Kinetics of the Titanate Causticization Reactions in a Potassium-Based Process

Abstract

The objective of this study was to model the kinetics of direct causticization of potassium-based chemical using titanium dioxide, TiO₂. The starting materials were K₂CO₃ and TiO₂. Potassium chemical was used because there is an indication that potassium carbonate, K₂CO₃, might offer benefits over sodium carbonate, Na₂CO₃, such as the elimination of potassium build-up in sodium-based pulping. Experiments were run at six different temperatures. Half were below potassium carbonate’s melting point while the other half were above. Reaction rates and conversions increased with temperature, and the maximum conversion achieved was 0.90. Several kinetic models were fitted to the data. Valensi-Carter showed a good fit for the solid-solid reaction, while ash diffusion control model was chosen to describe the solid-liquid reaction with TiO₂ stayed in solid phase. The samples from the heated experiments were then leached with water to produce KOH. The amount of KOH was found to increase with temperature. It implied that more 4K₂O•5TiO₂ was produced at higher temperatures. Reacting K₂CO₃ with K₂O•3TiO₂ might interest industry more because TiO₂ is added to the recovery system as a make up only. The models used did not show good fits for the whole conversions; therefore, additional study should be done to develop a model that could describe low conversions as well as high conversions.