Agilent 7890 Series GC with Prefractionator for Reliable Analysis of Crude Butadiene and Mixed C4 Streams

Significance of the Topic

The reliable characterization of crude 1,3-butadiene and mixed C4 streams is critical in petrochemical processing to ensure product quality and protect sensitive chromatography columns from polar contaminants and heavy oligomers. Inline precolumn backflushing preserves column life, improves precision, and reduces downtime.

Objectives and Study Overview

This study evaluates an Agilent 7890 Series GC equipped with a High Pressure Liquid Injector (HPLI) and a Capillary Flow Technology (CFT) purged union to implement midpoint backflushing. The goal is to remove water, polar solvents, and higher-molecular-weight components before they reach the alumina PLOT analytical column, while achieving robust separation of light hydrocarbons.

Methodology and Instrumentation

Samples are injected via HPLI into a 15 m × 0.53 mm, 1 µm HP-INNOWax precolumn that retains water, acetonitrile, and 1,3-butadiene dimer. At a programmed time point (1.7–2.0 min), the CFT purged union drops inlet pressure to reverse flow and backflush retained impurities through the split vent. The analytical column is a 50 m × 0.53 mm, 10 µm GS-Alumina operated at constant helium flow. Detection is performed with FID.

Main Results and Discussion

Optimized backflush timing effectively removes polar and heavy components, preventing alumina column fouling. Chromatograms demonstrate complete elution of C1–C5 hydrocarbons with clear peak resolution. Inline backflushing cuts cycle time by approximately 36 minutes compared to non-backflush methods. Analysis of a real mixed C4 plant sample confirms clean baseline and accurate quantification. Twenty sequential injections and a blank run after fifty samples show minimal carryover and sustained column performance. Retention time relative standard deviations improve from 0.07–0.84% without backflush to 0.02–0.11% with backflush.

Benefits and Practical Applications

• Extends PLOT column lifetime by excluding polar contaminants
• Enhances retention time repeatability for trace impurity analysis
• Reduces overall analysis duration and increases sample throughput
• Streamlines method development for QA/QC in petrochemical laboratories

Future Trends and Perspectives

Emerging developments include automated backflush control integrated into GC software, expansion of precolumn backflush to two-dimensional GC workflows, coupling with mass spectrometry for enhanced compound identification, and novel inert precolumn coatings to further improve robustness in demanding industrial environments.

Conclusion

An Agilent 7890 GC with HPLI and CFT purged union delivers a robust solution for crude butadiene and mixed C4 analysis. Precolumn backflushing protects the alumina PLOT column, maintains chromatographic performance over extended sequences, and accelerates analysis cycles while ensuring high precision in impurity quantification.

Instrumentation

• Agilent 7890 Series Gas Chromatograph
• High Pressure Liquid Injector (HPLI)
• CFT purged union controlled via AUX EPC channel
• HP-INNOWax precolumn (15 m × 0.53 mm, 1 µm)
• GS-Alumina analytical column (50 m × 0.53 mm, 10 µm)
• Flame Ionization Detector (FID)
• Helium carrier gas

References

1. Wang C. Improved Gas Chromatograph Method for Trace Hydrocarbon Impurities in 1,3-Butadiene. Agilent Technologies publication 5991-1499EN; 2012.
2. White WC. Butadiene Production Process Overview. Chemico-Biological Interactions. 2007;166:10–14.
3. Agilent Flow Calculator software. www.agilent.com/chem/flow-calculator.
4. Firor RL. Prefractionator for Reliable Analysis of the Light Ends of Crude Oil and other Petroleum Fractions. Agilent Technologies publication 5990-5070EN; 2009.