A method for preparing nano-titanium dioxide by using hydrochloric acid by-product of titanium dioxide production by chlorination method

Abstract

This invention discloses a method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the titanium dioxide production process via the chloride process, comprising the following steps: (1) distilling and concentrating the hydrochloric acid to obtain a titanium solution with a concentration of 4–10 mol / L; (2) diluting the titanium solution with water to obtain a diluted titanium solution with a concentration of 1–4 mol / L; (3) slowly adding an alkaline solution to the diluted titanium solution until it approaches the critical deposition point, at which point the addition of the alkaline solution is stopped, resulting in a critical deposition titanium solution; (4) heating and stirring the critical deposition titanium solution to deposit the solution, followed by filtration, washing, drying, calcination, and grinding to obtain rutile nano-titanium dioxide. This invention employs a critical homogeneous precipitation method, where alkali is slowly added at room temperature to neutralize the solution to the critical deposition point. This titanium solution serves as a homogeneous active reaction liquid, and low-temperature heating deposition is used to prepare nano-titanium dioxide with uniform particle size distribution.

Description

Technical Field

[0001] This invention relates to a technology for treating hydrochloric acid, a byproduct of titanium dioxide production via the chloride process, and more particularly to a method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of titanium dioxide production via the chloride process. Background Technology

[0002] Titanium dioxide, chemically known as titanium dioxide, is the most important compound of titanium, with the molecular formula TiO2. At room temperature, it hardly reacts with other compounds (including elements). Besides its highly stable chemical properties, titanium dioxide also possesses a high refractive index, ideal particle size distribution, excellent whiteness, gloss, dispersibility, wettability, hiding power, tinting strength, weather resistance (light resistance), and low oil absorption. It is a high-performance white pigment widely used in coatings, rubber, plastics, papermaking, printing inks, daily chemicals, electronics, microelectromechanical systems (MEMS), and environmental protection industries.

[0003] The chlorination process for producing titanium dioxide mainly involves mixing titanium-rich raw materials with petroleum coke and then carrying out a chlorination reaction in a chlorination furnace to produce a mixture containing titanium tetrachloride. The mixture exiting from the top of the chlorination furnace is separated from slag and dust by a cyclone dust collector to obtain crude titanium tetrachloride. Impurities such as VOCl3 in the crude titanium tetrachloride are then reacted with mineral oil to remove vanadium, and the crude titanium tetrachloride is further purified by distillation to obtain refined titanium tetrachloride. The refined titanium tetrachloride reacts with oxygen at high temperature to produce titanium dioxide, which is then further processed to obtain high-grade rutile titanium dioxide. The principle of the chlorination reaction is as follows:

[0004] TiO₂ + 2C + 2Cl₂ → TiCl₄ + 2CO

[0005] TiO₂ + C + 2Cl₂ → TiCl₄ + CO₂

[0006] During the chlorination reaction, a large amount of CO and CO2 gases are generated. Due to differences in process control, the proportions of CO and CO2 produced vary, generally containing 30-50% CO in the chlorination tail gas. In addition to large amounts of CO and CO2, the chlorination tail gas also contains small amounts of HCl and unreacted Cl2, requiring further treatment by a chlorination tail gas treatment system. Currently, chlorination tail gas is generally treated by acid washing and alkali washing, or by water washing and alkali washing. First, acidic gases such as HCl are removed by acid washing or water washing to generate hydrochloric acid as a byproduct. Then, alkali washing is used to treat the chlorine in the waste gas to generate 18%-30% hydrochloric acid as a byproduct. Due to the complex composition of the chlorination tail gas, the generated hydrochloric acid has a high impurity content, mainly containing silica gel, TiOCl2, and dust. Selling this byproduct hydrochloric acid directly as a hydrochloric acid product is impure and cannot be sold as high-quality hydrochloric acid, thus wasting titanium resources. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the titanium dioxide production process, in which titanium elements in the byproduct hydrochloric acid are prepared into nano-titanium dioxide, while high-purity hydrochloric acid is obtained.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the chloride process for titanium dioxide, comprising the following steps:

