Research octane number (RON) determination in isomerate

Significance of the topic

Light naphtha isomerization is a cornerstone process in modern refineries to boost gasoline octane values. Rapid, cost-effective determination of research octane number (RON) is essential for real-time process optimization and quality control, ensuring that final isomerate products meet stringent fuel specifications.

Objectives and overview of the study

This application note evaluates near-infrared spectroscopy (NIRS) as an alternative to the conventional CFR engine test (ASTM D2699) for RON determination. The goal was to develop and validate a calibration model that delivers accurate RON predictions in under one minute, without sample preparation or chemical reagents.

Methodology and instrumentation

A total of 63 isomerate samples spanning the full RON range were analyzed using a Metrohm DS2500 Liquid Analyzer in transmission mode across 400–2500 nm. Measurements were conducted at a controlled temperature of 35 °C. Disposable 8 mm glass vials eliminated the need for cleaning between runs. Data acquisition and chemometric model development were performed with Vision Air Complete software using cross-validation and partial least squares regression.

Main results and discussion

The NIR spectra captured key absorption features related to paraffin branching. A PLS regression model yielded a calibration R² of 0.986, with standard errors of calibration and cross-validation of 0.73 and 0.76 RON units, respectively. Correlation plots between NIR predictions and ASTM reference values demonstrated high agreement, confirming the robustness of the method for routine RON determination.

Benefits and practical applications of the method

• Rapid analysis: one-minute measurement versus 30 minutes per sample by CFR engine test.
• No reagents or extensive sample preparation required.
• Low operational cost and minimal maintenance.
• Applicability directly at-line or in production environments for real-time process monitoring.

Future trends and potential applications

• Integration of flow-through NIR cells and automation for high-throughput screening.
• Extension of calibration models to related streams such as reformate and alkylate.
• Deployment of advanced machine learning algorithms to further enhance prediction accuracy and detect process anomalies.

Conclusion

NIRS using the DS2500 Liquid Analyzer provides a fast, reliable, and cost-effective alternative to traditional engine tests for RON determination in isomerate. The method’s high precision and ease of use enable real-time process control, improving refinery efficiency and product quality.

Reference

No external literature was cited in the original application note.