KR20230096896A - Preparation method for ethylene-vinyl alcohol copolymer - Google Patents

Abstract

The present invention relates to a method for producing an ethylene-vinyl alcohol copolymer, which performs a supercritical extraction process after saponifying an ethylene-vinyl acetate copolymer in the presence of an alkaline catalyst, and minimizes the generation of waste liquid and effectively removes by-products such as catalyst residues without the need for complex equipment such as a multi-stage distillation column, pipe mixer, and water tank, thereby capable of effectively obtaining an ethylene-vinyl alcohol copolymer.

Description

Manufacturing method of ethylene-vinyl alcohol copolymer {PREPARATION METHOD FOR ETHYLENE-VINYL ALCOHOL COPOLYMER}

The present invention relates to a method for preparing an ethylene-vinyl alcohol copolymer.

Ethylene-Vinyl Alcohol (EVOH) is widely used as a material for films, sheets, containers, etc. because of its excellent gas barrier properties such as oxygen, transparency, oil resistance, non-static properties, and mechanical strength.

The EVOH may be prepared through a saponification reaction of ethylene-vinyl acetate (EVAc) prepared by copolymerization of ethylene and vinyl acetate. As a catalyst for the saponification reaction of EVAc, alkali catalysts such as sodium hydroxide, potassium hydroxide, and alkali metal alcoholates are mainly used.

Since EVOH exhibits excellent gas barrier properties as the saponification degree increases, EVOH used for food packaging and the like preferably has a high saponification degree of 99% or more. In order to achieve such a high degree of saponification, conventionally, a method of performing the saponification reaction at a higher temperature or increasing the amount of alkali catalyst used has been used.

However, in the case of a high-temperature reaction, side reactions tend to occur, and when a large amount of an alkali catalyst is used, there is a problem in that the amount of catalyst by-products in the saponified product increases. Since catalyst by-products cause discoloration of EVOH, a washing process to remove them is accompanied after the saponification reaction. When the content of catalyst by-products is high, an excessive washing process is required, reducing process efficiency and generating excessive wastewater.

In particular, after the saponification reaction of ethylene-vinyl acetate copolymer (Ethylene-Vinyl Acetate, EVAc), in addition to EVOH in the EVOH solution, catalyst by-products (Na component, etc.), reaction by-products (Methyl acetate, MeAc, etc.), residual alcohol solvent (methanol / MeOH etc.), a process in which EVOH is washed with water after the alcohol-dealcoholing process and then dried to obtain EVOH solids is known. Here, the dealcoholization process removes alcohol solvents (MeOH, etc.) using water vapor in a multi-stage distillation column, and excessive water vapor is required and waste liquid containing alcohol and water is excessively generated. In addition, when EVOH is washed with water, residues in the EVOH are removed using a mixing process with water, which requires an excessive amount of water and generates an excessive amount of waste liquid. In this process, problems such as the need for a multi-stage distillation column, a pipe mixer and a water tank for washing with water, and complicating the entire process occur.

Moreover, when recycling the alcohol solvent recovered through the alcohol-dealing process in the saponification reaction or the like, there is a difficulty in performing a process of additionally separating or removing water used in the alcohol-dealing process.

Accordingly, a multi-stage distillation column is required in the washing process, or a pipe mixer and a water tank are required during washing, and the efficiency of the entire process of preparing the ethylene-vinyl alcohol copolymer through a complicated process is greatly reduced.

The present invention is to solve the above problems, and can efficiently obtain an ethylene-vinyl alcohol copolymer having a high degree of saponification without complicated processes such as a multi-stage distillation tower or a pipe mixer and a water bath during water washing. Preparation of an ethylene-vinyl alcohol copolymer It aims to provide a method.

Accordingly, according to one embodiment of the present invention, the saponification reaction step of producing an ethylene-vinyl alcohol copolymer by reacting the ethylene-vinyl acetate copolymer in the presence of an alkali catalyst; and

Extracting the alcohol solvent contained in the saponification reaction product under supercritical carbon dioxide conditions; Including,

The supercritical carbon dioxide condition is, the pressure of CO ₂ is 80 bar or more to 150 bar or less, and the temperature is 40 ° C. or more to 60 ° C. or less,

A method for producing an ethylene-vinyl alcohol copolymer is provided.

According to the present invention, after the saponification of the ethylene-vinyl acetate copolymer in the presence of an alkali catalyst, the supercritical extraction process is performed under optimized conditions, so that the multi-stage distillation column or pipe mixer and water tank without deterioration of the physical properties of the ethylene-vinyl acetate copolymer An ethylene-vinyl alcohol copolymer having a high degree of saponification can be efficiently obtained while minimizing the generation of waste liquid without complicated equipment and equipment.

Accordingly, according to the present invention, the efficiency of the cleaning process for removing catalyst by-products contained in the ethylene-vinyl alcohol copolymer after the saponification process can be increased without deteriorating the physical properties of the ethylene-vinyl acetate copolymer, and the amount of wastewater generated in the cleaning process can be reduced. can be minimized.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, step, component, or combination thereof, but one or more other features or steps; It should be understood that the presence or addition of components, or combinations thereof, is not previously excluded.

Since the present invention can have various changes and various forms, specific embodiments will be exemplified and described in detail below. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Hereinafter, the present invention will be described in detail.

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; and

and extracting the alcohol solvent included in the saponification reaction product under supercritical carbon dioxide conditions.

Specifically, in the supercritical carbon dioxide conditions, the CO ₂ pressure is 80 bar or more to 150 bar or less, and the temperature is 40 °C or more to 60 °C or less.

In particular, the present invention is to saponify the ethylene-vinyl acetate copolymer in the presence of an alkali catalyst and then perform a supercritical extraction process of extracting an alcohol solvent under supercritical carbon dioxide conditions under optimized conditions to obtain the ethylene-vinyl acetate copolymer. Ethylene-vinyl alcohol copolymer can be efficiently obtained by minimizing the generation of waste liquid and effectively removing by-products such as catalyst residues without deterioration of physical properties and without complex equipment such as multi-stage distillation columns, pipe mixers, and water tanks.

