Preparation method of composite demulsifier for tar dehydration

Abstract

The invention discloses a preparation method of a composite demulsifier for tar dehydration, which comprises the following steps: adding cerium oxide nanoparticles and urea into deionized water to obtain a suspension, and carrying out ball milling treatment on the obtained suspension at a certain temperature to completely hydroxylate cerium oxide to obtain hydroxylated modified nano cerium oxide; the preparation method comprises the following steps: dissolving polyoxyethylene ether in water to obtain a polyoxyethylene ether solution, then adding organic acid and a functional monomer, carrying out a polymerization reaction under the action of an initiator, adding hydroxylation modified nano cerium oxide and a silane coupling agent for a reaction after the reaction is finished, and washing and drying an obtained product after the reaction is finished to obtain the modified nano cerium oxide. The modified polyoxyethylene ether high polymer doped with the cerium oxide nanoparticles is obtained; and mixing and uniformly stirring the cerium oxide nanoparticle-doped modified polyoxyethylene ether high polymer, the organic auxiliary agent, lauryl sodium sulfate and the balance of ethanol in percentage by weight to obtain the composite demulsifier. The demulsifier provided by the invention has good dehydration and demulsification performance on tar.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and more particularly, relates to a preparation method of a composite demulsifier for tar dehydration. Background Art

[0002] During the processing of coal tar, it is easy to form a relatively stable water-in-oil emulsion. Since coal tar contains a large amount of natural surfactant substances such as asphaltene, resin, and naphthenic acid, these surfactant substances are extremely easy to adsorb on the oil-water interface of the emulsion, forming a firm elastic "outer shell". This elastic "outer shell" prevents the possible mutual aggregation between small water droplets. In addition, due to the relatively high viscosity of coal tar, the small water droplets therein are difficult to settle and separate by themselves due to gravity. This is an important factor leading to the excessive salt and water content in coal tar.

[0003] "Demulsification" is an important means to break the elastic "outer shell" and promote the aggregation and settlement of small water droplets at present. The mechanism of demulsification is to add an emulsifier with higher interfacial activity to coal tar. This emulsifier can adsorb or partially replace the natural emulsifier on the oil-water interface, forming a mixed film with lower interfacial film strength than the original one. The interfacial film strength of the mixed film is lower, which weakens the interfacial strength between oil and water, shortens the film life, thins the thickness, and makes it easier to break, thus releasing the small water droplets wrapped in the film. The small water droplets coalesce and grow into large water droplets, and the large water droplets sink in the oil under the action of gravity, so that the oil and water phases are separated, thereby achieving the purpose of demulsification and dehydration. Summary of the Invention

[0004] The primary object of the present invention is to provide a composite demulsifier for tar dehydration and its preparation method, so as to effectively demulsify and dehydrate coal tar.

[0005] To this end, the present invention provides the following technical solutions.

[0006] One aspect of the present invention provides a preparation method of a composite demulsifier for tar dehydration, and the method includes the following steps:

[0007] Adding cerium oxide nanoparticles and urea to deionized water to obtain a suspension, subjecting the obtained suspension to ball milling treatment at a certain temperature to completely hydroxylate cerium oxide, removing the remaining urea and impurities after ball milling, and drying the product to obtain hydroxylated modified nano-cerium oxide;

[0008] Dissolving polyoxyethylene ether in water to obtain a polyoxyethylene ether solution with a concentration of 5-10 wt%, then adding an organic acid and a functional monomer, carrying out a polymerization reaction under the action of an initiator, adding hydroxylated modified nano-cerium oxide and a silane coupling agent for reaction after the reaction is completed, and washing and drying the obtained product after the reaction is completed to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles;

[0009] By weight percentage, 10 - 30% of a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 1 - 5% of an organic auxiliary, 1 - 5% of sodium dodecyl sulfate, and the balance of ethanol are mixed and stirred evenly to obtain a composite demulsifier.

[0010] In some preferred embodiments, the mass ratio of the cerium oxide nanoparticles, urea, and deionized water is 1:10 - 30:20 - 40.

[0011] In some preferred embodiments, the ball milling conditions are: temperature at room temperature, time 4 - 10 h.

[0012] In some preferred embodiments, the organic acid is selected from any one or a mixture of two or more of acrylic acid, crotonic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, citraconic acid, citraconic anhydride, mesaconic acid, glutaconic acid, aconitic acid, and methacrylic acid.

[0013] In some preferred embodiments, the addition amount of the organic acid is 0.5 - 1 times the mass of the polyoxyethylene ether.

