Modified graphene oxide, modified graphene oxide aqueous dispersion, and preparation method and application thereof

Abstract

The application relates to the field of graphene oxide, and discloses modified graphene oxide, which comprises graphene oxide and grafted polyoxyethylene chains, the chemical formula of the polyoxyethylene chains being -CH2CH(OH)CH2O(CH2CH2O) n CH2CH2OH, wherein n is any integer of 3-20; the grafting rate of the polyoxyethylene chains in the modified graphene oxide is 30-50%. The modified graphene oxide has good salt resistance, can resist acid / alkali aqueous solutions, and effectively inhibits the accumulation and agglomeration of graphene oxide.

Description

Technical Field

[0001] This invention relates to the field of graphene oxide, specifically to a modified graphene oxide, a modified graphene oxide aqueous dispersion, its preparation method, and its application. Background Technology

[0002] Graphene oxide sheets are the product of chemical oxidation and exfoliation of graphite powder. Graphene oxide is a single atomic layer, and its structure spans the typical scales of general chemistry and materials science. Its nanoscale sheet structure endows the material with a high specific surface area, and its surface contains abundant functional groups, thus making it a novel carbon material with excellent performance.

[0003] Graphene oxide can be considered a non-traditional type of flexible material, possessing properties similar to polymers, colloids, films, and amphoteric molecules, and can be well dispersed in water. However, graphene oxide has poor tolerance to inorganic salts and tends to agglomerate and precipitate in saline solutions, which greatly limits its application in life sciences, energy, and other fields. Therefore, developing graphene oxide materials with excellent dispersibility under high-salt conditions is currently a hot research topic.

[0004] The amidation reaction between the carboxyl groups on the surface of graphene oxide and polyetheramine is a widely studied modification method. Xu et al. disclosed a method for grafting 6-arm polyetheramine onto graphene oxide in their paper (ACS Appl Mater Interfaces. 2014; 6(19): 17268–17276.), which improved the dispersion stability of graphene oxide in buffer solution. However, the preparation process of polyetheramine requires the use of flammable and explosive chemicals such as palladium on carbon and sodium azide, which poses a significant safety hazard to the overall reaction route.

[0005] CN113277504A prepared polyetheramine-grafted modified graphene oxide through the same synthetic route, which improved the dispersion performance of graphene oxide nanomaterials. However, its preparation process requires sodium aminoborohydride, and the subsequent amino deprotection process requires palladium on carbon and hydrogen. The raw materials used pose safety risks and are not easy to scale up industrially.

[0006] CN113248669B employs an interfacial reaction method for asymmetric modification of nano-graphene oxide. It utilizes the reaction between long-chain organic amines and epoxy groups on the graphene oxide surface to graft alkyl tail chains. Simultaneously, compounds containing polyoxyethylene (PE) segments are introduced as monomers through grafting onto the graphene oxide surface. The text states that the introduction of PE segments can reduce the dispersion difficulty of amphiphilic graphene and improve its salt and temperature resistance and long-term dispersion stability. However, the hydrophilic modification method proposed in this patent is based on the polymerization reaction between the double bonds of the monomer compound and the double bonds of the graphene oxide skeleton under the initiation of an initiator. Its drawback lies in the lower steric hindrance and higher reactivity between the double bonds in the monomer, making self-polymerization of the monomer more likely. Grafting onto the graphene oxide surface is more difficult, ultimately leading to low grafting efficiency. Furthermore, the hydrophilic modified monomers used in this patent are easily hydrolyzed in alkaline environments.

[0007] CN111978944A describes a method for preparing hydrophilically modified microcrystalline graphene oxide via esterification between carboxyl groups on the surface of graphene oxide and hydroxyl groups in polyethylene glycol. However, ester bonds are easily hydrolyzed in alkaline environments, causing the polyoxyethylene groups grafted onto the material surface to leave, resulting in the loss of its inherent salt resistance. This makes the modified material unsuitable for use in conventional alkaline flooding systems in oilfields, and requires regular monitoring of pH and the degree of ester bond hydrolysis during application, leading to numerous inconveniences.

[0008] Therefore, the grafting modification method of graphene oxide needs to be optimized to improve the material's tolerance to inorganic salts and acid / alkali conditions in water. Summary of the Invention

[0009] The purpose of this invention is to overcome the problems of poor tolerance of graphene oxide to inorganic salts and acids / alkalis in the prior art, and its tendency to accumulate and agglomerate in water. This invention provides a modified graphene oxide, a modified graphene oxide aqueous dispersion, its preparation method and application. The modified graphene oxide has good salt resistance and can withstand acid / alkali aqueous solutions, effectively inhibiting the accumulation and agglomeration of graphene oxide.

[0010] To achieve the above objectives, a first aspect of the present invention provides a modified graphene oxide comprising graphene oxide and grafted polyethylene oxide chains, wherein the polyethylene oxide chains have the chemical formula -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer from 3 to 20;

[0011] The grafting rate of polyoxyethylene chains in the modified graphene oxide is 30-50%.

[0012] A second aspect of this invention provides a method for preparing a modified graphene oxide aqueous dispersion, the method comprising the following steps:

[0013] (1) Under alkaline conditions, the aqueous dispersion of graphene oxide was activated with cyclodextrin to obtain an activated solution;

[0014] (2) The activating solution and polyethylene glycol monoglycidyl ether were subjected to a grafting reaction to obtain the grafted product.

[0015] Preferably, the mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide is 5-100:1, and more preferably, the mass ratio is 10-30:1.

[0016] A third aspect of the present invention provides a modified graphene oxide aqueous dispersion prepared by the aforementioned preparation method.

[0017] A fourth aspect of the present invention provides a modified graphene oxide, wherein the modified graphene oxide is obtained by dialysis of the modified graphene aqueous dispersion described in the third aspect to remove unreacted raw materials.

[0018] The fifth aspect of the present invention provides the application of the aforementioned modified graphene oxide or the aforementioned modified graphene oxide aqueous dispersion in the field of oilfield flooding.

