Cellulose-based carbon hollow fiber membranes for high-pressure mixed gas separations of CO2/CH4 and CO2/N2

Carbonized cellulose-based hollow fiber membranes were prepared by dry-wet spinning phase inversion method, followed by carbonization and evaluated in terms of gas separation performance for CO2/N-2 and CO2/CH4 mixtures, under flow conditions. Permeability and real selectivity were measured for both mentioned mixtures, in a temperature range of 25 degrees C to 60 degrees C, a differential pressure range of 8 bar(a) to 20 bar(a) and a CO2 concentration range from 5% v/v to 15% v/v. The highest yielding mixture selectivity values were 42 for CO2/N-2 at 10% v/v CO2, 25 degrees C & 8 bar(a) and around 150 for CO2/CH4 at the same conditions, whereas the respective CO2 permeabilities were 110 and 45 Barrer. Additionally, experiments of varying head pressure, while maintaining differential pressure, transmembrane pressure, at 8 bar(a), have revealed that CO2/N-2 separation factor can be further enhanced with real selectivity being raised to 55 and permeability to 180 at 20 bar head pressure. The same approach had negligible effect on CO2/CH4 separation. This is an important finding by taking into consideration that natural gas treatment, i.e. sweetening and purification processes, is energetically and economically convenient if it takes place under the conditions, where the NG stream is extracted from the wells, or after a decompression. Moreover, Process simulation indicates that a two-stage system using the developed carbon membranes is technologically feasible to produce 96% methane with a low methane loss of < 4%. Further improving membrane gas permeance can significantly reduce the specific natural gas processing cost which is dominated by the membrane-related capital cost.