Agilent 355 Sulfur Chemiluminescence Detector (355 SCD): Odorants and Other Sulfur Compounds in Liquefied Petroleum and Natural Gases

Importance of the Topic

Accurate identification and quantification of volatile sulfur compounds in liquefied petroleum gases (LPG) and natural gas liquids (NGL) are vital for safety, regulatory compliance, and process efficiency. Sulfur species can corrode equipment, poison catalysts in downstream units, and contribute to odor nuisance. Moreover, deliberate addition of odorants such as ethyl mercaptan and tetrahydrothiophene requires stringent quality control to ensure reliable leak detection.

Objectives and Study Overview

This technical overview outlines the ASTM D5504-95 procedure for determining individual sulfur species and total sulfur in gaseous fuels. The focus is on demonstrating the capabilities of the Agilent 355 Sulfur Chemiluminescence Detector (SCD) to separate and quantify a broad range of volatile sulfur compounds in an NGL sample with approximately 100 ppm wt total sulfur content.

Methodology and Instrumentation

The analysis combines gas chromatography (GC) with sulfur‐selective chemiluminescence detection. Key elements of the method include:

• Sample injected into a GC for separation of sulfur analytes.
• Use of a temperature program starting at –10 °C, held for 3 min, then ramped at 10 °C/min to the final temperature.
• Sulfur compounds converted to excited SO radicals in the SCD and quantified by emitted light intensity.

Instrumentation Used

• Agilent 5890 Series II gas chromatograph.
• Agilent 355 Sulfur Chemiluminescence Detector operated under standard conditions.
• Analytics column: 30 m × 0.32 mm id, 4 μm methyl silicone WCOT fused silica.
• Alternative ambient‐temperature column options for H₂S and COS separation: Chrompack CP Sil 5 CB (0.32 mm), Chrompack CP SilicaPLOT (30 m × 0.32 mm) and Astec Gaspro (15 m × 0.32 mm).

Main Results and Discussion

The Agilent 355 SCD provides baseline resolution for at least 15 volatile sulfur compounds, including:

• Carbonyl sulfide, methyl and ethyl mercaptans.
• Dimethyl sulfide, carbon disulfide, propyl and butyl mercaptans.
• Di- and mixed disulfides, thiophene derivatives and ethyl methyl sulfide.

The detector’s sensitivity enabled clear speciation of odorants and trace sulfur species in under 25 minutes. The chemiluminescence response is linear across a wide concentration range, supporting reliable quantitation down to sub-ppm levels.

Benefits and Practical Applications

The GC–SCD method delivers:

• Rapid, selective detection of diverse sulfur analytes in LPG and NGL streams.
• Enhanced odorant quality control to maintain leak detection performance.
• Improved catalyst protection by monitoring corrosive sulfur species prior to downstream processes.
• Compliance with industry standards and environmental regulations through precise total sulfur measurement.

Future Trends and Prospects

Ongoing advances in capillary column technologies and detector designs are expected to further reduce analysis times and improve resolution for complex sulfur matrices. Integration with automated sampling systems and data analytics will enable real-time sulfur monitoring, supporting proactive process control and predictive maintenance in petrochemical operations.

Conclusion

The Agilent 355 Sulfur Chemiluminescence Detector coupled with optimized GC conditions offers a robust solution for comprehensive sulfur speciation in LPG and NGL. Its high sensitivity, selectivity, and compatibility with standard methods make it a valuable tool for quality assurance, environmental compliance, and operational safety in the gas industry.