Abstract:

 The aim of this paper is to study how to treat the experimental adsorption isotherms by the conventional Type－I isotherm theories in order to acquire the required information of the adsorption system under supercritical conditions. The study was carried out on manipulation of a set of adsorption data of supercritical hydrogen on activated carbon AX－21 over a temperature range of 77－298K. The results show that the Langmuir equation can well model the experimental data, but cannot provide any reliable information about the adsorption system considered; the Virial equation cannot model the whole set of data satisfactorily, but it can give Henry's law constants reliably， from which isosteric heat of adsorption can then be precisely determined. Some inspection of the adsorption mechanism was made on fitting data to Dubinin-Astakhov equation. Although this equation can best model the experimental data, the reality of any physical quantity evaluated from it might be doubtful since the parameters in the model interact each other during regression and some quantities in the equation are ill－defined under supercritical condition.

Key words: Hydrogen adsorption, Isotherm modeling, Langmuir equation, Virial equation, Dubinin-Astakhov equation