KR20230081450A - Method for Preparing Chemically Recycled PET - Google Patents

Abstract

(A) preparing a dicarboxylic acid-diol slurry containing a dicarboxylic acid compound and a diol compound; (B) mixing the dicarboxylic acid-diol slurry and bis-2-hydroxyethyl terephthalate (BHET) to obtain a mixed slurry; (C) subjecting the mixed slurry to an esterification reaction in the presence of a catalyst; And (D) a polycondensation reaction of the esterification reaction product in the presence of a catalyst; wherein at least one of steps (B) and (C) comprises introducing a basic compound, It relates to a method for manufacturing recycled PET.

Description

Manufacturing method of chemically recycled PET {Method for Preparing Chemically Recycled PET}

The present invention relates to a method for making chemically recycled PET.

The consumption of plastic products is increasing year by year. In particular, polyethylene terephthalate (PET) is widely used as a raw material for bottle containers, films, fibers, and the like, and among them, the increase in consumption as a bottle container is remarkable. However, plastic products such as PET do not decompose in the environment after use, and the need for recycling is constantly emphasized due to environmental problems, and efforts to improve the recovery rate and recycling rate of waste PET products are continuing worldwide. .

Recycling methods of PET products can be divided into physical recycling and chemical recycling of waste PET. Physical recycling involves washing, refining and sorting, grinding waste PET products, then refining and classifying them to produce flakes from which impurities are removed, and subsequently going through an extrusion-filtration step to produce recycled PET, and the recycled PET thus produced is being reused as a blend with virgin PET, thereby producing new products such as bottles, fibers and films. However, PET produced by this mechanical recycling method is difficult to apply to colored PET containing pigments, and cannot be used for food storage products such as beverages. follow

Accordingly, studies have recently been conducted on a chemical recycling method in which waste PET is depolymerized to produce bis(2-hydroxyethyl)terephthalate (BHET), and PET is polymerized using the same as a raw material to produce recycled PET. As an example of the chemical recycling method of the PET, Chinese Patent Publication No. 103132175 suggests a method of depolymerizing polyester waste using a metal catalyst.

BHET prepared by depolymerization of waste PET contains many metal ionic materials derived from the depolymerization catalyst, which can be removed using an ion exchange resin. At this time, the metal ionic material, which is an impurity, is replaced with hydrogen ions, so that the acid value of BHET increases. Furthermore, in order to reuse the ion exchange resin, an acidic material such as sulfuric acid is used, which causes the acidic material to remain in the manufactured BHET. BHET prepared as described above needs to lower the acid value of BHET and remove residual acidic substances through a purification process. However, in order to sufficiently lower the acid value of BHET and sufficiently remove residual acidic substances, an expensive purification process is required. problems may occur.

The present invention seeks to provide a manufacturing process for chemically recycled PET. Specifically, in the manufacture of chemically recycled PET, purification is insufficient, so even if BHET having a high acid value is used, polymerization of chemically recycled PET is possible and a method capable of minimizing deterioration in physical properties is provided.

An exemplary embodiment of the present invention includes (A) preparing a dicarboxylic acid-diol slurry including a dicarboxylic acid compound and a diol compound; (B) mixing the dicarboxylic acid-diol slurry and bis-2-hydroxyethyl terephthalate (BHET) to obtain a mixed slurry; (C) subjecting the mixed slurry to an esterification reaction in the presence of a catalyst; And (D) a polycondensation reaction of the esterification reaction product in the presence of a catalyst; wherein at least one of steps (B) and (C) comprises introducing a basic compound, A method for producing recycled PET is provided.

In the method for manufacturing chemically recycled PET according to an exemplary embodiment of the present invention, even when BHET having a high acid value is used, catalysts used in esterification and polycondensation reactions can prevent activity from being lowered by generating acidic substances and salts remaining in BHET. can Furthermore, the method for manufacturing chemically recycled PET according to an exemplary embodiment of the present invention has the advantage of minimizing degradation of physical properties and enabling polymerization of chemically recycled PET even when BHET having a high acid value is used.

In the present specification, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Hereinafter, the present invention will be described in detail.

