Modified graphene oxide, modified graphene oxide aqueous dispersion as well as preparation method and application of modified graphene oxide aqueous dispersion

Abstract

The invention relates to the field of graphene oxide, and discloses modified graphene oxide, the modified graphene oxide comprises graphene oxide and a grafted polyoxyethylene chain, the chemical formula of the polyoxyethylene chain is-CH2CH (OH) CH2O (CH2CH2O) nCH2CH2OH, and n is any integer from 3 to 20; the grafting rate of a polyoxyethylene chain in the modified graphene oxide is 30 to 50 percent. The modified graphene oxide has good salt resistance, can tolerate an acid / alkali aqueous solution, and effectively inhibits accumulation and agglomeration of graphene oxide.

Description

Technical Field

[0001] The present invention relates to the field of graphene oxide, and in particular to modified graphene oxide, a modified graphene oxide aqueous dispersion, and a preparation method and application thereof. Background Art

[0002] Graphene oxide flakes are the product of graphite powder after chemical oxidation and exfoliation. Graphene oxide is a single atomic layer, and its structure transcends the typical scale of general chemistry and materials science. Its nano-scale sheet structure gives the material a high specific surface area, and the surface contains rich functional groups, making it a new type of carbon material with excellent performance.

[0003] Graphene oxide can be considered as a non-traditional flexible material with the properties of polymers, colloids, films, and amphiphilic molecules, and can be well dispersed in water. However, graphene oxide has poor tolerance to inorganic salts and is prone to agglomeration and precipitation in salty water, which greatly limits the application of the material in life sciences, energy and other fields. Therefore, the development of graphene oxide materials with excellent dispersion properties under high-salt conditions is currently a hot research direction.

[0004] The amidation reaction between the carboxyl groups on the surface of graphene oxide and polyetheramine is a modification method that has been widely studied. 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. However, the preparation process of polyetheramine requires the use of flammable and explosive chemicals such as palladium carbon and sodium azide, which makes the overall reaction route have a great safety hazard.

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

[0006] CN113248669B uses an interfacial reaction method to asymmetrically modify nanographene oxide, using long-chain organic amines to react with epoxy groups on the surface of graphene oxide to graft alkyl tail chains; at the same time, a compound containing a polyoxyethylene segment is used as a monomer, and a polyoxyethylene segment is introduced through a grafting reaction on the surface of graphene oxide. The text points out that the introduction of polyoxyethylene segments can reduce the dispersion difficulty of amphiphilic graphene and improve its salt resistance, temperature resistance and long-term dispersion stability. However, the hydrophilic group modification method proposed in this patent is based on the polymerization reaction of the double bonds of the monomer compound and the double bonds of the graphene oxide skeleton under the initiation of an initiator. Its defect is that the reaction steric hindrance between the double bonds contained in the monomer is lower and the reaction activity is higher, making the monomer more likely to self-polymerize, and the difficulty of grafting on the surface of graphene oxide is greater, which ultimately leads to low grafting efficiency. In addition, the hydrophilic modified monomer used in this patent is easily hydrolyzed in an alkaline environment.

[0007] CN111978944A prepares hydrophilic modified microcrystalline graphene oxide by esterification reaction between carboxyl groups on the surface of graphene oxide and hydroxyl groups contained in polyethylene glycol. However, ester bonds are easily hydrolyzed in alkaline environments, resulting in the departure of polyoxyethylene groups grafted on the surface of the material and loss of the inherent salt resistance. This makes it impossible to apply the modified material provided by it to the conventional alkaline flooding system in the field of oil production, and the changes in pH and degree of hydrolysis of ester bonds should be monitored regularly during the application process, thus causing many 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 / base conditions in water. Summary of the invention

[0009] The purpose of the present invention is to overcome the problems in the prior art that graphene oxide has poor tolerance to inorganic salts and acids / alkalis and is prone to accumulation and agglomeration in water, and to provide a modified graphene oxide, a modified graphene oxide aqueous dispersion, and a preparation method and application thereof. The modified graphene oxide has good salt resistance, can tolerate acid / alkali aqueous solutions, and effectively inhibits the accumulation and agglomeration of graphene oxide.

