Method for continuously preparing weather-resistant titanium dioxide and titanium dioxide

Abstract

The invention relates to the technical field of chemical synthesis, and discloses a method for continuously preparing weather-resistant titanium dioxide and titanium dioxide. Comprising the following steps: continuously adding an organic dispersant into titanium dioxide slurry, adjusting the pH value of the slurry to an alkaline range, and curing to obtain slurry A, adding a silicon source solution and an acid solution into the slurry A to obtain slurry B, carrying out aging treatment on the slurry B, continuously feeding the slurry into a multi-stage reactor, and carrying out silicon film deposition under the condition of adding the acid solution to obtain slurry C; continuously feeding the slurry C into a subsequent reactor, and continuously adding a meta-aluminate solution and an aluminum salt solution to obtain slurry D with a silicon / aluminum composite inorganic coating layer; and washing, drying and crushing the slurry D to obtain the titanium dioxide. The prepared titanium dioxide inorganic coating is compact and uniform, low in acid solubility and good in weather resistance, and the continuous preparation method is high in process controllability, stable in operation and suitable for large-scale efficient production.

Description

Technical Field

[0001] This invention relates to the field of chemical synthesis technology, specifically to a method for continuous preparation of weather-resistant titanium dioxide and titanium dioxide. Background Technology

[0002] Titanium dioxide, due to its high refractive index, excellent optical stability, and chemical inertness, is one of the most widely used white pigments. Among its various crystal forms, the anatase and rutile forms are the most commercially valuable. These forms absorb almost no light in the visible light range, providing a strong light-scattering effect, thus achieving good hiding power with relatively low addition amounts. Titanium dioxide is widely used in coatings, plastics, rubber, papermaking, cosmetics, and other fields, and is an irreplaceable whitening and hiding component in many material systems.

[0003] However, titanium dioxide typically possesses photocatalytically active sites on its surface. When directly used in coating systems, it easily induces oxidative degradation of the substrate under light exposure, leading to wrinkling, chalking, peeling, and other phenomena in the coating, thus accelerating material aging. To reduce photocatalytic side effects, the industry commonly employs inorganic coatings such as silicon dioxide and alumina to shield ultraviolet light, forming a dense protective shell on the surface of titanium dioxide particles, thereby improving the pigment's weather resistance.

[0004] Existing inorganic coating technologies mostly employ intermittent processes, resulting in limited production cycles, high energy consumption, and significant batch-to-batch variations in properties. Dispersants are typically added before inorganic coating to fully disperse agglomerated titanium dioxide into individual particles, ensuring uniform deposition of the inorganic coating on each particle surface. However, commonly used dispersants often fail to achieve stable and sustained dispersion under continuous feeding conditions, leading to incomplete dispersion of some particles and ultimately, a less dense coating that affects the product's weather resistance.

[0005] Furthermore, during the inorganic coating process, the coating agent needs to preferentially nucleate and grow on the surface of titanium dioxide, so the supersaturation of the system must be strictly controlled. When the aggregation rate during the precipitation stage exceeds the growth rate, a large number of free particles will appear, making the coating layer discontinuous and loose; while if the concentration of the coating agent is too low, it is not conducive to achieving stable deposition in a continuously flowing slurry system, making it difficult to form a uniform inorganic shell.

[0006] Existing continuous coating schemes have also proposed using equipment with specific structures and multi-stage residence systems to achieve continuous deposition. However, such schemes often require complex equipment structures and are prone to problems such as uneven mixing, unstable deposition, or clogging in actual operation, making process control difficult. Summary of the Invention

[0007] This invention provides a method for continuously preparing weather-resistant titanium dioxide and titanium dioxide, to solve the problems of insufficient dispersion of titanium dioxide, imbalance between nucleation and growth during inorganic coating deposition, and difficulty in maintaining coating stability in continuous processes in the prior art.

[0008] In a first aspect, the present invention provides a method for continuously preparing weather-resistant titanium dioxide, comprising the following steps: (1) Organic dispersant is continuously added to titanium dioxide slurry, and the pH of the slurry is adjusted to the alkaline range and then aged to obtain slurry A. The organic dispersant includes acrylic acid modified polysiloxane. (2) Add silicon source solution and acid solution to slurry A to obtain slurry B. After aging treatment, slurry B is continuously fed into a multi-stage reactor and silicon film is deposited under the condition of adding acid solution to obtain slurry C. (3) The slurry C is continuously fed into the subsequent reactor, and aluminate solution and aluminum salt solution are continuously added to obtain slurry D with silicon / aluminum composite inorganic coating layer; (4) Wash, dry and pulverize the slurry D to obtain titanium dioxide.

[0009] The silicon / aluminum composite inorganic coating layer refers to a composite inorganic coating structure formed by a silicon film layer deposited from a silicon source and an aluminum film layer deposited from an aluminum source on the surface of titanium dioxide particles.

[0010] This invention achieves a uniform and dense silicon / aluminum composite inorganic coating layer by sequentially completing the organic dispersion, silicon film deposition, and aluminum film composite coating of titanium dioxide particles in a stable flow system. Specifically, acrylic acid-modified polysiloxane helps improve particle dispersibility and provides a sufficient reaction interface for the inorganic coating. Aging treatment and controlled deposition of the silicon film in a multi-stage reactor suppress the formation of free precipitates and promote continuous film formation of silicon species on the particle surface. Furthermore, the introduction of aluminates and aluminum salts further constructs a composite coating structure, effectively reducing the surface activity of titanium dioxide, thereby reducing acid solubility and improving weather resistance. Simultaneously, this method employs a continuous process, which is stable, easy to control, and suitable for large-scale, efficient production.

