Molecular Design Of Ionic Liquid As Catalyst For Lignin Degradation Reaction And Performance Research

With the development of economy and science technology,people have great demand for energy,resource crisis and environmental pollution have become the two major challenges to human society.15%-35%of biomass is lignin,it contains abundant aromatic rings and carbon elements,lignin provides structural basis for solving resource crisis and environmental pollution.Small molecular aromatic compounds can be obtained by breaking the chemical bonds in lignin.However,stable structure of lignin increase the difficulty of chemical degradation,it’s urgent to develop an environmentally friendly and efficient biomass degradation technology.As a new environmental green solvent,Ionic liquids have excellent catalytic performance in catalysis.However,it’s wasteful and infeasible to choose the best ionic liquid catalytic because of a wide variety of ionic liquid.In the dissertation,the molecular design of functional ionic liquid is accomplished by DFT theory from the microscopic point.1.24 kinds of ionic liquids were obtained by enumerating four cations and six anions.Through density functional theory,the interaction energy and HOMO-LUMO orbital energy of the complexes which consisted of ionic liquids and lignin model compounds（β-O-4,α-O-4,4-O-5,5-5 andβ-1）were calculated.The effects of anion and cation on reducing the energy of reaction system,enhancing the stability of the reaction system and improving catalytic degradation of ionic liquids were analyzed.The calculation results show that propyl sulfonate on the ionic liquid cationic imidazole ring and hydrogen sulfate anions can greatly reduce the energy,increase the stabilize and have high selective fragmentation for theβ-O-4 bond type.2.In order to test the accuracy of quantum calculation,1-propylsulfonate-3-methylimidazolium hydrogensulfate（[Pr SO₃HMIm]HSO₄）,1-propylsulfonate-3-methylimidazolium chloride（[Pr SO₃HMIm]Cl）and 1-butyl-3-methylimidazolium hydrogensulfate（[BMIm]HSO₄）were selected for experimental investigation.The catalytic degradation efficiencies of three ionic liquids under different reaction conditions were compared.The experimental results show that the catalytic efficiency of Pr SO₃HMIm]HSO₄is higher than the other two ionic liquids under different reaction condition.The highest degradation rate of lignin by Pr SO₃HMIm]HSO₄is 83.60%.While the highest degradation rate of lignin by[Pr SO₃HMIm]Cl and[BMIm]HSO₄were 82.22%and 80.89%respectively.The yield of guaiacol,one of the break products of theβ-O-4 bond,was used to evaluate the catalytic efficiency of breaking theβ-O-4bond.The highest yield of guaiacol was 24.23%when the catalyst was Pr SO₃HMIm]HSO₄,which was 0.64%and 1.4%higher than[Pr SO₃HMIm]Cl and[BMIm]HSO₄,respectively.Moreover,the catalyst kept high catalytic activity after cycles.The experimental results were in agreement with the simulation results,and the accuracy of quantum calculation was verified.3.The molecular design route of binuclear sulfonic acid functionalized ionic liquids was proposed.The catalytic efficiency of binuclear sulfonic was analyzed by NBO,charge transfer analysis,HOMO-LUMO theory and interaction energy.Compared with[Pr SO₃HMIm]HSO₄,binuclear ionic liquids could greatly reduce the HOMO-LUMO orbital energy,and the reaction system is more stable.According to NBO analysis,the hydrogen bond among anion,cation and lignin were the key to promote the fragmentation ofβ-O-4 bond.The results of charge transfer analysis show that the transfer was mainly concentrated in C_α-OH,C_β-O and C_β-H atoms.The total charge transfer of binuclear ionic liquids is greater than that of[Pr SO₃HMIm]HSO₄.In a word,the catalytic effect of binuclear ionic liquids was better than that of[Pr SO₃HMIm]HSO₄.4.Binuclear sulfonic acid ionic liquid was prepared.The structure of ionic liquid was characterized by FT-IR,NMR and MS,then the ionic liquid was applied to experiment.The results showed that the degradation rate of lignin was 93.72%after 3h,which was 10.12%and 11.15%higher than that of[Pr SO₃HMIm]HSO₄and[Pr SO₃HMIm]Cl respectively.The highest yield of guaiacol is 27.23%by binuclear sulfonic acid ionic liquid,which is 3%and 4.4%higher than that of[Pr SO₃HMIm]HSO₄and[Pr SO₃HMIm]Cl respectively.Moreover,the catalyst could keep high catalytic activity after cycles.