High and low concentration titanium liquid comprehensive hydrolysis process

Abstract

The application provides a high and low concentration titanium liquid comprehensive hydrolysis process and relates to the technical field of titanium liquid hydrolysis.The hydrolysis process comprises the following steps: in the initial stage, high concentration titanium liquid is added into lye to form primary crystal seeds;in the first boiling stage, the primary crystal seeds are added into the high concentration titanium liquid, the temperature is increased to boiling, microwave treatment is performed, and when the grey point is reached, stirring and heating are stopped;in the first boiling maintaining stage, low concentration titanium liquid is added at 1-5 DEG C lower than the boiling temperature;in the second boiling stage, the temperature is continuously increased to boiling, and the low concentration titanium liquid is additionally added;and the first adjusting agent and the second adjusting agent are respectively added in the initial stage and the first boiling maintaining stage, the first adjusting agent is a sodium salt, and the second adjusting agent is citric acid, ammonium persulfate and sodium hexametaphosphate.The process can reduce the use amount of high concentration titanium liquid, reduce energy consumption and cost, improve the quality of crystal seeds and increase the hydrolysis rate.

Description

Technical Field

[0001] This invention relates to the field of titanium liquid hydrolysis technology, and more specifically, to a comprehensive hydrolysis process for high and low concentration titanium liquids. Background Technology

[0002] Titanium dioxide, as an important inorganic pigment, has its particle size distribution, optical properties, and energy efficiency directly affected by the hydrolysis process in its production. Traditional sulfuric acid process for titanium dioxide production mostly adopts the self-generated seed hydrolysis method, but it has the following problems: (1) Dependence on high-concentration titanium solution: The existing self-generated seed process requires a high concentration of titanium solution, which needs to be increased through a concentration process, resulting in increased steam energy consumption (1.2-2.0 tons of steam per ton of titanium dioxide). (2) Limited application of low-concentration titanium solution: When low-concentration titanium solution is directly hydrolyzed, insufficient seed generation is easily caused by low hydrolysis rate (<90%) and uneven distribution of metatitanic acid particle size, which affects the tinting strength (<120) and brightness (<94.5%) of titanium dioxide.

[0003] To address these issues, existing technologies attempt to improve the base water formulation (such as replacing pure water with hot alkaline solution) or optimize the feeding rate, but it remains difficult to balance the seeding efficiency and energy consumption of low-concentration titanium solutions. Therefore, an innovative process is urgently needed that can combine the advantages of both high and low concentration titanium solutions, reduce concentration energy consumption, and improve seed quality. Summary of the Invention

[0004] The purpose of this invention is to provide a comprehensive hydrolysis process for high and low concentration titanium liquid, which can reduce the amount of high concentration titanium liquid used, reduce energy consumption and cost, and also improve the quality of seed crystals and increase the hydrolysis rate.

[0005] This invention is achieved through the following technical solution:

[0006] A combined high- and low-concentration titanium liquid hydrolysis process includes the following steps:

[0007] Initial stage: High-concentration titanium liquid is added to alkaline solution to form primary seed crystals;

[0008] First boiling stage: Add primary seed crystals to high-concentration titanium liquid, heat to boiling, microwave treatment, and stop stirring and heating when the ash point is reached;

[0009] During the first boiling stage: add a low concentration of titanium liquid at a temperature 1-5°C below the boiling point;

[0010] Second boiling stage: Continue heating to boiling point, and add low-concentration titanium liquid;

[0011] It also includes adding a first modifier and a second modifier in the initial stage and the first boil-holding stage, respectively. The first modifier is a sodium salt, and the second modifier is citric acid, ammonium persulfate, and sodium hexametaphosphate.

[0012] Preferably, the concentration of the high-concentration titanium solution is 160-250 g / L, the concentration of the alkali solution is 100-200 g / L, the alkali-to-titanium ratio of the high-concentration titanium solution to the alkali solution is 0.20-0.38, and the high-concentration titanium solution and the alkali solution are preheated to 70-96℃ before mixing. During the pretreatment process, the stirring speed is 5-10 r / min, which can reduce turbulent shear force and prevent premature agglomeration of seed crystals.

[0013] Preferably, the microwave processing is performed at a power of 300-500W, a frequency of 2.45GHz, and a time of 10-15min.

[0014] Preferably, the concentration of the low-concentration titanium liquid is 120-150 g / L, and the low-concentration titanium liquid is preheated to 60-85℃ before being added.

