Preparation method and application of modified chitosan Schiff base corrosion inhibitor

Abstract

The present invention relates to the field of metal corrosion and protection, and specifically to a preparation method and application of a modified chitosan Schiff base corrosion inhibitor. The preparation method comprises six steps: (1) preparing a gel-like chitosan dispersion; (2) preparing an ethanol solution of 2,6-dimethyl-5-heptenal; (3) adding the gel-like chitosan dispersion; (4) adding the ethanol solution of 2,6-dimethyl-5-heptenal and conducting a Schiff base reaction; (5) rotary evaporation and dehydration of the reaction product; and (6) washing, filtering, and drying. The present invention utilizes 2,6-dimethyl-5-heptenal, a common food additive, as a modifier to condense with natural polymer chitosan to prepare an acid corrosion-resistant corrosion inhibitor, with a simple process and low production cost. The invention is applied to N80 steel sheets in a hydrochloric acid medium for corrosion protection, uses a low concentration, and effectively improves the corrosion inhibition rate of the corrosion inhibitor on metals. The invention is a green, environmentally friendly, economical, and efficient corrosion inhibitor with good promotion prospects.

Description

Technical Field

[0001] The present invention relates to the field of metal corrosion and protection, and in particular to a preparation method and application of a modified chitosan Schiff base corrosion inhibitor. Background Art

[0002] Carbon steel is the most widely used and versatile steel in industrial applications. However, during use, carbon steel can spontaneously generate rust and scale layers due to environmental media, indirectly causing economic losses. According to data published by the American Society of Corrosion Engineers, global property losses from spontaneous metal corrosion account for 3.5% of global GDP. In the United States, corrosion in the oil and gas industry results in approximately $1.4 billion in annual losses. In China, direct economic losses from carbon steel corrosion account for 3% of the national economy each year. Therefore, surface cleaning of carbon steel is essential when using it.

[0003] There are two main methods for removing surface scale deposits from carbon steel: physical and chemical removal. Pickling is currently the most commonly used method, but the addition of hydrochloric acid can cause secondary corrosion to the metal surface. Currently, the use of corrosion inhibitors is one of the most effective corrosion prevention technologies in the oil and gas industry. Therefore, when pickling carbon steel, corrosion inhibitors are added to protect the metal. However, their use is often associated with high toxicity and environmental regulations. With the development of industrialization, environmental protection has become increasingly important, and the use of many corrosion inhibitors that pollute and threaten the environment has been restricted.

[0004] Chitosan is a natural polymer compound with the second-largest reserves in the world. Chitosan is green, environmentally friendly, and easily modifiable, making it one of the most popular green corrosion inhibitors due to its low toxicity. However, due to strong intermolecular and intramolecular hydrogen bonding, its solubility is poor and its corrosion inhibition is only effective at high concentrations, limiting its application. For example, the invention patent "A Chitosan-Based Carbon Steel Pickling Corrosion Inhibitor and Its Application" with application number CN200910016381.1 and publication number CN101580942A, for example, describes a corrosion inhibitor concentration in acid solutions of up to 3000 mg / L. The invention patent "A Carboxymethyl Chitosan and Its Preparation and Application" with application number CN201110364584.7 and publication number CN103113491A, for example, describes a corrosion inhibitor containing water-soluble chitosan phosphate at a concentration of up to 800 mg / L. Summary of the Invention

[0005] In order to overcome the defects of the prior art, the present invention provides a preparation method and application of a modified chitosan Schiff base corrosion inhibitor.

[0006] A method for preparing a modified chitosan Schiff base corrosion inhibitor, the technical solution of which comprises the following steps:

[0007] (1) Preparation of gel-like chitosan dispersion: Chitosan is dissolved in an acetic acid solution with a mass concentration of 0.5%-1.5%, with the amount of chitosan in the acetic acid solution being 20-40 g / L. After ultrasonic swelling for 1-2 hours, a gel-like chitosan dispersion is obtained;

[0008] (2) Preparation of ethanol solution of 2,6-dimethyl-5-heptenal: dissolve 2,6-dimethyl-5-heptenal in anhydrous ethanol, the dosage of 2,6-dimethyl-5-heptenal in anhydrous ethanol is 52.2-78.2 g / L, and after full dissolution, an ethanol solution of 2,6-dimethyl-5-heptenal is obtained;

