Superfine aluminum hydroxide micro powder as well as segmented preparation method and application thereof

Abstract

The invention belongs to the technical field of aluminum hydroxide micro powder preparation, and particularly relates to superfine aluminum hydroxide micro powder and a segmented preparation method and application thereof. According to the invention, the aluminum hydroxide seed crystal with D50 of 0.8-1.2 [mu] m is prepared by integrating and adjusting a carbonation decomposition process, and the aluminum hydroxide seed crystal can be directly used in the preparation of superfine aluminum hydroxide micro powder seed decomposition without subsequent grinding treatment; the technical problem that in the prior art, superfine aluminum hydroxide micro powder seed decomposition crystal seeds cannot be directly prepared through a chemical method is solved, and the production cost of the superfine aluminum hydroxide micro powder is greatly reduced. According to the invention, a segmented preparation method of two-stage seed precipitation decomposition is used, and a reaction system after one-stage seed precipitation decomposition is put into two-stage seed precipitation decomposition, so that the usage amount of crystal seeds in production can be greatly reduced, and the production cost of the superfine aluminum hydroxide micropowder can be effectively reduced. The superfine aluminum hydroxide micropowder prepared by the method can meet the use requirements of the flame retardant.

Description

Technical Field

[0001] The invention belongs to the technical field of aluminum hydroxide micropowder preparation, and specifically relates to ultrafine aluminum hydroxide micropowder and a segmented preparation method and application thereof. Background Art

[0002] With the widespread application of polymer composite materials such as plastics, rubber, and fibers in the fields of construction, chemical industry, military, and transportation, the safety of their use and the harm to the environment have gradually become the focus of attention, and it is urgent to improve their flame retardant and smoke suppression properties. Compared with other inorganic flame retardant additives, aluminum hydroxide micropowder has a larger specific surface area, higher surface energy, does not affect the mechanical properties and processing characteristics of the material, and has excellent flame retardant effect. It has become the first choice of inorganic flame retardant additives for polymer materials. It is often used in building insulation materials, silicone rubber insulation materials, heat shrinkable materials, and cable outer insulation additives, accounting for more than 80% of inorganic flame retardant consumers.

[0003] The particle size and particle size distribution of aluminum hydroxide products as flame retardants are the main factors affecting the performance. If the particle size is too fine, the product will have a large specific surface area, high viscosity, poor fluidity and cannot be used. The optimal particle size is D50 = 1.5-2.0 μm. If the particle size is too coarse, the specific surface area will be reduced, the fluidity will be poor after mixing with the resin, and the processing will be difficult. The specific surface area is 3.0-4.0 m 2 / g is more appropriate. Therefore, the particle size of aluminum hydroxide powder that meets the requirements of flame retardant is D50 = 1.5 ~ 2.0 μm, and the specific surface area is 3.0 ~ 4.0 m 2 / g, aluminum hydroxide powder with this characteristic is usually considered to be ultrafine aluminum hydroxide powder.

[0004] At present, the industrial production methods of aluminum hydroxide mainly include carbonation decomposition method and seed separation method, but the traditional carbonation decomposition method and seed separation method cannot directly obtain ultrafine aluminum hydroxide powder that meets the requirements of flame retardants. The method for preparing ultrafine aluminum hydroxide powder in the prior art is usually: adding specific aluminum hydroxide seeds to a supersaturated sodium aluminate solution with a caustic ratio of 1.55 to 1.9 to reduce the surface energy of aluminum hydroxide precipitation and make aluminum hydroxide crystallize and precipitate quickly. The key to this method is the preparation of active seeds. The seed preparation methods currently used include mechanical grinding method, aluminum sulfate method, amorphous gel method, etc. The active seeds are subsequently added to the sodium aluminate solution using a two-stage seed separation method to produce ultrafine products. However, the shortcomings of the prior art are: the seed preparation time is long, and the seeds are prone to particle size differentiation during the storage period, which will affect the particle size, specific surface area and other indicators of subsequent ultrafine products. Summary of the invention

[0005] In view of the problems existing in the prior art, the present invention provides an ultrafine aluminum hydroxide powder and a segmented preparation method and application thereof, which solves the problems in the preparation process of ultrafine aluminum hydroxide powder, that is, the seed preparation time is long, the seed crystals are prone to particle size differentiation during the storage period, and the particle size and specific surface area of ​​the subsequent ultrafine products are affected.

