JP2002060369A - Method for recycling polyester waste - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recycling a polyester waste, by which highly pure terephthalic acid as a valuable component can be recovered from the polyester waste containing polyethylene terephthalate as a main component. SOLUTION: This method for recycling the polyester waste is characterized by subjecting the polyester waste containing a polyalkylene terephthalate as a main component to a glycolysis reaction, a transesterification reaction, a recrystallization process, and a purification treatment to obtain the pure dimethyl terephthalate, and then hydrolyzing the pure dimethyl terephthalate under pressurized steam to recover the highly pure terephthalic acid as a valuable substance.

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 high-purity terephthalic acid from polyester waste containing polyethylene terephthalate as a main component.

[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.

The recovered polyester waste is subjected to a depolymerization reaction with ethylene glycol, followed by a substitution esterification reaction using methanol, and further separation and purification to obtain purified dimethyl terephthalate (hereinafter abbreviated as DMT in some cases). ) And ethylene glycol (hereinafter EG)
May be abbreviated. ) And further hydrolyze purified dimethyl terephthalate to recover as high-purity terephthalic acid (hereinafter sometimes abbreviated as PTA), leading to effective use of resources and reduction in total cost.

JP-B-43-2088 discloses that polyethylene terephthalate is added with an excess amount of ethylene glycol, heated, and depolymerized to form a bis (β-hydroxyethyl) terephthalate and a low-molecular-weight monomer having a terminal β-hydroxyethyl ester group. A method of obtaining a mixture of polymers, adding excess methanol (hereinafter, may be abbreviated as MeOH) to the mixture, and subjecting the mixture to a substitution esterification reaction in the presence of a catalyst to recover dimethyl terephthalate is described. ing.

However, terephthalic acid is the mainstream raw material for polyesters produced worldwide today, and it is necessary to recover the resulting recovered product as high-purity terephthalic acid that can be used as a polymer raw material.

There is also a method of directly recovering terephthalic acid by hydrolyzing polyethylene terephthalate waste. However, terephthalic acid has a low vapor pressure,
It was difficult to purify by distillation, and if impurities were mixed in polyethylene terephthalate waste, the purity was insufficient for use as a raw material for polymer synthesis.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to convert high-purity terephthalic acid as a valuable component from a polyester waste mainly composed of polyethylene terephthalate. To recover.

[0010]

In order to solve such a difficult problem, the present inventors have developed a method for recovering terephthalic acid and ethylene glycol from a polyester waste mainly composed of polyethylene terephthalate. As a result of intensive studies, the present invention has been completed.

That is, an object of the present invention is to recover valuable materials from polyester waste mainly composed of polyalkylene terephthalate, and successively pass the polyester waste through the following steps (a) to (d). This can be achieved by a method for recycling polyester waste, which comprises recovering high-purity terephthalic acid as a valuable resource. (A) a step of depolymerizing a polyester waste with an alkylene glycol; (B) a step of subjecting the depolymerized product obtained in step (a) to substitution esterification using methanol to obtain crude dimethyl terephthalate. (C) a step of recrystallizing the crude dimethyl terephthalate obtained in the step (b), washing with methanol and / or purifying by distillation to recover as purified dimethyl terephthalate; (D) a step of subjecting the purified dimethyl terephthalate obtained in step (c) to a hydrolysis reaction under pressurized steam to recover terephthalic acid of high purity.

[0012]

DETAILED DESCRIPTION OF THE INVENTION The subject of the present invention is a polyester waste mainly composed of polyalkylene terephthalate. Here, “mainly” means that if the polyalkylene terephthalate is less than 50 wt% based on the total polyester waste, the method of the present invention is not targeted.

In the recovery method of the present invention, it is necessary to first depolymerize polyester waste in ethylene glycol in the presence of a known depolymerization catalyst.

Next, if necessary, the mixture obtained in the depolymerization reaction is extracted with excess ethylene glycol used in the depolymerization reaction, and then introduced into a reactor together with methanol to obtain crude dimethyl terephthalate and substituted esterification. Let it.

The obtained crude dimethyl terephthalate is recrystallized, washed with methanol and / or purified by distillation to recover as purified dimethyl terephthalate.

Further, the purified dimethyl terephthalate is hydrolyzed using high-pressure steam by a known method, followed by purification such as washing with water and recrystallization with an aqueous solution.

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. It is sufficient that the pressure is about 230 ° C. and the pressure is about 0 to 0.2 MPaG. 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 carrying out 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 to 0.59 MPaG. The substitution esterification reaction is sufficiently performed. In addition, the substitution esterification reaction time is 30 minutes or more.
Preferably, it is 4 hours.

Here, any of known depolymerization catalysts and substituted esterification catalysts as depolymerization catalysts and substituted esterification catalysts can be used, but carbonates, bicarbonates, and alkali metal and alkaline earth metals can be used. 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,
In any case, it is particularly preferable to use sodium carbonate.

