Potentiometric determination of hydrogen sulfide, carbonyl sulfide and mercaptans in petroleum products

Importance of the Topic

Accurate quantification of hydrogen sulfide carbonyl sulfide and mercaptans in petroleum products is critical for product quality process safety and regulatory compliance Mercaptans and sulfides contribute to corrosion catalyst poisoning and environmental hazards making reliable analytical methods essential

Objectives and Study Overview

This bulletin presents a potentiometric titration approach for simultaneous determination of hydrogen sulfide carbonyl sulfide and mercaptans in both liquid and gaseous petroleum samples It outlines the procedure sample handling reagents titration conditions and calculation models for sulfur speciation

Methodology

Liquid samples are directly titrated without pretreatment by adding a measured aliquot into a solvent of isopropanol or ethanol blended with sodium acetate and ammonia or acetic acid depending on mercaptan molecular weight Gaseous samples are absorbed in alkaline caustic traps followed by titration of the collected solution All titrations employ an alcoholic silver nitrate titrant and Ag Titrode detection under inert nitrogen to prevent oxidation Key titration parameters include DET mode endpoint recognition stirring rates and controlled titrant addition to resolve multiple equivalence points

Instrumentation Used

United Metrohm Titrator equipped with DET mode Sample Changer and rod stirrer
Ag Titrode electrode with silver sulfide coating
Sealed titration vessel featuring a gas inlet and overflow tube

Main Results and Discussion

Titration curves exhibit one equivalence point for pure H2S or mercaptans and two points for mixed samples while a third plateau appears when elemental sulfur is present Formulas relate titrant volume and titer to sulfur content for each compound class The first peak corresponds to hydrogen sulfide the second to mercaptans and the third to disulfide formation with free sulfur An inert atmosphere and deoxygenated solvent are necessary to ensure accuracy due to oxidation sensitivity

Benefits and Practical Applications

The automated potentiometric method offers rapid precise and selective analysis across a wide range of petroleum matrices including fuels and refinery streams It supports quality control regulatory testing and process monitoring providing clear speciation of different sulfur forms

Future Trends and Opportunities

Emerging developments may include online integration for continuous monitoring microfluidic titration platforms advanced endpoint algorithms and coupling with spectroscopic detectors The adoption of artificial intelligence for data interpretation and smart automation could further enhance throughput and reliability

Conclusion

The described potentiometric titration procedure provides a robust approach to quantify hydrogen sulfide carbonyl sulfide and mercaptans in petroleum products Its automation versatility and clear equivalence point resolution make it a valuable tool for industrial and research laboratories

References

• ISO 3012:1999 Petroleum products – Determination of thiol mercaptan sulfur in light and middle distillate fuels – Potentiometric method
• ASTM D3227-04a Standard Test Method for Thiol Mercaptan Sulfur in Gasoline Kerosene Aviation Turbine and Distillate Fuels Potentiometric Method
• IP 342 Petroleum products – Determination of thiol mercaptan sulfur in light and middle distillate fuels – Potentiometric method
• UOP163-10 Hydrogen Sulfide and Mercaptan Sulfur in Liquid Hydrocarbons by Potentiometric Titration
• ISO 6326-3:1989 Natural gas – Determination of sulfur compounds – Part 3 Determination of hydrogen sulfide mercaptan sulfur and carbonyl sulfide sulfur by potentiometry
• IP 272 Determination of mercaptan sulfur and hydrogen sulfide content of liquefied petroleum gases LPG Electrometric titration method
• UOP212-05 Hydrogen Sulfide Mercaptan Sulfur and Carbonyl Sulfide in Hydrocarbon Gases by Potentiometric Titration