Dual-Channel Gas Chromatographic System for the Determination of Low-Level Sulfur in Hydrocarbon Gases

Importance of the topic

Trace level detection of sulfur compounds in hydrocarbon gases is critical to protect catalysts, ensure fuel cell performance, and meet environmental regulations. Conventional sulfur selective detectors often suffer from hydrocarbon interference, limiting accurate quantitation at low parts per billion levels.

Aims and overview of the study

The study demonstrates a dual‐channel gas chromatographic system equipped with parallel flame photometric detectors using two complementary capillary columns. The system aims to achieve sub‐20 ppb detection of volatile sulfur species in various gas matrices and to extend the method to arsine and phosphine analysis.

Methodology and used instrumentation

A 6890N GC was fitted with dual enhanced‐sensitivity flame photometric detectors operating in parallel. Heated 6‐port valves with Silcosteel or Sulfinert treated surfaces introduced samples at low split ratios. Column sets included a thick film DB‐1 and a 320 μm GS‐GasPro PLOT phase, selected according to application. Detector gas flows were configured for sulfur, phosphorus, and arsenic modes. Oven programs ranged from sub‐ambient cryogenic starts to 290 °C ramps at 20–25 °C/min. Dynamic blending of calibration standards at low ppb levels was achieved via an EPC autodilutor.

Main results and discussion

Dual‐column separation effectively resolves key sulfur species from hydrocarbon interferences. In fuel cell and natural gas matrices, eight common sulfur compounds at 45 ppb were quantified, with DB‐1 separating H2S and GS‐GasPro separating COS and mercaptans. In propylene streams, extended column lengths and cryogenic cooling improved H2S and COS resolution. By adjusting detector flows in automated runs, the system also measured arsine and phosphine down to 5–60 ppb.

Benefits and practical applications of the method

• Reliable quantitation of trace sulfur contaminants in diverse hydrocarbon matrices
• Simultaneous analysis via dual detection for increased throughput
• Flexibility to monitor phosphorus and arsenic species without hardware changes
• Applicability to process control in petrochemical, refining, and fuel cell industries

Future trends and potential applications

• On‐line integration for real‐time process monitoring and quality control
• Automated switching between detection modes for broad‐scope screening
• Enhanced sensitivity through advanced column chemistries and cryo‐trapping
• Extension to emerging fuel mixtures such as biogas and hydrogen‐rich streams

Conclusion

The Agilent dual‐channel GC with enhanced FPD delivers robust separation and sub‐ppb detection of sulfur, phosphorus, and arsenic contaminants in complex gas streams, supporting rigorous quality assurance and compliance with tightening regulations.

References

1. Agilent Technologies A comparison of sulfur selective detectors for low level analysis in gaseous streams publication 5988‐2426EN
2. Agilent Technologies Volatile sulfur in natural gas refinery gas and liquefied petroleum gas publication 5988‐2791EN
3. Agilent Technologies Automated dynamic blending system for the Agilent 6890 GC low level sulfur detection publication 5988‐2465EN