A temperature-resistant anti-wax drag-reducing pipeline inner wall coating and a preparation method thereof

Abstract

The application discloses a kind of temperature-resistant wax-proof drag-reducing pipeline inner wall coating and preparation method thereof, belong to wax-proof drag-reducing coating technical field.Specifically, a kind of temperature-resistant wax-proof drag-reducing pipeline inner wall coating is disclosed, by weight parts, including the following components: silicone modified epoxy resin 72-80 parts, alkylsilane-epoxy silane synergistic modified reduced graphene oxide 1.0-4.0 parts, dispersing agent 0.8-1.2 parts, leveling agent 0.3-0.4 parts, defoaming agent 0.2-0.3 parts, dimethylbenzene 7-10 parts, propylene glycol methyl ether acetate 5-7 parts, phenolic resin curing agent 13-18 parts, imidazole accelerator 0.15-0.40 parts.The coating of the application achieves a good overall balance in wax-proof rate, pipe flow pressure drop, surface roughness and adhesion, and is suitable for long-term protection needs of the inner wall of a pipeline containing waxy medium.

Description

Technical Field

[0001] This invention belongs to the field of anti-wax drag-reducing coating technology, specifically, it relates to a temperature-resistant anti-wax drag-reducing coating for the inner wall of a pipe and its preparation method. Background Technology

[0002] Crude oil and waxy media typically exhibit good fluidity at higher temperatures. However, during long-distance transport, wellbore lifting, or intermittent operation, the medium temperature gradually decreases along the pipeline. When the medium temperature approaches or falls below the wax precipitation temperature, wax crystals easily precipitate, grow, and adhere near the inner wall of the pipeline, leading to a reduction in the effective flow cross-sectional area and an increase in transport pressure drop, thereby increasing the costs of cleaning, heating, and maintenance. Wax deposition on the inner wall of the pipeline is not only related to the composition and temperature changes of the waxy medium itself, but also to the surface energy, roughness, heat transfer state, and coating stability of the inner wall of the pipeline. Rough surfaces easily provide attachment and growth sites for wax crystals, while high surface energy inner walls tend to enhance the interaction between wax crystals and the wall surface. Under fluctuating temperature conditions, if the coating's temperature resistance stability is insufficient, the low adhesion characteristics and adhesion of the coating surface will gradually decrease with thermal cycling.

[0003] In the prior art, epoxy resin, polyurethane, silicone resin, fluororesin or their composite systems are often used as film-forming materials for the coating of the inner wall of pipes to improve the anti-corrosion, wear resistance and anti-adhesion performance of the inner wall of pipes. For example, Chinese patent CN102268223A discloses an anti-wax-caking organic coating and a method for preparing an organic coating including the same. The anti-wax-caking organic coating includes silicone polyaspartic acid ester and isocyanate with structural formula (1). In formula (1), R is an alkane group. When X is -R′-[SiR″2O]nSiR″2-R′-, Y is H; or when X is -(CH2)P-, Y is the anti-wax-caking organic coating provided by the present invention, which reduces the raw material cost and shortens the curing time in the process of forming the organic coating. This technical solution uses silicone polyaspartic acid ester and isocyanate to form an anti-wax-caking organic coating, uses silicone segments to reduce surface energy, and reduces the adhesion of wax crystals on the pipe wall through the organic coating with lower roughness. However, the aforementioned organosilicon polyaspartic acid ester / isocyanate system mainly relies on the low surface energy of organosilicon segments and the rapid curing characteristics of polyaspartic acid ester system. Its technical focus is not on the heat resistance stability of the cross-linked network in the high-temperature pipeline inner wall environment. In reality, for some high-temperature gathering or deep well pipeline inner walls, the local temperature may reach above 200°C or even close to 260°C. Under such conditions, polyurethane or polyurea related structures formed by isocyanate curing are prone to segment relaxation, thermal aging, or decreased interfacial adhesion.

[0004] To address the issue of low surface energy and the problem of wax adhesion in micro / nano structures, Chinese patent CN119119826A discloses a superhydrophobic anti-wax epoxy composite coating, its preparation method, and its application. The method involves first modifying nano-silica with fluorinated silanes to obtain fluorinated silane-modified nano-silica. Then, a fluorinated modifier with epoxy groups is prepared via a mercaptoene click reaction and blended with epoxy resin to obtain a modified epoxy resin. Finally, the fluorinated silane-modified nano-silica is blended with the modified epoxy resin to obtain the composite coating. The composite coating obtained exhibits a water and diesel contact angle greater than 150° and a roll-off angle less than 5°, demonstrating superhydrophobic properties and an anti-wax adhesion efficiency ≥75%. This technical solution uses fluorinated silane-modified nano-silica and modified epoxy resin to form a superhydrophobic composite coating, thereby reducing the adhesion of paraffin wax to the coating surface. However, the superhydrophobic anti-wax route usually relies on micro-nano structures with high roughness and fluorine-containing low surface energy components. For the inner wall of the pipe, the rough structure may be worn, the filler may fall off and local failure may occur under long-term shearing, sand scouring or thermal cycling conditions of wax-containing media. Once the micro-nano structure is worn, not only will the anti-wax performance decrease, but the flow resistance may also increase due to local rough protrusions and form mechanical embedding points of wax crystals.

