Titanium oxide particles and method for producing the same

Abstract

To provide titanium oxide particles and a method for producing the same, the titanium oxide particles having a high anatase content, reduced coarse particles, and superior uniformity and dispersibility.SOLUTION: A method for producing titanium oxide particles is provided, comprising: a reaction step in which a raw material gas (G1), containing titanium tetrachloride and an inert gas, and an oxidizing gas (G2), containing at least one of oxygen gas and water vapor as well as an inert gas, are introduced into a reaction tube to generate a reaction gas; and a cooling step in which the reaction gas is cooled by introducing a cooling gas, thereby yielding titanium oxide particles, in which the ratio FG1T / FG1, which is the flow rate (FG1T) of titanium tetrachloride in G1 to the flow rate (FG1) of G1 in the reaction step, is 0.4 or more and less than 1.0, and the ratio of a TiO2 mass (kg) after introduction of the cooling gas in the cooling step to a total gas volume (m3), (TiO2 mass) / (total gas volume), is more than 0 and 0.21 kg / m3 or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to titanium oxide particles and a method for producing the same. [Background technology]

[0002] Titanium oxide has a very wide range of industrial applications, including cosmetics, UV shielding materials, and additives to silicone rubber, and in recent years has been used in a wide variety of applications, including photocatalysts, solar cells, dielectric materials, and electrode materials for Li-ion batteries. Although "titanium oxide" is listed as titanium dioxide in the Japanese Industrial Standards (JIS), titanium dioxide is widely used as the common name, so in this disclosure titanium dioxide (TiO2) will be abbreviated to titanium oxide.

[0003] Recently, titanium oxide has been attracting attention as a material for high-performance dielectric materials, such as BaTiO3, which can be obtained by the following reaction under heating. BaCO3+TiO2 →BaTiO3+CO2

[0004] The above reaction is a solid-phase reaction, and it is said that BaCO3 decomposes at high temperatures to produce BaO, and BaO diffuses and dissolves in TiO2 particles to become BaTiO3. Therefore, the size of BaTiO3 particles is governed by the size of TiO2 particles. In recent years, with the miniaturization of multilayer ceramic capacitors, the thinning of the dielectric layer has become an issue, and for this purpose, it is essential to make BaTiO3 particles finer and uniform. Furthermore, if BaTiO3 particles larger than the thickness of the dielectric layer are present, a short circuit will occur in the multilayer ceramic capacitor, leading to equipment failure. Therefore, it is necessary to make TiO2, the raw material of BaTiO3, finer and uniform, and it is preferable that it does not contain coarse TiO2 particles. Similarly, in other applications, titanium oxide particles are required to be finer and uniform, and it is also preferable that they do not contain coarse particles.

[0005] Methods for producing titanium oxide are roughly divided into a liquid phase method in which titanium tetrachloride or titanium sulfate is hydrolyzed, and a gas phase method in which titanium tetrachloride is reacted with oxygen or water vapor at high temperatures.

[0006] The liquid phase method has the advantage that titanium oxide can be produced under relatively mild conditions and fine primary particles can be easily obtained, but there is a problem that the use of titanium oxide in this state is limited because the titanium oxide is obtained in the form of a sol or slurry. In order to use the sol or slurry as titanium oxide particles, it is necessary to dry it, and after drying, it generally becomes severely aggregated. Such severely aggregated titanium oxide particles have a problem that the particle size distribution becomes non-uniform. There is also a problem that the titanium oxide particles obtained by drying have poor dispersibility when dispersed in a solvent. If the dispersibility is poor, when the raw materials are mixed to generate the above-mentioned BaTiO3, the titanium oxide particles and other raw materials are not mixed sufficiently, resulting in uneven distribution of the raw material components, which causes non-uniform growth during the reaction, resulting in quality variations, etc.

[0007] On the other hand, in the gas phase method, the primary particle size of the titanium oxide produced can be adjusted by adjusting the production conditions such as temperature. In addition, since the gas phase method does not use a solvent, titanium oxide is obtained as a powder, and the problems mentioned in the liquid phase method rarely occur. Furthermore, the gas phase method has the advantage that the reaction is carried out at a relatively higher temperature than the liquid phase method, so the resulting titanium oxide has high crystallinity.

[0008] However, in the gas phase method, the reaction is carried out at a higher temperature than in the liquid phase method. If the temperature in the reaction tube or in the cooling tube after the introduction of the cooling gas is too high, or if the residence time of the titanium oxide particles is too long, the titanium oxide particles will sinter excessively, making it difficult to obtain fine titanium oxide particles and resulting in a non-uniform particle size distribution. If the temperature of the reaction zone is too low to avoid sintering of the titanium oxide particles, the nucleation of titanium oxide will not be sufficient, making it difficult to obtain fine particles, or only titanium oxide with low crystallinity will be obtained. On the other hand, by immediately cooling the reaction gas with the cooling gas, the sintering of the titanium oxide particles can be suppressed, and fine titanium oxide particles can be obtained. If cooling is not performed immediately or if there is unevenness in the cooling, the particles will sinter unevenly, making it difficult to obtain uniform titanium oxide fine particles.

[0009] Patent Document 1 describes a method for producing titanium oxide particles, which is characterized by reacting a titanium halide gas with an oxidizing gas under specific conditions, with the aim of obtaining uniform titanium oxide particles by a gas phase method.

[0010] Furthermore, Patent Document 2 describes a method for producing titanium oxide particles, which is characterized by reacting TiCl4 vapor with hydrogen and oxygen, with the aim of obtaining uniform titanium oxide particles free of coarse particles by a gas phase method, and by having a small number of metal oxide particles with a diameter greater than 45 μm. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2022 / 244620 [Patent Document 2] Patent No. 4445972 specification Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, titanium oxide particles excellent in uniformity and dispersibility are desired, and the titanium oxide particles obtained by the gas phase method have the advantage of being superior in uniformity and dispersibility compared to those obtained by the liquid phase method.

