KR20010056826A - Preparation of polyester - Google Patents

Abstract

PURPOSE: A process for producing high quality polyester is provided for dividing untreated ethyleneglycol from impurity as a by-product in a preferred efficiency to reuse it in the polymerization process. CONSTITUTION: The process for preparing high quality polyester comprises providing terephthalic acid and/or its ester derivative and ethylene glycol as raw material into an esterification reactor; introducing the obtained low polymer into a polycondensation reactor; using centrifugal separator to precipitate impurities of the ethylene glycol containing efflux from the esterification and/or polycondensation reactors and to purify the ethylene glycol; and reusing the purified product in the polymerization process. The centrifugal separator satisfies the equation of >=T 2e(exp7)Z(exp1.8401), wherein Z and T represent the efficiency of centrifugal separation and the resident time in the separator, respectively.

Description

Production method of polyester {Preparation of polyester}

The present invention relates to a method for producing a polyester resin, and more particularly, to remove ethylene glycol that is recovered without being reacted by being introduced into a polymerization process and separated from impurities with improved efficiency and reused in polymerization. It is related with the manufacturing method of polyester.

The polymerization method of the polyester resin may be classified into a direct polymerization method and a transesterification method depending on raw materials, or may also be classified into a batch polymerization and a continuous polymerization method according to a manufacturing process. For example, when polyester is polyethylene terephthalate, the direct polymerization method (so-called TPA method) uses terephthalic acid (TPA) and ethylene glycol (EG) as raw materials, and the transesterification method (so-called DMT method) is dimethyl tere. Phthalates (DMT) and ethylene glycol are used. In the industrial production process, both the direct polymerization method and the transesterification method are used for the batch polymerization method, but the direct polymerization method is mainly used for the continuous polymerization method.

This polymerization reaction usually proceeds in two stages, in which the first stage reaction is an ester reaction (or transesterification reaction) to form a oligomer, and the two stage reaction is a polycondensation reaction to form a high polymer. In this polymerization reaction, mainly in the polycondensation reaction step, the unreacted material in the ethylene glycol input as a raw material is recovered in a vacuum system as the polycondensation reaction proceeds regardless of the polymerization method.

In addition to the ethylene glycol, the material recovered in the polymerization process contains a large amount of substances (hereinafter referred to as 'impurities') such as reaction catalysts, heat-resistant agents, moisture, diethylene glycol, carbides, solids (polyester oligomers), and the like. Since it is a state, impurity purification is essential to reuse the recovered ethylene glycol as a raw material in the polymerization process.

In other words, the water in the impurities in the ethylene glycol recovered in the vacuum system in the polyester polycondensation step is discharged to the rectification column of the esterification step when re-introduced into the polymerization process as a raw material, and some of them stay in the final polymer and However, since the amount thereof is very small, the physical properties of the final polymer are not significantly affected.

In addition, the metal catalyst and the heat-resistant agent can be corrected by the amount of the polymerization process catalyst by evaluating the remaining amount and activity. However, it is essential to remove carbides and solids since carbides and solids cannot be removed in the polymerization process and cause serious degradation in the final polymer.

Conventionally, a method of purifying ethylene glycol by the rectification method using the boiling point difference between ethylene glycol and impurities and the precipitation method by the specific gravity difference, and re-injecting the raw material into the process as a raw material has been proposed.

Korean Patent Application Publication No. 95-18137 (Application No. 94-35954) discloses a rectification method for recovering and purifying ethylene glycol using a difference in boiling point between ethylene glycol and impurities. However, this method is excellent in refining efficiency because it is rectified at a temperature above boiling point in order to separate impurities recovered with ethylene glycol, but the disadvantages of excessively expensive equipment cost and high heat consumption for ethylene glycol recovery are too high. have.

In an attempt to remedy these shortcomings, Korean Patent Application Publication No. 97-10824 (Application No. 96-35262) has proposed a precipitation method using a specific gravity difference between ethylene glycol and impurities. The characteristic of this method is that the recovered ethylene glycol is stored in the storage tank for precipitation, the supernatant is used again as a raw material, and the precipitate is separated by using the rectification method because of the high content of ethylene glycol, thus reducing the need for rectification. To reduce the recovery cost of ethylene glycol. In this method, however, carbides with a large difference in specific gravity among the impurities coexisting with ethylene glycol can be separated to some extent, but solid contents having a small difference in specific gravity have a low sedimentation rate and require excessive settling time. This will increase the required settling time.

Therefore, the present invention is to provide a method for refining ethylene glycol in a high purity in a simple yet economical manner in the material recovered in the polyester polymerization process to be reused in the polymerization process.

In the present inventor's research for solving the above problems, by using a high-speed centrifugation purification method that can increase the sedimentation rate, the recovered ethylene glycol can be purified with high purity and safely reused in the polymerization process with improved productivity and economy. I found out that I could.

1 is a block diagram schematically illustrating a process of recovering ethylene glycol of high purity by separating the ethylene glycol-containing effluent in the polyester manufacturing process according to the present invention and re-supplying it to the polymerization process. Where CEG stands for ethylene glycol-containing effluent and PEG stands for purified ethylene glycol.

