CN102527442B - A method for preparing an alumina support and the support obtained therefrom - Google Patents

Abstract

The invention relates to a method for preparing an aluminum oxide carrier used in the process of production of a silver catalyst for ethylene oxide through ethylene oxidation and the carrier prepared by the method. The carrier is prepared by substituting a beta-trihydrate aluminum oxide material for a trihydrate alpha-aluminum oxide material. The aluminum oxide carrier prepared by the method has larger specific surface area. In addition, according to the technology, the selecting range of the raw material of the aluminum oxide carrier is enlarged.

Description

A method for preparing an alumina support and the support obtained therefrom

technical field

The present invention relates to a method for preparing an alumina carrier and a carrier prepared thereby, more particularly, the present invention relates to a method for preparing an alumina carrier for a silver catalyst used in the oxidation of ethylene to produce ethylene oxide and thereby prepared carrier.

Background technique

Under the action of silver catalyst, the oxidation of ethylene mainly produces ethylene oxide, and at the same time, side reactions produce carbon dioxide and water. Among them, activity, selectivity and stability are the main performance indicators of silver catalyst. The so-called activity refers to the reaction temperature required when the production process of ethylene oxide reaches a certain reaction load. The lower the reaction temperature, the higher the activity of the catalyst. The so-called selectivity refers to the ratio of the moles of ethylene converted to ethylene oxide in the reaction to the total reaction moles of ethylene. The so-called stability is expressed as the decline rate of activity and selectivity, and the smaller the decline rate, the better the stability of the catalyst. The use of silver catalysts with high activity, high selectivity and good stability in the process of ethylene oxidation to produce ethylene oxide can greatly improve economic benefits, so the manufacture of silver catalysts with high activity, high selectivity and good stability is a silver catalyst research main direction. The performance of the silver catalyst not only has an important relationship with the composition and preparation method of the catalyst, but also has an important relationship with the performance of the carrier used in the catalyst and the preparation method.

The preparation method of silver catalyst in the prior art includes two processes of preparing a porous carrier (such as alumina) and applying active components and auxiliary agents to the carrier.

It is an important research direction to add other components to the alumina carrier to improve the carrier to improve the performance of silver catalysts, including adding alkaline earth metal oxides or other salt compounds. EP0150238 (US4428863) uses a small amount of barium aluminate or barium silicate binder in the manufacturing process of high-purity, low-surface alumina carrier, claiming that it can improve the crushing strength and wear resistance of the carrier, and the specific surface of the prepared carrier is less than 0.3m ² /g, the activity and selectivity of the prepared catalyst are relatively low. US5384302 claims that reducing the Na, K, Ca, and Al ion content in the carrier can improve the crushing strength and wear resistance of the carrier by pretreating α-Al ₂ O ₃ . US5739075 pre-deposits a booster of rare earth metals and another booster of metal salts (alkaline earth metals or VIII transition metals) on the surface of the alumina carrier, followed by calcination, and finally the treated carrier is made into a silver catalyst. The evaluation results show that the selectivity decline rate of the catalyst is smaller than that of the catalyst sample without pre-deposition treatment.