[0011] In an optional embodiment, in step (1), the acrylic acid-modified polysiloxane has the following structural formula (Ⅰ), where n is 8~20; .

[0012] In one optional embodiment, the mass ratio of the organic dispersant to TiO2 in the titanium dioxide slurry is (0.1% to 0.5%):1. For example, the mass ratio of the organic dispersant to TiO2 in the titanium dioxide slurry is 0.1%:1, 0.2%:1, 0.3%:1, 0.4%:1, or 0.5%:1.

[0013] In one optional embodiment, the mass fraction of SiO2 in the silicon source solution is 5% to 10%. For example, the mass fraction of SiO2 in the silicon source solution is 5%, 6%, 7%, 8%, 9%, or 10%.

[0014] In one optional embodiment, the mass ratio of SiO2 in the silicon source solution to TiO2 in the titanium dioxide slurry is (0.015~0.06):1. For example, the mass ratio of SiO2 in the silicon source solution to TiO2 in the titanium dioxide slurry is 0.015:1, 0.02:1, 0.03:1, 0.04:1, 0.05:1, or 0.06:1.

[0015] In one optional embodiment, in step (2), a silicon source solution and an acidic solution are added to slurry A, and the pH of the system is maintained at 9.0~9.5. After being kept at a temperature of 65℃~95℃ for 1h~3h, an aging treatment is performed; for example, the pH can be 9.0, 9.1, 9.2, 9.3, 9.4 or 9.5; the temperature can be 65℃, 70℃, 75℃, 80℃, 85℃, 90℃ or 95℃; and the time can be 1h, 1.5h, 2h, 2.5h or 3h.

[0016] Preferably, the aging treatment time is 1 hour to 3 hours, and the temperature is 65°C to 95°C. For example, the aging treatment time is 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours; and the aging treatment temperature is 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 95°C.

[0017] In one alternative embodiment, in step (2), the slurry is continuously fed into a multi-stage reactor to deposit a silicon film under conditions of progressively decreasing pH. Preferably, in step (2), the slurry is subjected to heat preservation treatment at pH 8.0~8.5, 7.0~7.5, and 6.0~6.5 in sequence to deposit a silicon film. The heat preservation temperature is 65℃~95℃ and the heat preservation time is 0.5h~2h.

[0018] By continuously feeding the slurry into a multi-stage reactor and depositing silicon films under progressively decreasing pH conditions, the hydrolysis and condensation rates of the silicon source on the titanium dioxide surface can be effectively controlled. This allows the silicon film to preferentially nucleate and grow on the surface of titanium dioxide particles, avoiding the formation of free silicon precipitation due to localized supersaturation. Through segmented temperature treatment within different pH ranges, the silicon film gradually transforms from loose to dense, facilitating the formation of a continuous, uniform, and firmly bonded inorganic coating layer. This significantly improves the controllability and stability of silicon film deposition, reduces the probability of coating defects, provides a good structural foundation for subsequent aluminum film composite coating, and ultimately enhances the weather resistance of titanium dioxide.

[0019] In one optional embodiment, in step (3), the reaction temperature is controlled at 65°C to 95°C; and / or the reaction time is controlled at 0.5h to 2h. In an optional embodiment, in step (3), the mass fraction of Al2O3 in the aluminate solution is 15wt%~18wt%; for example, the mass fraction of Al2O3 in the aluminate solution is 15 wt%, 16 wt%, 17 wt% or 18 wt%.

[0020] In an optional embodiment, in step (3), the mass fraction of Al2O3 in the aluminum salt solution is 7wt%~9wt%; for example, the mass fraction of Al2O3 in the aluminum salt solution is 7 wt%, 8 wt% or 9 wt%.

[0021] In an optional embodiment, in step (3), the total mass ratio of Al2O3 in the aluminate solution and aluminum salt solution to the mass ratio of TiO2 in the titanium dioxide slurry is (0.01~0.03):1; for example, the total mass ratio of Al2O3 to TiO2 is 0.01:1, 0.015:1, 0.02:1, 0.025:1 or 0.03:1.

[0022] In one optional embodiment, in step (1), after adding the organic dispersant, the temperature is first kept at 65℃~95℃ for 5~15 minutes; for example, the holding time is 5 minutes, 8 minutes, 10 minutes, 12 minutes or 15 minutes, and the holding temperature is 65℃, 75℃, 85℃ or 95℃.

[0023] In one optional embodiment, in step (1), an alkaline solution is added to the slurry to adjust the pH of the slurry to 9.0~10.5; for example, the pH of the slurry is adjusted to 9.0, 9.5, 10.0 or 10.5.

[0024] In one optional embodiment, in step (4), an organic coating agent is added during the pulverization process; Preferably, the organic coating agent includes one or more of trimethylolpropane, trimethylolethane, neopentyl glycol, and polyethylene glycol; Preferably, the mass ratio of the organic coating agent to TiO2 in the titanium dioxide slurry is (0.3% to 0.6%):1; for example, 0.3%:1, 0.4%:1, 0.5%:1 or 0.6%:1.