[0006] The present invention specifically includes the following contents:

[0007] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0008] (1) Carbonation decomposition to prepare seed crystals: a gas containing carbon dioxide is introduced into a sodium aluminate solution having an aluminum oxide concentration of 35-50 g / L, wherein the volume concentration of carbon dioxide in the carbon dioxide-containing gas is 27-50%, the reaction temperature is controlled to be 25-35° C., the reaction time is 3-7 min, and the aluminum oxide concentration at the reaction end point is 3-7 g / L, to obtain aluminum hydroxide seed crystals with a D50 of 0.8-1.2 μm;

[0009] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to the sodium aluminate solution to carry out a one-stage seed decomposition reaction, controlling the seed ratio to be 25-28 wt %, and obtaining a one-stage reaction system after the reaction is completed; it should be noted that the seed ratios described in the present invention are all in mass percentage;

[0010] (3) Two-stage seed decomposition: Add the first-stage reaction system to the sodium aluminate solution, control the volume of the sodium aluminate solution to be 3-5 times the volume of the first-stage reaction system, and perform a two-stage seed decomposition reaction to obtain D50 = 1.5-2.0 μm, specific surface area = 3.0-4.0 m 2 / g of ultrafine aluminum hydroxide powder.

[0011] The carbon dioxide-containing gas in step (1) can be tail gas produced by calcining lime.

[0012] Preferably, after the second-stage seed decomposition reaction in step (3) is completed, the process further comprises:

[0013] a. Separation and washing: After the second stage seed decomposition reaction is completed, the reaction system is subjected to solid-liquid separation to obtain a solid material, and the solid material is washed and then separated from the solid and liquid again to obtain ultrafine aluminum hydroxide wet material;

[0014] b. Drying and dispersing: flash drying the ultrafine aluminum hydroxide wet material to obtain ultrafine aluminum hydroxide, and dispersing the ultrafine aluminum hydroxide powder to obtain the ultrafine aluminum hydroxide.

[0015] Preferably, the moisture content of the ultrafine aluminum hydroxide wet material is less than 40wt%; and / or the moisture content of the ultrafine aluminum hydroxide obtained after drying is less than 0.2wt% and the sodium oxide content is less than 0.2wt%.

[0016] Preferably, the caustic ratio of the sodium aluminate solution in step (2) is 1.55-1.9, and the alumina concentration is 50-120 g / L; and / or the reaction temperature of the first-stage seed decomposition reaction is 50-70° C.; and / or the reaction time of the first-stage seed decomposition reaction is 2-3 h.

[0017] Preferably, the caustic ratio of the sodium aluminate solution in step (3) is 1.55-1.9, the alumina concentration is 50-120 g / L, and / or the reaction temperature of the second-stage seed decomposition reaction is 50-70° C.; and / or the reaction time of the second-stage seed decomposition reaction is 8-10 h.

[0018] The invention discloses an ultrafine aluminum hydroxide powder prepared by the method described in the invention.

[0019] A flame retardant containing the ultrafine aluminum hydroxide powder of the invention.

[0020] An application of the flame retardant of the present invention in building thermal insulation materials, insulating materials and heat shrinkable materials.

[0021] Beneficial effects of the present invention:

[0022] (1) The present invention prepares aluminum hydroxide seeds with D50 = 0.8-1.2 μm by integrating and adjusting the carbonation decomposition process. The aluminum hydroxide seeds can be directly used in the preparation of ultrafine aluminum hydroxide micropowder seed decomposition without subsequent grinding treatment, thereby overcoming the technical difficulty of the prior art that ultrafine aluminum hydroxide micropowder seed decomposition seeds cannot be directly prepared by chemical methods, and greatly reducing the production cost of ultrafine aluminum hydroxide micropowder.

[0023] (2) The method for preparing ultrafine aluminum hydroxide powder disclosed in the present invention innovatively uses a staged preparation method of two-stage seed decomposition, and the reaction system after the first-stage seed decomposition is put into the second-stage seed decomposition, which can greatly reduce the amount of seed crystals used in production and effectively reduce the production cost of ultrafine aluminum hydroxide powder.

