JP4935005B2 - Polyester production method, solid phase polycondensation method and high strength polyester fiber - Google Patents

Description

  The present invention provides a process for producing a polyester capable of improving process stability and producing a stable polyester by controlling the esterification reaction, a solid phase polycondensation method using the polyester, and the solid phase polycondensation. The present invention relates to a high-strength polyester fiber using a polyester obtained by a legal method.

  Polyester is used for various applications including films, fibers and bottles because of its excellent properties. Among these, polyethylene terephthalate is generally used because of its excellent mechanical strength, chemical resistance, and dimensional stability.

  In general, polyester is produced in two stages, an esterification reaction and a polycondensation reaction. In the production of polyethylene terephthalate, in order to stabilize the production process, the ratio of carboxyl end groups to hydroxyl end groups (hereinafter referred to as “end group ratio”) of the low polymer, which is an intermediate obtained by esterification reaction, is determined. It is important to adjust.

  For example, if the terminal group ratio fluctuates greatly, the progress rate of the polycondensation reaction fluctuates in the polycondensation step, resulting in problems such as fluctuations in the load of removing ethylene glycol or the polymer not reaching a predetermined degree of polymerization. . In terms of quality, a phenomenon occurs in which the hue of the polymer changes.

Therefore, for example, at least 1 comprising the temperature during the esterification reaction, the pressure residence time, and the ethylene glycol supply amount so that the esterification rate of the polyester oligomer supplied to the polycondensation step is constant within the range of 90 to 98%. A method for obtaining a polyester having a carboxyl end group amount of 20 to 50 eq / ton by adjusting the reaction conditions of the seeds, the esterification rate of the polyester oligomer supplied to the polycondensation step is in the range of 92 to 98%, and in all the end groups At least one kind consisting of a method of obtaining a polyester having a carboxyl end group amount of 35 eq / ton by adjusting the proportion of carboxyl end groups to 35% or less, the temperature during the first polycondensation reaction, the residence time, and the ethylene glycol supply amount Adjusting the reaction conditions or the esterification reaction rate of the esterification reactant first A method of adjusting the condensation reaction conditions to obtain a polyester having a carboxyl end group amount of 15 to 50 eq / ton and a method of supplying the polyester oligomer with a carboxyl end group amount of 9 to 30 eq / ton and supplying it to the polycondensation step are disclosed ( (See Patent Documents 1 to 4).
Japanese Patent Laid-Open No. 10-176043 Japanese Patent Laid-Open No. 10-251391 JP-A-11-106498 JP 2001-329058 A

Furthermore, the color tone of the product polymer is measured, the method of adjusting the esterification rate in the esterification process according to the deviation of the measured value from the target value, the color tone of the product polymer is measured, and the deviation of the measured value from the target value Of adjusting the residence time during the first polycondensation reaction according to the above, and measuring the color tone and intrinsic viscosity of the product polymer, and depending on the deviation of the measured value from the target value, ethylene glycol into the first stage polycondensation reaction can By adjusting the supply amount, the standard deviation of the color tone (b value) of the produced polyester is kept within 0.05 times the average value, and the standard deviation of the intrinsic viscosity is within 0.005 times the average value. The method of keeping is disclosed (see Patent Documents 5 to 7).
Japanese Patent No. 3375403 JP 2004-75955 A JP 2004-75957 A

  However, in the above method, since the polycondensation reaction has already progressed at the time when the color tone of the product polymer is measured, it cannot be said that the above problem has been solved because the adjustment of the esterification rate is delayed.

In addition, the density and concentration of the slurry of terephthalic acid and ethylene glycol supplied to the polyester manufacturing process are continuously measured, and esterification is performed based on the molar ratio of ethylene glycol to terephthalic acid in the slurry obtained from the measured value. A method for controlling the reaction and a method for controlling a change in the ratio of terephthalic acid and ethylene glycol in the slurry according to changes in the slurry concentration are disclosed (see Patent Documents 8 and 9).
JP-A-6-247899 JP 2004-75956 A

  The above method is a preferable method for stabilizing the quality of the polyester obtained in that it is supplied to the esterification reaction and controlled so that the polyester formation reaction is made constant by the slurry concentration, but has a great influence on the quality of the polyester. There is a problem that the degree of progress of the esterification reaction that gives rise to is not detected.

Moreover, the method of measuring the electrical conductivity of an esterification reaction product on-line and controlling esterification reaction by the result is disclosed (for example, refer patent documents 10-12 etc.). The method is a method for controlling the esterification reaction by utilizing the proportionality between the electrical conductivity of the esterification reaction product and the esterification reactivity, and the point that the esterification reactivity is directly measured. This is a control method that is one step ahead of the proposed method. However, this method has a problem that the influence of disturbance such as a change in the electric conductivity of the esterification reaction product due to the influence of water or unreacted ethylene glycol produced by the esterification reaction is large.
Japanese Patent Publication No.51-41679 JP-A-48-103537 JP 52-19634 A Japanese Patent Publication No. 5-32385

