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

分离化学性质相似的气体，如丙烯（一种烯烃）和丙烷（一种石蜡），是以石油为基础生产燃料和商品化学品的关键步骤。然而，分离具有相似分子大小和物理性质的气体是极具挑战性的，通常需要大量的能量消耗。使用膜（即分子过滤器）分离烯烃和石蜡是一种极具吸引力的节能替代方法。然而，由于目前的膜制造技术过于昂贵，目前还没有这种商业上可用的膜。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/石蜡气体的膜。经济高效地设计和生产能够高效分离烯烃/石蜡的膜的能力，有可能大大减少精炼过程中的能源消耗，从而减少碳排放。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方面的培训。每年夏天，研究者还将在实验室接待一名当地的高中教师，以便该地区的K-12学生可以间接从该项目中受益。演示相关项目内容的视频也将制作并发布在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来制备含有沸沸体-咪唑酸盐框架（ZIF）的混合基质中空纤维膜和模块，并为感兴趣的气体分离量身定制分子筛选特性。多晶ZIF-8膜已显示出对节能丙烯/丙烷分离的希望，但由于制备所需的复杂和缓慢的处理步骤，这种膜的商业应用成本过高。此外，晶体填充材料如ZIF-8和沸石的离散孔径不允许对选择性进行足够的控制。研究人员假设，采用聚合物修饰的原位金属有机骨架（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，可以制备具有亚微米厚选择性复合皮层的非对称混合基质中空纤维膜。第二个需要测试的相关假设是，这种膜的分子筛分性能可以通过设计带有多个连接体和/或金属中心的ZIF填料的结构来微调。三个目标将测试假设：(1)了解离子交换、离子扩散和反应过程如何塑造聚合物修饰的原位MOF形成过程，并制造具有亚微米厚选择性复合皮层的膜；(2)设计具有可调分子筛性能的膜及其组件的微观结构；(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/甲烷分离中的性能。该项目的结果将是开发高效气体分离膜的策略，克服现有聚合物基膜技术的许多局限性，以及基于mof的混合基质膜设计所需的基础知识。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。

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.