JPS5844652B2 - Method for esterifying aromatic dicarboxylic acids - Google Patents

Description

Detailed Description of the Invention The present invention relates to bis(hydroxyalkyl)terephthalate, its low polymer, or a mixture thereof, which is useful as an intermediate for producing polyalkylene terephthalate used in fibers, films, plastics, adhesives, etc. , by esterifying terephthalic acid or an aromatic dicarboxylic acid mainly consisting of terephthalic acid with a glycol having 2 to 10 carbon atoms.

By esterifying terephthalic acid with ethylene glycol,
Methods for producing bis-(2-hydroxyethyl) terephthalate and its oligomers useful as intermediates for producing polyethylene terephthalate are generally known.

However, in this case, various difficulties arise when carrying out the esterification reaction because terephthalic acid is insoluble at normal esterification temperatures and is insoluble or sparingly soluble in common solvents such as ethylene glycol.

For example, a mixture of terephthalic acid and ethylene glycol that is subjected to a normal esterification reaction is a highly viscous slurry, making it difficult to transport, and furthermore, when the above mixture is subjected to an esterification reaction, the slurry is highly viscous. As a result, heat transfer becomes poor at the beginning of the esterification reaction, which increases the time required for the reaction, or side reactions tend to occur in locally heated areas, resulting in poor quality of the reaction product obtained. descend.

Furthermore, the stirring power required to carry out the esterification reaction also increases, resulting in a large loss of energy.

Furthermore, there was a problem that the required ratio of ethylene glycol to terephthalic acid varied depending on the particle size of the terephthalic acid.

Various methods have been proposed to address the above-mentioned problems, particularly to reduce the viscosity of the slurry in the reaction system at the initial stage of the esterification reaction.

That is, (1) a method of adding water in advance to the esterification reaction system (Japanese Patent Publication No. 36-3840) or a method of adding hydrocarbons (Japanese Patent Publication No. 37-11546);
) A method in which terephthalic acid and ethylene glycol are reacted in the presence of bis(2-hydroxyethyl) terephthalate or a low polymer thereof (Japanese Patent Publication No. 43-22999).

However, method 1) requires a large heat loss for removing the solvent used, and is not expected to increase the reaction rate much.

Furthermore, depending on the type of solvent used, there are drawbacks such as a decrease in the quality of the obtained product.

On the other hand, in method (2), it is necessary to produce bis(2-hydroxyethyl) terephthalate or its low polymer by a separate operation, or to use a part of the product once produced remaining.

Therefore, the resulting product contains some products with a long thermal history, making it impossible to obtain a high quality product.

Furthermore, this method is by no means satisfactory in terms of operability and other aspects.

In view of the above points, the present inventors conducted a detailed study on the process of esterifying terephthalic acid with ethylene glycol, and as a result, the following findings were obtained.

That is, the above esterification reaction is divided into the following two processes.

(1) A process in which solid terephthalic acid is dissolved in ethylene glycol.

(2) A process in which the carboxyl group of dissolved terephthalic acid reacts with the hydroxyl group of ethylene glycol or bis(2-hydroxyethyl) terephthalate or its low polymer to form an ester bond.

When we examined the speed of the above two processes, we found that process (1) is faster and that a constant concentration of carboxyl groups always exists in the liquid phase of the esterification reaction system.

Therefore, in the esterification reaction, most of the solid terephthalic acid that is not dissolved in the liquid phase does not directly participate in the reaction, and the reaction system contains enough terephthalic acid in the liquid phase to reach saturation solubility. It is sufficient if a sufficient amount of solid terephthalic acid is present.

Even if the esterification reaction progresses, if a sufficient amount of solid terephthalic acid is present in the reaction system so that the terephthalic acid dissolved in the liquid phase reaches saturation solubility, the esterification rate will decrease. There's nothing to do.