  As a method for solving the above problems, the near infrared characteristics of one or more of raw materials, reaction intermediate products or final products in the production process of polyester are continuously measured, and the measured spectrum is used to measure A method for analyzing the physical properties of the polymer and controlling the reaction conditions during the production process based on the analysis data is disclosed (see Patent Document 14). In this patent document, the polyester is provided at the bottom of the polycondensation tank in the continuous production process. In addition, a near-infrared absorption spectrum detection terminal is installed at the outlet, and the carboxyl end group concentration of the polyester that always passes through the outlet is continuously measured, and the near-infrared absorption is also performed at the outlet of the second esterification reaction tank. A spectrum detection terminal is installed, and the esterification rate of the polyester oligomer passing through the detection terminal is continuously measured to obtain the target esterification rate. Fed back to the second esterification reaction tank temperature controller, a method of suppressing a carboxyl end group concentration change of product polyester is disclosed as. The method is effective as a control method for stabilizing the carboxyl end group concentration of the polyester, but is a method for detecting and controlling the characteristic values of the polyester and oligomer at two points in the polyester production process. There is a problem that the capital investment of the control device and the maintenance cost for maintaining its performance are high and the control system is complicated. Furthermore, there is a problem that the reaction control is performed by controlling the temperature of the second esterification reaction tank having a slow response speed. These challenges are one. That is, since the reaction control is performed by the temperature control of the second esterification reaction tank having a slow response speed, it is assumed that the above complicated control is required. Therefore, it is desired to establish a method that can stabilize the carboxyl end group concentration change of the produced polyester with a more simplified control system.

JP 11-315137 A

  In the above direct esterification method, the polyester is produced by preparing a slurry of an aromatic dicarboxylic acid and glycol in a slurry preparation tank and supplying the slurry to an esterification reaction tank. Since the aromatic dicarboxylic acid is solid and insoluble in glycol, these raw materials are supplied in a slurry form to the esterification reaction tank. In order to ensure the fluidity of this slurry, more than the theoretical amount of glycol is required. A method of supplying as a raw material and recovering an excess part is common. The esterified oligomer produces a polyester by deglycolization reaction in a polycondensation reaction tank. These excessively used glycols and glycols generated by the polycondensation reaction must be recovered and reused. Since methods for recovering and reusing these glycols greatly affect the production cost of polyester, various methods are disclosed.

A method of rectifying and removing a low-boiling fraction from a distillate in an esterification reaction tank, circulating it in a slurry preparation tank (see Patent Document 15), and a low-boiling fraction of ethylene glycol discharged from the esterification reaction tank Rectified and removed and supplied to the ethylene glycol storage tank, and a part of this is used as a circulating liquid for the wet condenser provided in the polycondensation reaction tank to supply the condensate to the ethylene glycol storage tank and the ethylene retained in the ethylene glycol storage tank. A method of reusing glycol for slurry preparation (see Patent Document 16), distillate generated from a polycondensation reaction tank is condensed in a wet condenser, and sent to a distillation column provided in the esterification reaction tank. After removing the fraction, a method of returning to the slurry preparation tank and reusing it (see Patent Document 17), the distillate generated in the polycondensation reaction tank is continuously simply distilled, A method in which the bottom extraction liquid of the continuous single distillation can is sent to a batch-type single distillation can for simple distillation, and the distilled liquid excluding the first distillation portion is used as a part of the polycondensation reaction gas condensation refrigerant liquid ( Patent Document 18), a part of the esterification reaction tank distillate and the polycondensation reaction tank distillate rectifies and removes the low boiling fraction, and the remaining part of the polycondensation reaction tank distillate has a low boiling point. A method of removing distillate and high-boiling fraction, circulating to slurry preparation and reusing (see Patent Document 19), distillate discharged from the second stage of the esterification reaction directly without purification by distillation , A method of reusing a part or the whole of the raw material (see Patent Document 20), distilling the distillate from the polycondensation reaction tank by rectifying and removing the low boiling fraction by flash distillation and reusing it as a part of the raw glycol A method of use (see Patent Document 21) is disclosed.
Japanese Patent Laid-Open No. 53-126096 JP-A-55-56120 JP-A-60-163918 JP-A-8-325363 Japanese Patent No. 3424755 Japanese Patent Laid-Open No. 10-279777 WO01 / 088382

            The glycol recovered by the above method includes, for example, a case where water generated by the reaction is reused without being completely removed. In the method, the use of the recovered glycol affects, for example, the progress of the esterification reaction, and consequently affects the quality and productivity of the polyester. However, the techniques disclosed in these patent documents are disclosures of techniques relating to a method for recovering and reusing raw glycol, and in a polyester production process for stabilizing the quality of polyester in a production method for reusing the recovered glycol. No mention is made regarding optimization of reaction conditions and the like.

  On the other hand, as a raw material polyester for high-strength fibers and direct blow molded bottles, a high molecular weight polyester is required. The raw material polyester is generally prepared by preparing a prepolymer having an intrinsic viscosity of 0.45 to 0.70 by a melt polycondensation method, and subjecting the prepolymer to solid phase polycondensation to produce a high molecular weight polyester. In the solid phase polycondensation, it is known that the polycondensation reaction rate varies greatly depending on the carboxyl end group of the prepolymer.

For example, a method in which solid-phase polycondensation is performed with a ratio of carboxyl end groups to total end groups of the prepolymer of 20 to 45 equivalent% is disclosed (see Patent Document 22).
Japanese Patent Laid-Open No. 8-188443

Further, a method for specifying the solid phase polycondensation time according to the amount of end groups of the prepolymer is disclosed (see Patent Document 23).
Japanese Patent Laid-Open No. 7-90064

Based on the background described above, the present inventors continuously detect the carboxyl end groups of the esterification reaction product before the start of polycondensation online, and based on the detected values, the carboxyl end groups and the hydroxyl end groups are detected. A method for adjusting the ratio was proposed (see Patent Document 24).
Japanese Patent Application No. 2003-431641

  By the above method, high quality polyester can be stably produced, and the quality of the polyester subjected to solid phase polycondensation can be improved by using it as a prepolymer for the polyester solid phase polycondensation method. However, for example, in order to achieve high stabilization of the spinning operability of high strength fibers, further stabilization of quality is necessary. Furthermore, from the economical point of view, establishment of a technology that maintains the above-mentioned stabilization of quality is desired in a method for producing a polyester in which glycol generated in the polyester production process is reused.

