Comparative analysis of diffusion mechanisms inside porous media for steam methane reforming over Ni-Al2O3 catalyst

Abstract

The catalyst particles are widely used in steam methane reforming. The main mass transport mechanism inside the catalyst particles is diffusion. Several diffusion mechanisms are used by researchers for the investigations, and no consensus has been reached on which one is more suitable. This study aims to find the appropriate diffusion mechanism for the steam methane reforming. The effect of various diffusion mechanisms on the predictive performances of the steam methane reforming process was investigated for Ni-Al${}_2$O${}_3$ catalyst particles. Four diffusion mechanisms were considered: constant diffusion coefficient, Lewis number correlation, kinetic theory, and Bosanquet approximation. The CH${}_4$ conversion, species and temperature distributions were compared for various operating temperatures, residence time, particle diameters, pressure and H${}_2$O/CH${}_4$ ratio ($\beta$). For the similar operating and design parameters, CH${}_4$ conversion obtained for Bosanquet approximation and Lewis number correlation showed close to similar results with average deviation of 2%. Other diffusion models have failed to correctly predict the CH${}_4$ conversion. It was shown that the choice of an appropriate diffusion mechanism is important for the numerical prediction of the steam methane reforming performances.