[0013] According to Patent Document 1, titanium oxide particles with few coarse particles can be produced. In Patent Document 1, the amount of coarse particles exceeding 16 times D50 is quantified using a scanning electron microscope, and this quantification method captures and evaluates images in which the number of primary particles per field of view is 8,000 to 12,000, so coarse particles of a level of several tens of μm cannot be evaluated. In addition, since the particle size is determined by image analysis, the amount of particles coarsened by aggregation (secondary particles) cannot be evaluated.

[0014] Patent Document 2 refers to a method for synthesizing titanium oxide particles with few coarse particles having a particle size of about several tens of μm. However, since a mixture of hydrogen and oxygen is used as the oxidizing gas and hydrogen combustion and TiCl4 oxidation are carried out simultaneously, the reaction temperature tends to be high and the anatase content tends to be low.

[0015] The present disclosure provides titanium oxide particles having a high anatase content, a small number of coarse particles, and excellent uniformity and dispersibility, and a method for producing the same. [Means for solving the problem]

[0016] The present inventors have discovered that in a method for producing titanium oxide particles, which comprises reacting a raw material gas containing titanium tetrachloride and an inert gas with an oxidizing gas containing at least one of oxygen gas and water vapor and an inert gas, and cooling the reaction gas with a cooling gas, the above-mentioned problems can be solved by setting the gas flow rate ratio in the reaction step and the total gas amount relative to the TiO2 mass in the cooling step within predetermined ranges, and have completed the present invention.

[0017] The present disclosure includes the following aspects. [Aspect 1] A reaction step of generating a reaction gas by introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas, and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube; a cooling step of introducing a cooling gas to cool the reaction gas to obtain titanium oxide particles; A method for producing titanium oxide particles, comprising: The flow rate of G1 in the reaction step (F G1 ) vs. the flow rate of titanium tetrachloride in G1 (F G1T ) ratio F G1T / F G1 is 0.4 or more and less than 1.0, and the TiO2 mass (kg) and the total gas amount (m 3 ) ratio (TiO2 mass) / (total gas amount) is more than 0.21 kg / m 3 The method for producing titanium oxide particles is as follows. [Aspect 2] The flow rate of the titanium tetrachloride (F G1T ) / (flow rate of the water vapor (F G2W ) + the flow rate of the oxygen gas (F G2O 2. The method for producing titanium oxide particles according to claim 1, wherein the ratio of [Aspect 3] 3. The method for producing titanium oxide particles according to aspect 1 or 2, wherein a ratio of an amount of the cooling gas to a total amount of gas in the cooling step is 0.3 or more and 0.6 or less. [Aspect 4] Flow rate of G1 (F G1 ) / G2 flow rate (F G2 4. The method for producing titanium oxide particles according to any one of aspects 1 to 3, wherein the ratio of the ratio of the number of particles to the total number of particles is 0.3 or more and 1.2 or less. [Aspect 5] The method for producing titanium oxide particles according to any one of aspects 1 to 4, wherein a purging medium outlet is provided on an inner wall or an upper portion of a reaction tube, and in a cross section of the reaction tube perpendicular to a central axis of the reaction tube, a blowing angle α of the purging medium with respect to a line connecting the blowing port of the purging medium and the central axis of the reaction tube is 50° or more, and a blowing flow velocity of the purging medium is 35 m / s or more. [Aspect 6] The method for producing titanium oxide particles according to any one of aspects 1 to 5, wherein a ratio (S1 / S2) of a cross-sectional area (S1) of the inlet of the reaction tube to a sum (S2) of a cross-sectional area of ​​an outlet of an inlet tube of the raw material gas (G1) and the oxidizing gas (G2) is 1.0 or more and 10.0 or less. [Aspect 7] BET specific surface area is 15-40m 2 / g, an anatase content of 70% or more, and when placed in water at 25°C and pH 7 and subjected to water sieving by ultrasonic dispersion at an ultrasonic intensity of 55 W and 38 kHz for 5 minutes, the concentration of residue that did not pass through a sieve with openings of 45 μm is 100 ppm or less. [Aspect 8] The titanium oxide particles according to embodiment 7, wherein the Cl content of the titanium oxide particles is 0.20 mass % or less as measured by silver nitrate potentiometric titration. [Aspect 9] The titanium oxide particles according to aspect 7 or 8, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb, and Zr are each 50 ppm by mass or less, and the contents of Si and C are each 500 ppm by mass or less. [Aspect 10] A slurry comprising the titanium oxide particles according to any one of aspects 7 to 9. [Aspect 11] A dispersion comprising the titanium oxide particles according to any one of aspects 7 to 9. [Aspect 12] A composition comprising the titanium oxide particles according to any one of aspects 7 to 9. [Aspect 13] A dielectric material comprising the titanium oxide particles according to any one of aspects 7 to 9. Effect of the Invention

[0018] According to the present disclosure, it is possible to provide titanium oxide particles having a high anatase content, few coarse particles, and excellent uniformity and dispersibility, and a method for producing the same. The titanium oxide particles of the present disclosure can be suitably used as a slurry, a dispersion, a composition, and a dielectric raw material. [Brief description of the drawings]

[0019] [Figure 1] FIG. 2 is a schematic diagram showing the blowing angles of a cooling gas and a purge medium in a cross section of a reaction tube in one embodiment of a method for producing titanium oxide particles. [Diagram 2] FIG. 2 is a schematic diagram showing the blowing angles of a cooling gas and a purge medium in a vertical cross section of a reaction tube in one embodiment of a method for producing titanium oxide particles. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, embodiments of the present invention will be described, however, it should be understood that the present invention is not limited to these embodiments and that various applications are possible within the spirit and scope of the present invention.

[0021] In this disclosure, when "~" is used for a numerical range, the numerical values ​​at both ends are the upper and lower limits, respectively, and are included in the numerical range. When multiple upper or lower limits are listed, numerical ranges can be created from all combinations of the upper and lower limits. Similarly, when multiple numerical ranges are listed, separate numerical ranges can be created by individually selecting and combining the upper and lower limits from those numerical ranges.

[0022] Numerical values ​​of various measurements in this disclosure are defined to include significant figures unless otherwise specified or the context indicates otherwise. For example, 0 ppm means less than 0.5 ppm.