[0019] The beneficial effects of the present invention through the above technical solution are as follows:

[0020] (1) The present invention grafts graphene oxide with polyethylene glycol monoglycidyl ether, and the resulting modified graphene oxide has good salt resistance and can withstand acid / alkali aqueous solutions, effectively inhibiting the accumulation and aggregation of graphene oxide.

[0021] (2) In this invention, the addition of cyclodextrin provides a suitable reaction site for the grafting reaction, enabling the ring-opening grafting reaction to proceed efficiently and significantly improving the grafting efficiency of hydrophilic groups on the surface of graphene oxide.

[0022] (3) The preparation method provided by the present invention has the advantages of easy-to-obtain reaction raw materials, low cost, simplicity, high efficiency and strong safety.

[0023] (4) The product obtained by the preparation method of the present invention can withstand brine with a mass fraction of up to 5%, and no precipitation will be generated in the pH range of 2-13. It also has good oil-water interface activity in alkaline water environment, which promotes the application of modified graphene oxide nanomaterials in the field of oil production. Attached Figure Description

[0024] Figure 1 This is the mass spectrum of polyethylene glycol monoglycidyl ether in Example 1 of the present invention;

[0025] Figure 2 These are the infrared spectra of graphene oxide and modified graphene oxide in Example 1 of this invention;

[0026] Figure 3 The results are the atomic force microscopy morphology characterization results of the microcrystalline graphene oxide in Example 3 of this invention. Detailed Implementation

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] The first aspect of this invention provides a modified graphene oxide comprising graphene oxide and grafted polyethylene oxide chains, wherein the polyethylene oxide chains have the chemical formula -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer from 3 to 20;

[0029] The grafting rate of polyoxyethylene chains in the modified graphene oxide is 30-50%.

[0030] In this invention, n in the polyoxyethylene chain is any integer from 3 to 20, for example, n is 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and any range formed by any two values, preferably any integer from 5 to 15.

[0031] In this invention, the modified graphene oxide is subjected to infrared spectroscopy. The structure of the modified graphene oxide is characterized and the contained functional groups are determined by the position of characteristic peaks in the infrared spectrum. The spectrum is located at 3432 cm⁻¹. -1 The characteristic absorption peak at 1730 cm⁻¹ represents the stretching vibration peak of the remaining unreacted hydroxyl groups in graphene oxide and the newly formed OH groups after ring opening of the epoxy groups. -1 The characteristic absorption peak at 1633 cm⁻¹ corresponds to the carbon-oxygen double bond of the carboxylic acid group on graphene oxide. -1 The characteristic absorption peak at 1101 cm⁻¹ corresponds to the carbon-carbon double bonds in graphene oxide. -1 The peak corresponds to the stretching vibration peak of COC in the polyoxyethylene group, at 845 cm⁻¹. -1 The peak at 1450 cm⁻¹ is the stretching vibration peak of Cc in polyoxyethylene groups. -1 and 2855cm -1 The peaks at the ellipse correspond to the CH vibration absorption peaks of the polyoxyethylene groups. These spectral peaks demonstrate that the polyoxyethylene chains are chemically bonded to the graphene oxide surface.

[0032] In this invention, the linking group between the obtained modified graphene oxide and polyoxyethylene is an ether bond, and the obtained modified graphene oxide has hydroxyl groups at the end, so it will not participate in the grafting reaction.

[0033] In this invention, preferably, the modified graphene oxide does not contain organic amines.

[0034] In this invention, the infrared spectrometer is a NICOLET 6700 infrared spectrometer with a testing range of 450-4000 cm⁻¹. -1 The results obtained are data after removing the background air.

[0035] According to the present invention, preferably, the grafting rate of polyoxyethylene chains in the modified graphene oxide is 35-46%, more preferably 40-46%.

[0036] In this invention, the grafting rate of the polyoxyethylene chain is calculated based on the difference in mass loss rate between the two graphene oxide materials before and after grafting modification, after heating at 800℃, that is: grafting rate = {(m[modified material] - m[modified material after heating at 800℃]) / m[modified material] - (m[graphene oxide] - m[graphene oxide after heating at 800℃]) / m[graphene oxide]}*100%.

[0037] According to the present invention, preferably, the modified graphene oxide is obtained by dialysis of a modified graphene oxide aqueous dispersion.

[0038] In this invention, the modified graphene oxide has good salt resistance and can withstand acid / alkali aqueous solutions, effectively inhibiting the accumulation and aggregation of graphene oxide.

[0039] A second aspect of the present invention provides a method for preparing a modified graphene oxide aqueous dispersion, wherein the method includes the following steps:

[0040] (1) Under alkaline conditions, the aqueous dispersion of graphene oxide was activated with cyclodextrin to obtain an activated solution;

[0041] (2) The activating solution and polyethylene glycol monoglycidyl ether were subjected to a grafting reaction to obtain the grafted product.

[0042] In this invention, compared to polyethylene glycol diglycidyl ether, the use of polyethylene glycol monoglycidyl ether to graft graphene results in modified graphene oxide with hydroxyl groups at the ends, which do not participate in the grafting reaction, thus avoiding chemical connections between graphene oxide sheets and inhibiting the accumulation and aggregation of modified graphene oxide. In contrast, if polyethylene glycol diglycidyl ether is used, the two epoxy groups at both ends of the molecule easily react with two different graphene oxide nanosheets. This "bridging" effect will promote the accumulation and aggregation of nanomaterials, making the modified graphene oxide difficult to disperse stably in water.

[0043] According to the present invention, the activation reaction conditions in step (1) include: a reaction temperature of 60-100℃, preferably 70-90℃; and a reaction time of 1-4h, preferably 2-3h.

[0044] In this invention, preferably, the activation reaction is carried out under the above conditions, which is beneficial to improve the activity of hydroxyl groups in the activation reaction and further improve the grafting efficiency of polyoxyethylene chains.

[0045] In this invention, the structure of the cyclodextrin is not particularly limited. Preferably, the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin, and more preferably β-cyclodextrin. In this invention, the cyclodextrin provides the microcavities required for the grafting reaction, enabling the ring-opening grafting reaction to proceed efficiently and significantly improving the grafting efficiency of hydrophilic groups on the surface of graphene oxide.