However, in the esterification reaction, more than a certain amount of
In other words, if a large excess of solid terephthalic acid is present,
These terephthalic acids not only do not participate in esterification, but also increase the viscosity of the slurry of the reaction mixture, lowering its fluidity, impairing the heat transfer of the reaction mixture, and requiring extra stirring power. causing problems such as

Furthermore, since the reaction between terephthalic acid and ethylene glycol is a heterogeneous reaction, it is significantly influenced by the particle size of the terephthalic acid used in the reaction.

Particularly when using terephthalic acid with a small particle size, the amount of ethylene glycol used relative to the terephthalic acid must be increased in order to obtain a slurry with electromotive properties.

However, if the amount of ethylene glycol used for terephthalic acid is too high, the dehydration reaction between ethylene glycol and terephthalic acid also occurs during the esterification reaction, resulting in an increase in the amount of diethylene glycol produced. The softening point of the polyester obtained by acid condensation is lowered.

On the other hand, from the cost perspective when producing polyester, it is desired that the molar ratio of ethylene glycol to terephthalic acid be 2.5 or less, preferably close to the stoichiometric value of 1.0.

However, with such a small molar ratio, it is impossible to obtain a fluid slurry mixture of terephthalic acid and ethylene glycol.

In other words, when esterifying terephthalic acid with ethylene glycol, it is necessary to satisfy two contradictory demands: reducing the amount of ethylene glycol used relative to terephthalic acid, and at the same time improving the fluidity of the slurry of the reaction mixture. There is.

In view of the above circumstances, the present inventors conducted various studies to improve the drawbacks of the conventional method in the esterification reaction of terephthalic acid and ethylene glycol, and as a result, they came to obtain the method of the present invention.

That is, the present invention uses terephthalic acid or an aromatic dicarboxylic acid mainly consisting of terephthalic acid having 2 to 1 carbon atoms.
When esterifying with 0 glycol, maintain the esterification reaction system so that the proportion of unesterified aromatic dicarboxylic acid to the total weight of the reaction mixture is 30 or less by weight throughout the esterification period. A method for esterifying terephthalic acid or an aromatic dicarboxylic acid mainly consisting of terephthalic acid, characterized by:

In the present invention, aromatic dicarboxylic acids other than terephthalic acid used for esterification include, for example, isophthalic acid, 2,6-naphthalene dicarboxylic acid, sodium 3,5-dicarboxybenzenesulfonate, and 4,4'-biphenyldicarboxylic acid. Examples include acids.

Ethylene glycol is preferred as the glycol having 2 to 10 carbon atoms used for esterification, but other examples include 1,2-propanediol, 1,3-propanediol, 4-butanediol, neopentyl glycol,
Examples include cyclohexane dimetatool and mixtures thereof.

In the present invention, the reaction system is maintained such that the amount of unesterified aromatic dicarboxylic acid is 30% by weight or less based on the total weight of the reaction mixture at any point in the esterification reaction. This feature makes it possible to minimize the viscosity of the reaction mixture during the esterification reaction, especially at the initial stage.

This point will be further explained in detail with reference to FIG.

Figure 1 shows the initial stage of esterification when a predetermined amount of terephthalic acid and ethylene glycol were supplied to an autoclave at 240°C, the total amount was kept constant, and the weight ratio of terephthalic acid and ethylene glycol in the autoclave was varied. This graph shows the change in the power applied to the stirrer for stirring the reaction mixture, and the power value on the vertical axis is expressed as a multiple of the power when only ethylene glycol is used, which is taken as 1.

It is recognized that as the concentration of terephthalic acid in the reaction mixture shown on the horizontal axis of the figure increases, the power of the stirrer on the vertical axis increases, but the increase is especially large when the concentration of terephthalic acid exceeds 30%. This was confirmed.

This shows that carrying out esterification at a concentration of terephthalic acid in the reaction mixture of 30φ or less as shown in the present invention is extremely advantageous in terms of stirring the reaction system.

As a specific method for carrying out the esterification reaction according to the method of the present invention, for example, 1 mole of terephthalic acid is added to 10 moles of ethylene glycol, mixed, heated under pressure, and a part of the terephthalic acid is added. Esterification is performed by dissolving in ethylene glycol.

