Study On The Conversion Of Carbohydrates Into Furan Chemicals In Deep Eutectic Solvents

Biomass is the most abundant and renewable resource on the earth,which has great potentiality of chemical conversion and wide application in energy,chemistry and medical fields.The conversion of carbohydrates into platform chemicals and value-added products is the key point for efficient utilization of the biomass resource.This thesis taking biomass carbohydrates as the raw material and the green chemical synthesis conversion as the research method,makes a series of study about the chemical conversion of biomass carbohydrates in the deep eutectic solvent system.This thesis mainly includes the synthesis of 5-HMF and 5-CMF from carbohydrates in DESs,and the preparation of the fossil fuel alternative 5-EMF.Moreover,this thesis also involves in the preparation and the characterization of catalysts.Some research results obtained from those studie are as follows.Firstly,the DES consisting of fructose and ChCl has been proved an excellent reaction system,in which the fructose could be effectively converted into 5-HMF in the presence of extremely low dosage of BrOnsted acids such as HCl and H2SO4.88.6%and 90.3%yields of 5-HMF were obtained with the H2SO4 and HCl being used as catalysts,respectively.This DES reaction system has good ability of water tolerance that could run normally with the water content as high as 40 wt%.The recycle ability of this DES system is also studied.In the DES/MeCN biphasic system,the DES mixture could be directly reused for the next time after the separation of DES phase from the organic solvent,and no obvious decrease of 5-HMF yield was observed after this DES system being reused for five times.Other carbohydrates such glucose,inulin and sucrose could also be dehydrated in the DES system,giving 60.3%,61.5%and 69.8%yield of 5-HMF especially.Moreover,the possible mechanism of the carbohydrate dehydration in the DES system has been put forward in our study.Then,a novel method was put forward in this thesis for the preparation of new platform molecule 5-CMF in the DES/MIBK biphasic reaction system.Compared with the traditional preparation method of 5-CMF,this method is milder and more environmental friendly.In the conversion of bio-based sugars to 5-CMF,types of metal chloride catalysts affected dramaticallythe experiment result.It was found that the catalyst with high Lewis acidity could effectively promote the conversion of carbohydrates.When AICl3·6H2O used as the catalyst,the fructose could be effectively converted into 5-CMF.In the reaction condition of substrates of 5 mmol fructose,5 mmol catalyst loading,25 mmol ChCl dosage,30 mL MIBK co-solvent,120?reaction temperature and 5 h reaction time,a highest yield 5-CMF of 50.3%was obtained.The DES mixture could be effectively recycled after the reaction,only 10%decrease of 5-CMF yield was detected after the DES system being recycled for three times.Other bio-based sugars such as glucose,inulin and sucrose were also exerted in this biphasic reaction,and suitable 5-HMF&5-CMF yields were achievedallowing this DES system with practical potentiality of application.Moreever,the possible mechanism of the carbohydrate dehydration into 5-CMF was schemed on the experimental data obtained.Compared with the extremely low acid,the solid acid catalyst possesses many advantages for its separation and recycling,and could be observed to effectively catalyze the carbohydrates dehydration into 5-HMF as well as.A variety of self-made solid acids including lignin-derived solid acid,graphene oxide,sulfonated solid-ball acid,molecular sieve based catalysts and silica-based catalyst were tasted in the carbohydrates dehydration with DES system.Under the optimized reaction conditions,a highest 5-HMF yield of 94%was obtained with the lignin-derived solid acid.Moreover,the lignin-derived solid acid and sulfonated solid-ball acid held appropriate reusability,and the inactivation of solid acid reactivation could be retrieved after simple sulfonation steps.Following,the metal-free catalyst Amberlyst-15 was used in the dehydration of fructose into 5-HMF.the CrC3 modified Amberlyst-15 could be found to effectively converse the glucose into 5-HMF.Moreover,the commercial ion exchange resin has many advantages for it economic efficiency and environmental friendship.In the DES biphasic reaction system,the obtained 5-HMF solvent could be used as the starting material for the 5-EMF preparation,therefore,77.3%yield of 5-EMF was achieved from fructose with one-pot and two-step reaction process in the presence of Amberlyst-15.The reaction conditions also strongly affect the 5-EMF and 5-HMF yields,such as time,temperature and catalyst loading.In this study,a maximum 94.3%yield of 5-HMF was obtained from fructose under the condition of 0.9 g fructose,20 wt%catalyst loading,3.6 g ChCl dosage,30 mL MeCN co-solvent,100? reaction temperature and 2 h reaction time.Moreover,the glucose could also be dehydrated into 5-HMF in the presence of 40 wt%Amberlyst-15-CrCl3,and a highest yield of 57.0%5-HMF was obtained with the reaction condition of 0.9 g glucose,3.6 g ChCl dosage,30 mL MeCN co-solvent,130? reaction temperature and 2 h reaction time.Other carbohydrates such as sucrose,maltose and starch could also dehydrated in the DES system,and 49.4%,37,8%and 35.7%yield of 5-EMF were obtained separately.Both Amberlyst-15 and Amberlyst-15-CrCl3 catalysts could be reused for several times,no obvious decrease of 5-EMF and 5-HMF yields was took place in the original third recycles.