Carbon quantum dot asphaltene inhibitor modified by hydrophobic long carbon chain as well as preparation method and application of carbon quantum dot asphaltene inhibitor

Abstract

The invention discloses a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain as well as a preparation method and application of the carbon quantum dot asphaltene inhibitor, and belongs to the technical field of oil field plug removal. The preparation method comprises the following steps: dissolving citric acid and ethidene diamine in distilled water, and after a heating reaction is finished, centrifugally collecting supernate to obtain a carbon quantum dot solution; adding an inorganic acid solution, and carrying out oxidation reaction, washing and drying to obtain carboxylated carbon quantum dots; the preparation method comprises the following steps: preparing a hydrophobic long carbon chain modified carbon quantum dot asphaltene inhibitor, uniformly mixing the hydrophobic long carbon chain modified carbon quantum dot asphaltene inhibitor with N-amino polyhexylamine and a solvent, adding a coupling agent, carrying out an amidation reaction, and carrying out rotary evaporation, water washing, centrifugation and drying to obtain the hydrophobic long carbon chain modified carbon quantum dot asphaltene inhibitor. Strong adsorption is formed through interaction with asphaltene molecules through pi-pi interaction, electrostatic attraction, hydrogen bonds, Van der Waals force and the like. The grafted hydrophobic long carbon chain forms large steric hindrance among asphaltene molecules, formation of large-scale parallel stacking is hindered, direct contact and aggregation of the asphaltene molecules are prevented, and the efficiency of the inhibitor is remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oilfield unblocking, and in particular relates to a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, and a preparation method and application thereof. Background Art

[0002] With the continuous growth of energy demand and the rapid development of the petroleum industry, the quality control and processing technology of petroleum products have become important research directions. In the process of petroleum refining, the presence of asphaltene brings many challenges to the refining process and the properties of the final product. Asphaltene, as a high molecular polymer in petroleum, has high viscosity and is not easily soluble. It can cause pipeline blockage, equipment wear and product quality degradation during processing. Therefore, the development of effective asphaltene inhibitors is crucial to improving petroleum processing efficiency and product quality.

[0003] Traditional asphaltene inhibitors mainly include some small molecule compounds and inorganic materials. Although these traditional inhibitors can alleviate the deposition problem of asphaltene to a certain extent, their effects are often restricted by problems such as insufficient solubility, poor stability and weak selectivity. In recent years, the emergence of nanomaterials has brought new breakthroughs in this field. Among them, carbon quantum dots (CQDs), as a new type of carbon nanomaterial, have become a research hotspot due to their unique optical properties, good biocompatibility and other chemical properties. Carbon quantum dots are a type of carbon nanomaterial with a size usually between 2-10 nanometers and good fluorescence properties and chemical stability. By introducing various functional groups on the surface of carbon quantum dots, their chemical properties and physical properties can be significantly changed. For example, by grafting long-chain alkyl or other hydrophobic groups on the surface of carbon quantum dots, their dispersibility and stability in oily media can be improved. This modification not only improves the hydrophobicity of carbon quantum dots, but also enhances their interaction with asphaltene molecules in the oil phase. Carbon quantum dots modified with hydrophobic long carbon chains have significant advantages: on the one hand, hydrophobic modification enables carbon quantum dots to exist stably in oily media, thereby effectively reducing the deposition and aggregation of asphaltene; on the other hand, the surface functional groups of carbon quantum dots can further inhibit their aggregation behavior by forming strong interactions with asphaltene molecules. This method can not only improve the performance of carbon quantum dots in oil recovery, but also effectively improve the shortcomings of traditional inhibitors in practical applications.

