Modified black phosphorus nanosheet as well as synthesis method and application thereof

Abstract

The invention relates to a modified black phosphorus nanosheet as well as a synthesis method and application thereof. Asphaltene in thick oil is dispersed by grafting a copolymerized oil-soluble polymer on one side of the black phosphorus nanosheet, so that the viscosity of the thick oil is reduced, and meanwhile, the acting force between the modified black phosphorus nanosheet and crude oil is also increased; the hydrophilic polymer grafted on the other side faces water, so that the modified black phosphorus nanosheet is stabilized at an oil-water interface to form an emulsion; the black phosphorus nanosheet is used as a core, the polymer is used as a shell, and good salt resistance and temperature resistance are achieved; meanwhile, the modified black phosphorus nanosheet is used as a thick oil viscosity reducer, and the self-demulsification effect can be achieved by adjusting the pH value of produced liquid.

Description

Technical Field

[0001] The present invention relates to the technical field of petroleum extraction, and in particular to a modified black phosphorus nanosheet, a synthesis method and application thereof. Background Art

[0002] With the increasing demand for oil and the large-scale development of conventional oil resources, heavy oil resources, due to their abundant reserves, have become a hot topic for development. Because heavy oil contains a large amount of natural W / O emulsifiers such as colloids and asphaltenes, its high viscosity makes it difficult to recover from oilfields. Using emulsification and viscosity reduction, the W / O emulsion is converted to an O / W emulsion by adding a certain amount of emulsifying viscosity reducer. The lower viscosity of water increases the fluidity of the system, facilitating the recovery of heavy oil.

[0003] Ahmed (Ahmed NS, Nassar AM, Zaki NN, Gharieb KH. Stability and Rheology of Heavy Crude Oil-in-Water Emulsion Stabilized by an Anionic-Nonionic Surfactant Mixture [J]. Petroleum Science and Technology, 1999, 17 (5-6): 553-576) selected an anionic surfactant triethanolamine dodecylbenzenesulfonate and a nonionic surfactant nonylphenol polyoxyethylene ether and successfully applied them to the emulsification and viscosity reduction of an Egyptian heavy oil. The study found that the anionic surfactant and the nonionic surfactant had a certain synergistic effect and could achieve the emulsification and viscosity reduction effect of a single surfactant at a lower dosage. It was also found that the anionic surfactant helped to stabilize the emulsion at a lower concentration, while the nonionic surfactant played a positive role in reducing the viscosity of the emulsion.

[0004] Li Juan (Li Juan. Synthesis and Properties of Water-Soluble Polymer Viscosity Reducers for Heavy Oil [D]. Shandong University, 2019. DOI: 10.27272 / d.cnki.gshdu.2019.000208.) copolymerized AM, dimethylacrylamide, and acryloylmorpholine to produce an amphiphilic terpolymer. A hydroxyl-terminated anionic copolymer was synthesized by free radical copolymerization of AM, sodium styrene sulfonate, and the chain transfer agent mercaptoethanol. These two copolymers were then used to produce a composite amphiphilic copolymer for heavy oil viscosity reduction. The composite system exhibited excellent heavy oil viscosity reduction performance, achieving a viscosity reduction rate exceeding 95% at a dosage of 1000 mg / L, and exhibited good salt tolerance.

[0005] Guo Na (Guo Na, Li Liang, Zhang Xiao, et al. Preparation and Performance Evaluation of Polymer Emulsified Viscosity Reducer [J]. Applied Chemical Industry, 2019, 48(10): 4.) prepared a polymer of ethylene glycol acrylate-acrylamide-alkyl hydrophobic monomer using polyethylene glycol acrylate and maleic acid hydrophobic long-chain monomer. The results showed that the emulsification viscosity reduction effect exceeded 98% when the oil-water volume ratio was 7:3 and the addition amount was 0.08%. After treatment at 180°C for 24 hours, the viscosity reduction rate of the polymer emulsifier decreased by about 3% and remained above 95%. The molecular structure was well maintained at high temperature, and it still had a good ability to emulsify heavy oil.

[0006] Liu Binlong (Liu Binlong. Preparation and Performance Evaluation of a pH-Responsive, High-Temperature-Resistant Pickering Emulsion Viscosity Reducer for Heavy Oil) functionalized the surface of SiO2 with amino groups. The amino-functionalized SiO2 then reacted with tolualdehyde via a Schiff base reaction, attaching hydrophobic chains to the surface of the amino-functionalized SiO2 to produce SiO2-B. Under the conditions of a SiO2-B concentration of 0.1 wt%, a pH of 7.8, and an oil-to-water volume ratio of 1:1, the resulting stable Pickering emulsion could be cyclically demulsified and emulsified by pH control, maintaining stable stability.

