Preparation method of high-purity pseudo-boehmite

Abstract

The invention relates to the technical field of preparation of pseudo-boehmite, in particular to a preparation method of high-purity pseudo-boehmite. The preparation method of the high-purity pseudo-boehmite comprises the following steps: firstly, reacting alcohol with aluminum under the action of a catalyst and an adsorbent to synthesize aluminum alkoxide; then hydrolyzing and aging the aluminum alkoxide to obtain a hydrolysis product, and finally filtering, pulping and drying the hydrolysis product to obtain the high-purity pseudo-boehmite. In the preparation process of aluminum alkoxide, aluminum isopropoxide is selected as a catalyst, other impurities are not introduced, pollution to the environment is avoided, modified chitosan is adopted as an adsorbent, the specific surface area is increased, the adsorption and complexation effects on impurity ions are enhanced, the purity of aluminum alkoxide is better improved, and then the purity of pseudo-boehmite is improved; in addition, the pseudo-boehmite is further pulped, the grain size is refined, the particle uniformity is improved, and the purity of the pseudo-boehmite is further improved.

Description

Technical Field

[0001] The present application relates to the technical field of preparation of pseudo-boehmite, and in particular to a method for preparing high-purity pseudo-boehmite. Background Art

[0002] Pseudo-boehmite, also known as pseudo-monohydrate soft boehmite, is mainly used in different industries such as catalysts, automobile exhaust treatment, and papermaking. In catalyst applications, pseudo-boehmite mainly plays the role of a binder and a carrier for active components. With the increase in national environmental protection efforts, the use of petroleum refining (desulfurization, denitrogenation, alkylation) catalysts, reforming catalysts, and automobile exhaust purification catalysts has increased dramatically. Therefore, the market prospect of pseudo-boehmite is very good, and the use will increase year by year.

[0003] At present, there are two main 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 a simple process, low cost, and small equipment investment, but impurities such as sodium, halogen, silicon, iron, sulfate, etc. in the product are difficult to control, and the impurity content is high, causing pseudo-boehmite to cause precious metal catalyst poisoning during the process of being used as a catalyst carrier. The organic aluminum salt method mainly prepares high-purity pseudo-boehmite. With the increasing requirements of modern chemical industry for catalysts, higher requirements are also placed on the purity of pseudo-boehmite products. Therefore, the research and development of high-purity pseudo-boehmite is very necessary and urgent.

[0004] The application document with publication number CN112939039A discloses a method for preparing low-sodium pseudo-boehmite, which is to use raw aluminum or refined high-purity aluminum as raw materials, first react with alcohol to generate aluminum alcohol salt after elution and drying, filter solid particles with a screen and then hydrolyze, and then evaporate the alcohol produced by hydrolysis to obtain crude pseudo-boehmite. A certain amount of deionized water and a dispersant are added to the crude pseudo-boehmite, and the pseudo-boehmite is treated at 50°C to 250°C for 2 to 12 hours to obtain a dispersion of pseudo-boehmite, and 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 effect 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 the pseudo-boehmite. Summary of the invention

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

[0006] A method for preparing high-purity pseudo-boehmite comprises the following steps: 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 is chitosan or 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: Filter the hydrolyzate, slurry the obtained solid product, filter and vacuum dry to obtain the product.

[0007] In the above technical scheme, first, in the presence of a catalyst, aluminum particles and alcohol react to generate alcohol aluminum salt; then, the alcohol aluminum salt is hydrolyzed and aged to obtain a hydrolysis product; finally, after the hydrolysis product is filtered, a solvent is added to the filter cake to perform slurrying, and the obtained uniform slurry is filtered and vacuum dried to obtain high-purity pseudo-boehmite.

