The effectiveness of catalytic hydroprocessing was also explored for co-processing of lipid feedstocks with petroleum fractions as catalytic hydroprocessing units are available in al­most all refineries. The first co-processing study involved experiments of catalytic hydro­treating of sunflower oil mixtures with heavy petroleum fractions aiming to produce high quality diesel [55]. The experiments were conducted in a continuous fixed-bed reactor over a wide range of temperatures 300-450°C employing a typical NiMo/Al2O3 hydrotreating cata­lyst. The study was focused on the hydrogenation of double C-C bonds and the subsequent paraffin formation via the three different reactions routes: decarbonylation, decarboxylation and deoxygenation. Furthermore the large carbon-chain paraffins can also undergo isomeri­zation and cracking leading to the formation of smaller paraffins. This study concluded that the selectivity of products on decarboxylation and decarbonylation is increasing as the tem­perature and vegetable oil content in the feedstock increase [55].

In a similar study catalytic hydrocracking over sunflower oil and heavy vacuum gas oil mix­tures was investigated [56]. The experiments were conducted in a continuous-flow hydro­processing pilot-plant over a range of temperatures (350-390°) and pressures (70-140bar). Three different hydrocracking catalysts were compared under the same conditions and four different feedstocks were employed, incorporating for 10% and 30%v/v of lipid bio-based feedstock and considering non-pretreated and pretreated sunflower oil as a bio-based feed­stock. The results indicated that a prior mild hydrogenation step of sunflower oil is necessa­ry before hydrocracking. Furthermore, conversion was increased with increasing sunflower oil ratio in the feedstock and increasing temperature, while the later decreased diesel selec­tivity.

The effect of the process parameters and the vegetable oil content of the feedstocks on the yield, physical properties, chemical properties and application properties during co-hydro­treating of sunflower oil and gas-oil mixtures utilizing a typical NiMo/Al2O3hydrotreating catalyst was also studied [57]. The experimental results of this study indicated that catalytic co-hydrogenation of gas oil containing sunflower oil in different percentages allowed both vegetable oil conversion reactions (saturation, deoxygenation) and the gas oil quality im­provement reactions (hetero atom removal, aromatic reduction). The optimal operating con­ditions (360-380°C, P=80 bar, LHSV=1.0h-1, H2/oil=600 Nm3/m3and 15% sunflower oil content of feed) resulted in a final diesel product with favorable properties (e. g. less than 10 wppm sulfur, ~20% aromatics) but poor cold flow properties (CFPP=3°C). The study also indicated that for sunflower content in the feedstock higher than 15% reduced the desulfurization effi­ciency. Furthermore, the authors also concluded that the presence of sunflower oil in the feedstock has augmented the normal and iso-paraffins content of the final product and as a result has increased the cetane number but degraded the cold flow properties, indicating that an isomerization step is required as an additional step.

The issue of catalyst development suitable for co-hydrotreating and co-hydrocracking of gas-oil and vegetable oil mixtures was recently addressed [10], as there are no commercial hydroprocessing catalysts available for lipid feedstocks. New sulfided Ni-W/SiO2-Al2O3 and sulfided Ni-Mo/Al2O3 catalysts were tested for hydrocracking and hydrotreating of gas­
oil and vegetable oil mixtures respectively. The results indicated that the hydrocracking cat­alyst was more selective for the kerosene hydrocarbons (140-250°C), while the less acidic hydrotreating catalyst was more selective for the diesel hydrocarbons (250-380°C). The study additionally showed that the deoxygenation reactions are more favored over the hy­drotreating catalyst, while the decarboxylation and decarbonylation reactions are favored over the hydrocracking catalyst.