An integrated model for adsorption-induced strain in microporous solids

Deformation of porous materials during adsorption of gases, driven by physico- or chemo-mechanical couplings, is an experimentally observed phenomenon of importance to adsorption science and engineering. Experiments show that microporous adsorbents exhibit compression and dilation at different stages of the adsorption process. A new integrated model based on the thermodynamics of porous continua (assumed to be linear, isotropic and poroelastic) and statistical thermodynamics is developed to calculate the adsorption-induced strain in a microporous adsorbent. A relationship between the strain induced in the adsorbent and the equilibrium thermodynamic properties of the adsorbed gas is established. Experimental data of CO₂ adsorption-induced strain in microporous activated carbon adsorbents (Yakovlev, V.Y., Fomkin, A.A., Tvardovskii, A.V., Sinitsyn, V.A., 2005. Carbon dioxide adsorption on the microporous ACC carbon adsorbent. Russian Chemical Bulletin, International Edition 54, 1373-1377) is used to fit the model parameters and to validate the model. Assuming that the initial contraction in a microporous adsorbent is caused due to an attractive interaction between the adsorbed gas and the adsorbent, we demonstrate that there also exists a repulsive interaction amongst the adsorbed gas molecules and that this repulsive interaction can be correlated to the adsorption-induced strain. The proposed correlation can be extended to take into account the adsorbate-adsorbent attractive interaction in order to offer an undisputed and complete explanation of the adsorption-induced strain in microporous adsorbents.