JPS61233651A - Production of glycol ester of terephthalic acid - Google Patents

Abstract

PURPOSE:To obtain efficiently and stably the titled compound in a low DEG concentration, by detecting the conversion at a specific time interval, and controlling the esterification of the esterification reaction product in obtaining the titled compound by reacting terephthalic acid (TPA) with ethylene glycol (EG). CONSTITUTION:Terephthalic acid (TPA) is reacted with ethylene glycol (EG) at 1.5-1.7 molar ratio between TPA and EG at 250-270 deg.C under 0.05 kg/cm<2> gauge pressure, and the reactant in the reaction tank are converted into an esterification reaction product containing suspended unreacted TPA particles. The above-mentioned reaction product is filtered to remove the TPA particles and give the aimed compound. In the process, the conversion is detected at a sampling interval of time expressed by formula I or less to control the esterification conversion of the esterification reaction product. The sampling interval is et at the time expressed by formula II or less in detecting the conversion by using the electric conductivity of the reactants. When the electric conductivity is measures by a measuring instrument connected to a microcomputer at 100 times/sec frequency (the average value is used as the measured value), the sampling interval is set at the time expressed by formula III or less.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention involves reacting terephthalic acid (hereinafter abbreviated as TPA) and ethylene glycol (hereinafter abbreviated as EG) to produce terephthalic acid glycol ester.

It relates to a method for producing bis-(β-hydroxyethyl)-terephthalate and/or its low polymer (hereinafter abbreviated as BHET), and in detail, it relates to a method for producing bis-(β-hydroxyethyl)-terephthalate and/or its low polymer (hereinafter abbreviated as BHET). The present invention relates to a method for controlling an esterification reaction for producing old +1ET capable of forming polyester.

(Prior art) Polyester, especially polyethylene terephthalate, has a high degree of crystallinity and a high softening point, and has excellent strength, chemical resistance, heat resistance,
In addition to fibers, it has excellent properties such as weather resistance and electrical insulation.

It is widely used industrially as bottles and other molded products.

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

For this purpose, D in the polyester resulting from side reactions is required.
Reducing the EC concentration is considered to be one of the important issues.

Polyester is usually produced by an esterification process followed by a polycondensation process, but conventionally DEC? J
In the esterification process, which has a large influence on reducing the
Development and improvement of catalysts and additives, and DE (Ji
ff: Processes have been developed that can reduce the degree of damage, but these methods also have some drawbacks.

For example, the addition of alkali metal compounds as catalysts or additives, which has been proposed many times including in Japanese Patent Publication No. 34-2594, contributes to the reduction of I)E c >3 degrees, but at the same time it reduces the color tone. ,viscosity.

The drawbacks include loss of strength or other physical properties and retardation of the double condensation rate.

On the other hand, as a process to reduce DEcli degree.

Conventionally, there was a transesterification method in which BHET was produced by transesterifying dimethyl terephthalate and EG, but it was unsuitable for continuous operation, dimethyl terephthalate was more expensive than TPA, and it was more expensive than the transesterification method. Since the esterification method using TPA and EG as starting materials has many advantages such as a simpler process, the process gradually shifted to the esterification method and continues to this day. Therefore, at present, the transesterification method is generally used only for products that particularly require a low DEC concentration, even if it increases the cost to some extent.

Now, even when the esterification method is adopted, high-quality B with a low DEC concentration that is as good as the transesterification method can be obtained.
Methods of manufacturing HETs have also been proposed.

For example, as disclosed in Japanese Patent Publication No. 46-22463, there is a method in which TPA is suspended in EG and gaseous EG is reacted at a temperature higher than the boiling point of EG;
As disclosed in Japanese Patent No. 24236, unreacted T
By separating unreacted TPA particles from the esterification product in which PA particles are suspended.

A method of obtaining BHET with a constant reaction rate and a low degree of DEGFI, ie, a filtration esterification method, etc., has been proposed.

However, even when these methods are adopted, variations in reaction rate and DEC concentration occur in the former case, which is a problem, and even in the latter case, if the reaction temperature is lowered, DEC? jt1 degree will be lower.

This method has problems in that productivity is poor and the system becomes extremely unstable when the reaction rate fluctuates due to disturbances.