[0010] In order to achieve the above object, the first aspect of the present invention provides a modified graphene oxide, wherein the modified graphene oxide comprises graphene oxide and a grafted polyoxyethylene chain, wherein the chemical formula of the polyoxyethylene chain is -CH 2 CH(OH)CH 2 O(CH 2 CH 2 O) n CH 2 CH 2 OH, wherein n is any integer from 3 to 20;

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

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

[0013] (1) Under alkaline conditions, an activation reaction is performed on a graphene oxide aqueous dispersion and cyclodextrin to obtain an activation solution;

[0014] (2) subjecting the activation solution and polyethylene glycol monoglycidyl ether to a grafting reaction to obtain a grafted product.

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

[0016] The third aspect of the present invention provides an aqueous dispersion of modified graphene oxide obtained by the aforementioned preparation method.

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

[0018] A fifth aspect of the present invention provides the use of the aforementioned modified graphene oxide or the aforementioned modified graphene oxide aqueous dispersion in the field of oil field recovery.

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

[0020] (1) The present invention grafts graphene oxide with polyethylene glycol monoglycidyl ether, and the obtained modified graphene oxide has good salt resistance, can tolerate acid / alkali aqueous solution, and effectively inhibits the accumulation and agglomeration of graphene oxide;

[0021] (2) In the present invention, the addition of cyclodextrin provides a suitable reaction site for the grafting reaction, so that the ring-opening grafting reaction can be carried out efficiently, which can greatly improve the grafting efficiency of the hydrophilic groups on the surface of graphene oxide;

[0022] (3) The preparation method provided by the present invention has the advantages of easy availability of 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 tolerate brine with a mass fraction of up to 5%, no precipitation will be generated in the pH range of 2-13, and has good oil-water interfacial activity in an alkaline water environment, thereby promoting the application of modified graphene oxide nanomaterials in the field of oil production. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 is the infrared spectrum of graphene oxide and modified graphene oxide in Example 1 of the present invention;

[0026] Figure 3 This is the result of atomic force microscopy morphology characterization of microcrystalline graphene oxide in Example 3 of the present invention. DETAILED DESCRIPTION

[0027] The endpoints and any values ​​of the ranges disclosed in this article 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 each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0028] The first aspect of the present invention provides a modified graphene oxide, wherein the modified graphene oxide comprises graphene oxide and a grafted polyoxyethylene chain, wherein the chemical formula of the polyoxyethylene chain is -CH 2 CH(OH)CH 2 O(CH 2 CH 2 O) n CH 2 CH 2 OH, wherein n is any integer from 3 to 20;

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

[0030] In the present 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 between any two values, preferably any integer from 5 to 15.

[0031] In the present invention, the modified graphene oxide is subjected to infrared spectroscopy test, and the structure of the modified graphene oxide is characterized and the groups contained are determined by the position of the characteristic peaks in the infrared spectrum. -1 The characteristic absorption peaks at 1730cm are the stretching vibration peaks of the remaining unreacted hydroxyl groups in graphene oxide and the newly generated hydroxyl groups after the epoxy groups open. -1 The characteristic absorption peak at 1633 cm -1 The characteristic absorption peak at 1101cm-1 The peak at 845 cm corresponds to the stretching vibration peak of COC in the polyoxyethylene group. -1 The peak at 1450cm is the stretching vibration peak of CC in the polyoxyethylene group. -1 and 2855cm -1 The peak at 40 corresponds to the CH vibration absorption peak of the polyoxyethylene group. The above peaks prove that the polyoxyethylene chain has been connected to the graphene oxide surface through chemical bonds.

[0032] In the present invention, the linking group between the obtained modified graphene oxide and the polyoxyethylene group is an ether bond, and the terminal of the obtained modified graphene oxide is a hydroxyl group, which will no longer participate in the grafting reaction.

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

[0034] In the present invention, the infrared spectrum test instrument is a NICOLET 6700 infrared spectrometer, and the test range is 450-4000cm -1 The results are the data after deducting the air background.

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

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

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

[0038] In the present invention, the modified graphene oxide has good salt resistance, can tolerate acid / alkali aqueous solutions, and effectively inhibits the accumulation and agglomeration 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 comprises the following steps:

[0040] (1) Under alkaline conditions, an activation reaction is performed on a graphene oxide aqueous dispersion and cyclodextrin to obtain an activation solution;

[0041] (2) subjecting the activation solution and polyethylene glycol monoglycidyl ether to a grafting reaction to obtain a grafted product.

