Preparation method of low oil absorption value single crystal particle aluminum hydroxide

Abstract

The invention uses crystal face protective agent and alkaline solution to dissolve and modify industrial aluminum hydroxide, and controls the process technology to obtain qualified slurry. The slurry is filtered, washed and dried to obtain low oil absorption value (10-18 ml / 100g, the oil absorption value can be reduced to 8-14 ml / 100 after modification) and low viscosity single crystal aluminum hydroxide (5-50 microns) product; the filtered alkaline solution returns to the seed system to continue seed decomposition or is integrated into the mother liquor process. The process has low cost, simple process and high industrial value, and the obtained aluminum hydroxide is an ideal material for heat conduction and high filling purposes (such as artificial stone).

Description

TECHNICAL FIELD

[0001] The present application relates to the field of inorganic material preparation, in particular to a production method of low oil absorption value single crystal particle aluminum hydroxide. BACKGROUND

[0002] In the field of ultra-fine aluminum hydroxide, the production method for preparing low oil absorption value aluminum hydroxide is mainly realized by process control of sodium aluminate solution decomposition (such as CN109422285A “Low oil absorption value aluminum hydroxide and its preparation method and application”, CN109422285 “A production method of aluminum hydroxide”), by surface modification (CN115011144A “Preparation method of low oil absorption value aluminum hydroxide flame retardant and its application”, CN110655095A “Preparation method of low oil absorption value aluminum hydroxide micropowder flame retardant”), mechanical processing (CN105110358A “Preparation method of low oil absorption value and low viscosity aluminum hydroxide”) and other methods. However, the particle size of ultra-fine aluminum hydroxide is generally below 3 μm, the oil absorption value is generally not less than 25 μm, and the viscosity is relatively high, which cannot meet the requirements of heat-conducting and other filler aluminum hydroxide.

[0003] In the aluminum oxide industry, to reduce the oil absorption value of aluminum hydroxide, the process conditions are generally controlled to make the effective agglomeration and growth of aluminum hydroxide and the product is graded to reduce the number of small particles and improve the strength of aluminum hydroxide. For example, CN200410037937 “High-strength large-particle aluminum hydroxide seed decomposition method” uses its own product as seed to achieve the purpose of large-particle aluminum hydroxide through agglomeration and growth. Low oil absorption value products can also be achieved by grading different particle sizes of aluminum hydroxide. However, such aluminum hydroxide is a non-single crystal agglomerate, which cannot meet the performance requirements for some special purposes of aluminum hydroxide.

[0004] In the field of energy storage, in order to prevent the overheating of the battery during rapid charging, the heat must be conducted from the battery stack to the outside through the battery shell, and the gap filler between the single battery packs of the battery module plays a key role, and its thermal conductivity is usually 2.5-3.0 W / mk. For the gap filler, although its inherent high thermal conductivity is advantageous, but high filling amount is more important. The filling amount of the gap filler usually needs to be higher than 80%, and the low oil absorption value aluminum hydroxide provides the possibility for high filling. Aluminum hydroxide has the properties of flame retardation, filling, smoke suppression and thermal conductivity, and large single crystal particle aluminum hydroxide has the characteristics of low viscosity, good compatibility with organic polymer materials and good processing performance, and the flame retardation effect is also better with the increase of the filling amount. SUMMARY

[0005] The purpose of the present application is to provide a method for preparing low oil absorption value single crystal large particle aluminum hydroxide.

[0006] The method for preparing low oil absorption value single crystal particle aluminum hydroxide according to the present application comprises the following steps:

[0007] 1) using industrial aluminum hydroxide as raw material, surface treatment is performed with an organic acid crystal face protective agent;

[0008] 2) adding the treated raw material into an alkaline solution, and controlling the temperature at 60-95°C to perform dissolution and decoration;

[0009] 3) filtering the slurry, washing and drying to obtain single crystal aluminum hydroxide.

[0010] Preferably, the particle size D50 of the industrial aluminum hydroxide raw material is 50-120 μm.

[0011] Preferably, the pKa value of the crystal face protective agent is between 2.5 and 5.0, and the crystal face protective agent is preferably an organic carboxylic acid.

[0012] Preferably, the addition amount of the crystal face protective agent is 4.0‰-10.0‰ of the mass of the aluminum hydroxide, and the preferred amount is 5.0‰-8.0‰.

