A thermal runaway or thermal explosion may be the consequence of an adiabatic process of a reaction or series of reactions. It occurs when heat produced by an exothermic reaction is accumulated leading to an increase in temperature of the reaction mixture. Subsequently, the reaction rate increases leading to an increased rate of heat generation.
The temperature increase may trigger secondary reactions, such as decomposition of the reaction mass, the intermediates or the final product leading to a thermal runaway. By conducting proper process safety studies at laboratory scale, the conditions leading to a thermal runaway can be identified and avoided before the process is scaled-up.
Studying both, the desired as well as potentially undesired reactions are of utmost importance. While the undesired reactions are investigated using adiabatic calorimeters, Dewar flasks, or DSC, the desired reaction is typically studied with a Reaction Calorimeter.
The Reaction Calorimeter can be used to determine key factors such as the Heat of Reaction, the accumulation, the Adiabatic Temperature Rise and MTSR in order to understand the consequence of a cooling failure. In fact, it is used to determine whether the desired synthesis reaction could cause the process to become unstable leading to a secondary reaction.
In most cases, the secondary reaction liberates more energy and faster than the desired reaction, with the production facility not being capable of safely removing this energy. Therefore, it is necessary to design the reaction so that potentially dangerous conditions cannot occur, or to define appropriate measures to ensure that the process remains under control safely at all times.