JPS60104125A - Esterification - Google Patents

Abstract

PURPOSE:To control esterification in high measurement accuracy without being influenced by disturbance and operation factor, by inserting a semiconductor sensor to vapor formed by esterification of terephthalic acid and ethylene glycol, measuring the reaction ratio. CONSTITUTION:In esterifying terephthalic acid or a dicarboxylic acid consisting essentially of it with ethylene glycol or a glycol consisting essentially of it, a semiconductor sensor is inserted into vapor formed by the reaction, electric conductivity of the sensor is detected, to control reaction ratio of esterification. The esterification is preferably carried out in a molar ratio of ethylene glycol/ terephthalic acid =1.5-1.7 at <=0.15kg/cm<2> gauge pressure at 240-260 deg.C. The semiconductor is preferably set in a measurement cell having the reaction product obtained by taking out partially formed vapor from a piping of extraction line of it, condensing volatile vapor such as acetaldehyde, etc. and removing it, controlling the reaction product at a fixed temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for esterifying terephthalic acid or a dicarboxylic acid having the L form thereof with ethylene glycol or a glycol mainly composed of terephthalic acid.

Polyester is used industrially today.

In particular, polyethylene terephthalate is highly crystalline.

Has a high softening point and excellent properties such as strength, chemical resistance, heat resistance, weather resistance, and electrical insulation? Because it has t, it is widely used industrially as fibers, films, bottles, and other molded products.

Polyethylene terephthalate is obtained by the transesterification reaction of dimethyl terephthalate and ethylene glycol or the direct esterification reaction of terephthalic acid and ethylene glycol to obtain bis(β-hydroxyethyl) terephthalate (including its low polymers), which is then catalyzed. However, in recent years, the direct esterification method, which is advantageous in terms of ease of continuous operation, reduction in raw material consumption, and energy savings, has been widely adopted. It has become.

By the way, when producing polyester by the direct esterification method, in order to obtain high quality polyester, it is necessary to control the esterification reaction rate when carrying out the esterification reaction.

The esterification reaction rate can be determined by sampling two reactants and measuring the acid value and saponification value.
Such manual analysis methods are not compatible with process automation.

As a method to solve this problem, a method of controlling the esterification reaction rate by measuring the electrical conductivity (hereinafter referred to as electrical conductivity) of the esterification reaction mixture (Japanese Patent Laid-Open No. 48-10
3537) and a method in which esterification is carried out while maintaining the electrical conductivity of one reaction system constant (Japanese Patent Application Laid-open No. 19634/1983) has been proposed.

However, such a method of controlling by the electrical conductivity of the esterification reactant has the following problems,9 and is not suitable for full-scale practical use.

(1) The conductivity in the actual operating range is extremely low and falls within the measurement error range of existing instruments, so the signal due to disturbances (noise) due to temperature, pressure, air bubbles, etc. and changes in the esterification reaction rate. It cannot be put to practical use because it is difficult to identify and a method for preventing disturbance factors has not been established.

(2) In the case of polyethylene terephthalate-1, if the average degree of polymerization is not 10 or more, preferably 15 or more, the relationship between esterification reaction rate and tli conductivity can be formulated due to the influence of ethylene glycol and water produced by the reaction. I can't do it,
The variation due to measurement becomes large. Therefore, although it is good for controlling the degree of polymerization of polymers, it is not practical for those having an average degree of polymerization of 10 or less, such as esterification reaction products.

(3) It is extremely difficult to make corrections based on temperature, pressure, the amount of ethylene glycol added, etc., and it is impossible to make one-time corrections that would require changing various conditions in the actual manufacturing process.

The present inventors have conducted intensive research on a method for controlling the esterification reaction rate that does not have such problems, that is, a practical method for controlling the esterification reaction rate that is not affected by disturbances or operating factors. The present invention was completed based on the discovery that the change in the conductivity of a semiconductor sensor inserted into the vapor generated by the esterification reaction closely follows the change in the esterification reaction rate.

That is, 9 the present invention uses terephthalic acid (TPA) or a dicarboxylic acid mainly composed of terephthalic acid and ethylene glycol (EG).
or a semiconductor sensor is placed in the vapor generated by the 9 reactions when esterifying a glycol mainly containing this, the conductivity of the sensor is detected, and the esterification reaction rate is controlled. The gist is the esterification method.

