Preparation method of polysaccharide corrosion inhibitor

Abstract

The invention provides a preparation method of a polysaccharide corrosion inhibitor, which comprises the following steps: a) carrying out nucleophilic substitution reaction on beta-cyclodextrin and allyl bromide in an aprotic polar solvent at 0 DEG C under an alkaline condition to obtain allyl beta-cyclodextrin with double bonds; b) dissolving xanthan gum in water under an anaerobic condition, adjusting the pH value to 3-7, adding an ammonium ceric nitrate initiator, then adding the allyl beta-cyclodextrin obtained in the step a), and carrying out a free radical graft copolymerization reaction at 50-80 DEG C; and after the reaction is completed, adding a terminating agent, precipitating, filtering and drying to obtain the xanthan gum grafted beta-cyclodextrin corrosion inhibitor. The natural polysaccharide beta-cyclodextrin and xanthan gum are used as main raw materials, so that the natural polysaccharide beta-cyclodextrin and xanthan gum are wide in source, renewable and biodegradable. Any toxic and harmful heteroatom (such as N, S, P and the like) or a high-toxicity catalyst is not used or introduced in the whole preparation process, and the final product is non-toxic and pollution-free and completely conforms to the concepts of green chemistry and sustainable development.

Description

Technical Field

[0001] This invention belongs to the technical field of polysaccharide corrosion inhibitors, and more specifically, relates to a method for preparing a polysaccharide corrosion inhibitor. Background Technology

[0002] Metal corrosion is a serious problem prevalent in nature and industrial production. It not only leads to the waste of vast amounts of metal resources and causes enormous economic losses, but also can trigger equipment failures, safety accidents, and environmental pollution, threatening the sustainable development of human society. In many fields such as oil extraction, chemical production, machinery manufacturing, power energy, and infrastructure construction, metallic materials, especially the inexpensive and widely used Q235 steel, are extremely susceptible to severe corrosion in acidic environments (such as pickling, descaling, and oil well acidizing).

[0003] To effectively control and mitigate metal corrosion, various protective technologies have been developed, primarily including the use of corrosion-resistant alloys, the application of protective coatings, electrochemical protection (such as cathodic protection), and the addition of corrosion inhibitors. Among these methods, corrosion inhibitor technology is widely used in various industrial processes due to its advantages of simple operation, low cost, significant effects, and ease of implementation, especially in dynamic and closed systems where it has irreplaceable advantages.

[0004] Organic corrosion inhibitors are an important component of the corrosion inhibitor field, and can be divided into synthetic and natural types based on their source. While traditional synthetic organic corrosion inhibitors are highly efficient, many contain heteroatoms such as nitrogen, sulfur, and phosphorus, which may exhibit certain biotoxicity, are difficult to biodegrade, and pose potential environmental hazards, thus contradicting current green chemistry and sustainable development principles. Natural corrosion inhibitors, such as plant extracts, are environmentally friendly, but the extraction process for their active ingredients is complex and costly, and their acid resistance and corrosion inhibition efficiency are often unstable, limiting their large-scale industrial application.

[0005] In recent years, with increasingly stringent environmental regulations and the growing acceptance of green chemistry concepts, the development of efficient, non-toxic, and biodegradable environmentally friendly (green) corrosion inhibitors has become a research hotspot. Natural polysaccharide polymers, such as xanthan gum (XG) and cyclodextrin (CD), are considered ideal candidates for preparing green corrosion inhibitors due to their wide availability, low cost, non-toxicity, renewability, and good water solubility and biocompatibility. Polysaccharide molecules are rich in polar groups such as hydroxyl (-OH), which theoretically can act as adsorption sites to interact with metal surfaces. However, single polysaccharide corrosion inhibitors often suffer from drawbacks such as low corrosion inhibition efficiency, poor thermal stability, or poor acid resistance.

[0006] To overcome these limitations, researchers have begun exploring the chemical modification of natural polysaccharides, synthesizing novel polymeric corrosion inhibitors through grafting, cross-linking, and other methods. These modified products can combine the advantages of different components, introducing more and stronger adsorption groups, thereby significantly improving corrosion inhibition performance. For example, grafting cyclodextrin with a special cavity structure onto the xanthan gum backbone via free radical polymerization holds promise for obtaining composite green corrosion inhibitors with both high adsorption capacity and excellent corrosion inhibition efficiency. However, existing modification methods may involve the introduction of toxic catalysts or heteroatoms, are complex processes, or fail to fully optimize reaction conditions to achieve optimal performance.

