Predictive equations in gas adsorption kinetics

The experimental method of determining the operative parameters of adsorptive capacity and rate in the gas adsorption kinetics of packed bed sorbents relies upon the linear relationship between gas breakthrough time and sorbent weight. The slope and intercept of the straight line, resulting from such a plot, yields values for the gas saturation capacity and adsorption rate constant of the adsorbent. This relationship is shown in the modified Wheeler adsorption equation, originally derived from a continuity equation of mass balance between the gas entering an adsorbent bed and the sum of the gas adsorbed by plus that penetrating through the bed. We have found that for wellpacked adsorbent beds, the Dubinin-Polanyi equations for predicting adsorption space at equilibrium, based upon prior characterization of an adsorbent with a reference gas, could also be applied to gas flow conditions, and the kinetic capacity of the adsorbent predicted within close limits. Although no theoretical relationship exists for prediction of the adsorption rate constant, recent gas tests at high linear flow velocities have shown experimental evidence of the mass transfer limiting value for the rate constant. The functionalities of the kinetic saturation capacity and the mass transfer limited value for the adsorption rate constant have been incorporated into the modified Wheeler adsorption equation to provide an expanded equation permitting prediction by calculation of the breakthrough time of a gas through a well-packed bed of adsorbent granules.