Sulfur compounds - Analysis of ethanethiol (ethyl mercaptan) in LPG

Importance of Sulfur Compound Analysis in LPG

LPG often contains sulfur additives like ethanethiol to enable odor detection. Accurate measurement of these compounds ensures compliance with fuel quality standards and protects downstream catalytic systems from sulfur poisoning. The method outlined here provides sensitive, reliable detection of ethanethiol at low ppm levels.

Study Objectives and Overview

This application note demonstrates separation and quantification of ethanethiol in LPG using gas chromatography with a wide-bore column and flame photometric detection. Key goals include method sensitivity at 10–20 ppm, chromatographic resolution of sulfur species, and reproducibility in LPG matrices.

Methodology and Instrumentation

• Instrument: Gas chromatograph with valve-loop injector and flame photometric detector (FPD)
• Column: Agilent CP-SilicaPLOT, 0.53 mm × 30 m, 6 μm PLOT stationary phase
• Column temperature: 120 °C
• Carrier gas: Helium at 175 kPa (1.75 bar)
• Injection: Nickel valve-loop at 120 °C
• Detection: FPD set to 175 °C for sulfur-selective response
• Calibration range: 10–20 ppm ethanethiol in propane/LPG matrix

Main Results and Discussion

The method achieved baseline separation between the bulk hydrocarbon peak and ethanethiol. In calibration samples, ethanethiol was detected at 10.3 ppm, consistent across replicates. Analysis of a commercial LPG sample yielded an ethanethiol concentration of 17 ppm. The CP-SilicaPLOT column demonstrated high inertness and retention characteristics essential for trace sulfur analysis.

Benefits and Practical Applications

• Sensitivity: Reliable quantification of ethanethiol at low ppm levels
• Speed: Rapid analysis with a 120 °C isothermal run
• Robustness: Inert column minimizes adsorption and peak tailing
• Quality control: Ensures compliance with odorant addition regulations in LPG production and distribution

Future Trends and Potential Applications

Advancements in detector technology, such as enhanced sulfur-selective detectors or mass spectrometry coupling, will further lower detection limits. Emerging microfabricated PLOT columns and automated sample introduction systems may increase throughput and reduce maintenance. The methodology may extend to other sulfur additives and volatile sulfur compounds in alternative fuels.

Conclusion

The presented GC-FPD method using the Agilent CP-SilicaPLOT column provides a straightforward, sensitive, and reproducible approach for ethanethiol determination in LPG. Its robustness and low detection limits make it suitable for routine quality control in fuel analysis.

References

• Agilent Technologies, Inc. Application Note A01452 (2011)
• Olofsson, M.; Borealis AB, Stenungsund, Sweden (Courtesy data)