Pickling agent and application thereof

Abstract

The invention discloses a pickling agent and application thereof, and relates to the technical field of corrosion inhibitors. According to the pickling agent provided by the invention, the nicotinoyl methionine is applied to the hydrochloric acid, the nicotinoyl methionine is used as an adsorption type corrosion inhibitor, and the nicotinoyl methionine can quickly form a film on the surface of the steel in the process of pickling the steel by the hydrochloric acid, so that corrosive substances such as H2O, H3O < + >, Cl <-> and the like in an acidic medium are prevented from being diffused on the surface of the steel, and the corrosion inhibition effect is achieved. After the nicotinoylmethionine is added into a hydrochloric acid medium as the corrosion inhibitor, the corrosion rate of the pickling agent on the surface of the steel is remarkably reduced, the corrosion inhibition performance is remarkably improved, the corrosion rate of the pickling agent on the surface of the steel at normal temperature can be reduced to 1.654 g.m <-2 > h <-1 > or below, and the corrosion inhibition rate can be improved to 92.99% or above.

Description

Technical Field

[0001] The present invention relates to the technical field of corrosion inhibitors, and specifically, to an acid pickling agent and its application. Background Art

[0002] Due to its low cost and easy processing, low-carbon steel is widely used in industries such as chemical engineering, pipelines, and automobiles. However, in actual industrial applications, low-carbon steel faces serious corrosion problems. When directly exposed to the natural environment, low-carbon steel is prone to an oxygen absorption reaction, resulting in the formation of surface corrosion products and oxide layers. Therefore, it is often necessary to remove the scale and rust on its surface through acid pickling (usually using hydrochloric acid as the acidic medium) to ensure the surface quality of the steel. However, in a highly acidic environment, low-carbon steel will undergo more severe corrosion. Therefore, substances such as corrosion inhibitors that can reduce metal corrosion are usually added during the acid pickling process.

[0003] Organic corrosion inhibitors usually contain atoms such as N, S, O, P and polar groups. These structures can interact with the electrons on the metal surface, enabling the organic corrosion inhibitor to be adsorbed onto the metal surface to achieve the protection of the metal. Therefore, extensive research has been conducted in recent years. Currently commonly used organic corrosion inhibitors such as benzotriazole are highly toxic, difficult to degrade, and harmful to human health and the ecological system. In the pursuit of environmental protection, green corrosion inhibitors represented by amino acids and their derivatives have received increasing attention in recent years. However, although existing green corrosion inhibitors are mild enough, their corrosion inhibition effects still need to be improved. Therefore, it is urgent to find green corrosion inhibitors with better corrosion inhibition effects, especially those that can exhibit excellent corrosion inhibition effects in an acidic medium such as hydrochloric acid, because hydrochloric acid is currently the most widely used acidic medium in the steel acid pickling process. Summary of the Invention

[0004] To solve the deficiencies of the prior art, the present invention provides an acid pickling agent. By applying nicotinoyl methionine to hydrochloric acid, the former, as an adsorption-type corrosion inhibitor, can quickly form a film on the surface of the steel during the acid pickling of the steel by hydrochloric acid, hindering the diffusion of corrosive substances such as H2O, H3O + , Cl - etc. on the surface of the steel, thereby exerting a corrosion inhibition effect.

[0005] Another object of the present invention is to provide the application of the above acid pickling agent in the acid pickling of the steel surface.

[0006] The above objects of the present invention are achieved through the following technical solutions:

[0007] An acid pickling agent comprising hydrochloric acid and nicotinoyl methionine.

[0008] In a specific embodiment of the present invention, the acid pickling agent further comprises a solvent, and the solvent comprises water.

[0009] The inventors of the present application have found through a large number of experimental studies that there is an unexpected synergistic effect between nicotinoyl methionine and hydrochloric acid. Hydrochloric acid, sulfuric acid, nitric acid, hydrofluoric acid, etc. are all commonly used acidic media in the pickling of steel surfaces, but the principles of the interaction between different acidic media and the steel surface during pickling are different. Among them, hydrochloric acid has a relatively fast corrosion rate on the steel surface, and the presence of Cl - is likely to cause pitting corrosion, but the chloride formed by the reaction of Cl - with the steel is easily soluble. After adding nicotinoyl methionine in combination with hydrochloric acid, nicotinoyl methionine can quickly form a film on the steel surface, hindering the diffusion of corrosive substances such as H2O, H3O + , Cl - in the acidic medium on the steel surface, and realizing the corrosion inhibition effect on the steel surface during pickling. The principle may be that nicotinoyl methionine, as an "adsorption-type" corrosion inhibitor, has a surface tension matching that of hydrochloric acid and high compatibility between the two. When nitric acid is used as the pickling medium, the steel surface will be quickly passivated, and it is difficult for nicotinoyl methionine to achieve corrosion inhibition through adsorption. Therefore, the corrosion inhibition effect in nitric acid is generally average; when sulfuric acid is used as the pickling medium, the steel surface easily reacts with sulfuric acid to form insoluble sulfates, which also hinders the adsorption of nicotinoyl methionine on the steel surface, resulting in a decrease in its corrosion inhibition effect. When hydrofluoric acid is used as the acidic medium, a corrosion inhibitor that can adsorb and form a film on the steel surface is usually also used, but the compatibility between nicotinoyl methionine and hydrofluoric acid decreases.

[0010] It should be noted that the nicotinoyl methionine referred to in the present invention has the following chemical structure as shown in formula (I):

[0011]

[0012] As can be seen from the above formula, the structural fragments of nicotinoyl methionine are respectively composed of nicotinic acid (also known as vitamin B3) and methionine (also known as methionine). Among them, both nicotinic acid and methionine are essential nutrients for the human body, with low toxicity and being environmentally friendly at the same time.

[0013] Preferably, the preparation method of the nicotinoyl methionine includes the following steps:

[0014] S1. Mix and react methyl methionine hydrochloride, nicotinic acid with a condensing agent and an activating agent, and obtain an intermediate product after the reaction;

[0015] S2. Mix and react the intermediate product obtained in step S1 with an acid-binding agent, and add an acid for acidification after the reaction to obtain nicotinoyl methionine.

