The solid state reaction between sodium tri-titanate and sodium carbonate, forming mainly sodium pentatitanate, was investigated. Experiments were carried out in a micro-differential reactor made of quartz glass at various temperatures between 800 degrees C and 880 degrees C and in a pilot fluidized bed reactor operated in a semi-batch mode, in the former reactor, basic kinetic data was obtained by measuring the release of carbon dioxide. Different kinetic models were considered to describe the conversion, such as the Valensi-Carter model for diffusion controlled reaction rates and the phase-boundary model for first-order reaction kinetics. Furthermore, a model that included both diffusion in the solid material and the chemical kinetics was derived. This model described the experimental data obtained in the micro-differential reactor very well. However, for the fluidized bed experiments, these different kinetic models did not accurately describe the experimental data. Therefore, an improved model was developed, which also took into account the time taken for the reactants to achieve physical contact. This model gave good agreement with the experimental data.