As a result of extensive research to solve these problems, the present inventors have discovered that it is possible to efficiently produce BIIET with a low D E G concentration using a specific method using a plurality of consecutive reaction vessels. I discovered what could be done and proposed it first (
Japanese Patent Application No. 58-179912 and No. 5B-187395.

5'8--197344).

However, even when these methods are adopted, Bl(ET) with a low nEc concentration can be efficiently produced, but on the other hand, the dynamic characteristics of the two reaction system are extremely unstable.

In other words, if BHET with a constant reaction rate is removed from the system by filtration while keeping the temperature at a constant value, the esterification reaction rate of the entire esterification reaction product before filtration (total esterification reaction rate)
Once it begins to increase, it continues to increase.

On the contrary, once it begins to decrease, it continues to decrease, resulting in a fatal problem that the overall esterification reaction rate is not stable.

(Problems to be Solved by the Invention) The present invention involves appropriately controlling the esterification reaction rate of the esterification reaction product when producing ET from +'TI'A and EG by a filtration esterification method. The present invention aims to provide a method that can efficiently and stably manufacture BIIET with a low DEC depth.

(Means for Solving the Problems) The present invention detects (monitors) the reaction rate at specific sampling intervals in accordance with the overall esterification reaction rate of the target esterification reaction product and controls the reaction rate. This solves this problem and has a first-order configuration.

When producing terephthalic acid glycol ester by reacting TPA and EG, the reactants in one reaction tank are converted into unreacted T.
In the method of forming an esterification reaction product in which PA particles are suspended, and filtering the reaction product from the reaction tank to remove unreacted TPA particles, sampling for a period of time or less shown by the following formula (T) A method for producing terephthalic acid glycol ester, which comprises controlling the esterification reaction rate of an esterification reaction product by detecting the reaction rate at intervals.

t = 0.5 + 3・f/100 (1) [Here, t is the sampling interval (hr), and f is the target overall esterification reaction rate (%) of the esterification reactants in the reaction tank. , 60% or more. ] First, a flow sheet showing one embodiment of the present invention is shown in FIG.

'' In Figure 1, 1 is the first reaction tank, 2 is the second reaction tank, 3 and 4 are raw material supply lines that supply slurry of TPA and EG to each reaction tank, and 5 is the line from the first reaction tank to the second reaction tank. Liquid feed line for the esterification reaction product to the reaction tank.

Reference numeral 6 indicates a pump for discharging the esterification reaction product from the second reaction tank, and 7 indicates a filtration device, in which unreacted TPA particles are removed by the filtration device. The remaining esterification reaction product, in which unreacted TPA particles have increased due to filtration, is returned to the second reaction tank via a recycle line 9. Further, 10 indicates an electrical conductivity (hereinafter abbreviated as type conductivity) measuring device for detecting the esterification reaction rate.

The esterification method in the present invention includes:
A method is used in which a slurry consisting of TPA and EG is supplied to a reaction tank in which BIIET is present and esterified.

This BHHT may optionally contain a dicarboxylic acid component other than TPA, such as isophthalic acid, 4. 71'
-Dicarboxybiphenyl, bis(4-carboxyphenyl)methane, 2.2'-bis(4-carboxyphenyl)propane, bis(4-carboxyphenyl)sulfone, bis(4-carboxyphenyl)ether, nuclic acid, 4 -Hydroxybenzoic acid, 5-sodium sulfoisophthalic acid, adipic acid, l-limerisotic acid, etc. Glycol or polyol component other than EG group 1 For example, diethylene glycol, neopentyl glycol, 1,4-cyclohexane dimetatool, pentaerythritol, etc. may be contained in an amount not exceeding 30 mol% of the constituent components.

=9- Further, BHET may be obtained by any known method, but it is preferable to use the BHET obtained by the above method as it is.

The raw material is usually supplied as a slurry consisting of TPA and EG, and the molar ratio of EG/TPA in the slurry is usually 1.
2-2.0. Preferably 1.4 to 1.8. Optimally 1.
It is preferable to set it to 5 to 1.7.

This slurry may contain components other than TPA and EG groups, ie, the dicarboxylic acid component and glycol component described above.