In general, the ethylene-vinyl alcohol copolymer manufacturing process involves polymerizing an ethylene-vinyl acetate copolymer (EVA) (step 1), producing EVOH through a saponification reaction using an alkali catalyst (step 2), and EVOH solution (EVOH + MeOH) is de-alcoholized and washed (Step 3), followed by pelletizing and drying (Step 4).

Here, after the above-mentioned dealcoholization and washing process (Step 3), most of the alcohol component (MeOH) of EVOH is removed and replaced with water to become “hydrous EVOH”. In this hydrous EVOH state, a process of adding additives such as carboxylic acid may be performed. That is, a step of adding an additive such as carboxylic acid during the dealcoholization and washing process (Step 3) or pelletizing and drying the "hydrous EVOH" obtained after the dealcoholization and washing process (Step 3) (Step 4). ) A process of separately introducing additives such as carboxylic acid may be introduced in the previous step. Among the conventional ethylene-vinyl alcohol copolymer manufacturing processes, the drying process refers to a process of reducing the moisture content in “hydrous EVOH” as described above.

In the present invention, the EVOH solution obtained after the saponification reaction (Step 2) using the alkali catalyst described above is subjected to a saponification reaction product through an extraction process under supercritical carbon dioxide conditions instead of the conventional dealcoholization and washing process (Step 3). It is characterized by performing a dealcoholization process to remove the alcohol solvent from.

Accordingly, in the method for preparing the ethylene-vinyl alcohol copolymer of the present invention, a specific saponification reaction process and a supercritical extraction process will be described in detail below.

Saponification Reaction Process

First, in the present invention, an ethylene-vinyl alcohol copolymer may be produced through a saponification reaction in which an ethylene-vinyl acetate copolymer is reacted in the presence of an alkali catalyst.

Specifically, the saponification reaction process consists of adding an alkali catalyst solution dropwise to the ethylene-vinyl acetate copolymer dispersed in an alcohol solvent and reacting. Preferably, the saponification reaction of the ethylene-vinyl acetate copolymer (EVAc) is carried out in two stages, and the alkali catalyst may be continuously added dropwise in each stage instead of all at once. At this time, 'dropwise addition' means that the solution is added dropwise.

In this way, when the alkali catalyst is continuously added dropwise, an ethylene-vinyl alcohol copolymer having a high degree of saponification can be obtained even with a small amount of catalyst compared to the case where the catalyst is added at once, and accordingly, the ethylene-vinyl alcohol produced after the saponification reaction A cleaning process for removing alkali catalyst by-products included in the alcohol copolymer can be simplified, thereby increasing the efficiency and economic efficiency of the process and minimizing the amount of wastewater generated.

In the present invention, the reactive material, ethylene-vinyl acetate copolymer, may be prepared using a commercially available product or by copolymerizing ethylene and vinyl acetate monomers.

The ethylene-vinyl acetate copolymer may be copolymerized by further including, in addition to ethylene and vinyl acetate, a monomer copolymerizable with them. 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, or monoalkyl or dialkyl esters thereof; nitriles such as acrylonitrile and methacrylonitrile; amides such as acrylamide and methacrylamide; Olefin sulfonic acid or its salt, such as ethylene sulfonic acid, aryl sulfonic acid, and metharyl sulfonic acid; vinyl monomers such as alkyl vinyl ethers, vinyl ketone, N-vinyl pyrrolidone, vinyl chloride, and vinylidene chloride; etc. can be mentioned.

The ethylene content of the ethylene-vinyl acetate copolymer may be appropriately adjusted according to the desired physical properties of the ethylene-vinyl alcohol copolymer. In one embodiment, the ethylene content of the ethylene-vinyl acetate copolymer may 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 prepared ethylene-vinyl alcohol may have excellent gas barrier properties while exhibiting high processability. Meanwhile, the ethylene content can be calculated from the peak integration ratio of ¹ H-NMR data of the ethylene-vinyl acetate copolymer.

The weight average molecular weight of the ethylene-vinyl acetate copolymer is not particularly limited, but is, for example, 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 greater than or equal to 100,000 g/mol, or greater than or equal to 150,000 g/mol, or greater than or equal to 180,000 g/mol, greater than or equal to 200,000 g/mol, or greater than or equal to 220,000 g/mol, and less than or equal to 290,000 g/mol, or less than or equal to 270,000 g/mol, 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, 50,000 g/mol or less, or 30,000 g /mol or less, or 25,000 g/mol or less, or 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 weight average molecular weight has 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, A range of 180,000 g/mol or less, 170,000 g/mol or less, or 160,000 g/mol or less may be satisfied. The weight average molecular weight of the ethylene-vinyl acetate copolymer and the ethylene-vinyl alcohol copolymer can be measured by styrene conversion method through gel permeation chromatography (GPC).

As the alcohol solvent, a solvent commonly used in the saponification reaction of ethylene-vinyl acetate copolymer may be used without limitation. For example, a lower alcohol solvent such as methanol, ethanol, propanol, isopropanol, or butanol may be used, preferably methanol.

The alkali catalyst is a group consisting of alkali catalysts such as alkali metal hydroxides or alcoholates such as sodium hydroxide, potassium hydroxide, sodium methoxide, potassium methoxide, sodium methylate, sodium ethirat, potassium methylate, and lithium methylate At least one selected from may be used, and in terms of ease of storage and handling of the catalyst (in the case of sodium methoxide, it is necessary to block air contact, a glove box is required when handling, and the catalyst is denatured when exposed to air), preferably sodium hydroxide or Potassium hydroxide can be used.

Specifically, the saponification reaction of the ethylene-vinyl acetate copolymer (EVAc) is divided into two steps, and the alkali catalyst solution may be continuously added dropwise in each step instead of all at once.

For example, the saponification reaction of the ethylene-vinyl acetate copolymer (EVAc) may include a first saponification reaction step of reacting by adding a first alkali catalyst dropwise to the ethylene-vinyl acetate copolymer dispersed in an alcohol solvent; and a second saponification reaction step of reacting by adding a second alkali catalyst dropwise to the first saponification reaction mixture.

The first saponification reaction step and the second saponification reaction step may be performed consecutively. That is, immediately after completion of the first saponification reaction step, the second alkali catalyst solution may be added dropwise to the reaction mixture to proceed with the second saponification reaction.

In addition, the first alkali catalyst and the second alkali catalyst may be the same as or different from each other, and preferably, the same material may be used as the first alkali catalyst and the second alkali catalyst.

