Process for producing titanium dioxide particles having reduced chlorides

Abstract

This disclosure relates to process for producing titanium dioxide pigment having reduced chlorides, comprising: a) reacting titanium tetrahalide vapor, rutile-forming agent and at least a stoichiometric amount of oxygen in a reactor to form a gaseous suspension comprising titanium dioxide particles; b) introducing silicon tetrachloride into the reactor at least one point downstream of the point of contact of the titanium tetrahalide, the rutile forming agent and the oxygen, and where at least 97% of the titanium tetrahalide has been converted to titanium dioxide to provide a substantially uniform encapsulation of pyrogenic SiOon the titanium dioxide; c) passing the gaseous suspension to a cooling conduit; d) introducing scouring material, typically selected from the group of calcined titanium dioxide and compressed titanium dioxide, and mixtures thereof, 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 and forming a cooled product having a solid and a vapor phase; e) separating the vapor phase from the cooled product to form a powder comprising the titanium dioxide particles, and a content of chlorine-containing material ranging from about 500 to about 3000 ppm of oxychloride, and the scouring material; and f) subjecting the powder to substantially uniform heating at a temperature of about 200° C. to about 600° C., in the presence of moisture, to reduce the content of chlorine-containing material to less than about 60 ppm oxychloride; wherein the moisture present is in at least a stoichiometric amount with the oxychloride.