Solid acid (heterogeneous) catalysts have a unique advantage in esterification and transesterification reactions which enhances the use of high acid value oil to be used as feedstock for synthesis of biodiesel. Various solid acid catalysts such as resins, tungstated and sulfated zirconia, polyaniline sulfate, heteropolyacid, metal complexes, sulfated tin oxide, zeolite, acidic ionic liquid, and others have been explored as potential heterogeneous catalysts. The activity of the catalyst differs slightly resulting in moderate to high conversion and yield. The reuse of the solid catalyst is governed by their deactivation, poisoning, and the extent of leaching in the reaction medium. The applicability of these catalysts for synthesis of biodiesel along with their reusability aspect is discussed in this review.
Sharma, Y. C., Singh, B., & Korstad, J. (2011). Advancements in solid acid catalysts for ecofriendly and economically viable synthesis of biodiesel. Biofuels, Bioproducts and Biorefining, 5(1), 69-92. doi:10.1002/bbb.253