WO2016111289A1 - Method for producing terephthalic acid and method for producing recycled polyethylene terephthalate - Google Patents

Abstract

This method for producing terephthalic acid has: a first hydrolysis step for hydrolyzing polyethylene terephthalate by exposing a material to be treated that contains polyethylene terephthalate, which has been stored in a sealed container, to an atmosphere of from normal pressure to saturated water vapor pressure, and obtaining a hydrolysate containing terephthalic acid and/or an ethylene terephthalate oligomer; and a second hydrolysis step for obtaining terephthalic acid by hydrolyzing, in hot water, the ethylene terephthalate oligomer obtained in the first hydrolysis step, the weight of hot water in the second hydrolysis step being twice or more the weight of the material to be treated used in the first hydrolysis step.

Description

Method for producing terephthalic acid and method for producing recycled polyethylene terephthalate

The present invention relates to a method for producing terephthalic acid and a method for producing recycled polyethylene terephthalate, for example, a production method for obtaining terephthalic acid as a synthetic raw material from a polyethylene terephthalate molded article such as a beverage bottle, film, or sheet, and The present invention relates to a method for producing recycled polyethylene terephthalate using the produced terephthalic acid.

Polyester resins are widely used for various applications because of their excellent properties. For example, polyethylene terephthalate (PET) is excellent in chemical stability, so it is produced in large quantities in the food field as life-related materials such as fibers, films, and resins, especially as bottles for drinking water and carbonated beverages. in use. However, the processing of fibers and films, resin product waste, non-standard molded products, etc., which are generated in large quantities as production and usage increases, is currently becoming a major social problem, From the viewpoint of effective utilization, a method for effectively recycling these polyester-based resin molded products is required.
As such a recycling method, various methods such as a material recycling method and a chemical recycling method have been proposed.

The Material Recycling Law means that the polyester resin is melted and reused at high temperatures without decomposing it, so the quality of the recycled product gradually decreases compared to the polyester resin before recycling due to its thermal history. There is a problem. Further, when a component (impurity) other than the polyester-based resin is contained, it is difficult to completely remove the impurity, so that there is a problem that the quality further deteriorates. Therefore, it is difficult to obtain the same quality as the polyester resin before recycling except in some cases such as using the runner generated during injection molding as it is after pulverization.

On the other hand, chemical recycling methods can generally be classified into four types: (1) raw materials, (2) reducing agents, (3) gas / oilification, and (4) thermal recycling. Among these, the raw material is attracting attention as an advantageous method because it can obtain a product having the same quality as the polyester resin before recycling.

In Patent Document 1, as an example of making polyethylene terephthalate as a raw material, polyethylene terephthalate is decomposed to dimethyl terephthalate and further to terephthalic acid by ethylene glycol decomposition / methanol treatment, and again condensed with ethylene glycol to form a “bottle”. A method of “to bottle” is disclosed.

Further, in Patent Document 2, when terephthalic acid as a hydrolysis catalyst is added to polyethylene terephthalate and hydrolyzed in hot water at 300 ° C., terephthalic acid is obtained in a yield of 100% in about 10 minutes. Has been reported.

Furthermore, Patent Document 3 discloses that an object to be processed containing polyethylene terephthalate is exposed to a water vapor atmosphere filled with a saturated water vapor pressure at the processing temperature, and saturated water vapor generated at the processing temperature causes the above object to be processed. Is disclosed in which polyethylene terephthalate contained in is hydrolyzed, and ethylene glycol is separated as a gas or liquid component and terephthalic acid is separated as a solid component.

Japanese Unexamined Patent Publication No. 2003-119316 Japanese Unexamined Patent Publication No. 2007-332361 Japanese Unexamined Patent Publication No. 2008-308416

However, the method of Patent Document 1 has problems such as complicated operations and high costs, and a large amount of capital investment. The method of Patent Document 2 has a high temperature of 150 to 350 ° C. without adding dicarboxylic acid. It has been shown that when polyester is hydrolyzed in water, it cannot be sufficiently hydrolyzed, suggesting that dicarboxylic acid as a hydrolysis catalyst is indispensable for hydrolysis in high-temperature water.
In addition, the method of Patent Document 3 requires the preparation of a pressure-resistant processing chamber provided with a stirring means inside and a cooling tower for recovering ethylene glycol, and the apparatus becomes large and there is room for improvement. there were. In addition, when polyethylene terephthalate contains impurities, there is a problem that the quality of terephthalic acid and ethylene glycol recovered by hydrolysis treatment is deteriorated.

Polyester resin is a synthetic resin obtained from limited petroleum resources, so the establishment of technology for chemically recycling polyester resin waste is an urgent issue in order to build a society that can sustain its supply. It is. In particular, polyethylene terephthalate is excellent in chemical resistance and heat resistance, and when used for foods, its safety is good, so it is widely used in various fields, and its recycling is an important issue. However, as described above, the establishment of a method in which both maintenance of quality and economy (suppression of running cost and initial cost) have not been established yet, and the development is urgently required.

Therefore, an object of the present invention is to treat a material to be treated containing polyethylene terephthalate by chemical recycling technology without using a large-scale apparatus or cost, and to synthesize the polyethylene terephthalate without using a special hydrolysis catalyst. It is to provide a method for producing terephthalic acid capable of recovering terephthalic acid which is a high quality and high yield, and a method for producing regenerated polyethylene terephthalate obtained using the obtained terephthalic acid.

