1. A preparation method of a nano composite pour point depressant is characterized by comprising the following steps: the preparation method comprises the following steps:

dissolving 1-3g of ethylene vinyl acetate in 10-40ml of dodecane, adding 20-50ml of methanol solution, fully mixing at 50-70 ℃ for 0.5-1 hour, dropwise adding 40-80ml of sodium hydroxide-methanol solution at 40-50 ℃ as an alkali catalyst, magnetically stirring for 2-4 hours, washing the product with methanol, filtering, and drying in a vacuum drying oven for 2.5-3.5 hours to obtain an ethylene-vinyl alcohol copolymer;

adding an organic solvent into a reaction kettle, dispersing the ethylene-vinyl alcohol copolymer in the organic solvent at the concentration of 8-12wt%, and after completely dissolving, adding graphene oxide into the solution, wherein the mass ratio of the graphene oxide to the ethylene-vinyl alcohol copolymer is 1: 200, stirring at a high speed for reaction for 2 to 5 hours at the temperature of between 80 and 100 ℃ to prepare the nano composite pour point depressant.

2. The method for preparing the nano composite pour point depressant according to claim 1, wherein the method comprises the following steps: the preparation method comprises the following steps:

dissolving 2g of ethylene vinyl acetate in 25ml of dodecane, adding 25ml of methanol solution, fully mixing at 60 ℃ for 0.5 hour, dropwise adding 50ml of sodium hydroxide-methanol solution at 45 ℃ as an alkali catalyst, magnetically stirring for 2 hours, washing the product with methanol, filtering, and drying in a vacuum drying oven for 2.5 hours to obtain an ethylene-vinyl alcohol copolymer;

adding an organic solvent into a reaction kettle, dispersing the ethylene-vinyl alcohol copolymer in the organic solvent at the concentration of 10wt%, and after completely dissolving, adding graphene oxide into the solution, wherein the mass ratio of the graphene oxide to the ethylene-vinyl alcohol copolymer is 1: 200, stirring at a high speed for reaction for 2.5 hours at the temperature of 90 ℃ to prepare the nano composite pour point depressant.

3. The method for preparing a nanocomposite pour point depressant according to claim 1 or 2, wherein the method comprises the following steps: the content of ester in the ethylene vinyl acetate is 26-40%.

4. The method for preparing a nanocomposite pour point depressant according to claim 1 or 2, wherein the method comprises the following steps: the mass ratio of the sodium hydroxide to the water in the alkali catalyst solution is 1 (2-10).

5. The method for preparing a nanocomposite pour point depressant according to claim 1 or 2, wherein the method comprises the following steps: the organic solvent is toluene, dodecane or hexadecane.

6. The method for preparing a nanocomposite pour point depressant according to claim 1 or 2, wherein the method comprises the following steps: the nano composite pour point depressant capable of reducing the pour point of the wax-containing crude oil can be obtained by the preparation method.

7. The method for preparing the nano composite pour point depressant according to claim 3, wherein the method comprises the following steps: the nano composite pour point depressant capable of reducing the pour point of the wax-containing crude oil can be obtained by the preparation method.

8. The method for preparing the nano composite pour point depressant according to claim 4, wherein the method comprises the following steps: the nano composite pour point depressant capable of reducing the pour point of the wax-containing crude oil can be obtained by the preparation method.

9. The method for preparing the nano composite pour point depressant according to claim 5, wherein the method comprises the following steps: the nano composite pour point depressant capable of reducing the pour point of the wax-containing crude oil can be obtained by the preparation method.

Background

Most of crude oil produced in oil fields in China is high wax content crude oil, and when the oil temperature is lower than the Wax Apparent Temperature (WAT), wax molecules precipitate due to supersaturation to form needle-shaped or flaky wax crystals. The separated wax crystals have strong tendency to form a network structure, so that the complex non-Newtonian fluid property is given to the crude oil, even the crude oil is gelled, and the extraction and transportation efficiency of the crude oil is reduced. The most common method for improving the low-temperature fluidity of crude oil is to add a pour point depressant into the crude oil, wherein most polar parts in the pour point depressant can be adsorbed on the surface of wax crystals to prevent the wax crystals from approaching each other and inhibit the generation of large-size wax crystals. Increasing the polarity of the pour point depressant molecules also increases the polarity of the wax crystal surface, i.e., increases the liquid crystal interfacial tension. Therefore, there is a current trend to develop crude oil pour point depressants to further increase the polarity in the molecule. On the other hand, in order to improve the performance of the conventional polymer pour point depressant, one of the methods is to synthesize a polymer nanocomposite by introducing inorganic nanoparticles/flakes into a polymer matrix, thereby significantly improving the performance and dispersion stability thereof.

