Open cycle cooling water system corrosion and scale inhibitor and preparation method thereof

Abstract

The application relates to the technical field of water treatment agents, and particularly discloses an open circulating cooling water system corrosion and scale inhibitor and a preparation method thereof. The preparation method of the open circulating cooling water system corrosion and scale inhibitor comprises the following steps: firstly, partially neutralizing a polycarboxylic acid dispersant, and then slowly adding imidazoline quaternary ammonium salt under low-temperature high-speed stirring to in-situ construct a stable polyelectrolyte composite nanodispersion, so that strong electrostatic association precipitation when anions and cations are directly mixed is effectively avoided, and the storage stability and the corrosion and scale inhibition performance of the product are improved.

Description

Technical Field

[0001] This application relates to the field of water treatment agent technology, and more specifically, to corrosion and scale inhibitors for open-loop circulating cooling water systems and their preparation methods. Background Technology

[0002] Open-type circulating cooling water systems are widely used in industrial production. During system operation, the water continuously evaporates and concentrates, which easily leads to scaling problems such as calcium carbonate and calcium sulfate. At the same time, the cooling water medium can corrode metal equipment materials such as carbon steel and cast iron. Scale and corrosion problems can reduce heat exchange efficiency and cause equipment pipeline perforation and leakage. Therefore, it is usually necessary to add corrosion and scale inhibitors to simultaneously inhibit metal corrosion and scale dispersion.

[0003] In the prior art, in order to take into account both corrosion inhibition and scale inhibition properties, a corrosion and scale inhibitor scheme has emerged that combines cationic imidazoline quaternary ammonium salt corrosion inhibitor with anionic polycarboxylic acid dispersant scale inhibitor. The imidazoline quaternary ammonium salt forms a protective film on the metal surface by molecular adsorption to inhibit metal corrosion, while the polycarboxylic acid dispersant inhibits scale formation through lattice distortion and chelation dispersion. Patent application CN117023817A discloses a corrosion and scale inhibitor and its preparation method. The corrosion and scale inhibitor, by mass percentage, comprises 10%–40% imidazoline quaternary ammonium salt, 5%–20% alkanolamine corrosion inhibitor, 5%–10% thiourea compound, 15%–30% polycarboxylic acid dispersant, 1%–5% reducing agent, and the balance being deionized water. The preparation method includes: adding deionized water to a stirred tank and heating to 60–80°C; adding imidazoline quaternary ammonium salt and thiourea compound to the stirred tank to obtain a first intermediate solution; stirring the first intermediate solution for 10–30 minutes to obtain a second intermediate solution; cooling the second intermediate solution to room temperature; and adding alkanolamine corrosion inhibitor and polycarboxylic acid dispersant to the second intermediate solution and stirring at room temperature. However, the high proportion of cationic imidazoline quaternary ammonium salt in the above-mentioned corrosion and scale inhibitor formulation, when directly combined with anionic polycarboxylate dispersant, easily leads to anionic-cationic charge association reactions, generating insoluble ion-pair precipitates. This not only causes turbidity, stratification, and storage stability issues with the precipitated solids in the agent system, but also consumes the effective components, weakening the adsorption and film-forming corrosion inhibition ability of imidazoline quaternary ammonium salt on the metal surface, as well as the lattice distortion and chelation scale inhibition effect of polycarboxylate dispersant. In addition, the preparation process involves dissolving the material at high temperature and then cooling it to room temperature before adding the polycarboxylate dispersant, further amplifying the risk of association precipitation. As a result, it is difficult for those skilled in the art to obtain a uniform and stable finished product when directly implementing the scheme. The corrosion inhibition and scale inhibition performance of the agent cannot be guaranteed during actual use, and it cannot well meet the usage requirements of stable operation in open circulating cooling water systems. Summary of the Invention

[0004] To improve the corrosion and scale inhibition performance of corrosion and scale inhibitors for open-loop circulating cooling water systems, this application provides corrosion and scale inhibitors for open-loop circulating cooling water systems and their preparation methods.

[0005] In the first aspect, this application provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, employing the following technical solution: A method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system includes the following steps: (1) Dissolve the polycarboxylic acid dispersant in deionized water, heat to 40-50°C, and stir until completely dissolved; add alcohol amine corrosion inhibitor dropwise, adjust the pH of the system to 6.5-7.5, keep warm and stir for 15-20 min to obtain a polycarboxylic acid-alcohol amine solution; (2) Cool the polycarboxylic acid-alcohol amine solution to 15-25°C, and add imidazoline quaternary ammonium salt dropwise while stirring at 500-1500 rpm; continue stirring for 25-35 min after the addition is complete to obtain polyelectrolyte composite nano-dispersion; (3) Add the thiourea compound to the polyelectrolyte composite nano-dispersion and stir until dissolved. Then add the reducing agent and stir until dissolved. Adjust the pH to 7.0-7.5 with an alcohol amine corrosion inhibitor or a polycarboxylic acid dispersant and stir and mature at below 40°C for 1-2 hours. Cool to room temperature, filter and collect to obtain the corrosion and scale inhibitor for open circulating cooling water systems.

