Quaternary ammonium salt modified carbon quantum dot corrosion inhibitors and their preparation and application

Abstract

This application discloses a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor and its preparation and application, belonging to the field of nanomaterials and water treatment technology. The preparation method includes: using citric acid as a carbon source, through hot melt polycondensation, purification, concentration, and drying, a carboxyl-containing carbon quantum dot precursor is obtained; benzyl chloride and triethanolamine undergo a quaternization reaction, followed by recrystallization and drying, to obtain a hydroxyl-containing quaternary ammonium salt precursor; then, the two undergo an esterification covalent composite reaction, followed by purification, concentration, and drying, to obtain the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor. This application grafts the corrosion-inhibiting active groups of the quaternary ammonium salt onto the surface of carbon quantum dots through esterification covalent bonding, giving the product both nanoscale effect and film-forming adsorption capacity, achieving a synergistic effect in corrosion inhibition. At a dosage of 50 mg / L, the corrosion inhibition rate for N80 steel sheets reaches 96.4%, with a corrosion rate as low as 0.0205 mm / a. It also has advantages such as low toxicity, good water dispersibility, and low cost, making it applicable to oilfield water treatment.

Description

Technical Field

[0001] This application relates to the fields of nanomaterials and water treatment technology, and in particular to quaternary ammonium salt modified carbon quantum dot corrosion inhibitors and their preparation and application. Background Technology

[0002] In the processes of oil and gas extraction, transportation, and processing, the high salinity of produced fluids and injected water can easily lead to uniform corrosion and pitting of metal equipment, seriously affecting production efficiency and equipment safety. In severe cases, it can even cause accidents such as pipeline perforation and crude oil leakage, significantly increasing operation and maintenance costs and safety risks.

[0003] Currently, oilfield corrosion prevention measures mainly include using corrosion-resistant pipes, coating corrosion protection, and electrochemical corrosion protection. However, these methods have drawbacks such as limited corrosion inhibition effect, limited application conditions, and high cost. In contrast, chemical corrosion protection (adding corrosion inhibitors) is currently the most economical and effective anti-corrosion method, with advantages such as small dosage, simple equipment, and good effect.

[0004] Carbon quantum dots, as a novel nanomaterial, have shown great potential due to their small size, good water dispersibility, high biocompatibility, and ease of functionalization. However, existing carbon quantum dot corrosion inhibitors still face key challenges: different functional group modifications lead to significant differences in corrosion inhibition properties; their mechanism of action on actual oilfield water samples remains unclear; and existing inhibitors suffer from problems such as limited functionality and high toxicity. Therefore, there is an urgent need to develop a highly efficient, low-toxicity, multifunctional, and synergistic carbon quantum dot corrosion inhibitor to meet the pressing needs of complex oilfield environments for corrosion inhibition solutions. Summary of the Invention

[0005] This application provides a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor, its preparation and application, which solves the problems mentioned in the background art.

[0006] In a first aspect, embodiments of this application provide a method for preparing a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor, comprising the following steps: S1: Using citric acid as a carbon source, a preliminary carbon quantum dot solution is obtained after hot melt polycondensation reaction and dissolution; S2: The initial carbon quantum dot solution is purified to obtain a purified carbon quantum dot solution; S3: The purified carbon quantum dot solution was concentrated and dried to obtain a carbon quantum dot precursor containing carboxyl groups; S4: Benzyl chloride and triethanolamine are subjected to a quaternization reaction. After the reaction is completed, the mixture is rotary evaporated and crystallized to obtain preliminary quaternary ammonium salt crystals. S5: The preliminary quaternary ammonium salt crystals are recrystallized and dried to obtain a quaternary ammonium salt precursor containing hydroxyl groups; S6: The carbon quantum dot precursor and the quaternary ammonium salt precursor are subjected to an esterification covalent complexation reaction to obtain a preliminary modified carbon quantum dot solution; S7: The preliminarily modified carbon quantum dot solution is purified to obtain a purified modified carbon quantum dot solution; S8: The purified modified carbon quantum dot solution is concentrated and dried to obtain a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor.

