Method for producing ethylene-vinyl alcohol copolymer

Abstract

The present invention relates to a method for producing an ethylene-vinyl alcohol copolymer, which can efficiently obtain an ethylene-vinyl alcohol copolymer by performing a supercritical extraction process after saponifying an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst, minimizing waste liquid generation without requiring complicated equipment such as a multi-stage distillation column, a pipe mixer, and a water tank, and effectively removing by-products such as catalyst residues.

Description

[Technical field]

[0001] [Cross-reference to related applications] This application claims the benefit of priority to Korean Patent Application No. 10-2021-0185641 filed December 23, 2021, and Korean Patent Application No. 10-2022-0182255 filed December 22, 2022, and all contents disclosed in the documents of the Korean patent applications are incorporated herein by reference. The present invention relates to a method for producing an ethylene-vinyl alcohol copolymer. [Background technology]

[0002] Ethylene-vinyl alcohol copolymer (EVOH) has excellent barrier properties against oxygen and other gases, transparency, oil resistance, antistatic properties, and mechanical strength, and is widely used as a material for films, sheets, containers, etc.

[0003] EVOH can be produced by saponification of ethylene-vinyl acetate (EVAc), which is produced by copolymerization of ethylene and vinyl acetate. Alkaline catalysts such as sodium hydroxide, potassium hydroxide, and alkali metal alcoholates are mainly used as catalysts for the saponification of EVAc.

[0004] Since the higher the saponification degree of EVOH, the better the gas barrier properties it exhibits, it is preferable that EVOH used in food packaging applications has a high saponification degree of 99% or more. Conventionally, in order to achieve such a high saponification degree, the saponification reaction was carried out at a higher temperature or the amount of alkaline catalyst used was increased.

[0005] However, high-temperature reactions are prone to side reactions, and when a large amount of alkaline catalyst is used, there is a problem that the amount of catalyst by-products in the saponification product increases.Since catalyst by-products cause discoloration of EVOH, a washing process is required to remove them after the saponification reaction, but if the amount of catalyst by-products is high, excessive washing processes are required, which reduces process efficiency and generates excessive wastewater.

[0006] In particular, after the saponification reaction of ethylene-vinyl acetate copolymer (EVAc), a process for removing catalyst by-products (such as Na), reaction by-products (such as methyl acetate, MeAc), and residual alcohol solvents (such as methanol / MeOH) from the EVOH solution in addition to EVOH has been known to involve washing the EVOH with water and then drying it to obtain EVOH solids. Here, the dealcoholization process involves removing the alcohol solvent (such as MeOH) using steam in a multi-stage distillation tower, which requires an excessive amount of steam and generates an excessive amount of waste liquid containing alcohol and water. In addition, when washing the EVOH with water, a mixing process with water is used to remove the residuals in the EVOH, which requires an excessive amount of water and generates an excessive amount of waste liquid. This process requires a multi-stage distillation tower, and water washing requires a pipe mixer and a water tank, which creates a problem of the overall process being complicated.

[0007] Furthermore, when the alcohol solvent recovered from the dealcoholization step is reused in a saponification reaction or the like, there is a difficulty in that a step of separating or removing the water used in the dealcoholization step must be further carried out.

[0008] Therefore, a multi-stage distillation column is required in the washing process, and a pipe mixer and a water tank are required during water washing, which complicates the process and significantly reduces the overall process efficiency of producing ethylene-vinyl alcohol copolymer. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention has been made to solve the above problems, and aims to provide a method for producing an ethylene-vinyl alcohol copolymer, which can efficiently obtain an ethylene-vinyl alcohol copolymer with a high degree of saponification without complicated processes such as a multi-stage distillation column or a pipe mixer and a water tank during water washing. [Means for solving the problem]

[0010] Thus, according to one embodiment of the present invention, a saponification step of reacting an ethylene-vinyl acetate copolymer in the presence of an alkaline catalyst to produce an ethylene-vinyl alcohol copolymer; and extracting the alcohol solvent contained in the saponification reaction product under supercritical carbon dioxide conditions; The supercritical carbon dioxide conditions are 2 The pressure is 80 bar or more and 150 bar or less, and the temperature is 40 ° C or more and 60 ° C or less. A method for producing an ethylene-vinyl alcohol copolymer is provided. Effect of the Invention

[0011] According to the present invention, ethylene-vinyl acetate copolymer is saponified in the presence of an alkali catalyst, and then a supercritical extraction process is carried out under optimized conditions, thereby minimizing waste liquid generation and efficiently obtaining an ethylene-vinyl alcohol copolymer with a high degree of saponification without complicating equipment such as a multi-stage distillation column, a pipe mixer, and a water tank, without deteriorating the physical properties of the ethylene-vinyl acetate copolymer.

[0012] Therefore, according to the present invention, it is possible to increase the efficiency of the washing process for removing catalyst by-products contained in the ethylene-vinyl alcohol copolymer after the saponification process without deteriorating the physical properties of the ethylene-vinyl acetate copolymer, and to minimize the amount of wastewater generated in the washing process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates a different meaning. In this specification, the terms "include", "comprise", "have" or "have" are intended to specify the presence of an implemented feature, step, component, or combination thereof, and should be understood as not precluding the possibility of the presence or addition of one or more other features, steps, components, or combinations thereof.

[0014] Since the present invention can be modified in various ways and can have various forms, specific embodiments are exemplified and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the spirit and technical scope of the present invention.

[0015] The present invention will be described in detail below. The method for producing an ethylene-vinyl alcohol copolymer of the present invention includes the steps of: reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst to produce an ethylene-vinyl alcohol copolymer; and extracting the alcohol solvent contained in the saponification reaction product under supercritical carbon dioxide conditions.

[0016] Specifically, the supercritical carbon dioxide conditions are 2 The pressure is between 80 bar and 150 bar, and the temperature is between 40°C and 60°C.

[0017] In particular, the present invention performs a supercritical extraction process under optimized conditions, in which ethylene-vinyl acetate copolymer is saponified in the presence of an alkali catalyst and then an alcohol solvent is extracted under supercritical carbon dioxide conditions, thereby efficiently obtaining ethylene-vinyl alcohol copolymer without deteriorating the physical properties of the ethylene-vinyl acetate copolymer, minimizing waste liquid generation without requiring complicated equipment such as a multi-stage distillation column, a pipe mixer, and a water tank, and effectively removing by-products such as catalyst residues.

[0018] Generally, the process for producing ethylene-vinyl alcohol copolymer involves polymerizing ethylene-vinyl acetate copolymer (EVA) (step 1), producing EVOH through a saponification reaction using an alkaline catalyst (step 2), dealcoholizing and washing the EVOH solution (EVOH+MeOH) (step 3), and pelletizing and drying the resulting product (step 4).

