Preparation method of monodisperse micron-sized barium metaphosphate

Abstract

The invention belongs to the technical field of preparation processes of barium metaphosphate, and particularly relates to a preparation method of monodisperse micron-sized barium metaphosphate. The preparation method comprises the following steps: mixing purified barium carbonate slurry and phosphoric acid according to a certain molar ratio, reacting to obtain barium dihydrogen phosphate slurry, adding ethanol and a particle size regulating agent, uniformly mixing, and carrying out spray drying to obtain a crude product; the particle size regulating agent comprises ammonium citrate, polyalcohol and barium metaphosphate; and calcining the crude product to obtain the product monodisperse micron-sized barium metaphosphate. According to the preparation method, a small amount of particle size regulating agent and a certain amount of ethanol are added, a crude product with uniform particle size distribution is prepared under a spray drying process condition, and then calcination is performed to obtain the micron-sized barium metaphosphate with uniform particle size distribution.

Description

Technical Field

[0001] This invention belongs to the technical field of barium metaphosphate preparation process, and particularly relates to a method for preparing monodisperse micron-sized barium metaphosphate. Background Technology

[0002] Barium metaphosphate, as an important inorganic functional material, plays a crucial role in the production of specialty optical glasses, particularly high-power laser glass. Furthermore, high-purity barium metaphosphate is essential in the fabrication of high-end lenses such as those used in high-definition cameras and mobile phone lenses. Micron-sized barium metaphosphate exhibits excellent optical properties in laser glass manufacturing, thus attracting widespread attention. However, currently, there is no effective process for the large-scale production of stable monodisperse products of micron-sized metaphosphates, including barium metaphosphate. Monodisperse metaphosphates, as raw materials for optical glasses, can reduce optical distortion and improve product quality.

[0003] Currently, the main preparation processes for barium metaphosphate are as follows: 1. High-temperature calcination method using barium carbonate: This method uses a mixture of barium carbonate and phosphate to prepare barium metaphosphate through high-temperature calcination. For example, CN115490221A discloses a method for producing barium metaphosphate using barium carbonate as raw material, including material reaction and dissolution, hydrogen sulfide gas absorption, hydrogen peroxide oxidation, impurity sedimentation and filtration, evaporation and crystallization, solid-liquid separation, and calcination. This method has a long process flow, high energy consumption, and uneven product particle size distribution, making it difficult to meet the requirements for micron-sized products. Furthermore, the phosphoric acid content in this process is far excessive, increasing costs and resulting in more free phosphorus in the product, affecting product quality. 2. Barium hydroxide-phosphoric acid synthesis method: CN1800000A discloses a method that uses the reaction of barium hydroxide and phosphoric acid followed by centrifugal spray drying technology, solving the problems of complex processes and high costs in barium metaphosphate production. Although this method can produce products with high purity, the spray-dried product is prone to agglomeration, making it difficult to accurately control the particle size distribution. III. Barium metaphosphate can be directly prepared in a one-step reaction by high-temperature calcination using barium sulfate and ammonium dihydrogen phosphate or phosphoric acid as raw materials. This method has low raw material costs, but the reaction is incomplete and the product purity is low. IV. CN113880065A discloses a method of slowly adding phosphoric acid solution and barium carbonate to a reactor in a specific ratio, recycling the filtrate, which solves the problems of high preparation cost and waste liquid recovery in existing barium metaphosphate production. However, current technologies mainly focus on how to prepare high-purity barium metaphosphate products, with little attention paid to the poor dispersion of micron-sized barium metaphosphate particles. Summary of the Invention

