A spherical alumina catalyst carrier and its preparation method

Abstract

The present invention belongs to the technical field of catalyst carriers, and relates to a spherical alumina catalyst carrier and a preparation method thereof. In the present invention, mercapto sodium alginate, an alumina precursor and a dispersant are mixed to form a suspension slurry, which is ground using alumina as a grinding medium, and then dropped into an aluminum salt solution to form gel beads for aging; after the aged gel beads are washed with deionized water, they are placed in a reaction solution containing ammonium aluminum sulfate for aging for 30-60 minutes, and then ammonium bicarbonate is added and heated in a sealed manner to obtain the spherical alumina catalyst carrier. The present invention combines mercapto sodium alginate and the alginate-assisted gel method to prepare a spherical alumina catalyst carrier. The obtained spherical alumina catalyst carrier beads have high strength, large specific surface area and high pore volume, and are easy to realize industrial continuous production.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalyst carriers, and relates to a spherical alumina catalyst carrier and a preparation method thereof. Background Art

[0002] Due to its special surface properties, pore structure and good stability, alumina has become the most widely used catalyst carrier material. Currently, the preparation process of alumina carrier materials usually involves first preparing an alumina precursor and then forming it into a corresponding shape through a certain forming method. Among them, spherical alumina is widely used in fixed beds and moving beds due to its good rollability, low abrasion and high strength.

[0003] Currently, the main methods for preparing spherical alumina are the rolling method and the oil (ammonia) column method. Recently, there have also been literature patents reporting the use of an aqueous phase forming method. The rolling method mainly utilizes the hydraulicity of fast powder removal. During the rolling process, mother balls are first formed, and then they aggregate and grow during the rolling process and are then cured, dried and calcined to obtain the finished product. This method has low production costs, but has high abrasion and small pore volume. The other two methods mainly use the sol-gel principle for forming, which can effectively solve these shortcomings of the rolling method. CN102718241A discloses a preparation method of spherical alumina. It drops a sodium alginate-pseudoboehmite suspension into an aqueous solution of aluminum, calcium, barium, copper, zinc, manganese or cobalt ions for forming, and after forming or during the forming process, it is treated in an aqueous solution with a pH of 1 to 4 for 10 to 120 minutes to increase the mechanical strength of the product, and then spherical alumina is obtained through drying and calcination. CN102441436A discloses a preparation method of an alumina carrier. The steps for preparing the alumina carrier by this method are as follows: pseudoboehmite dry gel powder and an extrusion aid are mixed evenly, and then an aqueous solution dissolving a physical pore former and a chemical pore former is added and mixed evenly, and then it is extruded into strips on an extruder and then dried and calcined to obtain the alumina carrier. Although using a physical pore former can increase the proportion of macropores, for industrial catalysts, in order to improve the activity of the catalyst, it also needs to have a certain specific surface area and mechanical strength. However, when increasing the macropores, the specific surface area and mechanical strength will be reduced. Therefore, when using a physical pore former for pore expansion, it will be restricted by other performance requirements of the catalyst and often cannot take both into account. Summary of the Invention

[0004] The purpose of the present invention is to solve the problem that mechanical strength and high pore volume cannot be taken into account at the same time.

[0005] Based on the above purpose, the present invention provides a spherical alumina catalyst carrier and a preparation method thereof to meet this need in the field.

[0006] In one aspect, the present invention relates to a method for preparing a spherical alumina catalyst carrier, comprising: mixing sodium mercaptoalginate, an alumina precursor, and a dispersant to form a suspension slurry, grinding the mixture with alumina as a grinding medium, dripping the mixture into an aluminum salt solution to form gel balls, and aging the mixture;

[0007] The aged gel balls are washed with deionized water, placed in a reaction solution containing ammonium aluminum sulfate for 30 to 60 minutes for aging, and then ammonium bicarbonate is added and heated in a sealed manner to obtain the spherical alumina catalyst carrier.

[0008] Furthermore, in the preparation method of the spherical alumina catalyst carrier provided by the present invention, the thiol content in the sodium thiol alginate is 0.4 to 0.8 mmol / g;

[0009] The alumina precursor is pseudo-boehmite;

[0010] The dispersant is one or more of polyethylene glycol, carboxyethyl cellulose, sodium carboxymethyl cellulose, and polyvinyl alcohol.

