This chapter provides an overview of biodiesel (basically a mixture of fatty esters) as renewable fuel, covering the market developments and trends, chemical composition and characteristics, properties and performance, complementary use as diesel fuel, main synthesis routes (e.g. esterification or transesterification), various catalysts used for manufacturing (e.g. homogeneous, solid acids and solid base catalysts) and industrial production processes (e.g. batch, continuous, supercritical, enzymatic, multi-step, reactive separations).Fatty esters are key products of the chemical process industry, involved in various specialty chemicals with applications in the food industry, cosmetics, pharmaceuticals, plasticizers, bio-detergents and biodiesel. However, the main interest has shifted nowadays to the larger scale production of biodiesel-a mixture of fatty acid alkyl esters-hence the current strong market drive for more innovative and efficient processes (Kralova and Sjoblom 2010).The increasing worldwide interest in biodiesel is illustrated by the tremendous increase of the production, mostly in Western Europe, North America and Asiaas shown in Fig. 2.1 (Blagoev et al. 2008;Kiss 2009). The market potential for biodiesel is actually defined and limited by the market size of the petroleum diesel. Remarkable, there is no major technical limitation on replacing fossil diesel with biodiesel, although a limitation on the feedstock-and the required arable farmland-availability does exist in practice.The biodiesel market share suffered some changes during the recent decade, being now rather stabilized-as shown in Fig. 2.1 (bottom). An interesting development over the past years is the shift in global biodiesel market share. Europe had over 80 % capacity in 2000, but it is no longer the dominant player of the biodiesel industry, its global share accounting presently about 40 % of global capacity. Other key players emerged-such as Asia, North America, Central and South America-and they have leveled out the global biodiesel market shares. For a complete picture of the current status, Fig. 2.2 shows the biodiesel consumption worldwide and in EU (Kiss 2009). The biodiesel consumption worldwide is actually expected to grow at an average annual rate of over 5 % during 2011 -2016(Blagoev et al. 2008. Biodiesel is an alternative renewable and biodegradable fuel with properties similar to petroleum diesel (Bowman et al. 2006;Balat et al. 2008; Knothe 2010). Actually it has several advantages over petroleum diesel: it is safe, renewable, non-toxic and biodegradable; it contains no sulfur and is a better lubricant. Despite the chemical differences these two fuels have similar properties and performance An important characteristic of diesel fuels is the ability to auto-ignite, quantified by the cetane number (cetane index). Biodiesel not only has a higher cetane number than petroleum diesel, but also a higher flash point meaning better and safer performance. Blends of biodiesel and petroleum diesel are designated by a 'B' fo...