As a mineralizer, fluoride is widely used in the preparation of alumina supports. CN1034678A Mix appropriate particle size and ratio with trihydrate α-alumina and false monohydrate α-alumina and carbonaceous materials, flux, fluoride, binder and water, knead and form, and dry and roast to make α- Alumina carrier. The specific surface of the carrier is 0.2-2m ² /g, and the pores with a pore radius larger than 30μm account for 25-10% of the total pore volume. The support is impregnated with silver compound and co-catalyst, dried and activated, and used for ethylene oxidation to produce ethylene oxide, with a selectivity as high as 83-84%. CN101007287A Mix a certain particle size of trihydrate α-alumina, false monohydrate α-alumina, a certain amount of burnable carbon-containing materials, flux, fluoride, and optional heavy alkaline earth metal compounds, mix well and then add The binder and water are uniformly kneaded, extruded, dried and calcined to make an α-alumina carrier. The specific surface of the carrier is 0.2-2.0m ² /g, the pore volume is 0.35-0.85ml/g, the water absorption rate is ≥30%, and the crushing strength is 30-120N/grain. The carrier is impregnated with the solution of silver amine complex, alkali metal compound and alkaline earth metal compound, dried and activated to prepare a silver catalyst for ethylene epoxidation to prepare oxirane. CN1634652A does not use a pore-forming agent in the preparation of the carrier, but directly mixes α-alumina trihydrate with pseudo-alumina monohydrate, flux, and fluoride in a certain proportion, and then adds binder and water after mixing evenly. Knead evenly, extrude, dry and roast to make α-alumina carrier. The specific surface of the carrier made by the invention is 0.2-2.0m ² /g, the pore volume is 0.35-0.85ml/g, the water absorption rate is more than 30%, and the crushing strength is 20-90N/grain. The carrier is impregnated with the solution of silver amine complex, alkali metal compound and alkaline earth metal compound, dried and activated to prepare silver catalyst for ethylene epoxidation to prepare oxirane.

Although the above-mentioned patent documents use methods such as adding alkaline earth metal compounds or fluorides to the alumina raw material to improve the alumina support, the activity and selectivity of the catalyst are improved to varying degrees, but with the increase of medium and high selectivity silver catalysts For large-scale industrial applications, the requirements for the performance of alumina carriers are also constantly improving. The present invention uses β-alumina trihydrate raw materials instead of α-alumina trihydrate raw materials to prepare carriers. This method can prepare alumina carriers with larger specific surface areas. The alumina support is ultimately beneficial to improve the activity of the silver catalyst. In addition, this technology also broadens the selection range of alumina carrier raw materials.

Contents of the invention

In view of the above-mentioned state of the art, the inventors of the present invention have carried out extensive and in-depth experimental research in the field of silver catalyst and its alumina carrier, and found that the carrier is prepared by using β-alumina trihydrate instead of α-alumina trihydrate , the α-alumina carrier with significantly larger specific surface area can be prepared by this method. Specifically, by adding an appropriate amount of β-alumina trihydrate to the alumina raw material, an α-alumina carrier with a larger specific surface area can be finally prepared. In addition, this technology also broadens the selection range of alumina raw materials.

Therefore, the object of the present invention is to provide a novel vector.

Another object of the present invention is to provide a preparation method of the above carrier.

These and other objects, features and advantages of the present invention will become more apparent after reading this specification.

One aspect of the present invention provides a method for preparing an α-alumina carrier for silver catalysts for ethylene oxidation to produce ethylene oxide, comprising the steps of:

1) Prepare a mixture comprising the following components:

a) beta-alumina trihydrate of 5-90% by weight based on the total weight of all solids of the mixture obtained in step I);

b) based on the total weight of all solids of the mixture obtained in step I) is 5-50% by weight of false monohydrate Al ₂ O ₃ ;

c) 0.01-3.0% by weight of a fluoride mineralizer based on the total weight of all solids in the mixture obtained in step I);

d) a heavy alkaline earth metal compound of 0-2.0% by weight based on the total weight of all solids of the mixture obtained in step I);

e) 10-45% by weight of binder different from components c)-d), based on the total weight of components a)-d); and

f) appropriate amount of water;

The sum of the contents of all solids of the mixture obtained in the above steps 1) is 100% by weight;

II) kneading and molding the mixture obtained in step I) to obtain a shaped body; and

III) drying the molded body obtained in step II), and then calcining it into an α-Al ₂ O ₃ support.

In order to prepare the α-alumina support of the present invention, it is necessary to use β-alumina trihydrate, ie component a). Based on the total weight of all solids in the mixture obtained in step I), the amount of β-alumina trihydrate is usually 5-90% by weight, preferably 15-80% by weight, more preferably 35-80% by weight, especially preferably 65-80% by weight.

