Numerical evidence for a thermal driving force during adsorption of butane in silicalite

Jean-Marc Simon (1, 2) , Isabella Inzoli (2) , Dick Bedeaux (2) , Signe Kjelstrup (2)

1 ICB - Laboratoire Interdisciplinaire Carnot de Bourgogne
2 Chemistry NTNU - Department of Chemistry [Trondheim]

The transport properties of nano-porous materials determine their applicability, e.g. as separators or catalysts [1, 2]. Adsorption in zeolites is explained as a two-step process; adsorption to the external crystal surface and subsequent intra-crystalline diffusion [3]. Both steps have been considered to be isothermal [4, 5]. Here we show, using non-equilibrium molecular dynamics simulations of n-butane in silicalite [6] that a significant temperature change accompanies adsorption and intra-crystalline transport, and leads to a significant varying thermal driving force across the crystal surface, in agreement with the proposition of Ruthven et al. [7]. The butane flux into the crystal is caused in the first stage by a chemical potential difference. In the second stage the temperature of the zeolite decreases due to a thermal force across the surface. This slow reduction in the zeolite temperature induces a small butane uptake, that may help explain why equilibrium techniques give larger diffusion coefficients than non-equilibrium techniques [5]. Descriptions of transport in nano-porous materials [1, 8] need to include a thermal driving force.

Mots clés: Physical Sciences

Jean-Marc Simon, Isabella Inzoli, Dick Bedeaux, Signe Kjelstrup. Numerical evidence for a thermal driving force during adsorption of butane in silicalite. Molecular Simulation, 2009, 33 (09-10), pp.839-841. ⟨10.1080/08927020701370620⟩. ⟨hal-00526214⟩