Determination of total fluorine, chlorine, bromine, and sulfur in liquefied petroleum gas by pyrohydrolytic combustion ion chromatography with sample preconcentration

Significance of the topic

Liquefied petroleum gas (LPG) is widely used as fuel and chemical feedstock. Trace halogen and sulfur species can damage catalysts and downstream processes, so reliable quantification at low μg/kg levels is crucial.

Goals and Overview of the Study

The study demonstrates a streamlined workflow combining pyrohydrolytic combustion with preconcentration and reagent-free ion chromatography to measure total fluorine, chlorine, bromine, iodine, and sulfur in n-butane LPG.

Methodology and Instrumentation

A constant volume sampling of 30 μL LPG undergoes oxidative pyrohydrolytic combustion, generating halide and sulfate ions absorbed in a peroxide–hydrazine solution. The absorbate is diluted to 10 mL and preconcentrated on an IonPac UTAC-ULP2 column before elution and chromatography.

Instrumentation Used

• Mitsubishi AQF-2100H Automatic Combustion Unit with ABC-210 controller, HF-210 furnace, GI-260 LPG injector, and GA-211 absorption module
• Thermo Scientific Dionex Integrion HPIC system with Reagent-Free IC pump, eluent generator, high-pressure degasser, conductivity detector, and IonPac AG20/AS20 columns
• Auxiliary AXP pump and TTL-controlled preconcentration interface

Main Results and Discussion

Calibration from 2 to 16 mg/kg using multiple combustions produced correlation coefficients above 0.998. Preconcentration enhanced responses for chlorine, bromine, and iodine compared to direct injection, achieving method detection limits from ~125 to 1 070 μg/kg. Blank analyses identified background contributions limiting fluorine and sulfur sensitivity. Recoveries for spiked LPG standards ranged from 88 to 116 % with repeatability below 3 % RSD.

Benefits and Practical Applications

• Automated, safe handling of pressurized LPG with built-in venting and purge controls
• Improved sensitivity for trace halogens and sulfur versus direct injection IC
• Efficient calibration by combusting incremental standard aliquots
• Compliance with ASTM D7994 and compatibility with existing IC infrastructure

Future Trends and Opportunities

Advances in micro-preconcentration, digital automation, and integrated combustion-IC platforms will extend detection to sub-μg/kg levels and enable rapid screening of diverse matrices in energy, petrochemical, and environmental applications.

Conclusion

The combined pyrohydrolytic combustion and preconcentration IC approach delivers fast, robust quantification of total halogens and sulfur in LPG. It achieves low detection limits, high accuracy, and reproducibility, supporting quality control and regulatory requirements.

References

1. International Energy Agency. Key word statistics, IEA Publications, November 2018.
2. Nadkarni, ed. Guide to ASTM Test Methods for the Analysis of Petroleum Products and Lubricants, 2nd ed., ASTM International, 2007.
3. Thermo Scientific Application Note AN72693: Determination of Total Fluorine, Chlorine, and Sulfur in Aromatic Hydrocarbons by Oxidative Pyrolytic Combustion Followed by Ion Chromatography, 2018.
4. Thermo Scientific AppsLab record: Determination of Chloride in Algal Oil Using Combustion Ion Chromatography, 2015.
5. Thermo Scientific AppsLab record: Determination of Halogens and Sulfur in Refuse Derived Fuel by Combustion Ion Chromatography, 2015.
6. Thermo Scientific AppsLab record: Determination of Chloride and Sulfate in Crude Oil by Combustion Ion Chromatography, 2017.
7. Thermo Scientific AppsLab record: Determination of Halogens and Sulfate in LPG Using Combustion Ion Chromatography, 2016.
8. Thermo Scientific Application Note AN1145: Determination of Halogens in Coal Using Combustion Ion Chromatography, 2015.
9. Thermo Scientific AppsLab record: Determination of Chlorine and Sulfur in Wood Chips Using Combustion Ion Chromatography, 2015.
10. ASTM D7994 Standard Test Method for Total Fluorine, Chlorine, and Sulfur in LPG by Oxidative Pyrohydrolytic Combustion Followed by IC Detection, 2011.
11. Thermo Scientific Application Note AN73105: Determination of total fluorine, chlorine, bromine, and sulfur in LPG by pyrohydrolytic combustion IC, 2019.