[0007] In conjunction with the first aspect, in one possible implementation, the hot melt polycondensation reaction in step S1 is as follows: citric acid is reacted at 200°C for 4 hours, and after the reaction is completed, it is cooled to room temperature, ultrapure water is added, and the mixture is stirred until fully dissolved.

[0008] In conjunction with the first aspect, in one possible implementation, the purification process described in step S2 is as follows: first, the carbon quantum dot solution is filtered through a microporous membrane, and then transferred to a dialysis bag for dialysis.

[0009] In conjunction with the first aspect, in one possible implementation, the concentration in step S3 is achieved by rotary evaporation, and the drying is achieved by vacuum drying.

[0010] In conjunction with the first aspect, in one possible implementation, the molar ratio of benzyl chloride to triethanolamine in step S4 is 1.5:1, the quaternization reaction is carried out at room temperature for 24 hours, and then crystallized at 4°C after rotary evaporation.

[0011] In conjunction with the first aspect, in one possible implementation, the good solvent used for recrystallization in step S5 is methanol, and the poor solvent is ethyl acetate.

[0012] In conjunction with the first aspect, in one possible implementation, the esterification reaction in step S6 is carried out at a temperature of 90°C for a reaction time of 6 hours.

[0013] In conjunction with the first aspect, in one possible implementation, the purification process described in step S7 is as follows: first, the modified carbon quantum dot solution is filtered through a microporous membrane, and then transferred to a dialysis bag for dialysis.

[0014] Secondly, this application provides a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor prepared according to the preparation method in the first aspect or any possible implementation of the first aspect.

[0015] Thirdly, regarding the application of the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor in oilfield water treatment according to the second aspect of this application, the dosage of the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor in the oilfield water sample is 25-75 mg / L.

[0016] One or more technical solutions provided in the embodiments of this application have at least the following technical effects: First, this application uses low-toxicity raw materials such as citric acid, benzyl chloride, and triethanolamine to obtain quaternary ammonium salt modified carbon quantum dot corrosion inhibitors through a green preparation process, reducing biotoxicity and environmental risks. Second, the corrosion inhibitor prepared in this application requires a small dosage (25-75 mg / L), the process is simple, and the raw materials are inexpensive, significantly reducing the operation and maintenance costs of corrosion prevention in oilfields. Third, this application uses esterification covalent bonding to integrate the corrosion-inhibiting active groups (-OH, -N) of the quaternary ammonium salt. + R3 was successfully grafted onto the surface of carbon quantum dots, enabling the product to simultaneously possess the nano-size effect of carbon quantum dots (particle size 1-3 nm, excellent water dispersibility) and the film-forming adsorption capacity of quaternary ammonium salts, achieving a synergistic effect in corrosion inhibition. Experimental data show that at a dosage of 50 mg / L, the corrosion inhibitor of this application achieves a corrosion inhibition rate of 96.4% for N80 steel sheets, with a corrosion rate as low as 0.0205 mm / a, significantly superior to the precursor carbon quantum dots (corrosion inhibition rate 72.1%) and the precursor quaternary ammonium salt (corrosion inhibition rate 82.01%). Fourth, the corrosion inhibitor of this application can form a dense adsorption film on the metal surface (SEM verification shows a smooth surface without pitting corrosion). The adsorption process conforms to the Langmuir model and is dominated by chemical adsorption (ΔG°≈-38 kJ / mol), effectively solving the problems of unstable adsorption and incomplete film formation of existing corrosion inhibitors in complex oilfield water environments in the background technology. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments of this application will be briefly introduced below. Obviously, the accompanying drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the preparation process of the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor of this application; Figure 2 This is a diagram of the experimental setup for the corrosion inhibitor pad weight loss in this application; Figure 3 Transmission electron microscopy (TEM) images and particle size distribution comparison diagrams of the precursor carbon quantum dots and the quaternary ammonium salt modified carbon quantum dot corrosion inhibitors of this application. Figure 4 This is a comparison of the Fourier transform infrared (FT-IR) spectra of the precursor and the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor of this application. Figure 5 The images show a comparison of the scanning electron microscope (SEM) morphologies of N80 steel sheets after experiments with the precursor carbon quantum dot group and the quaternary ammonium salt modified carbon quantum dot group of this application; among them, Figure 5 (a) and Figure 5Image (c) shows SEM images of the steel sheet surface at different magnifications after the addition of quaternary ammonium salt modified carbon quantum dot corrosion inhibitor. Figure 5 (b) and Figure 5 (d) in the figure represents SEM images of the steel sheet surface at different magnifications after the addition of the precursor carbon quantum dot corrosion inhibitor.

