Method for preparing porous alumina

Abstract

The invention belongs to the technical field of inorganic material preparation, and discloses a method for preparing porous alumina. The method comprises the following steps: mixing gibbsite serving as a raw material with an organic solvent, then carrying out high-temperature solvothermal reaction, and carrying out filtering, drying and high-temperature calcination on the obtained product to obtain porous alumina with different structures, including sponge-like pores, slit pores, accumulation pores and the like. Different from most pore-forming technologies at present, the preparation method has the advantages that an intermediate product does not need to be treated and additional materials such as a pore-forming agent do not need to be added in the preparation process, the cost is low, the operation steps are simple and convenient, and other impurities are not introduced in the preparation process.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic material preparation, and relates to a method for preparing porous aluminum oxide. Background Art

[0002] Porous alumina is an important type of inorganic material. Compared with other inorganic materials, porous alumina is an ideal adsorbent, catalyst or catalyst carrier due to its high stability, large specific surface area and pore volume, and adjustable surface acidity / alkalinity. At present, the common pore-forming methods for preparing alumina materials mainly include hard template method, soft template method and biological template method.

[0003] Patent CN 102531015 A discloses a method for preparing porous alumina using aluminum inorganic salt as raw material. The invention uses urea as a coprecipitant, adds urea to an inorganic aluminum salt solution, and performs a hydrothermal reaction at 120-180°C for 20 hours, then centrifuges, washes, and dries to obtain an alumina precursor, which is then calcined at 600-1000°C to obtain porous alumina powder.

[0004] Patent CN 102910656 B discloses a method for preparing porous alumina. The invention firstly conducts a sufficient neutralization and gelling reaction between an aluminum salt solution and a precipitant, obtains an alumina precursor through filtration and drying, and then obtains porous alumina through high-temperature calcination.

[0005] Patent CN 108258231 A discloses a method for preparing porous alumina using ammonium aluminum carbonate as an aluminum source. The invention firstly mixes polyvinyl pyrrolidone with an ethanol solution to obtain a dispersed alcohol solution, adds ammonium aluminum carbonate and sodium chloride to the dispersed alcohol solution to obtain a suspension, and then obtains porous alumina through reduced pressure distillation, drying, calcination and other steps.

[0006] Most of the above-mentioned porous alumina preparation technologies use aluminum salts as raw materials, and the corresponding by-products need to be treated. In addition, in order to obtain porous structure products, precipitants or templates need to be used, which will automatically decompose or be manually removed during the preparation process, making recycling difficult and costly; and some pore-forming agents need to be pre-treated by sealing, particle size screening, etc., making the preparation process more complicated.

[0007] Based on the above problems, the present invention uses gibbsite as raw material and proposes a method for preparing porous alumina in an organic solvent, which solves the problems of complicated and expensive preparation process in the existing process and opens up a new path for the preparation of porous inorganic materials. Summary of the invention

[0008] The present invention proposes a method for preparing porous alumina, which uses a simple solvent thermal method to successfully form pores in different organic solvents based on a small number of raw materials, and prepares porous alumina with various pore types and uniform pore size distribution, such as sponge-like pores, slit pores, stacked pores, etc. In order to solve the problems of the prior art that aluminum salts produce by-products, the preparation process is cumbersome and the cost is high, the present invention has found through a large number of experiments that gibbsite can be decomposed at high temperature in an organic solvent to generate a precursor of a porous structure, and the precursor can be calcined at high temperature to obtain porous alumina.

[0009] The technical solution of the present invention:

[0010] A method for preparing porous alumina comprises the following steps:

[0011] (1) After fully mixing gibbsite and an organic solvent, the mixture is placed in a high-pressure reactor, and after a high-temperature solvent thermal reaction, the reactor is naturally cooled;

[0012] (2) taking out the mixture from the reaction kettle, filtering and drying to obtain a precursor;

[0013] (3) The dried product is calcined at high temperature to obtain porous alumina with different pore shapes.

[0014] In step (1), the organic solvent is one or a mixture of two or more of methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, isooctyl alcohol, heptane, octane, toluene, N,N-dimethylformamide, acetylacetone, and tetrahydrofuran.

[0015] In step (1), the solid-to-liquid ratio of gibbsite to the organic solvent is 1:30 to 1:3 g / ml.

[0016] In step (1), the temperature of the high temperature solvent thermal reaction is 160 to 220° C., and the time is 1 to 24 hours.

[0017] In step (3), the calcination temperature is 500-800° C. and the calcination time is 1-6 hours.