[0015] Preferably, the amount of primary seed crystals added is 2-4% of the total mass of hydrolyzed titanium, the total amount of low-concentration titanium liquid added is 10-30% of the total mass of hydrolyzed titanium, and the mass ratio of low-concentration titanium liquid in the first boiling stage and the second boiling stage is 1:0.4-0.8.

[0016] Preferably, the heating rate during the first boiling stage is 0.5℃ / min; the heating rate during the second boiling stage is 1℃ / min, and the process is maintained at a gentle boil for 60-80 min.

[0017] Preferably, during the initial boiling stage, a 365nm ultraviolet light source is simultaneously introduced to irradiate the hydrolysis system, and this temperature is maintained for 30-60 minutes. The ultraviolet light source can excite the generation of hydroxyl radicals on the surface of titanium particles, which then react with organic acids in the solution to form complexes, creating a dynamic dispersion interface and improving the dispersibility of the titanium solution.

[0018] Preferably, during the second boiling stage, after adding a low-concentration titanium solution, the sulfuric acid concentration in the system is adjusted to 0.6 ± 0.02 mol / L. Adjusting the sulfuric acid concentration can induce uniform seed crystal growth and prevent heterogeneous nucleation caused by localized over-alkaliness.

[0019] Preferably, the mass ratio of the first modifier to the high-concentration titanium solution is 1:8-12, and the sodium salt is sodium sulfate, sodium chloride, or sodium sulfonate.

[0020] Preferably, the mass ratio of the second modifier to the low-concentration titanium liquid is 1:18-22, and the mass ratio of citric acid, ammonium persulfate and sodium hexametaphosphate is 1-3:1:1.

[0021] The technical solution of the present invention has at least the following advantages and beneficial effects:

[0022] In the initial stage, the high-concentration titanium solution, after mixing with the alkaline solution, forms primary seed crystals, providing growth sites for subsequent hydrolysis. However, the high-concentration titanium solution has a high degree of supersaturation, resulting in a rapid crystal nucleus formation rate and the formation of titanium oxide groups (such as [Ti(OH)2)). 2+ During nucleation, crystals are prone to agglomeration due to van der Waals forces or hydrogen bonding. To prevent premature agglomeration of seed crystals, a first modifier is used. Sodium salt can increase the ion concentration in the solution, compress the electric double layer around the colloidal particles, and reduce the electrostatic repulsion between particles, thereby inhibiting excessive agglomeration. At the same time, it can also inhibit local supersaturation, reduce heterogeneous nucleation, and promote the directional formation of crystal nuclei.

[0023] The first boiling point, the first boiling point maintenance stage, and the second boiling point are transitional stages. The system concentration is gradually reduced by adding low-concentration titanium solution, thus rationally controlling the titanium solution concentration gradient during hydrolysis and reducing the amount of high-concentration titanium solution used. This concentration gradient induces the stepwise growth of seed crystals, reducing the initial concentration requirement and improving seed crystal uniformity, thereby enhancing seed crystal quality. However, changes in the concentration gradient may lead to a decrease in seed crystal stability; therefore, a second modifier is used. Ammonium persulfate decomposes in the acidic titanium solution to generate sulfate free radicals, and Ti in the titanium oxide solution... 3+ To Ti 4+ Simultaneously generating active Ti 3+ Sites that enhance the hydrolysis activity of titanium solution, Ti 3+ / Ti 4+ The presence of redox pairs can regulate the hydrolysis equilibrium of titanium oxide groups, lower the nucleation energy barrier, and promote the effective hydrolysis of low-concentration titanium solutions. Citric acid can chelate Ti. 4+ Sodium hexametaphosphate slows down the hydrolysis rate, prevents excessively rapid particle growth, improves particle uniformity, and reduces secondary agglomeration. It can also prevent the agglomeration of hydrolysis products, optimize particle distribution, enhance seed crystal activity, and increase the hydrolysis rate.