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, based on 1 mol of the vinyl acetate unit of the ethylene-vinyl acetate copolymer.

In order to prepare an ethylene-vinyl alcohol copolymer having a high degree of saponification by the conventional method, 0.03 mol or more of an alcohol catalyst was required for 1 mol of vinyl acetate unit, but according to the production method of the present invention, while reducing the amount of alcohol catalyst used, An ethylene-vinyl alcohol copolymer having a degree of saponification can be produced. However, if the total amount of the alkali catalyst is less than 0.01 mol, the saponification reaction may be too slow, so it is preferable to satisfy the amount of the catalyst.

In addition, within the range satisfying the total usage amount, the first alkali catalyst and the second alkali catalyst are each 0.0025 mol or more, or 0.005 mol or more, and 0.02 mol or less, based on 1 mol of vinyl acetate unit of the ethylene-vinyl acetate copolymer. or less than 0.01 mole.

The first alkali catalyst and the second alkali catalyst may be used in a molar ratio of 1:1 to 1:4 or 1:1 to 1:2. In this way, an ethylene-vinyl alcohol copolymer having a higher degree of saponification can be prepared by increasing the amount of the second alkali catalyst equal to or greater than the amount of the first alkali catalyst.

Meanwhile, the alkali catalyst, for example, the first alkali catalyst and the second alkali catalyst are added dropwise to the ethylene-vinyl acetate copolymer dispersion in the form of a solution. At this time, the above-described alcohol solvent may be used as the solvent, and it is preferable to use the same solvent used in preparing the ethylene-vinyl acetate copolymer dispersion. The concentration of each alkali catalyst solution may be the same as or different from each other, and may be adjusted according to the concentration of the ethylene-vinyl acetate copolymer dispersion and the desired drop rate of the alkali catalyst solution.

For example, in the first saponification reaction step, a dispersion is first prepared by dispersing an ethylene-vinyl acetate copolymer in an alcohol solvent, and a first alkali catalyst is added dropwise thereto to proceed with the saponification reaction.

The amount of alcohol solvent used to prepare the ethylene-vinyl acetate copolymer dispersion may be appropriately adjusted according to the type of alcohol solvent, the type of ethylene-vinyl acetate copolymer, and the concentration of the alkali catalyst solution. For example, the alcohol solvent may be used in the range of 100 parts by weight to 1000 parts by weight, based on 100 parts by weight of the ethylene-vinyl acetate copolymer, or 200 parts by weight or more, or 300 parts by weight or more, 800 parts by weight, or 700 parts by weight Part by weight, or may be used in the range of 500 parts by weight or less, but is not limited thereto.

On the other hand, in the saponification reaction process, the drop rate of the alkali catalyst solution may be adjusted according to the reaction time. For example, the dropwise addition of the alkali catalyst solution is the amount of alkali catalyst per minute with respect to 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer. The input amount may be 1.0*10 ^-5 mol to 13*10 ^-5 mol. When the above dropwise acceleration rate range is satisfied, an ethylene-vinyl alcohol copolymer having a high degree of saponification may be prepared by increasing reaction efficiency without excessively lengthening the saponification reaction time.

From this point of view, the dropwise addition of the alkali catalyst solution is 2.0*10 −5 mol or more, or 3.0*10 ⁻⁵ mol or more, or 3.0*10 ⁻⁵ mol or more, or It is preferably 4.0*10 ^-5 mol or more and 11.0*10 ^-5 mol or less, or 10.0*10 ^-5 mol or less, or 9.0*10 ^-5 mol or less.

For example, the dropwise addition of the first alkali catalyst solution is 1.0*10 ^-5 mol or more, or 2.0*10 ^-5 mol or more of the first alkali catalyst added per minute per 1 mol of vinyl acetate unit of the ethylene-vinyl acetate copolymer. or more than 3.0*10 ^-5 moles, or more than 4.0*10 ^-5 moles, but less than or equal to 13*10 ^-5 moles, less than or equal to 11.0*10 ^-5 moles, or less than or equal to 10.0*10 ^-5 moles, or less than or equal to 9.0*10 moles It is preferably made so that it becomes ^-5 mol or less.

In addition, the dropwise addition of the second alkali catalyst solution is 2.0 * 10 ^-5 moles or more, or 3.0 * 10 ^-5 moles or more, Or 4.0*10 ^-5 mol or more, but preferably 8.0*10 ^-5 mol or less, or 7.0*10 ^-5 mol or less, 6.0*10 ^-5 mol or less.

As long as the above range is satisfied, the drop rate of the second alkali catalyst solution may be equal to or higher than the drop rate of the first alkali catalyst solution. In this case, the reaction efficiency is increased, and thus an ethylene-vinyl alcohol copolymer having a high degree of saponification can be obtained, which is preferable.

Meanwhile, the temperature of the saponification reaction may be 40 °C or higher, or 50 °C or higher, or 60 °C or higher, and 120 °C or lower, or 110 °C or lower, or 100 °C or lower. When the reaction temperature is less than 40 ° C., the saponification reaction rate may be excessively slow, and when the reaction temperature exceeds 120 ° C., side reactions easily occur, so it is preferable that the above range is satisfied.

For example, the temperature of the first saponification step is preferably 40 °C or higher, or 50 °C or higher, or 60 °C or higher, and 120 °C or lower, or 110 °C or lower, or 100 °C or lower.

In addition, the temperature of the second saponification step is preferably 60 °C or higher, or 70 °C or higher, or 80 °C or higher, and 120 °C or lower, or 110 °C or lower, or 100 °C or lower.

As long as the above range is satisfied, the temperature of the second saponification reaction step may be equal to or higher than the temperature of the first saponification reaction step. In this case, the reaction efficiency is increased, and thus an ethylene-vinyl alcohol copolymer having a high degree of saponification can be obtained, which is preferable.

Meanwhile, the pressure of the saponification reaction process may be 1 bar or more, 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 may be excessively slow, and in terms of reducing equipment cost and securing process safety in actual process implementation, it may be performed at 5 bar or less.

For example, the pressure in the first saponification reaction step may be 1 bar or more, 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.

In addition, the pressure of the second saponification reaction step is 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.

