Reaction calorimetry is an efficient tool used to obtain kinetic, thermodynamic, and safety data. A new tool, composed of a high-pressure reactor (HP350) coupled with a Mettler-Toledo RC1e reaction calorimeter, is developed for the investigation of chemical reactions, under supercritical conditions. The reactor (V = 1.2 L) can be pressurized up to 350 bar and heated to 300 °C. Results presented in this contribution are divided into three sections. The first part concerns some highlights of the technical challenge related to supercritical reaction calorimetry in comparison with the classical liquid calorimetry. The second part presents a Wilson plot analysis with pure supercritical CO2 and shows that, in contrast to classical liquids, the lower the temperature (above the critical point) the better the heat transfer coefficient. This tendency can be explained by the evolution of scCO2 thermodynamical and transport properties around the critical point. The third part contains preliminary results from the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide using poly(dimethylsiloxane) macromonomer as stabilizer. Poly (methyl methacrylate) can be produced with high yield, high molecular weight, and nar-row particle size distribution, using 10 wt % (with respect to monomer) stabilizer under efficient stirring. A polymerization enthalpy of −58.8 ± 3 kJ/mol has been calculated with high reproducibility, being in good agreement with previously reported data. This confirms that the employed heat balance model is correct and shows the important potential of reaction calorimetry for the promotion of supercritical fluid technologies at industrial scale, since it allows the determination of kinetics, thermodynamic, and safety data.

Calorimetry (adiabatic, isothermal, differential, oscillating or acoustic) is generally based on heat-flow measurements of the studied system. Most of its applications are dedicated to kinetic-parameter determination, safety studies and process optimization, phase equilibrium and phase transition studies. Heat flow calorimetry on the lab scale is currently limited to low viscosity fluids. An emerging new field is concerned with the use of calorimetry in the presence of supercritical fluids as solvent reaction, which will be named supercritical calorimetry. Supercritical carbon dioxide (CO 2 sc) represents an increasingly interesting media for a wide variety of reactions. To fulfill this need, a special supercritical calorimeter has been developed in collaboration with Mettler-Toledo, Schwerzenbach, CH and some preliminary results are presented. This paper explores supercritical calorimetry applied to the intrinsic properties of carbon dioxide in the liquid, gas and especially supercritical phase as well as applications and theory related to reaction calorimetry. The CO 2 sc heat capacity (c p ) is measured over the range of 33-112 °C and 77-206 bar using a reaction calorimeter (RC1e, Mettler-Toledo) coupled with a high-pressure HP350 metallic reactor. Measured values are compared to theoretical values obtained from Wagner and Span's equation of state. 3D representations of the predicted values for heat capacity, density and sound speed of carbon dioxide in the fluid phase are presented.

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Summary: Reaction calorimetry is an efficient tool used to obtain kinetic, thermodynamic and safety data. A reaction calorimeter, RC1e‐HP350, developed in collaboration with Mettler‐Toledo GmbH, allows investigating chemical reactions under supercritical conditions. The main technical difference, compared with a classical liquid system, is that the whole reactor volume is occupied by the media. Heat transfer analysis in supercritical carbon dioxide (scCO2) by the Wilson plot method shows that the behavior of the internal heat transfer coefficient in scCO2 is the opposite of the one observed for classical liquid. In scCO2 the lower the temperature (above the critical point) the better the internal heat transfer coefficient. The evolution of scCO2 thermodynamical and transport properties near the critical point are responsible for this behavior. The dispersion polymerization of methyl methacrylate in scCO2, with the polydimethylsiloxane monomethacrylate as stabilizer, is used as a model reaction. A polymerization reaction enthalpy of −56.9 ± 2.2 kJ · mol−1 is determined, being in good agreement with previously reported data. The results presented illustrate the accuracy of the heat balance model used and emphasize the potential of reaction calorimetry for the promotion of supercritical fluids technologies.Technical comparison between liquid and supercritical reaction calorimetry.magnified imageTechnical comparison between liquid and supercritical reaction calorimetry.

Efficient stirring is needed to realize heat flow analysis with a thermally homogeneous medium. Because dispersion polymerization with supercritical fluids can be destabilized under stirring, a preliminary target has been to find a compromise between synthesis and basic reaction calorimetry requirements. This paper describes the use of poly (dimethylsiloxane) macromonomer with a molecular weight 5000 g/mol as stabilizer for the dispersion polymerization of methyl methacrylate in supercritical carbon dioxide. The effect of stirring speed and stabilizer concentration has been examined. This study has shown that poly (methyl methacrylate) can be produced at high yield and molecular weight using 10 wt% (respect to monomer) poly (dimethylsiloxane) macromonomer at stirring speeds up to 600 rpm. A polymerization enthalpy of −57.6±2 kJ/mol has been calculated being in good agreement with previously reported data. Thus, preliminary results for the heat balance using the newly developed high pressure reaction calorimeter for supercritical fluid applications have shown the important potential of reaction calorimetry to promote supercritical fluid technologies at industrial scale allowing for the determination of kinetics and thermodynamic and safety data, respectively.