[0046] According to the present invention, preferably, based on a total volume of 1L of the mixed solution of graphene oxide aqueous dispersion and cyclodextrin, the content of cyclodextrin is 100-800mg, more preferably 300-500mg. In the present invention, if the mass concentration of cyclodextrin is too low, the grafting effect will be poor and the grafting rate will be low; if the mass concentration of cyclodextrin is too high, it will result in waste of raw materials.

[0047] In this invention, the activation reaction is carried out under stirring conditions, and the stirring rate of the activation reaction is 200-800 rpm, preferably 300-500 rpm.

[0048] According to the present invention, preferably, in step (1), an alkali is added to adjust the pH of the mixed solution to alkaline, wherein the alkali is sodium hydroxide and / or potassium hydroxide. In the present invention, the activation reaction is carried out under alkaline conditions, which can improve the activity of hydroxyl groups in the activation solution and increase the grafting rate of polyoxyethylene chains in the modified graphene oxide.

[0049] According to the present invention, the amount of alkali added can be adjusted adaptively by those skilled in the art as needed, so that the pH value of the mixed solution meets the requirements of the activation reaction. Preferably, the pH value of the mixed solution is 9-12, and more preferably, the pH value is 10-11.

[0050] According to the present invention, preferably, the mass concentration of graphene oxide in the graphene oxide aqueous dispersion in step (1) is higher than 20 mg / L, and more preferably 500-2000 mg / L.

[0051] According to the present invention, preferably, the raw material for the graphene oxide is microcrystalline graphite and / or flake graphite, and the sheet diameter of the graphene oxide does not exceed 2 μm, preferably 50-500 nm.

[0052] In this invention, the microcrystalline graphene oxide prepared using microcrystalline graphite can be stably dispersed in high-salinity formation water. Furthermore, the material exhibits strong dispersion stability and resistance to acids / alkalis, with interfacial tension reduced by an order of magnitude compared to the unmodified form. Therefore, it is suitable for application in various acid / alkali-based oil displacement systems. Additionally, the cost of using microcrystalline graphite as a raw material is lower than that of flake graphite, making the modified graphene oxide more economical in application.

[0053] According to the present invention, preferably, the polyethylene glycol monoglycidyl ether described in step (2) is prepared by the following method:

[0054] A mixture of polyethylene glycol, an alkaline substance, and epoxy halopropane was stirred and reacted. After the reaction was completed, polyethylene glycol monoglycidyl ether was obtained by extraction.

[0055] In this invention, the polyethylene glycol monoglycidyl ether has the following structural formula: n is any integer from 3 to 20, preferably any integer from 5 to 15.

[0056] According to the present invention, preferably, the reaction temperature is 20-50°C, more preferably 25-40°C; and the reaction time is 12-36 h, more preferably 20-30 h.

[0057] In this invention, the stirring rate is not particularly limited, and those skilled in the art can make adaptive adjustments as needed. Preferably, the stirring rate is 200-800 rpm, and more preferably 300-500 rpm.

[0058] According to the present invention, preferably, the molar ratio between polyethylene glycol, the alkaline substance, and the epoxy halide is 1:(0.1-1):(1.1-10), more preferably 1:(0.5-1):(1.5-10). The feed ratio of the mixture of polyethylene glycol, the alkaline substance, and the epoxy halide is adjusted so that the product obtained is polyethylene glycol monoglycidyl ether.

[0059] In this invention, preferably, the average molecular weight of the polyethylene glycol is 200-600. If the average molecular weight of the polyethylene glycol is too high, the polyethylene glycol exists in solid form, resulting in a low reaction yield; if the average molecular weight of the polyethylene glycol is too low, the stability of the obtained polyethylene glycol monoglycidyl ether is not good enough.

[0060] According to the present invention, preferably, the alkaline substance is selected from at least one of potassium carbonate, potassium hydroxide, potassium bicarbonate, sodium carbonate, sodium hydroxide and sodium bicarbonate, and more preferably from at least one of potassium carbonate, potassium hydroxide and potassium bicarbonate.

[0061] According to the present invention, preferably, the epoxy halopropane is epichlorohydrin and / or epibromopropane.

[0062] In this invention, after the reaction for preparing polyethylene glycol monoglycidyl ether is completed, the solvent is removed by extraction to obtain polyethylene glycol monoglycidyl ether. There are no particular limitations on the extraction process.

[0063] According to a preferred embodiment of the present invention, polyethylene glycol monoglycidyl ether can be extracted into the dichloromethane phase using a water / dichloromethane solvent system with a suitable volume ratio of 1:1. The dichloromethane phase is collected, and the solvent is removed to obtain polyethylene glycol monoglycidyl ether.

[0064] According to the present invention, preferably, the grafting reaction conditions in step (2) are: the reaction temperature is 60-100℃, preferably 70-90℃; the reaction time is 4-16h, preferably 6-12h.

[0065] According to the present invention, preferably, the mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide is 5-100:1, for example 5:1, 10:1, 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, 80:1, 90:1, 100:1, and any range between any two values, preferably 10-30:1.

[0066] According to the present invention, preferably, the method further includes: adjusting the pH of the grafted product obtained in step (2) to neutral, and then washing it.

[0067] According to the present invention, preferably, the pH of the grafted product is adjusted to neutral by adding acid.

[0068] According to the present invention, preferably, the acid is selected from at least one of hydrochloric acid, sulfuric acid and phosphoric acid.

[0069] According to the present invention, preferably, the washing agent is amylase and / or cyclodextrinase. In the present invention, by using the above-mentioned washing agent, cyclodextrin can be removed through enzymatic hydrolysis.

[0070] According to the present invention, preferably, the amount of the detergent is 50-800 mg, more preferably 100-400 mg, based on a total volume of 1 L of graphene oxide aqueous dispersion.

