Industrial production method of pseudo-boehmite seed and pseudo-boehmite micro-powder

Abstract

The present application relates to the technical field of pseudo-boehmite preparation, and particularly relates to a production method of pseudo-boehmite seed and pseudo-boehmite micro powder, and specifically comprises the following steps: (1) preparing pseudo-boehmite seed: adding water and pseudo-boehmite fine powder into a seed reaction kettle to make a slurry, controlling the flow of sodium metaborate and nitric acid and the reaction temperature, and preparing a pseudo-boehmite seed slurry; (2) preparing pseudo-boehmite micro powder: adding the pseudo-boehmite seed into a synthesis reaction kettle according to a proportion to prepare a pseudo-boehmite micro powder slurry; (3) filtering and washing the pseudo-boehmite slurry: filtering and countercurrent washing the pseudo-boehmite slurry; and (4) drying the product: flash drying the filter cake to obtain the pseudo-boehmite micro powder. The pseudo-boehmite micro powder has the following characteristics: (1) high purity: the purity is greater than or equal to 99%, the sodium oxide is less than or equal to 0.05%, and the iron oxide is less than or equal to 0.03%; (2) fine and uniform particle size: D 50 ≤2 microns, and D 90 ≤4 microns; and (3) the slurry of the pseudo-boehmite is in a mortar state, has good filtering performance, and is easy to be industrialized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pseudo-boehmite preparation, and particularly relates to a production method of pseudo-boehmite seed and pseudo-boehmite micro powder. BACKGROUND

[0002] Pseudo-boehmite is also known as monohydrated alumina and pseudo-one water soft gibbsite, and its crystallization water content is between 1.25% and 2.0%. It is one of the 12 known water and alumina crystal types, and has high crystal phase purity, good peptization performance and strong cohesiveness, and is often used as a binder and a catalyst carrier. Compared with conventional materials, the pseudo-boehmite micro powder has special effects such as small size effect, quantum size effect, macro quantum tunnel effect and surface effect, which determines its strong chemical adsorption capacity. The use of superfine particles with more surface active centers as a catalyst can control the reaction speed and improve the reaction efficiency, and the pseudo-boehmite micro powder has also begun to attract the attention of researchers.

[0003] The unique physical and chemical properties of pseudo-boehmite determine its wide application in many industries, and the physical and chemical properties of pseudo-boehmite and the preparation method and process are closely related. The present application realizes the preparation of pseudo-boehmite micro powder by adding seed crystals in the synthesis process. In industry, there is a similar operation of adding seed crystals in sodium metaaluminate liquor when preparing aluminum hydroxide powder, but the two processes are fundamentally different. First, the products are different. Although pseudo-boehmite and aluminum hydroxide both belong to alumina hydrates, their crystal structures are different, and their properties and uses also have great differences. Secondly, the process methods are different. The production of aluminum hydroxide by adding seed crystals in sodium metaaluminate liquor, i.e. seed division method, generally utilizes the characteristics that sodium metaaluminate is unstable and can decompose to generate aluminum hydroxide and sodium hydroxide, and the product is mainly in the form of gibbsite crystal phase.

[0004] Patent CN 111137911 A discloses a method for preparing high-purity superfine aluminum hydroxide flame retardant by decomposition. In the method, aluminum hydroxide gel is added into sodium metaaluminate liquor, and high-purity CO2 is introduced to decompose sodium metaaluminate, and the decomposition time is 10-25h, and the average particle size of the generated superfine aluminum hydroxide is 1-2μm. Since this method is a gas-liquid reaction, the reaction process is difficult to control, and the initial pH value of sodium metaaluminate is above 13, and the reaction time is 10-25h. Under the conditions of long time and high pH value, the generated product is mainly aluminum hydroxide in the form of gibbsite crystal. Therefore, this process can only be used for producing aluminum hydroxide, and cannot be used for producing superfine pseudo-boehmite product.

[0005] If you want to generate pseudo-boehmite crystal type, specific reaction pH value, temperature and reaction time are needed, and the simple use of acid and sodium metaaluminate neutralization reaction, due to the fast acid-base neutralization reaction rate, the agglomeration phenomenon between pseudo-boehmite particles is serious, it is difficult to prepare fine pseudo-boehmite product. At present, the reported preparation of ultra-fine pseudo-boehmite method has super gravity carbonization method, strong stirring carbonization method, sol-gel method.

