Production pigments

Tetrachloride-Reduction Process. Titanium tetrachloride for metal production must be of very high purity. The requited purity of technical-grade TiCl for pigment production is compared with that for metal production in Table 4. Titanium tetrachloride for metal production is prepared by the same process as described above, except that a greater effort is made to remove impurities, especially oxygen- and carbon-containing compounds. 

Titanium raw-material utilization can be broken down as illustrated in Figure 9. About 4% of the titanium mined is used as metal, 94% is used as pigment-grade Ti02, and 2% as ore-grade mtile for fluxes and ceramics. In 1995, the estimated U.S. Ti02 pigment production was valued at 2.6 biUion and was produced by five companies at 11 plants in nine states. About 47% was used in paint, 18% in plastics, 24% in paper, and 18% in other misceUaneous appHcations (56). 

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. 

Table 10. Annual World Capacity for Titanium Dioxide Pigment Production, t x 10 ...

W. Herbst and K. Hunger, Industrial Organic Pigments, Production, Properties, Applications, VCH, Weioheim, Germany, 1993, pp. 521—546. 

Hari, R.K., Patel, T.R., and Martin, A.M., An overview of pigment production in biological systems functions, biosynthesis, and apphcations in food industry, Food Rev. Int., 10, 49, 1994. 

Natural pigment production for food coloration includes the entire spectrum of biotechnologies. For example, biological production of carotenoid pigments has medical implications because carotenoids are nutritive (pro-vitamin A), antioxidant, and photoprotective. Carotenoids are produced alternately in agricultural systems (plants), industrial bioreactors (bacterial and fungi), and marine systems (cyanobacteria and algae). 

The microalgae are cultured in bioreactors under solar or artiflcial light in the presence of carbon dioxide and salts. The bioreactors may be closed systems made of polyethylene sleeves rather than open pools. Optimal conditions for pigment production are low to medium light intensity and medium temperatures (20 to 30°C). Pigment extraction is achieved by cell breakage, extraction into water or buffered solution, and centrifugation to separate out the filtrate. The filtrate may then be partly purified and sterilized by microfiltration and spray dried or lyophilized. 

Hamdi, M., Blanc, P.J., and Goma, G., A new process for red pigment production by Monascus purpureus culture on prickly pear juice and the effect of partial oxygen pressure. Bioprocess Eng., 17, 75, 1995. 

Organic synthesis 39 [OS 39) Formation of azobenzene derivatives for pigment production... 

OS 39] ]R 25] ]P 27] A 24 h run of a pilot-scale micro reactor for azo pigment production was performed using a diazo suspension [55], At the end of this period, the pressure loss of the micro reactor increased exponentially. Special means were developed to prevent clogging and unstable operation. By partial removal of the deposits, the pressure loss was brought back to normal. 

Emissions of dichlorobenzidine, chloroaniline, cuprous chloride and more during pigment production (17-20%)... 

The impact of UV radiation on the human skin not only enhances pigment production (tanning), but also causes erythema (skin injury, sun bum). There is a huge market for a small portable UV dosimeter that gives an indication when sunburn has to be anticipated. Whereas such a consumer product would have to be cheap and straightforward, serious UV-dosimetry remains quite a challenge. 

The most abundant titanium sand deposits are black sands in streams and on beaches of volcanic regions. The principal black minerals are magnetite, titanoferous magnetite and black silicates, chiefly angite and homblend. It is quite difficult to produce an ilmenite suitable for pigment product from black sand, but other sand deposits that contain rutile, ilmenite and often monazite are found in Australia, USA, India and Africa. These deposits are either alluvial or marine in origin. 

Excellent apatite results were achieved. An ilmenite concentrate was produced suitable for pigment production. 

Certain commercial developments in the last twenty years or so have had important effects on the pattern of pigments production. One is the rapid growth of textile production in the Asia Pacific region and another is the development of automated dyeing methods, coupled with instrumental methods of colour measurement and of computerised colour recipe prediction. 

The final crystals that ultimately constitute the crude pigment product are known as primary particles. These are true single crystals with the typical lattice disorders or combinations of several lattice structures that appear as units under X ray. 

Other common intermediates for azo pigment production are 2,4-dinitro-aniline, acetoacet-o-chloroanilide, acetoacet-o-toluidide, phenyl- and p-tolyl-methylpyrazolone, 2-hydroxy-3-naphthoic acid, Naphtol AS and its derivatives, and 2-chloro-4-aminotoluene-5-sulfonic acid. 

In most cases, diazonium salts are unstable in the dry state and are sensitive to heat and impact. Since isolation is not necessary for azo pigment production, the diazonium compound is coupled with the coupling component as it is formed in solution or suspension. 

The following factors determine the outcome of azo pigment production by continuous process ... 

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