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

利用分子模拟和量子化学计算研究无机膜的膜渗透机理和分子设计

基本信息

批准号：
11450291
负责人：
NITTA Tomoshige
金额：
$ 7.49万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B).
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2000
项目状态：
已结题

项目摘要

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

本工作的目标有两个：无机膜的气体渗透机理的分子模拟研究和利用从头计算的量子化学计算的表面改性方法的研究，以实现无机膜的分子设计。1．在分子模拟中，三种不同的碳膜。提出了多种孔形状（菱形、锯齿形和光滑狭缝类型）作为模型膜，并计算了甲烷/乙烷混合物的渗透率，以下是重要结果： (1) 气体的分子渗透和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入口和出口处的相对渗透阻力。(2) 对于菱形和锯齿形膜，扩散阻力和出口阻力占主导地位，而狭缝形膜仅出口阻力占主导地位。（3）增强强吸附分子渗透率的膜结构可能是此外，已经开发了一些柔性分子渗透的程序，并且已经进行了丁烷异构体通过沸石膜的渗透的模拟；但是，它们需要大量的计算时间，因此，我们已经采取了努力。重写并行处理程序，期望有一个新的并行计算系统。 2．提出了一种通过从头计算量子化学计算的方法来修改表面原子的策略：即选择候选原子以增强其性能。分子与表面（团簇）之间的稳定能因素被发现NH_3-TiO_2之间的分子间相互作用很大，并且对于未经修饰的CO_2-MgO和CO_2-TiO_2体系来说，可归为化学吸附。发现分子间势是物理吸附，对稳定化的最大贡献是从表面原子到CO_2分子的电荷转移，因此，Ca原子具有较小的尺寸。选择电负性高于 Mg 和 Ti 原子的，以增强电荷转移，这导致 CO_2 的吸附能增加，正如选择规则预测的那样，当分子极化是相互作用的主要因素时，我们可以选择。尽管我们最近的计算表明，极化项对分子间稳定的敏感性似乎较弱，但原子比原始表面原子更软。