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On-line determination of the conversion in a styrene bulk polymerization batch reactor using near-infrared spectroscopy



A fast on-line method for measuring the monomer conversion of a styrene batch polymerization reaction with near-infrared spectroscopy (NIR) has been developed. Multivariate calibration was performed, using polymer samples having temperatures around the set point of the batch reactor (75–85°C) and monomer conversions up to 35%. The calibration model was built in such a way that the effect of the temperature on the predicted conversion of the sample was minimized. The method was validated in a number of batch runs. In these runs, the batch temperature and molar mass distributions of the polymer were varied. At-line size-exclusion chromatography was used as a reference method for measuring the monomer conversion. Results show that on-line conversion monitoring with NIR offered overall an excellent accuracy (∼ 0.32% conversion). For high and low monomer conversions a small bias in the predicted conversion is present. The method proved to be insensitive to both relative large changes (10°C) of the batch temperature and to considerable changes of the molar mass distribution of the polymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 90–98, 2002; DOI 10.1002/app.10241

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