Method for controlling the particle size of titanium dioxide

Abstract

The present application relates to the production technical field, provide a kind of control method of titanium dioxide powder particle, including the following steps: metatitanic acid crude product is made into pulp after calcination, then carries out roll grinding, beating, colloid mill, ceramic mill, and then after screen, sand mill, again after screening, after cyclone separation, it is obtained intermediate material, in beating process, modified dispersing agent and lye are added to slurry;Finally, tetraethyl orthosilicate is added to intermediate material, reacts for a period of time, then continue to add sodium hexametaphosphate and zirconium sulfate to slurry, carries out surface coating treatment;The control method of the present application can obtain the titanium dioxide powder particle of uniform particle size and high whiteness quality.

Description

Technical Field

[0001] This invention relates to the field of production technology, and more specifically, to a method for controlling powder particles in titanium dioxide. Background Technology

[0002] Titanium dioxide is an important chemical material widely used in various fields. Its performance and quality are closely related to its particle size. The particle size of titanium dioxide refers to the size of the titanium dioxide particles, which is mainly measured by a laser particle size analyzer.

[0003] The titanium dioxide production process has extremely high requirements for particle fineness and particle size distribution. To ensure the desired particle size distribution, the crushing, grinding, and classification control of the intermediate powder is crucial. The intermediate powder is commonly represented by the D50 value (median diameter or median particle size), which is the particle size corresponding to 50% of the cumulative particle size distribution of the sample. Physically, it means that 50% of the particles are larger than this value, and 50% are smaller. A uniform and concentrated particle size distribution in the classified slurry is a prerequisite for the quality of the surface treatment coating and has a vital impact on product quality.

[0004] Therefore, controlling the particle size of titanium dioxide is a core and crucial step in controlling the type and quality grade of finished titanium dioxide products. How to control the particle size and optimize the particle size distribution of titanium dioxide has become an urgent problem to be solved. Summary of the Invention

[0005] To better control the particle size of titanium dioxide, this invention focuses on research into aspects such as raw material intake, slurry dispersion, wet milling process flow, and grinding media. Through production practice, the optimal process control conditions for raw material grinding have been determined. Specifically, the purpose of this invention is to provide a method for controlling the particle size of titanium dioxide, which can yield titanium dioxide particles with uniform particle size and high whiteness.

[0006] The embodiments of the present invention are achieved through the following technical solutions:

[0007] A method for controlling powder particles in titanium dioxide includes the following steps:

[0008] S1. Take crude metatitanic acid with a phosphorus content of 700ppm to 2000ppm, crush it in a crusher, add H3PO4 solution, and stir for 30 minutes to make a slurry with a concentration of 500 to 600 g / L; wherein, the amount of H3PO4 solution added is 0.1% to 0.2% of the mass of titanium dioxide in metatitanic acid, based on phosphorus pentoxide.

[0009] S2. The slurry is calcined, then first subjected to roller milling (80-200 r / min), followed by low-speed beating (20-50 r / min). This helps to avoid the generation of bubbles and ensures uniform mixing of the materials. During the low-speed beating process, a modified dispersant and alkali solution are added to the slurry. Then, it is successively treated by colloid milling and ceramic milling. After treatment, it is sieved, sand-milled, and sieved again. After separation by hydrocyclone, intermediate material is obtained. The intermediate material that has passed the grinding test is used for surface treatment. The modified dispersant is a copolymer synthesized by solution polymerization of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate as monomers.

[0010] Titanium dioxide particles treated with modified dispersants exhibit better uniformity and dispersion performance. This is mainly due to the steric hindrance effect of the hydrophilic polyether chains in polyethylene glycol monomethyl ether (PEGMEI) during dispersion, resulting in a more complete coating layer of the modified dispersant on the particle surface and a stronger dispersion and viscosity-reducing effect. The presence of acrylic acid and maleic acid enhances the adsorption force of PEGMEI, increasing its hydrophilic chains and further strengthening steric hindrance, thereby enhancing its dispersion ability and resulting in a uniform particle size distribution without excessively large or small particle agglomerates.

