Thermally rearranged poly(benzoxazole-co-imide) hollow fiber membranes for CO2 capture

• The addition of PEG 200 and propionic acid improved gas permeation performance.
• Major hollow fiber spinning conditions were optimized.
• A high CO2 permeance of 560 GPU and ideal CO2/N2 selectivity of 16.8 were achieved.
• A lab-scale module was prepared and examined with mixed-gas.

Thermally rearranged poly(benzoxazole-co-imide) (TR-PBOI) hollow fiber membranes were fabricated from a hydroxyl polyimide-co-polyimide (HD5) precursor containing equal molar amounts of non-TR-able DAM and TR-able HAB. A wide variety of spinning conditions were optimized in order to improve the gas permeation properties. A high bore flow rate (DI water) led to lowered gas permeation properties due to the generation of a dense, thick skin layer. The shear rate contributed significantly to manipulate the polymer chain packing density during spinning, therefore, CO2 permeance was critically enhanced in low shear rate. The addition of co-solvent (propionic acid) and pore forming agent (PEG 200) was shown to improve the gas permeation properties. The TR-PBOI hollow fiber membrane fabricated under optimal spinning conditions exhibited an excellent CO2 permeance of 560 GPU and CO2/N2 ideal selectivity of 16.8. A TR-PBOI hollow fiber module was successfully fabricated with an effective area of 106 cm2 for the mixed-gas permeation tests with a ternary gas mixture containing 14% CO2, 6% O2, and 80% N2. The results showed a permeate CO2 concentration around 50% and CO2 permeance of 400 GPU at a pressure ratio of 10.

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