[0019] Figure 6 The figure shows the thermodynamic fitting results of the precursor carbon quantum dots, the precursor quaternary ammonium salt, and the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor of this application. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] In the description of the embodiments of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the embodiments of this application and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. The terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. Furthermore, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0022] This application provides a method for preparing a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor, such as... Figure 1 As shown, the method includes the following steps: S1: Using citric acid as the carbon source, a preliminary carbon quantum dot solution is obtained after dissolution via a hot melt polycondensation reaction.

[0023] This application uses citric acid as a carbon source, which is inexpensive and widely available. Through hot-melt polycondensation, it can rapidly form a carbon quantum dot framework with carboxyl functional groups, providing reaction sites for subsequent functionalization modifications. Preferably, the hot-melt polycondensation reaction is as follows: citric acid is reacted at 200°C for 4 hours. After the reaction, it is cooled to room temperature, and ultrapure water is added and stirred until fully dissolved. Under these conditions, the carbon quantum dots have a high yield and uniform particle size, which is beneficial for forming a stable precursor for nano-corrosion inhibitors.

[0024] S2: The initial carbon quantum dot solution is purified to obtain a purified carbon quantum dot solution.

[0025] This application improves the purity of carbon quantum dots by removing unreacted citric acid and small molecule byproducts through purification, thereby ensuring the efficiency of subsequent esterification reactions. Preferably, the purification process involves filtering the carbon quantum dot solution through a microporous membrane and then dialyzing it in a dialysis bag. This purification method is simple to operate, low in cost, and can effectively obtain carbon quantum dots with a concentrated particle size distribution.

[0026] S3: The purified carbon quantum dot solution is concentrated and dried to obtain a carbon quantum dot precursor containing carboxyl groups.

[0027] Concentration and drying processes preserve carbon quantum dots in solid powder form, facilitating storage, weighing, and quantitative reaction with quaternary ammonium salt precursors. Preferably, concentration is achieved through rotary evaporation, and drying is performed using vacuum drying. This method removes the solvent at lower temperatures, preventing the deactivation of carboxyl groups on the carbon quantum dot surface due to high temperatures.

[0028] S4: Benzyl chloride and triethanolamine are subjected to a quaternization reaction. After the reaction is completed, the mixture is rotary evaporated and crystallized to obtain preliminary quaternary ammonium salt crystals.

[0029] Benzyl chloride reacts with triethanolamine to form a quaternary ammonium salt containing a hydroxyl functional group. The hydroxyl group provides a covalent bonding site for subsequent esterification with the carboxyl group of carbon quantum dots. Preferably, the molar ratio of benzyl chloride to triethanolamine is 1.5:1, the quaternization reaction is carried out at room temperature for 24 hours, and then crystallized at 4°C after rotary evaporation. This molar ratio yields the highest quaternary ammonium salt, and low-temperature crystallization at 4°C is beneficial for obtaining high-purity quaternary ammonium salt crystals.

[0030] S5: The preliminary quaternary ammonium salt crystals are recrystallized and dried to obtain a quaternary ammonium salt precursor containing hydroxyl groups.

[0031] Recrystallization can further remove unreacted raw materials and byproducts from the quaternary ammonium salt, improving its purity and thus enhancing the efficiency of subsequent esterification reactions. Preferably, methanol is a good solvent for recrystallization, while ethyl acetate is a poor solvent. This solvent system has good solubility and crystallization effect on the quaternary ammonium salt, yielding high-purity quaternary ammonium salt crystals.

