Catalytic Conversion Of Carbohydrates To Functional Platform Chemicals

The rapid depletion of fossil fuels has led to an international effort to increase the use of renewable energy. The replacement for fossil fuels in this aspect comes from biomass, with biorefineries being presented as the future substitutes for petroleum refineries. In the same way that petroleum refineries use certain chemicals as the building blocks for more complex molecules such as polymers, biorefinery will use simple molecules that can be readily obtained from a vast number of feedstock as a base for the synthesis of biopolymers and other large molecules. The most promising building blocks are 5-hydroxymethylfurfural (5-HMF) and levulinic acid (LA), which are the subject in this thesis.The preparation of 5-HMF and LA from monosaccharides was successfully established in aqueous medium catalyzed by InCl3 in an efficient fashion.60% 5-HMF yield (10 min) and 57% LA yield (60 min) were obtained from glucose at 180℃ with 2.5 mol% InCl3, while 79% 5-HMF yield (15 min) and 45% LA yield (60 min) were obtained from fructose under the optimized conditions. It showed that fructose has the faster conversion to 5-HMF, and the relatively high amount of LA was obtained using glucose as substrate under the same condition. The comparative studies of glucose/fructose mixture manifested that the isomerization from glucose to fructose was easier than the reversible process. Moreover, a catalytic mechanism of monosaccharides dehydration was proposed.A biphasic system consisting of THF and NaCl (aq. solution) was developed for converting cellulose to 5-HMF in the presence of catalytic InCl3. A good 5-HMF yield (40%) was obtained accompanied with a LA yield of 11% in 2 h at 200℃. The resulted 5-HMF was extracted by THF from aqueous phase, avoiding its rehydration to LA. Additionally, this biphasic system could also be used for other carbohydrates derivitives, such as the mono-, di-, and polysaccharides, suggesting an effective catalytic system towards different feedstocks.Solid acid, SO42-/In2O3-ATP, was used as an excellent catalyst for the preparation of 5-HMF from hexose. The catalytic property of solid acid which contained In(III) and ATP powder was superior to the pure ATP. The Bronsted and Lewis acid sites on SO42-/In2O3-ATP could catalyze the glucose isomerizaition and fructose dehydration, respectively.40% yield of 5-HMF from glucose was obtained at 180℃ with the reaction time of 60 min in biphasic GVL/H2O system. The use of this system allowed the homogeneous catalyst used for glucose isomerization to be replaced by solid acid catalyst. Besides, the catalyst can be recycled and reused for four times without significant loss in activity.A single-step process for the conversion of cellulose into valuable LA was developed in SO3H-functionalized ionic liquids with addition of water, where the highest yield of 39% was obtained in the presence of [BSMim]HSO4 ionic liquid. This approach offered significant improvements for production of LA from cellulose, regarding high selectivity and product separation. The catalyst was effectively recycled four times without significant loss of activity. It also indicated that [BSMim]HSO4 ionic liquid gave satisfactory yields (93%) in the condensation of phenol and LA, which derived from their special structures, and the selectivity to p,p’-DPA of nearly 100% was obtained under the optimized condition. Simple operation, insolubility in the organic phase, high yield, and the reusability are the key features of this methodology. Based on this combination of assets, it would appear that [BSMim]HSO4 ionic liquid has great potential for green process.