Therefore, according to the present invention, terephthalic acid and / or its ester-forming derivative and ethylene glycol are used as raw materials to be fed to an esterification reaction to perform an esterification reaction, and the resulting polyester oligomer is fed to a polycondensation reaction apparatus to carry out polycondensation. A method for producing a polyester, characterized in that the ethylene glycol-containing effluent discharged from the esterification reactor and / or the polycondensation reactor is centrifuged to settle impurities and the purified ethylene glycol is fed back to the polymerization process. A polyester production method is provided.

Further, according to the present invention, the centrifugation satisfies Equation 1, while the centrifugation effect (Z) is higher than 2000G (where G is gravity acceleration) and the retention time (T) satisfies at least 5 minutes. There is provided a process for producing a polyester characterized by centrifugation:

In the formula, Z represents the centrifugal effect, and T represents the residence time in minutes in the centrifuge.

In addition, the present invention provides a polyester chip characterized in that the ethylene glycol flowing out of the polymerization process of the polyester is re-supplied and manufactured, the color b value is 1.6 to 2.2, the diethylene glycol content is 1.33% by weight or less.

Hereinafter, the present invention will be described in more detail.

The present invention proposes a more efficient method for purifying ethylene glycol, which is introduced as a raw material in a polycondensation reaction step in a polyester resin polymerization process and then flows out into a vacuum system, to be re-supplied to the resin polymerization process.

According to the present invention, it is essential to separate impurities such as carbides and solids from the ethylene glycol-containing material flowing out into the vacuum system using the principle of centrifugation, and to re-feed high purity ethylene glycol to the polymerization process.

Centrifugation refers to an operation of separating the solid or liquid fine particles suspended in the fluid using the centrifugal force as the driving force. In the present invention such centrifugation is carried out under specially controlled conditions, i.e. , Centrifugal effect (Z) is performed under conditions satisfying at least 2000G and residence time (T) at least 5 minutes at the same time.

The centrifugal effect (Z) refers to the ratio (F _circle / F _in) of the centrifugal force (F _W) and gravity (F _in) represents the strength of the separation force in a centrifuge.

When a particle of arbitrary mass (m) [Kg] rotates at an arbitrary rotation radius (r) [m] at an arbitrary angular velocity (ω) [s-¹], the centrifugal force applied to the particle becomes Equation 2, gravity applied to the particles of the mass (F _in) is the equation (3).

Therefore, the centrifugal effect Z becomes (4).

Therefore, when the centrifugal effect is expressed in revolutions per minute, it is expressed by Equation 5.

As can be seen in Equation 5, the centrifugal separation effect is high when the rotation is accelerated or the rotation radius is increased. In addition, this centrifugal effect requires an appropriate residence time in order to be sufficiently separated by the precipitation rate of ethylene glycol.

According to the invention Centrifugal separation of ethylene glycol-containing effluent under conditions satisfying at least 2000G of centrifugal effect (Z) and residence time (T) of at least 5 minutes can separate the average particle diameter of the minimum particles to 10 μm or less, resulting in high purity ethylene glycol Can be fed back to the polymerization process. If the centrifugal effect is less than 2000G, it is impossible to separate particles having a low specific gravity, and if the residence time is 5 minutes or less, the centrifugal effect is not sufficiently applied and the centrifugal separation is not performed.

According to the present invention, when the ethylene glycol flowing out of the polymerization process is re-supplied to produce a polyester chip having a color b value of 1.6 to 2.2 and a diethylene glycol content of 1.33% by weight or less. If the polyester chip manufactured by re-feeding ethylene glycol flowing out from the polymerization process contains diethylene glycol (DEG) in an amount greater than 1.33% by weight, the dyeability difference occurs. And the like, and also when the color b value is less than 1.6 or more than 2.2, the problems as described with respect to the DEG content are likely to occur.

Features and other advantages of the present invention as described above will become more apparent from the following examples. However, the present invention is not limited to the following examples.

[Examples 1-3]

860 kg of terephthalic acid (TPA) and 390 kg of pure ethylene glycol (hereinafter referred to as 'NEG') were added to the reaction vessel to which the stirrer and the rectifier tube were attached, and the stirring was started, and the reaction was performed while removing the water generated by the reaction. When the esterification reaction is completed in this way, 0.030 kg of antimony compound, 0.30 kg of titanium oxide, and 0.010 kg of phosphoric acid are added to polycondensate at high vacuum of 20 Torr or lower and high temperature of 280 ° C., and when the viscosity reaches a certain viscosity, the reaction is terminated. It discharged and the chip-like polymer was obtained. On the other hand, in the vacuum system of the polycondensation step, the ethylene glycol-containing effluent (hereinafter referred to as 'CEG') was discharged out of the system. CEG was purified by centrifugation in a centrifuge and centrifugal effect and retention time as shown in Table 1, and the purified ethylene glycol (hereinafter referred to as "REG") was returned to the above polyester manufacturing process. Supplied. The resupply amount was the same as that of NEG. In other words, NEG: REG = 1: 1 to prepare a polyester chip.