[0032] S6: The carbon quantum dot precursor and the quaternary ammonium salt precursor are subjected to an esterification covalent complexation reaction to obtain a preliminary modified carbon quantum dot solution.

[0033] Quaternary ammonium salts are covalently grafted onto the surface of carbon quantum dots via esterification, giving the product both the small size effect of carbon quantum dots and the corrosion-inhibiting active groups (-OH, -N) of quaternary ammonium salts. + R3) achieves a synergistic effect in corrosion inhibition. Preferably, the esterification reaction temperature is 90℃ and the reaction time is 6h. Under these conditions, the esterification reaction proceeds fully, the grafting efficiency is high, and the structure of the carbon quantum dots is not damaged.

[0034] S7: The preliminarily modified carbon quantum dot solution is purified to obtain a purified modified carbon quantum dot solution.

[0035] Purification removes unreacted quaternary ammonium salts, free byproducts, and small molecule impurities, ensuring the purity of the final product. Preferably, the purification process involves filtering the modified carbon quantum dot solution through a microporous membrane and then transferring it to a dialysis bag for dialyzing. This purification method effectively retains the target product while removing impurities.

[0036] S8: The purified modified carbon quantum dot solution is concentrated and dried to obtain a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor.

[0037] Concentration and drying processes ensure the final product exists in solid powder form, facilitating storage, transportation, and quantitative dosing in practical applications. Preferably, concentration is achieved through rotary evaporation, and drying is achieved through vacuum drying.

[0038] It should be noted that, firstly, this application addresses the shortcomings of traditional corrosion inhibitors (such as chromates and nitrites) in the background technology, which are highly toxic and cause serious environmental pollution. It utilizes low-toxicity raw materials such as citric acid, benzyl chloride, and triethanolamine, and obtains a quaternary ammonium salt-modified carbon quantum dot corrosion inhibitor through a green preparation process, significantly reducing biotoxicity and environmental risks. Secondly, addressing the problems of high cost and limited implementation of traditional anti-corrosion measures such as corrosion-resistant pipes and coatings in the background technology, the corrosion inhibitor prepared in this application requires a small dosage (25-75 mg / L), has a simple process, and uses inexpensive raw materials, greatly reducing the operation and maintenance costs of oilfield corrosion prevention. Thirdly, addressing the key challenge of unclear structure-activity relationships and limited functionality of existing carbon quantum dot corrosion inhibitors in the background technology, this application uses esterification covalent bonding to integrate the corrosion-inhibiting active groups (-OH, -N) of the quaternary ammonium salt. +R3 was successfully grafted onto the surface of carbon quantum dots, enabling the product to simultaneously possess the nano-size effect of carbon quantum dots (particle size 1-3 nm, excellent water dispersibility) and the film-forming adsorption capacity of quaternary ammonium salts, achieving a synergistic effect in corrosion inhibition. Experimental data show that at a dosage of 50 mg / L, the corrosion inhibitor of this application achieves a corrosion inhibition rate of 96.4% for N80 steel sheets, with a corrosion rate as low as 0.0205 mm / a, significantly superior to the precursor carbon quantum dots (corrosion inhibition rate 72.1%) and the precursor quaternary ammonium salt (corrosion inhibition rate 82.01%). Fourth, the corrosion inhibitor of this application can form a dense adsorption film on the metal surface (SEM verification shows a smooth surface without pitting corrosion). The adsorption process conforms to the Langmuir model and is dominated by chemical adsorption (ΔG°≈-38 kJ / mol), effectively solving the problems of unstable adsorption and incomplete film formation of existing corrosion inhibitors in complex oilfield water environments in the background technology.

[0039] This application describes a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor prepared according to the above-described preparation method. The particle size distribution is between 1-3 nm, with uniform distribution and good water dispersibility. The molecular structure simultaneously contains carboxyl, hydroxyl, and quaternary ammonium ions, which can form a dense adsorption film on the metal surface, effectively inhibiting the erosion of the metal substrate by corrosive media.