[0024] The hydrolysis reaction is initiated at the first boil stage to promote seed crystal growth, providing growth sites for subsequent hydrolysis. The first boil-holding stage allows the seed crystals to grow fully and stabilize, preventing excessively rapid hydrolysis that could lead to uneven particle size. The second boil-holding stage accelerates the hydrolysis reaction, ensuring complete hydrolysis of titanate to generate hydrated titanium dioxide, while simultaneously regulating the product particle size and crystal form. During hydrolysis, the ionic system formed by the second modifier maintains the pH of the hydrolysis system within the range of 2.5-3.5, preventing excessive local acidity that could corrode the seed crystals. Simultaneously, the second modifier interacts with Ti... 3+ / Ti 4+ The reaction can expose the titanium oxide group ([Ti(OH))). + The active sites of the pre-dispersed seed crystals reduce the hydrolysis activation energy of low-concentration titanium liquid from 85 kJ / mol in the traditional process to 72 kJ / mol. The pre-dispersed seed crystals serve as heterogeneous nucleation templates, reducing the nucleation energy barrier of low-concentration titanium liquid and inducing it to be deposited on the seed crystal surface in an "epitaxical growth" mode, rather than generating new crystal nuclei.

[0025] Microwaves selectively heat polar molecules (such as H₂O and titanium oxide groups) through dielectric heating, raising the local reaction temperature and reducing the activation energy of the hydrolysis reaction. Microwave treatment can also physically promote the directional alignment of titanium liquid molecules, shortening the crystal nucleation time and inhibiting seed agglomeration. The high-temperature micro-boiling state in the later stages accelerates the hydrolysis reaction kinetics, while the low concentration reduces the supersaturation of the titanium liquid, inhibiting the formation of new crystal nuclei and promoting the directional growth of existing seeds, resulting in uniformly sized metatitanic acid particles. Detailed Implementation

[0026] 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.

[0027] Example 1

[0028] A combined high- and low-concentration titanium liquid hydrolysis process includes the following steps:

[0029] Initial stage: The high-concentration titanium liquid with a concentration of 250 g / L and the alkaline solution with a concentration of 200 g / L are preheated to 96℃ respectively. Then, the high-concentration titanium liquid is added to the alkaline solution with an alkaline-to-titanium ratio of 0.38. The stirring speed is 10 r / min. Sodium sulfate is added while stirring. The mass ratio of the first modifier to the high-concentration titanium liquid is 1:12 to form primary seed crystals.

[0030] First boiling stage: Add primary seed crystals to the hydrolysis pot at 4% of the total mass of hydrolyzed titanium, then add them to a high-concentration titanium liquid preheated to 80℃ with a concentration of 200g / L, heat to boiling at a rate of 0.5℃ / min, and microwave for 15min at a power of 500W and a frequency of 2.45GHz until the ash point is reached, then stop stirring and heating;

[0031] Maintaining the boiling point: Add a low-concentration titanium solution with a concentration of 120 g / L at a temperature 5°C below the boiling point, and then add a second modifier. The mass ratio of the second modifier to the low-concentration titanium solution is 1:22. The second modifier includes citric acid, ammonium persulfate, and sodium hexametaphosphate in a mass ratio of 1:1:1. Maintain this temperature for 60 minutes, and simultaneously introduce a 365 nm ultraviolet light source to irradiate the hydrolysis system.

[0032] Second boiling stage: Continue heating to boiling at a rate of 1℃ / min, add low-concentration titanium solution, adjust the sulfuric acid concentration of the system to 0.6±0.02mol / L, add water, and maintain a gentle boiling treatment for 80min.

[0033] The total amount of low-concentration titanium solution added is 30% of the total mass of hydrolyzed titanium. The mass ratio of low-concentration titanium solution in the first boiling stage and the second boiling stage is 1:0.4. The low-concentration titanium solution in each stage is added within 20 minutes.

[0034] Example 2

[0035] A combined high- and low-concentration titanium liquid hydrolysis process includes the following steps:

[0036] Initial stage: The high-concentration titanium liquid with a concentration of 200 g / L and the alkaline solution with a concentration of 150 g / L are preheated to 85°C. The high-concentration titanium liquid is then added to the alkaline solution for pretreatment. The alkaline-to-titanium ratio is 0.25, the stirring speed is 5 r / min, and sodium chloride is added while stirring. The mass ratio of the first modifier to the high-concentration titanium liquid is 1:8 to form primary seed crystals.

[0037] First boiling stage: Add primary seed crystals at 2% of the total mass of hydrolyzed titanium to the hydrolysis pot, then add it to a high-concentration titanium liquid preheated to 70℃ with a concentration of 180g / L, heat to boiling at a rate of 0.5℃ / min, and microwave for 10 minutes at a power of 300W and a frequency of 2.45GHz until the ash point is reached, then stop stirring and heating;

[0038] Maintaining the boiling point: Add a low-concentration titanium solution with a concentration of 130 g / L at a temperature 1°C below the boiling point, and then add a second modifier. The mass ratio of the second modifier to the low-concentration titanium solution is 1:18. The second modifier includes citric acid, ammonium persulfate, and sodium hexametaphosphate in a mass ratio of 2:1:1. Maintain this temperature for 30 minutes, and simultaneously introduce a 365 nm ultraviolet light source to irradiate the hydrolysis system.