[0011] Furthermore, in the preparation method of the spherical alumina catalyst carrier provided by the present invention, based on the total mass of the suspension slurry, the content of the sodium mercaptoalginate is 2-7w%, the content of the alumina precursor is 20-30w%, and the content of the dispersant is 1-5w%.

[0012] Furthermore, in the preparation method of the spherical alumina catalyst carrier provided by the present invention, the grinding time is 1 to 6 hours, and the grinding medium is alumina ceramic balls with a diameter of 10 mm and a purity greater than 95%.

[0013] Furthermore, in the preparation method of the spherical alumina catalyst carrier provided by the present invention, the aluminum salt solution is one or more of aluminum sulfate, aluminum nitrate or aluminum chloride;

[0014] The concentration of aluminum ions in the aluminum salt solution is 15-20w%.

[0015] Furthermore, in the preparation method of the spherical alumina catalyst carrier provided by the present invention, the aging temperature is 40-60°C.

[0016] Furthermore, in the preparation method of the spherical alumina catalyst carrier provided by the present invention, the concentration of ammonium aluminum sulfate in the reaction solution containing ammonium aluminum sulfate is 4 to 8 w%;

[0017] After the ammonium bicarbonate is added, the concentration of the ammonium bicarbonate in the reaction solution is 2-10w%.

[0018] Furthermore, in the preparation method of the spherical alumina catalyst support provided by the present invention, the first-stage heating is carried out before the sealed heating, and the second-stage heating and the third-stage heating are carried out after the sealed heating;

[0019] The first-stage heating is as follows: the heating rate is 10 - 20 °C / min and it is maintained at 60 - 80 °C for 2 - 4 h;

[0020] The second-stage heating is as follows: the heating rate is 5 - 10 °C / min and it is maintained at 200 - 230 °C for 2 - 4 h;

[0021] The third-stage heating is as follows: the heating rate is 5 - 10 °C / min and it is maintained at 600 - 700 °C for 4 - 6 h.

[0022] On the other hand, the present invention provides a spherical alumina catalyst support prepared by the above method.

[0023] The present invention has the following beneficial effects or advantages compared with the prior art:

[0024] The present invention uses thiolated sodium alginate with an appropriate thiol content to replace sodium alginate, which is beneficial to improving the strength and specific surface area of the spherical alumina catalyst support. The present invention uses alumina ceramic balls to grind the suspension slurry. On the one hand, it is beneficial to improve the mixing effect of the suspension slurry, and on the other hand, a small amount of alumina incorporated into the suspension slurry is more conducive to the formation and strength improvement of spherical alumina. The present invention controls the time of sealed heating, and through experiments, it is verified that maintaining at 200 - 230 °C for 2 - 4 h is more conducive to the formation of γ-Al2O3. The present invention uses ammonium aluminum sulfate and ammonium bicarbonate as the reaction solution, and NH4Al(OH)2CO3 is attached to the surface of the gel beads, and together with the gel beads, spherical alumina is formed during the final sealed heating process, so that the spherical alumina catalyst support beads have high strength, large specific surface area, and high pore volume. Specific Embodiments

[0025] The technical solutions of the present invention will be described in detail below with reference to specific embodiments. The following embodiments will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that those of ordinary skill in the art can make several modifications and improvements without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

[0026] In the following embodiments, the experimental methods and detection methods are all conventional methods unless otherwise specified; the reagents and materials can be obtained in the market unless otherwise specified.

[0027] Thiolated sodium alginate was purchased from Xi'an Ruixi Biotechnology Co., Ltd.

[0028] Example 1

[0029] This embodiment provides a preparation process of spherical alumina.

[0030] (1) Pseudoboehmite and polyethylene glycol were mixed with an appropriate amount of water, and sodium mercaptoalginate having a thiol content of 0.4 mmol / g was mixed with an appropriate amount of water. The mixture was then placed in a 5 L stirring tank to prepare 3 L of a suspension slurry having a sodium mercaptoalginate content of 2 w%, a pseudoboehmite content of 20 w%, and a polyethylene glycol content of 1 w%.

