Wood activated carbon with multi-pore structure and preparation method thereof

Abstract

The invention relates to a method for preparing wood activated carbon with a multi-porous structure, and belongs to the technical field of activated carbon. The preparation method comprises the following steps: 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; 2) grinding and sterilizing the mixture to obtain a mixed raw material; 3) adding the mixed raw material to a reactor, adding potassium hydroxide and deionized water to the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; 4) heating and activating the prefabricated activated carbon, cooling, washing, filtering, and drying to obtain wood activated carbon. The invention uses different raw materials of wood activated carbon, utilizes the different content structures of cellulose and lignin in the raw materials, and combines a plurality of pretreatment methods to pretreat the raw materials to obtain activated carbon with a multi-porous structure.

Description

Technical Field

[0001] The invention belongs to the technical field of activated carbon and relates to a wood activated carbon with a multi-pore structure and a preparation method thereof. Background Art

[0002] Activated carbon is a very fine carbon particle with a large surface area and tiny pores inside. Therefore, activated carbon has a strong adsorption capacity and can purify air or water. The principle of activated carbon purifying water is to use its porosity to adsorb one or more substances in the water into the pores on its surface. The objects to be removed include organic matter, synthetic detergents, microorganisms, viruses or heavy metals, so that the water has a decolorization and deodorization effect.

[0003] In recent years, people have become more and more interested in the adsorption, catalytic, and electrochemical performance of porous carbon materials with multiple pore sizes, because they show better performance than porous carbon with a single pore structure. Due to the complex spatial network structure of the lignin molecules in the raw material of wood activated carbon, it is extremely difficult to prepare multi-layered and hierarchical porous carbon materials by a simple or single method.

[0004] The Chinese patent with publication number CN104386685A discloses a method for preparing nitrogen-doped activated carbon from nitrogen-rich biomass raw materials. The activated carbon is prepared by activation with an activation gas (carbon dioxide, water vapor or air). Although the activated carbon prepared by this method can have the advantages of two different activation methods, this method is prone to pore structure collapse due to over-activation, energy waste, complicated steps, and reduced yield. Summary of the invention

[0005] The purpose of the present invention is to provide a wood activated carbon with a porous structure and a preparation method thereof. The present invention uses different raw materials of wood activated carbon, utilizes the different content structures of cellulose and lignin in the raw materials, and combines a variety of pretreatment methods to pretreat the raw materials to obtain activated carbon with a multi-porous structure, thereby enhancing the application range of the activated carbon; by adding carbon black to the raw material grinding process, adjusting the addition method of potassium hydroxide and deionized water, the activation temperature, etc., finally preparing an activated carbon material with an ultra-high specific surface area and extremely developed pores.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0008] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixed material;

[0009] 2) grinding the mixed material and sterilizing it to obtain a mixed raw material;

[0010] 3) adding the mixed raw materials into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon;

[0011] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon.

[0012] In the scheme of the present invention, potassium hydroxide is added for activation, and the mixed raw material reacts with potassium hydroxide at high temperature, and the reaction consumes C to form a porous structure. Potassium carbonate and potassium oxide are generated in this reaction process, and these two potassium compounds further react with C to generate metallic potassium. When the heating temperature exceeds the boiling point of metallic potassium, the potassium in the mixed raw material diffuses from the inside to the outside in a gaseous form, and further expands the pores longitudinally during the diffusion process, forming an activated carbon material with ultra-high specific surface area and extremely developed pores; wherein the water vapor formed by deionized water in the above activation process also plays a role in expanding the pores.

[0013] As a preferred technical solution of the present invention, in step 1), the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.2-3.5:5-8.

[0014] As a preferred technical solution of the present invention, in step 1), the drying condition is at a temperature of 75-80° C. and drying for 8-10 hours.

[0015] As a preferred technical solution of the present invention, in step 2), the grinding conditions are as follows: after adding carbon black, adjusting the rotation speed to 500-600r / min, the pressure to less than 0.5Pa, and grinding for 30-45min; by adding carbon black to adjust the carbon content of the mixture, the connection strength of the internal structure is strengthened, and at the same time, the added carbon black participates in the reaction between the mixed raw materials and potassium hydroxide, so that more potassium remains inside the mixed raw materials, which is beneficial to more gaseous diffusion from the inside to the outside during the activation process, further improving the gaseous pore expansion ability, further improving the specific surface area of ​​activated carbon and obtaining more pores; the addition of carbon black can effectively avoid the problems of pore structure collapse, energy waste, and reduced yield due to excessive activation in the subsequent mixed raw material activation process.

[0016] As a preferred technical solution of the present invention, in step 2), the mass ratio of the mixture to carbon black is 10-12:0.2-0.5.

