Polyacrylamide slow-swelling particle with coating layer growing on surface as well as preparation method and application of polyacrylamide slow-swelling particle

Abstract

The invention discloses a polyacrylamide slow-swelling particle with a coating layer growing on the surface and a preparation method and application thereof, and belongs to the technical field of composite functional materials.The preparation method comprises the steps that 1, micron-sized polyacrylamide powder serves as a core layer raw material, and a mixed solution containing the core layer raw material, an organic alcohol solvent, a catalyst and deionized water is prepared; (2) preparing an organic alcohol solution of a silicon source, mixing the organic alcohol solution with the mixed solution obtained in the step (1) drop by drop, carrying out a full reaction while carrying out gel curing, and carrying out further separation and drying so as to obtain polyacrylamide slow-swelling particles with coating layers grown on the surfaces, the coating layers being composed of silicon dioxide pellets; the average particle size of the micron-sized polyacrylamide is 10-30 [mu] m, and the average particle size of the silicon dioxide pellets is 0.1-0.8 [mu] m. The slow expansion particles prepared by the invention have excellent slow expansion performance and plugging capacity, are good in stability, and have good application prospects in the fields of oil exploitation, soil improvement or wastewater treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of composite functional materials, and particularly relates to a polyacrylamide slow-swelling particle with a coating layer grown on its surface, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of oil exploitation, the water shutoff and profile control technology is one of the important means to improve the crude oil recovery rate. As a commonly used water-soluble polymer, polyacrylamide has good thickening, flocculation and other properties, and is widely used in the water shutoff and profile control technology. However, there are some problems in the use of traditional polyacrylamide. For example, its water absorption and swelling rate is too fast and difficult to control, which may lead to premature blockage during the injection into the reservoir and cannot effectively reach the target high-permeability layer, thus affecting the water shutoff and profile control effect. In addition to the oil exploitation field, polyacrylamide also has good application prospects in soil improvement, wastewater treatment, etc., but also because of its too fast water absorption and swelling rate, it affects the long-term effectiveness and stability of its use. Therefore, it is of great significance to develop a polyacrylamide-based material with a controllable swelling rate.

[0003] Chinese patent document with publication number CN102993453A discloses a slow-swelling water-absorbing resin and a preparation method thereof. The slow-swelling water-absorbing resin includes a common water-absorbing resin as the core and an outer coating layer containing a film-forming material and a pore-forming agent. The film-forming material can be selected from hydroxypropyl methylcellulose, ethylcellulose, sodium carboxymethylcellulose, arabic gum, etc. This slow-swelling water-absorbing resin does not require external conditions to melt, dissolve or break the coating layer, but relies on the expansion force of the internal water-absorbing resin to split the particles. However, the film-forming material in this slow-swelling water-absorbing resin has low strength, cannot withstand large shear forces, and the slow-swelling effect needs to be improved, resulting in its inability to enter the deeper interior of the ground.

[0004] Chinese patent document with publication number CN118126250A discloses a coated profile control agent and a preparation method thereof. The coated profile control agent uses a nano-sphere emulsion as the core and a coating structure as the shell, wherein the core is a water-in-oil polyacrylamide nano-sphere emulsion, and the coating structure is obtained by reacting a reaction system containing N,N-dimethylacrylamide, a super-hydrophobic monomer, a temperature-resistant monomer, a salt-resistant monomer and a first cross-linking agent. The water absorption rate of this profile control agent is extremely small during the long-term migration process into the formation to ensure that it can enter the deep part of the formation, but it needs to be prepared by multi-step emulsion polymerization, the process is cumbersome, and the preparation process cost is high, which is inconvenient to implement and is not conducive to large-scale production and practical application. Summary of the Invention

[0005] Aiming at the deficiencies existing in the above-mentioned prior art, the present invention provides a preparation method of polyacrylamide slow-swelling particles with a coating layer grown on the surface. This method has simple and efficient process steps. The prepared slow-swelling particles have excellent slow-swelling performance, plugging ability, and good stability, and can effectively solve the problems of too fast swelling rate, poor stability, difficult control, and low strength of traditional polyacrylamide.