[0007] CN 113861957A discloses a dual-base nano-viscosity reducer and its application in heavy oil production and a production method. The dual-base nano-viscosity reducer is prepared from an organic-inorganic emulsion, amphiphilic nanosheets and water. The organic-inorganic emulsion is prepared from a polymer surfactant, an alkane organic solvent, water and a first emulsifier.

[0008] Therefore, the key to achieving viscosity reduction through emulsification is to make the viscosity reducer amphiphilic. Conventional approaches rely on surfactant compounding, adding hydrophobic chains to hydrophilic polymers, or attaching hydrophobic chains to hydrophilic nanoparticles. However, amphiphilic polymers are difficult to synthesize, have poor temperature resistance, and self-assemble in aqueous solutions, reducing their interaction with crude oil. Furthermore, polymer emulsions are difficult to demulsify. Furthermore, surfactant compounding also presents challenges with temperature resistance, salt tolerance, and chromatographic separation.

[0009] Therefore, in view of the shortcomings of the existing technology, it is necessary to provide a method for synthesizing a material with strong emulsification ability, high viscosity reduction efficiency, temperature and salt resistance, and self-demulsification characteristics. Summary of the Invention

[0010] The purpose of the present invention is to provide a modified black phosphorus nanosheet, a synthesis method and application thereof. The modified black phosphorus nanosheet is prepared by grafting polymers of different wettability onto both sides of the black phosphorus nanosheet. As a heavy oil viscosity reducer, the material has the characteristics of strong emulsification ability, high viscosity reduction efficiency, temperature and salt resistance, and self-demulsification.

[0011] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides a method for synthesizing modified black phosphorus nanosheets, the method comprising the following steps:

[0013] (1) performing a first reaction on a double-terminated carboxyl polyethylene glycol, calcium carbonate, and a first solvent, and washing the resulting solid phase to obtain a PEG-CaCO3 structure;

[0014] (2) subjecting the black phosphorus nanosheets, the catalyst, the second solvent, and the PEG-CaCO3 structure obtained in step (1) to a second reaction, and centrifuging and washing the resulting product to obtain a BP-PEG-CaCO3 structure;

[0015] (3) subjecting the polymer monomer, the third solvent, the polymerization initiator, and the BP-PEG-CaCO3 structure obtained in step (2) to a third reaction, and washing the resulting product to obtain a POLY-BP-PEG-CaCO3 structure;

[0016] (4) removing calcium carbonate from the POLY-BP-PEG-CaCO3 structure obtained in step (3), and washing and centrifuging the obtained product to obtain the modified black phosphorus nanosheets.

[0017] The invention provides a method for synthesizing modified black phosphorus nanosheets. The invention graft copolymerizes polymers of different types and molecular weights on both sides of the black phosphorus nanosheets, thereby maintaining the amphiphilicity of the overall structure, having strong emulsification ability and good emulsion stability. The graft copolymerized oil-soluble polymer has good permeability: the long carbon chain of the oil-soluble polymer easily interacts with the alkyl number in the side chain of the heavy oil, thereby entering between the colloid and asphaltene sheet molecules, breaking up some stacked molecular aggregates, and selecting polar groups as side chains to interact with the condensed aromatic hydrocarbons. Atoms such as N and O are easy to form hydrogen bonds, which can form hydrogen bonds with colloids and asphaltenes in heavy oil, thereby destroying the hydrogen bonds formed between the colloids and asphaltenes, thereby forming an O / W emulsion. For hydrophilic polymers grafted with PEG, the ethoxy group easily forms hydrogen bonds with water and has strong hydrophilicity, which is conducive to the adsorption of viscosity reducers at the emulsion interface and increases the stability of the emulsion, thereby preventing premature emulsion decomposition due to poor emulsion quality during transportation, thereby preventing pipeline blockage. The present invention uses black phosphorus nanosheets as the core and the polymer as the shell, and has good salt and temperature resistance.

[0018] Preferably, the molecular weight of the double-terminated carboxyl polyethylene glycol in step (1) is 1000-5000, for example, 1000, 2000, 3000, 4000 or 5000, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0019] Preferably, the particle size of the calcium carbonate in step (1) is 2-5 μm, for example, 2 μm, 3 μm, 4 μm, 4.5 μm or 5 μm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0020] Preferably, the mass ratio of the double-terminated carboxyl polyethylene glycol to calcium carbonate in step (1) is (10-30):1, for example, it can be 10:1, 15:1, 20:1, 25:1 or 30:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0021] Preferably, in step (1), the first solvent comprises deionized water.

[0022] Preferably, the temperature of the first reaction in step (1) is 80-90° C. and the time is 60-90 min.

