A method for producing titanium dioxide with added seed crystals via hydrolysis to stabilize particle size

Abstract

This invention relates to the field of titanium dioxide technology, specifically disclosing a method for producing titanium dioxide with added seed crystals via hydrolysis to stabilize particle size. The method includes the following steps: S1 Adding additive I to an alkaline solution and heating it to obtain a preheated alkaline solution; heating additive II into the titanium solution and heating it to obtain a preheated titanium solution; S2 Adding the preheated alkaline solution to a seed crystal preparation tank during time t1-t2, with a volume of V1; S3 Adding the preheated titanium solution to the seed crystal preparation tank during time t2-t3, with a volume of V2, until V1 / V2 is 0.5-1:1-2; S4 Performing isothermal ripening during time t3-t4, and releasing the seed crystals for the hydrolysis process during time t4-t5; Additive I is selected from hexadecyltrimethylammonium bromide, and additive II is selected from polyethylene glycol 400. This method can obtain added seed crystals with uniform particle size and improve the stability of the D50 of the hydrolyzed particles.

Description

Technical Field

[0001] This invention relates to the field of titanium dioxide technology, and specifically discloses a method for producing titanium dioxide by hydrolysis of added seed crystals to stabilize the particle size. Background Technology

[0002] In the sulfuric acid process for titanium dioxide production, the hydrolysis step is crucial for the transformation from liquid to solid phase. The particle size and distribution of the metatitanic acid produced directly determine the core performance of the final product. If the hydrolyzed particle size is too fine, the filtration and washing of the metatitanic acid become significantly more difficult, substantially extending the production cycle. Conversely, if the particle size is too coarse, impurities are easily trapped, damaging the whiteness and purity of the product. Therefore, industrially, precise control of parameters such as the total titanium concentration of the titanium solution, acidity coefficient, seed crystal addition amount, and hydrolysis temperature is typically achieved to balance nucleation and crystal growth, thus effectively controlling the hydrolyzed particle size.

[0003] In this process, the stability of the hydrolyzed seed crystals, as the externally introduced nanoscale crystal nuclei, is crucial, directly determining the uniformity of nucleation in the hydrolysis reaction and the consistency of subsequent particle growth. Insufficient stability of the hydrolyzed seed crystals is mainly manifested in a wider seed crystal size distribution, resulting in a large number of abnormally coarse particles or amorphous impurities. Insufficient seed crystal stability can cause the following problems in the hydrolysis process: 1. Unstable seed crystals lead to uneven nucleation during hydrolysis, resulting in a wider particle size distribution of the generated metatitanic acid, increasing the difficulty of filtration and washing, and significantly increasing water and energy consumption. 2. The unevenly sized metatitanic acid is prone to localized sintering during calcination, leading to a decrease in the bleaching power and whiteness of the final product.

[0004] Currently, hydrolyzed seed crystals are typically prepared using the sodium hydroxide neutralization method. To ensure the stability of these seed crystals, the industry mainly employs methods such as strictly controlling the parameters of the raw titanium liquid to prevent the introduction of impurities, and using segmented addition of titanium liquid or segmented temperature control to prepare the seed crystals. However, these traditional methods have limited effectiveness in improving seed crystal stability and cannot fundamentally solve the problem of poor seed crystal size uniformity.

[0005] To address the aforementioned technical issues, patent CN106186055A proposed using sodium phosphate instead of traditional sodium hydroxide to prepare hydrolyzed seed crystals, aiming to ensure particle size uniformity by controlling the size of the seed crystals. However, the high phosphate concentration in the reaction system promotes the formation of byproducts such as titanium phosphate and basic titanium phosphate. Simultaneously, phosphate ions strongly adsorb onto the surface of the seed crystals and embed themselves in the intercrystalline gaps. These phosphorus-containing substances are difficult to completely remove during subsequent hydrolysis, water washing, and metatitanic acid washing processes, ultimately being carried into the calcination stage as P2O5 residues. This results in a decrease in the whiteness and yellowish hue of the titanium dioxide, as well as a significant reduction in tinting strength and gloss, severely impacting the quality of the final product. Summary of the Invention

[0006] This invention provides a method for producing titanium dioxide by hydrolysis of added seed crystals to stabilize the particle size, which can obtain added seed crystals with uniform particle size.