As a result of intensive studies in view of the above problems, the present inventors first exposed a polyethylene terephthalate molded article (object to be treated) to an atmosphere of atmospheric pressure to a saturated water vapor pressure to hydrolyze, so that terephthalic acid or A first hydrolyzate containing an ethylene terephthalate oligomer is obtained, and further, the first hydrolyzate is hydrolyzed in a specific volume of hot water, so that it can be easily synthesized compared with the conventional chemical recycling method. The inventors have found that terephthalic acid can be obtained, and have completed the present invention.

That is, according to the present invention, after storing an object to be treated containing polyethylene terephthalate in a sealed container, the polyethylene terephthalate is hydrolyzed by exposure to an atmosphere of normal pressure to saturated water vapor pressure, from terephthalic acid, terephthalic acid and ethylene glycol. A first hydrolysis step to obtain a hydrolyzate containing at least one of the oligomers (ethylene terephthalate oligomer) to be obtained, and terephthalic acid by hydrolyzing the ethylene terephthalate oligomer obtained in the first hydrolysis step in hot water And the weight of hot water in the second hydrolysis step is at least twice the weight of the object to be treated used in the first hydrolysis step. To a method for producing terephthalic acid.

In the present invention, the temperature of hot water in the second hydrolysis step is preferably 150 to 300 ° C.

In addition, the weight of hot water in the second hydrolysis step is preferably 2 to 10 times the weight of the object to be treated used in the first hydrolysis step.

Moreover, it is preferable to transfer the total amount of the hydrolyzate containing at least one of terephthalic acid and ethylene terephthalate oligomer obtained in the first hydrolysis step to the second hydrolysis step.

Furthermore, it is preferable to perform the first hydrolysis step and the second hydrolysis step continuously in a closed container.

Furthermore, the present invention relates to a method for producing recycled polyethylene terephthalate, characterized in that polyethylene terephthalate is produced by condensation polymerization of the terephthalic acid obtained above with ethylene glycol.

In the method for producing terephthalic acid of the present invention, an object to be treated containing polyethylene terephthalate is hydrolyzed by exposure to an atmosphere of atmospheric pressure to saturated water vapor pressure, and terephthalic acid or an ethylene terephthalate oligomer (an oligomer comprising terephthalic acid and ethylene glycol). ), And the oligomer obtained in the first hydrolysis step is further hydrolyzed by heating in hot water having a weight twice or more that of the object to be processed to obtain terephthalic acid. It has a 2nd hydrolysis process. In the second hydrolysis step, the hydrolysis efficiency in hot water is markedly increased by setting the weight of hot water to be used to be twice or more the weight of the object to be treated used in the first hydrolysis step. Can be improved.

In the first hydrolysis step, polyethylene terephthalate in the object to be treated is decomposed by water vapor and the polyethylene terephthalate is oligomerized. A part of the oligomer decomposes to terephthalic acid. In the subsequent second hydrolysis step, the oligomer obtained in the first hydrolysis step is further hydrolyzed in an excess amount of hot water more than twice as much as the weight of the object to be treated. Among the raw materials constituting this oligomer, water-soluble ones such as ethylene glycol are dissolved in hot water, and non-water-soluble ones such as terephthalic acid are solid in hot water. The resulting raw material can be recovered with high quality simply and without cost.

By utilizing the technology of the present invention, the object to be treated is not only polyethylene terephthalate, but also used in large quantities such as polyethylene naphthalate, polybutylene terephthalate, polybutylene naphthalate, polytrimethylene terephthalate, and the amount thereof. Even in the case of other general-purpose polyester resins that are difficult to process due to their large number, the synthetic raw materials can be easily recovered with high quality without incurring costs.

Further, if the first hydrolysis step and the second hydrolysis step in the present invention are carried out continuously in a sealed container, the stirring means and cooling tower described in Patent Document 3 are not required, and at low cost, It becomes possible to obtain a terephthalic acid by hydrolyzing an object to be treated containing polyethylene terephthalate with high quality and high recovery rate.

Since the terephthalic acid obtained as described above is obtained by the chemical recycling method, it is possible to produce recycled polyethylene terephthalate without causing quality degradation by condensation polymerization reaction with ethylene glycol separately procured. Can do. Thus, the production method of the present invention is a very useful method for recycling (recycling) useful resources.

FIG. 1 is a production process diagram for explaining the production method of terephthalic acid of the present invention. 2 (a) to 2 (e) are schematic diagrams for explaining the processing method according to the preferred embodiment of the present invention.

Hereinafter, embodiments of the method for producing terephthalic acid and the method for producing recycled polyethylene terephthalate according to the present invention will be described in detail.

The object to be treated used in the method for producing terephthalic acid of the present invention contains polyethylene terephthalate, and there are no particular restrictions on the type and raw materials other than polyethylene terephthalate contained therein, which are conventionally known or publicly used. It can be various processed objects.

Polyethylene terephthalate as an object to be treated in the present invention is a general-purpose polyester resin obtained by condensation polymerization of ethylene glycol as a polyol component, which is a synthetic raw material, and terephthalic acid as a polycarboxylic acid component. In addition to the terephthalic acid, the polycarboxylic acid component may partially contain isophthalic acid or phthalic acid.