[0006] Mechanical crushing is to dry the industrial synthesis of pseudo-boehmite, and then grind to the required particle size range by ball mill, jet mill and other equipment. Carbon method refers to the introduction of CO2 gas into sodium metaaluminate of a certain concentration, and the purpose of preparing ultra-fine pseudo-boehmite is achieved by means of super gravity reactor, strong stirring and other technical means.

[0007] Among them, the super gravity carbonization method refers to the use of super gravity field formed by the rotation of the rotating packed bed in the rotating packed bed to micronize or form microfilm in the filler layer, so that the mass transfer surface is quickly updated, and the mass transfer rate is greatly improved. But the super gravity reactor has large equipment investment, and the reactor is easy to block during synthesis process, which affects the continuity of production and the stability of product. The principle of strong stirring carbonization method is similar to that of super gravity method, which is to reduce the agglomeration of pseudo-boehmite under the condition of high-speed rotation to generate large centrifugal force. The speed is generally above 600~800r / min, which requires high equipment, limiting the popularization of this method in industry.

[0008] The essence of sol-gel method is that the raw materials such as alkyl aluminum and aluminum alkyl are hydrolyzed into sol-gel under catalytic reaction, and then the fine particles are prepared by drying and heat treatment. The amorphous aluminum hydroxide or pseudo-boehmite obtained by sol-gel method can be controlled in terms of crystal type, crystallinity, particle size and morphology. But the preparation process is complex and difficult to control in industrial production.

[0009] The present application aims at the above problems, and controls the particle size of pseudo-boehmite by adding crystal seeds in the synthesis process from the aspect of pseudo-boehmite crystallization mechanism. The process of pseudo-boehmite precipitation can be roughly divided into: primary nucleation, secondary nucleation, mechanical nucleation, crystal growth, and crystal grain agglomeration. These processes are not sequential in the reaction system, and there is no primary and secondary, and they may exist at the same time. The nucleation process is the generation process of pseudo-boehmite fine crystal nucleus from nothing, which is more difficult to occur than other processes. The present application strengthens the crystal nucleus generation process by adding crystal seeds, generates more fine particles in a short time, and weakens the crystal grain agglomeration process which leads to the increase of product particle size. Thus, the pseudo-boehmite micropowder with finer particles and more uniform particle size distribution is prepared.

[0010] The preparation method is a pure inorganic reaction process, and the reaction conditions are mild, the process is easy to control, the equipment requirement is low, compared with several preparation methods currently disclosed, the production cost of pseudo-boehmite micro powder can be reduced, and the environmental pollution can be reduced, and the prepared pseudo-boehmite micro powder has high purity, uniform particle size, and average particle size D 50 ≤2 μm, D 90 ≤4 μm, and the pseudo-boehmite slurry is in a mortar state, and has good filtration performance.

[0011] The XRD pattern of the pseudo-boehmite micro powder produced by the industrial device is shown in Figure 1 The prepared pseudo-boehmite micro powder can be used for preparing γ-Al2O3 after high-temperature treatment, and the XRD pattern of the prepared γ-Al2O3 is shown in Figure 2 . SUMMARY

[0012] In order to solve the above technical problems, the application provides a production method of pseudo-boehmite seed and pseudo-boehmite micro powder, and the production process comprises the following steps:

[0013] (1) preparing pseudo-boehmite seed: after a certain amount of water and pseudo-boehmite powder are slurried, sodium metaborate and nitric acid are neutralized under the condition of a certain flow rate and temperature to synthesize pseudo-boehmite seed slurry;

[0014] (2) preparing pseudo-boehmite micro powder slurry: the pseudo-boehmite seed slurry prepared in step (1) is added to a synthesis reactor in a certain proportion, and sodium metaborate and nitric acid are mixed under the condition of a certain pH value and a certain reaction condition to synthesize pseudo-boehmite micro powder slurry;

[0015] (3) filtering and washing the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0016] (4) drying the product: the filter cake is dried by flash drying to obtain pseudo-boehmite product.

