Arora Gaurav, Sandler Stanley I
Center for Molecular and Engineering Thermodynamics, Department of Chemical Engineering, University of Delaware, Newark, Delaware 19716, USA.
J Chem Phys. 2005 Jul 22;123(4):044705. doi: 10.1063/1.1949172.
Separation of a nitrogen-oxygen mixture (air) by single wall carbon nanotubes has been studied using grand canonical Monte Carlo simulations at a range of nanotube diameters, temperatures, and pressures. It is demonstrated that depending on these operating parameters, the extent of adsorptive selectivity can vary significantly. Detailed calculations are also presented for the adsorption isotherms, energies, and isosteric heats of pure nitrogen, oxygen, and their mixture at 100 K in a carbon nanotube of 12.53-A diameter. In single-component simulations, it is found that near saturation loading nitrogen forms only an annular layer close to the nanotube wall, while smaller-sized oxygen also occupies the region near the center of the nanotube. In mixture adsorption, the energetically favored nitrogen is preferentially adsorbed at low loadings. However, at high loadings oxygen replaces nitrogen due to the dominant entropic effects, and therefore a high selectivity towards oxygen is observed close to the saturation loading. The effect of the entropic change on mixture adsorption is evident from the calculated isosteric heats of adsorption. The mixture isotherms obtained from simulations are found to be in good agreement with the predictions based only on the pure component simulation results.
已使用巨正则蒙特卡罗模拟，在一系列纳米管直径、温度和压力条件下，研究了单壁碳纳米管对氮 - 氧混合物（空气）的分离。结果表明，根据这些操作参数，吸附选择性的程度会有显著变化。还给出了直径为12.53埃的碳纳米管中，纯氮、纯氧及其混合物在100K时的吸附等温线、能量和等量吸附热的详细计算结果。在单组分模拟中，发现接近饱和负载时，氮仅在靠近纳米管壁处形成一个环形层，而尺寸较小的氧还占据纳米管中心附近的区域。在混合吸附中，能量上更有利的氮在低负载时优先被吸附。然而，在高负载时，由于主导的熵效应，氧会取代氮，因此在接近饱和负载时观察到对氧的高选择性。从计算出的等量吸附热可以明显看出熵变对混合吸附的影响。模拟得到的混合等温线与仅基于纯组分模拟结果的预测结果吻合良好。
