Synthesis of Tubular Faujasite X-Type Membranes with Mullite Supports and their Gas Permeances for N2/CO2 Mixtures

Abstract

The present work reports the synthesis of tubular faujasite (FAU) X-type membranes with mullite supports for the permeation separation of N2/CO2. The external surfaces of mullite supports were modified and seeded with X-type zeolite crystals prior to film growth in synthesis solutions. We investigated the effects of synthesis conditions including the composition of synthesis solution and the process of hydrothermal treatment on the formation of FAU X-type membranes. We also characterized the membrane morphology and phases using scanning electron microscopy (SEM) and X-ray diffraction (XRD). In addition, we evaluated the permeation separation of N2/CO2 with the as-synthesized membranes. The results indicated that increasing aging time accelerated the crystal growth rate, but overlong aging time could cause the generation of P-type zeolite and thicker membrane layer. Prolonging crystallization time and raising temperature would increase the rate of crystal nucleation, but readily made trans-crystallization phenomena occur. The Na/Si ratio did not play a significant role in synthesizing FAU X-type membranes in the tested range. The as-synthesized zeolite membranes with higher ratio of Si/Al accompanied with the formation of P-type crystal and the particle size on the membrane surface obviously increased. The membrane with a smoother zeolite surface and a thinner top layer was obtained with increasing H2O content. For single-gas permeation, CO2 had a lower permeance than N2. For the gas mixtures of N2/CO2, the separation factor α of 7.89 was gained.