RU2547490C2 - Method for synthesis of nanosize particles of titanium dioxide powder - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention can be used in chemical industry. The method for synthesis of nanosize particles of titanium dioxide powder includes gas-phase reaction of a titanium halide and oxygen in a plasma reactor channel and cooling the reaction product in quenching unit. Immediately before feeding into the reactant injection unit of the plasma reactor, titanium tetrachloride is mixed with a dry oxygen-containing gas. Separate control of flow rates of the reactants is performed before feeding into the injection unit of the plasma reactor. Reactants are fed into the plasma reactor channel at temperature of 293-700 K. The obtained gas-phase reaction semi-product, which contains titanium dioxide nanoparticles, is quenched in a countercurrent of a dry oxygen-containing quenching gas. Fractional and phase compositions of titanium dioxide nanoparticles are formed by varying the flow rate of the quenching gas. To this end, the distance between nozzle sections of the quenching unit is varied in the radial direction of feeding the quenching gas or the angle of feeding the quenching gas is varied in the range of 10-25° relative to the radial direction of feeding the quenching gas. The flow rate of the quenching gas is greater than the total flow rate of the mixture of gases in the plasma reactor channel.

EFFECT: invention enables to obtain especially pure titanium dioxide with the required fractional and phase composition, eg rutile or anatase, with high efficiency.

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Description

The invention relates to a technology for producing highly pure finely divided oxide powders, directly to a plasma-chemical method for the synthesis of simple and double oxides of a number of elements, for example, such as zirconium dioxide, alumina, titanium dioxide, zirconium dioxide doped with yttrium oxide, etc. The invention can be used with the production of ceramic materials, polishing compounds, oxide coatings and in other areas of technology.

The invention can also be used on an industrial scale to obtain powdered titanium dioxide of a rutile or anatase crystalline phase from its halides, as well as to obtain pigment titanium dioxide used in the manufacture of paints, varnishes, paper, rubbers and plastics, as well as the anatase form of titanium dioxide, serving as an important component in the creation of installations in water treatment and air treatment facilities, in solar panels and fiber optic resonators.

The prior art method in the art for producing finely dispersed oxides according to patent RU No. 2119454, IPC C01B 13/28, 1998. Finely dispersed oxide powders are obtained by oxidizing tetrachlorides with oxygen. In this case, liquid tetrachlorides are sprayed into an oxygen-containing plasma coolant. Spraying is carried out with an oxygen-containing gas at a ratio of the mass flow rate of oxygen to the mass flow rate of metal tetrachloride or metalloid of at least half the stoichiometrically necessary amount. Titanium, silicon, tin, and germanium tetrachlorides are sprayed. Titanium tetrachloride is sprayed at an angle of 10 to 25 ° to the direction of movement of the plasma coolant with at least four jets in pairs towards each other. Modifying additives, in particular aluminum trichloride, silicon tetrachloride and / or carbon tetrachloride, are introduced into the reaction zone in the form of a solution in titanium tetrachloride.

The method allows to accelerate the process of evaporation of droplets of dispersed liquid in a high-temperature gas and to reduce the particle size of the obtained titanium dioxide powder, however, the disadvantage is that the preliminary mixing of the reactants before entering the reactor is realized in different phase states of the reactants - liquid titanium tetrachloride and gaseous oxygen. This leads to uneven mixing of the reagents during the evaporation of droplets of titanium tetrachloride in a high-temperature jet and, consequently, to a large dispersion in particle sizes of the final product, which affects the quality of the pigment. In addition, microdrops of tetrachloride may not have time to evaporate completely and fall on the walls of the reactor, which leads to their corrosion and the formation of a skull.

The closest implementation of the plasma-chemical method for producing titanium dioxide by the chloride method is the plasma synthesis of metal oxide nanoparticles (US patent No. 7217407, IPC C01B 13/28, 2007) - selected for the prototype.