[0004] At present, although some studies have attempted to use carbon quantum dots to inhibit asphaltene deposition, they all focus on the basic properties of the original carbon quantum dots, and there is still a lack of systematic research on how to improve their inhibitory effect through surface modification technology. Therefore, the development of a preparation method for carbon quantum dot asphaltene inhibitors modified by hydrophobic long carbon chains will provide new ideas and solutions for asphaltene inhibition technology. This will not only help improve the inhibitory effect during oil recovery, but is also expected to play an important role in improving the quality of petroleum products and reducing processing costs. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain and its preparation method and application, so as to solve the technical problem of easy aggregation and deposition of asphaltene in crude oil extraction and refining processes.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention discloses a method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, comprising the following steps: S1: Dissolve citric acid and ethylenediamine in distilled water. After the temperature reaction is completed, collect the supernatant by centrifugation to obtain a carbon quantum dot solution. S2: adding an inorganic acid solution to the carbon quantum dot solution obtained in step S1, and obtaining carboxylated carbon quantum dots after oxidation reaction, washing, and drying; S3: Evenly mix N-aminopolyhexylamine, solvent and the carboxylated carbon quantum dots obtained in step S2, add a coupling agent, and after amidation reaction, obtain a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain by rotary evaporation, water washing, centrifugation and drying.

[0007] Preferably, in step S1, the mass ratio of citric acid, ethylenediamine and distilled water is 1:(1-2.5):(15-30).

[0008] Preferably, in step S1, the temperature of the temperature-raising reaction is 160-200° C., and the time is 4-10 hours.

[0009] Preferably, in step S2, the volume ratio of the carbon quantum dot solution to the inorganic acid solution is (30-50):1; the inorganic acid solution is any one of sulfuric acid, nitric acid and hydrochloric acid, and the mass concentration of the inorganic acid solution is 20%-60%.

[0010] Preferably, in step S2, the oxidation reaction temperature is 25-80° C. and the time is 2-8 hours.

[0011] Preferably, in step S3, the mass ratio of carboxylated carbon quantum dots, N-aminopolyhexylamine and solvent is 1:(2-3):(35-50); the solvent is any one of N,N-dimethylformamide, dimethyl sulfoxide and tetrahydrofuran.

[0012] Preferably, in step S3, the coupling agent is any one of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide; and the amount of the coupling agent added is 5% to 10% of the mass of the carboxylated carbon quantum dots.

[0013] Preferably, in step S3, the amidation reaction is carried out at a temperature of 25-35° C. and for a time of 6-12 h.

[0014] The present invention also discloses a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, which is prepared by the above preparation method. The general structural formula of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is: ; Where n is the degree of polymerization, and the value range of n is 10~30.

[0015] The present invention also discloses the use of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain obtained by the above preparation method in crude oil extraction and petroleum refining, characterized in that the dispersion stability at 30°C is 88.5%~91.8%; the dispersion stability at 150°C is 89.7%~95.9%.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention provides a method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain. Compared with a traditional asphaltene inhibitor, the present invention promotes the amidation reaction between the carboxyl group and N-aminopolyhexylamine on the surface of the carbon quantum dot under the action of a coupling agent, and connects the N-aminopolyhexylamine to the surface of the carbon quantum dot, thereby synthesizing a carbon quantum dot asphaltene inhibitor. The modified carbon quantum dot inhibitor can interact with the asphaltene molecules through π-π interaction, electrostatic attraction, hydrogen bonding and van der Waals force, effectively inhibiting its aggregation and deposition. At the same time, the carbon quantum dot inhibitor also has a nanometer size and a large specific surface area. By adsorbing on the asphaltene molecules, a large steric hindrance effect is formed, which effectively prevents direct contact and aggregation between asphaltene molecules, thereby significantly improving the inhibition efficiency and stabilizing the dispersed system. In addition, the hydrophobic long side chain structure hinders the formation of large-scale parallel stacking, keeps the asphaltene stable and dispersed, thereby effectively preventing the formation of organic scale and significantly improving the efficiency of the inhibitor. At the same time, it has a nanometer size and a large specific surface area, can enter the low-permeability and ultra-low-permeability reservoir, and has a good viscosity reduction and deposition prevention effect on the oil phase inside it.

