Study On Preparation Of Levulinic Acid And 5-hydroxymethylfurfural From Saccharides Catalyzed By Heteropolyacid Salts

Considering the increased consumption of fossil fuels,the use of other alternative fuels has become of particular interest.Biomass,as a renewable energy source,is an efficient alternative for the production of chemicals and transportation fuels.Biomass raw material has the following characteristics:Rich in products,which can be found everywhere in nature;Renewable,biomass energy is inexhaustible;Green environmental protection,the use of biomass resources generally produces less pollutants than fossil energy.Therefore,the utilization of biomass energy into high-value chemicals through reasonable ways has been a hot spot of research.Levulinic acid（LA）and 5-hydroxymethylfurfural（5-HMF）are two important platform chemicals with broad application prospects.Both of them can be transformed into higher value chemicals through specific transformation,and play a vital role in food,medicine,chemical industry and other fields.Generally speaking,macromolecular substances such as starch or lignocellulose in biomass are degraded into disaccharides,which can be further degraded into monosaccharides such as glucose and fructose,and monosaccharides can be converted into LA and 5-HMF.Heteropolyacid salt catalyst has the advantages of economy,green and easy recovery,and can be used for catalytic conversion of sugars.In this paper,three kinds of silicotungstate(Ag₄Si W₁₂O₄₀,Zn₂Si W₁₂O₄₀,Al_4/3Si W₁₂O₄₀)and three kinds of phosphotungstate(CrPW₁₂O₄₀,Ni_3/2PW₁₂O₄₀,Ag₃PW₁₂O₄₀)were synthesized by heteropoly-acid and transition metal ions,and they were used in the degradation of biomass sugar to the reaction of levulinic acid and 5-HMF with good results.The main conclusions were as follows:（1）Six catalysts were used for the degradation of glucose to prepare levulinic acid under the same conditions.It was found that the catalytic order of three kinds of silicotungstate salts was:Ag₄Si W₁₂O₄₀<Zn₂Si W₁₂O₄₀<Al_4/3Si W₁₂O₄₀,while the order of three kinds of silicotungstate salts was:Ag₃PW₁₂O₄₀<Ni_3/2PW₁₂O₄₀<CrPW₁₂O₄₀,and the catalytic effect of CrPW₁₂O₄₀is the best.The catalysts were characterized by FTIR,XRD and SEM,and the optimum reaction conditions were as follows:The glucose was 0.5 g,the dosage of the CrPW₁₂O₄₀was 0.3 g,the reaction temperature was 180℃,and the reaction time was 150 min.At this time,the conversion rate of glucose was 99.01%,and the yield of levulinic acid was51.33%.（2）Glucose was almost not transformed in the single-phase pure water system,and Na Cl had a little promotion effect on the reaction,while glucose was almost completely transformed in the Na Cl-H₂O/GVL two-phase system,and the optimal reaction conditions were as follows:The glucose was 0.5 g,the ultrapure water was 5 ml,the GVL was 20 ml,the Na Cl was 0.35 g,the reaction temperature was 160℃,the reaction time was 120 min,and the dosage of the CrPW₁₂O₄₀was 0.3 g.At this time,the conversion rate of glucose was 96.24%,and the yield of 5-HMF was 63.14%.（3）In view of the good performance of CrPW₁₂O₄₀catalyst in glucose degradation reaction,it was continued to be used in the reaction of synergistic catalytic degradation of sucrose to 5-HMF with hydrochloric acid,and the optimal reaction conditions were optimized as follows:The sucrose was 0.5 g,the ultrapure water was 5 ml,the GVL was 20 ml,the Na Cl was 0.35 g,the p H value of the solution was 1,the reaction temperature was 210℃,the reaction time was 90 min,and the dosage of the CrPW₁₂O₄₀was 0.4 g.At this time,the sucrose conversion rate was 98.37%,and the yield of 5-HMF was 54.81%.The recovery experiment of CrPW₁₂O₄₀catalyst also proved that the catalyst was stable.