CN108754510B

CN108754510B - Composite pickling corrosion inhibitor containing Schiff base and preparation method thereof

Info

Publication number: CN108754510B
Application number: CN201810651109.XA
Authority: CN
Inventors: 文家新
Original assignee: Chongqing Industry Polytechnic College
Current assignee: Chongqing Industry Polytechnic College
Priority date: 2018-06-22
Filing date: 2018-06-22
Publication date: 2020-10-09
Anticipated expiration: 2038-06-22
Also published as: CN108754510A

Abstract

The invention belongs to the technical field of carbon steel pickling, and discloses a composite pickling corrosion inhibitor containing Schiff base and a preparation method thereof. The composite corrosion inhibitor provided by the invention has excellent corrosion inhibition performance on carbon steel metal in 0.5M hydrochloric acid washing liquor, the corrosion inhibition efficiency can reach more than 94%, the consumption of the corrosion inhibitor is small, and the defects of a single methionine corrosion inhibitor in the using process are overcome.

Description

Composite pickling corrosion inhibitor containing Schiff base and preparation method thereof

Technical Field

The invention belongs to the technical field of carbon steel pickling, and particularly relates to a composite corrosion inhibitor and a preparation method thereof, in particular to a methionine Schiff base derivative 2- (N-picolylimide) -4-methylthiobutyric acid (MD) and sodium carboxymethylcellulose (MD) compound corrosion inhibitor and a preparation method thereof.

Background

Acid washing is one of the important methods for chemical cleaning, and is widely applied to scale removal and rust removal processes of carbon steel equipment (including boilers, power systems, heat exchangers and the like) and parts thereof due to the characteristics of high speed, high efficiency and the like. Hydrochloric acid, which is the most commonly used acid for pickling, can dissolve a carbon steel substrate while chemically reacting with scale or rust on the metal surface, and corrode equipment and parts thereof to different degrees, thereby not only affecting industrial production efficiency, but also having potential safety hazards. A corrosion inhibitor is a chemical substance or compound that is present in the environment (medium) in a suitable concentration and form to slow or prevent corrosion. The corrosion inhibitor is the most main anticorrosion measure in the pickling process, and has the advantages of low cost, simple and convenient process, strong applicability, good protection effect and the like, so the corrosion inhibitor is widely applied to the field of metal pickling. The amino acid substance has hydrophilic amino group, carboxyl group, hydrophobic substituent group and other groups, and has the advantages of no toxicity and harm to environment, good water solubility, good corrosion inhibition effect, low cost and the like, so that the amino acid substance is widely used as a metal corrosion inhibitor. Methionine (Met) is a sulfur-containing amino acid, S, N atoms contained in the methionine have potential corrosion inhibition performance on metal materials in an acid solution, and the methionine has the advantage of an amino acid corrosion inhibitor, and is a green corrosion inhibitor with great development potential. The corrosion inhibition performance of methionine can be effectively improved by introducing polar groups or hydrophobic groups containing N, O, S atoms into methionine molecules, and various groups are connected into the methionine molecules through amidation reaction on amino or carboxyl in the conventional synthesis method, but the method has the defects of harsh reaction conditions, complex steps, expensive reagents, high toxicity and the like, and the application development of the method is limited. In addition, with the improvement of corrosion control requirements and the progress of corrosion inhibitor technology, if several corrosion inhibitors are compounded for use, the synergistic effect of the corrosion inhibitors is utilized, so that higher corrosion inhibition efficiency can be obtained by using less corrosion inhibitors. However, the research on the methionine compound corrosion inhibition system mainly focuses on the synergistic corrosion inhibition performance between methionine and other amino acids, between methionine and organic small molecules or inorganic compounds, and few research reports exist on the synergistic corrosion inhibition performance between methionine and organic high molecules.

In summary, the problems of the prior art are as follows:

(1) the single methionine is used as the carbon steel pickling corrosion inhibitor, and the corrosion inhibition efficiency is low due to the defects of simple molecular structure, insufficient adsorption on the metal surface and the like, so that the requirement of practical application cannot be met.