[0018] Compared with other existing pore-forming technologies, the advantages of the present invention are: (1) an alumina precursor with uniform pore distribution can be prepared in one step by a solvothermal method, and the preparation process is very simple; (2) the raw materials used in the present invention only contain gibbsite and an organic solvent, and the pore-forming process does not require the addition of template agents, pore-forming agents and other materials, which avoids the introduction of other impurities, inorganic salts and other by-products in the preparation process, greatly reducing labor time, material costs and impurity content of the product; (3) the present invention prepares porous alumina with different pore types in different organic solvents, including sponge-like pores, slit pores, stacked pores, etc., and the pore type of each porous alumina is uniformly distributed, which provides a new idea for preparing porous inorganic materials with different pore types. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FE-SEM morphology of experimental raw material gibbsite.

[0020] Figure 2 XRD spectrum of porous alumina powder prepared in the experiment.

[0021] Figure 3 FE-SEM image of the microstructure of the sponge-like porous alumina prepared in the experiment.

[0022] Figure 4 FE-SEM images of the microstructure of the porous alumina prepared in the experiment; among them, (a) is the ethanol solvent thermal product, (b) is the n-propanol solvent thermal product, (c) is the n-butanol solvent thermal product, (d) is the tetrahydrofuran solvent thermal product, (e) is the N,N-dimethylformamide solvent thermal product, (f) is the isooctyl alcohol solvent thermal product, (g) is the 160°C methanol solvent thermal product, and (h) is the methanol solvent thermal product at a solid-liquid ratio of 1:30 g / ml.

[0023] Figure 5 SEM images of the morphology of the comparative samples prepared in the experiment. DETAILED DESCRIPTION

[0024] The specific implementation of the present invention is further described below in conjunction with the accompanying drawings and technical solutions.

[0025] Embodiment 1:

[0026] Weigh 10 g of gibbsite ( Figure 1) and 60 mL of methanol were put into a polytetrafluoroethylene liner, and a mixture was obtained by sufficient magnetic stirring for 20 min. The liner was then sealed with a stainless steel jacket to obtain an autoclave; the autoclave was placed in a heating box, kept warm at 200°C for 12 h, and then naturally cooled; the reaction mixture was filtered, and the filter cake was placed in a blast drying oven for sufficient drying, and kept warm at 80°C for 8 h to obtain a white solid; the obtained dry product was fully ground in an agate mortar and placed in a corundum crucible, and calcined at high temperature in a muffle furnace, and the temperature was increased to 600°C at a rate of 5°C / min and kept warm for 3 h. After the insulation was completed, it was naturally cooled to room temperature to obtain a product, namely porous alumina. Figure 2 (a) shows the XRD spectrum of the porous alumina obtained in Example 1, and its diffraction peaks correspond one to one with the peaks of the alumina standard card PDF#50-0741. Figure 3 The microscopic morphology of porous alumina obtained by methanol solvent thermal treatment is shown in Figure 1. The macropores of porous alumina formed by methanol solvent thermal treatment are sponge-like. The nitrogen adsorption and desorption test results show that the pore volume of the porous alumina obtained is 1.27 ml / g, the average pore diameter is 32 nm, and the specific surface area is 161 m 2 / g.

[0027] Embodiment 2:

[0028] The preparation process and parameters are the same as those in Example 1, except that ethanol is used as the solvent. Figure 2 Curve (d) shows the XRD spectrum of the calcined material prepared in Example 2, and its diffraction peaks correspond one to one with the peaks of the alumina standard card PDF#50-0741. Figure 4 (a) shows the microscopic morphology of porous alumina obtained under ethanol solvent heat. The macropores of porous alumina formed by ethanol solvent heat are stacked pores. The nitrogen adsorption and desorption test results show that the pore volume of the porous alumina is 0.96mL / g, the average pore diameter is 18nm, and the specific surface area is 211m 2 / g.

[0029] Comparative Example 1:

[0030] The preparation process and parameters are the same as those in Example 1, except that water is used as the solvent. Figure 5 The microscopic morphology of alumina obtained by hydrothermal treatment is shown in the figure. It can be seen that the hydrothermally prepared alumina is a dispersed rhombus block structure without a pore structure. The nitrogen adsorption and desorption test results show that the pore volume of the obtained alumina is 0.02mL / g, the average pore diameter is 3nm, and the specific surface area is 25m 2 / g.

[0031] By comparing the morphology and pore parameters of alumina obtained by hydrothermal and organic solvent thermal methods, it can be seen that organic solvent thermal method can greatly increase the pore volume, pore size and specific surface area of ​​alumina, and obtain porous alumina with different pore shapes and uniform pore size distribution. This proves that organic solvent thermal method has the ability to form pores, which provides a new idea for the preparation of porous materials.

[0032] Embodiment 3:

[0033] The preparation process and parameters are the same as those in Example 1, except that n-propanol is used as the solvent. Figure 2 Curve (e) shows the XRD spectrum of the calcined material prepared in Example 3, and its diffraction peaks correspond one-to-one with the peaks of the alumina standard card PDF#50-0741. Figure 4 (b) shows the microscopic morphology of porous alumina obtained by n-propanol solvent thermal treatment. The macropores of the porous alumina formed by n-propanol solvent thermal treatment are mostly stacked pores.

