A preparation method of pseudo-boehmite

Abstract

The present invention belongs to the technical field of inorganic material synthesis, and provides a preparation method of pseudo-boehmite. In the preparation method provided by the present invention, magnesium hydroxide is used as a precipitant, and a magnesium-aluminum composite hydroxide is prepared through a solid-liquid reaction; subsequently, based on the principle that ammonium ions can greatly increase the solubility of magnesium hydroxide, the prepared magnesium-aluminum composite hydroxide is corroded with an aqueous ammonium chloride solution, and the magnesium in the magnesium-aluminum composite hydroxide is selectively corroded, thereby obtaining pseudo-boehmite with a large specific surface area and high pore volume. Since the pseudo-boehmite obtained by the preparation method provided by the present invention has a large specific surface area and a rich pore structure, it has good application prospects in catalyst carriers and environmental protection. Compared with other preparation methods, the preparation method provided by the present invention does not introduce impurity sodium and silicon, has low cost, requires simple equipment, and mild synthesis conditions.

Description

Technical Field

[0001] The present invention relates to the technical field of inorganic material synthesis, and particularly relates to a method for preparing pseudo-boehmite. Background Art

[0002] Pseudo-boehmite (AlOOH·nH2O, n = 0.08 - 0.62) is a kind of incompletely crystallized hydrated alumina. The extremely thin wrinkled lamellar morphology and special spatial network structure endow pseudo-boehmite with the characteristics of high specific surface area, large porosity, adjustable pore size and good colloidal solubility. These characteristics make it widely used in industries such as industrial catalysis, fire protection, environmental protection, and papermaking.

[0003] There are many methods for preparing pseudo-boehmite. According to the raw material sources, they can be briefly divided into the alcohol-aluminum method, the carbonization method, and the aluminum salt neutralization method. Abroad, the long-chain alcohol-aluminum method is usually used to produce pseudo-boehmite. For example, high-carbon alcohol reacts with high-purity aluminum flakes to prepare high-purity pseudo-boehmite for catalysis. The higher alcohols generated by hydrolysis in this method are insoluble in water, which is more conducive to the recovery of higher alcohols and the pseudo-boehmite prepared has low impurity content. The product performance is significantly better than that obtained by the inorganic aluminum salt method, but the production cost, energy consumption and selling price are relatively high.

[0004] Currently, using the carbonization method to produce pseudo-boehmite is the process route with the lowest cost. CO2 is introduced into the NaAlO2 alkaline solution, and high-crystallinity pseudo-boehmite products are obtained through neutralization hydrolysis. However, since there are many phases involved in this reaction process, it is easy to cause uneven pore size distribution and poor pore structure performance. The obtained products are difficult to form and have poor quality. The aluminum salt neutralization method is to react aluminum salt with NaAlO2 or alkaline precipitants (such as ammonium bicarbonate, sodium hydroxide, etc.), and pseudo-boehmite products are obtained through neutralization hydrolysis. It is mainly used as a catalyst carrier and raw material for producing activated alumina. This preparation method is prone to generate Al(OH)3 impurity phases due to too high local concentration, and the pore volume is small, resulting in low catalyst loading rate and low catalytic efficiency. In addition, the sodium content in the pseudo-boehmite prepared by this method is relatively high, which affects the subsequent application of the product in high-end products, and a large amount of sodium-containing wastewater is generated by this method, resulting in huge environmental protection pressure. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a method for preparing pseudo-boehmite. The preparation method provided by the present invention can obtain pseudo-boehmite with rich pores, large pore volume and large specific surface area; and it does not contain sodium.

[0006] In order to achieve the above invention purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing pseudo-boehmite, comprising the following steps:

[0008] Mix magnesium hydroxide, triethanolamine and water to obtain a first mixed system;

[0009] Dissolve a water-soluble aluminum salt in water to obtain an aluminum salt solution;

[0010] Mix the first mixed system and the aluminum salt solution and carry out a precipitation reaction to obtain a magnesium-aluminum composite hydroxide;

[0011] Disperse the magnesium-aluminum composite hydroxide in an aqueous ammonium chloride solution and carry out corrosion to obtain the pseudo-boehmite;

[0012] Preferably, the concentration of magnesium hydroxide in the first mixed system is 0.2 - 1 mol / L.

[0013] Preferably, the water-soluble aluminum salt is one or more of aluminum sulfate, aluminum chloride and aluminum nitrate.

[0014] Preferably, the molar ratio of aluminum ions to magnesium hydroxide in the water-soluble aluminum salt is 0.35 - 2:1.

