The effectiveness of catalytic hydroprocessing was also explored for co­processing 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/Al2O3 hydrotreating 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/m3 and 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.