TRANSESTERIFICATIONPROCESS TO MANUFACTUREETHYL ESTER OF RAPE OIL
Roger A. Korus, Dwight S. Hoffman Narendra Barn,
Charles L. Peterson, and David C. Drown
Department of Chemical Engineering
University of Idaho
Moscow, ID 83843

ABSTRACT
A process for the production of the ethyl ester of winter rape [EEWR] for use as a biodiesel fuelhas been studied. The essential part of the process is the transesterificationof rape oil with ethanol, in thepresence of a catalyst, to yield the ethyl ester of rape oil as a product and glycerin as a by-product.
Experiments have been performed to determine the optimum conditions for the preparation of EEWR. The
process variables were. 1) temperature, 2) catalyst, 3) rate of agitation, 4) water content of the alcohol
used, and 5) the amount of excess alcohol used. The optimum conditions were: 1) room temperature, 2)
0.5% sodium me&oxide or 1% potassium hydroxide catalyst by weight of rapeseed oil, 3) extremely
vigorous agitation with some splashing during the initial phase of the reaction and agitation was notnecessary after the reaction mixture became homogeneous, 4) absolute ethanol was necessary for highconversion, and 5) 50% excess ethanol with NaOCH3
or 100% excess with KOH gave a maximum
conversion. Viscosity, cloud point and pour point of the EEWR were measured. A preliminary break-evencost for the commercial production of EEWR was found to be %0.55/liter [%2.08/U.S. gallon].

INTRODUCTION
Background
Vegetable oils have attracted attention as a potential renewable resource for the production of analternative for petroleum-based
diesel fuel. Various products derived from vegetable oils have been
proposed as an alternative fuel for diesel engines, including neat vegetable oil, mixtures of vegetable oilwith petroleum diesel fuel, and alcohol esters of vegetable oils. Alcohol esters of vegetable oils appear tobe the most promising alternative. Vegetable oils are triglycerides &lycerin esters] of fatty acids; alcohol
esters of fatty acids have been prepared by the transesterificationof the glycerides, wherein linear,monohydroxy alcohols react with vegetable oils in the presence of a catalyst to produce alcohol esters ofvegetable oils [AEVO] and glycerin as a by-product (Fig. 1). AEVO when used as an alternative diesel
fuel has been identified as a “biodiesel”.
Detailed literature reviews concerning the production and use of AEVO have been given byPeterson et al. (199 1) and Barn (199 1). Previous publications reported the use of methyl, ethyl, and butyl
alcohols for the transesterificationof rape oil, sunflower oil, cottonseed oil, peanut oil, soybean oil, andpalm oil to produce methyl, ethyl, and butyl esters. The transesterifications
were enhanced by the use ofpotassium hydroxide, sodium hydroxide, sodium me&oxide, or sodium e&oxide as a catalyst. Important
reaction parameters for the transesterifications are: 1) ratio of alcohol to vegetable oil, 2) temperature, 3)
rate of agitation, and 4) amount of water present in reaction mixture.
AEVO has a viscosity approximately twice that of diesel fuel. Viscosity is of prime concern
because of its effects on spray patterns and deposit formation. AEVO performs similarly to diesel in both
short- and long-term engine tests (Fig. 2) while the raw vegetable oil develops severe injector fouling after
200 hours of operation.
Alcohol esters of fatty acids have surprisingly good emission characteristics; the emissions ofmethyl esters of winter rape -1
gave significantly lower total particulates and lower polynuclear
aromatic hydrocarbons than #2 diesel fuel. However, combustion of MEWR gave higher levels of NO,
and aldehyde emissions than did #2 diesel fuel. Additional tests of emissions from biodiesel fuels areneeded to enhance their commercialization.
The use of neat vegetable oil, mixtures of vegetable oil and other components, and alcohol esters ofvegetable oils [AEVO] has been under study at the University of Idaho since 1979. Peterson et al. (199 I)
have given a complete description of the process for the production of the methyl ester of winter rape
VEWR].
MEWR has been manufactured in a 756-l&[200 - U.S. gallons] batch pilot plant scale (Fig.
3) using potassium hydroxide as a catalyst. The MEWR bicdiesel product has been used as a replacementfor diesel fuel in laboratory studies and in tractors using the ester under actual field conditions. A 20 KW(27 hp) Satoh tractor has been powered with 100% MEWR biodiesel since the spring of 1987. The tractor
has been performing satisfactorily to date. A preliminary economic analysis of the commercial productionof MEWR showeda breakevencostof $0,49iliter [$l.SS/U.S.gallon). Costsarein 1991U.S. dollars.
Research at the Uruversity of Idaho has been focused on alcohol esters of vegetable oils because
vegetable oils are a renewable enera resource. Earlier work has concentrated on methyl esters. The next
logical step is the use of ethanol rather than methanol and consequently produce the ethyl ester of vegetableoils. Ethanol can be produced from agricultural renewable resources, thereby attaining total independence
from petroleum-based alcohols. Consequently, a process for the production of the ethyl ester of winter rape
EEWR] for use as a biodiesel fuel has been studied. The process system which has been studied is similarto the process for production of MEWR as shown in Figs. 1 and 3 except ethanol was used instead of
methanol and catalysts other than KOH as well as KOH were tested.
Objective
Optimum conditions for the transesterificationof rape oil to produce EEWR were determinedwhich yielded a maximum conversion of rape oil to the ethyl ester. The variables were: 1) Temperature ofreaction; 2) Catalyst; 3) Rate of agitation of reaction mixture; 4) Water content of alcohol (ethanol); and5) Amount of excess alcohol.
METHODS
Materials
The rapeseed oil used for the experiments was extracted from Bridger rapeseed; Bridger is a wintervariety of rape. This oil has a high level of erucic acid (53.2%). Extraction of the oil from the rapeseed(Fig. 3) was done by the Department of Agricultural Engineering at the University of Idaho (Peterson et al.
1983). A Cecoco oil expeller press with an extraction efficiency of approximately
80% was an integral
part of their process. The automated and instrumented system was equipped with a seed preheater-auger,
seed bin, meal auger, and oil pump. Reagent grade absolute ethanol was used. Potassium hydroxidepellets with an assay of 85% were purchased from EM Science Company; Fisher Scientific Company
provided the purified, dry sodium methoxide powder; sodium ethoxide was provided by Aldrich Chemical
Company; and potassium methoxide was a product from Aldrich Chemical Company.
Fractional

