(592e) Sorbent Regeneration Energy Analysis of Phase-Changing Guanidine-Based Ligands Used for CO? Direct-Air Capture

Currently, solvents that are used for COâ‚‚ capture face issues regarding large energy penalties associated with regeneration and water vaporization. Bis-imino-guanidine (BIG)-based ligands, when combined with potassium salts of amino acids (e.g., potassium sarcosinate, K-SAR), react with COâ‚‚ to form an insoluble precipitate. Research conducted with BIG ligands suggests that this phase change has the potential to reduce the regeneration energy requirement to levels below that of current industry standards for direct air capture (calcium carbonate, CaCO₃) and flue gas capture (monoethanolamine, MEA). This study investigates the thermal regeneration of sorbents used for the direct air capture of COâ‚‚ using spectroscopic and calorimetric methods. In particular, the regeneration energy requirement for 3M K-SAR and a guanidine-based ligand (MGBIG) is quantified using differential scanning calorimetry (DSC) coupled with thermogravimetric analysis (TGA) and Fourier-transform infrared (FTIR) spectroscopy. In order to fully understand the different thermodynamic parameters contributing to the regeneration of K-SAR and MGBIG, the sensible heat, enthalpy of reaction, and enthalpy of vaporization are also estimated. DSC/TGA helps with understanding the regeneration from a thermodynamic perspective and provides information regarding the heat flow as a function of mass, time, and temperature. The gas generated during thermal regeneration is analyzed using FTIR, which provides real-time compositional information of the evolved gas as a function of reaction time and temperature. Using these three techniques, the total regeneration energy of 3M K-SAR and MGBIG was approximated to be 21.4 GJ/tCO₂ and 7 GJ/tCO₂, respectively. The enthalpy of reaction accounts for approximately 11% of the total regeneration energy for K-SAR and approximately 77% of the total regeneration energy for MGBIG. These results provide the fundamental basis for developing an effective carbon capture technology with phase-changing amino acid/guanidine absorbents that can be used to effectively capture atmospheric CO₂.

This research was funded by the US Department of Energy, Office of Technology Transitions, through a Technology Commercialization Fund (TCF-20-20118) supported by the Office of Fossil Energy and Carbon Management.