Continuous cycles of CO2 absorption and amine regeneration with aqueous alkanolamines: a comparison of the efficiency between pure and blended DEA, MDEA and AMP solutions by 13C NMR spectroscopy

This experimental study describes the performances of CO2 capture by aqueous solutions of pure alkanolamines (0.667, 1.33 and 2.00 M) 2,20-iminodiethanol (DEA), N-methyl-2,20-iminodiethanol (MDEA) and 2-amino-2-methy-1-propanol (AMP). The behaviour of some alkanolamine blends (2.00 M) has been also considered. In these experiments the CO2-loaded and the regenerated amine solutions were continuously circulated in a closed system between the absorber (set at 293 K) and the desorber (set at 363, 373 and 363-388 K). The absorption efficiency of the single amines at equilibrium is between 69 and 81% according to the desorber temperature and to the amine concentration. The CO2-amine reaction equilibria have been investigated by 13C NMR spectroscopy, which established the regeneration efficiency and the loading capacity for each single amine experiment. AMP displays the greatest absorption efficiency and MDEA the greatest regeneration efficiency at any amine concentration and desorber temperature. Blended AMP-MDEA and AMP-DEA systems (1/2 and 2/1 molar ratios) significantly enhance the absorption efficiency (in the range 7-14%) with respect to single amines under identical operating conditions. AMP-MDEA blends display better performances than AMP-DEA due to the lower efficiency of DEA carbamate in both CO2 absorption and amine regeneration. Owing to a higher thermal stability, AMP and MDEA solutions surpass DEA, as no degradation product has been detected by 13C NMR analysis after heating AMP and MDEA solutions at 403 K up to fourteen days.