JP3303370B2 - Depolymerization method of aromatic polyester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for depolymerizing an aromatic polyester. More specifically, the present invention relates to a method for depolymerizing aromatic polyester waste for performing a depolymerization reaction of aromatic polyester waste with an alkylene glycol in a short time and then regenerating the aromatic polyester waste again as a high-quality aromatic polyester.

[0002]

2. Description of the Related Art Polyethylene terephthalate (PET)
Aromatic polyesters (hereinafter simply referred to as polyester) represented by polyethylene naphthalate (PEN) and the like have excellent mechanical properties, weather resistance, electrical insulation properties, and chemical resistance. Widely used as film, fiber and other molded products.

[0003] However, these polyesters often generate debris during the resin production and molding stages, and are often discarded after use even after commercialization.

Therefore, various methods for collecting these wastes have been conventionally studied. For example, a method in which methanol is added to PET to decompose it into dimethyl terephthalate (DMT) and ethylene glycol (EG) (Japanese Patent Publication No. 32-80)
No. 69, Japanese Patent Publication No. 42-8855, etc.), PE
A method of adding EG to T to depolymerize and then adding methanol to recover DMT (JP-A-48-62732) is disclosed. Although relatively high-quality recycled PET can be obtained by these methods, there is a problem in that it is not economically preferable because the recovery device is complicated.
Further, for the purpose of shortening the depolymerization time when depolymerizing PET with EG, a method of depolymerizing PET under specific conditions (JP-A-60-248646) is disclosed.
This method also has a problem that the depolymerization reaction time is not sufficiently improved.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems in the prior art in the depolymerization of aromatic polyester waste, and in particular to improve the economic efficiency by shortening the depolymerization, and This will suppress the lowering of the softening point of the regenerated aromatic polyester.

[0006]

The object of the present invention is to provide a reaction system in which an aromatic dicarboxylate and a low polymer thereof are present in a molten state when an aromatic polyester is depolymerized with an alkylene glycol. was added to the aromatic polyesters perform depolymerization reaction at 200 to 250 ° C., then the alkylene glycol, 0.5 to 5.0-fold molar added to acids Ingredients constituting the added aromatic polyesters, further The problem is solved by a method for depolymerizing an aromatic polyester, which comprises supplying a part of an aromatic dicarboxylate and a low polymer obtained by performing a depolymerization reaction at 200 to 250 ° C. to a polymerization reaction system. be able to.

The aromatic polyester (hereinafter simply referred to as "polyester") in the present invention is an aromatic dicarboxylic acid such as terephthalic acid, 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, isophthalic acid, or a lower alkyl ester thereof as an acid component. And a polyester comprising, as a glycol component, EG, diethylene glycol, butanediol, cyclohexanedimethanol, and the like.

[0008] Specifically, PET, 2,6-PEN, polybutylene terephthalate and the like can be mentioned.
These polyesters may be homopolymers or copolymers, but it is preferable not to mix homopolymers and copolymers in quality control of the finally obtained polyester. In the case of a copolymer, it is preferable from the viewpoint of quality control of the polyester to separate each polyester constituting the copolymer component. Depending on the purpose, two or more of the above-mentioned dicarboxylic acid components and glycol components can be used. Further, polyalkylene glycols such as polyethylene glycol and polybutylene glycol, and aliphatic carboxylic acids such as adipic acid and sebacic acid can be used. 5-Natrium sulfoisophthalic acid, hydroxybenzoic acid and the like can also be used.

The shape of the polyester waste used in the present invention is not particularly limited. For example, film waste, flake waste obtained by cutting bottles, fibrous waste, block waste, and the like can be mentioned. However, if the flake waste is compressed and solidified into pellets, the apparent specific gravity becomes large, so it is preferable. It is preferable that the amount of the block-like waste is 1 cm ³ or less because the dissolution time of the polyester can be shortened.

A feature of the present invention is that, when an aromatic polyester is depolymerized with an alkylene glycol, an aromatic dicarboxylate which is a precursor compound of the aromatic polyester and a low polymer thereof (hereinafter referred to as a low polymer) are melted and stored. To the reaction system, a low polymer is first produced by adding an aromatic polyester to perform a depolymerization reaction, and then adding an alkylene glycol to further perform a depolymerization reaction,
It is to supply a part of the low polymer to the polycondensation reaction system.