Factorial

Experimental

DesignA fractional, factorial experimental
design was used to determine the optimum values oftemperature, degree of agitation, type of catalyst, and water content of ethanol used. A 24-1 fractional,
factorial design was chosen for this purpose. Using a 24-1 design four variables were studied at two levels
by performing eight experiments (2 4-1 = 8). The fractional, factorial design contains three quantitative
variables - temperature, agitation, and water content of ethanol - and one qualitative variable - catalyst.
The response is degree of conversion of rape oil to ethyl ester. The design matrix (Table 1) shows the twolevels of the variables and the response. Table 1 shows the recorded data with the levels coded so that aminus one (-1) represents the low level and a plus one (+l) represents the high level. The catalyst chosen
for the lower level was sodium e&oxide and potassium hydroxide was chosen for the higher level.
The levels which were chosen for the various variables in this study were based on previous
experiments and practical considerations.
The low level of temperature was chosen as room temperatureand the high level was chosen slightly higher below the boiling point of 190 proof ethanol. The lower levelof ethanol chosen was 190 proof (five wt percent water); the higher level was 200 proof (zero wt percent
water). The lower level of agitation was a gentle agitation and the higher level of agitation was anextremely vigorous agitation with some splashing.

Table1. Design

Matrixfor the Experimental

Parameters

Levels

1 - Agitation
2 - Temperature
3 - Catalyst
4 - Ethanol
Expt No.

