High-activity graphene quantum dot and preparation method thereof

Abstract

The invention discloses a high-activity graphene quantum dot and a preparation method thereof, and relates to the technical field of oilfield chemistry, and the preparation method comprises the following steps: uniformly ground carbon source and nitrogen source are mixed, heated, fully reacted and cooled, uniformly dispersed in deionized water by ultrasonic waves, and then subjected to suction filtration, dialysis and freeze drying to obtain the nitrogen-containing graphene quantum dot. The preparation method comprises the following steps: dispersing nitrogen-containing graphene quantum dots, fatty alcohol-polyoxyethylene ether carboxylic acid and a catalyst in absolute ethyl alcohol, carrying out ultrasonic oscillation for 30 minutes, carrying out reflux reaction, and carrying out reduced-pressure rotary evaporation, thereby obtaining the nitrogen-containing graphene quantum dots. The prepared high-activity graphene quantum dots are small in particle size, high in activity and capable of entering small pores to peel crude oil, so that the recovery efficiency can be remarkably improved, the point injection allocation process is simple, the high-activity graphene quantum dots can be rapidly dispersed into injected water, an additional injection allocation device is not needed, and the construction cost is low.

Description

Technical Field

[0001] The invention relates to the technical field of oilfield chemistry, in particular to a high-activity graphene quantum dot and a preparation method thereof. Background Art

[0002] Low-permeability and ultra-low-permeability reservoirs have the characteristics of complex pore structure, poor local physical properties, and strong intra-layer heterogeneity, which leads to the overall situation of "no water injection and no oil production", which seriously restricts the improvement of oilfield development effect and reserve utilization. Graphene quantum dots (GQDs) are small graphene fragments with a lateral size of less than 100nm and a longitudinal thickness of several layers. Not only does it have the excellent properties of graphene, but it also has stable fluorescence properties, low toxicity and good biocompatibility, so it has become a research hotspot in recent years. On the one hand, it can enter the deep part of the reservoir for plugging and profile adjustment, and on the other hand, the separation pressure formed can strip crude oil from the rock and significantly improve the recovery rate with extremely low dosage.

[0003] The preparation methods of GQDs are mainly divided into two categories: "bottom-up" and "top-down". The bottom-up method mainly uses small-molecule organic matter to prepare small-sized GQDs through solution chemistry and pyrolysis carbonization. Its advantage is that the size and shape of GQDs can be adjusted by controlling the reaction conditions, but it has the disadvantages of harsh and complex preparation process and long preparation cycle. The top-down method mainly uses chemical oxidation cutting, hydrothermal method, ultrasonic exfoliation method, electrochemical oxidation method, etc. to cut large-sized carbon materials (such as graphite, graphene, graphene oxide) into small-sized GQDs. These methods are relatively simple, but the cost is high, and toxic and corrosive reagents such as strong acids and strong bases are used in the preparation process. In order to avoid the shortcomings of the above methods, many scholars have improved and optimized the preparation methods of GQDs. For example, using deionized water and glucose as precursors, low-cost, high-yield, green-fluorescent single-layer graphene quantum dots (SLGQDs) with an average size of 8nm were synthesized; using de-oiled asphalt as the precursor material, high-quality GQDs were prepared in one step by a microwave-assisted method, emitting bright green fluorescence under 365nm ultraviolet excitation, with a size distribution between 1nm-6nm and an average size of 2.65nm, which is smaller and thinner than most reported GQDs; using citric acid as the raw material, a combination of thermal decomposition and hydrothermal methods was used to prepare blue-green graphene quantum dots with a high quantum yield. Compared with the single thermal decomposition method, the average quantum yield can reach about 67%; the existing improved GQDs preparation method avoids the use of toxic / corrosive solvents, but the prepared GQDs have low activity. Summary of the invention

[0004] In view of this, the present invention proposes a highly active graphene quantum dot and a preparation method thereof, and aims to solve the problems of complex preparation process and low activity of conventional graphene quantum dots, and provides a simple, green and low-cost method for synthesizing highly active graphene quantum dots.

