Phase Splitting Agent Regulated Biphasic Solvent for Efficient CO2 Capture with a Low Heat Duty.

A biphasic solvent features high absorption capacity and low heat duty for CO2 capture. Phase separation behavior is essential to cut down energy penalty. Four phase splitting agents with different hydrophobicities, such as 1,3-dimethyl-2-imidazolidinone (DMI), 1-methyl-2-pyrrolidinone (NMP), N,N-dimethylformamide, and sulfolane, were dosed to biphasic solvents, triethylenetetramine and 2-(diethylamino)ethanol. Experimental results revealed that they can tune the phase separation behavior during CO2 absorption. Generally, under the same CO2 loading, the volume ratio of the rich phase increased with their hydrophobicity (log P), which accounts for over 50%. Moreover, their influences on absorption capacity, kinetics, and thermodynamics were also investigated. After dosing NMP, the heat duty was decreased by 22%. Furthermore, a phase splitting agent with a positive log P was more conducive to reducing the heat duty, and one with a negative log P enhanced the absorption rate. With DMI, the absorption rate was 114% higher than that of MEA at rich loading. The 13C NMR analysis showed that the agents were not involved in CO2 absorption and did not affect the reaction mechanism. Furthermore, quantum calculation was used to verify the reaction mechanism, confirming that the phase splitting agent increases the reaction equilibrium constant and makes it proceed more thoroughly.