[0008] In the above-mentioned preparation process of alcohol aluminum salt, adding a catalyst can increase the reaction rate of aluminum particles and alcohol. After the reaction rate is increased, more impurities are dissolved or generated. At this time, the adsorbent is chitosan or modified chitosan, which has a large specific surface area, good adsorption, and is rich in amino and hydroxyl groups. It can adsorb solid impurities and impurity ions generated in the reaction process, such as iron, calcium, magnesium, etc. During the vacuum distillation, the adsorbent and the impurities adsorbed by it are separated from the alcohol aluminum salt, thereby reducing the content of impurities in the alcohol aluminum salt, and then reducing the content of impurities in the pseudo-boehmite, thereby effectively removing these solid impurities and impurity ions, and improving the purity of alcohol aluminum.

[0009] In the above hydrolysis reaction process, aluminum alcohol is very easy to be hydrolyzed when it meets water, and accompanied by the polycondensation reaction of aluminum alcohol. As the reaction time increases, aluminum alcohol is completely hydrolyzed to generate pseudo-boehmite hydrolysis products. Pseudo-boehmite is aluminum hydroxide. The pseudo-boehmite crystals just obtained by hydrolysis are incomplete and the particles are small. After a period of aging, the small particles are continuously dispersed, re-accumulated and grown to form a layered structure with stable structure, uniform pore distribution and increased specific surface area. The crystal form is more perfect, the crystal water or impurities between the crystals are less, and the crystals are more dense, which is conducive to improving the purity of pseudo-boehmite.

[0010] After the hydrolysis and aging are completed, the hydrolysis product is filtered, and the filtered pseudo-boehmite is further dispersed into a uniform suspension by beating, which improves the dispersibility of the pseudo-boehmite in the solution, and is more conducive to adjusting the particle size uniformity of the pseudo-boehmite, thereby further improving the purity of the pseudo-boehmite. In addition, the hydrolysis product includes pseudo-boehmite and liquid phase hydrolyzate, and the solid and liquid are separated through the filtering step, and impurities such as suspended matter, unreacted raw materials, and by-products in the hydrolysis product are removed, thereby improving the purity of the pseudo-boehmite. Preferably, in step S1, the catalyst is aluminum isopropoxide.

[0011] In the above technical scheme, the empty orbit of aluminum in aluminum isopropoxide can form a coordination bond with the lone pair of electrons of oxygen of alcoholic hydroxyl group, so that the electron cloud in alcoholic hydroxyl group is more biased towards oxygen atom, so that the hydrogen atom in alcoholic hydroxyl group is more easily ionized, at this time, the hydrogen ion concentration in the solution increases, hydrogen ion reacts with aluminum particles to generate aluminum ion, aluminum ion reacts with alcohol to generate alcohol aluminum salt and hydrogen ion, so that the cycle is repeated, and the catalyst continuously catalyzes the generation of alcohol aluminum salt, thereby improving the reaction efficiency. In addition, aluminum isopropoxide is used as a catalyst, not only other impurities are not introduced in the reaction process, but also the reaction product aluminum isopropoxide can also catalyze the reaction, promote the reaction rate to accelerate, therefore, only a small amount of aluminum isopropoxide needs to be added, a faster reaction rate can be obtained, and it is more conducive to obtaining high-purity pseudo-boehmite.

[0012] 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).

[0013] Preferably, in step S1, the conditions for the reduced pressure distillation are: firstly carry out reduced pressure distillation 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.

[0014] In the above technical scheme, the main components of the mixed liquid after the reaction of alcohol and aluminum are the alcohol aluminum salt generated by the reaction, the unreacted alcohol, water, catalyst and adsorbent, and the alcohol used to prepare the alcohol aluminum salt is mainly isopropanol, which has a boiling point of 82.5°C. It is firstly subjected to reduced pressure distillation at 82-83°C to collect the unreacted alcohol and use it in the alcohol aluminum reaction to reduce costs; then, it is further subjected to reduced pressure distillation to separate the alcohol aluminum salt from other substances, which is conducive to obtaining alcohol aluminum salt with higher purity.

