Study On The Selective Hydrodesulfurization Catalyst For FCC Gasoline

Fluid catalytic cracking (FCC) gasoline, accounting for about 70%?80% of commercial gasoline in China, contains very high levels of sulfur compounds and olefins. More than 90% of sulfur compounds come from FCC gasoline. With the enforcement of increasingly stringent environmental laws, strict regulations of the sulfur levels in gasoline have been carried out around the world. Therefore, it is highly required for the reduction of the sulfur contents in FCC gasoline. The technology of selective hydrodesulfurizaiton has obvious advantages in deep desulfurization and maintaining the octane value than other hydrodesulfurization technology. In this paper, the main purpose is to develop high selective hydrodesulfurization catalyst and study the influence of active component precursors, carriers and chelating agents on the catalytic activities of catalysts. The main research contents are as follows:(1) ?-Al2O3 was chosen as the support for the preparation of NiSO4/?-Al2O3 catalysts with NiSO4 as a precursor by impregnating method. And the results showed that there was a strong interaction between S=O in SO42- and Al2O3 supports, which creates a large amount of acid sites. Moreover, the NiSO4/?-Al2O3 catalyst can be in situ self-sulfided to NiSx by H2 at an elevated temperature, which is considered to be the acitive phase. And the catalysts showed higher activity in terms of high thiophene conversion and a high selectivity factor than those of the counterpart catalyst prepared by nickel nitrate.(2) The influence of carriers, containing nano HZSM-5 zeolites, nano silicate-1 (S-1), small particles titanium silicate-1 (TS-1) and ?-Al2O3 supports, on catalytic performance of CoMo supported catalysts was investigated. The results showed that MoS2 slabs were more uniform in the catalyst supported on HZSM-5, and the number of MoS2 slabs stacking is moderate. Compared with the catalysts using S-1, TS-1 and ?-Al2O3 as supports the CoMo/HZSM-5 catalyst showed higher isomerization, aromatization and desulfurization activities.(3) Effects of different chelating agents, containing citric acid (CA), ethylenediamine (EN), urea (Urea), nitrilotriacetic acid (NTA), ethylenediamine tetraacetic acid (EDTA), and trans-1,2-cyclohexanediamineetectraacetic acid (CDTA), on the catalytic performance of CoMo catalysts supported on nano ZSM-5-Al2O3 was investigated. The results indicated that the chelating agents weaken the interaction between active components and supports, and promoted the reduction of Mo species and the formation of Co-Mo-O mixture. The presence of chelating agents reduced the sulfidation temperature of Mo species and produced more MoS2 slabs of smaller size. And the average MoS2 stacking of the catalysts increased obviously with EDTA and NTA modification, showing much more active sites in catalysts.(4) The influences of HZSM-5 contents and hydrothermal treatment temperature of supports on selective hydrodesulfurization of EDTACoMO/HZSM-5-Al2O3 catalysts were also studied. The interaction between active components and supports was adjusted when nano ZSM-5 zeolite was introduced, which inhibited the formation of Al2(MoO4)3 species. Meanwhile, the proportion of 3-5 layers of MoS2 slabs was increased, while the amount of the monolayer of MoS2 slabs was decreased in the presence of ZSM-5 zeolite. The Lewis acid and Bronsted acid of catalysts were modulated when using the hydrothermal treatment treated ZSM-5-Al2O3 supports, and the crystallinity, specific surface area and pore volume were changed to some extent. The experimental results indicated that the CoMo/HZSM-5-Al2O3 catalyst showed high hydrodesulfurization activity and selectivity when the content of ZSM-5 was more than 70 wt.% and the hydrothermal treatment temperature was greater than or equal to 500?.(5) The EDTACoMo supported catalyst was prepared with high hydrodesulfurization activity and selectivity, and named as DQG-076. In order to verify the practical activity, selectivity, stability as well as adaptability to different feedstocks with different sulfur contents and processing conditions, the DQG-076 catalyst was tested on a pilot flow hydrogenation reactor with catalyst capacity of 100 mL. The experimental results demonstrated that DQG-076 catalyst showed high hydrodesulfurization activity, selectivity and stability for FCC gasoline. The results of 100 mL fixed bed and small fixed bed in laboratory for FCC gasoline were almost at the same level. For FCC gasoline with the sulfur contents< 300 ppm, the product meets the National V standard with sulfur content at around 10 ppm and the loss of RON less than 1.5 unit by the two steps process (deep selective hydrodesulfurization followed by aromatization). For FCC gasoline with the sulfur contents ?300 ppm, the DQG-076 catalyst also showed highly selective hydrodesulfurization and good stability with little RON loss, indicating that DQG-076 catalyst has a bright prospect for commercialization.