(2) When methionine is used as a carbon steel pickling corrosion inhibitor, a large amount of addition is often needed to obtain high corrosion inhibition efficiency, so that the cost is increased, the resource waste and the environmental pollution are caused, and the development and application of methionine as the corrosion inhibitor are limited.

(3) At present, the synthesis method of methionine derivatives by accessing various groups through amidation reaction has the defects of harsh reaction conditions, complex steps, expensive reagents, high toxicity and the like, and limits the application development of the methionine derivatives.

(4) The methionine composite corrosion inhibition system mainly focuses on synergistic corrosion inhibition between methionine and other amino acids, between methionine and small organic molecules or between methionine and inorganic compounds, and the composite corrosion inhibition systems generally have the problems of low corrosion inhibition efficiency, high toxicity of compounded compounds, high price and the like, and cannot meet the requirements of practical application.

The difficulty and significance for solving the technical problems are as follows:

firstly, the Schiff base contains a special structure of C ═ N double bonds, has good coordination capacity, can form a complex with a transition metal, can be firmly adsorbed on the metal surface, and effectively inhibits corrosion. In addition, according to the research on the relationship between the structure and the physical properties, the molecules containing atoms with larger electronegativity (such as N, O, S and other atoms) can provide lone electron pairs, and can just act with the d orbitals of metals to form a protective film on the surface; therefore, the methionine Schiff base derivative containing pyridine groups is synthesized, the corrosion inhibition performance of methionine can be obviously improved, meanwhile, the synthesis process of the Schiff base is simple, the operability is high, the synthesis cost is low, the defect of the existing methionine derivative synthesis can be effectively overcome, and the methionine Schiff base derivative has a high market application value.

And secondly, the sodium carboxymethylcellulose (CMC) is an organic high molecular compound, is nontoxic and harmless, has low cost, contains a large amount of polar groups (hydroxyl, carboxyl and the like), can be adsorbed on the surface of metal, makes up the defects of the corrosion inhibition film of the methionine Schiff base derivative, enhances the compactness of the corrosion inhibitor adsorption film, forms a synergistic corrosion inhibition effect, and further improves the corrosion inhibition performance, so that less corrosion inhibitors obtain higher corrosion inhibition efficiency, the consumption of the corrosion inhibitors of the methionine Schiff base derivative is reduced, and the CMC is of great significance for promoting the industrial application of the corrosion inhibitors of the methionine Schiff base derivative.

Disclosure of Invention

Aiming at the problems in the prior art, the invention provides a composite pickling corrosion inhibitor containing Schiff base and a preparation method thereof.

The preparation method of the methionine Schiff base derivative and the composite corrosion inhibitor of the methionine Schiff base derivative and sodium carboxymethyl cellulose comprises the following steps:

step one, adding 60mL of trichloromethane solution into a three-neck flask provided with an oil bath heating and magnetic stirring device, then adding 5.35g of pyridine-2-formaldehyde (PCD) and 7.45g of methionine (Met) into the flask, starting magnetic stirring, and heating and refluxing for 1h until the solid is completely dissolved;

step two, dropwise adding 5 drops of glacial acetic acid into a reaction flask to serve as a catalyst, adjusting the pH value of reaction liquid, continuously heating and refluxing for reaction for 24 hours, then stirring at room temperature for reaction for 2 hours, then putting the reaction liquid into a refrigerator for cooling and crystallization, carrying out reduced pressure suction filtration to remove a solvent to obtain a brown yellow solid, recrystallizing a product with methanol, and carrying out vacuum drying to obtain the methionine Schiff base derivative 2- (N-picolylamine) -4-methylthiobutyric acid (MD);

and step three, taking the methionine Schiff base derivative (MD) and the sodium carboxymethyl cellulose (CMC) according to a ratio of 4:3, and compounding to obtain the high-efficiency composite corrosion inhibitor.

