suitable regenerators, the gas is compressed to a pressure of 30 atmospheres (441 lb. per sq. inch) and then passes to the bottom of a high tower packed with flints, in which it meets a downward flow of water which absorbs the carbon dioxide, and also the sulphuretted hydrogen which is present in the gas to a very slight extent. The energy in the water leaving the tower is recovered in the form of power by letting it impinge on a Pelton wheel. The removal of the 2 per cent, of carbon monoxide is accomplished in a similar tower , only in this case a solution of ammoniacal solution of cuprous chloride is used instead of water. Given an adequate size of tower and volume of the cuprous chloride solution, the pressure at which the gas is introduced into the tower may be as low as 30 atmospheres (441 lb. per sq inch); however, where the gas is to be used for making synthetic ammonia it is usual to compress it to 200 atmospheres (2940 lb. per sq. inch) before passing it through the carbon monoxide absorbing tower. The use of this high pressure is ultimately necessary in the ammonia process and it reduces the size of the tower which has to be employed. The cuprous chloride solution, after leaving the absorption tower, is passed through a small vessel, in which it gives up its carbon monoxide. The gas evolved from

CHEMICAL METHODS

105

e solution is passed t h r o u g h water in o r d e r to p r e v e n t y ammonia loss. T h e a d v a n t a g e s of this process o v e r t h e I r o n C o n t a c t ocess are :— 1. It is continuous in operation. 2. It is more economical. 3. T h e whole of t h e sulphur c o m p o u n d s in the b l u e s are converted into sulphuretted h y d r o g e n a n d a r e mpletely absorbed b y t h e high p r e s s u r e w a t e r scrubT h e disadvantages as c o m p a r e d with t h e I r o n Con:t process a r e :— 1. G r e a t e r complexity of operation 2. F o r aeronautical purposes t h e p e r c e n t a g e of nitron is high. Description of Plant, — T h e d i a g r a m ( F i g . 12) ows the m e t h o d of operation of this process. Steam ters by the pipe A a n d mixes with blue w a t e r g a s tering b y t h e pipe B, t h e speed of flow of each b e i n g dicated o n separate g a u g e s a s shown. T h e m i x t u r e of iam and g a s p a s s e s ' t h r o u g h the r e g e n e r a t o r or supera t e r C a n d flows, as indicated b y t h e arrows, over fractory tubes, through which t h e h o t products of the action a r e flowing in t h e reverse direction. T h e h e a t e d xed gases flow via the p i p e F into t h e g e n e r a t o r and, :reasing in t e m p e r a t u r e , pass t h r o u g h t h e catalytic iterial, w h e r e reaction takes place with t h e evolution heat T h e y then flow a s indicated by t h e arrows ck t h r o u g h t h e regenerator, parting with their heat to e incoming m i x t u r e of blue water g a s and steam. Thermo-couples a r e placed in t h e contact mass so at its t e m p e r a t u r e may b e controlled by increasing or

MANUFACTURE OF H Y D R O G E N

io6

r e d u c i n g t h e q u a n t i t y of s t e a m in t h e i n c o m i n g g a s e o u s mixture. The

whole apparatus

is v e r y

effectively

lagged

to

reduce the heat losses to a minimum. To Milli -voltmeter

Thermo-couples for Temperatures —between 450 & 500'C Superheater or Regenerator Contact Material

WaterGas Inlet Orifice Gauge

Diatomite Brick Cover throughout, bound with Painted Cloth

Hydrogen and C02 Outlet

To Mi Hivoltmeter

FIG

i2.

T h e following p a t e n t s o n this process b y the B a d i s c h e A n a l i n a n d S o d a F a b r i k a r e in e x i s t e n c e : — English patent

French

„

27117.

1912.

27963.

1913.

459918.

1913.

CHEMICAL METHODS

iojr

T h e following p a t e n t s relating to the g e n e r a l chemi1 reaction in this process h a v e been taken o u t : — sssie du Motay. ,, ,, ,,

patent 229338. 229339. M IJ 229340. >> M English „ 22340. French ,, 355324 U.S. 854I57-

1880. 1880. 1880. 1891. 1905. 1907.

„ ,,

1909. 1910.

U . S.

i) >> J> illman & E l worthy. [worthy. His & Eldred. lem. F a b r i k Greisheim British Elektron German aber & Muller.

2523. 237283.

- U s i n g Lime.—If carbon monoxide together with :am is p a s s e d over lime a t a t e m p e r a t u r e of a b o u t o° C , t h e m o n o x i d e is a b s o r b e d with the formation of lcium carbonate, a n d h y d r o g e n is evolved in accordce with t h e following e q u a t i o n :— CaO + H 2 0 + CO = CaCO3 + H 2 . Investigation of the a b o v e reaction by Levi & P i v a x iicates t h a t t h e chemical c h a n g e takes place in two iges, in t h e first of which calcium formate is produced, lile in t h e second it is d e c o m p o s e d with t h e evolution hydrogen and carbon m o n o x i d e as is shown in the [lowing e q u a t i o n s . — (1) CaO + H 2 0 + 2CO = Ca(COOH)2j (2) Ca(COOH)2 - CaCO3 + CO + H a . It can, however, b e s e e n from these equations t h a t latever volume of carbon monoxide is p e r m a n e n t l y isorbed, an equal volume of hydrogen is evolved. Now, since blue water g a s is, roughly speaking, half r drogen a n d half carbon monoxide, by passing it over lc

'Journ Soc. Chem Ind," 1914, 310

108

MANUFACTURE OF HYDROGEN

lime under the conditions stated above, a gas equal in volume to the water gas, but wholly composed of hydrogen, is produced. In the commercial operation of this process, the lime is contained in a tower, which is initially heated to a temperature of about 5000 C , but since the absorption of the carbon monoxide is exothermic, after the process has started, no further heating is required. When the lime has become sluggish in its action, by the formation of a crust of calcium carbonate, the blue gas is diverted through a similar tower, while the contents of the original tower are heated m situ to a temperature sufficiently great to decompose the calcium carbonate, and thus the tower is again ready for use. This process is protected by the following patents :— Chem. Fabrik Greisheim Elektron. British patent 2523. 1909. Dieffenbach & Moldenhauer. „ „ 8734. 1910 Ellenberger. U.S. „ 989955 1912. Chem. Fabrik Greisheim Elektron. British „ 13049. 1912. (4) Miscellaneous Methods of Making Hydrogen* THE CARBONIUM GESELLSCHAFT PROCESS.

From Acetylene.—If acetylene is compressed and then subjected to an electric spark it undergoes dissociation into its elements. Acetylene can be most easily generated from the action of water on calcium carbide, thus :— CaC2 + 2H2O - C2H2 + Ca(OH)2.

CHEMICAL M E T H O D S

109

T h e acetylene produced is then compressed in very trong cylinders and subjected to an electric spark, when tie following reaction takes place :— C2H2 = Q + H 3 If the acetylene is produced from calcium carbide, pproximately 178 lb. of calcium carbide a n d 100 lb. of /ater are theoretically required to produce 1000 cubic set of h y d r o g e n at 40° F . and 30 inches barometer, /hile, at t h e s a m e time, 39 lb. of carbon in t h e form of imp-black is produced. This process is employed by t h e Carbonium Gesellchaft of F r e d e r i c k s h a v e n for the inflation of airships, irhile the carbon produced is sold a n d is used in m a k i n g irinters 1 ink. A s u s e d by this company, the g a s is ompressed to a b o u t 2 atmospheres (29*4 lb. p e r sq. nch) prior to sparking. T h e following patent, relative to this process, is in xistence:— Bosch. G e r m a n patent 268291.

1911.

T h e decomposition of acetylene m a y b e obtained b y leating ; thus, if acetylene derived from calcium carbide »r some other source is passed through a t u b e h e a t e d to bout 500° C. it decomposes, in accordance with t h e ollowing equation, with the evolution of h e a t : — CgHg = Ca + Hg. Such is t h e quantity of heat liberated t h a t after t h e emperature of t h e t u b e has been raised until decom)osition of the acetylene begins no further external heat s required. T h e carbon p r o d u c e d may be chiefly r e m o v e d b y iltering t h e gas, while t h e residue which still remains nay be removed b y scrubbing with water.

HO

M A N U F A C T U R E OF H Y D R O G E N This process is protected by t h e following p a t e n t s :— Picet. French p a t e n t English German

„ „

421838. 421839. 24256. 255733.

1910. — 1910. 1912.

