Energy Engineering: Biodiesel

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INTRODUCTION
India imported about 2/3rd of its petroleum requirements last year, which involved a cost of approximately Rs. 80,000 crores in foreign exchange. Even 5% replacement of petroleum fuel by bio-fuels can help India save Rs.4000 crores per year in foreign exchange. It is utmost important that the options for substitution of petroleum fuels be explored to control this rapidly growing import bill. With the stock of fossil fuels diminishing throughout the world and demand for energy based comforts and mobility ever increasing, time is ripe that we strike a balance between energy security and energy usage. Moreover having uplifted to such a sphere of engineering excellence, reverting back to the ages of the bull carts will prove next to impossible thereby compelling us to search for a variety of alternative fuels to derive energy to cater to our needs. Several sources of energy, especially for driving the automotives are being developed and tested.
This report presents detailed information on Biodiesel together with its emission benefits. The prospect of Biodiesel as an alternative to conventional fuels like gasoline and diesel and the experience of other countries are also mentioned.

BIODIESEL
Biodiesel is the name for a variety of ester-based oxygenated fuels derived from natural, renewable biological sources such as vegetable oils. Biodiesel operates in compression ignition engines like petroleum diesel thereby requiring no essential engine modifications. Moreover it can maintain the payload capacity and range of conventional diesel. Biodiesel fuel can be made from new or used vegetable oils and animal fats. Unlike fossil diesel, pure Biodiesel is biodegradable, nontoxic and essentially free of sulphur and aromatics. The concept of using vegetable oil as a fuel dates back to 1895 when Dr. Rudolf Diesel developed the first diesel engine to run on vegetable oil.

PRODUCTION
Vegetable oils can be chemically reacted with an alcohol (methanol or ethanol is the usual choice) to produce chemical compounds known as esters. Biodiesel is the name given to these esters when they are proposed for use as fuel. Currently Biodiesel is produced by a process called transesterification where the vegetable oil or animal fat is first filtered, then processed with alkali to remove free fatty acids. It is then mixed with an alcohol (usually methanol or ethanol) and a catalyst (usually sodium or potassium hydroxide). This transesterification process can also be carried out in presence of acid catalyst. The only problem with acid catalyzed process is that it is very slow. Generally base catalyzed process takes about 2 hours for completion while acid catalyzed process is much slower than this at about 700 C. The oil’s triglycerides react to form esters and glycerol, which are then separated from each other and purified. The yield of transesterification process is same for both, acid catalyzed and base catalyzed processes. Yield of process affected, Freedman B. et al. (1984), mainly by oil to alcohol ratio. For all practical purposes 100% excess alcohol is used. But more than this use of alcohol lead to problems during separation of glycerol. Glycerol obtained as by product is used pharmaceutical industry.