[0071] According to the present invention, preferably, the washing time is 1-4 hours, more preferably 2-3 hours. In the present invention, the washing is carried out under stirring conditions, and there is no particular limitation on the washing stirring rate. Those skilled in the art can make adaptive adjustments as needed. Preferably, the washing stirring rate is 200-800 rpm, more preferably 300-500 rpm.

[0072] In this invention, unless otherwise specified, percentage content refers to mass percentage content.

[0073] A third aspect of the present invention provides a modified graphene oxide aqueous dispersion prepared by the aforementioned preparation method.

[0074] A fourth aspect of the present invention provides a modified graphene oxide, wherein the modified graphene oxide is obtained by dialysis of the modified graphene aqueous dispersion described in the third aspect to remove unreacted raw materials.

[0075] This invention provides modified graphene oxide with polyoxyethylene groups grafted onto its surface. These nonionic hydrophilic groups effectively overcome the electrostatic shielding effect of inorganic salt cations on the carboxyl groups on the graphene oxide surface, significantly improving the salt resistance of the modified graphene oxide. Furthermore, the linking group between the modified graphene oxide and the polyoxyethylene group is an ether bond, which is more stable than ester bonds and can withstand acid / alkali aqueous solutions, thereby broadening the industrial application range of the modified graphene oxide material.

[0076] The fifth aspect of the present invention provides the application of the aforementioned modified graphene oxide or the aforementioned modified graphene oxide aqueous dispersion in the field of oilfield flooding.

[0077] In this invention, the modified graphene oxide aqueous dispersion can significantly reduce the oil-water interfacial tension of crude oil in oil fields.

[0078] In this invention, unless otherwise specified, all percentages, parts, ratios, etc. mentioned herein are based on weight, unless being based on weight does not conform to the conventional understanding of those skilled in the art.

[0079] According to a particularly preferred embodiment of the present invention, a method for preparing a modified graphene oxide aqueous dispersion includes the following steps:

[0080] (1) Under alkaline conditions, the aqueous dispersion of graphene oxide was activated with cyclodextrin to obtain an activated solution;

[0081] (2) The activation solution and polyethylene glycol monoglycidyl ether were subjected to a grafting reaction to obtain the grafted product;

[0082] The activation reaction conditions described in step (1) include: a reaction temperature of 70-90℃ and a reaction time of 2-3 hours;

[0083] With a total volume of 1L for the mixed solution of graphene oxide aqueous dispersion and cyclodextrin, the content of cyclodextrin is 300-500mg.

[0084] The amount of alkali added makes the pH of the mixed solution 10-11.

[0085] The present invention will be described in detail below through examples and comparative examples. Unless otherwise specified, all reagents used in the following examples and comparative examples are of analytical grade and commercially available.

[0086] The main raw materials used in the examples and comparative examples are as follows:

[0087]

[0088] Product Name source Product Parameters Polyethylene glycol 400 Inokai Average molecular weight 400 Polyethylene glycol 600 Inokai Average molecular weight 600 Polyethylene glycol 200 Acros Average molecular weight 200 Polyethylene glycol 1000 Inokai Average molecular weight 1000 α-Cyclodextrin Inokai 98％ β-Cyclodextrin Inokai 99％ epichlorohydrin Inokai 99％ amylase Adamas 90%+, 2000u / g Polyethylene glycol diglycidyl ether Acmec 99%, average molecular weight 400

[0089] Example 1

[0090] (1) Preparation of polyethylene glycol monoglycidyl ether

[0091] 16 g of polyethylene glycol 400 and 5.5 g of potassium carbonate were weighed into a single-necked flask. 10 g of epichlorohydrin was added under stirring at 25°C and a stirring rate of 500 rpm. The reaction was continued for 24 hours, after which stirring was stopped. Subsequently, polyethylene glycol monoglycidyl ether was extracted to the dichloromethane phase using 200 mL of a 1:1 (v / v) water / dichloromethane solvent system. The dichloromethane phase was collected, and the solvent was removed to obtain polyethylene glycol monoglycidyl ether.

[0092] The mass spectrum of the product is as follows Figure 1 As shown, since polyethylene glycol 400 is a mixture, its mass spectrum also shows multiple molecular ion peaks: 449.5 corresponds to the polyethylene glycol monoglycidyl ether product with an n value of 7, 493.5 corresponds to the polyethylene glycol monoglycidyl ether product with an n value of 8, and 537.5 corresponds to the polyethylene glycol monoglycidyl ether product with an n value of 9.

[0093] (2) Weigh 100 mL of graphene oxide aqueous dispersion A1 with a mass concentration of 500 mg / L, add 50 mg of β-cyclodextrin, and then add sodium hydroxide to adjust the pH of the system to 10. Stir at 80℃ for 2 hours at a stirring speed of 500 rpm. After the reaction has been going on for 2 hours, add 1.5 g of polyethylene glycol monoglycidyl ether and continue the reaction for 8 hours. Then stop heating and cool to room temperature.

[0094] (3) Add hydrochloric acid to the reaction system to adjust the pH to neutral. Then, add 10 mg of amylase and stir for 3 hours at a stirring speed of 500 rpm to obtain the modified graphene oxide aqueous dispersion.

[0095] Take 10 mL of the modified graphene oxide aqueous dispersion and dialyze it through a dialysis bag in distilled water for one week to remove unreacted raw materials. Then, freeze-dry the dialyzed graphene oxide aqueous dispersion and characterize the product structure by infrared spectroscopy.

[0096] The results are as follows Figure 2 As shown, the spectrum is at 3432 cm⁻¹ -1 The characteristic absorption peak at 1730 cm⁻¹ represents the stretching vibration peak of the remaining unreacted hydroxyl groups in graphene oxide and the newly formed OH groups after ring opening of the epoxy groups. -1 The characteristic absorption peak at 1633 cm⁻¹ corresponds to the carbon-oxygen double bond of the carboxylic acid group on graphene oxide. -1 The characteristic absorption peak at 1101 cm⁻¹ corresponds to the carbon-carbon double bonds in graphene oxide. -1 The peak corresponds to the stretching vibration peak of COC in the polyoxyethylene group, at 845 cm⁻¹. -1 The peak at 1450 cm⁻¹ is the stretching vibration peak of Cc in polyoxyethylene groups. -1 and 2855cm -1 The peaks at the ellipse correspond to the CH vibration absorption peaks of the polyoxyethylene groups. These spectral peaks demonstrate that the polyoxyethylene chains are chemically bonded to the graphene oxide surface.

