Water-lean triethylenetetramine/N,N-diethylethanolamine/n-propanol biphasic solvents: Phase-separation performance and mechanism for CO2 capture

The presence of a small amount of water has a significant effect on amine/alcohol absorbents. In this study, the absorption performance of polyamines DETA, TETA, and TEPA in aqueous and n-propanol solutions at 313 K were investigated, and TETA was selected as the amine to blend with DEEA to investigate the phase separation behavior in water-lean solvents. The influence of amine concentration and water content on the absorption–desorption loading, reaction rate, CO2 cycle capacity, and mass fraction of the CO2-rich phase were discussed. The regenerated products obtained from 1 TETA/4 DEEA/H2O (1T4D-H2O) and 1 TETA/4 DEEA/n-propanol/12 H2O (1T4DnP-12H) at 383 and 393 K were compared and analyzed. The CO2-rich phase capacity of 1T4DnP-12H was highest at 3.37 mol CO2 kg−1 solution. The pH value, conductivity, and ATR-FTIR spectra of the process products of 1T4DnP-12H were measured, analyzed, and compared with the results obtained using 13C NMR by other researchers. In addition to n-propanol, H2O, and DEEA/DEEAH+, a small amount of carbamate products was detected in the lean phase by ATR-FTIR analysis. The main components without regeneration in 1T4DnP-12H solution at 393 K were carbamates. In 1T4D-H2O and 1T4DnP-12H regenerated solutions, stratification occurred and the upper phases were mainly DEEA. The phase migration factors of DEEA (R1,t) and n-propanol (R2,t) were also defined, and the phase separation and species migration mechanisms of TETA/DEEA/n-propanol/H2O solutions were explored from the perspective of molecular structure. Quantitative analysis of the phase-migration factors showed that n-propanol underwent more migration between the two phases than DEEA. Absorption and desorption mechanisms have also been proposed for the TETA/DEEA/n-propanol/H2O/CO2 system.