CN1884082A - Method for preparing pseudo-boehmite with large pore volume and high specific surface area - Google Patents

Abstract

The present invention is a method for preparing pseudo-boehmite with large pore volume and high specific surface area. The steps include: firstly adding SB powder to a mixture containing 110-200g/L-Al ₂ O ₃ and a causticization coefficient of 1.30-1.75 In the sodium aluminate solution, the mass ratio of the amount of seed crystals added to the Al ₂ O ₃ in the solution is 1.0, and then it is decomposed under the hydrothermal condition of 100-150 ℃ for 3-16 hours; the decomposed product after cooling is suction filtered , washed with water until neutral, then washed with ethanol and dried to obtain single-phase pseudo-boehmite. The SB powder seed crystal adopted in the invention has high activity and good hydrothermal stability, and can obtain a higher solution decomposition rate at a very low seed crystal ratio and a short decomposition time. The method has the advantages of simple process, mild conditions, continuous recycling of seed crystals and strong operability, and provides a new alternative for preparing high value-added pseudo-boehmite from cheap sodium aluminate solution. path.

Description

A kind of preparation method of pseudo-boehmite with large pore volume and high specific surface area

technical field

The invention relates to the preparation of pseudo-boehmite, in particular to a method for preparing pseudo-boehmite with large pore volume and high specific surface area by hydrothermally decomposing sodium aluminate solution with SB powder as crystal seed.

Background technique

Pseudoboehmite is a chemical alumina with uncertain composition, incomplete crystallization and controllable properties. Its chemical formula is γ-AlOOH·nH ₂ O (n=0.08～0.62). Boehmite (γ-AlOOH) is similar, with a typical structure of very thin wrinkled sheets. The specific surface of γ-Al ₂ O ₃ obtained by calcination of pseudo-boehmite is higher, and it is widely used as a catalyst carrier in the field of petrochemical industry, while the specific surface of γ-Al ₂ O ₃ obtained by calcination of boehmite is lower. It is generally difficult to be used in the field of catalysis.

SB powder is a kind of high-quality pseudo-boehmite produced by high-purity aluminum rotary shavings and higher alcohols (n-pentanol, n-hexanol) successfully developed by German Condea company. SB powder is easy to control due to its good crystal form and pore structure. , specific surface and high purity, it is widely used in the field of catalysis. Its production has gone through the cycle process of aluminum hydroxide-aluminum oxide-aluminum-aluminum alcohol-aluminum hydroxide. However, the organic solvent used in this method is toxic and the production cost is relatively high. However, the Bayer process bauxite dissolution intermediate - cheap refined sodium aluminate solution is used as raw material, and the sodium aluminate solution seed crystal decomposition technology is used to directly produce high-quality pseudo-boehmite with properties similar to those of SB powder. It is possible to overcome the shortcomings of the SB powder manufacturing process.

The seed crystal decomposition of sodium aluminate solution is a key process in the production process of metallurgical grade alumina. The traditional seed crystal decomposition is based on adding gibbsite seed crystals and precipitation of aluminum hydroxide (Al(OH) ₃ ), not only the decomposition time Long, low decomposition rate, and the process of converting Al(OH) ₃ into alumina has high energy consumption and difficult to control the product quality.

A method for preparing boehmite by decomposing sodium aluminate solution with boehmite seeds has been reported. WO9,858,876 discloses a method for preparing boehmite by decomposing sodium aluminate solution at 90°C, the seed crystal is boehmite obtained after hydrothermal treatment of gibbsite. Under the condition that the seed crystal ratio is 1.76 and the composition of sodium aluminate solution is 90.0g/L-Na ₂ O and 99g/L-Al ₂ O ₃ , the decomposition rate of sodium aluminate solution is 40.53% when decomposed for 96 hours. The main disadvantage of this method is that the decomposition time is too long, and the decomposition products can only be used as precursors of metallurgical grade alumina.