[0006] By adopting the above technical solution, the polycarboxylic acid dispersant is partially neutralized with an alcohol amine, and then imidazoline quaternary ammonium salt is slowly added dropwise under low temperature and high speed stirring to form a polyelectrolyte composite nano-dispersion in situ. This effectively avoids the strong electrostatic association precipitation when imidazoline cations and polycarboxylic acid anions are directly mixed, allowing the two functional components to coexist stably in the concentrate. Subsequently, thiourea and a reducing agent are added and the pH is adjusted to further ensure the storage stability of the product and the effectiveness of the active components. After the resulting corrosion and scale inhibitor is added and diluted, the nano-dispersion dissociates, and imidazoline and polycarboxylic acid respectively play the roles of corrosion inhibition and scale inhibition, achieving integrated corrosion and scale inhibition.

[0007] Preferably, in step (3), before adding the thiourea compound, the polyethylene glycol-polylactic acid block copolymer is first added to the polyelectrolyte composite nano-dispersion. The polyethylene glycol-polylactic acid block copolymer is pre-dispersed by water-miscible organic solvent or by ultrasonic pretreatment before being added to the material. The mixture is stirred at 20-30°C for 15-25 minutes.

[0008] By adopting the above technical solution, before adding thiourea in step (3), polyethylene glycol-polylactic acid block copolymer (PEG-PLA) is first added to the polyelectrolyte composite nanodispersion and stirred. This allows the hydrophobic segments of PLA to be anchored to the surface of the nanoparticles through hydrophobic interactions, while the hydrophilic segments of PEG extend outward to form a hydrophilic brush layer. This hydrophilic brush layer provides additional steric hindrance and hydration, significantly improving the colloidal stability of the nanodispersion and preventing particles from agglomerating and settling under long-term storage or temperature fluctuations. At the same time, the presence of the PEG brush layer is beneficial for the uniform dispersion and encapsulation of thiourea in the subsequent process and provides a structural basis for the sustained release of the diluted active components.

[0009] Preferably, in step (3), a thiourea compound with a mass ratio of 1:(0.5-2) and a polyethylene glycol-polylactic acid block copolymer are used in deionized water, wherein the polyethylene glycol-polylactic acid block copolymer is pre-dispersed by water-miscible organic solvent or ultrasonic pretreatment, and stirred at 20-30°C for 10-15 min to obtain a mixture; the mixture is added to the polyelectrolyte composite nano-dispersion, stirred evenly, and then a reducing agent is added, and stirred at below 40°C until dissolved.

[0010] By employing the above technical solution, thiourea compounds are pre-mixed with PEG-PLA to form a mixture before being added to the nano-dispersion. This allows thiourea and the PLA segments in PEG-PLA to pre-assemble through intermolecular interactions such as hydrogen bonds. This pre-assembly process effectively anchors thiourea within the hydrophilic brush layer, reducing direct contact between thiourea and dissolved oxygen, inhibiting its oxidative decomposition, improving the chemical stability of thiourea during concentrated storage, extending the effective shelf life of the product, and ensuring the durability of its corrosion inhibition properties.

[0011] Preferably, the number-average molecular weight of the polyethylene glycol-polylactic acid block copolymer is 3000 to 5000.

[0012] By adopting the above technical solution, within this molecular weight range, the PLA segment length is sufficient to firmly anchor on the surface of nanoparticles through hydrophobic interaction, making it less likely to detach in the aqueous phase; at the same time, the PEG chain segment length is moderate, and the thickness of the formed hydrophilic brush layer is appropriate, which can provide sufficient steric hindrance to prevent nanoparticle aggregation, and will not hinder the dissociation of the diluted nanodispersion and the release of imidazoline due to an excessively thick brush layer. Thus, it takes into account both the concentration stability and the dilution release performance, ensuring the effective release and function of the active components of the corrosion and scale inhibitor during use.

[0013] Secondly, this application provides a corrosion and scale inhibitor for open-loop circulating cooling water systems, employing the following technical solution: The corrosion and scale inhibitor for open-loop circulating cooling water systems comprises the following raw materials in parts by weight: 15-30 parts imidazoline quaternary ammonium salt, 6-16 parts alkanolamine corrosion inhibitor, 2-6 parts thiourea compounds, 12-24 parts polycarboxylic acid dispersant, 1-4 parts reducing agent, and 0-3 parts polyethylene glycol-polylactic acid block copolymer.

[0014] By adopting the above technical solution, the components work synergistically. Imidazoline quaternary ammonium salt and thiourea provide corrosion inhibition, polycarboxylic acid dispersant provides scale inhibition and dispersion, alkanolamine adjusts pH and assists film formation, reducing agent protects thiourea, and PEG-PLA can further improve stability. The product does not contain betaine-type amphoteric surfactants and ethylene glycol cosolvents, reducing the risk of foaming and biomass growth. After dilution, the nanoparticles dissociate and release active components, exhibiting excellent corrosion inhibition, scale inhibition, and storage stability, making it suitable for long-term operation of open circulating cooling water systems.

[0015] Preferably, the polycarboxylic acid dispersant is one or more of polyepoxysuccinic acid, polyaspartic acid, and polymaleic acid-acrylic acid copolymer; more preferably, it is polyepoxysuccinic acid.