[0017] The present invention also discloses a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain obtained by the above-mentioned preparation method, which has a nano size and a large specific surface area, can effectively penetrate into low permeability and ultra-low permeability reservoirs, achieve a good viscosity reduction effect on the internal oil phase and effectively prevent deposition. At the same time, the fluidity of crude oil can be enhanced. The addition of the inhibitor helps to maintain the fluidity of crude oil, reduce the increase in fluid resistance caused by asphaltene deposition, make crude oil easier to be mined and transported, and thus improve the production efficiency of the oil field. The carbon quantum dot asphaltene inhibitor prepared by the present invention also has a cost advantage. The raw material for its preparation is low-cost and easily available citric acid, the reaction process is simple and easy to control, and it is suitable for large-scale production, which helps to reduce the production cost of the inhibitor and the overall operating cost of the oil field. In addition, the carbon quantum dot asphaltene inhibitor has good chemical stability, can maintain the inhibitory effect under different temperature and pressure conditions, and reduces the asphaltene deposition problem caused by fluctuations in conditions.

[0018] The present invention also discloses the use of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain prepared by the above preparation method in crude oil extraction and petroleum refining. The carbon quantum dot inhibitor prepared by the present invention has a unique molecular structure design, which strongly interacts with asphaltene molecules, effectively disperses asphaltene, and significantly reduces the risk of formation blockage. The addition of the inhibitor reduces the fluid resistance caused by asphaltene deposition, making the flow of crude oil smoother, thereby improving the extraction and transportation efficiency of the oil field. By effectively inhibiting asphaltene deposition, the inhibitor can also reduce blockage and corrosion inside the equipment, extend the service life of the equipment, and reduce maintenance costs and economic losses caused by downtime. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The synthetic route diagram of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain disclosed in the present invention; Figure 2 This is an infrared spectrum of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain prepared in Example 2 of the present invention.

[0020] Figure 3 The particle size distribution histogram of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain disclosed in the present invention. DETAILED DESCRIPTION

[0021] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0022] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0023] Unless otherwise specified, all technical and scientific terms used herein have the common meanings understood by those skilled in the art for the present invention. In case of conflict, the definitions in this specification shall prevail.

[0024] The theories or mechanisms described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, that is, the present invention can be implemented without being limited by any specific theory or mechanism.

[0025] In this article, all features such as values, quantities, contents and concentrations defined in the form of numerical ranges or percentage ranges are for simplicity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to have included and specifically disclosed all possible secondary ranges and individual values ​​within the range (including integers and fractions).

[0026] In this document, unless otherwise specified, “includes,” “including,” “contains,” “has,” or similar terms cover the meanings of “consisting of” and “mainly consisting of,” for example, “A includes a” covers the meanings of “A includes a and other” and “A only includes a.”

[0027] In this document, in order to make the description concise, not all possible combinations of various technical features in various embodiments or examples are described. Therefore, as long as there is no contradiction in the combination of these technical features, the various technical features in various embodiments or examples can be combined arbitrarily, and all possible combinations should be considered to be within the scope of this specification.

[0028] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0029] The following examples use conventional instruments and equipment in the art. The experimental methods in the following examples where specific conditions are not specified are usually carried out under conventional conditions or under conditions recommended by the manufacturer. The various raw materials used in the following examples are conventional commercial products unless otherwise specified, and their specifications are conventional specifications in the art. In the specification of the present invention and the following examples, unless otherwise specified, "%" means weight percentage, "part" means weight part, and ratio means weight ratio.

[0030] The present invention is further described in detail below in conjunction with the accompanying drawings: During crude oil extraction and refining, asphaltene often aggregates, flocculates and deposits due to temperature and pressure fluctuations and changes in crude oil composition. These phenomena can lead to blockage of oil well formations and oil pipelines, ultimately affecting recovery and production efficiency. To address this problem, the present invention aims to construct a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain to inhibit the aggregation and deposition of asphaltene particles, reduce the risks associated with crude oil production and transportation, and improve the stability and economic benefits of the oil extraction and refining process.

