Transforming Gas Separations with Scalable Carbon Molecular Sieve Membranes Enabled by Chemically Tuned Hollow‐Fiber Precursors

ABSTRACT Blending hydrogen into natural gas pipelines requires efficient separation, while helium recovery from natural gas via cryogenic distillation is energy‐ and capital‐intensive, driving demand for better membranes. This study develops ultraselective carbon molecular sieve (CMS) hollow fiber membranes from chemically modified Matrimid (pyrolyzed at 900°C). Two types of modifications are reported for both applications: treatment with vinyltrimethoxysilane (VTMS) or with diethyltoluenediamine/trimesoyl chloride (DETDA/TMC) and VTMS. The chemical modifications create highly economical new precursor hollow fibers that cannot be formed via conventional solvent dissolution and spinning. This establishes a broadly tunable network‐polymer platform for polyimide‐based precursor hollow fiber membranes, extendable to various diamines, which represents a transformative materials platform for scalable CMS membranes. Superior gas separation performance has been achieved, which is envisioned to be extendable across many gas pair cases. For 10% H 2 /90% CH 4 feeds, the membrane achieves 99.75% H 2 purity and 15.6 GPU H 2 permeance, enabling dual‐use hybrid pipelines. For He recovery, CMS membranes stabilized by VTMS avoid pyrolysis‐induced collapse, and VTMS treatment delivers 18.6 GPU He permeance with high selectivity. Alternatively, the DETDA/TMC+VTMS treatment thins the dense layer (to ∼1 µm), boosting permeance under mixed feeds (8.7 vs. 6.0 GPU) while retaining ∼99% He purity.