Stability of gel-supported facilitated transport membrane for carbon dioxide separation from model flue gas

摘要

The stability of a facilitated transport membrane for carbon dioxide (CO2) separation from CO2/N2 (nitrogen) mixed gas was studied. This membrane was composed of an aqueous potassium carbonate (K2CO3) solution and a vinylalcohol-acrylate copolymer (PVA-PAA, super absorbent polymer), in which the aqueous solution was immobilized. This facilitated transport membrane named a gel-supported membrane worked properly when the PVA-PAA polymer gel held sufficient amount of water. The amount of water in the gel membrane depended on the water vapor pressure above the membrane. Higher water retention was observed at the K2CO3 solution because of its ionic strength. The role of the polymer gel in retaining water was not observed clearly. The aqueous K2CO3 solution contributed greatly to keeping the membrane wet, and the polymer gel was suitable as substrate of a thin liquid membrane. The gel-supported membrane immobilizing an aqueous 2 mol/kg K2CO3 solution worked well even under the evacuating condition for 6 months by controlling the water vapor pressure. Sulfur dioxide (SO2) which was included in the flue gas obstructed CO2 transportation. SO2 may have the influences of restraining CO2 from dissolving into the carrier solution and of decreasing the concentration of a carrier at the gas-liquid interface. These undesirable effects of SO2 were weakened by the addition of potassium sulfite (K2SO3), and it appeared at low concentration of 0.1 mol/kg K2SO3. Nitrogen monoxide (NO) and nitrogen dioxide (NO2), which were included in the flue gas as well, had no influence to CO2 transportation through the membrane. As the results of these studies, it was believed that the gel-supported membrane had a potentiality for practical use to recover CO2 from the high humid gas mixture such as flue gas.