Stability of IRA-45 Solid Amine Resin as a Function of Carbon Dioxide Absorption and Steam Desorption Cycling

A solid-amine water (steam) desorbed (SAWD) carbon dioxide removal subsystem is a candidate for use on the proposed U.S. Space Station for removing carbon dioxide (CO₂) from the spacecraft cabin atmosphere. To evaluate the long-term stability of the solid amine resin, IRA-45, with respect to repeated CO₂ absorption and steam desorption cycling, an automated laboratory flow-test facility was assembled. Packed columns of IRA-45 resin were tested under simulated Space Station cabin conditions for 569 cycles to determine 1) the decrease in CO₂ absorption capacity as a function of the number of cycles and 2) the volatile organic compounds released by steam desorption cycling. Carbon dioxide capacity was measured in real-time during each cycle. Organic volatiles in the resin-desorbed CO₂ and in the simulated cabin air flow were trapped on graphitic carbon adsorbents. Analyses of the trapped volatiles were performed using gas chromatography (GC) and mass spectrometry (MS). The CO₂ adsorption capacity of the IRA-45 gradually decreased over time but the rate of degradation slowed significantly after about the first 10 cycles. After a 43% loss in capacity during the first 10 cycles, the additional loss in CO₂ capacity was only about 2.7% during the remaining 560 cycles. During the first 80 cycles, trimethylamine was present in the process air downstream of the resin bed in concentrations that were at or above the spacecraft maximum allowable limit (SMAC). The continued presence of trimethylamine after 569 cycles suggested that it is a principal resin breakdown product and that it may be necessary to post-treat the process air in order to minimize exposure of the Space Station crew to this toxic chemical.