Mass transfer coefficient in cyclic adsorption and desorption.

Abstract

Intraparticle distribution of adsorbate amount in cyclic adsorption and desorption is simulated by two methods: rigorous numerical solution of the particle-phase diffusion equation and the linear driving force (LDF) approximation. It becomes clear that the conventional value of 15 Ds/R2 as the intraparticle mass transfer coefficient, ksav, in the LDF method is not advisable for the simulation of transient adsorption and desorption. A mass transfer coefficient defined by including the cycle time is thus proposed. In this new conception, ksav increases with decreasing cycle time and approaches π2Ds/R2 with increasing cycle time. Simulations of cyclic mode by the LDF method using this new ksav agree well in the steady state with that obtained by numerical solution of the diffusion equation. In unsteady-state operation, however, the two simulations do not coincide with each other because of overestimation of driving force for adsorption and underestimation for desorption in the LDF method.