[0016] By adopting the above technical solution, polyepoxysuccinic acid (PESA), compared with polyaspartic acid and maleic acid-acrylic acid copolymers, has a molecular chain rich in a large number of unpolymerized side hydroxyl groups, possessing multiple technical advantages. Firstly, the side hydroxyl groups can form abundant intermolecular hydrogen bonds with the amino groups of thiourea and the hydroxyl groups of triethanolamine, effectively enhancing the molecular entanglement forces within the nanoparticle shell, significantly improving the embedding stability of thiourea within the polymer brush layer, and reducing thiourea precipitation and oxidation loss during storage. Secondly, the side chain hydroxyl groups of PESA can form auxiliary hydrogen bonds with the ester carbonyl groups of the PLA segments in PEG-PLA, further strengthening the overall tightness of the nanoparticle shell. In this invention, the interfacial anchoring of PEG-PLA on the particle surface is mainly based on hydrophobic interactions, supplemented by hydrogen bonds; these dual effects synergistically enhance the colloidal storage stability. Thirdly, PESA, with a weight-average molecular weight of 4000-6000, has a moderately long molecular chain, which can uniformly coat nanoparticles to form a complete and stable hydration shell, avoiding the problems of insufficient coating due to excessively low molecular weight and excessively high molecular weight leading to excessive system viscosity and decreased dispersibility. At the same time, PESA is a phosphorus-free, biodegradable, and green scale inhibitor with excellent lattice distortion and dispersion / scale inhibition properties, making it suitable for the environmental protection requirements of open-loop circulating cooling water systems and the optimal choice among the three types of polycarboxylic acid dispersants.

[0017] Preferably, the amine corrosion inhibitor is one or more of triethanolamine, diethanolamine, monoethanolamine, and morpholine; more preferably, it is triethanolamine.

[0018] By employing the above technical solution, triethanolamine molecules, containing three hydroxyl groups, form protonated amine cations with large spatial volume and strong hydration capacity. These cations can construct a dense and stable hydration layer on the outer shell of polyelectrolyte nanoparticles, significantly enhancing the anti-agglomeration and anti-settling capabilities of the nanodispersion. Simultaneously, the mild and controllable alkalinity of triethanolamine allows for precise and stable regulation of the neutralization degree of polycarboxylic acid, ensuring controllable uniformity of polyelectrolyte nucleation and avoiding particle agglomeration and system turbidity problems caused by excessively high or low neutralization. Furthermore, triethanolamine itself exhibits a mild adsorption and corrosion inhibition effect on carbon steel, forming a synergistic corrosion inhibition effect with naphthenic acid imidazoline quaternary ammonium salts, further improving overall corrosion inhibition efficiency. Its comprehensive performance surpasses that of diethanolamine and morpholine, making it the optimal amine selection.

[0019] Preferably, the imidazoline quaternary ammonium salt is a naphthenic acid imidazoline quaternary ammonium salt or an oleic acid imidazoline quaternary ammonium salt; the imidazoline quaternary ammonium salt is pre-diluted with deionized water to a mass fraction of 50% to 70%.

[0020] By adopting the above technical solution, compared with oleic acid imidazoline quaternary ammonium salt, naphthenic acid imidazoline quaternary ammonium salt has a hydrophobic tail chain containing a cyclic alkane structure and no carbon-carbon double bond unsaturated groups, resulting in stronger chemical stability. It is less prone to oxidation, deterioration, discoloration, and failure during storage, and has better long-lasting efficacy. Simultaneously, the larger spatial volume of the cyclic hydrophobic tail chain leads to a more significant hydrophobic aggregation effect during nucleation, forming a denser and more stable nano-hydrophobic core, providing ample binding sites for PLA block hydrophobic anchoring. Furthermore, naphthenic acid imidazoline quaternary ammonium salt has lower industrial raw material costs, offering a significant cost-performance advantage. In the preparation process, it is preferable to pre-dilute the naphthenic acid imidazoline quaternary ammonium salt with deionized water to a homogeneous solution before dropwise addition. This concentration range provides suitable viscosity, allowing precise control of the dropwise acceleration rate and local material concentration, avoiding micro-agglomeration caused by local concentration overload, and ensuring uniform particle size and homogeneous system stability in the final nanoparticles.

[0021] Preferably, the thiourea compound is one or more of thiourea, diphenylthiourea, and aminothiourea; more preferably, it is thiourea.

[0022] By adopting the above technical solution, thiourea has a simple molecular structure, excellent water solubility, and strong activity of the amino hydrogen bond donor in the molecule. It can rapidly form stable intermolecular hydrogen bonds with the PLA ester carbonyl group of PEG-PLA, efficiently completing supramolecular pre-assembly, and is suitable for the aqueous pre-assembly process of this invention. Compared with diphenylthiourea, thiourea has no large-volume aromatic ring steric hindrance, resulting in higher pre-assembly bonding efficiency and not hindering hydrogen bond recombination and polymer brush layer embedding effects. Compared with modified thiourea such as aminothiourea, thiourea has lower toxicity, wider raw material sources, and lower cost, with optimal overall compatibility, and can stably achieve the dual effects of anti-oxidation and auxiliary corrosion inhibition within the nanosystem.