Based on the total weight of all solids in the mixture obtained in step I), the amount of pseudo monohydrate Al ₂ O ₃ as component b) is usually 5-50% by weight, preferably 10-40% by weight, more preferably 15- 40% by weight, particularly preferably 15-30% by weight.

When preparing the α-alumina support of the present invention, the addition of the fluoride mineralizer as component c) is to accelerate the crystal transformation of alumina. The fluoride mineralizer used in the present invention is usually inorganic fluoride, including hydrogen fluoride, ammonium fluoride, aluminum fluoride, magnesium fluoride, cryolite, etc., preferably selected from hydrogen fluoride, aluminum fluoride, ammonium fluoride, fluoride One or more of magnesium and cryolite, particularly preferably ammonium fluoride. For the present invention, based on the total weight of all solids in the mixture obtained in step I), the fluoride mineralizer is usually added in an amount of 0.01-3.0% by weight, preferably 0.1-2.5% by weight, particularly preferably 1.2-2.0% by weight.

When preparing the α-alumina support of the present invention, a heavy alkaline earth metal compound, component d), may optionally be used in step I), the purpose of which is to improve the performance of the support. The heavy alkaline earth metal compound is a compound of strontium and/or barium, such as oxides, sulfates, acetates, nitrates and oxalates of strontium and/or barium. Particular preference is given to using barium oxide, barium sulfate, barium nitrate, barium carbonate or mixtures thereof as heavy alkaline earth metal compound. Based on the total weight of all solids in the mixture obtained in step I), the heavy alkaline earth metal compound is added in an amount of 0-2.0%, preferably 0-1.0% by weight, particularly preferably 0-0.5% by weight. When the heavy alkaline earth metal compound in component d) is a heavy alkaline earth metal fluoride, the heavy alkaline earth metal fluoride is not more than 5.0% by weight, preferably not more than 4.0% by weight based on the total weight of all solids in the mixture obtained in step I). When preparing the α-alumina carrier of the present invention, by adding the binder as component e), it forms aluminum sol with pseudo-monohydrate Al ₂ O ₃ in the mixture, and binds each component together to become Extrudable paste. The binders used include acids, such as nitric acid, formic acid, acetic acid, propionic acid and hydrochloric acid, etc., or use aluminum sol to partially or completely replace the fake monohydrate Al ₂ O ₃ and acid. When an acid is used as a binder, an aqueous solution of nitric acid is preferred, wherein the volume ratio of nitric acid to water is 1:1.25-1:10, preferably 1:2-1:4. For the purposes of the invention, the binder is generally added in an amount of 10-45% by weight, preferably 10-35% by weight, particularly preferably 15-30% by weight, based on the total weight of components a)-d).

In a preferred embodiment of preparing the α-alumina carrier of the present invention, in step I), the amount of component a) is 15-80% by weight, based on the total weight of all solids of the mixture obtained in step I), The amount of component b) is 10-40% by weight, the amount of component c) is 0.1-2.5% by weight, and the amount of component d) is 0-1.0% by weight, and/or component e) is based on the component The total weight of a)-d) is 10-35% by weight, wherein the total weight of all solids in the mixture obtained in step I) is 100% by weight.

In a more preferred embodiment of preparing the α-alumina support of the present invention, in step I), the amount of component a) is 35-80% by weight based on the total weight of all solids of the mixture obtained in step I) , the amount of component b) is 15-40% by weight, the amount of component c) is 1.2-2.0% by weight, and the amount of component d) is 0-0.5% by weight, and/or component e) is based on group The total weight of fractions a)-d) is 15-30% by weight, wherein the total weight of all solid fractions of the mixture obtained in step I) is 100% by weight.

