High-adsorption stability corrosion inhibitor and preparation method thereof

Abstract

This invention discloses a highly adsorption-stable corrosion inhibitor and its preparation method, belonging to the field of metal corrosion and protection technology. The corrosion inhibitor is a hyperbranched polyester functionalized with nitrocatechol. Its structure uses a hyperbranched polyester as a backbone, with terminal hydroxyl groups partially or completely linked to nitrocatechol groups via ester bonds. The preparation method includes: synthesizing 5-nitro-3,4-dihydroxybenzoic acid from 3,4-dihydroxybenzoic acid via nitration; synthesizing a hydroxyl-terminated hyperbranched polyester via melt condensation polymerization using a polyol as the core and polycarboxylic acid and polyol as monomers; and grafting nitrocatechol groups to the ends of the hyperbranched polyester via a DCC / DMAP condensation system. The corrosion inhibitor of this invention can form an ultra-highly stable adsorption film on the metal surface, with an anodic desorption potential 150-200 mV higher than that of traditional imidazoline corrosion inhibitors, and a corrosion inhibition efficiency of over 89% at 70℃.

Description

Technical Field

[0001] This invention belongs to the field of metal corrosion and protection technology, specifically relating to a highly adsorption stable corrosion inhibitor and its preparation method. Background Technology

[0002] Metallic materials, due to their excellent mechanical and processing properties, have become indispensable basic materials in modern industry, infrastructure, and daily life. However, metal corrosion is a widespread phenomenon, causing not only huge economic losses but also safety accidents, resource waste, and environmental pollution. Among numerous anti-corrosion technologies, adding corrosion inhibitors is a simple, cost-effective, and widely applicable protective strategy, and is widely used in petrochemical, pickling, industrial circulating water systems, and machinery manufacturing fields.

[0003] The mechanism of action of corrosion inhibitors mainly relies on the adsorption behavior of their molecules at the metal / solution interface. Corrosion inhibitor molecules, through active centers such as polar groups (e.g., heteroatoms containing N, O, S, and P), unsaturated bonds, or aromatic rings in their molecular structure, undergo physical adsorption (electrostatic interaction) or chemical adsorption (coordination bonds, back-bonding) with the metal surface, ultimately forming a dense hydrophobic protective film that blocks corrosive media (such as H₂O₂). + Cl － The contact between corrosion inhibitors (such as oxygen and oxygen) and the metal substrate inhibits electrochemical corrosion reactions. Therefore, the adsorption stability of corrosion inhibitors on metal surfaces, i.e., their ability to resist desorption and maintain long-term effective protection, is a key factor determining their final corrosion inhibition performance and service life.

[0004] Despite the wide variety of existing corrosion inhibitors, under complex working conditions, especially in environments with high temperature, high flow rate, strong acidity, or competitive adsorption ions, corrosion inhibitors generally suffer from insufficient adsorption stability, a core technical problem. This manifests primarily as easy desorption of the protective film, rapid failure, and the need for frequent replenishment to maintain effectiveness. One particularly prominent issue is anodic desorption induced by potential fluctuations. Anodic desorption refers to the sudden, large-scale desorption of the corrosion inhibitor molecules that were previously well adsorbed on the metal surface when the electrode potential of the metal shifts positively to a critical value due to external anodic polarization or the formation of a localized corrosion cell in an electrochemical corrosion system. This leads to a sharp increase in corrosion current and instantaneous failure of the corrosion inhibition performance. This critical potential value is called the anodic desorption potential (E-des). The root cause of anodic desorption lies in the imbalance of the dynamic interplay between electric field forces and chemical bond forces at the electrode / solution interface. On the one hand, when the electrode potential is much greater than the zero charge potential (PZC) of the metal, the metal surface carries a high density of positive charge, which generates a strong electrostatic repulsion force on the positively charged corrosion inhibitor molecules. When the repulsion force exceeds the adsorption bond energy, desorption occurs. On the other hand, the metal ions generated by anodic dissolution will physically impact the adsorption layer, forming a self-catalytic cycle of "damage → dissolution → impact → more severe damage".