[0024] (3) The preparation method disclosed in the present invention prepares a D50 of 1.5-2.0 μm and a specific surface area of ​​1.5-2.0 μm by comprehensively improving the raw material ratio and reaction parameters of the first-stage seed decomposition reaction and the second-stage seed decomposition reaction.

[0025] =3.0-4.0m 2 / g of ultrafine aluminum hydroxide powder can meet the use requirements of flame retardants. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a process flow diagram of the method disclosed in the present invention;

[0027] Figure 2 The laser particle size analyzer analysis result of the aluminum hydroxide micropowder prepared in Example 1 of the present invention;

[0028] Figure 3 The specific surface area test results of the aluminum hydroxide micropowder prepared in Example 1 of the present invention;

[0029] Figure 4 The laser particle size analyzer analysis result of the aluminum hydroxide micropowder prepared in Example 2 of the present invention;

[0030] Figure 5 The specific surface area test results of the aluminum hydroxide micropowder prepared in Example 2 of the present invention;

[0031] Figure 6 This is the analysis result of the aluminum hydroxide micropowder prepared in Comparative Example 1 of the present invention using a laser particle size analyzer. DETAILED DESCRIPTION

[0032] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. The embodiments shown below do not limit the invention content described in the claims. In addition, the entire contents of the structures represented by the following embodiments are not limited to those necessary as solutions to the invention described in the claims.

[0033] Reference Figure 1 The process flow is a segmented preparation method of ultrafine aluminum hydroxide powder, comprising the following steps:

[0034] (1) Carbonation decomposition to prepare seed crystals: a gas containing carbon dioxide (preferably tail gas produced by calcining lime) is introduced into a sodium aluminate solution having an aluminum oxide concentration of 35-50 g / L, wherein the volume concentration of carbon dioxide in the carbon dioxide-containing gas is 27-50%, the reaction temperature is controlled to be 25-35° C., the reaction time is 3-7 min, and the aluminum oxide concentration at the reaction end point is 3-7 g / L, to obtain aluminum hydroxide seed crystals with D50=0.8-1.2 μm; it should be noted that the carbonation decomposition described in the present invention is carbonation decomposition;

[0035] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to a sodium aluminate solution having a caustic ratio of 1.55-1.9 and an aluminum oxide concentration of 50-120 g / L to carry out a one-stage seed decomposition reaction, wherein the seed ratio is controlled to be 25-28 wt %, the reaction temperature is 50-70° C., and the reaction time is 2-3 h. After the reaction is completed, a one-stage reaction system is obtained;

[0036] (3) Two-stage seed decomposition: add the first-stage reaction system to a sodium aluminate solution with a caustic ratio of 1.55-1.9 and an alumina concentration of 50-120 g / L, control the volume of the sodium aluminate solution to be 3-5 times the volume of the first-stage reaction system, and carry out a two-stage seed decomposition reaction at a reaction temperature of 50-70°C and a reaction time of 8-10 h. After the second-stage seed decomposition reaction, the reaction system is subjected to solid-liquid separation to obtain a solid material. The solid material is washed and then subjected to solid-liquid separation again to obtain an ultrafine aluminum hydroxide wet material with a water content of less than 40 wt% and a washing liquid. The washing liquid is discharged (i.e., the washing liquid is discharged in the attached figure) to the alumina section for further use. The ultrafine aluminum hydroxide wet material is flash-dried to obtain ultrafine aluminum hydroxide, which is dispersed to obtain a D50 of 1.5-2.0 μm and a specific surface area of ​​1.5-2.0 μm.

[0037] =3.0-4.0m 2 / g, ultrafine aluminum hydroxide powder with a water content of less than 0.2wt% and a sodium oxide content of less than 0.2wt%.

[0038] The ultrafine aluminum hydroxide powder prepared by the method of the present invention can be prepared into a flame retardant and used in building thermal insulation materials, insulating materials and heat shrinkable materials.

[0039] Example 1

[0040] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0041] Step 1: Preparation of sodium aluminate solution for seed crystal decomposition. Sodium aluminate solution with a caustic ratio of 1.65 and an alumina concentration of 70 g / L was prepared to an alumina concentration of 45 g / L at a temperature of 30°C.