[0097] Example 2

[0098] (1) Weigh 24 g of polyethylene glycol 600 and 2.8 g of potassium carbonate into a single-necked flask. Add 18.5 g of epichlorohydrin dropwise under stirring at 40 °C and a stirring rate of 500 rpm. Continue the reaction for 24 hours and then stop stirring. Subsequently, extract polyethylene glycol monoglycidyl ether into the dichloromethane phase using a 200 mL water / dichloromethane solvent system (1:1 volume ratio). Collect the dichloromethane phase and remove the solvent to obtain the product.

[0099] (2) Weigh 100 mL of 2000 mg / L graphene oxide aqueous dispersion A2, add 30 mg of β-cyclodextrin, then add sodium hydroxide to adjust the pH of the system to 11, and then heat to 90 °C with a stirring speed of 500 rpm. After reacting for 2 hours, add 2 g of polyethylene glycol monoglycidyl ether, continue the reaction for 6 hours, stop heating, and cool to room temperature.

[0100] (3) Add hydrochloric acid to the reaction system to adjust the pH to neutral. Then, add 20 mg of amylase and stir for 3 hours at a stirring speed of 500 rpm to obtain the modified graphene oxide aqueous dispersion.

[0101] Example 3

[0102] Pretreatment: Preparation of microcrystalline graphene oxide

[0103] Oxidation process: Weigh 0.5g of microcrystalline graphite and 0.5g of sodium nitrate into a three-necked flask. Place the flask in an ice-water bath and add 25mL of 98% concentrated sulfuric acid while stirring at 500rpm. Mix thoroughly. Slowly add 3g of potassium permanganate. After mixing, the solution turns dark red. Stir in the ice-water bath for 0.5h. Remove the ice-water bath and transfer the flask to a 40℃ oil bath. Continue stirring for 1h. Add 40mL of deionized water to the flask, heat to 95℃, and react at 500rpm for 40min. After the reaction is complete, add another 100mL of deionized water. Finally, add 30% hydrogen peroxide solution in three portions (3mL each time). At this point, the solution color changes from dark red to orange-yellow.

[0104] Washing process: The reacted graphite oxide mixture was filtered and then washed with 100 mL of deionized water. After washing three times, the filter cake was placed in a centrifuge tube, mechanically stirred and dispersed, and centrifuged at 1000 rpm for 2 minutes to remove the supernatant. The washing, dispersion, and centrifugation process was repeated five times until the pH of the supernatant was neutral. Finally, the centrifuged graphite oxide precipitate was freeze-dried to obtain graphite oxide solid powder.

[0105] Dispersion process: Weigh 0.2g of graphene oxide and add it to 100mL of deionized water. Sonicate for 3h to obtain a microcrystalline graphene oxide aqueous dispersion.

[0106] The atomic force microscopy characterization results of the obtained microcrystalline graphene oxide are as follows: Figure 3 As shown, by Figure 3 It is known that the thickness of microcrystalline graphene is 1-2 nm, and the planar size is between 100-300 nm.

[0107] (1) Weigh 8 g of polyethylene glycol 200 and 4.5 g of potassium carbonate into a single-necked flask. Add 37 g of epichlorohydrin dropwise under stirring at 40 °C and a stirring rate of 500 rpm. Continue the reaction for 24 hours and then stop stirring. Subsequently, extract polyethylene glycol monoglycidyl ether into the dichloromethane phase using a 200 mL water / dichloromethane solvent system (1:1 volume ratio). Collect the dichloromethane phase and remove the solvent to obtain the product.

[0108] (2) Weigh 100 mL of 2000 mg / L graphene oxide aqueous dispersion, add 50 mg of β-cyclodextrin while stirring at 500 rpm, add sodium hydroxide to adjust the pH of the system to 11, and then heat to 80 °C. After reacting for 3 hours, add 2.2 g of polyethylene glycol monoglycidyl ether, continue the reaction for 12 hours, stop heating, and cool to room temperature.

[0109] (3) Add hydrochloric acid to the reaction system to adjust the pH to neutral. Then, add 40 mg of amylase and stir for 2 hours at a stirring speed of 500 rpm to obtain the modified graphene oxide aqueous dispersion.

[0110] Example 4

[0111] The modified graphene oxide aqueous dispersion was prepared according to the method of Example 1, except that the β-cyclodextrin in step (2) was replaced with an equal mass of α-cyclodextrin.

[0112] Example 5

[0113] The modified graphene oxide aqueous dispersion was prepared according to the method of Example 1, except that polyethylene glycol 400 was replaced with 40g of polyethylene glycol with an average molecular weight of 1000.

[0114] Example 6

[0115] Prepared according to the method of Example 1, except that the amount of polyethylene glycol monoglycidyl ether added was changed so that the mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide in step (2) was 5:1, and a modified graphene oxide aqueous dispersion was obtained.

[0116] Comparative Example 1

[0117] Prepared according to the method of Example 1, but without adding β-cyclodextrin during the activation reaction in step (2) and without adding amylase during the treatment after the grafting reaction.

[0118] Comparative Example 2

[0119] (1) First, microcrystalline graphene oxide and modified graphene oxide were prepared according to the method of Example 1 of CN111978944A.

[0120] (1-1) Take 250 mL of 98% concentrated sulfuric acid and pour it into a 500 mL glass beaker with a stir bar. Stir at 500 rpm. Slowly add 5.00 g of 15000 mesh microcrystalline graphite powder to the beaker. After stirring magnetically in an ice-water bath for 30 min, slowly add 25 g of ground potassium permanganate powder while stirring. Continue stirring in the ice-water bath for 120 min. Remove the ice-water bath and raise the temperature to 37℃. Continue stirring for 120 min. Slowly add deionized water and control the temperature below 60℃. Add water until the temperature of the reaction system no longer rises. Add 5 mL of 30% hydrogen peroxide solution.

