Studies on Membrane Permeation Mechanisms and Molecular Design of Inorganic Membranes by Using Molecular Simulations and Quantum Chemical Calculations

本论文的主要工作有两个方面：无机膜气体渗透机理的分子模拟研究和无机膜表面改性方法的量子化学从头计算研究，以实现无机膜的分子设计.在分子模拟中，提出了三种不同孔形状的碳膜（菱形，锯齿形，光滑狭缝型）作为模型膜和甲烷/乙烷混合物的渗透计算。（1）气体分子渗透分离机理可以用三个因素来解释：选择性吸附、孔内相对扩散阻力和膜进出口相对渗透阻力。(2)对于菱形和锯齿形膜，扩散阻力和出口阻力占主导地位，而对于狭缝形膜，仅出口阻力占主导地位。(3)增强渗透的膜结构 关于我们 强吸附的分子的速率可能是最好的。此外，一些程序的柔性分子的渗透已经开发和模拟丁烷异构体通过沸石膜的渗透已经进行，但是，他们被发现需要大量的计算时间。因此，我们一直在努力重写并行处理程序，期望有一个新的并行计算系统.通过量子化学从头计算，提出了一种表面原子修饰的策略：即选择一个候选原子，以提高分子与表面（团簇）之间的稳定能因子。NH_3-TiO_2间的分子间相互作用较大，属于化学吸附。对于CO_2-MgO和CO_2-TiO_2体系，分子间作用势主要是物理吸附，对稳定化的贡献最大的是表面原子向CO_2分子的电荷转移。因此，选择电负性比Mg和Ti小的Ca原子来增强电荷转移，导致CO_2的吸附能增加，这与选择规则的预测一致。在分子极化是相互作用的主要因素的情况下，我们可以选择比原始表面原子更软的原子，尽管我们最近的计算表明极化项对分子间稳定性的敏感性似乎很弱。少

The objectives of the present work are twofold : molecular simulation studies on gas permeation mechanisms through inorganic membranes and studies on surface modification method by using ab initio quantum chemical calculations, toward molecular design of inorganic membranes.1. In molecular simulations, three carbon membranes different in pore shape (diamond, zigzag, and smooth slit types) were proposed as model membranes and the permeation of methane/ethane mixtures were calculated. Followings are important results : (1) Molecular permeation and separation mechanisms of gases may be explained by three factors : selective adsorption, relative diffusion resistance in pores, and relative permeation resistance at the inlet and outlet of membranes.(2) For the diamond and zigzag shape membranes, the diffusion resistance and the outlet resistance are predominant while only the outlet resistance is predominant for the slit-shaped membrane.(3) The membrane structure that enhances the permeation … More rate of molecules strongly adsorbed may be the best. Furthermore, some programs for permeation of flexible molecules have been developed and simulations of permeation of butane isomers through a zeolite membrane have been carried out ; however, they are found to take a lot of computation time. Therefore, we have taken efforts to rewrite the programs for parallel processing, with expecting to have a new parallel computing system.2. A strategy for modification of surface atoms has been proposed by means of ab initio quantum chemical calculations : i.e. selecting a candidate atom so as to enhance the factors of stabilization energy between a molecule and the surface (a cluster). The intermolecular interaction between NH_3-TiO_2 was found to be large and to be classified into chemical adsorption without modification. For the CO_2-MgO and CO_2-TiO_2 systems, the intermolecular potentials were found to be physical adsorption and the largest contribution for the stabilization was the charge transfer from the surface atoms to a CO_2 molecule. Therefore, Ca atoms, which have smaller electronegativity than Mg and Ti atoms, were selected to enhance the charge-transfer, which resulted in the increase in adsorption energy of CO_2 as the selection rule predicted. In the case when the molecular polarization is the major factor for the interaction, we can choose softer atoms than the original surface atoms, though the sensitivity of the polarization term on the intermolecular stabilization seems to be weak, suggested by our recent calculations. Less