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The Role of Chemical Reactivity Data in Process Safety Management

Chemical reactivity is addressed throughout the requirements of OSHA’s PSM Standard. It is specifically required in the process safety information element. In addition, it is necessary input to process hazard analyses, operating procedure development, emergency relief system design, and mechanical integrity. As the understanding of the impact of chemical reactivity hazards on the operation of a chemical process continues to develop, it is important to have a method for developing this data. Equally important is a method for extracting meaningful reactivity information from the data and incorporating it into process safety. This paper will present a process for evaluating chemical reactivity hazards using an Accelerating Rate Calorimeter (ARC®). It will then explain how to extract information from this data to help define process safety elements such as safe upper and lower limits, emergency relief system design, etc. Read more

Thermo-Kinetic Analysis of Reactions Involved in the Manufacture of oNitroaniline

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. Read more