[0039] Second boiling stage: Continue heating to boiling at a rate of 1℃ / min, add low-concentration titanium solution, adjust the sulfuric acid concentration of the system to 0.6±0.02mol / L, add water, and maintain a gentle boil for 60min.

[0040] The total amount of low-concentration titanium solution added is 10% of the total mass of hydrolyzed titanium. The mass ratio of low-concentration titanium solution in the first boiling stage and the second boiling stage is 1:0.6. The low-concentration titanium solution in each stage is added within 20 minutes.

[0041] Example 3

[0042] A combined high- and low-concentration titanium liquid hydrolysis process includes the following steps:

[0043] Initial stage: The high-concentration titanium liquid with a concentration of 160 g / L and the alkaline solution with a concentration of 100 g / L are preheated to 70°C. The high-concentration titanium liquid is then added to the alkaline solution for pretreatment. The alkaline-to-titanium ratio is 0.20, the stirring speed is 8 r / min, and sodium sulfonate is added while stirring. The mass ratio of the first modifier to the high-concentration titanium liquid is 1:10 to form primary seed crystals.

[0044] First boiling stage: Add primary seed crystals to the hydrolysis pot at 3% of the total mass of hydrolyzed titanium, then add it to a high-concentration titanium liquid preheated to 96℃ with a concentration of 190g / L, heat to boiling at a rate of 0.5℃ / min, and microwave for 12min at a power of 400W and a frequency of 2.45GHz until the ash point is reached, then stop stirring and heating;

[0045] Maintaining the boiling point: Add a low-concentration titanium solution with a concentration of 150 g / L at a temperature 3°C below the boiling point, and then add a second modifier. The mass ratio of the second modifier to the low-concentration titanium solution is 1:20. The second modifier includes citric acid, ammonium persulfate, and sodium hexametaphosphate in a mass ratio of 3:1:1. Maintain this temperature for 40 minutes, and simultaneously introduce a 365 nm ultraviolet light source to irradiate the hydrolysis system.

[0046] Second boiling stage: Continue heating to boiling at a rate of 1℃ / min, add low-concentration titanium solution, adjust the sulfuric acid concentration of the system to 0.6±0.02mol / L, add water, and maintain a gentle boiling treatment for 70min.

[0047] The total amount of low-concentration titanium solution added is 20% of the total mass of hydrolyzed titanium. The mass ratio of low-concentration titanium solution in the first boiling stage and the second boiling stage is 1:0.8. The low-concentration titanium solution in each stage is added within 20 minutes.

[0048] Comparative Example 1

[0049] The difference between this comparative example and Example 1 is that the low-concentration titanium liquid was added completely during the first boil-holding stage.

[0050] Comparative Examples 2-3

[0051] The amount of primary seed crystals added was 1% and 10% of the total mass of hydrolyzed titanium, respectively, and the rest was the same as in Example 1.

[0052] Comparative Example 4-5

[0053] The total amount of low-concentration titanium liquid added was 5% and 40% of the total mass of hydrolyzed titanium, respectively, and the rest was the same as in Example 1.

[0054] Comparative Example 6

[0055] The difference between this comparative example and Example 1 is that microwave processing is not performed.

[0056] Comparative Example 7

[0057] The difference between this comparative example and Example 1 is that the hydrolysis system is not irradiated with ultraviolet light.

[0058] Comparative Example 8

[0059] The difference between this comparative example and Example 1 is that no first modifier is added.

[0060] Comparative Example 9

[0061] The difference between this comparative example and Example 1 is that no second modifier is added.

[0062] Comparative Example 10

[0063] The difference between this comparative example and Example 1 is that the second modifier consists only of citric acid.

[0064] Comparative Example 11

[0065] The difference between this comparative example and Example 1 is that the second modifier consists only of ammonium persulfate.

