Enhancing the Stability of Ethanol/Water Separation in MFI Zeolite Membranes via PDMS Coating

Pure-silica MFI zeolite membranes hold significant potential for the separation of an ethanol-water solution. However, their inadequate hydrophobicity and susceptibility to formation for surface defects limit further enhancement of separation performance. More critically, the silanol groups Si-OH in the framework are prone to react with the solution, accelerating defect formation and leading to progressive performance degradation during operation, and the instability hinders their industrial applicability. This study innovatively employed PDMS for interfacial modification of the MFI zeolite membrane, fabricating novel MFI/PDMS composite membranes. The strategy effectively minimized contact and reactions between the ethanol-water solution and the surface for the zeolite membrane; thereby, the stability was enhanced. Through systematic characterization, the composite conditions for MFI/PDMS membrane were optimized, and the optimal composite membrane demonstrated a permeation flux of 0.47 kg·m⁻²·h⁻¹ and a separation factor of 50 for 5 wt % ethanol-water solution at 60 °C, with no performance degradation observed after 120 h of continuous operation. These results confirmed the exceptional stability of the MFI/PDMS composite membrane, and the proposed composite strategy offered a novel perspective for enhancing the stability of the zeolite membrane.