Determination of TAN in engine oil with 859 Titrotherm

Importance of the Topic

The determination of the Total Acid Number (TAN) in engine oils is a critical quality control measure in the petroleum and lubricant industries. TAN provides insight into oil degradation, corrosion potential and performance under operating conditions. Rapid and accurate TAN measurements support maintenance scheduling, ensure engine protection and extend oil service life.

Objectives and Study Overview

This study outlines a robust thermometric titration method for quantifying TAN in used engine oil. The primary goals are:

• Establish a reliable titration protocol with the 859 Titrotherm system.
• Demonstrate automated titer and method blank calculations using paraformaldehyde-catalyzed titrations.
• Validate the procedure on a real used oil sample (“Turbo 254”).

Applied Methodology and Instrumentation

The oil sample is dissolved in a 1:1 mixture of toluene and 2-propanol. Total acid constituents are titrated with 0.1 mol/L tetrabutylammonium hydroxide (TBAOH) in 2-propanol/methanol. Paraformaldehyde acts as catalyst, enhancing the endothermic hydrolysis reaction and sharpening the thermometric endpoint. Constant titrant addition produces a steady temperature change until the inflection marks the endpoint. Automated regression analysis in the tiamo™ software calculates titrant titer and method blank from plotted data of standard and blank titrations.

Used Instrumentation:

• 859 Titrotherm (with Dosino units)
• 2 mL and 50 mL dosing units
• Thermoprobe temperature sensor
• 3-way stopper with antidiffusion tip
• Standard laboratory glassware

Main Results and Discussion

Titer determination yielded a mean endpoint volume of 4.9933 mL for the benzoic acid standard, resulting in a calculated titrant concentration of 0.1001 mol/L. The method blank for fresh engine oil was 0.0638 mL. Analysis of the used oil sample “Turbo 254” delivered a TAN value of 22.85 mg KOH/g with a relative standard deviation of 0.26% (n=5). High correlation coefficients (R² ≥ 0.9999) indicate excellent linearity and reproducibility.

Benefits and Practical Applications of the Method

This thermometric titration approach offers:

• Rapid endpoint detection without specialized insulated vessels.
• Automated calculations for titer, blank and TAN values.
• High precision and minimal sample handling.
• Compatibility with routine laboratory workflows for QA/QC.

Future Trends and Potential Applications

Advances may include integration with online sampling for real-time oil condition monitoring. Coupling thermometric titration with chemometric data analysis could further enhance predictive maintenance strategies. Miniaturized and portable titration units could expand field applications in remote or industrial environments.

Conclusion

The described titration protocol using the 859 Titrotherm provides a fast, accurate and reproducible determination of TAN in engine oils. Automated data processing in tiamo™ streamlines the workflow, making this method well suited for industrial quality control and routine maintenance laboratories.