JPH07228677A - Method for producing polyester - Google Patents

Abstract

(57) [Summary] [Structure] When a polyester is produced from a dicarboxylic acid and a dihydroxy compound by a process including an esterification step and a polycondensation step, a dihydroxy compound-containing distillate distilled in the polycondensation step. In the distillation process,
A method for producing polyester, which comprises performing a treatment including a filtration step, a decolorization step, and an iron removal step if necessary, and supplying the recovered dihydroxy compound and polycondensation catalyst to the esterification step. In the present invention, it is preferable to adjust the catalyst content by adding the polycondensation catalyst to the recovered dihydroxy compound containing the polycondensation catalyst. [Effect] Since the dihydroxy compound and the polycondensation catalyst distilled from the polycondensation step can be effectively reused without deteriorating the quality of the polyester, the production efficiency can be improved and the production cost can be reduced. .

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a polyester, and more specifically, it processes a dihydroxy compound-containing distillate distilled in a polycondensation step to esterify the recovered dihydroxy compound with a polycondensation catalyst. The present invention relates to a method for producing polyester to be supplied to a chemical conversion step.

[0002]

BACKGROUND OF THE INVENTION Polyester such as polyethylene terephthalate has been conventionally used as a material for molded articles such as bottles, fibers, films and sheets.

Such polyesters are usually produced by a process including an esterification process of esterifying a dicarboxylic acid and a dihydroxy compound and a polycondensation process of liquid phase polycondensation in the presence of a polycondensation catalyst. In this polycondensation step, polycondensation is carried out while dihydroxy compounds such as ethylene glycol are distilled out of the system, and 60 to 70% of the polycondensation catalyst added to the polymerization system is out of the system together with the dihydroxy compound. Distill in.

Since the dihydroxy compound distilled off from the polycondensation step as described above contains a polycondensation catalyst, the polycondensation catalyst and the dihydroxy compound can be efficiently used by supplying this to the polymerization system. . However, since this dihydroxy compound contains a large amount of impurities other than the polycondensation catalyst that deteriorate the quality of the polyester, it has been difficult to reuse it as it is in the production process of the polyester.

In order to solve such a problem, for example, Japanese Patent Application Laid-Open No. 57-26632 discloses a method in which a germanium-containing glycol generated in a polyester manufacturing process is treated with a cationic resin as shown in FIG. , A method of using it as a polyester raw material has been proposed. However, such a method has a problem that impurities cannot be sufficiently removed.

Therefore, there is a demand for a method of efficiently removing impurities from a dihydroxy compound containing a polycondensation catalyst that is distilled off from the polycondensation step and reusing it in the polyester production step without degrading the quality of the polyester. .

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made under the above-mentioned circumstances and removes impurities from a dihydroxy compound containing a polycondensation catalyst that is distilled off from the polycondensation step to obtain a dihydroxy compound and a polycondensation compound. It is an object of the present invention to provide a polyester production method capable of improving the production efficiency of polyester and reducing production cost by efficiently reusing a catalyst.

[0008]

SUMMARY OF THE INVENTION In the method for producing a polyester according to the present invention, when a polyester is produced from a dicarboxylic acid and a dihydroxy compound by a step including an esterification step and a polycondensation step, distilling is carried out in the polycondensation step. The dihydroxy compound-containing distillate has the following (a) to
A treatment including the step (c) is performed, and the recovered dihydroxy compound and the polycondensation catalyst are supplied to the esterification step; (a) distillation step (b) filtration step (c) decolorization step In the invention, in treating the dihydroxy compound-containing distillate, in addition to the steps (a) to (c), (d)
It is preferable to perform a treatment including an iron removal step.

Further, in the present invention, it is preferable that after treating the dihydroxy compound-containing distillate, the polycondensation catalyst is added to the recovered dihydroxy compound containing the polycondensation catalyst to adjust the catalyst content.

