Study On Selective Hydrodesulfurization Of Nanosized HZSM-5 For FCC Gasoline Upgrading

To protect the environment, the motor fuel compositions have been limited strictly to reduce emissions of harmful substances in the world. Production of low sulfur, high reaserch octane number(RON) clean gasoline has become an important issue of refining technological progress. Fluid catalytic cracking(FCC) gasoline of the total gasoline usually accounts for more than 70% in China. The process using traditional hydrodesulfurization catalyst will lead to the serious saturation of olefins in FCC gasoline, causing significant loss of RON. Therefore, our country needs urgently to develop high selective hydrodesulfurization catalyst.Nano-HZSM-5 has a unique pore structure and larger surface area, which can enhance the dispersion of active components and the loading amount and improve the selectivity and yield of target product in the reaction. In this article, nano-HZSM-5 zeolites had been modified by hydrothermal treatment, the physical properties of the modified catalysts were characterized. On this basis, the selective hydrodesulfurization performance of HZSM-5 zeolites after hydrothermal treatment and loading active component Co, Mo were investigated for FCC gasoline upgrading. The hydrodesulfurization performance of the catalysts for thiophene was compared with that of benzothiophene. Finally, the selective hydrodesulfurization performance of CoMo/HZSM-5 catalysts modified with chelating agent EDTA was also studied. Conclusions from the experiments were summarized mainly as follow:1. With hydrothermal treatment temperature increased, the surface area and the acid amount of the nano-HZSM-5 catalyst decreased and the weak acid strength and pore volume changed little. HZSM-5 zeolite maintained a good MFI topology after hydrothermal treatment.2. The selective hydrodesulfurization performance of HZSM-5 zeolites after hydrothermal treatment and loading active component Co, Mo were investigated in the full range FCC gasoline. The results showed that the hydrodesulfurization activity of modified catalysts was inhibited, but olefin saturation activity was improved with hydrothermal treatment temperature increased. As reaction temperature increased, the desulfurization activity and olefin saturation of the catalyst increased; The increase of WHSV was helpful for keeping olefin contents, but not beneficial to the desulfurization activity of the catalysts. The modified catalyst after hydrothermal treatment at 600℃and loading active component Co, Mo had better selective hydrodesulfurization performance than other catalysts, which the composition of reaction product is essentially as the same as raw oil and its RON loss was less than 1.The HZSM-5 catalysts after hydrothermal treatment and loading active component Co, Mo had good desulfurization activity for thiophene and benzothiophene. However, when the hydrothermal treatment temperature was over 700℃, the catalytic activity for them declined seriously. The desulfurization activity of these serial catalysts for benzothiophene is better than that of thiophene.3. The selective hydrodesulfurization performance of the CoMo/HZSM-5 catalys modified with chelating agent EDTA was investigated in FCC gasoline upgrading. The results showed that the catalyst after modified by EDTA can not meet the purpose of desulfurization and maintaining RON of FCC gasoline for its desulfurization activity significantly improved, but the olefin saturation degree aggravated and its RON loss was serious. The olefin saturation activity and HDS activity can not reach a good balance with the change of process conditions. To achieve high selectivity hydrodesulfurization performance, the catalytic activity of the catalysts must be further improved.