Analysis of Impurities in Ethylene by ASTM D6159-97

Significance of the Topic

Ethylene is produced at over 100 million metric tons per year and serves as a feedstock for polyethylene, ethylene oxide and many other chemicals. Trace hydrocarbon impurities can poison catalysts, reduce yields, and increase operational costs. Reliable detection and quantitation of these impurities are therefore essential for process control and product quality in petrochemical operations.

Objectives and Study Overview

This application note describes the implementation of ASTM D6159-97, a gas chromatographic method with flame ionization detection, for the analysis of C1–C5 hydrocarbon impurities in high-purity ethylene. The goal is to achieve baseline resolution of all relevant compounds to enable accurate quantitation at low ppmv levels.

Methodology and Instrumentation

The procedure employs a dual-column configuration: a 50 m × 0.53 mm ID Rt-Alumina BOND/KCl PLOT column (10 µm film) in series with a 30 m × 0.53 mm ID Rtx-1 column (5 µm film), connected via a press-tight connector. Key parameters include a 1 µL split injection with a split vent of 60 mL/min, injector temperature 200 °C, helium carrier gas at 8 psi, and linear velocity of 25.4 cm/sec at 35 °C. The oven program holds at 35 °C for 2 min, ramps to 190 °C at 4 °C/min with a 15 min hold. Detection is by FID at 200 °C on an Agilent 5890 GC.

Key Results and Discussion

Using the alumina PLOT column alone, coelution of several impurity pairs occurs: acetylene with isobutane, propadiene with n-butane, and methyl acetylene with n-pentane. Coupling the Rtx-1 column introduces differential retention of nonpolar hydrocarbons, resolving all C1–C5 species including methane, ethane, ethylene, propane, cyclopropane, propylene, acetylene, isobutane, propadiene, n-butane, various butenes, isopentane, methyl acetylene, n-pentane and 1 3-butadiene. This configuration achieves baseline separation, enabling precise quantitation.

Benefits and Practical Applications

• Accurate detection of trace hydrocarbons at ppmv levels supports catalyst protection and optimal process yield.
• High reproducibility of retention times and extended column lifetime are afforded by low‐particle-release PLOT technology.
• Method alignment with an established ASTM standard ensures regulatory and industry acceptance for QA/QC workflows.

Future Trends and Opportunities

Advances in column stationary phases may further enhance separation of complex hydrocarbon matrices. Integration with mass spectrometric detection could provide definitive compound identification. Online and automated sampling systems could enable real-time monitoring of ethylene purity in continuous production environments. Adaptation of similar dual-column approaches may benefit analysis of other olefinic feedstocks and petrochemical streams.

Conclusion

The ASTM D6159-97 GC/FID method using an alumina PLOT column coupled to an Rtx-1 column provides comprehensive separation of up to eighteen C1–C5 hydrocarbons in ethylene. This robust approach safeguards catalysts, supports product quality control, and enables efficient process troubleshooting in ethylene production.

References

1. ASTM D6159-97 Standard Test Method for Analysis of Hydrocarbon Impurities in Ethylene ASTM International 1997
2. Restek Corporation Application Note PCAN1174 Analysis of Impurities in Ethylene 2009