Kinetics of Palm Oil Transesterification
in a Batch Reactor
D. Darnoko1 and Munir Cheryan 2
University of Illinois, Department of Food Science and Human Nutrition,
Agricultural Bioprocess Laboratory, Urbdna, Illinois 61801

ABSTRACT: Methyl esters were produced by transesterificationof palm oil with methanol in the presence of a catalyst (KOH).
The rate of transesterification in a batch reactor increased withtemperature up to 60° C. (Higher temperatures did not reduce thetime to reach maximal conversion. The conversion of triglycerides (-TG), diglycerides (-DG) and monoglycerides (-MG) appeared to be second order up to 30 mins of reaction time. Reaction rate constants for TG, DG and MG hydrolysis reactions were0.018 -0.191 (wt % @min)-1, and were higher at higher temperatures and higher for the MG reaction than for the TG hydrolysis. Activation energies were : 14.7, 14.2 and 6.4 kcal/mol for the TG,DG and MG hydrolysis reactions respectively. The optimal catalyst concentration was 1% KOH.
Paper no. 19574 in JAOCS 77, 1263-1267 (December 2000).
KEY WORDS: Biodiesel, kinetics, methyl esters, palm oil, transesterification.
Methyl esters derived from vegetable oil (biodiesel) havegood potential as an alternative diesel fuel. The cetane number, energy content., viscosity, and phase changes of biodiesel
are similar to those of petroleum-based diesel fuel (1).
Biodiesel is produced by transesterification of large, branchedtriglycerides (TG) into smaller, straight-chain molecules ofmethyl esters, using an alkali or acid as catalyst (2). There arethree stepwise reactions with intermediate formation ofdiglycerides (DG) and monoglycerides (MG) resulting in theproduction of 3 mol of methyl esters (ME) and 1 mol of glycerol (GL) as follows (3,4).
The overall reaction is:CatalystTG + 3ROH)))))))))))> 3R'CO2-R + GL

[1]

2[2]

k 4.
1

Present address: Indonesian Oil Palm Research Institute, Jl. Brigjen
Katarnso 51, Medan20001)(H, Indonesia.
2
To whom correspondence should be addressed at(University of Illinois Department of Food Science and Human Nutrition, Agricultural Bioprocess
Laboratory, 1302 W. Pennsylvania Ave.. Urbana, IL 61801,
E-mail- mcheryan@uiue.edu

Copyright © 2000 by AOCS Frcss

W MG + R'CO R2[3]k5k3

MG + ROH

W GL + R'CO R
2[4]

k6.

Transesterification reactions have been studied for many vegetable oils such as .soybean, rapeseed, sunflower, and safflower seed (5,6). Common catalysts for transesterification
are NaOH, KOH, or sodium methoxide. However, sodium
methoxide causes formation of several by-products, mainly
sodium salts, which have to be treated as waste (7). In addition, a high-quality oil is required with this catalyst. Potassiurn hydroxide has an advantage in that, at the end of the reaction, the reaction mixture can be neutralized with phosphoric acid resulting in potassium phosphate, which can beused as fertilizer. Isigigur et al. (6) reported that potassiumhydroxide was superior to sodium hydroxide as a catalyst for
the transesterification of safflower seed oil.
A study of the kinetics of transesterification will provide
parameters that can be used to predict the extent of the reaction at any time under particular conditions. Among several
kinetic studies published on transesterifieation of simple esters, only a few were concerned with the transesterifieation ofvegetable oil fatty esters, such as those by Freedman et al. (3)and Noureddini and Zhu (4). Although methyl esters from palm
oil have been produced on a pilot scale in Malaysia,
there are no published reports on its kinetics.

Refined, bleached, and deodorized palm oil was obtained fromArcher, Daniels Midland (Decatur, IL). Reference standards
such as tripalmitin, triolein, diolein, monoolein, methyloleate, methyl palmitate, methyl heptanoate, and glycerol of>99% purity were purchased from Nu-Chek-Prep. Inc.
(Elysian, MN) and Sigma Chemical Co. (St. Louis, MO)..
Methanol and potassium hydroxide were of analytical grade
obtained from Fisher Scientific Co. (Pittsburgh, PA).
Batch reaction. Transesterifieation reactions were performed in a 1-L three-necked flask equipped with a reflux
condenser, a thermometer, and a sampling port. The reactor
was immersed in a constant-temperature water bath equippedk1

W DG + R'CO R

DG + ROH

EXPERIMENTAL PROCEDURES

The stepwise reactions are:

