Significance of pressure gradients in porous materials: Part II. Diffusion and flow in porous catalysts

Diffusion and flow rates through porous catalysts were measured under the conditions of finite pressure gradients for single‐ and two‐component systems. For large pore (low density) alumina pellets the diffusion rate counter to the pressure gradient was severely depressed, while for small pore Vycor the pressure gradient had little effect. The equations developed in Part I for flow and diffusion in a single capillary were extended to porous catalysts. The resulting prediction methods contain no parameters which require transport data for their evaluation, but pore size and void fraction information is needed. For the catalysts investigated, both the permeability and diffusion rates varied several thousand‐fold. The calculated results predict the same extensive range and show the same effects of pressure gradient and pore properties. Also the quantitative agreement between calculated and experimental results is such that the theory provides a useful method of predicting transport rates through certain types of porous media.