[0009] (3) Adding the gel-like chitosan dispersion: Add the gel-like chitosan dispersion obtained in step (1) into a two-necked flask, and place the two-necked flask in a heat-collecting constant-temperature heating magnetic stirrer;

[0010] (4) Adding the ethanol solution of 2,6-dimethyl-5-heptenal and Schiff base reaction: Using a constant pressure dropping funnel, add the ethanol solution of 2,6-dimethyl-5-heptenal obtained in step (2) dropwise into the two-necked flask containing the gel-like chitosan dispersion in step (3), so that the ethanol solution of 2,6-dimethyl-5-heptenal and the gel-like chitosan dispersion are fully reacted during stirring; set the reaction temperature to 60-80°C, the stirring speed to 600-800 r / min, and the reaction time to 6-8 h;

[0011] (5) Dehydrating the reaction product by rotary evaporation: placing the reaction product obtained in step (4) in a rotary evaporator to remove excess water from the reaction product to obtain a viscous extract;

[0012] (6) Washing, filtration and drying: The viscous extract obtained in step (5) was washed with acetone several times until a precipitate was precipitated, filtered, washed with anhydrous ethanol several times, and then dried in a vacuum drying oven to obtain a light yellow gel-like solid.

[0013] In the step (1), the mass concentration of the acetic acid solution is 1%-1.2%, the amount of chitosan added to the acetic acid solution is 30-35 g / L, and ultrasonic swelling is performed for 1.5 hours.

[0014] In the step (2), the dosage of 2,6-dimethyl-5-heptenal in anhydrous ethanol is 62.6-68.4 g / L.

[0015] In step (4), the reaction temperature is set at 70-75°C, the stirring speed is set at 700 r / min, and the reaction time is set at 7 h.

[0016] The viscous extract in step (6) is washed 2-3 times with acetone.

[0017] The mass ratio of the viscous extract to acetone in step (6) is 1:(80-150).

[0018] The mass ratio of the viscous extract to acetone is 1:(100-140).

[0019] The mass ratio of the viscous extract to acetone is 1:(120-130).

[0020] The vacuum drying temperature in step (6) is 40-50°C.

[0021] The invention discloses an application of a modified chitosan Schiff base corrosion inhibitor, namely, when performing an acid pickling operation to clean a scale layer on the surface of an N80 steel sheet, the modified chitosan Schiff base corrosion inhibitor prepared by the above method is added to a hydrochloric acid solution and fully swelled before use; the concentration of the hydrochloric acid solution is 1 mol / L, and the amount of the modified chitosan Schiff base corrosion inhibitor added to the hydrochloric acid solution is 100-400 mg / L.

[0022] The basic research and development idea of the present invention is: because chitosan contains amino groups, it is easy to react with aldehydes to form Schiff bases with good corrosion inhibition properties; taking advantage of this, 2,6-dimethyl-5-heptenal is introduced into chitosan through a Schiff base reaction, which not only increases the active adsorption points of chitosan and improves the adsorption capacity of chitosan for metals, but also conforms to the concept of green environmental protection and is expected to be developed and applied in industry.

[0023] The reaction formula of chitosan and 2,6-dimethyl-5-heptenal is as follows:

[0024]

[0025] Compared with the prior art, the present invention has the following outstanding technical effects:

[0026] 1. The present invention utilizes 2,6-dimethyl-5-heptenal, a common food additive, as a modifier to condense with the natural polymer chitosan to prepare an acid-corrosion-resistant corrosion inhibitor. On the one hand, the disadvantage of poor solubility of chitosan caused by intramolecular hydrogen bonds is improved. On the other hand, the corrosion inhibition rate of the corrosion inhibitor on metals is improved after modification. The invention is a green, environmentally friendly and efficient corrosion inhibitor.

[0027] 2. Applied to N80 steel sheet in hydrochloric acid medium for corrosion protection, with low concentration and good economy.

[0028] 3. The preparation process is simple and the process is easy to control.

