JPH10182802A - Production of polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to continuously analyze a sample, even in a small amount, at good accuracy within a short time without treating the sample and to thereby permit the stable supply of starting materials, the stabilization of reaction conditions and the stabilization of quality by controlling the composition of the reaction system on the basis of the specified analytical values on the diol concentration, diol condensate concentration, water content and catalyst concentration of the recycle liquid in an esterification reaction. SOLUTION: In producing a polyester by forming a slurry by dispersing a powder of an aromatic dicarboxylic acid such as terephthalic acid or isophthalic acid in a liquid diol such as ethylene glycol, reacting the slurry at 240-270 deg.C at normal pressure or under a pressure of 300,000Pa while removing the formed water from the reaction system, a solution containing unreacted diol from the polycondensation process and a catalyst is recirculated as a recycle liquid, the concentrations of the components in the liquid are analyzed with a near-infrared analyzer having a noise level of 50×10<-6> Abs or below and a wavelength reproducibility of 0.01nm or below and a fluorescent X-ray analyzer, and the composition of the total of the feed materials and the recycle liquid are controlled according to the analytical values.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyester by reacting an aromatic dicarboxylic acid and a diol, and more particularly to a method for producing a polyester by controlling a reaction condition by analyzing a recycled solution of an unreacted diol. Things.

[0002]

2. Description of the Related Art Polyesters such as polyethylene terephthalate are produced by supplying an aromatic dicarboxylic acid such as terephthalic acid, a diol such as ethylene glycol, and a catalyst to a reactor, followed by an esterification reaction and a polycondensation reaction. In this production method, it is important to produce polyester of uniform quality by keeping the reaction conditions constant.However, the analysis of diols and catalysts requires a long time for analysis, so the reaction conditions and quality must be kept accurately and consistently. Is difficult.

Conventionally, in order to control reaction conditions in the production of polyester, the acid value of dicarboxylic acid as a raw material, the hydroxyl value of diol, the ester value of polyester as a product, and water content are analyzed by a near infrared spectrometer. A method for controlling reaction conditions such as temperature, pressure and time based on the analysis value has been proposed (JP-A-2-306937).
However, it was difficult to quantify the concentration of diol only by applying such a method. The concentration of the diol compound has a strong influence on the heat resistance of a molded article such as a polyester bottle. Therefore, it is necessary to have a quantification accuracy of 3% or less, which is similar to that of gas chromatography analysis.
It turned out that it is not suitable for practical use unless the wavelength accuracy and the noise level are predetermined. Further, it is difficult to change reaction conditions such as temperature, pressure, and time.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for controlling a stable supply of raw materials by performing a continuous analysis with a small amount and a short time with high accuracy without processing a sample. And to propose a method for producing polyester with stable quality.

[0005]

SUMMARY OF THE INVENTION The present invention relates to a method for producing a polyester by dispersing an aromatic dicarboxylic acid powder in a liquid diol to form a slurry and subjecting the slurry to a esterification step and a polycondensation step in the presence of a catalyst. When circulating a liquid containing unreacted diol and catalyst in the polycondensation step as a recycled liquid to the esterification step, the diol concentration, the diol condensate concentration, the water concentration and the catalyst concentration in the recycled liquid are adjusted to a noise level of 50 ×. Analyze with a near-infrared spectrophotometer and a fluorescent X-ray analyzer having a wavelength reproducibility of not more than 10 ^-6 Abs and a wavelength of not more than 0.01 nm. A method for producing a polyester, characterized in that the composition is controlled so as to fall within a predetermined range.

The aromatic dicarboxylic acid used as a raw material in the present invention includes, for example, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and the like. Examples of the diol include ethylene glycol, propylene glycol, and butanediol. These are used alone or in combination of two or more.

In the method for producing a polyester of the present invention, the above-mentioned aromatic dicarboxylic acid powder is dispersed in a diol to form a slurry, and the polyester is produced through an esterification step and a polycondensation step. The slurry is formed by stirring the above-mentioned aromatic dicarboxylic acid powder and other carboxylic acid powder to be added as necessary in ethylene glycol and other liquid diols and other alcohol to be added as needed under stirring at normal temperature and normal pressure. The slurry is suspended and dispersed to form a slurry. The amount of the diol used is 1 to 2 mol, preferably 1.1 to 1 mol, per 1 mol of the aromatic dicarboxylic acid powder.
Preferably it is 2 moles.

