Page 239 - Biofuels Refining and Performance

222 Chapter Eight

diesel has given rise to studies for cracking of lipids (vegetable
oils/animal fat) into nonpolar hydrocarbons [12] to be used as a base for
fuels or chemical commodities. Decomposition studies with and without
catalysts (metallic salts, metal oxides) have been performed. Finally,
lipids (and proteins) in dead cellular matter such as sewage sludge or
meat and bonemeal may be converted by natural catalysts present in
the substrate to oil having properties similar to diesel fuel [13].
In the following sections, basic processes of converting lipids into non-
polar hydrocarbons with alkanes, alkenes, and arenes as main con-
stituents are discussed. Details of pure vegetable oils or biodiesel are
outlined elsewhere (see Chaps. 4, 5, 6).

8.2 Thermal Degradation Process

Thermal decomposition of vegetable oil was performed to prove the
theory of the origin of mineral oil from organic matter [14] as early as
1888. Literature up to 1983 has been reviewed by Schwab et al. [15]. In
many cases, inadequate characterization of products formed in pyrol-
ysis of vegetable oils was found. Therefore, analytical data obtained by
gas chromatography–mass spectrometry (GC-MS) from thermally
decomposed soybean oil and high oleic safflower oil in the presence of
air or nitrogen were reported [15].
The ASTM standard method for distillation of petroleum products
D86-82 has been used for decomposition experiments. Catalytic systems
were excluded in this destructive distillation. The actual temperature of
the oil in the feeder flask was about 100 C higher than the vapor temper-
ature throughout the distillation. Under these conditions, GC-MS analy-
sis showed that approximately 75% of the products were made up of
alkanes, alkenes, aromatics, and carboxylic acids with carbon numbers
ranging from 4 to more than 20 (see Table 8.1).
A comparison of fuel properties is given in Table 8.2. The carbon-
hydrogen ratio shows 79% C and 11.88% H for the pyrolyzate of soybean

TABLE 8.1 Composition Data of Pyrolyzed Oil
Percent by mass
high oleic safflower Soy
Class of compounds N 2 sparge Air N 2 sparge Air
Alkanes 37.5 40.9 31.3 29.9
Alkenes 22.2 22.0 28.3 24.9
Alkadienes 8.1 13.0 9.4 10.9
Aromatics 2.3 2.2 2.3 1.9
Unresolved unsaturates 9.7 10.1 5.5 5.1
Carboxylic acids 11.5 16.1 12.2 9.5
Unidentified 8.7 12.7 10.9 12.6