[0013] Preferably, the crystal face protective agent is prepared into a 10-50% solution, is fully mixed with the aluminum hydroxide, and stays for 30-180 minutes.

[0014] The alkaline solution used in the present application can be a sodium hydroxide solution, a potassium hydroxide solution, a mother liquor, a washing liquor, a sodium aluminate solution or a mixture thereof, wherein the concentration of the sodium hydroxide solution is N K 50-300 g / L, preferably the concentration of the sodium hydroxide solution is 100-150 g / L; the a k value of the mother liquor is 1.7-5.0, preferably the a k value of the mother liquor is 2.5-3.5; the a k value of the washing liquor is 2.0-5.5, preferably the a k value of the washing liquor is 3.0-4.5; the a k value of the sodium aluminate solution is between 1.7 and 4.0, and the preferred a k value is between 2.5 and 3.5

[0015] In the typical embodiment of the present application, the solid content of the aluminum hydroxide is 50-400 g / L, and the preferred solid content is 100-300 g / L.

[0016] Preferably, the dissolution and decoration time is 5-60 hours, and more preferably 10-30 hours.

[0017] The present application uses a crystal face protective agent and an alkaline solution to dissolve and modify industrial aluminum hydroxide, and through a simple process, qualified slurry is obtained. The slurry is filtered, washed, and dried to obtain low oil absorption value (10-18 ml / 100 g, the oil absorption value can be reduced to 8-14 ml / 100 after modification) and low viscosity single crystal aluminum hydroxide (5 μm-50 μm) products; the filtered alkaline solution is returned to the seed system for further seed decomposition or integrated into the mother liquor process. The process is low in cost, simple in process, and has great industrial value. The obtained aluminum hydroxide is an ideal material for heat conduction and high filling purposes (such as artificial stone, etc.). BRIEF DESCRIPTION OF DRAWINGS

[0018] Figures 1 to 8 are electron competitive scanning photos of the samples obtained in Examples 1 to 6, Comparative Examples 1 and 2, respectively. DETAILED DESCRIPTION

[0019] N k , α k has the general meaning in the art. Specifically, the Na2O content of the sodium aluminate solution, including the Na2O from the dissolution of alumina to form sodium aluminate and the free Na2O in the form of NaOH, both of which are caustic alkalis, is denoted as N k , with the unit of g / l. The molar ratio of caustic alkali Na2O to Al2O3 in the sodium aluminate solution is denoted as α k . D50, also known as median diameter or median particle size, refers to the particle size value corresponding to the cumulative percentage of 50%.

[0020] According to the present application, using industrial aluminum hydroxide with a selected particle size as the starting material, the time required for dissolution in an alkaline solution can obtain single crystal aluminum hydroxide with the desired particle size.

[0021] Another feature of the present application is that the industrial aluminum hydroxide is surface treated with a crystal face protective agent before dissolution. The crystal face protective agent suitable for use in the present application is an organic acid with a pKa value between 2.5 and 5.0, including but not limited to hexenoic acid, pentenoic acid, butenoic acid, benzenesulfonic acid, benzoic acid, malonic acid, propionic acid, acrylic acid, butyric acid, terephthalic acid, phthalic acid, fumaric acid, glyceric acid, succinic acid, adipic acid, hexanoic acid, formic acid, acetic acid, tartaric acid, citric acid, malic acid, lactic acid, sorbic acid, salicylic acid, glutaric acid, valeric acid, isobutyric acid, etc., among which an organic carboxylic acid is preferred.

[0022] The present application uses the above-mentioned organic acid with the above-mentioned acid strength to treat the surface of the raw material aluminum hydroxide, which can buffer the strong corrosion of the strong alkali (sodium hydroxide) to the aluminum hydroxide when it first contacts the aluminum hydroxide, and suppress the amplification of the irregular surface caused by the action of the strong alkali, so that the action of sodium hydroxide on the surface of aluminum hydroxide is more gentle and uniform.

[0023] For this purpose, the amount of organic acid can be 0.4-2.0% by mass of the mass of aluminum hydroxide, preferably not more than 1.0%. The organic acid can be prepared into an aqueous solution, and the mass percentage concentration of the aqueous solution can be 10-50%, preferably 10-30%. The concentration should be selected to ensure that the solution completely wets the surface of the raw material aluminum hydroxide, and preferably no significant amount of free solution exists after wetting. After mixing the raw material aluminum hydroxide with the crystal face protection agent solution, after sufficient stirring at 10-40°C, preferably at room temperature, and preferably after standing for 30 min to 180 min, preferably for 30-60 min.

