Isopropanol dehydration by batch extractive distillation under variable pressure

• A batch extractive distillation process is simulated and optimised. • Different pressure policies, including progressively reduced pressure are compared. • Dehydration of isopropanol with DMSO is optimised. • The profit of one batch is maximized under constraints with the Box-complex method. • The CO 2 emissions of the different policies are also compared. The recovery of isopropanol (IPA) in high purity in an industrial column from nearly azeotropic IPA(A)-water(B) mixture by batch extractive distillation is studied by dynamic simulation and optimization. The solvent DMSO (S) is much heavier than A and B. When the temperature of the heating steam is limited, the high boiling point of S (T BP,S ) may require the application of a lower pressure (e.g. vacuum) than that of A/B separation. Three different pressure policies are studied and compared: operation at atmospheric pressure, in vacuum and at progressively reduced pressure. The profit of one batch is maximized with the Box-complex method. The optimization parameters are the feed plate of S, purity and flow rate of S, reflux ratios and stopping criteria of several steps. The volume of the liquid in the reboiler and the purity of the IPA and that of wastewater sent to biological purification mean constraints for the optimization. The CO 2 emissions of the different policies are also compared. The profit obtained in vacuum was higher by 1.03 % than at progressively reduced pressure and by 6 % than at atmospheric pressure. However, the CO 2 emission was the lowest when the pressure was progressively reduced.