[0042] Step 2: Preparation of seed crystals. A carbonation reaction was carried out using a supergravity reactor and a vertical lime furnace to produce a gas with a volume concentration of 35% CO2 produced by calcining limestone. The alumina concentration at the end of the reaction was 5 g / L and the reaction time was controlled within 5 minutes to prepare seed crystals with D50 = 0.85 μm.

[0043] Step 3: Preparation of sodium aluminate solution for product decomposition. Sodium aluminate solution with a caustic ratio of 1.65 and an alumina concentration of 70 g / L is placed in a cooling tank and cooled to 55°C with circulating water.

[0044] Step 4: Second-stage seed decomposition. Add the seed crystals prepared in the second step into a sodium aluminate solution with a temperature of 55°C, a caustic ratio of 1.65, and an alumina concentration of 70 g / L, and place it in a second-stage seed decomposition tank. Start stirring, and react for 2.5 hours. The seed ratio is controlled at 25wt%.

[0045] Step 5: Three-stage seed decomposition. Add sodium aluminate solution with a temperature of 55°C, a caustic ratio of 1.65, and an alumina concentration of 70g / L into the three-stage seed tank, send the solution after the second-stage seed decomposition into the three-stage seed tank, start stirring, and continue the seed decomposition for 8 hours. The amount of sodium aluminate solution added is 4 times the volume of the second-stage solution.

[0046] Step 6: Separation, washing and filtration. The decomposed slurry enters the buffer tank and is sent to the vertical filter press to add evaporation return water for three reverse washings, so that the filter cake contains 39% water and 0.16% sodium oxide.

[0047] Step 7: Drying and breaking up the filter cake. The filter cake after filtration is fed into a flash dryer and a break-up machine through a sealed conveyor belt to obtain ultrafine aluminum hydroxide powder with 0.19% water content and 0.15% sodium oxide content. The ultrafine aluminum hydroxide powder obtained in this example is tested for particle size using a laser particle size analyzer. The results are as follows: Figure 2 As shown in the test results, it can be seen that the D50 of the ultrafine aluminum hydroxide powder prepared in this embodiment is 1.835 μm. The ultrafine aluminum hydroxide powder obtained in this embodiment is tested for specific surface area by nitrogen adsorption method. The results are as follows Figure 3 As shown in the test results, it can be seen that the specific surface area of ​​the ultrafine aluminum hydroxide powder prepared in this embodiment is 3.3464m 2 / g.

[0048] Example 2

[0049] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0050] Step 1: Preparation of sodium aluminate solution for seed crystal decomposition: Sodium aluminate solution with a caustic ratio of 1.8 and an alumina concentration of 112 g / L was prepared to an alumina concentration of 40 g / L and a temperature of 34°C.

[0051] Step 2: Preparation of seed crystals: A carbonation reaction was carried out using a supergravity reactor and a vertical lime furnace with a volume concentration of 36% CO2 gas, with an alumina concentration of 3g / L at the end of the reaction and a time control of 7 minutes to prepare seed crystals with a D50 of 0.80 μm.

[0052] Step 3: Preparation of sodium aluminate solution for product decomposition. Sodium aluminate solution with a caustic ratio of 1.8 and an alumina concentration of 112 g / L is placed in a cooling tank and cooled to 60°C with circulating water.

[0053] Step 4: Second stage seed decomposition. Add the seed crystals prepared in the second step into a sodium aluminate solution with a temperature of 60°C, a caustic ratio of 1.8, and an alumina concentration of 112 g / L, and load into the second stage seed decomposition tank. Start stirring, react for 3 hours, and control the seed ratio at 27 wt%.

[0054] Step 5: Three-stage seed decomposition. Add sodium aluminate solution with a temperature of 60°C, a caustic ratio of 1.8, and an alumina concentration of 112g / L into the three-stage seed tank, send the solution after the second-stage seed decomposition into the three-stage seed tank, start stirring, and continue seed decomposition for 9.5 hours. The amount of sodium aluminate solution added is 5 times the volume of the second-stage solution.

[0055] Step 6: Separation, washing and filtration. The decomposed slurry enters the buffer tank and is sent to the vertical filter press to add evaporation return water for three reverse washings, so that the filter cake contains 38% water and 0.15% sodium oxide.

[0056] Step 7: Drying and breaking up the filter cake. The filter cake after filtration enters the flash dryer and the breakers through a sealed conveyor belt to obtain ultrafine aluminum hydroxide powder with 0.16% water content and 0.13% sodium oxide content.