[0025] Secondly, the present invention provides a weather-resistant titanium dioxide, which is prepared by any of the preparation methods described in the above technical solutions; Preferably, the acid solubility of the weather-resistant titanium dioxide is 3.3% to 8.5%.

[0026] The technical solution of this invention has the following advantages: This invention introduces organic dispersion, silicon film deposition, and aluminum film composite coating steps sequentially into a continuous process, ensuring that titanium dioxide particles maintain a good dispersion state in a stable flow system. This facilitates the uniform nucleation and continuous growth of the inorganic coating on the particle surface. Acrylic acid-modified polysiloxane effectively inhibits titanium dioxide agglomeration and improves the interfacial accessibility of subsequent coating reactions. The synergistic arrangement of silicon film deposition and aluminum film composite coating results in a denser and more complete inorganic coating layer structure, significantly reducing the acid solubility of titanium dioxide and improving its weather resistance. Furthermore, the method employs a continuous process instead of traditional intermittent operation, resulting in high process stability and production efficiency, making it suitable for industrial-scale continuous production.

[0027] The weather-resistant titanium dioxide prepared by the method of this invention has a continuous and dense silicon / aluminum composite inorganic coating layer on its particle surface, which effectively shields the photocatalytic active sites of titanium dioxide and significantly reduces the corrosive effect of acidic media on the titanium dioxide particles, keeping the acid solubility of the product stably controlled within the range of 3.3% to 8.5%. This weather-resistant titanium dioxide exhibits excellent weather resistance and chemical stability, making it suitable for applications such as coatings and plastics that require high long-term weather resistance, while also demonstrating good batch consistency and industrial applicability. Detailed Implementation

[0028] The following embodiments are provided to better understand the present invention, but the following embodiments do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the scope of protection of the present invention.

[0029] (1) The test methods involved in the embodiments and comparative examples of the present invention are as follows: The acid solubility test was conducted using an Agilent Cary 3500 spectrophotometer. The specific test method is as follows: Accurately weigh 1.0000 g of spectroscopically pure titanium dioxide and transfer it to a 300 mL Erlenmeyer flask. Add 15 g of ammonium sulfate and 20 mL of concentrated sulfuric acid, shake to mix thoroughly, and then slowly heat until completely dissolved. Cool to room temperature, dilute with 80 mL of distilled water, and transfer to a 1 L volumetric flask. Rinse the Erlenmeyer flask with distilled water, add the rinsing solution to the volumetric flask, dilute to 800 mL with distilled water, then add 80 mL of concentrated sulfuric acid, mix, cool to room temperature, and dilute to 1000 mL with distilled water. The prepared TiO2 standard solution has a concentration of 0.001 g / mL and should be allowed to stand for one week before use.

[0030] Use a pipette to transfer 2, 4, 6, and 8 mL of TiO2 standard solution into 100 mL volumetric flasks, add 10 mL of 30% hydrogen peroxide, and dilute to the mark with 10% sulfuric acid. Shake well.

[0031] Prepare a reference solution by adding 10 mL of 30% hydrogen peroxide to a 100 mL volumetric flask and diluting to the mark with 10% sulfuric acid. The TiO2 concentrations of the four samples prepared above are 20 mg / L, 40 mg / L, 60 mg / L, and 80 mg / L. After standing for 1 hour, using the reference solution as a blank, measure the absorbance of the four standard solutions at 400 nm using a 10 mm cuvette, and retain the results to two decimal places. Plot a standard curve with TiO2 concentration on the x-axis and absorbance on the y-axis.

[0032] Turn on the power to the magnetic stirring oil bath and set the temperature to 185℃. Accurately weigh 0.2000g of the sample to be tested into a clean 100ml beaker, and record the mass as m1. Add 10ml of concentrated sulfuric acid and gently shake to ensure the sample is fully wetted with sulfuric acid. Once the oil bath temperature reaches the set temperature, place the beaker containing the sample into the oil bath for digestion. Cover the beaker with a watch glass to prevent acid fumes from carrying away the sample and to reduce errors. The entire digestion process takes 60 minutes. Three minutes before the end of digestion, place a container of ice water next to the oil bath. After one hour of digestion, remove the watch glass, hold the beaker with tongs, and quickly place it into the container of ice water to cool. After cooling, transfer the contents of the beaker to a 100mL volumetric flask. Rinse the beaker with distilled water, transfer the washings to the volumetric flask, dilute to the mark with distilled water, and mix well. Filter through two sheets of filter paper and collect the filtrate in a dry container, ensuring the filtrate is clean and clear. If it becomes cloudy, filter again. Transfer 10 mL of the filtrate to a 25 mL volumetric flask and add 2 mL of 30% hydrogen peroxide. Dilute to the mark with 10% sulfuric acid and mix well. Prepare a blank solution by adding 2 mL of 30% hydrogen peroxide to a 25 mL volumetric flask and diluting to the mark with 10% sulfuric acid. Mix well. After standing for 1 hour, measure the absorbance of the sample at 400 nm using a 10 mm cuvette.

[0033] The measured absorbance is compared with the prepared standard curve to obtain the concentration of TiO2 in the sample. Based on the concentration of TiO2 in the sample, the mass m2 of the sample dissolved in concentrated sulfuric acid is calculated. The acid solubility rate is calculated as m2 / m1×100%.

