The Automated On-Line Sampling and Analysis of Glycerol in Biodiesel

Importance of the Topic

Glycerol is a key by-product in biodiesel production and its efficient removal is essential to meet fuel quality standards and ensure engine performance. Monitoring glycerol content at low concentrations (down to 500 ppm) helps producers optimize purification steps and maintain compliance with regulatory limits.

Objectives and Study Overview

This application note describes the development of an automated on-line sampling and analysis method for quantifying glycerol in biodiesel streams. The goal is to achieve a reliable, fully automated workflow that delivers accurate glycerol measurements without manual intervention, enabling real-time quality control.

Instrumentation

• ATAS Optic 2-200 programmable injector
• Focus Autosampling Robot with flow cell
• HP 5890 gas chromatograph with flame ionization detector (FID)
• SGE SolGel Wax capillary column (30 m × 0.25 mm i.d., 0.25 µm film)

Methodology

The automated sequence involves:

• Sampling biodiesel directly from the process stream via the Focus flow cell
• Addition of internal standard and mixing with ethanol and n-hexane
• Injection of 1 µL aliquot in split mode into the GC system

The injector and GC temperature program are optimized for rapid vaporization and separation of glycerol:

• Injector initial temperature: 60 °C; ramp to 280 °C at 4 °C/s; total run time 20 min
• GC oven: hold 50 °C for 2 min, ramp to 280 °C at 10 °C/min, 16 min hold
• FID at 300 °C; split flow 10 mL/min

Main Results and Discussion

Chromatograms demonstrate clear separation of glycerol from biodiesel matrix components. The lower trace shows a distinct glycerol peak at approximately 19.5 min for a 500 ppm standard. Peak shape and retention time are reproducible, and the method achieves the target detection limit of 500 ppm. Automated sampling reduces variability and ensures consistent sample preparation.

Benefits and Practical Applications

• Fully automated workflow minimizes operator error and labor requirements
• On-line analysis enables real-time monitoring of glycerol removal in biodiesel production
• High sensitivity and reproducibility support stringent quality assurance protocols
• Integration with process control systems can optimize downstream purification steps

Future Trends and Potential Applications

Advancements may include coupling on-line sampling with mass spectrometric detection for enhanced specificity, smaller footprint micro-GC systems for decentralized testing, and integration into closed-loop process control platforms. Further research into faster column chemistries and multiplexed sampling could boost throughput.

Conclusion

The automated on-line GC-FID method provides a robust, sensitive, and reproducible solution for monitoring glycerol in biodiesel. Its implementation can streamline quality control, reduce operational costs, and support continuous production optimization.

Reference

Nicholas D. The Automated On-Line Sampling and Analysis of Glycerol in Biodiesel. Application Note No. 073. GL Sciences B.V.