Kinetic modeling and in-line monitoring using fiber optic raman spectroscopy of emulsion copolymerization reactions

In this research, kinetic modeling and in-line monitoring using fiber optic Raman spectroscopy of emulsion copolymerization reactions was studied. A model was developed for describing the kinetics of emulsion copolymerization of 2-ethylhexyl acrylate and acrylic acid. Experimental data of total conversion was obtained separately by gravimetric analysis and the analysis of Raman spectra taken continuously during the course of a reaction. Both the data sets were best fitted and the values of unknown parameters in the kinetic model were independently determined using these two techniques.

Use of in-line Raman spectroscopy was found to give slightly better results in estimation of best-fit parameters as compared to the off-line gravimetric analysis. The predictions of the kinetic model for a different set of reactions matched very well with the experimental results of both gravimetry and Raman spectroscopy. The kinetic model also predicted the individual conversions of 2-ethylhexyl acrylate and acrylic acid, which could not be determined from gravimetric and Raman spectra analysis.

A new method of normalization of the intensity of (C=C) peak in Raman spectra of the emulsion was used in calculating the monomer conversions, which resulted in less scatter m the calculated conversion profiles and also improved the accuracy of the final conversion values. In-line Raman spectroscopy was found sensitive in observing changes in the reaction rates due to the changes in the initiator and surfactant concentrations. Use of this fact can be made in designing control systems for emulsion copolymerization reactors.