Study of novel hindered amine/polyamine blends for improved carbon dioxide capture

Sterically hindered amines are used as solvents for bulk CO 2 removal by reactive absorption, because their loading capacity is high and regeneration is easy. However, these amines react more slowly with CO 2 than the conventional amines. Thus, the addition of rate promoters is beneficial. This work investigated CO 2 absorption into aqueous solutions of the hindered amine 2‐amino‐2‐hydroxymethyl‐1,3‐propanediol (AHPD) promoted with the polyamine triethylenetetramine (TETA) or tetraethylenepentamine (TEPA). Absorption kinetics was studied in a stirred cell reactor in the 308–318 K range. The reactions were investigated in the fast reaction regime. In this regime, the inequality 10 < Ha < < E i holds (here, Ha and E i denote Hatta number and enhancement factor for instantaneous reaction). At 308 K, the overall rate constant was equal to 6520 (for AHPD/TETA) and 8852 s −1 (for AHPD/TEPA). The respective values of the second‐order rate constant for the CO 2 reaction with TETA and TEPA were 11,107 and 16,014 m 3 /(kmol s). These values were higher than the rate constant for monoethanolamine (MEA). A vapour–liquid equilibrium (VLE) study for the two blends AHPD/TETA and AHPD/TEPA (2.5/0.5 M) was performed to find the equilibrium solubility of CO 2 at 308 K. The highest CO 2 loading capacity was found to be 0.68 (for AHPD/TETA) and 0.76 mol/mol (for AHPD/TEPA) at CO 2 partial pressure of 85 kPa. In comparison, aqueous AHPD (2.5 M) exhibited a highest loading of 0.54 mol/mol at 75 kPa CO 2 partial pressure, thus suggesting that polyamine addition improved CO 2 solubility. Desorption features of the chosen blends were studied at 358 K in a glass reactor and compared with MEA. The efficiency of desorption for AHPD/TETA (55%) and AHPD/TEPA blend (57%) was higher than that for MEA (40%). Thus, the chosen blends exhibited better desorption performance than the conventional amine MEA.