TW201630862A - 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 recovered polyethylene terephthalate

The present invention relates to a method for producing terephthalic acid and a method for producing recycled polyethylene terephthalate, for example, a polyethylene terephthalate for use in bottles or films, sheets, and the like. A method for producing terephthalic acid as a synthetic raw material, and a method for producing a recovered polyethylene terephthalate using terephthalic acid obtained by a molded article or the like.

Polyester resins are widely used in various applications due to their excellent properties. For example, polyethylene terephthalate (PET) is excellent in chemical stability, and is used as a living-related material such as fiber, film, or resin, especially as a bottle for drinking water or carbonated beverages, and is also produced in large quantities in the food field. And use. However, the processing of fibers or films, wastes of resin products, and molded articles of non-standard products that are produced in large quantities as the amount of production or usage increases is now becoming a major social problem, and resources are effective. From the viewpoint of the use, a method of efficiently recycling the polyester resin molded articles is also sought.

As such a recycling method, various methods such as a material recycling method or a chemical recycling method have been proposed.

The material recycling method does not decompose the polyester resin, and is melted and reused at a high temperature. Therefore, the quality of the recycled product is gradually lowered compared with the polyester resin before reuse due to the heat history. . Moreover, when a component (impurity) other than a polyester resin is contained, it is difficult to completely remove the impurity, and the quality is further lowered. Therefore, it is possible to obtain the same quality as the polyester resin before recycling, except directly after pulverization. It is a difficult problem other than the case where a part of a flow path generated at the time of injection molding is used.

On the other hand, as a chemical recycling method, it can be generally classified into (1) raw material, (2) reducing agent, (3) gas, oiling, and (4) heat recycling. Among them, since the raw material is obtained by the same quality as the polyester resin before recycling, it is attracting attention as an advantageous method.

In Patent Document 1, as an example of the materialization of polyethylene terephthalate, there is disclosed a method of decomposing polyethylene terephthalate into p-benzoic acid by ethylene glycol decomposition/methanol treatment. Dimethyl formate is further decomposed into terephthalic acid, which is again polycondensed with ethylene glycol to form a "bottle to bottle".

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

Further, Patent Document 3 discloses a method of exposing a processed object containing polyethylene terephthalate to a water vapor atmosphere filled with a pressure of a saturated water vapor pressure at a processing temperature, whereby the treatment is performed. The saturated water vapor generated at the temperature hydrolyzes the polyethylene terephthalate contained in the above-mentioned treated object, and recovers the ethylene glycol as a gas or a liquid component, and the terephthalic acid is in the form of a solid component. Recycling.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open Publication No. 2003-119316

Patent Document 2: Japanese Patent Laid-Open Publication No. 2007-332361

Patent Document 3: Japanese Patent Laid-Open Publication No. 2008-308416

However, the method of Patent Document 1 has a problem that the operation is complicated and costly, or the amount of equipment investment becomes large, and in the method of Patent Document 2, it is expressed that no dicarboxylic acid is added. When acid is used to hydrolyze a polyester in high-temperature water at 150 to 350 ° C, it is not sufficiently hydrolyzed, suggesting that dicarboxylic acid as a hydrolysis catalyst is indispensable in hydrolysis in high-temperature water.

Further, in the method of Patent Document 3, it is necessary to prepare a treatment chamber having a pressure resistance inside the stirring mechanism or a cooling tower for recovering ethylene glycol, and the apparatus becomes large-scale and has room for improvement. Further, when polyethylene terephthalate contains impurities, there is a problem that the quality of terephthalic acid and ethylene glycol recovered by the hydrolysis treatment is lowered.

Since the polyester resin is a synthetic resin obtained from a limited petroleum resource, it is a primary problem to establish a technique for chemically recycling waste of a polyester resin in order to construct a society in which supply is continued. In particular, polyethylene terephthalate is excellent in chemical resistance and heat resistance, and is excellent in safety when used in foods. Therefore, it is widely used in various fields, and its reuse has become an important issue. However, as described above, the method of establishing the quality and the economy (the suppression of the operating cost and the original cost) has not been established, so that the development as a practical situation is sought as soon as possible.

Accordingly, it is an object of the present invention to provide a method for producing terephthalic acid which is processed by a chemical recycling technique using a polyethylene terephthalate-containing material without requiring a large-scale apparatus or cost. Moreover, the terephthalic acid which is a synthetic raw material of the polyethylene terephthalate can be recovered with high quality and high yield without using a special hydrolysis catalyst, and a terephthalic acid obtained by using the same can be provided. A method for producing recovered polyethylene terephthalate obtained by formic acid.

The present inventors have made an effort to study the above problems, and as a result, it has been found that the molded article (object to be treated) of polyethylene terephthalate is first exposed to an environment of normal pressure to saturated water vapor pressure. Hydrolyzing to obtain a first hydrolyzate comprising terephthalic acid or ethylene terephthalate oligomer, and further hydrolyzing the first hydrolyzate in a specific volume of hot water to repeat with the previous chemical The present invention has been completed by simply obtaining terephthalic acid which is a synthetic raw material by a method.

