Biodiesel Production from Vegetable Oils: A Comparative Optimization Study

High viscosity and low volatility of vegetable oils compared to diesel lead to injector fouling and carbon deposits in engine cylinder while using them directly in engines. Biodiesel from these vegetable oils produced by transesterification process could reduce viscosity considerably and improve the volatility. The properties of methyl esters (biodiesels) produced from rubber seed oil, coconut oil and palm kernel oil, which are locally available especially in Kerala (India) are presented and found to be comparable with diesel fuel as per ASTM D6751-02. Biodiesel from rubber seed oil (with high free fatty acid) was produced by employing two-step pretreatment process (acid esterification) to reduce acid value from 48 to 1.72 mg KOH/g with 0.75 v/v methanol-oil ratio and 1.0% v/v H2SO4 as catalyst at a temperature of 63 (+/- 2)degrees C with one hour reaction time followed by transesterification using methanol-oil ratio of 0.30 v/v, 0.5 w/v KOH as alkaline catalyst at 55 (+/- 2)degrees C with 40 minutes reaction time to yield 98-99%. Coconut oil and palm oil, being edible oils, transesterification with 0.25 v/v methanol-oil ratio, 0.50% w/v KOH as at 58 (+/- 2)degrees C, 20 minutes reaction time for coconut oil and 0.25% v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 60 (+/- 2)degrees C for palm kernel oil will convert them to 98-99% biodiesel. It was observed that rubber seed methyl ester (being non edible) as a good alternative to diesel fuel even though viscosity of coconut methyl ester was found to be closer to that of diesel fuel.