A preparation method of high-purity pseudo-boehmite

Abstract

This application relates to the technical field of the preparation of pseudo-boehmite, and specifically relates to a method for preparing high-purity pseudo-boehmite. The method for preparing high-purity pseudo-boehmite in this application includes the following steps: First, under the action of a catalyst and an adsorbent, an alcohol reacts with aluminum to synthesize aluminum alkoxide; then the aluminum alkoxide undergoes hydrolysis and aging to obtain a hydrolysis product, and finally the hydrolysis product is filtered, slurried, and dried to obtain high-purity pseudo-boehmite; in the process of preparing the aluminum alkoxide mentioned above, isopropanol aluminum is selected as the catalyst, which does not introduce other impurities and will not cause pollution to the environment. The adsorbent uses modified chitosan, with an increased specific surface area, enhanced adsorption and complexation effects on impurity ions, which is more conducive to improving the purity of the aluminum alkoxide and thus the purity of the pseudo-boehmite; in addition, the pseudo-boehmite is further slurried to refine the grain size and improve the particle uniformity, further improving the purity of the pseudo-boehmite.

Description

Technical Field

[0001] This application relates to the technical field of preparing pseudo-boehmite, and specifically relates to a method for preparing high-purity pseudo-boehmite. Background Art

[0002] Pseudo-boehmite, also known as meta-boehmite, is mainly used in different industries such as catalysts, automotive exhaust treatment, and papermaking. In catalyst applications, pseudo-boehmite mainly acts as a binder and a carrier for providing active components. With the increasing national environmental protection efforts, the consumption of petroleum refining (desulfurization, denitrification, alkylation) catalysts, reforming catalysts, and automotive exhaust purification catalysts has increased sharply. Therefore, the market prospect of pseudo-boehmite is very good, and the consumption will increase year by year.

[0003] Currently, there are mainly two methods for producing pseudo-boehmite: the inorganic aluminum salt method and the organic aluminum salt method. The inorganic aluminum salt method is further divided into two categories: the aluminum salt neutralization method and the carbonization method. This method has simple process, low cost, and small equipment investment, but it is difficult to control impurities such as sodium, halogens, silicon, iron, and sulfate in the product, and the impurity content is high, resulting in poisoning of noble metal catalysts during the process of using pseudo-boehmite as a catalyst carrier. The organic aluminum salt method is mainly used to prepare high-purity pseudo-boehmite. With the increasing requirements of modern chemical industry for catalysts, higher requirements are also put forward for the purity of pseudo-boehmite products. Therefore, it is very necessary and urgent to research and develop the preparation of high-purity pseudo-boehmite.

[0004] The application document with publication number CN112939039A discloses a method for preparing low-sodium pseudo-boehmite. The preparation method uses primary aluminum or refined high-purity aluminum as raw materials. After leaching and drying, it first reacts with alcohol to form aluminum alkoxide. After screening and filtering solid particles, hydrolysis is carried out, and then the alcohol generated by hydrolysis is evaporated to obtain crude pseudo-boehmite. A certain amount of deionized water and dispersant are added to the crude pseudo-boehmite, and it is treated at 50°C to 250°C for 2 to 12 hours to obtain a dispersion of pseudo-boehmite. The precipitate in the dispersion is removed by high-speed centrifugation, and then the purified dispersion is spray-dried to obtain low-sodium pseudo-boehmite. The pseudo-boehmite obtained by the above preparation method has low sodium, iron, and silicon contents, but the catalyst used in the preparation process contains heavy metal mercury, which will have an adverse impact on the product and the environment. Moreover, although the dispersant used in the preparation process can improve the stability of the dispersion, it will also introduce new impurities, resulting in a decrease in the purity of pseudo-boehmite. Summary of the Invention

[0005] In order to improve the purity of pseudo-boehmite, this application provides a method for preparing high-purity pseudo-boehmite.

