Qualitative Analysis For Liquefaction Products From Lignocellulosic Biomass Catalyzed By Sulfuric Acid And The Reaction Mechanism Research

Significant progress has been made in the preparation of levulinic acid and its esters,furfural,5-HMF and other small molecular platform compounds by catalytic liquefaction of lignocellulosic biomass.However,the components of the lignocellulosic biomass liquefaction products are complex,in particular,the liquid phase products.This makes product separation difficult,and also brings challenges to the full composition of liquefied products.On the other hand,this also hinders the further research on the mechanism of lignocellulosic biomass liquefaction.In this thesis,gas chromatography with quadrupole time-of-flight mass spectrometry（GC/Q-TOF MS）,combined with post-target and non-target analysis,was used to analyze the liquid phase products generated from lignocellulosic biomass liquefaction.And on the basis of the results of qualitative analysis,the Carbon-Compound Specific Isotope Analysis（C-CSIA）technology were used to study the liquefaction mechanism of glucose.The main research contents and results were summarized as follows:1.GC/Q-TOF MS,combined with post-target analysis method,was used to analyze the liquid phase products generated from lignocellulosic biomass liquefaction,such as poplar wood,pine wood,cellulose model compounds,including glucose,cellobiose and microcrystalline cellulose,hemicellulose model compounds,including xylose,xylan,glucose and xylose mixture and microcrystalline cellulose and xylan mixture,liquefied in ethanol catalyzed by sulfuric acid.In the above 9 samples,36,35,25,16,18,22,28,18,17compounds were identified successively,and a total of 54 compounds were identified in all samples by this analysis method.The results show that the target analysis,using the library search for mass spectra combined with the quality retention index and accurate mass measurement,and combing with GC/（CI）-Q-TOF MS analysis accurate molecular ion peaks of the samples to get some of the components（[M+H]⁺）formula deduce the corresponding components,further to the unknown material qualitative,can greatly improve the accuracy of post-target analysis of unknown compounds qualitative.2.Based on the qualitative analysis of lignocellulosic biomass liquefaction products by post-target analysis method,the non-target analysis method was used to analyze the non-target compounds that could not be identified by post-target analysis.Eighteen unknown compounds were identified by non-target analysis for the first time.Among the 18 unknown compounds,six were intermediates of lignocellulosic biomass liquefaction and 12 were byproducts.The reaction mechanism of ethyl levulinate by catalytic liquefaction of lignocellulosic biomass acid was further clarified based on the intermediate compound ethyl 2-hydroxy-4-oxopentanoate（EHO）,which was first reported.The mechanism was as follows:（i）cellulose is hydrolyzed to generate glucose,from which 1,6-anhydro-Beta-d-Glucopyranose（AGP）,1,6-Anhydro-Beta-d-glucofuranose（AGF）,3-hydroxy-4-oxopentanoic acid（HOA）and EHO are gradually generated,and finally ethyl levulinate is produced;and（ii）cellulose was hydrolyzedintoglucose,whichgraduallygeneratedinto1,4:3,6-Dianhydro-alpha-d-glucopyranose（DGP）,HOA and EHO,and finally into ethyl levulinate.3.On the basis of the above liquefaction mechanism research,the liquefaction mechanism of sulfuric acid catalyzed liquefaction of cellulose to ethyl levulinate was further studied by Gas chromatography combustion isotope ratio mass spectrometer（GC-C-IRMS）using glucose as the model compound of cellulose.C-CSIA of target compounds in the liquefied products of glucose was established by GC-C-IRMS,and the standard deviation ofδ¹³C test value of the specific compounds was less than 0.3‰.Theδ¹³C value and fractionation characteristics of intermediate products 1,4;3,6-dianhydro-alpha-d-glucopyranose（DGP）were compared with different liquefaction temperatures.And combining with the variation tendency of the DGP’s yield,all of the above results show that,C-O,C-H bonds just participate in reacting in the process of glucose to generate DGP by dehydration.But during the generation of ethyl levulinate from DGP by decarboxylation and rearrangement isomerization reactions,there are not only breaking and forming C-O,C-H bonds,but also involving C-C,which leads to the latter having more significant carbon isotope kinetic effect.Therefore,it is speculated that the DGP directly generates levulinic acid through further decarboxylation and isomerization without undergoing 5-hydroxymethylfurfural.The results show that CSIA technology can effectively study reaction paths in complex systems such as glucose catalytic liquefaction and provide more information for liquefaction mechanism.