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Producing Biodiesel by the Transesterification Process

written by: Haresh Khemani•edited by: Lamar Stonecypher•updated: 11/17/2011

Biodiesel, a renewable fuel, is produced from vegetable oils and animal fats by a process called transesterification. It breaks down the molecules of vegetable oils into constituent molecules forming biodiesel as the main product and glycerin as the byproduct.

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    Sources of Biodiesel

    Biodiesel is manufactured from the vegetable oils like soya, canola, jatropha, sunflower seed, algae, etc. and animal fats. The chemical name for biodiesel is fatty acid alkyl esters. There are a few methods for production of biodiesel, but the most commonly used method for production of biodiesel is known as transesterification. It is the chemical conversion process of vegetable oil or animal fats to biodiesel.

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    Chemical Components of Vegetable Oil

    The main components used for production of biodiesel are vegetable oil or animal fats. Vegetable oils are triglycerides that are composed of three chains of fatty acids all connected together by a glycerin molecule. The triglycerides are not the individual atoms; instead they are esters. The esters in turn are the acids, say like fatty acids, that have been combined with alcohol. The chemical name for glycerin is glycerol, which is a form of alcohol.

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    Process of Transesterification

    Transesterification is a chemical reaction used for the conversion of vegetable oil to biodiesel. In this process vegetable oil is chemically reacted with an alcohol like methanol or ethanol in presence of a catalyst like lye. After the chemical reaction, various components of vegetable oil break down to form new compounds.

    The triglycerides are converted into alkyl esters, which is the chemical name of biodiesel. If methanol is used in the chemical reaction, methyl esters are formed, but if ethanol is used, then ethyl esters are formed. Both these compounds are biodiesel fuels with different chemical combinations. In the chemical reaction alcohol replaces glycerin.

    Glycerin that has been separated during the transesterification process is released as a byproduct of the chemical reaction. Glycerin will either sink to the bottom of the reaction vessel or come to the surface depending on its phase. It can be easily separated by centrifuges, and this entire process is known as transesterification.

    The biodiesel produced by the process of transesterification has much lower viscosity, which makes it capable of replacing petroleum diesel in diesel engines. In earlier years when the process of transesterification was not known, the viscosity of vegetable oil was the major hindrance for its use as a fuel for motor engines. The transesterification process has been able to remove this hindrance.

    The byproduct of the transesterification chemical reaction is the glycerin that originally formed the bond between the chains of fatty acids. Glycerin can be used for various purposes. Thus during transesterification process nothing goes to waste. All the products and byproducts are utilized for various purposes.


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