[0031] (2) The suspension slurry obtained in step (1) is pumped into the stirring tank using a diaphragm pump to transfer the suspension to a 0.6 m 3 The stirred mill is equipped with alumina ceramic balls with a diameter of 10 mm and a purity of >95%. The liquid passing through the stirred mill is returned to the stirring tank using a diaphragm pump and the reaction cycle is 1 hour.

[0032] (3) The suspension slurry obtained in step (2) was dripped into an aluminum sulfate solution with an aluminum ion concentration of 15w% through a 1.0mm pinhole to form gel beads. The gel beads were washed three times with deionized water, placed in a reaction solution of 4w% ammonium aluminum sulfate and aged at 40°C for 30 minutes, and then ammonium bicarbonate was added to the reaction solution until the concentration of ammonium bicarbonate was 2w%.

[0033] (4) The reaction solution obtained in step (3) was kept at a constant temperature of 60°C for 2 hours at a heating rate of 10°C / min, sealed, then kept at a constant temperature of 200°C for 2 hours at a heating rate of 5°C / min, and finally kept at a constant temperature of 600°C for 4 hours at a heating rate of 5°C / min, and naturally cooled to obtain.

[0034] Example 2

[0035] This embodiment provides a preparation process of spherical alumina.

[0036] (1) Pseudoboehmite and carboxyethyl cellulose were mixed with an appropriate amount of water, and sodium mercaptoalginate having a thiol content of 0.5 mmol / g was mixed with an appropriate amount of water. The mixture was then placed in a 5 L stirring tank to prepare 3 L of a suspension slurry having a sodium mercaptoalginate content of 5 w%, a pseudoboehmite content of 25 w%, and a carboxyethyl cellulose content of 3 w%.

[0037] (2) The suspension slurry obtained in step (1) is pumped into the stirring tank using a diaphragm pump to transfer the suspension to a 0.6 m 3 The stirred mill is equipped with alumina ceramic balls with a diameter of 10 mm and a purity of >95%. The liquid passing through the stirred mill is returned to the stirring tank using a diaphragm pump and the reaction cycle is 3 hours.

[0038] (3) The suspension slurry obtained in step (2) is dropped into an aluminum nitrate solution with an aluminum ion concentration of 18 w% through a 1.0 mm pinhole to form gel beads. After washing the gel beads three times with deionized water, they are placed in a reaction solution of 5 w% ammonium aluminum sulfate and aged at 50 °C for 45 min, and then ammonium bicarbonate is added until the concentration of ammonium bicarbonate in the reaction solution is 5 w%.

[0039] (4) The reaction solution obtained in step (3) is heated at a rate of 15 °C / min to 70 °C and held at a constant temperature for 3 h, then sealed, and then heated at a rate of 6 °C / min to 220 °C and held at a constant temperature for 3 h. Finally, it is heated at a rate of 6 °C / min to 650 °C and held at a constant temperature for 5 h, and then obtained after natural cooling.

[0040] Example 3

[0041] This example provides a preparation process of spherical alumina.

[0042] (1) Pseudoboehmite and polyvinyl alcohol are mixed with an appropriate amount of water, and sodium alginate with a thiol content of 0.8 mmol / g is mixed with an appropriate amount of water. Then, the above two are placed in a 5 L stirring tank to prepare 3 L of a suspension slurry with a sodium alginate content of 7 w%, a pseudoboehmite content of 30 w%, and a polyvinyl alcohol content of 5 w%.

[0043] (2) The suspension slurry obtained in step (1) is pumped into a stirred mill containing 10 mm diameter alumina ceramic balls with a purity > 95% using a diaphragm pump. The liquid passing through the stirred mill is pumped back into the stirring tank using a diaphragm pump, and the cyclic reaction is carried out for 6 h. 3 The liquid passing through the stirred mill is pumped back into the stirring tank using a diaphragm pump, and the cyclic reaction is carried out for 6 h.

[0044] (3) The suspension slurry obtained in step (2) is dropped into an aluminum chloride solution with an aluminum ion concentration of 20 w% through a 1.0 mm pinhole to form gel beads. After washing the gel beads three times with deionized water, they are placed in a reaction solution of 8 w% ammonium aluminum sulfate and aged at 60 °C for 60 min, and then ammonium bicarbonate is added until the concentration of ammonium bicarbonate in the reaction solution is 10 w%.