  An object of the present invention is to provide a method for stably producing a high-quality polyester by controlling an esterification reaction by a simplified and economical reaction control method.

In order to solve the above-mentioned problems, we intensively studied, and in the previously proposed quantification of carboxyl end groups by near infrared absorption, it is possible to quantitate hydroxyl end groups only by changing the measurement wavelength. It was also found that by measuring the hydroxyl end groups at the same time and controlling the esterification reaction using both measured values, the overresponse can be suppressed as compared with the control with the quantitative value of only the carboxyl end groups. Furthermore, the recovered glycol is reused by combining the above control with the water content in the recovered glycol and the slurry temperature comprising the carboxylic acid and glycol supplied to the esterification reaction tank being controlled within a specific temperature range. High-quality polyester can be stably produced in a highly economical polyester production method, and the above object can be achieved. For this reason, the quality of the obtained polyester can be further stabilized, and by performing solid phase polycondensation using the polyester as a prepolymer, the stability of the solid phase polycondensation reaction is improved. The present invention has been completed by finding that the spinning operability when producing high-strength polyester fibers can be further improved.
That is, the present invention is a method for producing a polyester characterized in that it is a continuous method for producing a polyester by a direct esterification method and satisfies the following conditions simultaneously.
(1) In the process of preparing a slurry consisting of carboxylic acid and glycol in a slurry preparation tank and continuously feeding it quantitatively to the esterification reaction tank, the temperature of the slurry is controlled within ± 4 ° C. of the set value. Supply to the chemical reaction tank.
(2) The carboxyl end group concentration and the hydroxyl end group concentration of the polyester low polymer at the end of the final esterification reaction tank are continuously detected online, and the esterification reaction is controlled based on the detected values.
In this case, in the distillation tower provided in the polyester production process, the glycol distilled from the polyester production process is fractionally removed from the low-boiling fraction containing water as a main component, and the residue taken out from the bottom of the distillation tower is removed. Is preferably reused as recovered glycol.
In this case, at least two distillation towers are provided, and the glycol distilled from the first esterification reaction tank and the glycol distilled from the second esterification reaction tank are separated, and water is the main component. It is preferable to distill off the low-boiling fraction.
In this case, it is preferable to return the distillate glycol residue from the first esterification reaction tank to the slurry preparation tank.
Moreover, in this case, it is preferable to return the distillate glycol residue from the second esterification reaction tank to the distillation column for fractionating the distillate glycol from the slurry preparation tank and / or the first esterification reaction tank.
In this case, the glycol is preferably ethylene glycol.
Further, in this case, in the fractionation, it is preferable to control the top pressure of the distillation column having a line for returning the slurry preparation tank using the residue as recovered glycol to 10 to 300 kPa.
In this case, the water content in the recovered glycol is preferably controlled within X ± 2.0% by mass (where X represents a number of 2 or more and 3 or less).
In this case, in the fractionation, it is preferable to control the middle temperature of the distillation tower having a line for returning the residue to the recovered glycol as the recovered glycol to 106 ± 3 ° C.
In this case, the temperature of the slurry preparation tank is detected and fed back to the glycol temperature supplied to the slurry preparation tank so that the temperature is within ± 3 ° C. of the set value. preferable.
In this case, the reaction control is performed by continuously changing the glycol addition amount supplied after the second esterification reaction tank by the feedback circuit based on the carboxyl end group concentration and the hydroxyl end group concentration detected by the above method. By carrying out, it is preferable to control the carboxyl end group concentration with a standard deviation (s) of 2.5 or less.
In this case, it is preferable that the carboxyl end group concentration and the hydroxyl end group concentration of the product are detected using a near infrared spectrophotometer.
In addition, the present invention is a solid phase polycondensation method of polyester characterized by solid phase polycondensation of the polyester obtained by the above polyester production method.
The present invention also provides a high-strength polyester fiber obtained by spinning the polyester obtained by the solid phase polycondensation method.

  The polyester production method of the present invention can suppress the quality fluctuation of the obtained polyester by a highly simplified and highly economical reaction control method. Therefore, the solid phase polycondensation reaction can be stabilized by using the polyester as a prepolymer, and the spinning operability of high strength fibers can be improved by using the solid phase polycondensation polyester. In addition, the polyester production method of the present invention is characterized by excellent cost performance because the above characteristics are maintained even when applied to a production method in which glycol generated in the polyester production process is recovered and reused.

  Hereinafter, an embodiment of a method for producing a polyester of the present invention will be described.

In the present invention, it is important to satisfy the following conditions simultaneously in the continuous production method of polyester by the direct esterification method. That is, in the continuous production method of polyester by the direct esterification method, it is preferable to satisfy the following conditions simultaneously.
(1) In the process of preparing a slurry consisting of carboxylic acid and glycol in a slurry preparation tank and continuously feeding it quantitatively to the esterification reaction tank, the temperature of the slurry is controlled within ± 4 ° C. of the set value. Supply to the chemical reaction tank.
(2) The carboxyl end group concentration and the hydroxyl end group concentration of the polyester low polymer at the end of the final esterification reaction tank are continuously detected online, and the esterification reaction is controlled based on the detected values.
Furthermore, in the distillation tower provided in the polyester production process, the low-boiling fraction mainly composed of water is fractionated and removed to recover the residue taken out from the bottom of the distillation tower. It is more preferable to recycle as glycol.

  The direct esterification method is advantageous in terms of economy as compared with the transesterification method. The continuous polycondensation method is advantageous in terms of quality uniformity and economy as compared to the batch polycondensation method.

  In the present invention, the number and size of the reactors in the esterification and polycondensation steps, the production conditions in each step, and the like can be appropriately selected without limitation.

