Descaling and rust removing agent and preparation method thereof

Abstract

According to the descaling and rust removing agent and the preparation method thereof, a permeation-chelation-corrosion inhibition-stabilization system is constructed by regulating and controlling the proportion of composite organic acid and introducing plant source modified corrosion inhibition components and a synergistic chelation mechanism, and the descaling and rust removing agent is prepared by compounding the composite organic acid, a plant source modified corrosion inhibitor and the like according to a specific proportion. The composite organic acid is composed of glycolic acid, citric acid and gluconic acid according to a ratio of 2: 1: 1.5; the corrosion inhibitor is formed by compounding corn protein modified tannic acid and methylbenzotriazole according to the ratio of 3: 2; the chelating agent is EDTA-2Na, and HEDTA and NTA-Na are compounded in a gradient manner. The descaling rate of the product is greater than or equal to 99.2%, the derusting time of carbon steel is less than or equal to 15min, the corrosion rate is less than or equal to 0.02 mm / a, and the biodegradation rate is greater than or equal to 95% The preparation adopts a segmented temperature control-nitrogen protection process, and is suitable for industrial production. The high-efficiency, low-corrosion, environment-friendly and high-efficiency synergic performance is achieved, and the high-efficiency, low-corrosion, environment-friendly and high-efficiency metal base material is suitable for metal base materials such as carbon steel, cast iron, copper alloy and stainless steel and the harsh environment-friendly industries such as food processing, pharmaceutical and chemical engineering and electronic precision manufacturing.

Description

Technical Field

[0001] In the field of metal surface treatment agents, this invention specifically relates to a highly efficient composite descaling and rust removal agent that integrates descaling and rust removal functions, is compatible with multiple substrates, and is environmentally friendly, as well as its preparation method. It is particularly suitable for removing scale and rust from the surfaces of various metal substrates, including industrial circulating water systems (such as power plant condensers and steel plant cooling water networks), heat exchange equipment (such as chemical reactor jackets and central air conditioning heat exchangers), petrochemical pipelines (such as crude oil pipelines and refined oil storage tanks), hardware and machinery parts (such as automotive parts and standard components), and marine engineering equipment (such as decks and cabin metal components). The technical solution of this invention is not only applicable to conventional room temperature cleaning scenarios but also adaptable to industrial cleaning processes such as high-pressure spray cleaning (pressure 0.5-1.0 MPa) and ultrasonic cleaning (frequency 20-40 kHz). It also meets the application needs of industries with stringent requirements for the environmental friendliness and safety of cleaning agents, such as food processing, pharmaceuticals, and precision electronics manufacturing. Background Technology

[0002] Currently, there are many types of descaling and rust removal agents on the market. Based on their mechanism of action and composition, they can be divided into inorganic acid type, organic acid type, chelating type, compound type, and bio-enzyme type, etc. All types of products have obvious technical defects and are difficult to meet the comprehensive requirements of modern industry for high efficiency, environmental protection, and compatibility with multiple substrates. 1. Inorganic acid-based descaling and rust removal agents: These agents use hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, etc., as the main active ingredients. They remove rust and scale through the dissolving action of strong acids, and are characterized by fast rust removal speed (rust removal time for carbon steel at 20℃ ≤ 10 min) and low cost (raw material cost ≤ 2 yuan / kg). However, they have fatal flaws: ① Extremely corrosive, with a corrosion rate of ≥ 0.5 mm / a on carbon steel. A large amount of corrosion inhibitor needs to be added during the cleaning process, and it easily leads to rough substrate surface and hydrogen embrittlement (especially for high-strength steel), shortening the service life of equipment; ② Poor environmental performance, generating a large amount of toxic and harmful gases during use (such as Cl2 produced by hydrochloric acid volatilization and HF produced by hydrofluoric acid volatilization), causing serious harm to the respiratory system of operators. The pH value of the waste liquid is ≤ 1, requiring neutralization treatment before discharge, resulting in high treatment costs (treatment cost ≥ 50 yuan per ton of waste liquid); ③ Narrow applicability, with greater corrosivity to stainless steel, copper alloys, and other precious metal substrates, easily causing intergranular corrosion, making it unsuitable for general use. For example, a machine shop used a 30% hydrochloric acid solution to clean carbon steel parts. Although the rust removal was completed within 10 minutes, the surface roughness of the parts increased from Ra1.6μm to Ra3.2μm, and obvious hydrogen embrittlement cracks appeared.

[0003] 2. Traditional organic acid-based descaling and rust removal agents: These agents mainly consist of acetic acid, formic acid, oxalic acid, etc., which have lower corrosiveness than inorganic acids (carbon steel corrosion rate ≤0.1mm / a). However, they suffer from low descaling and rust removal efficiency and are not effective in removing stubborn rust (thickness ≥0.5mm) and hard scale (such as calcium sulfate scale). The removal time at 20℃ is usually ≥60min. Furthermore, the chelating ability of a single organic acid is weak, requiring the addition of a large amount of chelating agent, which increases costs. Some organic acids (such as oxalic acid) are toxic and have poor biodegradability (≤60%), which does not meet environmental protection requirements.

[0004] 3. Chelating descaling and rust removal agents: These agents primarily consist of EDTA, aminotrimethylenephosphonic acid, etc. They remove rust and scale by forming stable chelates with metal ions. They exhibit extremely low corrosivity (corrosion rate of carbon steel ≤0.01mm / a), but their descaling and rust removal speed is extremely slow (removal time ≥120min at 20℃). Furthermore, the cost of chelating agents is high (market price of EDTA-2Na ≥20 yuan / kg), making it difficult to meet the efficiency and cost requirements of large-scale industrial cleaning. At the same time, traditional chelating agents (such as EDTA) have poor biodegradability and are prone to accumulating in the environment, causing pollution.

[0005] 4. Existing composite descaling and rust removal agents: Although they combine the advantages of organic acids and chelating agents, they generally suffer from unclear synergistic effects and poor performance balance. Some products, in pursuit of faster rust removal, still add more than 10% inorganic acid components, leading to excessive corrosion rates. Some products use chemically synthesized corrosion inhibitors (such as di-o-toluenethiourea and thiourea), with a biodegradation rate of ≤50% and high toxicity. Some products have poor compatibility with different metal substrates; the same product works well for cleaning carbon steel, but corrosion and discoloration occur when cleaning copper alloys.

[0006] 5. Bio-enzyme-based descaling and rust removal agents: These are novel products, primarily composed of proteases and lipases. While environmentally friendly, they suffer from low efficiency and a narrow range of applications. They are only effective against biologically formed rust and scale, showing poor performance against common industrial iron oxide and calcium carbonate scale. Furthermore, enzyme activity is easily affected by temperature and pH, resulting in poor storage stability and hindering industrial-scale application. In addition, existing descaling and rust removal agent preparation processes are generally crude, often employing a "room temperature mixing - simple stirring" approach. This lack of precise control over key parameters such as reaction temperature, stirring rate, and material addition order leads to uneven dispersion of components, preventing them from fully exerting their synergistic effects and resulting in poor batch-to-batch stability (performance fluctuation ≥10%). For example, some processes add corrosion inhibitors and organic acids simultaneously, causing the corrosion inhibitor molecules to be destroyed by the acid, reducing the corrosion inhibition effect by more than 50%. Other processes adjust the pH too quickly, leading to sudden pH changes that cause hydrolysis and inactivation of chelating agents, affecting the descaling effect. With increasingly stringent environmental regulations (such as the implementation of GB / T 38483-2020 "Environmental Protection Technical Requirements for Industrial Cleaning Agents") and the diversification of industrial equipment materials, the technical shortcomings of existing descaling and rust removal agents have become increasingly prominent. Developing products that combine high-efficiency descaling and rust removal performance, low corrosivity, high environmental friendliness, and compatibility with multiple substrates has become a technical challenge that the industry urgently needs to solve.

[0007] To address the shortcomings of inorganic acid-based products, organic acid-based descaling and rust-removing agents have been widely researched and applied, but existing technologies still have many deficiencies. For example, Chinese patent application CN106567084A discloses a metal rust remover and its preparation method, which uses acetic acid as the main acidic component (accounting for 20%), combined with sodium polyacrylate (chelating agent), tetrasodium EDTA (chelating agent), chitosan (corrosion inhibitor), di-o-toluenethiourea (corrosion inhibitor), etc. Although the product has lower corrosivity than inorganic acids (carbon steel corrosion rate 0.08mm / a), it has the following obvious technical defects: ① Low descaling and rust-removing efficiency. The penetration and chelating abilities of acetic acid alone are limited. It takes more than 60 minutes to remove a 0.5mm thick carbon steel rust layer, and the descaling rate for calcium carbonate scale is only 85%, which is difficult to meet the efficiency requirements of industrial cleaning; ② The product exhibits several drawbacks: ① Poor environmental performance: The corrosion inhibitor used is di-o-toluenethiourea, which is toxic (oral LD50 in rats is 300 mg / kg) and has a biodegradability rate of only 40%, failing to meet the requirement of ≥80% biodegradability in GB / T38483-2020. Wastewater discharge is likely to cause environmental pollution. ② Poor substrate compatibility: The corrosion rate on copper alloy substrates reaches 0.05 mm / a, resulting in noticeable discoloration on the copper surface after cleaning. ③ High cost: The formula includes trifluoroethanol (a co-solvent), which has a market price of ≥100 yuan / kg, leading to a raw material cost of over 15 yuan / kg, hindering large-scale industrial application. ④ Poor stability: The product is prone to stratification when stored below 0℃, affecting its performance. These existing technologies indicate that traditional organic acid-based descaling and rust-removing agents generally suffer from the technical contradiction of "difficulty in balancing environmental protection and high efficiency" and "poor compatibility with multiple substrates." The core reason lies in the lack of a scientifically sound synergistic component system: single or simply compounded organic acids cannot simultaneously achieve a balance between rapid penetration and gentle corrosion; corrosion inhibitors have poor compatibility with organic acids and chelating agents, making it difficult to form a stable synergistic effect; and chelating agents lack sufficient targeting for different metal ions, resulting in uneven descaling and rust-removing effects. This invention successfully solves the above-mentioned technical contradictions through precise design and synergistic optimization of the organic acid system, corrosion inhibitors, and chelating agents.

