Лако-красочные материалы — производство

The titanium in the raw material is converted to titanium tetrachloride in a reducing atmosphere. Calcined petroleum coke is used as the reducing agent because it has an extremely low ash content and, due to its low volatiles content, very little HCl is formed. The titanium dioxide reacts exothermically as follows:

TiO2 + 2Cl2 + C ^TiCl4 + CO2

As the temperature rises, an endothermic reaction in which carbon monoxide is formed from the carbon dioxide and carbon also occurs to an increasing extent. Therefore, oxygen must be blown in with the chlorine to maintain the reaction tem­perature between 800 and 1200 °C. The coke consumption per tonne of TiO2 is 250-300 kg. If CO2-containing chlorine from the combustion of TiCl4 is used, the coke consumption increases to 350-450 kg.

The older fixed-bed chlorination method is hardly used today. In this process, the ground titanium-containing raw material is mixed with petroleum coke and a binder, and formed into briquettes. Chlorination is carried out at 700-900 °C in brick-lined reactors.

Fluidized-bed chlorination was started in 1950. The titanium raw material (with a particle size similar to that of sand) and petroleum coke (with a mean particle size ca. five times that of the TiO2) are reacted with chlorine and oxygen in a brick-lined fluidized-bed reactor (c) at 800-1200 °C. The raw materials must be as dry as possible to avoid HCl formation. Since the only losses are those due to dust entrainment the chlorine is 98-100% reacted, and the titanium in the raw material is 95-100% reacted, depending on the reactor design and the gas velocity. Magnesium chloride and calcium chloride can accumulate in the fluidized-bed reactor due to their low volatility. Zirconium silicate also accumulates because it is chlorinated only very slowly at the temperatures used. All the other constituents of the raw materials are volatilized as chlorides in the reaction gases.

The ceramic cladding of the fluidized-bed reactor is rather rapidly destroyed by abrasion and corrosion. If chlorination is interrupted, there is a further danger that the raw materials may sinter and eventually cannot be fluidized.