Synthesis Of Micro-mesoporous Composite Materials Beta-FDU-12 And Its Hydrogenation Performance For DBT

With the increasingly stringent fuel regulations,the production of clean oil has become an irreversible trend.Based on the current status of China’s oil processing industry,FCC diesel is the main source of fuel for vehicles in China for a long time.In order to meet increasingly stringent fuel standards,FCC diesel hydrodesulfurization technology has become the key technology to the production of clean oil.In the current hydrogenation process,the desulfurization efficiency can be improved by increasing the reaction temperature,reducing the space velocity and increasing the H₂pressure,but it will increase the energy consumption and shorten the service life of the equipment.Therefore,the development of a catalyst with high desulfurization activity is of great significance to the hydrodesulfurization process.In this thesis,micro-mesoporous composite materials Beta-FDU-12 were successfully synthesized by in-situ assembly method with Beta crystallization and F127.At the same time,different micelle expanders（cyclohexane,1,4-dimethyl-benzene,1,3,5-trimethylbenzene and triisopropylbenzene）and different inorganic salts（KCl,Fe Cl₃,Mg Cl₂,Mn Cl₂and Cu Cl₂）were used to modify the pore properties and surface properties of Beta-FDU-12（BF）composite materials in the synthesis process.And the hydrothermal precipitation method were compared with the impregnation method to optimize the dispersion properties of active metals.The effects of different factors on the synthesis of catalysts were systematically investigated from three aspects:pore properties,surface properties and dispersion properties of active metals.Finally,the supported Ni Mo/Beta-FDU-12 composite catalysts with high hydrodesulfurization activity were synthesized base on the above modification.The properties of Beta-FDU-12 composite materials and the catalysts were systematically tested by various characterization methods,including XRD,BET,H₂-TPR,Py-IR,XPS and HRTEM.The Hydrodesulfurization Performance of Ni Mo/Beta-FDU-12 composite catalysts were investigated using feedstocks of DBT.And the best operating conditions were obtained by 252 h hydrodesulfurization reaction.The different micelle expanders mainly affected the pore properties of supports in this paper,such as pore size,pore volume and specific surface area,which indirectly influenced the dispersion and sulfidation of active metals.XRD and BET results showed that the pore size,pore volume,specific surface area and the crystallinity of BF composite materials increased with the rising of molecular sizes of micelle expanders.However,excessive molecular size of micelle expanders could destroy the framework structure of BF composite materials and led to the unsatisfactory pore properties.The BF composite materials synthesized with TMB as the micelle expander had the best pore properties(S_BET=861 m²·g^-1,V_BJH=0.68 cm³·g^-1and d=11.38 nm).Ni Mo/BF-TMB catalyst had good dispersion and sulfidation degree of active metals due to the best pore properties.In the meantime,Ni Mo/BF-TMB catalyst possessed the suitable acidity,and strong B acid sites.Consequently,Ni Mo/BF-TMB showed the best DBT hydrodesulfurization activity.When the weight hourly space velocity（WSHV）was 10h^-1,the desulfurization efficiency could reach 80.0%.The different inorganic salts mainly affected the acidity of catalysts,the dispersion and sulfidation of active metals in this paper.XRD and BET results demonstrated that different inorganic salts had no significant effect on the pore properties of BF composite materials.All materials maintained the larger specific surface area(850-950 m²·g^-1),pore volume(0.69-0.78 cm³·g^-1)and the larger pore size（10.96-12.22 nm）of BF composite materials.Raman and XPS results showed that Ni Mo/BF-Mg Cl₂catalyst showed the best active metal sulfidation(S_Mo61.3%).Py-IR results confirmed that Ni Mo/BF-Mg Cl₂catalyst had the highest amounts of total acid and moderate strong acid,as well as the largest weak and moderate strong B acid.HRTEM results revealed that Ni Mo/BF-Mg Cl₂catalyst exhibited the shortest average length of Mo S₂active phase(L_av=3.75)and the best dispersion of active phase(f _Mo=0.28).Therefore,in the hydrodesulfurization evaluation of DBT,Ni Mo/BF-Mg Cl₂catalyst displayed the best hydrodesulfurization performance.When the WHSV was 10 h^-1,the desulfurization efficiency could reach 98.6%,and the hydrogenation pathway ratio of HYD and DDS reached the highest value（0.29）.The hydrothermal precipitation method mainly affected the strength of the metal-support interaction（MSI）,the number of stacking layers of"Ni-Mo-S"active phase,the dispersion and the sulfidation degree of active metals.Many characterization results proved that the catalysts synthesized by hydrothermal precipitation method had the relatively weak MSI（H₂-TPR）,the higher dispersion of active metals（XRD,HRTEM）,more suitable stacking layer of"Ni-Mo-S"active phases（HRTEM）and the higher degree of sulfidation（XPS）than that of the catalysts synthesized by traditional impregnation method.The BET results of the catalysts using quaternary ammonium salts with different carbon chain lengths（dodecyl trimethyl ammonium bromide,tetradecyl trimethyl ammonium bromide and cetyltrimethyl ammonium bromide）indicated that the loss of specific surface area of the catalysts decreased gradually with the increase of carbon chain length.Among them,Ni Mo/BF-CTAB catalyst had the best pore properties,such as the specific surface area,pore volume and pore diameter(295.68 m²·g^-1,0.54 cm³·g^-1and 17.63 nm,respectively).At the same time,HRTEM results confirmed that the Ni Mo/BF-CTAB catalyst synthesized by hydrothermal precipitation method using CTAB had the best stacking layers of Mo S₂active phases（no more than 6 layers）,the best dispersion of active phase(f _Mo=0.32)and the best sulfidation degree of active metal Mo(S_Mo=60.19%).Therefore Ni Mo/BF-CTAB catalyst showed the best hydrodesulfurization performance in the hydrodesulfurization evaluation of DBT.When the WHSV was 10 h^-1,the desulfurization efficiency could reach 96.9%,and the hydrogenation pathway ratio of HYD and DDS reached the highest value（0.44）.