| Hydrothermal conversion of biomass in the presence of catalyst can produce bio-based liquid fuels.This is one of the most promising technical routes for biomass utilization.Furan platform compounds,represented by 5-hydroxymethylfurfural(HMF)and furfural,are critical intermediates in this route.These compounds are also the bridge between biomass and liquid fuels.This dissertation focuses on the development of renewable butanone-water reaction system with ionic liquid as the catalyst,and aims at the realization of high-efficiency conversion of biomass and its derived sugars to furan platform compounds.All the related work is supported by the National Key R&D Program of China,the National Science Fund for Distinguished Young Scholars,and the National Natural Science Foundation of China.Firstly,the most abundant C5 sugar unit in biomass,namely xylose,was selected as the reactant.Then the influence of the metal component and the imidazole component in ionic liquid catalyst on the dehydration of xylose to furfural was investigated.Based on the detailed structure characterization of ionic liquid and the quantification of xylulose,which was an important intermediate in xylose conversion,we found that proper proportion of each component in catalyst favored the isomerization-dehydration reaction route of xylose.This route required low activation energy than the direct dehydration route.However,excessive amount of some catalyst component could lead to frequent occurrence of side reactions,and therefore furfural yield would decrease with prolonging reaction time.At 140?,75% yield of furfural were achieved after catalyst screening.The proposed catalytic reaction system was also appropriate for biomass conversion,and a furfural yield of 48% was obtained from corn stalk.On the basis of the experimental results above,molecular dynamics simulation was carried out in order to study the mechanism of organic solvent effect from butanone on the conversion of xylose to furfural.The results showed that butanone could strengthen the interaction between water and xylose,thus accelerating the protonated dehydration of xylose and raising xylose conversion.Moreover,butanone had shielding effect against water molecules,and therefore side reactions were avoided.Arabinose is the second abundant C5 sugar unit in biomass,and it is also the aldopentose with the lowest reactivity.When using arabinose as the feedstock,60% yield of furfural could be reached in butanone-water solvent mixture with ionic liquid catalyst at 140?.Reaction kinetics analysis indicated that unwanted reactions primarily resulted from the condensation between furfural and dehydration intermediates from arabinose.Besides,butanone-water solvent mixture was found to increase the activation energy required by furfural degradation,so the formation of byproducts was hindered.Based on the mechanism and experimental research on the hydrothermal conversion of C5 sugars,we employed the same reaction system in the conversion of C6 sugars for the production of HMF.Widely available sugars including sucrose,maltose,cellobiose,lactose,inulin and cellulose was chosen as the feedstocks.Sulfonation of ionic liquid catalyst as well as microwave heating was adopted for improving the efficiency of the reaction.The experimental results suggested that the proposed reaction system could realize the rapid conversion of disaccharides and polysaccharides with high selectivity towards HMF.Complete conversion of each disaccharide was achieved within 1min and the best HMF yield was 65.1%.Sucrose and inulin,which are rich in fructose unit,had higher HMF selectivities than other sugars.The next were maltose,cellobiose,and cellulose,which mainly consist of glucose unit.They produced more oxygenated aliphatics than others.Lactose had the lowest HMF selectivity and tended to be converted into furan byproducts during the dehydration process. |
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