[0008] In the esterification step, the slurry obtained in the slurrying step is kept at 220 to 300 ° C, preferably at 240 ° C.
The reaction is carried out at a temperature of 270 ° C. under normal pressure or under pressure, preferably under normal pressure or 300,000 Pa, and the aromatic dicarboxylic acid is reacted with a diol to remove the generated water to esterify. The esterification reaction produces esters of aromatic dicarboxylic acids and diols and their multimers (oligomers). A catalyst may not be used for the esterification reaction, but a polycondensation catalyst used in the subsequent polycondensation step can be added at this stage.

The esterification step is preferably performed in a plurality of stages. Most of the diol is separated from the reaction mixture obtained in the esterification step and recycled to the esterification step.
The product ester and its multimer are sent to the polycondensation step in a state of being dispersed in a small portion of the diol together with the polycondensation catalyst.

In the polycondensation step, the ester and the polymer formed in the esterification step are treated at a temperature of 240 to 300 ° C., preferably 275 to 290 ° C., and under normal pressure or reduced pressure, preferably at a pressure of 14,000 to 60 Pa. Polycondensation produces a polyester while removing generated water. The polycondensation step can be performed in one stage, but is preferably performed in a plurality of stages.

The polycondensation reaction in the above-mentioned liquid phase polycondensation step is carried out in the liquid phase in the presence of a polycondensation catalyst. Examples of the polycondensation catalyst include germanium compounds such as germanium dioxide, germanium tetraethoxide, and germanium tetra-n-butoxide; antimony catalysts such as antimony trioxide; and titanium catalysts such as titanium tetrabutoxide. It is preferable that these polycondensation catalysts be used properly, taking advantage of the characteristics in the quality target.

In the liquid phase, a stabilizer can be used together with the polycondensation catalyst. Examples of the stabilizer include phosphates such as trimethyl phosphate, triethyl phosphate, tri-n-butyl phosphate, trioctyl phosphate, triphenyl phosphate and tricresyl phosphate, triphenyl phosphite, trisdodecyl phosphite, and trisnonyl phenyl phosphite. Phosphites such as methyl acid phosphate, isopropyl acid phosphate, butyl acid phosphate, dibutyl phosphate, monobutyl phosphate and dioctyl phosphate; and phosphorus compounds such as phosphoric acid and polyphosphoric acid.

The proportion of these catalysts or stabilizers used is usually expressed as the weight of the mixture of dicarboxylic acid and glycol or, in the case of a catalyst, the weight of the metal in the catalyst.
0.0005 to 0.2% by weight, preferably 0.001 to 0.2
In the range of 0.05% by weight, and in the case of stabilizers,
Usually 0.0001 to 0.0001 as the weight of phosphorus atom in the stabilizer.
It is in the range of 0.1% by weight, preferably 0.0002 to 0.02% by weight. For example, when two or more kinds of germanium-based catalysts are used in combination, or when a germanium-based catalyst and an antimony catalyst are used in combination, the calculation is performed as the total weight of metals in the total amount of these catalysts.

The method for supplying the polycondensation catalyst and the stabilizer can be supplied at the stage of the esterification step or can be supplied to each reactor in the polycondensation step.
In the liquid phase polycondensation step, the polycondensation catalyst and the stabilizer are used in a state of being dissolved or dispersed in the reaction liquid phase.

At the final stage of the polycondensation step in the liquid phase, the polyester produced from the reaction mother liquor is separated, and thereafter, if necessary, the granulation step, the crystallization step, the solid phase polycondensation step, etc., are carried out. obtain. A diol containing a catalyst and a stabilizer is recovered from the reaction mother liquor by a diol recovery step and, if desired, circulated as a recycle liquid to the esterification step via a purification step described in, for example, JP-A-7-228677.

In the present invention, the diol concentration, the diol condensate concentration, the water concentration, and the catalyst concentration in the recycled liquid are analyzed by a near-infrared spectroscopic analyzer and a fluorescent X-ray analyzer, and the reaction system is analyzed based on the analyzed values. The total composition of the raw materials (including aromatic carboxylic acids, diols, and catalysts) and the recycle liquid, for example, aromatic carboxylic acids, diols,
The supply amount of the raw material and / or the recycle amount of the recycle liquid are controlled so that the composition of the diol condensate, moisture, catalyst and the like becomes a predetermined value.

