Natural gas hydrate resistant coating

Abstract

The invention discloses an anti-natural gas hydrate coating which is obtained by coating the inner surface of a pipeline with a coating which can release phase change latent heat when the temperature drops and then curing the coating at low temperature, and the coating comprises the following raw materials in percentage by mass: 100% of dimethyl sulfoxide aqueous solution, 10% of gelatin and 10% of waterborne polyurethane. The mass fraction of the dimethyl sulfoxide aqueous solution is 60-90 wt%, the mass fraction of the waterborne polyurethane is 5-20 wt%, and the balance is gelatin. When the temperature drops, latent heat of phase change can be released, delayed freezing of the hydrate is achieved, the adhesive force of the hydrate is reduced, the self-repairing characteristic is achieved, and the problems that due to the too low temperature, the hydrate and the surface structure of the super-hydrophobic coating are mechanically interlocked, and the interior of the surface texture is coagulated are solved; and the problem of poor recycling performance of the existing super-hydrophobic coating is also solved.

Description

Technical field:

[0001] The invention relates to the technical field of coatings, and in particular to a natural gas hydrate resistant coating. Background technology:

[0002] During deep-sea oil and gas extraction and transportation, natural gas and light components in crude oil can form ice-like solid substances called natural gas hydrates with water under low temperature and high pressure conditions. If natural gas hydrates are formed in oil and gas pipelines and corresponding equipment, they will cause blockages. Moreover, 1 volume of natural gas hydrates can store 150-180 times the volume of natural gas under standard conditions. When hydrates form blockages, a large amount of gas will be produced in the blocked section. Any constraints will cause a surge in gas pressure. Therefore, the formation of natural gas hydrates in pipelines may block pipelines, bring serious safety hazards, cause production stagnation, and cause huge economic losses.

[0003] At present, the most common method to prevent and control hydrate pipeline blockage is to add chemical inhibitors. The inhibitors used mainly include thermodynamic hydrate inhibitors (THI), kinetic hydrate inhibitors (KHI) and anti-agglomeration agents (AA). Thermodynamic hydrate inhibitors (THI) are added in large quantities and require subsequent separation, which will increase the investment in fixed equipment. Moreover, some thermodynamic hydrate inhibitors (THI) are harmful to the environment and are prohibited from use in some areas. KHI and AA are still not used on a large scale due to the lack of cost-effective inhibitors, difficulty in degradation and other shortcomings. In recent years, designing a surface coating for hydrates to passively reduce hydrate blockage has been regarded as an alternative and effective method.

[0004] At present, most reported anti-hydrate coatings utilize superhydrophobic surfaces to reduce the adhesion of hydrates to the pipe wall. Such surfaces combine the characteristics of surface micro / nanostructures and low surface energy, which can effectively block air between surface irregularities and result in a reduced contact area between water and the solid surface, facilitating the rapid removal of liquid water from the surface before it forms hydrates (ice nuclei) with guest molecules. For example, CN 103189594 B discloses coating at least a portion of the inner surface of the pipeline with a non-metallic surface coating, where the non-metallic surface coating is selected from silicon coatings and coatings formed by applying crosslinked polymeric materials selected from siloxanes, fluorosiloxanes, and fluoropolymers. CN 109719013 A discloses adding polytetrafluoroethylene, polyphenylene sulfide, and hydrophobic fumed silica into a dispersant and ultrasonically dispersing to obtain a dispersion; stirring the dispersion with a magnetic stirrer, while dropping a leveling thickener and stirring evenly to obtain an anti-hydrate coating; then immersing the pretreated substrate in the coating, taking it out, standing still for natural leveling, and drying; and sintering at high temperature to obtain an anti-hydrate coating. This coating prevents the aggregation and adhesion of hydrate particles in pipelines and equipment by delaying the nucleation and growth of hydrates and reducing the adhesion force between hydrate particles and the inner walls of pipelines and equipment.

[0005] However, once water droplets penetrate into the pores of the micro / nanostructured surface of the superhydrophobic coating and condense, the mechanical interlocking of hydrates with the surface structure will lead to an increase in adhesion force. Additionally, repeated freeze / thaw cycles may cause the performance of the micro / nanostructures to fail, weakening the anti-hydrate performance of the superhydrophobic coating. Therefore, a new type of coating that can solve the problem of condensation occurring inside the surface texture and improve the cyclic use performance is needed. Summary of the Invention:

[0006] The objective of the present invention is to provide an anti-natural gas hydrate coating that releases latent heat of phase change when the temperature drops during phase change, realizes the delayed freezing of hydrates and reduces the adhesion force of hydrates, and has self-healing properties, solving the problems of mechanical interlocking between hydrates and the surface structure of the superhydrophobic coating due to too low temperature and condensation occurring inside the surface texture, and also solving the problem of poor cyclic use performance of existing superhydrophobic coatings.