That is, the present invention relates to a method for producing terephthalic acid, which has a first hydrolysis step of storing a material containing polyethylene terephthalate in a sealed container. The polyethylene terephthalate is hydrolyzed by exposure to an atmospheric pressure to a saturated water vapor pressure to obtain an oligomer containing terephthalic acid and terephthalic acid and ethylene glycol (p-benzene) a hydrolyzate of at least one of ethylene glycol formate oligomers; and a second hydrolysis step of hydrolyzing the ethylene terephthalate oligomer obtained in the first hydrolysis step in hot water The terephthalic acid is obtained; and the weight of the 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.

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

Moreover, it is preferable that the weight of the 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.

Moreover, it is preferable that 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.

Further, it is preferable to continuously carry out the first hydrolysis step and the second hydrolysis step in a sealed container.

Furthermore, the present invention relates to a method for producing recycled polyethylene terephthalate, which comprises polycondensing terephthalic acid obtained from the above and ethylene glycol to produce polyethylene terephthalate. .

The method for producing terephthalic acid of the present invention comprises: a first hydrolysis step of exposing a treated object comprising polyethylene terephthalate to an environment of from normal pressure to saturated water vapor pressure to obtain hydrolysis; Terephthalic acid or ethylene terephthalate oligomer (including oligomers of terephthalic acid and ethylene glycol); and second hydrolysis step, which is based on the treated object 2 The oligomer obtained in the above first hydrolysis step is heated in hot water having a weight of more than twice, thereby further hydrolyzing to obtain terephthalic acid. In the second hydrolysis step, the weight of the hot water to be used is set to be twice or more the weight of the object to be treated used in the first hydrolysis step, whereby the hydrolysis efficiency in the hot water can be remarkably improved.

In the first hydrolysis step, the polyethylene terephthalate in the object to be treated is decomposed by water vapor, and polyethylene terephthalate is oligomerized. Further, one of the oligomers is partially decomposed to terephthalic acid. The oligomer obtained in the first hydrolysis step is further subjected to hydrolysis treatment in the second aqueous hydrolysis step in the subsequent second hydrolysis step, thereby forming polyparaphenylene in an excess amount of hot water which is twice or more the weight of the material to be treated. The water-soluble one of ethylene glycol diester or the raw material of the oligomer is dissolved in hot water, and the water-insoluble one such as terephthalic acid becomes solid in hot water, so it is simple The raw material obtained as a hydrolyzate is recovered at a higher quality without cost.

Furthermore, by using the technique of the present invention, not only the polyethylene terephthalate as the object to be treated, but also polyethylene naphthalate or polybutylene terephthalate or polynaphthalene dicarboxylic acid. Other general-purpose polyester resins, such as butadiene diester and polytrimethylene terephthalate, which are used in large quantities and are difficult to handle due to their large amount, can be easily and recycled at a high quality without cost. raw material.

In addition, when the first hydrolysis step and the second hydrolysis step in the present invention are continuously carried out in a sealed container, the stirring mechanism or the cooling tower described in Patent Document 3 is not required, and the quality can be low, high, and high. Recovery rate The treated material containing polyethylene terephthalate was subjected to hydrolysis treatment to obtain terephthalic acid.

The terephthalic acid obtained as described above is obtained by the chemical recycling method, so that by performing polycondensation reaction with ethylene glycol additionally supplied, the recovered polyterephthalic acid can be produced without deterioration in quality. Ethylene glycol ester. Thus, the manufacturing method of the present invention is an extremely advantageous method in the recycling (reuse of useful resources).

20‧‧‧ Pressure container

21‧‧‧1st container

22, 23‧‧‧ second container

A‧‧‧孔部

H1‧‧‧1st hydrolysate

H2‧‧‧2nd hydrolyzate (ethylene glycol)

H3‧‧‧2nd hydrolysate (terephthalic acid)

H4‧‧‧Ethylene glycol

H5‧‧‧ terephthalic acid

S‧‧‧Processed objects

S1‧‧‧ residue

S10‧‧‧Preparing processed objects

S11‧‧‧ broken, cleaned

S12‧‧‧1st hydrolysis step

S13‧‧‧2nd hydrolysis step

S14‧‧‧Dissolved hot water of water-soluble hydrolyzate

S15‧‧‧ refined

S16‧‧‧Recycling

S17‧‧‧ terephthalic acid

S18‧‧‧3rd hydrolysis step

S19‧‧‧ refined

S20‧‧‧Recycling

W1, W3‧‧‧ hot water

W2‧‧‧Water vapor production

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing the manufacturing steps of a method for producing terephthalic acid of the present invention.

2(a) to 2(e) are schematic views for explaining a processing method in a suitable form of the present invention.

Hereinafter, embodiments of the method for producing terephthalic acid of the present invention and the method for producing recycled polyethylene terephthalate 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 is no particular difference with respect to the kind thereof or the raw materials other than the polyethylene terephthalate contained therein. The restrictions may be various processed objects known or common from the prior.