  For example, a slurry containing 1.02 to 2.0 moles, preferably 1.03 to 1.95 moles of ethylene glycol per mole of terephthalic acid is prepared and used in the esterification reaction step. Supply continuously. The esterification reaction is carried out using a multistage apparatus in which 1 to 3 esterification reaction tanks are connected in series while removing water generated by the reaction from the system with a rectification column. The temperature of the esterification reaction in the first stage is 240 to 270 ° C., preferably 245 to 265 ° C., and the pressure is normal pressure to 0.29 MPa, preferably 0.005 to 0.19 MPa. The temperature of the esterification reaction at the final stage is usually 250 to 290 ° C, preferably 255 to 275 ° C, and the pressure is usually 0 to 0.15 MPa, preferably 0 to 0.13 MPa. When carried out in three or more stages, the reaction conditions for the esterification reaction in the intermediate stage are conditions between the reaction conditions for the first stage and the reaction conditions for the final stage. The increase in the reaction rate of these esterification reactions is preferably distributed smoothly at each stage. Ultimately, it is desirable that the esterification reaction rate reaches 90% or more, preferably 93% or more. A low-order condensate having a molecular weight of about 500 to 2000 is obtained by these esterification reactions. Subsequently, it is transferred to a polycondensation reaction tank to carry out polycondensation. The number of reaction tanks in the polycondensation step is not limited. In general, a three-stage system of initial polycondensation, intermediate polycondensation and late polycondensation is employed. As for the polycondensation reaction conditions, the reaction temperature of the first stage polycondensation is 250 to 290 ° C., preferably 260 to 280 ° C., and the pressure is 0.065 to 0.0026 MPa, preferably 200 to 20 Torr. The temperature of the polycondensation reaction is 265 to 300 ° C., preferably 275 to 295 ° C., and the pressure is 0.0013 to 0.000013 MPa, preferably 0.00065 to 0.000065 MPa. When carried out in three or more stages, the reaction conditions for the intermediate stage polycondensation reaction are conditions between the reaction conditions for the first stage and the reaction conditions for the last stage. The degree of increase in intrinsic viscosity achieved in each of these polycondensation reaction steps is preferably distributed smoothly.

  In the production of the polyester as described above, the first constituent requirement in the present invention is that a slurry comprising a carboxylic acid and a glycol is prepared in a slurry preparation tank, and the slurry is continuously supplied quantitatively to the esterification reaction tank. In the method of continuously producing the slurry, it is important to control the temperature of the slurry to within ± 4 ° C. of the set value and supply it to the esterification reaction tank. The slurry temperature is more preferably controlled within ± 3 ° C. of the set value, and further preferably controlled within ± 2 ° C. It is particularly preferable to control within ± 1 ° C. When the temperature exceeds ± 4 ° C., the change in the progress of the esterification reaction becomes large, and the change in the carboxyl end group of the polyester oligomer (hereinafter sometimes simply referred to as an oligomer) becomes large. This is not preferable because it leads to quality fluctuations such as color tone and transparency of the product polyester. On the other hand, the lower limit is most preferably ± 0 ° C., which is unchanged, but from the viewpoint of cost performance, ± 0.1 ° C. is preferable, and ± 0.3 ° C. is more preferable.

  The method for controlling the slurry temperature is not limited, but it is preferable to detect the temperature of the slurry preparation tank or the terephthalic acid temperature and feed back to the glycol temperature supplied to the preparation tank. The slurry temperature control may be controlled by installing a heat exchanger in the slurry preparation tank or slurry transfer line. In addition, a circulation line may be provided in the slurry preparation tank to circulate the slurry in the slurry preparation tank to improve the accuracy of temperature control. In the case of this method, it is preferable to add a temperature control function also to the circulation line. The above methods may be performed alone or a plurality of methods may be combined. Further, a slurry storage tank may be provided between the slurry preparation tank outlet and the esterification reaction tank supply to improve the accuracy of the slurry temperature control. In the case of this method, a temperature control mechanism may be added to the slurry storage tank. As a method of providing the slurry storage tank, the slurry adjustment in the slurry preparation tank may be carried out by a batch method. The batch type slurry preparation method facilitates the management of the composition ratio of the carboxylic acid and the glycol in the slurry, which is an important process management item in slurry preparation, leading to the advantage that the control system for the management can be simplified. . In the case of this method, since the composition ratio between the carboxylic acid and the glycol can be adjusted in the slurry storage tank, there is an advantage that the composition ratio can be suppressed. In this method, slurry preparation may be carried out by a continuous method or a semibatch method. Moreover, you may implement combining this method and the former method.

  Although the said setting value is not limited, Room temperature to 180 degreeC is preferable. In the present invention, as described later, it is a preferred embodiment that the recovered glycol generated in the polyester production process is used with a part of the slurry-prepared glycol. The recovered glycol is in a warm state. Therefore, the set temperature is preferably a warmed state, and more preferably 70 to 160 ° C.

  The method of the present invention is extremely simple, the above-described slurry temperature, has high measurement accuracy, and has high cost performance because the esterification reaction is controlled by the measurement value with stable measurement value even after long-term operation. And the accuracy is maintained even in long-term operation.

  The temperature control suppresses the fluctuation of the carboxyl end group concentration of the polyester oligomer on the premise that the slurry is supplied in a fixed amount to the esterification reaction tank. The supply amount of the slurry is preferably controlled within a set value ± 3%. The set value is preferably within ± 2%, more preferably within the set value ± 1.5%. When the set value exceeds ± 3%, it is difficult to suppress the variation in the carboxyl end group concentration of the polyester oligomer within the preferable range of the present invention even if the slurry temperature is controlled within the above range. On the other hand, the lower limit is most preferably ± 0%, which is unchanged, but from the viewpoint of cost performance, ± 0.1% is preferable, and ± 0.3% is more preferable.

