Titanium dioxide

Titanium dioxide is the naturally occurring oxide of titanium. It has a wide range of applications, from paint to sunscreen to food coloring. When used as a food coloring, it has E number E171. Titanium dioxide has remarkable optical properties, with a very high refractive index close to that of diamond.  It is also a very stable compound.

Titanium dioxide is the most used white pigment and provides whiteness and opacity for paints (57% of the world production) and coatings, plastics (24%) and paper (12%). It has many specialty uses. It is resistant to UV radiations and thus does not discolor over a long period of time. Ultra-pure and fine crystal titanium dioxide grades are being increasingly used for sun screens. Titanium dioxide is also seeing growing demand in photocatalysts.

Manufacturing process

There are two main processes, the Sulfate Process and the Chloride Process which use the two principal ores, ilmenite and rutile, respectively.  Ilmenite contains 45 of 60% titanium dioxide (TiO₂) and rutile contains up to 99% of TiO₂.  The ores are mined worldwide but most production is in Australia and South Africa.

Each large producer of titanium dioxide balances its production between the two processes.  Each produces the oxide in the rutile crystal form but the Sulfate Process can also produce another form of the oxide, anatase, which is softer and which is used for a small number of specialist applications.

It is estimated that about 65% of the world's production is based on the Chloride Process.

Sulfate process

The chemistry of the sulfate process involves three main stages namely the dissolution of the ore, the formation of hydrated titanium dioxide, and the formation of hydrated titanium dioxide.

Dissolving the ore: The ore is usually ilmenite. It is ground finely and dissolved in sulfuric acid to form a mixture of sulfates. The iron ions must be removed from the solution so that the color of the final product is not spoiled. After filtration, the remaining solution contains titanyl sulfate, TiOSO4.

Formation of hydrated titanium dioxide: The next stage involves the hydrolysis of the titanyl sulfate in solution to give insoluble, hydrated titanium dioxide.

Formation of anhydrous titanium dioxide: The final stage of the process is the heating of the solid in a rotating furnace heated by gas flames. Heating evaporates the water and decomposes any remaining sulfuric acid in the solid. After cooling, the product is 'milled' to form crystals of the size needed.

Chloride process

The chemistry of the chloride process involves two main stages namely the conversion of rutile to titanium chloride and the oxidation of titanium chloride.

The conversion of rutile to titanium chloride: The rutile and chlorine are fed into a heated bed together with a source of carbon. Titanium and other metals chlorides are formed. Gaseous metal chlorides are separated. The titanium chloride vapor is then distilled to give a purer product.

The oxidation of titanium chloride: Liquid titanium chloride is vaporized and burnt in oxygen, together with a hydrocarbon fuel source to a high temperature to initiate the reaction and keep the temperature high enough for the reaction to proceed.
The titanium dioxide is formed (by adding seed crystals) as a fine solid in the gas stream and is filtered out of the waste gases using cyclones or filters. The chlorine is recycled to the chlorination stage of the process above.

GAB Neumann’s process equipment

The production of titanium dioxide involves the use and processing of large amounts of hydrochloric or sulfuric acids.

GAB Neumann provides sulfuric acid dilution coolers, graphite heaters, and graphite coolers to the titanium oxide manufacturers that use the sulfate process and graphite coolers, graphite heaters and graphite absorbers to the titanium oxide manufacturers that use the chloride process.

GAB Neumann has developed specific abrasion resistant solutions to cope with the erosive nature of titanium oxide crystals.

Associated products:

Sulfuric acid dilution coolers

Impervious graphite annular groove heavy-duty condensers

Impervious graphite annular groove partial condensers

Impervious graphite block heat exchangers

Impervious graphite annular groove isothermal absorbers

Impervious graphite columns

Hydrochloric acid recovery units