Preparation method of rubber filler

Abstract

The invention belongs to the technical field of inorganic filler modification, and particularly relates to a rubber filler preparation method, which comprises: (1) contacting fly ash with superheated steam in a fluidized bed jet mill, and grinding to obtain a crushed material; (2) after being separated by a grading wheel, the crushed materials and steam enter a connecting pipeline arranged between a fluidized bed jet mill and a first bag-type dust collector; a nozzle is mounted on the connecting pipeline, and a modifier solution and inert gas are respectively added into the connecting pipeline; under the conveying of inert gas, the ultrafine powder is suspended in the connecting pipeline and reacts with the atomized modifier; (3) separating the modified ultrafine powder from steam and inert gas; and (4) separating in a second bag-type dust collector arranged at the top of the buffer bin, and obtaining the superfine modified fly ash filler after separation. The modified filler prepared by the method has the characteristics of small particle size, narrow distribution and good dispersity, and meanwhile, the modification time is shortened on the basis of ensuring the modification effect.

Description

Technical Field

[0001] This invention belongs to the technical field of inorganic filler modification, and particularly relates to a method for preparing rubber fillers. Background Technology

[0002] Rubber is widely used in various fields due to its excellent properties. Natural or synthetic rubber requires the addition of different types of fillers before being processed into rubber products; its usage is the second largest after raw rubber. Rubber fillers include reinforcing and non-reinforcing fillers. Adding fillers can reduce the amount of rubber used, lowering costs, and reinforcing fillers can significantly improve the matrix strength of the rubber and enhance its performance. Currently, the most commonly used reinforcing filler in the rubber industry is carbon black, followed by silica; however, carbon black is expensive, ranging in price from 7,000 to 10,000 yuan per ton.

[0003] Fly ash is a bulk solid waste with characteristics such as low density, large specific surface area, and high mechanical strength. Studies have shown that SiO2 in fly ash can play an additive reinforcing role in rubber and can replace clay and silica; Al2O3 and CaO in fly ash can play an additive role in rubber and can replace special calcium carbonate; SO3 in fly ash plays a sulfur-adding role; and the unburned combustibles in fly ash play a reinforcing role similar to carbon black. It has obvious technical and economic advantages in rubber applications.

[0004] However, fly ash has a particle size range of 0.5 to 300 μm, which is large and unevenly distributed. When used directly in rubber, its reinforcing effect is not good, and it often needs to be ultra-fine processed. In addition, fly ash is an inorganic material, and its direct addition to rubber will result in poor compatibility with rubber. Therefore, its surface modification treatment is required to improve the dispersibility of ultrafine particles and its compatibility with rubber.

[0005] Currently, ultrafine treatment of fly ash includes grading and crushing. Graded ultrafine fly ash retains its original spherical microstructure, but due to limitations in the original fly ash particle size distribution, the quantity of smaller fly ash particles that can be graded is limited. Mechanical grinding has certain limitations on the lower limit of its product size, and it is time-consuming, energy-intensive, and prone to particle agglomeration.

[0006] When modifying fly ash inorganic fillers, it is usually processed to a certain particle size and then the resulting ultrafine powder is mixed with a modifier by stirring. However, this modification method requires a lot of equipment, and in order to ensure the coating rate of the modifier on the powder and improve the modification effect, the modification time is generally long.

[0007] Patent document CN 101654342A discloses a method and dedicated equipment for preparing fine fly ash using low-grade flue gas. The method involves using flue gas generated by boiler combustion to pneumatically convey high-temperature dry-discharge fly ash into a steam pulverizer powered by low-grade superheated steam for pulverization and grading. The pulverized fly ash is then collected by a steam dust collector to obtain an ultrafine fly ash product. The waste steam is discharged by an induced draft fan for use in curing concrete products or thermal insulation wall materials. This invention patent discloses a technique for grinding fly ash using low-grade superheated steam generated by a coal-fired boiler; however, it does not provide a detailed description of the specific fly ash product, its particle size, its uses, or how the pulverized ultrafine fly ash can be modified for application in specific technical fields.

