Methanol corrosion inhibitor and preparation method thereof

Abstract

The invention relates to the technical field of vehicle fuel additives, in particular to a methanol corrosion inhibitor and a preparation method thereof. The inhibitor is prepared from the following components in parts by weight: 30 to 40 parts of bis-imidazole-lanthanum-alkyl benzotriazole hybrid molecules, 20 to 30 parts of ethanol, 10 to 15 parts of n-butyl alcohol, 1 to 3 parts of isopropanol, 8 to 15 parts of triethanolamine, 3 to 5 parts of an antioxidant, 1 to 3 parts of a surfactant and 0.2 to 0.4 part of C9-C11 alkane, wherein the bis-imidazole-lanthanum-alkyl benzotriazole hybrid molecule is prepared by condensation of 1-methylimidazole-4-formaldehyde and malonic acid, reduction of borane, coordination with lanthanum acetylacetonate, formation of quaternary ammonium salt, acylation of 10-bromodecanoic acid and nucleophilic substitution of benzotriazole. The inhibitor can effectively inhibit corrosion of methanol to metal, and has good compatibility with rubber.

Description

Technical Field

[0001] The present invention relates to the technical field of vehicle fuel additives, in particular to a methanol corrosion inhibitor and a preparation method thereof. Background Art

[0002] With increasingly stringent environmental regulations, methanol fuel has attracted significant attention in the automotive sector as a clean alternative energy source. Its high oxygen content and low carbon emissions help improve engine combustion efficiency and meet stringent emission standards such as the National VI standard. However, methanol fuel (especially high-methanol gasoline above M15) has significant drawbacks in practical applications. First, the methanol combustion process easily produces acidic corrosion products such as formic acid, which can cause electrochemical corrosion of engine metal components (such as copper, brass, cast iron, and aluminum alloys in the cylinder block and oil system). Second, methanol's strong polarity and swelling properties can cause rubber seals (such as oil floats, injector seals, and pipelines) to harden, crack, or swell and fail. These issues have severely restricted the large-scale application of methanol fuel.

[0003] Existing methanol corrosion inhibitors mostly use a single corrosion inhibitor (such as benzotriazole or an organic amine). While these inhibitors offer some protection against specific metals, they suffer from the following drawbacks: ① They cannot simultaneously address the corrosion protection needs of multiple metals, including copper, aluminum, and steel; ② they lack optimized compatibility with rubber materials; and ③ in high-concentration methanol systems, inadequate molecular structure design leads to poor adsorption film stability and weak swelling resistance. Therefore, developing composite corrosion inhibitors that offer synergistic protection for multiple metals, excellent rubber compatibility, and resistance to methanol penetration has become a key technical challenge in the widespread application of methanol fuel. Summary of the Invention

[0004] The purpose of the present invention is to solve the shortcomings of the prior art and to provide a methanol corrosion inhibitor and a preparation method thereof.

[0005] Based on the above purpose, the present invention provides a methanol corrosion inhibitor, comprising the following raw materials in parts by weight: 30-40 parts of a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule, 20-30 parts of ethanol, 10-15 parts of n-butanol, 1-3 parts of isopropanol, 8-15 parts of triethanolamine, 3-5 parts of an antioxidant, 1-3 parts of a surfactant, and 0.2-0.4 parts of a C9-C11 alkane; The preparation method of the bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule is as follows: (1) Under nitrogen protection, 1-methylimidazole-4-carboxaldehyde, malonic acid and molecular sieves were added to anhydrous N,N-dimethylformamide, and then piperidine was added. The temperature was raised to 80-90°C and stirred for 4-6 hours. The mixture was filtered while hot and then cooled to room temperature. The mixture was added to deionized water to obtain a yellow solid. After filtration, the solid was washed with water until neutral to obtain 2-((1-methyl-1H-imidazole-4-yl)methylene)malonic acid. The chemical reaction equation is as follows:

[0006] The structure of the product was confirmed by H NMR. Malonic acid, a compound containing an active methylene group, undergoes deprotonation under the catalysis of piperidine to form a carbon anion, which attacks the aldehyde group of 1-methylimidazole-4-carboxaldehyde, forming an intermediate product followed by dehydration and condensation to produce an α,β-unsaturated carboxylic acid. The added molecular sieves adsorbed water from the reaction system, maintaining an anhydrous environment and preventing side reactions. In the resulting 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid, the nitrogen atom of the imidazole ring has a lone pair of electrons, which can be adsorbed on the metal surface through coordination, forming an initial adsorption layer. (2) Under nitrogen protection, 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid was added to anhydrous tetrahydrofuran, cooled to -5-5°C, and borane tetrahydrofuran solution was added with stirring. Then the temperature was restored to room temperature and reacted for 3-5 hours. The temperature was lowered to 0-5°C, and methanol was added to quench the reaction. The tetrahydrofuran was removed by distillation under reduced pressure. The crude product was subjected to silica gel column chromatography and gradient elution to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol as a white solid. The chemical reaction equation is as follows:

