Octans and Lower Boiling Hydrocarbons in Olefin-Free Gasolines

Importance of the Topic

Detailed profiling of C8 and lower hydrocarbons in gasoline is critical for quality control, regulatory compliance and performance optimization. Olefin-free gasolines require precise characterization of paraffins and naphthenes, as their boiling range and isomeric composition influence combustion behavior, emissions and compliance with industry standards.

Objectives and Overview

This study outlines a gas chromatographic method to identify and quantify C8 and lighter paraffins and naphthenes in olefin-free gasoline samples. Two chromatographic conditions are employed to enhance compound resolution and confirm identifications by comparing dual chromatograms. The workflow follows UOP-690 methodology, aiming to deliver robust and repeatable hydrocarbon profiles.

Methodology and Instrumentation

The analysis was performed on a Nexis GC-2030LBH3 system configured with a single splitless injector, a dedicated capillary column and flame ionization detection (FID). Key features include:

• Single-channel FID ensuring high sensitivity and simplicity
• Precision temperature programming for optimal separation of C4–C8 isomers
• Specialized software tools for peak identification and chromatogram comparison

Chromatograms were acquired under two sets of conditions, generating four traces that resolve up to 58 target compounds, including challenging isomeric species.

Main Results and Discussion

The dual-condition approach yielded clear separation of paraffinic and naphthenic isomers. Typical chromatograms demonstrate:

• Baseline resolution for key components such as isobutane, n-butane, pentanes and hexanes
• Successful discrimination of multiple trimethylpentanes and methylcyclopentane isomers
• Identification of aromatic co-elutions (e.g., xylenes, ethylbenzene) through retention time matching

Repeatability tests confirmed relative standard deviations below 2% for major peaks. Comparison of chromatograms under varied conditions improved confidence in peak assignments.

Benefits and Practical Application

The presented method offers:

• Streamlined setup with a single FID channel
• High repeatability and reproducibility for routine QC
• Comprehensive hydrocarbon profiling supporting compliance with UOP and ASTM standards
• Ease of software-assisted identification saving analyst time

It is well-suited for research laboratories, refinery quality control and industrial testing facilities.

Future Trends and Opportunities

Advancements may include coupling with mass spectrometry for increased specificity, faster column technologies for reduced analysis time, and integration of multivariate data analysis to enhance quantification and isomer discrimination. Real-time monitoring of production streams and portable GC solutions represent further application prospects.

Conclusion

The Nexis GC-2030LBH3 system, adhering to UOP-690, provides a reliable and detailed approach for C8 and lower hydrocarbon analysis in olefin-free gasolines. Its simplicity, precision and comprehensive identification capability make it a valuable tool for gas chromatography laboratories.

References

• Shimadzu Corporation. Nexis GC-2030LBH3 System Gas Chromatograph Application Note SGC-ADS-0180. First Edition, November 2017.
• UOP Method 690: Analysis of C8 and Lower Boiling Hydrocarbons in Olefin-Free Gasolines.