Linear driving force approximation for isothermal non-isobaric diffusion/convection with binary Langmuir adsorption

Abstract

This paper presents several reduced models for the intraparticle diffusion/convection mechanisms in spherical homoporous particles under isothermal conditions. These semi-empirical linear driving force approximations were developed for the cyclic steady state that is attained when a cyclic concentration and/or total pressure perturbation is imposed at the particle surface. The models are applicable to linear systems or those obeying bicomponent Langmuir isotherms. The linear driving force approximations have two or three parameters for each component and are presented for the following cases: Knudsen diffusion, molecular diffusion, molecular plus Knudsen diffusion in series, viscous flow, and also for both diffusion mechanisms in series, in parallel with the convective flow, as in the dusty gas model. Comparison between the results obtained with these approximations and with the complete models shows that on average the relative quadratic error is ≈10% for non-smooth and 5% for smoother perturbations.