[0016] Preferably, the methyl methionine hydrochloride in step S1 is L-methyl methionine hydrochloride.

[0017] More preferably, the molar ratio of the methyl methionine hydrochloride to nicotinic acid in step S1 is (1.05 - 1.5):1.

[0018] Making the methyl methionine hydrochloride slightly in excess of the nicotinic acid can enable the reaction in step S1 to proceed fully.

[0019] Preferably, the condensing agent in step S1 includes 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI hydrochloride).

[0020] More preferably, the molar ratio of the condensing agent to nicotinic acid in step S1 is (1 - 3):1.

[0021] Preferably, the activating agent in step S1 includes N-methylmorpholine.

[0022] More preferably, the molar ratio of the activating agent to nicotinic acid in step S1 is (2 - 4):1.

[0023] More preferably, the temperature of the reaction in step S1 is 20 - 25°C.

[0024] More preferably, the time of the reaction in step S1 is 10 - 14 h.

[0025] Preferably, the reaction in step S1 is carried out in a solution environment, and the solution includes dichloromethane.

[0026] Preferably, after the reaction in step S1, it further includes the steps of dilution, washing, drying, filtration, concentration, and purification.

[0027] The intermediate product obtained after the reaction in step S1 is a crude product, so preferably the subsequent steps include the above steps to obtain an intermediate product with higher purity.

[0028] More preferably, the reagent used for dilution includes dichloromethane.

[0029] More preferably, the reagents used for washing include water and physiological saline.

[0030] More preferably, the concentration is carried out under reduced pressure.

[0031] More preferably, the purification is carried out by column chromatography. The mobile phase used in the column chromatography includes dichloromethane and petroleum ether, and the stationary phase includes chromatographic silica gel powder with a particle size of 200 - 400 mesh. More preferably, the volume ratio of dichloromethane to petroleum ether is 1:1.

[0032] More preferably, after obtaining the intermediate product in step S1, it further includes the step of dissolving it in a solvent to obtain an intermediate product solution. More preferably, the solvent used for dissolution includes methanol and tetrahydrofuran. Dissolving the intermediate product first is beneficial for subsequent further reactions.

[0033] Preferably, the acid binding agent in step S2 comprises LiOH.

[0034] More preferably, the molar ratio of the acid binding agent in step S2 to the intermediate product obtained in step S1 is (4-6):1.

[0035] Preferably, the acid in step S2 comprises hydrochloric acid.

[0036] Using hydrochloric acid for acidification can reduce the generation of by-products.

[0037] More preferably, the reaction temperature in step S2 is 20-25°C.

[0038] More preferably, the concentration of the acid in step S2 is 1-2 mol / L.

[0039] More preferably, the pH after acidification in step S2 is 2-4.

[0040] More preferably, the reaction time in step S2 is 1 to 3 hours.

[0041] More preferably, the step S2 further comprises a step of evaporating the solvent before the acidification. More preferably, the step S2 further comprises a step of diluting after the evaporation of the solvent and before the acidification, and the solvent used for the dilution comprises water.

[0042] In step S2, a dilution step is also included after evaporating the solvent and before acidification, which is beneficial for adjusting the pH to obtain the product and extracting it.

[0043] More preferably, after the acidification in step S2, an extraction step is further included, and the solvent used in the extraction includes ethyl acetate.

[0044] More preferably, the extraction in step S2 further includes drying and concentrating steps.

[0045] Preferably, the pickling agent comprises the following components calculated by mass:

[0046] 100-4000 parts of nicotinylmethionine, 36500 parts of hydrochloric acid.

[0047] The ratio between pickling medium and corrosion inhibitor will affect the pickling and corrosion inhibition effects. If the concentration of corrosion inhibitor is too low, it is difficult to form a complete film on the steel surface, and the corrosion inhibition effect is reduced; if the concentration of corrosion inhibitor is too high, it may be difficult for excess corrosion inhibitor molecules to find active adsorption points on the adsorption layer, thus disturbing the adsorption layer, causing local desorption, and easily leading to a decrease in corrosion inhibition effect.

[0048] More preferably, the pickling agent comprises the following components calculated by mass:

[0049] 200 - 500 parts of nicotinoyl methionine and 36500 parts of hydrochloric acid.

[0050] More preferably, the concentration of the hydrochloric acid is 0.5 - 2 mol / L.

[0051] The present invention also protects the application of the above pickling agent in pickling the surface of steel.

[0052] Preferably, the steel includes low - carbon steel.

[0053] Preferably, the temperature of the pickling is 15 - 40 °C.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] After using nicotinoyl methionine as an inhibitor and adding it to the hydrochloric acid medium, the corrosion rate of the pickling agent on the surface of the steel decreases significantly, and the corrosion inhibition performance improves significantly. At room temperature, the corrosion rate of the pickling agent on the surface of the steel can be reduced to 1.654 g·m -2 h -1 Hereinafter, the corrosion inhibition rate can be increased to more than 92.99%. Description of the Drawings

[0056] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0057] Figure 1 For the structural formula, 1 H NMR spectrum and IR spectrum of nicotinoyl methionine prepared by the present invention, where Figure 1 (a) is the structural formula of nicotinoyl methionine, Figure 1 (b) is the IR spectrum, Figure 1 (c) is 1 the HNMR spectrum, Figure 1 (d) and (e) are respectively 1 the partial enlarged view of the HNMR spectrum at δ = 7.8 - 9.3 and the partial enlarged view at δ = 1.7 - 2.9.

[0058] Figure 2 (a) - (f) are the SEM images and AFM images of Q235 steel after being immersed in the blank control pickling agent, the pickling agent of Example 4, and the pickling agent of Comparative Example 3 for 24 h, where Figure 2 (a) and (d) are the SEM images of Q235 steel after being immersed in the blank control pickling agent for 24 h, Figure 2(b) and (e) are SEM images of Q235 steel after being immersed in the pickling solution of Example 4 for 24 h. Figure 2 (c) and (f) are SEM images of Q235 steel after being immersed in the pickling solution of Comparative Example 3 for 24 h. Figure 2 (g), (h), and (i) are AFM images of Q235 steel after being immersed in the blank control pickling solution, the pickling solution of Example 4, and the pickling solution of Comparative Example 3 for 24 h, respectively.

