Highly permeable polyethersulfone substrates with bicontinuous structure for composite membranes in CO2/N2 separation

Abstract

Substrate morphology has a significant effect on the CO2 transport performance of a thin-film composite (TFC) membrane. In this study, a new mixed solvent comprising 2-pyrrolidone (2-PD) and 2-methoxyethanol (2-ME) was used to prepare polyethersulfone (PES) substrates with bicontinuous structure by water vapor-induced phase separation, followed by immersion in water as nonsolvent. Compared with the commonly used solvent, N-methyl-2-pyrrolidone (NMP), the 2-PD/2-ME mixed solvent is more hydrophilic and can decrease the thermodynamic stability of the casting solution significantly. As a result, the phase separation was induced via the spinodal decomposition mechanism. The open morphology bestowed the optimized substrate with a very high CO2 permeance of 133,226 ± 3870 GPU (1 GPU = 10–6 cm3(STP) s–1 cm–2 cmHg–1 = 3.3464 × 10-9 kg-mol s–1 m–2 Pa–1), which was 5 times more permeable than the baseline substrate synthesized with NMP. By using this new substrate, the prepared TFC membrane containing amines showed an increased CO2 permeance of 908 ± 8 GPU at 57 °C, which was 48 GPU higher than that with the baseline substrate. Meanwhile, the CO2/N2 selectivity was retained at 162 ± 4 at 57 °C. In addition, the good scalability of the new PES substrate was demonstrated by roll-to-roll fabrication of a 50′ long scale-up PES substrate with a width of 21ʺ.