Application of modified cardanol aldehyde amine as corrosion inhibitor for acid medium

Abstract

The invention discloses application of modified cashew phenolic aldehyde amine as a corrosion inhibitor for an acid medium, the modified cashew phenolic aldehyde amine with a structure shown in a general formula (1) is directly added into a metal pickling solution as the corrosion inhibitor, and R is CH2CH2NHCH2CH2, (CH2CH2NH) 2CH2CH2 or # imgabs 1 #, and the adding amount of the modified cashew phenolic aldehyde amine in the metal pickling solution is 10 ppm to 1%. The modified cardanol aldehyde amine is used as the corrosion inhibitor for the acid medium, so that the corrosion inhibitor has good environmental protection performance and excellent corrosion inhibition performance, and has a great effect of prolonging the service life of a metal material in the acid medium. The preparation method of the modified cardanol aldehyde amine is simple in process, low in reaction temperature, short in reaction time, low in energy consumption, high in yield and good in environmental protection performance, and no other organic solvent except ethanol is adopted in the production process.

Description

Technical Field

[0001] The invention belongs to the technical field of organic corrosion inhibitors, and mainly relates to the use of modified cardamom aldehyde amine as a corrosion inhibitor for acid medium. Background Art

[0002] Corrosion inhibitors were first used in metal pickling processes. In oilfield mining, metal acid corrosion is an urgent problem to be solved. Researchers continue to study and develop different anti-corrosion measures, and the most effective and convenient method is to add corrosion inhibitors. So far, organic compounds containing polar groups (containing elements such as N, O, P, S) such as Mannich bases, amides, imidazolines, quaternary ammonium salts, etc. have been widely studied, and it is known that these substances have excellent corrosion inhibition properties.

[0003] Until the beginning of the 20th century, the research and application of corrosion inhibitors began to become more and more active, from the initial extraction from natural plants to the synthesis obtained by processing raw materials, so that the types of corrosion inhibitors also increased. By the 1930s, researchers from different countries had invested a lot of manpower and energy to study corrosion inhibitors, and began to extract and separate organic matter containing elements such as N, S, and O from coal tar. The corrosion inhibition properties of these substances were tested through experiments, and the results were used to determine whether they could be used as industrial corrosion inhibitors. It was not until the mid-1930s that the history of the development of corrosion inhibitors ushered in the first major breakthrough, and organic corrosion inhibitors were successfully synthesized artificially. From the 1940s to the 1950s, Uhlig.HH of the United States compiled the first edition of the Corrosion Handbook, which included 120 sulfuric acid corrosion inhibitors, most of which were sulfur-containing organic compounds (thiols, thioureas, thioethers, sulfates, etc.). In 1963, Yoshino Tsutomu of Japan compounded organic compounds with inorganic compounds and found that this method had a good anti-corrosion effect on low-carbon steel in solutions such as hydrochloric acid, sulfuric acid, and aminosulfonic acid. In the 1980s, the Soviet Union used cyclopentylphenol condensates as corrosion inhibitors in the petroleum industry to inhibit the corrosion of carbon steel in acid solutions.

[0004] It wasn't until 1953 that research on pickling inhibitors began in China. The Chemical Laboratory of the Tianjin Heavy Industry Bureau achieved the first success, successfully developing a pickling inhibitor mainly composed of o-tolylthiourea and putting it on the market under the brand name "May 4th Brand" Rohodine, which was successfully applied in sulfuric acid pickling at Tianjin Steel Mill. This product can slow down the corrosion of the metal substrate by hydrochloric acid, inhibit the generation of acid mist, and promote the cleaning of various scale deposits such as iron oxide scales and silicate scales. From the 1970s to the 1990s, China developed rapidly in the field of hydrochloric acid pickling inhibitors, and the products obtained could basically meet the requirements of China's hydrochloric acid pickling process. While researching the development and application of inhibitors, China also focused on studying the action mechanism and testing methods of inhibitors. Academician Cao Chunan et al. studied the electrochemical parameters of adsorption-type inhibitors in acidic media using steady-state polarization curves, linear polarization current, and AC impedance, analyzed their corrosion inhibition mechanisms, and proposed corrosion inhibition theoretical models such as geometric coverage effect and negative catalytic effect, as well as data analysis and processing methods. In-depth theoretical research has also promoted the development of new inhibitor products. The research characteristics of pickling inhibitors in China are that inhibitors are synthesized from chemical industrial and pharmaceutical by-products or extracted from plants and aquatic plants, and these products have achieved good corrosion inhibition effects during use.

[0005] Cardanol is a natural compound extracted from cashew nut shell liquid, which is a renewable biological resource. Developing and applying many products using cardanol can solve part of the petroleum energy crisis.

[0006] In the application of cardanol, it is mainly the preparation of cardanol curing agents. The prepared curing agents are cured with epoxy resins to obtain paint films with high stability, high temperature resistance, and good operability at low temperatures, which are mainly used as coatings for paint films on ships and containers.