[0019] Here, when the dealcoholization and washing process (step 3) is completed, most of the alcohol component (MeOH) of EVOH is removed and replaced with water, resulting in "hydrated EVOH". In this state of hydrated EVOH, a process of adding an additive such as a carboxylic acid is carried out. That is, an additive such as a carboxylic acid may be added during the dealcoholization and washing process (step 3), or a process of adding an additive such as a carboxylic acid separately may be introduced before the process (step 4) of pelletizing and drying the "hydrated EVOH" obtained after the dealcoholization and washing process (step 3). Among the conventional manufacturing processes of ethylene-vinyl alcohol copolymers, the drying process refers to a process of reducing the water content in the "hydrated EVOH" as described above.

[0020] The present invention is characterized in that, instead of the conventional dealcoholization and washing steps (step 3) for the EVOH solution obtained after the saponification reaction (step 2) using the above-mentioned alkaline catalyst, a dealcoholization step is carried out in which the alcohol solvent is removed from the saponification reaction product by an extraction step under supercritical carbon dioxide conditions.

[0021] In the method for producing the ethylene-vinyl alcohol copolymer of the present invention, the specific saponification reaction process and supercritical extraction process will be described in detail below.

[0022] Saponification reaction process First, in the present invention, an ethylene-vinyl acetate copolymer is reacted in the presence of an alkali catalyst to produce an ethylene-vinyl alcohol copolymer by a saponification reaction.

[0023] Specifically, the saponification reaction process is carried out by reacting an ethylene-vinyl acetate copolymer dispersed in an alcohol solvent while adding an alkaline catalyst solution dropwise. Preferably, the saponification reaction of the ethylene-vinyl acetate copolymer (EVAc) is carried out in two stages, and the alkaline catalyst is added dropwise continuously in each stage, rather than all at once. In this case, "dropwise addition" means that the solution is added dropwise.

[0024] When the alkali catalyst is continuously added dropwise, an ethylene-vinyl alcohol copolymer having a high degree of saponification can be obtained with a small amount of catalyst compared to the case where the catalyst is added all at once. Therefore, the washing process for removing the alkali catalyst by-products contained in the ethylene-vinyl alcohol copolymer produced after the saponification reaction is simplified, improving the efficiency and economy of the process and minimizing the amount of wastewater generated.

[0025] In the present invention, the ethylene-vinyl acetate copolymer, which is a reactant, may be a commercially available product or may be prepared by copolymerizing ethylene and vinyl acetate monomers. The ethylene-vinyl acetate copolymer may be a copolymer of ethylene and vinyl acetate with a monomer that can be copolymerized therewith. Examples of such monomers include α-olefins such as propylene, isobutylene, α-octene, and α-dodecene; unsaturated acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, and itaconic acid, salts thereof, anhydrides thereof, and mono- or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; ethylene sulfonic acid, Allylsulfonic acid , Methallyl Sulfonic Acid or salts thereof; vinyl monomers such as alkyl vinyl ethers, vinyl ketones, N-vinylpyrrolidone, vinyl chloride, and vinylidene chloride; and the like.

[0026] The ethylene content of the ethylene-vinyl acetate copolymer can be appropriately adjusted depending on the physical properties of the desired ethylene-vinyl alcohol copolymer. In one embodiment, the ethylene content of the ethylene-vinyl acetate copolymer can be 20 mol% or more, 25 mol% or more, or 30 mol% or more, and 40 mol% or less, 35 mol% or less, or 33 mol% or less. When the ethylene content of the ethylene-vinyl acetate copolymer satisfies the above range, the produced ethylene-vinyl alcohol can have high processability and excellent gas barrier properties. The ethylene content of the ethylene-vinyl acetate copolymer can be adjusted depending on the physical properties of the desired ethylene-vinyl alcohol copolymer. 1 It is calculated from the peak integral ratio of H-NMR data.

[0027] The weight average molecular weight of the ethylene-vinyl acetate copolymer is not particularly limited, but for example, it is 8,000 g / mol or more, 10,000 g / mol or more, or 12,000 g / mol or more, or 20,000 g / mol or more, or 50,000 g / mol or more, or 100,000 g / mol or more, or 150,000 g / mol or more, or 180,000 g / mol or more, 200,000 g / mol or more, or 220,000 g / mol or more, and 290,000 g / mol or more. In one embodiment, the molecular weight may be 100,000 g / mol or less, 270,000 g / mol or less, or 260,000 g / mol or less, or 240,000 g / mol or less, or 200,000 g / mol or less, or 150,000 g / mol or less, or 100,000 g / mol or less, or 80,000 g / mol or less, or 50,000 g / mol or less, or 30,000 g / mol or less, or 25,000 g / mol or less, 20,000 g / mol or less, or 18,000 g / mol or less. The ethylene-vinyl alcohol copolymer obtained by the saponification reaction of the ethylene-vinyl acetate copolymer satisfying the above weight average molecular weight satisfies the range of a weight average molecular weight of 120,000 g / mol or more, 130,000 g / mol or more, or 140,000 g / mol or more, and 180,000 g / mol or less, 170,000 g / mol or less, or 160,000 g / mol or less. The weight average molecular weight of the ethylene-vinyl acetate copolymer and the ethylene-vinyl alcohol copolymer can be measured by gel permeation chromatography (GPC) using styrene as a standard.

[0028] The alcohol solvent may be any solvent generally used in the saponification reaction of ethylene-vinyl acetate copolymer, without limitation, for example, lower alcohol solvents such as methanol, ethanol, propanol, isopropanol, or butanol, preferably methanol.

[0029] The alkaline catalyst may be at least one selected from the group consisting of alkaline metal hydroxides and alcoholates, such as sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium methylate, sodium ethylate, potassium methylate, and lithium methylate. From the standpoint of ease of storage and handling of the catalyst (in the case of sodium methoxide, it is necessary to block contact with air, and a glove box or the like is required when handling, and the catalyst is denatured when exposed to air), it is preferable to use sodium hydroxide or potassium hydroxide.

[0030] Specifically, the saponification reaction of the ethylene-vinyl acetate copolymer (EVAc) is carried out in two stages, and the alkaline catalyst solution is not added all at once, but is added dropwise in each stage continuously.

[0031] As an example, the saponification reaction of the ethylene-vinyl acetate copolymer (EVAc) may include a first saponification reaction step in which a first alkali catalyst is added dropwise to an ethylene-vinyl acetate copolymer dispersed in an alcohol solvent while reacting the copolymer; and a second saponification reaction step in which a second alkali catalyst is added dropwise to the first saponification reaction mixture while reacting the copolymer.

[0032] The first and second saponification reaction steps may be carried out consecutively, i.e., immediately after the completion of the first saponification reaction step, a second alkaline catalyst solution may be added dropwise to the reaction mixture to carry out the second saponification reaction.

