Template-Free Synthesis of Oriented Zeolite Membranes with Improved High-Activity Molecular Separation Characteristics

MFI型沸石膜是具有分子筛筛选能力的最稳定的微孔材料之一。在中空纤维载体上的高性能MFI沸石膜将通过显著提高纯度、提高通量并最大限度地降低资本和运营成本，为化工和石油工业开发新的、更有效的分离技术。由于MFI沸石晶体的独特孔结构，b取向的MFI沸石膜提供比随机取向的多晶MFI沸石膜更好的分子筛分离特性。这些性质使得b取向的MFI沸石膜对于包括二甲苯异构体分离的工业应用具有高度吸引力。然而，高质量的b-取向的MFI沸石膜已经通过包括使用昂贵的有机模板的复杂合成方法仅在盘支撑体上制造。这种模板化的MFI沸石膜还表现出分离性能的不利的压力依赖性，其特征在于随着进料二甲苯蒸气压的增加，渗透性和选择性降低。必须解决几个挑战，以进一步推进b-取向的MFI沸石膜的合成超过实验室规模。这些挑战包括在载体上合成高质量的b-取向MFI沸石膜，其可以通过具有成本效益和可扩展的方法布置成具有高填充密度的模块，以及理解在高蒸气压下与进料混合物接触的b-取向MFI沸石膜的分离特性。因此，本项目将开发在中空纤维载体上简便合成高质量b-取向MFI沸石膜的方法，并研究这种生长的b-取向MFI沸石膜的合成-结构-分离性能关系，用于在高蒸气压下分离二甲苯异构体。通过本项目开发的知识将可转化为其他取向的结晶微孔膜用于其他分离过程。除了研究生培训机会，该项目的更广泛影响包括旨在展示无机膜如何工作的公众宣传活动。该项目将重点关注通过可扩展的无模板合成方法在氧化铝中空纤维支撑物上合成b-取向MFI沸石膜。该方法将由使用2维MFI沸石纳米片的过滤“接种”，然后无模板二次生长组成。通过过滤使用二维MFI沸石纳米片制备沸石层提供了一种通用的和可扩展的制造方法，从而产生用于二次生长的高质量b-取向的MFI沸石晶种层。MFI沸石晶种层将优先生长成具有优化组成的无模板合成溶液的b-取向MFI沸石膜。无模板溶液的使用通过最小化或消除允许气体或液体混合物的非选择性扩散的晶间间隙而产生更高质量的沸石膜。它还减少了合成步骤的数量，并消除了昂贵的有机模板的使用。合成的模板剂和无模板剂，随机和b-取向的MFI沸石膜，使系统的研究的MFI沸石膜的合成-结构-分离性能的关系。特别是，该研究将集中在理解晶体形状/取向，晶间微观结构，和沸石骨架组合物上的进料压力依赖性的二甲苯渗透性和MFI沸石膜的选择性的影响。这项工作还将确定合成高性能b-取向MFI沸石膜的条件，以便在工业相关条件下有效分离二甲苯混合物。该奖项反映了NSF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。

MFI-type zeolite membranes are among the most stable microporous materials with molecular sieving capabilities. High-performing MFI zeolite membranes on hollow fiber supports will enable development of new and more efficient separation technologies for the chemical and petroleum industries by significantly improving purity, heightening flux, and minimizing capital and operating costs. Due to the unique pore structure of MFI zeolite crystals, b-oriented MFI zeolite membranes offer better molecular sieving separation characteristics than randomly oriented polycrystalline MFI zeolite membranes. These properties make b-oriented MFI zeolite membranes highly attractive for industrial applications including separation of xylene isomers. However, high quality b-oriented MFI zeolite membranes have been fabricated only on disk supports by complex synthesis methods that include the use of costly organic-templates. Such templated MFI zeolite membranes also exhibit unfavorable pressure dependence of separation properties, characterized by a decrease of permeability and selectivity with increasing feed xylene vapor pressure. Several challenges must be addressed to further advance the synthesis of b-oriented MFI zeolite membranes beyond the laboratory scale. These challenges include synthesis of high-quality b-oriented MFI zeolite membrane on supports that can be arranged into modules with high packing density by cost-effective and scalable methods and understanding the separation characteristics of b-oriented MFI zeolite membranes in contact with feed mixtures at high vapor pressures. This project will therefore develop methods for facile syntheses of high-quality b-oriented MFI zeolite membranes on hollow fiber supports and study the synthesis-structure-separation property relationship of such grown b-oriented MFI zeolite membranes for use in the separation of xylene isomers at high vapor pressures. The knowledge developed through this project will be translatable to other-oriented crystalline microporous membranes for other separation processes. In addition to graduate student training opportunities, the broader impacts of the project include a public outreach activity aimed at demonstrating how inorganic membranes work.This project will focus on the synthesis of b-oriented MFI zeolite membranes on alumina hollow fiber supports by a scalable, template-free synthesis method. The method will consist of filtration “seeding” using 2-dimensional MFI zeolite nanosheets, followed by template-free secondary growth. Preparation of a zeolite layer using 2-dimensional MFI zeolite nanosheets by filtration offers a versatile and scalable method of fabrication leading to a high-quality b-oriented MFI zeolite seed layer for secondary growth. The MFI zeolite seed layer will be preferentially grown into a b-oriented MFI zeolite membrane with a template-free synthesis solution of optimized composition. The use of a template-free solution produces zeolite membranes of higher quality by minimizing or eliminating intercrystalline gaps that permit non-selective diffusion of gas or liquid mixtures. It also reduces the number of synthesis steps and eliminates the use of costly organic templates. Synthesis of templated and template-free, randomly and b-oriented MFI zeolite membranes enables a systematic study of the synthesis-structure-separation property relationship of the MFI zeolite membranes. In particular, the study will be focused on understanding the effects crystal shape/orientation, intercrystalline microstructure, and zeolite framework composition on the feed pressure dependence of xylene permeability and selectivity of MFI zeolite membranes. This work will also identify conditions for the synthesis of high-performance b-oriented MFI zeolite membranes for effective separation of xylene mixture under industrially relevant conditions.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.