Further, in the step one: 0.05mol of pyridine-2-formaldehyde; methionine 0.05 mol.

Further, the synthesis reaction equation of the methionine Schiff base derivative 2- (N-picolyl imine) -4-methylthio butyric acid is as follows:

the invention also aims to provide the composite pickling corrosion inhibitor prepared by the preparation method of the composite pickling corrosion inhibitor containing Schiff base, the corrosion inhibitor is prepared by compounding a methionine Schiff base derivative 2- (N-picolylimide) -4-methylthiobutyric acid (MD) and sodium carboxymethylcellulose (MD) according to the mass ratio of 4:3, the corrosion inhibitor has excellent hydrochloric acid pickling corrosion inhibition performance on carbon steel equipment, the corrosion inhibition efficiency can reach more than 94%, the consumption is low, and the defects of a single methionine corrosion inhibitor in the using process are overcome.

Another object of the present invention is to provide a boiler corrosion prevention compound prepared from the heat exchanger.

Another object of the present invention is to provide a power system corrosion protection composite prepared from the heat exchanger.

Another object of the present invention is to provide a heat exchanger corrosion prevention compound prepared from the heat exchanger.

In summary, the advantages and positive effects of the invention are:

the corrosion inhibition performance of the corrosion inhibitor on carbon steel metal materials in 0.5M hydrochloric acid washing liquor is inspected by adopting a weight loss method and a polarization curve method, and the corrosion morphology of a carbon steel sample is observed by a metallographic microscope, so that the result shows that the composite corrosion inhibitor has excellent corrosion inhibition performance on carbon steel metal in 0.5M hydrochloric acid washing liquor, the corrosion inhibition efficiency can reach more than 94%, the consumption of the corrosion inhibitor is small, and the defects of a single methionine corrosion inhibitor in the using process are overcome. The Schiff base compound is prepared by introducing a pyridine ring into methionine molecules, so that electron-rich groups containing atoms such as N, O on the methionine molecules are increased, the adsorption capacity of the compound on the surface of carbon steel is further enhanced, and the corrosion inhibition performance of the compound on the carbon steel is improved. The high-efficiency metal composite corrosion inhibitor is prepared by compounding 2- (N-picolylamine) -4-methylthiobutyric acid and sodium carboxymethylcellulose in proportion by utilizing good corrosion inhibition synergistic effect between the 2- (N-picolylamine) -4-methylthiobutyric acid and the sodium carboxymethylcellulose.

Drawings

FIG. 1 is a flow chart of a preparation method of a composite pickling corrosion inhibitor containing Schiff base according to an embodiment of the invention.

FIG. 2 is a plot of the tafel polarization of carbon steel in 0.5M HCl washes containing different corrosion inhibition systems as provided by an example of the present invention.

FIG. 3 is a metallographic representation of the surface shape of a carbon steel coupon after 24 hours immersion in a 0.5M HCl bath containing no corrosion inhibitor or different corrosion inhibitors as provided by an example of the present invention;

in the figure: (a) blank sample; (b) no corrosion inhibitor is contained; (c) contains 40mg/L Met; (d) it contains 40mg/L MD +30 mg/LCMC.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The composite pickling corrosion inhibitor containing Schiff base is prepared by reacting methionine with pyridine-2-formaldehyde to prepare a methionine Schiff base derivative 2- (N-picolylimide) -4-methylthiobutyric acid, and then compounding the methionine Schiff base derivative with sodium carboxymethylcellulose.

