The Application Of Ionic Liquids In Dissolution, Regeneration And Liquefaction Of Biomass

Stalk is a renewable, cheap and widely available biomass resource. It is generally used asthe production of energy by combustion in most regions of China resulting in a tremendouswaste of resources. For the purpose of improving the situation, and enhance thecomprehensive utilization of straw, the straw is studied in this thesis. Firstly, the mechanismof lignin dissolution and regeneration in ionic liquid is investigated through theoretical andexperimental study. Then, liquefaction of wheat stalk with acidic ionic liquids as catalyst arediscussed.Firstly, Density functional theory （DFT）, atoms in molecules （AIM） theory, natural bondorbital （NBO） analysis and Wiberg bond index （WBI） are employed to investigate themechanism of lignin dissolution and regeneration in1-allyl-3-methylimidazolium chloride（AmimCl）. Lignin is modeled with1-（4-methoxyphenyl）-2-methoxyethanol （LigOH）. Fromthe theoretical results, it is observed that AmimCl interacts with LigOH mainly by hydrogenbonds （H-bonds） and the interaction of AmimCl with LigOH is stronger than that of LigOHwith LigOH, thus, it can be speculated that lignin can be dissolved in AmimCl. In addition,the H-bonds between LigOH and AmimCl are weakened or even destroyed by the addition ofwater. The experimental results also reveal that lignin can be easily regenerated from theAmimCl-lignin solution by the addition of water. The regenerated lignin is characterized byFT-IR, TG, SEM compared with the original one.Then, a series of acidic ionic liquids are synthesised: N-methylimidazoliumhydrogensulfate （[Hmim]HSO₄）,1-sulfobutyl-3-methyl imidazolium hydrosulfate（[C₄SO₃mim]HSO₄）,1-sulfopropyl-3-methyl imidazolium hydrosulfate （[C₃SO₃mim]HSO₄）,N-methyl-2-pyrrolidonium hydrogensulfate （[NMP]HSO₄）,1-（3-sulfopropyl）-3-methylimidazolium Methyl Sulphate （[C₃SO₃mim]CH3SO₃）, N-Methyl-2-Pyrrolidonium MethylSulphate （[NMP]CH3SO₃）. In order to meet the needs of the experiment, these acidic ionicliquids are characterized by FT–IR, TG and1HNMR to determine the purity and thermalstability.Finally，we investigate the liquefaction reaction of wheat straw from the following fiveaspects: time, temperature, the ratio of liquid and solid, kinds of catalysts and the dosage ofcatalyst with the acidic ionic liquids as catalyst, polyethylene glycol-400and glycerol （m（polyethylene glycol-400）: m （glycerol）=4:1） as the liquefaction reagents. As can be seenfrom the results, the optimum reaction conditions are that, reaction time is20min, reactiontemperature is160°C, the ratio of liquid and solid is8:1, the catalyst is [C₃SO₃mim]HSO₄,the dosage of catalyst is15%. The TG analysis shows that the thermal stability of residue islower than that of raw material. It is can be seen from the FT-IR analysis that the components of the raw material participate the liquefaction reaction and the liquefaction products is amixture of polyhydric alcohols and phenolic compounds. The molecular weight distributionshows that the molecular weight is small implying that the bonds breaks during theliquefaction process.