[0008] Patent document CN 106590066A discloses a method for preparing rubber filler, rubber filler, and composite rubber. The method involves washing and wet grinding fly ash aluminum extraction residue with water for 1.5 to 3 hours to obtain finely ground fly ash aluminum extraction slag with D90≤3μm. Then, water and surface modifier are added and surface modification is carried out at room temperature for 15 to 30 minutes. The modified fly ash aluminum extraction residue is then dried and dispersed to obtain rubber filler. However, this patented technology uses mechanical grinding, which takes a long time. Moreover, the modification process is wet modification, which consumes a lot of water. After modification, the filler is easy to agglomerate together, and it needs to be dispersed after drying. The process is complicated and involves many steps.

[0009] Patent document CN 110643074A discloses a reinforced, flame-retardant, and wear-resistant composite rubber filler made from all industrial solid waste and its preparation method. The method involves mixing industrial solid wastes such as stainless steel slag, fly ash, phosphorus slag, magnesium slag, and manganese slag with a composite grinding aid, grinding the mixture using a planetary ball mill for 90-120 minutes, followed by mechanical and chemical treatment for 72-96 hours to obtain an all-industrial solid waste composite ultrafine powder. This powder is then mixed with a surface modifier solution and stirred for 120-150 minutes to obtain the all-industrial solid waste composite rubber filler. However, this patented technology uses a mechanical grinding method, which takes tens of hours and consumes a lot of energy. Furthermore, it does not mention or disclose the particle size of the resulting filler; and the stirring modification method also suffers from a long modification time.

[0010] Patent document CN 102775816A discloses a method for modifying fly ash residue after acid-process aluminum extraction to prepare rubber filler. The method involves washing the fly ash residue after acid-process aluminum extraction until neutral, drying it, pulverizing it to 300 mesh, adding an organic modifier, mixing and grinding at high speed, and aging it to obtain the rubber filler. However, the fly ash used in this patent technology is 300 mesh, which has a large particle size, and the particle size of the modified filler is not mentioned or disclosed.

[0011] Therefore, further research is needed on how to improve the modification process and effect of inorganic fillers used in rubber. Summary of the Invention

[0012] The purpose of this invention is to address the aforementioned problems in the modification process of rubber fillers by providing a method for preparing rubber fillers. The modified filler obtained has small particle size and narrow distribution, and good dispersibility. At the same time, the modification time is shortened while ensuring the modification effect.

[0013] To achieve the above objectives, the present invention provides the following technical solution:

[0014] A method for preparing a rubber filler includes the following steps:

[0015] (1) In a fluidized bed air jet mill, fly ash is brought into contact with superheated steam (accelerated by a laval nozzle). The fly ash moves at high speed in the fluidized bed air jet mill under the drive of the superheated steam, and is crushed by collision with each other to obtain the crushed material.

[0016] (2) The crushed material obtained in step (1) is separated by the classifying wheel (not shown) at the top of the fluidized bed air jet mill. The separated (qualified particle size) ultrafine powder enters the connecting pipe between the fluidized bed air jet mill and the first bag filter together with steam.

[0017] The connecting pipe is equipped with a modifier atomizing nozzle and an inert gas nozzle. The modifier solution and the inert gas (such as nitrogen) are added into the connecting pipe through the nozzles respectively. The modifier solution is atomized through the nozzles. Under the delivery of the inert gas (such as nitrogen), the ultrafine powder is suspended in the connecting pipe and reacts with the atomized modifier to obtain the modified ultrafine powder.

[0018] (3) The modified ultrafine powder obtained in step (2) is introduced into the first bag filter along with steam and inert gas for separation to obtain the separated ultrafine powder.

[0019] (4) The ultrafine powder separated by the first bag filter is removed by the suction device (such as by using hot drying gas introduced by the hot drying gas inlet to replace and remove the entrained steam) and then enters the second bag filter set at the top of the buffer silo for separation. After separation, ultrafine modified fly ash filler with a particle size of 1-10μm (e.g., 2μm, 4μm, 5μm, 6μm, 8μm) is obtained.

[0020] According to the preparation method provided by the present invention, in some embodiments, in step (1), the process parameters of the superheated steam include: steam pressure of 0.5-1.2 MPa (e.g., 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, 1.0 MPa, 1.1 MPa), and steam temperature of 200-320℃ (e.g., 205℃, 210℃, 220℃, 240℃, 250℃, 260℃, 280℃, 285℃, 290℃, 300℃, 310℃, 315℃).

[0021] In some implementations, in step (2), the number of modifier atomizing nozzles and the number of inert gas nozzles in the connecting pipe are both non-zero even numbers (i.e., excluding 0), for example, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.

