Microwave Irradiation Aided Transesterification for Biodiesel Synthesis via Heterogeneous Catalysts

This review paper has examined, though not exhaustively, the synthesis of biodiesel through the transesterification reaction of non-edible and waste oils utilizing chemically-based heterogeneous catalysts activated by microwave irradiation. The production of biodiesel from such feedstock oils can significantly enhance the commercialization of biodiesel, as it presents a cost-effective alternative to fresh edible oils, thereby lowering raw material expenses. Another potential reduction in costs may stem from employing heterogeneous catalysts alongside microwave heating, which utilizes less energy and necessitates a shorter transesterification reaction time, exhibiting improved reaction kinetics without compromising the overall yield of biodiesel, in contrast to traditional heating methods. The findings from the reviewed studies indicate that microwave heating may surpass conventional heating in all assessed parameters, despite the more controlled reaction conditions associated with the former. It has also been observed that the acceleration of the transesterification reaction via microwave heating cannot be directly compared to that achieved through conventional heating under otherwise identical conditions. Moreover, microwave-assisted heterogeneously catalyzed transesterification reactions are distinguished by the emergence of hot spots, superheating, and selective heating of particular species. These phenomena improve the efficiency of the heating process, resulting in a higher rate of transesterification while minimizing the generation of by-products. The efficacy of heterogeneous catalysts in facilitating transesterification reactions is remarkable, showcasing high reactivity, stability, and selectivity when integrated with microwave technology.