Modeling and simulation of continuous fixed adsorptive distillation with adsorbent regeneration using thermal desorption

Abstract

Fixed adsorptive distillation (FAD), a hybrid separation method combining distillation and adsorption, was proven to be able to break the azeotropic point and to enhance the product purity of azeotropic solution. FAD consists of two conventional distillation columns, equipped with an inter-bed of adsorbent. To operate a continuous FAD, a pair of adsorbent beds must be utilized in which adsorption operation and adsorbent regeneration are carried out alternately. This work is a parametric study which aims to model and to simulate a continuous FAD with adsorbent regeneration using thermal desorption. The azeotropic solution model used is water-isopropyl alcohol (IPA) with adsorbent of silica. Variable analysis is conducted to derive the equations, to obtain the appropriate design variable/s, and to systematically calculate the state variables. The appropriate design variables are the adsorptive flow (A_df) and the bottom product of Column 2 (B₂); while the recycle variable is the distillate of Column 2 (D₂). The successful continuous FAD is measured based on the composition of IPA in the feed of Column 2 (x_F2) and that in the distillate of Column 2 (x_D2); both must be above the azeotropic point. To ensure the successful continuous FAD with a fresh feed of 100 mol/min. (30 % mole IPA), relatively pure water and IPA in both bottoms, and equal flow split of adsorptive-bypass flow (R_f = 1), the adsorptive flow and the flow rate of bottom product of Column 2 are operated at (25.00–107.00) mol/min. and (29.77–30.29) mol/min., respectively.