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 CH 4 , eventually results in an ultra-high CO 2 /CH 4 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%CO 2 /90 mol%CH 4 mixed gas at 60 °C and feed pressure ranging from 10 to 50 bar. The obtained remarkable CO 2 /CH 4 separation factor of 131 at 50 bar and good stability make these carbon membranes great potential candidates for CO 2 removal from high-pressure natural gas.