Adsorption isotherm for flexible molecules in random porous media. Can we regard the system as a binary mixture?

Abstract

Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. II. Binary and ternary mixtures and comparison with the experimental data The adsorption isotherm for repulsive n-alkanes in a random porous medium has been determined by computer simulation. The porous medium or matrix is obtained by quenching an equilibrium configuration of repulsive spheres. Keeping fixed this configuration of the matrix particles, Grand-Canonical Monte Carlo simulations were used to determine the adsorption isotherm of repulsive n-butane and n-hexane models in the random porous medium. In addition to that, canonical Monte Carlo simulations were performed for the equilibrium binary mixture in which the spherical and n-alkane particles are allowed to move. Chemical potential of the n-alkane molecule in the binary mixture is computed by using the test particle method. We found that, at the same chemical potential, the structure of the n-alkane in the binary mixture and in the quenched medium differs at high densities. However, at the same chemical potential, densities of the n-alkane in the random porous medium and in the binary mixture are quite similar. A consequence of that is that adsorption isotherms can be computed if the properties of the binary mixture are known. We have recently proposed an equation of state for mixtures of hard n-alkane molecules which contains as a particular case the sphereϩn-alkane mixture. The chemical potential of the n-alkane in the mixture can be computed analytically and we used this result for determining adsorption isotherms. Excellent agreement with simulation is found. The results of this work suggest that the knowledge of the properties of the binary mixture can be very useful for obtaining adsorption isotherms in random porous media. Finally, the effect of attractive forces on the properties of alkanes in binary mixtures and confined in a random porous medium was also studied. In general, the presence of attractive forces reduces the similarity between the properties of alkanes in these two systems.

Adsorption of a Hard Sphere Fluid in Disordered Microporous Quenched Matrix of Short Chain Molecules: Integral Equations and Grand Canonical Monte Carlo Simulations

“…The theoretical results obtained for simple fluids have been tested versus computer simulations. Complex fluids in complex matrices have been investigated less frequently (11)(12)(13)(14)(15), in spite of their importance for basic research and applications.…”

Connect the Thermodynamics of Bulk and Confined Fluids: Confinement-Adsorption Scaling

“…Such selectivity is extensively exploited in various chemical processes, for example, catalytic cracking in oil industry . Nowadays, it is widely recognized that the properties of fluids confined in porous media can be dramatically different from those of the bulk ones. − Understanding the behavior of confined fluids is important not only from a fundamental point of view but also for conceiving innovative industrial processes.…”

“…A large literature exists on the study of confined fluids by theoretical and simulation methods − ,− (references given here are just for illustration but far from being exhaustive). Models with simple pore geometry (e.g., slit or cylinder) are widely studied.…”

Fluids Confined in Porous Media: A Soft-Sponge Model

“…They showed how the statistical−mechanics approaches for liquids, that is, diagrammatic expansions and integral equations, can be extended to describe fluids confined in a random porous matrix. The work of Madden and Glandt has incited much interest in the theoretical study of fluid adsorption in random porous media. − …”