Study On Modification Of Co-Mo/γ-Al₂O₃ Catalysts And Selective Hydrodesulphurization For FCC Gasoline

In this paper, the CoMo/γ-Al₂O₃ catalysts modified with the transition metal additives such as Zn, Cu, Fe, Mn were prepared. The influence of additive types and the modifying methods on physicochemical properties of the catalyst and selectivity of the desulfurization was studied. The physicochemical properties of catalyst have characterized by XRD, BET, Py-FTIR, H2-TPR, NH3-TPD and HRTEM techniques.Experimental results show that the CoMoZn/γ-Al₂O₃ catalysts prepared by co-impregnation method have better activity and selectivity for hydrodesulfurization of FCC gasoline. The optimized preparation condition is that the content of CoO plus MoO3 is 12.0 wt%, the atomic ratio of Zn/Mo is 1.0. XRD and HRTEM verify that Zn added in the catalyst promotes the dispersion of active metals on the surface of supports, therefore, the nanoparticle of MoS2 has a smaller size and slab lengh, so that the better HDS selectivity is reached. The passivation of CoMoZn/γ-Al₂O₃ catalysts with basic nitrogen compound quinoline is investigated to improve the activity and selectivity for hydrodesulfurization of FCC gasoline. It is verified from experimentals that the selective adsorption of quinoline on the surface of the catalyst may modify the ratio of active sites for desulfurization/hydrogenation, so that the selectivity for desulfurization is improved. Experimental results show that the adsorption of quinoline has little impact on activity for desulfurization, however, it inhibits the activity for hydrogenation of olefins. When HDS percentage reaches 82%-90%, hydrogenation percentage of olefin (HDO) is only 17.4%～21%, the octane number loss of the FCC gasoline is 1 to 2.In order to verify the practical activity, selectivity, stability as well as adaptability to different feedstocks and processing conditions of the catalyst for hydrodesulfurization of FCC gasoline furthermore, the CoMoZn/γ-Al₂O₃ catalysts are tested on a pilot flow hydrogenation reactor with catalyst capacity of 100ml. The results indicate that the catalyst has high activity for desulfurization, HDS percentage could reach over 85% at conditions of 280°C, 1.6MPa, hydrogen-to-oil ratio of 300:1 and LHSV of 4h-1. For HDS of Shengli and Shenghua FCC gasoline, the low sulfur gasoline with 150μg/g S which is accordant to EU III specification is reached. For HDS of Dagang FCC gasoline, the low sulfur gasoline with 50μg/g S which is accordant to EU IV specification is reached.In order to verify the feasibility of TMD process, the Co-Mo-Zn/γ-Al₂O₃ catalyst was applied to couple with the aromatization catalyst to processing Dalian FCC gasoline with high olefin and low aromatic contents. This work is finished on a pilot flow unit with three 100ml fixed bed reactors located in the Catalyst Factory of Fushun Petrochemical Company. Experiments show that it can reduce the total sulfur in gasoline feedstocks from 195.7μg/g to 72.1μg/g with RON loss 0.4 units. Therefore, the coupling of the selective HDS catalyst with the aromatization catalyst has better performance in processing high olefin gasoline to meet the requirement of removing sulfur and reducing olefin with little RON loss, so that TMD process has a bright prospect for commercialization.