A non-equilibrium thermodynamics model for combined adsorption and diffusion processes in micro- and nanopores

摘要

A non-equilibrium thermodynamics model able to analyze the combined effect ofdiffusion and adsorption in porous materials is proposed. The model considersthe coupled dynamics of the diffusive phase, described by a diffusion typeequation, and the adsorbed phase governed by a generalized Langmuir equation.It is shown that the combination of diffusion and adsorption can be treated asdiffusion in an effective medium, with an effective diffusion coefficientdepending on the characteristics of the adsorption kinetics. The interplaybetween these effects leads to the appearance of different regimes in which theeffective diffusion coefficient exhibits peculiar behaviours such as a decreasedue to the presence of the adsorption process and a non-monotonous behaviorresulting from particle interactions. We outline applications of the modeldeveloped to diffusion in porous materials such as zeolites and bentonites, andto engineered highly porous materials.