Regarding the preferred depolymerization method of the present invention,
A description will be given of ET waste as an example. In depolymerizing PET waste in the present invention, first, bis (2-hydroxyethyl) terephthalate and its low polymer (hereinafter referred to as BHT) are added to the reaction system.
It is indispensable to store them in a molten state. BHT
Is not stored, in other words, P
When ET scrap and EG are supplied, the temperature of the reaction system is maintained at the boiling point of EG, so that not only the depolymerization time is delayed, but also the softening point of the recycled PET decreases.

The stored BHT includes BHT obtained from DMT and EG, and BH obtained from terephthalic acid and EG.
B or BHT obtained from PET waste and EG can be used. However, in order to continuously regenerate PET waste, BHT obtained from PET waste and EG is stored in BHT.
It is preferable that

The amount of BHT to be melted and stored depends on the PET to be added.
The molar ratio of the storage tank BHT component to 1 mole of the scrap acid component is 1
The range of / 4 to 2/1 is desirable because the depolymerization time can be shortened and the decrease in the softening point can be sufficiently suppressed.

[0014] In the present invention, PET waste is first added to the molten and stored BHT. Since the temperature of the depolymerization reaction after adding the PET waste can be made higher than the temperature of the melt-stored BHT, the rate of the depolymerization reaction is significantly improved. Usually, it is preferable that the reaction temperature after adding the PET waste be 5 to 30 ° C. higher than the temperature of the stored BHT before adding the PET waste.

EG is added to the relatively high molecular weight BHT thus obtained, and the depolymerization reaction is performed again. The amount of EG added at this time depends on the PET added to the stored BHT.
Molar ratio of scrap to acid component (hereinafter simply referred to as molar ratio)
Must be set to 0.5 to 5.0. More preferably, it is 1.0 to 3.0.

In general, foreign matters cannot be avoided to some extent in PET waste. It is necessary to remove such foreign matter by some means, such as a method of removing with a filter at the stage of BHT or a method of removing with a centrifuge proposed in Japanese Patent Application No. 4-94481. The method of centrifugation is more preferable because foreign substances can be removed with high accuracy. Regardless of the method, the lower the melting point, specific gravity and melt viscosity of BHT, the greater the foreign matter separating effect.

However, if the above molar ratio is less than 0.5 mole, the obtained BHT has a high melting point, specific gravity, melt viscosity, and the like. Therefore, it is necessary to remove foreign matter contained in the BHT by the above method. Is difficult. According to the method of the present invention, the melting point can be set to 200 ° C. or less, the specific gravity to 1.2 or less, and the melt viscosity to 10 cp or less.
Foreign substances in the inside can be efficiently removed. Here, the specific gravity and the melt viscosity are measured values at 180 ° C.

On the other hand, if the molar ratio exceeds 5.0, not only does the basic unit of EG and the energy unit required for removing EG during the polycondensation reaction increase, but also when the BHT is used as the stored BHT, Since the molar ratio of the system becomes high, the equilibrium boiling point of BHT becomes low, so that not only the depolymerization reaction time is delayed, but also the polycondensation reaction time of the next step is delayed. Further, the softening point of the recycled PET also decreases, which is not preferable.

The thus obtained BHT after depolymerization
Feeds a part of it to a polycondensation vessel,
The polymerization reaction is carried out at 80 to 300 ° C. and at a reduced pressure of 1 mmHg or less. At this time, as described above, the amount of BHT to be left in the depolymerization tank is the required amount (molar ratio to the acid component of PET waste; 1/4 to 2) when used as BHT for storage of the next batch.
/ 1). In this depolymerization reaction system, B
The reason why a part of the HT is left is that it is effective for removing foreign substances in the BHT for the following reason, in addition to being used as the BHT for storage of the next batch.

In general, when BHT after the completion of the depolymerization reaction is supplied to the polycondensation reactor, a method using a head difference between the depolymerization reactor and the polycondensation reactor or an inert gas or pump from the depolymerization reactor is used. And a method of supplying to a polycondensation can. When the entire amount of BHT in the depolymerization can is supplied to the polycondensation can, the inert gas is supplied to the filter or centrifuge installed between the depolymerization can and the polycondensation can. The foreign matter once separated comes into the clarified BHT again. Further, it is preferable that the water contained in the PET waste supplied to the depolymerization reaction system be separated using a rectification tower installed in the depolymerization can.

The reaction system at the time of the above depolymerization reaction may be either under normal pressure or under pressure, but it is preferable that the pressure be substantially at normal pressure from the viewpoint of equipment maintenance. Further, the method of the present invention may be either a batch process or a continuous process.

The BHT thus obtained is converted into regenerated PET in the presence of a polycondensation reaction catalyst. As the polycondensation reaction catalyst at this time, a glycol-soluble antimony compound, germanium compound, titanium compound or the like can be used. When the required amount of the polycondensation reaction catalyst is contained in the PET waste, it is not necessary to add it again.