[0023] [Titanium oxide particles] In one embodiment, the titanium oxide particles have a BET specific surface area of ​​15 to 40 m 2 The titanium oxide particles have a molecular weight of 10000000 / g and an anatase content of 70% or more. When the particles are placed in water at 25°C and pH 7 and subjected to water sieving by ultrasonic dispersion at an ultrasonic intensity of 55 W and 38 kHz for 5 minutes, the concentration of residue that did not pass through a sieve with openings of 45 μm is 100 ppm or less.

[0024] (BET specific surface area) In one embodiment, the titanium oxide particles have a BET specific surface area of ​​15 to 40 m due to their excellent uniformity and dispersibility. 2 / g. The BET specific surface area is 15m 2 From the same viewpoint, if the BET specific surface area is 17 m 2 / g or more is preferable, and 20m 2 / g or more is more preferable. 2 If the BET specific surface area is less than 35 m 2 / g or less is preferable, and 30m 2 In the present disclosure, the BET specific surface area is measured by the method described in the Examples.

[0025] (Anatase content) In one embodiment, the anatase content (molar basis) of the titanium oxide particles is 70% or more, and preferably 75% or more. If the anatase content is 70% or more, high photoelectrochemical activity is exhibited. The upper limit of the anatase content is not particularly limited, but can be, for example, 100% or less, 99% or less, or 98% or less. In the present disclosure, the anatase content means the content of anatase type crystals in the titanium oxide particles, and is measured by the method described in the Examples.

[0026] (Residue concentration) In one embodiment, when titanium oxide particles are placed in water at 25°C and pH 7, and subjected to water sieving by ultrasonic dispersion at an ultrasonic intensity of 55 W and 38 kHz for 5 minutes, the concentration of residues that do not pass through a sieve with a mesh size of 45 μm is 100 ppm or less. If the residue concentration is 100 ppm or less, the amount of coarse particles is small, and the uniformity and dispersibility are excellent. From the same viewpoint, the residue concentration is preferably 80 ppm or less, more preferably 50 ppm or less. The lower limit of the residue concentration is not particularly limited, but can be 1 ppm or more, 2 ppm or more, or 5 ppm or more. In the present disclosure, the residue concentration is determined by the method described in the examples. Titanium oxide particles with few coarse particles are highly uniform and can meet the high quality required for titanium oxide particles, and are therefore particularly useful in a wide range of applications such as cosmetics, ultraviolet shielding materials, additives to silicone rubber, photocatalysts, solar cells, dielectric raw materials, and electrode material raw materials for Li-ion batteries.

[0027] (Tap density) The tap density of titanium dioxide particles is 0.20 g / cm 3 More than 0.50g / cm 3 The tap density is preferably 0.20 g / cm or less. 3 If the density is more than 0.25g / cm3, the density is high and it is advantageous in terms of transportation costs. From the same viewpoint, the tap density is 0.25g / cm3 3 More preferably, 0.30 g / cm 3 More preferably, the tap density is 0.50 g / cm 3 From the same viewpoint, the tap density is 0.45 g / cm or less, and the dispersibility in water is excellent. 3 Less than 0.40 g / cm is more preferable. 3 The following is even more preferred: In this disclosure, the tap density is measured by the method described in the Examples.

[0028] (pH) When titanium oxide particles are dispersed in water, the pH is preferably 1.0 to 5.0. When the pH is within the above range, the particles are stable in water and tend to maintain a dispersed state. From the same viewpoint, the pH is more preferably 2.0 to 4.0, and even more preferably 2.5 to 3.0.

[0029] (Chlorine (Cl) content) The Cl (chlorine atom) content of the titanium oxide particles is preferably 0.20% by mass or less. If the Cl content is 0.20% by mass or less, problems are unlikely to occur in the subsequent process when the titanium oxide particles are used as a raw material. For example, when titanium oxide particles with a Cl content exceeding 0.20% by mass are used as a raw material for BaTiO3 or the like, flux may be generated during firing. The molten flux is likely to be localized, and the localized portion may become more aggregated, resulting in quality variations between the localized portion and other portions. In addition, when the particles aggregate, the crystals of the BaTiO3 particles grow to become abnormal particles, which may reduce the dielectric properties of BaTiO3. From this viewpoint, the Cl content of the titanium oxide particles is more preferably 0.18% by mass or less, and even more preferably 0.16% by mass or less. The lower limit of the Cl content of the titanium oxide particles is not particularly limited, but may be 0.01% by mass or more, 0.02% by mass or more, or 0.05% by mass or more. In this disclosure, the Cl content is measured using silver nitrate potentiometric titration as described in the Examples.

[0030] (Content of other impurities) The contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr in the titanium oxide particles are preferably 50 mass ppm or less, more preferably 10 mass ppm or less. The contents of Si and C in the titanium oxide particles are preferably 500 mass ppm or less, more preferably 100 mass ppm or less. When titanium oxide particles with few impurities are used as a raw material, problems are unlikely to occur in the subsequent process. For example, when a dielectric is obtained using titanium oxide particles as a raw material, the deterioration of dielectric properties due to the presence of impurities is suppressed. In addition, when the titanium oxide particles are used for photocatalysis or solar cell applications, the decrease in transparency due to coloring by Fe is prevented or suppressed, and the decrease in function as a photocatalyst or solar cell due to lattice defects caused by Al, S, etc. is also prevented or suppressed. In the present disclosure, the contents of other impurities are measured by the method described in the examples.

[0031] [Slurry, Dispersion, Composition and Dielectric Raw Material] The slurry, dispersion, composition, and dielectric raw material in one embodiment contain the above-mentioned titanium oxide particles. The slurry is a mixture in which particles are mixed in a liquid, but often refers to a highly viscous fluid. The dispersion refers to a mixture in which solid particles are dispersed in a liquid, and includes low-concentration dispersions. The composition refers to a composition composed of a plurality of components. The dielectric raw material refers to a raw material for producing a dielectric. The slurry, dispersion, composition, and dielectric raw material in one embodiment are suitable for photocatalyst applications, solar cell applications, dielectric applications, and the like. Other applications of the slurry, dispersion, and composition containing titanium oxide particles are known. A known method can be used as a method for producing the slurry, dispersion, composition, and dielectric raw material using the titanium oxide particles of the present disclosure. The slurry, dispersion, composition, and dielectric raw material containing titanium oxide particles in one embodiment do not contain coarse particles, and therefore can improve the uniformity and quality of the final product. In particular, in thinning the dielectric of a multilayer ceramic capacitor, not containing coarse particles prevents short circuits and contributes to improving quality.