[0006] The specific technical solutions adopted are as follows:

[0007] A preparation method of polyacrylamide slow-swelling particles with a coating layer grown on the surface, comprising the following steps:

[0008] (1) Using micron-sized polyacrylamide powder as the core layer raw material, prepare a mixed solution including the core layer raw material, organic alcohol solvent, catalyst, and deionized water;

[0009] (2) Prepare an organic alcohol solution of the silicon source. Dropwise mix the organic alcohol solution of the silicon source and the mixed solution in step (1), and after full reaction and gel aging, further separate and dry to obtain polyacrylamide slow-swelling particles with a coating layer grown on the surface, wherein the coating layer is composed of silicon dioxide spheres;

[0010] The average particle size of the micron-sized polyacrylamide powder is 10 - 30 μm, and the average particle size of the silicon dioxide spheres is 0.1 - 0.8 μm.

[0011] In the prior art, the preparation of polyacrylamide slow-swelling materials generally adopts the form of coating the surface of polyacrylamide with organic substances or the form of copolymerizing and doping with multiple monomers. The coating layer of the slow-swelling material obtained by coating the surface of polyacrylamide with organic substances is thin and has low strength, resulting in poor slow-swelling effect, inability to withstand high temperatures, and inability to withstand large shear forces. The process of preparing slow-swelling materials by copolymerizing and doping multiple monomers is complex and costly. Based on this, the present invention grows silicon dioxide spheres on the surface of micron-sized polyacrylamide through specific raw materials and the sol-gel method to prepare polyacrylamide slow-swelling particles with a coating layer grown on the surface, with a slow and controllable swelling rate and good stability.

[0012] Preferably, the micron-sized polyacrylamide powder is prepared by a ball milling method, and the parameters of ball milling are 600 - 1000 rpm and 5 - 20 h. The ball milling process can make the irregular core layer polyacrylamide more uniform, which is conducive to the growth of the shell layer on the surface of the core layer particles.

[0013] Optionally, the organic alcohol solvent includes but is not limited to methanol, ethanol, ethylene glycol, 3-pentanol, isopropanol, sec-butanol, etc.

[0014] Optionally, the catalyst is selected from acid solutions or alkali solutions with a concentration of 25 - 40 wt%; acid catalysts include hydrochloric acid or nitric acid, etc., and alkali catalysts include ammonia water or sodium hydroxide, etc.

[0015] Preferably, in the mixed solution of step (1), the ratio of the core layer raw material, organic alcohol solvent, catalyst and deionized water is 5 g: 40 - 80 mL: 1 - 10 mL: 0 - 10 mL.

[0016] Preferably, the silicon source is selected from at least one of hexamethyldisiloxane, trimethylbromosilane, tetraethyl orthosilicate, sodium silicate, phenylsilane; the concentration of the organic alcohol solution of the silicon source is 10 - 40 wt%.

[0017] Preferably, the organic alcohol solution of the silicon source and the mixed solution of step (1) are gradually dropped and mixed at the same rate by a peristaltic pump, and the propulsion speed of the peristaltic pump is 1 - 8 rpm.

[0018] During the reaction process, the color of the reaction system will gradually deepen. As the reaction time increases, it will gradually change from relatively clear to white. In this process, the solution grows silica in the form of sol - gel and adheres to the surface of polyacrylamide through intermolecular forces and a small amount of physical adsorption. In this process, core - shell structure coated slow - swelling particles with polyacrylamide as the core and silica as the shell layer can be obtained.

[0019] Preferably, in step (2), the reaction temperature is 10 - 30 °C, the reaction time is 5 - 20 h, and continuous stirring is carried out during the reaction process.