With the development of nanotechnology, researchers are gradually introducing nanoparticles into the preparation of pour point depressants. Graphene oxide is more active than graphene due to the increase of the number of oxygen-containing functional groups, and can improve properties thereof through various reactions with the oxygen-containing functional groups. Sharma prepared a polymer nanocomposite PMMA-GO from graphene oxide and polymethyl methacrylate (PMMA) by an in-situ radical polymerization method, and examined the influence of the product on the condensation point of Indian waxy crude oil. The related experiment results show that the graphene oxide is actually amphiphilic, and shows a property distribution from hydrophilic to hydrophobic from the edge to the center of the graphene sheet. Graphene oxide may exist at an interface as a surfactant and reduce energy between interfaces. Therefore, hydroxyl is introduced into an EVA side chain, and carboxyl on the surface of graphene oxide is utilized to stably combine the EVA side chain and the graphene oxide in a chemical bond form, so that the capability of pour point depression and wax crystal dispersion property improvement is further increased, the low-temperature flow property of the waxy crude oil is improved, the pipeline transportation efficiency is improved, and the transportation cost is reduced.

Most of nano composite pour point depressants adopt a physical blending mode to realize the performance regulation and control of nano particles on the traditional polymer pour point depressants, but the blending does not form stable chemical bonds, polymers on the surface of a nano material are easy to desorb, and the dispersion stability in an oil phase is still to be improved. The chemical grafting method is combined with the existing research and preparation method to prepare the novel nano composite pour point depressant system. The novel nano-composite pour point depressant EVAL-GO is prepared by depolymerizing Ethylene Vinyl Acetate (EVA) by using alkali-catalyzed alcohol to obtain an alcoholysis product (EVAL) and then by using an esterification reaction between graphene oxide and EVAL in a chemical grafting manner.

Disclosure of Invention

The invention aims to provide a preparation method of a nano composite pour point depressant and the pour point depressant prepared by the preparation method, wherein alcoholyzed Ethylene Vinyl Acetate (EVA) is grafted to the surface of graphene oxide through esterification reaction, so that the chemical assembly of nano particles and a polymer is realized, the dispersity and the stability of the nano composite pour point depressant are improved, the pour point depressant is uniformly and stably dispersed in an oil phase, and polymer molecules are not easy to separate from the surface of the nano particles, so that the condensation point of wax-containing crude oil can be greatly reduced, the low-temperature rheological property of the crude oil is improved, the pipeline transportation efficiency is improved, and the transportation cost is reduced.

The technical scheme adopted by the invention is as follows: a preparation method of a nano composite pour point depressant comprises the following steps:

dissolving 1-3g of Ethylene Vinyl Acetate (EVA) in 10-40ml of dodecane, adding 20-50ml of methanol solution, fully mixing at 50-70 ℃ for 0.5-1 hour, dropwise adding 40-80ml of sodium hydroxide-methanol solution at 40-50 ℃ as an alkali catalyst, magnetically stirring for 2-4 hours, washing the product with methanol, filtering, and drying in a vacuum drying oven for 2.5-3.5 hours to obtain ethylene-vinyl alcohol copolymer (EVAL);

adding an organic solvent into a reaction kettle, dispersing the ethylene-vinyl alcohol copolymer in the organic solvent at the concentration of 8-12wt%, and after completely dissolving, adding graphene oxide into the solution, wherein the mass ratio of the graphene oxide to the ethylene-vinyl alcohol copolymer is 1: 200, stirring at a high speed for reaction for 2-5 hours at the temperature of 80-100 ℃ to prepare the nano composite pour point depressant (EVAL-GO).

Further, the preparation method comprises the following steps: dissolving 2g of Ethylene Vinyl Acetate (EVA) in 25ml of dodecane, adding 25ml of methanol solution, fully mixing at 60 ℃ for 0.5 hour, dropwise adding 50ml of sodium hydroxide-methanol solution at 45 ℃ as an alkali catalyst, magnetically stirring for 2 hours, washing the product with methanol, filtering, and drying in a vacuum drying oven for 2.5 hours to obtain ethylene-vinyl alcohol copolymer (EVAL);

adding an organic solvent into a reaction kettle, dispersing the ethylene-vinyl alcohol copolymer in the organic solvent at the concentration of 10wt%, and after completely dissolving, adding graphene oxide into the solution, wherein the mass ratio of the graphene oxide to the ethylene-vinyl alcohol copolymer is 1: 200, and stirring at a high speed for reaction for 2.5 hours at the temperature of 90 ℃ to prepare the nano composite pour point depressant (EVAL-GO).