The polyethylene terephthalate which is the object to be treated in the present invention is obtained by polycondensation of ethylene glycol as a polyol component as a raw material of the synthesis thereof and terephthalic acid as a polycarboxylic acid component. Polyester resin. Further, as the polycarboxylic acid component, in addition to terephthalic acid, isophthalic acid or phthalic acid may be partially contained.

In addition, the form of the object to be treated in the present invention is not particularly limited, and various molded articles, and wastes of various molded articles which are typically reprocessed after use can be used, and examples thereof include fibers, films, and sheets. Bottles for bottles, drinking water or carbonated beverages, adhesive tapes (tapes), food trays, etc.

Further, in the various molded articles as the objects to be processed, various materials such as various additives other than polyethylene terephthalate are often used depending on the form of use. However, in the present invention, the types of these materials are used. , no restrictions.

As such an additive which can be added to various molded articles as a workpiece, for example, a known flame retardant or plasticizer, a lubricant, a colorant (pigment, dye, etc.), an ultraviolet absorber, and an antioxidant are mentioned. , anti-aging agent, filler, reinforcing agent, antistatic agent, surfactant, tension modifier, anti-shrinkage agent, fluidity modifier, surface treatment agent, etc.

Further, the object to be treated may be a molded article containing only polyethylene terephthalate or a composite with other materials. That is, it may be a composite product including a layer of polyethylene terephthalate and a laminate including a layer of a resin other than polyethylene terephthalate. Specifically, for example, when the object to be treated is an adhesive tape, a back-treated polyethylene terephthalate film and an acrylic-based adhesive or a rubber-based adhesive, and a polyoxygen-based adhesive are exemplified. a laminate of an adhesive layer such as a solvent; or a laminate having a release sheet containing a release agent such as a polyfluorene-based resin on one surface, on the surface of the adhesive layer, in the present invention, even in this case The laminate can also be processed.

However, from the viewpoint of the recovery efficiency of terephthalic acid obtained by the production method of the present invention, the content ratio of the polyethylene terephthalate in the object to be treated is preferably 40% by weight or more, for example. It is preferably 60% by weight or more.

In the present invention, the object to be treated may have a shape as it is, but the polyethylene terephthalate is hydrolyzed by the first hydrolysis step and the second hydrolysis step of the present invention described below, thereby efficiently Decomposed into terephthalic acid as a final target of the hydrolyzate, preferably as a pretreatment, the workpiece is previously crushed or cut to an appropriate size before the hydrolysis treatment, and the foreign matter adhering to the surface is removed by the cleaning treatment. .

The method for producing terephthalic acid of the present invention comprises at least a first hydrolysis step of pretreating a treated material comprising polyethylene terephthalate as needed, such as crushing, cutting, washing, etc., to be exposed to the usual The ester bond existing in the molecule of polyethylene terephthalate is hydrolyzed under a water vapor atmosphere saturated with a vapor pressure to obtain terephthalic acid, and oligomerization containing terephthalic acid and ethylene glycol. a first hydrolyzate of at least one of the substances (ethylene terephthalate oligomer); and a second hydrolysis step of heating the obtained first hydrolyzate in hot water to further hydrolyze The first hydrolyzate is obtained to obtain terephthalic acid as the second hydrolyzate.

The production method of the present invention includes the first hydrolysis step and the second hydrolysis step, characterized in that the weight of the hot water used in the second hydrolysis step (hereinafter also referred to as The "hot water amount" is twice or more the weight of the object to be treated used in the first hydrolysis step, and the ethylene terephthalate oligomerization obtained in the first hydrolysis step can be efficiently hydrolyzed in hot water. Things.

Hereinafter, the method for producing terephthalic acid of the present invention will be described in detail with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a view showing the manufacturing steps of a method for producing terephthalic acid of the present invention.

First, a material to be treated containing polyethylene terephthalate (step S10) is prepared, and the first hydrolysis step and the second hydrolysis step can be efficiently decomposed into terephthalic acid as a hydrolyzate. It is necessary to crush or cut the object to be appropriately sized, and then clean and remove foreign matter adhering to the surface or the like (step S11).

The pulverization method of the object to be processed can be carried out by a known method, and for example, a method of cutting by a cutting machine as needed and then pulverizing it can be mentioned. As the pulverizer, for example, a shear crusher such as a double-shaft rotary shear crusher or a uniaxial rotary shear crusher, a hammer mill, an impact crusher, or the like, a shredder or the like can be used. The size of the pulverized material is not particularly limited, and may be appropriately set depending on the hydrolysis time or the temperature at the time of hydrolysis. In the case where the container for accommodating the object to be treated is provided in the first hydrolysis step and has a hole portion, the object to be treated may be larger than the hole portion. The long diameter (maximum length) of the hole portion may be appropriately adjusted, for example, between 0.01 mm and 20 mm.

Examples of the method for cleaning the object to be treated include a method of performing watering washing on the ground material, and a method of washing the ground material while being conveyed to the water.

