Kinetic hydrate inhibitors and compounded hydrate inhibitors

Abstract

The application provides a kinetic hydrate inhibitor and a compound hydrate inhibitor. The chemical structural formula of the kinetic hydrate inhibitor is shown in the following formula: x:y=0.5-2, x=8-20, y=10-16; n=6-9. The compound hydrate inhibitor comprises the kinetic hydrate inhibitor and ethylene glycol with a mass ratio of 1:5-1:10, or comprises the kinetic hydrate inhibitor and methanol with a mass ratio of 1:15-1:30. The kinetic hydrate inhibitor and the compound hydrate inhibitor provided by the application have the characteristics of high cloud point and strong inhibition performance.

Description

Technical Field

[0001] This invention belongs to the field of natural gas pipeline flow protection technology, specifically relating to a high-efficiency, high-turbidity-point kinetic hydrate inhibitor and a compound hydrate inhibitor formed by combining the kinetic hydrate inhibitor. Background Technology

[0002] The formation of hydrates in natural gas pipeline systems can clog pipelines, potentially causing significant economic losses and even casualties in severe cases. Hydrate blockage has become a major threat to pipeline safety.

[0003] The oil and gas industry primarily employs the injection of inhibitors to suppress natural gas hydrate formation and prevent pipeline blockages caused by hydrates. Hydrate inhibitors are further categorized into kinetic inhibitors, thermodynamic inhibitors, and anti-polymerization agents. Thermodynamic inhibitors, such as methanol and ethanol, alter the thermodynamic conditions for hydrate formation, making them an effective and widely used method. However, they suffer from drawbacks such as high dosage and significant environmental impact. Anti-polymerization agents are unsuitable under high water content conditions. Kinetic inhibitors reduce the growth rate and formation rate of hydrates by adsorbing onto the surface of hydrate crystal nuclei, disrupting the nucleation and growth process, thus inhibiting hydrate formation. They offer the advantage of low dosage. Currently, widely used kinetic inhibitors mainly include polymer-based kinetic inhibitors such as PVP and PVCap. These polymer-based kinetic inhibitors have low cloud points (typically 30-40℃), and often precipitate out in areas of drastic temperature change, such as throttling elements and heating devices in natural gas pipeline systems, thus affecting their inhibitory performance.

[0004] Therefore, research is needed on high turbidity point hydrate inhibitors to effectively reduce the risk of hydrate formation and blockage in natural gas pipeline systems, which is of great significance for ensuring the flow of natural gas pipelines. Summary of the Invention

[0005] The purpose of this invention is to provide a hydrate inhibitor with a high cloud point and strong inhibitory performance.

[0006] To achieve the above objectives, the present invention provides the following technical solution.

[0007] In a first aspect, the present invention provides a kinetic hydrate inhibitor, wherein the chemical structural formula of the kinetic hydrate inhibitor is shown below:

[0008]

[0009] Among them, x:y=0.5-2.0, x=8-20, y=10-16; n=6-9.

[0010] According to a preferred embodiment of the first aspect, the weight-average molecular weight Mw of the kinetic hydrate inhibitor is 6000-10000 (e.g., 8933).

[0011] According to a preferred embodiment of the first aspect, the number-average molecular weight Mn of the kinetic hydrate inhibitor is 1000-3000 (e.g., 1727).

[0012] The kinetic hydrate inhibitor provided by this invention is based on the existing kinetic inhibitor polyvinylcaprolactam structure. By modifying polyvinylcaprolactam, adding polyethylene glycol methyl ether methacrylate as a reactant and simultaneously adding mercaptoacetic acid as a chain transfer agent to carry out the polymerization reaction, its cloud point is improved and its inhibitory performance is enhanced.

[0013] In a second aspect, the present invention provides a method for preparing the kinetic hydrate inhibitor provided in the first aspect, wherein the method includes:

[0014] N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, 2,2-azobisisobutyronitrile (2,2-azobisisobutyronitrile), and an organic solvent were mixed to obtain a homogeneous reaction system; wherein the ratio of N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, 2,2-azobisisobutyronitrile (2,2-azobisisobutyronitrile), and the organic solvent was 60-120 mmol: 10-20 mmol: 0.1-0.5 mmol: 1-3 mmol: 80 ml;

[0015] The homogeneous reaction system is deoxygenated and then reacted at 70-90℃ for 4-6 hours to obtain a solution containing the kinetic hydrate inhibitor.