[0023] Preferably, the reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium isoascorbate; more preferably, it is sodium sulfite.

[0024] By employing the above technical solution, the sodium sulfite aqueous solution is weakly alkaline, and its addition to the system will not significantly disturb the pH of the reagent. This allows for the stable maintenance of the charge structure of the nanoparticle shell and the integrity of the hydration layer, avoiding the defects of acidic reducing agents disrupting colloidal stability. Its moderate reducing properties enable it to efficiently capture dissolved oxygen in the system, fundamentally inhibiting the oxidative degradation of thiourea and ensuring the long-term storage activity of the reagent. Compared to sodium bisulfite, sodium sulfite lacks acidic dissociation characteristics, preventing the carboxyl grouping and shell loosening / detachment from the nanoparticle surface. Compared to sodium isoascorbate, sodium sulfite is lower in cost and more suitable for industrial application. It should be objectively noted that sodium sulfite exhibits slow self-oxidation loss in open aerobic environments, making it more suitable for closed storage conditions.

[0025] In summary, this application has the following beneficial effects: 1. This application obtains a negatively charged polyelectrolyte composite nano-dispersion in situ by partially neutralizing polycarboxylic acid with alkanolamine and adding imidazoline quaternary ammonium salt at low temperature and high speed, thus avoiding direct association and precipitation of anions and cations and stabilizing the concentrate. After dilution, the nanoparticles dissociate, and imidazoline and polycarboxylic acid respectively play the roles of corrosion inhibitor and scale inhibitor, achieving integrated treatment.

[0026] 2. Before adding thiourea, this application first introduces PEG-PLA, whose PLA segment is anchored on the surface of nanoparticles and PEG segment forms a hydrophilic brush layer. Through steric hindrance and hydration, the colloidal stability is improved, preventing aggregation and sedimentation. At the same time, it is conducive to the uniform dispersion and encapsulation of thiourea and provides a structural basis for the sustained release of the active component after dilution.

[0027] 3. In this application, thiourea and PEG-PLA are pre-mixed to form an assembly before being added, so that the thiourea is anchored in the hydrophilic brush layer, reducing contact with dissolved oxygen and inhibiting oxidative decomposition; combined with the addition of a reducing agent at low temperature, the thiourea is further protected, the product shelf life is extended and the corrosion inhibition is guaranteed to be durable. Detailed Implementation

[0028] The present application will be further described in detail below with reference to the embodiments.

[0029] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0030] Example 1 This embodiment provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, comprising the following steps: (1) 45g of polyepoxysuccinic acid (solid content 40%) and 5g of deionized water were heated to 45℃ and stirred at 400rpm until completely dissolved; while maintaining 400rpm, 10.5g of triethanolamine was slowly added dropwise at a rate of 0.7g / min. After the addition was complete, the pH of the system was measured to be approximately 6.9; the mixture was kept warm and stirred for 18min to obtain a polycarboxylic acid-ethanolamine solution. (2) Cool the solution obtained in step (1) to 20°C, dilute 22.5g of naphthenic acid imidazoline quaternary ammonium salt with 10g of deionized water, and add it dropwise at a rate of 0.54g / min under stirring at 1000rpm for 60min. After the addition is completed, continue stirring at 1000rpm for 30min to obtain polyelectrolyte composite nano-dispersion. (3) Add 4g of thiourea to the above nano-dispersion under stirring at 400rpm and stir until completely dissolved; then add 2.5g of sodium sulfite and continue stirring until dissolved; add 0.5g of triethanolamine dropwise at a rate of 0.5g / min to adjust the pH to 7.2; stir and mature at 35℃ and 300rpm for 1.5h; cool to room temperature, filter and collect to obtain corrosion and scale inhibitor for open circulating cooling water system.

[0031] Example 2 This embodiment provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, comprising the following steps: (1) 45g of polyepoxysuccinic acid (solid content 40%) and 3.5g of deionized water were heated to 45℃ and stirred at 400rpm until completely dissolved; while maintaining 400rpm, 10.5g of triethanolamine was slowly added dropwise at a rate of 0.7g / min. After the addition was complete, the pH of the system was measured to be approximately 6.9; the mixture was kept warm and stirred for 18min to obtain a polycarboxylic acid-ethanolamine solution. (2) Cool the solution obtained in step (1) to 20°C, dilute 22.5g of naphthenic acid imidazoline quaternary ammonium salt with 10g of deionized water, and add it dropwise at a rate of 0.54g / min under stirring at 1000rpm for 60min; after the addition is completed, continue stirring at 1000rpm for 30min to obtain polyelectrolyte composite nano-dispersion; (3) Under stirring at 500 rpm, 1.5 g of polyethylene glycol-polylactic acid block copolymer (number average molecular weight 4000) was added to 4.5 g of anhydrous ethanol at a PEG-PLA solid: anhydrous ethanol mass ratio of 1:3; the mixture was sealed in a 42°C water bath and stirred at 300 rpm for 12 min until completely dissolved to obtain a homogeneous mother liquor; the mother liquor was added to the above nano-dispersion and stirred at 25°C and 500 rpm for 20 min; then 4 g of thiourea was added at 400 rpm and stirred until completely dissolved; then 2.5 g of sodium sulfite was added and stirred at 35°C and 400 rpm until dissolved; 0.5 g of triethanolamine was added dropwise at a rate of 0.5 g / min to adjust the pH to 7.2; the mixture was stirred and matured at 35°C and 300 rpm for 1.5 h; cooled to room temperature, filtered and collected to obtain an open-loop circulating cooling water system corrosion and scale inhibitor.