Then, the object to be treated is subjected to a hydrolysis reaction in two stages of the first hydrolysis step and the second hydrolysis step (steps S12 and S13).

(first hydrolysis step)

In the first hydrolysis step in the present invention, the object to be treated containing polyethylene terephthalate is stored in a sealed container (pressure-resistant container) and exposed to an environment of normal pressure to saturated water vapor pressure. The ester bond in polyethylene terephthalate is hydrolyzed to obtain a first hydrolyzate.

As is generally known, a hydrolysis bond is ionicly broken, and one molecule of H ₂ O is classified into H ⁺ and OH ^- , and an addition reaction is carried out at the position of the bond.

In the present invention, in the first hydrolysis step, first, the object to be treated is exposed to a water vapor atmosphere, whereby the target first hydrolyzate is separated from impurities not derived from polyethylene terephthalate. The obtained first hydrolyzate is a hydrolyzate of 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 comprises terephthalic acid formed by decomposition of polyethylene terephthalate, and/or an oligomer comprising terephthalic acid and ethylene glycol. The mixture of (ethylene terephthalate oligomer) is in a flowing state in the first hydrolysis step or after the step, and is supplied to the second hydrolysis step described below in this 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") is appropriately determined. For example, it is preferably from 100 to 260 ° C, more preferably from 120 to 260 ° C, still more preferably from 140 to 260 ° C. By treating in the above temperature range, the polyethylene terephthalate contained in the object to be treated can be efficiently hydrolyzed in a water vapor environment. In particular, from the viewpoint of shortening of the hydrolysis reaction time and the melting point of polyethylene terephthalate (about 260 ° C), the water vapor ambient temperature is preferably below the melting point of polyethylene terephthalate, for example, 150~ It is carried out in the range of 260 ° C, more preferably 180 to 260 ° C, and further preferably 200 to 260 ° C.

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

Further, the first hydrolysis step of the present invention is carried out under normal pressure to pressurized conditions, that is, saturated water evaporation. The hydrolysis treatment is carried out under pressure. The pressurized water vapor pressure at the water vapor ambient temperature is preferably 0.4 to 5 MPa, more preferably 1 to 5 MPa, as the saturated water vapor pressure. By performing the hydrolysis treatment in the above range, the first hydrolyzate can be obtained efficiently in a short time.

Further, the water vapor pressure in the production method of the present invention preferably rises along the saturated water vapor pressure curve, and by such a step, thermal decomposition of the polyethylene terephthalate as the object to be treated can be prevented. And carbonization or modification. The water vapor can be supplied by various known methods, and examples thereof include a method of storing water in a sealed container subjected to hydrolysis treatment and heating the water, and introducing water vapor generated by the steam generating device into the sealed container. Method, etc.

Further, in the first hydrolysis step in the present invention, it is preferred to start the hydrolysis in a state of being exposed to a water vapor atmosphere in which the object to be treated containing polyethylene terephthalate is not in contact with water. By being exposed to the water vapor atmosphere without being in contact with water, the material to be treated is internally decomposed, so that the decomposition treatment can be performed efficiently.

The first hydrolyzate obtained in the first hydrolysis step contains terephthalic acid or ethylene terephthalate oligomer, and may contain other intermediate products and the like. The ethylene terephthalate oligomer is, for example, a monomer having 2 to 75 monomers (constituting unit), and the weight average molecular weight of the oligomer is, for example, 200 to 7,500.

Further, the above weight average molecular weight can be measured by a gel permeation chromatography (GPC) method in the form of an average molecular weight in terms of polystyrene.

In the present invention, the first hydrolyzate obtained in the first hydrolysis step is obtained as a fluid having a viscosity. The melt viscosity of the first hydrolyzate can be appropriately set by adjusting the kind of the object to be treated or the degree of 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 which is not melted by hydrolysis, it is necessary to separate them. As a separation method, for example, a mixture containing the first hydrolyzate and other impurities is transferred to a container having a hole through which the first hydrolyzate can pass, and a method of filtering to recover the first hydrolyzate passing through the pore portion; or storing the material to be treated in a vessel having a pore portion to perform a first hydrolysis step, and performing the hydrolysis treatment while obtaining the first hydrolyzate obtained from The method in which the pores of the container are sequentially flowed down, and the other container is used for recovery. When the hydrolyzate extraction hole portion is provided at at least the bottom portion of the container on which the workpiece is placed, it is preferable to use the first hydrolysis stream from the pore portion and directly supply it to the second hydrolysis step. In this case, it is preferred that the first hydrolyzate adjust the melt viscosity to such an extent that impurities other than the unmelted ones can be separated.

In the present invention, the object to be treated containing polyethylene terephthalate is preferably placed in a first container, and the first container is subjected to hydrolysis treatment by steam, and the first container is placed in a sealed state. In the container (pressure-resistant container), a hole portion through which the first hydrolyzate can pass without passing the object to be treated is provided at the bottom of the container.

The material of the first container is not particularly limited as long as it does not affect the hydrolysis reaction of the first hydrolyzate, and for example, a container containing a corrosion-resistant metal material or ceramics can be used.

