Analysis of Low-Level Sulfur Compounds in Natural Gas and Propylene Using a Pulsed Flame Photometric Detector

Importance of the Topic

Analysis of trace sulfur compounds is vital to ensure product quality, protect catalytic systems, and prevent corrosion in gas processing and petrochemical operations. Low-level detection down to tens of parts per billion is required for regulatory compliance and efficient downstream treatment.

Objectives and Study Overview

This study evaluates the performance of an Agilent 7890A GC equipped with an OI 5380 pulsed flame photometric detector for routine analysis of sulfur species in natural gas and propylene matrices at concentrations as low as 50 ppbv. Comparative selectivity over traditional detectors and chromatographic separation in complex light hydrocarbon streams are assessed.

Used Instrumentation

• Agilent 7890A gas chromatograph
• OI Analytical model 5380 pulsed flame photometric detector
• Volatiles interface inlet with six port gas sampling valve
• SilcoNert 2000 deactivated transfer lines and 1 mL sample loop
• Dynamic blending system for preparation of low level sulfur standards
• Columns: Select Low Sulfur PLOT 0.32 mm x 60 m and HP 1 nonpolar 0.32 mm x 60 m, 5 µm

Methodology

The pulsed flame photometric detector was tuned via WinPulse software to optimize gate settings. Standard mixtures containing H2S, COS, mercaptans and sulfides at 1 ppm in helium were serially diluted in methane using a blending system. GC oven programs and carrier gas flows were defined to achieve adequate resolution while maintaining detector stability. Calibration curves for hydrogen sulfide and carbonyl sulfide were generated over the 0.1 to 1 ppm range.

Results and Discussion

Using the HP 1 column, sulfur compounds were separated from methane, ethane, propane and other light hydrocarbons, though COS quantification was impacted by high propane levels. The Select Low Sulfur column provided baseline separation of H2S, COS and methyl mercaptan in propylene streams, preventing quenching and peak distortion. Sensitivity improvements of 3 to 5 fold relative to conventional FPD were demonstrated, with reliable detection limits of 50 ppbv for key sulfur species. Calibration linearity correlations exceeded 0.996.

Benefits and Practical Applications

• Enhanced sensitivity and selectivity for low level sulfur detection compared to flame photometric detectors
• Reduced quenching effects in complex hydrocarbon matrices
• Routine monitoring capability for natural gas quality control and petrochemical feedstock analysis
• Flexible method tuning via software interface for robust operation

Future Trends and Opportunities

Further advancements in detector miniaturization and integration with online monitoring platforms could enable real time surveillance of sulfur contaminants. Development of tailored stationary phases and AI guided data processing may enhance selectivity and reduce analysis time. Expansion to wider hydrocarbon and industrial gas matrices is anticipated.

Conclusion

The pulsed flame photometric detector on an Agilent 7890A GC provides a sensitive and selective approach for trace sulfur analysis in natural gas and propylene. Careful method setup and choice of stationary phase are key to avoiding matrix interferences. The technique supports routine detection down to 50 ppbv, offering a valuable tool for industry quality assurance.

References

• Wenmin Liu and Mario Morales Detection of Sulfur Compounds in Natural Gas According to ASTM D5504 with Agilents Dual Plasma Sulfur Chemiluminescence Detector G6603A on the 7890A Gas Chromatograph Agilent Technologies publication 5989-9234EN
• Roger L Firor Volatile Sulfur in Natural Gas Refinery Gas and Liquified Petroleum Gas Agilent Technologies publication 5988-2791EN
• Roger L Firor Use of GC MSD for Determination of Volatile Sulfur Application in Natural Gas Fuel Cell Systems and Other Gaseous Streams Agilent Technologies publication 5988-4453EN
• Roger L Firor and Bruce D Quimby A Comparison of Sulfur Selective Detectors for Low Level Analysis in Gaseous Streams Agilent Technologies publication 5988-2426EN
• ASTM D 6228 Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Flame Photometric Detection
• Helena Jacobse GC Analysis of Sulfur Components in Propylene using a Pulsed Flame Photometric Detector Agilent Technologies publication 5990-6990EN