The mixture obtained by the substitution esterification reaction contains DMT, MeOH, EG, monomers 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.

When the mixture is used as it is, a recrystallization operation is performed, or when the DMT crystals are not completely dissolved, a heating operation 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 separated into a solid and a liquid 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. If the MeOH amount is less than 1 time, the removal of the monomer derived from the copolymerized polyester becomes insufficient, and if it exceeds 5 times, it is not economically preferable. The number of times the MeOH is washed 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 can be further increased.

The DMT washed with MeOH is purified by distillation under known conditions to recover the purified DMT. Furthermore, the obtained purified DMT may be hydrolyzed under known conditions to obtain terephthalic acid.

[0026]

EXAMPLES The contents of the present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. The purity of terephthalic acid in the examples was determined according to the following method.

Terephthalic acid purity (%): A 2N aqueous solution of potassium hydroxide was mixed with 15 g of terephthalic acid as a sample to remove undissolved substances in the solution.
The difference between the absorbance using a wavelength of 0 nm and the absorbance of a blank (2N aqueous potassium hydroxide solution) was determined and defined as the purity.

Normally available PTA (purity 99.9)
%), The purity was 85% in each case.
９５95%.

Example 1 200 parts of EG was charged into a 500 ml separable flask, 50 parts of polyethylene terephthalate was further charged, and the temperature was raised to 185 ° C. while increasing the temperature at a stirring speed of 100 rpm. When this state was maintained for 4 hours, the PET was dissolved and the depolymerization reaction was completed. The obtained depolymerization reaction 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. The transesterification reaction was performed while maintaining the liquid temperature at 75 ° C. and stirring at 100 rpm for 1 hour at normal pressure.

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 was repeated twice.

DMT captured on the filter was charged into a distillation apparatus, and DMT was distilled off as a fraction by vacuum distillation at a pressure of 6.65 kPa. Forty fractions could be collected. When the amount of DMT was determined by measuring the residue in the tank, the amount was 2 parts. Based on the charged polyester, the reaction yield of DMT was 93% by weight.
Met.

Steam was continuously blown into 40 parts of the distilled DMT while maintaining the temperature at 250 ° C. and the pressure at 0.98 MPaG, and excess steam and generated MeOH were continuously extracted to carry out a hydrolysis reaction. The reaction proceeded almost quantitatively, and 33 parts of terephthalic acid were recovered. When the alkali transmittance of the obtained terephthalic acid was measured, it was 90%.
Met.

[Comparative Example 1] The same operation as in Example 1 was performed except that terephthalic acid was recovered by performing a direct hydrolysis reaction without performing DMT distillation. The recovered terephthalic acid was 30 parts, and the alkali transmittance was measured and found to be 20%.

[0035]

According to the present invention, high-purity terephthalic acid as a valuable component can be recovered from a polyester waste mainly composed of polyethylene terephthalate, and its industrial significance is great.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Sato 77 Kitayoshida-cho, Matsuyama-shi, Ehime Pref. BE08A CB35 DA05 EA01Y 4H006 AA02 AC91 AD11 AD15 AD17 BA02 BA06 BA32 BC10 BC11 BE60 BS30

Claims (6)

[Claims] When recovering valuable resources from polyester waste mainly composed of polyalkylene terephthalate, the polyester waste is passed through the following steps (a) to (d) sequentially to obtain valuable resources. A method for recycling polyester waste, comprising recovering high-purity terephthalic acid. (A) a step of depolymerizing a polyester waste with an alkylene glycol; (B) a step of subjecting the depolymerized product obtained in step (a) to substitution esterification using methanol to obtain crude dimethyl terephthalate. (C) a step of recrystallizing the crude dimethyl terephthalate obtained in the step (b), washing with methanol and / or purifying by distillation to recover the purified dimethyl terephthalate; (D) a step of subjecting the purified dimethyl terephthalate obtained in step (c) to a hydrolysis reaction under pressurized steam to recover terephthalic acid of high purity. 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 is carried out by using at least one selected from the group consisting of alkali metal carbonates, bicarbonates, and carboxylate salts, alkaline earth metal carbonates, bicarbonates, and carboxylate salts. The recycling method according to claim 1, wherein said compound is added as a depolymerization catalyst. 5. The method according to claim 1, wherein the substituted esterification is performed using at least one selected from the group consisting of carbonates, bicarbonates, and carboxylate salts of alkali metals, and carbonates, bicarbonates, and carboxylate salts of alkaline earth metals. The recycling method according to claim 1, wherein one or more compounds are added as a substituted esterification catalyst. 6. The polyester waste is a copolymer polyester, polyvinyl chloride, polyvinylidene chloride, polyethylene, polypropylene, polyethylene naphthalate, polyamide, polylactic acid, natural fiber, dye and colorant as components other than polyalkylene terephthalate. The recycling method according to claim 1, comprising at least one component selected from the group consisting of: not more than 50 wt% based on the weight of the polyester waste.