Experimental investigation on the low-pressure pyrolysis of cyclohexane initiated by 1-nitropropane in a flow tube reactor

An experimental study of 5% 1-nitropropane (1-NP)-initiated cyclohexane pyrolysis was carried out in a flow reactor at 30 Torr (4.0 kPa) over a temperature range of 673-1273 K. The pyrolysis species were detected with synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) technique. Pyrolysis species from m/z 15-106, including C1-C8 hydrocarbons, CO, NO, NO2, CH2O, CH3OH and C3H5NO, were identified with near-threshold photoionization efficiency (PIE) spectra and quantified at different temperatures. The experi-mental results indicated that the addition of 1-NP obviously reduced the initial pyrolysis temperature of cyclohexane from 1048 to 1098-723 K, and caused the decreases of the initial formation temperatures for the species from cyclohexane pyrolysis. Almost all the high-temperature pyrolysis species in the mechanisms pro-posed in the literature were identified in the experiments. Based on the experimental results in this work and rate coefficients proposed in the literature, the primary pyrolysis mechanisms of cyclohexane in the presence of 1-NP were discussed. The 1-NP pyrolysis occurs at a lower temperature than the cyclohexane does, and produces HONO, NO2, C3H7, etc. It was demonstrated that cyclohexane was mainly consumed via the H-atom abstractions by H and OH attacks in this work and the cyclohexyl radical formed via H-atom abstractions mainly isomerized into 1-C6H11-6 radical, which further combines with H to form 1-C6H12.