(19b) Considerations for the Safe Handling and Processing of Unstable Materials

The chemical industry handles and processes an increasing amount and variety of unstable chemicals. For example, certain chemicals used in the manufacture of plastics, including peroxide-based initiators and olefinic monomers, are known to be unstable. The quantity of plastics produced worldwide has increased 12% over the 5 years from 2017 – 2021[1] and is expected to grow at a rate of at least 5% per year through 2030.[2] Technological advancements will inevitably result in new products coming to market, including sustainable polymers, performance fibers used in textiles, biological-based medical-grade polymers, and composites developed for use in the next generation of automobiles and aircraft. Therefore, the production and use of the initiators and monomers used to build today’s plastics is expected to grow and new chemicals will likely be developed to meet increased and more rigorous requirements. Another relevant example is the pool chemicals industry, which develops and sells chlorine-containing compounds such as sodium dichloroisocyanurate or trichloroisocyanuric acid. Many of these are water reactive and once a reaction starts within bulk storage of these chemicals, it cannot be easily extinguished.

Increased demand and the anticipated development of new products is expected to increase the manufacture, storage, handling, and processing of reactive chemicals. Therefore, manufacturers should develop a consistent methodology to assess the hazards of unstable chemicals and mitigate their risk. Unstable chemicals typically generate heat at an accelerating rate as their storage and processing temperature increases. They can also release flammable and toxic gases that can increase the risk fires, explosions, and/or poisoning as the chemical reacts violently and/or decomposes. Therefore, chemical manufactures and plant operators often add chemical inhibitors to unstable chemicals and/or implement temperature control measures (i.e., refrigeration or vessel jacket quenching) to prevent or mitigate unwanted heating and runaway exothermic reactions.

We propose a lumped-capacitance methodology to evaluate the instability hazards of initiators, monomers, and other unstable materials within known storage configurations. We address the storage and handling of these chemicals in individual containers and pallets of containers, and within larger storage and process vessels. A simplistic model in which the temperature profile of an unstable chemical can be analyzed given heat transfer from/to the environment, heat generation due to decomposition and other reaction kinetics, and heat generated from auxiliary equipment (e.g., agitators/mixers, pumps, vessel jackets) can be very useful in evaluating the risk of a thermal runaway. We describe how to determine the self-accelerating decomposition temperature (SADT) within larger storage vessels from existing test data on smaller packages and predict the temperature profile of a chemical given exposure conditions (e.g., ambient temperature), packaging (e.g., storage vessel size and material type), decomposition kinetics, and additional sources of heat and insulation. Thermal analysis techniques used determine decomposition kinetics including thermogravimetry (TG), differential scanning calorimetry (DSC), and accelerated rate calorimetry (ARC) are reviewed. Various approaches to calculate the self-heating rate of unstable substances will be evaluated against recommendations by the Kinetics Committee of the International Confederation for Thermal Analysis and Calorimetry (ICTAC).

Case studies related to the storage and processing of solid chemicals (e.g., sodium dichloroisocyanurate and other chlorine-containing compounds) and liquid chemicals (e.g., tert-butyl cumyl peroxide and other peroxides) materials are presented. Finally, we provide recommendations regarding determining safe storage and processing temperatures.

[1] https://www.statista.com/statistics/282732/global-production-of-plastics...

[2] https://www.skyquestt.com/report/polymer-market