Preparation method for improving yield of ethylene-maleic anhydride alternating copolymer

Abstract

A method for improving the yield of an ethylene-maleic anhydride alternating copolymer comprises the steps that maleic anhydride, a free radical initiator and a polymerization catalyst are mixed and added into an organic solvent, ethylene gas is introduced for free radical polymerization, and the ethylene-maleic anhydride alternating copolymer is prepared, and the polymerization catalyst is obtained by taking SiO2 as a carrier to load heteropolyacid and then activating. The problem that the molecular weight of the polymer prepared by a solvent method is not high is solved, the molecular weight of the polymer and the yield of the product are improved while the reaction pressure is reduced and the use of the reaction solvent is reduced, the molecular weight distribution of the polymer is also reduced, and the occurrence of side reactions is also reduced. The number-average molecular weight of the prepared ethylene-maleic anhydride alternating copolymer is 60-90k, the molecular weight distribution is as low as 1.2, the performance stability is excellent, and the ethylene-maleic anhydride alternating copolymer can be applied as a high-efficiency binder and a dispersant of building thermal insulation materials, sound insulation materials and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of preparing copolymers by the solvent method, specifically to a preparation method for improving the yield of ethylene-maleic anhydride alternating copolymer based on the solvent method, and particularly to improving the yield of high-molecular-weight ethylene-maleic anhydride alternating copolymer. Background Art

[0002] Ethylene-maleic anhydride alternating copolymer is an alternating copolymer with a copolymerization ratio of ethylene to maleic anhydride of 1:1. In the structural unit of ethylene-maleic anhydride alternating copolymer, there are both hydrophobic ethylene structures and hydrophilic maleamide salts and maleate structures after amidation or hydrolysis. Therefore, it has amphiphilicity, so this polymer can be used as a fertilizer dispersant, special paper, a battery separator, or an additive in the production of special inks. At the same time, this polymer can also be used as a forging lubricant and quenching liquid, which can avoid serious pollution caused by a large amount of smoke generated by oil-based lubricants during hot forging, contribute to improving production safety and product quality, and prevent fire hazards and flying sparks.

[0003] In addition, the polymer can be used in different fields according to different molecular weights. Among them, in high-molecular-weight polymers, the maleic anhydride groups in the polymer structural units can undergo esterification reactions with hydroxyl groups in materials such as glass fibers and ceramics, and are also used in new formaldehyde-free adhesives, while this polymer with a lower molecular weight is often used as a dispersant.

[0004] Currently, the production of high-molecular-weight ethylene-maleic anhydride alternating copolymer often adopts the high-pressure method. However, the production of ethylene-maleic anhydride alternating copolymer by the high-pressure method requires an ethylene pressure of more than 20 MPa, and the cost is relatively high. Therefore, someone developed the solvent method for synthesizing ethylene-maleic anhydride alternating copolymer on this basis, and reduced the reaction pressure and shortened the reaction time by adding a Lewis acid catalyst. However, the copolymer prepared by the solvent method has a relatively small molecular weight. For example, Patent 202310395202.X obtained a polymer with Mn = 36800 in 2 h under the reaction conditions of a reaction pressure of 0.6 MPa and 60 °C by adding B(C6F5)3 to the system. When the pressure was increased to 2 MPa, the molecular weight Mn of the prepared polymer increased to 66000. However, 2 L of toluene was required as a solvent in the reaction, and the product concentration was only 6.55%, which increased the difficulty of subsequent solvent recovery and treatment, and the molecular weight distribution of the product was 1.53, and the uniform stability of the polymer performance could not be guaranteed. Although ethylene-maleic anhydride with a molecular weight of more than 80,000 was prepared in CN119060229A, the molecular weight distribution was large, the amount of solvent used was large, and the reaction time was also long. It can be seen that the molecular weight of ethylene-maleic anhydride prepared by the solvent method is either small or large, and the molecular weight distribution is also large, and the amount of solvent used is relatively large. Summary of the Invention

[0005] Based on the above problems existing in the preparation of ethylene-maleic anhydride by the solvent method, the object of the present invention is to provide a preparation method for regulating the molecular weight and yield of ethylene-maleic anhydride alternating copolymer based on the solvent method. Specifically, by adjusting the catalyst and the reaction solvent, the problem that the molecular weight of the polymer prepared by the solvent method is uncontrollable (too low or too high) is solved. While reducing the reaction pressure and reducing the use of the reaction solvent, the molecular weight of the polymer is regulated between 60 - 90k, the yield of the product is increased, and the molecular weight distribution of the polymer is also reduced.