[0010]

DETAILED DESCRIPTION OF THE INVENTION The method for producing the polyester of the present invention will be specifically described below. In the present invention, when a dicarboxylic acid or an ester-forming derivative thereof and a dihydroxy compound or an ester-forming derivative thereof are esterified in an esterification step and then liquid phase polycondensation is performed in a polycondensation step to produce a polyester, The dihydroxy compound-containing distillate distilled in the polycondensation step is subjected to treatments such as distillation, filtration and decolorization, and then the recovered dihydroxy compound and polycondensation catalyst are supplied to the esterification step. The production of such polyester is usually carried out in a continuous manner.

In the esterification step, a dicarboxylic acid or an ester-forming derivative thereof, a dihydroxy compound or an ester-forming derivative thereof, and optionally other components such as a monofunctional compound and a polyfunctional compound are included. Slurry and distillate from the polycondensation step described later, recovered by treatments such as distillation, filtration, decolorization, the catalyst content was adjusted as necessary, the dihydroxy compound containing a polycondensation catalyst was continuously supplied. It

The slurry contains 1.02 to 2.0 with respect to 1 mol of dicarboxylic acid or its ester-forming derivative.
Included are moles, preferably 1.03 to 1.5 moles of the dihydroxy compound or ester forming derivative thereof. In addition, the other component used as necessary is such that the total amount of the dicarboxylic acid or its ester-forming derivative and the dihydroxy compound or its ester-forming derivative is 100.
When defined as mol%, 0.01 to 2 mol%, preferably 0.02 mol%.
It is preferably contained in an amount of 05 to 1 mol%.

Examples of the dicarboxylic acid used in the present invention include aromatic dicarboxylic acids such as terephthalic acid, adipic acid, phthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, diphenoxyethanedicarboxylic acid; succinic acid and adipic acid. And aliphatic dicarboxylic acids such as azelaic acid, sebacic acid and decanedicarboxylic acid; and alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid.

As the dihydroxy compound, ethylene glycol, triethylene glycol, polyethylene glycol, diethylene glycol, cyclohexanediol, 1,3-bis (2-hydroxyethoxy) benzene, 1,4-
Bis (2-hydroxyethoxy) benzene, bis (4-β-
Hydroxyethoxyphenyl) sulfone and the like can be mentioned.

Examples of the monofunctional compound include benzoylbenzoic acid, diphenylsulfone monocarboxylic acid, stearic acid, methoxypolyethylene glycol and phenoxypolyethylene glycol, and examples of the polyfunctional compound include trimesic acid, trimethylolethane and trimethylol. Propane, trimethylolmethane, pentaerythritol and the like can be mentioned.

The esterification reaction is carried out by removing at least two esterification reactors in series using a reactor in which the dihydroxy compound is refluxed, and removing the water produced by the reaction from the system in a rectification column. While being carried out.

Regarding the reaction conditions for carrying out the esterification reaction, for example, when the esterification reaction is carried out in two stages, the temperature of the first stage esterification reaction is usually 240 to 270.
℃, preferably 245 ~ 265 ℃, the pressure is usually 0.2 ~ 3kg / cm ² -G, preferably 0.5 ~ 2kg /
cm ² -G. The temperature of the second stage esterification reaction is
It is usually 250 to 280 ° C, preferably 255 to 275 ° C, and the pressure is usually 0 to 1.5 kg / cm ² -G, preferably 0 to 1.3 kg / cm ² -G.

A low-order condensate is obtained by this esterification step, and the number-average molecular weight of the low-order condensate is usually from 500 to
It is 5000. Such an esterification reaction can be performed by using a tertiary amine such as triethylamine, tri-n-butylamine or benzyldimethylamine, or a quaternary hydroxide such as tetraethylammonium hydroxide, tetra-n-butylammonium hydroxide or trimethylbenzylammonium hydroxide. It is preferable to add ammonium and a small amount of a basic compound such as lithium carbonate, sodium carbonate, potassium carbonate or sodium acetate. By carrying out the esterification reaction in the presence of the basic compound, the proportion of the dioxyethylene terephthalate component unit in the main chain of the polyester can be maintained at a relatively low level.