An exemplary embodiment of the present invention includes (A) preparing a dicarboxylic acid-diol slurry including a dicarboxylic acid compound and a diol compound;

(B) mixing the dicarboxylic acid-diol slurry and bis-2-hydroxyethyl terephthalate (BHET) to obtain a mixed slurry;

(C) subjecting the mixed slurry to an esterification reaction in the presence of a catalyst; and

(D) subjecting the esterification reaction product to polycondensation in the presence of a catalyst;

At least one of steps (B) and (C) provides a method for producing chemically recycled PET, including introducing a basic compound.

According to an exemplary embodiment of the present invention, the dicarboxylic acid-diol slurry may be prepared by introducing a dicarboxylic acid compound and a diol compound into a mixing vessel and then mixing them.

According to an exemplary embodiment of the present invention, the basic compound is a hydrate of at least one alkali metal selected from among sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium acetate; Acetates of alkali metals; alkoxides of alkali metals; carbonates of alkali metals; Hydrates of alkaline earth metals; acetates of alkaline earth metals; oxides of alkaline earth metals; alkoxides of alkaline earth metals; and carbonates of alkaline earth metals; At least one of them may be included. Specifically, the basic compound may include at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, and sodium acetate, and more specifically, may be sodium hydroxide.

According to an exemplary embodiment of the present invention, step (B) may include introducing a basic compound into the mixed slurry. Further, step (C) may include a step of introducing a basic compound at or before the start of the esterification reaction. Specifically, the basic compound may be introduced in step (B), or may be introduced in both steps (B) and (C).

As described above, BHET that has not been sufficiently purified has a high acid value and may contain residual acidic substances. Such high acid value BHET or residual acidic substances may cause deterioration of catalyst activity by generating catalysts and salts used in esterification and polycondensation reactions. Such a decrease in catalytic activity may cause chemically recycled PET with low physical properties to be produced because the esterification reaction and/or polycondensation reaction do not proceed smoothly, or chemically recycled PET may not be synthesized because the esterification reaction and/or polycondensation reaction do not proceed. may be

The method for manufacturing chemically recycled PET according to the present invention removes acidic substances remaining in BHET and/or lowers the acid value of BHET using a basic compound during the manufacturing process, thereby reducing the catalytic activity in the esterification reaction and/or polycondensation reaction. It can be prevented.

According to an exemplary embodiment of the present invention, the basic compound may be added in an equivalent amount of 1 to 5 times the amount required for neutralization of the bis-2-hydroxyethyl terephthalate. Specifically, the basic compound may be added in an equivalent amount of 1 to 3 times the amount required for neutralization of the bis-2-hydroxyethyl terephthalate. When an equivalent amount of the basic compound is added in the above range, the acid value of BHET is sufficiently lowered to prevent a decrease in catalytic activity in an esterification reaction and/or a polycondensation reaction. Furthermore, when the basic compound equivalent to the above range is added, even when low quality, that is, high acid value BHET is applied, the intrinsic viscosity (I.V.) of the finally obtained chemically recycled PET and residues such as ethylene glycol are reduced. By adjusting the amount of diol to less than 2 wt%, high physical properties similar to those of virgin PET can be realized.

According to an exemplary embodiment of the present invention, the acid value of the bis-2-hydroxyethyl terephthalate may be greater than 5 mg KOH/g. Specifically, the acid value of the bis-2-hydroxyethyl terephthalate may be greater than 10 mg KOH/g, greater than 20 KOH/g, or greater than 25 KOH/g. Chemically recycled PET manufactured by applying BHET in the above acid value range to a general chemically recycled PET manufacturing process may have an excessively high intrinsic viscosity and residual diol content, and furthermore, may have a problem of having an excessively low melting temperature (Tm). . In addition, when BHET in the above acid value range is applied to a general process for manufacturing chemically recycled PET, polymerization into PET may be impossible. In contrast, in the method for manufacturing chemically recycled PET according to the present invention, polymerization into PET is possible even when BHET in the above acid value range is applied, and deterioration in physical properties can be minimized.

According to an exemplary embodiment of the present invention, the BHET is a polymerization reactant containing BHET, and the content of BHET may be 25 mol% to 50 mol%. In the case of 100 mol% of BHET, since an esterification reaction is not required, it is not suitable for the manufacturing process of chemically recycled PET in the present invention using the existing PET manufacturing process, so it is not preferable.