[0008] Chelating descaling and rust removal agents achieve their advantages by forming stable chelates (stability constants typically ≥10¹²) with metal ions through the amino and carboxyl functional groups in the chelating agent molecules. These agents have the advantages of low corrosivity (corrosion rate of carbon steel ≤0.01mm / a) and minimal damage to the substrate. However, these products have two major drawbacks: ① Slow descaling and rust removal speed: The chelation reaction between the chelating agent molecules and metal ions is a slow process, and the chelating agent molecules are relatively large with weak penetration ability, making it difficult to quickly enter the rust. For dense rust layers commonly found in industry, the removal time at 20℃ is typically ≥120min, which cannot meet the needs of large-scale continuous production. ② High cost: The market price of high-efficiency chelating agents (such as HEDTA) is generally above 30 yuan / kg. To achieve the ideal descaling effect, the chelating agent addition amount needs to be ≥15%, resulting in a raw material cost exceeding 20 yuan / kg, far higher than traditional inorganic acid-based products (2-5 yuan / kg), limiting their industrial application. For example, an electronics company used pure EDTA-2Na solution to clean precision copper parts. Although it did not cause corrosion, the cleaning time was as long as 4 hours, resulting in extremely low production efficiency. Composite descaling and rust-removing agents combine the penetrating and dissolving effects of organic acids with the chelating effects of chelating agents, becoming a current research hotspot. However, existing composite products still face several technical bottlenecks: ① The synergistic effect of components is unclear. Most products simply mix organic acids and chelating agents without considering the interactions between the components. In some cases, antagonistic effects even occur. For example, when oxalic acid and EDTA are mixed, oxalate ions compete with EDTA for metal ions, resulting in a decrease in chelation effect of more than 30%; ② The descaling and rust-removing effects are unbalanced. Some products add a high proportion of strong acids (such as hydrochloric acid and nitric acid) to pursue faster rust removal, which improves rust removal efficiency but exceeds the corrosion rate limit. Some products reduce the content of acidic components to reduce the corrosion rate, resulting in a significant decrease in descaling and rust-removing efficiency; ③ Environmental performance is insufficient. Most products use chemically synthesized corrosion inhibitors (such as thiourea and imidazoline), with a biodegradability rate of ≤60%, and some components have endocrine-disrupting effects, easily accumulating in the environment and causing long-term pollution; ④ Poor compatibility with various substrates means that a single product cannot meet the cleaning needs of multiple substrates such as carbon steel, stainless steel, and copper alloys. For example, a product that works well for carbon steel may cause intergranular corrosion when used for stainless steel, or cause surface discoloration when used for copper alloys. Furthermore, existing composite products typically have a fixed pH range of 1-2, making them highly acidic systems. While this improves descaling efficiency, it further exacerbates the risk of substrate corrosion and places extremely high demands on the corrosion resistance of cleaning equipment, increasing equipment investment costs for companies. With the diversification of industrial equipment materials and increasingly stringent environmental requirements, existing composite descaling and rust removal agents can no longer meet market demands. Developing a new composite system that combines "high-efficiency penetration, targeted chelation, mild corrosion, and environmental stability" has become an inevitable trend in the industry.

[0009] Besides the deficiencies in the formulation system, the existing preparation processes for descaling and rust removal agents also have significant shortcomings. They generally employ simple mixing and stirring processes, lacking precise control over key process parameters, resulting in poor product performance stability and large batch-to-batch fluctuations (performance deviation ≥10%). The main problems are as follows: ① Lack of temperature control: Most processes involve mixing at room temperature, without considering the impact of temperature on the dissolution of organic acids, chelation reactions, and the adsorption of corrosion inhibitors. For example, citric acid dissolves slowly at room temperature, requiring stirring for more than 30 minutes to completely dissolve, and the dissolution is uneven, easily leading to localized excessively high concentrations; while the chelation reaction is most efficient at 35-45℃, with efficiency decreasing by more than 50% at room temperature; ② The following issues were identified: 1. Inappropriate stirring parameters: Most processes use fixed stirring speeds (e.g., 300 r / min), which cannot meet the mixing requirements of different stages. For example, the surfactant compounding stage requires high-speed stirring (above 600 r / min) to form a stable micelle system, while the pH adjustment stage requires low-speed stirring (below 300 r / min) to avoid local pH changes. 2. Insufficient stirring time in some processes leads to uneven dispersion of components, resulting in stratification and precipitation. 3. Disordered material addition order: Some processes add all components to water at once, causing corrosion inhibitors to react directly with organic acids. The corrosion inhibitor molecules are destroyed by the acid, losing their corrosion inhibition effect. For example, tannic acid hydrolyzes when in direct contact with strong acids, destroying the phenolic hydroxyl groups and reducing the corrosion inhibition effect by more than 80%. Some processes add surfactants before organic acids, causing the organic acids and surfactants to form gels, affecting system stability. 4. Lack of online monitoring and quality control: Most processes do not use online detection equipment during preparation, making it impossible to monitor key indicators such as pH, viscosity, and concentration in real time. Testing can only be done after the product is finished, and if it fails, rework is required, increasing production costs. Without considering the introduction of impurities, some processes use ordinary tap water instead of deionized water. Calcium and magnesium ions in the water will react with the chelating agent, consuming the effective components of the chelating agent and reducing the descaling effect. No protective measures were taken during the stirring process, and oxygen in the air will oxidize organic acids, resulting in a decrease in the content of acidic components.

[0010] For example, a chemical plant used a traditional process to prepare a descaling and rust-removing agent, adding hydrochloric acid, EDTA, and thiourea to tap water in a single stirring process. Product testing revealed a descaling rate of only 70% (design value 90%) and a corrosion rate of 0.18 mm / a (design value 0.05 mm / a). Analysis showed that calcium and magnesium ions in the tap water consumed 20% of the EDTA, oxygen oxidation caused a 15% decrease in hydrochloric acid concentration, and thiourea reacted with hydrochloric acid to generate ineffective products. These defects in the preparation process directly lead to unstable product performance, making it difficult to meet the demands of large-scale industrial production and application. Therefore, developing precise, controllable, stable, and efficient preparation processes and formulation systems is equally important. Summary of the Invention

[0011] To address the shortcomings of existing technologies, the purpose of this invention is to provide a descaling and rust removal agent and its preparation method, which solves the problems of "high efficiency but high corrosion" and "environmentally friendly but inefficient" in existing products, and is applicable to various metal substrates and industries with stringent environmental requirements.

[0012] The above-mentioned objective of this invention is achieved through the following technical solutions: This invention provides a descaling and rust-removing agent, comprising the following components by weight: 15-25 parts of a complex organic acid system, 3-8 parts of a plant-derived modified corrosion inhibitor, 5-12 parts of a high-efficiency synergistic chelating agent, 2-6 parts of a green surfactant, 1-4 parts of a pH adjuster, 1-3 parts of a functional co-solvent, and 40-65 parts of deionized water; the complex organic acid system is composed of glycolic acid (≥99% purity), food-grade citric acid, and industrial-grade gluconic acid in a weight ratio of 2:1:1.5; the plant-derived modified corrosion inhibitor is a compound of corn protein-modified tannic acid and methylbenzotriazole in a weight ratio of 3:2, wherein the corn protein-modified tannic acid... The product was prepared by reacting tannic acid and corn protein in deionized water at a weight ratio of 5:1 at 50°C for 60 min, followed by freeze-drying and pulverizing to 100 mesh. The highly efficient synergistic chelating agent was prepared by compounding disodium ethylenediaminetetraacetate, hydroxyethyl ethylenediaminetriacetic acid, and sodium hypoaminotriacetate in a weight ratio of 2:1:1. The green surfactant was prepared by compounding fatty alcohol polyoxyethylene ether, sodium dodecylbenzenesulfonate, and alkyl glycoside in a weight ratio of 2:1:1. The pH adjuster was prepared by compounding flake sodium hydroxide and triethanolamine in a weight ratio of 1:2. The functional cosolvent was prepared by compounding ethylene glycol monobutyl ether and propylene glycol methyl ether in a weight ratio of 1:1.

[0013] According to one embodiment of the present invention, the high-efficiency synergistic chelating agent can be adjusted in composition and ratio according to the type of substrate being treated: when treating iron-based materials such as carbon steel and cast iron, disodium ethylenediaminetetraacetate and hydroxyethyl ethylenediaminetriacetic acid are compounded in a weight ratio of 1:1, and the chelating capacity of the chelating system for Fe³⁺ is ≥300 mg / g; when treating copper and copper alloy materials, hydroxyethyl ethylenediaminetriacetic acid and sodium hypoaminotriacetate are compounded in a weight ratio of 1:1, and the chelating capacity for Cu²⁺ is ≥280 mg / g; when treating multi-metal mixed substrates, disodium ethylenediaminetetraacetate, hydroxyethyl ethylenediaminetriacetic acid, and sodium hypoaminotriacetate are compounded in a weight ratio of 2:1:1, and the chelating constants of this chelating system for Fe³⁺, Ca²⁺, Mg²⁺, and Cu²⁺ are all ≥10¹ in the pH range of 2.5-4.0. 4 The purity of the chelating agent meets the following requirements: disodium ethylenediaminetetraacetate ≥ 99%, hydroxyethyl ethylenediaminetriacetate ≥ 98%, sodium ethylenediaminetriacetate ≥ 97%, and heavy metal content (as Pb) ≤ 10 ppm.

[0014] According to one embodiment of the present invention, the green surfactant is a ternary compound composed of a nonionic surfactant, an anionic surfactant, and a plant-derived glycoside surfactant in a weight ratio of 2:1:1; the nonionic surfactant is a fatty alcohol polyoxyethylene ether (AEO-9) with an HLB value of 13.3, the anionic surfactant is sodium dodecylbenzene sulfonate (LAS) with a biodegradability of ≥90%, and the plant-derived glycoside surfactant is an alkyl glycoside (APG-1214) with a carbon chain length of 12-14 prepared from corn starch and coconut oil; the critical micelle concentration of this ternary system is 0.08-0.12 g / L, the surface tension at 20°C is ≤30 mN / m, it has excellent compatibility with the composite organic acid system, and there is no stratification or precipitation after mixing, with a spreading coefficient ≥50 mm / min on the rust surface.

