The world population is growing rapidly as a result fuel demands are increasing. However, natural resources of energy (crude oil, gas and coal) are diminishing with the passage of time. According to the CIA World Fact book, we are finishing all of the known reserves of crude oil by 2052, gas by 2060 and coal by 2088. Due to the ever diminishing fossil fuels and, increasing fuel demands combined with environmental pollution concerns, the world has been focusing on the development of alternate renewable and cleaner energy resources.
Biodiesel is a cleaner form of fuel. It is produced from the biological based resources such as vegetable oils and animal fats. Biodiesel is the natural, biodegradable, non-toxic, cleaner and environment friendly source of energy. Crude oil or fat are used for the production of biodiesel which is obtained by pressing the natural vegetable oil and animal fat. These oils usually have free fatty acids, phospholipids and other molecules which effect quantity and quality of biodiesel. Animal fats and different plant based oils including Palm oil, Soybean oil, coconut oil, sunflower oil, rapeseed oil, tung oil are used in production of biodiesel. The developed world has made significant progress in production of biodiesel progressed over last two decades. In 2005 United States was the world largest biodiesel producing country. Now USA is producing about 3.75 billion US gallons per year that is about the one third of the total annual diesel requirement of Pakistan.
Vegetable oils have high viscosity that hinders its proper combustion in the engine and causes numerous problems such as coking, carbon deposition, sticking of oil ring and thickening and gelling of lubrication. Micro emulsion technique may be employed to solve high viscosity problems. Solvents (such as methanol, ethanol and 1-butanol) have been used in micro emulsion technique. Through this technique optically isotropic fluid microstructure, dispersed with the dimension generally in the 1-150 nm range and formed spontaneous mixture from two immiscible liquids. The diesel obtained from this type of technique has low octane number and energy. Thermal cracking make use of pyrolysis to produce biodiesel from vegetable oils and animal fats. In pyrolysis, vegetable oils and animal fats are heated at temperature between 450-850 ⁰C in oxygen/air free environment in the presence of catalyst (SiO2/ Al2O3) which cleavage the chemical bonds and yields small molecules. The remains (methyl ester) may directly be used as fuel. This technique was used during the World War-I for the production of diesel, gasoline and kerosene from the tung oil. Trans- esterification is the process by which the fat and oil reacts with the alcohols (methanol and ethanol) and the ester and glycerol are produced. Maximum ester may be produced with ratio of (1:3) reactant triglyceride and alcohol.
A catalyst (Alkalis, acids and enzymes) enhances the reaction rate. An example of alkali catalyst includes NaoH, KoH, carbonates, sodium methoxide and sodium peroxide. In acids Sulfuric acid, Sulfonic acid and Hydrochloric acid are usually used as acid catalyst. Lithium may also be used as catalyst in Trans-esterification.Glycerides and alcohols must be anhydrous when alkali catalysts are used because the presence of water may shift the reaction toward the saponification, a process by which soap is produced. This process is completed in series of reactions.
A mole of ester is liberated at each step during this process. This ester is used as the bio fuel. During this process, the glycerides should have pH less than one and anhydrous environment because if its having the moisture then there will be the formation of soap which affects the catalytic activity. Molar ratio should be 3:1 for vegetable oil and 6:1 for the animal fats, respectively.
There are numerous methods of producing the biodiesel from the natural renewable resources however; Trans esterification produces high quality biodiesel with desired qualities of low viscosity and, high combustion power. Biodiesel is cleaner energy source that would also reduce our reliance on ever diminishing fossil fuels.