In addition, the form of the object to be treated in the present invention is not particularly limited, and various molded articles, typically wastes of various molded articles that have been used and should be reprocessed can be used. Examples thereof include fibers, films, sheets, bottles for drinking water and carbonated drinks, adhesive tapes, food trays, and the like.

In addition, various molded products as the object to be treated are often mixed with raw materials such as various additives other than polyethylene terephthalate depending on the usage form, but in the present invention, the types of these raw materials are limited. It is not something.
Examples of additives that may be added to various molded articles as such objects to be treated include known flame retardants, plasticizers, lubricants, colorants (pigments, dyes, etc.), ultraviolet absorbers, and antioxidants. Anti-aging agents, fillers, reinforcing agents, antistatic agents, surfactants, tension modifiers, shrinkage inhibitors, fluidity modifiers, surface treatment agents, and the like.

Further, the object to be treated may be not only a molded product made of only polyethylene terephthalate but also a composite product with other materials. That is, it may be a composite product such as a laminate of a layer made of polyethylene terephthalate and a layer containing a resin other than polyethylene terephthalate. Specifically, for example, when the object to be treated is an adhesive tape, a laminate of a polyethylene terephthalate film that has been subjected to a back treatment and an adhesive layer made of an acrylic adhesive, a rubber adhesive, a silicone adhesive, or the like. And a laminate in which a release sheet having a release agent composed of a silicone resin or the like on one side is provided on the surface of the pressure-sensitive adhesive layer. In the present invention, even such a laminate can be treated. It is.
However, from the viewpoint of the recovery efficiency of terephthalic acid obtained by the production method of the present invention, the content of polyethylene terephthalate in the object to be treated is, for example, 40% by weight or more, preferably 60% by weight or more.

In the present invention, the object to be treated may be in the form as it is, but the final product is a hydrolyzate obtained by hydrolyzing polyethylene terephthalate in the first hydrolysis step and the second hydrolysis step of the present invention described later. In order to efficiently decompose even the terephthalic acid as the target product, as a pretreatment, the object to be treated is preliminarily crushed or cut into an appropriate size before the hydrolysis treatment, and further, foreign matter adhering to the surface by washing treatment is removed. It is preferable to remove it.

The method for producing terephthalic acid according to the present invention comprises subjecting an object to be treated containing polyethylene terephthalate to pretreatment such as crushing, cutting and washing, if necessary, and exposing to an atmosphere of water vapor from atmospheric pressure to saturated water vapor pressure. Hydrolyzing the ester bond existing in the molecule of the first hydrolyzing step to obtain a first hydrolyzate containing at least one of terephthalic acid and an oligomer composed of terephthalic acid and ethylene glycol (ethylene terephthalate oligomer); A second hydrolysis step of heating the obtained first hydrolyzate in hot water and further hydrolyzing the first hydrolyzate to obtain terephthalic acid as a second hydrolyzate; , At least.

The production method of the present invention includes the first hydrolysis step and the second hydrolysis step described above, but the weight of hot water used in the second hydrolysis step (hereinafter also simply referred to as “hot water amount”) is the first. It is characterized in that the ethylene terephthalate oligomer obtained in the first hydrolysis step can be efficiently hydrolyzed in hot water by making it twice or more the weight of the object to be used in 1 hydrolysis step. To do.

Hereinafter, the manufacturing method of the terephthalic acid of this invention is demonstrated in detail with reference to drawings.
FIG. 1 is a production process diagram for explaining the production method of terephthalic acid of the present invention.
First, an object to be treated containing polyethylene terephthalate is prepared (step S10), and an object to be treated is obtained as necessary so that it can be efficiently decomposed into terephthalic acid as a hydrolyzate by the first hydrolysis step and the second hydrolysis step. After the processed product is crushed or cut into an appropriate size, foreign substances adhering to the surface are removed by washing (step S11).
As a method for pulverizing the object to be processed, a known method can be used, and examples thereof include a method of cutting with a cutting machine if necessary and then pulverizing. Examples of the pulverizer include a shear crusher such as a biaxial rotary shear crusher and a uniaxial rotary shear crusher, an impact crusher such as a hammer mill and an impact crusher, and a shredder. The size of the pulverized product is not particularly limited, and may be appropriately set according to the hydrolysis time, the temperature at the time of hydrolysis, and the like. In the case where the container for storing the object to be processed for use in the first hydrolysis step has a hole, the object to be processed may be larger than the hole. The major axis (maximum length) of the hole may be appropriately adjusted between 0.01 mm and 20 mm, for example.
Examples of the method for cleaning the object to be treated include a method of spraying water from above the pulverized product, a method of cleaning the pulverized product while transporting it into water, and the like.

Subsequently, a two-stage hydrolysis reaction is performed on the object to be treated by the first hydrolysis step and the second hydrolysis step (steps S12 and S13).

