Abstract
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.
Highlights
Natural gas is considered one of the most attractive low carbon en ergy sources due to its availability, versatility and environmental benefit
Raw natural gas produced from gas wells/reservoirs usually contains impurities such as carbon dioxide (CO2), hydrogen sulfide (H2S), water, and heavy hydrocarbons (HHCs), which need to be removed or reduced before being transported and distributed to natural gas grids as those impurities will cause a series of issues related to pressure drop, plugging of a pipeline, and pipeline corrosions [1]
Various membrane materials have been developed for CO2 removal from natural gas, including glassy polymer membranes [5,6], metal-organic framework (MOF)-based hybrid membranes [7,8,9], fixed-site-carrier (FSC) membranes [10,11] and carbon molecular sieve (CMS) membranes [3,4,12,13]
Summary
Natural gas is considered one of the most attractive low carbon en ergy sources due to its availability, versatility and environmental benefit. Various membrane materials have been developed for CO2 removal from natural gas, including glassy polymer membranes [5,6], metal-organic framework (MOF)-based hybrid membranes [7,8,9], fixed-site-carrier (FSC) membranes [10,11] and carbon molecular sieve (CMS) membranes [3,4,12,13] Some polymeric membranes such as cellulose acetate, polyimide, and perfluoro mem branes have been successfully used for industrial natural gas sweetening [2,4]. CMS membranes with rigid pore structures, fabricated by controlled carbonization of polymeric precursors at high temperature, have shown attractive separation per formances for CO2 removal from natural gas [3]. A remarkable CO2/CH4 separation factor of 131 obtained from the mixed gas (10% CO2/90% CH4) permeation measurement at 60 ◦C and 50 bar shows attractive a great potential for high-pressure natural gas sweetening
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