Process for synthesizing mesoporous alumina by taking gibbsite as raw material

Abstract

The invention relates to the technical field of mesoporous alumina materials, and innovatively provides a novel raw material path, i.e., synthesis of an alumina precursor from gibbsite and preparation of high-performance mesoporous alumina through a pyrolysis process: gibbsite is used as an aluminum source, and amorphous alumina is prepared through activation roasting under specific conditions; a precursor is generated through a liquid phase reaction, and the mesoporous alumina material is obtained after roasting. A unique path for converting gibbsite into basic ammonium aluminum carbonate through an activation step is disclosed and reported for the first time. The production cost is greatly reduced by adopting the gibbsite, the synthesis process is pollution-free, and the repeated cyclic utilization of the filtrate is realized. The method ingeniously breaks through the limitation of poor pore structure of the gibbsite, the gibbsite is successfully converted into the mesoporous material with an excellent pore structure, and the specific expression is that the original pore volume of the gibbsite is 0.07 cm < 3 > / g, the aluminum oxide with the pore volume of 0.62 cm < 3 > / g is obtained after conversion, and a new research direction and industrial application prospects are developed for the field of mesoporous aluminum oxide.

Description

Technical Field

[0001] The present invention relates to a process for synthesizing mesoporous alumina using gibbsite as a raw material. The process comprises using gibbsite as an aluminum source and ammonium salts (ammonium carbonate, ammonium bicarbonate) or amide compounds (formamide, acetamide, urea) as modifiers. Basic ammonium aluminum carbonate is prepared by a hydrothermal method, and the mesoporous alumina material is obtained by pyrolysis of the substance. Background Art

[0002] Alumina is a very important catalyst support material. The random, staggered stacking of alumina nanoparticles creates numerous interparticle pores within the support, significantly increasing the catalyst's pore volume. In recent years, considerable research has been conducted on the preparation of alumina with excellent pore structures. Basic ammonium aluminum carbonate is a popular precursor for the synthesis of porous alumina. The alumina obtained by calcination inherits the porous structure of the precursor, and the alumina product obtained by pyrolysis exhibits advantages such as ultrafine quality and high purity, while also being simple to process and easy to operate.

[0003] In the synthesis of basic ammonium aluminum carbonate, researchers generally need to use aluminum salts and ammonium salts to carry out precipitation reaction for synthesis. CN118026231A uses sodium aluminate as the aluminum source, synthesizes AACH by hydrothermal method, and obtains porous nano alumina material after calcination. CN111498881A synthesizes the precursor basic ammonium aluminum carbonate with aluminum sulfate and ammonium bicarbonate, and then obtains alumina particles with uniform particle size through two gradient calcinations. Bai et al. use aluminum nitrate and urea as raw materials, and carry out hydrothermal crystallization in the presence of copolymer P123 to prepare basic ammonium aluminum carbonate with uniform fibrous morphology. The use of aluminum salts or templates in the above synthesis method process will pollute the environment. This research team has invented a method (CN108217702A) for synthesizing basic ammonium aluminum carbonate material by hydrothermal crystallization of urea and pseudo-boehmite, and the obtained basic ammonium aluminum carbonate has an ultra-microporous structure. However, the cost of pseudo-boehmite as a raw material is too high. Therefore, it is urgent to develop new methods to synthesize mesoporous alumina materials that are low-cost, easy to operate, and environmentally friendly.

[0004] Gibbsite is an aluminum hydroxide mineral with the chemical formula Al(OH)3. It belongs to the monoclinic crystal system and exhibits pseudohexagonal plate-like crystals with low surface area and extremely low pore volume. Gibbsite often coexists with minerals such as boehmite (AlO(OH)), diaspore (α-AlO(OH)), hematite, and kaolinite, forming the primary component of bauxite. Compared to gibbsite, gibbsite exhibits higher reactivity in the Bayer process, lowers energy consumption, and reduces costs. With an annual production exceeding 30 million tons, it is a preferred raw material for the development of the aluminum industry. Gibbsite can be used directly as an inorganic flame retardant, commonly used in polymer materials such as plastics and rubber; it can be processed into polyaluminum chloride (PAC) for wastewater treatment; and it can also be used as a separator coating for lithium-ion batteries to enhance high-temperature resistance. With the increasing demand for green manufacturing and resource recycling, the efficient utilization of gibbsite and the development of environmentally friendly processes will become key areas of future research. It would be of great significance if gibbsite could be used as raw material, modified to generate basic ammonium aluminum carbonate and used as a precursor to prepare mesoporous alumina. Summary of the Invention