[0014] In some preferred embodiments, the functional monomer is selected from any one or a mixture of two or more of N,N - dimethyl - N - acryloyloxyethyl - N - (3 - sulfopropyl) - ammonium betaine, N,N - dimethyl - N - acrylamidopropyl - N - (2 - carboxymethyl) - ammonium betaine, N,N - dimethyl - N - acrylamidopropyl - N - (3 - sulfopropyl) - ammonium betaine, and N,N - dimethyl - N - acrylamidopropyl - N - (2 - carboxymethyl) - ammonium betaine.

[0015] In some preferred embodiments, the addition amount of the functional monomer is 1 - 3 times the mass of the polyoxyethylene ether.

[0016] In some preferred embodiments, the initiator is selected from one or several of ammonium persulfate, potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, and tert - butyl peroxybenzoate.

[0017] In some preferred embodiments, the addition amount of the initiator is 0.2 - 0.6% of the total mass of the monomers.

[0018] In some preferred embodiments, the addition amount of the hydroxylated modified nano - cerium oxide is 0.1 - 0.5 times the mass of the polyoxyethylene ether.

[0019] In some preferred embodiments, the silane coupling agent is selected from any one of mercapto trimethoxysilane, mercapto triethoxysilane, mercapto methyl trimethoxysilane, mercapto methyl triethoxysilane, and mercapto methyl tripropoxysilane.

[0020] In some preferred embodiments, the addition amount of the silane coupling agent is 0.5-1% of the mass of the hydroxylated modified nano-ceria.

[0021] In some preferred embodiments, the organic auxiliary agent is selected from any one or a mixture of two or more of diethylenetriamine, hexamethylenetetramine, diethylamine, triethylamine, and monoethanolamine.

[0022] The second aspect of the present invention provides a composite demulsifier prepared by the preparation method of the composite demulsifier for tar dehydration as described above.

[0023] By means of the above technical solutions, the present invention has at least the following advantages:

[0024] The present invention uses nano-ceria particles as one of the raw materials, and obtains surface-hydroxylated ceria through modification. Using polyoxyethylene ether as the second raw material, by reacting with organic acids and zwitterionic monomers, various active groups are introduced into the polymer. Finally, under the action of a silane coupling agent, it is bridged with surface-hydroxylated nano-ceria to obtain a modified polyoxyethylene ether polymer doped with ceria nano-particles. Using this polymer as the main active substance and supplemented with organic auxiliary agents, etc., a composite demulsifier is obtained. This demulsifier has good penetration ability, excellent wetting performance, and sufficient flocculation and coalescence ability. It can quickly reach the oil-water interface to form a new unstable oil-water interface film, and has good dehydration and demulsification performance for tar. Moreover, it also has the advantages of saving time, manpower and material resources, and can be widely applied in fields such as crude oil extraction and petroleum refining.

[0025] The above description is only an overview of the technical solution of the present invention. In order to be able to understand the technical means of the present invention more clearly and implement it according to the content of the specification, the following will describe in detail with preferred embodiments of the present invention as follows. Detailed Embodiments

[0026] In order to make the technical means, creative features, achieved purposes and functions of the present invention easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0027] Unless otherwise specified, the percentage content involved in the present invention refers to the mass percentage for solid-liquid mixing and solid-solid mixing, and the volume percentage for liquid-liquid mixing.

[0028] Unless otherwise specified, the percentage concentrations involved in the present invention all refer to the final concentrations. The final concentration refers to the proportion of the added component in the system after adding the component.

[0029] The temperature parameters in the present invention, unless otherwise specified, allow both constant temperature treatment and treatment within a certain temperature range. The constant temperature treatment allows the temperature to fluctuate within the accuracy range controlled by the instrument.

[0030] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods.

[0031] Unless otherwise specified, the average particle size of the cerium oxide nanoparticles (JK-09-016, Nanjing Jike Biotechnology Co., Ltd.) used in the following examples is 50 nm, and materials, reagents, etc. can all be obtained from commercial channels.

