Pebax composite hollow fiber membranes by modulating PDMS surface hydrophilicity and coatability for CO2 capture

• The PES hollow fiber substrate has a dense outer surface and a porous inner surface by spinning optimization. • The PDMS gutter layer modified by argon plasma possesses desirable hydrophilicity to facilitate the Pebax coating. • A high-ethanol-to-water ratio in Pebax solutions enhances drying and reduces defects in the selective layer. • The Pebax/PDMS/PES composite hollow fiber membrane displays a superior CO 2 permeance and CO 2 /N 2 selectivity. • The Pebax/PDMS/PES hollow fiber membrane has stable mixed gas performance for CO 2 /N 2 separation in one month. Eco-friendly CO 2 capture technologies are essential to minimize global warming. In this study, the fundamentals of designing and fabricating composite hollow fiber membranes consisting of an inner polyethersulfone (PES) substrate, a polydimethylsiloxane (PDMS) gutter layer, and an outer Pebax selective layer were revealed for CO 2 /N 2 separation. The resultant Pebax/PDMS/PES composite hollow fiber membranes possess a CO 2 permeance of 1253 GPU and an ideal CO 2 /N 2 selectivity of 34.9 at 0.1 MPa and 25 °C. They have a comparable CO 2 /N 2 selectivity but a much higher CO 2 permeance of 1–2 times than other Pebax based composite hollow fiber membranes in literature. The much higher CO 2 permeance demonstrates the effectiveness of the proposed strategies to design multi-layer composite hollow fiber membranes for CO 2 capture. Two major challenges have been innovatively overcome when developing these composite membranes. Namely, the diminish of PDMS intrusion during its coating on PES substrates and the hydrophilization of inherently hydrophobic PDMS surfaces for the Pebax coating. The former was solved by optimizing the spinning conditions such as air gap distance, coagulation temperature, and bore fluid composition to design the substrates with a dense outer surface and a porous inner surface, thus minimizing PDMS intrusion and gas transport resistance. The latter was overcome using plasma to improve the wettability of PDMS surfaces. The optimal Pebax/PDMS/PES membranes also have stable mixed gas performance using an N 2 /CO 2 feed of 85/15 (mol/mol %) at 0.2 MPa and 25 °C over one month, achieving a CO 2 permeance of 829 GPU and a CO 2 /N 2 selectivity of 32.5.