Krishna Rajamani, van Baten Jasper M
Van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands.
ACS Omega. 2020 Dec 10;5(50):32769-32780. doi: 10.1021/acsomega.0c05269. eCollection 2020 Dec 22.
The separation performance of microporous crystalline materials in membrane constructs is dictated by a combination of mixture adsorption and intracrystalline diffusion characteristics; the permeation selectivity is a product of the adsorption selectivity and the diffusion selectivity, . The primary objective of this article is to gain fundamental insights into and by use of molecular simulations. We performed configurational-bias Monte Carlo (CBMC) simulations of mixture adsorption equilibrium and molecular dynamics (MD) simulations of guest self-diffusivities of a number of binary mixtures of light gaseous molecules (CO, CH, N, H, and CH) in a variety of microporous hosts of different pore dimensions and topologies. Irrespective of the bulk gas compositions and bulk gas fugacities, the adsorption selectivity, , is found to be uniquely determined by the adsorption potential, Φ, a convenient and practical proxy for the spreading pressure π that is calculable using the ideal adsorbed solution theory for mixture adsorption equilibrium. The adsorption potential Φ is also a proxy for the pore occupancy and is the thermodynamically appropriate yardstick to determine the loading and composition dependences of intracrystalline diffusivities and diffusion selectivities, . When compared at the same Φ, the component permeabilities, Π for CO, CH, and N, determinable from CBMC/MD data, are found to be independent of the partners in the various mixtures investigated and have practically the same values as the values for the corresponding unary permeabilities. In all investigated systems, the H permeability in a mixture is significantly lower than the corresponding unary value. These reported results have important practical consequences in process development and are also useful for screening of materials for use as membrane devices.
膜结构中微孔晶体材料的分离性能取决于混合物吸附和晶内扩散特性的综合作用；渗透选择性是吸附选择性和扩散选择性的乘积，即 。本文的主要目的是通过分子模拟深入了解 和 。我们对多种不同孔径和拓扑结构的微孔主体中轻质气态分子（CO、CH、N、H和CH）的二元混合物进行了构型偏置蒙特卡罗（CBMC）模拟以研究混合物吸附平衡，并进行了分子动力学（MD）模拟以研究客体自扩散系数。无论主体气体组成和主体气体逸度如何，吸附选择性 都被发现由吸附势Φ唯一确定，Φ是铺展压力π的一种方便实用的替代量，可使用理想吸附溶液理论计算混合物吸附平衡来计算π。吸附势Φ也是孔占有率的替代量，并且是确定晶内扩散系数和扩散选择性 的负载和组成依赖性的热力学合适标准。当在相同的Φ下进行比较时，可从CBMC/MD数据确定的CO、CH和N的组分渗透率Π被发现与所研究的各种混合物中的伙伴无关，并且实际上与相应的一元渗透率值相同。在所有研究的系统中，混合物中H的渗透率明显低于相应的一元值。这些报道的结果在工艺开发中具有重要的实际意义，并且对于筛选用作膜装置的材料也很有用。
