Ionic Liquids as Solvents

2019-02-22 23:19:05 adman 1

Amines are the most prevalent absorbent in postcombustion carbon capture technology today. In particular, monoethanolamine (MEA) has been used in industrial scales in postcombustion carbon capture, as well as in other CO2 separations, such as "sweetening" of natural gas.[1]However, amines are corrosive, degrade over time, and require large industrial facilities. Ionic liquids on the other hand, have low vapor pressures . This property results from their strong Coulombic attractive force. Vapor pressure remains low through the substance's thermal decomposition point (typically >300 °C).[2]In principle, this low vapor pressure simplifies their use and makes them "green" alternatives. Additionally, it reduces risk of contamination of the CO2 gas stream and of leakage into the environment.[3]

The solubility of CO2 in ionic liquids is governed primarily by the anion, less soby the cation.[4] The hexafluorophosphate (PF6) and tetrafluoroborate (BF4) anions have been shown to be especially amenable to CO2 capture.[4]

Ionic liquids have been considered as solvents in a variety of liquid-liquid extraction processes, but never commercialized.[5] Beside that, ionic liquids have replaced the conventional volatile solvents in industry such as absorption of gases or extractive distillation. Additionally, ionic liquids are used as co-solutes for the generation of aqueous biphasic systems, or purification of biomolecules.