[0016] The method for preparing the kinetic hydrate inhibitor provided by the present invention uses N-vinylcaprolactam and polyethylene glycol methyl ether methacrylate as reacting monomers, 2,2-azobisisobutyronitrile (2,2-thioglycolic acid) as chain transfer agent, and 2,2-azobisisobutyronitrile as initiator for polymerization reaction.

[0017] According to a preferred embodiment of the second aspect, the method for preparing the kinetic hydrate inhibitor further includes:

[0018] The organic solvent in the solution containing the kinetic hydrate inhibitor was removed by rotary evaporation.

[0019] The product obtained by rotary evaporation was then washed with n-hexane and tetrahydrofuran to remove unreacted substances and other impurities, thus obtaining the kinetic hydrate inhibitor.

[0020] The washing of the product obtained by rotary evaporation with n-hexane and tetrahydrofuran includes:

[0021] 1) First, add tetrahydrofuran dropwise to the product until the product dissolves;

[0022] 2) Add n-hexane to the solution obtained in step 1) to form a precipitate;

[0023] 3) Filter out the precipitate obtained in step 2);

[0024] 4) The precipitate is used as a product to repeat steps 1) to 3) at least twice more, and the final precipitate is the purified kinetic hydrate inhibitor.

[0025] According to a preferred embodiment of the second aspect, N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, 2,2-azobisisobutyronitrile (2,2-azobisisobutyronitrile), and an organic solvent are mixed to obtain a homogeneous reaction system comprising:

[0026] N-vinylcaprolactam was dissolved in an organic solvent to prepare an N-vinylcaprolactam solution;

[0027] Add 2,2-azobisisobutyronitrile to the N-vinylcaprolactam solution and mix thoroughly; then add polyethylene glycol methyl ether methacrylate and mercaptoacetic acid and mix thoroughly to obtain a homogeneous reaction system.

[0028] According to a preferred embodiment of the second aspect, the number-average molecular weight of polyethylene glycol methyl ether methacrylate is 475.

[0029] According to a preferred embodiment of the second aspect, the organic solvent is selected from toluene and / or carbon tetrachloride.

[0030] Thirdly, the present invention provides a compound hydrate inhibitor, wherein the compound hydrate inhibitor comprises a kinetic hydrate inhibitor provided in the first aspect of the present invention and ethylene glycol in a mass ratio of 1:5 to 1:10, or comprises a kinetic hydrate inhibitor provided in the first aspect of the present invention and methanol in a mass ratio of 1:15 to 1:30.

[0031] The compound hydrate inhibitor provided by this invention combines the advantages of thermodynamic hydrate inhibitors and kinetic hydrate inhibitors. Based on the special kinetic hydrate inhibitor provided by this invention, its inhibitory performance and cloud point are further improved by adding ethylene glycol (MEG) or methanol thermodynamic inhibitors.

[0032] The kinetic hydrate inhibitors and compound hydrate inhibitors provided by this invention possess excellent high turbidity point and high inhibition performance characteristics. This helps to reduce the negative impact of drastic temperature changes in areas such as throttling elements and heating devices on the effectiveness of the kinetic inhibitors, expanding the application range of kinetic hydrate inhibitors and playing a significant role in ensuring the flow of natural gas pipelines. Furthermore, the kinetic hydrate inhibitors and compound hydrate inhibitors provided by this invention require low dosages; only 1 wt% is needed to effectively inhibit the formation of natural gas hydrates. Attached Figure Description

[0033] Figure 1 The image shows the gel permeation chromatography elution curve of the kinetic hydrate inhibitor provided in Example 1.

[0034] Figure 2 This is a gel permeation chromatography molecular distribution curve of the kinetic hydrate inhibitor provided in Example 1.

[0035] Figure 3 The hydrogen-1 nuclear magnetic resonance spectrum of the kinetic hydrate inhibitor provided in Example 1.

[0036] Figure 4 This is a pressure / temperature-time curve inside the test vessel during the induction period test in Example 1, which is part of the inhibition performance testing.

[0037] Figure 5 This is a schematic diagram of the chemical shifts of the functional groups of the kinetic hydrate inhibitor provided in Example 1.