[0011] S3. Add tetraethyl orthosilicate to the intermediate material obtained in S2 and react for a period of time to coat the surface of titanium dioxide with a dense silica film using the sol-gel method. The coated intermediate material shows lower acid solubility and activity, and higher density and weather resistance. Then, sodium hexametaphosphate and zirconium sulfate are added for surface coating treatment. Finally, the coated intermediate material is washed with water to obtain a filter cake. Then, flash evaporation and steam pulverization are performed to obtain the finished titanium dioxide product.

[0012] After the above-mentioned coating treatment, the present invention forms a uniform and continuous dense protective film on the surface of titanium dioxide, which can not only effectively shield metal ion impurities, improve the whiteness of titanium dioxide, inhibit the excessive growth of TiO2 grains, and ensure the particle size distribution of titanium dioxide, but also reduce the surface energy of titanium dioxide, improve the dispersibility of titanium dioxide, and exhibit better optical properties, whiteness, brightness and weather resistance.

[0013] Furthermore, in S1, the phosphorus content in the crude product is 800 ppm to 1000 ppm.

[0014] Further, in S2, the method for preparing the modified dispersant is as follows:

[0015] (1) After mixing maleic acid, polyethylene glycol monomethyl ether acrylate and initiator, add organic solvent to dissolve them completely. Then, introduce nitrogen gas into the reaction system and heat it to 70-90°C for a period of time.

[0016] (2) After dissolving acrylic acid and initiator in an organic solvent and mixing them, slowly add them dropwise to the reaction system of step (1). After reacting for a period of time, evaporate the organic solvent. Dissolve the obtained product in water and add an appropriate amount of alkali solution to adjust the pH to 6-7. After purification, the modified dispersant is obtained.

[0017] Further, in step (1), the molar amount of the initiator is 0.5% to 2% of the total molar amount of maleic acid and polyethylene glycol monomethyl ether acrylate; in step (2), the molar amount of the initiator is 0.1% to 0.5% of the molar amount of acrylic acid.

[0018] Further, in step (1), the amount of organic solvent used is 50% to 100% of the total weight of the reactants (i.e., maleic acid, polyethylene glycol monomethyl ether acrylate and initiator); in step (2), the amount of organic solvent used is 50% to 100% of the total weight of the reactants (i.e., acrylic acid and initiator).

[0019] Further, the molar ratio of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate is 2-8:3-9:10-15; preferably, it is 5:6:10.

[0020] Furthermore, the organic solvent is ethyl acetate or propylene glycol methyl ether.

[0021] Furthermore, the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, or dimethyl azobisisobutyrate.

[0022] Further, in S2, 2.0‰ to 3.0‰ of a modified dispersant is added to the resulting slurry, and the pH value is adjusted to 9.5-10 with dilute alkali.

[0023] Furthermore, in S2, the calcination temperature is 935–945°C. Under the salt treatment method of this invention, the titanium dioxide particles obtained by calcination at 935–945°C are approximately spherical in shape, with relatively uniform particle size and a titanium dioxide particle diameter of up to 260 nm. The particle size distribution is narrow, the tinting strength is greater than 1500, and the blue phase is greater than 40. Otherwise, if the temperature is too low, the particles are small and the specific surface area is small, making it impossible to obtain relatively uniform medium-sized powder particles. If the calcination temperature is too high, the particles will sinter and agglomerate, resulting in inconsistent growth rates of titanium dioxide particles, leading to a wider particle size distribution and poorer pigment performance.

[0024] The amount of grinding media in ceramic mills and sand mills has a significant impact on the particle size. Larger grinding media diameters result in coarser slurry particles, but also increase production capacity; conversely, smaller grinding media diameters result in finer slurry particles, but decrease production capacity. To balance production capacity and quality, in S2, the ceramic balls used in the ceramic mill are selected in sizes of 10mm, 8mm, 6mm, and 4mm, with an addition ratio of 2:2:2:1. The slurry concentration is 500-600g / L, and the viscosity is controlled between 80mpa·s and 100mpa·s. Regular replenishment at 60-80mg / ton yields the best grinding effect. The slurry is then sieved through a 300-350 mesh screen, ensuring all residue passes through.