[0004] To overcome the shortcomings of poor particle size uniformity in existing micron-sized barium metaphosphate products, this invention proposes a method for preparing monodisperse micron-sized barium metaphosphate. Using reagent-grade high-purity barium carbonate and phosphoric acid as raw materials, barium dihydrogen phosphate is prepared. Then, a compound particle size modifier and ethanol are added, followed by spray drying and calcination to obtain a monodisperse micron-sized barium metaphosphate product. Specifically, this invention achieves the above objective through the following technical solutions: A method for preparing monodisperse micron-sized barium metaphosphate includes the following steps: (S1) Barium carbonate is added to water to prepare a barium carbonate slurry; (S2) The purified barium carbonate slurry was slowly added to the first phosphoric acid at a molar ratio of BaCO3:H3PO4 of 1:2.5-3.0. The system was heated to allow the reaction to proceed fully. Then, the second phosphoric acid was added at a molar ratio of BaCO3:H3PO4 of 1:0.5-1.0. After the reaction, barium dihydrogen phosphate slurry was obtained. (S3) Ethanol and particle size control agent are added to barium dihydrogen phosphate slurry, and after being mixed evenly, crude product is obtained by centrifugal spray drying; the particle size control agent includes ammonium citrate, polyol and barium metaphosphate. (S4) The crude product is calcined to obtain a monodisperse micron-sized barium metaphosphate product.

[0005] Furthermore, in step (S1), the solid content of the barium carbonate slurry is 15-20%.

[0006] Further, in step (S2), the phosphoric acid is electronic-grade phosphoric acid with a concentration of 75-85 wt%, diluted with deionized water to a concentration of 60-65 wt% before use; even further, the molar ratio of barium carbonate to the total molar ratio of the first and second phosphoric acids is 1:3.1-3.8; preferably 1:3.2-3.5. Barium carbonate is slowly added to the phosphoric acid. Initially, the phosphoric acid is in significant excess, and then more phosphoric acid is added to maintain the total molar ratio of phosphoric acid to barium carbonate within the aforementioned range. This yields high-purity barium dihydrogen phosphate while reducing the total amount of phosphoric acid added, thus reducing the difficulty and cost of subsequent processing of free phosphorus.

[0007] Furthermore, the solid content of the barium dihydrogen phosphate slurry obtained in step (S2) is 15-20%. Spray drying with the above-mentioned concentration of barium dihydrogen phosphate slurry is suitable and makes it easier to obtain a product with uniform particle size.

[0008] Further, in step (S3), the polyol is at least one of polyethylene glycol and polypropylene glycol with a number average molecular weight of 200-400.

[0009] Further, in step (S3), the mass ratio of barium dihydrogen phosphate slurry, ethanol and particle size control agent is 100:10-20:1-2; even further, the mass ratio of ammonium citrate, polypolyol and barium metaphosphate is 3-5:6-10:2-3.

[0010] This invention utilizes a compounded particle size control agent, namely ammonium citrate, polyol, and barium metaphosphate in a specific mass ratio, to directly and directly prepare monodisperse barium metaphosphate with a particle size of approximately 0.5-1 μm, preferably 0.7-0.9 μm, in a single step during subsequent spray drying. The inventors hypothesize that barium metaphosphate, acting as a seed crystal, guides the orderly and stable dehydration and crystallization of barium dihydrogen phosphate at the high temperature of spray drying, transforming the originally homogeneous nucleation into heterogeneous nucleation in the presence of ethanol, followed by simultaneous and stable crystal growth. Ammonium citrate adsorbs onto the seed crystal surface through complexation, adjusting the surface energy and achieving a regular morphology. The polyol provides steric hindrance protection, enhancing the stability of the slurry and preventing agglomeration. Note that ammonium citrate cannot be replaced with metal citrates such as sodium citrate or potassium citrate; otherwise, even if a barium metaphosphate product with uniform particle size is obtained, sodium / potassium impurities will be introduced, affecting the product's performance in high-purity applications. The molecular weight of the polyol should not be too large, and the dosage should not be too high; otherwise, the polymer chain will be too long, making atomization difficult and increasing the possibility of agglomeration. Extensive experiments have shown that a number-average molecular weight of 200-400 is optimal for polyols.

