Table 1. General preparation conditions, microstructure parameters and permeance of AAO membranes.

Sample code	AAO-25	AAO-40	AAO-60	AAO-100	AAO-120
Electrolyte for anodization	0.3 M H2SO4	0.3 M H2C2O4
Anodization voltage, V	25 (2 step)	40 (2 step)	60 (1 step)	100 (1 step)	120 (1 step)
Pore diameter, nm	21 ± 4	35 ± 4	49 ± 4	67 ± 10	82 ± 10
Average interpore distance, nm	55	104	145	216	265
Porosity, %	13.2	10.3	10.4	8.7	8.7
Gas	Permeance ∙ 103, L ∙ m−2 bar−1 ∙ h−1
CH4	14 ± 1	27 ± 3	32 ± 4	44 ± 3	48 ± 5
N2	13 ± 1	22 ± 3	25 ± 2	30 ± 2	38 ± 2
O2	11 ± 1	20 ± 2	23 ± 2	28 ± 3	33 ± 3
CO2	10 ± 1	18 ± 1	20 ± 1	25 ± 1	28 ± 2
C4H10	8.7 ± 0.5	17 ± 2	15 ± 1	24 ± 1	26 ± 1