[0017] As a preferred technical solution of the present invention, in step 3), the amount of the mixed raw material, potassium hydroxide and deionized water is 1g: 2.0-2.2g: 12-13mL.

[0018] As a preferred technical solution of the present invention, in step 3), the heating treatment condition is to keep warm at 150-160°C for 2.0-2.5h.

[0019] As a preferred technical solution of the present invention, in step 4), the heating activation treatment conditions are as follows: in a nitrogen atmosphere, the temperature is increased to 770-780°C at 3-5°C / min, the activation time is 25-30min, and then the temperature is increased to 880-900°C at 2-3°C / min, and the activation time is 60-65min; by adopting a two-stage heating activation treatment, at a lower activation temperature, the erosion of the mixed raw material can be reduced, the movement of the metallic potassium inside the mixed raw material is relatively gentle, and there is partial decomposition of organic matter. The introduction of carbon black can make more metallic potassium remain in the mixed raw material and strengthen the connection strength inside the mixed raw material. The intensity of the movement of metallic potassium is reduced by temperature control, and the decomposition of organic matter is coordinated to form more pores and prevent collapse.

[0020] As a preferred technical solution of the present invention, in step 4), the cooling condition is cooling to room temperature; the cleaning condition is washing with deionized water for 2-3 times; and the drying condition is drying at 105-110°C for 6-7h.

[0021] Beneficial effects of the present invention:

[0022] The present invention uses different raw materials of wood activated carbon, utilizes the different content structures of cellulose and lignin in the raw materials, and combines a variety of pretreatment methods to pretreat the raw materials to obtain activated carbon with a multi-pore structure, thereby enhancing the application range of the activated carbon; by adding carbon black to the raw material grinding process, adjusting the addition method of potassium hydroxide and deionized water, the activation temperature, etc., finally preparing an activated carbon material with an ultra-high specific surface area and extremely developed pores. DETAILED DESCRIPTION

[0023] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation methods, structures, features and effects of the present invention are described in detail below in combination with the embodiments.

[0024] Example 1

[0025] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0026] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.2:5; and the drying condition is at a temperature of 75° C. and drying for 8 hours;

[0027] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the rotation speed to 500 r / min, the pressure to less than 0.5 Pa, and grinding for 30 minutes; the mass ratio of the mixture to the carbon black is 10:0.2;

[0028] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.0g:12mL; and the heating treatment condition is to keep warm at 150°C for 2.0h;

[0029] 4) The prefabricated activated carbon is subjected to heat activation treatment, cooling, washing, filtering and drying to obtain wood activated carbon; wherein the heating activation treatment conditions are in a nitrogen atmosphere, heating to 770°C at 3°C / min, activation time 25min, then heating to 880°C at 2°C / min, activation time 60min; the cooling condition is cooling to room temperature; the washing condition is washing twice with deionized water; the drying condition is drying at 105°C for 6h.

[0030] Example 2

[0031] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0032] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.9:7.5; and the drying conditions are at a temperature of 78° C. and drying for 9 hours;

[0033] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the speed to 550 r / min, the pressure to less than 0.5 Pa, and grinding for 38 minutes; the mass ratio of the mixture to the carbon black is 11:0.35;

[0034] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.1g:12.5mL; and the heating treatment condition is to keep the temperature at 155°C for 2.2h;

[0035] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 775°C at 4°C / min, the activation time is 28min, and then the temperature is increased to 890°C at 2°C / min, and the activation time is 62min; the cooling condition is cooling to room temperature; the washing condition is washing with deionized water twice; the drying condition is drying at 108°C for 6.5h.

[0036] Example 3

[0037] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0038] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:3.5:8; and the drying condition is at a temperature of 80° C. and drying for 10 hours;

[0039] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the rotation speed to 600 r / min, the pressure to less than 0.5 Pa, and grinding for 45 minutes; the mass ratio of the mixture to the carbon black is 12:0.5;

[0040] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.2g:13mL; and the heating treatment condition is to keep the temperature at 160°C for 2.5h;

[0041] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered, and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 780°C at 5°C / min, the activation time is 30 minutes, and then the temperature is increased to 900°C at 3°C / min, and the activation time is 65 minutes; the cooling condition is cooling to room temperature; the washing condition is washing with deionized water for 3 times; the drying condition is drying at 110°C for 7 hours.