[0031] The present invention discloses a method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, comprising the following steps: S1: Dissolve citric acid and ethylenediamine in distilled water to form a uniform solution, then pour the solution into a high-pressure reactor and heat it for a period of time. After the reaction is completed, collect the supernatant by centrifugation to obtain a carbon quantum dot solution.

[0032] S2: adding an inorganic acid solution to the carbon quantum dot solution to introduce carboxyl groups on the surface of the carbon quantum dots through an oxidation reaction. After the reaction is completed, washing with excess distilled water is performed multiple times to remove the acidic solution, and carboxylated carbon quantum dots are obtained after drying.

[0033] S3: Carboxylated carbon quantum dots, N-aminopolyhexylamine and solvent are mixed evenly, a coupling agent is added to activate the reaction between the carboxyl group and the amino group, and the mixture is heated to a certain temperature and stirred to perform an amidation reaction. After the reaction is completed, a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is obtained by rotary evaporation, water washing, centrifugation and drying.

[0034] As an optional solution, in step S1, the mass ratio of citric acid, ethylenediamine and distilled water is 1:(1-2.5):(15-30), the reaction temperature is 160-200°C, and the reaction time is 4-10h.

[0035] As an optional scheme, in step S2, the inorganic acid solution is one of sulfuric acid, nitric acid and hydrochloric acid, and the mass concentration of the inorganic acid solution is 20%~60%; the volume ratio of the carbon quantum dot solution to the inorganic acid solution is (30~50):1; the oxidation reaction temperature is 25~80°C, and the reaction time is 2~8h.

[0036] As an optional scheme, in step S3, the solvent is one of N,N-dimethylformamide, dimethyl sulfoxide and tetrahydrofuran; the mass ratio of carboxylated carbon quantum dots, N-aminopolyhexylamine and solvent is 1: (2~3): (35~50); the coupling agent is one of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide; the amount of coupling agent added is 5~10wt% of the mass of carboxylated carbon quantum dots; the amidation reaction temperature is 25~35°C, and the reaction time is 6~12h.

[0037] The present invention provides a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain. The general structural formula of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is: ; Where n is the degree of polymerization, and the value range of n is 10~30.

[0038] Based on the analysis of the molecular structure of asphaltene, the present invention grafts N-aminopolyhexylamine on the edge of the carboxylated carbon quantum dot molecule through carboxylation reaction and amidation reaction. The formed carbon quantum dot asphaltene inhibitor can produce strong π-π interaction with the asphaltene molecules, and provides steric hindrance through the hydrophobic side chain, effectively preventing the further polymerization and deposition of the asphaltene molecules, and can effectively improve the recovery rate. In addition, the carbon quantum dot asphaltene inhibitor has a nanometer size and a large specific surface area, can enter the low-permeability and ultra-low-permeability reservoir, and has a good viscosity reduction and anti-deposition effect on the oil phase inside. At the same time, it has cost advantages, the raw material for its preparation is low-cost and easily available citric acid, the reaction process is simple and easy to control, and it is suitable for large-scale production.

[0039] The present invention provides a kind of carbon quantum dot asphaltene inhibitor modified by hydrophobic long carbon chain prepared according to the above preparation method, which is used in crude oil extraction and petroleum refining. When used as a scale inhibitor in the oil field, by grafting alkyl long chains on the surface of carbon quantum dots, its dispersibility and stability in oily media can be improved. There are also more hydrophobic side chains around, and the structure hinders the formation of large-scale parallel stacking, keeps asphaltene stable and dispersed, thereby effectively preventing the formation of organic scale and significantly improving the efficiency of the inhibitor. In addition, the carbon quantum dot asphaltene inhibitor has a nano size and a large specific surface area, can effectively penetrate into low permeability and ultra-low permeability reservoirs, achieve good viscosity reduction effect on the internal oil phase and effectively prevent deposition. At the same time, it can enhance the fluidity of crude oil. The addition of the inhibitor helps to maintain the fluidity of crude oil, reduce the increase in fluid resistance caused by asphaltene deposition, make crude oil easier to be mined and transported, and thus improve the production efficiency of oil fields. It can extend the service life of equipment. By effectively inhibiting the deposition of asphaltene, the inhibitor can reduce the blockage inside the equipment, thereby extending the service life of related equipment, reducing maintenance costs and downtime. The application of this inhibitor can significantly improve the economic benefits of oil fields by increasing recovery rates, reducing maintenance costs, extending equipment life, and reducing losses caused by production stoppages.

