EVALUATION OF DIFFUSION-COEFFICIENTS FOR INTRACRYSTALLINE TRANSPORT SUPERIMPOSED BY 1ST-ORDER PHENOMENA IN MOLECULAR-SIEVE CRYSTALS

First-order phenomena that may take place in molecular sieve structure s besides intracrystalline diffusion shift the effective diffusivity. This shift depends on the ratio of rates of mobilizing and immobilizin g the sorbate in the microporous structure. The corresponding uptake c urves obtain an unusual but characteristic shape. The phenomenon is ex emplified by the system p-xylene/microporous gallosilicate of MFI-type . For the quantification of the kinetic parameters [intracrystalline d iffusivities, (im)-mobilization rates], the Volterra integral equation technique is used.