[0015] Preferably, the molar ratio of triethanolamine to aluminum ions in the water-soluble aluminum salt is 0.1 - 1:1.

[0016] Preferably, the volume ratio of the first mixed system to the aluminum salt solution is 1:1.

[0017] Preferably, the temperature of the precipitation reaction is 60 - 95 °C and the time is 1 - 6 hours.

[0018] Preferably, the mass fraction of the aqueous ammonium chloride solution is 10% - 27%;

[0019] The dosage ratio of the magnesium-aluminum composite hydroxide to the aqueous ammonium chloride solution is 1 g:100 mL.

[0020] Preferably, the temperature of the corrosion is 35 - 80 °C and the time is 6 - 12 hours.

[0021] After the corrosion, it further includes: filtering the obtained corrosion feed liquid to obtain a filtrate and a filter residue; washing and drying the filter residue in sequence to obtain the pseudo-boehmite;

[0022] Adjust the pH value of the filtrate to be alkaline and recycle to obtain magnesium hydroxide.

[0023] The present invention provides a method for preparing pseudo-boehmite, comprising the following steps: mixing magnesium hydroxide, triethanolamine and water to obtain a first mixed system; dissolving a water-soluble aluminum salt in water to obtain an aluminum salt solution; mixing the first mixed system and the aluminum salt solution to carry out a precipitation reaction to obtain a magnesium-aluminum composite hydroxide; dispersing the magnesium-aluminum composite hydroxide in an aqueous ammonium chloride solution for erosion to obtain the pseudo-boehmite.

[0024] In the preparation method provided by the present invention, magnesium hydroxide is used as a precipitant, and a magnesium-aluminum composite hydroxide is prepared through a solid-liquid reaction; subsequently, based on the principle that ammonium ions can greatly increase the solubility of magnesium hydroxide, the prepared magnesium-aluminum composite hydroxide is eroded with an aqueous ammonium chloride solution, and magnesium in the magnesium-aluminum composite hydroxide is selectively eroded, thus obtaining pseudo-boehmite with a large specific surface area and high pore volume. Since the pseudo-boehmite obtained by the preparation method provided by the present invention has a large specific surface area and a rich pore structure, it has good application prospects in catalyst carriers and environmental protection. Compared with other preparation methods, the preparation method provided by the present invention does not introduce impurity sodium and silicon, has low cost, requires simple equipment, and has mild synthesis conditions.

[0025] Further, after the erosion, it further includes: filtering the obtained eroded feed liquid to obtain a filtrate and a filter residue; washing and drying the filter residue in sequence to obtain the pseudo-boehmite; adjusting the pH value of the filtrate to be alkaline to recover magnesium hydroxide. The present invention can realize the recycling of the precipitant magnesium hydroxide. Description of the Drawings

[0026] Figure 1 XRD pattern of the pseudo-boehmite obtained in Example 1;

[0027] Figure 2 N2 adsorption-desorption curve of the pseudo-boehmite obtained in Example 1;

[0028] Figure 3 Pore volume curve of the pseudo-boehmite obtained in Example 1;

[0029] Figure 4 XRD pattern of the pseudo-boehmite obtained in Example 2;

[0030] Figure 5 N2 adsorption-desorption curve of the pseudo-boehmite obtained in Example 2;

[0031] Figure 6 Pore volume curve of the pseudo-boehmite obtained in Example 2;

[0032] Figure 7 SEM image of the pseudo-boehmite obtained in Example 3;

[0033] Figure 8N2 adsorption - desorption curve of the pseudo - boehmite obtained in Example 3;

[0034] Figure 9 Pore size distribution diagram of the pseudo - boehmite obtained in Example 3. Detailed implementation mode

[0035] The present invention provides a method for preparing pseudo - boehmite, which comprises the following steps:

[0036] Mix magnesium hydroxide, triethanolamine and water to obtain a first mixed system;

[0037] Dissolve a water - soluble aluminum salt in water to obtain an aluminum salt solution;

[0038] Mix the first mixed system and the aluminum salt solution, carry out a precipitation reaction to obtain a magnesium - aluminum composite hydroxide;

[0039] Disperse the magnesium - aluminum composite hydroxide in an ammonium chloride aqueous solution, carry out corrosion to obtain the pseudo - boehmite.

[0040] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0041] The present invention mixes magnesium hydroxide, triethanolamine and water to obtain a first mixed system.

[0042] In the present invention, the water is preferably deionized water.

[0043] In the present invention, the concentration of magnesium hydroxide in the first mixed system is preferably 0.2 - 1 mol / L, and more preferably 0.4 - 0.8 mol / L.