It is effective to repeat the process of adding 1 mole of terephthalic acid to the reaction system as the esterification reaction progresses to continue the esterification reaction.

By sequentially adding terephthalic acid to the reaction system in this way, the molar ratio of ethylene glycol to terephthalic acid added to the reaction system was 1.0 by the end of esterification.
-25 preferably 10-2.0.

In this case, the amount of terephthalic acid added to the reaction system, the timing of addition, etc. can be determined by, for example, measuring the torque applied to the stirrer that is stirring the reaction system. If the reaction is being carried out while distilling water to the outside, this can also be determined by measuring the amount of water distilled out.

Conditions such as temperature, pressure, and stirring for esterification in the present invention may be arbitrarily selected from conventionally known methods.

Further, the method of the present invention can be carried out either continuously or batchwise.

An example of the latter method has already been shown, but the former method can be implemented using, for example, the apparatus shown in FIG.

FIG. 2 schematically shows an esterification apparatus for continuously performing esterification of the present invention, and 1 is an esterification reaction tank, which is heated by a jacket not shown in the drawing.

A partition plate 2 is installed in the reaction tank 1, and the reaction tank 1 is divided into a plurality of reaction chambers 3.

First, ethylene glycol is supplied to the first reaction chamber from the supply port 4, and terephthalic acid is supplied from the upper supply port 5.

The reaction mixture is stirred by the stirrer 6, the esterification reaction proceeds, and by-product water is removed from the volatile matter discharge lower.

The reaction mixture in which the esterification reaction has proceeded is sent to the next reaction chamber through piping 8.

Also in this reaction chamber, terephthalic acid is supplied from the upper supply port 5, and the esterification reaction proceeds in the same manner.

Similarly, in each reaction chamber, terephthalic acid is supplied from the upper supply port 5 to the reaction mixture supplied from the previous reaction chamber via the pipe 8 to complete the esterification.

The reaction product that has completed the esterification process in the last reaction chamber is taken out from the outlet 9.

In addition, even in this continuous esterification method, unreacted terephthalic acid in the reaction mixture in each reaction chamber is always maintained at 30% by weight or less, and the reaction mixture is
The total terephthalic acid supplied to the reaction mixture before being taken out from the first reaction chamber and the ethylene glycol supplied to the first reaction chamber are supplied to each reaction chamber such that the molar ratio is 1:1.0 to 2.5. The amount of terephthalic acid added is adjusted.

In the method of the present invention, when esterifying an aromatic dicarboxylic acid mainly consisting of terephthalic acid with glycol, it does not depart from the spirit of the present invention to add additives other than the aromatic dicarboxylic acid and glycol.

Examples of such additives include various metal compounds used as catalysts for esterification reactions, amines used as inhibitors of ether bond formation, nitrogen compounds such as acid amides, and pigments such as titanium oxide and carbon black. Can be mentioned.

The reaction mixture obtained by the method of the present invention is mainly composed of a diglycol ester of an aromatic dicarboxylic acid and/or a low polymer thereof, and a suitable polycondensation catalyst,
For example, a high-quality polyester can be obtained by adding antimony trioxide, germanium dioxide, or a titanyl oxalate compound and polycondensing the mixture by heating to a high temperature under reduced pressure.

Conventional esterification reactions were carried out in a highly viscous slurry state, which imposed various restrictions on the viscosity of the aromatic dicarboxylic acid and the solid-liquid ratio during esterification.However, in the present invention, , it has become possible to completely remove these restrictions.

Furthermore, since the esterification reaction of the present invention is carried out in a completely low-viscosity, almost homogeneous reaction system, the power required for stirring the reaction system is reduced, and the manufacturing cost of the esterification reaction apparatus is accordingly reduced. be able to.

Therefore, it has become possible to reduce the cost required for the esterification reaction.

Furthermore, according to the method of the present invention, the esterification reaction can proceed without locally overheating the reaction mixture, making it possible to prevent the quality of the product from deteriorating.

Therefore, the method of the present invention makes it possible to economically produce a polyester of higher quality than aromatic dicarboxylic acids and glycols.