[0033] The first and second alkaline catalysts may be the same or different, and it is preferable to use the same material as the first and second alkaline catalysts. The total amount of the alkali catalyst used may be 0.01 mol or more, or 0.015 mol or more, and less than 0.03 mol, or 0.02 mol or less, per mol of vinyl acetate units in the ethylene-vinyl acetate copolymer.

[0034] In order to produce an ethylene-vinyl alcohol copolymer having a high degree of saponification by the conventional method, 0.03 moles or more of vinyl acetate units are required per mole of vinyl acetate units. alkali A catalyst was previously required, but the production method of the present invention makes it possible to alkali It is possible to produce an ethylene-vinyl alcohol copolymer having a high degree of saponification while reducing the amount of catalyst used. However, if the total amount of alkali catalyst used is less than 0.01 mol, the saponification reaction is too slow, so it is preferable to satisfy the above amount of catalyst used.

[0035] In addition, within the range satisfying the above total usage amount, the first alkali catalyst and the second alkali catalyst can be used in an amount of 0.0025 mol or more, or 0.005 mol or more, and 0.02 mol or less, or 0.01 mol or less, per 1 mol of vinyl acetate units in the ethylene-vinyl acetate copolymer.

[0036] The first and second alkali catalysts can be used in a molar ratio of 1:1 to 1:4, or in a molar ratio of 1:1 to 1:2. In this way, the amount of the second alkali catalyst used is equal to or greater than the amount of the first alkali catalyst used, thereby producing an ethylene-vinyl alcohol copolymer having a higher degree of saponification.

[0037] The alkali catalysts, for example, the first and second alkali catalysts, are added dropwise to the ethylene-vinyl acetate copolymer dispersion in the form of a solution. In this case, the above-mentioned alcohol solvents can be used as the solvent, and it is preferable to use the same one as that used in preparing the ethylene-vinyl acetate copolymer dispersion. The concentrations of the alkali catalyst solutions may be the same or different from each other, and can be adjusted according to the concentration of the ethylene-vinyl acetate copolymer dispersion and the desired dripping speed of the alkali catalyst solutions.

[0038] For example, in the first saponification step, an ethylene-vinyl acetate copolymer is first dispersed in an alcohol solvent to prepare a dispersion, and a first alkali catalyst is then added dropwise thereto to carry out the saponification reaction. The amount of the alcohol solvent used to prepare the ethylene-vinyl acetate copolymer dispersion can be appropriately adjusted depending on the type of alcohol solvent, the type of ethylene-vinyl acetate copolymer, the concentration of the alkaline catalyst solution, etc. For example, the alcohol solvent can be used in a range of 100 parts by weight to 1000 parts by weight, or 200 parts by weight or more, or 300 parts by weight or more, and 800 parts by weight, 700 parts by weight, or 500 parts by weight or less, relative to 100 parts by weight of the ethylene-vinyl acetate copolymer, but is not limited thereto.

[0039] Meanwhile, the dripping rate of the alkaline catalyst solution in the saponification reaction process can be adjusted according to the reaction time. For example, the dripping rate of the alkaline catalyst solution is 1.0*10 per minute per 1 mole of vinyl acetate unit of ethylene-vinyl acetate copolymer. -5 Mol ~ 13 * 10 -5 When the dropping rate is within the above range, the saponification reaction time is not excessively long, and the reaction efficiency is increased, so that an ethylene-vinyl alcohol copolymer having a high degree of saponification can be produced.

[0040] From this viewpoint, the alkali catalyst solution is added dropwise at a rate of 2.0*10 per minute per mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer. -5 mol or more, or 3.0*10 -5 mol or more, or 4.0*10 -5 mol or more and 11.0*10 -5 Sub-molar, or 10.0*10 -5 Molar or less, or 9.0*10 -5 It is preferable to carry out the reaction so that the amount is less than 1 molar.

[0041] For example, the first alkaline catalyst solution is added dropwise at a rate of 1.0*10 per minute per mole of vinyl acetate unit of ethylene-vinyl acetate copolymer. -5 Molar or more, or 2.0*10 -5 mol or more, or 3.0*10 -5 mol or more, or 4.0*10-5 More than or equal to 13*10 -5 Molar or less, 11.0*10 -5 Sub-molar, or 10.0*10 -5 Molar or less, or 9.0*10 -5 It is preferable to make it so that it is less than 1 mole.

[0042] In addition, the second alkaline catalyst solution is added dropwise at a rate of 2.0*10 per minute per mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer. -5 mol or more, or 3.0*10 -5 mol or more, or 4.0*10 -5 mol or more and 8.0*10 -5 Molar or less, or 7.0*10 -5 Molar or less, 6.0*10 -5 It is preferable to make it so that it is less than 1 mole.

[0043] As long as the above range is satisfied, the drop speed of the second alkaline catalytic solution may be equal to or faster than the drop speed of the first alkaline catalytic solution, which is preferable because the reaction efficiency is increased and an ethylene-vinyl alcohol copolymer with a high degree of saponification can be obtained.

[0044] The temperature of the saponification reaction step may be 40° C. or more, 50° C. or more, or 60° C. or more, and 120° C. or less, 110° C. or less, or 100° C. or less. If the reaction temperature is less than 40° C., the saponification reaction rate becomes excessively slow, and if it exceeds 120° C., side reactions are likely to occur, so it is preferable to satisfy the above range.

[0045] As an example, the temperature of the first saponification reaction step is preferably 40°C or more, or 50°C or more, or 60°C or more, and 120°C or less, or 110°C or less, or 100°C or less.

[0046] The temperature of the second saponification reaction step is preferably 60°C or more, or 70°C or more, or 80°C or more, and 120°C or less, or 110°C or less, or 100°C or less.

[0047] As long as the temperature satisfies the above range, the temperature of the second saponification reaction step may be the same as or higher than the temperature of the first saponification reaction step, which is preferred because it increases the reaction efficiency and produces an ethylene-vinyl alcohol copolymer with a high degree of saponification.

[0048] Meanwhile, the pressure of the saponification reaction process may be 1 bar or more and 5 bar or less, or 4.5 bar or less, or 4 bar or less, or 3.5 bar or less, or 3.2 bar or less, or 3 bar or less. If the reaction pressure is less than 1 bar, the saponification reaction rate becomes too slow, and therefore, in terms of reducing equipment costs and ensuring process safety when implementing an actual process, the process is carried out at 5 bar or less.

[0049] As an example, the pressure in the first saponification reaction stage may be 1 bar or more and 2.5 bar or less, or 2 bar or less, or 1.8 bar or less, or 1.5 bar or less, or 1.2 bar or less.

[0050] Also, the pressure in the second saponification reaction step may be 1 bar or more, or 1.2 bar or more, or 1.5 bar or more, or 2 bar or more, or 2.8 bar or more, or 2.5 bar or more, and 5 bar or less, or 4.5 bar or less, or 4 bar or less, or 3.2 bar or less, or 3 bar or less. The temperature of the second saponification reaction step is preferably 60°C or more, 70°C or more, or 80°C or more, and 120°C or less, 110°C or less, or 100°C or less.