[0121] (1-2) Place the solution in a centrifuge, set the speed to 800 rpm and the time to 5 minutes. After standing, filter to remove large particulate impurities, transfer to a 1000 mL beaker, add deionized water to wash until pH≥6, and obtain microcrystalline graphite oxide gel.

[0122] (1-3) The microcrystalline graphene oxide gel was placed in an ultrasonic disperser and ultrasonically dispersed at 720W power and 20Hz frequency for 60 minutes for exfoliation. Then, it was transferred to a centrifuge and centrifuged at 3000rpm for 5 minutes to remove impurities and obtain a microcrystalline graphene oxide aqueous dispersion.

[0123] (2) The modification of microcrystalline graphene oxide was carried out in accordance with Example 7 of the patent application:

[0124] After drying the aqueous dispersion of microcrystalline graphene oxide, it was dissolved in dichloromethane, and 50g of polyethylene glycol, 1g of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and 1g of 4-dimethylaminopyridine were added. The mixture was stirred at 500rpm for 24 hours at room temperature, washed with dilute hydrochloric acid, washed with water, and filtered to obtain polyethylene glycol-modified nano-graphene oxide.

[0125] Comparative Example 3

[0126] Weigh 100 mL of 0.5 mg / mL graphene oxide aqueous dispersion A1 (sheet diameter 50-200 nm), add 1.5 g of polyethylene glycol 400, and stir until homogeneous.

[0127] Comparative Example 4

[0128] A modified graphene oxide aqueous dispersion was prepared according to the method of Example 1 in CN113248669A.

[0129] Comparative Example 5

[0130] The modified graphene oxide aqueous dispersion was prepared according to the method of Example 1, except that polyethylene glycol diglycidyl ether was added in step (2).

[0131] Test Example 1

[0132] 0.5 g of modified graphene oxide powder was weighed into a quartz boat and heated to 800 °C for 2 h using a tube furnace at a heating rate of 10 °C / min. The mass loss was measured, and the grafting rate of polyoxyethylene chains on the surface of the modified graphene oxide was calculated as shown in Table 1.

[0133] Table 1 Grafting rate of polyoxyethylene chains on the surface of modified graphene oxide

[0134]

[0135]

[0136] The modification method provided by this invention achieves a polyoxyethylene linking rate of 35-46% in modified graphene oxide.

[0137] Test Example 2: Salt Tolerance Test of Modified Graphene Oxide under Neutral Conditions

[0138] First, prepare a series of NaCl aqueous solutions. Then, take a certain amount of the modified graphene oxide aqueous dispersion and dilute it to 20 mL with NaCl aqueous solution. After dilution, the content of modified graphene oxide in the solution is 2 mg. Let it stand for 4 hours and observe whether any precipitation occurs. The results are shown in Table 2 below.

[0139] Table 2 Salt resistance properties of graphene oxide materials before and after modification

[0140]

[0141]

[0142] As shown in Table 2, the hydrophilic-modified graphene oxide materials in Examples 1-5 exhibited good salt resistance, remaining uniformly dispersed in water even at NaCl concentrations as high as 5%. In contrast, unmodified graphene oxide, regardless of sheet size, showed poor salt resistance, precipitating out in a 0.5% salt solution. In Example 6, due to the low grafting rate of the hydrophilic groups, the modified material could not withstand a 5% high-salt solution, but remained stable in a 1% salt solution.

[0143] Comparative Example 1 showed that the low grafting rate of hydrophilic groups in the graphene oxide material led to agglomeration and precipitation when the salt concentration reached 1% or higher. Comparative Example 3 indicated that after non-covalent modification of graphene oxide with polyethylene glycol, the material could withstand 0.5% saline solution, but not 1% or higher. These results demonstrate that covalently grafted polyoxyethylene groups improve the salt resistance of graphene oxide.

[0144] The modification method and modified structure of the hydrophilic modified graphene oxide in Comparative Example 2 are different from those of the present invention. Although it can be uniformly dispersed in water under neutral conditions, its dispersion stability under acidic and alkaline conditions is poor. The relevant test results will be shown later in the present invention.

[0145] The hydrophilic modified graphene oxide material in Comparative Example 4 could tolerate a salt concentration of 1%, but precipitation occurred when the salt concentration increased to 5%. The presence of long-chain amines in its structure weakened the hydrophilicity of the material, making it prone to aggregation and precipitation in high-salt water. In addition, since the polymers formed by the self-polymerization of hydrophilic monomers cannot be completely removed by dialysis, the actual grafting rate of hydrophilic groups on the surface of the modified graphene oxide material is lower than the measured value, which is also a possible reason for the precipitation of the material in high-salt water.

[0146] In Comparative Example 5, the two epoxy groups of polyethylene glycol diglycidyl ether react with different graphene oxide nanosheets, acting as a "bridging" mechanism, which makes the material more prone to aggregation in water.

[0147] Test Example 3: Salt tolerance of modified graphene oxide under alkaline conditions

[0148] First, prepare a series of NaCl aqueous solutions. Then, take a certain amount of modified graphene oxide aqueous dispersion and dilute it to 20 mL with NaCl aqueous solution. After dilution, the content of modified graphene oxide in the solution is 2 mg. Then, add NaOH to adjust the pH to 13, let it stand for 4 hours, and observe whether a precipitate is formed. The results are shown in Table 3.

[0149] Table 3. Salt resistance of graphene oxide materials before and after modification under alkaline conditions.