[0020] Optionally, the reaction product is separated by centrifugation, the centrifugation speed is 8000 - 12000 rpm, and the centrifugation time is 10 - 20 min; the drying temperature is 30 - 80 °C, and the drying time is 3 - 8 h.

[0021] The present invention also provides polyacrylamide slow - swelling particles with a coated film layer grown on the surface prepared by the preparation method of polyacrylamide slow - swelling particles with a coated film layer grown on the surface. The polyacrylamide slow - swelling particles with a coated film layer grown on the surface have a core - shell structure, with polyacrylamide as the core layer and a coated film layer composed of silica spheres as the shell layer.

[0022] The present invention also provides the application of the polyacrylamide slow - swelling particles with a coated film layer grown on the surface in the fields of oil exploitation, soil improvement or wastewater treatment.

[0023] The present invention also provides an oil - field processing aid, including the polyacrylamide slow - swelling particles with a coated film layer grown on the surface.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] (1) Excellent slow - swelling performance: The present invention effectively solves the technical problems of difficult controllable preparation of polyacrylamide swelling particles and poor slow - swelling effect by growing silica spheres on the surface of polyacrylamide. Since the silica nanosphere layer forms a stable microstructure on the surface of polyacrylamide, the contact angle of the slow - swelling particles prepared by the present invention increases, resulting in a hydrophobic effect, which hinders the contact distance between water molecules and polyacrylamide, effectively delaying the contact between polyacrylamide and the external environment. At the same time, water molecules need to bypass the spheres first and pass through the gaps between the silica spheres to reach the surface and inside of polyacrylamide, thus significantly reducing its initial water absorption and swelling rate, and can dynamically adapt to complex environments in practical applications.

[0026] (2) Enhanced stability: The coating layer composed of silica spheres in the present invention not only plays a role in slow - swelling, but also enhances the overall stability of the slow - swelling particles. Due to the high hardness and rigidity of silica spheres, when subjected to shear impact, friction or other physical effects, the spheres can share part of the force, reducing the damage to the polyacrylamide layer and thus improving the overall stability. According to the DLVO theory, the surface of silica spheres has a certain charge and forms an electric double layer in solution. When silica spheres grow on the surface of polyacrylamide, the charge distribution and electric double layer structure on its surface change, increasing the repulsive force between the particle spheres and making them less likely to aggregate and precipitate, thereby improving the stability of the system. Therefore, under complex environmental conditions, such as high temperature and high pressure in oil reservoirs, the slow - swelling particles can maintain the integrity of the structure, reduce the premature loss or failure of polyacrylamide, extend its action time, and provide guarantee for long - term and stable applications.

[0027] (3) Improved plugging ability: The micro - structure of silica spheres grown on the surface of polyacrylamide in the present invention provides a rougher surface for the slow - swelling particles, and the formation of the rough structure also increases the friction force between the slow - swelling particles, which is more conducive to plugging.

[0028] (4) The method of the present invention has a simple process, is easy to implement, has low cost, is convenient for large - scale production, and is conducive to practical application. Description of the Drawings

[0029] Figure 1 SEM image of micron - sized polyacrylamide powder in Example 1.

[0030] Figure 2 SEM image of polyacrylamide slow - swelling particles with a coating layer grown on the surface in Example 1.

[0031] Figure 3 Slow - swelling ratio diagram of polyacrylamide slow - swelling particles with a coating layer grown on the surface in Example 1.

[0032] Figure 4The thixotropic recovery stability characteristic diagram of the polyacrylamide slow-swelling particles with a coating layer grown on the surface in Example 1.

[0033] Figure 5 The thermal stability diagram of the polyacrylamide slow-swelling particles with a coating layer grown on the surface in Example 1.

[0034] Figure 6 The viscosity-shear force diagram of the polyacrylamide slow-swelling particles with a coating layer grown on the surface in Example 2.