(First hydrolysis step)
In the first hydrolysis step of the present invention, the object to be treated containing polyethylene terephthalate is stored in a sealed container (pressure-resistant container) and exposed to an atmosphere of normal pressure to saturated water vapor pressure to form an ester bond in polyethylene terephthalate. Hydrolyze to obtain a first hydrolyzate.
As is generally known, the hydrolysis is a decomposition reaction in which one bond is ionically cleaved and the H ₂ O1 molecule is divided into H ⁺ and OH ⁻ and added to the cleavage position.
In the present invention, in the first hydrolysis step, first, the target first hydrolyzate and impurities not derived from polyethylene terephthalate are separated by exposing the object to be treated in a steam atmosphere. The obtained first hydrolyzate is a hydrolyzate containing an oligomer formed by cleavage of an ester bond in polyethylene terephthalate, and exhibits a fluid state in the present invention. Specifically, the hydrolyzate obtained in the first hydrolysis step is a mixture containing terephthalic acid and / or an oligomer composed of terephthalic acid and ethylene glycol (ethylene terephthalate oligomer) produced by the decomposition of polyethylene terephthalate. Yes, during the first hydrolysis step or after the step, it becomes a fluid state, and is used in the second hydrolysis step described later in that state.

In the first hydrolysis step of the present invention, the temperature at which the object to be treated containing polyethylene terephthalate is exposed to a water vapor atmosphere (hereinafter also referred to as “water vapor atmosphere temperature”) may be appropriately determined. The temperature is preferably 260 ° C, more preferably 120 to 260 ° C, still more preferably 140 to 260 ° C. By treating within the temperature range, polyethylene terephthalate contained in the object to be treated can be effectively hydrolyzed in a water vapor atmosphere. In particular, from the viewpoint of shortening the hydrolysis reaction time and the melting point of polyethylene terephthalate (about 260 ° C.), the water vapor atmosphere temperature is preferably below the melting point of polyethylene terephthalate, for example, in the range of 150 to 260 ° C., more preferably 180 ° C. It is -260 ° C, more preferably 200-260 ° C.

The hydrolysis time in the first hydrolysis step is preferably, for example, 1 minute to 20 hours, and more preferably 5 minutes to 10 hours. By performing the hydrolysis treatment within the above range, the molecular weight of the obtained first hydrolyzate can be reduced, terephthalic acid can be efficiently produced, and the production of by-products can also be suppressed. In particular, from the viewpoint of further reducing the molecular weight of the resulting ethylene terephthalate oligomer and suppressing the by-products, the hydrolysis time is preferably in the range of 5 minutes to 10 hours, and more preferably 10 minutes to 5 hours. It's time.

In the first hydrolysis step of the present invention, the hydrolysis treatment is performed under normal steam pressure under saturated steam pressure. As the pressurizing condition, the saturated water vapor pressure at the water vapor atmosphere temperature is preferable. The saturated water vapor pressure is, for example, preferably 0.4 to 5 MPa, and more preferably 1 to 5 MPa. By performing the hydrolysis treatment within the above range, the first hydrolyzate can be obtained efficiently in a short time.

Note that the water vapor pressure in the production method of the present invention is preferably increased along the saturated water vapor pressure curve, and by adopting such a step, the polyethylene terephthalate as the object to be treated is thermally decomposed or carbonized. Denaturation can be prevented. For the supply of water vapor, various known means can be employed.For example, water is stored in an airtight container that performs hydrolysis treatment, and the water is heated, and water vapor generated by a water vapor generator is used. For example, a method of introducing into a hermetic container.

Further, in the first hydrolysis step in the present invention, it is preferable to start hydrolysis in a state where an object to be treated containing polyethylene terephthalate is exposed to a water vapor atmosphere that does not come into contact with water. By exposing to a water vapor atmosphere so as not to come into contact with water, the object to be processed is decomposed from the inside, so that the decomposition treatment can be efficiently performed.

The first hydrolyzate obtained in the first hydrolysis step contains terephthalic acid or ethylene terephthalate oligomer, but may contain other intermediate products. The ethylene terephthalate oligomer is composed of, for example, 2 to 75 monomers (constituent units), and the weight average molecular weight of the oligomer is, for example, 200 to 7500.
In addition, the said weight average molecular weight can be measured as an average molecular weight by polystyrene conversion by the gel permeation chromatography (GPC) method.

In the present invention, the first hydrolyzate obtained in the first hydrolysis step is obtained as a fluid having viscosity. The melt viscosity of the first hydrolyzate can be appropriately set by adjusting the type of the object to be processed and the progress of hydrolysis. Since the first hydrolyzate obtained in the first hydrolysis step is in a state of being mixed with impurities other than the first hydrolyzate that does not melt by hydrolysis, it is necessary to separate them. As the separation method, for example, the mixture containing the first hydrolyzate and other impurities is transferred to a container having a hole through which the first hydrolyzate can pass, filtered, and passed through the hole. A method for recovering the hydrolyzate, or a first hydrolyzing step in which the object to be treated is accommodated in a container having a hole, and simultaneously with the hydrolysis treatment, the obtained first hydrolyzate is stored in the container. The method of making it flow down sequentially from a hole and collect | recovering with another container etc. is mentioned. If a hole for taking out the hydrolyzate is provided at least at the bottom of the container on which the workpiece is placed, only the first hydrolyzate can flow down from the hole, and the second hydrolysis step is performed as it is. It is preferable because it can be used for In this case, it is preferable to adjust the melt viscosity of the first hydrolyzate to such an extent that other impurities that do not melt can be separated.

