Hydrocarbons, C1 – C4 - Analysis of impurities in propylene

Importance of the Topic

Propylene is a key feedstock and product in petrochemical and energy industries. Accurate quantification of trace hydrocarbons and common impurities (C1–C4) is vital for process optimization, product quality assurance, safety and regulatory compliance. Reliable analytical methods ensure consistent product performance and prevent catalyst poisoning or downstream equipment fouling.

Objectives and Study Overview

This application note describes a gas chromatographic method for the separation and quantification of low–molecular-weight hydrocarbons and related impurities in propylene. Using an Agilent CP-SilicaPLOT capillary column and direct injection, the study aims to demonstrate baseline resolution of key C1–C4 species—including methane, ethylene, acetylene, propane, cyclopropane and propylene—and to validate sensitivity in the ppm range.

Methodology and Instrumentation

The method employs capillary gas chromatography with flame ionization detection (FID). A narrow-bore (0.53 mm × 30 m, df = 6 μm) CP-SilicaPLOT column provides efficient separation of permanent gases, saturated and unsaturated hydrocarbons, sulfur species, halogenated volatiles and moisture.

Instrumentation

• Gas chromatograph: Capillary GC system compatible with direct injection
• Column: Agilent CP-SilicaPLOT, 0.53 mm id, 30 m length, 6 μm film thickness
• Carrier gas: Helium at 20 kPa (0.2 bar)
• Injector: Direct, 225 °C
• Detector: FID, 250 °C
• Temperature program: Initial 50 °C (5 min), ramp 5 °C/min to 225 °C
• Sample volume: 2 μL

Main Results and Discussion

The CP-SilicaPLOT column achieved clear baseline separation of 15 target analytes. Cyclopropane was fully resolved from propylene, preventing coelution errors. Retention times remained stable even in the presence of moisture, carbon dioxide and sulfur compounds. The method demonstrates linear response across ppm to percent concentration ranges and robust quantitation of trace impurities.

Benefits and Practical Applications

• High sensitivity for trace hydrocarbons supports quality control in polymer and chemical production.
• Broad analyte scope enables simultaneous monitoring of permanent gases, olefins, diolefins and trace contaminants.
• Direct injection simplifies sample handling and reduces cycle time.

Future Trends and Applications

Advances in column chemistry and detector technology will further improve sensitivity, reduce analysis time and extend the range of detectable impurities. Integration with automated sampling and data-analysis software will enhance throughput in refinery and petrochemical laboratories. Coupling with mass spectrometry may provide structural confirmation of unknown trace components.

Conclusion

The presented GC-FID method on an Agilent CP-SilicaPLOT column offers a robust and sensitive approach for comprehensive analysis of C1–C4 hydrocarbons and impurities in propylene. It supports stringent quality requirements in industrial applications by delivering reliable separation, repeatable retention times and broad dynamic range.

References

• Agilent Technologies, Inc. Application Note: Hydrocarbons, C1–C4: Analysis of Impurities in Propylene. Publication A01353, First published prior to May 11, 2010; printed October 31, 2011.