Hydrocarbon Diffusion in Mesoporous Carbon Materials: Implications for Unconventional Gas Recovery
Methane diffusion in micro- and mesopores of carbonaceous materials is dominated by molecular interactions with the pore walls. As a consequence, the fluid molecules are mainly in a diffusive regime and the laws of fluid mechanics are not directly applicable. A method called the “free volume theory” has been successfully used by different authors to study the diffusion of n -alkanes into microporous carbons. However, we show in this paper that such a method fails to describe the dynamical properties of methane in porous hosts presenting both micro- and mesopores. We further evidence that this theory is limited to structures whose pore diameters are lower than ∼ 3 nm. We then propose a simple scaling method based on the micro- and mesoporous volume fraction in order to predict diffusion coefficients. This method only requires the knowledge of (i) the host microporous volume fraction and (ii) the self-diffusion coefficient in micropores smaller than 3 nm, which can be obtained using the “free volume theory”, quasi-elastic neutron scattering experiments, or atomistic simulations.
Keywords: Molecular diffusion, Kerogen, Methane, Green−Kubo equation, Molecular dynamics, Electron Tomography
This work is the result of a collaboration between the joint MIT/CNRS laboratory “MultiScale Material Science for Energy and Environment” at the Massachusetts Institute of Technology, the Centre Interdisciplinaire de Nanoscience de Marseille and TOTAL SA as part of the “Flow and Adsorption Science&Tech for Enhanced Recovery in Shale (FASTER Shale)” project.
ACS Applied Nano Materials 2020, 3, 7604-7610