Application Of Ionic Liquids In Extractive Distillation And CO₂ Reduction

With the rapid development of the economy,energy and environment is facing huge problems,such as the use of volatile organic solvents in the separation process of chemical industry,environmental and global warming caused by a large amount of energy consumption.Among them,extractive distillation is a typical process with high energy consumption and large use of volatile organic extractants.Therefore,it is also important to find a suitable extractant to replace the currently used organic solvents.The main reason for global warming is the increasing concentration of carbon dioxide（CO₂）in the atmosphere.The conversion of atmospheric CO₂ into other high value-added products is also a global concern.Ionic liquids have obvious merits such as negligible vapor pressure,wide electrochemical window and non-flammability.The separation of azeotropic mixtures using ionic liquids as extractants is expected to solve the energy and environmental problems in the extractive distillation and improve the separation efficiency.At the same time,the research on electrochemical reduction of CO₂ with ionic liquid as electrolyte has also attracted extensive attention of researchers.Based on the unique advantages of ionic liquids in extractive distillation and electrocatalytic CO₂,the contents of this article are as follows:（1）Design and optimization of the efficient extractive distillation process for separating the binary azeotropic mixture based on the quantum chemistry and conceptual design.Firstly,ionic liquids,1-Methylimidazolium acetate（[MIM][OAc]）and 1-methylimidazolium 2-hydroxypropionate（[MIM][Hpr]）,were selected as candidate extractants for separating acetone-methanol mixtures through the analysis ofσ-profiles.Then,through the thermodynamic topology analysis,the feasibility of the two candidate schemes was further studied.The results showed that acetone was first separated as the overhead product,and ionic liquids and methanol were used as the bottom effluent.Finally,the design and optimization of extractive distillation with[MIM][OAc],[MIM][Hpr]and DMSO was conducted respectively.The simulation results are consistent with the thermodynamic topological analysis.And the results demonstrate that the total annual cost of the extractive distillation process using[MIM][Hpr]is significantly reduced by 31.39%and 21.70%compared with the dimethyl sulfoxide（DMSO）and[MIM][OAc]processes.（2）A novel method for the screening of organic solvents and ionic liquids as extractants along with the design of the corresponding homogeneous extractive distillation processes has been developed.The toxicity and the physical properties of two types of extractants（e.g.,19 organic solvents and 289）ionic liquids are first considered.Then,the properties related to separation performance are further evaluated and three organic solvents and 11 ionic liquids are found to conform to the process feasible restrictions.In the third step,glycerol,triethylene glycol,1-butyl-3-methylimidazolium thiocyanide[C₄MIM][SCN],and 1-pentyl-3-methylimidazolium thiocyanide[C₅MIM][SCN]are chosen as the representatives to perform thermodynamic topological analysis.Finally,the process design and optimization with four extractants are performed.And the process economic evaluation proves that the ability of glycerol in separating tert-butanol-water system is superior to that of triethylene glycol while that of[C₄MIM][SCN]is better than that of[C₅MIM][SCN].（3）With the aim of cleaning and energy-saving,herein,innovative energy-saving design for ionic liquids-based extractive distillation process has been proposed.The innovative energy-saving design focuses on the binary minimum azeotrope mixtures isopropanol（IPA）and water.An innovative ionic liquids based extractive distillation process combining distillation column and stripping column are designed and optimized with 1-ethyl-3-methyl-imidazolium dicyanamide（[EMIM][DCA]）and 1-butyl-3-methyl-imidazolium dicyanamide（[BMIM][DCA]）as extractants,respectively.The results demonstrate the TAC reduced by 19.9%with[EMIM][DCA]as extractant and by 24.3%with[BMIM][DCA]as extractant when compared to DMSO as extractant.（4）The ionic liquids[N₁₁₁₈][Triz]was prepared,and the research of electrocatalytic CO₂ reduction in the[N₁₁₁₈][Triz]medium is conducted.In this study,the new ionic liquids N-octyltrimethyl 1,2,4-triazole ammonium([N₁₁₁₈][Triz])shows outstanding performance for electrochemical reduction of CO₂ to CO on the commercial Ag electrode,and the current density can be up to 50.8 m A/cm² with a Faradaic efficiency of 90.6%.The current density of CO is much higher than those reported current density of the electrochemical reduction of CO₂ to CO in the ionic liquid electrolyte.In addition,density functional theory（DFT）calculation further proved that[N₁₁₁₈][Triz]interact with CO₂ to form[N₁₁₁₈]⁺[Triz-CO₂]^-complex which played a key role in reducing the activation energy of CO₂.According to the molecular orbital theory,the electrons obtained from ionic liquids was filled in the anti-bonding orbit（π*）of the CO₂,thus reducing the C=O bond energy.This work provides a new strategy to design novel ionic liquids for high efficiency electrochemical reduction of CO₂ to CO.