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

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% H2/90% CH4 feeds, the membrane achieves 99.75% H2 purity and 15.6 GPU H2 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.