[0015] According to one embodiment of the present invention, the pH adjuster is a composite buffer system composed of flake sodium hydroxide with a purity ≥96% and analytical grade triethanolamine in a weight ratio of 1:2. This system can suppress pH fluctuations, and the pH change during the cleaning process is ≤0.5. The pH of the descaling and rust-removing agent is adjusted to 2.5-4.0, wherein the pH is controlled at 2.5-3.0 when treating carbon steel substrates, at 3.0-3.5 when treating stainless steel substrates, and at 3.5-4.0 when treating copper alloy substrates. The pH adjuster is added dropwise at a rate of 0.5-1.0 mL / min, while simultaneously using magnetic stirring at 500 r / min to ensure uniform pH of the system.

[0016] According to one embodiment of the present invention, the functional co-solvent is a compound of ethylene glycol monobutyl ether and propylene glycol methyl ether in a weight ratio of 1:1. This system can improve the solubility of the components and the permeability of the product, and the penetration depth of the rust layer with a thickness of ≥1mm is ≥0.8mm / 10min. The descaling and rust removing agent has a viscosity of 5-15mPa·s at 20℃, a surface tension of 25-35mN / m, a flash point of ≥60℃, and is non-flammable. The product can be stored in the range of -5℃ to 45℃ for 6 months, and the change rate of various performance indicators is ≤5%. 0.1-0.3 parts of sodium fluorescein can be added as a fluorescent tracer with a fluorescence emission wavelength of 520nm and a detection sensitivity of ≤0.1ppm.

[0017] This invention also provides a method for preparing the descaling and rust-removing agent as described above, employing an integrated process of "segmented temperature control - nitrogen protection - gradient stirring - online monitoring," including the following steps: S1. Raw material pretreatment: ① Hydroxyacetic acid, citric acid, and gluconic acid are vacuum dried (vacuum degree -0.09MPa, temperature 60℃, time 2h) to control the moisture content ≤0.5%; ② Corn protein modified tannic acid is pulverized to 100 mesh and sieved; ③ Deionized water is treated with ion exchange resin to achieve a conductivity ≤10μS / cm; metered pretreated deionized water is added to the reactor, the anchor stirrer is turned on at a speed of 300-500r / min, nitrogen gas is introduced at a rate of 0.5-1.0L / min for protection, and the temperature is raised to 35-45℃ at a rate of 2℃ / min. The three pretreated organic acids are added sequentially, and each addition is stirred for 5min. After all the acids are added, stirring is continued for 15-25min until dissolved. The pH value is monitored by an online pH meter to be ≤1.5 to obtain a composite organic acid solution. S2. Preparation of corrosion inhibition-chelation composite system: Keep the reactor temperature at 35-45℃ and the nitrogen flow rate constant, add a high-efficiency synergistic chelating agent at a rate of 1-2 g / min, stir for 10-20 min until dissolved, and the pH value of the system rises to 1.8-2.2; add a plant-derived modified corrosion inhibitor, stir at 300 r / min for 10 min, then stir at 500 r / min for 20 min, and continue stirring for 20-30 min to form a corrosion inhibition-chelation composite system. The particle size distribution of this system, as detected by laser particle size analyzer, is 100-300 nm and there is no obvious agglomeration. S3. Compound surfactant ingredients: Reduce the temperature of the reactor to 25-30℃ at a rate of 1℃ / min, stop nitrogen flow, add the premix of fatty alcohol polyoxyethylene ether, sodium dodecylbenzene sulfonate and alkyl glycoside, stir at 400r / min for 10min, then stir at 600r / min for 25-35min. When the viscosity stabilizes at 5-15mPa·s (fluctuation ≤0.5mPa·s) monitored by an online viscometer, stop stirring and let stand for 5min. The system should be uniform and transparent with no foam or only a small amount of easily dissipated foam. S4. Adjustment and stabilization: Add a premixed solution of sodium hydroxide and triethanolamine dropwise at a rate of 0.5-1.0 mL / min, stir at 300 r / min and monitor the pH value online. Stop the dropwise addition after the target range of 2.5-4.0 is reached; add a compound of ethylene glycol monobutyl ether and propylene glycol methyl ether, stir for 15-20 min, cool to 25℃ and let stand for 30-45 min, and remove microbubbles by vacuum degassing (vacuum degree -0.08 MPa, time 10 min).

[0018] According to one embodiment of the present invention, in S1, the diameter of the anchor-type stirrer blade is 1 / 3 of the inner diameter of the reactor, and the blade immersion depth is 2 / 3 of the liquid level; nitrogen protection is provided throughout S1 and S2, the nitrogen purity is ≥99.9%, and after drying and impurity removal, the moisture content is ≤10ppm and the oxygen content is ≤50ppm; after S1, the concentration of the composite organic acid solution is detected by acid-base titration, and the deviation is ≤2%, otherwise, the corresponding organic acid or deionized water is added to adjust.

[0019] According to one embodiment of the present invention, the order of adding the high-efficiency chelating agent in S2 is as follows: first add disodium ethylenediaminetetraacetate and stir for 5 min, then add hydroxyethyl ethylenediaminetriacetic acid and stir for 5 min, and finally add sodium methylaminetriacetate (when ternary compound is used); the gradient stirring after adding the corrosion inhibitor can increase the adsorption energy of the corrosion inhibitor on the metal surface by more than 30%; after S2, the chelation capacity is detected by EDTA complexometric titration. If the chelation capacity of Fe³+ is ≥250 mg / g, otherwise, chelating agent is added.

[0020] According to one embodiment of the present invention, the pH adjuster in S4 is added dropwise by a constant flow pump with an accuracy of ±0.05 mL / min; the pH value is monitored by an online pH meter with an accuracy of ±0.01, and calibrated with standard buffer solutions of pH=2.00 and 4.00 before use; when treating sensitive substrates such as copper alloys, the pH control accuracy is improved to ±0.05.

[0021] According to one embodiment of the present invention, the finished product undergoes three levels of quality inspection: Level 1 inspection includes appearance (uniform, transparent, and free of sedimentation and stratification), pH value 2.5-4.0, viscosity 5-15 mPa·s, and surface tension 25-35 mN / m, with a pass rate of 100%; Level 2 inspection includes descaling rate ≥98% (GB / T 35454-2017 gravimetric method), rust removal rate ≥0.8 g / (m²·min) (GB / T 16545-2015 loss-in-weight method), carbon steel corrosion rate ≤0.02 mm / a and stainless steel ≤0.005 mm / a (measured by an electrochemical workstation), with a pass rate of ≥98%; Level 3 inspection includes biodegradation rate ≥85% (GB / T 38483-2020 CO2 release method), Pb ≤10 ppm and Cd ≤5 ppm (ICP-MS determination), and no stratification after storage at -5℃ for 72 h, with a pass rate of 100%; only qualified products can be shipped from the factory, and unqualified products are returned to the reaction vessel for adjustment.

[0022] In summary, compared with the prior art, the present invention includes at least one of the following beneficial technical effects: 1. High descaling and rust removal efficiency: This invention optimizes the composition and ratio of the composite organic acid system, combining the synergistic effect of highly efficient chelating agents and surfactants to achieve rapid and efficient removal of scale and rust. Experimental data shows that the descaling and rust removal agent of this invention removes rust from carbon steel surfaces in ≤15 min at 20℃, with a descaling rate ≥99.2% and a rust removal rate ≥0.8 g / (m²·min), far exceeding existing organic acid-based products (existing products generally have a descaling rate of 85%-95% and a rust removal time ≥25 min).

[0023] 2. Low Corrosion: This environmentally friendly corrosion inhibitor, formulated with natural tannic acid and methylbenzotriazole, combined with the corrosion-inhibiting effect of gluconic acid, significantly reduces the corrosion of metal substrates by organic acids. Testing shows that the corrosion rate of this descaling and rust-removing agent on carbon steel is ≤0.02 mm / a, and on stainless steel it is ≤0.005 mm / a, far below the corrosion rate limit specified in the national standard (GB / T23447-2009 specifies a corrosion rate of ≤0.1 mm / a for carbon steel). After use, the surface of the metal substrate is smooth, without hydrogen embrittlement, pitting, or other phenomena.

[0024] 3. Excellent Environmental Performance: The scale and rust remover of this invention uses natural plant-derived corrosion inhibitors, is free of phosphorus, heavy metals, and toxic or harmful solvents, has a biodegradability rate of ≥90%, and a volatile organic compound (VOC) content of ≤10g / L, meeting the environmental protection requirements of GB / T38508-2020 "Limits of Hazardous Substances in Cleaning Agents". Waste liquid treatment is simple; it can be directly discharged after neutralization, with minimal environmental impact.

[0025] 4. Wide range of applications: The descaling and rust removal agent of this invention is suitable for a variety of metal substrates such as carbon steel, stainless steel, cast iron, and copper alloys. It can be used for descaling and rust removal in various scenarios such as industrial pipelines, heat exchange equipment, boilers, hardware accessories, and automotive parts, solving the problem of the limited substrates applicable to existing products.

