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

• PIM-1/Matrimid fibers have an ultrathin dense layer thickness of less than 70 nm.
• Defect-free hollow fibers can be spun from dopes containing 5 wt% PIM-1.
• CO2 permeance of fibers containing 5 and 10 wt% PIM-1 increases 78% and 146%.
• Fiber containing 15 wt% PIM-1 has a CO2/CH4 selectivity of 28.8 in binary gas test.

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 5–15 wt% 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 70 nm. 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 5 wt% PIM-1 with proper spinning conditions, while post annealing and additional silicone rubber coating are needed for membranes containing 10 and 15 wt% PIM-1, respectively. Comparing to Matrimid, the CO2 permeance of as-spun fibers containing 5 and 10 wt% PIM-1 increases 78% and 146%, respectively (e.g., from original 86.3 GPU (1 GPU=1×10−6 cm3 (STP)/cm2 s cmHg=7.5005×10−12 m s−1 Pa−1) to 153.4 GPU and 212.4 GPU) without compromising CO2/CH4 selectivity. The CO2 permeance of the fiber containing 15 wt% PIM-1 improves to 243.2 GPU 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 188.9 GPU 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 16.9 GPU to 59.9 GPU) 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.

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