Preparation method of oil well cement suspending agent

Abstract

The invention discloses a preparation method of an oil well cement suspending agent, which comprises the following steps: monomers are subjected to free radical polymerization, the monomers comprise the following components in parts by mass: 25-45 parts of 2-acrylamido-2-methylpropanesulfonic acid, 30-45 parts of hydrophobic monomers and 20-40 parts of cationic monomers, and the oil well cement suspending agent is obtained. According to the preparation method of the oil well cement suspending agent, the temperature resistance of the polymer is improved by introducing the hydrophobic monomer and the cationic monomer, the cement discharging time is shortened, free liquid is eliminated, and the well cementation requirements of most deep wells are met.

Description

Technical Field

[0001] The present application relates to the field of cementing slurry, and in particular to a method for preparing an oil well cement suspension. Background Art

[0002] Cementing is an important part of oil drilling, which mainly includes casing and cementing. After the casing is lowered into the wellbore, cement slurry is pumped into the annulus outside the casing through special equipment, and then solidified to form a cement ring, so as to effectively seal complex formations, isolate oil, gas and water layers, and establish a safe channel for oil and gas production. As an important part of oil and gas well construction, cementing quality is directly related to the next step of safe production.

[0003] In order to ensure the quality of cementing under complex geological and working conditions, it is necessary to add additives such as fluid loss reducer, retarder, drag reducer, suspending agent, etc. to the cement slurry to adjust the performance of the cement slurry and meet the requirements of cementing construction. Among them, the suspending agent is an oil well cement additive that prevents the sedimentation of particles in the cement slurry and maintains the stability of the cement slurry system. Poor stability of cement slurry will lead to uneven cement ring, different development of compressive strength, and easy appearance of free liquid in the top cement slurry. At the same time, it will have an adverse effect on the sealing ability of the cement ring. Especially for the horizontal well section, the stability of cement slurry has a more serious impact on the cementing quality. Unstable cement slurry may cause channeling in the upper cement ring of the horizontal section, affecting the subsequent staged fracturing and production increase operations and interlayer isolation. When the cement slurry settles seriously, it may lead to the risk of pump blocking or the inability to pull out the central pipe during construction. With the development of downhole oil and gas resources, the pressure system is more complicated, blowout and leakage coexist, the safety density window is narrow, and the requirements for the rheology of cement slurry are getting higher and higher. The improvement of rheological properties seriously affects the sedimentation stability of cement slurry. Such problems are more prominent at high temperatures. In order to solve the problem of cement slurry sedimentation stability, scholars have paid more and more attention to the research of suspending agents. In the synthesis of existing suspending agent polymers, the temperature resistance of suspending agent molecules is improved to solve the defect of traditional suspending agent varieties becoming thinner at high temperatures, but it affects the slurry preparation and takes a long time to set the ash. Summary of the invention

[0004] The present application provides a method for preparing an oil well cement suspension agent, which can solve the problems of low-temperature thickening and ash removal of organic suspension agents, as well as high-temperature dilution of cement slurry.

[0005] This application adopts the following technical solutions:

[0006] The present application provides a method for preparing an oil well cement suspension agent, comprising the following steps: subjecting monomers to free radical polymerization, wherein the monomers comprise the following components in parts by weight: 25 to 45 parts of 2-acrylamide-2-methylpropane sulfonic acid, 30 to 45 parts of a hydrophobic monomer, and 20 to 40 parts of a cationic monomer, to obtain an oil well cement suspension agent.

[0007] Furthermore, the preparation method comprises the following steps: adding 25 to 45 parts of 2-acrylamide-2-methylpropanesulfonic acid, 30 to 45 parts of hydrophobic monomers and 20 to 40 parts of cationic monomers to 300 parts of deionized water to mix into an aqueous solution system. Stirring is started, and after each component in the aqueous solution system is dissolved, the pH of the mixed solution obtained after each component is dissolved is adjusted to 6 with NaOH under ice bath conditions, heating is started, and the temperature is raised to an initiation temperature of 55 to 60° C. under nitrogen protection, 0.05 to 0.35 parts of initiator are added at one time, and the reaction is kept warm for 2 to 5 hours, and finally cooled to room temperature to obtain an oil well cement suspension agent.

[0008] Further, the hydrophobic monomer includes at least two of methacrylamide, N-ethylacrylamide, N-n-propylacrylamide, N,N-dimethylacrylamide, N-tetradecylacrylamide, and N,N-diethyl-2-acrylamide.