Next, the low-order condensate obtained in the esterification step is supplied to the polycondensation step. In the polycondensation process,
In the presence of a polycondensation catalyst, under reduced pressure, heated to a temperature above the melting point of the resulting polyester (usually 270-300 ℃),
Polycondensation is carried out while distilling a dihydroxy compound-containing distillate containing a dihydroxy compound such as ethylene glycol produced during polycondensation out of the system. The dihydroxy compound-containing distillate contains a dihydroxy compound such as ethylene glycol, a polycondensation catalyst, water and an oligomer.

The dihydroxy compound-containing distillate distilled out of the system is subjected to treatments including (a) a distillation step, (b) a filtration step, (c) a decolorization step, and (d) an iron removal step, if necessary. The dihydroxy compound and the polycondensation catalyst recovered by removing impurities are supplied to the esterification step as a polyester raw material and a catalyst.

The distillate-containing distillate that has been distilled off is treated in the order of (a) distillation step, (b) filtration step, (c) decolorization step, or (b) filtration step, (a) distillation step, It is preferable that the step (c) is performed in the order of the bleaching step. Further, when the dihydroxy compound-containing distillate treatment includes (d) iron removal step, (a) distillation step, (b) filtration step,
(C) decoloring step, (d) iron removing step, or (b) filtering step, (a) distillation step, (c) decolorizing step,
(D) It is preferable to perform the iron removal step in this order. FIG. 1 shows a schematic process diagram of the method for producing polyester according to the present invention.

In the distillation step (a), water, low-temperature distillate, etc. in the dihydroxy compound-containing distillate are removed. The pressure when distilling the dihydroxy compound-containing distillate is 20 to
The pressure is 600 Torr, preferably 50 to 150 Torr, and the temperature is 100 to 200 ° C., preferably 120 to 1
It is preferably 70 ° C. The water content in the dihydroxy compound-containing distillate that has undergone this distillation step is desirably 1.0% or less, preferably 0.5% or less. In the distillation step, the water content in the dihydroxy compound-containing distillate,
Since low-temperature distillate is removed, it has the effect of reducing the load on the decolorization process and iron removal process, and prolonging the breakthrough time, compared to dihydroxy compound-containing distillate that has not undergone the distillation process. .

(B) In the filtration step, oligomers and the like in the dihydroxy compound-containing distillate are removed. The temperature at which the dihydroxy compound-containing distillate is filtered is 10 to 80.
It is desirable that the temperature is ° C, preferably 20 to 60 ° C. Further, it is preferable to use a filter aid during filtration, and examples of the filter aid include celite and cellulose-based filter aids. Such a filter aid is 10 to 200 parts by weight, preferably 50 to 10 parts by weight, based on 100 parts by weight of the precipitated oligomer in the dihydroxy compound-containing distillate.
It is preferably used in an amount of 0. It is desirable that the amount of precipitated oligomer in the dihydroxy compound-containing distillate that has been subjected to this filtration step is 0.05% or less, preferably 0.01% or less. In the filtration step, oligomers and the like in the dihydroxy compound-containing distillate are removed, so it is possible to prevent clogging in the (c) decolorization step and (d) iron removal step described below.

In the (c) decolorization step, the dihydroxy compound-containing distillate is brought into contact with activated carbon to remove the coloring matter from the dihydroxy compound-containing distillate. The temperature at which the dihydroxy compound-containing distillate is brought into contact with activated carbon is 50 to 100 ° C., preferably 70 to 90 ° C.,
The superficial velocity is 0.1 to 6.0 hr ^−1, preferably 0.16
7 to 4.0 hr ^−1, more preferably 0.20 to 2.0 hr
It is preferably r ⁻¹ . In this decolorization step, it is desirable that the T ₃₈₀ of the dihydroxy compound-containing distillate after treatment is 97% or more, preferably 98% or more. When the T ₃₈₀ of the dihydroxy compound-containing distillate is 98% or more, the quality of the obtained polyester, particularly the hue is not deteriorated. Note that T ₃₈₀ is the transmittance of light having a wavelength of 380 nm and is measured as follows.

