JPS5833855B2 - Esterification method - Google Patents

Description

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

Bis-β-hydroxyethyl terephthalate and/or its low polymer (hereinafter referred to as BHT) is obtained from terephthalic acid (hereinafter referred to as TPA) and ethylene glycol (hereinafter referred to as EG) through an esterification reaction, and then subjected to a polycondensation reaction. Polyethylene terephthalate 1.
(hereinafter referred to as PET) is a direct polymerization method that is well known.

However, in the conventional batch esterification method, TPA and EG are individually charged into a reaction tank containing BHT, and the boiling point is lowered by applying pressure (1.0 to 3.0 kg/crAG pressure). The method was to raise the temperature and esterify it.

However, in this method, there is a large amount of free ethylene glycol in the reaction system, resulting in a large amount of diethylene glycol (hereinafter referred to as DEC) as a by-product, which lowers the softening point of PET obtained by polycondensing the esterified product. There is.

In order to improve such problems, a semi-continuous method (JP-A-49-129791, JP-A-50-53342) has been developed in which a slurry of a mixture of TPA and EG is continuously fed into BHT and reacted.
is proposed.

The feature of this method is that in order to suppress the amount of free EG in the esterification reaction system, the EG of the mixture of TPA and EG is reduced.
The aim is to keep the molar ratio of /TPA low and the reaction temperature and reaction rate high.

However, the drawback of such a semi-continuous method is that TPA and EG are mixed before the reaction, and the mixed slurry is sent to the reaction system through a supply pipe using a pump, etc., and the mixing processability in this process is low. , it is necessary to improve the stability of the slurry.

Therefore, when a mixed slurry of TPA and EG is continuously fed into BHT for esterification, a TPA raw material of a specific quality is used in order to improve the above-mentioned problem of slurry undling. Method (Tokuko Showa 50-1931
Publication No. 3) has been proposed.

However, such an improvement method is still insufficient as a method for stably and quantitatively supplying a slurry of TPA and EG over a long period of time.

For this reason, the present inventors previously proposed a method (Japanese Patent Application No. 131527/1982) using a non-compressible pump as a method for stably and quantitatively supplying a slurry of TPA and EG.

However, this method is also not preferred when strict metrology is required.

That is, in the non-compressible pump, when the temperature changes, for example, the level of the primary pressure and/or secondary pressure of the pump changes, so the amount of liquid sent per rotation of the pump changes.

In addition, when used for a long period of time, the stator inside the pump wears out and the supply amount gradually decreases.

For this reason, it is difficult to accurately supply slurry at a constant rate using a non-compressible pump.

The present inventors have conducted studies with the aim of providing a stable slurry supply method and management method when a slurry of TPA and EG is continuously supplied into BHT and esterified in a batch manner, and the present invention has been made. It was reached.

That is, in the present invention, a slurry consisting of TPA and EG,
A feature of this method is that when BHT is continuously supplied to a system where BHT is present and esterification is performed in a batch manner, the amount of slurry to be supplied consisting of terephthalic acid and ethylene glycol is measured within the reaction system and the amount of the supplied liquid is controlled. This is an esterification method.

The feature of the present invention is that the supply amount of slurry from TPA and EG is measured within the reaction system, and the slurry supply amount is corrected and the total supply amount is confirmed, thereby enabling stable operational management. Conventionally, in a reaction system in which supply of slurry of TPA and EG as raw materials and esterification reaction are carried out in parallel,
No effective means for managing the greatly fluctuating liquid level has been found.

The amount of liquid in the esterification reaction tank may be measured by any method as long as it can withstand high temperatures and can be measured at any time before, during, or after the reaction, but methods such as inert gas purge level gauges, float type, etc. It is preferable to measure using a mechanical or electrical detection device such as a liquid level gauge, diaphragm level gauge, ultrasonic level gauge, radiation level gauge, capacitive level gauge, or thermometer. .

Among the liquid level gauges described above, a purge pipe level gauge using an inert gas, particularly N2, is particularly preferable.

This is due to the large amount of steam in the reaction system, the fact that it is a special reaction in which raw materials are supplied and the reaction is carried out in parallel, the reaction temperature is not constant, the reaction is heterogeneous, and there is no sublimate in the gas phase. This is due to the following reasons: the liquid level changes due to vortex flow due to stirring, etc., and the system is pressurized during transfer of BHT after the reaction.