[0009] Furthermore, the cationic monomer includes one or two of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and octadecyldimethylallylammonium chloride.

[0010] Furthermore, the initiator includes one or two of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisobutyramidine hydrochloride.

[0011] Furthermore, the reaction time is 4 h.

[0012] Furthermore, the initiation temperature is 60°C.

[0013] Compared with the prior art, this application has the following beneficial effects:

[0014] The preparation method of the present application introduces cationic monomers to alleviate the strong electrostatic repulsion caused by the sulfonic acid anions on the polymer, prevents the sedimentation of solid phase particles in the cement slurry through the charge effect, and improves the suspension performance of the suspending agent; at the same time, the introduction of cationic monomers is beneficial to the infiltration of cement particles and reduces the ash laying time. The preparation method of the present application introduces hydrophobic monomers to improve the hydrophobicity of the polymer, enhance the hydrophobic association effect, and effectively compensate for the problem of decreased viscosity of the cement slurry system due to temperature increase. In general, the preparation method of the oil well cement suspending agent provided in the present application improves the temperature resistance of the polymer by introducing hydrophobic monomers and cationic monomers, reduces the ash laying time, eliminates free liquid, and meets most deep well cementing needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a graph showing the effect of different amounts of suspending agent on the stability of cement slurry at 150°C in this application;

[0016] Figure 2This is a thickening curve of the cement slurry to which the suspending agent prepared in Example 1 is added at 150° C. and 94.4 MPa;

[0017] Figure 3 This is a thickening curve of the cement slurry to which the commercially available suspending agent A is added at 150°C and 94.4MPa in this application;

[0018] Figure 4 This is a thickening curve of the cement slurry to which the commercially available suspending agent B is added at 150°C and 94.4MPa in this application;

[0019] Figure 5 This is a thermal analysis curve of the suspension prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0020] The technical methods in the embodiments of the present application are described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present application.

[0021] The embodiment of the present application provides a method for preparing an oil well cement suspension agent, comprising the following steps:

[0022] The monomers are subjected to free radical polymerization, the monomers include the following components by weight: 25-45 parts of 2-acrylamido-2-methylpropanesulfonic acid, 30-45 parts of hydrophobic monomers, and 20-40 parts of cationic monomers, to obtain an oil well cement suspension agent. The oil well cement suspension agent is a multipolymer prepared from monomers by a free radical polymerization method.

[0023] Specifically, the preparation method comprises the following steps:

[0024] (1) adding 25-45 parts of 2-acrylamido-2-methylpropanesulfonic acid, 30-45 parts of hydrophobic monomer and 20-40 parts of cationic monomer to 300 parts of deionized water to form an aqueous solution system; (2) starting stirring, after each component in the aqueous solution system is dissolved, adjusting the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, starting heating, raising the temperature to an initiation temperature of 55-60° C. under nitrogen protection, adding 0.05-0.35 parts of initiator at one time, keeping the temperature for reaction for 2-5 hours, and finally cooling to room temperature to obtain a solution product-oil well cement suspension agent.

[0025] The amount of 2-acrylamide-2-methylpropanesulfonic acid used can be 25, 30, 45 parts, etc.

[0026] The amount of the hydrophobic monomer can be 30, 40, 45 parts, etc. The hydrophobic monomer can include at least two of methacrylamide, N-ethylacrylamide, N-n-propylacrylamide, N,N-dimethylacrylamide, N-tetradecylacrylamide, and N,N-diethyl-2-acrylamide. For example, the hydrophobic monomer can be a mixture of methacrylamide and N-ethylacrylamide; it can also be a mixture of N-n-propylacrylamide, N,N-dimethylacrylamide, and N-tetradecylacrylamide; it can also be a mixture of methacrylamide, N-ethylacrylamide, N-n-propylacrylamide, N,N-dimethylacrylamide, N-tetradecylacrylamide, and N,N-diethyl-2-acrylamide.

[0027] The amount of the cationic monomer can be 20, 30, 40 parts, etc. The cationic monomer can include one or two of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and octadecyldimethylallylammonium chloride. For example, the cationic monomer can be dimethyldiallylammonium chloride; it can also be a mixture of methacryloyloxyethyltrimethylammonium chloride and octadecyldimethylallylammonium chloride; it can also be a mixture of dimethyldiallylammonium chloride and octadecyldimethylallylammonium chloride.

