Ether-, Allyl- Imidazolium Ionic Liquids And Their Application In The Capture Of Carbon Dioxide

The rising level of atmospheric carbon dioxide has been drawing worldwide attention. Some conventional strategies for CO2 capture such as absorption with aqueous amine solution and solid alkali have been applied in industry, which have several shortcomings of high energy and severe equipment corrosion and secondary pollution to be overcome. Ionic liquids(ILs), as a novel designable solvent, have been successfully used in CO2 capture. However, ionic liquids which have a good absorption capacity of CO2 have many drawbacks such as high viscosity, expensive price, complex synthesis, low thermal stability and others. Besides, the systematic research on the interaction mechanism of ionic liquids as CO2 absorbent is insufficient. These factors have greatly limited the further application and progress of ILs. Therefore, it is necessary to design new ionic liquids with potentially solvents for CO2 capture in industry and study on the interaction between ionic liquids and CO2.In this paper, two types of functionalized ionic liquids based on imidazolium cation have been synthesized, the performance for CO2 capture of ionic liquids was studied and controlled by changing the type of the anion, pressure, temperature and water trace. The nuclear magnetic resonance(NMR) and infrared spectroscopy(IR) techniques were used to study microscopic interaction between ionic liquids and CO2, which would provide a theoretical basis on design more useful ionic liquid absorbents for CO2 capture. The main contents of this work are as follows:1. Ten ionic liquids, composed by two kinds of cation, 1-methoxyethyl-3-methyllimidazolium cation([C1OC2mim]+) and 1-allyl-3-methyllimidazolium cation([Amim]+) and five anions([Tf2N]-, [SCN]-, [N(CN)2]-, [Lact]-, [Ac]-) were synthesized. Besides, two imidazolium acetate ionic liquids that the C2 proton in the imidazole ring was substituted by methyl group were also synthesized. [C1OC2mim]Lact, [C1OC2mim]Ac and [C1OC2mmim]Ac were first reported. All synthesized ILs were characterized by NMR. The thermal stability and melting point or glass transition temperature of twelve ionic liquids were determined. The influence of cation and anion structure on those physical and chemical properties were analyzed.2. Absorption performance of ether functionalized ILs with five different anions was measured, and the effect of structures of cation and anion on the solubility of CO2 was analyzed. Ionic liquid [C1OC2mim]Ac was selected, the effects of pressure, temperature and water contents on absorption capacities were discussed in details. This ionic liquid also display a good cycle performance.3. Five kinds allyl functionalized ILs with lower viscosity were applied to the field of CO2 capture for the first time. [Amim]Ac was picked as a representative to study the influence by the factors with pressure, temperature and trace moisture on absorption capacity. Finally, the recyclability of ionic liquid [Amim]Ac was investigated.4. The interaction between ionic liquids [C1OC2mim]Ac and[Amim]Ac with CO2 was investigated by means of NMR and IR techniques and the effect of water contents on absorption process was studied by 13 C NMR. Absorption mechanism was proposed from the studied results, which would offer a new strategy on how to design potential absorbents on CO2 capture by changing the structures of ionic liquids.