Research octane number (RON) determination in isomerate

Determination of Research Octane Number (RON) in Isomerate Using Near-Infrared Spectroscopy

Significance of the Topic

The research octane number (RON) is a critical quality parameter for gasoline blending components. In light naphtha isomerization processes, achieving a high and consistent RON value ensures compliance with fuel specifications and optimal engine performance. Conventional RON determination relies on CFR engine tests, which are time-consuming and costly. Near-infrared spectroscopy (NIRS) offers a rapid, low-cost alternative, enabling refineries to optimize production parameters in real time and improve overall efficiency.

Objectives and Study Overview

This application note investigates the feasibility of using NIRS to predict RON in isomerate samples. Key objectives include:

• Measuring a diverse set of 63 isomerate samples with known RON values.
• Developing and validating a chemometric model correlating Vis-NIR spectra to reference RON values (ASTM D2699).
• Comparing analysis time and precision against the standard CFR engine test.

Applied Methodology and Instrumentation

Samples were analyzed in transmission mode across the full spectral range (400–2500 nm) using the Metrohm DS2500 Liquid Analyzer. Key instrumentation and software:

• DS2500 Liquid Analyzer with built-in temperature control (35 °C).
• 8 mm disposable vials to eliminate cleaning steps.
• Vision Air Complete software for data acquisition and model development.

Main Results and Discussion

Vis-NIR spectra of the 63 samples were processed using a chemometric regression algorithm and evaluated by cross-validation. Figures of merit:

• Coefficient of determination (R2): 0.986
• Standard error of calibration (SEC): 0.73 RON units
• Standard error of cross-validation (SECV): 0.76 RON units

The high R2 value demonstrates strong agreement between NIRS predictions and the ASTM D2699 reference method. Model precision supports reliable routine use.

Benefits and Practical Applications

NIRS analysis of RON in isomerate delivers:

• Rapid results in under one minute without chemical reagents or sample preparation.
• Significant time savings compared to the 30 minutes per sample required by the CFR engine test.
• Lower operational costs and reduced maintenance effort.
• Potential for inline or at-line quality control in refinery environments.

Future Trends and Opportunities

Advancements that could enhance NIRS-based RON determination:

• Integration with process control systems for automatic feedback and optimization.
• Development of robust multivariate models accommodating feedstock variability.
• Application of advanced machine learning techniques for improved prediction accuracy.
• Expansion to other fuel quality parameters such as MON, density, or sulfur content.

Conclusion

The study confirms that near-infrared spectroscopy with the Metrohm DS2500 Liquid Analyzer provides a fast, accurate, and cost-effective alternative to traditional CFR engine tests for RON determination in isomerate. Implementation of this technique can streamline quality control workflows and support real-time refinery optimization.

Reference

1. ASTM D2699 Standard Test Method for Research Octane Number of Spark-Ignition Engine Fuel.
2. Metrohm Application Note AN-NIR-113: Research Octane Number (RON) Determination in Isomerate by NIRS.