Also, the pressure for the esterification reaction may be either normal pressure or increased pressure, but DEC? In order to suppress the am degree, the gauge pressure is usually 0.5 kg/c♂ or less, preferably 0.5 kg/c♂ or less. ], 5
It is best to keep it at a constant value of Kg/cl or less, optimally 0.05 Kg/cJ or less.

On the other hand, the temperature of the esterification reaction is at least a temperature at which the esterification reaction substantially proceeds (220°C).

Below 290°C to suppress DEGtM degree, ie.

Usually 220-290°C, preferably 240-270°C,
The optimum temperature is 250 to 270°C.

=10- Now, when the esterification reaction is carried out in this way, when the reaction rate exceeds a certain value, there will be no unreacted TPA particles suspended in the esterification reaction product, although it depends on the temperature of the esterification reaction. The 5 reactants become transparent.

By the way, if the reaction rate of the esterification reactant supplied to the polycondensation step, which is the second step of polyester production, is too low, the 1st reaction rate will decrease, the 2nd polycondensation reaction will be delayed, or BIIET with a low degree of polymerization will occur. This is undesirable as it increases the amount of scattering, which worsens the raw material consumption rate and causes blockage in the extraction system for distilled steam in the 5-polycondensation process.
It is necessary to carry out the reaction until a relatively high reaction rate of B HET is produced, preferably 93-98%, optimally 94-96%, and as a result, there is a decrease in productivity and
This will lead to an increase in viscosity. Moreover, when the filtration esterification method 2 is adopted as described above, the overall esterification reaction rate in the reaction tank begins to decrease due to disturbance.

The esterification reaction rate of the esterification reaction product after removing unreacted TPA particles remains constant.9 As a result, unreacted TPA particles accumulate in the reaction tank, and the volume ratio occupied by unreacted TPA particles increases. increases, the effective reaction volume decreases, and the esterification reaction rate decreases.

At the same time, the fluidity of the esterification reaction product in the reaction tank deteriorates and the esterification reaction rate decreases, both of which work to decrease the overall esterification reaction rate, and conversely, the esterification reaction rate of one reaction tank decreases. When it starts to increase, unreacted TPA
Until the particles are gone, both of them work in the direction of increasing the overall esterification reaction rate (a so-called positive feed hack occurs), so the overall esterification reaction rate only decreases or increases, making stable operation impossible. .

However, according to the method of the present invention, in order to control the esterification reaction rate of the esterification reactant, the esterification reaction rate is controlled by detecting the reaction rate at a sampling interval equal to or less than the time shown by the above formula (I). However, when the esterification reaction product is filtered to remove unreacted TPA particles B) IET is supplied to the next step, the polycondensation step, the dynamic characteristics of the reaction system described above are stabilized.

The degree of DEGtH can be suppressed while keeping the overall esterification reaction rate stable.

In order to detect the esterification reaction rate, the esterification reaction rate may be determined by sampling the esterification reaction product at an interval equal to or less than the time indicated by the above formula (1) and measuring the acid value and saponification value. However, a preferred method is to measure the electrical conductivity of the esterification reactant.

When controlling the esterification reaction rate by measuring the conductivity of the esterification reaction product, the sampling interval (conductivity measurement interval)
It is desirable that the time is less than or equal to the time expressed by the following formula (IT).

t=0.2 + f/100 (Tl) The most preferable method is to use a measuring device connected to a microcomputer to measure the following formula (III) at a rate of 100 times or more per second.
) or less (preferably 1/60 hr or more)
This is a method of reading the conductivity and using the average value as the actual measurement value. [Conductivity is read continuously, but t
Since one measurement value is averaged every (hr), t is the sampling interval. ]t=0.1 +0.1
- f/100 (1) Thus, in the present invention, in order to control the esterification reaction rate, it is necessary to set the interval at which the esterification reaction product is sampled to be equal to or less than the time indicated by the above formula (1). . In addition, when controlling the esterification reaction rate by measuring the electrical conductivity of the esterification reaction product, the sampling interval is set to the time shown by the above formula (U) or less, and the esterification reaction is performed using a measuring device connected to a microcomputer. When controlling the esterification reaction rate by measuring the conductivity of a substance, the sampling interval is determined by the above formula (I
It is preferable that the time is less than the time shown in 'll). If the sampling interval is outside this range, it is not preferable because the stability of the overall esterification reaction rate of the esterification reactants in one reaction tank will be impaired.