[0032] Example 1:

[0033] Cerium oxide nanoparticles and urea were added to deionized water in a mass ratio of 1:20:30 to obtain a suspension. The obtained suspension was ball-milled at room temperature for 7 h to completely hydroxylate the cerium oxide. The mixture obtained after ball-milling was diluted with deionized water to 1 mg / ml. The diluted solution was repeatedly subjected to the operations of dilution-ultrasonic dispersion-centrifugation at room temperature to remove excess urea and impurities, and then the lower-layer precipitate was taken and dried to obtain hydroxylated modified nano-cerium oxide. Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 7.5 wt%. Then acrylic acid (the addition amount was 0.75 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine (the addition amount was 2 times the mass of polyoxyethylene ether) were added, and a polymerization reaction was carried out under the action of ammonium persulfate (the addition amount was 0.4% of the total mass of N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine). After the reaction ended, hydroxylated modified nano-cerium oxide (the addition amount was 0.3 times the mass of polyoxyethylene ether) and mercapto trimethoxysilane (the addition amount was 0.75% of the mass of hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0034] By weight percentage, 20% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 3% of diethylenetriamine, 3% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0035] Example 2:

[0036] Cerium oxide nanoparticles and urea were added to deionized water in a mass ratio of 1:30:40 to obtain a suspension. The obtained suspension was ball-milled at room temperature for 10 h to completely hydroxylate the cerium oxide. After ball-milling, the obtained mixture was diluted with deionized water to 1 mg / ml. The diluted solution was repeatedly subjected to the operations of dilution-ultrasonic dispersion-centrifugation at room temperature to remove excess urea and impurities. Then, the lower-layer precipitate was taken and dried to obtain hydroxylated modified nano-cerium oxide. Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 5 wt%. Then, methacrylic acid (the addition amount was 0.5 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine (the addition amount was 3 times the mass of polyoxyethylene ether) were added. A polymerization reaction was carried out under the action of potassium persulfate (the addition amount was 0.2% of the total mass of N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine). After the reaction ended, hydroxylated modified nano-cerium oxide (the addition amount was 0.5 times the mass of polyoxyethylene ether) and mercapto-triethoxysilane (the addition amount was 0.5% of the mass of hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0037] By weight percentage, 10% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 5% of triethylamine, 5% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0038] Example 3:

[0039] Cerium oxide nanoparticles and urea were added to deionized water in a mass ratio of 1:10:20 to obtain a suspension. The obtained suspension was ball-milled at room temperature for 4 h to completely hydroxylate cerium oxide. The mixture obtained after ball-milling was diluted with deionized water to 1 mg / ml. The diluted solution was repeatedly subjected to the operations of dilution - ultrasonic dispersion - centrifugation at room temperature to remove excess urea and impurities. Then, the lower-layer precipitate was taken and dried to obtain hydroxylated modified nano-cerium oxide. Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 10 wt%. Then, maleic acid (the addition amount was 1 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-(3-(acrylamido)propyl)-N-(2-carboxyethyl)ammonium betaine (the addition amount was 1 times the mass of polyoxyethylene ether) were added. A polymerization reaction was carried out under the action of sodium persulfate (the addition amount was 0.6% of the total mass of N,N-dimethyl-N-(3-(acrylamido)propyl)-N-(2-carboxyethyl)ammonium betaine). After the reaction ended, hydroxylated modified nano-cerium oxide (the addition amount was 0.1 times the mass of polyoxyethylene ether) and mercaptomethyltrimethoxysilane (the addition amount was 1% of the mass of hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0040] By weight percentage, 30% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 1% of diethylenetriamine, 1% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0041] Example 4:

[0042] Cerium oxide nanoparticles and urea were added to deionized water in a mass ratio of 1:15:25 to obtain a suspension. The obtained suspension was ball-milled at room temperature for 6 h to completely hydroxylate cerium oxide. After ball-milling, the resulting mixture was diluted with deionized water to 1 mg / ml. The diluted solution was repeatedly subjected to the operations of dilution-ultrasonic dispersion-centrifugation at room temperature to remove excess urea and impurities. Then, the lower-layer precipitate was taken and dried to obtain hydroxylated modified nano-cerium oxide. Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 9 wt%. Then, maleic anhydride (the addition amount was 0.8 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-(3-sulfopropyl)-N-(acrylamidopropyl) ammonium betaine (the addition amount was 3 times the mass of polyoxyethylene ether) were added. A polymerization reaction was carried out under the action of azobisisobutyronitrile (the addition amount was 0.5% of the total mass of N,N-dimethyl-N-(3-sulfopropyl)-N-(acrylamidopropyl) ammonium betaine). After the reaction ended, hydroxylated modified nano-cerium oxide (the addition amount was 0.2 times the mass of polyoxyethylene ether) and mercaptomethyltriethoxysilane (the addition amount was 0.6% of the mass of hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0043] By weight percentage, 25% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 2% of diethylamine, 3% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0044] Example 5:

