JP2002167363A - Dimethylterephthalate composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for distinguishing dimethylterephthalate recovered from polyester from vergin dimethylterephthalate newly produced from paraxylene. SOLUTION: Dimethylterephthalate recovered from polyester can be distinguished from vergin dimethylterephthalate newly produced from paraxylene by adding and uniformly dispersing an isotope of DMT as a distinguishing agent into dimethylterephthalate recovered from polyester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a dimethyl terephthalate recovered from a polyester as a raw material of a polyester using ethylene glycol and methanol,
A method of discriminating and judging by adding dimethyl terephthalate, which is newly produced through oxidation and esterification from para-xylene, to a dimethyl terephthalate isotope compound as a labeling compound, and uniformly dispersing the compound. About.

[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, polyester is depolymerized with ethylene glycol (hereinafter sometimes abbreviated as EG), and then methanol (hereinafter sometimes abbreviated as MeOH) is used. A method for purifying and recovering high-purity dimethyl terephthalate (hereinafter sometimes abbreviated as DMT) and EG, which are raw materials for the production of polyester products, by subjecting them to a substitution esterification reaction followed by separation and purification. Are known. This method has the advantage that by purifying as DMT, it is relatively easy to separate and purify it from additives and a small amount of the third component contained in the polyester.

In Japanese Patent Publication No. 43-2088, bis-β-hydroxyethyl terephthalate (hereinafter sometimes abbreviated as BHET) and an ethylene glycol are added to polyethylene terephthalate in an excess amount, heated and depolymerized. A method has been proposed in which a lower oligomer is obtained, excess methanol is added to the mixture, and a substitution esterification reaction is performed in the presence of a catalyst to recover DMT.

DMT recovered and purified using EG and MeOH as described above (hereinafter sometimes abbreviated as recovered DMT) has high quality, appearance, acid value, freezing point, melting colorimetric, sulfuric acid. Due to its quality characteristics such as ash content and trace impurities, DMT newly obtained from para-xylene
(Hereinafter sometimes abbreviated as “virgin DMT”).

However, in order for the chemical recycling method of polyester to contribute to the formation of a recycling-oriented society, it is important to surely use the raw materials recovered from polyester and to regenerate it as polyester. It is also conceivable that confusion between virgin DMT and recovered DMT may hinder the formation of a recycling-based society. Therefore, there has been a demand for a method capable of clearly distinguishing recovered DMT from virgin DMT.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art by providing a DMT composed of carbon and / or hydrogen isotopes as an identification compound in DMT recovered from polyester. A method for discriminating and determining that the DMT is a polyester-recovered DMT by adding a small amount of the DMT and uniformly dispersing the DMT.

[0010]

Means for Solving the Problems To achieve the above object, the present inventors can easily add and uniformly disperse DMT recovered from polyester, and easily identify and quantitate the added identification compound. We have intensively studied a method for selecting a compound which can be easily identified and quantified even among polyester polymers produced from DMT and which is added in a small amount to the recovered DMT so as to be distinguishable.

As a result, the polyester is subjected to a depolymerization reaction with ethylene glycol, followed by a substitution esterification reaction with methanol, and the DMT obtained by further purification is melted and is composed of carbon and / or hydrogen isotopes. D
The present inventors have found that it is possible to discriminate and determine virgin DMT by adding a small amount of MT and uniformly dispersing the same, and have completed the present invention.

That is, an object of the present invention is to provide a DMT recovered from a polyester using EG and MeOH in an amount of 1 to 1%.
2,000 ppm by weight, preferably 1-50 ppm by weight, of DMT composed of isotopes of carbon and / or hydrogen, preferably an isotope of DMT wherein the isotope of carbon is 13 C and the isotope of hydrogen is deuterium It is characterized in that a compound is added as a discriminating compound, and by detecting this, discrimination between the recovered DMT and the virgin DMT can be determined.