[0025] In addition, during sand milling in S2, a Netzsch 1000L sand mill is selected, and the grinding media consists of zirconia beads or zirconium oxide beads with a diameter of 5-10mm. The one-time filling amount is 2300kg. Preferably, 6mm, 8mm, and 10mm zirconium beads are selected, with an addition ratio of 3:2:1. The slurry concentration is controlled at 500-600g / L, and the viscosity is controlled at 20mpa·s to 50mpa·s. Regular replenishment is made at 80mg to 120mg / ton, and the particle size of the slurry after sand milling is tested to ensure it meets the production quality requirements. During sand milling, the rotation speed is adjusted to 1000-2000r / min, and stirring is performed for 0.5-1h. Furthermore, two-stage sand milling is performed. The first-stage mill uses 4-6mm zirconium beads as the grinding media, and the second-stage mill uses 6-10mm zirconium oxide beads as the grinding media. This combination yields the best grinding effect and the most uniform and concentrated particle size distribution of the resulting medium powder.

[0026] Furthermore, in S2, before sand milling, the material is passed through a 300-350 mesh sieve; after sand milling, it is passed through a 450-550 mesh sieve.

[0027] Furthermore, in S3, the amount of tetraethyl orthosilicate added is 1-5% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 1-3% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.5-1% of the mass of the intermediate material.

[0028] Furthermore, in S3, the surface coating process is controlled at 50-70℃. The specific operation is as follows: Tetraethyl orthosilicate is added to the intermediate material at a uniform rate, and then aged for 0.5-1h; then sodium hexametaphosphate and zirconium sulfate are added at a uniform rate. During this process, acid or alkali solution is added dropwise to control the pH of the system between 6.5 and 8.5, and aged for 0.5-1h. After aging, it is washed and dried.

[0029] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0030] This invention controls titanium dioxide production from aspects such as raw material intake, slurry dispersion, wet milling process flow, and grinding media to obtain titanium dioxide particles with uniform particle size and high whiteness. More specifically, this invention improves the uniformity and dispersion of titanium dioxide particles by adding a modified dispersant during the grinding process, and performs surface coating treatment on the titanium dioxide particles to form a uniform and continuous dense protective film on the surface of the titanium dioxide. This film not only effectively shields metal ion impurities, improves the whiteness of titanium dioxide, inhibits excessive growth of TiO2 grains, and ensures the particle size distribution of titanium dioxide, but also reduces the surface energy of titanium dioxide, improves its dispersibility, and exhibits better optical properties, whiteness, brightness, and weather resistance. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a particle size distribution diagram of the titanium dioxide product obtained in Example 1 of the present invention;

[0033] Figure 2 This is a particle size distribution diagram of the titanium dioxide product obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0035] Example 1

[0036] A method for controlling powder particles in titanium dioxide includes the following steps:

[0037] S1. Take crude metatitanic acid with a phosphorus content of 1000ppm, crush it in a crusher, add 0.1% H3PO4 solution (calculated as P2O5, which is 0.1% of the mass of titanium dioxide in metatitanic acid), and stir for 30 minutes to make a slurry with a concentration of 550g / L.

[0038] S2. The slurry is calcined at 940℃, then rolled at 150 r / min, and then slowly pulped at 35 r / min. During the slow pulping process, 2‰ of a modified dispersant is added to the slurry, and the pH is adjusted to 9.8 with sodium bicarbonate solution. Then, it is sequentially processed by a colloid mill (2000 r / min) and a ceramic mill. The ceramic mill balls are selected with sizes of 10 mm, 8 mm, 6 mm, and 4 mm, and the addition ratio is... The ceramic slurry concentration is 550 g / L, and the viscosity is controlled at 90 MPa·s, with 70 mg / ton added regularly. The slurry is then sieved through a 330-mesh screen until all residue is passed through. It then undergoes two-stage sand milling: the first-stage mill uses 4mm and 6mm zirconium beads at a ratio of 3:2, and the second-stage mill uses 6mm, 8mm, and 10mm zirconium beads at a ratio of 3:2:1. The slurry is then sieved through a 500-mesh screen and separated by a hydrocyclone to obtain the intermediate material.

