Study On Catalyst Preparation And Process For Selective Hydrodesulfurization Of FCC Gasoline

With the growing awareness of environmental protection and promulgated legislation for controlling the exhaust gas emission from motor vehicles, ultraclean gasoline production has been an urgent subject of oil-refining industry in recent years. 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. This paper studies the influence of adding rare earth element on CoMo/γ-Al2O3 catalyst reaction performance, aiming at developing a novel catalyst with high hydrodesulfurization selectivity for FCC gasoline.The co-impregnation preparation methods was improved as well as the influences of rare earth metal type, including load of La, and the load of active metal CoMo on the physicochemical properties of the catalyst and selectivity of the desulfurization were investigated. The experimental results show that the catalyst with La has the best performance of hydroesulfurization. This is because rare earth metal adding which greatly weakened the interaction between the active component and the support. After the addtion of La,the average slab length of MoS2 particles was slightly decreased and the predominant slab was increased,to some extent, affecting the performance of the catalysts. As a result, the CoMoLa/γ-Al2O3 has weaker DDS activity and stronger HYD activity than CoMo/γ-Al2O3, which indicates CoMo La/γ-Al2O3 has the best activity and selectivity. It is also found that with the increase of La load, the hydrodesulfurization selectivity demonstrates a trend of increasing followed by its decreasing. The CoMo La/γ-Al2O3 catalysts have the best hydrodesulfurization selectivity when La load is 1.0wt%. Under the experimental reaction conditions, with the increase of CoMo load, the hydrodesulfurization selectivity demonstrates a trend of increase followed by its decrease. The sulfided catalyst has the best hydrodesulfurization selectivity when the CoMo load of catalysts is 18%.During the process of catalysts production, the influences of calcination temperature, organic acid types, and the introduce method of rare earth metal(total impregnation method, step by step impregnation method and kneading method) on catalyst activity and selectivity of hydrodesulfurization catalyst were studied. The results show that the olefin saturation activity has been restrained when it is made from high-temperature calcination whichleads to higher hydrodesulfurization selectivity. Calcination has changed the acting force between activity component and support and changed the construction of active phases. It also shows that the best catalyst is made from using citric acid as organic acid when producing impregnation liquid. Experimental results show that the CoMoLa/γ-Al2O3 catalyst prepared by step by step impregnation method has better activity and selectivity than kneading method and co-impregnation method. Based on the plausibility of industrial application and its low cost,total impregnation method has more advantage over the others.The catalysts perform high activity and selectivity with HDS of 97.4% and HYD of 17.7% under conditions of 260°C, 1.5MPa, hydrogen-to-oil ratio of 300:1 and LHSV of 4h-1.