[0024] In the present application, the raw material aluminum hydroxide is an industrial aluminum hydroxide with a D50 in the range of 50 μm to 120 μm, which is readily available on the market, and is usually an agglomerate, i.e. an agglomerate of smaller single crystals of aluminum hydroxide. It is thus readily understood that the raw material aluminum hydroxide can also be replaced by seed aluminum hydroxide obtained by the Bayer process from an enterprise. At present, the industrial aluminum hydroxide obtained by the seed method is always an agglomerate. In a typical embodiment of the present application, a high-white seed aluminum hydroxide is used, which is suitable for scenarios with special requirements for whiteness, such as artificial stone or other high-whiteness polymer products, etc. Its sodium aluminate solution is a sintering method liquor or a Bayer method liquor that has been deeply decolorized, and the raw material is readily available.

[0025] In the case of self-seeding to obtain aluminum hydroxide, the attached alkali is preferably washed off sufficiently to avoid consumption of the crystal face protection agent in the present application by the strong alkali. The attached alkali is preferably washed off to an amount of not more than 0.03%.

[0026] In the present application, after surface treatment of the raw material aluminum hydroxide or self-seeding of the aluminum hydroxide, the process of further treatment at an elevated temperature and in an alkaline solution is a dissolution process. The dissolution temperature is suitably in the range of 60-95°C. In this process, the agglomerated aluminum hydroxide particles are disaggregated into single crystals, and the single crystals grow to some extent, and in the process of growth, the pores on the surface of the particles, if present, are modified.

[0027] The alkaline solution used in the present application can be various, and a typical way is to use a sodium hydroxide solution. The N k value of the sodium hydroxide is suitably between 50 g / L and 300 g / L, and the preferred N K concentration is 100-150 g / L. Another way is to use the mother liquor in the process cycle, which is the liquid phase obtained after filtering off the aluminum hydroxide product at the end of the dissolution process, and the a k value of the mother liquor can be between 1.7 and 4.0, and the preferred a k value is between 2.5 and 3.5. In another embodiment, the washing solution in the process is used as the alkaline solution, which is the liquid phase obtained by washing the surface of the aluminum hydroxide to remove the attached alkali, and the ak The value can be between 2.0 and 6.0, preferably the washing solution a k is between 3.0 and 4.5. In another embodiment, the prepared sodium aluminate solution is used as the leaching solution, and the ak value of the sodium aluminate solution can be between 1.7 and 4.0, preferably the a k value is between 2.5 and 3.5. Regardless of the way of the alkaline solution, the N K value is suitably between 50 g / L and 300 g / L, preferably in the range of 100-150 g / L.

[0028] In the leaching system of the present application, the solid content of aluminum hydroxide can be between 50 g / L and 400 g / L, preferably between 100 g / L and 200 g / L. If the solid content is too low, the process control is difficult and the cost is high, and if the solid content is too high, the leaching time is too long and the leaching effect is poor.

[0029] In the present application, the leaching is suitably between 60°C and 95°C, and if it is too low or too high, it is easy to cause poor leaching effect. In the present application, the leaching time is usually between 5h and 60h, and preferably the leaching time is between 10h and 30h.

[0030] The test method of oil absorption value: 100.00 grams (g) of the sample to be tested is weighed on a clean surface dish, castor oil is added dropwise, and a clean glass rod is used to stir the paste during the dropping process until the sample is completely pasted on the glass dish, and the amount of castor oil at this time is recorded as AmL. The oil absorption value (X) = A (mL / 100g).

[0031] Example 1:

[0032] 150g (dry basis) of industrial aluminum hydroxide raw material is weighed, the particle size D 50 is 60μm; and the attached alkali is ≤0.03%.

[0033] 0.75g of citric acid is weighed to prepare a 30% solution and added to the prepared aluminum hydroxide, which is stirred uniformly at room temperature and stays for 60min.

[0034] The solution is added to 1L of 70°C mother liquor for leaching. The mother liquor a K is 2.8, and the Al2O3 concentration is 80g / L; the leaching time is 10h.

[0035] The leached slurry is filtered, washed and dried to obtain the single crystal aluminum hydroxide product. The electron microscope is seen Figure 1 . The particle size D 50 of the product is 10μm, and the oil absorption value is 16mL / 100g.