CN1186046A discloses a method in which CO ₂ is introduced into sodium aluminate solution first, and after the causticization coefficient α _K of the solution is reduced to 1.20-1.30, the method of decomposing and preparing boehmite by seed crystals of sodium aluminate solution is disclosed. The decomposition rate of sodium aluminate solution is 48 when the sodium aluminate solution is decomposed for 30 hours under the conditions of 90～110g/L-Al ₂ O ₃ , caustic coefficient 1.40～1.60, 110～120℃ and seed ratio 2.0～2.5. ~52%. This method has a high utilization rate of aluminum in the solution, but the decomposition product can only be used as a precursor of metallurgical grade alumina, and the introduction of CO ₂ also consumes NaOH with high utilization value in subsequent processes, and the range of main operating parameters is too narrow Also be unfavorable for the operation of sodium aluminate solution decomposition process.

CN1733607A discloses a method for preparing relatively active boehmite seed crystals and decomposing sodium aluminate solution to prepare micron-sized boehmite. _In this method, 8-30 _% H ₂ O ₂ solution _containing 50-250g/L-Al _{2 O 3} A sodium aluminate solution with a caustic coefficient α _K of 1.30 to 3.50, and then the boehmite obtained by filtering, washing with water, ethanol dispersion and washing and drying in sequence as the seed crystal, in the sodium aluminate solution to form 60 to 180g/ L-Al ₂ O ₃ , caustic coefficient 1.30-1.80 and low seed crystal ratio can be decomposed, and the highest decomposition rate can reach more than 50%.

Some researchers [Filippou D, Paspaliafris I. Light Metals. New York: the Minerals, Metals & Materials Society, 1993.119] believe that boehmite is the only decomposition that can be obtained by decomposition of sodium aluminate solution between 100 and 150 °C products, but if a special decomposition technique is used, for example, adding a certain amount of alcohol to reduce the activity of water, it is possible to obtain pseudo-boehmite. The defect of the existing sodium aluminate solution seed crystal decomposition technology is that the decomposition products are usually low value-added metallurgical grade alumina products such as gibbsite or boehmite.

Contents of the invention

The technical problem to be solved by the present invention is to provide a method for preparing pseudo-boehmite with large pore volume and high specific surface area by hydrothermal seed crystal decomposition of sodium aluminate solution, which can prepare pseudo-boehmite with higher added value stone products.

The technical solution adopted by the present invention to solve the technical problem is: use SB powder as crystal seed, hydrothermally decompose sodium aluminate solution to prepare pseudo-boehmite with large pore volume and high specific surface area, and the specific steps include:

1. Use SB powder as a seed crystal, add it to a sodium aluminate solution containing 110-200g/L-Al ₂ O ₃ and a caustic coefficient of 1.30-1.75 for decomposition, the amount of seed crystal added and the Al ₂ O The mass ratio of ₃ is 1:1, and then decomposed under closed hydrothermal conditions to obtain decomposition products;

2. After the decomposition product is cooled and vacuum filtered, it is washed with water until neutral to obtain a neutral filter cake;

3. Disperse and wash the neutral filter cake once with 2.0 to 4.0 times the volume of ethanol, and after drying, single-phase pseudo-boehmite can be obtained;

4. The decomposition product in step 1 can also be returned to the previous process as a seed crystal, and then the above-mentioned sodium aluminate solution hydrothermal seed crystal decomposition step is repeated.

Compared with the preparation technology of existing pseudo-boehmite, the present invention has the following main advantages:

1. The SB powder seed crystal adopted in this method has very high activity, and the hydrothermal decomposition of the sodium aluminate solution by the seed crystal is efficient and economical, and can be performed within a very low seed crystal ratio (SR=1.0) and decomposition time (3h) Obtain a high solution decomposition rate, the decomposition rate can reach more than 30%;

2. The method for preparing pseudo-boehmite by hydrothermally decomposing sodium aluminate solution of SB powder provided by this method is not only simple in process, mild in condition, and the crystal seed can be continuously recycled for many times, and the product has large pore volume and high specific surface area. Some properties even exceed the technical indicators of SB powder, showing its potential application prospects as catalyst carriers and adsorbents in petrochemical and other industries;

3. After the SB powder hydrothermally decomposes the sodium aluminate solution in this method, the pH of the decomposed filtrate is greatly improved compared with that before the decomposition. After being combined with the process of producing metallurgical grade alumina by alkaline process such as Bayer process, the decomposed filtrate can be returned to the dissolution stage of bauxite in the process of producing alumina by alkaline process for recycling.

