Thermodynamics analysis on the adsorption behaviors of VOCs on various adsorbents

The adsorption and desorption behaviors of n-hexane, toluene and ethyl acetate on activated carbon, 5A, NaY, 13X, ZSM-5 (SiO₂/Al₂O₃=27, 300), Hβ and MCM-41 at different temperatures were investigated by chromatography method and thermogravimetry (TG).And the adsorption thermodynamic parameters (ΔH, ΔS and ΔG) were calculated based on the results obtained by inverse gas chromatography, by which, the interactions between adsorbent and VOC molecules were elucidated. In addition, the adsorption mechanisms of VOC molecules on molecular sieves were confirmed based on FT-IR results. There are two modes of spontaneous adsorption involving physical and chemical adsorptions. The physical adsorption strength is dependent on the pore size distribution of the adsorbent and the molecular diameter of the adsorbate, while the chemical adsorption strength is associated with the Si/Al ratio of the molecular sieve, the cations of Ca²⁺, Na⁺, H⁺, and the dipole moment of the adsorbate molecules. Meanwhile, the presence of strong chemical adsorption makes desorption temperature up to 200℃.