TG + ROH

k21263

PDF created with FinePrint pdfFactory trial version http://www.fineprint.com

JAOCS. Vof, 77, no, 12 (2000)

1264

with a temperature controller, that was capable of maintaining the temperature within ± 0.2° C. Agitation was provided
with a magnetic stirrer, which was set at a constant speed
throughout the experiment. Initially, the reactor was filledwith 500 g palm oil and heated to the desired temperature. A
known amount of potassium hydroxide (the catalyst) was dissolved in the required amount of methanol and heated separately to the desired temperature. This methanolic KOH wasthen added to the base of the reactor (to prevent evaporationof methanol) at which point the reaction was assumed to havestarted. The molar ratio of methanol/oil was fixed at 6:1 since
the literature suggests that this is the optimal ratio for veg
etable oil transesterification. The weight of 1 mol oil was determined from the calculated average molecular weight ofpalm oil based on the known fatty acid composition of the oil.
At various times, a sample was withdrawn quickly fromthe reactor with a Pasteur pipet. About 300 mg of the sample
mixture was placed in a vial and diluted with 5 mL high-performance liquid chromatography grade tetrahydrofuran, andthen one drop of 0.6 N hydrochloric acid was added to neutralize the catalyst. Separate studies had determined that thisdilution and neutralization stopped the reaction immediately.
The sample was then filtered through 0.2 µ m poly tetra fluoroethylene syringe filter and kept at -20/C until further analysis.
Analysis. The samples were analyzed for TG, DG, MG,
total methyl esters, and glycerol content by gel permeation
chromatography (8). The composition of the methyl esters
was analyzed by gas chromatography (9,10) using an HP
6890 Series Gas Chromatograph System equipped with asplit/splitless injection system, a flame-ionization detector,and an HP ChemStation software (Hewlett-Packard, Wilmington, DE). The column was a 30 m x 0.25 mm, 0.25 µ m
DB-Wax capillary column (J &. W Scientific, Folsom, CA)with He at 25 cm/s as the carrier gas and a split ratio of 50:1.
Injector and detector temperatures were 250° C, oven temperature started at 120° C tor 2 min, increased to 230° C at a rateof 5° C/min, and held at this temperature for 5 min. Methyl
heptanoate was used as the internal standard.
RESULTS AND DISCUSSIONFigure 1 shows the progress of the transesterification reaction
for palm oil in the first 90 min of reaction time. The temperature was 50° C, the catalyst was 1 % potassium hydroxide, andthe methanol/oil molar ratio was 6:1. In the initial stages of
the reaction, production of ME was rapid. The rate then diminished and finally reached equilibrium in about 60 min.
The increase in ME concentration was followed by an increase in glycerol concentration as it was liberated from TG
molecules. However, the relative proportion of GL produced
was not always the same as that of the esters produced. Thisis due to intermediate products such as DG and MG. TG concentration decreased as the reaction proceeded; after 60 min,TG concentration was only 0.54%. The highest concentrationsof DG and MG were observed in the first minute; their levels

D. DARNOKO AND MUN1R CHERYAN

FIG. 1. Composition of reaction products during palm oil transesterification at 50/C. Molar ratio of oil/methanol was b, catalyst was 1% KOH

then decreased and reached equilibrium after 60 min. Data atother temperatures followed a similar pattern (II).
Effect of temperature. The effect of temperature on palm
oil transesterification was studied at a catalyst (KOH) concentration of 1 % and a methanol/oil molar ratio of 6:1. Owing
to the semisolid nature of palm oil at room temperature, theminimum temperature used in this work was 50° C. Below
50° C, the high viscosity of the oil caused problems in pumping and stirring. Storage temperatures for palm oil were about
55° C to maintain its liquidity. The maximum temperaturestudied was 65° C because the boiling point of methanol is68° C. Temperature had a small but noticeable effect on thetransesterification reaction, as shown in Figure 2.
Figure 3 shows a typical distribution of products and intermediates at 4 min of reaction time. At 50° C, conversion of
TG to ME was 73% as compared to 82% conversion at 65° C.
Freedman et al. (5) also reported rapid formation of ME during transesterification of soybean oil and sunflower oil: after
1 min, 80% of TG were converted to ME and after 1 h, ME
concentration was 93-98% of the reaction mixture.
Reaction kinetics. The best kinetic model for our data appears to be a pseudo second-order model for the initial stagesof the reaction, followed by first-order or zero-order kinetics.
To test this hypothesis, a model was developed based on thekinetics of TG hydrolysis (1 2). The second-order reaction ratefor TG in Equation 2 would be as follows (13):