[0013]

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 isotope compound of DMT as an identification compound is required. DM
Among the isotopic compound T, then terephthalic acid - carboxy - ¹³ C-dimethyl ester, terephthalic acid - carboxy - ¹³ C ₂ - dimethyl ester, terephthalic acid - ¹³ C ₆ - dimethyl ester, terephthalic acid -d- dimethyl ester, terephthalic acid -d ₄ - is preferably at least one isotopic compound selected from the group consisting of dimethyl ester.

First, a polyester is subjected to a depolymerization reaction in EG in the presence of a known depolymerization catalyst. 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, and the crude DMT is subjected to substitution esterification reaction and cooling crystallization. obtain. Furthermore, by distilling and purifying the obtained crude DMT, high-purity DMT can be obtained.

The high-purity recovered D obtained through the above steps
The MT is kept in a molten state at 140 to 170 ° C., the DMT isotope compound can be added by a known method, and a batch type or a continuous type can be employed without any problem.
For example, when the isotope compound is added, the form is a fine powder of the isotope compound or a slurry state of an organic solvent represented by, for example, methanol. After the addition, the mixture is uniformly mixed in DMT by stirring or liquid circulation. And a method of dispersing them.

The added DMT isotope compound is ¹³ CN
Analysis by MR, ¹ HNMR, gas chromatograph mass spectrometer, or the like makes it possible to determine the discrimination from virgin DMT.

The depolymerization reaction of the polyester by EG may be performed at a temperature of about 110 to 230 ° C. and a pressure of about 0.0 to 0.2 MPa (gauge pressure).
The 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 this 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 separated into a solid and a liquid by a centrifugal separation operation, 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 carried out under 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.

[0028]

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 isotope compound in DMT is FT-
NMR apparatus (JEOL A-60 manufactured by JEOL Ltd.)
The analysis was performed using 0).

Example 1 200 parts of ethylene glycol were 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 were introduced 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 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.

The recovered DMT (40 parts) purified by distillation was further melted at 150 ° C., and terephthalic acid-carboxy-
2.0 × 10−3 parts of ¹³ C ₂ -dimethyl ester was added, and the mixture was stirred at a stirring speed of 100 rpm for 30 minutes.

When the obtained recovered DMT was analyzed by ¹³ C NMR, the signal intensity of the carboxyl group carbon considered to be derived from terephthalic acid-carboxy- ¹³ C ₂ -dimethyl ester was compared with the signal intensity of the other carbons in the amount added. It was detected correspondingly higher and clearly different from the known DMT spectrum.

Comparative Example 1 A virgin DMT manufactured from a commercially available product PX was analyzed by 13 C NMR. As a result, the signal intensity of each carbon was almost the same as the known DMT physical property data.

[0036]

According to the identification method of the present invention, dimethyl terephthalate recovered from polyester can be easily distinguished from dimethyl terephthalate newly produced from para-xylene through oxidation and esterification. ,
It helps prevent misidentification and misinformation, and contributes to the formation of a recycling-oriented society by a chemical recycling method in which raw materials recovered from polyester are regenerated as polyester again.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiro Sato 77 Kitayoshida-cho, Matsuyama-shi, Ehime Prefecture Teijin Limited Matsuyama Office F-term (reference) 4H006 AA05 AD40

Claims (5)

[Claims] 1. A dimethyl terephthalate composition comprising dimethyl terephthalate composed of carbon and / or hydrogen isotopes as an identification compound in an amount of 1 to 1000 ppm by weight based on dimethyl terephthalate. 2. The dimethyl terephthalate composition according to claim 1, wherein the carbon isotope is ¹³ C. 3. The method according to claim 1, wherein the isotope of hydrogen is deuterium.
Dimethyl terephthalate composition. 4. The dimethyl terephthalate composition according to claim 1, wherein the dimethyl terephthalate is obtained by depolymerizing polyalkylene terephthalate with ethylene glycol and then transesterifying with methanol. 5. A method for producing a dimethyl terephthalate composition, comprising adding dimethyl terephthalate composed of carbon and / or hydrogen isotopes to dimethyl terephthalate, melting and uniformly dispersing the mixture.