The shape or size of the hole of the first container is not particularly limited as long as the object to be treated does not pass through and the first hydrolyzate passes. The shape may be a circle, a polygon, an amorphous shape or the like, and the size (the maximum length of the pores) is preferably set as appropriate according to the melt viscosity of the first hydrolyzate.

(second hydrolysis step)

In the second hydrolysis step following the first hydrolysis step, the first hydrolyzate obtained in the first hydrolysis step is heated in hot water to further hydrolyze the first hydrolyzate to obtain a target pair as the second hydrolyzate. Phthalic acid. In this case, the first hydrolyzate containing terephthalic acid and/or ethylene terephthalate oligomer obtained in the first hydrolysis step is supplied to the second hydrolysis step, preferably The total amount is transferred to the second hydrolysis step, and the transfer may be carried out in a continuous or batchwise manner.

In addition, in order to improve the hydrolysis efficiency of the terephthalic acid used as the target hydrolyzate At the rate, the first hydrolyzate is further hydrolyzed in the second hydrolysis step, whereby the water-soluble impurities or ethylene glycol mixed in the hydrolyzate can be extracted in hot water, and the second hydrolyzate can be obtained in high purity. The second hydrolyzate contains a hydrolyzate of terephthalic acid and ethylene glycol as a synthetic raw material of polyethylene terephthalate. From the obtained hydrolyzate, terephthalic acid and ethylene glycol can be separately recovered by a purification step.

The second hydrolysis step is preferably carried out under pressure. Further, in the aspect in which the first hydrolysis step and the second hydrolysis step are continuously performed in the same pressure-resistant container as described below, the second hydrolysis step can be, for example, the normal pressure used in the first hydrolysis step. It is carried out under an environment of saturated water vapor pressure. The pressurizing condition is, for example, preferably 0.4 to 10 MPa, more preferably 1 to 10 MPa.

The temperature of the hot water in the second hydrolysis step is, for example, preferably from 150 to 300 ° C, more preferably from 180 to 300 ° C, still more preferably from 200 to 300 ° C. By carrying out the above temperature range, the molecular weight of the obtained second hydrolyzate can be lowered, the target terephthalic acid can be obtained, the formation of by-products can be suppressed, and impurities can be reduced. The heating time in the hot water is, for example, preferably from 1 minute to 10 hours, more preferably from 5 minutes to 5 hours. By carrying out in the above range, the molecular weight of the obtained second hydrolyzate can be lowered, the target terephthalic acid can be obtained, and the formation of by-products can be suppressed, thereby reducing impurities.

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 of polyethylene terephthalate, and includes a small amount in addition to the second. An unhydrolyzed ethylene terephthalate oligomer or other intermediate product in the hydrolysis step. Further, the water-soluble ethylene glycol is dissolved in hot water, and the water-insoluble terephthalic acid is precipitated as a solid in hot water, and can be separately recovered.

In the manufacturing method of the present invention, the first hydrolyzate of the first container provided in the sealed container (pressure-resistant container) is stored in the second container provided in the pressure-resistant container, and further in hot water. Hydrolysis treatment. In this case, the first hydrolyzate may be contained in the second container in which hot water is placed in advance, or heat may be added to the first hydrolyzate in the second container. water. Further, in either case, water may be initially used instead of hot water, and then heated in such a manner as to become hot water at a temperature within the preferred range of the present invention. Further, the condensed water generated by the steam may be replaced by hot water.

In the production method of the present invention, it is important that the weight of the hot water placed in the second container is twice or more, preferably 2%, the weight of the object to be treated used in the first hydrolysis step. 10 times. The second hydrolysis step is carried out by adjusting the amount of hot water to the above range, whereby the hydrolysis rate of the obtained second hydrolyzate is increased to 90% or more. When the weight of the hot water is less than 2 times, a sufficient hydrolysis rate cannot be obtained, and if the amount of hot water exceeds 10 times, the volume of the second container becomes too large, and the hydrolysis apparatus for carrying out the production method of the present invention becomes large. Never economical.

As described above, in the second hydrolysis step, the ethylene terephthalate oligomer as the first hydrolyzate is hydrolyzed in hot water instead of the water vapor to obtain a para-benzene as the second hydrolyzate. Dicarboxylic acid.

That is, it is presumed that in the first hydrolysis step, the polyethylene terephthalate as a solid matter is exposed to a water vapor atmosphere, whereby the exposed surface of the high-energy water molecule and polyethylene terephthalate is exposed. In the collision, the ester bond of the main chain is hydrolyzed and slowly oligomerized from the surface portion thereof. In the first hydrolysis step, since the oligomer formed in a high-temperature environment is in a molten state and has fluidity, it is supplied to the hot water in the second hydrolysis step.