[0040] Example 1 A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain comprises the following steps: S1: Dissolve 10g of citric acid and 10g of ethylenediamine in 150g of distilled water to form a uniform solution. Pour the solution into a high-pressure reactor and heat it at 160°C for 4h. After the reaction, collect the supernatant by centrifugation to obtain a carbon quantum dot solution.

[0041] S2: Take 30mL of carbon quantum dot solution, add 1mL of 30% sulfuric acid solution to introduce carboxyl groups on the surface of carbon quantum dots through oxidation reaction, the oxidation reaction temperature is 25℃, and the reaction time is 2h. After the reaction is completed, 10g of carboxylated carbon quantum dot solid is obtained after washing and drying.

[0042] S3: 1 g of carboxylated carbon quantum dot solid was mixed with 2 g of N-aminopolyhexylamine and 35 g of N,N-dimethylformamide, and 0.05 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide was added. The mixture was heated to 25 °C and stirred for 6 h, and then rotary evaporated, washed with water, centrifuged and dried to obtain a carbon quantum dot asphaltene inhibitor modified with a hydrophobic long carbon chain.

[0043] Example 2 A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain comprises the following steps: S1: Dissolve 12g of citric acid and 24g of ethylenediamine in 180g of distilled water to form a uniform solution. Pour the solution into a high-pressure reactor and heat it at 200°C for 10h. After the reaction is completed, collect the supernatant by centrifugation to obtain a carbon quantum dot solution.

[0044] S2: Take 40mL of carbon quantum dot solution, add 1mL of 20% nitric acid solution to introduce carboxyl groups on the surface of carbon quantum dots through oxidation reaction, the oxidation reaction temperature is 80℃, and the reaction time is 8h. After the reaction is completed, 11g of carboxylated carbon quantum dot solid is obtained after washing and drying.

[0045] S3: 1.5 g of carboxylated carbon quantum dot solid was mixed with 3 g of N-aminopolyhexylamine and 52.5 g of dimethyl sulfoxide, and 0.15 g of 1,3-dicyclohexylcarbodiimide was added. The mixture was heated to 35 °C and stirred for 12 h, and then rotary evaporated, washed with water, centrifuged and dried to obtain a carbon quantum dot asphaltene inhibitor modified with a hydrophobic long carbon chain.

[0046] Example 3 A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain comprises the following steps: S1: 8g of citric acid and 20g of ethylenediamine were dissolved in 240g of distilled water to form a uniform solution. The solution was poured into a high-pressure reactor and heated at 160°C for 5h. After the reaction, the supernatant was collected by centrifugation to obtain a carbon quantum dot solution.

[0047] S2: Take 30mL of carbon quantum dot solution, add 1mL of 30% hydrochloric acid solution to introduce carboxyl groups on the surface of carbon quantum dots through oxidation reaction, the oxidation reaction temperature is 35°C, and the reaction time is 4h. After the reaction is completed, 6g of carboxylated carbon quantum dot solid is obtained after washing and drying.

