Molecular Simulation Studies on Adsorption of Propane/Propylene in NaA Zeolite by Using a Monte Carlo Technique
Molecular Simulation Studies on Adsorption of Propane/Propylene in NaA Zeolite by Using a Monte Carlo Technique
复制标题
蒙特卡罗技术对 NaA 沸石吸附丙烷/丙烯的分子模拟研究
DOI：
10.1252/jcej.36.1085
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发表时间：
2003
影响因子：
0.8
通讯作者：
T. Nitta
中科院分区：
文献类型：
--
作者：
Yi Zhang;S. Furukawa;T. Nitta
采用μ VT系综定向偏置Monte Carlo方法，模拟了298.15K时丙烷/丙烯在NaA分子筛上的吸附等温线。Catlow等（1991）和Oie等（1981）的原子势模型能满意地代表实验等温线。模拟结果揭示了丙烯吸附比丙烷强得多的原因，即丙烯的吸附能比丙烷大10 kJ/mol，这主要是通过丙烯分子与沸石原子/Na离子之间的库仑相互作用实现的。用Langmuir、多中心占据、二维货车der Waals流体和Ruthven+U模型对模拟得到的丙烷/丙烯纯吸附等温线进行了关联。后三个模型被发现适合得多，因为它们考虑到吸附分子之间的相互作用，其贡献已被澄清是显着的模拟比朗缪尔模型。在100 kPa总压和298.15 K下计算的丙烷/丙烯混合物的模拟等温线显示了混合气体吸附的一个新特征，即弱吸附质丙烷的吸附量随丙烷分压的降低而增加，并在丙烯摩尔分数较低时达到最大值。这种不寻常的混合气体吸附已被归因于吸附效果，通过分子间的相互作用丙烯分子明显吸附在沸石。模拟混合气体等温线定性预测上述三个模型，而Langmuir模型与IAST（理想吸附溶液理论）未能预测丙烷的最大吸附的存在。
A μVT-ensemble Orientational-Bias Monte Carlo technique has been utilized to simulate adsorption isotherms of pure and mixed propane/propylene in NaA zeolite at 298.15 K. An atomic potential model of Catlow et al. (1991) and Oie et al. (1981) is found to represent the experimental isotherms satisfactorily. The simulations reveal the reason why propylene is adsorbed much more strongly than propane; i.e. the adsorption energy of propylene is 10 kJ/mol larger than that of propane, mainly through the Coulomb interactions between propylene molecules and zeolite atoms/Na ions. Pure adsorption isotherms of propane/propylene obtained from the simulations are correlated with four theoretical models: Langmuir, multi-site occupancy, two-dimensional van der Waals fluid and Ruthven+U models. The latter three models are found to fit much better than the Langmuir model because they take account of interactions between adsorbed molecules, the contribution of which has been clarified to be significant from the simulations. The simulation isotherms of propane/propylene mixtures, calculated at 100 kPa in total pressure and 298.15 K, show a novel feature of mixed-gas adsorption; i.e. the adsorption of propane, a weak adsorbate, increases with the decrease in the partial pressure of propane and reaches a maximum in a low mole fraction of proylene. This unusual mixed-gas adsorption has been ascribed to a sorption effect through the molecular interactions of propylene molecules appreciably adsorbed in zeolite. The simulation mixed-gas isotherms are qualitatively well predicted by the above three models, while the Langmuir model with the IAST (Ideal Adsorbed Solution Theory) fails to predict the existence of a maximum adsorption of propane.