Transesterification of Triglyceride

CBE301. Chemical and Biomolecular Engineering Laboratory
(2015 spring)
Experiment 3
Production of Biodiesel through
Transesterification of Palm oil
Transesterification of Triglyceride
Biodiesel properties
Physical property
Density (g/ml) at 15 oC
Viscosity (cP) at 40 oC
Rapeseed oil
Biodiesel
Diesel fuel
0.92
Max 36.0
0.88
4.3
0.83
3.2
Biomass Bioenerg. 42 (2012) 164-171
 Direct use of vegetable oils and animal fats as combustion fuel is not suitable due to their
high kinematic viscosity and low volatility.
 Furthermore, its long term use posed serious problems such as deposition, ring sticking and
injector chocking in engine.
Transesterification of triglycerides
H 2C
OCOR1
R1COOCH3
OH
HC
OCOR2
H 2C
OCOR3
Triglyceride
+
3
OH
KOH or NaOH
HO
OH
+
R2COOCH3
R3COOCH3
Methanol
Glycerol
Methyl esters
(FAME)
Biotechnol. Adv. 28 (2010) 500-518
Application of Transesterification Technologies
Type of
Catalyst
Base
Advantages


Homogeneous
Catalyst


Heterogeneous
Catalyst
Acid
Homogeneous
Catalyst
Reaction can occur at mild reaction condition and less energy
intensive
Very fast reaction rate - 4000 times faster than acid-catalyzed
transesterification
Catalysts such as NaOH and KOH are widely available and
economical


Relatively faster reaction rate than acid-catalyzed
transesterification
Easy separation of catalyst from product
High possibility to reuse and regenerate the catalyst



Insensitive to FFA and water content in the oil
Preferred method if low-grade oil is used
Esterification and transesterification occur simultaneously

Reaction can occur at mild reaction condition and less energy
intensive
Disadvantages




Poisoning of the catalyst when exposed to ambient air

Leaching of catalyst active sites may result to product
contamination

High reaction temperature, high alcohol to oil molar ratio and
long reaction time are required


Very slow reaction rate
Corrosive catalyst such as H2SO4 can lead to corrosion on
reactor and pipelines
Separation of catalyst from product is problematic

Heterogeneous
Catalyst


Easy separation of catalyst from product
High possibility to reuse and regenerate the catalyst
Enzyme



Insensitive to FFA and water content in the oil
Preferred method if low-grade oil used
Tranesterification can be carried out at low reaction
temperature, even lower than homogeneous base catalyst
Only simple purification step is required

Sensitive to FFA content in the oil
Soap will formed if the FFA content in the oil is more than 2
wt%
Too much soap formation will decrease the biodiesel yield and
cause problem during product purification



Complicated catalyst synthesis procedures lead to higher cost
Energy intensive
Leaching of catalyst active sites may result to product
contamination

Very slow reaction rate, even slower than acid-catalyzed
transesterification
High cost
Sensitive to alcohol, typically methanol that can deactivate the
enzyme


