JP3690768B2 - Continuous production method of polyester - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a process for continuously producing a polyester having a low carboxyl end group amount.
[0002]
[Prior art]
Polyester, especially polyethylene terephthalate, has various excellent properties, especially excellent mechanical strength, and is widely used as fibers, films, sheets, bottles, and other molded articles.
[0003]
Polyethylene terephthalate is generally produced by esterifying terephthalic acid and ethylene glycol to make an oligomer, which is heated under reduced pressure for polycondensation.
As a method for producing such a polyester, there are a batch method and a continuous method, but in the case of mass production, a continuous method which is advantageous in terms of quality and cost is generally adopted.
[0004]
In the case of producing a molded product from polyester obtained by melt polymerization, usually, a method of once forming chips and then remelting and molding is employed. At that time, if the amount of the carboxyl terminal group of the raw material polyester is large, hydrolysis due to residual moisture of the polyester is likely to occur during remelting. Since this hydrolysis is promoted by acid catalysis by the carboxyl end groups of the polyester, the degree of hydrolysis increases as the amount of the carboxyl end groups of the raw material polyester increases. If hydrolysis occurs during molding by remelting, desirable properties inherent to the molded article such as insufficient strength of the product and deterioration of color tone due to a decrease in viscosity are impaired.
[0005]
In order to solve such a problem, various methods for producing a polyester having a low carboxyl end group amount have been proposed.
For example, based on the knowledge that the amount of carboxyl end groups increases with the progress of the thermal decomposition reaction, a method for reducing the amount of carboxyl end groups by lowering the reaction temperature has been proposed. However, if the polymerization reaction temperature is lowered, the apparent polymerization reaction rate decreases, so that it is necessary to extend the polymerization reaction time, resulting in a problem that productivity is lowered and costs are increased.
[0006]
In addition, a method using an end-capping agent such as a carbodiimide compound that reacts with a carboxyl end group of polyester is also known. According to this method, the amount of the carboxyl end group can be effectively reduced. However, in this method, it is necessary to seal the carboxyl terminal group of the total amount of the polyester to be manufactured, and after the polyester is once manufactured, the complexity of adding a post-process for reacting the polyester with the terminal blocking agent is added, It was difficult to apply to the method of manufacturing polyester continuously from economical efficiency.
[0007]
Furthermore, it is known that a polyester having a low carboxyl end group amount can be obtained by increasing the esterification reaction rate of the oligomer during the esterification reaction. However, when the esterification reaction rate is increased, the color tone of the polyester is deteriorated or the content of diethylene glycol component (DEG) as a by-product is increased, and the polycondensation reaction rate is decreased and the productivity is decreased. There was a problem.
[0008]
[Problems to be solved by the invention]
The present invention seeks to provide a method for continuously producing a polyester capable of obtaining a polyester having a low carboxyl end group amount without impairing general polyester characteristic values such as color tone, DEG content and viscosity, and productivity. To do.
[0009]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have adjusted the polymerization degree of the oligomer while maintaining the esterification reaction rate of the oligomer constant by adjusting the reaction conditions during the esterification reaction. It is possible to change the apparent polycondensation reaction rate by controlling the proportion of carboxyl end groups in the total end groups, and there is a correlation between the esterification reaction rate and the DEG content of the product polyester The inventors have found that there is a relationship and that there is a correlation between the color tone of the polyester and the esterification reaction conditions, and have reached the present invention.
[0010]
That is, the present invention relates to a method for continuously producing a polyester having a carboxyl end group amount of 35 g equivalent / 10 ⁶ g or less from terephthalic acid and ethylene glycol through an esterification reaction and a polycondensation reaction. A continuous production of a polyester, characterized in that an oligomerization reaction rate is in the range of 92 to 98% and an oligomer having a carboxyl end group ratio of 35% or less in all terminal groups is subjected to a polycondensation reaction under reduced pressure. The summary of the method is as follows.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
[0012]
The polyester which is the subject of the present invention is a polyester from terephthalic acid and ethylene glycol, that is, polyethylene terephthalate, but within the range that does not greatly change its properties, isophthalic acid, phthalic anhydride, 5-sodium sulfoisophthalic acid, Naphthalenedicarboxylic acid, diphenylenedicarboxylic acid, diphenoxyethanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, decanedicarboxylic acid, dodecanedicarboxylic acid, cyclohexanedicarboxylic acid, 1,4-butanediol, neopentyl glycol, 1,4 -Copolymerization components such as cyclohexanedimethanol, p-xylene glycol, ethylene oxide adduct of bisphenol A, and 4-hydroxybenzoic acid may be used in combination. Further, a trifunctional or higher polyfunctional compound such as trimellitic acid or glycerin may be used in combination as a copolymerization component as long as the thermoplasticity is not impaired.