In the present invention, the object to be treated containing polyethylene terephthalate is provided in a closed container (pressure-resistant container) with a hole that does not allow the object to be treated and allows the first hydrolyzate to pass therethrough. It is preferable to place it in a first container provided at the bottom and to perform hydrolysis treatment with water vapor in this first container.

The material of the first container is not particularly limited as long as it does not affect the hydrolysis reaction for obtaining the first hydrolyzate. For example, a container made of a corrosion-resistant metal material or ceramics can be used.
The shape and size of the hole of the first container are not particularly limited as long as the object to be processed and the first hydrolyzate can be passed therethrough. Examples of the shape include a circle, a polygon, and an indeterminate shape, and the size (maximum length of pores) is preferably set as appropriate according to the melt viscosity of the first hydrolyzate.

(Second hydrolysis step)
In the second hydrolysis step subsequent to the first hydrolysis step described above, the first hydrolyzate obtained in the first hydrolysis step is heated in hot water, and the first hydrolyzate is further added. Hydrolyze to obtain the desired terephthalic acid as the second hydrolyzate. In this case, the first hydrolyzate containing terephthalic acid and / or ethylene terephthalate oligomer obtained in the first hydrolysis step is subjected to the second hydrolysis step, but all of these are transferred to the second hydrolysis step. Is preferable, and it may be transferred continuously or batchwise.

Moreover, in order to improve the hydrolysis efficiency for obtaining the terephthalic acid as a target hydrolyzate, it mixes in a hydrolyzate by further hydrolyzing the 1st hydrolyzate in a 2nd hydrolysis process. Water-soluble impurities and ethylene glycol can be extracted into hot water, and the second hydrolyzate can be obtained with high purity. The second hydrolyzate is a hydrolyzate containing terephthalic acid and ethylene glycol, which are raw materials for synthesizing polyethylene terephthalate. From the obtained hydrolyzate, terephthalic acid and ethylene glycol can be recovered by fractionation and purification steps, respectively.

The second hydrolysis step is preferably performed under pressure. In addition, as described below, in a mode in which the first hydrolysis step and the second hydrolysis step are continuously performed in the same pressure-resistant container, the second hydrolysis step is employed in the first hydrolysis step, for example. Can be performed in an atmosphere of normal pressure to saturated water vapor pressure. The pressurizing condition is, for example, preferably 0.4 to 10 MPa, and more preferably 1 to 10 MPa.

The temperature of hot water in the second hydrolysis step is preferably 150 to 300 ° C., for example, more preferably 180 to 300 ° C., and still more preferably 200 to 300 ° C. By carrying out within the temperature range, the molecular weight of the obtained second hydrolyzate can be reduced to obtain the desired terephthalic acid, the production of by-products can be suppressed, and impurities can be reduced. The heating time in hot water is, for example, preferably 1 minute to 10 hours, more preferably 5 minutes to 5 hours. By performing within the said range, while reducing the molecular weight of the obtained 2nd hydrolyzate and obtaining the target terephthalic acid, the production | generation of a by-product can be suppressed and an impurity can be reduced further.

The second hydrolyzate obtained in the second hydrolysis step in the present invention is mostly ethylene glycol and terephthalic acid, which are synthetic raw materials for polyethylene terephthalate, and was not hydrolyzed in the second hydrolysis step. It contains a small amount of ethylene terephthalate oligomer and other intermediate products. In addition, water-soluble ethylene glycol is dissolved in hot water, and water-insoluble terephthalic acid is precipitated as a solid in hot water, enabling fractional collection.

In the production method of the present invention, the first hydrolyzate that has passed through the first container installed in the sealed container (pressure container) is accommodated in the second container installed in the pressure container, and further heated. Hydrolysis is performed in water. In this case, the first hydrolyzate may be stored in a second container in which hot water has been added in advance, or hot water may be added to the first hydrolyzate in the second container. . In either case, water may be used first instead of hot water, and then heated to become hot water having a temperature within the preferred range of the present invention. Furthermore, dew condensation water generated from water vapor can be used as a substitute for hot water.

In the production method of the present invention, the weight of hot water put into the second container is set to be 2 times or more, preferably 2 to 10 times the weight of the object to be treated used in the first hydrolysis step. is important. By adjusting the amount of hot water within the above range and performing the second hydrolysis step, the hydrolysis rate to the obtained second hydrolyzate is increased to 90% or more. When the weight of hot water is less than twice, a sufficient hydrolysis rate cannot be obtained, and when the amount of hot water exceeds 10 times, the volume of the second container becomes too large and the production of the present invention is performed. The hydrolysis apparatus for carrying out the method becomes large and is not economical.

As described above, in the second hydrolysis step, ethylene terephthalate oligomer, which is the first hydrolyzate, is hydrolyzed in hot water instead of in a water vapor atmosphere to obtain terephthalic acid as the second hydrolyzate. .
That is, in the first hydrolysis step, solid polyethylene terephthalate is exposed to a water vapor atmosphere, so that high-energy water molecules collide with the exposed surface of polyethylene terephthalate, and the ester bond of the main chain is hydrolyzed. Thus, it is presumed that it gradually oligomerizes from the surface portion. Since the first hydrolysis step is in a high-temperature atmosphere, the generated oligomer is in a molten state and has fluidity, and is supplied to the hot water of the second hydrolysis step.