According to an exemplary embodiment of the present invention, the dicarboxylic acid compound includes at least one selected from the group consisting of an aromatic dicarboxylic acid compound having 8 to 20 carbon atoms and an aliphatic dicarboxylic acid compound having 4 to 12 carbon atoms. can do. The aromatic dicarboxylic acid compound may be at least one selected from the group consisting of terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, and diphenyl dicarboxylic acid. In addition, the aliphatic dicarboxylic acid compound is at least one selected from the group consisting of cyclohexanedicarboxylic acid, phthalic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, adipic acid, glutaric acid and azelaic acid can be Specifically, the dicarboxylic acid compound may include at least one of terephthalic acid and isophthalic acid.

According to an exemplary embodiment of the present invention, the diol compound may include at least one selected from the group consisting of an aromatic diol compound having 8 to 40 carbon atoms and an aliphatic diol compound having 2 to 12 carbon atoms. The aromatic diol compound is polyoxyethylene-(a)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene-(b)-2,2-bis(4-hydroxyphenyl)propane and poly It may include at least one selected from the group consisting of oxypropylene-(c)-polyoxyethylene-(d)-2,2-bis(4-hydroxyphenyl)propane. Here, (a), (b), (c), and (d) may mean the number of polyoxyethylene or polyoxypropylene units. In addition, the aliphatic diol compound is at least one selected from the group consisting of ethylene glycol, diethylene glycol, triethylene glycol, propanediol, butanediol, pentanediol, hexanediol, neopentyl glycol, cyclohexanediol, and cyclohexanedimethanol. can include Specifically, the diol compound may include at least one of ethylene glycol and diethylene glycol.

According to an exemplary embodiment of the present invention, the catalyst may include at least one metal catalyst selected from the group consisting of a titanium compound, an antimony compound, a germanium compound, an aluminum-based compound, a tin-based compound, or a mixture thereof. The catalyst is for accelerating the esterification reaction and the polycondensation reaction sequentially performed in the PET polymerization process, and any catalyst used in the art may be appropriately used. The catalyst may be introduced in an amount of 1 ppm or more and 500 ppm or less based on the central atom with respect to the chemically recycled PET to be polymerized.

According to an exemplary embodiment of the present invention, a phosphorus-based stabilizer may be used in the esterification reaction and the polycondensation reaction. Specifically, in the esterification reaction and polycondensation reaction, a phosphorus stabilizer selected from the group consisting of phosphoric acid, trimethyl phosphate, triethyl phosphate, triphenyl phosphate, triethyl phosphono acetate, or a mixture of two or more thereof may be added.

According to an exemplary embodiment of the present invention, the esterification reaction of step (C) may be performed in a pressure range of 0 kg/cm 2 to 10.0 kg/cm 2 and a temperature range of 150° C. to 330° C. At this time, the esterification reaction conditions may be appropriately adjusted according to the desired characteristics of the chemically recycled PET to be produced and/or the molar ratio of the dicarboxylic acid component to glycol. More specifically, the esterification reaction may be carried out under a pressure range of 0 kg/cm 2 to 5.0 kg/cm 2 or 0.1 kg/cm 2 to 3.0 kg/cm 2 , and also at 200° C. to 330° C. or 230° C. to 280° C. It can be performed under a range of temperatures. The effluent generated during the esterification reaction is immediately removed, and the esterification reaction can be terminated when no more effluent is generated.

According to an exemplary embodiment of the present invention, the polycondensation reaction in step (D) may be carried out in a temperature range of 250 °C to 330 °C, specifically 270 °C to 290 °C, and also, 0.1 torr to 5 torr, specifically It may be performed under a pressure range of 0.5 torr to 2 torr. It may be necessary to immediately remove diol components such as ethylene glycol and by-products generated from the polycondensation reaction to prevent deterioration of physical properties of chemically recycled PET.

According to an exemplary embodiment of the present invention, the intrinsic viscosity of the PET composition in a molten state obtained through the esterification reaction and the polycondensation reaction is 0.50 dl/g or more and 0.90 dl/g or less, specifically 0.58 dl/g or more and 0.80 dl. /g or less. The intrinsic viscosity range is an intrinsic viscosity range suitable for use in PET products (eg, PET fibers or PET containers), and can be measured more conveniently than molecular weight measurement, through which the molecular weight of PET can be predicted.

According to an exemplary embodiment of the present invention, the PET composition in a molten state obtained through the esterification reaction and the polycondensation reaction may further increase the intrinsic viscosity through the polycondensation reaction, and the polycondensation reaction is performed at a temperature of 190 ° C. to 100 ° C. It may be performed under a temperature range of 240 °C and a pressure range of 0.2 torr to 2 torr. Further, the polycondensation reaction may be carried out under an inert atmosphere, for example, a nitrogen atmosphere.