[0038] Figure 6 This is a schematic diagram showing the fog-like appearance of the aqueous solution of the test sample during the turbidity point test in Example 1. Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0040] Example 1

[0041] This embodiment provides a kinetic hydrate inhibitor, which is prepared by the following method:

[0042] (1) Dissolve 68 mmol of the first monomer N-vinylcaprolactam (PVCap, 99% GC) in 80 ml of toluene to prepare an N-vinylcaprolactam solution;

[0043] (2) Add 1.6 mmol of initiator 2,2-azobisisobutyronitrile (AIBN, 99% recrystallization) to the N-vinylcaprolactam solution prepared in step (1) and mix well; then add 12 mmol of the second monomer polyethylene glycol methyl ether methacrylate (PEOMA, >98% GC) and 0.2 mmol of chain transfer agent mercaptoacetic acid (>95% AR) and mix well to obtain a homogeneous reaction system;

[0044] (3) The uniformly mixed reaction system was deoxygenated and then reacted at 80°C for 3.5 hours to obtain a solution containing a kinetic hydrate inhibitor;

[0045] (4) The solution containing the kinetic hydrate inhibitor obtained in step (3) was subjected to rotary evaporation using a rotary evaporator to remove the organic solvent; then the product obtained by rotary evaporation was filtered and washed with n-hexane and tetrahydrofuran to remove unreacted substances and other impurities, and the kinetic hydrate inhibitor PV-S was obtained.

[0046] The washing of the product obtained by rotary evaporation with n-hexane and tetrahydrofuran includes:

[0047] 1) First, add tetrahydrofuran dropwise to the product until the product dissolves;

[0048] 2) Add n-hexane to the solution obtained in step 1) to form a precipitate;

[0049] 3) Filter out the precipitate obtained in step 2);

[0050] 4) The precipitate is used as a product and steps 1) to 3) are repeated twice. The final precipitate is the kinetic hydrate inhibitor PV-S.

[0051] Kinetic hydrate inhibitor performance test

[0052] 1. The prepared kinetic hydrate inhibitor PV-S was characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance spectroscopy (NMR). GPC was mainly used to obtain the molecular weight range of the product, while NMR was used to obtain the molecular configuration of the product.

[0053] Gel permeation chromatography detection: The kinetic hydrate inhibitor PV-S prepared by gel permeation chromatography was tested using an Agilent 1260 instrument. The elution curve and molecular distribution curve were obtained by the chromatograph. Figure 1 , Figure 2 As shown, the average molecular weight of the kinetic hydrate inhibitor was obtained, with a weight-average molecular weight Mw of 8933 and a number-average molecular weight Mn of 1727.

[0054] 1H NMR spectroscopy: The kinetic hydrate inhibitor PV-S prepared was analyzed using a Bruker AVANCE III HD 400M instrument. The 1H NMR spectrum of the kinetic hydrate inhibitor was obtained as follows: Figure 3 As shown.

[0055] The kinetic hydrate inhibitor PV-S was obtained by copolymerization of two monomers: N-vinylcaprolactam and polyethylene glycol methyl ether methacrylate. The structural formula of the reaction product is as follows:

[0056]

[0057] The structure of the kinetic hydrate inhibitor PV-S was verified by proton nuclear magnetic resonance (H-NMR) spectroscopy. Combining the structural formula and common chemical shifts from H-NMR, the chemical shifts corresponding to different groups in the molecular formula were obtained, such as... Figure 5 As shown, only four groups—b, c, i, and h—have chemical shifts greater than 3 ppm. For example... Figure 3 As shown, the corresponding absorption peaks can be found in the spectrum. Peak c corresponds to a triplet, consistent with the CH-N chemical environment. Peak b has an excessively strong signal, making it difficult to distinguish the number of splits. Peak j represents -O-CH3 bonded only to oxygen. Peak i corresponds to the chemical shift of the ester oxygen group. Peaks greater than 5 ppm are solvent peaks and other impurities. The number of protons is quantitatively calculated by integrating the peak areas. Since a hydrogen atom has only one proton, the ratio of hydrogen atoms in the groups can also be obtained. Therefore, the hydrogen atom ratio of group a to group c is 0.48:1. Considering the ratio of hydrogen atoms attached to a single group of both groups is 1:3, the x:y ratio is 1.44. Thus, the structural formula of the kinetic hydrate inhibitor PV-S is shown above, where x / y = 1.44, and its average molecular weight Mw is 8933, and Mn is 1727.