  The method for controlling the supply amount of the slurry is not limited. For example, a method of changing the feed pump rotation speed so as to achieve a set flow rate using a flow meter, a bypass line returning to the slurry preparation tank is provided after the feed pump of the feed line, and the revolution speed of the feed pump is set. Method of adjusting the opening of the control valve provided in the bypass line so that the flow rate of the flow meter provided in the liquid feed line is constant, and the position of the slurry preparation tank and the first esterification reaction tank For example, and by feeding the slurry with the head pressure and adjusting the opening of a control valve provided in the liquid feed line so that the flow rate of the flow meter provided in the liquid feed line is constant. The type of flow meter is not limited. For example, a rotor flow meter, a rotor piston flow meter, an oval flow meter, a micro motion flow meter, and the like can be given. Moreover, you may adjust so that the liquid level of a 1st esterification reaction tank may become fixed.

  The stabilization of the slurry temperature also leads to the stabilization of the slurry flow rate.

  Moreover, since the molar ratio of carboxylic acid and glycol in the slurry also affects the esterification reaction, it is preferably controlled within a certain range. As the variation range, the range of the known technique described above is sufficient. A setting value within ± 0.3% is preferable. A set value within ± 0.25% is more preferable, and a set value within ± 0.2% is even more preferable. On the other hand, the lower limit is most preferably ± 0% which is unchanged, but from the viewpoint of cost performance, ± 0.01% is preferable, and ± 0.02% is more preferable.

  The method for adjusting the molar ratio is not limited, but a method of continuously measuring online and adjusting the amount of carboxylic acid and / or glycol supplied to the slurry preparation tank is preferable. The measuring method is not limited. The method of measuring with a densitometer or a near-infrared spectrophotometer is mentioned.

  In the production method as described above, the second constituent requirement in the present invention is to continuously detect the carboxyl end group and hydroxyl end group concentrations of the polyester low polymer at the outlet of the final esterification reaction tank on-line, and detect the detected value. Is to control the esterification reaction. In this case, by performing reaction control by changing the amount of glycol added continuously after the second esterification reaction tank by a feedback circuit based on the carboxyl end group concentration detected by the above method, It is preferable to control the base concentration so that the standard deviation (s) is 2.5 or less. The standard deviation (s) is more preferably 2.3 or less, and further preferably 2.0 or less. When the standard deviation (s) exceeds 2.5, it is not preferable because it leads to the progress of the subsequent polycondensation reaction and the fluctuation of the carboxyl end group concentration of the final polyester.

  The average value of the carboxyl end group concentration is not limited. It is set as appropriate depending on the progress of the subsequent polycondensation reaction, the carboxyl end group concentration of the final product polyester, and the like. For example, regarding the progress of the subsequent polycondensation reaction, that is, the polycondensation activity, the optimum range varies depending on the type of polycondensation catalyst used in the production of polyester. In addition, regarding the setting of the carboxyl end group concentration of the final polyester, the optimum range varies depending on the intended use of the polyester. For example, a higher setting is preferable when the polycondensation of the subsequent solid phase polycondensation is taken into consideration, and a lower setting is preferable when the hydrolytic stability of the polyester is used in a field where it is required. In general, the range of 100 to 1000 eq / ton is preferable. 200 to 900 eq / ton is more preferable.

  In this case, it is preferable to detect the carboxyl end group concentration of the product using a near infrared spectrophotometer.

  Detection of the carboxyl end group concentration of the oligomer before the start of the polycondensation is preferably carried out continuously using a near-infrared spectrophotometer in a portion where the oligomer is flowing, such as a reaction can or a pipe. There is no particular limitation as long as it is a near-infrared spectrophotometer that can be continuously measured online. For example, commercial products such as NIRS Systems (Nireco), BRAN LUEBBE, and Yokogawa Electric's near-infrared on-line analyzer may be used, or a systemized device for this purpose may be manufactured. May correspond.

  In the method of the present invention, the detection cell of the near-infrared spectrophotometer needs to be installed in a high temperature region, and a design for the correspondence is necessary. Also, when installing between esterification reaction cans, it must be in a pressurized state, and when installing in the transfer line from the esterification reaction can to the initial polycondensation can, it must be structured to withstand both pressurization and decompression. There is. It is preferable to implement this measure as appropriate depending on the installation location.

  In the present invention, the installation location of the measurement cell of the near-infrared spectrophotometer may be set at any location from the start of the esterification reaction to just before the start of the polycondensation reaction. You may set to an esterification reaction can and you may install in the transfer line of each reaction can. You may install directly in each reaction can and a transfer line, and you may provide a bypass line and install in this bypass line. When detecting the inside of the reaction can when it is installed in the bypass line, it is preferable to provide a circulation line through which the reaction contents circulate in the target reaction can and install it in the circulation line. Since the installed measurement cell may require maintenance, it is preferably installed in the bypass line.

  Two near-infrared spectrophotometer measurement cells for the carboxyl end group and hydroxyl end group may be provided for separate measurement, or the measurement wavelength is changed alternately using one cell. By doing so, both terminal group concentrations may be measured. When measuring using two cells, they may be installed in the same place or in different places. Even when the concentration of both terminal groups is measured using a single cell, cells may be installed at a plurality of locations, and information on the plurality of locations may be taken to improve control accuracy.

