Ionic Liquids-water Systems Controlled By Carbon Dioxide And Their Applications In Reactionand Separation

Ionic liquids(ILs) are attracting extensive attention from academia and industry because of their potential application as "green solvents" in chemical reaction and liquid-liquid biphasic catalysis. In particular, ILs are playing an important role in separation science. Hydrophobic ILs-H2 O biphasic systems have been used to separate and extract neutral organic compounds and metal ion. However, many of hydrophobic ILs contain fluorine-containing anions, which are expensive and not friendly for environment. Hydrophilic ILs overcome the shortcomings of hydrophobic ILs. However, hydrophilic ILs have to be used together with inorganic salt to form IL/inorganic salt/H2 O aqueous two-phase systems(ATPSs) for the purpose of separation. In this case, the concentration of inorganic salts in the salt-rich phase is very high, which can cause environmental problems. Therefore, it is highly necessary to develop non-fluorine-containing anions based hydrophobic ILs-H2 O biphasic systems and recyclable hydrophilic ILs based ATPSs for homogeneous chemical reaction and heterogeneous separation process.CO2 has been used as the reversible "switch" for the formation of "switchable solvents". The formation of such switchable materials is ascribed to the reversible reaction of additives containing nitrogenous base with CO2 at ambient pressure. As reversible "switch", CO2 has two significant advantages:(i) it is not necessary to employ a specialized high-pressure device;(ii) the use of high concentration salts can be avoided because of the recyclability of the generated ammonium salts. Based on the above analysis, the combination of ILs, CO2 and aliphatic amines has been used, in this work, to design a series of CO2 induced ILs/ammonium salts/H2 O ATPSs at ambient pressure. At the same time, hydrophobic ILs in which the cation or anion is functionalized by the groups containing nitrogen have been designed and synthesized. Thus, these functionalized ILs form CO2 controlled ILs-H2 O biphasic systems. Then, physicochemical property, phase behavior and molecular interactions in the CO2 controlled ILs-H2 O systems are studied. The effects of chemical structures of the ILs and amines on the recovery of ILs and selective separation of aliphatic from aromatic amines with CO2 switchable ILs/ammonium salts/H2 O ATPSs are examined. CO2 controlled ILs-H2 O biphasic systems utilized for coupling of chemical reaction, product separation and recovery of ILs are also developed. The main contents are as follows.1. The effects of the heterocyclic structure of the cations, the nature of the anions of the ILs, and the structure of the amines(1,2-PDA, MEA, DEA, MMEA, MDEA and TEA) upon the formation of ATPSs and recovery of the ILs were studied systematically. A simple, effective and sustainable approach was proposed for the beneficial use of CO2 in combination with recyclable amines to recover ILs from aqueous solution at room temperature and ambient pressure.2. The effects of chemical structures of the ILs, aliphatic and aromatic amines on the separation efficiency of aliphatic and aromatic amines were investigated. The interactions between ILs and aniline derivatives(AN, 2-MA, 3-MA, 4-MA, 2,6-DMA, 3-CA, 4-CA and 3-NA) were also examined. Then the main driving forces for this selective separation were analyzed, and an efficient and environmentally friendly strategy was developed for selective separation of aliphatic and aromatic amines with CO2 switchable IL/ammonium salt ATPSs.3. A novel class of ILs with the anions functionalized by azoles, such as [CnDIPA][Im], [CnDIPA][Pyr] and [CnDIPA][Triz],(n = 4, 6, 8), was developed through carefully design of chemical structures of the cations and anions. This type of ILs exhibited unique phase behavior with water: monophase in the presence of CO2, but biphase by removing CO2 at room temperature and atmospheric pressure. The mechanism of hydrophobic_hydrophilic transition was investigated by the means of NMR spectroscopy and DFT calculations. These unique ILs-H2 O mixtures were used for facile and efficient synthesis of Au nanochain_built 3D netlike porous films in the presence of CO2, while three phase system(porous film, the IL and aqueous solution) was formed after removing of CO2. Thus coupling of homogeneous synthesis and heterogeneous separation including IL recovery was achieved.4. A new class of ILs with the anions functionalized by nitrogen-containing heterocyclic compounds([CnDEA][2-Op], [CnDEA][3-Op], [CnDEA][4-Op], [CnDEA][Pyr] and [CnDEA][Triz]; n = 6, 8) was designed and synthesized. It was found that these ILs had LCST type phase behavior in water: the mixture existed in biphase at higher temperature, but completely miscible at lower temperature. Meanwhile, phase behavior of the IL-H2 O mixture could also be controlled by CO2: it was monophase in the presence of CO2, but biphase by bubbling of CO2 at room temperature and atmospheric pressure. The mechanism of such a hydrophobic_hydrophilic transition was investigated by NMR spectroscopy. These unique ILs are expected to have more important applications in reaction and separation engineering.