JP2001322967A - Method for distilling and purifying bis-beta- hydroxyethyl terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for efficiently obtaining purified bis-β- hydroxyethyl terephthalate having excellent quality without retarding smooth performance of a distillation step in distilling bis-β-hydroxyethyl terephthalate. SOLUTION: This method for distilling and purifying bis-β-hydroxyethyl terephthalate comprises distilling a solution composed of the bis-β-hydroxyethyl terephthalate as the main solute and ethylene glycol as the main solvent after adding 3-300 ppm calculated as phosphorus atom at least one of phosphorus compound selected from acidic phosphorus compounds and ester derivatives thereof based on the bis-β-hydroxyethyl terephthalate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying bis-β-hydroxyethyl terephthalate by distillation.

[0002]

2. Description of the Related Art Polyethylene terephthalate has excellent physical and chemical properties and is widely used in various applications such as fibers, films and resins. In recent years, their uses have been increasingly diversified, and therefore their required performance has been diversified and advanced.

[0003] Polyethylene terephthalate is currently used to convert bis-β-hydroxyethyl terephthalate by direct esterification of terephthalic acid with ethylene glycol or by transesterification of lower alkyl esters of terephthalic acid, especially dimethyl terephthalate with ethylene glycol. It is mainly produced by a method of producing an intermediate containing the compound and then subjecting it to a polycondensation reaction under high temperature and high vacuum. In such a reaction, a reaction catalyst is usually used.

As described above, polyethylene terephthalate basically contains various metal compounds such as an antimony compound, a titanium compound, a germanium compound, and a manganese compound as a polymerization catalyst under a high temperature and a high vacuum, and is kept in a molten state for a long time. However, it is not easy to exhaustively satisfy the various required characteristics described above. Therefore, as a means for enhancing the function and quality of polyethylene terephthalate, there have been conventionally proposed methods of introducing a novel copolymer component into a polymer, improving a polymerization catalyst, and adding various additives. But it can't be drastic.

[0005]

In order to improve the quality of polyethylene terephthalate, first, the quality of the raw material is basically improved, and it will be possible to obtain a polymer of essentially higher quality. This raw material terephthalic acid,
Alternatively, various proposals have been made for the purification of dimethyl terephthalate, which is a lower alkyl ester, but the quality of bis-β-hydroxyethyl terephthalate, which is closer to the final polymer, is still being improved. No practical means to achieve has been developed. If it were achieved, it would be a very useful tool for obtaining essentially upgraded polymers.

As a method for purifying bis-β-hydroxyethyl terephthalate, a method for improving the quality by recrystallization without using evaporation or distillation has been proposed. However, in this method, although it looks as if the quality is improved, in practice, impurities still remain in many cases, which often become obstacles to obtaining a high quality polymer. In particular, when polyethylene terephthalate is recovered and depolymerized to bis-β-hydroxyethyl terephthalate with ethylene glycol to obtain a polyester again, the adverse effects are remarkably recognized. On the other hand, proposals have been made to purify bis-β-hydroxyethyl terephthalate by evaporation or distillation.In such a case, crude bis-β-hydroxyethyl terephthalate is usually prepared by subjecting crude bis-β-hydroxyethyl terephthalate to evaporation or distillation. In addition, a condensed condensation reaction, which is an obstacle, occurred remarkably, and it was difficult to practically obtain a purified bis-β-hydroxyethyl terephthalate fraction.

[0007]

The present inventors have studied this distillation purification method and found that such an adverse effect on the evaporation or distillation of bis-β-hydroxyethyl terephthalate is due to the fact that bis-β-
Substances having a boiling point lower than the boiling point of hydroxyethyl terephthalate are substantially removed, and thereafter, the
It has been found out that bis-β-hydroxyethyl terephthalate, which is less than 0 ° C., can be substantially suppressed by evaporating or distilling under reduced pressure in a temperature range in which quality deterioration is unlikely to occur, and has previously been proposed. But,
Even in such a case, the smooth execution of the distillation purification step was sometimes hindered. The present inventor has worked diligently to solve the problem, and as a result, by carrying out the distillation purification in the presence of a specific phosphorus compound, purified bis-β of excellent quality was obtained.
It has been found that -hydroxyethyl terephthalate can be efficiently obtained, and the present invention has been completed.

