(W1130-02-14) Contactless, Real-Time Thermal Profiling and Control of Exothermic and Endothermic Reactions

Purpose: eal-time temperature monitoring is essential for accurately characterizing exothermic and endothermic reactions, particularly during rapid thermal transitions. In this study, we monitored real-time temperature shifts during different exothermic and endothermic reactions, using thermopile technology. The results were compared to those obtained using a conventional temperature probe. The aim was to explore the suitability of thermopiles and temperature probes for providing chemists with rapid and accurate temperature measurements and control. Experiments were conducted in a multiple, small-scale reactor system with automated sampling (ReactALL).

Methods: First, to validate the accuracy of the thermopile sensor, a slow heating and cooling thermal profile was generated, ranging from 20 ºC to close to boiling point, for different solvent systems, then cooled back to 20 °C at a rate of 1 ºC/min and compared with those from a conventional temperature probe. Additionally, exothermic and endothermic reactions were conducted to further evaluate this technology’s performance across reactions with varying enthalpy changes and to assess its ability to monitor and control reaction heat. For the exothermic reaction, 4 mL of 2M HCL was added to a 16 mL reactor vial and cooled to 20 ºC while stirring at 350 rpm. Once stabilized, 4 mL of 2M NaOH was added was added through the Smartcap port of the reactor system via automated dosing. HCl (aq) + NaOH (aq) » NaCl (aq) + H2O (l) ΔH < 0. For the endothermic reaction, ~1.7 g of potassium chloride (KCl) was added to a 16 mL reactor vial and maintained at 20 ºC. After equilibration, 5 mL of distilled water was added through the Smartcap port of the reactor system. KCl (s) » K+ (aq) + Cl- (aq) ΔH > 0

Results: Temperature measurements obtained using the contactless thermopile technology closely matched those from a conventional temperature probe, as illustrated in Figure 3, which depicts a slow heating and cooling thermal profile for different solvents. The difference between the two technologies was as low as 0.1 ºC. In temperature control experiments involving both exothermic and endothermic reactions, the thermopile-based feedback system effectively regulated the reactor jacket temperature, restoring the internal reactor temperature to 20 ºC within a few minutes. As illustrated by the red line in Figure 4, the reactor jacket temperature was dynamically adjusted via thermopile feedback to maintain the internal reactor temperature at the target setpoint. This was achieved within few minutes for exothermic (Figure 4b) and endothermic (Figure 4d) reactions. In contrast, experiments without active thermopile control required significantly more time to return to baseline, as shown in Figures 3a and 3c. The time for thermal stabilization depends on factors like reaction enthalpy and solvent properties, especially boiling point and specific heat capacity. As such, we anticipated that the time needed to reach baseline conditions would vary between systems. Nevertheless, the thermopile technology demonstrated rapid stabilization, achieving thermal control within just a few minutes, whereas other technologies require more time.

Conclusion: In exothermic and endothermic reaction experiments, contactless thermopile technology restored the reactor temperature to 20 ºC within few minutes – significantly faster than systems without active thermopile control. These results demonstrate this novel technology’s ability to provide rapid and accurate temperature measurement and control, which is essential for precise thermal profiling in dynamic processes. Additionally, this approach enhances temperature resolution while minimizing environmental disturbances, making it ideal for small-scale chemical reactions.

Figure 1. Illustration of the automated sampling process and Figure 2. Thermopile technology

Figure 3. Experimental heating and cooling thermal profile comparing temperature measurements from the thermopile sensor and a conventional
temperature probe, for a set of solvents at 1º C/min heat/cool rate

Figure 4. Temperature profiles during the experiments: a) Exothermic reaction (without thermopile control); b) Exothermic reaction (with thermopile control); c) Endothermic reaction (without thermopile control); d) Endothermic reaction (with thermopile control)