JP2002121173A - METHOD FOR PURIFYING CRUDE BIS-beta-HYDROXYETHYL TEREPHTHALATE AND THE THUS PURIFIED BIS-beta-HYDROXYETHYL TEREPHTHALATE - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for obtaining highly purified bis-β-hydroxyethyl terephthalate. SOLUTION: This method for purifying bis-β-hydroxyethyl terephthalate comprises the following two steps: (1) crude bis-β-hydroxyethyl terephthalate containing a total of <=50 ppm of (i) cations consisting of Na, Mg, Ca, Fe, Co, Zn, Ti, Sn Sb, Ge and P and (ii) anions consisting of halogens, NO2, NO3, PO4 and SO4 is put to crystallization and (2) the thus crystallized bis-β- hydroxyethyl terephthalate is evaporated or distilled under reduced pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a novel method for purifying crude bis-β-hydroxyethyl terephthalate and a method for producing polyethylene terephthalate using the same. Bis-β-hydroxyethyl terephthalate is widely used industrially as a raw material for polyethylene terephthalate, which is a very useful polyester in various molded article fields such as fibers, films and resins.

[0002]

2. Description of the Related Art As described above, polyesters, particularly polyesters containing ethylene terephthalate as a main component, are widely used for various purposes. The method for producing the bis-β-hydroxyethyl terephthalate includes direct esterification of terephthalic acid and ethylene glycol or transesterification of a lower alkyl ester of terephthalic acid, particularly dimethyl terephthalate with ethylene glycol. Currently, a method of subjecting it to a step of subjecting it to condensation polymerization under high temperature and high vacuum after passing through an intermediate containing is mainly practically used at present. In recent years, polyesters have been used in a wide variety of applications based on their excellent performance, and thus the performance required for high quality has been diversified and advanced.

[0003]

Polyethylene terephthalate is basically produced by allowing various metal compounds to exist as a polymerization catalyst under a high temperature and a high vacuum, and maintaining the molten state for a long time to increase the degree of polymerization. . It is not easy to exhaustively satisfy various required qualities with polyethylene terephthalate. Therefore, as a means for satisfying various required qualities and improving the quality of polyester, conventionally, methods such as adding a novel copolymer component to polyester, improving a polymerization catalyst, and adding various additives have been proposed. It has been. However, it cannot be a drastic measure.

[0004]

SUMMARY OF THE INVENTION The inventor of the present invention believes that high quality polyester is based on the high quality of the raw material of the polyester, whereby it is possible to obtain essentially high quality polyester. Therefore, various examinations were repeated while positioning the above-mentioned various upgrading means as auxiliary means to be used together as necessary. Various proposals have been made for the purification of terephthalic acid or dimethyl terephthalate, which is a lower alkyl ester thereof, as a raw material of polyester, but a raw material closer to the final polymer or bis-β-hydroxy which is an intermediate has been proposed. As for ethyl terephthalate, practical means for achieving high quality has not been clarified. The present invention relates to bis-β
-A means for purifying hydroxyethyl terephthalate to a high degree of purity, thereby making it an extremely useful means for obtaining a high-quality polyester.

That is, according to the present invention, (1) (i)
Na, Mg, Ca, Fe, Co, Zn, Ti, Sn, S
b, a cation consisting of Ge and P and (ii) a crude bis-β-hydroxyethyl terephthalate having a total content of anion consisting of halogen, NO ₂ , NO ₃ , PO ₄ and SO ₄ of 50 ppm or less, are subjected to crystallization. And (2) purifying bis-β-hydroxyethyl terephthalate by evaporating or distilling the crystallized bis-β-hydroxyethyl terephthalate under reduced pressure to purify bis-β-hydroxyethyl terephthalate. A method is provided.

