Toluene and water vapor adsorption characteristics and selectivity on hydrophobic resin-based activated carbon

Abstract

The competitive adsorption between volatile organic compounds (VOCs) and water vapor seriously decreases the adsorption capacity of adsorbents. In this paper, a series of hydrophobic spherical resorcinol-formaldehyde resin-based activated carbons (CRFs) were prepared and characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmet-Teller (BET) techniques. The adsorption equilibrium and selectivity of toluene and water vapor on CRFs were investigated systematically. Compared to other adsorbents, HCRF800 treated by hydrogen reduction exhibited the highest toluene uptake (8.64 mmol/g at 293 K) and the strongest hydrophobicity, which was much superior to commercial activated carbon. The results of isosteric heats showed that toluene on HCRF800 was higher than that of water vapor, indicating a stronger interaction between the adsorbent and toluene than water vapor. The adsorption selectivity of toluene/water vapor on CRFs was estimated by the Difference of Isosteric Heats (DIH) equation, and the results suggested that HCR800 possessed the highest selectivity, and the value was in the range of 9.5–52.3. Furthermore, HCRF800 also displayed good toluene uptake at different humidities and faster intra-particle diffusion behavior due to its lower content of surface oxygen groups. Temperature-programmed desorption experiments and Density Functional Theory calculations further revealed that surface oxygen groups had a negative effect on the selectivity of toluene/water, and the negative effect followed the order as O-CO > C-O > CO. Moreover, HCRF800 possessed excellent reversibility. These results demonstrated that HCRF800 would be a superior adsorbent for VOCs recycling from a humid atmosphere.