[0007] This invention is achieved through the following technical solution: A method for producing titanium dioxide by hydrolysis with added seed crystals to stabilize particle size includes the following steps: S1 Add auxiliary agent I to the alkaline solution and heat it to obtain a preheated alkaline solution; Additive II was heated into the titanium liquid and heated to obtain a preheated titanium liquid. S2 adds preheated alkaline solution to the seed crystal preparation tank during the time interval t1-t2, with a volume of V1. S3 During the time interval t2-t3, preheated titanium liquid with a volume of V2 is added to the seed crystal preparation tank until V1 / V2 is 0.5-1:1-2; S4 undergoes isothermal ripening during the time interval t3-t4, and seed crystals are placed during the time interval t4-t5 to proceed with the hydrolysis process; Additive I is selected from hexadecyltrimethylammonium bromide, and additive II is selected from polyethylene glycol 400.

[0008] In this invention, during the isothermal ripening stage, the absorbance of the seed crystals is measured using a spectrophotometer. The specific steps are as follows: S31 uses a peristaltic pump to extract seed samples from the seed preparation tank to the mixing tank, adds water to the mixing tank, and mixes the seed samples with water at a volume ratio of 1:10-15. The gravity switch is turned on, and the absorbance of the mixed liquid is measured by a spectrophotometer. S32 If the absorbance is 1.1-1.3, the seed crystal preparation is complete; If the absorbance exceeds 1.1-1.3, maintain the reaction temperature and retest every 1-2 minutes until the absorbance is 1.1-1.3.

[0009] In this invention, the concentration of the alkali solution is 100-150 g / L, and the F value of the titanium solution is 1.8-2.0.

[0010] In this invention, the alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution.

[0011] In this invention, the temperature of the preheated alkaline solution is 79-88℃, and the temperature of the preheated titanium solution is 86-92℃.

[0012] In this invention, the amount of additive I added is 0.05-0.2% of the mass of TiO2 in the titanium liquid, and the amount of additive II added is 0.5-1.5% of the mass of TiO2 in the titanium liquid.

[0013] In this invention, t1-t2 is 4-8 min, t2-t3 is 5-8 min, t3-t4 is 4-5 min, and t4-t5 is 4-6 min.

[0014] In this invention, the constant temperature curing temperature is 90-103℃, and ultrasonic assistance is introduced during the constant temperature curing stage, with ultrasonic treatment at 40kHz and 40W for 2-3 minutes.

[0015] Because the titanium liquid will burst into nucleation instantly when injected into the alkaline solution, the nascent crystal nuclei will undergo irreversible chemical condensation and hard agglomeration due to the exposure of the surface active Ti-OH, resulting in an inherently widened initial particle size distribution. Furthermore, the growth rate of each crystal face is different and the particle size continues to widen, thus making the seed crystal particle size distribution wider and the stability poor.

[0016] This invention, by pre-adding additive I to the alkaline solution, allows additive I to be uniformly distributed throughout the reaction system before nucleation occurs. Upon the addition of the titanium liquid, it acts on the surface of the nascent crystal nuclei, inhibiting grain agglomeration. Rapidly injecting the hot titanium liquid into the hot alkaline solution within a very short time triggers a rapid nucleation explosion, ensuring that all crystal nuclei are formed almost simultaneously, resulting in highly uniform initial particle sizes. Simultaneously, additive II passivates the active sites of the crystal nuclei, slowing down the condensation rate and ensuring uniform crystal growth rather than disordered aggregation.

[0017] Hexadecyltrimethylammonium bromide can anchor itself on the surface of crystal nuclei, preventing newly formed nuclei from colliding and agglomerating, resulting in a narrow initial particle size distribution. It can effectively guide the growth of crystal nuclei along specific directions, controlling the shape and final particle size from the source. It continuously provides electrostatic repulsion, increasing the energy barrier required to overcome for material exchange between grains, slowing down the dissolution of small grains and the growth rate of large grains, thus regulating the particle size distribution. Polyethylene glycol 400 can adsorb onto the surface of crystal nuclei, passivating active hydroxyl groups, and fill the gaps between hexadecyltrimethylammonium bromide molecules, reducing the number of active sites accessible to the titanium precursor, inhibiting the Ti-OH condensation rate, thereby suppressing the chemical bonding growth between crystal nuclei at the source, slowing down the particle growth rate, and allowing the crystal nuclei to grow uniformly, resulting in an external seed crystal with a relatively uniform particle size distribution.

