Research On The Application Of Deep Eutectic Solvents(DESs)for Extractive Distillation Process

The separation of acetonitrile-water(strong polar azeotrope system)and n-hexanemethylcyclopentane(non-polar near azeotrope system)has strong industrial background.In recent years,China has put forward the requirements of energy saving,consumption reduction,green and low carbon for the chemical industry,and the traditional extractive distillation technology does not conform to the development trend of the chemical industry.Low eutectic solvent(DESs),a popular material in recent years,has the advantages of low cost,green and no pollution,and can be used in extractive distillation.At present,there are few studies on the synthesis mechanism of DESs and the separation mechanism of enhanced extractive distillation,lacking of theoretical guidance.Accurate and rapid screening of suitable solvents is also the key point of DESS application in extractive distillation.Based on the above analysis,in order to reduce the workload of solvent screening,this paper calculated the infinite dilution activity coefficient of DESs for the system by computer aided(COSMO-SAC model),and carried out solvent screening with the solubility and selectivity in the infinite dilution state as the indicators.The selected solvents were synthesized and processed.The ternary vapor-liquid equilibrium experimental data of the two systems and DESS were measured respectively and thermodynamic correlation was carried out.The reliability of the prediction model and the feasibility of the solvent were analyzed by the phase diagram.The synthesis mechanism of DESs was studied by FT-IR and intermolecular interaction energy.The enhanced separation mechanism of DESs was studied by σ-profiles,intermolecular interaction energy and independent gradient model.The COSMO-SAC model was used to screen two kinds of DESs with high performance indexes.The selected DESs was successfully synthesized,and DESs was accurately defined by physical property determination.The NRTL model was used to successfully correlate the experimental data of three-element gas-liquid phase equilibrium containing DESs.By comparing with the traditional solvent phase diagram,the feasibility of DESs as extractant was verified,and the data basis for the design and optimization of extractive distillation process was provided.By comparing the deviation between the experimental data and the prediction model,the reliability of the screening method is verified.FT-IR and intermolecular interaction energy analysis showed that the synthesis of DESs is mainly the formation of intermolecular hydrogen bonding,and the strong hydrogen bonding.The independent gradient model analysis showed that DESs exhibited hydrogen bonding for system 1(water + acetonitrile)and van der Waals interaction for system 2(n-hexane + methylcyclopentane).Using σ-profiles and intermolecular interaction energy analysis,it was found that DESs had higher solubility and selectivity for water in system 1 and for methylcyclopentane in system 2,and the addition of DESs could achieve the purpose of enhanced separation.The analysis of DESs synthesis mechanism and enhanced separation mechanism can provide guidance for the design of DESs solvents in extractive distillation in the future.