JPH047339B2 - - 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, including BHET that has a low diethylene glycol (DEG) concentration and can form a polyester with 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, even if it 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 these problems, the present inventors have discovered that not only a plurality of consecutive reaction vessels are used for the reaction and the reactants from the final reaction vessel are taken out as products, but also the first A portion of the reactant from the reaction tank is removed by filtering the reactant and unreacted TPA.
By removing particles and extracting them as products, we can produce products with different properties, including BHET with low DEG concentrations.
They discovered that BHET can be obtained efficiently and completed the present invention.

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 materials consisting of TPA and EG are supplied to the first reaction vessel, and the insufficient EG is supplied to the second and subsequent reaction vessels. A part of the esterification reaction product in which unreacted TPA particles are suspended from the first reaction tank is filtered to remove unreacted TPA particles and taken out as a product.
This is characterized in that the remainder is transferred to a second reaction tank.

As the esterification method in the present invention, a method is usually used in which raw materials consisting of TPA and EG are continuously supplied to a reaction tank in which BHET is present and esterified. This BHET includes some TPA and EG.
may contain components other than residues, and
BHET may be obtained by any known method, but it is preferable to use the BHET obtained by the above method as is. Raw materials consisting of TPA and EG are usually supplied as a slurry, and 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 continuously producing BHET using two continuous tanks, the overall esterification reaction rate in the first reaction tank is set to a state where unreacted TPA particles are suspended,
A portion of the reactant from the first reactor is filtered to remove unreacted TPA particles to produce a product (BHET).
The object of the present invention is achieved by taking out the polymer as BHET from the final reaction tank and supplying it to the next polycondensation reaction step in accordance with the final polymer application.

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 the temperature at a constant temperature of 250°C or less, which has the disadvantage of slowing down the reaction rate and not increasing productivity.

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 today's era when polyester is desired in small quantities and in many varieties, polyester is an intermediate product.
It goes without saying that BHET also requires a wide variety of products.

According to the method of the present invention, by changing the temperature, pressure, and raw material supply rate of the first reaction tank to change the overall esterification reaction rate, it is possible to simultaneously obtain BHET of different qualities that can meet current demands. becomes possible.

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.

It is also 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, but it is also possible to install an independent filtration device outside and have one inlet and two outlets. It is preferable to use 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. A filtration device having an outlet for delivering BHET (corresponding to the actual production amount) to be fed to the reaction process and an outlet for recycling or transferring the increased reactant of remaining unreacted TPA particles to the next reaction tank is preferred. By using such a filtration device, the filtration process can be performed smoothly and with a long service life.

FIG. 4 is a flow sheet showing one embodiment of the present invention, in which 1 is a first reaction tank, 2 is a second (final) reaction tank, 3 is a raw material supply line that supplies a slurry of TPA and EG, and 4 is a flow sheet showing an embodiment of the present invention. is the EG supply line, 5 is the liquid feeding line from the first reaction tank to the second reaction tank, 6 is the reactant dispensing pump, and 7 is the filtration device. The reactant is sent to the polycondensation step via a liquid line 8, and the remaining reactant, which has an increased amount of unreacted TPA particles due to filtration, is recycled to the first reaction tank via a recycle line 9. Also, from the second reaction tank
BHET is sent to the polycondensation process via a liquid feed line 10.

FIG. 5 is a flow sheet showing another embodiment of the present invention, in which the reactant from the first reaction tank is supplied to a total filtration device, and the remaining reactant with an increased amount of unreacted TPA particles is sent to the liquid through filtration. The reactor is transferred to the second reaction tank via a line 11.

As shown in the embodiment examples, it is preferable to attach the filtration device only to the first reaction tank and not to the other reaction layers because control is easier.

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, 102 parts/Hr of slurry with an EG/TPA molar ratio of about 1.6 was placed in the first reaction tank 1 containing BHET, and 5 parts/Hr of EG was placed in the second reaction tank 2.
The temperature of the first reaction tank is 255%.
℃, pressure 0.05Kg/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. Summary of the first reaction tank. The esterification reaction rate is 80%, the overall esterification reaction rate of the second reaction tank is 94%, and the esterification reaction rate of BHET after filtering the reactant from the first reaction tank is
94% DEG of BHET from the first and second reactor
The concentrations were 0.80 mol% and 1.12 mol%.

The amount transferred from the first reaction tank to the second reaction tank is
52 parts/hour. In addition, a stainless steel plain-woven wire mesh with a mesh size of 40μ was used as a filter, the supply amount to the filtration device was 125 parts/Hr, and BHET was used as the first
25 parts/Hr from the reaction tank, 52 parts/Hr from the second reaction tank
was sent to the polycondensation step at a ratio of .

Example 2 Using the apparatus shown in Figure 5, the slurry supply amount to the first reaction tank was 110 parts/Hr, the EG supply amount to the second reaction tank was 6 parts/Hr, and under the same conditions as Example 1. Made it react.

The properties of the esterification reaction product and BHET were almost the same as in Example 1, and the production amount of BHET was 20 parts/Hr from the first reaction tank and 63 parts/Hr from the second reaction tank.

Comparative Example In Example 1, a filtration device was not attached to the first reaction tank, and the entire amount of the reactant from the first reaction tank was transferred to the second reaction tank as it was, so that the amount of slurry supplied to the first reaction tank was reduced. 110 parts/Hr, to the second reaction tank
The reaction was carried out under the same conditions as in Example 1, with the EG supply amount being 8 parts/Hr.

The obtained BHET had an esterification reaction rate of 94%,
The DEG concentration was 1.10%, and the production amount was 83 parts/Hr.

Thus, according to the method of the present invention, low DEG
It is possible to efficiently produce BHET with a high concentration of BHET and BHET with a normal DEG concentration at the same time.

[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 4 and 5 showing the relationship between BHET and reaction rate after filtration, respectively.
The figure is a flow sheet showing an embodiment of the invention. 1...First reaction tank, 2...Second reaction tank, 3...
Raw material supply line, 7...filtration device.

Claims (1)

[Claims] 1. When reacting terephthalic acid and ethylene glycol to continuously produce terephthalic acid glycol ester, the reaction is carried out using two or more consecutive reaction vessels, and the first reaction vessel is filled with terephthalic acid and ethylene glycol. A raw material is supplied, and only the insufficient ethylene glycol is supplied to the second and subsequent reactors, and a part of the esterification reaction product in which unreacted terephthalic acid particles are suspended from the first reactor is reacted. The product is filtered to remove unreacted terephthalic acid particles and taken out as a product, and the remainder is added to the second
A method for continuous production of terephthalic acid glycol ester, characterized by transferring the terephthalic acid glycol ester to a reaction tank.