Precision tuning of micropore flexibility in polysilsesquioxane membranes for enhanced helium extraction

Helium (He) is a strategically scarce resource primarily occurring in helium-bearing natural gas. The generally low helium content in natural gas resources results in significant extraction challenges and high costs. Gas separation membrane technology offers an attractive opportunity for the cost-effective extraction of He from natural gas. Highly selective and permeable gas membranes are urgently needed to address the extremely low He concentration in natural gas mixtures. In this study, polysilsesquioxane (PSQ) membranes with ultramicropores (0.4–0.5 nm) were constructed via co-polymerization of an organic-rich precursor (bis3-(trimethoxysilyl)propylethylene diamine (BTPDA)) and another organic-lean precursor (1,2-bis(triethoxysilyl)ethane (BTESE)). Such a strategy led to the formation of a novel hybrid PSQ network structure, which possesses rigid network skeleton and flexible ultramicropores, allowing for the precise molecular sieving for separation of He from its mixtures. The resulted membranes displayed excellent structural stability, He permeability (>1570 GPU, measured with pure He) and He/CH₄ selectivity (>100) upon the optimization of the molar ratio of these two precursors during the sol-gel process. Compared to traditional PSQ membranes fabricated via homopolymerization of single precursor with either organic-rich or organic-lean properties, as well as other reported polymer and inorganic membranes, the membranes with tailored flexible ultramicropores tended to overcome the trade-off of He permeability and He/CH₄ selectivity, showing great promise for the industrial He extraction from natural gas field.