That is, the present invention relates to a solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent, and at least one phosphorus compound selected from the group consisting of acidic phosphorus compounds and ester derivatives thereof. Of bis-β-hydroxyethyl terephthalate as a phosphorus atom per bis-β-hydroxyethyl terephthalate, and subjecting the mixture to distillation.

In the present invention, the solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent may be a solution (product) obtained by depolymerizing polyethylene terephthalate with ethylene glycol, For example, a solution in which the solute concentration is adjusted by, for example, adding ethylene glycol is preferably used. Solute concentration is 5-5
It is preferably 0% by weight, more preferably 10 to 30% by weight.

In the present invention, polyethylene terephthalate is a polyester having ethylene terephthalate as a main structural unit, and includes, for example, an ethylene terephthalate homopolymer and a copolymer obtained by copolymerizing at least one of other structural components in a small proportion. The allowable range of the copolymerization component is, for example, usually 40 mol% or less, preferably 30 mol% or less, more preferably 2 mol% or less, based on all constitutional units.
0 mol% or less. Examples of the copolymerization component, as a dicarboxylic acid component, for example, isophthalic acid, diphenyldicarboxylic acid, diphenylsulfonedicarboxylic acid, diphenyletherdicarboxylic acid, naphthalenedicarboxylic acid,
Aromatic dicarboxylic acids such as diphenoxyethane dicarboxylic acid, sodium sulfoisophthalic acid; sebacic acid,
Examples thereof include aliphatic dicarboxylic acids such as adipic acid; and alicyclic dicarboxylic acids such as hexahydroterephthalic acid. Examples of the diol component include trimethylene glycol, tetramethylene glycol, hexamethylene glycol, cyclohexanedimethanol, bis-β-hydroxyethylbisphenol A, bis-β
-Hydroxyethoxydiphenylsulfone, bis-β
-Hydroxyethoxydiphenyl ether, diethylene glycol, polyethylene glycol and the like. Also, hydroxycarboxylic acids such as p
-Hydroxyethoxyphenylcarboxylic acid can be mentioned as a copolymerization component. Further, the use of a trifunctional or higher polyfunctional compound and / or a monofunctional compound is also possible as long as the polyester maintains a linear shape. Examples of trifunctional or higher polyfunctional compounds include, for example, trimesic acid, glycerin, pentaerythritol, and the like. Examples of monofunctional compounds include, for example, 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, and they may be used alone or in combination of two or more. In the production reaction of such polyethylene terephthalate, a polymerization catalyst known per se, for example, an antimony compound, a titanium compound,
A germanium compound or the like is used.

[0011] The polyethylene terephthalate to be subjected to depolymerization with ethylene glycol can be one generally called a waste polymer or a recovered polymer. Its shape can be arbitrary, for example fibers,
It can be preferably used as a molded product such as a film or a bottle, which has been made fine by means such as cutting or pulverization, or further processed by melting, for example, flakes, chips, pellets and the like. In that case, the polymer to be depolymerized is
Even if it is in the form of a product and is mixed with other materials or mixed with foreign matter such as garbage, if necessary, apply a foreign matter removal process such as sorting, filtering, etc. Thereby, the present invention can be implemented without any trouble.

In such a specific example, the waste polymer and the recovered polymer may be mixed with different kinds of fibers when the polymer is in the form of a fibrous product, or may contain titanium oxide as a matting agent. Out, or mixed with other types of film materials in the form of a film, containing various additives such as lubricants in the polymer, or other molded products,
For example, in the form of a bottle, it may be crushed and mixed with other materials such as polyethylene used for the lid and bottom parts, or mixed with other materials such as paper or plastics used for labels, etc. This situation is rather a normal situation. In the present invention, the present invention can be practiced without hindrance by applying a foreign matter removing step such as sorting or filtering as necessary.