In a particularly preferred embodiment of the preparation of the α-alumina support according to the invention, in step I), the amount of component a) is 65-80% by weight, based on the total weight of all solids of the mixture obtained in step I) , component b) in an amount of 15-30% by weight, component c) in an amount of 1.2-2.0% by weight, and component d) in an amount of 0-0.5% by weight, and/or component e) based on group The total weight of fractions a)-d) is 15-30% by weight, wherein the total weight of all solid fractions of the mixture obtained in step I) is 100% by weight.

After kneading the mixture in step I), a paste is usually obtained. It is beneficial to the present invention that usually the components a, b and d are mixed uniformly and then transferred to the kneader, then the components c, e and f are added and kneaded, kneaded into a moldable paste, for example kneaded into a Extruded paste. After the obtained paste is molded, for example, extruded, a molded body is obtained. The molded body can be dried to a moisture content of less than 10% by weight, the drying temperature is 80-120° C., and the drying time is controlled within 1-24 hours according to the moisture content. The shape of the obtained molded body can be annular, spherical, cylindrical or porous cylindrical, or other shapes.

The dried molded body is usually calcined at a temperature of 900-1600°C, preferably 1100-1400°C, for not less than 1 hour, preferably 3-8 hours. By roasting, almost all of the alumina is converted into α-Al ₂ O ₃ , for example, more than 90% of it is converted into α-Al ₂ O ₃ , and the α-Al ₂ O ₃ carrier is obtained.

Therefore, according to another aspect of the present invention, there is also provided an α-alumina support prepared by the above method, the specific surface area of the support is 0.2-2.0m ² /g, and the water absorption rate is not lower than 30%, and The amount of the heavy alkaline earth metal compound is 0.0-2.0% of the carrier weight in terms of alkaline earth metal.

In this paper, the specific surface area of the support was determined by nitrogen physical adsorption BET method. The lateral compressive strength is obtained by using the DL II intelligent particle strength tester, selecting the carrier sample, measuring the radial crushing strength and taking the average value. Water absorption is measured according to the boiling method. The crystal phase composition of alumina was determined by XRD powder diffraction method.

The α-alumina support obtained according to the support preparation method of the present invention can be in a common form in the art, such as a ring, a sphere, a column or a porous column, or other shapes.

After the α-alumina support of the present invention is prepared, the silver catalyst can be prepared by means known to those skilled in the art or conventionally, for example by impregnating the above-mentioned alumina support with a solution containing a silver compound and an organic amine .

The active component silver can be added by traditional impregnation methods, for example, by immersing the support in a silver amine complex solution containing ethylenediamine and ethanolamine, followed by leaching to remove excess solution and heat treatment. As the silver compound used, silver precursor compounds such as silver nitrate and silver oxalate can be used, preferably silver oxalate. In order to ensure the uniform and full loading of silver, it is better to vacuumize the carrier in advance, and after impregnation and leaching, it should be quickly activated in the flow of air or inert gas such as nitrogen, argon, etc. at 200-500 ° C for more than 2 minutes. In order to ensure that the catalyst has high activity, the heat treatment temperature should not be higher than 500°C. In order to further improve the performance of the catalyst, the silver catalyst can also be prepared by adding alkali metal lithium, sodium, potassium, rubidium, cesium compounds or their mixtures, alkaline earth metals such as calcium, strontium, barium compounds or their mixtures, and rhenium compounds. And other additives such as synergistic additives of rhenium, these catalyst additives can be applied to the support before, at the same time or after impregnating silver, and can also be impregnated on the support after the silver compound is reduced.

Example

The present invention will be further described below in conjunction with specific examples, but the scope of the present invention is not limited to these examples.

Carrier Preparation Example 1 (comparison)

Put 3995g α-Al ₂ O ₃ trihydrate, 820g false monohydrate Al ₂ O ₃ and 10g BaSO ₄ into the mixer and mix evenly, then mix another part according to this raw material ratio, and then mix the two parts together Transfer to a kneader. 160 g of NH ₄ F was completely dissolved in 1.90 liters of dilute nitric acid aqueous solution (nitric acid: water = 1: 3, volume ratio), poured into a kneader, and kneaded into a paste that could be extruded. Finally, put the paste into the extruder, extrude it into a column with a diameter of 8.0mm and a length of 6.0mm, and dry it at 80-120°C for more than 2 hours to reduce the free water content to below 10% by weight .