[0006] The object of the present invention is achieved by the following technical solutions: A method for increasing the yield of ethylene-maleic anhydride alternating copolymer, characterized in that maleic anhydride, a radical initiator and a polymerization catalyst are mixed and added into an organic solvent, and ethylene gas is introduced for radical polymerization. The polymerization catalyst is obtained by loading a heteropolyacid on SiO2 as a carrier and then activating it.

[0007] Further, the loading is to dissolve the heteropolyacid in deionized water, stir at 50 - 60 °C to form an aqueous solution, drop the aqueous solution into the dry carrier SiO2 for impregnation, after dropping, let it stand for 10 - 15 h, and then dry to obtain the loaded catalyst.

[0008] Further, the activation is to heat the loaded catalyst in a nitrogen atmosphere at a rate of 3 - 5 °C / min to 200 °C - 250 °C and keep it warm for 2 - 3 h to obtain the polymerization catalyst.

[0009] Further, the heteropolyacid is any one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or silicomolybdic acid.

[0010] Further, the mass-volume ratio of SiO2, heteropolyacid and deionized water is 100g : 15 - 25g : 100mL.

[0011] Further, the organic solvent is composed of solvent A and solvent B in a volume ratio of 7:3 - 9:1, where solvent A is one of toluene, xylene, cyclohexane, and solvent B is one of ethyl acetate, acetone and methyl ethyl ketone.

[0012] Further, the radical initiator is at least one of azobisisobutyronitrile, azobisisoheptonitrile, benzoyl peroxide, diisopropylbenzene peroxide, and preferably azobisisobutyronitrile.

[0013] Further, the radical initiator added to the composite solvent is 20 - 30 mmol / L, maleic anhydride is 3 mol / L, and the dosage of the polymerization catalyst is 20 - 30 g / L.

[0014] Furthermore, the ethylene pressure in the catalytic reaction is 0.3 - 0.8 MPa, the reaction temperature is 50 - 60 °C, and the reaction time is 2 - 5 h.

[0015] Most specifically, a method for increasing the yield of ethylene - maleic anhydride alternating copolymer, characterized by comprising the following steps: (1) Dissolve the heteropolyacid in deionized water, stir at 50 - 60 °C to form an aqueous solution, drop the aqueous solution onto dry SiO2 for impregnation, after dropping, let it stand for 10 - 15 h, then dry at 100 °C, and then in a nitrogen atmosphere, heat it to 200 - 250 °C at a rate of 3 - 5 °C / min and keep it warm for 2 - 3 h to obtain a polymerization catalyst. The heteropolyacid is any one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid, or silicomolybdic acid. The mass - volume ratio of SiO2, heteropolyacid, and deionized water is 100 g: 15 - 25 g: 100 mL; (2) Add a composite solvent, a radical initiator azobisisobutyronitrile, maleic anhydride, and the polymerization catalyst into a high - pressure reactor, displace with nitrogen 3 times, introduce ethylene with a pressure of 0.3 - 0.8 MPa, react at an oil - bath temperature of 50 - 60 °C for 2 - 5 h, and then discharge the remaining ethylene to obtain a milky suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 7:3 - 9:1. Solvent A is any one of toluene, xylene, and cyclohexane, and solvent B is any one of ethyl acetate, acetone, and methyl ethyl ketone. The dosage ratio of maleic anhydride, radical initiator, polymerization catalyst, and composite solvent is 1.5 mol: 10 - 15 mmol: 10 - 15 g: 500 mL. The radical initiator is at least one of azobisisobutyronitrile, azobis(2,4 - dimethylvaleronitrile), benzoyl peroxide, and di - isopropylbenzene peroxide; (3) Filter the suspension through a 200 - mesh filter to obtain a supported catalyst and a suspension. After subjecting the suspension to suction filtration, wash it twice with ethanol to remove unreacted maleic anhydride, and vacuum - dry the washed solid to obtain an ethylene - maleic anhydride polymer. The recovered supported catalyst can be reused after washing with DMF.