[0048] S3: 0.8 g of carboxylated carbon quantum dot solid was mixed with 2.4 g of N-aminopolyhexylamine and 40 g of tetrahydrofuran, 0.04 g of N-hydroxysuccinimide was added, the mixture was heated to 25 °C and stirred for 6 h, and then rotary evaporated, washed with water, centrifuged and dried to obtain a hydrophobic long-chain modified carbon quantum dot asphaltene inhibitor.

[0049] Example 4 A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain comprises the following steps: S1: Dissolve 15g of citric acid and 15g of ethylenediamine in 300g of distilled water to form a uniform solution. Pour the solution into a high-pressure reactor and heat it at 200°C for 7h. After the reaction is completed, collect the supernatant by centrifugation to obtain a carbon quantum dot solution.

[0050] S2: Take 50mL of carbon quantum dot solution, add 1mL of 60% sulfuric acid solution to introduce carboxyl groups on the surface of carbon quantum dots through oxidation reaction, the oxidation reaction temperature is 25°C, and the reaction time is 8h. After the reaction is completed, 12g of carboxylated carbon quantum dot solid is obtained after washing and drying.

[0051] S3: 2 g of carboxylated carbon quantum dot solid was mixed with 6 g of N-aminopolyhexylamine and 100 g of N,N-dimethylformamide, and 0.1 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide was added. The mixture was heated to 35 °C and stirred for 12 h, and then rotary evaporated, washed with water, centrifuged and dried to obtain a hydrophobic long-chain modified carbon quantum dot asphaltene inhibitor.

[0052] Example 5 A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain comprises the following steps: S1: Dissolve 10g of citric acid and 25g of ethylenediamine in 150g of distilled water to form a uniform solution. Pour it into a high-pressure reactor and heat it at 170°C for 4h. After the reaction is completed, collect the supernatant by centrifugation to obtain a carbon quantum dot solution.

[0053] S2: Take 35mL of carbon quantum dot solution, add 1.5mL of 60% nitric acid solution to introduce carboxyl groups on the surface of carbon quantum dots through oxidation reaction, the oxidation reaction temperature is 50°C, and the reaction time is 2h. After the reaction is completed, 8g of carboxylated carbon quantum dot solid is obtained after washing and drying.

[0054] S3: 1.2 g of carboxylated carbon quantum dot solid was mixed with 3.6 g of N-aminopolyhexylamine and 42 g of dimethyl sulfoxide, 0.12 g of N-hydroxysuccinimide was added, the mixture was heated to 32 °C and stirred for 10 h, and then rotary evaporated, washed with water, centrifuged and dried to obtain a hydrophobic long-chain modified carbon quantum dot asphaltene inhibitor.

[0055] Example 6 A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain comprises the following steps: S1: Dissolve 9g of citric acid and 9g of ethylenediamine in 135g of distilled water to form a uniform solution. Pour the solution into a high-pressure reactor and heat it at 175°C for 5h. After the reaction, collect the supernatant by centrifugation to obtain a carbon quantum dot solution.

[0056] S2: Take 30mL of carbon quantum dot solution, add 1mL of 30% hydrochloric acid solution to introduce carboxyl groups on the surface of carbon quantum dots through oxidation reaction, the oxidation reaction temperature is 80℃, and the reaction time is 8h. After the reaction is completed, 8g of carboxylated carbon quantum dot solid is obtained after washing and drying.

[0057] S3: 1 g of carboxylated carbon quantum dot solid was mixed with 2.8 g of N-aminopolyhexylamine and 38 g of tetrahydrofuran, and 0.1 g of 1,3-dicyclohexylcarbodiimide was added. The mixture was heated to 28 °C and stirred for 8 h, and then rotary evaporated, washed with water, centrifuged and dried to obtain a hydrophobic long-chain modified carbon quantum dot asphaltene inhibitor.

[0058] See also Figure 1 This is a reaction mechanism diagram for the preparation of the carbon quantum dot asphaltene inhibitor disclosed in the present invention; as can be seen from the figure, citric acid and ethylenediamine are used as raw materials, and after a high-pressure autoclave temperature reaction, an acidic solution is added to introduce a carboxyl group, and after the reaction is completed, the carboxylated carbon quantum dot solid and N-aminopolyhexylamine are subjected to an amidation reaction by washing and drying, and then the N-aminopolyhexylamine hydrophobic long chain is introduced to impart surface activity to obtain a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long chain.