[0032] The above-mentioned polyethylene glycol-polylactic acid block copolymer was obtained by the following method: 260g of methoxy polyethylene glycol monohydroxy (number average molecular weight 2600) was dried under vacuum at 110℃ for 2h, cooled to 85℃, protected by high-purity nitrogen, and 140g of L-lactide crystals were added. The temperature was further increased to 130℃, and stannous octoate (0.3% of the total molar amount of the system) was added. The mixture was stirred at a constant temperature for 12h. Heating was stopped, and the copolymer was completely dissolved in anhydrous dichloromethane while hot. The solid was then precipitated in cold anhydrous diethyl ether and collected by filtration. The process of dissolving in anhydrous dichloromethane and precipitating in cold anhydrous diethyl ether was repeated twice. The copolymer was dried under vacuum at 40℃ to constant weight. The number average molecular weight was determined to be approximately 4000 by gel permeation chromatography (GPC).

[0033] Example 3 This embodiment provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, comprising the following steps: (1) 45g of polyepoxysuccinic acid (solid content 40%) and 3g of deionized water were heated to 45℃ and stirred at 400rpm until completely dissolved; while maintaining 400rpm, 10.5g of triethanolamine was slowly added dropwise at a rate of 0.7g / min. After the addition was complete, the pH of the system was measured to be approximately 6.9; the mixture was kept warm and stirred for 18min to obtain a polycarboxylic acid-ethanolamine solution. (2) Cool the solution obtained in step (1) to 20°C, dilute 22.5g of naphthenic acid imidazoline quaternary ammonium salt with 10g of deionized water, and add it dropwise at a rate of 0.54g / min under stirring at 1000rpm for 60min; after the addition is completed, continue stirring at 1000rpm for 30min to obtain polyelectrolyte composite nano-dispersion; (3) Take 2.0g of polyethylene glycol-polylactic acid block copolymer (number average molecular weight 4000, preparation method is the same as in Example 2), add 6.0g of anhydrous ethanol, seal in a 42℃ water bath, stir at 300rpm for 12min until completely dissolved, and obtain PEG-PLA ethanol mother liquor; add the mother liquor and 4g of thiourea to 2g of deionized water, stir at 25℃ and 400rpm for 12min to obtain thiourea-PEG-PLA mixture; add the mixture to the nano-dispersion obtained in step (2) under stirring at 500rpm, and stir evenly; then add 2.5g of sodium sulfite at 400rpm, and stir at 35℃ until dissolved; add 0.5g of triethanolamine dropwise at a rate of 0.5g / min to adjust the pH to 7.2; stir and mature at 35℃ and 300rpm for 1.5h; cool to room temperature, filter and collect to obtain corrosion and scale inhibitor for open circulating cooling water system.

[0034] Example 4 This embodiment provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, comprising the following steps: (1) 30g of polyepoxysuccinic acid (solid content 40%) and 35g of deionized water were heated to 40℃ and stirred at 300rpm until completely dissolved; while maintaining 300rpm, 5.6g of triethanolamine was slowly added dropwise at a rate of 0.4g / min. After the addition was complete, the pH of the system was measured to be approximately 6.5; the mixture was kept warm and stirred for 15min to obtain a polycarboxylic acid-ethanolamine solution. (2) Cool the solution obtained in step (1) to 15°C, dilute 15g of naphthenic acid imidazoline quaternary ammonium salt with 10g of deionized water, and add it dropwise at a rate of 0.47g / min under stirring at 500rpm for 30min; after the addition is completed, continue stirring at 500rpm for 25min to obtain polyelectrolyte composite nano-dispersion. (3) Take 2.0g of polyethylene glycol-polylactic acid block copolymer (number average molecular weight 3000), add 3.0g of anhydrous ethanol, seal in a 42℃ water bath, stir at 300rpm for 10min until completely dissolved, and obtain PEG-PLA ethanol mother liquor; add the mother liquor and 2g of thiourea to 1g of deionized water, stir at 25℃ and 300rpm for 10min to obtain thiourea-PEG-PLA mixture; add the mixture to the nano-dispersion obtained in step (2) under stirring at 400rpm, and stir evenly; then add 1g of sodium sulfite at 300rpm, and stir at 30℃ until dissolved; add 0.4g of triethanolamine dropwise at a rate of 0.5g / min to adjust the pH to 7; stir and mature at 30℃ and 200rpm for 1h; cool to room temperature, filter and collect to obtain corrosion and scale inhibitor for open circulating cooling water system.

