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) reversible arrow 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.