A method for preparing high surface area metal fluorides from aqueous phase polyamines

Abstract

This invention discloses a method for preparing high specific surface area metal fluorides using aqueous polyamines. This method is suitable for preparing magnesium fluoride and aluminum fluoride. The preparation of magnesium fluoride includes: adding polyamine to an aqueous solution of a soluble magnesium salt at 30℃–60℃ with stirring, then adding hydrofluoric acid dropwise, and continuing stirring for 10–70 minutes after the addition is complete; adding ammonia dropwise to adjust the pH to 8–10, and continuing stirring for 60–180 minutes; filtration, washing the filter cake with deionized water until the pH of the filtrate is ~7, drying at 80℃–120℃, and calcining at 260℃–400℃. The preparation of aluminum fluoride includes: adding polyamine to an aqueous solution of a soluble aluminum salt at 30℃–60℃ with stirring, then adding hydrofluoric acid dropwise, and continuing stirring for 30–90 minutes after the addition is complete; filtration, washing the filter cake with deionized water until the pH of the filtrate is ~7, drying at 80℃–120℃, and calcining at 260℃–400℃. This invention can effectively reduce the preparation cost of high specific surface area metal fluorides and has industrial application value.

Description

Technical Field

[0001] This invention relates to a method for preparing metal fluorides, specifically to a method for preparing high specific surface area metal fluorides from aqueous polyamines. Background Technology

[0002] Metal fluorides, particularly aluminum fluoride and magnesium fluoride, are widely used as catalysts or catalyst supports. Metal fluorides can exist stably for extended periods in high-temperature HF atmospheres and are important catalysts for the industrial synthesis of CFC substitutes such as hydrofluorocarbons (HFCs) and hydrofluoroolefins (HFOs). For metal fluorides to be used as catalysts or supports, they must possess a high specific surface area to achieve considerable catalytic activity. Therefore, the preparation of metal fluorides with high specific surface area has been a key research focus in the CFC substitute manufacturing industry.

[0003] In the existing technology, there are examples of preparing amorphous AlF3 and amorphous MgF2 by anhydrous sol-gel fluorination, and there are also examples of preparing α-AlF3 and MgF2 by sol-gel method in aqueous system. However, the current preparation methods of aluminum fluoride and magnesium fluoride still have at least the following problems: (1) Anhydrous sol-gel fluorination uses expensive organometallic salts as metal sources and anhydrous HF organic solvent as fluorine source, resulting in high preparation costs of aluminum fluoride and magnesium fluoride. Moreover, this method must be operated under anhydrous conditions, the process is complicated, and it is difficult to apply to industrial production. At the same time, the obtained aluminum fluoride has an amorphous structure, is unstable at high temperature, and is easy to crystallize into fluorides with low specific surface area; (2) The preparation process of sol-gel method in aqueous system requires the use of a large amount of expensive polyols as solvent, resulting in high preparation costs of aluminum fluoride and magnesium fluoride. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing high specific surface area metal fluorides from aqueous polyamines. This preparation method is simple, mild, and has low production costs.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for preparing high specific surface area metal fluorides from aqueous polyamines, which can prepare magnesium fluoride and aluminum fluoride;

[0007] The preparation of the magnesium fluoride includes the following steps:

[0008] Step a1: While stirring, add polyamine to a soluble magnesium salt aqueous solution at 30℃~60℃, then add hydrofluoric acid dropwise. After the addition is complete, continue stirring for 10min~70min.

[0009] Step a2: Add ammonia dropwise to adjust the pH to 8-10, and continue stirring for 60-180 minutes.

[0010] Step a3: Filter by suction, wash the filter cake with deionized water until the pH of the filtrate is 7, dry at 80℃~120℃, and calcine at 260℃~400℃;

[0011] The preparation of the aluminum fluoride includes the following steps:

[0012] Step b1: While stirring, add polyamine to the soluble aluminum salt aqueous solution at 30℃~60℃, then add hydrofluoric acid dropwise. After the addition is complete, continue stirring for 30min~90min.

[0013] Step b2: Filter by suction, wash the filter cake with deionized water until the pH of the filtrate is 7, dry at 80℃~120℃, and calcine at 260℃~400℃.

[0014] The present invention also includes the following technical features:

[0015] Specifically, the soluble magnesium salt is magnesium chloride, magnesium nitrate, or magnesium sulfate.

[0016] Specifically, the soluble aluminum salt is aluminum chloride, aluminum nitrate, or aluminum sulfate.

[0017] Specifically, the polyamine is ethylenediamine, 1,2-propanediamine, or 1,3-propanediamine.

[0018] Specifically, in step a1, the amount of polyamine used is 0.5% to 5% of the mass of the soluble magnesium salt aqueous solution; in step b1, the amount of polyamine used is 0.5% to 5% of the mass of the soluble aluminum salt aqueous solution.

