Effective diffusion coefficients and tortuosity factors for commercial catalysts

The effective diffusion coefficients of 13 commercial catalysts and supports were measured under nonreacting conditions by a dynamic tracer-response method using a single pellet string reactor (SPSR). Helium, nitrogen, and n-butane were used as tracers. Axial dispersion in SPSR was measured independently by using identical nonporous glass particles and was found to be low. It was observed that the possibility of convective flow through the catalyst pores was small. An analysis of the diffusion results using simple pore models showed that the most reasonable values of tortuosity factors were obtained for a cylindrical pore model. The diffusivities predicted by a random pore model were nearly twice the measured values in many cases. The tortuosity factor was found to vary strongly with the particle porosity.