JP2001294552A - Method for recovering dimethyl terephthalate from polyalkylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for constructing a recovering system capable of providing stable facility productivity and labor productivity without much cost investment in recovering dicarboxylic acid components and glycol components from polyester wastes by glycolysis-transesterification reaction. SOLUTION: This method comprises using a conventional DMT(dimethyl terephthalate) producing process from paraxylene also as a DMT recovery system from polyester wastes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering dimethyl terephthalate from polyalkylene terephthalate. More specifically, the present invention relates to a method for recovering dimethyl terephthalate from polyalkylene terephthalate using a dimethyl terephthalate production process.

[0002]

2. Description of the Related Art Polyalkylene terephthalate is widely used in various fields, such as bottles for drinking water, fibers, films and resins.

[0003] However, the disposal of a large amount of nonstandard products and used polyalkylene terephthalate (hereinafter sometimes abbreviated as polyester waste) generated with an increase in the production and use amount is not only a disposal cost but also a disposal cost. It has become a major problem, including environmental issues.

[0004] As a method of treating polyester waste, there is a so-called material recycling method in which after removing plastics and metals other than polyalkylene terephthalate, pellets or flakes are reused as short fibers made from the pellets or flakes. The so-called thermal recycling that converts polyester waste into fuel, that is, the so-called chemical recycling, in which polyalkylene terephthalate is returned to dimethyl terephthalate (hereinafter sometimes referred to as DMT) or terephthalic acid, which is a raw material of polyalkylene terephthalate, and recovered. is there.

[0005] In material recycling, the quality of polyalkylene terephthalate deteriorates, so its use is limited, and the quality decreases every time it is collected, so that it is difficult to finally avoid disposal.

[0006] Further, in the thermal recycling, there is a problem that the calorific value of the polyester waste is relatively low, and there is a problem of loss of the polyalkylene terephthalate raw material, which is not preferable from the viewpoint of energy saving and resource saving.

On the other hand, in contrast to the above two methods, chemical recycling converts polyester waste into its constituent components.
By recovering, the compounds can be recycled and reused, which is the most preferable from the viewpoint of resource saving.

As chemical recycling, polyalkylene terephthalate is converted into D
Methanolysis which decomposes to MT, alkali decomposition which decomposes to terephthalic acid with alkali, supercritical methanol decomposition which decomposes with supercritical methanol, bishydroxyalkyl terephthalic acid with alkylene glycol to depolymerize glycolysis, and the product obtained by glycolysis A method of transesterifying the product with methanol to obtain DMT.

[0009] In particular, a method of depolymerizing polyester waste with an alkylene glycol and then transesterifying with methanol to obtain DMT is widely known as a glycolysis-transesterification reaction method and has been practiced industrially.

[0010] However, the glycolysis-transesterification reaction method is a mild reaction condition and consumes less heat than other methods, but has a disadvantage that the equipment investment is increased due to a longer process.

[0011] Further, using only polyester waste as a raw material, D
Producing the MT may hinder continuous operation due to a shortage of raw materials or the like, and is not preferable from the viewpoint of stable equipment productivity and labor productivity.

The present inventors can use not only an apparatus for producing DMT from para-xylene but also an apparatus for collecting polyester waste by methanolysis without significantly changing the existing process for producing DMT from para-xylene. (Japanese Patent Laid-Open No. 11-29)
No. 2826). However, the recovery of polyester waste by methanolysis requires a large amount of energy because a large amount of methanol is reacted at high temperature, and the reaction conditions are severe. Occurs and reduces the quality of the recovered active ingredient.

Here, the reaction conditions of the glycolysis-ester exchange reaction are milder, and the glycolysis-ester exchange reaction is superior to methanolysis from the viewpoint of energy saving. -If transesterification is performed, even if impurities are mixed in the polyester waste, thermal decomposition of the impurities does not progress,
It has been found that the quality of the recovered active ingredient is not reduced.

[0014]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a stable equipment productivity without significant cost investment in the recovery of dicarboxylic acid component and glycol component from polyester waste by the glycolysis-ester exchange reaction method. Another object of the present invention is to establish a method of constructing a recovery device that provides labor productivity.

