Impact of surface characteristics of activated carbon on adsorption of BTEX

Five residues of botanical origin were tested as potential activated carbon precursors; these are: date pits (DP), cotton stalks (CS), peach stones (PS), almond shells (ALS), and olive stones (OS). A standard activation procedure was followed (impregnation with 50% H3PO4 and heat treatment at 773 K) for the sake of comparison. Texture characteristics were determined by analysis of the N2/77 K isotherms. Highly to good adsorbing carbons were obtained in the order: PS, ALS, CS, OS and DP, respectively. Acidity/basicity characteristics were estimated by the selective titration method of Boehm. All carbons contained residual phosphates and showed high content of surface oxygen complexes mostly of acidic type. Removal of benzene, toluene, ethylbenzene and p-xylene (BTEX) was evaluated for each component in the mixture and in terms of total uptake. Low amounts of BTEX were adsorbed, which were irregularly correlated to either of the porosity or surface–chemical parameters. It is assumed that the complexity of the carbon surface with developed porosity and high content of hydrophilic oxygen functionalities determine the uptake of the hydrophobic organic molecules. In general, the order of uptake appears consistent to previous investigations as B<T<E<X, as related to decreased water solubility and increased molecular weight. A single air oxidized activated carbon at 625 K (OSA) showed a considerable reduction in porosity as well as increased acidity and improved removal capacity of BTEX per unit area.