Hitherto, various proposals have been made to improve the quality of crude bis-β-hydroxyethyl terephthalate by recrystallization operation without evaporation or distillation. However, with such a method, although it appears as if the quality has been improved, it is often the case that impurities still remain, which often hinders obtaining a high quality polyester. Was. In particular, the used polyester is recovered, and bis-β-
In a case where polyester is to be obtained again by depolymerization to hydroxyethyl terephthalate, adverse effects due to foreign substances adhering to or accompanying a used polyester product have been often noticeable. On the other hand, proposals have been made to obtain purified bis-β-hydroxyethyl terephthalate by evaporation or distillation purification. In such a case, however, crude bis-β-hydroxyethyl terephthalate is usually subjected to evaporation or distillation operation. , A contaminating condensation reaction occurs remarkably, making it difficult to practically obtain a bis-β-hydroxyethyl terephthalate fraction.

According to the results of the study by the present inventors, bis-β-
Such an adverse effect on the evaporation or distillation of hydroxyethyl terephthalate is caused by decationization and / or deanionization before the evaporation or distillation operation, and furthermore, a substance having a boiling point lower than that of bis-β-hydroxyethylterephthalate. It is substantially removed, and thereafter, it can be substantially suppressed by evaporating or distilling under reduced pressure in a temperature range of 130 to 250 ° C. where bis-β-hydroxyethyl terephthalate does not easily deteriorate in quality. Was proposed to the headline. The present inventor has further studied and, prior to the evaporation or distillation under reduced pressure, crystallizing bis-β-hydroxyethyl terephthalate makes it possible to obtain purified polyester which is very suitable for obtaining a high-quality polyester. −
They have found that β-hydroxyethyl terephthalate can be obtained, and have reached the above-mentioned method of the present invention.

In the present invention, in order to practically obtain a bis-β-hydroxyethyl terephthalate fraction purified from crude bis-β-hydroxyethyl terephthalate, it is necessary to carry out evaporation or distillation under reduced pressure. . To practice it practically, the evaporation or distillation of the crude bis-β-hydroxyethyl terephthalate is not evaporation or boiling point evaporation or distillation under distillation temperature and pressure, ie, equilibrium evaporation or distillation, but rather the once evaporated bis-β-hydroxyethyl terephthalate. It is preferable to perform non-equilibrium evaporation or distillation in which the unidirectional transfer of molecules from the evaporation surface to the condensation surface is performed without substantially returning the molecules of hydroxyethyl terephthalate to the evaporation surface, and thus a special evaporation or evaporation suitable for it. The use of distillation means is desirable. Such an evaporation or distillation operation may be commonly referred to by the name of molecular distillation.

In the present invention, in carrying out such an evaporation or distillation operation, the yield of purified bis-β-hydroxyethyl terephthalate from crude bis-β-hydroxyethyl terephthalate is to be obtained to a practically more advantageous level. The composition comprising the crude bis-β-hydroxyethyl terephthalate which is subjected to evaporation or distillation is substantially decationized and / or deanionized and crystallizes bis-β-hydroxyethylterephthalate. It is desirable that the substance which has been subjected to the step and has a boiling point lower than that of bis-β-hydroxyethyl terephthalate be sufficiently removed.

In this case, the crude bis-β in the step (1)
-Hydroxyethyl terephthalate includes (i) N
a, Mg, Ca, Fe, Co, Zn, Ti, Sn, S
A cation consisting of b, Ge and P and (ii) anion consisting of halogen, NO ₂ , NO ₃ , PO ₄ and SO ₄ are deionized to a total ion content of 50 ppm or less.

[0011] The total ion content is preferably 40 ppm or less, more preferably 30 ppm or less. A lower total ion content is advantageous, but lowering the total ion content below 10 ppm requires more complicated deionization steps and is uneconomical. When the total ion content is about 30 ppm, there is substantially no hindrance to evaporation or distillation. The most preferred total ion content is less than 10 ppm. The total content of anions is suitably 1 ppm or less.

