Calorimetry and Thermo-Kinetic Modeling to Determine SAPT and Safe Shipping Conditions for Self-Reactive Materials

Transportation of self reactive materials such as monomers can potentially hazardous if the conditions of shipping (temperature, inhibition level of the material during transport etc.) are favorable for a runaway reaction. The United Nations Recommendations on the Transport of Dangerous Goods, Model Regulations, Rev.19 (2015) has a new requirement for the determination of the SAPT (Self-Accelerating Polymerization Temperature) for polymerizing substances. Accordingly, depending upon their SAPT and type of transportation packaging polymerizing substances may be subject to temperature monitoring or temperature control. The new regulation states that SAPT shall be determined in accordance with the test procedures established for the SADT (Self Accelerating Decomposition Temperature) for self-reactive substances. There are multiple strategies for determination of SADT, each of which differ in their measurement techniques. Recent work published for Acrylic Acid has shown that SAPT results can differ significantly depending upon which SADT method was applied. To ensure consistent SAPT values for safe transportation, several industry consortia committees (Basic Acrylic Monomer Manufacturers, European Basic Acrylate Manufacturers and Methacrylate Producers Association) met in a joint session, of which Dow is a member, and agreed to an inter-company effort to identify the best method on the basis of good science, readily available technology, and flexibility in packaging applications. This paper highlights the technical approach developed and validated at Dow for inhibited methyl methacrylate (MMA) using isothermal microcalorimetry, modeling, simulations, and SADT H1 testing. In this study, the effect of inhibitor level, headspace volume, and mixing during sample preparation on polymer induction times (PIT) were carefully examined and managed. Several kinetic models were evaluated based on their fit to PIT data, full heat profiles, and accuracy of measured and predicted data. The H1 test results for MMA were consistent with the SAPT values predicted by simulation using kinetics obtained from microcalorimetry tests, and the measured heat transfer coefficient for the 1-gallon package. With the successful completion of this proof of concept study, Dow advocates for the determination of SAPT utilizing isothermal calorimetric data and modeling. This approach can be easily and safely implemented at smaller companies using commercially available calorimeters, and can accommodate variations in size and shape of common transportation containers.