[0051] As long as the above range is satisfied, the pressure in the second saponification reaction step may be the same as or higher than the pressure in the first saponification reaction step, which is preferred because it increases the reaction efficiency and produces an ethylene-vinyl alcohol copolymer with a high degree of saponification. The saponification reaction may be carried out under an inert gas atmosphere, and in order to increase the conversion rate, the reaction may be carried out while continuously discharging the by-product methyl acetate out of the system.

[0052] For example, the first saponification reaction step may be terminated when the dropwise addition of the first alkaline solution is completed. In other words, the dropwise addition of the first alkaline solution may be performed continuously from the start to the end of the first saponification reaction. By adding the first alkaline solution dropwise throughout the reaction time in this manner, the conversion rate of EVAc to EVOH may be increased while minimizing side reactions.

[0053] After the first saponification reaction is completed, a second alkali catalyst solution, which is separately prepared, is added dropwise to the reaction mixture to carry out a second saponification reaction. The first and second saponification reaction steps may be carried out consecutively, i.e., immediately after the completion of the first saponification reaction step, a second alkaline catalyst solution may be added dropwise to the reaction mixture to carry out the second saponification reaction.

[0054] As with the first saponification reaction step, the second saponification reaction step may be terminated when the dropwise addition of the second alkaline solution is completed. That is, the dropwise addition of the second alkaline solution may be performed continuously from the start to the end of the second saponification reaction. By adding the second alkaline solution dropwise throughout the reaction time, the conversion rate of EVAc to EVOH can be increased while minimizing side reactions.

[0055] According to the above-mentioned manufacturing method, an ethylene-vinyl alcohol copolymer having a high saponification degree of 99% or more can be obtained using a small amount of alkali catalyst compared to the conventional batch-type saponification process of ethylene-vinyl acetate copolymer. The ethylene-vinyl alcohol copolymer has a high saponification degree and therefore exhibits excellent gas barrier properties, making it useful for food packaging applications.

[0056] Specifically, the ethylene-vinyl alcohol copolymer produced by the above-mentioned production method may have a saponification degree of 99% or more, or 99% to 99.9%; an ethylene content of 20 mol% or more, or 25 mol% or more, or 27 mol% or more, or 30 mol% or more, and 60 mol% or less, or 50 mol% or less, or 48 mol% or less, or 35 mol% or less; and a weight average molecular weight of 120,000 g / mol or more, or 130,000 g / mol or more, or 140,000 g / mol or more, and 180,000 g / mol or less, or 170,000 g / mol or less, or 160,000 g / mol or less. Such an ethylene-vinyl alcohol copolymer may exhibit excellent moldability and gas barrier properties.

[0057] As an example, the saponification degree of the ethylene-vinyl alcohol copolymer is 1 It can be calculated from the peak integral number ratio of H-NMR data. The specific measurement method is as shown in the test examples.

[0058] In addition, the ethylene-vinyl alcohol copolymer may have a yellowness index (YI) of 13 or less, or 12 or less, or 11 or less, or 10 or less, or 9.8 or less, or 9.5 or less, or 9 or less, or 8.9 or less, or 8.5 or less, or 8.2 or less, or 8 or less, or 7.9 or less, thereby exhibiting excellent hue characteristics.

[0059] For example, the yellowness of the ethylene-vinyl alcohol copolymer can be measured using a color difference meter (UltraScan VIS, Hunterlab). A specific measurement method is as shown in the test examples.

[0060] Supercritical extraction process In the method for producing the ethylene-vinyl alcohol copolymer of the present invention, the ethylene-vinyl alcohol copolymer obtained by the above-mentioned saponification reaction is subjected to a supercritical extraction process under optimized conditions, and by-products such as an alcohol solvent are effectively removed, so that a post-treatment process, for example, a dipping process using a carboxylic acid-containing aqueous solution can be immediately carried out without an additional washing process.

[0061] In particular, the present invention is characterized in that, instead of carrying out the conventional dealcoholization and washing processes on the ethylene-vinyl alcohol copolymer obtained by the saponification reaction using the above-mentioned alkali catalyst, an extraction process is carried out under supercritical carbon dioxide conditions to extract the alcohol solvent contained in the saponification reaction product.

[0062] Specifically, in the present invention, after the above-mentioned saponification reaction is performed, the saponification reaction product containing the ethylene-vinyl alcohol copolymer is introduced into a supercritical extractor and CO 2 can be injected to extract the alcohol.

[0063] Such supercritical extraction processes involve the extraction of hydrous polymers or water (H 2 Since it is not used to remove water from compounds containing excessive amounts of CO, it is difficult to apply it to the process of drying "water-containing EVOH" in the conventional manufacturing process of ethylene-vinyl alcohol copolymers. 2 After passing through the supercritical extractor, the fluid is finally recondensed and cooled to return to a liquefied state, but if there is an excess of water, the water that is not 100% condensed in the separator is converted into CO 2 CO flows into the supercritical equipment line and is cooled 2 This causes the EVOH to freeze, clogging the line and generating abnormally high pressure, which can lead to the risk of a high-pressure explosion and equipment failure, making it difficult to use the "water-containing EVOH" in the drying process to reduce the moisture content.

[0064] The supercritical carbon dioxide conditions in the extraction step of the present invention are 2Specifically, the present invention is directed to a method for effectively removing catalyst by-products contained in the ethylene-vinyl alcohol copolymer after the saponification process without deteriorating the physical properties of the ethylene-vinyl alcohol copolymer, thereby increasing the recovery rate of the alcohol solvent. 2 The pressure is between 80 bar and 150 bar, and the temperature is between 40°C and 60°C.

[0065] Specifically, the CO injected into the supercritical extractor 2 The pressure may be 80 bar or more, more specifically 85 bar or more, or 90 bar or more, or 95 bar or more, or 98 bar or more, or 100 bar or more, or 105 bar or more, or 110 bar or more, or 115 bar or more, or 120 bar or more, from the viewpoint of increasing the extraction efficiency of the alcohol solvent. However, from the viewpoint of preventing the deterioration of the physical properties of the ethylene-vinyl alcohol copolymer, it may be 150 bar or less, more specifically 148 bar or less, or 145 bar or less, or 143 bar or less, or 140 bar or less. In addition, the temperature of the supercritical extraction step may be 40° C. or more, more specifically 42° C. or more, or 43° C. or more, or 45° C. or more, from the viewpoint of increasing the extraction efficiency of the alcohol solvent. However, from the viewpoint of preventing the deterioration of the physical properties of the ethylene-vinyl alcohol copolymer, it may be 60° C. or less, more specifically 55° C. or less, or 53° C. or less, or 52° C. or less. Here, the CO 2 If the pressure and temperature of the CO2 extractor are too high, 2 The flow rate increases, which can cause problems such as an increase in the capacity of devices such as separators and a corresponding increase in the energy required for heating and cooling.