Put the dried column into a natural gas kiln, raise the temperature from room temperature to 1250°C over 18 hours, and then keep the temperature for 4 hours to obtain a white solid product. The XRD analysis of the solid shows that it is α-Al ₂ O ₃ , numbered as carrier 1, and the relevant physical performance data of the carrier are shown in Table 1.

Carrier Preparation Example 2

Put 3995g β-alumina trihydrate, 820g false monohydrate Al ₂ O ₃ and 10g BaSO ₄ into the mixer and mix evenly, then mix another part according to this raw material ratio, and then transfer both parts to in a kneader. 160 g of NH ₄ F was completely dissolved in 2.8 liters of dilute nitric acid solution (nitric acid: water = 1:3, volume ratio), poured into a kneader, and kneaded into a paste that could be extruded. Finally, put the paste into the extruder, extrude it into a column with a diameter of 8.0mm and a length of 6.0mm, and dry it at 80-120°C for more than 2 hours to reduce the free water content to below 10% by weight .

Put the dried column into a natural gas kiln, raise the temperature from room temperature to 1250°C over 18 hours, and then keep the temperature for 4 hours to obtain a white solid product. The XRD analysis of the solid shows that it is α-Al ₂ O ₃ , numbered as carrier 2, and the relevant physical performance data of the carrier are shown in Table 1.

Carrier Preparation Example 3

Put 3995g of β-alumina trihydrate and 820g of false monohydrate Al ₂ O ₃ into the mixer and mix evenly, then mix another part according to this raw material ratio, and then transfer the two parts into the kneader. 160 g of NH ₄ F was completely dissolved in 2.5 liters of dilute nitric acid solution (nitric acid:water=1:3, volume ratio), poured into a kneader, and kneaded into a paste that could be extruded. Finally, put the paste into the extruder, extrude it into a column with a diameter of 8.0mm and a length of 6.0mm, and dry it at 80-120°C for more than 2 hours to reduce the free water content to below 10% by weight .

Put the dried column into a natural gas kiln, raise the temperature from room temperature to 1250°C over 18 hours, and then keep the temperature for 4 hours to obtain a white solid product. The XRD analysis of the solid shows that it is α-Al ₂ O ₃ , numbered as carrier 3, and the relevant physical performance data of the carrier are shown in Table 1.

Carrier Preparation Example 4

Put 3995g of β-alumina trihydrate and 820g of false monohydrate Al ₂ O ₃ into the mixer and mix evenly, then mix another part according to this raw material ratio, and then transfer the two parts into the kneader. 160 g of NH ₄ F was completely dissolved in 2.5 liters of dilute nitric acid solution (nitric acid:water=1:3, volume ratio), poured into a kneader, and kneaded into a paste that could be extruded. Finally, put the paste into the extruder, extrude it into a column with a diameter of 8.0mm and a length of 6.0mm, and dry it at 80-120°C for more than 2 hours to reduce the free water content to below 10% by weight .

Put the dried column into a natural gas kiln, raise it from room temperature to 1300°C over 19 hours, and then keep the temperature for 4 hours to obtain a white solid product. XRD analysis of the solid shows that it is α-Al ₂ O ₃ , numbered as carrier 4, and the relevant physical performance data of the carrier are shown in Table 1.

Table 1 Physical property data of carriers 1-4

It can be clearly seen from Table 1 that at the same calcination temperature, compared with the comparative carrier 1, the carrier 2 and the carrier 3 made of β-alumina trihydrate raw material have larger specific surface areas. Moreover, the carrier 4 produced at a higher calcination temperature still has a larger specific surface area than the carrier 1 .

