Measurement of Intracrystalline Diffusion in Molecular SieveZeolites by the Tracer-Pulse Method - Renewal

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The measurements of equilibrium and diffusional parameters of gases in microporous solids is very important for the design of many separation and catalytic processes. These properties are measured by use of the pulse chromatography method, which is unique in that it is a macroscopic method that operates under equilibrium conditions. Comparison of the tracer pulse results with previously published NMR diffusion coefficients is used to determine the origin of discrepancies commonly observed between the two techniques. Equilibrium isotherms and diffusion data for the ethane-silicalite system are measured at various temperatures and loadings, allowing investigation of the effect of adsorbed phase concentration on the micropore diffusion coefficient. The effect of co-adsorbed molecules on the diffusional behavior of ethane in ideal and nonideal adsorbed mixtures is investigated by a modification of the original tracer pulse technique. Equilibrium isotherms for each component of the binary mixtures are also measured by the 'concentration-tracer pulse' method. Since industrial applications always involve multicomponent systems, a study if diffusion in mixtures is of great interest. Finally, two variations of perturbation chromatography (tracer and concentration pulse) are used to investigate the validity of the Darken equation at various adsorbed concentrations. The tracer-pulse chromatography apparatus is unique in this respect, since other experimental techniques are not able to measure both the transport and self diffusion coefficients.