[0040] This application describes the application of the aforementioned quaternary ammonium salt modified carbon quantum dot corrosion inhibitor in oilfield water treatment. The dosage of the corrosion inhibitor in the oilfield water sample is 25-75 mg / L. Within this dosage range, the corrosion inhibitor can fully exert its corrosion inhibition effect. Preferably, at a dosage of 50 mg / L, the corrosion inhibition efficiency for N80 steel sheets can reach 96.4%, with a corrosion rate as low as 0.0205 mm / a, significantly superior to commercially available conventional corrosion inhibitors.

[0041] Example 1 The preparation process in this embodiment is as follows: Figure 1 As shown, the process mainly includes three core stages: the synthesis of carbon quantum dot precursors, the synthesis of quaternary ammonium salt precursors, and the covalent compounding of the two through esterification.

[0042] (I) Preparation of Quaternary Ammonium Salt Modified Carbon Quantum Dot Corrosion Inhibitor S1: Synthetic precursors of carboxyl-containing carbon quantum dots Accurately weigh 10.0 g of citric acid and place it in a round-bottom flask. Carbonize the mixture at 200 °C for 4 h. After the reaction is complete, allow it to cool naturally to room temperature. Add 100 mL of ultrapure water to the flask and stir magnetically for 30 min until the solid is fully dissolved to obtain a preliminary carbon quantum dot solution.

[0043] S2: Purified carbon quantum dot solution The carbon quantum dot solution obtained in step S1 was first filtered through a 0.22 μm microporous membrane, the filtrate was collected, and then transferred to a dialysis bag with a 1000 Da cutoff. Ultrapure water was used as the dialysis solution, and the solution was dialyzed for 24 hours. The dialysis solution was changed every 6 hours during the process to obtain the purified carbon quantum dot solution.

[0044] S3: Concentration and drying to obtain carbon quantum dot precursors The purified carbon quantum dot solution obtained in step S2 was placed in a rotary evaporator and concentrated to a viscous state at 65°C. Then it was transferred to a vacuum drying oven and dried at 60°C for 4 hours to obtain a brownish-yellow powder containing carboxyl groups as carbon quantum dot precursors (CQDs).

[0045] S4: Synthesis of hydroxyl-containing quaternary ammonium salt precursors Benzyl chloride and triethanolamine were added to a beaker at a molar ratio of 1.5:1 and the mixture was magnetically stirred at room temperature for 24 hours. After the reaction was completed, the reaction solution was placed in a rotary evaporator and concentrated at 40°C. The concentrated solution was then transferred to a refrigerator at 4°C and allowed to stand for crystallization for 12 hours to obtain preliminary quaternary ammonium salt crystals.

[0046] S5: Recrystallization and purification of quaternary ammonium salt The preliminary quaternary ammonium salt crystals obtained in step S4 were dissolved in methanol (a good solvent), and then ethyl acetate (a poor solvent) was slowly added dropwise until the solution became slightly turbid. The solution was allowed to stand and recrystallized. The crystals were collected after filtration. The recrystallization operation was repeated twice. Finally, the solution was dried in a vacuum drying oven at 40°C for 6 hours to obtain a white crystalline quaternary ammonium salt precursor containing hydroxyl groups (QAS).

[0047] S6: Esterified covalent complex The carbon quantum dot precursor (CQDs) obtained in step S3 and the quaternary ammonium salt precursor (QAS) obtained in step S5 were added to a round-bottom flask purged with nitrogen at a mass ratio of 5:3. DMF (N,N-dimethylformamide) was added as a solvent, with the amount of solvent used to make the solid content of the reaction system 10-20 mg / mL (for example, when taking 0.5 g of CQDs and 0.3 g of QAS, 40-80 mL of DMF was added). The reaction was refluxed in an oil bath at 90 °C for 6 h. After the reaction was completed, the mixture was naturally cooled to room temperature to obtain a preliminary modified carbon quantum dot solution.

