Direct Air Capture (DAC) of CO2 accomplished by different alkanolamines

The chemical capture of carbon dioxide from ambient air (Direct Air Capture - DAC) represents one of the negative carbon technologies (NETs) with the potential of reduce the global atmospheric CO2 concentration. Moreover, the capture of CO2 from air is suitable to supply pure CO2 wherever it is needed. Because of the very low concentrations (about 400 ppm), to date the most widespread technologies for CO2 removal from the air are based on alkaline aqueous solutions, but the process is high energy demanding and prohibitively expensive. In recent papers, we have reported some experimental studies on the CO2 capture from gas mixture by different amine-based sorbents. Herein, we have investigated the possibility of transferring our previous studies to DAC technology, with the goal of formulating absorbents capable to efficiently react with aerial CO2 featuring lower energy demand for thermal regeneration. To this purpose, we have selected 2-aminoethanol (monoethanolamine, MEA), the benchmark in CCS technologies, 2-(2-aminoethoxy)ethanol (diethylene glycol amine, DGA), 2-amino-2-methyl-1-propanol (AMP) and 2-(butylamino)ethanol (BUMEA), and we have investigated their performances for low-concentrated CO2 capture either in aqueous and non-aqueous solutions. The 2-(2-methoxyethoxy)ethanol (diethylene glycol monomethyl ether, DEGMME) was used as non-aqueous solvent because of the solubility of most of the carbonated compounds in this solvent, the high boiling temperature and low viscosity of the solutions. We have carried out batch experiments to evaluate the CO2 loading capacity, the rate of CO2 capture and the efficiency of amine regeneration. The heat of CO2 absorption (?Habs), which is a significant parameter to evaluate the overall energy demand of the CO2 capture process, has been calculated by the Gibbs-Helmholtz equation. Finally, we used 13C NMR spectroscopy to identify and quantify the carbonated species in the solution equilibria originated by CO2 absorption, to better understand the absorption mechanisms.