Molecular-level mixed matrix membranes comprising Pebax® and POSS for hydrogen purification via preferential CO2 removal

The molecular-level mixed matrix membranes (MMMs) comprising Pebax® and POSS have been developed by tuning the membrane preparation process in this work. They exhibit a simultaneous enhancement in CO2 permeability and CO2/H2 selectivity by optimizing the POSS content at extremely low loadings. This is mainly attributed to the large cavity of POSS itself and its effect on the segmental-level polymeric chain packing. More interestingly, the Pebax®/POSS MMMs reveal a much higher separation performance in the mixed gas test than that in the pure gas test. The highest CO2/H2 selectivity reaches 52.3 accompanied by CO2 permeability of 136 Barrer at 8 atm and 35 °C. This is due to the CO2-induced plasticization that improves the free volume and polymer chain mobility, hence benefiting the interaction between the polymer matrix and penetrant CO2. These features may ensure the superiority of Pebax®/POSS molecular-level MMMs as CO2-selective membranes in the industrial application of hydrogen purification.