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 CO2/CH4 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 NH2-MIL-53(Al)/ZIF-8 (1:1 ratio). The CO2/CH4 selectivity increased significantly from 23 to 40 from pure PSF to the 16 wt.-% MIL-101(Cr)/ZIF-8 membrane. Separation of CO2/CH4 is relevant for purification (sweetening) of natural gas (CH4 as main component) which is soured with up to over 40 % CO2 and N-2 and only useable at low CO2 concentrations.