Emulsion polymerizations monitoring

Bauer et al. describe the use of a noncontact probe coupled by fiber optics to an FT-Raman system to measure the percentage of dry extractibles and styrene monomer in a styrene/butadiene latex emulsion polymerization reaction using PLS models [201]. Elizalde et al. have examined the use of Raman spectroscopy to monitor the emulsion polymerization of n-butyl acrylate with methyl methacrylate under starved, or low monomer [202], and with high soUds-content [203] conditions. In both cases, models could be built to predict multiple properties, including solids content, residual monomer, and cumulative copolymer composition. Another study compared reaction calorimetry and Raman spectroscopy for monitoring n-butyl acrylate/methyl methacrylate and for vinyl acetate/butyl acrylate, under conditions of normal and instantaneous conversion [204], Both techniques performed well for normal conversion conditions and for overall conversion estimate, but Raman spectroscopy was better at estimating free monomer concentration and instantaneous conversion rate. However, the authors also point out that in certain situations, alternative techniques such as calorimetry can be cheaper, faster, and often easier to maintain accurate models for than Raman spectroscopy, hi a subsequent article, Elizalde et al. found that updating calibration models after... 

C. Bauer, B. Amram, M. Agnely, D. Charmot, J. Sawatzki, M. Dupuy and J.-P. Huvenne, On-hne monitoring of a latex emulsion polymerization by fiber-optic FT-Raman spectroscopy. Part I Cahbration, Appl. Spectrosc., 54, 528-535 (2000). 

O. Elizalde, J.R. Leiza and J.M. Asua, On-hne monitoring of all-acrylic emulsion polymerization reactors by Raman spectroscopy, Macromol. Symp., 206, 135-148 (2004). 

O. Elizalde, M. Azpeitia, M.M. Reis, J.M. Asua and J.R. Leiza, Monitoring emulsion polymerization reactors calorimetry versus Raman spectroscopy, Ind. Eng. Chem. Res., 44, 7200-7207 (2005). 

Monitoring monomer conversion during emulsion polymerization... 

Chabot et al. at Atofina Chemicals (King of Prussia, PA, USA) used in-line NIR to monitor monomer conversion in real time in a batch emulsion polymerization process. The business value of this monitoring... 

Figure 15.1 Effect of temperature on the rate of emulsion polymerization as monitored by in-line NIR. Reprinted with permission from Chabot et al. (2000). ...

Wenz and colleagues at Bayer Polymers Inc. describe the use of Raman spectroscopy to monitor the progress of a graft emulsion polymerization process, specifically the manufacture of ABS graft copolymer, in order to select the appropriate reaction termination point.40 Early termination reduces product yield and results in an extra product purification step termination too late reduces product quality. As Figure 5.5 illustrates, the reaction composition over time is not smooth and predictable, making it unlikely that off-line analysis would ever be fast enough to ensure correct control decisions. 

McCaffery etal. discuss the use of a low-resolution Raman spectrometer to directly monitor a batch mini-emulsion polymerization.41 While this kind of equipment is unlikely to be installed in an industrial facility, the article raises several important points. In order to compensate for laser-power fluctuations, a functional group present in both the reactants and the product, the phenyl ring in styrene, was used as an internal standard. Since internal standards cannot be added to industrial reactions, this approach can be quite helpful. However, scientists must be certain that the internal standard will remain unchanged by the reaction and that changes in its signal only reflect laser-power fluctuations. 

Bauer, C. Amram, B. Agnely, M. etal On-Line Monitoring of a Latex Emulsion Polymerization by Fiber-Optic FT-Raman Spectroscopy. Part I Calibration Appl. Spectrosc. 2000, 54, 528-535. 

Chabot, Paul, Hedhli, Lotfi Olmstead, Christyn On-line NIR Monitoring of Emulsion Polymerization AT-Process 2000, 5(1, 2), 1-6. 

The use of a precision digital density meter as supplied by Mettler Instruments (Anton Paar, Ag.) appeared attractive. Few references on using density measurements to follow polymerization or other reactions appear in the literature. Poehlein and Dougherty (2) mentioned, without elaboration, the occasional use of y-ray density meters to measure conversion for control purposes in continuous emulsion polymerization. Braun and Disselhoff (3) utilized an instrument by Anton Paar, Ag. but only in a very limited fashion. More recently Rentsch and Schultz(4) also utilized an instrument by Anton Paar, Ag. for the continuous density measurement of the cationic polymerization of 1,3,6,9-tetraoxacycloundecane. Ray(5) has used a newer model Paar digital density meter to monitor emulsion polymerization in a continuous stirred tank reactor train. Trathnigg(6, 7) quite recently considered the solution polymerization of styrene in tetrahydrofuran and discusses the effect of mixing on the reliability of the conversion data calculated. Two other references by Russian authors(8,9) are known citing kinetic measurements by the density method but their procedures do not fulfill the above stated requirements. 

On-Line Monitoring of Emulsion Polymerization Reactor Dynamics... 

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. 

For the purposes of conversion monitoring of emulsion polymerization, we have found the DMA40D with a precision of +1 x 10 g/cm capable of resolving monomer conversion to +0.2% in the absence of thermostating and sampling errors. On-line, in the presence of such possible errors, a resolution of at least +0.5% can be expected. Care must be taken to ensure a representative sample and good temperature control of the sample stream before introducing it into the instrument. Some example results with this instrument are presented below. 

It would appear that these sensors are quite valuable in exploring the dynamics of emulsion polymerization systems both at the laboratory and pilot plant scales. In addition, it appears that these instruments, in more rugged design would have applications for monitoring, alarm, and control functions in industrial-scale installations. Further refinements and applications are under study at present. 

This work has shown that by monitoring conversion curves by a computer, emulsifier metering can be varied to produce a desired particle size distribution of smalls in a seeded PVC emulsion polymerization. 

Computerized HDC for Monitoring the Latex Emulsion Polymerization Particle Growth Patterns. 

It has been advantageous to use the FT-Raman method to study various dynamic processes of interest in the paint industry. One such study was the study of an emulsion polymerization reaction whereby a FT-Raman system actually monitored the process (1). 

This study illustrates a particular use of FT-Raman spectroscopy (Section 2.4.2) to monitor an emulsion polymerization of an acrylic/methacrylic copolymer. There are four reaction components to an emulsion polymerization water-immiscible monomer, water, initiator, and emulsifier. During the reaction process, the monomers become solubilized by the emulsifier. Polymerization reactions were carried using three monomers BA (butyl acrylate), MMA (methyl methacrylate), and AMA (allyl methacrylate). Figure 7-1 shows the FT-Raman spectra of the pure monomers, with the strong vC=C bands highlighted at 1,650 and 1,630 cm-1. The reaction was made at 74°C. As the polymerization proceeded, the disappearance of the C=C vibration could be followed, as illustrated in Fig. 7-2, which shows a plot of the concentration of the vC=C bonds in the emulsion with reaction time. After two hours of the monomer feed, 5% of the unreacted double bonds remained. As the... 

The above argument suggests that the initial droplet size distribution may play an important role in super-swelling or colloidal instability. This indicates that one should monitor the emulsification procedure for controlled free radical emulsion polymerization closely. 

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