[0023] The temperature of the first reaction is 80-90°C, for example, 80°C, 82°C, 85°C, 88°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0024] The time of the first reaction is 60-90 min, for example, 60 min, 70 min, 80 min or 90 min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the first reaction in step (1) is carried out under stirring conditions of 500-1500 rpm, for example, 500 rpm, 800 rpm, 1000 rpm, 1200 rpm or 1500 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the cleaning in step (1) is centrifugal cleaning with deionized water 3 times.

[0027] Preferably, the size of the black phosphorus nanosheets in step (2) is 50-150 nm, for example, 50 nm, 80 nm, 100 nm, 120 nm or 150 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the mass ratio of the black phosphorus nanosheets to the PEG-CaCO3 structure in step (2) is (10-20):1, for example, it can be 10:1, 12:1, 15:1, 18:1 or 20:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the catalyst in step (2) comprises 4-dimethylaminopyridine.

[0030] Preferably, the amount of the catalyst used in step (2) is 8-10wt% of the mass of the black phosphorus nanosheets, for example, it can be 8wt%, 8.5wt%, 9wt%, 9.5wt% or 10wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0031] Preferably, in step (2), the second solvent comprises N,N-dimethylformamide.

[0032] Preferably, the temperature of the second reaction in step (2) is 30-50° C. and the time is 8-12 h.

[0033] The temperature of the second reaction is 30-50°C, for example, 30°C, 35°C, 40°C, 45°C or 50°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0034] The time of the second reaction is 8-12 hours, for example, 8 hours, 9 hours, 10 hours, 11 hours or 12 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] Preferably, the second reaction in step (2) is carried out under stirring conditions of 500-1500 rpm, for example, 500 rpm, 800 rpm, 1000 rpm, 1200 rpm or 1500 rpm, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0036] Preferably, the second reaction in step (2) is carried out in an argon atmosphere.

[0037] Preferably, the centrifugation and washing steps in step (2) include: centrifuging the obtained product at 5000 rpm for 10 minutes, and then washing with deionized water three times.

[0038] Preferably, the polymer monomer in step (3) includes any one or a combination of at least two of styrene, acrylamide, eicosyl acrylate, behenyl acrylate, sodium allyl sulfonate or vinyl acetate. Typical but non-limiting combinations include a combination of styrene, eicosyl acrylate and acrylamide, a combination of sodium allyl sulfonate, behenyl acrylate and vinyl acetate, a combination of behenyl acrylate, styrene and vinyl acetate, or a combination of styrene, acrylamide, eicosyl acrylate, behenyl acrylate, sodium allyl sulfonate and vinyl acetate.

[0039] Preferably, the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer in step (3) is (10-50):1, for example, 10:1, 20:1, 30:1, 40:1 or 50:1, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the amount of the polymerization initiator used in step (3) is 0.5-1wt% of the mass of the polymer monomer, for example, it can be 0.5wt%, 0.6wt%, 0.8wt%, 0.9wt% or 1wt%, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0041] Preferably, the polymerization initiator in step (3) includes any one of azobisisobutyronitrile, azobisisoheptanenitrile or dimethyl azobisisobutyrate, or a combination of at least two thereof. Typical but non-limiting combinations include a combination of azobisisobutyronitrile and azobisisoheptanenitrile, a combination of azobisisoheptanenitrile and dimethyl azobisisobutyrate, or a combination of azobisisobutyronitrile, azobisisoheptanenitrile and dimethyl azobisisobutyrate.

[0042] Preferably, the third solvent in step (3) comprises a mixed solution of toluene and ethanol.

[0043] Before use, the first solvent, the second solvent and the third solvent in the present invention need to be purged with nitrogen for 30 minutes to remove oxygen therein.

[0044] Preferably, the specific steps of the third reaction in step (3) include: dispersing the polymer monomer and the BP-PEG-CaCO3 structure obtained in step (2) in a third solvent, introducing nitrogen gas, and then adding a polymerization initiator to carry out the third reaction.

[0045] Preferably, the temperature of the third reaction in step (3) is 50-90° C., and the time is 6-12 h.

[0046] The temperature of the third reaction is 50-90°C, for example, 50°C, 60°C, 70°C, 80°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] The time of the third reaction is 6-12 hours, for example, 6 hours, 7 hours, 8 hours, 10 hours or 12 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the washing reagent in step (3) includes methanol.

[0049] Preferably, the reagent used for removing calcium carbonate in step (4) includes ethylenediaminetetraacetic acid at a concentration of 0.1-0.2 mol / L, for example, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L or 0.2 mol / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0050] Preferably, the cleaning in step (4) is performed using deionized water.

[0051] In a second aspect, the present invention provides a modified black phosphorus nanosheet, which is synthesized by the synthesis method described in the first aspect.