[0009] (1) The hydrochloric acid byproduct of the chloride process titanium dioxide is concentrated by distillation to obtain a titanium liquid with a concentration of 4-10 mol / L;

[0010] (2) Dilute the titanium solution with water to obtain a diluted titanium solution with a concentration of 1-4 mol / L;

[0011] (3) Slowly add an alkaline solution to the diluted titanium solution until it approaches the critical point of deposition, then stop adding the alkaline solution to obtain the titanium solution solution at the critical deposition point.

[0012] (4) After heating and stirring the critically deposited titanium liquid solution to deposit, the solution is filtered, washed, dried, calcined and ground to obtain rutile nano titanium dioxide.

[0013] Furthermore, the hydrochloric acid distilled in step (1) has a mass concentration of 25% to 30%.

[0014] Furthermore, the vacuum degree of the distillation concentration in step (1) is 0.1 to 0.3 MPa, and the temperature is 60 to 80 °C.

[0015] Furthermore, step (3) involves slowly adding an alkaline solution at room temperature for 0.5 to 3 hours.

[0016] Furthermore, the alkaline solution in step (3) is a solution of sodium hydroxide, ammonia, or sodium carbonate, and the concentration of the alkaline solution is 50 g / L to 200 g / L.

[0017] Furthermore, in step (4), the critically deposited titanium liquid solution is heated to 40-60°C for reaction, and after the solution turns blue, deposition continues for 0.5-2 hours.

[0018] Furthermore, the calcination temperature in step (4) is 600-800℃, and the calcination time is 2-6h.

[0019] Furthermore, in step (3), the critical amount of alkali used to reach the deposition critical point is the amount of alkali used (L) that causes the solution to change from clear to turbid during the slow addition of alkali solution to the titanium solution. The amount used to reach the deposition critical point is 0.8 L to 0.9 L. Generally, the critical amount of alkali used (L) is obtained after the solution changes from clear to turbid after adding alkali solution to the titanium solution for 30 to 60 minutes.

[0020] This invention utilizes reduced-pressure, low-temperature evaporation to concentrate and purify byproduct hydrochloric acid, while simultaneously recovering titanium elements through low-temperature concentration, yielding a titanium oxychloride concentrate. The concentrate is then diluted to a specific concentration and slowly neutralized with alkali at room temperature. The neutralization endpoint marks the critical point for deposition, at which point the titanium solution forms a homogeneous active reaction solution. Subsequently, the solution is stirred and heated to a specific temperature for a period of time to obtain nano-titanium dioxide with uniform particle size distribution. This method not only effectively utilizes hydrochloric acid from the chlorination process to obtain high-purity hydrochloric acid but also leverages its titanium content to prepare nano-titanium dioxide with uniform particle size distribution, achieving titanium resource recovery. Furthermore, the preparation method for nano-titanium dioxide is simple and easily controlled to ensure a homogeneous reaction, guaranteeing product quality stability. Additionally, by adjusting the titanium solution concentration and critical deposition temperature, the average particle size can be effectively controlled, resulting in high deposition efficiency, which is beneficial for high-capacity production. Adding titanium oxychloride solution to alkaline solution will cause a rapid reaction between the small amount of titanium oxychloride and the large amount of alkali in the solution, resulting in precipitation. Furthermore, the alkali in the solution is constantly being consumed, leading to a heterogeneous deposition process and making it difficult to control the particle size distribution of titanium dioxide. Adding alkaline solution under heating conditions will result in a more vigorous reaction, making particle size control difficult and leading to a product with larger particle size and a less concentrated particle size distribution.

