JPS5826741B2 - Esther Kahouhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a direct esterification method for obtaining a substance mainly consisting of bis-β-hydroxyethyl terephthalate and/or its low condensate from terephthalic acid and ethylene glycol.

From terephthalic acid (hereinafter referred to as TPA) and ethylene glycol (hereinafter referred to as EG), bis-β-hydroxyethyl terephthalate (hereinafter referred to as BH
T) and/or its lower condensate are obtained, and then polyethylene terephthalate (T) is obtained by polycondensation reaction.
The direct polymerization method for producing PET (hereinafter referred to as PET) is well known.

Although the direct esterification method described above is theoretically superior to the transesterification method, it has many problems in practice.

In other words, in order to accelerate the reaction rate to an economical range, it is necessary to increase the molar ratio of EG/TPA, but EG
/TPA molar ratio (if this is done, a large amount of diethylene glycol (hereinafter referred to as DEC), which is a dehydrated condensation product of EG, will be produced, and the quality of the final PET obtained will deteriorate.

In addition, in order to solve the problem of increasing DEC, EG/TPA
A method has been proposed to increase the reaction rate k by lowering the molar ratio and increasing the pressure.

However, when the EG/TPA molar ratio is lowered, solid TPA and E
It becomes necessary to handle a highly viscous slurry consisting of a mixture of G, which impedes the fluidity of the reaction liquid at the initial stage of the reaction, hindering the smooth progress of the reaction, and causing problems such as coloring due to local overheating of TPA. .

In order to eliminate these drawbacks of the direct clam method, an EG+TPA slurry prepared using TPA with specific slurry properties and an EG/TPA molar ratio of 1.3 or less was continuously added to the reaction system in which BHT was present at 240°. Method of reacting at C or higher (Special Publication No. 50-19313.5O-19314), EG
+ A method in which TPA slurry is continuously supplied and the reaction rate is maintained at 85 to 95% during the esterification reaction (Japanese Patent Application Laid-Open No.
053342), a continuous esterification method in which TPA+EG is continuously supplied to the reaction system and the reaction is carried out so that the free EG in the reaction system is in the range of 2 to 15% by weight (Japanese Patent Application Laid-Open No. 4885550). A method of esterification at the boiling point (Japanese Patent Publication No. 47-45958) has been proposed.

Although these methods are recognized to be effective in improving the initial fluidity of the reaction system, they are not necessarily satisfactory in terms of the esterification reaction rate.

The present inventors used a slurry with a low EG/TPA molar ratio as a BH
In an esterification method in which T is continuously supplied to a system in which T is present, the present invention was achieved by considering the provision of a method that suppresses the by-product of DEC, keeps unreacted TPA constantly at a low level, and increases the reaction rate. This is what I did.

That is, in the present invention, when synthesizing terephthalic acid and ethylene glycol, lahisto-β-hydroxyethyl terephthalate, and/or its low condensate, a slurry consisting of terephthalic acid and ethylene glycol is continuously bis-condensed.
An ester characterized by supplying β-hydroxyethyl terephthalate and/or its low condensate to a system and carrying out the reaction while distilling water produced under normal pressure together with 0.3 to 30% by weight of ethylene glycol. It is a method of conversion.

The EG/TPA molar ratio of the supplied slurry is 1.05 to 2.
0 is preferable, and 1.1 to 1.5 are more preferable.

If the molar ratio is less than 1.05, it is difficult to prepare a uniform slurry, and the fluidity is extremely poor, making it impossible to supply the slurry.

If the molar ratio exceeds 2.0, the EG/TPA ratio in the reaction system will become too high, making it impossible to raise the reaction temperature.

In the present invention, the slurry is added continuously in order to raise the reaction temperature, but it may be added intermittently as long as the reaction temperature is not extremely lowered.

Further, if a large amount is added at once, the temperature of the reaction system will drop due to the sensible heat of the slurry, and the reaction temperature determined from the amount of BHT and the amount of EG cannot be kept high, which is not preferable.

A suitable pump is used in the present invention to continuously add the EG/TPA slurry.

In this case, a water cooling jacket is attached to the inlet to the esterification reactor to prevent heat from the reactor from being transmitted to the slurry supply piping and deteriorating the fluidity of the slurry.

Ball valves or flush valves are also recommended for the valves attached to the piping.

BHT and/or its low condensate stored in the esterification reactor have an average degree of polymerization of 1 to 20, and the BHT
The storage amount is % to % of the total storage amount and supply in TPA units.
is preferred.

If it exceeds %, the productivity will be poor, and if it is less than %, the reaction will take a long time, and in either case, the production of DEC will become significant, which is not preferable.

The esterification reaction is carried out substantially at normal pressure (0.02~0.30k
g/ca gauge pressure).

The pressurized reaction is not preferred because it increases the DEC and makes the equipment expensive.

The temperature of the esterification reaction is preferably 200 to 260°C,
220-240°C is more preferable.