[0026] 5. Stable and controllable preparation process: The preparation method of this invention adopts segmented temperature control, gradient stirring, and precise pH adjustment to ensure that all components are fully dissolved and exert synergistic effects, resulting in good product performance stability. The batch-to-batch descaling rate difference is ≤1%, and the corrosion rate difference is ≤0.002mm / a, which is far superior to products prepared by existing simple mixing processes and is suitable for large-scale industrial production. Detailed Implementation

[0027] The technical solutions in the embodiments of this application will be clearly and completely described below with reference to the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0028] As a basic material in industrial production, the surface condition of metallic materials directly affects the performance, lifespan, and production safety of equipment. During processing, storage, and use, metal surfaces are inevitably corroded by environmental factors. On the one hand, corrosive media such as oxygen, moisture, carbon dioxide, and sulfides in the environment will undergo electrochemical corrosion reactions with the metal, forming a rust layer on the surface. The main components of the rust layer on carbon steel are iron oxide (Fe2O3), iron hydroxide (Fe(OH)3), and their hydrates, while copper alloys will form rust such as basic copper carbonate (Cu2(OH)2CO3). These rust layers have a loose structure, which not only affects the appearance quality but also accelerates further corrosion of the metal. On the other hand, in industrial water systems, calcium and magnesium ions in the water easily combine with anions such as carbonate, sulfate, and silicate to form scale such as calcium carbonate (CaCO3), magnesium carbonate (MgCO3), and calcium sulfate (CaSO4). The thermal conductivity of scale is only 1 / 10 to 1 / 50 that of metal (e.g., the thermal conductivity of carbon steel is 45 W / (m·K), while that of calcium carbonate scale is only 0.6 W / (m·K)), which will seriously reduce the heat transfer efficiency of equipment. According to statistics from the industrial cleaning industry, for every 1mm of scale buildup on the surface of industrial equipment, heat transfer efficiency decreases by 10%-15%, leading to a 15%-20% increase in energy consumption. The presence of rust increases pipeline resistance, raising fluid transport energy consumption, and in severe cases, causing pipeline blockage, equipment corrosion and perforation, and production accidents. For example, a thermal power plant experienced an 8% reduction in unit power generation efficiency due to scale buildup in condenser pipelines, resulting in an additional consumption of over 5,000 tons of standard coal annually. A petrochemical company experienced a 24-hour production stoppage and economic losses of several million yuan due to rust flaking off and clogging filters in its oil pipelines. Therefore, developing efficient, environmentally friendly, low-corrosion descaling and rust-removing agents compatible with various substrates has significant industrial application value and economic significance for improving the operating efficiency of industrial equipment, extending its service life, reducing energy consumption, and mitigating safety risks.

[0029] Addressing the dual deficiencies of existing technologies in terms of formulation systems and preparation processes mentioned above, this invention, based on the core concepts of "molecular synergistic design," "targeted action," and "precise process control," achieves a comprehensive improvement in the performance of descaling and rust removal agents through systematic research. The specific innovative ideas are as follows: 1. Synergistic optimization of the composite organic acid system: Abandoning single organic acids or simple compounding models, this invention selects three organic acids with different structures and properties: glycolic acid (small molecule, strong penetration), citric acid (medium molecule, strong chelation), and gluconic acid (large molecule, mild corrosion inhibition). The optimal ratio (2:1:1.5) is determined through molecular simulation calculations. The three organic acids form stable composite acid clusters through intermolecular hydrogen bonding. The small molecule structure of glycolic acid rapidly penetrates the interior of rust and scale, disrupting the crystal structure; the carboxyl groups of citric acid form chelates with metal ions, promoting dissolution; and the polyhydroxyl structure of gluconic acid forms a temporary protective film on the metal surface, slowing corrosion. The three synergistically achieve a balance between "rapid penetration - efficient chelation - mild corrosion." 2. Development of Plant-Derived Modified Corrosion Inhibitors: Addressing the challenge of balancing environmental friendliness and corrosion inhibition effectiveness in traditional corrosion inhibitors, this study modifies plant-extracted tannic acid using corn protein. The amino groups of corn protein form amide bonds with the phenolic hydroxyl groups of tannic acid, enhancing the stability and long-lasting corrosion inhibition of tannic acid. This is then combined with methylbenzotriazole, leveraging the strong metal adsorption of methylbenzotriazole and the environmental friendliness of tannic acid to form a "strong adsorption-biodegradation-synergistic corrosion inhibition" system. This solves the problems of high toxicity and low biodegradability of traditional corrosion inhibitors. 3. Design of High-Efficiency Synergistic Chelating Agents: Based on the chelation requirements of different metal ions, three chelating agents—EDTA-2Na (strong chelating ability), HEDTA (good biodegradability), and NTA-Na (strong targeting)—are selected and blended in a gradient. By adjusting the proportions, high-efficiency targeted chelation of various metal ions such as Fe³⁺, Ca²⁺, Mg²⁺, and Cu²⁺ is achieved. Simultaneously, these agents work synergistically with the corrosion inhibitors to further reduce the corrosion rate. 4. Construction of a green surfactant system: Plant-derived alkyl glycosides (APG) are introduced and compounded with AEO-9 and LAS to form a ternary surfactant system, improving the product's wettability, penetration, and emulsification, while ensuring a biodegradability rate of ≥90%, meeting environmental protection requirements. 5. Development of a precise and controllable preparation process: Addressing the shortcomings of existing processes, an integrated process of "segmented temperature control - nitrogen protection - gradient stirring - online monitoring" is developed. By precisely controlling the temperature, stirring rate, material addition sequence, and reaction time at each stage, and using online pH meters, viscometers, and other detection equipment, the synergistic effect of each component is ensured, improving batch stability of the product.

[0030] This invention, through dual innovation in formulation and process, aims to provide a descaling and rust removal agent and its preparation method that is highly efficient in removing scale and rust, has low corrosivity, excellent environmental performance, is compatible with multiple substrates, and has a stable and controllable preparation process. It solves the technical problems of "high efficiency inevitably leads to high corrosion", "environmental protection inevitably leads to low efficiency", "incompatibility with multiple substrates", and "batch instability" in the existing technology, and provides a high-performance, green and environmentally friendly new solution for the industrial cleaning industry.

[0031] Experimental methods not specified in the examples were generally performed under standard conditions or conditions recommended by the manufacturer. All raw materials used were commercially available analytical grade or industrial grade raw materials. Hydroxyacetic acid (purity ≥99%), citric acid (purity ≥99.5%), and gluconic acid (purity ≥98%) were purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; tannic acid (plant extract, purity ≥98%) was purchased from Xi'an Lvtian Bioengineering Co., Ltd.; methylbenzotriazole (purity ≥99%) was purchased from Changzhou Shanfeng Chemical Co., Ltd.; disodium ethylenediaminetetraacetate, hydroxyethylethylenediaminetriacetic acid, and sodium hypoaminotriacetate were purchased from Sinopharm Chemical Reagent Co., Ltd.; fatty alcohol polyoxyethylene ether (AEO-9) and sodium dodecylbenzenesulfonate were purchased from Shandong Deshi Chemical Co., Ltd.

[0032] The primary objective of this invention is to overcome the four major defects of existing descaling and rust removal agents: ① The contradiction between descaling and rust removal efficiency and corrosivity, i.e., high-efficiency descaling and rust removal inevitably leads to high substrate corrosion; ② The contradiction between environmental performance and corrosion inhibition effect, i.e., environmentally friendly corrosion inhibitors usually have poor corrosion inhibition effect, while high-efficiency corrosion inhibitors are highly toxic and have low biodegradability; ③ Poor compatibility with multiple substrates, i.e., the same product cannot meet the cleaning needs of various metal substrates such as carbon steel, stainless steel, and copper alloys; ④ Poor batch stability of products, i.e., the performance of different batches of products fluctuates greatly. Based on this, the primary objective of this invention is to provide a high-efficiency, environmentally friendly, low-corrosion, and multi-substrate-compatible composite functional descaling and rust-removing agent. This product must simultaneously meet the following performance indicators: descaling rate ≥98% (for calcium carbonate scale, soaking at 20℃ for 30 min), rust removal rate ≥0.8 g / (m²·min) (for carbon steel rust layer at 20℃), carbon steel corrosion rate ≤0.02 mm / a, stainless steel corrosion rate ≤0.005 mm / a, copper alloy corrosion rate ≤0.01 mm / a, biodegradability ≥90%, and stable storage at -5℃ to 45℃. Meanwhile, the raw material cost should be controlled within 10 yuan / kg, making it suitable for industrial promotion.

[0033] Another objective of this invention is to provide a method for preparing the aforementioned descaling and rust-removing agent. This method addresses problems in existing preparation processes, such as lack of temperature control, unreasonable stirring parameters, chaotic material addition sequence, and lack of online monitoring. Specific objectives include: ① Achieving uniform dispersion and full synergy among the components, ensuring the formation of stable acid clusters in the composite organic acid system, and achieving synergistic effects between the corrosion inhibitor and chelating agent; ② Precisely controlling key performance indicators (pH value, viscosity, concentration) with a deviation range of ≤5%; ③ Improving batch-to-batch stability, with fluctuations in core indicators such as descaling rate and corrosion rate between different batches ≤3%; ④ Simplifying the operation process, reducing reliance on operator skills, and making it suitable for large-scale continuous industrial production; ⑤ Reducing raw material loss during production, with a raw material utilization rate ≥98%, thereby reducing production costs.

[0034] To achieve the above objectives, this invention, through extensive experimental research and theoretical analysis, breaks through the traditional formulation design approach and constructs a quaternary synergistic system of "composite organic acid - modified corrosion inhibitor - synergistic chelating agent - green surfactant," employing the following technical solution: A highly efficient and environmentally friendly descaling and rust-removing agent, by weight, comprises the following components: 15-25 parts of a complex organic acid system, 3-8 parts of a plant-derived modified corrosion inhibitor, 5-12 parts of a highly efficient synergistic chelating agent, 2-6 parts of a green surfactant, 1-4 parts of a pH adjuster, 1-3 parts of a functional co-solvent, and 40-65 parts of deionized water. The content ranges of each component were determined through extensive orthogonal experiments, based on the following key criteria: The complex organic acid system, as the main active ingredient for descaling and rust removal, results in insufficient acid concentration and a significant decrease in descaling and rust removal efficiency when its content is below 15 parts, with the rust removal time for carbon steel exceeding 30 minutes at 20°C. While the content is above 25 parts, although efficiency is improved, corrosiveness increases dramatically, with the corrosion rate of carbon steel exceeding 0.05 mm / a, and raw material costs rise. When the content of the plant-derived modified corrosion inhibitor is below 3 parts, the corrosion inhibition effect is insufficient, and the corrosion rate exceeds the standard. When the content is above 8 parts, the improvement in corrosion inhibition is not significant, and it reduces the descaling and rust-removing activity of the organic acid, leading to a decrease in efficiency. When the content of the highly efficient synergistic chelating agent is less than 5 parts, the chelating ability is insufficient, failing to effectively chelate dissolved metal ions and easily leading to secondary deposition; when the content is higher than 12 parts, the chelating ability is saturated, and the cost increases significantly. When the content of the green surfactant is less than 2 parts, the wetting and penetration are insufficient, making it difficult for the agent to spread on the rust and scale surface; when the content is higher than 6 parts, a large amount of foam will be generated, affecting the cleaning operation and the stability of the finished product. The content of the pH adjuster is determined according to the target pH value, ensuring that the pH value of the system is within the range of 2.5-4.0. This range can ensure the activity of organic acids while avoiding excessive corrosion. When the content of the functional co-solvent is less than 1 part, the solubilizing and penetration effects are insufficient; when the content is higher than 3 parts, it will increase the volatility and irritation of the product. The content of deionized water as a solvent needs to be adjusted according to the concentration requirements of each active ingredient to ensure the stability and homogeneity of the system.

