Analysis of Sulphur Compounds in Various Liquefied Petroleum Gases

Significance of the Topic

The analysis of trace sulphur compounds in liquefied petroleum gas (LPG) is critical for ensuring product quality, compliance with environmental and safety regulations, and protecting downstream catalysts and equipment from corrosion and poisoning.

Objectives and Study Overview

This application note presents a two-channel gas chromatography (GC) method using pulsed flame photometric detectors (PFPD) to quantify low-level hydrogen sulfide, carbonyl sulfide and various mercaptans in propane- and butane-based LPG samples.

Methodology

Samples of LPG are introduced as a fully gaseous stream via dual gas sampling valves and a micro-gasifier. An inert Ultimetal-deactivated flow path prevents adsorption of sulphur species. Channel A employs a non-polar SCION-5 capillary column for H₂S and mercaptans in propane matrices; Channel B uses a polar BOND Q column to resolve COS and methyl mercaptan in butane matrices. Carrier gas is helium at 2 mL/min, with temperature programming from 35 °C to 250 °C at 12 °C/min.

Used Instrumentation

• SCION 456 GC system with dual channels
• Micro-gasifier for direct LPG introduction
• Ultimetal-deactivated sampling path
• SCION-5 non-polar column (30 m × 0.32 mm × 5 µm)
• BOND Q polar column (25 m × 0.32 mm)
• Pulsed flame photometric detectors in sulphur mode
• Helium carrier gas and controlled air/H₂ flows

Main Results and Discussion

Calibration with a sulphur standard demonstrated baseline separation of H₂S and mercaptans on Channel A, while COS co-eluted with propane but was resolved on Channel B. In butane matrices, methyl mercaptan co-eluted on the non-polar column but was quantified reliably on the BOND Q column. Fifteen replicate analyses yielded relative standard deviations below 2.5% across all analytes, confirming excellent repeatability and minimal detector quenching by bulk hydrocarbons.

Benefits and Practical Applications

• Direct coupling of LPG stream to GC avoids sample pretreatment.
• Inert flow path prevents analyte loss and system contamination.
• Two-channel approach offers flexible analysis regardless of hydrocarbon matrix.
• High sensitivity and selectivity of PFPD enables reliable quantification at low concentration levels.

Future Trends and Applications

Advances in micro-GC and novel sulphur-selective detectors may further reduce analysis time and increase portability. Integration with automated QC workflows and real-time process monitoring will enhance industrial applications. Coupling with mass spectrometry could provide complementary structural information.

Conclusion

The dual-channel SCION GC configuration with PFPD detectors offers a robust, sensitive and repeatable solution for low-level sulphur analysis in LPG. Its inert sample path and selective detection ensure accurate quantification of H₂S, COS and mercaptans in diverse hydrocarbon matrices, supporting quality control and regulatory compliance in petrochemical operations.