Synthesis Of Task-specific Ionic Liquids And Absorption Of SO₂and CO₂from Flue Gas By The Ionic Liquids

Ionic liquids (ILs) are organic salts, the molten temperatures ofwhich are near room temperature. They are composed of anions andcations and regared as a kind of environmentally benign solvents. Themost important property of ILs is their extremely low vapor pressure.Besides this, high thermal and chemical stability, designable structure arealso the excellent properties of ILs. At room temperature, ILs have highsolubilities for many organic or inorganic gases, such as SO₂, CO₂, H₂S,ethane and ethane. Nowadays, ILs have been studied in many researchfields, especially the absorption of SO₂and CO₂. In this thesis, as themechanism of the absorption of SO₂by ILs is still unclear, themechanism was studied. Meanwhile, the effect of other components offlue gas, such as water, oxygen and ash, were investigated. After that,based on the new mechanism, a new kind of ILs was synthesized andused to capture CO₂at high temperatures. This thesis consisted of thefollowing parts:1. Some new task-specific ILs have been synthesized and a new way to purify ILs—sweeping solvents by N2, has been found. This method canremove quickly volatile impurities, such as water and organic solvents, inILs. The mass fraction of these impurities decreases from0.05to0.001inseveral hours even0.5h. This method can also avoid the degradation ofILs, save energy and analyze the interaction between solvents and ILs.2. The viscosity, density and conductivity of ILs during theabsorption of SO₂by different kinds of ILs were studied. Based on theresults and the FT-IR and NMR spectrum, a new mechanism of theabsorption was proposed. For task-specific ILs, the absorption of SO₂isconsisted of chemical and physicial absorptions, and the stoichiometricratio of SO₂to ILs is0.5; for normal ILs, the absorption is resulted fromthe physical solution.3. The effect of water on the absorption of SO₂by IL was studied. Itis found that when7.3%of water (V/V) is present in the flue gas, bothwater and SO₂can be absorbed by the IL. The IL can abosorb0.098gH2O/g IL and0.153g SO₂/g IL, and the absorption of SO₂show a goodagreement with that without water,0.157g SO₂/g IL. The absorption ofwater cannot decrease the absorption of SO₂, but it can decrease greatlythe viscosity of ILs during the absorption from8797mPa·s to254mPa·s.4. The absorption of water in different kinds of ILs was investigated.And it was found that decreasing the water content in simulated gas orusing the nonproton ILs and hydrophobic ILs could decrease the absorption of water in ILs. Based on the Raoult's law, the activity ofwater in ILs was obtained. For protic hydrophilic IL, the interactionbetween IL and water is strong and the the activity coefficient of water isless than1. For hydrophobic IL, the interaction between IL and water isweak and the the activity coefficient of water is more than1. For aprotichydrophilic IL, the interaction between IL and water is similar with thatbetween water and water, and the the activity coefficient of water is morethan1.5. The effect of oxygen on the absorption of SO₂by an IL wasstudied. It was found that the existence of oxygen caused the traceoxidation of SO₂. Increasing absorption temperatures, concentration ofoxygen, time and ash can enhance the oxidation. Some ways to decreasethe oxidation were proposed. Meanwhile, we studied the effect of CO₂onthe absorption of SO₂and found that CO₂present in flue gas could notinfluence the absorption.6. The effect of sulfuric acid on the absorption of SO₂by IL and theregeneration of IL were investigated. It was found that when sulfuric acidexisted in ILs, the absorption of SO₂in IL decreased. When the mole ratioof IL to sulfuric acid reached0.5, the IL could not absorb SO₂. But whenNaOH, CaO or CaCO3were added into the mixture of IL and sulfuricacid, sulfuric acid can be easily removed and the IL regenerated.7. Based on the absorption mechanism of SO₂, a new kind of ILs was synthesized and used to capture CO₂at high temperatures andambient condition. These ILs can absorb large amount of CO₂. Forexample, triethylenetetramine lactate can absorb0.94mol CO₂/mol IL at110oC. There is strong chemical interaction between CO₂and the freeamino in ILs. These ILs can be easily synthesized by neutralization ofamine with organic acid and the number of free amino can be adjusted bythe mole ratio of organic acid and amine.8. Several kinds of task-specific ILs for CO₂absorption weresynthesized, and effects of water, SO₂and temperature on the absorptionof CO₂were studied. It was found that all the task-specific ILs used forCO₂capture can absorb SO₂. And water, SO₂and temperature influencedthe absorption of CO₂.