F r o m Hydrocarbon Oils*—While the decomposition of acetylene is attended with the evolution of heat, most other hydrocarbon gases absorb heat when they decompose into their constituents; consequently, to produce hydrogen from other hydrocarbon g a s or volatilised hydrocarbon oils, it is necessary to supply h e a t during t h e process. T h e necessary heat may be supplied by passing t h e hydrocarbon g a s or vaporised oil t h r o u g h a t u b e of r e fractory material which is externally heated, or t h e ingenious Rincker-Wolter method may b e used. I n this process t h e rough principle is to use a g e n e r a t o r similar to a " blue-gas " generator filled with coke. B y m e a n s of a n air blast t h e t e m p e r a t u r e of the coke is raised to about 1200° C , then, when this t e m p e r a t u r e h a s b e e n reached, the air supply is stopped and crude oil is blown in a t the bottom of the h o t coke. T h e oil is immediately volatilised, a n d passes by expansion u p through t h e h o t coke, during which process it is decomposed into hydrogen and carbon, t h e latter to a large extent attaching itself to the coke a n d becoming a source of fuel. W h e n the t e m p e r a t u r e h a s fallen too low t o effect a complete decomposition of t h e crude oil the injection is stopped and t h e t e m p e r a t u r e of t h e coke again raised by m e a n s of t h e air b l a s t T h e g a s produced b y this process is stated to h a v e t h e following composition :—

CHEMICAL

METHODS

in Per Cent, by Volume 96*0 1*3

Hydrogen . Nitrogen Carbon monoxide

T h e cost of h y d r o g e n m a d e by this process must lepend almost entirely on t h e price of crude o i l ; it is tated that, with crude oil at twopence a gallon, hydrogen can b e produced for about seven shillings a t h o u s a n d ubic feet. 1 T h e following patents deal with this o r s o m e w h a t imilar p r o c e s s e s : — xeisenberger. lincker & W o l t e r . Jerlin Anhaltische /[aschinenbau A. G

). Ellis.

F r e n c h patent ,, ,,

German French English U.S.

„ „ „ „

361462. 391867. 391868.

1905. r9o8. 1908.

267944. 466040. 2054. 1092903.

1913. 1913. 1914 1914.

F r o m S t a r c h . — W h e n yeast, which is a living rganism, is introduced into a solution containing jgar, fermentation results with t h e production of [cohol a n d carbon dioxide, which m a y b e e x p r e s s e d in n equation as follows :— A n analogous process to the above is employed )mmercially for t h e production of acetone a n d butyl cohol. W h e n what is k n o w n as t h e F e r n b a c h bacillus is inoduced into starch jelly, »(C 6 H I O O 5 ), acetone, ( C H 3 ) 2 C O , * Ellis, "The Hydrogenation of Oils" (Constable).

112

MANUFACTURE OF HYDROGEN

and butyl alcohol, CH3CH3CHaCH3OH, are produced ; at the same time there is an evolution of gas which is chiefly hydrogen and carbon dioxide, but it also contains a little nitrogen. As there is a great demand for acetone in certain localities, large quantities of hydrogen in this impure form are being produced as a by-product. If the carbon dioxide is absorbed by passing the gas under pressure through water (Bedford method), a gas is produced of about the following composition •— Hydrogen . . . 94fo Nitrogen . . . . 6'o The above is not a process for the production of hydrqgen, but the hydrogen produced may be frequently usefully employed if there is a local demand for it.

CHAPTER

IV.

THE MANUFACTURE OF HYDROGEN. CHEMICO-PHYSICAL

METHODS.

Lindc*Frank'Caro P r o c e s s * — T h e m o s t i m p o r t a n t ethod of producing hydrogen, in which chemical a n d lysical m e t h o d s are employed, is one in which t h e emical process results in t h e production of blue w a t e r s, and t h e physical in t h e separation of t h e chemical mpounds (chiefly carbon monoxide) from t h e h y d r o g e n liquefaction. 'HE SEPARATION OF H Y D R O G E N FROM B L U E

WATER

GAS.

T h e separation of mixed gases by liquefaction is subject of very great complexity a n d o n e into the ricacies of which it is not intended to g o in this work, t for further information the attention of t h e reader directed to t h e t w o following books :— " T h e Mechanical Production of Cold," by J. A. ving. ( C a m b r i d g e University Press.) " Liquid Air, O x y g e n , Nitrogen," by G. Claude. & A. Churchill.) All gases a r e capable of being liquefied, but in t h e e of h y d r o g e n and h e l i u m l t h e difficulties a r e so g r e a t 1

This gas, which was the last to resist liquefaction, was first efied on ioth July, 1908, by Professor Kamerhngh-Onnes. (113) 8

H4

MANUFACTURE OF HYDROGEN

t h a t it is only b y m e a n s of t h e highest technical skill a n d very costly a p p a r a t u s t h a t this can b e accomplished. Originally it was considered that to obtain a g a s in t h e liquid state t h e sole necessity was p r e s s u r e ; however, all g a s e s possess a physical property k n o w n as critical temperature} T h e critical t e m p e r a t u r e of a g a s is t h a t t e m p e r a t u r e a b o v e which the g a s cannot b e liquefied, h o w e v e r g r e a t the pressure to which it is subjected. Prior to the realisation of the existence of t h e critical temperature, chemists a n d physicists subjected various gases to enormous pressures in t h e hope of causing t h e m to liquefy, and, t h o u g h they failed, it is interesting to observe from t h e accounts of their experiments that t h e compressed gas attained a density g r e a t e r than t h e s a m e g a s in t h e liquid state at atmospheric pressure. Besides critical t e m p e r a t u r e , a n o t h e r term requires definition, that is, criticalpressure\ which is the pressure which must b e exerted on a g a s cooled to its critical t e m p e r a t u r e to p r o d u c e liquefaction. T h e following t a b l e of critical t e m p e r a t u r e s a n d pressures of the constituents of blue water g a s is interesti n g :— Gas

"

Hydrogen . . Carbon monoxide „ dioxide. Nitrogen Methane Sulphuretted hydrogen Oxygen 1

Template

Cnfcal Pressure.

- 2 34*0° C. — 136 o + 3° 9 2 - 146 o - 82*0 + 100 o - 118-0

294 lb. per sq in 492 „ "3* „ 485 ,, 820 ,, 1304 „ 735

Discovered by Andrews, 1863

CHEMICO-PHYSICAL METHODS

115

F r o m this t a b l e it is seen that t h e critical temperaure of h y d r o g e n is 88° C. below t h a t of its nearest .ssociate, n i t r o g e n ; consequently, if t h e blue water g a s vere cooled to — 146 0 C. while subjected to a pressure of o m e w h e r e a b o u t 500 lb. per s q u a r e inch, the whole of he gas, with t h e exception of t h e hydrogen, would iquefy; t h e r e f o r e , separation of a liquid from a g a s >eing a simple m a t t e r , t h e problem of the production of lydrogen from b l u e water g a s would be solved. If a g a s is c o o l e d below its critical t e m p e r a t u r e t h e >ressure which h a s to b e applied to p r o d u c e liquefaction 3 much r e d u c e d . N o w , since t h e boiling point of a [quid a n d the c o n d e n s i n g point of a vapour u n d e r the a m e pressure a r e t h e s a m e temperature, t h e boiling ioints of t h e v a r i o u s g a s e s contained in blue water g a s an b e studied w i t h a d v a n t a g e . BOILING P O I N T S

OF SOME PHERIC

Gas Hydrogen . . . Carbon monoxide . ,, dioxide . Nitrogen . Methane . . . . Sulphuretted hydrogen Oxygen

L I Q U I D G A S E S AT A T M O S PRESSURE.

.

.

.

. . . . .

Boiling Point. - 253*0° C. - 190 o - 8o#o - 195*5 . - 164 7 . - 61 "6 - 182-5 .

Therefore, it can b e seen that, if blue water g a s rere cooled a t a t m o s p h e r i c pressure to a temperature elow - 195 '5° C , the whole of t h e constituents of t h e as, other t h a n h y d r o g e n , would b e liquefied, a n d consquently a n e a s y separation could b e made. T o s u m m a r i s e , t h e liquefaction of the constituents of

n6

M A N U F A C T U R E OF H Y D R O G E N

blue water gas, other t h a n h y d r o g e n , can b e accomplished either b y a m o d e r a t e d e g r e e of cooling a n d t h e application of pressure, or by intense cooling a n d no application of pressure. PRODUCTION OF HYDROGEN FROM WATER GAS BY THE LINDE PROCESS

H2S COa Sulphuretted Carbon Hydrogen. Dioxide. •5% 3-5%

CH 4 Meth

-47O

CO N2 Carbon ^ 6 Monoxide. 39 67. 4°/.

