Pressure changes during diffusion with chemical reaction in a porous pellet

Abstract

A method is proposed for evaluation of the pressure change in an isothermal porous pellet within which a single chemical reaction takes place, accompanied by mass transfer by Knudsen diffusion, bulk diffusion and viscous convective flow of the reacting mixture. The dimensionless pressure is expressed as a function of two dimensionless parameters which characterize transport mechanism and mixture properties respectively. The pressure change also depends on the reaction and on the mixture composition on the pellet surface. The method requires numerical integration of an initial-value problem. A simple analytical method is also proposed for estimation of the maximum possible pressure changes in the system, both for the Knudsen diffusion control regime and for the bulk diffusion with viscous convective flow control regime. Both methods are illustrated by the computed results for a general two-molecule reaction and for the ammonia synthesis reaction.