[0007] The product's structure was confirmed by H NMR. Borane, acting as a strong reducing agent, reacts with the carboxylic acid to form a borate ester intermediate, which is then hydrolyzed to the corresponding alcohol. Borane preferentially reduces the carboxylic acid without affecting other functional groups, such as the imidazole ring, resulting in high chemoselectivity. The resulting diol structure provides an active site for subsequent reactions. (3) Under nitrogen protection, lanthanum acetylacetonate hydrate and 4-bromobutyric acid were added to anhydrous tetrahydrofuran, stirred, heated to 70-80°C, reacted for 4-6 hours, cooled to room temperature, filtered, washed, and dried to obtain a rare earth complex as a yellow powder. The chemical reaction equation is as follows: The structure of the product was confirmed by H NMR. This reaction is a coordination substitution reaction. The acetylacetonate ligand (β-diketone) in lanthanum acetylacetonate undergoes ligand exchange with the carboxylate of 4-bromobutyric acid. The carboxylate forms a coordination bond with the lanthanum ion through the oxygen atom to generate a stable rare earth complex. The rare earth ion lanthanum has a strong coordination ability and can bind to defect sites (such as vacancies and dislocations) on the metal surface to fill the pores of the oxide film. At the same time, the rare earth complex can catalyze the oxidation reaction of the decomposition products of methanol, reducing the accumulation of corrosive substances (such as formic acid). 3+ It is adsorbed on the negatively charged metal surface through electrostatic interaction. Its high coordination number can form a chelate structure with multiple functional groups (such as hydroxyl groups and imidazole nitrogen), thereby enhancing the cross-linking degree of the methanol corrosion inhibitor after film formation on the metal surface, thereby improving the swelling resistance and anti-permeation ability of the inhibitory film; (4) Under nitrogen protection, 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, rare earth complex and potassium iodide were added to acetonitrile, heated to 60-70°C, reacted for 8-12 hours, cooled to room temperature, and acetonitrile was removed by distillation under reduced pressure. Deionized water was added, and then extracted three times with ethyl acetate. The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. After silica gel column chromatography using gradient elution, imidazole-rare earth quaternary ammonium salt was obtained as a light beige solid. The chemical reaction equation is as follows: The structure of the product was confirmed by H NMR. The reaction is a nucleophilic substitution reaction. The nitrogen atom on the imidazole ring attacks the bromine atom of bromobutyric acid in the rare earth complex to form a quaternary ammonium bond. Potassium iodide acts as a catalyst to accelerate the reaction by increasing the leaving ability of the bromide ion. The positive charge in the quaternary ammonium salt structure can be electrostatically adsorbed on the negatively charged metal surface to form a cationic adsorption layer, thereby forming a corrosion inhibition film, which hinders the formation of Cl - OH - The migration of corrosive ions such as chlorinated ions and imidazole rings can be prevented. At the same time, the coordinated coordination of rare earth ions and imidazole rings can form "double-site adsorption", enhancing the stability of the membrane. The surface activity of the quaternary ammonium salt causes it to be oriented at the metal-methanol interface, with the hydrophobic groups facing outward to form a barrier. The coordination bond between the rare earth ions and imidazole nitrogen improves the mechanical strength of the membrane and reduces membrane damage. This step constructs a dual action mechanism of "charge adsorption-coordination enhancement" and is the core structural unit for improving corrosion inhibition efficiency. (5) Under nitrogen protection, 10-bromodecanoic acid was added to anhydrous tetrahydrofuran, cooled to -5-5°C, and then dicyclohexylcarbodiimide DCC was added. The mixture was stirred for 10-20 min, and then 4-dimethylaminopyridine DMAP and imidazole-rare earth quaternary ammonium salt were added. The mixture was returned to room temperature and stirred for 8-10 h. The mixture was filtered and the filtrate was concentrated to one third of the original volume. Then, n-hexane was added. The precipitated solid was filtered, washed, and dried to obtain imidazole-rare earth quaternary ammonium salt containing long-chain alkyl groups as a white waxy solid. The chemical reaction equation is as follows:

[0008] The product was characterized by H NMR. This reaction is a carboxylic acid activation-acylation reaction. DCC acts as a dehydrating agent, reacting with 10-bromodecanoic acid to form an active intermediate. DMAP acts as a nucleophilic catalyst, promoting the acylation reaction between the carboxylic acid and the hydroxyl group on the quaternary ammonium salt to form an ester bond and introduce a long-chain alkyl group. The hydrophobic properties of the long-chain alkyl group form a physical barrier on the metal surface, preventing the penetration of methanol molecules. At the same time, the steric hindrance effect of the alkyl chain reduces the contact area between the corrosive particles and the metal. The long-chain alkyl group interacts through van der Waals forces, forming a dense hydrophobic layer on the inhibitory membrane surface, reducing the permeability of methanol. Its flexible chain structure fills the pores of the membrane and improves its integrity. The alkyl chain is a key component of the "hydrophobic protective layer" and can significantly reduce the electrochemical corrosion rate of the metal, especially in high-concentration methanol systems. (6) Under nitrogen protection, in a reaction vessel equipped with a water separator, imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, benzotriazole, potassium carbonate and toluene are added, the temperature is raised to 100-120°C, the reaction is carried out for 6-10 hours, the potassium carbonate is removed by filtration, and the toluene is removed by vacuum distillation. The crude product is subjected to silica gel column chromatography using gradient elution to obtain a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule as a light yellow solid. The chemical reaction equation is as follows: The product is passed through H NMR confirmed the structure, and the reaction is also a nucleophilic substitution reaction. Under the action of potassium carbonate, the nitrogen atom of benzotriazole deprotonates and attacks the carbon atom adjacent to the bromine atom in the quaternary ammonium salt, undergoing an aromatic nucleophilic substitution reaction and forming a C-N bond. Toluene is used as the solvent, and a water separator removes the water generated by the reaction, pushing the equilibrium toward the forward reaction. Potassium carbonate acts as a base to promote the formation of the nucleophilic reagent. BTA benzotriazole is a highly effective metal corrosion inhibitor that forms stable complexes with metals such as Cu and Fe, forming a passivating film on the metal surface. Furthermore, the hybrid structure of BTA with imidazole and rare earth elements produces a synergistic effect, enhancing the corrosion resistance of the film. The triazole ring of BTA interacts with the imidazole ring through π-π stacking, enhancing intermolecular forces. Its nitrogen atom forms a coordination bond with the metal, forming a dense passivating film that inhibits anodic dissolution. This step combines the passivation effect of BTA with the adsorption effect of imidazole and rare earth elements through multi-component synergy, enabling the inhibitor to form a highly effective protective film on the surfaces of various metals, such as engine aluminum alloys and copper pipelines.

