Size-Dependent Adsorption Models in Microporous Materials. 1. Thermodynamic Consistency and Theoretical Analysis

Size-Dependent Adsorption Models in Microporous Materials. 2. Comparison with Experimental Data

“…A detailed analysis of the applicability of the Keller model to adsorption equilibrium data on molecular sieves was performed by Staudt et al (1993a), Staudt (1994), and Giustiniani et al (1995). Figures 1 and 2 show two examples of the agreement between the Keller model and experimental adsorption data for singlecomponent mixtures.…”

“…It should again be stressed that the slope of log a vs 1/T, according to the Keller model, is equal to EiaJR and not to Ei/R. This observation is particularly important since it represents an aspect peculiar to the Keller model deriving from the constraints of thermodynamic consistency (see also Giona and Giustiniani (1995)). Therefore, the effective adsorption energy evaluated from the analysis of the plot c¿ vs 1/RT is greater than the slope of this curve by a factor equal to l/o¿.…”

“…The analysis of the temperature dependences provides a clearer understanding of the role and the physical meaning of the parameters appearing in the model. In particular, as discussed by Giona and Giustiniani (1995), the temperature behavior of the exponents a¿ helps us to interpret the physical origin of the Freundlich exponents.…”

“…Our previous article in this issue (Giona and Giustiniani, 1995) provides a detailed analysis of the thermodynamic and statistical mechanical derivation of Keller adsorption isotherms (AIs) (Keller, 1988(Keller, , 1990). As previously discussed (Giustiniani et al, 1995; Giona and Giustiniani, 1995), Keller AIs are particularly interesting from the theoretical and practical points of view since they enable us to separate the effects of geometric roughness, expressed by means of some intrinsic parameter characterizing the adsorbent (such as fractal dimension), from the role of energetic heterogeneity.…”

“…An important point on which analysis of the experimental data may furnish conclusive results is the temperature behavior of the parameters n«,(D, a¿(T), and a(D appearing in eq 1 (Giustiniani et al, 1995; Giona and Giustiniani, 1995). The temperature dependence of a¿ is particularly interesting with regard to the physical origin of non-Henry (Freundlich) behavior at low pressures and the possible appearance of a phase transition in the adsorbed phase.…”