[0013]
Next, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic process diagram showing an example of an embodiment of a method for continuously producing polyester. In FIG. 1, 1 is a first stage esterification reaction tank, 2 is a slurry supply pipe, 3 is a second stage esterification reaction tank, 4 is an ethylene glycol supply pipe, 5 is a first stage polycondensation reaction tank, and 6 is a first stage. A two-stage polycondensation reaction tank, 7 is a third-stage polycondensation reaction tank, 8 is a die head, 9 is a cutter, and 10 is a pellet.
[0014]
Although FIG. 1 shows an example in which polyester is continuously produced by a two-stage esterification reaction and a three-stage polycondensation reaction, the number of stages of the esterification reaction and the polycondensation reaction is not limited to this. .
[0015]
In the continuous production method of polyester as shown in FIG. 1, generally, a slurry of terephthalic acid and ethylene glycol is supplied from a slurry supply pipe 2 to a first stage esterification reaction tank 1 in which an oligomer is present in advance, and is subjected to normal pressure. Or it is made to react by heating and stirring under slight pressure, and the esterification reaction rate is 80 to 90%, more preferably 83 to 87%. Next, this is sequentially fed to the second stage esterification reaction tank 3, and heated and stirred at normal pressure or under pressure to increase the esterification reaction rate to 92-98%, more preferably 94-98%. Oligomer.
[0016]
If the esterification reaction rate is out of the above range, the polycondensation reaction rate in the subsequent process will be significantly reduced. It is necessary to raise the temperature. If the pressure in the polycondensation reaction tank is too high, the oligomer will evaporate, causing process trouble. On the other hand, when the reaction temperature is raised, the degradation of the polyester is accelerated, and accordingly, the color tone of the product polyester is lowered, the by-products are increased, and the amount of carboxyl end groups is increased.
[0017]
Also, when the esterification reaction rate of the oligomer is less than 92%, the oligomer is volatilized much and the oligomer adheres to the vapor phase can wall of the polycondensation reaction tank, and the melting point increases with time. As a result, it falls into the reaction product, clogs the filter in the process, and degrades the quality of the product polyester.
[0018]
On the other hand, the esterification reaction rate of the oligomer from the esterification reaction tank 3 is known to affect the color tone of the polyester, and the esterification reaction rate is changed as means for adjusting the color tone. . At this time, the esterification reaction rate is mainly adjusted by increasing or decreasing the amount of ethylene glycol supplied from the ethylene glycol supply pipe 4.
[0019]
As a result of studies by the present inventors, in order to make the carboxyl end group amount of the final polyester 35 g equivalent / 10 ⁶ g or less, the esterification reaction rate of the oligomer remains at a constant value in the range of 92 to 98%, By adjusting the reaction conditions such as the reaction temperature, reaction pressure and residence time in the final esterification reaction tank 3 and lowering the degree of polymerization of the oligomer, the proportion of carboxyl end groups in all end groups should be 35% or less. I found it good.
[0020]
The proportion of carboxyl end groups in all end groups of the oligomer varies depending on the degree of polymerization even if the esterification reaction rate is the same. The carboxyl end group undergoes esterification reaction with the hydroxyl end group, but since the parallel constant of this esterification reaction is close to 1, hydrolysis occurs at the same rate as the amount of carboxyl end group decreased by the esterification reaction in the polycondensation reaction step. Progresses.
[0021]
Since the polycondensation reaction is performed under reduced pressure, water generated by the esterification reaction is quickly removed out of the system at the beginning of the polycondensation reaction, but the melt viscosity increases as the polycondensation reaction proceeds, Since the mass transfer of the produced water becomes slow, the amount of carboxyl end groups is difficult to decrease from a certain value, and conversely, the amount of carboxyl end groups increases due to the thermal decomposition reaction of polyester.
[0022]
The value at which the carboxyl end group amount is minimized correlates with the proportion of carboxyl end groups in all the end groups of the oligomer, and in order to make the carboxyl end group amount of the final polyester 35 g equivalent / 10 ⁶ g or less, It has been found that the proportion of carboxyl end groups in all end groups of the oligomer should be 35% or less.
[0023]
The esterification reaction rate of the oligomer remains a constant value in the range of 92 to 98%, and the condition of the esterification reaction is adjusted so that the proportion of carboxyl end groups in all end groups is 35% or less. This adjustment is performed in the following range in consideration of operability and the like.
