Ernst A. Stadlbauer and Sebastian Bojanowski

8.1 Introduction

Lipids [1] in the form of fat and edible oils are important energy sources for humans due to the high calorific value of triacylglycerols (~37 kJ/g, or ~9 kcal/g) and the nutritional benefits of both essential fatty acids and phosphate. In addition, energy stored in lipids may be technically realized by either direct use in combustion or by upgrading into a more versatile fuel. In this respect, lipids play an important role for providing lighting and warmth.

Historically, whale oil lamps and tallow candles were gradually dis­placed by kerosene lamps and electric bulbs [2]. Nowadays, lipids are attracting interest as a renewable source of fuels and chemical feedstock. Therefore, segmentation in the marketplace for lipids is noticeable [3]. In emerging economies of eastern Asia, there is a demand for cheap, edible commodity oils, such as soybean or palm oils. In developed economies, a nutritionally led demand for niche oils, such as low-trans­fat oils, high-omega-3 oils, and enhanced lipophilic vitamins (especially A and E), prevails. More recently, nonedible uses of lipids arise from the proliferating demand for alternative fuels [4] to substitute liquid hydro­carbons derived from mineral oil [5]. Such strategies fall into four broad categories. One is aimed at fueling diesel engines with pure vegetable oils [6] or vegetable oil-fossil fuel blends [7]. The other focuses on biodiesel (alkyl esters of fatty acids), which is mainly sourced from rapeseed and palm oils [8-10]. Problems [11] associated with the more polar charac­teristics of vegetable oil and biodiesel in comparison to conventional

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diesel has given rise to studies for cracking of lipids (vegetable oils/animal fat) into nonpolar hydrocarbons [12] to be used as a base for fuels or chemical commodities. Decomposition studies with and without catalysts (metallic salts, metal oxides) have been performed. Finally, lipids (and proteins) in dead cellular matter such as sewage sludge or meat and bonemeal may be converted by natural catalysts present in the substrate to oil having properties similar to diesel fuel [13].

In the following sections, basic processes of converting lipids into non­polar hydrocarbons with alkanes, alkenes, and arenes as main con­stituents are discussed. Details of pure vegetable oils or biodiesel are outlined elsewhere (see Chaps. 4, 5, 6).