(398c) Recent Advances in Microreactor-Based Calorimetry for Monitoring Rapid and Strong Exothermic Processes

Powerful process analytical techniques which provide a high level of information while simultaneously keeping experimentation times short are essential for the process design of energetic materials syntheses. For example, calorimetry is a universal analytical method for investigating thermal effects resulting from chemical reactions and/or changes in physical states. Calorimetric measurements make it possible not only to make direct statements about thermodynamics but also about kinetics and physical constitutions. Knowing the heat flows that occur during a reaction therefore provides crucial information for the successful and safe design of processes producing energetic materials.

In this context, the combination of calorimetric measurement technologies with continuously operated microreactor processes offers an extremely promising methodical approach. The technical advantages offered by microreaction technology make it particularly suited for use in processes with an increased hazard potential – such as removing strong reaction heat, preventing unwanted side or decomposition reactions or handling explosive and other unstable products and intermediates in small hold-ups under short residence times.

Here we report on the development of various small-volume, continuously operated calorimeters on the basis of microreactor chips which permit rapid screening of thermokinetic key data of chemical processes. At the heart of the calorimeters are sensor arrays based on miniaturized Seebeck elements for the localized, quantitative characterization of heat flows. The sensor arrays consist of up to 40 individual sensors, which can collect data concerning the reaction heat generated in a microreactor with a high degree of temporal and spatial resolution. Due to the large surface-to-volume ratio of microreactors and the resulting small time constants of just a few seconds, it is also possible to perform isothermal calorimetric measurements for rapid and strong exothermic reactions. The test volume is extremely small (< 100 μL), which enables a fast reaction screening.

The combination of continuous microreaction technology and efficient heat flow sensors thus opens the way to rapid and extremely efficient screening of chemical reaction parameters and allow acquisition of safety data. During screening experiments, the influence of individual process parameters (e. g. concentration, stoichiometry, use of alternative reactants, temperature, residence time, etc.) can be followed directly by observing the altered heat signal – both in a qualitative and quantitative manner. The measurement of the heat flows is in real-time; time-consuming calibrations of the heat transfer are not required. Even targeted and quantitative analysis of the energetic potential of critical process conditions (worst case scenarios) can be conducted safely.