Production of Biodiesel by Enzymatic Transesterification: Review

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.

Recent developments in microbial oils production: a possible alternative to vegetable oils for biodiesel without competition with human food?

“…Lipid bio-fuels are the renewable resource which seems to be a promising alternative for partial or total replacement of fossil fuels (Liu et al 2008). Biodiesel is defined as a mixture of fatty acid alkyl esters which can be produced from renewable sources and can be in solid or liquid state (Ghaly et al 2010). The technical properties of biodiesel must be the availability (Demirbas, 2008), lack of negative effect upon environment, biodegradability (Zhang et al 2003), low potential risk (no explosive vapour) (Muniyappa et al 1996) and easy portability to existent storage places (Zhang et al 2003;Demirbas, 2006;Fisher et al 2008).…”

The challenge of biodiesel production from oil palm feedstock in Nigeria

“…Of these, microbes have been found to produce high yields of lipases compared to the animal and plants (Ghaly et al, 2010). Because their bulk production is easy, the commercialization of microbial lipases and their involvement in biodiesel production are common compared to that from plants and animals (Akohet al, 2007).…”

“…Lipases hydrolyze TG (Saliset al, 2005) and are capable of catalyzing other unnatural reactions. They act on the ester bonds of carboxylic acids allowing them to carry out their primary reaction of hydrolyzing fats (Joseph et al, 2008).This involves the soaking of enzyme in a medium prior to use in the transesterification reaction (Ghaly et al, 2010). This pretreatment helps to minimize the deactivation of the enzyme which is most commonly due to the use of lower chained alcohols (Ranganathan et al, 2008).…”

“…In a typical acid pretreatment procedure, FFA are esterified to the corresponding FAME in the presence of heat, excess methanol, and acid catalyst, usually sulfuric acid, hydrochloric acid (Ghaly et al, 2010;Nebel and Mittelbach, 2006;Kumartiwari et al, 2007;Meng et al, 2008). The two-step procedure readily accommodates high FFA-containing low-cost feedstocks for the preparation of biodiesel Van Gerpen 1999, 2001).…”

“…Transesterification is the exchange of the alcohol moiety of an ester with another alcohol moiety (Ghaly et al, 2010;Ranganathan et al, 2008) (Fig. 1).…”