Kinetic analysis via microwave dielectric measurements

In the chemical industry, a key step for the assessment of thermal risk and runaway is the identification of autocatalytic reactions. In this field, many estimation methods based on dynamic differential scanning calorimetry (DSC) measurements have been developed. As a rule, a screening of the most hazardous chemicals is conducted. In the first step, the measured heat release curve from dynamic DSC gives the apparent activation energy level. In the second step, the characteristic behaviour of a possible autocatalytic decomposition is pointed out with an isothermal DSC measurement. Unfortunately, when an endothermic process precedes the exothermic decomposition, identification is rather difficult or even impossible. A new method based on microwave dielectric measurements of chemicals has been developed. This method consists of a preliminary recording of the initial reactants and final product dielectric properties. Then the normalized extent of a chemical process is determined from the behaviour of its complex permittivity. As an illustration, the thermal decomposition of a well known curing agent, 2,2'-azobis-isobutyronitrile is studied.