Numerical simulation of unsteady continuous countercurrent adsorption system with nonlinear adsorption isotherm

Abstract

A theoretical dispersed plug flow model that includes a mass-transfer resistance represented by a linear driving force approximation is developed for unsteady-state continuous countercurrent adsorption systems having nonlinear equilibrium isotherms. The model is solved from unsteady state to steady state using Danckwert's boundary conditions. The system consists of two sections having 11 adsorption columns. The model is used to investigate the effects of various process parameters on the performance of the system. It is demonstrated that as the nonlinearity changes, the optimal choice of bed length, feed and eluent flow rates, and switch times must be suitably adapted. The results are compared with the “pore diffusion” and “equilibrium” models of Morbidelli et al.¹⁴ and are found to lie between these two models. To establish the consistency of the model the results are compared with one of the limiting asymptotes, namely, the linear isotherm with the experimental data of Ching and Ruthven^12,13 and are found to agree well.