The Research On Conversion Of Biomass Over Phosphotungstic Acid-based Ionic Liquids

With the increasing demand of energy sources and depletion of fossil fuels, the world is faced with a serious energy sources crisis. At the same time, gas and water generated from the production and use of fossil fuels caused serious environmental pollution. Biomass can serve as a source for both energy and carbon, and being renewable, it is the only sustainable source of energy and organic carbon for our industrial society. Producing biofuel and chemicals from lignocelluloses by chemical transformation is considered to be one of the effective ways to relieve the energy sources crisis.In this dissertation, catalytic transformation of typical agricultural residual lignocelluloses such as corn stalk and catalytic hydrolysis of duckweed for reducing sugar by phosphotungstic acid-based ionic liquids, which advantaged both heterogeneous and homogeneous catalysts were investigated. Results demonstrated that this catalytic system is efficient for not only catalytic transformation of lignocelluloses but also catalytic hydrolysis of duckweed. Furthermore, The ionic liquids are easy to recycle and can be used without significant loss of activity after several runs. Thus, the research method provided in this dissertation will be a significant references for the future efficient utilization of renewable carbon-rich resource.Some details are as follows:(1)Catalytic transformation of agricultural biomass such as corn stalk was investigated with phosphotungstic acid-based ionic liquids as catalysts. Modern instrumental analysis methods such as GC-MS、GPC、FT-IR、TG、NMR and elemental analysis were applied to characterize the physical and chemical properties of raw material, products and residue. The catalytic mechanism was also elucidated based on the intensive discussion and analysis. Results showed that: the optimum reaction conditions for the reaction system: [C4H8SO3Hmim]3PW12O40 catalyst dosage: 0.2 mmol; reaction temperature: 473 K; 1 g corn straw powder; reaction time: 60 min; volume of ethanol concentration is: 80%.In the conditions of corn stalk powder conversion rate as high as 95.80%, GC-MS and GPC of products revealed that biomass was completely transformed into small molecules. The main products were furfural(27.4%), ethyl levulinate(16.38%), guaiacol(5.36%), 4-ethylguaiacol(7.79%)and the yield of total reducing sugar was 14%. FT-IR and TG analysis displayed that some aromatic refractory components of raw materials were hard to be degraded.(2)The catalytic hydrolysis of duckweed for reducing sugar was further investigated. Modern instrumental analysis methods such as GPC、FT-IR、TG、NMR and elemental analysis were applied to characterize the physical and chemical properties of raw material, products and residue. The results showed that, phosphotungstic acid-based ionic liquids had the good performance in hydrolysis of duckweed. The best yield of total reducing sugar is 79.8% under the condition of 140 oC, 3 h, 0.4 mmol IL catalyst.Catalytic transformation of biomass by phosphotungstic acid-based ionic liquids in mild condition has practical significance: This is the path to sustainable development of social economy that transforms biomass to chemicals. It reveals broad application prospects though still in the stage of base research.