A GAS CHROMATOGRAPHIC STUDY OF THE ADSORPTIVE PROPERTIES OF A SERIES OF ACTIVATED CHARCOALS

Abstract

From measurements of the gas chromatographic retention volumes, the initial slopes of the adsorption isotherms of nitrogen and the simpler hydrocarbons on a series of steam-activated coconut charcoals were determined. The initial heats of adsorption were obtained in the usual way from the temperature dependence. It was found for all gases that both the initial slope of the isotherm and the initial heat of adsorption decreased with increasing degree of activation of the charcoal (i.e. with increasing surface area per g). This suggests that the higher affinity for the very small pores in less activated material more than counterbalances the lower total surface.Measurements at several different carrier gas flow rates of the relative band width for the charcoals of least and of greatest activation demonstrated, as might be expected, a greater resistance to mass transfer for the former. However, the apparent diffusion coefficients calculated on the assumption that all transport is by gas phase in the pores were nearly the same for each charcoal and showed relatively little variation among the different gases.