Hydrocarbons, C3 – C4 - Analysis of impurities in cis-2-butene

Significance of the Topic

The accurate determination of trace hydrocarbons in industrial gases is critical for quality control, process optimization, and safety in petrochemical and gas processing operations. Monitoring C3 and C4 impurities in cis-2-butene ensures product purity, protects downstream catalysts, and meets regulatory specifications.

Study Objectives and Overview

This application note describes a rapid gas chromatographic method to separate and quantify ten C3–C4 impurities in cis-2-butene using an Agilent CP-Al2O3/Na2SO4 capillary column. The goal is to achieve baseline resolution of key hydrocarbon contaminants within a 12-minute run time over a wide concentration range (5–1000 ppm).

Methodology

A split injection gas chromatography approach was employed. Key parameters:

• Column dimensions: 0.32 mm × 50 m fused-silica WCOT, 5 µm film thickness (Agilent CP-Al2O3/Na2SO4, part no. CP7565)
• Oven temperature: 110 °C isothermal
• Carrier gas: Nitrogen at 120 kPa (1.2 bar)
• Injector: Split mode at 20 mL/min, 150 °C
• Detector: Flame ionization detector at 200 °C
• Sample size: 100 µL
• Calibration range: 5–1000 ppm of each analyte

Instrumentation Used

The analysis utilized an Agilent gas chromatograph equipped with a capillary injector and flame ionization detector. The CP-Al2O3/Na2SO4 stationary phase selectively separates light hydrocarbons and olefins based on adsorption and volatility differences.

Main Results and Discussion

The method achieved clear resolution of eleven peaks, including ten impurities and the target compound, cis-2-butene, within 12 minutes. Identified compounds in elution order:

1. Propane
2. Propene (propylene)
3. Isobutane
4. n-Butane
5. Acetylene
6. Cyclobutane
7. trans-2-Butene
8. 1-Butene
9. Isobutene
10. cis-2-Butene
11. 1,2-Butadiene

Chromatograms demonstrated baseline separation with sharp, symmetric peaks and reproducible retention times, supporting reliable quantitation across the specified concentration range.

Benefits and Practical Applications

• Fast analysis suitable for high-throughput quality control laboratories.
• Wide dynamic range allows monitoring of trace to major impurities.
• Robust separation minimizes interferences among isomeric and homologous hydrocarbons.
• Applicable to petrochemical, specialty gas production, and regulatory compliance testing.

Future Trends and Potential Applications

Advances in microfabricated columns and alternative detectors (e.g., mass spectrometry) could further reduce analysis time and enhance sensitivity. Integration with real-time process monitoring and chemometric data analysis may enable predictive maintenance and tighter process control in continuous gas production.

Conclusion

The described GC-FID method using an Agilent CP-Al2O3/Na2SO4 column provides a rapid, reliable, and sensitive approach for quantifying C3–C4 impurities in cis-2-butene. Its speed, resolution, and broad concentration capability make it well-suited for routine industrial and research laboratories.

References

1. Agilent Technologies, Inc. Application Note A00593: Analysis of impurities in cis-2-butene using GC and Agilent CP-Al2O3/Na2SO4 column, 2011.