High performance PIM-1/Matrimid hollow fiber membranes for CO₂/CH₄, O₂/N₂ and CO₂/N₂ separation

Polymers of intrinsic microporosity (PIM-1) have received worldwide attention but most PIM-1 researches have been conducted on dense flat membranes. For the first time, we have fabricated PIM-1/Matrimid membranes in a useful form of hollow fibers with synergistic separation performance. The newly developed hollow fibers comprising 5-15wt% of highly permeable PIM-1 not only possess much higher gas-pair selectivity than PIM-1 but also have much greater permeance than pure Matrimid fibers. Data from positron annihilation lifetime spectroscopy (PALS), field emission scanning electron microscopy (FESEM) and apparent dense layer thickness indicate that the blend membranes have an ultrathin dense layer thickness of less than 70nm. PIM-1 and Matrimid are partially miscible. The effect of partial miscibility on dense selective layer was studied. Defect-free hollow fibers with gas pair selectivity more than 90% of the intrinsic value can be spun directly from dopes containing 5wt% PIM-1 with proper spinning conditions, while post annealing and additional silicone rubber coating are needed for membranes containing 10 and 15wt% PIM-1, respectively. Comparing to Matrimid, the CO₂ permeance of as-spun fibers containing 5 and 10wt% PIM-1 increases 78% and 146%, respectively (e.g., from original 86.3GPU (1GPU=1×10^-6cm³ (STP)/cm²scmHg=7.5005×10^-12ms^-1Pa^-1) to 153.4GPU and 212.4GPU) without compromising CO₂/CH₄ selectivity. The CO₂ permeance of the fiber containing 15wt% PIM-1 improves to 243.2GPU with a CO₂/CH₄ selectivity of 34.3 after silicon rubber coating. Under mixed gas tests of 50/50 CO₂/CH₄, this fiber shows a CO₂ permeance of 188.9GPU and a CO₂/CH₄ selectivity of 28.8. The same fiber also has an impressive O₂ permeance of 3.5 folds higher than the pristine Matrimid (e.g., from original 16.9GPU to 59.9GPU) with an O₂/N₂ selectivity of 6.1. The newly developed membranes may have great potential to be used for natural gas purification, air separation and CO₂ capture.