Design and control of pressure‐swing distillation for separating ternary systems with three binary minimum azeotropes

Abstract

The separation of ternary nonideal systems with multi‐azeotrope is very important because they are often found in the waste of chemical and pharmaceutical industries, which is much more difficult due to the formation of multi‐azeotrope and distillation boundary. We propose a systematic procedure for design and control of a triple‐column pressure‐swing distillation for separating ternary systems with three binary minimum azeotropes. This procedure involves thermodynamic insights, a two‐step optimization method, and effective control strategy. The separation of tetrahydrofuran (THF)/ethanol/water is used to illustrate the capability of the proposed procedure. It is found that the pressure limits in columns can be determined through the analysis of residue curve maps, distillation boundary, and isovolatility curves. The optimal triple‐column pressure‐swing distillation is generated with the minimum total annual cost (TAC) of $2.181 × 106 in sequence A. The operating conditions are well controlled approaching their desired specifications in an acceptable time when disturbances occur. © 2019 American Institute of Chemical Engineers AIChE J, 65: 1281–1293, 2019

Distributed Control Strategy with Smith's Predictor in a Pilot‐Scale Diabatic Distillation Unit

“…Pressure-swing distillation has stood out in recent years for the good capacity of separating azeotropic systems with energy and environmental advantages [45]. Yang et al [46] proposed an innovative, robust, plant-wide control strategy of feedforward and dual-temperature difference control to reduce deviations and offsets of products purities. Cong and Liu [47] presented a sensitive stage temperature control scheme with adaptive set-point corrections (SC-PID) for the high-purity control of a heat-integrated distillation column, another important advanced configuration.…”

Separation of a ternary mixture with multiple azeotropes via pressure‐swing distillation

“…In the work of Yang et al, two sequences of W L E M T H and W L T H E M were also proposed to separate this mixture with a different flow rate and composition, but have various optimization parameters. In addition, the medium pressure steam is used for the THF column at 10 atm.…”

“…On the basis of these works, Zhang et al also developed various dynamic control structures for the conventional extractive distillation configuration. Yang et al investigated the conceptual design of PSD separation sequences via some extended feasibility rules (i.e. isovolatility lines and volatility order) as well as the robust plant‐wide control.…”

Pressure swing distillation for the separation of methyl acetate‐methanol azeotrope

“…For ternary azeotropes, PSD is more complex. Taking the separation of tetrahydrofuran/ethanol/water as an example, Yang et al proposed a new systematic procedure for a triple‐column PSD, which involved the process simulation, optimization, and control.…”