A method for synthesizing nanosized particles of titanium dioxide in a plasma process involves a gas-phase reaction of titanium halide and oxygen, and oxygen is taken in an amount that is excessive in comparison with the stoichiometric required for the reaction with titanium. A reaction in the presence of a hydrogen source to form particles of metallic titanium dioxide, where the average particle size is less than 100 nm in diameter, with a smaller fraction of particle aggregates larger than 100 nm in diameter, and the amount of hydrogen is sufficient to provide a smaller fraction of particle aggregates. A method for the synthesis of nanosized particles containing titanium dioxide in a plasma chemical reactor, including:

(a) injection of a feed gas containing oxygen and titanium halide vapors, the oxygen in the feed gas in an excess amount compared to the stoichiometric required for the reaction with titanium;

(b) injection from a hydrogen source into the reactor;

(c) generating a plasma jet;

(d) contact of the supply gas with plasma in the presence of hydrogen in an amount sufficient to form a mixture of reaction products containing titanium dioxide nanoparticles with an average particle size of less than 100 nm in diameter and with a smaller fraction of particle aggregates whose size exceeds 100 nm in diameter.

The method further includes quenching the mixture of reaction products and disposing of the formed nanoparticles.

The disadvantages of this method include, first of all, the dependence of the flow rate of one reagent - titanium tetrachloride - on the flow rate of bubble oxygen, the second reagent. In addition, the introduction of hydrogen into the reactor may lead to the formation of hydrogen chloride vapor, which requires the absence of moisture in the reactor to prevent corrosion of the walls of the reactor.

The objective of the invention is to obtain the target product is a nanosized titanium dioxide powder with an adjustable fractional and phase composition due to efficient mixing of reagents in a plasma reactor and controlled quenching.

The technical result is achieved by the fact that the method for the synthesis of nanosized particles of titanium dioxide powder involves a gas-phase reaction of titanium tetrachloride and oxygen in the channel of a plasma reactor, followed by controlled cooling of the reaction products in the quenching unit. According to the invention, titanium tetrachloride vapors are immediately mixed with the dried oxygen-containing gas immediately before being fed to the injection unit of the plasma reactor reactors; moreover, the flow rates of the reactants are separately controlled before being fed to the injection site of the plasma reactor, the reactants are fed into the plasma reactor channel at a temperature of 293-700 K, after which the obtained gas-phase reaction intermediate containing titanium dioxide nanoparticles is subjected to quenching in a counter flow of a dried oxygen-containing quenching g aza, forming the fractional and phase composition of titanium dioxide nanoparticles by changing the quenching gas flow rate, which is carried out by changing the distance between the sections of the nozzles of the quenching unit in the radial direction of quenching gas supply or by changing the angle of supply of quenching gas within 10-25 ° relative to the radial direction of flow quenching gas, and the flow rate of quenching gas exceeds the total flow rate of the gas mixture in the channel of the plasma reactor.

The proposed method for the synthesis of nanosized particles of titanium dioxide powder allows one to obtain ultrafine highly pure oxides of the desired crystal structure, for example, rutile or anatase crystalline phases, and is characterized by high productivity and relatively low energy intensity of the process.

In FIG. 1 shows a diagram of a flow-type plasma chemical reactor for implementing a method for the synthesis of nanosized particles of titanium dioxide powder.

In FIG. 2 shows the angle of rotation of the nozzles of the quenching unit.

The plasma-chemical reactor (Fig. 1) consists of a direct current plasma torch 1, a reagent injection unit 2 with holes for radial injection of components, the reactor itself, consisting of a working channel of the reactor 3 and a hardening unit 4 with nozzles 5 for supplying quenching gas to the reactor channel. The plasma torch DC 1, the working channel of the reactor 3 and the hardening unit 4 are made water-cooled.

Installation of a plasma-chemical reactor also contains a plasma-forming gas unit 6 with a gas supply line 7 to the plasmatron; a quenching gas supply unit 8 with a gas supply line 9 through nozzles 5 to the quenching unit 4 and an outlet gas path 10 connecting

a quenching unit 4 with a collection of 11 particles of the target product powder - titanium dioxide nanoparticles, and a chlorine neutralization and separation unit (not shown in Fig. 1).

The installation is also equipped with a reservoir 12 of transporting gas (dried nitrogen, argon or circulating chlorine), inert with respect to titanium tetrachloride with a conveying line 13; capacity 14 with liquid titanium tetrachloride (TiCl ₄ ) and a conveyor line 15, as well as a node 16 with a dried oxygen-containing gas and a conveyor line 17.

