Study On The Transformation Of Carbohydrates To Furfural And 5-alkoxymethylfurfural By Tandem Catalysis

Vigorously developing abundant and green biomass resources meets the needs of current green and low-carbon development,and is an effective technical way to achieve the carbon peaking and carbon neutrality goals.A variety of high value-added chemicals and fuels can be produced from biomass-based carbohydrates.The platform chemical furfural and biofuel 5-alkoxymethylfurfural can be prepared from five-carbon and six-carbon sugars,respectively.A large number of studies on the preparation of furfural and 5-alkoxymethylfurfural have been carried out at home and abroad,but there are still problems such as high cost,low efficiency,harsh catalytic conditions,unclear mechanism and environmental pollution.Therefore,this thesis has carried out the following research work aiming at the above problems:（1）The Sn Cl₄/1-ethyl-3-methylimidazolium bromide（EMIMBr）homogeneous system was constructed for the catalytic conversion of furfural.The catalytic activity of a series of metal chlorides on the dehydration of xylose to furfural in different ionic liquids was explored.The reaction system consisted of metal chloride salt Sn Cl₄ and EMIMBr is effective.In the Sn Cl₄/EMIMBr system,when the initial addition amount of xylose was 20 wt%（relative to the mass of ionic liquid）,the furfural yield could reach 71.1%.Moreover,when the composite catalyst composed of 5 mol%Mg Cl₂ and5 mol%Sn Cl₄was used to replace 10 mol%Sn Cl₄,the yield of furfural could still reach68.8%.Compared with the single aqueous system,the biphasic system composed of water and organic solvent can improve the furfural yield.However,compared with the single-phase reaction system of EMIMBr,the biphasic system composed of EMIMBr and organic solvent adversely affects the formation of furfural.In addition,adding an appropriate amount of water to the Sn Cl₄/EMIMBr system can effectively convert xylan and corn stover into furfural.（2）A heterogeneous system for the conversion of carbohydrates to 5-hydroxymethylfurfural（HMF）and furfural was constructed by tandem catalysis.A series of metal aluminum and tin modified hydroxyapatite catalysts were prepared by impregnation method.By characterizing the morphology,structure（pore size,specific surface area,pore volume,etc.）,acid site characteristics of the solid acid catalyst,it was found that the Al and Sn co-modified hydroxyapatite（Al/Sn-HAP）has higher specific surface area,pore size and Lewis acid density.The activation energy for the conversion of glucose was only 68.4 k J/mol catalyzed by Al/Sn-HAP in EMIMBr medium.The HMF yields were 70.5 and 46.6%at glucose loadings of 10 and 40 wt%,respectively.The furfural yield of xylose（10 wt%）could reach 56.4%.Moreover,this system can realize the efficient conversion of disaccharides and even polysaccharides into HMF by tandem catalysis of hydrolysis,isomerization and dehydration.Besides,the Al/Sn-HAP catalyst exhibits high cycling stability.（3）The hierarchical porous carbon materials with abundant mesopores and micropores were prepared without additional templates from chicken bones.Subsequently,the porous carbon material was functionalized with-PHSO₃H groups（SCCs）by a mild chemical reduction method,which introduced a high density of-PHSO₃H groups（2.33 mmol/g）,and preserved the mesoporous structure of the carbon precursor to a certain extent.High yields（63.6-94.7%）of 5-ethoxymethylfurfural（EMF）can be obtained from raw materials such as HMF,fructose and inulin in the ethanol system using SCC-700 as catalyst.The low apparent activation energies（29.1and 49.5 k J/mol）of SCC-700 for the conversion of HMF and fructose further confirmed its superior catalytic activity.In addition,compared with other kinds of sulfonic acid-based catalysts,the SCC-700 exhibited stable catalytic activity in cycling experiments.（4）The combination of metal phosphate and acidic ionic liquid 1-butylsulfonate-3-methylimidazolium chloride（BSO₃HMIMCl）to catalyze the conversion of glucose to EMF is effective.The EMF yield of 52.6%from glucose catalyzed by Tin phosphate（Sn PO）/BSO₃HMIMCl in ethanol medium could be obtained.The intermediate products of the reaction system were determined by LC-MS,GC-MS and ¹³C NMR,and the possible reaction pathways in the reaction system could be speculated.By comparing Sn PO combined with different acidic ionic liquids（BMIMHSO₄ and BSO₃HMIMHSO₄）and different heterogeneous Lewis acid catalysts（H-USY and Sn-beta molecular sieves）combined with BSO₃HMIMCl to catalyze the conversion of glucose in ethanol,the synergy of Sn PO and BSO₃HMIMCl was confirmed in the Sn PO/BSO₃HMIMCl system,and main pathway in the reaction was revealed.Through the optimization of parameters such as reaction temperature,substrate loading,catalyst dosage and solvent additives,the yield of EMF was further increased to 61.7%.In addition,the Sn PO/BSO₃HMIMCl system can also effectively catalyze the conversion of cellobiose and starch to EMF.In this study,a series of catalytic systems were constructed by rationally designing catalysts and screening solvents to realize the tandem catalysis of carbohydrates to prepare furfural,HMF,and EMF.The Sn Cl₄/EMIMBr system could efficiently catalyze the conversion of high concentrations of xylose,xylan and corn stover into furfural;Al/Sn-HAP/EMIMBr coould catalyze the triple reaction of hydrolysis,isomerization and dehydration,and realize the efficient conversion of disaccharides and polysaccharides into HMF;sulfonated carbon materials（SCC）with a large number of benzenesulfonic acid groups and a large number of mesopores were prepared from waste chicken bones,which could catalyze the rapid conversion of fructose and HMF to EMF in an ethanol system（yield 63.6-94.7%）;the Sn PO/BSO₃HMIMCl system can catalyze the efficient preparation of EMF from glucose,which broken the bottleneck of preparing EMF from glucose and the EMF yield increased.Through a series of experiments and characterizations,the main pathways in the reaction were determined,and the synergistic effect of Sn PO and BSO₃HMIMCl in the reaction was confirmed.This study can provide theoretical basis and technical support for the preparation of furfural,HMF and EMF from biomass carbohydrates.