[0032] [Method of manufacturing titanium oxide particles] A method for producing titanium oxide particles according to one embodiment includes a reaction step in which a raw material gas (G1) containing titanium tetrachloride and an inert gas and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas are introduced into a reaction tube to generate a reaction gas, and a cooling step in which a cooling gas is introduced to cool the reaction gas to obtain titanium oxide particles, and the flow rate (F G1 ) vs. the flow rate of titanium tetrachloride in G1 (F G1T ) ratio F G1T / F G1 is 0.4 or more and less than 1.0, and the TiO2 mass (kg) and the total gas amount (m 3 ) ratio (TiO2 mass) / (total gas amount) is more than 0.21 kg / m 3 The following is the result.

[0033] (Reaction tube) The reaction tube may be a horizontal reaction tube, but a vertical reaction tube is preferred because it is easier to make the flow of various gases uniform, and a reaction tube with a circular cross section is preferred. In the case of a circular vertical reaction tube, a preheated raw material gas (G1) and an oxidizing gas (G2) are introduced from the top end of the heated reaction tube toward the bottom of the reaction tube through their respective supply pipes to generate a reaction gas. This process is called the reaction process. A cooling gas outlet is provided on the inner wall of the reaction tube, and the cooling gas is blown out from there and mixed with the reaction gas to cool the reaction gas. This process is called the cooling process.

[0034] The area from the raw material gas inlet to the cooling gas outlet in the reaction tube is called the reaction region, and the area from the cooling gas outlet to the exhaust outlet is called the cooling region. If there are multiple cooling gas outlets, the area from the raw material gas inlet to the first cooling gas outlet in the reaction tube is called the reaction region, and the area from the first cooling gas outlet to the exhaust outlet is called the cooling region.

[0035] The cooled titanium oxide particles and the remaining gas are discharged to the outside at the bottom of the reaction tube. The reaction gas may contain titanium oxide as a reaction product.

[0036] The raw material gas (G1) and the oxidizing gas (G2) are introduced from the inlet (end face side) of the reaction tube in the axial direction of the reaction tube. The ratio (S1 / S2) of the cross-sectional area (S1) of the reaction tube inlet (end face or cross section of the reaction tube) to the sum (S2) of the cross-sectional areas of the inlet of the raw material gas (G1) and the oxidizing gas (G2) is preferably 1.0 or more and 10.0 or less. By setting it in this range, the temperature or high temperature zone time of the reaction region can be made closer to uniform. In the present disclosure, the cross-sectional area (S1) of the reaction tube inlet is a cross-sectional area including the cross-sectional area (S2) of the inlet of the raw material gas (G1) and the oxidizing gas (G2). The ratio (S1 / S2) is more preferably 1.5 or more and 7.0 or less, even more preferably 3.0 or more and 7.0 or less, and particularly preferably 6.0 or more and 7.0 or less. The raw material gas (G1) and the oxidizing gas (G2) are preferably introduced in the gas flow direction in the reaction tube.

[0037] The temperature of the reaction zone into which the raw material gas (G1) and the oxidizing gas (G2) are introduced is preferably 800°C or more and less than 1,200°C, more preferably 800°C or more and less than 1,100°C. If the temperature of the reaction zone is 800°C or more, the reaction proceeds sufficiently, the particle size distribution of the titanium oxide particles becomes uniform, and the crystallinity can be increased. By increasing the temperature of the reaction zone, the reaction can be completed simultaneously with mixing, uniform nucleation can be promoted, and the reaction zone can be made small. On the other hand, if the temperature of the reaction zone is less than 1,200°C, particle growth proceeds moderately, but aggregation is unlikely to occur, so that coarse particles are unlikely to be generated. In addition, the anatase content can be increased by setting the temperature of the reaction zone to less than 1,200°C.

[0038] (Raw material gas (G1)) The raw material gas (G1) contains titanium tetrachloride (G1T) and an inert gas (G1I). The titanium tetrachloride in the raw material gas is in a gaseous state.

[0039] Flow rate of source gas (F G1 ) is 1.0Nm 3 / hr or more is preferable. 3 / hr shortens the residence time of the raw gas (G1) in the reaction zone, making it difficult for over-sintering and coarsening of titanium oxide to occur. G1 is 8.0Nm 3 / hr or more is preferable, 15.0Nm 3 / hr or more is more preferable. G1 The upper limit of can be appropriately set depending on the production conditions such as the size of the reaction tube and the temperature of the reaction zone, but is not particularly limited. For example, 3 / hr or less, 50Nm 3 / hr or less, or 40Nm 3 / hr or less.

[0040] Flow rate of titanium tetrachloride (F G1T ) is set at 1.0 Nm2 in order to increase the yield per hour. 3 / hr or more is preferable, and 8.0 Nm 3 / hr or more is preferable, 15.0Nm3 / hr or more is more preferable. From the viewpoint of suppressing the growth of sintered grains due to reaction heat, F G1T is preferably 50.0 Nm 3 / hr or less, more preferably 40.0Nm 3 / hr or less, more preferably 30.0 Nm 3 / hr or less.

[0041] Examples of the inert gas include nitrogen gas, helium gas, and argon gas, with nitrogen gas being preferred from an economical standpoint.

[0042] Flow rate of source gas (F G1 ) in G1 versus titanium tetrachloride (F G1T ) flow rate ratio F G1T / F G1 is greater than or equal to 0.4 and less than 1.0. G1T / F G1 By setting F to 0.4 or more, the reaction can be promoted, and titanium oxide particles having a low specific surface area can be obtained. From the same viewpoint, G1T / F G1 is preferably 0.45 or more, and more preferably 0.47 or more. G1T / F G1 By making F less than 1.0, it is possible to suppress the generation of coarse particles due to sintering of the titanium oxide particles obtained. G1T / F G1 is preferably 0.99 or less.