[0011] During the spray drying process, this invention creatively incorporates a certain amount of ethanol. On one hand, ethanol reduces the surface tension of the system; the reduced surface tension of the spray-dried slurry makes it easier to form smaller, more uniform droplets at the same centrifugal speed, reducing the number of irregular small droplets generated during atomization. On the other hand, ethanol has a lower boiling point and higher volatility, allowing the solution to evaporate and dry more quickly during spray drying, preventing droplet aggregation and adhesion. Through the synergistic effect of ethanol and a particle size modifier, this invention produces micron-sized barium metaphosphate with a uniform particle size distribution via spray drying, satisfying the requirements of a micron-sized barium metaphosphate product line.

[0012] Furthermore, in step (S3), the centrifugal spray drying parameters are: inlet air temperature 240-280℃, outlet air temperature 110-140℃, and atomizer centrifugal speed 15000-20000 rpm.

[0013] Further, in step (S4), the calcination temperature is 400-600℃ to fully dehydrate the crude product and remove free phosphorus, yielding the final product as monodisperse micron-sized barium metaphosphate. After spray drying, barium dihydrogen phosphate undergoes preliminary dehydration and conversion, and further calcination can further remove moisture and free phosphorus from the semi-finished product.

[0014] Compared with the prior art, the present invention has at least the following beneficial effects: I. In this invention, after preparing barium dihydrogen phosphate, it is not directly calcined. Instead, a small amount of particle size control agent and a certain amount of ethanol are added, and a crude product with uniform particle size distribution is obtained under spray drying conditions. Then, it is calcined to obtain micron-sized barium metaphosphate with uniform particle size distribution.

[0015] Second, the raw materials of this invention are basically the same as those of traditional high-purity barium metaphosphate. The addition of a spray drying process allows for the completion of the process conditions of this invention simply by adding spray drying equipment to existing traditional processes. There is no need to purchase large-scale equipment, making it convenient for process upgrades. Attached Figure Description

[0016] Figure 1 This is a SEM image of barium metaphosphate obtained in Example 1. Detailed Implementation

[0017] The technical solution of the present invention will be further explained and described below by way of embodiments.

[0018] Barium carbonate is reagent grade, with a purity ≥99.9% and a metal impurity content ≤20ppm; phosphoric acid is electronic grade, with a purity ≥99.99% and a metal impurity content ≤1ppm.

[0019] Example 1 (S1) Add 15 parts by mass of barium carbonate to 85 parts by mass of deionized water to prepare a barium carbonate slurry with a solid content of 15%. (S2) The purified barium carbonate slurry was slowly added to 60 wt% primary phosphoric acid at a BaCO3:H3PO4 molar ratio of 1:2.5 over 1 hour. The mixture was heated to 60°C and stirred to ensure complete reaction. The stirring and constant temperature of 60°C were maintained. Secondary phosphoric acid was added at a BaCO3:H3PO4 molar ratio of 1:0.7. After the reaction, barium dihydrogen phosphate slurry was obtained. The solid content of the barium dihydrogen phosphate slurry was adjusted to 15 wt% by concentration or by adding deionized water. (S3) Add 10 parts by mass of ethanol and 1 part by mass of particle size regulator to 100 parts by mass of barium dihydrogen phosphate slurry. The particle size regulator is a compound of ammonium citrate, PEG200 and barium metaphosphate in a mass ratio of 3:10:2. After mixing evenly, the crude product is obtained by spray drying. The spray drying process parameters are: inlet air temperature 260℃, outlet air temperature 120℃, and atomizer centrifugal speed 20000rpm. (S4) The crude product was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min. It was held at this temperature for 2 hours, then cooled to room temperature, washed with deionized water, and dried to obtain the product barium metaphosphate. Figure 1 This is a SEM image of barium metaphosphate obtained in Example 1.

