JPH11302367A - Production of polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for industrially and advantageously producing a high-quality polyester by reutilizing a distilled glycol produced in each step as a part or the total amount of raw materials. SOLUTION: Terephthalic acid and a glycol are fed to esterification reactors 3 and 4 to carry out the esterification reaction and the resultant ester low polymer is then fed to polycondensation reactors 11 to 13 to conduct the polycondensation. Thereby, a polyester is produced. A distillate discharged from the polycondensation reactors 11 to 13 or esterification reactors 3 and 4 and consisting essentially of the glycol as a cooling liquid for condensing a gas produced in the esterification reaction is sprayed into a partial condenser 5. The resultant partial condensate is filtered to separate undissolved substances. The separated filtrate is subsequently reutilized as a part or the total amount of the raw materials.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing polyester, and more particularly to terephthalic acid (hereinafter referred to as TP).
A. ) And glycols such as ethylene glycol (hereinafter referred to as EG) and 1,4-butanediol (hereinafter referred to as BD) are minimized, and
The present invention relates to a method for producing polyester with stable quality.

[0002]

2. Description of the Related Art In the case of polyester, for example, polyethylene terephthalate, TPA and EG slurried by a slurry mixer are sent to an esterification reactor to perform an esterification reaction to form a polyester low polymer, and then a polycondensation reactor. And is produced by a polycondensation reaction.

Here, in order to improve the reactivity, EG is usually supplied in an amount of 1.1 to 2.0 times the amount of TPA, and catalyst components and additives added in each reaction are added. Most of the polyesters are used after being dissolved in EG, and in the process, EG in excess of the theoretical amount of EG contained in the polyester exists. As a result, it is necessary to extract a part of the EG from the esterification reactor or the polycondensation reactor, and the EG (hereinafter referred to as distillate EG) contains water, a low-boiling substance, and a polyester low polymer entrained by droplets. Will be included.

[0004] In addition, a polyester polymerization facility usually includes a distillate EG generated from the process and an EG that is additionally supplied.
Is collectively purified into high-purity EG, and the high-purity EG purified here is reused as a raw material. However, it is practically impossible to make the yield in the recovery step 100%, and the amount of EG used increases,
It was one of the causes of cost increase.

[0005] In addition, the substances removed in the recovery of EG are:
In addition to water and low-boiling substances and polyester low polymers,
High-melting polymers, catalysts, modified polymers of additives, etc.
The use amount of A and EG is greatly increased, which is a major cause of cost increase.

Hitherto, various studies have been made in order to solve the cost increase factor. One of the main methods for solving this problem is a method in which distillate EG generated from an esterification reactor or a polycondensation reactor is directly reused as a raw material without going through a recovery / purification step (Japanese Unexamined Patent Publication (Kokai) No. 53-53). 126
No. 096, JP-B-59-48058). With this method, it is possible to solve the cost problem described above. However, the above-mentioned distillate EG contains solid or semi-solid high-melting components (hereinafter referred to as high-melting substances), and these components are reacted in an esterification reactor or a polycondensation reactor. The polyester does not dissolve therein and becomes a foreign substance, which deteriorates the quality of the polyester, and hence the quality of the polyester, which is produced as a raw material, because the polyester is present as a foreign substance. These solids,
There is a method of removing with a filter before entering the reactor, but those with a filtration accuracy below are not removed, and if the filtration accuracy is fine, filter clogging is likely to occur due to a large amount of low polymer, and maintenance There is a problem.

As a method for solving this problem, Japanese Patent Application Laid-Open
No. 241368 proposes a method for separating solid or semi-solid matter in a distillate EG by utilizing a specific gravity difference. However, this method has a problem that the amount of TPA or EG used cannot be significantly reduced because undissolved low polymer present in a large amount in the distilled EG is also separated and removed.

[0008]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, recycles the distillate glycol generated from each step as a part or all of the raw material, and industrially provides a high-quality polyester. It is an object of the present invention to provide a manufacturing method.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, the distillate glycol generated from each step is directly converted into a raw material without passing through a distillation purification step, and is significantly reduced. It is always manufactured by dissolving the low polymer contained in the generated distillate by the heat of condensation of the high-temperature esterification reaction gas, and then filtering and separating the high-melting-point product while reducing the cost. The inventors have found that the quality of polyester can be stabilized, and have completed the present invention.

That is, the present invention relates to a polyester obtained by supplying terephthalic acid and glycol to an esterification reactor to carry out an esterification reaction, and then supplying the resulting ester low polymer to a polycondensation reactor for polycondensation. In the method for producing a distillate, a distillate mainly composed of glycol discharged from the polycondensation reaction device and / or the esterification reaction device is sprayed as a cooling liquid for condensing the gas generated by the esterification reaction into the condensing device. A method for producing a polyester, characterized in that the obtained fractionated liquid is filtered to separate undissolved substances and then reused as part or all of the raw material.