[0015]

DISCLOSURE OF THE INVENTION In view of the above-mentioned problems, the present inventors have developed a method for producing DMT from para-xylene without significantly changing the existing DMT production process from para-xylene.
The present invention has been found that if it can be used not only as a T manufacturing device but also as a polyester waste collecting device, it is possible to provide a collecting device that provides stable equipment productivity and labor productivity without investing much cost. It has been reached.

That is, an object of the present invention is to provide an oxidation step by reacting a mixture of para-xylene and methyl toluate with oxygen molecules, and removing unreacted para-xylene and unreacted methyl toluate from the product. A stripping step, an esterification step of subsequently reacting the product with methanol, a distillation step of taking out methyl toluate from the esterification product and transferring it to an oxidation step, and taking out dimethyl terephthalate; In a dimethyl terephthalate production process comprising a recrystallization process of recrystallizing dimethyl terephthalate with methanol, an intermediate tank in a stripping process or a process for storing an intermediate product is used as a depolymerization process of alkylene glycol and polyalkylene terephthalate, and oxidation is performed. Process, or esterification process, or The crystals step is used as the transesterification process of methanol and depolymerization process products can be achieved by dimethyl terephthalate process for recovering from polyalkylene terephthalamide terpolymer rate.

[0017]

DETAILED DESCRIPTION OF THE INVENTION DMT from existing para-xylene
The production process includes an oxidation step by reacting a mixture of para-xylene and methyl toluate with molecular oxygen, a stripping step of removing unreacted para-xylene and unreacted methyl toluate from the product, Esterification step of reacting the product with methanol, methyl toluate is taken out of the esterification product and transferred to the oxidation step, and dimethyl terephthalate is taken out, and dimethyl terephthalate after distillation is re-used with methanol. It consists of a recrystallization step for crystallization.

In the present invention, as an apparatus used for the depolymerization reaction of polyester waste with an alkylene glycol, an efficient tank is used by using a stripping step in a dimethyl terephthalate production step or an intermediate tank in a step for storing an intermediate product. Can be used.

As an apparatus used for the transesterification reaction between the depolymerized product and methanol, an oxidizing apparatus, an esterifying apparatus, and a recrystallization apparatus in the dimethyl terephthalate production step can be used efficiently. .

For the purification of the product obtained by the transesterification reaction, the existing distillation apparatus or recrystallization apparatus in the DMT production process from para-xylene can be used as it is.

In the depolymerization of the polyester waste, the alkylene glycol used for the reaction is preferably a glycol constituting the recovered polyalkylene terephthalate. The alkylene glycol is used in an amount of 0.5 to 20 times, preferably 1 to 5 times, the weight ratio of the raw material polyester waste.

In the present invention, the catalyst for depolymerization is at least one selected from the group consisting of carbonates and oxides of alkali metals, carbonates and oxides of alkaline earth metals, manganese acetate and zinc acetate. Preferably, a compound is used. The amount of the depolymerization catalyst to be added is preferably 0.1 to 10% by weight based on the weight of the polyester waste, and when it is within the above range, the depolymerization time can be shortened.

[0023] The depolymerization reaction is carried out at a temperature of 110 ° C to 210 ° C, preferably at 140 ° C to 190 ° C. When the reaction temperature is 110 ° C. or lower, the time required for depolymerization becomes long, which is not efficient. When the reaction temperature is 210 ° C. or higher, thermal decomposition of impurities mixed into the polyester waste becomes remarkable, and the quality of the recovered active ingredient is deteriorated. The depolymerization reaction is completed by heating and holding under these conditions for 1 to 10 hours, and converted into oligomers of repeating units 1 to 4.

In the transesterification reaction of the depolymerized product with methanol, if a large amount of alkylene glycol is present, the recovery rate of DMT becomes low. Therefore, the alkylene glycol is distilled off from the depolymerized product by means such as distillation. Preferably, the weight ratio between the alkylene glycol and the raw material polyester waste is 0.5 to 2.0.

In the transesterification reaction, methanol is added 2 to 4 times in weight as compared with polyester waste.

