(643d) Innovative Manufacturing of Porous Oxide Hollow Fiber Membranes

Inorganic membranes (e.g., zeolite, ultramicroporous silica, ion-transport perovskite) can outperform polymer membranes by providing high productivity, high selectivity, and excellent thermal and chemical stability. Inorganic membranes often rely on porous oxide hollow fibers as substrates, which are traditionally manufactured by high-temperature methods. For example, the phase inversion-sintering method is based on sintering of polymer hollow fibers consisting of preformed nonporous alumina particles at 1500 °C. These high-temperature manufacturing processes are expensive and have limited inorganic membranes to a few niche applications.

In this talk, we will present innovative manufacturing of porous oxide hollow fiber membranes via petrification of polymer hollow fiber templates.¹ This novel petrification method represents a breakthrough in inorganic membrane manufacturing and consists of three simple steps of (1) silane soaking, (2) moisture exposure, and (3) air heating. The method allows formation of porous oxide hollow fiber membranes, which we name “petrified hollow fiber membranes”, at temperatures far below the traditional phase inversion-sintering method. The lower temperature reduces the manufacturing cost of inorganic membranes, thereby potentially broadening the scope of their applications.

These petrified hollow fiber membranes have a unique hierarchical micro-/meso-/macroporous structure, giving both high surface area (650 m²/g) and large pore volume (2.5 cm³/g). Interestingly, like petrified wood reproduces the geometry and cell structure of wood, petrified hollow fiber membranes reproduce the hollow fiber geometry and asymmetric macropore structure of polymer hollow fiber templates. Their asymmetric macropore structure allows the petrified hollow fiber membranes to efficiently reject macromolecular solutes (e.g., protein) in cross-flow filtration tests. They are also highly gas permeable (helium permeance ~30,000 GPU), and therefore are potentially suitable as substrates of inorganic membranes for gas and vapor separations.

References:

¹Liu, L.; Ku, C.-E.; Zhang, C., Petrified Hollow Fiber Membranes with Hierarchical Pores. ACS Materials Letters 2022, 938-943.