Alkene Quantitation in Plastic Waste-Derived Alternative Fuels using GC×GC FID

Significance of Topic

Engine performance can be compromised by high olefin content, which leads to gum formation and deposit accumulation
Reliable quantitation of unsaturated hydrocarbons in fuels derived from plastic and tire pyrolysis is essential for quality assurance and broader adoption of recycled fuels

Objectives and Study Overview

The study presents a comprehensive GC×GC-FID method to quantify various classes of olefins in complex fuel mixtures
It aims to differentiate and determine iso-alkenes, mono- and poly-unsaturated linear and cyclic olefins before and after derivatization

Methodology

Samples are derivatized with dimethyl disulfide and iodine to stabilize double bonds and suppress coelution
Internal standards and sodium thiosulfate ensure quantitative recovery
Helium is used as carrier gas at 1.5 mL/min with split injection (1:20)
Temperature programming ramps from 40 °C to 200 °C at 3 °C/min with a modulation period of 1.5 s (0.45 s hot pulse)

Used Instrumentation

LECO QuadJet GC×GC-FID system with liquid nitrogen thermal modulator
Reversed-phase primary column (30 m × 0.25 mm × 0.25 µm Rxi-17 Sil MS) and secondary column (0.9 m × 0.25 mm × 0.10 µm DB-1HT)
Flame ionization detector at 280 °C and front injector at 275 °C
Pegasus BT 4D GC×GC-TOFMS was employed for validation

Main Results and Discussion

Quantitation of scrap tire pyrolysis oil revealed distributions of n-alkanes (1.54 wt %) and various olefin classes including iso-alkenes, mono-enes, di-enes, and tri-enes
Post-derivatization data showed improved separation and reduced overlap, enabling precise weight percent calculations for each olefin category
Comparison with conventional ASTM methods (D4607, D1159, D1319) across nine gasoline-like samples demonstrated strong correlation and enhanced specificity of the GC×GC-FID approach

Benefits and Practical Applications

The method provides detailed olefin profiles crucial for engine fuel specification, deposit control, and regulatory reporting
It supports the advancement of alternative fuels from polymer waste streams, contributing to environmental sustainability and circular economy goals

Future Trends and Opportunities

Integration of high-resolution mass spectrometry for detailed structural elucidation of complex isomers
Automation of data analysis workflows with advanced software for rapid quantitation in quality control laboratories
Extension of this analytical framework to bio-derived and other unconventional fuel matrices to promote standardized olefin measurement across industries

Conclusion

The presented GC×GC-FID approach, combined with derivatization, delivers robust and detailed quantitation of olefins in complex recycled fuel samples
Validation against established ASTM protocols confirms its accuracy and potential for widespread adoption in fuel analysis laboratories

Reference

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