The depolymerization can be carried out by a method known per se. For example, the method can be carried out by a method in which debris or recovered polyethylene terephthalate flakes and ethylene glycol are heated and mixed to depolymerize. Further, it is also preferable to carry out a method separately proposed by the present inventors, that is, a method in which waste or recovered polyethylene terephthalate is preliminarily depolymerized using bis-β-hydroxyethyl terephthalate, and then ethylene glycol is added to further depolymerize. . The solution obtained by the depolymerization usually contains cations and anions contained in the raw material polyethylene terephthalate. In addition, as understood from the above description, the polymer may contain another kind of polymer, such as polyolefin, mixed in the polymer recovery process.

In the present invention, at least one phosphorus compound selected from the group consisting of an acidic phosphorus compound and its ester derivative is added to a solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent. 3 to 300 ppm of phosphorus atoms per bis-β-hydroxyethyl terephthalate are added and subjected to distillation. The addition amount of the phosphorus compound is 3 ppm to 300 ppm as phosphorus atoms based on bis-β-hydroxyethyl terephthalate. Addition of more than this amount has a disadvantage such as formation of scale on the heat transfer surface of the molecular still, while addition of lesser amount causes a problem such that oligomerization is caused when the residence time becomes longer. The addition amount of the phosphorus compound is further 5 to 100 ppm as a phosphorus atom.
Is preferable.

Preferable examples of such phosphorus compounds include phosphoric acid, phosphorous acid and esters thereof.
Examples thereof include alkyl esters such as trimethyl ester, dimethyl ester, triethyl ester and diethyl ester, and triaryl esters such as triphenyl ester and diphenyl ester. These can be used alone or in combination of two or more. As an example of the ester, a lower alkyl ester having 1 to 6 carbon atoms is particularly suitable.

The phosphorus compound may be added all at once, or, if necessary, may be added for each type, or a part or the whole may be added arbitrarily. The phosphorus compound may be added as it is, but is preferably added as a suitable solution such as an ethylene glycol solution. By adding such a phosphorus compound, the distillation step is smoothly performed, and the reason why bis-β-hydroxyethyl terephthalate of excellent quality can be efficiently obtained is not clear, but it is not clear why the remaining cations are trapped and the activity is improved. Is considered to be due to suppression of

In the present invention, the distillation treatment is performed after the addition of the specific phosphorus compound.
For practically obtaining a β-hydroxyethyl terephthalate fraction, the distillation is preferably carried out under specific temperature and reduced pressure conditions. In addition, in order to carry out the method in a practically advantageous manner, the distillation of bis-β-hydroxyethyl terephthalate is not carried out by boiling distillation, that is, by equilibrium distillation. It is preferable to perform the non-equilibrium evaporation or distillation in which molecules unilaterally move from the evaporation surface to the condensation surface without returning to the evaporation surface. And, of course, such non-equilibrium evaporation or distillation is preferably carried out using a distillation means suitable for it. Such a distillation operation may be generally referred to by the name of molecular distillation.

[0018] Such a distillation treatment is preferably carried out in a temperature range of more than 190 ° C and less than 200 ° C, more preferably 160 ° C.
In the temperature range of up to 220 ° C. and preferably under reduced pressure, more preferably 133.3 Pa (1 mmHg) (absolute pressure)
Hereinafter, particularly preferably, 67 Pa (0.5 mmHg)
(Absolute pressure) It is advantageous to carry out under reduced pressure. Also,
Advantageously, the average residence time of bis-β-hydroxyethyl terephthalate in the evaporation or distillation apparatus is preferably less than 2 hours, more preferably less than 1.5 hours.

In carrying out the molecular distillation, a substance having a boiling point lower than that of bis-β-hydroxyethyl terephthalate, particularly a substance such as ethylene glycol as a solvent, is previously removed by distillation, and its content is preferably reduced. It is at most 10% by weight, more preferably at most 5% by weight, particularly preferably at most 2% by weight. Thereby, the efficiency of molecular distillation can be increased. In the present invention, the solution is subjected to a decolorizing treatment at a stage prior to the addition of the phosphorus compound, or a crystallization treatment at a stage prior to the addition of the phosphorus compound, and further to a phosphorus compound In a stage prior to the addition of decolorization treatment,
Thereafter, crystallization treatment is preferably performed.