[0066] Specifically, the method may further include, prior to the supercritical extraction step, a step of gelling or solidifying the saponification reaction product including the ethylene-vinyl alcohol copolymer from the saponification reaction mixture.

[0067] As an example, the method for producing an ethylene-vinyl alcohol copolymer of the present invention includes a saponification step of reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst to produce an ethylene-vinyl alcohol copolymer;

[0068] gelling or solidifying a saponification reaction product comprising the ethylene-vinyl alcohol copolymer from the saponification reaction mixture; and The gelled or solidified saponification reaction product containing the ethylene-vinyl alcohol copolymer is introduced into a supercritical extractor and CO 2 a supercritical extraction step in which alcohol is extracted by injecting

[0069] At this time, the conditions of the supercritical carbon dioxide are: 2 The pressure is 80 bar or more and 150 bar or less, and the temperature is 40° C. or more and 60° C. or less, and the specific conditions for supercritical carbon dioxide are as described above.

[0070] In this case, the gelation or solidification method is performed by cooling the saponification reaction product to about 5°C or less or about -10°C to about 5°C or less during or after the recovery of the saponification reaction product. For example, the saponification reaction product may be cooled in a transfer pipe to about 5°C or less or about -10°C to about 5°C or less during the recovery of the saponification reaction product and discharged in the form of strands, or the saponification reaction product may be cooled to about 5°C or less or about -10°C to about 5°C or less for about 3 hours to 12 hours after the recovery of the saponification reaction product and gelled or solidified in the form of cakes. For example, the strands are cylindrical, and the cakes are rectangular. However, in terms of increasing the extraction efficiency of the alcohol solvent, it is preferable to cool the saponification reaction product to about -10°C to about 5°C or less to gel or solidify it in the form of strands, and then extract the alcohol solvent under supercritical carbon dioxide conditions.

[0071] Specifically, in the supercritical extraction step, the saponification reaction product has an external surface area per volume of about 5 cm2 / cm 3 More than or about 5cm 2 / cm 3 More than about 50cm 2 / cm 3 More specifically, the external surface area per volume of the saponification reaction product may be less than about 5 cm 2 / cm 3 or more, or about 6 cm 2 / cm 3 or more, or about 8 cm 2 / cm 3 or more, or about 9 cm 2 / cm 3 or more, or about 10 cm 2 / cm 3 or more, or about 11 cm 2 / cm 3 or more, or about 12 cm 2 / cm 3 or more, or about 13 cm 2 / cm 3 However, taking into consideration the actual process efficiency of gelling or solidifying the saponification reaction product, it may be about 45 cm 2 / cm 3 Less than or equal to 40cm 2 / cm 3 Less than or equal to 35cm 2 / cm 3 Less than or equal to 30cm 2 / cm 3 Less than or equal to 28cm 2 / cm 3 Less than or equal to 25cm 2 / cm 3 Less than or equal to 22cm 2 / cm 3 Less than or equal to 20cm 2 / cm 3 Less than or equal to 18cm 2 / cm 3 Less than or equal to 16cm 2 / cm 3 Less than or equal to 15cm 2 / cm 3 In one example, the external surface area per volume of the saponification reaction product may be about 9 cm 2 / cm 3~about 20cm 2 / cm 3 , or about 10 cm 2 / cm 3 ~Approx. 18cm 2 / cm 3 , or about 10 cm 2 / cm 3 ~Approx. 15cm 2 / cm 3 , or about 10 cm 2 / cm 3 ~Approx. 12cm 2 / cm 3 The external surface area per volume of the saponification reaction product may be measured by various methods known to measure the volume and external surface area of ​​a polymer, and may be applied without particular limitation. For example, when the saponification reaction product is in the form of a strand or cake, the length, diameter, width, height, etc., which are measured by appearance, may be measured, and the volume and surface area may be calculated based on the measured length, diameter, width, height, etc.

[0072] On the other hand, in the present invention, the ethylene-vinyl alcohol copolymer obtained by the above-mentioned saponification reaction is subjected to a supercritical extraction process using CO 2 The method may further include a step of filtering the solid ethylene-vinyl alcohol copolymer from the extract discharged from the supercritical extractor into which the ethylene-vinyl alcohol copolymer is injected, using a filtering device. The filtering device is not limited as long as it is a device capable of filtering the solid ethylene-vinyl alcohol copolymer, and may be, for example, a filter. The specifications of the filter are not particularly limited.

[0073] In one embodiment of the present invention, the method may further include a step of subjecting the extract filtered by the filtration device to gas-liquid separation using a separator. The separator is a device for separating carbon dioxide and an alcohol solvent from the extract discharged from the supercritical extractor, and may be, for example, a gas-liquid separator including a flash separator or a multi-stage distiller.

[0074] The separator may separate and discharge gaseous carbon dioxide through the upper part of the separator device, and separate and discharge liquid alcohol solvent and other components through the lower part of the device. The carbon dioxide separated and discharged from the upper part may be condensed into a liquid form and recycled to the supercritical extractor in a subsequent process, and the alcohol solvent discharged in a liquid form may be reused as a raw material for the saponification process after undergoing a purification process. An additional gas-liquid separation process may also be performed before the purification process.

[0075] Meanwhile, the supercritical extraction process can exhibit a high recovery rate of the alcohol solvent of 88% by weight or more, and preferably 90% by weight or more, or 92% by weight or more, or 93% by weight or more, or 95% by weight or more, or 96% by weight or more, or 97% by weight or more, or 98% by weight or more, or 98.5% by weight or more, or 99% by weight or more, or 99.5% by weight or more, or 99.9% by weight or more.

[0076] Specifically, the recovery rate of the alcohol solvent was measured by measuring the weight (A) of the ethylene-vinyl alcohol copolymer (EVOH) before supercritical extraction, the weight (B) of the EVOH after supercritical extraction, and the weight (C) of the alcohol solvent recovered by the supercritical extraction process in grams (g) after the saponification reaction of the ethylene-vinyl acetate copolymer in the presence of the above-mentioned alkali catalyst, and then measuring the recovery rate (%) of the alcohol solvent in the supercritical extraction process after the saponification reaction according to the following formula 1.

[0077] [Formula 1] Recovery rate of alcohol solvent in supercritical extraction process (%) = C / (AB) x 100 In the above formula 1, A is the weight (g) of ethylene-vinyl alcohol copolymer (EVOH) before the supercritical extraction process; B is the weight (g) of ethylene-vinyl alcohol copolymer (EVOH) after the supercritical extraction process; C is the weight (g) of alcohol solvent recovered from the supercritical extraction process.