[0034] Embodiment 4:

[0035] The preparation process and parameters are the same as those in Example 1, except that n-butanol is used as the solvent. Figure 2 Curve (f) shows the XRD spectrum of the calcined material prepared in Example 4, and its diffraction peaks correspond one to one with the peaks of the alumina standard card PDF#50-0741. Figure 4 (c) shows the microscopic morphology of porous alumina obtained by n-butanol solvent thermal treatment. The macropores of the porous alumina formed by n-butanol solvent thermal treatment are mostly stacked pores.

[0036] Embodiment 5:

[0037] The preparation process and parameters are the same as those in Example 1, except that tetrahydrofuran is used as the solvent. Figure 2 Curve (g) shows the XRD spectrum of the calcined material prepared in Example 5, and its diffraction peaks correspond one to one with the peaks of the alumina standard card PDF#50-0741. Figure 4 (d) shows the microscopic morphology of porous alumina obtained by tetrahydrofuran solvent thermal treatment. The macropores of porous alumina formed by tetrahydrofuran solvent thermal treatment are mostly slit pores.

[0038] Embodiment 6:

[0039] The preparation process and parameters are the same as those in Example 1, except that N,N-dimethylformamide is used as the solvent. Figure 2 Curve (h) shows the XRD spectrum of the calcined material prepared in Example 6, and its diffraction peaks correspond one to one with the peaks of the alumina standard card PDF#50-0741. Figure 4(e) shows the microscopic morphology of porous alumina obtained by N,N-dimethylformamide solvent thermal treatment. The macropores of porous alumina formed by N,N-dimethylformamide solvent thermal treatment are mostly stacked pores.

[0040] Embodiment 7:

[0041] The preparation process and parameters are the same as those in Example 1, except that isooctyl alcohol is used as the solvent. Figure 2 (i) Curve 1 shows the XRD spectrum of the calcined material prepared in Example 7, and its diffraction peaks correspond one-to-one to the peaks of the alumina standard card PDF#50-0741. Figure 4 (f) shows the microscopic morphology of porous alumina obtained by isooctanol solvent thermal treatment. The macropores of porous alumina formed by isooctanol solvent thermal treatment are mostly slit pores.

[0042] Embodiment 8:

[0043] The preparation process and parameters are the same as those in Example 1, except that the solvent thermal temperature is 160°C. Figure 2 Curve (b) shows the XRD spectrum of the calcined material prepared in Example 8, and its diffraction peaks correspond one to one with the peaks of the alumina standard card PDF#50-0741. Figure 4 (g) shows the microscopic morphology of the alumina precursor and porous alumina obtained at a solvothermal temperature of 160°C, compared with the product obtained at a solvothermal temperature of 200°C ( Figure 3 )Comparison shows that a slight decrease in the solvothermal temperature will not change the sponge-like pore shape of porous alumina, but the product growth is incomplete when the solvothermal temperature is low, and its pore structure is slightly smaller.

[0044] Embodiment 9:

[0045] The preparation process and parameters are the same as those in Example 1, except that the mass of gibbsite is 2 g. Figure 2 Curve (c) shows the XRD spectrum of the calcined material prepared in Example 9, and its diffraction peaks correspond one-to-one with the peaks of the alumina standard card PDF#50-0741. Figure 4 (h) shows the microscopic morphology of porous alumina obtained when the mass of gibbsite is 2 g, and ( Figure 3 )Comparison shows that reducing the mass of raw materials will not change the sponge-like pore shape of porous alumina, but the product is thicker and has lower crystallinity.

Claims

1. A method for preparing porous alumina, characterized in that: The following steps are involved: (1) After fully mixing gibbsite and an organic solvent, the mixture is placed in a high-pressure reactor, and after a high-temperature solvent thermal reaction, the reactor is naturally cooled; (2) taking out the mixture from the reaction kettle, filtering and drying to obtain a precursor; (3) The dried product is calcined at high temperature to obtain porous alumina with different pore shapes.

2. The method according to claim 1, characterized in that In step (1), the organic solvent is one or a mixture of two or more of methanol, ethanol, n-propanol, n-butanol, n-pentanol, n-hexanol, isooctyl alcohol, heptane, octane, toluene, N,N-dimethylformamide, acetylacetone, and tetrahydrofuran.

3. The method according to claim 1, characterized in that In step (1), the solid-to-liquid ratio of gibbsite to the organic solvent is 1:30 to 1:3 g / ml.

4. The method according to claim 1, characterized in that: In step (1), the temperature of the high temperature solvent thermal reaction is 160 to 220° C., and the time is 1 to 24 hours.

5. The method according to claim 1, characterized in that: In step (3), the calcination temperature is 500-800° C. and the calcination time is 1-6 hours.

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