JPS5828266B2 - Kaibunshikiester 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 consisting mainly of bis-β-hydroxyethyl terephthalate and/or its lower condensate, mainly terephthalic acid and ethylene glycol.

From terephthalic acid (hereinafter referred to as TPA) and ethylene glycol (hereinafter referred to as EG), bis-β-hydroxyethyl/L/terephthalate and/or its low polymer (hereinafter referred to as BHT) is obtained by an esterification reaction,
A direct polymerization method in which polyethylene terephthalate (hereinafter referred to as PET) is then produced by polycondensation reaction 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
When the /TPA molar ratio is increased, a large amount of diethylene glycol (hereinafter referred to as DEC), which is a dehydrated condensation product of EG, is produced as a by-product, resulting in a decrease in the quality of the PET finally obtained.

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

However, when the E G/T P A molar ratio is lowered, solid TP
Since it is necessary to handle a highly viscous slurry consisting of a mixture of A and EG, the fluidity of the reaction liquid at the initial stage of the reaction is inhibited, hindering the smooth progress of the reaction, and causing local TPA.
Problems such as coloring occur due to overheating.

In order to overcome these drawbacks of the direct method, an EG + TPA slurry with an EG/TPA molar ratio of 1.3 or less prepared with TPA having specific slurry properties was continuously added to the reaction system in which BHT was present240. Method of reacting at temperatures above ℃ (
Special Publication Showa 50-19313, Special Publication No. 50-19314),
A method of continuously supplying EG+TPA slurry to perform an esterification reaction and keeping the reaction rate between 85 and 95% (% opening/closing 5055342). Cooling method to prevent solidification
) etc. have been proposed.

Although these methods are effective in improving the initial fluidity of the reaction system, there are problems in stably supplying a homogeneous slurry with a low EG/TPA molar ratio to the reaction system on an industrial scale. .

The present inventors used a slurry with a low EG/TPA molar ratio as a BH
In a batch esterification method in which T is continuously supplied to a system in which T is present, we have considered providing a method for obtaining a uniform slurry of EG+TPA and stably supplying the slurry with a high degree of quantitative property, and have developed the present invention. It was reached.

That is, in the present invention, when synthesizing bis-β-hydroxyethyl terephthalate and/or its low condensate from terephthalic acid and ethylene glycol, a slurry consisting of terephthalic acid and ethylene glycol is stored in a storage tank, and the slurry is pumped through a snake pump. This is a batch esterification method characterized by continuously supplying bis-β-hydroxyethyl terephthalate and/or its low condensate to a reaction system containing bis-β-hydroxyethyl terephthalate and reacting under substantially normal pressure.

The method of the present invention will be explained with the aid of figures.

FIG. 1 is a schematic diagram of an apparatus suitable for carrying out the method of the invention, in which TPA is stored in a hopper 1 and fed quantitatively to a kneader 3 via a TPA metering system 2.

A stirrer may be attached to the hopper 1 so that the TPA can be transferred to the TPA weighing machine without any trouble.

Note that it is important to pass inert gas from the bottom of the hopper.
It is suitably employed for the purpose of preventing the formation of bridging structures between particles.

On the other hand, EG is quantitatively supplied to the kneader 3 from a separate port to form a uniform EG+TPA slurry within the kneader 3.

The slurry discharged from the kneader 3 is stored in a slurry storage tank 4 equipped with an agitator (the stirring blade should be shaped so that it can scoop up the slurry in the tank), and the slurry can be added to the slurry storage tank 4 as needed.
The snake pump 5 installed at the bottom of the reactor is operated to continuously supply slurry to the esterification reactor.

The purpose of providing the slurry storage tank 4 in the present invention is to absorb the imbalance between the slurry supply time and the esterification reaction time;
The slurry prepared in a kneader or the like is matured by stirring in the storage tank 4 to prevent clogging in the slurry supply pipe.