The choice of a direct current plasma torch as a coolant for heating reagents is due to its high performance in the target product, the ability to reduce the contamination of the resulting powder by erosion products to an acceptable level, as well as low ripple electric power.

The method of synthesis of nanosized particles of titanium dioxide powder in a plasma-chemical flow reactor is implemented as follows.

Plasma-forming gas is supplied from the unit 6 through the gas line 7 to the channel of the plasma torch 1, then it enters the channel of the reactor into the region of the unit 2 for injection of reagents. As a plasma-forming gas, air or nitrogen with a constant flow rate is used.

Independent control of reagent costs - titanium tetrachloride (TiCl ₄ ) and dried oxygen-containing gas is implemented as follows.

Vapors of low-vapor titanium tetrachloride are transported by one of the following gases inert to it: dried nitrogen, argon, or circulating chlorine, which is supplied from tank 12 via line 13 and sparged through liquid titanium tetrachloride (TiCl ₄ ) located in tank 14, increasing evaporation liquid from the surface. In this case, the flow rate of titanium tetrachloride is determined both by the flow rate of the gas transporting it, and by the properties of the most volatile liquid at a given temperature, as well as by the surface area of the mirror. The carrier gas with titanium tetrachloride vapors passes through line 15, where it is mixed with dried oxygen-containing gas supplied from unit 16 in a predetermined ratio along gas line 17. Next, the reagent gas mixture enters injection unit 2, where it is radially blown into the plasma torch and is effectively mixed with it due to the high range of the vapor phase of titanium tetrachloride. The mixture of reagents should have a temperature not exceeding 700 K, since above this temperature a reaction begins between oxygen and titanium tetrachloride.

Further, the chemical reaction of titanium tetrachloride (TiCl ₄ ) vapors and dried oxygen-containing gas proceeds in the working channel of reactor 3, while nucleation of titanium dioxide nuclei from its supersaturated vapors is formed and further

particle growth of titanium dioxide (TiO ₂ ). Estimates show that in the working zone the jet has a mass-average temperature in the range of 1000–2500 K, and the passage time of the zone is a few milliseconds.

Downstream in the quenching unit 4, the heterophase stream is mixed with cold quenched, dried oxygen-containing gas supplied from the unit 7 via a gas line 8, where the particles of the target product are cooled and the chemical reaction is sharply slowed down and the coagulation of particles of titanium dioxide (TiO ₂ ) powder begins. Quenching oxygen-containing gas is injected radially or at an angle relative to the radial direction of quenching gas supply through nozzles 5 with a controlled flow rate exceeding the total gas mixture flow rate in the working channel of reactor 3. The quenching stage is the most important, since the average particle size and crystal lattice structure depend on the cooling rate the target product is titanium dioxide: a rutile or anatase crystalline phase from its tetrachloride.

The oxygen-gas supply rate is controlled by changing the flow rate in the nozzles of the quenching unit: by changing the distance between the sections of the nozzles of the quenching unit, or by changing the angle α between the nozzles of the quenching unit and the radial direction of supply of the quenching gas within 10–25 ° (see Fig. 2).

For example, to obtain anatase, a high quenching rate is required, which is achieved with the same quenching gas consumption by reducing the distance between the sections of the nozzles of the quenching unit, respectively, to obtain a rutile crystalline phase, a lower quenching speed is required and the distance between the sections of the nozzles must be increased.

After quenching, a gas suspension of cold nanoparticles of titanium dioxide (TiO ₂ ) is formed in a mixture of gases containing chlorine (chlorine gas). The resulting conglomerates of powder particles are carried out by chlorine gas through the gas path 10 and captured on a bag or cermet filter in the collection of the target product 11, and the mixture of gases with chlorine enters the neutralization or chlorine separation unit (not shown in the figures).

An advantage of the proposed method is the controlled preliminary homogeneous mixing of the reagents before feeding the plasma torch into the injection unit, which provides more favorable conditions for a uniform reaction in the entire volume of the working zone of the reactor channel 3. It is possible to mix the dried oxygen-containing gas with titanium tetrachloride, as well as all the gases accompanying the titanium tetrachloride vapors, should not contain moisture, since the hydrolysis of titanium tetrachloride proceeds very intensively even at room temperature with strong heat. This leads to precipitation,

consisting of hydrates of titanium tetrachloride, and clogging of the feed line of the reagents with hydrolysis products.

