Exothermic reaction processing must be concerned with potential consequences when heat released by the reaction exceeds that removed by the reactor coolant system, a situation known commonly as a runaway reaction. We have investigated a complicated reaction process in which two exotherms can occur — the process of making the desired product, o-nitroaniline (o-NA), from ammonia and o-chloronitrobenzene (T Onset around 140° C), and the decomposition of the product, o-NA (T Onset around 225° C). A severe industrial loss occurred in 1971 at a plant producing o-nitroaniline, an incident that has been the subject of several AIChE loss prevention presentations and papers. In this article, we take a closer look at the chemistry involved, and the ability to use thermo-kinetic analyses to understand the reactions involved, and how these influenced the accident that occurred. Further, we present the progress we've made towards predictive models for the kinetics and the pressure-time data. Several useful generalizations have evolved. First, is the need to include experiments that use stoichiometric mixtures when assessing exothermic reactions. Second, is the need to understand the role of reaction intermediates, and how they may influence the operation of the plant.
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