Experimental and kinetic study on the low-temperature oxidation of pyridine as a representative of fuel-N compounds

The low-temperature oxidation (LTO) of pyridine was studied in a jet-stirred reactor over the temperature range of 700–1000 K at atmospheric pressure and equivalence ratio of 2.0. Mole fraction profiles of the reaction products were obtained based on molecular beam mass spectrometry and tunable vacuum ultraviolet synchrotron photoionization techniques. Hydrogen peroxide, methanamine, acetylenamine, ethenamine, acetaldimine, ethylamine, allyamine, and methylformamide were newly identified compared with previous studies of pyridine flame and pyrolysis. HCN was found to be the dominant N-containing species of pyridine LTO. Pyrrole, acrylonitrile, acetonitrile, and ammonia were also found at the same level of N₂O and NO. Based on the new measurements and updated rate constants of several reactions including the H-abstractions of pyridine as well as the oxidation of ortho-pyridyl using density functional theory calculations, a new pyridine LTO kinetic model consisting of 588 species and 3516 reactions was developed with a reasonable agreement with the experimental results. In general, the predictions of the predominant species have been improved compared with the existing model. Rate-of-production analysis indicates that pyridine mainly consumes via C₅H₅N→C₅H₄N→C₅H₄NO₂→HCN+CO+CH₂CHC˙O, and C₅H₅N→C₅H₅NO→C₂H₂+HCN+CH₂CO. Sensitivity analysis shows that C₅H₄N+O₂=>C₅H₄NO₂, and C₅H₅N+OH[dbnd]C₅H₄N+H₂O have significant promoting effect on pyridine consumption, while the reverse of C₅H₄N+HO₂[dbnd]C₅H₄NO+OH has strong inhibiting effect. The results will enrich the understanding of pyridine low-temperature oxidation mechanism, which can be applied to the fields of coal pre-treatment, staged combustion and mild combustion.