983675 - Developing Amine-Grafted Silica Materials for CO₂ Capture from Enclosed Environments

Exposure to high CO2 levels in enclosed environments such as spacecraft, submarines, and lunar habitats may result in adverse health impacts, namely headaches, dizziness, difficulty breathing, tiredness, asphyxia, and even coma. In order to provide a safe and healthy environment for the crew, the CO2 and water vapor originating from exhalation must be removed from cabin air through a process called “Air Revitalization”. Currently, NASA enforces a Spacecraft Maximum Allowable Concentration (SMAC) of 0.5% CO2 over a 1000-day period, using a multi-bed system known as the Carbon Dioxide Removal Assembly (CDRA). The process involves cyclic adsorption-desorption using zeolite 5A molecular sieves. Owing to the presence of humidity in the cabin air and the hydrophilic nature of zeolite 5A, the removal of CO2 and water vapor must be conducted separately via two adsorption beds that are arranged in series, resulting in additional capital and operating costs. The objective of this study is to address this shortcoming via developing alternative adsorbent materials capable of integrating and intensifying the process. Amine-grafted silica materials, also known as aminosilicas, were synthesized via covalent bonding of primary amines onto SBA-15 silica. The adsorptive properties of the aminosilicas, namely equilibrium uptake and adsorption kinetics, were investigated in the presence of 1 vol.% CO2 in N2 at 25 °C. Similar experiments were completed on beaded and powdered zeolite 5A for comparison. Whereas aminosilicas and zeolite 5A achieved comparable equilibrium CO2 uptakes, the adsorption kinetics was much faster on the aminosilicas, particularly relative to beaded zeolite 5A. Moreover, aminosilicas required lower regeneration temperature compared to zeolite 5A, while being capable of concurrent removal of CO2 and water vapor. These results indicate the high potential of aminosilicas as an alternative adsorbent for life support applications in space.