JP2002060543A - Method for recycling polyester waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover low-molecular weight oligomers mainly composed of bis-β- hydroxyethyl terephthalate with high quality from polyester waste. SOLUTION: From polyester wastes mainly composed of polyethylene terephthalate, dimethyl terephthalate is recovered as useful components. Subsequently, the reaction mixture is heated and subjected to a reaction with large excess of EG under normal pressure using no catalyst, and a lower-polymeric mixture mainly composed of bis-β-hydroxyethyl terephthalate and containing a hydroxyethyl ester group at the terminal is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recycling polyester waste, and more particularly, to a method for recovering and reusing an effective component from a polyester waste containing polyalkylene terephthalate as a main component by chemical recycling. .

[0002]

2. Description of the Related Art Polyethylene terephthalate is rapidly used in daily life-related materials such as fibers, films and resins, and in the food field such as drinking water and carbonated beverage bottles because of its excellent chemical stability. Is growing.

However, used polyethylene terephthalate, which is generated in large quantities with the increase in the amount of use as described above, or an unqualified product generated in the stage of producing polyethylene terephthalate (hereinafter sometimes referred to as polyester waste). The treatment of ()) is a major social problem.

In order to solve the above-mentioned problem, so-called chemical recycling, in which polyester waste is converted into a monomer and recovered, and the monomer is used as a raw material to produce and reuse polyethylene terephthalate by a polymerization reaction has been studied. This method basically enables loss-free recycling of compounds and resource recycling.

As a chemical recycling method,
(1) The recovered polyester waste is subjected to a depolymerization reaction with ethylene glycol (hereinafter sometimes abbreviated as EG), and bis-β-hydroxyethyl terephthalate (hereinafter sometimes abbreviated as BHET) and a terminal. To obtain a mixture of low polymers containing a hydroxyethyl ester group (hereinafter sometimes abbreviated as lower oligomer).
A method of purifying this and recovering it as an intermediate material for the production of polyester products (JP-A-2000-53802, etc.), and (2) collecting the collected polyester waste in EG
, Followed by a substitution esterification reaction using methanol, followed by separation and purification to obtain high-purity dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) and a raw material for producing polyester products. A method of purifying and recovering EG is known. However, the method of obtaining BHET by the one-stage depolymerization method using EG in the above (1) is based on the additive and small amount of the third component contained in the polyester waste, substances such as diethylene glycol by-produced in the depolymerization reaction, and the reverse. The substance produced by the reaction was easily affected by quality and was difficult to purify.

On the other hand, the method (2) for purifying and recovering DMT and EG is as follows:
There is an advantage that separation and purification from additives and a small amount of the third component contained in the polyester waste are relatively easy.

[0007] JP-B-43-2088 discloses that an excess amount of ethylene glycol is added to polyethylene terephthalate and heated to obtain a BHET and a lower oligomer by a depolymerization reaction, and excess methanol (hereinafter referred to as M
Sometimes abbreviated as OH. ) And in the presence of a catalyst,
A method of recovering dimethyl terephthalate by performing a substitution esterification reaction has been proposed.

However, terephthalic acid is the mainstream raw material of polyester currently produced worldwide, and in many existing polyester resin manufacturing processes, the obtained recovered DMT may not be used as a polymer raw material.

When a polyester resin is produced using DMT as a raw material, a catalyst is required for the transesterification reaction. Therefore, in some applications, the catalyst may hinder the improvement of the quality of the polyester resin.

[0010] Therefore, it has been desired to provide a method capable of recovering a high-quality polyester production intermediate material containing no additives and containing few impurities when performing chemical recycling of polyester waste.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to reduce a polyester waste containing polyethylene terephthalate as a main component.
It contains no additives and is an intermediate raw material for the production of polyester products, and recovers high-quality lower oligomers mainly composed of bis-β-hydroxyethyl terephthalate.
An object of the present invention is to provide a method for recycling polyester waste.

[0012]

DISCLOSURE OF THE INVENTION In view of the above-mentioned prior art, the present inventors converted high quality bis-β-hydroxyethyl terephthalate lower oligomers from polyester waste mainly composed of polyethylene terephthalate. We conducted intensive research on the method of recovery.

As a result, the polyester waste is once highly purified as DMT which is relatively easy to purify, and then a part / or all of the resulting high-purity DMT is subjected to a large excess of EG at normal pressure and no pressure. By reacting under a catalyst, it is found that it can be recovered as a high-quality lower oligomer containing BHET as a main component, which is an intermediate material for the production of polyester products without any additives such as a transesterification catalyst, The present invention has been completed.