[0024]
The temperature of the esterification reaction is 240 to 270 ° C, preferably 245 to 268 ° C, more preferably 255 to 265 ° C. If the reaction temperature is too low, the fluidity will be lowered, and not only will it be difficult to send the oligomer, but there will be problems such as poor stirring, non-uniform reaction, and even higher stirring power. On the other hand, if the esterification reaction temperature is too high, the volatilization of oligomers will increase, thermal decomposition will occur, the color of the final polyester will deteriorate, and the amount of by-products such as DEG will increase.
[0025]
The pressure of the esterification reaction is 0 to 200 kPa · G, preferably 0 to 180 kPa · G, more preferably 0 to 150 kPa · G. If the reaction pressure is too low, oligomer volatilization increases. Conversely, if the reaction pressure is too high, the amount of by-products increases.
[0026]
The residence time in the esterification reaction tank is 0.5 to 4 hours, preferably 0.5 to 3 hours, more preferably 1.02 to 2.5 hours. If this residence time is too short, problems such as poor agitation due to insufficient amount of liquid in the reaction tank and heat transfer from a coil through a heating medium will occur. There arises a problem that the amount of product produced increases and the stirring power increases.
[0027]
Next, an oligomer satisfying the above predetermined conditions is fed to the first stage polycondensation reaction tank 5, a polycondensation catalyst such as antimony trioxide and germanium dioxide is added, and the first stage polycondensation reaction tank 5 is added. The second-stage polycondensation reaction tank 6 and the third-stage polycondensation reaction tank 7 are sequentially passed, and a polycondensation reaction is performed until a polyester having a predetermined polymerization degree is obtained, thereby obtaining a polyester having a high polymerization degree. The obtained polyester having a high degree of polymerization is discharged into a strand shape with the die head 8 and granulated with a cutter 9 to obtain pellets 10.
[0028]
【Example】
Next, the present invention will be specifically described with reference to examples.
In addition, the measuring methods, such as a characteristic, are as follows.
(a) Color tone (b value)
Measured with a Nippon Denshoku Industries 300A color difference meter.
(b) DEG content The polyester was hydrolyzed with an aqueous potassium hydroxide solution, and then measured using a GC-14B gas chromatograph manufactured by Shimadzu Corporation.
(c) The mixture was measured at a temperature of 20 ° C. using an equal weight mixture of intrinsic viscosity phenol and tetrachloroethane as a solvent.
(d) Weigh accurately 0.15 g of carboxyl end-group polyester, add 5 ml of benzyl alcohol, heat to 202-203, dissolve by heating, and titrate with 0.1 mol / L potassium hydroxide in methanol. It was.
(e) Esterification reaction rate The total carboxyl terminal group amount A and the unreacted carboxyl terminal group amount B of the oligomer are determined by the following method, and calculated by the following formula.
Esterification reaction rate (%) = [(A−B) / A] × 100
Total carboxyl end group amount A: Weigh accurately 0.3 g of oligomer, add 20 ml of 0.5 mol / L potassium hydroxide aqueous solution, reflux for 1 hour, hydrolyze, and titrate with 0.5 mol / L hydrochloric acid. Ask.
Unreacted carboxyl end group amount B: 2.0 g of oligomer was precisely weighed, 20 ml of N, N-dimethylformamide was added to this, dissolved by refluxing for 1 hour, and titrated with a 0.1 mol / L potassium hydroxide methanol solution. Ask.
[0029]
Example 1
Using the continuous polyester production apparatus shown in Fig. 1, a slurry in which the molar ratio of ethylene glycol to terephthalic acid is 1.5 to 1 is reacted at an average residence time of 4.6 hours at a rate of 5902 kg per hour from the slurry supply pipe 2. It is continuously fed to the first stage esterification tank 1 controlled at a temperature of 260 ° C. and a reaction pressure of 33 kPa · G to form an oligomer having an esterification rate of 85.0%, and then this oligomer is continuously produced with an average residence time of 2.1 hours. The reaction temperature is 254 ° C and the reaction pressure is controlled to 33kPa · G. The solution is sent to the second-stage esterification reaction tank 3, and at the same time, ethylene glycol from the supply pipe 4 to the reaction tank 3 is equivalent to a molar ratio of terephthalic acid of 0.2. The oligomer was reacted while being fed to obtain an oligomer having an esterification reaction rate of 95.0% at a rate of 4442 kg per hour.
The degree of polymerization of this oligomer was calculated from the intrinsic viscosity, and the ratio of the amount of carboxyl end groups in all end groups was calculated to be 32.5%.