[0007] Therefore, there is an urgent need to develop a polysaccharide corrosion inhibitor preparation method that is simple to produce, does not introduce harmful heteroatoms, is environmentally friendly, and has high corrosion inhibition efficiency, in order to meet the urgent needs of modern industry for efficient and green anti-corrosion technology. Summary of the Invention

[0008] To address the aforementioned problems, the present invention aims to prepare a xanthan gum-grafted cyclodextrin polymer (β–CD–XG) and provide a method for preparing a polysaccharide corrosion inhibitor without introducing other heteroatoms. First, an allyl cyclodextrin (A–β–CD) intermediate was synthesized using a nucleophilic substitution reaction mechanism. Then, based on the principle of solution polymerization, the xanthan gum-grafted cyclodextrin polymer (β–CD–XG) was synthesized to prepare a polysaccharide corrosion inhibitor.

[0009] A method for preparing a polysaccharide corrosion inhibitor includes the following steps:

[0010] a) Under alkaline conditions, β-cyclodextrin and allyl bromide undergo a nucleophilic substitution reaction in an aprotic polar solvent at 0°C to obtain allyl β-cyclodextrin with a double bond. Specifically, β-cyclodextrin is stirred with N,N-dimethylformamide (DMF) until completely dissolved. After the β-cyclodextrin is completely dissolved, sodium hydroxide is added, and the mixture is stirred at room temperature for 1 h. The temperature is then slowly cooled to approximately 0°C, and finally, allyl bromide is added dropwise to the reaction system in two portions, with vigorous stirring for 48 h. After the reaction is complete and the mixture is allowed to stand for 2 h, the contents of the three-necked flask are transferred to a rotary evaporator for concentration under reduced pressure. Finally, the residue is washed repeatedly with alcohol, filtered, and the final product is dried in an oven at 40°C for 12 h to obtain allyl β-cyclodextrin.

[0011] Furthermore, in step a), the mass ratio of β-cyclodextrin to allyl bromide is 1:87.4. In step a), the mass ratio of β-cyclodextrin to sodium hydroxide is 1:50.2.

[0012] b) Under anaerobic conditions, xanthan gum is dissolved in water, the pH is adjusted to 3-7, cerium ammonium nitrate initiator is added, followed by allyl β-cyclodextrin obtained in step a), and a free radical graft copolymerization reaction is carried out at 50-80℃. After the reaction is completed, a terminator is added, and the mixture is precipitated, filtered, and dried to obtain xanthan gum-grafted β-cyclodextrin corrosion inhibitor. Specifically, first, xanthan gum is dissolved in boiled deionized water and stirred vigorously until completely dissolved. An appropriate amount of dilute hydrochloric acid is added to adjust the pH of the solution. After the pH stabilizes, cerium ammonium nitrate is added to the solution and stirred vigorously for 2 h. Subsequently, a certain proportion of allyl cyclodextrin is added, and the mixture is stirred continuously at a certain temperature for 8 h. After the reaction is completed, a saturated hydroquinone solution is added to terminate the polymerization reaction. The graft copolymer is precipitated with anhydrous ethanol, filtered to obtain a crude product, and the crude product is washed three times with anhydrous ethanol and dried in a 60 ℃ oven for 12 h to obtain xanthan gum-grafted β-cyclodextrin corrosion inhibitor.

[0013] Furthermore, in step b), the concentration of xanthan gum in water is 1.67 g / L, and the mass ratio of cerium ammonium nitrate to xanthan gum is 0.6:1.

[0014] Furthermore, in step b), the free radical graft copolymerization reaction time is 8 hours.

[0015] Furthermore, in step b), the mass ratio of allyl β-cyclodextrin to xanthan gum is 1:0.86.

[0016] Furthermore, the terminator is a saturated aqueous solution of hydroquinone, and the amount added is approximately 2 mL per 150 mL reaction system.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) By grafting β-cyclodextrin with a special cavity structure onto the xanthan gum backbone, the xanthan gum-grafted β-cyclodextrin polymer (β-CD–XG) is prepared. This polymer contains a large number of polar groups such as hydroxyl (-OH), ether bonds (-CH2-O-CH2), and carboxyl groups (-COOH). These groups can interact strongly with metal surfaces (such as iron) through electrostatic and chemical adsorption, forming a dense and stable protective film that effectively isolates corrosive media (such as H₂O₂). + Cl - Its performance in contact with metals is significantly better than that of xanthan gum or cyclodextrin alone.

[0019] (2) This invention uses natural polysaccharide β-cyclodextrin and xanthan gum as the main raw materials, which are widely available, renewable and biodegradable. The entire preparation process does not use or introduce any toxic or harmful heteroatoms (such as N, S, P, etc.) or highly toxic catalysts. The final product is non-toxic and pollution-free, which fully complies with the concept of green chemistry and sustainable development. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the preparation process of allyl cyclodextrin.

