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

Abstract

Chemical crosslinking is the most commonly used solution to address the issue of poor structure stability and low plasticization resistance of polymer membranes for gas separation. However, the general crosslinking route requires the introduction of reactive groups into the polymer chain and is very likely to weaken the separation performance of membranes. Here, we report a new and nondestructive benzyl-induced crosslinking strategy. Owing to the high reactivity and wide existence in most polymers, the benzyl-induced crosslinking could universally happen in unmodified polymer membranes. Our crosslinked polyimide membrane exhibits unprecedented performance with a CO 2 /CH 4 selectivity > 70, three times that of non-crosslinked membranes, and with CO 2 plasticization pressures above 42 bar, the highest value among the polyimide membranes reported so far. The comprehensive performance surpasses the state-of-the-art 2018 upper bound for mixed gas. Our work provides a facile and reliable route for constructing polymer membranes with highly improved stability and performance.

Covalent and non-covalent approaches to suppress plasticization of polymer membranes for gas separation

“…36 In addition, the stability of thermal oxidation crosslinking is greatly improved with the use of reactivity of a benzyl moieties and thermal crosslinking can be conducted at a relatively low temperature of 250 1C due to the high reactivity of the -CH 3 group. 37 Benzyl polyimide membranes were synthesized via a polycondensation reaction of (4,4 0 -hexafluoroisopropylidene) diphthalic anhydride (6FDA) and para-phenylenediamine. This crosslinked membrane has a CO 2 /CH 4 selectivity of more than 70 and a plasticization resistance that is three times higher than non-crosslinked membranes in CO 2 , allowing it to withstand up to 42 bar without sustaining damage.…”

Poly(hydrazide–imide) Membranes with Enhanced Interchain Interaction for Highly Selective H2/CO2 Separation

“…Because of its inherent interchain interaction, it shows high membrane density (1.27 g/mL) and denser chain packing than other glassy polymers. − To further increase chain rigidity and decrease free volumes, Lin’s group reported the use of H 3 PO 4 and terephthaloyl chloride to cross-link PBI to improve its size-sieving ability, thereby increasing the H 2 /CO 2 selectivity by almost 100%. , In addition, H 2 /CO 2 selectivity of polyimides could be improved via diamine cross-linking to manipulate chain rigidity and chain-packing efficiency. Chung’s group reported that a polyimide (6FDA-durene) membrane could be cross-linked by various amines such as ethylenediamine (EDA), diethylenetriamine (DETA), diaminobutane (DAB) dendrimers, and other diamines, and H 2 /CO 2 selectivity increased by more than 260%. − This approach involves the reaction of the imide ring of polyimide with a cross-linker molecule to produce a polymer network structure. ,− Their results showed that chemical cross-linking of polyimide membranes remains one of the most promising methods for improving H 2 enrichment. However, these methods mentioned above usually face several challenges: (1) only a few polymers with rigid structure that can be directly used to separate H 2 and CO 2 ; (2) the serious loss of permeability due to the denser chain packing after modification; (3) the destruction of the main chain of the polyimide caused by excessive reaction and the decrease of molecular weight of the polymer after cross-linking.…”

Fabrication of Ultralarge Curvature Folding-Resistant Polyimide Films by Widening the Elastic Range and Intermolecular Slippery Spacing

“…The ionic liquid-embedded PI films could withstand a low folding radius, but the affordable amount of folding was only 4, which was far away from 200,000 . The PI films crosslinked by a covalent or hydrogen bond network exhibited good folding resistance under a folding radius about 2–3 mm, but the crosslinked films with brittleness cannot afford the increased strain with the decrease in folding radius. ,,− In addition, the exponential impact of folding radius on the tested folding reliability of PI films was further confirmed in this work. Thus, there were still difficulties in preparing large curvature folding-resistant PI films, and a novel strategy was an urgent need for enhancing the folding resistance of PI films under a large curvature.…”