Hereinafter, examples will be described in detail to explain the present invention in detail. However, embodiments according to the present invention can be modified in many different forms, and the scope of the present invention is not construed as being limited to the embodiments described below. The embodiments herein are provided to more completely explain the present invention to those skilled in the art.

[Reference Example 1]

In a slurry tank, 1563 g of terephthalic acid, 58 g of isophthalic acid, and 565 g of monoethylene glycol were added, and 600 ppm of antimony oxide catalyst (256 ppm based on antimony metal atoms) based on the total weight of the final PET resin produced was dissolved in the monoethylene glycol and added. Furthermore, after adding 827 g of BHET having an acid value of 1.6 mg KOH/g, the mixture was stirred at a temperature of about 50° C. for about 5 minutes to prepare a dicarboxylic acid-diol slurry.

After transferring the dicarboxylic acid-diol slurry to an ester reactor, an esterification reaction was performed at a temperature of about 260° C. and an atmospheric pressure, and the reaction was continued until no more effluent was generated. Then, the reaction product was transferred to a polycondensation reactor, and 145 ppm of triethylphosphonoacetate (20 ppm based on elemental phosphorus content) was added as a heat stabilizer, followed by stirring for about 5 minutes. In addition, the reaction was performed for about 2 hours while reducing the pressure to a final degree of vacuum of about 1 torr and raising the temperature to about 280 ° C. After the reaction was completed, the polycondensation reaction product was discharged and cut into chips, and intrinsic viscosity (I.V.), diethylene glycol content (DEG), and melting temperature (Tm) were measured.

[Comparative Example 1]

A polycondensation reaction product was obtained in the same manner as in Reference Example 1, except that BHET having an acid value of 7.6 mg KOH/g was applied, and its intrinsic viscosity (I.V.), diethylene glycol content (DEG) and melting temperature were obtained. (Tm) was measured.

[Example 1]

In the preparation of the dicarboxylic acid-diol slurry, a condensation polymerization reaction product was obtained in the same manner as in Reference Example 2, except that sodium hydroxide was added in an amount twice the equivalent amount capable of adjusting the acidity of BHET to neutral. , its intrinsic viscosity (I.V.), diethylene glycol content (DEG) and melting temperature (Tm) were measured.

[Comparative Example 2]

A polycondensation reaction product was obtained in the same manner as in Reference Example 1, except that BHET having an acid value of 23.2 mg KOH/g was applied, and its intrinsic viscosity (I.V.), diethylene glycol content (DEG) and melting temperature were obtained. (Tm) was measured.

[Example 2]

A polycondensation reaction product was obtained in the same manner as in Comparative Example 2, except that sodium hydroxide was added in an amount twice the amount of the equivalent to adjust the acidity of BHET to neutral, and its intrinsic viscosity (I.V.) , diethylene glycol content (DEG) and melting temperature (Tm) were measured.

[Comparative Example 3]

A polycondensation reaction product was obtained in the same manner as in Reference Example 1, except that BHET having an acid value of 35.4 mg KOH/g was applied, and its intrinsic viscosity (I.V.), diethylene glycol content (DEG) and melting temperature were obtained. (Tm) was measured.

[Example 3]

A condensation polymerization reaction product was obtained in the same manner as in Comparative Example 3, except that sodium hydroxide was added in an amount one-times the equivalent amount capable of adjusting the acidity of BHET to neutral, and its intrinsic viscosity (I.V.) , diethylene glycol content (DEG) and melting temperature (Tm) were measured.

[Example 4]

A polycondensation reaction product was obtained in the same manner as in Comparative Example 3, except that sodium hydroxide was added in an amount twice the equivalent amount to adjust the acidity of BHET to neutral, and its intrinsic viscosity (I.V.) , diethylene glycol content (DEG) and melting temperature (Tm) were measured.

[Example 5]

A polycondensation reaction product was obtained in the same manner as in Comparative Example 3, except that sodium hydroxide was added in an amount three times the amount of equivalent to adjust the acidity of BHET to neutral, and its intrinsic viscosity (I.V.) , diethylene glycol content (DEG) and melting temperature (Tm) were measured.

