Characterization and Quantitative Hydrocarbon Group-Type Analysis of Plastic-Derived Pyrolysis Oils by GCxGC-TOFMS/FID

Significance of the topic

Characterizing plastic-derived pyrolysis oils at the molecular level is vital for evaluating their suitability as fuel or chemical feedstocks and for monitoring process efficiency. Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GCxGC-TOFMS) and flame ionization detection (FID) enables detailed profiling of hydrocarbon classes and heteroatom species, supporting quality control and research in sustainable waste valorization.

Study Objectives and Overview

This work demonstrates a workflow for group-type and heteroatomic analysis of pyrolysis oils derived from polyethylene/polypropylene at different process stages. Key aims include:

• Quantify bulk distributions of hydrocarbon classes
• Identify and map heteroatomic compounds (N, S species)
• Compare sample variability using statistical tools

Methodology and Instrumentation

Samples were collected from condenser lines, product tanks, collection tanks, and knock tanks. Multiple GCxGC configurations were evaluated:

• QuadJet SD with FID for quantitative group analysis
• Paradigm Shift with simultaneous FID and MS acquisition
• Pegasus BT 4D for fast acquisition and library matching
• Pegasus HRT+ 4D for high-resolution accurate-mass identification with EI, PCI, and ECNI

Two column sets (nonpolar–polar and polar–nonpolar) were compared to optimize separation of paraffins and aromatics. Data processing employed ChromaTOF software for tile-based statistics, group-region classification with an alignment algorithm, high-resolution deconvolution (HRD®), mass-defect and Kendrick plots.

Main Results and Discussion

GCxGC structured chromatograms resolved distinct clusters of alkanes, alkenes/cycloparaffins, monocyclic, dicyclic, and tricyclic aromatics. Quantitative FID area% provided bulk composition of each hydrocarbon class. Tile-based statistics and PCA highlighted differences across sample points. High-resolution MS enabled confident assignment of N- and S-containing species via mass-defect filtering and multi-mode ionization. The combination of GCxGC separation and accurate mass data resolved isomeric bands of benzothiophenes and related heterocycles.

Benefits and Practical Applications

• Comprehensive qualitative and quantitative profiling of complex pyrolysis oils
• Enhanced sensitivity and selectivity for trace heteroatom species
• Simultaneous MS and FID acquisition ensures robust quantitation
• Statistical workflows facilitate sample comparison and process monitoring

Future Trends and Potential Applications

Advances in high-resolution GCxGC-MS and multi-mode ion sources will further improve speciation of trace compounds. Integration with machine learning for automated feature extraction and real-time monitoring promises to streamline process control. Expanding this approach to diverse feedstocks and coupling with bio-derived pyrolysis streams will support circular economy initiatives.

Conclusion

The presented GCxGC-TOFMS/FID workflow delivers detailed group-type composition and heteroatom speciation of plastic-derived pyrolysis oils. Instrument flexibility and advanced data processing enable both routine quality assessment and in-depth research applications in waste-to-energy and sustainable chemistry.