Experimental Investigation And Optimization For Titanium Dioxide Hydrolysis Process

The hydrolysis is an important step in the production of titanium dioxide through sulphate process. The particle mean size and size distribution as well as its purity are affected directly by operating conditions of hydrolysis process.Stabilizing the product quality is always a challenge to many TiO2 producers, since all the processes involved are in batch mode. Among all the batch operating steps, hydrolysis is one of the most important stages to the quality of the end product. Therefore, hydrolysis process is experimentally studied in this thesis in order to improve and stabilize the product quality.The effect of seeding was studied. The influence of feed rate on the quantity and quality of crystal seeds, the primary crystal sizes of the product and particle size distribution (PSD) was also investigated.An on-line instrument for particle chord length measurements, FBRM (Focused Beam Reflectance Measurement), was employed for detecting the transient variations of PSD during the process to give a better understanding of hydrolysis mechanism. Hydrolysis process can be divided to four stages: induction, aggregation, breakage companying with further reaction and ripening. Particle growth during hydrolysis process follows the sigmoid model. From this study, an on-line monitoring and controlling system was developed for the stability of the product.Through the analysis of the production process, four major operating conditions affecting the process most were selected for process optimization, which are stirring speed, feed fluid rate, heating profile and initial adding water volume. Response Surface Method (RSM) was used for the experimental design, in which four factors and three levels were determined according to the actual conditions. To analyze the experimental results, the four operating conditions that influence mean particle size and size distribution, filtration time and the rate of hydrolysis of titanyl sulfate solutions are evaluated, four fitting models between responses and its influence factors are obtained. Optimum operating conditions are predicted. An experiment for validation of predicted conditions was carried out, and confirms the estimations are correct. The results from the study can been use as a guideline for the process operation.Fluid dynamics condition is also very important to hydrolysis process. Influence of different types of impellers on hydrolysis rate, hydrous TiO2 particle size and filtration time was investigated. The flow fields in the reactor with different impellers were simulated using a commercial CFD code, Fluent, to identify mixing efficiency, which will give a design basis for the industrial application.