A new class of single-component absorbents for reversible carbon dioxide capture under mild conditions

Some inexpensive and commercially available secondary amines reversibly react with CO2 at room temperature and ambient pressure to yield carbonated species in the liquid phase in the absence of any additional solvent. These solvent-free absorbents have a high CO2 capture capacity (0.63-0.65 mol CO2/mol amine) at 1.0 bar (=100 kPa), combined with low-temperature reversibility at ambient pressure. 13C NMR spectroscopy analysis identified the carbonated species as the carbamate salts and unexpected carbamic acids. These absorbents were used for CO2 (15 and 40% in air) capture in continuous cycles of absorption-desorption carried out in packed columns, yielding an absorption efficiency of up to 98.5% at absorption temperatures of 40-45°C and desorption temperatures of 70-85 °C at ambient pressure. The absence of any parasitic solvent that requires to be heated and stability towards moisture and heating could result in some of these solvent-free absorbents being a viable alternative to aqueous amines for CO2 chemical capture.