[0035] Figure 7 The time creep and recovery diagram of the polyacrylamide slow-swelling particles with a coating layer grown on the surface in Example 3. Detailed implementation manners

[0036] To make the objectives, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description through specific implementation manners. Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined correspondingly without conflict.

[0037] The operation methods of the following examples without specifying specific conditions are generally in accordance with conventional conditions or the conditions recommended by the manufacturer. The content not described in detail in this specification belongs to the prior art well-known to those skilled in the art. The experimental materials used in the following examples can be obtained from conventional biochemical reagent companies without special instructions.

[0038] Example 1

[0039] (1) Add polyacrylamide powder into a ball mill, and ball mill it to the micron level at a ball milling speed of 800 rpm and a ball milling time of 5 h to obtain the core layer raw material (as shown in the SEM diagram Figure 1 ), and the average particle size of the core layer raw material is 10 - 30 μm;

[0040] (2) Prepare three independent reaction vessels. Add 40 mL of ethanol into the first reaction vessel, accurately weigh 5 g of the core layer raw material obtained in step (1) and add it therein, then add 10 mL of hydrochloric acid (concentration 38 wt%) and 1 mL of deionized water to obtain a mixed solution;

[0041] (3) Then add 10 g of tetraethyl orthosilicate into the second reaction vessel, and then add 40 mL of ethanol. During the dropping process, continuously stir to make the solution mix evenly to obtain a clear and transparent silicon source solution;

[0042] (4) Next, the mixed solution in step (2) and the silicon source solution in step (3) are slowly added dropwise into a third reaction vessel using a peristaltic pump at the same rate. The rotational speed of the peristaltic pump is 1 rpm. Under the condition of ultrasonic oscillation, it reacts fully at 20 °C for 20 h while the gel matures. Then, the reaction product is centrifuged at 12,000 rpm for 10 min and washed, and then transferred to an oven at 80 °C for drying for 4 h to obtain polyacrylamide slow-swelling particles with a coating layer grown on the surface. The coating layer is composed of silica spheres with an average particle size of 0.1 - 0.8 μm.

[0043] In this example, the submicroscopic morphology of the obtained polyacrylamide slow-swelling particles with a coating layer grown on the surface is as Figure 2 shown. It can be observed that a silica sphere layer is formed on the outer surface of the polyacrylamide through the growth process, achieving a good coating effect; Figure 3 shown is the slow-swelling performance curve of the slow-swelling particles. It can be seen that the polyacrylamide swelling particles in Comparative Example 1 reached a very high swelling ratio at the initial stage of water absorption and reached the swelling peak within 1 h. However, the slow-swelling particles prepared in this example showed almost no swelling in the initial few hours, and the entire slow-swelling process could last for dozens of hours, up to 30 h, having good slow-swelling performance and significantly reducing the water absorption swelling rate. Testing the shear thixotropic recovery performance of the slow-swelling particles, the results are as Figure 4 shown. It can be known from the test curve that as the applied shear rate increases, the slow-swelling particles will bear a large shear stress. However, after the shear force is slowly reduced or even removed, the slow-swelling particles will recover, and the recovery can reach 98%, having good shear stability and still being able to be used normally after being subjected to shear force in deep underground, and the effect is stable. At the same time, through the characterization of the thermal stability of the slow-swelling particles ( Figure 5 ), due to the presence of the silica layer grown on the surface, the slow-swelling particles can still exist stably at higher temperatures, with a temperature resistance of up to 300 °C, and the decomposition rate at high temperatures is significantly reduced, and its decomposition is also correspondingly improved.

[0044] Thus, it can be seen that the slow-swelling particles can still maintain the structural integrity and stability under complex conditions such as high temperature and high shear, reduce the premature loss or failure of polyacrylamide, have excellent slow-swelling performance, extend the action time of polyacrylamide, provide guarantee for long-term stable application, and the reagents used in the preparation process are few, and the preparation process is very simple, which is conducive to cost savings and production.