[0018] V1 ensures a constant total amount and concentration of alkali solution, providing a homogeneous reaction system for nucleation; V1 / V2 guarantees a fixed ratio of titanium solution to alkali solution, determining the final supersaturation and pH endpoint of the system. The combination of these two factors eliminates batch-to-batch differences in seed crystal size and activity caused by variations in the total amount of materials.

[0019] The strict control over the addition time of the titanium solution from t2 to t3 compresses the generation time of all crystal nuclei within an extremely narrow window, achieving synchronous nucleation and fundamentally determining the uniformity of the initial particle size distribution. The ripening time from t3 to t4 is quantitatively determined by absorbance to confirm the optimal ripening point for balancing seed activity and particle size, avoiding fluctuations and lags caused by manual judgment. Once the absorbance meets the standard, the prepared external seed crystals can be placed into the hydrolysis process within the time frame of t4 to t5 to prevent over-ripening and subsequent decrease in activity.

[0020] During the isothermal ripening process, a spectrophotometer is used to measure the absorbance of the seed crystals, transforming the evaluation of seed crystal quality from subjective experience into a quantifiable optical threshold. This ensures reproducibility between different batches, fundamentally solving the problem of batch variations due to manual judgment. Once the absorbance reaches the threshold, it indicates that the seed crystal size and activity have reached the optimal balance point, and the material is immediately discharged to the hydrolysis process, effectively avoiding under- or over-ripening. If the standard is not met, the ripening time is extended until the conditions are met. This accommodates batch fluctuations in raw materials, ensuring consistent seed crystal quality throughout the process.

[0021] Introducing ultrasonic treatment during the isothermal curing stage allows the cavitation effect of ultrasound to break up loose soft agglomerates that may form during curing, enabling the additives to be redistributed evenly on the surface of the crystals, further narrowing the particle size distribution and improving the monodispersity of the seed crystals.

[0022] The technical solution of the present invention has at least the following advantages and beneficial effects: This invention employs liquid level control to adjust the ratio of alkali solution and titanium solution, and regulates seed nucleation and growth through additives I and II, thereby narrowing the seed particle size distribution and improving seed particle size uniformity. A spectrophotometer is used to detect seed stability, which is convenient, accurate, and avoids human error, thus improving the stability of particle D50 during the titanium solution hydrolysis stage. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the absorbance detection of added seed crystals provided in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described below with reference to specific embodiments, but the embodiments do not limit the present invention in any way. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0025] Example 1 A method for producing titanium dioxide by hydrolysis with added seed crystals to stabilize particle size includes the following steps: S1. Hexadecyltrimethylammonium bromide is added to a sodium hydroxide or potassium hydroxide solution with a concentration of 130 g / L and heated to 85 °C to obtain a preheated alkaline solution; the amount of hexadecyltrimethylammonium bromide added is 0.1% of the mass of TiO2 in the titanium solution; Polyethylene glycol 400 was added to a titanium melt with an F value of 1.88 and heated to 90°C to obtain a preheated titanium melt. The amount of polyethylene glycol 400 added was 1% of the mass of TiO2 in the titanium melt. S2 Add 1 cubic meter of preheated alkali solution to the seed crystal preparation tank within 6 minutes; S3 Add 1 cubic meter of preheated titanium liquid to the seed crystal preparation tank within 7 minutes; S4 was subjected to isothermal ripening over 5 minutes at a temperature of 100℃, with simultaneous ultrasonic assistance, and ultrasonic treatment at 40kHz and 40W for 2 minutes. The absorbance of the seed crystals was measured using a spectrophotometer. The specific steps are as follows: S31 Reference Figure 1 A peristaltic pump was used to draw 10 mL of seed sample from the seed preparation tank into the mixing tank. 120 mL of water was added to the mixing tank, and the gravity switch was turned on. The absorbance of the mixed liquid was measured using a spectrophotometer; the absorbance was 1.18, indicating the addition of seed crystals. The seed crystals were then placed in the hydrolysis process within 5 minutes.

