KR20210067555A - Method for chemical recycling waste plastics including crystallization - Google Patents

Abstract

The present invention relates to a method for regenerating a crystal filtrate after recovering BHET crystals during a waste plastic chemical recycling process and reusing the same. More specifically, the present invention provides a method for chemical recycling of waste plastics comprising the following steps: depolymerizing waste PET in a reaction solvent to produce a depolymerization solution containing BHET; crystallizing BHET in the depolymerization solution, separating and recovering BHET crystals, and obtaining a crystal filtrate; and removing impurities from the crystal filtrate to obtain a regenerated crystal filtrate.

Description

Method for chemical recycling of waste plastics including crystallization {METHOD FOR CHEMICAL RECYCLING WASTE PLASTICS INCLUDING CRYSTALLIZATION}

The present invention relates to a method for chemically recycling waste plastics by regenerating a crystal filtrate after recovering BHET crystals during a chemical recycling process of waste plastics and reusing them.

In general, in chemical recycling of waste plastics, specifically waste PET, BHET is generated by depolymerizing waste PET to obtain a depolymerization solution, and the temperature of the depolymerization solution is lowered to produce BHET (bis(2-hydroxyethyl) terephthalate). By crystallizing and solid-liquid separation, the desired product, BHET crystal, is obtained with high purity.

In this process, after recovering the BHET crystals obtained by crystallization, the crystal filtrate remains. The crystal filtrate contains ethylene glycol as a reaction solvent, a depolymerization catalyst, and BHET remaining dissolved in the reaction solvent.

Conventionally, the crystal filtrate was immediately discarded without reuse, or the crystal filtrate was distilled and purified to recover and reuse only ethylene glycol as a reaction solvent.

For example, Japanese Patent Laid-Open No. 2000-169623 discloses a method of recycling polyethylene terephthalate (PET) waste by depolymerizing waste PET under the boiling point condition of ethylene glycol, a reaction solvent, and distilling and evaporating the obtained depolymerization solution to ethylene Disclosed is a method for obtaining concentrated BHET by concentrating BHET by evaporating off glycol, or by cooling a depolymerization solution to crystallize BHET and then separating solid BHET crystals by solid-liquid separation. The ethylene glycol separated by evaporation is directly recycled back to the depolymerization process and recycled, or the ethylene glycol separated in the concentration process is purified by a method such as distillation and remanipulation, and then as a reaction solvent of the depolymerization process. A method for chemical recycling of recycled waste is disclosed.

However, a lot of energy is consumed to separate ethylene glycol by the BHET concentration process through the distillation and evaporation operation, and a lot of energy is consumed even when ethylene glycol separated by solid-liquid separation is purified by refining operation such as distillation. . In addition, unreacted raw materials and depolymerization catalysts in solution are included in the purification process of ethylene glycol, but these useful components are eventually discarded and cannot be recycled, so there is a problem of loss of raw materials.

In addition, Japanese Patent Laid-Open No. 2008-088096 discloses a process of obtaining BHET by mixing a raw material containing polyethylene terephthalate and a depolymerization catalyst with ethylene glycol to depolymerize it, and a process of recovering BHET from the depolymerization solution obtained in the depolymerization reaction process. technology is launched. In the process of recovering BHET, a residue is obtained by evaporating substances such as ethylene glycol having a lower boiling point than BHET, and BHET is recovered from the residue. However, the above patent does not disclose the recycling of the depolymerization catalyst used in the depolymerization reaction and ethylene glycol as the reaction solvent, and the treatment method for unreacted waste PET is not disclosed, resulting in a loss of raw and subsidiary materials.

In performing the chemical recycling process of waste PET, by reusing the depolymerization catalyst, reaction solvent, unreacted waste PET, etc., which are useful components contained in the crystal filtrate that were conventionally discarded, the economic feasibility of the process is improved, and the productivity of the process The development of technologies that can improve

The crystal filtrate remaining after recovering BHET crystals during the chemical recycling process of waste plastics contains useful components, such as a depolymerization catalyst, unreacted waste PET, and a reaction solvent. The present invention reprocesses the crystal filtrate containing these useful components Accordingly, it is intended to provide a method for chemical recycling of waste plastics that is reused as a reaction solution for depolymerization.