[0042] Example 4

[0043] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0044] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.9:7.5; and the drying conditions are at a temperature of 78° C. and drying for 9 hours;

[0045] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the speed to 550 r / min, the pressure to less than 0.5 Pa, and grinding for 38 minutes; the mass ratio of the mixture to the carbon black is 11:0.42;

[0046] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.1g:12.5mL; and the heating treatment condition is to keep the temperature at 155°C for 2.2h;

[0047] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 775°C at 4°C / min, the activation time is 28min, and then the temperature is increased to 890°C at 2°C / min, and the activation time is 62min; the cooling condition is cooling to room temperature; the washing condition is washing with deionized water twice; the drying condition is drying at 108°C for 6.5h.

[0048] Compared with Example 2, the difference is that the mass ratio of the mixture to carbon black in Example 4 is 11:0.42; the other components, preparation steps and parameters are the same.

[0049] Example 5

[0050] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0051] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.9:7.5; and the drying conditions are at a temperature of 78° C. and drying for 9 hours;

[0052] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the speed to 550 r / min, the pressure to less than 0.5 Pa, and grinding for 38 minutes; the mass ratio of the mixture to the carbon black is 11:0.5;

[0053] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.1g:12.5mL; and the heating treatment condition is to keep the temperature at 155°C for 2.2h;

[0054] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 775°C at 4°C / min, the activation time is 28min, and then the temperature is increased to 890°C at 2°C / min, and the activation time is 62min; the cooling condition is cooling to room temperature; the washing condition is washing with deionized water twice; the drying condition is drying at 108°C for 6.5h.

[0055] Compared with Example 2, the difference is that the mass ratio of the mixture to carbon black in Example 4 is 11:0.5; the other components, preparation steps and parameters are the same.

[0056] Example 6

[0057] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0058] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.9:7.5; and the drying conditions are at a temperature of 78° C. and drying for 9 hours;

[0059] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the speed to 550 r / min, the pressure to less than 0.5 Pa, and grinding for 38 minutes; the mass ratio of the mixture to the carbon black is 11:0.35;

[0060] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.2g:12.5mL; and the heating treatment condition is to keep warm at 155°C for 2.2h;

[0061] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 775°C at 4°C / min, the activation time is 28min, and then the temperature is increased to 890°C at 2°C / min, and the activation time is 62min; the cooling condition is cooling to room temperature; the washing condition is washing with deionized water twice; the drying condition is drying at 108°C for 6.5h.

[0062] Compared with Example 2, the difference is that the amount of the mixed raw material, potassium hydroxide and deionized water used in Example 6 is 1g:2.2g:12.5mL; the other components, preparation steps and parameters are the same.

[0063] Example 7

[0064] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0065] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.9:7.5; and the drying conditions are at a temperature of 78° C. and drying for 9 hours;

[0066] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the speed to 550 r / min, the pressure to less than 0.5 Pa, and grinding for 38 minutes; the mass ratio of the mixture to the carbon black is 11:0.35;

[0067] 3) adding the mixed raw material into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; wherein the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.1g:12.5mL; and the heating treatment condition is to keep the temperature at 155°C for 2.2h;

[0068] 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 775°C at 4°C / min, the activation time is 28min, and then the temperature is increased to 890°C at 2°C / min, and the activation time is 62min; the cooling condition is cooling to room temperature; the washing condition is washing with deionized water twice; the drying condition is drying at 108°C for 6.5h.

[0069] Compared with Example 2, the difference is that the heating activation treatment conditions described in Example 7 are under a nitrogen atmosphere, the temperature is increased to 775°C at 5°C / min, the activation time is 28 minutes, and then the temperature is increased to 890°C at 3°C / min, and the activation time is 62 minutes; the other components, preparation steps and parameters are the same.

[0070] Comparative Example 1

[0071] Compared with Example 2, the difference is that in step 2), no carbon black is used in Comparative Example 1, and the other components, preparation steps and parameters are the same.

[0072] Comparative Example 2

[0073] Step 2) grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the rotation speed to 550 r / min and grinding for 38 min; the mass ratio of the mixture to the carbon black is 11:0.35;

[0074] Compared with Example 2, the difference is that in Example 2, no pressure adjustment is performed during the grinding process in step 2), and the other components, preparation steps and parameters are the same.

