Revisit the PAH and soot formation in high-temperature pyrolysis of methane

As the major component of natural gas, most basic and stable hydrocarbon molecule, methane (CH4) is an important source in industrial processing. The polycyclic aromatic hydrocarbons (PAHs) and the soot produced in the utilization of CH4 also attract particular attention. In this work, CH4 pyrolysis was studied with gas chromatographs (GCs) and a gas chromatography-mass (GC-MS) spectrometry within the temperature range of 1073-1623 K at atmospheric pressure. Mole fraction profiles of 11 species, including CH4, C2H2, C2H4, C2H6, aC3H4, pC3H4, C3H6, C4H6, C6H6, C10H8 (naphthalene) and C12H8 (acenaphthylene) were quantified. C10H8 and C12H8 were detected during the pyrolysis of CH4. A detailed kinetic model involving 300 species and 1840 reactions was proposed with reasonable prediction against the measured data. During pyrolysis, CH4 is mainly consumed by the H-abstraction reactions. 2CH3=C2H5+H and C9H7+C3H3=A2R5+H2 are the two major reactions controlling CH4 consumption according to sensitivity analysis. In addition, the soot generated in the reactor was analyzed by Raman spectroscopy and Scanning Electron Microscope (SEM), showing the morphology and structural characteristics of the soot. The detailed formation and consumption pathways of PAHs such as naphthalene and acenaphthylene were analyzed. This work will enrich the understanding of CH4 pyrolysis and promote experimental and theoretical studies on the formation of PAHs and soot.