A Review on the Use of Bio/Nanostructured Heterogeneous Catalysts in Biodiesel Production

Abstract

The continuous increase in the growth of the world's population is also drastically increasing energy demands in both industrial and domestic sectors. Moreover, public awareness about pollution due to overuse of fossil fuels has led to a rise in interest in research into alternative renewable energy sources. Among the various options for renewable energies for road transportation, biodiesel is considered the most suitable replacement for petro-diesel. In terms of industrial applications for biodiesel production, homogeneous catalysts such as NaOH, KOH, H2SO4, and HCl are usually preferred, but their removal is rather complex and somewhat polluting, bringing extra cost to the final product. The application of heterogeneous catalysts, both solid acid and solid base, for the transesterification reaction can resolve the biodiesel purification problems associated with homogeneous catalysts. However, heterogeneous catalysts are currently somewhat slow and inefficient, and present some mass-transfer limitations. In this context, nanocatalysts represent a new generation of heterogeneous catalysts with promising advantages over homogeneous and conventional heterogeneous ones. Other alternatives also exist. Enzymatic catalysis has been used in biodiesel production, employing lipases as biocatalysts. However, for economic reasons and due to issues of reusability and recycling, the lipases must be immobilized on suitable supports, bringing into play the concept of heterogeneous biocatalysis. Like other heterogeneous catalytic materials, this presents similar issues with inefficiency and mass-transfer limitations. A solution may be the use of nanostructured supports for enzyme immobilization as new heterogeneous biocatalysts. This chapter mainly focuses on the application of heterogeneous basic, acidic, and enzymatic catalysts, as well as nanocatalysts and nano(bio)catalysts, in transesterification reactions, and their multiple methods of synthesis.