[0021] Figure 2 Schematic diagram of the synthesis reaction of xanthan gum grafted with β-cyclodextrin corrosion inhibitor;

[0022] Figure 3 Consider the response surfaces and interactions between A and B;

[0023] Figure 4 The response surfaces and interactions of A and C;

[0024] Figure 5 Corrosion polarization curves of Q235 steel sheets at different temperatures: (A) 293 K; (B) 303 K; (C) 313 K;

[0025] Figure 6 To fit the equivalent circuit diagram;

[0026] Figure 7 Nyquist plots of corrosion of Q235 steel sheets at different temperatures: (A) 293 K; (B) 303 K; (C) 313 K

[0027] Figure 8 Bode plots for Q235 steel sheets at different temperatures: (A) 293 K; (B) 303 K; (C) 313 K;

[0028] Figure 9 SEM analysis of steel sheet surface in corrosive medium: (A) without corrosion inhibitor, (B) with corrosion inhibitor;

[0029] Figure 10 EDS analysis of steel sheet surface in corrosive medium: (A) with corrosion inhibitor added, (B) without corrosion inhibitor added;

[0030] Figure 11 Adsorption isotherms for different models: (a) Frumkin; (b) Freundlich; (c) Langmuir; (d) Temkin;

[0031] Figure 12 The linear relationship between Kads and 1000 / T;

[0032] Figure 13 This is a schematic diagram illustrating the corrosion inhibition mechanism of xanthan gum-grafted β-cyclodextrin corrosion inhibitor. Detailed Implementation

[0033] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0034] Example 1:

[0035] A method for preparing a polysaccharide corrosion inhibitor includes the following steps:

[0036] like Figure 1 As shown, a) 2.27 g of β-cyclodextrin and 70 mL of N,N-dimethylformamide were added to a three-necked flask and stirred until homogeneous. After complete dissolution, a certain amount of sodium hydroxide (NaOH) was added, and the mixture was stirred at room temperature for 1 h. The temperature was then slowly cooled to approximately 0 °C. Finally, a certain amount of allyl bromide was added dropwise to the reaction system in two portions, and the mixture was stirred vigorously for 48 h. After the reaction was completed and allowed to stand for 2 h, the contents of the three-necked flask were transferred to a rotary evaporator for concentration under reduced pressure. Finally, the residue was washed repeatedly with alcohol, filtered, and the final product was placed in an oven and dried at 40 °C for 12 h to obtain allyl β-cyclodextrin.

[0037] In step a), the mass ratio of β-cyclodextrin to allyl bromide is 1:87.4.

[0038] In step a), the mass ratio of β-cyclodextrin to sodium hydroxide is 1:50.2.

[0039] like Figure 2 As shown in b), under anaerobic conditions, a suitable amount of deionized water was boiled with an alcohol lamp. 0.25 g of xanthan gum was dissolved in 150 mL of the boiled deionized water and stirred vigorously until completely dissolved. A suitable amount of dilute hydrochloric acid was added to adjust the pH of the solution to 3. After the pH stabilized, 0.15 g of cerium ammonium nitrate was added to the solution and stirred vigorously for 2 h. Subsequently, a certain proportion of allyl cyclodextrin was added, and the mixture was stirred continuously at 50 °C for 8 h to carry out a free radical graft copolymerization reaction. After the reaction was completed, 2 mL of saturated hydroquinone solution was added to a three-necked flask to terminate the polymerization reaction. The graft copolymer was precipitated with anhydrous ethanol, filtered to obtain the crude product, washed three times with anhydrous ethanol, and then dried in a 60 °C oven for 12 h to obtain the xanthan gum-grafted β-cyclodextrin corrosion inhibitor.

[0040] In step b), the mass ratio of allyl β-cyclodextrin to xanthan gum is 1:0.86.

[0041] Example 2

[0042] This embodiment is the same as Embodiment 1, except that in step b), an appropriate amount of dilute hydrochloric acid is added to adjust the pH of the solution to 5. The free radical graft copolymerization reaction is carried out by continuous stirring at 80°C for 8 hours.

[0043] Example 3

[0044] This embodiment is the same as Embodiment 1, except that in step b), an appropriate amount of dilute hydrochloric acid is added to adjust the pH of the solution to 7. The free radical graft copolymerization reaction is carried out by continuous stirring at 65°C for 8 hours.

[0045] The products prepared in Examples 1-3 were subjected to weight loss tests at room temperature to calculate the corrosion inhibition rate.

[0046] In this scheme, the steel sheet used for the weight loss method test is Q235 steel. The composition (wt.%) of the Q235 steel is: C (0.14~0.22), Mn (0.30~0.65), Si (≤0.30), S (≤0.05), P (≤0.045), with the remainder being Fe. Before each experiment, the sample is polished to a smooth surface using a series of 240~1500 grade diamond sandpaper, the surface of the steel is rinsed with ethanol, and after air drying, it is immersed in the experimental solution.