[0029] 4. Low production cost and good promotion prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 (a) is the infrared spectrum of chitosan (CTS);

[0031] Figure 1 (b) IR spectrum of modified chitosan (CTS-melonal) prepared in Example 1;

[0032] Figure 2 This is the thermogravimetric analysis diagram of chitosan (CTS) and modified chitosan (CTS-melonal) prepared in Example 1. DETAILED DESCRIPTION

[0033] The present invention will be described in further detail below with reference to the embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0034] If no specific techniques or conditions are specified in the examples, the procedures were carried out according to the techniques or conditions described in the literature in the field or according to the product instructions. If the raw materials used are not specified by the manufacturer, they are all conventional products that can be purchased commercially.

[0035] Chitosan used in the following examples was purchased from Sinopharm Chemical Reagent Co., Ltd. (CAS: 9012-76-4, degree of deacetylation ≥ 95%); 2,6-dimethyl-5-heptenal was from MacLean (CAS: 106-72-9, ≥ 85% (GC)); anhydrous ethanol was from Tianjin Fuyu Fine Chemical Co., Ltd. (CAS: 64-17-5); acetone was from Sinopharm Chemical Reagent Co., Ltd. (CAS: 67-64-1); and acetic acid was from Sinopharm Chemical Reagent Co., Ltd. (CAS: 64-19-7).

[0036] Example 1

[0037] Weigh 3.00 g of chitosan and 2.61 g of 2,6-dimethyl-5-heptenal into 100 mL of a 1.0% acetic acid solution, ultrasonically swell the chitosan for 1 hour, then pour the mixture into a 250 mL two-necked flask and place it in a heat-collecting, constant-temperature, magnetic stirrer. Dissolve 2,6-dimethyl-5-heptenal in 50 mL of anhydrous ethanol and slowly add it dropwise to the flask using a constant-pressure dropping funnel. The reaction temperature was set at 70°C, the stirring speed at 600 rpm, and the reaction was allowed to proceed for 7 hours. After the reaction was complete, the product was placed in a rotary evaporator to remove excess water, yielding a viscous extract. The extract was then washed 2-3 times with acetone (1:140, by mass) until a precipitate formed. The extract was then filtered, rinsed several times with anhydrous ethanol, and dried in a vacuum drying oven (40°C) to yield a pale yellow gel-like solid.

[0038] Example 2

[0039] Weigh 2.00 g of chitosan and 3.13 g of 2,6-dimethyl-5-heptenal into 100 mL of a 1.5% acetic acid solution, ultrasonically swell the chitosan for 2 hours, then pour the mixture into a 250 mL two-necked flask and place it in a heat-collecting, constant-temperature, magnetic stirrer. Dissolve 2,6-dimethyl-5-heptenal in 50 mL of anhydrous ethanol and slowly add it dropwise to the flask using a constant-pressure dropping funnel. Set the reaction temperature to 60°C and the stirring speed to 800 rpm for 8 hours. After the reaction is complete, place the reaction product in a rotary evaporator to remove excess water, yielding a viscous extract. Wash the product with acetone (mass ratio: 1:150) 2-3 times until a precipitate forms. Filter the extract, rinse several times with anhydrous ethanol, and dry it in a vacuum drying oven (45°C) to yield a pale yellow gel-like solid.

[0040] Example 3

[0041] Weigh 3.50 g of chitosan and 3.42 g of 2,6-dimethyl-5-heptenal into 100 mL of 0.5% acetic acid solution, ultrasonically swell the chitosan for 1.5 hours, then pour the mixture into a 250 mL two-necked flask and place it in a heat-collecting, constant-temperature, magnetic stirrer. Dissolve 2,6-dimethyl-5-heptenal in 50 mL of anhydrous ethanol and slowly add it dropwise to the flask using a constant-pressure dropping funnel. Set the reaction temperature to 75°C and stir at 600 rpm for 6 hours. After the reaction is complete, place the reaction product in a rotary evaporator to remove excess water, yielding a viscous extract. Wash the product with acetone (mass ratio: 1:130) two to three times until a precipitate forms. Filter the extract, rinse several times with anhydrous ethanol, and dry it in a vacuum drying oven at 50°C to yield a pale yellow gel-like solid.