In addition, the temperature of the second saponification step is preferably 60 °C or higher, 70 °C or higher, or 80 °C or higher, and 120 °C or lower, 110 °C or lower, or 100 °C or lower.

As long as the above range is satisfied, the pressure of the second saponification reaction step may be equal to or higher than the pressure of the first saponification reaction step. In this case, the reaction efficiency is increased, and thus an ethylene-vinyl alcohol copolymer having a high degree of saponification can be obtained, which is preferable.

Meanwhile, the saponification reaction may be performed under an inert gas atmosphere, and the reaction may proceed while continuously discharging methyl acetate, which is a by-product, out of the system to increase the conversion rate.

For example, the first saponification reaction step may be terminated at the time when the dropwise addition of the first alkali solution is completed. In other words, dropwise addition of the first alkali solution may be continuously performed from the start to the end of the first saponification reaction. As such, by adding the first alkali solution dropwise throughout the reaction time, the conversion rate of EVAc to EVOH may be increased while minimizing side reactions.

After completion of the first saponification reaction, a second alkali catalyst solution prepared separately is added dropwise to the reaction mixture to perform a second saponification reaction.

The first saponification reaction step and the second saponification reaction step may be performed consecutively. That is, immediately after completion of the first saponification reaction step, the second alkali catalyst solution may be added dropwise to the reaction mixture to proceed with the second saponification reaction.

Similar to the first saponification reaction step, the second saponification reaction step may be completed at the time when the dropwise addition of the second alkali solution is completed. That is, dropwise addition of the second alkali solution may be continuously performed from the start to the end of the second saponification reaction. As such, by adding the second alkali solution dropwise throughout the reaction time, the conversion rate of EVAc to EVOH can be increased while minimizing side reactions.

According to the above preparation method, an ethylene-vinyl alcohol copolymer having a high degree of saponification of 99% or more can be obtained using a smaller amount of an alkali catalyst compared to the conventional batch saponification process of ethylene-vinyl acetate copolymer. Since the ethylene-vinyl alcohol copolymer exhibits excellent gas barrier properties due to its high degree of saponification, it can be usefully used for food packaging.

Specifically, the ethylene-vinyl alcohol copolymer prepared according to the above production method has a saponification degree of 99% or more, or 99% to 99.9%; the ethylene content is at least 20 mol%, or at least 25 mol%, or at least 27 mol%, or at least 30 mol%, and is 60 mol% or less, or 50 mol% or less, or 48 mol% or less, or 35 mol% or less; ; The weight average molecular weight may be 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.

For example, the saponification degree of the ethylene-vinyl alcohol copolymer can be calculated through the peak integral number ratio of ¹ H-NMR data. The specific measurement method is as shown in the test example.

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 may be satisfied to exhibit excellent color characteristics.

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

Supercritical extraction process

In the method for producing an ethylene-vinyl alcohol copolymer of the present invention, a supercritical extraction process is performed under optimized conditions for the ethylene-vinyl alcohol copolymer obtained through the above-described saponification reaction to effectively remove by-products such as alcohol solvents, and additional A post-treatment process, for example, an immersion process using a carboxylic acid-containing aqueous solution, may be immediately performed without a washing process.

In particular, the present invention is an ethylene-vinyl alcohol copolymer obtained through the saponification reaction using the above-described alkali catalyst, instead of performing the dealcoholization and washing process in the conventional method, an extraction process under supercritical carbon dioxide conditions It is characterized in that the alcohol solvent included in the saponification reaction product is performed by performing an extraction process.

Specifically, in the present invention, after performing the above-described saponification reaction, the saponification reaction product including the ethylene-vinyl alcohol copolymer is put into a supercritical extractor and CO ₂ is injected to extract alcohol.

This supercritical extraction process is not used to remove water from hydrated polymers or compounds with excess water (H ₂ O). difficult to apply to the process. In _particular , after the supercritical CO ₂ fluid passes through the supercritical extractor, it is finally recondensed and cooled to return to the liquefied state. It is difficult to use in the drying process that reduces the moisture content of “hydrous EVOH” because it freezes by the cooled CO ₂ and blocks the line, causing abnormal high pressure to occur, resulting in high pressure explosion risk and equipment failure.

In the extraction step of the present invention, the supercritical carbon dioxide conditions correspond to the critical temperature and pressure at which CO ₂ becomes supercritical, and specifically, the ethylene-vinyl alcohol copolymer after the saponification process without degrading the physical properties of the ethylene-vinyl alcohol copolymer In terms of effectively removing catalyst by-products contained in and increasing the alcohol solvent recovery rate, the pressure of CO ₂ is 80 bar or more to 150 bar or less, and the temperature is 40 °C or more to 60 °C or less.

Specifically, the pressure of CO ₂ injected into the supercritical extractor is 80 bar or more in terms of increasing alcohol solvent extraction efficiency, 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. However, in terms of preventing degradation of physical properties of the ethylene-vinyl alcohol copolymer, it may be 150 bar or less, and 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 process may be 40 ° C. or higher, more specifically, 42 ° C. or higher, 43 ° C. or higher, or 45 ° C. or higher in terms of increasing alcohol solvent extraction efficiency. However, it may be 60 °C or less, more specifically, 55 °C or less, 53 °C or less, or 52 °C or less in terms of preventing the degradation of physical properties of the ethylene-vinyl alcohol copolymer. Here, if the pressure and temperature of the CO ₂ are too high, the CO ₂ flow rate at the rear end of the extractor increases correspondingly, and problems such as an increase in the capacity of a device such as a separator and the corresponding increase in cooling and heating energy may occur.

Specifically, prior to the supercritical extraction step, gelling or solidifying the saponification reaction product including the ethylene-vinyl alcohol copolymer from the saponification reaction mixture; may be further included.

As an example, the method for preparing an ethylene-vinyl alcohol copolymer of the present invention includes a saponification reaction step of producing an ethylene-vinyl alcohol copolymer by reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst;

gelling or solidifying a saponification reaction product including the ethylene-vinyl alcohol copolymer from the saponification reaction mixture; and

A supercritical extraction step of introducing the gelled or solidified saponification reaction product including the ethylene-vinyl alcohol copolymer into a supercritical extractor and injecting CO ₂ to extract alcohol.