That is, an object of the present invention is a recycling method for recovering an active ingredient from a polyester waste mainly composed of polyalkylene terephthalate, wherein the polyester waste is sequentially subjected to the following steps (a) to (e). By recycling as a low-polymer mixture containing bis-β-hydroxyalkylene terephthalate as a main component and having a hydroxyalkylene ester group at its terminal. Can be. (A) A step of pulverizing and pretreating polyester waste. (B) a step of depolymerizing the polyester waste treated in step (a) with an alkylene glycol in the presence of a catalyst. (C) a step of subjecting the depolymerized product obtained in step (b) to a substitution esterification reaction with methanol in the presence of a catalyst to obtain crude dimethyl terephthalate. (D) a step of recrystallizing the crude dimethyl terephthalate obtained in the step (c), purifying the crude dimethyl terephthalate by washing with methanol and / or distillation, and recovering it as high-purity dimethyl terephthalate; (E) reacting the purified dimethyl terephthalate obtained in the step (d) with a large excess of 2 times or more moles of the alkylene glycol under normal pressure without a catalyst to obtain bis-β-hydroxyalkylene terephthalate as a main component; And recovering the mixture as a low polymer mixture containing a hydroxyalkylene ester group at a terminal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the recovery method of the present invention, it is necessary to first crush and pretreat polyester waste. The treatment is carried out from crushed polyester waste discharged from the crusher, metal, stone, glass, as foreign matter,
Sand and the like may be separated, and a dehydration treatment may be performed if necessary.

Here, the polyester waste is a polyester waste mainly composed of polyalkylene terephthalate, and other components than the polyalkylene terephthalate include copolymerized polyester, polyvinyl chloride, and the like.
Polyvinylidene chloride, polyethylene, polypropylene,
At least one component selected from the group consisting of polyethylene naphthalate, nylon, vegetable natural fibers, dyes and coloring agents may be contained in a range of 50% or less based on the weight of the polyester waste.

Further, specific examples of polyalkylene terephthalate include polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate.

The pulverized product of the polyester waste obtained by the above-described process must be first subjected to a depolymerization reaction in an alkylene glycol, preferably ethylene glycol, in the presence of a known depolymerization catalyst. Next, if necessary, the mixture obtained by the depolymerization reaction is extracted with excess ethylene glycol used in the depolymerization reaction, and then introduced into a reactor together with methanol to be substituted and esterified with crude dimethyl terephthalate.

The obtained crude dimethyl terephthalate is recrystallized, washed with methanol and / or purified by distillation, and recovered as high-purity dimethyl terephthalate.

Further, a part / or all of the high-purity dimethyl terephthalate is reacted with a large excess of ethylene glycol at least 2 times the molar amount thereof under normal pressure without a catalyst to remove by-produced methanol out of the system. Meanwhile, it is recovered as a low-polymer mixture mainly composed of high-quality bis-β-hydroxyethyl terephthalate, which is an intermediate raw material for the production of polyester products, and having a hydroxyethyl ester group at a terminal.

In the recovery method of the present invention, the system for depolymerizing the polyester waste may be any of a batch system and a continuous system without any problem. The temperature may be about 230 ° C. and the pressure is about 0.0 to 0.2 MPa (gauge pressure). In this range, the EG depolymerization reaction is sufficiently performed. Here, if the depolymerization reaction temperature is lower than 110 ° C., the depolymerization time becomes extremely long and the efficiency becomes inefficient. On the other hand, if the temperature exceeds 230 ° C., a reactor corresponding to a high pressure is required, which is not preferable in terms of operation and safety.

The reaction temperature for performing the substitution esterification reaction is preferably in the range of 50 to 150 ° C., and the reaction pressure is preferably in the range of 0.0 to 0.59 MPa (gauge pressure). When it is within the range, the substitution esterification reaction is sufficiently performed. In addition, the substitution esterification reaction time is preferably set to 30 minutes to 4 hours.

Here, any of known depolymerization catalysts and substituted esterification catalysts as depolymerization catalysts and substituted esterification catalysts can be used, but carbonates, hydrogencarbonates, alkali metal and alkaline earth metals, and the like. It is preferable to use at least one compound selected from the group consisting of carboxylate and carboxylate from the viewpoint of high catalytic ability. Furthermore, it is particularly preferable to use sodium carbonate in all cases.

The mixture obtained by the substitution esterification reaction contains DMT, MeOH, EG, a monomer derived from the copolymerized polyester and water, dioxane, which are by-products of the EG depolymerization reaction and the substitution esterification reaction. Dimethyl ether and the like.