As the transesterification catalyst, at least one compound selected from the group consisting of alkali metal carbonates and oxides, alkaline earth metal carbonates and oxides, manganese acetate and zinc acetate can be used. Preferably, the amount is 1 to 10% by weight based on the weight of the raw polyester waste. As the transesterification catalyst, it is preferable to use the same catalyst as that used for the depolymerization reaction of the polyester waste.

The transesterification is carried out at a reaction temperature of 65 ° C. to 85 ° C. at about atmospheric pressure and is completed in 0.5 to 3 hours.

After the transesterification reaction is completed, DM
It becomes a slurry of T, methanol, and alkylene glycol. A solid-liquid separator can be used to recover DMT from the slurry.

When a solid-liquid separation device is used after the transesterification reaction, after the esterification reaction, the mixture is cooled sufficiently to perform solid-liquid separation. The separated liquid contains alkylene glycol, methanol, a catalyst, and dissolved DMT, but the alkylene glycol and methanol are separately purified for use in the process again. This separation and purification need not be limited to a distillation operation, but distillation is preferred from the viewpoint of effective use of existing DMT manufacturing equipment. In this case, first, methanol having a low boiling point is separated by distillation, and the liquid remaining at the bottom of the column is supplied to the next distillation column to separate the alkylene glycol by distillation. The bottom can be supplied to a depolymerization apparatus to recover the active ingredient again, or discarded to reduce the impurity concentration in the process.

The solid separated by the solid-liquid separation can be purified by washing with methanol, distillation under reduced pressure, and recrystallization according to the required quality. The bottom of the distillation under reduced pressure may be supplied to a depolymerization apparatus to recover the active ingredient again, or may be discarded in order to reduce the impurity concentration in the process.

Hereinafter, the recovery method of the present invention will be specifically described with reference to FIG. 1 showing one embodiment of the recovery method of the present invention.
The present invention is not limited by this.

When this apparatus is used in an apparatus for producing DMT from para-xylene, the oxidation reactor 1 shown in FIG. 1 is an apparatus for performing an oxidation reaction of a mixture of para-xylene and methyl toluate. The object is transferred from the lower part to the tank 2 via the pipe 9.

The tank 2 is for stripping unreacted paraxylene and methyl toluate from a solution containing paraxylene and an oxide of methyl toluate, and supplies the product after the oxidation reaction. In addition to the pipe 9, a steam supply pipe for stripping is installed (the pipe is not shown).

The stripped para-xylene and methyl toluate are fed back to the oxidation reactor 1 (the piping is not shown), and the oxides of para-xylene and methyl toluate are esterified via the feed pipe 10. It is supplied to the reactor 3.

The esterification reactor 3 has a feed pipe 10 for the product from the tank 2 and a blow-out port (not shown) for the heated methanol from the bottom of the tower, and has sufficient tray trays for the esterification reaction. In a high-pressure reactor, an esterification reaction is performed to form a mixture of methyl toluate and DMT from paraxylene and an oxide of methyl toluate.

The overhead fraction of the esterification reactor 3 is
And methanol is recovered from the top of the column via a pipe 19.

After the esterification reaction, the mixture of methyl toluate and DMT is separated into DMT, methyl toluate, and a bottom residue by distillation columns 4 and 5 via line 11, and DMT is separated from line 16. Is transferred to the tank 6 via. Methyl toluate is fed back to the oxidation reactor 1 described above, and the residue in the kettle is purged via a pipe 15. The DMT transferred to the tank 6 is recrystallized with methanol. The DMT after the recrystallization is separated by the solid-liquid separator 7, and the solid DMT is taken out as a product via the pipe 17. The liquid methanol is transferred to the distillation column 8 via the pipe 18 and purified and separated.

On the other hand, when the apparatus is used for recovering DMT from polyester waste, the operation is as follows.

The oxidation reaction apparatus 1 is not used, and the depolymerization reaction between the polyester waste and ethylene glycol is performed in the tank 2. Here, the depolymerization reaction is a reaction in which ethylene glycol and polyester waste are reacted to convert them into oligomers having 1 to 4 repeating units.

For this reason, the tank 2 needs pipes 21 and 22 for charging the raw material polyester waste and ethylene glycol.

