Influence of water on the dynamic adsorption of chlorinated VOCs on active carbon: Relative humidity of the gas phase versus pre-adsorbed water

The present work deals with the influence of water on the adsorption of two chlorinated volatile organic compounds (VOCs) on activated carbons (ACs) having very different pore textures and surface chemistry. Two kinds of moisture were considered, viz. pre-adsorbed on the AC or present as steam in the gaseous phase, at various relative humidities ranging from 30% to 75%. It is shown that the adsorption of the VOCs depends on the kind of moisture. If the latter is pre-adsorbed, water is just displaced by the VOCs (overshoot). The adsorption capacities of the AC remain unchanged and only some minor changes in the shape of the breakthrough front, corresponding to hindered diffusion, may sometimes occur. In contrast, the simultaneous adsorption of steam and VOC leads to competition between water and the chlorinated compound, with direct consequences on the adsorption kinetics and capacities of the AC. However, the decrease of the water-induced adsorption performances depends strongly on the AC and the VOC (through different VOC/AC and water/NOC interactions), and on the concentration of the VOC.