[0059] Figure 3 (a) - (f) are the surface profile maps, contour lines, and isometric three - dimensional morphology maps of Q235 steel after being immersed in the blank control pickling solution, the pickling solution of Example 4, and the pickling solution of Comparative Example 3 for 24 h, respectively. Among them, Figure 3 (a) is the surface profile map of Q235 steel after being immersed in the blank control pickling solution for 24 h. Figure 3 (b) is the surface profile map of Q235 steel after being immersed in the pickling solution of Example 4 for 24 h; Figure 3 (c) is the surface profile map of Q235 steel after being immersed in the pickling solution of Comparative Example 3 for 24 h; Figure 3 (d) is the contour line of Q235 steel after being immersed in the blank control pickling solution for 24 h; Figure 3 (e) is the contour line of Q235 steel after being immersed in the pickling solution of Example 4 for 24 h; Figure 3 (f) is the contour line of Q235 steel after being immersed in the pickling solution of Comparative Example 3 for 24 h; Figure 3 (g) is the isometric three - dimensional morphology map of Q235 steel after being immersed in the blank control pickling solution for 24 h; Figure 3 (h) is the isometric three - dimensional morphology map of Q235 steel after being immersed in the pickling solution of Example 4 for 24 h; Figure 3 (i) is the isometric three - dimensional morphology map of Q235 steel after being immersed in the pickling solution of Comparative Example 3 for 24 h.

[0060] Figure 4 is the XPS high - resolution energy spectrum of the steel surface of Q235 steel after being immersed in the pickling solution of Example 4 for 24 h; among them, (a) is the total spectrum; (b) is the Fe 2p spectrum; (c) is the C1s spectrum; (d) is the O1s spectrum; (e) is the N1s spectrum; () is the S2p spectrum.

[0061] Figure 5 is the frontier molecular orbital and ESP distribution map of nicotinoyl - methionine in the present invention; among them, (a) is the HOMO distribution; (b) is the LUMO distribution; (c) is the ESP distribution.

[0062] Figure 6Figure showing the Monte Carlo simulation results of the adsorption of nicotinoyl methionine in a vacuum environment and in an acidic medium, where (a) is the vacuum environment and (b) is the acidic medium. Detailed implementation manners

[0063] The present invention will be further described below in conjunction with the detailed implementation manners, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw material reagents used in the embodiments of the present invention are raw material reagents purchased conventionally. Among them, the raw material information used in each embodiment and the comparative example is as follows:

[0064] Nicotinoyl methionine: CAS No. 17274-90-7. Its preparation method includes the following steps:

[0065] S1. Add 1.1 mol of methionine methyl ester hydrochloride, 1 mol of nicotinic acid, 2 mol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and 3 mol of N-methylmorpholine to dichloromethane solvent, mix well, stir and react at room temperature for 12 h. After the reaction, obtain the crude product of the intermediate product, dilute it with dichloromethane, and then wash it twice with water and physiological saline respectively, dry, filter and concentrate under reduced pressure, and purify it by column chromatography (mobile phase volume ratio of dichloromethane: petroleum ether = 1:1) to obtain the intermediate product Dissolve 1 mol of the intermediate product in a mixed solvent including methanol and tetrahydrofuran to obtain an intermediate product solution;

[0066] S2. Add 5 mol of LiOH to the intermediate product solution obtained in step S1, stir and react at room temperature for 2 h. After the reaction, evaporate the solvent, dilute it with water and adjust the pH to 2-4 with 1.5 mol / L hydrochloric acid, and then add ethyl acetate for extraction, dry and concentrate to obtain nicotinoyl methionine. According to Figure 1 (b) to (e) characterization can clarify that the present invention can prepare nicotinoyl methionine with a structure as Figure 1 (a) shown.

[0067] Nicotinic acid: commercially available.

[0068] Methionine: commercially available.

[0069] tert-Butylbenzoylmethionine: CAS No. 86123-95-7. Its preparation method comprises the following steps: Under ice-water bath conditions, methionine (0.75 g, 5 mmol) is added to a 50 mL round-bottom flask containing NaOH (0.4 g, 10 mmol) and 5 mL of water. After stirring evenly, 4-tert-butylbenzoyl chloride (0.98 mL, 5 mmol) is added dropwise, and the reaction is continuously stirred for 24 hours. After the reaction is completed, the pH is adjusted to 1-2 with dilute hydrochloric acid. Then the aqueous phase after the reaction is extracted with ethyl acetate multiple times, the extracted organic phase is collected, and dried with anhydrous magnesium sulfate. After concentration by rotary evaporation, purification is carried out by column chromatography, and the eluent is DCM (dichloromethane) and MeOH (methanol), and the eluent ratio is DCM:MeOH = 9:1, and the product is obtained by separation and purification.

[0070] 3-Thienylcarbonylmethionine: CAS No. 97692-58-5. Its preparation method comprises the following steps: 3-Thiophenecarboxylic acid (0.64 g, 5 mmol) and 40 mL of DCM are added to a 100 mL round-bottom flask. Under ice-water bath stirring, oxalyl chloride (COCl)2 (0.85 mL, 10 mmol) is added dropwise, and then two drops of N,N-dimethylformamide (DMF) are added, and the reaction is stirred for 2 hours. After the reaction is completed, the solvent DCM is removed by distillation under reduced pressure, and 10 mL of 1,4-dioxane is added to the round-bottom flask and mixed well. Under ice-water bath conditions, methionine (0.75 g, 5 mmol) is added to a 50 mL round-bottom flask containing NaOH (0.4 g, 10 mmol) and 5 mL of water. After stirring evenly, a dioxane solution of 3-thiophenecarbonyl chloride is added dropwise, and the reaction is continuously stirred for 24 hours. After the reaction is completed, dioxane is first removed by distillation under reduced pressure, and the pH is adjusted to 1-2 with dilute hydrochloric acid. Then the aqueous phase after the reaction is extracted with ethyl acetate multiple times, the extracted organic phase is collected, and dried with anhydrous magnesium sulfate. After concentration by rotary evaporation, purification is carried out by column chromatography, and the eluent is petroleum ether (PE) and ethyl acetate (EA), and the eluent ratio is PE:EA = 8:2, and the product is obtained by separation and purification.