Spectrophotometer (U-1100 manufactured by Hitachi Ltd.)
The dihydroxy compound-containing distillate after treatment was put into a 10 mm quartz cell using distilled water, and distilled water was used as a control solution.
The transmittance is measured at a wavelength of 380 nm.

In the decoloring step, since the dihydroxy compound-containing distillate is contacted with the activated carbon, the amount of the polycondensation catalyst in the dihydroxy compound-containing distillate is hardly reduced and Colorants can be removed.

In the iron removal step (d), the iron content in the dihydroxy compound-containing distillate is removed. (D) In the iron removal step,
The distillate is contacted with the ion exchange resin. Examples of the ion exchange resin include a cation exchange resin, an anion exchange resin and an amphoteric ion exchange resin, and among these, a cation exchange resin, particularly a strongly acidic cation exchange resin is preferable.

The contact between the distillate and the ion exchange resin is 50
To 100 ° C., preferably 70 to 90 ° C., and superficial velocity 0.1 to 6.0 hr ^−1, preferably 0.167 to 4.0 h.
It is desirable that r ^{−1 is} more preferably 0.20 to 2.0 hr ⁻¹ .

It is desirable that the dihydroxy compound-containing distillate subjected to the iron removal step (d) has an iron content of 2 ppm or less, preferably 0.5 ppm or less. When the iron content in the dihydroxy compound-containing distillate is removed in the iron removal step, the hue of the obtained polyester is not lowered.

The dihydroxy compound-containing distillate treated as described above is usually recovered as a dihydroxy compound containing a polycondensation catalyst. You may adjust a catalyst content etc. by adding the stabilizer etc. which consist of phosphorus compounds. The polycondensation catalyst, the stabilizer, etc. are added in an amount to supplement the polycondensation catalyst, the stabilizer, etc. discharged out of the reaction system together with the produced polyester. Specifically, the amount of the polycondensation catalyst and the stabilizer in the polycondensation reactor is
It is added in an amount so as to be within the range described below.

In the present invention, the dihydroxy compound-containing distillate distilled from the polycondensation step is subjected to (a) a distillation step, (b) a filtration step, (c) a decolorization step, and (d) an iron removal step if necessary. Since the recovered dihydroxy compound and the polycondensation catalyst are supplied as a raw material and a catalyst to the esterification step after the treatment including, the dihydroxy compound and the polycondensation catalyst distilled from the polycondensation step are efficiently used. In addition, the production efficiency of polyester is not lowered, and the quality of polyester is not lowered.

The polycondensation reaction in the liquid phase may be carried out in one step or in a plurality of steps. For example, when carrying out the polycondensation reaction in two stages, the polycondensation reaction conditions are:
The reaction temperature of the first stage polycondensation is usually 250 to 290.
℃, preferably 260-280 ℃, the pressure is usually
500-20 Torr, preferably 200-30 Torr
r. The temperature of the second stage polycondensation reaction is usually 26
5 to 300 ° C, preferably 270 to 295 ° C, the pressure is usually 10 to 0.1 Torr, preferably 5 to 0.5T.
orr.

The amount of the polycondensation catalyst in the polycondensation reactor is usually 0.0005 to 0.2 mol%, preferably 0.001 to 100 mol% of the dicarboxylic acid in terms of metal atoms in the polycondensation catalyst. It is preferably in the range of 0.1 mol%.
The amount of the stabilizer in the polycondensation reactor is usually 0.00 as the weight of phosphorus atom in the stabilizer with respect to the weight of the esterified product of dicarboxylic acid and dihydroxy compound.
It is desirable to be in the range of 1 to 0.1% by weight, preferably 0.002 to 0.02% by weight.

The intrinsic viscosity [η] of the polyester obtained from these polycondensation steps is usually 0.40 to 1.0 dl /
g, preferably 0.50 to 0.90 dl / g.

In the present invention, germanium compounds such as germanium dioxide, germanium tetraethoxide and germanium tetra n-butoxide, antimony catalysts such as antimony trioxide and titanium catalysts such as titanium tetrabutoxide can be used as polycondensation catalysts. Among these catalysts, it is preferable to use a germanium dioxide compound.