PDF created with FinePrint pdfFactory trial version http://www.fineprint.com

KINETICS OF PALM OIL TRANSESTERIFICATION-d[TG]/dt = k[TG]21265[5]
Similarly, the same procedure applied to Equations 3 and 4would result in:

Integration of Equation 5 yields:
kTG @t = 1/[TG] - l/[TG0]kDG @t = 1/[DG] - l/[DG0][7]

kMG @t = 1/[MG] - l/[MG0]

[8]

[6]

where k is the overall pseudo rate constant, t is the reaction
time, TG0 is the initial triglyceride concentration, DG0 is theinitial highest diglyceride concentration, and MG0 is the initial highest monoglyceride concentration.
For the hydrolysis of TG, a plot of reaction time (t) vs.
1/[TG] will be a straight line if the model (Equation 6) is valid.
Figure 4 shows such plots at the four temperatures in the earlystages of the reaction (up to 30 min of reaction lime). The slope
is kTG with the units (wt%@min)-1. Similar straight lines wereobtained for DG and MG hydrolysis (11). The values of k andits corresponding correlation coefficient are shown in Table 1.
There is an increase in k at higher temperatures, and the order

TABLE 1Reaction Rate Constant k (wt% min) -1 for Triglyceride (TG),Diglyceride (DG), and Monoglyceride (MG) Hydrolysis
at Different TemperaturesGlycerideTG

6 DG

DG

6 MGMG6 GLaTemperature°CReaction rateconstant(wt%@@min)-1R2

50
55
60
65
505560
65
5055
60
65

0.018
0.024
0.036
0.048
0.036
0.051
0.070
0.098
0.112
0.158
0.141
0.191

0.98650.9966
0.98220.99030.99400.99740.98600.96780.97330.96190.98620.9843aGL, glycerol.

PDF created with FinePrint pdfFactory trial version http://www.fineprint.com

1266

D.DARNOKO AND MUNIR CHERYANTABLE 3Distribution of Methyl Esters Derived from Palm Oil(expressed as concentration in weight %)of magnitude of k is kMG > kDG > kTG. These data were used todetermine the Arrhenius energy of activation from a plot of thereaction rate constant (k) vs. the reciprocal of absolute temperature (T), according to the equation:
log10k = (-Ea/2.303R)/T+C[9]

where Ea is the energy of activation, R is the gas constant, andC is a constant. The plot is shown in Figure 5, and activationenergies are shown in Table 2. Our values of Ea are in thesame range as other work (3) for the TG-DG and DG-MG reactions, but our value for the MG-GL reaction is smaller.
Effect of catalysi concentration. Figure 6 shows the effectof concentration of the KOH catalyst, expressed as a. weightpercentage of the oil. At the lowest catalyst concentration.
(0.5%) there was a lag, in ME production, followed by a rapid
increase in rate after 6 min. The rate then decreased after 30min. Noureddini and Zhu (4) also observed a sigmoidal pattern for the production of ME from soybean oil, Boocock etal. (14) suggested the lag is because this is a two phase reaction mixture. The oil concentration in the methanol phase islow at the start of the reaction leading to mass transfer limitations. As the reaction proceeds, the concentration of oil inthe methanol phase increases, leading to higher rates. No
large differences were observed in TG conversion to ME between 1% and 1.2% KOH. Others have also observed 1%
KOH to be optimum for transesterification of safflower seed

TABLE 2
Activation Energy for Hydrolysis of TG, DG, and MG During
Transesterification of Palm Oil4

Reaction

Ea (kcal/mol)

R2TG

6 DG14.70.9959

DG6MG

14.20.9998

MG

6 GL

6.40.7457

Methyl ester
Methyl laurate (2:0)
Methyl myristate (14:0)
Methyl palmitate (16:0
Methyl palmitoleate (16:1)
Methyl stearate (18:0)
Methyl oleate (18:1).Methyl linoleate (18:2)
Methyl linolenate (18:3)
Methyl arachidate (20:0This Work
0.35
l.08
43.79
0.15
4.42
39.90
9.59
0.17
0.38