Next, this oligomer is continuously fed to the first stage polycondensation reaction tank 5, and antimony trioxide is added to the reaction tank 5 as a polycondensation catalyst at a molar ratio of 1.7 × 10 ⁻⁴ to terephthalic acid, Polycondensation reaction is carried out in a polycondensation reaction tank 5-7 controlled at a reaction temperature of 270 to 275 ° C and a reaction pressure of 2.7 kPa · G to 140 Pa · G. Manufactured.
The obtained polyethylene terephthalate had a color tone of 5.4, a DEG content of 1.39 mol%, an intrinsic viscosity of 0.687, and a carboxyl end group amount of 31.5 g equivalent / 10 ⁶ g.
[0030]
Example 2
Using the same polyester continuous production apparatus as in Example 1, a slurry in which the molar ratio of ethylene glycol to terephthalic acid is 1.5 to 1 is 5902 kg per hour from the slurry supply pipe 2 at an average residence time of 4.6 hours. The first stage esterification tank 1 controlled at a reaction temperature of 260 ° C. and a reaction pressure of 33 kPa · G was continuously fed to form an oligomer having an esterification rate of 85.0%. The solution was sent to the second stage esterification reaction tank 3 controlled at a time, a reaction temperature of 249 ° C., and a reaction pressure of 33 kPa · G. At the same time, ethylene glycol was supplied from the supply pipe 4 to the reaction tank 3 to a molar ratio of terephthalic acid to 0.25. The reaction was conducted while supplying the corresponding amount, and an oligomer having an esterification reaction rate of 96.0% was obtained at a rate of 4442 kg per hour.
The ratio of the amount of carboxyl end groups in all the end groups of this oligomer was 30.3%.
Next, this oligomer is continuously fed to the first stage polycondensation reaction tank 5, and antimony trioxide is added to the reaction tank 5 as a polycondensation catalyst at a molar ratio of 1.7 × 10 ⁻⁴ to terephthalic acid, Polycondensation reaction is carried out in a polycondensation reaction tank 5-7 controlled at a reaction temperature of 270 to 275 ° C and a reaction pressure of 2.7 kPa · G to 140 Pa · G. Manufactured.
The obtained polyethylene terephthalate had a color tone of 5.4, a DEG content of 1.39 mol%, an intrinsic viscosity of 0.687, and a carboxyl end group amount of 28.5 g equivalent / 10 ⁶ g.
[0031]
Comparative Example 1
In Example 1, the conditions in the first stage esterification tank were changed to an average residence time of 5.0 hours, a reaction temperature of 260 ° C., and a reaction pressure of 29 kPa · G to obtain an oligomer with an esterification reaction rate of 85.1%. The conditions in the conversion tank were changed to an average residence time of 2.1 hours, a reaction temperature of 254 ° C., and a reaction pressure of 29 kPa · G to obtain an oligomer having an esterification reaction rate of 94.6%.
The ratio of the amount of carboxyl end groups in all the end groups of this oligomer was 39.0%.
When this oligomer was subjected to a polycondensation reaction in the same manner as in Example 1, the obtained polyethylene terephthalate had a color tone of 5.6, a DEG content of 1.45 mol%, an intrinsic viscosity of 0.687, and a carboxyl end group content of 45.4 g equivalent / 10 ⁶ g. there were.
[0032]
【The invention's effect】
According to the present invention, it is possible to continuously produce a polyester having a low carboxyl end group amount without impairing general polyester characteristic values such as color tone, DEG content and viscosity, and productivity.
[Brief description of the drawings]
FIG. 1 is a schematic process diagram showing an example of an embodiment of a method for continuously producing polyester.
[Explanation of symbols]
1 First stage esterification reaction tank 2 Slurry supply pipe 3 Second stage esterification reaction tank 4 Ethylene glycol supply pipe 5 First stage polycondensation reaction tank 6 Second stage polycondensation reaction tank 7 Third stage tree condensation reaction tank 8 Die head 9 cutter
10 pellets

Claims (1)

In a method of continuously producing a polyester having a carboxyl terminal group amount of 35 g equivalent / 10 ⁶ g or less from terephthalic acid and ethylene glycol through an esterification reaction and a polycondensation reaction, the esterification reaction rate is 92 to 92 by the esterification reaction. A method for continuously producing a polyester, characterized in that it is in the range of 98% and an oligomer having a carboxyl end group ratio of 35% or less in all terminal groups is subjected to a polycondensation reaction under reduced pressure.

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