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Molecular Simulation Studies on Membrane Permeation and Molecular Design of Membranes

膜渗透的分子模拟研究和膜的分子设计

基本信息

批准号：
09450286
负责人：
NITTA Tomoshige
金额：
$ 7.74万
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：
1997
资助国家：
日本
起止时间：
1997 至 1998
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09450286/
关键词：
Inorganic Membrane Carbon Membrane Molecular Dynamics Non-Equilibrium Zeolite Membrane Quantum Chemistry Wave function

项目摘要

The objectives of the present work are twofold : molecular simulation studies of gas permeation mechanisms through inorganic membranes and an attempt of surface modification method by use of ab initio quantum chemical calculations. Followings are important results : (1) The gammaVT-NEMD method has been effectively used to simulate permeation of pure and mixed gases through carbon membranes ; it is found that the separation mechanism of mixed gases through a membrane composed of heterogeneous surfaces of belt-like potential barrier changes from adsorption-control to diffusion-control as the potential barrier increases. (2) One of interesting observations is a blocking phenomenon where ethane molecules, which are strongly adsorbed on carbon surfaces, cover outer mouths of slit pores, resulting in preventing small methane molecules to enter. (3) Simulations of permeation of helium, nitrogen, carbon dioxide, methane, ethane through the pure silica ZSM-5 membrane have been carried out and d … More ensity profiles of gases are found to provide quantitative estimations of permeation-resistance through the entrance, inside and exit of the membrane. (4) A wavepacket analysis method was firstly. introduced to investigate the statistical behavior of molecules that penetrate a slit-shaped micropore ; the effect of kinetic energy vertical to the wall surface on gas permeation from inside to outside was investigated by the new method.A strategy has been suggested to modify surface atoms through ab initio quantum chemical calculations : the GAUSSIAN is used to optimize the geometry of a molecule and a cluster imitating a surface and the GAMESS is used to decompose the molecular interaction energy into various energy terms : electrostatic, exchange, polarization, charge-transfer and others. It is found that the charge-transfer term is the largest in the above interaction terms for molecular interactions between CO^2 and a cluster of MgO (electron charge is transferred from the surface to the CO^2 molecule) ; therefore, Ca atoms, which have smaller electronegativity than Mg atoms, are selected to enhance the charge-transfer effect from surface to the CO^2 atom. A partial exchange of Mg atoms with Ca atoms resulted in lower potential energy for adsorption of CO^2 on the modified surface as expected, which suggests that the proposed method will be a rational tool for the evaluation of atoms to be modified. Less

本工作的目的有两个：一是通过分子模拟研究气体透过无机膜的机理，二是尝试用从头算方法进行表面修饰。(1)用GammaVT-NEMD方法有效地模拟了纯气体和混合气体在碳膜中的渗透过程，发现随着势垒的增大，混合气体通过由带状势垒非均质表面组成的膜的分离机理由吸附控制转变为扩散控制。(2)有趣的观察之一是一种堵塞现象，即强烈吸附在碳表面的乙烷分子覆盖裂隙孔的外口，从而阻止小甲烷分子进入。(3)对氦、氮、二氧化碳、甲烷、乙烷等气体在纯二氧化硅zsm-5膜中的渗透过程进行了模拟计算，并用d…进行了模拟。发现更多的气体密度分布可以提供通过膜的入口、内部和出口的渗透阻力的定量估计。(4)首次提出了波包分析方法。研究了分子穿透狭缝状微孔的统计行为；用新方法研究了垂直于壁面的动能对气体由内向外渗透的影响。提出了一种通过从头计算对表面原子进行修饰的策略：用高斯优化分子和模拟表面的团簇的几何结构，用GamesS将分子相互作用能分解成各种能量项：静电、交换、极化、电荷转移等。结果表明，在上述相互作用项中，CO^2与一团簇MgO(电荷从表面转移到CO^2分子)之间的电荷转移项最大，因此选择电负性比镁原子小的Ca原子来增强从表面到CO^2原子的电荷转移效应.镁原子与钙原子的部分交换降低了CO^2在修饰表面的吸附势能，这表明该方法将是评价待修饰原子的一种合理工具。较少