A kinetic expression for the pyrolytic decomposition of polytetrafluoroethylene

Despite the fact that the thermal decomposition of polytetrafluoroethylene has been extensively studied over the past six decades, some inconsistencies regarding the kinetic parameters, e.g. the order of the reaction, remain. Representative kinetic data are essential for practical purposes such as reactor design and scaling. In general the literature data refer to homogeneous bulk heating, whereas the case of the non-homogeneous heating of a single particle has not received attention. Data (reaction rate and pre-exponential factor) applicable to this latter case were experimentally determined from isothermal thermogravimetric analyses of the depolymerisation reaction of PTFE. The kinetic data obtained on coarse granules (800–1000 μm) are reported here. The rate law is consistent with a shrinking particle kinetic model, with chemical kinetics controlling phase-boundary movement. The mass loss rate is directly proportional to surface area. A rate law applicable to this case, and useable for geometries of arbitrary shape, is derived.

Graphical abstractThe reaction rate for the thermal depolymerization of PTFE is shown to be directly proportional to the surface area and, to a reasonable accuracy, the mass flux from the surfaces of decomposing granular PTFE can be expressed as:−j(r(t))=−1dA(r(t))dmA(s)dt=k=8×1012e−260000/RTkg m−2 s−1.Figure optionsDownload full-size imageDownload as PowerPoint slide