The first method for production of biodiesel is by pyrolysis reaction in which oils or fats are thermally cracked to similar chemical compositions of fossil fuels in the absence of oxygen (Ma and Hanna 1999). However, pyrolyzed vegetable oils are contaminated with trace amounts of sulfur, water, and sediment, and these could lead to corrosion problems in the engine. This process usually requires high main­tenance cost especially the distillation unit for various fractions separation (Ma and Hanna 1999). The removal of oxygen during the thermal processing of pyrolysis eliminates the benefits of using oxygenated fuel.

Another method for production of biodiesel is by microemulsion. It is defined as a colloidal equilibrium dispersion of optically isotropic fluid microstructures with dimensions generally 1-150 nm range formed spontaneously from two normally immiscible liquids and one or more ionic or nonionic amphiphiles (Schwab et al. 1987). Ionic and nonionic microemulsions of aqueous ethanol in soybean oil have good performances as diesel fuel oil. Emulsion of 53% (vol) alkali-refined and win­terized sunflower oil, 13.3% (vol) 190-proof ethanol, and 33.4% (vol) 1-butanol when undergoing 200 h laboratory screening endurance test, irregular injector nee­dle sticking, heavy carbon deposits, incomplete combustion, and an increase of lubricating oil viscosity were reported (Ziejewski et al. 1984).

Transesterification is the most widely used process producing biodiesel from vegetable oils. Transesterification is the alcoholysis of triglyceride esters, resulting
in a mixture of mono-alkyl esters and glycerol (Fukuda et al. 2001). This process has been used to reduce the viscosity of triglycerides and enhance the physical prop­erties of renewable fuels with the aim to improve the performance in engine (Clark et al. 1984). Transesterification can be carried out through a variety of ways in the presence of alkali catalyst, acid catalyst, biocatalyst, heterogeneous catalyst, or using alcohols under supercritical conditions without catalyst.

Microemulsions of vegetable oils would reduce the biofuel viscosity, but engine performance problems of injector coking and carbon deposits still persist (Bala 2005). Pyrolysis of triglycerides produces compounds with incompatible biodiesel quality in terms of ash, carbon residues, and pour point (Schwab et al. 1987). Among all the conversion methods, transesterification of vegetable oils is the most promising route to produce biofuel with similar properties and performances as hydrocarbon-based diesel fuels (Fukuda et al. 2001).