[0150] 0.5% NaCl 1% NaCl 5% NaCl Example 1 homogeneous solution homogeneous solution homogeneous solution Example 2 homogeneous solution homogeneous solution homogeneous solution Example 3 homogeneous solution homogeneous solution homogeneous solution Example 4 homogeneous solution homogeneous solution homogeneous solution Example 5 homogeneous solution homogeneous solution homogeneous solution Example 6 homogeneous solution homogeneous solution precipitation Comparative Example 1 homogeneous solution precipitation precipitation Comparative Example 2 precipitation precipitation precipitation Comparative Example 3 homogeneous solution precipitation precipitation Comparative Example 4 precipitation precipitation precipitation Comparative Example 5 precipitation precipitation precipitation Example 1 (before modification) precipitation precipitation precipitation Example 2 (before modification) precipitation precipitation precipitation Example 3 (before modification) precipitation precipitation precipitation

[0151] As shown in Table 3, in Examples 1-5, the modified graphene oxide maintained good salt resistance under alkaline conditions, while the unmodified graphene oxide in Examples 1-3 and Comparative Example 3, which was not covalently modified, still exhibited poor salt resistance. Furthermore, Comparative Examples 2 and 4 lost their salt resistance under alkaline conditions, precipitating in a 0.5% salt solution. The modified graphene oxide in Example 6 and Comparative Example 1 could still tolerate 0.5% saline solution under alkaline conditions, but when the salt concentration exceeded 1%, the material agglomerated and precipitated due to the low grafting rate of hydrophilic groups. In Comparative Example 5, the two epoxy groups of polyethylene glycol diglycidyl ether reacted with different graphene oxide nanosheets, acting as a "bridging" mechanism, making the material more prone to agglomeration and precipitation.

[0152] The above results demonstrate that the modified graphene oxide provided in the embodiments of the present invention has superior salt resistance under alkaline conditions.

[0153] Test Example 4: Salt resistance of modified graphene oxide under acidic conditions

[0154] First, prepare a series of NaCl aqueous solutions. Then, take a certain amount of the modified graphene oxide aqueous dispersion and dilute it to 20 mL with NaCl aqueous solution. After dilution, the content of modified graphene oxide in the solution is 2 mg. Then, add hydrochloric acid to adjust the pH to 2, let it stand for 8 hours, and observe whether a precipitate is formed. The results are shown in Table 4 below.

[0155] Table 4. Salt resistance of graphene oxide materials before and after modification under acidic conditions.

[0156] 0.5% NaCl 1% NaCl 5% NaCl Example 1 homogeneous solution homogeneous solution homogeneous solution Example 2 homogeneous solution homogeneous solution homogeneous solution Example 3 homogeneous solution homogeneous solution homogeneous solution Example 4 homogeneous solution homogeneous solution homogeneous solution Example 5 homogeneous solution homogeneous solution homogeneous solution Example 6 homogeneous solution homogeneous solution precipitation Comparative Example 1 homogeneous solution homogeneous solution precipitation Comparative Example 2 homogeneous solution homogeneous solution precipitation Comparative Example 3 homogeneous solution precipitation precipitation Comparative Example 4 homogeneous solution homogeneous solution precipitation Comparative Example 5 precipitation precipitation precipitation Example 1 (before modification) precipitation precipitation precipitation Example 2 (before modification) precipitation precipitation precipitation Example 3 (before modification) precipitation precipitation precipitation

[0157] As shown in Table 4, in Examples 1-5, the hydrophilically modified graphene oxide materials maintained good salt resistance under acidic conditions, while the unmodified graphene oxide in Examples 1-3 and the non-covalently modified comparative example 3 still exhibited poor salt resistance. Comparative examples 2 and 4 showed some salt resistance under acidic conditions; the materials could be uniformly dispersed in a 1% salt solution, but precipitated in a 5% salt solution. The modified graphene oxide materials in Examples 6 and 1 could withstand 1% salt water under acidic conditions, but when the salt concentration increased to 5%, the materials agglomerated and precipitated due to the low grafting rate of the hydrophilic groups. In Comparative example 5, the two epoxy groups of polyethylene glycol diglycidyl ether reacted with different graphene oxide nanosheets, acting as a "bridging" agent, making the material more prone to agglomeration and precipitation.

[0158] Test Example 5: Evaluation of the interfacial properties of modified graphene oxide aqueous dispersion

[0159] The oil-water interfacial tension of the graphene oxide materials in the examples and comparative examples was measured using a TX-500C interfacial tensiometer with the rotating droplet method. The test oil was crude oil from the Louzi block of Henan Oilfield (its viscosity at 50℃ was measured to be 300 mPa·s using a Haake VT550 rotational viscometer). The test temperature was 50℃, and the rotation speed was 5000 rpm. The crude oil from this block was extracted through alkaline ternary flooding. The formation water had a salt concentration of 50000 mg / L and a pH of 9.52. The test water was prepared according to these parameters, and the results are shown in Table 5.

[0160] Table 5. Oil-water interfacial tension in the examples and comparative examples.

[0161] Interfacial tension (mN / m) Example 1 0.35 Example 2 0.98 Example 3 0.50 Example 4 1.02 Example 5 0.98 Example 6 1.17 Comparative Example 1 2.88 Comparative Example 2 1.31 Comparative Example 3 5.20 Comparative Example 4 3.25 Comparative Example 5 6.22

[0162] Table 5 shows that the hydrophilic-modified graphene oxide obtained by this invention has a hydrophilic-lipophilic balance value that is more conducive to the adsorption of the material at the oil-water interface and its interaction with crude oil components, thus exhibiting certain interfacial activity. It can reduce the oil-water interfacial tension to less than 1.2 mN / m, and under optimal conditions, the interfacial tension can be reduced to as low as 0.35 mN / m. The modified graphene oxide nanomaterials prepared in Examples 5 and 6 have lower grafting rates and their interfacial activity is lower than that of Examples 1-3, but still better than the comparative examples, and they can be stably dispersed in formation water. In contrast, the modified graphene oxide with a lower grafting rate used in Comparative Example 1, the esterified grafted modified graphene oxide used in Comparative Example 2, the system of graphene oxide and polyethylene glycol 400 in Comparative Example 3, and the modified graphene oxide used in Comparative Examples 4 and 5 all agglomerated and precipitated in the alkaline brine used in this experiment, and their oil-water interfacial tensions were all higher than 1.2 mN / m.