[0011]

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

The polyester of the present invention refers to a polyester containing TPA as a dicarboxylic acid component and EG, BD or the like as a glycol component, and is preferably polyethylene terephthalate or polybutylene terephthalate.

[0013] Some of the acid components include, for example, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 2,6-naphthalenedicarboxylic acid, adipic acid,
Use dicarboxylic acids such as sebacic acid, or use trimethylene glycol, hexamethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, 1,4-cyclohexanedimethanol, ethylene oxide adduct of bisphenol II, etc. as part of the glycol component. And may be used for copolymerization. The method for producing the polyester of the present invention may be a continuous type or a batch type.

Next, the method for producing the polyester of the present invention will be described with reference to the drawings.

FIG. 1 is a schematic process diagram showing an embodiment of the present invention. In FIG. 1, TPA and EG are supplied to a slurry mixing tank 1 at a constant molar ratio to form a slurry. This slurry is sent to the esterification reactor 3 by the pump 2. In the method shown in FIG. 1, TPA and EG are slurried.
PA and EG may be separately supplied to the esterification reactor 3. In the esterification reactor 3, the reaction is preferably performed at 230 to 270 ° C. and 100 kPa to 400 kPa to a predetermined reaction rate, and then sent to the second-stage esterification reactor 4 until the ester conversion reaches the predetermined reaction rate. The reaction is carried out.

The gas generated in the esterification reactors 3 and 4 enters the decomposer 5 and is cooled and condensed by the EG liquid distilled from the polycondensation step sprayed from the shower nozzle 6. The EG liquid distilled from the polycondensation step is usually supplied as a liquid at 30 ° C. or lower,
It is sprayed in the decomposer 5 and receives heat from the gas generated during the esterification reaction to raise the temperature to about 130 to 230 ° C. It enters the rectification tower 9 together with the reaction product gas. In the rectification column 9, low-boiling substances and water are separated and discharged from the top of the column, and EG (hereinafter, referred to as recovered EG) is extracted from the bottom of the column. The recovered EG is supplied to the slurry mixer 1 as a part of the raw material by the recovered EG supply pump 10.

On the other hand, in the decomposer 5, the low polymer is completely dissolved by the high-temperature EG, and is discharged together with the EG as a decomposed liquid (hereinafter referred to as a decomposed EG). And supplied to the slurry mixer 1 as a part of the raw material through the EG filter 8. At this time,
High melting point components such as undissolved polyester high melting point polymer and catalyst present in the decomposed EG, and modified polymers of additives,
The separated EG filter 8 completely separates and removes. The object of the split EG filter 8 used here is an EG having a high temperature of 130 ° C. to 230 ° C. In consideration of the danger of burns during clogging removal work and the maintenance work, a self-cleaning regeneration filter system is used. Is best.
Specifically, SUP manufactured by Yak Filter Systems Co., Ltd.
ER-Z or # 200-50A manufactured by IM Co., Ltd. can be used. In addition, the filtration accuracy of the filter is selected in consideration of the allowable size of the undissolved material and the cost of equipment.

When the temperature of the shrinkage EG is lower than 130 ° C., a part of the low polymer is not dissolved, and when the temperature exceeds 230 ° C., a side reaction such as formation of a large amount of a glycol dimer is caused. Absent. Further, the temperature of the divided EG can be adjusted by the spray amount of the distilling EG liquid supplied to the divided unit 5 or the pressure of the divided unit 5. As described above, since the high melting point component is completely removed from the reduced EG, the slurry mixer 1 and the esterification reactors 3 to 4 are used as a part of the raw material.
And a high-quality low polymer can be obtained.

Here, a device for directly extracting the reduced EG from the divider 5 has been described. However, a device for circulating the reduced EG to the divider 5 and extracting a part thereof may be used. Good. Further, the distillate EG of the polymerization step may be directly added to the condensed EG circulated to the condensing device 5 and sprayed to the condensing device 5.

The low polymer thus obtained is sent to a polycondensation reaction apparatus in the next step. Polycondensation reactors 11-13
Then, preferably 250 to 295 ° C., 0.05 to 10 k
When the temperature and the degree of vacuum are gradually increased within the range of Pa, polyester is synthesized.

The polycondensation apparatuses 11 to 13 are provided with wet condensers 14 to 16, respectively. Distilled EG generated by the polycondensation reaction is condensed here and stored in circulation EG tanks 17 to 19, respectively. At the same time, it is sent again to each of the wet condensers 14 to 16 as a circulation EG, and is used as a spray liquid for condensing the distillate EG. Each of the wet condensers 14 to 16 is connected to a vacuum generator by a pipe.