[0035] The above-mentioned polyethylene glycol-polylactic acid block copolymer was obtained by the following method: 160g of methoxy polyethylene glycol monohydroxy (number average molecular weight 1600) was dried under vacuum at 110℃ for 2h, cooled to 85℃, protected by high-purity nitrogen, and 140g of L-lactide crystals were added. The temperature was further increased to 130℃, and stannous octoate (0.3% of the total molar amount of the system) was added. The mixture was stirred at a constant temperature for 12h. Heating was stopped, and the copolymer was completely dissolved in anhydrous dichloromethane while hot. The solid was then precipitated in cold anhydrous diethyl ether and collected by filtration. The process of dissolving in anhydrous dichloromethane and precipitating in cold anhydrous diethyl ether was repeated twice. The copolymer was dried under vacuum at 40℃ to constant weight. The number average molecular weight was determined to be approximately 3000 by gel permeation chromatography (GPC).

[0036] Example 5 This embodiment provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, comprising the following steps: (1) 60g of polyepoxysuccinic acid (solid content 40%) and 9.5g of deionized water were heated to 50°C and stirred at 500rpm until completely dissolved; while maintaining 500rpm, 15.5g of triethanolamine was slowly added dropwise at a rate of 0.9g / min. After the addition was complete, the pH of the system was measured to be approximately 7.5; the mixture was kept warm and stirred for 20min to obtain a polycarboxylic acid-ethanolamine solution.

[0037] (2) Cool the solution obtained in step (1) to 25°C, dilute 30g of naphthenic acid imidazoline quaternary ammonium salt with 10g of deionized water, and add it dropwise at a rate of 0.58g / min under stirring at 1500rpm for 90min; after the addition is completed, continue stirring at 1500rpm for 35min to obtain polyelectrolyte composite nano-dispersion; (3) Take 3.0g of polyethylene glycol-polylactic acid block copolymer (number average molecular weight 5000), add 9.0g of anhydrous ethanol, seal in a 42℃ water bath, stir at 300rpm for 15min until completely dissolved, and obtain PEG-PLA ethanol mother liquor; add the mother liquor and 6g of thiourea to 3g of deionized water, stir at 25℃ and 500rpm for 15min to obtain thiourea-PEG-PLA mixture; add the mixture to the nano-dispersion obtained in step (2) under stirring at 600rpm, and stir evenly; then add 4g of sodium sulfite at 500rpm, and stir at 40℃ until dissolved; add 0.5g of triethanolamine dropwise at a rate of 0.5g / min to adjust the pH to 7.5; stir and mature at 40℃ and 400rpm for 2h; cool to room temperature, filter and collect to obtain corrosion and scale inhibitor for open circulating cooling water system.

[0038] The above-mentioned polyethylene glycol-polylactic acid block copolymer was obtained by the following method: 360g of methoxy polyethylene glycol monohydroxy (number average molecular weight 3600) was dried under vacuum at 110℃ for 2h, cooled to 85℃, protected by high-purity nitrogen, and 140g of L-lactide crystals were added. The temperature was further increased to 130℃, and stannous octoate (0.3% of the total molar amount of the system) was added. The mixture was stirred at a constant temperature for 12h. Heating was stopped, and the copolymer was completely dissolved in anhydrous dichloromethane while hot. The solid was then precipitated in cold anhydrous diethyl ether and collected by filtration. The process of dissolving in anhydrous dichloromethane and precipitating in cold anhydrous diethyl ether was repeated twice. The copolymer was dried under vacuum at 40℃ to constant weight. The number average molecular weight was determined to be approximately 5000 by gel permeation chromatography (GPC).

[0039] Comparative Example 1 The corrosion and scale inhibitor provided in this comparative example is the corrosion and scale inhibitor prepared in Example 1 of the patent application document CN117023817A for an open circulating cooling water system. Specifically, deionized water is added to a stirred tank and heated to 70°C. Then, 80g of thiourea and 30g of sodium ascorbate are added sequentially. The stirrer is turned on at 80rpm and stirred until completely dissolved. After cooling to room temperature, 200g of oleic acid imidazoline quaternary ammonium salt, 150g of ethanolamine, and 200g of sodium polyaspartate are added. The mixture is stirred at room temperature for 30min to obtain the corrosion and scale inhibitor.

[0040] Comparative Example 2 This embodiment provides a method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, comprising the following steps: (1) 45g of polyepoxysuccinic acid (solid content 40%) and 5g of deionized water were heated to 45℃ and stirred at 400rpm until completely dissolved; while maintaining 400rpm, 10.5g of triethanolamine was slowly added dropwise at a rate of 0.7g / min. After the addition was complete, the pH of the system was measured to be about 6.9; the system was kept warm and stirred for 18min to obtain a polycarboxylic acid-ethanolamine solution.

[0041] (2) 22.5g of naphthenic acid imidazoline quaternary ammonium salt was diluted with 10g of deionized water beforehand; the polycarboxylic acid-alcohol amine solution was cooled to 20℃ and added dropwise to the imidazolium solution at a rate of 0.54g / min under stirring at 1000rpm; after the addition was completed, stirring was continued at 1000rpm for 30min to obtain a mixture; (3) Add 4g of thiourea to the above mixture under stirring at 400rpm and stir until completely dissolved; then add 2.5g of sodium sulfite and continue stirring until dissolved; add 0.5g of triethanolamine dropwise at a rate of 0.5g / min to adjust the pH to 7.2; stir and mature at 35℃ and 300rpm for 1.5h; cool to room temperature, filter and collect to obtain corrosion and scale inhibitor for open circulating cooling water system.