In short, this method breaks through the traditional production process of pseudo-boehmite, greatly shortens the process flow, and reduces production costs. It is expected to develop into traditional high-value-added pseudo-boehmite and γ- _{Complementary} approach to _Al2O3 preparation technology.

Description of drawings

Fig. 1 is the XRD spectrum of embodiment 1～embodiment 4 decomposition product and SB powder.

Detailed ways

The present invention provides a method for preparing pseudo-boehmite with large pore volume and high specific surface area by hydrothermally decomposing sodium aluminate solution with SB powder as crystal seed, and the specific steps include:

1. Use SB powder as the original crystal seed, add it to the sodium aluminate solution to decompose, the amount of the species added and the mass ratio of Al ₂ O ₃ in the solution are 1:1, and then under closed hydrothermal conditions (reaction temperature 100 ~ 150°C, reaction time 3 to 16 hours) to decompose and obtain decomposition products. The decomposition product can also be returned to the previous process as a seed crystal to reduce the amount of SB powder seed crystals and reduce production costs. The specific surface area and pore volume of the original seed crystals are about 227.2m ² /g and 0.40cm ³ /g respectively.

The control of the above decomposition conditions is critical.

The concentration of Al ₂ O ₃ in the sodium aluminate solution should be controlled between 110-200g/L-Al ₂ O ₃ and the caustic coefficient between 1.30-1.75 to ensure a higher decomposition rate of the sodium aluminate solution and reduce the subsequent The difficulty of removing Na ⁺ by process. If the concentration of Al ₂ O ₃ in the solution is 200g/L, the causticization coefficient of the solution should be 1.30; if the concentration of Al ₂ O ₃ in the solution is 110g/L, the causticization coefficient of the solution should be 1.75. If the concentration of Al ₂ O ₃ in the solution is between 110g/L and 200g/L, the caustic coefficient of the solution should also be between 1.75 and 1.30. In short, the concentration of Al ₂ O ₃ in the sodium aluminate solution and the caustic coefficient should be negatively correlated.

When SB powder decomposes sodium aluminate solution, by controlling the decomposition time at different hydrothermal decomposition temperatures, the aluminum in the solution is precipitated in the form of pseudo-boehmite with large pore volume and high specific surface area. The hydrothermal decomposition time of sodium aluminate solution at 100°C is not less than 16h, and the hydrothermal decomposition time of sodium aluminate solution at 125°C is not less than 3h. When the temperature for decomposing the sodium aluminate solution is between 100°C and 125°C, the corresponding hydrothermal decomposition time should also be between 16h and 3h. In conclusion, there should be a negative correlation between the selected hydrothermal decomposition temperature and hydrothermal decomposition time.

2. After the decomposition product is cooled and vacuum filtered, it is washed with water until neutral to obtain a neutral filter cake.

3. Disperse and wash the neutral filter cake with 2.0-4.0 times the volume of ethanol, and then dry it at 100-120°C for 10-12 hours to obtain a specific surface area of 176.8-213.6m ² /g and a pore volume Single-phase pseudo-boehmite with a size of 0.59-0.86 cm ³ /g.

In this step, the neutral filter cake is washed with ethanol, mainly to effectively eliminate the hard agglomeration of the washed product due to the rich wet water in the subsequent drying process, resulting in a decrease in the pore volume and specific surface of the decomposition product.

The present invention will be further described below in conjunction with several specific examples.

Example 1: A certain amount of SB powder is added to 40ml of sodium aluminate solution containing 140g/L-Al ₂ O ₃ and the caustic coefficient α _K is _1.30 . The weight ratio of ₃ is 1:1, continuous hydrothermal decomposition at 125°C for 3 hours, and the decomposition rate is 31.7%. After dispersing and washing, the filter cake was dried at 100°C for 12 hours, and the dried product was detected by XRD as 100% pseudo-boehmite. The specific surface area and pore volume measured by the automatic specific surface and porosity analyzer were respectively 176.8m ² /g and 0.59cm ³ /g.

