| As a class of new media and functional materials, ionic liquids (ILs) have obtained remarkable achievement in green chemistry during recent years. ILs have been successfully applied in organic synthesis, catalytic chemistry, electrochemistry, and materials science due to thier unique properties such as non-detectable vapor pressures, high stability, non-flammability, easy recovery, and physico-chemical tunabilities. However, the application of ILs in the seperation of biomass components is still in its infant stage, very few studies have been conducted to explore the influence of the anionic structure of ILs on the dissolution performance of cellulose. The existing ILs show some drawbacks like high melting point, high viscosity or lower solubility at room temperature and so forth. As a part of the project supported by the National High Technology Research and Development Program (863 Program, No.2007AA05Z454), in this thesis, a series of anion-functionalized ILs which possess a stronger capacity of dissolving cellulose were synthesized, solubility property of cellulose in the ionic liquids, the influence of addition of lithium salts as well as polar aprotic solvents in [C4mim][CH3COO] on cellulosic solubility, and the possible mechanisms of the ILs and composite systems in dissolution of cellulose were investigated. On that basis, the selective separation of model biomass components was successfully realized by using ILs. The main contents are as follows:1. A series of anion-functioned ILs were designed and synthesized by coupling 1-butyl-3-methylimidazolium cation [C4mim]+with the anions such as [CH3COO]-, [HCOO]-[CH3CHOHCOO]-, [H2NCH2COO]-, [HOCH2COO]-, [(C6H5]COO]-and [N(CN)2]-based on the relationship between structure and property. The ILs were characterized by means of'H NMR spectra. The physico-chemical data such as densities (p), viscosities (η) and electrical conductivities (σ) were determined at the temperature range from 303.15 to 343.15 K. The results indicate that with increasing temperature, the densities of the ILs slightly decrease, and the viscosities along with electrical conductivities increase markedly. The alkyl chain length of anions of the ILs has a considerable effect on their physico-chemical properties. The increase of alkyl chain length would lead to the decrease of densities and electrical conductivities and the increase in viscosities. The temperature dependence of densities of the ILs could be described with the Tait equation. The temperature dependence of viscosities of [C4mim][HCOO], [C4mim][HOCH2COO] and [C4mim][N(CN)2] is more consistent with the VFT equation, whereas the Arrhenius equation is more suitable for other ILs. In addition, the temperature dependence of the conductivity of the ILs can be described well by VFT equation.2. Solubilities of cellulose in the ILs at different temperatures were systematically measured, and the main factors of the effect of the ILs on the solubility property were investigated by means of 1H NMR chemical shift and solvatochromic UV/vis probe. The anionic structure of the ILs was found to have a significant impact on cellulosic solubility, and the hydrogen bond accepting ability of anions of the ILs predominated the solubility performance of cellulose. The replacement of H in [CH3COO]- anion of [C4mim][CH3COO] by an electron-withdrawing group such as OH, SH, NH2 or CH3OH leads to the decreased solubility.3. As an example, the influence of the addition of a small amount of lithium salt LiX(X=Cl-,Br-, NO3-, ClO4-, [CH3COO]-) into [C4mim][CH3COO] on cellulose solubility was investigated, and the possible mechanism was analyzed by 13C NMR technology. The results indicate that the addition of a small amount of lithium salts increase cellulose solubility, and this is mainly due to the disruption of the inter-molecular hydrogen bond, O(6)H…O(3) owing to the interaction of Li+with the hydroxyl oxygen O(3) of cellulose. The non-derivatizing cellulose can be regenerated by adding water into [C4mim][CH3COO]/LiX/cellulose system, indicating that [C4mim][CH3COO]/LiX is the direct solvent of cellulose. The regenerated cellulose exhibited a quite similar thermal stability to the original cellulose.4. The effect of the additon of polar aprotic solvents like dimethyl sulfoxide(DMSO), N,N-dimethylformamide(DMF) and N,N-dimethyl-acetamide(DMAc) in [C4mim][CH3COO] on the solubility of cellulose and the possible mechanism were studied. The results indicate that the addition of the polar aprotic solvents drastically increase solubility of cellulose in [C4mim][CH3COO]. At 25℃, cellulose is insoluble in a single solvent of [C4mim][CH3COO], DMSO, DMF or DMAc. However, after [C4mim][CH3COO] is mixed with DMSO, DMF or DMAc at a suitable ratio, cellulose becomes efficiently soluble. The results from 1H NMR and 13C NMR indicate that the [C4mim]+cations are solvated preferentially by polar aprotic solvent, more [C4mim][CH3COO] ion pairs were dissociated into free [CH3COO]- and solvated [C4mim]+ions, and the free [CH3COO]- is more beneficial to disrupting the hydrogen bonds of cellulose and therefore promoting cellulose dissolution. The impact of differnt polar aprotic solvents on cellulose solubility depends on the interaction between solvent molecules and the catons of the ILs. On this basis, the IL based composite solvents which could quickly dissolve significant amounts of cellulose were developed.5. Based on the solubility difference of cellulose, hemicellulose and lignin in the ILs, the selective separation of three components of model biomass was conducted. The weight percentage of the separated cellulose, hemicellulose and lignin was 99.7,75.4 and 76.9%, respectively. The recovery and recycling usage of the ILs were investigated as well. This provides a new way for the seperation and use of biomass components.
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