Dual Alkali Solvent System for CO Capture from Flue Gas.

A novel two-aqueous-phase CO capture system, namely the dual alkali solvent (DAS) system, has been developed. Unlike traditional solvent-based CO capture systems in which the same solvent is used for both CO absorption and stripping, the solvent of the DAS system consists of two aqueous phases. The upper phase, which contains an organic alkali 1-(2-hydroxyethyl) piperazine (HEP), is used for CO absorption. The lower phase, which consists of a mixture of KCO/KHCO aqueous solution and KHCO precipitate, is used for CO stripping. Only a certain kind of amine (such as HEP) is able to ensure the phase separation, satisfactory absorption efficiency, effective CO transfer from the upper phase to the lower phase, and regeneration of the upper phase. In the meantime, due to the presence of KCO/KHCO in the lower phase, HEP in the upper phase is capable of being regenerated from its sulfite/sulfate heat stable salt, which enables the simultaneous absorption of CO and SO/SO from the flue gas. Preliminary experiments and simulations indicate that the implementation of the DAS system can lead to 24.0% stripping energy savings compared to the Econamine process, without significantly lowering the CO absorption efficiency (∼90%).