[0017] Beneficial effects: the application provides a production method of pseudo-boehmite seed and high-purity pseudo-boehmite micro powder, the preparation method is a pure inorganic reaction process, the reaction conditions are mild and easy to control, the equipment requirement is low, the method is simple and suitable for industrial production. The filtrate and mother liquor after multi-stage countercurrent washing are concentrated by multi-effect evaporation and used as by-product sodium nitrate, and wastewater and waste residue are discharged in the production process. The prepared pseudo-boehmite micro powder has high purity, uniform particle size, and average particle size D 50 ≤2 μm, D 90 ≤4 μm, and the pseudo-boehmite slurry is in a mortar state, and has good filtration performance. The pseudo-boehmite micro powder can be used for preparing active alumina, catalyst carrier and the like. DETAILED DESCRIPTION

[0018] The present application can be more readily understood with reference to the following detailed description of the preferred embodiments of the application and the included examples. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. If there is a conflict between the definitions in the specification and those in the patent, the definitions in the specification are intended to prevail. As used herein, the term "prepared from" is synonymous with "comprising." As used herein, the terms "comprise", "comprises", "comprising", "include", "includes", "including", "have", "has", "having", or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0019] The present application provides a method for producing pseudo-boehmite seed crystals and high-purity pseudo-boehmite micropowder, which comprises the following steps:

[0020] (1) Preparing pseudo-boehmite seed crystals: a certain amount of water and pseudo-boehmite fine powder are added to a seed crystal reactor, and then a neutralization precipitation reaction of sodium metaaluminate and nitric acid is carried out to synthesize a pseudo-boehmite seed crystal slurry;

[0021] (2) Preparing a pseudo-boehmite micropowder slurry by neutralization reaction: the pseudo-boehmite seed crystal slurry prepared in step (1) is added to a synthesis reactor, and an isopH value mixed reaction is carried out in the synthesis reactor to obtain a pseudo-boehmite micropowder slurry;

[0022] (3) Filtering and washing the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter and then washed by multiple-stage countercurrent washing to obtain a filter cake;

[0023] (4) Drying: the filter cake is dried by flash drying to obtain a pseudo-boehmite product.

[0024] Preferably, the average particle size D50 of the pseudo-boehmite fine powder added to the seed crystal reactor in step (1) is 1-5 μm;

[0025] More preferably, the average particle size D50 of the pseudo-boehmite fine powder added to the seed crystal reactor in step (1) is ≤ 3.5 μm;

[0026] Preferably, in step (1), the mass of the pseudo-boehmite fine powder added to the seed crystal reactor is 1%-5% of the total amount;

[0027] More preferably, in step (1), the mass of the pseudo-boehmite fine powder added to the seed crystal reactor is 2%-3% of the total amount;

[0028] Preferably, in step (1), the mass ratio of water to pseudo-boehmite fine powder added to the seed crystal reactor is 5-10:1.

[0029] As more preferably, in the step (1), the mass ratio of water to pseudo-boehmite fine powder added into the seed reactor is 6-7:1;

[0030] As preferably, in the step (1), the flow rate of sodium aluminate added into the seed reactor is 1.3-1.8 m³ / h, and the flow rate of nitric acid is 2-3 m³ / h;

[0031] As more preferably, in the step (1), the flow rate of sodium aluminate added into the seed reactor is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h;

[0032] As preferably, in the step (1), the reaction process of sodium aluminate and nitric acid added into the seed reactor is an equal-pH value reaction process, and the pH value is controlled to be 6-9;

[0033] As more preferably, in the step (1), the reaction process of sodium aluminate and nitric acid added into the seed reactor is an equal-pH value reaction process, and the pH value is controlled to be 7-8;

[0034] As preferably, in the step (2), the pseudo-boehmite seed slurry prepared in the step (1) is added into the synthesis reactor, and the seed slurry is added in an amount of 10%-20% of the total amount;

[0035] As more preferably, in the step (2), the pseudo-boehmite seed slurry prepared in the step (1) is added into the synthesis reactor, and the seed slurry is added in an amount of 13%-15% of the total amount;

[0036] As most preferably, the method for preparing the high-purity ultrafine aluminum hydroxide flame retardant by the decomposition method according to the application comprises the following steps in the production process:

[0037] (1) Preparation of pseudo-boehmite seed: pseudo-boehmite fine powder is added into a seed reactor, the average particle size D 50 ≤3.5 μm, and the mass is 2%-3% of the total amount; the mass ratio of water to pseudo-boehmite fine powder added is 6-7:1; the flow rate of sodium aluminate added is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h; the reaction process of sodium aluminate and nitric acid is an equal-pH value reaction process, and the pH value is controlled to be 7-8; neutralization and precipitation reaction of sodium aluminate and nitric acid is carried out to synthesize pseudo-boehmite seed slurry;

