1.1 Background

Over the past decade, interest in biodiesel use has grown due to the increasing price of petroleum and the effect of carbon emissions on climate change. Biodiesel is a non-toxic and biodegradable alternative fuel, which can be used in conjunction with or as a substitute for petroleum diesel fuel. The first account for the production of biodiesel was in 1937 by the Belgian professor G. Chavanne of the University of Brussels, who applied for a patent (Belgian Patent 422,877) for the “Procedure for the transformation of vegetable oils for their uses as fuels” [12]. The chemical structure of biodiesel is that of a fatty acid alkyl ester, which is clean burning [13]. Biodiesel contains no polycyclic aromatic hydrocarbons, and emits very little sulfur dioxide, carbon monoxide, carbon dioxide, and particulates, which greatly reduces health risks when compared to petroleum diesel.

The first diesel engine was created in 1893 by a German mechanical engineer, Rudolph Diesel. The diesel engine is an internal compression-ignition engine that uses the compression of the fuel to cause ignition, instead of a spark plug for gaso­line engines. As a result, a higher compression ratio is required for a diesel engine, which for the same power output (when compared to a gasoline engine), is more efficient and uses less fuel. The higher compression ratio requires the diesel engine to be built stronger so it can handle the higher pressure; consequently, the longevity of a diesel engine is generally higher than its gasoline equivalent. These vehicles therefore require less maintenance and repair overall, thus saving money [14]. In the European markets, over 40% of new car sales are diesel. This is due to a large influx of highly efficient diesel engines used in small cars.

An advantage of biodiesel is that current compression-ignition (diesel) engines, 15 years old or newer, can operate with pure biodiesel, or any blend, with no engine modifications. Older engine systems may require replacement of fuel lines and other rubber components in order to operate on biodiesel. The current infrastruc­ture for petroleum diesel fuel can be utilized for biodiesel, thus reducing costs and widespread implementation criteria. The Environmental Protection Agency (EPA) in 2006 limited sulfur emission in diesel fuels to 15 ppm. New trucks and buses with diesel engines, from model year 2007, are now required to use only ultra low sul­fur diesel (ULSD) with new emissions control equipment. The higher sulfur levels aided in diesel fuel lubrication; however, biodiesel is oxygenated and therefore is naturally a better lubricant and has similar material compatibility to ULSD. Many countries are utilizing biodiesel’s lubrication properties to blend with ULSD so that expensive lubricating additives are not needed [15].

The production of biodiesel is from the transesterification of triglycerides or by the esterification of fatty acids, which are both found in grease, vegetable oils, and animal fat. The transesterification of the triglycerides with a short chain alcohol (such as methanol, ethanol, propanol, or butanol) along with a catalyst, results in fatty acid esters (biodiesel) and glycerol as a by-product. The generalized transesterification reaction is given by the following stoichiometry

1[triglyceride] + 3[alcohol] ^ 3[fatty acid ester (biodiesel)] + 1[glycerol]

The fatty acids are almost entirely straight chain, mono-carboxylic acids that typically contain 8-22 even number carbons. Fatty acids are obtained mainly from soybean, palm kernel, and coconut oils and from the hydrolysis of hard animal fats. The esterification of the fatty acids with a short chain alcohol along with a catalyst, results in a fatty acid ester (biodiesel) and water as a by-product. The generalized esterification reaction is given by the following stoichiometry

1[fatty acid] + 1[alcohol] ^ 1[fatty acid ester (biodiesel)] + 1[water]