A PRACTICAL ISOTHERM EQUATION FOR ADSORPTION ON A HETEROGENEOUS SURFACE AND ITS APPLICATIONS TO SINGLE AND MIXED GAS-ADSORPTION ON AN ACTIVATED CARBON-FIBER

A practical isotherm equation based on the scaled-particle theory and a patchwise model has been developed for single- and multi-component adsorption on a heterogeneous surface. The surface energy distribution function used in the model is the asymmetric Gaussian function; however, the continuous distribution is formally changed to four discrete patches, called the four-point approximation model, by means of the Hermite-Gauss quadrature formula in the numerical integration. The model is applied to single-gas adsorption on an activated carbon fiber, KF-1500, at elevated pressures and three temperatures with satisfactory agreement. Four binary gas adsorption data on KF-1500 at 298.15 K and 500 kPa have been obtained and analyzed by the model. The geometric mean assumption for the binary interaction parameters between adsorbed molecules is adequate for binary mixtures of methane + ethane and methane + ethylene, while an adjustable parameter for the binary interactions, k(ij), is required for binary mixtures of carbon dioxide + ethane and carbon dioxide + ethylene.