[0042] In the present invention, compared with polyethylene glycol diglycidyl ether, polyethylene glycol monoglycidyl ether is used to graft graphene oxide, and the modified graphene oxide obtained has a hydroxyl terminal, which will no longer participate in the grafting reaction, avoiding the chemical connection between the graphene oxide sheets, thereby inhibiting the accumulation and agglomeration of the modified graphene oxide. In contrast, if polyethylene glycol diglycidyl ether is used, the two epoxy groups at both ends of the molecule are easy to react with two different graphene oxide nanosheets, and this "bridging" effect will promote the accumulation and agglomeration of nanomaterials, resulting in the modified graphene oxide being difficult to stably disperse in water.

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

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

[0045] In the present invention, there is no particular limitation on the structure of the cyclodextrin. Preferably, the cyclodextrin is selected from at least one of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin, and β-cyclodextrin is more preferably selected. In the present invention, the cyclodextrin provides microcavities required for the grafting reaction, so that the ring-opening grafting reaction can be carried out efficiently, which can greatly improve the grafting efficiency of the hydrophilic groups on the surface of graphene oxide.

[0046] According to the present invention, preferably, the content of cyclodextrin is 100-800 mg, preferably 300-500 mg, based on the total volume of the mixed solution of graphene oxide aqueous dispersion and cyclodextrin being 1 L. In the present invention, if the mass concentration of cyclodextrin is too low, the grafting effect is not good and the grafting rate is low; if the mass concentration of cyclodextrin is too high, it will cause waste of raw materials.

[0047] In the present 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), alkali is added to adjust the pH of the mixed solution to alkaline, and the alkali is sodium hydroxide and / or potassium hydroxide. In the present invention, the activation reaction is carried out under alkaline conditions, which can increase the activity of the hydroxyl groups in the activation solution and increase the grafting rate of the polyoxyethylene chains in the modified graphene oxide.

[0049] According to the present invention, the amount of the base added can be adaptively adjusted 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, preferably 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, preferably 500-2000 mg / L.

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

[0052] In the present invention, microcrystalline graphene oxide prepared by using microcrystalline graphite can be stably dispersed in high-salinity formation water, and the dispersion stability of the material has strong tolerance to acid / alkali, and the interfacial tension is reduced by one order of magnitude compared with that before modification, so it is suitable for application in conjunction with different acid / alkali flooding systems. At the same time, 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 in step (2) is prepared by the following method:

[0054] A mixture of polyethylene glycol, alkaline substance and epihalohydrin is stirred for reaction, and polyethylene glycol monoglycidyl ether is extracted after the reaction is completed.

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

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

[0057] In the present 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, preferably 300-500 rpm.

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

[0059] In the present invention, preferably, the average molecular weight of the polyethylene glycol is 200-600. When the average molecular weight of the polyethylene glycol is too high, the polyethylene glycol exists in a solid form, and the reaction yield is low; when the average molecular weight of the polyethylene glycol is too low, the obtained polyethylene glycol monoglycidyl ether has insufficient stability.

[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, preferably selected from at least one of potassium carbonate, potassium hydroxide and potassium bicarbonate.

[0061] According to the present invention, preferably, the epihalohydrin is epichlorohydrin and / or epibromohydrin.

[0062] In the present invention, after the reaction for preparing polyethylene glycol monoglycidyl ether is completed, the solvent is removed by extraction to obtain polyethylene glycol monoglycidyl ether, and the extraction process is not particularly limited.

[0063] According to a preferred embodiment of the present invention, polyethylene glycol monoglycidyl ether can be extracted into a dichloromethane phase using a water / dichloromethane solvent system with a 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: reaction temperature is 60-100° C., preferably 70-90° C.; reaction time is 4-16 h, preferably 6-12 h.

[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 comprises: adjusting the pH of the grafted product obtained in step (2) to neutral, and then washing.

[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, the above-mentioned washing agent can be used to remove cyclodextrin by enzymatic hydrolysis.