Here, the pressure loss caused by the vapor pressure of low boiling components such as water contained in the distillate EG in the wet condenser 16 attached to the polycondensation reactor 13 requiring a high degree of vacuum is particularly required. In order to prevent the increase and prevent the adhesion of low polymers generated by entrainment to various devices and pipes, a new EG
Is preferably added to the circulation EG storage tank 19.

In the circulating EG storage tank 19, a part is extracted so that the liquid level is constant, and is sent to the circulating EG storage tank 18. The distillate EG sent to the circulation EG storage tank 18 is used as a spray liquid of the wet condenser 15. Also, the circulation EG
A part is withdrawn so that the liquid level of the storage tank 18 is constant, and sent to the circulation EG storage tank 17. Circulating EG storage tank 17
Is sent to the wet condenser 14 as a spray liquid. A part of the liquid level of the circulating EG storage tank 17 is also extracted so as to have a constant height, and is supplied by the distilling EG transfer pump 20 to the condensing device 5 in the esterification step.

In FIG. 1, the transfer destination from the distilling EG transfer pump 20 is shown by a single series of decomposers, but it may be transferred to a plurality of series of decomposers. Further, a part of this can be transferred to a conventional distillation purification step.

[0025]

Next, the present invention will be described specifically with reference to examples. In Examples and Comparative Examples, a polyester continuous production apparatus was used in both the esterification step and the polycondensation step.

Example 1 Using the manufacturing apparatus shown in FIG.
G and EG to be added are controlled so that the total is always 22 kg / h.
, And supplied to the esterification reactor 3 via the pump 2. Then, an esterification reaction and a polycondensation reaction were performed under the conditions shown in Table 1. The distillate EG generated in the polycondensation reaction step is supplied to the total amount decomposer 5, and the decomposed EG filter 8 is a self-cleaning regenerative filter having a filtration accuracy of 100 μm (SU manufactured by Yak Filter Systems Co., Ltd.).
PER-Z) was used. The pressure of the decompressor 5 is 10
At 0 kPa, the temperature of the split solution was 170 ° C.

[0027]

[Table 1]

Operation was continued under these conditions for one month, but the process was stable. In addition, as a result of a yarn production test using the obtained polyester, there was no problem with yarn breakage during spinning or drawing, strong elongation, dyeability, etc., and a yarn of the same quality as the conventional product was obtained. .

Comparative Example 1 An operation was carried out under the same reaction conditions using the same production equipment as in Example 1 except that the distillate EG solution from the polycondensation reaction was directly supplied to the slurry mixer. Note that a wire mesh filter having a filtration accuracy of 800 μm was used for filtering the polymerization distillate. The operation was continued for one month under these conditions, during which time the filter of polymerization distillate EG liquid was clogged 32 times, and labor was required for replacing and cleaning the filter. Other steps were stable. A yarn-making test was performed using the obtained polyester. As a result, there was no problem with the strength and elongation and the dyeability, and the same quality yarn as the conventional product was obtained. There were many 35 times.

[0030]

According to the present invention, the distilled glycol can be reused without being purified by distillation, and a high-quality polyester can be stably produced for a long period of time.

[Brief description of the drawings]

FIG. 1 is a schematic process chart showing one embodiment of a method for producing a polyester of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slurry mixing tank 2 Slurry supply pump 3-4 Esterification reactor 5 Splitter 6 Shower nozzle 7 Reduced EG supply pump 8 Reduced EG filter 9 Rectification tower 10 Recovery EG supply pump 11-13 Polycondensation reactor 14 -16 Wet condenser 17-19 Circulating EG storage tank 20 Distillation EG transfer pump

Claims (4)

[Claims] 1. A method for producing a polyester by supplying terephthalic acid and glycol to an esterification reactor to carry out an esterification reaction, and supplying the resulting ester low polymer to a polycondensation reactor for polycondensation. In the above, the distillate mainly composed of glycol discharged from the polycondensation reaction device and / or the esterification reaction device was sprayed into a condensing device as a cooling liquid for condensing a gas generated in the esterification reaction, and the obtained product was obtained. A method for producing a polyester, characterized in that the separated liquid is filtered to separate undissolved substances and then reused as part or all of the raw material. 2. The method according to claim 1, wherein the glycol is ethylene glycol or 1,4-butanediol. 3. The method for producing a polyester according to claim 1, wherein the temperature of the split solution is 130 ° C. to 230 ° C. 4. The method for producing a polyester according to claim 1, wherein the filtration separation method is a method using a self-cleaning regeneration type filter.