[0021] The beneficial effects of this invention are: This invention adopts the critical homogeneous precipitation method, which slowly neutralizes the titanium solution to the critical point of deposition at room temperature, and uses this titanium solution as a homogeneous active reaction solution to prepare nano-titanium dioxide with uniform particle size distribution by low-temperature heating and deposition. Detailed Implementation

[0022] The present invention will be further described below with reference to embodiments.

[0023] Example 1:

[0024] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0025] The concentrated titanium solution was diluted with water to 2 mol / L. 230 ml of this 2 mol / L titanium solution was taken, and its deposition critical point was experimentally calculated. The experimental method was as follows: the deposition critical point was determined by continuously adding alkali until the deposit no longer dissolved, and the amount added was the critical deposition amount. In this example, 60 g / L sodium hydroxide alkali solution was slowly added to 230 ml of the 2 mol / L titanium solution at room temperature, with the addition time controlled at 1 hour. When 750 ml of sodium hydroxide alkali solution was added, the deposit no longer dissolved, and the critical deposition amount in this example was 750 mL.

[0026] Subsequently, 675 ml of 60 g / L sodium hydroxide alkaline solution was added to 230 ml of 2 mol / L titanium solution within 30 min and stirred. After the addition was completed, the mixture was stirred for 30 min. Then, the titanium solution at critical deposition was heated and stirred at 50 °C for 20 min. The solution began to turn blue and continued to deposit for 1 h.

[0027] The supernatant was filtered, then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m, then dried at 105℃ until the moisture content was below 0.3%, and finally calcined at 800℃ for 3 hours. After grinding, rutile nano-titanium dioxide with an average particle size of 60 nm was obtained, of which D10 was 33 nm and D90 was 116 nm.

[0028] Example 2:

[0029] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0030] The concentrated titanium solution was diluted with water to 4 mol / L. 230 ml of this 4 mol / L titanium solution was taken, and its deposition critical point was tested. The experimental method was as follows: the deposition critical point was determined by continuously adding alkali at room temperature until the deposit no longer dissolved, and the amount added was the critical deposition amount. In this example, 60 g / L sodium hydroxide alkali solution was slowly added to 230 ml of 4 mol / L titanium solution at room temperature, with the addition time controlled at 1 hour. When 1700 ml of sodium hydroxide alkali solution was added, the deposit no longer dissolved, and the critical deposition amount was found to be 1750 mL.

[0031] Subsequently, 1530 ml of 60 g / L sodium hydroxide alkaline solution was added to 230 ml of 4 mol / L titanium solution within 30 min and stirred. After the addition was completed, the mixture was stirred for 30 min. Then, the titanium solution at critical deposition was heated and stirred at 60 °C for 20 min. The solution began to turn blue and continued to deposit for 1 h.

[0032] The supernatant was filtered, then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m, then dried at 105℃ until the moisture content was below 0.3%, and finally calcined at 800℃ for 3 hours. After grinding, rutile nano-titanium dioxide with an average particle size of 80 nm was obtained, of which D10 was 45 nm and D90 was 147 nm.

[0033] Comparative Example 1: (Alkali solution was added during heating; otherwise, it was the same as in Example 1)

[0034] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0035] The concentrated titanium solution was diluted with water to 2 mol / L. 230 ml of the 2 mol / L titanium solution was taken and heated to 50 °C. Then, 750 ml of 60 g / L sodium hydroxide alkaline solution was slowly added to the 230 ml of 2 mol / L titanium solution, and the addition time was controlled to be 1 h. After the alkaline solution was completely added, the deposition continued for another 1 h.

[0036] The supernatant was filtered, then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m, then dried at 105℃ until the moisture content was below 0.3%, and finally calcined at 800℃ for 3 hours. After grinding, rutile nano-titanium dioxide with an average particle size of 68 nm was obtained, of which D10 was 18 nm and D90 was 134 nm.

