| Vapor-liquid equilibrium data is the basic data for the design and optimization of extractive distillation process,and screening appropriate solvents is the key to achieve low energy consumption and high efficiency separation.In this paper,five organic solvents including N-methylpyrrolidone,N,N-dimethylformamide,butyl butyrate,cyclohexanol and N-formylmorpholine were selected to separate p-xylene and pentanol azeotrope.The vapor-liquid equilibrium data of pentanol+butyl butyrate,N-formylmorpholine+pentanol and p-xylene+butyl butyrate binary systems were measured using modified Rose-type circulating still at 101.3 k Pa.The thermodynamic consistency of three groups of binary vapor-liquid equilibrium data is verified by Herington,Van Ness and Frdunlund methods.The results show that the data have good thermodynamic consistency.The measured vapor-liquid equilibrium data were correlated and regressed by NRTL,UNIQUAC and Wilson models to obtain the binary interaction parameters.The root mean square deviation and average absolute deviation of vapor phase molar composition/temperature between experimental data and model prediction data are calculated,and the maximum values are 0.009 and 0.006,0.92 K and 0.62 K respectively.The regression results show that the three thermodynamic models can well describe the phase behavior of the system.The sequential iterative method was used to optimize the extractive distillation process of N-formylmorpholine separation of p-xylene and pentanol.The effects of regression thermodynamic model parameters and built-in thermodynamic model parameters on extractive distillation process were compared.It was found that the total annual cost difference between the two processes was 5.9×10~5$·year-1.The interaction between organic solvents,deep eutectic solvents,low transition temperature mixture and ionic liquid and p-xylene-pentanol was studied by quantum chemical calculation,and the separation mechanism was studied at the molecular level.They are quantitatively studied based on the energy decomposition analysis based on forcefield.The order of total non bond interaction is[BMIM]Cl>(Ch Cl:MA)1:2>(Ch Cl:HL)1:1>N-formylmorpholine.Using the interaction region indicator function analysis,it is found that the interaction between solvents and p-xylene-pentanol is mainly weak interaction.Electrostatic interaction and van der Waals interaction are the key interactions in the compound.The electron density difference can judge that(Ch Cl:MA)1:2,[BMIM]Cl and pentanol-p-xylene are dominated by electrostatic interaction.Using van der Waals potential,it can be judged that(Ch Cl:G)1:2,(Ch Cl:HMA)1:1 and pentanol-p-xylene are dominated by van der Waals interaction.In addition,because the molecular structure of the optimal compound is inevitably accompanied by orbital overlap,the orbital interaction is analyzed by using natural bond orbital.The results showed that both organic solvents and green solvents were easier to form C-H···O or O-H···O with pentanol.Quantum chemical calculation results show that the introduction of solvent has a significant effect on the molecular interaction of azeotropes,which is the main factor for the solvent to reduce the relative volatility between azeotropes. |
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