Facile suppression of intensified plasticization in glassy polymer thin films towards scalable composite membranes for propylene/propane separation

Membrane-based propylene/propane (C₃H₆/C₃H₈) separation has the potential to significantly reduce the extremely high energy consumption in the conventional distillation process. However, no large-scale commercialization case currently exists despite decades of remarkable advancements in membrane materials. This challenge can potentially be attributed to a lack of understanding of the close relationship between material properties and membrane configurations, including confinement-driven transitions in polymer dynamics from the bulk to thin films (<1 μm). We first report design aspects of thin-film composite (TFC) membranes for C₃H₆/C₃H₈ separation based on a cost-effective, versatile, and scalable fabrication method. An unprecedented acceleration in C3 hydrocarbon-induced plasticization is observed in TFC membranes as the selective layer thickness decreases, causing anomalous gas transport properties and poor mixed-gas selectivities, which deviate from those of bulk membranes. To overcome this issue, a plasticization resistant (PR) layer is additionally coated onto the TFC membranes. Advanced thin-film characterization techniques, including quartz crystal microbalance (QCM) and nanomechanical analyses, demonstrate effective suppression of intensified plasticization in glassy polymer thin films by introducing a PR layer. Ultimately, the PR layer-coated TFC membranes exhibited excellent mixed-gas C₃H₆/C₃H₈ separation performances close to industrial requirements, which can be further extended to prepare large-area TFC membranes by roll-to-roll processes.