| With the increasing consumption of coal, petroleum and other non-renewable resources, it is very urgent to seek the strategy of sustainable resources to be the replacement for fossil resources. Biomass is the most abundant renewable resource in the world. Form lignocelluloses, important platform chemicals such as 5-hydroxymethyl furfural (HMF), levulinic acid (LA) can be prepared. These platform chemicals have good reaction activity, from which a variety of high value-added chemicals can be produced and they are mainly applied in the field of chemical, materials, medicine, etc. Inorganic acids are commonly used as the catalyst for the preparation of levulinic acid from biomass. During the production process, however, a large amount of acidic wastewater will be produced, which is difficult to handle and harmful for the environment. Therefore, it is of great significance to develop an efficient, environmental benign and catalyst-recyclable technology for the preparation of LA.In this thesis, the kinetics of the degradation of cellulose and glucose to LA catalyzed by ionic liquids in high temperature lipid water were studied, and the technology for the preparation of LA from furfural residues was developed. The study screened and found the efficient and recyclable ionic liquids for the degradation of biomass to LA, revealed the regularity of ionic liquids, provided theoretical evidence and experimental basis for the development of efficient catalysis system of LA, and facilitated the industrialization process of efficient and low-cost preparation of LA.Firstly, glucose, fructose and cellulose were selected as the raw materials, and conversion of reactant, yield of LA were employed as the evaluation indexes. The degradation behaviors of the raw materials with 19 kinds of ionic liquids were studied. The results showed that 1-propylsulfonic-3-methylimidazolium chloride had the best catalytic activity, which can make fructose, glucose converted completely and a LA yield of 65% was achieved. The regularity for the catalytic activity of ionic liquids was demonstrated based on the experimental results:the kind of anions significantly impact the catalytic acitivity, and the catalytic activities followed the sequence of "Cl->HSO4>CH3SO3-".Secondly, glucose and cellulose were selected as the raw materials, and conversion of reactant, yield of LA were employed as the evaluation indexes. The kinetics of the degradation of the raw materials catalyzed by 1-propylsulfonic-3-methylimidazolium chloride and 1-butylsulfonic-3-methylimidazoliumhydrogensulfate were studied. The results showed that the highest yield of LA from cellulose catalyzed by 1-propylsulfonic-3-methylimidazolium chloride was 63.5% and the activation energy for the degradation of cellulose was 173.9kJ/mol. However, this IL is difficult to be reused because its structure changed during the process of reaction and recycle. The highest yield of LA from glucose and cellulose catalyzed by 1-butylsulfonic-3-methylimidazolium hydrogensulfate were 63.4% and 58.4%, and the activation energies for the degradation of glucose and cellulose were 148.4 and 151.2kJ/mol, respectively. This IL has good reusability.Thirdly, a near-critical water continuous flow reactor is designed for the study of the degradation of glucose catalyzed by 1-butylsulfonic-3-methylimidazoliumhydrogensulfate. The effects of reaction temperature and residence time on the degradation were studied. The conversion of glucose increased with the rise of reaction temperature and residence time. A glucose conversion of 98.7% and LA yield of 55.3% were achieved within the residence time of 16.7 min at 200℃. The results of the degradation of glucose in the batch reactor and flow reactor were compared. At the same temperature, the rate constant for degradation in the flow reactor was smaller than that in the batch reactor.Fourthly, furfural residues were selected as the raw materials to prepare LA in high temperature liquid water with dilute sulfuric acid. The effects of ratio of liquid to solid, acid concentration, reaction time and reaction temperature on the yield of LA from the decomposition of furfural residue were investigated, and the kinetic data were fitted. The optimized reaction condition was also obtained:ratio of liquid to solid is 1:10; concentration of sulfuric acid is 2%; reaction temperature is 180℃; and reaction time is 2 h. The yield of levulinic acid was 66.6% at this reaction condition. The activation energy for the decomposition of cellulose was obtained as 122.7kJ/mol. The study provided basic data for further research and evidence for the integrated utilization of furfural residues. |
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