[0016] The present invention has the following technical effects: In the present invention, by using a specific supported catalyst after activation in combination with a composite solvent, the solubility of maleic anhydride and ethylene in the solvent is effectively increased, the reaction activity is improved, the problem of low tunability of the molecular weight of the polymer prepared by the solvent method is solved, while reducing the reaction pressure and the use of the reaction solvent, the molecular weight of the polymer is adjusted, the yield of the product is increased, the molecular weight distribution of the polymer is also reduced, and at the same time, the occurrence of side reactions is reduced. The number average molecular weight of the prepared ethylene-maleic anhydride alternating copolymer is between 60 and 90k, the molecular weight distribution is as low as 1.2, and the performance stability is excellent. The ethylene-maleic anhydride can be used as an efficient binder and dispersant for building thermal insulation materials, sound insulation materials, etc.; in addition, the catalyst can be recovered and recycled. Detailed implementation manners

[0017] The present invention will be specifically described below through examples. It is necessary to point out here that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention according to the above content of the present invention.

[0018] Example 1 A method for increasing the yield of an ethylene-maleic anhydride alternating copolymer, comprising the following steps: (1) Dissolve phosphomolybdic acid in deionized water, stir at 55 °C to form an aqueous solution, drop the aqueous solution onto dry SiO2 for impregnation, let it stand for 12 h after dropping, then dry at 100 °C, and then in a nitrogen atmosphere, heat to 230 °C at a rate of 4 °C / min and hold for 3 h to obtain a polymerization catalyst, where the mass-volume ratio of SiO2, phosphomolybdic acid and deionized water is 100 g: 20 g: 100 mL; (2) Add 500 mL of composite solvent, 12 mmol of free radical initiator azobisisobutyronitrile, 1.5 mol of maleic anhydride and 15.0 g of polymerization catalyst to a high-pressure reactor, displace with nitrogen 3 times, introduce ethylene with a pressure of 0.6 MPa, and react at an oil bath temperature of 60 °C for 2 h, then discharge the remaining ethylene to obtain a milky suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, where solvent A is toluene and solvent B is methyl ethyl ketone; (3) Filter the suspension through a 200-mesh filter to obtain a polymerization catalyst and a suspension. After collecting the polymerization catalyst, filter the suspension by suction, wash it twice with ethanol to remove unreacted maleic anhydride, and vacuum dry the washed solid to obtain an ethylene-maleic anhydride polymer.

[0019] Measure the weight average molecular weight (M w ) and number average molecular weight (M n), the M of the ethylene-maleic anhydride polymer prepared in this example w is 78,800, and the M n is 65,700. The yield of the ethylene-maleic anhydride polymer is 158.3 g. The collected polymerization catalyst is 12.8 g.

[0020] According to the preparation process of Example 1, by adjusting the ratio of Solvent A and Solvent B in the composite solvent, the ethylene-maleic anhydride alternating copolymer prepared is shown in Table 1.

[0021] Table 1:

[0022] It can be seen that as the proportion of Solvent B in the composite solvent increases, the yield and molecular weight of the prepared ethylene-maleic anhydride alternating copolymer show a trend of first increasing and then decreasing, while the influence on the molecular weight distribution is first decreasing and then increasing, but the overall change in the molecular weight distribution is not significant. Among them, when the volume ratio of Solvent A and Solvent B is 8:2, the polymer yield is the highest. This is because the excessive ester and ketone solvents increase the polarity of the composite solvent, resulting in that although the solubility of maleic anhydride increases, the solubility of ethylene gas is greatly reduced, which is not conducive to the reaction. Through the use of the composite solvent and the catalyst, through their synergistic effect, the polymer yield can be effectively increased to more than 300 g / L of solvent under a lower ethylene pressure.

[0023] According to the preparation process of Example 1, the ethylene-maleic anhydride alternating copolymer prepared by adjusting the ethylene pressure is shown in Table 2.

[0024] Table 2:

[0025] As can be seen from the above table, the molecular weight of the polymer generated by the reaction gradually increases with the increase of the ethylene pressure, but the change in pressure has little effect on the molecular weight distribution. In addition, we have tried to further increase the ethylene pressure. As the pressure increases, the molecular weight of the prepared ethylene-maleic anhydride gradually increases, but the molecular weight distribution basically does not change much. On the basis of Example 1, when the ethylene pressure is increased to 2 MPa, the M n of the prepared ethylene-maleic anhydride reaches 146,000, the molecular weight distribution is 1.24, and the polymer yield is 170.5 g. It can be expected that if the ethylene pressure is further increased, the molecular weight of the prepared ethylene-maleic anhydride copolymer will further increase, and the yield of the copolymer will also further increase.

