An extension of the NPK method to include the pressure dependency of solid state reactions

An novel method to identify the pressure dependency for reactions of the type A(s) ⇌ B(s) + C(g) is proposed. It is an extension of the non-parametric kinetic analysis (NPK) method as it identifies the pressure dependency in addition to the temperature and conversion dependency of the reaction. This is done by analyzing kinetic data in a three-dimensional data space (conversion, temperature, pressure) and attributing the variation of the conversion rate to these independent variables. Thus a reduction from a three-dimensional problem to three one-dimensional problems is achieved. The derivation of a kinetic model can then be performed for each dependency independently, which is easier than deriving a model directly from the data. This work presents the basic approach of the identification and combination of the three dependencies to build a full kinetic model. Also, the interpretation of the model to achieve a physically motivated model is illustrated. Then the method is applied to identify the complex reaction kinetics of the decomposition of CdCO3 based on a set of thermogravimetric measurements. It is shown that it is possible to identify interaction terms between the dependency terms.