Sorption and Mobility of CO2 and H2O in Zeolite Y

CO₂ selectivities of >5000 over N₂, CH₄ and CO were measured for supported zeolite Y (ZY) membranes, which makes them attractive for energy-efficient CO₂ capture applications. The CO₂ selectivity of ZY membranes is ascribed to a very favorable combination of mobility and sorption of CO₂ molecules w.r.t. other molecules. However the selectivity and permeance of CO₂ depends strongly on conditions. For instance H₂O exhibits a similar if not greater sorption affinity and, consequently, can severely affect CO₂ transport properties. The removal of H₂O prior to CO₂ capture is undesirable since it diminishes the energy efficiency of the process. So membrane materials and operating conditions that favor CO₂ over H₂O transport must be identified via complete and accurate transport descriptions before the technology can be fully developed. In the work presented, high-pressure thermo gravimetric analysis (HP-TGA), spectroscopic ellipsometry (SE) and transport measurements were used to determine the sorption affinities and molecular mobilities of CO₂ and H₂O in Zeolite NaY. Both HP-TGA and SE were used to obtain sorption isotherms in stationary mode, and mobilities from transient measurements. HP-TGA was performed on bulk samples. It provides accurate sorption data but transient measurements are affected by sorption heating effects. The reverse is the case for SE which makes that both methods are complimentary. Based on the results, a prognosis is given for the viability of ZY-based membranes for CO₂ capture.