Method and system for producing ethylene-vinyl alcohol copolymers

Abstract

The present application discloses a method for preparing an ethylene-vinyl alcohol copolymer and a system for preparing an ethylene-vinyl alcohol copolymer, wherein the method comprises hydrolyzing an ethylene-vinyl acetate copolymer in a solvent containing alcohol and water in the presence of a catalyst to prepare a reaction product containing an ethylene-vinyl alcohol copolymer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to and the benefit of Korean Patent Application No. 10-2023-0133220 filed in the Korean Intellectual Property Office on October 6, 2023, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] Embodiments of the present disclosure are directed to methods and systems for preparing ethylene-vinyl alcohol copolymers. Background Art

[0004] Ethylene vinyl alcohol copolymers are processed into a wide variety of films, sheets, containers and fibers, and are used in a variety of applications such as fresh food packaging and automotive fuel tanks due to their excellent gas barrier properties, solvent resistance and mechanical strength.

[0005] The conventional method for industrially preparing ethylene-vinyl alcohol copolymer includes first synthesizing ethylene-vinyl acetate copolymer by free radical solution polymerization using vinyl acetate and ethylene as raw materials, and then reacting the ethylene-vinyl acetate copolymer with alcohol to prepare ethylene vinyl alcohol copolymer.

[0006] However, this method for preparing ethylene-vinyl alcohol copolymers has two major limitations. First, because the transesterification between ethylene-vinyl acetate (EVA) copolymers and alcohols is a reversible reaction, the alkyl acetate obtained as a by-product must be continuously removed to increase the ethylene

[0007] -ethylene alcohol (EVOH) copolymer conversion. Therefore, a reactive distillation column (RDC) capable of simultaneous reaction / distillation is used in industrial processes such as the Kuraray process. Another limitation is that in order to make the ethylene-vinyl alcohol copolymer with a high conversion exist in a solution state instead of precipitating in the reactive distillation column, high pressure and high temperature conditions are required.

[0008] Therefore, the conventional method of preparing ethylene-vinyl alcohol copolymer using ethylene-vinyl acetate copolymer has difficulties and disadvantages.

[0009] The information disclosed in this section is only for enhancement of understanding of the background of the present disclosure and therefore it may contain information that does not constitute prior art. Summary of the invention

[0010] Embodiments of the present disclosure provide a method for preparing an ethylene-vinyl alcohol copolymer by hydrolysis, which is a reaction of an ethylene-vinyl acetate copolymer with water in an aqueous solution, without transesterification, which is a reaction between an ethylene-vinyl acetate copolymer and an alcohol.

[0011] A method of preparing an ethylene-vinyl alcohol copolymer according to one embodiment of the present disclosure includes hydrolyzing an ethylene-vinyl acetate copolymer in a solvent containing alcohol and water in the presence of a catalyst to prepare a reaction product containing the ethylene-vinyl alcohol copolymer.

[0012] The hydrolysis can be carried out at a temperature of 90°C or below without precipitation.

[0013] The catalyst may include at least one selected from the group consisting of an alkali metal hydroxide, an alkali metal alkoxide, an alkali metal alkyl, an alkali metal alcoholate, and a carboxylic acid.

[0014] The alcohol may be a C1 to C4 alcohol.

[0015] The solvent may include alcohol and water in a weight ratio of 3:1 to 3:5.

[0016] The ethylene-vinyl acetate copolymer may be added in an amount of 10 parts by weight to 50 parts by weight based on 100 parts by weight of the solvent.

[0017] The ethylene-vinyl acetate copolymer may have a weight average molecular weight (Mw) of about 50,000 g / mol to about 500,000 g / mol.

[0018] The ethylene-vinyl acetate copolymer may contain 20 to 40 mol % of ethylene and 60 to 80 mol % of vinyl acetate.

[0019] The hydrolysis may be carried out at a temperature of 50°C to 80°C.

[0020] The hydrolysis can be carried out at a pressure of 1 bar to 3 bar.

[0021] The ethylene-vinyl alcohol copolymer may contain 20 to 40 mol % of ethylene and 60 to 80 mol % of vinyl alcohol.

[0022] The conversion rate of the ethylene-vinyl alcohol copolymer may be 90% or more.

[0023] The ethylene-vinyl alcohol copolymer may be present in the reaction product in a liquid phase.