[0047] When performing the weight loss test, Q235 carbon steel sheets with dimensions of 40 mm × 13 mm × 2 mm were placed in 0.1 M H2SO4 solutions with and without different concentrations of corrosion inhibitors. The solutions were left to stand for 12 h at different temperatures. After 12 h, the steel sheets were removed and rinsed with deionized water and anhydrous ethanol to remove corrosion products from the surface of the steel sheets. After air drying, the sheets were weighed.

[0048] The corrosion rate of Q235 steel sheet and the corrosion inhibition efficiency of the corrosion inhibitor are calculated by formula (1) and formula (2), respectively.

[0049]

[0050]

[0051] In the formula: W is the weight change of the metal before and after corrosion (g); A is the area of ​​the metal exposed to the corrosive medium (cm²). 2 ); t is the time of the weight loss test (h); ρ is the density of the metal (g / cm³). 3 ); %IE represents the corrosion inhibition efficiency of the corrosion inhibitor on Q235 steel in corrosive media; CR0 and CR i The values ​​represent the corrosion rates (mm / year) of the corrosion pads in sulfuric acid solutions containing and without corrosion inhibitors.

[0052] The steps in this scheme will be analyzed in detail below. First, we will analyze step a) for the preparation of allyl β-cyclodextrin. Considering that there are many factors affecting the corrosion inhibition rate in this step, and that some of these factors have mutual influences, in order to determine the optimal conditions, we will comprehensively consider each reaction condition and use the final corrosion inhibition rate as the evaluation index. We will use orthogonal experiments (Table 1) to explore and determine the optimal synthesis conditions.

[0053]

[0054] As shown in Table 1, the optimal reaction conditions for allyl β-cyclodextrin as a corrosion inhibitor are as follows: when the temperature is around 0 °C, n(β-cyclodextrin):n(allyl bromide) = 1:87.4, n(β-cyclodextrin):n(NaOH) = 1:50.2, and the reaction time is 48 h, allyl β-cyclodextrin synthesized under these conditions exhibits a high corrosion inhibition rate.

[0055] Furthermore, it can be seen from orthogonal table 1 that both experimental conditions affect the final experimental results, but the proportion of influence is different. The amount of NaOH added has a greater impact on the corrosion inhibition rate than the amount of allyl bromide added.

[0056] The second step of synthesis was carried out at a certain temperature using allyl β-cyclodextrin and xanthan gum as raw materials and cerium ammonium nitrate as an initiator under anaerobic conditions. Considering the influence of various factors on the corrosion inhibition rate, it was finally determined that X (reactant ratio (mass ratio)), Y (temperature), and Z (pH) had the greatest impact on the corrosion inhibition rate. Based on this, an orthogonal experiment was designed, and the orthogonal factor level table for the synthesis of the xanthan gum-grafted β-cyclodextrin corrosion inhibitor is shown in Table 2. The orthogonal table of the specific experiments is shown in Table 3.

[0057]

[0058]

[0059] Analysis of the range data from the orthogonal experiments in Table 3 shows that all three experimental factors affect the final corrosion inhibition rate, with Z > Y > X. That is, the order of influence of the three experimental factors on the corrosion inhibition rate from largest to smallest is pH, temperature, and reactant ratio. Analysis of the orthogonal experimental data indicates that when the reaction time is controlled at 8 h, the optimal process conditions for synthesizing the xanthan gum-grafted β-cyclodextrin corrosion inhibitor are a reactant ratio of 1:0.86, a temperature of 65 ℃, and pH=7.

[0060] Corrosion inhibitor response surface analysis

[0061] To comprehensively evaluate the impact of each factor on the corrosion inhibition rate and explore the relationship between the various factors, this scheme uses Design-export to design 14 central composite experiments as shown in Table 4. A represents the reactant ratio (mass ratio), B represents the reaction temperature (°C), and C represents the pH. The specific influencing factors are shown in Table 5. The model analysis of the results calculated by the software is shown in Table 6.

[0062]

[0063]

[0064]

[0065] In the regression model of this experiment, R 2 =0.9385, and as shown in the table, F is greater than 0.05, indicating a high degree of significance. This means that the equation has a high degree of fit and the model is correctly selected. From the F values ​​of A, B, and C, we can see that C has the greatest influence, followed by B, and A has the smallest influence. That is, pH has the greatest influence on the corrosion inhibition rate, followed by temperature, and finally the reactant ratio.

[0066] By analyzing the response surface and contour lines, the relationships between various factors are derived, and the optimal response conditions are inferred. The response surfaces and contour plots under different conditions are shown below.

[0067] like Figure 3 The diagram shows the combined effect of temperature and reactant ratio on the corrosion inhibition rate. Figure 3 It is evident that changes in temperature and reactant ratio significantly affect the corrosion inhibition rate. With a fixed reactant ratio, the higher the temperature, the higher the corrosion inhibition rate. However, when the temperature exceeds a certain value, the corrosion inhibition rate begins to decrease. Therefore, the optimal temperature was selected as 65 ℃.

