Structural Design Of Ionic Liquids For The Extraction Of Carboxylic Acids Containing And Ester Containing Systems

Liquid-liquid extraction is an important separation unit operation of chemical engineering.Nowadays,with the development of green chemical engineering,there is growing attention to search green solvents to replace the organic solvents for liquid-liquid extractions.Ionic liquids(ILs)as tunable green solvents are increasingly used in the extraction processes.The C2/C4 routes for methyl methacrylate(MAA)synthesis contain several typical separation systems,such as methacrylic acid(MAA)-water(H2O),MAA-acetic acid(HAc),propionic acid(PA)-HAc,ethyl acetate(EA)-H2O.In this work,a series of novel ILs were designed and synthesized to separate MAA-H2O,MAA-HAc,PA-HAc and EA-H2O systems.The basic data of the ILs extraction processes were obtained by experiments.Then the molecular mechanisms of the ILs extraction processes were revealed by combining experimental characterization analyses with quantum chemical calculations.The results are expected to provide the guidance for the molecular design and application of ILs as extractants.The main contents and the results of the dissertation are as follows:Firstly,the imidazolium-based ILs and quaternary ammonium salt ILs were designed and synthesized to recover MAA from dilute aqueous solution.The effects of the IL's structure on the MAA extraction were evaluated.The results showed that the anion of IL has the higher effect on the extraction of MAA than the cation and the effect of the anion followed as[BF4]->[NTf2]->[PF6]-.In addition,the solvatochromic study showed that the partition coefficients of MAA are positive correlation with the hydrogen bond basicity of ILs.Moreover,the FT-IR and quantum chemical calculation results indicated the important role of hydrogen bond between IL and MAA,and the hydrogen bond between anion and MAA has the dominant position.Then,[N8,8,8,1]Cl with strong hydrogen bond basicity was used to extract MAA form dilute aqueous solution.At the optimal extraction conditions,the partition coefficient of MAA for[N8,8,8,1]C1 achieves 42.15,which is 49 times higher than the industrial solvent of hexane.Secondly,the carboxyl-functionalized quaternary ammonium ILs tricaprylmethylammonium succinate([A336]Suc),tricaprylmethylammonium aspartate([A336]Asp),tricaprylmethylammonium glutamate([A336]Glu),tricaprylmethylammonium trifluoroacetate([A336]TFA)and tricaprylmethylammonium phthalate([A336]Pha)with strong hydrophobicity were designed and synthesized to separate MAA and HAc from an aqueous solution.The[A3 3 6]-based ILs has strong hydrogen bond basicity due to the carboxylate group in anion of ILs.[A336]Suc has shown the better extraction performance than the other ILs because of the stronger hydrogen bond basicity.Thus,[A3 3 6]Suc was selected as extractant to separate MAA and HAc.The selectivity of MAA to HAc achieves54.70 at the optimized extraction conditions,which is two times higher than trioctylamine.The hydrogen bonding interaction was detected by FT-IR analysis.Moreover,the quantum chemical calculation was employed to analyze the interaction between[A336]Suc and MAA/HAc.The computational studies demonstrated that the stronger hydrogen bonding interaction between carboxylate group of[A3 3 6]Suc and MAA than HAc is the key of the selective separation of MAA and HAc.Third,low viscosity ILs for the selective separation of PA-HAc were designed and prepared.Three kinds of low viscosity ILs,tricaprylmethylammonium malonate([A336]Mal),trihexyltetradecylphosphonium malonate([P6,6,6,:4]Mal)and trihexyltetradecylphosphonium maleate([P6,6,6,14]Male)were used to separate PA and HAc from an aqueous solution.[P6,6,6,,4]Male exhibited lower viscosity than the other ILs due to the weak interaction between cation and anion as well as the weak intermolecular interaction of IL.The viscosity of[P6,6,6,14]Male at 303.15K is 292.82mPa s,which is 75.89%lower than[A336]Suc.Then[P6,6,6,i4]Male was used to selective separate PA and HAc.The selectivity of PA to HAc achieves 10.09,which is higher than tributyl phosphate.Fourth,hydrophilic ILs for the separation of EA-H20 mixture were designed and prepared.The dehydration of EA-H2O mixtures is difficult due to the form EA-H20 binary azeotrope.H2O can be easily removed by hydrophilic ILs through liquid-liquid extraction.Among the ILs,1-ethyl-3-methyl-imidazolium acetate([C2mim]OAc)showed best extraction performance for the separation of EA-H2O mixtures.The partition coefficient of H2O is obtained 711.26 and selectivity of H20 to EA achieves 26444.81.After three stages extraction,the water content in EA is reduced to 0.0084wt%.Moreover,the quantum chemical calculation showed that the strong hydrogen bond is formed between[C2mim]OAc and H2O,which makes the stronger interaction than[C2mim]OAc with EA and H2O with EA.The results indicated the important role of hydrogen bond for the separation of EA-H2O mixtures.