As a typical example of the method of the present invention, a control method using an N2 purge level gauge will be explained with reference to the drawings.

Figure 1 shows pressurized N21 with pressure reduced by pressure reducing valve 2.
An appropriate amount is set using the flow rate setting devices 3 and 3'.

In this case, the amounts of N2 flowing through the flow rate setters 3 and 3' are approximately the same.

The N2 set at a specified amount is discharged into the liquid level from the submerged purge pipe 6, and into the gas phase from the pressure equalization pipe 6' on the other hand.

At this time, a differential pressure is generated due to the height of the liquid level, and the differential pressure transmitter 4 sends an electrical indication to the liquid level indicator 5 to detect this differential pressure.

The submerged purge pipe 6 may be provided with one or more notches in order to stabilize the N2 discharge part at its tip.

In addition, the submerged purge pipe 6 may be left as a single pipe so that the reaction product BHT does not solidify in the reverse flow, or may be provided with a heating jacket capable of maintaining the temperature at 210° C. or higher.

It is necessary to take measures to prevent the submerged purge pipe from coming into contact with heating parts (such as heating coils) with an ester ratio of 11 (not shown) or the rotating stirring blades 9. It is preferable that the length be below the liquid level of the BHT stored before the reaction, but it may be above the liquid level.

The N2 discharged from the submerged purge pipe 6 and the pressure equalization pipe 6' may be allowed to flow out during the reaction, or may be allowed to flow only during measurement, but may be allowed to flow out all the time.

Further, stirring may or may not be stopped during measurement, but it is preferable to do so.

A slurry of TPA and EG is supplied to an ester ratio of 11 from a slurry supply pipe 10 by a slurry feed pump 13.

The amount of reaction liquid within an ester ratio of 11 times can be monitored almost constantly during slurry supply using the N2 purge level meter mentioned above, and the actual measured value of the amount of slurry supplied in a certain period of time (slurry supply rate) It is possible to check.

By checking the deviation between the measured slurry supply speed and the set slurry supply speed, the rotation speed of the slurry feed pump 13 at the source of the slurry supply pipe 100 is reset as appropriate.
Correction can be made while supplying slurry so that a prescribed amount of slurry is supplied at a prescribed time.

In addition, since the N2 purge level gauge allows monitoring of the total amount of slurry supplied by a certain time, it is possible to confirm that the specified amount of slurry to be supplied in that batch has been supplied, and then turn on the slurry feed pump 13. Slurry supply can be stopped by stopping the rotation.

Furthermore, even greater effects can be expected by automating the above operations.

Storage B before esterification reaction when carrying out the method of the present invention
The amount of HT is 20% to 70% of the total amount of BHT after reaction.
It is preferable that the degree of polymerization of the stored BHT is 1.5 to
30 is preferable, and 2.5 to 20 is more preferable.

It is also desirable to leave a portion of the BIT produced after the reaction.

The amount of BHT transferred to the polymerization reactor and the amount remaining in the esterification reaction reactor can be easily measured by using the liquid level gauge described above.

That is, the liquid level indicator 5 in FIG. 1 and the ester ratio doubling valve 7 are linked, and when the transition occurs, the valve 7 is opened and the valve T is closed at the set liquid level.

The preferred range of the EG/TPA molar ratio of the feed slurry is 1.0.
2 to 1.80, more preferably 1.08 to 1.40.

The esterification reaction temperature is 215-280°C, 230°C
~260°C is preferable, and the reaction pressure is O~2.5 kg/
The pressure can be selected from a pressure range of caG pressure, but preferably atmospheric pressure to slight pressurization of 0 to 0.4 kg/crAG pressure.

In the case of a pressurized reaction, it is convenient to maintain pressurization using N2 released from the N2 purge level gauge used in the present invention.

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 copolymer components other than TPA and EG may be present during the esterification reaction.

By subjecting the esterification reaction product to a polycondensation reaction, high-quality PET with a low DEC content can be obtained, but in this case, known antifouling agents, additives, complementary colorants, etc. may be used. can.

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

■ A constant amount of raw materials can be supplied at a constant time, allowing for stable production.