[0026] Comparative Example 1 Under the condition of a composite solvent with a volume ratio of solvent A to solvent B of 8:2, according to the process steps of Example 1, replace the polymerization catalyst of the present invention with Lewis acid B(C6F5)3 (the addition amount is 20 mmol, and under this process, the polymer M synthesized with this addition amount n is the largest), and the remaining steps are the same as those in Example 1. The M of the ethylene-maleic anhydride alternating polymer prepared n is 38900, the molecular weight distribution is 1.39, and the polymer yield is 44.6 g. By adjusting the ethylene pressure to increase to 0.8 MPa, M n rises to 46100, the molecular weight distribution is 1.36, and the polymer yield is 51.7 g.

[0027] It can be seen that even if a composite solvent is used, but the catalyst used is not suitable and cannot produce a synergistic effect with the composite solvent, the molecular weight of the polymer is too low and the yield is also poor. Even if the ethylene pressure is increased, the improvement effect on the molecular weight and yield of the polymer is not obvious.

[0028] Comparative Example 2 Compared with Example 1, cyclohexanone is used to replace methyl ethyl ketone in the composite solvent, and the remaining steps are the same as those in Example 1. The M of the ethylene-maleic anhydride alternating polymer prepared n is 41600, the molecular weight distribution is 1.33, and the polymer yield is 95.9 g.

[0029] Example 2 A method for improving the yield of ethylene-maleic anhydride alternating copolymer, comprising the following steps: (1) Dissolve phosphotungstic acid in deionized water, stir at 60 °C to form an aqueous solution, drop the aqueous solution onto dry SiO2 for impregnation, let it stand for 10 h after dropping, then dry at 100 °C, and then in a nitrogen atmosphere, heat to 250 °C at a rate of 5 °C / min and hold for 2 h to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphotungstic acid and deionized water is 100 g:15 g:100 mL; (2) Add 500 mL of composite solvent, 12 mmol of free radical initiator, 1.5 mol of maleic anhydride and 10.0 g of polymerization catalyst into a high-pressure reactor, displace with nitrogen 3 times, introduce ethylene with a pressure of 0.3 MPa, and react at an oil bath temperature of 60 °C for 2 h, then discharge the remaining ethylene to obtain a milky suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, where solvent A is toluene and solvent B is ethyl acetate; (3) Filter the suspension through a 200-mesh filter to obtain a polymerization catalyst and a suspension. After collecting the polymerization catalyst, filter the suspension by suction, wash it twice with ethanol to remove unreacted maleic anhydride, and vacuum-dry the washed solid to obtain an ethylene-maleic anhydride polymer.

[0030] The weight-average molecular weight (M w ) and number-average molecular weight (M n ) of the ethylene-maleic anhydride polymer prepared in this example were measured by gel permeation chromatography (GPC). The M w of the ethylene-maleic anhydride polymer was 70300, the M n was 58300, and the yield of the ethylene-maleic anhydride polymer was 138.1 g. The collected polymerization catalyst was 9.5 g.

[0031] Example 3 A method for increasing the yield of ethylene-maleic anhydride alternating copolymer, comprising the following steps: (1) Dissolve phosphotungstic acid in deionized water, stir at 60 °C to form an aqueous solution, drop the aqueous solution onto dry SiO2 for impregnation, let it stand for 10 h after dropping, then dry at 100 °C, and then heat to 250 °C at a rate of 5 °C / min in a nitrogen atmosphere and hold for 2 h to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphotungstic acid and deionized water is 100 g: 15 g: 100 mL; (2) Add 500 mL of composite solvent, 12 mmol of free radical initiator diisopropylbenzene peroxide, 1.5 mol of maleic anhydride and 10.0 g of polymerization catalyst into a high-pressure reactor, displace with nitrogen 3 times, introduce ethylene with a pressure of 0.3 MPa, and react at an oil bath temperature of 50 °C for 5 h, then discharge the remaining ethylene to obtain a milky suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 9:1, where solvent A is toluene and solvent B is acetone; (3) Filter the suspension through a 200-mesh filter to obtain a polymerization catalyst and a suspension. After collecting the polymerization catalyst, filter the suspension by suction, wash it twice with ethanol to remove unreacted maleic anhydride, and vacuum-dry the washed solid to obtain an ethylene-maleic anhydride polymer.