Claims (14)

1. a method of producing the alpha-alumina supports of oxirane silver catalyst for the preparation of ethylene, comprises the steps:

I) mixture that preparation comprises following component:

A) based on step I) all solids of the gained mixture gross weight of dividing is the β-gibbsite of 5-90% weight;

B) based on step I) all solids of the gained mixture gross weight of dividing is the vacation one water Al of 5-50% weight ₂o ₃;

C) based on step I) all solids of the gained mixture gross weight of dividing is the fluoride-mineralization agent of 0.01-3.0% weight;

D) based on step I) all solids of the gained mixture gross weight of dividing is the heavy alkaline earth metal compound of 0-2.0% weight;

E) be different from amount of component b)-d) based on component a)-gross weight d) is the binding agent of 10-45% weight; With

F) appropriate water;

Above-mentioned steps I) all solids of the gained mixture content sum of dividing is 100% weight;

II) by step I) in the mixture that obtains mediate evenly and moulding, obtain formed body; And

III) drying steps II) in the formed body that obtains, then roasting becomes α-Al ₂o ₃carrier.

2. the method for claim 1, wherein step I) described in as amount of component b) fluoride-mineralization agent be inorganic fluoride.

3. the method for claim 1, wherein step I) described in as amount of component b) fluoride-mineralization agent be to be selected from one or more in hydrogen fluoride, aluminum fluoride, ammonium fluoride, magnesium fluoride and ice crystal.

4. the method for claim 1, wherein step I) described in as amount of component b) fluoride-mineralization agent be ammonium fluoride.

5. the method for claim 1, wherein step I) described in be selected from oxide, sulfate, acetate, nitrate and the oxalates of strontium and/or barium as component heavy alkaline earth metal compound d).

6. the method for claim 1, wherein step I) described in be barium monoxide, barium sulfate, barium nitrate, brium carbonate or its mixture as component heavy alkaline earth metal compound d).

7. the method as described in any one in claim 1-6, wherein step I) described in as component binding agent e) be acid.

8. method as claimed in claim 7, wherein with aluminium sol-fraction or whole acid and false water Al of replacing ₂o ₃.

9. method as claimed in claim 7, wherein said acid is aqueous solution of nitric acid, wherein the volume ratio of nitric acid and water is 1:1.25-1:10.

10. method as claimed in claim 9, wherein the volume ratio of nitric acid and water is 1:2-1:4.

11. methods as described in any one in claim 1-6, wherein at step I) in, based on step I) all solids of the gained mixture gross weight of dividing, component amount a) is 15-80% weight, components b) amount be 10-40% weight, amount of component b) amount be 0.1-2.5% weight, with component amount d) be 0-1.0% weight, and/or component e) based on component a)-gross weight d) is 10-35% weight, wherein step I) all solids of the gained mixture gross weight of dividing is 100% weight.

12. methods as described in any one in claim 1-6, wherein at step I) in, based on step I) all solids of the gained mixture gross weight of dividing, component amount a) is 35-80% weight, components b) amount be 15-40% weight, amount of component b) amount be 1.2-2.0% weight, with component amount d) be 0-0.5% weight, and/or component e) based on component a)-gross weight d) is 15-30% weight, wherein step I) all solids of the gained mixture gross weight of dividing is 100% weight.

13. methods as described in any one in claim 1-6, wherein at step I) in, based on step I) all solids of the gained mixture gross weight of dividing, component amount a) is 65-80% weight, components b) amount be 15-30% weight, amount of component b) amount be 1.2-2.0% weight, with component amount d) be 0-0.5% weight, and/or component e) based on component a)-gross weight d) is 15-30% weight, wherein step I) all solids of the gained mixture gross weight of dividing is 100% weight.

14. 1 kinds of alpha-alumina supports of preparing according to the method described in any one in claim 1-13, it has following feature: specific area is 0.2-2.0m ²/ g; Water absorption rate is not less than 30%; And the amount of heavy alkaline earth metal compound is counted the 0.0-2.0% of vehicle weight with alkaline-earth metal.