Maycock(17)
0.2
1.1
44.0
0.1
4.5
39.2
10.1
0.4
0.4

oil (6) and rapeseed oil (15) although Vicente et a!. (16) suggested higher levels of alkali were better for the transesterification reaction,
Composition of ME. There were no significant changes in
the concentration of nine major ME during the entire 90 minof reaction, as analyzed by gas chromatography (11). The distribution of ME is shown in Table 3.
ACKNOWLEDGMENTS
This study was partly supported by the Illinois Agricultural Experiment Station, University of Illinois. The authors acknowledge Indonesian Oil Paim Oil Research Institute for the leave of absence
and scholarship provided for D. Darnoku.
REFERENCES
1. Muniyappa, P.R., S.C. Brammer, and H. Noureddini, Improved
Conversion of Plant Oils and Animal Fats into Biodiesel andCo-product, Bioresour. Technol. 56:19-24 (1996).
2. Sridharan, R., and I.M. Mathai, Transesterification Reactions, J,Sri.Ind. Res. 33:178-187(1974).
3. Freedman, B., R.O. Butterfield, and E.H. Pryde, Transesterification Kinetics of Soybean Oil, J. Am. Oil Chem. Soc.
63:1375-1380 (1986).

PDF created with FinePrint pdfFactory trial version http://www.fineprint.com

KINETICS OF PALM OIL - TRANSESTERIFICATION1267

4. Noureddini, H., and D. Zhn, Kinetics of Transesterification ofSoybean Oil, Ibid. 74:1457-1463 (1997),
5. Freedman, B., E.H- Pryde and T.L. Mounts, Variables Affecting the Yield of Fatty Esters from Transesterified Vegetable Oil,//?ir/.rt/:1638-1643(I984).
6. Isigigur, A., F. Karaosmanoglu, iind H-A. Aksoy, Methyl Ester
from Safflower Seed Oil of Turkish Origin as a Biofuel for
Diesel Engines, App. Biochi'm. Riotechiwl. 45/46:103-112(1994).
7. Ahn, E., M. Koncar, M. Mittelbach, and R- Man', A Low-waste
Process for the Production of Biodiesel, Sep. Sci. Technol. 30:
2021-2033(1995).
8. Darnoko, D., M. Cheryan, and E.G. Perkins, SimultaneousAnalysis of Vegetable Oil Transesterification Products by Gel Permeition Chromatography. J. Ui{. Chrom. 23:2327-2335 (2000).
9. Off'ictcii mul Tentative Methods, 3rd edn., American Oil
Chemists' Society, Champaign, 1985, Method Ce 1-62.
10. Freedman, B., W.F. Kwoiek, and E-H. Pryde, Quantitation in
The Analysis of Transesterified Soybean Oil by Capillary Gas
Chromatography, J. Am. Oil Chem. s(k: 6^:1370-1375(1986).
11. Darnoko, D., Continuous Production of Methyl Esters fromPalm Oil and Recovery of Beta-Carotene by Membrane Technology, Ph.D. Thesis, University of Illinois, Urbana, 1999.

12. Dandik, L., and H.A. Aksoy, The Kinetics of Hydrolysis ofNige/lti .vativci (black cumin) Seed Oil Catalyzed by Native Lipase in Ground Seed, J. Am. Oil Chem. Soc- 69:1239-1 24 I
(1992).
13- Smith, J.M., Chemical Engineering Kinetics, 3rd cdn.,
McGrawHill Publishing Co., New York, 1981.
14. Boocock, G.B., S-K. Konar, V- Mao, C, Lee, anti S, Eiiligan,
Fast Formation of High-Purity Methyl Esters from VegetableOils, ./.Am. Oil Chem. Soc. 75:1 167-1172(1998),
15. Filiieres, R., B. Benjelloun-Mlayah, and M- Deimiis,
Ellianolysis of Rapeseed Oil: Quantitation of Ethyl Esters, Mono-, Di-,and Trigiycerides and Glycerol by High-Performance Si/,e-Exclusion Chromalography, Ihiil. 72:427-432 (1995).
16. Vicente, G-, A. Coteron, M. Martine-', and J. Aracil.
Application of the Factorial Design of Experiments and Response Surface Methodology to Optimize Biodiesel Production, liui. Crops
Prod. ^:29-35(1998).
17. Maycock, J.H., Extraction of Crude Palm Oil, in Palm. Oil,edited by F.D. Gunstone, Cril. Rep. Appi. Chem., John Wiley &Sons, New York, Vol. 15, 1987, pp. 29-38,[Received March 29, 2000; accepted August 26, 2000]

PDF created with FinePrint pdfFactory trial version http://www.fineprint.com