1 2

Rama Raju Baadhe, Ravichandra Potumarthi2’*, Vijai K. Gupta
^Department of Biotechnology, National Institute of Technology, Warangal, Andhra Pradesh, India,
^Department of Chemical Engineering, Monash University, Clayton, Victoria, Australia,
3Molecular Glycobiotechnology Group, Department of Biochemistry, School of Natural Sciences,
National University of Ireland Galway, Galway, Ireland
*Corresponding author email: ravichandra. potumarthi@monash. edu; pravichandra@gmail. com

OUTLINE

Introduction 119

Chemistry of Biodiesel 120

Transesterification 120

Disadvantages of Chemical Transesterification 120

Advantages of Using Lipases in

Biodiesel Production 121

Historical Background of Lipase 121

Lipase-Catalyzed Transesterification Done

in Two Approaches 121

Advantages of Immobilized Lipase 122

Technical Challenges 123

Feedstock 123

Vegetable Oils 123

Animal Oils/Fats	123
Waste Oils/Fats	123
Algae Oils	124
Choice of Enzyme	124
Molar Ratio (Alcohol/Oil)	124
Temperature	124
Water Content	126
Acyl Acceptors	126
Solvents	126
Reactor System	126
Conclusions	127
References	127

INTRODUCTION

World’s commercial primary energy needs are mostly supplied through fossil fuels and accounts about 87% of total energy source (OPEC, 2011, 2012). Primary energy demand by 2035 increases to 54% and still fossil fuels con­tributes 82% of the global total by 2035 (OPEC, 2012). All fossil-fuel sources are finite and if the crude oil con­sumption continued at current usage rates, it will last
only for 54.2 years (British Petroleum Statistical Review, 2012). Projected demand for oil reaches 110 mb/day by 2035. Among the fossil fuel, diesel fuels have an essen­tial function in the industrial, transportation and agri­cultural sectors in developing countries. Gradual depletion of crude oil and emission of greenhouse gases in to the environment triggers the alarm for suitable alternative fuels for use in diesel engines (Ganesan et al., 2009). Biodiesel is one of the attractive and

Bioenergy Research: Advances and Applications http://dx. doi. org/10.1016/B978-0-444-59561-4.00008-5

alternative fuels along with bioethanol. Biodiesel or fatty acid methyl esters (FAMEs) are mono-alkyl esters of long-chain fatty acids, derived from transesterification of triglycerides (plant or animal or algal origin). It can be used directly in its pure form or as a blend with con­ventional diesel fuel in diesel engines (Ma and Hanna,

1999) . This fuel is biodegradable and nontoxic and has low emission profiles when compared to petroleum diesel (Krawczyk, 1996). But the cost of biodiesel, how­ever, is the main obstacle to commercialize the product. There are four primary ways of making biodiesel: direct use and blending (Ma and Hanna, 1999), micro emulsions (Schwab et al., 1987), thermal cracking (pyrol­ysis) (Sonntag, 1979) and transesterification. However, the first three have some limitations and drawbacks in case of physiochemical properties of biodiesel (Schwab et al., 1987). Transesterification is the well-known method and involves conversion of oils or fat to FAMEs or fatty acid ethyl esters in the presence of a catalyst such as acid, base or lipase (Bisen et al., 2010). The conventional method for producing biodiesel involves acid and base catalysts to form fatty acid alkyl esters. Processing expenses and environmental concerns associated with biodiesel production and difficulties connected with by-products recovery have led to the search for alterna­tive production methods and alternative sources (Bisen et al., 2010). Enzyme-mediated transesterification can be a moderate alternative to produce biodiesel in its pure form, which also makes its separation easy against the by-product (glycerol). But still due to the cost of enzyme, commercialization of biodiesel has not come to reality. Though there are many attempts made for bio­diesel production through enzyme-mediated method (Ranganathan et al., 2008; Sanchez and Vasudevan, 2006; Lai et al., 2005; Noureddini et al., 2005; De Oliveira et al., 2004; Xu et al., 2004; Sha et al., 2003; Belafi-Bako et al., 2002; Iso et al., 2001; Fukuda et al., 2001; Freedman et al., 1984), profitable commercial production was not achieved for industrial utilization. Recombinant DNA and protein engineering technologies improved the quantities and catalytic efficiency of lipase (Akoh et al.,

2007) . There are several technical challenges that need to be addressed to make biodiesel production profitable. Some of them associated with enzyme transesterification process. In this chapter, some of the technical challenges

О

II

r’co-ch2

о

II

R’CO-CH2 + 3 ROH

I Alcohol

R’CO-CH2

Triacylglycerol (vegetable oil)

3 CH2-O-CO-R I

2 H-C-O-CO-R’

I

1 CH2-O-CO-R»

1,2,3,-O-tri-acyl -glycerol R’, Rand R» are saturated or unsaturated chains

FIGURE 8.1 Chemical structure of triacylglycerol. Source: Bisen et al. (2010).

involved in the lipase-catalyzed biodiesel production were discussed.

CHEMISTRY OF BIODIESEL

Chemically biodiesel is defined as mono-alkyl (methyl or ethyl) esters of triacylglycerol. All vegetable oils, algal lipids and animal fats (triacylglycerol/triglyc — eride molecules) consist of a three-carbon chain forms the glycerol backbone, which consists of three long fatty acid chains (Figure 8.1). Amounts of each fatty acid pre­sent in molecules determine the properties of triacylgly — cerol (Knothe, 2001).

TRANSESTERIFICATION

In chemical transesterification process, fatty acid re­acts with any alcohol and forms mono-alkyl ester (bio­diesel) in the presence of a catalyst (acid, base and enzyme). General reaction scheme of biodiesel produc­tion is shown in Figure 8.2. The reaction has two inputs: triacylglycerol and the alcohol—commonly ethanol or methanol is used (Meher et al., 2004).