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

[0071] According to the present invention, preferably, the washing time is 1-4h, preferably 2-3h. 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 200-800rpm, preferably 300-500rpm.

[0072] In the present invention, unless otherwise specified, percentages refer to percentages by mass.

[0073] The third aspect of the present invention provides an aqueous dispersion of modified graphene oxide obtained by the aforementioned preparation method.

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

[0075] The present invention provides modified graphene oxide, the surface of which is grafted with polyoxyethylene groups, which, as nonionic hydrophilic groups, can effectively overcome the electrostatic shielding effect of inorganic salt cations on the carboxyl groups on the surface of graphene oxide, so that the salt resistance of the modified graphene oxide is significantly improved. On the other hand, the linking group between the modified graphene oxide obtained by the present invention and the polyoxyethylene groups is an ether bond, which is more stable than an ester bond and can withstand acid / alkali aqueous solutions, thereby broadening the industrial application range of the modified graphene oxide material.

[0076] A fifth aspect of the present invention provides the use of the aforementioned modified graphene oxide or the aforementioned modified graphene oxide aqueous dispersion in the field of oil field recovery.

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

[0078] In the present invention, unless otherwise specified, all percentages, parts, ratios, etc. mentioned in the present invention are based on weight, unless the weight basis does not conform to the common 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 comprises the following steps:

[0080] (1) Under alkaline conditions, an activation reaction is performed on a graphene oxide aqueous dispersion and cyclodextrin to obtain an activation solution;

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

[0082] The activation reaction conditions in step (1) include: reaction temperature of 70-90° C.; reaction time of 2-3 h;

[0083] Based on the total volume of the mixed solution of graphene oxide aqueous dispersion and cyclodextrin being 1 L, the content of cyclodextrin is 300-500 mg;

[0084] The amount of the base added is such that the pH value of the mixed solution is 10-11.

[0085] The present invention will be described in detail below through examples and comparative examples. In the following examples and comparative examples, unless otherwise specified, the reagents used in the present invention are all analytically pure and are commercially available;

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

[0087]

[0088] Product Name source Product Parameters Polyethylene glycol 400 Inokay Average molecular weight 400 Polyethylene glycol 600 Inokay Average molecular weight 600 Polyethylene glycol 200 Acros Average molecular weight 200 Polyethylene glycol 1000 Inokay Average molecular weight 1000 α-Cyclodextrin Inokay 98％ β-Cyclodextrin Inokay 99％ Epichlorohydrin Inokay 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] Weigh 16g of polyethylene glycol 400 and 5.5g of potassium carbonate in a single-mouth bottle, add 10g of epichlorohydrin under stirring at 25°C, stirring at a rate of 500rpm, continue the reaction for 24 hours and then stop stirring. Then use 200mL of a water / dichloromethane solvent system with a volume ratio of 1 / 1 to extract the polyethylene glycol monoglycidyl ether into a dichloromethane phase. Collect the dichloromethane phase and remove the solvent to obtain polyethylene glycol monoglycidyl ether;

[0092] The mass spectrum of the product is Figure 1 As shown. Since polyethylene glycol 400 is a mixture, its mass spectrum also shows multiple molecular ion peaks accordingly. 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 500 mg / L graphene oxide aqueous dispersion A1, add 50 mg of β-cyclodextrin, then add sodium hydroxide to adjust the pH value of the system to 10, stir at 80° C. for 2 hours at a stirring rate of 500 rpm. After reacting for 2 hours, add 1.5 g of polyethylene glycol monoglycidyl ether, continue the reaction for 8 hours, stop heating, and cool to room temperature.

[0094] (3) Adding hydrochloric acid to the reaction system to adjust the pH value to neutral. Subsequently, adding 10 mg of amylase and stirring for 3 hours at a stirring rate of 500 rpm to obtain a modified graphene oxide aqueous dispersion.

[0095] 10 mL of the modified graphene oxide aqueous dispersion was dialyzed in distilled water for 1 week through a dialysis bag to remove unreacted raw materials. The dialyzed graphene oxide aqueous dispersion was then freeze-dried, and the product structure was characterized by infrared spectroscopy.