  The measurement wavelength of near infrared rays for determining the carboxyl end group concentration and the hydroxyl end group concentration is not limited. It is preferable to use a model oligomer corresponding to the measurement location and investigate and set the wavelength with high sensitivity and less disturbance. For example, it is preferable to use a wavelength of 1444 nm for the carboxyl end group concentration and 2030 nm for the hydroxyl end group concentration. Moreover, you may calculate from the analytical curve which combined the some wavelength.

  The calibration curve for the concentration of both end groups determined by the above method is preferably prepared using the above model oligomer. In this case, it is preferable to use values measured by the NMR method for the carboxyl end group concentration and the hydroxyl end group concentration of the model oligomer.

  In the present invention, the polyester obtained by continuously detecting the carboxyl end group concentration and the hydroxyl end group concentration of the oligomer in real time by the above-mentioned method, calculating from a program previously incorporated in a computer, and controlling the production conditions of the polyester To stabilize the quality of

  Although the reaction control method is not limited, for example, a method of changing the amount of diol added to the esterification reaction step by a feedback circuit based on the detection information is a preferred embodiment. When measuring the concentrations of both end groups at the same location, the carboxyl end group concentration and the hydroxyl end group concentration show an inversely proportional fluctuation behavior, but this method also detects the carboxyl end group concentration previously proposed to react. Since the over-response is suppressed as compared with the control method, there is an advantage that the accuracy of reaction control is improved and the quality fluctuation of the obtained polyester is reduced. In the method of obtaining information at two or more locations, it is possible to lead to finer control, so that the control accuracy can be further improved.

  Although the reaction control method is not limited, for example, a method of changing the amount of diol added to the esterification reaction step by a feedback circuit based on the detection information is a preferred embodiment. This method has a higher response speed and can be controlled with higher accuracy than the above-described conventional methods for controlling the esterification reaction temperature. Of course, you may implement in combination with control of this esterification reaction temperature.

  For example, it is preferable to add glycol adjusted to a temperature as close as possible to the reactor so that the reactor temperature does not fluctuate. By this method, fluctuations in the esterification reaction due to fluctuations in the reaction temperature can be suppressed. Moreover, when the addition amount of glycol exceeds a certain range or more, a method of adjusting the temperature of the esterification reaction tank may be taken. Although the esterification reaction tank which adjusts the temperature in this method is not limited, it is preferable to control the temperature of the first esterification reaction tank.

  In the present invention, the low-boiling fraction containing water as a main component is fractionated and removed from the bottom of the distillation column using a distillation column in which the glycol distilled from the polyester production step is provided in the polyester production step. The residue is preferably recycled and reused. This measure can reduce the production cost of the polyester.

  The method for fractionating the glycol is not limited, but at least two distillation towers are provided to classify the glycol distilled from the first esterification reaction tank and the glycol distilled after the second esterification reaction tank. Then, the low-boiling fraction containing water as a main component is removed by fractional distillation, the distillate glycol residue from the first esterification reaction tank is returned to the slurry preparation tank, and from the reaction tank after the second esterification reaction tank It is preferable to supply the residue of the distillate glycol from the first esterification reaction tank to the middle stage of the distillation column for fractionating the distillate and / or the slurry preparation tank.

  In general, the esterification reaction in a polyester production method is often carried out in a multistage reaction system in which two or more reaction vessels are used. In this method, the glycol distilled from the esterification reaction tank and the amount of water contained in the glycol decrease as the latter stage. In addition, the glycol generated in the polycondensation step has a lower water content. In particular, the glycol from the first esterification reaction tank often occupies about 70% or more of the glycol generated in the polyester production process, and the amount of water is overwhelmingly large. Therefore, it is better to separate the distillate glycol from the first esterification reaction tank and the glycol distillate after the second esterification reaction tank and perform fractional distillation in separate distillation towers. This is economically advantageous because it leads to a reduction in the running cost of the distillate. The number of the distillation tower is not limited, but two is preferable. Three or more groups may be used. Moreover, you may fractionally fractionate the whole amount of distillate glycol with one distillation column, without carrying out the said division.

  In the case of fractional distillation in two or more distillation towers according to the above preferred embodiment, the distillate glycol from the first esterification reaction tank is obtained by fractionating and removing the low boiling fraction mainly composed of water. It is preferable to return to the slurry preparation tank and reuse it (hereinafter, glycol to be returned to the slurry preparation tank and reused is referred to as recovered glycol). On the other hand, the glycol distilled from the reaction tank after the second esterification reaction tank may be reused by returning the residue obtained by fractional removal of the low-boiling fraction mainly composed of water to the slurry preparation tank, The distillate glycol in the 1 esterification reaction tank may be supplied to a distillation column for fractional distillation and may be re-distilled together with the residual distillate glycol from the first esterification reaction tank to return the slurry preparation tank. . Moreover, you may use both together. In particular, the glycol distilled from the reaction tank after the second esterification reaction tank is fractionated from the distillate glycol of the first esterification reaction tank with the total amount of the residue obtained by fractionating and removing the low-boiling fraction mainly composed of water. The method of supplying to the distillation column and re-distilling together with the residue of the glycol distilled from the first esterification reaction tank and returning it to the slurry preparation tank can improve the precision of the fractionation. Furthermore, a double effect that the control of the amount of water in the recovered glycol, which will be described later, becomes one place and the control is simplified is exhibited.

  The performance of the distillation column used in the above method is not limited, but 8 to 18 stages are preferable. 9 to 15 stages are more preferable. Either a bubble column or a packed column may be used. In the case where a plurality of distillation towers are provided and used, all distillation towers having the same performance may be used, or the respective performances may be changed. When the fraction from the second esterification reaction tank is fed to the distillation tower for fractionation from the first esterification reaction tank and re-fractionated, distillation is installed in the first esterification reaction tank. The distillation column installed in the second esterification reactor from the column has a lower number of stages.