[0059] Performance Characterization Taking Example 2 as an example, the hydrophobic long carbon chain modified carbon quantum dot asphaltene inhibitor prepared in this example was characterized by infrared spectroscopy. The results are as follows: Figure 2 shown.

[0060] Figure 2 This is an infrared spectrum of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain prepared in Example 2 of the present invention. Figure 2 It can be seen that the absorption peak at 3410 cm⁻¹ is attributed to the stretching vibration of the -OH bond; at 2923 cm⁻¹ and 2815 cm⁻¹, the stretching vibration absorption peaks of the -CH bond appear respectively; the absorption peak at 1728 cm⁻¹ is due to the stretching vibration of the -C=O bond; the absorption peak at 1678 cm⁻¹ corresponds to the stretching vibration of the -C=O bond of the amide group; the absorption peak at 1076 cm⁻¹ is the -CN vibration of the amine alkyl group. According to the infrared spectral characteristics, it can be inferred that the hydrophobic long carbon chain has been successfully introduced into the edge of the molecular structure of the carbon quantum dots, and the carbon quantum dot asphaltene inhibitor has been successfully synthesized.

[0061] In order to characterize the particle size characteristics of a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, the particle size distribution of the carbon quantum dot asphaltene inhibitor was measured by a nano-laser particle size analyzer to characterize its particle size characteristics, such as Figure 3 shown.

[0062] Figure 3 The particle size distribution histogram of the carbon quantum dot asphaltene inhibitor modified by the hydrophobic long carbon chain disclosed in the present invention. Figure 3It can be seen that the particle size distribution of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is uniform, concentrated in (9±0.5) nanometers, and the main particle size is below 10 nanometers, which is consistent with the particle size characteristics of typical carbon quantum dots. In addition, the particle size of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is slightly larger than that of pure carbon quantum dots, which is mainly due to the introduction of a hydrophobic long carbon chain structure on its surface. The long carbon chain modification not only increases the volume of the particles, but also gives them special properties such as hydrophobicity, steric hindrance effect and chemical stability, further enhancing their dispersibility and inhibition performance in oilfield applications. This structural design achieves efficient inhibition of asphaltene by enhancing the interaction between carbon quantum dots and asphaltene molecules.

[0063] In order to characterize the effect of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain on the asphaltene dispersion inhibition effect, the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain and the carboxylated carbon quantum dots prepared in Examples 1, 2, 4, and 6 of the present invention were respectively used for dispersion stability test. The test method is: the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is dissolved in toluene at a mass ratio of 1:2 and dispersed for standby use. The heavy oil sample extracted from Changqing Oilfield has an asphaltene content of 16.9% and a density of 0.9677g / cm³. To determine its dispersion stability, 1g of heavy oil sample was taken, 13mL of n-heptane was added, and a carbon quantum dot asphaltene inhibitor or carboxylated carbon quantum dots modified by a hydrophobic long carbon chain at a concentration of 770 ppm was added, stirred evenly, and placed at different temperatures for 24h. After centrifugation, the solid phase mass was measured to be m2. The dispersion stability calculation formula is: m1- m2 / m1. The experimental results are shown in Table 1.

[0064] Table 1 Dispersion stability test results under different temperature conditions

[0065] From the results in Table 1, it can be seen that the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain prepared in the examples of the present invention shows significant advantages in dispersion stability. Specifically, the dispersion stability of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain in each example exceeds 88%, which is much higher than the dispersion effect of the unmodified carboxylated carbon quantum dots. This result shows that the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain developed by the present invention not only shows excellent performance in inhibiting the aggregation and precipitation of asphaltene particles, but also can maintain a good dispersion state for a long time, significantly improving the stability of the material. This excellent performance provides a reliable technical guarantee for preventing the blockage of equipment such as oil wells and oil pipelines under complex working conditions, and further verifies the potential value of the present invention in practical applications.

