Research of novel polyamine-based biphasic absorbents for CO2 capture using alkanolamine to regulate the viscosity and mechanism analysis.

[Display omitted] • Using alkanolamine to regulate the viscosity of biphasic solvents is proposed. • A novel polyamine-based biphasic solvent with low costs is developed. • The phase split mechanism is investigated by NMR analysis. • A molecular-scale understanding of the viscosity regulation mechanism is revealed. Biphasic solvent has attracted widespread attention in CO 2 chemical absorption technology due to its significant potential for reducing capture energy consumption. However, the high viscosity of CO 2 -rich phase after phase split could lead to issues such as high flow resistance, low heat transfer efficiency, and phase separation instability in application. To address these limitations, a strategy of using alkanolamine as a viscosity regulator for biphasic solvents was proposed. Diethanolamine(DEA), an alkanolamine regulator, was introduced to a system of polyamine/amide absorbent, and then a novel biphasic solvent of diethylenetriamine (DETA)/diethanolamine(DEA)/N, N-Dimethylacetamide(DMAC)/water(H 2 O) was developed. The viscosity of the CO 2 -rich phase solvent was reduced to 19.02 mPa⋅s, a significant decrease compared to the solution without DEA regulation. The novel solvent exhibited a high cyclic capacity of 2.08 mol/kg, which was 43.4 % higher than that of the solution without DEA, and a desorption rate twice as high as 30 wt% monoethanolamine(MEA). Quantitative 13C Nuclear Magnetic Resonance (NMR) and Molecular Dynamics (MD) simulations revealed the phase split and viscosity regulation mechanisms. It was proved that DETA species, especially carbamates, tend to self-aggregate with each other due to intermolecular hydrogen bonding with the CO 2 loading increases, which leads to phase split and high viscosity of the saturated solution. Through DEA regulation, the protonation of carbamates and the generation of HCO 3 –/CO 3 2– were promoted, which weakened the self-aggregation of carbamates species, decreasing the viscosity and the regeneration energy of saturated CO 2 -rich phase solution. The regeneration energy reached 2.19 GJ/ton CO 2 , which exhibited a 42.4 % reduction compared with that of 30 wt% MEA. [ABSTRACT FROM AUTHOR]