SELECTIVE ANALYSIS OF TRACE LEVEL CARBONYL SULFIDE IN PROPYLENE BY GAS CHROMATOGRAPHY AND CHEMILUMINESCENCE AS ALTERNATIVE DETECTION FOR ASTM D5303

Significance of the Topic

Trace levels of carbonyl sulfide (COS) in propylene streams pose a serious threat to polymerization catalysts, leading to deactivation and costly process interruptions. Reliable detection of COS at concentrations below 30 ppb mole is essential for maintaining catalyst performance, ensuring product quality and minimizing downtime in industrial operations.

Objectives and Study Overview

This study aimed to develop and validate a selective gas chromatographic method with chemiluminescence detection for quantifying COS in propylene at trace levels. The goal was to surpass the lower detection limits of ASTM D5303 (0.5 – 4.0 ppm m) and to extend applicability to even more stringent requirements such as those of ASTM D5504.

Methodology and Instrumentation

A gas chromatograph equipped with the PAC SeNse Sulfur Chemiluminescence Detector (SCD) was employed to achieve optimum selectivity and sensitivity. Key methodological elements included:

• A boiling point GC column compatible with ASTM D5504 applications.
• Helium as carrier gas and hydrogen/oxygen reagent gases for the chemiluminescent reaction.
• External standard calibration using a 1.5 ppm m sulfur gas mixture dynamically diluted to low-ppb levels with propylene via mass flow controllers.
• System configuration featuring a back inlet maintained under helium flow and a chemiluminescence cell for sulfur-specific detection.

Key Results and Discussion

Selectivity and detection limit were evaluated by analyzing 15 ppb m COS in a pure propylene matrix. No baseline disturbances were observed, and a signal-to-background ratio exceeding 5 × 10^7 was achieved. The method detection limit for COS was determined to be below 30 ppb m.

Recovery studies involved diluting a 1.5 ppm m sulfur standard to 60 ppb m COS in propylene. Measured recoveries for several sulfur species were within ±10 % of target values:

• H₂S: 98 % recovery
• COS: 102 % recovery
• MeSH: 100 % recovery
• EtSH: 99 % recovery
• DMS: 109 % recovery

These results demonstrate that coeluting species, including COS with propylene, can be quantitated accurately using the chemiluminescence detector.

Benefits and Practical Applications

The presented method delivers:

• Sub-30 ppb m detection limits for COS in propylene.
• High selectivity against hydrocarbon matrix interferences.
• Robust quantitation with recoveries near 100 % for multiple sulfur compounds.
• Compliance with or exceedance of ASTM D5303 and D5504 requirements.

This analytical approach supports quality control and process monitoring in petrochemical and polymerization plants, helping to prevent catalyst poisoning and unscheduled shutdowns.

Future Trends and Applications

Advancements may include integration of real-time, inline monitoring systems with automated sampling, further miniaturization of detection modules, and application to other trace sulfur species in diverse petrochemical streams. Coupling chemiluminescence detection with advanced data analytics could enhance predictive maintenance and process optimization.

Conclusion

A selective GC–chemiluminescence method has been established for trace-level COS analysis in propylene, achieving detection limits below 30 ppb m and robust recoveries across multiple sulfur compounds. This approach outperforms traditional ASTM D5303 protocols and extends to more demanding applications, offering a reliable tool for catalyst protection and process control.

References

• ASTM D5303: Standard Test Method for Trace Hydrogen Sulfide and Carbonyl Sulfide in Propylene by Gas Chromatography.
• ASTM D5504: Standard Test Method for Determination of Sulfur Compounds in Natural Gas by Gas Chromatography.