Method for preparing pseudo-boehmite from waste used alumina

Abstract

The application discloses a method for preparing pseudo-boehmite by using waste alumina, and relates to the technical field of compound synthesis, and comprises the following steps: reacting alumina and sodium hydroxide in a molten state; adding hydrazine hydrate into a water solution of the above soluble substance to fully react, and collecting a filtrate; adding ammonium bicarbonate solution dropwise into the filtrate, and keeping the solution alkaline, and collecting a filter cake; washing the filter cake with water until neutral, and then washing with water to remove sodium ions, and finally calcining at high temperature to obtain pseudo-boehmite. The application avoids the problems of poor reproducibility in each crystallization process and unstable microstructure such as specific surface area and pore volume of the product in the crystallization preparation method; after adding hydrazine hydrate, metal impurities except aluminum are reduced into insoluble elements; sodium ions are removed in the previous step of synthesizing pseudo-boehmite by means of water washing, and the technical problem that sodium ions cannot be effectively removed from pseudo-boehmite produced by a conventional method even after a large amount of water washing is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of compound synthesis, and particularly relates to a method for preparing pseudoboehmite by using waste alumina. BACKGROUND

[0002] Pseudoboehmite is a series of aluminum oxides with uncertain composition, incomplete crystallization, evolution from disorder to order and from weak crystalline state to crystalline state, and the typical structure is very thin wrinkled sheet layer. Pseudoboehmite has the characteristics of high specific surface area and large pore volume, and the product gamma-Al2O3 calcined at (400-700) DEG C is widely used as a catalyst carrier, a catalyst and an adsorbent, etc. Alpha-Al2O3 calcined at (1100-1200) DEG C is widely used in coatings, additives, high-grade ceramics, high-efficiency catalysts for petroleum chemical industry, submicron / nanometer grinding materials and polishing materials, etc.

[0003] The main preparation method of pseudoboehmite is the aluminum alcohol method (industrial catalysis, 2020, 28 (1): 24-31). First, aluminum is reacted with isopropyl alcohol to prepare isopropyl aluminum, and then the isopropyl aluminum is hydrolyzed, filtered and dried to obtain pseudoboehmite. The main preparation methods in China include using carbon dioxide and sodium metaaluminate as raw materials, neutralizing to prepare pseudoboehmite. Ammonium aluminum sulfate or aluminum nitrate is neutralized with an alkaline substance to prepare pseudoboehmite (petroleum refining and chemical industry, 2021, 52 (6): 6-10). Sodium metaaluminate is neutralized with an acid to prepare pseudoboehmite (refining and chemical industry, 2004, 15 (1): 21-22). Sodium metaaluminate and aluminum sulfate are neutralized to prepare pseudoboehmite (contemporary chemical industry, 2012, 41 (9): 934-936). The pseudoboehmite prepared by the alcohol aluminum method has high quality, but the cost is high, and it is mainly used for the research and development of high-end catalyst carriers.

[0004] At present, the main problem of the domestic preparation method is that the product quality is unstable, and it is difficult to meet the requirements of large-scale production. Although improvements have been made in specific surface area, pore volume and other aspects, there are still problems such as harsh operating conditions, poor repeatability, difficulty in controlling sodium ions and difficulty in large-scale production. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing pseudoboehmite by using waste alumina. The method uses used waste alumina as a carrier of a catalyst as raw material, reacts with solid sodium hydroxide under melting to prepare a solid of sodium metaaluminate, adds hydrazine hydrate to reduce metal impurities other than aluminum into insoluble elements, dissolves in water to remove other impurities, drops into ammonium bicarbonate solution to prepare aluminum ammonium carbonate solid, removes sodium ions by filtration, and calcines at 250-350 DEG C to prepare pseudoboehmite.

