【作者】 许爱荣；

【导师】 王键吉；

【作者基本信息】 兰州大学 ， 物理化学， 2010， 博士

【摘要】 离子液体是近十多年来在绿色化学的框架下发展起来的一类新的介质和功能材料。由于其具有几乎可以忽略的蒸汽压、热稳定性高、不燃烧、易回收、结构和性质可调变等优良性能,离子液体已被成功地应用于有机合成、催化化学、电化学以及材料科学等领域。然而,离子液体在纤维素材料和生物质原料分离方面的研究还处于起步阶段,人们对离子液体尤其是离子液体的阴离子对纤维素的溶解规律缺乏系统的研究,现有的离子液体存在着熔点高、粘度大、或者室温下溶解度较低等缺陷。作为国家863项目(No.2007AA05Z454)的一部分,本文通过阴离子的功能化设计合成了一系列对纤维素具有较强溶解能力的离子液体,研究了这些离子液体对纤维素的溶解性能、锂盐和极性非质子溶剂的加入对纤维素溶解性能的影响,以及离子液体和复合体系对纤维素溶解的可能机理。在此基础上,研究了离子液体对生物质原料组分的选择性分离。主要研究内容包括：1、根据离子液体结构与性能的关系,设计合成了一系列1-丁基-3-甲基咪唑基阴离子功能化的离子液体：1-丁基-3-甲基咪唑的乙酸盐,甲酸盐,乳酸盐,甘氨酸盐,乙醇酸盐,苯甲酸盐以及二氰胺盐。借助1HNMR核磁技术对这些离子液体进行了表征,并在303.15K至343.15K的温度范围内测定了这些离子液体的密度(ρ)、粘度(η)、电导率(σ)等物理化学数据,考察了这些性质随温度的变化关系。结果表明,随着温度的升高,离子液体的密度稍有降低,粘度明显降低,而电导率显著增加。阴离子烷基链的长度对离子液体的物理化学性质有重要的影响,烷基链上CH2的增加会导致密度和电导率的降低,粘度的增加。离子液体的密度可以用Tait方程进行描述；离子液体[C4mim][HCOO]、[C4mim][HOCH2COO]和[C4mim][N(CN)2]的粘度随温度的变化更适合用VFT方程来描述,而其它几种离子液体的粘度随温度的变化更适合用Arrhenius方程来描述；离子液体的电导率随温度的变化用VFT方程比用Arrhenius方程描述更合适。2、系统地测定了不同温度下纤维素在上述离子液体中的溶解度,并利用1H NMR化学位移和溶剂化显色紫外／可见光探针研究了影响离子液体对纤维素溶解性能的主要因素。离子液体的阴离子的结构对纤维素的溶解度具有显著的影响,离子液体阴离子的氢键接受能力对纤维素的溶解度起支配作用。离子液体[C4mim][CH3COO]的阴离子[CH3COO]-上的H原子被吸电子基团OH、SH、NH2以及CH3OH取代后会导致纤维素溶解度的降低。3、以[C4mim][CH3COO]离子液体为代表,研究了少量锂盐LiX(X=Cl-,Br-, NO3-, ClO4-, [CH3COO]-)的加入对纤维素在离子液体中溶解度的影响,并用13C NMR技术分析了可能的影响机制。研究结果表明,少量锂盐的加入即可增加纤维素的溶解度,主要原因是：Li+与纤维素中的O(3)有较强的相互作用,导致纤维素分子链之间的氢键O(6)H…O(3)被打开。向[C4mim][CH3COO]/LiX/纤维素体系中加入水,可使纤维素沉淀再生,再生纤维素没有发生衍生化反应,说明[C4mim][CH3COO]/LiX是纤维素的直接溶剂。再生纤维素表现出与原生纤维素相似的热稳定性。4、研究了极性非质子溶剂二甲基亚砜(DMSO)、N,N二甲基甲酰胺(DMF)和N,N二甲基乙酰胺(DMAc)的加入对离子液体溶解纤维素性能的影响以及可能的机制。实验结果表明,这些非质子溶剂的加入均可以较大幅度地增加纤维素在离子液体中的溶解。250C时,无论是[C4mim][CH3COO]还是DMSO、DMF或DMAc均不能溶解纤维素,但是将[C4mim][CH3COO]以一定的比例与DMSO、DMF或DMAc混合后,纤维素能够高效地溶解到这些溶剂中。1H NMR和13C NMR核磁结果表明,这是由于[C4mim]+被极性非质子溶剂溶剂化,更多的离子液体的阴离子[CH3COO]-由缔合状态转化为解离状态,解离状态的[CH3COO]-离子更有利于打开纤维素分子内氢键,从而促进了纤维素的溶解。极性非质子溶剂对纤维素溶解度的影响取决于这些溶剂分子与离子液体阳离子相互作用的强弱。在此基础上,开发了在室温下能快速、大量溶解纤维素的离子液体复合溶剂体系。5、根据不同离子液体对纤维素、半纤维素、木质素溶解性能的差异,首次尝试用离子液体对模拟生物质原料三组分进行选择性逐级分离,纤维素、半纤维素、木质素的分离百分比例分别为99.7%,75.4%和76.9%。同时研究了离子液体的回收和循环使用。为生物质原料组分的分离和利用提供了新的思路。更多还原

【Abstract】 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.更多还原