Adsorption characteristics of synthesized mordenite membranes

Nitrogen adsorption at 77 K was measured for a self-supporting mordenite membrane synthesized on, and detached from, a polytetrafluoroethylene (PTFE) substrate, and for a simultaneously formed powder. The adsorption by the membrane saturated at an amount which was about half that found for adsorption by the powder. To examine this difference in adsorption characteristics, both of powder and membrane were measured for adsorption for water, methanol, n-hexane and tert-butyl alcohol. For methanol, n-hexane and tert-butyl alcohol, the powder and membrane both showed the same adsorption behavior as for nitrogen. When water molecules were adsorbed, however, there was no difference in saturated adsorption amount between powder and membrane, suggesting the presence of ''deformed pores'' in the rectangular crystal layer of the mordenite membrane. The deformed pores are assumed to occur as gaps among crystallites which displaced along the ab planes of the rectangular crystals, forming the rectangular crystal layer. The channel bonding sites resulting from such displacement were found to serve as pore walls against adsorbable molecules which have a cross-sectional area greater than that of the water molecule, and so to hinder their entrance into the deformed pores. X-ray diffraction analysis revealed that the rectangular crystals have no periodic, continuous structure along the c-axis; they show a slight distortion of the crystallite shift from the plane perpendicular to the c-axis.