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Common principles for producing rutile titanium white powder and this method is similar to chlorination, but the process more complex and accurate control condition. In the initial reaction, TiCl 4 and oxygen generating a homogeneous chemical reaction to produce TiO 2 precursor molecules, clusters of molecules or particles formed TiO 2 by nucleation. Since the heterogeneous nucleation ratio is homogeneous, it is thermodynamically easier. As the reaction proceeds, TiCl 4 adsorbs on the surface of the TiO 2 particles and undergoes heterogeneous reaction to make the particles larger. The reaction formula is as follows:
TiCl 4 (g) + O 2 (g) ===TiO 2 (s) + 2Cl 2 (g)
Shi Liyi and others used N 2 to carry TiCl 4 gas, and after preheating to 435 ° C, the inner tube of the casing nozzle enters the high temperature tubular reactor, and the oxygen is preheated to 870 ° C, and then enters through the outer tube of the casing nozzle. The reactor, TiCl 4 and O 2 are reacted at 900~1400 ° C, and the nano titanium dioxide particles generated by the reaction are subjected to gas-solid separation by a particle trapping system. They studied the effects of oxygen preheating temperature, nitrogen flow rate at the reactor tail, reaction temperature, residence time and aluminum content on the particle size, morphology and crystal form of TiO 2 . The results show that increasing the oxygen preheating temperature and increasing the nitrogen flow rate at the tail of the reactor are favorable for controlling the particle size of the product. The particle size of the nano-TiO 2 particles increases with the increase of the reaction temperature and the residence time. When the reaction temperature is 1373K, AlCl When the molar ratio of 3 to TiCl 4 is 0.25:1 and the residence time is 1.73 s, the particle size distribution of pure rutile nano TiO 2 particles is 30-50 mm.
East China University of Science and Technology first combines combustible gas with excess oxygen to produce a high-temperature oxygen-containing gas stream, and then cross-mixes with preheated gaseous TiCl 4 (containing a small amount of crystal form conversion promoter) at an angle to allow the reaction to proceed at high speed. . At the same time, the external quenching method is used to rapidly cool the reactants, thereby obtaining a high rutile content of nano titanium dioxide.
TiCl 4 gas oxidation method, because chlorine gas can be recycled, has the advantages of energy saving, environmental protection, low cost and high degree of automation, and can prepare anatase type, mixed crystal type and rutile type nano titanium white powder separately. However, due to the complexity of this process, on the one hand, chemical reactions and nucleation and growth occur, while TiO 2 molecules, molecular clusters and particles collide, agglomerate and form agglomerates, and at high temperatures Solid phase reactions such as sintering and crystal transformation occur, and the processes are not simple parallel and series processes; on the other hand, because the reactor involves complex engineering problems such as flow, transfer, and mixing, these problems also affect the nano titanium dioxide. Structure and performance. In order to achieve effective control of nano titanium dioxide particle state, particle size distribution, specific surface area and crystal form, the characteristics of the process, kinetics and influencing factors must be further studied.
At present, the key to realize the large-scale production of TiCl 4 gas phase oxidation method is to solve the structural design of the oxidation reactor. The reactor must achieve the following two purposes: 1. The reactants reach a high degree of agitation and intense in a very short time. Momentum exchange, so that the reactants reach a predetermined temperature and the mixing of the human level is uniform, while avoiding the reverse flow of any macro to ensure uniform reaction conditions; 2 there is a large temperature gradient in the reactor, so that the nucleation of the particles Growth is carried out as much as possible. The reaction process should be carried out at a higher temperature to increase the reaction rate, thereby increasing the supersaturation of the product, facilitating the formation of nano-titanium dioxide, and promoting the transformation of anatase to rutile. After the reaction, the product must be rapidly formed. Cooling prevents the aggregation and sintering of the nanoparticles and makes the particles larger.
The by-product of the method is highly corrosive, has large investment, complicated equipment structure, high material requirements, high temperature resistance and corrosion resistance, and the device is difficult to maintain, and the research and development is difficult.