Chlorination of titanias modified by alkali and/or phosphorus additives

Abstract

The role of surface alkali and phosphorus additives on the time-dependence of the reaction of TiO₂ with COCl₂ has been studied by a reactive thermogravimetric method. At conversions below 0.7 apparent fractional orders with respect to the solid were found to be 1 (for TiO₂-Li(s) and TiO₂-Na(s)) and 2 (for TiO₂-K(s)); these formal orders, however, provided insufficient information for describing the conversion vs. time curves above α = 0.7. The proposed kinetic model which enables satisfactory curve fitting even for high conversions involves a non-uniform particle size distribution, together with the surface enrichment of phosphorus as retardant during the shrinking of the particles, which results in a steady decrease in the linear reaction rate.