QSPR Models Of Azeotropic Characteristics And The Special Distillation Separation Strategy For Binary Azeotropes Containing Lower Alcohols

In this paper,the study of pressure-swing distillation was carried out from three different aspects,including thermodynamics analysis,process design and intensification,and dynamic control.Quantitative structure-property relationship(QSPR)was proposed to study the relationship between molecular structure of azeotrope component and the azeotropic characteristics,thermodynamic property,optimal operation parameters and optimal dynamic control structure of pressure-swing distillation.The descriptors of 80 binary azeotropes containing lower alcohols were calculated,and 336 structure parameters such as composition descriptors,topological descriptors,and space descriptors were obtained.7 closely related molecule descriptors were selected using genetic algorithm to establish azeotropic temperature and composition models for binary azeotropes containing lower alcohols.The reliability of the models was tested with internal validation and external validation.Determination coefficient(R~2)and cross validation correlation coefficient(R~2CV)of optimal azeotropic temperature model were both above 0.9,R~2 and R~2 CV of optimal azeotropic composition model were 0.87 and 0.82,respectively.The validation results show that the models established have high stability and predictive ability.Vapor-liquid equilibrium data of isobutanol and n-heptane were obtained with built-in database of Aspen Plus software.1,2-propanediol,dimethyl sulfoxide(DMSO),and n-methyl pyrrolidone(NMP)were selected as alternative entrainers for extractive distillation process separating isobutanol and n-heptane through qualitative judgment.NMP was selected as optimal entrainer by comparing the influence of different entrainers on the relative volatility of isobutanol and n-heptane and analysing the residue curve map of isobutanol/ n-heptane/NMP ternary system.The smallest ratio of solvent flow rate/feed flow rate(S/F)was confirmed as 0.95 through sensitivity analysis.The extractive distillation process was optimized with optimization tool of Visual Basic based on sequential iterative method taking the minimal total annual cost(TAC)as objective function.The optimal operating parameters were obtained and minimal TAC was 1.086?10 $/y.Based on the optimal TAC process,the control structures with composition and temperature controller were explored using Aspen Plus Dynamics software.By comparing the control performance of control structure with different S/F ratios(1.0-1.3),we found that the control performance can be improved through increasing the S/F ratio at the expense of increasing TAC.