An IGC and TA study of acetaldehyde adsorption on activated carbons

Abstract

Two samples of activated carbons of various origins were modified using oxidation with nitric acid and impregnation with urea followed by thermal treatment. The surface of carbons was characterized using sorption of nitrogen, Boehm titration, and thermal analysis. Inverse gas chromatography was used to study the adsorption of acetaldehyde at infinite dilution. From the retention volumes the heats of acetaldehyde adsorption were calculated. The results showed that on materials with very small pores interactions of acetaldehyde are strongest. This is due to dispersive interactions of hydrocarbon moiety with the activated carbon pore walls. Introduction of functional groups containing oxygen or nitrogen results in creation of additional adsorption centers which start to play a role when all high energy centers, small pores, are filled with acetaldehyde molecules. After modification of carbon surfaces the isosteric heat of acetaldehyde adsorption decreased. This is due to changes in the pore structure and an increase in the density of surface groups that results in partial blocking of the pore entrances and thus decreases the contact of hydrocarbon moiety with the carbon surface.