乙二酸和苯甲酸在活性炭上的脱附行为

低挥发性有机酸不仅自身污染环境而且显著促进颗粒污染物形成,对其吸脱附性能的研究有助于这类物质的控制。采用程序升温脱附(TPD)技术对乙二酸、苯甲酸在活性炭(AC)上的脱附行为进行了研究。结果表明,吸附主要发生在粗微孔(0.7~2 nm)、细微孔(<0.7 nm)中,对应TPD曲线中的吸附位Ⅰ、Ⅱ。粗微孔对乙二酸、苯甲酸的脱附活化能为101.63、112.43 kJ·mol^-1,吸附量均大于总吸附量的91%。细微孔对乙二酸、苯甲酸的脱附活化能为118.01、130.87 kJ·mol^-1,吸附量均小于总吸附量的9%。细微孔吸附强度高于粗微孔,但吸附量远低于粗微孔,因为细微孔对吸附质的迁移阻力较大,仅少量吸附质能进入细微孔中。苯甲酸在迁移中受到阻力较乙二酸大,在细微孔中吸附量更小,表现为分子筛分作用。

Desorption behavior of ethanedioic acid and benzoic acid on activated carbon

Low-volatility organic acids are harmful to the environment. Adsorption/desorption study of organic acids on adsorbents is of great significance to control these pollutants. Here temperature programmed desorption method was used to study the desorption behavior of ethanedioic and benzoic acids on activated carbon. Results show that textural characteristics of activated carbon play a critical role since wide micropores (0.7-2 nm) and narrow micropores (<0.7 nm) dominate the adsorption at active sites Ⅰ and Ⅱ, respectively. Interactions of ethanedioic and benzoic acids with active site Ⅰ (E_d = 101.63, 112.43 kJ·mol^-1) are weaker than those with active site Ⅱ (E_d =118.01, 130.87 kJ·mol^-1), whereas the adsorption amount on active site Ⅰ is much larger than that on active site Ⅱ. Molecular sieving effect is shown to explain the fact that ethanedioic acid with a chain structure and smaller kinetic diameter is easier to be adsorbed into narrow micropores as compared to benzoic acid with a circular structure and larger kinetic diameter.