Benzyl-Induced Crosslinking of Polymer Membranes for Highly Selective CO2/CH4 Separation with Enhanced Stability

Tröger's Base Polyimide Membranes with Enhanced Mechanical Robustness for Gas Separation

The rigid V-shaped Tröger's base (TB) unit has been proven efficacious in creating microporosity, making TB-based polyimides (PIs) exhibiting significant advantages in simultaneously increasing gas permeability and selectivity for the separation industry. However, TB-based PIs commonly display undesired mechanical performance due to the low molecular weight resulting from the evident steric hindrance and low reactivity of TB-containing diamines. Herein, a novel diamine-containing bisimide linkage (BIDA) has been synthesized and then polymerized with paraformaldehyde via a moderate "TB polymerization" strategy to furnish polymers simultaneously, including imide linkages and TB units in the polymer main chains, namely, TB-PIs. This TB polymerization strategy avoids the direct polymerization of dianhydride with low-reactivity TB diamine. After incorporating a meta-methyl substituent into BIDA diamine, the m-MBIDA diamine-derived m-MTBPI ultimately exhibits a high molecular weight, good tensile strength (90.4 MPa) and an outstanding fracture toughness (45.1 MJ/m3). And more importantly, the m-MTBPI membrane displays an evidently enhanced gas separation ability in comparison with BIDA-derived TBPI, with overall separation properties much closer to the 1991 Robeson upper bound. Moreover, no sign of plasticization appears for the m-MTBPI membrane when separating a high-pressure CO2/CH4 mixture (v/v = 1/1) up to 20 bar, with the CO2/CH4 mixed-gas separation performance approaching the 2018 upper bound.

Synergistic Tuning of Microstructure and Morphology in Carbon Molecular Sieve Hollow Fibers for Propylene/Propane Separation

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro- and macro-structural morphologies for energy efficient propylene-propane separation are reported here. A sub-glass transition temperature (sub-Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS "skin" derived from the 6FDA : BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2-doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

Healable, Recyclable, and Upcyclable Gel Membranes for Efficient Carbon Dioxide Separation

Ionic liquids (ILs) are prized for their selective dissolution of carbon dioxide (CO2), leading to their widespread use in ionogel membranes for gas separation. Despite their advantages, creating sustainable ionogel membranes with high IL contents poses challenges due to limited mechanical strength, leakage risks, and poor recyclability. Herein, we leverage copolymerized and supramolecularly bound ILs to develop ionogel membranes with high mechanical strength, zero leakage, and excellent self-healing and recycling capabilities. These membranes exhibit superior ideal selectivity for gas separation compared to other reported ionogel membranes, achieving a CO2/nitrogen selectivity of 61.7 and a CO2/methane selectivity of 24.6, coupled with an acceptable CO2 permeability of 186.4 Barrer. Additionally, these gas separation ionogel membranes can be upcycled into ionic skins for sensing applications, further enhancing their utility. This research outlines a strategic approach to molecularly engineer ionogel membranes, offering a promising pathway for developing sustainable, high-performance materials for advanced gas separation technologies.