ABSTRACT Helium/methane (He/CH 4 ) separation is of strategic importance for energy and industrial applications, yet it remains technically challenging due to the need to simultaneously achieve ultrahigh selectivity and helium productivity. In this work, we report ultraselective Matrimid‐derived asymmetric carbon molecular sieve (CMS) hollow fibers in which ultramicropore and fiber geometry are deliberately co‐engineered to enable precise He/CH 4 separation with high He productivity at the module level. We showed that pyrolysis temperature tuning tightens ångström‐scale ultramicropores and enhances He/CH 4 discrimination; while a targeted post‐pyrolysis hyperaging enables selective refining of the ultramicropores, thereby offering high He permeance with exceptional He/CH 4 selectivity. For a 5/95 He/CH 4 mixed gas feed, the hyperaged CMS‐700 hollow fibers achieve permeate helium purities of up to 98.6% with He/CH 4 selectivities exceeding 1300 and a stable He permeance of approximately 26 GPU. Beyond this material achievement, fiber geometry optimization through reduction of the outer diameter was achieved to increase the packable membrane area without compromising mechanical integrity or intrinsic separation performance, leading to enhanced module‐level He productivity. This integrated co‐engineering strategy provides an energy‐efficient and industrially viable platform for He recovery and is readily extendable to other challenging small/large gas‐pair separations.
Liu et al. (Mon,) studied this question.