Screening zeolites for gas separation applications involving methane, nitrogen, and carbon dioxide

Abstract

An experimental evaluation of the kinetics and equilibrium capacities of pure fluids as a fast and effective means to screen an adsorbent's gas separation potential is described. Equilibrium adsorption capacities for pure N 2, CH 4, and CO 2 have been determined using a Micromeritics ASAP2020 sorption analyzer, for three commercially available zeolites: natural chabazite, H + mordenite, and Linde 4A molecular sieve over the temperature range from (248 to 302) K and pressure range from (0.001 to 120) kPa. Toth models were regressed to the equilibrium data for each gas and used to generate inferred equilibrium selectivity maps over a wider range of temperature and pressure for the purpose of targeting any future mixture measurements. For each gas, the rate of adsorption at 100 kPa was measured as a function of temperature and used with a linear driving force model to calculate mass transfer coefficients. In most cases the ratio of the mass transfer coefficients for each pair of gases was close to unity and did not give rise to a significant kinetic selectivity. However the Linde 4A molecular sieve at 273 K and 100 kPa had a kinetic selectivity for CO 2 over CH 4 of 6.2. This approach to screening adsorbents with pure fluids can assist in optimizing the design of subsequent mixture measurements by identifying the most promising temperature and pressure ranges to target. © 2011 American Chemical Society.