Separation Performance and Controllability Improvement for Pressure-Swing Distillation Based on the Relationship between Feed Composition and Distillation Boundaries

Methanol/ethyl acetate/cyclohexane ternary azeotropes are separated by pressure-swing distillation (PSD) in this paper. Through analyzing the phase diagram, three processes with different separation sequences are proposed. The TAC and the gas emission are used as objective functions to optimize the processes via multiobjective optimization. The results show that PSD with a high-medium-low sequence performs better than the other two processes. The relationship between the separation performance and the normal distance, which is calculated through the feed composition and the distillation boundaries, is studied. The normal distance is verified as an efficient indicator to estimate the process performance without complex calculation of evaluation factors. Different control structures are explored to investigate the dynamic responses of the PSD process. It is found that controllability can be improved by making the feed composition locate in the suitable distillation region, but the economy needs to be sacrificed to some extent. Besides, the model prediction control is studied and applied to realize further enhancement of the control performance.