The Study On CO₂/SO₂ Capture By Tuning Imidazolium Ionic Liquids

Carbon dioxide ?CO₂? and Sulfur dioxide ?SO₂? are main parts of air pollutants, which will threaten natural environment as well as human health, where the capture of CO₂ and SO₂ has attracted extensive attention. Ionic liquids ?ILs? exhibit excellent properties which are superior to other adsorbents in the area of acidic gas absorption owing to their unique properties such as low vapour pressure, wide liquid temperature ranges, high thermal stability and excellent designable property, so they can act as a novel kind of solvents, which provides much prospect for developing new technology of acidic gas absorption. Imidazolium ILs are widely applied for CO₂ and SO₂ capture, but there are some drawbacks such as low CO₂ absorption capacity and much difficulty in regeneration due to the carbene formation in the process of CO₂ capture. Furthermore, it is necessary to improve imidazolium ILs CO₂ absorption properties through reducing the carbene formation.Firstly, a new strategy on improving the capture of CO₂ through tuning the structure of imidazolium ILs to reduce carbene-CO₂ pathway was proposed. On the basis of quantitative method of calculating carbene ratio by NMR method, the formation of carbene was reduced through reducing the anion's basicity and enlarging the cation's steric hindrance. It was found that lower basicity could reduce less carbene formation, which also induced lower CO₂ absorption capacity. However, low carbene content and enhanced CO₂ absorption capacity were achieved through increasing cation's steric hindrance. The results of quantum chemical calculation indicated that the binding between the anion of the IL with CO₂ was strengthened by introducing certain steric hindrance substituent to the cation, which resulted in increasing CO₂ absorption capacity. Through spectroscopic investigation and calorimetric data, we found that [Ipmim][Triz] exhibited excellent reversibility and high CO₂ mass absorption capacity of 0.21 g CO₂/g IL.Secondly, as with the application in SO₂ capture of imidazolium ILs, a computer-aided design strategy of imidazolium ILs through quantitative prediction for SO₂ absorption and desorption behavior from flue gas was reported. Through a combination of Langmuir model and quantum chemical calculation method, SO₂ absorption and desorption performance from flue gas by imidazolium ILs were predicted. Afterwards, the predicted results were verified by carrying out SO₂ absorption experiment, where the experimental values were in good agreement with the predicted values. An ideal ionic liquid [Emim][Tetz] showed the highest available absorption capacity of 0.24 g SO₂ per g ionic liquid and excellent reversibility.In summary, the article studied the application of functionalized imidazolium ILs in CO₂ and SO₂ capture. On the one hand in CO₂ absorption, CO₂ absorption and desorption reversibility properties of imidazolium ILs was improved though tuning the structure. CO₂ absorption mechanism was also explained through spectroscopic investigation and quantum chemical calculation. On the other hand in SO₂ absorption, with a combination of quantum chemical calculation, a new method for predicting SO₂ absorption and desorption performance effectively was set up, which opens a door for researchers to develop new functionalized ILs for CO₂/SO₂ capture.