Generalized approach to model pyrolysis of flammable materials

• Published in: Thermochimica acta 2014-08, Vol.590, p.242-250
• Main Author: Snegirev, A.Yu
• Format: Article
• Language: English
• Subjects: Flammability; Global reaction; Microscale combustion calorimetry; Modeling; Multi-step kinetics; Pyrolysis
• ISSN: 0040-6031; 1872-762X
• DOI: 10.1016/j.tca.2014.07.009

•A single global reaction can describe a multi-step pyrolysis of arbitrary complexity.•Dependencies of kinetic parameters on conversion accommodate information about multi-step pyrolysis.•These dependencies can be derived from thermal analysis data using iso-conversional Friedman method.•Measurements at multiple heating rates are required. Generalized approach is suggested to model pyrolysis of solid materials. Generalization implies use of conversion-dependent, rather than constant, formal kinetic parameters. Within this approach, two functions characterizing thermochemical stability of a material are evaluated: the apparent activation energy and the product of pre-exponential factor and conversion function. Both functions are obtained by the iso-conversional Friedman method and tabulated depending on the global conversion variable. The key advantage of this approach is application of a single global reaction to model pyrolysis with multi-step reaction mechanism of arbitrary complexity. This approach has been applied to five flammable materials (polystyrene, polycarbonate, polymethyl methacrylate, polyvinyl chloride, and wood) decomposing in ether single- or multi-step manner. To derive generalized pyrolysis kinetic models, material decomposition was studied by microscale combustion calorimetry and thermogravimetry. The advantage of MCC is highlighted. The proposed kinetic model is shown to replicate MCC measurements to a very good accuracy in a range of the heating rates from 0.25 to 1.5°C/s. The generalized global kinetic models can be readily applied to predict ignition and burning of flammable materials with no need to develop multi-step reaction schemes. Favorable performance of the generalized approach has been demonstrated when it was applied as a component of the Pyropolis model to predict thermal decomposition, flaming ignition, and burning of the material (PVC) with complex multi-step decomposition chemistry.