[0005] To address the anodic desorption problem, existing technologies mainly employ two strategies: one is to strengthen the molecular structure by introducing atoms such as S and P into the corrosion inhibitor framework to enhance coordination bond energy; the other is to use film-forming corrosion inhibitors instead of adsorbent film-forming ones. However, while the former can increase the desorption potential, it cannot completely eliminate the desorption phenomenon, while the latter has stringent requirements for medium conditions, a slow film formation rate, and limited applications. Summary of the Invention

[0006] The technical problem this invention aims to solve is to address the shortcomings of existing corrosion inhibitors, which are prone to anodic desorption under anodic polarization conditions, leading to a sharp drop in protective performance. This invention provides a corrosion inhibitor with high adsorption stability and its preparation method. This corrosion inhibitor should be able to form a strong and tough adsorption film on the metal surface in acidic corrosive media through multiple supramolecular anchoring mechanisms, significantly increasing the anodic desorption potential and achieving long-term stable corrosion protection.

[0007] To achieve the above objectives, this application adopts the following technical solution:

[0008] In a first aspect, the present invention provides a highly adsorption-stable corrosion inhibitor, wherein the corrosion inhibitor is a hyperbranched polyester functionalized with nitrocatechol, the structure of which is based on the hyperbranched polyester skeleton, and the terminal hydroxyl groups of the hyperbranched polyester are connected to nitrocatechol groups through ester bonds.

[0009] Preferably, the nitrocatechol group is 5-nitro-3,4-dihydroxybenzoyl.

[0010] Secondly, the preparation method of the above-mentioned highly adsorption stable corrosion inhibitor of the present invention includes the following steps:

[0011] Step 1: 3,4-Dihydroxybenzoic acid is reacted with a nitrating agent in the presence of an acidic catalyst to carry out an electrophilic substitution reaction to prepare 5-nitro-3,4-dihydroxybenzoic acid.

[0012] Step 2: Using polyols as the core molecule and polycarboxylic acids and / or polyols as monomers, hydroxyl-terminated hyperbranched polyesters are synthesized through melt polycondensation in the presence of an esterification catalyst.

[0013] Step 3: The 5-nitro-3,4-dihydroxybenzoic acid obtained in Step 1 is subjected to an esterification reaction with the terminal hydroxyl hyperbranched polyester obtained in Step 2 in the presence of a condensing agent and a catalyst, so that the nitrocatechol group is grafted to the end of the hyperbranched polyester through ester bonds, thereby obtaining nitrocatechol functionalized hyperbranched polyester.

[0014] Step 4: Dissolve the nitrocatechol-functionalized hyperbranched polyester obtained in Step 3 in an organic solvent and add a stabilizer to prepare a corrosion inhibitor mother liquor.

[0015] As a preferred embodiment, in the first step, the nitrating agent is concentrated nitric acid or fuming nitric acid, the acidic catalyst is concentrated sulfuric acid, the reaction temperature is 0-10℃, the reaction time is 1-4 hours, and the molar ratio of 3,4-dihydroxybenzoic acid to nitric acid is 1:1.0-1.5.

[0016] As a preferred embodiment, in the second step, the polyol core molecule is pentaerythritol or dipentaerythritol; the polycarboxylic acid monomer is adipic acid, sebacic acid, or citric acid; the polyol monomer is glycerol or trimethylolpropane; the esterification catalyst is p-toluenesulfonic acid, tetrabutyl titanate, or dibutyltin oxide; the polycondensation reaction temperature is 140-200℃, the reaction time is 4-8 hours, the reaction is carried out under nitrogen protection, and the generated water is removed by a water separator.

[0017] As a preferred option, the number-average molecular weight (Mn) of the hydroxyl-terminated hyperbranched polyester synthesized in the second step is 1500-5000, and the hydroxyl value is 200-400 mg KOH / g.

[0018] As a preferred embodiment, in the third step, the condensing agent is dicyclohexylcarbodiimide (DCC) or 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC·HCl); the catalyst is 4-dimethylaminopyridine (DMAP); the reaction solvent is N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or N-methylpyrrolidone (NMP); the reaction temperature is 20-40℃, and the reaction time is 12-36 hours; the molar ratio of 5-nitro-3,4-dihydroxybenzoic acid to the hydroxyl groups in the terminal hydroxyl hyperbranched polyester is 1:1.5-2.5.