I-k& (+1)
75 c
KOH
200 proof
Parameters
1 2 3 4-1 -1 -1 -1+l -1 -1 +l-1 +1 -1 +1+1 +l -1 -1-1 -1 +1 +1+1 -1 +1 -1-1 +l +1 -1+l +1 +1 +l

Experimental

Setup

DesignLow (-1)
30 c
NaOC2H5
190 proof% Conversion

51
98
81.5
45
91.7
29
77.8
100

and ProcedureThree operations were studied in the experimental work which was performed. These are shown in
Figure 3; they are: 1) transesterification,2) phase separation, and 3) washing. Figure 1 shows thetranesterification;in this study ethanol, in presence of a catalyst, instead of methanol was used and ethyl
ester was produced. After the reaction was complete, the reaction products separated into two layers; theester product formed the upper layer and the by-product glycerin formed the lower layer. The residual
catalyst and unreacted excess alcohol were distributed between the two phases. After separation of thephases, the catalyst and alcohol were washed from the ester with water.

Transesfefification
The transesterification
experiments were performed in conical flasks using 250 g of rapeseed oil.
Catalysts were 2.5 g (1% by weight of the oil) of potassium hydroxide or 1.25 g (0.5% by weight of oil) of
sodnun ethoxide The catalyst was first dissolved in 72 g of ethanol which represented a 100% excess ofthe stolchiometnc amount required for the transesterification.
It was necessary to heat the ethanol slightly
with stirring to completely dissolve the catalyst The ethanol and dissolved catalyst were then added to the011and stlrrmg was begun. Samples of approximately 3-4 ml of the reaction mixture were pipetted out at 1,30, 60, and 120 minutes respectively. The reaction was arrested in the samples by adding one or two
drops of water. The samples were analyzed to determine the degree of completion of the reaction.
Additional experiments were conducted to study the effects of temperature and sodium methoxideand potassium me&oxide catalysts on ester yields. Experiments were also performed to determine ester
yelds using the stoichiometric amount and amounts of alcohol equal to 50%, 7S%, and 100% excess.

Phaseseparation

After 120 minutes of reaction time, the reaction was stopped and the reaction mixture was allowed
to stand overnight while phase separations occurred.
The ester phase was then decanted from theequihbnum mixture.
Washing
Excess alcohol and residual catalyst were washed from the ester with water. The ester phase wasplaced in a glass column 1.26 cm in diameter and 100 cm in length. Water was sprayed into the top of thecolumn at a low velocity. The excess alcohol and catalyst were removed by the water as it percolated
through the column. During the washing, some of the ester formed an emulsion with the water; a time of
24-48 hours was required for the water phase containing alcohol, catalyst, and emulsified ester to settle andthe ester phase to become clear.

Analyses
The analyses have been described by Barn (1991). High Performance Liquid Chromatography(HPLC) was used to determine the composition of the reaction mixture and the ester conversion. The
composition of the ester was determined by Gas Chromatography (GC). Viscosity measurements of theester were made by following ASTM standards (ASTM D445 or IP 71). The ester was analyzed for cloudand pour points by following ASTM Standards D2500-81 and D97, respectively.

RESULTS AND DISCUSSION
Statistical Analysis of Experimental

DesignThe results obtained from the eight experiments performed according to the fractional factorial
design (Table 1) were analyzed using Statistical Analysies System (SAS). The results of this analysis wereused to develop an equation which shows the relationships between degrees of conversion, rate ofagitation. temperature, water content of ethanol, and catalyst.
CON-V = 71.75 - 3.75(A) + 4.3250

where A = rate of agitation; T = temperature;+ 21.05(ALC)+ 9.95(T)(C)- 6.37(T)(ALC)(1)

ALC = water content of alcohol; C = catalyst; and CONV=

percentage conversron of oil to ester.
In this equation, the values of A are either -1 (low agitation) or +l (high agitation); values of T areeither -1 (30C) or +l (75C); values of ALC are either -1 (190 proof) or +l (200 proof); values of C areeither -1 (NaOC2H5)
or +l (KOH).
For example, with high agitation, with temperature = 75C, using
NaOC2H5 as catalyst, and 190 proof ethanol,
CONV= 71.75 - 3.75(+1) + 4.325(+1)= 47.7%+ 21.05(-l)+ 9.95 [(+1)(-l)]- 6.375[(+1)(-l)]

Inspection of Equation (1) shows that water content of alcohol is the most important independent factor
affecting degree of conversion and that increasing water content (lowering proof) decreases degree of
conversion.
Further inspection shows that the interaction between temperature and catalyst and thetnteraction between temperature

and water constant of alcohol are significant.