[0019] Specifically, in step a1, the molar ratio of hydrofluoric acid to soluble magnesium salt is 2 to 4:1.

[0020] Specifically, in step b1, the molar ratio of hydrofluoric acid to soluble aluminum salt is 3 to 6:1.

[0021] Compared with the prior art, the present invention has the following technical effects:

[0022] (1) Compared with the anhydrous sol-gel fluorination method, the present invention uses inexpensive inorganic aluminum source, inorganic magnesium source and hydrofluoric acid aqueous solution, and does not need to be operated under anhydrous conditions, resulting in low preparation cost and simple preparation process.

[0023] (2) Compared with the sol-gel method in aqueous systems, the present invention does not use expensive polyols as solvents, but only uses a very small amount of polyamines, resulting in low preparation cost and high specific surface area of ​​the aluminum fluoride and magnesium fluoride produced. Detailed Implementation

[0024] This invention provides a method for preparing high specific surface area metal fluorides using aqueous polyamines. Water is used as the solvent to prepare a solution of a soluble magnesium salt. A polyamine is then introduced into this aqueous solution. On one hand, the polyamine adjusts the pH of the soluble magnesium salt solution, generating magnesium hydroxide precipitate. On the other hand, the nitrogen (N) in the polyamine can coordinate with Mg, altering the properties of the generated magnesium hydroxide. Hydrofluoric acid is then added dropwise to the newly formed magnesium hydroxide precipitate, converting the magnesium hydroxide into magnesium fluoride sol. After precipitation with ammonia, magnesium fluoride with a high specific surface area is obtained. Alternatively, water can be used as the solvent to prepare a solution of a soluble aluminum salt. A polyamine is then introduced into this aqueous solution. The nitrogen (N) in the polyamine can coordinate with Al, and the pH of the aqueous solution can be adjusted, thereby altering the properties of the precipitate formed after the addition of hydrofluoric acid, resulting in aluminum fluoride with a high specific surface area. This method for preparing high specific surface area metal fluorides is suitable for preparing magnesium fluoride and aluminum fluoride.

[0025] The preparation of magnesium fluoride includes the following steps: Under stirring, a polyamine is added to an aqueous solution of a soluble magnesium salt at 30℃~60℃, followed by the dropwise addition of hydrofluoric acid. After the addition is complete, stirring continues for 10min~70min. Ammonia water is added dropwise to adjust the pH to 8~10, and stirring continues for 60min~180min. The solution is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate reaches ~7. The solution is dried at 80℃~120℃ and calcined at 260℃~400℃. The soluble magnesium salt is magnesium chloride, magnesium nitrate, or magnesium sulfate.

[0026] The preparation of aluminum fluoride includes the following steps: Under stirring, a polyamine is added to an aqueous solution of a soluble aluminum salt at 30℃~60℃, followed by the dropwise addition of hydrofluoric acid. After the addition is complete, stirring continues for 30min~90min. The solution is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate reaches ~7. The solution is dried at 80℃~120℃ and calcined at 260℃~400℃. The soluble aluminum salt is aluminum chloride, aluminum nitrate, or aluminum sulfate.

[0027] The amount of polyamine used is 0.5% to 5% of the mass of the soluble magnesium salt aqueous solution or the soluble aluminum salt aqueous solution.

[0028] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments. All equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0029] Example 1:

[0030] This embodiment provides a method for preparing high specific surface area metal fluorides from aqueous polyamines, comprising the following steps: Under stirring, at 30°C, 18.0g of ethylenediamine is added to a solution prepared by dissolving 60.99g of magnesium chloride in 300g of water. Then, 30.00g of hydrofluoric acid is added dropwise. After the addition is complete, stirring continues for 10 minutes. Ammonia water is added dropwise to adjust the pH to 8. Stirring continues for 60 minutes. The mixture is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate is ~7. The filtrate is dried at 80°C and calcined at 260°C to obtain magnesium fluoride. The specific surface area is 236 m² / g as determined by nitrogen physical adsorption-desorption testing. 2 / g.

[0031] Example 2:

[0032] This embodiment provides a method for preparing high specific surface area metal fluorides from aqueous polyamines, comprising the following steps: Under stirring, at 40°C, 8.05 g of 1,2-propanediamine is added to a solution prepared by dissolving 102.56 g of magnesium nitrate in 300 g of water. Then, 60.00 g of hydrofluoric acid is added dropwise. After the addition is complete, stirring continues for 40 min. Ammonia water is added dropwise to adjust the pH to 9. Stirring continues for 120 min. The mixture is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate is ~7. The filtrate is dried at 100°C and calcined at 350°C to obtain magnesium fluoride. The specific surface area is 192 m² / g as determined by nitrogen physical adsorption-desorption testing. 2 / g.

