Simultaneous Analysis of Trace Oxygenates and Hydrocarbons in Ethylene Feedstocks Using Agilent 7890A GC Capillary Flow Technology

Importance of the Topic

Trace hydrocarbons and oxygenates in ethylene feedstocks can impair catalyst function and polymer quality. Efficient monitoring of these contaminants is essential for process reliability and product performance.

Study Objectives and Overview

This study integrates two-dimensional gas chromatography on an Agilent 7890A GC to detect C1–C4 hydrocarbons and oxygenates in a single run, enhancing ASTM D6159. Goals include streamlining analysis, boosting productivity, and safeguarding sensitive columns.

Methodology and Instrumentation

• First-dimension separation on a polar HP-INNOWax column isolates oxygenates from hydrocarbons.
• A Deans switch heart-cuts the hydrocarbon fraction onto an alumina HP-PLOT M column for detailed C1–C4 analysis.
• Auxiliary EPC channels dynamically blend gas standards for automated calibration.
• Key parameters: 40 °C initial oven, helium flows of 2.5 and 6 mL/min, 250 °C detector temperature, 5:1 split injection.

Main Results and Discussion

Methanol and C1–C4 hydrocarbons in technical-grade ethylene were resolved in under 25 minutes. The wax column prevented polar compounds from damaging the PLOT phase, maintaining peak shape and retention precision. Precision testing at ~2 ppmV impurity levels yielded RSDs below 3.8%.

Practical Benefits and Applications

• Simultaneous quantitation accelerates quality control workflows.
• Upstream trapping of oxygenates protects expensive columns and extends service life.
• Automated calibration reduces manual handling and improves reproducibility.

Future Trends and Potential Use

Advances in GC flow control and multi-dimensional separations may enable faster heart-cutting, integration with mass spectrometry, and broader automation. Dynamic blending calibration could be applied to sulfur, nitrogen, and VOC analyses.

Conclusion

The Agilent 7890A GC with Capillary Flow Technology and enhanced EPC offers a robust, single-run solution for trace oxygenate and hydrocarbon analysis in ethylene, complementing ASTM D6159 while reducing runtime and maintenance.

Used Instrumentation

• Agilent 7890A Gas Chromatograph
• Capillary Flow Technology with Deans switch
• HP-INNOWax column (30 m × 0.32 mm × 0.5 µm)
• Alumina HP-PLOT M column (30 m × 0.53 mm × 15 µm)
• Flame ionization detector at 250 °C
• Auxiliary electronic pneumatics control

References

1. ASTM D6159: Standard Practice for Analysis of Hydrocarbons in Ethylene by Gas Chromatography.
2. McCurry JD. Fast Determination of Denatured Fuel Ethanol Purity by Two-Dimensional Gas Chromatography. Agilent Technologies. 2003.
3. Firor RL, Quimby BD. Automated Dynamic Blending System for Low Sulfur Detection on Agilent 6890 GC. Agilent Technologies. 2001.