Predicting second gas-solid virial coefficients using calculated molecular properties on various carbon surfaces

Gas-solid chromatography was used to obtain values of the second gas-solid virial coefficient, B-2s, in the temperature range from 343 to 493 K for seven adsorbate gases: methane, ethane, propane, chloromethane, chlorodifluoromethane, dimethyl ether, and sulfur hexafluoride. Carboxen-1000. a 1200 m(2)/g carbon molecular sieve (Supelco Inc.), was used as the adsorbent. These data were combined with earlier work to make a combined data set of 36 different adsorbate gases variously interacting with from one to four different carbon surfaces. All B-2s values were extrapolated to 403 K to create a set of 65 different gas-solid B-2s values at a fixed temperature. The B-2s value for a given as-solid system can be converted to a chromatographic retention time at any desired flow rate and can be converted to the amount of gas adsorbed at any pressure in the low-coverage, Henry's law region. Beginning with a theoretical equation for the second gas-solid virial coefficient. various quantitative structure retention relations (QSRR) were developed and used to correlate the In B-2s values for different gas adsorbates with different carbon surfaces. Two calculated adsorbate molecular parameters (molar refractivity and connectivity index), when combined with two adsorbent parameters (surface area and a surface energy contribution to the gas-solid interaction), provided an effective correlation (r(2) = 0.952) of the 65 different In B-2s values. The two surface parameters provided a simple yet useful representation of the structure and energy of the carbon surfaces and thus our correlations considered variation in both the adsorbate gas and the adsorbent solid. (C) 2003 Elsevier Inc. All rights reserved.