Hydrocarbon Diffusion in Mesoporous Carbon Materials: Implications for Unconventional Gas Recovery

Abstract

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 ∼3nm. We then 1 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 3nm, which can be obtained using the "free volume theory", Quasi-Elastic Neutron Scattering experiments, or atomistic simulations.

A Step in Carbon Capture from Wet Gases: Understanding the Effect of Water on CO2 Adsorption and Diffusion in UiO-66

“…In eq , the flow velocity v scales linearly with the pressure gradient −∇ P and depends on the ratio of the pore network permeability k and the molecular viscosity η, two intrinsic parameters related to the porous host and the flowing fluid under given thermodynamic conditions, respectively. However, for pores below 50 nm, Darcy’s law fails due to slippage, friction, surface tension, nonviscous effects, excess density depending on pore size, and, more generally, to the adsorption dominating transport at the small pore scale. − Corrections such as the one proposed by Klinkenberg, accounting for slippage, have been included in Darcy’s equation . However, such an empirical correction does not capture the phenomenon of molecule adsorption at the pore walls, paramount to describe transport behavior.…”

Nanoscale Accessible Porosity as a Key Parameter Depicting the Topological Evolution of Organic Porous Networks

“…Other methods such as lattice Boltzmann method (LBM) or computational fluid dynamics (CFD) cannot be directly used below 50 nm as the adsorption of the fluid on the pore walls is not considered and where parameters that originate from collective interactions as viscosity are meaningless. Atomistic simulations are thus the only way of integrating these effects as discussed in ref . This full-atom approach can then be upscaled using hybrid molecular dynamics and lattice Boltzmann method (LBM). , These approaches would provide more insights into the governing transport regimes of hydrocarbon production from source rock formation.…”

“…Atomistic simulations are thus the only way of integrating these effects as discussed in ref . This full-atom approach can then be upscaled using hybrid molecular dynamics and lattice Boltzmann method (LBM). , These approaches would provide more insights into the governing transport regimes of hydrocarbon production from source rock formation.…”

Development of Atomistic Kerogen Models and Their Applications for Gas Adsorption and Diffusion: A Mini-Review

“…The 4 different systems correspond to different scaling degrees indicating the level of increase of the volume of the mesoporous phase so as to decrease the microporous fraction x ϕ . The orange circle stands for the self-diffusion coefficient evaluated for the bulk microporous kerogen, the empty squares for the ones predicted by the 1 / x ϕ scaling, and the empty stars for the estimate of the collective diffusion coefficients adding the 1/ x φ scaling that quantifies the collective effects on the diffusion properties (Reproduced with permission from ref . Copyright 2020 American Chemical Society).…”

“…The natural inclusion of mesoporosityas opposed to former studies where it is imposed via sacrificial spacers − , or by cutting larger pores within initially microporous modelsis also a challenge that remains to be solved for more realistic and consistent (i.e., in the sense that mesopores would not fall apart when removing the artificial dummy particles) micro-/mesoporous models. Considering the discussions above, as long as their molecular weights stay on the low end, molecular models do not seem to be the most relevant ones here.…”