Study On Hydrothermal Conversion Of Lignocellulosic Biomass To Furfural And Levulinic Acid

Lignocellulosic biomass can be produced to platform chemicals such as furfural and levulinic acid through hydrothermal conversion and further converted into a series of high-value-added chemicals and high-grade hydrocarbon liquid fuels through condensation,hydrodeoxygenation and other processes.It is helpful to realize the highvalue utilization of biomass,alleviate the environmental pollution problems caused by fossil energy,and meet national strategic needs.Based on this,with the support of National Key Research and Development Program of China,this paper has developed a dilute acid hydrolysis coupled solid acid catalytic conversion technology based on a new carbon-based solid acid catalyst,which realizes the efficient directional conversion of cellulose biomass to furfural and levulinic acid.Firstly,xylose,the most abundant pentose unit in biomass,was taken as the research object,and a sulfonated carbon-based solid acid catalyst was synthesized to catalyze the conversion of xylose to furfural,and the catalyst was characterized and analyzed in detail,focusing on the influence of different catalyst preparation conditions on catalytic performance.By optimizing the reaction time,temperature,substrate concentration,and solvent composition,the best performance condition of the catalyst was obtained,and the difference in catalytic performance between the catalyst in pure water solvent and organic solvent was verified.Further,the catalyst cycle test was carried out to study the stability of the catalyst.The results showed that the solid sulfonated acid had both weak acid sites and strong acid sites.The functional group distribution of the solid acids SP-150,SP-170,and SP-190 prepared at three sulfonation temperatures showed similar characteristics.In GVL/water solvent,the highest furfural yield obtained with SP-170 as catalyst reached 80.4 mol.%.In addition,the catalyst is also suitable for the conversion of pentose and its polysaccharide to furfural.The furfural yields of arabinose and xylan are 71.2 mol.% and 67.3 mol.%,respectively.Aiming at the problems of the low conversion rate of raw materials and easy deactivation of catalyst in the process of biomass hydrothermal conversion to furfural and levulinic acid in pure water solvent system,a new resin-based carbon-based acid fixing catalyst with high catalytic activity and hydrothermal stability was synthesized by condensation.The catalytic performance of the catalyst for dehydration of typical biomass-derived sugars to FF and LA was tested in a pure water solvent,carried out catalyst recycling test and analyze the causes of catalyst deactivation.Among them,the highest furfural yield of xylose is 57.4 mol.%.Through further optimization of working conditions,the yield of levulinic acid of glucose is 62.5 mol.%,the yield of levulinic acid of sucrose is 56.9 mol.%,and the yield of levulinic acid of maltose is 61.7 mol.%.Through the test of catalyst recycling and the characterization of the catalyst after recycling,it was found that the enrichment of depolymerization residue on the catalyst surface and the loss of sulfonic acid functional groups during recycling were the main reasons for catalyst deactivation,and the macroporous structure of catalyst could effectively reduce the impact of depolymerization residue aggregation.Based on the new resin-type carbon-based solid acid,the dilute acid hydrolysis coupled with a solid acid catalytic conversion process was developed,which realized the efficient and directional conversion of cellulose biomass to furfural and levulinic acid.First,xylose and glucose with yield distribution of 91.3 mol.% and 79.3 mol.%were obtained by hydrolysis under the catalysis of 0.9 wt.% dilute sulfuric acid,and the corresponding conversion rates of hemicellulose and cellulose were 100% and 97.3%,respectively.Under the synergetic catalysis of solid acid and dilute acid,xylose and glucose in the hydrolysate obtained 68.7 mol.% of the furfural yield and 70.3 mol.% of the yield of levulinic acid.The yield of furfural and levulinic acid based on dry biomass reached 27.3 wt.%.The catalytic system has good adaptability to typical cellulosic biomass,such as rice straw,cotton straw,wheat straw,barley straw,sorghum straw,willow eucalyptus,and scotch pine.The yield of furfural and levulinic acid is more than23 wt.%.After 28 cycles,the catalyst performance can still maintain 83% of the initial catalytic performance.Finally,the physicochemical properties and pyrolysis behavior of the depolymerization residue,the primary solid by-product produced in the hydrothermal conversion of cellulose biomass,were systematically studied.It was found that the liquid phase depolymerization residues(H-CS,H-ES,and H-PS)from three kinds of biomass,namely corn stalk,eucalyptus salicifolia,and pinus sylvestris,were complex polymers based on aromatic and furan rings.The macro kinetic simulation of thermal cracking based on DG-DAEM shows that the parallel reaction of H-CS degradation has a lower activation energy(144.7 k J/mol),and the parallel reaction of condensation is the dominant reaction of H-CS.PY-GC/MS and TG-TOF-MS were used to analyze the escape behavior of the pyrolysis products,and the relationship between the typical chemical structure of the polymer residue and the pyrolysis behavior was obtained.The three depolymerization residues have good thermal stability and high coke yield and have the potential to prepare excellent solid fuels and further pyrolysis to prepare liquid biofuels.In addition,the pyrolysis products of the depolymerization residues contain rich furan platform compounds,which can be further refined into high-value-added chemicals and high-grade fuels.