[0026] Example 2 S1. Add hexadecyltrimethylammonium bromide to a sodium hydroxide or potassium hydroxide solution with a concentration of 150 g / L, and heat to 88 °C to obtain a preheated alkaline solution; the amount of hexadecyltrimethylammonium bromide added is 0.2% of the mass of TiO2 in the titanium solution; Polyethylene glycol 400 was added to a titanium melt with an F value of 2.0 and heated to 92°C to obtain a preheated titanium melt. The amount of polyethylene glycol 400 added was 1.5% of the mass of TiO2 in the titanium melt. S2 Add 1.0 cubic meter of preheated alkali solution to the seed crystal preparation tank within 8 minutes; S3. Within 8 minutes, add 2 cubic meters of preheated titanium liquid to the seed crystal preparation tank; S4 was subjected to isothermal ripening over 5 minutes at a temperature of 103℃, with simultaneous ultrasonic assistance, and ultrasonic treatment at 40kHz and 40W for 3 minutes. The absorbance of the seed crystals was measured using a spectrophotometer. The specific steps are as follows: S31 uses a peristaltic pump to draw 10 mL of seed sample from the seed preparation tank into the mixing tank. 100 mL of water is added to the mixing tank for mixing. The gravity switch is then turned on. The absorbance of the mixed liquid is measured using a spectrophotometer; the absorbance is 1.25, indicating the addition of seed crystals. The seed crystals are then placed in the hydrolysis process within 6 minutes.

[0027] Example 3 A method for producing titanium dioxide by hydrolysis with added seed crystals to stabilize particle size includes the following steps: S1. Hexadecyltrimethylammonium bromide is added to a 100 g / L sodium hydroxide or potassium hydroxide solution and heated to 79 °C to obtain a preheated alkaline solution; the amount of hexadecyltrimethylammonium bromide added is 0.05% of the mass of TiO2 in the titanium solution. Polyethylene glycol 400 was added to a titanium melt with an F value of 1.8 and heated to 86°C to obtain a preheated titanium melt. The amount of polyethylene glycol 400 added was 0.5% of the mass of TiO2 in the titanium melt. S2 Add 0.5 cubic meters of preheated alkaline solution to the seed crystal preparation tank within 4 minutes; S3. Add 1 cubic meter of preheated titanium liquid to the seed crystal preparation tank within 5 minutes; S4 was subjected to isothermal ripening at 90℃ for 4 minutes, with ultrasonic assistance, and ultrasonic treatment at 40kHz and 40W for 2 minutes. The absorbance of the seed crystals was measured using a spectrophotometer. The specific steps are as follows: S31 uses a peristaltic pump to draw 10 mL of seed sample from the seed preparation tank into the mixing tank. 150 mL of water is added to the mixing tank for mixing. The gravity switch is turned on, and the absorbance of the mixed liquid is measured by a spectrophotometer. The absorbance is 1.13, indicating the addition of seed crystals. The seed crystals are then placed in the hydrolysis process within 4 minutes.

[0028] Example 4 A method for producing titanium dioxide by hydrolysis with added seed crystals to stabilize particle size includes the following steps: S1. Hexadecyltrimethylammonium bromide is added to a 120 g / L sodium hydroxide or potassium hydroxide solution and heated to 85 °C to obtain a preheated alkaline solution; the amount of hexadecyltrimethylammonium bromide added is 0.15% of the mass of TiO2 in the titanium solution. Polyethylene glycol 400 was added to a titanium melt with an F value of 1.95 and heated to 88°C to obtain a preheated titanium melt. The amount of polyethylene glycol 400 added was 0.8% of the mass of TiO2 in the titanium melt. S2 Add 0.8 cubic meters of preheated alkaline solution to the seed crystal preparation tank within 5 minutes; S3. Within 6 minutes, add 1.5 cubic meters of preheated molten titanium to the seed crystal preparation tank; S4 was subjected to isothermal ripening over 4 minutes at a temperature of 95°C. The absorbance of the seed crystals was measured using a spectrophotometer. The specific steps are as follows: S31 uses a peristaltic pump to draw 10 mL of seed sample from the seed preparation tank into the mixing tank. 120 mL of water is added to the mixing tank for mixing. The gravity switch is then turned on. The absorbance of the mixed liquid is measured using a spectrophotometer; the absorbance is 1.16, indicating the addition of seed crystals. The seed crystals are then placed in the hydrolysis process within 5 minutes.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that cetyltrimethylammonium bromide is not added to the alkaline solution.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that polyethylene glycol 400 is not added to the titanium solution.

