Carbon Capture via Crystallization with a Guanidine Ligand
Carbon capture and storage (CCS) is an important strategy aimed at stabilizing the atmospheric CO2 concentration and thereby the global temperature. In conventional fossil fuel-fired power plants, the resulting flue gas is released into the air without any carbon dioxide scrubbing, which gradually increases the atmospheric CO 2 concentration (currently at approximately 409 ppm). Implementation of post-combustion capture (PCC) of carbon dioxide, whereby the CO 2 emitted by power plants is captured and stored into geological repositories, would enable us to continue to use relatively cheap fossil fuels such as coal, natural gas, and oil, but with significantly reduced CO 2 emissions. A recent report by the International Energy Agency indicated that by 2050 CCS could reduce the annual CO 2 emissions by almost 6 gigatones, which represents about 14% of the total carbon emission reduction necessary to limit the global temperature increase by 2 ºC by the end of the 21st century (International Energy Agency, 2016). This goal will be accomplished by developing inexpensive materials that can be used to effectively capture CO 2 and be regenerated with minimal energy penalty. This project helped address this need by introducing new materials and mechanisms for CO 2 capture. The goal of this project was to demonstrate a bench-scale CO 2 capture process based on a novel guanidinium (bi)carbonate crystallization approach, and ultimately develop an energy-efficient and cost-effective technology for CO 2 capture from flue gas. The project built on our recent discovery of a new class of aqueous guanidine sorbents that react with carbon dioxide and crystallize as carbonate or bicarbonate salts of very low aqueous solubility (Brethomé, 2018; Williams, 2019). The resulting guanidinium (bi)carbonate crystals release the CO 2 upon mild heating at 80-120 ºC, which regenerates the guanidine ligands quantitatively (Figure 1). The potential advantage of this crystallization-based approach over traditional amine scrubbing methods (i.e., using aqueous MEA) is that it allows sorbent regeneration by heating the solid crystals alone, without the bulk solution, making this process more energy-efficient.