[0058] 2. The cloud point and inhibition performance of the prepared kinetic hydrate inhibitor PV-S and the N-vinylcaprolactam PVCap used to prepare PV-S were tested.

[0059] Cloud point detection: A. First, dissolve the sample to be tested in deionized water to form a 1 wt% aqueous solution; B. Place the aqueous solution in a transparent reagent bottle and then place the bottle in a heat-stable water bath; C. Slowly increase the water bath temperature from room temperature (20°C) at a rate of 0.5°C per minute, observing the aqueous solution in the transparent reagent bottle. Measure the water bath temperature using a digital thermometer with an accuracy of ±0.1K; D. The aqueous solution begins to show a cloud point... Figure 6The temperature of the hazy appearance is recorded as the cloud point temperature; E. Steps A to D are repeated three times for each sample to be tested, and the average of the three cloud point temperatures is taken as the cloud point temperature of the sample to be tested.

[0060] The results are shown in Table 1. Compared with the traditional kinetic inhibitor PVCap, the kinetic hydrate inhibitor PV-S increased the cloud point by 9℃, and compared with the original PVCap, the cloud point increased by 23.7%, showing significant effects.

[0061] Table 1

[0062] PVCap 38℃ PV-S 47℃

[0063] Inhibition performance testing: A five-vessel linkage swing reactor was used to conduct hydrate formation experiments, testing the hydrate formation induction period of the system with the added sample, thereby characterizing the inhibition performance of the sample; specifically including:

[0064] A. Solution preparation: Dissolve the sample to be tested in deionized water to form an aqueous solution with a mass concentration of 1 wt%; B. Liquid addition and gas injection: Introduce the prepared aqueous solution of the sample to be tested into the test vessel. Open the inlet valve and fill the test vessel with natural gas. After filling with natural gas, to ensure no leakage, maintain the gas pressure inside the vessel at 9 MPa for 30 minutes without significant change. C. Induction period test: Set the initial temperature to 20℃, then start the power swing device to fully mix the liquid inside the test vessel. Adjust the temperature to the target temperature for hydrate formation (1℃), wait for the temperature inside the test vessel to reach the target temperature for hydrate formation, and collect and record the pressure and temperature inside the test vessel. After the temperature and pressure inside the test vessel stabilize (pressure and temperature must remain constant within 10 minutes), the induction period test ends. D. Post-experiment work: After the induction period test, first adjust the temperature to 20℃ and wait for the test vessel to reach a stable state. Then, disassemble the experimental equipment and clean it thoroughly. After cleaning, turn off the power of the equipment and allow it to cool naturally. E. Repeat the experiment three times for each sample and take the average value of the induction period.

[0065] Figure 4 The dynamic changes in temperature and pressure within the test vessel over time are demonstrated. Based on the evolution of these parameters, the hydrate formation process can be divided into four main stages:

[0066] Natural gas dissolution stage: In this stage, the test vessel is maintained under high pressure; the experimental gas is fully mixed with the liquid under the action of dynamic stirring and gradually dissolves in the liquid; until a stable state is reached, at which point hydrates have not yet formed;

[0067] Hydrate nucleation induction stage: As the temperature of the test vessel continues to decrease, when the temperature and pressure reach the conditions for hydrate formation, water molecules and gas molecules begin to aggregate to form clusters, which gradually grow to the critical size. This stage ends when the pressure in the system changes significantly.

[0068] Hydrate growth stage: Hydrates initially form at the gas-liquid interface; during this stage, as the gas is continuously consumed, the volume of the hydrate increases, which leads to a significant decrease in pressure inside the test vessel.

[0069] Hydrate decomposition stage: Since the induction period test has ended, the water bath temperature for this stage is set to 20℃. As the system temperature continues to rise, the hydrate begins to decompose, accompanied by the release of natural gas from the hydrate, and the system pressure continuously increases. Finally, as the system pressure stabilizes, the hydrate decomposition stage is complete.

[0070] The duration of the hydrate nucleation induction phase, i.e. the induction period, is used as an evaluation index for the inhibitory performance.

[0071] Table 2 shows the induction period data for each group of samples. The characterization results indicate that the kinetic hydrate inhibitor PV-S has significantly improved inhibitory performance compared to the traditional kinetic inhibitor PVCap, with the hydrate induction period of 12.62 h, an increase of 25.7%, compared to 10.04 h in the 1 wt% PVCap system.

