Synthesis of Biodiesel through In Situ Transesterification of Jatropha curcas

Biodiesel is a renewable fuel synthesized through a chemical reaction of alcohol
and vegetable or animal oils, fats or greases. Currently most of the biodiesel
production is based on edible oils and use methanol and alkaline catalysts in two
step transesterification process. The main limitation of biodiesel production is due
to the high feedstock and production cost. The use of non edible oil sources, such
as Jatropha curcas, can reduce the high feedstock cost since it does not compete
with food supply and this leads to a cheaper feedstock source. Moreover, it is
hoped that these problems can be counterbalanced by combining both extraction
and reaction steps. This method is known as in situ transesterification.
The experiments were carried out in a batch reactor equipped with a reflux
condenser, a magnetic stirrer and a thermometer. Effect such as types of base
catalyst (KOH, NaOH and NaOMe), their concentrations (0.5, 1.0, 1.5, 2.0 and
2.5 (wt.%)), reaction time (2, 4 and 6 hours), reaction temperature (30, 40, 50, 60
and 70oC), stirrer speed (100, 200, 400 and 600 rpm) and types of alcohol such as
methanol, ethanol and mixture of methanol-ethanol (50% : 50%) (v/v) were
studied. The kinetics of transesterification of Jatropha curcas seeds were also
investigated.
The liquid products which consist of methyl ester, ethyl ester or mixtures of both
were analyzed using Thin Layer Chromatography (TLC) and Gas
Chromatography (GC). TLC was used to determine the content of the alkyl ester
in the biodiesel sample qualitatively. However, it can not be used to quantify the
amount of the alkyl ester in the biodiesel sample. Therefore, GC was used to
determine the amount of the fatty acid alkyl ester in the biodiesel sample. The
analysis of the biodiesel samples was conducted based on ASTM D 6854 – 00. It
was found that the highest yield of the alkyl ester (99.97%) was obtained at 30°C,
with 2.00 wt.% sodium methoxide concentration and stirrer speed of 600 rpm for
2 hours of reaction time.
However, the methanolysis in situ transesterification of the Jatropha curcas seed
was unsuccessful because the yield of the biodiesel was only 39.42%. At the
optimum conditions, the acid value, viscosity and total glycerin were 0.04 mg
KOH/g of sample, 5.5 mm2/s and 0.003 (wt.%), respectively. At 30oC, the
reaction order and reaction rate constant was found to be 1.24 and 0.009
liter0.24/mol0.24.s, respectively. The mechanism of the biodiesel production through
in situ transesterification of Jatropha curcas seed was determined by solid-liquid
kinetics. Then, it was found that the reaction rate was most probably ash diffusion
controlled.