Energy-saving dividing-wall column design and control for benzene extraction distillation via mixed entrainer

Benzene and cyclohexane form an azeotrope (Benzene, 49.7 w.t%, 1 atm), which can be separated by extractive distillation. In this study, o-xylene is added into the sulfolane entrainer for mixed entrainer to make the operation conditions more convenient and controllable. The TAC (total annual cost, generally utilized in global economic optimization) of the process with o-xylene as mixed entrainer is less than that of the process with SULF as entrainer. In addition, as the most energy saving process, the process of extractive dividing wall column (EDWC) is proposed, for it can save 44.0% of energy and 35.8% of TAC, compared with the conventional extractive distillation arrangement with pure entrainer. Besides, two control structures are established for EDWC, and their dynamic performances are evaluated by feed flow rate disturbances and feed composition disturbances. Finally, it is found that the disturbances are well handled with the second control structure.