[0038] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed slurry prepared in the step (1) is added into a synthesis reactor in an amount of 13%-15% of the total amount, and an equal-pH value mixed reaction is carried out in the synthesis reactor, the pH value is controlled to be 7-8, and pseudo-boehmite fine powder slurry is obtained;

[0039] (3) Filtering and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0040] (4) Drying: the filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0041] In the present application, the particle size of the pseudo-boehmite is controlled by adding seed crystals during the reaction process, and the pseudo-boehmite powder prepared has high purity, uniform particle size, and an average particle size D 50 ≤2 μm, D 90 ≤4 μm, and the pseudo-boehmite slurry is in the form of mortar, and has good filtering performance. The particle size of the product can be controlled by controlling the amount of seed crystals added.

[0042] The present application will be described in detail below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present application, and cannot be understood as limiting the protection scope of the present application, and some non-essential improvements and adjustments made by the person skilled in the art based on the content of the present application still belong to the protection scope of the present application.

[0043] In addition, if not otherwise specified, the raw materials used are commercially available. Example

[0044] Example 1

[0045] (1) Preparation of pseudo-boehmite seed crystals: pseudo-boehmite fine powder with an average particle size D50≤3.5 μm is added to a seed crystal reactor, and the mass of the pseudo-boehmite fine powder is 2% to 3% of the total amount, and the mass ratio of water to pseudo-boehmite fine powder is 6 to 7:1; the flow rate of sodium metaaluminate is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h; the reaction process of sodium metaaluminate and nitric acid is an isopH value reaction process, and the pH value is controlled to be 7 to 8; the neutralization and precipitation reaction of sodium metaaluminate and nitric acid is carried out to synthesize a pseudo-boehmite seed crystal slurry;

[0046] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed crystal slurry prepared in step (1) is added to a synthesis reactor in an amount of 13% to 15% of the total amount, and an isopH value mixed reaction is carried out in the synthesis reactor, the pH value is controlled to be 7 to 8, and the reaction temperature is 95°C, to obtain a pseudo-boehmite fine powder slurry;

[0047] (3) Filtering and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0048] (4) Drying: the filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0049] Product analysis: the average particle size D 50 of the pseudo-boehmite product is 1.63 μm, D90 3.10 μm

[0050] Comparative Example 1

[0051] (1) Preparation of pseudoboehmite seed crystals: Add aluminum hydroxide powder with an average particle size D50≤3.5 μm to a seed crystal reactor, the mass being 2% to 3% of the total amount, and add water in a mass ratio of 6 to 7:1 to the pseudoboehmite powder; add sodium aluminate at a flow rate of 1.5 m3 / h and nitric acid at a flow rate of 2.5 m3 / h; the reaction process of sodium aluminate and nitric acid is an equal-pH value reaction process, with the pH value controlled at 7 to 8; carry out the neutralization precipitation reaction of sodium aluminate and nitric acid to synthesize a pseudoboehmite seed slurry;

[0052] (2) Preparation of a pseudoboehmite powder slurry by neutralization reaction: add the pseudoboehmite seed slurry prepared in step (1) in an amount of 13% to 15% of the total amount to a synthesis reactor, and carry out an equal-pH value mixing reaction in the synthesis reactor, with the pH value controlled at 7 to 8 and the reaction temperature controlled at 95°C, to obtain a pseudoboehmite powder slurry;

[0053] (3) Filtration and washing of the pseudoboehmite slurry: separate the pseudoboehmite slurry obtained in step (2) by a filter, and then carry out multi-stage countercurrent washing to obtain a filter cake;

[0054] (4) Drying: dry the filter cake by flash drying to obtain a pseudoboehmite product.

[0055] Product analysis: the average particle size D 50 of the pseudoboehmite product is 10.3 μm, and the D 90 is 26.51 μm

[0056] Comparative Example 2

[0057] (1) Pseudoboehmite seed synthesis process without adding pseudoboehmite powder: carry out an equal-pH value mixing reaction of sodium aluminate and nitric acid in a product synthesis reactor, with the pH value controlled at 7 to 8, to obtain pseudoboehmite seed crystals;

[0058] (2) Preparation of a pseudoboehmite powder slurry by neutralization reaction: add the pseudoboehmite seed slurry prepared in step (1) in an amount of 13% to 15% of the total amount to a synthesis reactor, and carry out an equal-pH value mixing reaction in the synthesis reactor, with the pH value controlled at 7 to 8 and the reaction temperature controlled at 95°C, to obtain a pseudoboehmite powder slurry;

[0059] (3) Filtration and washing of the pseudoboehmite slurry: separate the pseudoboehmite slurry obtained in step (2) by a filter, and then carry out multi-stage countercurrent washing to obtain a filter cake;

[0060] (4) Drying: dry the filter cake by flash drying to obtain a pseudoboehmite product.