When the oligomer obtained in the first hydrolysis step is carried out in the same water vapor atmosphere as in the first hydrolysis step, it takes much time for hydrolysis and is not practical. 2 It is characterized by performing a hydrolysis process in hot water. By performing the second hydrolysis step in hot water, polyethylene terephthalate having a low molecular weight has a higher hydrolysis rate than in a water vapor atmosphere, and ethylene glycol obtained together with terephthalic acid is dissolved in hot water. Water-insoluble terephthalic acid is precipitated in hot water, so that it can be easily separated and recovered. If the amount of hot water used in the second hydrolysis step is too small, the concentration of ethylene glycol dissolved in the hot water becomes high, the ethylene terephthalate oligomer is depolymerized, and ethylene glycol causes a condensation polymerization reaction with terephthalic acid. It becomes easy and the yield of terephthalic acid tends to decrease, so adjustment of the amount of hot water is important.

The material of the second container is not particularly limited as long as it does not affect the reaction for obtaining the second hydrolyzate. For example, a container made of a metal material or ceramics can be used. It is more preferable to employ a material that does not cause elution of metal ions or the like, which becomes a problem when used to produce recycled polyethylene terephthalate.

Note that the second hydrolyzate may be further purified by a known purification method, if necessary, and further collected after increasing its purity.

Since the second hydrolyzate after the second hydrolysis step in the present invention is ethylene glycol as a water-soluble hydrolyzate and terephthalic acid as a water-insoluble hydrolyzate, it is water-soluble as described above. The hydrolyzate is dissolved in hot water, and the water-insoluble hydrolyzate is not dissolved in hot water but precipitates to become a solid. Therefore, solid terephthalic acid is separated from hot water in which a water-soluble hydrolyzate (ethylene glycol) is dissolved (steps S14 and S17).
It does not specifically limit as a separation method, A well-known method can be used, What is necessary is just to isolate | separate by filtration, aspiration, centrifugation, decanting, etc.

The dissolved water-soluble hydrolyzate (such as ethylene glycol) is subjected to a known purification treatment as necessary (step S15) and recovered (step S16). On the other hand, the solid water-insoluble hydrolyzate (terephthalic acid) is similarly subjected to a known purification treatment as necessary (step S19) and recovered (step S20).

In addition, the first hydrolysis step and the second hydrolysis step may be performed continuously as described later, or the first hydrolyzate obtained in the first hydrolysis step is once recovered, Then, you may employ | adopt what is called a batch system which uses this 1st hydrolyzate for a 2nd hydrolysis process.

According to the production method of the present invention, the polyethylene terephthalate as an object to be treated is first hydrolyzed (divided) by the first hydrolysis step, with the ester bond of polyethylene terephthalate being steam from atmospheric pressure to saturated steam pressure. As a result, an ethylene terephthalate oligomer containing an ethylene glycol unit or a terephthalic acid unit is produced. In the subsequent second hydrolysis step, these oligomers are hydrolyzed to a minimum monomer unit of ethylene glycol monomer unit and terephthalic acid monomer unit in a large amount of hot water, and the water-soluble ethylene glycol monomer unit is heated. The terephthalic acid monomer unit which dissolves in water and is hardly soluble in water is solidified in hot water and can be recovered in high yield.

In the second hydrolysis step in the present invention, when only crude terephthalic acid having a low purity can be obtained due to insufficient hydrolysis to terephthalic acid, a hydrolysis reaction (third hydrolysis step) is further performed in hot water. ) Is preferably performed (FIG. 1, step S18). In this case, sufficient hydrolysis is unlikely to occur only by increasing the reaction time of the second hydrolysis step. That is, since ethylene glycol, which is a hydrolyzate obtained in the second hydrolysis step, is dissolved in hot water, the hydrolysis reaction occurs reversibly even if the hydrolysis reaction is continued as it is. This may result in an equilibrium state and may not be fully hydrolyzed to terephthalic acid. Therefore, in such a case, the hot water used in the second hydrolysis step in which a large amount of ethylene glycol is dissolved is temporarily removed from the system and replaced with new hot water. Is preferable because the hydrolysis reaction can be accelerated. Thus, by performing a hydrolysis process in new hot water, the hydrolysis to terephthalic acid is accelerated and terephthalic acid with high purity can be obtained.

When performing the third hydrolysis step, the treatment conditions, specifically, the hydrolysis environment, the temperature of hot water, the heating time, and the like are the same as in the second hydrolysis step.

Next, a further preferred embodiment of the production method of the present invention will be described.
According to a preferred aspect of the present invention, the first hydrolysis step and the second hydrolysis step are continuously performed in a sealed container (pressure-resistant container). The pressure-resistant container is preferably provided with a heater for heating the entire system. By using a pressure-resistant container provided with a heater, the treatment pressure and heating temperature with water vapor in the first hydrolysis step and the second hydrolysis step can be arbitrarily adjusted. For example, an operation for increasing the water vapor along the saturated water vapor pressure curve as described above can be easily performed. The increase and decrease in pressure and temperature can be controlled by appropriately applying known control means. Furthermore, by performing the first hydrolysis step and the second hydrolysis step in one container, a simple processing operation can be performed, and the equipment cost and the processing cost can be reduced.

