Nonisothermal adsorption of water by synthetic NaX zeolite pellets

Abstract

Experimental measurements and theoretical analysis of the uptake and surface temperature are presented for adsorption of water by synthetic NaX zeolite pellets of different sizes. It is shown that, under the present experimental conditions, the heat dissipation effect plays a dominant role in the adsorption kinetics, after a short initial stage which is controlled essentially by both the macropore diffusion and the micropore diffusion. An excellent agreement is obtained between the experimental data and theoretical results given by a nonisothermal model for a bidisperse structure, both for the uptake and for the surface temperature curves. The values of diffusivities determined by the curve-fitting method over an initial stage are of the order of D p ∼ 3 × 10 −5 m 2/s for the macropore diffusion and D ie / R i 2 ∼ 0.003 s −1 for the micropore diffusion, and these values exhibit an independence of the pellet size for all the tested pellets. Furthermore, it is demonstrated that the use of an effective model for the monodisperse structure may also give a good agreement, but the values of diffusivities determined by the best fit are not very meaningful because of their dependence on the pellet size.