[0015] Preferably, in step S2, the alcohol-water mixed solution is prepared by mixing isopropanol and pure water in a mass ratio of 1:1; and the mass ratio of the alcohol aluminum to the alcohol-water mixed solution is 1:(0.4-2.4).

[0016] In the above technical scheme, the hydrolysis solution is prepared by alcohol and water in a certain proportion, and when the added amount of alcohol aluminum is certain, the added amount of the hydrolysis solution should be controlled within a certain range. If the added amount of the hydrolysis solution is too small, the alcohol aluminum is not completely hydrolyzed, the yield of the obtained pseudo-boehmite is reduced, and the purity of the pseudo-boehmite may be reduced; if the added amount of the hydrolysis solution is too large, excess water remains in the hydrolysis product. During aging, there is more crystallization water between the pseudo-boehmite grains, and the formed grains are larger, but the density of the grains is lower, thereby affecting the purity of the pseudo-boehmite, and also reducing the concentration of the pseudo-boehmite in the hydrolysis product, reducing the crystallization rate of the pseudo-boehmite, and forming smaller grains, which is not conducive to improving the purity of the pseudo-boehmite.

[0017] Preferably, 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.

[0018] In the above technical solution, the hydrolysis reaction conditions and aging conditions will affect the hydrolysis rate and the size of the grains, thereby affecting the quality of the pseudo-boehmite. If the hydrolysis reaction conditions are not suitable, it may lead to incomplete hydrolysis, or a high hydrolysis rate, but the pseudo-boehmite grains are small; if the aging conditions are not suitable, it may lead to grain growth failure, grain defects, etc., which will also affect the purity of the pseudo-boehmite.

[0019] Preferably, 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.

[0020] Preferably, 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 product is obtained by suction filtration, washing, and drying.

[0021] In the above technical scheme, firstly, chitosan is partially carbonized after the hydrothermal reaction, the specific surface area of ​​chitosan is increased, and there are more adsorption sites. Through adsorption, the impurity particles generated during the alcohol aluminum reaction 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, aluminum ions can form layered hydroxides after the hydrothermal reaction, which further increases the specific surface area and makes the adsorption of chitosan stronger. Moreover, the introduction of aluminum can also increase the reaction rate of isopropanol and aluminum to a certain extent, and promote the formation of aluminum isopropoxide.

[0022] Then, the uncarbonized chitosan on the surface of the composite microspheres is carboxymethylated. After carboxymethylation, the surface of the composite microspheres contains more carboxyl groups. The carboxyl group is an acidic group that can ionize hydrogen ions in aqueous solution to form carboxylate anions, which can be electrostatically attracted to positively charged ions, such as iron, calcium, magnesium and other ions. Moreover, the oxygen in the carboxyl group and the nitrogen atom in the amino group have lone pairs of electrons, which can form stable complexes with ions that can provide empty orbitals. This complexation and electrostatic action work together to make the composite microspheres more adsorbent and stable to impurity ions, which is more conducive to the removal of impurities in the alcohol aluminum synthesis process.

[0023] Preferably, in step (1), the mass ratio of chitosan, aluminum nitrate and urea is 1:(0.1-0.2):(0.2-0.5).

[0024] Preferably, in step (2), the mass ratio of the composite microspheres to chloroacetic acid is 1:(1.2-3).

[0025] The above technical solution of the present application includes at least the following beneficial effects: 1. The adsorbent of the present application has a large specific surface area and strong adsorption, and can reduce the influence of impurities on aluminum alcohol during the synthesis of aluminum alcohol; 2. The present application uses a non-toxic catalyst to catalyze the alcohol aluminum reaction process, thereby increasing the reaction rate and not introducing other impurities, which is beneficial to increasing the purity of pseudo-boehmite; 3. After filtering the alcohol aluminum hydrolysis product, the present application adjusts the particle size uniformity of the pseudo-boehmite through a slurrying step to further improve the quality of the pseudo-boehmite. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 3 is a microscopic morphology of pseudo-boehmite prepared by comparative example and example 1. DETAILED DESCRIPTION

[0027] The present application is further described in detail below in conjunction with embodiments.

