Experimental and kinetic study of pyridine pyrolysis with tunable synchrotron VUV photoionization and molecular beam mass spectrometry

The pyrolysis of pyridine, a model compound for fuel-nitrogen in coal, biomass, and tar, was investigated in a flow reactor at a pressure of 30 Torr and a temperature range from 773 to 1473 K. Twenty-seven species, including three radicals, three sets of isomers, nine hydrocarbons and nine nitrogenous species, were identified and quantified by synchrotron vacuum ultraviolet photoionization mass spectrometry. Several intermediates were newly detected compared with previous pyridine pyrolysis studies based on the photoionization efficiency spectra including cyanides, a benzene isomer, and resonance-stabilized radicals (propargyl and benzyl radicals). A new kinetic model for pyridine pyrolysis was developed and validated against the measured data. Kinetic modeling, rate-of-production and sensitivity analysis were performed to reveal the pyrolysis kinetics of pyridine and the formation of the key products. The results indicate that the decomposition of pyridine is dominated by the H-abstraction reactions. Hydrocarbon radicals, alkenes and alkynes are mainly produced by the elimination of HCN from nitrogenous intermediates. The formation of nitrogenous products relates to the removal of acetylene from pyridine. A new growth route from C 3 HN to C 5 HN and C 7 HN was observed and analyzed, which has not been reported previously regarding the pyrolysis studies of fuel-N. By comparing the pyridine pyrolysis with pyrrole pyrolysis experiments, the influence of different C-N bond structures on reaction mechanisms and product distributions was revealed. Results of this work are helpful in deepening the understanding of pyridine conversion behaviors related to coal and biomass combustion and conversion processes.