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

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.