Catalytic properties of CoMo/Al2O3 sulfide catalysts in the hydrorefining of straight-run diesel fraction mixed with rapeseed oil
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CoMo/Al2O3 sulfide catalysts varying in preparation method and Co/Mo ratio have been tested in the hydrorefining of a mixture of straight-run diesel fraction and rapeseed oil in a flow reactor at a temperature of 340–360°C, a hydrogen pressure of 4.0–7.0 MPa, and a liquid hourly space velocity of 1–2 h−1. A comparison between catalysts prepared using citric acid (CoMo/Al2O3-1.5) and both citric and orthophosphoric acids (CoMoP/Al2O3-1.5) as promoters, with Co/Mo = 0.3 and 0.5, has demonstrated that the most active catalyst in hydrodesulfurization and hydrodenitrogenation is the phosphorus-containing Co/Mo ≈ 0.5 sample. The addition of rapeseed oil to straight-run diesel fraction lowers the hydrodesulfurization and hydrodenitrogenation activities of the CoMo sulfide catalysts, irrespective of the method by which they were prepared. The fatty acid triglyceride conversion selectivity of these catalysts depends on the Co/Mo ratio and on reaction conditions: decreasing the Co/Mo ratio from 0.46 to 0.26, lowering the reaction temperature, and raising the hydrogen pressure and hydrogen-to-feedstock ratio increase the C18/C17 hydrocarbon ratio in the hydrogenated product. The addition of rapeseed oil improves the quality of the product; however, for attaining the preset residual sulfur level in this case, the process needs to be conducted at a higher temperature than the hydrorefining of straight-run diesel fraction containing no admixture.
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