[0066] The invention discloses a method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain. First, the carbon quantum dots are carboxylated by an acidic solution, and then the hydrophobic long carbon chain N-amino polyhexylamine is connected to the carboxyl group on the carbon quantum dots by an amidation reaction, so as to finally obtain a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain. The inhibitor can interact with asphaltene molecules through π-π interaction, electrostatic attraction, hydrogen bonding and van der Waals force, and the asphaltene molecules form strong adsorption. The grafted hydrophobic long carbon chain forms a large steric hindrance between the asphaltene molecules, hindering the formation of large-scale parallel stacking, effectively preventing the direct contact and aggregation of asphaltene molecules, thereby maintaining the stable dispersion of the system, effectively preventing the formation of organic scale, and significantly improving the inhibitor efficiency. The advantages of the carbon quantum dot inhibitor are that it has a nano size and a large specific surface area, can enter a low-permeability and ultra-low-permeability reservoir, and has a good viscosity reduction and deposition prevention effect on the oil phase inside it. At the same time, it has a cost advantage, and its preparation raw material is low-cost and easily available citric acid, the reaction process is simple and easy to control, and it is suitable for large-scale production.

[0067] The above contents are only for explaining the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, characterized in that: The following steps are involved: S1: Dissolve citric acid and ethylenediamine in distilled water. After the temperature reaction is completed, collect the supernatant by centrifugation to obtain a carbon quantum dot solution. S2: adding an inorganic acid solution to the carbon quantum dot solution obtained in step S1, and obtaining carboxylated carbon quantum dots after oxidation reaction, washing, and drying; S3: Evenly mix N-aminopolyhexylamine, solvent and the carboxylated carbon quantum dots obtained in step S2, add a coupling agent, and after amidation reaction, obtain a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain by rotary evaporation, water washing, centrifugation and drying.

2. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S1, the mass ratio of citric acid, ethylenediamine and distilled water is 1:(1-2.5):(15-30).

3. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S1, the temperature of the temperature-raising reaction is 160-200° C., and the time is 4-10 hours.

4. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S2, the volume ratio of the carbon quantum dot solution to the inorganic acid solution is (30-50):1; the inorganic acid solution is any one of sulfuric acid, nitric acid and hydrochloric acid, and the mass concentration of the inorganic acid solution is 20%-60%.

5. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S2, the temperature of the oxidation reaction is 25-80° C. and the time is 2-8 hours.

6. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S3, the mass ratio of the carboxylated carbon quantum dots, N-aminopolyhexylamine and the solvent is 1:(2-3):(35-50); the solvent is any one of N,N-dimethylformamide, dimethyl sulfoxide and tetrahydrofuran.

7. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S3, the coupling agent is any one of 1-ethyl-(3-dimethylaminopropyl)carbodiimide, 1,3-dicyclohexylcarbodiimide and N-hydroxysuccinimide; the amount of the coupling agent added is 5% to 10% of the mass of the carboxylated carbon quantum dots.

8. The method for preparing a carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain according to claim 1, characterized in that: In step S3, the amidation reaction is carried out at a temperature of 25-35° C. and for a time of 6-12 h.

9. A carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain, characterized in that: The carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain is prepared by the preparation method according to any one of claims 1 to 8, and the general structural formula is: ； Where n is the degree of polymerization, and the value range of n is 10~30.

10. Use of the carbon quantum dot asphaltene inhibitor modified by a hydrophobic long carbon chain obtained by the preparation method according to any one of claims 1 to 8 in crude oil extraction and petroleum refining, characterized in that: The dispersion stability at 30°C is 88.5%~91.8%; the dispersion stability at 150°C is 89.7%~95.9%.

Images