Trace Oxygenated Hydrocarbons in Liquid Hydrocarbon Streams Nexis GC-2030OAS3 GC-2014OAS3

Importance of the Topic

Trace oxygenated hydrocarbons—such as ethers, aldehydes, ketones and alcohols—in liquefied petroleum gas (LPG) can significantly affect product quality, process safety and regulatory compliance. Precise measurement of these components at ppm levels is crucial for refining operations, petrochemical feedstock monitoring and ensuring consistency in downstream applications.

Goals and Overview of the Study

This method outlines a robust gas chromatographic approach for the simultaneous determination of over 60 oxygenated hydrocarbon species in C4 LPG streams. It leverages an automated sampling system with backflush capability to achieve reliable quantitation across a wide concentration range (1–100 000 ppm), meeting UOP-960 specifications.

Methodology

• Automatic sampling with backflush to minimize carryover and matrix interference.
• Dual injection paths for parallel analysis and system performance monitoring.
• Split capillary column arrangement to optimize separation of structurally similar compounds.
• Flame Ionization Detection (FID) for universal response to oxygenates.
• Calibration covering low (1 ppm) to high (100 000 ppm) concentration levels.

Instrumentation Used

• Nexis GC-2030OAS3 gas chromatograph (Shimadzu)
• GC-2014OAS3 gas chromatograph (Shimadzu)
• Dual sample loop injectors and two multi-port valves
• Two capillary columns configured for backflush sequencing
• Dual FID detectors (one dedicated to analyte detection, the other monitoring backflush timing)

Main Results and Discussion

Chromatographic separations demonstrated baseline resolution for key oxygenated compounds within a 30 min run time. Detection limits consistently reached 1 ppm for all target analytes, with excellent repeatability (RSD <2 %). Typical chromatograms confirmed the effective removal of high-boiling matrix components post-backflush, preserving column life and maintaining signal stability.

A representative FID chromatogram identified early-eluting simple ethers (methyl ether, ethyl methyl ether) followed by aldehydes, alcohols and ketones in increasing retention order. Multi-component coelutions (e.g., isopropanol/n-propanol/cyclopropyl methyl ketone) were resolved by optimized temperature programming.

Benefits and Practical Applications

• Wide dynamic range suitable for trace-level monitoring and bulk impurity analysis.
• High throughput with minimal manual intervention due to automated sampling and backflush.
• Improved method robustness and reduced downtime by protecting columns from heavy hydrocarbons.
• Compliance with industry standard UOP-960 enhances data comparability across laboratories.

Future Trends and Opportunities

Advances in detector technology (e.g., high-resolution time-of-flight MS) may further enhance selectivity for complex oxygenates. Integration with online process analyzers and predictive maintenance software will support real-time quality control. Emerging miniaturized GC platforms could enable on-site monitoring in decentralized facilities.

Conclusion

The described GC method offers a comprehensive solution for quantifying trace oxygenated hydrocarbons in LPG streams. Its combination of automated backflush, dual-channel FID detection and extensive calibration range ensures accurate, reproducible results for routine quality assurance and process control.

References

1. UOP-960: Determination of Trace Oxygenates in LPG, 2012.
2. Shimadzu Corporation. SGC-ADS-0188 System Gas Chromatograph, First Edition, November 2017.