[0044] In the present invention, the mixing of magnesium hydroxide, triethanolamine and water preferably includes: dispersing magnesium hydroxide in water, carrying out a first mixing, and then adding triethanolamine for a second mixing; both the first mixing and the second mixing are preferably carried out under stirring conditions, and the stirring time is preferably 20 min.

[0045] The present invention dissolves a water - soluble aluminum salt in water to obtain an aluminum salt solution.

[0046] In the present invention, the water - soluble aluminum salt is preferably one or more of aluminum sulfate, aluminum chloride and aluminum nitrate. In the present invention, the water is preferably deionized water. In the present invention, the concentration of aluminum ions in the aluminum salt solution is preferably 0.05 - 1 mol / L, and more preferably 0.1 - 0.8 mol / L.

[0047] In the present invention, the molar ratio of aluminum ions to magnesium hydroxide in the water-soluble aluminum salt is preferably 0.35 to 2:1, more preferably 0.5 to 1.8:1, and still more preferably 1.0 to 1.5:1.

[0048] In the present invention, the molar ratio of triethanolamine to aluminum ions in the water-soluble aluminum salt is preferably 0.1 to 1:1.

[0049] In the present invention, the dissolution of the water-soluble aluminum salt in water is preferably carried out under stirring, and the stirring time is preferably 20 min.

[0050] After obtaining the first mixed system and the aluminum salt solution, the present invention mixes the first mixed system and the aluminum salt solution to carry out a precipitation reaction to obtain a magnesium-aluminum composite hydroxide.

[0051] In the present invention, the volume ratio of the first mixed system to the aluminum salt solution is preferably 1:1.

[0052] In the present invention, the temperature of the precipitation reaction is preferably 60 to 95 °C, and the time is preferably 1 to 6 hours.

[0053] After the precipitation reaction, the present invention preferably further includes: cooling the obtained precipitation reaction stock solution to room temperature, filtering, and then washing and drying the obtained filter residue in sequence; the washing includes water washing and alcohol washing in sequence; the reagent for water washing is preferably deionized water; the reagent for alcohol washing is preferably absolute ethanol. In the present invention, the drying temperature is preferably 50 °C.

[0054] After obtaining the magnesium-aluminum composite hydroxide, the present invention disperses the magnesium-aluminum composite hydroxide in an ammonium chloride aqueous solution for corrosion to obtain the pseudo-boehmite.

[0055] In the present invention, the mass fraction of the ammonium chloride aqueous solution is preferably 10% to 27%, more preferably 15% to 25%. In the present invention, the dosage ratio of the magnesium-aluminum composite hydroxide to the ammonium chloride aqueous solution is preferably 1 g: 100 mL.

[0056] In the present invention, the temperature of the corrosion is preferably 35 to 80 °C, and the time is preferably 6 to 12 hours.

[0057] After the corrosion, the present invention preferably further includes: filtering the obtained corrosion stock solution to obtain a filtrate and a filter residue; washing and drying the filter residue in sequence; the washing preferably includes water washing and alcohol washing in sequence; the reagent for water washing is preferably deionized water; the reagent for alcohol washing is preferably absolute ethanol. In the present invention, the drying temperature is preferably 50 °C and the time is preferably 12 h.

[0058] In the present invention, it is preferably further included that: adjusting the pH value of the filtrate to be alkaline to recover magnesium hydroxide; the reagent for adjusting the pH value of the filtrate is preferably ammonia water.

[0059] The following is a detailed description of the preparation method of pseudo-boehmite provided by the present invention with reference to embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0060] Example 1

[0061] Weigh 1.16 g (0.02 mol) of magnesium hydroxide and place it in a 100 mL beaker. Add 50 mL of deionized water, and after magnetic stirring at room temperature for 20 minutes, add 0.15 g (0.01 mol) of triethanolamine. Continue stirring for 20 minutes to obtain the first mixed system; weigh 15 g (0.04 mol) of aluminum nitrate nonahydrate, place it in a 100 mL beaker, add 50 mL of deionized water, and after magnetic stirring at room temperature for 20 minutes, obtain an aluminum nitrate solution (concentration: 0.8 mol / L); pour the first mixed system and the aluminum nitrate solution into a rapidly stirred reaction kettle (rotation speed: 3000 r / min) simultaneously. After the reaction, the slurry is crystallized at 80 °C for 3 hours, then centrifugally washed with deionized water and absolute ethanol, and dried in an oven at 50 °C to obtain a magnesium-aluminum composite hydroxide.

