Gas separation and water desalination performance of defect-free interfacially polymerized para-linked polyamide thin-film composite membranes

Abstract

Abstract Introduction of interfacially polymerized (IP) polyamide thin-film composite (TFC) membranes in the 1980s revolutionized the reverse osmosis desalination industry. However, IP-derived TFCs have not achieved industrial success for gas separation applications due to the presence of membrane defects in their dry state. In this work, we report defect-free crosslinked polyamide thin-film composite membranes prepared from para-substituted aromatic and cycloaliphatic diamines, p-phenylenediamine (PPD) and piperazine (PIP), reacted with trimesoyl chloride (TMC). The key parameters in our modified IP process to mitigate defects are long reaction time (∼5\u202fmin) and high organic solution temperature (100\u202f°C). The gas separation and desalination properties of the para-linked polyamide membranes were compared to previously reported polyamide TFCs made from meta-phenylenediamine (MPD) and TMC. The gas- and water permeances of the TFCs increased in the order: MPD-TMC\u202f \u202fPPD-TMC\u202f≥\u202fPIP-TMC. Elimination of defects allowed exploitation of the ultra-selective nature of polyamide TFCs, specifically for hydrogen and helium separations. At 23\u202f°C, PIP-TMC, PPD-TMC and MPD-TMC exhibited H2/CH4 selectivities of 312, 362 and 1290, respectively, with moderate H2 permeances of 37.4, 32.6 and 25.8 GPU (1 GPU\u202f=\u202f10−6\u202fcm3(STP) cm−2 s−1 cmHg−1). Furthermore, the TFCs demonstrated excellent performance for H2/CO2 separation with pure-gas selectivities of 10-14\u202fat 23\u202f°C. The strong size-sieving capability of the polyamide TFCs originated from tight interchain packing induced by strong hydrogen bonding. Wide-angle X-ray diffraction confirmed a dominant fraction of submicropores of less than ∼4\u202fA within PPD-TMC and PIP-TMC polyamide networks.