Prospects of heterogeneous catalysts in biodiesel development

Abstract

Biodiesel is gaining popularity among the researchers and the public in general who are using diesel as fuel in agriculture and automobiles. The positive aspects of biodiesel is its renewable nature, less emissions of toxic substances, being biodegradable in nature and reduction in the major contributor of global warming such as carbon dioxide. Constituents of biodiesel are basically fatty acid alkyl esters which can be derived from a variety of raw materials. These include vegetable oils, animal fats and algae. The process employed is transesterification reaction where the fatty acids react with lower group alcohol in presence of a catalyst to get converted into fatty acid alkyl esters. Till recently, homogeneous catalysts were commonly employed in research and at industrial level also for biodiesel production. These catalysts still dominate in biodiesel production but few of their demerits have given the scope for search of heterogeneous catalysts. These heterogeneous catalysts work on the mechanism similar to that of homogeneous catalysts. A variety of compounds have been used as heterogeneous catalysts based on their surface area, basicity, porosity and other factors. These catalysts are mainly grouped as acid catalysts, base catalyst and enzymes. Solid base catalysts have shown good performance in transesterification reaction. Acid catalysts have the advantage of esterification of free fatty acids (FFAs) in addition to transesterification. FFAs are constituents of various non-edible oils which are used as feedstock for biodiesel development. Acid and base catalysts along with their method of preparation, mechanism, yield and conversion obtained from them under optimized conditions have been discussed in this chapter. Activity of these heterogeneous catalysts improved by calcination at high temperature to modify their characteristics has also been discussed. Leaching test has been carried out by several authors to justify their heterogeneous nature. As per the findings of several authors, some of these catalysts have shown high yield and conversion which could be a definite alternative to their homogeneous counterparts. With this pace of research and the advantage of the heterogeneous catalyst in the form of their easy separation and reusability, these catalysts have potential to be applied at industrial level for the production of biodiesel. On the basis of their better performance and simplicity in their handling, the heterogeneous catalysts will prove to be 'master substances' of tomorrow. © 2010 by Nova Science Publishers, Inc. All rights reserved.