Pyrolysis gasoline (Pygas) is a byproduct of ethylene production, which contains unwanted conjugated diolefins making it unsuitable as a motor fuel. To overcome this limitation, the olefin content needs to be reduced below 2 mg/g pygas in a selective hydrogenation unit (SHU). The diene value, or maleic anhydride value (MAV), is usually determined by the Diels-Alder wet chemical method (UOP326-17).
This wet chemical method requires several hours to perform by highly trained analysts. In contrast to the primary method, near-infrared spectroscopy (NIRS) is a cost-efficient and fast analytic solution for the determination of diene value in pyrolysis gasoline.
99 pygas samples were analyzed on a NIRS XDS RapidLiquid Analyzer equipped with 8 mm disposable glass vials. All measurements were performed in transmission mode from 400 nm to 2500 nm. The temperature control was set to 40 °C, to provide a stable sample environment. For convenience reasons disposable vials with a path length of 8 mm were used, which made a cleaning procedure obsolete. The Metrohm software package Vision Air Complete was used for data acquisition and prediction model development.
|XDS RapidLiquid Analyzer||2.921.1410|
|Disposable vials, 8 mm diameter, transmission||6.7402.000|
|Vision Air 2.0 Complete||6.6072.208|
The obtained Vis-NIR spectra (Figure 2) were used to create a prediction model for the diene value determination. To verify the quality of the prediction model, correlation diagrams were created which display the correlation between Vis-NIR prediction and primary method values (Figure 3). The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.
|Figures of merit||Value|
|Standard error of calibration||0.42 mg/g|
|Standard error of cross-validation||0.46 mg/g|
This application note shows the feasibility of NIR spectroscopy for the analysis of diene value in pyrolysis gasoline. In comparison to the wet chemical method UOP326-17 (Table 3), the time to result is a major advantage of NIR spectroscopy, since a single measurement is performed within one minute.
|Parameter||Method||Time to result and workflow|
|Diene value||Diels Alder (UOP326-17)||∼6 hr; reflux, hydrolysis, titration|