[0012] As described above, in order to obtain the total ion content of the specific cation and the anion, it is preferable to deionize using an ion exchanger, particularly an ion exchange resin. In this case, it is practical to decationize and / or deanionize the composition containing bis-β-hydroxyethyl terephthalate in a solution containing ethylene glycol as a main solvent and bis-β-hydroxyethyl terephthalate as a main solute. It is. The decationization and / or deanionization treatment does not matter in any order, and either may be performed first or after. Examples of ion exchange resins for decationization include Amberlite cation exchange resins (manufactured by Organo), and examples of ion exchange resins for deanionization include Amberlite anion exchange resins (manufactured by Organo).
Can be mentioned. The deionization step using such an ion exchange resin can be performed by a method known per se. Preferably, during the decation and / or deanion operation, bis-β-hydroxyethyl terephthalate precipitates in a solution in which ethylene glycol is the main solvent and bis-β-hydroxyethyl terephthalate is the main solute. The temperature conditions and the concentration of bis-β-hydroxyethyl terephthalate in the solution are selected so that the ion-exchange resin can stably withstand use.

In the present invention, as described above, step (1)
, A crystallization step of extracting bis-β-hydroxyethyl terephthalate as a crystal is performed once or more. In the step of taking out bis-β-hydroxyethyl terephthalate as crystals, preferably, in a solution containing ethylene glycol as a main solvent and bis-β-hydroxyethyl terephthalate as a main solute, its concentration is maintained in a solution state in a high temperature range. In a low temperature range, the reaction is carried out under such conditions as to precipitate bis-β-hydroxyethyl terephthalate. In many cases, the high-temperature condition for maintaining the solution state can be within the heat-resistant temperature of the ion-exchange resin in the above-described deionization step.

The crude bis-β-hydroxyethyl terephthalate used in step (1) of the purification method of the present invention has a total ion content in the above range and a boiling point of bis-β-hydroxyethyl terephthalate. It is desirable that the substance having a lower boiling point is preferably 10% by weight or less, more preferably 5% by weight or less, and further preferably 2% by weight or less.

When the above-mentioned specific crude bis-β-hydroxyethyl terephthalate used in the present invention and bis-β-hydroxyethyl terephthalate which does not satisfy the requirements of the present invention which are generally present in the prior art are placed under the same conditions. Is surprisingly completely different. For example, a composition comprising a comparative crude bis-β-hydroxyethyl terephthalate in which the weight of the cation is 2,080 ppm and the weight of the anion is 22 ppm can be obtained without decationization and deanionization. When the substance having a boiling point lower than the boiling point of ethyl terephthalate is concentrated to a content of 5.0% by weight and subjected to molecular distillation, the obtained bis-β-hydroxyethyl terephthalate is colored to such an extent that it can be visually recognized. The oligomer formation rate during molecular distillation is as high as 9.2%,
At the same time, the precipitates adhered and deposited on the heat transfer surface of the distillation apparatus, hindering stable heat transfer during distillation, and the recovery of bis-β-hydroxyethyl terephthalate was reduced to about 70% or less. on the other hand,
Through a process of decationizing and deanionizing and extracting bis-β-hydroxyethyl terephthalate as crystals, the crude bis-β-hydroxyethyl terephthalate deionized to the cation weight of 15 ppm and the anion weight of 1 ppm is concentrated to the same conditions. When subjected to molecular distillation under the same conditions, the obtained bis-β-hydroxyethyl terephthalate does not have any visually distinguishable coloring, and the oligomer formation rate during molecular distillation is about 1 to 1.5%. Could hardly adhere to the heat transfer surface of the distillation machine and stable continuous operation was possible, and the recovery of bis-β-hydroxyethyl terephthalate was about 98% or more.

In the present invention, the crude bis-β-hydroxyethyl terephthalate is dissolved in an ethylene glycol solution before performing the evaporation or distillation in step (2), preferably before performing the deionization treatment in step (1). It is desirable to perform a decolorization treatment. An adsorbent treatment such as activated carbon is advantageous for the decolorization treatment. This decolorization treatment can also be carried out in combination with the crystallization step of bis-β-hydroxyethyl terephthalate in the step (1). In this case, the decolorization treatment is carried out under a temperature and concentration condition such that bis-β-hydroxyethyl terephthalate does not precipitate bis-β-hydroxyethyl terephthalate in an ethylene glycol solution, and an adsorbent such as activated carbon is separated and removed. Bis-β
Bis-β-hydroxyethyl terephthalate can be collected under temperature and concentration conditions under which -hydroxyethyl terephthalate precipitates.