[0034] (2) The raw materials involved in the embodiments and comparative examples of the present invention are as follows: Titanium dioxide slurry: sourced from Anada Co., Ltd., with a titanium dioxide mass concentration of 370 g / L and a density of 1.293 g / cm³; Acrylic acid-modified polysiloxane: sourced from Wanhua Chemical Co., Ltd.; Sodium silicate: derived from INNOCHEM, purity 99%; Sodium aluminate: derived from INNOCHEM, purity 99%; Aluminum sulfate: derived from INNOCHEM, 99% purity; Concentrated sulfuric acid: derived from INNOCHEM, mass fraction 98%; Trimethylolpropane: derived from INNOCHEM, 99% purity; Hydrogen peroxide solution: derived from INNOCHEM, mass fraction 32%.

[0035] Unless otherwise specified, the experimental steps or conditions in the examples were performed in accordance with conventional experimental procedures and conditions in the art. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0036] Example 1 This embodiment provides a method for continuously preparing weather-resistant titanium dioxide and the titanium dioxide itself, as detailed below: (1) In reactor A, titanium dioxide slurry was continuously added at a flow rate of 328 kg / min at 85°C, and acrylic acid-modified polysiloxane was continuously added as an organic dispersant, with the amount added accounting for 0.3% of the weight of TiO2 in the titanium dioxide slurry. The pH of the slurry was adjusted to 10.5 using sodium hydroxide solution, and it was matured at this temperature for 10 min. After the maturation was completed, slurry A was obtained, and slurry A was continuously transported to reactor B.

[0037] The structural formula (Ⅰ) of the acrylic acid-modified polysiloxane is as follows, where n is 15; ; (2) In reactor B, a sodium silicate aqueous solution with a concentration of 10 wt% (based on SiO2) was continuously added at a flow rate of 29 kg / min, and a dilute sulfuric acid solution with a concentration of 10 wt% was continuously added at a flow rate of 300 g / min, so that the mass ratio of SiO2 to TiO2 was 0.03:1, to obtain slurry B. The pH of the system was controlled at 9.0-9.5, the reaction temperature was maintained at 85℃, and the residence time was 2.5 h.

[0038] After the reaction was completed, the slurry in reactor B was continuously transported to reactor C at a flow rate of 357 kg / min and aged at 85°C for 1 h to form an initial silicon film layer.

[0039] Subsequently, the reaction solution in reactor C was continuously added to reactor D at a flow rate of 357 kg / min. The pH of the reaction solution was controlled at 8.0–8.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 85℃ and the temperature was maintained for 30 min.

[0040] The reaction solution in reactor D was continuously added to reactor E at a flow rate of 357 kg / min. The pH of the reaction solution was controlled at 7.0–7.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 85℃ and the temperature was maintained for 30 min.

[0041] The reaction solution in reactor E was continuously added to reactor F at a flow rate of 357 kg / min. The pH of the reaction solution was controlled at 6.0–6.4 by adding dilute sulfuric acid in a co-current flow. The reaction temperature was 85℃ and the mixture was kept at that temperature for 30 min to obtain slurry C. (3) The slurry from reactor F is continuously fed into reactor G, and sodium aluminate solution with a concentration of 17 wt% based on Al2O3 and aluminum sulfate solution with a concentration of 8.2 wt% based on Al2O3 are added in parallel. The flow rate of sodium aluminate solution is 7.6 kg / min and the flow rate of aluminum sulfate solution is 11.1 kg / min. The total mass ratio of Al2O3 in the aluminate solution and aluminum salt solution to the mass ratio of TiO2 in the titanium dioxide slurry is 0.02:1. The reaction temperature is set to 65℃ and kept at that temperature for 45 min. The aluminum film coating is completed to obtain slurry D.

[0042] (4) The slurry D is subjected to pressure filtration and demineralized water washing. The resulting filter cake is flash dried and then subjected to air jet milling. During the milling process, trimethylolpropane, an organic coating agent, is added. The amount of the organic coating agent used is based on the mass of TiO2 contained in the titanium dioxide slurry before entering this step, and the amount added is 0.5% of the mass of TiO2. Finally, titanium dioxide that has been fully milled and has formed an organic coating on its surface is collected in the air jet bag filter.

[0043] The acid solubility of titanium dioxide was determined to be 3.7%.

[0044] Example 2 This embodiment provides a method for continuously preparing weather-resistant titanium dioxide and the titanium dioxide itself, as detailed below: (1) In reactor A, titanium dioxide slurry was continuously added at a flow rate of 328 kg / min at 85°C, and acrylic acid-modified polysiloxane was continuously added as an organic dispersant, with the amount added accounting for 0.3% of the weight of TiO2. The pH of the slurry was adjusted to 10.5 using sodium hydroxide solution, and it was matured at this temperature for 10 min. After the maturation was completed, slurry A was obtained, and slurry A was continuously transported to reactor B.

[0045] The acrylic acid-modified polysiloxane used in Example 1 is the same as in Example 1. (2) In reactor B, a sodium silicate aqueous solution with a concentration of 10 wt% (based on SiO2) was continuously added at a flow rate of 15 kg / min, and a dilute sulfuric acid solution with a concentration of 10 wt% was continuously added at a flow rate of 270 g / min, so that the mass ratio of SiO2 to TiO2 was 0.015:1, to obtain slurry B. The pH of the system was controlled at 9.0-9.5, the reaction temperature was maintained at 85℃, and the residence time was 2.5 h.