[0042] Example 4

[0043] Weigh 4.00 g of chitosan and 3.91 g of 2,6-dimethyl-5-heptenal into 100 mL of a 1.2% acetic acid solution, ultrasonically swell the chitosan for 2 hours, then pour the mixture into a 250 mL two-necked flask and place it in a heat-collecting, constant-temperature, magnetic stirrer. Dissolve 2,6-dimethyl-5-heptenal in 50 mL of anhydrous ethanol and slowly add the mixture dropwise to the flask using a constant-pressure dropping funnel. The reaction temperature was set at 80°C, the stirring speed at 700 rpm, and the reaction was allowed to proceed for 7 hours. After the reaction was complete, the product was placed in a rotary evaporator to remove excess water, yielding a viscous extract. The extract was then washed 2-3 times with acetone (1:80 by mass) until a precipitate formed. The extract was then filtered, rinsed several times with anhydrous ethanol, and dried in a vacuum drying oven (45°C) to yield a pale yellow gel-like solid.

[0044] Example 5

[0045] Weigh 3.00 g of chitosan and 2.61 g of 2,6-dimethyl-5-heptenal into 100 mL of a 1.1% acetic acid solution, ultrasonically swell the chitosan for 1.5 hours, then pour the mixture into a 250 mL two-necked flask and place it in a heat-collecting, constant-temperature, magnetic stirrer. Dissolve 2,6-dimethyl-5-heptenal in 50 mL of anhydrous ethanol and slowly add it dropwise to the flask using a constant-pressure dropping funnel. Set the reaction temperature to 75°C and stir at 600 rpm for 7 hours. After the reaction is complete, place the reaction product in a rotary evaporator to remove excess water, yielding a viscous extract. Wash the product with acetone (1:120, by mass) two to three times until a precipitate forms. Filter the extract, rinse several times with anhydrous ethanol, and dry it in a vacuum drying oven at 50°C to yield a pale yellow gel-like solid.

[0046] Example 6

[0047] Weigh 4.00 g of chitosan and 3.91 g of 2,6-dimethyl-5-heptenal into 100 mL of a 1.0% acetic acid solution, ultrasonically swell the chitosan for 2 hours, then pour the mixture into a 250 mL two-necked flask and place it in a magnetic stirrer with a constant-temperature heating system. Dissolve 2,6-dimethyl-5-heptenal in 50 mL of anhydrous ethanol and slowly add the mixture dropwise to the flask using a constant-pressure dropping funnel. The reaction temperature was set at 80°C, the stirring speed at 700 rpm, and the reaction was allowed to proceed for 7 hours. After the reaction was complete, the product was placed in a rotary evaporator to remove excess water, yielding a viscous extract. The extract was then washed 2-3 times with acetone (1:100 by mass) until a precipitate formed. The extract was then filtered, rinsed several times with anhydrous ethanol, and dried in a vacuum drying oven (45°C) to yield a pale yellow gel-like solid.

[0048] In order to verify the performance of the modified chitosan Schiff base corrosion inhibitor prepared by the present invention, a corrosion inhibition performance test was conducted on it:

[0049] The corrosion inhibition performance of the modified chitosan Schiff base corrosion inhibitor prepared according to the preparation method of Example 1 was studied using an electrochemical method and analyzed and verified.

[0050] Electrochemical tests were performed using a Gamry Reference 600 electrochemical workstation (Gamry Instrument Co.). Test steel sheets (N80 steel) were purchased from Xiangwei Machinery Co., Ltd., Yangzhou, Jiangsu Province. N80 steel was used as the working electrode; a platinum electrode was used as the auxiliary electrode; and a calomel electrode was used as the reference electrode. The working electrode dimensions were 10 mm × 10 mm × 2 mm, with a 100 mm gap left. 2The working surface of the tooth was sealed with denture base resin. Before the experiment, the working surface was polished step by step with 400-1500 grit sandpaper, rinsed with distilled water, wiped with ethanol, and degreased before use. The strong polarization curve scan range was set to -400 mV to +400 mV, and the scan speed was 0.5 mV·s. -1 , scanning from cathode to anode; the electrochemical impedance spectroscopy setting parameters are: scanning from high frequency to low frequency, range 5×10 -2 Hz~5×10 5 Hz, with an amplitude of 10mV.