[0006] A method for preparing high-purity pseudo-boehmite includes the following steps:

[0007] S1: Mix aluminum particles, a catalyst, an adsorbent, and isopropyl alcohol, heat up to 100 - 160 °C, react for 6 - 12 h, and perform vacuum distillation to obtain aluminum alkoxide; the adsorbent is chitosan or modified chitosan;

[0008] S2: Mix the aluminum alkoxide and an alcohol - water mixed solution evenly, carry out a hydrolysis reaction, and perform aging after hydrolysis is completed to obtain a hydrolysis product;

[0009] S3: Filter the hydrolysis product, pulp the obtained solid product, and then filter and vacuum - dry it to obtain the product.

[0010] In the above - mentioned technical solution, first, in the presence of a catalyst, aluminum particles react with alcohol to generate an aluminum alkoxide salt; then, the aluminum alkoxide salt undergoes hydrolysis and aging to obtain a hydrolysis product; finally, after the hydrolysis product is filtered, a solvent is added to the filter cake for pulping, and the obtained uniform slurry is filtered and vacuum - dried to obtain high - purity pseudo - boehmite.

[0011] During the preparation process of the above - mentioned aluminum alkoxide salt, adding a catalyst can increase the reaction rate of aluminum particles and alcohol. After the reaction rate increases, more impurities are dissolved out or generated. At this time, the adsorbent is chitosan or modified chitosan, which has a relatively large specific surface area, good adsorption performance, and is rich in amino and hydroxyl groups. It can adsorb solid impurities and impurity ions generated during the reaction, such as iron, calcium, magnesium, etc. When performing vacuum distillation, the adsorbent and the impurities it adsorbs are separated from the aluminum alkoxide salt, thereby reducing the impurity content in the aluminum alkoxide salt, further reducing the impurity content in pseudo - boehmite, and effectively removing these solid impurities and impurity ions to improve the purity of the aluminum alkoxide.

[0012] During the above - mentioned hydrolysis reaction process, aluminum alkoxide is extremely easy to hydrolyze when encountering water, and at the same time, a polycondensation reaction of aluminum alkoxide occurs. As the reaction time extends, the aluminum alkoxide is completely hydrolyzed to generate a pseudo - boehmite hydrolysis product. Pseudo - boehmite is a hydroxide of aluminum. The pseudo - boehmite obtained just after hydrolysis has an incomplete crystal structure and small particles. After a period of aging process, the small particles are continuously dispersed, re - stacked, and grown to form a layered structure with a stable structure, uniform pore distribution, and increased specific surface area. The crystal form is more perfect, the crystal water or impurities between crystals are less, and the crystals are more dense, which is beneficial to improving the purity of pseudo - boehmite.

[0013] After the above - mentioned hydrolysis and aging are completed, filter the hydrolysis product. The filtered pseudo - boehmite is further dispersed into a uniform suspension by pulping to improve the dispersibility of pseudo - boehmite in the solution, which is more conducive to adjusting the particle size uniformity of pseudo - boehmite, thereby further improving the purity of pseudo - boehmite. In addition, the hydrolysis product includes pseudo - boehmite and a liquid - phase hydrolysis solution. After the filtration step, the solid - liquid separation is carried out to remove impurities such as suspended substances, unreacted raw materials, and by - products in the hydrolysis product, and improve the purity of pseudo - boehmite.

[0014] Preferably, in step S1, the catalyst is aluminum isopropoxide.

[0015] In the above technical solution, the empty orbital of aluminum in aluminum isopropoxide will form a coordination bond with the lone pair electrons of the oxygen in the alcohol hydroxyl group, making the electron cloud in the alcohol hydroxyl group more biased towards the oxygen atom. As a result, the hydrogen atom in the alcohol hydroxyl group is more likely to ionize. At this time, the concentration of hydrogen ions in the solution increases, and the hydrogen ions react with the aluminum particles to generate aluminum ions. The aluminum ions react with the alcohol to generate alcohol aluminum salt and hydrogen ions, and so on in a cycle. The catalyst continuously catalyzes the generation of alcohol aluminum salt, improving the reaction efficiency. In addition, using aluminum isopropoxide as the catalyst not only does not introduce other impurities during the reaction process, but also the reaction product aluminum isopropoxide can catalyze the reaction to promote the reaction rate to increase. Therefore, only a very small amount of aluminum isopropoxide needs to be added to obtain a relatively fast reaction rate, which is more conducive to obtaining high-purity pseudo-boehmite.