H2 Hydrogen. J

6

5»7.

Oxide Boxes. H2S partly absorbed. Compressor. Pressure Water Scrubber

20 Atmospheres (294 lb / Q " ) . COa & HaS almost entirely absorbed.

Caustic Soda Scrubber (NaOH 307J, last traces CO2 & H2S absorbed Ammonia Cooler. Water Vapour condensed, Temperature reduced to - 25° C. Linde Still. Final Temperature - 2050 C. Methane, Carbon Monoxide & Nitrogen liquified.

Gaseous Hydrogen Ha 977O by Volume CO 2„ „ N2 1„ „

Methane, Carbon Monoxide & Nitrogen. On evaporation to gas engine operating the whole plant.

In t h e L i n d e - F r a n k - C a r o process t h e b l u e w a t e r g a s is compressed to 20 atmospheres, a n d under pressure it is passed t h r o u g h water, which r e m o v e s

CHEMICO-PHYSICAL M E T H O D S

117

practically t h e whole of the carbon dioxide a n d sulphuretted h y d r o g e n . It is t h e n passed t h r o u g h t u b e s :ontaining caustic soda, which r e m o v e s t h e r e m a i n i n g traces of c a r b o n dioxide, sulphuretted h y d r o g e n , a n d water. T h e g a s thus purified from these constituents n o w passes to t h e separator proper ; the r e a s o n for this p r e liminary removal of s o m e of the constituents of t h e blue water g a s is d u e to t h e fact that, in t h e separation of t h e zarbon monoxide a n d nitrogen, such low t e m p e r a t u r e s have to b e reached t h a t t h e water, sulphuretted h y d r o g e n , i n d carbon dioxide would b e in t h e solid state, a n d would, therefore, tend to block up t h e pipes of t h e a p paratus. T h e a p p a r a t u s operates in t h e following manner, which will b e more readily understood by consulting t h e diagram ( F i g . 1 3 ) : — T h e purified w a t e r g a s passes d o w n t h e t u b e A, through coils in the vessel B, which is filled with liquid carbon monoxide boiling at a t m o s p h e r i c p r e s s u r e ( — 190° C ) . N o w , since the water gas is u n d e r pressure and is p a s s i n g t h r o u g h coils cooled t o its t e m p e r a ture of liquefaction a t atmospheric pressure, t h e b u l k of it liquefies (theoretically m o r e g a s should b e liquefied in the tubes t h a n is e v a p o r a t e d outside t h e m ) . T h e gas, containing a considerable a m o u n t of liquid saturated with hydrogen, passes into t h e vessel C, which is surrounded by liquid nitrogen boiling u n d e r reduced pressure g i v i n g a t e m p e r a t u r e of — 205° C. H e r e t h e remainder of the carbon m o n o x i d e a n d t h e nitrogen originally contained in t h e g a s liquefies a n d hydrogen of approximately the following composition passes u p t h e t u b e E :—

US

MANUFACTURE OF

HYDROGEN

ki

s ! _AJVaterGasIn/et A **i ""*

Carbon Monoxide Outlet

=njU

D Nitrogen Outlet D. u

Liquid Nitrogen Inlet

°

o

o

o

o

o

o

o

o

o

0

F I G

13 — D i a g r a m

s h o w i n g

L i n d e - F r a n k - C a r o

Process.

Per by 1

H y d r o g e n

Nitrogen C a r b o n

.

m o n o x i d e

.

h y d r o g e n

sulphur

W h e n

t h e

Messrs

.

97*0 -

i

O r g a n i c

supplied

.

.

Sulphuretted

1

.

Cent,

Volume

A r d o l

t h e author

.

.

c o m p o u n d s

g a s

i s

r e q u i r e d

of Selby, with

this

. .

. .

t o

o f

Yorks, w h o e m p l o y information

.

nil.

.

b e

h i g h

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2 0

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p u r i t y

this process,

it

is

kindly

CHEMICO-PHYSICAL M E T H O D S

119

lbsequently passed over calcium carbide or s o d a lime, le reactions of which processes will b e dealt with later. D u r i n g t h e operation of the process liquid c a r b o n lonoxide a n d s o m e liquid n i t r o g e n collects in C. Tow this liquid g a s is u n d e r pressure a n d can therefore 2 run b a c k t h r o u g h t h e tube F via t h e cock G Lto t h e vessel B ; b u t B is at a t m o s p h e r i c pressure, Dnsequently some of t h e liquid g a s passing t h r o u g h G ill be volatilised, with consequent fall in t e m p e r a ire of t h e remainder. T h e liquid nitrogen used in t h e vessel D is prouced in a special L i n d e machine from the a t m o s p h e r e . T h e vapour of carbon monoxide, with a little itrogen a n d h y d r o g e n , from t h e vessel B is used to ool the incoming purified water gas, as is shown in t h e iagram. T h i s m e t h o d of using t h e cold s e p a r a t e d ases for cooling t h e g a s g o i n g into the a p p a r a t u s is ;rmed " Cooling by counter-current heat exchangers," nd it m a y b e r e g a r d e d as the essence of efficiency in 11 low t e m p e r a t u r e g a s separation. T h e consumption of power in this process is theoetically v e r y small, as much carbon monoxide should >e liquefied in t h e coil in the vessel B as is volatilised >utside it (this is theoretically t r u e w h e n t h e pressure >f the g a s passing t h r o u g h the coil is atmospheric) -lowever, in practice, the necessity for p o w e r c o n s u m p 1011 arises from t h e fact t h a t liquid n i t r o g e n must )e continuously supplied to the vessel D in order to jrevent t h e t e m p e r a t u r e of the plant rising from exernal infiltration of heat, which t a k e s place in spite of he most effective lagging. In practice, t h e p o w e r obtained from using t h e sepa*ated carbon monoxide as a fuel is sufficient to run all

120

MANUFACTURE OF HYDROGEN

the machines necessary for the operation of a plant producing 3500 cubic feet of hydrogen or more per hour. Thus, to very roughly indicate the cost of operation of this process, neglecting all depreciation, etc., it may be said that, on a plant of the size mentioned above, unit volume of blue water gas yields "4 volume of hydrogen of about 97 per cent, purity, or, on the basis of a coke consumption of 35 lb. per 1000 cubic feet of water gas, the hydrogen yield is 25,500 cubic feet per ton of coke. Purification of Hydrogen.—Where very pure hydrogen is required it is necessary to employ chemical methods to remove the 3 per cent, of impurity, which may be done by passing the gas through heated soda lime, where the carbon monoxide is absorbed in accordance with the following equation :— 2Na0H + CO = Na2CO3 + H2, or, on the other hand, it may be passed through heated calcium carbide (over 300° C), which possesses the advantage of not only removing the carbon monoxide but also the nitrogen. The reactions taking place are indicated in the following equations :— CaCa + CO = CaO + 3C, CaC2 + N2 - CaCN2 + C. The following is given as an analysis of the gas purified by means of soda lime .— Per Cent, by Volume, Hydrogen . . . . 9 9 2-99-4 Carbon monoxide . . nil Nitrogen . . . . o*8-o 6 The following patents are in existence for the pro-

CHEMICO-PHYSICAL METHODS

121

ztion of h y d r o g e n by liquefaction m e t h o d s from blue ter g a s : — worthy. ank. aude. :s-fur Linde's E i s tnaschinen A . G . von Linde.

French patent English „ French „ >] U.S.

lemical purification— ank. French

ti

37599L

1905. 1906. 1906

4179831020102. 1020103. 1027862 1027863

1911. 1912. 1912. 1912 1912.

371814.

1906.

35532426928.