[0052] The modified black phosphorus nanosheets have a POLY-BP-PEG structure. Through the organic combination of the black phosphorus nanosheets and the polymer, the grafted oil-soluble polymer significantly increases the interaction of heavy components, reducing the viscosity of the heavy oil and facilitating emulsification. The grafted water-soluble polymer imparts amphiphilicity to the overall structure, significantly enhancing the stability of the emulsion. Finally, with the black phosphorus nanosheets as the core, the material combines the dual advantages of the nanomaterial's temperature and salt resistance with its ability to degrade and break down under alkaline conditions.

[0053] In a third aspect, the present invention provides a use of the modified black phosphorus nanosheets as described in the second aspect, wherein the modified black phosphorus nanosheets are used as a heavy oil viscosity reducer in heavy oil production.

[0054] Preferably, the modified black phosphorus nanosheets are used as a heavy oil viscosity reducer at a concentration of 500-2000 mg / L, for example, 500 mg / L, 800 mg / L, 1000 mg / L, 1500 mg / L or 2000 mg / L, but are not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] Preferably, the pH value of the produced fluid from heavy oil production is adjusted to 9-11, and demulsification is achieved after stirring for 3-5 hours.

[0056] The pH value of the produced fluid is adjusted to 9-11, for example, 9, 9.5, 10, 10.5 or 11, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0057] The stirring time is 3-5 hours, for example, 3 hours, 3.5 hours, 4 hours, 4.5 hours or 5 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0058] Since black phosphorus nanosheets will accelerate degradation in an alkaline environment, the modified black phosphorus nanosheets provided by the present invention can achieve the effect of self-demulsification by adjusting the pH value of the produced fluid, thereby reducing the post-processing cost of the produced fluid and simplifying the post-processing process of the produced fluid.

[0059] Compared with the prior art, the present invention has the following beneficial effects:

[0060] (1) The present invention provides a method for synthesizing modified black phosphorus nanosheets, wherein polymers of different types and molecular weights are grafted and copolymerized on both sides of the black phosphorus nanosheets, thereby maintaining the amphiphilicity of the overall structure, having strong emulsification ability and good emulsion stability: the asphaltene in the heavy oil is dispersed by the grafted copolymerized oil-soluble polymer, thereby reducing the viscosity of the heavy oil and increasing the interaction between the modified black phosphorus nanosheets and the crude oil; the hydrophilic polymer grafted on the other side faces the water, so that the modified black phosphorus nanosheets are stabilized at the oil-water interface to form an emulsion, that is, the stronger the interaction between the viscosity reducer and the heavy oil, the easier it is to form an emulsion, the increased hydrophilicity helps to increase the stability of the emulsion; by first dispersing the asphaltene to reduce the viscosity of the heavy oil and then emulsifying and dispersing to significantly reduce the viscosity of the heavy oil, not only can the amount of viscosity reducer added be reduced, but also a better viscosity reduction effect can be achieved;

[0061] (2) The modified black phosphorus nanosheets synthesized by the present invention have black phosphorus nanosheets as cores and polymers as shells, and have good salt and temperature resistance. At the same time, the modified black phosphorus nanosheets can be used as a heavy oil viscosity reducer to achieve the effect of self-demulsification by adjusting the pH value of the produced fluid, thereby reducing the post-processing cost of the produced fluid and simplifying the post-processing process of the produced fluid. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] Example 1

[0064] This embodiment provides a modified black phosphorus nanosheet. The synthesis method of the modified black phosphorus nanosheet comprises the following steps:

[0065] (1) Dispersing a double-end carboxyl polyethylene glycol with a molecular weight of 3000 and calcium carbonate with a particle size of 4 μm in deionized water, performing a first reaction at 85°C and 1000 rpm for 70 min, and washing the resulting solid phase three times by centrifugation with deionized water to obtain a PEG-CaCO3 structure; the mass ratio of the double-end carboxyl polyethylene glycol to calcium carbonate is 20:1;

[0066] (2) dispersing black phosphorus nanosheets with a size of 100 nm and the PEG-CaCO3 structure obtained in step (1) in N,N-dimethylformamide, then adding 4-dimethylaminopyridine in an amount of 9 wt% of the mass of the black phosphorus nanosheets, and performing a second reaction under argon atmosphere, 40° C. and stirring at 1000 rpm for 10 hours. The obtained product was centrifuged at 5000 rpm for 10 minutes and then washed three times with deionized water to obtain a BP-PEG-CaCO3 structure; the mass ratio of the black phosphorus nanosheets to the PEG-CaCO3 structure was 15:1;