The stabilizers include phosphoric acid esters such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate, triphenyl phosphite, trisdodecyl phosphite, trisnonyl phenyl phosphite. And the like, and acid phosphates such as methyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate, dioctyl phosphate, and phosphorus compounds such as phosphoric acid and polyphosphoric acid.

These catalysts and stabilizers are supplied to the esterification step together with the dihydroxy compound recovered by treating the dihydroxy compound-containing distillate distilled from the polycondensation step as described above. It may be supplied to the step or the polycondensation step.

The polyester obtained in such a liquid phase polycondensation step is usually formed into particles (chips) by a melt extrusion molding method. The polyester thus obtained has almost the same quality as the polyester produced by the conventional production method.

[0039]

INDUSTRIAL APPLICABILITY The method for producing a polyester of the present invention can effectively reuse the dihydroxy compound and the polycondensation catalyst distilled from the polycondensation step without deteriorating the quality of the obtained polyester. The efficiency can be improved and the production cost can be reduced.

[0040]

The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited to these examples.

[0041]

Example 1 When a polyester is produced from terephthalic acid and ethylene glycol by a process including an esterification step and a polycondensation step, an ethylene glycol-containing distillate (dihydroxy compound-containing distillate containing dihydroxy compound) Distillate) was obtained. The composition of the obtained distillate containing ethylene glycol was: ethylene glycol: 87.1% by weight,
Diethylene glycol: 0.6% by weight, water: 12.0% by weight, and precipitated oligomer: 0.3% by weight.

13 parts of this distillate containing ethylene glycol
After distillation at 7 ° C and 80 Torr, cellulosic filter aid K
0.3 part by weight of S-100 (manufactured by Kojin) was added, stirred and dispersed, and filtered with a membrane filter (0.45 μm). The filtrate was clear and no suspended matter could be visually confirmed. At this time, the T ₃₈₀ of the filtrate was 93.7%. Then, the filtrate was heated to 70 ° C., and iron removal treatment and decolorization treatment were performed at a superficial velocity of 0.5 hr ⁻¹ . Amberlyst 15WET (manufactured by Organo) was used for iron removal treatment, and Kuraray Coal GLC (manufactured by Kuraray Chemical) was used for decolorization treatment. The composition of the obtained purified ethylene glycol-containing distillate was as follows: ethylene glycol: 98.4% by weight, diethylene glycol: 0.9% by weight, water: 0.5% by weight, F
e: 0.0002% by weight, Ge: 0.2% by weight,
_T380 : It was 99.5%.

Next, a polyester was produced using this purified ethylene glycol-containing distillate. Elephthalic acid 100 parts by weight, ethylene glycol 38.2 parts by weight,
6.7 parts by weight of the purified ethylene glycol-containing distillate,
And 0.019 parts by weight of germanium equivalent to germanium dioxide (germanium in the distillate containing purified ethylene glycol) were used for esterification reaction by a conventional method, and then 0.029 parts by weight of trimethyl phosphate was added. Was subjected to a polycondensation reaction to obtain a polyester chip having an intrinsic viscosity of 0.56. Further, this polyester chip was subjected to solid-state polymerization at 215 ° C. for 21 hours under nitrogen flow to obtain a polyester chip having an intrinsic viscosity of 0.80.

The polyester chip was measured with a 45 ° diffusion type color difference meter (Suga tester: SC-2-CH type). Color tone is L value (brightness): 90.4, a value (+ red, -green):-
2.5, b value (+ yellow, -blue): +4.2. Further, this chip was heated and melted at 275 ° C. to form a stepped rectangular plate. The haze of the square plate having a thickness of 5 mm was 6.6%.