[0028] Unless otherwise specified, the raw materials used in the examples and comparative examples of the present application are all commercially available.

[0029] Example Example 1 The preparation method of high-purity pseudo-boehmite in this embodiment comprises the following steps: S1: Weigh 100 g of aluminum particles, 1 g of aluminum isopropoxide, and 0.5 g of chitosan with a deacetylation degree of 80%, place them in a reactor, heat them to 100° C., and continuously add 500 g of isopropanol, react and reflux for 12 h, then perform vacuum distillation on the reaction system at 82° C., collect unreacted isopropanol, and after the collection is completed, continue to perform vacuum distillation, collect the fraction at 130-150° C., and obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 80° C. for 6 h, and then age them at 160° C. for 2 h after the hydrolysis is completed to obtain a hydrolysis product; S3: The hydrolysis product is filtered, and the obtained solid product is placed in a blender, and a mixed solution of alcohol and water is added, and the mixture is slurried at a rotation speed of 300 rpm for 15 minutes to form a stable slurry, which is then filtered and vacuum dried to obtain the product.

[0030] Example 2 The preparation method of high-purity pseudo-boehmite in this embodiment comprises the following steps: S1: Weigh 100 g of aluminum particles, 3 g of aluminum isopropoxide and 2 g of chitosan with a deacetylation degree of 80%, place them in a reactor, heat them to 160° C., and continuously add 1200 g of isopropanol, react and reflux for 6 hours, then perform vacuum distillation on the reaction system at 83° C., collect unreacted isopropanol, and after the collection is completed, continue to perform vacuum distillation, collect the fraction at 130-150° C., and obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 160° C. for 2 h, and then age them at 90° C. for 6 h to obtain a hydrolyzate; S3: The hydrolysis product is filtered, and the obtained solid product is placed in a blender, and a mixed solution of alcohol and water is added, and the mixture is beaten at a rotation speed of 450 rpm for 30 minutes to form a stable slurry, which is then filtered and vacuum dried to obtain the product.

[0031] Example 3 The preparation method of high-purity pseudo-boehmite in this embodiment comprises the following steps: S1: Weigh 100 g of aluminum particles, 2.5 g of aluminum isopropoxide, and 1.2 g of chitosan with a deacetylation degree of 80%, place them in a reactor, heat them to 120°C, and continuously add 1000 g of isopropanol, react and reflux for 8 hours, then perform vacuum distillation on the reaction system at 82.5°C, collect the unreacted isopropanol, and after the collection is completed, continue to perform vacuum distillation, collect the fraction at 130-150°C, and obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 120° C. for 4 h, and then age them at 120° C. for 4 h after the hydrolysis is completed to obtain a hydrolysis product; S3: The hydrolysis product is filtered, and the obtained solid product is placed in a blender, and a mixed solution of alcohol and water is added, and the mixture is slurried at a speed of 400 rpm for 30 minutes to form a stable slurry, which is then filtered and vacuum dried to obtain the product.

[0032] Example 4 The preparation method of high-purity pseudo-boehmite in this embodiment is different from that in Example 3 in that: S1: Weigh 100 g of aluminum particles, 2.5 g of aluminum isopropoxide, and 1.2 g of chitosan with a deacetylation degree of 80%, place them in a reactor, heat them to 120°C, and continuously add 1000 g of isopropanol, react and reflux for 8 hours, then perform vacuum distillation on the reaction system at 82.5°C, collect the unreacted isopropanol, and after the collection is completed, continue to perform vacuum distillation, collect the fraction at 130-150°C, and obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 120° C. for 4 h, and then age them at 120° C. for 4 h after the hydrolysis is completed to obtain a hydrolyzate; S3: The hydrolysis product is filtered, and the obtained solid product is placed in a blender, and a mixed solution of alcohol and water is added, and the mixture is slurried at a speed of 400 rpm for 30 minutes to form a stable slurry, which is then filtered and vacuum dried to obtain the product.