[0061] Product analysis: the average particle size D 50 of the pseudo-boehmite product is 12.43 μm, D 90 of 32.89 μm

[0062] Example 2

[0063] (1) Preparation of pseudo-boehmite seed crystals: pseudo-boehmite fine powder with an average particle size D 50 ≤ 3.5 μm and a mass of 2% to 3% of the total amount is added to the seed reactor, and the mass ratio of water to the pseudo-boehmite fine powder is 6 to 7:1. The flow rate of sodium aluminate is 1.5 m3 / h, and the flow rate of nitric acid is 2.5 m3 / h. The reaction process of sodium aluminate and nitric acid is an isopH value reaction process, and the pH value is controlled to be 7 to 8. The neutralization precipitation reaction of sodium aluminate and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry.

[0064] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed slurry prepared in step (1) is added to the synthesis reactor in an amount of 5% of the total amount, and an isopH value mixing reaction is carried out in the synthesis reactor, with the pH value controlled to be 7 to 8 and the reaction temperature controlled to be 95°C, to obtain the pseudo-boehmite fine powder slurry.

[0065] (3) Filtration and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained.

[0066] (4) Drying: the filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0067] Product analysis: the average particle size D 50 of the pseudo-boehmite product is 5.32 μm, D 90 of 20.24 μm

[0068] Example 3

[0069] (1) Preparation of pseudo-boehmite seed crystals: pseudo-boehmite fine powder with an average particle size D 50 ≤ 3.5 μm and a mass of 2% to 3% of the total amount is added to the seed reactor, and the mass ratio of water to the pseudo-boehmite fine powder is 6 to 7:1. The flow rate of sodium aluminate is 1.5 m3 / h, and the flow rate of nitric acid is 2.5 m3 / h. The reaction process of sodium aluminate and nitric acid is an isopH value reaction process, and the pH value is controlled to be 7 to 8. The neutralization precipitation reaction of sodium aluminate and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry.

[0070] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed slurry prepared in step (1) is added to the synthesis reactor in an amount of 20% of the total amount, and an isopH value mixing reaction is carried out in the synthesis reactor, with the pH value controlled to be 7 to 8 and the reaction temperature controlled to be 95°C, to obtain the pseudo-boehmite fine powder slurry.

[0071] (3) The pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0072] (4) The filter cake is dried by flash drying to obtain a pseudo-boehmite product.

[0073] Product analysis: The average particle size D50 of the pseudo-boehmite product is 1.07 μm, and D90 is 2.02 μm. 50 90 The solid-liquid separation effect is poor.

[0074] Comparative Example 3

[0075] (1) The pseudo-boehmite fine powder slurry is prepared by neutralization reaction: no seed is added, and the pH value is mixed in the synthesis reactor, the pH value is controlled at 7-8, the reaction temperature is 95°C, and the pseudo-boehmite fine powder slurry is obtained;

[0076] (2) The pseudo-boehmite slurry is filtered and washed: the pseudo-boehmite slurry obtained in step (1) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0077] (3) The filter cake is dried by flash drying to obtain a pseudo-boehmite product.

[0078] Product analysis: The average particle size D50 of the pseudo-boehmite product is 7.35 μm, and D90 is 24.4 μm. 50 90

[0079] Example 4

[0080] (1) The pseudo-boehmite seed is prepared: the pseudo-boehmite fine powder with an average particle size D50≤3.5 μm is added to the seed reactor, the mass is 2%-3% of the total amount, the mass ratio of water to pseudo-boehmite fine powder is 6-7:1; the flow rate of sodium metavanadate is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h; the reaction process of sodium metavanadate and nitric acid is an equal-pH value reaction process, and the pH value is controlled at 7-8; the neutralization and precipitation reaction of sodium metavanadate and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry;

[0081] (2) The pseudo-boehmite fine powder slurry is prepared by neutralization reaction: the pseudo-boehmite seed slurry prepared in step (1) is added to the synthesis reactor, the pH value is mixed in the synthesis reactor, the pH value is controlled at 6-9, the reaction temperature is 95°C, and the pseudo-boehmite fine powder slurry is obtained;

[0082] (3) The pseudo-boehmite slurry is filtered and washed: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0083] ​​​(4) Drying: The filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0084] Product analysis: The average particle size D 50 of the pseudo-boehmite product is 1.78 μm, and D 90 is 3.34 μm.