[0096] The results are as follows Figure 2 As shown, the spectrum is at 3432cm -1 The characteristic absorption peaks at 1730cm are the stretching vibration peaks of the remaining unreacted hydroxyl groups in graphene oxide and the newly generated hydroxyl groups after the epoxy groups open. -1 The characteristic absorption peak at 1633 cm -1 The characteristic absorption peak at 1101cm -1 The peak at 845 cm corresponds to the stretching vibration peak of COC in the polyoxyethylene group. -1 The peak at 1450cm is the stretching vibration peak of CC in the polyoxyethylene group. -1 and 2855cm -1 The peak at 40 corresponds to the CH vibration absorption peak of the polyoxyethylene group. The above peaks prove that the polyoxyethylene chain has been connected to the graphene oxide surface through chemical bonds.

[0097] Example 2

[0098] (1) Weigh 24 g of polyethylene glycol 600 and 2.8 g of potassium carbonate in a single-necked bottle, add 18.5 g of epichlorohydrin dropwise at 40° C. under stirring conditions, with a stirring rate of 500 rpm, and continue the reaction for 24 hours before stopping stirring. Then, use 200 mL of a water / dichloromethane solvent system with a volume ratio of 1 / 1 to extract the polyethylene glycol monoglycidyl ether into a dichloromethane phase. Collect the dichloromethane phase, remove the solvent, and 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 value of the system to 11, then heat to 90° C., stir at 500 rpm. After reacting for 2 hours, add 2 g of polyethylene glycol monoglycidyl ether, continue to react for 6 hours, stop heating, and cool to room temperature.

[0100] (3) Adding hydrochloric acid to the reaction system to adjust the pH value to neutral, then adding 20 mg of amylase and stirring for 3 hours at a stirring rate of 500 rpm to obtain a 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 respectively in a three-necked flask, place the three-necked flask in an ice-water bath, add 25mL of 98% concentrated sulfuric acid at a stirring rate of 500rpm, and mix evenly; slowly add 3g of potassium permanganate, and the solution turns dark red after mixing. Stir in the ice-water bath for 0.5h, remove the ice-water bath, transfer the three-necked flask to a 40℃ oil bath, and continue stirring for 1h. Add 40mL of deionized water to the flask, heat to 95℃, react at a stirring speed of 500rpm for 40min, and after the reaction is completed, add 100mL of deionized water, and finally add 30% hydrogen peroxide solution three times (3mL each time). At this time, the color of the solution changes from dark red to orange-yellow.

[0104] Cleaning process: Filter the reacted graphite oxide mixture, and then wash it with 100 mL of deionized water. After washing three times, put the filter cake into a centrifuge tube, mechanically stir and disperse it, centrifuge it at 1000 rpm for 2 minutes, and remove the supernatant. Repeat the washing, dispersion, and centrifugation for 5 times until the pH value of the supernatant is neutral. Finally, freeze-dry the centrifuged graphite oxide precipitate to obtain a solid graphite oxide powder.

[0105] Dispersion process: Weigh 0.2 g of graphite oxide, add it to 100 mL of deionized water, and ultrasonicate for 3 h 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 can be seen that the thickness of microcrystalline graphene is 1-2nm, and the plane size is between 100-300nm.

[0107] (1) 8 g of polyethylene glycol 200 and 4.5 g of potassium carbonate were weighed into a single-necked bottle, and 37 g of epichlorohydrin was added dropwise under stirring at 40° C. The stirring rate was 500 rpm, and the reaction was continued for 24 hours, and then the stirring was stopped. Then, polyethylene glycol monoglycidyl ether was extracted into a dichloromethane phase with 200 mL of a water / dichloromethane solvent system with a volume ratio of 1 / 1. The dichloromethane phase was collected, and the solvent was removed to obtain the product.

[0108] (2) Weigh 100 mL of 2000 mg / L graphene oxide aqueous dispersion, add 50 mg of β-cyclodextrin at a stirring rate of 500 rpm, add sodium hydroxide to adjust the pH value 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 value to neutral. Then, add 40 mg of amylase and stir for 2 hours at a stirring rate of 500 rpm to obtain a 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 by an equal mass of α-cyclodextrin to obtain a modified graphene oxide aqueous dispersion.

[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 40 g of polyethylene glycol having an average molecular weight of 1000 to prepare polyethylene glycol monoglycidyl ether, thereby obtaining the modified graphene oxide aqueous dispersion.