In the case where the oligomer obtained in the first hydrolysis step is carried out in the same steam atmosphere as in the first hydrolysis step, the time required for the hydrolysis is necessary and is not practical, and thus it is characterized in that it is characterized in that it is characterized in that The second hydrolysis step is carried out in hot water. By carrying out the second hydrolysis step in hot water, the low molecular weight polyethylene terephthalate is more rapidly hydrolyzed than in the water vapor environment, and the ethylene glycol obtained together with the terephthalic acid is dissolved in the hot water. Among them, terephthalic acid which is insoluble in water is precipitated in hot water, so separation and recovery are easy. Further, if the amount of hot water used in the second hydrolysis step is too small, the concentration of ethylene glycol dissolved in hot water is increased, and the ethylene terephthalate oligomer is depolymerized and contained. It is easy to cause the polycondensation reaction of ethylene glycol and terephthalic acid, and the yield of terephthalic acid is lowered, so the 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 containing a metal material or a ceramic can be used, and it is more preferable to use a benzene which does not cause the use of the benzene. The dicarboxylic acid is produced by dissolving a metal ion or the like which is a problem when polyethylene terephthalate is recovered.

Further, the second hydrolyzate can be further purified by a known purification method as needed, and the purity can be further increased and recovered.

The second hydrolyzate after the second hydrolysis step in the present invention is a water-soluble hydrolyzate, which is a water-soluble hydrolyzate, and a terephthalic acid which is a water-insoluble hydrolyzate. Dissolved in hot water, the water-insoluble hydrolyzate precipitates in hot water and becomes a solid. Therefore, the solid terephthalic acid is separated from the hot water in which the water-soluble hydrolyzate (ethylene glycol) is dissolved (steps S14 and S17).

The separation method is not particularly limited, and may be carried out by filtration, suction, centrifugation, decantation or the like using a known method.

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

Further, the first hydrolysis step and the second hydrolysis step may be continuously performed as described below, or the first hydrolyzate obtained in the first hydrolysis step may be temporarily recovered, and then the first hydrolyzate may be supplied to the first hydrolyzate. The so-called batch method of the second hydrolysis step.

According to the production method of the present invention, the polyethylene terephthalate as the object to be treated is firstly subjected to the first hydrolysis step, and the ester bond of the polyethylene terephthalate is from normal pressure to saturated water. The steam is vaporized and the molecular chain is hydrolyzed (broken) to produce an ethylene terephthalate oligomer comprising ethylene glycol units or terephthalic acid units. Then borrow In the subsequent second hydrolysis step, the oligomers are hydrolyzed in a large amount of hot water to the ethylene glycol monomer unit and the terephthalic acid monomer unit as the smallest monomer unit, and are water-soluble ethylene glycol. The monomer unit is dissolved in hot water, and the water-insoluble terephthalic acid monomer unit is solidified in hot water, so that each can be recovered in a higher yield.

In the second hydrolysis step in the present invention, in the case where only the crude terephthalic acid having a low purity is obtained because the hydrolysis to terephthalic acid is insufficient, it is preferred to further carry out the hydrolysis reaction in hot water. (Third hydrolysis step) (Fig. 1, step S18). In this case, if only the reaction time of the second hydrolysis step is extended, it is difficult to generate sufficient hydrolysis. In other words, since the ethylene glycol as the hydrolyzate obtained in the second hydrolysis step is dissolved in the hot water, the hydrolysis reaction can be reversed even if the hydrolysis reaction is continued in the original state, and the equilibrium reaction state is impossible. Fully hydrolyzed to the case of terephthalic acid. Therefore, in such a case, the hot water used in the second hydrolysis step of dissolving a large amount of ethylene glycol is temporarily removed to the outside of the system, and replaced with fresh hot water for treatment, whereby the hydrolysis reaction can be promoted, so that it is preferable. . The hydrolysis treatment is carried out in the fresh hot water in this manner, whereby the hydrolysis to terephthalic acid can be accelerated, and the terephthalic acid having a higher purity can be obtained.

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

Next, a more suitable form 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 preferably has a heater for heating the entire system. The treatment pressure by the steam and the heating temperature in the first hydrolysis step and the second hydrolysis step can be arbitrarily adjusted by using a pressure-resistant container having a heater. For example, the operation of raising the water vapor along the saturated water vapor pressure curve as described above or the like can be simply performed. Furthermore, the rise and fall of pressure and temperature can be controlled by appropriate application of known control methods. Further, the first hydrolysis step and the second hydrolysis step are carried out in one container, whereby a simple processing operation can be realized, and equipment cost and processing can be reduced. cost.

Moreover, the first container is provided in the pressure-resistant container, and is provided with a hole having a size sufficient to pass the first hydrolyzate obtained by hydrolyzing polyethylene terephthalate without passing the object to be treated at the bottom. And a second container attached to the lower portion of the first container as a first hydrolyzate. Furthermore, it is preferable that the first hydrolysis step is performed on the workpiece in the first container, and the first hydrolyzate passing through the first container is received by the second container, and the first container is in the first container. The hydrolyzate is subjected to a second hydrolysis step. According to this aspect, the treatment of the object containing polyethylene terephthalate can be treated continuously and at low cost, high quality, and high recovery rate.