[0007] For example, patent document CN113061105A discloses a cardanol-modified curing agent, its preparation method and application. Cardanol reacts with 3-mercaptopropionic acid under catalyst conditions to introduce a mercapto group, and an acrylic compound is attached through click chemistry "thiol-eoe" to obtain cardanol-polyacrylic acid. Cardanol-polyacrylic acid and formaldehyde and fatty amines are synthesized through Mannich reaction to prepare polyacrylic acid-cardanol aldehyde amine resin, that is, cardanol-modified curing agent; this curing agent is used in waterborne epoxy resins, and the formed coating has corrosion resistance and is suitable for metal protection in acidic environments.

[0008] Patent document CN111763151A discloses a preparation method of a cardanol-modified polyamine curing agent. Cardanol, paraformaldehyde and an amine compound are subjected to a Mannich reaction. After the reaction is completed, a water-soluble initiator is added for an olefin polymerization reaction. After the reaction is completed, water and the excessive amine compound are removed by distillation under reduced pressure to obtain the cardanol-modified polyamine. The polymerization reaction temperature is 70-100°C, and the polymerization time is 3-5h. The water-soluble initiator is azodiisobutyramidine hydrochloride, etc., and the amine compound is ethylenediamine. It is used in the heavy anti-corrosion fields such as ships and containers.

[0009] However, there is no literature mentioning cardanol derivatives as corrosion inhibitors for metal pickling. Summary of the Invention

[0010] Cardanol contains phenolic hydroxyl groups and long-chain alkyl groups. As an active hydrogen compound, it can replace part of the phenolic compounds to participate in chemical reactions. For example, it can undergo a Mannich reaction with polyamines and paraformaldehyde to prepare a new type of Mannich base - modified cardanol aldehyde amine:

[0011]

[0012] In the process of studying modified cardanol aldehyde amine, the inventors of the present invention accidentally found that the lone pair electrons on N and O of the modified cardanol aldehyde amine form coordination bonds with the empty orbitals of atoms on the metal surface, so that the modified cardanol aldehyde amine can be firmly adsorbed on the metal surface, and has a good inhibitory effect on the corrosion of metals in acid solutions. Therefore, the purpose of the present invention is to provide the use of modified cardanol aldehyde amine as a corrosion inhibitor for acid media.

[0013] The technical solution of the present invention is as follows:

[0014] A use of a modified cardanol aldehyde amine as a corrosion inhibitor for acid media, wherein the modified cardanol aldehyde amine having the structure of general formula (1) is directly added to a metal pickling solution as a corrosion inhibitor.

[0015]

[0016] Wherein: R are respectively: CH2CH2NHCH2CH2, (CH2CH2NH)2CH2CH2 or

[0017] The addition amount of the modified cardanol aldehyde amine in the metal pickling solution depends on the acid concentration of the metal pickling solution. The higher the acid concentration, the more the addition amount of the corrosion inhibitor should be. Preferably, the addition amount of the modified cardanol aldehyde amine in the metal pickling solution is 10 ppm to 1%, the preferred addition amount is 50 to 2000 ppm, and the more preferred addition amount is 100 to 500 ppm.

[0018] Preferably, the modified cardanol phenolic amine is used as a pickling inhibitor for carbon steel; the metal pickling solution is at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, citric acid solution, and oxalic acid solution, with a concentration of 1-5 mol / L; preferably a hydrochloric acid solution with a concentration of 1-3 mol / L.

[0019] Further preferably, in a 1.0 mol / L HCl solution, the addition amount of the modified cardanol phenolic amine is 150-400 ppm, more preferably 200-350 ppm.

[0020] The modified cardanol phenolic amine is prepared by the Mannich reaction from cardanol, paraformaldehyde, and organic amine according to a molar ratio of n(phenol):n(aldehyde):n(amine) = 1:(1-2):(1-2); the organic amine is ethylenediamine and / or triethylenetetramine.

[0021] Furthermore, the preparation method of the modified cardanol phenolic amine includes the following steps:

[0022] (1) Stir and heat the cardanol and organic amine in a reactor to 50-60 °C to make them evenly mixed;

[0023] (2) Slowly add the paraformaldehyde to the reactor; after the paraformaldehyde is completely dissolved, add anhydrous ethanol to the reactor to completely dissolve the reaction mixture in anhydrous ethanol; heat to 60-70 °C and react for 5-8 h;

[0024] (3) After the reaction is completed, perform vacuum distillation to remove ethanol, water generated during the reaction, and unreacted amine to obtain a brownish-red transparent liquid, and the obtained product is the modified cardanol phenolic amine corrosion inhibitor.

[0025] Preferably, in step (2), the reaction temperature is 70 °C and the reaction time is 6 h, and the obtained corrosion inhibitor has the best performance. At this time, the yield of the modified cardanol phenolic amine is about 90%.

[0026] Preferably, the amount of anhydrous ethanol is 1-2 times the total molar amount of the reaction mixture.

[0027] The paraformaldehyde should be added in small batches at intervals of at least 10 min to ensure the dissolution of paraformaldehyde and reduce the further condensation of paraformaldehyde.

[0028] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0029] The present invention uses the modified cardanol phenolic amine as a corrosion inhibitor for acid media, which has good environmental protection performance, excellent corrosion inhibition performance, and plays a great role in improving the service life of metal materials in acidic media.

[0030] Furthermore, the preparation method of the modified cardanol phenolic amine of the present invention has a simple process, low reaction temperature, short time, low energy consumption, high yield, good environmental protection performance, and does not use any organic solvents other than ethanol during the production process, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is the relationship between the corrosion inhibition rate of A3 carbon steel in 1.0 mol / L HCl solution obtained by the weight loss method and the inhibitor concentration at different temperatures.

