Two-Surface Virial Analysis of Alkane Adsorption on Carbopack C with and without Hydrogen Treatment

Abstract

Second gas–solid virial coefficients for propane, butane, pentane, and hexane were found for Carbopack C and Carbopack C-HT (Supelco Inc.) within the temperature range of 323 to 471 K using gas–solid chromatography in the Henry's law region of adsorption. Carbopack C and Carbopack C-HT are both graphitized carbon black powders. Treatment of Carbopack C with hydrogen at 1273 K converts it to Carbopack C-HT and is believed to remove certain high energy sites or “hot spots” from the carbon surface. These two surfaces provide appropriate model systems to test a two-surface virial analysis. Surface areas for both powders were calculated using a uniform single-surface model and a two-surface model. Only the two-surface virial model which is based on gas–solid interaction parameters determined by an iterative process and numerical integration gave reasonable areas for the two surfaces: 13.2 and 13.9 m2/g for Carbopack C and Carbopack C-HT, respectively. The percentage of high energy sites on the Carbopack C was found to be 2.6% and for Carbopack C-HT was found to be 1.5%. The gas–solid interaction energy for the high energy sites was found to be 1.80 times greater than the corresponding value for the low energy portion of the surface. In addition, the gas–solid adsorption energies for the four alkane adsorbates were found to have a linear correlation with their boiling points and with the ratio of their critical temperatures divided by the square root of their critical pressures.