NWO/CW Project Nr. 700.54.653
Continuous Biodiesel Production Reactive Distillation Makes It Happen Tony KISS, A.C. Dimian, G. Rothenberg, F. Omota
UNIVERSITY OF AMSTERDAM van ‘t Hoff Institute for Molecular Sciences Nieuwe Achtergracht 166, 1018 WV Amsterdam Tel.+31-20-525.6468, E-mail:
[email protected] Web: staff.science.uva.nl/~ktony
Acknowledgement Jurriaan Beckers Marjo C. Mittelmeijer-Hazeleger STW – Dutch Technology Foundation NWO/CW Project Nr. 700.54.653
Entrainer-Based Reactive Distillation for Synthesis of Fatty Acids Esters
k n a h T ! you ☺
Cognis, Oleon, Sulzer and Uniquema
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2/24
Biodiesel = green energy
Emission type
CO2 Light
B20 = 20% biodiesel
B20
B100
Biodiesel = mono-alkyl esters of fatty acids Total unburned hydrocarbons –20% –67% Safe,monoxide renewable, Carbon (CO) non-toxic, biodegradable –12% –48% –16% –79% Carbon dioxide (CO2) Raw materials: vegetable oils, fat, recycled grease Particulate matter –12% –47% Positive life cycle energy balance Nitrogen oxides (NOx) +2% +10% –20% –100% Sulphur oxides (SOx) impact Positive social Polycyclic Aromatic Hydrocarbons (PAH) –13% –80% Less emissions than regular petroleum diesel Nitrated PAH's (nPAH)
Biomass
–50%
CO2
–90%
Biodiesel
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3/24
Project goals Development of an active and selective solid acid catalyst for fatty acids esterification. Continuous biodiesel production process based on catalytic reactive distillation. Catalyst requirements Water-tolerant Long life Inexpensive
Active, selective, stable Easy to use Available on industrial scale
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Applications
O CH3
O
CH3 CH3
Cosmetics
Food
Why fatty esters? Food industry Pharmaceuticals Cosmetics Plasticizers Bio-detergents Pharmaceuticals
Bio-diesel
Bio-stuff
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Industrial key players
STEARINERIE-DUBOIS
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Process comparison Current process
Novel process
Batch esterification High alcohol / acid ratios Homogeneous catalysis Difficult separation Corrosive & toxic • Reduced investment costs • Reduced energy consumption • Increased process controllability • Enhanced overall rates
Continuous esterification Reactive distillation Heterogeneous catalysis Easy separation Environmentally friendly
Make up Fatty acid
Steam Water
Alcohol Fatty ester
The key to success is an active & selective solid acid catalyst.
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Fatty acids & alcohols Saturated fatty acids: CH3-(CH2)n-COOH Lauric acid Myristic acid Palmitic acid Stearic acid Arachidic acid
(n=10) (n=12) (n=14) (n=16) (n=18)
Aliphatic alcohols: Methanol Ethanol Propanol … 2-Ethyl hexanol
Unsaturated fatty acids Palmitoleic acid: Oleic acid:
CH3(CH2)5CH=CH(CH2)7COOH CH3(CH2)7CH=CH(CH2)7COOH
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Reaction pathways REACTANTS Fatty Acid
Alcohol
esterification
dehydration
etherification
Fatty Ester Main product
Excess of alcohol
Ether
Water
Alkene
Secondary products
Water removal by distillation
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Reaction mechanism Catalyst H
O
RCOOH + R’OH ↔ RCOOR’ + H2O
+
OH
OH
+
C R
R
OH
OH
Secondary reactions:
C
C R
+
2 Alcohol Ether + H2O Alcohol Alkene + H2O 2 Acid Anhydride + H2O
OH
R'
C
HO OH
R
OH +
HO
R'
Catalyst
R
OH
OH
C
C
OH +
HO
R
OH
OH2
O R'
+
+
C R
OH R'
C
H 2O
O
+
R
R' O
R
+
O
H
C
R' O
R'
Similar mechanism for hetero- and homogeneous catalysis.
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10/24
Surface hydrophobicity Water tolerant. Not enough acid sites.
C O
OH
H+
hydrophobic surface with isolated acid site
O
C
H+
OH
O
C H+
O
OH
C
H+
OH
Proper trade-off hydrophobicity-acidity. Good catalytic activity.
hydrophobic surface with adjacent acid site H 2O
Water sensitive. Easy deactivation.
H 2O H 2O
H+
H 2O
H
+
H 2O
H2O
H + OH
H 2O
H2O
H+
OH
H+ H+
H 2O
hydrophilic surface/ numerous acid sites
Influence of surface hydrophobicity on catalytic activity.
