High-Performance FAU Zeolite Membranes Derived from Nano-Seeds for Gas Separation

In this study, high-performance FAU (NaY type) zeolite membranes were successfully synthesized using small-sized seeds of 50 nm, and their gas separation performance was systematically evaluated. Employing nano-sized NaY seeds and an ultra-dilute reaction solution with a molar composition of 80 Na₂O: 1Al₂O₃: 19 SiO₂: 5000H₂O, the effects of synthesis temperature, crystallization time, and porous support (α-Al₂O₃ or mullite) on the formation of FAU membranes were investigated. The results illustrated that further extending the crystallization time or increasing the synthesis temperature led to the formation of a NaP impurity phase on the FAU membrane layer. The most promising FAU membrane with a thickness of 2.7 µm was synthesized on an α-Al₂O₃ support at 368 K for 8 h and had good reproducibility. The H₂ permeance of the membrane was as high as 5.34 × 10⁻⁷ mol/(m² s Pa), and the H₂/C₃H₈ and H₂/i-C₄H₁₀ selectivities were 183 and 315, respectively. The C₃H₆/C₃H₈ selectivity of the membrane was as high as 46, with a remarkably high C₃H₆ permeance of 1.35 × 10⁻⁷ mol/(m² s Pa). The excellent separation performance of the membrane is mainly attributed to the thin, defect-free membrane layer and the relatively wide pore size (0.74 nm).