Molecular simulation of self- and transport diffusion of mixtures in metal-organic frameworks

Molecular dynamics (MD) simulations of self- and transport diffusion in metal-organic frameworks (MOFs) were performed. Self-diffusion coefficients in MOF-5 for methane, n-pentane, n-hexane, n-heptane, and cyclohexane were presented. They were of the same order of magnitude as in silicalite. Almost simultaneously, diffusion of argon in another MOF, Cu-BTC, was also carried out. This study probed the dependence of self- and transport diffusion over a wide range of pore loadings at room temperature. The two diffusivities differed by almost two orders of magnitude at high pore loadings. Detailed molecular simulations of mixture diffusion were presented in various MOFs topologies, i.e., the IRMOFs of Yaghi et al., Cu-BTC and some of the paddlewheel structures synthesized by the Hupp group. The self- and transport diffusivities were obtained from the Einstein equation using MD. The effect of confinement and topology on the selectivity in a mixture was evaluated. Adsorption isotherms and diffusion coefficients were presented for binary mixtures of CO₂/N₂ as well as ternary mixtures of hexane/2-methylpentane/2,2-dimethylbutane. For reference, the single component adsorption isotherms and diffusivities were also calculated. This is an abstract of a paper presented at the 2006 AIChE National Meeting (San Francisco, CA 11/12-17/2006).