New Frequency Response Method for Measuring Adsorption Rates via Pressure Modulation: Application to Oxygen and Nitrogen in a Carbon Molecular Sieve

A new frequency response method based on a sinusoidal modulation of pressure is developed to measure gas adsorption equilibria and kinetics simultaneously. The transfer phenomena of pure N 2 and O 2 gases on carbon molecular sieve are investigated for different pressures and particle sizes by this method. The mass-transfer mechanism for N 2 can be explained by a surface barrier using a linear driving force model, but that for O 2 requires a combination of a surface barrier and micropore diffusion using a combined resistance model. Alternatively, a distribution of surface barrier resistances is introduced to take into account heterogeneity of the surface and describes the experimental data well. The linear driving force mass-transfer coefficients increase with increasing pressure but depend on the particle size only slightly. The effects of pressure on the transfer coefficients for N 2 are less pronounced than those for O 2 . The apparatus is shown to be useful in providing accurate and rapid transfer coefficient measurements and in identifying the rate-controlling adsorption mechanism.