Validation by Heat Generation Simulation

This result, together with the accuracy of thermodynamical parameters previously measured, confirms that the supercritical calorimeter is operating correctly and validates the equipment for calorimetric evaluation of reactions in supercritical media. 

Several analytical techniques that could be used to monitor reactions in supercritical fluids have been presented in the preceding sections. In this section, the dispersion polymerization of MMA in SCCO2 will be discussed in the light of on-line monitoring. 

It can be seen in Fig. 5.14 that the heat flow measured with respect to the total weight of monomer does not depend on stirring speed. Moreover, the good reproducibility of the reaction calorimeter is confirmed. By integration of the thermal curves, the enthalpy of polymerization can be calculated as -56.9 2.2 kj mol and is in good agreement with the literature s value of -57.8 kj mol obtained in conventional solvent [32]. The error of 2.2 kJ mol is a standard deviation calculated from a series of seven measurements [33]. 

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. 

In order to validate the system, external sampling under pressure during the reaction was performed. The reactant contents were analyzed by dynamic head space gas chromatography and the polymer molecular weight distribution by size exclusion chromatography with triple detection. 

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