Changes in Gas Permeability and Permselectivity of Natural Zeolite Disk by Heat Treatment

The changes in the gas permeability and permselectivity of natural zeolite disk by heat treatment were examined. The natural zeolite disks were fired for several hours at temperatures of 673 to 1273 K. The gas permeability and separation factor of the disks were measured by the gas permeation experiments with nitrogen-hydrogen gaseous mixture. The pore size distributions of the disks were evaluated by mercury porosimetry. The gas permeation experiments showed that gas permeability and separation factor simultaneously improved under a proper heat treatment condition. However, the measured mean pore diameters of the heat-treated samples was found to increase as the heat treatment temperature was increased. Such phenomenon could not be interpreted with considering conventional gas molecule transport mechanism through straight pores. Based on the observations, a qualitative model for pore structure change by neck growth due to sintering was proposed to account for the simultaneous improvement of the gas permeability and separation factor.