A method for reducing the basicity of alumina

Abstract

The application relates to the technical field of alumina preparation, and particularly discloses a method for reducing the alkalinity of alumina, which comprises the following operations: firstly, mixing alumina with an additive and an organic acid, then performing ball milling, and finally performing calcination; the additive can promote the adhesion of the organic acid and the alumina; the additive and the organic acid are both decomposed into water and carbon dioxide after calcination. The method for reducing the alkalinity of alumina can effectively reduce the pH value of the alumina, does not introduce other impurity ions, is simple to operate, has low energy consumption, and can be used as an adsorbent, a catalyst carrier and an additive in a battery material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alumina preparation, in particular to a method for reducing the basicity of alumina. BACKGROUND

[0002] In modern chemical production, alumina is a very important adsorbent, catalyst carrier and battery material additive. In order to meet the needs of different basicity alumina in the above applications, the prepared alumina with high basicity needs to be modified to reduce its basicity.

[0003] Chinese patent application No. 201611052881.7 (publication No. CN 108097200 A) discloses a method for preparing modified alumina: alumina is mixed with deionized water, stirred, dried; then mixed with ethanol, stirred, dried, and then treated at a certain temperature; then mixed with an additive, deionized water, stirred, and then directly filtered, dried, the additive is selected from one of magnesium sulfate, ammonium chloride, ferrous sulfate and ferric nitrate; finally, the modified alumina product is obtained by high temperature treatment. Chinese patent application No. 201611052882.1 (publication No. CN 108101081 A) discloses a method for preparing modified alumina, which selects alumina same as the above patent and has similar preparation method, but the additive is selected from copper nitrate or aluminum chloride. Although the above two patents can obtain alumina with adjustable basicity, since any one of sulfate, chloride and nitrate is selected to treat alumina to reduce the basicity of alumina, on the one hand, the treatment effects of different salts are quite different, on the other hand, these salts will introduce other impurity ions, which may affect the performance of the material and have adverse effects on its application.

[0004] Chinese patent application No. 202011197406.5 (publication No. CN 114524444 A) discloses a method for modifying alumina, comprising the following steps: (1) mixing alumina with deionized water, then drying at 90-220℃ for 9-24h; (2) mixing the solid obtained in step (1) with alcohol, then drying at 90-220℃ for 9-24h, and then treating at 280-410℃ for 1-6h; (3) mixing the solid obtained in step (2) with aluminum nitrate and deionized water, then directly filtering; (4) washing the solid obtained in step (3) with a mixture of acetic acid and deionized water; (5) treating the solid obtained in step (4) at 80-150℃ for 1-12h to obtain modified alumina. The alumina obtained by the method has the characteristics of low basicity and can be used as an adsorbent and a catalyst carrier. However, the treatment method frequently involves deionized water washing and drying, which is not only complicated to operate, but also has high energy consumption, resulting in high treatment cost, which is not suitable for popularization and application in industrial production.

[0005] Therefore, it is urgent to design a new modification method to reduce the alkalinity of alumina at a lower cost and with relatively simple operation without introducing impurity ions. SUMMARY

[0006] In view of the above-mentioned shortcomings of the prior art, the present application provides a method for reducing the alkalinity of alumina, which solves the problems of easy introduction of impurity ions, high energy consumption, high cost and complicated operation existing in the prior treatment methods.

[0007] In order to achieve the above-mentioned purposes, the main technical solutions adopted by the present application include:

[0008] The method for reducing the alkalinity of alumina comprises the following operations: firstly, mixing alumina with an additive and an organic acid; secondly, ball milling; and finally, calcining. The additive can promote the adhesion of the organic acid to the alumina. Both the additive and the organic acid are decomposed into water and carbon dioxide after calcination.

[0009] During the ball milling, the alumina, the additive and the organic acid are fully mixed and contacted. The organic acid adheres to the alumina under the action of the additive, and the acid groups provided by the organic acid consume the alkali amount of the alumina itself through acid-base neutralization reaction, so as to finally achieve the purpose of reducing the alkalinity of the alumina. If the additive is not added, the alkali amount of the alumina will not be effectively consumed even if the alumina and the organic acid are ball milled for a longer time, and the pH value of the alumina will not be reduced.

[0010] Optionally, the alumina is α-Al2O3. α-alumina has high mechanical strength, hardness, melting point, and excellent chemical stability and corrosion resistance, and is one of the most widely used crystal forms of alumina. It can be added to battery materials to enhance the thermal stability of the battery and prevent high-temperature explosion accidents caused by battery heat release.