[0043] The raw material gas (G1) is introduced into the reaction tube at a temperature of preferably 600°C or higher and lower than 1,200°C, more preferably 700°C or higher and lower than 1,200°C, and further preferably 800°C or higher and lower than 1,200°C.

[0044] (Oxidizing gas (G2)) The oxidizing gas (G2) contains at least one of oxygen gas (G2O) and water vapor (G2W), and an inert gas (G2I).

[0045] Flow rate of oxidizing gas (F G2 ) is 1.0Nm 3 / hr or more is preferable. 3 / hr shortens the residence time of the oxidizing gas (G2) in the reaction zone, making it difficult for the titanium oxide particles to become oversintered and coarse. G2 is 15.0Nm 3 / hr or more is more preferable, 30.0Nm 3 / hr or more is more preferable. G2 The upper limit of can be appropriately set depending on the production conditions such as the size of the reaction tube and the temperature of the reaction zone, but is not particularly limited. For example, 3 / hr or less, 80Nm 3 / hr or less, or 60Nm 3 / hr or less.

[0046] The flow rate ratio of at least one of oxygen gas and water vapor in the oxidizing gas (G2) ((F G2W +F G2O ) / F G2 ) is preferably from 0.8 to 0.999, more preferably from 0.9 to 0.998, and even more preferably from 0.99 to 0.997.

[0047] Flow rate of titanium tetrachloride (F G1T ) vs. water vapor flow rate (F G2W ) and oxygen gas flow rate (F G2O ) and the ratio F G1T / (F G2W +F G2O ) is preferably 0.3 or more and 0.6 or less. G1T / (F G2W +F G2O ) is 0.3 or more, the yield can be increased. From the same viewpoint, F G1T / (F G2W +F G2O ) is more preferably 0.40 or more, and even more preferably 0.45 or more. G1T / (F G2W +F G2O ) is 0.6 or less, the number of nuclei generated from titanium oxide particles increases, making it easier to obtain ultrafine particles, and it also makes it easier to reduce oxygen defects and suppress the generation of colored titanium oxide. G1T / (FG2W +F G2O ) is more preferably 0.55 or less, and even more preferably 0.50 or less.

[0048] Flow rate of source gas (F G1 ) vs. the flow rate of oxidizing gas (F G2 ) ratio F G1 / F G2 is preferably 0.3 or more and 1.2 or less. G1 / F G2 By making F 0.3 or more, mixing of the raw material gas (G1) and the oxidizing gas (G2) can be promoted, and titanium oxide with a low specific surface area can be obtained. G1 / F G2 is more preferably 0.40 or more, and even more preferably 0.45 or more. G1 / F G2 By keeping F at 1.20 or less, the number of nuclei generated from titanium oxide particles increases, making it easier to obtain ultrafine particles. In addition, the high-temperature residence time is shortened, improving the uniformity of the primary particle size. G1 / F G2 is more preferably 0.55 or less, and even more preferably 0.50 or less.

[0049] The oxidizing gas (G2) is preferably introduced into the reaction tube at a temperature of 600°C or higher and lower than 1,200°C.

[0050] Examples of the inert gas include nitrogen gas, helium gas, argon gas, etc., and from an economical viewpoint, nitrogen gas is preferred. It is preferable that the inert gas in the oxidizing gas (G2) is the same chemical species as the inert gas in the raw material gas (G1).

[0051] (cooling gas) In one embodiment, a cooling gas outlet is provided on the inner wall of the reaction tube, and the cooling gas is blown out and mixed with the reaction gas to cool the reaction gas.

[0052] The cooling gas may be, for example, air, nitrogen gas, or carbon monoxide. From the viewpoint of enhancing the cooling effect, the temperature of the cooling gas is preferably 0° C. to 100° C., more preferably 10° C. to 90° C. Sprayed water may also be used in combination with the cooling gas.

[0053] The blowing angle γ of the cooling gas Q (see FIG. 1) is defined as the angle at which the cooling gas Q is blown out (the angle of the blowing outlet 3 of the cooling gas Q with respect to the central axis 4 direction) in a cross section perpendicular to the central axis 4 (flow direction of the reaction gas) of the reaction tube 1, when the line connecting the blowing outlet 3 of the cooling gas Q and the central axis 4 of the reaction tube 1 is set to 0°, and is preferably 0° or more and less than 50°. By making the angle γ 0° or more and less than 50°, the cooling gas can be made to flow near the center of the reaction tube, and can be sufficiently mixed with the reaction gas to obtain a high cooling effect. From the same viewpoint, the angle γ is more preferably 0° or more and 30° or less.

[0054] The blowing angle δ of the cooling gas Q (see FIG. 2) is preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more, in a vertical cross section including the central axis of the reaction tube 1 (flow direction of the reaction gas G1), when the flow direction of the reaction gas along the central axis of the reaction tube 1 is set to 0°. The blowing angle δ of the cooling gas Q is preferably 90° or less. By setting the blowing angle δ of the cooling gas Q to such an angle, a high cooling effect can be obtained.

[0055] The number of cooling gas outlets is one or more, preferably two or more, from the viewpoint of promoting mixing of the cooling gas and the reaction gas. From the same viewpoint, the number of cooling gas outlets may be one, two or more in the same cross section of the reaction tube. The number of cooling gas outlets may be one, two or more in the same vertical cross section of the reaction tube along the central axis of the reaction tube.

[0056] (Purge medium) A purging medium outlet may be provided on the inner wall or upper part of the reaction tube, and the purging medium may be introduced through the outlet. By flowing the purging medium while swirling along the inner wall of the reaction tube, adhesion of titanium oxide particles to the inner wall of the reaction tube can be prevented. The shape of the purging medium outlet may be, for example, a single hole or a slit.

