Preparation of titania powders in a fluidized-bed reactor

Abstract

Titania powder was prepared in a fluidized-bed crystallizer at 25 °C by mixing titanium isopropoxide in 2-propanol with water at various ratios with two peristaltic pumps at equal flow rates. The column was packed with quartz glass beads of broad size distribution (0.2–0.8 mm). The flow rates of the feed solutions were selected to achieve optimal fluidization of the quartz beads. Various parameters, including the residence time of the reactants in the bed, the excess water with respect to the stoichiometric amounts (Ti:H₂O), the presence of foreign ions and the role of the quartz filling beads, were investigated with respect to their importance in the physicochemical and morphological characteristics of the particles formed. The concentration of titanium at the top of the bed was kept constant during the crystallization process after the establishment of a steady state. The difference in concentration from the corresponding value of the feedstock solution was used to calculate the rates of titania formation. The presence of Li⁺, Nb⁵⁺ and W⁶⁺ in the aqueous medium resulted in the incorporation of these ions in the titania lattice and the reduction of the rates of formation of the particles from the resulting supersaturated solutions.