Deep Catalytic Oxidation Desulfurization Of Fuel By Polyoxometalate-based Poly(Ionic Liquids)

Nowadays,green development is deeply rooted in the hearts of the people and there is a long way to go to protect our ecology and environment.Fuel with high sulfur concentration will corrode transportation pipelines and processing equipment.The combustion of sulfur-containing fuel will produce a large amount of sulfur oxides（SOx）,which has a harmful impact on public health and the ecosystem.Therefore,the removal of sulfur compounds from the fuel is an essential step.Hydrodesulfurization technology is more popular in industry.It is easier to remove aliphatic sulfur compounds,but the removal of aromatic sulfur compounds is not effective,and it will cause a large loss of octane number.Therefore,non-hydrodesulfurization technology has been developed to cope with the limitations of hydrodesulfurization.Oxidative desulfurization has attracted attention due to its mild reaction conditions and good removal of thiophene sulfides.This thesis revolves around polyacid-based poly ionic liquids,by adjusting the molar ratio of polyoxometallate and poly ionic liquid anion,change the valence state of polyoxometalate to form molybdenum blue-based poly ionic liquid,cross-linking method used to synthesize poly acid cross-linked poly ionic liquid materials.The relationship between its structural properties and oxidative desulfurization performance is explored by a series of characterization.Firstly,we use the anion exchange method to synthesize the polyacid-based poly ionic liquid PIL-PMo through changing the molar ratio of the poly ionic liquid and phosphomolybdic acid.Explore the influence of materials synthesized in different molar ratios on the effect of oxidative desulfurization.Characterization methods such as FT-IR,XRD proved the successful preparation of the catalyst and its excellent stability,and the obtained catalyst has a good specific surface area.When the molar ratio of poly ionic liquid to phosphomolybdic acid is 3:1,the catalytic oxidative desulfurization effect is the best.Under the optimal conditions（the reaction temperature is 30°C,the catalyst dosage is 0.01 g,and the extractant1-octyl-3-methylimidazole tetrafluoroborate is 1 m L,O/S=5）,the desulfurization efficiency can reach 99.90%after 60 minutes.The catalyst can be recycled 7 times without significant activity decrease.Through characterization analysis such as GC-MS,it was verified that the oxidation product was DBTO₂.Secondly,using the solid-phase chemical etching method to thermally mix the polystyrene and PIL-PMo utilizing the property that the?electrons of the benzene ring in aromatic molecules can interact with metals.Then the above mixture is purified with an organic solvent to obtain heteropoly blue material with the high content and stable Mo（V）.The influence of polystyrene on the formation and stability of low-valent molybdenum was explored,and the molybdenum blue-based poly ionic liquid composite material was obtained,which solved the problem of deep desulfurization requiring the addition of extractant.In the desulfurization process,the reaction is carried out for 60 minutes and the optimal conditions are tested（the catalyst dosage is 0.01g,reaction temperature is 60 ^oC,O/S=5）and the deep desulfurization can reach 99.95%.It can be recycled for 6 times,without significant reduction of desulfurization effect.The experimental results of GC-MS,ESR,and free radical capture show that both superoxide free radicals and hydroxyl free radicals are produced during the reaction process,which together promote the oxidative desulfurization rate.Finally,a cross-linked poly ionic liquid is synthesized by a cross-linking method,which exchanged with phosphomolybdic acid anion to obtain a catalyst with high cross-linking degree and strong thermal stability.The amphiphilic catalyst is obtained by adjusting the molar ratio of the ionic liquid monomer and divinylimidazole and adjusting the carbon chain length of the ionic liquid monomer.SEM characterization proves that the crosslinked catalyst has a larger specific surface area and abundant pores,which can uniformly disperse the active sites,strengthen the affinity of the active sites for organic substrates and oxidants,and greatly improve the performance of oxidative desulfurization.Under the optimal reaction conditions of 0.02 g catalyst mass,50^oC reaction temperature and O/S=5,the desulfurization rate can reach 99.86%without using extracting agent.In addition,the desulfurization rate can reach 87%after 5 cycles of the catalyst.Through GC-MS and ESR characterization,it was proved that two active species were produced during the desulfurization process,andthe reaction mechanism of the catalyst was speculated.