A generalization of the Dubinin-Radushkevich equation for the filling of heterogeneous micropore systems in strongly activated carbons

A generalization of the Dubinin-Radushkevich equation, recently proposed by Stoeckli as an alternative to the Dubinin-Astakhov equation, is discussed theoretically and is tested with new experimental data. The extended equation applies to the filling of heterogeneous micropore systems in strongly activated carbons. It is based on the assumption that the original DR equation only applies to relatively homogeneous systems of micropores, if adsorption is considered over a large range of temperature and pressure. This is suggested by adsorption experiments on carbons with marked molecular-sieve properties. Heterogeneity is dealt with by introducing weighted contributions from the various systems, all following the DR equation, but with different structural parameters. A Gaussian distribution of the micropore volumes with respect to constant B leads to a satisfactory general isotherm, with an extended range of applicability. This isotherm is also compared with the generalization of Dubinin and Astakhov.