Remarkably enhanced gas separation properties of PIM-1 at sub-ambient temperatures

In-Situ Formation of Three-Dimensional Network Intrinsic Microporous Ladder Polymer Membranes with Ultra-High Gas Separation Performance and Anti-Trade-Off Effect

The global quest for clean energy and sustainable processes makes advanced membrane extremely attractive for energy-intensive industrial gas separations. Here, we disclose a series of ultra-high-performance gas separation membranes (PIM-3D-TB) from novel network polymers of intrinsic microporosity (PIM) that combine the advantages of solution processible PIM and small pore size distribution (PSD) of porous organic polymers (POP), which was synthesized by in situ copolymerization of triptycene-2,6-diamine as linear part and triptycene-2,6,13(14)-triamine (TTA) as crosslinker. The resulting PIM-3D-TB membranes demonstrated outstanding separation properties that outperformed the latest trade-off lines for H2/CH4 and O2/N2. They also showed an anti-trade-off effect by simultaneously enhancing gas permeability and gas-pair selectivity with increasing TTA content. The TTA crosslinking node increased the microporosity, and, shifted the PSD from the ultramicropore (<7 Å) toward the more size sieving submicropore (<4 Å) region. The post-treated TTA-75 displayed an exceptional H2 permeability of 8000 Barrer and H2/CH4 selectivity of 208. These PIM-3D-TB membranes and their design protocol have unparalleled potential in the next generation of membranes for hydrogen purification and air separations.

Effect of Temperature-Induced Aging on the Gas Permeation Behavior of Thin Film Composite Membranes of PIM-1 and Carboxylated PIM-1

Polymers of intrinsic microporosity (PIMs) are a class of promising gas separation materials due to their high membrane permeabilities and reasonable selectivities. When processed into thin film composite (TFC) membranes, their high gas throughput aligns closely with industrial requirements, but they are prone to physical aging and plasticization effects. TFC membranes based on the prototypical PIM-1 and its carboxylated derivative cPIM-1 exhibit temperature-dependent gas permeation behavior, which has not been extensively studied before. In single CO2 permeation tests, measurable physical aging occurred when the temperature was raised to 55 °C within a period of 90 min, and the aging rate accelerated as temperature was raised further. TFC membranes prepared from cPIM-1 exhibited a faster aging rate compared to PIM-1 at the same temperature. The decreased permeance could be at least partially recovered through a 5 day methanol vapor treatment. In mixed gas experiments, all membranes showed decreased permselectivities at elevated temperatures. The plasticization pressure of TFC membranes occurred at around 1 bar of CO2 partial pressure, independent of temperature. Significant plasticization was particularly evident for cPIM-1 TFC membranes under CO2/CH4 conditions with increasing temperature, which resulted in increased gas permeance for both components.

Impact of Sub-Ambient Temperature on Aging Rate and Gas Separation Properties of Polymers of Intrinsic Microporosity

Aging in polymers of intrinsic microporosity has slowed exploitation due to a decay in performance over time since densification makes them unsuitable for industrial applications. This work aimed to study the impact of the operation and storage temperature on the gas separation properties and aging rates of PIM-1 self-standing films. The permeability, diffusivity, and solubility of the tested membranes were monitored through permeation tests for pure carbon dioxide and nitrogen at a maximum upstream pressure of 1.3 bar for temperatures ranging from -20 °C to 25 °C. This study found significant benefits in the operation of glassy polymeric membranes at low temperatures, resulting in a favourable trade-off in separation performance and a reduction in the aging rate by three orders of magnitude. This brings new opportunities for the industrial application of PIMs in innovative carbon capture processes.