Phase Equilibrium And Mechanism Study On The Separation Of Esters And Low-carbon Alcohols Using Choline-deep Eutectic Solvents

In the production process of diclofenac drugs,the composite solvent of isopropyl acetate and low-carbon alcohol is often used as the synthesis and aftertreatment process of drugs,resulting in a large amount of waste liquid containing mixtures.Isopropyl acetate and low-carbon alcohol belong to azeotropic systems,and liquid-liquid extraction is a common method for separating azeotropic systems.In this work,a deep eutectic solvent with simple preparation,low cost,and low vapor pressure was used to separate the two azeotropic compounds of isopropyl acetate methanol and isopropyl acetate ethanol.In addition,quantum chemistry and molecular dynamics simulation were used to analyze the microscopic mechanism and explore the mechanism of the extraction process.A conductor like shielded fragment activity coefficient model was used to analyze the hydrogen bonding ability of several common hydrogen bond acceptors with an azeotropic system,the performance characteristics of infinite dilution activity coefficient were compared,choline chloride was finally selected as the hydrogen bond acceptor,and three deep eutectic solvents were synthesized using environmentally friendly and widely applied ethylene glycol,urea and glycerol as hydrogen bond donors.Then the liquid-liquid equilibrium experimental data of isopropyl acetatemethanol-deep eutectic solvent and isopropyl acetate-ethanol-deep eutectic solvent system at atmospheric pressure and 25 ℃ were measured,the calculated selection factor is greater than 1,indicating that deep eutectic solvents can achieve effective separation of low-carbon alcohols.the experimental data were fitted with Othmer-Tobias and Hand equations,the fitting results verified the better reliability of the experimental data.The NRTL model was chosen to correlate the results of liquid-liquid equilibrium experiments,and the root mean square deviation calculated indicated that the phase equilibrium data had high accuracy.The mechanism analysis was carried out using quantum chemical methods of electrostatic potential,atoms in molecules,and independent gradient models.The results showed that the hydrogen bond acceptor of deep eutectic solvents and their hydrogen bond donors rely on hydrogen bond interactions to bind.Deep eutectic solvents mainly separate azeotropic systems through hydrogen bonds and van der Waals interactions,and the former plays a major role in separation.Using molecular dynamics simulation to reveal the mechanism of the structure of hydrogen bond donor and hydrogen bond acceptor on the extraction process at the molecular level,The analysis results of nonbonded interaction energy,radial distribution function and spatial distribution function showed that hydrogen bond acceptor was the main influencing factor during the separation process,in which the interaction of chloride ions with low-carbon alcohols mainly led the separation process,and this result was corroborated with the analysis results of quantum chemistry.In addition,the extraction process of isopropyl acetate and low-carbon alcohol was simulated,which can meet the purity requirements of the product under the optimized operating conditions.This shows that the selected deep eutectic solvent can realize the effective separation of azeotropic system.In addition,a heat integrated separation process proposed can effectively reduce process energy consumption.In summary,the feasibility and effectiveness of choline-deep eutectic solvents for the separation of isopropyl acetate and low-carbon alcohol azeotropic systems were verified from solvent screening,liquid-liquid equilibrium experiments,mechanistic analysis and process simulation.The reasons for the difference in separation performance of different deep eutectic solvents were illustrated from a microscopic point of view,which provided a reference for selecting suitable deep eutectic solvents for the separation of azeotropic systems.