[0045]

Example 2 A polyester was produced using the purified ethylene glycol-containing distillate obtained in Example 1. 100 parts by weight of terephthalic acid, ethylene glycol 3
1.4 parts by weight, 13.5 parts by weight of the above-mentioned purified ethylene glycol-containing distillate, and 0.
Using 038 parts by weight of germanium (germanium with distillate containing purified ethylene glycol), an esterification reaction was carried out in the same manner as in Example 1, and then 0.029 parts by weight of trimethyl phosphate was added to carry out polycondensation. React,
A polyester chip having an intrinsic viscosity of 0.56 was obtained. Further, this polyester chip was subjected to 1 at 215 ° C. under nitrogen flow.
Solid-state polymerization was carried out for 8 hours to obtain a polyester chip having an intrinsic viscosity of 0.80.

The color tone of this polyester chip is L value:
91.7, a value: -2.6, b value: +3.8.
Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of a square plate having a thickness of 5 mm was 10.5%.

[0047]

Example 3 An ethylene glycol-containing distillate was purified in the same manner as in Example 1 except that the iron removing treatment was not carried out. The composition of the obtained purified ethylene glycol-containing distillate was as follows: ethylene glycol: 98.6% by weight, diethylene glycol: 0.8% by weight, water: 0.
It was 4% by weight, Fe: 0.0014% by weight, Ge: 0.2% by weight, and T ₃₈₀ : 99.1%.

Using the purified distillate containing ethylene glycol, polyester was produced in the same manner as in Example 1 to obtain a polyester chip having an intrinsic viscosity of 0.56. Further, this polyester chip was subjected to solid phase polymerization in the same manner as in Example 1 to obtain a polyester chip having an intrinsic viscosity of 0.78.

The color tone of this polyester chip has an L value:
90.7, a value: -2.3, b value: +3.6.
Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of a square plate having a thickness of 5 mm was 10.2%.

[0050]

Example 4 The treatment of the distillate containing ethylene glycol in Example 1 was carried out by the steps of distillation, filtration, decolorization,
The ethylene glycol-containing distillate was purified in the same manner as in Example 1 except that the iron removal step was performed in this order. The composition of the obtained purified ethylene glycol-containing distillate was as follows: ethylene glycol: 96.9% by weight, diethylene glycol:
0.8% by weight, water: 2.1% by weight, Fe: 0.0000
4% by weight, Ge: 0.20% by weight, T ₃₈₀ : 99.4%
Met.

Using the purified distillate containing ethylene glycol, polyester was produced in the same manner as in Example 1 to obtain a polyester chip having an intrinsic viscosity of 0.55. Further, this polyester chip was subjected to solid phase polymerization at 215 ° C. for 18 hours under a nitrogen flow to obtain a polyester chip having an intrinsic viscosity of 0.77.

The color tone of this polyester chip is L value:
91.1, a value: -2.7, b value: +3.6.
Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of a 5 mm-thick square plate was 9.9%.

[0053]

COMPARATIVE EXAMPLE 1 Example 1 was repeated except that 6.7 parts by weight of ethylene glycol was used in place of the purified ethylene glycol-containing distillate and 0.019 parts by weight of germanium dioxide was used in producing the polyester in Example 1. A polyester chip having an intrinsic viscosity of 0.56 was obtained in the same manner as in.
Further, this polyester chip was subjected to solid phase polymerization in the same manner as in Example 1 to obtain a polyester chip having an intrinsic viscosity of 0.80.

The color tone of this polyester chip has an L value:
91.0, a value: -2.5, b value: +3.5.
Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of a 5 mm-thick square plate was 10.6%.

[0055]

Comparative Example 2 Example 2 was repeated except that 13.5 parts by weight of ethylene glycol was used in place of the purified ethylene glycol-containing distillate and 0.038 parts by weight of germanium dioxide was used in producing the polyester in Example 2. A polyester chip having an intrinsic viscosity of 0.56 was obtained in the same manner as in. Further, this polyester chip was subjected to solid phase polymerization in the same manner as in Example 2 to obtain a polyester chip having an intrinsic viscosity of 0.80.

The color tone of this polyester chip is L value:
91.3, a value: -2.6, b value: +3.4.
Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of a square plate having a thickness of 5 mm was 10.5%.