The product of the depolymerization reaction is supplied to the tank 6 via the pipe 23. Vessel 6 contains DM from para-xylene
In the production of T, since it is used as a recrystallization apparatus, the supply pipe of methanol necessary for transesterification can be used as it is.

After the transesterification reaction is completed in the tank 6, solid DMT and liquid are separated by the solid-liquid separation device 7,
Is sent to the distillation column 5 via the pipe 24. The liquid is sent to the distillation column 8 via the pipe 18 and recovers methanol from the pipe 19. Further, the bottom of the distillation column 8 is connected to the pipe 2
The liquid is sent to the distillation column 4 via 5 and ethylene glycol is recovered from the pipe 28. DMT sent to distillation unit 5
Is purified by distillation and taken out as product DMT.

As described above, according to the present invention, it is possible to recover DMT from polyester waste by using an existing reactor only by attaching a part of piping or the like to a usual apparatus for producing DMT from para-xylene. .

[0044]

The present invention will be described below with reference to examples. However, the present invention is not limited to this embodiment. In the examples, "parts" means "parts by weight" unless otherwise specified.

Example 1 DMT from polyester waste
The recovery was performed using the apparatus of FIG. 1 as follows. As the raw material polyester waste, a crushed colorless polyethylene terephthalate bottle was used. In tank 2, 100 parts of polyester waste, 400 parts of ethylene glycol,
3 parts of sodium carbonate was charged and the temperature was raised to 185 ° C. After 4 hours in this state, the polyester waste was dissolved and the depolymerization was completed.

The depolymerized product was transferred to the tank 6 and 3 parts of sodium carbonate and methanol 2 were used as transesterification catalysts.
00 parts were charged. At normal pressure, the liquid temperature was 75 ° C., and the transesterification was completed in 2 hours. The resulting mixture is
The mixture was cooled to 0 ° C. and separated into a liquid and a solid by a solid-liquid separator 7. The solid was distilled under reduced pressure in the distillation column 5 at a pressure of 6.65 kPa, and 87 parts of DMT having a purity of 99.9% could be recovered as a fraction. The liquid separated by the solid-liquid separator was subjected to atmospheric distillation in the distillation column 8 to recover 150 parts of methanol. Further, the distillation residue was sent to the distillation column 4 and distilled under reduced pressure at 40 kPa to recover 430 parts of ethylene glycol.

Further, after the completion of the above-mentioned reaction, the inside of the reactor was drained, and then DMT from para-xylene was removed using the apparatus shown in FIG.
When synthesized, it could be produced without any problem.

[0048]

According to the present invention, the production of DMT from para-xylene and the recovery of dimethyl terephthalate from polyester waste can be performed by the same apparatus, and the equipment can be used effectively.

[Brief description of the drawings]

FIG. 1 is a flow chart schematically showing one embodiment of the process of the present invention for specifically describing the present invention. In FIG. 1, a thin line portion is necessary only when producing DMT from para-xylene. The piping and bold line are DM from polyester waste.
The pipes required when collecting T are shown below.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Oxidation reactor 2 tank 3 Esterification reactor 4 Distillation tower 5 Distillation tower 6 Tank 7 Solid-liquid separation device 8 Distillation tower 9-28 Piping

 ────────────────────────────────────────────────── ─── Continued on front page (72) Inventor Kazuhiro Sato 77 Kitayoshida-cho, Matsuyama-shi, Ehime Pref. BC10 BJ50 KA03

Claims (1)

[Claims] 1. An oxidation step by reacting a mixture of para-xylene and methyl toluate with oxygen molecules, a stripping step of removing unreacted para-xylene and unreacted methyl toluate from the product, An esterification step of reacting the product with methanol; a distillation step of taking out methyl toluate from the esterification product and transferring it to an oxidation step; and a distillation step of taking out dimethyl terephthalate. In the dimethyl terephthalate production step comprising a recrystallization step of recrystallizing, an intermediate tank in a stripping step or a step for storing an intermediate product is used as a depolymerization step of alkylene glycol and polyalkylene terephthalate, and an oxidation step or an esterification step Or recrystallization step with methanol Used as transesterification step of the polymerization step product, dimethyl terephthalate process for recovering from polyalkylene terephthalamide terpolymer rate.