[0035] One of the core innovations of this invention lies in the precise design and synergistic effect of the composite organic acid system, which is key to achieving a balance between "high-efficiency descaling and rust removal and low substrate corrosion". The composite organic acid system consists of glycolic acid, citric acid, and gluconic acid in a weight ratio of 2:1:1.5. This ratio was determined through molecular simulation and orthogonal experiments. The molecular structures and properties of the three organic acids are complementary, forming a synergistic effect. The specific mechanism is as follows: 1. Single-component properties of various organic acids: ① Glycolic acid: With the molecular formula HOCH2COOH, it is the smallest α-hydroxy acid, with a small molecular size (molecular diameter approximately 0.5 nm). It has extremely strong penetrating power, enabling it to quickly penetrate the dense structure of rust and scale, reaching the metal surface and reacting chemically with iron oxide in rust and calcium carbonate in scale, thus destroying their crystal structure. Simultaneously, glycolic acid has strong acidity (pKa = 3.83), providing sufficient H+ to promote the dissolution of rust and scale. At 20℃, a 10% glycolic acid solution achieves a rust removal rate of 0.6 g / (m²·min) on carbon steel rust layers. However, when used alone, it is highly corrosive, with a carbon steel corrosion rate reaching 0.1 mm / a. ② Citric acid: With the molecular formula C6H8O7, it is a ternary organic acid containing three carboxyl groups and one hydroxyl group. It has excellent chelating ability, forming stable chelates with metal ions such as Fe³⁺, Ca²⁺, and Mg²⁺ (the stability constant with Fe³⁺ is 10²⁻¹). 5 . 0 Citric acid promotes the dissolution of rust and scale; citric acid has mild acidity (pKa1=3.13) and lower corrosiveness than glycolic acid. A 10% citric acid solution has a corrosion rate of 0.05 mm / a on carbon steel, but its penetration ability is weak, and its effect on removing dense rust is poor. At 20℃, the rust removal rate is only 0.3 g / (m²·min). ③ Gluconic acid: molecular formula C6H 12 O7, belonging to the class of hexonic acids, contains six hydroxyl groups and one carboxyl group in its molecule. It has extremely mild acidity (pKa=3.86) and very low corrosiveness. The corrosion rate of carbon steel by a 10% gluconic acid solution is only 0.01 mm / a. Its polyhydroxy structure can enhance the wettability of the system and promote the spread of other organic acids on the rust surface. At the same time, gluconic acid molecules can form a temporary physical adsorption film on the metal surface, slowing down the corrosion of metal by organic acids. However, when used alone, its descaling and rust removal efficiency is extremely poor, with a descaling rate of only 50% at 20°C.

[0036] 2. Synergistic Mechanism of the Composite Organic Acid System: When three organic acids are compounded in a 2:1:1.5 ratio, they form a stable composite acid cluster structure through intermolecular hydrogen bonding (infrared spectroscopy analysis shows a characteristic hydrogen bond absorption peak at 3200-3400 cm⁻¹). This structure achieves complementary performance of the three acids: ① Penetration-Scale Degradation Synergy: The small molecular structure of glycolic acid acts as a "leader," rapidly penetrating into the rust scale, disrupting its crystal structure and forming microchannels. Citric acid and gluconic acid enter the rust scale through these channels, reacting with metal ions, avoiding the difficulty of penetration associated with citric acid alone. ② Chelation-Dissolution Synergy: The carboxyl groups of citric acid form stable chelates with metal ions, carrying away dissolved metal ions from the rust scale surface and promoting continuous reaction. The H+ provided by glycolic acid accelerates the dissolution of the rust scale; both synergistically enhance the efficiency of scale and rust removal. ③ Corrosion Inhibition-Protection Synergy: The polyhydroxyl groups of gluconic acid form a temporary adsorption film on the metal surface, slowing down the corrosion of metals by glycolic acid and citric acid; at the same time, the hydroxyl groups of gluconic acid and the carboxyl groups of citric acid form hydrogen bonds, further stabilizing the complex acid cluster structure and avoiding pitting corrosion caused by excessive local acid concentration.

[0037] 3. Optimization Experiment Verification: To determine the optimal ratio, an orthogonal experiment was conducted, using descaling rate (A), rust removal rate (B), and carbon steel corrosion rate (C) as evaluation indicators. A comprehensive scoring method was adopted (A accounts for 40%, B for 40%, and C for 20%), with the weight ratio of glycolic acid (A), citric acid (B), and gluconic acid (C) as the factor. The levels were as follows: Level 1: 1:1:1; Level 2: 2:1:1; Level 3: 2:1:1.5; Level 4: 3:1:1.5. The experimental results showed that the highest comprehensive score of 92 was achieved when the ratio was 2:1:1.5.

[0038] Another core innovation of this invention is the plant-derived modified corrosion inhibitor, which is a compound of corn protein-modified tannic acid and methylbenzotriazole in a weight ratio of 3:2. The corn protein-modified tannic acid is prepared by adding tannic acid and corn protein to deionized water in a weight ratio of 5:1, stirring at 50°C for 60 minutes, freeze-drying, and then pulverizing to 100 mesh. In the modified tannic acid molecule, the phenolic hydroxyl groups form amide bonds with the amino groups of corn protein, improving corrosion inhibition durability by more than 40%. Its natural plant-derived characteristics ensure a biodegradability rate of ≥95%, and it is non-toxic and harmless. Methylbenzotriazole has a strong adsorption and corrosion inhibition effect on metals such as copper and iron. After the two are combined, tannic acid compensates for its environmental deficiencies, while methylbenzotriazole enhances the corrosion inhibition stability of tannic acid, forming a system that combines environmental protection and corrosion inhibition effects. Compared with the di-o-toluenethiourea used in the prior art, the corrosion inhibitor of this invention has a biodegradability rate increased by more than 80% and toxicity reduced by more than 90%.

[0039] The highly efficient synergistic chelating agent is a compound of disodium ethylenediaminetetraacetate (EDTA-2Na), hydroxyethylethylenediaminetriacetic acid (HEDTA), and sodium nitrilotriacetate (NTA-Na) in a weight ratio of 2:1:1. EDTA-2Na has strong chelating ability (with a stability constant of 10² for Fe³⁺). 5 . 0 The system exhibits a biodegradability of ≥85% for HEDTA and excellent targeted chelation of Cu²⁺, achieving a synergistic effect of "strong chelation, high degradation, and targeted targeting" when combined with NTA-Na. The system has a chelation capacity of ≥300 mg / g for Fe³⁺ and ≥280 mg / g for Cu²⁺, representing a chelation capacity increase of over 25% and a biodegradability increase of over 50% compared to EDTA-2Na alone. Furthermore, in synergy with corrosion inhibitors, it reduces the erosion of the substrate by free ions through chelation of metal ions, further lowering the corrosion rate.

[0040] The green surfactant is a ternary system composed of fatty alcohol polyoxyethylene ether (AEO-9, HLB value 13.3), sodium dodecylbenzenesulfonate (LAS, biodegradability ≥90%), and alkyl glycoside (APG-1214, carbon chain 12-14, prepared from corn starch and coconut oil) in a weight ratio of 2:1:1. AEO-9 provides excellent wettability, LAS enhances detergency and dispersibility, and APG-1214 improves biocompatibility. The critical micelle concentration of the three components is 0.08-0.12 g / L, the surface tension at 20℃ is ≤30 mN / m, and the spreading coefficient on rust and scale surfaces is ≥50 mm / min. This system can reduce the interfacial tension between the agent and rust and scale, accelerate penetration, and stably disperse dissolved rust and scale particles to prevent secondary deposition, improving the descaling efficiency by more than 15% compared to binary compound systems.

[0041] The pH adjuster is a buffer system composed of flake sodium hydroxide (purity ≥96%) and triethanolamine (analytical grade) in a weight ratio of 1:1:2. This system can precisely adjust the pH of the descaling and rust-removing agent to 2.5-4.0: pH 2.5-3.0 for carbon steel, pH 3.0-3.5 for stainless steel, and pH 3.5-4.0 for copper alloys. This system can suppress pH fluctuations ≤0.5 during cleaning, preventing pitting corrosion caused by excessively high local acid concentrations. The functional co-solvent is composed of ethylene glycol monobutyl ether and propylene glycol methyl ether in a weight ratio of 1:1. It penetrates rust layers ≥1mm thick to a depth ≥0.8mm / 10min, improving the solubility of each component, preventing stratification and precipitation when the product is stored below -5℃, and enhancing system stability.

[0042] The present invention also provides a method for preparing the above-mentioned descaling and rust-removing agent, comprising the following steps: S1. Preparation of the composite organic acid solution: Add metered deionized water to the reactor, turn on the anchor-type stirrer, set the speed to 300-500 r / min, and raise the temperature inside the reactor to 35-45℃. Add glycolic acid, citric acid, and gluconic acid sequentially, stirring for 15-25 min until completely dissolved to obtain the composite organic acid solution. Using an anchor-type stirrer ensures uniform mixing of the system, and the temperature range of 35-45℃ is conducive to the dissolution of organic acids, increasing the dissolution rate. Nitrogen protection is used during stirring, with a nitrogen flow rate of 0.5-1.0 L / min, which prevents the organic acids from being oxidized and degraded at high temperatures, ensuring the effective content of the organic acids.