[0071] Nicotinoyl-L-phenylalanine: PubChem CID is 5307679. Its preparation method comprises the following steps: First, nicotinic acid (1 equivalent), L-phenylalanine methyl ester hydrochloride (1.1 equivalents), EDCI hydrochloride (2 equivalents), and N-methylmorpholine (3 equivalents) are added to a flask containing dichloromethane, and stirred at room temperature for 12 h. Subsequently, it is diluted with dichloromethane, washed with water and brine, dried, filtered and concentrated under reduced pressure, and purified by column chromatography (dichloromethane:petroleum ether = 1:1) to obtain the ester. Then, LiOH (5 equivalents) is added to a solution of the ester (1 equivalent) in methanol and THF, and stirred at room temperature for 2 hours. Finally, the solvent is evaporated, diluted with water, acidified with 1.5N HCl, extracted with ethyl acetate, dried and concentrated to obtain the target product.

[0072] Nicotinoyl tryptophan: PubChem CID is 44304898. Its preparation method includes the following steps: First, add nicotinic acid (1 equivalent), L-tryptophan methyl ester hydrochloride (1.1 equivalents), EDCI hydrochloride (2 equivalents), and N-methylmorpholine (3 equivalents) into a flask containing dichloromethane, and stir at room temperature for 12 h. Subsequently, dilute with dichloromethane, wash with water and brine, dry by filtration and concentrate under reduced pressure, and purify by column chromatography (dichloromethane: petroleum ether = 1:1) to obtain the ester. Then, add LiOH (5 equivalents) to the solution of the ester (1 equivalent) dissolved in methanol and THF, and stir at room temperature for 2 hours. Finally, evaporate the solvent, dilute with water, acidify with 1.5N HCl, extract with ethyl acetate, dry and concentrate to obtain the target product.

[0073] 3-(2,5-Dibromothiophenyl)carbonyl methionine: Add 2,5-dibromothiophene-3-carboxylic acid (0.86 g, 3 mmol) and 40 mL of DCM into a 100 mL round-bottom flask. While stirring in an ice-water bath, add oxalyl chloride (COCl)2 (0.51 mL, 6 mmol) dropwise, and then add two drops of N,N-dimethylformamide (DMF), and stir the reaction for 2 hours. After the reaction is completed, distill off the solvent DCM under reduced pressure, and add 10 mL of dioxane to the round-bottom flask and mix well. Under the condition of an ice-water bath, add methionine (0.75 g, 5 mmol) to a 50 mL round-bottom flask containing NaOH (0.4 g, 10 mmol) and 5 mL of water, stir evenly, and then dropwise add the dioxane solution of 2,5-dibromothiophene-3-carbonyl chloride, and continuously stir the reaction for 24 hours. After the reaction is completed, first distill off dioxane under reduced pressure, and adjust the pH to 1-2 with dilute hydrochloric acid. Extract the aqueous phase with ethyl acetate multiple times, collect the organic phase after extraction, and dry it with anhydrous magnesium sulfate. After concentration by rotary evaporation, purify by column chromatography, and the eluent is PE and EA, and the ratio of the eluent is PE:EA = 8:2, and the product is obtained by separation and purification.

[0074] Examples 1 to 5

[0075] This example provides a series of pickling agents with different mass fractions of nicotinoyl methionine, where the concentration of hydrochloric acid is 1 mol / L and the solvent is water. The mass fractions of nicotinoyl methionine and hydrochloric acid in Examples 1 to 5 are shown in Table 1 below:

[0076] Table 1. Components and their mass fractions in Examples 1 to 5

[0077]

[0078] The nicotinoyl methionine used in this example 1 1H NMR and IR spectra are as Figure 1(as shown in (b) to (e)).

[0079] According to Figure 1 (b), the following characteristic absorption peaks can be read out: 3300 cm -1 and 1710 cm -1 near which there appear characteristic absorption peaks belonging to the O-H bond and C=O in the carboxyl group respectively; 2950 cm -1 belongs to the bending vibration peak of the S-CH3 bond; 1637 cm -1 belongs to the characteristic absorption peak of the amide.

[0080] According to Figure 1 (c) to (e), the following characteristic peaks can be read out: δ9.02 (s, 1H), 8.77 (d, J = 5.5 Hz, 1H), 8.56 (d, J = 8.1 Hz, 1H), 7.85 (dd, J = 8.2, 5.4 Hz, 1H), 4.59 (dd, J = 9.3, 4.6 Hz, 1H), 2.61 (ddq, J = 21.1, 13.7, 7.8 Hz, 2H), 2.29 to 2.16 (m, 1H), 2.08 (d, J = 5.9 Hz, 4H).

[0081] According to Figure 1 the characterization in, it can be confirmed that nicotinoyl methionine can be prepared by using the preparation method of the present invention.

[0082] Comparative Example 1

[0083] An acid cleaning agent, which is only different from Example 4 in that:

[0084] nicotinoyl methionine is replaced with nicotinic acid in an equal mass fraction.

[0085] Comparative Example 2

[0086] An acid cleaning agent, which is only different from Example 4 in that:

[0087] nicotinoyl methionine is replaced with methionine in an equal mass fraction.

[0088] Comparative Example 3

[0089] An acid cleaning agent, which is only different from Example 4 in that:

[0090] nicotinoyl methionine is replaced with a mixture of nicotinic acid and methionine with a molar ratio of 1:1, and the total mass fraction of the obtained mixture is 400 parts.

