Automated determination of Total Acid Number in oils

Importance of the Topic

Determination of the total acid number in lubricating and crude oils is essential for assessing oil degradation corrosiveness and quality assurance In industrial settings regular TAN measurement helps prevent equipment wear and ensures compliance with industry standards Automated approaches enhance throughput reduce operator variability and support predictive maintenance strategies

Objectives and Study Overview

This application note describes an automated thermometric titration method for evaluating TAN in new and used lubricating oils as well as crude oils using a sample processor equipped system Key goals include establishment of a robust protocol comparison with a semi automated procedure and demonstration of repeatability across multiple oil types

Methodology and Instrumentation

The method is based on dissolution of oil in a toluene propan2ol mixture followed by addition of paraformaldehyde which serves as an endpoint indicator The sample is titrated with 0.1 or 0.01 mol per liter potassium hydroxide in isopropanol The endpoint is detected thermometrically as an endothermic inflection due to base catalyzed paraformaldehyde depolymerization Critical parameters include titrant rate solvent pre dose mixing rate and timing of reagent addition to preserve paraformaldehyde activity Blank titrations are performed for each oil type by weighing sets of samples in defined mass increments Standardization of KOH molarity is achieved using automated dispense of benzoic acid aliquots resulting in precise calibration

Used Instrumentation

• 859 Titrotherm thermometric titrator
• Thermoprobe temperature sensor
• Dosino dispensers 10 and 50 milliliter
• 802 propeller rod stirrer
• 814 USB Sample Processor with 14 place rack
• Macro titration head and related stoppers sleeves and cups

Main Results and Discussion

Automated titration of a used oil sample yielded a TAN of 5.33 plus minus 0.13 milligram KOH per gram based on seven replicates Comparable semi automated measurements returned 5.48 plus minus 0.16 milligram KOH per gram indicating close agreement The KOH standardization curve exhibited a slope corresponding to 0.1006 mol per liter with excellent linearity Blank determination as a function of sample mass produced an R2 of 0.9967 Thermometric titration curves displayed sharp temperature and derivative inflections confirming reliable endpoint detection

Benefits and Practical Applications

• High precision and reproducibility across oil types
• Reduced manual intervention and faster analysis
• Clear and objective thermometric endpoint detection
• Suitability for routine quality control in industrial and environmental laboratories
• Adaptable to different sample matrices with minimal method adjustment

Future Trends and Possibilities

Integration of automated thermometric titration with laboratory information management systems and further miniaturization of titration vessels are anticipated Development of advanced endpoint detection algorithms and coupling with spectroscopic techniques may expand applicability to other analytes Moreover remote operation and application of machine learning to interpret titration data represents a promising direction for enhanced process analytical technology

Conclusion

The described automated thermometric titration method provides a robust accurate and efficient means to determine total acid number in oils Implementation of a sample processor enables consistent reagent delivery and endpoint detection achieving results comparable to conventional approaches while enhancing throughput and reproducibility

References

• M J D Carneiro M A Feres Junior and O E S Godinho Determination of the acidity of oils using paraformaldehyde as a thermometric endpoint indicator J Braz Chem Soc volume 13 issue 5 pages 692 694 year 2002