[0022] In some implementations, in step (2), the radial angle between the modifier atomizing nozzle and the connecting pipe is 30° to 50°, for example, 32°, 34°, 35°, 36°, 38°, 40°, 42°, 45°, 48°.

[0023] In some implementations, in step (2), the radial angle between the inert gas nozzle and the connecting pipe is 30° to 50°, for example, 32°, 34°, 35°, 36°, 38°, 40°, 42°, 45°, 48°.

[0024] In this paper, the radial angles between the modifier atomizing nozzle and the connecting pipe, and the radial angles between the inert gas nozzle and the connecting pipe, can be the same or different. This invention selects the connecting pipe as the site for modification; by setting a certain angle between the nozzle and the connecting pipe, sufficient contact between the ultrafine powder and the modifier can be ensured during the inert gas phase transport process, promoting their reaction or coating.

[0025] In some implementations, in step (2), the contact time between the ultrafine powder and the modifier solution in the connecting pipe is 5 seconds or less, preferably 1 second or less.

[0026] In some implementations, in step (2), the steam pressure in the connecting pipe is -1.5 kPa to -0.5 kPa, for example, -0.6 kPa, -0.7 kPa, -0.8 kPa, -1.0 kPa, -1.2 kPa, -1.4 kPa, or -1.5 kPa.

[0027] In some implementations, in step (2), the total flow rate of the inert gas in the connecting pipe is 310-560 kg / h, for example, 325 kg / h, 320 kg / h, 330 kg / h, 350 kg / h, 380 kg / h, 400 kg / h, 420 kg / h, 450 kg / h, 480 kg / h, 500 kg / h, 520 kg / h, 540 kg / h, 550 kg / h;

[0028] The modification reaction temperature within the connecting pipe is controlled within the range of 105-120℃ (e.g., 110℃, 115℃, 118℃).

[0029] The connecting pipe can also be equipped with a temperature monitoring system and an inert gas delivery monitoring system. By interlocking the temperature monitoring device with the inert gas delivery monitoring, the temperature inside the connecting pipe can be controlled between 105-120℃ by adjusting the inert gas flow rate, ensuring excellent modification effects. Controlling the temperature inside the connecting pipe by the inert gas flow rate prevents water vapor condensation when the modification temperature inside the connecting pipe is below 105℃. When the modification temperature inside the connecting pipe exceeds the 105-120℃ range, the inert gas flow rate can be increased to lower the pipe temperature, preventing excessively high temperatures from adversely affecting the modifier's effect.

[0030] In step (3), the process conditions and operation procedures for separating the material in the first bag filter can be conventional choices in the field, and will not be elaborated here.

[0031] In some embodiments, in step (4), the modifier solution is a hydrolysate containing a modifier (e.g., the modifier solution includes a modifier and a water / alcohol mixture, wherein the modifier is hydrolyzed in an appropriate amount of water / alcohol mixture);

[0032] In some embodiments, the mass ratio of the modifier to the water / alcohol mixture in the modifier solution is 1:(4-160), for example, 1:5, 1:10, 1:15, 1:20, 1:30, 1:50, 1:80, 1:100, 1:120, 1:140, 1:150.

[0033] In some embodiments, the modifier is selected from one or more of silane coupling agents, aluminate coupling agents, titanate coupling agents, and stearic acid.

[0034] In some embodiments, the mass ratio of silane coupling agent, titanate coupling agent, aluminate coupling agent, and stearic acid in the modifier is 1:(0-1):(0-0.5):(0-0.5). For example, if a titanate coupling agent is present in the modifier, the mass ratio of silane coupling agent to titanate coupling agent can be 1:0.2, 1:0.4, 1:0.5, 1:0.6, 1:0.8, or 1:1; if an aluminate coupling agent is present, the mass ratio of silane coupling agent to aluminate coupling agent can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, or 1:0.5; and if stearic acid is present, the mass ratio of silane coupling agent to stearic acid can be 1:0.1, 1:0.2, 1:0.3, 1:0.4, or 1:0.5.

[0035] In some implementations, in step (4), the amount of the modifier added is 1wt%-5wt% of the mass of the fly ash to be modified, for example, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%.

