Reaction calorimetry monitoring polymerization reactions

Monitoring Polymerization Reactions by Means of Reaction Calorimetry... 

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... 

Areas of application of reaction calorimetry include determination of calorimetric data for reactions and process design, for the kinetic characterization of chemical reactions and of physical changes, for on-line monitoring of heat release and other analytical parameters needed in subsequent process development as well as for the development and optimization of chemical processes with the objective, for instance, to increase yield or profitability, control the morphology or degree of polymerization and/or index of polydispersity, etc. 

Anionic polymerization of L6 in aliphatic solvents was monitored on-line using both isothermal and non-isothermal reaction calorimetry in combination with Vis-spectrometry. 

The pressure can also be used to monitor the polymerization, because when the pressure reaches a plateau this means that the conversion is higher than 90%, as also reported by Lepilleur and Beckman [12] and Wang et al. [26]. It should be noted that the thermal signal obtained by calorimetry is much more sensitive than the pressure and gives more information. This result reveals aU the potential of reaction calorimetry for supercritical fluid investigations and polymerization monitoring. 

Combination of Equations 6.51 and 6.54 allows the estimation of the polymerization rate from temperature measurements. This technique, which is called reaction calorimetry, is a powerful non-invasive on-line monitoring technique, and it has been extensively applied to polymerization reactors. This subject is discussed in detail in Chapter 8. 

Other non-invasive (e.g., calorimetry and ultrasounds) and invasive (e.g., densimetry) techniques can also be used for monitoring of monomer concentration in homopolymerization reactions. However, in multimonomer formulations the individual monomer concentrations cannot be obtained with these techniques, meaning that a state estimator is required [66, 67, 69]. The use of reaction calorimetry is appealing because the hardware is very cheap and, when coupled with a state estimator, provides good estimation of the monomer concentration. The performance of calorimetry was compared with that of the Raman spectroscopy in emulsion polymerization to monitor overall and individual monomer conversions [68]. Calorimetry was as good as FT-Raman spectroscopy when monomer concentrations in the reactor were relatively high, but the performance of calorimetry was poorer when monomer concentrations were low. 

The experimental procedure involves initiation of the polymerization by irradiation followed by cutting off the light after a certain time at a degree of conversion chosen, and monitoring the reaction in the dark. As experimental methods, both isothermal differential scanning calorimetry (photocalorimetry, photo-DSC) [2,6, 7, 18-32] and real-time infrared... 

Reaction Calorimetry. The easiest way to follow a polymerization is to monitor the temperature of the reaction mixture or to use reaction calorimetry (cf above). Landau gives an excellent review on reaction calorimetry, its principles and application in chemical research in Reference 425. Table 23 summarizes papers dealing with reaction calorimetry of heterophase polymerizations. Reaction calorimetry gives on-line information with regard to the overall heat released during the reaction. This heat release is directly connected with the monomer conversion (eq. 49). 

Postdoctorate Fellow at the TotalFinaElf and a year and a half as an associate researcher at the National Research Council of France at the Blaise Pascal University of Clermont-Ferrand, France, with J.P. Grolier. His research interests focus on anionic polymerization of lactams in organic media, electroactivated stimuli responsive polymer gels, combined techniques for on-line monitoring of chemical processes, with an emphasis on the use of reaction calorimetry. Dan has authored more than 30 research papers, two invited book chapters, and holds one patent. 

Reaction calorimetry is probably the cheapest, easiest, and most robust monitoring technique for polymerization reactors, due to the large enthalpy of polymerization of most monomers. The technique is noninvasive (basically, only temperature sensors are required), and it is industrially applicable [151, 152]. It yields continuous information on the heat released by polymerization and hence it is also very useful for safety issues. The main drawback is that only overall polymerization rates can be obtained. Consequently, the determination of the individual rates requires estimation techniques [114, 153-155]. 

Reaction calorimetry is an appropriate technique to monitor polymerization reactions because of the exothermic nature of the conversion of monomer(s) to (co)polymer (enthalpies... 

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... 

BenAmor S, Colombie D, McKenna T. Online reaction calorimetry. Applications to the monitoring of emulsion polymerization without samples or models of the heat-transfer coefficient. Ind Eng Chem Res 2002 41 4233-4241. 

Several reports have been published on the in-line monitoring of vinyl acetate emulsion polymerization reactions in semibatch mode [22]. With appropriate models, this approach can provide good feedback about the polymerization reaction kinetics. Heat flow calorimetry (Hfc) is frequently used to... 

There are several methods available to monitor emnision polymerization reactions, such as gravimetric and GC analysis, nonetheless, they are time consuming. Others snch as densitometry, ultrasound velocity, and calorimetry can be applied for online analysis, but they are ledpe specific and are unable to discriminate between monomers in a copolymerization. More recently, advanced analytical techniqnes such as Fourier transform infrared spectroscopy (FT IR) and Raman spectroscopy have been developed for online and in-line monitoring of emulsion polymerization processes. The major drawback of the near-infrared (NIR) spectroscopic... 

Esposito M, Sayer C, Hermes de Araujo PH. In-line monitoring of emulsion polymerization reactions combining heat flow and heat balance calorimetry. Macromol React Eng 2010 4 682-690. 

Theoretical treatment of this polymerization is difficult because of the presence of both primary and secondary amine reactions as well as tertiary amine catalyzed epoxy homopolymerization. To obtain kinetic and viscosity correlations, empirical methods were utilized. Various techniques that fully or partially characterize such a system by experimental means are described in the literature ( - ). These methods Include measuring cure by differential scanning calorimetry, infra-red spectrometry, vlsco-metry, and by monitoring electrical properties. The presence of multiple reaction mechanisms with different activation energies and reaction orders (10) makes accurate characterizations difficult, but such complexities should be quantified. A dual Arrhenius expression was adopted here for that purpose. 

Differential Photocalorimetry (DPC) (19.201. The polymerization being an exothermal process, the reaction can be monitored in real time by differential scanning calorimetry (DSC). From the recorded thermogram which shows the variation of the heat flow with the irradiation time, the rate of polymerization can be directly calculated, provided the standard heat of polymerization (AHq) is known. For acrylic monomers, AHg values are usually in the range of 78 to 86 kJ mol depending on the monomer considered. 

Polymerization rate can be measured by several techniques, although calorimetry (the heat of reaction, Qr, is monitored by solving the energy balances of the reactor and the cooling jacket) is often the most convenient one for industrial reactors. 

Before an examination of the propagation and termination reactions individually, a brief overview of the methods that have been used to obtain profiles of the polymerization rate as a function of time is provided. The photopol5unerization rate can be monitored by any technique that measures a physical quantity which changes as the reaction progresses. In theory, a wide variety of analytical techniques could be used for this purpose (139-148), and new methods are continuously being developed (149). The commonly used methods for obtaining complete polymerization rate profiles are differential scanning calorimetry, fluorescence spectroscopy, and vibrational spectroscopies such as Raman and infrared. 

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