[0051] The electrochemical tests were divided into five groups. The first group used 1 mol·L -1 HCl solution was used as the corrosion medium (100 ml) without adding corrosion inhibitor; the second group used 1 mol·L -1 HCl solution was used as the corrosion medium (100 ml), and 10 mg of corrosion inhibitor was added; the third group used 1 mol·L -1 HCl solution was used as the corrosion medium (100 ml), and 20 mg of corrosion inhibitor was added; the fourth group used 1 mol·L -1 HCl solution was used as the corrosion medium (100 ml), and 30 mg of corrosion inhibitor was added; the fifth group used 1 mol·L -1 HCl solution was used as the corrosion medium (100 ml), and 40 mg of corrosion inhibitor was added. Before starting the test, different amounts of modified chitosan Schiff base corrosion inhibitor were added at 1 mol·L -1 Fully swelled in HCl solution.

[0052] Potentiodynamic polarization curve test: The obtained polarization curve data are shown in Table 1.

[0053] Table 1 Potentiodynamic polarization curve test fitting results

[0054]

[0055] Electrochemical impedance spectroscopy (EIS) data are shown in Table 2.

[0056] Table 2 AC impedance spectrum test fitting results

[0057]

[0058] The detailed analysis of Table 1 and Table 2 is as follows:

[0059] Table 1 shows the fitting results of the potentiodynamic polarization curve test. Experimental group 1, in which no corrosion inhibitor was added, constitutes the blank group. Experimental groups 2 through 5, in which varying amounts of corrosion inhibitor were added, constitute the experimental groups. The corrosion current density in the experimental groups significantly decreased, and the slopes of the Tafel curves for both the cathode and cathode changed, with the cathode slope changing significantly. At 25°C, the addition of the corrosion inhibitor significantly inhibited the corrosion of N80 steel in hydrochloric acid solution. The inhibition rate was positively correlated with the experimental concentration, reaching 86.43% at 400 mg / L. This demonstrates that the corrosion inhibitor is a mixed inhibitor that primarily inhibits the cathodic reaction in hydrochloric acid solution.

[0060] Table 2 shows the fitting results of the AC impedance spectrum test. In the first experimental group, no corrosion inhibitor was added, which was the blank group. In the second to fifth experimental groups, different amounts of corrosion inhibitor were added, which were the experimental groups. ct When the concentration of the corrosion inhibitor is 400 mg / L, the highest corrosion inhibition rate reaches 91.69%, R ct Reaching 652.1Ω·cm 2 . It is proved that the addition of corrosion inhibitor increases the resistance and hinders the electrode reaction.

[0061] In addition, the present invention conducted infrared and thermogravimetric analysis on chitosan (CTS) and modified chitosan (CTS-melonal) prepared in Example 1, see Figure 1 (a), Figure 1 (b) and Figure 2 , a detailed comparative analysis of its characterization characteristics is as follows:

[0062] FIG1 is an infrared spectrum of 2,6-dimethyl-5-heptenal modified chitosan and chitosan prepared in Example 1. In FIG1 CTS, 1387 cm -1 OH bending vibration; 1067cm -1 and 1011cm -1 The peak is the asymmetric hydroxyl vibration peak located at the C3 and C6 positions on the CTS skeleton; 1262 cm -1 and 885 cm -1 CTS sugar absorption band; 3417 cm -1 The peaks of 1666 cm-1 are the vibration peaks of the hydrogen-oxygen bond and the nitrogen-hydrogen bond in the CTS molecule. -1 A new larger peak appeared, which is the characteristic absorption peak of -C=N- double bond, proving that chemical modification occurred; 828cm -1 -C=C- absorption peak; 726 cm -1 -CH2- absorption peak; 2961cm -1 -CH3 vibration peak; 1458 cm -1 -CH3 absorption peak; 1260 cm-1 The in-plane bending vibration of OH at the position shifted, and it can be inferred that the amino group on chitosan reacted with the aldehyde group on 2,6-dimethyl-5-heptenal to form 2,6-dimethyl-5-heptenal-modified chitosan Schiff base.

