Biodiesel is currently obtained from the transesterification reaction of vegetable oils. A pos­sible drawback of this technology is that large investment is required to build up new bio­diesel plants. An interesting alternative is to directly feed the vegetable oil into the hydrotreating unit of a petroleum refinery, for instance, vegetable oil can be co-fed with heavy vacuum oil HVO. Under typical hydrotreating conditions (300-450°C, 50 bar H2 pres­sure, sulfidedNiMo/Al2O3 catalyst), vegetable oils are transformed into alkanes through three different pathways: decarboxylation, decarbonylation and HDO. The straight chain al­kanes can undergo isomerization and cracking to produce lighter and isomerized alkanes (Figure 8) [37]. It was reported that mixing the sunflower oil with HVO does not decrease the rate of desulfurization. Moreover, the rate of vegetable oil hydrotreating is faster that the rate of HVO desulfurization. For industrial application, corrosion problems should be taken into account and the formation of waxes should be minimized, as they can plug the reactor.

Isomerization lso"^i5

Propane

Cracking lighter alkanes

HsO

Figure 8. Reaction pathway for conversion of tri-glycerides to alkanes [37].

Fatty alcohols can be obtained by catalytic hydrogenolysis of fatty acid methyl esters. Small- chain fatty alcohols are used in cosmetics and food and as industrial solvents or plasticizers, while the large-chain fatty alcohols are important as biofuels and as nonionic surfactants or
emulsifiers. Fatty alcohols are produced by hydrogenolysis, in the presence of Cu based het­erogeneous hydrogenation catalysts, operating under H2 pressures between 20 and 30 bar and temperatures in the range of 97-197°C [38]. High hydrogen pressures are required to in­crease the solubility of hydrogen in the reaction mixture, in order to boost the availability of H2 at the catalyst surface and to reduce mass transport limitations [39].The stoichiometry of the reaction is presented below:

R-COOCH3+ 2H2 — R-CH2OH + CH3OH