JP2006070227A - Method for producing polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polyester by making a slurry by mixing directly a wet dicarboxylic acid cake, obtained from solid-liquid separation of a slurry mainly containing a dicarboxylic acid and water, with an alkylene glycol, and followed by a subsequent esterification reaction and polycondensation reaction, and to provide a method for producing a polymer having a good color tone and a stable color tone with little dispersion. <P>SOLUTION: This method comprise a step of hydrolyzing a dicarboxylic acid dimethyl ester to produce the dicarboxylic acid and a subsequent step of the esterification reaction with an alkylene glycol and the polycondensation reaction to produce the polyester, wherein an internal pressure of units, selected from a unit that handles the slurry containing the dicarboxylic acid and the water, a unit that handles the water to be applied for the hydrolysis reaction and a unit that handles the dicarboxylic acid, is maintained lower than an atmospheric pressure, and the slurry containing the dicarboxylic acid and the water, the water to be applied for the hydrolysis reaction and the dicarboxylic acid are kept under an inert gas atmosphere of oxygen density of ≤1% by volume. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing a polyester having a stable color tone (b value) with little coloring.

  Polyesters typified by polyethylene terephthalate (hereinafter sometimes abbreviated as PET) and polybutylene terephthalate (hereinafter sometimes abbreviated as PBT) have excellent properties and are used for clothing fibers, industrial fibers and films. It is widely used as various molded products such as bottles. In these polyester products, in order to obtain good quality, it is important to reduce the coloration of the polyester, manage the color tone in a stable state, and reduce the variation.

  On the other hand, as an industrial method for producing terephthalic acid, which is one of polyester raw materials, a liquid phase oxidation method of para-xylene, a hydrolysis method of dimethyl terephthalate, and the like are employed. In particular, for the latter method, there is a method in which polyester waste is chemically decomposed to recover monomers, and then a recycled polyester resin is integrated from polyester waste through the subsequent hydrolysis, esterification, and polycondensation steps. It has been proposed (see, for example, Patent Document 1), and a hydrolysis method of dimethyl terephthalate is employed as part of the process. As an industrial production method of polyester, a direct polymerization method in which terephthalic acid and a glycol component are directly esterified and then polycondensed is widely employed.

  Therefore, as a method for controlling the color tone of polyester in this production method, a method for controlling the esterification reaction rate has been proposed (see, for example, Patent Document 2). In addition, a method of changing the amount of phosphide compound added as a stabilizer has been proposed (see, for example, Patent Document 3). In addition, a method for maintaining a slurry of terephthalic acid and alkylene glycol in an inert gas atmosphere has been proposed (see, for example, Patent Document 4).

  However, regarding the method of producing terephthalic acid by hydrolyzing dimethyl terephthalate and then producing polyester by esterification reaction with alkylene glycol and polycondensation reaction, the color tone of the polyester is managed in a stable state, and variations are not observed. The current situation is that the problems to be reduced have not been completely solved.

JP 2003-119316 A JP-A-7-173268 JP-A-10-87808 JP 2003-128774 A

  In the present invention, a slurry mainly composed of a dicarboxylic acid and water is subjected to solid-liquid separation, and the obtained wet dicarboxylic acid cake is directly mixed with an alkylene glycol to form a slurry, and then the polyester is obtained by a subsequent esterification reaction and polycondensation reaction. It is an object of the present invention to provide a method for producing a polymer having a stable color tone with good color tone and little variation.

  The present invention deals with a slurry mainly composed of dicarboxylic acid and water in a method for producing a polyester by hydrolyzing a dicarboxylic acid dimethyl ester to produce a dicarboxylic acid, followed by an esterification reaction with an alkylene glycol and a polycondensation reaction. Among the apparatus, the apparatus that handles water supplied to the hydrolysis reaction, and the apparatus that handles dicarboxylic acid, the slurry in which the internal pressure of the apparatus is maintained under a pressure lower than atmospheric pressure, the slurry comprising the dicarboxylic acid and water, the hydrolysis This can be achieved by a polyester production method characterized in that water and dicarboxylic acid supplied to the reaction are kept in an inert gas atmosphere having an oxygen concentration of 1% by volume or less.

