JP2006249394A - Method for producing polybutylene terephthalate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing polybutylene terephthalate, capable of exchanging spray nozzles of a condenser without deteriorating a degree of vacuum during polycondensation reaction and capable of being continuously operated for a long period. <P>SOLUTION: In this method for producing the polybutylene terephthalate, the reduced-pressure polycondensation reaction is conducted by a reaction apparatus having the wet condenser 2 which has a plurality of the spray nozzles 3, 4, a seal tank 7, an ejector 12 which uses 1,4-butanediol as a vapor, and a hot well 15, wherein the spray nozzles 3, 4 are changeable during operation and comprise two or more kinds of which the spray patterns are different from each other. Therefore, the polybutylene terephthalate is continuously produced. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  In the present invention, the spray nozzle can be replaced even during the polycondensation reaction without deteriorating the degree of vacuum in the reactor, and the polycondensation reaction can be achieved by the shape, combination and baffle of the spray nozzle in the wet condenser. It is related to a continuous polybutylene terephthalate production method that can realize stable decompression polycondensation reaction and can produce stable polybutylene terephthalate of stable quality over a long period of time. is there.

  Since polybutylene terephthalate has excellent physical and chemical properties, it is widely used in various applications such as fibers, films, and other molded articles. In addition, since it is excellent in mechanical properties such as strength and elastic modulus, heat resistance and the like, it is widely used particularly as an engineering plastic.

  As one method for producing such polybutylene terephthalate, an esterification step for obtaining bishydroxybutyl terephthalate and its low polymer by esterification of terephthalic acid and 1,4 butanediol, and bishydroxybutyl terephthalate and its low polymerization There is a direct polymerization method comprising a polycondensation step for obtaining a polybutylene terephthalate having a high degree of polymerization while distilling excess 1,4 butanediol under high temperature and high vacuum.

  In this polycondensation step, a deaeration device is required to reduce the pressure in the polycondensation reaction apparatus, and a liquid ring pump, an oil rotary pump, a roots pump, a steam ejector, etc. are generally used.

  Among them, a combination of a steam ejector, a condenser, and a hot well is widely used because the apparatus is simple and easy to maintain (Patent Document 1).

  However, in the steam ejector using water vapor, there is a problem that tetrahydrofuran generated in the polycondensation reaction of polybutylene terephthalate is collected by a condenser and finally flows into waste water.

  In order to solve this problem, the raw material 1,4 butanediol vapor is used in the ejector instead of water vapor, and tetrahydrofuran is separated from 1,4 butanediol in the hot well and used as repeated vapor for waste water. It is known to reduce the internal load (Patent Document 2).

  However, in this method, although the load on the environment is reduced, in the long-term operation by continuous polymerization, solid substances such as oligomers entrained together with 1,4 butanediol from the polycondensation reactor are sprayed on the wet condenser. There have been problems such as clogging of the circulating liquid feed piping of 1,4 butanediol used for circulation as the nozzle and its spray liquid and the heat exchange part of the condenser, resulting in a decrease in the flow rate of the spray.

  In order to solve this problem, it is known to install a centrifuge in the circulation pipe of 1,4 butanediol to remove solid substances such as oligomers (Patent Document 3).

However, in this method, although solids can be removed, since the spray nozzle of the wet condenser is single and no baffle is installed, the collection of tetrahydrofuran is insufficient and the degree of vacuum is deteriorated. The ejector is overloaded, which ultimately causes problems such as lowering the intrinsic viscosity, deterioration of color tone, and generation of foreign matter in the product polymer quality obtained, or when installing a centrifuge or a spray nozzle. When clogged, the degree of vacuum in the polycondensation reaction apparatus had to be returned to normal pressure once, which had problems such as having a significant effect on polymer quality.
JP-A-57-135828 Japanese Patent Application Laid-Open No. 2004-169013 Japanese Patent Publication No. 10-50448

  In the present invention, the spray nozzle can be replaced without deteriorating the vacuum degree even during the polycondensation reaction, and efficiently collects 1,4 butanediol and tetrahydrofuran in a wet condenser. To provide a method for continuously producing long-term stable polybutylene terephthalate with stable quality by collecting with a filter in the circulation pipe so as not to cause blockage of spray or circulation pipe. It was made for the purpose.

