| Nowadays, energy crisis become increasingly serious. It is urgent to hunt for alternative fuel source to solve the problem all over the world. Biomass resources is renewable resources that was produced abundantly as waste during agricultural products processing. 5-hydroxymethylfurfural(5-HMF), prepared from carbohydrate in biomass resources, could be used as an precursor to synthesis clean fuels and prevent cardiovascular disease effectively. Therefore, how to produce 5-HMF efficiently from biomass resources has attract a promising focus.First, the 5-HMF formation regulation of monosaccharide, disaccharide and polysaccharide catalyzed by acid was explored. Then, solid acid phosphate catalysts separated from products easily were synthesized and the catalytic properties were researched. Finally, the effect of pretreatment on the conversion from agricultural products processing waste carbohydrate resources to 5-HMF was discussed. The primary research contents and results were as follows:(1)The regulation of 5-HMF of monosaccharide(glucose(G), fructose(F)),disaccharide(D-cellobiose(C), sucrose(S)) and polysaccharide(microcrystalline cellulose(Cm), soluble starch(Ss)) catalyzed by organic triprotic acid citric acid(Ac)and inorganic triprotic acid phosphoric acid(Ap) was researched. And the temperature was 383 K, 393 K and 403 k. The reaction activation energy(Ea) was calculated.The maximum yield of 5-HMF(Ymax-5-HMF) was the highest with 44.3±0.48%from 60 min to 480 min. The higher temperature the higher Ymax-5-HMF. The carbohydrate with α-glucosidic bond in molecular structure converted more easily was indicated by the result that Ymax-5-HMF and Y5-HMF in the same condition converted from carbohydrate with α-glucosidic bond were higher than β-glucosidic bond.The order of kinetic models and reaction activation energy in carbohydrate acid systems were as follows: 0 order and 84.25 kJ/mol in F/Ap system, 0 order and128.86 kJ/mol in F/Ac system, 0.25 order and 79.27 kJ/mol in G/Ap system, 0.25 order and 57.49 kJ/mol in G/Ac system, 0 order and 70.68 kJ/mol in S/Ap system, 0order and 105.89 kJ/mol in S/Ac system, 0.25 order and 119.64 kJ/mol in C/Ap system, 0.25 order and 128.29 kJ/mol in C/Ac system, 0.5 order and 118.69 kJ/mol in Ss/Ap system, 0.5 order and 161.28 kJ/mol in Ss/Ac system, 0.75 order and 63.55kJ/mol in Cm/Ap system, 0.25 order and 128.31 kJ/mol in Cm/Ac system. The Ea catalyzed by Ap was lower than Ac in the same sugar system. The temperature had an greater effect on the formation of 5-HMF catalyzed by Ap. But the catalyst was not conducive to separate from product as Ap was liquid acid.(2)The catalytic characteristic of solid acid phosphate on monosaccharide(G, F),disaccharide(C, S) and polysaccharide(Cm, Ss) was researched by analyzing Y5-HMF after fostering at 393 K.The solid phosphate catalysts performed greater catalytic activity when reacted for 5h in terms of Y5-HMF compared to calcium phosphate, strontium phosphate and magnesium phosphate and was more easily to separated from products with practical significance. The Y5-HMF catalyzed by solid acid calcium phosphate(SPA-Sr) was higher than strontium phosphate(SPA-Ca).The product in carbohydrate dehydration solution reacted for 5h and 2h. Then analyze the materials(F, G, C, M(maltose) and S): In G/SPA-Sr system, the yield of F(YF) was detected as 0.52±0.02% when reaction time was 2h, and the yield of S(YS)was detected as 1.60±0.08% when it was 5h. In F/SPA-Sr system C was not detected when reaction time was 2h, and the yield of C(YC) was detected as was 4.89±0.04%when it was 5h. It was indicated that SPA-Sr could effect the isomerization reaction between G and F, and polymerizazed C and S. There was no such phenomenon in SPA-Ca system. The conversion rate of sucrose(ConS 60.3±1.64%) in S/SPA-Ca system when the reaction time was 2h was higher than S/SPA-Ca(50.5±2.89%), and the conversion rate of D-cellobiose(ConC, 11.2±0.06%) was higher than C/SPA-Sr(7.74±0.19%). It was indiated that SPA-Ca could break glucosidic bond more easily.The Ss became transparent liquid when heated for 5h, the yield of G and M was building up. The YG increased from 2.72 0.24% at 2h to 6.42 0.80% at 5h in Ss/SPA-Ca system, and increased from 1.14 0.06% at 2h to 5.58 0.47% at 5h. TheM was not detected at 2h, and was detected as 11.16 0.18% in SPA-Ca system and7.41 0.06% in SPA-Sr system. The disaccharide were not detected and monosaccharide were decrease in Cm/SPA-Ca system and Cm/SPA-Sr system. A large amount of precipitate was remained. It was indicated that almost all of the dissolved Cm had hydrated to small molecule carbohydrate and anticipated to reactions. So improving the solubility of carbohydrate by effected on the supramolecular structure was the key to conversion to 5-HMF.(2) Microcrystalline cellulose(Cm), corn stalk core(Co), wheat straw(Wh) was pretreated with water, 0.1 M H2SO4, 0.2 M NaOH, ionic liquid([C4mim]Cl), then catalyzed by SPA-Ca and SPA-Sr. The results were as follows:The mass loss rate of biomass pretreated by acid was higher than other methods,and so was the yield of reducing sugar. The Y5-HMF could be increased by pretreatment with different degree. The YTrs-enzy(the yield of reducing sugar in carbohydrate enzymolysis liquid) and Y5-HMF of Co and Cm pretreated by ionic liquid was higher than other methods. The YTrs-enzy and Y5-HMF of Wh pretreated by alkalinity were higher than other methods.Analysis the structure from FTIR spectrum: The pretreatment had an great effect on FTIR feature peak of carbohydrate. The pretreatment of acid and ionic liquid had an greater effect on α-glucosidic bond at 788 cm-1 and β-glucosidic bond at 898 cm-1 in Co. The molecular structure of Co could be effected by acid and ionic liquid pretreatment. The feature peaks of 1727cm-1 C=O and 833 cm-1α-glucosidic bond were disappeared in Wh preteated by alkalinity. And 1512cm-1aromatic rings of lignin was just disappeared after alkalinity pretreatment which was indicated that ligin could be removed by alkalinity and made it more easier to transformed and utilized. As a result, the effect of pretreatment varied from different materials, the pretreatment should be different according to the biomass. |
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