Phase Behavior And Process Optimization Of Extractive Distillation For Separation Of C₆ Hydrocarbons By DMF And NMP

Extractive distillation,as an important separation technology,is not only popularized and applied in the field of chemical production,but also often used in the fields of medical production,petroleum refining,biological research,environmental protection and so on.In this paper,the Aspen Plus simulation software was used to optimize and design the extractive distillation process for the separation of benzene-cyclohexane-toluene with N,N-Dimethylformamide(DMF)and N-methyl-2-pyrrolidone(NMP)as solvent,respectively.The phase behavior between DMF,NMP and benzene-cyclohexane-toluene was studied by analyzing the vapor-liquid equilibrium data reported in the literature.The influence of the regressed thermodynamic model parameters and the built-in thermodynamic model parameters on the extractive distillation process is investigated.In this paper,DMF and NMP were selected as solvent to separate benzene-cyclohexane-toluene,and the phase behavior of the solvent and separation system was studied.The results show that the phase behavior of toluene-DMF and cyclohexane-NMP systems described by the Aspen Plus built-in binary interaction parameters were deviated from the experimental data.The vapor-liquid equilibrium data of toluene-DMF,benzene-NMP and cyclohexane-NMP system at 101.3 kPa were measured by a modified Rose vapor recirculating type equilibrium still.The Herington and Van Ness tests are used to verify the thermodynamic consistency of the measured isobaric vapor-liquid equilibrium data and the isothermal vapor liquid equilibrium data reported in the literature,and the experimntal data were correlated by the NRTL,Wilson and UNIQUAC activity coefficient models experimental data,and the regressed thermodynamic model parameters are obtained.Based on the sequential iterative method and the annual total cost(TAC)minimum target,extractive distillation optimization softwares are applied to optimize the extractive distillation processes for separating benzene-cyclohexane-toluene with DMF as solvent and separating benzene-cyclohexane with NMP as solvent,and the influence of the different thermodynamics model parameters on the separation process was compared.The results show that the operating cost and TAC for separating benzene-cyclohexane-toluene with DMF as solvent are 7.58 % and 9.72 % lower than the literature process which was designed using the built-in thermodynamic model parameters;the operating cost and TAC for separating benzene-cyclohexane with NMP as solvent are 31.17 % and 36.82 % lower than the process which was designed using the built-in thermodynamic model parameters.The results show that the regression thermodynamic model parameters can accurately describe the phase behavior of the mixtures,and the importance of the thermodynamic model parameters was further illustrated by the calculation of TAC.The phase behavior and thermodynamic model parameters should receive more attention during the research and development of extractive distillation processes.