[0036] Compared with the prior art, the beneficial effects of the technical solution of the present invention are at least as follows:

[0037] (1) The preparation process of ultrafine powder of the present invention uses superheated steam to grind the powder, which can improve the product flowability and grinding efficiency, and the obtained product has small particle size and narrow distribution. At the same time, since superheated steam does not carry static electricity, it avoids the phenomenon of agglomeration of the powder obtained after grinding, avoids agglomeration, and has the characteristics of good dispersibility.

[0038] (2) The high temperature during superheated steam pulverization can affect the modification effect of the modifier on the powder. After classification, the qualified ultrafine powder is carried by superheated steam through the connecting pipe to the downstream bag filter for product collection and gas-solid separation due to the suction effect of the subsequent induced draft fan. Since the temperature of the superheated steam is around 170-180℃, the excessively high temperature can lead to side reactions during modification. Therefore, in order to ensure the modification effect of the modifier while preventing the generation of condensate, this invention introduces an appropriate amount of inert gas (such as N2) into the connecting pipe to reduce the temperature. Combined with the temperature control system and the interlocking control system, the material modification reaction temperature in the connecting pipe is ensured to be between 105-120℃. When the temperature in the connecting pipe exceeds the range, the flow rate of the inert gas (such as N2) can be increased to reduce the pipe temperature, and vice versa. This ensures that the modification process in the pipe is carried out at a suitable temperature, thereby improving the modification effect of the powder.

[0039] The modification process of this invention is carried out under dilute phase flow, which can greatly shorten the modification time. The ultrafine powder is transported by inert gas, and the modifier is atomized and enters the connecting pipe. The atomizing nozzle is at a certain angle to the pipe, which enables the powder and modifier to spiral forward in the pipe, thus promoting full contact between the modifier and the ultrafine powder, and shortening the modification time while ensuring the modification effect. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the apparatus used in a preparation method according to one embodiment of the present invention;

[0041] Figure 2 for Figure 1 The diagram shows a pipe (connecting pipe between the fluidized bed air jet mill and the first bag filter) in the device, which includes a modifier atomizing nozzle and an inert gas nozzle.

[0042] The labels in the diagram are explained as follows:

[0043] 1- Fluidized bed air jet mill, 2- Connecting pipe, 21- Inert gas nozzle, 22- Modifier atomizing nozzle, 3- First bag filter, 4- Suction equipment, 5- Second bag filter, 6- Buffer silo. Detailed Implementation

[0044] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.

[0045] In the following examples and comparative examples, the sources of some reagents or raw materials used, unless otherwise specified, are all conventional products that can be purchased commercially; among them,

[0046] The main components and their contents of the fly ash used in each embodiment and comparative example are shown in Table 1:

[0047] Table 1. Main components and content of fly ash

[0048]

[0049] Note: The balance refers to trace amounts of other components.

[0050] Example 1

[0051] The preparation method of rubber filler is referred to Figure 1 The schematic diagram includes the following steps:

[0052] (1) In the fluidized bed air jet mill 1, the feed of fly ash to be modified (particle size 100-200μm) is brought into contact with superheated steam accelerated by the laval nozzle. The fly ash moves at high speed under the conditions of steam pressure of 0.9MPa and steam temperature of 240℃, and is crushed by mutual collision to obtain the crushed material.

[0053] (2) The crushed material obtained in step (1) is separated by the classifying wheel (not shown) at the top of the fluidized bed air jet mill. The separated ultrafine powder and steam enter the connecting pipe 2 between the fluidized bed air jet mill 1 and the first bag dust collector 3.

[0054] like Figure 2 As shown, two modifier atomizing nozzles 22 and two inert gas nozzles 21 are installed on the connecting pipe 2. The radial angle between the modifier atomizing nozzle and the connecting pipe is 45°, and the radial angle between the inert gas nozzle and the connecting pipe is 45°. Modifier solution and N2 are added into the connecting pipe through the nozzles, respectively, and the total flow rate of N2 is controlled at 390 kg / h. Combined with the temperature control device and interlocking system, the modification temperature in the connecting pipe is maintained at 110°C, and the steam pressure in the connecting pipe is -1.0 kPa.

[0055] In a 10wt% modifier solution, the solute is silane coupling agent KH570 and the solvent is a water / alcohol mixture. The amount of silane coupling agent added is 2wt% of the mass of the fly ash to be modified.

