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

建议编号：1604375，PI：Sholl，DavidTitle：确定和利用基于扩散的分离的上限使用金属有机框架批量化学分离对世界范围内的化学品和燃料行业至关重要。由于这些分离在很大程度上是用热驱动的方法(例如蒸馏)来执行的，因此它们消耗了大量的能量。膜分离为一系列大容量的化学分离提供了一种替代传统分离的有效方法。工业气体分离膜的应用主要是由聚合物膜主导的，但这些膜受到选择性和通量之间的基本权衡的限制。近年来，利用包括金属有机骨架(MOF)在内的多孔材料制膜已取得了长足的进展。MOF的结晶性质意味着聚合物膜存在的基本权衡原则上是可以克服的。然而，其他物理现象似乎很可能会限制MOF膜的最终性能。该项目将使用原子细节建模和实验相结合的方法来确定作为气体分离膜的MOF的性能上限。这项工作将对指导这些用于关键工业应用的膜的开发至关重要。该项目将专注于小孔MOF，如沸石咪唑骨架(ZIF)和杂化ZIF，其中可以通过吸附和扩散选择性实现分离。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预测此类材料中的分子扩散系数的能力。这些计算依赖于自由能采样技术，因为实际感兴趣的物种的扩散发生得太慢，无法使用直接的分子动力学模拟。同样重要的是，考虑到吸附剂框架中所有自由度的模型应该用来准确地描述缓慢扩散的物种。将对一系列小孔MOF进行详细的分子模拟，以探索分子扩散上限关系在MOF中存在的假设。模拟将使用选定材料中扩散的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.