Important Petroleum Separations Using a New SPB™-Octyl Capillary Column

Importance of the Topic

Accurate separation of complex hydrocarbon and oxygenate mixtures is critical for petroleum quality control, environmental monitoring, and regulatory compliance. Traditional nonpolar phases like squalane and polydimethylsiloxane (PDMS) present limitations in thermal stability and selectivity. The SPB-Octyl bonded phase offers an advanced nonpolar alternative approaching squalane’s polarity while providing a wider temperature range and enhanced resolution for key petroleum analyses.

Objectives and Study Overview

This work evaluates the performance of a novel SPB-Octyl capillary column (50% methyl/50% n-octyl polysiloxane) in resolving important hydrocarbon and oxygenate pairs that are challenging on conventional nonpolar columns. Specific goals include resolving aromatic/olefin pairs, MTBE contaminants, methanol/isobutane, and complex pyrolysis gasoline mixtures.

Methodology and Instrumentation

Gas chromatography with flame ionization detection was used to compare SPB-Octyl against SPB-1 and Petrocol DH columns. Typical conditions included:

• Column dimensions: 100 m × 0.25 mm ID, 0.5 µm film
• Carrier gas: helium at constant pressure or linear flow
• Temperature ramps: subambient (35 °C) to 200 °C at 1 °C/min or 50 °C to 180 °C at 10 °C/min
• Injection: split ratios of 200:1 to 215:1, injection port at 250 – 310 °C

Key Results and Discussion

• Benzene/1-methylcyclopentene and toluene/2,3,3-trimethylpentene pairs were baseline-resolved on SPB-Octyl, unlike on SPB-1.
• MTBE oxygenate contaminants (tert-butanol, cis/trans-2-pentene) eluted in a distinct window, improving quantitation.
• Methanol and isobutane were separated at ambient initial temperature without subambient programming.
• Complex pyrolysis gasoline samples showed clear separation of disproportionate aromatics, olefins, and xylenes over 75 minutes.
• Oxygenates such as ethanol, isopropanol, and ETBE exhibited shifted retention indices versus hydrocarbons, enhancing selectivity.

Benefits and Practical Applications

The SPB-Octyl phase combines low polarity with bonded-phase stability, offering:

• Improved resolution for environmentally relevant oxygenates and petroleum streams.
• Wide operational temperature range (-60 °C to 280 °C) for diverse sample matrices.
• Enhanced throughput for gasoline quality control, MTBE purity analysis, and reformate characterization.

Future Trends and Applications

Further developments may include coupling SPB-Octyl columns with mass spectrometry for high-confidence identification, miniaturized fast GC applications, and extension into food, fragrance, pharmaceutical, and environmental analyses requiring robust nonpolar separations.

Conclusion

The SPB-Octyl capillary column demonstrates squalane-equivalent nonpolarity with bonded-phase advantages, delivering superior separations of critical hydrocarbon and oxygenate mixtures for petroleum and related industries.

References

1. ASTM D5441: Test Method for Analysis of Methyl tert-Butyl Ether by Gas Chromatography.
2. HP US Patent No. 4,293,415: Fused Silica Capillary Column Technology.