Characterization Of Biomass And Its Pyrolysis Products And Catalytic Mechanism Of Model Compounds By Nuclear Magnetic Resonance Technique

Pyrolysis is one of the most promising methods in the thermal conversion of biomass,which will convert biomass into complex and diverse products.It hinders subsequent research.Therefore,the in-depth analysis and characterization of biomass pyrolysis products is the basis for studying its reaction mechanism and upgrading process.Based on various NMR characterization techniques combined with isotope tracer methods,a series of reactions in the pyrolysis process of biomass were studied,which facilitates quantitative and qualitative analysis of complex products.It further promotes the determination of the relevant reaction mechanism and provides valuable data for upgrading process and catalyst design.Firstly,the activation of common chemical bonds（C-H bonds）in biomass were studied.The isotope labeling method and ¹HNMR were used to study the activation reactions of C-H bonds in several biomass model compounds using different reactors and catalysts,including methanol,ethanol,ethylene glycol,glycerol,and anisole.Affected by molecular characteristics and the orientation of molecular adsorption on the catalyst surface,the degree of C-H bond activation of different model compounds is different.Methylene is more susceptible to cleavage by metal catalysts than methyl and methine.Glycerol is the only model compound that can be catalyzed by Pt/C and Pd/C to break C-C bond.Two types of waste biomass（pine bark and residue）and four biomass components（cellulose,hemicellulose,lignin and tannin）were pyrolyzed in a tube furnace.Furthermore,the C-H bond in the pyrolysis oil was characterized by using HSQCNMR.It has been found in the study that rearrangement of methyl groups occured during the pyrolysis of bark and residue.The components of the pyrolysis oil produced are mainly catechol,guaiacol,and aromatic C-H bonds.The aromatic C-H bonds were produced by lignin and tannins.Pyrolysis oil has disadvantages such as high oxygen content,and its upgrading process is necessary.An innovative high-pressure in situ NMR characterization method for the isotope tracer upgrading process was proposed.Ring-opening reactions of two basic pyrolysis oil model compounds（methylcyclopentane and cyclohexane）catalyzed by four precious metal catalysts（including Ir,Pt,Ru and Pd alumina supported catalysts）in the study.The results show that Ru/γ-Al₂O₃ can better promote the C-C and C-H bonds in methylcyclopentane and cyclohexane to break,which makes it as a good ring-opening catalyst.The hydroxyl functional group in pyrolysis oil is one of the main functional groups in which oxygen exists.³¹PNMR was used to study the derivatization processes of four alcohol model compounds,four carboxylic acid model compounds and two types of pyrolysis oil.Carboxylic acids were less stable during derivatization than alcohol.Model compounds can decompose and produce water during the derivatization process.The pyrolysis oil prepared from pine bark was relatively stable in the first 2 hours,while the pyrolysis oil of residue was unstable in the derivatization experiment.Therefore,the optimal time for the preparation and testing of pyrolysis oil samples can be determined,which provides accurate and detailed data for studying the aging of pyrolysis oil and subsequent upgrading processes.