[0066] The test data for the examples and comparative examples were recorded, and the results are as follows:

[0067] Table 1. Experimental Results

[0068] Hydrolysis rate % 96 95.9 95.7 94.68 94.75 94.81 94.98 D10(μm) 1.879 1.948 1.891 1.109 1.039 1.309 1.349 D50(μm) 3.133 3.39 3.453 3.642 3.715 2.712 2.851 D90(μm) 5.333 5.172 5.701 5.882 5.918 4.382 4.458 Horizontal distance (μm) 1.162 0.951 1.103 1.264 1.218 1.294 1.285 Blue light whiteness 92.9 91.9 92.4 90.7 90.7 90.7 91.7 brightness 95.2 95.0 95.1 92.6 92.1 91.7 92.5 Decolorizing power ≥130 ≥130 ≥130 ≥120 ≥120 ≥120 ≥120 Group Comparative Example 5 Comparative Example 6 Comparative Example 7 Comparative Example 8 Comparative Example 9 Comparative Example 10 Comparative Example 11 Hydrolysis rate % 94.5 95.0 95.3 94.12 94.35 94.51 94.68 D10(μm) 1.579 1.436 1.299 1.266 1.325 1.471 1.352 D50(μm) 4.133 3.179 2.961 2.888 3.025 3.289 3.173 D90(μm) 5.933 5.566 5.097 4.896 5.118 5.677 5.487 Horizontal distance (μm) 1.195 1.299 1.283 1.257 1.254 1.279 1.303 Blue light whiteness 90.9 92.5 92.4 89.7 90.1 91.2 91.5 brightness 93.2 94.5 95.1 91.6 90.7 92.2 92.8 Decolorizing power ≥120 ≥120 ≥120 ≤120 ≤120 ≤120 ≤120

[0069] As shown in Table 1, compared with the comparative examples, Examples 1-3 have higher hydrolysis rate, blue light whiteness, brightness and tinting strength, narrower seed particle size distribution and higher product uniformity.

[0070] 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 comprehensive hydrolysis process for high and low concentration titanium liquid, characterized in that: Includes the following steps: Initial stage: High-concentration titanium liquid is added to alkaline solution to form primary seed crystals; First boiling stage: Add primary seed crystals to high-concentration titanium liquid, heat to boiling, microwave treatment, and stop stirring and heating when the ash point is reached; During the first boiling stage: add a low concentration of titanium liquid at a temperature 1-5°C below the boiling point; Second boiling stage: Continue heating to boiling point, and add low-concentration titanium liquid; It also includes adding a first modifier and a second modifier in the initial stage and the first boil-holding stage, respectively. The first modifier is a sodium salt, and the second modifier is citric acid, ammonium persulfate, and sodium hexametaphosphate.

2. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 1, characterized in that: The concentration of the high-concentration titanium solution is 160-250 g / L, the concentration of the alkaline solution is 100-200 g / L, the alkali-to-titanium ratio of the high-concentration titanium solution to the alkaline solution is 0.20-0.38, and the high-concentration titanium solution and the alkaline solution are preheated to 70-96℃ respectively before mixing.

3. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 1, characterized in that: During microwave processing, the power is 300-500W, the frequency is 2.45GHz, and the time is 10-15min.

4. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 1, characterized in that: The concentration of the low-concentration titanium liquid is 120-150 g / L, and it should be preheated to 60-85℃ before being added.

5. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 4, characterized in that: The amount of primary seed crystals added is 2-4% of the total mass of hydrolyzed titanium, and the total amount of low-concentration titanium liquid added is 10-30% of the total mass of hydrolyzed titanium. The mass ratio of low-concentration titanium liquid in the first boiling stage and the second boiling stage is 1:0.4-0.

8.

6. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 5, characterized in that: The heating rate during the first boiling stage is 0.5℃ / min; the heating rate during the second boiling stage is 1℃ / min, and the process is maintained at a gentle boil for 60-80 min.

7. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 6, characterized in that: During the first boiling stage, a 365nm ultraviolet light source is simultaneously introduced to irradiate the hydrolysis system, and the temperature is maintained for 30-60 minutes.

8. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 1, characterized in that: During the second boiling stage, after adding low-concentration titanium liquid, the sulfuric acid concentration in the system was adjusted to 0.6±0.02mol / L.

9. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 1, characterized in that: The mass ratio of the first modifier to the high-concentration titanium liquid is 1:8-12, and the sodium salt is sodium sulfate, sodium chloride, or sodium sulfonate.

10. The integrated hydrolysis process for high and low concentration titanium liquid according to claim 1, characterized in that: The mass ratio of the second modifier to the low-concentration titanium liquid is 1:18-22, and the mass ratio of citric acid, ammonium persulfate and sodium hexametaphosphate is 1-3:1:1.