[Comparative Example 4]

A polycondensation reaction product was obtained in the same manner as in Reference Example 1, except that BHET having an acid value of 52 mg KOH/g was applied, and its intrinsic viscosity (I.V.), diethylene glycol content (DEG) and melting temperature were obtained. (Tm) was measured.

[Example 6]

A polycondensation reaction product was obtained in the same manner as in Comparative Example 4, except that sodium hydroxide was added in an amount 1.5 times the equivalent amount to adjust the acidity of BHET to neutral, and its intrinsic viscosity (I.V.) , diethylene glycol content (DEG) and melting temperature (Tm) were measured.

[Example 7]

A condensation polymerization reaction product was obtained in the same manner as in Comparative Example 4, except that sodium hydroxide was added in an amount twice the amount of equivalent to adjust the acidity of BHET to neutral, and its intrinsic viscosity (I.V.) , diethylene glycol content (DEG) and melting temperature (Tm) were measured.

The results of measuring the physical properties of the compositions and prepared polycondensation reaction products (PC products) according to the Reference Examples, Examples and Comparative Examples are shown in Table 1 below.

[Table 1]

- Measurement of IV (intrinsic viscosity) : 0.4 g of the PC reaction product was added to 100 ml of a 6:4 mixed solution of phenol and 1,1,2,2-Tetrachloroethane, dissolved at 120 ° C for 90 minutes, and then removed using a filter. After filtering, the sample was sucked into an Ubbelohde viscometer at a temperature of 30 ° C., the solution was dropped, the number of seconds of falling was measured, and IV was calculated by substituting into the following formula.

* I.V. = 1/4(R.V.-1)/C + 3/4(ln R.V./C)

- Analysis of DEG: After putting 1 g of the PC reaction product in a 50 mL container, 3 mL of monoethanolamine was added and heated to completely dissolve the sample, and then cooled to 100 ° C, followed by 0.005 g of 1,6-hexanediol. was added in 20 mL of methanol, and neutralized by adding 10 g of terephthalic acid. After filtering the obtained neutralization solution using a funnel and filter paper, the filtrate was subjected to gas chromatography to measure DEG (diethylene glycol) content. DEG becomes the starting point of providing radicals during thermal oxidative decomposition within the PET chain, which can cause yellowing, and can form dioxane in effluent from esterification, so it is important to control the DEG content. .

In the results of Table 1, in the case of Example 1 in which BHET having an acid value of 7.6 mg KOH/g was applied, the addition of sodium hydroxide had the effect of increasing the melting temperature of the polycondensation reaction product by 1 ° C, but the addition of sodium hydroxide had no significant effect. However, in Examples 2 to 7, in which BHET having an acid value exceeding 10 mg KOH/g was applied, sodium hydroxide was added to control the DEG content, which causes yellowing of PET products, and to reduce the melting temperature of polycondensation products. I was able to confirm that I could control it. In particular, referring to Comparative Example 4, when BHET having an acid value of 52 mg KOH/g was applied, it was confirmed that the polycondensation reaction did not proceed without adding sodium hydroxide.

Claims (5)

(A) preparing a dicarboxylic acid-diol slurry containing a dicarboxylic acid compound and a diol compound;
(B) mixing the dicarboxylic acid-diol slurry and bis-2-hydroxyethyl terephthalate (BHET) to obtain a mixed slurry;
(C) subjecting the mixed slurry to an esterification reaction in the presence of a catalyst; and
(D) subjecting the esterification reaction product to polycondensation in the presence of a catalyst;
At least one step of step (B) and step (C) includes the step of introducing a basic compound,
Manufacturing method of chemically recycled PET. The method of claim 1,
Characterized in that the acid value of the bis-2-hydroxyethyl terephthalate is greater than 5 mg KOH / g, a method for producing chemically recycled PET. The method of claim 1,
The basic compound is added in an equivalent amount of 1 to 5 times the amount required for neutralization of the bis-2-hydroxyethyl terephthalate. The method of claim 1,
The dicarboxylic acid compound comprises at least one selected from the group consisting of an aromatic dicarboxylic acid compound having 8 to 20 carbon atoms and an aliphatic dicarboxylic acid compound having 4 to 12 carbon atoms, chemically recycled PET. Manufacturing method of. The method of claim 1,
The method for producing chemically recycled PET, characterized in that the diol compound includes at least one selected from the group consisting of an aromatic diol compound having 8 to 40 carbon atoms and an aliphatic diol compound having 2 to 12 carbon atoms.