Howard E. Thomas

Gas—solid chromatography and virial analysis of chlorofluorocarbon adsorption on a microporous carbon

Abstract Gas-solid chromatography was used to determine the second gas-solid virial coefficients in the temperature range 373–512 K for ethane, propane, chloromethane, dichloromethane, fluoromethane, chlorodifluoromethane (Freon 22), and dichlorodifluoromethane (Freon 12), with Super Sorb, a microporous carbon adsorbent. The temperature dependence of the second gas-solid virial coefficients of these adsorbates was used in conjunction with a Lennard-Jones and Devonshire cell model to determine the effective structural parameters of cavity radius and number of cavities per gram of adsorbent, as well as gas-cavity interaction energies. The interaction energies were correlated with adsorbate boiling points and energetic additivity rules based on molecular structure including the number of atoms of different types in the molecule and the dipole moment of the molecule.

Gas—solid chromatography and virial analysis of hydrocarbon adsorption on 13X zeolite

Abstract Gas-solid chromatography was used to determine the second gas-solid virial coefficients in the temperature range 343–597 K for ethane, propane, n-butane, 2-methylpropane, n-pentane, 2-methylbutane, 2,2-dimethylpropane, n-hexane, 2,2-dimethylbutane, and cyclohexane with 13X zeolite. The temperature dependence of the second gas-solid virial coefficients of these 10 hydrocarbons along with the available methane data was used in conjunction with a Lennard-Jones and Devonshire cell model to determine the 13X zeolite structural parameters of cavity radius and number of cavities per gram of adsorbent, as well as gas-cavity interaction energies. The 13X structural parameters were compared to X-ray crystallographic values. The interaction energies were found to be linearly dependent on the number of carbon atoms in the adsorbate hydrocarbon with the more highly branched molecules having somewhat lower energies. The interaction energies were correlated with hydrocarbon boiling points and energetic additivity rules on the basis of molecular structure.

Binding energies for alkane molecules on a carbon surface from gas-solid chromatography and molecular mechanics.

Gas-solid chromatography was used to determine B(2s) (gas-solid virial coefficient) values for 12 alkanes (10 branched and 2 cyclic) interacting with a carbon powder (Carbopack B, Supelco). B(2s) values were determined by multiple size variant injections within the temperature range of 393 to 623 K with each alkane measured at 5 or 6 different temperatures. The temperature variations of the gas-solid virial coefficients were used to find the experimental adsorption energy or binding energy values (E( *)) for each alkane. A molecular mechanics based, rough-surface model was used to calculate the molecule-surface binding energy (E(cal)( *)) using augmented MM2 parameters. The surface model consisted of three parallel graphene layers with each layer containing 127 interconnected benzene rings and two separated nanostructures each containing 17 benzene rings arranged in a linear strip. As the parallel nanostructures are moved closer together, the surface roughness increases and molecule-surface interactions are enhanced. A comparison of the experimental and calculated binding energies showed excellent agreement with an average difference of 3.8%. Linear regressions of E( *) versus E(cal)( *) for the current data set and a combined current and prior alkane data set both gave excellent correlations. For the combined data set with 18 linear, branched and cyclic alkanes; a linear regression of E( *)=0.9848E(cal)( *) and r(2)=0.976 was obtained. The results indicate that alkane-surface binding energies may be calculated from MM2 parameters for some gas-solid systems.