An improved chromatographic method to determine the propane diffusivity in CHA/AEI-SAPO zeolite.

Diffusion limitations may quick arise in small pore zeolite. Since each zeolite has its specific pore structure, much effort need to be put in meauring and understanding the mass transport phenomena in these systems. A 3-zone-column chromatographic model that includes the effects of system non-ideal behavior, the pressure drop of the packed bed, the particle size distribution, and nonlinear adsorption equilibrium for the measurement of diffusivities in nanopores was solved numerically in the time domain. A CHA/AEI intergrowth SAPO zeolite was successfully synthesized using hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), physisorption analyzer and Malvern Mastersizer etc. The diffusion behavior of propane in the CHA/AEI-SAPO zeolite was systematically studied to obtain diffusion coefficient. The apparent diffusivity at 100 degrees C is 3.1 ± 0.5 x 10(-16) m2/s and the activation energy is 35 ± 4 kJ/mol. This provides reliable data to obtain anticipated product selectivity by controlling the diffusion rates of specific gases in the nanopores.