Step (2) of the present invention is carried out by subjecting the bis-β-hydroxyethyl terephthalate crystallized in step (1) to evaporation or distillation under reduced pressure. The distillation temperature is preferably in the range of 130 to 250 ° C.
The range of 0 to 220C is more preferable. The pressure is 30
The pressure is preferably reduced to 0 Pa (2.25 mmHg) (absolute pressure) or less, and more preferably 70 Pa (0.5 mmHg) (absolute pressure) or less. Furthermore, the average residence time of the bis-β-hydroxyethyl terephthalate in the evaporator or in the distiller is 2 hours or less, preferably 1.5 hours.
Advantageously it is less than an hour.

Step (2) The purified bis-β-hydroxyethyl terephthalate recovered by evaporation or distillation is extremely high quality, and the total content of the cations and anions is 15 ppm or less, preferably 5 ppm or less. . Further, the content of bis-β-hydroxyethyl terephthalate is 97% by weight or more, preferably 98% by weight or more. The thus obtained purified bis-β-hydroxyethyl terephthalate is suitably used for producing polyethylene terephthalate or a copolymerized polyester thereof.

The purified bis-β-hydroxyethyl terephthalate obtained by the present invention is suitable as at least a part of the polyester raw material widely used in various applications as described above, for example, alone or in combination with terephthalic acid. It is something. Specifically, as the polymerization catalyst, those known per se can be used. For example, an antimony compound, a titanium compound or a germanium compound can be used.

Such polyesters have ethylene terephthalate as a main structural unit, and also include those obtained by copolymerizing at least one of other structural components in a small proportion. The allowable range of the other components is, for example, usually 40 mol% or less, preferably 30 mol% or less, more preferably 20 mol% or less, based on all the constituent units. Examples of other components that can be copolymerized include dicarboxylic acid components such as isophthalic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenyletherdicarboxylic acid, naphthalenedicarboxylic acid, diphenoxyethanedicarboxylic acid, and sodium sulfoisophthalic acid. Aromatic dicarboxylic acids; aliphatic dicarboxylic acids such as sebacic acid and adipic acid; and alicyclic dicarboxylic acids such as hexahydroterephthalic acid. As the diol component, for example, trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanedimethanol, bis-β-
Examples thereof include hydroxyethyl bisphenol A, bis-β-hydroxyethoxydiphenyl sulfone, bis-β-hydroxyethoxydiphenyl ether, diethylene glycol, and polyethylene glycol. Also, hydroxycarboxylic acids, for example, p-hydroxyethoxyphenylcarboxylic acid, can be mentioned as examples of other copolymerization components. Further, a trifunctional or higher functional polyfunctional compound and / or a monofunctional compound can be used in combination as another copolymer component. These other components are possible as long as the polyester remains linear.
Examples of trifunctional or higher polyfunctional compounds include trimesic acid, glycerin, pentaerythritol and the like, and examples of monofunctional compounds include diphenylmonocarboxylic acid,
Examples thereof include diphenyl ether monocarboxylic acid and phenoxy polyethylene glycol. These various copolymer components can be used as functional derivatives, for example, in the form of an ester. These can be used alone or in combination of two or more.

According to the results of studies by the present inventors, polyesters obtained by using the purified bis-β-hydroxyethyl terephthalate obtained by the method of the present invention as at least a part of the raw materials for the production thereof include fibers, films, bottles and the like. It can be used as various molded products without any problem. Further, in the case where various polyester molded products are depolymerized to substantially return to the stage of purified bis-β-hydroxyethyl terephthalate, it is usually obtained by performing a depolymerization step using ethylene glycol. The depolymerized product can be obtained as a solution containing ethylene glycol as a main solvent, and the solution is used as it is or after adjusting the concentration to an appropriate concentration to remove the cation and / or anion described above. The composition containing crude bis-β-hydroxyethyl terephthalate to be used in the method of the present invention is subjected to a step of removing hydroxyethyl terephthalate as a crystal and, if necessary, before, during and / or after the decolorization step. Bis-β-hydrido purified by applying the purification method of the present invention thereto It can be obtained carboxyethyl terephthalate.