D i f f u s i o n . — T h e separation of h y d r o g e n from t h e ler constituents of blue w a t e r g a s h a s b e e n proposed, lploying diffusion for t h e purpose. G r a h a m expressed 2 law of diffusion of gases as .— " T h e relative velocities of diffusion of a n y t w o ses are inversely as the s q u a r e roots of their densities." T h a t is to say, if a m i x t u r e of t w o gases of different nsities is passed t h r o u g h a p o r o u s t u b e , e.g. unglazed rcelain, in a given time, m o r e of t h e lighter g a s would ve passed t h r o u g h t h e walls of t h e t u b e t h a n of t h e avier, or, t o t a k e a concrete example, s u p p o s e t h e ixture of g a s e s was o n e composed of equal p a r t s b y •lume of h y d r o g e n a n d o x y g e n , then, since their nsities a r e as 1 t o 16, a n d since, therefore, t h e roots their densities a r e as 1 to 4, in a g i v e n t i m e four nes as much h y d r o g e n would diffuse t h r o u g h t h e sdium a s o x y g e n . T h e densities a n d t h e s q u a r e r o o t s of the densities the constituents of blue water g a s a r e g i v e n below ;—

122

MANUFACTURE OF HYDROGEN

Hydrogen . Carbon monoxide ,, dioxide Nitrogen Methane . Sulphuretted hydrogen Oxygen

Density.

jW

i 14 22 14 8 17 16

1 3*7 47 37 28 41 4'°

From which it will be seen that, if blue gas were passed continuously through a porous tube, the gas diffusing through the tube would contain more hydrogen than the blue gas originally contained. Of course, in the successful operation of a diffusion separation it is necessary to remove the gas which diffuses through the porous medium as well as the residue which is left undiffused. The former may be done by maintaining a constant pressure by means of a suction pump, while the latter can be done by regulating the speed of flow through the diffusion tube. It is, of course, essential that the undiffused gsCs must be removed from contact with the porous medium after a certain time, as it is only a matter of time before the whole of the gas will diffuse through the medium, and thus destroy the work of separation. THE DIFFUSION MEDIUM.

The selection of the diffusion material is a subject of considerable difficulty , if the porosity of the material is too great no diffusion takes place, but the gas passes through the material without any appreciable separation taking place. Thus, if a mixture of hydrogen and oxygen is passed through a fine capillary tube, the gas

CHEMICO-PHYSICAL M E T H O D S

123

i n g will b e found to b e of the same composition as original g a s . It is interesting to note in this connection that, if 2 h y d r o g e n were first passed t h r o u g h t h e t u b e a n d 1 p u r e oxygen, in a g i v e n time m o r e h y d r o g e n by ime would pass through the t u b e t h a n oxygen. s differential rate of flow t h r o u g h tubes is called ranspiration ". If the porosity of t h e material is insufficient, t h e time lired to effect separation is unduly long. It m a y , in connection, b e mentioned that it has from t i m e to i been s u g g e s t e d that by means of diffusion it would )ossible t o separate a mixture of gases of different sities without t h e consumption of power. 1 How-, in practice this has not been found to b e the case, n order to obtain a reasonable speed of separation, fference of pressure between the two sides of t h e ision material has to b e maintained. J o u v e a n d Gautier h a v e employed a diffusion hod in o r d e r to separate h y d r o g e n from blue w a t e r and it is stated that, by a single p a s s a g e t h r o u g h a JUS partition, the p e r c e n t a g e of carbon m o n o x i d e in g a s passing through the medium was reduced from jer cent, in the original g a s to 8 per c e n t Whether process h a s been employed on a commercial scale ot known to the author, nor h a s h e a n y k n o w l e d g e 0 the a m o u n t of power required to obtain a definite ime of h y d r o g e n practically free from carbon monle. T h e following patents, in which diffusion h a s b e e n 1

It is theoretically impossible to separate a mixture of two gases DUt the consumption of power, but the theoretical requirements ilmost negligible.

i24

MANUFACTURE OF HYDROGEN

employed for separating mixed gases, have been taken out:— Jouve & Gautier. French patent 372045. 1908 Hoofnagle. U.S. „ 1056026. 1913 Separation by Centrifugal Force,—When a mass is compelled to move in a circular course a force acts on it which is a function of its mass, linear velocity, and the radius of curvature of its path, which may be expressed as— Centrifugal force = —5— is. where m = mass of the body5 v = its linear velocity, R =» the radius of curvature of its path. Therefore, since a greater force is acting on the heavier of two particles moving on the same course with the same velocity, the heavier particle will tend to move outward from its centre of rotation to a greater extent than the lighter. This principle of centrifugal force is employed industrially for many purposes, such as the separation of cream from milk, water from solid bodies, honey from the comb, etc., and it has been suggested that it might be used to separate hydrogen from blue water gas. However, though a certain amount of work has been done on this problem by Elworthy1 and Mazza,2 as far as the author knows no satisfactory results have been obtained. The special physical questions involved in the separation of gases of different densities by means of a centrifugal machine have been considered theoretically 1 2

Elworthy, English patent, 1058 rgo6. Mazza, English patent, 7421 1906

CHEMICO-PHYSICAL METHODS

125

a n u m b e r of physicists, whose conclusions a r e t h a t y high velocities must b e given t o the g a s t o obtain 7 appreciable separation ; it has b e e n s h o w n that, if a im 3 feet in diameter a n d one foot l o n g filled with a cture at 15 0 C , containing 80 per cent, of h y d r o g e n 1 20 per cent, of air, is rotated a t 20,000 revolutions minute, a condition of dynamical equilibrium will se w h e n t h e peripheral g a s a n d t h e axial g a s will re the following composition :— Hydrogen Air .

. .

.

Axial Gas. 97 8 . 2 - 2

Peripheral Gas 66§i 33-9

Since t h e density of air a n d that of carbon m o n o x i d e almost t h e s a m e (14*4 a n d 14*0) almost identical oretical results could b e obtained b y g i v i n g a similar ary motion to a mixture of 80 per cent, h y d r o g e n a n d per cent, carbon monoxide. H o w e v e r , t h e enormous ed of rotation a n d a practical m e t h o d of r e m o v i n g t h e al and peripheral gases makes this question one of the atest technical difficulty, a n d it m a y well b e t h a t t h e ver consumption to p r o d u c e a g i v e n v o l u m e of h y d r o 1 from blue w a t e r gas may b e g r e a t e r t h a n t h a t uired t o produce a n equal v o l u m e of h y d r o g e n b y ctrolysis.

CHAPTER

V.

THE MANUFACTURE OF HYDROGEN. PHYSICAL

METHODS.

E l e c t r o l y s i s . — W h e n an electric current passes through a solid conductor a magnetic field is created round t h e conductor and the conductor is h e a t e d b y the passage of t h e current, both of which effects bear a definite relationship to the m a g n i t u d e of the current passing. S o m e liquids are also conductors of electricity, e.g. m e r c u r y ; the passage of a current through such a conductor produces results identical with those produced in solid conductors. O t h e r liquids a r e also conductors, but, besides the passage of the current creating a m a g netic field a n d a heating effect, a portion of the liquid is split u p into two parts which m a y each b e a chemical element, or one or either may be a chemical group. T h u s , if two platinum plates a r e placed as shown in the diagram, one plate being connected to the positive pole of the battery and the other to the negative, then, if a s t r o n g aqueous solution of hydrochloric acid is put in the vessel containing the plates, decomposition of the liquid will take place ; hydrogen will b e given off at the negative plate or cathode, and chlorine at t h e positive or anode. If t h e solution of hydrochloric acid is replaced by o n e of caustic soda t h e caustic soda is split up b y the current (126)

PHYSICAL METHODS

127

ito oxygen, which is liberated at t h e anode, a n d metallic idium which is deposited on the c a t h o d e ; b u t since letallic sodium cannot exist in contact with water, t h e •llowing reaction t a k e s place a t t h e c a t h o d e •— 2Na + 2H2O » 2NaOH + H 2 . T h u s , b y a secondary reaction, h y d r o g e n is libered at t h e cathode, or, in other words, water is split into 3 constituents, while t h e caustic soda is reformed. N o w , let t h e caustic soda solution b e replaced by a n jueous solution of sulphuric acid. I n this case h y d r o m will b e liberated a t t h e cathode a n d t h e g r o u p SO* the anode, but t h e g r o u p S O 4 c a n n o t exist in contact ith water, as t h e following reaction takes p l a c e : — 2SO4 + 2H2O - 2H2SO4 +0^. T h u s , by a secondary reaction, oxygen is liberated the anode, or, in other words, w a t e r is split into its •nstituents while t h e sulphuric acid is reformed.

I ^

1 Electrolyte

1

FIG

Battery 14.—Electrolytic Cell.

Liquids which, under

t h e i n f l u e n c e of t h e e l e c t r i c

r r e n t , b e h a v e in t h e m a n n e r of t h e a b o v e a r e t e r m e d i l e c t r o l y t e s , " a n d t h e process w h e r e b y t h e y a r e split • is c a l l e d " E l e c t r o l y s i s ".

