Mechanism And Performance Of Functionalized Ionic Liquids In Denitrogenation Of Fuel Oils

The removal of N-compounds from fuel oils has attracted extensive attention from researchers with the increasingly strict environmental regulations in recent years.As a new denitrogenation technique,the extraction denitrogenation with ionic liquids?ILs?shows greater potential than other techniques,due to its advantages such as mild conditions,simple process operation,and limited environmental pollution caused by volatility of conventional organic solvents.However,the previous researches showed a paucity on the simultaneous efficient removals of both basic and non-basic N-compounds by ILs,and the theoretical study on denitrogenation mechanism with ILs still lacked deepness and system.Three types of ionic liquids were synthesized herein and used to remove basic and non-basic N-compounds from diesel oil simutaneously.The structure of ionic liquid and interaction between ionic liquid and N-compounds?e.g.quinoline and indole?were studied with density functional theory calculations,which can provide some theoretical advice for the design of ionic liquids.Br?nsted acidic ionic liquids 1-butyl-3-methylimidazolium hydrosulphates?[Bmim]HSO₄?was synthesized,and it exhibited an excellent performance of simultaneous efficient removal of both basic and non-basic N-compounds compared with other investigated imidazolium-based ILs with different anionic characteristics?i.e.,[CF₃COO]^-,[CH₃COO]^-,[BF₄]^-,Br^-,Cl^-?,achieving more than 99.0%extraction efficiency of quinoline and indole.Additionally,compared with the reported removal of indole by[?CH₃CH₂?₃N?CH₂?₃SO₃H]HSO₄,a shorter equilibrium time was attained by[Bmim]HSO₄.The geometrical structures and electronic properties of[Bmim]HSO₄ and the interactions between[Bmim]HSO₄ and quinoline,indole were investigated by density functional theory at B3LYP/6-311+G?d,p?level.Natural bond orbital?NBO?analyses suggested that the orbital interaction from the anion to cation occurred mainly through the LPO?BD*C-H interactions.The strong interaction occurred between active hydrogen of HSO₄^-and the N atom of quinoline molecule,while in the case of indole,the interaction derived from the hydrogen bond formed between the H atom of N-H in indole molecule and the O atom of HSO₄^-,which were the main driving force of denitrogenation with[Bmim]HSO₄.The interaction energy between[Bmim]HSO₄ and quinoline,indole were calculated to be 32.95 KJ/mol and 44.29KJ/mol,respectively.Eutectic ionic liquids?EILs?[Bmim]Br-polyacids?or alcohols?were synthesized for the first time.Taking[Bmim]Br-malonic acid as an example,its structure was characterized by FT-IR and ¹H NMR,meanwhile its geometrical structure and electronic property was studied in detail by density functional theory.AIM and NBO analyses showed electrostatic interaction and hydrogen bond existed between components in EILs[Bmim]Br-malonic acid,which was consistent with characterization results of EILs.The research on denitrogenation performance of EILs indicated[Bmim]Br-malonic acid?molar ratio=1:0.8?presented good performance of simultaneous efficient removal of both basic and non-basic N-compounds,and its denitrogenation mechanism was same with that of[Bmim]HSO₄.The removal efficiency of quinoline and indole by[Bmim]Br-0.8 malonic acid can reach 97.0%and 95.7%at ILs/oil?w/w?1:7,respectively,and the removal efficiency of quinoline and indole can still reach 85.1%and 88.7%during four recycles of the EILs,respectively.FeCl₃ and ZnCl₂ based bromide imidazolium ionic liquids were synthesized,and it was found that low viscous FeCl₃-based ILs?[Bmim]Br/FeCl₃?presented better performance of simultaneous removal of both basic and non-basic N-compounds at lower temperature,achieving 99.1%quinoline and 89.3%indole removal efficiency,respectively.Moreover,the extraction performance of[Bmim]Br for quinoline was significantly improved by the co-presence of FeCl₃,which can be attributed to the interaction of Lewis acidic Fe^?species with Lewis basic quinoline,as well as the good fluidity of[Bmim]Br/FeCl₃.Removal efficiency of quinoline can still reach 92.3%after four cycles of[Bmim]Br/FeCl₃.Fushun shale diesel distillate with a large amount of N-compounds was selected as actual oil for further investigation of removal performance of[Bmim]HSO₄,[Bmim]Br/FeCl₃and[Bmim]Br-malonic acid?molar ratio=1:0.8?for basic and non-basic N-compounds.Under the condition with temperature of 30?,oil:IL?w/w?7:1,H₂O:IL?w/w?2:1,extraction time of 20 min and settling time of 120 min,about 90.0%basic N-extraction efficiency and 71.3%total N-extraction efficiency were achieved when[Bmim]HSO₄ was used in denitrogenation from the shale diesel distillate.In the case of denitrogenation with[Bmim]Br/FeCl₃ and[Bmim]Br-0.8 malonic acid from shale diesel distillate,the basic N-removal efficiency and the total N-removal efficiency can reach 95.3%,89.8%and 88.9%,83.0%at IL/oil?w/w?1:1,respectively.Further investigation indicated that the N-compounds in shale diesel distillate were removed effectively and sulfur compounds can also be removed to some extent after treatment with ionic liquid.In addition,the density,viscosity and pouring point of refined oil were decreased and the oil quality was improved.