Study On Preparation Of 5-Hydroxymethylfurfural From Cellulose In A Biphasic System

Due to the increasing consumption of traditional fossil resources,the use of biomass resources to produce a variety of chemicals,including fuels,platform compounds and multifunctional materials,provides the opportunity to replace some of the traditional fossil energy sources as a raw material for the production and preparation of bulk chemicals.Among them,the preparation of 5-hydroxymethylfurfural（5-HMF）through the catalytic conversion of cellulose is a feasible method to efficiently and rationally produce high value-added chemicals using biomass resources.As an important platform compound,5-HMF can be transformed into a variety of high-value chemicals.Therefore,this paper designs and synthesizes a phosphate-supported catalyst with Si O₂ microspheres as a carrier to convert cellulose into 5-HMF in a two-phase system,and studies the reaction mechanism of the catalytic system.1.In this paper,hafnium phosphate（Hf P）,tin phosphate（Sn P）,zirconium phosphate（Zr P）,lanthanum phosphate（La P）and cerium phosphate（Ce P）are prepared.Through characterization and experimental results,it was found that Hf P had the best catalytic effect,while the yield of5-HMF reaching 45.5%.However,considering the high price of Hf,in order to reduce its use and improve the atomic utilisation,Si O₂ microspheres were chosen as the carrier for the preparation of the loaded catalysts and the effect of different Hf P loadings on the catalytic reaction was investigated.The most suitable loading amount of Hf P/Si O₂ catalyst was selected as 10 wt%based on the experimental results.The catalytic performance of the Si O₂,H₃PO₄-Si O₂,Hf P and Hf P/Si O₂ catalysts was also compared.,and it was found that the catalytic activity of Si O₂ on cellulose convertion is very weak,and after treatment with 1 mol·L^-1 H₃PO₄,the catalytic effect on the hydrolysis of cellulose was enhanced due to the increased amount of Brφnsted acid on its surface,and its conversion rate was increased from 10.2%to 23.8%.A 5-HMF yield of 45.5%was obtained using Hf P,while the Hf P/Si O₂ catalyst gave a 5-HMF yield of 48.6%,where the Hf P content was only 10 wt%of unsupported ones.2.To further reduce the amount of Hf used and to adjust the relative proportions of Lewis acid and Brφnsted acid in the catalyst,Zr P and Hf P were co-loaded onto the Si O₂ surface to obtain Hf_xZr_1-xP/Si O₂.The experimental results showed that the highest 5-HMF yield of 58.5%could be obtained when using Hf_0.7Zr_0.3P/Si O₂.Py-FTIR and NH₃-TPD was used to analyze the acidic type and strength of the catalysts,it was found that Hf_0.7Zr_0.3P/Si O₂ has a suitable ratio of Brφnsted acid to Lewis acid,which can synergistically catalyze the hydrolysis of cellulose and the isomerization of glucose,and has the best catalytic activity for the preparation of 5-HMF.The effects of the type of extracted phase in the reaction system,the amount of catalyst,the reaction temperature and the time on the catalytic reaction were also investigated.It was found that the optimum reaction:30 mg of Hf_0.7Zr_0.3P/Si O₂ is used as the catalyst,a biphasic H₂O-THF system containing 3.5 g Na Cl as the reaction solvent,the reaction temperature is190°C,the reaction time is 4 h,the conversion rate of cellulose is 89.2%,and the yield of 5-HMF is 62.1%.Due to the formation of P-O-Si on the Si O₂ carrier with Hf P,which reduces the loss of catalytically active components from the surface and enhances the stability of the catalyst,the catalyst was subjected to five cycles of experiments and the yield of 5-HMF was only reduced by 3.1%.3.In addition,the reaction mechanism of Hf_0.7Zr_0.3P/Si O₂ catalyzed cellulose preparation of 5-HMF was explored in combination with experimental results and characterization tests,which mainly included three steps:hydrolysis of cellulose,isomerization of glucose and dehydration of fructose.Firstly,hydrogen protons provided by hydroxyl groups on the catalyst act as Brφnsted acid centres to hydrolyse cellulose to glucose,then Hf⁴⁺and Zr⁴⁺act as Lewis acid centres to isomerise glucose to fructose,and finally,Brφnsted acid dehydrates fructose to produce 5-HMF.