[0005] The invention discloses a highly active graphene quantum dot and a preparation method thereof, comprising the following steps:

[0006] Step S1: mixing the uniformly ground carbon source and nitrogen source, heating and reacting them fully, cooling them, and uniformly dispersing them in deionized water by ultrasonication, followed by suction filtration, dialysis and freeze drying to obtain nitrogen-containing graphene quantum dots;

[0007] Step S2: adding nitrogen-containing graphene quantum dots, fatty alcohol polyoxyethylene ether carboxylic acid and catalyst into anhydrous ethanol for dispersion, ultrasonically vibrating for 30 minutes, and performing reflux reaction followed by reduced pressure rotary evaporation to obtain the product.

[0008] One embodiment of the present invention is that the carbon source is sodium lignin sulfonate and the nitrogen source is urea.

[0009] In one embodiment of the present invention, the catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide.

[0010] An embodiment of the present invention is that, in terms of molar fractions, the ratio of the nitrogen source to the carbon source is 1:0.5 to 2.5.

[0011] One embodiment of the present invention is that, in terms of molar fractions, the ratio of the nitrogen-containing graphene quantum dots to the fatty alcohol polyoxyethylene ether carboxylic acid is 1:2-5.

[0012] One implementation mode of the present invention is that the amount of the catalyst is 2-5% of the total mass of the nitrogen-containing graphene quantum dots and the fatty alcohol polyoxyethylene ether carboxylic acid.

[0013] An embodiment of the present invention is that the heating reaction conditions of the carbon source and the nitrogen source are: heating at 180-220° C. in a muffle furnace for 1-2 hours.

[0014] An embodiment of the present invention is that the reflux reaction conditions are: condensation reflux for 12 to 14 hours in a water bath at 80 to 100°C.

[0015] And highly active graphene quantum dots prepared by the method.

[0016] The technical effects of the present invention are:

[0017] (1) The highly active graphene quantum dots prepared by the present invention have a small particle size and high activity, and can enter small pores to strip crude oil, thereby significantly improving the recovery rate.

[0018] (2) The highly active graphene quantum prepared by the present invention has good temperature resistance (>120°C) and salt resistance (>200,000), which can meet the requirements for use in high-temperature and high-salt oil reservoirs.

[0019] (3) The high-activity graphene quantum dots in the present invention have a simple injection process and can be quickly dispersed into the injected water without the need for additional injection equipment, thus having a low construction cost.

[0020] (4) The preparation method of the present invention avoids the use of strong acids, strong bases and toxic, corrosive solvents, and is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a microscopic morphology of the highly active graphene quantum dots in Example 1 of the present invention;

[0022] Figure 2 The oil-water interfacial tension test results of various embodiments of the present invention are shown in FIG.

[0023] Figure 3 This is a diagram showing the results of an oil displacement experiment in Example 4 of the present invention;

[0024] Figure 4 This is a diagram showing the results of the oil displacement experiment of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with the examples, but the embodiments of the present invention are not limited thereto. The experimental methods used in the following examples are conventional methods unless otherwise specified; the materials, reagents, etc. used therein are all commercially available unless otherwise specified.

[0026] Example 1

[0027] (1) 6 g of urea and 53.5 g of sodium lignin sulfonate were fully ground to make them completely contact, and then added to a ceramic crucible; the ceramic crucible was placed in a muffle furnace at 200° C. and reacted for 1.5 h; after the reaction, the product was ground and then added to 200 mL of deionized water, ultrasonically dispersed for 30 min, and filtered through a filter membrane with a pore size of 0.22 μm. The resulting solution was placed in a dialysis bag with a molecular weight cutoff of 1000 and dialyzed for 48 h, and then freeze-dried for 24 h to obtain nitrogen-containing graphene quantum dots.

