Processing biomass in conventional oil refineries: Production of high quality diesel by hydrotreating vegetable oils in heavy vacuum oil mixtures

Renewable liquid alkanes can be produced by hydrotreating of vegetable oils and vegetable oil–heavy vacuum oil (HVO) mixtures at standard hydrotreating conditions (i.e. 300–450°C) with conventional hydrotreating catalysts (sulfided NiMo/Al2O3). The reaction pathway involves hydrogenation of the CC bonds of the vegetable oils followed by alkane production by three different pathways: decarbonylation, decarboxylation and hydrodeoxygenation. The straight chain alkanes can undergo isomerization and cracking to produce lighter and isomerized alkanes. The carbon molar yield of straight chain C15–C18 alkanes was 71% on a carbon basis (the maximum theoretical yield for these products is 95%) for hydrotreating of pure vegetable oil under optimal reaction conditions. The rate of alkane production from pure sunflower oil is greater than the rate of hydrodesulfurization of a HVO with a 1.48wt% sulfur content (e.g. 100% conversion of sunflower oil at 350°C compared to 41% conversion of sulfur). The yield of straight chain alkanes increases when sunflower oil is mixed with HVO, illustrating that dilution of HVO can improve the reaction chemistry. For example, with a 5wt% sunflower oil–95wt% HVO feed the maximum theoretical straight chain C15–C18 yield from the sunflower oil was higher (87%) than it was with the pure sunflower oil (75%). Mixing the sunflower oil with HVO does not decrease the rate of desulfurization indicating that sunflower oil does not inhibit the hydrotreating of HVO.