As a result of intensive studies to achieve the above object, the present inventors have reached the present invention.
That is, the present invention
(1) In the method for producing polybutylene terephthalate, a wet condenser having a plurality of two or more spray nozzles having different spray patterns that can be replaced during operation, a seal tank, an ejector using 1,4 butanediol as steam, and A method for producing polybutylene terephthalate, characterized by continuously performing a reduced pressure polycondensation reaction in a reaction apparatus having a hot well,
(2) The method for producing polybutylene terephthalate according to (1), wherein the spray pattern of the spray nozzle of the wet condenser is a full cone type or a holo cone type,
(3) The method for producing polybutylene terephthalate according to (1) or (2), wherein the full cone type spray nozzle installation position of the wet condenser is located below the installation position of the hollow cone type,
(4) The method for producing polybutylene terephthalate according to any one of (1) to (3), wherein there is a baffle on the side of the wet condenser.
(5) The method for producing polybutylene terephthalate according to any one of (1) to (4), wherein a filter is provided before and after the seal tank, and the filter is 3 to 100 mesh.
(6) The polybutylene terephthalate according to any one of (1) to (5), wherein 1,4 butanediol used in the spray liquid in the wet condenser is directly reused as a raw material without being purified. Manufacturing method,
Consists of.

  According to the method for producing polybutylene terephthalate of the present invention, the spray nozzle can be replaced even during the polycondensation reaction, and 1,4 butanediol and tetrahydrofuran are collected efficiently in a wet condenser, and other oligomers, etc. Since solids can be collected by a filter in a circulation pipe and a stable reduced pressure state can be realized, polybutylene terephthalate having stable quality can be obtained in the long term.

  Hereinafter, the present invention will be described in detail.

  The polybutylene terephthalate produced in the present invention is a high molecular weight thermoplastic polyester having an ester bond in the main chain using terephthalic acid as an acid component and 1,4-butanediol as a diol component. Components include cyclophthalic dicarboxylic acids such as isophthalic acid, orthophthalic acid, naphthalene dicarboxylic acid, diphenyldicarboxylic acid, sodium sulfoisophthalic acid, cyclohexanedicarboxylic acid, decalin dicarboxylic acid, oxalic acid, malonic acid, succinic acid , Sebacic acid, adipic acid, aliphatic carboxylic acid such as dodecanedioic acid, etc., and other diol components specifically include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol , Neopentyl glycol, 1,6-hexanediol, polypropylene glycol, polytetramethylene glycol and other aliphatic diols, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and other alicyclic diols, 2,2 -Aromatic diols such as -bis (4'-hydroxyphenyl) propane can also be used in part. These copolymer components are each preferably 40 mol% or less based on terephthalic acid or 1,4-butanediol.

 Although there is no restriction | limiting in particular about the continuous polymerization method in the manufacturing method of the polybutylene terephthalate of this invention, It is preferable to superpose | polymerize continuously using a series continuous tank reactor. Specifically, a raw material mainly composed of a diol component and a dicarboxylic acid component is prepared as a slurry, the slurry is supplied to an esterification reaction tank, an esterification reaction is performed, and an oligomer as an esterification reaction product obtained is preliminarily prepared. The polycondensation reaction can be carried out through the polycondensation reaction tank and the final polymerization machine. The obtained polybutylene terephthalate is preferably extracted in the form of a strand from the bottom of the final polymerization machine through a die, water-cooled with cooling water, and then cut with a pelletizer to form pellets or other granular materials.

  In a preferred embodiment of the present invention, the charged molar ratio of the diol component to the dicarboxylic acid component is preferably 1.0 to 2.0, and more preferably 1.2 to 1.8.

  The type of the esterification reaction tank used in the present invention is not particularly limited.For example, a vertical stirring complete mixing tank, a vertical heat convection mixing tank, a shelf-type reaction tank, and the like can be used. When a plurality of reaction vessels are used, a plurality of vessels of the same kind or different types can be used in series.

  It is preferable to attach a rectifying column at the distillation outlet of the esterification reaction tank, and water and tetrahydrofuran and 1,4-butanediol in the distillate can be separated by the rectifying column. A distillate containing water and tetrahydrofuran as main components is distilled from the top of the rectification column, condensed in a condenser, and sent to a recovery step. The distillate containing 1,4 butanediol as a main component is condensed at the bottom of the rectifying column and is returned to the esterification reaction tank. At that time, in order to adjust the molar ratio in the esterification reaction tank, a part of 1,4 butanediol returned to the esterification reaction tank may be distilled out of the system. In this case, the distillate having 1,4-butanediol distilled as a main component can be used again as a raw material, and may be used after rectification or may be used as it is.

