Quality control of pyrolysis gasoline

Importance of the Topic

Pyrolysis gasoline (Pygas) is a byproduct of ethylene production containing unwanted conjugated diolefins that render it unsuitable as motor fuel. Rapid and accurate determination of its diene content is essential for quality control and process optimization in selective hydrogenation units.

Objectives and Study Overview

This work aims to establish a near-infrared spectroscopy (NIRS) method for quantifying the diene (maleic anhydride) value in Pygas in under one minute, benchmarking its performance against the conventional UOP326-17 Diels-Alder wet chemical assay.

Methodology and Instrumentation

Ninety-nine Pygas samples were measured using a NIRS XDS RapidLiquid Analyzer in transmission mode over 400–2500 nm at a controlled temperature of 40 °C. Eight-millimeter disposable glass vials were used to eliminate cleaning steps. Spectral data acquisition and chemometric model development were performed with Vision Air Complete software.

Used Instrumentation

• XDS RapidLiquid Analyzer (Metrohm 2.921.1410)
• Disposable glass vials, 8 mm transmission (Metrohm 6.7402.000)
• Vision Air 2.0 Complete spectroscopy software (Metrohm 6.6072.208)

Main Results and Discussion

The calibration model correlating NIRS predictions with reference values (UOP326-17) produced:

• Coefficient of determination (R²): 0.9253
• Standard error of calibration (SEC): 0.42 mg/g
• Standard error of cross-validation (SECV): 0.46 mg/g

These results indicate strong predictive accuracy suitable for routine quality control.

Benefits and Practical Applications

• Analysis time reduced to under one minute per sample
• No hazardous reagents or lengthy sample preparation
• Minimal operator training required
• Cost-effective, high-throughput screening in production environments

Future Trends and Opportunities

Implementing NIRS inline within production streams could enable real-time process adjustments. Further expansion to other petrochemical byproducts and advanced chemometric techniques may enhance robustness and broaden applicability.

Conclusion

Near-infrared spectroscopy demonstrates a rapid, reliable, and reagent-free alternative to traditional wet chemical methods for determining diene value in pyrolysis gasoline, offering significant advantages in speed, safety, and operational efficiency.

Reference

• UOP326-17 Diels-Alder wet chemical method for maleic anhydride value determination