The esterification method in the present invention is 2 usually bis(
TPA was added to the reaction tank containing β-hydroxyethyl) terephthalate (including its low polymer) (BIIE1').
A method is used in which a slurry consisting of EG and EG is continuously supplied for esterification. This BIIET may partially contain components other than TPA and EG residues,
BIIET may be obtained by any known method, but it is preferable to use the BIIET obtained by the above method as is.

The molar ratio of the slurry consisting of TPA and EG to r;G/'l'P is usually 1.2 to 2.0. Preferably 1.4・
~1.8. The optimum value is 1.5 to 1.7. Of course, this slurry also contains some other acid components, such as isophthalic acid, 5-sulfoisulfoisophthalic acid, adipic acid, sebacic acid, and knack dicarboxylic acid.

Diphenylsulfone dicarboxylic acid or the like or other glycol components, such as tetramethylene glycol.

Neopentyl glycol, 1,4-cyclohexane dimetatool, etc. may be present in an amount not exceeding 30 mol%.

In addition, the esterification reaction is performed using diethylene glycol (DE
C) Normal cage pressure 0.2 to suppress tlit degree.
It is suitable to carry out at 5 kg/crA or less, preferably 0.15 kg/cJ or less.

On the other hand, the temperature of the esterification reaction is usually 220 to 270°C.
5 Preferably 230-260°C 5 Optimally 240-2
The temperature is 60°C. Below 220°C, the esterification reaction does not substantially proceed; on the other hand, above 270°C, 1) IE
G'IQ increases, both of which are undesirable.

The reaction rate of BNET supplied to the next step, polycondensation step, is usually 90% or more, preferably 90 to 98%, and optimally 90% or more.
However, as the reaction rate of the obtained BIIET changes, the polycondensation reaction rate in the polycondensation process changes, and the quality of the obtained polyester varies. It is essential to stably produce IIET with a constant reaction rate.

Now, regarding the relationship between the reaction rate of the esterification reactant and the conductivity of the semiconductor sensor placed in the vapor generated by the reaction, which is the gist of the present invention, the higher the esterification reaction rate, the more the esterification reaction The amount of EG vapor due to the 9-polycondensation reaction increases relative to the amount of water produced, and the conductivity of the semiconductor sensor placed in the produced vapor increases
It is predicted that the esterification reaction rate and the electric conductivity will be in a 1:1 ratio, faithfully reflecting the changes due to the 111 formation change (correspondingly, as the esterification reaction rate increases, the electric conductivity of the semiconductor will decrease). be done.

The reaction rate actually calculated from the acid value and saponification value of the esterification reaction product according to a conventional method and the SnO placed in the reaction gas
The resistance of the semiconductor sensor is measured with an electrometer manufactured by Kugada Riken Co., Ltd., and when the average value of the converted value is plotted, the result is as shown in Figure 1.

However, in reality, the conductivity of the semiconductor sensor in the reaction gas has considerable bias and variation due to the influence of volatile vapors such as low polymers and DEC and acetaldehyde generated as a result of reactions in water and EG vapor. Avoid installing the sensor in the generated vapor at the upper part of the reactor, and extract a portion of the vapor from the piping of the extraction line to condense volatile vapors such as ace-1-aldehyde. It is preferable to remove the sample and place it in a measurement cell controlled at a constant temperature for measurement. Still, there is some variation in the conductivity of semiconductor sensors.

Therefore, in order to detect a slight difference in reaction rate, it is necessary to use a considerably large number of samples and take the average value. One means for realizing this is ttil inventory technology including microcomputers. Recent advances in microcontrollers have made it possible to monitor each reaction online.
There are extremely many examples of practical use for controlling.

Also in the method of the present invention, it is preferable to use a system as shown in FIG. 2 for the above-mentioned reasons.

Also, it is economically advantageous to use a microcomputer.

In FIG. 2, the electrode section and the detection section (electromake) 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 the control room, the electrical signal from the detection section is weak, and noise is likely to enter when the field and control room are far apart, so it is preferable to install the operational amplifier section on site. . When a command is input from the input section, the signal is amplified by the operational amplifier section, converted to digital by an 8/1) converter, inputted to the microcomputer, subjected to necessary calculations, and displayed on a display section such as a CRT.

Furthermore, the electric power of the semiconductor sensor placed in the esterification reaction gas is affected by temperature, pressure, etc.
It is preferable to sufficiently quantify the influence of temperature and pressure in order to improve the accuracy of reaction rate measurement.

Note that when using the method of the present invention, temperature is a suitable factor for controlling the reaction rate, and it is preferable to keep the amount of EG supplied to one reaction tank constant.

