CN105753027A - A solid phase preparation method of γ-Al2O3 carrier with high specific surface area - Google Patents

Abstract

The invention discloses a method for preparing solid phases of gamma-Al2O3 carriers with high specific surface areas.Solid-phase reaction is carried out on aluminum salt and additives at the room temperature on the premise that optional solvents are omitted, and then reaction products are roasted to obtain Al2O3.The method includes steps of (1), weighing certain quantities of the aluminum salt and the additives, mixing the aluminum salt and the additives to obtain solid mixtures and grinding the solid mixtures; (2), directly roasting the solid mixtures in air atmosphere to obtain the aluminum oxide carrier.The method has the advantages that the method is easy to implement, short in preparation cycle and high in synthesis efficiency, the optional solvents are omitted, and reaction procedures are easy to control; the aluminum oxide carriers prepared by the aid of the method have the high specific surface areas and large pore volumes and are applicable to hydrotreatment on catalysts.

Description

A solid-phase preparation method of gamma-Al2O3 carrier with high specific surface area

technical field

The invention relates to a method for preparing a gamma-Al ₂ O ₃ carrier with a high specific surface area.

Background technique

γ-Al ₂ O ₃ can be used as a catalyst carrier due to its large specific surface area, porosity, surface acidity and good thermal stability, and is widely used in petrochemical and environmental protection fields. Usually, γ-Al ₂ O ₃ is obtained by heating and dehydrating pseudo-boehmite at a certain temperature. The preparation methods of pseudo-boehmite mainly include carbonization method, aluminum alcohol hydrolysis method, acid method and so on. The carbonization method uses NaAlO ₂ and CO ₂ as raw materials to prepare pseudo-boehmite through the steps of gelation, aging, separation, washing and drying. Large impact, poor process stability. The aluminum alcohol hydrolysis method is that metal aluminum and alcohol generate aluminum alcohol under the action of a catalyst, which is then hydrolyzed, aged, filtered, and dried. The organic solvent used in this method has certain toxicity and high production cost. The acid method is made by adding aluminum sulfate, aluminum nitrate or aluminum chloride and other aluminum salts as raw materials, adding NaAlO ₂ , NaOH, Na ₂ CO ₃ or ammonia water to neutralize it, and then making it through the processes of gelling, aging, washing, and drying. The method has cumbersome steps, many interference factors, and a long preparation period.

Patent USP4448896 provides a method of adding a carbon black pore-enlarging agent during the preparation of alumina, mixing the powdered pore-enlarging agent with pseudo-boehmite dry rubber powder, and extruding them into strips. During carrier calcination, the pore-enlarging agent generates gas after oxidation and combustion, and leaves large pores on the surface of the carrier after volatilization. However, this method has low mechanical strength, scattered and uneven pore distribution, and is difficult to meet industrial requirements. On this basis, patent CN1768946A discloses a method for preparing alumina carrier using starch as a pore-enlarging agent, wherein starch is added in powder form, and the added amount is 10-20wt% of alumina. Pseudo-boehmite dry rubber powder, extrusion aid, water, and starch are mixed and kneaded together, and then dried and roasted to obtain large-pore alumina. For the selection of extrusion aids, refer to patent CN1289825A, which proposes to use squash powder, methylcellulose, starch, and polyvinyl alcohol as extrusion aids, and the amount of extrusion aids is 4-6%. However, starch is rarely used as an extrusion aid because of its high viscosity, which is unfavorable to molding, and it has not been mentioned in the implementation cases. Compared with the carbon black pore expander method, the alumina carrier prepared by the starch pore expander has the characteristics of high strength, large pore size, and concentrated pore distribution, and the preparation process is simple, and the raw material cost and production cost are lower, which is suitable for mass industrial production.

