Analysis of Sulfur Compounds in Petroleum Gases and Natural Gas

Importance of the Topic

Monitoring sulfur compounds in petroleum gases and natural gas is essential to protect catalysts, ensure product quality, and safeguard environmental and human health. Trace levels of reactive, polar sulfur species require specialized analytical approaches to deliver reliable results.

Study Objectives and Overview

This application note evaluates the performance of the Agilent J&W DB-Sulfur SCD GC column configured with an inert flow path GC/SCD system. Following ASTM D5504, the work encompasses analysis of 22 sulfur standards and real samples of liquefied petroleum gas (LPG) and natural gas before and after desulfurization.

Methodology and Instrumentation

Analyses were conducted on Agilent 7890A gas chromatographs equipped with Agilent 355 dual-plasma sulfur chemiluminescence detectors. Key parameters included a 70 m × 0.53 mm × 4.3 µm DB-Sulfur SCD column, a 1 m deactivated fused silica restrictor, and helium carrier at constant pressure. The oven program ranged from 35 °C to 220 °C, and sample introduction used a six-port gas valve with point-of-use blending for low-level mixes.

• Gas chromatograph: Agilent 7890A with inert flow path
• Detector: Agilent 355 Sulfur Chemiluminescence Detector
• Column: Agilent J&W DB-Sulfur SCD
• Restrictor: 1 m deactivated fused silica tubing
• Carrier gas: Helium, 8.6 psi

Main Results and Discussion

• Resolution: Baseline separation of H₂S and COS (Rs ≈ 0.8) at ambient temperature without cryogenic cooling.
• Selectivity: Improved separation of coeluting thiols (e.g., 1-methyl-1-propanethiol, thiophene, 2-methyl-1-propanethiol) over nonpolar phases.
• Linearity and Sensitivity: Wide dynamic range (10 ppb to 10 ppm) with R² > 0.997 for major analytes.
• Repeatability: RSD < 2.25% for replicate injections of calibration gas.
• Real Sample Analysis: Total sulfur in natural gas decreased from ~20 ppm pre-treatment to 1 ppm post-desulfurization; H₂S reduced from 8.98 ppm to 0.01 ppm.
• No hydrocarbon interferences detected, confirming detector specificity.

Benefits and Practical Applications

• Equimolar response minimizes quantification bias across sulfur species.
• Low-bleed, inert stationary phase reduces adsorption and catalytic losses.
• Ambient-temperature start simplifies laboratory operations.
• Applicable to quality control, environmental monitoring, and catalyst protection in gas processing.

Future Trends and Potential Applications

• Coupling GC/SCD with mass spectrometry for enhanced identification of sulfur species.
• On-line, automated monitoring for real-time process control in petrochemical plants.
• Field-deployable, miniaturized GC/SCD systems for environmental surveys.
• Development of advanced column chemistries targeting emerging sulfur compounds.

Conclusion

The Agilent inert flow path GC/SCD configuration with the DB-Sulfur SCD column delivers robust, sensitive, and selective analysis of sulfur compounds in fuel gases. Meeting ASTM D5504 requirements, it offers excellent resolution, linearity, and repeatability, making it a valuable tool for industrial and environmental applications.

Reference

• ASTM D5504-12: Standard Test Method for Determination of Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence. ASTM International, Philadelphia, PA, USA, 2012.
• Liu W., Morales M. Detection of Sulfur Compounds in Natural Gas According to ASTM D5504 with Agilent’s Dual Plasma Sulfur Chemiluminescence Detector. Agilent Technologies, Application Note 5988-9234EN, 2008.
• Agilent Technologies. Agilent 355 Sulfur Chemiluminescence Detector (355 SCD): Odorants and Other Sulfur Compounds in Liquefied Petroleum and Natural Gases. Technical Overview 5989-6788EN, 2007.
• Agilent Technologies. Application D5504: Trace Sulfur Gas Analyzer for Natural Gas and Gaseous Fuels. Technical Overview 5988-7674EN, 2002.