[0091] Comparative Example 4

[0092] An acid cleaning agent, which is only different from Example 4 in that:

[0093] Replace nicotinoyl methionine with an equal mass fraction of tert-butylbenzoyl methionine, where the structure of benzoyl methionine is shown in the following formula (II):

[0094]

[0095] Comparative Example 5

[0096] An acid cleaning agent, which is different from Example 4 only in that:

[0097] Replace nicotinoyl methionine with an equal mass fraction of 3-thienylcarbonyl methionine, where the structure of 3-thienylcarbonyl methionine is shown in the following formula (III):

[0098]

[0099] Comparative Example 6

[0100] An acid cleaning agent, which is different from Example 4 only in that:

[0101] Replace nicotinoyl methionine with an equal mass fraction of nicotinoyl phenylalanine, where the structure of nicotinoyl phenylalanine is shown in the following formula (IV):

[0102]

[0103] Comparative Example 7

[0104] An acid cleaning agent, which is different from Example 4 only in that:

[0105] Replace nicotinoyl methionine with an equal mass fraction of nicotinoyl tryptophan, where the structure of nicotinoyl tryptophan is shown in the following formula (V):

[0106]

[0107] Comparative Example 8

[0108] An acid cleaning agent, which is different from Example 4 only in that:

[0109] Replace nicotinoyl methionine with an equal mass fraction of 3-(2,5-dibromothienyl)carbonyl methionine, where the structure of 3-(2,5-dibromothienyl)carbonyl methionine is shown in the following formula (VI):

[0110]

[0111] Comparative Example 9

[0112] An acid cleaning agent, which is different from Example 4 only in that:

[0113] Replace hydrochloric acid with an equal mass fraction of sulfuric acid.

[0114] Comparative Example 10

[0115] An acid pickling agent, which is only different from that of Example 4 in that:

[0116] Hydrochloric acid is replaced with nitric acid in an equal mass fraction.

[0117] Performance Test

[0118] I. Room Temperature Corrosion Inhibition Performance Test

[0119] The following uses the acid pickling agents provided by the examples and comparative examples to pickle Q235 steel at room temperature to test the corrosion inhibition performance of the corrosion inhibitor in the hydrochloric acid medium in the acid pickling agent.

[0120] The Q235 steel used in the test has the following elemental composition (wt%): 0.062% C, 0.326% Mn, 0.009% P, 0.013% S, and the rest is Fe.

[0121] The size of the weight loss specimen used in the test is 20.0 mm × 25.0 mm × 2.0 mm, and the size of the electrochemical specimen is 10.0 mm × 10.0 mm × 5.0 mm. The specimens are polished successively with 400#, 800#, 1200#, 1500# and 2000# sandpapers before the test. When performing electrochemical tests, a copper wire is welded to the back of each specimen as a wire and sealed with epoxy resin. The exposed area of the specimen is 1 cm 2 .

[0122] 1.1 Weight Loss Test

[0123] Place the weight loss specimens in a blank control acid pickling agent (1 mol / L hydrochloric acid aqueous solution) and the acid pickling agents provided by the examples and comparative examples, soak them in a constant temperature water bath for 24 h, and use an analytical balance (0.1 mg) to record the weight of the specimens before and after the test. The corrosion rate (V R ) and the corrosion inhibition rate η w % are determined by Formula 1 and Formula 2 respectively:

[0124]

[0125] In the formula, W (g) is the mass loss of specimen corrosion, S (m 2 ) is the total area of the specimen, T (h) is the soaking time; V0 and V are the corrosion rates of the Q235 specimens in the blank control and the solution with the added corrosion inhibitor, g·m -2 ·h -1 .

[0126] 1.2 Electrochemical Test

[0127] Electrochemical measurements were carried out using an electrochemical workstation PARSTAT 2273. A standard three-electrode system was adopted, with a saturated calomel electrode (SCE) as the reference electrode and graphite as the auxiliary electrode. Polarization curves were measured at a scanning rate of 0.5 mV / s and a potential range of (E0 ± 250 mV). The corrosion potential (E corr ), corrosion current density (i corr ), and cathodic Tafel slope (b c ) were obtained by analyzing the polarization curves. The inhibition efficiency (η P %) of the corrosion inhibitor was calculated according to Equation 3

[0128]

[0129] wherein, i 0 corr and i corr are the measured corrosion current densities in the blank control or the solution added with the corrosion inhibitor, respectively.

[0130] The specific data of the above tests are shown in Table 2 below:

[0131] Table 2. Inhibition efficiency and corrosion rate of the pickling agents provided by the blank control, examples, and comparative examples

[0132] Group <![CDATA[Corrosion rate g·m -2 ·h -1 > <![CDATA[Corrosion inhibition rate η w %]]> Example 1 1.654 92.99 Example 2 1.273 94.60 Example 3 0.994 95.79 Example 4 0.871 96.31 Example 5 / 98.50 Comparative Example 1 10.271 56.45 Comparative Example 2 7.448 68.42 Comparative Example 3 2.723 88.45 Comparative Example 4 3.370 85.71 Comparative Example 5 7.466 68.34 Comparative Example 6 5.376 77.20 Comparative Example 7 2.049 91.31 Comparative Example 8 4.176 82.29 Comparative Example 9 3.759 84.06 Comparative Example 10 169.677 45.22 Blank control pickling agent 23.581 /

[0133] Note: " / " in Table 2 above refers to no test being carried out.

[0134] As can be seen from Table 2 above, compared with the blank control pickling agent containing only hydrochloric acid, after adding nicotinoyl methionine as a corrosion inhibitor to the pickling agent provided by the examples of the present invention, the corrosion rate of the pickling agent on the steel surface decreased significantly, and the inhibition performance improved significantly. Moreover, according to Examples 1 to 5, within a certain range, as the concentration of the corrosion inhibitor in the pickling agent increased, the inhibition performance of the pickling agent on the steel surface also increased. This shows that the addition of the corrosion inhibitor in the pickling agent can adsorb and form a film on the steel surface, forming a stable protective layer, isolating it from the corrosive acidic medium, and thus the effect of corrosion inhibition can be achieved.

[0135] According to Example 4 and Comparative Examples 1 to 2, replacing nicotinoyl methionine with nicotinic acid or methionine in its preparation raw materials would result in an increase in the corrosiveness of the obtained pickling agent on the steel surface and a decrease in the corrosion inhibition effect. Combining nicotinic acid and methionine (Comparative Example 3) could improve the corrosion inhibition effect of the pickling agent. However, the inhibition performance was still inferior to that of the pickling agent provided by the present invention, indicating that the intramolecular synergistic corrosion inhibition effect is stronger than the intermolecular synergistic corrosion inhibition effect.