[0005] Therefore, how to provide a high-temperature resistant, wax-resistant, and drag-reducing pipe inner wall coating and its preparation method, which can maintain its high-temperature resistance, wax resistance, drag reduction, and erosion resistance for a long time at high temperatures, is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the deficiencies in the aforementioned technical solutions, the present invention aims to provide a heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating and its preparation method.

[0007] To achieve the above objectives, the present invention provides a temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating, comprising, by weight: 72-80 parts of organosilicon-modified epoxy resin, 1.0-4.0 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 0.8-1.2 parts of dispersant, 0.3-0.4 parts of leveling agent, 0.2-0.3 parts of defoamer, 7-10 parts of xylene, 5-7 parts of propylene glycol methyl ether acetate, 13-18 parts of phenolic resin curing agent, and 0.15-0.40 parts of imidazole accelerator.

[0008] The alkylsilane-epoxysilane synergistic modified reduced graphene oxide is prepared by synergistic hydrolysis grafting of long-chain alkylsilanes and epoxysilanes, mild reduction and post-treatment of graphene oxide.

[0009] The organosilicon-modified epoxy resin is a resin whose molecular structure contains both epoxy groups and organosilicon segments. The epoxy groups of the organosilicon-modified epoxy resin can undergo a cross-linking reaction with the phenolic resin curing agent.

[0010] The dispersant is any one of BYK-110, BYK-163, and BYK-180; The leveling agent is any one of BYK-306, BYK-333, and BYK-354; The defoamer is any one of BYK-066N, BYK-088, and BYK-A530; The phenolic resin curing agent is a thermosetting phenolic resin curing agent; The imidazole promoter is 2-methylimidazole, 2-ethyl-4-methylimidazole, or a combination of both.

[0011] The preparation method of the alkylsilane-epoxysilane synergistic modification of reduced graphene oxide includes the following steps: Step 1: After pre-drying the graphene oxide, add it to deionized water, and then wet, ultrasonically disperse and high-speed shear disperse to obtain a graphene oxide dispersion. Step 2: Add long-chain alkylsilanes and epoxysilanes to an alcohol-water system and hydrolyze them under acidic conditions to obtain silane hydrolysate; Step 3: Add the graphene oxide dispersion obtained in Step 1 to the silane hydrolysate obtained in Step 2, and carry out the grafting reaction under nitrogen protection, so that the hydrolyzed silane and the oxygen-containing functional groups on the surface of graphene oxide undergo condensation grafting. Step 4: After the grafting reaction is complete, a reducing agent is added for gentle reduction to reduce graphene oxide to synergistically modified reduced graphene oxide. Step 5: After the reaction is completed, solid-liquid separation, washing, drying, grinding and sieving are performed to obtain black powder alkylsilane-epoxysilane synergistic modified reduced graphene oxide.

[0012] The long-chain alkylsilane in step 2 is hexadecyltrimethoxysilane; The epoxy silane in step 2 is 3-glycidoxypropyltrimethoxysilane.

[0013] The graphene oxide sheets have a diameter of 0.5-5 μm and a thickness of 1-5 layers; The alkylsilane-epoxysilane synergistic modified reduced graphene oxide, after being ultrasonically dispersed in a xylene / propylene glycol methyl ether acetate mixed solvent for 30 min, had a sedimentation rate of no more than 2.0% after 24 h.

[0014] Further, by weight, the coating comprises: 76 parts of silicone-modified epoxy resin, 2.6 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 1.0 part of dispersant, 0.4 parts of leveling agent, 0.2 parts of defoamer, 8 parts of xylene, 6 parts of propylene glycol methyl ether acetate, 16 parts of phenolic resin curing agent, and 0.30 parts of 2-methylimidazole.

[0015] Furthermore, the silicone-modified epoxy resin is either Shin-Etsu Chemical ES-1001N or Evonik SILIKOPON® EF; Furthermore, the phenolic resin curing agent is either PHENODUR®PR-401 or PHENODUR®PR-516.