As the esterification catalyst used in the present invention, an organic titanium compound is preferably used. The organic titanium compound preferably used in the present invention is
(R1O) nTi (OR2) 4-n
(Wherein R1 and R2 are aliphatic, alicyclic or aromatic hydrocarbon groups having 1 to 10 carbon atoms, and n is a number of 0 to 4 (including decimal numbers)) and Represented by condensates.

  Specifically, the organic titanium compound used in the present invention includes titanic acid methyl ester, tetra-n-propyl ester, tetraisopropyl ester, tetra-n-butyl ester, tetraisobutyl ester, tetra-tert-butyl ester, tetra- Examples include 2-ethylhexyl ester, tetraoctyl ester, phenyl ester, benzyl ester, tolyl ester, and mixed esters thereof. Among these, tetra-n-propyl ester (tetra-n-propyl titanate), tetraisopropyl ester (tetra-isopropyl titanate), and tetra-n-butyl ester (tetra-n-butyl titanate) of titanic acid are available at low cost. The tetra-n-butyl ester of titanic acid (tetra-n-butyl titanate) is particularly preferably used. These organic titanium compounds may use only 1 type and can use 2 or more types together. Further, the same species may be used during the esterification reaction and polycondensation, or different organic titanium compounds may be used. Further, this organic titanium compound may be added together with a suitable organic solvent. Examples of the organic solvent in this case include isopropanol, n-butanol, isobutanol, ethylene glycol, propylene glycol, and 1,4-butanediol. In consideration of the influence on quality, etc., 1,4-butanediol is preferable. Used.

  The addition amount of the organic titanium compound as an esterification catalyst is preferably 30 to 75 ppm, preferably 35 to 70 ppm, based on the total weight of the polymer in terms of Ti atom. If the amount added is less than 30 ppm, the esterification rate may be slow, and the secondary property of tetrahydrofuran may increase. On the other hand, if it exceeds 75 ppm, problems such as an increase in polymer solution haze may occur. Absent.

  The method for adding the esterification catalyst is not particularly limited, but specifically, a method for directly supplying to the esterification reaction tank, a method for simultaneously adjusting the slurry, and a line for supplying the raw slurry to the esterification reaction tank. Examples include a method of supplying with a metering pump.

  In the present invention, when an organic titanium compound is added as a polymerization catalyst, it is preferable to further add an organic titanium compound after the reaction rate of the dicarboxylic acid component is set to 98% or more, preferably 98.5% or more. If a polymerization catalyst is added at a reaction rate of the dicarboxylic acid component of less than 98%, problems such as an increase in polymer solution haze may occur, which is not preferable.

  The esterification reaction in the present invention is carried out in the presence of an organic titanium compound, the reaction temperature is preferably 210 to 260 ° C, more preferably 220 to 250 ° C, and the pressure is preferably 13.3 to 93 kPa, more preferably 20 to 87 kPa. It is mentioned as preferable conditions to carry out under reduced pressure. The reaction rate of the dicarboxylic acid component discharged from the esterification reaction tank is preferably 90 to 97.5%, more preferably 92 to 97%.

  In the present invention, when a preliminary polycondensation reaction tank is used, the type thereof is not particularly limited. For example, a vertical stirring polymerization tank, a horizontal stirring polymerization tank, a thin film evaporation polymerization tank, and the like can be used.

  The preliminary polycondensation reaction tank may be a single tank or a plurality of tanks in which a plurality of tanks of the same kind or different kinds are connected in series. The reaction temperature of the preliminary polycondensation reaction is preferably 210 to 270 ° C., more preferably 220 to 260 ° C., and the pressure is preferably 7 kPa or less, more preferably 1 to 6 kPa.

  In the present invention, when the final polymerization machine is used, the type thereof is not particularly limited. For example, a horizontal single-axis reactor, a horizontal twin-axis reactor, or the like can be used.

  The reaction temperature of the final polymerization machine is preferably 220 to 260 ° C., more preferably 230 to 250 ° C., and the pressure is preferably 1.3 kPa or less, more preferably 0.67 kPa or less. .