[0057] If the generated titanium oxide particles adhere to and remain on the inner wall of the reaction tube, they will become coarse due to sintering grain growth. If the coarse particles detach from the inner wall and are mixed into the titanium oxide particles obtained as the product, this can cause the particle size distribution to become non-uniform. By introducing a purging medium, it is possible to prevent the titanium oxide particles from adhering to and remaining on the inner wall of the reaction tube. The purging medium can be introduced continuously or intermittently.

[0058] The purge medium may be a gas or a liquid. Examples of the purge medium include air, nitrogen gas, carbon monoxide gas, and sprayed water. The temperature of the purge medium is preferably 0°C to 100°C, and more preferably 10°C to 90°C. The temperature of the purge medium is preferably not higher than the temperature of the cooling gas. This can enhance the cooling effect of the cooling gas.

[0059] The blowing angle α of the purge medium P (see FIG. 1) is defined as the angle at which the purge medium P is blown out (the angle of the blowing port 5 of the purge medium P relative to the central axis 4 direction) in a cross section perpendicular to the central axis 4 (flow direction of the reaction gas) of the reaction tube 1, when the line connecting the blowing port 5 of the purge medium P and the central axis 4 of the reaction tube 1 is set to 0°, and is preferably 45° or more. By making the angle α 45° or more, the purge medium can be rotated near the inner wall of the reaction tube, and the adhesion of titanium oxide to the inner wall of the reaction tube can be effectively prevented. From the same viewpoint, the angle α is preferably 50° or more. The angle α is less than 90°.

[0060] The blowing angle β of the purging medium P (see FIG. 2) is preferably 60° or more, more preferably 70° or more, and even more preferably 80° or more, in a vertical cross section including the central axis of the reaction tube 1 (flow direction of the reaction gas G1), when the flow direction of the reaction gas along the central axis of the reaction tube 1 is set to 0°. The blowing angle β of the purging medium P is preferably 90° or less. By setting the blowing angle β of the purging medium P at such an angle, adhesion of titanium oxide to the inner wall of the reaction tube can be effectively prevented.

[0061] The number of outlets for the purge medium is preferably one or more, more preferably two or more, from the viewpoint of preventing adhesion of titanium oxide particles to the inner wall of the reaction tube. From the same viewpoint, the number of outlets for the purge medium is preferably one or more, more preferably two or more, in the same cross section of the reaction tube. In general, the number of outlets per circumference of the cross section of the reaction tube can be reduced as the angle α increases or the flow rate of the purge medium increases. The number of outlets for the purge medium may be one, two or more, along the central axis of the reaction tube in the same vertical cross section of the reaction tube. The outlet for the purge medium may be arranged in a spiral shape on the inner wall of the reaction tube. The outlet for the purge medium is installed in the reaction zone, and preferably also in the cooling zone. It is preferable that a swirling flow of the purge medium is formed along the inner wall of the reaction tube in both the reaction zone and the cooling zone.

[0062] From the viewpoint of effectively preventing the generated titanium oxide particles from adhering to the inner wall of the reaction tube, the blowing flow velocity of the purging medium is preferably 35 m / s or more, more preferably 50 m / s or more, and even more preferably 55 m / s or more. In the present disclosure, the blowing flow velocity of the purging medium is determined by the flow rate (m 3 / s) is calculated by dividing the cross-sectional area of ​​the purge medium outlet (m 2 ) divided by (m / s).

[0063] (Titanium oxide mass / total gas volume) In one embodiment, the mass of titanium oxide (kg) after the introduction of the cooling gas and the total gas amount (m 3) ratio (TiO2 mass) / (total gas amount) is greater than 0.21 kg / m 3 The mass of titanium oxide is calculated assuming that all the titanium tetrachloride introduced has become titanium oxide, that is, it is defined as the mass of titanium tetrachloride introduced (kg) x 79.87 / 189.71. Total gas amount = gas amount remaining after reaction x temperature correction (based on the temperature of the reaction area) + amount of purge medium introduced + amount of cooling gas introduced, and the amount of gas remaining after reaction = amount of gas generated (Cl component) + amount of remaining oxidizing gas + amount of inert gas. (TiO2 mass) / (total gas amount) is 0.21 kg / m 3 If the amount is less than 0.18 kg / m, the occurrence of agglomeration during the cooling process can be suppressed. From the same viewpoint, (TiO2 mass) / (total gas amount) is 0.18 kg / m 3 Less than 0.15kg / m is preferable. 3 From the viewpoint of obtaining titanium oxide, the ratio (mass of TiO2) / (total amount of gas) is more than 0 and is preferably 0.10 kg / m 3 The above is preferred.

[0064] (cooling gas volume / total gas volume) The amount of cooling gas (m 3 ) / total gas volume (m 3 ) is preferably 0.3 or more and 0.6 or less. When the ratio is 0.3 or more, cooling is sufficient and coarse particles are unlikely to be generated. From the same viewpoint, the ratio is preferably 0.40 or more, and more preferably 0.45 or more. When the ratio is 0.6 or less, excessive cooling gas is prevented from flowing back into the reaction region, and the reaction can proceed smoothly. From the same viewpoint, the ratio is preferably 0.58 or less, and more preferably 0.56 or less.

[0065] (Dechlorination process) The produced titanium oxide particles are preferably dechlorinated in a dechlorination step. Dechlorination of titanium oxide particles by heating is preferably performed by heating the titanium oxide particles to a temperature of 200°C to 550°C, preferably 250°C to 450°C, while contacting the titanium oxide particles with steam, so that the mass ratio of water to titanium oxide particles (mass of steam / mass of titanium oxide particles) is 0.01 or more, preferably 0.04 or more. By setting the temperature to 550°C or less, sintering of the titanium oxide particles can be suppressed and the primary particle size can be made uniform. By setting the temperature to 200°C or more, the efficiency of dechlorination can be increased. If the mass ratio of water to titanium oxide particles is 0.01 or more, particle growth can be effectively suppressed. The mass ratio of water to titanium oxide particles is preferably 0.01 to 3, more preferably 0.05 to 2, and even more preferably 0.2 to 1.8.

[0066] The water vapor is preferably used by mixing with a gas that plays a role in efficiently transferring chlorine separated from the titanium oxide particles to the outside of the system, for example, air. When air is used, the water vapor is preferably contained in the air at 0.1 volume % or more, more preferably 5 volume % or more, and even more preferably 10 volume % to 80 volume %. The air containing water vapor is preferably heated to 200°C to 1,000°C, more preferably 450°C to 850°C.

