Thermal runaway, closed reaction vessel

Possible Haystack-Type Reaction Associated with Thermal Runaway in a Closed Reaction Vessel 329... 

Imagine a closed reaction vessel in which an exothermic reaction proceeds at room temperature at a finite rate. Although the temperature in the reaction vessel is initially the same as room temperature, it rises gradually until the rate of heat generation due to the exothermic chemical reaction is equal to the rate of heat escape from the reaction vessel surface. However, if a thermal balance is not established for such a chemical reaction, the reaction rate is accelerated by self-heating as the temperature rises, leading to thermal runaway. The temperature change in a reaction vessel is represented by Eq. (1),... 

In the production of formic acid, a slimy of calcium formate in 50% aqueous formic acid containing urea is acidified with strong nitric acid to convert the calcium salt to free acid, and interaction of formic acid (reducant) with nitric acid (oxidant) is inhibited by the urea. When only 10% of the required amount of urea had been added (unwittingly, because of a blocked hopper), addition of the nitric acid caused a thermal runaway (redox) reaction to occur which burst the (vented) vessel. A small-scale repeat indicated that a pressure of 150-200 bar may have been attained. A mathematical model was developed which closely matched experimental data. 

Figure 8. Clock or haystack-type reaction associated with thermal runaway derived from self-heating due to exothermic reactions in a closed vessel. Parameters ...

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