[0042] Performance testing The corrosion inhibitors obtained in each embodiment and comparative example were tested as follows, and the test results are recorded in Table 1 and Table 2.

[0043] (1) Average particle size: Measured using dynamic light scattering (DLS) with a Malvern Zetasizer NanoZS nanoparticle size potentiometer. For uniformly dispersed example samples: Take an appropriate amount of corrosion and scale inhibitor sample, dilute with deionized water to the instrument's recommended count rate range, and measure after equilibration at 25°C for 120 seconds. For comparative sample samples that exhibited precipitation and stratification: Shake the sample vigorously for 5 minutes before testing, immediately take the upper suspension, dilute with deionized water, and measure under the above conditions. If the sample cannot form a measurable suspension, record it as "unable to form a stable dispersion". Each sample was measured three times, and the average particle size and polydispersity index (PDI) were recorded.

[0044] (2) Zeta potential: Measured using electrophoretic light scattering with a Malvern Zetasizer NanoZS nanoparticle size potentiometer. For uniformly dispersed example samples: a suitable amount of sample was diluted with deionized water and injected into the capillary sample cell, then measured at 25°C. For comparative sample samples that underwent precipitation and stratification: the sample was shaken well before testing, and the upper suspension was immediately diluted and measured. If no analyte suspension was available, it was recorded as "unable to measure". Each sample was repeated three times, and the average value was taken. The Zeta potential was automatically calculated by the instrument based on the Henry equation.

[0045] (3) Changes in appearance and particle size after standing at 60℃ for 30 days: The finished corrosion and scale inhibitor was sealed in a glass bottle and placed in a 60℃ constant temperature drying oven for 30 days. After being taken out and brought back to room temperature, the appearance was first visually observed to see if there was any precipitation, layering, or significant change in turbidity. Appearance judgment criteria: "No precipitation": No visible sediment at the bottom of the bottle, and the system is homogeneous; "Slight precipitation": A small amount of sediment at the bottom of the bottle, and the upper layer is still a suspension; "Large amount of precipitation": Most of the solids have settled, and the upper layer is basically clear. Particle size determination: For homogeneous samples, an appropriate amount was directly taken to determine the average particle size; for samples with precipitation, the upper suspension was taken immediately after shaking to determine the average particle size. The particle size change rate was calculated by comparing it with the initial average particle size.

[0046] (4) Corrosion inhibition performance: The rotating plate method was used, referring to GB / T18175-2014 "Determination of Corrosion Inhibition Performance of Water Treatment Agents - Rotating Plate Method". A3 carbon steel test pieces were used, and the test water was simulated circulating cooling water (prepared by concentrating pure water 10 times, Ca...). 2+ 250mg / L, HCO3 - 200mg / L, Cl -150 mg / L). The corrosion and scale inhibitor was added to the test water to a concentration of 50 mg / L, and the test was run continuously for 7 days at 50℃ and a specimen rotation speed of 0.35 m / s. For the comparative sample that precipitated, it was thoroughly shaken before testing, and the supernatant was immediately added to the test water. After the test, corrosion products on the specimen surface were removed with acid pickling solution. After washing with water, cleaning with acetone, and drying, the specimen was weighed, and the corrosion rate and corrosion inhibition rate were calculated. The corrosion inhibition rate was calculated using the following formula: Corrosion inhibition rate = (blank corrosion rate - chemically treated corrosion rate) / blank corrosion rate × 100%.

[0047] (5) Scale inhibition performance: Static scale inhibition method was adopted, referring to GB / T16632-2008 "Determination of Scale Inhibition Performance of Water Treatment Agents - Calcium Carbonate Deposition Method". A solution containing Ca was prepared. 2+ 400mg / L, HCO3 - For the comparative sample, using 300 mg / L simulated water, shake well before testing and immediately add the supernatant suspension to the simulated water to achieve a reagent concentration of 30 mg / L. Let it stand in an 80℃ water bath for 10 hours. After cooling, determine the remaining Ca in the clarified solution using EDTA titration. 2+ Concentration, and a blank test was also conducted. The scale inhibition rate was calculated using the following formula: Scale inhibition rate = (Remaining Ca after chemical addition) / (Calcium content of the chemically added product) 2+ Concentration - Blank Residual Ca 2+ (concentration) / (initial Ca) 2+ Concentration - Blank Residual Ca 2+ (Concentration) × 100%.

[0048] (6) Thiourea stability: The thiourea content was determined by high performance liquid chromatography. The finished corrosion and scale inhibitor was sealed and stored in a 60℃ constant temperature oven for 30 days for accelerated storage. For the comparative sample that showed precipitation, the sample was shaken well before testing, and the upper suspension was taken to determine the thiourea content. The thiourea content in the initial sample was also determined. The thiourea retention rate was calculated using the following formula: Retention rate = Thiourea content after 30 days of storage / Initial thiourea content × 100%.

