JPH0361660B2 - - Google Patents

Description

Detailed Description of the Invention The present invention produces terephthalic acid glycol ester, that is, bis(β-hydroxyethyl) terephthalate and/or its low polymer (BHET) by reacting terephthalic acid (TPA) and ethylene glycol (EG). It provides a method for simultaneously and efficiently producing BHET with different properties that can form a polyester with a low diethylene glycol (DEG) concentration and good heat resistance.

Polyester, which is used industrially today,
In particular, polyethylene terephthalate has a high degree of crystallinity and a high softening point, and has excellent strength, chemical resistance, heat resistance, and
Because it has excellent properties in terms of weather resistance and electrical insulation, it is widely used industrially as fibers, films, and other molded products.

Generally, when polyester is used in various industrial fields, it usually has heat resistance during forming processes such as melt extrusion, drawing, stretching, and heat treatment, or in the case of films, heat resistance during magnetic layer coating and metal vapor deposition. Heat resistance is required in the secondary processing process when molded products are made, and heat resistance is required when the products are made into final products.

To this end, one important issue is to reduce the DEG concentration in polyester that occurs as a result of side reactions. Polyester is normally produced through an esterification process followed by a polycondensation process, but in the past, in order to reduce the DEG concentration, the esterification process, which has a large influence, has required the development and improvement of catalysts and additives, or the development and improvement of DEG. Although processes have been developed that can reduce concentrations, they also have certain drawbacks.

For example, the addition of alkali metal compounds as catalysts or additives, which has been proposed in many ways, including in Japanese Patent Publication No. 34-2594, is itself
Although it contributes to reducing the DEG concentration, it also has the drawback of impairing color tone, viscosity, strength, and other physical properties, and causing a delay in the polycondensation rate.

On the other hand, as a process to reduce the DEG concentration, there has been a transesterification method that produces BHET by transesterifying dimethyl terephthalate and EG, but it is not suitable for continuous operation and dimethyl terephthalate is less suitable than TPA. It is expensive and compared to the transesterification method, it is more expensive than TPA.
The so-called direct esterification method, in which EG is directly esterified, has the advantage of simplifying the process, so the direct esterification method has gradually been used to this day. Therefore, at present, the transesterification method is generally used only for varieties that require a particularly low DEG concentration, which increases the cost to some extent.

Now, even when the above-mentioned direct esterification method is adopted, a method has also been proposed for producing high-quality BHET with a low DEG concentration that is as good as the transesterification method.

For example, as disclosed in Japanese Patent Publication No. 46-22463, TPA is suspended in BHET and gaseous EG is reacted at a temperature higher than the boiling point of EG, or as disclosed in Japanese Patent Publication No. 50-24236. As has been said,
By separating unreacted TPA particles from the esterification reaction product in which unreacted TPA particles are suspended, the reaction rate is constant and the DEG concentration is low.
Methods for obtaining BHET have been proposed.

However, even when these methods are adopted, in the former case, there are problems due to variations in reaction rate and DEG concentration, and in the latter case,
Lowering the reaction temperature will reduce the DEG concentration, but
This method has problems in that productivity is poor and the system becomes extremely unstable when the reaction rate fluctuates due to disturbances.

As described above, a method for continuously and efficiently producing high-quality BHET with a low DEG concentration by a direct esterification method has not yet been fully completed industrially.

As a result of extensive research in order to solve this problem, the present inventors conducted a reaction using a plurality of consecutive reaction vessels, and not only the first reaction vessel, but also
By supplying a slurry consisting of raw materials TPA and EG to the final reaction tank, and filtering the reactants from both reaction tanks to remove unreacted TPA particles,
The present invention was completed by discovering that BHET with different properties can be efficiently obtained at low DEG concentrations.

That is, the present invention involves reacting TPA and EG.
When producing BHET continuously, the reaction is carried out using two or more consecutive reaction vessels, and the raw material is
The reactant is supplied to the reaction tank and the final reaction tank and reacted to form an esterification reaction product in which unreacted TPA particles are suspended, and the reactant from the first reaction tank and the final reaction tank is filtered to remove unreacted TPA. It is characterized by removing particles.