[0033] Example 5 The preparation method of high-purity pseudo-boehmite in this embodiment is different from that in Example 3 in that: S1: Weigh 100 g of aluminum particles, 2.5 g of aluminum isopropoxide, and 1.2 g of chitosan with a deacetylation degree of 80%, place them in a reactor, heat them to 120°C, and continuously add 1000 g of isopropanol, react and reflux for 8 hours, then perform vacuum distillation on the reaction system at 82.5°C, collect the unreacted isopropanol, and after the collection is completed, continue to perform vacuum distillation, collect the fraction at 130-150°C, and obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 120° C. for 4 h, and then age them at 120° C. for 4 h after the hydrolysis is completed to obtain a hydrolysis product; S3: The hydrolysis product is filtered, and the obtained solid product is placed in a blender, and a mixed solution of alcohol and water is added, and the mixture is slurried at a speed of 400 rpm for 30 minutes to form a stable slurry, which is then filtered and vacuum dried to obtain the product.

[0034] Example 6 The preparation method of the high-purity pseudo-boehmite in this embodiment is the same as that in Example 5; The modified chitosan of this embodiment is prepared by a method comprising the following steps: (1) Weigh 10 g of chitosan, 1 g of aluminum nitrate and 500 mL of deionized water, mix them evenly, add 2 g of urea while stirring, place the mixture in a high-pressure reactor, react at 110 °C for 12 h, centrifuge the product, wash it with anhydrous ethanol and deionized water until it is neutral, and dry it to obtain composite microspheres; (2) Weigh 2 g of the composite microspheres, add 20 mL of isopropanol, stir for 10 min, slowly add 10 mL of 5 mol / L sodium hydroxide solution and 2.4 g of chloroacetic acid, stir at 65 °C for 4 h, add 4 mL of distilled water, adjust the pH to neutral with glacial acetic acid, filter, wash with anhydrous ethanol, and dry.

[0035] Example 7 The preparation method of the high-purity pseudo-boehmite in this embodiment is the same as that in Example 5; The modified chitosan of this embodiment is prepared by a method comprising the following steps: (1) Weigh 10 g of chitosan, 2 g of aluminum nitrate and 500 mL of deionized water, mix them evenly, add 5 g of urea while stirring, place the mixture in a high-pressure reactor, react at 140 ° C for 6 h, centrifuge the product, wash it with anhydrous ethanol and deionized water until it is neutral, and dry it to obtain composite microspheres; (2) Weigh 2 g of the composite microspheres, add 20 mL of n-butanol, stir for 10 min, slowly add 10 mL of 5 mol / L sodium hydroxide solution and 6 g of chloroacetic acid, stir and react at 80 °C for 2 h, add 4 mL of distilled water, adjust the pH to neutral with glacial acetic acid, filter, wash with anhydrous ethanol, and dry.

[0036] Comparative Example Comparative Example 1 The preparation method of the high-purity pseudo-boehmite in this comparative example comprises the following steps: S1: Weigh 100 g of aluminum particles and 1 g of aluminum isopropoxide and place them in a reactor, heat to 100° C., and continuously add 500 g of isopropanol, react and reflux for 12 hours, then perform vacuum distillation on the reaction system at 82° C., collect unreacted isopropanol, and after collection, continue vacuum distillation to collect fractions at 130-150° C. to obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 80° C. for 6 h, and then age them at 160° C. for 2 h after the hydrolysis is completed to obtain a hydrolysis product; S3: Filter and vacuum dry the hydrolyzate to obtain.