In order to stably carry out the reaction in the esterification and polycondensation steps in order to obtain a high quality polyester product, it is important to keep the composition of the raw materials introduced into the reaction system at a predetermined value. It is necessary to keep the total composition of raw materials and recycle liquid newly supplied to the reaction system at a predetermined value. For example, when the diol concentration in the recycle liquid increases, the supply amount of the raw material is reduced or the recycle amount is reduced, so that the total introduction amount of the newly supplied raw material and the recycle liquid is controlled to a predetermined value.
In this case, the reaction conditions and the like may be further adjusted. In addition, it is preferable to similarly analyze and control the concentrations of the stabilizer and the metal in the recycle solution.

A near-infrared spectrometer generally has a wavelength of 500 to
An apparatus that irradiates a sample with near-infrared light of 3000 nm, preferably 800 to 2500 nm, and more preferably 1000 to 2000 nm, detects transmitted light or reflected light, and analyzes the physical properties, components, and the like of the sample based on the absorption spectrum. . In the present invention, without pre-processing the recycled liquid,
In the process of recycling, analysis is performed as a sample as it is, and control is performed based on the result. Control is performed using a control device such as a computer so that the total composition of the raw materials and the recycle liquid supplied to the reaction system is within a predetermined range.

The near-infrared spectrometer has a noise level of 5
0 × 10 ⁻⁶ Abs or less, preferably 20 × 10 ⁻⁶ Abs
Hereinafter, a high-precision wavelength reproducibility of 0.01 nm or less is required. The measuring method of the noise level and the wavelength accuracy is as follows.

Measurement method of noise level If the measurement method is a reflection type, a ceramic plate is measured twice. If the measurement method is a transmission type, the measurement is performed twice in air.
Measure 0 sets. The standard deviation of the difference (effective value) between the first measurement value and the second measurement value is defined as the noise level.

Measurement Method of Wavelength Reproducibility Using a standard of JIS K0117-1979 infrared spectroscopy, a standard polystyrene film is put in an optical path and measured.
At this time, the reference near-infrared absorption wavelength is 1143.6330 n.
m, 1684.2700 nm, 2166.4000 nm
And 2305.9300 nm. Ten standard deviations are the values of the wavelength reproducibility.

The objects to be measured by the near-infrared spectroscopic analysis include the diol concentration, the diol condensate concentration, and the water concentration in the recycled liquid. Near-infrared rays have less energy than ultraviolet rays and do not change sample components. Also, unlike the case of visible light, the analysis is based on the absorption spectrum, and is not affected by the transparency or other form of the sample, so that adjustment of the film thickness or the like is not required.

Therefore, the recycled liquid can be used as a sample without any pretreatment. In addition, since the recycled liquid is not subjected to any chemical change by the analysis, the analyzer can be continuously analyzed for a long period without contamination of the analyzer.

An X-ray fluorescence analyzer generally performs analysis by detecting X-ray fluorescence in secondary X-rays generated when a sample is irradiated with primary X-rays of a constant intensity. This fluorescent X-ray analyzer can analyze elements, particularly inorganic elements. In the present invention, elements such as germanium in a catalyst, elements such as phosphorus in a stabilizer, and iron etc. Analyze metal elements. An X-ray fluorescence analyzer can also perform analysis without pre-processing the sample.

As the control device, a computer or the like can be used. In the near-infrared analyzer, wavelength calibration, spectral waveform processing, numerical calculation processing, supply control, and in the fluorescent X-ray analyzer, calibration, secondary X-ray detection , Signal formation / amplification, spectrum formation, numerical calculation processing, supply amount control, and the like.

[0026]

According to the method for producing a polyester of the present invention,
The esterification step and the polycondensation are performed by controlling the total composition of the raw materials and the recycle liquid to be supplied to the reaction system based on the analysis results of the respective components changing in the recycle liquid so as to be within a predetermined range. The reaction in the process is performed in a stable state, and a uniform quality polyester can be produced.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in which terephthalic acid (hereinafter referred to as TA) is used as an aromatic dicarboxylic acid, ethylene glycol (hereinafter referred to as EG) is used as a diol, and polyethylene terephthalate (hereinafter referred to as a polyester) is used as a polyester. , PET) will be described with reference to the drawings. FIG. 1 is a system diagram of the embodiment.

In the method for producing PET, first, the raw materials TA and EG are introduced into the esterification step 1. The raw material aromatic dicarboxylic acid may be any one containing TA as a main component, and may contain other dicarboxylic acids such as phthalic acid, isophthalic acid, and naphthalenedicarboxylic acid in an amount of 20 mol% or less in addition to TA.

