Construction Of Imidazolyl Heteropoly Acid Catalytic System And Study On Deep Desulfurization Of Fuel Oil

The consumption of huge fossil fuels releases SO_x,leading to dramatically serious air pollution and some other environmental issues.Countries and regions worldwide have launched increasingly strict regulations on sulfur contents in fuel oils.Therefore,reducing or even removing sulfur contents in fuel oils is an inevitable trend,which is also significant for improving the global environment and achieving sustainable development.At present,fuel desulfurization technology can be divided into two categories:hydrodesulfurization（HDS）and non-hydrodesulfurization.Among them,HDS needs to be carried out under high-temperature and high-pressure conditions,inducing the high cost of HDS.Compared with aliphatic sulfur compounds,aromatic sulfide（RS）is difficult to remove on account of larger steric hindrances and stable chemical properties.In non-hydrodesulfurization methods,oxidative desulfurization（ODS）has been proven to be efficient,in which organic sulfides are oxidized to sulfoxides or sulfones with higher polarities under mild conditions.In this paper,1-vinyl imidazole was used as raw material to prepare linear and cross-linked polyvinyl imidazole.A series of imidazole-based catalysts were prepared by the reaction of monomer,linear chain,and cross-linked vinyl imidazole with heteropoly acids such as phosphotungstic acid,phosphomolybdic acid,and molybdovanadic acid,which were applied to the catalytic oxidation desulfurization of fuel oil.Firstly,the phosphomolybdenum-vanadium heteropoly acid(H₅PMo₁₀V₂O₄₀)was prepared by hydrothermal synthesis.Then 1-vinylimidazole monomer was reacted with different kinds of heteropoly acids to prepare imidazolyl heteropoly acid catalyst HPA-VIM（HPW-VIM,HPMo-VIM and HPMo V-VIM）by a one-pot method.The chemical bonds and functional groups contained in the catalyst were characterized by FT-IR and Raman spectra;The thermal stability of the catalyst was tested by TG analysis.In addition,the effects of different heteropoly acids,reaction temperature and the amount of oxidant on the catalytic desulfurization activity were investigated.Finally,the recycle performance of the catalyst was studied.The desulfurization rate of the prepared imidazolyl heteropoly acid catalyst can reach99.9%under mild conditions,and the desulfurization activity remains at 97.7%after seven times of recovery.In addition,the mechanism of high desulfurization activity was clarified by density functional theory（DFT）calculation.The results show that the energy barrier of imidazolyl heteropoly acid（HPW-VIM）as catalyst is much lower than that of phosphotungstic acid（HPW）as catalyst.Secondly,linear polyvinylimidazole（n%Pvim）with different chain lengths were prepared from 1-vinylimidazole and initiator AIBN.A series of supported catalysts with different ratios of n%Pvim HPW-m were obtained by introducing phosphotungstic acid（HPW）through hydration.The structure and morphology of the catalyst were characterized by FT-IR,XRD,SEM,and XPS.The best reaction conditions were obtained by changing the type of reaction catalyst,reaction temperature and the content of oxidant in the reaction process.The desulfurization efficiency of 2.5%Pvim-HPW-2 catalyst is 99.80%at 50℃and O/S=5.Under the same conditions,the desulfurization efficiency of catalyst 5%Pvim-HPW-1is 99.15%,and the catalytic activity is still above 95.0%after 8 cycles.The interaction of electron transfer and oxygen vacancy in the catalyst was discussed and the mechanism of ODS was revealed.Finally,the supported catalyst VE-HPW was synthesized by bulk polymerization and hydrothermal method using 1-vinylimidazole,ethylene glycol dimethyl acrylate and phosphotungstic acid as raw materials.VE-HPMo and VE-HPMo V were prepared by changing the type of heteropoly acid.The morphology,structure,pore size and specific surface area of the catalyst were investigated by FT-IR,XRD,SEM,BET and XPS.At the same time,the thermal stability and hydrophilicity of the catalysts were observed by TG-DTG and CA tests.In addition,the effects of catalyst type,reaction temperature and amount of oxidant on catalytic activity were investigated.Finally,the recycle performance of the catalyst was tested.At 50℃,the desulfurization efficiency can reach 99.68%in 60 min.VE-HPW has good desulfurization performance.It is worth noting that the catalyst is recyclable for 9consecutive times and the removal rate is stable,reaching 98.60%.The reaction mechanism of oxidative desulfurization was finally proposed based on a free radical capture experiment and GC-MS analysis.