[0033] Example 3:

[0034] This embodiment provides a method for preparing high specific surface area metal fluorides from aqueous polyamines, comprising the following steps: Under stirring, at 60°C, 1.75 g of 1,3-propanediamine is added to a solution prepared by dissolving 49.30 g of magnesium sulfate in 300 g of water. Then, 40.00 g of hydrofluoric acid is added dropwise. After the addition is complete, stirring continues for 60 min. Ammonia water is added dropwise to adjust the pH to 10. Stirring continues for 180 min. The mixture is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate is ~7. The filtrate is dried at 120°C and calcined at 400°C to obtain magnesium fluoride. The specific surface area is 175 m² / g as determined by nitrogen physical adsorption-desorption testing. 2 / g.

[0035] Example 4:

[0036] This embodiment provides a method for preparing high specific surface area metal fluorides from aqueous polyamines, comprising the following steps: Under stirring, 3.72 g of ethylenediamine is added to a solution prepared by dissolving 72.49 g of aluminum chloride in 300 g of water at 50 °C. Then, 45.00 g of hydrofluoric acid is added dropwise. After the addition is complete, stirring continues for 30 min. The mixture is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate reaches ~7. The filtrate is dried at 90 °C and calcined at 300 °C to obtain aluminum fluoride. A nitrogen physical adsorption-desorption test shows a specific surface area of ​​249 m² / g. 2 / g.

[0037] Example 5:

[0038] This embodiment provides a method for preparing high specific surface area metal fluorides from aqueous polyamines, comprising the following steps: Under stirring, 13.50 g of 1,2-propanediamine is added to a solution prepared by dissolving 150.05 g of aluminum nitrate in 300 g of water at 45 °C. Then, 100.00 g of hydrofluoric acid is added dropwise. After the addition is complete, stirring continues for 70 min. The mixture is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate reaches ~7. The filtrate is dried at 110 °C and calcined at 320 °C to obtain aluminum fluoride. A nitrogen physical adsorption-desorption test shows a specific surface area of ​​227 m² / g. 2 / g.

[0039] Example 6:

[0040] This embodiment provides a method for preparing high specific surface area metal fluorides from aqueous polyamines, comprising the following steps: Under stirring, 14.66 g of 1,3-propanediamine is added to a solution prepared by dissolving 66.64 g of aluminum sulfate in 300 g of water at 40°C. Then, 30.00 g of hydrofluoric acid is added dropwise. After the addition is complete, stirring continues for 90 min. The mixture is then filtered, and the filter cake is washed with deionized water until the pH of the filtrate reaches ~7. The filtrate is dried at 100°C and calcined at 360°C to obtain aluminum fluoride. The specific surface area is 193 m² / g as determined by nitrogen physical adsorption-desorption testing. 2 / g.

Claims

1. A process for the preparation of high surface area metal fluorides from aqueous phase polyamines, characterized in that, This method can prepare magnesium fluoride; The preparation of the magnesium fluoride includes the following steps: Step a1: While stirring, add polyamine to a soluble magnesium salt aqueous solution at 30℃~60℃, then add hydrofluoric acid dropwise. After the addition is complete, continue stirring for 10min~70min. Step a2: Add ammonia water dropwise, adjust the pH to 8-10, and continue stirring for 60-180 minutes; Step a3: Filter by suction, wash the filter cake with deionized water until the pH of the filtrate is 7, dry at 80℃~120℃, and calcine at 260℃~400℃; The soluble magnesium salt is magnesium chloride, magnesium nitrate, or magnesium sulfate; The polyamine is ethylenediamine, 1,2-propanediamine, or 1,3-propanediamine; In step a1, the amount of polyamine used is 0.5% to 5% of the mass of the soluble magnesium salt aqueous solution.

2. The method for preparing high specific surface area metal fluorides from aqueous polyamines as described in claim 1, characterized in that, In step a1, the molar ratio of hydrofluoric acid to soluble magnesium salt is 2~4:

1.

3. A method for preparing high specific surface area metal fluorides from aqueous polyamines, characterized in that, This method can prepare aluminum fluoride; The preparation of the aluminum fluoride includes the following steps: Step b1: While stirring, add polyamine to the soluble aluminum salt aqueous solution at 30℃~60℃, then add hydrofluoric acid dropwise. After the addition is complete, continue stirring for 30min~90min. Step b2: Filter by suction, wash the filter cake with deionized water until the pH of the filtrate is 7, dry at 80℃~120℃, and calcine at 260℃~400℃; The soluble aluminum salt is aluminum chloride, aluminum nitrate, or aluminum sulfate; The polyamine is ethylenediamine, 1,2-propanediamine, or 1,3-propanediamine; In step b1, the amount of polyamine used is 0.5% to 5% of the mass of the soluble aluminum salt aqueous solution.

4. The method for preparing high specific surface area metal fluorides from aqueous polyamines as described in claim 3, characterized in that, In step b1, the molar ratio of hydrofluoric acid to soluble aluminum salt is 3~6:1.