Adsorption and Desorption Behavior of Benzene on Activated Carbons from Different Precursors in Dry and Humid Conditions

Activated carbons (ACs) prepared by CO2 activation of five different precursors and commercial coconut shell AC are used for benzene adsorption (5 ppmv) from air at relative humidities (RHs) of 0%, 50% and 70%. Benzene adsorption capacities of the ACs prepared in the laboratory are similar at RH 0%, but differ significantly in the presence of moisture. The negative influence of moisture on benzene uptake is greater in a case of the ACs with large amounts of surface polar sites. The average micropore sizes of the ACs up to 0.8 nm are beneficial for benzene adsorption at RH 70%, while the average micropore sizes above 0.8 nm are beneficial for benzene adsorption at RH 50%. The desorption of benzene from the ACs after adsorption has been examined by temperature programmed desorption (TPD) method. It was found that the desorption profiles of the ACs are similar at the same RH, suggesting that the adsorption of benzene occurred on similar adsorption sites in all ACs, despite the differences in their origin and in pore and chemical properties. At RH 70%, benzene is adsorbed only on the high-energy sites, which results in a shift of desorption profiles to higher temperatures.