Amaël Obliger (UMI CNRS-MIT, Mutiscale Material Science for Energy and Environment), présentera un séminaire le 11 décembre à 11h dans la bibliothèque du laboratoire PHENIX (7e étage, bâtiment F, porte 754) intitulé :
Transport of hydrocarbon mixtures in disordered nanoporous media
Résumé
Despite the recent major focus on shale-gas, no model has been provided to understand the transport of hydrocarbon mixtures in shales subnanoporous matrix (kerogen). Since continuum descriptions such as Darcy’s law cannot be used to describe transport of linear alkanes through subnanoporous carbon membranes (pore size below 2 nm), we use molecular dynamics and statistical mechanics to rationalize the behaviour of both equilibrium and non-equilibrium transport coefficients of hydrocarbon mixtures. As kerogen replicas we use the numerical model of disorderd carbon structures from the work of Bousige et al. [1].
Under applied pressure gradient, the velocity of each component of the mixtures at steady-state is still proportional to the pressure gradient. The coefficients of proportionality, called permeances, depend on the density and on the solid-fluid interactions. We use the Fluctuation Dissipation Theorem in order to derive a Green- Kubo expression that allows us to express the permeances as function of the Onsager coefficients that can be evaluated at equilibrium. Due to strong adsorption effects, it appears that the hydrocarbon transport behaviour is mostly influenced by the interactions with the solid matrix. As a consequence, the permeances of the different components of the mixtures scale in a simple way with the alkane length, independently of the nature of the mixture (number of components, composition). Moreover, this scaling is the same as for the pure component case described previously by Falk et al. [2] with a free volume theory. In this framework, the effects of the solid-fluid interactions and of the crowding on the transport are decoupled and captured respectively by a friction and an overlapping coefficient.
To get further insights on hydrocarbon transport in kerogen, we investigate in detail how these coefficients can be linked to the topology of the host matrix. We aim at proposing simple relations between the transport coefficients of the free volume theory and the porosity of the solid matrix.
Work in collaboration with R. J.-M. Pellenq, F.-J. Ulm and B. Coasne.
[1] Bousige, C. ; Botan, A. ; Ulm, F.-J. ; Pellenq, R. J.-M. ; Coasne, B. Optimized molecular reconstruction procedure combining hybrid reverse Monte Carlo and molecular dynamics. The Journal of Chemical Physics 2015, 142, 114112.
[2] Falk, K. ; Coasne, B. ; Pellenq, R. ; Ulm, F.-J. ; Bocquet, L. Subcontinuum mass transport of condensed hydrocarbons in nanoporous media. Nature Communications 2015, 6, 7949.
