Design and control of triple-column pressure swing distillation process for acetone-methanol-hexane separation

The mixture of acetone-methanol-hexane is used in the industry as a solvent, an extraction agent and for cleaning purposes. This mixture belongs to the topological class of 3.1-2 in Serafimov's classification with three binary and one ternary minimum boiling homogeneous azeotropes (Shen et al., 2016). To our knowledge, steady-state design studies for this class of azeotropes are very rare, and there is no dynamic control study in the literature. In this study, a triple-column pressure swing distillation (PSD) process is designed for separation of three components with a 99.9 mole % purity. The process is optimized based on total annual cost (TAC), and a plant-wide control structure is designed for the optimal steady-state case. The control structure including inferential temperature controllers shows an effective base-level regulatory control with acceptable offsets in compositions. This work hereby demonstrates that a ternary mixture which forms three binary and one ternary azeotropes can be separated using a triple-column PSD process, and this process system can be controlled robustly using a decentralized control structure.