[0056] Inside the connecting pipe, the modifier solution is atomized through a nozzle. Under the delivery of N2, the ultrafine powder is suspended in the connecting pipe and reacts with the atomized modifier to obtain the modified ultrafine powder. Inside the connecting pipe, the contact time between the ultrafine powder and the modifier solution is 1 second or less.

[0057] (3) The modified ultrafine powder obtained in step (2) is introduced into the first bag filter 3 together with steam and N2 for separation to obtain the separated ultrafine powder.

[0058] (4) The ultrafine powder separated by the first bag filter is removed by the hot drying gas introduced by the hot drying gas inlet under the action of the suction device 4, and then enters the second bag filter 5 set at the top of the buffer silo 6 for separation. The ultrafine modified fly ash filler obtained after separation flows into the buffer silo 6 located below.

[0059] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 5.184 μm and an activation index of 81%.

[0060] Example 2

[0061] The preparation process of the rubber filler is the same as in Example 1, except that the radial angle between the modifier atomizing nozzle and the connecting pipe is 30° and the radial angle between the inert gas nozzle and the connecting pipe is 30°; the rest of the steps are the same as in Example 1.

[0062] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 6.527 μm and an activation index of 79%.

[0063] Example 3

[0064] The preparation process of the rubber filler is the same as in Example 1, except that: in step (2), the total flow rate of N2 is adjusted to 310 kg / h, so that the modification temperature in the connecting pipe is 120°C; the rest of the steps are the same as in Example 1.

[0065] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 5.861 μm and an activation index of 72%.

[0066] Example 4

[0067] The preparation process of the rubber filler is the same as in Example 1, except that: in step (2), the total flow rate of N2 is adjusted to 420 kg / h, so that the modification temperature in the connecting pipe is 105°C; the rest of the steps are the same as in Example 1.

[0068] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 5.377 μm and an activation index of 83%.

[0069] Comparative Example 1

[0070] The preparation process of the rubber filler is the same as in Example 1, except that: in step (2), the total flow rate of N2 is adjusted to 820 kg / h, so that the modification temperature in the connecting pipe is 90°C; the rest of the steps are the same as in Example 1.

[0071] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 20.479 μm and an activation index of 32%.

[0072] Comparative Example 2

[0073] The preparation process of the rubber filler is the same as in Example 1, except that the radial angle between the modifier nozzle and the connecting pipe is 0° and the radial angle between the inert gas nozzle and the connecting pipe is 0°; the rest of the steps are the same as in Example 1.

[0074] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 10.742 μm and an activation index of 65%.

[0075] Comparative Example 3

[0076] The preparation process of the rubber filler is the same as in Example 1, except that: in step (2), the connecting pipe is not equipped with a modifier atomizing nozzle and the modifier solution is not sprayed into the pipe; instead, in step (4), the obtained ultrafine powder is mixed with the modifier solution in the buffer silo 6 for modification, and the stirring time is 30 min; the remaining steps are the same as in Example 1.

[0077] The obtained ultrafine modified fly ash was tested and found to have a particle size D90 of 6.941 μm and an activation index of 58%.

[0078] The ultrafine modified fly ash (rubber filler) prepared in each embodiment and comparative example is applied in rubber preparation, wherein the formulation is as follows:

[0079]

[0080]

[0081] In the table, the dosage of each of the other components is based on a rubber dosage of 100 parts.

[0082] According to the formula shown in Table 1, the raw rubber was plasticized by passing it through a two-roll mill for 2 minutes. Zinc oxide (ZnO) and stearic acid were added and mixed for 2 minutes. Then carbon black and ultrafine modified fly ash prepared in Examples 1-4 and Comparative Examples 1-3 were added and mixed for 5 minutes. After wrapping the mill with rollers, sulfur and accelerator TBBS (at 45-50℃) were added. After the material was fed, it was cut 4 times on each side and passed through the mill 6 times. It was then left to stand at room temperature for 16 hours. After that, it was vulcanized using a flat vulcanizing machine at a vulcanization temperature of 150℃. After vulcanization for a certain time, it was left to stand for 24 hours to obtain the rubber product.

[0083] The rubber products prepared as described above were subjected to relevant tests, and the test results are shown in Table 2 below.