[0020] Example 2 (S1) Add 15 parts by mass of barium carbonate to 85 parts by mass of deionized water to prepare a barium carbonate slurry with a solid content of 15%. (S2) The purified barium carbonate slurry was slowly added to 65 wt% primary phosphoric acid at a BaCO3:H3PO4 molar ratio of 1:3 over 1 hour. The mixture was heated to 60°C and stirred to ensure a complete reaction. The stirring and temperature were maintained at 60°C. Secondary phosphoric acid was added at a BaCO3:H3PO4 molar ratio of 1:0.5. After the reaction, barium dihydrogen phosphate slurry was obtained. The solid content of the barium dihydrogen phosphate slurry was adjusted to 15 wt% by concentration or by adding deionized water. (S3) Add 20 parts by mass of ethanol and 2 parts by mass of particle size control agent to 100 parts by mass of barium dihydrogen phosphate slurry. The particle size control agent is a compound of ammonium citrate, PEG400 and barium metaphosphate in a mass ratio of 5:6:3. After mixing evenly, the crude product is obtained by spray drying. The spray drying process parameters are: inlet air temperature 240℃, outlet air temperature 110℃, and atomizer centrifugal speed 15000rpm. (S4) The crude product was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min. It was held at this temperature for 2 hours, then cooled to room temperature, washed with deionized water, and dried to obtain the product barium metaphosphate.

[0021] Example 3 (S1) Add 20 parts by mass of barium carbonate to 80 parts by mass of deionized water to prepare a barium carbonate slurry with a solid content of 20%. (S2) The purified barium carbonate slurry was slowly added to 62 wt% primary phosphoric acid at a BaCO3:H3PO4 molar ratio of 1:2.7 over 1 hour. The mixture was heated to 60°C and stirred to ensure complete reaction. The stirring and constant temperature of 60°C were maintained. Secondary phosphoric acid was added at a BaCO3:H3PO4 molar ratio of 1:0.8. After the reaction, barium dihydrogen phosphate slurry was obtained. The solid content of the barium dihydrogen phosphate slurry was adjusted to 20 wt% by concentration or by adding deionized water. (S3) 16 parts by mass of ethanol and 1.7 parts by mass of particle size control agent are added to 100 parts by mass of barium dihydrogen phosphate slurry. The particle size control agent is a compound of ammonium citrate, PEG200 and barium metaphosphate in a mass ratio of 3:8:2. After mixing evenly, the crude product is obtained by spray drying. The spray drying process parameters are: inlet air temperature 280℃, outlet air temperature 140℃, and atomizer centrifugal speed 18000rpm. (S4) The crude product was placed in a tube furnace and heated to 500°C at a heating rate of 5°C / min. It was held at this temperature for 2 hours, then cooled to room temperature, washed with deionized water, and dried to obtain the product barium metaphosphate.

[0022] Example 4 The other conditions are the same as in Example 3, except that in step (S3), the amount of ethanol added is 8 parts by mass.

[0023] Example 5 The other conditions are the same as in Example 3, except that in step (S3), the amount of ethanol added is 24 parts by mass.

[0024] Example 6 The other conditions are the same as in Example 3, except that in step (S3), the particle size control agent is ammonium citrate, and PEG200 and barium metaphosphate are compounded in a mass ratio of 2:10:1.

[0025] Example 7 The other conditions are the same as in Example 3, except that in step (S3), the particle size control agent is a mixture of ammonium citrate, PEG200 and barium metaphosphate in a mass ratio of 5:5:3.

[0026] Example 8 The other conditions are the same as in Example 3, except that in step (S3), PEG200 is replaced with an equal mass of PEG500.

[0027] Example 9 The other conditions are the same as in Example 3, except that in step (S3), PEG200 is replaced with an equal mass of PEG100.

[0028] Comparative Example 1 The other conditions are the same as in Example 3, except that in step (S3), the particle size control agent is a mixture of ammonium citrate and barium metaphosphate in a mass ratio of 3:2, that is, PEG200 is not added to the particle size control agent.