[0057] The ultrafine aluminum hydroxide powder obtained in this example was tested for particle size using a laser particle size analyzer. Figure 4 As shown in the test results, it can be seen that the D50 of the ultrafine aluminum hydroxide powder prepared in this embodiment is 1.603 μm. The ultrafine aluminum hydroxide powder obtained in this embodiment is tested for specific surface area by nitrogen adsorption method. The results are as follows Figure 5 As shown in the test results, it can be seen that the specific surface area of ​​the ultrafine aluminum hydroxide powder prepared in this embodiment is 3.1971m 2 / g.

[0058] Example 3

[0059] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0060] (1) Carbonation decomposition to prepare seed crystals: Carbon dioxide gas was introduced into a sodium aluminate solution with an aluminum oxide concentration of 35 g / L, and the volume concentration of the carbon dioxide was controlled to be 27%. The reaction temperature was controlled to be 25° C., the reaction time was controlled to be 3 min, and the aluminum oxide concentration at the reaction end point was controlled to be 3 g / L, to obtain aluminum hydroxide seed crystals with D50=0.8 μm;

[0061] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to a sodium aluminate solution having a caustic ratio of 1.55 and an aluminum oxide concentration of 50 g / L to carry out a one-stage seed decomposition reaction, wherein the seed ratio is controlled to be 25 wt %, the reaction temperature is 50° C., and the reaction time is 2 h. After the reaction is completed, a one-stage reaction system is obtained;

[0062] (3) Two-stage seed decomposition: add the first-stage reaction system to a sodium aluminate solution with a caustic ratio of 1.55 and an aluminum oxide concentration of 50g / L, control the volume of the sodium aluminate solution to be 3 times the volume of the first-stage reaction system, and carry out a two-stage seed decomposition reaction. The reaction temperature is 50°C and the reaction time is 8h. After the second-stage seed decomposition reaction, the reaction system is subjected to solid-liquid separation to obtain a solid material. The solid material is washed and then subjected to solid-liquid separation again to obtain an ultrafine aluminum hydroxide wet material with a water content of 38wt%; the ultrafine aluminum hydroxide wet material is flash dried to obtain ultrafine aluminum hydroxide, and after dispersion, an ultrafine aluminum hydroxide micropowder with a water content of 0.17wt% and a sodium oxide content of 0.18wt% is obtained. The particle size of the ultrafine aluminum hydroxide micropowder prepared in this embodiment is detected by a laser particle size analyzer, and D50=1.512μm is obtained. The specific surface area is detected by nitrogen adsorption method, and the specific surface area is 4.0m 2 / g.

[0063] Example 4

[0064] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0065] (1) Carbonation decomposition to prepare seed crystals: Carbon dioxide gas was introduced into a sodium aluminate solution with an aluminum oxide concentration of 50 g / L, and the volume concentration of the carbon dioxide was controlled to be 50%. The reaction temperature was controlled to be 35° C., the reaction time was controlled to be 7 min, and the aluminum oxide concentration at the reaction end point was controlled to be 7 g / L, to obtain aluminum hydroxide seed crystals with D50=1.2 μm;

[0066] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to a sodium aluminate solution having a caustic ratio of 1.9 and an aluminum oxide concentration of 120 g / L to carry out a one-stage seed decomposition reaction, wherein the seed ratio is controlled to be 28 wt %, the reaction temperature is 70° C., and the reaction time is 3 h. After the reaction is completed, a one-stage reaction system is obtained;

[0067] (3) Two-stage seed decomposition: add the first-stage reaction system to a sodium aluminate solution with a caustic ratio of 1.9 and an aluminum oxide concentration of 120 g / L, control the volume of the sodium aluminate solution to be 5 times the volume of the first-stage reaction system, and carry out a two-stage seed decomposition reaction at a reaction temperature of 70°C and a reaction time of 10 h. After the second-stage seed decomposition reaction, the reaction system is subjected to solid-liquid separation to obtain a solid material. The solid material is washed and then subjected to solid-liquid separation again to obtain an ultrafine aluminum hydroxide wet material with a water content of 35 wt%; the ultrafine aluminum hydroxide wet material is flash dried to obtain ultrafine aluminum hydroxide, and after dispersion, an ultrafine aluminum hydroxide micropowder with a water content of 0.1 wt% and a sodium oxide content of 0.13 wt% is obtained. The particle size of the ultrafine aluminum hydroxide micropowder prepared in this embodiment is detected by a laser particle size analyzer, and D50 = 2.011 μm is obtained. The specific surface area is detected by nitrogen adsorption method, and the specific surface area is 3.0 m2 / g.

