Comparison of adsorption properties of a chemically activated and a steam-activated carbon, using inverse gas chromatography

Adsorption properties of two different activated carbons, steam and chemically activated, respectively, were examined by inverse gas chromatography (IGC). The influence of acid, basic and combined washings, carried out in order to remove ashes, on the adsorption properties of these materials was also tested using this technique. Chemical and textural characterization was carried out by nitrogen adsorption, ICP-MS and temperature programmed desorption, whereas thermodynamic properties (enthalpy of adsorption, surface free energy characteristics) have been determined by IGC. Washing procedures (specially those involving acid washing) removes almost completely the mineral ashes of the carbons. Concerning to the effect on porous structure, this procedures only affect significantly to the properties of chemically activated carbon, with increases of micropore volume of up to 43%. The steam activated carbon shows the best adsorptive behaviour, with an enthalpy of adsorption up to 16% higher than the corresponding to chemically activated one, as well as a large amount of micropores. The removal of these ashes enhances the adsorption of studied compounds, especially for alkanes and chlorinated ones. Washing procedures also modify the chemical structure of the organic functionalities, but this effect does not seem to be very important on the adsorption properties of these materials.