In this case, the supercritical carbon dioxide condition is, the pressure of CO ₂ is 80 bar or more to 150 bar or less, the temperature is 40 °C or more to 60 °C or less, and the specific supercritical carbon dioxide conditions are as described above.

At this time, as the gelation or solidification method, the saponification reaction product may be cooled to about 5 ° C or less, or about -10 ° C or more to about 5 ° C or less after recovering or recovering the saponification reaction product. For example, while recovering the saponification reaction product, a method of line cooling to about 5 ° C or less or about -10 ° C or more to about 5 ° C or less in a transfer pipe and discharging it in the form of a strand is applied, or the saponification reaction product is After recovery, gelation or solidification may be applied in the form of a cake by cooling at less than about 5° C. or less than about -10° C. to less than about 5° C. for about 3 hours or more to about 12 hours or less. For example, the strand may have a cylindrical shape, and the cake may have a rectangular parallelepiped shape. However, in terms of increasing the alcohol solvent extraction efficiency, after cooling the saponification reaction product to about -10 ℃ or more to about 5 ℃ or less to gel or solidify in the form of a strand (strand), extracting the alcohol solvent under supercritical carbon dioxide conditions desirable.

Specifically, in performing the supercritical extraction step, the saponification reaction product may have an external surface area per volume of about 5 cm ² /cm ³ or more or about 5 cm ² /cm ³ or more to about 50 cm ² /cm ^{3 or} less. . More specifically, the external surface area per volume of the saponification reaction product is greater than or equal to about 5 cm ² /cm ³ , or greater than or equal to about 6 cm ² /cm ³ , or greater than or equal to about 8 cm ² /cm ³ , or greater than or equal to 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 or more. However, considering the actual process efficiency of gelation or solidification of the saponification reaction product, about 45 cm ² /cm ³ or less, or about 40 cm 2 /cm ^{3 or} less, or about 35 cm ² /cm 3 or less, or about 30 cm ² /cm ³ or less cm ² /cm ³ or less, or about 28 cm ² /cm ³ or less, or about 25 cm ² /cm ^{3 or} less, or about 22 cm ² /cm ^{3 or} less, or about 20 cm 2 /cm 3 or less, or about 18 cm ² /cm ³ or less cm ² /cm ³ or less, or about 16 cm ² /cm ³ or less, or about 15 cm ² /cm ³ or less. In one example, the external surface area per volume of the saponification reaction product is about 9 cm ² /cm ³ to about 20 cm ² /cm ³ , or about 10 cm ² /cm ³ to about 18 cm ² /cm ³ , or about 10 cm ² /cm ³ to about 15 cm ² /cm ³ , or about 10 cm ² /cm ³ to about 12 cm ² /cm ³ . The external surface area per volume of the saponification reaction product can be measured by various methods known to be capable of measuring the volume and external surface area of a polymer, and can be applied without particular limitation. For example, when the saponification reaction product is in the form of a strand or a cake, the length, diameter, width, height, etc. measured in appearance are measured, and the volume and surface area can be calculated through this.

On the other hand, with respect to the ethylene-vinyl alcohol copolymer obtained through the saponification reaction described above in the present invention, in the supercritical extraction process, the extract liquid discharged from the supercritical extractor into which CO ₂ is injected is filtered into solid ethylene-vinyl alcohol air A process of filtering out coalescence may be further included. The filtering device is not limited as long as it is capable of filtering out the solid ethylene-vinyl alcohol copolymer, and may be, for example, a filter. The specifications of the filter are not particularly limited.

In addition, in one example of the present invention, a step of gas-liquid separation using a separator may be further included with respect to the extract filtered through the filtering device.

The separator is a device for separating carbon dioxide and an alcohol solvent from the extract liquid discharged from the supercritical extractor, and may be, for example, a gas-liquid separator including a flash separator or a multi-stage distiller.

The separator may, for example, separate and discharge carbon dioxide in a gas phase through an upper part of the separator device, and separate and discharge alcohol, solvent, and other components in a liquid phase through a lower part of the separator device. The carbon dioxide separated and discharged upwards may be condensed into a liquid phase in a subsequent process and recycled to the supercritical extractor, and the alcohol solvent discharged as a liquid phase may be reused as a raw material for the saponification process after going through a purification process. In addition, an additional gas-liquid separation process may be performed prior to the purification process.

Meanwhile, through the supercritical extraction process, the recovery rate of the alcohol solvent may be as high as 88% by weight or more, 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 at least 96%, or at least 97%, or at least 98%, or at least 98.5%, or at least 99%, or at least 99.5%, or at least 99.9%.

Specifically, the alcohol solvent recovery rate is the weight (A ), the EVOH weight (B) after supercritical extraction, and the weight (C) of the alcohol solvent recovered through the supercritical extraction process are measured in grams (g), respectively, and the alcohol solvent in the supercritical extraction process after saponification as shown in Equation 1 below The recovery rate (%) of was measured.

[Equation 1]

Recovery of alcohol solvent in supercritical extraction process (%) = C / (A-B) × 100

In Equation 1 above,

A is the weight (g) of ethylene-vinyl alcohol copolymer (EVOH) before performing the supercritical extraction process,

B is ethylene-vinyl alcohol copolymer (EVOH), weight (g) after performing a supercritical extraction process,

C is the weight (g) of alcohol solvent recovered through the supercritical extraction process.

In addition, the product containing the ethylene-vinyl alcohol copolymer obtained after performing the supercritical extraction process may have an alcohol solvent content of 12% by weight or less, preferably 10% by weight or less, based on the total weight of the product, or 8% or less, or 10% or less, or 8% or less, or 7% or less, or 5% or less, or 4% or less, or 3% or less, or 2% or less, or 1.5% or less % or less, or 1 wt% or less, or 0.5 wt% or less, or 0.1 wt% or less. More preferably, the alcohol solvent may not be substantially detected in the ethylene-vinyl alcohol copolymer obtained after the extraction step and the product including the same.