[0046] After the reaction was completed, the slurry in reactor B was continuously added to reactor C at a flow rate of 343 kg / min and aged at 85°C for 1 h to form an initial silicon film layer.

[0047] Subsequently, the reaction solution in reactor C was continuously added to reactor D at a flow rate of 343 kg / min. The pH of the reaction solution was controlled at 8.0–8.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 85℃ and the temperature was maintained for 30 min.

[0048] The reaction solution in reactor D was continuously added to reactor E at a flow rate of 343 kg / min. The pH of the reaction solution was controlled at 7.0–7.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 85℃ and the reaction was maintained for 30 min.

[0049] The reaction solution in reactor E is continuously added to reactor F. The pH of the reaction solution is controlled at 6.0-6.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature is 85℃ and the temperature is maintained for 30 min to obtain slurry C. (3) The slurry from reactor F is continuously fed into reactor G, and sodium aluminate solution with a concentration of 17 wt% based on Al2O3 and aluminum sulfate solution with a concentration of 8.2 wt% based on Al2O3 are added in parallel. The flow rate of sodium aluminate solution is 7.6 kg / min and the flow rate of aluminum sulfate solution is 11.1 kg / min. The total mass ratio of Al2O3 in the aluminate solution and aluminum salt solution to the mass ratio of TiO2 in the titanium dioxide slurry is 0.02:1. The reaction temperature is set to 65℃ and kept at that temperature for 45 min. The aluminum film coating is completed to obtain slurry D.

[0050] (4) The slurry D is subjected to pressure filtration and demineralized water washing. The resulting filter cake is flash dried and then subjected to air jet milling. Trimethylolpropane is added during the milling process. The amount of the organic coating agent used is based on the mass of TiO2 contained in the titanium dioxide slurry before entering this step, and the amount added is 0.5% of the mass of TiO2. Finally, titanium dioxide that is fully milled and has an organic coating formed on its surface is collected in the air jet bag filter.

[0051] The acid solubility of the obtained weather-resistant titanium dioxide was determined to be 7.9%.

[0052] Example 3 This embodiment provides a method for continuously preparing weather-resistant titanium dioxide and the titanium dioxide itself, as detailed below: (1) In reactor A, titanium dioxide slurry was continuously added at a flow rate of 328 kg / min at 85°C, and acrylic acid-modified polysiloxane was continuously added as an organic dispersant at a rate of 0.3% of the weight of TiO2. The pH of the slurry was adjusted to 10.5 using sodium hydroxide solution and matured at this temperature for 10 min. After maturation, slurry A was obtained and continuously transported to reactor B.

[0053] The acrylic acid-modified polysiloxane is the same as in Example 1.

[0054] (2) In reactor B, a sodium silicate aqueous solution with a concentration of 10 wt% (based on SiO2) was continuously added at a flow rate of 57 kg / min, and a dilute sulfuric acid solution with a concentration of 10 wt% was continuously added at a flow rate of 330 g / min, so that the mass ratio of SiO2 to TiO2 was 0.06:1, to obtain slurry B. The pH of the system was controlled at 9.0-9.5, the reaction temperature was maintained at 85℃, and the residence time was 2.5 h.

[0055] After the reaction was completed, the slurry in reactor B was continuously added to reactor C at a flow rate of 385 kg / min and aged at 85°C for 1 h to form an initial silicon film layer.

[0056] Subsequently, the reaction solution in reactor C was continuously added to reactor D at a flow rate of 385 kg / min. The pH of the reaction solution was controlled at 8.0–8.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 85℃ and the temperature was maintained for 30 min.

[0057] The reaction solution in reactor D was continuously added to reactor E at a flow rate of 385 kg / min. The pH of the reaction solution was controlled at 7.0–7.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 85℃ and the temperature was maintained for 30 min.

[0058] The reaction solution in reactor E is continuously added to reactor F. The pH of the reaction solution is controlled at 6.0-6.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature is 85℃ and the temperature is maintained for 30 min.

[0059] (3) The slurry from reactor F is continuously fed into reactor G, and sodium aluminate solution with a concentration of 17 wt% based on Al2O3 and aluminum sulfate solution with a concentration of 8.2 wt% based on Al2O3 are added in parallel. The flow rate of sodium aluminate solution is 7.6 kg / min and the flow rate of aluminum sulfate solution is 11.1 kg / min. The total mass ratio of Al2O3 in the aluminate solution and aluminum salt solution to the mass ratio of TiO2 in the titanium dioxide slurry is 0.02:1. The reaction temperature is set to 65℃ and kept at that temperature for 45 min. The aluminum film coating is completed to obtain slurry D.

[0060] (4) The slurry D is subjected to pressure filtration and demineralized water washing. The resulting filter cake is flash dried and then subjected to air jet milling. Trimethylolpropane is added during the milling process. The amount of the organic coating agent used is based on the mass of TiO2 contained in the titanium dioxide slurry before entering this step, and the amount added is 0.5% of the mass of TiO2. Finally, titanium dioxide that is fully milled and has an organic coating formed on its surface is collected in the air jet bag filter.

[0061] The acid solubility of the obtained weather-resistant titanium dioxide was determined to be 3.3%.

