Hydrocarbons, C1 – C2 - Impurity determination in ethylene

Importance of the Topic

The purity of ethylene is vital in chemical manufacturing and polymer production. Even trace levels of C1–C2 hydrocarbon impurities can affect catalyst performance, product quality and process efficiency. A rapid and reliable analytical approach for quantifying these impurities supports quality control and process optimization in industrial settings.

Objectives and Study Overview

This application note presents a gas chromatographic method for the simultaneous determination of five common C1 and C2 hydrocarbon impurities—methane, ethane, propane, propylene and acetylene—in an ethylene matrix. The goal is to achieve complete separation and accurate quantitation within a short analysis time suitable for routine laboratory and process analysis.

Methodology

A capillary gas chromatography technique employing a porous layer open tubular (PLOT) column coated with Al₂O₃/Na₂SO₄ was adopted. A temperature program initiates at 60 °C (held for 3 minutes) and ramps to 150 °C at 10 °C/min, enabling elution of light hydrocarbons within eight minutes. The split injection mode and flame ionization detection ensure sensitive, stable response for low-level analytes.

Instrumental Setup

• Gas chromatograph: Agilent with capillary inlet and FID detector
• Column: Agilent CP-Al₂O₃/Na₂SO₄ PLOT, 0.53 mm × 50 m, 10 µm film thickness
• Carrier gas: Helium at 100 kPa (1.0 bar)
• Injector: Split ratio 1:100, temperature 200 °C
• Detector: FID at 300 °C
• Sample volume: 1 mL injected loop

Main Results and Discussion

The optimized method achieved baseline separation of methane, ethane, propane, propylene and acetylene with ethylene as the major component. Calibration at impurity levels from tens to hundreds of ppm provided excellent linearity and reproducibility. Analysis time per run was under eight minutes, with clear resolution between adjacent peaks and minimal tailing.

Benefits and Practical Applications

• Rapid turnaround supports high-throughput quality control.
• High sensitivity down to low ppm levels ensures compliance with purity specifications.
• Robustness of the PLOT column minimizes maintenance and downtime.
• Method adaptability allows integration into process analytical technology (PAT) frameworks.

Future Trends and Potential Applications

The technique can be further enhanced by coupling with mass spectrometry for unambiguous identification of unexpected contaminants. Automation of sample introduction and data processing can enable real-time monitoring in production facilities. Emerging column chemistries and detectors may reduce analysis time and improve detection limits for ultratrace impurities.

Conclusion

This application note demonstrates a fast, reliable GC-FID method for determining C1–C2 hydrocarbon impurities in ethylene. Its simplicity, speed and sensitivity make it well suited for routine quality assurance in chemical and petrochemical laboratories.

References

• Agilent Technologies, Inc. (2011). Hydrocarbons, C1 – C2: Impurity Determination in Ethylene. Application Note A00579.