[0063] Figure 2 This is a thermogravimetric analysis of chitosan modified with 2,6-dimethyl-5-heptenal and chitosan prepared in Example 1. Before modification, there are two stages of weight loss: the first, from approximately 47-150°C, is due to water molecules in the chitosan; the second, from approximately 247-500°C, is due to polymer chain segment breakage and combustion. After modification, there are two stages of weight loss: the first, from approximately 47-130°C, is due to water loss; the second, from approximately 150-500°C. This indicates that the decomposition rate of the modified chitosan is significantly greater than that of the unmodified chitosan, resulting in reduced thermal stability.

Claims

1. A method for preparing a modified chitosan Schiff base corrosion inhibitor, characterized in that: The steps include: (1) Preparation of gel-like chitosan dispersion: Chitosan is dissolved in an acetic acid solution with a mass concentration of 0.5%-1.5%, with the amount of chitosan in the acetic acid solution being 20-40 g / L. After ultrasonic swelling for 1-2 hours, a gel-like chitosan dispersion is obtained; (2) Preparation of ethanol solution of 2,6-dimethyl-5-heptenal: dissolve 2,6-dimethyl-5-heptenal in anhydrous ethanol, the dosage of 2,6-dimethyl-5-heptenal in anhydrous ethanol is 52.2-78.2 g / L, and after full dissolution, an ethanol solution of 2,6-dimethyl-5-heptenal is obtained; (3) Adding the gel-like chitosan dispersion: Add the gel-like chitosan dispersion obtained in step (1) into a two-necked flask, and place the two-necked flask in a heat-collecting constant-temperature heating magnetic stirrer; (4) Adding the ethanol solution of 2,6-dimethyl-5-heptenal and Schiff base reaction: Using a constant pressure dropping funnel, add the ethanol solution of 2,6-dimethyl-5-heptenal obtained in step (2) dropwise into the two-necked flask containing the gel-like chitosan dispersion in step (3), so that the ethanol solution of 2,6-dimethyl-5-heptenal and the gel-like chitosan dispersion are fully reacted during stirring; set the reaction temperature to 60-80°C, the stirring speed to 600-800 r / min, and the reaction time to 6-8 h; (5) Dehydrating the reaction product by rotary evaporation: placing the reaction product obtained in step (4) in a rotary evaporator to remove excess water from the reaction product to obtain a viscous extract; (6) Washing, filtration and drying: The viscous extract obtained in step (5) was washed with acetone several times until a precipitate was precipitated, filtered, washed with anhydrous ethanol several times, and then dried in a vacuum drying oven to obtain a light yellow gel-like solid.

2. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 1, wherein: In the step (1), the mass concentration of the acetic acid solution is 1%-1.2%, the amount of chitosan added to the acetic acid solution is 30-35 g / L, and ultrasonic swelling is performed for 1.5 hours.

3. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 1, wherein: In the step (2), the dosage of 2,6-dimethyl-5-heptenal in anhydrous ethanol is 62.6-68.4 g / L.

4. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 1, characterized in that: In step (4), the reaction temperature is set at 70-75°C, the stirring speed is set at 700 r / min, and the reaction time is set at 7 h.

5. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 1, characterized in that: The viscous extract in step (6) is washed 2-3 times with acetone.

6. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 1, characterized in that: The mass ratio of the viscous extract to acetone in step (6) is 1:(80-150).

7. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 6, characterized in that: The mass ratio of the viscous extract to acetone is 1:(100-140).

8. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 7, characterized in that: The mass ratio of the viscous extract to acetone is 1:(120-130).

9. The method for preparing a modified chitosan Schiff base corrosion inhibitor according to claim 1, characterized in that: The vacuum drying temperature in step (6) is 40-50°C.

10. An application of a modified chitosan Schiff base corrosion inhibitor, characterized in that: When performing pickling operation to clean the scale layer on the surface of N80 steel sheet, the modified chitosan Schiff base corrosion inhibitor prepared by the method according to any one of claims 1 to 9 is added to a hydrochloric acid solution and fully swelled before use; the concentration of the hydrochloric acid solution is 1 mol / L, and the amount of the modified chitosan Schiff base corrosion inhibitor added to the hydrochloric acid solution is 100-400 mg / L.

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