[0009] Preferably, the antioxidant refers to one or both of 2,6-di-tert-butyl-p-cresol and N-phenyl-α-naphthylamine, and the surfactant refers to polyoxyethylene ether.

[0010] Preferably, the molar ratio of 1-methylimidazole-4-carboxaldehyde to malonic acid in (1) is 1:1.1-1.3.

[0011] Preferably, the weight ratio of 1-methylimidazole-4-carboxaldehyde, molecular sieve, piperidine, anhydrous N,N-dimethylformamide and deionized water in (1) is 1:0.3-0.7:0.01-0.03:5-7:7-9.

[0012] Preferably, the weight ratio of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid, borane tetrahydrofuran solution and anhydrous tetrahydrofuran in (2) is 1:4-5:5-7.

[0013] Preferably, the concentration of the borane tetrahydrofuran solution in (2) is 2 mol / L.

[0014] Preferably, the gradient elution in (2) refers to the volume ratio of dichloromethane to methanol in each step of the eluent being successively from 1:0, 20:1 to 9:1.

[0015] Preferably, the molar ratio of lanthanum acetylacetonate hydrate to 4-bromobutyric acid in (3) is 1:1.1-1.3.

[0016] Preferably, the weight ratio of lanthanum acetylacetonate hydrate to anhydrous tetrahydrofuran in (3) is 1:5-7.

[0017] Preferably, the molar ratio of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, rare earth complex and potassium iodide in (4) is 1:1-1.2:0.2-0.4.

[0018] Preferably, the weight ratio of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, acetonitrile and deionized water in (4) is 1:8-12:8-12.

[0019] Preferably, the gradient elution in (4) refers to the volume ratio of dichloromethane to methanol in each step of the eluent being successively from 1:0, 20:1, 10:1 to 4:1.

[0020] Preferably, the molar ratio of 10-bromodecanoic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine and imidazole-rare earth quaternary ammonium salt in (5) is 2.2-2.4:2.5-3:0.2-0.3:1.

[0021] Preferably, the weight ratio of imidazole-rare earth quaternary ammonium salt, anhydrous tetrahydrofuran and n-hexane in (5) is 1:7-10:6-8.

[0022] Preferably, the molar ratio of the imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, benzotriazole, and potassium carbonate in (6) is 1:2.1-2.3:2-3.

[0023] Preferably, the weight ratio of the imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group and toluene in (6) is 1:8-12.

[0024] Preferably, the gradient elution in (6) refers to the volume ratio of dichloromethane / methanol / water in each step of the eluent being successively from 9:1:0, 8:2:0, 6:4:0 to 4:1:0.1.

[0025] Furthermore, the present invention also provides a method for preparing a methanol corrosion inhibitor, comprising the following steps: mixing a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule with ethanol, n-butanol, and isopropanol, heating the mixture to 40-50°C, stirring the mixture for 10-20 minutes, then adding triethanolamine, an antioxidant, a surfactant, and a C9-C11 alkane, stirring the mixture evenly, cooling the mixture to room temperature, and filtering out impurities through a filter membrane to obtain a methanol corrosion inhibitor.

[0026] Beneficial effects of the present invention: 1. The present invention utilizes a hybrid molecular design of imidazole rings, rare earth lanthanum ions, long-chain alkyl groups, and benzotriazole (BTA) to form a multi-action mechanism of chemical adsorption, coordination crosslinking, hydrophobic barrier, and passivation protection. The dinitrogen heterocyclic structures of imidazole and BTA provide strong coordination capabilities, forming stable chelate bonds with metal surfaces such as Fe, Cu, and Al. The rare earth lanthanum ions, with their high coordination numbers, construct molecular crosslinking centers, enhancing the mechanical strength of the inhibitory film. The long-chain alkyl groups form a physical barrier on the metal surface through hydrophobic interaction, preventing methanol penetration. BTA promotes the formation of a metal passivation film. The four synergistic effects give the inhibitor excellent protection against a variety of metals in methanol systems.

[0027] 2. The quaternary ammonium salt structure and rare earth ions in the hybrid molecule synthesized in this invention impart strong polarity to the inhibitor, enabling uniform dispersion in methanol while preventing swelling damage to the rubber. The introduction of long-chain alkyl groups modulates the molecule's hydrophobicity, forming a protective film on the rubber surface through van der Waals forces, reducing methanol's erosion of the rubber molecular chains. This design ensures the inhibitor's ability to form a film on metal surfaces while maintaining compatibility with fuel system rubber components, addressing the challenges of metal corrosion and rubber degradation in methanol fuel.

