Preparation of Carbon Molecular Sieve Membranes with Remarkable CO₂/CH₄ Selectivity for High-pressure Natural Gas Sweetening

Carbon hollow fiber membranes (CHFMs) were fabricated based on cellulose hollow fiber precursors spun from a cellulose/ionic liquid system. By a thermal treatment on the precursors using a preheating process before carbonization, the micropores of the prepared CHFMs were tightened and thus resulting in highly selective carbon molecular sieve (CMS) membranes. By increasing the drying temperature from RT to 140 °C, the cellulose hollow fiber precursors show a substantial shrinkage, which results in a reduction of average pore size of the derived CHFMs from 6 to 4.9 Å. Although the narrowed micropore size causes the decrease of gas diffusion coefficient, stronger resistance to the larger gas molecules, such as CH₄, eventually results in an ultra-high CO₂/CH₄ ideal selectivity of 917 tested at 2 bar for CHFM-140C due to the simultaneously enhanced diffusion and sorption selectivity. The CHFM-140C was further tested with a 10 mol%CO₂/90 mol%CH₄ mixed gas at 60 °C and feed pressure ranging from 10 to 50 bar. The obtained remarkable CO₂/CH₄ separation factor of 131 at 50 bar and good stability make these carbon membranes great potential candidates for CO₂ removal from high-pressure natural gas.