Study On Catalyst And Process For Ultra-Deep Selective Hydrodesulfurization Of FCC Gasoline

People’s growing environmental awareness and the increasingly stringent environmental regulations are accelerating improvements in new catalysts for the ultraclean gasoline production.Except for high level of sulfur impurities,FCC gasoline also contains massive olefins which are important to maintain the high octane number of the final product.However,the olefins could be easily hydrogenated in the HDS reaction.For ultra-deep HDS of FCC gasoline,preparation of catalysts with high activity and selectivity for HDS of FCC gasoline is arguably the most important part to be addressed.In this paper,the sulfided CoMoS/γ-Al₂O₃ catalyst was prepared by a new composite sulfuring agent-ex situ presulfiding,while a conventional in situ presulfided catalyst was selected as the reference agent,to investigate the effect of vulcanization on catalytic performance.The results showed that the CoMoS/γ-Al₂O₃ catalyst prepared by composite sulfuring agent-ex situ presulfiding had higher stacked layers,larger slab lengths and higher edge/corner ratio.Its selectivity factor was 6⁷ times larger than that of in-situ presulfided catalyst.The vulcanization of sulfided CoMoS/γ-Al₂O₃ catalyst prepared by composite sulfuring agent was that the composite sulfuring agent reacted with MoO₃,generating thiosulfate at lower temperatures.As the temperature increased,the interaction between this precursor and the support would not be strong,and almost all active ingredients translated into high-stacked-layer Co-Mo-S（II）active phase.Meanwhile,under this sulfidation condition,Co would not be sulfured,which would lead to the growth of the MoS₂ due to the weaken interaction between Co and Mo during the generation of MoS₂,so high-stack-layer and long-slab length MoS₂ was formed,and then highest HDS selectivity was exhibited.When the temperature was 120oC,the amount of sulfuring agent was 120%of the theoretical amount,the hydrodesulfurization catalyst had higher activity and selectivity.The active phases of Co（Ni）Mo/γ-Al₂O₃ catalysts were built by the ex situ presulfiding and the in-situ presulfiding with different sulfidation atmosphere to investigate the effect of the sulfidation methods on the active phase morphology.The results showed that the average slab lengths and predominant slabs of MoS₂ particles over the catalysts sulfided in a stream of H₂S/N₂ were larger than those of the catalysts sulfided in other methods.This growth of the slab length was profitable to the DBT HDS over the CoMo catalysts and was unprofitable to the DBT HDS over the NiMo catalysts,mainly due to the different reaction paths:tended to the direct desulfurization pathway（DDS）on the CoMo catalysts and tended to the hydrogen pathway（HYD）on the NiMo catalysts,further confirming that the corner site of Co（Ni）-Mo-S phase was the active site for hydrogenation reaction,whereas the edge site for the hydrogenolysis reaction.The processing conditions of hydrogenation was also investigated over the CoMoS/γ-Al₂O₃ catalyst prepared by the optimum condition.Under the reaction pressure of1.8 MPa,volume space velocity of 2 h^-1,hydrogen to oil volume ratio of 300/1（V/V）and reaction temperature of 260oC and 280oC,respectively,the product sulfur content of the FCC gasoline(179.2μg·g^-1 and 323.0μg·g^-1)reduced to below 10.0μg·g^-1 and the loss of octane number was less than 1.5 units.