Patent CN102275963A proposes a method of adding a structure-directing agent during the preparation of alumina, mixing inorganic aluminum salt, urea and structure-directing agent with hydrothermal heat for 12 hours, wherein the molar ratio of structure-directing agent and aluminum ion is 0-0.4:1, urea and aluminum ion The ion molar ratio is 3-12:1. After drying and roasting, rod-shaped, aloe-shaped, flake-shaped and spindle-shaped alumina can be prepared respectively, and the specific surface area is 190-820m ² /g. And patent CN103787394A has proposed a kind of method that does not add structure directing agent to prepare high specific surface area alumina, this method is aluminum source with inorganic aluminum salt, urea is precipitating agent, urea and aluminum ion molar ratio 2-10: 1, in different Under the premise of using a structure-directing agent, seal the solution at 140-200°C for 2-12 hours of hydrothermal reaction to obtain pseudo-boehmite, which can be directly dried and roasted without filtering and washing to obtain a higher specific surface area. and aluminum oxide with larger pores. Its advantages are: without filtering and washing, the ammonium nitrate and ammonium carbonate produced by the reaction can be well supported by water and alumina structure, and will not cause the sheet structure to collapse due to drying and loss of water, so that the carrier has a higher At the same time, when these salts are roasted and decomposed by heat, a large amount of gas is generated, which has a good pore expansion effect.

CN101255356A discloses a non-supported catalyst and its preparation method. The catalyst is to mix several metal component precursors with urea and react in a molten state. The molar ratio of urea to metal is 1-5:1, wherein the metal component It can use its metal precursors such as metal oxides, salts, acids, etc., the reaction temperature is 100-200 ° C, the reaction time is 2-10 h, the calcination temperature is 200-500 ° C, the calcination time is 2-8 h, and a kind of nanopore and Catalyst particles with high specific surface area. The advantage of this method is to overcome the disadvantages of hydrothermal reaction and co-precipitation method, adopt the synthesis technology of urea melting reaction, and the reaction speed is fast, so that the prepared metal compound particles themselves have relatively developed pores and large specific surface area, which can provide Abundant active sites for catalytic hydrogenation.

Patent CN1727063A discloses a method for preparing an alumina carrier with a bimodal pore structure. In this method, water, alumina and ammonium aluminum carbonate are mixed, formed and roasted, wherein the weight mixing ratio of water, alumina and ammonium aluminum carbonate is 20-90 : 10-80, the calcination temperature is 450-1000°C and the time is 1-8h. And the patent CN102849763A discloses a solid-phase preparation method of γ-Al ₂ O ₃ with gradient distribution pores. The method is to grind aluminum nitrate, ammonium bicarbonate and inducer polyethylene glycol at room temperature, and obtain aluminum carbonate through aging ammonium, then dried at 50-180°C for 1-20 hours, and then calcined at 350-900°C to obtain alumina. During the decomposition of ammonium aluminum carbonate, gases such as ammonia and carbon dioxide are generated, and the generation and escape of these gases will create some large pores. The slower heating rate during the calcination process is conducive to the slow escape of gaseous substances, which is not easy to cause the collapse of the carrier. The advantage of this method is that it is easy to operate and does not need to add any pore-enlarging agent. The above two methods use the solid-phase method to synthesize the alumina carrier, which is a new way, and compared with the traditional hydrothermal synthesis method, it is simple and easy to operate.

To sum up, the existing methods for preparing γ-Al ₂ O ₃ include pseudo-boehmite roasting method, hydrothermal synthesis method, and solid phase method. Use the hydrothermal synthesis method to prepare intermediates such as pseudo-boehmite or ammonium aluminum carbonate, and then dry and roast to obtain the carrier. The preparation method is cumbersome, has many interference factors, long preparation period, and uses solvents, which have certain environmental impacts. pollution, and the specific surface area and pore volume of the alumina carrier prepared without template agent are relatively small. Using the solid-phase method, the operation is simple, there is no solvent pollution, and a relatively large specific surface area and pore volume are obtained.

Contents of the invention

Aiming at the deficiencies of the prior art, the present invention provides a method for preparing a high specific surface area γ-Al ₂ O ₃ carrier by a solid-phase method. The method does not use any solvent in the preparation process, the preparation method is simple, the production cycle is short, and the obtained Aluminum oxide has a large specific surface area and pore volume and pore size, and is suitable for hydrorefining catalysts.

