Photometric titration of acid value in biodiesel according to EN 14104

Significance of the topic

Monitoring the acid value of biodiesel is essential for ensuring fuel purity, stability and protection of engine components. Elevated acid numbers signal potential degradation or production issues, which may cause corrosion and reduce operational safety.

Objectives and study overview

This application note demonstrates a rapid photometric titration method for determining the acid value of fatty acid methyl ester (FAME) biodiesel. The procedure follows the EN 14104 standard, covering values from 0.10 to 1.00 mg KOH/g sample.

Methodology and instrumentation

Sample and preparation:

• 100 % biodiesel derived from waste cooking oil.
• No additional sample pretreatment required.

Analytical setup:

• OMNIS Professional Titrator with OMNIS Dosing Modules.
• Optrode M2 photometric sensor with selectable wavelength.

Procedure:

1. Weigh biodiesel into the titration beaker.
2. Add pre-neutralized 2-propanol and phenolphthalein indicator.
3. Titrate with standardized KOH in 2-propanol until the photometric endpoint is reached.

Main results and discussion

The method delivers high repeatability and reproducibility in accordance with EN 14104 requirements. A set of six replicates yielded:

• Mean acid value: 0.41 mg KOH/g
• Absolute SD: 0.01 mg KOH/g
• Relative SD: 1.8 %

The smooth titration curve confirms reliable endpoint detection by the Optrode sensor.

Benefits and practical applications of the method

• Fast and reliable determination of acid value in biodiesel.
• Minimal sample preparation and reagent consumption.
• Chemically resistant Optrode sensor ensures maintenance-free operation.
• Modular OMNIS system allows easy expansion for parallel analyses.

Future trends and potential applications

Advancements in photometric titration may include in-line monitoring of fuel quality in production, integration with automated sampling systems and expansion to other non-aqueous titrations. Customizable wavelengths and software automation will further enhance method versatility.

Conclusion

The photometric titration method using the Optrode M2 and OMNIS titrator provides a robust, compliant and efficient approach for acid value determination in biodiesel. Its high precision and adaptability make it suitable for quality control in research and industrial laboratories.

Reference

EN 14104: Fatty acid methyl ester (FAME) – Determination of acid value – Photometric titration