Preparation of ITQ-29 (Al-free zeolite A) membranes

Membranes consisting of Al-free ITQ-29 (a zeolite with the LTA-type structure) have been prepared on alumina tubular supports by seeded liquid phase hydrothermal synthesis. A supramolecular organic structure-directing agent (SDA) was used for the synthesis of ITQ-29 that must be removed from the zeolite pores to activate the membrane for permeation. The high temperature needed to decompose SDA from small-pore zeolites could create thermal stresses that affect the final membrane quality. Because of this, the effect of the atmosphere (N2, O2, air and O3/air) and temperature of the membrane calcination process has been studied. An ITQ-29 membrane activated by means of the combination of pyrolytic (at 723 K) and ozonization (at 473–573 K) treatments gave the best results, with N2/CH4 and N2/propane selectivities well above the corresponding Knudsen values.