Tuning Fluorination of Carbon Molecular Sieve Membranes with Enhanced Reverse‐Selective Hydrogen Separation From Helium
Zeyuan Gao, Yongchao Sun, Lu Bai, Tianyou Li, Jianyu Guan, Fake Sun, Fangxu Fan, Gaohong He, Canghai Ma
Abstract
Abstract Membrane technology has been explored for separating helium from hydrogen in natural gas reservoirs, a process that remains extremely challenging due to the sub‐Ångstrom size difference between H 2 and He molecules. Reverse‐selective H 2 /He separation membranes offer multiple advantages over conventional helium‐selective membranes, which, however, suffer from low H 2 /He selectivity. To address this hurdle, a novel approach is proposed to tune the ultra‐micropores of carbon molecular sieves (CMS) membranes through fluorination of the polymer precursor. By incorporating ‐CF 3 units into the backbone of Tröger's base polymers, the microporosity of CMS is tailored and reverse‐selective H 2 /He CMS membranes are deployed with remarkable separation performance, surpassing most reported membranes. These CMS membranes exhibit a H 2 permeability of 1505.2 Barrer with a notable H 2 /He selectivity of 3.8. Barometric sorption tests reveal preferential sorption of H 2 over He in the fluorinated CMS membranes, which also demonstrate a significantly higher H 2 /He diffusion selectivity compared to unfluorinated samples. Material studio calculations indicate that the “slim” hydrogen molecule penetrates ultra‐micropores more readily than the spherical He molecule, thus achieving reverse H 2 /He selectivity. This design approach offers a promising pathway for developing molecularly sieving membranes to tackle the challenging helium separation from natural gas.