Optimizing the Stabilization Environment of the Carbon Molecular Sieve Membranes Derived from the Porous Hollow Fibers for Gas Separation

Carbon molecular sieve (CMS) hollow fiber membranes (HFMs) are very promising for efficient gas separation. However, their gas separation performance was hindered by the thick selective skin layer. In this work, defect-free CMS HFMs with a very thin selective layer (about 1.5 μm) were prepared successfully by the pristine porous fiber precursors. Furthermore, the porous fibers were thermally pretreated in different conditions (vacuum, N₂ and air) near T_g of the polyimide to stabilize the structure of the HFM precursors, and the CMS membranes derived from the pretreated porous fibers exhibited attractive enhanced gas separation properties. As a result, the CMS membranes which derived from the porous hollow fibers thermally treated in vacuum and N₂ exhibited the obvious enhancement of gas permeance and the comparable H₂/CH₄, H₂/N₂, CO₂/CH₄, CO₂/N₂, and O₂/N₂ selectivity. When they were pretreated in air condition, the H₂ (242 GPU), CO₂ (57 GPU), and O₂ (19 GPU) permeance values increased 158%, 300%, and 405% with the slightly decreased selectivity of H₂/CH₄ (64), H₂/N₂ (53), CO₂/CH₄ (15.7), CO₂/N₂ (12.9), and O₂/N₂ (4.3), respectively. The thermal pretreatment of the porous HFM precursors near T_g was a very facile but effective way to enhance the gas separation properties.