  According to the method of the present invention, it is possible to provide a method for producing a polyester having good hue, small variation in hue, and excellent transparency.

  The present invention relates to a method for producing a polyester by hydrolyzing a dicarboxylic acid dimethyl ester to produce a dicarboxylic acid, followed by an esterification reaction and a polycondensation reaction with an alkylene glycol. Hereinafter, the production method of the present invention will be specifically described with reference to FIGS. 1 and 2 showing an example of the process diagram.

  In the present invention, the dimethyl dicarboxylate is specifically preferably dimethyl aromatic dicarboxylate, more preferably dimethyl terephthalate as the main component or dimethyl 2,6-naphthalenedicarboxylate as the main component. . The main component means that it is 90 mol% or more of the total dicarboxylic acid dimethyl ester. Examples of other dimethyl dicarboxylates include dimethyl phthalate, dimethyl isophthalate, dimethyl naphthalenedicarboxylate other than 2,6 substitution, dimethyl adipate, dimethyl sebacate or dimethyl cyclohexanedicarboxylate.

Then, in the present invention, dicarboxylic acid dimethyl ester is hydrolyzed.
In the present invention, among the apparatus that handles the slurry mainly composed of dicarboxylic acid and water, the apparatus that handles the water supplied to the hydrolysis reaction, and the apparatus that handles the dicarboxylic acid, the internal pressure of the apparatus is maintained under a pressure below atmospheric pressure. In the apparatus, the slurry composed of the dicarboxylic acid and water, the water supplied to the hydrolysis reaction, and the dicarboxylic acid must be kept in an inert gas atmosphere having an oxygen concentration of 1% by volume or less. Here, the apparatus includes a tank such as a reaction tank and a storage tank, an apparatus having a non-tank shape such as a solid-liquid separator, and a pipe connecting these. In addition, in the production process of the polyester of the present invention, an apparatus that handles a slurry mainly composed of dicarboxylic acid and water, an apparatus that handles water supplied to the hydrolysis reaction, and an apparatus that handles dicarboxylic acid and dicarboxylic acid and alkylene glycol slurry are below atmospheric pressure. Even if the pressure is not maintained, it is more preferable to keep the oxygen concentration in a nitrogen atmosphere of 1% by volume or less. Further, even when the polyester polymerization process is not actually operated and the above-mentioned two kinds of slurry and water are stored under atmospheric pressure, the inert gas atmosphere with an oxygen concentration of 1% by volume or less is used. Is preferably maintained. An oxygen concentration exceeding 1% by volume is not preferable because it causes coloring of the polyester obtained by the influence of the mixed acid. In addition, “mainly” means that, in addition to these, monomethyl esters and the like that are not completely hydrolyzed may be contained within a range that does not affect the subsequent steps.

  In the present invention, dicarboxylic acid dimethyl ester is always maintained in an atmosphere maintained in an inert gas atmosphere during the production process, and preferably in a molten state. First, dicarboxylic acid dimethyl ester is supplied from the pipe: 11 to the hydrolysis reaction tank: 1 and the water from which dissolved oxygen has been removed by the deaerator: 5 is also added from the reaction water storage tank: 4 through the reaction water pipe: 12 The decomposition reaction tank is supplied to 1. In this case, the hydrolysis reaction may be batch or continuous.

  When the hydrolysis reaction is carried out batchwise, for example, when the hydrolysis reaction tank is at atmospheric pressure or lower when the raw material is charged, an inert gas atmosphere in which the oxygen concentration is 1 vol% or lower in the reaction tank before the raw material is charged. Need to be below.