[0067] As a method for transferring the chlorine removed from the titanium oxide particles to the outside of the system, a method of reducing the pressure inside the container used for dechlorination can be mentioned. The degree of reduced pressure inside the container is preferably 0.5 kPa or more, more preferably 0.5 kPa or more and 3.5 kPa or less. In the present disclosure, the degree of reduced pressure is the pressure difference between the pressure inside the reduced pressure container and the atmospheric pressure.

[0068] Since the titanium oxide particles of the present disclosure have almost no chlorine inside the particles and most of the chlorine is present on the particle surface, it is possible to reduce the chlorine content by a wet method, for example, by removing the chlorine by washing with water. As a wet method, for example, there is a method in which the titanium oxide particles are suspended in pure water and the chlorine that has migrated to the liquid phase is separated outside the system using an ultrafiltration membrane, a reverse osmosis membrane, a filter press, or the like. EXAMPLES

[0069] Examples and comparative examples will be specifically described below, but the present invention is not limited to these in any way.

[0070] The physical properties of the titanium oxide particles were measured as follows.

[0071] (1)BET specific surface area In accordance with JIS R 1626:1996, a fully automatic BET specific surface area measuring device ("Macsorb (trademark) HM model-1208", manufactured by Mountec Co., Ltd.) was used. The sample was heated to 180°C as a pretreatment, and nitrogen gas was passed through it for 20 minutes. The BET specific surface area was measured by the BET three-point method using nitrogen gas as the adsorbate. The applicable range of the BET method was P / P0 = 0.00 to 0.95.

[0072] (2) Anatase content The content of anatase crystals in titanium oxide particles (anatase content) was measured by powder X-ray diffraction. Specifically, X-ray diffraction measurement was performed on dried titanium oxide particles using a measuring device "X'pertPRO" manufactured by PANalytical Co., Ltd., a copper target, and Cu-Kα1 radiation under the conditions of tube voltage 45 kV, tube current 40 mA, measurement range 2θ = 10 to 80 deg, sampling width 0.0167 deg, and scanning speed 0.0192 deg / s. The peak height (Ha) of the maximum peak corresponding to anatase crystals, the peak height (Hb) of the maximum peak corresponding to brookite crystals, and the peak height (Hr) of the maximum peak corresponding to rutile crystals were calculated, and the content of anatase crystals in titanium oxide particles (anatase content) was calculated by the following calculation formula. Anatase content (%) = {Ha / (Ha+Hb+Hr)} x 100

[0073] (3) Residue (coarse particles) concentration 300 g of the sample was showered on a mesh with 45 μm openings at a water pressure of 300 ± 20 kPa until it became transparent. Then, it was placed in pure water at 25 ° C and pH 7, and sieved by ultrasonic dispersion for 5 minutes at an ultrasonic intensity of 55 W and 38 kHz using a tabletop ultrasonic cleaner (Sonocleaner, Kaijo Co., Ltd.). The residue concentration was calculated by dividing the mass of the residue remaining on the sieve by the total amount of the sample.

[0074] (4) Tap density Titanium oxide particles were placed in a cup and tapped for 3 minutes, then transferred to a 100 mL container. The tap density (g / cm) was calculated from the mass of titanium oxide particles in the container. 3 ) was calculated.

[0075] (5) pH A 10% suspension of titanium oxide particles was prepared according to JIS K 5101-17-2: 2004, and the pH of the suspension was measured. The suspension was prepared using water as the dispersion medium, without using a wetting agent.

[0076] (6) Chlorine (Cl) content The Cl content in the titanium oxide particles was measured by silver nitrate potentiometric titration. Specifically, 0.5 g of titanium oxide particles was weighed. Next, a silver nitrate solution (concentration: 0.02 mol) was dropped into the solution of the titanium oxide particles, and the mass of chlorine atoms in the solution was obtained by measuring the potential difference, and the chlorine content (mass%) was calculated.

[0077] (7) Content of other impurities The method for measuring each impurity is as follows. Fe: Atomic absorption spectrometry (Hitachi High-Tech Z-2300 atomic absorption spectrophotometer) Al, Si: X-ray fluorescence analysis (XRF) (Simultex 10, manufactured by Rigaku Electric Co., Ltd.) C, S: High-frequency induction furnace combustion and infrared absorption method Na, Ni, Cr, Nb, Zr: Inductively Coupled Plasma-Mass Spectrometry

[0078] Example 1 <1st process> In a vertical reaction tube with a circular cross section, a raw material gas (G1) consisting of titanium tetrachloride (purity of titanium tetrachloride is 99.99 mass% or more) and nitrogen gas was heated to 965°C and a flow rate of 26.2 Nm 3 / hr, an oxidizing gas (G2) consisting of oxygen gas, water vapor, and nitrogen gas was heated to 845°C and had a flow rate of 55.4 Nm 3 / hr from the top of the reaction tube to generate the reaction gas. The purge medium (nitrogen gas) was introduced from the inner wall of the reaction tube in the reaction zone. In the cooling zone, the cooling gas (air) was introduced at the rate of TiO2 mass (kg) / total gas amount (m 3 ) is 0.19 kg / m 3 The titanium oxide particle raw material was obtained by introducing the titanium oxide particle raw material into the reaction tube so that the titanium oxide particle raw material was collected at the bottom of the reaction tube using a polytetrafluoroethylene bag filter. The production conditions, including other conditions, are shown in Table 1.

[0079] <Second process> The obtained titanium oxide particle raw material was passed through a cylindrical rotary heating furnace, and dechlorinated at a mass ratio of steam mixed with air to titanium oxide raw material (mass of steam / mass of titanium oxide particle raw material) of 0.06 at a temperature of 450°C to obtain titanium oxide particles. Various physical properties of the obtained titanium oxide particles were measured. The physical property evaluation results are shown in Table 2.