[0019] As a preferred embodiment, in the fourth step, the organic solvent is ethanol, ethylene glycol, or isopropanol; the stabilizer is ascorbic acid or citric acid, and its addition amount is 0.5-2% of the mass of the nitrocatechol functionalized hyperbranched polyester; the active ingredient content of the corrosion inhibitor mother liquor is 30-60 wt%.

[0020] As the preferred embodiment, the preparation method includes the following specific steps:

[0021] 1) Synthesis of 5-nitro-3,4-dihydroxybenzoic acid: In a reaction flask equipped with a stirrer and thermometer, 200 mL of concentrated sulfuric acid was added and cooled to 0-5 °C in an ice bath; 77.05 g (0.5 mol) of 3,4-dihydroxybenzoic acid was added in portions with stirring, and the temperature was controlled not to exceed 10 °C; after it was completely dissolved, 49.2 mL (0.55 mol) of 65% concentrated nitric acid was slowly added dropwise using a constant pressure dropping funnel, and the dropping rate was controlled to maintain the reaction temperature at 0-5 °C; after the addition was completed, the reaction was stirred at this temperature for 2 hours; after the reaction was completed, the reaction solution was slowly poured into a 1 L ice-water mixture, and a yellow precipitate was precipitated; the precipitate was filtered, the filter cake was washed 3 times with ice water, and the crude product was recrystallized from ethanol-water (1:3) to obtain 5-nitro-3,4-dihydroxybenzoic acid, which was dried under vacuum at 50 °C for 12 hours.

[0022] 2) Synthesis of hydroxyl-terminated hyperbranched polyester: In a four-necked flask equipped with a stirrer, nitrogen inlet tube, thermometer, and water separator, 134.17 g (1.0 mol) of trimethylolpropane, 146.14 g (1.0 mol) of adipic acid, 13.61 g (0.1 mol) of pentaerythritol, and 3.5 g of p-toluenesulfonic acid were added sequentially; nitrogen gas was introduced to purge air, the temperature was raised to 140 °C, and stirring was started; the reaction was carried out at this temperature for 1 hour, and then the temperature was raised to 160 °C for further reaction. The reaction was carried out for 2 hours, and then the temperature was raised to 180℃ for 3 hours. During this period, the generated water was continuously removed through a water separator until the acid value of the reaction system dropped below 10 mg KOH / g. Heating was stopped, and the temperature was lowered to below 100℃. 500 mL of DMF was added to dissolve the product. The DMF solution was slowly poured into 5 L of anhydrous ethanol, and a viscous precipitate was formed. The upper layer of ethanol was decanted, and the precipitate was washed twice with fresh ethanol and dried under vacuum at 60℃ for 24 hours to obtain the hydroxyl-terminated hyperbranched polyester.

[0023] 3) Synthesis of nitrocatechol-functionalized hyperbranched polyester: 285 g (0.1 mol, based on a number-average molecular weight of 2850) of the hydroxyl-terminated hyperbranched polyester obtained in step two was dissolved in 500 mL of LDM and added to a 2 L three-necked flask; 47.5 g (0.22 mol) of 5-nitro-3,4-dihydroxybenzoic acid obtained in step one and 2.7 g of DMAP were added and stirred to dissolve; the mixture was cooled to 0-5 °C in an ice bath, and 45.4 g (0.22 mol) of DCC solution was slowly added dropwise using a constant pressure dropping funnel. The solution was added dropwise over approximately 1 hour in 100 mL of DMF. After the addition was complete, the ice bath was removed, and the temperature was naturally raised to 25°C. The reaction was continued with stirring for 24 hours. After the reaction was completed, the white precipitate dicyclohexylurea (DCU) was removed by filtration. The filtrate was concentrated under reduced pressure to approximately 200 mL. The concentrate was then slowly added dropwise to 2 L of ice-cold diethyl ether, and the mixture was stirred vigorously to precipitate a yellowish-brown precipitate. The precipitate was allowed to stand, the supernatant was discarded, and the precipitate was washed twice with fresh diethyl ether and dried under vacuum at 40°C for 24 hours to obtain nitrocatechol-functionalized hyperbranched polyester.