Further, in order to improve the thermal stability of the obtained recycled PET, a known thermal stabilizer or an antioxidant may be added. Furthermore, inert particles such as calcium carbonate, titanium oxide, silicon dioxide, talc, kaolin, and alumina can be added according to the purpose of the recycled PET.

[0024]

The present invention will be specifically described below with reference to examples. The parts in this example are parts by weight, and the measured values of the properties of each polymer were in accordance with the following methods. A. Intrinsic viscosity of polymer Measured at 25 ° C. using o-chlorophenol as a solvent. B. Softening point Measured with a penetrometer and expressed in SP (° C). C. Color tone b value Using a direct-reading color difference meter (Suga Test Instruments Co., Ltd.), it was measured in the form of a chip and indicated by b value.

D. Number of Foreign Substances in Polymer Foreign substances present in 50 g of the chip were counted with the naked eye.

[0026] Example 1 stirrer, heating coils, and PET chips 100 parts of a solution polymerization reactor equipped with a fractionating column, EG64.6 parts (EG / PET structure
Molar ratio of the acid component to be formed (hereinafter, this ratio is referred to as the EG / PET model).
Ratio, or simply the molar ratio) is 2.0)
HT164.6 parts melted and stored at 220 ° C
100 parts of PET waste was added. The heating was started at the same time as the addition of the PET waste.
G was added in an amount of 64.6 parts (molar ratio: 2.0). The temperature in the can at the end of the EG addition was 215 ° C. Thereafter, heating was further continued, and the temperature reached 220 ° C. after 30 minutes. All of the polymer was dissolved. The reaction was further continued at 220 ° C. for 15 minutes to terminate the depolymerization reaction. The total depolymerization time was 1.0 hour. Except when the top of the rectification column showed the boiling point of water immediately after the start of heating, the entire amount of the distilled EG was refluxed to the depolymerization reactor.

Next, the depolymerization can was adjusted to 0.2 fkg / cm ² .
164.6 parts of BHT (100 parts of PET)
Equivalent) to a disk-type centrifuge to separate foreign matter.
After that, it is transferred to the polycondensation reactor, where the polycondensation
(Experiment No. 1). Recycled PET polymer
Properties: intrinsic viscosity 0.623, softening point 259.7 ° C, color tone b
The value was 5.4 and the number of foreign substances was 0. Experiment No. The number of batches was repeated by the same operation as in Example 1 to obtain a recycled PET (actual
Experiment No. 2-4). Table 1 shows the polymer characteristics. Either
Is also a good polymer with good reproducibility.

Comparative Example 1 100 parts of PET waste and EG64.6 were added to the depolymerization can of Example 1.
And heating was started. Except when the top of the rectification column showed the boiling point of water immediately after the start of heating, the entire amount of the distilled EG was refluxed to the depolymerization reactor. For a while after starting the temperature rise, P
Since a large amount of ET debris and unreacted EG are present,
It took 2.0 hours to raise the temperature from the boiling point of 197 ° C. to 200 ° C. Thereafter, the mixture was further heated, and reached 220 ° C. 4 hours after the start of heating. All of the polymer was dissolved. The reaction was further continued at 220 ° C. for 15 minutes to terminate the depolymerization reaction. The total depolymerization time required 4 hours and 15 minutes. Next, 164 parts of BHT (0.6 parts remained)
Is separated in the same manner as in Example 1, and then a polycondensation reaction is performed.
The mixture was transferred to a can to terminate the polycondensation reaction (Experiment No. 5).
In this example in which BHT is not present when adding PET and EG, the depolymerization time is long, the intrinsic viscosity is 0.625,
Recycled PET with a softening point of 259.3 ° C and a color tone b value of 6.2
Was also unfavorable in polymer properties.

Comparative Example 2 In Example 1, BHT 16 at 220 ° C. was left in the depolymerization vessel.
To a reaction system in which 4.6 parts were stored BHT, 100 parts of PET waste and 64.5 parts of EG were simultaneously added, and the temperature was raised. The temperature in the can at the end of the addition was 205 ° C. Further, the inside of the can was continued in the same manner as in Example 2, and after 1 hour and 45 minutes 220
° C was reached. The waste polymer was completely dissolved. 2 more
The reaction was continued at 20 ° C. for 15 minutes to terminate the depolymerization reaction (Experiment No. 6). The total depolymerization time was 2 hours, and the depolymerization time was long. Table 2 summarizes the depolymerization conditions, the depolymerization time, and the polymer characteristics of the recycled PET in the above (Experiment No. 6).

