Influence of NIPS on the structure and gas separation performance of asymmetric carbon molecular sieve membranes

摘要

Abstract Asymmetric carbon molecular sieve (ACMS) membranes derived from PMDA-ODA polyimide were prepared via nonsolvent-induced phase separation (NIPS) and carbonization. The effects of NIPS parameters on the asymmetric structure and gas separation performance of ACMS membranes and evolution of the asymmetric structure and microstructure during carbonization were investigated systematically with scanning electron microscopy (SEM), X-ray diffraction (XRD), positron annihilation lifetime spectroscopy (PALS) and gas permeation tests. The parameters of the NIPS process significantly influenced the asymmetric structure and gas separation performance of ACMS membranes. The asymmetric structure of ACMS membrane was inherited from the polymeric membrane and could be tuned with parameters of the NIPS process. During carbonization, the pore and carbon structures of the ACMS membrane were well developed and were further regulated with the carbonization temperature and holding time. A dense top layer and more ultramicropores in the ACMS membrane enhanced the gas selectivity, and an abundance of micropores increased the gas permeance. The ACMS membrane prepared under optimized conditions exhibited a high O2 permeance of 49.3 GPU with a reasonable O2/N2 selectivity of 4.5, which showed good O2/N2 permeation property.