[0032] Figure 2 It is the polarization curve of A3 carbon steel in 1.0 mol / L HCl solution with blank and different concentrations of inhibitor.

[0033] Figure 3 It is the EIS electrochemical parameters of A3 carbon steel tested in 1.0 M HCl solution with blank and different concentrations of inhibitor.

[0034] Figure 4 It is the equivalent circuit diagram.

[0035] Figure 5 It is calculated from the test results of the Langmuir isothermal adsorption model by the weight loss method of the inhibitor.

[0036] Figure 6 It is the plot of ln(W coor ) against 10 3 / T.

[0037] Figure 7 It is the plot of ln(W coor / T) against 10 3 / T.

[0038] Figure 8 It is the SEM image of the apparent morphology of the A3 carbon steel specimen without immersion test.

[0039] Figure 9 It is the SEM image of the apparent morphology of the A3 carbon steel specimen after immersion in 1.0 mol / L HCl solution.

[0040] Figure 10 It is the SEM image of the apparent morphology of the specimen after immersion in 1.0 mol / L HCl solution containing 300 ppm of this inhibitor. DETAILED DESCRIPTION OF THE INVENTION

[0041] Those of ordinary skill in the art of the present technology should recognize that this embodiment is only used to illustrate the present invention and is not used as a limitation to the present invention. As long as changes and variations are made to the embodiment within the scope of the implementation of the present invention, they can all be within the scope of the claims of the present invention.

[0042] Example 1

[0043] Preparation method of modified cardanol phenolic amine corrosion inhibitor for acid medium, comprising the following steps:

[0044] (1) Put 0.2 mol of cardanol and 0.4 mol of ethylenediamine into a four-necked flask equipped with a tetrafluoroethylene stirring paddle, a thermometer and a reflux condenser, stir and heat up to 50 °C, and stir for 20 min to make it uniform;

[0045] (2) Add 0.4 mol of paraformaldehyde to the four-necked flask in batches, with an interval of 10 min between each batch; after the paraformaldehyde is completely dissolved, add 2 mol of absolute ethanol to the four-necked flask to completely dissolve the reaction solution in the solvent; heat up to 60 °C and react for 6 h;

[0046] (3) After the reaction is completed, carry out vacuum distillation to remove ethanol, water generated during the reaction and unreacted amine, and obtain a brownish-red transparent liquid. The obtained product is the modified cardanol phenolic amine corrosion inhibitor.

[0047] Example 2

[0048] Preparation method of modified cardanol phenolic amine corrosion inhibitor for acid medium, comprising the following steps:

[0049] (1) Put 0.2 mol of cardanol and 0.3 mol of ethylenediamine into a four-necked flask equipped with a tetrafluoroethylene stirring paddle, a thermometer and a reflux condenser, stir and heat up to 50 °C, and stir for 20 min to make it uniform;

[0050] (2) Add 0.3 mol of paraformaldehyde to the four-necked flask in batches, with an interval of 10 min between each batch; after the paraformaldehyde is completely dissolved, add 1.5 mol of absolute ethanol to the four-necked flask to completely dissolve the reaction solution in the solvent; heat up to 70 °C and react for 6 h;

[0051] (3) After the reaction is completed, carry out vacuum distillation to remove ethanol, water generated during the reaction and unreacted amine, and obtain a brownish-red transparent liquid. The obtained product is the modified cardanol phenolic amine corrosion inhibitor.

[0052] Example 3

[0053] Preparation method of modified cardanol phenolic amine corrosion inhibitor for acid medium, comprising the following steps:

[0054] (1) Put 0.2 mol of cardanol and 0.35 mol of ethylenediamine into a four-necked flask equipped with a tetrafluoroethylene stirring paddle, a thermometer and a reflux condenser, stir and heat up to 50 °C, and stir for 20 min to make it uniform;

[0055] (2) Add 0.35 mol of paraformaldehyde to the four-necked flask in batches, with an interval of 10 min between each batch; after the paraformaldehyde is completely dissolved, add 2 mol of absolute ethanol to the four-necked flask to completely dissolve the reaction solution in the solvent; raise the temperature to 60 °C and react for 6 h;

[0056] (3) After the reaction is completed, perform vacuum distillation to remove ethanol, water generated during the reaction, and unreacted amine, and obtain a brownish-red transparent liquid. The obtained product is the modified cashew phenol aldehyde amine corrosion inhibitor.

[0057] Example 4

[0058] A preparation method of a modified cashew phenol aldehyde amine corrosion inhibitor for acid medium, comprising the following steps:

[0059] (1) Place 0.2 mol of cashew phenol and 0.25 mol of ethylenediamine in a four-necked flask equipped with a tetrafluoroethylene stirring paddle, a thermometer, and a reflux condenser, stir and raise the temperature to 50 °C, and stir for 20 min to make it uniform;

[0060] (2) Add 0.25 mol of paraformaldehyde to the four-necked flask in batches, with an interval of 10 min between each batch; after the paraformaldehyde is completely dissolved, add 1 mol of absolute ethanol to the four-necked flask to completely dissolve the reaction solution in the solvent; raise the temperature to 60 °C and react for 6 h;

[0061] (3) After the reaction is completed, perform vacuum distillation to remove ethanol, water generated during the reaction, and unreacted amine, and obtain a brownish-red transparent liquid. The obtained product is the modified cashew phenol aldehyde amine corrosion inhibitor.

