Robust Control of Partially Heat-Integrated Pressure-Swing Distillation for Separating Binary Maximum-Boiling Azeotropes

Previous studies of partially heat-integrated pressure-swing distillation (PHI-PSD) for separating the binary maximum-boiling azeotropes methanol/trimethoxysilane and ethylenediamine/water have demonstrated difficulties in dynamic control due to the complexity of these processes. In this paper, efforts are made to find new robust control structures to improve the dynamic controllability of these processes in three different types of PHI-PSD sequences. First, for the high-pressure column (HPC) -> low-pressure column (LPC) sequence of PHI-PSD for separating the methanol/trimethoxysilane azeotrope, five new control structures are established and three of them are robust. Second, the dynamic controllability of the LPC -> HPC sequence of PHI-PSD for separating the methanol/trimethoxysilane azeotrope is investigated for the first time and four robust control structures are proposed. Finally, two new robust control structures are proposed for PHI-PSD for separating the ethylenediamine/water azeotrope. The crucial elements in establishing robust control of these processes are that the reboiler duty of the HPC should be manipulated to control the sump level of the HPC and the bottom flow rate of the HPC should be flow controlled. The feedforward control of the ratio of the recycling flow rate or the connecting bottom flow rate to the feed flow rate leads to worse results. In addition, the best control structure of the HPC -> LPC sequence of PHI-PSD for separating the methanol/trimethoxysilane mixture and the best control structure of PHI-PSD for separating the ethylenediamine/water mixture are compared with the robust control structures of the previous studies. All the robust control structures are valuable in practice for the control of PHI-PSD for separating maximum-boiling azeotropes.