Increased Selectivity in CO₂/CH₄ Separation with Mixed‐Matrix Membranes of Polysulfone and Mixed‐MOFs MIL‐101(Cr) and ZIF‐8

Combination of two hydrothermally stable MOFs MIL‐101(Cr) and ZIF‐8 in a 1:1 ratio in a polysulfone (PSF) mixed‐matrix membrane (MMM) showed a significant higher selectivity in mixed‐gas CO 2 /CH 4 permeation tests for 16 wt.‐% MIL‐101(Cr)/ZIF‐8 compared to analogous single‐filler MMMs [MIL‐101(Cr) or ZIF‐8] or to the also tested combination NH 2 ‐MIL‐53(Al)/ZIF‐8 (1:1 ratio). The CO 2 /CH 4 selectivity increased significantly from 23 to 40 from pure PSF to the 16 wt.‐% MIL‐101(Cr)/ZIF‐8 membrane. Separation of CO 2 /CH 4 is relevant for purification (“sweetening”) of natural gas (CH 4 as main component) which is soured with up to over 40 % CO 2 and N 2 and only useable at low CO 2 concentrations.