Too low a reaction temperature will increase the reaction time; too high a reaction temperature will increase the DEC and impart undesirable coloration to the reaction product.

What is important in the esterification method of the present invention is that the amount of water produced is 0.3 to 3.0% by weight, more preferably 0.3 to 2.0% by weight.
The reaction is allowed to proceed while distilling together with EG in a weight percent.

Setting the amount of distilled EG to less than 0.3% by weight is preferable from the viewpoint of increasing the purity of the distilled water, but this requires excessive rectification during the reaction and increases the amount of reflux liquid. This method has the drawbacks of worsening the utility consumption rate and returning water to the system, increasing the contribution of the reverse reaction and reducing the reaction rate.

Furthermore, it becomes difficult for substances with a boiling point lower than EG contained in the raw materials and substances with a boiling point lower than EG produced during the esterification reaction to be distilled out of the reaction system. There are drawbacks such as an increase in the amount of DEG and a decrease in quality such as coloring of the polymer.

On the other hand, if the amount of distilled EG exceeds 3% by weight, the EG/T of the reaction system
Although the PA molar ratio does not change significantly, surprisingly, the amount of DEC in the product becomes extremely high.

This is thought to be because when the EG fraction in the gas phase is increased, the amount of free EG in the system also changes, resulting in a situation that is not similar to DEGO raw materials.

Furthermore, in order to distill out of the reaction system substances with a boiling point lower than EG contained in the raw materials and substances with a lower boiling point than EG produced during the esterification reaction, it is sufficient to set the amount of distilled EG to 3%. and the DEC in the polymer due to these substances
It is possible to suppress the increase in color of the polymer and the coloring of the polymer.

Note that the amount of EG in the distilled water does not necessarily need to be 0.3 to 3.0% by weight throughout the entire process of the esterification reaction.

Sometimes, in the early or late stages of the reaction, the amount of steam generated from the system is small compared to the main reaction process, and even if the amount of EG in the distilled water deviates from the 0.3 to 3.0% by weight of the present invention during this period, the present invention is still effective. Since the effect of the invention is not impaired, the amount of EG may be deviated from the range of the EG amount of the present invention during this period.

The method of carrying out the reaction while maintaining the amount of distilled EG contained in the distilled water at 0.3 to 3.0% by weight can be used if the TPA used as a raw material contains a certain amount of impurities. 4-carboxybenzaldehyde to 5
The effect is particularly great for those containing 0 ppm or more or 30 ppm or more of P-toluic acid.

On the one hand, TPA containing relatively large amounts of these compounds may also contain other substances with lower boiling points than EG, and on the other hand, 4-carboxybenzaldehyde, P-)ruyl acid and other impurities. As a result, there is a possibility that a substance having a boiling point lower than that of EG may be produced during the esterification reaction, and it is thought that deterioration in the quality of the polymer can be suppressed by distilling such a product out of the reaction system.

In addition, in the main esterification reaction process, the E in the distillate water described above is
Although it is not preferable to deviate from the G amount range, deviating for a short time does not hinder the reaction.

As a specific means for controlling the amount of EG in distilled water to 0.3 to 3.0% by weight, for example, there is a method of setting the temperature distribution of a rectification column installed in the reaction apparatus to an appropriate value.

That is, when the esterification reaction proceeds while rectifying two parts of the distillate back to the rectification column, the temperature is detected at the middle stage of the rectification column or at an appropriate point or at multiple points, and the temperature distribution in the rectification column is detected. This can be achieved by performing reflux according to the conditions.

Of course, a decentralizer is installed at the bottom of the rectification column, and the E
Partial condensation of G can reduce the size of the rectification column and improve the responsiveness of the reflux liquid.

Note that the reaction apparatus can be equipped with an external heat exchanger other than the rectification column, for example, to perform the same role.

In this case, the temperature can be detected at an appropriate point and the degree of heat exchange can be adjusted in the same way as above.Also, in addition to the method of refluxing two parts of the distillate as described above, it is also possible to introduce all of the distillate to the receiving tank. There is also a method of controlling the amount of EG in the distillate by sending externally cooled water or distillate received in a receiver tank to the top of the rectification column using a pump and adjusting the amount of reflux liquid in the rectification column. good.

Furthermore, it is also possible to adopt a method of adjusting the amount of EG in the distillate by changing the supply rate of the TPA+EG slurry.

Specifically, when the EG ratio of the distillate remains high, the slurry supply rate is reduced or the slurry supply is stopped; when the EG ratio of the distillate remains low, the slurry supply rate is reduced. This is a method of increasing the feed rate.

It is also possible to adjust the EG ratio by changing the temperature of the reaction system depending on the EG ratio of the distillate.

An easy way to detect the weight percent of EG in the distilled water in the esterification reaction is to measure the specific gravity and refractive index of the distilled water, but to obtain accurate values, gas chromatography is recommended. It is preferable to use a method of measuring .