Examples 2 to 4 and Comparative Examples 3 to 4 Experiment No. 1 of Example 1 was conducted except that the amounts of EG and PET were changed and the molar ratio during the depolymerization reaction was changed. After supplying the BHT having undergone the depolymerization reaction in the same manner as in Example 1 to a disk-type centrifugal separator, the polycondensation reaction was completed (Experiment Nos. 7 to 7).
11).

When the molar ratio was less than the range of the present invention, the separation of foreign matters was insufficient (Comparative Example 3, Experiment N
o. 10). When the molar ratio exceeds the range of the present invention, a polymer having a long depolymerization time, poor polycondensation reactivity (slow rise in intrinsic viscosity), and a low softening point was obtained (Comparative Example 4, experiment). No. 11).

Table 2 shows the depolymerization conditions, the depolymerization time and the polymer characteristics of the recycled PET in the above (Experiments Nos. 7 to 11).
3

Examples 5 to 6 and Comparative Examples 5 to 8 The temperature of the stored BHT at the time of addition of PET waste, the depolymerization temperature after addition of PET waste, and the depolymerization temperature after addition of EG under the conditions shown in Tables 3 and 4. A depolymerization reaction was performed (Experiment Nos. 12 to 1).
7).

When PET waste is added to a temperature where the stored BHT temperature at the time of addition of PET waste does not fall within the range of the present invention, BHT in the system is solidified, uneven stirring occurs, and the depolymerization time is delayed (Comparative Example 5, experiment). No. 14), when the stored BHT temperature at the time of addition of PET scrap exceeded the range of the present invention, only a polymer having a low softening point and an undesirable color tone was obtained (Comparative Example 6, Experiment No. 15). ).

On the other hand, when the depolymerization temperature after the addition of EG is less than the range of the present invention, the depolymerization temperature is remarkably delayed, and a polymer having a favorable softening point and color tone cannot be obtained (Comparative Example 7, experiment No. 16), even when it exceeds the scope of the present invention,
Only a polymer having a low softening point and an undesirable color tone was obtained (Comparative Example 8, Experiment No. 17). Above (Experiment N
o. Tables 3 and 4 summarize the depolymerization conditions, depolymerization times and polymer properties of the recycled PET described in 12 to 17).

Comparative Example 9 B remaining after transferring the BHT of No. 4 to the polycondensation can
HT164.6 parts of the total amount of Experiment No. 4 similarly to the depolymerization reactor pressurized with nitrogen to 0.2fkg / cm ² was shifted to Juchijimi if the can through the centrifuge. After the transfer was completed, the nitrogen pressure was released from the polycondensation vessel via a centrifuge. Then, in Experiment No. A polymer was obtained in the same manner as in Example 4 (Experiment No. 4).
18).

In this example, since a part of the BHT was not left in the depolymerization vessel at the end of the BHT transfer, nitrogen gas was supplied directly to the centrifugal separator installed between the depolymerization vessel and the polycondensation vessel.
As a result, the foreign matter once separated by the centrifugal separator was mixed into the clarified BHT again, and the foreign matter in the regenerated polymer was remarkably increased to 35.

[0038]

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[0039]

According to the depolymerization method of the present invention, the polyester for depolymerization and the glycol are melted under specific conditions to obtain a molten BH.
Since T is added to the existing depolymerization reaction system, the depolymerization reaction time is shortened, and the thus obtained regenerated B
By repolymerizing HT, that is, the aromatic dicarboxylate and its low polymer, a high-grade aromatic polyester can be produced and can be regenerated as a fiber or a film. In particular, . In the production of recycled polyester, the depolymerization reaction time is greatly reduced, so that the economic efficiency and productivity are significantly improved. . The number of foreign substances in the recycled polymer is greatly reduced. . The regenerated polymer has a high softening point and excellent color tone. It has excellent effects such as.

Claims (1)

(57) [Claims] When depolymerizing an aromatic polyester with an alkylene glycol, an aromatic polyester is first added to a reaction system in which an aromatic dicarboxylate and a low polymer thereof are present in a molten state, and the aromatic polyester is added at 200 to 250 ° C. 0.5 in performed depolymerization reaction, then to an acid Ingredients constituting the aromatic polyester with the addition of alkylene glycol
It is characterized in that the aromatic dicarboxylate and a part of its low polymer obtained by adding a depolymerization reaction at 200 to 250 ° C. are added to the polymerization reaction system by adding the compound to the polymerization reaction system at 200 to 250 ° C. A method for depolymerizing an aromatic polyester.