Comparative Studies of Biodiesel Production from Rubber Seed Oil, Coconut Oil, and Palm Oil Including Thermogravimetric Analysis

Abstract

High viscosity and low volatility of vegetable oils compared to diesel lead to injector fouling and carbon deposits in engine cylinders while using them directly in engines. Biodiesel from the vegetable oils produced by a transesterification process could reduce viscosity considerably and improve the volatility. The properties of methyl esters produced from rubber seed oil, coconut oil, and palm kernel oil, which are locally available, especially in Kerala (India), are presented here. The viscosity of methyl esters of these oils is found to be comparable with diesel fuel as per ASTM D6751-02. Biodiesel from rubber seed oil (with high FFA) was produced by employing a two-step pretreatment process (acid esterification) to reduce acid value from 48 to 1.72 mgKOH/g with 0.40 and 0.35 v/v methanol-oil ratio and 1.0% v/v H₂SO₄ as catalyst at a temperature of 63(±2)°C with 1 h reaction time followed by transesterification using a methanol-oil ratio of 0.30 v/v, 0.5 w/v KOH as an alkaline catalyst at 55(±2)°C with 40 min reaction time to yield 98–99% biodiesel. Coconut oil and palm oil, being edible oils and having similarities in fatty acid composition, transesterification with 0.25 v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 58(±2)°C, 20 min reaction time for coconut oil and 0.25% v/v methanol-oil ratio, 0.50% w/v KOH as alkaline catalyst at 60(±2)°C for palm kernel oil converted them to 98–99% biodiesel. The viscosity of coconut biodiesel was more comparable to diesel fuel than that of other biodiesels, such as rubber seed oil biodiesel and palm oil biodiesel. Furthermore, thermogravimeric analysis indicated that coconut oil biodiesel is more volatile than other biodiesels and the volatility is nearer to diesel fuel.

Keywords:

• biodiesel
• coconut methyl ester
• palm methyl ester
• rubber seed methyl ester
• thermogravimetric analysis
• transesterification