[0163] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A modified graphene oxide, characterized in that, The modified graphene oxide comprises graphene oxide and grafted polyethylene oxide chains, the chemical formula of which is -CH2CH(OH)CH2O(CH2CH2O). n CH2CH2OH, where n is any integer from 3 to 20; The grafting rate of polyoxyethylene chains in the modified graphene oxide is 35-46%. The modified graphene oxide does not contain organic amines.

2. The modified graphene oxide according to claim 1, wherein, In the polyoxyethylene chain, n is any integer from 5 to 15.

3. The modified graphene oxide according to claim 1, wherein, The modified graphene oxide was obtained by dialysis of a modified graphene oxide aqueous dispersion.

4. A method for preparing a modified graphene oxide aqueous dispersion, characterized in that, The method includes the following steps: (1) Under alkaline conditions, the aqueous dispersion of graphene oxide was activated with cyclodextrin to obtain an activated solution; (2) The activating solution and polyethylene glycol monoglycidyl ether were subjected to a grafting reaction to obtain the grafted product.

5. The preparation method according to claim 4, wherein, The activation reaction conditions described in step (1) include: a reaction temperature of 60-100℃ and a reaction time of 1-4h.

6. The preparation method according to claim 5, wherein, The activation reaction conditions described in step (1) include: a reaction temperature of 70-90℃ and a reaction time of 2-3h.

7. The preparation method according to claim 4, wherein, With a total volume of 1L for the mixed solution of graphene oxide aqueous dispersion and cyclodextrin, the content of cyclodextrin is 100-800 mg.

8. The preparation method according to claim 7, wherein, With a total volume of 1L for the mixed solution of graphene oxide aqueous dispersion and cyclodextrin, the content of cyclodextrin is 300-500mg.

9. The preparation method according to claim 4, wherein, In step (1), an alkali is added to adjust the pH of the mixed solution to alkaline, wherein the alkali is sodium hydroxide and / or potassium hydroxide.

10. The preparation method according to claim 9, wherein, The amount of alkali added makes the pH of the mixed solution 9-12.

11. The preparation method according to claim 10, wherein, The amount of alkali added makes the pH of the mixed solution 10-11.

12. The preparation method according to claim 4, wherein, The mass concentration of graphene oxide in the graphene oxide aqueous dispersion in step (1) is higher than 20 mg / L; And / or, the raw material for the graphene oxide is microcrystalline graphite and / or flake graphite, and the sheet diameter of the graphene oxide does not exceed 2 μm.

13. The preparation method according to claim 12, wherein, The mass concentration of graphene oxide in the graphene oxide aqueous dispersion mentioned in step (1) is 500-2000 mg / L; And / or, the graphene oxide sheet diameter is 50-500 nm.

14. The preparation method according to claim 4, wherein, The polyethylene glycol monoglycidyl ether described in step (2) is prepared by the following method: A mixture of polyethylene glycol, an alkaline substance, and epoxy halopropane was stirred and reacted. After the reaction was completed, polyethylene glycol monoglycidyl ether was obtained by extraction.

15. The preparation method according to claim 14, wherein, The reaction temperature is 20-50℃; the reaction time is 12-36h.

16. The preparation method according to claim 15, wherein, The reaction temperature is 25-40℃; the reaction time is 20-30h.

17. The preparation method according to claim 14, wherein, The molar ratio of the polyethylene glycol, the alkaline substance, and the epoxy halogenated propane is 1:(0.1-1):(1.1-10).

18. The preparation method according to claim 17, wherein, The molar ratio of the polyethylene glycol, the alkaline substance, and the epoxy halogenated propane is 1:(0.5-1):(1.5-10).

19. The preparation method according to claim 14, wherein, The average molecular weight of the polyethylene glycol is 200-600.

20. The preparation method according to claim 14, wherein, The alkaline substance is selected from at least one of potassium carbonate, potassium hydroxide, potassium bicarbonate, sodium carbonate, sodium hydroxide, and sodium bicarbonate. And / or, the epoxy halopropane is epichlorohydrin and / or epibromopropane.

21. The preparation method according to claim 20, wherein, The alkaline substance is selected from at least one of potassium carbonate, potassium hydroxide, and potassium bicarbonate.

22. The preparation method according to claim 4, wherein, The grafting reaction conditions described in step (2) include: a reaction temperature of 60-100℃ and a reaction time of 4-16h; And / or, the mass ratio of the polyethylene glycol monoglycidyl ether to graphene oxide is 5-100:

1.

23. The preparation method according to claim 22, wherein, The grafting reaction conditions described in step (2) include: a reaction temperature of 70-90℃ and a reaction time of 6-12h; And / or, the mass ratio of the polyethylene glycol monoglycidyl ether to graphene oxide is 10-30:

1.

24. The preparation method according to claim 4, wherein, The method further includes: adjusting the pH of the grafted product obtained in step (2) to neutral, and then washing it.

25. The preparation method according to claim 24, wherein, The pH of the grafted product was adjusted to neutral by adding acid.

26. The preparation method according to claim 25, wherein, The acid is selected from at least one of hydrochloric acid, sulfuric acid, and phosphoric acid.

27. The preparation method according to claim 24, wherein, The washing agent used is amylase and / or cyclodextrinase.

28. The preparation method according to claim 27, wherein, Based on a total volume of 1L for the graphene oxide aqueous dispersion, the amount of the detergent is 50-800mg. And / or, the washing time is 1-4 hours.

29. The preparation method according to claim 28, wherein, Based on a total volume of 1L for the graphene oxide aqueous dispersion, the amount of the detergent is 100-400mg. And / or, the washing time is 2-3 hours.

30. A modified graphene oxide aqueous dispersion prepared by the preparation method according to any one of claims 4-29.

31. A modified graphene oxide, characterized in that, The modified graphene oxide is obtained by dialysis of the modified graphene aqueous dispersion of claim 30 to remove unreacted raw materials.

32. The application of the modified graphene oxide according to any one of claims 1-3 and 31 or the modified graphene oxide aqueous dispersion according to claim 30 in the field of oilfield flooding.

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