[0007] The present invention is achieved through the following technical solutions:

[0008] An anti-natural gas hydrate coating is obtained by coating the inner surface of a pipeline with a coating that releases latent heat of phase change when the temperature drops and then curing at a low temperature of 0 - 5°C. The raw materials of the coating are dimethyl sulfoxide aqueous solution, gelatin, and waterborne polyurethane. Calculated based on the total mass percentage of the coating raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 60 - 90 wt%, the mass fraction of the waterborne polyurethane is 5 - 20 wt%, and the balance is gelatin.

[0009] The method for preparing the coating is as follows: Gelatin is added to an aqueous solution of dimethyl sulfoxide. After heating and stirring at 60 °C until it is uniform and free of suspended matter, aqueous polyurethane is added, and stirring is continued to obtain an aqueous solution of dimethyl sulfoxide encapsulated in a polymer network.

[0010] Specifically, the mass fraction of dimethyl sulfoxide in the aqueous solution of dimethyl sulfoxide is 60%-90%, preferably 90%.

[0011] Dimethyl sulfoxide (DMSO) is colorless, non-toxic, water-soluble and hygroscopic. It can undergo a phase change at low temperature to form solid DMSO (SD), increasing its anti-solubility and anti-evaporation. Moreover, it can interact with water or ice (natural gas hydrate) to form a self-lubricating, non-freezing, aqueous (DMSO-water) liquid layer, thereby inhibiting the formation and propagation of ice crystals (natural gas hydrates). DMSO can be cross-linked with polymers into a three-dimensional network to form organic hydrogels (OHGs), expanding its scope of application. Gelatin is an abundant, environmentally friendly and multifunctional polymeric organic gelling agent with self-healing properties, which can restore its initial properties after damage through reversible hydrogen bonds. Aqueous polyurethane (WPU) has good biocompatibility, adjustable molecular structure and high mechanical properties, and can be used to enhance the mechanical properties of the coating.

[0012] The material of the pipeline is stainless steel, and the coating method is selected from any one of brushing, drop coating and dip coating. The coating thickness is 1.1-1.5 mm, and the curing time is 46-48 h.

[0013] The present invention also protects the application of the anti-natural gas hydrate coating, which is applied to the inner surface of oil and gas transmission pipelines, with an applicable pressure of 1-15 MPa and a temperature of -10 °C to 25 °C.

[0014] The beneficial effects of the present invention are as follows:

[0015] 1) The coating raw materials of the present invention are convenient to obtain, safe and reliable, and simple to prepare. They will release latent heat of phase change when the temperature drops, realizing the delayed freezing of hydrates and reducing the adhesion of hydrates, and solving the problem of mechanical interlocking of the surface structure of hydrates and superhydrophobic coatings and condensation occurring inside the surface texture due to too low temperature.

[0016] 2) The coating of the present invention introduces gelatin with self-healing properties, encapsulates the aqueous solution of dimethyl sulfoxide in a polymer network, and introduces aqueous polyurethane (WPU) to enhance mechanical strength and scope of application, greatly increasing the durability and mechanical stability of the material, and solving the problem of poor recycling performance of existing superhydrophobic coatings. Description of the drawings:

[0017] Figure 1 It is a schematic diagram of the physical cross-linking of dimethyl sulfoxide and gelatin. Detailed implementation manners:

[0018] The following is a further description of the present invention, rather than a limitation thereof.

[0019] Example 1:

[0020] An anti-natural gas hydrate coating, which is obtained by applying a coating material that releases latent heat of phase change when the temperature drops on the surface of a stainless steel sheet and then curing at 5°C for 48 hours, and the coating thickness is 1.3 mm.

[0021] The raw materials of the coating material are dimethyl sulfoxide aqueous solution, gelatin and waterborne polyurethane. Based on the total mass percentage of the coating material raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 70 wt%, the mass fraction of the waterborne polyurethane is 20 wt%, and the balance is gelatin.

[0022] The preparation method of the coating material is as follows: Gelatin is added to the dimethyl sulfoxide aqueous solution, heated and stirred at 60°C until it is uniform and free of suspended matter, and then waterborne polyurethane is added and stirring is continued to obtain it. The mass fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 90%.

[0023] Comparative Example 1:

[0024] Referring to Example 1, the difference is that there is no dimethyl sulfoxide aqueous solution in the raw materials of the coating material.

[0025] Comparative Example 2:

[0026] Referring to Example 1, the difference is that no coating material is applied on the stainless steel surface.

[0027] Example 2:

[0028] Referring to Example 1, the difference is that based on the total mass percentage of the coating material raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 75 wt%, the mass fraction of the waterborne polyurethane is 15 wt%, and the balance is gelatin. The mass fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 60%.