That is, in the batch esterification reaction, the supply of the EG + TPA slurry must be stopped during the latter half of the reaction and while transferring BHT to the polycondensation reactor, and on the other hand, the preparation of the slurry must be stopped in line with the supply of the slurry. is unfavorable for the operation of kneaders, etc.

In other words, if the kneader or the like is stopped with TPA and EG filled, too much load will be placed on stirring when restarting, causing mechanical trouble.

For this reason, it is preferable to continue preparing the slurry using a kneader or the like even while the snake pump is stopped and slurry supply is stopped.

Furthermore, if slurry prepared in a kneader or the like is directly supplied using a snake pump and kept stationary within the supply piping, clogging will occur in a short period of time.

However, if a single slurry prepared using a slurry or the like is stored in a slurry storage tank, clogging becomes less likely to occur even if the slurry is left stationary within the supply pipe.

This is because the slurry prepared with a kneader etc. is mixed with some gas mixed in, so the gas near the particles is not sufficiently removed, but by stirring the slurry in a slurry storage tank at normal pressure, This seems to be due to deaeration.

A slurry circulation line may be attached to the slurry storage tank, and a supply port to the esterification reactor may be branched from this line, or a supply line may be provided to the storage tank separately from the circulation line.

In this case, the circulation line can also be pumped with a snake pump.

The maturation time of the slurry in the slurry storage tank is 10 minutes or more, preferably 30 minutes or more.

In addition to the kneader shown in FIG. 1, a flow jet mixer, a blender, or the like can be used to prepare the slurry.

In this case, the slurry preparation apparatus may be either a continuous type or a batch type, but a continuous type is preferable from the viewpoint of operation.

The molar ratio of E G / T P A of the slurry to be prepared is 1.0.
5 to 1.8 are preferable, and 1.1 to 1.5 are more preferable.

When the molar ratio is less than 1.05, it is difficult to prepare and supply a uniform slurry.

On the other hand, if the molar ratio exceeds 1.8, it is easy to prepare and supply the slurry, but the molar ratio for the esterification reaction inevitably becomes high, resulting in the disadvantage that DEGO production is significant.

Note that the lower limit of the molar ratio is roughly determined by the particle size of TPA, so if the particle size is small, it may be higher than the above value.

On the other hand, if the particle size is large, a slurry with a lower value than the above value can be prepared and supplied.

The snake pump referred to in the present invention is a non-compressible pump that pumps liquid by utilizing the movement of a gap formed by planetary motion of a single thread male screw rotor inside a double thread female stator. As shown in the figure.

That is, the EG+TPA slurry adjusted to a predetermined molar ratio is supplied from A into a closed housing through which the shaft of the rotor 8 passes.

The rotor 8 has irregularities on its surface, and is rotated by a shaft 9 connected to a driving source.

Further, the stator 6 containing the rotor 8 is configured to have the same pitch as the rotor 8 and a gap 7 on its inner surface.

The cavity 7 is moved and propelled from the housing portion toward the outflow portion as the rotor 8 rotates.

Therefore, the slurry to be supplied can be supplied continuously and quantitatively through the gap.

Preferred materials for use in the snake pump include metal for a portion of the rotor and rubber for a portion of the stator, but the materials are not necessarily limited to these.

In order to facilitate feeding to the rotor, spiral blades may be attached to the inlet portion of the snake pump housing to the rotor 8, ie, the rotating shaft portion at the drop point from A.

That is, the purpose of using a snake pump to supply the EG+TPA slurry in the present invention is to facilitate the supply of a slurry with a low EG/TPA molar ratio and to supply the slurry with excellent quantitative properties.

Slurry with a high EG/TPA molar ratio can be sufficiently supplied by plunger pumps, gear pumps, etc., but if the molar ratio is low and is less than 1.8 mol, especially less than 1.6, TPA and EG will separate and become trapped inside the pump. , TPA forms a block in the pipe, causing a clogging phenomenon.

