Development and investigation of a multilayer PDMS/zeolite composite membrane for CO2 separation applications

This work aims to investigate and develop a concept for CO2 separation based on PDMS/SSZ-13 (high-Si CHA) composite membranes. Firstly, an Al2O3 support was coated with SSZ-13 zeolite layer, then to increase the performance of the membrane, a Polydimethylsiloxane layer was effectively deposited homogeneously to cover the cracks and defects of the zeolite layer. The results of single gas permeation measurements displayed a notable increase in ideal CO2/CH4 selectivity up to 428 at the lowest PDMS concentration of 0.5 vol%. Moreover, a coating time of 10 min preserved CO2 permeance while increasing CO2/CH4 selectivity from 5 to 120. A twentyfold increase in CO2/CH4 selectivity was noted with mixed gas permeation without a reduction in CO2 permeance. Quantitative and qualitative microscopic analyses were also carried out on the coated membrane to better understand its morphology and microstructure. The outcomes indicated that PDMS layer decreased the permeation of N2 and CH4 and enhanced surface affinity toward CO2, resulting in reduced defects in the zeolite membranes and enhanced selectivity for CO2/N2 and CO2/CH4.