[0016] The present invention also provides a method for preparing the coating, comprising the following steps: Step A, preparation of graphene functional masterbatch: The alkylsilane-epoxysilane synergistic modified reduced graphene oxide is premixed with a portion of solvent and dispersant, and then subjected to ultrasonication and sand milling to obtain graphene functional masterbatch; Step B, Preparation of coating component A: Mix the organosilicon modified epoxy resin, the graphene functional masterbatch obtained in step A, the remaining solvent, the leveling agent and the defoamer evenly, and filter to obtain component A; Step C, Preparation and application of component B: Mix phenolic resin curing agent and imidazole accelerator evenly to obtain component B; before application, mix component A and component B according to the set equivalent ratio, degas, and then coat them onto the inner wall of the surface-treated steel pipe. Step D, curing into a film: After coating, first level at 25℃ for 20-40 min, then pre-cur at 70-90℃ for 0.5-1.5 h, then cure at 150-170℃ for 1.5-2.5 h, and finally post-cur at 210-230℃ for 1.5-2.5 h, thus obtaining a temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating.

[0017] Further, the graphene functional masterbatch in step A is prepared by the following method: alkylsilane-epoxysilane synergistic modification of reduced graphene oxide, a dispersant, and a portion of a mixed solvent are premixed. During premixing, the dispersant is first dissolved in the mixed solvent, and then the modified reduced graphene oxide is added in small amounts multiple times. The mixture is stirred at 500 r / min for 20 min to completely wet the powder. After wetting, it is ultrasonically dispersed for 30 min at an ultrasonic power of 400-600 W, with the system temperature controlled below 35℃. Subsequently, it is dispersed by sand milling for 1.5 h using 0.8-1.0 mm zirconium oxide beads at a milling speed of 1000-1500 r / min. After sand milling, a small amount of large particles are removed by filtering with a 100-mesh filter, thus obtaining a graphene functional masterbatch with a fineness of no more than 25 μm.

[0018] Furthermore, in step B, the filter mesh size of component A is not less than 100 mesh, and the applicable period of the mixed coating is 2-4 hours.

[0019] The beneficial effects of this invention are: 1. This invention uses an organosilicon-modified epoxy resin and a phenolic thermosetting system as the main framework. The phenolic resin curing agent undergoes an addition curing reaction with the epoxy groups in the organosilicon-modified epoxy resin through its phenolic hydroxyl groups under the catalysis of an imidazole accelerator, forming a three-dimensional cross-linked network. The organosiloxane segments mainly provide heat resistance, low surface energy, and flexibility. This curing system is suitable for high-temperature baking processes, which can impart excellent thermal stability to the coating. Furthermore, the organosiloxane segments reduce the tendency of interfacial adhesion, allowing the coating to maintain relatively stable anti-wax and protective properties even after high-temperature treatment. 2. This invention synergistically modifies reduced graphene oxide with alkylsilanes and epoxysilanes, so that the same graphene sheet simultaneously has a long-chain alkyl low-adhesion interface and an epoxysilane compatible interface. This structure not only helps to weaken the nucleation and adhesion of wax crystals on the coating surface, but also helps to reduce the aggregation and erosion of graphene in the resin. This results in a better overall balance of performance in terms of wax resistance, pipe flow pressure drop, surface roughness, and adhesion, making it particularly suitable for long-term protection of the inner wall of pipes containing wax. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. The illustrative embodiments and descriptions of this invention are for explanation only and are not intended to limit the invention. Furthermore, regarding numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0021] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0022] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0023] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0024] Example 1 A heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating, by weight, comprises the following: 72 parts of silicone-modified epoxy resin, 1.0 part of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 0.8 parts of dispersant, 0.3 parts of leveling agent, 0.2 parts of defoamer, 10 parts of xylene, 7 parts of propylene glycol methyl ether acetate, 13 parts of phenolic resin curing agent, and 0.15 parts of 2-methylimidazole.

[0025] The organosilicon-modified epoxy resin is a resin whose molecular structure contains both epoxy groups and organosiloxane segments; its epoxy groups can undergo a cross-linking reaction with phenolic resin curing agents. The silicone-modified epoxy resin is Shin-Etsu Chemical ES-1001N, with a solid content of 70 wt%. The phenolic resin curing agent is PHENODUR®PR-516, with a solid content of 70 wt%. The dispersant is BYK-110, the leveling agent is BYK-333, and the defoamer is BYK-A530.

