The Chemistry of Biodiesel Production - Term Paper Example

Biodiesel is one such form of hydrocarbon based fuels. The American Society for Testing and Materials (ASTM) defines biodiesel fuel as monoalkyl esters of long chain fatty acids derived from a renewable lipid feedstock, such as vegetable oil or animal fat (Zhang et al. 1). It is made by chemically combining any natural oil, fat or recycled grease with a suitable alcohol in the presence of a catalyst. The general equation that can be used to predict the amount of biodiesel that will be made from fats and oils is as shown: 100 pounds of oil + 10 pounds of methanol > 100 pounds of biodiesel + 10 pounds of glycerol Biodiesel can be used as neat (B 100) or in a blend with petroleum diesel for example a blend of 20 % biodiesel with 80 % petro-diesel by volume, is termed “B 20” (van Gerpen et al. 22). .

The Biox process involves the use of a co-solvent, tetrahydrofuran (THF), to solubilize the methanol. THF enhances solubility of the alcohol in the triglyceride phase and thus hastens the otherwise slow reaction (van Gerpen et al. 38). With THF the reaction takes 5 to 10 minutes at a low temperature of 30°C. On the other hand, in the supercritical process a high alcohol to oil ratio (42:1) mixture is subjected to supercritical conditions – temperatures of 350 – 400 °C and pressures of 1200 pounds per square inch and above.

So far, the huge capital and operating costs incurred in performing the supercritical reactions have made scaling up of this process to be quite difficult (van Gerpen et al. 40). The most common way to produce biodiesel is through transesterification. Transesterification refers to a catalyzed chemical reaction involving vegetable oil and an alcohol to yield fatty acid alkyl esters (which is the biodiesel) and glycerol. Catalyzed processes can be further subdivided into three major processes: acid catalyzed processes, alkali catalyzed processes and enzyme catalyzed processes (Zhang et al. 2). The alkali catalyzed process involves use of a basic catalyst such as sodium hydroxide or potassium hydroxide whereas the acid catalyzed process involves the use of an acid such as sulfuric, phosphoric, hydrochloric, or organic sulfonic acids as the catalyst.

In enzyme catalyzed processes, lipases are used to catalyze transesterification in either aqueous or non-aqueous systems. Acid catalyzed and alkali catalyzed processes are the ones that continue to receive the most attention largely because the production of enzymes is significantly costly and their reactions remarkably slower (Zhang et al. 2). As mentioned previously,