[0045] Example 2

[0046] (1) Add polyacrylamide powder to a ball mill and ball mill it to the micron level at a ball milling speed of 800 rpm and a ball milling time of 5 h to obtain the core layer raw material. The average particle size of the core layer raw material is 10 - 30 μm;

[0047] (2) Prepare three independent reaction vessels. Add 40 mL of ethanol to the first reaction vessel, accurately weigh 5 g of the core layer raw material obtained in step (1) and add it thereto. Then add 8 mL of hydrochloric acid (concentration 38 wt%) and 3 mL of deionized water to obtain a mixed solution.

[0048] (3) Then add 15 g of tetraethyl orthosilicate to the second reaction vessel, and then add 40 mL of ethanol. During the dropping process, continuously stir to make the solution mix evenly to obtain a clear and transparent silicon source solution.

[0049] (4) Next, slowly drop the mixed solution in step (2) and the silicon source solution in step (3) into the third reaction vessel at the same rate using a peristaltic pump. The rotational speed of the peristaltic pump is 3 rpm. Under the condition of ultrasonic oscillation, make it react fully at 25 °C for 15 h while the gel matures. Then, centrifuge the reaction product at a speed of 10000 rpm for 15 min and wash it. Subsequently, transfer it to an oven at 60 °C and dry it for 6 h to obtain polyacrylamide slow-swelling particles with a coating layer grown on the surface, where the coating layer is composed of silica spheres with an average particle size of 0.1 - 0.8 μm.

[0050] Perform rheological tests on the slow-swelling particles prepared in this example, and the results are as Figure 6 shown, indicating that the slow-swelling particles have good rheological properties and have a certain shear thinning phenomenon. This is very beneficial for the slow-swelling particles to still be able to enter the deep underground high-permeability layer to exert the slow-swelling effect under the action of a higher shear force and have good shear stability.

[0051] Example 3

[0052] (1) Add polyacrylamide powder to a ball mill and ball mill it to the micron level at a ball milling speed of 600 rpm and a ball milling time of 10 h to obtain a core layer raw material with an average particle size of 10 - 30 μm.

[0053] (2) Prepare three independent reaction vessels. Add 40 mL of ethanol to the first reaction vessel, accurately weigh 5 g of the core layer raw material obtained in step (1) and add it thereto. Then add 6 mL of hydrochloric acid (concentration 38 wt%) and 5 mL of deionized water to obtain a mixed solution.

[0054] (3) Then add 20 g of tetraethyl orthosilicate to the second reaction vessel, and then add 40 mL of ethanol. During the dropping process, continuously stir to make the solution mix evenly to obtain a clear and transparent silicon source solution.

[0055] (4) Next, the mixed solution in step (2) and the silicon source solution in step (3) are slowly added dropwise into a third reaction vessel using a peristaltic pump at the same rate. The rotational speed of the peristaltic pump is 5 rpm. Under the condition of ultrasonic oscillation, it reacts fully at 30 °C for 10 h while the gel matures. Then, the reaction product is centrifuged at a speed of 8000 rpm for 20 min and washed. Subsequently, it is transferred to an oven at 40 °C and dried for 8 h to obtain polyacrylamide slow-swelling particles with a coating layer grown on the surface, where the coating layer is composed of silica spheres with an average particle size of 0.1 - 0.8 μm.

[0056] The relationship between time and creep of the slow-swelling particles prepared in this example was tested, and the results are as Figure 7 shown, indicating that the slow-swelling particles have good recovery performance and can recover well after being sheared for a certain period of time, enabling them to enter the deep underground high-permeability layer to exert the slow-swelling effect.

