Analysis of high molecular weight compounds in pyrolysis liquids from scrap tires using Fourier transform ion cyclotron resonance mass spectrometry

• Analysis of pyrolysis liquids from scrap tires by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS).
• Laser desorption ionization (LDI) using graphite powder as support was used and parameters influencing mass spectra appearance was investigated.
• Assignment of molecular formulas revealed mainly hydrocarbon, but also heteroatomic highly aromatic compounds.
• The compositional change of the high molecular weight content in the pyrolysis liquids during a pyrolysis experiment was investigated.

Liquids from the pyrolysis of scrap tires are known to be mixtures of a huge variety of organic molecules ranging from low to high boiling compounds. While the low to medium boiling fraction has been investigated using gas chromatography, virtually no information exists regarding high molecular weight compounds. Although size exclusion chromatography has been used to prove their existence no structural information has been obtained yet. In this study Fourier-transform ion-cyclotron-resonance mass-spectrometry (FT-ICR-MS) using laser desorption ionization (LDI) was applied to analyze the high molecular weight fraction of pyrolysis liquids from a fixed bed reactor. Samples were prepared as graphite slurry on conventional steel target plates and mass spectra were compared to those obtained from preparations without graphite. The influence of the graphite to sample ratio and the impact of laser fluence were examined. Using graphite as support during laser desorption increased the spot capacity and enabled the acquisition of a multitude of scans which significantly increased S/N ratios and led to the identification of a range of hydrocarbon and heteroatomic molecular formulas. Molecular formulas of highly unsaturated hydrocarbon compounds with 35–70 carbon atoms and compounds of the type CcHhOoNnSs with o = 0,…,2, n = 0,…,1 and s = 0,…,1 could be identified.