Determination of Total Acid Number in Biodiesel

Significance of the Topic

The determination of Total Acid Number (TAN) in biodiesel is critical for assessing fuel quality, stability, and compliance with industry specifications. Accurate TAN measurement prevents engine wear, corrosion, and deposit formation, ensuring reliable performance and extending equipment lifespan.

Objectives and Overview of the Study

This application note presents a thermometric titration method for quantifying TAN in biodiesel samples with a detection limit below 0.05 mg KOH/g. The approach employs paraformaldehyde as a catalyst and endpoint indicator to generate a distinct thermal signal.

Methodology and Instrumentation

The procedure involves weighing 5–10 mL of biodiesel, dissolving it in 30 mL of 2-propanol, and adding approximately 0.5–0.6 g of paraformaldehyde. Titration is performed with 0.01 mol/L KOH in 2-propanol at a delivery rate of 5 mL/min, with stirring speed set to 15 (802 stirrer) and a 10-second delay before initiation. Endpoint detection relies on an endothermic response associated with paraformaldehyde depolymerization, monitored via solution temperature and its second derivative.

Instrumentation

The titration system includes a Dosino delivery unit protected by a soda-lime guard tube to prevent CO2 ingress. Temperature changes are recorded with high sensitivity to capture the thermal inflection at the endpoint.

Main Results and Discussion

Biodiesel from company A (samples A–batch 62, 72, 74) exhibited TAN values of 0.062–0.073 mg KOH/g (n=5). A sample from company B showed a significantly higher acidity at 0.421 mg KOH/g (n=5). Blank determinations across 4–12 g sample masses yielded a regression intercept of 0.3739 mL (R2=0.9992), accounting for baseline titrant consumption required to trigger the indicator reaction.

Benefits and Practical Applications

This thermometric titration technique offers rapid, precise, and low-reagent-consumption analysis of biodiesel acidity. Its sensitivity to low TAN values makes it suitable for quality control in biodiesel production, feedstock evaluation, and regulatory compliance.

Future Trends and Applications

Future developments may focus on further automation, integration with inline process monitoring, and adaptation to other lipid-based materials. Enhancements in data processing and instrument miniaturization could improve throughput and lower detection limits.

Conclusion

The paraformaldehyde-catalyzed thermometric titration method provides a robust, sensitive, and efficient solution for TAN determination in biodiesel, meeting stringent industry requirements for fuel quality assurance.

Reference

M. J. D. Carneiro, M. A. Feres Júnior, and O. E. S. Godinho. Determination of the acidity of oils using paraformaldehyde as a thermometric end-point indicator. J. Braz. Chem. Soc. 13(5) 692–694 (2002).