The method of the present invention will be specifically explained below with reference to Examples, but the present invention is not necessarily limited to these Examples.

In addition, in the examples, parts represent parts by weight.

The esterification rate (ES%) of aromatic dicarboxylic acid is determined by measuring the acid value (AV) and hydration value (SV) by a conventional method.
It was calculated according to the following formula.

*V-AV ES coefficient 2□XI 00 SV The intrinsic viscosity ([η]) was measured at 30°C using a mixed solvent of phenol:tetrachloroethane=6:4 (weight ratio).

Further, the diethylene glycol content (DEG) was expressed as the mole φ of diethylene glycol in all the glycol units of the polymer.

Furthermore, the hunter scale b value, which indicates the color tone of the polymer, is measured in the form of pellets, and is a measure of yellowness, and the smaller the b value, the better the color tone.

Reference Example: 0 parts of ethylene glycol was supplied to an autoclave equipped with a stirrer, a rectification column, a pressure regulator, and a device for continuously supplying terephthalic acid, and after replacing the air in the space of the autoclave with nitrogen, With gas, 4.5
While pressurizing to kg/i (gauge pressure) and maintaining constant pressure,
The temperature was raised to 240°C.

The stirring power when this temperature change is reached is measured, and then terephthalic acid with an average particle size of 50μ is gradually added to change the terephthalic acid concentration in the mixture, and the stirring power is adjusted according to the terephthalic acid concentration. The rise was measured.

The stirring power when no terephthalic acid is added is 1,
The magnification of the stirring power for each terephthalic acid concentration is shown in Table 1 below, and FIG. 1 is a plot of it.

The terephthalic acid concentration was calculated from the amount of ethylene glycol initially charged and the amount of terephthalic acid added, and the stirring power was calculated from the voltage and current applied to the stirrer motor.

Example 1 100 parts of terephthalic acid with an average particle size of 50μ, ethylene glycol 4
After supplying 48 parts of N,N-dimethylformamide and 0.09 parts of N,N-dimethylformamide and replacing air with nitrogen in the autoclave space, pressurize to 4.5 kg/i (gauge pressure) with nitrogen gas and maintain a constant pressure. Esterification was carried out while raising the temperature to 240° C. and removing the produced water from the system through a rectification column.

Twenty minutes after the start of the reaction, the internal temperature reached 240°C.

Ten minutes after reaching 240°C, terephthalic acid was started to be added to the reaction system according to the following method.

That is, the amount of water distilled from the reaction system was measured every 5 minutes,
Terephthalic acid equivalent to 1 part and 2 times water in molar ratio was supplied to the reaction system.

By this method, the amount of unreacted terephthalic acid relative to the total amount of the reaction system mixture could always be kept at 30 parts or less.

After starting to add terephthalic acid to the reaction system, 900 parts of terephthalic acid was added in 100 minutes.

Since water corresponding to an esterification rate of 86 was distilled out 160 minutes after the start of the esterification reaction, the autoclave was depressurized and the esterification process was completed.

A total of 10 terephthalic acids were supplied to the esterification reaction system.
00 parts, and ethylene glycol is 448 parts, so the molar ratio of ethylene glycol to terephthalic acid (hereinafter expressed as EG/TPA).

) was 12.

The current applied to the stirrer motor during the esterification reaction was almost constant.

The characteristic values of the polymer obtained by adding 0.262 parts of antimony trioxide to the obtained reaction product and polycondensing it under reduced pressure according to a conventional method are as follows: [η] is 0628 and DEG is 20.
9φ and b value was 3.0.

Comparative Example 1 In the same autoclave used in Example 1, ooo parts of the same terephthalic acid used in Example 1 (approximately 70 weight φ),
448 parts of ethylene glycol N.

"-Supplying 0.09 parts of dimethylformamide at once,
After replacing the air with nitrogen in the autoclave space, the pressure was increased to 4.5 kg/cIIL (gauge pressure) with nitrogen gas, and the temperature was raised to 240°C while maintaining a constant pressure. The water produced was passed through a rectification column to the system. The esterification reaction was carried out while removing the mixture from the outside.