[0078] In addition, the product containing the ethylene-vinyl alcohol copolymer obtained after the supercritical extraction process may have an alcohol solvent content of 12 wt% or less, preferably 10 wt% or less, 8 wt% or less, 10 wt% or less, 8 wt% or less, 7 wt% or less, 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1.5 wt% or less, 1 wt% or less, 0.5 wt% or less, or 0.1 wt% or less, based on the total weight of the product. More preferably, the ethylene-vinyl alcohol copolymer obtained after the extraction step and the product containing the same may have substantially no alcohol solvent.

[0079] Meanwhile, the removal rate of the alkaline component contained in the catalyst used in the saponification reaction by the supercritical extraction process may be 25% or more, and preferably 26% or more, or 27% or more, or 28% or more, or 29% or more, or 30% or more, or 31% or more, or 33% or more, or 35% or more, or 40% or more, or 45% or more, or 50% or more. Specifically, the removal rate of the alkaline component is measured by measuring the content (a) of the alkaline component in ethylene-vinyl alcohol copolymer (EVOH) before supercritical extraction and the content (b) of the alkaline component in EVOH after extraction, respectively, and calculating the removal rate (%) of the alkaline component according to the following formula 2.

[0080] [Formula 2] Alkaline component removal rate (%) = 100 x (1-b / a) In the formula 2, a is the residual amount (ppm) of catalytic alkali component contained in ethylene-vinyl alcohol copolymer (EVOH) before the supercritical extraction process; b is the residual amount (ppm) of catalytic alkali component contained in EVOH after the supercritical extraction process.

[0081] The residual amount (ppm) of the catalytic alkaline component contained in the ethylene-vinyl alcohol copolymer (EVOH) obtained by the supercritical extraction process, i.e., the residual amount (ppm) of the alkaline component contained in the catalyst used in the saponification reaction, can be measured using inductively coupled plasma optical emission spectrometry (ICP-OES), and specifically, can be measured under the following conditions. - Pretreatment: microwave digestion, 250℃, 30min heating, 250℃, 15min maintenance (90bar) - ICP-OES analysis conditions: RF power(W):1300 Plasma Gas Flow (L / min): 15 Aux.Gas flow (L / min):0.20 Neb.Gas flow (L / min):0.80 Internal Standard: Sc

[0082] In addition, the residual amount of the alkali component in the product containing the ethylene-vinyl alcohol copolymer obtained after the supercritical extraction process, i.e., the residual amount of the alkali component contained in the catalyst used in the saponification reaction relative to the total weight of the product, may be 100,000 ppm or less, preferably 9000 ppm or less, or 8700 ppm or less, or 7000 ppm or less, or 5000 ppm or less, or 3000 ppm or less, or 2500 ppm or less, or 2200 ppm or less, or 2100 ppm or less, or 2000 ppm or less, or 1500 ppm or less, or 1000 ppm or less, or 800 ppm or less, or 500 ppm or less, or 300 ppm or less, or 100 ppm or less. More preferably, the ethylene-vinyl alcohol copolymer obtained after the extraction step and the product containing the same may not substantially contain the alkali component contained in the catalyst used in the saponification reaction.

[0083] As an example, in the present invention, the ethylene-vinyl alcohol copolymer obtained by the above-mentioned saponification reaction is put into a supercritical extractor and CO2 After injecting CO to control the inside of the extractor at 50°C and 150 bar, a steady phase was run for 20 minutes with additional CO 2 The temperature and pressure were maintained without CO flow, and then the CO circulation phase was repeated for 20 min. 2 is continuously injected at a rate of 6.5 L / min at 50° C. and 150 bar, and this can be repeated three or more times to carry out the supercritical extraction process for a total of 120 minutes.

[0084] The supercritical extraction process according to the present invention does not use steam or water and effectively recovers an alcohol solvent such as methanol, so that the alcohol solvent can be reused in the saponification reaction without the need for an additional process of separating water and the alcohol solvent when reusing the alcohol solvent, greatly improving the overall process efficiency.

[0085] In particular, according to the present invention, the deterioration of the physical properties of the ethylene-vinyl alcohol copolymer produced by the saponification reaction can be minimized by carrying out the supercritical extraction process under the conditions of the pressure and temperature ranges as described above.

[0086] Therefore, the ethylene-vinyl alcohol copolymer obtained after carrying out the supercritical extraction process according to the present invention may have a degree of saponification of 99% or more, or 99% to 99.9%; an ethylene content of 20 mol% or more, or 25 mol% or more, or 27 mol% or more, or 30 mol% or more and 60 mol% or less, or 50 mol% or less, or 48 mol% or less, or 35 mol% or less; and a weight average molecular weight of 120,000 g / mol or more, or 130,000 g / mol or more, or 140,000 g / mol or more and 180,000 g / mol or less, or 170,000 g / mol or less, or 160,000 g / mol or less. In addition, the ethylene-vinyl alcohol copolymer has a yellowness index (YI) of 13 or less, or 12 or less, or 11 or less, or 10 or less, or 9.8 or less, or 9.5 or less, or 9 or less, or 8.9 or less, or 8.5 or less, or 8.2 or less, or 8 or less, or 7.9 or less, thereby exhibiting excellent color characteristics. Here, the saponification degree and yellowness of the ethylene-vinyl alcohol copolymer can be measured by the method described in the saponification reaction step, and the specific measurement method is as shown in the test examples.

[0087] Post-processing stage Meanwhile, in the method for preparing the ethylene-vinyl alcohol copolymer according to the present invention, after the above-mentioned saponification reaction process and supercritical extraction process, a post-treatment step of immersing in an additive-containing aqueous solution and drying may be additionally performed. Specifically, after performing the supercritical extraction process, the method may further include a step of immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing a carboxylic acid, and then drying the water.

[0088] As an example, the method for producing an ethylene-vinyl alcohol copolymer of the present invention includes a saponification step of reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst to produce an ethylene-vinyl alcohol copolymer; extracting the alcohol solvent contained in the saponification reaction product under supercritical carbon dioxide conditions; and After the supercritical extraction process, the method may further include a step of immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing a carboxylic acid, and then drying the water.

[0089] As another example, the method for producing an ethylene-vinyl alcohol copolymer of the present invention includes the steps of: reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst to produce an ethylene-vinyl alcohol copolymer; gelling or solidifying a saponification reaction product comprising the ethylene-vinyl alcohol copolymer from the saponification reaction mixture; extracting the alcohol solvent contained in the gelled or solidified saponification reaction product under supercritical carbon dioxide conditions; and After the supercritical extraction process, the method may further include a step of immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing a carboxylic acid, and then drying the water.

[0090] At this time, the conditions of the supercritical carbon dioxide are: 2 The pressure is 80 bar or more and 150 bar or less, and the temperature is 40° C. or more and 60° C. or less, and the specific conditions for supercritical carbon dioxide are as described above. Specifically, the aqueous carboxylic acid solution may contain acetic acid. The concentration of the carboxylic acid-containing aqueous solution may be 0.01% by weight to 1% by weight.