On the other hand, through the supercritical extraction process, the removal rate of the alkali component contained in the catalyst used for the saponification reaction may be 25% or more, preferably 26% or more, or 27% or more, or 28% or more, or 29% or greater than or equal to 30%, or greater than or equal to 31%, or greater than or equal to 33%, or greater than or equal to 35%, or greater than or equal to 40%, or greater than or equal to 45%, or greater than or equal to 50%. Specifically, the alkali component removal rate was determined by measuring the alkaline component content (a) of the ethylene-vinyl alcohol copolymer (EVOH) before supercritical extraction and the alkaline component content (b) of the EVOH after extraction, respectively, as shown in Equation 2 below. Component removal rate (%) is measured.

[Equation 2]

Alkaline component removal rate (%) = 100 × (1 - b/a)

In Equation 2 above,

a is the residual amount (ppm) of the catalytic alkali component contained in the ethylene-vinyl alcohol copolymer (EVOH) before performing the supercritical extraction process,

b is the residual amount (ppm) of the catalytic alkali component included in the ethylene-vinyl alcohol copolymer (EVOH) after performing the supercritical extraction process.

Through the supercritical extraction process, the residual amount (ppm) of the catalyst alkali component contained in the ethylene-vinyl alcohol copolymer (EVOH), that is, the residual amount (ppm) of the alkali component contained in the catalyst used for the saponification reaction is inductively bonded It can be measured using plasma emission spectrometry (ICP-OES), and can be specifically measured under the following conditions.

- Pretreatment: microwave digestion, 250 ℃, 30 min temperature increase, 250 ℃, 15 min maintenance (90 bar)

- 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

In addition, the residual amount of the alkali component in the product including the ethylene-vinyl alcohol copolymer obtained after performing the supercritical extraction step is, that is, the residual amount of the alkali component included in the catalyst used for the saponification reaction relative to the total weight of the product 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 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, in the ethylene-vinyl alcohol copolymer obtained after the extraction step and the product including the same, the alkali component included in the catalyst used for the saponification reaction may not be substantially detected.

For example, in the present invention, the ethylene-vinyl alcohol copolymer obtained through the above-described saponification reaction is put into a supercritical extractor, CO ₂ is injected, and the inside of the extractor is controlled at 50 ° C. and 150 bar, followed by 20 minutes During the Steady step, the temperature and pressure were maintained without additional CO ₂ flow, and then CO ₂ was continuously injected at a rate of 6.5 L/min at 50 °C and 150 bar in the circulating step for another 20 minutes, and this was repeated three or more times to achieve a total A supercritical extraction process can be performed for 120 minutes.

The supercritical extraction process according to the present invention effectively recovers an alcohol solvent such as methanol without using steam or water, so that it can be reused in the saponification reaction without an additional process of separating water and alcohol solvent when recycling the alcohol solvent. The overall process efficiency can be greatly improved.

In particular, according to the present invention, by performing the supercritical extraction process under pressure and temperature range conditions as described above, it is possible to minimize the deterioration of the physical properties of the ethylene-vinyl alcohol copolymer prepared by the saponification reaction.

Accordingly, the ethylene-vinyl alcohol copolymer obtained after performing the supercritical extraction process according to the present invention has a saponification degree of 99% or more, or 99% to 99.9%; the ethylene content is 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; ; The weight average molecular weight may be 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 may be satisfied to exhibit excellent color characteristics. Here, the degree of saponification and yellowness of the ethylene-vinyl alcohol copolymer can be measured by the same method as described in the saponification reaction step, and the specific measurement method is as shown in the test example.

Post-processing step

Meanwhile, in the method for preparing an ethylene-vinyl alcohol copolymer according to the present invention, after performing the above-described 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, immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing carboxylic acid and then drying the water; may be further included.

As an example, the method for preparing an ethylene-vinyl alcohol copolymer of the present invention includes a saponification reaction step of producing an ethylene-vinyl alcohol copolymer by reacting an ethylene-vinyl acetate copolymer in the presence of an alkali catalyst;

Extracting the alcohol solvent contained in the saponification reaction product under supercritical carbon dioxide conditions; and

After performing the supercritical extraction process, immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing carboxylic acid and then drying the water.

As another example, the method for producing an ethylene-vinyl alcohol copolymer of the present invention includes a saponification reaction step of producing an ethylene-vinyl alcohol copolymer by reacting the ethylene-vinyl acetate copolymer in the presence of an alkali catalyst;

gelling or solidifying a saponification reaction product including the ethylene-vinyl alcohol copolymer from the saponification reaction mixture;

extracting an alcohol solvent included in the saponification reaction product under the gelled or solidified supercritical carbon dioxide condition; and

After performing the supercritical extraction process, immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing carboxylic acid and then drying the water.

In this case, the supercritical carbon dioxide condition is, the pressure of CO ₂ is 80 bar or more to 150 bar or less, the temperature is 40 °C or more to 60 °C or less, and the specific supercritical carbon dioxide conditions are as described above.

Specifically, the carboxylic acid aqueous solution may include acetic acid.

In addition, the concentration of the carboxylic acid-containing aqueous solution may be 0.01% by weight to 1% by weight.

The immersion process may be performed 1 to 5 times at 20 °C to 50 °C for 10 minutes to 60 minutes each time.

For example, after performing the supercritical extraction process, the ethylene-vinyl alcohol copolymer is mixed with an aqueous solution containing 0.01% by weight to 1% by weight of carboxylic acid, 1 to 5 times, each time 10 to 10 times. After soaking and stirring for 60 minutes, it can be dried.

In addition, the step of drying the water after being immersed in the above-described carboxylic acid-containing aqueous solution may be performed for 3 hours to 50 hours under a condition of 40 ℃ to 100 ℃, and may be dried through a single or a plurality of times.

The moisture drying process may be performed so that the moisture content is less than 5% or less than 1%, more preferably less than 0.5%.

Hereinafter, preferred embodiments are presented to aid understanding of the present invention, but the following examples are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It goes without saying that changes and modifications fall within the scope of the appended claims.

Example 1

1-1. Saponification Reaction Process

A mixed solution (total solid content: 20%) containing 100 parts by weight of an ethylene-vinyl acetate copolymer (EVAc) with an ethylene content of 32 mol% and 400 parts by weight of methanol (MeOH) was put into a saponification reactor, and 0.27 wt% of NaOH relative to EVAc solid content 20 parts by weight (sodium hydroxide/vinyl acetate unit = 0.01/1, molar ratio) of a methanol solution of sodium hydroxide (16 g/L) in a 1% dilution state in MeOH was added to a saponification reactor at atmospheric pressure (about 1 bar) at 60 ° C. The saponification reaction proceeded by continuously adding dropwise for 2.5 hours. At this time, the rate of addition was such that the number of moles of sodium hydroxide added per vinyl acetate unit of EVAc was 1.4×10 ^-6 moles per second. As described above, the first saponification reaction (reactor temperature: 60 °C, reactor pressure: atmospheric pressure, reaction time: 2.5 hours) was performed.

