Fully automated determination of TAN/TBN in industrial samples according to ASTM standards D 664 and D 2896

Significance of TAN/TBN Analysis

Accurate determination of Total Acid Number (TAN) and Total Base Number (TBN) is vital in the petroleum and lubricant industry for monitoring oil degradation, additive consumption, and corrosion potential. These metrics indicate oxidative aging and alkaline reserve, directly impacting equipment longevity, maintenance schedules, and product quality.

Objectives and Overview of the Study

This study presents a fully automated workflow for measuring TAN and TBN in industrial oil samples in accordance with ASTM D 664 and D 2896 standards. The main goals are to streamline sample handling, reduce manual labor, enhance safety by limiting solvent exposure, and achieve high reproducibility even at low analyte concentrations.

Instrumentation

• 864 Robotic Balance Sample Processor – automates sample weighing, solvent dosing, mixing, and electrode conditioning.
• 809 Titrando with Solvotrode – performs potentiometric titration and endpoint detection for acid/base titrations.
• 800 Dosinos – delivers precise volumes of titrants and electrolyte solutions.
• Precisa XR 205 A Analytical Balance – ensures accurate sample mass measurement directly on the robotic rack.

Methodology

A small aliquot of oil is placed on the robotic balance rack and weighed automatically. The system adds a defined volume of solvent mixture (toluene, isopropanol, water) and mixes until complete dissolution. For TAN, titration is carried out with standardized KOH in alcohol; for TBN, perchloric acid in glacial acetic acid or chlorobenzene is used. All titrant additions and electrode conditioning steps occur under computer control, and the titration curves are recorded potentiometrically. After each run, the unit performs an automated cleaning cycle tailored to oil residues.

Main Results and Discussion

The automated protocol yielded TAN and TBN values with relative standard deviations below 2%, demonstrating high precision across replicate measurements in both standard oils and industrial samples. Endpoint volumes correlated closely with manual methods while offering faster throughput. Titration curves showed well-defined inflection points and consistent baselines, confirming reliable electrode performance and reagent delivery.

Benefits and Practical Applications

• Significant reduction in hands-on time and operator errors.
• Enhanced laboratory safety by minimizing contact with toxic solvents.
• Improved data integrity through integrated software management and database storage.
• Rapid turnaround enables real-time monitoring of production and field samples.

Future Trends and Potential Applications

Automation of TAN/TBN determination can be extended by integrating inline sampling for continuous process monitoring, coupling with spectroscopic sensors for multi-parameter analysis, and employing machine-learning algorithms for endpoint prediction and anomaly detection. Miniaturization of reagent volumes and green solvent alternatives are promising directions to reduce cost and environmental impact.

Conclusion

The fully automated system described here delivers robust, reproducible TAN and TBN measurements in compliance with ASTM D 664 and D 2896. It combines precise sample handling, controlled titration, and thorough cleaning to meet the demands of modern oil analysis laboratories, offering significant gains in efficiency, safety, and data quality.

References

• Risse H. Fully automated determination of TAN/TBN in industrial samples according to ASTM standards D 664 and D 2896. Metrohm AG, Herisau, Switzerland.