As the esterification method in the present invention, a method is usually used in which a slurry consisting of TPA and EG is continuously supplied to a reaction tank in which BHET is present and esterification is performed. This BHET includes some TPA and
BHET may contain components other than EG residues, and BHET may be obtained by any known method, but it is preferable to use the one obtained by the above method as is. . Raw materials are usually
It is supplied as a slurry consisting of TPA and EG, but the molar ratio of EG/TPA in the slurry is usually 1.2 to 2.0.
It is preferably between 1.4 and 1.8, most preferably between 1.5 and 1.7. This slurry may of course contain in part other acid components such as isophthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, sebacic acid, naphthalene dicarboxylic acid, diphenylsulfone dicarboxylic acid, etc. or other glycol components such as tetramethylene glycol. , neopentyl glycol, 1,4-cyclohexanedimethanol, etc. may be contained to an extent not exceeding 30 mol%.

The esterification reaction may be carried out at normal pressure or under increased pressure, but in order to suppress the DEG concentration, the gauge pressure is usually 0.5 Kg/cm 2 or less, preferably 0.15 Kg/cm ² or less.
It is preferable to set it to below cm ² , most preferably below 0.05 Kg/cm ² .

On the other hand, the temperature of esterification reaction is usually 220-270
℃, preferably 240-270℃, optimally 250-260℃
It is. If the temperature is lower than 220°C, the esterification reaction will not substantially proceed, while if the temperature exceeds 270°C, the DEG concentration will increase, both of which are undesirable.

When esterifying in the usual way, when the esterification reaction rate reaches about 90%, unreacted
Suspension of TPA particles is no longer visible and the reactant becomes transparent. However, if it is fed as it is to the polycondensation step, which is the second step in polyester production, the reaction rate will decrease, causing a delay in the polycondensation time, and increasing the amount of BHET with a low degree of polymerization, which will worsen the raw material consumption rate. The esterification reaction rate is usually lowered to 90% because this is undesirable as it may cause blockage in the distillate vapor extraction system in the polycondensation process.
~98%, preferably 93-98%, optimally 94-96%
It is necessary to carry out the reaction until BHET is produced at a relatively high reaction rate, resulting in a decrease in productivity and an increase in DEG concentration.

It has been known to increase the reaction efficiency and suppress the increase in DEG concentration by carrying out the esterification reaction using several consecutive tanks, but it is not economical to increase the number of tanks unnecessarily. However, there are naturally limits to the suppression of DEG concentration.

However, according to the method of the present invention, a plurality of tanks as many as normally used, preferably 2 to 3 tanks,
Optimally, when producing BHET continuously using two continuous tanks, it is necessary to not only supply raw materials to the first reaction tank, but also to supply raw materials to the final reaction tank and to control the overall production of the final reaction tank. Unreacted esterification reaction rate
The next polycondensation reaction step is to adjust the BHET to the final polymer use by reducing the TPA particles to a suspended state and filtering the reactants from the first reaction tank and the final reaction tank to remove unreacted TPA particles. The object of the present invention is achieved by supplying each of them to the following.

The fact that if the temperature and pressure of the reaction tank are kept constant, BHET after filtration exhibits constant characteristic values such as esterification reaction rate and number average degree of polymerization is disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 1973-
As disclosed in Publication No. 24236, etc.,
Specifically, it is shown in FIGS. 1 to 3. Figure 1 shows the relationship between reaction temperature and reaction rate of BHET after filtration.
Figure 2 shows the overall esterification reaction rate and the
Figure 3 shows the relationship between the overall esterification reaction rate and the reaction rate of BHET after filtration (for reaction temperatures of 250°C and 260°C).

When the reaction is carried out using only one tank, the temperature and pressure must be kept constant in order to obtain BHET with stable characteristics, and as shown in Figure 1, the esterification reaction is the most suitable for the polycondensation process. Rate of 94-96%
In order to obtain BHET, it is necessary to maintain a constant temperature of 250°C or less, which has the disadvantage that the reaction rate decreases and productivity does not increase.

