Tuning critical solution temperature for CO2 capture by aqueous solution of amine

Abstract

Aqueous solution of amine is a mature technology to selectively absorb CO2 from an industrial exhaust. Monoethanolamine (MEA) is still considered as the reference amine and unfortunately, the energy necessary to desorb CO2 and recycle the solvent is limiting its use at industrial scale. The main cost of the process is the energy needed to heat the solvent over 100 °C to desorb the CO2. Several options to decrease this expense have been considered including the use of phase separation to reduce the volumes to be treated. It was then proposed to use aqueous solution of an amine exhibiting a lower critical solution temperature (LCST) at an adequate temperature. However, it is challenging to found a solvent able to absorb large quantity of CO2 and having an LCST at a suitable temperature. Deep eutectic solvent (DES) composed of oleic acid (hydrophobic) and lidocaine (amphiphilic) can be separated from water with either temperature or CO2 as stimuli. This DES has been used to adjust the critical solution temperature after sorption of CO2 in an aqueous solution of demixing amine. By only changing the ratio of the two components of the DES, the critical solution temperature can be tuned from around 30 to 70 °C. The addition of this DES into an aqueous solution of demixing amine could then substantially help to adapt the critical solution temperature of a solvent to the require conditions of CO2 capture process.