Structural characterization and transformation of nitrogen compounds in waste tire pyrolysis oils

The waste tire pyrolysis oil (WTPO) has been widely concerned because it's a promising recycling method of waste tires. However, the high content of nitrogen in WTPO is unfavorable to its application. In this work, nitrogen compounds in the full distillation range of a waste tire pyrolysis oil were characterized by gas chromatograph-nitrogen chemiluminescence detector (GC-NCD), gas chromatograph-mass spectrometry (GC-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). In the gasoline fraction of WTPO, the most abundant nitrogen compounds were benzonitrile, aniline and small molecule nitriles. In the diesel fraction of WTPO, the most abundant nitrogen compounds were benzothiazole, quinoline derivatives, p-phthalodinitrile, benzonitrile derivatives, hexadecanenitrile and octadecanenitrile. In the heavy fraction of WTPO, significant amounts of N_xO_y (x = 2-3 and y = 1-2) species were discovered after the separation of solvent dissolution and solid phase extraction. The molecular structures of these N_xO_y species were determined as amide derivatives of diphenylamine by tandem mass spectra of FT-ICR MS. Therefore, the origin of nitriles in the light fractions of WTPO was suspected as the pyrolysis of these amides in the heavy fractions. Finally, the nitrogen transformation during the pyrolysis of waste tires was suggested based on the results of quantum chemistry simulations. These results would be helpful for the treatment and removal of these undesirable nitrogen compounds in WTPO.