[0037] Comparative Example 2: (Deposition temperature is less than the specified range, other conditions are the same as in Example 1)

[0038] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0039] The concentrated titanium solution was diluted with water to 2 mol / L. 230 ml of this 2 mol / L titanium solution was taken, and its deposition critical point was experimentally calculated. The experimental method was as follows: the deposition critical point was determined by continuously adding alkali until the deposit no longer dissolved, and the amount added was the critical deposition amount. In this example, 60 g / L sodium hydroxide alkali solution was slowly added to 230 ml of the 2 mol / L titanium solution at room temperature, with the addition time controlled at 1 hour. When 750 ml of sodium hydroxide alkali solution was added, the deposit no longer dissolved, and the critical deposition amount in this example was 750 mL.

[0040] Subsequently, 675 ml of 60 g / L sodium hydroxide alkaline solution was added to 230 ml of 2 mol / L titanium solution within 30 min and stirred. After the addition was completed, the mixture was stirred for 30 min. Then, the titanium solution at critical deposition was heated and stirred at 35 °C for 20 min, and then deposition was continued for 1 h.

[0041] The supernatant was filtered and then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m. It was then dried at 105 °C until the moisture content was below 0.3%. Finally, it was calcined at 800 °C for 3 hours and ground to obtain rutile nano-titanium dioxide with an average particle size of 45 nm. However, the Ti recovery rate was very low, less than 40%, because the temperature was too low and the reaction was incomplete.

[0042] Comparative Example 3: (Deposition temperature is greater than the range, other conditions are the same as in Example 1)

[0043] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0044] The concentrated titanium solution was diluted with water to 2 mol / L. 230 ml of this 2 mol / L titanium solution was taken, and its deposition critical point was experimentally calculated. The experimental method was as follows: the deposition critical point was determined by continuously adding alkali until the deposit no longer dissolved, and the amount added was the critical deposition amount. In this example, 60 g / L sodium hydroxide alkali solution was slowly added to 230 ml of the 2 mol / L titanium solution at room temperature, with the addition time controlled at 1 hour. When 750 ml of sodium hydroxide alkali solution was added, the deposit no longer dissolved, and the critical deposition amount in this example was 750 mL.

[0045] Subsequently, 675 ml of 60 g / L sodium hydroxide alkaline solution was added to 230 ml of 2 mol / L titanium solution within 30 min and stirred. After the addition was completed, the mixture was stirred for 30 min. Then, the titanium solution at critical deposition was heated and stirred at 80 °C for 20 min, and then deposition was continued for 1 h.

[0046] The supernatant was filtered, then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m, then dried at 105℃ until the moisture content was below 0.3%, and finally calcined at 800℃ for 3 hours. After grinding, rutile nano-titanium dioxide with an average particle size of 75 nm was obtained, of which D10 was 38 nm and D90 was 136 nm.

[0047] Comparative Example 4: (Titanium liquid concentration is greater than the range, other aspects are the same as in Example 1)

[0048] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0049] Take 230 ml of 5 mol / L concentrated titanium solution and calculate its deposition critical point. The experimental method is as follows: the deposition critical point is determined by continuously adding alkali at room temperature until the deposit no longer dissolves, and the amount added is the critical deposition amount. In this example, 60 g / L sodium hydroxide alkali solution is slowly added to 230 ml of 5 mol / L titanium solution at room temperature, and the addition time is controlled to be 1 h. When 2100 ml of sodium hydroxide alkali solution is added, the deposit no longer dissolves, and the critical deposition amount is 2100 ml.

[0050] Subsequently, 1890 ml of 60 g / L sodium hydroxide alkaline solution was added to 230 ml of 5 mol / L titanium solution within 30 min and stirred. After the addition was completed, the mixture was stirred for 30 min. Then, the titanium solution at critical deposition was heated and stirred at 50 °C for 20 min, and then deposition was continued for 1 h.

[0051] The supernatant was filtered, then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m, then dried at 105℃ until the moisture content was below 0.3%, and finally calcined at 800℃ for 3 hours. After grinding, rutile nano-titanium dioxide with an average particle size of 95 nm was obtained, of which D10 was 43 nm and D90 was 152 nm.

