Physicochemical Properties Of New Hydroxyl Functionalized Ionic Liquids And Their Extraction Mechanism For Phenol From Oil

One of the most prominent features of ionic liquids（ILs）is their ability to introduce specific functional groups required and rationalize their properties by selecting components.In this paper,eight hydroxyl functionalized ionic liquids（HFILs）were designed and synthesized:1-（2-hydroxyethyl）-3-methyl-imidazolium propionate ionic liquid（[HEMIM][Pro]）,1-（2-hydroxyethyl）-3-methyl-imidazole acetate ionic liquid（[HEMIM][Ac]）,1-（2-Hydroxyethyl）-3-methyl-imidazolium glycine ionic liquid（[HEMIM][Gly]）,1-（2-hydroxyethyl）-3-methylimidazole lactate ionic liquid（[HEMIM][Lac]）,choline propionate ionic liquid（[Ch][Pro]）,choline acetate ionic liquid（[Ch][Ac]）,choline glycine ionic liquid（[Ch][Gly]）,choline lactate ionic liquid（[Ch][Lac]）.The eight HFILs were characterized by ¹H NMR,¹³C NMR,EA,FT-IR and TGA,respectively.Through the analysis results,the synthesized substances were determined as target products and the mass fraction of the eight HFILs were all greater than 0.99,which met the requirements of further physicochemical properties’determination.In view of ILs’water absorption and the property characteristics of the internal water which are difficult to remove,in the temperature range of 288.15 K-333.15 K,the density,viscosity,surface tension and refractive index of the eight synthesized HFILs were obtained.On this basis,the surface entropy,surface energy,thermal expansion coefficient,molar polarization and molar susceptibility of eight HFILs were calculated,and the variation of the above properties with the type of anion and cation of ionic liquids and temperature were discussed.Method for predicting the molar surface Gibbs energy and surface tension of the eight synthesized HFILs were proposed and verified,and the predicted values showed good consistent trend with the experimental values.The viscosity value of binary mixtures in the full concentration range（x₁=0-1）were determined by Anton Paar Lovis 2000 ME viscometer in a dry environment.By exploring the hydrogen bonding and solvation between solvent molecules and HFILs,the effect of molecular solvent addition on the viscous fluidity of HFILs was explored.The viscous flow activation energy of binary mixed solution were obtained by Arrhenius equation,and the influence of molecular solvent addition on the viscous flow activation energy of binary mixture solution was explored.The excess properties of binary mixture solutions were discussed by introducing the viscosity deviation and relative viscosity,extending from basic thermodynamic properties to excess thermodynamic properties.The factors influencing the viscosity value of the actual solutions relative to the ideal solution were discussed by measuring the excess properties relative to the ideal solution.Phenolic compounds are mainly the products of coal pyrolysis oil,coal liquefied oil and biomass pyrolysis oil.Due to the large number of phenolic compounds contained in coal tar or coal-converted oil,which seriously increases their production cost and transportation difficulty.Method for efficient separation of phenolic compounds in low-temperature coal tar is of great industrial significance.The synthesized HFILs with functional hydroxyl groups that can interact with phenolic hydroxyl groups were applied to the extraction of phenol in model oil.The separation effect of HFILs on phenol was explored,and the extraction mechanism was analyzed.Effects of HFILs structure,temperature,molar ratio of HFILs to phenol,phenol concentration in the oil phase and extraction time on the efficiency were also investigated.The results showed that the synthesized HFILs all had good extraction performance for phenol,and the[Ch][Pro]ionic liquid showed the best extraction effect on phenol and was selected as the best extraction agent.By ¹H NMR and FT-IR,the extraction mechanism was analyzed.It was found that there was an optimal distance between ionic liquid anions and cations to form hydrogen bonds with phenol,and there also anπ-πeffect between the imidazole ring in IMe-HFILs and the benzene ring in phenol,which contributed to the extraction of phenol from IMe-HFILs.In addition,ionic liquids exhibited good recyclability and continue to maintain good extraction properties after 5 cycles.In this paper,eight kinds of HFILs are selected as research objects,their basic physicochemical data were determined,and the internal changes of solutions during homogenization were deeply revealed,which was more conducive to discovering the relationship between the structure and properties of ionic liquids,and the established database was also of practical value,which was helpful to predict and estimate their thermodynamics and chemical properties of solutions.Based on the establishment of the database of physical and chemical properties of ionic liquids,the quantitative structure-property correlation（QSAR）research of ionic liquids opens up a convenient way for the design and selection of ionic liquids,and provides new systems,new methods and new theories for the molecular design,controllable preparation and functional application of ionic liquids as efficient extractant,which shows high research value.