[0068] like Figure 4 The diagram shows the combined effect of reactant ratio and pH on corrosion inhibition rate. Figure 4 It can be seen that changes in the reactant ratio and pH have a significant impact on the corrosion inhibition rate. When the reactant ratio is fixed, the corrosion inhibition rate increases with increasing pH, but begins to decrease when the pH exceeds a certain value. Therefore, the optimal pH is 7.

[0069] The corrosion inhibition behavior of the xanthan gum-grafted β-cyclodextrin corrosion inhibitor obtained in this scheme will be further analyzed below.

[0070] Weightlessness analysis

[0071] To test the corrosion inhibition efficiency of xanthan gum-grafted β-cyclodextrin corrosion inhibitor under different conditions, Q235 steel sheets were placed in 0.1 mol / L sulfuric acid media with different temperatures and concentrations of corrosion inhibitor. The corrosion inhibition performance of the inhibitor was evaluated using the weight loss method. Specific corrosion parameters are shown in Table 7.

[0072]

[0073] As shown in Table 7 above, at 293 K, the corrosion rate of the steel sheet without xanthan gum-grafted β-cyclodextrin corrosion inhibitor was 4.395 mm / y. However, when the temperature increased to 313 K, the corrosion rate reached 14.0361 mm / y, indicating a sharp increase in corrosion rate with rising temperature. With the addition of xanthan gum-grafted β-cyclodextrin corrosion inhibitor, the corrosion rate decreased significantly with increasing inhibitor concentration. At 293 K, the inhibitor concentration was only 150 mg / L, yet the corrosion inhibition efficiency reached 90.71%. This is likely due to the greater adsorption of xanthan gum-grafted β-cyclodextrin on the metal surface, thus inhibiting corrosion. Even at 313 K, the corrosion inhibition rate remained at 87.72%, demonstrating that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor still exhibits strong anti-corrosion effects at higher temperatures.

[0074] The results of the weight loss method indicate that, at a certain temperature, the corrosion inhibition efficiency gradually increases with the increase of the concentration of xanthan gum-grafted β-cyclodextrin corrosion inhibitor; at a certain concentration, the corrosion inhibition efficiency gradually decreases with the increase of temperature, but the decreasing trend is not significant, indicating that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor still has a high corrosion inhibition rate at higher temperatures.

[0075] Polarization curve method

[0076] To investigate the effect of xanthan gum-grafted β-cyclodextrin corrosion inhibitor on the polarization behavior of Q235 carbon steel, polarization experiments were conducted in 0.1 M H2SO4 at different concentrations of xanthan gum-grafted β-cyclodextrin corrosion inhibitor and at different temperatures. The obtained polarization curves are shown below. Figure 5 As shown in the figure. The extrapolated kinetic parameters, such as corrosion potential (Ecorr) and corrosion current density (icorr), are shown in Table 8. For the sample without xanthan gum-grafted β-cyclodextrin corrosion inhibitor, it is clear that when xanthan gum-grafted β-cyclodextrin corrosion inhibitor is added as a corrosion inhibitor to carbon steel with 0.1 M H2SO4, the corrosion current density shifts in the negative direction. This means that the addition of xanthan gum-grafted β-cyclodextrin corrosion inhibitor can effectively inhibit the corrosion of carbon steel.

[0077]

[0078] If the Ecorr value in the system with added corrosion inhibitor shifts by >85 mV relative to the system without added corrosion inhibitor, the corrosion inhibitor can be considered a cathodic or anodic corrosion inhibitor. If the Ecorr shift is <85 mV, it can be considered a hybrid corrosion inhibitor. (From Table 8 and...) Figure 5It can be seen that the addition of xanthan gum-grafted β-cyclodextrin corrosion inhibitor only causes a small change in the Ecorr value, and Ecorr increases with the addition of xanthan gum-grafted β-cyclodextrin corrosion inhibitor, indicating that xanthan gum-grafted β-cyclodextrin corrosion inhibitor is a mixed corrosion inhibitor with anodic inhibition as the main function, which may be due to adsorption on the electrode surface and the formation of a barrier film. Figure 5 It can also be seen that when the temperature and the concentration of xanthan gum-grafted β-cyclodextrin corrosion inhibitor change, the shape of the polarization curve does not change significantly, indicating that the addition of xanthan gum-grafted β-cyclodextrin corrosion inhibitor does not cause a change in the corrosion mechanism.

