The measurement of gas diffusivity in porous materials by temporal analysis of products (TAP)

The pulsing of argon in a temporal analysis of products (TAP) reactor and reactor modeling of the response curves were used to measure the effective intraparticle diffusivities in porous materials. The diffusivity that can be measured is limited: (1) at the low end by intraparticle diffusion being too slow such that just a small fraction of the pulse gets into the pores to give an indistinguishable tail, which only measures that the diffusivity is smaller than an upper limit and (2) at the high end by intraparticle diffusion being too fast such that it gives a constant concentration in the pores, which only measures that the diffusivity is larger than a lower limit. The limits and range are slightly different for different particle and bed dimensions. A 9 mm long packed bed has a sensitive range of about 300-fold where there are discernible changes in the normalized pulse shape due to diffusivity changes. If small particles of about 50 μm are used, the range is from 1 × 10−10 to 3 × 10−8 m2/s, and if large particles of about 500 μm are used, the range is from 2 × 10−9 to 5 × 10−7 m2/s.