Representative longevity testing of direct air capture materials

Direct-air CO2 capture (DAC) is a rapidly expanding field of research driven by a growing need for net-negative technologies. One leading class of materials for DAC is amine-based adsorbents, however these may have limited lifetime due to oxidative degradation. Material longevity is a critical parameter; however, most studies test the stability of these materials under inert atmospheres, removing the oxidation pathway. Consequently, more realistic longevity testing is needed. This work presents a method using ambient air and partial vacuum conditions to assess the stability of DAC materials realistically. A custom-built, automated system was developed whereby CO2 adsorption was conducted in ambient air and desorption under vacuum. In this study, the novel method presented here is compared to a TGA method for analysis of the commercial ion exchange resin Lewatit VP OC 1065. A novel crosslinked polyamine designated here as CA-1 is also examined using the system under various conditions. The method involves the measurement and re-measurement of adsorption capacity between adsorption/ desorption cycles. The Lewatit resin was cycled 180 times with desorption at 80 degrees C and 100 mbar absolute. In this test, it lost 31.20 % of original capacity, contrasted with a 5.47 % loss from the inert TGA method. The CA-1 crosslinked polyamine was then cycled 500 times at three sets of desorption conditions: 80 degrees C and atmospheric pressure, 80 degrees C and 500 mbar absolute, and 75 degrees C and 200 mbar absolute. The sample at 200 mbar lost only 2.79 % original uptake, compared to 28.74 % in atmospheric pressure.