[0028] The amount of the initiator can be 0.05, 0.2, 0.35 parts, etc. The initiator can include one or two of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile, and azobisisobutyramidine hydrochloride. For example, the initiator can be ammonium sulfate; it can also be a mixture of potassium persulfate and azobisisobutyronitrile; it can also be a mixture of azobisisoheptanenitrile and azobisisobutyramidine hydrochloride.

[0029] The reaction time can be 2, 3, 5 hours, etc. Further, the reaction time can be 2.5-4.5 hours. Further, the reaction time can be 4 hours.

[0030] The initiation temperature may be 55, 58, 60°C, etc. Further, the initiation temperature may be 60°C.

[0031] The preparation method of the present application alleviates the strong electrostatic repulsion caused by the sulfonic acid anions on the polymer by introducing cationic monomers, prevents the sedimentation of solid phase particles in the cement slurry through the charge effect, and improves the suspension performance of the suspending agent; at the same time, the introduction of cationic monomers is beneficial to the infiltration of cement particles and reduces the ash laying time. The preparation method of the present application improves the hydrophobicity of the polymer and enhances the hydrophobic association effect by introducing hydrophobic monomers, effectively compensating for the problem of decreased viscosity of the cement slurry system due to temperature increase. In general, the preparation method of the oil well cement suspending agent provided in the present application improves the temperature resistance of the polymer by introducing hydrophobic monomers and cationic monomers, reduces the ash laying time, eliminates free liquid, and meets most deep well cementing needs.

[0032] The following is a detailed description with reference to specific embodiments:

[0033] Example 1

[0034] (1) adding 30 parts of 2-acrylamido-2-methylpropanesulfonic acid, 20 parts of N,N-dimethylacrylamide, 20 parts of N-ethylacrylamide and 20 parts of dimethyldiallylammonium chloride to 300 parts of deionized water to form an aqueous solution system; (2) starting stirring, after the components in the aqueous solution system are dissolved, adjusting the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, starting heating, raising the temperature to an initiation temperature of 60°C under nitrogen protection, adding 0.2 parts of ammonium persulfate at one time, keeping the temperature for reaction for 4 hours, and finally cooling to room temperature to obtain a solution product - oil well cement suspension agent, marked as sample 1#.

[0035] Example 2

[0036] (1) Add 35 parts of 2-acrylamido-2-methylpropanesulfonic acid, 20 parts of N,N-dimethylacrylamide, 10 parts of methacrylamide, 10 parts of N-ethylacrylamide and 20 parts of dimethyldiallylammonium chloride to 300 parts of deionized water, and mix to form an aqueous solution system; (2) Start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 55°C under nitrogen protection, add 0.2 parts of ammonium persulfate and 0.05 parts of azobisisobutylamidine hydrochloride at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product-oil well cement suspension agent, marked as sample 2#.

[0037] Example 3

[0038] (1) Add 40 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of N,N-dimethylacrylamide, 10 parts of methacrylamide, 10 parts of N-ethylacrylamide, 10 parts of N,N-diethyl-2-acrylamide and 20 parts of dimethyldiallylammonium chloride to 300 parts of deionized water to form an aqueous solution system; (2) Start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 60°C under nitrogen protection, add 0.25 parts of ammonium persulfate at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product-oil well cement suspension agent, marked as sample 3#.

[0039] Example 4

[0040] (1) Add 35 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of N,N-dimethylacrylamide, 10 parts of methacrylamide, 10 parts of N-ethylacrylamide, 10 parts of N,N-diethyl-2-acrylamide, 5 parts of N-n-propylacrylamide and 20 parts of dimethyldiallylammonium chloride to 300 parts of deionized water, and mix to form an aqueous solution system; (2) Start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 55°C under nitrogen protection, add 0.15 parts of ammonium persulfate and 0.15 parts of azobisisobutylamidine hydrochloride at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product-oil well cement suspension agent, marked as sample 4#.

[0041] Example 5

[0042] (1) Add 25 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of N,N-dimethylacrylamide, 10 parts of methacrylamide, 10 parts of N,N-diethyl-2-acrylamide, 5 parts of N-n-propylacrylamide, 10 parts of dimethyldiallyl ammonium chloride and 10 parts of methacryloyloxyethyltrimethylammonium chloride to 300 parts of deionized water, and mix to form an aqueous solution system; (2) Start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 60°C under nitrogen protection, add 0.3 parts of ammonium persulfate at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product-oil well cement suspension agent, marked as sample 5#.