[0029] Example 3:

[0030] Referring to Example 1, the difference is that based on the total mass percentage of the coating material raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 75 wt%, the mass fraction of the waterborne polyurethane is 20 wt%, and the balance is gelatin. The mass fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 90%.

[0031] Example 4:

[0032] Referring to Example 1, the difference is that based on the total mass percentage of the coating raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 85 wt%, the mass fraction of the waterborne polyurethane is 5 wt%, and the balance is gelatin. The mass fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 70%.

[0033] Example 5:

[0034] Referring to Example 1, the difference is that based on the total mass percentage of the coating raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 85 wt%, the mass fraction of the waterborne polyurethane is 5 wt%, and the balance is gelatin. The mass fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 80%.

[0035] Control the temperature and examine the onset time of surface hydrate formation of the stainless steel sheets coated with the anti-natural gas hydrate coating obtained in Examples 1-5 and the stainless steel sheets obtained in Comparative Examples 1-2.

[0036] The natural gas hydrate-forming gas uses a mixed gas. The composition of Mixed Gas 1 is: methane 92 vol%, ethane 5 vol%, and propane 3 vol%. The composition of Mixed Gas 2 is n-pentane 0.208 vol%, isopentane 0.201 vol%, isobutane 0.493 vol%, n-butane 0.789 vol%, propane 3.13 vol%, ethane 7.51 vol%, nitrogen 0.398 vol%, and methane 87.271 vol%.

[0037] The device for testing the influence of the coating on hydrate formation uses a flow loop. The loop is 30 meters long, built of 316 stainless steel, with an inner pipe diameter of 2.54 cm. The loop contains a 30-cm-long transparent section and a transparent window for observing the flow of hydrates at different positions inside the pipe. The temperature of the loop is cooled by a refrigeration unit through a jacket. The temperature range of the refrigeration unit is -20 to 50 °C. The maximum design pressure is 15 MPa. The loop is equipped with 8 temperature sensors at different positions, with an accuracy of 0.15 °C; 8 pressure sensors, with an accuracy of 0.25% grade; 2 differential pressure gauges, with an accuracy of ±0.065% F.S; 1 liquid flowmeter, with an accuracy of ±0.065% F.S; all data such as temperature, pressure, differential pressure, and flow are collected and recorded by a computer. The liquid flow in the loop is achieved by a piston pump. In this experiment, both the gas and liquid do not flow and it is carried out under static conditions. The two ends of the stainless steel sheet coating are fixed on the protruding fixed columns in the stainless steel pipe and are suspended as a whole in the transparent section. The microscope observes the induction time of hydrate formation on the coating surface through the transparent section. The results are shown in Tables 1 and 2.

[0038] Table 1 Test results of the anti-natural gas hydrate surface under different experimental conditions for Mixed Gas 1

[0039]

[0040] Table 2 Test results of the surface resistance to natural gas hydrate under different experimental conditions for Gas Mixture 2

[0041]

[0042]

Claims

1. An anti-natural gas hydrate coating, characterized in that, the coating is obtained by coating the inner surface of a pipeline with a coating material that releases latent heat of phase change when the temperature drops and undergoes a phase change, and then curing at a low temperature of 0-5°C. The raw materials of the coating material are dimethyl sulfoxide aqueous solution, gelatin and waterborne polyurethane. Based on the total mass percentage of the coating material raw materials being 100%, the mass fraction of the dimethyl sulfoxide aqueous solution is 60-90wt%, the mass fraction of the waterborne polyurethane is 5-20wt%, and the balance is gelatin.

2. The anti-natural gas hydrate coating according to claim 1, characterized in that, the mass fraction of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 60%-90%.

3. The anti-natural gas hydrate coating according to claim 1, characterized in that, the preparation method of the coating material is as follows: gelatin is added to the dimethyl sulfoxide aqueous solution, heated and stirred at 60°C until uniform and free of suspended matter, and then waterborne polyurethane is added and stirring is continued to obtain it.

4. The anti-natural gas hydrate coating according to claim 1, characterized in that, the material of the pipeline is stainless steel.

5. The anti-natural gas hydrate coating according to claim 1, characterized in that, the coating method is selected from any one of brush coating, drop coating and dip coating.

6. The anti-natural gas hydrate coating according to claim 1, characterized in that, the coating thickness is 1.1-1.5 mm.

7. The anti-natural gas hydrate coating according to claim 1, characterized in that, the curing time is 46-48 h.

8. The application of the anti-natural gas hydrate coating according to claim 1, characterized in that: it is applied to the inner surface of oil and gas transmission pipelines, and the applicable pressure is 1-15 MPa and the temperature is -10°C to 25°C.

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