Optimization of two step karanja biodiesel synthesis under microwave irradiation

The free fatty acid of crude karanja oil (Pongamia pinnata) was reduced and biodiesel was synthesized from pretreated oil under microwave irradiation. The process variables such as irradiation time, methanol–oil ratio and sulfuric acid concentration for pretreatment step; irradiation time, methanol–oil ratio and KOH concentration were optimized through the Box–Behnken experimental design. The free fatty acid of crude karanja oil was reduced to 1.11 ± 0.07% with an optimal combination of 190 s irradiation time (180 W), 33.83 (w/w)% methanol–oil ratio and 3.73 (w/w)% sulfuric acid concentration. An optimal combination of 150 s irradiation time, 33.4 (w/w)% methanol–oil ratio and 1.33 (w/w)% KOH concentration yielded 89.9 ± 0.3% biodiesel. The model was validated by conducting experiments at optimal design conditions. The present work confirmed that the microwave energy has a significant effect on esterification and transesterification reaction.