[0136] According to Example 4 and Comparative Examples 4-9, replacing the methionine structural fragment in nicotinoyl methionine with other amino acids or replacing the nicotinic acid structural fragment with other structures results in a decrease in the corrosion inhibition effect of the resulting corrosion inhibitor in hydrochloric acid medium, indicating that nicotinoyl methionine formed by the combination of nicotinic acid fragment and methionine structural fragment has better compatibility and interaction with hydrochloric acid medium.

[0137] 1.3 Surface analysis of specimens

[0138] At 25 °C, the weight-loss specimens were respectively immersed in the blank control pickling agent and the pickling agents provided in the examples and comparative examples for 24 h. After immersion, the specimens were taken out, rinsed with deionized water, dried, and then the surface of the specimens was characterized by scanning electron microscope (SEM), atomic force microscope (AFM), and white light confocal three-dimensional profiler to analyze the surface morphology and roughness of the specimens.

[0139] Figure 2 (a)-(f) are SEM images of Q235 steel immersed in the blank control pickling agent, the pickling agent of Example 4, and the pickling agent of Comparative Example 3 for 24 h, respectively, where Figure 2 (a) and (d) are SEM images of Q235 steel immersed in the blank control pickling agent for 24 h. It can be seen from the figure that after immersion in the blank control pickling agent for 24 h, a large amount of corrosion products appear on the surface of Q235 steel; Figure 2 (b) and (e) are SEM images of Q235 steel immersed in the pickling agent of Example 4 for 24 h. According to Figure 2 (b) and (e), after adding the corrosion inhibitor, the corrosion products of the pickling agent on the steel surface are greatly reduced, and the surface of the steel can remain relatively smooth, indicating that the corrosion degree of the steel surface is reduced; Figure 2 (c) and (f) are SEM images of Q235 steel immersed in the pickling agent of Comparative Example 3 for 24 h. According to Figure 2 The comparison of (b)-(f) shows that compared with adding the raw materials nicotinic acid and methionine, adding nicotinoyl methionine as a corrosion inhibitor has a relatively higher corrosion inhibition effect.

[0140] To deeply understand the corrosion inhibition effect of nicotinoyl methionine on Q235 steel in hydrochloric acid medium, atomic force microscope was used to take micrographs of the surface of Q235 steel after immersion. The results are as Figure 2As shown in (g) - (i). It can be found from the figure that when 1 mmol / L of nicotinoyl methionine (Example 4) or a mixture of nicotinic acid - methionine with a total concentration of 1 mmol / L (where the molar ratio of nicotinic acid to methionine is 1:1) (Comparative Example 3) is added to the pickling agent, the surface of the steel after pickling can have a high degree of smoothness and uniformity. Table 3 lists the average roughness (Ra), root mean square roughness (Rq), and maximum peak - valley value (Rmax) of the steel surface obtained in different groups after immersion:

[0141] Table 3. Roughness data of the steel surface of Q235 steel after being immersed in the blank control pickling agent, the pickling agent of Example 4, and the pickling agent of Comparative Example 3 for 24 h

[0142] Group Ra (nm) Rq (nm) Rmax (nm) Blank control pickling agent 356.3 446.7 3000 Pickling agent of Example 4 23.88 32.05 310.3 Pickling agent of Comparative Example 3 182.6 242.5 2045

[0143] It can be found from Table 3 that after adding 1 mmol / L of nicotinoyl methionine, Ra, Rq, and Rz are the smallest, being 23.88 nm, 32.05 nm, and 310.3 nm respectively. These results clearly show that nicotinoyl methionine has excellent protective effects on the corrosion of Q235 steel in hydrochloric acid solution.

[0144] The corrosion inhibition performance of the corrosion inhibitors in the pickling agents provided in Example 4 and Comparative Example 3 was further studied using a white - light confocal three - dimensional profiler. The results are as Figure 3 shown, and the three - dimensional morphology and contour line height data of the specimen surface can be obtained. For the specimen immersed in the blank control pickling agent, its maximum height reaches 40.29 μm, which is much higher than that of the specimens immersed in nicotinoyl methionine (12.34 μm) and nicotinic acid + methionine (19.79 μm). In addition, Figure 3 the contour lines shown in (b)(e)(h) and Figure 3 the isometric three - dimensional images shown in (c)(f)(i) further confirm that the addition of the corrosion inhibitor makes the surface of Q235 steel smoother and the corrosion lessened.

[0145] II. Exploration of Synergistic Effects

[0146] 2.1 Intermolecular Synergistic Effects

[0147] Next, by changing the concentrations and temperatures of the corrosion inhibitors provided in Comparative Examples 1 - 3, the synergistic effects between nicotinic acid and methionine were explored.

[0148] The specific data are shown in Tables 4 - 5 as follows:

[0149] Table 4. Corrosion inhibition effect data obtained by changing the concentrations and temperatures of the corrosion inhibitors in Comparative Examples 1 - 3

[0150]

[0151]

[0152] Note: " / " in Table 4 above indicates that the test was not conducted.

[0153] According to Table 4 above, compared with the blank control pickling agent (containing only hydrochloric acid), the addition of the corrosion inhibitor reduced the corrosion rate of Q235 steel to varying degrees. Moreover, the corrosion rates of Q235 steel in the blank and in the presence of the corrosion inhibitor increased with the increase in the experimental temperature. Meanwhile, the inhibition efficiency always showed the pattern of nicotinic acid < methionine < nicotinic acid + methionine < nicotinyl methionine.

[0154] Synergistic inhibition coefficient: It is calculated according to the following formula 4:

[0155]

[0156] In the formula, η1, η2, and η3 are the inhibition efficiencies of nicotinic acid, methionine, and nicotinic acid + methionine, respectively.