[0045] Cerium oxide nanoparticles and urea were added to deionized water in a mass ratio of 1:25:25 to obtain a suspension. The obtained suspension was ball-milled at room temperature for 8 h to completely hydroxylate the cerium oxide. The mixture obtained after ball-milling was diluted with deionized water to 1 mg / ml. The diluted solution was repeatedly subjected to the operations of dilution - ultrasonic dispersion - centrifugation at room temperature to remove excess urea and impurities. Then, the lower-layer precipitate was taken and dried to obtain hydroxylated modified nano-cerium oxide. Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 6 wt%. Then, fumaric acid (the addition amount was 0.6 times the mass of the polyoxyethylene ether) and N,N-dimethyl-N-(3-(acrylamido)propyl)-N-(2-carboxymethyl)ammonium betaine (the addition amount was 2 times the mass of the polyoxyethylene ether) were added. A polymerization reaction was carried out under the action of azodiisobutyronitrile (the addition amount was 0.3% of the total mass of N,N-dimethyl-N-(3-(acrylamido)propyl)-N-(2-carboxymethyl)ammonium betaine). After the reaction ended, hydroxylated modified nano-cerium oxide (the addition amount was 0.4 times the mass of the polyoxyethylene ether) and mercaptomethyltriethoxysilane (the addition amount was 0.9% of the mass of the hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0046] By weight percentage, 15% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 5% of triethylamine, 5% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0047] Example 6:

[0048] Cerium oxide nanoparticles and urea were added to deionized water in a mass ratio of 1:15:35 to obtain a suspension. The obtained suspension was ball-milled at room temperature for 6 h to completely hydroxylate cerium oxide. The mixture obtained after ball-milling was diluted with deionized water to 1 mg / ml. The diluted solution was repeatedly subjected to the operations of dilution-ultrasonic dispersion-centrifugation at room temperature to remove excess urea and impurities. Then, the lower-layer precipitate was taken and dried to obtain hydroxylated modified nano-cerium oxide. Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 8 wt%. Then, itaconic acid (the addition amount was 0.8 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine (the addition amount was 1 times the mass of polyoxyethylene ether) were added. Polymerization reaction was carried out under the action of benzoyl peroxide (the addition amount was 0.5% of the total mass of N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine). After the reaction ended, hydroxylated modified nano-cerium oxide (the addition amount was 0.2 times the mass of polyoxyethylene ether) and mercaptomethyltripropoxysilane (the addition amount was 0.8% of the mass of hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0049] By weight percentage, 25% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 5% of monoethanolamine, 5% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0050] Comparative Example 1:

[0051] Polyoxyethylene ether was dissolved in water to obtain a polyoxyethylene ether solution with a concentration of 7.5 wt%. Then, acrylic acid (the addition amount was 0.75 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine (the addition amount was 2 times the mass of polyoxyethylene ether) were added. Polymerization reaction was carried out under the action of ammonium persulfate (the addition amount was 0.4% of the total mass of N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine). After the reaction ended, cerium oxide nanoparticles (the addition amount was 0.3 times the mass of polyoxyethylene ether) and mercapto trimethoxysilane (the addition amount was 0.75% of the mass of hydroxylated modified nano-cerium oxide) were added for reaction. After the reaction ended, the obtained product was washed and dried to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles.

[0052] By weight percentage, 20% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 3% of diethylenetriamine, 3% of sodium dodecyl sulfate, and the balance of ethanol were mixed and stirred evenly to obtain a composite demulsifier.

[0053] Comparative Example 2:

[0054] Dissolve polyoxyethylene ether in water to obtain a polyoxyethylene ether solution with a concentration of 7.5 wt%, then add acrylic acid (the addition amount is 0.75 times the mass of polyoxyethylene ether) and N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine (the addition amount is 2 times the mass of polyoxyethylene ether), and carry out a polymerization reaction under the action of ammonium persulfate (the addition amount is 0.4% of the total mass of N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine). After the reaction is completed, wash and dry the obtained product to obtain a modified polyoxyethylene ether polymer.

[0055] Mix 20% of the modified polyoxyethylene ether polymer, 3% of diethylenetriamine, 3% of sodium dodecyl sulfate and the balance of ethanol by weight percentage and stir evenly to obtain a composite demulsifier.

[0056] Comparative Example 3:

[0057] Mix 20% of polyoxyethylene ether, 3% of diethylenetriamine, 3% of sodium dodecyl sulfate and the balance of ethanol by weight percentage and stir evenly to obtain a composite demulsifier.

