Intrapellet diffusivities from TAP pulse responses via moment-based analysis

Moment-based anal. was applied to det. successfully inter- and intrapellet diffusion coeffs. from exptl. TAP (temporal anal. of products) outlet pulse responses over a one-zone bed with porous particles. Different temps., gas molar masses, and pellet sieve fractions were used to validate the Knudsen diffusion relation for inert gases inside porous catalyst pellets. The zeroth to third moments of the outlet pulse response were anal. derived for rectangular, cylindrical and spherical pellets. The third moment provides a significantly more accurate access to the intrapellet diffusivity than the second moment does. The exptl. window of the TAP reactor is explored for porous silica as catalyst support bed filling. The relevance of concn. gradients inside the pellet is illustrated with model simulations.