Heterogeneous basic catalysts for transesterification of vegetable oils: A review

Abstract

Biodiesels are biofuels made from renewable sources such as vegetable oils originating from plants and animal fats. Transesterification reaction is carried out by reacting triglycerides in oil/fat with an alcohol in presence of a catalyst. Important process variables are reaction temperature, time, reactant concentration and the catalyst. Catalysts can be homogeneous or heterogeneous. Homogeneous catalysts are liquid phase ionic acid and base, enzymes, and non-ionic organic base compounds. Heterogeneous catalysts are acid and base type. Examples of acid heterogeneous catalysts are ion-exchange resins, tungstated and sulphated zirconia, metal complexes and zeolite. Base heterogeneous catalysts consist of metal oxides in pure form or over support, zeolites, clays and nonoxides. Paper gives a brief introduction of catalytic transesterification process and a detailed review of solid basic catalysts. It is found that these catalysts are selective to feed and preparation method. Acid solid catalysts are suitable for high free fatty acid feed. Basic solid catalyst give a better yield compared to acid solid catalysts but lead to soap formation if feed has high free fatty acid.