128

M A N U F A C T U R E OF

HYDROGEN

T h e laws relating to this decomposition of liquids by the electric current were enunciated by F a r a d a y as follows:— 1. T h e quantity of a n electrolyte d e c o m p o s e d is proportional to t h e quantity of electricity which p a s s e s . 2. T h e mass of a n y substance liberated b y a given quantity of electricity is proportional to t h e c h e m i c a l equivalent weight of t h e substance. By t h e chemical equivalent weight of a s u b s t a n c e is meant in the case of elements, t h e figure w h i c h is obtained by dividing its atomic weight b y its v a l e n c y , while in the case of compounds, it is t h e m o l e c u l a r weight divided b y t h e valency of the c o m p o u n d . However, m a n y elements h a v e more t h a n one v a l e n c y , therefore they h a v e m o r e than o n e chemical e q u i v a l e n t weight, as can be seen from the following t a b l e : —

Eleme t

»-

Hydrogen Oxygen . Gold . Tm . Phosphorus Tungsten .

. . . .

..,.„ Weigh?

ValenC

i 16 197 118 31 184

i 2 3 or 4 „ 5 „ 6 ,,

y-

Chemical Equivalent Weight, ^ T ' .

1 2 3 4

i 8 65 6 or 29-5 „ 6*02 „ 306 „

197 59 10-03 46 o

F r o m F a r a d a y ' s laws it can b e seen that, if the weight of any substance liberated by a definite c u r r e n t in a definite time is known, the theoretical w e i g h t of a n y substance which should be liberated by a definite c u r r e n t in a definite time can b e calculated, if t h e chemical e q u i v a lent weight of this substance is known. V e r y careful experiments h a v e been m a d e with regard to t h e a m o u n t

PHYSICAL M E T H O D S

129

silver deposited b y a current of o n e a m p e r e flowing • one second (one c o u l o m b ) ; this current deposits 'ooi 118 g r a m of silver •m a n aqueous solution of a silver salt. N o w t h e atomic weight of silver is 107-94 d its valency is unity, therefore its chemical equivalt weight is 107-94, t t h e atomic weight of hydrogen is I'O d its valency is unity, therefore its chemical equivalent ight is I'O, :refore it follows from

F a r a d a y ' s second law

that

= -000010357 g r a m of h y d r o g e n will be liberd by one "ampere flowing for o n e second, or the mass hydrogen liberated by a n y current in any time m a y be Dressed as 1-0357 x i o " 5 A / ere A is the current in amperes a n d t the t i m e it flows seconds ; which is equivalent to saying that, at o C. i 760 mm. barometric pressure (29^92 inches), one pere-hour will liberate •0147 cubic foot of hydrogen. So far t h e relationship between current a n d v o l u m e l y d r o g e n which would b e produced theoretically h a s :n considered; it now remains to d e t e r m i n e t h e itionship between power a n d the volume of hydrogen 9

130

MANUFACTURE OF HYDROGEN

which should be theoretically liberated. To refer to the diagram, it will be at once appreciated that, to get the current to flow through the electrolyte requires an electrical pressure, or, in other words, there will be found to be a voltage drop between the anode and cathode. This voltage drop is due to two types of resistance, one of which is identical to the resistance of any conductor and is dependent on the cross-sectional area of the path of flow of the current and on the length of the path, i.e. the distance between the plates. The other resistance is one that is due to a condition analogous to the back E M. F. of an electric motor. Assume that electrolysis has been taking place in the diagrammatic cell and that the battery has been removed ; if a voltameter is then placed between the anode and cathode it will be found that there is a difference of potential between the two plates and that the direction of this electromotive force is the reverse of that of the current which was supplied in the first instance by the battery. This resistance is called the back E M.F. of the cell, or the polarisation resistance. While the first type of resistance can be practically eliminated by placing the plates close together, the second is not a function of the cell design^ but a constant of the electrolyte in the cell; therefore, to obtain electrolysis in a cell it is- necessary that the current must have a certain theoretical potential to overcome the polorisation resistance of the electrolyte. The minimum voltage to produce continuous electrolysis in a cell whose resistance other than that due to polarisation is negligible is given below for various aqueous solutions of bases, acids and salts containing

PHYSICAL METHODS

131

aeir chemical equivalent weight in g r a m s p e r litre ; with Dnsiderable variation in the degree of concentration of le solution it has been found that those solutions given elow whose minimum voltage is about 1 7 require n o ppreciable variation in pressure to p r o d u c e continuous 'ectrolysis .— Solution of

11

Zinc sulphate Cadmium sulphate „ nitrate Zinc bromide Cadmium chloride Orthophosphonc acid Nitric acid Caustic soda „ potash . Lead nitrate Hydrochloric acid Silver nitrate

Minimum Voltage for Continuous Electrolysis . 2*35 volts 1 2 03 1 1 98 1 i'8o 1 • 1-78 170 1 1*69 1 1 69 11 . 1*67 11 I-S2 1 1-31 11 1 70 1

Now it h a s been previously deduced from F a r a d a y ' s ws that a current of one a m p e r e for one hour should oduce "0147 cubic foot of hydrogen (at o° C. a n d 760 m. pressure), but if a solution of caustic s o d a was used e current would h a v e h a d to be supplied a t 1 '69 volts, erefore 1 x 1 "69 watt-hour produces '0147 cubic foot hydrogen, or 1000 watt-hours produce

, ° = 8*7 cubic feet. r 69 it, at t h e same time a s the h y d r o g e n is liberated a t 2 cathode, o x y g e n is being liberated at t h e anode, a n d ice from F a r a d a y ' s laws the volume of oxygen is o n e If of that of the hydrogen, on t h e electrolysis of a 1

Determined by Le Blanc.

132

MANUFACTURE OF HYDROGEN

solution of caustic soda i kilowatt-hour (B.T. U) theoretically produces 87 cubic feet of hydrogen at o° C. 760 mm. (29*92"). and 4-4 „ „ oxygen - „ The theory of electrolysis having been considered, it remains to describe some of the more important applications of this phenomenon for the production of hydrogen and oxygen. To refer again to the diagrammatic cell, if the distance between the anode and cathode is great the resistance of the cell is high, and consequently the production of hydrogen is much below the theoretical, but if, on the other hand, the distance between the two plates is small, the gases liberated are each contaminated with the other, hence the design of a cell for the commercial production of oxygen and hydrogen has of necessity to be a compromise between these extremes. A large number of commercial cells put the anode and cathode comparatively close together, but, in order to obtain reasonably high purity in the gaseous products, a porous partition is placed between the electrodes: this, like increasing the distance between the plates, creates a certain amount of resistance, but it has one advantage of the latter procedure in that it makes for compactness, which is very desirable in any plant and particularly so in the case of electrolytic ones, as one of the greatest objections to their use is the floor space which they occupy. A glance at the list of patents at the end of the chapter will show what an amount of ingenuity has been expended in the design of electrolytic plant for the production of oxygen and hydrogen. On account of this multiplicity of different cells it is intended merely

PHYSICAL METHODS ) describe rpes:— J. 2. 3. 4.

t h e following,

133

which are

representative

Filter press type. T a n k type. Non-porous non-conducting partition type. Metal partition type. Section on Line A B E

Porous Partition

sz f

C

9

'bber

9

Electrode

H Section on CD.

Section onE.E

Hydrogen Liberated ! SS S23 3 2 SEE ^ "T Hydrogen Outlet

Oxygen Liberated FIG.

Filter P r e s s T y p e , — I f , :

ig.

15. in t h e d i a g r a m m a t i c

15), a p l a t e of c o n d u c t i n g m a t e r i a l w a s

cell

placed

•tween t h e a n o d e a n d c a t h o d e a n d t h e c u r r e n t s w i t c h e d L, h y d r o g e n w o u l d b e l i b e r a t e d a t t h e o r i g i n a l c a t h o d e d o x y g e n a t t h e o r i g i n a l a n o d e , b u t , b e s i d e s t h i s , it

134

MANUFACTURE OF HYDROGEN

would be found that on the side of the plate facing the original cathode oxygen would be liberated, while on its

other side hydrogen would be given off ; thus it is seen that the intermediate plate becomes on one face an anode