[0084] Table 2 Performance Tests of Rubber Products

[0085]

[0086] This invention utilizes a connecting pipe as the modification site for the powder, and the introduction of inert gas not only controls the modification temperature within a suitable range, promoting the modification effect, but also ensures sufficient contact between the ultrafine powder and the modified agent after atomization, due to the inert gas transport of the ultrafine powder and the atomizing nozzle being at a certain angle to the pipe. This allows the powder and modified agent to spiral forward within the pipe. The resulting modified rubber filler product has a small particle size (1-10 μm) and narrow distribution, while avoiding agglomeration of the powder obtained after grinding, thus preventing clumping and exhibiting good dispersibility. Furthermore, it shortens the modification time while maintaining the modification effect. The test results in Table 2 also show that the modified rubber filler obtained by this invention has a good modification effect, and its application in rubber processing results in products with excellent mechanical properties and wear resistance.

[0087] Although Comparative Example 1 modified fly ash within the connecting pipe, the improper control of the modification temperature resulted in a modified rubber filler product with a large particle size and a low activation index. In Comparative Example 2, the modifier nozzle and inert gas nozzle within the connecting pipe were not set at an angle to the radial direction of the connecting pipe, leading to poor modification of the inorganic filler. In Comparative Example 3, the powder was not modified within the connecting pipe, also resulting in poor modification of the inorganic filler. The modified rubber fillers obtained in each comparative example showed poor modification effects, and their application in rubber processing resulted in products with poor mechanical properties and wear resistance.

[0088] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. A method for preparing a rubber filler, characterized in that, Includes the following steps: (1) In a fluidized bed air jet mill, fly ash is brought into contact with superheated steam. The fly ash moves at high speed in the fluidized bed air jet mill under the drive of the superheated steam, and is crushed by mutual collision to obtain the crushed material. (2) The pulverized material obtained in step (1) is separated by the classifier wheel at the top of the fluidized bed air jet mill. The separated ultrafine powder and steam enter the connecting pipe between the fluidized bed air jet mill and the first bag filter. The connecting pipe is equipped with a modifier atomizing nozzle and an inert gas nozzle. Modifier solution and inert gas are added into the connecting pipe through the nozzles, respectively. The modifier solution is atomized through the nozzles. Under the delivery of inert gas, the ultrafine powder is suspended in the connecting pipe and reacts with the atomized modifier to obtain modified ultrafine powder. (3) The modified ultrafine powder obtained in step (2) is introduced into the first bag filter for separation along with steam and inert gas; (4) After the ultrafine powder separated by the first bag filter is removed by the suction device, it enters the second bag filter set at the top of the buffer silo for separation. After separation, ultrafine modified fly ash filler with a particle size of 1-10μm is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), the process parameters of the superheated steam include: steam pressure of 0.5-1.2 MPa and steam temperature of 200-320℃.

3. The preparation method according to claim 1 or 2, characterized in that, In step (2), the number of modifier atomizing nozzles and the number of inert gas nozzles in the connecting pipe are both non-zero even numbers.

4. The preparation method according to any one of claims 1-3, characterized in that, In step (2), the radial angle between the modifier atomizing nozzle and the connecting pipe is 30° to 50°; the radial angle between the inert gas nozzle and the connecting pipe is 30° to 50°.

5. The preparation method according to any one of claims 1-4, characterized in that, In step (2), the contact time between the ultrafine powder and the modifier solution in the connecting pipe is 5 seconds or less, preferably 1 second or less.

6. The preparation method according to any one of claims 1-5, characterized in that, In step (2), the steam pressure in the connecting pipe is -1.5 kPa to -0.5 kPa.

7. The preparation method according to any one of claims 1-6, characterized in that, In step (2), the flow rate of the inert gas in the connecting pipe is 310-560 kg / h; The temperature of the modification reaction within the connecting pipe is controlled within the range of 105-120℃.

8. The preparation method according to any one of claims 1-7, characterized in that, In step (4), the modifier solution is a hydrolysate containing a modifier; In the modifier solution, the mass ratio of the modifier to the water / alcohol mixture is 1:(4-160).

9. The preparation method according to claim 8, characterized in that, The modifier is selected from one or more of silane coupling agents, aluminate coupling agents, titanate coupling agents, and stearic acid; Preferably, the mass ratio of silane coupling agent, titanate coupling agent, aluminate coupling agent and stearic acid in the modifier is 1:(0-1):(0-0.5):(0-0.5).

10. The preparation method according to any one of claims 1-9, characterized in that, In step (4), the amount of the modifier added is 1wt%-5wt% of the mass of the fly ash to be modified.

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