[0048] The basis for using a mass ratio of 5:3 in this application is that, since carbon quantum dots (CQDs) have no regular molecular structure, the surface carboxyl content cannot be accurately obtained through theoretical molar calculation. Therefore, the surface carboxyl loading of CQDs is measured by acid-base titration to determine that a mass ratio of 5:3 is the optimal ratio, at which the quaternary ammonium salt grafting rate reaches the maximum and the corrosion inhibition performance is optimal.

[0049] S7: Purified modified carbon quantum dots The modified carbon quantum dot solution obtained in step S6 was first filtered through a 0.22 μm microporous membrane, the filtrate was collected, and then transferred to a dialysis bag with a 500 Da cutoff. Ultrapure water was used as the dialysis solution, and the solution was dialyzed for 48 hours. The dialysis solution was replaced every 8 hours during the process to obtain the purified modified carbon quantum dot solution.

[0050] S8: Concentrate and dry to obtain the final product. The purified modified carbon quantum dot solution obtained in step S7 was placed in a rotary evaporator and concentrated to a viscous state at 65°C. Then it was transferred to a vacuum drying oven and dried at 60°C for 4 hours to obtain a light yellow powdery quaternary ammonium salt modified carbon quantum dot corrosion inhibitor (QAS-CQDs).

[0051] (ii) Product characterization 1. Morphology and particle size characterization The morphology of the precursor carbon quantum dots and the quaternary ammonium salt-modified carbon quantum dot corrosion inhibitor prepared in this example was characterized using transmission electron microscopy. The results are as follows: Figure 3 As shown. Figure 3 The left image shows the TEM image and particle size distribution of the precursor carbon quantum dots, while the right image shows the TEM image and particle size distribution of the quaternary ammonium salt modified carbon quantum dots (QAS-CQDs). Figure 3 It can be seen that both are uniformly distributed, with a predominantly spherical morphology, exhibiting good dispersibility and no agglomeration. The precursor carbon quantum dots have a particle size distribution between 1 and 4 nm, with an average particle size of 2.1 nm; the carbon quantum dots modified with quaternary ammonium salt have a particle size distribution between 1 and 3 nm, with an average particle size of 1.8 nm. Figure 3 The magnified images also show that both CQDs and QAS-CQDs contain lattice fringes in graphite regions, with lattice spacings of approximately 0.21 nm and 0.22 nm, respectively, indicating that both have crystallinity similar to graphite. These results demonstrate that quaternary ammonium salt modification did not disrupt the core structure of carbon quantum dots, and that the modified particles showed a slight decrease in size and improved uniformity.

[0052] 2. Infrared spectroscopy characterization Functional group analysis was performed on the precursor carbon quantum dots, the precursor quaternary ammonium salt, and the quaternary ammonium salt-modified carbon quantum dot corrosion inhibitor prepared in this example using Fourier transform infrared spectroscopy. The results are as follows: Figure 4 As shown. Figure 4 In the diagram, the green curve represents precursor carbon quantum dots (CQDs), the cyan curve represents precursor quaternary ammonium salt (QAS), and the purple curve represents quaternary ammonium salt-modified carbon quantum dots (QAS-CQDs). Comparing the three curves reveals that the QAS-CQDs surface retains the characteristic absorption peaks of the original CQDs, and also exhibits a peak at 3432.7 cm⁻¹. - The characteristic peak of the stretching vibration of -OH is observed at ¹, at 1384.8 cm⁻¹. - ¹ R4N is present at this location. +The bending vibration peak is at 1714.9 cm⁻¹. - The characteristic stretching vibration peak of the ester group (-COO-) is observed at position ¹. These results indicate that a covalent bond is formed between the quaternary ammonium salt and carbon quantum dots via esterification, successfully achieving covalent recombination of QAS and CQDs.

