JP2002167354A - Terephthalic acid component - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to distinguish terephthalic acid recovered from polyester from virgin terephthalic acid newly produced. SOLUTION: A discrimination of terephthalic acid recovered from polyester from virgin terephthalic acid newly produced from paraxylene, is made possible by adding and dispersing uniformly an inorganic compound as a discriminating compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a marker which is used as a marker between terephthalic acid recovered as a raw material of polyester from polyester by a chemical recycling method and virgin terephthalic acid newly produced from para-xylene through an oxidation reaction. The present invention relates to a method of discriminating and judging by adding a substance and detecting this.

[0002]

2. Description of the Related Art Polyethylene terephthalate (hereinafter referred to as PE)
Sometimes abbreviated as T. ) Is rapidly increasing its use 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.

[0003] However, treatment of used PET, which is generated in large quantities as the amount of used PET increases, or non-qualified products generated at the PET manufacturing stage, is a major social problem.

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

As one of the chemical recycling methods, there is known a method in which high-purity terephthalic acid (hereinafter, may be abbreviated as PTA) is regenerated from polyester to be recovered as a raw material for producing polyester products. I have.

[0006] PTA is a mainstream raw material for polyester products that are currently produced worldwide.
The advantage of being recycled and recovered as A is that it can be used in many existing polyester resin manufacturing processes,
The bottle-to-bottle in the T-bottle field, that is, the recycling of the product from the collected PET bottle to the PET bottle can be realized again.

As a method for recovering PTA from polyester, a method for directly recovering PTA by hydrolyzing PET (Japanese Patent Publication No. 32-8068, etc.) is known. However, this method cannot be purified by distillation due to the properties of PTA, and is difficult to purify by recrystallization because of low solubility in various solvents. Possibly poor quality for use as a raw material for polymer synthesis.

On the other hand, (1) JP-B-43-2088 discloses that an excessive amount of ethylene glycol (hereinafter, sometimes abbreviated as EG) is added to PET and heated, and bis-β is added by a depolymerization reaction. -Hydroxyethyl terephthalate (hereinafter sometimes abbreviated as BHET) and a lower oligomer are obtained, and excess methanol (hereinafter sometimes abbreviated as MeOH) is added to the mixture, and the mixture is substituted in the presence of a catalyst. There has been proposed a method of recovering high-purity dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) by performing an esterification reaction.

Further, (2) Japanese Patent Publication No. 57-53332
In Japanese Patent Application Publication No. JP-A-2005-264, a method of obtaining high-purity PTA by performing an oxidation reaction and an esterification reaction with methanol from para-xylene and further subjecting the obtained DMT to a hydrolysis reaction under high-pressure steam is proposed.

By combining the above-mentioned known techniques (1) and (2), it becomes possible to recover high-purity PTA from polyester.

That is, from polyester, EG and MeO
DMT collected and purified using H (hereinafter referred to as “collected DMT”).
May be abbreviated. ) Is further hydrolyzed under known high-pressure steam to obtain high-purity PTA. In this way, PTA once recovered from PET via DMT (hereinafter sometimes abbreviated as “recovered PTA”) can provide stable quality as a high-purity recovered product, so that its appearance and transmittance (T340% )-It is difficult to distinguish from PTA newly obtained by oxidizing para-xylene (hereinafter, may be abbreviated as virgin PTA) due to quality characteristics such as composition of contained impurities.

However, in order to contribute to the formation of a recycling-oriented society by the chemical recycling method, it is important to use the raw materials recovered from polyester without fail and regenerate it as polyester. If PTA is confused with recovered PTA, there is a possibility that it may hinder the formation of a recycling-based society. Therefore, a method for clearly identifying the recovered PTA and the virgin PTA has been desired.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art by converting polyester to D.
An object of the present invention is to provide a method for discriminating and determining that the PTA is a polyester-recovered PTA by adding a trace amount of an inorganic compound as a discriminating compound to the PTA recovered through MT.

[0014]

Means for Solving the Problems In order to achieve the above object, the present inventors can easily add and uniformly disperse PTA recovered from polyester, and can easily identify and quantify a discriminating compound, and We are keenly studying a method to select an inorganic compound that can be easily identified and quantified even in the polyester polymer produced from the recovered PTA, and to add it in the recovery PTA production stage so that it can be contained in a small amount in the recovered PTA to make it identifiable. I have piled up.