  The inert gas is a gas that does not cause adverse effects during the reaction when the polyester is produced from the obtained dicarboxylic acid and alkylene glycol by hydrolyzing dicarboxylic acid dimethyl ester as in the present invention. It is. Specifically, nitrogen gas, argon gas, helium gas, or the like can be used, but nitrogen gas is preferable from an economical viewpoint. As the nitrogen gas, a commercially available gas can be supplied by a cylinder, or a gas produced by a pressure swing method, a cryogenic separation method, or the like can be used. These inert gases are sealed in the reaction tank at a pressure higher than atmospheric pressure, or purged out of the system while being continuously supplied, thereby maintaining the inside of the hydrolysis reaction tank at a low oxygen concentration and reducing the oxygen concentration. It becomes possible to make it 1 volume% or less.

  However, since the hydrolysis reaction is generally carried out in a closed system under high temperature and pressure, if the oxygen concentration is kept at 1% by volume or less in the raw material preparation stage before the start of the hydrolysis reaction, the inside of the reaction tank will be used later. It is unlikely that the oxygen concentration will exceed that value. When the hydrolysis reaction is carried out batchwise, generally the temperature is 230 to 260 ° C., the pressure is 2.9 to 5.0 MPa, and the time is 1 to 5 hours to hydrolyze the dicarboxylic acid dimethyl ester to the dicarboxylic acid and methanol. I can do it. The generated methanol is discharged from the hydrolysis tank to the outside. It is also preferable to collect this methanol as necessary and use it again when producing dicarboxylic acid dimethyl ester from dicarboxylic acid.

  When the hydrolysis reaction is carried out continuously, the inside of the hydrolysis reaction tank is purged out of the system while sealing or continuously supplying an inert gas in the hydrolysis reaction tank before starting the operation of the equipment. Usually, a method in which an inert gas atmosphere is used is used. However, the hydrolysis reaction is usually carried out under conditions of about 230 to 260 ° C. and 2.9 to 5.0 MPa, and is always under high pressure, and the dicarboxylic acid dimethyl ester and water supplied into the hydrolysis reaction tank are reduced. By maintaining the atmosphere under an oxygen concentration atmosphere, it is possible to maintain a low oxygen atmosphere state without supplying an inert gas into the hydrolysis reaction tank during continuous operation. For the hydrolysis reaction, a method of increasing the reaction rate by adding a catalyst is also appropriately used, but it may be omitted. The reaction time varies depending on the amount of dicarboxylic acid dimethyl ester supplied, but is approximately 1 to 5 hours.

  The slurry mainly composed of dicarboxylic acid and water generated in the hydrolysis step is depressurized to atmospheric pressure, passes through the pipe 14 as the dicarboxylic acid + water slurry, and is stored in the slurry tank (a): 2. Slurry tank (a): 2 and piping: 14 is a device that handles a slurry mainly composed of dicarboxylic acid and water, and is a device that is maintained under atmospheric pressure. Of the slurry tank (a) at a pressure higher than atmospheric pressure, or purged out of the system through the gas phase part of the slurry tank (a) while continuously supplying to the gas phase part of the slurry tank (a). It is possible to keep the oxygen concentration in the gas phase part at 1% by volume or less. Further, the slurry in the slurry tank (a) passes through the pipe 14 as the terephthalic acid + water slurry, is guided to the solid-liquid separator 3 and is separated into the solid and liquid, and as a result, is separated into the wet dicarboxylic acid cake and the filtrate. As a solid-liquid separation method, a usual method such as a centrifugal separation method or a filtration method can be adopted. Solid-liquid separator: 3 is also maintained under atmospheric pressure, and a slurry composed of dicarboxylic acid and water is processed, so that it is necessary to have a nitrogen atmosphere with an oxygen concentration of 1% by volume or less. In the solid-liquid separator, the inert gas is sealed into the solid-liquid separator vapor phase at a pressure higher than atmospheric pressure, or purged outside the system through the vapor-phase part of the solid-liquid separator while continuously supplying it. It is possible to keep the gas phase part of the solid-liquid separator at a low oxygen concentration.