[0043] Example 6

[0044] (1) Add 20 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10 parts of N,N-dimethylacrylamide, 10 parts of methacrylamide, 10 parts of N-ethylacrylamide, 10 parts of N,N-diethyl-2-acrylamide, 5 parts of N-n-propylacrylamide, 20 parts of dimethyldiallylammonium chloride and 20 parts of octadecyldimethylallylammonium chloride to 300 parts of deionized water, and mix to form an aqueous solution system; (2) Start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 60°C under nitrogen protection, add 0.35 parts of ammonium persulfate at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product-oil well cement suspension agent, marked as sample 6#.

[0045] Comparative Example 1

[0046] Add 45 parts of 2-acrylamido-2-methylpropanesulfonic acid and 40 parts of dimethyldiallylammonium chloride to 300 parts of deionized water, and mix to form an aqueous solution system; (2) start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 60°C under nitrogen protection, add 0.2 parts of ammonium persulfate at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product - oil well cement suspension agent, marked as sample 7#.

[0047] Comparative Example 2

[0048] Add 45 parts of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts of N,N-dimethylacrylamide and 20 parts of N-ethylacrylamide to 300 parts of deionized water, and mix to form an aqueous solution system; (2) start stirring, after the components in the aqueous solution system are dissolved, adjust the pH of the mixed solution obtained after the components are dissolved to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 60°C under nitrogen protection, add 0.2 parts of ammonium persulfate at one time, keep the temperature for reaction for 4 hours, and finally cool to room temperature to obtain a solution product - oil well cement suspension agent, marked as sample 8#.

[0049] Test Example 1

[0050] (1) The sedimentation stability evaluation results of cement slurries containing the suspending agents prepared in Examples 1 to 6 of the present application (1# to 6# samples), the suspending agents prepared in Comparative Examples 1 to 2 (7# to 8# samples) and commercially available suspending agents (A, B) at 150°C were compared. The data results are shown in Table 1.

[0051] Cement slurry formula: 600 parts of Jiahua G grade cement, 210 parts of silica fume, 30 parts of fluid loss reducer (BXF-200L), 18 parts of retarder (BCR-300L), 0.5 parts of defoamer (G603), 30 parts of suspending agent and 278 parts of fresh water, liquid-to-solid ratio: 0.44, 150℃.

[0052] Table 1 Results of cement slurry stability test at 150℃

[0053]

[0054]

[0055] It can be seen from the test results that compared with the suspension agent 7# sample prepared in comparative example 1 of the present application, the suspension agent 1#~6# samples prepared by adding the examples of the present application have better stability and can effectively eliminate free liquid; compared with the suspension agent 8# sample prepared in comparative example 2 of the present application, the suspension agent 1#~6# samples prepared by adding the examples of the present application have a shorter ash-lowering time for slurry preparation and do not affect the slurry preparation of the cement slurry; compared with commercially available suspension agents A and B, the suspension agent prepared by adding the examples of the present application does not affect the slurry preparation of the cement slurry, has a shorter ash-lowering time, can effectively eliminate free liquid, and improves the sedimentation stability of the cement slurry at 150°C.

[0056] (2) The suspension agent samples 1# to 4# prepared in this application were preferably used to test the effect of different dosages of the suspension agent on the stability of cement slurry at 150°C. The test results are shown in Figure 1 and Table 2.

[0057] Weigh the components according to the following mass proportions: G-grade oil well cement: 600 parts; silica fume: 210 parts; fluid loss reducer BXF-200L: 30 parts; retarder BCR-300L: 18 parts; defoamer G603: 0.5 parts; suspending agent: 18-30 parts; fresh water 278-290 parts. The liquid-to-solid ratio of the cement slurry is 0.44, and the density is 1.89g / cm 3 of cement slurry.

[0058] Table 2 Effect of different suspending agent dosages on cement slurry stability at 150℃

[0059]

[0060] From the above test results, it can be seen that with the increase of the suspending agent dosage, the density difference of cement slurry gradually decreases and the stability of cement slurry is significantly improved.

[0061] (3) The thickening curves of cement slurries containing different suspending agents at 150°C and 94.4 MPa were compared. Figure 2 This is a thickening curve of the cement slurry added with the suspending agent prepared in Example 1 at 150°C and 94.4MPa. Figure 3 and Figure 4 The thickening curves of cement slurries with commercially available suspending agents A and B added at 150°C and 94.4MPa are shown respectively.