[0057]

Comparative Example 3 An ethylene glycol-containing distillate was purified in the same manner as in Example 1 except that the iron removal treatment and the decolorization treatment were not performed in the above Example 1. The composition of the obtained purified ethylene glycol-containing distillate was as follows: ethylene glycol: 98.5% by weight, diethylene glycol: 0.9% by weight, water: 0.4% by weight, Fe: 0.0010% by weight,
Ge was 0.2% by weight and T ₃₈₀ was 92.5%.

Using this purified ethylene glycol-containing distillate, polyester was produced in the same manner as in Example 1 to obtain a polyester chip having an intrinsic viscosity of 0.55. Furthermore, this polyester chip was subjected to solid phase polymerization at 215 ° C. for 25 hours under a nitrogen stream to obtain a polyester chip having an intrinsic viscosity of 0.82.

The color tone of this polyester chip has an L value:
91.0, a value: -2.2, b value: +3.9, which was slightly yellowish. Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of the 5 mm-thick square plate was 17.5%, and it was slightly hazy.

[0060]

Comparative Example 4 The same esterification step as in Example 1 above,
An ethylene glycol-containing distillate was obtained which was distilled from the esterification step and the polycondensation step when a polyester was produced by a step including a polycondensation step. The composition of this ethylene glycol-containing distillate was ethylene glycol: 8
1.5% by weight, diethylene glycol: 2.3% by weight,
Water: 15.9% by weight, precipitated oligomer: 0.3% by weight.

After precipitating oligomers in the distillate containing ethylene glycol were separated by standing, Amberlyst 15 WET
(Manufactured by Organo) was used to remove iron at a superficial velocity of 1.0 hr ⁻¹ and room temperature. Further, after distillation treatment at 175 ° C. under atmospheric pressure, decolorization treatment was performed at a superficial velocity of 0.5 hr ⁻¹ and normal temperature using Calgon CPG (manufactured by Toyo Calgon) to obtain a purified ethylene glycol-containing distillate. . The composition of the obtained purified ethylene glycol-containing distillate was ethylene glycol: 94.5% by weight, diethylene glycol: 2.9.
% By weight, water: 2.6% by weight, Fe: 0.0001% by weight, Ge: 0.032% by weight, T ₃₈₀ : 95.0%.

Next, polyester was produced using this purified ethylene glycol-containing distillate. 100 parts by weight of terephthalic acid, 34.7 parts by weight of ethylene glycol,
Using 10.8 parts by weight of the purified ethylene glycol-containing distillate and 0.0013 parts by weight of germanium dioxide, an esterification reaction was carried out by a conventional method, and then 0.017 parts by weight of trimethyl phosphate was added to carry out polycondensation. By reacting, a polyester chip having an intrinsic viscosity of 0.59 was obtained. Further, this polyester chip was subjected to solid phase polymerization at 215 ° C. for 13 hours under a nitrogen flow to obtain a polyester chip having an intrinsic viscosity of 0.78.

The color tone of this polyester chip is L value:
It was 88.0, a value: -1.8, b value: +4.6.
Further, using this chip, a stepped square plate was formed in the same manner as in Example 1. The haze of a square plate having a thickness of 5 mm was 14.2%.

[Brief description of drawings]

FIG. 1 is a schematic process diagram showing a glycol treatment method in a conventional polyester manufacturing process.

FIG. 2 is a schematic process diagram showing a method for producing a polyester according to the present invention.

Claims (3)

[Claims] 1. When a polyester is produced from a dicarboxylic acid and a dihydroxy compound by a process including an esterification step and a polycondensation step, the dihydroxy compound-containing distillate distilled in the polycondensation step has the following (a): ) To (c), and a method for producing a polyester, characterized by supplying the recovered dihydroxy compound and a polycondensation catalyst to the esterification step; (a) distillation step (b) filtration step (C) Decolorization process 2. The method for producing a polyester according to claim 1, wherein when the dihydroxy compound-containing distillate is treated, a treatment including a (d) iron removing step is performed in addition to the (a) to (c) steps. . 3. The method according to claim 1, wherein after the dihydroxy compound-containing distillate is treated, the polycondensation catalyst is added to the recovered dihydroxy compound containing the polycondensation catalyst to adjust the catalyst content. Method for producing polyester.