[0085] Comparative Example 4

[0086] (1) Preparation of pseudo-boehmite seed crystals: Pseudo-boehmite fine powder with an average particle size D 50 ≤ 3.5 μm and a mass of 2% to 3% of the total amount is added to the seed crystal reactor, and the mass ratio of water to the pseudo-boehmite fine powder is 6 to 7:1. The flow rate of sodium aluminates is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h. The reaction process of sodium aluminates and nitric acid is an isopH value reaction process, and the pH value is controlled at 7 to 8. The neutralization and precipitation reaction of sodium aluminates and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry.

[0087] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: The pseudo-boehmite seed slurry prepared in step (1) is added to the synthesis reactor in an amount of 13% to 15% of the total amount, and an isopH value mixing reaction is carried out in the synthesis reactor, with the pH value controlled at 5 to 6 and the reaction temperature at 95°C, to obtain the pseudo-boehmite fine powder slurry.

[0088] (3) Filtration and washing of the pseudo-boehmite slurry: The pseudo-boehmite slurry obtained in step (2) is separated by a filter and washed by multiple countercurrent washing to obtain a filter cake.

[0089] (4) Drying: The filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0090] Product analysis: The average particle size D 50 of the pseudo-boehmite product is 12.5 μm, and D 90 is 15.62 μm.

[0091] Comparative Example 5

[0092] (1) Preparation of pseudo-boehmite seed crystals: Pseudo-boehmite fine powder with an average particle size D 50 ≤ 3.5 μm and a mass of 2% to 3% of the total amount is added to the seed crystal reactor, and the mass ratio of water to the pseudo-boehmite fine powder is 6 to 7:1. The flow rate of sodium aluminates is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h. The reaction process of sodium aluminates and nitric acid is an isopH value reaction process, and the pH value is controlled at 7 to 8. The neutralization and precipitation reaction of sodium aluminates and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry.

[0093] (2) Neutralization reaction to prepare pseudo-boehmite micro powder slurry: the pseudo-boehmite seed slurry prepared in step (1) is added into the synthesis reactor in an amount of 13% to 15% of the total amount, and an equal pH value mixing reaction is carried out in the synthesis reactor, the pH value is controlled to be 9 to 10, and the reaction temperature is 95°C, so as to obtain a pseudo-boehmite micro powder slurry;

[0094] (3) Filtration and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained.

[0095] (4) Drying: the filter cake is dried by flash drying to obtain a pseudo-boehmite product.

[0096] Product analysis: the average particle size D 50 of the pseudo-boehmite product is 7.03 μm, and the average particle size D 90 is 14.23 μm.

[0097] Example 5

[0098] (1) Preparation of pseudo-boehmite seeds: pseudo-boehmite fine powder with an average particle size D 50 ≤ 3.5 μm is added into a seed reactor, and the mass of the pseudo-boehmite fine powder is 2% to 3% of the total amount, the mass ratio of water to the pseudo-boehmite fine powder is 6 to 7:1, the flow rate of sodium metaaluminate is 1.5 m³ / h, and the flow rate of nitric acid is 2.5 m³ / h; the reaction process of sodium metaaluminate and nitric acid is an equal pH value reaction process, the pH value is controlled to be 7 to 8, and a neutralization and precipitation reaction of sodium metaaluminate and nitric acid is carried out to synthesize a pseudo-boehmite seed slurry.

[0099] (2) Neutralization reaction to prepare pseudo-boehmite micro powder slurry: the pseudo-boehmite seed slurry prepared in step (1) is added into the synthesis reactor in an amount of 13% to 15% of the total amount, and an equal pH value mixing reaction is carried out in the synthesis reactor, the pH value is controlled to be 7 to 8, the reaction temperature is 85°C, and a pseudo-boehmite micro powder slurry is obtained.

[0100] (3) Filtration and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained.

[0101] (4) Drying: the filter cake is dried by flash drying to obtain a pseudo-boehmite product.

