Identifying and Utilizing Upper Bounds for Diffusion-based Separations using Metal Organic Frameworks

提案号：1604375，PI: shull， david标题：使用金属有机框架确定和利用基于扩散的分离的上限散装化学分离对世界范围内的化学品和燃料工业至关重要。因为这些分离主要是用热驱动的方法（如蒸馏）进行的，它们消耗大量的能量。膜基分离为大容量化学分离的常规分离提供了一个强大的替代方案。膜的商业气体分离应用主要是聚合物膜，但这些膜受到选择性和吞吐量之间的基本权衡的限制。近年来，包括金属有机骨架（MOFs）在内的多孔材料制备膜的研究取得了很大进展。mof的结晶性质意味着存在于聚合物膜的基本权衡在原则上可以被克服。然而，似乎有可能的是，其他物理现象将限制MOF膜的最终性能。本项目将使用原子细节建模和实验相结合的方法来确定mof作为气体分离膜的性能上限。这项工作将对指导这些膜的关键工业应用的发展至关重要。该项目将重点关注小孔mof，如沸石咪唑盐框架（ZIFs）和混合ZIFs，它们可以通过吸附和扩散选择性来实现分离。这项工作将建立在pi最近的工作基础上，该工作证明了使用分子模拟来预测这类材料中的分子扩散率的能力。这些计算依赖于自由能采样技术，因为实际感兴趣的物种扩散发生得太慢，无法直接用于分子动力学模拟。同样重要的是，考虑吸附剂框架中所有自由度的模型被用来准确地描述缓慢扩散的物种。我们将对选定的一系列小孔mof进行详细的分子模拟，以探索mof中分子扩散存在上界关系的假设。模拟将通过对选定材料的扩散进行直接实验测量进行测试和验证。

Proposal Number: 1604375, PI: Sholl, DavidTitle: Identifying and Utilizing Upper Bounds for Diffusion-based Separations using Metal Organic FrameworksBulk chemical separations are vital to the world-wide chemicals and fuels industries. Because these separations are largely performed with thermally-driven methods (e.g. distillation), they consume vast amounts of energy. Membrane-based separations offer a powerful alternative to conventional separations for a range of large-volume chemical separations. Commercial gas separations applications of membranes are dominated by polymeric membranes, but these membranes are limited by a fundamental trade-off between selectivity and throughput. Considerable progress has been made in recent years in making membranes from porous materials including metal-organic frameworks (MOFs). The crystalline nature of MOFs means that the fundamental tradeoff that exists for polymeric membranes can in principle be overcome. It seems likely, however, that other physical phenomena will place bounds on the ultimate performance that is possible with MOF membranes. This project will use a combination of atomically-detailed modeling and experiments to establish upper bounds on the performance of MOFs as membranes for gas separations. This work will be critical in guiding the development of these membranes for key industrial applications.The project will focus on small pore MOFs such as zeolitic imidazolate frameworks (ZIFs) and hybrid ZIFs in which separations can be achieved by both adsorption and diffusion selectivity. The work will build upon recent work by the PIs that demonstrates the ability to predict molecular diffusivities in materials of this kind using molecular simulations. These calculations rely on free energy sampling techniques, since the diffusion of species that is of practical interest occurs far too slowly for direct molecular dynamics simulations to be used. It is also vital that the models accounting for all degrees of freedom in the adsorbent framework be used to accurately describe slowly diffusing species. Detailed molecular simulations will be performed for a series of small pore MOFs that have been selected to explore hypotheses about the existence of upper bound relationships for molecular diffusion in MOFs. Simulations will be tested and validated using direct experimental measurements of diffusion in selected materials.