[0053] (III) Evaluation of corrosion inhibition performance 1. Experimental Apparatus and Methods This embodiment uses a corrosion-inhibiting plate weight loss test device for performance evaluation. The device is as follows: Figure 2 As shown (top left: blank group; top right: QAS-CQDs group; bottom left: CQDs group; bottom right: QAS group), the apparatus includes a constant temperature water bath, a suspension bracket, N80 steel sheet samples, and a reaction vessel. The experiment was conducted according to the petroleum and natural gas industry standard "Performance Inhibitors and Evaluation Methods for Oilfield Produced Water Treatment" (SY-T5273-2014), using the static weight loss method.

[0054] The experimental water sample was produced in the WZ12-2A oilfield in the western South China Sea. The water quality parameters are as follows: Na + +K + It is 11403 mg / L, Ca² + 700 mg / L, Mg² + It is 208 mg / L, Cl - The concentration of HCO3 was 20111 mg / L. - It is 547 mg / L, SO4² - The concentration of particulate matter (SS) was 281 mg / L, the concentration of suspended solids (SS) was 2 mg / L, and the concentration of dissolved oxygen was 6 mg / L.

[0055] N80 steel sheets were suspended in the above-mentioned oilfield water samples and placed in a constant temperature water bath at 60°C for 72 hours. The corrosion inhibition performance of the blank group, the group with carbon quantum dot precursor (50 mg / L), the group with quaternary ammonium salt precursor (50 mg / L), and the group with product of this example (25, 50, 75 mg / L) were tested respectively.

[0056] The corrosion inhibition efficiency η is calculated according to formula 1: η = (Δm0 - Δm1) / Δm0 × 100%; Corrosion rate r c Calculate according to formula 2: r c =8.76×10 4 ×(m-m1) / (S×t×ρ); In the formula: Δm0 is the mass loss of the blank group steel sheet (g), Δm1 is the mass loss of the added group steel sheet (g); m is the mass of the steel sheet before the test (g), m1 is the mass of the steel sheet after the test (g), S is the total area of ​​the steel sheet (cm²), ρ is the density of the steel sheet (g / cm³), and t is the test time (h).

[0057] 2. Experimental Results:

[0058] The results showed that the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor prepared in this embodiment achieved a corrosion inhibition rate of up to 96.4% at a dosage of 50 mg / L, with a corrosion rate of only 0.0205 mm / a, which was significantly better than that of carbon quantum dots (corrosion inhibition rate of 72.1%) and quaternary ammonium salt (corrosion inhibition rate of 82.01%) as the single precursor. This indicates that the covalent combination of carbon quantum dots and quaternary ammonium salt produced a significant synergistic effect.

[0059] 3. Surface morphology analysis of steel sheets To further verify the corrosion inhibition effect, scanning electron microscopy was used to observe the surface morphology of N80 steel sheets after the experiments, including the blank group, the precursor carbon quantum dot group, and the quaternary ammonium salt modified carbon quantum dot group. The results are as follows: Figure 5 As shown. Figure 5 middle, Figure 5 (a) and Figure 5 (c) shows the surface morphology of the steel sheet after the addition of quaternary ammonium salt modified carbon quantum dot corrosion inhibitor (at different magnifications). Figure 5 (b) and Figure 5 (d) in the figure shows the surface morphology of the steel sheet after the addition of the precursor carbon quantum dot corrosion inhibitor (at different magnifications).

[0060] Depend on Figure 5 (b) and Figure 5 As can be seen in (d), even after adding the precursor carbon quantum dots, obvious corrosion marks and pitting pits still exist on the surface of the steel sheet, resulting in a relatively rough surface. However, due to... Figure 5 (a) and Figure 5 As can be seen in (c), after adding the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor, the surface of the steel sheet is smooth and flat, with no obvious pitting corrosion and corrosion product accumulation. This indicates that the corrosion inhibitor forms a dense protective film on the surface of the steel sheet, effectively blocking the contact between the corrosive medium and the metal substrate.