[0114] Example 6

[0115] The modified graphene oxide aqueous dispersion was 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, thereby obtaining a modified graphene oxide aqueous dispersion.

[0116] Comparative Example 1

[0117] The preparation was carried out according to the method of Example 1, except that β-cyclodextrin was not added during the activation reaction in step (2), and amylase was not added during the treatment process after the grafting reaction.

[0118] Comparative Example 2

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

[0120] (1-1) 250 mL of 98% concentrated sulfuric acid was poured into a 500 mL glass beaker with a stirrer and stirred at a rate of 500 rpm. 5.00 g of 15000 mesh microcrystalline graphite powder was slowly added into the beaker. After magnetic stirring in an ice-water bath for 30 min, 25 g of ground potassium permanganate powder was slowly added while stirring. The mixture was stirred in the ice-water bath for 120 min. The ice-water bath was removed and the temperature was raised to 37° C. The mixture was stirred for 120 min. Deionized water was slowly added to control the temperature below 60° C. Water was added until the temperature of the reaction system stopped rising. 5 mL of 30% hydrogen peroxide solution was added dropwise.

[0121] (1-2) placing the solution in a centrifuge at 800 rpm for 5 minutes, filtering to remove large particles after standing, transferring the solution into a 1000 mL beaker, and washing with deionized water until the pH value is ≥ 6 to obtain microcrystalline graphite oxide gel;

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

[0123] (2) The modification of microcrystalline graphene oxide is carried out with reference to Example 7 of the patent application:

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

[0127] Comparative Example 4

[0128] The modified graphene oxide aqueous dispersion was prepared by referring to the method of Example 1 of CN113248669A.

[0129] Comparative Example 5

[0130] The method of Example 1 was used for preparation, except that polyethylene glycol diglycidyl ether was added in step (2) to obtain a modified graphene oxide aqueous dispersion.

[0131] Test Example 1

[0132] 0.5 g of modified graphene oxide dry powder was weighed into a quartz boat and heated to 800 °C at a heating rate of 10 °C / min in a tube furnace for 2 h. The mass loss was measured and the grafting rate of the polyethylene oxide chain 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] Through the modification method provided by the present invention, the grafting rate of the polyoxyethylene chains of the modified graphene oxide is between 35% and 46%.

[0137] Test Example 2: Salt resistance test of modified graphene oxide under neutral conditions

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

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

[0140]

[0141]

[0142] From the results in Table 2, it can be seen that the hydrophilically modified graphene oxide materials of Examples 1-5 have good salt resistance and can still be evenly dispersed in water when the NaCl concentration is as high as 5%. In contrast, the unmodified graphene oxide, regardless of the size of the sheet, has poor salt resistance and precipitates in a 0.5% salt solution. Due to the low hydrophilic group grafting rate of Example 6, the modified material cannot tolerate 5% high salt water, but can remain stable in 1% salt water.

[0143] In Comparative Example 1, due to the low grafting rate of hydrophilic groups in the graphene oxide material, it agglomerates and precipitates when the salt concentration rises to 1% or above. The results of Comparative Example 3 show that after the graphene oxide is non-covalently modified by adding polyethylene glycol, the material can tolerate 0.5% salt water, but cannot tolerate 1% and higher concentrations of salt water. The above results show that covalent grafting of polyethylene oxide groups can 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 of Comparative Example 4 can tolerate a salt concentration of 1%, but precipitates when the salt concentration increases to 5%. The presence of long-chain amines in its structure weakens the hydrophilicity of the material, and it is easy to aggregate and precipitate in high salt water. In addition, since the polymer after the self-polymerization of the hydrophilic monomer cannot be completely removed by dialysis, the actual grafting rate of the hydrophilic group on the surface of the modified graphene oxide material is lower than the test value, which is also a possible reason for the precipitation of the material in high salt water.

[0146] In Comparative Example 5, since the two epoxy groups of polyethylene glycol diglycidyl ether reacted with different graphene oxide nanosheets respectively, they played a "bridging" role, causing the material to aggregate more easily in water.