The decolorization treatment is desirably performed with a solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent.
For this decolorization treatment, treatment with an adsorbent such as activated carbon is useful. The decolorizing treatment can be performed by passing the solution through an adsorbent packed layer, or by adding an adsorbent to the solution, stirring and mixing, and separating the adsorbent. As described above, the decolorizing treatment can be performed in combination with the crystallization step of extracting bis-β-hydroxyethyl terephthalate as crystals. That is, an ethylene glycol solution of bis-β-hydroxyethyl terephthalate is brought into contact with an adsorbent such as activated carbon at a temperature and a concentration condition at which a solute does not precipitate, and then the adsorbent is separated and removed. It is a useful embodiment to precipitate bis-β-hydroxyethyl terephthalate at a temperature and concentration condition under which hydroxyethyl terephthalate precipitates, and to separate and collect the bis-β-hydroxyethyl terephthalate.

The crystallization treatment, that is, the treatment of separating and separating bis-β-hydroxyethyl terephthalate as crystals, may be performed immediately before the purification by distillation. In short, what is necessary is just to select suitably according to the balance between the quality of the target bis- (beta) -hydroxyethyl terephthalate, and a yield, and any aspect is in the scope of the present invention. The crystallization treatment can be performed one or more times, which is a preferable embodiment.

In the present invention, it is preferable that the step of extracting bis-β-hydroxyethyl terephthalate as a crystal as described above is performed one or more times before the distillation is carried out. The step of removing the bis-β-hydroxyethyl terephthalate as crystals is usually performed in a solution containing ethylene glycol as a main solvent and bis-β-hydroxyethyl terephthalate as a main solute.
In the high temperature range, the solution state is maintained, and in the low temperature range, the concentration is selected so as to precipitate bis-β-hydroxyethyl terephthalate. In such a case, the high-temperature region condition for maintaining the solution state can often be in the range of 20 ° C. to 120 ° C., and it is preferable to take an aspect in which these are combined. If necessary, operations such as dilution and concentration can be added within the scope of the present invention.

The purified bis-β-hydroxyethyl terephthalate purified by distillation in the method of the present invention has an extremely high quality, and the content of bis-β-hydroxyethyl terephthalate is preferably 97% by weight or more, more preferably Can be 98% by weight or more. And
The purified bis-β-hydroxyethyl terephthalate is
It is advantageously used for the production of polyesters, especially polyethylene terephthalate. For example, the purified bis-β-hydroxyethyl terephthalate is suitably used as at least a part of a raw material of polyethylene terephthalate widely used for various applications as described above. The obtained polyethylene terephthalate (PET) can be used without any problem as various molded products such as fibers, films, and bottles.

[0024]

EXAMPLES The present invention will be described more specifically with reference to the following examples. The present invention is not limited to these examples.

Example 1 A PET bottle recovered from the city was wet-pulverized to a size of 8 to 10 mm, washed and dried, and 50 kg of PET bottle flakes and 0.25 sodium methylate were obtained.
kg and 360 kg of ethylene glycol were charged into a 700-liter autoclave equipped with a heating medium oil pump circulation heating jacket reflux condenser and a stirrer.
The depolymerization reaction was performed under the condition of 15 MPa for 150 minutes.
Next, the temperature of the heating medium oil in the jacket was lowered to 50 to 6
After keeping at 0 ° C. for 3 hours, precipitated oligomers and contaminants such as caps and labels were filtered off with a 0.8 μm filter, and then subjected to decolorization treatment. Conductivity is 370 μS / m
Met.