[0024] 4) Preparation of corrosion inhibitor stock solution: Take 500g of the above-mentioned nitrocatechol functionalized hyperbranched polyester, add 500g of anhydrous ethanol, stir and dissolve evenly, then add 5g of ascorbic acid, stir and dissolve to obtain a corrosion inhibitor stock solution with 50wt% active ingredient content; adjust the pH of the stock solution to 7.0-8.0 with triethanolamine.

[0025] This invention reduces the electron cloud density of the hydroxyl groups on the catechol ring by using the nitro group on nitrocatechol, and then reacts with Fe... 2+ / Fe 3+The formation of a more stable five-membered ring chelate significantly shifts the anodic desorption potential in the positive direction. By functionalizing hyperbranched polyester with nitrocatechol, anchoring groups are formed, achieving optimal spatial orientation and multi-point contact with surface Fe atoms, resulting in a significant synergistic enhancement effect and greatly increasing the total adsorption free energy to a level similar to covalent bonds. Furthermore, nitrocatechol, after partial deprotonation in acidic media, becomes negatively charged. When anodic polarization leads to the accumulation of positive charges on the metal surface, electrostatic attraction rather than repulsion occurs, causing the adsorption strength to increase rather than decrease within a certain anodic polarization range, fundamentally reversing the desorption mechanism of traditional corrosion inhibitors. The anchored nitrocatechol groups can capture Fe dissolved due to localized film damage. 2+ In situ, an insoluble [Fe(catecholate)3] type complex precipitate is formed on the surface of the adsorption layer, which automatically fills the defects in the adsorption film and forms a second barrier against anodic desorption.

[0026] Compared with the prior art, this application has the following beneficial effects:

[0027] 1) Ultra-high adsorption stability: Through multiple supramolecular anchoring mechanisms, the adsorption free energy of the corrosion inhibitor on the metal surface is significantly higher than that of traditional imidazoline corrosion inhibitors, and the adsorption of carbon steel in acidic media is extremely strong.

[0028] 2) Significantly improves anodic desorption potential: Compared with traditional imidazoline corrosion inhibitors, the anodic desorption potential of the corrosion inhibitor of the present invention can be positively increased by 150-200mV, which can effectively resist potential fluctuations caused by anodic polarization or localized corrosion cells.

[0029] 3) Long-term corrosion inhibition performance: It can still maintain a corrosion inhibition efficiency of over 89% at a high temperature of 70℃, demonstrating excellent resistance to thermal desorption.

[0030] 4) Wide applicability: Not only is it suitable for strongly acidic environments such as pickling and oil and gas well acidification, but its "potential self-adaptive" characteristics and in-situ film formation ability also make it applicable to industrial circulating water, marine engineering, and other environments with potential fluctuations and Cl... － It has broad application prospects in corrosive environments. Attached Figure Description

[0031] Figure 1 Infrared spectrum of the nitrocatechol-functionalized hyperbranched polyester prepared in Example 1 of this invention.

[0032] Figure 2 Example 1 of this invention: Flowchart of the preparation of a highly adsorption stable corrosion inhibitor. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the following embodiments are only for explaining the invention and not for limiting it. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0034] Test method description:

[0035] Example 1

[0036] A highly adsorption-stability corrosion inhibitor was prepared according to a preferred technical solution of the present invention (see reference). Figure 2 ).

[0037] Step 1: Synthesis of 5-nitro-3,4-dihydroxybenzoic acid (NC)

