Titanium dioxide finishing process

Abstract

This disclosure relates to process for producing titanium dioxide (TiO 2 ) pigments, comprising the following steps: a) oxidizing a mixture of titanium tetrahalide and a rutile forming agent, such as aluminum halide, present in the vapor phase and in the presence of a nucleant to form a gaseous suspension comprising titanium dioxide particles; b) passing the gaseous suspension to a cooling conduit; c) introducing scouring material into the cooling conduit; wherein the particles of the scouring material have a diameter in the range of about 0.25 mm to about 12.7 mm; d) separating the vapor phase to form a powder comprising the titanium dioxide particles and the scouring material; and e) simultaneously subjecting the powder to substantially uniform heating at a temperature of about 300° C. to about 600° C. and reducing the size of the titanium dioxide particles and the particles of the scouring material in the powder to a mean particle size of about 50 nm to about 1000 nm, whereby the titanium dioxide pigment has a chloride content of less than about 500 ppm. The so treated powder may have a residual free chlorine content of less than about 1 ppm.

1 - 13 . (canceled) 
     
     
         14 . A dehalidized titanium dioxide pigment having a mean particle size of about 50 nm to about 1000 nm and a chloride content of less than about 500 ppm prepared by heating a powder comprising titanium dioxide particles having halides adsorbed thereon and scouring material at a temperature of about 300° C. to about 600° C. in a fluid energy mill to deadsorb at least a portion of the halides from the titanium dioxide particles. 
     
     
         15 . The titanium dioxide pigment of  claim 14  wherein the fluid energy mill is a micronizer. 
     
     
         16 . The titanium dioxide pigment of  claim 15  wherein the heating of the micronizer is accomplished by a heated fluid selected from the group of steam, air, argon, helium, nitrogen and mixtures thereof. 
     
     
         17 . The titanium dioxide pigment of  claim 15  wherein the heated fluid is steam. 
     
     
         18 . The titanium dioxide pigment of  claim 14  in which the titanium dioxide particles have chlorides adsorbed thereon. 
     
     
         19 . The titanium dioxide pigment of  claim 14  in which the powder further comprises an amount of residual free halogens which are reduced to an amount less than about 1 ppm. 
     
     
         20 . A system for dehalidizing titanium dioxide pigment, comprising:
 (a) an oxidation zone, for vapor phase oxidizing a feedstock comprising titanium tetrachloride, oxygen, a nucleant and a rutile forming agent to form a gaseous suspension comprising titanium dioxide particles, the oxidation zone having a cooling conduit located downstream therefrom, the cooling conduit having a scouring material inlet;   (b) a fluid micronizer having a steam inlet,   wherein the cooling conduit is located between the oxidation zone and the fluid micronizer, the cooling conduit for contacting the gaseous suspension comprising titanium dioxide particles with a scouring material introduced to the gaseous suspension via the inlet and for cooling and transferring the gaseous suspension comprising cooled titanium dioxide particles from the oxidation zone to the fluid micronizer, the fluid micronizer for substantially uniformly heating the titanium dioxide particles to a temperature ranging from 300° C. to about 600° C. by contacting the cooled gaseous suspension with steam introduced to the fluid micronizer through the steam inlet and for simultaneously reducing the size of the titanium dioxide particles to a mean particle size of about 50 nm to about 1000 nm to form dehalidized titanium dioxide pigment having a chloride content of less than about 500 ppm.