Hydrophobic modified activated carbon using PDMS for the adsorption of VOCs in humid condition

In engineering applications, moisture is inevitable in waste gas containing VOCs, which leads to the problem of poor adsorption performance of activated carbon under humid conditions. To improve the adsorption selectivity of VOCs, walnut based activated carbon was modified by polydimethylsiloxane (PDMS) and characterized by FTIR analysis, SEM&EDS and the static water contact angle. Dynamic adsorption column experiments were conducted and Yoon-Nelson (Y-N) model was used to identify adsorption effect for benzene on ACs when relative humidity was 0%, 30%, 60%, 90%. The results show that the activated carbon modified by PDMS increases Si and O elements and forms a hydrophobic coating on the surface in the form of Si-O-Si group. The hydrophobicity changed positively with the increase of modification temperature, but the collapse and blockage of pores were more serious. Adsorption capacity of hydrophilic Bare-AC decreased by 55.9% when the relative humidity increased from 0% to 90%. However, the activated carbon covered with PDMS modified at 200 °C decreased by only 19.3%. Changes in the mass transfer rate of benzene during adsorption under different conditions have also been discovered. This study provides a method to solve the problem of serious deterioration of adsorption capacity of adsorbents in wet environment.