High Surface Area Oxidation – Development of an Improved Open Cup ARC Vessel and Validation

PresentationEasily oxidized, low volatility organic liquids absorbed/dispersed on inorganic solid materials such as insulation, absorbents, and molecular sieves can result in spontaneous ignition incidents. This is due to increased rates of oxidation of the organic when it is spread out over the very high surface area inherent in these types of solid materials. Similarly, high surface area organic solids that are either self-reactive or oxidizable may self-heat when accumulated in a pile of sufficient size, resulting in thermal runaways, gas generation, and/or fire. Understanding and quantifying this behavior is critical to identifying hazards and developing appropriate mitigative measures. Previously, an Open Cup Accelerating Rate Calorimeter technique was developed at Dow using an open, stainless steel container, purged with air heated to testing temperatures to maintain adiabaticity. This method has been used for many years to understand the reaction kinetics of “auto-oxidation” reactions and high surface area runaway reactions. While the method has been shown to be reliable and able to accurately predict large scale hazards, the exposure of the gaseous decomposition and oxidation products of the reactions is destructive to the ARC calorimeter. The open-cup system vents directly into the ARC, resulting in accelerated corrosion or potentially exposing the internals to fire. A new ARC container design has been developed that has been demonstrated to produce comparable results and removes the concerns associated with damaging the equipment. The new design of the Open Cup ARC test cell, validation, and discussion of the data application will be included in this article

A Case Study: Autocatalytic Behavior and its Consideration for a Chemical Process with General application to Handling, Shipping, and Reactive Relief Design

PresentationAutocatalysis is a generally well understood phenomenon. However, since autocatalytic molecules do not have a fixed energy release rate for a given temperature, like nth order reactions, additional considerations are required to ensure safe shipping, handling and relief device sizing. Also, unlike nth order reactions, autocatalytic reactions have an induction time and it is associated with reaching a critical concentration of a catalytic species. Once the induction time is exhausted the reaction accelerates even under isothermal conditions (i.e. dT/dt = f (T,Ccat). Often a thermo- kinetic model is required for adequate hazard evaluation. During model development a first order reaction scheme is often used as a starting point. Such an approach typically leads to an unrealistically high apparent activation energy to get a reasonable fit to the data. Since time impacts the reaction rate, induction times need to be determined to build an accurate kinetic model. Once induction times are determined as a function of temperature, adequate layers of protection and operating discipline can be determined for safe handling. This paper describes: 1) Identification and confirmation of autocatalytic behavior, 2) Induction time model development, and 3) Application to storage, shipping, and reactive relief design. For reactive relief vent sizing, consideration is given not only to credible failure scenarios that may result in relief device activation, but also recovery from contained unplanned events