Therefore, in order to supply a slurry with a low molar ratio as in the present invention without causing a clogging phenomenon, a pump with a mechanism that does not have a compressive action is suitable, and from this point of view, it is suitable to employ a snake pump.

Furthermore, the snake pump has excellent quantitative performance when supplying EG+TPA slurry, and does not require a special slurry metering system.

That is, the amount of slurry supplied to the esterification reactor can be determined from the rotation speed of the snake pump.

The amount of slurry to be supplied can also be determined by controlling the liquid level in the slurry storage tank or the esterification reactor.

It is preferable to attach a water cooling jacket to the feed port from the snake pump to the reactor to prevent heat from the reactor from being transmitted to the slurry supply piping and deteriorating the fluidity of the slurry.

Further, the valve attached to the supply pipe is preferably a ball valve or a flush valve.

The esterification reaction is carried out at substantially normal pressure.

Substantially normal pressure includes a slightly pressurized state equivalent to the pressure loss of the rectification column as the pressure of the reaction vessel, and is 0.02 to 0.5 kg.
/crA gauge pressure range is preferred.

Within this range, in addition to the pressure naturally generated from the reaction system, an inert gas such as N2 is introduced before or during the reaction,
It is also good to apply slight pressure.

In this case, first, 60% to 20% of BHT is stored in TPA units, and EG+TPA slurry is continuously supplied thereto.

When the amount of BHT stored exceeds 60%, productivity deteriorates.
If it is less than 20%, the reaction time will be long.

Further, in either case, the formation of DEC becomes significant, which is not preferable.

Note that the purpose of continuously adding the slurry is to raise the reaction temperature, and it may be added intermittently as long as the reaction temperature is not extremely lowered.

The reaction temperature for esterification is 200 to 260°C, and 22
0 to 240°C is more preferable.

If the reaction temperature is less than 200°C, the reaction time will be longer and 26
When the temperature exceeds 0°C, the amount of DEG increases and gives an undesirable color to the reaction product.

Known catalysts and softening point lowering inhibitors can be used in the esterification reaction of the present invention.

In addition, any known method can be applied to the polycondensation of the esterification reaction product, and known polycondensation catalysts, color inhibitors,
Other various additives used during polyester production may also be added.

The effects of the esterification method of the present invention are listed below.

(1) By installing a slurry storage tank, the imbalance between the slurry supply time and the esterification reaction time can be absorbed, and the slurry prepared in a kneader etc. can be aged by stirring in the storage tank to prevent clogging in the supply piping. can.

(2) By installing a snake pump, it is possible to supply slurry with a low EG/TPA molar ratio, and it is also possible to supply slurry with excellent quantitative properties.

(3) The normal pressure reaction by continuous supply of slurry can reduce the amount of free EG in the system, suppress the generation of DEC, and keep the amount of solid TPA in the system at a constant level, making stirring easy. Because it is a pressure reaction, the reaction vessel and attached instruments are inexpensive.

The esterification method using a slurry tank and a snake pump according to the present invention can be applied to a conventionally known pressurized esterification reaction using EG+TPA liquid feeding.

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

Example In the apparatus shown in FIG. 1, TPA was fed through a hopper 1 and a weighing machine 2 at a rate of 50 kg/hr, and EG was fed through a continuous kneader 3 at a rate of 21.3 kg/hr.
supplied.

The rotation speed of the kneader was 58 rpm, and the residence time in the kneader at this time was 10 minutes.

The homogeneous slurry from the kneader was transferred to a 3001 capacity slurry storage tank.

After the slurry storage tank 4 is stirred at 18 rpm and retained for 30 minutes, it is pumped with a snake pump 5 connected to the bottom of the storage tank.
was operated to supply the slurry to the esterification reactor.

The snake pump runs at 5 rpm and 70 k.
It was fed at a rate of g/hr.

The slurry supply piping had an inner diameter of 2 inches, a vertical portion of 5 μm, and was connected to the esterification reactor with a total length of 15 m.