The present invention is a method for preparing gamma _{- Al2O3} carrier by solid phase method, comprising the following specific steps:

(1) take a certain proportion of aluminum salt and additives respectively;

Preferably, in the step (1), the aluminum salt is selected from aluminum chloride, aluminum nitrate, aluminum sulfate or aluminum isopropoxide;

Preferably, in the step (1), the additives are obtained from urea, starch, citric acid and polyethylene glycol;

Preferably, in the step (1), the relative molecular mass of the additive polyethylene glycol is 2000, 6000, 20000;

Preferably, in the step (1), two combinations of additives are selected, one is to select only a single component of urea, starch, citric acid or polyethylene glycol as an additive, and the other is to select urea, starch, citric acid and Two or more components in polyethylene glycol are used as additives;

Preferably, the weight ratio of one or more of the additives urea, starch, citric acid to polyethylene glycol is 0.2-1;

Preferably, in the step (1), the mass ratio of the total amount of additives to the synthetic Al ₂ O ₃ is 0.5-9;

(2) mixing a certain proportion of aluminum salt and additives, and grinding;

Preferably, in the step (2), the grinding time is 20min～2h;

(3) directly calcining the solid mixture prepared in step (2) in an air atmosphere to obtain the target alumina carrier.

Preferably, in the step (3), the solid mixture is calcined, the calcining temperature is 400-600° C., and the calcining time is 2-5 hours.

The additive used in the present invention decomposes and escapes during the roasting process to produce CO ₂ and NH ₃ .

Compared with the existing hydrothermal synthesis technology, the gamma _{- Al2O3} support prepared by the present invention has the following advantages:

(1) The method of the present invention is to directly utilize aluminum salt and additives to carry out mixed grinding between solid phases, and then obtain the carrier through roasting, that is, the so-called solid phase method, which omits the aging in the preparation process of the intermediate pseudo-boehmite , washing, filtering, drying and a series of steps, the operation process is simple and completed in one step, which greatly shortens the production cycle.

(2) No solvent is used in the whole preparation process of the present invention, which reduces environmental pollution. The aluminum salts and additives used are all environmentally friendly materials, which are harmless to the environment. After the roasting is complete, the gas volatilizes and no impurities remain , in line with the requirements of green chemistry.

(3) Most of the raw materials used in the method of the present invention are cheap and easy to obtain, the production cost and mature technology can be controlled, the requirements for production equipment are not high, and it can be applied to large-scale industrial production.

(4) Compared with the carrier prepared by the hydrothermal synthesis method, the alumina carrier prepared by the method of the present invention has higher specific surface area, pore volume and pore diameter. The characteristics of large pore size and high specific surface area provided by the carrier can be applied to hydrofinishing treatment technologies such as hydrodesulfurization reaction or hydrodemetallization reaction.

Description of drawings

Fig. 1 is the adsorption-desorption curve of the alumina carrier prepared in Example 1.

2 is a pore size distribution diagram of the alumina carrier prepared in Example 1.

detailed description

The following examples are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

The specific preparation method of the alumina carrier provided by the present invention is: take a certain amount of aluminum salt and additives, the aluminum salt is one of aluminum nitrate, aluminum sulfate, aluminum chloride or aluminum isopropoxide, and the additives are urea, One, two or more of starch, citric acid and polyethylene glycol, the mass ratio of the amount of the additive to the synthetic Al ₂ O ₃ is 0.5-9. The aluminum salt and the additive are mixed and ground, and the grinding time is 20 minutes to 2 hours. Then, the solid mixture is calcined at 400-600° C. for 2-5 hours in an air atmosphere to obtain an alumina carrier.

Example 1

The method for preparing alumina: Weigh 7.95g of aluminum chloride respectively, add 15g of polyethylene glycol (M=2000) as an additive, mix and grind for 30min. The solid mixture was then placed in an air atmosphere and calcined at 500° C. for 3 hours to obtain alumina carrier No. 1. The properties of the carrier are shown in Table 1.

Example 2

A method for preparing alumina: weigh 11.9g of aluminum nitrate, add 0.85g of polyethylene glycol (M=6000) as an additive, mix and grind for 60min. The solid mixture was then placed in an air atmosphere and calcined at 400° C. for 5 hours to obtain alumina carrier No. 2. The properties of the carrier are shown in Table 1.

Example 3

A method for preparing alumina: Weigh 7.3g of aluminum isopropoxide, add 6g of polyethylene glycol (M=20000) as an additive, mix and grind for 2 hours. The solid mixture was then placed in an air atmosphere and calcined at 600° C. for 2 hours to obtain alumina carrier No. 3. The properties of the carrier are shown in Table 1.

