Determination of effective diffusivities in commercial single pellets: Effect of water loading

Single industrial adsorbent pellets of zeolites 5A and 13X were mounted with a polymer capable of withstanding high temperatures. Adsorbents were characterized by mercury-porosimetry and low-temperature N-2 adsorption. Isobars of water on these adsorbents at 5 torr were measured using a gravimetric method. Micropores in the pellets were blocked with water loading. Different water loadings in the mounted single pellets were achieved by flowing water-saturated helium through the diffusion cell at different temperatures. Transport through single pellets was studied by measuring steady-state and transient responses in a Wicke-Kallenbach type system. Shift in transient responses was observed as a result of the water loading. Effective diffusivities were calculated from steady-state measurements. A "macropore, micropore, and macropore-micropore-in-series" model was used to estimate the relative contributions from each mode. Effective diffusivities were not affected by water loading in 5A pellets but were affected by water loading in 13X pellets due to increased contribution from the micropores.