On-line Monitoring in Emulsion Polymerization Reactors

In the production of dispersed polymers, the main objectives to be fulfilled are  

In order to implement the process conditions that lead to the required specifications of safety, production rate, and product quality, it is necessary to develop suitable control strategies. Reaction control strategies rely on both efficient monitoring techniques and state estimation and filtering techniques. In this section the main focus is on the instrumentation available for monitoring emulsion polymerization reactors. Detailed reviews for on-line monitoring techniques for polymerization reactors are available [124—126]. 

Other properties, such as molecular weight distribution of nonlinear polymers and particle morphology, are currently neither measurable nor observable. 

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Because of its importance, continuous on-line monitoring of emulsion polymerization reactors continues to be an area of considerable investment in terms of research and development. It is evident that to better understand the nucleation mechanisms, and to develop better control strategies,... 

Fig. 6.13. On-line monitoring of emulsion polymerization reactor by means of calorimetric measurements (a) free monomer in VAc/BA/AA semibatch emulsion polymerization (b) terpolymer composition in the VAc/MMA/BA semibatch emulsion polymerization.

Liotta, V. Sudol, E.D. El-Aasser, M.S. Georgakis, C. On-line monitoring, modeling, and model validation of semibatch emulsion polymerization in an automated reactor control facility. J. Polym. Sci. Pt. A Polym. Chem. 1998, 36 (10), 1553-1571. 

The available data from emulsion polymerization systems have been obtained almost exclusively through manual, off-line analysis of monomer conversion, emulsifier concentration, particle size, molecular weight, etc. For batch systems this results in a large expenditure of time in order to sample with sufficient frequency to accurately observe the system kinetics. In continuous systems a large number of samples are required to observe interesting system dynamics such as multiple steady states or limit cycles. In addition, feedback control of any process variable other than temperature or pressure is impossible without specialized on-line sensors. This note describes the initial stages of development of two such sensors, (one for the monitoring of reactor conversion and the other for the continuous measurement of surface tension), and their implementation as part of a computer data acquisition system for the emulsion polymerization of methyl methacrylate. 

Real time continuous monitoring of the emulsion polymerization reactions was achieved using transmission and reflectance techniques. Transmission spectra were obtained on-line using the automatic sampling and dilution system. The reflectance probes were immersed in the reactor and the spectra recorded as function of time. Figure 3 shows a schematic of the probes in the reactor. In all cases special care was taken to ensure that the tip of the probe was well immersed in the reacting mixture. The lattices prepared were also used to study the effect of particle concentration on the reflectance measurements. 

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