Example 4

A method for preparing alumina: weigh 7.95g of aluminum chloride, add 1g of additives urea, citric acid, and starch, mix and grind for 90 minutes. The solid mixture was then placed in an air atmosphere and calcined at 580° C. for 140 min to obtain alumina carrier No. 4. The properties of the carrier are shown in Table 1.

Example 5

The method for preparing alumina: weigh 10.8g of aluminum sulfate, the additive is a mixture of polyethylene glycol (M=6000) and urea, both of which have a mass of 7.5g, mix and grind for 45min. The solid mixture was then placed in an air atmosphere and calcined at 450° C. for 4 hours to obtain alumina carrier No. 5. The properties of the carrier are shown in Table 1.

Example 6

The method for preparing alumina: Weigh 11.9g of aluminum nitrate, the additive is a mixture of polyethylene glycol (M=20000), urea, and citric acid, the masses of which are 1g, 0.1g, and 0.1g, respectively, mix and grind for 75min. The solid mixture was then placed in an air atmosphere and calcined at 550° C. for 2.5 hours to obtain alumina carrier No. 6. The properties of the carrier are shown in Table 1.

Example 7

The method for preparing alumina: weigh 7.3g of aluminum isopropoxide, add 2g of additive starch, mix and grind for 20min. The solid mixture was then placed in an air atmosphere and calcined at 480° C. for 140 min to obtain alumina carrier No. 7. The properties of the carrier are shown in Table 1.

Example 8

The method for preparing alumina: Weigh 10.8g of aluminum sulfate, the additive is a mixture of polyethylene glycol (M=2000) and starch, the masses of which are 5g and 1g respectively, mix and grind for 60min. The solid mixture was then placed in an air atmosphere and calcined at 550° C. for 3 hours to obtain alumina carrier No. 9. The properties of the carrier are shown in Table 1.

Example 9

A method for preparing alumina: Weigh 7.95g of aluminum chloride, add polyethylene glycol (M=20000) and citric acid mixture, the mass is 5g and 3g respectively, mix and grind for 60min. The solid mixture was then placed in an air atmosphere and calcined at 450° C. for 4 hours to obtain alumina carrier No. 10. The properties of the carrier are shown in Table 1.

Example 10

The method for preparing alumina: Weigh 7.95g of aluminum chloride without adding any additives, directly place it in an air atmosphere, and calcinate it at 500°C for 3 hours to obtain alumina carrier No. 8. The properties of the carrier are shown in Table 1.

The characterization data of the above carriers were all measured by Tristar II 3020 instrument. The sample tube is pretreated at 300°C for 3 hours, and then the sample tube is hung and installed, and the following data can be obtained.

The properties of the alumina support prepared by the above-mentioned examples of table 1

Claims (7)

1. a high-specific surface area γ-Al₂O₃The method for preparing solid phase of carrier, comprises the following steps:

(1) a certain amount of aluminium salt and additive are weighed, mixing, grind；

(2) by solid mixture directly roasting in air atmosphere obtained in step (1), γ-Al is i.e. obtained₂O₃Carrier；

Aluminium salt in described step (1) is the one in aluminum chloride, aluminum sulfate, aluminum nitrate or aluminum isopropylate.；

Additive in described step (1) is one or more in carbamide, starch, citric acid or Polyethylene Glycol.

Method the most according to claim 1, it is characterised in that: the molecular weight of described Polyethylene Glycol is 2000,6000 or 20000.

Method the most according to claim 1, it is characterised in that: described additive carbamide, starch, one or more of citric acid are 0.2～1 with the weight ratio of Polyethylene Glycol.

4. according to the method described in any one of claims 1 to 3, it is characterised in that: the addition of additive is 0.5～9 with the Al2O3 mass ratio of synthesis.

5. according to the method described in any one of claims 1 to 3, it is characterised in that: milling time controls at 20min～2h.

6. according to the method described in any one of claims 1 to 3, it is characterised in that: described roasting refers to roasting 2～5h at 400～600 DEG C.

7. γ-the Al obtained according to the method described in any one of claims 1 to 3₂O₃Carrier application in hydrodesulfurization reaction or HDM react.