Automatic determination of the bromine number and the bromine index in petroleum products

Significance of the Topic

The bromine number and bromine index are fundamental quality parameters for petroleum products, reflecting the degree of unsaturation in aliphatic and aromatic hydrocarbons. Accurate measurement of these parameters supports product specification, process control in refining, environmental compliance and performance evaluation of fuels, lubricants and petrochemical feedstocks.

Objectives and Study Overview

This Application Bulletin outlines automated potentiometric titration methods for determining the bromine number (expressed in g Br2 per 100 g sample) and the bromine index (mg Br2 per 100 g sample) across a wide range of petroleum fractions. It integrates multiple international standards—including ASTM D1159, ISO 3839, BS 2000-130, IP 130, GB/T 11135, DIN 51774-1 for bromine number; ASTM D2710, IP 299, GB/T 11136, DIN 51774-2 for aliphatic bromine index; and ASTM D5776, SH/T 1767 for aromatic bromine index—while avoiding toxic solvents and improving safety and reproducibility.

Methodology and Instrumentation

Titrations are performed on an automated titrator equipped with dual potentiometric detection modes (DETIpol and METIpol), a double platinum-wire electrode and a Pt1000 temperature sensor. Key components include a thermostatted titration vessel, magnetic stirrer and precision buret.

Reagent and solvent preparation uses dried KBr/KBrO3 for Br2 generation, glacial acetic acid, toluene, methanol and controlled additions of H2SO4 or HCl. Sodium thiosulfate serves as titrant for back-titration. The titration solvent mixture is cooled to approximately 4.5 °C, and blank corrections are applied to ensure accuracy.

Sample sizes are selected according to the expected bromine value, either by direct weighing or by dilution in toluene. Typical ranges span low-unsaturation products (0–10 g Br2/100 g) to highly unsaturated fractions (>150 g Br2/100 g) for bromine number, and from 0–20 mg Br2/100 g up to 500–1000 mg Br2/100 g for bromine index analyses.

Main Results and Discussion

The automated protocols deliver precise detection of equivalence points with clear potential jumps and minimal drift. Blank titrations confirm stable background consumption. Comparison across standards reveals that slight variations in acid concentration or solvent composition do not compromise precision. Reproducibility better than 1 % relative is routinely achieved over the full dynamic range.

Benefits and Practical Applications

Automated potentiometric titration of bromine parameters offers:

• High precision and reproducibility with minimal operator influence
• Clear endpoint identification via potentiometric detection
• Elimination of ozone-depleting or highly toxic chlorinated solvents
• Wide applicability to fuels, olefins, aromatic extracts and biofuel analysis
• Full compliance with multiple international test methods

Future Trends and Possibilities for Use

Emerging developments may include miniaturized titration cells for lower reagent consumption, integration of in-line sensors for real-time process monitoring and application of machine-learning algorithms to optimize titration parameters. Expansion into biofuel unsaturation profiling and real-time environmental monitoring of unsaturated contaminants is anticipated.

Conclusion

The described automated potentiometric methods provide a robust, flexible and standardized approach for accurate determination of bromine number and bromine index in petroleum products. By combining precise endpoint detection with safer solvent systems and broad compliance to global standards, these protocols enhance laboratory productivity, safety and data reliability.

References

• ASTM D1159 Standard Test Method for Bromine Numbers of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titration
• ISO 3839 Petroleum Products – Determination of Bromine Number of Distillates and Aliphatic Olefins – Electrometric Method
• BS 2000-130 Petroleum Products – Determination of Bromine Number
• IP 130 Petroleum Products – Determination of Bromine Number of Distillates and Aliphatic Olefins
• GB/T 11135 Standard Test Method for Bromine Numbers of Petroleum Distillates and Commercial Aliphatic Olefins by Electrometric Titration
• DIN 51774-1 Determination of Bromine Acceptance by Electrometric Dead-Stop Method
• ASTM D2710 Standard Test Method for Bromine Index of Petroleum Hydrocarbons by Electrometric Titration
• IP 299 Determination of Bromine Index – Electrometric Titration Method
• GB/T 11136 Petroleum Hydrocarbons – Determination of Bromine Index
• DIN 51774-2 Testing of Liquid Fuels; Determination of Bromine Acceptance by Electrometric Dead-Stop Method
• ASTM D5776 Standard Test Method for Bromine Index of Aromatic Hydrocarbons by Electrometric Titration
• SH/T 1767 Determination of Bromine Index of Aromatic Hydrocarbons by Electrometric Titration