Hydrocarbons, C1 – C4 - Analysis of impurities in trans-2-butene

Significance of the Topic

Ensuring high purity of trans-2-butene is vital in petrochemical manufacturing and product quality control. Trace levels of C1–C4 hydrocarbons can affect polymerization catalysts, downstream processes, and final product specifications. A rapid, reliable analytical method enables routine monitoring, minimizes downtime, and supports regulatory compliance.

Objectives and Overview

The primary goal of this study is to develop a gas chromatography (GC) method capable of separating and quantifying 16 C3–C4 hydrocarbon impurities in trans-2-butene within a 15-minute runtime. The approach leverages a specialized Agilent CP-Al2O3/Na2SO4 capillary column to achieve baseline resolution of light hydrocarbons, facilitating accurate impurity profiling.

Methodology and Instrumentation

The analytical method employs capillary GC with the following parameters:

• Column: Agilent CP-Al2O3/Na2SO4, 0.32 mm × 50 m fused silica, df = 5 μm (Part no. CP7565)
• Oven Temperature: 110 °C isothermal
• Carrier Gas: Nitrogen at 110 kPa (1.1 bar, 16 psi)
• Injection: Split mode at 20 mL/min, injector temperature 150 °C, sample volume 100 μL
• Detection: Flame ionization detector (FID) at 200 °C, hydrogen flow of 4 × 10⁻¹² Afs
• Concentration Range: 5–1000 ppm for each impurity

Main Results and Discussion

The optimized method achieves separation of 16 hydrocarbons, including methane, ethane, ethylene, propane, propylene, isobutane, n-butane, cyclobutane, isobutene, cis- and trans-2-butene, 1-butene, and 1,3-butadiene in under 15 minutes. Peak identification is unambiguous, and retention times exhibit high reproducibility. The method demonstrates linear response across the specified concentration range, low detection limits, and minimal interference from the trans-2-butene matrix.

Benefits and Practical Applications

The rapid analysis supports high-throughput quality control in petrochemical plants and research laboratories. Key advantages include:

• Short analysis time for efficient sample turnaround
• Broad dynamic range accommodating trace to mid-level impurities
• Compatibility with standard GC instrumentation and readily available columns
• Robust performance under isothermal conditions, reducing complexity

Future Trends and Potential Applications

Advances in column technologies and detection systems may further reduce analysis time and enhance sensitivity. Coupling GC methods with mass spectrometry could enable simultaneous identification of unknown contaminants. Automation and inline sampling will support real-time monitoring in process analytical technology (PAT) frameworks, optimizing plant operations and product consistency.

Conclusion

The presented GC method utilizing an Agilent CP-Al2O3/Na2SO4 column delivers fast, reliable separation and quantification of C1–C4 impurities in trans-2-butene. Its robustness, simplicity, and throughput make it an ideal choice for routine quality control in industrial and research settings.

Instrumentation Used

• Agilent GC system equipped with CP-Al2O3/Na2SO4 capillary column (0.32 mm × 50 m, df = 5 μm)
• Split injector and flame ionization detector (FID)
• Nitrogen carrier gas setup