Application of cyclic operation to acetic / water separation

Abstract

Abstract Acetic acid is an important bulk chemical, used as raw material in the production of vinyl acetate, terephtalic acid, acetate esters and acetic anhydride. All these processes include a step for separating the acetic acid from water, both high-purity and high-recovery of acetic acid being required. Although acetic acid and water do not form an azeotrope, the separation is difficult due to the tangent pinch present on the pure water end. A common industrial practice to overcome the tangent pinch is to add an entrainer and, therefore, to use heterogeneous azeotropic distillation. This work investigates the applicability of cyclic distillation to this difficult separation. A mathematical model is presented and used for sizing and optimization considering the total annual cost as objective function and the number of trays, feed tray location, and the duration of vapor-flow period as decision variables.