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离子液体结构性质及其溶解木质素的机理研究
张雅琴
学位类型硕士
导师张锁江 ; 何宏艳  
2017-07
学位授予单位中国科学院研究生院
学位授予地点北京
学位专业化学工程
关键词离子液体 氢键 Dft 超额红外 木质素 Β-o-4
摘要

离子液体作为一种新型溶剂,被广泛应用到催化过程、气体吸收、电解质和生物质处理等诸多领域。但目前对离子液体的结构性质和离子液体溶解木质素的机理缺乏深入的探究。本文采用量子化学计算和实验相结合的方法,研究了共溶剂对离子液体结构性质的影响,并着重研究了木质素在咪唑类离子液体中的溶解机理。主要工作总结如下:(1) 采用超额红外光谱(Excess IR)和密度泛函理论(DFT)计算的方法,研究了不同摩尔浓度配比的二甲基亚砜(DMSO)与N-丁基吡啶双氰基胺盐([Bpy][DCA])二元溶液中的氢键作用。研究结果表明,DMSO能同时与离子液体的阴阳离子之间形成氢键,并且与阳离子之间的氢键更强。DMSO共溶剂的存在减弱了阴阳离子之间的氢键作用,同时增强了二元混合体系的氢键作用。阴离子超额红外光谱的结果表明,溶液中存在稳定的Cring-H…NC, Calkyl-H…NC和CDMSO-H…NC作用体。当DMSO摩尔分数在0.3-0.4范围时,二元体系的氢键作用最强。二维红外分析表明,阳离子Cring-H将优先于Calkyl-H与DMSO发生作用。核磁共振氢谱中,阳离子的C-H化学位移向低场移动表明[Bpy][DCA]与DMSO之间形成了氢键,阳离子吡啶环的屏蔽区使CDMSO-H向高场移动。DFT计算得到的核磁结果与实验值相符合,并且[Bpy][DCA]与DMSO的各种作用方式的强弱顺序是:2[Bpy]+-2[DCA]--DMSO> [Bpy]+-[DCA]--DMSO> [Bpy]+-[DCA]-> DMSO-[Bpy]+> DMSO-[DCA]-。(2) 采用DFT计算了离子液体4种阴离子([OAc]-、[Cl]-、[MeSO4]-、[PF6]-)、4种阳离子([Mmim]+、[Emim]+、[Bmim]+、[Hmim]+)和16种离子对与木质素模型化合物愈创木酚-β-愈创木基醚(GG)之间的相互作用,并阐述了木质素在离子液体中的微观溶解机理。计算结果表明,单个阴离子或阳离子与GG之间容易形成氢键,阴离子与GG之间的氢键作用要强于单个阳离子与GG之间的氢键作用。阴离子与GG的α-OH位置作用最强,不同阴离子与之形成氢键的能力顺序符合:[OAc]-> [Cl]-> [MeSO4]-> [PF6]-。阳离子与GG的γ-OH位置作用最强,不同阳离子与之形成氢键的能力顺序符合:[Mmim]+> [Emim]+> [Bmim]+> [Hmim]+。阳离子烷基侧链长度的改变对阳离子与GG之间的相互作用影响较小,而阴离子种类不同则对阴离子与GG的相互作用影响显著。B3LYP-D3/6-311+g**计算水平发现阴离子同时与GG的α-OH和阳离子的C2-H形成氢键,阳离子咪唑环与GG的苯环之间存在π-π作用和CH-π作用。较强的氢键以静电作用为主,较弱的氢键以范德华作用为主,阳离子与GG之间的π-π作用和CH-π作用的性质为色散作用。氢键和π-π作用的协同作用是咪唑离子液体溶解木质素的至关因素。

其他摘要

Ionic liquids as novel solvents have been applied to processes, such as catalysis, gas absorption, electrolytes and biomass treatment. However, the structural properties of ionic liquids and the mechanism of lignin dissolution in ionic liquids lack in-depth exploration. In this work, the effect of co-solvent on the structure of ionic liquids is studied by computational chemistry in combination with experiments, and the mechanism of lignin dissolution in imidazolium-based ionic liquids is particularly studied by DFT calculations. The main research is summarized as following:(1) Excess infrared (Excess IR) and DFT calculations were applied to study the hydrogen bonding interactions between dimethyl sulfoxide (DMSO) and N-butyl-pyridinium dicyanamide ([Bpy][DCA]). The results show that DMSO forms H-bonds with [Bpy]+ and [DCA]- simultaneously and H-bond between DMSO and [Bpy]+ is stronger than that between [DCA]- and DMSO. H-bonds between ionic cations and anions are gradually weakened and the whole hydrogen bonding interactions in the solutions are enhanced by DMSO. Positive and negative peaks at fixed positions in excess IR of [DCA]- show the presence of stable interactions of Cring-H…NC, Calkyl-H…NC and CDMSO-H…NC. When the molar fraction of DMSO is in the range from 0.3 to 0.4, hydrogen bonding interaction reaches the maximum than that in other solutions. The sequence of the interactions in the binary solutions is: 2[Bpy]+-2[DCA]--DMSO > [Bpy]+-[DCA]--DMSO > [Bpy]+-[DCA]- > DMSO-[Bpy]+ > DMSO-[DCA]-.(2) The interactions between anions ([OAc]-, [Cl]-, [MeSO4]-, [PF6]-), cations ([Mmim]+, [Emim]+, [Bmim]+, [Hmim]+), 16 kinds of ion pairs and lignin model compound guaiacyl glycerol-β-guaiacyl ether (GG) is studied by DFT calculations to reveal the dissolution mechanism of lignin in ionic liquids. The results show that one single anion forms stronger H-bond with GG than cation does. The optimal position for anion-GG interactions is the α-OH of GG and anions follow [OAc]-> [Cl]-> [MeSO4]-> [PF6]-. The optimal position for cation-GG interactions is the γ-OH of GG and cations follow [Mmim]+> [Emim]+> [Bmim]+> [Hmim]+. It seems that the alkyl chain lengths do not have obvious effects on cation-GG interactions, but the types of anions have significant effects on anion-GG interactions. Further calculations at the B3LYP-D3/6-311+g** level confirm that anions form H-bonds with C2-H of cations andα-OH of GG, and π-π stacking effect exist between pyridinium ring and benzene ring of GG. The stronger H-bonds are dominated by electrostatic interaction, and the weaker H-bonds and π-π stacking effect are dominated by van der Waals interaction. H-bonds and π-π interaction are essential for the dissolution of lignin in ionic liquids.

语种中文
文献类型学位论文
条目标识符http://ir.ipe.ac.cn/handle/122111/24214
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张雅琴. 离子液体结构性质及其溶解木质素的机理研究[D]. 北京. 中国科学院研究生院,2017.
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