[0062] Example 4 This embodiment provides a method for continuously preparing weather-resistant titanium dioxide and the titanium dioxide itself, as detailed below: (1) In reactor A, titanium dioxide slurry was continuously added at a flow rate of 328 kg / min at 65°C, and acrylic acid-modified polysiloxane was continuously added as an organic dispersant, with the amount added accounting for 0.1% of the weight of TiO2 in the titanium dioxide slurry. The pH of the slurry was adjusted to 9 using sodium hydroxide solution, and it was matured at this temperature for 15 min. After the maturation was completed, slurry A was obtained, and slurry A was continuously transported to reactor B.

[0063] The acrylic acid-modified polysiloxane has the same structural formula as in Example 1, where n is 20.

[0064] (2) In reactor B, a sodium silicate aqueous solution with a concentration of 5 wt% (based on SiO2) was continuously added at a flow rate of 38 kg / min, and a dilute sulfuric acid solution with a concentration of 5 wt% was continuously added at a flow rate of 300 g / min, so that the mass ratio of SiO2 to TiO2 was 0.02:1, to obtain slurry B. The pH of the system was controlled at 9.0-9.5, the reaction temperature was maintained at 65℃, and the residence time was 3 h.

[0065] After the reaction was completed, the slurry in reactor B was continuously transported to reactor C at a flow rate of 366 kg / min and aged at 65°C for 3 h to form an initial silicon film layer.

[0066] Subsequently, the reaction solution in reactor C was continuously added to reactor D at a flow rate of 366 kg / min. The pH of the reaction solution was controlled at 8.0–8.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 65 °C and the temperature was maintained for 30 min.

[0067] The reaction solution in reactor D was continuously added to reactor E at a flow rate of 366 kg / min. The pH of the reaction solution was controlled at 7.0–7.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 65℃ and the reaction was maintained for 30 min.

[0068] The reaction solution in reactor E was continuously added to reactor F at a flow rate of 366 kg / min. The pH of the reaction solution was controlled at 6.0–6.4 by adding dilute sulfuric acid in a co-current flow. The reaction temperature was 65℃ and the mixture was kept at that temperature for 120 min to obtain slurry C. (3) The slurry from reactor F is continuously fed into reactor G, and sodium aluminate solution with a concentration of 15 wt% (based on Al2O3) and aluminum sulfate solution with a concentration of 7 wt% (based on Al2O3) are added in parallel. The flow rate of sodium aluminate solution is 3.8 kg / min and the flow rate of aluminum sulfate solution is 6.2 kg / min. The total mass ratio of Al2O3 in the aluminate solution and aluminum salt solution to the mass ratio of TiO2 in the titanium dioxide slurry is 0.01:1. The reaction temperature is set to 80℃ and kept at that temperature for 30 min. The aluminum film coating is completed to obtain slurry D.

[0069] (4) The slurry D is subjected to pressure filtration and demineralized water washing. The resulting filter cake is flash dried and then subjected to air jet milling. During the milling process, trimethylolpropane, an organic coating agent, is added. The amount of the organic coating agent used is based on the mass of TiO2 contained in the titanium dioxide slurry before entering this step, and the amount added is 0.3% of the mass of TiO2. Finally, titanium dioxide that is fully milled and has an organic coating formed on its surface is collected in the air jet bag filter.

[0070] The acid solubility of titanium dioxide was determined to be 8.3%.

[0071] Example 5 This embodiment provides a method for continuously preparing weather-resistant titanium dioxide and the titanium dioxide itself, as detailed below: (1) In reactor A, titanium dioxide slurry was continuously added at a flow rate of 328 kg / min at 95°C, and acrylic acid-modified polysiloxane was continuously added as an organic dispersant, with the amount added accounting for 0.5% of the weight of TiO2 in the titanium dioxide slurry. The pH of the slurry was adjusted to 10 using sodium hydroxide solution, and it was matured at this temperature for 5 min. After the maturation was completed, slurry A was obtained, and slurry A was continuously transported to reactor B.

[0072] The acrylic acid-modified polysiloxane has the same structural formula as in Example 1, where n is 8.

[0073] (2) In reactor B, an aqueous solution of sodium silicate with a concentration of 8 wt% (based on SiO2) was continuously added at a flow rate of 47 kg / min, and a dilute sulfuric acid solution with a concentration of 10 wt% was continuously added at a flow rate of 300 g / min, so that the mass ratio of SiO2 to TiO2 was 0.04:1, to obtain slurry B. The pH of the system was controlled at 9.0-9.5, the reaction temperature was maintained at 95℃, and the residence time was 1 h.

[0074] After the reaction is complete, the slurry in reactor B is continuously transported to reactor C at a flow rate of 375 kg / min and aged at 95°C for 2.5 h to form an initial silicon film layer.

[0075] Subsequently, the reaction solution in reactor C was continuously added to reactor D at a flow rate of 375 kg / min. The pH of the reaction solution was controlled at 8.0–8.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 95 °C and the temperature was maintained for 30 min.

[0076] The reaction solution in reactor D was continuously added to reactor E at a flow rate of 375 kg / min. The pH of the reaction solution was controlled at 7.0–7.4 by adding dilute sulfuric acid in a parallel flow. The reaction temperature was 95℃ and the temperature was maintained for 30 min.

