Collaborative Research: Crossing the percolation threshold for selective gas transport using interconnected crystals of metal–organic frameworks in polymer-based hybrid membranes

合作研究：利用聚合物杂化膜中金属有机框架的互连晶体跨越选择性气体传输的渗滤阈值

• 批准号: 2034742
• 负责人: Zachary Smith
• 金额: $ 26万
• 依托单位: Massachusetts Institute of Technology
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-07-15 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2034742&HistoricalAwards=false
• 关键词: Collaborative; Research; Crossing; percolation; threshold

Light gases such as methane, ethane, and ethylene play an important role in industrial applications, including their use as gas and liquid fuels and as precursors in polymer manufacturing. Access to high purity gases is typically required for these applications necessitating an industrial gas separation process. Gas separation technology is also required to reduce the concentration of carbon dioxide and other greenhouse gases in the atmosphere. Accordingly, the development of low-energy and low-cost separations of gas mixtures is critically important to meet industrial demand, address environmental concerns, and improve standards of living. Separating gas molecules from a mixture requires materials (molecular sieves) containing holes with uniform dimensions that are comparable with the sizes of the small gas molecules to be separated. However, suitable molecular sieve particles are usually difficult to form into the geometries necessary for scales relevant to industrial applications or environmental remediation. This project will advance the fundamental science of forming molecular sieve particles into well-connected networks, which will enable the development of large-scale separation technologies. In the networks, the particles will be held together by polymer interfaces designed to minimize any adverse effects on the particle sieving function and, at the same time, preserve the structural integrity of the material. The separation performance, gas transport properties, and structural properties of such networks will be quantified on all relevant length scales. The outcomes of this project will lay the foundation for rationally designed molecular sieve morphologies that can be optimized for the desired gas separation. The investigators will also initiate a new research mentoring program with the objective of teaching and training students from underrepresented groups in STEM. Existing institutional programs will be leveraged, and the use of online tools will be emphasized to enhance the program's effectiveness.Metal-organic frameworks (MOFs) are high porosity molecular sieves exhibiting extraordinary property sets when applied in membrane-based gas separations. However, these materials cannot be easily formed into defect-free membrane geometries. Hence, it is challenging to leverage the intrinsic transport benefits of MOFs for membrane separations. Mixing MOF crystals with polymers to make mixed-matrix membranes (MMMs) is a well-known strategy to form MOF-based membranes. However, the typical separation performance of MMMs is usually lower than that of the corresponding MOFs because MMM transport properties are unfavorably affected by the polymer phase and, in some cases, by interfacial MOF–polymer defects. A clear route to improve MMM performance is to increase MOF concentrations and even reach a percolation threshold to enable diffusion predominantly through the MOF phase, i.e., a situation when gas diffusion in MMMs can proceed mostly over interconnected MOF crystals. The investigators will develop the fundamental science of crossing the percolation threshold for gas transport in the MOF phase of MOF–polymer MMMs to enable separation performance comparable with that of pure MOF membranes. Membrane fabrication strategies will be developed based on a novel functionalization of the external surface of MOF crystals in combination with the development of fundamental understanding of intramembrane gas transport. Advanced nuclear magnetic resonance will be used to investigate changes of all relevant types of microscopic gas transport in MMMs as a function of increasing MOF loading and the diffusion length scale. MOF surface functionalization will also be optimized with respect to enhancing the mechanical properties of the membranes. This project will lead to the development of fundamental chemical separations knowledge related to percolation theory in composites. If successful, this concept will enable pure MOF-like transport properties to be accessed in membranes without the requirement of forming pure MOF films. In this way, new performance limits may be achieved for MMMs, including percolated transport for MOFs that are not easily formed into crystalline films. As a design platform, this approach could be used to improve the productivity and efficiency of chemical separations for membranes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

轻气体如甲烷、乙烷和乙烯在工业应用中发挥着重要作用，包括用作气体和液体燃料以及用作聚合物制造的前体。对于这些需要工业气体分离过程的应用，通常需要获得高纯度气体。气体分离技术还需要降低大气中二氧化碳和其他温室气体的浓度。因此，开发低能耗和低成本的气体混合物分离技术对于满足工业需求、解决环境问题和提高生活水平至关重要。从混合物中分离气体分子需要材料（分子筛）含有尺寸均匀的孔，这些孔与待分离的小气体分子的大小相当。然而，合适的分子筛颗粒通常难以形成与工业应用或环境修复相关的尺度所需的几何形状。该项目将推进将分子筛颗粒形成连接良好的网络的基础科学，这将使大规模分离技术的发展成为可能。在网络中，颗粒将通过聚合物界面结合在一起，旨在最大限度地减少对颗粒筛分功能的不利影响，同时保持材料的结构完整性。这种网络的分离性能、气体输运特性和结构特性将在所有相关的长度尺度上进行量化。该项目的研究成果将为合理设计分子筛形态，优化分子筛结构以达到理想的气体分离效果奠定基础。调查人员还将启动一项新的研究指导计划，目的是教授和培训来自STEM中代表性不足群体的学生。将利用现有的机构项目，并强调使用在线工具来提高项目的有效性。金属有机骨架（MOFs）是一种高孔隙率的分子筛，在膜基气体分离中表现出非凡的性能。然而，这些材料不能轻易形成无缺陷的膜几何形状。因此，利用mof固有的传输优势进行膜分离是一项挑战。将MOF晶体与聚合物混合制备混合基质膜（MMMs）是一种众所周知的制备MOF基膜的方法。然而，MMMs的典型分离性能通常低于相应的mof，因为MMMs的输运性能受到聚合物相的不利影响，在某些情况下，受到mof -聚合物界面缺陷的影响。提高MMM性能的一个明确途径是增加MOF浓度，甚至达到一个渗透阈值，使扩散主要通过MOF相进行，即MMMs中的气体扩散可以主要通过相互连接的MOF晶体进行。研究人员将开发MOF聚合物MMMs的MOF相中气体传输的渗透阈值的基础科学，以实现与纯MOF膜相当的分离性能。膜制造策略将基于MOF晶体外表面的新功能化，结合对膜内气体传输的基本理解的发展。先进的核磁共振将用于研究mmmm中所有相关类型的微观气体输运随MOF载荷和扩散长度尺度的变化。MOF表面功能化也将得到优化，以提高膜的机械性能。该项目将导致与复合材料渗透理论相关的基础化学分离知识的发展。如果成功，这一概念将使在不需要形成纯MOF薄膜的情况下，在膜中获得纯MOF类输运特性。通过这种方式，可以实现mm的新性能限制，包括不易形成结晶膜的mof的渗透传输。作为一个设计平台，该方法可用于提高膜化学分离的生产率和效率。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。