Production of Biodiesel by Enzymatic Transesterification: Review

Ghaly Ghaly

doi:10.3844/ajbbsp.2010.54.76

Abstract

Problem Statement: The research on the production of biodiesel has increased significantly in recent years because of the need for an alternative fuel which endows with biodegradability, low toxicity and renewability. Plant oils, animal fats, microalgal oils and waste products such as animal rendering, fish processing waste and cooking oils have been employed as feedstocks for biodiesel production. In order to design an economically and environmentally sustainable biodiesel production process, a proper understanding of the factors affecting the process and their relative importance is necessary. Approach: A comprehensive review of the literature on the subject of biodiesel production was carried out. Traditionally biodiesel has been produced using either acid or base catalysts. The multi-step purification of end products, wastewater treatment and energy demand of the conventional process has lead to search for alternative option for production of biodiesel. The use the enzyme lipase as a biocatalyst for the transesterification reaction step in biodiesel production has been extensively investigated. Lipase is produced by all living organisms and can be used intracellularly or extracellularly. Conclusion: To date, the most popular microbes used for their lipases have been filamentous fungi and recombinant bacteria. A summary of lipases used in transesterification and their optimum operating conditions is provided. In addition to the choice of lipase employed, factors which make the transesterification process feasible and ready for commercialization are: enzyme modification, the selection of feedstock and alcohol, use of common solvents, pretreatment of the lipase, alcohol to oil molar ratio, water activity/content and reaction temperature. Optimization of these parameters is necessary in order toreduce the cost of biodiesel production. Use of no/low cost waste materials as feedstocks will have double environmental benefits by reducing the environmental pollution potential of the wastes and producing an environmentally friendly fuel.

Highlights

Finite fossil fuel reserves, political, economic, health and environmental issues and/or concerns have promoted biodiesel as an alternative renewable and eco-friendly fuel
As a green renewable and potentially unlimited, biodiesel has recently come out as the superlative alternative fuel which can be used in compression ignition engines with minor or no modifications (Xu and Wu, 2003; Vasudevan and Briggs, 2008; Robles et al, 2009; Leung et al, 2010)
Using a mixture containing 20% biodiesel reduces carbon dioxide net emissions by 15.66% (Fukuda et al, 2001) while using pure biodiesel makes the net emission of carbon dioxide zero (Vasudevan and Briggs, 2008)

Summary

INTRODUCTION

Political, economic, health and environmental (ozone depletion, global warming, greenhouse gases) issues and/or concerns have promoted biodiesel as an alternative renewable and eco-friendly fuel. The most popular plant derived oils used for biodiesel production are: canola, coconut, cottonseed, groundnut, jatropha, karanj, olive, palm, peanut, rapeseed, safflower, soybean and sunflower oils (Demirbas, 2003; Akoh et al, 2007; Robles et al, 2009). The choice of feedstock depends on where the biodiesel is being produced and used which could meet norms of internationally accepted ASTM standards Parameters such as saponification number, iodine value and cetane number of fatty acid methyl esters of the oil, play an important role in selection of feedstock for biodiesel production (Sharma and Singh, 2010). Biodiesel produced from oils with large chain fatty acids (greater than 18 carbons) have a high cetane index and combustion temperature but have low cloud and pour points and greater viscosity (Robles et al, 2009).

MATERIALS AND METHODS

RESULTS AND DISCUSSION

Methods