Adsorption Kinetics of Propane and Propylene in 13X Zeolite

This paper presents the properties of single component diffusion of propane and propylene in zeolite 13X obtained by Molecular Dynamics (MD) simulations, especially its dependence on temperature and concentration. The potential form and parameters used to describe the interactions between propane and the zeolite framework atoms, including the cations, are based on the force field from Calero et al. (J. Am. Chem. Soc., 126, 11377, 2004). The interaction parameters for propylene were taken from our previous work on equilibrium adsorption of propylene in 13X zeolite (Granato et al., Ind. Eng. Chem. Res. 46, 7239, 2007). Each simulation was performed in two steps. In the first step, a configurational-bias Monte Carlo in the NVT ensemble is used to generate an equilibrated system, minimizing the energy. The MD simulations are executed in the NVT ensemble, using the Nosé-Hoover thermostat to maintain constant temperature conditions.

Self-diffusion coefficients (DS) were calculated from the mean squared displacements. Transport diffusivities (DT) were estimated by using the Darken equation. The simulations show that DS decreases with increasing loadings, either for propane or propylene. The results compared well with literature data, although different measurement techniques may show enormous discrepancies between results.