Study On Preparation Of Mesoporous Alumina Supported Molybdenum Oxide Catalysts And Its Deep Oxidative Desulfurization Of Fuel Oil

In recent years,with increasingly stringent environmental regulations,oxidative desulfurization?ODS?is becoming a hot deep desulfurization research topic,because ODS has the advantages of mild reaction conditions,high desulfurization efficiency and effective removal of thiophene and its derivatives which are stubborn for hydrodesulfurization?HDS?.In this dissertation,the development of deep desulfurization in recent years was reviewed.Then three mesoporous alumina supported molybdenum oxide catalysts with different structures were fabricated,then the catalysts were applied in the ODS system with H₂O₂ as oxidant.The ODS process ofmodeloil?dibenzothiophene?DBT?,benzothiophene?BT?and4,6-dimethyldibenzothiophene?4,6-DMDBT??were researched.The main conclusions were as follows:Firstly,MoO₃/Al₂O₃ was in situ synthesized and applied in the catalytic oxidative desulfurization system.When MoO₃/Al₂O₃ was employed as the catalyst,the oxidative removal rate of DBT,4,6-DMDBT and BT were close to 100%after 50 min,60 min and 100 min,respectively.The rate constants of these oxidative reactions were 0.051min^-1,0.043 min^-1 and 0.022 min^-1,and the apparent activation energies of these oxidation reactions were 45.39 kJ/mol,48.55 kJ/mol and 54.21 kJ/mol.The recycling experiments indicated that the removal rates of DBT,4,6-DMDBT and BT could still reach 90.81%,89.22%and 88.33%after five cycles.Secondly,F127-MoO₃/Al₂O₃ whose pore structure was modified by the template polyethylene oxide-polypropylene oxide-polyethylene oxide?F127?,was in situ synthesized and applied in the catalytic oxidative desulfurization system.Pore structure analysis showed that the pore structure?the increase of specific surface area,pore volume and average pore size?was effectively improved.When F127-MoO₃/Al₂O₃ was employed as the catalyst,the oxidative removal rates of DBT,4,6-DMDBT and BT were close to 100%after 10 min,12 min and 25 min,respectively.The rate constants of these oxidative reactions were 0.184 min^-1,0.170 min^-1 and 0.151min^-1,and the apparent activation energies of these oxidation reactions were 39.16kJ/mol,39.66 kJ/mol and 49.47 kJ/mol.The recycling experiments indicated that the removal rates of DBT,4,6-DMDBT and BT could still reach 97.91%,95.68%and93.82%after five cycles.The catalytic activity of the catalyst was obviously improved by the using of F127.Lastly,F127-Ca/MoO₃/Al₂O₃ modified by Ca²⁺was synthesized by in-situ method and applied in the ODS system.XPS analysis showed the binding energy of the Mo 3d on the F127-Ca/MoO₃/Al₂O₃ catalyst was increased by 0.7 eV with F127-MoO₃/Al₂O₃.UV-Vis analysis indicated the number of molybdenum oxide octahedral geometry in the catalyst was increased by the introduction of Ca²⁺.These changes were beneficial to improve the desulfurization activity of the catalyst.When F127-Ca/MoO₃/Al₂O₃ was employed as the catalyst,the oxidative removal rates of DBT,4,6-DMDBT and BT were close to 100%after 8 min,10 min and 16 min,respectively.The rate constants of these oxidative reactions were 0.294 min^-1,0.283min^-1 and 0.190 min^-1,and the apparent activation energies of these oxidation reactions were 33.01 kJ/mol,34.67 kJ/mol and 40.16 kJ/mol.The recycling experiments indicated that the removal rates of DBT,4,6-DMDBT and BT could still reach 97.92%,95.64%and 93.83%after five cycles.The oxidative desulfurization activity of the catalyst was further improved by the modification of Ca²⁺.The order of the catalysts for the removal of sulfur compounds was:F127-Ca/MoO₃/Al₂O₃>F127-MoO₃/Al₂O₃>MoO₃/Al₂O₃.Under the same reaction system,the catalytic oxidation reactivity of sulfur-containing compounds was in the order of DBT>4,6-DMDBT>BT.The oxidation product of 4,6-DMDBT,DBT and BT were corresponding sulfones,which were adsorbed by the surface active groups of the solid catalysts.The oxidative desulfurization process could effectively reduce the separation operation of the oxidized products and fuel oil,which could improve economic efficiency.