2(a) to 2(e) are schematic views for explaining a treatment method in a suitable form of the present invention, and are a mode of a treatment apparatus for continuously performing the first hydrolysis step and the second hydrolysis step. Figure.

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), and the first container 21 is placed in the first container 21 The second container 22 is provided at the lower portion. The first container 21 is provided with a plurality of holes A that can pass the first hydrolyzate without passing the workpiece S, and accommodates the workpiece S in the first container 21. Further, the hot water W1 is stored in the second container 22. Water W2 for generating water vapor used in the hydrolysis treatment of polyethylene terephthalate is stored at the bottom of the pressure-resistant container 20. Further, the water vapor can be supplied into the pressure-resistant container 20 by a water vapor generating device (not shown) provided outside without using the water W2.

As shown in Fig. 2 (b), when the first hydrolysis step is performed, the material S to be treated is hydrolyzed to become the first hydrolyzate H1, and is dropped from the hole portion A of the first container 21 as indicated by the arrow. The dropped first hydrolyzate H1 is received in the hot water W1 of the second container 22, and is applied to the second hydrolysis step to produce a second hydrolyzate in the hot water.

Next, as shown in FIG. 2(c), ethylene glycol as a water-soluble hydrolyzate and terephthalic acid which is a water-insoluble hydrolyzate are contained in the second hydrolyzate, so that the water-soluble second is contained. The hydrolyzate (ethylene glycol) H2 is dissolved in the hot water W1. On the other hand, the water-insoluble second hydrolyzate (terephthalic acid) H3 is not dissolved in the hot water W1 and is precipitated as a solid. The second hydrolyzates H2 and H3 are subjected to a known purification treatment as needed, and are collected. Further, in the first container 21, the high molecular weight residue S1 which was not hydrolyzed in the first hydrolysis step did not pass through the pore portion A and remained.

In the present invention, it is preferable to cool the inside of the pressure-resistant container 20 by natural cooling or forced cooling while controlling the pressure and temperature in the pressure-resistant container 20 after the completion of the second hydrolysis step. By this operation, deterioration of the quality of the recovered raw material can be suppressed.

Further, the conditions of the hydrolysis are the same as described above.

The first container 21 and the second container 22 are preferably made of a metal which can sufficiently withstand the hydrolysis conditions of the first hydrolysis step and the second hydrolysis step. For example, the first container 21 can be made of a known perforated metal or wire mesh. .

Further, in the case where the hydrolysis in the second hydrolysis step is insufficient, and the yield of the target terephthalic acid is insufficient, the hot water W1 can be removed from the second container, as shown in Fig. 2(d). It is shown that the new hot water W3 is added to further continue the hydrolysis treatment. By performing the treatment as described above, as shown in Fig. 2(e), the second hydrolyzate is sufficiently hydrolyzed into terephthalic acid H5 and ethylene glycol H4, and terephthalic acid H5 can be obtained in a high yield.

In the present invention, recovered polyethylene terephthalate can be produced using terephthalic acid obtained as described above. Specifically, the terephthalic acid obtained through the first hydrolysis step and the second hydrolysis step and the separately prepared ethylene glycol can be polycondensed to obtain recycled polyethylene terephthalate. The method of polycondensation can be carried out by a method known per se, and the obtained recovered polyethylene terephthalate can be processed into various molded articles in the form of pellets or the like.

[Examples]

Hereinafter, the present invention will be specifically described by way of examples and comparative examples, but various applications can be made without departing from the spirit of the invention, and are not limited to the following examples. Recorded.

(Example 1)

The process of forming a polyethylene terephthalate film (thickness: 35 μm, weight average molecular weight: 20000) as a material to be processed was carried out using the apparatus shown in Fig. 2 (a) to Fig. 2 (e).

First, as shown in FIG. 2(a), a pressure-resistant container 20 including a heater (not shown), a first container 21, and a second container 22 is prepared.

The internal volume of the first container 21 was 5 L, and 500 g of a film as a workpiece was placed therein. 3 kg of water was placed in advance in the second container 22. The water W2 for generating water vapor may be stored at the bottom of the pressure-resistant container 20, and the amount of water vapor required for the hydrolysis treatment is generated by the heater.

The first container 21 is provided with a plurality of holes A having a size that allows passage of the object to be treated and allows the first hydrolyzate generated in the first hydrolysis step to pass. The hole portion A is formed of a perforated metal made of stainless steel, and the size of the hole portion A is set to 1 mm square.

Then, as shown in FIGS. 2(b) and 2(c), the first hydrolysis step and the second hydrolysis step are continuously performed in the pressure-resistant container 20. In the first hydrolysis step and the second hydrolysis step, the water vapor atmosphere temperature of the pressure-resistant container 20 is 230 ° C, the temperature of the hot water W1 is 230 ° C, and the saturated water vapor pressure (pressure 2.8 MPa) is used. The film of polyethylene terephthalate as a material to be treated is subjected to hydrolysis. The second hydrolyzate H3 in the second container 22 was partially sampled after the water vapor atmosphere temperature in the pressure-resistant container reached 230 ° C for 2 hours, and the hydrolyzate was investigated by high-speed liquid chromatography (HPLC). The composition. Further, HPLC analysis conditions were as follows.

