Experimental Study On Catalytic Preparation Of 5-HMF From Corn Stover By Fenton/Deep Eutectic Solvent Pretreatment

5-Hydroxymethylfurfural?Abbreviated as 5-HMF?is a kind of chemical raw material can be directly produced by the catalytic conversion of cellulose in crop straw,which is widely used in fine chemical.As a typical agricultural waste in the northern region in China,corn stover is still in a state of high pollution and low production capacity.Its unique advantage of high value utilization has not been used efficiently.Therefore,the development of high-efficiency,environmentally friendly,and high-value-added practical technologies to catalyze corn stover conversion into 5-HMF has certain significance for the high-value utilization of biomass resources.In order to weaken the natural barrier effect of lignin in biomass structure,different Fenton reactions was used to pretreat corn stover to promotes the high-value utilization rate of cellulose.First,low concentration of hydrogen peroxide was put in Fenton's reagent to pretreat corn stover for enhancing the yield of reducing sugar after enzymolysis.Secondly,Fe²⁺was used to stimulate Fenton reaction to pretreat corn stover in two ways:direct input and continuous input.At the same time,Fourier infrared spectroscopy?FTIR?,scanning electron microscopy?SEM?,X-ray diffraction?XRD?and thermogravimetric analysis?TG?was combined to analyze the characteristics of corn stover properties before and after pretreatment.The optimal result of the low hydrogen peroxide concentration test is the combination of 0.2 mol?L^-11 Fe²⁺and 0.2%H₂O₂ for 24 h.Under this condition,the yield of reducing sugar was 1.21 times higher than that of untreated corn stover after enzymatic hydrolysis of 72 hours.The crystallinity of the cellulose decreased by 7%,and the content of the acid-insoluble lignin decreased by 16.27%.However,there was no significant change in the lignin content in the corn stover treated by the two feeding methods after the Fenton reaction was stimulated.The hemicellulose content increased slightly,and the enzymolysis efficiency of cellulose after 1 FPU/g cellulase hydrolysis increased by 1.5 times.Some analysis show that Fenton pretreatment can reduce the ineffective adsorption of lignin to cellulase,destroy the microstructure of straw,and reduce its thermal stability.In view of the fact that Fenton pretreatment failed to extract lignin,deep eutectic solvent was used to separate lignin from corn stover.Equal molar ratio of choline chloride and urea was formulated into DES solvent,and corn stover were treated under microwave conditions at80?and 100?,respectively.The content of heald fiber in the obtained coarse pulp was higher than 70%,and the enzymolysis efficiency of cellulose after 15 FPU/g cellulase digestion for 72 h was slightly higher than that of untreated corn stover.The dissolution rate of lignin is about 10%and FTIR analysis shows that the extracted lignin contains more G and H monomers.Based on the concept of biorefining,a unique MAAL?maleic acid and aluminum chloride?combined catalyst was used to directly catalyze the pretreated corn stover,and the yield of target product 5-HMF and by-product furfural was quantitatively analyzed.The results showed that the highest conversion rate of cellulose in Fenton modified corn stover was 82%,and the highest conversion rate of hemicellulose was 95.03%.It shows that the Fenton reaction can improve the reactivity of cellulose and hemicellulose in corn stover and increase the yield of 5-HMF.In the single water phase and water-organic solvent two-phase system,MAAL catalyzed the crude cellulose fractionated by DES.The results showed that the highest yield of 5-HMF was only 6.53%,and the highest yield of furfural was 37.47%.It shows that the cellulose prepared by DES solution is not ideal for the catalytic preparation of5-HMF,and its utilization method needs to be further explored.