[0049] Table 1 Performance test data of Examples 1-5 and Comparative Examples 1-2

[0050] Table 2 Performance test data of Examples 1-5 and Comparative Examples 1-2

[0051] As shown in Tables 1 and 2, all embodiments of the present invention can form nano-dispersions with moderate particle size, negative Zeta potential, and good storage stability. Among them, Example 5 exhibits the best corrosion inhibition and scale inhibition performance due to its high degree of neutralization and fine particle size. Examples 2 and 3 with added PEG-PLA are superior to Example 1 without added PEG-PLA in terms of storage stability and thiourea protection. Moreover, Example 3, which uses a pre-assembly method of thiourea and PEG-PLA, has the most outstanding stabilizing effect on thiourea. Comparative Example 1 was prepared according to the existing technology. Because the imidazoline quaternary ammonium salt and polycarboxylic acid are directly mixed, a large amount of precipitation is generated, and a stable dispersion cannot be formed. Its corrosion inhibition, scale inhibition, and thiourea retention performance are significantly reduced. Comparative Example 2's performance is further deteriorated due to excessive aggregation of polyelectrolyte caused by reverse droplet addition. This indicates that the process steps of partial neutralization of polycarboxylic acid, slow droplet addition of imidazoline at low temperature, and PEG-PLA stabilization treatment used in the present invention play a key role in obtaining high-performance corrosion and scale inhibitors.

Claims

1. A method for preparing a corrosion and scale inhibitor for an open-loop circulating cooling water system, characterized in that, Includes the following steps: (1) Dissolve the polycarboxylic acid dispersant in deionized water, heat to 40-50°C, and stir until completely dissolved; add alcohol amine corrosion inhibitor dropwise, adjust the pH of the system to 6.5-7.5, keep warm and stir for 15-20 min to obtain a polycarboxylic acid-alcohol amine solution; (2) Cool the polycarboxylic acid-alcohol amine solution to 15-25°C, and add imidazoline quaternary ammonium salt dropwise while stirring at 500-1500 rpm; continue stirring for 25-35 min after the addition is complete to obtain polyelectrolyte composite nano-dispersion; (3) Add the thiourea compound to the polyelectrolyte composite nano-dispersion and stir until dissolved. Then add the reducing agent and stir until dissolved. Adjust the pH to 7.0-7.5 with an alcohol amine corrosion inhibitor or a polycarboxylic acid dispersant and stir and mature at below 40°C for 1-2 hours. Cool to room temperature, filter and collect to obtain the corrosion and scale inhibitor for open circulating cooling water systems.

2. The method for preparing the corrosion and scale inhibitor for an open-loop circulating cooling water system according to claim 1, characterized in that, In step (3), before adding thiourea compounds, polyethylene glycol-polylactic acid block copolymer is added to the polyelectrolyte composite nanodispersion and stirred at 20-30°C for 15-25 minutes.

3. The method for preparing the corrosion and scale inhibitor for an open-loop circulating cooling water system according to claim 1, characterized in that, In step (3), a thiourea compound with a mass ratio of 1:(0.5-2) and a polyethylene glycol-polylactic acid block copolymer are used in deionized water and stirred at 20-30°C for 10-15 minutes to obtain a mixture. The mixture is then added to the polyelectrolyte composite nano-dispersion and stirred until homogeneous. A reducing agent is then added and stirred at 40°C or below until dissolved.

4. The method for preparing the corrosion and scale inhibitor for an open-loop circulating cooling water system according to claim 3, characterized in that, The number-average molecular weight of the polyethylene glycol-polylactic acid block copolymer is 3000-5000.

5. A corrosion and scale inhibitor for an open-type circulating cooling water system, characterized in that, The corrosion and scale inhibitor for an open-circulating cooling water system is prepared by the preparation method of any one of claims 1-4; the corrosion and scale inhibitor for the open-circulating cooling water system comprises the following raw materials in parts by weight: 15-30 parts of imidazoline quaternary ammonium salt, 6-16 parts of alkanolamine corrosion inhibitor, 2-6 parts of thiourea compound, 12-24 parts of polycarboxylic acid dispersant, 1-4 parts of reducing agent, and 0-3 parts of polyethylene glycol-polylactic acid block copolymer.

6. The corrosion and scale inhibitor for an open-loop circulating cooling water system according to claim 5, characterized in that, The polycarboxylic acid dispersant is one or more of polyepoxysuccinic acid, polyaspartic acid, and polymaleic acid-acrylic acid copolymer.

7. The corrosion and scale inhibitor for open-type circulating cooling water systems according to claim 5, characterized in that, The alkanolamine corrosion inhibitor is one or more of triethanolamine, diethanolamine, monoethanolamine, and morpholine.

8. The corrosion and scale inhibitor for open-type circulating cooling water systems according to claim 5, characterized in that, The imidazoline quaternary ammonium salt is either cycloalkanoic acid imidazoline quaternary ammonium salt or oleic acid imidazoline quaternary ammonium salt; the imidazoline quaternary ammonium salt is pre-diluted with deionized water to a mass fraction of 50% to 70%.

9. The corrosion and scale inhibitor for an open-loop circulating cooling water system according to claim 5, characterized in that, The thiourea compounds are one or more of thiourea, diphenylthiourea, and aminothiourea.

10. The corrosion and scale inhibitor for an open-loop circulating cooling water system according to claim 5, characterized in that, The reducing agent is one or more of sodium sulfite, sodium bisulfite, and sodium isoascorbate.

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