(455e) Sub-Ambient Direct Air Capture with Mixed Diluent/Aqueous Amino Acid Solvent-Based Processes

Direct Air Capture (DAC) is an effective way to mitigate greenhouse gas emissions and can be deployed anywhere to capture carbon dioxide from the atmosphere. One of the leading DAC processes is aqueous solvent-based CO₂ absorption utilizing chemically reactive amino acid solutions that have low vapor pressure, slower evaporation rates, and reasonably high CO₂ solubility, making them suitable for large-scale deployment. However, the freezing points of aqueous amino acids that can be used for DAC are above seasonal changes in colder climates, limiting their adoption to certain geographical areas. To address this potential limitation, this study aims to develop solvent formulations for DAC that can operate within a wider temperature range, particularly at sub-ambient climate conditions, while maintaining high CO₂ solubility, kinetics, and mass transfer rates. This research has demonstrated that certain additives, such as glycols, can significantly reduce the freezing point of aqueous amino acid solvents to below -40 degrees Celsius, while maintaining CO₂ solubility. Relevant physical properties of the new solvent system such as freezing point, viscosity, density, and regeneration energy, which impact the operational implementation, CO₂ removal performance, CO₂ capacity, and reaction kinetics in cross-flow absorption systems, have been investigated. This research provides fundamental physical property data and understanding of DAC solvent deployment that are directly applicable to the scale-up of this DAC technology.