Impact of Humidity on the CO2/N2 Separation Performance of Pebax-MOF Mixed Matrix Membranes

Postcombustion capture has been an important field for CO2 capture, but its high H2O content has been a significant barrier to the performance of mixed matrix membranes (MMMs). In this study, a series of humidity values were established, and two types of MOFs (SUM-1 and SUM-9) were used in Pebax 2533 (poly(ether-block-amide)) to prepare MMMs to explore CO2/N-2 separation performance. At 35 degrees C and 2 bar, the CO2 permeability of Pebax-SUM-1 was 380.9, 433.1, 405.4, and 401.7 Barrer, respectively, when the relative humidity (RH) changed from 0, 30, 60, to 100%, and the CO2/N-2 selectivity was 20.5, 19.0, 18.1, and 17.0, respectively. The CO2 permeability of Pebax-SUM-9 was 390.9, 387.4, 412.5, and 452.4 Barrer, with the CO2/N-2 selectivities being 18.5, 19.9, 20.0, and 19.7, respectively. The CO2/N-2 selectivity had no significant fluctuations. A hypothesis has been proposed that the large-pore MOFs could only provide transport channels and could not screen CO2, and the CO2/N-2 selectivity would mainly be provided by the polymer matrix. Under high humidity conditions, the CO2 transport channels with large-pore MOFs might fail due to competition between H2O and CO2. This study investigated the influence of a series of RH on MMMs separation performance. The proposed theory suggests that there might be an optimal humidity range for the CO2 permeability of MMMs in humid conditions, which can be useful to guide the design of porous fillers for future MMMs development.