If the mixture is used as it is, a recrystallization operation is performed, or if the DMT crystals do not completely dissolve, heating is performed to dissolve the copolymer composition in a mixed solution. At this time, the substitution esterification reaction temperature as it is or after heating once in the range of 60 to 150 ° C. depending on the composition of the mixture, the monomer derived from the copolymerized polyester for the purpose of removal is dissolved in the solution side, Then, 10-50 ° C
Cool to the range. If necessary, use the latent heat of the solvent,
Preferably, the mixture is cooled.

The DMT concentration in the mixed solution is 10 to 40.
It is preferable to be in the range of wt%. DMT concentration of 1
If the amount is less than 0 wt%, the amount of the solvent used increases, which is not economically preferable. If the amount exceeds 40 wt%, the removal of the monomer derived from the copolymerized polyester is insufficient, which is not preferable.

The recrystallized mixture is subjected to solid-liquid separation by a centrifugal separation operation or the like, and then the obtained cake is washed with MeOH.

The amount of MeOH added here is preferably in the range of 1 to 5 times the amount of DMT, and when it is within this range, the removal of the monomer derived from the copolymerized polyester is sufficient, and economically. preferable.

The number of times of MeOH washing is preferably about 1 to 3 times. However, depending on the amount of the monomer derived from the copolymerized polyester, if the removal of impurities is insufficient, the number of times of washing may be further increased. The MeOH-washed DMT is purified by distillation under known conditions and recovered as high-purity DMT.

Further, the obtained high-purity DMT is heated to 180 to 250 ° C. using a large excess of EG in a molar excess of 2 times or more, and transesterification is carried out under normal pressure without a catalyst. DM
T and EG form an equilibrium state even without a catalyst by heating and holding. However, when a large excess of EG is used, the equilibrium state is further improved by B.
A significant shift to the HET side can be achieved. The amount of EG used in the reaction is preferably about 2 to 30 mol times, and particularly preferably 4 to 10 mol times, relative to DMT. Further, MeOH by-produced by the transesterification reaction needs to be effectively distilled out of the system. However, since EG and DMT are entrained along with the distillation of MeOH, at least two or more fractionation towers are required. It is desirable to provide them, and it is also important to control the temperature of each fractionation tower. By performing these, purified DMT
Is based on BHET and has a molecular weight of 254-1300.
And can be recovered as intermediate raw materials for high quality polyester products. Since this transesterification reaction is carried out under normal pressure and without a catalyst, it takes about 4 to 10 hours to complete the reaction. However, since the reaction proceeds slowly without a catalyst, by-products such as diethylene glycol are produced. Also less.

[0031]

EXAMPLES The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited by these examples. The obtained DMT, BHET and lower oligomer components were analyzed by gas chromatography (apparatus: HP5890 manufactured by Hewlett-Packard Company, capillary column: TC-1701 manufactured by GL Sciences) and GPC (apparatus: L-4000 manufactured by Hitachi, Ltd.) Using liquid chromatography and tetrahydrofuran solvent), the component composition and the molecular weight distribution were determined.

Example 1 200 parts of ethylene glycol were charged into a 500 ml separable flask, and 50 parts of polyethylene terephthalate were further charged.
The temperature was raised to 185 ° C. at 0 rpm. When this state was maintained for 4 hours, the PET was dissolved and the depolymerization reaction was completed.
The obtained depolymerized product was concentrated by distillation under reduced pressure of 6.65 kPa, and 150 parts of EG was recovered as a fraction.

To this concentrated solution, 0.5 part of sodium carbonate and 100 parts of MeOH were added as a transesterification catalyst, and the liquid temperature was kept at 75 ° C. and the stirring speed was 100 rpm at normal pressure for 1 hour to carry out the transesterification reaction. did.

The resulting mixture of DMT, EG and MeOH was cooled to 40 ° C. and filtered through a glass 3G-4 filter. The DMT collected on the filter was put into 45 parts of MeOH, heated to 40 ° C., washed with stirring, and filtered again with a glass filter. This washing was repeated twice.

The DMT captured on the filter was charged into a distillation apparatus, and vacuum distillation at a pressure of 6.65 kPa was performed.
DMT was obtained as a fraction. Forty fractions could be collected. When the amount of DMT was measured by measuring the residue, the amount was 2 parts. Based on the charged polyester, the conversion of DMT was 93% by weight.

40 parts of DMT purified by distillation and EG
75 parts into a separable flask and 100 rpm
As the temperature was increased under stirring, MeOH was generated at around 200 ° C., and the start of the reaction was confirmed. The distilled MeOH was distilled out of the system with two separation towers, and the accompanying EG and DMT fractions were returned to the flask.

