@article {135, title = {Effect of Chain Length and Pore Accessibility on Alkane Adsorption in Kerogen}, journal = {Energy \& Fuels}, volume = {29}, year = {2015}, month = {Oct-28-2015}, pages = {7889 - 7896}, abstract = {
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Configurational-biased Grand Canonical Monte Carlo and Molecular Dynamics simulations were used to investigate the adsorption and structure of n-alkanes in realistic models of kerogen (the organic phase in gas shales). Both the effects of the n-alkane length (from methane to dodecane) and of the adsorbent porosity/density and connectivity were considered. For all n-alkanes, due to the subnano pore size of kerogen, adsorption follows a Langmuir-type adsorption isotherm as the adsorbed amount increases continuously with pressure until maximum loading is reached. While all n-alkanes get adsorbed very efficiently in low density kerogen, size exclusion in high density kerogen lead to low adsorbed amounts for molecules larger than hexane. Using Molecular Dynamics simulations reflecting the setup of actual adsorption experiments, we also probed the effect of pore accessibility on n-alkane adsorption in kerogen. All pores are connected to the surface and, hence, accessible for the low density kerogen. In contrast, most pores are isolated and inaccessible in the kerogen with the high density. We also address the effect of mesoporosity and its connection to nanoporosity on alkane adsorption in kerogen.

}, issn = {0887-0624}, doi = {10.1021/acs.energyfuels.5b02015}, author = {Kerstyn I. Falk and Roland Jean-Marc Pellenq and Franz-Josef Ulm and Benoit A. Coasne} } @article {182, title = {Effect of Surface Texture on Freezing in Nanopores: Surface-Induced versus Homogeneous Crystallization}, journal = {Langmuir}, volume = {31}, year = {2015}, month = {Mar-10-2015}, pages = {2706 - 2713}, abstract = {
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Freezing of argon in ordered and disordered carbon pores of a similar diameter D \∼ 2.4 nm is investigated using extensive molecular simulations with large system sizes up to 104 atoms. While crystallization in the atomistically smooth pore consists in a surface-induced phase transition occurring at a temperature larger than the bulk, crystallization in the disordered pores, which is only partial as it is spatially restricted to the pore center, occurs through homogeneous crystallization. These results shed light on solidification in pores by showing that there is a crossover between surface-induced and homogeneous crystallization upon increasing the surface disorder of the host material. In the latter case, the Gibbs\–Thomson equation, in which crystallization is assumed to occur when the crystal size equals the pore size corrected for the thickness of the unfreezable layer at the pore surface, is in reasonable agreement with the observed freezing temperature.

}, issn = {0743-7463}, doi = {10.1021/la5041213}, author = {Benoit A. Coasne} } @article {89, title = {Effect of Gas Adsorption on Acoustic Wave Propagation in MFI Zeolite Membrane Materials: Experiment and Molecular Simulation}, journal = {Langmuir}, volume = {30}, year = {2014}, month = {Aug-04-2014}, pages = {10336-10343}, type = {Article}, abstract = {
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The present study reports on the development of a characterization method of porous membrane materials which consists of considering their acoustic properties upon gas adsorption. Using acoustic microscopy experiments and atomistic molecular simulations for helium adsorbed in a silicalite-1 zeolite membrane layer, we showed that acoustic wave propagation could be used, in principle, for controlling the membranes operando. Molecular simulations, which were found to fit experimental data, showed that the compressional modulus of the composite system consisting of silicalite-1 with adsorbed He increases linearly with the He adsorbed amount while its shear modulus remains constant in a large range of applied pressures. These results suggest that the longitudinal and Rayleigh wave velocities (VL and VR) depend on the He adsorbed amount whereas the transverse wave velocity VT remains constant.

}, issn = {0743-7463}, doi = {10.1021/la502182k}, author = {Manga, Etoungh D. and Blasco, Hugues and J. Philippe Da-Costa and Drobek, Martin and Ayral, Andre and Le Clezio, Emmanuel and Despaux, Gilles and Benoit A. Coasne and Julbe, Anne} } @article {101, title = {Effect of temperature on adsorption of mixtures in porous materials}, journal = {Molecular Simulation}, volume = {40}, year = {2014}, month = {Jan-02-2014}, pages = {45-51}, type = {Article}, abstract = {

The effect of temperature on the adsorption of a simple mixture (Ar/Kr) in disordered porous materials is investigated by means of molecular simulation. In the larger mesopores of porous silica glasses, capillary condensation occurs upon decreasing the temperature. At temperatures above the capillary condensation temperature, Kr is preferentially adsorbed at the pore surface and Ar adsorption occurs in regions of low Kr density. For temperatures below the capillary condensation temperature, Ar density surprisingly increases as temperature increases, the behaviour that is consistent with an over-solubility effect. In contrast, in the disordered sub-nanoporous carbon, filling of the pores occurs in a reversible and continuous way upon decreasing the temperature, owing to the small size and amorphous shape of the pores. These results show that the crossover between capillary condensation and continuous reversible filling observed for pure fluids in pores also exists for mixtures. We also show that the Kr selectivity exhibits a minimum in the disordered porous silica that is located at the capillary condensation temperature. In contrast, in the disordered porous carbon where no capillary condensation occurs, the selectivity decreases monotonically with increasing the temperature. These results shed light on low-temperature adsorption of mixtures confined in porous materials and provide a guide to design efficient phase separation processes.

}, keywords = {Adsorption, grand canonical Monte Carlo simulations, Mixtures, porous materials}, issn = {0892-7022}, doi = {10.1080/08927022.2013.852192}, author = {Kerstyn I. Falk and Benoit A. Coasne and Roland Jean-Marc Pellenq} } @article {85, title = {Enhanced H-2 Uptake of n-Alkanes Confined in Mesoporous Materials}, journal = {Journal of Physical Chemistry C }, volume = {118}, year = {2014}, month = {Apr-30-2014}, pages = {10720-10727}, type = {Article}, abstract = {
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The hydrogen uptake in hybrid sorbents consisting of n-alkane solvents confined in mesoporous silica aerogel is measured at different temperatures from 273 to 313 K and pressures up to 40 bar. An apparent \“oversolubility\” effect is observed as the H2 uptake in the hybrid sorbents is much larger than that in bulk solvents. The H2 uptake in the hybrid sorbents is found to increase with increasing temperature, which suggests that the flexibility and conformation of n-alkane molecules confined in the aerogel play a crucial role; high-entropy (disordered) alkane configurations lead to the creation of numerous cavities which make it possible to solubilize a larger number of H2 molecules. This departs from adsorption-driven solubility effects for which the number of solubilized molecules decreases with increasing temperature. For a given temperature and pressure, it is found that the number of solubilized H2 molecules per unit volume increases with decreasing alkane chain length. Such an effect, which is observed for both the bulk alkanes and the alkanes confined in the silica aerogel, can be rationalized by considering the number density of CHx (x = 2 or 3) groups; for a given temperature, the latter number density decreases with decreasing alkane chain length so that the free volume available to solubilize H2 molecules increases.

}, issn = {1932-7447}, doi = {10.1021/jp411526f}, author = {St{\'e}phanie Clauzier and Linh Ngoc Ho and Pera-Titus, M. and David Farrusseng and Benoit A. Coasne} }