[0024] The method may further include isolating the ethylene-vinyl alcohol copolymer from the reaction product.

[0025] A system for preparing an ethylene-vinyl alcohol copolymer according to another embodiment of the present disclosure includes a reactor configured to receive a solvent containing an alcohol and water and an ethylene-vinyl acetate copolymer, and hydrolyze the ethylene-vinyl acetate copolymer in the solvent in the presence of a catalyst to prepare a reaction product containing the ethylene-vinyl alcohol copolymer.

[0026] The system may further include a temperature control unit configured to control the temperature of the reactor at 90° C. or below.

[0027] The system may further include a purification unit configured to receive the reaction product from the reactor and separate the ethylene-vinyl alcohol copolymer from the reaction product. DETAILED DESCRIPTION

[0028] The embodiments are provided in order to more fully explain the present disclosure to those of ordinary skill in the art. The following embodiments may be modified in various other forms, and the scope of the present disclosure is not limited to the following embodiments.

[0029] A method of preparing an ethylene-vinyl alcohol copolymer according to one embodiment includes hydrolyzing an ethylene-vinyl acetate copolymer in a solvent containing alcohol and water in the presence of a catalyst to prepare a reaction product containing the ethylene-vinyl alcohol copolymer.

[0030] In the conventional method for industrially preparing ethylene-vinyl alcohol copolymer, ethylene-vinyl acetate copolymer is first synthesized by free radical solution polymerization using vinyl acetate and ethylene as raw materials, and then reacted with alcohol to prepare ethylene vinyl alcohol copolymer.

[0031] This method cannot prepare ethylene-vinyl alcohol with a high conversion rate in ordinary glassware or flasks because the transesterification between the ethylene-vinyl acetate (EVA) copolymer and the alcohol is a reversible reaction, and the alkyl acetate obtained as a by-product needs to be continuously removed to increase the conversion rate of the ethylene-vinyl alcohol (EVOH) copolymer. In addition, this method has difficulties in preparing the ethylene-vinyl alcohol copolymer using the ethylene-vinyl acetate copolymer because high pressure and high temperature conditions are required in order to make the ethylene-vinyl alcohol copolymer with a high conversion rate exist in a solution state instead of precipitating in a reactive distillation tower.

[0032] In contrast, in the present disclosure, ethylene-vinyl alcohol copolymer is prepared by hydrolyzing ethylene-vinyl acetate copolymer using a solvent containing alcohol and water. In this case, hydrolysis is an irreversible reaction, and ethylene-vinyl alcohol copolymer with high conversion can be prepared without distillation for separating by-products. In addition, this improves conversion even in a batch reactor rather than a tower, thereby providing simple operation. The method can be carried out under mild conditions because the copolymer exists in a solution state under atmospheric pressure conditions.

[0033] In one embodiment, the hydrolysis can be carried out at a temperature of 90° C. or less without precipitation. For example, the hydrolysis can be carried out at a temperature of 50° C. to 80° C. or 60° C. to 80° C. When the hydrolysis is carried out within the above temperature range, the reaction is completed at a sufficient reaction rate without precipitation, and occurs in a liquid phase, which is advantageous for a continuous process.

[0034] The hydrolysis can be carried out under a pressure of 1 bar to 3 bar. For example, the hydrolysis can be carried out under 1 bar to 2 bar or under atmospheric pressure. According to the present disclosure, even under mild pressure conditions, especially under atmospheric pressure conditions, ethylene-vinyl alcohol copolymers with high conversion rates can be continuously prepared, and the reaction can be carried out in a liquid phase without precipitating the ethylene-vinyl alcohol copolymers.

[0035] In one embodiment, the catalyst may include at least one selected from the group consisting of alkali metal hydroxides, alkali metal alkoxides, alkali metal alkylates, alkali metal alcoholates, and carboxylic acids, but is not limited thereto. For example, the catalyst may include at least one selected from the group consisting of alkali metal hydroxides such as sodium hydroxide and potassium hydroxide; alkali metal ethanolates such as sodium methoxide and potassium methoxide; alkali metal alkylates such as sodium methylate, sodium ethylate, potassium methylate, and lithium methoxide; alkali metal alcoholates such as sodium methoxide, sodium ethoxide, sodium isopropoxide, and sodium n-butoxide; and carboxylic acids such as acetic acid, sulfuric acid, and hydrochloric acid.