[0028] 3. The rare earth complex in the methanol corrosion inhibitor prepared by this invention catalyzes the oxidation of corrosive substances such as formic acid produced by methanol decomposition, reducing the acidity of the system. The conjugated structure of imidazole and BTA enhances the membrane's resistance to swelling. The flexible long-chain alkyl segments fill the membrane's pores, adapting to changes in the membrane's structure under environmental fluctuations. This design enables the inhibitor to form a dense protective layer even under the complex operating conditions of an engine, broadening the application of methanol fuel. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The H NMR spectrum of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid prepared in Example 2 of the present invention; Figure 2 The H NMR spectrum of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol prepared in Example 2 of the present invention; Figure 3 This is the H NMR spectrum of the rare earth-based complex prepared in Example 2 of the present invention; Figure 4 The H NMR spectrum of the imidazole-rare earth quaternary ammonium salt prepared in Example 2 of the present invention; Figure 5 The H NMR spectrum of the imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group prepared in Example 2 of the present invention; Figure 6 This is the H NMR spectrum of the bisimidazolyl-lanthanum-alkylbenzotriazole hybrid molecule prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0030] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to specific embodiments.

[0031] Example 1: A specific preparation method of a methanol corrosion inhibitor, comprising the following steps: (1) Under nitrogen protection, 10 g of 1-methylimidazole-4-carboxaldehyde, 10.39 g of malonic acid and 3 g of molecular sieves were added to 50 g of anhydrous N,N-dimethylformamide, and 0.1 g of piperidine was added. The temperature was raised to 80 ° C. and stirred for 4 h. The mixture was filtered while hot and then cooled to room temperature. The yellow solid was added to 70 g of deionized water. After filtration, the yellow solid was washed with water until neutral to obtain 2-((1-methyl-1H-imidazole-4-yl)methylene)malonic acid; (2) Under nitrogen protection, 15 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid was added to 75 g of anhydrous tetrahydrofuran, cooled to -5 °C, and 60 g of 2 mol / L borane tetrahydrofuran solution was added under stirring. The temperature was then restored to room temperature and reacted for 3 h. The temperature was then lowered to 0 °C, methanol was added to quench the reaction, and tetrahydrofuran was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography using gradient elution to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol. (3) Under nitrogen protection, 30 g of lanthanum acetylacetonate hydrate and 12.13 g of 4-bromobutyric acid were added to 150 g of anhydrous tetrahydrofuran, stirred, heated to 70 ° C, reacted for 4 h, cooled to room temperature, filtered, washed, and dried to obtain a rare earth complex; (4) Under nitrogen protection, 10 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, 29.91 g of rare earth complex and 1.97 g of potassium iodide were added to 80 g of acetonitrile, heated to 60 ° C, reacted for 8 h, cooled to room temperature, and acetonitrile was removed by vacuum distillation. 80 g of deionized water was added, and then extracted three times with ethyl acetate. The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. After that, it was subjected to silica gel column chromatography using gradient elution to obtain imidazole-rare earth quaternary ammonium salt; (5) Under nitrogen protection, 15.54 g of 10-bromodecanoic acid was added to 140 g of anhydrous tetrahydrofuran, and the temperature was lowered to -5 °C. 15.37 g of dicyclohexylcarbodiimide was added, and the mixture was stirred for 10 min. Then 0.73 g of 4-dimethylaminopyridine and 20 g of imidazole-rare earth quaternary ammonium salt were added, and the mixture was returned to room temperature. The mixture was stirred for 8 h, and filtered. After the filtrate was concentrated to one third of the original volume, 120 g of n-hexane was added, and the precipitated solid was filtered, washed, and dried to obtain imidazole-rare earth quaternary ammonium salt containing long-chain alkyl groups; (6) Under nitrogen protection, 30 g of imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, 6.76 g of benzotriazole, 7.47 g of potassium carbonate and 240 g of toluene were added to a reaction vessel equipped with a water separator, the temperature was raised to 100 ° C, the reaction was carried out for 6 h, the potassium carbonate was removed by filtration, and the toluene was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography using gradient elution to obtain a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule; (7) 30 g of bisimidazolyl-lanthanum-alkylbenzotriazole hybrid molecule was mixed with 20 g of ethanol, 10 g of n-butanol, and 1 g of isopropanol, heated to 40 °C, and stirred for 10 min. Then, 8 g of triethanolamine, 3 g of antioxidant, 1 g of surfactant, and 0.2 g of C9-C11 alkane were added. After stirring evenly, the mixture was cooled to room temperature and impurities were filtered through a filter membrane to obtain a methanol corrosion inhibitor.