Furthermore, unless the overall esterification reaction rate including unreacted TPA particles is about 85%, the actual reaction capacity will decrease and the reaction efficiency will deteriorate. By the way, in the current era where small quantities of polyester are desired in many varieties, it goes without saying that BHET, which is an intermediate product, is also required in many varieties.

According to the method of the present invention, by changing the temperature, pressure, and raw material supply rate of the first reaction tank and the final reaction tank to change the overall esterification reaction rate, BHET of different quality can be produced to meet current demands. can be obtained from each tank at the same time.

For example, if BHET with a DEG concentration of 0.8 mol% is required, the overall esterification reaction rate must be at the 80% level as shown in Figure 2, but if you operate at such a low reaction rate, esterification will not be directly involved in the reaction. Since there are many unreacted TPA particles that do not react, the actual reaction volume decreases, so a reaction tank with a large capacity must be installed, and from the viewpoint of reaction engineering, it is better to use a multi-stage reaction tank for better reaction efficiency.

In the present invention, any known filtration device can be used to filter the reactant, but usually
It is effective to use a filter with a mesh size of 100μ, preferably 20-60μ, optimally 30-50μ. If the mesh size is finer than this range, not only will the filtration effect become saturated, but it will also undesirably increase the pressure loss unnecessarily and shorten the filter life. If it is coarser than this range, unreacted TPA particles will not be sufficiently filtered and will come out through the filter, which is undesirable.

Also, for the final reaction tank, it is possible to install this filter at the bottom of the reaction tank and take out only the BHET that does not contain unreacted TPA particles.
Installing an independent filtration device externally, and using a filtration device with one inlet and two outlets, is
preferable. That is, a polycondensation process in which unreacted TPA particles passed through an inlet and a filtration layer in which an amount of reactant in excess of the actual production amount, preferably several times the production amount, was introduced into which unreacted TPA particles were suspended, and the unreacted TPA particles were removed. BHET supplied to the reaction process (corresponds to the actual production amount)
A filtration device having an outlet for sending out TPA particles and an outlet for recycling the increased reactant of remaining unreacted TPA particles to the reaction tank is preferable, and by using such a filtration device, the filtration process can be carried out smoothly. Moreover, it can be operated with a long life.

FIG. 4 is a flow sheet showing one embodiment of the present invention, 1 is the first reaction tank, 2 is the second (final) reaction tank, and 3 and 3' are the slurry of TPA and BG in each reaction tank. A raw material supply line, 4 is a liquid feeding line from the first reaction tank to the second reaction tank, 5 and 5' are reactant discharging pumps, 6 and 6' are filtration devices,
BHET with unreacted TPA particles removed by filtration device
is sent to the polycondensation process via liquid feed lines 7 and 7',
The remaining reactant containing unreacted TPA particles due to filtration is recycled to each reaction tank through recycling lines 8 and 8'.

Hereinafter, the present invention will be specifically explained with reference to Examples.

In the examples, "parts" indicate parts by weight, and the characteristic values were measured by the following method.

(1) DEG concentration (mol%) Alcoholysis for 2 hours under methanol reflux,
The generated EG and DEG were analyzed and quantified using gas chromatography.

(2) Reaction rate f (%) Calculated using the following formula from the acid value (AV) and saponification value (SN) determined by the method described below.

f%=SN−AV/SN×100 Γ Acid value (AV) (equivalent/ton) Accurately weigh about 3 g of sample, dissolve it in 40 ml of dimethylformamide under reflux, and after cooling, add 1/10 normal methanol water. It was determined by potentiometric titration with a potassium oxide solution.

Γ Saponification number (SN) (equivalent/ton) Accurately weigh approximately 0.5 g of the sample and perform alkaline hydrolysis with excess 1/2 N ethanolic potassium hydroxide solution at 20°C for 1 hour to remove excess potassium hydroxide. It was determined by back titration with 1/2 normal hydrochloric acid.

