| The research work using the ionic liquid of imidazolium-water system to dissolve the lignin. But the dissolving mechanism is unclear. Which limits the ionic liquid- water- lignin system in-depth research in some extent. Due to the lignin is a natural polymer, with complex functional and spatial structure, to investigate the interactions between ionic liquid water and behavior is more difficult. We take the lignin model compound 2,6-dimethoxy phenol(2,6-DMP) as a probe, which can be used to study the dissolved mechanism in ionic liquid-water system. Using spectroscopic method resolution lignin model compounds, ionic liquid, interaction between and among water molecules, thus to provide reasonable theoretical basis for the mechanism of dissolved lignin.This paper studies content included the main research contents include: 1. preparation of different kinds and concentrations of ionic liquid solution, selected 2,6-dimethoxyphenol as simple phenolic lignin model compound, and determine its solubility in ionic liquid-water mixtures; 2.Fixed ionic liquids and the molar ratio of 2,6-DMP(1:0.4), the means of spectroscopy investigation on intermolecular interaction force. Such as attenuated total reflection infrared spectroscopy(ATR-IR), and two-dimensional correlation infrared spectrum, Raman spectrum in different concentrations of ionic liquids in aqueous solution, and with the presence of ionic liquid and water form when 2,6-DMP join, at the same time the ternary system of water clusters in the collective and the change of the ionic liquid aggregate; 3.By the different solubility in different mole fraction of ionic liquid water phenomenon, explain the dissolution mechanism of 2,6-DMP predict lignin dissolved characteristics under different ionic liquid water system. Through experimental analysis, get the following conclusion:1. Dissolution behavior of 2,6-dimethoxyphenol(2,6-DMP) in 1-butyl-3-methyl imidazolium tetrafluoroborate([C4mim]BF4) aqueous solutions(ionic liquid mole fraction x IL=1.0-0.02) was investigated by attenuated total reflectance infrared(ATR-IR) spectroscopy. The experimental results indicated that 2,6-DMP solubility increased and then decreased with adding water into [C4mim]BF4. The corresponding threshold of x IL is 0.1. The results of ATR-IR and two dimensional correlation IR spectroscopy analyses showed that ionic clusters of [C4mim]BF4 could be destroyed by water with the increase of water amount, and be converted into ionic pairs. This change of microstructure influences the behavior of 2,6-DMP dissolution greatly.2. The ternary system of alkylimidazolium bromine-water-lignin model compound(2,6-Dimethoxyphenol, 2,6-DMP) and the binary system of alkylimidazolium bromine-water were investigated by Raman spectroscopy. The results indicated that the imidazolium ring and alkyl chains on ILs interacted with water or 2,6-DMP through different intermolecular forces. And there was the transformation of the gauche or trans configuration of alkyl chains of ILs in the mixed systems. The gauche configuration of alkyl chains existed in 1-ethyl-3-methyl imidazolium bromine([Emim]Br), whereas the gauche and trans configurations were found in 1-hexyl-3-imidazole bromine([Hmim]Br). The configuration of alkyl chains was affected by the formation of water cluster instead of adding 2,6-DMP. |
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