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Refiners use the catalytic reforming process to produce high-octane reformate. This reformate is used for premium gasoline blends or petrochemical feedstock. The determination of key quality parameters of reformate—namely research octane number (RON, ASTM D2699), aromatic content (ASTM D5769), benzene content, olefin content, and density—requires time-consuming and laborious conventional methods.

In contrast, all of these parameters (and more) can be measured by near-infrared (NIR) spectroscopy. The Metrohm DS2500 Liquid Analyzer, operating in the visible and near-infrared spectral region (Vis-NIR), provides results within one minute without any sample preparation.

507 different reformate samples were measured on the Metrohm DS2500 Liquid Analyzer (Figure 1). All measurements were performed in transmission mode from 400–2500 nm using 8 mm disposable vials. The temperature control of the analyzer was set to 35 °C for all measurements to ensure the best performance and highest quality data. Data acquisition and prediction model development was performed with the Metrohm software package Vision Air Complete.

Figure 1. Metrohm DS2500 Liquid Analyzer used for the determination of research octane number (RON), aromatics, benzene, olefins, and density in reformate.

Table 1. Hardware and software equipment overview.

Equipment Article number
DS2500 Liquid Analyzer 2.929.0010
DS2500 Holder 8 mm vials 6.7492.020
Vision Air 2.0 Complete 6.6072.208

The measured Vis-NIR spectra (Figure 2) were used to create a prediction model for quantification of all five parameters. The quality of the prediction models was evaluated using correlation diagrams which display a high correlation (R2 > 0.98) between the Vis-NIR prediction and the reference methods for all parameters. The respective figures of merit (FOM) display the expected precision and confirm the feasibility during routine analysis (Figures 3–7).

Figure 2. Selection of Vis-NIR spectra of reformate samples analyzed on a Metrohm DS2500 Liquid Analyzer with 8 mm vials.
Figure 3. Correlation diagram and the respective figures of merit for the prediction of RON value using a DS2500 Liquid Analyzer. The lab value was evaluated according to ASTM D2699.
Figures of Merit Value
R2 0.996
Standard Error of Calibration 0.34
Standard Error of Cross-Validation 0.36
Figure 4. Correlation diagram and the respective figures of merit for the prediction of aromatic content using a DS2500 Liquid Analyzer. The lab value was evaluated using gas chromatography (GC).
Figures of Merit Value
R2 0.999
Standard Error of Calibration 0.88 vol%
Standard Error of Cross-Validation 0.91 vol%
Figure 5. Correlation diagram and the respective figures of merit for the prediction of benzene content using a DS2500 Liquid Analyzer. The lab value was evaluated using gas chromatography (GC).
Figures of Merit Value
R2 0.984
Standard Error of Calibration 0.066 vol%
Standard Error of Cross-Validation 0.088 vol%
Figure 6. Correlation diagram and the respective figures of merit for the prediction of olefin content using a DS2500 Liquid Analyzer. The lab value was evaluated using gas chromatography (GC).
Figures of Merit Value
R2 0.982
Standard Error of Calibration 0.71 vol%
Standard Error of Cross-Validation 0.87 vol%
Figure 7. Correlation diagram and the respective figures of merit for the prediction of benzene content using a DS2500 Liquid Analyzer. The lab value was evaluated using a density meter.
Figures of Merit Value
R2 0.993
Standard Error of Calibration 0.0029 kg/L
Standard Error of Cross-Validation 0.0034 kg/L

This Application Note demonstrates the feasibility of the Metrohm DS2500 Liquid Analyzer for the determination of RON, aromatic content, benzene content, olefin content, and density in reformate samples. Compared to the conventional methods, Vis-NIR spectroscopy enables fast determination (Table 2) without any sample preparation. Significant gains are achieved through time savings as well as the reduction in chemical usage and waste.

Table 2. Time to result overview for the parameters of RON, aromatic content, benzene content, and olefin content by standard methods.

Parameter Method Time to result
RON CFR engine test ∼30 minutes per sample
Aromatic content Gas Chromatography ∼45 minutes per sample
Benzene content Gas Chromatography ∼45 minutes per sample
Olefin content Gas Chromatography ∼45 minutes per sample
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