[0016] Preferably, in step S1, the mass ratio of the aluminum particles, isopropanol, catalyst, and adsorbent is 1:(5 - 12):(0.01 - 0.03):(0.005 - 0.02).

[0017] Preferably, in step S1, the conditions for vacuum distillation are as follows: first, perform vacuum distillation at 82 - 83 °C to collect the unreacted alcohol. After the collection is completed, continue vacuum distillation to collect the fraction at 130 - 150 °C.

[0018] In the above technical solution, in the mixed solution after the reaction of alcohol and aluminum, the main components are the alcohol aluminum salt generated by the reaction, the unreacted alcohol, as well as water, the catalyst, and the adsorbent. The alcohol used to prepare the alcohol aluminum salt is mainly isopropanol, whose boiling point is 82.5 °C. First, perform vacuum distillation at 82 - 83 °C to collect the unreacted alcohol for use in the alcohol aluminum reaction to reduce costs; then continue vacuum distillation to separate the alcohol aluminum salt from other substances, which is conducive to obtaining a higher purity of alcohol aluminum salt.

[0019] Preferably, in step S2, the alcohol-water mixed solution is prepared by mixing isopropanol and pure water at a mass ratio of 1:1; the mass ratio of the alcohol aluminum to the alcohol-water mixed solution is 1:(0.4 - 2.4).

[0020] In the above technical solution, the hydrolysis solution is prepared by mixing alcohol and water in a certain proportion. Moreover, when the addition amount of aluminum alkoxide is fixed, the addition amount of the hydrolysis solution should be controlled within a certain range. If the addition amount of the hydrolysis solution is too small, the hydrolysis of aluminum alkoxide is incomplete, the yield of pseudo-boehmite obtained is reduced, and the purity of pseudo-boehmite may be lowered. If the addition amount of the hydrolysis solution is too large, excessive water remains in the hydrolysis product. During aging, there is more crystal water between the pseudo-boehmite grains, and the formed grains are larger, but the density of the grains is lower, thus affecting the purity of pseudo-boehmite. Moreover, it will also reduce the concentration of pseudo-boehmite in the hydrolysis product, lower the crystallization rate of pseudo-boehmite, form smaller grains, and is also not conducive to improving the purity of pseudo-boehmite.

[0021] Preferably, in step S2, the temperature of the hydrolysis reaction is 80 - 160 °C, and the time of the hydrolysis reaction is 2 - 6 h; the temperature of the aging is 90 - 160 °C, and the time of the aging is 2 - 6 h.

[0022] In the above technical solution, the hydrolysis reaction conditions and the aging conditions will affect the hydrolysis rate and the grain size, thus affecting the quality of pseudo-boehmite. If the hydrolysis reaction conditions are inappropriate, it may lead to incomplete hydrolysis, or a higher hydrolysis rate, but the formed pseudo-boehmite grains are smaller. If the aging conditions are inappropriate, it may lead to the grains not growing, grain defects, etc., and will also affect the purity of pseudo-boehmite.

[0023] Preferably, in step S3, the specific steps of pulping are as follows: The filtered solid product and the alcohol-water mixed solution are stirred at a speed of 300 - 450 rpm for 15 - 30 min to form a uniform slurry.

[0024] Preferably, in step S1, the modified chitosan is prepared by a method including the following steps:

[0025] (1) Mix chitosan with an aqueous solution of aluminum nitrate, add urea, react at 110 - 140 °C for 6 - 12 h, centrifuge, wash until neutral, and dry to obtain composite microspheres;

[0026] (2) Mix the composite microspheres and alcohol evenly, add an alkali solution and chloroacetic acid, carry out the reaction, adjust the pH value to neutral after the reaction, and obtain the product through suction filtration, washing, and drying.

[0027] In the above technical solution, first, after the hydrothermal reaction, chitosan is partially carbonized, resulting in an increased specific surface area of chitosan and more adsorption sites. Through the adsorption effect, the impurity particles generated during the reaction of aluminum alkoxide can be adsorbed on the surface or in the pores of the microspheres, and the adsorption of impurities is more stable, which is more conducive to the removal of impurities. In addition, after the hydrothermal reaction, aluminum ions can form layered hydroxides, further increasing the specific surface area, making the adsorption effect of chitosan stronger. Moreover, the introduction of aluminum can also improve the reaction rate of isopropanol and aluminum to a certain extent, promoting the formation of aluminum isopropoxide.

