A novel solid–liquid 'phase controllable' biphasic amine absorbent for CO2 capture.

[Display omitted] • Solid-liquid 'phase controllable' biphasic amine was firstly proposed for CO 2 capture. • The reaction rule of multistage amines was studied. • The activation barrier to form AMP+CO 2 -was higher than that of TETA+CO 2 –. • TETA+CO 2 – had two deprotonation pathways: self-deprotonation and AMP deprotonation. • The controllability was ascribed to the interaction of TETA intermediates was weak. The main issues in the application of biphasic amine absorbent include the inconvenient separation of the liquid–liquid biphase and the clogging that is associated with the solid–liquid mixture. A novel solid–liquid 'phase controllable' biphasic amine absorbent was therefore developed, in which the phase separation occurred only when the absorbent was near saturation. The absorbent, composed of triethylene tetramine (TETA), 2-amino-2-methyl-1-propanol (AMP), and N-methylformamide (NMF), turned into solid–liquid biphase under CO 2 loading of 0.85 mol mol−1, which is close to saturation (0.92 mol mol−1). The solid phase comprised white powder that accounted for only 42 % of the total volume while absorbing 91 % of the total load. Turbidity and particle size tests showed that the phase separation was self-aggregating. The mechanisms of absorption and regulation were obtained using 13C NMR and molecular simulation. During the absorption, CO 2 first combined with TETA to generate TETAH+CO 2 –/TETACO 2 – through the zwitterion mechanism, and then combined with AMP to generate AMPCO 2 – because of the lower reaction activity between CO 2 and AMP. The TETA-carbamate was found to greatly weakened the strength of the hydrogen bonds and the van der Waals forces between AMPH+ and AMPCO 2 –, increasing the solubility of the intermediate products, and therefore achieved the purpose of controlling the phases separation inherent in the reaction. [ABSTRACT FROM AUTHOR]