[0079] Table 8 shows that when xanthan gum-grafted β-cyclodextrin corrosion inhibitor is added, the corrosion inhibition efficiency gradually increases with the increase of the concentration of xanthan gum-grafted β-cyclodextrin corrosion inhibitor, but the corrosion inhibition efficiency decreases slightly with increasing temperature. When the corrosion inhibitor concentration is 150 mg / L, the corrosion current density reaches its minimum and the corrosion inhibition efficiency reaches its maximum at all temperatures. The corrosion inhibition efficiency reaches 91.72% at 293 K, and even at 313 K, the corrosion inhibition efficiency is still 88.73%. Based on the results of the polarization curve test, xanthan gum-grafted β-cyclodextrin corrosion inhibitor has a good corrosion inhibition effect.

[0080] Electrochemical impedance spectroscopy

[0081] Electrochemical impedance spectroscopy was used to investigate the corrosion mechanism of corrosion inhibitors on the surface of steel materials, and Nyquist and Bode plots were performed using an electrochemical workstation. Figure 6 The electrochemical parameters were obtained by fitting the equivalent circuit diagram. Table 9 details the electrochemical parameters and their corresponding corrosion inhibition efficiencies under different temperature conditions and concentration ranges. The data in this table shows that as the concentration of xanthan gum-grafted β-cyclodextrin corrosion inhibitor gradually increases, the value of Rct shows a corresponding increasing trend, and the corrosion inhibition efficiency also steadily increases. For example, when the temperature is set at 293 K and the concentration of xanthan gum-grafted β-cyclodextrin corrosion inhibitor reaches 150 mg / L, the corrosion inhibition efficiency is as high as 92.34%. Although the increase in temperature may have some impact on the corrosion inhibition efficiency, this change is not significant. Even in high-temperature environments (such as 313 K), the corrosion inhibition efficiency can still maintain a relatively high level of 87.78%.

[0082]

[0083] The obtained impedance spectrum was fitted and analyzed using Zsimpwin, and the Nyquist plot was obtained as follows: Figure 7 As shown, the impedance can be represented by the diameter of the semicircle. (Refer to Table 9 and...) Figure 7It can be seen that the arc diameter decreases significantly with increasing temperature, indicating a significant decrease in impedance and an accelerated corrosion rate. When xanthan gum-grafted β-cyclodextrin corrosion inhibitor is added, the arc radius is much larger than that of the control group, indicating a significant increase in impedance and inhibition of steel corrosion. The impedance value is highest and the corrosion inhibition efficiency is highest when the xanthan gum-grafted β-cyclodextrin corrosion inhibitor concentration reaches 150 mol / L. The figures also show that the fitted curves approximate a single capacitive arc, indicating that the addition of xanthan gum-grafted β-cyclodextrin corrosion inhibitor does not affect the corrosion mechanism and that it is an adsorption-type corrosion inhibitor.

[0084] Figure 8 The figure shows the Bode plot of Q235 steel sheet during the testing process. As can be seen from the figure, under various temperature conditions, the impedance modulus in the low-frequency range gradually increases with the increase of the xanthan gum-grafted β-cyclodextrin corrosion inhibitor concentration. When the concentration reaches 150 mg / L, the impedance modulus increases almost tenfold compared to the blank control group. This undoubtedly reveals that the impedance value is gradually increasing, and also means that the metal corrosion process is effectively inhibited. This phenomenon is consistent with the law revealed by the Nyquist plot. Near the mid-frequency region, we can clearly observe a relatively good linear correlation between frequency and impedance modulus, and its slope is close to -1. This means that a typical capacitance effect has been generated on the surface of Q235 steel, further confirming that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor has indeed formed a stable adsorption layer on the surface of Q235 steel. In addition, compared with the blank solution, the phase angle diagram of the solution with xanthan gum grafted β-cyclodextrin corrosion inhibitor is significantly wider, and the phase angle values ​​are generally higher than those of the blank solution, indicating that the xanthan gum grafted β-cyclodextrin corrosion inhibitor is adsorbed on the metal surface.

[0085] Surface Analysis

[0086] To further investigate the surface morphology of Q235 carbon steel corroded in 0.1 M sulfuric acid solution, SEM and EDS were used to analyze its surface morphology. The SEM and EDS results of the steel immersed in corrosion solutions with and without corrosion inhibitors are shown below. Figure 9 and Figure 10 As shown.

[0087] Due to the corrosive effect of sulfuric acid solution, the steel without corrosion inhibitor was severely corroded, resulting in the expected localized deep pits. In the presence of corrosion inhibitor, even at higher magnification, the damage to the polished lines in the image was much less, further confirming that the corrosion inhibitor molecules covered the active sites of the metallic steel, forming a protective film that prevented the steel surface from contacting the corrosive medium, thus effectively inhibiting corrosion.