[0091] The immersion step is carried out once to five times at 20° C. to 50° C. for 10 minutes to 60 minutes each time. As an example, after the supercritical extraction step, the ethylene-vinyl alcohol copolymer can be immersed in an aqueous solution containing 0.01% by weight to 1% by weight of a carboxylic acid 1 to 5 times for 10 to 60 minutes each time, stirred, and then dried.

[0092] The step of drying the water after immersion in the carboxylic acid-containing aqueous solution described above may be carried out at 40° C. to 100° C. for 3 hours to 50 hours, and drying may be performed once or multiple times. The moisture drying step may be carried out so that the moisture content is less than 5% or less than 1%, more preferably less than 0.5%.

[0093] In the following, preferred examples are presented to deepen understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope of the scope and technical idea of ​​the present invention. It goes without saying that such changes and modifications fall within the scope of the appended claims.

[0094] Example 1 1-1.Saponification reaction process A mixture containing 100 parts by weight of ethylene-vinyl acetate copolymer (EVAc) with an ethylene content of 32 mol% and 400 parts by weight of methanol (MeOH) (total solid content 20%) was placed in a saponification reactor, and 20 parts by weight of a methanol solution of sodium hydroxide (16 g / L) (sodium hydroxide / vinyl acetate unit = 0.01 / 1, molar ratio) in a state of 1% dilution with MeOH, with 0.27 wt% NaOH based on the EVAc solid content, was continuously added dropwise to the saponification reactor at 60°C and normal pressure (about 1 bar) for 2.5 hours to carry out the saponification reaction. At this time, the dropping rate was 1.4 x 10 moles of sodium hydroxide per vinyl acetate unit of EVAc per second. -6 As described above, while continuously feeding the sodium hydroxide methanol solution (NaOH / MeOH solution) into the reactor, nitrogen gas was blown into the reactor to remove the by-product methyl acetate together with methanol from the system, and the first saponification reaction (reactor temperature: 60° C., reactor pressure: normal pressure, reaction time: 2.5 hours) was carried out.

[0095] Then, 20 parts by weight of a methanol solution of sodium hydroxide (16 g / L) (sodium hydroxide / vinyl acetate unit = 0.01 / 1, molar ratio) was added dropwise to the reaction mixture for 3 hours, and the second saponification reaction was carried out. The rate of addition was 9.3 x 10 moles of sodium hydroxide per vinyl acetate unit of EVAc per second. The sodium hydroxide was added dropwise to the reaction mixture for 3 hours. The sodium hydroxide was added dropwise to the vinyl acetate unit of EVAc for 3 hours. The second saponification reaction was carried out.-7 As described above, the methanol solution of sodium hydroxide was continuously fed into the reactor while nitrogen gas was blown into the reactor, and the by-product methyl acetate was removed from the system together with methanol to carry out the second saponification reaction (reactor temperature: 90°C, reactor pressure: 3 bar, reaction time: 3 hours).

[0096] After the addition of NaOH was completed, the reaction was continued for 1 hour under the above-mentioned conditions (reactor temperature: 90° C., reactor pressure: 3 bar).

[0097] Then, 120 parts by weight of an aqueous solution of acetic acid (9 g / L) (acetic acid / sodium hydroxide = 1 / 1, molar ratio) was added to the reaction mixture, which was the same molar equivalent as NaOH, and the reaction was stopped by neutralizing it with stirring for 30 minutes, and the reaction solution was concentrated at 60-70 °C until the total solid content (TSC) was 15-20%. At this time, an EVOH methanol / aqueous solution consisting of 60 parts by weight of ethylene-vinyl alcohol copolymer (EVOH), 120 parts by weight of methanol, and 120 parts by weight of water was obtained. The EVOH solution was cooled to 5 °C during line transfer to solidify it and discharged as a cylindrical ethylene-vinyl alcohol strand (EVOH strand) with a diameter of about 2 mm. At this time, the external surface area per volume of the ethylene-vinyl alcohol strand (EVOH strand) was 10-12 cm 2 / cm 3 It was.

[0098] 1-2.Supercritical extraction process Then, 64g of the EVOH strand (extraction process after saponification reaction) before The weight of EVOH, A) was put into a 70L supercritical extractor and CO 2 After injecting CO to control the inside of the extractor at 50°C and 150 bar, a steady phase was run for 20 minutes with additional CO 2 The temperature and pressure were maintained without flowing CO (Steady phase: CO 2 No injection, CO from extractor to separator 2Then, again for 20 minutes, a CO circulation phase was performed. 2 was continuously injected at a rate of 6.5 L / min at 50 °C and 150 bar (circulation stage: CO 2 Reservoir → Extractor → Separator → CO 2 CO in the reservoir 2 This was repeated three times to perform the supercritical extraction process for a total of 120 minutes. Then, the carbon dioxide and the extract were separated into gas and liquid at 50 bar and 40°C using a separator connected to the supercritical extractor, resulting in the gaseous CO 2 and liquid methanol were recovered. The amount of methanol recovered by the supercritical extraction process was 51.939 g (the weight of MeOH recovered after the extraction process, C). After that, the supercritical extractor was changed to normal pressure and temperature (about 20 to 23°C, about 1 bar), and the ethylene-vinyl alcohol copolymer (EVOH) that had completed the dealcohol extraction was recovered. At this time, the amount of EVOH was 11.8 g (the weight of EVOH after the extraction process, B).

[0099] 1-3. Post-treatment stage (immersion, drying) The EVOH thus obtained was immersed once in a 0.5% acetic acid solution for 1 hour, then immersed once in deionized water (DIW) for 1 hour, and extruded in an extruder at 90°C and 120 rpm (water content: about 25% by weight), and then dried under reduced pressure at 80°C for 16 hours to produce EVOH with a water content of 0.01% by weight.

[0100] Example 2 The saponification reaction step, the supercritical extraction step, and the immersion drying step as a post-treatment step were carried out in the same manner as in Example 1, and the supercritical carbon dioxide conditions in the supercritical extraction step were set to CO 2 The temperature and pressure were 40° C. and 100 bar to produce the EVOH of Example 2.

[0101] Example 3 The saponification reaction process, supercritical extraction process, and post-treatment process, immersion drying process, were carried out in the same manner as in Example 1. After the saponification reaction, neutralization, and concentration were completed, the EVOH solution was drained into a container or plate, cooled at -5°C for 6 hours, and solidified to obtain an external surface area of ​​6 to 8 cm per volume. 2 / cm 3 After obtaining the cubic EVOH cake, a supercritical extraction process was carried out to produce the EVOH of Example 3.

[0102] Comparative Example 1 The saponification reaction step, the supercritical extraction step, and the immersion drying step as a post-treatment step were carried out in the same manner as in Example 1, and the supercritical carbon dioxide conditions in the supercritical extraction step were set to CO 2 The temperature and pressure were set at 35° C. and 80 bar to produce the EVOH of Comparative Example 1.

