Synthesis of Biodiesel from a Crude Blend of Palm Oil and Rubber Seed Oil

Biodiesel industry is expanding as new challenges arise from environmental impacts
caused by hydrocarbon based fuels. However, the industry has shown some downfall
recently due to the increasing demand of vegetable oils for human nutrition's need.
Crude rubber seed and palm oils were used in this study to synthesize biodiesel since
both can be extracted and produced here in Malaysia from their abundant plantations.
The respective oils and the blends were characterized. An equi-volume blend of crude
palm oil and rubber seed oil was chosen for biodiesel synthesis and exhibited the
following properties: density of0.91754 g/cm3, viscosity of39.35cP, heating value of
38.1 MJ/Kg, acid value 31.4, FFA 11.9%, refractive index of 1.465, mono-,di- and
triglycerides were 2.5, 7.3 and 70 wt%. Sulfur content was acceptable at 0.03 lwt%.
Fstty acid composition for the oil blend was established and the calculated iodine
value was 106.3. Two stage transesterification is performed in this study to remedy
the high acid value of the oil blend. Design of experiments using taguchi technique
was used to study the interaction of parameters involved in the production.
Temperature, alcohol and catalyst amount were studied independently for both acid
and base reactions to find their relevant effects. The optimum operating conditions for
acid esterification which could reduce the FFA% to lower than 0.6% were 65°C, 15/1
methanol to oil ratio and 0.5wt% catalyst. The optimum operating conditions for base
transesterification were 55°C, 8/1 methanol to oil ratio and 2wt% potassium
hydroxide which could achieve the highest possible conversion to methyl esters
exceeding 98 %. The quality of biodiesel produced matched that of international
standards. The kinetics of free fatty acids alcoholysis in acid esterification was
investigated and the rate equation had a reaction order of (2.24). Rate constant was
(6.769xl03 lit/gmol.min) while the activation energy and Arrhenius constant were
60.289 and 14.06 x 109 KJ/g respectively. A nonlinear model was developed and
with experimental data to predict FFA concentration change throughout the reaction.
Kinetics of methyl ester formation in base transesterification was studied using
differential method. Three techniques were applied, namely, graphical method, finite
difference and linear regression. None of which could predict a rate law to represent
the reaction. Consequently, a model was developed to represent the rate of reaction
and the system using nonlinear regression of the experimental data.