Linearization of adsorption isotherms for high-pressure applications

The adsorption data in the range of 77-298 K and 0-7 MPa for supercritical hydrogen were linearized by adopting the coordinates of ln ln (n) vs 1/ln P. Compared to conventional isotherm equations, the proposed model for linear isotherms avoids the use of any fictitious physical quantity and thus does not display such abnormal behaviors as have been observed previously. Use of the linearization strategy includes: 1. Modification of the Dubinin-Astakhov equation for applications under supercritical conditions. The common intersection point of the bundle of linear isotherms defines a special reference state, which modifies the D-A equation but preserves the temperature invariance of the characteristic curve. 2. Identification of the effect of adsorbate volume on adsorption isotherms. A special formulation of the linearized isotherms can be used to quantify this effect. 3. Evaluation of isosteric heats of adsorption. The linearized model excludes the effect of non-ideal conditions, and therefore produces more precise values of isosteric heats of adsorption. (C) 1998 Elsevier Science Ltd. All rights reserved.