Development of dual-functionalized ionic liquids for biphasic solvents: Enhancing the CO2 absorption through two-stage reaction and promoting the energy-saving regeneration

Abstract

A dual-functionalized ionic liquid was synthesized by facile neutralizing routes from Diethylenetriamine (DETA) and lysine (Lys), which was designated as [DETA]Lys. It could absorb CO2 through a two-stage reaction, achieving a CO2 capacity of up to 2.16 mol CO2/mol ILs. And N-methyl-2-pyrrolidone (NMP) was validated as a good phase splitting agent for [DETA]Lys-based biphasic solvent by tailoring the polarity and hydrogen bonding effect. Thus, DETA-carbamate, Lys-carbamate, and HCO3−/CO32− were formed during CO2 absorption and gathered in the lower layer, while most of the NMP stayed in the upper layer. Finally, the CO2-rich phase took up 53.84 % of the total volume and 99.03 % of the captured CO2, exhibiting a CO2 loading of 4.78 mol CO2/L. The significantly enhanced CO2 loading (4.78 mol/L), decreased stripping volume (53.84 %), and reduced desorption energy (1.28 GJ/ton CO2) allowed for a great reduction in regeneration energy to 1.89 GJ/ton CO2, which was merely 47.37 % of 5 M MEA (3.80 GJ/ton CO2). The regeneration efficiency of the solvent remained at 91.5 % after the 3rd absorption/desorption cycle. Furthermore, the corrosion speeds of the rich and lean phases were merely 0.18 % and 12.35 % of 5 M MEA. The excellent CO2 capture performance and good energy-saving potential enabled the [DETA]Lys + NMP + H2O system an effective absorbent for carbon capture.