A matrix was designed which contained sodium methoxide and potassium methoxide in place ofpotassium hydroxide and sodium ethoxide as shown in Table 1. The conversions obtained wereapproximately
the same for all catalysts except potassium methoxide.
The conversion obtained withpotassium methoxide was significantly lower.
Phase separation was also treated as the dependent variable as a function of agitation, temperature,catalyst and water content of alcohol. The type of catalyst used was an important variable affecting theseparation of the ester phase from the glycerin phase. Temperature, alcohol, and the interaction between
temperature and alcohol also had significant effects on phase separation.
Optimum

Conditions

for Ethyl

Ester

Preparation

Transesterification
Temperature had no detectable effect on the ultimate conversion to ester. However, higher temperatures
decrease the time required to reach maximum conversion. It is believed the cost of energy for heating
would exceed the value of time saved by using higher temperatures.
Therefore, room temperature isconsidered to be the optimum temperature for conversion.
A high degree of conversion could be obtained only if the oil and alcohol phases have been blended into
one homogeneous phase. This requires extremely vigorous agitation with some splashing at the start of thereaction.
When the reaction mixture is homogeneous, the conversion and time to reach maximum
conversion are independent of agitation.
The presence of water in the reaction mixture markedly reduces the conversion of oil to ester (seeEquation 1). 200 proof ethanol must be used in order to obtain a high degree of conversion.
Theexperiments in which different amounts of excess alcohol were used in the reaction mixture showed that an
amount in 50% excess of the stoichiometric ratio gave a high conversion when sodium methoxide was thecatalyst. Potassium hydroxide catalyst required 100% excess alcohol to achieve similar conversion andphase separation from the glycerin.
Although SAS indicated sodium e&oxide, sodium methoxide, and potassium hydroxide all gave good
conversions during transesterification,
sodium me&oxide was chosen as the most promising catalyst due tophase separation considerations described below. Experiments were performed in which the concentrationof sodium me&oxide varied from 0.3% to 0.5% by weight of rapeseed oil used. Conversion was maximum
for 0 5% concentration of catalyst.
Phase

Separation

The QF of catalyst used during the transesterification has an important effect on the subsequent phaseseparation. Phase separation was erratic and dependent upon the amount of excess alcohol present in thecase of potassium hydroxide. No phase separation occurred when potassium methoxide was used. Whensodium me&oxide or sodium ethoxide was used, separation was good; however, sodium methoxide wasjudged to give the better result.
The impact of variables other than catalyst and excess alcohol on phase separation was consideredminor relative to their impact on transesterification.

Washing
During the washing of the ester phase care must be taken to add water slowly in a fine spray.
Agitation of the ester with the flow of water caused a loss of as much as 18% of the ester due to theformation of an emulsion.
The importance of washing is the removal of residual catalyst from the ester. The effluent wash water
was monitored for sodium content and washing continued until the sodium content of the effluent was thesame as the sodium content of the entering wash water. Complete removal of catalyst from the ester was
assured by determinin g the amount of sodium in the glycerin phase and the total sodium removal from theester phase. The sum of these accounted for all of the sodium entering the reaction as a constituent of thecatalyst.
Physical

Properties

of EEWRThe measured viscosity of the ethyl ester was 7.0 centistokes at 25C. The viscosity of the rapeseed
methyl ester is 6 cs at 40C and 2.39 cs at 1OOC; the viscosity of #2 diesel is 3.2 cs at 40C and 1.26 cs at
1OOC. The cloud and pour points of the ethyl ester was found to be -7C and -16C, respectively.
Preliminary