  The recovered glycol recovered by the above method contains water generated in the esterification step. In the production of polyester, the amount of water affects, for example, the progress of the esterification reaction, and consequently affects the quality and productivity of the polyester. Accordingly, high quality polyester cannot be stably produced unless the moisture content is controlled. As a method for avoiding this problem, there is a method for improving the performance of the above-mentioned distillation column to obtain a glycol substantially free of moisture. This method is effective in stabilizing the reaction and quality of the polyester, but it requires a high-performance distillation column and is disadvantageous in terms of economy. On the other hand, the higher the water content, the better the economics of glycol recovery, but this is disadvantageous in terms of stabilizing the quality of the polyester. The amount of water in the recovered glycol is preferably controlled within X ± 2.0% by mass (where X represents a number of 2 or more and 3 or less). Within X ± 1.5% by mass (where X represents a number of 2 or more and 3 or less) is more preferable, and within X ± 1.0% by mass (where X represents a number of 2 or more and 3 or less) is more preferable. On the other hand, the lower limit of the fluctuation range is most preferably ± 0%, which is unchanged, but from the viewpoint of cost performance, ± 0.1% by mass is preferable, and ± 0.3% by mass is more preferable. By implementing this method, in addition to stabilizing the influence of the water content on the esterification reaction and reducing the recovery cost, the fluidity of the slurry composed of carboxylic acid and glycol is improved by the water in the recovered glycol. In addition, the esterification reaction is stabilized, and as a result, the effect that the quality of the polyester is stabilized is exhibited. In other words, compared to the case where the production of polyester is produced only with a new glycol, or the water content of the recovered glycol is recovered and manufactured in a substantially anhydrous state, the fluidity of the slurry is improved by the water in the recovered glycol, The supply accuracy of the slurry to the esterification reaction tank can be improved, and the process and quality can be stabilized. Further, since the supply stability of the slurry can be ensured even if the amount of glycol used during slurry preparation is reduced, stable production is possible even if the ratio of the amount of glycol in the slurry is lowered, which is economically advantageous.

  The method for setting the amount of water in the recovered glycol to the above range is not limited, but the pressure and temperature of the distillation column are controlled to control the amount of water in the residue of the fraction taken from the bottom of the distillation column. preferable.

  The pressure in the distillation column is not limited, but it is preferably set in conjunction with the pressure setting in the esterification reaction tank which is a generation source of glycol supplied to the distillation column. It is preferable to carry out the interlocking with the pressure of the esterification reaction tank and the balance between the distillation efficiency and the energy required for distillation in a slightly pressurized state from the overall performance.

  In the method of setting in conjunction with the pressure setting of the esterification reaction tank, the distillation tower preferably keeps the top pressure at 10 to 300 kPa (gauge pressure). The entire distillation column may be controlled within the pressure range. 20-250 kPa (gauge pressure) is more preferable, and 80-200 kPa (gauge pressure) is more preferable. If it is less than 10 kPa (gauge pressure), it will be influenced by the pressure fluctuation by atmospheric pressure fluctuation, and will lead to the fall of the temperature management precision of a distillation column. Moreover, since the pressure of an esterification reaction tank changes with the fluctuation | variation of atmospheric pressure and it leads to the fluctuation | variation increase of esterification reaction, it is unpreferable. On the other hand, when it exceeds 300 kPa (gauge pressure), it leads to the fall of fractionation precision. Further, in the method of adjusting the pressure in the esterification reaction tank with the tower top pressure, by-product of diethylene glycol in the esterification reaction step is increased, which is not preferable. Furthermore, an increase in the pressure of the esterification reaction tank increases the degree of influence on the esterification reaction due to the pressure fluctuation, and therefore the fluctuation of the esterification reaction increases.

  The method for controlling the top pressure of the distillation column is not limited. For example, a pressure regulating valve is installed in the vent pipe of a distillation column, and the method of adjusting with the pressure regulating valve, the method of adjusting the vent pipe with water, and adjusting by changing the position of the liquid surface of the water seal or the pipe of the water sealed portion, etc. Is mentioned.

The present invention is preferably applied to a method for producing a polyester using ethylene glycol as the glycol. In the case of using ethylene glycol as the glycol, it is preferable to control the middle temperature of the distillation column having a line for returning the residue as recovered glycol and returning the slurry preparation tank to 106 ± 3 ° C. in the fractionation. The control is preferably performed in conjunction with the pressure control described above. In general, the control of the distillation column is controlled by the top temperature of the distillation column, but in the fractionation of the present invention, the amount of water in the residue discharged from the bottom of the distillation column is controlled by controlling the top temperature. In order to control, it is necessary to control the temperature in a very narrow range. On the other hand, when the temperature is controlled by the temperature at the bottom of the column, the temperature at the top of the column is determined and the variation in the amount of ethylene glycol in the low-boiling fraction mainly composed of water discharged from the column increases.
In general, since the low boiling fraction is discarded, an increase in the amount of ethylene glycol in the low boiling fraction is not preferable because it leads to a change in the treatment load of the waste liquid and the environmental load increases. The above problems can be balanced by controlling the temperature of the middle stage of the distillation column. In addition, the middle stage temperature means a substantially central part of the shelf of the distillation column. That is, when the number of shelves is an odd number, the temperature is at the center shelf, and when the number is even, it indicates the temperature of one of the shelves on the center side of each of the divided parts. The temperature range is more preferably 106 ± 2 ° C. If the temperature is less than 103 ° C., the amount of water in the residue is more than the above range, which is not preferable. On the other hand, when the temperature exceeds 109 ° C., the amount of water in the residue is less than the above range, and the amount of ethylene glycol in the low-boiling fraction is increased. Since it increases, it is not preferable.

