Production Of 5-Hydroxymethylfurfural From Hexose Catalyzed By Solid Acid In Aqueous System

Accelerating the development and utilization of biomass meets the major strategic needs of the global energy transition.The conversion of biomass into platform compounds is one of the most promising routes for biomass utilization.5-hydroxymethylfurfural（HMF）,as an important biomass-based platform compound,can be prepared from the dehydration of economical and abundant natural resources of hexose,and can be further converted into high value-added compounds such as fuel,lubricant,solvent,polymer materials.Production of HMF is of great significance to alleviating the global energy crisis.On the basis of the existing research,this subject aims to promote the efficient production and industrialization of HMF in the water phase,focusing on the various characteristics of solid acid catalysts,and systematically discussing how its acid center,acid content,surface hydrophilicity and process conditions in the reaction process influence on the conversion of hexose to HMF:（1）The influence of acid sites and content in the solid catalyst was studied.Regenerated cellulose was used as a carbon source to prepare regenerated cellulose carbonaceous solid acid catalysts with different carbonization times.The results showed that the catalyst contained a large amount of-SO₃H and a small amount of-COOH and-OH groups on the surface,and had a high amount of BrΦnsted acid;the carbonization time affected the amount of surface acid,and the amount of acid gradually decreased with the increase of time;In the reaction of fructose dehydration to produce HMF,the relationship between catalytic activity and surface acid content was affected by temperature:at 140℃and 150℃,the higher the acid content,the higher the catalytic activity;at 160℃,the catalytic activity of three catalysts is comparable.In the water phase system,the optimal reaction conditions were:regenerated cellulose carbonaceous solid acid with a carbonization time of 12 h was used as catalyst,reaction was conducted at 160℃for 180 min,the HMF yield reached 50.2%,and the fructose conversion rate can reach 85.4%.（2）The influence of the surface hydrophilic and hydrophobic properties of solid catalysts was studied.[MIM]₃HSi W₁₂O₄₀ was synthesized using 1-methylimidazole to replace part of the protons in H₄Si W₁₂O₄₀.The results showed that:[MIM]₃HSi W₁₂O₄₀ contains hydrophilic Keggin and lipophilic imidazole ring structures,which were micellar catalysts.Compared with H₄Si W₁₂O₄₀.[MIM]₃HSi W₁₂O₄₀ can catalyze the conversion of fructose to HMF more effectively.This was because the hydrophilic end of the micellar catalyst can promote fructose aggregation and increased the conversion rate,and the hydrophobic end inhibited the hydration reaction of HMF and increased the yield of HMF（up to 47.5%）.In addition,[MIM]₃HSi W₁₂O₄₀also had catalytic activity for the conversion of glucose,and the yield of HMF reached 13.6%.The reason for the low yield was the lack of Lewis acid sites in the catalyst.（3）The influence and recovery performance of the solid catalyst Lewis acid center were studied.Fe/Fe₃O₄@ZSM was synthesized by hydrothermal method coupled with impregnation method.The results showed that the surface of the catalyst contained both BrΦnsted acid center and Lewis acid center,and was a core-shell structure in which magnetic iron oxide was wrapped by a molecular sieve;in the reaction of glucose dehydration to generate HMF,the maximum yield of HMF was 32.0%.The catalytic activity was much higher than that of HZSM-5（1.5%）;magnetism made the separation process of the catalyst simple.After three times of reuse,the yield of HMF can still reach 30.0%.（4）The influence of process conditions in the reaction process was studied.The hybrid catalyst(SO₄^2-/B₂O₃/Zr O₂)was prepared by the impregnation method and combined with the pressure release to promote the dehydration of glucose to prepare HMF.The results showed that:SO₄^2-/B₂O₃/Zr O₂ contained BrΦnsted acid center and Lewis acid center,which was a typical mesoporous catalyst—effective structure for mass transfer;pressure reduction promoted water boiling,which can effectively promote the HMF in the mesoporous catalyst to diffusion and mass transfer,and played an important role in inhibiting the occurrence of HMF side reactions.Under the optimal conditions,the yield of HMF significantly increased from 9.3%to35.2%.