[0028] (2) Add 10 g of nitrogen-containing graphene quantum dots, 20 g of fatty alcohol polyoxyethylene ether carboxylic acid and 1.2 g of catalyst into a beaker, then add 200 mL of anhydrous ethanol, and perform ultrasonic oscillation for 30 min to ensure that the reactants are fully in contact. Then, condense and reflux for 13 h in an 80 °C water bath, and evaporate under reduced pressure to obtain highly active graphene quantum dots.

[0029] Example 2

[0030] (1) 12 g of urea and 53.5 g of sodium lignin sulfonate were fully ground to make them completely contact, and then added to a ceramic crucible; the ceramic crucible was placed in a muffle furnace at 200° C. and reacted for 1.5 h; after the reaction, the product was ground and then added to 210 mL of deionized water, ultrasonically dispersed for 30 min, filtered through a filter membrane with a pore size of 0.22 μm, and the resulting solution was placed in a dialysis bag with a molecular weight cutoff of 1000 for 48 h, and then freeze-dried for 24 h to obtain nitrogen-containing graphene quantum dots.

[0031] (2) Add 10 g of nitrogen-containing graphene quantum dots, 20 g of fatty alcohol polyoxyethylene ether carboxylic acid and 1.2 g of catalyst into a beaker, then add 200 mL of anhydrous ethanol, and perform ultrasonic oscillation for 30 min to ensure that the reactants are fully in contact; then condense and reflux for 13 h in an 80 ° C water bath, and vacuum rotary evaporate to obtain highly active graphene quantum dots.

[0032] Example 3

[0033] This embodiment is substantially the same as embodiment 2, except that the amount of urea used in this embodiment is 6 g, and the amount of sodium lignin sulfonate used is 107 g.

[0034] Example 4

[0035] This embodiment is substantially the same as Embodiment 3, except that the amount of fatty alcohol polyoxyethylene ether carboxylic acid used in this embodiment is 30 g.

[0036] Comparative Example 1

[0037] Nitrogen-containing graphene quantum dots were prepared according to the method (1) in Example 4, and the nitrogen-containing graphene quantum dots were directly mixed with fatty alcohol polyoxyethylene ether carboxylic acid in a mass ratio of 1:3.

[0038] In order to better illustrate the technical effects of the present invention, performance evaluation of relevant embodiments is provided below.

[0039] 1. Microscopic morphology characterization

[0040] Figure 1 This is a microscopic morphology of the highly active graphene quantum dots in Example 1. It can be seen that most of the prepared highly active graphene quantum dots are spherical or nearly spherical, and a small part is elliptical or irregular in shape, with a particle size of about 4 nm.

[0041] 2. Evaluation of the ability to reduce interfacial tension

[0042] The highly active graphene quantum dots prepared in Examples 1 to 4 were subjected to an interfacial tension evaluation experiment at 90°C with a mineralization degree of 10×10 4 mg / L, Ca 2+The interfacial tension of the liquid was measured by mixing 5000 mg / L experimental water with crude oil (taken from the Northwest Oilfield). The results are as follows: Figure 2 As shown. Figure 2 The results show that as the amount of each example increases, Examples 1 to 4 all have a good interfacial tension reduction effect, which is beneficial to improving the oil displacement efficiency.

[0043] 3. Core flooding experiment

[0044] Example 4 was prepared into a highly active graphene quantum dot dispersion with a concentration of 0.4% (the mineralization degree of the experimental water was 10×10 4 mg / L, of which Ca 2+ The oil displacement experiment was carried out at 90°C with a concentration of 5000 mg / L. The experimental conditions were: gas permeability of homogeneous core: 10 mD; porosity: 9.42%; oil saturation: 44.4%; diameter: 2.5 cm, length: 5 cm; injection rate during displacement was 0.2 mL / min.

