Titanium dioxide production process

Sulfate-resisting cement, 5 498 Sulfate surfactants, 24 145 Sulfate titanium dioxide production process, 29 388-391 Sulfathiazole, 28 684 Sulfation, 23 513, 514, 536-538 higher aliphatic alcohols, 2 4 in higher olefins, 27 713 Sulfation operations, industrial changes affecting, 23 515-516 Sulfation processes, general overviews of, 23 555... 

Because sulfur suppHes, either as elemental sulfur or by-product sulfuric acid, have grown owiag to iacreased environmental awareness, demand for sulfur has decreased ia some consuming iadustries for the same reason. Industries such as titanium dioxide productions, which traditionally utilized sulfuric acid, have concerted to more environmentally friendly processes. In addition, many consumers who contiaue to use sulfuric acid are puttiag an emphasis on regenerating or recycling spent acid. 

An excellent example of the differing energy requirements of competing processes is provided by titanium dioxide production. There are two competing processes ... 

A typical plant production of titanium dioxide (sulfate process) is shown in the process diagram (Figure 22.16). 

In the titanium dioxide production plant where the chlorine process is employed, the wastewater from the kiln, the distillation column, bottom residue, and those from other parts of the plant first settle in a pond. The overflow from this pond is neutralized with ground calcium carbonate in a particular reactor, while the scrubber wastewater is neutralized with lime in another reactor. The two streams are sent to a settling pond before being discharged. 

A typical wastewater treatment process flow diagram in a titanium dioxide production plant (the chlorine process) is shown in Figure 22.19. 

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. 

The chief mined ore of titanium is ilmenite (iron titanium oxide, FeTiC>3) and it occurs as vast deposits of sand in Western Australia, Canada and the Ukraine. Large deposits of rutile (titanium dioxide, TiO ) are known in North America, and South Africa. World production of the metal itself is around 90,000 tonnes per year, small compared to titanium dioxide production which is 4.3 million tonnes per year. Reserves of titanium amount to more than 600 million tonnes and while there is an abundance of this element it is extremely costly because it has to be extracted by a complicated process, and yet it could be so much more useful if it was cheaply available. 

Meng. X.G. et al.. Methods of preparing a surface-activated titanium dioxide product and of using same in water treatment processes, U.S. Patent 6 919 029, 2005, cited in [2110]. 

The other important process for production of titanium dioxide is termed the chloride process [7]. The raw material used in this process is natural rutile, which is first heated at 9S0°C in the presence of carbon (in the form of coke) and chlorine. This produces crude TiC, and this product is heated at l(XX) C in the presoice of oxygen to produce the final titanium dioxide product. Under these conditions, the final product is the rutile phase. 

There are two crystalline forms widely used in papermaking applications, anatase and rutile. The major difference between the two is crystal uniformity and size, which yields a slightly higher index of refraction in the rutile crystal (Fig. 6.8). There are two chemical processing manufacturing routes commercially viable for titanium dioxide production, the sulphate and the chlorine process. The older sulphate method may be used to produce both anatase and rutile, while the more recent chlorine process is utilised only for rutile crystal production. 

Low-Residue Process for Titanium Dioxide Production (Example from Kronos International)... 

Regeneration of process solutions used in titanium dioxide production, pickling plants, viscose fibre production, etc. 

In the Huelva factoiy, the oldest and most common process for titanium dioxide production is used the sulphate process. This process uses concentrated sulphuric acid (H2SO4) to dissolve the titaniferous feedstocks which are milled and dried beforehand to aid the digestion process. 

Chloride process. The chloride process yields the rutile form of titanium dioxide. At temperatures between 800 and 1200 C, chlorine is reacted in a fluidized-bed reactor with a titanium-containing mineral under reducing conditions (in the presence of coke) to form anhydrous TiCh- Further purification requires separa-hon by fractional condensation. The conversion of TiCl, to Ti02 may be accomplished by either direct thermal oxidation, or by reaction with steam in the vapor phase at temperatures in the range of 900—1400 °C. A smaU amount of AICI3 is generaUy added to promote formation of the rutile form. The titanium dioxide product is then washed, calcined, and packaged (Kuznetsof, 2006). 

Within the last several years, a number of companies have investigated the application of Raman spectroscopy to process analysis. A review of the scholarly and patent literature reveals several examples PCI3 reactions, titanium dioxide production, diamondlike carbon (DLC) films production, polymeric fiber property detection, applications to gasoline, aromatic production, chlorosilane production, and gas-phase measurements. In Section in, some of these applications will be reviewed in order to illustrate the application of Raman spectroscopy to process chemistry and control. 

In titanium dioxide production, there are two processes used the chloride process and the sulfate process. While the demand for titanium dioxide has historically been growing rapidly, the supply has sometimes exceeded demand and sometimes lagged. So in the past there was a history of shortages and allocations due to tight supply. Also there were periods of excess supply. 

The sulfuric acid is often used for other on-site processes (e.g., titanium dioxide production) or sold. 

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

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). 

Precipitation of a hydrated titanium oxide by mixing aqueous solutions of titanium chloride with alkaU forms the precipitation seeds, which are used to initiate precipitation in the Mecklenburg (50) variant of the sulfate process for the production of pigmentary titanium dioxide. Hydrolysis of aqueous solutions of titanium chloride is also used for the preparation of high purity (>99.999%) titanium dioxide for electroceramic appHcations (see Ceramics). In addition, hydrated titanium dioxide is used as a pure starting material for the manufacture of other titanium compounds. 

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. 

---