Note that the targeted overall esterification reaction rate of the esterification reactants in one reaction tank must be 60% or more. As mentioned above, since the dynamic characteristics of one reaction system are inherently extremely unstable, once the overall esterification reaction rate is reduced to less than 60%.

Even after that, the reaction rate continues to drop rapidly, and in reality, it is nearly impossible to return the reaction rate to its original level.

In the present invention, any known filtration device can be used to filter the esterification reaction product.

Usually 10-100μ, preferably 20-60μ, optimally.

It is preferred to use a filter with a mesh size of 30 to 50 microns. If the mesh size is smaller than this range, the filtration effect will not only reach saturation, but it will also undesirably increase the pressure loss unnecessarily and shorten the filter life. If it is made coarser, unreacted TPA particles will not be sufficiently filtered and will come out through the filter, which is not preferable.

Alternatively, this filter may be installed at the bottom of the reaction tank so that only BHET that does not contain unreacted TPA particles is taken out from the bottom of the reaction tank. It is preferable to use a filtration device having two outlets. That is, the esterification reaction product in which unreacted TPA particles are suspended is mixed with unreacted TPA particles.
Transparent HET fed to polycondensation process without PA particles
Transparent HET (corresponding to the actual production amount) without unreacted TPA particles fed into the inlet and the 9-polycondensation step is introduced in excess of the actual production amount, preferably several times the actual production amount. A filtration device having an outlet and an outlet for recycling the esterified reactants increased in remaining unreacted TPA particles to the reaction vessel is preferred; 60% reaction rate
By doing so, the filtration process can be operated smoothly and with a long service life.

Next, a method for controlling the esterification reaction rate of the two esterification reactants in the present invention will be explained.

The esterification reaction rate can be detected by sampling the esterification reaction product by an appropriate means and manually measuring its acid value and saponification value. In the present invention, this method may also be used to manually measure the esterification reaction rate. It cannot be easily automated and one analysis takes time, so it may not be possible to respond immediately to sudden changes in the process, and manual analysis is uneconomical. A method of monitoring the esterification reaction rate is preferred.

The relationship between the esterification reaction rate and the electrical conductivity of the esterification product is that as the esterification reaction rate increases, the amount of unreacted TPA decreases.
Since the carboxyl end groups of the partially esterified esterification product are reduced, the conductivity is expected to decrease proportionally as the esterification reaction rate increases.

However, when we actually plot the esterification reaction rate and electrical conductivity measured from the acid value and saponification value of the esterification reaction product according to a conventional method, we get the result shown in Figure 2, which shows a simple linear relationship. There isn't.

Furthermore, the electrical conductivity of the esterified product varies considerably due to the influence of unreacted TPA dissolved in BHET and water and EG produced as a result of the reaction. Therefore, in order to detect slight changes in the esterification reaction rate, it is preferable to use a considerably large number of samples and calculate the average value. One way to achieve this is control technology that uses microcomputers.

The recent development of control technology using microcomputers has been remarkable and there are many examples of practical use for online monitoring and control of two reactions.

In the method of the present invention, it is particularly preferable to employ a system using a microcomputer for the above-mentioned reasons, and the system shown in FIG. 3 is preferable. In FIG. 3, the electrode section and the detection section (electrometer) must of course be installed on site, but the rest can be installed in the control room. However, if the operational amplifier section is installed in a control room, the electrical signal from the detection section is weak.

Also, when the distance between the site and the control room is large.

Since it is easy for noise to enter, it is preferable to install the operational amplifier section on-site. A command is input from the input section, and the signal is amplified by the operational amplifier section, passes through the A/D converter, is input to the microcomputer, performs necessary calculations, and is displayed on the CR7 screen.

When calculating the esterification reaction rate from the electrical conductivity using a microcomputer, the average value of electrically conductive dust is used for the reasons described above, but the number of measurements is more than 100 times per second. ) denoted by t (hr)
It is preferable to measure for a period of less than 1/60 hr or more (preferably 1/60 hr or more) and take the average value as one measured value.

III.If the constant number of times is 100 times per second, noise cannot be removed sufficiently and accuracy deteriorates, which is not preferable. On the other hand, if the sampling interval exceeds the time t shown by the above formula (TIT), the time delay will become large, which is not preferable.