[0038] In a 500 mL three-necked flask equipped with a mechanical stirrer and thermometer, 200 mL of concentrated sulfuric acid (98%) was added, and the flask was cooled to 0-5 °C in an ice-salt bath. While stirring, 77.05 g (0.5 mol) of 3,4-dihydroxybenzoic acid was slowly added in portions, controlling the temperature during addition to not exceed 10 °C. After the addition was complete, stirring continued until completely dissolved, yielding a pale yellow, clear solution. 49.2 mL (0.55 mol) of concentrated nitric acid (65%) was slowly added dropwise to the above solution using a constant-pressure dropping funnel, strictly controlling the dropping rate to maintain the reaction system temperature between 0-5 °C, and the addition was completed in approximately 1.5 hours. After the addition was complete, the reaction was continued at 0-5 °C with stirring for 2 hours. After the reaction was complete, the reaction solution was slowly poured into a large beaker containing a 1 L mixture of ice and water under vigorous stirring, immediately precipitating a large amount of yellow precipitate. The precipitate was allowed to stand until complete, filtered, and the filter cake was washed three times with 200 mL of ice water and then dried. The crude product was recrystallized from an ethanol-water mixture (V ethanol:V water = 1:3) to obtain pale yellow needle-like crystals. The crystals were placed in a vacuum drying oven and dried at 50°C for 12 hours. The product was weighed, yielding 82.5 g, with a yield of 86.2%. Melting point: 224-226°C.

[0039] Step 2: Synthesis of hydroxyl-terminated hyperbranched polyester (HBPE)

[0040] In a 2L four-necked flask equipped with a mechanical stirrer, nitrogen inlet tube, thermometer, and water separator (connected to a reflux condenser), 134.17g (1.0mol) of trimethylolpropane, 146.14g (1.0mol) of adipic acid, 13.61g (0.1mol) of pentaerythritol, and 3.5g of p-toluenesulfonic acid were added sequentially. High-purity nitrogen was introduced to purge the air from the flask, and a nitrogen atmosphere was maintained throughout the reaction. Stirring and heating were initiated, and the temperature was raised to 140℃. The reactants gradually melted, and water began to evaporate and be collected in the water separator. The reaction was maintained at 140℃ for 1 hour. Then, the temperature was raised to 160℃ and the reaction was continued for 2 hours. Finally, the temperature was raised to 180℃ and the reaction was continued for 3 hours. Acid value was measured every 30 minutes during the reaction. The reaction was stopped when the acid value dropped below 10mgKOH / g. At this point, the total amount of water collected in the water separator was approximately 36mL (theoretical output 40mL). Stop heating and cool the mixture to below 100°C with cooling water. Add 500 mL of DMF to the reaction flask and stir to dissolve the product. Slowly pour the DMF solution into 5 L of anhydrous ethanol while stirring vigorously; a viscous precipitate immediately forms. Let stand, discard the supernatant, and wash the precipitate twice with fresh anhydrous ethanol. Place the obtained product in a vacuum drying oven and dry at 60°C for 24 hours to obtain a pale yellow, transparent, viscous, hydroxyl-terminated hyperbranched polyester, weighing approximately 310 g, with a yield of 88%. GPC determination: Mn = 3020, Mw = 4980, PDI = 1.65. Hydroxyl value determination: 278 mg KOH / g.

[0041] Step 3: Synthesis of Nitrocatechol Functionalized Hyperbranched Polyester (NC-HBPE)

[0042] In a dry 2L three-necked flask, 302g (0.1mol, based on Mn=3020) of HBPE obtained in step 2 was dissolved in 500mL of anhydrous DMF and stirred until dissolved. 47.5g (0.22mol) of NC and 2.7g (0.022mol) of DMAP obtained in step 1 were added and stirred until completely dissolved. The reaction flask was placed in an ice bath to cool to 0-5°C. 45.4g (0.22mol) of DCC was dissolved in 100mL of anhydrous DMF and transferred to a constant-pressure dropping funnel. The solution was slowly added dropwise to the reaction flask with stirring, controlling the dropping rate to complete the addition over approximately 1 hour. After the addition was complete, the ice bath was removed, and the reaction system was allowed to warm naturally to room temperature (approximately 25°C). The reaction was continued at this temperature with stirring for 24 hours. The reaction progress was monitored by TLC (developing solvent: dichloromethane:methanol = 9:1) until the NC point essentially disappeared. After the reaction was complete, the reaction mixture was filtered to remove a large amount of white precipitate dicyclohexylurea (DCU). The filtrate was concentrated under reduced pressure (bath temperature ≤50℃) to approximately 200 mL using a rotary evaporator. The concentrate was slowly added dropwise to 2 L of ice-cold diethyl ether under vigorous stirring, and a yellowish-brown viscous precipitate immediately formed. After standing, the supernatant was discarded, and the precipitate was washed twice with fresh diethyl ether. The product was placed in a vacuum drying oven and dried at 40℃ for 24 hours to obtain a yellowish-brown viscous nitrocatechol-functionalized hyperbranched polyester (FTIR(KBr, cm⁻¹)). -1 ): 3420 (broad peak, OH), 2955, 2925, 2854 (CH), 1735 (ester group C=O), 1530, 1350 (nitro group N=O), 1450 (benzene ring C=C), 1240 (COC), 1170, 1080 (CO). See Figure 1 The sample weighed approximately 285g, with a yield of 86%. Hydroxyl value was determined to be 38mgKOH / g, indicating a grafting rate of approximately 87% (i.e., approximately 12 NC groups were grafted onto each HBPE molecule).