[0011] Optionally, the additive is stearic acid. The present application surprisingly finds that stearic acid, as an additive, plays a bridging role in promoting the adhesion of the organic acid to the alumina. The carboxyl group of stearic acid can be combined with alumina, and the carbon chain of stearic acid can be crosslinked with the organic acid. This bridging role can ensure that the acid-base neutralization reaction between the organic acid and the alumina proceeds more completely, thereby achieving the purpose of reducing the alkalinity of the alumina. Moreover, stearic acid is stable at room temperature, and will decompose into water and carbon dioxide when heated to above 200℃, without introducing or leaving any impurity ions that are detrimental to the performance of the alumina into the alumina.

[0012] Optionally, the organic acid includes oxalic acid, citric acid, succinic acid and tartaric acid. Specifically, the organic acid can be any one or more of the above-mentioned four organic acids.

[0013] Oxalic acid is a weak acid and stable at room temperature, but its stability is poor after heating, and it decomposes at 189.5℃; citric acid is a strong tricarboxylic acid compound, colorless and odorless, and its decomposition temperature is 175℃; succinic acid, also known as succinic acid, is colorless and sour, and its decomposition temperature is 235℃; tartaric acid is low-toxic, odorless, and sour, with a melting point of 204-206℃ and a decomposition temperature of 210℃; the acid radicals provided by the above four organic acids can consume the self-alkali amount of alumina, and can be completely removed by high-temperature calcination without introducing or leaving any impurity ions that are not conducive to the performance of alumina. Considering the cost, environmental friendliness and use effect, oxalic acid is the best. Of course, other organic acids that meet the conditions can also be used.

[0014] Further, in the present application, stearic acid is used as an additive, and oxalic acid is used as an organic acid. Alumina, stearic acid and oxalic acid are reacted in a weight ratio of 1:(0.01-0.1):(0.3-0.5). By controlling the weight ratio of each component, the pH value of α-Al2O3 can be flexibly adjusted, and the pH value of α-Al2O3 can be reduced from 9.4-9.6 to 6.88 at the highest.

[0015] The self-alkali amount of α-Al2O3 is consumed by the acid radical provided by oxalic acid. The amount of oxalic acid has a greater impact on the pH value. Once the pH value of α-Al2O3 is determined, the amount of oxalic acid is also determined. If the amount of oxalic acid is too small, it is not conducive to the consumption of the alkali amount of α-Al2O3. If the amount of oxalic acid is too large, it may damage the structure of α-Al2O3 and change the crystal phase or even cause the decomposition of α-Al2O3. Stearic acid is used as an additive to promote the adhesion of oxalic acid and α-Al2O3. The amount of stearic acid increases with the increase of oxalic acid. If the amount of stearic acid is too small, it cannot promote the complete adhesion of oxalic acid and α-Al2O3, and then cannot effectively consume the alkali amount of α-Al2O3. If the amount of stearic acid is too large, it is not only useless for the adhesion of oxalic acid and α-Al2O3, but also increases the cost and may damage the structure of α-Al2O3.

[0016] It should be noted that basic alumina with a pH value outside the range of 9.4-9.6 can also be effectively reduced by the method described in the present application, but the weight ratio of alumina, stearic acid and oxalic acid will change. The amount of oxalic acid is determined by the self-alkali amount of alumina. The larger the self-alkali amount of alumina, the greater the amount of oxalic acid. The amount of stearic acid is determined by the amount of oxalic acid. The greater the amount of oxalic acid, the greater the amount of stearic acid.

[0017] Optionally, the ball milling is low-speed ball milling, preferably with a rotation speed ranging from 200 to 300 r / min. In the present application, the ball milling is only used to promote the full mixing and contacting of various materials, and is not used to reduce the particle size of the alumina, so that the low-speed ball milling can be used; it should be noted that the material of the ball milling medium is not limited in the present application, and any ball milling medium that can fully mix and contact the α-Al2O3, the additive and the organic acid without introducing other impurities can be used; the ball milling time should not be too long or too short, too long will not have a beneficial effect on the ball milling effect, but will increase the energy consumption and the production cost, and too short may result in insufficient contacting of various materials, and the effective crosslinking and adhesion cannot be formed, which is not conducive to the consumption of the self-contained alkali amount of the alumina by the organic acid, and the preferred ball milling time is 1-2 h.