[0072] Table 2

[0073] Inhibitor-free blank group 0.52 1.00 PVCap 10.04 19.31 PV-S 12.62 24.27

[0074] Example 2

[0075] This embodiment provides a compound hydrate inhibitor PV-S+MEG.

[0076] The compound hydrate inhibitor PV-S+MEG comprises the kinetic hydrate inhibitor provided in Example 1 of the present invention and ethylene glycol MEG in a mass ratio of 3:20.

[0077] Performance testing of compound hydrate inhibitors

[0078] 1. The turbidity point of the compound hydrate inhibitor PV-S+MEG and the compound hydrate inhibitor PVCap+MEG provided in this embodiment was detected; wherein, the compound hydrate inhibitor PVCap+MEG includes N-vinylcaprolactam PVCap and ethylene glycol MEG used in Example 1 in a mass ratio of 3:20.

[0079] Cloud point detection: A. First, dissolve the sample to be tested in deionized water to form an aqueous solution; the mass concentration of MEG in the aqueous solution is 10%, and the mass concentration of PVCapB or PV-S is 1.5%; place the aqueous solution in a transparent reagent bottle and place the transparent reagent bottle in a heat-stable water bath; C. Slowly increase the water bath temperature from room temperature (20℃) at a rate of 0.5℃ per minute, observing the aqueous solution in the transparent reagent bottle, and measure the water bath temperature using a digital thermometer with an accuracy of ±0.1K; D. The aqueous solution begins to show the cloud point... Figure 6 The temperature of the hazy appearance is recorded as the cloud point temperature; E. Steps A to D are repeated three times for each sample to be tested, and the average of the three cloud point temperatures is taken as the cloud point temperature of the sample to be tested.

[0080] The results are shown in Table 3.

[0081] Table 3

[0082] PV-S+MEG 55℃ PVCap+MEG 42℃

[0083] As shown in Tables 1 and 3, the addition of the thermodynamic hydrate inhibitor ethylene glycol can improve the low cloud point of single inhibitors. The combination of PV-S and MEG is particularly effective, raising the cloud point to 55℃, which is 44.7% higher than that of the traditional commercial inhibitor PVCap. This helps to reduce the negative impact of drastic temperature changes in areas such as throttling elements and heating devices on the efficacy of the kinetic inhibitor.

[0084] 2. The inhibitory performance of the compound hydrate inhibitor PV-S+MEG, compound hydrate inhibitor PVCap+MEG, and ethylene glycol MEG provided in this embodiment was tested; wherein, the compound hydrate inhibitor PVCap+MEG includes N-vinylcaprolactam PVCap and ethylene glycol MEG used in Example 1 in a mass ratio of 3:20.

[0085] Inhibition performance testing: A five-vessel linkage swing reactor was used to conduct hydrate formation experiments, testing the hydrate formation induction period of the system with the added sample, thereby characterizing the inhibition performance of the sample; specifically including:

[0086] A. Solution preparation: Dissolve the sample to be tested in deionized water to form an aqueous solution of the sample to be tested; the mass concentration of MEG in the aqueous solution of the sample to be tested is 10%, and when it contains PVCapB or PV-S, the mass concentration of PVCapB or PV-S is 1.5%; B. Liquid addition and gas injection: Introduce the prepared aqueous solution of the sample to be tested into the test vessel. Open the inlet valve and fill the test vessel with natural gas. After filling with natural gas, to ensure no leakage, maintain the gas pressure inside the vessel at 9 MPa for 30 minutes without significant change. C. Induction period test: Set the initial temperature to 20℃, then start the power swing device to fully mix the liquid inside the test vessel. Adjust the temperature to the target temperature for hydrate formation (1℃), wait for the temperature inside the test vessel to reach the target temperature for hydrate formation, and collect and record the pressure and temperature inside the test vessel. After the temperature and pressure inside the test vessel stabilize (pressure and temperature must remain constant within 10 minutes), the induction period test ends. D. Post-experiment work: After the induction period test, first adjust the temperature to 20℃ and wait for the test vessel to reach a stable state. Then, disassemble the experimental equipment and clean it thoroughly. After cleaning, turn off the power of the equipment and allow it to cool naturally. E. Repeat the experiment three times for each sample and take the average value of the induction period.

[0087] The results are shown in Table 4.