[0043] S2. Preparation of the corrosion-inhibiting-chelating composite system: Maintaining a constant reactor temperature, add a high-efficiency chelating agent to the composite organic acid solution obtained in S1. After stirring for 10-20 minutes, add an environmentally friendly corrosion inhibitor and continue stirring for 20-30 minutes to form a homogeneous and stable corrosion-inhibiting-chelating composite system. Adding the chelating agent first, followed by the corrosion inhibitor, avoids a direct and rapid reaction between the corrosion inhibitor and the organic acid, ensuring the corrosion inhibitor is fully dissolved. A gradient stirring method is used: first stir at 300 rpm for 10 minutes, then at 500 rpm for 20 minutes. Low-speed stirring facilitates the dissolution of the chelating agent, while high-speed stirring promotes the synergistic effect between the corrosion inhibitor and the chelating agent, improving the system stability.

[0044] S3. Compounding of surfactant components: Lower the reactor temperature to 25-30℃, add the surfactant, and stir for 25-35 minutes, monitoring the system viscosity using an online viscometer until the viscosity stabilizes at 5-15 mPa·s. Lowering the temperature to 25-30℃ prevents the surfactant from decomposing due to high temperatures, which would affect its surface activity; real-time monitoring with an online viscometer ensures that the surfactant is fully dispersed, the system viscosity meets design requirements, and the wettability and dispersibility of the product are guaranteed.

[0045] S4. Adjustment and Stabilization: Slowly add the pH adjuster to the system obtained in S3 at a rate of 0.5-1.0 mL / min, stirring continuously while monitoring the pH value. Stop adding the pH when the pH reaches 2.5-4.0. Then add the co-solvent, stir for 15-20 minutes, and let stand for 30-45 minutes to remove tiny air bubbles, obtaining the finished descaling and rust removal agent. Slowly adding the pH adjuster avoids sudden changes in local pH, preventing the chelating agent from becoming ineffective due to drastic pH fluctuations. Allowing the system to stand to remove air bubbles ensures that the product evenly covers the metal surface during use, preventing incomplete descaling and rust removal due to air bubbles.

[0046] After the product is finished, a quality inspection step is also included. The inspection items and standards are formulated in accordance with relevant national standards (such as GB / T23447-2009 "General Technical Conditions for Metal Surface Treatment Agents" and GB / T38508-2020 "Limits of Hazardous Substances in Cleaning Agents") and international standards (such as ISO11130-2021 "Metals and Alloys - Corrosion Testing") to ensure that the product performance meets the requirements of industrial applications.

[0047] Example 1: A descaling and rust removal agent, with the following components by weight: The mixture contains 15 parts of a complex organic acid system (6 parts of glycolic acid, 3 parts of citric acid, and 4.5 parts of gluconic acid), 3 parts of a plant-derived modified corrosion inhibitor (1.8 parts of corn protein-modified tannic acid and 1.2 parts of methylbenzotriazole), 5 parts of a highly efficient synergistic chelating agent (2.5 parts of disodium ethylenediaminetetraacetate, 1.25 parts of hydroxyethyl ethylenediaminetriacetate, and 1.25 parts of sodium hypoaminotriacetate), 2 parts of a green surfactant (1 part of fatty alcohol polyoxyethylene ether, 0.5 parts of sodium dodecylbenzenesulfonate, and 0.5 parts of alkyl glycoside), 1 part of a pH adjuster (0.33 parts of sodium hydroxide and 0.67 parts of triethanolamine), 1 part of a functional cosolvent (0.5 parts of ethylene glycol monobutyl ether and 0.5 parts of propylene glycol methyl ether), and 65 parts of deionized water.

[0048] The preparation method is as follows: S1. Preparation of composite organic acid solution: Add 65 kg of deionized water to a 500 L reactor, turn on the anchor stirrer, set the speed to 300 r / min, introduce nitrogen for protection, nitrogen flow rate is 0.5 L / min, raise the temperature inside the reactor to 35 °C, add 6 kg of glycolic acid, 3 kg of citric acid and 4.5 kg of gluconic acid in sequence, stir for 15 min until completely dissolved, and obtain composite organic acid solution; S2. Preparation of corrosion-inhibiting-chelating composite system: Keeping the reactor temperature constant at 35℃, add 2.5 kg of disodium ethylenediaminetetraacetate and 2.5 kg of hydroxyethyl ethylenediaminetriacetic acid to the solution obtained in S1. After stirring for 10 min, add 1.8 kg of tannic acid and 1.2 kg of methylbenzotriazole. Stir at 300 r / min for 10 min and then at 500 r / min for 20 min to form a corrosion-inhibiting-chelating composite system. S3. Compounding of surfactant components: Reduce the temperature of the reactor to 25°C, add 1.33 kg of fatty alcohol polyoxyethylene ether and 0.67 kg of sodium dodecylbenzene sulfonate, stir for 25 min, and stop stirring when the viscosity of the system stabilizes at 5 mPa·s by monitoring with an online viscometer. S4. Adjustment and Stabilization: Slowly add a mixed solution of 0.4 kg sodium hydroxide and 0.6 kg triethanolamine to the system obtained in S3 at a rate of 0.5 mL / min while stirring. Monitor the pH value in real time. Stop adding when the pH value reaches 4.0. Add 1 kg ethylene glycol monobutyl ether, stir for 15 min, and let stand for 30 min to remove bubbles to obtain the finished descaling and rust removal agent.

[0049] Example 2: A descaling and rust removal agent, with the following components by weight: The mixture contains 20 parts of a complex organic acid system (8 parts of glycolic acid, 4 parts of citric acid, and 6 parts of gluconic acid), 5 parts of a plant-derived modified corrosion inhibitor (3 parts of corn protein-modified tannic acid and 2 parts of methylbenzotriazole), 8 parts of a highly efficient synergistic chelating agent (4 parts of disodium ethylenediaminetetraacetate, 2 parts of hydroxyethyl ethylenediaminetriacetate and 2 parts of sodium hypoaminotriacetate), 4 parts of a green surfactant (2 parts of fatty alcohol polyoxyethylene ether, 1 part of sodium dodecylbenzenesulfonate and 1 part of alkyl glycoside), 2 parts of a pH adjuster (0.67 parts of sodium hydroxide and 1.33 parts of triethanolamine), 2 parts of a functional cosolvent (1 part of ethylene glycol monobutyl ether and 1 part of propylene glycol methyl ether), and 53 parts of deionized water.

[0050] The preparation method is as follows: S1. Preparation of composite organic acid solution: Add 53 kg of deionized water to a 500 L reactor, turn on the anchor stirrer, set the speed to 400 r / min, introduce nitrogen for protection, nitrogen flow rate is 0.8 L / min, raise the temperature inside the reactor to 40 °C, add 8 kg of glycolic acid, 4 kg of citric acid and 6 kg of gluconic acid in sequence, stir for 20 min until completely dissolved, and obtain composite organic acid solution; S2. Preparation of corrosion inhibition-chelation composite system: Keep the reactor temperature constant at 40℃, add 4kg of disodium ethylenediaminetetraacetate, 2kg of hydroxyethyl ethylenediaminetriacetic acid and 2kg of sodium thiamintriacetate to the solution obtained in S1, stir for 15min, then add 3kg of tannic acid and 2kg of methylbenzotriazole, stir at 300r / min for 10min, then stir at 500r / min for 20min to form corrosion inhibition-chelation composite system; S3. Compounding of surfactant components: Reduce the temperature of the reactor to 28℃, add 2.67kg of fatty alcohol polyoxyethylene ether and 1.33kg of sodium dodecylbenzene sulfonate, stir for 30min, and stop stirring when the viscosity of the system stabilizes at 10mPa·s by monitoring with an online viscometer. S4. Adjustment and Stabilization: Slowly add a mixed solution of 1 kg triethanolamine and 1 kg ammonia water to the system obtained in S3 at a rate of 0.8 mL / min, stirring while adding. Monitor the pH value in real time. Stop adding when the pH value reaches 3.0. Add 2 kg ethylene glycol monobutyl ether, stir for 18 min, and let stand for 40 min to remove bubbles to obtain the finished descaling and rust removal agent.

[0051] Example 3: A descaling and rust removal agent, with the following components by weight: The mixture contains 25 parts of a complex organic acid system (10 parts of glycolic acid, 5 parts of citric acid, and 7.5 parts of gluconic acid), 8 parts of a plant-derived modified corrosion inhibitor (4.8 parts of corn protein-modified tannic acid and 3.2 parts of methylbenzotriazole), 12 parts of a highly efficient synergistic chelating agent (6 parts of disodium ethylenediaminetetraacetate, 3 parts of hydroxyethyl ethylenediaminetriacetate, and 3 parts of sodium hypoaminotriacetate), 6 parts of a green surfactant (3 parts of fatty alcohol polyoxyethylene ether, 1.5 parts of sodium dodecylbenzenesulfonate, and 1.5 parts of alkyl glycoside), 4 parts of a pH adjuster (1.33 parts of sodium hydroxide and 2.67 parts of triethanolamine), 3 parts of a functional cosolvent (1.5 parts of ethylene glycol monobutyl ether and 1.5 parts of propylene glycol methyl ether), and 40 parts of deionized water.

[0052] The preparation method is as follows: S1. Preparation of composite organic acid solution: Add 40 kg of deionized water to a 500 L reactor, turn on the anchor stirrer, set the speed to 500 r / min, introduce nitrogen for protection, and the nitrogen flow rate is 1.0 L / min. Raise the temperature inside the reactor to 45 °C, and add 10 kg of glycolic acid, 5 kg of citric acid and 7.5 kg of gluconic acid in sequence. Stir for 25 min until completely dissolved to obtain composite organic acid solution; S2. Preparation of corrosion-inhibiting-chelating composite system: Keeping the reactor temperature constant at 45℃, add 6 kg of disodium ethylenediaminetetraacetate, 3 kg of hydroxyethyl ethylenediaminetriacetic acid and 3 kg of sodium thiamintriacetate to the solution obtained in S1. After stirring for 20 min, add 4.8 kg of tannic acid and 3.2 kg of methylbenzotriazole. Stir at 300 r / min for 10 min and then at 500 r / min for 20 min to form a corrosion-inhibiting-chelating composite system. S3. Compounding of surfactant components: Reduce the temperature of the reactor to 30℃, add 4kg of fatty alcohol polyoxyethylene ether and 2kg of sodium dodecylbenzene sulfonate, stir for 35min, and monitor the system viscosity with an online viscometer. Stop stirring when the viscosity of the system stabilizes at 15mPa·s. S4. Adjustment and Stabilization: Slowly add a mixed solution of 1 kg sodium hydroxide, 2 kg triethanolamine and 1 kg ammonia water to the system obtained in S3 at a rate of 1.0 mL / min, stirring while adding. Monitor the pH value in real time. Stop adding when the pH value reaches 2.5. Add 3 kg ethylene glycol monobutyl ether, stir for 20 min, and let stand for 45 min to remove bubbles to obtain the finished descaling and rust removal agent.

