CO2 absorption by binary mixture of ionic liquids-monoethanolamine at lower pressure

• Mixtures of imidazolium ILs and monoethanolamine (MEA) were developed for CO2 capture.
• Such mixtures are water-free, and ILs are easily prepared with cheap raw materials.
• Performances of CO2 absorption and desorption in such mixtures were studied.
• Such mixtures are comparable to aqueous amines in CO2 absorption, typically 0.5 mol CO2/mol MEA.
• Such absorbents can be regenerated and recycled with no remarkable activity loss.

We studied the absorption capability for CO2 of four binary mixtures of [BMIM][BF4]-MEA, [EMIM][BF4]-MEA, [BMIM][PF6]-MEA and [EMIM][PF6]-MEA at 298–318 K and 0.1–0.6 MPa, where BMIM is 1-butyl-3-methylimidazolium, EMIM is 1-ethyl-3-methylimidazolium, BF4 is tetrafluoroborate, PF6 is hexafluorophosphate, and MEA is monoethanolamine. Some factors such as ILs nature, MEA concentration, temperature, pressure, absorption rate and regeneration and recycling of absorbent were investigated. Compared with traditional aqueous amine, such water-free ILs-MEA does not suffer from water volatile loss and resulting corrosion that are typical problems in traditional aqueous amine process. With the addition of MEA, CO2 absorption capacity in such ILs-MEA is much larger than that in the pure ILs and is comparable to that in some aqueous amines and tertiary mixture of ILs-amine-H2O, typically, the CO2 absorption capacity of [BMIM][BF4]-MEA (50 v% MEA) is 0.519 mol CO2/mol MEA at 298 K and 100 KPa. ILs nature has important effect, and the absorption capacity of BF4 ILs-MEA for CO2 is about 30% higher than that of PF6 ILs-MEA where a precipitate is observed for the former while the absorption product of carbamate is soluble for the latter. Reasonable lower temperature and higher MEA concentration is favorable for CO2 absorption. The absorbents can be regenerated and recycled with no remarkable change in CO2 absorption.