Further, the pressure-resistant container is provided with a first hole portion having a hole at a bottom that is large enough to pass a first hydrolyzate obtained by hydrolyzing polyethylene terephthalate without passing an object to be processed. The container and the 2nd container as a receiving tray of a 1st hydrolyzate are installed in the lower part of this 1st container. Then, the first hydrolysis step is performed on the workpiece in the first container, the first hydrolyzate that has passed through the first container is received by the second container, and the first hydrolysis in the second container is performed. The aspect which performs a 2nd hydrolysis process to a thing is further more preferable. According to this aspect, it becomes possible to process the processing object containing polyethylene terephthalate continuously and at low cost with high quality and high recovery rate.

FIGS. 2 (a) to 2 (e) are schematic diagrams for explaining the treatment method in the preferred embodiment of the present invention, and the first hydrolysis step and the second hydrolysis step are continuously performed. It is a schematic diagram of the processing apparatus for.
As shown in FIG. 2 (a), a first container 21 is placed above the pressure-resistant container 20 in a sealed container (pressure-resistant container) 20 having a heater (not shown). Each of the second containers 22 is installed. The first container 21 includes a plurality of holes A that do not allow the workpiece S to pass through and allows the first hydrolyzate to pass through, and the workpiece S is accommodated in the first container 21. . Further, hot water W1 is stored in the second container 22. Water W2 for generating water vapor used for the hydrolysis treatment of polyethylene terephthalate is stored at the bottom of the pressure-resistant container 20. The water vapor may be supplied into the pressure-resistant container 20 by a water vapor generator (not shown) provided outside without using the water W2.

As shown in FIG. 2 (b), when the first hydrolysis step is performed, the workpiece S is hydrolyzed to become the first hydrolyzate H1, and the holes of the first container 21 are indicated by arrows. Drop from part A. The first hydrolyzate H1 that has fallen is received in the hot water W1 of the second container 22 and is subjected to the second hydrolysis step, whereby a second hydrolyzate is generated in the hot water.

Next, as shown in FIG. 2 (c), the second hydrolyzate contains water-soluble hydrolyzate ethylene glycol and water-insoluble hydrolyzate terephthalic acid. The water-soluble second hydrolyzate (ethylene glycol) H2 is dissolved in hot water W1, while the water-insoluble second hydrolyzate (terephthalic acid) H3 is not dissolved in hot water W1. And become a solid. These second hydrolysates H2 and H3 are recovered by performing a known purification treatment as necessary. In the first container 21, the high molecular weight residue S1 that has not been hydrolyzed in the first hydrolysis step remains without passing through the hole A.

In the present invention, after the second hydrolysis step is completed, it is preferable to lower the temperature of the pressure resistant container 20 by natural cooling or forced cooling while controlling the pressure and temperature in the pressure resistant container 20. Deterioration of the quality of the raw material recovered by this operation can be suppressed.
The various conditions for hydrolysis are the same as described above.

The first vessel 21 and the second vessel 22 are preferably made of metal that can sufficiently withstand the hydrolysis conditions of the first hydrolysis step and the second hydrolysis step. For example, the first vessel 21 is a known punching metal. And metal mesh can be used.

In addition, when the target terephthalic acid yield is not sufficient due to insufficient hydrolysis in the second hydrolysis step, the hot water W1 is removed from the second container, and then FIG. As shown in Fig. 2, the hydrolysis process can be continued by adding new hot water W3. By treating in this way, as shown in FIG. 2 (e), the second hydrolyzate is sufficiently hydrolyzed to terephthalic acid H5 and ethylene glycol H4 to obtain terephthalic acid H5 in a high yield. Can do.

In the present invention, recycled polyethylene terephthalate can be produced using the terephthalic acid obtained as described above. Specifically, regenerated polyethylene terephthalate can be obtained by polycondensing terephthalic acid obtained through the first hydrolysis step and the second hydrolysis step with ethylene glycol separately prepared. The method of condensation polymerization can be carried out by a method known per se, and the obtained recycled polyethylene terephthalate can be processed into various molded products in the form of pellets.

Hereinafter, the present invention will be specifically described by way of examples and comparative examples, but various applications are possible without departing from the technical idea of the present invention, and the present invention is not limited to the description of the following examples.

(Example 1)
Using the apparatus shown in FIGS. 2 (a) to 2 (e), a polyethylene terephthalate film (thickness 35 μm, weight average molecular weight 20000) was processed as an object to be processed.

First, as shown to Fig.2 (a), the pressure resistant container 20 provided with the heater (not shown), the 1st container 21, and the 2nd container 22 was prepared.
The internal volume of the first container 21 is 5 L, and 500 g of a film as an object to be processed is put therein. In the 2nd container 22, 3 kg of water was put beforehand. Water W2 for generating water vapor is stored at the bottom of the pressure-resistant container 20, and an amount of water vapor necessary for the hydrolysis treatment can be generated by the heater.
The first container 21 is provided with a plurality of holes A having a size that allows the first hydrolyzate generated in the first hydrolysis step to pass through without passing the workpiece. The hole A was made of a punching metal made of stainless steel, and the size of the hole A was set to 1 mm square.