Example 1 Using the apparatus shown in FIG. 4, the EG/TPA molar ratio was approximately 1.6 in the first and second reaction vessels 1 and 2 (the capacity of 1 was more than 4 times that of 2) where BHET was present. slurry at a rate of 110 parts/Hr and 25 parts/Hr, respectively.
Kg/cm ² G, average residence time 6 hours, second reaction tank temperature 255℃, pressure 0.05Kg/cm ² G, average residence time 3.5 hours, the overall esterification reaction rate of the first reaction tank is 80%, the overall esterification reaction rate of the second reaction tank is 85%, and the reaction rate after filtering the reactants from each reaction tank is 85%.
The esterification reaction rate of BHET is 94% in both cases.
DEG concentrations were 0.80 mol% and 0.90 mol%.

The amount transferred from the first reaction tank to the second reaction tank is
53 parts/Hr. In addition, a stainless steel plain-woven wire mesh with a mesh size of 40μ was used as a filter, and the amount supplied to the filtration device was 150 parts/Hr for both tanks, and BHET from which unreacted TPA particles had been removed was fed from the first reaction tank.
It was sent to the polycondensation step at a rate of 30 parts/Hr and 70 parts/Hr from the second reaction tank, and the remainder was recycled to each reaction tank.

Comparative Example 1 Example except that both the first and second reaction tanks were not equipped with a filtration device, the temperature was 260°C, the pressure was 0.05Kg/cm ² G, and the slurry was not supplied to the second reaction tank. When the reaction was carried out in the same manner as in 1, the esterification reaction rate in the first reaction tank was 85%, the DEG concentration was 0.90 mol%, the esterification reaction rate in the second reaction tank was 94.5%,
DEG concentration was 1.10 mol%. Also, BHET
The production volume was 83 parts/Hr.

Comparative Example 2 The first and second reaction tanks are made independent, each reaction tank is equipped with a filtration device, and the slurry supply amount is 90 parts/90 parts to the first reaction tank.
The reaction temperature in each reaction tank was 255℃, the reaction pressure was 0.05Kg/ ^cm2G , and the average residence time was 5 hours in the first reaction tank and 4 hours in the second reaction tank.
It was reacted over time. The overall esterification reaction rate of the first reaction tank was 85%, the esterification reaction of BHET after filtration was 94%, the DEG concentration was 0.90 mol%, and the production amount was 70 parts/Hr. In addition, the overall esterification reaction rate of the second reaction tank was 80%, the esterification reaction rate of BHET after filtration was 94%, and the DEG concentration was 0.80 mol%.
The production amount was 20 parts/Hr, but because the throughput was small, the overall esterification reaction rate in the second reaction tank decreased, and the supply of slurry had to be frequently stopped.

From the above results, it can be seen that according to the method of the present invention, BHET of high quality equivalent to that of Comparative Example 2 can be produced with better operability and productivity than the method of Comparative Example 2.

[Brief explanation of drawings]

Figure 1 shows the relationship between the reaction temperature and the reaction rate of BHET after filtration, Figure 2 shows the relationship between the overall esterification reaction rate and the DEG concentration in BHET after filtration, and Figure 3 shows the relationship between the overall esterification reaction rate and the reaction rate of BHET after filtration. Graphs showing the relationship between the BHET and the reaction rate after filtration, and FIG. 4 are flow sheets showing one embodiment of the present invention. 1...First reaction tank, 2...Second reaction tank, 3,
3'... Raw material supply line, 6,6'... Filtration device.

Claims (1)

[Claims] 1. When reacting terephthalic acid and ethylene glycol to continuously produce terephthalic acid glycol ester, the reaction is performed using two or more consecutive reaction tanks, and the raw materials are supplied to the first reaction tank and the final reaction tank. and reacting to form an esterification reaction product in which unreacted terephthalic acid particles are suspended, and filtering the reaction product from the first reaction tank and the final reaction tank to remove the unreacted terephthalic acid particles. Continuous production method of terephthalic acid glycol ester.