One aspect of the present invention relates to a method for recycling waste plastics that are used as a reaction solvent by regenerating a crystal filtrate generated in a chemical recycling process of waste plastics. generating; crystallizing BHET in the depolymerization solution, separating and recovering BHET crystals, and obtaining a crystal filtrate; and removing impurities from the crystal filtrate to obtain a regenerated crystal filtrate.

According to the method of the present invention, the loss of raw and subsidiary materials can be minimized by recovering raw and subsidiary materials and recycling them in the process, and BHET productivity can be improved.

According to one embodiment of the present invention, the crystal filtrate can be reused without a distillation operation, energy use can be minimized, and cost reduction can be achieved by recycling raw and subsidiary materials.

In addition, according to one embodiment of the present invention, in reusing the crystal filtrate, the quality of the BHET product can be prevented from being deteriorated due to the concentration of impurities contained in the crystal filtrate, and the production efficiency of BHET can be improved. can

1 is a view schematically showing a process waste recycling facility to which the method of the present invention is applied.

The present invention relates to a method for chemical recycling of waste PET, through reuse of depolymerization catalyst and reaction solvent, which are useful components contained in a crystal filtrate obtained by recovering BHET after depolymerization reaction of waste PET and crystallization of BHET, to reduce raw and subsidiary material costs and It aims to improve the productivity of the process.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The accompanying drawings are for explanation of the present invention, and are not intended to limit the present invention thereby.

In the method of the present invention, a waste PET product may be used as a waste plastic raw material for chemical recycling. As the waste PET product, if it is made of PET, it may be suitably used in the present invention, for example, it may be collected from containers, films, resins, textile products, and the like.

The waste PET product may be pulverized and used in the form of flakes. However, the shape and size of the flakes are not particularly limited.

The waste PET may generally contain impurities such as glass, metal, other plastics, wood, paper, and other inorganic materials in an amount of less than 2% by weight, preferably less than 1% by weight.

and putting the waste PET into a depolymerization reactor and performing a depolymerization reaction. In the depolymerization reaction, waste PET, a depolymerization catalyst, and a reaction solvent are added into a depolymerization reactor, and the depolymerization reaction may be performed in a predetermined temperature range.

In the depolymerization reaction, the reaction solvent is not particularly limited, but polyhydric alcohol may be used, and examples thereof include ethylene glycol, diethylene glycol, tripropylene glycol, 1,2-propylenediol, 1,3-propylenediol, 1 _{and (C 2} -C ₆ )alkylenediol such as ,2-butanediol, 1,4-butanediol, and 2,3-butanediol. The reaction solvent is not particularly limited, but may be added in an amount of 0.1 parts by weight or more and 40 parts by weight or less based on 1 part by weight of waste PET as raw material.

Furthermore, the depolymerization catalyst is not particularly limited as long as it is a catalyst that is commonly used in the depolymerization of PET, and can be suitably used in the present invention. For example, metal acetate or a hydrate thereof may be used. The metal acetate may include, for example, zinc acetate, sodium acetate, tin acetate, antimony acetate, manganese acetate, cobalt acetate, and the like, and any one of these may be used alone, as well as a mixture of two or more. can also be used. The depolymerization catalyst may be added, for example, in an amount of 0.1 parts by weight or more and 5 parts by weight or less based on 100 parts by weight of waste PET as a raw material.

As the reaction conditions for the depolymerization reaction, a conventional method applied to the depolymerization reaction of PET may be used, and the present invention is not particularly limited. For example, it can be carried out at a temperature equal to or higher than the boiling point of the reaction solvent. For example, when the reaction solvent is ethylene glycol, it can be carried out at a temperature of about 197 ° C., and also at a temperature higher than the melting point of PET, for example , it can be carried out in a temperature range of 240 °C or higher and 300 °C or lower. Furthermore, the depolymerization reaction may be carried out under atmospheric pressure, as well as under pressure conditions, for example, pressure conditions of 2 bar or more and 10 bar or less.

