A COMPARISON OF THE ADSORPTION BEHAVIOR OF NITROGEN, ALCOHOLS, AND WATER TOWARDS ACTIVE CARBONS

The adsorption behaviour of a range of vapours, of varying polarity, for two commercial carbons is reported. Type 5 (BDDT) isotherms are observed for water vapour adsorption where polar interactions predominate. Nitrogen gives type 1 isotherms, indicating that the major interaction is of the dispersion type. The initial regions of isotherms for the alcohols methanol to butanol suggest an increase in the relative dispersion to polar interaction with increasing molar volume, although the dispersion interaction appears dominant in all cases and the overall isotherms are all of type 1 character. Saturation volumes and Dubinin-Radushkevich micropore volumes from N2 and the alcohols are consistent for each carbon. Saturation volumes for water adsorption are much lower than those from the other vapours. The high pressure regions of Polanyi characteristic curves for N2 and the alcohols can be superimposed using beta-shifting factors based on molar volume or parachor data, low pressure deviations cannot be explained by molecular sieve effects and are most likely due to differential packing of adsorbate within the micropores. The Dubinin-Astakhov equation does not appear to offer any advantages for analysis of the data presented.