Significantly improved gas separation properties of sulfonated PIM-1 by direct sulfonation using SO3 solution

One of the biggest challenges in membrane-based gas separation application is how to obtain highly efficient membranes with both high permeability and selectivity. To achieve this target, we reported a novel simple method to modify polymer of intrinsic microporosity (PIM-1) membranes by direct sulfonation using sulfur trioxide (SO3)/dichloromethane solution to get a series of sulfonated PIM-1 (SPIM-1) membranes. The SO3H group was bonded to the main chain of the SPIM-1 and distributed homogeneously in the entire membrane that was confirmed by FTIR, XPS and SEM/EDS mapping. As the sulfonation time increased from 2 to 6 min, the concentration of sulfonic acid (SO3H) group in the repeat unit increased from 12.3% to 30.1%. The introduction of SO3H groups resulted in a decreased surface area and denser polymer chain packing. The resulting SPIM-1 membranes exhibited huge improved selectivity with separation performance much better than the pristine PIM-1. In which, the 6 min sulfonated PIM-1 membrane (SPIM-1-6) showed excellent gas separation properties with its performance approaches or even exceeds the latest trade-off curves for O2/N2, CO2/N2, H2/N2, and CO2/CH4. This is due to the SO3H group induced a compact packing of polymer main chain that remarkably enhanced the diffusion selectivity. The 60 days aged SPIM-1-6 demonstrated even higher gas pair selectivity, and the H2/N2 and O2/N2 selectivity reached as much as 125 and 8.43 coupled with H2 and O2 permeability of 1077 and 73.4 Barrer, respectively. Additionally, the SPIM-1-6 also showed excellent mixed-gas separation properties, with CO2/CH4 mixed-gas selectivity over 40 coupled with CO2 permeability of 296 Barrer even at the upstream pressure of 20 bar. These results suggested the great potential for this mild sulfonation method and sulfonated PIM-1 membranes in advanced membrane-based gas separation applications.