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N-octane diffusivity enhancement via carbon dioxide in silica slit-shaped nanopores – a molecular dynamics simulation

Le, T; Ogbe, S; Striolo, A; Cole, DR; (2015) N-octane diffusivity enhancement via carbon dioxide in silica slit-shaped nanopores – a molecular dynamics simulation. Molecular Simulation , 42 (9) pp. 745-752. 10.1080/08927022.2015.1089991. Green open access

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Abstract

Equilibrium molecular dynamics simulations were conducted to study the competitive adsorption and diffusion of mixtures containing n-octane and carbon dioxide confined in slit-shaped silica pores of width 1.9 nm. Atomic density profiles substantiate strong interactions between CO2 molecules and the protonated pore walls. Non-monotonic change in n-octane self-diffusion coefficients as a function of CO2 loading was observed. CO2 preferential adsorption to the pore surface is likely to attenuate the surface adsorption of n-octane, lower the activation energy for n-octane diffusivity, and consequently enhance n-octane mobility at low CO2 loading. This observation was confirmed by conducting test simulations for pure n-octane confined in narrower pores. At high CO2 loading, n-octane diffusivity is hindered by molecular crowding. Thus, n-octane diffusivity displays a maximum. In contrast, within the concentration range considered here, the self-diffusion coefficient predicted for CO2 exhibits a monotonic increase with loading, which is attributed to a combination of effects including the saturation of the adsorption capacity of the silica surface. Test simulations suggest that the results are strongly dependent on the pore morphology, and in particular on the presence of edges that can preferentially adsorb CO2 molecules and therefore affect the distribution of these molecules equally on the pore surface, which appears to be required to provide the effective enhancement of n-octane diffusivity.

Type: Article
Title: N-octane diffusivity enhancement via carbon dioxide in silica slit-shaped nanopores – a molecular dynamics simulation
Open access status: An open access version is available from UCL Discovery
DOI: 10.1080/08927022.2015.1089991
Publisher version: http://dx.doi.org/10.1080/08927022.2015.1089991
Language: English
Additional information: Copyright © 2015 Taylor & Francis. This is an Accepted Manuscript of an article published by Taylor & Francis in Molecular Simulation, vol 42, issue 9, 2016, available online: http://www.tandfonline.com/doi/full/10.1080/08927022.2015.1089991
Keywords: Mixture, competitive adsorption, preferential adsorption
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Chemical Engineering
URI: https://discovery.ucl.ac.uk/id/eprint/1470708
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