Quality control of pyrolysis gasoline

Importance of the Topic

Pyrolysis gasoline is a valuable by-product of ethylene production but contains conjugated diolefins that impair its use as a motor fuel. Accurate determination of the diene value is essential to ensure effective selective hydrogenation and to meet fuel quality specifications.

Objectives and Study Overview

The study aimed to develop and validate a rapid near‐infrared spectroscopy (NIRS) method for determining the diene (maleic anhydride) value in pyrolysis gasoline. Key goals included:

• Reducing analysis time compared to the conventional Diels–Alder wet chemistry method (UOP326-17).
• Establishing a robust calibration model correlating NIR spectra with reference values.
• Demonstrating adequate precision and accuracy for routine quality control.

Methodology and Instrumentation

Samples and measurements:

• 99 pyrolysis gasoline samples measured in transmission mode over 400–2500 nm.
• Temperature control at 40 °C to stabilize sample conditions.
• Disposable 8 mm glass vials to eliminate the need for cleaning between measurements.

Instrumentation:

• XDS RapidLiquid Analyzer (Metrohm 2.921.1410).
• Disposable borosilicate vials, 8 mm diameter (Metrohm 6.7402.000).
• Vision Air Complete software (Metrohm 6.6072.208) for data acquisition and model development.

Main Results and Discussion

A multivariate calibration model was built from the Vis-NIR spectra and validated against the UOP326-17 reference method. Figures of merit included:

• Coefficient of determination (R²) of 0.9253 indicating strong correlation.
• Standard error of calibration (SEC) of 0.42 mg/g diene value.
• Standard error of cross-validation (SECV) of 0.46 mg/g demonstrating reliable predictive performance.

Correlation plots confirmed close agreement between NIRS predictions and wet chemistry results, supporting the model’s suitability for routine use.

Benefits and Practical Applications

NIRS offers significant advantages for quality control of pyrolysis gasoline:

• Rapid single-measurement analysis (<1 minute) versus ~6 hours for Diels–Alder wet chemistry.
• Minimal sample preparation and no solvent use.
• Cost savings through reduced labor and consumables.
• Potential integration into process monitoring for real‐time feedback.

Future Trends and Potential Applications

Expanding the approach to other petrochemical by-products and refining process streams could further streamline quality control. Combining NIRS with online sampling and advanced chemometric algorithms may enable continuous monitoring of multiple analytes and in-line process optimization.

Conclusion

The NIR spectroscopy method developed for diene value determination in pyrolysis gasoline provides a fast, accurate, and cost-effective alternative to conventional wet chemical analysis. Its robustness and ease of use make it well suited for routine quality assurance in petrochemical operations.

Reference

• UOP326-17 Diels–Alder wet chemical method for determination of diene value.