Studies On The Catalysts’ Design And Processes’ Development For Catalytic Conversion Of Biomass Into Furanic Compounds

With rapid development of economy and increase of population size, the global crisis of energy emerges in the twenty-one century. Meanwhile, due to the excessive exploit of non-renewable fossil fuels, the problems of environment pollution and ecological damage have come out, and how to develop new technical route to produce renewable biofuels has become a focus of scientific research. Lignocellulosic biomass has been regarded as renewable green-energy, and efficient production of fine chemicals and biofuels from lignocellulosic biomass would meet with the growing demand of economic development. In this thesis, from the point of catalytic chemistry and reducing the production costs, a series of novel catalysts have been prepared and used to convert lignocellulosic biomass to fine chemicals and liquid biofuels. The main research results are achieved as follows:1. A novel carbon-based solid acid catalyst with high concentration of acid sites, bearing-SO3H,-COOH and-OH groups, has been easily synthesized via one-step hydrothermal carbonization approach. Such carbonaceous catalyst was used in the dehydration of fructose into5-hydroxymethylfurfural (HMF). Fructose can be completely converted in DMSO solvent under mild conditions, and the yield of HMF was up to91.2%. When the concentration of fructose increased from initial7to20wt.%, the yields of HMF maintained around80%. Compared to other acidic catalysts, the multiple functional groups on the carbonaceous catalyst enhanced the adsorption of fructose, but did not inhibit the fast desorption of HMF from the catalyst surface. Meanwhile, the synergic effect between surface carboxylic acid and sulfonic acid groups promoted the efficient conversion of fructose to HMF.2. Fructose can be fully converted in THF/DMSO mixed-solvent (7:3, v/v) catalyzed by a novel carbon-based solid acid catalyst with high surface area (189m2·g-1) under mild conditions, and the yield of HMF was up to98%. From the results of kinetic analysis, the extraordinary activity of carbonaceous catalyst was attributed to its greatly lowering down the energy barrier of the dehydration reaction of fructose, and the activation energy was50.3kJ·mol-1, which was much lower than that catalyzed by sulfuric acid or ion-exchanged acid resin. Especially, with the addition of DEE and H2O into the reaction system to extract HMF from the reaction solution, high purity of HMF (96.4%) can be obtained, realizing the goal of separation of HMF from high boiling point solvent of DMSO.3. A novel Sn-Mont solid acid catalyst, which had moderate to strong acid strength and contained both Lewis and Bronsted acid sites was synthesized easily via an ion-exchanged method. Single Sn-Mont catalyst can be directly used to completely convert glucose to HMF in THF and DMSO mixed solvent under mild conditions, and the yield of HMF was up to53.5%. It was found that Sn ions in the structure of Sn-Mont catalyst was used as the Lewis acid sites to isomerize glucose to fructose and these active Sn-OH groups was used as the Bronsted acid sites to convert the generated fructose to HMF. Especially, the yields of HMF were up to44.4and39.1%from starch and cellulose in THF/H2O-NaCl biphasic system, where THF was used as the extraction agent to promote the generated HMF from aqueous phase transferring to organic phase.4. The mixtures of xylose and glucose can be simultaneously and completely converted catalyzed by single Sn-Mont catalyst in THF/H2O-NaCl biphasic system under mild conditions, and the yields of furfural and HMF were about50and65%, respectively. Besides, the yields of furfural and HMF can be enhanced to76.8and68.6%at the same reaction conditions with addition of another NbOPO4solid acid catalyst with similar ratio of Bronsted to Lewis acid sites and higher acid amounts. Such excellent performances were attributed to the synergistic effect between Sn-Mont and NbOPO4catalyst, where Sn-Mont catalyst was beneficial for conversion of glucose to HMF and NbOPO4catalyst was used to efficiently convert xylose to furfural. This mixed catalysts also have exhibited excellent performances in the conversion of lignocellulosic biomass, and the total mass yields of furfural and HMF were always around20%. Meanwhile, lignin and inorganic salts in lignocellulosic biomass did not affect the conversion of hemicellulose and cellulose into furfural and HMF.5. A Ru/Co3O4catalyst easily prepared via co-precipitation method has showed extraordinary catalytic performances in the simultaneously hydrogenolysis of furfural and HMF. Meanwhile, furfural and HMF in the reaction mixture from dehydration of mixed sugars or lignocellulosic biomass can be directly converted to MF and DMF catalyzed by such Ru/Co3O4catalyst under mild conditions, and the yields of MF and DMF were around90%. This approach not only avoided the complicated separation and purification processes of furfural and HMF from the reaction mixture, but also lowered down the costs of biofuels production, realizing the goal of efficient production of liquid biofuels from renewable lignocellulosic biomass. It was confirmed that the Ru particles in the reduced catalyst were used to activate hydrogen, and active CoOx species have played important roles in the adsorption of intermediates and breakage C-O bonds, resulting in the formation of MF and DMF from furfural and HMF.