[0032] Example 2: A specific preparation method of a methanol corrosion inhibitor, comprising the following steps: (1) Under nitrogen protection, 10 g of 1-methylimidazole-4-carboxaldehyde, 11.34 g of malonic acid and 5 g of molecular sieves were added to 60 g of anhydrous N,N-dimethylformamide, and 0.2 g of piperidine was added. The temperature was raised to 85 ° C. and stirred for 5 h. The mixture was filtered while hot and then cooled to room temperature. The yellow solid was added to 80 g of deionized water. After filtration, the yellow solid was washed with water until neutral to obtain 2-((1-methyl-1H-imidazole-4-yl)methylene)malonic acid; (2) Under nitrogen protection, 15 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid was added to 80 g of anhydrous tetrahydrofuran, cooled to 0 ° C, and 67.5 g of 2 mol / L borane tetrahydrofuran solution was added under stirring. Then the temperature was restored to room temperature and reacted for 4 h. The temperature was lowered to 3 ° C, methanol was added to quench the reaction, and tetrahydrofuran was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography and gradient elution to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol. (3) Under nitrogen protection, 30 g of lanthanum acetylacetonate hydrate and 5.31 g of 4-bromobutyric acid were added to 180 g of anhydrous tetrahydrofuran, stirred, heated to 75 ° C, reacted for 5 h, cooled to room temperature, filtered, washed, and dried to obtain a rare earth complex; (4) Under nitrogen protection, 10 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, 32.90 g of rare earth complex and 2.96 g of potassium iodide were added to 100 g of acetonitrile, heated to 65 ° C, reacted for 10 h, cooled to room temperature, and acetonitrile was removed by vacuum distillation. 100 g of deionized water was added, and then extracted three times with ethyl acetate. The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. After that, it was subjected to silica gel column chromatography using gradient elution to obtain imidazole-rare earth quaternary ammonium salt; (5) Under nitrogen protection, 24.37 g of 10-bromodecanoic acid was added to 240 g of anhydrous tetrahydrofuran, and the temperature was lowered to 0 ° C. Then, 24.89 g of dicyclohexylcarbodiimide was added and stirred for 15 min. Then, 1.36 g of 4-dimethylaminopyridine and 30 g of imidazole-rare earth quaternary ammonium salt were added and the mixture was returned to room temperature. The mixture was stirred for 9 h and filtered. After the filtrate was concentrated to one third of the original volume, 210 g of n-hexane was added. The precipitated solid was filtered, washed and dried to obtain imidazole-rare earth quaternary ammonium salt containing long-chain alkyl groups. (6) Under nitrogen protection, 40 g of imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, 9.46 g of benzotriazole, 12.46 g of potassium carbonate and 400 g of toluene were added to a reaction vessel equipped with a water separator, and the temperature was raised to 110°C. The reaction was carried out for 8 h. The potassium carbonate was removed by filtration and the toluene was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography using gradient elution to obtain a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule. (7) 35 g of bisimidazolyl-lanthanum-alkylbenzotriazole hybrid molecule was mixed with 25 g of ethanol, 13 g of n-butanol, and 2 g of isopropanol, heated to 45 °C, and stirred for 15 min. Then, 12 g of triethanolamine, 4 g of antioxidant, 2 g of surfactant, and 0.3 g of C9-C11 alkane were added, stirred evenly, cooled to room temperature, and impurities were filtered through a filter membrane to obtain a methanol corrosion inhibitor.

[0033] Example 3: A specific preparation method of a methanol corrosion inhibitor, comprising the following steps: (1) Under nitrogen protection, 10 g of 1-methylimidazole-4-carboxaldehyde, 12.28 g of malonic acid and 7 g of molecular sieves were added to 70 g of anhydrous N,N-dimethylformamide, and 0.3 g of piperidine was added. The temperature was raised to 90 ° C. and stirred for 6 h. The mixture was filtered while hot and then cooled to room temperature. The mixture was added to 90 g of deionized water. The yellow solid was filtered and washed with water until neutral to obtain 2-((1-methyl-1H-imidazole-4-yl)methylene)malonic acid; (2) Under nitrogen protection, 15 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid was added to 105 g of anhydrous tetrahydrofuran, and the temperature was lowered to 5°C. 75 g of a 2 mol / L borane tetrahydrofuran solution was added under stirring, and then the temperature was restored to room temperature. The reaction was allowed to react for 5 h, and the temperature was lowered to 5°C. Methanol was added to quench the reaction, and tetrahydrofuran was removed by distillation under reduced pressure. The crude product was subjected to silica gel column chromatography using gradient elution to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol. (3) Under nitrogen protection, 40 g of lanthanum acetylacetonate hydrate and 19.12 g of 4-bromobutyric acid were added to 280 g of anhydrous tetrahydrofuran, stirred, heated to 80 ° C, reacted for 6 h, cooled to room temperature, filtered, washed, and dried to obtain a rare earth complex; (4) Under nitrogen protection, 10 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, 35.89 g of rare earth complex and 3.95 g of potassium iodide were added to 120 g of acetonitrile, heated to 70 ° C, reacted for 12 h, cooled to room temperature, and acetonitrile was removed by vacuum distillation. 120 g of deionized water was added, and then extracted three times with ethyl acetate. The organic phase was washed with saturated brine and dried over anhydrous sodium sulfate. After that, it was subjected to silica gel column chromatography using gradient elution to obtain imidazole-rare earth quaternary ammonium salt; (5) Under nitrogen protection, add 25.43 g of 10-bromodecanoic acid to 300 g of anhydrous tetrahydrofuran, cool to 5 ° C, add 27.66 g of dicyclohexylcarbodiimide, stir for 20 min, then add 1.64 g of 4-dimethylaminopyridine and 30 g of imidazole-rare earth quaternary ammonium salt, return to room temperature, stir and react for 10 h, filter, concentrate the filtrate to one third of the original volume, add 240 g of n-hexane, filter the precipitated solid, wash and dry to obtain imidazole-rare earth quaternary ammonium salt containing long-chain alkyl groups; (6) Under nitrogen protection, 40 g of imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, 9.88 g of benzotriazole, 14.95 g of potassium carbonate and toluene were added to a reaction vessel equipped with a water separator. The temperature was raised to 120 °C and the reaction was carried out for 10 h. The potassium carbonate was removed by filtration and the toluene was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography using gradient elution to obtain a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule. (7) 40 g of bisimidazolyl-lanthanum-alkylbenzotriazole hybrid molecule was mixed with 30 g of ethanol, 15 g of n-butanol, and 3 g of isopropanol, heated to 50 °C, and stirred for 20 min. Then, 15 g of triethanolamine, 5 g of antioxidant, 3 g of surfactant, and 0.4 g of C9-C11 alkane were added, stirred evenly, cooled to room temperature, and impurities were filtered through a filter membrane to obtain a methanol corrosion inhibitor.