[0036] The product of (4) is modified (1‰ addition, dry modification) using silane coupling agent KH570, and the oil absorption value is reduced to 13 mL / 100 g.

[0037] Example 2:

[0038] Take 150 g (dry basis) of seed aluminum hydroxide raw material, particle size D 50 70 μm; wash with attached alkali to ≤0.03%;

[0039] Take 0.90 g of formic acid to prepare a 20% solution and add to the seed aluminum hydroxide of (6), fully stir and uniform at room temperature, and stay for 40 min;

[0040] Add (7) aluminum hydroxide to 1 L of mother liquor at 75°C, and stir and dissolve. The mother liquor a K 3.0, Al2O3 concentration 60 g / L; dissolution time 20 h;

[0041] Filter, wash and dry the slurry after dissolution of (8) to obtain the single crystal aluminum hydroxide product. The electron microscope is seen Figure 2 . The product particle size D 50 is 20 μm, and the oil absorption value is 10 mL / 100 g.

[0042] The product obtained from (9) is modified (1‰ addition, dry modification) using titanium coupling agent 201, and the oil absorption value is 8 mL / 100 g.

[0043] Example 3:

[0044] Take 150 g (dry basis) of industrial aluminum hydroxide raw material, particle size D 50 90 μm; test attached alkali wash ≤0.03%;

[0045] Take 1.20 g of acetic acid to prepare a 30% solution and add to the aluminum hydroxide of (11), fully stir and uniform at room temperature, and stay for 90 min.

[0046] Add the treated aluminum hydroxide of (12) to 1 L of mother liquor at 85°C, and stir and dissolve. The mother liquor a K 2.9, Al2O3 concentration 65 g / L, dissolution time 30 h;

[0047] Filter, wash and dry the slurry after dissolution of (13) to obtain the single crystal aluminum hydroxide product. The electron microscope is seen Figure 3 . The product particle size D 50 is 30 μm, and the oil absorption value is 14 mL / 100 g.

[0048] Example 4:

[0049] Take 150g (dry basis) seed aluminum hydroxide raw material, particle size D50 is 100μm, wash with alkali to ≤0.03%; 50 3.8, and the Al2O3 concentration is 15g / L; dissolution time is 20h;

[0050] Take 0.90g propionic acid to prepare a 20% solution and add to the seed aluminum hydroxide of (15), fully stir and mix uniformly at room temperature, and stay for 90min.

[0051] Add the treated aluminum hydroxide of (16) to 1L of 80℃ washing solution, and stir and dissolve.

[0052] Washing solution a K 3.8, and the Al2O3 concentration is 15g / L; dissolution time is 20h;

[0053] Filter, wash and dry the slurry after dissolution of (17) to obtain the single crystal aluminum hydroxide product. The electron microscope is shown in Figure 4 . The product particle size D50 is 40μm, and the oil absorption value is 16mL / 100g.

[0054] Example 5:

[0055] Take 150g (dry basis) seed aluminum hydroxide raw material, particle size D50 is 110μm, wash with alkali to ≤0.03%; 50 3.8, and the Al2O3 concentration is 15g / L; dissolution time is 20h;

[0056] Take 0.80g of formic acid, acetic acid and propionic acid together to prepare a 30% solution and add to the seed aluminum hydroxide of (19), fully stir and mix uniformly at room temperature, and stay for 120min.

[0057] Add the treated aluminum hydroxide of (20) to 1L of 62℃ sodium hydroxide solution, and stir and dissolve for 20h. The sodium hydroxide solution Nk is 100g / L;

[0058] Filter, wash and dry the slurry after dissolution of (21) to obtain the single crystal aluminum hydroxide product. The electron microscope is shown in Figure 5 . The product particle size D50 is 50μm, and the oil absorption value is 17mL / 100g.

[0059] Example 6:

[0060] Take 150g (dry basis) high-white seed aluminum hydroxide, particle size D50 is 70μm, wash with alkali to ≤0.03%;

[0061] Take 0.50g of citric acid to prepare a 20% solution and add to the high-white seed aluminum hydroxide of (23), fully stir and mix uniformly at room temperature, and stay for 120min.

[0062] The treated high white aluminum hydroxide (24) was added into 1 L of 75°C sodium aluminate solution and stirred and dissolved. The solution aK was 3.0, the Al2O3 concentration was 70 g / L, and the dissolution time was 20 h;

[0063] The slurry after dissolution (25) was filtered, washed, and dried to obtain the single-crystal aluminum hydroxide product. The electron microscope image is shown in Figure 6 The product particle size D50 was 20 μm, and the oil absorption value was 16 mL / 100 g.

