Biomass‐based heterogeneous catalysts for biodiesel production: A comprehensive review

Abstract

Biodiesel is one of the most widely used alternative fuels to reduce exhaust emissions and the use of conventional fossil fuels. It can be synthesized from a transesterification reaction from vegetable oils or animal fats in the presence of homogeneous or heterogeneous catalysts. Some drawbacks of using homogeneous catalysts increased attention to heterogeneous catalysts for biodiesel production. Recently, heterogeneous catalysts derived from biomass have risen to the forefront of biodiesel production due to their sustainability, economical and eco-friendly nature. In addition, they are easily recovered and constitute an alternative to eliminate biomass residues. This review highlights several biomass sources used as precursors for the production of heterogeneous catalyst. Furthermore, methods for preparing heterogeneous catalysts, the reaction mechanisms, catalyst advantages and drawbacks, their performance in biodiesel production, as well as the methodologies developed for their effective recovery are discussed in detail. Among lignocellulosic biomass-based precursors, the paper takes into account those based on biochar, ash, carbonaceous substrate, and seed oil cake. Those catalysts obtained by both preparation methods (calcination and activation) have good catalytic activity for waste cooking oil or neat oils. Biomass ash or biochar-based catalysts are also promising routes in biodiesel synthesis, but significant reductions in catalyst load, reaction time, temperature, and methanol-to-oil ratio must be reached.