The rate of quenching of titanium dioxide powder is controlled by adjusting the flow rate in the nozzles 5 of the quenching unit 4, or by changing the distance between the sections of the nozzles of the quenching unit, or by changing the angle (10-25 °) between the nozzles of the quenching unit and the radial direction of supply of the quenching gas, so that the jet quenching gas had a velocity component opposite to the direction of motion of the high-temperature flow.

The preparation of a finely dispersed titanium dioxide (TiO ₂ ) powder (of a particular fractional and phase composition) is carried out by separately controlling the reagent costs before feeding them to the plasma torch injection unit, efficient mixing in the plasma torch channel and controlling the quenching rate in the oncoming stream of the obtained intermediate and quenched, dried oxygen-containing gas.

Example 1. Plasma-forming gas, nitrogen, is fed into the reactor with a flow rate of 0.8-1.2 * 10 ^-3 kg / s and a thermal power of 10-14 kW. TiCl ₄ vapors are transported by dried nitrogen or argon in the reagent supply line, then they are pre-mixed with the dried oxygen-containing gas at a temperature of 293 K, and then radially injected into the reactor through the reagent injection unit (4 holes with a diameter of 1 mm). The total excess of titanium tetrachloride against stoichiometry in the feed line of 20-50%. The temperature in the upper zone of the reactor is 2000-2500 K.

Dried oxygen-containing gas (air) is radially blown into the quenching unit through nozzles with a flow rate of 2-3 g / s (through 8 holes with a diameter of 5 mm), while the reaction of the unreacted part of TiCl ₄ with quenching gas (air) oxygen continues. The temperature after quenching is less than 800 K. Then, a nanosized TiO ₂ powder with an average fractional particle size of 0.1-0.2 μm and a rutile phase content of 80-99% is unloaded from the filter. The shape of the particles is spherical and oval.

Example 2. Plasma-forming gas — nitrogen — is fed into the reactor with a flow rate of 0.8-1.2 * 10 ^-3 kg / s and a thermal power of 8-10 kW. TiCl ₄ vapors are transported by nitrogen in the reagent supply line, then pre-mixed with dried oxygen-containing gas at a temperature of 293 K, and then radially injected into the reactor channel through the reagent injection unit (4 holes with a diameter of 1 mm). The total excess of titanium tetrachloride against stoichiometry in the feed line 80-90%. The temperature in the upper zone of the reactor is 1500-2000 K.

At the quenching unit, through the nozzles installed at an angle of 10 ° to the axis of the radial direction of quenching gas supply, the dried quenched oxygen-containing gas is blown

(air) at a rate of 6-8 g / s, and the reaction of the unreacted portion of TiCl ₄ with the dried oxygen of the quenching air continues. The final product is unloaded from the filter - nanosized TiO ₂ powder with an average fractional particle size of 0.03-0.06 microns and an anatase content of 70-80%. The shape of the particles is spherical and oval.

Information sources

1. Patent RU No. 2119454, IPC С01В13 / 28, 1998.

2. US patent No. 7217407, IPC С01В13 / 28, 2007 - prototype.

Claims (1)

A method for synthesizing nanosized particles of titanium dioxide powder, comprising a gas-phase reaction of titanium halide and oxygen in the channel of a plasma reactor with subsequent cooling of the reaction products in the quenching unit, characterized in that the titanium tetrachloride vapor is mixed directly with the dried oxygen-containing gas before being fed to the injection unit of the plasma reactor reagents, moreover, the reagent costs are separately controlled before they are fed to the injection site of the plasma reactor, and the reagents are fed into the channel of the plasma ctor is fed at a temperature of 293-700 K, after which the obtained gas-phase reaction semi-product containing titanium dioxide nanoparticles is quenched in the counter flow of a dried oxygen-containing quenching gas, thereby forming the fractional and phase composition of titanium dioxide nanoparticles by changing the quenching gas flow rate, which is carried out by changing the distance between the sections of the nozzles of the quenching unit in the radial direction of supply of quenching gas or by changing the angle of supply of quenching gas within 10-25 ° relates the radial direction of quenching gas supply, and the quenching gas flow rate exceeds the total flow rate of the gas mixture in the channel of the plasma reactor.

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