[0034] Comparative Example 1: The difference between Comparative Example 1 and Example 2 is that steps (3) and (4) are omitted. A specific method for preparing a methanol corrosion inhibitor comprises the following steps: (1) Under nitrogen protection, 10 g of 1-methylimidazole-4-carboxaldehyde, 11.34 g of malonic acid and 5 g of molecular sieves were added to 60 g of anhydrous N,N-dimethylformamide, and 0.2 g of piperidine was added. The temperature was raised to 85 ° C. and stirred for 5 h. The mixture was filtered while hot and then cooled to room temperature. The yellow solid was added to 80 g of deionized water. After filtration, the yellow solid was washed with water until neutral to obtain 2-((1-methyl-1H-imidazole-4-yl)methylene)malonic acid; (2) Under nitrogen protection, 15 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid was added to 80 g of anhydrous tetrahydrofuran, cooled to 0 ° C, and 67.5 g of 2 mol / L borane tetrahydrofuran solution was added under stirring. Then the temperature was restored to room temperature and reacted for 4 h. The temperature was lowered to 3 ° C, methanol was added to quench the reaction, and tetrahydrofuran was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography and gradient elution to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol. (3) Under nitrogen protection, 32.43 g of 10-bromodecanoic acid was added to 90 g of anhydrous tetrahydrofuran, and the temperature was lowered to 0 °C. 33.12 g of dicyclohexylcarbodiimide was added and stirred for 15 min. Then 1.82 g of 4-dimethylaminopyridine and 10 g of 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol were added and the mixture was returned to room temperature. The mixture was stirred for 9 h and filtered. After the filtrate was concentrated to one third of the original volume, n-hexane was added and the precipitated solid was filtered, washed and dried to obtain an imidazole containing a long-chain alkyl group. (4) Under nitrogen protection, 20 g of imidazole containing a long-chain alkyl group, 8.64 g of benzotriazole, 11.40 g of potassium carbonate and 200 g of toluene were added to a reaction vessel equipped with a water separator, and the temperature was raised to 110°C. The reaction was carried out for 8 h. The potassium carbonate was removed by filtration, and the toluene was removed by vacuum distillation. The crude product was subjected to silica gel column chromatography using gradient elution to obtain a bisimidazole-alkylbenzotriazole hybrid molecule. (5) 20 g of bisimidazolyl-lanthanum-alkylbenzotriazole hybrid molecule was mixed with 14.29 g of ethanol, 7.43 g of n-butanol, and 1.14 g of isopropanol, heated to 45 °C, and stirred for 15 min. Then, 6.86 g of triethanolamine, 2.29 g of antioxidant, 1.14 g of surfactant, and 0.17 g of C9-C11 alkane were added. After stirring evenly, the mixture was cooled to room temperature and impurities were filtered through a filter membrane to obtain a methanol corrosion inhibitor.

[0035] Comparative Example 2: The difference between Comparative Example 2 and Example 2 is that 10-bromodecanoic acid is replaced by bromoacetic acid.

[0036] Comparative Example 3: The difference between Comparative Example 3 and Example 2 is that 10-bromodecanoic acid is replaced by 6-bromohexanoic acid.

[0037] Comparative Example 4: The difference between Comparative Example 4 and Example 2 is that 10-bromodecanoic acid is replaced by 12-bromodecanoic acid.

[0038] Comparative Example 5: The difference between Comparative Example 5 and Example 2 is that 10-bromodecanoic acid is replaced by 15-bromopentadecanoic acid.

[0039] Comparative Example 6: The difference between Comparative Example 6 and Example 2 is that step (6) is omitted, and the imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group obtained in step (5) and ethanol are mixed, heated to 50°C, stirred for 20 minutes, and then triethanolamine, an antioxidant, and a surfactant are added. After stirring evenly, the mixture is cooled to room temperature and impurities are filtered through a filter membrane to obtain a methanol corrosion inhibitor.

[0040] Performance testing: 1. Metal corrosion inhibition test: Test materials: Copper: Meets the corrosion requirements of copper sheets in GB / T 5096; Brass: Meet the requirements of H70 copper in GB 5332; Chemical composition of cast iron: carbon mass fraction is 3.0% to 3.3%, silicon mass fraction is 1.8% to 2.2%, and iron is the balance; 20# steel: in accordance with GB 699 requirements; Chemical composition of aluminum flakes: silicon mass fraction is 5.5% to 6.5%, copper mass fraction is 3.0% to 4.0%, iron mass fraction is less than 1.2%, manganese mass fraction is 0.8%, magnesium mass fraction is 0.1% to 0.5%, nickel mass fraction is less than 0.5%, zinc mass fraction is less than 1.0%, and aluminum is the remainder; Tin sheet: The mass fraction of tin is 29.0% to 30.0%, with the remainder being lead.

[0041] Six test pieces were immersed in 92# gasoline, M30 methanol gasoline, and M30 methanol gasoline containing 1% of the methanol corrosion inhibitor prepared in Examples 1-3 and Comparative Examples 1-6. After two months, the test pieces were taken out for observation and weighed to calculate the change in mass per unit area. The metal corrosion indices of the different groups are shown in Table 1.

[0042] 2. Rubber corrosion inhibition test: Rubber materials such as automobile fuel tank floats, engine sealing collars, and pipelines were immersed in 92# gasoline, M30 methanol gasoline, and M30 methanol gasoline containing 1% of the methanol corrosion inhibitors prepared in Examples 1-3 and Comparative Examples 1-6. After two months, the rubber was removed and observed to see if it had hardened or turned white, if the immersion solution was not noticeably turbid, and if the components were still functioning properly. The experimental results are shown in Table 2.

