Study of thermal decomposition mechanism of methylene diphenyl diisocyanate (MDI) through accelerating rate calorimeter and theoretical approach

Methylene diphenyl diisocyanate (MDI) serves as a primary component of polyurethane in various applications, including household appliances, architectural structures, automobiles, and adhesives. A recent MDI plant explosion in China highlighted the importance of studying MDI’s thermal stability and parameters to prevent accidental thermal decomposition. In this study, an extensive array of analytical techniques, including differential scanning calorimetry, thermogravimetric analysis, and adiabatic accelerating calorimeter, was employed to determine the thermokinetic constants of MDI, providing a solid foundation for further in-depth investigations. The findings revealed that MDI containing water reacts at substantially lower temperatures, while pure MDI can release heat and gases in an adiabatic environment, posing a considerable explosion risk. The kinetic constant of MDI was calculated using the Flynn–Wall–Ozawa method, yielding apparent activation energy values ranging from 51.78 to 96.70 kJ mol⁻¹ across a conversion degree range of 0.05–0.70. The Coats–Redfern model pinpointed the kinetic reaction mechanism as a two-stage chemical process based on the apparent activation energy. Molecular optimization, following the energy minimisation principle, was conducted using Gaussian 09 software, which led to the identification of the optimal pathway for generating carbodiimide and carbon dioxide. This investigation offers valuable insights for the effective management of MDI during production, transportation, and storage, contributing to improve loss prevention practices in the industry.