Isotherm Equation for Water Vapor Adsorption onto Activated Carbon

Abstract

A simple isotherm model has been developed for the type-5 equilibrium adsorption systems by considering the effects of both primary and secondary adsorptive sites. The model was applied to interpret experimental data describing water vapor adsorption capacities of four activated carbon adsorbents for relative vapor pressures from 0.0 to 0.95 and temperatures between 288 and 308 K. Good agreement was observed between the model and experimental results. The isotherm parameters were found to either correlate well to the Brunauer, Emmett, and Teller specific surface area or have limited effect on describing the adsorption onto adsorbents made from the same precursor but activated with different degrees of burnout. The limiting pore volumes of the adsorbents obtained from the model based on water vapor adsorption compared favorably with those measured using volatile organic compounds.