(8b) Continuous Flow Calorimetry for the Thermal Characterization of Highly Exothermic and Fast Reactions

A key parameter for reactor design and safety evaluation is the reaction enthalpy (ΔH_rxn). However, the calorimetric characterization of high-energetic, fast reactions is very difficult within conventional batch calorimeters due to their inherent limitations. Consequently, there is an absence of calorimetric data for these reaction systems within the literature. “Flash chemistry” based on high-resolution residence time control within microstructured continuous flow reactors enables fast consecutive reactions involving unstable intermediates to be accomplished.¹ Recently, a modular 3D printed continuous flow calorimeter isothermal heat flow calorimeter was developed to facilitate the study of reactions that are difficult to perform in batch.² In this talk, we present examples from our own research to make the argument that robust calorimetric data for highly exothermic, fast reactions can indeed be obtained within a continuous flow calorimeter.

Initially, a benchmarking study for a very exothermic reaction will be presented to compare the performance against existing literature values. Subsequently, a more complex organolithium transformation which resulted in the formation three products will be discussed. The selectivity towards the different products was carefully optimized (flow rate, reagent equivalents, temperature) through a design of experiments (DoE) study. The influence of mixing efficiency on conversion and product selectivity was investigated through computational fluid dynamics (CFD) simulations. The understanding obtained from the DoE study and CFD simulations was then used to identify the best flow conditions to measure the calorimetric data. Finally, the utilization of continuous flow calorimetry to investigate the ΔH_rxn for a gas-liquid ozonolysis reaction using ozone (O₃) (Fig. 1) operating within an annular flow regime will be highlighted.³

(1) J. Yoshida et al., Chem. Commun. 2013, 49, 9896-9904.

(2) M. C. Maier et al., React. Chem. Eng. 2020, 5, 1410-1420.

(3) D. Polterauer, et al., React. Chem. Eng. 2021, 6, 2254-2258.