[0102] Product analysis: the average particle size D 50 of the pseudo-boehmite product is 2.13 μm, and the average particle size D 90 is 3.53 μm

[0103] Example 6

[0104] (1) Preparation of pseudo-boehmite seeds: pseudo-boehmite fine powder with an average particle size D 50≤3.5 μm, 2%~3% of the total mass, the mass ratio of water to pseudo-boehmite fine powder added is 6~7:1; the flow rate of sodium metaaluminate added is 1.5 m3 / h, and the flow rate of nitric acid is 2.5 m3 / h; the reaction process of sodium metaaluminate and nitric acid is an equal-pH value reaction process, the pH value is controlled to be 7~8; the neutralization and precipitation reaction of sodium metaaluminate and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry;

[0105] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed slurry prepared in step (1) is added into the synthesis reactor at an amount of 13%~15% of the total amount, and an equal-pH value mixing reaction is carried out in the synthesis reactor, the pH value is controlled to be 7~8, and the reaction temperature is 75°C, to obtain the pseudo-boehmite fine powder slurry;

[0106] (3) Filtration and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0107] (4) Drying: the filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0108] Product analysis: the average particle size D 50 of the pseudo-boehmite product is 2.62 μm, and the average particle size D 90 is 4.01 μm

[0109] Comparative Example 6

[0110] (1) Preparation of pseudo-boehmite seed: pseudo-boehmite fine powder is added into a seed reactor, the average particle size D 50 of the pseudo-boehmite fine powder is ≤3.5 μm, 2%~3% of the total mass, the mass ratio of water to pseudo-boehmite fine powder added is 6~7:1; the flow rate of sodium metaaluminate added is 1.5 m3 / h, and the flow rate of nitric acid is 2.5 m3 / h; the reaction process of sodium metaaluminate and nitric acid is an equal-pH value reaction process, the pH value is controlled to be 7~8; the neutralization and precipitation reaction of sodium metaaluminate and nitric acid is carried out to synthesize the pseudo-boehmite seed slurry;

[0111] (2) Preparation of pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed slurry prepared in step (1) is added into the synthesis reactor at an amount of 13%~15% of the total amount, and an equal-pH value mixing reaction is carried out in the synthesis reactor, the pH value is controlled to be 7~8, and the reaction temperature is 65°C, to obtain the pseudo-boehmite fine powder slurry;

[0112] (3) Filtration and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained;

[0113] (4) Drying: the filter cake is dried by flash drying to obtain the pseudo-boehmite product.

[0114] Product analysis: the average particle size D 50 of the pseudo-boehmite product was 3.26 μm, and D 90 of the pseudo-boehmite product was 5.19 μm

[0115] Comparative Example 6

[0116] (1) Preparation of pseudo-boehmite seed crystals: pseudo-boehmite fine powder with an average particle size D 50 ≤ 3.5 μm and a mass of 2% to 3% of the total amount was added to a seed reactor, and water was added in a mass ratio of 6 to 7:1 to the pseudo-boehmite fine powder; the flow rate of sodium aluminates was 1.5 m³ / h, and the flow rate of nitric acid was 2.5 m³ / h; the reaction process of sodium aluminates and nitric acid was an isopH value reaction process, and the pH value was controlled at 7 to 8; the neutralization precipitation reaction of sodium aluminates and nitric acid was performed to synthesize a pseudo-boehmite seed slurry;

[0117] (2) Preparation of a pseudo-boehmite fine powder slurry by neutralization reaction: the pseudo-boehmite seed slurry prepared in step (1) was added to a synthesis reactor in an amount of 13% to 15% of the total amount, and an isopH value mixing reaction was performed in the synthesis reactor, the pH value was controlled at 7 to 8, and the reaction temperature was room temperature, to obtain a pseudo-boehmite fine powder slurry;

[0118] (3) Filtration and washing of the pseudo-boehmite slurry: the pseudo-boehmite slurry obtained in step (2) was separated by a filter, and after multi-stage countercurrent washing, a filter cake was obtained;

[0119] (4) Drying: the filter cake was dried by flash drying to obtain a pseudo-boehmite product.