Furthermore, the conductive dust of the esterification product depends on the temperature, pressure, air bubbles, IEG and water content of the esterification reactant.

Because it is affected by the content of other compounds (impurities such as acetic acid, 4-carboxyhenzaldehyde, phosphorus compounds, and various transition metal compounds), the temperature and EC
It is even better if the influence of other factors such as the amount of addition is determined in advance and inputted into a microcomputer to correct for conductive dust. In addition, it is preferable to keep the pressure at a constant value in order to eliminate the influence of pressure to prevent bubbles from forming. 3. The pressure during conductivity measurement is usually 5 kg/ci or more, preferably 10 kg
It is desirable to have a score of /c or higher -19=.

Note that the current passed between the electrodes for measuring conductive dust may be either direct current or alternating current; however, in the case of direct current, a slight polarization effect may occur, leading to undesirable phenomena.

On the other hand, the voltage applied between the electrodes is not unique and should be variable, but generally 5 to 1000V, preferably 10 to 100V is suitable.

When carrying out the method of the present invention, it is preferable to use an electrode section configured as shown in FIG.

In FIG. 3, 11 is a flow path for transferring the esterification reaction product;
12 is a heat medium flow path, 13.14 is a valve, 15.16
17 is an insulator, 17 is a ten-electrode, 18 is a boost pump, 19 is a temperature detection end, and 20 is a pressure detection end.

A portion of the esterification reaction product flowing through the flow path 11 is transferred to the valve 1.
3 to a branch pipe, pressurized with a boost pump 18, and measured conductive dust with an electrode 17.

Conductive dust is calculated using the following formula.

V: applied voltage, ■ = current, C: distance between electrodes.

S: Electrode surface area Furthermore, the amount of conductive dust in the esterification reaction product is extremely low.

For example, ionic compounds used as catalysts.

Salts of alkali metals and alkaline earth metals such as sodium, potassium, calcium, and magnesium acetates, or manganese, cobalt, and tin.

When compounds such as various transition metal compounds such as zinc or organic sulfonic acid compounds such as sulfosalicylic acid and 0-sulfobenzoic anhydride are present, these may exhibit extremely high conductive dust, so esterification of these compounds is necessary. Correction is required depending on the concentration in the reactant.

(Example) Hereinafter, the method of the present invention will be specifically explained with reference to Examples.

In the examples, "1 part" indicates parts by weight, and the characteristic values were measured by the following method.

(1) DEC concentration (mol%) Cipul was alcoholyzed for 2 hours under refluxing methanol,
The generated EG and DEC were analyzed by gas chromatography (2) Esterification reaction rate f (%) Calculated using a quadratic formula from the acid value (AV) and saponification value (SN) determined by the method described below.

SN -8V f =
cc under reflux, and after cooling, it was determined by potentiometric titration with a 0.1N methanolic potassium hydroxide solution.

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

Examples 1 to 3 Using the apparatus shown in FIG. 1, a first reaction tank 1 containing BHET was prepared. The EG/TP^ molar ratio is approximately 1 in the second reaction tank 2.
．． 6 slurry at 110 parts/hr and 20 parts/hr, respectively.
hr, and the first reaction tank has a reaction temperature of approximately 255°C3.
Reaction pressure 0.05Kg/cfflG, average residence time 6
hr, the reaction temperature in the second reaction tank was approximately 255°C, the reaction pressure was 0.05 h/cJG, and the addition rate of EG was 0.2 mol/cJG.
The esterification reaction was carried out using TPA and an average residence time of 3 hours. At that time, use the system shown in Fig. 4 as shown in Fig. 3.

The electrical conductivity of the esterification reaction product before filtration was measured at a pressure of 5 kg/cJ, and read using a microcomputer at the frequency and time (sampling interval) shown in Table 1.

Determine the esterification reaction rate from the average value of the measured values.

As a control factor, the reaction IM□ degree was slightly manipulated to control the overall esterification reaction rate in each reaction tank to be 86%. A stainless steel plain-woven wire mesh with a mesh size of 40 μm was used as the filter, and the amount of esterification reaction product supplied to the filtration device was 200 parts/hr.

