Research On Decarboxylation Reaction And C-C/C-O Breaking Law Of Coal-Like Model Compounds During Pyrolysis

In this thesis,Py-GC/MS is used to detect the pyrolysis products of different coal-like model compounds.The quantum chemistry calculation software Gaussian is used to calculate the decarboxylation reaction path and the effect of different substituents on the activation energy of the reaction.The wave function analysis software Multiwfn is used in combination with the pyrolysis experiment results to analyze the C-C bond and C-O bond breaking rules.The results show that the temperature of the decarboxylation reaction of benzoic acid,p-Toluylic acid and p-hydroxybenzoic acid decreases in turn.Using Gaussian software to calculate the reaction path,it was found that the benzoic acid decarboxylation reaction is similar to the electrophilic reaction.During the reaction,the hydrogen atoms on the carboxyl group will attack the aromatic ring.Eventually,the hydrogen atom will replace the carboxyl group and form a bond with the benzene ring.In the case of little change in aromaticity,the reactivity of the decarboxylation reaction is determined by the atomic charge of the carbon atom connected to the carboxyl group on the aromatic ring.The substituents affect the activation energy of the reaction by affecting the number of atomic charges on the carbon atom.According to quantum chemistry calculations,the activation energy of the decarboxylation reaction is positively related to the Hirshfeld charge,and R² is greater than 0.9.The effect of electron localization on the decarboxylation reaction is greater than the number of atomic charges.During the decarboxylation reaction,the F-type?—?interaction can significantly reduce the activation energy of the decarboxylation reaction,and the T-type?—?interaction has little effect on the decarboxylation reaction.Ethylbenzene,bibenzyl,anisole and dibenzyl ether were pyrolyzed and it was found that C_al-O,C_al-C_al,and C_ar-C_al break at 400?,450?,and 500?,respectively.Through quantum chemical calculations combined with the results of pyrolysis experiments of model compounds,it is found that the widely used bond dissociation energy cannot correctly describe the chemical bond strength in the pyrolysis reaction,and the Laplacian bond order not only accurately describes the carbon-oxygen bond and carbon-carbon bond strength but also reflects the characteristics that C_al-O,C_al-C_all and C_ar-C_al have similar bond strength on the bridge bond and side chain respectively.The Laplacian bond order was used to investigate the effect of oxygen-containing functional groups on the strength of chemical bonds.It was found that?1?When-OH and-OCH₃ exist in the alkyl side chain,the strength of the C_ar-C_al and C_al-C_al bonds on the side chain is very close.?2?The-OH and-OCH₃ on the side chain can increase the strength of the C_al-O bond on the anisole,but the bond strength of the C-O bond is always lower than that of the C-C bond.