Pyrolysis products of C2 hydrocarbons using thermal plasma

• Thermal-plasma pyrolysis of ethylene and acetylene was investigated. • Ethylene pyrolysis produces film-like morphology. • Ethylene yields more PAHs than acetylene. Film-like carbon is expected to have various applications, and establishing a method for its mass production is highly desirable. Although there have been reports of obtaining film-like solid carbon using thermal plasma, knowledge about the growth behavior of this film-like carbon has not been sufficient. We analyzed the products and their growth behavior by pyrolysis experiments of C2 hydrocarbons with thermal plasma and investigated the pyrolysis behavior of C2 hydrocarbons with thermal plasma by numerical analysis. Solid products with different residence times were sampled from a sampling port in the reactor, observed by electron microscopy, and analyzed for crystallinity by Raman spectroscopy and X-ray diffraction. The solid products collected by a filter at the reactor outlet were measured by pyrolysis gas chromatography-mass spectrometer (GC/MS). The pyrolysis of acetylene yielded particulate carbon as in the pyrolysis in the electric furnace, whereas the pyrolysis of ethylene yielded a film-like carbon. The HRTEM image of ethylene pyrolysis products, however, shows lines indicating a stacked graphite structure of several tens of nanometers, indicating a different structure. In the pyrolysis GC/MS of ethylene pyrolysis products, various compounds were detected, whereas in the pyrolysis of acetylene, polycyclic aromatic hydrocarbons (PAHs) from three to seven rings were not detected. Reaction kinetic calculations using electron collision reactions were performed to examine the important reactions. The amount of ions produced tends to be larger for the pyrolysis of ethylene than for the pyrolysis of acetylene, indicating that the electron collision reaction is more likely to occur with ethylene in this calculation.