  In the present invention, a distillate mainly composed of excess 1,4 butanediol distilled from a prepolymerization tank and / or a final polymerization machine is condensed in a wet condenser, and then a seal tank installed in the lower part thereof. The water is stored in the condenser, cooled by a condenser in the circulation pipe, and then circulated as a spray. In this case, specifically, the apparatus shown in FIG. 1 is used.

  A plurality of wet condenser spray nozzles are preferably installed, and more preferably 2 to 4 spray nozzles. By installing multiple spray nozzles at different heights, the spray area can be greatly increased, the distillate can be condensed efficiently, and one of the multiple spray nozzles is blocked by solid matter. When maintenance is required, spraying can be continued with the remaining spray nozzles during the maintenance. When the number is less than two, only one type of spray pattern of the spray nozzle described below can be installed. When the number is more than four, the cost and maintenance are disadvantageous.

  Moreover, although the spray pattern of a spray nozzle includes a flat, full cone, holo cone, solid, air atomizing type, etc., a full cone type (omnidirectional) and a holo cone type (liquid film) are preferably used.

  As for the installation positions of the plurality of injection nozzles, the upper stage is preferably a holocorn type and the lower stage is a full cone type, and a distillate from the polycondensation step (1,4 butanediol, tetrahydrofuran is selected depending on the combination of the installation positions. Etc.) is mostly condensed by an omnidirectional full cone type spray located in the lower stage, and the distillate that could not be collected partially is a liquid film type holo cone located in the upper part. Can be fully condensed with a type of spray.

  In addition, it is preferable to install at least one baffle inside the wet conditioner, and it is more preferable to install in the vicinity of the inlet where the distillate from the polycondensation reaction apparatus is introduced into the wet condenser. By installing at the inlet, the sprayed 1,4 butanediol flows through the baffle, creating a liquid film locally at the inlet and strengthening the condensate of the distillate from the polycondensation reactor. can do. Further, the spray liquid cooled to about 40 ° C. in the condenser in the circulation pipe is sprayed on the pipe connecting the polycondensation reaction apparatus kept at about 250 ° C. and the wet condenser to prevent precipitation of oligomers and the like, and heat distortion occurs. It is possible to prevent the spray liquid from flowing back to the polycondensation reaction apparatus through the piping.

  In addition, solid substances such as oligomers entrained from the polycondensation reaction are mixed into the 1,4-butanediol that has been circulated over a long period of time, and the spray nozzle, circulation piping, and condenser are clogged. It is necessary to install at least one filter before and after the seal tank, and it is preferable to install one filter on each of the upper part of the seal tank and the secondary side of the circulation pump from the seal tank.

  About the opening of the filter to install, it is required that it is 3-100 mesh, Preferably it is 5-50 mesh. In the case of 100 mesh or more, solid substances such as oligomers are clogged immediately and need to be replaced each time. If it is smaller than 3 mesh, there is a problem that the sublimate is not sufficiently removed and the condenser or spray nozzle is blocked. .

  In addition, when the degree of vacuum deteriorates during the polycondensation reaction, the spraying of one spray nozzle is stopped, it is separated from the vacuum system of the polycondensation reaction tank, and only the spray part can be replaced. During the reaction, only the spray portion can be replaced in a short time, and the reaction can be continued.

  Further, 1,4 butanediol, which is circulated and used as a spray for a wet condenser, can be extracted and reused as a raw material.

  In addition, one or more filters can be attached to the piping connecting the reaction vessels used in the present invention or from the final polymerization machine to the discharge port for the purpose of filtering foreign substances in the polymer. Includes a pipe between the prepolymerization tank, a pipe between the prepolymerization tank and the final polymerization machine, and a pipe from the final polymerization machine to the discharge port. In addition, the filter type is not particularly limited, but examples include pleated cylindrical type, flat cylindrical type, tube type, basket type, etc., and the opening is preferably 1 to 100 μm, preferably 2 to 50 μm. Are more preferably used. In addition, it is preferable to install two or more filters in parallel in one place for easy replacement.

  In the production of PBT by the method of the present invention, conventional additives such as ultraviolet absorbers, heat stabilizers, lubricants, mold release agents, colorants including dyes and pigments, etc., are within the range not impairing the object of the present invention. 1 type (s) or 2 or more types can be added.

