Designation Of Low Viscous Ionic Liquid Systems And Investigation Of Dissolution Of Biomass Macromolecules

In recent years, ionic liquids(ILs) have made a notable advance in the dissolution of cellulose and lignin. However, very few studies have been conducted to explore the influence of the structural skeleton of cation, alkyl chain length and the types of functional groups in anion or cation. Moreover, the existing ILs show some draws like higher viscosity, higher solution temperature or lower solubility, and so forth. As a part of the National Natural Science Foundation of China(No. 21373078), in this paper, a series of anion/cation-functioned imidazolium-based ILs and anionfunctioned choline carboxylate ILs were synthesized. For the sake of reducing solvent viscosity, a series of IL-based solvents were also designed. The main contents are as follows:1. 23 kinds of ILs were designed and synthesized, and they were 1,3-diallylimidazolium acetate([A2im][CH3COO]) 、 propionate([A2im][CH3CH2COO]) 、 butyrate([A2im][CH3CH2CH2COO]) 、 methoxyacetate([A2im][CH3OCH2COO])、ethoxyacetate([A2im][CH3CH2OCH2COO])、acrylate([A2im][CH2=CHCOO]) 、 glycollate([A2im][HOCH2COO]) 、 nicotinate([A2im][(C5H4N)COO]) 、 acetonate([A2im][CH3C=OCOO]) 、 levalinate([A2im][CH3C=OCH2CH2COO]) 、 1-methyl-3-allylimidazolium methoxyacetate([C1Aim][CH3OCH2COO]) 、 1-ethyl-3-allylimidazolium methoxyacetate([C2Aim][CH3OCH2COO]) 、 1-butyl-3-allylimidazolium methoxyacetate([C4Aim][CH3OCH2COO]) 、 1-ethoxyl-3-allylimidazolium methoxyacetate([HOCH2CH2Aim][CH3OCH2COO]) 、 1-ethoxyethyl-3-allylimidazolium methoxyacetate([CH3CH2OCH2CH2Aim][CH3OCH2COO]) 、 1,2-dimethyl-3-allylimidazolium methoxyacetate([(CH3)2Aim][CH3OCH2COO]) 、 1,2,4,5-qumethyl-3-allylimidazolium methoxyacetate([(CH3)4Aim][CH3OCH2COO]) 、 Nbutyl-N-methylpyrrolidine methoxyacetate(N(C4C1)Py][CH3OCH2COO])、N-butylN-methylpiperidine methoxyacetate([N(C4C1)Pp][CH3OCH2COO]) 、 Nbutylpiperidine methoxyacetate([N(C4)Pyr][CH3OCH2COO]) 、 4-methyl-Nbutylpyridine methoxyacetate([C1N(C4)Pyr][CH3OCH2COO])、1-prop-carboxyl-3-allylimidazolium chlorine([HOOCCH2CH2Aim][Cl]) and 1-propyl-3-allylimidazolium chlorine([CH3CH2CH2Aim][Cl]). The ILs were characterized by 1H NMR spectra.2. Solubilities of cellulose in the ILs at different temperatures were measured, and systematic studies were conducted to explore the influence of the structural skeleton of cation, alkyl chain length and the types of functional groups in anion or cation. Possible dissolution mechanism of cellulose in the ILs was investigated. The influence of solution temperature and time on molecular structure and thermal stability of the regenerated cellulose was also estimated.3. The effect of the addition of polar aprotic solvents like dimethyl sulfoxide(DMSO), N,N-dimethylformamide(DMF), N,N-dimethyl-acetamide(DMAc), Nmethylimidazole(MIM) in [A2im][CH3OCH2COO] on the solubility of cellulose and the possible mechanism were studied. The influence of solution temperature and time on molecular and thermal stability of the regenerated cellulose was also investigated.4. 13 kinds of choline carboxylate ILs including choline acetate([Ch][CH3COO]) 、 choline propionate([Ch][CH3CH2COO]) 、 choline butyrate([Ch][CH3(CH2)2COO]) 、 choline caproate([Ch][CH3(CH2)4COO]) 、 choline dodecanoate([Ch][CH3(CH2)10COO]) 、 choline acrylate([Ch][CH2=CHCOO]) 、choline lactate([Ch][CH3HOCH2COO])、 choline glycollate([Ch][HOCH2COO])、choline glycinate([Ch][H2NCH2COO]) 、 choline gluconate([Ch][HOCH2(CHOH)4COO]) 、 choline succinate([Ch]2[OOC(CH2)2COO]) 、choline tartrate([Ch]2[COO(HCOH)2COO]) and choline citrate([Ch]3[OOCCH2(HO)C(COO)CH2COO])were synthesized and characterized by 1H NMR spectra. Their thermal properties such as glass transition and thermal stability were measured.5. Choline carboxylate IL/H2 O solvent were designed, and the effect of addition of H2 O and anion structure on the solubility of lignin was studied. The possible dissolution mechanism of lignin in choline carboxylate IL/H2 O solvent was studied by the means of 15 N NMR, 13 C NMR and UV/Vis technology. At the same time, the influence of solution temperature and time on molecular structure and thermal stability of the regenerated lignin were also investigated.