[0068] Example 5

[0069] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0070] (1) Carbonation decomposition to prepare seed crystals: Carbon dioxide gas was introduced into a sodium aluminate solution with an aluminum oxide concentration of 38 g / L, and the volume concentration of the carbon dioxide was controlled to be 30%. The reaction temperature was controlled to be 28° C., the reaction time was controlled to be 4 min, and the aluminum oxide concentration at the reaction end point was controlled to be 4 g / L, to obtain aluminum hydroxide seed crystals with a D50 of 1.0 μm;

[0071] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to a sodium aluminate solution having a caustic ratio of 1.6 and an aluminum oxide concentration of 60 g / L to carry out a one-stage seed decomposition reaction, wherein the seed ratio is controlled to be 26 wt %, the reaction temperature is 55° C., and the reaction time is 2.5 h. After the reaction is completed, a one-stage reaction system is obtained;

[0072] (3) Two-stage seed decomposition: add the first-stage reaction system to a sodium aluminate solution with a caustic ratio of 1.6 and an aluminum oxide concentration of 60g / L, control the volume of the sodium aluminate solution to be 4 times the volume of the first-stage reaction system, and carry out a two-stage seed decomposition reaction at a reaction temperature of 55°C and a reaction time of 8.5h. After the second-stage seed decomposition reaction, the reaction system is subjected to solid-liquid separation to obtain a solid material. The solid material is washed and then subjected to solid-liquid separation again to obtain an ultrafine aluminum hydroxide wet material with a water content of 34wt%; the ultrafine aluminum hydroxide wet material is flash-dried to obtain ultrafine aluminum hydroxide, which is dispersed to obtain an ultrafine aluminum hydroxide powder with a water content of 0.14wt% and a sodium oxide content of 0.11wt%. The particle size of the ultrafine aluminum hydroxide powder prepared in this embodiment is detected by a laser particle size analyzer, and D50=1.613μm is obtained. The specific surface area is detected by nitrogen adsorption method, and the specific surface area is 3.9m 2 / g.

[0073] Example 6

[0074] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0075] (1) Carbonation decomposition to prepare seed crystals: Carbon dioxide gas was introduced into a sodium aluminate solution having an aluminum oxide concentration of 42 g / L, and the volume concentration of the carbon dioxide was controlled to be 35%. The reaction temperature was controlled to be 30° C., the reaction time was controlled to be 5 min, and the aluminum oxide concentration at the reaction end point was controlled to be 5 g / L, to obtain aluminum hydroxide seed crystals with a D50 of 1.1 μm;

[0076] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to a sodium aluminate solution having a caustic ratio of 1.7 and an aluminum oxide concentration of 80 g / L to carry out a one-stage seed decomposition reaction, wherein the seed ratio is controlled to be 27 wt %, the reaction temperature is 60° C., and the reaction time is 2.8 h. After the reaction is completed, a one-stage reaction system is obtained;

[0077] (3) Two-stage seed decomposition: add the first-stage reaction system to a sodium aluminate solution with a caustic ratio of 1.7 and an aluminum oxide concentration of 80 g / L, control the volume of the sodium aluminate solution to be 5 times the volume of the first-stage reaction system, and carry out a two-stage seed decomposition reaction at a reaction temperature of 60°C and a reaction time of 9 hours. After the second-stage seed decomposition reaction, the reaction system is subjected to solid-liquid separation to obtain a solid material. The solid material is washed and then subjected to solid-liquid separation again to obtain an ultrafine aluminum hydroxide wet material with a water content of 30 wt%; the ultrafine aluminum hydroxide wet material is flash-dried to obtain ultrafine aluminum hydroxide, which is dispersed to obtain an ultrafine aluminum hydroxide powder with a water content of 0.11 wt% and a sodium oxide content of 0.09 wt%. The particle size of the ultrafine aluminum hydroxide powder prepared in this embodiment is detected by a laser particle size analyzer, and D50 = 1.837 μm is obtained. The specific surface area is detected by nitrogen adsorption method, and the specific surface area is 3.6 m 2 / g.

