JPS5833217B2 - Batch esterification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improved 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. More specifically, it relates to a method for supplying a slurry consisting of terephthalic acid and ethylene glycol with a stable esterification value.

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.

However, 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 if the molar ratio of EG/TPA is high (then diethylene glycol, which is a dehydrated condensate of EG), A large amount of DEC (hereinafter referred to as DEC) is generated, and the quality of the finally obtained PET deteriorates.

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

However, when the E G/T P A molar ratio is lowered, solid TP
It becomes necessary to handle a highly viscous slurry consisting of a mixture of A and EG, which inhibits 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. occurs.

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 using TPA with a specific slurry property, is continuously added to the reaction system in which BHT is present at 240°C or higher. (Special Publication No. 50-19313.5O-19314), E
A method of continuously supplying G + TPA slurry to maintain the reaction rate at 85 to 95% during esterification reaction (Japanese Unexamined Patent Application Publication No. 1983-53342), in which EG + TPA is added to the esterification equipment.
When supplying slurry, a cooling method to prevent slurry from solidifying in the slurry-forming to supply process
9119) 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. .

Furthermore, even if an E G/T P A slurry is obtained with an arbitrary molar ratio, when it is transported and measured in batches to a reaction vessel, sedimentation of the slurry may occur during the waiting time between batches.
This method has disadvantages such as the fact that a flow meter suitable for measuring the slurry cannot be obtained industrially.

For example, considering only slurry transportation, the chemical engineering handbook (Chemical Engineering Society, 4th edition, 1960), page 908, states that normal pumps that compress and compress liquid, such as centrifugal pumps, reciprocating pumps, gear pumps, and screw pumps, use TPA. and EG separated,
Unable to send liquid.

The present inventors used slurry with a low EG/TPA molar ratio as BH
To provide a method for stably supplying a slurry in a batch-type esterification method in which T is continuously supplied to a system in which it is kept in a homogeneous state and having a high degree of quantitative property for a plurality of esterification values. The present invention was arrived at after studying the following.

That is, the present invention involves the batch production of bis-β-hydroxyethyl terephthalate and/or its low polymer from terephthalic acid and ethylene glycol, using a snake pump to produce a slurry of terephthalic acid and ethylene glycol for a plurality of esterification values. This is a batch esterification method characterized in that esterification is carried out by circulating the ester using a snake pump, and measuring and charging the required amount from the circulation system for each of the plurality of mono-esterification values using a snake pump.

The method of the present invention will be explained with reference to the drawings.

FIG. 1 is a schematic diagram suitable for carrying out the method of the present invention, in which an EG/TPA slurry having a molar ratio of 0.95 or more is stored in a slurry storage tank 2 from a pipe 1, and a primary Slurry is circulated through a take-out pipe 4 using a snake pump 3, and the slurry is taken out from any part of the circulation line by branching to each reaction vessel. and feed it to the esterification number 9.

At this time, the rotation speed of the pump is detected by a counter 8 to measure the amount of slurry supplied.

After a predetermined amount of supply is completed, the branch valve 5 is closed, and the secondary snake pump 7 is stopped when the pressure gauge 6 confirms that the pressure in the piping between the branch valve 5 and the secondary snake pump 7 has decreased. do.

During operation, a timer is installed in place of pressure gauge 6, and valve 5 is
The pump 7 may be stopped after a predetermined period of time (for example, 3 to 5 seconds) has passed after closing the pump.

In the present invention, a snake pump is a non-compressible pump that pumps liquid by utilizing the gap formed by the planetary movement of a rotor with a single thread male thread inside a stator with a double thread female thread. It is what is shown.

That is, the EG/TPA slurry adjusted to a predetermined concentration is supplied from A into a closed housing through which the shaft of the rotor 13 passes.

The rotor 13 has irregularities on its surface, and is rotated by a shaft 14 connected to a drive source.

Further, the stator 11 containing the rotor 13 is configured to have the same pitch as the rotor 13 and a gap 12 on its inner surface.

As the rotor 13 rotates, the cavity 12 is propelled from the nozzle portion toward the outflow portion.

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

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.

The molar ratio of E G/T P A of the slurry used is 0.
95 to 1.8 are preferable, and 1.1 to 1.5 are more preferable.

However, if the molar ratio is less than 1.0, it is necessary to dissolve or disperse the catalyst or additive in EG, or add EG to make the molar ratio 1.0 or more.

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.

If the pressure at the pump suction port immediately after slurry is supplied is even slightly reduced from atmospheric pressure, it can be confirmed that no slurry remains, so it is desirable to have a control system that detects the degree of pressure reduction and automatically stops the pump.

In other words, it is common knowledge that each batch type esterification unit is operated in a time cycle of a certain amount of time, so there are times when slurry is fed in and times when it is not fed in, but generally the latter time is shorter. long.