[0043] Table 1 Metal corrosion inhibition

[0044] Table 2 Rubber corrosion inhibition

[0045] Performance Analysis: The experimental data in Tables 1 and 2 demonstrate that the methanol corrosion inhibitors prepared using the present invention in Examples 1-3 exhibit excellent performance. In metal corrosion inhibition tests, the unit area mass changes for copper, brass, cast iron, 20# steel, aluminum sheet, and tin sheet were close to those observed with 92# gasoline, and significantly lower than those observed with M30 methanol gasoline and the comparative examples, demonstrating excellent corrosion inhibition for a variety of metals. In rubber corrosion inhibition tests, the rubber products remained unchanged in appearance, the soaking solution remained clear, and the devices operated normally, demonstrating excellent compatibility with the rubber material. Among these, Example 2 exhibited the best overall performance, with various indicators closest to those observed with 92# gasoline among Examples 1-3, demonstrating the most outstanding corrosion inhibition effects on metals and protective effects on rubber.

[0046] The excellent performance of Example 2 may be because in the hybrid molecule prepared in Example 2, the imidazole ring and benzotriazole (BTA) form a "bis-nitrogen heterocyclic adsorption unit" through a conjugated π bond - the nitrogen atom of the imidazole ring and the triazole ring of BTA synergistically provide multi-site coordination ability, which can form a stable coordination bond with the empty orbitals on the surfaces of metals such as Fe and Cu. This "bicyclic conjugated" structure has improved adsorption capacity compared to a single imidazole; the rare earth lanthanum ion is centered on the +3 charge, coordinated with 4-bromobutyric acid through oxygen atoms, and constructs a "metal ion cross-linking center" with the imidazole ring, so that the molecule forms an adsorption film on the metal surface; the decyl long chain forms an oleophilic and hydrophobic layer on the membrane surface through the hydrophobic properties of the carbon chain. This gradient structure of "adsorption unit-cross-linking center-hydrophobic layer" realizes full-chain protection from chemical adsorption to physical barrier; secondly, the quaternary ammonium salt structure in the molecule is positively charged, which can be preferentially attracted by electrostatic attraction. It first adsorbs on the negatively charged metal surface to form a cationic repulsive layer, hindering the migration of corrosion ions; the coordination effect of lanthanum ions and imidazole rings further enhances the mechanical strength of the membrane, and this effect forms a "double driving force" with the charge adsorption of quaternary ammonium salts, making the adsorption membrane denser; the hydrophobic carbon chains of the decyl chain are tightly arranged through van der Waals forces to form a physical barrier, and its hydrophobic properties form an interfacial repulsion with methanol, directly reducing the penetration rate of the solvent to the metal surface. The three effects are synergistically associated through intramolecular chemical bonds to form a composite protective layer; finally, from a chemical point of view, the triazole ring of BTA has a strong electron-donating ability, which can form a stable chelate with metal ions, promote the formation of a passivation film in the anode area, and inhibit the metal dissolution reaction; the lanthanum ion in the rare earth complex acts as a Lewis acid, which can catalyze the oxidation of formic acid produced by the decomposition of methanol to CO2, thermodynamically reducing the corrosion driving force; the steric hindrance effect of the decyl chain reduces H + The effective collision probability with the metal surface kinetically slows down the corrosion rate. This multi-dimensional effect significantly increases the change in Gibbs free energy of the corrosion reaction, thereby inhibiting the corrosion process.

[0047] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A methanol corrosion inhibitor, characterized in that: The method comprises the following raw materials in parts by weight: 30-40 parts of a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule, 20-30 parts of ethanol, 10-15 parts of n-butanol, 1-3 parts of isopropanol, 8-15 parts of triethanolamine, 3-5 parts of an antioxidant, 1-3 parts of a surfactant, and 0.2-0.4 parts of a C9-C11 alkane. The preparation method of the bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule is as follows: (1) 1-Methylimidazole-4-carboxaldehyde, malonic acid and piperidine are added to anhydrous N,N-dimethylformamide to react to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid; (2) Add 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid to anhydrous tetrahydrofuran, and use borane tetrahydrofuran solution to reduce the carboxyl group of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid to alcohol to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol; (3) adding lanthanum acetylacetonate hydrate and 4-bromobutyric acid to anhydrous tetrahydrofuran to react and obtain a rare earth complex; (4) adding 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, a rare earth complex and potassium iodide to acetonitrile to react and obtain an imidazole-rare earth quaternary ammonium salt; (5) adding 10-bromodecanoic acid and dicyclohexylcarbodiimide to anhydrous tetrahydrofuran, and then adding 4-dimethylaminopyridine and imidazole-rare earth quaternary ammonium salt to react to obtain imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group; (6) Imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, benzotriazole, and potassium carbonate are added to toluene to react to obtain a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule.

2. The methanol corrosion inhibitor according to claim 1, characterized in that The antioxidant refers to one or both of 2,6-di-tert-butyl-p-cresol and N-phenyl-α-naphthylamine, and the surfactant refers to polyoxyethylene ether.

3. The methanol corrosion inhibitor according to claim 1, characterized in that The specific preparation method of (1) is as follows: under nitrogen protection, 1-methylimidazole-4-carboxaldehyde, malonic acid and molecular sieves are added to anhydrous N,N-dimethylformamide, and then piperidine is added, the temperature is raised to 80-90°C, the reaction is stirred for 4-6 hours, the mixture is filtered while hot, and then cooled to room temperature, and the mixture is added to deionized water. The obtained solid is filtered and washed with water until neutral to obtain 2-((1-methyl-1H-imidazole-4-yl)methylene)malonic acid; the molar ratio of 1-methylimidazole-4-carboxaldehyde and malonic acid is 1:1.1-1.3, and the weight ratio of 1-methylimidazole-4-carboxaldehyde, molecular sieves, piperidine, anhydrous N,N-dimethylformamide and deionized water is 1:0.3-0.7:0.01-0.03:5-7:7-9.