The purified bis-β-hydroxyethyl terephthalate can be used as at least a part of a raw material for producing a high-quality polyester again. According to the present invention, the polyester molded product to be depolymerized is in a state where it is mixed with other materials as in the case of a product form or is mixed with foreign matter such as dust. However, if necessary, a crude bis-β-hydroxyethyl terephthalate that enables the practice of the present invention can be obtained by applying a foreign matter removing step such as sorting and filtering.

Examples of such specific examples include, for example, when the polyester molded product is in the form of a fibrous product, it may be mixed with heterogeneous fibers, or may be titanium oxide used in polyester. Situations that include inorganic substances, when polyester is in the form of a film, mixed with other kinds of film materials, or situations that include various lubricants used in polyester, etc. In the case of molded products, for example, in the form of bottles, the materials may be crushed and mixed with other materials such as polyethylene used for the lid and bottom, and paper or plastics used for labels etc. Such a situation where it is mixed with another kind of material is rather a usual situation. Etc. and solid-liquid separation, by applying the conventionally known method, and the method of the present invention, by using a variety of techniques such as those as required above, it is possible to high quality desired product.

[0024]

The present invention will be described in more detail with reference to the following examples. The invention is not limited only to these examples.

Example 1 53 kg of crushed flakes of used PET bottles (made of polyethylene terephthalate resin) and 386 kg of ethylene glycol were charged into a 0.5 m ³ autoclave equipped with a stirrer, and sodium methylate, a well-known transesterification catalyst, was added. Add 27 kg, 220 ° C, 0.15MP
The solution was depolymerized for 3.3 hours under the condition (a) to obtain a solution containing ethylene glycol as a main solvent and bis-β-hydroxyethyl terephthalate as a main solute.
℃ 350, decolorize with activated carbon, 350k
g of the stock solution was obtained. The total cation weight in the concentrated solute of the stock solution was 2,080 ppm, and the total anion weight was 22 ppm. 150 kg of this stock solution was treated at a temperature of 55 ° C. with a cation ion exchange resin (Amberlite IR1 manufactured by Organo Corporation).
20-B), followed by anion ion exchange resin (Amberlite IRA-40 manufactured by Organo Corporation).
Deanion was carried out according to 0). The total cation weight in the concentrated solute of the solution after deionization was 9.4 ppm, and the total anion weight was 0 ppm. The decationized / deanionized solution is placed in a stirred crystallization tank equipped with a jacket. After cooling to 5 ° C. with 5 ° C. brine and crystallization for 3 hours, bis-β-hydroxyethyl terephthalate precipitated by a basket type centrifuge and ethylene glycol were centrifuged to obtain bis-β-hydroxy. A wet cake of ethyl terephthalate was obtained. At this time, the solid content was 57.6% by weight. 90-
Heated and melted at 100 ° C with 500 liter stirrer.
Charge into an autoclave with vacuum generator at 135 ° C, 1
Ethylene glycol was distilled off under a condition of 0.670 Pa (80 mmHg) until the residual weight of ethylene glycol in the solution became 20%, and then 150 ° C., 200 Pa (1 mm) by a vacuum thin film evaporator having a heat transfer area of 0.5 m ^2. Under a condition of 0.5 mmHg), 25.2 kg of a composition containing crude bis-β-hydroxyethyl terephthalate was concentrated by concentrating the substance having a boiling point lower than that of bis-β-hydroxyethyl terephthalate to 5.0% by weight. Obtained.