[Analysis conditions]

Analytical device: Product name UltiMate3000 manufactured by Thermo Fisher Scientific

Column: CAPCELLPAK (4.6mm ×150mm, 5μm, manufactured by Shiseido Co., Ltd.)

Solvent composition: aqueous formic acid / methanol gradient

Flow rate: 1mL/min

Detector: DAD (diode array detector, 190nm~800nm, 242nm extraction)

Column temperature: 40 ° C

Injection volume: 5μL

(Example 2)

A film of polyethylene terephthalate as a material to be treated was formed by the same conditions and methods as in Example 1 except that the amount of water was reduced to 2 kg in the second container 22 of the first embodiment. The hydrolysis treatment is carried out.

(Example 3)

A film of polyethylene terephthalate as a material to be treated was formed by the same conditions and methods as in Example 1 except that the amount of water was reduced to 1 kg in the second container 22 of the first embodiment. The hydrolysis treatment is carried out.

(Comparative Example 1)

In the second container 22 of the first embodiment, the amount of water was reduced to 0.5 kg, and the same conditions and methods as in Example 1 were used to prepare polyethylene terephthalate as a material to be treated. The membrane is subjected to hydrolysis treatment.

(Comparative Example 2)

In the second container 22 of the first embodiment, the amount of water was reduced to 0.2 kg, and the same conditions and methods as in Example 1 were used to prepare polyethylene terephthalate as a material to be treated. The membrane is subjected to hydrolysis treatment.

(Comparative Example 3)

The polyethylene terephthalate film as the object to be treated was subjected to the same conditions and methods as in Example 1 except that no water was placed in the second container 22 in the first embodiment. Hydrolysis treatment.

The terephthalic acid in the second hydrolyzate obtained in each of the above examples and the comparative examples was measured. The formic acid content rate is shown in Table 1 as the hydrolysis rate.

According to the results of Table 1, it is understood that if the amount of the hot water added to the adherend (the polyethylene terephthalate film) is twice or more in the second container in the second hydrolysis step, the hydrolysis is performed. The rate of the terephthalic acid in the second hydrolyzate was 90% by weight or more (Example 1, Example 2, and Example 3).

On the other hand, when the amount of water added to the adherend was 1 time or less, the hydrolysis rate was less than 80% (Comparative Examples 1, 2, and 3).

According to the above results, in the production method of the present invention, the amount of hot water in the second hydrolysis step is twice or more the weight (addition amount) of the workpiece, whereby the hydrolysis efficiency is improved to 90% by weight. The above yield obtained terephthalic acid.

The present invention has been described in detail with reference to the preferred embodiments of the present invention. It is understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The present application is based on Japanese Patent Application No. 2015-001081, filed on Jan.

[Industrial availability]

The present invention can provide a treatment method which can treat a processed material containing polyethylene terephthalate without consuming a large-scale apparatus or cost, and can be recovered as a polyethylene terephthalate with higher quality. The terephthalic acid which constitutes the raw material of the ester. Therefore, through chemical recycling technology, it can help to build a society that can sustain the supply of limited petroleum resources.

S10‧‧‧Preparing processed objects

S11‧‧‧ broken, cleaned

S12‧‧‧1st hydrolysis step

S13‧‧‧2nd hydrolysis step

S14‧‧‧Dissolved hot water of water-soluble hydrolyzate

S15‧‧‧ refined

S16‧‧‧Recycling

S17‧‧‧ terephthalic acid

S18‧‧‧3rd hydrolysis step

S19‧‧‧ refined

S20‧‧‧Recycling

Claims (6)

A method for producing terephthalic acid, comprising: a first hydrolysis step of storing a material containing polyethylene terephthalate in a sealed container, and exposing it to a normal pressure to a saturated water vapor pressure The polyethylene terephthalate is hydrolyzed under the environment to obtain an oligomer (ethylene terephthalate oligomer) containing terephthalic acid and terephthalic acid and ethylene glycol. a hydrolyzate of at least one of; and a second hydrolysis step of hydrolyzing the ethylene terephthalate oligomer obtained in the first hydrolysis step to obtain terephthalic acid in hot water; and the second The weight of the hot water in the hydrolysis step is twice or more the weight of the object to be treated used in the first hydrolysis step. 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. The method for producing terephthalic acid according to claim 1 or 2, wherein the weight of the 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. The method for producing terephthalic acid according to any one of claims 1 to 3, wherein at least one of terephthalic acid and ethylene terephthalate oligomer obtained in the first hydrolysis step is obtained The total amount of the hydrolyzate is transferred to the second hydrolysis step. 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 sealed container. A method for producing recycled polyethylene terephthalate, which is obtained by polycondensing terephthalic acid and ethylene glycol obtained by the production method according to any one of claims 1 to 5 Ethylene phthalate.