Speciation of Nitrogen-Containing Molecules in the Distilled Fractions of Plastic Pyrolysis Oils Using Comprehensive Two-Dimensional Gas Chromatography Coupled With High-Resolution Mass Spectrometry and a Nitrogen Chemiluminescence Detector

Plastic pyrolysis oils (PPOs) as potential steam cracker feedstocks contain several undesired molecules, such as oxygenates, nitrogenates, halogenated species, and metals. In this context, the speciation of these components is crucial to define an effective upgrading process before feeding PPO into steam crackers. In this work, a methodology is presented to identify and quantify nitrogen-containing molecules in PPOs using a comprehensive two-dimensional gas chromatography system coupled to a high-resolution time-of-flight mass spectrometer (GC×GC-HR-TOFMS) and a (comprehensive two-dimensional) gas chromatography system coupled to a nitrogen chemiluminescence detector (GC(×GC)-NCD). In addition, spectra analysis tool, a toolkit paired with the Leco ChromaTOF software, was used to filter HR-TOFMS data and allowed identifying fragments which contained nitrogen. A crude PPO and its distilled fractions were analyzed. The analysis of different boiling point ranges of PPO allowed the identification of several compounds which would be challenging in the full-range oil and provided additional insights into the sample composition, especially regarding the heavier fractions containing several branched paraffinic nitriles. Nitrogen species such as benzonitrile, caprolactam, benzenedicarbonitrile, hexadecanenitrile, and others were identified and quantified. The nitrogen content of all distilled fractions of PPOs obtained with GC-NCD was similar to the values from elemental analysis, with a recovery of approximately 100%. Therefore, the GC-NCD method proved to be robust for quantifying nitrogen species in PPOs and can potentially be implemented in quality control labs, while GC×GC-HR-TOFMS and GC(×GC)-NCD are powerful tools for speciation of unknown N-compounds.