The present invention will be described more specifically with reference to the following examples. However, the present invention is not limited to the following examples. In the examples, each measured value was determined as follows.
(1) Color tone (color coordinate b value)
The color coordinate b value of Hunter's color difference formula in the Lab color system described in Reference 1 of JIS Z 8730 was measured by a reflection method using a color tester SC-3-CH type manufactured by Suga Test Instruments Co., Ltd. The measurement is allowed to stand for 4 hours or more after the power is turned on, and after sufficiently stabilizing the apparatus in advance, the sample pellet is filled to the cut-off position in a measurement cell having an inner diameter of 60 mm, a depth of 30 mm, and a light receiving portion made of quartz glass. Measurements were made by changing the direction by 90 degrees in four directions, and the average value was taken as the value.
(2) Intrinsic Viscosity Using a Ubbelohde viscometer and o-chlorophenol, the solution viscosities of polybutylene terephthalate at concentrations of 1.0 g / dl, 0.5 g / dl and 0.25 g / dl were measured at 25 ° C. The viscosity number was extrapolated to a concentration of 0.
(3) Tetrahydrofuran concentration in the ejector-containing vapor A part of the vapor is extracted from the pipe connecting the wet condenser and the ejector, cooled to a liquid, and then 1,4-dioxane is used as an internal standard by Hitachi gas chromatography G-3500. Tetrahydrofuran content was determined using a calibration curve prepared in advance as a liquid.

Example 1
A production apparatus in which a slurrying tank, a slurry storage tank, one esterification reaction tank, one preliminary polymerization tank, one final polymerization machine, and a pelletizer were used in series was used. As a decompression device for the prepolymerization tank and the final polymerization machine, an ejector using 1,4 butanediol vapor was used, and a wet condenser, a seal tank, and a condenser were installed between the polymerization reaction tank and the ejector. Also, inside the wet condenser, one baffle is installed at the connection with the polymerization machine, and four spray nozzles that can be replaced during operation are the upper two for the hollow cone type and the lower two for the full cone type. One 10-mesh filter was installed at the top of the seal tank, and one 10-mesh filter was installed at the circulation pump from the seal tank. First, both raw materials were supplied to the slurrying tank at a ratio of 692 parts by weight of 1,4 butanediol with respect to 754 parts by weight of terephthalic acid, and the slurry was prepared by adjusting the slurry. The slurry was transferred to a slurry storage tank having a constant temperature of 0 ° C., and the slurry was supplied from the slurry storage tank by a pump to a fully mixed tank type esterification reaction tank having a rectifying column at a constant rate of 1446 parts by weight / hour. A 1,4-butanediol solution of n-butyl titanate (TBT) was continuously fed to the esterification reactor at 4 parts by weight / hour. The amount of TBT added is 56 ppm based on the total polymer weight in terms of Ti atoms.

  The reaction conditions of this esterification reaction tank were maintained at a temperature of 230 ° C. and a pressure of 73 kPa, a residence time of 1.8 hours, tetrahydrofuran and water were distilled from the top of the rectification column, and 1,4 butanediol was rectified. Refluxed from the tower bottom. Further, an oligomer having a reaction rate of 95% of the dicarboxylic acid component was obtained in this esterification reaction tank.

  Subsequently, this oligomer was supplied to the prepolymerization tank by a gear pump, and a 1,4 butanediol solution having a concentration of 10% TBT was added at 4 parts by weight / hour (the addition amount of TBT was based on the total weight of the polymer in terms of Ti atoms). 56 ppm). The reaction was carried out at a temperature of 245 ° C. and a pressure of 3.3 kPa, and a residence time of 2 hours, to obtain an oligomer having a reaction rate of 99.2% of the dicarboxylic acid component and an intrinsic viscosity of 0.30.

  This oligomer was supplied to the final polymerization machine (horizontal biaxial reactor) and reacted at a temperature of 240 ° C., a pressure of 200 Pa, and a residence time of 1.5 hours to obtain a polymer. This polymer was discharged in a strand from the system through a die by a gear pump, cooled by cooling water, and pelletized by a pelletizer.

