Zeoletic support of HDS catalysts for deep hydrodesulfurization to achieve 10PPM sulfur level

A two layer catalyst bed was prepared to achieve desulfurization without H₂S (NH₃) removal between layers. The functions of the catalysts in each layer were defined as follows. first layer: complete removal of reactive sulfur species and 95% removal of refractory sulfur species. second layers: remaining refractory sulfur species (∼ 400-500 ppm) must be removed to < 10 ppm in the presence of H₂S and NH₃. Several types of zeolite containing supports for HDS catalysts were prepared to be studied in the first and second layers. 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 straight run gas oil (SRGO), hydrodesulfurized SRGO + H₂S + NH₃. On the other hand, zeolite having strong acidity was easily deactivated and could crack and isomerizes hydrocarbons. Alumina-zeolite composite catalyst showed very high activity in HDS of HSRGO, while it did not crack the substrate so much. Thus, modified zeolite alumina catalyst might have longer life time than any other zeolite containing catalyst, with high cracking activity. Appropriate sets of two catalysts with successive layers were very active to achieve regulated sulfur level of gas oil.