Next, while cooling with brine at -5 ° C,
Crystallization is performed at 0 to 2 ° C. in a cooling classification crystallization tank for 180 minutes,
The crystals were separated by a decanter to obtain 102 kg of a cake of crude bis-β-hydroxyethyl terephthalate. The solids in the cake obtained were 63.1% by weight. 1.4 g of 85% phosphoric acid for 50 kg of this cake
And 1.8 g of tri-n-butyl phosphite and add 90-
Heat to 98 ° C. to dissolve. Subsequently, ethylene glycol was distilled off at 5.33 kPa (40 Torr) and 121 ° C. by a vacuum evaporator to concentrate the crude bis-β-hydroxyethyl terephthalate, followed by 15 Pa (0.11 kPa).
Under a vacuum of 3 Torr), the internal condenser was maintained at 120 ° C. at 196 ° C., and the distillation purification could be carried out smoothly without any problem for 38 minutes through a thin film evaporator having a heat transfer area of 0.5 m ² . The obtained purified bis-β-hydroxyethyl terephthalate was 29.3 kg and the residue was 1.77 k.
g, low boiling point distillate was about 0.5 kg. The quality of the obtained purified bis-β-hydroxyethyl terephthalate is as follows:
The optical density was 0.003 (10% methanol solution), the degree of coloring L was 99.4, the a value was -0.9, the b value was 1.3, no metal was observed, and the melting point was 112.1 ° C.

Comparative Example 1 The same operation was carried out using 50 kg of the cake obtained in Example 1 without adding the phosphoric acid and tri-n-butyl phosphite added in Example 1, and the evaporation purification was performed. 1 to start
After 3 minutes, the power of the stirrer gradually starts to increase, and at the same time, the degree of vacuum gradually decreases.
a, reached an equilibrium at 55 Pa and then at 87 Pa, the amount of distilling bis-β-hydroxyethyl terephthalate was reduced, and the removal of the residue resulted in impossible clogging and was stopped 27 minutes after starting the evaporative purification. I had to help. Since an ethylene glycol fraction was found in the cold trap installed at the vacuum pump inlet of the molecular still, it is apparent that a polycondensation reaction had occurred. The molecular distillation apparatus was disassembled and the melting point of the clog was measured.
showed that.

[0028]

According to the present invention, high-quality purified bis-β-hydroxyethyl useful for the production of polyethylene terephthalate from a solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent is used. Terephthalate can be obtained efficiently.

Continuation of the front page F term (reference) 4H006 AA02 AC91 AD11 AD15 AD40 BB14 BC52 BD10 BE04 BJ50 BN10

Claims (10)

[Claims] 1. A solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent is provided with at least one phosphorus compound selected from the group consisting of acidic phosphorus compounds and ester derivatives thereof. A method for purifying bis-β-hydroxyethyl terephthalate by adding 3 to 300 ppm of phosphorus atoms per β-hydroxyethyl terephthalate and subjecting the mixture to distillation. 2. The amount of the phosphorus compound added is 5 as phosphorus atoms per bis-β-hydroxyethyl terephthalate.
2. The method according to claim 1, wherein the amount is from ppm to 100 ppm. 3. The method according to claim 1, wherein the phosphorus compound is at least one selected from the group consisting of phosphoric acid, phosphorous acid and esters thereof.
2. The method of claim 1, which is a compound of the species. 4. The method according to claim 3, wherein the phosphorus compound is at least one compound selected from the group consisting of phosphoric acid, phosphorous acid and lower alkyl esters thereof. 5. The method according to claim 1, wherein the solution has been subjected to a decolorization step before adding the phosphorus compound. 6. The method according to claim 1, wherein the solution contains bis-β-hydroxyethyl terephthalate which has been subjected to a crystallization step before adding the phosphorus compound. 7. The method according to claim 1, wherein the solution contains bis-β-hydroxyethyl terephthalate which has been subjected to a decolorization step and then to a crystallization step before adding the phosphorus compound. 8. The distillation is carried out after the solvent has been substantially removed.
The method according to claim 1, wherein the method is carried out at a temperature in the range of greater than 190 ° C. and less than 200 ° C. 9. The distillation is carried out after the solvent has been substantially removed.
The method according to claim 1, which is carried out under a reduced pressure of not more than 133.3 Pa (1.0 mmHg) (absolute pressure). 10. A solution containing bis-β-hydroxyethyl terephthalate as a main solute and ethylene glycol as a main solvent is a product obtained by depolymerizing polyethylene terephthalate with ethylene glycol or a solution in which the solute concentration of the product is adjusted. The method of claim 1, wherein