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11/24
Solid acid catalysts Zeolites and clays Beta, Y, MOR, ZSM-5
HeteropolyAcids Oxides, sulphates Composite materials
CH3-(CH2)10-COOH + C8H15OH Dodecanoic acid
2 Ethyl hexanol Acid catalyst
CH3-(CH2)10-COOC8H15 + H2O 2 Ethyl hexyl dodecanoate
Amberlyst Nafion
Carbon-based catalysts Polysulfonated aromatics = Not tested yet …
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12/24
Catalyst screening Reaction profiles for esterification of dodecanoic acid with 2-ethylhexanol 100
H2SO4 1%wt Amberlyst 5%wt
80 60
Zeolites
40
Non-catalyzed
20
Conversion / [%]
Conversion / [%]
100
Amberlyst
80
SZ Nafion
60 Non-catalyzed
40 20
Alcohol:Acid = 1:1 T=130°C
0
Alcohol:Acid = 1:1 T=150°C, 3%wt catalyst
0 0
30
60
90
120
Time / [min]
0
30
60
90
120
Time / [min]
Organic resins are not thermo-stable. Zeolites have low activity.
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Zeolites – structure
*BEA – Beta, tetragonal
MFI – ZSM-5, orthorhombic
Diffusion limitations ?!
MOR – Mordenite, orthorhombic 12.82 Å 3.06 Å
CH3
2-ethylhexyl dodecanoate
7.78 Å
O O
CH3
4.86 Å
CH3
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Sulphated zirconia Reaction profiles for esterification of dodecanoic acid with 2-ethylhexanol
SZ 2%w
60
160°C
-1
180°C Non-catalyzed
40
2.3% min
20 0
-1
20 min
SZ
Nafion
Non-Catalyzed
40
SZ
60
Nafion
-1
7.3% min -1 3.4% min
180°C
80 Non-Catalyzed
80
Amberlyst
Conversion / [%]
Initial rate
Alcohol:Acid = 1:1 2%wt SZ Catalyst
Amberlyst
100
60 min
1.2% min
160°C 100
20 0 0
20
40
60
80
Conversion / [%]
Conversion / [%]
100
0%
1%
2%
3%
SZ
80 60 40 20 0
Time / [min]
T=150°C
T=160°C
T=170°C
Similar activity for esterification with 1-propanol and methanol.
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15/24
Experiments + Simulations Integration of experimental results with simulations of the reactive distillation (RD) setup, in AspenTech AspenPlus™ Distillate
RD column sections
Reflux a
a.
Rectifying section (water)
b
b.
Recovery of alcohol
Feeds
c
c.
Reaction zone
Alcohol
d
d.
Recovery of fatty acid
e.
Stripping section (ester)
Fatty acid
Recycle e Biodiesel
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Thermodynamic analysis Water Tb=100 ºC
Tb=298 ºC
Dodecanoic acid
Tb=334 ºC
2-Ethylhexyl dodecanoate O
2-Ethylhexanol Tb=186 ºC
O
CH3
CH3 CH3
Tb=302 ºC
n-Propyl dodecanoate n-Propanol Tb=97 ºC
O
CH3
O
CH3
Tb=267 ºC
Methyl dodecanoate Methanol Tb=65 ºC
O O
CH3
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CH3
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CPE analysis VLE One liquid phase • T > 100ºC • low conversion • open system • alcohol excess • water removal • T < 100ºC Chemical reaction and phase equilibrium • T > 100ºC • T < 100ºC • closed system • reactants molar ratio=1 • P > 1 bar LLE VLLE
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RD process – methanol Acid, 298ºC
Ester, 267ºC 1
X2 (acid+ester)
0.8
Feasible RD process. High purity products.
0.6 0.4 0.2 0
Alcohol, 65ºC
RDC Dodecanoic acid
0
0.2
0.4
0.6
X1 (water+acid)
0.8
1
Water, 100ºC
Distillation column Water ≥ 99.9 %
Feed ratio 1:1 Methanol Evaporator Ester ≥ 99.9 %
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Effect of reflux ratio Fatty acid
Partial alcohol conversion Highest reaction rate
Fatty acid
Total alcohol conversion
Highest reaction rate
Alcohol
Total acid conversion
Alcohol
Total acid conversion
Maximum reaction rate is located in the centre of RD column for an optimum reflux ratio
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Entrainer-based RD flowsheet 100
Feasible process. High purity products >99.9% Acid conversion, %
Entrainer Make up
No entrainer
99
98 100
Decanter
Fatty acid
With entrainer
Stripper
150
200
250
Catalyst loading, kg/m
300 3
Steam Water
Alcohol
Evaporator
Biodiesel
Reactive distillation column
Enhanced mass transfer and reduced catalyst loading when entrainer is used.
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RDC profiles Liquid composition and temperature profiles Separation zone
Reaction zone
Separation 500
0.8 0.6
1-Propanol
0.4
n-Propyl acetate
n-Propyl laurate
Water
0.2
Temperature, K
Liquid mole fraction
1
Reaction
Lauric acid
450
400
350
0 0
5
10
15 Stage
20
25
30
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0
5
10 15 20 25 Stage 22/24
Reactive distillation – advantages • No external recycles • Reduced investment costs • Reduced energy consumption • Increased process controllability
Reaction
Separation
• Equilibrium shifted to products • Enhanced overall rates • Improved selectivity
• Break azeotropes • Handle difficult separations
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Conclusions Surface hydrophobicity and acid sites density determines catalyst's activity & selectivity. Catalysts with small pores (e.g. zeolites) are not suitable. Resins are active but not thermally-stable. Sulphated zirconia is active, selective and stable. Biodiesel production by reactive distillation is feasible.
GREEN ENERGY
Biodiesel
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