[0018] Optionally, the calcination temperature is 200-300℃, and the time is 1-3 h. The calcination temperature should not be too high or too low, too high will increase the energy consumption and the production cost, and too low may result in incomplete decomposition and insufficient removal of the oxalic acid and the stearic acid, and affect the various properties of the alumina.

[0019] The method for reducing the basicity of the alumina provided in the present application can not only effectively reduce the pH value of the alumina, but also has simple process, convenient operation and low energy consumption, and more importantly, does not introduce impurity ions into the alumina, and is suitable for popularization and application in industrial production, and the alumina treated by the present application can be used as an adsorbent, a catalyst carrier and an additive in a battery material. BRIEF DESCRIPTION OF DRAWINGS

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced, and obviously, the drawings in the following description are only some embodiments of the present application, and any person skilled in the art can obtain other drawings according to the drawings without any creative effort.

[0021] Figure 1 XRD patterns of the modified alumina prepared for the blank group and examples 1-9;

[0022] Figure 2 XRD patterns of the modified alumina prepared for examples 9-12. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application, and obviously, the described embodiments are only some embodiments of the present application, but not all the embodiments. Based on the embodiments in the present application, any person skilled in the art can obtain all other embodiments without any creative effort, which all belong to the protection scope of the present application.

[0024] The inventors found in the research on the alkaline regulation of alumina that there are mainly two methods for reducing the alkalinity of alumina in the prior art: one is to treat alumina with sulfate or chloride or nitrate to reduce the alkalinity of alumina, however, the treatment effects of different salts are quite different, and the above salts will introduce other impurity ions into the alumina, which may affect the adsorption and catalytic properties of the material, and may also result in its inability to be used as an additive of battery material; the other is to treat alumina with alcohol, first mixed with ionized water, then mixed with aluminum nitrate and deionized water, then directly filtered, then filtered and washed with a mixture of acetic acid and deionized water, and finally treated at high temperature to obtain modified alumina, the alumina treated by this method retains less than 1% of the original alumina in terms of alkalinity, but has high energy consumption and cost, and the steps are more and the operation is more complicated, which is not suitable for popularization and application in industrial production.

[0025] In view of the above defects, the present application provides a method for reducing the alkalinity of alumina, in order to reduce the alkalinity of alumina at a relatively low cost and with relatively simple operation without introducing impurity ions.

[0026] The α-Al2O3 involved in the following experiments is Al2O3 in ordinary irregular shape calcined by high-temperature jet melting method (prior art), the pH value of which is 9.6, and the same batch of α-Al2O3 is used in the blank group, each example and each comparative example; of course, it can also be self-made by other prior art or directly purchased; the raw material is not the originality of the present application and is also not within the protection scope of the present application. The ball milling involved in the following experiments is carried out by using a quartz sand ball mill, and the rotation speed of the quartz sand ball mill is 200-300 r / min.

[0027] The pH value of the modified alumina involved in the following experiments is tested by using a PHS-3E type pH meter (brand: Shanghai Yilian Science (Leicai)), and the specific testing method is as follows: 100 ml of distilled water is added into a 150 ml beaker and heated to boiling; 25 g of modified alumina after drying is added into the beaker and boiled for 5 minutes; the beaker is taken out, cooled to room temperature, and then water is added to 100 ml, the pH meter is turned on and tested after preheating and calibration, the magnetic rotor is placed in the solution to be tested during testing and placed on a magnetic stirrer, and the testing is carried out under magnetic stirring, and the average value of three independent tests is taken. Of course, it is not limited to the above testing method, and other conventional pH value testing methods can also be used.

[0028] The modified alumina prepared in the following examples was characterized by XRD using a Rigaku Miniflex-600 X-ray diffractometer. The X-ray used was Cu target Kα line, and the characterization conditions were: normal temperature XRD, scanning between 10°-60°, scanning speed 10°·min-1, step size 0.02°, and the test method was: taking an appropriate amount of powder in the sample table groove, and using a glass sheet to compact. -1 , step size 0.02°, and the test method was: taking an appropriate amount of powder in the sample table groove, and using a glass sheet to compact.

[0029] blank group

[0030] 50 g of α-Al2O3 and 15 g of oxalic acid were mixed uniformly, ball milled for 1 h, and then calcined at 300°C for 1 h to obtain modified alumina, and the sample was numbered D-0.

[0031] Example 1

[0032] 50 g of α-Al2O3, 5 g of stearic acid, and 15 g of oxalic acid were mixed uniformly, ball milled for 1 h, and then calcined at 300°C for 1 h to obtain modified alumina, which was numbered A-1.