[0039] The modified dispersant is a copolymer synthesized by solution polymerization of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate monomers in a molar ratio of 5:6:10. Specifically, the preparation method of the modified dispersant is as follows: (1) Maleic acid, polyethylene glycol monomethyl ether acrylate, and azobisisobutyronitrile are mixed, and ethyl acetate is added to dissolve them completely. Then, nitrogen gas is introduced into the reaction system and the temperature is raised to 80°C, and the reaction is carried out for 0.5 h. (2) Acrylic acid and azobisisobutyronitrile are dissolved in ethyl acetate and mixed evenly. Then, the mixture is slowly added dropwise to the reaction system of step (1). After reacting for 0.5 h, the ethyl acetate is evaporated. Ester; the obtained product is dissolved in water and an appropriate amount of sodium bicarbonate is added to adjust the pH to 6.5. After purification, the modified dispersant is obtained; wherein, in step (1), the molar amount of the initiator is 1% of the total molar amount of maleic acid and polyethylene glycol monomethyl ether acrylate; in step (2), the molar amount of the initiator is 0.3% of the molar amount of acrylic acid; in step (1), the amount of organic solvent is 90% of the total weight of the reactants (i.e., maleic acid, polyethylene glycol monomethyl ether acrylate and initiator); in step (2), the amount of organic solvent is 80% of the total weight of the reactants (i.e., acrylic acid and initiator);

[0040] S3. At 60℃, tetraethyl orthosilicate is added uniformly to the intermediate material obtained in S2, and then aged for 0.5 h. Then, sodium hexametaphosphate and zirconium sulfate are added uniformly. During this process, hydrochloric acid or sodium hydroxide is added dropwise to control the pH of the system at around 7. After aging for 0.5 h, it is washed and dried. The amount of tetraethyl orthosilicate added is 3% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 2% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.7% of the mass of the intermediate material. Finally, the intermediate material after the above coating treatment is washed with water to obtain a filter cake. Then, it is flash-evaporated and steam-powdered to obtain the finished titanium dioxide. The L value of the obtained finished titanium dioxide is 98.43%, the a value is -0.75, and the b value is -0.19.

[0041] Example 2

[0042] The difference between this embodiment and Example 1 is that in S2, the molar ratio of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate is 3:7:12; the L value of the resulting titanium dioxide product is 98.38%, the a value is -0.73, and the b value is -0.24.

[0043] Example 3

[0044] The difference between this embodiment and Example 1 is that in S3, the amount of tetraethyl orthosilicate added is 2% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 1.5% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.9% of the mass of the intermediate material; the L value of the resulting titanium dioxide product is 98.40%, the a value is -0.71, and the b value is -0.22.

[0045] Example 4

[0046] The difference between this embodiment and Embodiment 1 is that in S3, the surface coating process is controlled at 65°C. The specific operation is as follows: Tetraethyl orthosilicate is added to the intermediate material at a uniform rate, and then cured for 1 hour; then sodium hexametaphosphate and zirconium sulfate are added at a uniform rate. During this process, acid or alkali solution is added dropwise to control the pH of the system at about 7.5, and cured for 1 hour. After curing, it is washed and dried. The resulting titanium dioxide product has an L value of 98.24%, an a value of -0.74, and a b value of -0.22.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that sodium citrate is used as a dispersant in S2; the L value of the resulting titanium dioxide product is 98.12%, the a value is -0.82, and the b value is -0.43.

[0049] Comparative Example 2

[0050] The difference between this comparative example and Example 1 is that in S3, the intermediate material was not coated on the surface, but was directly washed with water to obtain a filter cake; then flash evaporation and steam pulverization were performed to obtain the finished titanium dioxide product; the L value of the obtained finished titanium dioxide product was 98.03%, the a value was -0.83, and the b value was -0.43.

[0051] Comparative Example 3

[0052] The difference between this comparative example and Example 1 is that in S2, only one-stage sand milling is performed, without the hydrocyclone separation step. The resulting titanium dioxide product has an L value of 98.15%, an a value of -0.80, and a b value of -0.39.

