(700h) A Molecular Dynamics and Grand Canonical Monte Carlo Study of Small Gas Molecules in Siliceous Decadodecasil 3R

Hydrogen separation and combustion subsequent to coal gasification is an attractive process for environmentally benign methods of energy generation. Siliceous zeolites are thermally and chemically stable ultramicroporous materials that can satisfy the function of a separation membrane for such high temperature (>500°C) processes. Ensuing steam generation via hydrogen combustion can consequently occur without significant energy loss. All-silica Decadodecasil 3R (DD3R), with pore diameter 3.6x4.4 Å, is attractive for the separation of smaller H₂ (2.89 Å) from larger CO, CO₂, CH₄, N₂ and O₂ molecules with kinetic diameters of 3.76, 3.3, 3.8, 3.64 and 3.46 Å, respectively. The current study employs a molecular dynamics and grand canonical Monte Carlo approach to predict single-component gas diffusion coefficients and adsorption isotherms for H₂, CO, CO₂, CH₄, N₂ and O₂ in DD3R at 0 ? 1000°C. The respective diffusion coefficients and adsorption loadings determined in this study enabled prediction of separation characteristics of DD3R zeolite employed as a H₂-separation membrane material. These separation characteristics in a form of gas fluxes are presented and discussed in this talk.

Adsorption of CO, CO₂, CH₄, N₂ and O₂ in DD3R plays a significant role in overall mass transport and separation selectivity with respect to hydrogen than their diffusivity at low temperatures. Hydrogen adsorption is relatively low at all temperatures. At elevated temperatures (>200°C) gas adsorption in DD3R is insignificant, and the molecular diffusivity provides a dominant contribution to mass transport and selectivity.

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