Synthesis Of Fe-Based Magnetic Ionic Liquids And Their Oxidative Desulfurization Performance Of Fuel Oil

In recent years,the emission of SO_x from fuel combustion has become a serious environmental problem.As a substitute and supplement of traditional hydrodesulfurization process?HDS?,the extraction catalytic oxidation desulfurization?ECODS?is one of the most promising processes to coordinate with the existing HDS methods.The process can realize sustainable deep desulfurization of fuel by using green oxidant under mild conditions.As a new type of green solvent,ionic liquids?ILs?have the characteristics of high thermal stability,extremely low vapor pressure,high electrical conductivity and non-flammability.Because of these advantages,ILs have been widely used in ECODS and many achievements have been obtained.However,the separation of ILs is generally carried out by dumping method,which is not only inconvenient to operate,but also inefficient in recovery.Magnetic ionic liquids?MILs?is a kind of functional ionic liquid with magnetism,which not only has the high catalytic activity of ILs,but also can realize the efficient separation of ILs after desulfuration with the presence of magnetic field.In this work the dinuclear imidazole based magnetic ionic liquids[C_n?mim?₂]Cl₂/mFeCl₃?n=2,4,6;m=1,2,3?were synthesized by two-step method.FT-IR and UV-Vis were used to analyze the structure of the prepared MILs,TG-DSC and VSM were used to characterize the thermal stability and magnetic properties of the MILs,and HPCL was used to measure the solubility of MILs in model oil.The results showed that the hydrophobicity,acidity and viscosity of ionic liquids had an important influence on their catalytic activity.The highest desulfurization efficiency was obtained when[C₄?mim?₂]Cl₂/2FeCl₃ was used as catalyst.The removal of DBT was above 97%at the condition of 313 K,V?oil?=5 ml,the initial sulfur content of 500 ppm,m?mils?=0.02 g,O/S=6,and the reaction time of 10 min.The desulfurization system of[C₄?mim?₂]Cl₂/2FeCl₃ conformed to the pseudo-first-order kinetic model.The high-efficiency separation of[C₄?mim?₂]Cl₂/2FeCl₃ was achieved by using the external magnetic field.After six regeneration cycles,the desulfurization efficiency slightly decreased.The desulfurization products were determined to be DBT and its corresponding sulfone and sulfoxide by XPS and FT-IR,and the desulfurization mechanism was also predicted.Secondly,[C₄DBU]/Cl was obtained by the alkylation of 1,8-diazabicyclo[5.4.0]non-7-ene?DBU?,and then a series of new magnetic ionic liquids[C₄DBU]Cl/nFeCl₃?n=1,2,3?were prepared by coordination with FeCl₃ of different molar amounts.FT-IR,UV-Vis,TG-DSC and VSM were used to analyze the molecular structure and physicochemical properties of the prepared MILs.The extraction desulfurization and the extraction catalytic oxidation desulfurization of model oil were studied using[C₄DBU]Cl/nFeCl₃?n=1,2,3?as the extractant and catalyst,H₂O₂ as the oxidant.The results showed that the addition of oxidants could significantly improve the desulfurization performance of[C₄DBU]Cl/nFeCl₃?n=1,2,3?,and the desulfurization rate follows the following order:[C₄DBU]Cl/2FeCl₃>[C₄DBU]Cl/3FeCl₃>[C₄DBU]Cl/FeCl₃.Taking[C₄DBU]Cl/2FeCl₃ as the research object,the effect of operation conditions on the desulfurization efficiency were investigated.Under the conditions of 333 K,V?oil?=10 ml,initial sulfur content 1000 ppm,V?MILs?=1.0 ml,O/S=5,reaction time 90 min,the DBT removal reached 98.75%.The catalytic activity of[C₄DBU]Cl/2FeCl₃ remained unchanged after 8 times of regeneration,indicating the high stability of[C₄DBU]Cl/2FeCl₃.The active substance of reaction was determined by the experiment of capture agent,and the mechanism of desulfuration was further verified.