Innovative Strategies for Scalable Mixed-Matrix Hollow Fiber Membranes with Sub-micron thick Molecular-Sieve-Containing Composite Skin Layers for Tailorable Gas Separations

丙烯（一种烯烃）和丙烷（一种石蜡）等化学性质相似的气体的分离是以石油为基础生产燃料和日用化学品的关键步骤。然而，具有相似分子尺寸和物理性质的气体的分离极具挑战性，通常需要大量的能量消耗。膜的使用（即，分子过滤器）来分离烯烃和链烷烃是一种有吸引力的节能替代方案。然而，没有这样的市售膜，因为目前的膜制造技术过于昂贵。该项目的目标是开发一种可扩展的、具有成本效益的工艺，用于生产能够分离烯烃/烷烃气体的膜。具有成本效益地设计和生产能够高性能烯烃/链烷烃分离的膜的能力具有大幅减少精炼过程中的能源使用并随后减少碳排放的潜力。研究生和本科生研究人员将直接参与项目的完成，接受化学合成，材料表征方法和专业技能的培训。研究人员还将在实验室每年夏天举办一个当地的高中教师，使该地区的K-12学生可以间接受益于该项目。展示相关项目内容的视频也将被制作并发布在YouTube上，作为公众和K-12教育工作者的资源。该项目的总体目标是开发可扩展的方法，用于制备含沸石-咪唑酯骨架（ZIF）的混合基质中空纤维膜和模块，并定制用于感兴趣的气体分离的分子筛性能。多晶ZIF-8膜已经显示出用于节能的丙烯/丙烷分离的前景，但是考虑到制备所需的复杂和缓慢的加工步骤，这种膜的商业应用过于昂贵。此外，结晶填料材料如ZIF-8和沸石的离散孔不允许对选择性的充分控制。研究人员假设，可以通过使用聚合物改性使能的原位金属有机框架（MOF）形成技术将中空纤维纺丝过程与混合基质形成过程解耦来制备具有亚微米厚的选择性复合材料皮层的不对称混合基质中空纤维膜。待测试的第二个相关假设是，这种膜的分子筛性质可以通过工程化具有多个连接体和/或金属中心的ZIF填料的结构来微调。本论文的研究目标有三：（1）了解离子交换、离子扩散和反应过程如何影响聚合物改性的原位MOF形成过程，并制备具有亚微米厚选择性复合表层的膜;（2）设计具有可调分子筛性能的膜及其模块的微观结构;和（3）在工业相关条件下测试膜和组件在丙烯/丙烷、乙烯/乙烷和氮气/甲烷分离中的性能。该项目的成果将是一个战略，以开发有效的气体分离膜，克服了现有的聚合物为基础的膜技术的许多限制和随之而来的基础知识，为基于MOF的混合基质膜设计所必需的。这一奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的知识价值和更广泛的影响审查标准的支持。

The separation of chemically similar gases such as propylene (an olefin) and propane (a paraffin) is a key step in the petroleum-based production of fuels and commodity chemicals. However, the separation of gases with similar molecular sizes and physical properties is extremely challenging, often requiring extensive energy consumption. The use of membranes (i.e., molecular filters) to separate olefins and paraffins is an appealing energy-efficient alternative. However, there are no such commercially available membranes because current membrane manufacturing technologies are prohibitively expensive. The goal of this project is to develop a scalable, cost-effective process for producing membranes capable of olefin/paraffin gas separation. The ability to cost-effectively design and produce membranes capable of high-performance olefin/paraffin separation has the potential to substantially reduce energy usage in refining processes and, subsequently, reduce carbon emissions. Graduate and undergraduate student researchers will be directly engaged in completion of the project, receiving training in chemical synthesis, material characterization methods, and professional skills. The investigator will also host a local high school teacher in the lab each summer so that area K-12 students may indirectly benefit from the project. Videos demonstrating related project content will also be developed and published on YouTube as resources for the public and K-12 educators. The overall goals of this project are to develop scalable approaches for the preparation of zeolitic-imidazolate framework (ZIF)-containing mixed-matrix hollow fiber membranes and modules and to tailor the molecular sieving properties for gas separations of interest. Polycrystalline ZIF-8 membranes have shown promise for energy-efficient propylene/propane separation, but commercial application of such membranes is prohibitively expensive given the complex and slow processing steps required for preparation. Moreover, the discrete apertures of crystalline filler materials like ZIF-8 and zeolites does not allow for sufficient control over selectivity. The investigator hypothesizes that asymmetric mixed-matrix hollow fiber membranes with sub-micron thick selective composite skin layers can be prepared by decoupling the hollow-fiber spinning process from the mixed-matrix formation process using a polymer-modification-enabled in situ metal-organic framework (MOF) formation technique. A second, related hypothesis to be tested is that the molecular sieving properties of such a membrane can be fine-tuned by engineering the structures of the ZIF fillers with multiple linkers and/or metal centers. Three objectives will test the hypotheses: (1) understand how ion-exchange, ion-diffusion, and reaction processes shape the polymer-modification-enabled in situ MOF formation process and fabricate membranes with sub-micron thick selective composite skin layers; (2) engineer the microstructure of the membranes and their modules with tunable molecular sieving properties; and (3) test the performance of the membrane and modules in propylene/propane, ethylene/ethane, and nitrogen/methane separations under industrially-relevant conditions. The outcome of the project will be a strategy to develop efficient gas separation membranes that overcomes many of the limitations of existing polymer-based membrane technologies and the attendant fundamental knowledge necessary for MOF-based mixed-matrix membrane design.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.