Titanium dioxide is the whitest pigment widely used in the manufacture of paints and enamels. It may be manufactured by two major processes: the chloride and the sulfate process.These processes were compared and the chloride process was selected and analyzed. Titanium dioxide containing feed stock is subjected to high temperature carbo chlorination to produce titanium tetra chloride, which is thereafter converted to titanium dioxide by oxidation.This project involves the studying and collecting all preliminary information required for Titanium dioxide manufacture, generating mass and energy balances for the plant, designing the various equipment used in the plant and estimating the cost involved in setting up the plant.
Titanium dioxide is produced either in the anatase or rutile crystal form. Most titanium dioxide in the anatase form is produced as a white powder, whereas various rutile grades are often off-white and can even exhibit a slight color, depending on the physical form, which affects light reflectance. Titanium dioxide may be coated with small amounts of alumina and silica to improve technological properties.Commercial titanium dioxide pigment is produced by either the sulfate process or the chloride process. The principal raw materials for manufacturing titanium dioxide include ilmenite. (FeO/TiO2), naturally occurring rutile, or titanium slag. Both anatase and rutile forms of titanium dioxide can be produced by the sulfate process, whereas the chloride process yields the rutile form.
Titanium dioxide can be prepared at a high level of purity. Specifications for food use currently contain a minimum purity assay of 99.0%. Titanium dioxide is the most widely used white pigment in products such as paints, coatings, plastics, paper, inks, fibers, and food and cosmetics because of its brightness and high refractive index (> 2.4), which determines the degree of opacity that a material confers to the host matrix. When combined with other colors, soft pastel shades can be achieved. The high refractive index, surpassed by few other materials, allows titanium dioxide to be used at relatively low levels to achieve its technical effect.
The food applications of titanium dioxide are broad. US regulations authorize its use as a color additive in foods in general at levels not to exceed 1%. The European Union also permits its use in foods, in general, with some specified exceptions, at quantum satis levels. India restricts its uses to chewing gum and bubble gum at not more than 1% and to powdered concentrate mixes for fruit beverage drinks not to exceed 100 mg/kg. Japan lists its use as a food color without limitation, other than specifying certain foods in which it is not permitted. Finally, titanium dioxide is listed in Table 3 of the Codex General Standard for Food Additives, which lists additives that may be used in food, in general, unless otherwise specified, in accordance with GMP.
ORES AND NATURAL OCCURRENCE
Titanium is the world's ninth most abundant element. Titanium dioxide occurrences in nature are never pure, it occurs in complex oxides, usually in combination with iron and also with the alkaline earth elements. These impurities color the ores from buff to black and they are therefore far removed from the requirements of a clean white titanium dioxide pigment. The important ores are
- Ilmenite (FeTiO3)
- Mineral Rutile tetrag (TiO2)
- Brookite rhombic (TiO2)
- Perovskite (CaTiO3)
- Sphene (CaTiSiO5)
The oxides can be mined and serve as a source for commercial titanium. The original commercial ore, first used by the sulfate process is ilmenite. This occurs mainly as a black sand: in Australia, South Africa, India, the USA and Malaysia, and also as a hard rock deposit: in Canada, Norway and the USA. Ilmenite typically contains 45-65% TiO2 with iron making up the majority of the remainder. The second most available ore is the buff colored mineral rutile, which contains around 95% TiO2 with smaller amounts of iron and other impurities. Rutile sands are mostly found in Australia, Sierra Leone and South Africa. These are produced either by acid leaching of the iron and other impurities or via a slagging process to separate molten iron, producing a Titania rich slag which is then solidified and ground to the desired particle size. This beneficiation process allows fine ore sand to be converted to a more desirable, coarser TiO2 feed stock with iron produced as a by-product.
Titanium dioxide is one of the most important chemicals, finding a variety of applications in the Paint and Paper industries and many other fields. For the manufacture of Titanium dioxide in this project, we have used the Chloride process, a process that has many advantages over its alternative process. As the first step, preliminary analysis was carried out on the basis of properties and applications of Titanium dioxide and the various processes used in its manufacture. The material and energy balances for the various operations involved in the process were done. Next, the equipment's involved in the manufacturing process were designed. Cost estimation was done and the payback period for the operation of the plant was calculated. The plant layout and locations were decided upon to complete the conception of the whole process of manufacture of Titanium dioxide.
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