Biodiesel production: a review

Biodiesel has become more attractive recently because of its environmental bene®ts and the fact that it is made from renewable resources. The cost of biodiesel, however, is the main hurdle to commercialization of the product. The used cooking oils are used as raw material, adaption of continuous transesteri®cation process and recovery of high quality glycerol from biodiesel by-product (glycerol) are primary options to be considered to lower the cost of biodiesel. There are four primary ways to make biodiesel, direct use and blending, microemulsions, thermal cracking (pyrolysis) and transesteri®cation. The most commonly used method is transesteri®cation of vegetable oils and animal fats. The transesteri®cation reaction is a€ected by molar ratio of glycerides to alcohol, catalysts, reaction temperature, reaction time and free fatty acids and water content of oils or fats. The mechanism and kinetics of the transesteri®cation show how the reaction occurs and progresses. The processes of transesteri®cation and its downstream operations are also addressed. Ó 1999 Published by Elsevier Science B.V. All rights reserved.