[0033] Example 2

[0034] 50 g of α-Al2O3, 5 g of stearic acid, and 15 g of oxalic acid were mixed uniformly, ball milled for 1 h, and then calcined at 300°C for 1 h to obtain modified alumina, which was numbered A-2.

[0035] Example 3

[0036] 50 g of α-Al2O3, 5 g of stearic acid, and 25 g of oxalic acid were mixed uniformly, ball milled for 1 h, and then calcined at 300°C for 1 h to obtain modified alumina, which was numbered A-3.

[0037] Example 4

[0038] 50 g of α-Al2O3, 5 g of stearic acid, and 15 g of oxalic acid were mixed uniformly, ball milled for 2 h, and then calcined at 300°C for 1 h to obtain modified alumina, which was numbered A-4.

[0039] Example 5

[0040] 50 g of α-Al2O3, 5 g of stearic acid, and 15 g of oxalic acid were mixed uniformly, ball milled for 1 h, and then calcined at 200°C for 1 h to obtain modified alumina, which was numbered A-5.

[0041] Example 6

[0042] 50 g of α-Al2O3, 5 g of stearic acid, and 15 g of oxalic acid were mixed uniformly, ball milled for 1 h, and then calcined at 300°C for 2 h to obtain modified alumina, which was numbered A-6.

[0043] Example 7

[0044] Take 50 g of α-Al2O3, 5 g of stearic acid, 15 g of oxalic acid, mix uniformly, ball mill for 1 h; then calcine at 300℃ for 3 h to obtain modified alumina, which is numbered as A-7.

[0045] Example 8

[0046] Take 50 g of α-Al2O3, 0.5 g of stearic acid, 15 g of oxalic acid, mix uniformly, ball mill for 1 h; then calcine at 300℃ for 1 h to obtain modified alumina, which is numbered as A-8.

[0047] Example 9

[0048] Take 50 g of α-Al2O3, 2.5 g of stearic acid, 15 g of oxalic acid, mix uniformly, ball mill for 1 h; then calcine at 300℃ for 1 h to obtain modified alumina, which is numbered as A-9.

[0049] Comparative Example 1

[0050] Take 50 g of α-Al2O3, 5 g of stearic acid, 15 g of oxalic acid, mix uniformly, ball mill for 3 h; then calcine at 300℃ for 3 h to obtain modified alumina, which is numbered as D-1.

[0051] Comparative Example 2

[0052] Take 50 g of α-Al2O3, 5 g of stearic acid, 15 g of oxalic acid, mix uniformly, ball mill for 1 h; then calcine at 300℃ for 4 h to obtain modified alumina, which is numbered as D-2.

[0053] Comparative Example 3

[0054] Take 50 g of α-Al2O3, 5 g of stearic acid, 15 g of oxalic acid, mix uniformly, ball mill for 1 h; then calcine at 400℃ for 1 h to obtain modified alumina, which is numbered as D-3.

[0055] As shown in Figure 1 : The modified aluminas obtained in Examples 1-9 all crystallize well, the diffraction peaks are very sharp, the crystal phase is all α-Al2O3, and all have the typical 2θ of α-Al2O3: 43.36°, 35.15°, 57.50°, 25.58°, 37.78°. The modified aluminas obtained in the blank group and Comparative Examples 1-3 are also α-Al2O3. The technical parameters of the blank group, Examples 1-9, and Comparative Examples 1-3 and the pH values of the obtained products are shown in Table 1 below:

[0056] Table 1 Technical parameters of the blank group, Examples 1-9, and Comparative Examples 1-3 and the pH values of the obtained products

[0057]

[0058]

[0059] From the comparison of blank group and example 1, it can be seen that: without adding stearic acid, simply using oxalic acid mixed with α-Al2O3 for ball milling, the pH value of α-Al2O3 before ball milling is 9.6, and the pH value of α-Al2O3 after ball milling is 9.58, and the pH value has no change before and after ball milling. It can be seen that only under the action of stearic acid, oxalic acid can effectively consume the self-alkali amount of α-Al2O3 and reduce the alkalinity of α-Al2O3. The above fully shows that stearic acid is an essential condition for oxalic acid and α-Al2O3 ball milling to reduce the alkalinity of α-Al2O3.