[0062] Example 5

[0063] A preparation method of modified cashew phenol aldehyde amine, comprising the following steps:

[0064] (1) Place 0.15 mol of cashew phenol and 0.25 mol of ethylenediamine in a four-necked flask equipped with a tetrafluoroethylene stirring paddle, a thermometer, and a reflux condenser, stir and raise the temperature to 50 °C, and stir for 20 min to make it uniform;

[0065] (2) Add 0.25 mol of paraformaldehyde to the four-necked flask in batches, with an interval of 10 min between each batch; after the paraformaldehyde is completely dissolved, add 2 mol of absolute ethanol to the four-necked flask to completely dissolve the reaction solution in the solvent; raise the temperature to 60 °C and react for 6 h;

[0066] (3) After the reaction is completed, perform vacuum distillation to remove ethanol, water generated during the reaction, and unreacted amine, and obtain a brownish-red transparent liquid. The obtained product is the modified cashew phenol aldehyde amine corrosion inhibitor.

[0067] Example 6

[0068] The modified cardanol phenolic amine of Example 1 was diluted in 1.0 mol / L HCl solution at different concentrations, and the corrosion inhibition efficiency of the modified cardanol phenolic amine as a corrosion inhibitor for A3 carbon steel was tested at different temperatures: the concentration gradients of the modified cardanol phenolic amine in the hydrochloric acid solution were: 50 ppm, 100 ppm, 150 ppm, 200 ppm, and 300 ppm; then the A3 carbon steel specimens were completely immersed in the hydrochloric acid solution containing different concentrations of corrosion inhibitor and the blank hydrochloric acid solution, and kept at a constant temperature for 9 h; after taking out the specimens, the surface corrosion products were removed with a brush, rinsed with tap water, then wiped with anhydrous ethanol, then dried with filter paper, and finally dried with natural air and weighed. Table 1 shows the influence of corrosion inhibitors with different concentrations at different temperatures on the corrosion inhibition rate of A3 carbon steel in 1.0 mol / L HCl solution.

[0069] 1. Weight loss method

[0070] The steel specimens used in the experiment were A3 carbon steel specimens, and their main element compositions were: 0.14 - 0.2% C, 0.3 - 0.7% Mn, 0.3% Si, 0.045% S, 0.045% P, and Fe; the size of the A3 carbon steel specimens was 4.0×1.3×0.2 cm 3 . Before each experiment, all A3 carbon steel specimens were polished with different grades of metallographic sandpaper (600, 800, and 1200 mesh), degreased with acetone scrubbing, finally scrubbed clean with deionized water and anhydrous ethanol, dried with filter paper, and then sealed and stored.

[0071] The acidic medium used in the experiment was 1.0 mol / L HCl solution (abbreviated as 1.0 M HCl solution), which was prepared by diluting 88.3 mL of 37% AR concentrated hydrochloric acid to a 1000 mL volumetric flask.

[0072] The corrosion inhibition rate (%IE) and coverage rate (θ) can be calculated respectively by formulas (1) and (2):

[0073]

[0074] In formulas (1) and (2), w0 is the corrosion rate of carbon steel in the blank experiment, and w i is the corrosion rate of A3 carbon steel after adding different concentrations of corrosion inhibitor.

[0075] The corrosion rate (CR(W), unit mg·cm -2 ·h -1 ) is calculated by the following formula (3):

[0076]

[0077] In formula (3), Δm is the average value of weight loss (mg), S is the surface area of the A3 carbon steel specimen (cm 2 ), and t is the immersion time (h).

[0078] Table 1

[0079]

[0080] Figure 1 shows the relationship between the corrosion inhibition rate of A3 carbon steel in 1.0 M HCl solution obtained by the weight loss method and the inhibitor concentration at different temperatures. It can be seen from Figure 1 that as the inhibitor concentration increases, the corrosion inhibition rate %IE shows a gradually increasing trend at all temperatures; and it tends to be stable after 200 ppm, which confirms that the inhibitor has a good corrosion inhibition effect on the corrosion of A3 carbon steel in 1.0 mol / L HCl solution. When the inhibitor concentration reaches 300 ppm, the corrosion inhibition rate basically does not change, indicating that the protective film formed by the inhibitor molecules completely covers the metal surface, and the protection of the film reaches the best state at this concentration, thus making the corrosion inhibition rate reach the highest.

[0081] As the temperature increases, the corrosion inhibition rate %IE changes significantly when the inhibitor concentration is 50 ppm, mainly because there are not enough inhibitor molecules adsorbed on the A3 carbon steel specimen; while when the inhibitor concentration reaches 100 - 300 ppm, within this concentration range, the adsorption rate of the inhibitor on the metal surface is higher than the desorption rate, and the inhibitor molecules on the A3 carbon steel specimen are already close to saturation. At this time, as the temperature increases, the corrosion inhibition rate %IE only changes slightly.

