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The Biodiesel Production Process from Vegetable Oil.

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Dev. Chem. Eng. Mineral Process. 13(5/6), pp. 687-692, 2005.
The Biodiesel Production Process from
Vegetable Oil
Supranto
Department of Chemical Engineering, Gaa'jah Mada University,
Yogyakurta 55281, Indonesia
Research has been conducted on the production of biodiesel fiom vegetable oil by
means of the transesterfication process. The vegetable oils used were palm oil and
kapok oil. The experiments involved reacting the vegetable oil and methanol in a
tank-type reactor equipped with stirrer and temperature controller. The sodium
hydroxide is used as the catalyst. Theprocess conditions of the reaction, including the
reaction time and reaction temperatures can be controlled independently. Reaction
product was separatedfiom the reactants and used as biodieselfirel for diesel engine.
Experimental results showed that the conversion of the triglycerides to methyl ester
was affected by the process conditions. The transesterification processes with
temperature of about 7@C, and methanol ratio to the triglyceride of about 5 times its
stoichiometry, and the NaOH catalyst of 0.4 WPA, appear to be the acceptable
process conditionsfor biodiesel process production fiom palm oil and kapok oil.
Keywords: biodiesel, vegetable oil, transesterif cation, process production.
Introduction
Renewable energy resources are seen as future requirements to support human life.
Future uses of renewable energy will also have to meet environmental considerations.
World oil reserves are depleting and the biotechnology and alternative fuels will have
to take a more important role for fiture world energy supplies. In addition, global air
pollution increases day by day due to the large usage of low-grade oils, which release
C02, NOx and SOX into the atmosphere. Renewable energy resources need to be
developed, and also fuels that are more environmentally friendly. Based on these
considerations, it is believed that bio-diesel produced from vegetable oil will
eventually become one of the most important renewable energy sources for
transportation and household uses.
Authorfor correspondence (supranto@chemeng.ugm.ac.id).
68 7
Supranto
Indonesia has recently started developing bio-diesel derived from vegetable oils.
Sumiarso (2001) stated that Indonesia, with a large suitable area, has the possibility to
expand its oil palm and other plantations to provide a significant amount of crude oil
for development of a bio-diesel industry. Currently Indonesia is the second largest
palm oil producer after Malaysia, with a total production of 6.5 million tons of crude
palm oil (CPO) in 2000. This CPO was produced from 3.2 million ha of oil palm
plantations and the development of oil plantation is continuing. In the future, oil
plantations will expand in new and marginal areas. Following Sumatera, Kalimantan
and Irian Jaya will be the new development areas due to the availability of suitable
land (Pakpahan, 2001).
The chemical and physical properties of biodiesel closely resemble those of diesel
fuel. This has been documented by many workers (Clark et al., 1984; Mittelbach and
Tritthart, 1988; Pakpahan, 2001; Legowo E., 2001). The biodiesel cetane number,
energy content, viscosity and phase changes are similar to those of petroleum-based
diesel fuel, and biodiesel is essentially sulfur free. Engines fueled by biodiesel emit
significantly fewer particulates, hydrocarbons and less carbon monoxide than those
operating on conventional diesel fuel. However, emissions of NOx are slightly higher
than those of diesel engines operating on conventional diesel fuels (Mittelbach and
Tritthart,1988).
Biodiesel offers enhanced safety characteristics when compared to diesel fuel. It
has a higher flash point and does not produce explosive aidfuel vapors. Biodiesel is
biodegradable and less toxic than petroleum fuel, and emissions from an engine
operating on these fuels are less toxic due to an absence of aromatic hydrocarbons.
The esterified vegetable oils have a higher cloud point than diesel fuels and require
engine and fuel heaters when used as pure fuel in climates where the temperature dips
below O'C. However, for 20 to 25% blend of esterified oil and petroleum-based
diesel, no heater is required (Muniyappa et al., 1996).
Biodiesel is chemically defined as a methyl ester derived from natural oils such as
vegetable oils, animal fats or used frylng oils. Biodiesel is made by transesterification
of triglyceride in the natural oils with methanol. The transesterification of palm oil
and kapok oil for fuel purposes was studied in this work.
Experimental Details
The transesterification of vegetable oils or fats can be performed in a simple process.
However, the process conditions must be carefully controlled in order to acheve an
optimal yield at the optimal temperature and reaction time. The reactor is initially
charged with vegetable oil, methanol (in an amount of 3 to 15 equivalents), and
sodium hydroxide catalyst in an amount 0.1 to 1.O wt% based on the free fatty acid
concentration of the glycerides. The reaction mixture is then heated to the boiling
temperature of methanol and refluxed for a controlled time with agitation. The
reaction is at atmospheric pressure. With the agitation stopped, the reaction mixture
separates into an upper layer of methyl esters and a lower layer of glycerol diluted
with un-reacted methanol. The fatty ester product in the upper layer should be
neutralized, and vacuum distilled for the removal of any excess methanol before used
as a fuel.