[0052] Comparative Example 5: (Titanium liquid concentration is less than the range, other aspects are the same as in Example 1)

[0053] Hydrochloric acid, a byproduct of the chloride process titanium dioxide containing 6000 ppm titanium (with a mass concentration of 28%), was distilled under reduced pressure (0.1 MPa) at 60°C to concentrate the titanium solution to a concentration of 5 mol / L. The distilled hydrochloric acid had a mass concentration of 26%.

[0054] The concentrated titanium solution was diluted with water to 0.5 mol / L. 230 ml of this 0.5 mol / L titanium solution was taken, and its deposition critical point was calculated. The calculation method was as follows: the deposition critical point was determined by continuously adding alkali until the deposit no longer dissolved, and the amount added was the critical deposition amount. In this example, 60 g / L sodium hydroxide solution was slowly added to 230 ml of 0.5 mol / L titanium solution at room temperature, with the addition time controlled at 1 hour. When 180 ml of sodium hydroxide solution was added, the deposit no longer dissolved, and the critical deposition amount was found to be 180 ml.

[0055] Subsequently, 162 ml of 60 g / L sodium hydroxide alkaline solution was added to 230 ml of 2 mol / L titanium solution within 30 min and stirred. After the addition was completed, the mixture was stirred for 30 min. Then, the titanium solution at critical deposition was heated and stirred at 50 °C for 20 min, and then deposition was continued for 1 h.

[0056] The supernatant was filtered and then washed with deionized water until the resistivity of the filter cake was above 100 Ω·m. It was then dried at 105 °C until the moisture content was below 0.3%. Finally, it was calcined at 800 °C for 3 hours and ground to obtain rutile nano-titanium dioxide with an average particle size of 25 nm. However, its Ti recovery rate was less than 30% due to low concentration and low reactivity.

Claims

1. A method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the titanium dioxide production process via the chloride process, characterized in that, Includes the following steps: (1) The hydrochloric acid byproduct of the chloride process titanium dioxide is concentrated by distillation to obtain a titanium liquid with a concentration of 4-10 mol / L; (2) Dilute the titanium solution with water to obtain a diluted titanium solution with a concentration of 1-4 mol / L; (3) Slowly add an alkaline solution to the diluted titanium solution until it approaches the critical point of deposition, and then stop adding the alkaline solution to obtain a titanium solution at critical deposition. Step (3) involves slowly adding the alkaline solution at room temperature for 0.5 to 3 hours. The critical amount of alkaline solution used in step (3) is the amount of alkaline solution used when the solution changes from clear to turbid during the slow addition of the alkaline solution to the titanium solution, and the amount used when it approaches the critical point of deposition is 0.8 L to 0.9 L. (4) After heating and stirring the critically deposited titanium liquid solution to deposit, filter, wash, dry, calcinate and grind to obtain rutile nano titanium dioxide; in step (4), the critically deposited titanium liquid solution is heated to 40-60℃ to react, and when the solution turns blue, it continues to deposit for 0.5-2h.

2. The method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the chloride process for titanium dioxide production, as described in claim 1, is characterized in that: The hydrochloric acid distilled in step (1) has a mass concentration of 25% to 30%.

3. The method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the chloride process for titanium dioxide production, as described in claim 1, is characterized in that: The vacuum degree of the distillation concentration in step (1) is 0.1-0.3 MPa, and the temperature is 60-80°C.

4. The method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the chloride process for titanium dioxide production, as described in claim 1, is characterized in that: The alkaline solution in step (3) is a solution of sodium hydroxide, ammonia or sodium carbonate, and the concentration of the alkaline solution is 50 g / L to 200 g / L.

5. The method for preparing nano-titanium dioxide using hydrochloric acid, a byproduct of the chloride process for titanium dioxide production, as described in claim 1, is characterized in that: The calcination temperature in step (4) is 600-800℃, and the calcination time is 2-6h.