[0060] From the comparison of example 1, example 2 and example 3, it can be seen that: under the premise of other conditions being consistent, when the amount of oxalic acid is 15g, 20g and 25g respectively, the pH value of the product is 8.93, 7.69 and 6.88 respectively, and the pH value decreases with the increase of the amount of oxalic acid. It can be seen that the greater the amount of oxalic acid, the more the consumption of the self-alkali amount of α-Al2O3, and the more obvious the reduction of the pH value of α-Al2O3. The amount of oxalic acid plays a decisive role in the pH value of α-Al2O3.

[0061] From the comparison of example 1, example 4 and comparative example 1, it can be seen that: under the premise of other conditions being consistent, when the ball milling time is prolonged from 1h to 2h and 3h, the pH value of the product is reduced from 8.93 to 8.86 and 8.85. Considering the experimental results and experimental cost, the preferred ball milling time is 1-2h, and the ball milling time more than 2h has little effect on the pH value of the product, and also leads to greater energy consumption and increases the production cost. In addition, the ball milling time should not be less than 1h, and less than 1h may lead to that various materials cannot form effective cross-linking and adhesion due to insufficient contact, which is not conducive to the consumption of the self-alkali amount of alumina by organic acid.

[0062] From the comparison of example 1, example 6, example 7 and comparative example 2, it can be seen that: under the premise of other conditions being consistent, when the calcination time is prolonged from 1h to 2h, 3h and 4h, the pH value of the product is increased from 8.93 to 9.21, 9.35 and 9.55 respectively. Considering the experimental results and experimental cost, the preferred calcination time is 1-3h, and the calcination time more than 3h has little effect on the pH value of the product, and also leads to greater energy consumption and increases the production cost. In addition, the calcination time should not be less than 1h, and less than 1h may lead to incomplete decomposition of oxalic acid and stearic acid, which introduces impurities and affects the performance of alumina.

[0063] As can be seen from the comparison of Example 5, Example 1 and Comparative Example 3, under the condition of other conditions being the same, when the calcination temperature is 200℃, 300℃ and 400℃, the pH value of the product is 9.15, 8.93 and 8.87 respectively. Considering the experimental results and the experimental cost, the preferred calcination temperature is 200-300℃, and the calcination temperature exceeding 300℃ has little effect on the pH value of the product, but will result in greater energy consumption and increase the production cost. In addition, the calcination temperature should not be lower than 200℃, and lower than 200℃ may result in incomplete decomposition of oxalic acid and stearic acid, introducing impurities and affecting the performance of aluminum oxide.

[0064] In addition to the above Examples 1-9, the following Examples are also carried out according to the present application:

[0065] Example 10

[0066] In addition to replacing oxalic acid in Example 9 with an equal amount of citric acid, the other technical parameters are the same as those in Example 9, and the product is numbered as A-10.

[0067] Example 11

[0068] In addition to replacing oxalic acid in Example 9 with an equal amount of succinic acid, the other technical parameters are the same as those in Example 9, and the product is numbered as A-11.

[0069] Example 12

[0070] In addition to replacing oxalic acid in Example 9 with an equal amount of tartaric acid, the other technical parameters are the same as those in Example 9, and the product is numbered as A-12.

[0071] It is determined that the pH values of the products obtained in Examples 10-12 are 9.32, 9.66 and 9.41 respectively. As can be seen from the table, Examples 10-12 can also obtain well-crystallized α-Al2O3, and the corresponding products also have the typical 2θ of α-Al2O3: 43.36°, 35.15°, 57.50°, 25.58° and 37.78°. Figure 2

[0072] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can modify, replace, substitute and deform the above embodiments within the scope of the present application. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.​

Claims

1. A method of reducing the basicity of alumina, characterized by, The method comprises the following steps: firstly, mixing alumina, stearic acid and organic acid according to the weight ratio of 1:(0.01-0.1):(0.3-0.5), then ball milling for 1-2 hours, and finally calcining at the temperature of 200-300 DEG C for 1-3 hours; the stearic acid can promote the adhesion of the organic acid and the alumina, and both the stearic acid and the organic acid are decomposed into water and carbon dioxide after calcining.

2. The method of reducing the basicity of alumina according to claim 1, wherein, The alumina is alpha-Al2O3.

3. The method of reducing the basicity of alumina of claim 1, wherein, The organic acid comprises any one or more of oxalic acid, citric acid, succinic acid and tartaric acid.

4. The method of reducing the basicity of alumina of claim 2, wherein, The pH value of the alpha-Al2O3 is 9.4-9.

6.

5. The method of reducing the basicity of alumina of claim 1, wherein, The rotating speed of the ball milling is 200-300 r / min.

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