As shown in fig. 1, a preparation method of a composite pickling inhibitor containing Schiff base according to an embodiment of the present invention includes the following steps:

s101: adding 60mL of trichloromethane solution into a three-neck flask provided with an oil bath heating and magnetic stirring device, then adding 5.35g of pyridine-2-formaldehyde (PCD) and 7.45g of methionine (Met) into the flask, starting magnetic stirring, and heating and refluxing for 1h until the solid is completely dissolved;

s102: dropwise adding 5 drops of glacial acetic acid into a reaction flask as a catalyst, adjusting the pH value of a reaction solution, continuously heating and refluxing for 24 hours, stirring at room temperature for reaction for 2 hours, then putting the reaction solution into a refrigerator for cooling and crystallization, carrying out vacuum filtration to remove a solvent to obtain a brown yellow solid, recrystallizing the product with methanol, and carrying out vacuum drying to obtain the methionine Schiff base derivative 2- (N-picolylimine) -4-methylthiobutyric acid (MD);

s103: by utilizing the good synergistic corrosion inhibition effect between the synthesized product 2- (N-pyridylmethylimine) -4-methylthiobutyric acid (MD) and sodium carboxymethylcellulose (CMC), the ratio of MD to sodium carboxymethylcellulose (CMC) is selected according to 4:3, and compounding to obtain the high-efficiency composite corrosion inhibitor.

The synthesis reaction equation of the 2- (N-picolylmethylimine) -4-methylthiobutyric acid provided by the embodiment of the invention is as follows:

sodium carboxymethylcellulose has the molecular formula:

adding 60mL of trichloromethane solution into a three-neck flask provided with an oil bath heating and magnetic stirring device, then adding 5.35g of pyridine-2-formaldehyde (PCD) and 7.45g of methionine (Met) into the flask, starting magnetic stirring, heating and refluxing for 1h until the solid is completely dissolved, then dropwise adding 5 drops of glacial acetic acid as a catalyst, adjusting the pH value of the reaction solution, continuing to reflux for 24h, continuing to stir at room temperature for 2h, then placing the reaction solution into a refrigerator for cooling and crystallizing, removing the solvent by vacuum filtration to obtain a brown yellow solid, recrystallizing the product with methanol, and performing vacuum drying to obtain the methionine Schiff base derivative 2- (N-picolylimine) -4-methylthiobutyric acid (MD).

Weighing MD and sodium carboxymethylcellulose (CMC) according to the weight ratio of 4:3, and mixing and compounding to obtain the carbon steel hydrochloric acid pickling composite corrosion inhibitor. The composite corrosion inhibitor is added into hydrochloric acid pickling solution according to the concentration of 70mg/L, so that the corrosion of the hydrochloric acid solution to the carbon steel substrate in the pickling process can be effectively prevented.

1. Weight loss method test

Polishing a batch of carbon steel sheet samples with the same size step by step (600# -2000 #) by using sand paper for brightening, cleaning with acetone for removing oil, drying by blowing with cold air, accurately weighing with an electronic balance (accurately to 0.0001g), then soaking the samples into 0.5M hydrochloric acid solution at 25 ℃, simultaneously taking out after a certain time, washing with deionized water, drying and accurately weighing, performing parallel test for three times, and calculating the corrosion inhibition efficiency eta according to the formula (1).

In the formula,. DELTA.m_οAnd Δ m represents the average weight loss, g, of the steel sheet without and with corrosion inhibitor, respectively.

TABLE 1 Corrosion inhibition efficiency of carbon steels in 0.5M hydrochloric acid wash containing different corrosion inhibitors

As shown in Table 1, in 0.5M hydrochloric acid solution, the single methionine corrosion inhibitor has a maximum corrosion inhibition efficiency of 65.66% for carbon steel at a concentration of 40mg/L, and has a maximum corrosion inhibition efficiency of 85.37% for carbon steel at a concentration of 160mg/L, which has the problems of low corrosion inhibition efficiency or excessive dosage. The corrosion inhibition efficiency of the composite corrosion inhibitor of 40mg/L MD +30mg/L CMC can reach 95.97 percent, the consumption is small, the corrosion inhibition efficiency is high, and the requirement of practical application can be met.