Biotechnol. Adv. 28 (2010) 500-518
Soap Formation by Base Catalyst (Saponification)
O
O
+ ROH
+ H2O
R'
R'
OR
OH
O
O
+ H2O
+ NaOH
R'
OH
R´ = Carbon chain of fatty acid
R'
ONa
R = Alkyl group of alcohol
 The free fatty acid (FFA) in the reactant can react with the alkali catalyst to form soap and
water which results in the loss of alkali catalysts.
 When the FFA level is above 5%, the soap will inhibit separation of the methyl esters and
glycerol and causes emulsion formation during the water washing.
Appl. Energ. 87 (2010) 38-46
Treatment of Free Fatty Acids in Triglyceride
: Two-step Process
O
O
Step. 1.
+
R'
OH
H2SO4
+
R'
OH
H2O
OCH3
Esterification by acid catalyst. R´ = Carbon chain of fatty acid
Step. 2.
H 2C
OCOR1
R1COOCH3
OH
HC
OCOR2
H 2C
OCOR3
Triglyceride
+
3
OH
KOH or NaOH
HO
OH
+
R2COOCH3
R3COOCH3
Glycerol
Methanol
Methyl esters
(FAME)
Reaction condition
Catalyst
Temperature
(oC)
Alcohol/oil
(mol/mol)
Catalyst
loading (%)
Reaction
time (h)
Yield (%)
1st Ferric sulfate
2nd KOH
Acid : 95
Base : 65
Acid : 10
Base : 6
Acid : 2
Base : 1
Acid : 2
Base : 1
97
1st Ferric sulfate
2nd CaO
Acid : 60
Base : 60
Acid : 7
Base : 7
Acid : 0.4
Base : Not
specified
Acid : 3
Base : 3
81
J. Appl. Sci. 9 (2009) 3098-3103
J. Mol. Catal. A:Chem 252 (2006) 107-112
Heterogeneous Base Catalysts for Transesterification
CaO
MgO
Anion exchange resin
H2
C
H
C
CH3
H 2C
N
+
CH3 Cl
-
CH3
 Advantages
- High basic strength
- Low solubility in MeOH
 Advantages
- High stability in H2O
- High yield of FAME
 Advantage
- Easy recovery &
regeneration
 Disadvantages
 Disadvantages
 Disadvantages
- Poisoned by FFA adsorption
- Leaching of Mg and Al
- Low thermal stability
- Soap synthesis
- High reaction temperature
- Fast deactivation (~ 5 h)
Reaction condition
Catalyst
Temperature
(oC)
Alcohol/oil
(mol/mol)
Catalyst
loading (%)
Reaction
time (h)
Yield (%)
CaO
65
12
0.85
1
66
Hydrotalcite
180
4
5
1
90
Anion exchange resin
50
10
40
1
80
Fuel 87 (2008) 2798-2806
Appl. Catal. A:Gen 331 (2007) 138-148
Bioresource Technol. 98 (2007) 416-421
Heterogeneous Acid Catalysts for Transesterification
Sulfated ZrO2
Carbon-based catalyst
Heteropolyacids
S
O
Zr
 Advantage
- High acid strength
 Advantages
- High acid strength
- High stability
 Advantage
- High acid strength
 Disadvantages
 Disadvantage
- Leaching of sulfate
- High reaction temperature
- Regeneration is difficult
- Alcohol/oil ratio is too high
 Disadvantages
- Soluble in the reaction media
- Alcohol/oil ratio is too high
Reaction condition
Catalyst
Temperature
(oC)
Alcohol/oil
(mol/mol)
Catalyst
loading (%)
Reaction
time (h)
Yield (%)
Sulfated ZrO2
200
6
3
4
86
Carbon-based
80
30
10
8
92
Zr0.7H0.2PW12O40
65
20
2.1
8
99
Chem. Eng. J. 116 (2006) 61-66
Bioresource Technol. 99 (2008) 8752-8758
Energy Fuels 23 (2009) 4640-4646
Current Status of Transesterification Catalysts
Commercial transesterification using heterogeneous catalyst,
Zn-Al mixed oxide (Esterfip-H, France)
 Disadvantages of traditional homogeneous base-catalyzed transesterification process
- Low yield of FAME (presence of large amounts of free fatty acid)
- Soap (saponification product) causes product separation problems (emulsion formation)
Catal. Today 106 (2005) 190-192
Green Chem. 11 (2009) 1285-1308
Homogeneous & Heterogeneous Catalysis
Property
Homogeneous catalysts
Heterogeneous catalysts
Catalyst recovery
Difficult and expensive
Easy and cheap
Thermal stability
Poor
Good
Selectivity
Excellent/good (single active site)
Good/poor (multiple active site)
 If the catalyst stays in the same phase with the reaction media, it called as ‘homogeneous
catalyst’. On the other hand, if the catalyst stays in the different phase as a solid, it is
classified as ‘heterogeneous catalyst’.
 In this experiment, NaOH will be used as ‘homogeneous catalyst’ and CaO as
‘heterogeneous catalysts’.
Experimental
15 mL Methanol
+ 0.5 g NaOH or CaO
60 oC, 700 rpm
52.5 g
Palm oil
52.5 g
Palm oil
FAME
+ Glycerol
Pre-heated at 60 oC
with stirring (700 rpm)
FAME
Crude
glycerol
1 mL FAME
+ 9 mL n-hexane
Gas Chromatography
Injector
Detector
Oven
 FID is based on the detection of ions formed during combustion of organic compounds in a
hydrogen flame.
 Hydrocarbons generally have molar response factors that are equal to number of carbon
atoms in the molecule.
Peak Assign
 GC result
Methyl oleate
CH3(CH2)7CH=CH(CH2)7COOCH3
Methyl stearate
CH3(CH2)16COOCH3
n-hexane
Methyl palmitate
CH3(CH2)14COOCH3
36.3%
Methyl myristate
CH3(CH2)12COOCH3
48.5%
1.5%
9.5%
4.3%
Methyl lioleate
CH3(CH2)3(CH2CH=CH)2(CH2)7COOCH3
 Palm oil composition
Composition (%)
Chemical structure
Trimyristin
3
C45H86O6
Tripalmitin
40.5
C51H98O6
Tristearin
5
C57H110O6
Triolein
42
C57H104O6
Trilnolein
9.5
C57H98O6
Conversion & Selectivity
𝑛𝑛𝑖𝑖,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 − 𝑛𝑛𝑖𝑖,𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢𝑢
𝑛𝑛𝑖𝑖,𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶𝐶 % =
× 100 =
× 100
𝑛𝑛𝑖𝑖,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓
𝑛𝑛𝑖𝑖,𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓
 Reference data
𝑛𝑛𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 % =
× 100
𝑛𝑛𝑖𝑖,𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
- n-C6 area : 478207
- Total FAME area(at 100% conversion) : 21200
 Ratio of n-C6 to total FAME area : 22.5
 You can calculate the triglyceride conversion and FAME selectivity by using above equation
 Example
- n-C6 area : 521809
- Total FAME area : 14165
- If 100% conversion, total FAME area = 521809/22.5 = 23191
- So, conversion (%) = 14165/23191 x 100 = 61.1 %
Questions