Biodiesel Production From Palm Oil Crude

Bioresource Technology 70 (1999) 1±15

Biodiesel production: a review1
Fangrui Maa, Milford A. Hannab,*
b a Department of Food Science and Technology, University of Nebraska, Lincoln, NE, USA Industrial Agricultural Products Center, University of Nebraska, 211 L.W. Chase Hall, Lincoln, NE 68583-0730, USA

Received 24 March 1998; revised 16 December 1998; accepted 2 February 1999

AbstractBiodiesel 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, reactiontemperature, 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.
Keywords: Biodiesel; Transesteri®cation; Blending; Microemulsion;Thermal cracking

1. Introduction Biodiesel, an alternative diesel fuel, is made from renewable biological sources such as vegetable oils and animal fats. It is biodegradable and nontoxic, has low emission pro®les and so is environmentally bene®cial (Krawczyk, 1996). One hundred years ago, Rudolf Diesel tested vegetable oil as fuel for his engine (Shay, 1993). With the advent of cheap petroleum,appropriate crude oil fractions were re®ned to serve as fuel and diesel fuels and diesel engines evolved together. In the 1930s and 1940s vegetable oils were used as diesel fuels from time to time, but usually only in emergency situations. Recently, because of increases in crude oil prices, limited resources of fossil oil and environmental concerns there has been a renewed focus on vegetable oilsand animal fats to make biodiesel fuels. Continued and increasing use of petroleum will intensify local air pollution and magnify the global warming problems caused by CO2 (Shay, 1993). In a particular case, such as the emission of pollutants in
* Corresponding author. Fax: +1-402-472-6338; e-mail: mhanna@unl.edu 1 Journal Series #12109, Agricultural Research Division, Institute of Agriculture andNatural Resources, University of Nebraska±Lincoln.

the closed environments of underground mines, biodiesel fuel has the potential to reduce the level of pollutants and the level of potential or probable carcinogens (Krawczyk, 1996). Fats and oils are primarily water-insoluble, hydrophobic substances in the plant and animal kingdom that are made up of one mole of glycerol and three moles offatty acids and are commonly referred to as triglycerides (Sonntag, 1979a). Fatty acids vary in carbon chain length and in the number of unsaturated bonds (double bonds). The fatty acids found in vegetable oils are summarized in Table 1. Table 2 shows typical fatty acid compositions of common oil sources. Table 3 gives the compositions of crude tallow. In beef tallow the saturated fatty acidcomponent accounts for almost 50% of the total fatty acids. The higher stearic and palmitic acid contents give beef tallow the unique properties of high melting point and high viscosity. Natural vegetable oils and animal fats are extracted or pressed to obtain crude oil or fat. These usually contain free fatty acids, phospholipids, sterols, water, odorants and other impurities. Even re®ned oils and fats...