[0032] The weight-average molecular weight (M w ) and number-average molecular weight (M n ) of the ethylene-maleic anhydride polymer were measured by gel permeation chromatography (GPC). The M w of the ethylene-maleic anhydride polymer prepared in this example was 90800, the M n was 76900, and the yield of the ethylene-maleic anhydride polymer was 135.3 g. The collected polymerization catalyst was 9.7 g.

[0033] Example 4 A method for increasing the yield of ethylene-maleic anhydride alternating copolymer, comprising the following steps: (1) Dissolve phosphomolybdic acid in deionized water, stir at 50 °C to form an aqueous solution, dropwise add the aqueous solution to dry SiO2 for impregnation, let it stand for 15 h after dropping, then dry at 100 °C, and then in a nitrogen atmosphere, heat to 200 °C at a rate of 3 °C / min and hold for 2.5 h to obtain a polymerization catalyst. The mass-volume ratio of SiO2, phosphomolybdic acid and deionized water is 100 g: 25 g: 100 mL; (2) Add 500 mL of composite solvent, 15 mmol of radical initiator benzoyl peroxide, 1.5 mol of maleic anhydride and 15 g of polymerization catalyst into a high-pressure reactor, displace with nitrogen 3 times, introduce ethylene with a pressure of 0.8 MPa, react at an oil bath temperature of 60 °C for 2 h, and then discharge the remaining ethylene to obtain a milky suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, where solvent A is xylene and solvent B is acetone; (3) Filter the suspension through a 200-mesh filter to obtain a polymerization catalyst and a suspension. After collecting the polymerization catalyst, filter the suspension by suction filtration, wash it twice with ethanol to remove unreacted maleic anhydride, and vacuum dry the washed solid to obtain an ethylene-maleic anhydride polymer.

[0034] Measure the weight-average molecular weight (M w ) and number-average molecular weight (M n ) of the polymer by gel permeation chromatography (GPC). The M w of the ethylene-maleic anhydride polymer prepared in this example is 82,800, and the M n is 67,300. The yield of the ethylene-maleic anhydride polymer is 164.9 g. The collected polymerization catalyst is 13.3 g.

[0035] Example 5 A method for improving the yield of ethylene-maleic anhydride alternating copolymer, comprising the following steps: (1) Dissolve silicomolybdic acid in deionized water, stir at 55 °C to form an aqueous solution, dropwise add the aqueous solution to dry SiO2 for impregnation, let it stand for 12 h after dropping, then dry at 100 °C, and then in a nitrogen atmosphere, heat to 220 °C at a rate of 4 °C / min and hold for 2 h to obtain a polymerization catalyst. The mass-volume ratio of SiO2, silicomolybdic acid and deionized water is 100 g: 20 g: 100 mL; (2) Add 500 mL of composite solvent, 10 mmol of azobisisobutyronitrile, 1.5 mol of maleic anhydride and 15 g of polymerization catalyst into a high-pressure reactor, displace with nitrogen 3 times, introduce ethylene with a pressure of 0.8 MPa, react at an oil bath temperature of 60 °C for 4 h, and then discharge the remaining ethylene to obtain a milky suspension. The composite solvent is composed of solvent A and solvent B in a volume ratio of 8:2, where solvent A is cyclohexane and solvent B is ethyl acetate; (3) Filter the suspension through a 200-mesh sieve to obtain the polymerization catalyst and the suspension. After collecting the polymerization catalyst, subject the suspension to suction filtration, wash it twice with ethanol to remove unreacted maleic anhydride, and vacuum-dry the washed solid to obtain the ethylene-maleic anhydride polymer.

[0036] Measure the weight-average molecular weight (M w ) and number-average molecular weight (M n ) of the polymer by gel permeation chromatography (GPC). The M w of the ethylene-maleic anhydride polymer prepared in this example is 92,200, the M n is 75,800, and the yield of the ethylene-maleic anhydride polymer is 177.7 g. The collected polymerization catalyst is 13.1 g.