[0157] Based on the data in Table 4 and formula 4, the synergistic inhibition coefficient S when nicotinic acid and methionine are used in combination can be calculated as shown in Table 5 below:

[0158] Table 5. Synergistic inhibition coefficient S of the combination of nicotinic acid and methionine in the corrosion inhibitor provided in Comparative Example 3

[0159]

[0160] As can be seen from Table 5 above, the synergistic inhibition coefficient S obtained by combining nicotinic acid and methionine is basically greater than 1, indicating that the combination of the two substances has a synergistic effect.

[0161] 2.2 Comparison between intramolecular and intermolecular synergistic effects

[0162] Next, the pickling agents provided in Example 4 and Comparative Example 3 were used to pickle Q235 steel for 5 - 30 D (days), and the inhibition efficiency and corrosion rate were tested every 5 days. The specific data are shown in Table 6 below:

[0163] Table 6. Inhibition effects of the pickling agents in Comparative Example 3 and Example 4

[0164]

[0165]

[0166] From Table 6 above, the inhibition efficiency of nicotinyl methionine is much higher than that of nicotinic acid + methionine, indicating that the intramolecular synergistic corrosion inhibition effect is stronger than the intermolecular synergistic corrosion inhibition effect.

[0167] The long-term (30D) immersion experiment tracked the corrosion inhibition performance of adding 1 mmol / L of nicotinoyl methionine (Example 4) or nicotinic acid-methionine mixture (Comparative Example 3) to Q235 steel at 25°C. It was found that within the immersion time range of 5 - 30D, the η w showed a downward trend with the prolongation of the immersion time. Among them, compared with Example 4, the η w of Comparative Example 3 decreased more significantly with time. These results indicate that not only is the corrosion inhibition effect of nicotinoyl methionine far better than that of the nicotinic acid-methionine mixture, but the former also has better stability in acid, enabling Q235 steel to have excellent corrosion inhibition and stability in 1 mol / L hydrochloric acid medium.

[0168] III. Exploration of the corrosion inhibition mechanism of nicotinoyl methionine

[0169] 3.1 XPS test

[0170] XPS test was carried out on the surface of the steel after pickling corrosion to obtain the elemental content data and the binding energy data of each element distributed on its surface. The results are as follows Figure 4 shown in Tables 7 - 8.

[0171] Table 7. Elemental content on the surface of the steel after pickling with the pickling agents of Example 4 and Comparative Example 3

[0172] Group Fe C O N S Example 4 11.00 47.61 37.24 3.23 0.92 Comparative Example 3 7.08 49.52 39.09 3.41 0.91

[0173] According to Table 7, the N and S elements are contained on the surface of the steel after pickling, confirming the adsorption of the inhibitors in Example 4 and Comparative Example 3 on the surface of Q235 carbon steel.

[0174] Table 8. Binding energy of each element and its source data

[0175]

[0176] Figure 4 is the XPS high-resolution energy spectrum of Fe 2p, C 1s, O 1s, N 1s, S2p on the surface of the steel after pickling corrosion. The corresponding binding energy of each peak is shown in Table 8. The peak position at 399.8 eV in the N 1S spectrum corresponds to the amino group (-NH2) in the inhibitor molecule or the N-Fe bond formed between the N atom in the amino group and Fe; the peaks at 163.9 eV and 162.1 eV in the S2P spectrum correspond to C-S-C in the C-SH molecule and the S-Fe bond formed between the S atom and Fe respectively. According to Figure 4 and the data in Tables 7 - 8, it can be known that the N and S elements provided by nicotinoyl methionine can be adsorbed on the surface of the steel by forming bonds.

[0177] 3.2 Quantum chemical calculation

[0178] Based on density functional theory (DFT), quantum chemical calculations of the corrosion inhibitor were carried out using Gaussian 09 at the B3LYP / 6-311G* level to obtain the geometrically optimized structure and the distribution of frontier orbitals (HOMO, LUMO). At the same time, their sum and electrostatic potential (ESP) distributions were analyzed to explore the possible adsorption sites and strengths of the corrosion inhibitor. After the calculation was completed, Multiwfn and VMD were used to post-process the data and visualize the optimized structure.

[0179] Figure 5 Shows the frontier orbitals, energy levels, and the energy gap between them after the geometric structure of the nicotinoyl methionine molecule was optimized. According to Figure 5 (a), the HOMO orbital in the nicotinoyl methionine molecule is mainly distributed at C=S; according to Figure 5 (b), its LUMO orbital is mainly distributed at the pyridine ring and amide group. Figure 5 (c) shows the electrostatic potential (ESP) distribution on the van der Waals (vdW) surface of the optimized nicotinoyl methionine molecule, which can predict the possible adsorption sites of the corrosion inhibitor molecule on the metal surface. It can be found from the figure that the ESP on the vdW surface around the N and S atoms is more negative than other regions, indicating that the N and S atoms may be the adsorption sites of nicotinoyl methionine.

[0180] 3.3 Monte Carlo simulation

[0181] The Monte Carlo simulation was carried out using the Adsorption Locator module. Under the COMPASSⅡ force field, the adsorption behavior of the corrosion inhibitor molecule on the Fe(110) surface was studied. Among them, the Fe(110) crystal plane is composed of 6 layers of iron atoms, and a vacuum layer with a thickness of was added on the top to avoid the influence of periodic boundary conditions.

[0182] The simulation results and data are as Figure 6 shown in Tables 9-10.

[0183] Table 9. Monte Carlo simulation results of the adsorption of nicotinoyl methionine on the Fe(110) surface in a vacuum environment

[0184]

[0185] Table 10. Monte Carlo simulation results of the adsorption of nicotinoyl methionine on the Fe(110) surface in a solution environment

[0186]

[0187] As Figure 6(a) As shown, nicotinoyl methionine molecules are adsorbed on the Fe(110) surface in an approximately parallel adsorption manner. This adsorption configuration can maximally hinder the diffusion of Cl in an acidic medium - and the corrosive substances formed by its reaction with steel to the metal surface. In the Monte Carlo simulation, the adsorption energy of the inhibitor molecule consists of the rigid adsorption energy and the deformation energy. As shown in Table 9, both the adsorption energy and the deformation energy of nicotinoyl methionine molecules are negative values, indicating that this inhibitor can spontaneously adsorb on the Fe(110) surface. The corrosion inhibition rate of the inhibitor for steel is related to the adsorption configuration and adsorption strength of the inhibitor on the steel surface. Therefore, according to Figure 6 (a) and Table 9, it can be known that in the present invention, nicotinoyl methionine can not only achieve spontaneous adsorption on the steel surface in hydrochloric acid medium, but also has excellent adsorption strength, so the corrosion inhibition performance is excellent.