[0088] Table 4

[0089] Inhibitor-free blank group 0.52 1.00 MEG 0.55 1.05 PV-S+MEG ＞68 ＞130.77 PVCap+MEG 23.64 45.46

[0090] As shown in Tables 2 and 4, the compound hydrate inhibitor provided by this invention combines the advantages of both mechanodynamic and kinetic hydrate inhibitors. Compared with single hydrate kinetic inhibitors, it significantly improves inhibitory performance while increasing the cloud point. Characterization results show that the modified product combined with ethylene glycol (PV-S+MEG) has the best effect, extending the induction period to more than 68 hours, which is more than 130 times higher than the blank group without inhibitor. It also has superior inhibitory performance compared with the traditional commercial inhibitor PVCap, with an induction period extended by more than 58 hours.

[0091] In summary, the hydrate inhibitor provided by this invention has excellent high turbidity point and high inhibition performance characteristics, which helps to reduce the negative impact of drastic temperature changes in areas such as throttling elements and heating devices on the effect of kinetic inhibitors, expands the application range of kinetic hydrate inhibitors, and is of great significance for ensuring the flow of natural gas pipelines.

[0092] The embodiments described above are for the purpose of better explaining the present invention. For those skilled in the art, it is not difficult to make various modifications to these embodiments without departing from the principles and spirit of the present invention. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and variations made to the present invention by those skilled in the art based on the principles and spirit of the present invention should be within the scope of protection of the present invention.

Claims

1. A kinetic hydrate inhibitor, wherein, The chemical structural formula of this kinetic hydrate inhibitor is shown below: Among them, x:y=0.5-2.0, x=8-20, y=10-16; n=6-9; Among them, the weight-average molecular weight (Mw) of the kinetic hydrate inhibitor is 6000-10000; Among them, the number-average molecular weight Mn of the kinetic hydrate inhibitor is 1000-3000.

2. The method for preparing the kinetic hydrate inhibitor according to claim 1, wherein, The method includes: N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, mercaptoacetic acid, 2,2-azobisisobutyronitrile, and an organic solvent were mixed to obtain a homogeneous reaction system; wherein the ratio of N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, mercaptoacetic acid, 2,2-azobisisobutyronitrile, and organic solvent was 60-120 mmol: 10-20 mmol: 0.1-0.5 mmol: 1-3 mmol: 80 ml; The homogeneous reaction system is deoxygenated and then reacted at 70-90°C for 4-6 hours to obtain a solution containing the kinetic hydrate inhibitor.

3. The preparation method according to claim 2, wherein, The preparation methods for kinetic hydrate inhibitors also include: The organic solvent in the solution containing the kinetic hydrate inhibitor was removed by rotary evaporation. The product obtained by rotary evaporation was then washed with n-hexane and tetrahydrofuran to remove unreacted substances and other impurities, thus obtaining the kinetic hydrate inhibitor.

4. The preparation method according to claim 3, wherein, The product obtained by rotary evaporation was washed with n-hexane and tetrahydrofuran, including: 1) First, add tetrahydrofuran dropwise to the product until the product dissolves; 2) Add n-hexane to the solution obtained in step 1) to form a precipitate; 3) Filter out the precipitate obtained in step 2); 4) The precipitate is used as a product to repeat steps 1) to 3) at least twice more, and the final precipitate is the purified kinetic hydrate inhibitor.

5. The preparation method according to claim 2, wherein, N-vinylcaprolactam, polyethylene glycol methyl ether methacrylate, mercaptoacetic acid, 2,2-azobisisobutyronitrile, and an organic solvent were mixed to obtain a homogeneous reaction system comprising: N-vinylcaprolactam was dissolved in an organic solvent to prepare an N-vinylcaprolactam solution; Add 2,2-azobisisobutyronitrile to the N-vinylcaprolactam solution and mix thoroughly; then add polyethylene glycol methyl ether methacrylate and mercaptoacetic acid and mix thoroughly to obtain a homogeneous reaction system.

6. The preparation method according to claim 2, wherein, The number average molecular weight of polyethylene glycol methyl ether methacrylate is 475.

7. The preparation method according to claim 2, wherein, Toluene and / or carbon tetrachloride are selected as the organic solvents.

8. A compound hydrate inhibitor, wherein, The compound hydrate inhibitor comprises the kinetic hydrate inhibitor of claim 1 and ethylene glycol in a mass ratio of 1:5 to 1:10, or comprises the kinetic hydrate inhibitor of claim 1 and methanol in a mass ratio of 1:15 to 1:30.

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