[0026] The preparation method of the alkylsilane-epoxysilane synergistic modification of reduced graphene oxide: Step 1: Place graphene oxide in a vacuum drying oven at 60℃ for 8 hours and cool it for later use; take 10.0 parts of graphene oxide and add it to 2000 parts of deionized water, first wet it at 300 r / min for 20 min, then disperse it by ultrasonication for 45 min, with ultrasonic power of 500-700W and water bath temperature controlled at 25-35℃; then shear it at 1800-2200 r / min for 20 min to obtain a graphene oxide dispersion with a concentration of about 5 mg / mL; Step 2: Add 800 parts of anhydrous ethanol and 80 parts of deionized water to another dry four-necked flask, stir at 400-600 rpm, and adjust the pH to 4.8-5.2 with glacial acetic acid; then add 3 parts of hexadecyltrimethoxysilane and 4 parts of 3-glycidyl etheroxypropyltrimethoxysilane to the alcohol-water system, and hydrolyze at 25°C for 60 min; the system should remain milky white to semi-transparent throughout the hydrolysis process. Step 3: The graphene oxide dispersion prepared in Step 1 is added dropwise to the silane hydrolysate over 30 min. During the addition, the mixture is stirred at 400-600 r / min and nitrogen gas is introduced to maintain a slightly positive pressure nitrogen protection in the reaction system. After all the addition is completed, the temperature is raised to 55℃ and the reaction is maintained at this temperature for 5 h, so that the hydrolyzed silane undergoes condensation grafting near the oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups on the surface of graphene oxide. Step 4: After the grafting reaction is complete, the reaction system is heated to 85℃ again, 20 parts of ascorbic acid are added, and the reaction is continued for 3 hours under nitrogen protection to gently reduce the graphene oxide. During the reaction, the pH is controlled between 5.5 and 7.0. If the pH is lower than 5.0, it can be slowly adjusted to above 5.5 with dilute ammonia. The use of ascorbic acid for reduction can not only reduce the residue of strong reducing agent and retain some oxygen-containing groups, but also facilitate good interfacial bonding with organosilicon-modified epoxy resin in the future. Step 5: After the reaction is complete, allow the mixture to cool naturally to room temperature. Centrifuge at 8000 r / min for 15 min to collect the solid. Wash the solid three times with a 1:1 ethanol / water mixture, and then wash it twice with anhydrous ethanol until the pH of the supernatant is 6.5-7.5 and there is no obvious silane odor. Finally, dry the obtained wet filter cake under vacuum at 60℃ for 12 h. After drying, grind the filter cake gently and pass it through a 200-mesh sieve to obtain alkylsilane-epoxysilane synergistic modified reduced graphene oxide.

[0027] In specific implementation, the graphene oxide is a commercially available powder with a sheet diameter of 0.5-5 μm and a thickness of 1-5 layers.

[0028] A method for preparing a temperature-resistant, wax-resistant, and drag-reducing coating for the inner wall of a pipe includes the following steps: Step A, preparation of graphene functional masterbatch: The alkylsilane-epoxysilane synergistic modified reduced graphene oxide is premixed with a portion of solvent and dispersant, and dispersed by ultrasonication and sand milling to a fineness of no more than 25 μm to obtain graphene functional masterbatch; Step B, Preparation of coating component A: Mix the organosilicon modified epoxy resin, the graphene functional masterbatch obtained in step A, the remaining solvent, the leveling agent and the defoamer evenly, and filter to obtain component A; Step C, Preparation and application of component B: Mix phenolic resin curing agent and imidazole accelerator evenly to obtain component B; before application, mix component A and component B according to the set equivalent ratio, degas, and then coat them onto the inner wall of the surface-treated steel pipe. Step D, curing into a film: After coating, first level at 25℃ for 20-40 min, then pre-cur at 70-90℃ for 0.5-1.5 h, then cure at 150-170℃ for 1.5-2.5 h, and finally post-cur at 210-230℃ for 1.5-2.5 h, thus obtaining a temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating.

[0029] In specific implementation, the graphene functional masterbatch in step A is prepared by the following method: alkylsilane-epoxysilane synergistic modification of reduced graphene oxide, a dispersant, and a portion of the mixed solvent are first premixed. During premixing, the dispersant is first dissolved in the mixed solvent, and then the modified reduced graphene oxide is added in small amounts multiple times, while stirring at 500 r / min for 20 min to completely wet the powder. After sufficient wetting, ultrasonic dispersion is performed for 30 min at an ultrasonic power of 400-600 W, and the temperature of the reaction system is controlled below 35℃. Subsequently, the powder is dispersed by sand milling for 1.5 h using 0.8-1.0 mm zirconium oxide beads at a milling speed of 1000-1500 r / min. After sand milling, a small amount of large particles are removed by filtering with a 100-mesh filter, and finally, a graphene functional masterbatch with a fineness of no more than 25 μm is obtained.

[0030] In specific implementation, the mixed solvent is composed of xylene and propylene glycol methyl ether acetate in a mass ratio of 6:4.

[0031] Example 2 A heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating, by weight, comprises the following: 74 parts of silicone-modified epoxy resin, 1.8 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 0.9 parts of dispersant, 0.3 parts of leveling agent, 0.2 parts of defoamer, 9 parts of xylene, 6 parts of propylene glycol methyl ether acetate, 15 parts of phenolic resin curing agent, and 0.25 parts of imidazole accelerator.