As a result, the polyester is subjected to a depolymerization reaction with EG, followed by a substitution esterification reaction with MeOH, purified by distillation as DMT, and further subjected to a hydrolysis reaction under a known pressurized steam to give a recovered PTA. The present inventors have found that it is possible to discriminate and judge from virgin PTA by adding a small amount of an inorganic compound, and have completed the present invention.

That is, an object of the present invention is to provide 1 to 1000 ppm by weight, preferably 1 to 50 ppm by weight, of an inorganic compound, preferably ruthenium, rhodium, palladium, silver, osmium, iridium, in PTA recovered from polyester. At least one selected from the group consisting of platinum and gold
The present invention is characterized in that a simple substance and / or an inorganic compound composed of a kind of noble metal is contained as an identification compound, and by detecting this, it is achieved by a method capable of discriminating between recovered PTA and virgin PTA. be able to.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the identification method of the present invention, first, an inorganic compound to be an identification compound is required. Among the inorganic compounds, it is preferable that the inorganic compound is a simple substance composed of at least one noble metal selected from the group consisting of noble metals ruthenium, rhodium, palladium, silver, osnium, iridium, platinum and gold, and / or an inorganic compound. . Further, among these compounds, compounds having properties such that the analysis method is easy and easy to detect, that they can be easily made into a fine powder, that they are chemically stable, and that they have low toxicity are desirable, such as ruthenium, ruthenium oxide, and chloride. Ruthenium, rhodium, rhodium oxide, rhodium chloride, palladium, palladium oxide, palladium chloride, palladium nitrate, palladium sulfate, silver, silver oxide, silver chloride, silver bromide, silver sulfide, silver nitrate, osnium, iridium, iridium oxide, iridium chloride And at least one compound selected from the group consisting of iridium sulfide, platinum, platinum oxide and gold.

By adding a small amount of the above metal compound to the PTA recovered from the polyester, the virgin P
Thus, the object of the present invention is achieved. First, a polyester was prepared by adding E
A depolymerization reaction is performed in G. Here, the polyester is polyethylene terephthalate, polytrimethylene terephthalate, or polybutylene terephthalate. If necessary, the mixture obtained in the depolymerization reaction is extracted with excess EG used in the depolymerization reaction, then introduced into the reactor together with MeOH, substituted esterification reaction, and cooling crystallization,
Obtain crude DMT. Then, the obtained crude DMT is purified by distillation, whereby a high-purity recovered DMT can be obtained. Further, by performing the hydrolysis reaction under a known high-pressure steam condition, high-purity recovered PTA can be obtained. By adding an inorganic compound as an identification compound to the obtained recovered PTA by a known method, a recovered PTA containing a trace amount of the target identification compound can be obtained.

The inorganic compound added to the recovered PTA can be analyzed by fluorescent X-ray analysis, atomic absorption analysis, inductively coupled plasma (hereinafter referred to as I
Sometimes abbreviated as CP. ) By detecting a metal component by emission analysis or the like, it is possible to determine the discrimination from virgin PTA.

In the method for recovering the polyester, the system for the depolymerization reaction may be any of a batch system and a continuous system without any problem. The depolymerization reaction of the polyester by EG is performed at a temperature of 110 to 230 ° C. and a pressure of 0 ° C. 0.0-0.
The pressure may be about 2 MPa (gauge pressure), and when the pressure is 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 at the time of performing the substitution esterification reaction with MeOH is in the range of 50 to 150 ° C.
The reaction pressure is preferably in the range of 0.0 to 0.59 MPa (gauge pressure), and in this 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, and by-products from the EG depolymerization reaction and the substitution esterification reaction.

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 mixed solution. At this time, after heating once at the substituted esterification reaction temperature as it is or at a temperature in the range of 60 to 150 ° C. depending on the composition of the mixture,
Cool to 0-50 ° C. If necessary, the mixture is preferably cooled using the latent heat of the solvent.

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.

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, from the viewpoint of washing effect, handling property of solid-liquid slurry, and economical. Further, the number of times of cleaning is preferably 1 to 3 times, but there is no problem even if the number of times of cleaning is further added.

Crude DMT after MeOH washing and solid-liquid separation
The cake is heated and melted to further remove MeOH,
Finally, distillation and purification were performed under reduced pressure, and purified DM
T is taken out. In the purification of the recovered DMT, the distillation is usually performed under a reduced pressure of 5.3 to 13.3 kPa at a bottom temperature of 170 to 250 ° C. and a reflux ratio of 0.1 to 2.0.

