Preparation Of Furfural Platform Compounds From Biomass Resources In Deep Eutectic Solvent

5-hydroxymethylfurfural?5-HMF?is an important platform compounds,which can derive a number of downstream products by further reaction.In this paper,a simple and cheap deep eutectic solvent?DES?was used as solvent to study the dissolution of cellulose,and degradation of cellulose to 5-HMF by deep eutectic solvent was studied.The specific research contents were as follows:Firstly,the synthesis of choline DES and its dissolution mechanism of cellulose were studied.The dissolution of cellulose by four deep eutectic solvents which were cholinechloride/glycerolChCl/Glycerol),cholinechloride/urea?ChCl/Urea?,cholinechloride/Citric acid?ChCl/Citric acid?and cholinechloride/oxalic acid?ChCl/Oxalic acid?was studied from three aspects:temperature,viscosity and conductivity.The results showed that the viscosity decreased with the increase of temperature.However,the conductivity and solubility of cellulose increased.ChCl/Oxalic acid had a better dissolution effect on cellulose.The micromorphology of cellulose was observed by scanning electron microscopy.It was found that the solvent system could dissolve cellulose effectively.The structure of regenerated cellulose was similar to original cellulose,but the crystal form of cellulose had changed from type I to II.The dissolution of cellulose in ChCl/Oxalic acid was preliminarily analyzed:The anions and cations of DES dissolve cellulose effectively by splitting and recombining hydrogen bonds and glycoside bonds with cellulose.Secondly,the preparation of 5-HMF and glucose in the DES homogeneous system was studied.Microcrystalline cellulose,DES,metal chloride was used as raw material,solvent and catalyst,respectively.The effects of types of DES,kinds of metal chloride,ratio of DES to cellulose,dosages of catalyst,reaction temperature and reaction time on the yields of glucose and 5-HMF were investigated.In this work,ChCl/Oxalic acid and SnCl₄ were confirmed as reaction solvent and catalyst respectively,and optimal conditions were as follows:microcrystalline cellulose 1 g and SnCl₄ 1.42 wt%were added to 25 g ChCl/Oxalic acid at 160?.After 1.5 h of reaction,the yield of glucose was 22%,the maximum yield of 5-HMF was 11%.Finally,the preparation of glucose and 5-HMF in ChCl/Oxalic acid-organic solvent biphasic phase system was studied in the same material ratio.The results showed ethyl n-butyrate was the optimal extractant.When the reaction temperature was 140?,the reaction time was 2 h,the yield of 5-HMF reached the maximum.The yield of glucose and 5-HMF were 23.5%and 29.8%,respectively.Compared with the homogeneous system,the yield of 5-HMF in the biphasic phase system increased12.5%.It showed that the biphasic phase system was more suitable for cellulose degradation to prepare 5-HMF.The mechanism of the degradation of 5-HMF by SnCl₄in DES was analyzed as follows:cellulose is first hydrolyzed to glucose,then glucose is isomerized to fructose,and finally fructose is removed three molecules of water to form 5-HMF.In the meantime,it found that DES could be re-utilized after the investigation of the reaction system re-utilization.Comparing the different systems for preparing 5-HMF by dissolving cellulose,the research system provides a new idea for the degradation of cellulose to prepare 5-HMF.