[0088] Energy dispersive spectroscopy (EDS) results showed the proportions of each element on the surface of Q235 steel sheets. After immersion in 0.1 mol / L sulfuric acid for 12 h, the iron content (At.%) of carbon steel leached in 0.1 M sulfuric acid was 68.65% and 43.7% with and without corrosion inhibitor, respectively; the carbon content was 22.2% and 16.2%, respectively; and the oxygen content was 7.78% and 38.24%, respectively. The steel sheet without corrosion inhibitor had only 43.7% iron and 38.24% oxygen, indicating severe oxidative corrosion. With the addition of corrosion inhibitor, not only did the iron content increase, but the oxygen content also decreased significantly, indicating that the oxidative corrosion of the metal surface was inhibited. The increased oxygen content was most likely due to the adsorption of xanthan gum-grafted β-cyclodextrin corrosion inhibitor on the steel sheet surface. The increase in carbon content also confirms the adsorption of xanthan gum-grafted β-cyclodextrin corrosion inhibitor on the steel sheet surface.

[0089] Thermodynamic studies

[0090] Basic information about the interaction between the corrosion inhibitor and the metal surface can be obtained from various adsorption isotherms. This scheme attempts different adsorption isotherm models, namely Frumkin (equation (1), Freundlich (equation (2), Langmuir (equation (3), and Temkin (equation (4)). The fitting results are as follows: Figure 11 As shown, the results indicate that the adsorption of xanthan gum-grafted β-cyclodextrin corrosion inhibitor on the metal surface best conforms to the Langmuir adsorption isotherm model.

[0091]

[0092]

[0093]

[0094]

[0095] Where C is the inhibitor concentration, θ is the surface coverage, which can be expressed as the corrosion inhibition efficiency (%IE / 100), and K is the adsorption equilibrium constant.

[0096] Depend on Figure 11It can be seen that the adsorption isotherms fitted by the Langmuir model have an R² value closest to 1, all greater than 0.999; the adsorption isotherms simulated by the Temkin model have a maximum R² value of 0.9875 and a minimum of 0.9234; the adsorption isotherms simulated by the Freundlich model have a maximum R² value of 0.9859 and a minimum of 0.9301; and the adsorption isotherms simulated by the Frumkin model have a maximum R² value of 0.9787 and a minimum of only 0.7797. Compared with other models, the Langmuir model has the smallest R² value and the most successful fit. Therefore, it can be determined that the adsorption of xanthan gum-grafted β-cyclodextrin corrosion inhibitor on the surface of Q235 steel sheet conforms to the Langmuir isothermal adsorption model, indicating that the adsorption of this type of corrosion inhibitor on the metal surface is a monolayer adsorption.

[0097] The adsorption isotherm of Langmuir obtained by fitting can be used to calculate Kads under different temperature conditions, and then the adsorption Gibbs free energy ΔGads (kJ / mol) can be obtained by Equation 5. When the temperature difference is small, ΔH0 can be approximately regarded as constant. The adsorption heat ΔH0 of xanthan gum-grafted β-cyclodextrin corrosion inhibitor on the steel sheet surface can be obtained by Equation 6, and the Origin fitting is used to obtain... Figure 12 ΔH0 is obtained by calculating the slope of the straight line. The standard adsorption entropy ΔS0 can be obtained using Formula 7. The final calculation results are shown in Table 10.

[0098]

[0099]

[0100]

[0101] In the formula: ΔGads is the standard adsorption Gibbs free energy; R is the molar gas constant; T is the adsorption process temperature, K; Kads is the adsorption equilibrium constant; 55.5 is the molar concentration of H2O molecules, mol / L.

[0102]

[0103] K ads K represents the adsorption capacity of the corrosion inhibitor on the metal surface. ads The larger the K value, the stronger the adsorption effect of the corrosion inhibitor. Table 10 shows that when the temperature is 293 K, K... ads The value is the largest, at 6.77 × 10. 8 This indicates that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor exhibits the strongest adsorption capacity at this temperature. However, as the temperature increases, K... adsThe adsorption capacity of xanthan gum-grafted β-cyclodextrin corrosion inhibitor gradually decreased, but the overall decrease was not significant, indicating that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor could still adsorb onto the metal surface with a relatively strong effect. Table 10 also shows that ΔG ads The negative value indicates that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor can spontaneously adsorb onto the metal surface, and ΔG ads Since the values ​​are all less than -41 kJ / mol, the adsorption of xanthan gum-grafted β-cyclodextrin corrosion inhibitor is considered to be chemisorption. Furthermore, the table shows that the adsorption heat ΔH... 0 The value of -4.21 kJ / mol indicates that the entire adsorption process is exothermic. Increasing the temperature is detrimental to adsorption, which will lead to a decrease in the corrosion inhibition efficiency of the xanthan gum-grafted β-cyclodextrin corrosion inhibitor. This is consistent with the conclusions of the weight loss method and polarization curves. The adsorption of the corrosion inhibitor is an entropy-decreasing process, while the entropy in the data in the table is positive, indicating an entropy increase. This is because the xanthan gum-grafted β-cyclodextrin corrosion inhibitor is a type of bulky polymer corrosion inhibitor. When one molecule of the corrosion inhibitor is adsorbed onto the metal surface, it occupies more positions for water molecules, leading to an increase in the total entropy of the system.

