Methane transport through hierarchical silica micro-mesoporous materials: From non-equilibrium atomistic simulations to phenomenological correlations

Abstract

Methane transport through hierarchical silica micromesoporous materials: From non-equilibrium atomistic simulations to phenomenological correlations,

Probing Pore Size and Connectivity in Porous Silicas Using 13C MAS NMR Spectroscopy of Supercritical Methane

“…The smaller pore size reaches an EXSY intensity plateau at a slower rate (5.88 vs 12.1 s –1 ) and plateaus at a higher fraction of the total CH 4 population (0.73 ± 0.01 for 25 Å vs 0.35 ± 0.01 for 100 Å). This is consistent with molecular modeling data that shows CH 4 transport scales as a power function with porosity in porous silicas . A majority of the EXSY-derived exchange rates are values associated with CH 4 in the slow-exchange regime where we would expect to observe separate resonances for pore versus bulk CH 4 in the 1D 13 C NMR spectra, in agreement with those data.…”

“…This is consistent with molecular modeling data that shows CH 4 transport scales as a power function with porosity in porous silicas. 30 A majority of the EXSY-derived exchange rates are values associated with CH 4 in the slow-exchange regime where we would expect to observe separate resonances for pore versus bulk CH 4 in the 1D 13 C NMR spectra, in agreement with those data. The plateau values also suggest that the nanopore CH 4 peak should be of greater relative intensity with respect to the bulk CH 4 peak for the 25 Å porous silica compared to the 100 Å silica sample, also in full agreement with the 1D 13 C data.…”

Quantifying Pore Width Effects on Diffusivity via a Novel 3D Stochastic Approach with Input from Atomistic Molecular Dynamics Simulations

“…Although atomistic simulations can provide an accurate understanding of the transport mechanisms in confinement, upscaling to larger time and length scales requires significant, sometimes prohibitive computational effort. As a result, the systems investigated are frequently composed of a single pore, and a limited number of pore sizes/chemistries are explicitly considered. , To bridge the gap from atomistic simulations in single narrow pores to large scale systems, transport models that correlate diffusivity and/or permeability to pore characteristics have been developed. Typically, these models account for three diffusion mechanisms: Fickian, Knudsen, and surface diffusion. − The contribution of each mechanism to the overall fluid transport is described by coefficients, derived either from experimental or computational data.…”

Evidence of Facilitated Transport in Crowded Nanopores

“…A comprehensive understanding of the fundamental mechanisms responsible for carbon bearing-fluid migration in the presence of CO 2 /H 2 S is crucial for risk assessment and site selection for geologic CCS, monitoring H 2 S emissions, and perhaps identifying innovative enhanced oil recovery (EOR) processes that use CO 2 and H 2 S. , Because a thorough quantification of the phenomena that govern fluid transport in the complex heterogeneous pore networks found in organic-rich shale caprocks, which consist of crowded nanopores that provide poor connections between dispersed pockets of organic matter, remains elusive, because of practical difficulties in observing fluid transport in such complicated systems, computational approaches could be helpful. − …”