Research On Extraction And Separation Of DEM-ethanol Based On Deep Eutectic Solvents

Diethyloxymethane（DEM）is an excellent organic solvent,which has been widely used in organic synthesis,drug extraction and chemical industry.However,there is a binary azeotropic mixture of DEM and ethanol in the process of preparing DEM from formaldehyde and ethanol,which is difficult to be separated by ordinary distillation.Extraction is one of the common separation technologies in chemical process,which has the advantages of simple equipment,easy operation and low energy consumption.The selection of extractant is the key to determine the separation effect.With the vigorous development of green chemistry,the development of green solvents has attracted much attention.As a new type of green solvent,deep eutectic solvent（DES）has many advantages,such as simple preparation,low cost,low toxicity,good biodegradability and compatibility.It has great application potential in liquid-liquid extraction and other chemical separation processes.Based on this,this paper explored the extraction effect and analyzed the microscopic mechanism of DESs and DESs mixed solvents on DEM-ethanol system.In this paper,the COSMO-SAC model was applied to select ethylene glycol-benzyl trimethylammonium chloride 3:1（DES1）,glycerol-benzyl trimethyl ammonium chloride 3:1（DES2）and ethylene glycol-tetraethyl ammonium chloride 3:1（DES3）as the single solvents for DEM-ethanol separation,and then distribution coefficient,selectivity and performance index of DESs on DEM-ethanol system at different temperatures were obtained by liquid-liquid equilibrium experiment.The results show that high temperature is beneficial to the extraction of DESs,and DES2 has the best extraction performance globally at different temperatures.DES1 has better extraction performance when the ethanol content is lower.Since ethylene glycol is a common organic solvent to separate the system,the liquid-liquid equilibrium experiments were carried out with different mass ratios of DES1 and DES2(MD₁₂),DES2 and ethylene glycol（MD₂EG）as extractants in this paper.The experimental results show that the mixed solvents MD₁₂ and MD₂EG can greatly reduce the viscosity of DES2 while maintaining a good extraction separation effect.The consistency of the above experimental data was verified by Othmer-Tobias equation,Hand equation and Bachman equation.The linear correlation coefficients were close to 1,which confirmed the reliability of the experimental data.In this paper,the microscopic mechanism of DEM and ethanol extraction separation by DESs single solvent was analyzed based on the quantum chemistry theory.The interaction energy calculation results show that the interaction energy between DES2 and ethanol is highest,and the interaction energy difference between DES2 and DEM or ethanol is the largest.The study of weak interaction between molecules through independent gradient model and atom in the molecule show that there are mainly hydrogen bonding forces and van der Waals forces between DESs and DEM/ethanol.The mechanism of extracting and separating DEM and ethanol by MD₁₂ and MD₂EG mixed solvents was analyzed by IR and NMR.The results show that hydrogen bond is forming between the mixed solvent and ethanol and the hydrogen bond of DESs itself was broken.This paper explored the extraction performance of DESs and DESs mixed solvents in the separation of DEM and ethanol,and studied the microscopic mechanism through quantum chemistry and experimental methods.The paper also provide a reference for the screening of new solvents and mechanism analysis of extraction separation in other azeotropic systems.