| 5-Hydroxymethylfurfural(HMF)and furfural(FF)are the typical furanic compounds that are listed as the high value added platform chemicals from renewable biomass resource.HMF and FF,the dehydration products of C6 and C5 carbohydrates,respectively,can be used to synthesis a series of chemicals and liquid fuels,which is significant to gradually substitute the current fossil products.On this basis,novel and efficient reaction systems were developed to convert biomass carbohydrates into furanic platform chemicals in this thesis from the financial support from the National Basic Research Program of China(No.2013CB228101)and the National Natural Science Foundation of China(No.51476142).To convert hexose into HMF,fructose was investigated in a CO2-water system and it was found that this system could promote the formation of HMF compared to pure water system,as CO2 improved the acidity of the system.Then isopropanol was introduced into CO2-water system and HMF formation was remarkably improved because the solvent effect of isopropanol increased the tautomeric composition of fructofuranose,which was easy to form HMF.Additionally,the existence of isopropanol greatly suppressed the secondary reactions of HMF,and a high HMF yield of 67.14%was obtained under optimized conditions.With respect to the production of FF from pentose,the conversion of xylose into FF was studied in the CO2-water-isopropanol system.Higher initial CO2 pressure favored the dehydration of xylose to FF,and the addition of isopropanol slowed down the reaction rate of xylose to FF.The effect of NaCl on the conversion of xylose to FF in the CO2-water-isopropanol system was further investigated.The results showed that NaCl significantly promoted the formation of FF because the Cl can catalyze the enolization to form a key 1,2-enol intermediate,and a high FF yield of 69.12%was obtained under optimized condition.To improve the HMF yield from glucose,a simple single-phase reaction system consisting of water-DMOE-AlCl3 was developed.The results showed that introduction of DMOE can substantially enhance HMF production because of the polar aprotic solvent effect provided by DMOE.Under optimal condition,a high HMF yield(58.56%)was obtained.GC/MS analysis revealed that the liquid-phase products mainly included furans,oxygenated aliphatics,cyclopenten-1-ones,and pyrans,which were formed by complex reactions including retro-edol,fragment,dehydration and cyclization.Meanwhile,the formation of humins was greatly depressed in this system.The effect of Lewis acid AlCl3 and Bronsted acid H3PO4 on cellulose decomposition was also investigated in the water-DMOE system.Both the solvent composition and the ratio of L/B acids influenced the formation of HMF,and a maximum HMF yield of 49.42%when the ratio of water-DMOE was 1:7 and the ratio of L/B acids was 1:0.8.Further GC/MS analysis revealed that more glucose and anhysugars were formed from cellulose at the condition rich in B acid,while more furanic compounds were generated at the condition rich in L acid.Humin,a solid by-product formed during the acid-catalyzed conversion of carbohydrate to platform chemical,can be further utilized by pyrolysis technology.Two humins derived from glucose(humin-g)and xylose(humin-x)were characterized by elemental analysis,FTIR and 13C-NMR.Both humins were polymers rich in furan rings,and their carbon contents were more than 66%.Thermogravimetry and pyrolysis kinetic analyses based on Flynn-Wall-Ozawa and Friedman methods suggested that the activation energies for both humins increased as their conversion rates increased,and humin-g had better thermal stability following the removal-of weak linkages at low temperature.Further Py-GC/MS analysis showed the pyrolysis product distribution from humins were dominant in furans and phenols,and higher pyrolysis temperature favored aromatization of the products,enhancing the formation of benzenes,benzofurans,indenes and naphthalenes,and increased the heat value of the chars. |
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