Analysis And Formation Mechanism Of Nitrogen-Containing Compounds In Coal Tar

China is one of the countries with abundant coal resources in the world,and coal is an important part of the energy composition.In today’s carbon peak and carbon-neutral environment,the clean and refined use of coal has become a hot topic of research.Medium and low temperature coal tar is a raw material pool for fine chemicals,so how to use coal tar in a targeted and regulated way becomes a key point of the coal chemical industry,and the study of the pyrolysis process and mechanism is one of the important ways for direct conversion and efficient utilization of coal.To this end,the coal-related model compound was studied and allowed to co-pyrolyze with water and hydroxide isotopes of water to initially exploring the technical method of combining pyrolysis with isotopes and to try to capture the possible free radicals in the pyrolysis system with free radical trapping agents in this paper.This method is used to study the formation mechanism of nitrogenous compounds and add nitrogenous substances to coal to enhance the content of nitrogenous compounds in coal,and the results provide an important theoretical basis and experimental reference for the directional regulation and fine utilization of coal.The main study contents and results are as follows:（1）Preliminary exploration of the combination of isotope techniques and pyrolysis in the study of pyrolysis mechanisms.After screening 15 coal-related model compounds,it was found that 1-naphthalenemethanol produced new substances after co-pyrolysis.Therefore,1-naphthalenemethanol was chosen as the object of study and allowed to co-pyrolyze with water and hydroxide isotopes of water as well as free radical trapping agents to investigate the bond breaking mode and cleavage pathway of 1-naphthalenemethanol during the pyrolysis in this thesis.The results showed that hydrogen and hydroxyl radicals in the pyrolysis system were found by radical trapping agent and isotope techniques,and the hydroxyl radicals were very reactive and easily dehydrogenated to form aldehyde groups during the pyrolysis process.This indicated that rapid bond breaking,radical exchange and isotopic substitution were occurred in the system,and the traced product has a clear response on the mass spectra and NMR spectra,thus "labeling" the pyrolysis reaction.（2）Study of the formation mechanism of nitrogenous compounds.The processes of co-pyrolysis of coal-related model compounds with nitrogen-containing substances were investigated on the previously established method combining pyrolysis and isotope techniques.The analysis of the products after co-pyrolysis of seven coal-related model compounds revealed that 2-methylcinnamic acid produced new nitrogenous compounds after co-pyrolysis with ammonium chloride.The results show that 2-methylcinnamic acid underwent decarboxylation reactions during pyrolysis to form different intermediates,which then produced 1-ethyl-2-methylbenzene,indene,2-methylbenzaldehyde and other products through a series of complex processes such as radical addition,elimination and cyclization.The most probable structure of 5-methylquinolin-2（1H）-one was deduced by GC/MS and NMR spectroscopy;it was proved that the free radical reaction was dominant in the pyrolysis process,and other reactions were also accompanied.（3）Study of co-pyrolysis of coal with nitrogenous materials.Co-pyrolysis of coal with nitrogenous materials was used to increase the content of nitrogenous compounds in coal tar,and the pyrolysis tar products were examined by GC/MS and NMR.The results showed that the content of nitrogenous compounds increased the most by 17.53%after the addition of melamine compared with the original coal,while the thick ring aromatic hydrocarbons decreased by 9.13%.It is indicated that during the pyrolysis process,the thick-ringed aromatic hydrocarbons opened their rings by heat,and their-N,-NH,-NH₂,etc.seized the free radical sites to combine with their ring-opened aromatic hydrocarbons or small molecules to form other heterocyclic nitrogen-containing compounds or amines,which indirectly prevent the recondensation of thick rings with monocyclic aromatic hydrocarbons.