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

[0148] First, a series of NaCl aqueous solutions were prepared, and then a certain amount of modified graphene oxide aqueous dispersion was taken and diluted to 20 mL with NaCl aqueous solution. After dilution, the content of modified graphene oxide in the solution was 2 mg. NaOH was then added to adjust the pH to 13, and the solution was allowed to stand for 4 hours to observe whether precipitation was produced. 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] It can be seen from the results in Table 3 that in Examples 1-5, the modified graphene oxide still maintains good salt resistance under alkaline conditions, while the non-covalently modified graphene oxide in the unmodified Examples 1-3 and Comparative Example 3 still has poor salt resistance. In addition, Comparative Example 2 and Comparative Example 4 lose their salt resistance under alkaline conditions, and the materials precipitate in a 0.5% salt solution. The modified graphene oxide of Example 6 and Comparative Example 1 can still tolerate 0.5% salt water under alkaline conditions, but when the salt concentration is higher than 1%, the material agglomerates and precipitates due to the low hydrophilic group grafting rate. In Comparative Example 5, the two epoxy groups of polyethylene glycol diglycidyl ether react with different graphene oxide nanosheets respectively, playing a "bridging" role, causing the material to agglomerate and precipitate more easily.

[0152] The above results indicate that the modified graphene oxide provided by the embodiment of the present invention has excellent 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 modified graphene oxide aqueous dispersion, dilute it to 20 mL with NaCl aqueous solution, the content of modified graphene oxide in the solution after dilution is 2 mg, then add hydrochloric acid to adjust the pH to 2, let it stand for 8 hours, and observe whether precipitation occurs. 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] It can be seen from the results in Table 4 that in Examples 1-5, the hydrophilically modified graphene oxide materials still maintain good salt resistance under acidic conditions, while the unmodified examples 1-3 and the non-covalently modified comparative example 3 still have poor salt resistance. Comparative Examples 2 and 4 have certain salt resistance under acidic conditions, and the materials can be evenly dispersed in a 1% salt solution, but precipitate in a 5% salt solution. The modified graphene oxide materials of Example 6 and Comparative Example 1 can tolerate 1% salt water under acidic conditions, but when the salt concentration rises to 5%, the materials agglomerate and precipitate due to the low grafting rate of the hydrophilic group. In Comparative Example 5, the two epoxy groups of polyethylene glycol diglycidyl ether react with different graphene oxide nanosheets respectively, playing a "bridging" role, causing the material to agglomerate and precipitate more easily.

[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 material in the embodiment and the comparative example was measured by the rotating drop method using a TX-500C interfacial tension meter. The test oil was crude oil from the Louzi block of Henan Oilfield (the viscosity at 50°C was 300mPa·s measured by a Haake VT550 rotational viscometer), the test temperature was 50°C, and the rotation speed was 5000rpm. The crude oil in this block was produced by alkali-containing ternary flooding, the formation water salt concentration was 50000mg / L, and the pH value was 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 of the embodiments 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] The results in Table 5 show that the hydrophilic-lipophilic balance value of the graphene oxide after hydrophilic modification by the present invention is more conducive to the adsorption of the material at the oil-water interface and the interaction with the crude oil components, thus showing a certain interfacial activity, and being able to reduce the oil-water interfacial tension to less than 1.2 mN / m. Under the preferred conditions, the interfacial tension can be reduced to 0.35 mN / m at the lowest. The modified graphene oxide nanomaterials prepared in Examples 5 and 6 have a low grafting rate, and the interfacial activity is reduced compared with Examples 1-3, but are still better than the comparative example, and can be stably dispersed in formation water. In contrast, the modified graphene oxide with a low 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 simply compounded in Comparative Example 3, and the modified graphene oxide used in Comparative Examples 4 and 5 are all agglomerated and precipitated in the alkaline brine used in this experiment, and their oil-water interfacial tensions are all higher than 1.2 mN / m.

[0163] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A modified graphene oxide, It is characterized in that The modified graphene oxide comprises graphene oxide and grafted polyoxyethylene chains, wherein the chemical formula of the polyoxyethylene chains is -CH 2 CH(OH)CH 2 O(CH 2 CH 2 O) n CH 2 CH 2 OH, wherein n is any integer from 3 to 20; The grafting rate of the polyoxyethylene chains in the modified graphene oxide is 30-50%.