[0043] Step 4: Preparation of corrosion inhibitor stock solution

[0044] Take 500g of NC-HBPE obtained in step 3, add 500g of anhydrous ethanol, and stir to dissolve evenly at room temperature. Then add 5g of ascorbic acid as a stabilizer and stir to dissolve. Finally, slowly adjust the pH of the solution to 7.0-8.0 with triethanolamine to obtain a brownish-yellow transparent corrosion inhibitor stock solution with 50wt% active ingredient content, labeled as IE-1.

[0045] Example 2

[0046] Corrosion inhibitors were prepared by changing the grafting ratio.

[0047] Other conditions were the same as in Example 1, except that the dosage of NC was changed in step 3. The dosage of NC was changed to 31.6 g (0.15 mol), and the dosage of DCC was changed accordingly to 31.0 g (0.15 mol). The final product hydroxyl value was measured to be 105 mg KOH / g, and the grafting rate was calculated to be approximately 62% (approximately 8.5 NC groups were grafted onto each HBPE molecule). The resulting corrosion inhibitor mother liquor was labeled IE-2.

[0048] Example 3

[0049] Modify the hyperbranched polyester skeleton.

[0050] Other conditions were the same as in Example 1, except that the monomers used to synthesize the hyperbranched polyester were changed in step 2. In step 2, adipic acid was replaced with an equimolar amount of sebacic acid (202.25 g, 1.0 mol), which was polycondensed with trimethylolpropane (134.17 g, 1.0 mol) and pentaerythritol (13.61 g, 0.1 mol). GPC determination showed Mn = 3350 and hydroxyl value of 255 mg KOH / g. Subsequent steps 3 and 4 were the same as in Example 1. The resulting corrosion inhibitor mother liquor was labeled IE-3.

[0051] Comparative Example 1

[0052] Commercially available oil-soluble imidazoline corrosion inhibitors.

[0053] Oleic acid imidazoline corrosion inhibitor (oil-soluble) (effective content 97%) produced by Shandong Taihe Technology Co., Ltd. was selected and diluted with anhydrous ethanol to prepare a 50wt% stock solution, labeled CE-1. This type of corrosion inhibitor is a typical product commonly used in existing technologies for acidizing oil and gas wells and inhibiting CO2 corrosion.

[0054] Comparative Example 2

[0055] Unnitrated catechol-functionalized hyperbranched polyester.

[0056] Other conditions were the same as in Example 1, except that nitration was not performed in step 1; instead, 3,4-dihydroxybenzoic acid (unnitrated) was used to replace 5-nitro-3,4-dihydroxybenzoic acid in the grafting reaction of step 3. Specifically, 302g of HBPE obtained in step 2 was grafted with 40.7g (0.264mol, equivalent to the molar amount of NC in Example 1) of 3,4-dihydroxybenzoic acid in the presence of DCC / DMAP to obtain unnitrated catechol-functionalized hyperbranched polyester. Subsequent step 4 was the same as in Example 1. The resulting corrosion inhibitor mother liquor was labeled CE-2.