[0078] Example 7

[0079] A segmented preparation method of ultrafine aluminum hydroxide powder comprises the following steps:

[0080] (1) Carbonation decomposition to prepare seed crystals: Carbon dioxide gas was introduced into a sodium aluminate solution having an aluminum oxide concentration of 45 g / L, and the volume concentration of the carbon dioxide was controlled to be 45%. The reaction temperature was controlled to be 32° C., the reaction time was controlled to be 6 min, and the aluminum oxide concentration at the reaction end point was controlled to be 6 g / L, to obtain aluminum hydroxide seed crystals with a D50 of 1.1 μm;

[0081] (2) One-stage seed decomposition: adding the aluminum hydroxide seed to a sodium aluminate solution having a caustic ratio of 1.8 and an aluminum oxide concentration of 100 g / L to carry out a one-stage seed decomposition reaction, wherein the seed ratio is controlled to be 27 wt %, the reaction temperature is 65° C., and the reaction time is 3 h. After the reaction is completed, a one-stage reaction system is obtained;

[0082] (3) Two-stage seed decomposition: add the first-stage reaction system to a sodium aluminate solution with a caustic ratio of 1.7 and an aluminum oxide concentration of 80 g / L, control the volume of the sodium aluminate solution to be 4 times the volume of the first-stage reaction system, and carry out a two-stage seed decomposition reaction. The reaction temperature is 62°C and the reaction time is 9.5 h. After the second-stage seed decomposition reaction, the reaction system is subjected to solid-liquid separation to obtain a solid material. The solid material is washed and then subjected to solid-liquid separation again to obtain an ultrafine aluminum hydroxide wet material with a water content of 28 wt%; the ultrafine aluminum hydroxide wet material is flash dried to obtain ultrafine aluminum hydroxide, and after dispersion, an ultrafine aluminum hydroxide micropowder with a water content of 0.1 wt% and a sodium oxide content of 0.09 wt% is obtained. The particle size of the ultrafine aluminum hydroxide micropowder prepared in this embodiment is detected by a laser particle size analyzer, and D50 = 1.881 μm is obtained. The specific surface area is detected by nitrogen adsorption method, and the specific surface area is 3.7 m 2 / g.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is that the sodium aluminate solution with a caustic ratio of 1.65 and an alumina concentration of 70 g / L is adjusted to an alumina concentration of 55 g / L, and other conditions are the same. Figure 6 As shown, the aluminum hydroxide product prepared in this comparative example has a D50 of 3.173 μm and a specific surface area of ​​1.2 m 2 / g, because the particle size is too large, it does not meet the requirements of flame retardant.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that the sodium aluminate solution with a caustic ratio of 1.65 and an alumina concentration of 70 g / L is adjusted to an alumina concentration of 25 g / L, and other conditions are the same. The test results show that the aluminum hydroxide product prepared in this comparative example has a D50 of 1.130 μm and a specific surface area of ​​5.3 m 2 / g, because the particle size is too small, it does not meet the requirements of flame retardant.

[0087] Comparative Example 3

[0088] The difference between this comparative example and Example 2 is that the reaction temperature of carbon decomposition is 40°C, and other conditions are the same. The test results show that the aluminum hydroxide product prepared in this comparative example has a D50 of 3.102 μm and a specific surface area of ​​1.0 m 2 / g, does not meet the requirements of flame retardants.

[0089] Comparative Example 4

[0090] The difference between this comparative example and Example 2 is that the reaction temperature of carbon decomposition is 20°C, and other conditions are the same. The test results show that the aluminum hydroxide product prepared in this comparative example has a D50 of 1.100 μm and a specific surface area of ​​5.5 m 2 / g, does not meet the requirements of flame retardants.

[0091] Comparative Example 5

[0092] The difference between this comparative example and Example 3 is that the concentration of aluminum oxide in the sodium aluminate solution used for the first and second stage seed decomposition is 150 g / L, and other conditions are the same. The test results show that the aluminum hydroxide product prepared in this comparative example has a D50 of 3.517 μm and a specific surface area of ​​1.1 m 2 / g, does not meet the requirements of flame retardants.