[0082] After the experiment, observing the surface of the A3 carbon steel specimen after corrosion immersion in the blank and 1.0 M HCl solution containing different concentrations of inhibitor, it can be found that a layer of black corrosion substance appears on the surface of the A3 carbon steel specimen in the blank group. When scrubbing with a brush, it can be found that these corrosion substances are very easy to detach from the specimen surface, and the surface of the rinsed specimen completely turns black, which can obviously show that the corrosion of the specimen surface is very serious, and as the temperature increases, the corrosion will be more serious. The addition of the inhibitor makes the surface of the A3 carbon steel specimen not show the black corrosion products in the blank group, but dark strip-shaped corrosion patterns; and as the concentration of the inhibitor increases, the dark stripes generated by corrosion gradually decrease, and the pitting phenomenon also decreases accordingly. When the inhibitor concentration reaches 300 ppm, the surface of the A3 carbon steel specimen obtained after the experiment is very bright with few dark lines, and it can be observed from Table 1 that at this concentration, the corrosion inhibition rate is as high as 98%, and as the inhibitor concentration further increases, its corrosion inhibition rate does not change significantly, which is mainly due to the fact that the adsorption of the inhibitor molecules on the A3 carbon steel surface is close to saturation. As the inhibitor concentration increases, the corrosion rate of A3 carbon steel in the corrosive medium continuously decreases.

[0083] 2. Electrochemical Tests

[0084] The modified cardanol phenolic amine of Example 1 was diluted in 1.0 M HCl solution at different concentrations, and the corrosion inhibition efficiency of the modified cardanol phenolic amine as a corrosion inhibitor for A3 carbon steel at different temperatures was tested electrochemically:

[0085] The concentration gradients of the modified cardanol phenolic amine in the hydrochloric acid solution were: 50 ppm, 100 ppm, 150 ppm, 200 ppm, and 300 ppm; then the A3 carbon steel specimens were completely immersed in the hydrochloric acid solutions containing different concentrations of corrosion inhibitor and the blank hydrochloric acid solution, and kept at a constant temperature for 9 h; after taking out the specimens, the surface corrosion products were removed with a brush, rinsed with tap water, then wiped with anhydrous ethanol, and then dried with filter paper and natural air, and then weighed.

[0086] Both the polarization Tafel curve and the electrochemical impedance spectroscopy curve were measured by a PARSTAT2273 electrochemical workstation. The test used a three-electrode system, including a reference electrode (saturated calomel electrode), a counter electrode (platinum electrode), and a working electrode (a 1.0×1.0×0.2 cm 3 A3 carbon steel specimen. Copper wires were welded to the surface of the specimen, and the specimen was sealed with epoxy resin, leaving only 1 cm 2 of the surface exposed to the corrosive medium). In all tests, the three-electrode system was in direct contact with air. During the test, the 1 cm 2 platinum electrode should be parallel to the working electrode. And before all electrochemical tests, the working electrode system must be immersed in the test solution for 60 min to obtain a stable open-circuit potential (OCP). In the test of the Tafel curve, the scanning potential amplitude was from -250 mV to +250 mV, and the scanning speed was 5 mV. The test frequency in the EIS test was from 100 kHz to 10 mHz, and the amplitude of the alternating current signal was 10 mV. The impedance spectrogram obtained was a Nyquist curve, and fitting analysis was carried out through software.

[0087] At room temperature, the polarization (Tafel) curves of A3 carbon steel in the blank and 1.0 M HCl solutions containing different concentrations of corrosion inhibitor were tested, as Figure 2 shown. The corrosion potential E coor , corrosion current I coor , anodic polarization curve Tafel slope b a , cathodic polarization curve Tafel slope b c and other parameters can be obtained from the figure, and the corrosion inhibition rate was calculated according to the following formula (4), and the results are listed in Table 2.

[0088]

[0089] In the formula, I coor(b) and I coor(i) are the corrosion current densities in the blank and in the presence of different concentrations of the corrosion inhibitor, respectively.

[0090] Table 2 Electrochemical parameters of the polarization curves obtained for A3 carbon steel in 1.0 M HCl solution in the blank and in the presence of different concentrations of the corrosion inhibitor

[0091]

[0092] From Figure 2 and Table 2, it can be seen that the corrosion current density I coor decreases significantly with the increase in the concentration of the corrosion inhibitor; on the contrary, the inhibition efficiency %IE increases with the increase in the concentration of the corrosion inhibitor. When the offset value ΔE coor of the corrosion potential E coor is greater than 85 mV, the organic substance can be classified as an anodic or cathodic corrosion inhibitor. From Table 2, it can be seen that E coor shifts towards the positive direction, and the maximum value of ΔE coor is 51.0 mV, which is less than 85 mV. Therefore, it is proved that the corrosion inhibitor of the present invention is a mixed-type corrosion inhibitor. In addition, with the increase in the concentration of the corrosion inhibitor, the slope b c of the Tafel cathodic curve increases from 52 mV / dec to 133 mV / dec, while the slope b a of the Tafel anodic curve decreases from 63 mV / dec to 46 mV / dec, further proving that the corrosion inhibitor of the present invention is a mixed-type corrosion inhibitor. However, the increase value of b c is significantly higher than the decrease value of b a , indicating that the influence of this corrosion inhibitor on the hydrogen evolution reaction is stronger than that on the anodic metal dissolution reaction. Therefore, the modified cardanol phenolic amine as a corrosion inhibitor is a mixed-type corrosion inhibitor biased towards the cathodic reaction. It can be calculated from the corrosion current density obtained from the Tafel curve that the inhibition efficiency increases with the increase in the concentration of this corrosion inhibitor and reaches a maximum value of 96.0% at 300 ppm.