Economic

Evaluation

Between

Methyland Ethyl

Esters

The economic viability of the rapeseed ethyl esters was compared to that of methyl esters. This wasdone by comparing the breakeven cost of methyl ester with that of ethyl ester. Breakeven costs were foundby deterrninin g the sales value of product which would be required to operate a manufacturing
facility atzero profit. At zero profit the total of all annual costs equals the sales value. In the comparison made inthis study, annual costs were separated into raw material costs and all other costs which were identified asprocessing costs. Figure 4 shows the breakeven cost for four different situations. These are 1) methyl ester
using KOH as catalyst and methyl alcohol, 2) ethyl ester using KOH as catalyst and denatured 200 proofethanol, 3) ethyl ester using sodium methoxide as catalyst and denatured 200 proof ethanol, and 4) ethyl
ester using sodium me&oxide as catalyst and 200 proof absolute alcohol. It can be noted that oil is the
major cost in all cases. Raw material costs were based on a rapeseed oil cost of %0.44/kg [%0.20ilb]. The
breakeven cost for methyl ester is $1.85AJ.S. gallon and the maximum cost for ethyl ester is %2.39/U.S.
gallon.

CONCLUSIONS
Rapeseed oil ethyl ester can be made successfully under the following conditions for transesterification:2) 0.5% sodium methoxide catalyst based on weight of rapeseed oil and 50%
excess of the stoichiometricamount of required 200 proof alcohol; or 3) 1.0% potassium hydroxide
catalyst and 100% excess of the stoiciometric amount of 200 proof alcohol;
4) Extremely vigorous
agitation with a little splashing until the reaction mixture becomes homogeneous.
1) Room temperature;

Since the ester has an extremely high tendency to form an emulsion on contact with water, care must be
taken to maintain low levels of agitation during washing.
The economic viability can be significantly improved if lower valued oil feedstocks can be obtained.
Waste animal fats from meat processing facilities waste frying oils from French fried potatces and otherfood frying operations, and low-grade residue oils from food grade oil crushing and refining plants could besubstnuted for the rapeseed oil used in this study. The ethanol must be moisture free, but can be denatured
with small amounts of gasoline
ACKNOWLEDGEMENTS
The authors thank the Department of Agricultural Engineering, University of Idaho for furnishing the
rapeoil used in this study. The assistance given by members of the Agricuhural Engineering Department isgreatly appreciated. Dr. Rico Cruz assisted with the experimental setup and with the analyses performed
during the research. This work was supported by a U.S. Department of Agriculture-AIG
Cooperative
Agreement #58-43YK-7-0045
Amendment #4.

REFERENCES
Barn, Narendra (199 1). Process development of rapeseed oil ethyl ester as a dieselfirel substitute. MS
thesis, Department of Chemical Engineering, University of Idaho, U.S.A.
Peterson. C.L., Auld, D.L.,

and Thompson,

J.C. (1983).

“Experimentswith vegetable oil expression.”Transachons of the ASAE, 26(5), 1298-1302.
Peterson, C.L., Feldman, M., Korus, R. and Auld, D.L. (1991). “Batch type tranesterification
winter rape oil.” Applied Engineenng In Agriculture, 7(6), 7 1 l-7 16.

process for

Correspondence should be addressed to: Dr. David C. Drown, Associate Professor, Department
Chemical Engineering, University of Idaho, Moscow, ID 83844-1021, Phone: (208)-8857848.

of

+

+

200 H
so:50
RAPE
#2 DI

200

#2

HOUR

EMA

ENGINE

TEST

CYCLE

RAPE
METI

Figure 2. Injector nozzles: 200 hour EMA Engine Test CycleSEED

ALCOHOI-z---x---OIL PRESS

I

-

Raw

OIL

REACTOR

Glycerin

layer

WAT R

FUEL GRADEESTER d-CL..Wash’ PERCOLATOR

Figure 3. Biodesel Transesterification

Process Flowsheet

By-Product-GLYCERIN

.. .. .. .. .. ..
.. .. .. .. .. ..
. .. ... . .. .. .
. .. ... . .. ...
. ... .. .. . .. .

Methanol
KOHmEthanol
KOH
Type

Ethanol
MeOCHzof Ester

Alcoholm......
.
......
.
......
.
H......

Catalyst

Figure 4. Cost of Ester Production

Abs.

Ethanol

MeOCH 3

Ea

Process