[0031] Comparative Example 3 The difference between this comparative example and Example 1 is that, in S1, both hexadecyltrimethylammonium bromide and polyethylene glycol 400 were added to a sodium hydroxide solution and then heated.

[0032] Comparative Example 4 The difference between this comparative example and Example 1 is that, in S1, both hexadecyltrimethylammonium bromide and polyethylene glycol 400 are added to the titanium liquid and then heated.

[0033] Comparative Example 5 The difference between this comparative example and Example 1 is that the preheated titanium liquid, hexadecyltrimethylammonium bromide, and polyethylene glycol 400 were simultaneously added to the preheated alkaline solution in the seed crystal preparation tank.

[0034] Test case The hydrolysis process was consistent with that of the comparative examples, and the particle size of the added seed crystals and the D50 of the hydrolyzed particles obtained in the examples and comparative examples were detected.

[0035] Table 1. Particle size detection results

[0036] As shown in Table 1, the particle size distribution of the added seed crystals in the examples is 6.5-12.1 nm, and the D50 of the hydrolyzed particles is 2.6-4.3 μm. Compared with the comparative examples, the added seed crystals and hydrolyzed particles prepared in the examples have narrower particle size distribution and narrower D50 distribution. This indicates that the method of the present invention can improve the uniformity of the added seed crystals and enhance the stability of the D50 of the hydrolyzed particles.

[0037] The above are merely preferred embodiments of the present invention and are not intended to limit the present 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 producing titanium dioxide by hydrolysis with added seed crystals to stabilize particle size, characterized in that, Includes the following steps: S1 Add auxiliary agent I to the alkaline solution and heat it to obtain a preheated alkaline solution; Additive II was heated into the titanium liquid and heated to obtain a preheated titanium liquid. S2 adds preheated alkaline solution to the seed crystal preparation tank during the time interval t1-t2, with a volume of V1. S3 During the time interval t2-t3, preheated titanium liquid with a volume of V2 is added to the seed crystal preparation tank until V1 / V2 is 0.5-1:1-2; S4 undergoes isothermal ripening during the time interval t3-t4, and seed crystals are placed during the time interval t4-t5 to proceed with the hydrolysis process; Additive I is selected from hexadecyltrimethylammonium bromide, and additive II is selected from polyethylene glycol 400.

2. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, During the isothermal ripening stage, the absorbance of the seed crystals was measured using a spectrophotometer. The specific steps are as follows: S31 uses a peristaltic pump to extract seed samples from the seed preparation tank to the mixing tank, adds water to the mixing tank, and mixes the seed samples with water at a volume ratio of 1:10-15. The gravity switch is turned on, and the absorbance of the mixed liquid is measured by a spectrophotometer. S32 If the absorbance is 1.1-1.3, the seed crystal preparation is complete; If the absorbance exceeds 1.1-1.3, maintain the reaction temperature and retest every 1-2 minutes until the absorbance is 1.1-1.

3.

3. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, The concentration of the alkali solution is 100-150 g / L, and the F value of the titanium solution is 1.8-2.

0.

4. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, The alkaline solution is either sodium hydroxide solution or potassium hydroxide solution.

5. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, The temperature of the preheated alkaline solution is 79-88℃, and the temperature of the preheated titanium solution is 86-92℃.

6. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, The amount of additive I added is 0.05-0.2% of the mass of TiO2 in the titanium liquid, and the amount of additive II added is 0.5-1.5% of the mass of TiO2 in the titanium liquid.

7. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, t1-t2 is 4-8 min, t2-t3 is 5-8 min, t3-t4 is 4-5 min, and t4-t5 is 4-6 min.

8. The method for producing titanium dioxide with added seed crystals via hydrolysis according to claim 1, characterized in that, The constant temperature curing temperature is 90-103℃. Ultrasonic assistance is introduced during the constant temperature curing stage, and ultrasonic treatment is carried out at 40kHz and 40W for 2-3 minutes.

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