The present invention also includes an esterification reaction to obtain a polyester in which 80 mol% or more of the constituent units of the finally obtained polyester consist of ethylene terephthalate,
Less than 0 mol% of co-condensation components other than TPA and EG may be present during the esterification reaction.

In addition, a known esterification catalyst can be used during the esterification reaction of the present invention, and the polycondensation of the esterification reaction product can be carried out by any known method. and various other known additives used during polyester production may be added to the reaction system.

The effects of the esterification method of the present invention are as follows.

(1) EG in the system can be reduced by carrying out the atmospheric pressure esterification reaction by continuously supplying TPA + EG slurry.D
Generation of EG can be suppressed.

Furthermore, since the amount of solid TPA in the system can be kept small, stirring becomes easy and the reaction temperature can be raised to complete the reaction in a short time.

Furthermore, because the reaction takes place under normal pressure, the reaction container and attached instruments are inexpensive.

(2) Since water is distilled out together with a specific amount of EG under normal pressure, the water in the system efficiently turns into steam, making it possible to reduce the moisture content in the system.

Furthermore, since EG is distilled out, excessive rectification does not occur, and the energy transferred from the outside to the reaction system can be reduced.

Moreover, since substances with a lower boiling point than EG are easily distilled out of the reaction system, the quality of the obtained polymer is improved.

The present invention will be explained in detail with reference to Examples below.

Example 1 TPA used in the esterification reaction had a 4-carboxybenzaldehyde content of 10 ppm and a p-toluic acid content of 140 ppm.

61.6 kg of BHT with an average degree of polymerization of 5 and its oligomer (esterification reaction rate 98%, DECo, 7% by weight) were
Placed in a reactor maintained at 40°C, T
The PA+EG slurry was added continuously at a constant rate.

The reactor is equipped with a rectification column with a theoretical plate number of 2.5 filled with % inch Pall rings, and the vapor generated during the reaction is guided out of the system through this column, cooled and condensed, and the = fraction is rectified. It was refluxed from the upper part of the tower, and the remainder was led to a receiving tank.

Here, the ratio of the flow rate guided to the receiving tank and the reflux flow rate is assumed to be R.

During the reaction, if the thermometer placed in the middle of the rectification column indicates 120°C or lower, the reflux ratio is 1160°C or lower.
3, and when the temperature was between that range, the temperature was changed to R2.

Table 1 shows the composition of the distillate and the quality of the reaction product when the rectification column conditions were changed.

As is clear from Experiment Nos. 1 to 6 and Comparisons 1 to 5 in Group 1, when the EG content in the distillate is less than the lower limit of the present invention, the reaction time becomes longer and the DEC content of the product decreases. There will be more.

On the other hand, when the EG content in the distillate is high, the reaction time is short but the DEC content of the product increases.

Example 2 The TPA used in the esterification reaction had a 4-carboxybenzaldehyde content of 680 ppm and a p-toluic acid content of 20 ppm.

BHT with an average degree of polymerization of 71 and its oligomer (1 stellation reaction rate 99.1%, DECo, 66% by weight) 500k
g was fed to two reactors arranged in series.

The first reactor has a ratio of 1 to 0.015 per amount of TPA added.
A mixture of weight percent m-butyltin hydroxyoxide and its multimers was provided.

The temperature of each reactor was maintained at 235°C and 240'C, respectively.

The pre-adjusted TPA+EG slurry was continuously fed into the first reactor at a constant rate, while the product was fed at a reaction rate of 83.
It was continuously taken out and led to the second reactor while taking a residence time so as to maintain the same percentage.

Similarly, from the second reactor, the residence time was taken so as to maintain the reaction rate at 96%, and the reactor was taken out continuously.

A rectification column with 3 theoretical plates was installed in the first reactor, and a rectification column with 1.5 theoretical plates was installed in the second reactor, and the reflux ratios were set to R1 and R2, respectively.

Table 2 shows the composition of the distillate stream and the quality of the product when the rectification column reflux ratio was changed.

As is clear from Experiment Nos. 7 to 12 and Comparisons 6 to 8 in Group 2, when the EG content in the distillate from the first reactor is less than the lower limit of the present invention, the reaction time becomes longer and the formation of The DEC content of the product increases.

On the other hand, if the EG content in the distillate exceeds the upper limit of the present invention, the reaction time will be shortened, but the DEC content will be extremely high.

Regarding the second reactor, the requirements of the present invention do not apply in that it does not supply TPA/E G slurry, but the effect referred to in the present invention is achieved in comparison of the EG amount in the distillate and the DEC content in BHT. It is not always clear.

Claims (1)

[Claims] 1 Bis-β from terephthalic acid and ethylene glycol
- When synthesizing hydroxyethyl terephthalate and/or its lower condensates, a slurry consisting of terephthalic acid and ethylene glycol is continuously fed to a system consisting of bis-β-hydroxyethyl terephthalate and/or its lower condensates. The water produced under pressure is 0.3 to 3.
An esterification method characterized in that the reaction is carried out while distilling together with 0% by weight of ethylene glycol.