[0062] From the comparison of the test results, it can be seen that the suspension agent prepared in Example 1 has little effect on the initial consistency of the cement slurry, the cement slurry consistency curve is relatively stable, there is no core phenomenon, the system consistency decreases slightly with the increase of temperature, and the stability of the cement slurry at high temperature can be better maintained; while the cement slurry mixed with commercially available suspension agents A or B has a higher initial consistency, and the consistency decreases seriously with the increase of temperature. The cement slurry mixed with the suspension agent prepared in Example 1 does not significantly thicken at low temperatures, and can improve the sedimentation stability of the cement slurry at high temperatures, compensating for the problem of decreased viscosity of the cement slurry system due to temperature increase.

[0063] (4) Figure 5 The thermal analysis curve of the suspension prepared in Example 1 is shown in Figure 1. TG is thermogravimetric analysis, and DTG is the weight loss rate of a substance per unit time. Figure 5 It can be seen that the thermal decomposition of suspension agent molecules is mainly divided into three stages:

[0064] The first stage is thermal degradation in the temperature range of 201-262℃, with a mass loss of 12.2%. The DTG curve shows a trough at 239.5℃. The main reason for the weight loss in this stage is that the adjacent amide groups in the suspending agent molecules undergo imidization reaction at high temperature to generate imide groups and lose some water molecules. The second stage is thermal degradation in the temperature range of 270-360℃, with a mass loss of 28.8%. The DTG curve shows a trough at 307.8℃. The main reason for the weight loss in this stage is the large-scale decomposition and breakage of side chain groups such as amide and sulfonic acid groups in the suspending agent molecules. The third stage is thermal degradation in the temperature range of 362-500℃, with a mass loss of 35.5%. The DTG curve shows a trough at 420.2℃. The main reason for the weight loss in this stage is that the main chain in the suspending agent molecules begins to break. Above 500℃, the thermogravimetric curve tends to be stable, leaving only a small amount of carbonaceous residue. In summary, polymer BCJ-W begins to decompose at 270 °C, and the suspension agent has excellent thermal stability and can meet most deep well cementing needs.

[0065] To sum up the above, the temperature resistance of the suspension agent of the present application can reach 150°C, which can effectively compensate for the problem of decreased viscosity of the cement slurry system caused by temperature increase, effectively improve the sedimentation stability of oil well cement, eliminate free liquid, reduce ash laying time, and meet most deep well cementing needs.

[0066] The above shows and describes the basic principles, main features and advantages of the present application. Those skilled in the art should understand that the present application is not limited by the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present application. Without departing from the spirit and scope of the present application, the present application may have various changes and improvements, and the scope of protection required by the present application is defined by the attached claims, description and their equivalents.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A method for preparing an oil well cement suspension agent, characterized in that: The following steps are involved: The monomers are subjected to free radical polymerization, wherein the monomers include the following components in parts by weight: 25 to 45 parts of 2-acrylamide-2-methylpropane sulfonic acid, 30 to 45 parts of hydrophobic monomers, and 20 to 40 parts of cationic monomers, to obtain the oil well cement suspension agent.

2. The preparation method according to claim 1, characterized in that The following steps are involved: Add 25-45 parts of 2-acrylamide-2-methylpropane sulfonic acid, 30-45 parts of hydrophobic monomers and 20-40 parts of cationic monomers to 300 parts of deionized water, and mix to form an aqueous solution system; start stirring, wait for each component in the aqueous solution system to dissolve, adjust the pH of the mixed solution obtained by dissolving each component to 6 with NaOH under ice bath conditions, start heating, raise the temperature to an initiation temperature of 55-60° C. under nitrogen protection, add 0.05-0.35 parts of initiator at one time, keep the temperature for reaction for 2-5 hours, and finally cool to room temperature to obtain the oil well cement suspension agent.

3. The preparation method according to claim 1, characterized in that: The hydrophobic monomers include at least two of methacrylamide, N-ethylacrylamide, N-n-propylacrylamide, N,N-dimethylacrylamide, N-tetradecylacrylamide, and N,N-diethyl-2-acrylamide.

4. The preparation method according to claim 1, characterized in that: The cationic monomer includes one or two of dimethyldiallylammonium chloride, methacryloyloxyethyltrimethylammonium chloride, and octadecyldimethylallylammonium chloride.

5. The preparation method according to claim 1, characterized in that: The initiator includes one or two of ammonium persulfate, potassium persulfate, azobisisobutyronitrile, azobisisoheptanenitrile and azobisisobutyramidine hydrochloride.

6. The preparation method according to claim 1, characterized in that: The reaction time is 4h.

7. The preparation method according to claim 1, characterized in that: The initiation temperature was 60°C.

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