A novel solid–liquid ‘phase controllable’ biphasic amine absorbent for CO2 capture

Abstract

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 CO2 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, CO2 first combined with TETA to generate TETAH+CO2–/TETACO2– through the zwitterion mechanism, and then combined with AMP to generate AMPCO2– because of the lower reaction activity between CO2 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 AMPCO2–, increasing the solubility of the intermediate products, and therefore achieved the purpose of controlling the phases separation inherent in the reaction.