[0093] Figure 3 is the Nyquist curve of A3 carbon steel in 1.0 M HCl solution in the blank and in the presence of different concentrations of the corrosion inhibitor at room temperature. It can be clearly seen from the figure that the Nyquist curves of A3 carbon steel in the inhibited and non-inhibited solutions are both semicircular rather than circular, indicating that the corrosion process is mainly related to charge transfer. The formed Nyquist curve is elliptical mainly due to the inhomogeneity of the working electrode surface caused by the rough surface and interfacial action. Although the shapes of the individual curves in the Nyquist curve are similar, the diameter of the curve increases with the increase in the concentration of the corrosion inhibitor. The Randle's equivalent circuit diagram selected for this system is asFigure 4 as shown, where R s is the solution resistance, R ct is the charge transfer resistance, and C dl is the double-layer capacitance.

[0094] The inhibition efficiency (%IE) is calculated by Equation (5):

[0095]

[0096] In the formula, R ct(b) and R ct(i) are the charge transfer resistances in the blank and in the presence of different concentrations of the inhibitor, respectively.

[0097] The double-layer resistance (C dl ) is calculated by the following Equation (6):

[0098]

[0099] In the formula, f max is the maximum frequency in the Nyquist curve.

[0100] Table 3 shows the charge transfer resistance R ct , the double-layer resistance C dl , and the inhibition efficiency obtained from the Nyquist curve. It can be found from Table 3 that the addition of the modified cardanol phenolic amine as an inhibitor leads to an increase in the charge transfer resistance and a decrease in the double-layer resistance. This is because after the addition of the inhibitor, a protective film is formed on the surface of the A3 carbon steel specimen, isolating the reactive sites, hindering the transfer of charges from the metal surface to the corrosion medium, and resulting in an increase in the charge transfer resistance R ct . The decrease in the double-layer resistance C dl is due to the low dielectric constant of the inhibitor. After it forms a protective film on the metal surface, the local dielectric constant decreases, and the thickness of the double-layer also increases. The above conclusions all prove that the inhibitor molecules produce an inhibitory effect by replacing water molecules adsorbed at the metal / solution interface.

[0101] Table 3 Electrochemical impedance spectroscopy (EIS) parameters of A3 carbon steel tested in blank and 1.0 M HCl solutions containing different concentrations of inhibitor

[0102] C (ppm) <![CDATA[Rct (Ω·cm 2 )]]> <![CDATA[Cdl(μF·cm -2 )]]> % IE θ 0 94 43.66 - - 50 950 13.48 90.1 0.901 100 1050 8.58 91.0 0.910 150 1150 7.62 91.8 0.918 200 1450 6.34 93.5 0.935 300 1528 6.02 93.8 0.938

[0103] 3. Adsorption mode

[0104] The interaction between the inhibitor molecules and the surface of A3 carbon steel is called the adsorption isotherm equation. The inhibitor molecules replace the water molecules and adsorb on the metal surface, thus achieving the corrosion inhibition effect. To verify the adsorption mode of the inhibitor, in this invention, the data in Table 1 were used to fit three isothermal adsorption modes: Langmuir, Frumkin, and Temkin. The results show that the adsorption on the surface of A3 carbon steel follows the Langmuir adsorption isotherm equation. Plotting the inhibitor concentration C against C / θ gives a straight line, as Figure 5 shown.

[0105] The calculated data are shown in Table 4. The adsorption free energy (ΔG ads ) is negative, indicating that the adsorption process of the inhibitor on the surface of A3 carbon steel is spontaneous and there is a strong interaction between the inhibitor molecules and the metal surface. Generally, when ΔG ads is greater than -20 KJ·mol -1 , the adsorption of the inhibitor molecules on the metal surface is a physical adsorption. When ΔG ads is less than -40 KJ·mol -1 , the inhibitor molecules are adsorbed on the metal surface through chemical adsorption. In this process, the organic molecules form coordination bonds by transferring electrons to the metal surface or sharing electrons with the metal surface atoms. In this study, the calculated free energy ΔG ads is greater than -20 KJ·mol -1 , indicating that the adsorption process of this inhibitor on the metal surface belongs to physical adsorption. An endothermic adsorption process is obviously chemical adsorption, while an exothermic adsorption process can be physical adsorption or chemical adsorption, or it may be a combination of both. As can be seen from Table 4, the enthalpy change of adsorption (ΔH ads ) is positive, meaning that the adsorption process is endothermic, indicating that this inhibitor is adsorbed on the metal surface through chemical action. Therefore, it can be determined that this inhibitor is a complex mixed-type inhibitor, with both physical adsorption and chemical adsorption. And the entropy change ΔS ads is positive, indicating an increase in the degree of disorder during the formation of the adsorption of the inhibitor molecules on the metal surface in the HCl solution.

