The potential for use of cellulose triacetate membranes in post combustion capture

Cellulose triacetate (CTA) membranes occupy much of the gas separation market in natural gas processing. With a high CO2/N-2 selectivity, this material may also be prospective for post-combustion carbon capture, if the permeance can be optimised. In capture applications, the impacts of liquid water condensate of variable pH, SOX and NOX on the gas separation performance are of critical interest to ensure maximum membrane lifetime. In this work, dense CTA membranes were aged in pH solutions of 3, 7 and 13 for a total of 60 days. It was found that the plasticisation of the CTA membrane when aged in pH 3 and pH 7 solutions enhanced the permeability of CO2 and N-2 by over 30% with little impact on CO2/N-2 selectivity. Conversely, the membrane aged at pH 13 failed due to hydrolysis reactions. The membrane was selective for SO2 over CO2 with a SO2 permeability of 20 Barrer. Conversely, NO did not readily permeate, so that the permeate composition was below the level of detection. CTA membranes stored in SO2/N-2 and pure N-2 for a 120 day period at 22 degrees C were relatively stable, with a slight loss in permeability due to membrane aging. Conversely, a significant loss in permeability was observed when these membranes were exposed to 0.74 kPa of NO for the same period. The performance loss appeared to relate to reaction of alcohol groups within the cellulose acetate structure with trace levels of NO2 in the gas mixture. The results highlight the possibility for use of CTA membranes in post-combustion capture, if the active layer thickness can be reduced to enhance gas flux. (C) 2016 Elsevier Ltd. All rights reserved.