In the esterification step 1, EG is added in an amount of 1 to 2 mol, preferably 1.1 to 1.2 mol, per 1 mol of TA, followed by stirring to suspend and disperse TA in EG to form a slurry. . The diol as a raw material / dispersion medium may be one containing EG as a main component, and may contain other diols such as trimethylene glycol and propylene glycol in an amount of 20 mol% or less.

Further, a catalyst such as a germanium compound such as germanium oxide and / or an antimony compound such as antimony acetate is contained in the slurry at a metal concentration of 5 to 1000 wtppm, preferably 1 to 1000 wtppm, based on the slurry.
0.00-300 wtppm is added.

The resulting slurry is subjected to the esterification step 1 at a temperature of from 220 to 300 ° C., preferably from 240 to 260 ° C., under normal pressure or under pressure, preferably at normal pressure to 30 ° C.
The reaction is carried out under a pressure of 000 Pa to form an ester while esterifying TA and EG to remove water produced. The esterification step 1 is a step of producing BHT (bis-β-hydroxyethyl terephthalate) by an esterification reaction of TA and EG (a reaction between an acid and an alcohol to produce water). Is represented by the following equations [1] to [4]. MHT is mono-β
-Hydroxyethyl terephthalate.

[0032]

Embedded image

In the esterification step 1, the above formulas [1] to
The reaction of [4] has occurred, and a mixture of several BHTs (collectively referred to as BHT) is formed. EG
In the case of / TA = 2 (molar ratio), the reaction of the formula [2] is mainly performed. However, in the actual reaction, the reaction is performed under the condition that the EG / TA molar ratio is low. The reaction also proceeds. Usually, it is said to be a 1- to 4-mer, but actually, a multimer exists up to the 10-mer position. In the esterification reaction, the heat of reaction is almost “zero”.

The ester formed in the esterification step (BH
The reaction solution containing T) and EG as a dispersion medium is treated with 240 to 3 in the polycondensation step 2 after removing most of EG.
The reaction is carried out at a temperature of 00 ° C., preferably 260 to 290 ° C., under normal pressure or reduced pressure, preferably at a pressure of 14,000 to 60 Pa to carry out polycondensation to produce PET. Polycondensation step 2
Is a step of producing a PET resin by a polycondensation reaction of drawing out EG from BHT under high temperature and high vacuum and performing polycondensation. In order to efficiently perform the polycondensation reaction, a multistage reactor is used. Perform the reaction.

In the polycondensation step 2, a thermal decomposition reaction, a hydrolysis reaction, a DEG (diethylene glycol) forming reaction, an oligomer forming reaction, and the like occur as side reactions in addition to the main reactions of the polycondensation reaction and the esterification reaction. As shown in the following formula [5], the polycondensation reaction is a reaction in which EG is extracted from BHT and BHT is successively bonded.
The reaction proceeds by removing. As shown in formula [6], the esterification reaction is an esterification reaction between carboxylic acid that has not been reacted in the esterification step and carboxylic acid generated by the thermal decomposition reaction with ethylene glycol, and generates water.

[0036]

Embedded image

In the above reaction, ethylene glycol is condensed to form diethylene glycol (DE
G) is generated. When this DEG is produced, it reacts with MHT according to equation [8] to produce a DEG ester.

[0038]

Embedded image

The PET produced by the polycondensation reaction in the polycondensation step 2 is subjected to a granulation treatment,
A product is obtained by crystallization or the like.

The reaction mother liquor separated from the polycondensation step 2 and the EG separated from the esterification step remove unnecessary substances in the EG purification step 3 and thereafter circulate to the esterification step 1 as a recycle liquid. At this time, a part of the recycled liquid is bypassed as a sample, and the near-infrared spectrometer 4 and the X-ray fluorescence analyzer 5 analyze the EG concentration, the DEG concentration, the water concentration, the catalyst concentration, and the like.

The near-infrared spectrometer 4 measures EG, DEG and moisture concentration on stream without using the recycled liquid as a sample and performing pretreatment. For example, EG
At 1710 nm, DEG at 1728 nm and 1914
nm and moisture can be measured at 1922 nm. The measurement results are input to the control device 6, where the respective densities are calculated. The arithmetic expression for each concentration is given by the following expression or its approximate expression.