[0057] Performance testing and effect comparison

[0058] The corrosion inhibitors IE-1, IE-2, and IE-3 prepared above, as well as comparative examples CE-1 and CE-2, were subjected to electrochemical tests according to the aforementioned test methods (using a Gamry Reference 600+ electrochemical workstation, a three-electrode system: the working electrode was a Q235 carbon steel electrode (1 cm² area)). 2 The reference electrode was a saturated calomel electrode (SCE), and the auxiliary electrode was a platinum sheet electrode. The test medium was a 1M HCl solution, and the corrosion inhibitor dosage was 100 mg / L. Before testing, the working electrode was immersed in the test solution for 30 min, and the test was performed after the open circuit potential (OCP) stabilized. The potentiodynamic polarization curve scan range was -250 mV vs OCP to +800 mV vs OCP, and the scan rate was 0.5 mV / s. The constant potential polarization test was performed at -200mV vs. OCP for 3600s. A weight loss experiment was also conducted (Q235 carbon steel specimens (50mm×25mm×2mm) that had been polished, cleaned, dried, and weighed were suspended in 1M HCl solutions with or without corrosion inhibitors, and immersed at 30℃ and 70℃ for 72 hours respectively. After the experiment, the specimens were removed, cleaned, dried, and weighed, and the corrosion rate and corrosion inhibition efficiency were calculated. The corrosion rate v = (Δm) / (S·t), where Δm is the weight loss (g) and S is the surface area of ​​the specimen (m²). 2 ), where t is the immersion time (h). Corrosion inhibition efficiency IE = (v0-v) / v0×100%, where v0 is the corrosion rate of the blank group and v is the corrosion rate of the chemically treated group. The effective concentration of the corrosion inhibitor in all tests was 100 mg / L (based on active material).

[0059] The results are as follows:

[0060] Table 1: Electrochemical test results (1M HCl, 30℃)

[0061]

[0062] Results analysis:

[0063] As can be seen from the potentiodynamic polarization curve test results in Table 1, the current in the blank group increased rapidly during anodic polarization. The commercially available imidazoline corrosion inhibitor CE-1 showed a sudden increase in current density and significant anodic desorption when the potential shifted positively to approximately -130 mV vs SCE. In contrast, the anodic desorption potential E_des of IE-1 prepared in Example 1 of this invention reached +68 mV vs SCE, which is 198 mV higher than that of CE-1. This indicates that the corrosion inhibitor of this invention has a very strong ability to resist anodic polarization and can effectively inhibit anodic desorption. IE-3 also showed similar performance, while IE-2, with a lower grafting rate, although better than CE-1, was slightly worse than IE-1, indicating that a higher grafting rate is beneficial for enhancing adsorption stability. The comparative example CE-2 (unnitrated catechol functionalized compound) had an E_des of -85 mV vs SCE, which is higher than CE-1 (approximately 45 mV), but much lower than IE-1. This indicates that the introduction of nitro groups plays a key role in enhancing coordination and increasing desorption potential.

[0064] As shown in Table 1, at an anodic polarization potential of -200 mV vs SCE, the current density of CE-1 began to increase significantly after approximately 60 minutes, indicating that large-scale desorption of the adsorbed film had occurred. In contrast, the current density of IE-1 remained at an extremely low level (~11.2 μA / cm²) throughout the entire 3600-second test. 2 It exhibits an extremely stable adsorption state.

[0065] Table 2: Results of corrosion inhibition efficiency test by weight loss method (1MHCl, 72h)

[0066]

[0067] Table 2 shows the weight loss experiment results, indicating that all corrosion inhibitors exhibited good corrosion inhibition performance at 30℃. IE-1 of this invention showed the highest corrosion inhibition efficiency, while IE-2 and IE-3 also outperformed CE-1 at high temperatures. However, IE-1 was the best, reaching 96.7%, which is superior to the 92.6% of commercially available CE-1. When the temperature rose to 70℃, the performance of corrosion inhibitors generally decreased, but the corrosion inhibition efficiency of IE-1 of this invention remained as high as 89.4%, far exceeding the 77.0% of CE-1, demonstrating excellent high-temperature adsorption stability.

[0068] The high-adsorption stability corrosion inhibitor provided by this invention can be widely used in the fields of petrochemical acid washing, oil and gas well acid fracturing, industrial circulating cooling water systems, and corrosion protection of marine engineering equipment and infrastructure.

