Intensification of synthesis of biodiesel from non-edible oil using sequential combination of microwave and ultrasound

The present work reports the intensification of synthesis of biodiesel from the high acid value Nagchampa oil using sequential effect of microwave and ultrasound in a two-step synthesis method and its comparison with individual approaches of microwave, ultrasound and conventional approach. Esterification processing was employed for reducing the initial acid value of the oil from 18.9 to 1.7 mg of KOH/g of oil, in order to avoid saponification reaction during the alkaline transesterification. The molar ratio and catalyst concentration have been optimized for the esterification and transesterification stages for the microwave, ultrasound and sequential approach. It has been observed that the optimum molar ratio required for esterification is 1:4, 1:3, and 1:2 for the ultrasound, microwave and sequential approach respectively whereas for transesterification the optimum ratio in same order is 1:6, 1:6, and 1:4. The reaction time for the esterification and transesterification using ultrasound alone was 60 min and 20 min respectively and it reduced to only 15 min and 6 min for the sequential approach. The key intensification parameter is that the required excess of the alcohol is significantly reduced, which can lead to substantial energy savings in the downstream separations. (c) 2012 Elsevier B.V. All rights reserved.