[0053] Comparative Example 1 (Single Organic Acid System): Except for replacing the complex organic acid system with 20 parts of single glycolic acid, the other components (5 parts of plant-derived modified corrosion inhibitor, 8 parts of high-efficiency synergistic chelating agent, 4 parts of green surfactant, etc.) and preparation methods are exactly the same as in Example 2.

[0054] Comparative Example 2 (Single Corrosion Inhibitor): Except for replacing the plant-derived modified corrosion inhibitor with 5 parts of single corn protein modified tannic acid, the other components and preparation methods are exactly the same as in Example 2.

[0055] Comparative Example 3 (Existing Patented Product): The metal rust remover formula and preparation method disclosed in Chinese patent application CN106567084A are adopted, specifically: 25 parts sodium polyacrylate, 4 parts trifluoroethanol, 4 parts nonylphenol polyoxyethylene ether, 4 parts sodium citrate, 5 parts tetrasodium EDTA, 5 parts chitosan, 5 parts sodium dodecyl sulfonate, 4 parts acetic acid, 4 parts ethylene glycol, 4 parts triethanolamine, 4 parts di-o-toluenethiourea, 4 parts sodium gluconate, 4 parts carboxymethyl cellulose, 4 parts sodium oleate, 4 parts sodium pyrophosphate, 4 parts silica, 4 parts nonionic surfactant, 3 parts anionic surfactant, 3 parts defoamer, 3 parts trisodium phosphate, 3 parts stabilizer, and 50 parts deionized water. The product is prepared according to the steps disclosed in the patent.

[0056] Performance testing: Performance tests were conducted on the products of Examples 1-3 and Comparative Examples 1-3. The test items and methods are as follows: 1. Descaling rate test: Referring to GB / T23447-2009 "General Technical Conditions for Metal Surface Treatment Agents", a calcium carbonate scale simulation sample (size 50mm×50mm×3mm, scale thickness 0.5mm) was used. The sample was immersed in the descaling and rust removal agent at 20℃ for 30min. The descaling rate was calculated as: (scale mass before immersion - residual scale mass after immersion) / scale mass before immersion × 100%.

[0057] 2. Rust removal rate test: Referring to ISO11130-2021 "Metals and alloys - Corrosion test", carbon steel rust flakes (size 50mm×50mm×3mm, rust layer thickness 0.3mm) were used. The samples were immersed in a descaling and rust removal agent at 20℃. The sample mass was weighed every 5 minutes. The rust removal rate was calculated as (rust flake mass before immersion - rust flake mass after immersion) / (sample surface area × immersion time), with the unit being g / (m²·min).

[0058] 3. Corrosion rate test: Referring to ASTM G48-2022 "Test method for critical pitting temperature of stainless steel", a rust-free carbon steel test piece (size 50mm×25mm×2mm) was used. The test piece was immersed in a descaling and rust removal agent at 20℃ for 24h. The corrosion rate was calculated as (mass of test piece before immersion - mass of test piece after immersion) × 87600 / (surface area of ​​test piece × immersion time × metal density), with the unit being mm / a (carbon steel density is calculated as 7.85g / cm³).

[0059] 4. Biodegradation rate test: Referring to GB / T38508-2020 "Limits of Hazardous Substances in Cleaning Agents", the biodegradation rate of the product is tested using the carbon dioxide release method, with a test period of 28 days.

[0060] 5. VOC content test: Refer to GB / T38508-2020 "Limits of Hazardous Substances in Cleaning Agents" and use gas chromatography to test the VOC content of the product.

[0061] The test results are shown in Table 1 below:

[0062] As shown in Table 1, the descaling and rust-removing agents of Examples 1-3 of this invention exhibit superior performance in terms of descaling rate, rust removal rate, corrosion rate, biodegradation rate, and VOC content, significantly outperforming comparative examples 1-3. Specific analysis is as follows: 1. Synergistic effect of the composite organic acid system: Comparative Example 1 uses glycolic acid as the acidic component. Its descaling rate (88.3%) and rust removal rate (0.56 g / (m²·min)) are much lower than those of Example 2 (descaling rate 99.4%, rust removal rate 1.05 g / (m²·min)), and its corrosion rate (0.045 mm / a) is significantly higher than that of Example 2 (0.012 mm / a). This indicates that the composite organic acid system formed by compounding glycolic acid, citric acid and gluconic acid in a specific ratio has a significant synergistic effect, which can simultaneously improve the descaling and rust removal efficiency and reduce corrosion.

[0063] 2. Advantages of the environmentally friendly corrosion inhibitor: Comparative Example 2 uses tannic acid as a single corrosion inhibitor, and its corrosion rate (0.032 mm / a) is higher than that of Example 2 (0.012 mm / a), indicating that the combination of tannic acid and methylbenzotriazole can enhance the corrosion inhibition effect; Comparative Example 3 uses chitosan and di-o-toluenethiourea as corrosion inhibitors, and its biodegradation rate (45%) is much lower than that of Example 2 (95%), and its VOC content (28.6 g / L) is much higher than that of Example 2 (7.2 g / L), indicating that the environmentally friendly corrosion inhibitor of the present invention has significant environmental advantages.

[0064] 3. Synergistic performance of the overall formulation: Example 2 is the optimal embodiment, and all its performance indicators have reached the best level. The descaling rate is ≥99.4%, the rust removal rate is ≥1.05g / (m²·min), the corrosion rate is ≤0.012mm / a, the biodegradation rate is ≥95%, and the VOC content is ≤7.2g / L. This fully demonstrates the synergistic effect between the components in the formulation system of this invention and solves the technical defects of existing products.

[0065] The descaling and rust-removing agent prepared in Example 2 of this invention was applied to the cleaning project of heat exchange equipment in a petrochemical enterprise. This heat exchange equipment is made of carbon steel, has a service life of 5 years, and has an internal scale thickness of approximately 0.8 mm and a rust layer thickness of approximately 0.2 mm, resulting in a 40% decrease in heat transfer efficiency. The descaling and rust-removing agent of this invention was used for circulating cleaning under the following conditions: temperature 25℃, circulation flow rate 1.5 m / s, and cleaning time 20 min. The results after cleaning are as follows: 1. Descaling effect: Scale and rust inside the equipment are completely removed, leaving the metal surface smooth and residue-free, with a descaling rate of 99.6%; 2. Corrosion status: The wall thickness of the equipment was measured using an ultrasonic thickness gauge. The change in wall thickness before and after cleaning was ≤0.01mm, and the corrosion rate was calculated to be 0.011mm / a, which meets the equipment safety requirements. 3. Heat transfer efficiency: After cleaning, the heat transfer efficiency of the equipment is restored to 98% of that of a new equipment, and energy consumption is reduced by 38%; 4. Environmental indicators: After neutralization treatment, the pH value of the cleaning wastewater reaches 6.5 and the chemical oxygen demand (COD) is ≤100mg / L, which meets the national wastewater discharge standards and can be directly discharged.

[0066] This application example demonstrates that the descaling and rust removal agent of the present invention has significant industrial application value, effectively solving the problem of rust and scale on industrial equipment, reducing energy consumption, extending equipment lifespan, and meeting environmental protection requirements.

[0067] The implementation principle of this invention is as follows: This invention discloses a descaling and rust-removing agent and its preparation method, belonging to the field of metal surface treatment. It constructs a "penetration-chelation-corrosion inhibition-stabilization" system by controlling the ratio of composite organic acids, introducing plant-derived modified corrosion inhibitors, and a synergistic chelation mechanism. The system is composed of composite organic acids, plant-derived modified corrosion inhibitors, etc., in a specific ratio. The composite organic acid is composed of glycolic acid, citric acid, and gluconic acid in a ratio of 2:1:1.5; the corrosion inhibitor is a mixture of corn protein-modified tannic acid and methylbenzotriazole in a ratio of 3:2; and the chelating agent is a gradient mixture of EDTA-2Na, HEDTA, and NTA-Na. The product has a descaling rate ≥99.2%, a carbon steel rust removal time ≤15 min, a corrosion rate ≤0.02 mm / a, and a biodegradation rate ≥95%. The preparation adopts a segmented temperature-controlled nitrogen protection process, suitable for industrial production. This invention resolves the technical contradiction of existing products being "highly efficient but highly corrosive" and "environmentally friendly but inefficient," achieving synergistic performance of high efficiency, low corrosion, and environmental friendliness. It is applicable to metal substrates such as carbon steel, cast iron, copper alloys, and stainless steel, as well as environmentally demanding industries such as food processing, pharmaceuticals, chemicals, and precision electronics manufacturing, providing a compliant solution for related fields.

[0068] The embodiments described in this specific embodiment are preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made according to the structure, shape, and principle of the present invention should be covered within the scope of protection of the present invention. For example, the weight parts of the composite organic acid system can be arbitrarily adjusted between 15 and 25 parts, and the weight parts of the environmentally friendly corrosion inhibitor can be arbitrarily adjusted between 3 and 8 parts. As long as the core composition and proportion meet the requirements of the present invention, the technical effects of the present invention can be achieved.

[0069] It should be emphasized that the scope of protection of this invention is defined by the claims. Any modifications, equivalent substitutions, and improvements based on this specification should be included within the scope of protection of this invention. The descaling and rust-removing agent and its preparation method of this invention are not only suitable for industrial equipment cleaning, but can also be extended to household hardware, automobile repair, ship maintenance, and other fields, possessing broad market prospects.

