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Biodiesel Production Process

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BIODIESEL PRODUCTION PROCESS

 Rajeew Kumar

G.B.Pant University of Agriculture & Technology, Pantnagar-Uttrakhand


The process of converting vegetable oil into biodiesel fuel is called transesterification and is luckily less complex than it sounds. Chemically, transesterification means taking a triglyceride molecule or a complex fatty acid, neutralizing the free fatty acids, removing the glycerin, and creating an alcohol ester. This is accomplished by mixing methanol (wood alcohol) with lye (sodium hydroxide) to make sodium methoxide. This dangerous liquid is then mixed into vegetable oil. The entire mixture then settles. Glycerin is left on the bottom and methyl esters, or biodiesel, is left on top. The glycerin can be used to make soap (or any one of 1,600 other products) and the methyl esters is washed and filtered. The resulting biodiesel fuel when used directly in a Diesel engine will burn up to 75% cleaner than petroleum diesel fuel. Transesterification was conducted as early as 1853. One of the first uses of biodiesel (transesterified vegetable oil) was powering heavy vehicles in South Africa before World War II.  Biodiesel can be made by several ways. A chemical process called transesterification is used to transform the raw vegetable oil into biodiesel and glycerin. This process is not as complicated as it may sound, though it does require the use of toxic chemicals-most commonly methanol alternative to this, ethanol and potassium hydroxide, which are less hazardous, can be used, but they generally take more time and yield less fuel. In general, biodiesel can be produced from bio-oils using three different methods

  1. Base catalysed transesterification and esterification of oil with an alcohol.
  2. Direct acid catalysed esterification of oil with methanol.
  3. Conversion of oil to fatty acids, and then to alkyl esters with acid catalysis.

The base catalysed reaction is most often used because:

  • It uses low temperature (60°C) and pressure (20 psi) processing.
  • It achieves high conversion (98%) with minimal side reactions and low reaction time.
  • Conversion to methyl ester is direct with no intermediate steps.

Using the following reactions, biodiesel can even be produced at home using appropriate small-scale equipment. The process occurs in two stages as below. Note that although any alcohol can be used, either ethanol or methanol is the most common. In areas where sugar cane is grown, ethanol is most likely.

Stage 1
potassium hydroxide + ethanol › potassium ethoxide + water

KOH + CH3CH2OH › CH3CH2OK + H2O

Stage 2
Potassium ethoxide + water + fatty acid triglyceride (oil) › biodiesel (methyl ester) + glycerine + potassium hydroxide

CH3CH2OK + H2O + C3H5(OOCR)3 › 3RCOOCH3 + C3H5(OH)3 + KOH

R = hydrocarbon chain

From this it can be seen that the potassium hydroxide is reused and the only outputs are biodiesel, glycerine and fatty acids - all of which are harmless. : A common automated process for biodiesel production is depicted in Figure 1.

Production Process of Biodiesel


Formatted and uploaded by Priyanka Shukla
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Please note that this is the opinion of the author and is Not Certified by ICAR or any of its authorised agents.