Further, the current passed between the electrodes may be either direct current or alternating current, but in the case of direct current, a slight polarization effect may occur, causing variations, which may lead to undesirable phenomena. The voltage applied between the electrodes is determined by the properties of the BHET to be manufactured, such as the constituent raw materials and the desired reaction rate, and is not unambiguous, so it is desirable to make it variable, but it is usually 25~
1000V, preferably 50-500V is suitable.

As a semiconductor sensor used in the present invention.

These are recently known as chemical sensors, such as 5nOz, Pd/SnO2, ZnO, Pd/
7. nO.

Pd/CdS, Pd/Ti0z, Pd/MO3-
FET, (La-5r-Co)Oz.

T-Few O, 1, TiOz, Coo/MgO are used, and SnO is particularly preferred.

As explained above, the reaction rate control method of the present invention is characterized in that the reaction rate is known by detecting the conductivity of a semiconductor sensor placed in the esterification reaction gas. Not only does it enable rapid continuous control of the process, but it also provides a reaction rate that is as high as 6", which is superior to conventional single-man analysis methods.2If the present invention is utilized for process automation, and quality direction,
In addition to the above, the effect of reducing man-hours and labor is enormous.

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

([Parts] indicate parts by weight.) Example I A slurry having a molar ratio of TIIA/EG of 1/1.6 was continuously supplied at a rate of 100 parts/hr to an esterification tank in which BIIET was present.

Reaction temperature 250℃, pressure 0.05kg/cm”G,
Esterification was carried out with an average residence time of 8 hours. At that time, a semiconductor sensor was placed in a reaction gas, and the conductivity of the semiconductor sensor was measured using the system shown in Figure 2. The conductivity of the semiconductor sensor was measured using a microcomputer 10 times per minute, and the esterification reaction rate was determined from the average value of 100 dQl plantings. When the reaction temperature was manipulated as a control factor and the reaction rate was controlled to be 85%, the average value of the esterification reaction rate over 10 days was 85.37%, the standard deviation was 0.52%, and 82. The reaction rate was never less than 88% or less than 88%.

Example 2 The ester product obtained in Example 1 was continuously fed into an esterification tank containing BIIET at a reaction temperature of 260°C.

The reaction was carried out in the same manner as in Example 1, except that the reaction was carried out at a pressure of 0.05 kg/cm2G and an average residence time of 2 hours, and the esterification reaction rate was controlled to be 96%. The average value was 95.80% and the standard deviation was 0.29%, and the reaction rate was never less than 95% or more than 97%.

Comparative Example 1 The same procedure as in Example 1 was carried out except that the reaction rate was determined from the acid value and saponification value measured once per hour.The average value of the esterification reaction rate over 10 days was 84. 78%, standard deviation was 1.83%, and there were 11 times when it was less than 82% or more than 88%.

Comparative Example 2 The same procedure as in Example 2 was carried out except that the reaction rate was determined from the acid value and saponification value measured once per hour.The average value of the esterification reaction rate over 10 days was 96. 07%, standard deviation was 0.96%, and there were three times when it was less than 95% or 97%.

As is clear from the above examples, the esterification reaction rate can be well controlled by the present invention.

[Brief explanation of the drawing]

Figure 1 shows the relationship between the reaction rate of the esterification reactant and the conductivity of a semiconductor sensor placed in the vapor generated by the reaction, and Figure 2 shows an example of a reaction rate control system for the esterification reactant. FIG. Patent applicant Yu Kodama, agent for Nippon Ester Co., Ltd. Santan Ei Mu (%) Figure 1 Procedure amendment written form) March y, 1980 1, case indication patent application No. 1982-212135 2, Name of the invention: Esterification method 3, relationship with the person making the amendment Patent applicant address: 1-1 Hinakita-cho, Okazaki City, Aichi Prefecture Representative: Shigeru Nakai 4, Agent 5, Date of amendment order: February 1980 February 8th (Delivery date: February 28, 1982) 6. Full text of the specification to be amended 7. Engraving of the amended specification (no change in content)

Claims (1)

[Claims] (1) When esterifying terephthalic acid or a dicarboxylic acid mainly composed of terephthalic acid and ethylene glycol or a glycol mainly composed of terephthalic acid. A semiconductor sensor is placed in the vapor generated by the reaction,
An esterification method characterized in that the esterification reaction rate is controlled by detecting the electrical conductivity of the sensor.