Therefore, sedimentation of the slurry on the suction side of the pump becomes a problem when the slurry supply is stopped, but the present inventors have found that the pump continues to flow from the switching valve in the circulation system to the pump suction port even after the switching valve is closed. They discovered the fact that when the pump is driven, the pressure decreases, and conversely found a method to stop the pump when the pressure decreases, thus solving the above problem.

This is because the above-mentioned pump has very excellent sealing properties, and by utilizing this property, we have found a method for intermittent supply of sedimentary slurry.

Further, it is also desirable that part or all of the circulation line and each supply line be cooled with a water jacket or the like in order to preferably maintain the fluidity of the slurry.

In particular, it is desirable to install a water jacket to cool the area near the inlet to the esterification reactor, as heat from the reactor may be transmitted to the slurry supply piping and deteriorate the fluidity of the slurry.

The esterification reaction is carried out under substantially normal pressure (0.02 to 0.3 kg
/cA gauge pressure).

In this case, first, BHT and/or its oligomer is TP
Preferably 1/2 to 115 is stored in A unit, and EG is stored there.
+Continuously feed TPA slurry.

When the storage amount of BHT exceeds 1/2, productivity decreases and 1/2
If it is less than 15, 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 preferably 200 to 260°C, more preferably 220 to 240°C.

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 present invention are listed below.

In other words, ■ Low E G / T P A by installing a snake pump.
It is possible to supply slurry with the same molar ratio, and the amount of EG in the system can be reduced through normal pressure reaction due to continuous supply of slurry.
DEC by-products can be controlled.

■ Since the slurry, including the slurry storage tank, is constantly flowing in the circulation system, it is possible not only to maintain a constant uniformity and molar ratio, but also to prevent clogging in the supply piping.

Therefore, the subsequent esterification can be operated stably.

■ Since there is almost no slurry to settle between the switching valve installed at each branch and the secondary snake pump, it is possible to prevent pipe clogging due to settling of residual slurry.

■ Since the excess amount of the amount to be supplied to each reaction vessel is always stored and maintained at the supplied amount, even if the number of reaction vessels to be supplied changes due to time cycle discrepancies, it can be responded to immediately. can be supplied.

■ The amount of slurry supplied to the esterification value can be accurately supplied while the slurry is being pumped by detecting the rotation of the snake pump and measuring the slurry, which is kept homogeneous.

Benefits include:

Example: 714.6 parts by weight of the EG/TPA slurry (molar ratio 1.2) stored in the slurry storage tank 2 was circulated through the circulation line 4 via the secondary snake pump 3 at a rate of 900.0 parts by weight/hour. do.

159.7 parts by weight of bis β-hydroxyethyl terephthalate with an esterification reaction rate of 98% was stored at 240° C. to an esterification value of 9, and a slurry was metered by a secondary snake pump 7 from a circulation line 4 via a branch valve 5. The slurry was then fed at a rate of 53.0 parts by weight/hour.

During the supply, the reactants in the esterification value were maintained at 238 to 240°C to carry out the esterification reaction.

After the EG/TPA slurry was supplied, it was stored for an additional hour to obtain bis-β-hydroxyethyl terephthalate with an esterification reaction rate of 98%.

COMPARATIVE EXAMPLE Without using the circulation line 4 in the example, EG/
The TPA slurry was directly supplied from the slurry storage tank 2 to the esterification value 9 using the secondary snake pump 7, and the esterification reaction was carried out to produce bis-β-hydroxyethyl terephthalate with an esterification reaction rate of 98% as in the example. Obtained.

Half of the reaction product was subjected to the next step of polycondensation.

Next, when the EG/TPA slurry in the slurry storage tank 2 was supplied to the remaining reactant with an esterification value of 9 through the secondary snake pump 7 and an esterification reaction was attempted, the secondary snake pump 7 and the esterification can 90 The slurry supply pipe in between was blocked and could not be supplied.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a preferred process of the present invention, and FIG. 2 is a schematic diagram for explaining a snake pump used in the present invention. 1...Piping, 2...Slurry storage tank, 3
・・・・・・−Secondary snake pump, 4・・・・・・Circulation line, 5・・・・・・Branch valve, 6・・・Pressure gauge, 1・・・・・・Secondary Snake pump, 8...
...Counter, 9... Esterification value, 11.
... Stator, 12 ... Void part, 13
...Rotor 14 ...Axis.

Claims (1)

[Claims] 1 Bis-β from terephthalic acid and ethylene glycol
- When producing hydroxyethyl terephthalate and/or its low polymer in a batch manner, a slurry of terephthalic acid and ethylene glycol is circulated using a snake pump for a plurality of esterification values, and each of the plurality of mono-esters is A batch esterification method characterized by measuring and charging the required amount using a snake pump from the circulation system to perform esterification.