[0077] The reaction solution in reactor E was continuously added to reactor F at a flow rate of 375 kg / min. The pH of the reaction solution was controlled at 6.0–6.4 by adding dilute sulfuric acid in a co-current flow. The reaction temperature was 95℃ and the mixture was kept at that temperature for 60 min to obtain slurry C. (3) The slurry from reactor F is continuously fed into reactor G, and sodium aluminate solution with a concentration of 18 wt% (based on Al2O3) and aluminum sulfate solution with a concentration of 9 wt% (based on Al2O3) are added in parallel. The flow rate of sodium aluminate solution is 8.4 kg / min and the flow rate of aluminum sulfate solution is 14.7 kg / min. The total mass ratio of Al2O3 in the aluminate solution and aluminum salt solution to the mass ratio of TiO2 in the titanium dioxide slurry is 0.03:1. The reaction temperature is set at 95℃ and kept at that temperature for 120 min. The aluminum film coating is completed to obtain slurry D.

[0078] (4) The slurry D is subjected to pressure filtration and demineralized water washing. The resulting filter cake is flash dried and then subjected to air jet milling. During the milling process, trimethylolpropane, an organic coating agent, is added. The amount of the organic coating agent used is based on the mass of TiO2 contained in the titanium dioxide slurry before entering this step, and the amount added is 0.6% of the mass of TiO2. Finally, titanium dioxide that is fully milled and has an organic coating formed on its surface is collected in the air jet bag filter.

[0079] The acid solubility of titanium dioxide was determined to be 3.5%.

[0080] Example 1-1 The only difference between this embodiment and embodiment 1 is that in step (2), the pH is no longer controlled to decrease in stages during the silicon film deposition stage, but instead a constant pH of 8.0 is used to complete the entire deposition process; the other raw material ratios, temperatures, and residence times are consistent with those in embodiment 1.

[0081] Examples 1-2 The only difference between this embodiment and embodiment 1 is that in step (2), multi-stage reactors D, E, and F are not set up. Instead, dilute sulfuric acid solution is added directly after reactor C is aged to adjust the pH of the slurry to 6.0 in one go. Then, the silicon film is deposited by keeping it at 85°C for 90 min. Other conditions are the same as in embodiment 1.

[0082] Examples 1-3 Except for the pH control method in the silicon film deposition stage, all other process conditions in this embodiment are the same as in Example 1. The only difference between this embodiment and Example 1 is that only two pH control ranges are set in the silicon film deposition stage, that is, the pH of reactor D and reactor E are controlled in the ranges of 8.4~7.4 and 7.4~6.0 respectively. The third-stage pH control step in reactor F is omitted, and the slurry in reactor E is directly transported to aluminum-coated reactor G.

[0083] Comparative Example 1 The only difference between this comparative example and Example 1 is that the type of dispersant is different. Sodium hexametaphosphate is continuously added as a dispersant in this comparative example, and the amount of dispersant added is 0.3% of the weight of TiO2.

[0084] The acid solubility of the obtained titanium dioxide product was determined to be 15.4%.

[0085] Comparative Example 2 The only difference between this comparative example and Example 1 is that the type of dispersant is different. Sodium polyacrylate is continuously added as an organic dispersant in this comparative example, and the amount of dispersant added is 0.3% of the weight of TiO2.

[0086] The acid solubility of the obtained titanium dioxide product was determined to be 9.1%.

[0087] Comparative Example 3 The only difference between this comparative example and Example 1 is that no dispersant is added in this comparative example.

[0088] The acid solubility of the obtained titanium dioxide product was determined to be 35.3%.

[0089] Test Example 1 This test example evaluates the performance of weather-resistant titanium dioxide prepared according to the embodiments and comparative examples of the present invention. Acid solubility was selected as the weather resistance characterization index in this test example; a lower acid solubility indicates a more uniform and dense inorganic coating layer and better weather resistance. All samples were prepared and tested under the same conditions, and the test results are listed in Table 1.

[0090] Table 1: Acid solubility test results of the examples and comparative examples

[0091] As shown in Table 1, the titanium dioxide prepared using the technical solution of this invention has a significantly lower acid solubility than the comparative sample. Acid solubility reflects the shielding ability of the inorganic coating layer against acidic media; a lower value indicates a more uniform and dense coating layer with better weather resistance. The titanium dioxide of this invention exhibits a low acid solubility, indicating that the silicon / aluminum composite inorganic coating constructed through a continuous process can effectively cover the surface of titanium dioxide particles, weakening the dissolution behavior of titanium dioxide under acidic conditions.

[0092] In Comparative Example 3, no dispersant was added, and its acid solubility was significantly higher. This indicates that if the titanium dioxide particles are not sufficiently dispersed during the continuous coating process, agglomerates are easily formed, leading to uneven deposition of the silicon and aluminum sources on the particle surface, resulting in a discontinuous or loose coating layer. Although Comparative Examples 1 and 2 added dispersants, their acid solubility was still higher than that of the embodiments of the present invention. It is evident that the use of acrylic acid-modified polysiloxane as a dispersant in the present invention is more conducive to the full dispersion of titanium dioxide particles during the alkaline curing stage, thereby providing a stable interfacial foundation for the subsequent uniform deposition of silicon and aluminum films.