[0045] (4) The reaction solution obtained in step (3) is heated at a rate of 20 °C / min to 80 °C and held at a constant temperature for 4 h, then sealed, and then heated at a rate of 10 °C / min to 230 °C and held at a constant temperature for 4 h. Finally, it is heated at a rate of 10 °C / min to 700 °C and held at a constant temperature for 6 h, and then obtained after natural cooling.

[0046] Comparative Example 1

[0047] This comparative example provides a preparation process of spherical alumina. The test process is the same as that of Example 2, except that sodium alginate is used to replace sodium alginate with thiol groups.

[0048] Comparative Example 2

[0049] This comparative example provides a preparation process of spherical alumina. The test process is the same as that of Example 2, except that the mercapto group content in sodium mercapto alginate is 1.0 mmol / g.

[0050] Comparative Example 3

[0051] This comparative example provides a preparation process of spherical alumina. The test process is the same as that of Example 2, except that grinding is not carried out.

[0052] Comparative Example 4

[0053] This comparative example provides a preparation process of spherical alumina. The test process is the same as that of Example 2, except that the second-stage heating is: maintaining at a constant temperature of 160 °C for 3 h at a heating rate of 6 °C / min.

[0054] Example 4

[0055] This example provides the properties of the above spherical alumina. 100 spherical aluminas were measured in each test, and the results are shown in Table 1 and Table 2.

[0056] Table 1: Specific surface area, pore volume and strength

[0057]

[0058]

[0059] It can be seen from Table 1 that the spherical alumina prepared by the method of Examples 1 to 3 of the present invention has a relatively high specific surface area, a large pore volume, and high strength. In addition, it can be seen from Comparative Examples 1 to 2 that replacing sodium alginate with sodium mercapto alginate helps to improve the strength of spherical alumina, but when the mercapto group content is too high, it will affect other properties of spherical alumina.

[0060] As described above, the present invention can be preferably implemented. The above examples are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various changes and improvements made by those of ordinary skill in the art to the technical solutions of the present invention should fall within the protection scope determined by the present invention.

Claims

1. A preparation method of a spherical alumina catalyst support, characterized in that Comprising: Mix sodium alginate mercapto, alumina precursor and dispersant to make a suspension slurry, grind it with alumina as the grinding medium, then drop it into an aluminum salt solution to form gel beads, and age them; After washing the aged gel beads with deionized water, place them in a reaction solution containing ammonium aluminum sulfate and age for 30 - 60 min, then add ammonium bicarbonate and seal and heat to obtain the spherical alumina catalyst support; The mercapto content in the sodium alginate mercapto is 0.4 - 0.8 mmol / g; The alumina precursor is pseudo-boehmite; The dispersant is one or more of polyethylene glycol, carboxyethyl cellulose, sodium carboxymethyl cellulose, and polyvinyl alcohol; Based on the total mass of the suspension slurry, the content of sodium alginate mercapto is 2 - 7 w%, the content of the alumina precursor is 20 - 30 w%, and the content of the dispersant is 1 - 5 w%; The aging temperature is 40 - 60 °C; The concentration of ammonium aluminum sulfate in the reaction solution containing ammonium aluminum sulfate is 4 - 8 w%; The concentration of ammonium bicarbonate in the reaction solution after adding ammonium bicarbonate is 2 - 10 w%; The aluminum salt solution is one or more of aluminum sulfate, aluminum nitrate, or aluminum chloride; The concentration of aluminum ions in the aluminum salt solution is 15 - 20 w%; Perform the first-stage heating before the sealed heating, and perform the second-stage heating and the third-stage heating after the sealed heating; The first-stage heating is: a heating rate of 10 - 20 °C / min and maintain at 60 - 80 °C for 2 - 4 h; The second-stage heating is: a heating rate of 5 - 10 °C / min and maintain at 200 - 230 °C for 2 - 4 h; The third-stage heating is: a heating rate of 5 - 10 °C / min and maintain at 600 - 700 °C for 4 - 6 h; The grinding time is 1 - 6 h, and the grinding medium is alumina ceramic balls with a diameter of 10 mm and a purity > 95%; 2. A spherical alumina catalyst support, characterized in that, Prepared by the preparation method described in claim 1.

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