  The separated wet dicarboxylic acid cake is transferred to the slurry adjusting tank (b): 6 with the alkylene glycol through the pipe: 15. The slurry adjusting tank (b) is also an apparatus that handles dicarboxylic acid and is maintained under atmospheric pressure, so it needs to be in a nitrogen atmosphere with an oxygen concentration of 1% by volume or less. It is possible to keep the gas phase part of the slurry adjustment tank (b) at a low oxygen concentration by sealing the inert gas into the gas phase part at a pressure higher than atmospheric pressure or purging it outside the system while continuously supplying it. It is. Furthermore, in this slurry preparation tank (b), an alkylene glycol is added to the obtained dicarboxylic acid cake to form a slurry. In order to make a slurry, the slurry can be easily made by mixing them together and carrying out normal stirring.

  The alkylene glycol used here is preferably an alkylene glycol having 2 to 12 carbon atoms, more preferably an alkylene glycol having 2 to 6 carbon atoms. Specific examples include ethylene glycol, 1,2-propanediol, trimethylene glycol, 1,4-butanediol, 1,6-hexanediol, diethylene glycol, triethylene glycol, and the like. More preferred are ethylene glycol and 1,4-butanediol. It is preferable to use alkylene glycol as a raw material for the polyester in the subsequent step.

  The filtrate separated by the solid-liquid separator is collected and guided to the reaction water storage tank 4 through the pipe 16. It is an economically preferable aspect that it is recovered and supplied again to the hydrolysis reaction tank as reaction water for the hydrolysis reaction. The reaction water storage tank 4 is also a device that handles water supplied to the hydrolysis reaction and is maintained under atmospheric pressure, and therefore needs to be in a nitrogen atmosphere with an oxygen concentration of 1% by volume or less. Specifically, the inert gas is sealed in the gas phase part at a pressure higher than atmospheric pressure, or purged out of the system while continuously supplying the gas to the gas phase part of the slurry adjustment tank (b): 6 with low oxygen. It is possible to keep the concentration.

  A part of the filtrate is purged, and water lost by the reaction and a deficient water generated by purging the filtrate are replenished with water from which dissolved oxygen in the water is removed by the deaerator 5. As the deaeration device, a vacuum type, a nitrogen blowing type, a membrane separation type, an ejector type, etc. are commercially available, but any type of deaeration device may be used.

  Other tower tanks such as a dicarboxylic acid dimethyl ester, a slurry mainly composed of dicarboxylic acid and water, and a reaction tank that holds reaction water and is maintained at a pressure lower than atmospheric pressure, are used as cushion tanks. It is desirable to keep the gas phase part of the slurry adjusting tank (b) at a low oxygen concentration by sealing it into the gas phase part at a pressure higher than the internal pressure of the tanks or purging outside the system while continuously supplying it.

  The slurry mainly composed of dicarboxylic acid and alkylene glycol in the slurry adjusting tank (b) is supplied to the esterification reaction tank: 7 for performing the esterification reaction continuously through the pipe: 19. The esterification reaction and the subsequent polycondensation reaction may be carried out by ordinary methods. The reaction may be batch or continuous. More specifically, for example, first, by a direct esterification reaction of a dicarboxylic acid such as terephthalic acid and an alkylene glycol such as ethylene glycol, the glycol ester of dicarboxylic acid and / or its lower A polymer is produced. Next, the reaction product is heated under reduced pressure in the presence of a polymerization catalyst and subjected to a polycondensation reaction until a predetermined degree of polymerization is obtained, thereby producing the desired aromatic polyester. Even when other polyesters other than the aromatic polyester are included, a method of producing a copolymer with the aromatic polyester or a production method generally known for the polyester and employing a method such as blending after polymerization should be adopted. Can do. The polycondensation step may be a method using a plurality of reaction tanks such as prepolymerization in the initial polycondensation reaction tank: 8 depending on the melt viscosity of the polyester and reacting until the predetermined polymerization degree is reached in the late polycondensation reaction tank: 9. . The obtained polyester is granulated into pellets with a chip cutter: 10 to obtain a polyester polymer product: 20. Under the present circumstances, b value is measured with a color difference meter about a part of product polyester.

