Non-isothermal sorption kinetics and NMR diffusion studies

Due to heat effects on ad- and desorption the non-isothermicity of the sorption process has to be taken into account for the evaluation of diffusion coefficients. A mathematical treatment derived recently has been successfully tested. In the case of mesoporous solids and strongly adsorbable molecules, the concept of a two channel mechanism of mass transport in the pore volume and along pore surfaces is appropriate. The question is open to what extent the transport processes are affected by the rate of molecular exchange between the two regions. Self-diffusion coefficients in mesoporous solids, as obtained from non-isothermal kinetics and NMR measurements are in the same order of magnitude. The concentration dependence of the various diffusion coefficients is discussed. 23 refs.; 6 figs