PHYSICAL METHODS

135

i d on the other a cathode. Further, it will b e found that le polarisation or back E . M F . resistance of t h e cell om the original a n o d e to t h e original cathode is doubled ; IUS the placing of a conductor, to which n o electrical mnections h a v e been made, turns t h e original cell into vo cells. T h e filter press cell is constructed on lines lalogous to t h e above. T h e filter press cell is composed of a series of iron ates, which are recessed on either side as s h o w n in t h e agram, from which it will be seen that, if two of these ates are p u t together, a space will b e enclosed b y them f virtue of the recess In each plate there are three holes, o n e at X and vo along the line A B , so that, when t h e plates are aced together, the enclosed recess could b e filled with ater by means of the hole X. A small hole comlunicates with recess and the holes on A B , but in t h e ise of o n e this communication is on the right-hand side hile on t h e other it is on t h e left. N o w , b e t w e e n a n y vo plates is placed a partition, the shape a n d holes in hich exactly coincide with those in the plates. The i g e of this partition is composed of rubber, while t h e sntre portion, which is of the same size as t h e recess in le plate, is m a d e of asbestos cloth. If four of these plates are pressed together with the artitions between, they will m a k e t h r e e symmetrical dls which can b e filled with electrolyte by blocking u p le hole X in one outside plate and r u n n i n g it in t h r o u g h lis hole in the other outside plate. Since the asbestos ortion of t h e partition is porous, the electrolyte will oon reach the same level in each cell Now, if a positive electric connection is m a d e to one utside plate and a negative to the other, w h a t current

136

MANUFACTURE OF HYDROGEN

passes must flow through the electrolyte and consequently electrolysis will take place. Since each plate is insulated from the other by the rubber edge of the partition each plate becomes on one face an anode and on the other a cathode, as was described in the diagrammatic cell, but the two plates which go to make the recess are divided by the asbestos partition, so the gases liberated have little opportunity of mixing. Since, as has been already mentioned, one of the holes in the top of the plate is in communication with one side of the recess and the other hole with the opposite side, the hydrogen and oxygen formed pass via separate passages to different gasholders. The description is applicable to all filter press type cells. The actual voltage of the electrical supply determines the number of plates which are in the complete unit, for the individual resistances are in series. In practice, using a 10 per cent solution of caustic potash as the electrolyte, the voltage drop j>er plate is 2 '3-2 "5. The current density is generally about 18-25 amperes per square fodlt, while the production is 5*9 cubic feet of hydrogen ajid 3 cubic feet of oxygen, at mean temperature and pressure, per kilowatt-hour, the purity of the hydrogen being about 99*0 per cent, and that of the oxygen 97*5 per cent.1 The filter press type of"cell has a considerable advantage by being compact, but, on the other hand, since 1

The reason for the difference in purity is due to the fact that a small amount of diffusion takes place through the porous partitions, and since on account of its density the volume of hydrogen diffusing into the oxygen will be greater than the amount of oxygen diffusing into the hydrogen, the purity of the oxygen must of necessity be less than that of the hydrogen.

PHYSICAL METHODS

137

ie water and g a s tightness of the individual cells d e 5nds on the rubber in the partition and on the m e t h o d pressing t h e plates together, both t h e s e require a •rtain a m o u n t of attention ; probably a cell of this type ould require overhauling in these particulars about once every t w o a n d a half months, if it w e r e kept r u n n i n g mtinuously.

H

•!-__ //_ *_ -

A

K

_-"»

B \ m ''

•

B •

£ 0 0 0 0 0

p o o

_^H --^.,

*

Similar Holes frilled &I1 Wtr CylmderC

»

FIG 17.—Tank Cell. T h e following are probably the best-known com;rcial cells of this type . Oerlikon a n d S h r i v e n T h e T a n k Cell.—This type of cell will b e readily derstood by looking at the diagram ( F i g . 17). It nsists of a circular tank H m a d e of dead mild steel,

138

M A N U F A C T U R E OF H Y D R O G E N

standing o n insulators M, with an annular ring a t t h e top. In this tank a n iron cylinder C, perforated with holes, is h u n g from t h e cast-iron lid of the cell K b y means of an electrode E . Between the side of t h e t a n k

--

-—^i ii ail

FIG. I 8 —International Oxygen Company's Cell. H a n d t h e cylinder C an asbestos curtain A f r o m a p l a t e of n o n - c o n d u c t i n g m a t e r i a l B .

is h u n g

T h e lid of

t h e t a n k , w h i c h is i n s u l a t e d from b o t h H a n d C, h a s t w o f l a n g e s O a n d N w h i c h form a n a n n u l a r r i n g . t w o outlet pipes G a n d F .

It also has

P H Y S I C A L METHODS

139

T h e annular space in the tank H is filled with water, hile the interior of the tank is filled with a 10 p e r cent, 'lution of caustic soda in distilled water. T h e m e t h o d of operation of the cell is a s follows: If e negative lead of t h e circuit is connected t o D , which metallically fastened to t h e t a n k body H , a n d the >sitive lead is connected t o E , electrolysis will t a k e place id h y d r o g e n will b e liberated on t h e side of t h e tank , rising t h r o u g h the electrolyte into t h e a n n u l a r space lclosed by t h e flanges N and O on t h e lid K, from hence it is free to circulate to the outlet pipe G. W h i l e ^drogen is b e i n g liberated on the sides of the t a n k H , cygen will b e liberated on both sides of t h e cylinder C, om whence it will rise up, ultimately finding its way rough holes in the plate B into the annular space lclosed by the flange N , a n d thus on t o the outlet pe F . T h e r e is a trapped inlet pipe (not shown) in t h e cover . for introducing further distilled w a t e r from time to Tie, to replace that decomposed by the operation of the 'ocess T h e voltage drop between a n o d e a n d cathode is Dout 2'5 volts. T h e outlet pipes G and F are usually trapped in a lass-sided vessel, which enables the w o r k i n g of t h e cell ) be examined. F i g . 18 shows a t a n k cell of t h e International >xygen C o m p a n y , which is not unlike the diagrammatic 2II which has j u s t been explained. T e s t s on four of lese cells by t h e Electrical T e s t i n g Laboratories of lew Y o r k give t h e following figures1:— 1

Ellis, "The Hydrogenation of Oils" (Constable)

I4O

MANUFACTURE OF HYDROGEN Temp. 20° C. and Bar. 29*92 In8.

» . Max. o u TJ. TJ Cubic Ft. per Average Average Average ^le"IT Cubic Ft. per Hr K W Hr Amps. Volts Watts. £ P

39 2 '7

2609

1022

30 l°

Oxygen.

Hydro- Oxygen gen.

3 114

6075

3OSI

gen.

95°

Hydrogen Outlet

6lass

Plan View

FIG

19.

T h e purity of the oxygen was 98*34 per cent, a n d that of t h e hydrogen (from another test) 9 9 7 0 per cent. T h e best-known plant of this type is that of the International O x y g e n Company. The Non-Conducting, Non^Porous Partition T y p e . — T h i s cell, which is illustrated by the d i a g r a m ( F i g . 19), consists of a metal tube A, which forms the

PHYSICAL METHODS

141

Iectrode a n d g a s outlet, a n d which is m a d e of lead w h e r e n acid electrolyte is used, a n d of iron w h e r e an alkaline ne is employed. T h i s metal electrode is s u r r o u n d e d y a glass or porcelain t u b e perforated at t h e b o t t o m . T h e r e are four of these electrodes per cell, which re a r r a n g e d as indicated in the diagram. W h e n the urrent is switched on t h e gases are liberated o n t h e lectrodes within t h e glass tube ; consequently no mixing f the liberated gases can take place. T h e best-known commercial cell of this t y p e is t h e Jchoop. T h e Metal Partition T y p e . — I n t h e preliminary escription of t h e filter press t y p e of cell it was s t a t e d hat a conducting partition between t h e a n o d e a n d a t h o d e itself b e c a m e on o n e face a n a n o d e and o n t h e •ther face a cathode ; this, however, requires modificaion, as it is only t r u e w h e n the voltage d r o p b e t w e e n he original a n o d e or cathode a n d t h e metal partition is sss t h a n t h e m i n i m u m voltage required for continuous 'lectrolysis. I n t h e metal partition t y p e of cell a m e t a l partition s placed between t h e a n o d e a n d cathode. T h i s partiion is insulated from the poles, is not so d e e p a s t h e ilectrodes, a n d is perforated on the lower e d g e with •mall holes which, t h o u g h reducing t h e electrical resistince, do not allow of the gases mixing. T h e best-known cell of this t y p e is the G a r u t i , Arhich, since the t r u e electrodes a r e only a b o u t half a n nch apart, gives a m o r e compact cell t h a n if a non:onducting partition w e r e employed. Since t h e voltage d r o p b e t w e e n electrodes is slightly less for t h e s a m e electrolyte t h a n if a non-conducting

