title: Confined Water Determines Transport Properties of Guest Molecules in Narrow Pores.
abstract: We computed the transport of methane through 1 nm wide slit-shaped pores carved out of solid substrates. Models for silica, magnesium oxide, and alumina were used as solid substrates. The pores were filled with water. The results show that the methane permeability through the hydrated pores is strongly dependent on the solid substrate. Detailed analysis of the simulated systems reveals that local properties of confined water, including its structure, and more importantly, evolution of solvation free energy and hydrogen bond structure are responsible for the pronounced differences observed. The simulations are extended to multicomponent systems representative of natural gas, containing methane, ethane, and H2S. The results show that all pores considered have high affinity for H2S, moderate affinity for methane, and low affinity for ethane. The H2S/methane transport selectivity through the hydrated alumina pore is comparable, or superior, to that reported for existing commercial membranes. A multiscale approach was then implemented to demonstrate that a Smoluchowski one-dimensional model is able to reproduce the molecular-level results for short pores when appropriate values for the local self-diffusion coefficients are used as input parameters. We propose that the model can be extended to predict methane transport through uniform hydrated pores of macroscopic length. When verified by experiments, our simulation results could have important implications in applications such as natural gas sweetening and predictions of methane migration through hydraulically fractured shale formations.
authors.affiliation: Department of Chemical Engineering, University College London , London WC1E 7JE, U.K.
authors.forename: Anh
authors.initials: A
authors.lastname: Phan
authors.affiliation: School of Earth Sciences, The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: David R
authors.initials: DR
authors.lastname: Cole
authors.affiliation: Institut für Physik, Humboldt-Universität zu Berlin , Newtonstrasse 15, D-12489 Berlin, Germany.|Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin , Hahn-Meitner Platz 1, D-14109 Berlin, Germany.
authors.forename: R Gregor
authors.initials: RG
authors.lastname: Weiß
authors.affiliation: Institut für Physik, Humboldt-Universität zu Berlin , Newtonstrasse 15, D-12489 Berlin, Germany.|Soft Matter and Functional Materials, Helmholtz-Zentrum Berlin , Hahn-Meitner Platz 1, D-14109 Berlin, Germany.
authors.forename: Joachim
authors.initials: J
authors.lastname: Dzubiella
authors.affiliation: Department of Chemical Engineering, University College London , London WC1E 7JE, U.K.
authors.forename: Alberto
authors.initials: A
authors.lastname: Striolo
keywords: aqueous systems; confined fluids; molecular simulation; permeability; solvation free energy