[0028] Then, the chitosan on the surface of the composite microspheres that has not been carbonized is carboxymethylated. After carboxymethylation, the surface of the composite microspheres contains more carboxyl groups. Carboxyl group is an acidic group, which can ionize hydrogen ions in aqueous solution to form carboxylate anions, and can have electrostatic attraction with positively charged ions such as iron, calcium, magnesium ions. Moreover, the oxygen in the carboxyl group and the nitrogen atom in the amino group have lone pair electrons, which can form stable complexes with ions that can provide empty orbitals. This complexation and electrostatic interaction cooperate with each other, making the adsorption stability of the composite microspheres for impurity ions stronger, and more conducive to the removal of impurities during the synthesis of aluminum alkoxide.

[0029] Preferably, in step (1), the mass ratio of chitosan, aluminum nitrate, and urea is 1:(0.1 - 0.2):(0.2 - 0.5).

[0030] Preferably, in step (2), the mass ratio of the composite microspheres to chloroacetic acid is 1:(1.2 - 3).

[0031] The above technical solution of this application has at least the following beneficial effects:

[0032] 1. The adsorbent of this application has a large specific surface area and strong adsorption, which can reduce the influence of impurities on aluminum alkoxide during the synthesis of aluminum alkoxide;

[0033] 2. This application uses a non-toxic catalyst to catalyze the aluminum alkoxide reaction process, improving the reaction rate, and at the same time not introducing other impurities, which is beneficial to improving the purity of pseudo-boehmite;

[0034] 3. After filtering the hydrolysis product of aluminum alkoxide in this application, through the pulping step, the particle size uniformity of pseudo-boehmite is adjusted, further improving the quality of pseudo-boehmite. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the microscopic morphology diagram of pseudo-boehmite prepared by the comparative example and Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The following further elaborates on this application in conjunction with embodiments.

[0037] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0038] Example

[0039] Example 1

[0040] The preparation method of high-purity pseudo-boehmite in this example includes the following steps:

[0041] S1: Weigh 100 g of aluminum pellets, 1 g of aluminum isopropoxide, and 0.5 g of chitosan with a deacetylation degree of 80%, place them in a reaction kettle, heat up to 100 °C, and continuously add 500 g of isopropanol. React under reflux for 12 h, then carry out vacuum distillation on the reaction system at 82 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide;

[0042] S2: Prepare an alcohol-water mixed solution by mixing high-purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 40 g of the alcohol-water mixed solution, mix them evenly, hydrolyze at 80 °C for 6 h, and then age at 160 °C for 2 h to obtain a hydrolysis product;

[0043] S3: Filter the hydrolysis product, place the obtained solid product in a blender, add the alcohol-water mixed solution, and beat it into a slurry at a speed of 300 rpm for 15 min to form a stable slurry, and then filter and vacuum dry to obtain the product.

[0044] Example 2

[0045] The preparation method of high-purity pseudo-boehmite in this example includes the following steps:

[0046] S1: Weigh 100 g of aluminum pellets, 3 g of aluminum isopropoxide, and 2 g of chitosan with a deacetylation degree of 80%, place them in a reaction kettle, heat up to 160 °C, and continuously add 1200 g of isopropanol. React under reflux for 6 h, then carry out vacuum distillation on the reaction system at 83 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide;

[0047] S2: Prepare an alcohol-water mixed solution by mixing high-purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 40 g of the alcohol-water mixed solution, mix them evenly, hydrolyze at 160 °C for 2 h, and then age at 90 °C for 6 h to obtain a hydrolysis product;

[0048] S3: Filter the hydrolysis product, place the obtained solid product in a blender, add the alcohol-water mixed solution, and beat it into a slurry at a speed of 450 rpm for 30 min to form a stable slurry, and then filter and vacuum dry to obtain the product.

