The worldwide transport sector depends almost totally on fossil fuels. While the production of electricity is more diversified, vehicles require gasoline, diesel, or natural gas for the mobilization. Only in specific cases, has the total substitu­tion of gasoline with liquid biofuels been achieved, as in the case of the ethanol obtained from energy-rich crops such as sugarcane. The advantage of liquid bio­fuels compared to solid ones consists in their ease of transport and in the utiliza­tion of the supply chains of fossil fuels. Biodiesel and bioethanol are the two main liquid biofuels.

1.1.2.1 Biodiesel

Biological diesel is an oxygenated fuel obtained as a result of the transesterifica­tion of vegetable oils and animal fats with an alcohol in the presence of a cata­lyst (Figure 1.1). In general, the employed alcohol is methanol or ethanol. Thus, the biodiesel is a mixture of methyl or ethyl esters of fatty acids from oil and fats. Usually, rapeseed oil (in central Europe), sunflower oil (in southern Europe), and palm oil (in tropical countries of Southeast Asia and South America) are employed as a source of triglycerides. Used frying oil of animal or vegetable origin is employed for their conversion into biodiesel as well. For biodiesel pro­duction, acid, basic, and biological (enzymes) catalysts are used, with KOH and NaOH being the most utilized catalysts worldwide.

CH2 — OOC —Ri Rj— OOC— C2H5 CH2 — OH

KOH

CH2 — OOC —R2 + 3C2H5OH < > R2 —OOC —C2H5 + CH — OH

I I

CH2 — OOC —R3 R3— OOC— C2H5 CH2 — OH

Triglyceride Ethanol Ethyl esters Glycerol

FIGURE 1.1 Transesterification reaction of triglycerides.

Biodiesel is employed in heating systems and as an oxygenating additive (oxygenate) in diesel engines. For these purposes, blends containing 10% (B10) or 20% (B20) of biodiesel and the remaining fossil diesel are being utilized. In some cases and depending on its purity, the biodiesel is directly used in internal combustion engines (Ma and Hanna, 1999). The main advantages offered by the diesel usage are the reduction of polluting gases (mostly CO) and particulate mat­ter emissions, as well as the net equilibrium in the balance of atmospheric CO2. Unlike the oil-derived diesel, the biodiesel does not contain sulfurs, making its combustion much cleaner.

Worldwide biodiesel production achieved about 7.70 billion liters in 2007. The production of biodiesel in the United States was about 1.82 billion liters in 2007, whereas the production in the EU was about 5.71 billion liters (European Biodiesel Board, 2008). Germany is the world leader in biodiesel utilization. In this country, pure biodiesel is used in adapted vehicles, while in France, 30% and 50% biodiesel blends with fossil diesel are employed (Demirbas and Balar, 2006). In Colombia, the agro-industry of oilseeds is being developed through the production of biodiesel to be used as an oxygenate of local diesel in B5 blends. Thus, the productive chain of the oil palm can be boosted.