[0032] The silicone-modified epoxy resin is Shin-Etsu Chemical ES-1001N, with a solid content of 70 wt%. The phenolic resin curing agent is PHENODUR®PR-401, with a solid content of 70 wt%. The dispersant is BYK-110, the leveling agent is BYK-306, and the defoamer is BYK-066N; The imidazole promoter is a combination of 2-methylimidazole and 2-ethyl-4-methylimidazole.

[0033] The preparation methods of alkylsilane-epoxysilane synergistic modification and reduction of graphene oxide and the preparation methods of temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coatings in Example 2 are the same as those in Example 1.

[0034] Example 3 A heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating, by weight, comprises the following: 76 parts of silicone-modified epoxy resin, 2.6 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 1.0 part of dispersant, 0.4 parts of leveling agent, 0.2 parts of defoamer, 8 parts of xylene, 6 parts of propylene glycol methyl ether acetate, 16 parts of phenolic resin curing agent, and 0.30 parts of 2-ethyl-4-methylimidazole.

[0035] The silicone-modified epoxy resin is Shin-Etsu Chemical ES-1001N, with a solid content of 70 wt%. The phenolic resin curing agent is PHENODUR®PR-516, with a solid content of 70 wt%. The dispersant is BYK-163, the leveling agent is BYK-333, and the defoamer is BYK-088; The preparation methods of alkylsilane-epoxysilane synergistic modification and reduction of graphene oxide and the preparation methods of temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coatings in Example 3 are the same as those in Example 1.

[0036] Example 4 A heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating, by weight, comprises the following: 78 parts of silicone-modified epoxy resin, 3.2 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 1.1 parts of dispersant, 0.4 parts of leveling agent, 0.2 parts of defoamer, 8 parts of xylene, 5 parts of propylene glycol methyl ether acetate, 17 parts of phenolic resin curing agent, and 0.35 parts of 2-methylimidazole.

[0037] The silicone-modified epoxy resin is EvonikSILIKOPON® EF, with a solid content of 70 wt%. The phenolic resin curing agent is PHENODUR®PR-401, with a solid content of 70 wt%. The dispersant is BYK-180, the leveling agent is BYK-354, and the defoamer is BYK-A530; The preparation methods of alkylsilane-epoxysilane synergistic modification and reduction of graphene oxide and the preparation methods of temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coatings in Example 4 are the same as those in Example 1.

[0038] Example 5 A heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating, by weight, comprises the following: 80 parts of silicone-modified epoxy resin, 4.0 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 1.2 parts of dispersant, 0.4 parts of leveling agent, 0.3 parts of defoamer, 7 parts of xylene, 5 parts of propylene glycol methyl ether acetate, 18 parts of phenolic resin curing agent, and 0.40 parts of 2-methylimidazole.

[0039] The silicone-modified epoxy resin is EvonikSILIKOPON® EF, with a solid content of 70 wt%. The phenolic resin curing agent is PHENODUR®PR-516, with a solid content of 70 wt%. The dispersant is BYK-110, the leveling agent is BYK-354, and the defoamer is BYK-066N; The preparation methods of alkylsilane-epoxysilane synergistic modification and reduction of graphene oxide and the preparation methods of temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coatings in Example 5 are the same as those in Example 1.

[0040] Comparative Example 1 The difference between this comparative example and Example 3 is that: no alkylsilane-epoxysilane synergistic modification of reduced graphene oxide is added, but xylene and propylene glycol methyl ether acetate are used to maintain the application viscosity close to that of Example 3; the dosage of other components, coating mixing method, coating method and curing method are the same as those of Example 3.

[0041] Comparative Example 2 The difference between this comparative example and Example 3 is that unmodified reduced graphene oxide is used instead of alkylsilane-epoxysilane synergistic modified reduced graphene oxide. The unmodified reduced graphene oxide is obtained by reducing graphene oxide with ascorbic acid, washing, and drying, without the addition of hexadecyltrimethoxysilane and 3-glycidoxypropyltrimethoxysilane. Apart from this, the amounts of other components, the coating mixing method, the coating method, and the curing method are the same as in Example 3.

[0042] Comparative Example 3 The difference between this comparative example and Example 3 is that hexadecylsilane is used to modify reduced graphene oxide alone instead of alkylsilane-epoxysilane synergistic modification of reduced graphene oxide. Furthermore, only hexadecyltrimethoxysilane is added during preparation, and 3-glycidoxypropyltrimethoxysilane is not added. Apart from this, the amounts of other components, the coating mixing method, the coating method, and the curing method are the same as in Example 3.

