Carbon molecular sieve/ZSM-5 mixed matrix membranes with enhanced gas separation performance and the performance recovery of the aging membranes

Abstract

Carbon molecular sieve (CMS)/ZSM-5 mixed matrix membranes (MMMs) were prepared by pyrolysis of PMDA-ODA polyimide/ZSM-5 precursors. The morphology and structure of the CMS/ZSM-5 MMMs were investigated by scanning electron microscope (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM). The results indicated that ZSM-5 particles were well dispersed in the carbon matrix and maintained their microstructure during pyrolysis. The gas separation performance of the CMS/ZSM-5 MMMs was evaluated using single gases (H2, CO2, O2, N2, CH4) and mixed gases (21/79 mol.% O2/N2 and 50/50 mol.% CO2/H2). Compared with pure CMS membranes, the CMS/ZSM-5 MMMs exhibited outstanding permeability without significantly sacrificing selectivity. The gas permeabilities of the CMS/ZSM-5 MMMs increased with the increase of ZSM-5 loading and decreased with the increase of pyrolysis temperature. The aging of the CMS/ZSM-5 MMMs in a humid environment was also investigated. After simple thermal treatment, the pure gas permeabilities of the aging membrane were recovered to 39% (CH4), 66% (N2), 74% (H2), 77% (O2) and 83% (CO2) of the non-aging membrane, respectively, and the mixed gas permeabilities of the aging membrane were recovered to 63% (N2), 70% (O2), 82% (CO2) and 90% (H2) of the non-aging membrane, respectively.