A thermodynamic model for gas adsorption isotherms

In this paper based on the principle of solution thermodynamics for gas-sol id equilibrium, a relation is developed to express gas adsorption isotherms . An activity coefficient model based on weight fraction of sorbate in the solid phase has been derived that well describes the behavior of various ga ses on different types of adsorbents. The proposed model has been evaluated and compared with four other models commonly used for gas adsorption isoth erms in the literature. For 12 different systems at various isotherms for t he temperature range -128 to 100 degrees C and the pressure range 0.02 to 1 219 kPa for 689 data points, the proposed model predicts equilibrium pressu re with an average deviation of 5.3%, which is about half of the error obta ined from other methods. The proposed model clearly outperforms other avail able methods such as the vacancy solution theory, the ideal adsorption solu tion model, and other various modified forms of the Langmuir isotherm. Uniq ue features of the proposed model are its simplicity, generality, and accur acy over the entire pressure and temperature ranges. (C) 1999 Academic Pres s.