[0043] Comparative Example 4 The difference between this comparative example and Example 3 is that epoxy silane is used to modify reduced graphene oxide alone instead of alkyl silane-epoxy silane synergistic modification of reduced graphene oxide. Furthermore, only 3-glycidyl etheroxypropyltrimethoxysilane is added during preparation, and hexadecyltrimethoxysilane is not added. Apart from this, the amounts of other components, the coating mixing method, the coating method, and the curing method are the same as in Example 3.

[0044] Comparative Example 5 The difference between this comparative example and Example 3 is that the amount of alkylsilane-epoxysilane synergistic modified reduced graphene oxide is reduced to 0.3 parts. Otherwise, the amounts of other components, the coating mixing method, the coating method, and the curing method are the same as in Example 3.

[0045] Comparative Example 6 The difference between this comparative example and Example 3 is that the amount of alkylsilane-epoxysilane synergistic modified reduced graphene oxide is increased to 6 parts. Otherwise, the amounts of other components, the coating mixing method, the coating method, and the curing method are the same as in Example 3.

[0046] Comparative Example 7 The difference between this comparative example and Example 3 is that the silane hydrolysis grafting and reduction steps are omitted. Instead, unmodified reduced graphene oxide, hexadecyltrimethoxysilane, and 3-glycidyl etheroxypropyltrimethoxysilane are directly added to the coating system in the corresponding proportions of Example 3 for physical blending. The amounts of other components, coating mixing methods, coating methods, and curing methods are all the same as in Example 3.

[0047] Experimental Example 1 Cold finger anti-wax deposition and surface wettability tests: The coatings obtained in Examples 1-5 and Comparative Examples 1-7 were prepared on 50mm×50mm×3mm steel sheets, respectively, with the dry film thickness controlled at 300±20μm; uncoated steel sheets were used as the blank group. The test oil sample was a formulated wax oil with a wax content of 20wt% and a wax precipitation temperature of 38℃; the oil sample temperature was maintained at 55℃, and the cold finger tip temperature was maintained at 25℃, with a test time of 6h; after the test, the mass of wax deposited on the cold finger surface was scraped and weighed.

[0048] The wax resistance rate is calculated using the following formula: Wax resistance rate = (Wax deposition mass of blank group - Wax deposition mass of coated sample) / Wax deposition mass of blank group × 100%.

[0049] In this experiment, the wax deposition mass of the blank group was 1.820 g; the static contact angle of the coating surface with respect to deionized water and wax oil samples was measured using a contact angle meter, with 5 locations taken for each sample and the average value recorded; the test results are shown in Table 1: Table 1 Experimental Example 2 Heat resistance and wax resistance retention tests after high-temperature treatment: Samples were cut after curing the coatings of the examples and comparative examples, and thermogravimetric analysis was used to test the 5% mass loss temperature. The samples were also placed in a 260℃ hot air circulating oven for 8 hours, cooled to room temperature, and the mass loss rate was measured. The water contact angle and cold finger wax resistance performance were tested repeatedly. The wax resistance retention rate after 260℃ treatment was calculated as the ratio of the wax resistance rate after heat treatment to the wax resistance rate before heat treatment. The test results are shown in Table 2. Table 2 Experimental Example 3 Pipe flow pressure drop, surface roughness, and adhesion tests: The coatings of the examples and comparative examples were prepared on the inner wall of steel pipes with an inner diameter of 20 mm and a length of 1 m, respectively, with a dry film thickness of 300 ± 20 μm; wax oil prepared at 50 °C was circulated at a flow rate of 0.8 m / s for 30 min, and the stable pressure drop was recorded. The relative pressure drop reduction rate was calculated based on the pressure drop of the uncoated steel pipe; the arithmetic mean roughness Ra of the coating surface was tested using a surface profilometer; the adhesion was tested using the pull-out method, and the maximum pull-out strength before failure was recorded. The test results are shown in Table 3. Table 3 As can be seen from the data analysis in Tables 1 to 3, the coatings prepared in Examples 1-5 all exhibit good anti-wax, temperature resistance, drag reduction and erosion resistance properties.

[0050] Compared to Example 3, Comparative Example 1, without the addition of alkylsilane-epoxysilane synergistic modification of reduced graphene oxide, showed an increase in wax deposition mass from 0.438 g to 0.884 g, a decrease in wax resistance from 75.9% to 51.4%, a decrease in water contact angle from 116.8° to 95.8°, a decrease in wax oil sample contact angle from 61.5° to 41.0°, and a decrease in relative pressure drop from 17.4% to 8.6%. Meanwhile, Comparative Example 1 exhibited a 5% mass loss temperature of 340°C and an Ra of 0.54 μm, indicating that the main resin itself could still form a relatively dense and smooth heat-resistant coating. However, without the alkylsilane-epoxysilane synergistic modification of reduced graphene oxide, the near-surface layer of the coating lacked the low-shear interface regulation of long-chain alkyl low-surface-energy segments and graphene sheets, making it easier for wax crystals to nucleate, spread, and adhere to the resin surface.

