Monitoring a diethylbenzene isomer separation process

The challenges in this work concerned the fundamental limits of NIR spectroscopy. Eirst, would NIR, with its typically broad and highly overlapped bands, have enough spectral resolution to distinguish the ortho, meta, and para isomers from each other and from the extractant Second, would NIR, with its typically weak overtone and combination bands, have enough sensitivity to quantify the minor components of the stream, especially the ortho isomer, typically present at only 1%  

The NIR monitoring was done off-line using a Eoss NIRSystems Model 6500 analyzer in transmission mode and a quartz cuvette with 0.5-mm path length. The spectra had 10-nm wavelength resolution with data 

The NIR spectra of the pnre isomers and the extractant are shown in Fignre 15.2. Although the spectra of the three isomers and the extractant are qnite similar overall, there are distinct, reproducible spectral differences, especially in the 2100-2500 nm region. The anthors did extensive stndies involving mid-IR spectra, spectral simulations, and PCA in order to understand the origins of these differences to ensure that they were related to the isomers themselves and not to coincidental impurities. 

The results indicate that NIR does indeed have both the resolution (specificity) and the sensitivity needed for this application. The NIR method was successfully implemented in the plant, replacing the conventional GC method and allowing real-time control and optimization of the PDEB separation process. 

The composition of the 152 samples in the calibration sample set is shown in the first three columns of Table 11.2 the second and third columns of the table indicate the maximum and minimum concentrations (in volume %) found in the calibration sample set for the components listed in the first column. 

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