Study On The Separation Of Azeotropic Compounds Of Alcohol-Containing By Extraction Distillation With Choline Deep Eutectic Solvents

In the process of chemical production,many azeotropes of alkanes and alcohols that are difficult to separate are often produced,and it is necessary to separate and recover them to obtain higher economic and environmental benefits.Extractive distillation is a highly efficient azeotropic separation process,but traditional organic extractants have drawbacks such as high relative consumption,strong volatility,and high toxicity.Emerging deep eutectic solvents(DESs)have good potential applications in extractive distillation due to their environmentally friendly,low volatility,and adjustable structural properties.However,there are few reports on the effect of using DESs as an extractant on the separation efficiency of azeotropes.Therefore,exploring the extractive distillation separation mechanism and effect of DESs for azeotropes is of great significance for the design and development of new DESs and the research of green chemical processes.Firstly,the effect of different DESs with choline chloride(ChCl)as hydrogen bonding acceptor(HBA)and different carbon chain lengths of binary alcohols or dicarboxylic acids as hydrogen bonding donors(HBD)as extractants on the separation efficiency of n-heptane/ethanol system was explored.The effect of six different DESs on the relative volatility of n-heptane/ethanol system was studied through experiments.With the growth of HBD carbon chain,the separation effect of DESs on the separation system is better.The contribution and interaction of different HBDs to the separation process of n-heptane/ethanol system were explored at the micro scale by using quantum chemical theory calculation and molecular dynamics simulation.With the growth of HBD carbon chain,the hydrogen bond and van der Waals force of DESs to ethanol are enhanced,which enhances the attraction of DESs to ethanol in the system.However,the interaction between DESs and n-heptane did not increase with the growth of HBD carbon chain.Secondly,the separation effect and mechanism of cyclohexane/ethanol azeotrope system with different combinations and ratios of HBA(betaine(Bet),ChCl)and HBD(ethylene glycol(EG),levulinic acid(La))were studied.Based on the vapor-liquid phase equilibrium experiment,the effect of different DESs as solvent on the phase behavior of cyclohexane-ethanol azeotrope was investigated,and the DESs combination with the best separation performance(Bet-EG(1:1),ChCl-La(1:1),ChCl-La(1:2))was obtained.The electrostatic potential and interaction region between different DESs and azeotropic system were analyzed by quantum chemical calculation,and the separation mechanism of DESs for cyclohexane/ethanol system was revealed from the microscopic level.The effective separation of DESs from azeotropes is mainly because the interaction between DESs and ethanol formed by the combination of HBD and HBA is stronger than that between DESs and cyclohexane,and the interaction between DESs and ethanol is stronger than that between HBD and HBA ethanol alone.