[0062] Weigh 2 g of the magnesium-aluminum composite hydroxide and place it in a 500 mL beaker. Add 200 mL of a 20% ammonium chloride solution by mass, then heat up to 70 °C, keep warm for 6 hours, and then centrifuge to obtain a precipitate. Wash it three times with deionized water and then twice with absolute ethanol, and dry it in an oven at 50 °C for 12 hours to obtain pseudo-boehmite.

[0063] Figure 1 is the XRD pattern of the obtained pseudo-boehmite. From Figure 1 it can be seen that: the prepared substance exhibits the characteristic diffraction peaks of pseudo-boehmite and has no obvious impurity peaks, indicating that the prepared substance is pseudo-boehmite. Figure 2 is the N2 adsorption-desorption curve of the obtained pseudo-boehmite. It is calculated that the specific surface area of the prepared pseudo-boehmite is 385 m 2 / g, which is much higher than the specific surface area of the currently commercially available pseudo-boehmite (about 290 m 2 / g), and also higher than the specific surface area of the high-specific-surface-area pseudo-boehmite prepared in Patent ZL202110904450.3. Figure 3 is the pore volume curve diagram of the obtained pseudo-boehmite. From Figure 3 it can be known that the pore volume of the prepared pseudo-boehmite is 2.2 mL / g.

[0064] Example 2

[0065] Weigh 2.32 g (0.04 mol) of magnesium hydroxide and place it in a 100 mL beaker. Add 50 mL of deionized water, and after magnetic stirring at room temperature for 20 minutes, add 0.3 g (0.02 mol) of triethanolamine. Continue stirring for 20 minutes to obtain the first mixed system. Weigh 9.66 g (0.04 mol) of aluminum chloride hexahydrate, place it in a 100 mL beaker, add 50 mL of deionized water, and after magnetic stirring at room temperature for 20 minutes, obtain an aluminum chloride solution (0.8 mol / L). Pour the first mixed system and the aluminum chloride solution into a rapidly stirred autoclave (rotation speed 3000 r / min) simultaneously. After the reaction, the slurry is crystallized at 60 °C for 6 hours, then centrifugally washed with deionized water and absolute ethanol, and dried in an oven at 50 °C to obtain magnesium-aluminum composite hydroxide.

[0066] Weigh 2 g of the magnesium-aluminum composite hydroxide and place it in a 500 mL beaker. Add 200 mL of a 20% ammonium chloride solution by mass fraction, then heat up to 70 °C, keep warm for 8 hours, and then centrifuge to obtain a precipitate. Wash it three times with deionized water and then twice with absolute ethanol, and dry it in an oven at 50 °C for 12 hours to obtain pseudo-boehmite.

[0067] Figure 4 is the XRD pattern of the obtained pseudo-boehmite. From Figure 4 it can be seen that: the prepared substance shows the characteristic diffraction peaks of pseudo-boehmite and there are no obvious impurity peaks, indicating that the prepared substance is pseudo-boehmite. Figure 5 is the N2 adsorption-desorption curve of the obtained pseudo-boehmite. After calculation, the specific surface area of the prepared pseudo-boehmite is as high as 593 m 2 / g. Figure 6 is the pore volume curve graph of the obtained pseudo-boehmite. From Figure 6 it can be known that the pore volume of the prepared pseudo-boehmite is 2.02 mL / g, which is much higher than that of the pseudo-boehmite prepared by the conventional method (about 0.3 mL / g), and is also significantly higher than that of the high-pore-volume pseudo-boehmite prepared in Patent ZL202211031993.X.

[0068] Example 3

[0069] Weigh 4.64 g (0.02 mol) of magnesium hydroxide and place it in a 100 mL beaker. Add 50 mL of deionized water. After magnetic stirring at room temperature for 20 minutes, add 0.30 g (0.02 mol) of triethanolamine, and continue stirring for 20 minutes to obtain the first mixed system; weigh 6.66 g (0.01 mol) of aluminum sulfate octadecahydrate, place it in a 100 mL beaker, add 50 mL of deionized water, and obtain an aluminum sulfate solution after magnetic stirring at room temperature for 30 minutes; pour the first mixed system and the aluminum sulfate solution into a rapidly stirred reaction kettle (rotation speed 3000 r / min) simultaneously. After the reaction, the slurry is crystallized at 60 °C for 6 hours, then centrifugally washed with deionized water and absolute ethanol, and dried in an oven at 50 °C to obtain magnesium-aluminum composite hydroxide.

