Synthesis and CO2/N2 gas permeation characteristics of ZSM-5 zeolite membranes

ZSM-5 zeolite membranes for CO2 separation have been synthesized via hydrothermal-treating various porous α-alumina tubes in template reaction mixtures. The effect of each support acted as an Al source in high pH solution during hydrothermal treatment, and of the SiO2 molar ratio in reaction mixtures on the formation of ZSM-5 crystalline layers was investigated. The synthesized membranes were also surface-modified by dip-coating with polymeric silica sol which filled up the intercrystalline voids in order to improve the CO2 separation efficiency. The ZSM-5 zeolite membranes have been evaluated by the CO2/N2 separation factor and permeance measured as a function of the stage cut, the helium sweeping rate, the feed pressure, and the permeation temperature. The maximum separation factor of the ZSM-5 zeolite membrane for a CO2/N2 (50% CO2) gas mixture was about 54.3 at 25 °C and 14.9 at 100 °C, respectively, and its permeance was 3.6 × 10−8 mol/m2 s Pa. In particular, it was found that the separation factor of the ZSM-5 zeolite membranes were nearly independent of the moisture in the feed.