[0057] Example 4

[0058] (1) Polyacrylamide powder is added to a ball mill and ball milled to the micron level at a ball milling speed of 800 rpm for 5 h to obtain the core layer raw material, and the average particle size of the core layer raw material is 10 - 30 μm;

[0059] (2) Prepare three independent reaction vessels. Add 40 mL of ethanol to the first reaction vessel, accurately weigh 5 g of the core layer raw material obtained in step (1) and add it thereto. Then add 1 mL of ammonia water (concentration 28 wt%) and 4 mL of deionized water to obtain a mixed solution;

[0060] (3) Then add 10 g of tetraethyl orthosilicate to the second reaction vessel, and then add 40 mL of ethanol. During the dropping process, continuously stir to make the solution mix evenly to obtain a clear and transparent silicon source solution;

[0061] (4) Next, the mixed solution in step (2) and the silicon source solution in step (3) are slowly added dropwise into a third reaction vessel using a peristaltic pump at the same rate. The rotational speed of the peristaltic pump is 6 rpm. Under the condition of ultrasonic oscillation, it reacts fully at 25 °C for 10 h while the gel matures. Then, the reaction product is centrifuged at a speed of 10000 rpm for 15 min and washed. Subsequently, it is transferred to an oven at 50 °C and dried for 7 h to obtain polyacrylamide slow-swelling particles with a coating layer grown on the surface, where the coating layer is composed of silica spheres with an average particle size of 0.1 - 0.8 μm.

[0062] Example 5

[0063] (1) Add polyacrylamide powder to a ball mill and mill it to the micron level at a ball milling speed of 1000 rpm and a ball milling time of 5 h to obtain the core layer raw material, and the average particle size of the core layer raw material is 10 - 30 μm;

[0064] (2) Prepare three independent reaction vessels. Add 40 mL of ethanol to the first reaction vessel, accurately weigh 5 g of the core layer raw material obtained in step (1) and add it thereto, and then add 5 mL of ammonia water (concentration 28 wt%) to obtain a mixed solution;

[0065] (3) Then add 20 g of tetraethyl orthosilicate to the second reaction vessel, and then add 40 mL of ethanol. During the dropping process, continuously stir to make the solution mix evenly to obtain a clear and transparent silicon source solution;

[0066] (4) Next, slowly drop the mixed solution in step (2) and the silicon source solution in step (3) into the third reaction vessel at the same rate using a peristaltic pump. The peristaltic pump speed is 8 rpm. Under the condition of ultrasonic oscillation, make it react fully at 25 °C for 5 h while the gel matures. Then, centrifuge the reaction product at a speed of 8000 rpm for 20 min, wash it, and then transfer it to an oven at 70 °C to dry for 5 h to obtain polyacrylamide slow swelling particles with a coating layer grown on the surface, where the coating layer is composed of silica spheres with an average particle size of 0.1 - 0.8 μm.

[0067] Comparative Example 1

[0068] (1) Add polyacrylamide powder to a ball mill and mill it to the micron level at a ball milling speed of 800 rpm and a ball milling time of 5 h to obtain the core layer raw material, and the average particle size of the core layer raw material is 10 - 30 μm;

[0069] (2) Prepare three independent reaction vessels. Add 40 mL of ethanol to the first reaction vessel, accurately weigh 5 g of the core layer raw material obtained in step (1) and add it thereto to obtain a mixed solution;

[0070] (3) Then add 40 mL of ethanol to the second reaction vessel;

[0071] (4) Next, slowly drop the mixed solution in step (2) and the ethanol in step (3) into the third reaction vessel at the same rate using a peristaltic pump. The peristaltic pump speed is 3 rpm. Under the condition of ultrasonic oscillation, make it react fully at 25 °C for 15 h while the gel matures. Then, centrifuge the reaction product at a speed of 10000 rpm for 15 min, wash it, and then transfer it to an oven at 60 °C to dry for 6 h to obtain polyacrylamide swelling particles without silica spheres grown on the surface.

