Ein neues µ-Kalorimeter zur isothermen Bestimmung von thermodynamischen und kinetischen Kenngrößen stark exothermer Reaktionen

The Fraunhofer ICT has developed a small volume/-calorimeter that permits kinetic and thermodynamic characteristic values and strongly exothermic reactions to be determined isothermally. The reaction heat developed in a micro-reactor induces a thermoelectric force in Seebeck elements above and below the reactor that can be translated to the corresponding heat performance of the reaction. The Peltier element serves to adjust a constant temperature difference between the micro-reactor and the heat withdrawal block that is under the stack of reactor, Seebeck element, and Peltier element. The system is calibrated using an integrated hot supporting foil. These minimal losses are considered in the calorimetric balancing through a temperature and output dependent loss factor. The example reaction was the nitration of toluene the kinetic and thermodynamic characteristic values of which are well documented. The heat of reaction in the micro-reactor agreed well with published val ues. The continuous -calorimeter is suitable to characterize exothermic reactions in micro-reactors. Because of the large surface/volume ratio and the thereby resulting small time constants of a few seconds (RC 1 of Mettler-Toledo RC1 reaction calorimeter: 60 sec) for the first time as well an isothermal measurement is possible of rapid exothermic reactions. Also, critical process conditions can be studied with respect to their energy potential and quantitatively analyzed. The test volume is especially small (70 L) so that especially with cost intensive chemicals the use of substance can be reduced to a minimum.