  The oxygen concentration in the slurry tank (a): 2, the slurry adjustment tank (b): 6, the reaction water tank: 4, and other atmospheric and sub-atmospheric towers are purged from the tank gas phase part or the inert gas. It can be measured by installing an oxygen concentration meter in the middle of the line or in the middle of the line for supplying the inert gas into the tank. As the oxygen concentration meter, a galvanic cell type, a polarographic type, a thermomagnetic wind type and the like are commercially available, but any type of oxygen concentration meter may be used. In (1) to (3) of FIG. 2, the slurry tank (a): 2, the reaction water tank: 4, the slurry adjustment tank (b): 6 are described in more detail, nitrogen pipe: 21, nitrogen purge pipe: 22, oxygen Densitometer: The drawing in which 23 is installed is shown.

Examples in which the main component of the dimethyl ester of dicarboxylic acid is dimethyl terephthalate and the main component of the alkylene glycol is ethylene glycol are shown in the following examples, but are not limited thereto. In the present invention, the oxygen concentration and the polymer color b value were measured as follows.
(Oxygen Concentration) An oxygen concentration meter was installed in the middle of a line for purging a detector (model GD-F4A-SC) manufactured by Riken Keiki Co., Ltd. from the gas phase in the tank to the outside of the system, and continuously monitored.
(Hue) The obtained polymer was subjected to a dry crystallization treatment at 150 ° C. for 1 hour, and the color tone of the surface was measured using a colorimetric color difference meter (ZE-2000) manufactured by Nippon Denshoku Co., Ltd. The color b value indicates that the greater the value, the greater the degree of yellow.

[Example 1]
The reactor shown in FIG. 1 was used to continuously supply dimethyl terephthalate at 5000 kg / hr and reaction water at 5000 kg / hr to a continuous hydrolysis reactor and maintained at 250 ° C. and 4.0 MPa. It was made to react with. Next, the reaction solution was continuously supplied to a slurry tank (a) maintained at 100 ° C. and atmospheric pressure. The liquid in the slurry tank (a) was sent to a centrifuge and separated into a terephthalic acid cake and a filtrate. The cake was transferred to a slurry adjusting tank (b) and adjusted so that the molar ratio of terephthalic acid to ethylene glycol was 1.2. The slurry mixed and adjusted in the slurry adjusting tank (b) was continuously fed to the esterification reaction tank 7 and reacted at 265 ° C. Next, the esterified oligomer was transferred to an initial polycondensation reaction tank 8 and polymerized under the conditions of 280 ° C. and 2 kPa. Next, in the latter polycondensation reaction tank: 9, the polymerization reaction was carried out under the conditions of 280 ° C. and 0.13 kPa. The polymer exiting the late polymerization reactor was granulated into pellets with a chip cutter: 10 and sampled for color tone measurement every 5 hours. During this time, nitrogen is continuously supplied to all of the slurry tank (a), the centrifugal separator, the slurry adjusting tank (b), and the reaction water storage tank so that the oxygen concentration in each nitrogen purge is 0.2% or less. Managed.
When the b value of the chip was measured at 10 points, the average value of the b values was -1.53 and the standard deviation was 0.15. The results are summarized in Table 1.

[Comparative Example 1]
Using the same equipment as in Example 1, polymerization was carried out by stopping only the supply of nitrogen to the slurry tank (a). The oxygen concentration in the slurry tank (a) fluctuated in the range of 2 to 5%, and the b value of the polymer chip after polymerization was measured at 10 points every 5 hours as in Example 1. The average value of b values was 0.11, and the standard deviation was 0.24. The results are summarized in Table 1.

[Comparative Example 2]
Using the same equipment as in Example 1, polymerization was carried out by stopping only the supply of nitrogen to the centrifuge shown in FIG. The oxygen concentration of the centrifuge fluctuated within a range of 5 to 11%, and the b value of the polymer chip after polymerization was measured at 10 points every 5 hours as in Example 1. The average value of b values was -0.57, and the standard deviation was 0.30. The results are summarized in Table 1.

