(462g) Continuous Zeolite MFI Membranes from 2D MFI Nanosheets on Ceramic Hollow Fibers: Fabrication Processes and Hydrocarbon Separation Properties

The advent of 2D zeolite nanosheet materials has created new possibilities of accelerating the large-scale application of zeolitic membranes. In this regard, an important issue is the development of economical and scalable membrane fabrication processes that incorporate 2D zeolite nanosheets into thin membranes with high flux and selectivity. Such processes should be amenable to the use of low-cost, scalable supports that do not require any specialty materials, surface modifications, or microstructural engineering. This talk will focus on the fabrication of thin (submicron), b-oriented, selective MFI-type zeolitic membranes on low-cost ceramic hollow fibers (< 800 micron diameter), starting from 2D MFI nanosheet materials. First, 2D MFI nanosheet coatings are prepared on α-alumina hollow fiber supports via application of vacuum filtration. As-prepared 2D MFI nanosheet coatings are uniform and preserve the desirable (0k0) out-of-plane orientation; under optimized conditions no significant voids (such as delaminated areas, or uncovered areas) are found via microscopy. However, this 2D MFI coating contains uncovered regions between the stacked nanosheets where gas molecules can freely diffuse, which must be selectively filled to render the film capable of molecular sieving, while preserving the out-of-plane orientation of the molecular sieving channels. This is achieved by two-step hydrothermal treatments; the first involving a tetrapropylammonium fluoride (TPAF) structure-directing agent, and the second involving a tetraethylammonium hydroxide (TEAOH) structure directing agent. The two-step hydrothermal treatments with an appropriate choice of structure directing agents are effective in improving adhesion of the membrane on the support, closing macroscopic voids/nanoscale gaps between the 2D nanosheets, as well as highly suppressing the overgrowth/twinning of crystals and maintaining a high degree of out-of-plane b-orientation. This microstructurally optimized 2D MFI-based hollow fiber membranes are demonstrated to have excellent performance in a number of binary and multicomponent hydrocarbon separations, including for the separation of butane isomers and removal of natural gas liquid (NGL) components from methane. Overall, our findings have significant implications for utilizing zeolite nanosheets to accelerate scale-up and applications of thin and selective membranes.

Reference

B. Min, S. Yang, A. Korde, Y. H. Kwon, C. W. Jones, and S. Nair, “Continuous Zeolite MFI Membranes Fabricated from 2D MFI Nanosheets on Ceramic Hollow Fibers”, Angew. Chem. Int. Ed., 2019, Accepted