Gas Solid Chromatography Measurements of the Change in the Heat Capacity during Adsorption on Graphitized Thermal Carbon Black

Gas chromatography is widely used to measure the thermodynamic functions of adsorption on the homogeneous surface of graphitized thermal carbon black in the region where Henry's adsorption law is valid. A high-precision instrument with computer data acquisition measures the isosteric heat of adsorption and the change of the heat capacity during adsorption. The method is used to study the adsorption of benzene and n-pentane on different graphitized thermal carbon black samples. The data are directly comparable with the values calculated from statistical thermodynamics on graphite since it is shown that adsorbateadsorbate interactions are negligible and that the behavior of the bulk gas phase is nearly ideal. The results obtained for benzene could be compared with the molar heat capacity of adsorbed benzene measured by calorimetric methods and extrapolated at zero surface coverage. With n-pentane, however, the gas solid chromatographic method is unique, as extrapolation of calorimetric measurements is impossible because of strong adsorbate-adsorbate interactions at relatively low surface coverage.