[0106] Table 4 Adsorption parameters of the inhibitor on the surface of A3 carbon steel in 1.0 M HCl solution at different temperatures

[0107]

[0108] 4. Influence of temperature on adsorption

[0109] This patent calculates the activation energy of the corrosion process and observes the corrosion inhibition mechanism. From the results of the weight loss method test, it can be found that the corrosion rates of steel in pure acid solution and acid solution containing inhibitors both increase with the increase of temperature. The dependence of the corrosion rate on temperature can be demonstrated by the Arrhenius equation. At different temperatures, the thermodynamic activation parameters (activation energy E a , activation entropy ΔS, activation enthalpy ΔH) of A3 carbon steel specimens in blank and 1.0 M HCl solutions containing different concentrations of corrosion inhibitors can be calculated by the Arrhenius equations (7) and (8):

[0110]

[0111] In the formula, W coor is the corrosion rate, A is the Arrhenius constant, E a is the activation energy, R is the universal gas constant, T is the absolute temperature, N A is the Avogadro constant, h is the Planck constant, ΔS is the activation entropy, and ΔH is the activation enthalpy.

[0112] Table 5 Thermodynamic parameters of corrosion inhibitors on the surface of A3 carbon steel in 1.0 M HCl solution at different temperatures

[0113] C (ppm) <![CDATA[E a (KJ·mol -1 )]]> <![CDATA[ΔH(KJ·mol -1 )]]> <![CDATA[ΔS (J·mol -1 ·K -1 )]]> 0 43.56 41.00 -105.22 50 79.19 76.64 -108.58 100 45.00 42.39 -125.91 150 41.57 38.96 -171.18 200 37.75 35.01 -153.78 300 35.80 33.23 -160.66

[0114] According to the above formula, ln(W coor ) and ln(W coor / T) are plotted against 10 3 / T respectively, as shown in Figure 6 , 7 . In the obtained straight lines, the slopes are -E a / R and -ΔH / R respectively, and the intercepts are A and [ln(R / Nh)+(ΔS / R)] respectively. Thus, ΔH and ΔS after adding different concentrations of corrosion inhibitors are calculated, as shown in Table 5. The positive value of ΔH indicates that the dissolution process of the metal is a spontaneous endothermic process. It can be seen from Table 5 that the values of ΔH and E a increase with the addition of the corrosion inhibitor, reflecting that the energy barrier of the corrosion reaction increases with the addition of the corrosion inhibitor. However, when the concentration of the corrosion inhibitor is in the range of 150 - 300 ppm, the values of ΔH and E a show a decreasing trend. Such results have also appeared in other studies. The value of E a in the corrosion process containing the corrosion inhibitor is lower than that in the pure acid solution because the corrosion inhibitor is adsorbed on the steel surface through chemical action, including the charge distribution or charge transfer of the corrosion inhibitor molecules on the carbon steel surface.

[0115] In summary, it can be known that when the inhibitor concentration is in the range of 50 - 100 ppm, its adsorption is mainly physical adsorption, while when it is in the range of 150 - 300 ppm, it is mainly chemical adsorption. ΔS is negative both before and after adding the inhibitor, indicating that adsorption is the rate-determining step rather than desorption, and the degree of disorder decreases during the formation of the activated complex by the inhibitor molecules. In addition, with the addition of the inhibitor, the absolute value of the entropy change ΔS decreases, indicating that the presence of the inhibitor makes the system approach a state close to corrosion equilibrium.

[0116] 5. SEM Surface Morphology Analysis

[0117] According to the weight loss method, when the concentration of the modified cardanol phenolic amine in Example 1 as an inhibitor reaches 300 ppm, the inhibition rate reaches the maximum value. Therefore, A3 carbon steel specimens with a size of 1.0×1.0 cm 2 were immersed in blank and 1.0 M HCl solution containing 300 ppm inhibitor at 318 K for 9 h; the specimens were taken out, the corrosion products on the surface were removed with a brush, then rinsed with deionized water, wiped with anhydrous ethanol, and dried at room temperature after being blotted dry with filter paper. In the experiment, the SEM morphology of the specimen surface was photographed using a HITACHI scanning electron microscope (Model S-4800 FES).

[0118] Figures 8 - 10 are SEM pictures, including an untested A3 carbon steel specimen ( Figure 8 ), an A3 carbon steel specimen immersed and tested in blank 1.0 mol / L HCl solution ( Figure 9 ), and an A3 carbon steel specimen immersed in 1.0 mol / L HCl solution containing 300 ppm inhibitor ( Figure 10 ). As can be seen from Figure 9 , in the blank test without inhibitor, the surface of the A3 carbon steel specimen is rough, showing a typical uniform corrosion phenomenon, indicating that the acidic environment completely destroys the surface of the A3 carbon steel. Figure 10 As can be seen from

[0119] Example 8

[0120] The modified cardanol phenolic amine in Example 2 was used as an inhibitor and diluted in 1.0 mol / L HCl solution at different concentrations to test the corrosion inhibition efficiency for A3 carbon steel at a temperature of 338 K.

[0121] Table 6 Influence of Corrosion Inhibitors with Different Concentrations on the Corrosion Inhibition Rate of A3 Carbon Steel in 1.0 mol / L HCl Solution

[0122]

[0123] Example 9

[0124] Take the modified cashew phenol aldehyde amine in Example 3 as the corrosion inhibitor, dilute it in 1.0 mol / L HCl solution according to different concentrations, and test the corrosion inhibition efficiency on A3 carbon steel at 338 K.