That is, in the method proposed in Japanese Patent Application No. 50131527, the variation in the amount of raw material charged was more than ±7.5% from the specified amount, but by using the method of the present invention, it can be suppressed to about ±2.0% or less. .

Therefore, even in the polycondensation step following the esterification step,
Since the amount of BHT charged is constant, the reaction time is almost constant, and differences in polymer amount and quality between batches are reduced.

■ To measure and manage the liquid volume in the esterification reactor,
It is possible to easily determine the amount of BHT transferred to the polymerization can and the amount remaining in the ester ratio.

(2) By constantly performing N2 purge of the N2 purge liquid level gauge during the reaction, the distilled water can be distilled out of the system more quickly and the reaction can be accelerated.

The polyester obtained by polycondensing the esterification product of the method of the present invention is useful for fibers, films, and molding resins.

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

Example 1 BHT912 with an average degree of polymerization of 6.4 under atmospheric pressure. g(Il
ookg, reaction rate 98.4%) was stored in the esterification reactor shown in Figure 1, and heated to 247°C by a steam coil.
heated to.

The N2 flow rate is 2.0 each from the liquid purge pipe 6 and the pressure equalization pipe 6'.
±1. ol: Constantly released at a rate of 7 minutes.

The liquid level indicator 5 before the reaction shows 10%, and EG/T
A slurry with a PA molar ratio of 1.17 was heated for 70.01710 minutes (9
The liquid level indicator was linked to the rotational speed of a snake pump (NE-15, manufactured by Heishin Giki Co., Ltd.) i3 for slurry feeding, and the slurry was charged into the reaction vessel at a ratio of 7.4 kg (710 min).

That is, by measuring the amount of reaction liquid with a liquid level indicator every io minutes from the start of slurry supply and checking the amount of slurry supplied for each 10 minutes, the initial setting value of 70 is determined.
．． Snake pump 13 according to the deviation from 073710 minutes
The rotation speed was automatically increased or decreased.

When 3.0 hours have passed since the start of slurry supply, the liquid level indicator shows 58.0% and the liquid level is 20801! Met.

4 hours and 28 minutes after slurry supply started, the liquid level indicator was 80.0.
%, liquid volume 2741? After confirming that this was the case, slurry supply was stopped.

The reaction temperature remained at 238°C for most of the time when the slurry was supplied.
After the reaction was completed, the temperature was 246°C.

The reaction rate was 78.4% at the end of the slurry supply, and reached 98.7% 1 hour and 23 minutes after the slurry supply was completed, and the reaction was completed.

At this time, the N2 purge level gauge indicated 80.0%.

After the esterification reaction is completed, the inside of the esterification tank is charged at 0.8kg/c.
N2 pressure was applied to the yrtG pressure, and the ester ratio doubling valve 7 was opened to transfer BHT to the polymerization vessel.

The N2 purge level gauge is operated during the transition, and the level gauge indicates 10.
% ester ratio and closed the lower valve.

The transferred amount is 182511, the residual BHT amount is 9151,
This was used in the next esterification.

BHT transferred to polycondensation reaction is used as a catalyst in 5b2030.
04% by weight, orthophosphoric acid 0.03% by weight as an anti-adhesion agent, and 0.5% by weight Ti0 as a matte remover, and 1 in 60 minutes.
2 in 120 minutes while creating a high vacuum of 0mrnHg or less.
The temperature was raised to 85°C and polycondensation was continued for 4 hours after the start of the reaction.
The reaction was completed in 0 minutes.

The amount of polymer obtained was 2088.7 kg, and the intrinsic viscosity was 0.6.
50, and the softening point was 259.9°C.

When the above operation was repeated 40 times, the average slurry supply time per batch was 4 hours 29 minutes, R-5 minutes, the average esterification reaction time was 5 hours 42 minutes, R-24 minutes, and the average amount of polymer was 2098.91y. , R=35.4 kg,
The average intrinsic viscosity of the polymer is 0.649, R=0.00
6. Average softening point was 259.9°C, R=0.8°C.

Example 2 Except for not linking the rotation speed of the liquid level indicator and the snake pump for slurry supply, that is, without checking the slurry supply speed during slurry supply with the liquid level indicator, the rotation speed of the snake pump was kept constant. The reaction was carried out using the same reaction apparatus and under the same reaction conditions as in Example 1, except that the slurry was supplied as it was (with the set value fixed).