[0093] Comparative Example 6

[0094] The difference between this comparative example and Example 3 is that the concentration of aluminum oxide in the sodium aluminate solution used for the first and second stage seed decomposition is 40 g / L, and other conditions are the same. The test results show that the aluminum hydroxide product prepared in this comparative example has a D50 of 1.340 μm and a specific surface area of ​​4.8 m 2 / g, does not meet the requirements of flame retardants.

[0095] Comparative Example 7

[0096] The difference between this comparative example and Example 5 is that the seed ratio of the first stage seed decomposition is 20wt%, the volume of the sodium aluminate solution in the second stage seed decomposition is 8 times the volume of the first stage reaction system, and the other conditions are the same. The test results show that the aluminum hydroxide product prepared in this comparative example has a D50 of 3.007μm and a specific surface area of ​​1.2m 2 / g, does not meet the requirements of flame retardants.

[0097] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A staged preparation method of ultrafine aluminum hydroxide powder, characterized in that: The following steps are involved: (1) Preparation of seed crystals by carbonation decomposition: A gas containing carbon dioxide is introduced into a sodium aluminate solution having an aluminum oxide concentration of 35-50 g / L, wherein the volume concentration of carbon dioxide in the carbon dioxide-containing gas is 27-50%, and the reaction temperature is controlled to be 25-35° C., the reaction time is 3-7 min, and the aluminum oxide concentration at the reaction end point is 3-7 g / L, to obtain aluminum hydroxide seed crystals with a D50 of 0.8-1.2 μm; (2) One-stage seed decomposition: adding the aluminum hydroxide seed crystals to the sodium aluminate solution to carry out a one-stage seed decomposition reaction, controlling the seed ratio to be 25-28 wt %, and obtaining a one-stage reaction system after the reaction is completed; (3) Two-stage seed decomposition: Add the first-stage reaction system to the sodium aluminate solution, control the volume of the sodium aluminate solution to be 3-5 times the volume of the first-stage reaction system, and perform a two-stage seed decomposition reaction to obtain D50 = 1.5-2.0 μm, specific surface area = 3.0-4.0 m 2 / g of ultrafine aluminum hydroxide powder.

2. The method for preparing ultrafine aluminum hydroxide powder in stages according to claim 1, characterized in that: After the second-stage seed decomposition reaction in step (3) is completed, the method further comprises: a. Separation and washing: After the second stage seed decomposition reaction is completed, the reaction system is subjected to solid-liquid separation to obtain a solid material, and the solid material is washed and then separated from the solid and liquid again to obtain ultrafine aluminum hydroxide wet material; b. Drying and dispersing: flash drying the ultrafine aluminum hydroxide wet material to obtain ultrafine aluminum hydroxide, and dispersing the ultrafine aluminum hydroxide powder to obtain the ultrafine aluminum hydroxide.

3. The method for preparing ultrafine aluminum hydroxide powder in stages according to claim 2, characterized in that: The moisture content of the ultrafine aluminum hydroxide wet material is less than 40wt%; and / or the moisture content of the ultrafine aluminum hydroxide obtained after drying is less than 0.2wt% and the sodium oxide content is less than 0.2wt%.

4. The method for preparing ultrafine aluminum hydroxide powder in stages according to claim 1, characterized in that: In step (2), the caustic ratio of the sodium aluminate solution is 1.55-1.9, and the alumina concentration is 50-120 g / L; and / or, the reaction temperature of the first-stage seed decomposition reaction is 50-70° C.; and / or, the reaction time of the first-stage seed decomposition reaction is 2-3 h.

5. The method for preparing ultrafine aluminum hydroxide powder in stages according to any one of claims 1 to 4, characterized in that: In step (3), the caustic ratio of the sodium aluminate solution is 1.55-1.9, the alumina concentration is 50-120 g / L, and / or the reaction temperature of the second-stage seed decomposition reaction is 50-70° C.; and / or the reaction time of the second-stage seed decomposition reaction is 8-10 h.

6. An ultrafine aluminum hydroxide powder prepared by the staged preparation method of ultrafine aluminum hydroxide powder according to any one of claims 1 to 5.

7. A flame retardant containing the ultrafine aluminum hydroxide powder according to claim 6.

8. Use of the flame retardant according to claim 7 in building thermal insulation materials, insulating materials and heat shrinkable materials.

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