In this case, it took 90 minutes from the start of esterification for the internal temperature to reach 240°C.

Then, over a period of 155 minutes, water corresponding to an esterification rate of over 85 was distilled out, so the autoclave was depressurized and the esterification step was terminated.

The maximum current applied to the stirrer motor during the esterification reaction was four times that of Example 1, and it was found that stirring in the autoclave at the initial stage of the esterification reaction was extremely difficult.

The characteristic values of the polymer obtained by polycondensing the obtained reaction product in exactly the same manner as in Example 1 are as follows: [η] is 0.625;
The DEG was 2.88 and the b value was 4.4.

Example 2 To the autoclave used in Example 1, 90 parts of terephthalic acid, 10 parts of 4,4'-biphenyl dicarboxylic acid, 448 parts of ethylene glycol, and 0.211 parts of calcium acetate used in Example 1 were supplied, Esterification was carried out in the same manner as in Example 1.

After the start of esterification, the internal temperature reached 240°C in 30 minutes.

A mixture of 180 parts of terephthalic acid and 20 parts of 4,4'-biphenyldicarboxylic acid was then added to the autoclave four times at 20 minute intervals.

The timing and amount of addition of aromatic dicarboxylic acid were determined according to the method of the present invention based on the results of measuring distilled water.

After 180 minutes after the start of esterification, water equivalent to 85% of the esterification rate of aromatic dicarboxylic acid was distilled out of the system.
The pressure inside the autoclave was released to complete the esterification process.

The current applied to the stirrer motor during the esterification reaction was almost constant.

The characteristic values of the polymer obtained by polycondensing the obtained reaction mixture in exactly the same manner as in Example 1 are as follows: [η] is 0621;
The DEG was 227, and the b value was 3.2.

Comparative Example 2 In the autoclave used in Example 2, 810 parts of terephthalic acid used in Example 2, 90 parts of 4,4'-biphenyl dicarboxylic acid (approximately 62 parts by weight as fully aromatic dicarboxylic acid), and 448 parts of ethylene glycol were added. , calcium acetate 0.
Esterification was carried out in the same manner as in Comparative Example 1 by supplying 211 parts.

After the start of esterification, the internal temperature reached 240°C in 90 minutes, and the esterification rate of aromatic dicarboxylic acid reached 85 in 245 minutes.
Since water corresponding to the amount of water was distilled out, the pressure inside the autoclave was released to terminate the esterification process.

The maximum current applied to the stirrer motor during the esterification reaction was 3.5 times that of Example 2, and stirring in the autoclave at the initial stage of the esterification reaction was particularly difficult.

The characteristic values of the polymer obtained by polycondensing the obtained reaction product in exactly the same manner as in Comparative Example 1 are as follows: [η] is 0619, D
The EG was 3.24φ and the b value was 4.5.

[Brief explanation of drawings]

Figure 1 is a plot of the power applied to the stirrer to stir the reaction mixture in the early stage of esterification when esterifying a mixture of terephthalic acid and ethylene glycol as the concentration of terephthalic acid in the reaction mixture is varied. This is the graph. FIG. 2 is a vertical sectional view schematically showing an esterification apparatus for carrying out esterification of the present invention. 1... Esterification reaction tank, 2... Partition plate, 3... Reaction chamber, 4... Ethylene glycol supply port, 5...・Terephthalic acid supply port,
6... Stirrer, 7... Volatile substance discharge port, 8... Piping, 9... Output port.

Claims (1)

[Claims] 1. When esterifying terephthalic acid or an aromatic dicarboxylic acid mainly consisting of terephthalic acid with a glycol having 2 to 10 carbon atoms, the unesterified aromatic dicarboxylic acid is added to the total weight of the reaction mixture during the entire esterification period. A method for esterifying terephthalic acid or an aromatic dicarboxylic acid mainly consisting of terephthalic acid, characterized in that the esterification reaction system is maintained such that the acid concentration is 30% by weight or less.