Biodiesel Production from Waste Cooking Oil for Use as Fuel: Integrating Environmental,Economic, and Social Aspects

Biodiesel is a substitute to petroleum-based diesel, mainly because of its environmentally friendly nature, and is a renewable resource. Biodiesel is defined as monoalkyl esters of long chain fatty acids derived from a renewable lipid feedstock, such as vegetable oil or animal fat, for use in diesel engines (Figure 1). More specifically, biodiesel is defined as an oxygenated, sulfur-free, biodegradable, non-toxic, and eco-friendly alternative diesel oil. It is typically produced by a catalyzed trans-esterification reaction in which vegetable oil or animal fat reacts with an alcohol and alkali. As an alternative fuel, biodiesel can be used in the neat-form or mixed with petroleum-based diesel. No engine modifications are required, and the result is a less-expensive, renewable, clean-burning fuel. It is designated as B100, and it must meet the special requirements such as the ASTM and the European standards. For these to be considered as viable transportation fuels, they must meet stringent international quality standards. Biodiesel is made from a variety of natural oils such as soybeans, rapeseeds, coconuts, and even recycled cooking oil. Rapeseed oil dominates the growing biodiesel industry in Europe. In the United States, biodiesel is made from soybean oil because more soybean oil is produced in the USA than all other sources of fats and oil combined. We can also use vegetable oil in the diesel engines; however, the injection and atomization characteristics of the vegetable oils are significantly different from those of petroleum derived diesel fuels, mainly as the result of their high viscosities. Modern diesel engines have fuel-injection system that is sensitive to viscosity change. One way to avoid these problems is to reduce fuel viscosity of vegetable oil in order to improve its performance. The conversion of vegetable oils into biodiesel is an effective way to overcome all the problems associated with the vegetable oils. Dilution, micro-emulsification, pyrolysis, and trans-esterification are the four techniques applied to solve the problems encountered with the high fuel viscosity. Trans-esterification is the most common method and leads to mono alkyl esters of vegetable oils and fats, now called biodiesel when used for fuel purposes. The methyl ester produced by trans-esterification of vegetable oil has a high cetane number, low viscosity and improved heating value compared to those of pure vegetable oil, which results in shorter ignition delay and longer combustion duration, and hence low particulate emissions. Biodiesel is also a product of great interest for its environmental characteristics. It has the advantages of dramatically reduced sulfate and hydrocarbon emissions and reduces particulate matter. It runs a diesel engine just as petroleum-based diesel would.