[0070] Weigh 2 g of magnesium-aluminum composite hydroxide and place it in a 500 mL beaker. Add 200 mL of ammonium chloride solution with a mass fraction of 25%, then heat up to 70 °C, keep warm for 10 hours, and then centrifuge to obtain a precipitate. Wash it three times with deionized water and then twice with absolute ethanol, and dry it in an oven at 50 °C for 12 hours to obtain pseudo-boehmite.

[0071] Figure 7 is the SEM image of the obtained pseudo-boehmite. From Figure 7 it can be seen that the prepared pseudo-boehmite presents a distorted two-dimensional sheet structure. Figure 8 is the N2 adsorption-desorption curve of the obtained pseudo-boehmite. After calculation, the specific surface area of the prepared pseudo-boehmite is 531 m 2 / g. Figure 9 is the pore volume curve of the obtained pseudo-boehmite. From Figure 9 it can be known that the pore volume of the prepared pseudo-boehmite is 1.7 mL / g.

[0072] Example 4

[0073] The difference from Example 1 is that the mass of aluminum nitrate nonahydrate is 2.63 g (0.007 mol).

[0074] The specific surface area of the obtained pseudo-boehmite is 342 m 2 / g, and the pore volume is 1.4 mL / g.

[0075] Example 5

[0076] The difference from Example 1 is that the mass of aluminum nitrate nonahydrate is 7.5 g (0.02 mol).

[0077] The specific surface area of the obtained pseudo-boehmite is 402 m 2 / g, and the pore volume is 2.4 mL / g.

[0078] Example 6

[0079] The difference from Example 1 is that the mass of aluminum nitrate nonahydrate is 11.25 g (0.03 mol).

[0080] The specific surface area of the prepared pseudo-boehmite is 435 m 2 / g, and the pore volume is 2.5 mL / g.

[0081] Application Example 1

[0082] Removal of hexavalent chromium in wastewater: Weigh 0.1 g of the pseudo-boehmite prepared in Example 2 into a 500 mL beaker, add 100 mL of an aqueous solution containing hexavalent Cr, where the concentration of hexavalent chromium Cr is 150 mg / L. After magnetic stirring at room temperature for 120 minutes, take the upper layer solution, filter it through a 0.22 μm filter membrane, and then measure the concentration of Cr in it by ICP-MS. The results show that the removal rate of chromium by the prepared pseudo-boehmite reaches 99%, and its maximum adsorption capacity is 148 mg / g, showing a very good application prospect.

[0083] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing pseudo-boehmite, characterized in that: The following steps are involved: Mixing magnesium hydroxide, triethanolamine and water to obtain a first mixed system; dissolving a water-soluble aluminum salt in water to obtain an aluminum salt solution; mixing the first mixed system and an aluminum salt solution to perform a precipitation reaction to obtain a magnesium-aluminum composite hydroxide; The magnesium-aluminum composite hydroxide is dispersed in an ammonium chloride aqueous solution and dissolved to obtain the pseudo-boehmite.

2. The preparation method according to claim 1, characterized in that The concentration of magnesium hydroxide in the first mixed system is 0.2-1 mol / L.

3. The preparation method according to claim 1, characterized in that The water-soluble aluminum salt is one or more of aluminum sulfate, aluminum chloride and aluminum nitrate.

4. The preparation method according to claim 1, 2 or 3, characterized in that: The ratio of the amount of aluminum ions to the amount of magnesium hydroxide in the water-soluble aluminum salt is 0.35 to 2:

1.

5. The preparation method according to claim 1 or 3, characterized in that The molar ratio of the triethanolamine to the aluminum ion in the water-soluble aluminum salt is 0.1 to 1:

1.

6. The preparation method according to claim 1, characterized in that The volume ratio of the first mixed system to the aluminum salt solution is 1:

1.

7. The preparation method according to claim 1 or 6, characterized in that The temperature of the precipitation reaction is 60-95° C., and the time is 1-6 hours.

8. The preparation method according to claim 1, characterized in that The mass fraction of the ammonium chloride aqueous solution is 10% to 27%; The usage ratio of the magnesium-aluminum composite hydroxide and the ammonium chloride aqueous solution is 1 g:100 mL.

9. The preparation method according to claim 1 or 8, characterized in that The dissolution temperature is 35 to 80° C., and the dissolution time is 6 to 12 hours.

10. The preparation method according to claim 9, characterized in that After the dissolution, the method further comprises: filtering the obtained dissolution liquid to obtain a filtrate and a filter residue; washing and drying the filter residue in sequence to obtain the pseudo-boehmite; The pH value of the filtrate is adjusted to be alkaline, and magnesium hydroxide is recovered.

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