Gas Permeation Property of 6FDA-mPDA and Its Asymmetric Hollow Fiber Membranes

2,2′-Bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)-1,3-phenylenediamine(mPDA) polyimide was synthesized by chemical imidization in a two-step procedure.The density of the polymer dense membrane,the fractional free volume and the glass transition temperature were measured.The ultra-thin hollow fiber membranes with a dense skin were fabricated with different air gap.The hollow fiber membranes have an O2 permeance of 19.10 GPU and a CO2 permeance of 106.34 GPU with the O2/N2 selectivity of 5.99 and the CO2/CH4 selectivity of 82.00 at 25 ℃,0.5 MPa.The calculated thickness of the dense skin based on O2 permeance is 96 nm.The temperature effect on the gas separation performance was investigated.The permeances of the O2,N2,CH4 and CO2 increase with an increase in temperature,while the selectivities of O2/N2 and CO2/CH4 decrease.The physical aging phenomenon of the asymmetric hollow fiber membranes spun with different air gap distances was investigated.The results show the permeance of the ultra-thin membranes sharply decreases and the selectivity increases.And the thickness of the dense skin affected the aging behavior.