Estimation of surface diffusion through porous media

✍ Scribed by S. Sircar; M. B. Rao

• Publisher: American Institute of Chemical Engineers
• Year: 1990
• Tongue: English
• Weight: 586 KB
• Volume: 36
• Category: Article
• ISSN: 0001-1541
• DOI: 10.1002/aic.690360814

✦ Synopsis

Abstract

A mathematical model is developed to describe steady‐state nonequilibrium surface diffusion of an adsorbing gas through an energetically homogeneous porous medium by assuming that the adsorption isotherm is linear and that the gas‐surface mass transfer can be described by the linear driving force model. Analytical solutions for the model are reported. It is found that the conventional assumption of local thermodynamic equilibrium between the gas and surface phases within the porous medium can seriously underestimate the surface diffusivity when the mass transfer rate is finite. Also, the length of the porous medium becomes a critical variable in that case.

Meaningful estimation of surface diffusivity also requires that the gas phase diffusivity through the porous medium be accurately known. The estimated surface diffusivity is model dependent when local thermodynamic equilibrium is not established instantaneously. Modeling surface diffusion can be very complex when the surface is energetically heterogeneous.