[0049] Example 3

[0050] The preparation method of high-purity pseudo-boehmite in this example includes the following steps:

[0051] S1: Weigh 100 g of aluminum pellets, 2.5 g of aluminum isopropoxide, and 1.2 g of chitosan with a degree of deacetylation of 80%, place them in a reaction kettle, heat up to 120 °C, and continuously add 1000 g of isopropanol. React under reflux for 8 h, then carry out vacuum distillation on the reaction system at 82.5 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide;

[0052] S2: Prepare an alcohol-water mixed solution by mixing high-purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 40 g of the alcohol-water mixed solution, mix them evenly, hydrolyze at 120 °C for 4 h, and then age at 120 °C for 4 h after hydrolysis to obtain a hydrolysis product;

[0053] S3: Filter the hydrolysis product, place the obtained solid product in a blender, add the alcohol-water mixed solution, and beat it at a speed of 400 rpm for 30 min to form a stable slurry, and then carry out filtration and vacuum drying to obtain the product.

[0054] Example 4

[0055] The difference between the preparation method of high-purity pseudo-boehmite in this example and that in Example 3 is as follows:

[0056] S1: Weigh 100 g of aluminum pellets, 2.5 g of aluminum isopropoxide, and 1.2 g of chitosan with a degree of deacetylation of 80%, place them in a reaction kettle, heat up to 120 °C, and continuously add 1000 g of isopropanol. React under reflux for 8 h, then carry out vacuum distillation on the reaction system at 82.5 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide;

[0057] S2: Prepare an alcohol-water mixed solution by mixing high-purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 240 g of the alcohol-water mixed solution, mix them evenly, hydrolyze at 120 °C for 4 h, and then age at 120 °C for 4 h after hydrolysis to obtain a hydrolysis product;

[0058] S3: Filter the hydrolysis product, place the obtained solid product in a blender, add the alcohol-water mixed solution, and beat it at a speed of 400 rpm for 30 min to form a stable slurry, and then carry out filtration and vacuum drying to obtain the product.

[0059] Example 5

[0060] The difference between the preparation method of high-purity pseudo-boehmite in this example and that in Example 3 is as follows:

[0061] S1: Weigh 100 g of aluminum pellets, 2.5 g of aluminum isopropoxide, and 1.2 g of chitosan with a degree of deacetylation of 80%, place them in a reaction kettle, heat up to 120 °C, and continuously add 1000 g of isopropanol. React under reflux for 8 h, then carry out vacuum distillation on the reaction system at 82.5 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide;

[0062] S2: Prepare an alcohol - water mixed solution by mixing high - purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 180 g of the alcohol - water mixed solution, mix them evenly, hydrolyze at 120 °C for 4 h, and then age at 120 °C for 4 h to obtain a hydrolysis product;

[0063] S3: Filter the hydrolysis product, place the obtained solid product in a blender, add the alcohol - water mixed solution, and beat it into a slurry at a speed of 400 rpm for 30 min to form a stable slurry, and then filter and vacuum - dry to obtain it.

[0064] Example 6

[0065] The preparation method of the high - purity pseudo - boehmite in this example is the same as that in Example 5;

[0066] The modified chitosan in this example is prepared by a method including the following steps:

[0067] (1) Weigh 10 g of chitosan, 1 g of aluminum nitrate, and 500 mL of deionized water. After mixing evenly, add 2 g of urea while stirring, place the mixed solution in a high - pressure reaction kettle, react at 110 °C for 12 h. After the product is centrifuged, wash it with anhydrous ethanol and deionized water until neutral, and after drying, obtain composite microspheres;

[0068] (2) Weigh 2 g of the composite microspheres, add 20 mL of isopropanol, stir for 10 min, slowly add 10 mL of a sodium hydroxide solution with a concentration of 5 mol / L and 2.4 g of chloroacetic acid, stir and react at 65 °C for 4 h, add 4 mL of distilled water, adjust the pH value to neutral with glacial acetic acid, carry out suction filtration, wash with anhydrous ethanol, and dry to obtain it.

