The Study Of Formation Mechanism Of Cyclic Compounds During Lignin Pyrolysis Based On Quantum Chemistry Theory

With an increasingly serious problem of energy shortages and environmental pollution, more and more attention have been paid to the development and utilization of biomass energy around the world. Biomass is mainly composed of cellulose, hemicellulose and lignin. The research on pyrolysis mechanism of lignin has great significance for establishing the theoretical system of biomass gasification, guiding experiments and providing a new solution of engineering application. This thesis is sponsored by the National Natural Science Foundation Project named “Reaction Mechanisms research of Biomass Gasification using High Temperature Air / Steam based on Theoretical of Quantum Chemistry”?NO.51276023?, and it makes a systemic study on the pyrolysis process of lignin. The research employs density functional theory, puts forward possible pyrolysis reaction and optimizes a variety of reactants, products, intermediates, and the structure of transition state. It calculates the standard pyrolysis parameters for analyzing the formation mechanism of the main products. It analyzes the product of lignin thermal cracking by means of the Py-GC/MS, and finally makes a comparison between simulation experimental results.In this thesis, the main research work are as follows:?1? The study on pyrolysis formation of monocyclic compounds in lignin. Five paths are designed for main pyrolysis mode and eight paths have been designed for secondary pyrolysis mode, The calculation shows that C?-O keys and C₄-O key is easy to break, and the phenol and benzyl are the highest conversion ratio in secondary pyrolysis mode. According to the thermodynamic calculation,the result shows the priority support paths.?2? The study on pyrolysis formation of polycyclic compounds in lignin. Three paths are designed for cracking and aggregation of benzene ring.The calculation results show that these paths are all exothermic reactions. The heat released along with temperature increasing and enthalpy changes decreasing. Six paths are designed for the formation of polycyclic compounds. The calculation results show that all the paths are spontaneous, and the effect of temperature on some paths are not obvious. In addition, some paths' quantity of released heat in 400? to 700? reach the highest heat, and the rest of the path decreases with the increase of temperature.?3?The study on lignin pyrolysis experiments. The products of lignin pyrolysis is studied by Py-GC/MS. The result showed that majority products containing methoxyl at 300? and 400?, which mainly including phenolic compounds and their derivatives. At 800?,it appears PAHs. The comparison of the experimental data and simulation data is to show that the formation mechanism of ring compounds in lignin pyrolysis.