[0029] Comparative Example 2 The other conditions are the same as in Example 3, except that in step (S3), the particle size control agent is a mixture of ammonium citrate and PEG200 in a mass ratio of 3:8, that is, barium metaphosphate is not added to the particle size control agent.

[0030] Comparative Example 3 The other conditions are the same as in Example 3, except that in step (S3), the particle size control agent is a mixture of PEG200 and barium metaphosphate in a mass ratio of 4:1, that is, ammonium citrate is not added to the particle size control agent.

[0031] Comparative Example 4 The other conditions are the same as in Example 3, except that ethanol is not added in step (S3).

[0032] Comparative Example 5 The other conditions are the same as in Example 3, except that step (S3) is changed to: 100 parts by mass of barium dihydrogen phosphate slurry is evaporated and crystallized to obtain barium dihydrogen phosphate slurry, centrifuged, and the solid is calcined for the first time at 200°C for 4 hours, and then calcined for the second time at 400°C for 2 hours.

[0033] Application examples The barium metaphosphate obtained in the above examples and comparative examples was tested, and the impurity results met the following requirements: free phosphorus (calculated as P2O5) content ≤ 0.05%, total metal impurity content ≤ 15 ppm, of which Fe impurity content ≤ 2 ppm, and S (calculated as SO3) content ≤ 15 ppm. The results are shown in Table 1 below, where the span was calculated according to the following formula. The lower the span, the narrower the particle size distribution: Span = (D90 - D10) / D50 Table 1. Test results of barium metaphosphate performance indicators .

Claims

1. A method for preparing monodisperse micron-sized barium metaphosphate, characterized by, The method comprises the following steps: (S1) preparing barium carbonate slurry by adding barium carbonate into water; (S2) slowly adding the purified barium carbonate slurry into the first phosphoric acid to make the molar ratio of BaCO3:H3PO4 1:2.5-3.0, heating to make the system fully react, and then adding the second phosphoric acid according to the molar ratio of BaCO3:H3PO4 1:0.5-1.0, to obtain barium dihydrogen phosphate slurry after reaction; (S3) adding ethanol and particle size control agent into the barium dihydrogen phosphate slurry, uniformly mixing, and then obtaining the crude product by centrifugal spray drying; the particle size control agent comprises ammonium citrate, polyhydric alcohol and barium metaphosphate; (S4) calcining the crude product to obtain the product monodisperse micron-sized barium metaphosphate.

2. The production method according to claim 1, characterized by, In step (S1), the solid content of the barium carbonate slurry is 15-20%.

3. The production method according to claim 1, characterized by, In step (S2), the phosphoric acid is electronic-grade phosphoric acid with a concentration of 75-85wt%, which is diluted to a concentration of 60-65wt% with deionized water before use; further, the ratio of the amount of substance of barium carbonate to the total amount of substance of the first phosphoric acid and the second phosphoric acid is 1:3.1-3.8; preferably 1:3.2-3.

5.

4. The production method according to claim 1, characterized by, The solid content of the barium dihydrogen phosphate slurry obtained in step (S2) is 15-20%.

5. The production method according to claim 1, characterized by, In step (S3), the polyhydric alcohol is at least one of polyethylene glycol and polypropylene glycol with a number average molecular weight of 200-400.

6. The production method according to claim 1, characterized by, In step (S3), the mass ratio of the barium dihydrogen phosphate slurry, ethanol and particle size control agent is 100:10-20:1-2.

7. The production method according to claim 1, characterized by, In step (S3), the mass ratio of ammonium citrate, polyhydric alcohol and barium metaphosphate is 3-5:6-10:2-3.

8. The production process according to claim 1, characterized in that, In step (S3), the centrifugal spray drying parameters are an inlet air temperature of 240-280℃, an outlet air temperature of 110-140℃, and a centrifugal speed of the atomizer of 15000-20000rpm.

9. The production process according to claim 1, characterized in that, In step (S4), the calcination temperature is 400-600℃, and the calcination time is 1-3h.

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