Synthesis Of Novel Functionalized Ionic Liquids And Their Application In CO₂ Absorption And Extraction Of Rare Earth Elements

Ionic liquids (ILs) are novel "green" solvents, having a variety of excellent properties compared with conventional organic solvents, such as negligible volatility, thermal stability, low melting point, adjustable ions and recyclability. Therefore, ILs have been extensively used as catalysis for organic synthesis, electrolyte bases, polymer chemistry, solvent extraction, as well as in the area of gas absorption. Therefore, they deserve being studied widely and applied in broad areas. In my dissertation, three kinds of functionalized ionic liquids have been synthesized, including dicationic amino acid ILs, imidazolate ILs and carboxyl functionalized ILs. In addition, their glass transition temperature, thermal decomposition temperature, as well as the density, conductivity and viscosity data at temperature from 20 to 70?, have been measured carefully. For these three different kinds of ILs, dicationic amino acid ILs and imidazolate ILs are basicity, and will be used in absorption of CO2. Whereas, carboxyl functionalized ILs is acidity, and will be applied in extraction of rare earth ions from aqueous solutions and separation of rare earth ions and transition metals.In six dicationic ILs, there are four amino acid functionalzied ILs and two conventional ILs. The experimental results have proven that all these dicationic ILs are effective for CO2 capture, and their absorption ability have been elevated compared with another cationic analogous. For example, the CO2 absorption capacity of [Bis(mim)C4][Pro]2 can reach 2 mol·mol-1. After the absorption equlibrium, the calculation and analysis of absorption rate curves reveal that the absorption process of [Bis(mim)C4][Gly]2 and [Bis(mim)C4][Pro]2 is different. In addition, the absorption mechanisms are proved through FT-IR and 13C NMR. [Bis(mim)C4][Gly]2 and [Bis(mim)C4][Pro]2 can absorb equimolar and two molar equivalent amount of CO2, respectively. Furthermore, the used ILs can be regenerated by heating under vacuum or bubbling N2.For six imidazolate ILs, they can be divided into three different parts according to their different kinds of cations. Specifically, there are the conventional cations, the amino and hydroxyl functionalized cations or the dications, respectively. Through measuring the CO2 absorption capacity, one mole of the conventional ILs can absorb 0.5 mole of CO2. In addition, the CO2 absorption results are enhanced by using amino functionalized cation, but the improved performance is not observed by using the hydroxyl functionalized one. Furthermore, the dicationic ILs have good performance in CO2 capture, but the absorption rate will decrease because of their increasing viscosity. Finally, the analysis of 13C NMR, FT-IR and ESI-MS were utilized to provide the evidence of the mechanism of interaction between CO2 and the studied IL, leading to the formation of carboxylate connected with imidazolium ring of cation on C2 position.Aqueous [Bis(mim)C4][Im]2 solution is used as CO2 absorbent in a counter-current packed-column. The conditions of absorption process, consisting of liquid rate, liquid concentration and absorption temperature, are mainly discussed towards the absorption results. And the experimental results exhibit that it helps increasing the CO2 removal efficiency through increasing the liquid concentration and liquid rate, meanwhile, the CO2 capacity of ILs will decrease. Compared with another three absorbents, the CO2 removal efficiency and CO2 capacity of ILs absorbents at the outlet of the column are both higher than those of MEA, MEA+MDEA and DBU+Hexanol solutions. Furthermore, with the increasing liquid concentration and liquid rate, the changes in the CO2 removal efficiency and CO2 capacity of ILs absorbents are also more obvious than another three absorbents.In double stirred absorption cell, Aqueous [Bis(mim)C4][Im]2 solution is also the typical CO2 absorbent, and to be used in the kinetic study during absorption process. Combining with the experimental data and calculation analysis, several chemical parameters are obtained, such as Henry's law of ILs solution, diffusivity, gas and liquid mass transfer coefficients. In addition, the first pseudo-first order reaction occurs during the absorption process. The absorption rate and enhancement factor can be higher through increasing the initial CO2 concentration, ILs concentration and temperature. Furthermore, the CO2 removal efficiency increases by decreasing CO2 concentration or elevating the ILs concentration and temperature. Meanwhile, the CO2 loading will decrease. More importantly, the activation energy of the absorption is deduced (70.9 kJ·mol-1), and higher than those of MEA, DEA, [N1111][Gly] and [Hmim][Gly].Hydrophobic, non-fluorinated and carboxyl functionalized ILs, (4-carboxyl)butyl-trioctyl-phosphonium chloride ([P888C4COOH][Cl]), is mainly studied in extraction and separation of rare earth elements. The experimental results show that 3 mole of ILs can extract one mole of Nd(?) ion. And there is a similar conclusion about the extraction capacity according to the "slope analysis" method. However, when using (4-carboxyl)butyl-trioctyl-phosphonium nitrate ([P888C4COOH][NO3]3) and Nd(NO3)3 solutions, two mole of ILs can extract one mole of Nd(?) ion. The difference between them is that one chloride ion contributes to one coordination bond with the Nd(?) ion, but nitrate ion can coordinating as bidentate ligand occupying more coordination sites than chloride ions. Therefore, two mole of inner salt and one mole of Nd(?) ion formed to an ion-coordinated complex, associated with another three mole of nitrate anions. This extraction mechanism is also studied as well for La(?) and Eu(?) ions in order to support the proposed extraction mechanism. Furthermore, a separation between the different rare earths or rare earths and the transition metals nickel and cobalt is discussed. The results show that scandium (?) ion can selectively be separated from another five trivalent lanthanide ions with solvent extraction. And the separation factors of 800 and 1500 were observed for lanthanum from nickel and samarium from cobalt, respectively.