[0067] (3) dispersing the polymer monomer and the BP-PEG-CaCO3 structure obtained in step (2) in a mixed solution of toluene and ethanol, introducing nitrogen, adding 0.8 wt% of azobisisobutyronitrile in an amount of the polymer monomer mass, and conducting a third reaction at 70° C. for 10 h. The resulting product is washed with methanol to obtain a POLY-BP-PEG-CaCO3 structure; the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer is 30:1; the polymer monomer comprises dodecyl acrylate, styrene, and vinyl acetate in a mass ratio of 1:1:1;

[0068] (4) Using 0.15 mol / L ethylenediaminetetraacetic acid to remove calcium carbonate from the POLY-BP-PEG-CaCO3 structure obtained in step (3), the obtained product is washed with deionized water and centrifuged to obtain the modified black phosphorus nanosheets, which are POLY-BP-PEG structures.

[0069] Example 2

[0070] This embodiment provides a modified black phosphorus nanosheet. The synthesis method of the modified black phosphorus nanosheet comprises the following steps:

[0071] (1) Dispersing a double-end carboxyl polyethylene glycol with a molecular weight of 1000 and calcium carbonate with a particle size of 2 μm in deionized water, performing a first reaction at 80°C and 500 rpm for 90 min, and washing the resulting solid phase three times with deionized water by centrifugation to obtain a PEG-CaCO3 structure; the mass ratio of the double-end carboxyl polyethylene glycol to calcium carbonate is 10:1;

[0072] (2) dispersing black phosphorus nanosheets with a size of 50 nm and the PEG-CaCO3 structure obtained in step (1) in N,N-dimethylformamide, then adding 4-dimethylaminopyridine in an amount of 8 wt% of the mass of the black phosphorus nanosheets, and performing a second reaction under argon atmosphere, 30° C. and stirring at 500 rpm for 12 hours. The obtained product was centrifuged at 5000 rpm for 10 minutes and then washed three times with deionized water to obtain a BP-PEG-CaCO3 structure; the mass ratio of the black phosphorus nanosheets to the PEG-CaCO3 structure was 10:1;

[0073] (3) dispersing the polymer monomer and the BP-PEG-CaCO3 structure obtained in step (2) in a mixed solution of toluene and ethanol, introducing nitrogen, adding 0.5 wt% of azobisisobutyronitrile in an amount of the polymer monomer mass, and conducting a third reaction at 50° C. for 12 h. The resulting product is washed with methanol to obtain a POLY-BP-PEG-CaCO3 structure; the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer is 10:1; the polymer monomer includes styrene, eicosyl acrylate, and acrylamide in a mass ratio of 2:2:1;

[0074] (4) Using 0.1 mol / L ethylenediaminetetraacetic acid to remove calcium carbonate from the POLY-BP-PEG-CaCO3 structure obtained in step (3), the obtained product is washed with deionized water and centrifuged to obtain the modified black phosphorus nanosheets, which are POLY-BP-PEG structures.

[0075] Example 3

[0076] This embodiment provides a modified black phosphorus nanosheet. The synthesis method of the modified black phosphorus nanosheet comprises the following steps:

[0077] (1) Dispersing a double-end carboxyl polyethylene glycol with a molecular weight of 5000 and calcium carbonate with a particle size of 5 μm in deionized water, performing a first reaction at 90°C and 1500 rpm for 60 min, and washing the resulting solid phase three times by centrifugation with deionized water to obtain a PEG-CaCO3 structure; the mass ratio of the double-end carboxyl polyethylene glycol to calcium carbonate is 30:1;

[0078] (2) dispersing black phosphorus nanosheets with a size of 150 nm and the PEG-CaCO3 structure obtained in step (1) in N,N-dimethylformamide, then adding 4-dimethylaminopyridine in an amount of 10 wt% of the mass of the black phosphorus nanosheets, and performing a second reaction under argon atmosphere, 50° C. and stirring at 1500 rpm for 8 hours. The obtained product was centrifuged at 5000 rpm for 10 minutes and then washed three times with deionized water to obtain a BP-PEG-CaCO3 structure; the mass ratio of the black phosphorus nanosheets to the PEG-CaCO3 structure was 20:1;

[0079] (3) dispersing the polymer monomer and the BP-PEG-CaCO3 structure obtained in step (2) in a mixed solution of toluene and ethanol, introducing nitrogen, adding 1 wt% of azobisisobutyronitrile based on the mass of the polymer monomer, and conducting a third reaction at 90° C. for 6 h. The resulting product is washed with methanol to obtain a POLY-BP-PEG-CaCO3 structure; the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer is 50:1; the polymer monomer comprises sodium allyl sulfonate, dodecyl acrylate, and vinyl acetate in a mass ratio of 2:1:2;

[0080] (4) Using 0.2 mol / L ethylenediaminetetraacetic acid to remove calcium carbonate from the POLY-BP-PEG-CaCO3 structure obtained in step (3), the obtained product is washed with deionized water and centrifuged to obtain the modified black phosphorus nanosheets, which are POLY-BP-PEG structures.