Further, the content of ester in the ethylene vinyl acetate is 26-40%.

Further, the mass ratio of the sodium hydroxide to the water in the alkali catalyst solution is 1 (2-10).

Further, the organic solvent is toluene, dodecane or hexadecane.

Further, the volume of the alkali catalyst solution is 50-200 ml.

Further, a product EVAL is obtained through alcoholysis reaction of Ethylene Vinyl Acetate (EVA) copolymer, and an esterification reaction between carboxyl on the surface of graphene oxide and hydroxyl on the surface of EVAL is utilized to obtain a pour point depressant product.

The invention has the beneficial effects that: the alcoholysis-performed Ethylene Vinyl Acetate (EVA) is grafted to the surface of graphene oxide through an esterification reaction, so that the chemical assembly of nano particles and a polymer is realized, the dispersity and the stability of the nano composite pour point depressant are improved, the pour point depressant is uniformly and stably dispersed in an oil phase, and polymer molecules are not easy to separate from the surfaces of the nano particles, so that the condensation point of wax-containing crude oil can be greatly reduced, the low-temperature rheological property of the crude oil is improved, the pipeline transportation efficiency is improved, and the transportation cost is reduced.

Description of the drawings:

FIG. 1 is a wax crystal appearance of crude oil without any treatment in example one;

FIG. 2 is a wax crystal appearance of a crude oil to which a nanocomposite pour point depressant was added according to example one;

FIG. 3 is a shear viscosity profile of any of the treated crude oils of example one and the crude oil to which the nanocomposite pour point depressant was added;

FIG. 4 is a graph of the viscosity temperature curves of any of the treated crude oils and the crude oil with the addition of the nanocomposite pour point depressant according to one of the examples;

FIG. 5 is a graph of yield values for any of the treated crude oils of example one and the crude oil to which the nanocomposite pour point depressant was added.

The specific implementation mode is as follows:

example one

A preparation method of a nano composite pour point depressant comprises the steps of dissolving 2g of Ethylene Vinyl Acetate (EVA) in 25ml of dodecane, adding 25ml of methanol solution, fully mixing for 0.5 hour at 60 ℃, dropwise adding 50ml of sodium hydroxide-methanol solution as an alkali catalyst at 45 ℃, magnetically stirring for 2 hours, washing the product with methanol, filtering, and drying in a vacuum drying oven for 2.5 hours to obtain an ethylene-vinyl alcohol copolymer (EVAL), wherein the ester content in the ethylene vinyl acetate is 33%, and the mass ratio of sodium hydroxide to water in the alkali catalyst solution is 1: 6;

adding an organic solvent into a reaction kettle, dispersing the ethylene-vinyl alcohol copolymer in the organic solvent (toluene, dodecane or hexadecane) at the concentration of 10wt%, and after completely dissolving, adding graphene oxide into the solution, wherein the mass ratio of the graphene oxide to the ethylene-vinyl alcohol copolymer is 1: 200, and stirring at a high speed for reaction for 2.5 hours at the temperature of 90 ℃ to prepare the nano composite pour point depressant (EVAL-GO).

Adding 800ppm pour point depressant EVAL-GO into the wax-containing crude oil, controlling the temperature at about 70 ℃, fully stirring for ten minutes, and then testing and observing the condensation point, the shear viscosity, the wax prevention rate, the yield value and the wax crystal morphology. The shear viscosity, viscosity-temperature curve, yield value and wax crystal morphology of the untreated crude oil and the crude oil added with the nano-composite pour point depressant are shown in figures 1-5, the solidifying point of the untreated crude oil is 30 ℃, and the solidifying point of the crude oil added with the nano-composite pour point depressant is 20 ℃; the wax control rate of the crude oil added with the nano composite pour point depressant is up to 83.5 percent.

The alcoholysis-performed EVA is grafted to the surface of graphene oxide through an esterification reaction, so that the chemical assembly of nano particles and a polymer is realized, the dispersity and the stability of the nano composite pour point depressant are improved, the pour point depressant is uniformly and stably dispersed in an oil phase, polymer molecules are not easy to separate from the surface of the nano particles, and the pour point depressant can greatly reduce the pour point of wax-containing crude oil and improve the low-temperature rheological property of the crude oil according to measurement data of the pour point, the viscosity and the yield value. From microscopic morphology analysis of wax crystals, EVAL-GO can enable the wax crystals to form spherical crystals taking graphene oxide as a growth center, so that the wax crystals are difficult to connect, and the increase of pore space promotes the release of more liquid oil.