Hydrocarbon-rich pyrolysis oils produced
from landfill waste and
recycled plastics are potential sources for fuels and chemicals. It
is well established that feedstock composition significantly affects
pyrolysis oil composition and, hence, its potential uses. For example,
plastics waste pyrolysis oils contain a high concentration of hydrocarbons,
whereas biomass pyrolysis oils have high oxygen content. Previous
studies have shown that the addition of plastics to a biomass feedstock
increases the hydrocarbon content; however, a detailed analysis of
hydrocarbons and polar species from pyrolysis oils produced from “real
world” mixed municipal waste materials has not yet been done.
Here, the silica gel fractions from unsorted landfill waste and mixed
recycled plastics pyrolysis oils are analyzed by two-dimensional gas
chromatography (GC × GC), field ionization mass spectrometry
(FI-MS), Fourier transform infrared spectroscopy (FT-IR), and Fourier
transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Gravimetric
results show that the plastics pyrolysis oil has a much greater concentration
of saturated hydrocarbons than the more aromatic landfill pyrolysis
oil. GC × GC and FI-MS for the saturated hydrocarbons show a
range of alkanes, cycloalkanes, olefins, and 1-ring aromatics. Molecular
elemental compositions from FT-ICR MS were correlated with structural
assignments from GC × GC to expand the structural understanding
of the aromatic hydrocarbons from plastics and landfill pyrolysis
oils and showed that the aromatic hydrocarbons from the landfill are
both peri- and cata-condensed. In contrast, plastics pyrolysis oil
consists of polyphenyls and cata-condensed aromatic hydrocarbons.
The polar species from the plastics pyrolysis oil contain more alcohol
functionalities than the landfill pyrolysis oil, which contains non-carboxyl
carbonyl functional groups. Improved structural understanding of both
pyrolysis oils will provide better understanding of their properties
and potential uses.