Adsorption of Volatile Organic Compounds at Medium-High Temperature Conditions by Activated Carbons

Activated carbon (AC) adsorption is an effective method for abatement of volatile organic compounds (VOCs) in coal-fired power plants. The adsorption behaviors of VOCs (toluene and chlorobenzene) for ACs (coconut shell-based AC (CSAC) and wood-based AC (WAC)) under medium-high temperature (MHT: 90-150 degrees C) conditions were investigated in a fixed-bed reactor. The results indicated that the adsorption capacity of VOCs was reduced with increasing temperature. CSAC had a higher adsorption capacity and adsorption rate for the two VOCs than WAC at the same adsorption temperature. The adsorption capacity of toluene was within the range of 13.9-49.9 mg/g, while that for chlorobenzene was 26-80.3 mg/g. The content of oxygen-containing groups on the AC surface was increased with acid modification and decreased with alkali modification. The adsorption capacity of AC was improved to varying degrees after chemical modification. Adsorption was mainly controlled by physical adsorption, whereas the effects of chemisorption became evident with increasing temperature. The interactions between oxygen-containing groups and VOCs were more beneficial for improving adsorption capacity than pi-pi interactions. The pseudofirst-order kinetic model better described the adsorption of VOCs by ACs. The MHT conditions promoted the intraparticle diffusion; lower VOC concentration resulted in the external mass transfer of AC becoming the adsorption rate-limiting step. Increasing the external surface area and micropore volume of AC and enriching the content of surface oxygen-containing groups were useful in enhancing the VOC removal efficiency.