2-Amino-2-methyl-1-propanol regulated triethylenetetramine-based nonaqueous absorbents for solid-liquid phase-change CO2 capture: Formation of crystalline powder products and mechanism analysis

[Display omitted] •AMP as a regulator was used to tune the viscosity of the solid products of SLPCAs.•The AMP-regulated SLPCAs successfully yielded easily separated crystalline powders.•The TETA/AMP/NMP SLPCA was found to exhibit the best CO2 capture performance.•The phase-change mechanism of CO2 absorption into TETA/AMP/NMP was elucidated.•The regulatory effect of AMP on the physical form of the solid products was studied. Solid-liquid phase-change absorbents (SLPCAs) have a great potential to reduce the energy consumption of CO2 capture. The main issue in the practical application of SLPCAs is the difficulty in the phase separation of gelatinous solid products. In this study, 2-amino-2-methyl-1-propanol (AMP) was used as a regulator to tune the physical form of the solid products of triethylenetetramine (TETA)-based SLPCAs. Experimental results showed that the AMP-regulated TETA-based SLPCAs successfully avoided the formation of gelatinous products (viscosity up to more than 1000 mPa·s) and yielded easily separated crystalline powders. Among the investigated SLPCAs, TETA/AMP/N-methyl-2-pyrrolidone (NMP) (TETA:AMP = 2:8, 1 M) exhibited the best CO2 capture performance with a high CO2 loading of 0.94 mol·mol−1 and a high regeneration efficiency of 84.14 %. XRD, FT-IR and 13C NMR analyses indicated that TETA/AMP/NMP absorbed CO2 to form highly polar carbamate species and protonated amines, which could break the original assimilation state of the SLPCA system; thus, the polar products precipitated out from less polar NMP, leading to a phase change. The theoretical calculations revealed that in the absence of AMP, the TETA-derived products had a tendency to form gelatinous aggregation with large amounts of hydrogen bonds; with the introduction of AMP, the AMP-derived products tended to combine with the TETA-derived products via strong electrostatic attraction and Van der Waals force and effectively inhibited the aggregation formation. Since there was only one hydrogen bond forming between the AMP- and TETA-derived product molecules, the amount of hydrogen bonds was significantly reduced. Eventually, the TETA/AMP/NMP SLPCA avoided the formation of gelatinous products and yielded crystalline powder products.