Hung Hsu-Wen, Lin Tsair-Fuh
Sustainable Environment Research Center, National Cheng Kung University, Tainan City, Taiwan, Republic of China.
J Air Waste Manag Assoc. 2007 Apr;57(4):497-506. doi: 10.3155/1047-3289.57.4.497.
Prediction of the adsorption capacity for volatile organic compounds (VOCs) onto activated carbons is elucidated in this study. The Dubinin-Radushkevich (D-R) equation was first used to predict the adsorption capacity of nine aromatic and chlorinated VOCs onto two different activated carbons. The two key parameters of the D-R equation were estimated simply from the properties of the VOCs using quantitative structure-activity relationship and from the pore size distribution of the adsorbent. The approach based on the D-R equation predicted well the adsorption capacity at high relative pressures. However, at the relative pressures lower than -1.5 x 10(-3), the D-R approach may significantly overestimate adsorption capacity. To extrapolate the approach to lower relative pressures, the integration of the D-R equation and the Langmuir isotherm, called the D-R-L model, was proposed to predict adsorption capacity over a wide range of relative pressures of VOCs. In this model, the Langmuir isotherm parameters were extracted from the predicted D-R isotherm at high relative pressures. Therefore, no experimental effort was needed to obtain the parameters of the D-R-L model. The model successfully predicted the adsorption capacity of aromatic and chlorinated hydrocarbons tested onto BPL and Sorbonorit B carbons over relative pressures ranging from 7.4 x 10(-5) to 0.03, suggesting that the model is applicable at the low relative pressures of VOCs often observed in many environmental systems. In addition, the molecular size of organic compounds may be an important factor affecting the adsorption capacity of activated carbons. For BPL carbon, an ultramicroporous adsorbent, the limiting pore volume Wo of the D-R equation decreased when the kinetic diameter of the adsorbate was larger than 6 angstroms. However, for Sorbonorit B carbon, no reduction of Wo was found, suggesting that the Wo may be related to the pore size distribution of the adsorbents, as well as to their molecular size. This size exclusion effect may play an important role in predicting the adsorption capacity of VOCs onto microporous adsorbents in the D-R-L model and in the corresponding D-R equation.
本研究阐述了对挥发性有机化合物（VOCs）在活性炭上吸附容量的预测。首先使用杜比宁-拉杜什凯维奇（D-R）方程来预测9种芳香族和氯化VOCs在两种不同活性炭上的吸附容量。D-R方程的两个关键参数可通过使用定量构效关系从VOCs的性质以及从吸附剂的孔径分布简单估算得出。基于D-R方程的方法在高相对压力下能很好地预测吸附容量。然而，在相对压力低于-1.5×10⁻³时，D-R方法可能会显著高估吸附容量。为了将该方法外推到更低的相对压力，提出了将D-R方程与朗缪尔等温线相结合的方法，即D-R-L模型，以预测在广泛的VOCs相对压力范围内的吸附容量。在该模型中，朗缪尔等温线参数是从高相对压力下预测的D-R等温线中提取的。因此，无需进行实验来获取D-R-L模型的参数。该模型成功预测了芳香族和氯化烃在BPL和Sorbonorit B活性炭上在相对压力范围从7.4×10⁻⁵到0.03时的吸附容量，这表明该模型适用于许多环境系统中经常观察到的VOCs低相对压力情况。此外，有机化合物的分子大小可能是影响活性炭吸附容量的一个重要因素。对于BPL碳这种超微孔吸附剂，当被吸附物的动力学直径大于6埃时，D-R方程的极限孔体积Wo会减小。然而，对于Sorbonorit B碳，未发现Wo减小，这表明Wo可能与吸附剂的孔径分布以及它们的分子大小有关。这种尺寸排阻效应在D-R-L模型以及相应的D-R方程中预测VOCs在微孔吸附剂上的吸附容量时可能起重要作用。
