Analysis of Non-Sulfur Natural Gas Odorants Using the Agilent 990 Micro GC System

Significance of the Topic

Natural gas is inherently odorless, requiring reliable additives to enable leak detection. Traditional sulfur-based odorants, such as tetrahydrothiophene and tert-butyl mercaptan, can react with pipeline materials and elastomers, increasing maintenance costs and producing harmful SO2 and SO3 upon combustion. Methyl acrylate and ethyl acrylate represent the first commercially available sulfur-free odorants, offering corrosion mitigation and reduced environmental impact. Robust analytical methods for these esters are essential for ensuring safety and regulatory compliance.

Objectives and Study Overview

This application note evaluates the Agilent 990 Micro GC system with a CP-TCEP MES column for rapid and sensitive quantitation of methyl acrylate and ethyl acrylate in natural gas. Key goals include determining detection limits, assessing precision, and demonstrating selectivity against hydrocarbon matrices in both standard mixtures and real gas samples.

Methodology

Two gas standards were analyzed: Standard 1, a simulated natural gas containing approximately 11 ppm of each acrylate; and Standard 2, a hydrocarbon blend with n-C11, n-C12, and methanol. Carrier gas was helium at 200 kPa. Injector temperature was 80 °C, column oven 60 °C. Injection times of 40 ms and 150 ms were tested to optimize sensitivity. A residential natural gas sample spiked to 5 ppm evaluated real-world performance.

Used Instrumentation

• Agilent 990 Micro GC system
• 15 m CP-TCEP MES capillary column
• Helium carrier gas at 200 kPa
• Injector temperature set to 80 °C
• Column oven temperature set to 60 °C

Main Results and Discussion

• The high-polarity CP-TCEP MES phase resolved methyl acrylate (RT ~1.74 min) and ethyl acrylate (RT ~2.10 min) from light and heavy hydrocarbon interferences.
• Twenty consecutive injections of Standard 1 yielded retention time RSDs below 0.1% and area RSDs under 5.1%.
• Limits of detection were established at 1.1 ppm for methyl acrylate and 1.5 ppm for ethyl acrylate (99% confidence, n=20).
• Extending injection time to 150 ms increased peak heights approximately threefold without significant noise elevation.
• Collaborator data showed area precision at 5 ppm of 7.1% for methyl acrylate and 3.6% for ethyl acrylate, with real gas concentrations measured at 3.5 ppm and 4.3 ppm, respectively.

Benefits and Practical Applications

• Fast analysis time (<2.2 min) enables high throughput monitoring.
• Low detection limits support regulatory odorant concentration requirements.
• Separation from complex hydrocarbon matrices ensures reliable quantitation.

Future Trends and Potential Applications

Ongoing developments in micro GC technology, including advanced column chemistries and automated calibration routines, may enable broader screening of emerging non-sulfur odorants. Field-deployable systems with enhanced detector sensitivity could facilitate real-time, on-site leak detection and odorant monitoring.

Conclusion

The Agilent 990 Micro GC system with a CP-TCEP MES channel delivers rapid, sensitive, and reproducible measurement of methyl acrylate and ethyl acrylate in natural gas. Its high selectivity and low detection limits make it a robust solution for routine monitoring of sulfur-free odorants, improving safety and reducing environmental impact.

References

1. Schmeer F.; Reimert R.; Kaesler H.; Henke F.; Mansfeld G. Development of a Sulphur-Free Odorant. 22nd World Gas Conference, Tokyo, 2003.
2. Zhang J. Analysis of Tetrahydrothiophene (THT) in Natural Gas Using the Agilent 990 Micro GC; Agilent Technologies Application Note 5994-1042EN, 2019.