[0051] Comparative Example 2 replaced the bissilane-modified reduced graphene oxide with unmodified reduced graphene oxide. Compared with Example 3, the wax resistance of Comparative Example 2 decreased from 75.9% to 55.7%, Ra increased from 0.46 μm to 1.22 μm, the relative pressure drop reduction rate decreased from 17.4% to 5.2%, the pull-off adhesion decreased from 10.8 MPa to 6.4 MPa, and the wax resistance retention rate after treatment at 260°C decreased from 92.5% to 71.3%. A possible reason is that the unmodified reduced graphene oxide has insufficient compatibility with the silicone-modified epoxy resin, making it easy for the sheets to overlap, accumulate, and form local protrusions in the coating. These protrusions not only increase fluid shear resistance but also provide mechanical embedding sites for wax crystals, ultimately becoming the starting point for peeling during the scouring process.

[0052] Comparative Example 3 used hexadecylsilane to modify reduced graphene oxide alone to replace the duosilane synergistic modification material. Compared with Example 3, the water contact angle of Comparative Example 3 was 121.0°, which was higher than that of Example 3, but its wax resistance rate was only 67.3%, Ra increased to 0.84 μm, the pull-off adhesion decreased to 6.8 MPa, and the wax resistance rate retention rate decreased to 78.2% after treatment at 260°C. The significant performance difference shown above may be due to the following reasons: the single alkyl silane modification used in Comparative Example 3 gave the graphene surface strong hydrophobicity, indicating that long-chain alkyl groups can indeed improve the initial hydrophobicity; however, Comparative Example 3 lacked an epoxy silane structure that could form a compatible or reactive bond with the organosilicon-modified epoxy resin, which may make the graphene sheets more prone to phase separation in the resin and form a weak interface; and the subsequent wax resistance rate also shows that simply pursuing a higher water contact angle does not directly equate to obtaining better and more durable wax resistance, drag reduction, and erosion resistance in the future.

[0053] Comparative Example 4 used epoxy silane alone to modify reduced graphene oxide instead of the duosilane synergistic modifier. Compared with Example 3, Comparative Example 4 had a Ra of 0.58 μm and a pull-off adhesion of 9.9 MPa, but its wax resistance decreased from 75.9% to 58.5%, its water contact angle decreased from 116.8° to 103.0°, and its wax oil sample contact angle decreased from 61.5° to 46.6°. After treatment at 260°C, the wax resistance retention rate decreased to 78.8%. This indirectly demonstrates that epoxy silane modification is indeed beneficial for improving compatibility and structural stability. However, single epoxy silane modification mainly solves the problem of interfacial bonding between graphene and resin, but cannot fully provide a long-chain alkyl low surface energy interface. The adhesion of wax crystals to the coating surface is still strong. Comparative Example 4 and Comparative Example 3 corroborate each other, which may be because: alkyl silanes tend to reduce wax adhesion, while epoxy silanes tend to improve compatibility and durability. No matter which part is missing, the comprehensive effect presented in Example 3 cannot be achieved.

[0054] Comparative Example 5 reduced the amount of bissilane-modified reduced graphene oxide to 0.3 parts. When the amount of functional material is too low, the long-chain alkyl low-adhesion sheets and the graphene low-shear structure cannot form a sufficiently continuous functional distribution on the coating surface and near the surface, thus only providing limited wax prevention and drag reduction contributions.

[0055] In Comparative Example 6, the amount of silane-modified reduced graphene oxide was increased to 6.0 parts. Adding excessive layered filler increases the probability of overlap, stacking, and agglomeration between layers, resulting in insufficient coating of the continuous resin phase and the formation of rough protrusions, weak interfaces, and erosion weak points. This demonstrates that more alkylsilane-epoxysilane synergistic modification of reduced graphene oxide is not necessarily better; rather, a balance must be struck between low surface energy, anti-waxing properties, low roughness, and low flow resistance.

[0056] Comparative Example 7 used ungrafted reduced graphene oxide, hexadecylsilane, and epoxysilane in a physical blend. Compared with Example 3, the wax deposition mass of Comparative Example 7 increased from 0.438 g to 0.835 g, the wax resistance decreased from 75.9% to 54.1%, the water contact angle decreased from 116.8° to 99.4°, Ra increased from 0.46 μm to 1.18 μm, the relative pressure drop reduction rate decreased from 17.4% to 6.6%, the pull-off adhesion decreased from 10.8 MPa to 6.3 MPa, and the wax resistance retention rate after treatment at 260°C decreased from 92.5% to 69.0%.