2. Polarization curve test experiment

Performing electrochemical test by using CHI660E electrochemical workstation, packaging the cylindrical Q235 steel sheet with diameter of 1.13cm as working electrode except the working surface with epoxy resin, polishing with sand paper to mirror surface, cleaning, and removing oil. Taking a calomel electrode (SCE) equipped with a Lujin capillary salt bridge as a reference electrode, 4cm²The platinum sheet electrode of (2) is used as an auxiliary electrode. Open circuit potential of electrode to be worked in test solution (E)_OCP) After stabilization, the polarization curve test was performed.

TABLE 2 Tafel polarization curves of carbon steels in 0.5M hydrochloric acid wash with different corrosion inhibition systems testing of the main electrochemical parameters

Note: e_corrDenotes the self-corrosion potential of the metal, β_c、β_aRespectively represent the Tafel slopes of the cathode and anode, I_cIndicating corrosion current density, η indicating corrosion inhibition efficiency.

As shown in Table 2 and FIG. 2, the test results of tafel polarization curves of carbon steel in 0.5M hydrochloric acid washing liquor containing a composite corrosion inhibition system show that the composite corrosion inhibitor has excellent corrosion inhibition performance on carbon steel in 0.5M hydrochloric acid washing liquor, the corrosion inhibition efficiency is increased along with the increase of MD concentration, when the MD concentration is 40mg/L and the CMC concentration is 30mg/L, the corrosion inhibition efficiency can reach 94.72 percent and is much higher than the corrosion inhibition efficiency of 63.60 percent of 40mg/L single methionine.

3. The photograph of the etching profile is shown in FIG. 3.

As shown in fig. 3, fig. 3a is a blank sample, polished scratches are clearly visible, and no corrosion phenomenon is evident, and fig. 3b shows obvious and densely distributed corrosion products on the surface of the sample, and the surface is uneven, which indicates that the sample is severely corroded. The surface of fig. 3c still shows more corrosion products, but the concentration is obviously reduced compared with that of fig. 3b, which shows that methionine (Met) has a certain corrosion inhibition effect on the sample. The surface of the sample of fig. 3d is relatively flat and polished scratches are visible with only a few fine pits, which illustrates the MD vs CMC ratio of 4: the compound corrosion inhibitor with the mass ratio of 3 has good corrosion inhibition synergistic effect on the carbon steel sample, and is obviously better than the methionine corrosion inhibitor.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A preparation method of a composite pickling corrosion inhibitor containing Schiff base is characterized by comprising the following steps:

step one, adding 60mL of trichloromethane solution into a three-neck flask provided with an oil bath heating and magnetic stirring device, then adding 5.35g of pyridine-2-formaldehyde and 7.45g of methionine into the flask, starting magnetic stirring, and heating and refluxing for 1h until all solids are dissolved;

step two, dropwise adding 5 drops of glacial acetic acid into a reaction flask to serve as a catalyst, adjusting the pH value of reaction liquid, continuously heating and refluxing for reaction for 24 hours, then stirring at room temperature for reaction for 2 hours, then putting the reaction liquid into a refrigerator for cooling and crystallization, carrying out reduced pressure suction filtration to remove a solvent to obtain a brown yellow solid, recrystallizing the product with methanol, and carrying out vacuum drying to obtain the methionine Schiff base derivative 2- (N-picolylamine) -4-methylthiobutyric acid;

thirdly, compounding the methionine Schiff base derivative and the sodium carboxymethyl cellulose according to the mass ratio of 4:3 by utilizing the good synergistic corrosion inhibition effect between the synthesized methionine Schiff base derivative and the sodium carboxymethyl cellulose to obtain the composite corrosion inhibitor;

the synthesis reaction equation of the 2- (N-picolylmethylimine) -4-methylthiobutyric acid is as follows:

2. a composite restrainer prepared by the method of claim 1, comprising Schiff base.

3. A boiler corrosion inhibiting composition prepared from the composite restrainer of claim 2.

4. A power system corrosion inhibiting composition made from the composite restrainer of claim 2.

5. A heat exchanger corrosion inhibiting composition prepared from the composite restrainer of claim 2.