Hierarchical MFI Zeolite Membranes for Superior Xylene Separation

The separation of p-xylene from its xylene isomers (o-xylene, m-xylene) is a significant concern in the petrochemical industry. MFI zeolite membranes offer great potential for energy-efficient and high-selective xylene separation. Synthesizing ultrathin (< 1 µm) MFI zeolite membrane for high-flux separation is highly desired but remains challenging. Herein, a novel and facile strategy for synthesizing hierarchical MFI zeolite membranes on ceramic hollow fibers from multi-dimensionally assembled (2D@0D) seed layers is demonstrated. Owing to the rapid growth of 0D MFI seeds and the voids-preserved growth of stacked 2D MFI seeds, the hierarchical MFI membrane synthesized for 2 h yielded an ultrathin skin layer (≈255 nm thick) and many macro-voids within the sublayer (void fraction: 14.86%), which facilitated molecular permeation and simultaneously maintained high separation selectivity of zeolitic pores. The membrane exhibited over sevenfold higher p-xylene permeance (2.81 × 10⁻⁷ mol m⁻² s⁻¹ Pa⁻¹) and over threefold improved p-/o-xylene separation factor (1228) than the conventional MFI membrane.