Analysis of Ultra low Sulfur Compounds in Natural Gas and Gaseous Fuels by Gas Chromatography and Chemiluminescence according to ASTM D 5504

Significance of the Topic

The precise measurement of ultra low sulfur compounds in natural gas and gaseous fuels is essential to ensure safety odorization, prevent catalyst poisoning, and comply with environmental and industry standards. Sulfur species in the low ppb range pose challenges due to their corrosive and toxic nature and can degrade process performance in gas processing and energy production.

Objectives and Study Overview

This study outlines the application of a gas chromatography method coupled to chemiluminescence detection according to ASTM D5504 using a PAC SeNse detector. The main goals include the speciated quantification of hydrogen sulfide, carbonyl sulfide, methanethiol, ethanethiol and dimethyl sulfide at ultra low detection levels down to single digit ppb while demonstrating sensitivity, repeatability, linearity and robustness for routine laboratory analysis.

Methodology and Instrumentation

The analytical workflow integrates the following components

• Sample introduction via switching sample loop in carrier gas stream
• Separation on a thick phase methyl silicone capillary column under temperature programmed conditions starting at 35 degrees C
• Dual plasma furnace conversion of sulfur compounds to sulfur dioxide followed by reduction to reactive sulfur species
• Reaction with ozone to generate excited sulfur dioxide monitored by photomultiplier based chemiluminescence detection
• Mass flow controllers for dynamic dilution in linearity experiments

The system configuration conforms to ASTM D5504 specifications with emphasis on controlled temperature, pressure and flow to achieve high reproducibility and minimal interference.

Main Results and Discussion

Key performance metrics include

• Chromatographic baseline separation of hydrogen sulfide and carbonyl sulfide without cryogenic cooling
• Retention time repeatability with RSD below 0.05 minute across eight consecutive runs
• Concentration repeatability with RSD values below 0.6 percent at 500 ppb levels
• Linearity demonstrated over four orders of magnitude from 10 ppb to 10 ppm with correlation coefficients above 0.9999
• Detection limits calculated between 2.5 and 4.1 ppb for common sulfur compounds
• Equimolar detector response factors within 5 percent deviation confirming consistent sulfur sensitivity across analytes
• Application to real natural gas samples showing tetrahydrothiophene concentration matching supplier odorant specifications and detection of additional sulfur species at single digit ppb

Benefits and Practical Applications

The described method offers

• Ultra low detection capability enhancing safety monitoring and catalyst protection
• High repeatability and stability facilitating quality control and regulatory compliance
• Equimolar chemiluminescence response simplifying quantification of diverse sulfur compounds
• Robust design suitable for routine laboratory and process analytical environments

Future Trends and Possibilities for Application

Emerging developments may include

• Integration of online real time monitoring for process control in gas production and transmission
• Miniaturization and field deployable versions for rapid on site analysis
• Advanced calibration approaches using permeation devices or isotopic standards
• Coupling with mass spectrometry or alternative detectors to broaden compound scope
• Application to sustainability efforts in sulfur management and emissions monitoring

Conclusion

The gas chromatography chemiluminescence method using a PAC SeNse detector according to ASTM D5504 demonstrates superior sensitivity, repeatability, linearity and equimolar response. It provides a reliable solution for ultra low sulfur analysis in natural gas and gaseous fuels supporting safety, regulatory compliance and catalyst integrity in industrial applications.