2.5. Experimental Method

A custom-made gas permeation device was utilized to test the permeation properties of the membrane, and the details of the gas permeability testing device were the same as reported in the literature [26]. The membrane was sealed into the membrane cell, and the downstream of the membrane was evacuated for 12 h to eliminate all gas in the membrane, and then the upstream and downstream of the system were evacuated. The tested gas was fed into upstream and permeated through the membrane to downstream. The downstream gas pressure was measured by a vacuum flowmeter. In detail, the permeability (P) and the ideal gas selectivity (aA/B) could be calculated according to the following equations [26]:

where P is the permeability (barrer), V_d is the calibrated permeate volume (cm³), l is the membrane thickness (cm), p_up represents the upstream pressure (cmHg), A and T denote the effective membrane area (cm²) and the operating temperature (308 K), R is the gas constant (0.278 cm³ cm Hg cm⁻³ (STP) K⁻¹) and dp/dt is the steady-state downstream pressure increase (cm Hg s⁻¹).

where P_A and P_B represent permeability of gases A and B, respectively.