While repeating the above operation, the time when the internal temperature of the flask reached 220 to 250 ° C. was regarded as the reaction end point, and the required time was about 8 hours.

When the composition of the resulting mixture was analyzed by gas chromatography, DMT was completely consumed by the reaction, and no by-product was detected. The analysis and GPC confirmed that BHET was 45% by weight. The other components each showed a sharp molecular weight distribution, and it was confirmed that all of the components were linear dimers to pentamers and lower oligomers.

Example 2 B obtained in Example 1
Polymerization reactivity was confirmed using a lower oligomer having HET as a main component and a commercially available product BHET having a purity of 95% by weight. Each was charged into a flask, and a condensation polymerization reaction was performed using a germanium dioxide polymerization catalyst at 285 ° C. under a high vacuum of 0.10 kPa for 1.7 hours under the same conditions to evaluate. As a result, polyethylene terephthalate having [η] = 0.63 and a melting point of 253 ° C. was obtained without any difference, and it was confirmed that there was no problem in reactivity.

Comparative Example 1 In Example 1, excess EG was completely removed from the reaction mixture obtained by one-step depolymerization using EG to obtain crude BHET. Investigations were made to see if this could be used as an intermediate raw material for the production of polyester products.
５5% by weight was detected.

[Comparative Example 2] In Example 1, BHET synthesis was attempted using crude DMT before purification by distillation, and the catalyst (sodium carbonate) used in the transesterification was 0.6% by weight.
The purpose of the present invention is to remain in the crude DMT,
It was not possible to obtain intermediate raw materials for the production of polyester products without additives.

[0042]

According to the recovery method of the present invention, a polyester waste containing polyethylene terephthalate as a main component, containing no additives and containing few by-product impurities, is an intermediate raw material for the production of polyester products. Quality screw
It can be recovered as a lower oligomer containing β-hydroxyethyl terephthalate as a main component, and in many existing polyester production processes using terephthalic acid or DMT as a raw material, it becomes possible to regenerate and produce polyester products.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Sato 77 Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Limited Matsuyama Office F-term (reference) 4F301 AA25 AB03 CA09 CA23 CA24 CA53 CA72 CA73 4H006 AA02 AC48 AC91 BA02 BA32 BJ50 BS30 BT32

Claims (6)

[Claims] 1. A recycling method for recovering an active ingredient from a polyester waste mainly composed of polyalkylene terephthalate, wherein the polyester waste is sequentially passed through the following steps (a) to (e): Screw-
A method for recycling polyester waste, comprising recovering a low-polymer mixture containing β-hydroxyalkylene terephthalate as a main component and having a hydroxyalkylene ester group at a terminal. (A) A step of pulverizing and pretreating polyester waste. (B) a step of depolymerizing the polyester waste treated in step (a) with an alkylene glycol in the presence of a catalyst. (C) a step of subjecting the depolymerized product obtained in step (b) to a substitution esterification reaction with methanol in the presence of a catalyst to obtain crude dimethyl terephthalate. (D) a step of recrystallizing the crude dimethyl terephthalate obtained in the step (c), purifying the crude dimethyl terephthalate by washing with methanol and / or distillation, and recovering it as high-purity dimethyl terephthalate; (E) reacting the purified dimethyl terephthalate obtained in the step (d) with a large excess of 2 times or more moles of the alkylene glycol under normal pressure without a catalyst to obtain bis-β-hydroxyalkylene terephthalate as a main component; And recovering the mixture as a low polymer mixture containing a hydroxyalkylene ester group at a terminal. 2. The recycling method according to claim 1, wherein the polyalkylene terephthalate is at least one polyalkylene terephthalate selected from the group consisting of polyethylene terephthalate, polytrimethylene terephthalate, and polybutylene terephthalate. 3. The recycling method according to claim 1, wherein the alkylene glycol is ethylene glycol. 4. The depolymerization catalyst is at least one compound selected from the group consisting of carbonates, bicarbonates, and carboxylate salts of alkali metals and alkaline earth metals.
The recycling method according to claim 1. 5. The method according to claim 1, wherein the substituted esterification catalyst is at least one compound selected from the group consisting of carbonates, bicarbonates, and carboxylate salts of alkali metals and alkaline earth metals. Recycling method. 6. Polyester waste is produced from copolymer polyester, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polyethylene naphthalate, nylon, vegetable natural fiber, dye and colorant as components other than polyalkylene terephthalate. 2. The composition according to claim 1, comprising at least one component selected from the group consisting of not more than 50% by weight of the polyester waste.
The recycling method described.