[0005] In view of the above research background, the present invention uses ammonium salts (ammonium carbonate, ammonium bicarbonate) or amide compounds (formamide, acetamide, urea, etc.) as modifiers and industrial gibbsite (Ziboshan Aluminum) as raw material to prepare basic ammonium aluminum carbonate. Gibbsite is used as the aluminum source, which is calcined and activated, and then ammonium salts or amide compounds are used as modifiers to prepare basic ammonium aluminum carbonate by a hydrothermal method. The aluminum source used in this experimental method does not produce polluting anions and cations during the synthesis process compared to other aluminum salts and aluminates. The synthesized AACH has a high specific surface area (>350m 2 / g), the pore volume reaches 0.6cm 3 / g, the pore size is concentrated in 5-10nm. AACH is decomposed by heating at 300℃ and then calcined at 600℃ to obtain alumina with a pore volume of 0.5cm 3 / g, and the pore size is concentrated in the range of 3-10nm.

[0006] The typical synthesis process is (taking AACH-100-1 as an example):

[0007] a. Dissolve a certain amount of modifier in an appropriate amount of deionized water and stir until the solution is clear; b. Add activated gibbsite in a certain molar ratio to the clarified solution of step a and stir for 30 minutes until uniform. Transfer the turbid solution to a crystallization kettle and crystallize at 100°C for 24 hours. The crystallized solid is washed and dried to obtain basic ammonium aluminum carbonate.

[0008] Compared with the previous preparation method, the present invention has the following advantages:

[0009] (1) The present invention uses a simple physical method—high-temperature calcination—to activate gibbsite. This process effectively destroys the originally dense crystal structure of gibbsite, prompting dehydroxylation reactions between intralayer hydroxyl groups and interlayer hydroxyl groups, creating defects in the gibbsite crystal structure, reducing its crystallinity, significantly enhancing the activity of gibbsite, and creating favorable conditions for subsequent modification. Through inorganic ion intercalation technology, the activated gibbsite is converted into an alumina precursor with a well-developed pore structure, which is then calcined to ultimately produce a high-performance mesoporous alumina material.

[0010] (2) The present invention uses low-cost and easily available gibbsite as an aluminum source and selects ammonium salts or amide compounds as modifiers, which not only avoids the use of expensive templates but also avoids the generation of polluting anions and cations. At the same time, the filtrate can be recycled. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 XRD wide-angle diffraction patterns of the alumina precursor AACH obtained in Examples 1-6 and the comparative example;

[0012] Figure 2 N2 adsorption-desorption isotherms of the alumina precursor AACH obtained in Examples 1-6 and the comparative example;

[0013] Figure 3 is a pore size distribution curve diagram of the alumina precursor AACH obtained in Examples 1-6 and the comparative example;

[0014] Figure 4 N2 adsorption and desorption isotherms of the aluminum oxide obtained in Examples 5-6 and the comparative example;

[0015] Figure 5 The pore size distribution curves of the aluminum oxide obtained in Examples 5-6 and the comparative example are shown;

[0016] Figure 6 The SEM images of the aluminum oxide obtained in Example 6 and the comparative example are shown; DETAILED DESCRIPTION

[0017] The technical solution of the present invention is further described below with reference to some specific examples, but the protection scope of the present invention is not limited thereto.

[0018] Example 1: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared. Then, gibbsite activated in a muffle furnace at 400°C was added at a molar ratio of ammonium bicarbonate to Al of 1. The mixture was stirred for 30 minutes until uniformly dispersed. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-1 was 344.4 m 2 / g, pore volume is 0.44cm 3 / g, and the average pore diameter is 5.13nm.

[0019] Example 2: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared, and then gibbsite activated at 450°C was added at a molar ratio of ammonium bicarbonate to Al of 2.5. The solution was stirred for 30 minutes until the solution was uniform. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-2 was 410.6 m 2 / g, pore volume is 0.56cm 3 / g, and the average pore diameter is 5.43nm.

[0020] Example 3: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared, and then gibbsite activated at 500°C was added at a molar ratio of ammonium bicarbonate to Al of 5. The solution was stirred for 30 minutes until the solution was uniform. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-3 was 407.0 m 2 / g, pore volume is 0.60cm 3 / g, and the average pore diameter is 5.93nm.

[0021] Example 4: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared, and then gibbsite activated at 550°C was added at a molar ratio of ammonium bicarbonate to Al of 7.5. The solution was stirred for 30 minutes until the solution was uniform. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-4 was 339.7 m 2 / g, pore volume is 0.63cm 3 / g, and the average pore diameter is 6.35nm.

