Defect-Healing Strategy via PDMS Modification for Enhancing CO ₂ /CH ₄ Separation Performance and Humidity Resistance in SSZ-13 Membranes

Zeolite SSZ-13 membranes have emerged as highly promising candidates for the separation of CO2/CH4 mixtures due to their intrinsic molecular sieving properties. Nevertheless, the formation of nonzeolitic defects during hydrothermal synthesis and postcalcination remains a significant obstacle, compromising membrane selectivity and long-term stability. In this study, a facile and effective surface modification strategy was employed utilizing hydrophobic polydimethylsiloxane (PDMS) as a defect-healing agent to enhance both separation performance and moisture resistance of SSZ-13 membranes. The influence of PDMS concentration on defect mitigation was systematically investigated. Single-gas permeation measurements (H2, CO2, N2, CH4, and SF6) demonstrated that PDMS effectively sealed nonselective defects, thereby restoring the molecular sieving behavior. Optimal performance was achieved at a PDMS concentration of 10 wt %, resulting in a 28-fold enhancement in ideal CO2/CH4 selectivity and only 44.8% reduction in CO2 permeance at 1.2 MPa and 298 K. Moreover, surface hydrophobicity was significantly enhanced, as evidenced by an increase in water contact angle, attributed to the strong adhesion of long-chain alkyl groups in PDMS to the membrane surface. As a result, under humid conditions, the CO2/CH4 selectivity of the PDMS-modified membrane increased by 68.9% compared to that in dry conditions, whereas the unmodified membrane exhibited a 90.5% decline. Long-term operational stability tests confirmed the robust performance of the modified membrane in humid environments at high pressure and room temperature. These results demonstrate the potential of PDMS surface modification as a scalable and effective approach to enhance the defect tolerance and humidity resistance of SSZ-13 membranes for industrial CO2/CH4 separation applications.