Batch Esterification of Free Fatty Acid in Crude Palm Oil with Ethanol Assisted by Ultrasonic Irradiation

One of the obstacles in transesterification of crude palm oil (CPO), a raw material in biodiesel production, is its free fatty acid (FFA) content which causes soap formation and lowers the ester yield. This study investigated FFA reduction using batch esterification of FFA with ethanol, having sulfuric acid as a catalyst together with ultrasonic irradiation. Taguchi method was used in the experimental design. Results showed that FFA content could be reduced from 5.1 to 0.5 wt%. The optimum conditions were: sulfuric acid content at 60 wt% of FFA, 30:1 molar ratio of ethanol to FFA, 60 degrees C reaction temperature, 1 h reaction time, and 75% amplitude of acoustic power. The esterification not only reduced the FFA content, but also simultaneously lowered the phosphorus content from 11.24 to 1.46 mg/kg. One obvious advantage of this method is that no external source of heat is required for the reaction; the heat could be generated by cavitation resulting from ultrasonic activity. Comparing with the traditional stirring method, esterification by ultrasonic irradiation yielded no significant difference on FFA reduction. The esterification process had also been proven an efficient alternative to simultaneously reduce FFA and phosphorus content in the CPO.