[0042]

[Equation 1] EG concentration = 14.8380 + 70.7468 × absorbance (1710 nm) ··· [I] DEG concentration = 7.1835-379.4968 × absorbance (1728 nm) – 16.3079 × absorbance (1914 nm) ···· [II] Water concentration = 0.1351-14.9260 × absorbance (1922nm) ・ ・ ・ ・ [III]

In the X-ray fluorescence spectrometer 5, the liquid is flowed in series or parallel with the near-infrared spectroscopy analyzer 4 without performing pretreatment using the recycled liquid as a sample, and the elements such as Ge, Fe, P and the like are streamed on-stream. Perform analysis. For example, Ge is 9.876 KeV, Fe is 6.400 KeV, P
Performs analysis at an energy of 2.013 KeV. The analysis result is directly input to the control device 6.

The control unit 6 compares the measured and calculated values with the set values, and outputs a control signal so that the total composition of the raw material and the recycle liquid is maintained within a predetermined range. And reaction conditions and the like.

By controlling the amount of raw material supplied and / or the amount of recycle so as to maintain the total composition of the newly supplied raw material and the recycle liquid within the above range, the esterification step and the polycondensation step are always performed. The reaction is carried out under substantially the same conditions, the esterification and the polycondensation reaction can be stably performed, and a polyester of uniform quality can be obtained.

[0046]

EXAMPLES Examples of the present invention and comparative examples will be described below. In each case,% and ppm are based on weight.

Example 1 EG 98%, DEG 1.5%, moisture 0.3%, G
e 2000ppm, Fe 0.5ppm, P 70p
pm recycled liquid at 500 ml / min, near infrared spectrometer (OL-6 manufactured by NIRS Systems) shown in Table 1.
500, noise level 20 × 10 ^-6 Abs)
Wavelength 1710 nm, 1728 nm, 1914 nm, 19
After measuring the absorbance at 22 nm, an X-ray fluorescence analyzer (Mitsuisekka & Technos Onstream 600)
9.876 KeV, 6.400
It was measured at KeV, 2.013 KeV.

The above measurement was completed within 2 minutes. The results were calculated by the above-mentioned formulas [I] to [III] by the control device, and this was repeated 30 times to confirm the reproducibility. The results shown in Table 2 were obtained. The apparatus of Example 1 had good correlation coefficients and standard errors for both the water concentration and the DEG concentration. In addition, stable operation was possible for 6 months or more without correction or cleaning for a long time.

Comparative Example 1 EG and DEG in the recycle liquid were subjected to gas chromatography (DB-WAX, temperature 150 ° C., carrier gas H
e 5 ml / min), it took 20 minutes for the measurement, and column degradation was observed in about 10 samples,
Maintenance, such as column replacement, is required once every eight hours. In order to extend the life, pretreatment is required. When water was analyzed by Karl Fischer quantitative titration method,
The titration took 5 minutes. Ge, Fe, and P were analyzed by atomic absorption spectrometry (ICP plasma gas: 1.2 liter, high frequency 1.2 liter).
As a result of the analysis using KW), it takes 30 minutes for the measurement, and it is necessary to cope with the changing concentration, which leads to variation in quality and impaired economy.

Comparative Example 2 The NIR apparatus of Example 1 was changed to the apparatus shown in Table 1, and reproducibility was confirmed. As a result, as shown in Table 2, the apparatus of Comparative Example 2 having poor reproducibility of the noise level and the wavelength was inferior to the apparatus of Example 1 in both the moisture concentration and the DEG concentration in the correlation coefficient and the standard error. . The analysis of moisture did not affect the difference in the performance of the apparatus, but the analysis of DEG showed a low correlation coefficient and was not suitable for use.

[0051]

[Table 1]

[0052]

[Table 2] * Lab values in Table 2 are values measured by the method of Comparative Example 1.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a manufacturing method according to an embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Esterification process 2 Polycondensation process 3 EG purification process 4 Near-infrared spectroscopy device 5 X-ray fluorescence analyzer 6 Control device

Claims (1)

[Claims] 1. A method for producing a polyester by dispersing an aromatic dicarboxylic acid powder in a liquid diol to form a slurry and subjecting it to an esterification step and a polycondensation step in the presence of a catalyst; When a liquid containing a diol and a catalyst is recycled as a recycled liquid to the esterification process, the diol concentration, the diol condensate concentration,
The water concentration and catalyst concentration were adjusted to a noise level of 50 × 10
^-6 Abs or less, reproducibility of wavelength is 0.01 nm or less, analyzed by near-infrared spectrometer and X-ray fluorescence analyzer, and based on the analysis values, the total of raw materials and recycle liquid supplied to the reaction system was calculated. A method for producing a polyester, wherein the composition is controlled to fall within a predetermined range.