Molecular Simulation of Argon Adsorption and Diffusion in a Microporous Carbon with Poroelastic Couplings

Neglected for a long time in molecularsimulations offluid adsorptionand transport in microporous carbons, adsorption-induced deformationsof the matrix have recently been shown to have important effects onboth sorption isotherms and diffusion coefficients. Here we investigatein detail the behavior of a recently proposed 3D-connected maturekerogen model, as a generic model of aromatic microporous carbon withatomic H/C & SIM; 0.5, in both chemical and mechanical equilibriumwith argon at 243 K over an extended pressure range. We show thatunder these conditions the material exhibits some viscoelasticity,and simulations of hundreds of nanoseconds are required to accuratelydetermine the equilibrium volumes and sorption loadings. We also showthat neglecting matrix internal deformations and swelling can leadto underestimations of the loading by up to 19% (swelling only) and28% (swelling and internal deformations). The volume of the matrixis shown to increase up to about 8% at the largest pressure considered(210 MPa), which induces an increase of about 33% of both pore volumeand specific surface area via the creation of additional pores, yetdoes not significantly change the normalized pore size distribution.Volume swelling is also rationalized by using a well-known linearizedmicroporomechanical model. Finally, we show that self-diffusivitydecreases with applied pressure, following an almost perfectly linearevolution with the free volume. Quantitatively, neglecting swellingand internal deformations tends to reduce the computed self-diffusivities.

Automated summary

Neglected for a long time, the adsorption-induced deformations of the matrix in microporous carbons have been shown to have significant effects on sorption isotherms and diffusion coefficients. In this study, a 3D-connected mature kerogen model is used to investigate the behavior of aromatic microporous carbon in both chemical and mechanical equilibrium with argon. It is found that neglecting matrix internal deformations and swelling can lead to underestimations of the sorption loadings and self-diffusivities.