[0036] The catalyst is dispersed in a solvent containing alcohol and water and is easily contacted with the ethylene-vinyl acetate copolymer, thereby promoting the conversion of the ethylene-vinyl acetate copolymer into the ethylene-vinyl alcohol copolymer through hydrolysis.

[0037] The catalyst may be added in an amount of 5 to 50 parts by weight, 10 to 40 parts by weight, or 20 to 30 parts by weight based on 100 parts by weight of the ethylene-vinyl acetate copolymer. By adding the catalyst in an amount within the above range, the hydrolysis of the ethylene-vinyl acetate copolymer can be effectively performed, a large amount of waste water can be prevented from being generated in a subsequent washing process due to excessive use of the catalyst, and problems such as discoloration or poor appearance of articles due to the presence of catalyst residues therein can be prevented.

[0038] In one embodiment, the solvent can be a mixture of alcohol and water in an appropriate ratio. For example, the solvent can include alcohol and water in a weight ratio of 3:1 to 3:5. As a specific example, the solvent can include alcohol and water in a weight ratio of 3:1 to 3:4, 3:1 to 3:3 or 3:1.5 to 3:3. When a mixture of alcohol and water in the above-mentioned range is used as a solvent, it can not only dissolve ethylene-vinyl acetate copolymers at a temperature of 90°C or less and under mild pressure conditions, but also dissolve ethylene-vinyl alcohol copolymers, thereby continuously preparing ethylene-vinyl alcohol copolymers with high conversion rates through a liquid phase process, and by-products are not separated during the reaction.

[0039] The alcohol may be a C1 to C4 alcohol. For example, the alcohol may include at least one of ethanol, methanol, propanol, isopropanol or butanol. In a specific embodiment, the alcohol is ethanol.

[0040] The ethylene-vinyl acetate copolymer may be added in an amount of 10 to 50 parts by weight based on 100 parts by weight of the solvent. For example, the ethylene-vinyl acetate copolymer may be added in an amount of 10 to 35 parts by weight or 10 to 25 parts by weight based on 100 parts by weight of the solvent. By adjusting the contents of the solvent and the ethylene-vinyl acetate copolymer within the above range, a viscous product having sufficient fluidity may be obtained, and production with economic efficiency may be ensured.

[0041] The ethylene-vinyl acetate copolymer may have a weight average molecular weight (Mw) of 50,000 g / mol to 500,000 g / mol or 100,000 g / mol to 400,000 g / mol. When an ethylene-vinyl alcohol copolymer is prepared by hydrolyzing an ethylene-vinyl acetate copolymer having a weight average molecular weight within the above range, a product having sufficient heat resistance and mechanical resistance may be obtained.

[0042] The ethylene-vinyl acetate copolymer may be composed of 20 mol% to 40 mol% of ethylene and 60 mol% to 80 mol% of vinyl acetate. For example, the ethylene-vinyl acetate copolymer may be composed of 28 mol% to 32 mol% of ethylene and 68 mol% to 72 mol% of vinyl acetate. When an ethylene-vinyl alcohol copolymer is prepared by hydrolyzing an ethylene-vinyl acetate copolymer having a composition within the above range, a product having sufficiently good oxygen barrier properties and fluidity suitable for food packaging materials can be obtained.

[0043] In one embodiment, the ethylene-vinyl acetate copolymer can be converted into an ethylene-vinyl alcohol copolymer by hydrolysis in a solvent containing alcohol and water in the presence of a catalyst. Here, the ethylene-vinyl acetate copolymer may refer to a copolymer having ethylene-derived units and vinyl acetate-derived units, and the ethylene-vinyl alcohol copolymer may refer to a copolymer having ethylene-derived units and vinyl alcohol-derived units.

[0044] The hydrolysis is a saponification reaction in the presence of a catalyst, whereby part or all of the vinyl acetate-derived units in the ethylene-vinyl acetate copolymer are converted into repeating units containing hydroxyl groups.