A depolymerization solution in which BHET is generated is obtained by the depolymerization reaction as described above. The depolymerization solution produced may contain heterogeneous polymers or other impurities other than PET contained in waste PET, which is the raw material, and, in some cases, unreacted PET. have. Therefore, it is preferable to remove them from the depolymerization solution if necessary. These solid impurities from the neutral pressure solution can be removed by filtration or the like, for example, a filter or the like can be used.

BHET is separated and recovered from the depolymerization solution produced by the depolymerization reaction. The separation and recovery of BHET is not particularly limited as a commonly used method can be applied, but for example, the depolymerization solution is cooled to a temperature of 0°C or higher and 100°C or lower to obtain BHET. A crystallization solution is obtained by crystallization, and BHET crystals can be concentrated and separated from the crystallization solution by solid-liquid separation. More preferably, it can cool to the temperature of 0 degreeC or more and 10 degrees C or less.

For the solid-liquid separation, the solid-liquid separation means 103 as shown in FIG. 1 can be applied, and although not necessarily limited thereto, commonly used solid-liquid separation means such as a filter and a centrifuge can be used. The solid-liquid separation means 103 can be used to separate solid BHET crystals and crystal filtrate from the crystallization solution. The filter may use, for example, a filter cloth having a filter size of 0.1 mm or more and 10 mm or less.

In the solid-liquid separation, the temperature of the crystallization solution may be set to 0°C or higher and 100°C or lower. In the case of solid-liquid separation of the crystallization solution under the above temperature range, BHET in the crystallization solution can be maintained in a crystalline state, thereby further improving the solid-liquid separation efficiency.

A crystal filtrate can be obtained by solid-liquid separation of the BHET crystal, and the crystal filtrate may contain ethylene glycol as a reaction solvent and a depolymerization catalyst as useful components. For example, the crystal filtrate obtained after solid-liquid separation such as filtration is mostly occupied by a reaction solvent such as ethylene glycol, and contains a metal salt, which is a depolymerization catalyst, at a level of 0.1 wt% or more and 10 wt% or less. Accordingly, process economy can be promoted by recycling these useful components in the depolymerization process.

On the other hand, the crystal filtrate contains not only useful components as described above, but also impurities. In general, BHET is mainly produced by depolymerization of PET, but mono-(2-hydroxyethyl) terephthalate (MHET), 2-hydroxyethyl [2-(2-hydroxyethoxy) ethyl] terephthalate Ester compounds other than BHET such as (DEG-ester) and by-products such as diethylene glycol (DEG) may be generated, and colorable impurities used in waste PET products used as raw materials, that is, colorants, etc. may exist. can

When the crystal filtrate containing the above impurities is reused for the depolymerization reaction in order to utilize the useful components, since there is a risk of lowering the quality of the BHET produced by the depolymerization reaction, it is preferable to remove it. Removal of such impurities removes ester compounds other than BHET such as colorants and DEG-esters, and thereafter, organic acid salts such as MHET may be removed. However, the removal of the impurities is not necessarily performed in the above order, and may be performed in the reverse order.

Among the impurities contained in the crystal filtrate, colorants and ester compounds other than BHET such as DEG-ester may be removed from the crystal filtrate by adsorption by the adsorber 104 as shown in FIG. 1 . The adsorption of ester compounds other than BHET such as the colorant component and DEG-ester can be performed by activated carbon, and the colorant and DEG contained in the crystal filtrate by passing the crystal filtrate through an adsorber 104 containing activated carbon as an adsorbent -Ester can be removed, and a part of MHET can also be removed by adsorption.