[0057] The performance gap mentioned above may be due to the fact that simple physical blending cannot guarantee that silanes are stably fixed on the surface of graphene sheets. Long-chain alkyl and epoxy silanes are prone to migrate, condense into small agglomerates or be embedded in the continuous resin phase during coating preparation or curing, resulting in low surface energy segments and compatible segments not being able to act precisely on the graphene interface.

[0058] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A temperature-resistant, wax-resistant, drag-reducing coating for the inner wall of a pipe, characterized in that, By weight, it comprises the following components: 72-80 parts of silicone-modified epoxy resin, 1.0-4.0 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 0.8-1.2 parts of dispersant, 0.3-0.4 parts of leveling agent, 0.2-0.3 parts of defoamer, 7-10 parts of xylene, 5-7 parts of propylene glycol methyl ether acetate, 13-18 parts of phenolic resin curing agent, and 0.15-0.40 parts of imidazole accelerator.

2. The temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 1, characterized in that, The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating, by weight, comprises: 76 parts of silicone-modified epoxy resin, 2.6 parts of alkylsilane-epoxysilane synergistic modified reduced graphene oxide, 1.0 part of dispersant, 0.4 parts of leveling agent, 0.2 parts of defoamer, 8 parts of xylene, 6 parts of propylene glycol methyl ether acetate, 16 parts of phenolic resin curing agent, and 0.30 parts of imidazole accelerator; The alkylsilane-epoxysilane synergistic modified reduced graphene oxide is prepared by synergistic hydrolysis grafting of long-chain alkylsilanes and epoxysilanes, mild reduction and post-treatment of graphene oxide.

3. The temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 1, characterized in that, The dispersant is any one of BYK-110, BYK-163, and BYK-180.

4. The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 1, characterized in that, The leveling agent is any one of BYK-306, BYK-333, and BYK-354.

5. The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 1, characterized in that, The defoamer is any one of BYK-066N, BYK-088, and BYK-A530.

6. The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 1, characterized in that, The imidazole promoter is 2-methylimidazole, 2-ethyl-4-methylimidazole, or a combination of both.

7. The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 1, characterized in that, The preparation method of the alkylsilane-epoxysilane synergistic modification of reduced graphene oxide includes the following steps: Step 1: After pre-drying the graphene oxide, add it to deionized water, and then wet, ultrasonically disperse and high-speed shear disperse to obtain a graphene oxide dispersion. Step 2: Add long-chain alkylsilanes and epoxysilanes to an alcohol-water system and hydrolyze them under acidic conditions to obtain silane hydrolysate; Step 3: Add the graphene oxide dispersion obtained in Step 1 to the silane hydrolysate obtained in Step 2, and carry out the grafting reaction under nitrogen protection, so that the hydrolyzed silane and the oxygen-containing functional groups on the surface of graphene oxide undergo condensation grafting. Step 4: After the grafting reaction is complete, a reducing agent is added for gentle reduction to reduce graphene oxide to synergistically modified reduced graphene oxide. Step 5: After the reaction is completed, solid-liquid separation, washing, drying, grinding and sieving are performed to obtain black powder alkylsilane-epoxysilane synergistic modified reduced graphene oxide.

8. The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 7, characterized in that, The long-chain alkylsilane in step 2 is hexadecyltrimethoxysilane.

9. The heat-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to claim 7, characterized in that, The epoxy silane in step 2 is 3-glycidoxypropyltrimethoxysilane.

10. A method for preparing a temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating according to any one of claims 1 to 9, characterized in that, The preparation method includes the following steps: Step A, preparation of graphene functional masterbatch: The alkylsilane-epoxysilane synergistic modified reduced graphene oxide is premixed with solvent and dispersant, and then subjected to ultrasonication and sand milling to obtain graphene functional masterbatch; Step B, Preparation of coating component A: Mix the organosilicon modified epoxy resin, the graphene functional masterbatch obtained in step A, the remaining solvent, the leveling agent and the defoamer evenly, and filter to obtain component A; Step C, Preparation and application of component B: Mix phenolic resin curing agent and imidazole accelerator evenly to obtain component B; before application, mix component A and component B according to the set equivalent ratio, degas, and then coat them onto the inner wall of the surface-treated steel pipe. Step D, curing into a film: After coating, first level at 25℃ for 20-40 min, then pre-cur at 70-90℃ for 0.5-1.5 h, then cure at 150-170℃ for 1.5-2.5 h, and finally post-cur at 210-230℃ for 1.5-2.5 h, thus obtaining a temperature-resistant, wax-resistant, and drag-reducing pipe inner wall coating.

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