Quantitative Analysis of Aliphatic Olefins in Fuels made from Plastic Waste by Comprehensive Two-Dimensional Gas Chromatography

Importance of Topic

The accumulation of plastic waste has become a critical environmental challenge, with projections indicating that by 2050 the oceans could contain more plastic than fish. Comprehensive two-dimensional gas chromatography (GC×GC) enables detailed separation and quantification of aliphatic olefins in complex fuel mixtures derived from plastic waste.

Objectives and Study Overview

This study aimed to develop and validate a quantitative GC×GC-FID method for determining aliphatic olefins in diesel-range fractions produced by pyrolysis and hydrotreating of plastic waste. The focus was on achieving high peak capacity and specificity in complex matrices.

Methodology and Instrumentation

• Sample preparation: Dimethyl disulfide (DMDS) derivatization with iodine catalyst at 70 °C for structural stabilization, followed by quenching with sodium thiosulfate.
• Chromatographic system: GC×GC with primary nonpolar column and secondary polar column connected via a QuadJet thermal modulator.
• Detection: Flame ionization detector (FID) for quantitative analysis. Future validation planned using GC×GC-TOFMS (Pegasus BT 4D) with thermal desorption/pyrolysis unit.

Main Results and Discussion

• Quantitative comparison before and after hydrotreatment showed consistent n-alkane content (~1.5 wt %) and aromatic levels (~54 wt %).
• Mono- and polyolefin classes decreased after hydrotreatment: olefins with one double bond dropped from 4.43 wt % to 3.47 wt %, and those with two double bonds from 27.01 wt % to 25.20 wt %.
• DMDS derivatization improved resolution of heavier isoalkenes by shifting them out of the aromatic region, allowing accurate peak assignment.
• Method validation against ASTM standards (iodine value, bromine number, FIA) demonstrated strong correlation and enhanced specificity of the GC×GC approach.

Practical Applications and Benefits

• Enables detailed quality control of fuels derived from plastic waste, ensuring compliance with industry specifications.
• Supports process optimization for pyrolysis and hydrotreatment by providing detailed olefin distribution profiles.
• Offers superior resolving power for complex hydrocarbon mixtures, beneficial for environmental monitoring and regulatory compliance.

Future Trends and Potential Uses

• Integration of high-resolution time-of-flight MS detection (GC×GC-TOFMS) for simultaneous structural identification and quantification.
• Application of advanced data processing tools such as ChromaTOF Tile for pattern recognition and automated classification.
• Exploration of alternative derivatization chemistries (e.g., ozonolysis or single oxygen oxidative methods) to extend analyte scope.
• Extension to diverse feedstocks including mixed plastic streams and emerging bio-based polymers.

Conclusion

The developed GC×GC-FID method with DMDS derivatization provides a robust and validated approach for quantifying aliphatic olefins in plastic-derived diesel fuels. Its high resolution, reproducibility, and agreement with ASTM benchmarks make it a valuable analytical tool for fuel characterization and process control.

Reference

• Vozka P., Mo H., Šimáček P., Kilaz G. Quantitative Analysis of Aliphatic Olefins in Fuels made from Plastic Waste by Comprehensive Two-Dimensional Gas Chromatography. Talanta. 2018;186C:140–146.