CONTAMINANTS IN ETHYLENE AND PROPYLENE ULTRA TRACE LEVEL DETECTION

Significance of the Topic

Monitoring ultra-trace contaminants in polymer-grade ethylene and propylene is critical for safeguarding catalyst performance, maintaining process uptime, and ensuring product quality. Early detection of arsine, phosphine, hydrogen sulfide, and carbonyl sulfide at sub-part-per-billion levels enables timely corrective action in olefin production.

Objectives and Overview of the Study

This study evaluates a gas chromatograph–mass spectrometer system equipped with a High Efficiency Source (HES) and JetClean self-cleaning ion source for the selective, sensitive determination of four key contaminants in ethylene and propylene matrices. Key goals include:

• Achieving baseline separation of target impurities from the main olefin peaks
• Demonstrating sub-picogram detection limits
• Ensuring long-term signal stability during extended sequence runs

Methodology and Instrumentation Used

Samples were introduced via a gas sampling valve into an Agilent 7890B GC coupled to a 5977B MSD. A 120 m × 0.32 mm column with 8 µm film provided high chromatographic capacity, while continuous hydrogen cleaning of the JetClean ion source minimized column bleed. Calibration standards spiked into real ethylene and propylene matrices were used to assess:

• Chromatographic resolution
• Linearity (5–50 ppb)
• Repeatability (%RSD)
• Instrument detection limits (IDL) and method detection limits (MDL)

Main Results and Discussion

Chromatographic separation was achieved for all four contaminants in ethylene; phosphine was partially resolved on the shoulder of the ethylene peak but yielded reproducible quantitation. In propylene, carbonyl sulfide coeluted with propylene, so only three analytes were quantified. Key performance metrics included:

• %RSD below 6 % for all compounds over 50 injections in matrix
• IDLs below 1 ppb (0.045–0.715 ppb) and MDLs below 2 ppb
• Long-term precision of better than 5 % RSD across 300 runs over 4.5 days

Background levels of H2S and COS were detected at sub-ppb concentrations in blank matrices, highlighting system sensitivity.

Benefits and Practical Applications of the Method

This approach delivers:

• Ultra-trace detection of catalyst-poisoning impurities
• Robust, self-cleaning source for stable long-term operation
• High throughput thanks to long, thick-film columns

Olefin producers can implement real-time monitoring to prevent catalyst deactivation and unplanned shutdowns.

Instrumentation

• Agilent 7890B GC
• Agilent 5977B MSD with High Efficiency Source
• 120 m × 0.32 mm, 8 µm Select Olefins column
• Agilent JetClean self-cleaning ion source (continuous H2 flow)

Future Trends and Potential Applications

Advances may include integration with online process analytics, coupling to high-resolution mass spectrometry for isomer differentiation, and automated data analytics for predictive maintenance. Expanding the method to other olefin impurities or integrating with reactive sampling could further enhance catalyst life management.

Conclusion

The combination of a long, thick-film capillary column, Agilent HES, and JetClean ion source enables reliable, ultra-trace measurement of arsine, phosphine, hydrogen sulfide, and carbonyl sulfide in ethylene and propylene streams. The system achieves sub-ppb detection limits, excellent precision, and stable performance over extended sequences, providing a robust solution for industrial olefin quality control.