TITANIUM DIOXIDE FINISHING PROCESS

摘要

This disclosure relates to process for producing titanium dioxide (TiO<SUB>2</SUB>) 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 3000C to about 6000C 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. The Figure is a simplified flow diagram of one embodiment of the process of the disclosure wherein feedstreams comprising oxygen, titanium tetrachloride, a nucleant and a rutile forming agent are introduced to an oxidation zone 10 wherein, in the vapor phase, the titanium tetrachloride is oxidized to form a gaseous suspension comprising titanium dioxide particles, the gaseous suspension is transferred to a cooling conduit 12 wherein the gaseous suspension is contacted with scouring material to form a cooled product having a solid phase and a vapor phase. The vapor phase is separated from the solid phase via separator 14 to form a powder comprising titanium dioxide particles and the scouring material which is passed to a particle size reducing unit 16. The powder withdrawn from the unit can be subjected to surface treating in finishing unit 18.