Claims

1. A descaling and rust-removing agent, characterized in that, By weight, it includes the following components: 15-25 parts of complex organic acid system, 3-8 parts of plant-derived modified corrosion inhibitor, 5-12 parts of high-efficiency synergistic chelating agent, 2-6 parts of green surfactant, 1-4 parts of pH adjuster, 1-3 parts of functional cosolvent, and 40-65 parts of deionized water. The composite organic acid system is composed of glycolic acid with a purity ≥99%, food-grade citric acid, and industrial-grade gluconic acid in a weight ratio of 2:1:1.

5. The plant-derived modified corrosion inhibitor is a compound of corn protein modified tannic acid and methylbenzotriazole in a weight ratio of 3:

2. The corn protein modified tannic acid is obtained by reacting tannic acid and corn protein in deionized water at a weight ratio of 5:1 at 50°C for 60 minutes, followed by freeze-drying and pulverizing to 100 mesh. The highly efficient synergistic chelating agent is composed of disodium ethylenediaminetetraacetate, hydroxyethyl ethylenediaminetriacetate and sodium ethylenetriacetate in a weight ratio of 2:1:

1. The green surfactant is a compound of fatty alcohol polyoxyethylene ether, sodium dodecylbenzene sulfonate and alkyl glycoside in a weight ratio of 2:1:

1. The pH adjuster is a mixture of sodium hydroxide flakes and triethanolamine in a weight ratio of 1:

2. The functional cosolvent is a mixture of ethylene glycol monobutyl ether and propylene glycol methyl ether in a weight ratio of 1:

1.

2. The descaling and rust-removing agent according to claim 1, characterized in that, The composition and ratio of the highly efficient synergistic chelating agent can be adjusted according to the type of substrate being treated: When processing iron-based materials such as carbon steel and cast iron, a mixture of disodium ethylenediaminetetraacetate and hydroxyethyl ethylenediaminetriacetic acid in a weight ratio of 1:1 is used. The chelation capacity of the chelation system for Fe³⁺ is ≥300mg / g. When processing copper and copper alloy materials, a mixture of hydroxyethyl ethylenediamine triacetic acid and sodium hypoaminotriacetate at a weight ratio of 1:1 is used, which has a chelation capacity for Cu²⁺ ≥280mg / g. When processing multi-metal mixed substrates, a compound of disodium ethylenediaminetetraacetate, hydroxyethylethylenediaminetriacetic acid, and sodium hypoaminotriacetate in a weight ratio of 2:1:1 was used. This chelation system exhibited chelation constants ≥10¹ for Fe³⁺, Ca²⁺, Mg²⁺, and Cu²⁺ within a pH range of 2.5-4.

0. 4 ; The purity of the chelating agent meets the following requirements: disodium ethylenediaminetetraacetate ≥ 99%, hydroxyethyl ethylenediaminetriacetate ≥ 98%, sodium ethylenediaminetriacetate ≥ 97%, and heavy metal content ≤ 10 ppm.

3. The descaling and rust-removing agent according to claim 1, characterized in that, The green surfactant is a ternary compound composed of a nonionic surfactant, an anionic surfactant, and a plant-derived glycoside surfactant in a weight ratio of 2:1:

1. The nonionic surfactant is a fatty alcohol polyoxyethylene ether with an HLB value of 13.3, the anionic surfactant is sodium dodecylbenzene sulfonate with a biodegradability of ≥90%, and the plant-derived glycoside surfactant is an alkyl glycoside with a carbon chain length of 12-14, prepared from corn starch and coconut oil. The critical micelle concentration of this ternary system is 0.08-0.12 g / L, the surface tension at 20℃ is ≤30 mN / m, it has excellent compatibility with the composite organic acid system, and there is no stratification or precipitation after mixing. The spreading coefficient on the rust and scale surface is ≥50 mm / min.

4. The descaling and rust-removing agent according to claim 1, characterized in that, The pH adjuster is a composite buffer system composed of flake sodium hydroxide with a purity ≥96% and analytical grade triethanolamine in a weight ratio of 1:

2. This system can suppress pH fluctuations, and the pH change during the cleaning process is ≤0.

5. The pH value of the descaling and rust-removing agent is adjusted to 2.5-4.0, wherein the pH value is controlled at 2.5-3.0 when treating carbon steel substrates, at 3.0-3.5 when treating stainless steel substrates, and at 3.5-4.0 when treating copper alloy substrates. The pH adjuster is added dropwise at a rate of 0.5-1.0 mL / min, while simultaneously using magnetic stirring at 500 r / min to ensure uniform pH values ​​in the system.

5. The descaling and rust-removing agent according to claim 1, characterized in that, The functional co-solvent is a compound of ethylene glycol monobutyl ether and propylene glycol methyl ether in a weight ratio of 1:

1. This system can improve the solubility of the components and the permeability of the product, with a penetration depth of ≥0.8mm / 10min for rust layers with a thickness of ≥1mm. The descaling and rust-removing agent has a viscosity of 5-15mPa·s at 20℃, a surface tension of 25-35mN / m, a flash point of ≥60℃, and is non-flammable. The product can be stored in the range of -5℃ to 45℃ for 6 months with a change rate of ≤5% for various performance indicators. 0.1-0.3 parts of sodium fluorescein can be added as a fluorescent tracer with a fluorescence emission wavelength of 520nm and a detection sensitivity of ≤0.1ppm.

6. A method for preparing a descaling and rust-removing agent as described in any one of claims 1-5, characterized in that, The integrated process of "segmented temperature control - nitrogen protection - gradient stirring - online monitoring" includes the following steps: S1. Raw material pretreatment: ① Hydroxyacetic acid, citric acid, and gluconic acid are vacuum dried to control the moisture content ≤0.5%; ② Corn protein modified tannic acid is pulverized to 100 mesh and sieved; ③ Deionized water is treated with ion exchange resin to achieve a conductivity ≤10μS / cm; metered pretreated deionized water is added to the reactor, the anchor stirrer is turned on at a speed of 300-500r / min, nitrogen gas is introduced at a rate of 0.5-1.0L / min for protection, and the temperature is increased to 35-45℃ at a rate of 2℃ / min. The three pretreated organic acids are added sequentially, stirring for 5min after each addition. After all the acids are added, stirring is continued for 15-25min until dissolved. The pH value is monitored by an online pH meter to be ≤1.5 to obtain a composite organic acid solution. S2. Preparation of corrosion inhibition-chelation composite system: Keep the reactor temperature at 35-45℃ and the nitrogen flow rate constant, add a high-efficiency synergistic chelating agent at a rate of 1-2 g / min, stir for 10-20 min until dissolved, and the pH value of the system rises to 1.8-2.2; add a plant-derived modified corrosion inhibitor, stir at 300 r / min for 10 min, then stir at 500 r / min for 20 min, and continue stirring for 20-30 min to form a corrosion inhibition-chelation composite system. The particle size distribution of this system, as detected by laser particle size analyzer, is 100-300 nm and there is no obvious agglomeration. S3. Compound surfactant ingredients: Reduce the temperature of the reactor to 25-30℃ at a rate of 1℃ / min, stop nitrogen flow, add the premix of fatty alcohol polyoxyethylene ether, sodium dodecylbenzene sulfonate and alkyl glycoside, stir at 400r / min for 10min, then stir at 600r / min for 25-35min. When the viscosity stabilizes at 5-15mPa·s using an online viscometer, stop stirring and let stand for 5min. The system should be uniform and transparent with no foam or only a small amount of easily dissipated foam. S4. Adjustment and stabilization: Add a premixed solution of sodium hydroxide and triethanolamine dropwise at a rate of 0.5-1.0 mL / min, stir at 300 r / min and monitor the pH value online. Stop the dropwise addition after the target range of 2.5-4.0 is reached; add a compound of ethylene glycol monobutyl ether and propylene glycol methyl ether, stir for 15-20 min, cool to 25℃ and let stand for 30-45 min, and remove microbubbles by vacuum degassing.

7. The method for preparing a descaling and rust-removing agent according to claim 6, characterized in that, In S1, the diameter of the anchor-type agitator blade is 1 / 3 of the inner diameter of the reactor, and the blade immersion depth is 2 / 3 of the liquid level. Nitrogen protection is maintained throughout S1 and S2, with nitrogen purity ≥99.9%. After drying and impurity removal, the moisture content is ≤10ppm and the oxygen content is ≤50ppm. After S1, the concentration of the composite organic acid solution is tested by acid-base titration, and the deviation is ≤2%. Otherwise, the corresponding organic acid or deionized water is added to adjust.

8. The method for preparing a descaling and rust-removing agent according to claim 6, characterized in that, The order of adding the high-efficiency chelating agent in S2 is as follows: first add disodium ethylenediaminetetraacetate and stir for 5 min, then add hydroxyethyl ethylenediaminetriacetic acid and stir for 5 min, and finally add sodium ethylenediaminetriacetate. Gradient stirring after adding the corrosion inhibitor can increase the adsorption energy of the corrosion inhibitor on the metal surface by more than 30%. After S2, the chelation capacity is detected by EDTA complexometric titration. The chelation capacity of Fe³+ is ≥250 mg / g, otherwise, chelating agent is added.

9. The method for preparing a descaling and rust-removing agent according to claim 6, characterized in that, In S4, the pH adjuster is added dropwise using a constant flow pump with an accuracy of ±0.05 mL / min; the pH value is monitored using an online pH meter with an accuracy of ±0.01, and calibrated with standard buffer solutions of pH=2.00 and 4.00 before use; when treating sensitive substrates such as copper alloys, the pH control accuracy is improved to ±0.

05.

10. The method for preparing a descaling and rust-removing agent according to claim 6, characterized in that, The finished product undergoes three levels of quality testing: Level 1 testing includes appearance, pH value (2.5-4.0), viscosity (5-15 mPa·s), and surface tension (25-35 mN / m), with a 100% pass rate; Level 2 testing includes descaling rate ≥98%, rust removal rate ≥0.8 g / (m²·min), carbon steel corrosion rate ≤0.02 mm / a, and stainless steel corrosion rate ≤0.005 mm / a, with a pass rate ≥98%; Level 3 testing includes biodegradation rate ≥85%, Pb ≤10 ppm and Cd ≤5 ppm, and no stratification after 72 hours of storage at -5℃, with a 100% pass rate; only products that pass the tests can be shipped, and unqualified products are returned to the reactor for adjustment.

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