[0045] In one embodiment, the ethylene-vinyl alcohol copolymer contained in the reaction product can be composed of 20 mol% to 40 mol% of ethylene and 60 mol% to 80 mol% of vinyl alcohol. For example, the ethylene-vinyl alcohol copolymer can be composed of 25 mol% to 35 mol% of ethylene and 65 mol% to 75 mol% of vinyl alcohol, or 28 mol% to 32 mol% of ethylene and 68 mol% to 72 mol% of vinyl alcohol. The ethylene-vinyl alcohol copolymer having the above composition can prepare a product having oxygen barrier properties and fluidity suitable for food packaging materials.

[0046] In one embodiment, the conversion rate (i.e., saponification degree) of the ethylene-vinyl alcohol copolymer in the reaction product can be 90% or more, 95% or more, or 99.9% or more. Using the method according to the present disclosure, thanks to the irreversible reaction, even if the by-products generated during the reaction are not removed, the ethylene-vinyl alcohol copolymer with a high conversion rate can be continuously prepared.

[0047] The ethylene-vinyl alcohol copolymer can exist in the reaction product in a liquid phase. As described above, by using a solvent containing alcohol and water, not only the ethylene-vinyl acetate copolymer as a raw material but also the ethylene-vinyl alcohol copolymer as a target product exists in a liquid state even without high pressure conditions, thereby providing an easy preparation method through a continuous process.

[0048] In one embodiment, the method may further include separating the ethylene-vinyl alcohol copolymer from the reaction product obtained through the reaction.

[0049] The reaction product may include solvent, unreacted residue, by-products and ethylene-vinyl alcohol copolymer, and the ethylene-vinyl alcohol copolymer may be separated from the reaction product by a typical purification process. In addition, due to the low temperature and low pressure during the hydrolysis process, the reaction product may be easily processed.

[0050] A system for preparing an ethylene-vinyl alcohol copolymer according to one embodiment includes a reactor configured to receive a solvent containing an alcohol and water and an ethylene-vinyl acetate copolymer, and hydrolyze the ethylene-vinyl acetate copolymer in the solvent in the presence of a catalyst to prepare a reaction product containing the ethylene-vinyl alcohol copolymer.

[0051] In one embodiment, the reactor may be selected from various reactors, such as a glass vessel or a batch reactor instead of a tower. Specifically, since the ethylene-vinyl acetate copolymer is prepared by hydrolysis (which is an irreversible reaction) instead of by transesterification between the ethylene-vinyl acetate copolymer and an alcohol to produce the ethylene-vinyl alcohol copolymer, the necessity of continuously removing the alkyl acetate by-product during the reaction to increase the conversion rate can be eliminated, and thus the ethylene-vinyl alcohol copolymer with a high conversion rate can be prepared using a glass vessel or a batch reactor.

[0052] The reactor may include a raw material supply line. The raw material may include a catalyst, a solvent, and ethylene-vinyl acetate copolymer. Here, the raw material supply line may be provided as a line configured to supply each of the catalyst, the solvent, and the ethylene-vinyl acetate copolymer, and may be connected to the reactor, or the individual lines may be merged into one line, which is connected to the reactor.

[0053] The reactor may include a reaction product discharge line. The reaction product may include solvent, unreacted residues, by-products and ethylene-vinyl alcohol copolymer.

[0054] The preparation system may further include a temperature control unit configured to control the temperature of the reactor at or below 90° C. For example, the temperature of the reactor may be controlled within a temperature range of 50° C. to 80° C. or 60° C. to 80° C. When the hydrolysis is performed within the above temperature range, the hydrolysis may occur at a sufficient reaction rate without precipitation, and the reaction is performed in a liquid phase, which is advantageous for a continuous process.

[0055] The pressure of the reactor can be controlled within the range of 1 bar to 3 bar. For example, the pressure of the reactor can be controlled within the range of 1 bar to 2 bar or atmospheric pressure. According to the present disclosure, even under mild pressure conditions, especially under atmospheric pressure conditions, ethylene-vinyl alcohol copolymer with high conversion rate can be continuously produced, and the reaction can be carried out in liquid phase without precipitation of ethylene-vinyl alcohol copolymer.

[0056] The preparation system may further include a purification unit configured to receive the reaction product from the reactor and separate the ethylene-vinyl alcohol copolymer from the reaction product. Specifically, the reaction product discharged through the reaction product discharge pipeline may be supplied to the purification unit, and the purification unit may separate the ethylene-vinyl alcohol copolymer as the target product from the reaction product.

