VOCs在吸附剂上吸附性能的热力学研究

采用色谱法与热重(TG)法,测量了正己烷、甲苯和乙酸乙酯在活性炭、5A、NaY、13X、ZSM-5 (SiO_2/Al_2O_3=27、300)、Hβ以及M CM-41等吸附剂上不同温度下的吸脱附行为,并基于反相气相色谱法测得的数据,计算了其吸附热力学参数ΔH、ΔS和ΔG,分析了上述VOCs分子与吸附剂之间的作用机制,并借助FT-IR验证了吸附质在分子筛表面的吸附机制。结果表明,上述吸附过程存在物理吸附和化学吸附两种方式,其中,物理吸附的作用力大小与吸附剂的孔径分布和分子直径相关,而化学吸附的作用力大小依赖于分子筛硅铝比和Ca~(2+)、Na~+、H~+等阳离子及吸附质分子的偶极矩,且强的化学吸附使得部分吸附质分子的脱附温度高于200℃。

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℃.