A Sacrificial Seed Layer Strategy for Hierarchical MFI Zeolite Membranes With Enhanced Butane Isomer Separation...

Zeolite membranes hold significant promise for industrially relevant gas separations; however, balancing high permeance and selectivity remains a persistent challenge. Although thinning the selective layer improves permeance, achieving precise fabrication remains a major bottleneck. Herein, we demonstrate a sacrificial seed layer strategy enabling the fabrication of hierarchical MFI zeolite membranes (HMFI) on commercial α-Al₂O₃ tubes. Through precise modulation of synergistic ionic interactions within the synthetic gel and the nutrient supply rate during crystallization, the seed layer functions as both a porogen to generate a macroporous sublayer and a "fertilizer" to promote surface gel crystallization, forming a dense top layer. The resulting HMFI membrane delivers more than a fourfold enhancement in the ideal selectivity of n-butane and isobutane (n-/i-butane), accompanied by a 37% rise in n-butane permeance compared with conventional MFI membranes. Moreover, with a 10/90 n-/i-butane mixture, it exhibits an excellent separation factor of 158, along with a high n-butane permeance (188 × 10^-9 mol m^-2 s^-1 Pa^-1), representing the highest performance for reported membranes on tubular supports. The strategy not only enables a novel route to high-performance membranes, but also enriches the conceptual framework of the conventional secondary growth protocol, offering new avenues for microstructural engineering.