Лако-красочные материалы — производство

Titanium tetrachloride is reacted with oxygen at 900-1400 °C to form TiO2 pigment and chlorine (n). The purified TiCl4 is vaporized (k) and the vapor is indirectly heated to ca. 500 — 1000 °C (l). The reaction

TiCl4 + O2 ^2Cl2 + TiO2

is moderately exothermic, and requires a high reaction temperature, so that the oxy­gen must also be heated to >1000 °C (m). This can be achieved with an electric plasma flame, by reacting part of the oxygen with carbon monoxide, or by indirect heating. HotTiCl4 and oxygen (110-150% of the stoichiometric amount) are fed sep­arately into a reaction chamber where they must be mixed as rapidly and completely as possible to give a high reaction rate. For this reason, and also because the TiO2 has a strong tendency to cake onto the walls [2.35-2.37], many different reactor designs have been proposed and used. The same considerations apply to the cooling unit (o) where the pigment is very rapidly cooled to below 600 °C. Cooling zones of various geometries are used. Usually, the material is prevented from sticking to the walls by introducing abrasive particles like sand, coarse TiO2 particles, sodium chloride or other materials [2.38, 2.39].

The mixture of gases (Cl2, O2, CO2) and pigment can be further cooled during dry separation of the pigment either indirectly or directly by solid particles, e. g., sand. The pigment is separated from the gas by filtration (p). The gas stream is recycled to the cooling zone (o) of the combustion reactor and to the chlorination process as oxygen-containing chlorine via the liquefaction unit (u). The chlorine adsorbed on the pigment can be removed by heating or by flushing with nitrogen or air.

The wet separation process, in which the pigment-containing gas mixture (Cl2, O2, and CO2) is quenched in water, has not found application.

2.1.3.3