Claims

1. A method for improving the yield of ethylene-maleic anhydride alternating copolymer, characterized in that: The method is prepared by mixing maleic anhydride, a free radical initiator and a polymerization catalyst into an organic solvent, introducing ethylene gas to carry out free radical polymerization, wherein the polymerization catalyst is obtained by using SiO2 as a carrier to load a heteropoly acid and then activating the catalyst.

2. A method for improving the yield of ethylene-maleic anhydride alternating copolymer as claimed in claim 1, characterized in that: The loading is performed by dissolving the heteropoly acid in deionized water, stirring at 50-60° C. to form an aqueous solution, dropping the aqueous solution into the dry carrier SiO2 for impregnation, standing for 10-15 hours after the dropping is completed, and then drying to obtain the loaded catalyst.

3. A method for improving the yield of ethylene-maleic anhydride alternating copolymer according to claim 1 or 2, characterized in that: The activation is to heat the supported catalyst to 200°C-250°C at 3-5°C / min in a nitrogen atmosphere and keep the temperature for 2-3 hours to obtain a polymerization catalyst.

4. A method for improving the yield of ethylene-maleic anhydride alternating copolymer as claimed in claim 1 or 2, characterized in that: The heteropoly acid is any one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or silicomolybdic acid.

5. A method for improving the yield of ethylene-maleic anhydride alternating copolymer as claimed in claim 4, characterized in that: The organic solvent is composed of solvent A and solvent B in a volume ratio of 7:3 to 9:1, wherein solvent A is one of toluene, xylene, and cyclohexane, and solvent B is one of ethyl acetate, acetone, and methyl ethyl ketone.

6. A method for improving the yield of ethylene-maleic anhydride alternating copolymer according to any one of claims 1 to 5, characterized in that: The free radical initiator is at least one of azobisisobutyronitrile, azobisisoheptanenitrile, dibenzoyl peroxide, and dicumyl peroxide, preferably azobisisobutyronitrile.

7. A method for improving the yield of ethylene-maleic anhydride alternating copolymer according to any one of claims 1 to 6, characterized in that: The amount of free radical initiator added to 1L of the composite solvent is 20-30mmol, the amount of maleic anhydride is 3mol, and the amount of the polymerization catalyst is 20-30g.

8. A method for improving the yield of ethylene-maleic anhydride alternating copolymer according to any one of claims 1 to 7, characterized in that: The catalytic reaction has an ethylene pressure of 0.3-0.8 MPa, a reaction temperature of 50-60° C., and a reaction time of 2-5 h.

9. A method for improving the yield of ethylene-maleic anhydride alternating copolymer, characterized in that: The steps include: (1) dissolving a heteropoly acid in deionized water, stirring at 50-60° C. to form an aqueous solution, dropping the aqueous solution into dry SiO2 for impregnation, standing for 10-15 h after the dropping is completed, and then drying at 100° C., and then heating to 200° C.-250° C. at a rate of 3-5° C. / min in a nitrogen atmosphere and keeping the temperature for 2-3 h to obtain a polymerization catalyst, wherein the heteropoly acid is any one of phosphotungstic acid, phosphomolybdic acid, silicotungstic acid or silicomolybdic acid, and the mass volume ratio of SiO2, heteropoly acid and deionized water is 100 g:15-25 g:100 mL; (2) Add a composite solvent, a free radical initiator azobisisobutyronitrile, maleic anhydride and a polymerization catalyst into a high-pressure reactor, replace with nitrogen for 3 times, introduce ethylene at a pressure of 0.3-0.8 MPa, react at an oil bath temperature of 50-60°C for 2-5 hours, then discharge the remaining ethylene to obtain a milky white suspension, wherein the composite solvent is composed of solvent A and solvent B in a volume ratio of 7:3-9:1, wherein solvent A is any one of toluene, xylene and cyclohexane, and solvent B is any one of ethyl acetate, acetone and methyl ethyl ketone, and the amount ratio of maleic anhydride, free radical initiator, polymerization catalyst and composite solvent is 1.5 mol: 10-15 mmol: 10-15 g: 500 mL; (3) The suspension is filtered through a 200-mesh filter to obtain a polymerization catalyst and a suspension. The suspension is filtered and then washed twice with ethanol to remove unreacted maleic anhydride. The washed solid is vacuum dried to obtain an ethylene-maleic anhydride polymer. The recovered polymerization catalyst can be reused after washing with DMF.

Images