2. The modified graphene oxide according to claim 1, in, In the polyoxyethylene chain, n is any integer from 5 to 15; Preferably, the grafting rate of the polyethylene oxide chain in the modified graphene oxide is 35-46%; Preferably, the modified graphene oxide is obtained by dialyzing a modified graphene oxide aqueous dispersion.

3. A method for preparing a modified graphene oxide aqueous dispersion, It is characterized in that The method comprises the following steps: (1) Under alkaline conditions, an activation reaction is performed on a graphene oxide aqueous dispersion and cyclodextrin to obtain an activation solution; (2) subjecting the activation solution and polyethylene glycol monoglycidyl ether to a grafting reaction to obtain a grafted product.

4. The preparation method according to claim 3, in, The activation reaction conditions in step (1) include: reaction temperature of 60-100° C., preferably 70-90° C.; reaction time of 1-4 h, preferably 2-3 h; Preferably, based on the total volume of the mixed solution of graphene oxide aqueous dispersion and cyclodextrin as 1L, the content of cyclodextrin is 100-800 mg, preferably 300-500 mg; Preferably, in step (1), a base is added to adjust the pH of the mixed solution to alkaline, and the base is sodium hydroxide and / or potassium hydroxide; Preferably, the amount of base added is such that the pH value of the mixed solution is 9-12, preferably 10-11.

5. The preparation method according to claim 3 or 4, in, The mass concentration of graphene oxide in the graphene oxide aqueous dispersion in step (1) is higher than 20 mg / L, preferably 500-2000 mg / L; Preferably, the raw material of the graphene oxide is microcrystalline graphite and / or flake graphite, and the flake diameter of the graphene oxide does not exceed 2 μm, preferably 50-500 nm.

6. The preparation method according to any one of claims 3 to 5, in, The polyethylene glycol monoglycidyl ether in step (2) is prepared by the following method: Stirring a mixture of polyethylene glycol, alkaline substance and epihalohydrin to react, and extracting to obtain polyethylene glycol monoglycidyl ether after the reaction is completed; Preferably, the reaction temperature is 20-50°C, preferably 25-40°C; the reaction time is 12-36h, preferably 20-30h.

7. The preparation method according to claim 6, in, The molar ratio of the polyethylene glycol, the alkaline substance and the epihalohydrin is 1:(0.1-1):(1.1-10), preferably 1:(0.5-1):(1.5-10); Preferably, the average molecular weight of the polyethylene glycol is 200-600; Preferably, the alkaline substance is selected from at least one of potassium carbonate, potassium hydroxide, potassium bicarbonate, sodium carbonate, sodium hydroxide and sodium bicarbonate, preferably selected from at least one of potassium carbonate, potassium hydroxide and potassium bicarbonate; Preferably, the epihalohydrin is epichlorohydrin and / or epibromohydrin.

8. The preparation method according to any one of claims 3 to 7, in, The grafting reaction conditions in step (2) include: reaction temperature of 60-100° C., preferably 70-90° C.; reaction time of 4-16 h, preferably 6-12 h; Preferably, the mass ratio of polyethylene glycol monoglycidyl ether to graphene oxide is 5-100:1, and the preferred mass ratio is 10-30:

1.

9. The preparation method according to any one of claims 3 to 8, in, The method further comprises: adjusting the pH of the grafted product obtained in step (2) to neutral, and then washing; Preferably, the pH of the grafted product is adjusted to neutral by adding acid; Preferably, the acid is selected from at least one of hydrochloric acid, sulfuric acid and phosphoric acid; Preferably, the washing detergent is amylase and / or cyclodextrinase; Preferably, based on the total volume of the graphene oxide aqueous dispersion as 1 L, the amount of the detergent is 50-800 mg, preferably 100-400 mg; Preferably, the washing time is 1-4 hours, preferably 2-3 hours.

10. A modified graphene oxide aqueous dispersion obtained by the preparation method according to any one of claims 3 to 9.

11. A modified graphene oxide, It is characterized in that The modified graphene oxide is obtained by removing unreacted raw materials from the modified graphene aqueous dispersion according to claim 10 through dialysis.

12. Use of the modified graphene oxide according to claim 1, 2 or 11 or the modified graphene oxide aqueous dispersion according to claim 10 in the field of oil field recovery.

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