Transesterification of used vegetable oil catalyzed by barium oxide under simultaneous microwave and ultrasound irradiations

• Synergistic effect of simultaneous microwave/ultrasound irradiations was evaluated.
• Yields were higher for the MW/US reactions compared to MW or US individually.
• BaO catalyzed MW/US transesterification reaction is more environmental-friendly.
• BaO catalyzed MW/US transesterification reaction provides better biodiesel yields.
• Optimum power density must be identified for energy-efficient biodiesel production.

This study presents a novel application of simultaneous microwave and ultrasound (MW/US) irradiations on transesterification of used vegetable oil catalyzed by barium oxide, heterogeneous catalyst. Experiments were conducted to study the optimum process conditions, synergistic effect of microwave and ultrasound irradiations and the effect of power density. From the process parametric optimization study, the following conditions were determined as optimum: 6:1 methanol to oil ratio, 0.75% barium oxide catalyst by wt.%, and 2 min of reaction time at a combined power output rate of 200 W (100/100 MW/US). The biodiesel yields were higher for the simultaneous MW/US mediated reactions (∼93.5%) when compared to MW (91%) and US (83.5%) irradiations individually. Additionally, the effect of power density and a discussion on the synergistic effect of the microwave and ultrasound mediated reactions were presented. A power density of 7.6 W/mL appears to be effective for MW, and MW/US irradiated reactions (94.4% and 94.7% biodiesel yields respectively), while a power density of 5.1 W/mL was appropriate for ultrasound irradiation (93.5%). This study concludes that the combined microwave and ultrasound irradiations result in a synergistic effect that reduces the heterogeneity of the transesterification reaction catalyzed by heterogeneous catalysts to enhance the biodiesel yields significantly.

Transesterification reaction mediated by simultaneous microwave and ultrasound irradiations with barium oxide (BaO) heterogeneous catalyst.Figure optionsDownload as PowerPoint slide