[0022] Example 5: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared, and then gibbsite activated at 600°C was added at a molar ratio of ammonium bicarbonate to Al of 10. The solution was stirred for 30 minutes until the solution was uniform. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-5 was 332.8 m 2 / g, pore volume is 0.55cm 3 / g, and the average pore diameter is 6.60nm.

[0023] The AACH-100-5 solid was heated to 600°C at a heating rate of 2°C / min in air atmosphere and calcined at this temperature for 3 hours. The obtained solid was recorded as Example 5-600. The specific surface area of the obtained mesoporous alumina was 220.4 m 2 / g, pore volume is 0.58cm 3 / g, and the average pore diameter is 10.60nm.

[0024] Example 6: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared, and then gibbsite activated at 650°C was added at a molar ratio of ammonium bicarbonate to Al of 12.5. The mixture was stirred for 30 minutes until the solution was uniform. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-6 was 276.2 m 2 / g, pore volume is 0.50cm 3 / g, and the average pore diameter is 7.19nm.

[0025] The AACH-100-6 solid was heated to 600°C at a heating rate of 2°C / min in air atmosphere and calcined at this temperature for 3 hours. The obtained solid was recorded as Example 6-600. The specific surface area of the obtained mesoporous alumina was 210.2 m 2 / g, pore volume is 0.62cm 3 / g, and the average pore diameter is 11.85nm.

[0026] Comparative Example: At room temperature, a certain concentration of ammonium bicarbonate solution was prepared, and then unactivated gibbsite was added at a molar ratio of ammonium bicarbonate to Al of 1. The solution was stirred for 30 minutes until the solution was uniform. The uniform turbid solution was transferred to a crystallization kettle and reacted in an oven at 100°C for 24 hours. The solid material obtained after the reaction was filtered, washed, and dried at 100°C overnight. The specific surface area of the obtained AACH-100-0 was 59.4 m 2 / g, pore volume is 0.07cm 3 / g, and the average pore diameter is 4.76nm.

[0027] The AACH-100-1 solid was heated to 600°C at a heating rate of 2°C / min in air atmosphere and calcined at this temperature for 2 hours. The obtained solid was recorded as Comparative Example-600. The specific surface area of the obtained mesoporous alumina was 206.3 m 2 / g, pore volume is 0.31cm 3 / g, and the average pore diameter is 5.95nm.

[0028] As can be seen from the above embodiments, the present invention discloses a new method for synthesizing a new material of basic ammonium aluminum carbonate and a new method for preparing raw materials of mesoporous alumina by pyrolysis thereof. The synthesis method is simple and cleverly overcomes the limitation of the poor pore structure of the raw material itself, successfully converting it into a mesoporous material with excellent pore structure.

[0029] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A process for synthesizing mesoporous alumina using gibbsite as raw material, characterized in that: The synthesis steps are as follows: (1) calcining and activating gibbsite under certain conditions to obtain amorphous alumina powder; (2) Grind and mix the amorphous alumina powder and the modifier, add an appropriate amount of deionized water and mix and stir for 30 minutes until uniform, transfer to a crystallization kettle, and place the crystallization kettle in an oven for crystallization for 24 hours; (3) The product obtained by crystallization in step (2) is filtered, washed, and dried to obtain an alumina precursor, which is basic ammonium aluminum carbonate; (4) Calcinate basic ammonium aluminum carbonate at 150-800°C to obtain mesoporous alumina.

2. The process for synthesizing mesoporous alumina using gibbsite as raw material according to claim 1, characterized in that: The calcination activation atmosphere of the gibbsite in step (1) is one or more of air atmosphere, nitrogen atmosphere, carbon dioxide atmosphere, etc.

3. The process for synthesizing mesoporous alumina using gibbsite as raw material according to claim 1, characterized in that: The calcination temperature of the gibbsite in step (1) is 100-800°C, preferably 500-700°C.

4. The process for synthesizing mesoporous alumina using gibbsite as raw material according to claim 1, characterized in that: The molar ratio of the modifier to the Al element in step (2) is 0.5-10, preferably 1-3.

5. The process for synthesizing mesoporous alumina using gibbsite as raw material according to claim 1, characterized in that: The modifier in step (2) is an ammonium salt (ammonium carbonate, ammonium bicarbonate) or an amide compound (formamide, acetamide, urea, etc.).

6. The process for synthesizing mesoporous alumina using gibbsite as raw material according to claim 1, characterized in that: The crystallization temperature in step (2) is 50-180°C, preferably 90-120°C.

7. The process for synthesizing mesoporous alumina using gibbsite as raw material according to claim 1, characterized in that: The calcination temperature in step (4) is 300-1000° C., preferably 400-600° C.; the calcination time is 1-6 hours, preferably 1-2 hours.

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