The Isomerization Of Glucose Into Fructose Over Alkaline Ionic Liquids

The production of fuels and chemicals from biomass by chemical catalytic conversion method is an important way for the comprehensive utilization of biomass resources,which can effectively alleviate current energy crisis and environmental pollution.Recently,the reasearch is focused on the catalytic conversion of cellulose into 5-hydroxymethyl furfural and other small molecules.Catalytic conversion of cellulose to 5-hydroxymethyl furfural requires three steps,namely,hydrolysis of cellulose,isomerization of glucose and dehydration of fructose.Among them,the isomerization of glucose is a key step,so it is quite important to realize the highly efficient catalytic isomerization of glucose.Based on the shortcomings of current isomerization catalysts,an environment-friendly ionic liquid catalyst was developed to catalyze the isomerization reaction of glucose,and a highly efficient catalytic isomerization of glucose was achieved under mild conditions.Some details are as follow:(1)In this paper,a series of alkaline functionlized ionic liquids with carboxylate,hydroxide,carbonate,or proline as anions were prepared through ion exchange method.The structure and physicochemical properties of alkaline ionic liquids were characterized by FT-IR,NMR,TG and potentiometric titration,and their catalytic performance of glucose isomerization was investigated.In the optimum reaction condition,catalyst [N4,4,4,4]Pro dosage: 20 mol% relative to glucose,reaction temperature: 80 oC,reaction time: 30 min,the yield and selectivity of fructose were 36.8% and 73.8%,respectively.The results show that the reaction process is in accordance with the first order reaction kinetics and the activation energy of the reaction is 34.42 KJ/mol.The activation energy of the reaction is lower than the current literature reporting level,which is the main reason for high activity.Furthermore,isotope labeling method was used to investigate the isomerization mechanism of glucose by alkaline ionic liquids.The results of 2D-HSQC spectra showed that the isomerization mechanism of glucose was the same as Lobry de Bruyn-van Ekenstein mechanism.(2)Conventional alkaline ionic liquids have excellent activity in catalyzing the isomerization of glucose,but its biosafety has received wide attention in recent years.For this reason,we developed a series of low toxicity and biodegrable ionic liquis for catalyzing the isomerization of glucose.In this paper,a series of cholinium amino acids ionic liquids was successfully prepared.The structure and physicochemical properties of cholinium amino acids ionic liquids were characterized by FT-IR,NMR,TG and potentiometric titration,and their catalytic performance of glucose isomerization was investigated.In the optimum reaction condition,catalyst [Ch]Pro dosage: 20 mol% relative to glucose,reaction temperature: 70 oC,reaction time: 30 min,the yield and selectivity of fructose were 37.6% and 77.2%,respectively.