[0045] The experimental results are as follows Figure 3 As shown, the recovery rate of the front water flooding stage is 19.8%; then a high-activity graphene quantum dot dispersion with a total concentration of 0.4% is injected, and the injection pressure increases during the injection process, indicating that the high-activity graphene quantum dot dispersion can be adsorbed on the pore throat wall to improve the microscopic heterogeneity and expand the sweep efficiency. At the same time, the crude oil is stripped through the wedge separation pressure, the oil-water interfacial tension is coordinated to decrease, and the oil washing efficiency is increased, so that the final recovery rate is increased by 24.4%.

[0046] Furthermore, in order to compare the oil displacement performance of the high-activity graphene quantum dots and the nitrogen-containing graphene quantum dots / fatty alcohol polyoxyethylene ether carboxylic acid mixture, the comparative example 1 was prepared into a solution with a concentration of 0.4% (the mineralization degree of the experimental water was 10×10 4 mg / L, of which Ca 2+ The oil displacement experiment was carried out at 90°C with a concentration of 5000 mg / L. The experimental conditions were: the gas permeability of the homogeneous core was 10 mD; the porosity was 9.51%; the oil saturation was 46.3%; the diameter was 2.5 cm and the length was 5 cm; the injection rate during the displacement process was 0.2 mL / min.

[0047] The experimental results are as follows Figure 4 As shown, the recovery rate of the initial water flooding stage was 20.2%; then the nitrogen-containing graphene quantum dots / fatty alcohol polyoxyethylene ether carboxylic acid mixture with a total concentration of 0.4% was injected, and the final recovery rate increased by 18.9%. Compared with the highly active graphene quantum dot dispersion, the pressure during the injection of the mixed system is lower, the ability to improve microscopic heterogeneity is weaker, and the recovery rate increase is less than the 24.4% of the highly active graphene quantum dots.

[0048] It can be seen that the present invention introduces fatty alcohol polyoxyethylene ether carboxylic acid into nitrogen-containing graphene quantum dots by chemical grafting. Compared with the direct mixing of the two, the highly active graphene quantum dots prepared by the present invention have a better effect of improving microscopic heterogeneity and a greater effect of improving the final recovery rate, which proves that the highly active graphene quantum dots in the present invention have the effect of significantly improving the recovery rate.

[0049] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the embodiments of the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A method for preparing highly active graphene quantum dots, characterized in that: The following steps are involved: Step S1: mixing the uniformly ground carbon source and nitrogen source, heating and reacting them fully, cooling them, and uniformly dispersing them in deionized water by ultrasonication, followed by suction filtration, dialysis and freeze drying to obtain nitrogen-containing graphene quantum dots; Step S2: adding nitrogen-containing graphene quantum dots, fatty alcohol polyoxyethylene ether carboxylic acid and a catalyst into anhydrous ethanol for dispersion, ultrasonically vibrating for 30 minutes, and performing reflux reaction followed by reduced pressure rotary evaporation to obtain the product.

2. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: The carbon source is sodium lignin sulfonate, and the nitrogen source is urea.

3. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: The catalyst is 1-ethyl-(3-dimethylaminopropyl)carbodiimide.

4. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: In terms of molar fraction, the ratio of the nitrogen source to the carbon source is 1:0.5-2.

5.

5. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: In parts by weight, the ratio of the nitrogen-containing graphene quantum dots to the fatty alcohol polyoxyethylene ether carboxylic acid is 1:2-5.

6. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: The amount of the catalyst used accounts for 2-5% of the total mass of the nitrogen-containing graphene quantum dots and the fatty alcohol polyoxyethylene ether carboxylic acid.

7. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: The heating reaction conditions of the carbon source and the nitrogen source are: heating in a muffle furnace at 180-220° C. for 1-2 hours.

8. The method for preparing highly active graphene quantum dots according to claim 1, characterized in that: The reflux reaction conditions are: condensation reflux for 12 to 14 hours in a water bath at 80 to 100°C.

9. A highly active graphene quantum dot, characterized in that: The method is prepared by any one of claims 1 to 8.

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