4. The methanol corrosion inhibitor according to claim 1, characterized in that The specific preparation method in (2) is as follows: under nitrogen protection, 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid is added to anhydrous tetrahydrofuran, cooled to -5-5°C, borane tetrahydrofuran solution is added under stirring, and then the temperature is restored to room temperature, reacted for 3-5h, cooled to 0-5°C, methanol is added to quench the reaction, and tetrahydrofuran is removed by vacuum distillation. The crude product is subjected to silica gel column chromatography and gradient elution to obtain 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol; the weight ratio of 2-((1-methyl-1H-imidazol-4-yl)methylene)malonic acid, borane tetrahydrofuran solution and anhydrous tetrahydrofuran is 1:4-5:5-7, the concentration of borane tetrahydrofuran solution is 2 mol / L, and gradient elution refers to the volume ratio of dichloromethane and methanol in each step of the eluent being 1:0, 20:1 to 9:

1.

5. The methanol corrosion inhibitor according to claim 1, characterized in that The specific preparation method in (3) is as follows: under nitrogen protection, lanthanum acetylacetonate hydrate and 4-bromobutyric acid are added to anhydrous tetrahydrofuran, stirred, heated to 70-80°C, reacted for 4-6 hours, cooled to room temperature, filtered, washed, and dried to obtain a rare earth complex; the lanthanum acetylacetonate hydrate and 4-bromobutyric acid are in a molar ratio of 1:1.1-1.3, and the lanthanum acetylacetonate hydrate and anhydrous tetrahydrofuran are in a weight ratio of 1:5-7.

6. The methanol corrosion inhibitor according to claim 1, characterized in that The specific preparation method in (4) is as follows: under nitrogen protection, 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, rare earth complex and potassium iodide are added to acetonitrile, the temperature is raised to 60-70°C, the reaction is carried out for 8-12 hours, the reaction is cooled to room temperature, the acetonitrile is removed by distillation under reduced pressure, deionized water is added, and then the mixture is extracted three times with ethyl acetate. The organic phase is washed with saturated brine and then dried over anhydrous sodium sulfate, and then subjected to silica gel column chromatography using gradient elution to obtain imidazole-rare earth quaternary ammonium Salt; the 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, rare earth complex and potassium iodide are in a molar ratio of 1:1-1.2:0.2-0.4, and the 2-((1-methyl-1H-imidazol-4-yl)methylene)propane-1,3-diol, acetonitrile and deionized water are in a weight ratio of 1:8-12:8-12. Gradient elution refers to the volume ratio of dichloromethane and methanol in each step of the eluent being successively from 1:0, 20:1, 10:1 to 4:

1.

7. The methanol corrosion inhibitor according to claim 1, characterized in that The specific preparation method of (5) is as follows: under nitrogen protection, 10-bromodecanoic acid is added to anhydrous tetrahydrofuran, the temperature is lowered to -5-5°C, dicyclohexylcarbodiimide is added, and the mixture is stirred for 10-20 minutes, and then 4-dimethylaminopyridine and imidazole-rare earth quaternary ammonium salt are added, the temperature is restored to room temperature, the reaction is stirred for 8-10 hours, and the mixture is filtered. After the filtrate is concentrated to one-third of the original volume, n-hexane is added, and the precipitated solid is filtered, washed, and dried to obtain an imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group; the molar ratio of 10-bromodecanoic acid, dicyclohexylcarbodiimide, 4-dimethylaminopyridine and imidazole-rare earth quaternary ammonium salt is 2.2-2.4:2.5-3:0.2-0.3:1, and the weight ratio of imidazole-rare earth quaternary ammonium salt, anhydrous tetrahydrofuran and n-hexane is 1:7-10:6-8.

8. The methanol corrosion inhibitor according to claim 1, characterized in that The specific preparation method of (6) is as follows: under nitrogen protection, in a reaction vessel equipped with a water separator, imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, benzotriazole, potassium carbonate and toluene are added, the temperature is raised to 100-120°C, the reaction is carried out for 6-10 hours, the potassium carbonate is removed by filtration, the toluene is removed by vacuum distillation, and the crude product is subjected to silica gel column chromatography and gradient elution to obtain a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule; the imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group, benzotriazole and potassium carbonate are in a molar ratio of 1:2.1-2.3:2-3, the imidazole-rare earth quaternary ammonium salt containing a long-chain alkyl group and toluene are in a weight ratio of 1:8-12, and the gradient elution refers to the volume ratio of dichloromethane / methanol / water in each step of the eluent being successively from 9:1:0, 8:2:0, 6:4:0 to 4:1:0.

1.

9. The method for preparing the methanol corrosion inhibitor according to claims 1-8, characterized in that: The method comprises the following steps: mixing a bisimidazole-lanthanum-alkylbenzotriazole hybrid molecule with ethanol, n-butanol and isopropanol, heating the mixture to 40-50°C, stirring the mixture for 10-20 minutes, then adding triethanolamine, an antioxidant, a surfactant and a C9-C11 alkane, stirring the mixture evenly, cooling the mixture to room temperature, filtering out impurities through a filter membrane and obtaining a methanol corrosion inhibitor.

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