[0081] Example 4

[0082] This embodiment provides a modified black phosphorus nanosheet, which is different from Example 1 in that, except that the mass ratio of the black phosphorus nanosheet to the PEG-CaCO3 structure in step (2) is adjusted to 5:1, the rest is the same as Example 1.

[0083] Example 5

[0084] This embodiment provides a modified black phosphorus nanosheet, which differs from Example 1 in that, except for adjusting the mass ratio of the black phosphorus nanosheet to the PEG-CaCO3 structure in step (2) to 25:1, the rest is the same as Example 1.

[0085] Example 6

[0086] This embodiment provides a modified black phosphorus nanosheet, which differs from Example 1 in that, except for adjusting the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer in step (3) to 5:1, the rest is the same as Example 1.

[0087] Example 7

[0088] This embodiment provides a modified black phosphorus nanosheet, which differs from Example 1 in that, except for adjusting the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer in step (3) to 55:1, the rest is the same as Example 1.

[0089] Comparative Example 1

[0090] This comparative example provides a modified black phosphorus nanosheet, which differs from Example 1 in that steps (1), (2) and (4) are omitted, and the BP-PEG-CaCO3 structure of step (3) is replaced by black phosphorus nanosheets to adaptably obtain a POLY-BP structure. The rest is the same as in Example 1.

[0091] Comparative Example 2

[0092] This comparative example provides a modified black phosphorus nanosheet, and the synthesis method of the modified black phosphorus nanosheet comprises the following steps:

[0093] (1) Black phosphorus nanosheets with a size of 100 nm and double-terminated carboxyl polyethylene glycol were dispersed in N,N-dimethylformamide, and then 4-dimethylaminopyridine was added in an amount of 9 wt% of the mass of the black phosphorus nanosheets. A second reaction was carried out under argon atmosphere, 40°C and stirring conditions of 1000 rpm for 10 hours. The obtained product was centrifuged at 5000 rpm for 10 minutes and then washed three times with deionized water to obtain a BP-PEG structure; the mass ratio of the black phosphorus nanosheets to the double-terminated carboxyl polyethylene glycol was 15:1;

[0094] (2) The polymer monomer and the BP-PEG structure obtained in step (1) are dispersed in a mixed solution of toluene and ethanol, and after nitrogen is introduced, 0.8 wt% of azobisisobutyronitrile is added in an amount of the polymer monomer. A third reaction is carried out at 70° C. for 10 h, and the resulting product is washed with methanol to obtain a BP-PEG-POLY structure; the mass ratio of the BP-PEG structure to the polymer monomer is 30:1; the polymer monomer includes dodecyl acrylate, styrene, and vinyl acetate in a mass ratio of 1:1:1.

[0095] Comparative Example 3

[0096] This comparative example provides a modified black phosphorus nanosheet, which differs from Example 1 in that step (3) is omitted and step (4) is adaptively adjusted as follows: calcium carbonate is removed from the BP-PEG-CaCO3 structure obtained in step (2) using ethylenediaminetetraacetic acid at a concentration of 0.15 mol / L, and the resulting product is washed with deionized water and centrifuged to obtain the modified black phosphorus nanosheet. The modified black phosphorus nanosheet is a BP-PEG structure, and the rest is the same as Example 1.

[0097] Test Example 1

[0098] This test example evaluates the viscosity reduction rate of the modified black phosphorus nanosheets synthesized in Examples 1-7 and Comparative Examples 1-3, including the following steps:

[0099] (1) Determination of heavy oil viscosity: The heavy oil sample was preheated at 80°C and stirred continuously for 1 h before measurement, then cooled to 50°C. The viscosity of the heavy oil was measured using a digital viscometer to eliminate experimental errors caused by local inhomogeneity or differences in physical properties of the heavy oil.

[0100] (2) First, a certain amount of heavy oil was placed in a beaker, which was sealed and placed in a 60°C constant temperature oven for preheating for 1 hour. Then, a modified black phosphorus nanosheet solution with a concentration of 500 mg / L was prepared using deionized water. After 1 hour, 100 g of heavy oil and modified black phosphorus nanosheet solution were weighed according to an oil-water ratio of 7:3. The mixed solution was then placed on a heat-collecting magnetic stirrer and stirred at 60°C and 200 rpm for 30 minutes. The viscosity of the heavy oil after adding the modified black phosphorus nanosheets was measured using a digital viscometer, and the viscosity reduction rate was calculated according to the following formula:

[0101]

[0102] Where W is the viscosity reduction rate of heavy oil, %; η0 is the original viscosity of heavy oil, mPa·s; η is the viscosity of heavy oil after adding modified black phosphorus nanosheets, mPa·s.