[0057] Hereinafter, specific examples of the present disclosure will be described. However, the examples described below are only used to illustrate or explain the present disclosure in detail, and should not be construed as limiting the scope of the present disclosure. In addition, other details that are technically conceivable by those skilled in the art will not be described.

[0058] (Preparation of ethylene-vinyl alcohol copolymer)

[0059] Example 1

[0060] Sodium hydroxide as a catalyst, a solvent containing ethanol and water in a weight ratio of 2:1, and 15 parts by weight of ethylene-vinyl acetate copolymer based on 100 parts by weight of the solvent were supplied to the reactor and hydrolyzed to prepare a reaction product containing ethylene-vinyl alcohol copolymer. At this time, the temperature of the reactor was adjusted to 80° C., and the pressure was adjusted to atmospheric pressure.

[0061] Then, the ethylene-vinyl alcohol copolymer was separated from the reaction product. The obtained ethylene-vinyl alcohol copolymer was found to contain 31 mol% of ethylene-derived units and 69 mol% of vinyl alcohol-derived units.

[0062] Example 2

[0063] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that the temperature of the reactor was adjusted to 60°C.

[0064] Example 3

[0065] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that the temperature of the reactor was adjusted to 40°C.

[0066] Example 4

[0067] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that a solvent containing ethanol and water in a weight ratio of 3:1 was used.

[0068] Example 5

[0069] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that a solvent containing ethanol and water in a weight ratio of 3:3 was used.

[0070] Example 6

[0071] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that a solvent containing ethanol and water in a weight ratio of 3:5 was used.

[0072] Comparative Example 1

[0073] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that ethanol was used as a solvent.

[0074] Comparative Example 2

[0075] An ethylene-vinyl alcohol copolymer was prepared in the same manner as in Example 1, except that ethanol was used as a solvent, and a high-pressure reactor was used to adjust the reaction pressure and the reaction temperature to 6 bar and 130° C., respectively.

[0076] Test 1: Measurement of Ethylene-Vinyl Alcohol Copolymer Conversion

[0077] The conversion rates of the ethylene-vinyl alcohol (EVOH) copolymers prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were measured. Specifically, the prepared ethylene-vinyl alcohol (EVOH) copolymers were separated from the solution and dried, and H-NMR was measured to calculate the conversion rate based on the areas of the vinyl acetate peak and the vinyl alcohol peak. Here, the following equation 1 was used for calculation, and the results are shown in the following Table 1:

[0078] [Equation 1]

[0079] Conversion rate (%) = (area of ​​vinyl alcohol peak) / (area of ​​vinyl alcohol peak + area of ​​vinyl acetate peak) * 100

[0080] Test 2: Measurement of the amount of ethylene-vinyl alcohol copolymer precipitation in the reaction product

[0081] After the reaction of Examples 1 to 6 and Comparative Examples 1 to 2 was performed for 2 hours, the amount of precipitated ethylene-vinyl alcohol copolymer formed in the reaction product was measured. Specifically, the reaction solution was filtered through a filter while maintaining the temperature, the weight of the product residue on the filter was measured, and it was compared with the amount of precipitated ethylene-vinyl alcohol copolymer in Comparative Example 1 to calculate the amount of precipitated ethylene-vinyl alcohol copolymer. The results are shown in Table 1 below. Here, the precipitate amount was calculated based on 100% of the amount of precipitated ethylene-vinyl alcohol copolymer in Comparative Example 1.

[0082] [Table 1]

[0083]

[0084] As can be seen from Table 1, the composition of alcohol and water in Examples 1 and 2 enables ethylene-vinyl acetate (EVA) copolymer and ethylene-vinyl alcohol (EVOH) copolymer with high conversion to be dissolved under atmospheric pressure, so that the copolymer exists in a solution state during the reaction (i.e., from the beginning to the end of the reaction) and is easy to handle in a continuous process. In addition, it was found that the conversion rate by hydrolysis was about 99% or more. At the same time, in Example 3 where the reaction temperature was lowered, and in Examples 4 and 6 where the composition of alcohol and water was changed, the conversion rate was slightly reduced and the precipitation amount was slightly increased compared with Example 1.

