The CO₂ Absorption in Flue Gas Using Mixed Ionic Liquids

Because of the appealing properties, ionic liquids (ILs) are believed to be promising alternatives for the CO₂ absorption in the flue gas. Several ILs, such as [NH₂emim][BF₄], [C₄mim][OAc], and [NH₂emim[OAc], have been used to capture CO₂ of the simulated flue gas in this work. The structural changes of the ILs before and after absorption were also investigated by quantum chemical methods, FTIR, and NMR technologies. However, the experimental results and theoretical calculation showed that the flue gas component SO₂ would significantly weaken the CO₂ absorption performance of the ILs. SO₂ was more likely to react with the active sites of the ILs than CO₂. To improve the absorption capacity, the ionic liquid (IL) mixture [C₄mim][OAc]/ [NH₂emim][BF₄] were employed for the CO₂ absorption of the flue gas. It is found that the CO₂ absorption capacity would be increased by about 25%, even in the presence of SO₂. The calculation results suggested that CO₂ could not compete with SO₂ for reacting with the IL during the absorption process. Nevertheless, SO₂ might be first captured by the [NH₂emim][BF₄] of the IL mixture, and then the [C₄mim][OAc] ionic liquid could absorb more CO₂ without the interference of SO₂.