[0103] The results are shown in Table 1.

[0104] Table 1

[0105] Viscosity reduction rate (%) Example 1 97.65 Example 2 95.33 Example 3 96.01 Example 4 75.63 Example 5 77.91 Example 6 84.73 Example 7 85.89 Comparative Example 1 64.97 Comparative Example 2 67.12 Comparative Example 3 63.69

[0106] Test Example 2

[0107] With reference to Experimental Example 1 and the Petroleum and Natural Gas Industry Standard SY / T 5280-2018 of the People's Republic of China "General Technical Requirements for Crude Oil Demulsifiers", the demulsification rates of the modified black phosphorus nanosheets synthesized in Examples 1-7 were evaluated. The specific steps are as follows:

[0108] (1) First, a certain amount of heavy oil was placed in a beaker, which was sealed and placed in a 60°C constant temperature oven for preheating for 1 h. Then, a modified black phosphorus nanosheet solution with a concentration of 500 mg / L was prepared using deionized water. After 1 h, 100 mL of heavy oil and modified black phosphorus nanosheet solution were weighed according to an oil-water ratio of 7:3 and placed in an open container. The pH value of the solution was then adjusted to 10 and stirred at 60°C and 1000 rpm for 3 h.

[0109] (2) Add the above solution to a graduated colorimetric tube, let it stand and read the dewatered volume V, and calculate the demulsification rate according to the following formula:

[0110]

[0111] Wherein, η is the demulsification rate, %; V is the volume of dewatered water, mL.

[0112] The results are shown in Table 2.

[0113] Table 2

[0114] Demulsification rate / % Example 1 97.86 Example 2 96.31 Example 3 96.94 Example 4 80.54 Example 5 78.97 Example 6 70.45 Example 7 71.12

[0115] As can be seen from Tables 1 and 2, the modified black phosphorus nanosheets provided by the present invention have a high viscosity reduction rate as a heavy oil viscosity reducer. As a heavy oil viscosity reducer, the modified black phosphorus nanosheets have amphiphilicity, strong interaction with heavy oil, and good emulsification effect. At the same time, demulsification can be achieved by adjusting the pH value of the produced fluid.

[0116] From the comparison between Example 1 and Examples 4-7, it can be seen that the content of each structural component in the modified black phosphorus nanosheets needs to be limited to a reasonable range. If it exceeds the limited range, the viscosity reduction rate of the modified black phosphorus nanosheets will decrease.

[0117] Comparison between Example 1 and Comparative Example 1 shows that the oil-soluble polymer has a certain viscosity-reducing effect, but it is poorly dispersed in aqueous solution and the formed emulsion is unstable. Comparison between Example 1 and Comparative Example 2 shows that the black phosphorus nanosheets are uniformly modified, that is, PEG is first attached to their surface and then the oil-soluble polymer is polymerized on the outer surface. Similarly, due to its oil solubility, the emulsification is poor. Comparison between Example 1 and Comparative Example 3 shows that the black phosphorus nanosheets are uniformly modified with PEG to obtain a hydrophilic polymer, but its molecular chain is short and cannot disperse the asphaltene in crude oil. Moreover, the polymer is strongly hydrophilic as a whole, resulting in poor emulsification performance.

[0118] In summary, the synthesis method of modified black phosphorus nanosheets provided by the present invention is to graft copolymerize polymers of different types and different molecular weights on both sides of the black phosphorus nanosheets, thereby maintaining the amphiphilicity of the overall structure, having strong emulsification ability and good emulsion stability: the asphaltenes in the heavy oil are dispersed by the grafted copolymerized oil-soluble polymer, thereby reducing the viscosity of the heavy oil and increasing the interaction force between the modified black phosphorus nanosheets and the crude oil; the hydrophilic polymer grafted on the other side faces the water, so that the modified black phosphorus nanosheets are stabilized at the oil-water interface to form an emulsion, that is, the stronger the interaction force between the viscosity reducer and the heavy oil, the easier it is to form an emulsion, the increased hydrophilicity helps to increase the stability of the emulsion; by first dispersing the asphaltenes to reduce the viscosity of the heavy oil and then emulsifying and dispersing to significantly reduce the viscosity of the heavy oil, not only can the amount of viscosity reducer added be reduced, but also a better viscosity reduction effect is achieved;

[0119] The modified black phosphorus nanosheets synthesized by the present invention have black phosphorus nanosheets as a core and a polymer as a shell, and have good salt and temperature resistance. At the same time, the modified black phosphorus nanosheets can be used as a heavy oil viscosity reducer to achieve a self-demulsification effect by adjusting the pH value of the produced fluid, thereby reducing the post-processing cost of the produced fluid and simplifying the post-processing process of the produced fluid.