[0085] On the other hand, in Comparative Example 1, a solution state was maintained at the beginning of the reaction, but as the conversion rate of the ethylene-vinyl alcohol copolymer increased, the ethylene-vinyl alcohol copolymer precipitated in the solid phase, which resulted in deterioration of contact and dispersion with the sodium hydroxide catalyst. In addition, since it was difficult to remove the by-product alkyl acetate at a temperature of 80° C., a reverse reaction occurred in the reversible reaction, so the conversion rate was about 80% to 90%.

[0086] In addition, in Comparative Example 2, a high-pressure reactor was used to maintain 130° C. (the lowest temperature at which the ethylene-vinyl alcohol copolymer is dissolved in ethanol), and the internal pressure and temperature of the reactor were maintained at 6 bar and 130° C., respectively, to maintain the ethylene-vinyl alcohol copolymer in a solution phase. However, when the temperature was lowered, the ethylene-vinyl alcohol copolymer precipitated, thus disadvantageously making it difficult to process the reaction product at high temperature and high pressure, and having a conversion rate of about 95% due to a low removal rate of by-products.

[0087] As apparent from the above description, when the ethylene-vinyl alcohol copolymer is prepared using hydrolysis instead of transesterification according to the present disclosure, the hydrolysis is an irreversible reaction, thereby obtaining the ethylene-vinyl alcohol copolymer with a high conversion rate even without distilling and separating by-products.

[0088] Furthermore, when preparing the ethylene-vinyl alcohol copolymer according to the present disclosure, the operation is simple because the conversion rate can be increased even in a batch reactor rather than a tower, and the process can be performed under mild conditions because the reaction system contains alcohol and water, so the ethylene-vinyl alcohol copolymer with a high conversion rate exists in a solution state under atmospheric pressure conditions.

[0089] Although the preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.

Claims

1. A method for preparing an ethylene-vinyl alcohol copolymer, comprising hydrolyzing an ethylene-vinyl acetate copolymer in a solvent containing an alcohol and water in the presence of a catalyst to prepare a reaction product containing the ethylene-vinyl alcohol copolymer.

2. The method according to claim 1, wherein the hydrolysis is performed at a temperature of 90°C or below without precipitation. 3 . The method according to claim 1 , wherein the catalyst comprises at least one selected from the group consisting of alkali metal hydroxides, alkali metal alkoxides, alkali metal alkylates, alkali metal alcoholates, and carboxylic acids. The method according to claim 1 , wherein the alcohol is a C1 to C4 alcohol. The method according to claim 1 , wherein the solvent comprises alcohol and water in a weight ratio of 3:1 to 3:

5.

6. The method according to claim 1, wherein: The ethylene-vinyl acetate copolymer is added in an amount of 10 parts by weight to 50 parts by weight based on 100 parts by weight of the solvent. 7 . The method of claim 1 , wherein the ethylene-vinyl acetate copolymer has a weight average molecular weight (Mw) of 50,000 to 500,000 g / mol.

8. The method of claim 1, wherein the ethylene-vinyl acetate copolymer comprises 20 to 40 mol% ethylene and 60 to 80 mol% vinyl acetate.

9. The method of claim 1, wherein the hydrolysis is performed at a temperature of 50°C to 80°C.

10. The process according to claim 1, wherein the hydrolysis is carried out at a pressure of 1 bar to 3 bar.

11. The method of claim 1, wherein the ethylene-vinyl alcohol copolymer comprises 20 to 40 mol% of ethylene and 60 to 80 mol% of vinyl alcohol.

12. The method according to claim 1, wherein the conversion rate of the ethylene-vinyl alcohol copolymer is 90% or more.

13. The method according to claim 1, wherein the ethylene-vinyl alcohol copolymer is present in the reaction product in a liquid phase.

14. The method of claim 1, further comprising separating the ethylene-vinyl alcohol copolymer from the reaction product.

15. A system for preparing an ethylene-vinyl alcohol copolymer, comprising a reactor configured to receive a solvent containing an alcohol and water and an ethylene-vinyl acetate copolymer, and to hydrolyze the ethylene-vinyl acetate copolymer in the solvent in the presence of a catalyst to prepare a reaction product containing the ethylene-vinyl alcohol copolymer. 16 . The system of claim 15 , further comprising a temperature control unit configured to control the temperature of the reactor at 90° C. or below.

17. The system of claim 15, further comprising a purification unit configured to receive a reaction product from the reactor and separate the ethylene-vinyl alcohol copolymer from the reaction product.

Images