[0069] Example 7

[0070] The preparation method of the high - purity pseudo - boehmite in this example is the same as that in Example 5;

[0071] The modified chitosan in this example is prepared by a method including the following steps:

[0072] (1) Weigh 10 g of chitosan, 2 g of aluminum nitrate and 500 mL of deionized water. After mixing them evenly, add 5 g of urea while stirring. Place the mixed solution in a high-pressure reactor and react at 140 °C for 6 h. After centrifuging the product, wash it with absolute ethanol and deionized water until neutral, and then dry it to obtain composite microspheres.

[0073] (2) Weigh 2 g of the composite microspheres, add 20 mL of n-butanol, stir for 10 min, slowly add 10 mL of a sodium hydroxide solution with a concentration of 5 mol / L and 6 g of chloroacetic acid, stir and react at 80 °C for 2 h, add 4 mL of distilled water, adjust the pH value to neutral with glacial acetic acid, filter by suction, wash with absolute ethanol, and dry to obtain the product.

[0074] Comparative Example

[0075] Comparative Example 1

[0076] The preparation method of high-purity boehmite in this comparative example includes the following steps:

[0077] S1: Weigh 100 g of aluminum pellets and 1 g of aluminum isopropoxide and place them in a reactor. Heat up to 100 °C and continuously add 500 g of isopropanol. React under reflux for 12 h, then carry out vacuum distillation on the reaction system at 82 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide.

[0078] S2: Prepare an alcohol-water mixed solution by mixing high-purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 40 g of the alcohol-water mixed solution, mix them evenly, hydrolyze at 80 °C for 6 h, and then age at 160 °C for 2 h after hydrolysis to obtain a hydrolysis product.

[0079] S3: Filter and vacuum dry the hydrolysis product to obtain the product.

[0080] Comparative Example 2

[0081] The preparation method of high-purity boehmite in this comparative example includes the following steps:

[0082] S1: Weigh 100 g of aluminum pellets and 1 g of aluminum isopropoxide and place them in a reactor. Heat up to 100 °C and continuously add 500 g of isopropanol. React under reflux for 12 h, then carry out vacuum distillation on the reaction system at 82 °C, collect the unreacted isopropanol. After the collection is completed, continue vacuum distillation and collect the fraction at 130 - 150 °C to obtain aluminum isopropoxide.

[0083] S2: Prepare an alcohol-water mixed solution by mixing high-purity water and isopropanol according to a mass ratio of 1:1. Weigh 100 g of aluminum isopropoxide and 40 g of the alcohol-water mixed solution, mix them evenly, hydrolyze at 80 °C for 6 h, and then age at 160 °C for 2 h after hydrolysis to obtain a hydrolysis product.

[0084] S3: Filter the hydrolysis product, place the obtained solid product in a blender, add an alcohol-water mixed solution, and beat it into a slurry at a speed of 300 rpm for 15 min to form a stable slurry, and then filter and vacuum dry it to obtain the product.

[0085] Performance detection test

[0086] 1. Scanning electron microscope observation

[0087] Perform scanning electron microscope observation on the pseudo-boehmite prepared in Example 1 and Comparative Example 1, and its microscopic morphology is as Figure 1 shown.

[0088] 2. Purity test

[0089] Analyze the composition of the pseudo-boehmite prepared in Examples 1-7 and Comparative Examples 1-2, and the results are shown in Table 1.

[0090] Table 1 Analysis results of pseudo-boehmite composition

[0091]

[0092] Result analysis

[0093] From Figure 1 the comparison of the two figures, it can be seen that the pseudo-boehmite particles prepared in Comparative Example 1 and Example 1 are both stacked together, the particle shapes are irregular, and the particle size distribution of the pseudo-boehmite in Comparative Example 1 is uneven, with different sizes. However, the particle size of the pseudo-boehmite in Example 1 is smaller than that in Comparative Example 1, and the distribution is relatively uniform. It may be because the purity of the pseudo-boehmite in Example 1 is higher, and after the beating step, there are fewer crystal defects, which is more conducive to the formation of particles with smaller particle size and more uniform distribution.

[0094] In Table 1, LoI mainly refers to the water content. Since no other organic impurities are introduced during the preparation process, the carbon content in the pseudo-boehmite is very low and can be ignored. The impurities in the pseudo-boehmite mainly include the adsorbed impurity ions. From the data in Table 1, it can be seen that the purity of the pseudo-boehmite prepared by the examples is above 99.9%, and even can reach 99.99%.