Example 2: A certain amount of SB powder is added to 40ml of sodium aluminate solution containing 110g/L-Al ₂ O ₃ and the caustic coefficient α _K is 1.75. The amount of SB powder added is the same as that of Al ₂ O in sodium aluminate solution The weight ratio of ₃ is 1:1, continuous hydrothermal decomposition at 100°C for 16 hours, and the decomposition rate is 16.2%. After dispersing and washing, the filter cake was dried at 120°C for 10 hours, and the dried product was detected by XRD as 100% pseudo-boehmite. The specific surface and pore volume measured by the automatic specific surface and porosity analyzer were respectively 195.2 m ² /g and 0.86 cm ³ /g.

Example 3: A certain amount of SB powder is added to 40ml of sodium aluminate solution containing 200g/L-Al ₂ O ₃ and the caustic coefficient α _K is 1.30. The amount of SB powder added is the same as that of Al ₂ O in sodium aluminate solution The weight ratio of ₃ is 1:1, continuous hydrothermal decomposition at 150°C for 9 hours, and the decomposition rate is 23.1%. After dispersing and washing, the filter cake was dried at 110°C for 11 hours, and the dried product was detected by XRD as 100% pseudo-boehmite. The specific surface and pore volume measured by the automatic specific surface and porosity analyzer were respectively 181.3m ² /g and 0.78cm ³ /g.

Example 4: A certain amount of SB powder is added to 40ml of sodium aluminate solution containing 140g/L-Al ₂ O ₃ and the caustic coefficient α _K is 1.45. The amount of SB powder added is the same as that of Al ₂ O in sodium aluminate solution The weight ratio of ₃ is 1:1, continuous hydrothermal decomposition at 125°C for 3 hours, and the decomposition rate is 22.1%. After dispersing and washing, the filter cake was dried at 100°C for 12 hours, and the dried product was detected by XRD to be 100% pseudo-boehmite, and its specific surface and pore volume were 182.5m ² /g and 0.64cm ³ /g, respectively. Take the same steps as the above-mentioned method. The seeds used in each cycle of hydrothermal decomposition of sodium aluminate solution experiments are the decomposition products of the previous decomposition experiment. After continuous hydrothermal decomposition for 3 times, the decomposition rate is 21.8%. The XRD detection is 100% pseudo-boehmite, and its specific surface and pore volume are 213.6m ² /g and 0.84cm ³ /g, respectively.

Claims (6)

1. the preparation method of a large pore volume, high-ratio surface pseudo-boehmite, it is characterized in that a kind of is crystal seed with the SB powder, and the hydrothermal decomposition sodium aluminate solution prepares the method for large pore volume, high-ratio surface pseudo-boehmite, and concrete steps comprise:

1) with the SB powder as crystal seed, join and contain 110～200g/L-Al ₂O ₃With the causticization coefficient is to decompose Al in the add-on of crystal seed and the solution in 1.30～1.75 the sodium aluminate solution ₂O ₃Mass ratio be 1: 1, under airtight hydrothermal condition, decompose subsequently, degradation production;

2) degradation production is washed with water to neutrality behind cooling, vacuum filtration, gets neutral filter cake;

3) neutral filter cake is disperseed with its 2.0～4.0 times of volume of ethanol and washing once, after the drying operation, can obtain single-phase pseudo-boehmite.

2. the preparation method of large pore volume according to claim 1, high-ratio surface pseudo-boehmite is characterized in that described original crystal seed is the SB powder, and its specific surface area and pore volume size are respectively 227.2m ²/ g and 0.40cm ³About/g.

3. the preparation method of large pore volume according to claim 1, high-ratio surface pseudo-boehmite is characterized in that described airtight hydrothermal condition, and its processing parameter is: 100～150 ℃ of temperature of reaction, 3～16 hours reaction times.

4. the preparation method of large pore volume according to claim 1, high-ratio surface pseudo-boehmite is characterized in that described drying process, and its processing parameter is: bake out temperature is 100～120 ℃, and drying time is 10～12 hours.

5. the preparation method of large pore volume according to claim 1, high-ratio surface pseudo-boehmite is characterized in that described crystal seed, and its crystal seed can be a SB powder hydrothermal decomposition sodium aluminate solution resulting decomposition product in confined conditions.

6. the preparation method of large pore volume according to claim 1, high-ratio surface pseudo-boehmite is characterized in that described single-phase pseudo-boehmite, and its specific surface area is 176.8～213.6m ²/ g, the pore volume size is 0.59～0.86cm ³/ g.

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