First, BHT912J (9 to 1100, reaction rate 98.4%
) was heated to 247°C and added with an EG/TPA molar ratio of 1.
17 slurry for 7.00137 minutes (9.74ky/min)
The rotation speed of the snake pump was set to the rotation speed that we had confirmed in advance that it could be supplied with.

When 3.0 hours had passed after the start of slurry supply, the liquid level indicator showed 57.0%, and the liquid amount was 20,501.

4 hours and 31 minutes after slurry supply started, the liquid level indicator was 80.0%.
It was confirmed that the liquid amount was 27,401, and the slurry supply was stopped.

One hour and 22 minutes after the end of slurry supply, the reaction rate reached 98.5% and the reaction was completed.

After the reaction, the N2 purge level gauge was operated as in Example 1, and when the level gauge indicated 10%, the transfer to the polymerization reactor was completed, and the amount of residual BHT was 9121 times the ester ratio.

The polymerization method in the polymerization tank was carried out in the same manner as in Example 1, yielding 2096.4 kg of polymer.

When the above operation was repeated 40 times, the average slurry supply time per batch was 4 hours 39 minutes, R24 minutes, and the average esterification reaction time was 5 hours 57 minutes, R-42 minutes. Since the time varied, the range of variation in the esterification reaction time was wider than in Example 1.

However, the average polymer amount is 2097.1 kg, R = 33
．． 8 kg, and the average intrinsic viscosity of the polymer is 0.65.
0. RO,005, average value of softening point 259.6°C, R=
The temperature was 0.9°C, and as in Example 1, a specified amount of BHT was transferred to the polymerization can, so there was no particular problem in terms of polymer quality.

Comparative Example 1 A reaction was carried out without using a liquid level measuring device using an esterification reactor shown in FIG. 2, which was provided with a horizontally split transfer circuit so that 9121 minutes of stored BHT could be transferred in the reactor.

First, BHT9121 (1100 kg, reaction rate 98.7%)
) was heated to 248°C, and an EG/TPA molar ratio of 1.
A slurry of No. 17 was supplied and the reaction was carried out.

The slurry supply method used the same snake pump for slurry supply as in Example 1, the rotation speed of the snake pump was fixed at a constant setting value, and the slurry supply was finished after a constant time (4 hours and 30 minutes). We adopted the method of

One hour and 28 minutes after the end of slurry supply, the amount of distilled water reached 3791, and the reaction was completed.

The reaction rate of the produced HT was 98.1%.

After the reaction, 9121 remained in the BHT, and the rest was transferred to the polymerization reactor through a transfer circuit.

The polymerization method in the polymerization tank was carried out in the same manner as in Example 1, and Polymer 2095. I got Okg.

After repeating the above operation 8 times, the amount of polymer in the 2nd and 3rd batches was 2102.4 kg and 2085.5 kg, respectively.
kg, and the first 3 batches were able to supply almost the specified amount of slurry, but after the 4th batch, it became impossible to supply the slurry at a constant rate.
The amount of polymer is 2062.8 kg for the 4th batch, 2 for the 5th batch
018.3kg, 6th batch 1896.0kg, 7th batch 1982, Okg, 8th batch 2153.6kg, ■ Batch average 2049.5kg, R = 257.
It was 6ky.

[Brief explanation of drawings]

FIG. 1 is a sectional view of an esterification reactor preferably used in the method of the present invention, and FIG. 2 is a sectional view of an esterification reactor used in Comparative Example 1. 1: Pressure N2.2: Pressure reducing valve, 3.3': Flow rate setting device, 4
: Differential pressure transmitter, 5: Liquid level indicator, 6: Liquid purge, 6'
: Pressure equalization pipe, 10 Nislari supply pipe, 11: Ester ratio times.

Claims (1)

[Claims] 1. Continuously feeding a slurry consisting of terephthalic acid and ethylene glycol to a system in which bis-β-hydroxyethyl terephthalate and/or its low polymer is present,
An esterification method characterized by measuring the amount of a slurry containing terephthalic acid and ethylene glycol to be supplied in a reaction system and controlling the amount of the supplied liquid when carrying out batchwise esterification.