[0069] Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A highly adsorption-stable corrosion inhibitor, characterized in that, The corrosion inhibitor is prepared by dissolving nitrocatechol-functionalized hyperbranched polyester in an organic solvent and adding a stabilizer. The nitrocatechol-functionalized hyperbranched polyester has a hyperbranched polyester backbone, and the terminal hydroxyl groups of the hyperbranched polyester are connected to nitrocatechol groups through ester bonds. The stabilizer is ascorbic acid or citric acid, and its addition amount is 0.5-2% of the mass of the nitrocatechol-functionalized hyperbranched polyester.

2. The high adsorption stability corrosion inhibitor according to claim 1, characterized in that, The nitrocatechol group is 5-nitro-3,4-dihydroxybenzoyl.

3. A method for preparing a high-adsorption-stability corrosion inhibitor as described in claim 1 or 2, characterized in that, Includes the following steps: Step 1: 3,4-Dihydroxybenzoic acid is reacted with a nitrating agent in the presence of an acidic catalyst to prepare 5-nitro-3,4-dihydroxybenzoic acid via an electrophilic substitution reaction. Step 2: Using polyols as the core molecule and polycarboxylic acids and / or polyols as monomers, hydroxyl-terminated hyperbranched polyesters are synthesized through melt polycondensation reaction in the presence of an esterification catalyst. Step 3: The 5-nitro-3,4-dihydroxybenzoic acid obtained in Step 1 is subjected to an esterification reaction with the terminal hydroxyl hyperbranched polyester obtained in Step 2 in the presence of a condensing agent and a catalyst, so that the nitrocatechol group is grafted to the end of the hyperbranched polyester through ester bonds to obtain nitrocatechol functionalized hyperbranched polyester. Step 4: Dissolve the nitrocatechol-functionalized hyperbranched polyester obtained in Step 3 in an organic solvent and add a stabilizer to prepare the product.

4. The method for preparing the highly adsorption stable corrosion inhibitor according to claim 3, characterized in that, In the first step, the nitrating agent is concentrated nitric acid or fuming nitric acid, the acidic catalyst is concentrated sulfuric acid, the reaction temperature is 0-10℃, the reaction time is 1-4 hours, and the molar ratio of 3,4-dihydroxybenzoic acid to nitric acid is 1:1.0-1.

5.

5. The method for preparing the highly adsorption stable corrosion inhibitor according to claim 3, characterized in that, In the second step, the polyol core molecule is pentaerythritol or dipentaerythritol; the polycarboxylic acid monomer is adipic acid, sebacic acid or citric acid; the polyol monomer is glycerol or trimethylolpropane; and the esterification catalyst is p-toluenesulfonic acid, tetrabutyl titanate or dibutyltin oxide.

6. The method for preparing the high-adsorption stability corrosion inhibitor according to claim 3, characterized in that, In the second step, the polycondensation reaction temperature is 140-200℃, the reaction time is 4-8 hours, the reaction is carried out under nitrogen protection, and the generated water is removed through a water separator.

7. The method for preparing the highly adsorption stable corrosion inhibitor according to claim 6, characterized in that, The number-average molecular weight (Mn) of the hydroxyl-terminated hyperbranched polyester synthesized in the second step is 1500-5000, and the hydroxyl value is 200-400 mg KOH / g.

8. The method for preparing the highly adsorption stable corrosion inhibitor according to claim 3, characterized in that, In the third step, the condensing agent is dicyclohexylcarbodiimide or 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; the catalyst is 4-dimethylaminopyridine; the reaction solvent is N,N-dimethylformamide, dimethyl sulfoxide or N-methylpyrrolidone; the reaction temperature is 20-40℃ and the reaction time is 12-36 hours.

9. The method for preparing the highly adsorption stable corrosion inhibitor according to claim 3, characterized in that, In the third step, the molar ratio of 5-nitro-3,4-dihydroxybenzoic acid to the hydroxyl groups in the hydroxyl-terminated hyperbranched polyester is 1:1.5-2.

5.

10. The method for preparing the highly adsorption stable corrosion inhibitor according to claim 3, characterized in that, In the fourth step, the organic solvent is ethanol, ethylene glycol, or isopropanol.

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