[Comparative Example 3]
Using the same equipment as in Example 1, polymerization was carried out by stopping only the supply of nitrogen to the slurry adjusting tank (b). The oxygen concentration of the slurry adjusting tank (b) fluctuated in the range of 3 to 7%, and the b value of the polymer chip after polymerization was measured at 10 points every 5 hours as in Example 1. The average value of b values was -0.05, and the standard deviation was 0.22. The results are summarized in Table 1.

[Comparative Example 4]
Using the same equipment as in Example 1, polymerization was carried out by stopping only the supply of nitrogen to the reaction water storage tank. The oxygen concentration in the reaction water tank fluctuated within a range of 7 to 10%, and the b value of the polymer chip after polymerization was measured at 10 points every 5 hours as in Example 1. The average value of b values was −0.44 and the standard deviation was 0.12. The results are summarized in Table 1.

[Comparative Example 5]
Using the same equipment as in Example 1, the polymerization was carried out by stopping the supply of nitrogen to all of the slurry tank (a), the centrifuge, the slurry adjusting tank (b), and the reaction water storage tank. The oxygen concentration of the reaction water storage tank fluctuated in the range of 7 to 10%, and the b value of the polymer chip after polymerization was measured at 10 points every 5 hours as in Example 1. The average value of b values was 0.59, and the standard deviation was 0.22. The results are summarized in Table 1.

  As shown in Table 1, in Example 1 in which the present invention was specifically implemented, the average value of b values was small, so that the yellowness was small, and the standard deviation of b values was small, so the variation was small.

  A method for producing a polyester having good hue and excellent transparency can be provided, and polyester fibers, polyester films, polyester bottles and other polyester molded articles having good hue can be obtained from the polyester obtained by the production method. It comes out. Also, since the variation in hue is small, it can be said that the quality is stable. This is very significant in terms of industry.

It is the schematic which shows an example of the polyester manufacturing apparatus used for implementation of this invention. (1): Slurry tank (a) and its peripheral devices, (2): Reaction water storage tank, (3): Schematic diagram of inert gas introduction method to solid-liquid separator and slurry adjustment tank (b).

Explanation of symbols

1 Hydrolysis reaction tank 2 Slurry tank (a)
3 Solid-liquid separator 4 Reaction water storage tank 5 Deaerator 6 Slurry adjustment tank (b)
7 Esterification reaction tank 8 Initial polycondensation reaction tank 9 Late polycondensation reaction tank 10 Chip cutter 11 Dicarboxylic acid dimethyl ester piping 12 Reaction water piping 13 Makeup water piping 14 Dicarboxylic acid + water slurry piping 15 Dicarboxylic acid cake piping 16 Filtrate piping 17 Purge pipe 18 Alkylene glycol pipe 19 Dicarboxylic acid + alkylene glycol slurry pipe 20 Polyester polymer 21 Nitrogen pipe 22 Nitrogen purge pipe 23 Oxygen meter 24 Nitrogen flow

Claims (5)

  In a method for producing a polyester by hydrolyzing a dicarboxylic acid dimethyl ester to produce a dicarboxylic acid, followed by an esterification reaction with an alkylene glycol and a polycondensation reaction, an apparatus for handling a slurry mainly composed of a dicarboxylic acid and water, Among the devices that handle the water supplied to the decomposition reaction and the devices that handle the dicarboxylic acid, the device in which the internal pressure of the device is maintained at a pressure lower than atmospheric pressure is supplied to the slurry consisting of the dicarboxylic acid and water and to the hydrolysis reaction Water and the dicarboxylic acid are maintained in an inert gas atmosphere having an oxygen concentration of 1% by volume or less.   The method for producing a polyester according to claim 1, wherein the main component of the dimethyl dicarboxylate is dimethyl terephthalate.   The method for producing a polyester according to claim 1, wherein the main component of dimethyl ester of dicarboxylic acid is dimethyl 2,6-naphthalenedicarboxylate.   The method for producing a polyester according to any one of claims 1 to 3, wherein the main component of the alkylene glycol is ethylene glycol.   The polyester production method according to any one of claims 1 to 3, wherein the main component of the alkylene glycol is 1,4-butanediol.

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