[0093] In the embodiments of the present invention, the acid solubility varies depending on the proportion of silicon source added. When the proportion of silicon source added is low, the acid solubility is relatively high, indicating that the coverage of the silicon film layer is insufficient; while within a suitable range of silicon source proportions, the acid solubility is significantly reduced, indicating that the formed silicon film layer can completely coat the titanium dioxide particles and provide a continuous deposition substrate for subsequent aluminum film composite, thereby improving the overall compactness of the coating layer.

[0094] Comparing Examples 1, 1-1, 1-2, and 1-3, it is evident that the pH control method during the silicon film deposition stage significantly impacts the coating effect. Without segmented pH control, the acid solubility of the resulting product is significantly increased. This indicates that during continuous deposition, progressively decreasing the pH and using a multi-stage reactor helps suppress the formation of free precipitates, allowing silicon species to preferentially nucleate and grow on the titanium dioxide surface, thereby forming a more continuous and dense silicon film layer.

[0095] This invention achieves stable construction of inorganic coatings on the surface of titanium dioxide under continuous production conditions through the synergistic effects of organic dispersant-assisted dispersion, segmented deposition of silicon film, and composite coating of aluminum film. This significantly reduces the acid solubility of the product, improves the weather resistance of titanium dioxide, and ensures the controllability and repeatability of the process.

[0096] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for continuous preparation of weather-resistant titanium dioxide, characterized in that, Includes the following steps: (1) Organic dispersant is continuously added to titanium dioxide slurry, and the pH of the slurry is adjusted to the alkaline range and then aged to obtain slurry A. The organic dispersant includes acrylic acid modified polysiloxane. (2) Add silicon source solution and acid solution to slurry A to obtain slurry B. After aging treatment, slurry B is continuously fed into a multi-stage reactor and silicon film is deposited under the condition of adding acid solution to obtain slurry C. (3) The slurry C is continuously fed into the subsequent reactor, and aluminate solution and aluminum salt solution are continuously added to obtain slurry D with silicon / aluminum composite inorganic coating layer; (4) Wash, dry and crush the slurry D to obtain titanium dioxide.

2. The method for continuous preparation of weather-resistant titanium dioxide according to claim 1, characterized in that, In step (1), the acrylic acid-modified polysiloxane has the following structural formula (Ⅰ), where n is 8~20; 。 3. A method for continuous preparation of weather-resistant titanium dioxide according to claim 1 or 2, characterized in that, The mass ratio of the organic dispersant to TiO2 in the titanium dioxide slurry is (0.1% to 0.5%):

1.

4. A method for continuous preparation of weather-resistant titanium dioxide according to any one of claims 1-3, characterized in that, The mass fraction of SiO2 in the silicon source solution is 5% to 10%.

5. A method for continuous preparation of weather-resistant titanium dioxide according to any one of claims 1-4, characterized in that, The mass ratio of SiO2 in the silicon source solution to TiO2 in the titanium dioxide slurry is (0.015~0.06):

1.

6. A method for continuous preparation of weather-resistant titanium dioxide according to any one of claims 1-5, characterized in that, In step (2), a silicon source solution and an acidic solution are added to slurry A, and the pH of the system is maintained at 9.0~9.

5. After being kept at a temperature of 65℃~95℃ for 1h~3h, an aging treatment is carried out. Preferably, the aging treatment time is 1h to 3h and the temperature is 65℃ to 95℃.

7. The method for continuous preparation of weather-resistant titanium dioxide according to claim 6, characterized in that, In step (2), the slurry is continuously fed into a multi-stage reactor, and a silicon film is deposited under the condition of gradually decreasing pH. Preferably, in step (2), the slurry is subjected to heat preservation treatment at pH 8.0~8.5, 7.0~7.5, and 6.0~6.5 in sequence to deposit a silicon film. The heat preservation temperature is 65℃~95℃ and the heat preservation time is 0.5h~2h.

8. A method for continuous preparation of weather-resistant titanium dioxide according to any one of claims 1-7, characterized in that, In step (3), the reaction temperature is controlled at 65℃~95℃; and / or the reaction time is controlled at 0.5h~2h; And / or, in step (3), the mass fraction of Al2O3 in the aluminate solution is 15wt%~18wt%; And / or, in step (3), the mass fraction of Al2O3 in the aluminum salt solution is 7wt%~9wt%; And / or, in step (3), the total mass of Al2O3 in the aluminate solution and aluminum salt solution is in the mass ratio of TiO2 in the titanium dioxide slurry to (0.01~0.03):1; And / or, in step (1), after adding the organic dispersant, the temperature is first kept at 65℃~95℃ for 5~15 minutes; And / or, in step (1), an alkaline solution is added to the slurry to adjust the pH of the slurry to 9.0~10.

5.

9. A method for continuous preparation of weather-resistant titanium dioxide according to any one of claims 1-8, characterized in that, In step (4), an organic coating agent is added during the pulverization process; Preferably, the organic coating agent includes one or more of trimethylolpropane, trimethylolethane, neopentyl glycol, and polyethylene glycol; Preferably, the mass ratio of the organic coating agent to TiO2 in the titanium dioxide slurry is (0.3% to 0.6%):

1.

10. A weather-resistant titanium dioxide, characterized in that, It is prepared by any of the preparation methods described in claims 1-9 above; Preferably, the acid solubility of the weather-resistant titanium dioxide is 3.3% to 8.5%.

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