[0061] 4. Thermodynamic Fitting Analysis The adsorption behavior of precursor carbon quantum dots, precursor quaternary ammonium salt, and the quaternary ammonium salt-modified carbon quantum dot corrosion inhibitor prepared in this example was thermodynamically fitted, and the results are as follows: Figure 6 As shown. Figure 6In the diagram, the first image on the left shows the fitting curve for the precursor carbon quantum dots (CQDs), the second image shows the fitting curve for the precursor quaternary ammonium salt (QAS), and the third image shows the fitting curve for quaternary ammonium salt modified carbon quantum dots (QAS-CQDs). The fitting results indicate that the adsorption behavior of the three corrosion inhibitors on the N80 steel sheet surface conforms to the Langmuir isotherm adsorption model. Calculations show that QAS-CQDs has the largest adsorption equilibrium constant, with a standard adsorption free energy ΔG° of approximately -38 kJ / mol. This indicates that the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor undergoes a mixed adsorption process on the steel sheet surface, involving both chemical and physical adsorption, with chemical adsorption being dominant, resulting in a more stable and dense adsorption film.

[0062] (iv) Application methods In actual oilfield applications, the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor prepared in this embodiment is directly added to the oilfield produced water treatment system at a dosage of 50 mg / L. This can effectively control the corrosion rate of pipelines and equipment to below 0.05 mm / a, meeting the oilfield's corrosion prevention requirements.

[0063] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0064] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of this application.

Claims

1. A method for preparing a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor, characterized in that, Includes the following steps: S1: Using citric acid as a carbon source, a preliminary carbon quantum dot solution is obtained after hot melt polycondensation reaction and dissolution; S2: The initial carbon quantum dot solution is purified to obtain a purified carbon quantum dot solution; S3: The purified carbon quantum dot solution was concentrated and dried to obtain a carbon quantum dot precursor containing carboxyl groups; S4: Benzyl chloride and triethanolamine are subjected to a quaternization reaction. After the reaction is completed, the mixture is rotary evaporated and crystallized to obtain preliminary quaternary ammonium salt crystals. S5: The preliminary quaternary ammonium salt crystals are recrystallized and dried to obtain a quaternary ammonium salt precursor containing hydroxyl groups; S6: The carbon quantum dot precursor and the quaternary ammonium salt precursor are subjected to an esterification covalent complexation reaction to obtain a preliminary modified carbon quantum dot solution; S7: The preliminarily modified carbon quantum dot solution is purified to obtain a purified modified carbon quantum dot solution; S8: The purified modified carbon quantum dot solution is concentrated and dried to obtain a quaternary ammonium salt modified carbon quantum dot corrosion inhibitor.

2. The preparation method according to claim 1, characterized in that, The hot melt polycondensation reaction described in step S1 is as follows: citric acid is reacted at 200°C for 4 hours. After the reaction is completed, it is cooled to room temperature, ultrapure water is added, and the mixture is stirred until fully dissolved.

3. The preparation method according to claim 1, characterized in that, The purification process described in step S2 is as follows: first, the carbon quantum dot solution is filtered through a microporous membrane, and then transferred to a dialysis bag for dialysis.

4. The preparation method according to claim 1, characterized in that, The concentration in step S3 is achieved by rotary evaporation, and the drying is achieved by vacuum drying.

5. The preparation method according to claim 1, characterized in that, In step S4, the molar ratio of benzyl chloride to triethanolamine is 1.5:1, the quaternization reaction is carried out at room temperature for 24 hours, and then crystallized at 4°C after rotary evaporation.

6. The preparation method according to claim 1, characterized in that, The good solvent used for recrystallization in step S5 is methanol, and the bad solvent is ethyl acetate.

7. The preparation method according to claim 1, characterized in that, The esterification reaction in step S6 is carried out at a temperature of 90°C for 6 hours.

8. The preparation method according to claim 1, characterized in that, The purification process described in step S7 is as follows: first, the modified carbon quantum dot solution is filtered through a microporous membrane, and then transferred to a dialysis bag for dialysis.

9. The quaternary ammonium salt modified carbon quantum dot corrosion inhibitor prepared by the preparation method according to any one of claims 1-8.

10. The application of the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor according to claim 9 in oilfield water treatment, characterized in that, The dosage of the quaternary ammonium salt modified carbon quantum dot corrosion inhibitor in oilfield water samples is 25-75 mg / L.

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