142

M A N U F A C T U R E OF

partition were employed the yield is good, b ^ i ^ g a b o u t 6*i cubic feet of h y d r o g e n at mean t e m p e r ^ - t l a r e a n < ^ pressure per kilowatt-hour. T h e current d e n s i t y is a s high as 25 to 28 amperes per square foot, u s i n g f a 10 p e r cent, solution of caustic soda. T h e a d v a n t a g e of this type of cell is its c o r £ " * P a c t n e s s , due to t h e small distance between t h e electr*<=> c les, a n d its lightness, due to the fact that it is m a d e t £ * r ° u g h o u t (with the exception of t h e insulating strips) o f : r r i i l d steel sheet. H o w e v e r , t h e small distance b e t w e e n t h e electrodes necessitates care being taken to p r e v e n t a n internal short circuit in the individual cells. C a s t n e i v K e l l n e r Cell.—Besides those c e l l s already described, the object of which is to p r o d u c e oxygen and hydrogen, t h e r e a r e some which, t h o u g h not designed for t h e production of hydrogen, y i e l d it as a by-product. Probably the m o s t important of t h e s e e l e c t r o l y t i c processes yielding h y d r o g e n as a b y - p r o d u c t is t h e Castner-Kellner. T h e primary purpose of t h i s p r o c e s s is to m a k e caustic soda from a solution o f b r i n e ; b u t both hydrogen a n d chlorine are produced a t t h e same time. T h e working of this process can be u n d e r s t o o d from the diagram ( F i g . 20). T h e plant consists of a box A, d i v i d e d i n t o t h r e e compartments by t h e partitions B, which, h o w e v e r , d o not touch the b o t t o m of t h e box A. O n t h e floor of this box t h e r e is a l a y e r of mercury, which is o f sufficient depth to m a k e a fluid seal between the c o m p a r t m e n t s . In t h e two end c o m p a r t m e n t s there a r e c a r b o n electrodes, connected t o a positive electric s u p p l y , w h i l e in

PHYSICAL METHODS

143

le middle t h e r e is a n iron electrode, connected t o t h e egative supply. O n e side of t h e box A is carried on a inge H , while the other is slowly lifted u p a n d down y an eccentric G, which gives a rocking motion t o t h e ontents of-the box. In t h e two e n d c o m p a r t m e n t s is placed a s t r o n g olution of brine, while t h e middle is filled with water. ) n t h e current b e i n g switched on electrolysis takes ilace, t h e current passing from t h e positive c a r b o n elecrodes t h r o u g h t h e brine to the mercury, a n d from t h e

Hydrogen Outlet

B

r ^ X ~ & J

f

~i "Mercury

FIG. 20—'-Castner-Kellner Cell m e r c u r y t o t h e n e g a t i v e electrode in t h e c e n t r e c o m p a r t ment. N o w , c o n s i d e r i n g o n e of t h e e n d c o m p a r t m e n t s , b y t h e s p l i t t i n g u p of t h e s o d i u m c h l o r i d e , c h l o r i n e will b e l i b e r a t e d a t t h e p o s i t i v e e l e c t r o d e , a n d will u l t i m a t e l y p a s s o u t a t E , t o b e u s e d for m a k i n g b l e a c h i n g p o w d e r , o r for s o m e o t h e r p u r p o s e , w h i l e s o d i u m will b e d e p o s i t e d o n t h e m e r c u r y , w i t h w h i c h it will a m a l g a m a t e . O w i n g t o t h e r o c k i n g of t h e b o x , t h e s o d i u m m e r c u r y a m a l g a m will p a s s i n t o t h e c e n t r e c o m p a r t m e n t , w h e r e

144

M A N U F A C T U R E OF H Y D R O G E N

it is decomposed at the negative electrode, in accordance with the following equation :— 2Na + 2H2O - 2NaOH + H3. T h u s , b y the operation of t h e process, chlorine is produced in the end compartments, and caustic soda a n d hydrogen in the centre one. T h e following patents h a v e been t a k e n out for t h e production of h y d r o g e n electrolytically :— Delmard. Garuti. Baldo. Garuti. Garuti & Pompili.

G e r m a n patent English „

58282. 16588 18406. 534259. 23663 629070. 111131. 646281. 12950. 2820 27249.

1890. 1892.

1905. 1906. 1906. 1907.

11 U.S. English U.S. 11 n Schmidt. German H azard-Flamand. U . S . G a r u t i & Pompili. English

11

.1 i. 11 ii Vareille. ,, Aigner. Cowper- Coles. E y c k e n Leroy & Moritz. Schuckert. Fischer, L u e n i n g & Collins. Moritz. Hazard-Flamand L'Oxhydrique Francaise.

11 11 French U.S. German English

>.

„ „

355652. 823650. 198626. 14285

French German

„ ,,

397319. 231545.

1908. 1910

11 11

1004249. 981102. 1003456.

1911. 1911. 1911.

„ „ ,, II

„

U.S. 11 11 French

1895. 1895. 1896. 1899. 1899. 1900. 1900. 1902. 1903.

1012

P H Y S I C A L METHODS Benker. F r e n c h patent Knowles O x y g e n Co. & G r a n t . English ,, Maschinenfabrik Surth. French ,, Burdett. U.S. Ellis. Levin.

145 461981.

1913.

1812.

1913.

462394. 1086804. 1087937. 1092903. 1094728.

1913. 1914. 1914. 1914. 1914.

APPENDIX. PHYSICAL CONSTANTS. PHYSICAL PROPERTIES OF HYDROGEN.

Critical temperature . . . — 2340 C. „ pressure . 20 atmospheres [elting point at atmospheric pressure - 259° C. \ -T>avers oiling point „ „ - 252-7° C.J D E N S I T Y OF L I Q U I D

HYDROGEN.

At boiling point . At melting point

•07 •086

VAPOUR PRBSSURB OF LIQUID HYDROOEN (Travers & Jacquerod, 1902).

'emperature°C - 258 2 - 256 7 - 2557 - 255-0 - 254 3 - 253 7 - 253 2 - 252 9 'ressure mm

100

200

LATENT

300

400

500

600

700

760

H E A T OF HYDROGEN.

123 cal. per grm, IO

146

MANUFACTURE OF HYDROGEN DENSITY OF GASEOUS HYDROGEN.

At o° C. and 760 mm. •08987 grm. per litre. 5*607 1b. per 1000 cubic feet SPECIFIC HEAT OF GASEOUS HYDROGEN.

At constant pressure. At atmospheric pressure 30 atmospheres . At constant volume At 500 C .

. 3'4°2) . 3-788/ Lussana ' .

2 402 (Joly, 1891).

VELOCITY OF SOUND IN HYDROGEN.

At o° C. => 12 86 x io4 cm. per sec. (Zoch, 1866) SOLUBILITY OK HYDROGEN IN WATER.

The coefficient of absorption is that volume of gas (reduced to o° and 760 mm.) which unit volume of a liquid will take up when the pressure of the gas at the surface of the liquid, independent of the vapour pressure of the liquid, is 760 mm. Temperature. Coefficient of Temperature Coefficient of " C. AbHorption. " C. Abnorptinn. o . . . . 0214H11 do . . . . oi44aa 10 . . . 01955l 70 . . 'oi46 20 . *oi8iy1 80 . . oi491Ju 30 . 'oifiyy yo . . •oi55 a 40 '0152" 100 . . . *oi66 50 . . . 014ft' TUANM'IKATION O|- G\SEf)llS I IVDHOCKN. Oxygt-tJ . .1*0 Hydrogen . . *4.1 1 Wmrklcr (Her., 1 Sy 1, yy). -Bohr and Berk (Wicd. Ann., i8yi, 44, 316)

PHYSICAL CONSTANTS REFRACTIVITY OF

„ . ' Hydrogen .

.

RELATIONSHIP BETWEEN

' .

147

HYDROGEN

l ooo

\ Ramsay & Travers. -473!

P R E S S U R E AND V O L U M E

W e r e Boyle's L a w correct then the product of t h e ressure multiplied by the volume would be a c o n s t a n t ; owever, Boyle's Law is only an approximation, all ases near to their critical temperature being much m o r e ompressible than the law indicates. A t atmospheric smperature the common gases, such as oxygen and ltrogen, are very slightly more compressible t h a n would »e expected from theory. H y d r o g e n a n d helium under he same conditions are less compressible, hence R e g Lault's description of hydrogen as " g a s plus que >arfait". T h e behaviour of hydrogen at low pressures (from >5O to 25 mm. of mercury) was investigated b y Sir Afilliam R a m s a y and Mr. E . C. C. Baly, who found hat, at atmospheric temperature, Boyle's L a w held hroughout this r a n g e of pressure. T h e relationship between volume a n d pressure when he latter is great has been investigated by A m a g a t a n d Witkowski, whose results are incorporated in the g r a p h Fig. 21), which shows the relationship between t h e heoretical volume of h y d r o g e n which should be obtained Dn expansion to atmospheric pressure a n d t h a t which s obtained from a standard h y d r o g e n cylinder. From this it is seen that, on expansion from 2000 lb. per square inch t o atmospheric pressure, 9 2 per c e n t less volume of h y d r o g e n is obtained t h a n is indicated b y theory.

