Study On Catalyzed Degradation Of Lignin Of Rice Straw In Imidazole Ionic Liquids

With the development of human society, resource crisis and environmental pollution have become the two major challenges to human society. The exploitation and utilization of biomass is the key to solve these two puzzles. However, biomass is very difficult for chemical degradation due to the complex structure. As a result, the new approach of biomass degradation technology, which should be environmentally friendly and efficient, has become a hot topic for chemists. Among them, ionic liquids showed vast potential for application prospects in biomass processing and degradation owing to its excellent physical and chemical properties, especially the strong dissolving capacity, reported by some recent researches. In this thesis:1. Three kinds of neutral ionic liquids, including 1-Ethyl-3-methylimidazolium bromide salt （[Emim]Br） （Ⅰ）, 1-Butyl-3-methylimidazolium bromide salt （[Bmim]Br） （Ⅱ） and 1-Octyl-3-methylimidazolium bromide salt （[Omim]Br） （Ⅲ）, were synthesized via one-step reaction. Their yields were 92.80%,96.80% and 95.20%, respectively. Then, seven kinds of functional ionic liquids including [Emim]OH, [Emim]im, [Emim]OAc, [Bmim]im, [Bmim]OH, [Bmim]HS04, [Bmim]OAc were synthesized via the reaction between the compounds Ⅰ or Ⅱ and H₂SO₄, NaOH, CH₃COOH or imidazole.2. Seven kinds of functional ionic liquids were used as catalysts for the degradation of lignin in rice straw. The straw was added into a solution of ionic liquids in water. The reaction mixture was stirred at 110℃ with reflux for 4 h. Among the seven ionic liquids, the catalytic capacity of [Bmim]im and [Emim]im was better than others, the degradation rates of lignin in rice straw were 69.76% and 75.89%, respectively.3. Then, the catalyzed degradation conditions of lignin in rice straw by [Bmim]im and [Emim]im was optimized. For the [Bmim]im, the optimum conditions were that the reaction temperature is 120 ℃, the time is 6 h, the ratio of straw/catalyst （m: m）1:1, the ratio of straw/water（m: m）=1:10. Under the conditions, the content of lignin in rice straw reduced from 18.9% to 5.09% and the degradation rate was 69.37% with RSD of 4.53%（n=6）. For the [Emim]im, the optimum conditions were similare in reaction time, the ratio of straw/catalyst and the ratio of straw/water, but the reaction temperature of 110 ℃. Under the conditions, content of lignin in rice straw reduced from 18.9% to 3.14% and the degradation rate was 83.37% with RSD of 3.27% （n=3）.4. The products obtained from degradation reaction of rice straw have confirmed by more than one of TLC, IR, HPLC, LC, GC-MS and other analytical methods. The results revealled that the products are mainly ethers, aldehydes and phenolics.