25.2 kg of the composition containing the crude bis-β-hydroxyethyl terephthalate was transferred with a heat transfer area of 0.5 m ^2.
200 ° C, 24 Pa (0.1
8 mmHg) under the condition of molecular distillation over 75 minutes to obtain 23.9 kg of purified bis-β-hydroxyethyl terephthalate.
I got Table 1 shows the quality analysis values of the obtained purified bis-β-hydroxyethyl terephthalate. Next, 500 g of the obtained room temperature powder of the purified bis-β-hydroxyethyl terephthalate was put into a 1,000 cc glass polymerization apparatus equipped with a stirrer, sufficiently replaced with nitrogen gas, and heated to 130 ° C. in a nitrogen gas atmosphere. After melting bis-β-hydroxyethyl terephthalate by heating, 27.2 g of 0.2 parts by weight of germanium dioxide obtained by completely dissolving hexagonal germanium dioxide in ethylene glycol in a boiling state in advance was used as a polymerization catalyst under a nitrogen gas atmosphere. With stirring and 2
The temperature was raised to the boiling point of ethylene glycol (197 ° C.) over 0 minutes, and the mixture was further heated and stirred at normal pressure and 197 ° C. for 45 minutes to obtain an oligomer of polyethylene terephthalate. Subsequently, the oligomer was subjected to 280 ° C, 90P
Polycondensation was carried out for 2 hours under the condition of a (0.7 mmHg) to obtain polyethylene terephthalate. Table 2 shows the quality analysis values of the obtained polyethylene terephthalate. Both purified bis-β-hydroxyethyl terephthalate and polyethylene terephthalate were at extremely high quality levels in practice.

[0027]

[Table 1]

The optical density in the table is a method for evaluating the quality of bis-β-hydroxyethyl terephthalate, and is an amount proportional to the content of the coloring matter. The absorbance of a 10% methanol solution was measured at a wavelength of 380 μm and a cell length of 10 mm. The whiteness was measured with a colorimetric colorimeter and represented by L (brightness), a (redness) and b (yellowness) values according to the Hunter method.

[0029]

[Table 2]

The intrinsic viscosities in the table were measured at 30 ° C. in orthochlorophenol. The whiteness was measured with a colorimetric colorimeter and represented by L (brightness), a (redness) and b (yellowness) values according to the Hunter method.

Comparative Example 1 The same operation as in Example 1 was carried out without cooling and crystallizing 100 kg of the stock solution decolorized, deanionized and decationized in Example 1. In the obtained bis-β-hydroxyethyl terephthalate, an extremely pale yellow color, which was slightly discernible by visual observation, was observed in the overlapping portion of the crystal masses. There was no hindrance to the operation of the molecular still. The obtained bis-β
Table 3 shows the quality analysis values of hydroxyethyl terephthalate.
Shown in

[0032]

[Table 3]

The optical density in the table is a method for evaluating the quality of bis-β-hydroxyethyl terephthalate and is an amount proportional to the content of the coloring matter. The absorbance of a 10% methanol solution was measured at a wavelength of 380 μm and a cell length of 10 mm. The whiteness was measured with a colorimetric colorimeter and represented by L (brightness), a (redness) and b (yellowness) values according to the Hunter method.

Next, 500 g of room temperature powder of the obtained purified bis-β-hydroxyethyl terephthalate was added to 1,000 c
c into a glass polymerization vessel with a stirrer, sufficiently replaced with nitrogen gas, and heated to 130 ° C. in a nitrogen gas atmosphere to melt bis-β-hydroxyethyl terephthalate.
Germanium dioxide 0.2 in which hexagonal germanium dioxide is completely dissolved in ethylene glycol in a boiling state in advance
27.2 g of the liquid by weight was added as a polymerization catalyst under a nitrogen gas atmosphere, and the temperature was raised to the boiling point of ethylene glycol (197 ° C.) over 20 minutes with stirring.
The mixture was heated and stirred at 7 ° C. for 45 minutes to obtain an oligomer of polyethylene terephthalate. Subsequently, the oligomer was polycondensed at 280 ° C. and 90 Pa (0.7 mmHg) for 2 hours to obtain polyethylene terephthalate. Table 4 shows the quality analysis values of the obtained polyethylene terephthalate.

