Study On The Catalytic Conversion Of Cellulose To Furfural And Levulinic Acid

Levulinic acid and 5-HMF are two important chemical intermediates.Their various derivatives can be used in many fields,such as fuel,medicine,multifunctional materials and so on.They are rated as one of the 12 large bio-based platform chemicals by DOE.In this paper,four kinds of biodegradable deep eutectic solvents(DESS)were synthesized.Their physical properties were measured and their degradation effects on cellulose were explored.In the DES/MIBK two-phase system,microcrystalline cellulose and nano cellulose were degraded to prepare 5-HMF and levulinic acid with metal chloride as catalyst.The factors affecting the yields of the products were determined,and the system of preparing the target products with two different materials was compared.The research and conclusions were as follows:(1)The melting point of four DESs was lower than that of any component.Among the four DESs,The water content of O-DES was the highest,followed by T-DES and M-DES.The solubility of O-DES to cellulose was the highest,because the viscosity of it was the smallest,and oxalic acid,the raw material for O-DES synthesis,was a strong organic acid.The acidic environment was conducive to the dissolution of cellulose.The viscosity of DESs was inversely proportional to the solubility of cellulose and the smaller the viscosity was,the greater the solubility was.The conductivity of DESs was directly proportional to the solubility of cellulose and the greater the conductivity was,the greater the solubility of cellulose was.Through FTIR,SEM and XRD,we could get the theoretical mechanism of DESs dissolving cellulose.The dissolution of cellulose by DES was to destroy the amorphous area and intramolecular hydrogen bond of cellulose.The crystal form of cellulose changed from typical cellulose I to cellulose II.Based on the investigation of the solubility of cellulose by DESs,it is proved that O-DES can effectively dissolve cellulose.It is feasible to use it to degrade cellulose to prepare 5-HMF and levulinic acid.(2)The extraction effects of ethyl acetate,methyl isobutyl ketone,toluene and tetrahydrofuran on 5-HMF and levulinic acid and the dissolution on DESs were investigated.Finally,methyl isobutyl ketone(MIBK)was selected as the extractant because of the solubility and boiling point.When the best experimental conditions: O-DES: MCC=100,200wt% MIBK,3wt% Cr Cl3,the maximum yield of 5-HMF was 15.7% at 150℃ for 1.5h,and the maximum yields of levulinic acid and glucose were 14.3% and 28.4% respectively at 170℃ for 2h.By measuring the recovery effect of O-DES,it was determined that the recovery times of O-DES were three times,which caused little effect on the products yields.(3)The particle size of nanocellulose(NCC)prepared by sulfuric acid hydrolysis was analyzed by particle size analyzer and scanning electron microscope.The particle size was 100-200 nm,the width was 6-8nm,the average particle size was 170 nm,and the particle size consistency was 0.265.It was proved that the synthesized cellulose reached the nano level and could be used for subsequent reactions.5-HMF and levulinic acid were prepared from NCC and the effects of various factors on the yields of the products were investigated.It was found that the three products increased first and then remained unchanged with the increase of the ratio of O-DES: NCC and extractant dosage and increased first and then decreased with the increase of catalyst dosage.When the temperature was lower,the yields of the three products were all on the rise.As the increase of temperature,the maximum yield of 5-HMF was 5.7% at 150℃ for 2 h,and 4.5% and 14.2% yields of levulinic acid and glucose at 170℃ for 3h and 2h,respectively.Comparing the preparation of target products by degrading MCC and NCC,it could be seen that under the same reaction conditions,the yields of products obtained by catalyzing NCC was much lower than that of catalyzing MCC.The yields of products from two materials under the optimal conditions was also very different.The yields of the former was significantly lower than that of the latter.The most likely reason was that the degree of polymerization and crystallinity of MCC was much lower than that of NCC.NCC with high degree of polymerization and crystallinity was difficult to be dissolved in a large amount in the solvent system,so the products yields was low.