Polymerization reaction monitoring online

Alb AM, Reed WF. Fundamental measurements in online polymerization reaction monitoring and control with a focus on ACOMP. Macromol React Eng 2010 4 470-485. 

Depending on the type of polymerization performed and the number of target criteria for the control of the process, one or multiple in-line systems may be installed to achieve the expected qualified product. An excellent example of monitoring online polymerization reactions by multiple detection was reported [8]. Mostly individual methodologies are described as follows sometimes, the reader will notice a combination of techniques used to obtain the data sought. 

As noted earlier, fused silica optical fiber is used for remote NIR measurements. The same type of fiber optic probe can be used for Raman spectroscopy, and enables remote measurement of samples and online process measurements. In situ reaction monitoring by Raman spectroscopy has been used to study catalytic hydrogenation, emulsion polymerization, and reaction mechanisms. Remote sensing of molecules in the atmosphere can be performed by Raman scattering measurements using pulsed lasers. 

The foregoing overview of polymer characteristics leads up to a consideration of which of these are important candidates for online monitoring. There is a long history of attempts at online monitoring using GPC, in order to obtain MWD at discrete intervals during polymerization reactions. 

Because the reaction medium is normally quite concentrated, however, rheological and other measurements often only indirectly measure molecular mass and other single chain properties, because the interactions between polymer chains often dominate signals from undiluted reactor contents. Automatic continuous online monitoring of polymerization reactions (ACOMP) provides a solution for this. ACOMP is covered in Chapters 11-13. 

It is important to emphasize that the development of fiber optics technology is a fundamental cornerstone that allowed for the development of real in-line and in-situ monitoring spectroscopic techniques, as the sampling device can be placed at very harmful environments, while the spectrometer still sits in a process control room. Without the support of fiber optics technology, samples have to be prepared and placed inside the illuminated chambers (as performed in the lab since the nineteenth century) or pumped through sampling windows (as performed in advanced systems intended for process and product development, such as automatic continuous online monitoring of polymerization reactions (ACOMP) [37- 1] in order for spectral data to be obtained. 

Alb AM. Automatic Continuous Online Monitoring of Polymerization Reactors (ACOMP) Progress in Characterization of Polymers and Polymerization Reactions. PhD Thesis, Tulane University, New Orleans. 

Florenzano FH, Enohnyaket P Fleming V, Reed WF. Coupling of near infrared spectroscopy to automatic continuous online monitoring of polymerization reactions. Eur Polym J 2005 41 535-545. 

Santos JC, Reis MM, Machado RAF, Bolzan A, Sayer C, Giudici R, Aradjo PHH. Online monitoring of snspension polymerization reactions using Raman spectroscopy. Ind Eng Chem Res 2004 43 7282-7289. 

The overall heat transfer coefficient can be estimated online by using an additional process measurement (e.g., gravimetric conversion or solids content) together with state (parameter) estimation techniques to update the value of the overall heat transfer coefficient. This approach referred as adaptive calorimetry has been mainly exploited by Fevotte and coworkers [12] to monitor emulsion (co) polymerization reactions. They used a dependence of U with conversion... 

The electrical conductivity of a fluid is a quantitative measure of its ability to carry an electrical current, and therefore depends to a large extent on the concentration of ionic species. Given that the conductivity of pure water is extremely low (limited to 0.0548 xScm" at 25 °C by the HjO dissociation constant into H and OH" when no added ions are present), this technique will be sensitive to changes in ionic concentration. So, while it is not impossible to be used for the online monitoring of solution or melt phase processes, it is better suited for use in emulsion and miniemulsion polymerization reactions where ionic surfactants and initiators are commonly employed. 

During a homogenous (bulk or solution) polymerization reaction, both the concentration of polymer and molar mass change and hence viscosity should also change. Therefore, online monitoring of the viscosity could give... 

Rotational (torque measurements) or capillary process viscometers, as well as ultrasound and tube oscillations [58] can be used to measure viscosity online during a polymerization reaction. The first two techniques have been widely applied in the monitoring of both chain growth polymerizations and step-growth polymerizations. 

Torque measurements have been used for online monitoring of the viscosity of polymerization reactions. The advantage of the torque measurement as compared with that of the capillary is that no treatment (dilution and flow) of the reaction medium is needed. Several examples of monitoring chain-growth polymerization reactions [62, 63] and step-growth polymerization reactions (specially curing reactions) can be found in the hterature [64]. 

Dietrich T, Ereitag A, Schlecht U. New micro viscosity sensor—A novel analytical tool for online monitoring of polymerization reactions in a micro reaction plant. Chem Eng J 2010 160 823-826. 

CatalgU-Giz H, Giz A, Alb A, Reed W. Absolute online monitoring of a stepwise polymerization reaction polyurethane synthesis. J Appl Polym Sci 2001 82 2070-2077. 

While H NMR and NMR spectroscopy were proved to be useful tools for the online monitoring of polymerization reactions, their limitations, such as the intrinsic low sensitivity of the measurements and the time-consuming signal averaging, the use of expensive deuterated solvents ( H NMR) that limits their application in industrial processes, led to the development of the so-called hyperpolarization methods which overcome the lack of sensitivity of NMR... 

AUTOMATIC CONTINUOUS ONLINE MONITORING OF POLYMERIZATION REACTIONS (ACOMP)... 

Automatic continuous online monitoring of polymerization reactions surmounts this problem and allows to be measured in a single solvent because the instantaneous composition of copolymers can be determined during synthesis, which, together with the hght scattering data stream yields M at each instant. 

Automatic continuous online monitoring of polymerization reactions allows all the required variables to be measured at each point in time total comonomer conversion f apparent... 

Mignard E, Guerret O, Berlin D, Reed WF. Automatic Continuous Online Monitoring of Polymerization reactions (ACOMP) of high viscosity reactions. Polym Mat Sci Eng 2003 88 314-316. 

All cases presented earlier offer highlights on some of the multiple copolymer features determined during the online monitoring of (co)polymerization reactions via ACOMP for comonomers with similar or very different reactivity ratios. 

A new advance with regard to the instrumentation and methods available for online monitoring of heterogeneous polymerization reactions was made by using ACOMP for monitoring the evolution of multiple characteristics during polymerization. The information-rich data collected simultaneously by multiple detectors provide absolute, model-independent determination of quantities such as conversion, composition, and molar mass distribution and avoid potentially damaging effects of the reactor environment. 

FIGURE 12.7 Automatic Continuous Online Monitoring of Polymerization Reactions detectors response (LS90 ° and viscosity) to the different components of the diluted, phase inverted polyacrylamide emulsion (top) determination of dissolution time, from RI data for polyacrylamide in emulsion and in dry form. Reprinted (adapted) with permission from Alb AM, Farinato F, Calbick J, Reed WF. Online monitoring of polymerization reactions in inverse emulsions. Langmuir 2006 22 831-840. 2006 American Chemical Society. 

The method has been extensively used in the online monitoring of MMA and BA (co)polymerization reactions under a variety of concentration conditions, with and without surfactant [39]. A number of features were captured, such... 

In this context, the adaptation of ACOMP to online monitoring of NMP copolymerization offered the opportunity to study in more detail CRP reaction kinetics and mechanisms and to control the composition profile formation during the polymerization reaction. 

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