[0037] Comparative Example 2 The preparation method of the high-purity pseudo-boehmite in this comparative example comprises the following steps: S1: Weigh 100 g of aluminum particles and 1 g of aluminum isopropoxide and place them in a reactor, heat to 100° C., and continuously add 500 g of isopropanol, react and reflux for 12 hours, then perform vacuum distillation on the reaction system at 82° C., collect unreacted isopropanol, and after collection, continue vacuum distillation to collect fractions at 130-150° C. to obtain aluminum isopropoxide; S2: prepare an alcohol-water mixed solution with high-purity water and isopropanol in 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 them at 80° C. for 6 h, and then age them at 160° C. for 2 h after the hydrolysis is completed to obtain a hydrolysis product; S3: The hydrolysis product is filtered, and the obtained solid product is placed in a blender, and a mixed solution of alcohol and water is added, and the mixture is slurried at a rotation speed of 300 rpm for 15 minutes to form a stable slurry, which is then filtered and vacuum dried to obtain the product.

[0038] Performance testing 1. Scanning electron microscope observation The pseudo-boehmite prepared in Example 1 and Comparative Example 1 was observed by scanning electron microscope, and its microscopic morphology is as follows: Figure 1 shown.

[0039] 2. Purity test The components of the pseudo-boehmite prepared in Examples 1-7 and Comparative Examples 1-2 were analyzed, and the results are shown in Table 1.

[0040] Table 1 Analysis results of pseudo-boehmite components

[0041] Results Analysis from Figure 1 From the comparison of the two figures, it can be seen that the pseudo-boehmite particles prepared in Comparative Example 1 and Example 1 are piled together, the particle shapes are irregular, and the pseudo-boehmite particles of Comparative Example 1 are unevenly distributed in size, while the pseudo-boehmite particles of Example 1 are smaller in size than those of Comparative Example 1 and are relatively evenly distributed. This may be because the pseudo-boehmite of Example 1 has a higher purity and has fewer crystal defects after the pulping step, which is more conducive to forming particles with smaller particle size and more even distribution.

[0042] LoI in Table 1 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 impurity ions adsorbed by it. It can be seen from the data in Table 1 that the purity of the pseudo-boehmite prepared in the embodiment is above 99.9%, and can even reach 99.99%.

[0043] It can be seen from the data of Comparative Examples 1-2 and Examples 1-3 in Table 1 that in the process of preparing alcohol aluminum salt, the addition of adsorbent is beneficial to improving the purity of pseudo-boehmite, and with the increase in the amount of adsorbent added, the purity of pseudo-boehmite increases to a certain extent, which may be because the addition of adsorbent increases the purity of alcohol aluminum salt, thereby increasing the purity of pseudo-boehmite; in addition, after filtering the hydrolysis product, further pulping to form a uniform slurry is also beneficial to improving the purity of pseudo-boehmite.

[0044] It can be seen from the data of Examples 3-5 in Table 1 that in the hydrolysis process of alcohol aluminum salt, when the amount of alcohol aluminum salt added is constant, the amount of hydrolysis solution added has a greater influence on the hydrolysis reaction. As the amount of hydrolysis solution added increases, the hydrolysis is more complete and the impurity content in the hydrolysis product is less. Therefore, the purity of pseudo-boehmite is higher.

[0045] It can be seen from the data of Examples 5-7 in Table 1 that when modified chitosan is used as the adsorbent, the purity of pseudo-boehmite 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 alcohol aluminum salt and further improving the purity of pseudo-boehmite.

[0046] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

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 is chitosan or 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: Filter the hydrolyzate, slurry the obtained solid product, filter and vacuum dry to obtain the product.

2. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S1, the catalyst is aluminum isopropoxide.

3. 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).

4. 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.

5. 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).

6. 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.

7. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S3, the specific steps of slurrying are: 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.

8. The method for preparing high-purity pseudo-boehmite according to claim 1, characterized in that: In step S1, the modified chitosan is prepared by a method comprising the following steps: (1) Mix chitosan with aluminum nitrate aqueous solution, 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 product is obtained by suction filtration, washing, and drying.

9. The method for preparing high-purity pseudo-boehmite according to claim 8, 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).

10. The method for preparing high-purity pseudo-boehmite according to claim 8, 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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