Subsequently, as shown in FIGS. 2 (b) and 2 (c), the first hydrolysis step and the second hydrolysis step were continuously performed in the pressure resistant container 20. In the first hydrolysis step and the second hydrolysis step, the water pressure atmosphere temperature of the pressure-resistant vessel 20 is 230 ° C., the temperature of the hot water W 1 is 230 ° C., and the saturated water vapor pressure (pressure 2.8 MPa). A polyethylene terephthalate film was hydrolyzed. A part of the second hydrolyzate H3 in the second container 22 is sampled after two hours have passed since the steam atmosphere temperature in the pressure resistant container reaches 230 ° C., and the hydrolyzate is obtained by high performance liquid chromatography (HPLC). The composition of was investigated. The HPLC analysis conditions are as follows.

〔Analysis conditions〕
Analyzing apparatus: Product name UltimateMate 3000 manufactured by Thermo Fisher Scientific
Column: CAPCELLPAK (4.6 mmφ × 150 mm, 5 μm, manufactured by Shiseido Co., Ltd.)
Eluent composition: Formic acid aqueous solution / methanol gradient Flow rate: 1 mL / min
Detector: DAD (diode array detector, 190 nm to 800 nm, 242 nm extraction)
Column temperature: 40 ° C
Injection volume: 5 μL

(Example 2)
A polyethylene terephthalate film as an object to be treated was hydrolyzed under the same conditions and method as in Example 1 except that the amount of water in the second container 22 in Example 1 was reduced to 2 kg.

(Example 3)
A polyethylene terephthalate film as an object to be treated was hydrolyzed under the same conditions and method as in Example 1 except that the amount of water was reduced to 1 kg in the second container 22 in Example 1.

(Comparative Example 1)
A polyethylene terephthalate film as an object to be processed was hydrolyzed under the same conditions and method as in Example 1 except that the amount of water in the second container 22 in Example 1 was reduced to 0.5 kg.

(Comparative Example 2)
A polyethylene terephthalate film as an object to be treated was hydrolyzed under the same conditions and method as in Example 1 except that the amount of water in the second container 22 in Example 1 was reduced to 0.2 kg.

(Comparative Example 3)
A polyethylene terephthalate film as an object to be treated was hydrolyzed under the same conditions and method as in Example 1 except that water was not put into the second container 22 in Example 1.

The terephthalic acid content in the second hydrolyzate obtained in each of the above Examples and Comparative Examples was measured and listed in Table 1 as the hydrolysis rate.

As is clear from the results in Table 1, when hot water of 2 times or more with respect to the charged amount of the adherend (polyethylene terephthalate film) is used in the second container in the second hydrolysis step, the hydrolysis rate is 90. %, That is, the content of terephthalic acid in the second hydrolyzate was 90% by weight or more (Example 1, Example 2, Example 3).
On the other hand, when 1 time or less of water was used with respect to the charged amount of the adherend, the hydrolysis rate was less than 80% (Comparative Examples 1, 2, and 3).

From the above results, in the production method of the present invention, the hydrolysis efficiency is improved by setting the amount of hot water in the second hydrolysis step to be twice or more the weight (preparation amount) of the object to be treated. It is clear that terephthalic acid is obtained with a yield of more than% by weight.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on a Japanese patent application filed on January 6, 2015 (Japanese Patent Application No. 2015-001081), the contents of which are incorporated herein by reference.

An object of the present invention is to provide a treatment method capable of treating an object to be treated containing polyethylene terephthalate without costly equipment or cost and recovering terephthalic acid, which is a constituent material of the polyethylene terephthalate, with high quality. Can do. Therefore, chemical recycling technology can help build a society that can sustain the supply of limited petroleum resources.

20 pressure resistant container 21 first container 22, 23 second container A hole H1 first hydrolyzate H2 second hydrolyzate (ethylene glycol)
H3 Second hydrolyzate (terephthalic acid)
H4 Ethylene glycol H5 Terephthalic acid S Object to be treated S1 Residues W1, W3 Hot water W2 Water for water vapor generation

Claims (6)

1. After storing the object to be treated containing polyethylene terephthalate in a sealed container, the polyethylene terephthalate is hydrolyzed by exposure in an atmosphere of normal to saturated water vapor pressure, and terephthalic acid and an oligomer composed of terephthalic acid and ethylene glycol ) And a second hydrolysis to obtain terephthalic acid by hydrolyzing the ethylene terephthalate oligomer obtained in the first hydrolysis step in hot water. A process,
   A method for producing terephthalic acid, wherein the weight of hot water in the second hydrolysis step is twice or more the weight of the object to be treated used in the first hydrolysis step.
2. The method for producing terephthalic acid according to claim 1, wherein the temperature of the hot water in the second hydrolysis step is 150 to 300 ° C.
3. The method for producing terephthalic acid according to claim 1 or 2, wherein the weight of hot water in the second hydrolysis step is 2 to 10 times the weight of the object to be treated used in the first hydrolysis step.
4. The total amount of the hydrolyzate containing at least one of terephthalic acid and ethylene terephthalate oligomer obtained in the first hydrolysis step is transferred to the second hydrolysis step. A method for producing terephthalic acid according to 1.
5. The method for producing terephthalic acid according to any one of claims 1 to 4, wherein the first hydrolysis step and the second hydrolysis step are continuously carried out in a closed container.
6. A method for producing regenerated polyethylene terephthalate, wherein polyethylene terephthalate is produced by condensation polymerization of terephthalic acid obtained by the production method according to any one of claims 1 to 5 with ethylene glycol.

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