(392c) Dynamic Mean Field Theory for Mixtures Confined In Porous Materials

Recently we have developed a dynamic mean field theory (DMFT) for fluids in porous materials [P. A. Monson, J. Chem. Phys., 128, 084701 (2008); J. R. Edison and P. A. Monson, Faraday Discussions, 146, 167-184 (2010)]. The theory can be used to describe the relaxation processes in the approach to equilibrium or metastable equilibrium states for fluids in pores after a change in the bulk pressure or chemical potential. It is especially useful for studying systems where there are capillary condensation or evaporation transitions. Nucleation processes associated with these transitions are emergent features of the theory and can be visualized via the time dependence of the density distribution in the system. In this presentation we describe the extension of DMFT to mixtures. In addition we present some applications that illustrate the utility of the approach.

We consider two applications of DMFT for mixtures in a finite slit pore in contact with the bulk. We choose parameters in the model relevant to methane/ethane or methane/carbon dioxide mixtures in a carbon-like pore. The theory predicts the evolution of the density and composition in the pore in the approach to equilibrium. In the first case we study the dynamic uptake of a binary mixture in the pore by changing the bulk pressure at fixed temperature and composition. We do this for several temperatures up to the critical temperature of the less volatile component. In the second case we study the displacement of the more volatile component by the less volatile one. The latter case is relevant to the displacement of methane by carbon dioxide in coal seams as a possible sequestration process.