Adsorption rate constants from chromatography

A new method for determining adsorption equilibrium constants, rate constants, and intraparticle diffusivities is described and applied for the adsorption of ethane, propane, and n-butane on silica gel. The method rests upon recently developed theory for relating the moments of the effluent concentration wave from a bed of adsorbent particles to the rate constants associated with the various steps in the overall adsorption process. It is necessary to operate at concentrations of adsorbable gas such that the adsorption isotherm is linear. However, it is possible to take into account effects of longitudinal dispersion and diffusion to the particle surface as well as the intraparticle processes of diffusion and adsorption on the pore surface. The method gave reasonable values for intraparticle diffusivities and adsorption rate constants. Intraparticle diffusion was a major resistance for all particle sizes studied and for the largest size (R = 0.50 mm.) this step controlled the overall rate. From the constants determined chromatographically it is possible to predict breakthrough curves for the adsorption of these hydrocarbons on silica gel. The predicted curves agree well with experimentally established breakthrough curves.