(40a) Assessing Reactive Hazards: What’s the Right Tool for Me?

Evaluating chemical hazards is a crucial part of plant safety. Reactive chemical hazards are a special subset of chemical hazards that can be present whether the reaction is intended or not, and the results can have catastrophic consequences such as explosion, fires, or harmful chemical releases. It is critical to study both desired and undesired reactions to ensure that the proper safeguards, procedures, or safety related equipment are installed to provide adequate protection during process operations.

There are many ways of assessing and then addressing reactive hazards, and selecting the best experimental approach depends on a variety of factors. The first point of consideration when determining the approach is identifying the objective of the assessment. Is the goal to prevent, mitigate, or eliminate the reaction? Is the goal to determine the likelihood of a reaction occurring or understand the severity or consequence if the reaction occurs? Depending on the answers to these questions, there are a variety of important safety parameters such as heat of reaction, adiabatic temperature rise, instantaneous heat flow, adiabatic time to maximum rate (TMR), self-accelerating decomposition temperature (SADT), emergency relief requirement, and more that can be used to meet these goals, and there are different experimental techniques that are optimal for collecting the data needed to determine them.

The second point of consideration when determining the experimental approach to meet the assessment objective is reviewing details on the reaction and potential equipment limitations. Factors such as the temperature range, pressure range, sensitivity, material of construction and compatibility, sample size, stirring, and desired or undesired reaction procedure can all change the recommended approach. Different experimental approaches have different capabilities and limitations, and it is important to select the right tool to successfully study the reactive hazard.

This paper provides an overview of various laboratory experimental techniques recommended for developing a safe chemical process. Focus will be on evaluating heat and pressure generation through the use of calorimetry. Techniques discussed include Differential Scanning Calorimetry (DSC), Accelerating Rate Calorimetry (ARC), reaction/isothermal calorimetry, and low thermal inertia calorimetry (VSP2 & ARSST). The pros and cons of the various techniques, recommendations for collecting excellent data, and their typical safety applications are discussed while highlighting the two crucial points of consideration discussed above. Example DSC, ARC, ARSST, VSP2, TAM, and CalvetHT data are shared, and several case studies are highlighted:

1. Analyzing styrene polymerization heat flow data with various inhibitor levels to assess thermal stability,
2. Comparing data from different heat flow calorimeters to show the impact of differences in sensitivity, material of construction, sample size, and/or headspace,
3. Applying adiabatic calorimetry data from a 4-methyl-3-nitrophenol runaway reaction to design an emergency relief system,
4. Assessing data from ARC, ARSST, and/or VSP2 adiabatic calorimeters to determine how differences in phi-factor, stirring, sensitivity, tracking, and/or thermocouple location can affect the results, and
5. Evaluating heat flow and adiabatic calorimetry data on allyl phenyl ether to describe how each type of data or combination of data can be used to evaluate important safety parameters.