In addition, 20 parts by weight (sodium hydroxide / vinyl acetate unit = 0.01/1, molar ratio of sodium hydroxide / vinyl acetate unit = 0.01 / 1) ) was continuously added dropwise to the saponification reactor for 3 hours to proceed with the second saponification reaction. At this time, the drop rate was such that the number of moles of sodium hydroxide added per vinyl acetate unit of EVAc was 9.3 × 10 ^-7 moles per second. As described above, the second saponification reaction (reactor temperature: 90 ° C., reactor pressure : 3 bar, reaction time: 3 hours).

After the addition of NaOH was completed in this way, the reaction was further conducted for 1 hour under the above-described conditions (reactor temperature: 90 °C, reactor pressure: 3 bar).

Then, 120 parts by weight (acetic acid/sodium hydroxide = 1/1, molar ratio) of acetic acid aqueous solution (9 g/L) having the same molar equivalent to NaOH was added to the reaction mixture, stirred for 30 minutes to neutralize, and the reaction was stopped. , The reaction solution was concentrated to a total solid content (TSC, total solid contents) of 15 to 20% at 60 to 70 °C. At this time, an EVOH methanol/water 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 solidified by cooling at 5° C. during line transfer, and discharged as an ethylene-vinyl alcohol strand having a cylindrical shape 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 to 12 cm ² /cm ³ .

1-2. Supercritical extraction process

Then, 64 g of the EVOH Strand (EVOH weight after saponification reaction and extraction process, A) was put into a 70 L supercritical extractor, and CO ₂ was injected to control the inside of the extractor to 50 ° C. and 150 bar, The temperature and pressure were maintained without additional CO ₂ flow in the Steady stage for 20 minutes (Steady stage: no CO ₂ input to the extractor, no CO ₂ exiting the separator from the extractor). Thereafter, CO ₂ was continuously injected at a rate of 6.5 L/min at 50 °C and 150 bar as a circulation step for another 20 minutes (circulation step: CO ₂ reservoir -> extractor -> separator -> CO ₂ flow into the CO ₂ reservoir) . This was repeated three times to perform a supercritical extraction process for a total of 120 minutes. Then, gas-liquid separation was performed at 50 bar and 40° C. through a separator connected to the supercritical extractor, and gaseous CO ₂ and liquid methanol were recovered through the gas-liquid separation. The amount of methanol recovered through the supercritical extraction process was 51.939 g (the weight of MeOH recovered after the extraction process, C). Thereafter, the supercritical extractor was changed to normal pressure and room temperature (about 20 to 23 ° C., about 1 bar), and then the dealcohol extraction was completed, and the ethylene-vinyl alcohol copolymer (EVOH) was recovered. At this time, EVOH was 11.8 g (EVOH weight after extraction process, B).

1-3. Post-processing steps (soaking, drying)

The obtained EVOH was immersed once in an aqueous solution of 0.5% acetic acid for 1 hour, then immersed once in deionized water (DIW) for 1 hour, and then immersed in deionized water (DIW) once for 1 hour at 90 °C and 120 rpm. After extruding with an extruder under conditions (moisture content of about 25% by weight), EVOH having a moisture content of 0.01% by weight was prepared by drying under reduced pressure at 80 ° C. for 16 hours.

Example 2

In the same manner as in Example 1, the saponification reaction process, the supercritical extraction process, and the immersion drying process were performed as post-treatment steps, but in the supercritical extraction process, the temperature and pressure of CO ₂ were set to 40 °C and 100 bar under supercritical carbon dioxide conditions. Proceeding, the EVOH of Example 2 was prepared.

Example 3

In the same manner as in Example 1, the saponification reaction process, the supercritical extraction process, and the immersion drying process were performed as post-treatment steps, but after completing the saponification reaction to neutralization and concentration, the EVOH solution was drained into a container or plate, and then -5 ℃ 6h It was cooled and solidified to obtain an EVOH Cake having an external surface area of 6 to 8 cm ² /cm ³ per volume in the form of a cube, and then a supercritical extraction process was performed to prepare the EVOH of Example 3.

Comparative Example 1

In the same manner as in Example 1, the saponification reaction process, the supercritical extraction process, and the immersion drying process were performed as post-treatment steps, but in the supercritical extraction process, the temperature and pressure of CO ₂ were set to 35 °C and 80 bar under supercritical carbon dioxide conditions. Proceeding, the EVOH of Comparative Example 1 was prepared.

Comparative Example 2

In the same manner as in Example 1, the saponification reaction process, the supercritical extraction process, and the immersion drying process were performed as post-treatment steps, but the temperature and pressure of CO ₂ were set to 80 °C and 160 bar under supercritical carbon dioxide conditions in the supercritical extraction process. Proceeding, the EVOH of Comparative Example 1 was prepared.

<Test Example>

Regarding the ethylene-vinyl alcohol copolymers according to the above Examples and Comparative Examples, each physical property was measured in the following manner, and the measurement results are shown in Table 1 below.

(1) MeOH removal rate according to the alcohol-dealing extraction process after saponification reaction

EVOH weight (A) measured before the supercritical extraction process, supercritical extraction process The EVOH weight (B) and the weight (C) of the alcohol solvent (MeOH) recovered through the supercritical extraction process were measured in grams (g), respectively, and MeOH in the dealcohol extraction process after the saponification reaction as shown in Equation 3 below Recovery (%) was measured.

[Equation 3]

MeOH recovery (%) = C / (A-B) × 100 in the alcohol-dealing supercritical extraction process

(2) Removal rate of residual alkali components according to the alcohol-dealing extraction process after saponification reaction

After saponification of ethylene-vinyl acetate copolymer (EVOH) in the presence of an alkali catalyst according to Examples and Comparative Examples, an alcohol deal extraction process was performed, and then the removal rate of residual alkali components such as Na was measured under the following conditions. .

