Biodiesel Production from Castor Oil under Subcritical Methanol Conditions

Abstract

Biodiesel is a potentially sustainably renewable fuel for diesel engines; transesterification is the most used method to produce it and high quality vegetable oils are the most usual raw material. Non-edible vegetable oils such as castor oil can provide an alternative feedstock. In this work biodiesel was obtained by transesterification of castor oil with subcritical methanol; the reaction was carried out in an hermetic reactor at temperatures higher than methanol boiling point and with a small amount of potassium methoxide as catalyst. The effect of methanol:oil molar ratios were analyzed, observing that high proportion of alcohol is needed to reach high ester content, the best results were reached with 24:1 MeOH:oil molar ratio. Regarding catalyst concentration, 8.7 mM (0.12 wt%) were enough to achieve good results. A temperature of 150 º C and 1 h of reaction, at 10 bar, were the mildest conditions to reach an ester content higher than 90 wt %. The highest ester content, 94.7 wt %, was achieved at 220 º C, 36 bar and 4 h of reaction time. Hence good quality biodiesel from castor oil can be produced in subcritical methanol conditions,