[0103] Comparative Example 2 The saponification reaction step, the supercritical extraction step, and the immersion drying step as a post-treatment step were carried out in the same manner as in Example 1, and the supercritical carbon dioxide conditions in the supercritical extraction step were set to CO 2 The temperature and pressure were 80°C and 160 bar, and the comparative example 2 The company produced EVOH.

[0104] <Test Example> The ethylene-vinyl alcohol copolymers according to the above examples and comparative examples were measured for various physical properties by the following methods, and the measurement results are shown in Table 1 below. (1) Removal rate of MeOH by dealcoholization extraction process after saponification reaction In the examples and comparative examples, ethylene-vinyl acetate copolymer ( EVAc ) was subjected to a saponification reaction, and then in the dealcoholization extraction step, the weight of EVOH (A) measured before the supercritical extraction step, the weight of EVOH (B) measured after the supercritical extraction step, and the weight of the alcohol solvent (MeOH) (C) recovered by the supercritical extraction step were each measured in grams (g), and the MeOH recovery rate (%) in the dealcoholization extraction step after the saponification reaction was calculated according to the following formula 3. [Formula 3] MeOH recovery rate (%) in the dealcoholization supercritical extraction process = C / (AB) x 100

[0105] (2) Removal rate of residual alkaline components by dealcohol extraction process after saponification reaction In the examples and comparative examples, ethylene-vinyl acetate copolymer ( EVAc ) was subjected to a saponification reaction, and then a dealcohol extraction process was carried out. The removal rate of residual alkaline components such as Na was then measured under the following conditions.

[0106] Specifically, the content (a) of the alkaline component in ethylene-vinyl alcohol copolymer (EVOH) measured before the supercritical extraction process and the content (b) of the alkaline component in EVOH measured after the supercritical extraction process were measured in ppm, and the removal rate (%) of the alkaline component was calculated according to the following formula 4. [Formula 4] Alkaline component removal rate (%) = 100 x (1-b / a)

[0107] The content (ppm) of the above-mentioned alkaline component was measured by inductively coupled plasma optical emission spectrometry (ICP-OES), specifically under the following conditions. - Pretreatment: microwave digestion, 250℃, 30min heating, 250℃, 15min maintenance (90bar) - ICP-OES analysis conditions: RF power(W):1300 Plasma Gas Flow (L / min): 15 Aux. Gas flow(L / min):0.20 Neb. Gas flow (L / min): 0.80 Internal Standard: Sc

[0108] (3) Degree of saponification of ethylene-vinyl acetate copolymer EVOH 1The saponification degree (%) of the produced EVOH was calculated from the peak integral number ratio of the H-NMR data. in particular, 1 The integrals of the -OH peaks (δ4.05-4.72) derived from the vinyl alcohol unit and the -CH peaks derived from the vinyl acetate unit in the H-NMR data are shown in Table 1. 3 The integral value of the COO-peak (δ 1.99) was derived, and the percentage (%) of vinyl alcohol units relative to the total of vinyl alcohol units and vinyl acetate units was calculated to derive the degree of saponification.

[0109] (4) Yellowness index (YI) of ethylene-vinyl acetate copolymer The EVOH prepared in the examples and comparative examples was cut by a pelletizer to obtain EVOH pellets, and the pellets were placed in a measurement cell and the yellowness index (YI) was measured using a color difference meter (UltraScan VIS, Hunterlab).

[0110] [Table 1]

[0111] As shown in Table 1, the present invention Ria It was confirmed that ethylene-vinyl acetate copolymer is saponified in the presence of an alkali catalyst, and then the supercritical extraction process is carried out at optimal pressure and temperature ranges. This minimizes the generation of waste liquid without the need for complex equipment such as multi-stage distillation columns, pipe mixers, and water tanks, and effectively removes by-products such as catalyst residues, thereby efficiently obtaining ethylene-vinyl alcohol copolymer (EVOH) with a high degree of saponification without deterioration (yellowing).

[0112] Furthermore, a comparison of Examples 1, 2 and 3 shows that when the saponification reaction product is formed into a shape with a large surface area, such as a strand, a higher MeOH recovery rate can be achieved even under the same supercritical carbon dioxide conditions.

[0113] On the other hand, from the results of Comparative Examples 1 and 2, CO 2 When the pressure and temperature of 80 bar and 35 °C were applied, a significant drop in the recovery of MeOH was observed at 83%, and the recovery of CO 2 When the pressure and temperature were 160 bar and 80°C, it was confirmed that EVOH deteriorated and the yellowness index (YI) increased significantly to 15.2.

[0114] As described above, the present invention provides an excellent effect of significantly improving the overall process efficiency by performing supercritical extraction under optimized conditions for ethylene-vinyl alcohol copolymer, effectively recovering alcohol solvent such as methanol without using steam or water, without deteriorating the physical properties of ethylene-vinyl alcohol copolymer, and reusing the alcohol solvent in the saponification reaction without adding a process for separating water and the alcohol solvent.

Claims

1. a saponification step in which an ethylene-vinyl acetate copolymer is reacted in the presence of an alkaline catalyst to produce an ethylene-vinyl alcohol copolymer; and extracting the alcohol solvent contained in the saponification reaction product under supercritical carbon dioxide conditions; Including, The supercritical carbon dioxide conditions are ２ The pressure is 80 bar or more and 150 bar or less, and the temperature is 40° C. or more and 60° C. or less.

2. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the saponification reaction step is carried out by reacting an ethylene-vinyl acetate copolymer dispersed in an alcohol solvent while adding an alkali catalyst solution dropwise thereto.

3. The method for producing an ethylene-vinyl alcohol copolymer according to claim 2, wherein the alcohol solvent is at least one selected from the group consisting of methanol, ethanol, propanol, and butanol.

4. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the alkaline catalyst is lithium hydroxide, sodium hydroxide, or potassium hydroxide.

5. 2. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the total amount of the alkali catalyst used is 0.01 mol or more and less than 0.03 mol per mol of vinyl acetate units in the ethylene-vinyl acetate copolymer.

6. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the temperature in the saponification reaction step is 40° C. or higher and 120° C. or lower.

7. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the pressure in the saponification reaction step is 1 bar or more and 5 bar or less.

8. 2. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, further comprising: gelling or solidifying a saponification reaction product comprising the ethylene-vinyl alcohol copolymer from the saponification reaction mixture.

9. The supercritical carbon dioxide conditions are ２ The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the pressure is 100 bar or more and 150 bar or less, and the temperature is 40° C. or more and 50° C. or less.

10. 2. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, wherein the product containing the ethylene-vinyl alcohol copolymer obtained after the extraction step has an alcohol solvent content of 15 wt% or less based on the total weight of the product.

11. The method for producing an ethylene-vinyl alcohol copolymer according to claim 1, further comprising the step of: immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing a carboxylic acid after the extraction step, and then drying the water.

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