Particle size distribution, intrinsic viscosity, color b value and diethylene glycol (DEG) content were measured by the method described below in order to compare the characteristics of the purified REG and the characteristics of the prepared chip. The measurement results are shown in Table 1.

-Particle size distribution: Measurement of average particle diameter (μm) of solids in CEG and REG using a particle size distribution analyzer (model number BI-DCPH) manufactured and sold by BIC

-Intrinsic viscosity: Melt 2.0 g of chip in 25 ml of orthochlorophenol, a solvent, at 25 ° C to measure the viscosity.

-Color b value: Measured b value of chip using color meter (model number CR-200) manufactured and sold in Minolta, Japan.

DEG content: Determination of the weight content of diethylene glycol in the chip. Hydrolysis of the chip with methanol measured by gas chromatography (GC). GC column uses CARBOWAX 20M 10% CHROMOSORB W and 1,6-hexanediol as EXTERNAL STANDARD.

[Comparative Examples 1 and 2]

The same procedure as in Example 1 was repeated except that the CEG was filled with a cylinder of 1 meter in diameter and 3.5 meters in height to 3 meters in the cylinder, and after a certain precipitation time, more than 2 meters of height was recovered to REG and re-supplied to the polymerization process. It was.

Comparative Example 3

The same procedure as in Example 1 except that the REG was recovered and re-supplied to the polymerization process by operating at a tube temperature of 150 ° C. and a vacuum degree of 12 Torr in a process equipped with a rectifying tube equipped with a conventional heating system and a rectifying tower for gas-liquid separation by distillation. Was repeated.

[Comparative Example 4]

The same procedure as in Example 1 was repeated except that the CEG was resupplied to the polymerization process without purification.

[Control experiment]

The same procedure as in Example 1 was repeated except that only NEG was supplied to the polymerization process and ethylene glycol discharged to the vacuum system was completely discharged out of the system.

division Ethylene glycol Chip property Way Treatment condition Particle Size Distribution (㎛) Intrinsic viscosity Color b value DEG content (wt%) CEG REG contrast - Use only NEG 150 - 0.640 1.5 1.03 Example 1 Centrifugation Centrifugal effect: 2000G Stay time: 25 minutes 150 8 0.640 1.6 1.10 Example 2 Centrifugation Centrifugal effect: 3000G Stay time: 12 minutes 150 9 0.642 1.6 1.11 Example 3 Centrifugation Centrifugal effect: 4000 G Stay time: 6 minutes 150 6 0.638 1.6 1.09 Comparative Example 1 Precipitation Settling time: 60 minutes 150 120 0.638 2.6 1.15 Comparative Example 2 Precipitation Settling time: 120 minutes 150 100 0.642 2.3 1.13 Comparative Example 3 distillation - 150 2 0.641 1.6 1.35 Comparative Example 4 - Do not process 150 150 0.637 3.0 1.12

[evaluation]

When the ethylene glycol recovered in the polymerization process was separated by a centrifuge, the total amount of carbides was separated, and the particle distribution was confirmed to remove more than 10μm solids.

As a result, the intrinsic viscosity and the b value in the chip physical properties were obtained at the same level as in the conventional method, and there was no degradation of physical properties by carbides. The content of diethylene glycol, which causes the deterioration of physical properties in the manufacture of polyester filaments, was also shown to be at a level comparable to that of the normal. The particle distribution was superior to the precipitation method, and also superior to the separation by the precipitation method in comparing the content of ethylene glycol in the separated solids. In the energy consumption during operation, since the centrifuge does not consume energy other than the power of the motor for rotating the screw, there is an advantage that the energy cost can be reduced compared to the distillation method using the difference in boiling point.

As will be apparent from the results of Table 1, according to the present invention, a high-purity REG can be recovered from the CEG and re-supplied to the polymerization process using a centrifugal separation method requiring a low facility investment cost and a low energy cost. Therefore, the productivity and quality of the polyester manufacturing process can be improved.

Claims (3)

A polyester is produced by supplying terephthalic acid and / or its ester-forming derivative and ethylene glycol as a raw material to an esterification reaction device to effect esterification, and feeding the obtained polyester oligomer to a polycondensation reaction device to polycondensate. Process for producing a polyester, characterized in that the ethylene glycol-containing effluent discharged from the esterification reactor and / or the polycondensation reactor is centrifuged to precipitate impurities and replenish the purified ethylene glycol to the polymerization process. Way. The method of claim 1, wherein the centrifugation satisfies the following equation, (Where Z is the centrifugal effect and T is the residence time in minutes in the centrifuge) A method for producing a polyester, characterized in that the centrifugation effect (Z) is a high-speed centrifugation under a condition in which 2000 G (where G is gravity acceleration) or more and a residence time (T) satisfies 5 minutes or more. Ethylene glycol effluent from the polymerization process of the polyester is re-supplied, the polyester b, characterized in that the color b value is 1.6 to 2.2, diethylene glycol content is 1.33% by weight or less.