[0104] Corrosion Inhibition Mechanism Analysis

[0105] like Figure 13 As shown, the corrosion inhibition mechanism of xanthan gum-grafted β-cyclodextrin as a corrosion inhibitor in 0.1 M H2SO4 is as follows: Figure 13 As shown in the figure. Both the weight loss method and electrochemical analysis results indicate that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor has good corrosion inhibition performance on metals. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) suggest that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor is adsorbed onto the metal surface. Adsorption model analysis indicates that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor adheres to the metal surface through chemisorption. Figure 13 It can be seen that the xanthan gum-grafted β-cyclodextrin corrosion inhibitor has a large number of –OH groups on its molecules. As electron-donating groups, –OH can be adsorbed onto the anodic position of the metal surface through electrostatic interaction, while protonated groups such as –COOH, –COOCH3, –CH2–O–CH2 can be adsorbed onto the cathodic position of the metal surface through chelation. The xanthan gum-grafted β-cyclodextrin corrosion inhibitor forms an adsorption film on the metal surface through these two mechanisms to prevent corrosion.

[0106] In summary, this process uses natural polysaccharides as raw materials, introduces no toxic heteroatoms or harmful reagents, and produces non-toxic, biodegradable products that fully meet the stringent requirements of modern industry for environmentally friendly materials. Secondly, the production process is extremely simple, employing conventional nucleophilic substitution and free radical grafting reactions under mild conditions, using common equipment, and with a clear process, facilitating large-scale industrial production. More importantly, the prepared xanthan gum-grafted β-cyclodextrin polymer (β-CD–XG) exhibits excellent corrosion inhibition properties. Its molecular structure is rich in various polar groups, enabling it to form a dense adsorption protective film on metal surfaces. The corrosion inhibition efficiency for carbon steels such as Q235 steel in acidic media can reach over 90%, significantly superior to single-component methods. Furthermore, this method also boasts advantages such as low cost and high raw material utilization, and through graft copolymerization, it achieves a synergistic effect between xanthan gum and cyclodextrin, further enhancing protective performance and demonstrating broad application prospects.

[0107] The embodiments of the present invention are given for illustrative and descriptive purposes only, and are not intended to be exhaustive or to limit the invention to the forms disclosed. Many modifications and variations will be apparent to those skilled in the art. The embodiments were chosen and described in order to better illustrate the principles and practical application of the invention, and to enable those skilled in the art to understand the invention and to design various embodiments with various modifications suitable for a particular purpose.

Claims

1. A method for preparing a polysaccharide corrosion inhibitor, characterized in that, Includes the following steps: a) Under alkaline conditions, β-cyclodextrin and allyl bromide undergo a nucleophilic substitution reaction in an aprotic polar solvent at 0°C to obtain allyl β-cyclodextrin with double bonds. b) Under anaerobic conditions, xanthan gum is dissolved in water, the pH is adjusted to 3-7, cerium ammonium nitrate initiator is added, and then allyl β-cyclodextrin obtained in step a) is added. Free radical graft copolymerization reaction is carried out at 50-80°C. After the reaction is completed, a terminator is added, and after precipitation, filtration and drying, xanthan gum grafted β-cyclodextrin corrosion inhibitor is obtained.

2. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step a), the aprotic polar solvent is N,N-dimethylformamide or N-methylpyrrolidone.

3. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step a), after the nucleophilic substitution reaction is completed, the reactants need to be allowed to stand for 2 hours before being transferred to a rotary evaporator for vacuum concentration. The residue is washed multiple times with alcohol, filtered, and the final product is placed in an oven to dry at 40 °C for 12 hours.

4. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step a), the alkaline conditions are provided by sodium hydroxide, and the mass ratio of β-cyclodextrin to sodium hydroxide is 1:50.

2.

5. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step a), the mass ratio of β-cyclodextrin to allyl bromide is 1:87.4, and the reaction time is 48 hours.

6. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step b), the concentration of xanthan gum in water is 1.67 g / L, and the mass ratio of cerium ammonium nitrate to xanthan gum is 0.6:

1.

7. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step b), the free radical graft copolymerization reaction time is 8 hours.

8. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, In step b), the mass ratio of allyl β-cyclodextrin to xanthan gum is 1:0.

86.

9. The method for preparing a polysaccharide corrosion inhibitor according to claim 1, characterized in that, The terminator is a saturated aqueous solution of hydroquinone, and the amount added is approximately 2 mL per 150 mL reaction system.

Images