[0095] From the data of Comparative Examples 1-2 and Examples 1-3 in Table 1, it can be seen that during the preparation of the alcohol aluminum salt, adding an adsorbent is beneficial to improving the purity of the pseudo-boehmite, and with the increase of the adsorbent addition amount, the purity of the pseudo-boehmite increases to a certain extent. It may be because the addition of the adsorbent improves the purity of the alcohol aluminum salt, and then improves the purity of the pseudo-boehmite; in addition, after the hydrolysis product is filtered, it is further beaten into a uniform slurry, which is also beneficial to improving the purity of the pseudo-boehmite.

[0096] From the data of Examples 3 - 5 in Table 1, it can be seen that during the hydrolysis of aluminum alkoxide, when the amount of aluminum alkoxide added is constant, the amount of hydrolysis solution added has a great influence on the hydrolysis reaction. As the amount of hydrolysis solution added increases, the hydrolysis is more complete, the impurity content in the hydrolysis product is less, and therefore, the purity of pseudoboehmite is higher.

[0097] From the data of Examples 5 - 7 in Table 1, it can be seen that when the adsorbent is modified chitosan, the purity of pseudoboehmite is further improved. This may be because the modified chitosan has a stronger adsorption and stabilization effect on impurity particles and has a certain promoting effect on the reaction between isopropanol and aluminum, thereby improving the purity of aluminum alkoxide and further enhancing the purity of pseudoboehmite.

[0098] This specific embodiment is only an interpretation of the present application and does not limit the present application. After reading this specification, those skilled in the art can make modifications to this embodiment without creative contributions as needed, but as long as it is within the scope of the claims of the present application, it is protected by the patent law.

Claims

1. A method for preparing high-purity pseudo-boehmite, characterized in that: The steps include: S1: mixing aluminum particles, a catalyst, an adsorbent and isopropanol, heating to 100-160°C, reacting for 6-12 hours, and performing reduced pressure distillation to obtain aluminum alcohol; the adsorbent modified chitosan; S2: mixing the aluminum alcoholate and the alcohol water mixed solution uniformly, performing a hydrolysis reaction, and performing aging after the hydrolysis is completed to obtain a hydrolysis product; S3: filtering the hydrolyzate, beating the obtained solid product, filtering and vacuum drying to obtain the solid product; In step S1, the catalyst is aluminum isopropoxide; In step S1, the modified chitosan is prepared by a method comprising the following steps: (1) Mix chitosan with an aqueous solution of aluminum nitrate, add urea, react at 110-140°C for 6-12 hours, centrifuge, wash until neutral, and dry to obtain composite microspheres; (2) The composite microspheres and alcohol are mixed evenly, and alkali solution and chloroacetic acid are added to react. After the reaction, the pH value is adjusted to be neutral, and the mixture is filtered, washed, and dried to obtain the product; In step S3, the specific step of slurrying is: stirring the filtered solid product and the alcohol-water mixed solution at a rotation speed of 300-450 rpm for 15-30 minutes to form a uniform slurry.

2. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S1, the mass ratio of the aluminum particles, isopropanol, catalyst, and adsorbent is 1:(5-12):(0.01-0.03):(0.005-0.02).

3. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S1, the conditions for the reduced pressure distillation are: firstly, distill under reduced pressure at 82-83°C to collect the unreacted alcohol, and after the collection is completed, continue the reduced pressure distillation to collect the fraction at 130-150°C.

4. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S2, the alcohol-water mixed solution is prepared by mixing isopropanol and pure water in a mass ratio of 1:1; the mass ratio of the alcohol aluminum to the alcohol-water mixed solution is 1:(0.4-2.4).

5. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S2, the temperature of the hydrolysis reaction is 80-160°C, and the time of the hydrolysis reaction is 2-6 hours; the temperature of the aging is 90-160°C, and the time of the aging is 2-6 hours.

6. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step (1), the mass ratio of chitosan, aluminum nitrate and urea is 1:(0.1-0.2):(0.2-0.5).

7. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step (2), the mass ratio of the composite microspheres to chloroacetic acid is 1:(1.2-3).

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