148

MANUFACTURE OF HYDROGEN

aSgggss-gggsgssgs

s__s s_

THE JOULE-THOMSON EFFECT.

Down to at least - So° C. hydrogen on expansion by simple''outflow rises in temperature, which, is unlike all other gases with the possible exception of helium. The variation in temperature for drop in pressure of unit atmosphere for air and hydrogen is given below :—

PHYSICAL CONSTANTS

149

1 Variation per Atmospheric Pressure.

Air

.

1 \ 91 6

J

'8 90-3

6

Lift

of

ydrogen -

-

6

Hydrogen

Lift

Hydrogen* " ' 3 4 * 460 +

J_* T

B

,

+ +

of

0*203 o o 8

9 0-046

1000

cubic

of

feet

b

h e r e P =» P u r i t y o f h y d r o g e n b y v o l u m e e x p r e s s e d

in

percentage.

B = B a r o m e t r i c pressure in inches. T •» T e m p e r a t u r e

of air

in

degrees Fahrenheit

on the

dry

thermometer This formula

i s c o r r e c t if t h e a i r i s d r y .

small correction must sllowing

b e applied, which

in t h e a s s u m p t i o n of

wet

in

the

curve.

T h e purity of t h e h y d r o g e n

as

If it is

is g i v e n

is

expressed

that the impurity

t h e s a m e specific g r a v i t y as

by

volume

is a i r o r s o m e air

under

other

the

same

o n d i t i o n s ; if t h e i m p u r i t y i s n o t a i r d u e a l l o w a n c e

must

>e m a d e . Humidity

of

urve gives the correction

Correction

which

h e lift f o r m u l a

for

for

humidity

of

A i r — T h e must the

be

attached

employed

atmosphere.

in T h e

hfference b e t w e e n t h e t e m p e r a t u r e of t h e air o n t h e Liid

dry

thermometers

he graph ; the Iry

t e m p e r a t u r e of t h e a i r a s s h o w n

thermometer

)erpendiculars

is f o u n d o n t h e l e f t - h a n d

is

from

found these

on

the

two

bottom; points

Joule and Lord Kelvin.

side on

find

intersect

wet of the

where and

I5O

MANUFACTURE OF HYDROGEN

estimate the value of the correction from the position of the point of intersection relative to the curved lines. EXAMPLE.—Let the air temperature be

Dry. 6o° F.

Wet 5o°F

•

t h e n difference is io° F . , a n d the intersection of t h e perpendiculars is between the curved lines '35 a n d '4 at •05 i -15 Z Z5-3-35«4-«+5€-55

30 ,, ,

•5

75

' ! •

,' ' / / ; 'tf i

•' 3

r

20

Z$

10

7 t

'

T J ' J

35 4p 4S

i i I

r

l ,

r

I

/ r /

I it

i w

i * /

i

$b 95 60

l

l

i

I »

i

I

i

I

I ii

i I

I

I

i

i

\ i I

I

f

6ft TO "75 80

Temperature of Dry Thermometer/n F? F I G . 22.—Correction for Humidity m lb per i o o o Cubic Feet. a p o s i t i o n w h i c h m a y b e e s t i m a t e d a t '2,6 l b . ; t h e r e f o r e •36 feet

lb. m u s t b e s u b t r a c t e d f r o m of h y d r o g e n as determined

t h e lift p e r

1 0 0 0 cubic

b y t h e formula

when

t h e t e m p e r a t u r e of t h e air b y t h e d r y t h e r m o m e t e r w a s 6o° F. a n d the difference b e t w e e n w e t a n d dry i o ° F .

INDEX. ABSORPTION of hydrogen by metals, 15 Air, composition of, 7. — hydrogen in, 7 Aluminal process, 44. Ammonia, 26. — absorption by charcoal, 29 — liquefaction, 29. — properties, 27. — solubility, 28. — uses, 27. Arsme, 32. — production in Silicol process, 32.

Electrolysis, 126. Explosions of mixtures of hydrogen and oxygen, 14 FAT hardening, 35 Ferro-sihcon, 50

HEAT produced by ignition of hydrogen and oxygen, 17. Hydrik process, 44 Hydriodic acid, 24. Hydrobromic acid, 23. Hydrochloric acid, 21. Hydrogen and arsenic, 32. BADISCHE Catalytic process, 101. bromine, 23. patents, 106. carbon, 20 plant, 105. chlorine, ai preparation of catalyst, 103. iodine, 24. Bergius process, 63. nitrogen, 36 patents, 66. oxygen, 9. Boiling point of gases, 115 phosphorus, 30 hydrogen, 145 selenium, 25 Bronze, hydrogen in, 4. sulphur, 24 tellurium, 26. CALCIUM hydride, 34. Carbomum-Gesellschaft process, 108 — physical constants, 145. Centrifugal separation of hydrogen, 124 — production. See Production of hydrogen. Cerium hydride, 34 Hydrogenite process, 60 Clays, hydrogen in, 7. Hydrohth process, 67. Critical pressure, 114. of hydrogen, 145 IGNITION temperature of hydrogen and — temperature, 114. oxygen, 10. of hydrogen, 145 Iron Contact process, 86 Fuel consumption, 97. DENSITY of gaseous hydrogen, 145 Oxidising, go. liquid hydrogen, 145. Diffusion, separation of hydrogen by, Patents, gg. Plant— 121 Multi-retort type, 93. Discovery of hydrogen, 2. Single retort type, gs Draper effect, 22. Purging, 8g Purification of hydrogen, go. ELECTROLYTIC cells— Reducing, 88 Castner-Kellner cell, 142. Secondary reactions, 91 filter press type, 133 metal partition type, 141 Sulphuretted hydrogen in, g3 non-conducting, non-porous partition JouLE-Thomson effect, 148. type, 140 patents, 144 LATENT heat of hydrogen, 145 tank cell, 137. (I 5 0

1-52

MANUFACTURE OF HYDROGEN

Lift of hydrogen) 149. Lmde-Frank-Caro process, 113. — patents, iai. — purification of gas, 120 Lithium hydride, 33. MAGNESIUM hydride, 34

Manufacturing processes— Badische Catalytic, 101. Bergiue, 63 Carbomum-Gesellschaft, 108. Electrolytic, 132. Hydnk, 44. Hydrogenite, 60 HydroHth, 67. Iron Contact, 86. Linde-Frank-Caro, 113. Sical, 69. Silicol, 45. Meteoric iron, hydrogen in, 3.

Production from water and aluminium amalgam, 69. silicide, 68. metallic hydrides, 66. metals, 61. hydrocarbon oils, no starch, n r steam and barium sulphide, 100 iron, 86 water gas, 101. REFRACTIVITY of hydrogen, 147.

Rocks, hydrogen in, 3.

SELENURETTKD hydrogen, 25.

Sical process, 69 Silicol process, 45. composition of sludge, 55. lime, use of, 53. mineral grease, use of, 57. patents, 59 OCCURRENCE of hydrogen, 2. Oil and gas wells, hydrogen in discharge plant, 47. precautions to be taken, 57 from, 5 Oxygen, explosion of hydrogen and, 14. purity of hydrogen produced, 45 — heat produced by ignition of hydro- strength ot caustic, 52 Sodium hydride, 33. gen and, 17. — ignition temperature of hydrogen Solubility of hydrogen in water, 146. Sound, velocity in hydrogen, 146 and, io, 15. Specific heat of hydrogen, 146 — reaction of hydrogen with, 9 Sulphuretted hydrogen, 24 removal from water gas, 84 PHOSPHINB, 30 — action on metals, 31. Phosphoretted hydrogen, 30 TBLLURHTTED hydrogen, 26 Physical constants of hydrogen, 145 Transpiration of hydrogen, 146. Polarisation resistance, 130. Potassium hydride, 33. USES of hydrogen, 1 Production of hydrogen, 39. — from acetyline, 108 VOLCANOES, hydrogen in gases from, 5 acid and iron, 40. acid and zinc, 42. WATER gas manufacture, 72. alkali and aluminium, 44 carbon, 60. Dellwick method, 75 formate, 60. English method, 74. oxalate, 61. Swedish method, 75 silicon, 45 purification of, 82 zinc, 43. removal of sulphuretted hydrogen water and aluminium alloy, 71. from, 84.