Preparation Of Imidazole-based Polyacid Catalysts And Their Investigation On Catalytic Oxidative Desulfurization Of Fuels

With more and more serious environmental pollution caused by fuel combustion and increasingly demanding of people on the environment,it is a tendency to obtain ultra-low sulfur content fuels.With conventional methods,hydrodesulfurization?HDS?is efficient for the removal of thiols,sulfides and disulfides,but less effective for removing refractory sulfur compounds.To remove these refractory sulfur compounds,high temperatures and pressures are needed,which increases the cost of fuel.Therefore,non-HDS reaction processes have received a great deal of attention.Recently,oxidative desulfurization of organic sulfur compounds in fuels under mild environment has always been a rather important research subject,especially the oxidative desulfurization with the green oxidants?hydrogen peroxide?.From this point of view,liquid-liquid extraction and catalytic oxidative desulfurization?ECODS?system are used for the deep removal of sulfur compounds in fuels.The sulfur-containing compounds are oxidized to polarity sulfones by hydrogen peroxide.Sulfones are easily extracted into ionic liquid phase or other polar solvents,and achieved the aim of the deep desulfurization.The research contents of this dissertation are shown as following.1.Three peroxophosphorus molybdate catalysts,[C₄mim]₃{PO₄[MoO?O₂?₂]₄},[C₈mim]₃{PO₄[MoO?O₂?₂]₄}and[C₁₆mim]₃{PO₄[MoO?O₂?₂]₄},were synthesized.The structure characteristic of three catalysts were confirmed and discussed by elemental analysis,peroxide content determination,FT-IR,UV-Vis,and TG-DSC.The results indicated that ECODS system showed the best activity and the removal of DBT could reach 98.3%,when[C₁₆mim]₃{PO₄[MoO?O₂?₂]₄}was used as catalyst and[C₄mim]BF₄was used as the extractantat,V?H₂O₂?=24?L,n?DBT?/n?catalyst?=10:1,V?[C₄mim]BF₄?=1 mL at 60oC for 1 h.The system could be recycled for 8 times without significant decrease in activity.The sulfur removal was still higher than 98%.2.Three peroxophosphorus tungstate catalysts,[C₄mim]₃{PO₄[WO?O₂?₂]₄},[C₈mim]₃{PO₄[WO?O₂?₂]₄},[C₁₆mim]₃{PO₄[WO?O₂?₂]₄},were synthesized.The structure characteristic of three catalysts were confirmed and discussed by elemental analysis,peroxide content determination,FT-IR,UV-Vis,and TG-DSC.Researches showed that ECODS system exhibited the best activity in ionic liquid[C₄mim]BF₄.The optimal reaction conditions were shown as follows:n?DBT?/n?catalyst?=10:1,V?H₂O₂?=32?L,V?[C₄mim]BF₄?=1 mL,T=60oC,t=1 h.The DBT removal could reach up to 99.2%.The system could be recycled 5 times without significant decrease in activity.After been recycled for 5 times,sulfur removal with the reused catalyst decreased from 99.2%to 96.0%.3.Imidazole type peroxomolybdate[C₁₆mim]₂Mo₂O₃?O₂?₄?H₂O was designed and synthesized.And the as-prepared catalyst was characterized by NMR,elemental analysis,FT-IR,ESI-MS,TG-DSC etc.The catalyst exhibited reaction control foam phenomenon during the reaction.The catalyst was solid powder before reaction and then changed to foam-like status during the reaction process,after the reaction,it turned into powder status again.This change in the reaction process made catalyst to show highly active catalytic ability,and catalyst was easy to be recycling use after the reaction.The removal of DBT could achieve up to 98.4%with using H₂O₂ as the oxidant.The optimal reaction conditions were shown as follows:n?DBT?:n?catalyst?:n?H₂O₂?=30:1:180,T=50oC,t=1 h.The sulfur removal could reach 78.0%after 2 h for 4,6-DMDBT,which is the catalyst that most difficult to be removed in the HDS process.The system could be recycled 6 times without significant decrease in activity and the sulfur removal still reached 93.9%.4.A magnetic mesoporous silica-supported ionic liquid phosphomolybdic heteropoly acid salt heterogeneous catalyst?MPMS?was designed and synthesized.The active center[C₁₆mim]₃PMo₁₂O₄₀ was supported in mesoporous SiO₂.And the active center was then reacted with magnetic iron oxide to obtain a catalyst.Then,FT-IR,Raman,XPS,XRD,SEM and TEM demonstrated that ionic liquids and magnetic iron oxides were successfully supported in mesoporous SiO₂.The magnetic propertie of the0.5-MPMS catalyst showed superparamagnetic propertie.It could realize rapid separation from the oil under the action of external magnetic field.Through the activity test,it was found that under the reaction conditions:m?catalyst?=0.01g,T=70oC,V?H₂O₂?=32?L,the reaction could achieve deep desulfurization within 30 min.The sulfur removal reached 100%after 1 h.The catalyst showed higher removal activity for3-MBT,4-MDBT and 4,6-DMDBT.Moreover,the cycling experiment of the catalyst showed that the catalyst still retained 94%of catalytic activity after 10 cycles,showing a good industrial application prospect.