At first glance vegetable oil offers a favorable CO2 balance. However, when the extra N2O emission from biofuel production is calculated in “CO2-equivalent” global warming terms, and compared with the quasi­cooling effect of “saving” emissions of fossil fuel derived CO2, the out­come is that production of commonly used biofuels can contribute as much or more to global warming by N2O emissions than cooling by fossil fuel savings [33]. In addition, widespread use of vegetable oil fuels is lim­ited by high viscosity, low volatility, poor cold flow behavior, and lack of oxidation stability during storage [6, 7]. Partial conversion of vegetable oil to hydrocarbons offers the possibility to preserve the favorable envi­ronmental characteristics of vegetable oil-based fuels while improving viscosity and cold flow behavior [34, 35]. Figure 8.2 depicts thermo­gravimetry of vegetable oil without pure oil (dashed line) and in the pres­ence of a Y-zeolite (Koestrolith). The dotted line represents the first derivative from the catalyzed conversion reaction.

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H

Q

The efficiency of the decarboxylation effect of Y-zeolite activity on pure vegetable oil at T = 450°C may be seen by comparing the IR spec­trum of pure vegetable oil fuel in Fig. 8.3 with the corresponding spec­trum of the conversion product in Fig. 8.4. The carbonyl band at around 1700 cm 1 is an indicator for conversion efficiency.

Table 8.3 summarizes physical and chemical parameters of vegetable oil fuel and conversion products at different temperatures. The change

in viscosity is quite remarkable. In accordance with Fig. 8.2, a reaction temperature of T = 450°C is preferred.