[0075] Comparative Example 3

[0076] A method for preparing wood activated carbon with a multi-pore structure, the preparation method comprising the following steps:

[0077] 1) drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixture; wherein the mass ratio of the Sargassum, peanut shells and corn cobs is 1:2.9:7.5; and the drying conditions are at a temperature of 78° C. and drying for 9 hours;

[0078] 2) Grinding the mixture and sterilizing it to obtain a mixed raw material; wherein the grinding conditions are as follows: after adding carbon black, adjusting the speed to 550 r / min, the pressure to less than 0.5 Pa, and grinding for 38 minutes; the mass ratio of the mixture to the carbon black is 11:0.35;

[0079] 3) adding the mixed raw materials into a reactor and heating them to obtain prefabricated activated carbon; wherein the heating treatment condition is to keep the temperature at 210° C. for 2.2 h;

[0080] 4) Add potassium hydroxide and deionized water to the prefabricated activated carbon, stir and mix, heat and activate, cool, wash, filter and dry to obtain wood activated carbon; in step 3)-step 4), the amount of the mixed raw material, potassium hydroxide and deionized water is 1g:2.1g:12.5mL; in step 4), the heating activation treatment conditions are in a nitrogen atmosphere, heating to 775°C at 4°C / min, activation time 28min, and then heating to 890°C at 2°C / min, activation time 62min; the cooling condition is cooling to room temperature; the washing condition is washing twice with deionized water; the drying condition is drying at 108°C for 6.5h.

[0081] Compared with Example 2, the difference lies in the step of adding potassium hydroxide and deionized water in Comparative Example 3; the other components, preparation steps and parameters are the same.

[0082] Comparative Example 4

[0083] Step 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered, and dried to obtain wood activated carbon; wherein the heating and activation treatment conditions are in a nitrogen atmosphere, the temperature is increased to 890°C at 4°C / min, and the activation time is 90 minutes; the cooling conditions are cooling to room temperature; the washing conditions are washed twice with deionized water; and the drying conditions are dried at 108°C for 6.5 hours.

[0084] Compared with Example 2, the difference lies in the heating activation treatment conditions in Comparative Example 4; the other components, preparation steps and parameters are the same.

[0085] The specific surface area, total pore volume and pore size distribution of the activated carbons prepared in Examples 1-7 and Comparative Examples 1-4 were measured. The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] It can be seen from the test results in Table 1 that compared with comparative examples 1-4, the specific surface area and total pore volume of the activated carbon prepared in Examples 1-7 of the present invention are significantly better than those prepared in comparative examples 1-4; and the activated carbon prepared in Examples 1-7 of the present invention has a variety of pore sizes and the proportions are relatively balanced; it can be seen that the present invention finally prepares an activated carbon material with ultra-high specific surface area and extremely developed pores by adding carbon black to the raw material grinding process, adjusting the addition method of potassium hydroxide and deionized water, the activation temperature, etc.

[0089] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as a preferred embodiment as above, it is not used to limit the present invention. Any technical personnel in this field can make some changes or modify the technical contents disclosed above into equivalent embodiments without departing from the scope of the technical solution of the present invention. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing wood activated carbon with a multi-pore structure, characterized in that: The preparation method comprises the following steps: 1) Drying and crushing Sargassum, peanut shells and corn cobs to obtain a mixed material; 2) Grinding and sterilizing the mixed material to obtain a mixed raw material; 3) adding the mixed raw materials into a reactor, adding potassium hydroxide and deionized water into the reactor, stirring and mixing, and heating to obtain prefabricated activated carbon; 4) The prefabricated activated carbon is heated and activated, cooled, washed, filtered and dried to obtain wood activated carbon; In step 2), the grinding conditions are as follows: after adding carbon black, adjusting the rotation speed to 500-600 r / min, the pressure to less than 0.5 Pa, grinding for 30-45 min, and the mass ratio of the mixture to carbon black is 10-12:0.2-0.5; In step 3), the heating treatment condition is to keep the temperature at 150-160°C for 2.0-2.5h; In step 4), the heating activation treatment conditions are as follows: in a nitrogen atmosphere, the temperature is increased to 770-780°C at 3-5°C / min, the activation time is 25-30min, and then the temperature is increased to 880-900°C at 2-3°C / min, the activation time is 60-65min.

2. The method for preparing a wood activated carbon with a multi-pore structure according to claim 1, characterized in that: In step 1), the mass ratio of the sargassum, peanut shells and corn cobs is 1:2.2-3.5:5-8.

3. The method for preparing a wood activated carbon with a multi-pore structure according to claim 1, characterized in that: In step 1), the drying condition is at a temperature of 75-80° C. and drying for 8-10 hours.

4. The method for preparing a wood activated carbon with a multi-pore structure according to claim 1, characterized in that: In step 3), the amount of the mixed raw material, potassium hydroxide and deionized water is 1 g: 2.0-2.2 g: 12-13 mL.

5. The method for preparing a wood activated carbon with a multi-pore structure according to claim 1, characterized in that: In step 4), the cooling condition is cooling to room temperature; the cleaning condition is washing with deionized water for 2-3 times; and the drying condition is drying at 105-110° C. for 6-7 hours.

6. A wood activated carbon with a multi-pore structure prepared by the preparation method according to any one of claims 1 to 5.

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