Under the above conditions, the continuous operation time until the spray nozzle of the wet condenser was clogged and the spray flow rate was reduced without maintenance was measured. As a result, the continuous operation time was 340 Hr, the concentration of tetrahydrofuran in the vapor containing the ejector was 60%, the intrinsic viscosity of the obtained PBT polymer was 0.83, and the color tone (color coordinate b value) was 4.3. A good polymer was obtained. The results are shown in Table 1. Also, spray nozzles with reduced flow rates were replaced and maintained during the polycondensation reaction, and the polycondensation reaction could continue.
Examples 2-7
The same procedure as in Example 1 was performed except that the number, combination, presence / absence of baffles, and filter openings of the wet condenser were changed. The results are shown in Table 1.

Comparative Example 1
It was carried out in the same manner as in the example except that the spray nozzle was made into a hollow cone type with only one stage and the spray nozzle could not be replaced during the polycondensation reaction. Since the number of spray nozzles is small, tetrahydrofuran cannot be collected sufficiently, and it becomes a burden on the ejector, and only a polymer subjected to thermal decomposition with an intrinsic viscosity of 0.69 and a b value of 6.0 can be obtained. The operation time was as short as 100 hours. When the spray nozzle was replaced, the polycondensation reaction tank had to be returned to normal pressure once, and the polymer in the meantime had to be layered. The results are shown in Table 1.

Comparative Example 2
It implemented by the method similar to the comparative example 1 except having deleted the baffle in a wet condenser. Similarly, tetrahydrofuran could not be collected efficiently and the degree of vacuum was deteriorated. As a result, only a polymer having undergone thermal decomposition and having reduced intrinsic viscosity and increased b value was obtained. The results are shown in Table 1.

Comparative Example 3
The same method as in Comparative Example 2 was performed except that the input / output filter of the seal tank was deleted. During a long-term continuous operation, solid substances such as oligomers entrained by the polycondensation reaction are clogged with the spray nozzle, leading to a decrease in the flow rate of circulating 1,4 butanediol, thereby collecting tetrahydrofuran. Since the efficiency dropped and the ejector was loaded, the time during which it could be continuously operated without maintenance was as short as 50 hours, and the resulting polymer was also thermally decomposed. The results are shown in Table 1.

It is the schematic of the manufacturing apparatus of the polybutylene terephthalate which is one preferable embodiment of this invention.

Explanation of symbols

1. 1. Pipe connecting the polycondensation reactor and the wet condenser 2. Wet condenser Spray nozzle (hollow cone type)
4). Spray nozzle (full cone type)
5. Supply piping to ejector 6. Baffle 7. 7. Seal tank Filter 9. 9. Seal tank circulation pump 11. Condenser for seal tank 11.1, 4 Butanediol vapor Ejector 13. Barometric capacitor14. Vacuum pump 15. Hot well 16. Hot well circulation pump 17. Condenser for hot well

  When PBT is produced by this production method, the reduced pressure polycondensation reaction can be performed more stably than when produced by a conventional method, and even when the degree of vacuum deteriorates, the degree of vacuum in the system is affected. Since the degree of vacuum can be improved by exchanging only the spray nozzles without affecting the PBT, it is possible to obtain a PBT excellent in color tone and retention stability. Since the PBT obtained by the present invention is excellent in quality and retention stability, it can be usefully used for various automobile parts, electric / electronic parts and the like.

Claims (6)

In a method for producing polybutylene terephthalate, a wet condenser having a plurality of two or more spray nozzles having different spray patterns that can be replaced during operation, a seal tank, an ejector using 1,4 butanediol as steam, and a hot well are provided. A process for producing polybutylene terephthalate, which comprises continuously performing a polycondensation reaction under reduced pressure in a reactor having the same. 2. The method for producing polybutylene terephthalate according to claim 1, wherein the spray pattern of the spray nozzle of the wet condenser is a full cone type or a hollow cone type. 3. The method for producing polybutylene terephthalate according to claim 1, wherein the installation position of the full cone type spray nozzle of the wet condenser is lower than the installation position of the hollow cone type. 4. The method for producing polybutylene terephthalate according to any one of claims 1 to 3, wherein a baffle is provided on the side of the wet condenser. The method for producing polybutylene terephthalate according to any one of claims 1 to 4, wherein a filter is provided before and after the seal tank, and the filter is 3 to 100 mesh. The method for producing polybutylene terephthalate according to any one of claims 1 to 5, wherein the 1,4-butanediol used in the spray liquid in the wet condenser is directly reused as a raw material without being purified. .

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