Determination of sulfur compounds in various light hydrocarbon matrices by Sulfur Chemiluminescence Detector

Importance of the Topic

The accurate determination of sulfur compounds at low ppb levels in light hydrocarbon streams is critical for product purity, catalyst protection and regulatory compliance. Trace levels of hydrogen sulfide, carbonyl sulfide and mercaptans can poison downstream catalysts and degrade final products in petrochemical, environmental monitoring and food-grade applications.

Objectives and Study Overview

This study aims to demonstrate a robust gas chromatography method for quantifying sulfur impurities in C1–C5 matrices using a Sulfur Chemiluminescence Detector (SCD). Key goals include:

• Achieving reliable detection limits down to 20 ppb for H2S, COS and mercaptans
• Minimizing matrix-induced quenching and column adsorption losses
• Validating instrument settings for both SCD-only and SCD mounted on FID configurations

Methodology and Instrumentation

Gas chromatographic separation was performed on an Agilent J&W Select Low Sulfur PLOT column (60 m × 0.32 mm) optimized for inertness toward volatile sulfurs. Detector and system parameters included:

• Injector temperature: 200 °C; injection volume: 1 mL (split ratios varied from 10:1 to 100:1)
• Oven program: initial hold at 65 °C with ramps to 170–185 °C
• Carrier gas: helium, constant flow 2.0 mL/min
• SCD settings: burner 800 °C, hydrogen flow 40 mL/min, air flow 5–65 mL/min, ozone 5 psig
• FID settings (when SCD mounted on FID): temperature 300 °C, hydrogen 30 mL/min, air 400 mL/min, N2 makeup 30 mL/min

Results and Discussion

The novel PLOT column provided near-100 % response for H2S, COS and mercaptans at concentrations from 20 to 300 ppb. Chromatograms in LPG and propylene matrices showed:

• Effective separation of sulfur species from hydrocarbon peaks, eliminating quenching effects
• Minor peak broadening for methyl mercaptan under high matrix loads
• Excellent linearity (R2 > 0.995) across low ppb ranges

Matrix overloading and sampling of only 10 % of FID exhaust into the SCD were identified as key factors affecting sensitivity when the detector is mounted above an FID.

Benefits and Practical Applications

This method enables:

• Trace-level monitoring of sulfur contaminants in petrochemical and gas processing streams
• Protection of downstream catalysts from sulfur poisoning
• Quality assurance in food-grade CO2 and beverage gas analysis
• Environmental and industrial hygiene surveillance of volatile sulfur species

Future Trends and Opportunities

Advances may include development of more inert column materials, integration of pulsed flame photometric detectors with improved transfer efficiency, and online or at-line automation. Emerging data analysis algorithms and machine-learning tools could further enhance sensitivity and specificity in complex matrices.

Conclusion

The combination of a low-adsorption PLOT column and Sulfur Chemiluminescence Detection provides reliable, low-ppb quantification of reactive sulfur compounds in light hydrocarbons. Optimized GC parameters and detector configurations mitigate matrix effects and deliver robust performance for diverse analytical needs.

Reference

• Firor RL. Volatile Sulfur in Natural Gas, Refinery Gas, and Liquified Petroleum Gas. Agilent Technologies Publication 5988-2791EN.
• Duvekot C, Hollebrandse E. The Analysis of Sulfur Components in Various LPGs. Agilent Technologies Publication SI-01589.
• Ellis J, Vickers AK, George C. Capillary Column Selectivity and Inertness for Sulfur Gas Analysis in Light Hydrocarbon Streams by Gas Chromatography. Fuel Chemistry Division Preprints 2002;47(2):703.
• Agilent Technologies. Installing the FID Adapter for the Dual Plasma Burner. Publication G6600-90024.