Near the inlet to the esterification reactor, the piping is equipped with a water cooling jacket and a ball valve is installed.
A pressure gauge was attached to the supply piping between the snake pump and the esterification reactor.

BHT (average degree of polymerization 6.0
, esterification reaction rate 98.7%, DEC content 0.7% by weight) was melted and stored at 245° C., and slurry was continuously supplied thereto at a rate of 70 kg/hr for 4 hours using a snake pump.

During this time, the pressure gauge in the piping showed a gauge pressure of 0.8 kg/ctA, and the reaction temperature was 245-235°C.

One hour after the slurry supply was stopped, the amount of water distilled was 42.
kg, and the reaction was stopped, but the reaction temperature at this time was 2.
The temperature was 45°C.

After stopping the supply of slurry to the esterification reactor, the quantitative performance of the snake pump was checked, and the result was 70 kg/hr, the same as before supply.

The obtained BHTO saponification value was 556.6 KOH/P, oxidation value was 11.2 KOH/P, DE
The G content was 0.65% by weight and the color tone was excellent.

A portion of the obtained BHT was transferred to a polycondensation apparatus, and 120 kg was stored in an esterification reaction apparatus.

As before, the slurry was continuously supplied using a snake pump to carry out the esterification reaction of the next batch.

At this time, the snake pump stopped for 1 hour and 15 minutes, but when the snake pump restarted, there was no blockage in the slurry, and the pressure gauge attached to the piping showed 0.8 kg/
It was crt't gauge pressure and could be supplied smoothly like last time.

Comparative Example 1 Slurry was supplied to an esterification reactor containing BIT under the same conditions as in Example except that a kneader and a snake pump were directly connected without installing a slurry storage tank.

When the slurry supply was stopped after 4 hours as in the example,
After 1 hour, the amount of distilled water was 42.2 kg, the amount of distilled water was low, and the reaction was completed.

During this period, the pressure in the piping changed from the initial 0.8 kg/ca gauge pressure to 4.6 k61/crA gauge pressure.

The quality of the obtained BHT is saponification value 558.17% KOH
/f, oxidation value 9.8 ■KOH/? , D E C0
, 69% by weight.

After partially storing the obtained BHT and its oligomers and transferring them to the polymerization equipment, when trying to supply the slurry for the next batch, the pressure inside the piping exceeded 20 kg/cm gauge pressure, and the slurry supply stopped. It was impossible.

The stop time of the kneader and snake pump was 1 hour and 15 minutes as in the example.

Comparative Example 2 Slurry was started to be supplied to the esterification reactor in which BHT was present under the same conditions as in the example except that the snake pump in the example was changed to a gear pump.

The rotation speed of the gear pump was 56 rpm, which was the same as in the example.
Feed was started at a rate of 0 icg/hr.

40 minutes after the start of supply, the esterification reaction state became abnormal and an inspection revealed that normal slurry was not being supplied stably, and slurry with a high EG content was gradually being supplied to the esterification reactor, and the slurry supply was interrupted. It was found that the supply of slurry had been cut off 35 minutes after the start.

When the gear pump was dismantled and inspected, it was discovered that TPA had stuck to the teeth of the gear pump, and that the TPA had formed a block on the primary side of the pump, clogging the piping.

From this, it is clear that a pump supplying slurry with a low EG/TPA molar ratio is inappropriate.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus suitable for carrying out the invention. FIG. 2 is a schematic diagram for explaining a snake pump suitable for use in the present invention. 1...TPA Hotsuha, 2...TPA
Weighing machine, 3...Kneader, 4...-Slurry storage tank, 5...Snake pump, 6...
Stator 7...Gap, 8...Rotor 9...Shaft.

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 stored in a storage tank, and the slurry is pumped using a snake pump to produce bis-β-hydroxyethyl terephthalate and/or its lower condensates. A batch esterification method characterized in that a low condensate is continuously supplied to a reaction system containing a low condensate and the reaction is carried out under substantially normal pressure.