The highly purified recovered DMT is then
By performing a hydrolysis reaction under known high-pressure steam, high-purity recovered PTA can be obtained.

Further, by adding an inorganic compound to the obtained recovered PTA in order to enable discrimination from virgin PTA, a recovered PTA containing an inorganic compound as a target discriminating substance can be obtained.

As a method for adding the inorganic compound as the discriminating substance, any known method can be adopted. For example, the inorganic compound is added at the time of transporting the obtained recovered PTA,
A method of mixing powders in a pipe is exemplified.

[0033]

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 metal component of the labeling compound in the PTA was measured using a fluorescent X-ray analyzer (manufactured by Rigaku Denki Kogyo KK, Sys.
qualification and quantification were performed using tem3270).

Example 1 200 parts of ethylene glycol was charged into a 500 ml separable flask, 1.5 parts of sodium carbonate and 50 parts of polyethylene terephthalate were further charged, and the temperature was raised to 185 ° C. 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. 6.65k of the obtained depolymerized product
The mixture was concentrated by distillation under reduced pressure of Pa, 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 as a transesterification catalyst were added, 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 transesterification. did.

The resulting mixture was cooled to 40 ° C. and filtered through a glass 3G-4 filter. The crude DMT collected on the filter was put into 45 parts of MeOH,
The mixture was heated to 0 ° C., washed with stirring, and filtered again with a glass filter. This washing was repeated twice. This crude DMT was charged into a distillation apparatus, and vacuum distillation at a pressure of 6.65 kPa was performed to obtain DMT as a fraction. Forty fractions could be collected. The amount of DMT was 2 parts when the residue was measured and the DMT amount was measured, and the DMT reaction rate was 9 based on the charged polyester.
It was 3% by weight.

Further, 40 parts of the obtained DMT was mixed with 250 parts of DMT.
While maintaining the temperature and the pressure at 0.98 MPaG, steam was continuously blown, 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 was produced.

30 parts of the obtained terephthalic acid and 300 parts of water were put in an autoclave, and terephthalic acid was once dissolved in water at 250 ° C. and 4.1 MPaG, then cooled to 40 ° C., and terephthalic acid was filtered off. , Silver chloride fine powder 2 × 10
-4 parts were added and mixed. The obtained recovered PTA was fluorescent X
Upon line analysis, 6 ppm by weight of silver was detected in the recovered PTA.

The alkali permeability of the obtained recovered terephthalic acid (340% using 2N aqueous potassium hydroxide solution)
As a result of measuring a transmittance at a wavelength of nm, a known analysis method), it was 90%, and there was no significant difference from the commercially available PTA.

Comparative Example 1 X-ray fluorescence analysis was performed on virgin PTA manufactured from commercially available PX. As a result, bromine and iron, which are considered to be derived from the catalyst and the piping of the plant, were both detected at 0.1 ppm by weight, but noble metal components such as silver were not detected.

[0042]

According to the identification method of the present invention, terephthalic acid recovered from polyester and terephthalic acid newly produced from para-xylene through an oxidation reaction can be easily distinguished. Help prevent
It is possible to contribute to the formation of a recycling-based society by a chemical recycling method, in which raw materials recovered from polyester are recycled as polyester again.

Continuing on the front page (72) Inventor Minoru Nakajima 77, Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Co., Ltd. Matsuyama Office (72) Inventor Kazuhiro Sato 77, Kitayoshida-cho, Matsuyama-shi, Ehime Teijin Co., Ltd. Matsuyama Office F term (reference) 2G042 BC09 BC10 4H006 AA05 AD40 BJ50 BS30

Claims (4)

[Claims] 1. A terephthalic acid composition comprising an inorganic compound as a discriminating compound in an amount of 1 to 1000 ppm by weight based on terephthalic acid. 2. The inorganic compound is a simple substance and / or an inorganic compound composed of at least one noble metal selected from the group consisting of ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold. Terephthalic acid composition. 3. The terephthalic acid composition according to claim 1, wherein the inorganic compound is added and dispersed uniformly in the terephthalic acid production stage. 4. Terephthalic acid is obtained by depolymerizing polyalkylene terephthalate with ethylene glycol, then purifying it as dimethyl terephthalate by transesterification using methanol, and further hydrolyzing under high-pressure steam. The terephthalic acid composition of claim 1, which is