Isotope exchange technique for measurement of gas adsorption equilibria and kinetics

The isotope exchange technique (IET) can be used to simultaneously measure multicomponent gas adsorption equilibria and self‐diffusivities of the components in a single isothermal experiment without disturbing the overall adsorbed phase. An experimental protocol for the IET and corresponding data analysis procedures is described. Isotherms and self‐diffusivities for adsorption of N 2 as a pure gas were measured on commercial samples of a carbon molecular sieve and a 4‐Å zeolite using IET, as well as those of O 2 and N 2 from their binary mixtures. The carbon molecular sieve did not exhibit thermo‐dynamic selectivity for air separation, but had a kinetic selectivity of O 2 over N 2 Mass‐transfer resistances for self‐diffusion of N 2 and O 2 on the carbon molecular sieve were controlled by pore mouth restrictions in the carbon, but those for adsorption of N 2 into the 4‐Å zeolite by Fickian diffusion inside the adsorbent. A linear driving force model described the uptakes of N 2 and O 2 in the carbon molecular sieve. The Fickian diffusion model described the N 2 uptake in the 4‐Å zeolite. Mass‐transfer coefficients for both O 2 and N 2 on the carbon molecular sieve increased linearly with increasing gas‐phase partial pressure of these gases, and the pressure of O 2 did not affect mass‐transfer coefficients for N 2 . The self‐diffusivity of N 2 in the 4‐Å zeolite decreased with increasing adsorbate loading.