At this time, the activated carbon is not limited thereto, and may be used in an amount of 0.1 parts by weight or more and 20 parts by weight or less based on the total weight of the crystal filtrate in terms of economic efficiency. Furthermore, in performing the adsorption process, the crystal filtrate is passed through the adsorber 104 at a temperature range of 100° C. or less, for example, 50° C. or more, and 100° C. or less for 0.1 hours or more and 2 hours or less. have.

The crystal filtrate contains an organic acid salt such as MHET at a level of 0.1 wt% or more and 15 wt% or less, and a metal salt at a level of 0.1 wt% or more and 10 wt% or less, based on the total weight of the crystal filtrate. Among them, the organic acid salt may be removed through the ion exchanger 105 including the weakly basic anion exchange resin, as shown in FIG. 1 . The organic acid salt such as MHET may be partially adsorbed by activated carbon, but since the removal efficiency is relatively low, it is more preferable to remove it through an ion exchanger.

At this time, by bringing the crystal filtrate into contact with the ion exchanger 105 at a temperature of pH 7 or more, 10 or less, and 100° C. or less, for example, 50° C. or more, and 100° C. or less for 0.1 hours or more and 2 hours or less, the organic acid salt can be removed. By passing the ion exchanger 105 including the ion exchange resin through, while maintaining the content of the metal salt present in the crystal filtrate, only the organic acid salt is selectively removed to reduce the organic acid salt content to a level of 1 wt% or less. .

As described above, by treating the crystal filtrate through the adsorber 104 and the ion exchanger 105 according to the method of the present invention, the content of impurities contained in the crystal filtrate can be significantly reduced, and the organic acid salt as a catalyst and the reaction solvent It can be regenerated with a reaction solution containing , and can be reused as a reaction solution for depolymerization of PET. The regenerated reaction solution may be used alone or by adding a new reaction solvent and catalyst for depolymerization of waste PET.

Usually, the reaction solvent is used in an amount of 0.1 parts by weight or more and 40 parts by weight or less based on 1 part by weight of waste PET, and the depolymerization catalyst is used in the range of 0.1 to 5 parts by weight based on 100 parts by weight of the raw material. can be reused as a regenerated reaction solution, thereby reducing the amount of use of a new reaction solvent and a new catalyst.

In addition, the reaction solution regenerated from the crystal filtrate according to the present invention has the same level of PET depolymerization performance as the new reaction solution because impurities are removed, so the regenerated reaction solution can be suitably used in the chemical recycling process of waste PET. , even when PET is depolymerized using such a regeneration reaction solution, the impurity content is low, and high-quality BHET can be manufactured.

Example

Hereinafter, embodiments of the present invention will be described in detail. The following examples are only for understanding of the present invention, and are not intended to limit the present invention.

Example One

(1) After adding 1 g of zinc acetate as a depolymerization catalyst to 400 g of ethylene glycol, it was added to the depolymerization reactor 100 together with 100 g of waste PET flakes (diameter 10 mm).

After raising the temperature of the depolymerization reactor 100 to 197° C., the depolymerization reaction was performed for 2 hours to produce a depolymerization solution containing BHET.

Subsequently, the depolymerization solution containing BHET was cooled to 5° C. to crystallize BHET, and then filtered through a filter 103 equipped with a 1 mm filter cloth to obtain BHET crystals and crystal filtrate, respectively.

(2) At a temperature of 50° C., 400 g of the obtained crystal filtrate was passed through an adsorber 104 filled with 20 g of activated carbon over a total contact time of 30 minutes to remove organic matter and colorants.

Then, the 50 ℃ crystal filtrate (pH 8) passed through the adsorber was passed through the ion exchanger 105 filled with a weakly basic anion exchange resin (DIAION WA20, manufactured by Samyang Corporation) over a contact time of 30 minutes.

Thereby, it was regenerated from the crystal filtrate to obtain a regenerated reaction solution.

The regenerated reaction solution was introduced into the depolymerization reactor 100, and 100 g of waste PET was depolymerized at 197° C. for 2 hours to obtain a BHET product.

The yield and BHET b-value of the obtained BHET crystals were analyzed, and the results are shown in Table 1. A high BHET b-value indicates a high content of impurities such as ester compounds other than BHET.