[0006] The technical scheme adopted by the present application is as follows:

[0007] A method for preparing pseudo-boehmite from waste used alumina, comprising the following steps:

[0008] (1) reacting alumina with sodium hydroxide in a molten state, cooling, and leaching the soluble matter with water;

[0009] (2) adding hydrazine hydrate to the aqueous solution of the soluble matter and reacting thoroughly, filtering, and collecting the filtrate;

[0010] (3) adding ammonium bicarbonate solution dropwise to the filtrate and reacting, and keeping the solution alkaline, filtering, and collecting the filter cake;

[0011] (4) washing the filter cake to neutral with water, drying, grinding, washing again to remove sodium ions, heating the washed filter cake, and calcining at high temperature to obtain pseudo-boehmite.

[0012] The specific process for synthesizing pseudo-boehmite in the present application is as follows: grinding the waste catalyst into fine powder of not less than 300 mesh, uniformly mixing the waste catalyst with sodium hydroxide in the amount of waste catalyst (g): sodium hydroxide (g) = 1:1.5-1.8, melting and reacting at 450-500°C for 2-3h, taking out after cooling, adding water in the amount of waste catalyst (g): water (g) = 1:10-15, leaching the soluble matter at room temperature, adding water (g): hydrazine hydrate (g) = 1:0.005-0.01, filtering after 4-5h, extracting precious metals from the insoluble matter, and using the filtrate. The filtrate is added dropwise to ammonium bicarbonate at a speed of 50-200ml per minute, the amount of waste catalyst (g): ammonium bicarbonate (g) = 1:10-20, the concentration of ammonium bicarbonate is 100-150g / L, and the pH of the solution is kept at 8.5-9.5 during the reaction by using ammonium bicarbonate solution, filtering after the reaction, washing the filter cake to neutral, drying, grinding the solid, and washing with purified water until the sodium ion content in the washing water is 10-20mg / L, heating at a speed of 1-2h, and obtaining pseudo-boehmite at 250-350°C for 3-4h.

[0013] In the synthesis of the key product aluminum ammonium carbonate, the existing method has harsh synthesis conditions and is not easy to control, and aluminum hydroxide byproduct is easily generated, which affects the final result. The method used in the present application is as follows: adding a strong alkali solution of sodium metaaluminate to ammonium bicarbonate, since the reaction system is alkaline, even if aluminum hydroxide is generated, it will be dissolved again to form sodium metaaluminate, and aluminum ammonium carbonate is insoluble in alkaline solution, so this method can only obtain aluminum ammonium carbonate, thereby ensuring the stability and directionality of the result.

[0014] The raw material used in the prior art production of pseudo-boehmite contains sodium ions, which have a great influence on the catalyst. The specific surface area of the pseudo-boehmite is large, and the adsorption force is strong. Even if the product produced by the conventional method is washed with a large amount of water, it is still difficult to effectively remove the sodium ions. In addition, the existing method is directly prepared by aluminum hydroxide crystallization. The reproducibility is poor in the process of crystallization each time, and the specific surface area and pore volume of the product are unstable. The present application avoids the problems of poor reproducibility in the process of crystallization each time and the instability of the specific surface area and pore volume of the product obtained in the crystallization preparation method by using the reaction of waste catalyst alumina and sodium hydroxide in a molten state. After adding hydrazine hydrate, the metal impurities except aluminum are reduced to insoluble elements, and the sodium aluminate solution is further purified. The Na ions in the aluminum ammonium carbonate are washed out, and the sodium ions existing in the previous step of synthesizing pseudo-boehmite are removed, solving the technical problem that the pseudo-boehmite produced by the conventional method is still difficult to effectively remove the sodium ions even if it is washed with a large amount of water.

[0015] Further, in step 1, the mass ratio of the alumina to sodium hydroxide is 1:1.5-1.8, and the mass ratio of the alumina to water is 1:10-15.

[0016] Further, in step 1, the alumina is a used waste alumina carrier catalyst, and the alumina is a powder with a particle size of ≥300 mesh.

[0017] Further, in step 1, the reaction temperature in the molten state is 450-500℃, and the reaction time is 2-3h.

[0018] Further, in step 2, the mass ratio of water to hydrazine hydrate in the aqueous solution is 1:0.005-0.01, and the reaction time is 4-5h.