[0125] Table 7 Influence of Corrosion Inhibitors with Different Concentrations on the Corrosion Inhibition Rate of A3 Carbon Steel in 1.0 mol / L HCl Solution

[0126]

[0127] Example 10

[0128] Take the modified cashew phenol aldehyde amine in Example 4 as the corrosion inhibitor, dilute it in 1.0 mol / L HCl solution according to different concentrations, and test the corrosion inhibition efficiency on A3 carbon steel at 338 K.

[0129] Table 8 Influence of Corrosion Inhibitors with Different Concentrations on the Corrosion Inhibition Rate of A3 Carbon Steel in 1.0 mol / L HCl Solution

[0130]

[0131] Example 11

[0132] Take the modified cashew phenol aldehyde amine in Example 5 as the corrosion inhibitor, dilute it in 1.0 mol / L HCl solution according to different concentrations, and test the corrosion inhibition efficiency on A3 carbon steel at 338 K.

[0133] Table 9 Influence of Corrosion Inhibitors with Different Concentrations on the Corrosion Inhibition Rate of A3 Carbon Steel in 1.0 mol / L HCl Solution

[0134]

[0135] It can be seen from Tables 6 - 9 that as the concentration of the corrosion inhibitors in Examples 2 - 5 increases, the corrosion inhibition rate %IE shows a gradually increasing trend at all temperatures, confirming that cashew phenol polyethylenediamine has a good corrosion inhibition effect on the corrosion of A3 carbon steel in 1.0 mol / L HCl solution; when the concentration of the corrosion inhibitor reaches 300 ppm, the change in the corrosion inhibition rate slows down, indicating that the protective film formed by the corrosion inhibitor molecules completely covers the metal surface, and the protection of the film on the metal gradually reaches the best state at this concentration.

Claims

1. The use of modified cardanol aldehyde amine as a corrosion inhibitor for acid medium, characterized in that: The modified cardanol aldehyde amine having the structure of general formula (1) is directly added to the metal pickling solution as a corrosion inhibitor. Where: R is: CH2CH2NHCH2CH2, (CH2CH2NH)2CH2CH2 or 2. The use of the modified cardanol aldehyde amine according to claim 1 as a corrosion inhibitor for acid medium, characterized in that: The modified cardanol aldehyde amine is added in an amount of 10ppm to 1% in the metal pickling solution.

3. The use of the modified cardanol aldehyde amine according to claim 1 as a corrosion inhibitor for acid medium, characterized in that: The modified cardanol aldehyde amine is added in an amount of 50 to 2000 ppm in the metal pickling solution.

4. The use of the modified cardanol aldehyde amine according to claim 1 as a corrosion inhibitor for acid medium, characterized in that: The modified cardanol aldehyde amine is added in an amount of 100 to 500 ppm in the metal pickling solution.

5. The use of the modified cardanol aldehyde amine according to claim 1 as a corrosion inhibitor for acid medium, characterized in that: The modified cashew phenol aldehyde amine is used as a pickling corrosion inhibitor for carbon steel; the metal pickling solution is at least one of hydrochloric acid solution, sulfuric acid solution, nitric acid solution, citric acid solution, and oxalic acid solution, and the concentration is 1 to 5 mol / L.

6. The use of the modified cardanol aldehyde amine according to claim 1 as a corrosion inhibitor for acid medium, characterized in that: In a 1.0 mol / L HCl solution, the added amount of the modified cardanol aldehyde amine is 150 to 400 ppm, and more preferably 200 to 350 ppm.

7. The use of the modified cardanol aldehyde amine according to claim 1 as a corrosion inhibitor for acid medium, characterized in that: The modified cardanol aldehyde amine is prepared by Mannich reaction of cardanol, polyformaldehyde and organic amine in a molar ratio of n(phenol):n(aldehyde):n(amine)=1:(1-2):(1-2); the organic amine is ethylenediamine and / or triethylenetetramine.

8. Use of the modified cardanol aldehyde amine according to any one of claims 1 to 7 as a corrosion inhibitor for acid medium, characterized in that: The preparation method of the modified cardanol aldehyde amine comprises the following steps: (1) heating the cardanol and the organic amine to 50-60° C. in a reactor while stirring to mix them evenly; (2) slowly adding the paraformaldehyde into the reactor; after the paraformaldehyde is completely dissolved, adding anhydrous ethanol into the reactor to completely dissolve the reaction mixture in the anhydrous ethanol; heating to 60-70° C. and reacting for 5-8 hours; (3) After the reaction is completed, vacuum distillation is performed to remove ethanol, water produced during the reaction, and unreacted amine to obtain a brown-red transparent liquid. The obtained product is a modified cashew phenol amine corrosion inhibitor.

9. The use of the modified cardanol aldehyde amine according to claim 8 as a corrosion inhibitor for acid medium, characterized in that: In step (2), the reaction temperature is 70° C. and the reaction time is 6 h. The corrosion inhibitor obtained has the best performance. At this time, the yield of modified cashew phenol aldehyde amine is about 90%.

10. The use of the modified cardanol aldehyde amine according to claim 8 as a corrosion inhibitor for acid medium, characterized in that: The amount of the anhydrous ethanol is 1 to 2 times the total molar amount of the reaction mixture.

Images