Titanium dioxide production technology - chlorination production technology

The main steps of the chlorination process are as follows:
1 chlorination, using titanium chloride in a reducing atmosphere of titanium chloride raw materials;
2 rectification, titanium tetrachloride condensation, rectification and purification;
3 oxidation, titanium tetrachloride is oxidized to form Ti0 ₂ .
At the same time, there are various process schemes for hydrolyzing TiCl ₄ , but these processes have no commercial economic value. The advantage of the oxidation process is that chlorine can be recycled, ie the chlorine produced at this stage can be recycled back to the chlorination process.
1. Chlorination Titanium tetrachloride (TiC1 ₄ ) is first produced in the process of producing titanium dioxide by chlorination. It is produced by mixing titanium raw materials with sintered petroleum coke cake and preheated chlorine gas, and reacting at 800-1 000 degrees Celsius. Its usual chlorination reactor is a fluidized bed reactor, and there are other reactors.
The chlorination reactor is made of steel-lined refractory material, and the inside is cooled by jacket. Chlorine gas and titanium tetrachloride are highly corrosive under high temperature conditions. Therefore, even high-quality refractory materials are used, and their service life is limited.
Petroleum coke carbon primary object of the chlorination reaction is removed titanium chlorine, the chlorine content is reduced as much as possible the reaction with the metal, the reducing agent chloride Ti0 ₂ always sufficient.
The initial reaction heat is provided by electrical energy. The use of a graphite electrode requires a large amount of heat to start the reaction. When entering the chlorination reactor, the ratio of the coke cake to Ti0 ₂ needs to be carefully controlled. The temperature is too low and the conversion of TiO ₂ to TiCl ₄ is low. The unreacted chlorine gas passes through the reactor with low utilization; if the temperature is too high, the reactor material will melt and block the pores.
Some companies currently use titanium concentrate and high titanium slag or rutile or brookite mixed feed technology and commercial production capacity. The feed to the mine can reach Ti0 ₂ 60% content, the purpose of which is to reduce the production cost of raw materials. Other chlorination companies use the amount of blended raw materials not less than Ti _{2 2} 85%. Also required is natural rutile, synthetic rutile, titanium slag with low MgO, CaO. If Ca, Mg is too high, in the case of chlorination, the formation of liquid chlorides such as MgCl ₂ and CaCl ₂ will block the fluidized bed slag, resulting in abnormal production and shutdown.
From the gas out of the chlorination reaction, not only of TiCl, and carbon dioxide, and ash and coke cake has various chlorinated derivatives from the feed _{impurities, FeCl 3, SiCl 4, ZrC1} 3, MnCl 2 VOCl _3, and the like. From the reactor, the gas is separated by dust from the bag filter gas, and the main FeC1 ₃ is separated by a condenser maintained at a temperature of 200 ° C. In the case of using titanium concentrate and brookite doped feed, the amount of separated FeCl ₃ is significantly increased, which brings about a problem of large amount of waste by-treatment.
2. Rectification Purification This section is to condense and purify Ti0 ₂ gas. After the gas exits the chlorination reactor, it is cooled and condensed by an adjustable spray; the purpose is to lower the gas temperature to 13 degrees Celsius, which is just the boiling point of TiCl ₄ , under which FeCl ₂ , MnCl ₂ , CaCl ₂ , MgCl ₂ Separated in solid form and removed.
The TiCl ₄ gas after condensing and separating most of the solid impurities still contains many impurities similar to its boiling point such as SnCl ₄ , Sicl ₄ , FeCl ₃ , MnCl ₂ and VOC1 _{3 ,} etc. Reducing the amount of these impurities is the key to the operation of titanium chloride white powder. One of the factors.
VOC1 ₃ is separated by complexing iron manner alkylene or mineral oil. The impurity-containing TiCl _{4 was} treated with H ₂ S at 90 ° C, VOCl _{3 was} reduced to VOCl ₂ , and then separated by precipitation of iron and vanadium sulfide, and AIC1 _{3 was} converted into a complex salt and separated.
The precipitated impurities were filtered off TiCl ₄ further purified by careful control of distillation to obtain pure TiCl _4, can be sold as a commercial grade here, titanium dioxide plant or as an intermediate product, its quality was 98.5%, the main The trace impurities are CoCl ₂ , SiCl ₄ , VOC1 ₃ .
3. Oxidation This section is to oxidize TiCl ₄ with air or oxygen to form pure TiO ₂ and chlorine. When the oxidation temperature is lower than 600 ° C, the reaction rate is negligible; the reaction temperature increases rapidly beyond the reaction temperature, and the final reaction temperature ranges from 1300 to 1800 ° C. The oxidation reaction is the key to the control of the fineness and quality of the product. [next]
Chlorine and titanium tetrachloride are extremely corrosive under the oxidation temperature conditions used. The usual reactor is made of stainless steel lining refractory. The oxidation reaction heat can not maintain sufficient reaction temperature, and must provide auxiliary heat. The usual practice is: 1TiC1 ₄ and oxygen/air mixed with a small amount of steam, respectively preheated to the required temperature and separately into the reactor; 2 by burning CO to CO ₂ provides auxiliary heat; 3 oxygen is heated by electric spark.
In the oxidation, in order to increase the yield of TiO ₂ , seed crystals are usually added to promote the formation of TiO ₂ . AICI ₃ is a common auxiliary material added to the TiC1 ₄ feed, and Al ₂ is formed as solid particles during oxidation. 0 ₃ to provide the desired seed crystal, or to spray human droplets in air or oxygen during oxidation, as a seed crystal to promote the formation of TiO ₂ particles.
Oxidation tends to cause Ti0 _{2 to} stick to the reactor wall, gas inlet nozzles and other surfaces, and therefore must be prevented. The oxidation process is very difficult. The resulting TiO ₂ adheres rapidly and steadily to the wall of the oxidation reactor, to the outer wall of the inlet nozzle, and is not completely carried away by the gas.
Some nitrogen plants using the continuous reaction gas inlet portion, which is kept cool to prevent scarring precipitate Ti0 _2. It is also useful for sand and sand to prevent crusting. The difficulty of crusting in an oxidizing furnace is especially difficult to overcome on small devices. The 15,000-ton chlorination titanium dioxide plant in Jinzhou Ferroalloy Plant is currently the world's smallest production plant; after years of hard work, it has basically overcome the difficulty of oxidizing furnace crusting; from the original hours of operation to the current continuous operation 11 days. The removal measures are oxidizer gas film protection and salt removal.
After the reaction material is rapidly cooled, the titanium dioxide and the gas are separated by filtration using a cyclone, a cloth bag, an electric dust removal or the like. The exhaust gas is condensed to recover chlorine gas, stored as liquid chlorine, and recycled to the chlorination section for reuse.
Separated from the filter containing a large amount of TiO ₂ in chlorine adsorption, need to be removed by heating, steam is the most common treatment, chlorine is washed out and converted into the hydrochloric acid is removed and further treated with steam containing 0.1% of boric acid Traces of chlorine and hydrochloric acid give TiO ₂ .
The TiO _{2 is} finally taken out from the filter, slurried in water, wet-milled, depolymerized, and sent to a post-treatment to be processed in the same manner as the sulfuric acid method.
4. Material balance The main chemical reactions are as follows:

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