[0019] Further, in step 3, the mass ratio of the ammonium bicarbonate to the alumina is 1:10-20, and the concentration of the ammonium bicarbonate solution is 100-150g / L.

[0020] Further, in step 3, the dropping speed of the ammonium bicarbonate solution is 50-200ml / min.

[0021] Further, in step 3, the pH of the solution is 8.5-9.5.

[0022] Further, in step 4, in the sodium ion removal step by washing, the concentration of sodium ions in the water after washing is 10-20mg / L.

[0023] Further, in step 4, the heating rate is 125-250℃ / h, the high-temperature calcination temperature is 250-350℃, and the time is 3-4h.

[0024] The source of the old catalyst of the application is mainly FCC catalyst with alumina as the carrier, platinum content of 0.1%-0.2%.

[0025] Hydrazine hydrate: also known as hydrazine hydrate, is an inorganic compound, chemical formula is N2H4H2O, is colorless transparent smoke liquid, has a faint ammonia smell, smoke in the wet air, has strong alkaline and hygroscopicity. At normal pressure, hydrazine can form azeotrope with water (azeotrope hydrazine content is about 69%). Hydrazine hydrate liquid exists in the form of dimer, soluble in water and ethanol, insoluble in diethyl ether and chloroform; decomposed into N2, NH3 and H2 at high temperature; hydrazine hydrate has very strong reducing property, reacts violently with halogen, HNO3, KMnO4, etc. can absorb CO2 in the air, produce smoke.

[0026] Ammonium bicarbonate: NH4HCO3;

[0027] Sodium hydroxide: NaOH;

[0028] Sodium metaaluminate: NaAlO2.

[0029] The beneficial effects of the application are:

[0030] 1. The method adopted by the application: the strong alkali solution of sodium metaaluminate is added to ammonium bicarbonate. Because the reaction system is alkaline, even if aluminum hydroxide is generated, it is re-dissolved to form sodium metaaluminate, and aluminum ammonium carbonate is insoluble in alkaline solution. Therefore, only aluminum ammonium carbonate can be obtained by this method, thereby ensuring the directional nature and stability of the results, greatly reducing the generation of by-products, and the solution drop speed has little effect on the results, greatly improving the repeatability of the method, which is of great significance for large-scale production.

[0031] 2. The method adopted by the application is to use the used waste alumina carrier and sodium hydroxide to prepare sodium metaaluminate. Except for a small amount of amphoteric metals, other metal impurities are separated from the filtrate in the form of insoluble hydroxide. After adding hydrazine hydrate, the metal impurities except aluminum are reduced to insoluble elements, and the sodium metaaluminate solution is further purified.

[0032] 3. The method of the application obtains aluminum ammonium carbonate intermediate by the reaction of sodium metaaluminate and ammonium bicarbonate, and removes the ammonium salt by high-temperature burning to obtain pseudo-boehmite. Because the specific surface area of aluminum ammonium carbonate is small, the adsorption capacity is not strong, and sodium ions can be effectively removed by water washing. The pseudo-boehmite prepared by this method is sintered at high temperature by the molecules of aluminum ammonium carbonate, and does not need to pass through the crystallization process, so the microstructure of the product is stable. In addition, the volatilization of ammonium salt in the sintering process of aluminum ammonium carbonate can play the role of "explosion", so as to increase the specific surface area and pore volume of the product. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 Process flow chart of the present application;

[0034] Figure 2 XRD pattern of aluminum ammonium carbonate;

[0035] Figure 3 XRD pattern of pseudoboehmite. DETAILED DESCRIPTION

[0036] The technical solutions of the present application are described below clearly and completely. Obviously, the embodiments described herein are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0037] Example 1

[0038] Take 10 kg of waste alumina ground to 300 mesh, mix with 16 kg of sodium hydroxide, melt and react at 500°C for 3 hours, take out after cooling, add 120 kg of water, add 50 g of hydrazine hydrate after the water-soluble substance is completely leached out, stand for 4 hours, filter, and the filtrate is ready for use. Take 150 kg of ammonium bicarbonate, dissolve in 1500 liters of water, add the filtrate to the ammonium bicarbonate solution at a speed of 80 mL / min, and use the ammonium bicarbonate solution to keep the pH of the reaction at 8.5, filter after the reaction is complete, wash the filter cake to neutral, and dry. Grind the dry filter cake into powder, wash with water until the sodium ion in the washing water is less than 20 mg / L, filter, and dry the filter cake at 300°C for 4 hours within 2 hours to obtain pseudoboehmite, with a yield (calculated as aluminum) of 85.3%.