The yield of the product (BHET) obtained by using the regeneration reaction solution was determined by performing qualitative and quantitative analysis using LC-UV/MS on the solution obtained after depolymerization to measure the BHET concentration in the solution, and then the following formula (1) was calculated. The results are shown in Table 1.

(1)

(One)

On the other hand, the content of impurities (MHET, DEG-ester) in the crystal filtrate and the regenerated reaction solution after removing the BHET crystal is confirmed by changing the b-value of the product (BHET) obtained using the regenerated reaction solution, and the The results are shown in Table 1.

Example 2

In Example 1, depolymerization was carried out in the same manner as in Example 1, except that 200 g of a reaction solution containing 200 g of an ethylene glycol reaction solvent and 0.5 g of a fresh depolymerization catalyst was mixed in a weight ratio of 1:1 to the regenerated reaction solution. The reaction was carried out to obtain BHET crystals.

The yield and BHET b-value of the obtained BHET crystals were analyzed in the same manner as in Example 1, and the results are shown in Table 1.

comparative example One

BHET crystals were obtained in the same manner as in Example 1, except that the depolymerization reaction was performed using 400 g of the same crystal filtrate as in Example 1.

The yield and BHET b-value of the obtained BHET crystals were analyzed in the same manner as in Example 1, and the results are shown in Table 1.

comparative example 2

BHET crystals were obtained by carrying out the depolymerization reaction in the same manner as in Example 1, except that 200 g of the same crystal filtrate as in Example 1 and 200 g of a reaction solution containing a fresh depolymerization catalyst were mixed in a 1:1 ratio to carry out the depolymerization reaction. did.

The yield and BHET b-value of the obtained BHET crystals were analyzed in the same manner as in Example 1, and the results are shown in Table 1.

Reference example One

BHET crystals were obtained from the depolymerization solution obtained in the process of (1) in Example 1.

The yield and BHET b-value of the obtained BHET crystals were analyzed in the same manner as in Example 1, and the results are shown in Table 1.

Item Example 1 Example 2 Comparative Example 1 Comparative Example 2 Reference Example 1 pH in the ion exchanger 8 8 - - - Regeneration reaction solution usage ratio (compared to new reaction solution) 100% 50% 100% 50% 0% BHET yield (%) 78.5 82.4 67.3 75.2 83.5 BHET b-value 0.8 0.5 3.7 2.5 0.4

As can be seen from Table 1, when the crystal filtrate is reused as a reaction solution after removing impurities according to the method of the present invention as in Examples 1 and 2, it is possible to minimize the change in physical properties of the BHET product, BHET can be produced, and furthermore, the crystal filtrate can be reused, so that the economic feasibility of the process can be secured, and the auxiliary materials can be recycled, thereby improving productivity.

100: depolymerization reactor
103: solid-liquid separation means
104: adsorber
105: ion exchanger

Claims (6)

depolymerizing waste PET in a reaction solvent to produce a depolymerization solution containing BHET;
crystallizing BHET in the depolymerization solution, separating and recovering BHET crystals, and obtaining a crystal filtrate; and
removing impurities from the crystal filtrate to obtain a regenerated crystal filtrate
A method for chemical recycling of waste plastics, comprising: The chemical recycling method of waste plastic according to claim 1, wherein the impurities are removed by an activated carbon adsorbent or an ion exchange resin. The chemical recycling method of waste plastic according to claim 2, wherein the activated carbon adsorbent adsorbs and removes at least one of an ester compound and a colorant other than BHET. The chemical recycling method of waste plastic according to claim 2, wherein the organic acid salt is removed with the ion exchange resin. The method for chemical recycling of waste plastics according to any one of claims 1 to 4, wherein the regenerated crystal filtrate is used as the reaction solvent. The chemical recycling method of waste plastic according to claim 5, wherein a new depolymerization catalyst and a reaction solvent are additionally added to the regenerated crystal filtrate.

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