Specifically, the alkaline component content (a) of the ethylene-vinyl alcohol copolymer (EVOH) measured before the supercritical extraction process and the alkaline component content (b) of EVOH measured after the supercritical extraction process (b) were measured in ppm units, respectively, and the following As shown in Equation 4, the alkali component removal rate (%) was measured.

[Equation 4]

Alkaline component removal rate (%) = 100 × (1 - b/a)

In addition, the above-mentioned alkali component content (ppm) was measured using inductively coupled plasma emission spectrometry (ICP-OES), and was specifically measured under the following conditions.

- Pretreatment: microwave digestion, 250 ℃, 30min temperature increase, 250 ℃, 15min maintenance (90 bar)

- 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

(3) Degree of saponification of ethylene-vinyl acetate copolymer

The saponification degree (%) of the prepared EVOH was calculated through the peak integral number ratio of ¹ H-NMR data of EVOH.

Specifically, the integral value of the -OH peak (δ 4.05-4.72) derived from the vinyl alcohol unit of the ¹ H-NMR data and the -CH ₃ COO- peak (δ 1.99) derived from the vinyl acetate unit were derived, , The degree of saponification was derived by calculating the percentage (%) of vinyl alcohol units to the total of vinyl alcohol units and vinyl acetate units.

(4) Yellowness (YI) of ethylene-vinyl acetate copolymer

After obtaining EVOH pellets by cutting the EVOH prepared in Examples and Comparative Examples with a pelletizer, the pellets are placed in a cell for measurement and yellowness (YI, YI, Yellowness Index) was measured.

Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 saponification
reaction EVAc ethylene content (mol%) 32 32 32 32 32 Catalyst addition method continuous dropping continuous dropping continuous dropping continuous dropping continuous dropping Catalyst content (wt%) 1st 0.27wt% 2nd 0.53wt% Primary 0.27wt%
2nd 0.53wt% Primary 0.27wt%
2nd 0.53wt% Primary 0.27wt%
2nd 0.53wt% Primary 0.27wt%
2nd 0.53wt% Gelled/solidified form Strand Strand Cake Strand Strand saponification
after reaction
De-alcohol extraction process Dealcoholization process method supercritical extraction supercritical extraction supercritical extraction supercritical extraction supercritical extraction Temperature (℃) 50 40 50 35 80 pressure (bar) 150 100 150 80 160 total time (min) 120 120 120 120 120 MeOH recovery rate (%) in dealcoholic extraction process 99.5 98.6 93.7 83 99.8 After de-alcohol extraction process
Na removal rate (%) 30 27 31 19 32 additive
immersion compound Acetic acid Acetic acid Acetic acid Acetic acid Acetic Acid Concentration (%) 0.5 0.5 0.5 0.5 0.5 total time (min) 60 60 60 60 60 Saponification degree of EVOH (%) 99.9 99.9 99.9 99.9 99.9 Yellowness (YI) 7.9 6.7 8.9 10.1 15.2

As shown in Table 1, after the saponification of the ethylene-vinyl acetate copolymer in the presence of a salt alkali catalyst according to the present invention, the supercritical extraction process is performed at the optimal pressure and temperature range, so that the multi-stage distillation column or pipe mixer and Confirmation that high saponification ethylene-vinyl alcohol copolymer (EVOH) can be efficiently obtained without deterioration (yellowing) by minimizing the generation of waste liquid and effectively removing by-products such as catalyst residues without complicated equipment such as a water tank did

In addition, when comparing Examples 1, 2 and 3, it can be seen that a higher recovery rate of MeOH can be achieved even under the same supercritical carbon dioxide conditions when the saponified reaction product is applied in a form having a large surface area such as a strand.

On the other hand, through the results of Comparative Examples 1 _and 2, it was confirmed that the MeOH recovery rate dropped significantly to 83% when the pressure and temperature of CO ₂ were applied at 80 bar and 35 ° C. When applied at bar and 80 ℃, it was confirmed that the ethylene-vinyl alcohol copolymer (EVOH) deteriorated and the yellowness index (YI) increased significantly to 15.2.

As described above, in the present invention, by performing supercritical extraction under conditions optimized for ethylene-vinyl alcohol copolymer, alcohol solvents such as methanol are effectively recovered without using steam or water without deteriorating the physical properties of the ethylene-vinyl alcohol copolymer, In the case of recycling of the alcohol solvent, there is an excellent effect of greatly improving the overall process efficiency in that it can be reused for the saponification reaction without an additional process of separating water and the alcohol solvent.

Claims (11)

A saponification reaction step 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;
including,
The supercritical carbon dioxide condition is, the pressure of CO ₂ is 80 bar or more to 150 bar or less, and the temperature is 40 ° C. or more to 60 ° C. or less,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The saponification reaction process consists of reacting by adding dropwise an alkali catalyst solution to the ethylene-vinyl acetate copolymer dispersed in an alcohol solvent,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 2,
The alcohol solvent is at least one selected from the group consisting of methanol, ethanol, propanol, and butanol,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The alkali catalyst is lithium hydroxide, sodium hydroxide, or potassium hydroxide,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The total amount of the alkali catalyst used is 0.01 mol or more to less than 0.03 mol with respect to 1 mol of vinyl acetate units of the ethylene-vinyl acetate copolymer,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The temperature of the saponification reaction step is 40 ℃ or more to 120 ℃ or less,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The pressure of the saponification reaction process is 1 bar or more to 5 bar or less,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
Gelling or solidifying the saponification reaction product including the ethylene-vinyl alcohol copolymer from the saponification reaction mixture; further comprising,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The supercritical carbon dioxide condition is, the pressure of CO ₂ is 100 bar or more to 150 bar or less, and the temperature is 40 ° C. or more to 50 ° C. or less,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
The product containing the ethylene-vinyl alcohol copolymer obtained after performing the extraction step has an alcohol solvent content of 15% by weight or less relative to the total weight of the product,
A method for producing an ethylene-vinyl alcohol copolymer.
According to claim 1,
After performing the extraction process,
Drying the water after immersing the ethylene-vinyl alcohol copolymer in an aqueous solution containing carboxylic acid; further comprising,
A method for producing an ethylene-vinyl alcohol copolymer.