Homepage
Team Members
Bibliography
Technical Papers
Search this website or internet for biodiesel related material
Contact Us
Course Material
Digressions

Page 2

 The Chemistry of Biodiesel

It is not necessary to be a chemist to understand where biodiesel comes from and how it is used.  However, it is useful to review some of the fundamental chemical principles that are behind biodiesel so that its properties can be understood. 

 All vegetable oil and animal fats consist primarily of triglyceride molecules as shown schematically below.

R1, R2, and R3 represent the hydrocarbon chain of the fatty acid elements of the triglyceride.  Note that there is a three-carbon chain called the glycerol backbone that runs along the left side of the molecule.  Extending away from this backbone are the three long fatty acid chains.
In their free form, the fatty acids have the configuration shown below.

where R is a hydrocarbon chain of greater than 10 carbon atoms

The properties of the triglyceride and the biodiesel fuel will be determined by the amounts of each fatty acid that are present in the molecules. 

Fatty acids are designated by two numbers: the first number denotes the total number of carbon atoms in the fatty acid and the second is the number of double bonds. For example, 18:1 designates oleic acid which has 18 carbon atoms and one double bond. Table 1 shows the fatty acid compositions of a number of common vegetable oils and animal fats.
  
 Table 1 - Composition of Various Oils and Fats.
Oil or fat 14:0 16:0 18:0 18:1 18:2 18:3 20:0 22:1
Soybean   6-10 2-5 20-30 50-60 5-11    
Corn 1-2 8-12 2-5 19-49 34-62 trace    
Peanut   8-9 2-3 50-65 20-30      
Olive   9-10 2-3 73-84 10-12 trace    
Cottonseed 0-2 20-25 1-2 23-35 40-50 trace    
Hi linoleic Safflower   5.9 1.5 8.8 83.8      
Hi Oleic Safflower   4.8 1.4 74.1 19.7      
Hi Oleic Rapeseed   4.3 1.3 59.9 21.1 13.2    
Hi Erucic Rapeseed   3.0 0.8 13.1 14.1 9.7 7.4 50.7
Butter 7-10 24-26 10-13 28-31 1-2.5 .2-.5    
Lard 1-2 28-30 12-18 40-50 7-13 0-1    
Tallow 3-6 24-32 20-25 37-43 2-3      
Linseed Oil   4-7 2-4 25-40 35-40 25-60    
Tung Oil   3-4 0-1 4-15   75-90*    
Yellow grease 1.27 17.44 12.38 54.67 7.96 0.69 0.25 0.52

Peterson, C.L., "Vegetable Oil as a Diesel Fuel: Status and Research Priorities," ASAE Transactions, V. 29, No. 5, Sep.-Oct. 1986, pp. 1413-1422.
Linstromberg, W.W., Organic Chemistry, Second Edition, D.C. Heath and Company, Lexington, Mass., 1970.
 Tat, M.E., and  J. H. Van Gerpen, "Fuel Property Effects on Biodiesel," ASAE Paper No. 036034, American Society of Agricultural Engineering Annual Meeting, Las Vegas, NV. July 27-30, 2003.

 * The dominant fatty acid in tung oil is a conjugated isomer of linolenic acid called eleostearic acid. The three double bonds in eleostearic acid are located at 9:10, 11:12, and 13:14 instead of at 9:10, 12:13 and 15:16 as in linolenic acid.

The names of the fatty acids given in Table 1 are as follows:

14:0 Myristic Acid (tetradecanoic acid)
16:0 Palmitic Acid (hexadecanoic acid)
18:0 Stearic Acid (octadecanoic acid)
18:1 Oleic Acid
18:2 Linoleic Acid
18:3 Linolenic Acid
20:0 Arachidic Acid (eicosanoic acid)
22:1 Erucic Acid



sdfdfsdfsdfsdfsdfdsfd dsfsdfsdfsdfsdf