[0039] Example 2

[0040] Take 150 kg of waste catalyst ground to 350 mesh, mix with 270 kg of sodium hydroxide, melt and react at 500°C for 3 hours, take out after cooling, add 2000 kg of water, add 750 g of hydrazine hydrate after the water-soluble substance is completely leached out, stand for 5 hours, filter, and the filtrate is ready for use. Take 2250 kg of ammonium bicarbonate, dissolve in 15000 liters of water, add the filtrate to the ammonium bicarbonate solution at a speed of 100 mL / min, and use the ammonium bicarbonate solution to keep the pH of the reaction at 9.5, filter after the reaction is complete, wash the filter cake to neutral, and dry. Grind the dry filter cake into powder, wash with water until the sodium ion in the washing water is less than 20 mg / L, filter, and dry the filter cake at 300°C for 4 hours within 1.5 hours to obtain pseudoboehmite, with a yield (calculated as aluminum) of 90.1%.

[0041] Example 3

[0042] Take 200 kg of waste catalyst ground to 400 mesh, mix with 360 kg of sodium hydroxide, melt and react at 500℃ for 3 hours, cool, take out, add 3000 kg of water, wait for the water-soluble matter to be completely leached out, add 1000 g of hydrazine hydrate, stand for 5 hours, then filter, the filtrate is ready for use. Take 4000 kg of ammonium bicarbonate, dissolve in 20000 liters of water, then add the filtrate to the ammonium bicarbonate solution at a rate of 150 mL / min, and use the ammonium bicarbonate solution to keep the pH of the reaction at 9.0, after the reaction is complete, filter, wash the filter cake to neutral, and dry. Grind the dried filter cake into powder, wash with water until the sodium ion in the washing water is less than 15 mg / L, filter, and dry the filter cake at 350℃ for 4 hours, to obtain pseudoboehmite, yield (calculated as aluminum) 93.2%.

[0043] Comparative Example 1

[0044] Take 100 kg of sodium metaaluminate, dissolve in an aqueous solution of sodium hydroxide, adjust the pH to 7-7.5 with dilute sulfuric acid solution, stand, filter, dry, and sinter to obtain pseudoboehmite, sintering temperature: sintering temperature 250℃, time 3 hours.

[0045] Comparative Example 2

[0046] Take 100 kg of aluminum sulfate, dissolve in water, add ammonium bicarbonate solution, stand after the solution pH is 7-7.5, filter, dry, and sinter to obtain pseudoboehmite, sintering temperature: sintering temperature 250℃, time 3 hours.

[0047] Comparative Example 3

[0048] Take 100 kg of aluminum sulfate, dissolve in water, add sodium metaaluminate solution, stand after the solution pH is 7-7.5, filter, dry, and sinter to obtain pseudoboehmite, sintering temperature: sintering temperature 250℃, time 3 hours.

[0049] Figure 2 The XRD pattern of aluminum ammonium carbonate is consistent with the literature: Preparation of ultrafine Al2O3 by thermal decomposition of aluminum ammonium carbonate [J]. Xiao Ji, Wan Ye, Deng Hua, et al. Light Metals, 2006, 11:21-24. Figure 3 The XRD pattern of pseudoboehmite is consistent with the literature: XRD identification of aluminum oxide and aluminum hydroxide [J]. Li Bo, Shao Lingling. Inorganic Salt Industry, 2008, 40[2]:54-57.

