Formation of polycyclic aromatic hydrocarbons coincident with pyrolytic carbon deposition

Ethane was pyrolysed in a flow reactor system at residence times from 0.5 to 20 s, at 1185 K and a pressure of 40 kPa. Liquid products were trapped and analyzed by liquid chromatography, gas chromatography and mass spectrometry using atmospheric pressure chemical ionization and electron impact ionization. At least 90 products (with m/z ratios up to 700) were present: of these products 19 were identified, and eight were quantified. Benzene was the major liquid product, with a maximum yield of 16% by weight of the feed gas. Products with even numbers of carbon atoms were prominent, which is consistent with theories proposing that PAHs grow by the addition of acetylene. Most of the aromatics quantified had maximum yields at about 6 s, coinciding with the maximum rate of carbon deposition in the reactor, as recorded by a micro-balance. This observation is consistent with theories proposing that pyrolytic carbon is formed from aromatics. (C) 2001 Elsevier Science Ltd. All rights reserved.