[0080] Examples 2 to 4, Comparative Examples 1, 2, 4 to 6 The first step was carried out in the same manner as in Example 1 to obtain a titanium oxide particle raw material, except that the conditions of the raw material gas (G1), oxidizing gas (G2), cooling gas, purge medium, and total gas amount in the first step were changed. The conditions are shown in Table 1. The second step was carried out in the same manner as in Example 1 to obtain titanium oxide particles. The physical property evaluation results are shown in Table 2. Comparative Example 1 was produced according to the method of Example 5 of Patent Document 1 (WO 2022 / 244620), and Comparative Example 2 was produced according to the method of Example 3 of Patent Document 1 (WO 2022 / 244620).

[0081] Comparative Example 3 Titanium oxide particles were produced according to the method of Example A4 in Japanese Patent No. 4445972. The physical property evaluation results are shown in Table 2.

[0082] [Table 1]

[0083] [Table 2]

[0084] As shown in Table 2, in Examples 1 to 4, titanium oxide particles were obtained that had a BET specific surface area within the prescribed range, a high anatase content, and a low residue concentration. In Comparative Example 1, the ratio of TiO2 mass (kg) / total gas volume (m 3 ) is 0.21kg / m 3 In Comparative Examples 2 and 4 to 6, F G1T / F G1 Since the BET specific surface area was low at less than 0.4, the BET specific surface area was high.

[0085] In Comparative Example 3, a mixed gas of hydrogen and oxygen was used as the oxidizing gas, and the combustion of hydrogen and the oxidation of TiCl4 were carried out simultaneously, resulting in a high reaction temperature and a low anatase content.

[0086] According to the present disclosure, there are provided titanium oxide particles having fewer coarse particles and a higher anatase content than conventional titanium oxide particles having a comparable BET specific surface area, and a method for producing the same. [Industrial Applicability]

[0087] The titanium oxide particles of the present disclosure are suitable for photocatalyst applications, solar cell applications, dielectric applications, and the like, and since they do not require a crushing process or can be carried out using extremely minor equipment, they are of extremely great practical value industrially. [Explanation of symbols]

[0088] 1 Reaction tube 3 Cooling gas outlet 4. Reactor tube center 5 Purge medium outlet G1 Raw material gas G2 Oxidizing gas P Purging medium Q Cooling gas α Purge medium blowing angle (in a plane perpendicular to the reaction gas flow direction) β Purge medium blowing angle (within the plane including the reaction gas flow direction) γ Cooling gas blowing angle (in a plane perpendicular to the reaction gas flow direction) δ Cooling gas blowing angle (within the plane including the reaction gas flow direction)

Claims

1. A reaction step of generating a reaction gas by introducing a raw material gas (G1) containing titanium tetrachloride and an inert gas, and an oxidizing gas (G2) containing at least one of oxygen gas and water vapor and an inert gas into a reaction tube; a cooling step of introducing a cooling gas to cool the reaction gas to obtain titanium oxide particles; A method for producing titanium oxide particles, comprising: The flow rate of G1 in the reaction step (F Ｇ１ ) vs. the flow rate of titanium tetrachloride in G1 (F Ｇ１Ｔ ) ratio F Ｇ１Ｔ / F Ｇ１ is 0.4 or more and less than 1.0, and TiO after the introduction of the cooling gas in the cooling step ２ Mass (kg) and total gas volume (m ３ ) ratio (TiO ２ Mass) / (total gas amount) is greater than 0.21 kg / m ３ The method for producing titanium oxide particles is as follows.

2. The flow rate of the titanium tetrachloride (F Ｇ１Ｔ ) / (flow rate of the water vapor (F Ｇ２Ｗ ) + the flow rate of the oxygen gas (F Ｇ２Ｏ 2. The method for producing titanium oxide particles according to claim 1, wherein the ratio of the y-axis direction to the y-axis direction is 0.3 or more and 0.6 or less.

3. 3. The method for producing titanium oxide particles according to claim 1, wherein a ratio of an amount of the cooling gas to a total amount of gas in the cooling step is 0.3 or more and 0.6 or less.

4. Flow rate of G1 (F Ｇ１ ) / G2 flow rate (F Ｇ２ 3. The method for producing titanium oxide particles according to claim 1, wherein the ratio of the y-axis of the titanium oxide particle to the y-axis of the titanium oxide particle is 0.3 or more and 1.2 or less.

5. 3. The method for producing titanium oxide particles according to claim 1, wherein an outlet for a purging medium is provided on an inner wall or an upper portion of a reaction tube, and in a cross section of the reaction tube perpendicular to a central axis of the reaction tube, a blowing angle α of the purging medium with respect to a line connecting the outlet for the purging medium and the central axis of the reaction tube is 50° or more, and a blowing flow velocity of the purging medium is 35 m / s or more.

6. 3. The method for producing titanium oxide particles according to claim 1, wherein a ratio (S1 / S2) of a cross-sectional area (S1) of the inlet of the reaction tube to a sum (S2) of cross-sectional areas of outlets of inlet tubes for the raw material gas (G1) and the oxidizing gas (G2) is 1.0 or more and 10.0 or less.

7. BET specific surface area is 15 to 40 m ２ The titanium oxide particles have an anatase content of 70% or more and, when placed in water at 25° C. and pH 7 and subjected to water sieving by ultrasonic dispersion at an ultrasonic intensity of 55 W and 38 kHz for 5 minutes, the concentration of residue that did not pass through a sieve with openings of 45 μm is 100 ppm or less.

8. 8. The titanium oxide particles according to claim 7, wherein the Cl content of the titanium oxide particles is 0.20% by mass or less as measured by silver nitrate potentiometric titration.

9. 9. The titanium oxide particles according to claim 7 or 8, wherein the contents of Na, Al, S, Fe, Ni, Cr, Nb and Zr are each 50 ppm by mass or less, and the contents of Si and C are each 500 ppm by mass or less.

10. A slurry comprising the titanium oxide particles according to claim 7 or 8.

11. A dispersion comprising the titanium oxide particles according to claim 7 or 8.

12. A composition comprising the titanium oxide particles according to claim 7 or 8.

13. A dielectric material comprising the titanium oxide particles according to claim 7 or 8.

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