[0050] After sintering the pseudoboehmite obtained in Comparative Examples 1-3 and Examples 1-3 at 550℃ for 3 hours, the elemental analysis is shown in Table 1.

[0051] Table 1 Elemental analysis results

[0052] Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Na20 (%) 0.026 0.021 0.019 0.45 0.41 0.57 SiO2(%) 0.0029 0.0037 0.0017 0.031 0.0092 0.045 Fe203(%) 0.0093 0.0085 0.0071 0.072 0.067 0.049 Heavy metal as Pb (%) <0.0001 <0.0001 <0.0001 <0.001 <0.001 <0.001

[0053] From Table 1, it can be seen that the sodium ion content, SiO2content, Fe2O3content and heavy metal content (as Pb) of the pseudo-boehmite of Examples 1-3 are significantly lower than the corresponding contents of the pseudo-boehmite of Comparative Examples 1-3, indicating that the pseudo-boehmite prepared by the method of the present application has higher purity than the pseudo-boehmite of Comparative Examples 1-3.

[0054] Table 2 is the specific surface area and pore volume of the pseudo-boehmite after sintering at 550°C for 3 hours.

[0055] Table 2 Specific surface area and pore volume

[0056] Item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Specific surface area (m 2 / g) 305 327 318 201 198 215 Pore volume (ml / g) 1.49 1.29 1.50 0.43 0.51 0.49

[0057] From Table 2, it can be seen that the specific surface area and pore volume of the pseudo-boehmite of Examples 1-3 are significantly greater than those of Comparative Examples 1-3, indicating that the pseudo-boehmite prepared by the method of the present application has a greater specific surface area and pore volume than the pseudo-boehmite prepared by Comparative Examples 1-3.

Claims

1. A method for preparing pseudo-boehmite from used alumina, characterized by, The application comprises the following steps: (1) reacting waste alumina with sodium hydroxide in a molten state, cooling, and leaching soluble substances with water; (2) adding hydrazine hydrate to the aqueous solution of the soluble substances and fully reacting, filtering, and collecting the filtrate; (3) adding ammonium bicarbonate solution dropwise to the filtrate and reacting while keeping the solution alkaline, filtering, and collecting the filter cake; (4) washing the filter cake with water until neutral, drying, grinding, washing again to remove sodium ions, heating the washed filter cake, and then calcining at high temperature to obtain pseudo-boehmite. In step 3, the pH of the solution is 8.5-9.

5. In step 4, the concentration of sodium ions in the water after washing is 10-20 mg / L.

2. The method according to claim 1, wherein the spent alumina is used to prepare pseudo-boehmite. In step 1, the mass ratio of alumina to sodium hydroxide is 1:1.5-1.8, and the mass ratio of alumina to water is 1:10-15.

3. The method for preparing pseudo-boehmite from waste old alumina according to claim 1, characterized in that, In step 1, the alumina is a used waste alumina carrier catalyst, and the alumina is a powder with a particle size of ≥300 mesh.

4. The method for preparing pseudo-boehmite from waste old alumina according to claim 1, characterized in that, In step 1, the reaction temperature in the molten state is 450-500℃, and the reaction time is 2-3 h.

5. The method for preparing pseudo-boehmite from waste old alumina according to claim 1, characterized in that, In step 2, the mass ratio of water to hydrazine hydrate in the aqueous solution is 1:0.005-0.01, and the reaction time is 4-5 h.

6. The method for preparing pseudo-boehmite from waste old alumina according to claim 1, characterized in that, In step 3, the mass ratio of ammonium bicarbonate to alumina is 1:10-20, and the concentration of the ammonium bicarbonate solution is 100-150 g / L.

7. The method for preparing pseudo-boehmite from waste old alumina according to claim 1, characterized in that, In step 3, the dropping speed of the ammonium bicarbonate solution is 50-200 ml / min.

8. The method for preparing pseudo-boehmite from waste old alumina according to claim 1, characterized in that, In step 4, the heating rate is 125-250℃ / h, the high-temperature calcination temperature is 250-350℃, and the time is 3-4 h.

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