[0072] Sample Analysis

[0073] The swelling rate, shear recovery, and contact angle of the polyacrylamide slow-swelling particles with a coating layer grown on the surface prepared in the examples and the polyacrylamide swelling particles without silica spheres grown on the surface in the comparative examples were tested to characterize the slow-swelling effect and stability. The results are shown in Table 1, indicating that the polyacrylamide slow-swelling particles with a coating layer grown on the surface have better slow-swelling effect and stability.

[0074] Table 1 Statistical results of the slow-swelling effect and stability tests for the examples and comparative examples

[0075]

[0076] The above-described examples have elaborated on the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, or substitutions in a similar manner within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing polyacrylamide slow-swelling particles with a coating layer grown on the surface, characterized in that: The following steps are involved: (1) using micron-sized polyacrylamide powder as a core layer raw material, preparing a mixed solution including the core layer raw material, an organic alcohol solvent, a catalyst and deionized water; (2) preparing an organic alcohol solution of a silicon source, mixing the organic alcohol solution of the silicon source with the mixed solution of step (1) dropwise, allowing them to fully react and gel-mature, and then further separating and drying to obtain polyacrylamide slow-swelling particles with a coating layer grown on the surface, wherein the coating layer is composed of small silicon dioxide spheres; The average particle size of micron-grade polyacrylamide powder is 10-30 μm, and the average particle size of silica spheres is 0.1-0.8 μm.

2. The method for preparing polyacrylamide slow-swelling particles with a coating layer grown on the surface according to claim 1, characterized in that: The micron-sized polyacrylamide powder is prepared by a ball milling method, and the ball milling parameters are 600-1000 rpm and 5-20 hours.

3. The method for preparing polyacrylamide slow-swelling particles with a film layer grown on the surface according to claim 1, characterized in that: The organic alcohol solvent includes methanol, ethanol, ethylene glycol, 3-pentanol, isopropanol or sec-butanol, and the catalyst is selected from acid solution or alkaline solution with a concentration of 25-40wt%.

4. The method for preparing polyacrylamide slow-swelling particles with a coating layer grown on the surface according to claim 1, characterized in that: In the mixed solution of step (1), the ratio of the core layer raw material, the organic alcohol solvent, the catalyst and deionized water is 5g:40-80mL:1-10mL:0-10mL.

5. The method for preparing polyacrylamide slow-swelling particles with a coating layer grown on the surface according to claim 1, characterized in that: The silicon source is selected from at least one of hexamethyldisiloxane, trimethylsilyl bromide, tetraethyl silicate, sodium silicate and phenylsilane; the concentration of the organic alcohol solution of the silicon source is 10-40wt%.

6. The method for preparing polyacrylamide slow-swelling particles with a coating layer grown on the surface according to claim 1, characterized in that: The organic alcohol solution of the silicon source and the mixed solution of step (1) are mixed dropwise at the same rate using a peristaltic pump, and the propulsion speed of the peristaltic pump is 1-8 rpm.

7. The method for preparing polyacrylamide slow-swelling particles with a film layer grown on the surface according to claim 1, characterized in that: In step (2), the reaction temperature is 10-30° C., the reaction time is 5-20 h, and stirring is continued during the reaction.

8. The polyacrylamide retarding swelling particles with a film layer grown on the surface prepared by the method for preparing polyacrylamide retarding swelling particles with a film layer grown on the surface according to any one of claims 1 to 7, characterized in that: The polyacrylamide slow-swelling particles with a coating layer grown on the surface have a core-shell structure, wherein the polyacrylamide is the core layer and the coating layer composed of silicon dioxide spheres is the shell layer.

9. Use of the polyacrylamide slow-swelling particles with a film layer grown on the surface according to claim 8 in the fields of oil extraction, soil improvement or wastewater treatment.

10. An oilfield processing aid, characterized in that: The invention comprises the polyacrylamide slow-swelling particles with a coating layer grown on the surface as described in claim 8.

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