[0120] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for synthesizing modified black phosphorus nanosheets, characterized in that: The synthesis method comprises the following steps: (1) performing a first reaction on a double-terminated carboxyl polyethylene glycol, calcium carbonate, and a first solvent, and washing the resulting solid phase to obtain a PEG-CaCO3 structure; (2) subjecting the black phosphorus nanosheets, the catalyst, the second solvent, and the PEG-CaCO3 structure obtained in step (1) to a second reaction, and centrifuging and washing the resulting product to obtain a BP-PEG-CaCO3 structure; (3) subjecting the polymer monomer, the third solvent, the polymerization initiator, and the BP-PEG-CaCO3 structure obtained in step (2) to a third reaction, and washing the resulting product to obtain a POLY-BP-PEG-CaCO3 structure; (4) removing calcium carbonate from the POLY-BP-PEG-CaCO3 structure obtained in step (3), and washing and centrifuging the obtained product to obtain the modified black phosphorus nanosheets.

2. The synthesis method according to claim 1, characterized in that The molecular weight of the double-terminated carboxyl polyethylene glycol in step (1) is 1000-5000; Preferably, the particle size of the calcium carbonate in step (1) is 2-5 μm; Preferably, the mass ratio of the double-terminated carboxyl polyethylene glycol to calcium carbonate in step (1) is (10-30):1; Preferably, in step (1), the first solvent comprises deionized water; Preferably, the temperature of the first reaction in step (1) is 80-90°C and the time is 60-90 minutes; Preferably, the first reaction in step (1) is carried out under stirring conditions of 500-1500 rpm.

3. The synthesis method according to claim 1 or 2, characterized in that The size of the black phosphorus nanosheets in step (2) is 50-150 nm; Preferably, the mass ratio of the black phosphorus nanosheets to the PEG-CaCO3 structure in step (2) is (10-20):1; Preferably, the catalyst in step (2) comprises 4-dimethylaminopyridine; Preferably, the amount of the catalyst in step (2) is 8-10 wt% of the mass of the black phosphorus nanosheets; Preferably, in step (2), the second solvent comprises N,N-dimethylformamide.

4. The synthesis method according to any one of claims 1 to 3, characterized in that Step (2) the second reaction temperature is 30-50°C and the time is 8-12h; Preferably, the second reaction in step (2) is carried out under stirring conditions of 500-1500 rpm; Preferably, the second reaction in step (2) is carried out in an argon atmosphere.

5. The synthesis method according to any one of claims 1 to 4, characterized in that The polymer monomer in step (3) comprises any one or a combination of at least two of styrene, acrylamide, eicosyl acrylate, docosyl acrylate, sodium allyl sulfonate or vinyl acetate; Preferably, the mass ratio of the BP-PEG-CaCO3 structure to the polymer monomer in step (3) is (10-50):1; Preferably, the amount of the polymerization initiator in step (3) is 0.5-1 wt% of the mass of the polymer monomer; Preferably, the polymerization initiator in step (3) comprises any one of azobisisobutyronitrile, azobisisoheptanenitrile or dimethyl azobisisobutyrate, or a combination of at least two thereof; Preferably, the third solvent in step (3) comprises a mixed solution of toluene and ethanol.

6. The synthesis method according to any one of claims 1 to 5, characterized in that The specific steps of the third reaction in step (3) include: dispersing the polymer monomer and the BP-PEG-CaCO3 structure obtained in step (2) in a third solvent, introducing nitrogen gas and then adding a polymerization initiator to carry out the third reaction; Preferably, the temperature of the third reaction in step (3) is 50-90° C. and the time is 6-12 h; Preferably, the washing reagent in step (3) includes methanol.

7. The synthesis method according to any one of claims 1 to 6, characterized in that The reagent used for removing calcium carbonate in step (4) includes ethylenediaminetetraacetic acid with a concentration of 0.1-0.2 mol / L.

8. A modified black phosphorus nanosheet, characterized in that: The modified black phosphorus nanosheets are synthesized by the synthesis method according to any one of claims 1 to 7.

9. A use of the modified black phosphorus nanosheets according to claim 8, characterized in that: The modified black phosphorus nanosheets are used as a heavy oil viscosity reducer in heavy oil production.

10. The use according to claim 9, characterized in that The modified black phosphorus nanosheets are used as a heavy oil viscosity reducer at a concentration of 500-2000 mg / L; Preferably, the pH value of the produced fluid from heavy oil production is adjusted to 9-11, and demulsification is achieved after stirring for 3-5 hours.

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