[0035]

[Table 4]

[Brief description of the drawings]

FIG. 1 is a visible spectrum diagram of bis-β-hydroxyethyl terephthalate crystal taken as a sample from each step of Example 1.

[Explanation of symbols]

a crystal after depolymerization b crystal after activated carbon decolorization c crystal after activated carbon decolorization, decation, deanion, molecular distillation d crystal after activated carbon decolorization, decation, deanionization, crystallization, molecular distillation

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4H006 AA01 AA02 AB46 AD11 AD15 BB14 BC51 BC52 BJ50 BN10 4J029 AA03 AB04 AB07 AC01 AC02 BA02 BA03 BA04 BA05 BB13A BD03A BF09 BF25 BF26 BH02 CB06A DB13 FB07 KD07 FC03 KD07 KE02 KE03 KG01 KG02 KG03

Claims (15)

[Claims] (1) (1) (i) Na, Mg, Ca, Fe,
Cations consisting of Co, Zn, Ti, Sn, Sb, Ge and P, and (ii) halogens, NO ₂ , NO ₃ , PO
Total content of anions consisting of ₄ and SO ₄ is 50 pp
m of crude bis-β-hydroxyethyl terephthalate, and then (2) crystallized bis-β-hydroxyethyl terephthalate.
A method for purifying bis-β-hydroxyethyl terephthalate, comprising evaporating or distilling hydroxyethyl terephthalate under reduced pressure to purify bis-β-hydroxyethyl terephthalate. 2. The crystallization of bis-β-hydroxyethyl terephthalate uses ethylene glycol as a main solvent,
The purification method according to claim 1, wherein the solution obtained by subjecting a solution containing bis-β-hydroxyethyl terephthalate as a main solute to a deionization step is carried out. 3. The method according to claim 1, wherein the evaporation or distillation is carried out at a temperature in the range of 130 to 250 ° C. 4. Evaporation or distillation is conducted at 300 Pa (2.25 Pa).
The method is carried out under a reduced pressure of not more than (mmHg) (absolute pressure).
Purification method as described. 5. A crude bis-β-hydroxyethyl terephthalate having a total content of said cations and anions of 4
The purification method according to claim 1, wherein the content is 0 ppm or less. 6. A crude bis-β-hydroxyethyl terephthalate having a total content of said cations and anions of 3
The purification method according to claim 1, wherein the content is 0 ppm or less. 7. The method according to claim 1, wherein the crude bis-β-hydroxyethyl terephthalate is derived from ethylene glycol depolymerization of polyethylene terephthalate. 8. The crude bis-β-hydroxyethyl terephthalate is derived from a product obtained by decationizing and / or deanionizing a reaction mixture obtained by ethylene glycol depolymerization of polyethylene terephthalate. 2. The purification method according to 1. 9. The reaction mixture is decolorized before decation treatment and / or deanion treatment.
Purification method as described. 10. The purification method according to claim 1, wherein a purified bis-β-hydroxyethyl terephthalate having a total content of the cation and the anion of 15 ppm or less is obtained. 11. The method according to claim 1, wherein a purified bis-β-hydroxyethyl terephthalate having a total content of the cation and the anion of 5 ppm or less is obtained. 12. A purified bis-β-hydroxy-ester having a bis-β-hydroxyethyl terephthalate content of 97% by weight or more.
The purification method according to claim 1, wherein hydroxyethyl terephthalate is obtained. 13. Use of purified bis-β-hydroxyethyl terephthalate obtained by the purification method according to claim 1 for producing polyethylene terephthalate. 14. A method for producing polyethylene terephthalate, comprising polymerizing the purified bis-β-hydroxyethyl terephthalate obtained by the purification method according to claim 1 in the presence of a polycondensation catalyst. 15. A method for producing polyethylene terephthalate, comprising polymerizing purified bis-β-hydroxyethyl terephthalate and terephthalic acid obtained by the purification method according to claim 1 in the presence of a polycondensation catalyst.