Study On The Pyrolysis Mechanism Of β-O-4 Lignin Model Compounds Catalyzed By Alkali And Alkaline Earth Metals

In recent years,the urgent expectation for the commercialization and profitability improvement of biomass pyrolysis,and the guidance of the concept of lignin priority,the research on the mechanism and modeling of lignin pyrolysis has attracted the interest of researchers.At this stage,there are still many problems in the research on the mechanism of lignin pyrolysis,and the use of DFT theoretical calculation to carry out research on lignin pyrolysis is still insufficient.In this regard,based on theβ-O-4 linkage,this paper analyzes the effects of different pyrolysis temperatures,oxygen-containing functional groups on C_α,and inherent metal elements on the pyrolysis mechanism of lignin by means of calculation and experimental comparison.The main innovations and work are as follows:（1）Rapid pyrolysis at different temperatures was carried out on Py-GC/MS by synthesizing two model compounds ofβ-O-4 type lignin polymer model compounds with carbonyl or hydroxyl groups linked at C_αand adding potassium acetate or calcium acetate.Through analysis and comparison,it can be seen that the oxygen-containing functional groups on C_αnot only lead to differences in the initial pyrolysis reactions of the model compounds,but also change the distribution of pyrolysis products;both K⁺and Ca²⁺additions can reduce the temperature required for pyrolysis of the two polymers;K⁺exhibits a stronger catalytic effect than Ca²⁺based on changes in tar production.（2）Based on the density functional theory,the pyrolysis reaction paths of the C=O dimer model compound and the OH dimer model compound were designed,and the calculation was carried out using the Gaussian 16 program package.The calculation results show that the C_β-O homolytic reaction dominates the initial pyrolysis reaction of the two model compounds,and the main pyrolysis products inferred from the energy comparison are consistent with the experimental results.In addition,activation free energy is more suitable than activation enthalpy as an indicator to explain the pyrolysis reaction mechanism of lignin model compounds.（3）Determine the catalytic site of metal ions by quantum chemical molecular simulation calculation method,and study the catalytic effect of K⁺and Ca²⁺on the C=O dimer model compound and the OH dimer model compound according to the designed reaction pathways.The Gaussian 16 program package was used to carry out the calculation,and the catalytic mechanism of K⁺and Ca²⁺on the pyrolysis of lignin model compounds was obtained by comparative analysis with the experimental results.The results show that the addition of K⁺is more favorable for the occurrence of the pathways containing only simple homolytic reactions,while the addition of Ca²⁺is more favorable for the occurrence of the pathways containing the transition state reaction.