[0058] Test 1: Performance detection of the demulsifier

[0059] Carry out indoor crude oil dehydration and demulsification tests on the composite demulsifiers prepared in Examples 1-6 and Comparative Examples 1-3 respectively. The crude oil is taken from Renqiu Oilfield. Add 50 mg of the demulsifier to 1 L of crude oil, vibrate, and observe the oil-water interface after standing at room temperature for 30 min. Calculate the dehydration rate and demulsification rate of the demulsifier. The results are shown in Table 1:

[0060] Table 1 Demulsification rate and dehydration rate of the demulsifier

[0061] Group Demulsification rate (%) Dehydration rate (%) Color of dehydrated water Example 1 99.92 92.37 Clear Example 2 98.64 91.58 Clear Example 3 99.13 92.05 Clear Example 4 99.75 92.41 Clear Example 5 98.41 91.22 Clear Example 6 98.18 91.01 Clear Comparative Example 1 92.37 88.36 Clear Comparative Example 2 85.62 82.19 Relatively clear Comparative Example 3 57.49 62.76 Turbid

[0062] It can be seen from the results in Table 1 that the composite demulsifiers in Examples 1-6 of the present invention have higher demulsification rates and dehydration rates compared with Comparative Examples 1-3.

[0063] The above is only the preferred embodiment of the present invention, and it does not impose any form of limitation on the present invention. Although the present invention has been disclosed as above with the preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can make some changes or modifications to the equivalent embodiments by using the methods and technical contents disclosed above without departing from the technical scope of the present invention. However, as long as it does not depart from the content of the technical solution of the present invention, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A preparation method of a composite demulsifier for tar dehydration, characterized in that, The method includes the following steps: Adding cerium oxide nanoparticles and urea into deionized water to obtain a suspension, subjecting the obtained suspension to ball milling treatment at a certain temperature to completely hydroxylate the cerium oxide, removing the remaining urea and impurities after ball milling and drying the product to obtain hydroxylated modified nano-ceria; Dissolving polyoxyethylene ether in water to obtain a polyoxyethylene ether solution with a concentration of 5 - 10 wt%, then adding an organic acid and a functional monomer, carrying out a polymerization reaction under the action of an initiator, adding hydroxylated modified nano-ceria and a silane coupling agent for reaction after the reaction ends, and washing and drying the obtained product after the reaction ends to obtain a modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles; Mixing 10 - 30% of the modified polyoxyethylene ether polymer doped with cerium oxide nanoparticles, 1 - 5% of an organic auxiliary agent, 1 - 5% of sodium dodecyl sulfate and the balance of ethanol by weight percentage and stirring evenly to obtain a composite demulsifier.

2. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that, The mass ratio of the cerium oxide nanoparticles, urea and deionized water is 1:10 - 30:20 - 40.

3. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that, The ball milling conditions are: temperature at room temperature, time 4 - 10 h.

4. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that, The organic acid is selected from any one or a mixture of two or more of acrylic acid, crotonic acid, methacrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, itaconic anhydride, citraconic acid, citraconic anhydride, mesaconic acid, glutaconic acid, aconitic acid, methacrylic acid; The addition amount of the organic acid is 0.5 - 1 times the mass of the polyoxyethylene ether.

5. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that The functional monomer is selected from any one or a mixture of two or more of N,N-dimethyl-N-acryloyloxyethyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(3-sulfopropyl)-ammonium betaine, N,N-dimethyl-N-acrylamidopropyl-N-(2-carboxymethyl)-ammonium betaine; The addition amount of the functional monomer is 1 - 3 times the mass of the polyoxyethylene ether.

6. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that, The initiator is selected from one or several of ammonium persulfate, potassium persulfate, sodium persulfate, azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl perbenzoate; The addition amount of the initiator is 0.2 - 0.6% of the total mass of the monomers.

7. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that, The addition amount of the hydroxylated modified nano-ceria is 0.1 - 0.5 times the mass of the polyoxyethylene ether.

8. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that, The silane coupling agent is selected from any one of mercapto trimethoxysilane, mercapto triethoxysilane, mercapto methyl trimethoxysilane, mercapto methyl triethoxysilane, mercapto methyl tripropoxysilane; The addition amount of the silane coupling agent is 0.5 - 1% of the mass of the hydroxylated modified nano-ceria.

9. The preparation method of the composite demulsifier for tar dehydration according to claim 1, characterized in that The organic auxiliary agent is selected from any one or a mixture of two or more of diethylenetriamine, hexamethylenetetramine, diethylamine, triethylamine, monoethanolamine.

10. A composite demulsifier prepared by the preparation method of the composite demulsifier for tar dehydration according to any one of claims 1 - 9.