COUNTING DOUBLE BONDS: GC×GC–FID FOR PLASTIC PYROLYSIS OILS

Importance of the Topic

The conversion of plastic waste into fuels by pyrolysis is a promising approach to reduce plastic pollution and recover energy.
Olefin content strongly influences fuel stability and combustion properties, making precise quantification essential for industrial and environmental applications.

Study Objectives and Overview

This study reviews analytical strategies for detailed olefin quantification in complex plastic pyrolysis oils.
Key goals include comparing titration, spectroscopic, chromatographic and selective methods, and developing improved quantification workflows leveraging GC×GC–FID and selective adsorption.

Methodology and Instrumentation

Multiple approaches were evaluated:

• Titration methods (bromine number, iodine value)
• Spectroscopy (FTIR, Raman, NMR)
• Chromatography: one-dimensional GC, GC–VUV, HPLC, SFC
• Comprehensive two-dimensional GC coupled with FID, TOFMS and HRMS
• Selective adsorption using Ag-SiO2 SPE cartridges
• Derivatization of olefins using disulfides (DMDS, DBuDS, Ph2S2, DBzDS, di-tert-dodecyl disulfide)

Instrument resolution and selectivity were enhanced by optimized sample preparation, selective adsorption and chemical derivatization steps.

Main Results and Discussion

GC×GC–FID provided unparalleled resolution of paraffins, olefins, cycloparaffins and aromatics across wide boiling ranges.
Selective adsorption on Ag-SiO2 effectively removed olefins from sample matrices, allowing accurate discrimination of n-alkanes and isoalkanes.
Disulfide derivatization at 70 °C for 24 h with DMDS achieved complete aliphatic olefin conversion in gasoline-range samples, confirmed by 1H-NMR.
Heavier disulfides and optimized reaction conditions are required for diesel and jet-range olefins to ensure full derivatization and clear chromatographic separation.

Benefits and Practical Applications

• Accurate, reproducible olefin quantification supports quality assurance and process control in plastic-to-fuel operations.
• SPE with Ag-SiO2 is cost-effective and adaptable to routine laboratory workflows.
• GC×GC–FID combined with selective sample preparation enables detailed compositional profiling of complex pyrolysis oils.

Future Trends and Opportunities

Innovations include photoinitiator alternatives to iodine, novel disulfide reagents, room-temperature derivatization protocols and integration with advanced mass spectrometry and data analytics.
Machine learning and chemometric methods may further improve peak deconvolution and quantitation accuracy in complex samples.

Conclusion

An integrated analytical strategy combining GC×GC–FID, selective adsorption and chemical derivatization validated by NMR provides accurate olefin quantification in plastic pyrolysis oils.
Ongoing method refinements will extend applicability to heavier fuel fractions and enhance throughput for industrial adoption.

References

• Auersvald M., Barzallo G., Gieng H., Patel J., Sharma A., Van Geem K. M., Straka P., Vozka P. Toward Accurate Olefin Quantification in Plastic Waste Oils: Analytical Strategies and Future Directions. Trends in Analytical Chemistry 2025.
• Auersvald M., Šiman M., Vozka P., Straka P. Quantitative Determination of Olefins in Pyrolysis Oils from Waste Plastics and Tires Using Selective Adsorption by Ag-SiO2 Followed by GC×GC–FID. Talanta 2025, 281, 126792.
• Barzallo G., Gieng H., Sharma A., Patel J., Auersvald M., Straka P., Vozka P. Quantitative Analysis of Aliphatic Olefins in Alternative Fuels Made from the Conversion of Plastic Waste via GC×GC–FID. Journal of Chromatography A, in preparation.