2-SURFACE VIRIAL ANALYSIS OF ALKANE ADSORPTION ON CARBOPACK-C WITH AND WITHOUT HYDROGEN TREATMENT

Second gas-solid virial coefficients for propane, butane, pentane, and hexane were found for Carbopack C and Carbopack C-HT (Supelco Inc.) w ithin the temperature range of 323 to 471 K using gas-solid chromatogr aphy in the Henry's law region of adsorption. Carbopack C and Carbopac k C-HT are both graphitized carbon black powders. Treatment of Carbopa ck C with hydrogen at 1273 K converts it to Carbopack C-HT and is beli eved to remove certain high energy sites or ''hot spots'' from the car bon surface. These two surfaces provide appropriate model systems to t est a two-surface virial analysis. Surface areas for both powders were calculated using a uniform single-surface model and a two-surface mod el. Only the two-surface virial model which is based on gas-solid inte raction parameters determined by an iterative process and numerical in tegration gave reasonable areas for the two surfaces: 13.2 and 13.9 m( 2)/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 C arbopack C-HT was found to be 1.5%. The gas-solid interaction energy f or the high energy sites was found to be 1.80 times greater than the c orresponding value for the low energy portion of the surface. In addit ion, 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 ro ot of their critical pressures. (C) 1997 Academic Press.