688
The Biodiesel Production Process from Vegetable Oil
H
I
H-C-OCORI
I
H-C-OCOR2
I
H-C-OCOR3
I
H
H
I
CH3-OCORI
+
3 CH3-OH
+
H-C-OH
+
I
CH3-OCORt + H-C-OH
+
I
CH3-OCOR3
H-C-OH
I
H
~~
~
~~~
~
Figure 1. Transesterificationprocess of triglycerides with methanol.
Results and Discussion
The transesterification process involves the transformation of the large, branched,
triglyceride molecule into smaller, straight-chain molecules as illustrated in Figure 1.
Experimental investigations of the transesterification of the kapok oil and palm oil
were performed according to the procedures described above. Results selected and
representative experiments are presented in Figures 2 to 5.
The degree of homogeneity (or emulsification) of methanol in the triglyceride
phase is induced through mechanical mixing and by increasing the temperature of the
reactor. The reaction lunetics of the transesterification was approximated as a nonequilibrium pseudo-homogenous-first-order-reaction.The reaction rate coefficient can
be calculated from:
-dC/dt
=
kC
(1)
c
=
C,(1-x)
(2)
h(1-X)
=
k(t-tJ
(3)
-
where C is concentration of triglycerides; x is conversion of triglycerides; k is
reaction rate coefficient of the transesterifation process; t is the reaction time.
The reaction rate constants of the transesterification processes are presented in
Figures 6 and 7.
Using the value of the reaction rate constant obtained from the experiments, then
the transesterification process of vegetable oils with other process conditions can be
predicted as shown in Figure 8. The methyl ester product of the transesterification can
be separated from the product mixture by utilizing the physical property differences
(i.e. density, solubility in solvent, volatility) between the methyl ester and the other
chemicals in the mixture (i.e. methanol, glycerol, triglyceride, catalyst).
689
Supranto
Figure 2. Effect of time on the transesterijkation oftriglyceride in vegetable oil # I .
subject to 0.4 wt% of catalyst (NaOH).
I
0
I0
2a
30
41
60
00
time, min
Figure 3. Effect of time on the transesterifcation process of vegetable oil #2.
subject to 0.4 wt% catalyst (NaOH).
1W
I
0
10
20
30
40
50
60
0
rims min
Figure 4. Effect oftime on the transesterifcation process of vegetable oil #I,
subject to 3x stoichiometry of MET/TGE.
690
The Biodiesel Production Process fiom Vegetable Oil
-
0.10 at% C a t d y s l
a y *
....o.... 0 . a wt96 c
0.30 at% c a i s t
90.4) wt96 catdymb
4
0 3 wt96 catdymb
-t-
-
I
0
10
20
30
40
60
50
time, min
Figure 5. Effect of time on the transesterijkation process of vegetable oil #2,
subject to 3x stoichiometry of METflGE.
-
0-
0.028 i0.024 51 0.022 0.020
t
./
:1; :
0.016
-
0014
-
m
o
OM2 -
umbbkM
upbbhm
U'
0.010 -l
0.025
a
1
3
0.020
0.M
s
0 01 0
0.0
0.1
02
0.3
0.4
calalyrt
0.5
0.6
0.7
0.6
lRt%
Figure 7. Effect of ratio of methanol (MET) to triglyceride (TGE) on the reaction rate
coeficient.
691
Supranto
,
Figure 8. Conversion of triglyceride to methyl ester in the transesteri’jlcation process with the
ratio of methanol to triglyseride of about 5x stoichiometv.
Conclusions
The transesterification of triglycetides involves two immiscible liquid phases. The
degree of contact or solubility of these phases limits the extent of the reaction. The
use of an excess methanol of about 5 times its stoichiometry may increase the degree
of contact between the reactants.
References
1. Clark, S.J., Wagner, L.,Schrock, M.D., and Pinnaar, P.G. 1984. Methyl and ethyl esters as renewable
fuels for diesel engines. J. Amer. Oil Chem. SOC.,61, 1632-1638.
2. Legowo, E. 2001, Experience in Palm Biodiesel Uses for Transportation, Proceedings of the
International Biodiesel Workshop, Medan, Indonesia.
3. Mittelbach, M., and Tritthart, P. 1988. Diesel fuel derived from vegetable oils, 111. Emission test using
methyl esters of used frylng oils. J. Amer. Oil Chem. SOC.,65, 1185-1 187.
4. Muniyappa, P.R., Brammer, S.C., and Noureddini, H. 1996. Improved conversion of plant oils and
animal fats into biodiesel and co-product, Bioresource Technology, 56, 19-24.
5 . Pakpahan, A. 2001. Palm Biodiesel: Its Potency. Technology, Business Prospect, and Environmental
Implication in Indonesia, Proceedings of the International Biodiesel Workshop, Medan, Indonesia.
6. Sumiarso, L. 2001. Indonesian Policy on Renewuble Energy Development. Proceedings of the
International Biodiesel Workshop, Medan, Indonesia.
692
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