[0053] Experimental Example 1

[0054] The particle size of the titanium dioxide products prepared in each embodiment and comparative example was measured, and the results are shown in Table 1. The particle size distribution diagram is shown in [the table below]. Figure 1 ;

[0055] Table 1 - Comparison of particle size of titanium dioxide products obtained in each example and comparative example

[0056]

[0057]

[0058] As shown in Table 1, in Comparative Example 1, the titanium dioxide particles that were not dispersed by the modified dispersant of this invention grew at inconsistent rates, resulting in a wider particle size distribution and ion agglomeration, leading to larger particle size and specific surface area. In Comparative Example 2, the intermediate material was not coated, making it impossible to form a uniform and continuous dense protective film on the surface of the titanium dioxide, resulting in excessive grain growth and uneven particle size distribution. The particle size obtained in Comparative Example 3 was coarser than that in Example 1, mainly because the slurry was not sufficiently ground and sieved.

[0059] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling powder particles in titanium dioxide, characterized in that, Includes the following steps: S1. Take crude metatitanic acid with a phosphorus content of 700ppm~2000ppm, crush it with a high-efficiency crusher, add H3PO4 solution, and stir for 30 min to make pulp with a concentration of 500~600 g / L. S2. The slurry is calcined at a temperature of 935-945℃, then subjected to roller milling and pulping. During pulping, 2.0‰-3.0‰ of a modified dispersant is added to the slurry, and the pH value is adjusted to 9.5-10 with dilute alkali. Then, it is processed by colloid milling and ceramic milling in sequence. After processing, it is sieved, sand milled, and sieved again. After separation by hydrocyclone, the intermediate material is obtained. In ceramic milling, the grinding media is ceramic balls with diameters of 10 mm, 8 mm, 6 mm, and 4 mm, added in a ratio of 2:2:2:

1. In sand milling, two-stage sand milling is performed. The first-stage sand mill uses 4 mm and 6 mm zirconium beads with an addition ratio of 3:2, and the second-stage sand mill uses 6 mm, 8 mm, and 10 mm zirconium beads with an addition ratio of 3:2:

1. The modified dispersant is a copolymer synthesized by solution polymerization of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate as monomers; the preparation method of the modified dispersant is as follows: (1) After mixing maleic acid, polyethylene glycol monomethyl ether acrylate and initiator, add organic solvent to dissolve them completely. Then, introduce nitrogen gas into the reaction system and heat it up, and react for a period of time. The molar amount of initiator is 0.5% to 2% of the total molar amount of maleic acid and polyethylene glycol monomethyl ether acrylate; the amount of organic solvent is 50% to 100% of the total weight of maleic acid, polyethylene glycol monomethyl ether acrylate and initiator. (2) After dissolving acrylic acid and initiator in an organic solvent and mixing them, slowly add the mixture dropwise to the reaction system of step (1). After reacting for a period of time, evaporate the organic solvent. Dissolve the obtained product in water and add an appropriate amount of alkali solution to adjust the pH to 6-7. After purification, the modified dispersant is obtained. The molar amount of initiator is 0.1%-0.5% of the molar amount of acrylic acid. The amount of organic solvent is 50%-100% of the total weight of acrylic acid and initiator. The molar ratio of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate is 2-8:3-9:10-15; the organic solvent is ethyl acetate or propylene glycol methyl ether; and the initiator is one of azobisisobutyronitrile, azobisisoheptanenitrile, or dimethyl azobisisobutyrate. S3. Add tetraethyl orthosilicate to the intermediate material obtained in S2 and react for a period of time. Then, continue to add sodium hexametaphosphate and zirconium sulfate to the slurry for surface coating treatment. Finally, wash the intermediate material after the above coating treatment with water to obtain filter cake. Then, perform flash evaporation and steam powdering to obtain titanium dioxide finished product. The amount of tetraethyl orthosilicate added is 1-5% of the mass of the intermediate material, the amount of sodium hexametaphosphate added is 1-3% of the mass of the intermediate material, and the amount of zirconium sulfate added is 0.5-1% of the mass of the intermediate material.

2. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that, In S1, the phosphorus content in the crude product is 800 ppm to 1000 ppm.

3. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that, The molar ratio of acrylic acid, maleic acid, and polyethylene glycol monomethyl ether acrylate is 5:6:

10.

4. The method for controlling powder particles in titanium dioxide according to claim 1, characterized in that, In S2, before sand milling, the material is passed through a 300-350 mesh sieve; after sand milling, it is passed through a 450-550 mesh sieve.

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