Screening Study of Different Amine-Based Solutions as Sorbents for Direct CO2 Capture from Air

Direct air capture (DAC) is an emerging technology that can help limit the global temperature rises, as it has the potential to contrast the dispersed CO2 emissions coming from transport and heating that cannot be captured with traditional CCS methods. Although recent improvements are bringing DAC closer to commercial feasibility, an obstacle to its diffusion is the high regeneration energy required by the most common liquid sorbents, Na or K hydroxides. To develop efficient and more sustainable sorbents, in this screening study, several alkanolamines, particularly those already known for their utilization in CCS, were tested for DAC. The percentage of CO2 absorbed from compressed air of their 1.5 mol dm–3 aqueous solutions was evaluated in 24 h capture experiments, and the species formed were identified and quantified by means of 13C NMR spectroscopy. For selected amines, their performance in organic diluents was also evaluated. The correlations between aerial CO2 absorption, chemical structures of the different amines, and species formed in solution have shown that a high yield production of amine carbamate is the decisive factor for an effective CO2 capture and that aqueous primary unhindered amines are as efficient as aqueous alkali hydroxides, with the potential of a lower regeneration energy.