Composition of Vegetable Oils

Vegetable oils may or may not be edible, as explained in Section 2.1.1. Even though most efforts in producing biodiesel have been using edible oils, biofuel and, in particular, biodiesel can also be produced using inedible oils [6].

The most frequently used method of characterizing the chemical structure of a vegetable oil is the fatty acid composition, which shows the distribu­tion of different kinds of fatty acids, the carbon numbers of ingredient fatty acids, location of double bonds in the fatty acid molecular structure, ratio of saturated versus unsaturated fatty acids, and more. Table 2.3 shows fatty

TABLE 2.2

Typical Oil Extraction Efficiency of Various Extraction Methods

Extraction Method

Percentage Extracted (%)

Expeller Method

34-37

Solvent Extraction

40-43

Supercritical Fluid Extraction

35-80

acid compositions of common edible oils in terms of percent by weight of total fatty acids.

The specific gravity of most edible vegetable oil ranges between 0.91 and 0.93, depending upon the kind of vegetable oil, specific composition of the oil, purity, and other factors. The specific gravity of castor oil, an inedible oil, is approximately 0.957-0.961.