Dual Alkali Solvent System for CO₂ Capture from Flue Gas

A novel two-aqueous-phase CO₂ capture system, namely the dual alkali solvent (DAS) system, has been developed. Unlike traditional solvent-based CO₂ capture systems in which the same solvent is used for both CO₂ 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 CO₂ absorption. The lower phase, which consists of a mixture of K₂CO₃/KHCO₃ aqueous solution and KHCO₃ precipitate, is used for CO₂ stripping. Only a certain kind of amine (such as HEP) is able to ensure the phase separation, satisfactory absorption efficiency, effective CO₂ transfer from the upper phase to the lower phase, and regeneration of the upper phase. In the meantime, due to the presence of K₂CO₃/KHCO₃ 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 CO₂ and SO₂/SO₃ 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 CO₂ absorption efficiency (∼90%). (Figure Presented).