A new adsorption model for analyzing gas-solid equilibria in porous materials

Equilibria involving three probe gases adsorbed on two porous carbonaceous supports are measured at various temperatures. A novel analysis of the data is offered which uses multiple process equilibria to calculate adsorption equilibrium constants for the interaction of the gas with the solid. Equilibria involving three distinct processes are found. The equilibrium constants (K-1,K-ads, K-2,K-ads, and K-3,K-ads) are obtained as well as the capacity of the solid for each type of process (n(1), n(2), and n(3)), in millimoles of adsorptive per gram of solid. The first process, K-1,K-ads, involves adsorption of the gas in the solid's micropores which are of molecular dimensions. The second process, K-2,K-ads, involves adsorption in the larger micropores. The third process, K-3,K-ads, involves adsorption by the remaining surface. Multilayer formation is likely involved in some processes. The temperature dependencies of the K-ads's produce the enthalpy of adsorption for these processes. This analysis is important for, in contrast to BET analyses, it provides thermodynamic data for different adsorptives that can be interpreted in terms of those molecular properties that facilitate probe-solid interactions and can provide a quantitative definition of solid reactivity.