(443g) Control of a Pressure-Swing Distillation System for Methanol-Chloroform Separation

If the composition of a binary homogeneous azeotrope changes significantly with pressure, a process called pressure-swing distillation could be used to separate these chemical components. Thus, the large shift in the composition from 63.32 mol % chloroform at 1 atm (327 K) to 40.83 mol % chloroform at 10 atm (404 K) makes the pressure-swing distillation process feasible for a methanol-chloroform binary system. In addition, a large difference between the reflux drum temperature in the high-pressure column and the reboiler temperature in the low-pressure column makes the heat integration attractive for pressure-swing systems. In a fully heat-integrated system, the condenser duty of the high-pressure column is equal the reboiler duty of the low-pressure column. Thus, the only energy input is the reboiler duty in the high-pressure column. However, a full heat-integration results in a loss of one control degree of freedom, since the heat input to the reboiler of the low-pressure column cannot be independently set. The aim of this study is a dynamic comparison between pressure-swing distillation columns with and without heat integration for a methanol-chloroform binary system. Several control structures including a pressure-compensated temperature control structure are presented for these systems. The effectiveness of these control structures are tested against feed flow rate and composition disturbances.