[0120] Product analysis: the average particle size D 50 of the pseudo-boehmite product was 6.77 μm, and D 90 of the pseudo-boehmite product was 15.43 μm

[0121] Table 1 Particle size analysis results of pseudo-boehmite products of example samples

[0122] Item D50 / pm D90 / pm Example 1 1.63 3.10 Comparative Example 1 10.3 26.51 Comparative Example 2 12.43 32.89 Example 2 5.32 20.24 Example 3 1.07 2.02 Comparative Example 3 7.35 24.4 Example 4 1.78 3.34 Comparative Example 4 12.5 15.62 Comparative Example 5 7.03 14.23

[0123] As can be seen from the particle sizes of the pseudo-boehmite products prepared in Comparative Example 1, Comparative Example 1, and Comparative Example 2, the addition of pseudo-boehmite fine powder in the preparation process of the seed crystals has a great influence on the use effect of the seed crystals and the particle size of the final product.

[0124] As can be seen from the particle sizes of the pseudo-boehmite products prepared in Comparative Example 1, Example 2, Example 3, and Comparative Example 3, increasing the amount of seed crystals helps to reduce the particle size of the product, but when the amount of seed crystals is increased to 20%, the effect of the slurry solid-liquid part after the reaction will be affected, the production efficiency will be affected, and the particle size of the pseudo-boehmite product synthesized without adding seed crystals is larger.

[0125] The particle size of the pseudo-boehmite fines produced in Comparative Example 1, Example 5, Example 6, Comparative Example 6, and Comparative Example 7 is shown in Table 2. As can be seen, increasing the reaction temperature helps to decrease the average particle size of the product and increase the filtration rate.

[0126] Table 2 Particle Size Analysis Results for Pseudo-Boehmite Product

[0127] Item D 50 / μm D 90 / μm Filtration time / min Example 5 2.13 3.53 3 Example 6 2.62 4.01 4 Comparative Example 6 3.26 5.29 7 Comparative Example 7 6.77 15.43 10

[0128] The foregoing examples are illustrative only and are not meant to limit the scope of the methods described herein. The appended claims are intended to claim as broad a range as is allowed under the law. The examples presented herein are merely illustrative of selected embodiments in accordance with a combination of all possible embodiments. Therefore, the applicant intends that the appended claims not be limited to the choice of features set forth in the examples. Some numerical ranges recited in the claims are inclusive of the endpoints and sub-ranges falling within the ranges. Changes in these ranges can also be made under the applicable law.

Claims

1. A method for preparing pseudo-boehmite seeds, characterized by, The method comprises the following steps: (1) adding water and pseudo-boehmite fine powder into the seed reactor, the mass of the pseudo-boehmite fine powder is 1%~5% of the total mass of the slurry after reaction, the average particle size D 50 of the pseudo-boehmite fine powder is 1~5μm, the content of sodium oxide is ≤0.05%, the content of iron oxide is ≤0.05%, the mass ratio of the water to the pseudo-boehmite fine powder is 5~10:1; (2) heating the reactor to 60℃~80℃, adding sodium metaaluminate and nitric acid for neutralization reaction, the flow rate of the sodium metaaluminate is 1.3~1.8m³ / h, the flow rate of the nitric acid is 2~3m³ / h, the reaction process of the sodium metaaluminate and the nitric acid is an equal-pH value reaction process, the pH value is controlled to 6~9, and the pseudo-boehmite seed slurry is synthesized.

2. A method for producing pseudo-boehmite fine powder, characterized by, The production method comprises the following steps: (1) The pseudo-boehmite seed slurry of claim 1 is added into a synthesis reactor at a seed slurry addition amount of 10-20% of the total mass of the slurry after reaction, and the reactor is heated to 75-95°C; sodium metaaluminate and nitric acid are mixed at a pH value of 7-8 in the synthesis reactor, the sodium metaaluminate is added at a flow rate of 0.65-0.9 m³ / h, and the nitric acid is added at a flow rate of 1-1.5 m³ / h to obtain a pseudo-boehmite micro-powder slurry; (2) The pseudo-boehmite micro-powder slurry obtained in step (1) is separated by a filter, and after multi-stage countercurrent washing, a filter cake is obtained; (3) The filter cake is subjected to flash drying to obtain a pseudo-boehmite micro-powder product.

3. The method of producing pseudo-boehmite fine powder according to claim 2, characterized by, The prepared pseudo-boehmite micro-powder product has a pseudo-boehmite content of more than 99%, sodium oxide ≤0.05%, iron oxide ≤0.03%, average particle size D 50 ≤2μm, and D 90 ≤4μm.

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