A review of biomass-derived heterogeneous catalyst for a sustainable biodiesel production

Biodiesel production is commonly carried out through the process of transesterification reaction. The reaction is expedited with a suitable catalyst either homogeneous or heterogeneous. The selection of an appropriate catalyst depends on the amount of free fatty acids in the oil. Recently, homogeneous catalysts are widely chosen for biodiesel production in large scale operation. However, they are toxic, highly flammable and corrosive in nature. Furthermore, the use of homogeneous catalyst produced soaps as by-product and large amount of wastewater that required additional processing technologies and cost for proper disposal. On the contrary, heterogeneous catalysts are capable to overcome the problems faced by the former ones. However, they were mostly derived from non-renewable resources, highly expensive with low stability. Recently, heterogeneous catalysts derived from biological waste have gotten more attention. This type of catalysts offers several advantages, including renewable resources, non-toxic, reusable, high catalytic activity, stability in both acidic and basic conditions and high water tolerance properties, which depend on the amount and strengths of active acid or basic sites. Basic catalyst can be subdivided based on the type of metal oxides and their derivatives. Similarly, acidic catalyst can be subdivided depending upon their active acidic sites. In this article, efforts have been taken to review the bio-based heterogeneous catalyst utilized for sustainable biodiesel production and their suitability for industrial application. Catalyst generated from bio-waste and other biocatalysts, which are heterogeneous in nature and extensively reported in literature are also reviewed. The utilization of these biomass derived catalysts provides a greener synthesis route for biodiesel production.