Determination of Olefin Content in Denatured Ethanol According to ASTM D7347

Significance of the Topic

Denatured ethanol is widely used as an oxygenate additive in spark ignited engine fuels. The presence of olefinic hydrocarbons in this matrix can contribute to photochemical smog formation and must be controlled to meet environmental regulations such as California Air Resources Board limits. Reliable quantification of total olefin content is therefore critical for fuel producers and regulatory bodies.

Objectives and Study Overview

This application note presents an automated method for determining olefin content in denatured ethanol according to ASTM D7347-07. Using the Agilent 1260 Infinity Analytical SFC System coupled with a SIM flame ionization detector, the study demonstrates compliance with precision, calibration, and retention requirements without any sample pretreatment and within a 10-minute analysis time.

Methodology and Instrumentation

The analytical setup comprises:

• Agilent 1260 Infinity Binary SFC Pump with CO₂ as main eluent and hexane purge for the backpressure regulator
• Two thermostatted column compartments housing in series: a PVA guard column, silver‐loaded ChromSpher Lipids column, and silica column with time-based valve switching
• SIM Flame Ionization Detector operated at 300 °C with H₂, air, and N₂ makeup gases
• CTC Analytics PAL autosampler configured for 1 µL injections and hexane washes

Valve positions are actuated at predetermined times (0, 0.75, 3.0, 5.15, and 7.5 min) to trap ethanol, separate saturates, retain olefins on the silver column, and elute aromatic fractions.

Key Results and Discussion

Valve switching times were optimized using test mixtures to ensure baseline return before each step. A performance test mixture (PTM) containing saturates, olefins, mono- and polynuclear aromatics showed reproducible retention times (RSD < 0.2%) and resolution > 6 between olefins and aromatics over 20 injections. Calibration from 0.1 to 1.0 mass% olefins in ethanol yielded linear response (R² = 0.9979). Repeatability tests on PTM, a 0.25% QC sample, and a 0.5% spiked ethanol sample all met ASTM D7347-07 repeatability limits for peak area and content.

Benefits and Practical Applications

• Fully automated, no sample preparation required
• Rapid 10-minute analysis time with high precision
• Validated linear calibration range covering regulatory limits
• Robust valve switching protects columns and ensures clean separations

Future Trends and Potential Uses

The integration of supercritical fluid chromatography with dedicated FID hardware can be extended to other fuel analyses (e.g., aromatics in diesel per ASTM D5186). Future developments may include multiplexed valve assemblies for simultaneous multi-component screening, real-time process monitoring, and miniaturized portable SFC-FID systems for field applications.

Conclusion

The Agilent 1260 Infinity Analytical SFC System combined with the SIM FID provides a robust, precise, and rapid method for measuring olefin content in denatured ethanol in full compliance with ASTM D7347-07. The approach delivers repeatable retention times, accurate quantification down to 0.1% mass, and minimal column fouling through strategic valve switching.

Reference

1. ASTM D7347-07, Standard Test Method for Determination of Olefin Content in Denatured Ethanol by Supercritical‐Fluid Chromatography
2. California Air Resources Board, The California Reformulated Gasoline Regulations, Title 13, Sections 2250–2273.5
3. ASTM D6550-10, Standard Test Method for Determination of Olefin Content of Gasolines by Supercritical-Fluid Chromatography
4. Noll-Borchers M., Hölscher T., Naegele E., Becker M., Agilent Technologies Application Note 5991-6434EN, 2015