[0188] The Monte Carlo simulation can also calculate the differential adsorption energy corresponding to various adsorbed substances in the system, and realize the study of the competitive adsorption of inhibitor molecules and corrosive particles on the metal surface. As Figure 6 (b) shown, in the presence of corrosive particles (H2O, Cl - ), nicotinoyl methionine molecules still adsorb on the Fe(110) surface approximately parallelly. As shown in Table 10, the adsorption energy of nicotinoyl methionine molecules on the Fe(110) surface in the system is significantly lower than that of H2O and Cl - , indicating that nicotinoyl methionine molecules can adsorb on the metal surface prior to corrosive particles. By comparing Table 9 and Table 10, it can be found that the adsorption energy of nicotinoyl methionine molecules increases in the presence of corrosive particles, indicating that solvation can promote the adsorption process of inhibitor molecules.

[0189] 3.4 Molecular dynamics simulation

[0190] Through the Focite module in Materials Studio, in order to explore the hindering effect of the adsorbed inhibitor film on the diffusion of corrosive substances (H2O, H3O + , Cl - ), the diffusion coefficient (D i ) of corrosive substances was analyzed using Equation 5. First, a blank aqueous phase model containing 500 H2O, 5 H3O + and 5 Cl - (only hydrochloric acid is contained in the pickling agent) and an inhibitor film phase model containing 200 inhibitor molecules, 5 H2O, 5 H3O + and 5 Cl - were constructed. Then, under the COMPASSⅡ force field, the NPT ensemble was used to simulate for 200 ps to achieve density equilibrium, and then the NVT ensemble was used to simulate for 500 ps to achieve energy and temperature equilibrium.

[0191]

[0192] where N α is the number of particles, r i (0) and r i (t) are the positions of the particles at the initial time and at time t, respectively.

[0193] The corresponding diffusion coefficient (D i ) is calculated using Equation 5, and the results are shown in Table 11.

[0194] Table 11. Diffusion Coefficients of Different Corrosive Substances in Blank Aqueous Phase and Inhibitor Film Phase (Nicotinoyl Methionine)

[0195] Blank aqueous phase <![CDATA[D(m 2 / s)]]> Inhibitor film phase <![CDATA[D(m 2 / s)]]> <![CDATA[H2O]]> <![CDATA[2.489×10 -8 > <![CDATA[H2O]]> <![CDATA[7.993×10 -10 > <![CDATA[H3O + > <![CDATA[1.904×10 -8 > <![CDATA[H3O + > <![CDATA[6.005×10 -10 > <![CDATA[Cl - > <![CDATA[1.896×10 -8 > <![CDATA[Cl - > <![CDATA[3.128×10 -10 >

[0196] According to Table 11, it can be found that the diffusion rate of the corrosive substance in the inhibitor is much smaller than that in the blank solution, indicating that the inhibitor can block the corrosive substance after adsorbing on the metal surface.

[0197] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An acid cleaning agent, characterized in that, Includes hydrochloric acid and nicotinyl methionine.

2. The pickling agent according to claim 1, wherein The preparation method of nicotinylmethionine comprises the following steps: S1. mixing methionine methyl ester hydrochloride, nicotinic acid, a condensing agent and an activating agent to react to obtain an intermediate product; S2. The intermediate product obtained in step S1 is mixed with an acid-binding agent for reaction, and after the reaction, an acid is added for acidification to obtain nicotinylmethionine.

3. The pickling agent according to claim 2, wherein Include at least one of the following (a) to (d): (a) In the method for preparing nicotinylmethionine, the condensing agent in step S1 includes 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride; (b) In the method for preparing nicotinylmethionine, the activator in step S1 comprises N-methylmorpholine; (c) In the method for preparing nicotinylmethionine, the acid-binding agent in step S2 comprises LiOH; (d) In the method for preparing nicotinylmethionine, the acid in step S2 comprises hydrochloric acid.

4. The pickling agent according to claim 2 or 3, characterized in that, Including at least one of the following (e) to (i): (e) In the method for preparing nicotinylmethionine, the molar ratio of methionine methyl ester hydrochloride to nicotinic acid in step S1 is (1.05-1.5):1; (f) In the method for preparing nicotinylmethionine, the molar ratio of the condensing agent to nicotinic acid in step S1 is (1-3):1; (g) In the method for preparing nicotinylmethionine, the molar ratio of the activator to nicotinic acid in step S1 is (2-4):1; (h) In the method for preparing nicotinylmethionine, the molar ratio of the acid-binding agent in step S2 to the intermediate product obtained in step S1 is (4-6):1; (i) In the method for preparing nicotinylmethionine, the pH after acidification in step S2 is 2-4.

5. The pickling agent according to claim 2, wherein Including at least one of the following (j) to (k): (j) In the method for preparing nicotinylmethionine, the reaction temperature in step S1 is 20 to 25°C; (k) In the method for preparing nicotinylmethionine, the reaction temperature in step S2 is 20-25°C.

6. The pickling agent according to claim 1, wherein It includes the following components calculated by mass: 100-4000 parts of nicotinylmethionine and 36500 parts of hydrochloric acid.

7. The pickling agent according to claim 6, wherein It includes the following components calculated by mass: 200-500 parts of nicotinylmethionine and 36500 parts of hydrochloric acid.

8. The pickling agent according to claim 6 or 7, characterized in that, The concentration of the hydrochloric acid is 0.5-2 mol / L.

9. Use of the pickling agent according to any one of claims 1 to 8 in pickling of steel surfaces.

10. The application according to claim 9, characterized in that, Including at least one of the following (l) to (m): (l) the steel material comprises low carbon steel; (m) The pickling temperature is 15 to 40°C.

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