[0064] Comparative Example 1:

[0065] 150 g (dry basis) of seed aluminum hydroxide was weighed, with a particle size D 50 of 70 μm, and an attached alkali of 0.1%;

[0066] was added into 1 L of 50°C mother liquor and stirred and dissolved for 30 h. The mother liquor aK was 2.8, the Al2O3 concentration was 80 g / L, and the dissolution time was 80 h;

[0067] The slurry after dissolution (2) was filtered, washed, and dried to obtain the agglomerated aluminum hydroxide. The electron microscope image is shown in Figure 7 . The product particle size D 50 was 60 μm, and the oil absorption value was 25 mL / 100 g.

[0068] Comparative Example 2:

[0069] 150 g (dry basis) of seed aluminum hydroxide was weighed, with a particle size D 50 of 60 μm, and an attached alkali of ≤0.03% after washing;

[0070] (4) was added into 1 L of 70°C mother liquor and stirred and dissolved. The mother liquor a K was 2.8, the Al2O3 concentration was 80 g / L, and the dissolution time was 10 h;

[0071] The slurry after dissolution (5) was filtered, washed, and dried to obtain the aluminum hydroxide product. The electron microscope image is shown in Figure 8 . The product particle size D 50 was 21 μm, and the oil absorption value was 22 mL / 100 g.

[0072] Referring to the electron microscope images in the drawings and the test results of the examples, in the above examples, Examples 1-6 used the scheme of the present application; Comparative Example 1 used a low-temperature dissolution process without adding a crystal face protective agent, and the dissolution time was prolonged, the crystal grains were still agglomerates, and the particle size D 50 reached 60 μm, close to the original particle size. Comparative Example 2 was the same as Example 1 except that no crystal face protective agent was added, and the result was that the grain surface was poor and the oil absorption value increased. The particle size of Example 1 was 10 μm, the oil absorption value was 16 mL / 100 g, and the grain surface had no obvious flaws.

[0073] The examples selected herein for the purpose of illustrating the present application should be understood as being illustrative only and not limitative of the scope of the present application, which is defined by the claims. Some non-essential improvements and modifications to the present application, which do not depart from the spirit and scope of the present application, can be made by those skilled in the art.

Claims

1. A method for preparing single-crystal aluminum hydroxide particles with low oil absorption value, comprising the following steps: 1) Using industrial aluminum hydroxide as raw material, surface treatment is performed with an organic acid crystal surface protectant, wherein the crystal surface protectant is an organic carboxylic acid with a pKa value between 2.5 and 5.0; 2) Add the treated raw materials to an alkaline solution, and perform the solvent treatment at a temperature controlled between 60℃ and 95℃. The alkaline solution is sodium hydroxide solution, potassium hydroxide solution, mother liquor, washing solution, sodium aluminate solution, or a mixture thereof. The alkaline solution contains N K :50g / L~300g / L, the concentration of the washing solution (a) k The value is 2.0~5.5; the a value of the mother liquor k The value is 1.7~5.0; the a value of sodium aluminate solution k The value is between 1.7 and 4.0; 3) Filter the slurry, wash and dry it to obtain single-crystal aluminum hydroxide.

2. The preparation method according to claim 1, wherein, The particle size D50 of the industrial aluminum hydroxide raw material is 50μm to 120μm.

3. The preparation method according to claim 1, wherein, The amount of the crystal surface protectant added is 4.0‰ to 10.0‰ of the mass of aluminum hydroxide.

4. The preparation method according to claim 2, wherein, The crystal surface protectant is prepared as a 10-50% solution, thoroughly mixed with aluminum hydroxide, and left to stand for 30-180 minutes.

5. The preparation method according to claim 1, wherein, a of the washing solution k The value is 3.0~4.5; the a value of the mother liquor k The value is 2.5~3.5; the a value of sodium aluminate solution k The value is between 2.5 and 3.

5.

6. The preparation method according to claim 1, wherein, The solid content of aluminum hydroxide ranges from 50 g / L to 400 g / L.

7. The preparation method according to claim 1, wherein, The melting time is 5h~60h.

8. The preparation method according to claim 1, wherein, The industrial aluminum hydroxide was replaced by aluminum hydroxide obtained by the seed fractionation method.

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