A comparative study of vegetable oil methyl esters (biodiesels)

In the present study, rubber seed oil, coconut oil and palm kernel oil, which are locally available especially in Kerala (India), are chosen and their transesterification processes have been investigated. The various process variables like temperature, catalyst concentration, amount of methanol and reaction time were optimized. 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 1.72mg KOH/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 1h 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)°C with 40min reaction time to yield 98–99% biodiesel. 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)°C, 20min 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 will convert them to 98–99% biodiesel. The brake thermal efficiency of palm oil biodiesel was higher with lower brake specific fuel consumption, but rubber seed oil biodiesel(ROB) showed less emission (CO and NOx) compared to other biodiesels.