An approach to design the catalyst for deep hydrodesulfurization to achieve 10ppm sulfur level

Several NiMo and CoMo sulfide catalysts were examined in first and second layers with or without H₂S and NH₃ reduction between the layers. The two layers of the best HDS catalysts with appropriate activity under respective conditions can be a logical approach to achieve deep HDS of gas oil. The first layer catalyst must eliminate 100% of reactive sulfur species. Hence, the catalyst must have larger surface area, slightly smaller pore being allowed for the larger surface area. Acidity helps higher activity, 95% of refractory sulfur species must be also eliminated. Moderate acidity is helpful for the hydrogenative HDS. The second layer catalyst eliminates the refractory sulfur species of 100-500 ppm to < 10 ppm in the presence of H₂S and NH₃. The hydrodesulfurized straight run gas oil contains 20 ppm nitrogen. The catalyst must have larger pores to accept the refractory sulfur species of tri aromatic rings with methyl groups more than di aromatic rings. Acidity is important to enhance HDS of the refractory sulfur species in the hydrogenation route by moderate H₂S inhibition. Zeolite containing CoMo and NiMo showed higher activity in SRGO, HSRGO and HSRGO + H₂S. However, zeolite having strong acidity is easily deactivated. Appropriate sets of two catalysts with successive layers are very active to achieve regulated Sulfur level of gas oil. It is always discussed whether CoMo or NiMo is better catalyst for the first and second layers. High dispersion in designed shape of the sulfides must be practiced in any supports.