The Chloride Process

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 litde HCl is formed. The titanium dioxide reacts exothermically as follows  

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 torme of H02 is 250-300 kg. If CO2-containing chlorine from the combustion of TiCU 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-Uned 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 Ti02) are reacted with chlorine and oxygen in a brick-Uned 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 eventuaUy cannot be fluidized. 

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Chloride Process. The flow chart of the chloride process is presented in Figure 4. In the chloride process, finely ground mtile reacts with chlorine in the presence of calcined petroleum coke. At a temperature between 800 and 1200°C, the following reaction occurs ... 

Fig. 4. Flow chart for the chloride process for production of the pigment titanium dioxide.

Factors such as reaction temperature, excess of oxygen, water addition, addition of other minor reactants, eg, AlCl to promote the formation of mtile, mixing conditions inside the reactor, and many others influence the quaUty of Ti02 pigment. In general, titanium white pigments produced by the chloride process exhibit better lightness than those produced by the sulfate process. 

Paints. Paints account for perhaps 3% of sulfur consumption (see Paint). The main sulfur use is for the production of titanium dioxide pigment by the sulfate process. Sulfuric acid reacts with ilmenite or titanium slag and the sulfur remains as a ferrous sulfate waste product. Difficulties with this process have led to the development of the chloride process (see Pigments, inorganic Titanium compounds). 

Chloride Process. In the chloride process (Fig. 3), a high grade titanium oxide ore is chlorinated in a fluidized-bed reactor in the presence of coke at 925-1010°C ... 

A high purity titanium dioxide of poorly defined crystal form (ca 80% anatase, 20% mtile) is made commercially by flame hydrolysis of titanium tetrachloride. This product is used extensively for academic photocatalytic studies (70). The gas-phase oxidation of titanium tetrachloride, the basis of the chloride process for the production of titanium dioxide pigments, can be used for the production of high purity titanium dioxide, but, as with flame hydrolysis, the product is of poorly defined crystalline form unless special dopants are added to the principal reactants (71). 

Two pigment production routes ate in commercial use. In the sulfate process, the ore is dissolved in sulfuric acid, the solution is hydrolyzed to precipitate a microcrystalline titanium dioxide, which in turn is grown by a process of calcination at temperatures of ca 900—1000°C. In the chloride process, titanium tetrachloride, formed by chlorinating the ore, is purified by distillation and is then oxidized at ca 1400—1600°C to form crystals of the required size. In both cases, the taw products are finished by coating with a layer of hydrous oxides, typically a mixture of siUca, alumina, etc. 

Although ilmenites and leucoxenes can be used in the chloride process, ores having higher Ti02 contents, eg, mineral mtile, which is not readily attacked by sulfuric acid, are preferred in order to minimise loss of chlorine in iron chloride by-product. 

Chloride Process. A flow diagram for the chloride process is shown ia Eigure 1. The first stage ia the process, carbothermal chlorination of the ore to ... 

It is most economical when high-grade ores are used, becoming less economical with poorer feed materials containing iron, because of the production of chloride wastes from which the chlorine cannot be recovered. By contrast the sulfate process cannot make use of rutile which does not dissolve in sulfuric acid, but is able to operate on lower grade ores. However, the capital cost of plant for the sulfate process is higher, and disposal of waste has proved environmentally more difficult, so that most new plant is designed for the chloride process. 

Ironically, this episode proved beneficial to DuPont. DuPont became the dominant source of TEL after the niid-1920s because they perfected the chloride process and were far more experienced than Jersey Standard in producing and handling toxic substances. 

By contrast the chloride process can, for simplicity, be broken down into two relatively energy-efficient steps ... 

There is a difference of a factor of five in energy consumption between the two processes, largely due to the avoidance of evaporation of large amounts of water in the latter process. Despite this both processes still operate, although the chloride process does dominate. There are two main reasons for this first the sulfate process can use lower grade and therefore less expensive ores and secondly it produces anatase pigments as well as rutile, which is the sole product of the chloride process. 

Two processes are used in the manufacture of titanium dioxide pigments the sulfate process and the chloride process. The chemistry of the sulfate process, the longer established of the two methods, is illustrated schematically in Scheme 9.1. In this process, crude ilmenite ore, which contains titanium dioxide together with substantial quantities of oxides of iron, is digested with concentrated sulfuric acid, giving a solution containing the sulfates of Ti(iv), Fe(m) and Fe(n). Treatment of this... 

Summary of Raw Waste Loading Found in Screening and Verification Sampling of Titanium Dioxide (the Chloride Process)... 

The process was developed by Du Pont in the 1940s and its first plant started operating in 1958. It has progressively replaced the older Sulfate Process because it produces less effluent in 1998, 56 percent of the world capacity for titanium dioxide production used the Chloride Process. See also ICON. 

ICON [Integrated chlorination and oxidation] An improved version of the Chloride Process for making titanium dioxide pigment. It operates at above atmospheric pressure and is claimed to be cheaper to build. Chlorine from the oxidation section, under pressure, is introduced directly to the chlorinator. Developed by Tioxide Group, and first operated at its plant at Greatham, UK, in 1990. 

Emission rate enhancement, 14 852 Emissions. See also Emission Emissions. See also Fugitive emissions from the chloride process, 25 63 dioxin and furan, 13 181 effect of fuels on, 26 719-721 from ethylene oxide formation, 10 653-654... 

In the chloride process, developed in about 1960, the titanium in the ore is converted to titanium(IV) chloride by heating it to 800 °C with chlorine in the presence of carbon, which combines with the released oxygen. The purified chloride is then oxidised to titanium dioxide at 1000 °C and the chlorine formed is recycled. Technical problems arise because the oxidation of titanium(IV) chloride is not sufficiently exothermic to make the reaction self-sustaining but these can be overcome by pre-heating the reactants and by burning carbon monoxide in the reactor to raise the temperature. By careful control of the conditions, it is possible to produce pure rutile particles of a mean size of 200 nm. 

Titanium dioxide, in the form of either rutile or anatase, can also be obtained from ilmenite by treatment with sulfuric acid (the sulfate process), followed by hydrolysis and then thermal dehydration of the resulting TiO(OH)2. The chloride process, however, is now more widely used than... 

Figure 16. Flow diagram of Ti02 production by the chloride process...

The continually increasing demand for environmentally friendly industrial processes has also led to the development of techniques for recycling of the remaining 5-30% sulfate contained in the acidic wash water [2.55]. In modern processes, up to 99 % of sulfuric acid can be recovered and reused in production. In the chloride process, wastewater problems arise if the raw material contains < 90% Ti02. The metal chloride by products are sometimes disposed of in solution by the deep well method (e.g., at Du Pont). The metal chloride solutions are pumped via deep boreholes into porous geological strata. Special geological formations are necessary to avoid contamination of the groundwater by impurities. 

Increasing restrictions also apply to the chloride process, so that efforts are continually being made to use the iron chloride byproduct, e.g., in water treatment and as a flocculation agent [2.56], Another process for treating metal chorides with cement and alkaline compounds to produce rock-like aggregates for road building is described in [2.57]. 

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