BIIET after removing unreacted TPAP particles is 100/
The remaining esterification reaction product was recycled into the second reaction tank.

Average value of esterification reaction rate for 20 days, deviation of standard 4L, and I]IEG of BHET? The i degree is shown in Table 1.

Examples 4-6. Comparative Example 1 In Example 1, the overall esterification reaction rate in each reaction tank was controlled by manually measuring the acid value and saponification value at the sampling intervals shown in Table 1. (In Comparative Example 1, the overall esterification reaction rate became too low, and the filter was clogged with unreacted TP 8 particles, so the reaction was stopped on the 8th day.) The results are shown in Table 1.

Examples 7 to 9 In Example 1, the residence time was adjusted to control the overall esterification reaction rate in each reaction tank to be 88%, 909A, and 70%.

The results are shown in Table 1.

Example 10 In Example 9, the overall esterification reaction rate in each reaction tank was controlled at the sampling intervals shown in Table 1.

The results are shown in Table 1.

Comparative Examples 2 to 3 In Examples 10 and 5, the sampling intervals were controlled as shown in Table 9. (In Comparative Example 2, the reaction was stopped on the 6th day, and on the 100th day in Comparative Example 3, because the filter was clogged with unreacted TPAP particles.) The results are shown in Table 1.

Table 1 ” ■ ] (Effect of the invention) According to the present invention, the following effects are achieved.

(1) Even if the overall esterification reaction rate regarding TPAP including unreacted TPA particles changes, 2. If the reaction temperature is kept approximately constant, the esterification reaction product excluding unreacted TPAP particles (transparent part) The reaction rate of will be constant.

BHET with constant reaction rate is obtained. Therefore, by controlling the reaction temperature in a cascade manner to such an extent that the influence of disturbances can be absorbed, the reaction rate of the esterification reactant (transparent part) excluding unreacted TPAP molecules can be adjusted to a desired level.

(2) Regarding fluctuations in the overall esterification reaction rate due to disturbances.

It is possible to respond quickly, prevent large fluctuations in the overall esterification reaction rate, and enable stable operation.As a result, R is the most suitable raw material for heat-resistant polyester with excellent physical properties. ) IRT can be obtained.

(3) If a method is adopted to detect the esterification reaction rate by measuring the electrical conductivity of the esterification reaction product, rapid online continuous control will be possible and it will be superior to the conventional analysis method that requires nine people. Accurate esterification reaction rate can be detected, and high quality B It ET can be manufactured stably with good productivity.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing one embodiment of the present invention;
The figure shows the relationship between the esterification reaction product and the electrical conductivity.
The figure shows the configuration of an electrode section for measuring electrical conductivity, and FIG. 4 is a block diagram showing an example of a reaction rate control system for esterification reaction. 1-first reaction tank, 2-second reaction tank, 3.4-raw material supply line, 7-filtration device, 10-conductivity measuring device, 11-esterification reaction product transfer channel, 17-electrode.

Claims (1)

[Claims] (1) In producing terephthalic acid glycol ester by reacting terephthalic acid and ethylene glycol,
In the method of forming a reactant in a reaction tank into an esterification reaction product in which unreacted terephthalic acid particles are suspended, and filtering the reactant from the reaction tank to remove unreacted terephthalic acid particles, the following method is used: A method for producing terephthalic acid glycol ester, which comprises controlling the esterification reaction rate of an esterification reaction product by detecting the reaction rate at a sampling interval equal to or less than the time shown by formula (I). t=0.5+3・f/100(I) [Here, t is the sampling interval (hr), f is the target overall esterification reaction rate (%) of the esterification reactants in the reaction tank, and 60 % or more. ] (2) The terephthalic acid glycol ester according to claim 1, wherein the esterification reaction rate is detected by measuring the electrical conductivity of the esterification reaction product at a sampling interval equal to or less than the time represented by the following formula (II). manufacturing method. t=0.2+f/100 (II) (3) The electrical conductivity of the esterification reaction product was measured using a measuring device connected to a microcomputer at a frequency of 100 times or more per second and less than or equal to the time shown by the following formula (III). The method for producing terephthalic acid glycol ester according to claim 2, wherein the esterification reaction rate is detected from the average value measured at sampling intervals of . t=0.1+0.1・f/100(III)