Quantitative Analysis of Olefins in Alternative Fuels Made From Conversion of Plastic Waste via GC×GC-FID

Significance of the topic

The increasing accumulation of plastic waste and scrap tires has driven interest in converting these materials into alternative fuels. Characterizing olefin content is crucial since high concentrations of unsaturated hydrocarbons can lead to gum formation and engine deposits. However, existing analytical techniques lack the specificity and sensitivity to quantify olefins in complex, high-olefin matrices.

Objectives and Study Overview

This study aimed to develop a robust analytical method for detailed quantitation of olefin classes in alternative fuels derived from plastic waste pyrolysis. Using comprehensive two-dimensional gas chromatography with flame ionization detection, the work focused on separating and quantifying iso-alkenes, linear alkenes, and cycloalkenes bearing one to three double bonds across broad boiling ranges.

Methodology and Instrumentation

Sample preparation involved addition of internal standard, derivatization reagents (DMDS and iodine), heating at 70 °C, and phase separation before analysis.
Instrumentation

• LECO QuadJet GC×GC-FID equipped with a liquid nitrogen thermal modulator
• Primary polar or mid-polar column coupled to a secondary non-polar column
• Flame ionization detector for selective hydrocarbon response

Key Results and Discussion

In scrap tire pyrolysis oil, total olefin content prior to derivatization was approximately 4.4 weight percent. After derivatization and chromatographic separation, diene olefins represented the largest class at around 25 weight percent, followed by triene olefins at 3.5 weight percent, mono-olefins at 2.4 weight percent, and iso-alkenes at 0.22 weight percent. Aromatics constituted over 50 percent of the fuel. Validation against standard ASTM methods (iodine value D4607, bromine number D1159, and FIA D1319) across nine gasoline-like samples demonstrated that the GC×GC-FID approach provides class-specific olefin quantitation that correlates well with conventional bulk measures while offering enhanced compositional detail.

Benefits and Practical Applications

• Enables targeted monitoring of problematic olefin classes to predict engine performance and deposit formation
• Supports quality control and specification of alternative fuels from plastic waste
• Facilitates compliance with regulatory requirements by providing detailed hydrocarbon profiles

Future Trends and Opportunities

Integration of time-of-flight mass spectrometry (GC×GC-TOFMS) could enable structural identification of olefin isomers. Automation of derivatization and data processing workflows will improve throughput. Expanding this methodology to other waste-derived fuel streams and standardizing protocols may promote wider adoption in research and industry.

Conclusion

The comprehensive GC×GC-FID method developed here fills a critical gap in the quantitation of olefin classes in complex, high-olefin alternative fuels. It offers precise, class-based measurements that outperform bulk ASTM tests and supports the advancement of sustainable fuel technologies.

References

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