  In the present invention, the performance of the distillation column may be improved so that the water content in the recovered ethylene glycol is 1% by mass or less, and water may be added to the recovered ethylene glycol to adjust the water content range. In addition, the moisture content in the residue discharged from the bottom of the distillation column is measured online using, for example, a near-infrared spectrophotometer to improve the control accuracy of the moisture content in recovered ethylene glycol. May be.

  In the case of a distillation column that does not have a line for returning the residue to the slurry preparation tank using the recovered glycol, for example, two distillation towers are used, and the residue of the distillation tower that processes the distillate after the second esterification reaction tank is the second. When the distillate from the 1 esterification reaction tank is supplied to a distillation column to be treated and re-distilled together with the glycol distilled from the first esterification reaction tank to obtain recovered glycol, the second esterification reaction tank For the distillation column for treating the subsequent distillate, the application of the above temperature control is optional, and it is preferable to set in consideration of the conditions for the best recovery yield and energy consumption. In the case of carrying out by this method, it is preferable to supply the middle part of the distillation column for treating the distillate in the first esterification reaction tank as the residue from the second esterification reaction tank. This method enables efficient re-fractionation. On the other hand, in the method of fractionating using the two distillation columns, in the method of reusing the residue of both distillation columns as recovered glycol and reusing them, both distillation columns can be controlled within the above temperature range. preferable.

In the above-described glycol recovery method, it is preferable that fraction removal of the low-boiling fraction of the distillate from the esterification reaction tank is continuously performed by the heat of the distillate itself. This can further reduce operating costs and simplify equipment. If necessary, auxiliary heating may be performed by heating the pipe or heat exchange. On the other hand, the distillate from the polycondensation reaction tank is recovered by cooling and condensing in a wet condenser, so it is necessary to heat it and supply it to the distillation column.
Further, in the case of glycol distilled from the esterification reaction tank, the solid content contained in the glycol has a low melting point and is dissolved in the reaction system in the esterification reaction step and reacted and taken into the polyester, so it is not necessary to remove it. . However, when the temperature of the residue discharged from the bottom of the distillation column is lowered, the solid content is solidified and the liquid feed line is clogged. Therefore, the temperature of the residue is preferably maintained at 160 or higher. Moreover, it is preferable to circulate a part of the residue to the middle part of the distillation column. The circulation amount is preferably 30 to 75% by mass of the residual amount. The pump used for circulation may be either a reverse type or a non-reverse type, but the reverse type is preferred.

  On the other hand, the solid content contained in the fraction distilled from the polycondensation reaction tank has a high melting point, and if it is contained in recovered glycol and recycled to the polyester production process, it does not react with the polyester in the polyester production process and generates foreign matter. It is not preferable because it may lead to. Therefore, it is preferable to take measures to prevent the solid content from being mixed into the recovered glycol. Although this method is not limited, it is preferable to remove the solid content in the condensate recovered by cooling and condensing with a wet condenser and supplying it to the distillation column. The method for removing the solid content is not limited. For example, it is preferable to carry out by filtration, centrifugal separation, natural sedimentation or the like and a combination thereof.

  The method for reusing the recovered glycol recovered by the above method is not limited. It is preferably stored in a glycol storage tank and reused. The volume at the bottom of the distillation column may be increased and stored in this portion. Further, the recovered glycol may be directly supplied to the slurry preparation tank.

  In the present invention, the ratio of the recovered glycol used for slurry preparation is not limited, but the total amount of glycol generated in the polyester production process is used, and the self-balance method is used to supply the shortage with new glycol. preferable.

  In the present invention, the recovered glycol recovered by the above method and / or the residue discharged from the bottom of the distillation column may be used as glycol supplied to the reaction vessel after the second esterification.

  In the present invention, the standard deviation (s) of the carboxyl end group concentration of the obtained polyester is preferably 0.3 or less. 0.2 or less is more preferable.

  In the present invention, solid phase polycondensation is preferably performed using the polyester obtained by the above method. Furthermore, by spinning using the high polymerization degree polyester obtained by the solid phase polycondensation, for example, high strength fibers used for tire cord raw yarns, fish nets, filter nonwovens, safety belts and the like can be obtained. Is preferred.

  As described above, the polyester obtained by the method of the present invention suppresses fluctuations in the amount of carboxyl end groups, so that the solid-phase polycondensation reaction rate is stabilized, and the quality of the obtained polyester, particularly the intrinsic viscosity, is stabilized. . For example, the standard deviation (s) of the intrinsic viscosity of the polyester when solid phase polycondensation is carried out under certain conditions is preferably 0.0015 or less.

  The polyester used in the present invention is a polymer synthesized from a dicarboxylic acid and a diol, and is not particularly limited as long as it can be used as a molded product such as a film, fiber, or bottle. In particular, it is preferably applied to the production of a prepolymer for solid phase polycondensation polyester used for high strength fibers.

  Specific examples of such polyester include polyethylene terephthalate, polytetramethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polyethylene-1,2-bis (2-chlorophenoxy). Examples include ethane 4,4'-dicarboxylate, polypropylene terephthalate, and the like. Especially this invention is suitable in manufacture of the polyester copolymer which consists of the repeating unit of the polyethylene terephthalate generally used or the polyethylene terephthalate mainly used.

  The dicarboxylic acid used for obtaining the polyester is not particularly limited as long as it is an aromatic, aliphatic, or alicyclic dicarboxylic acid. Specifically, terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, aromatic dicarboxylic acid such as 4,4-diphenyldicarboxylic acid, aliphatic dicarboxylic acid such as adipic acid and sebacic acid, and alicyclic such as cyclohexanedicarboxylic acid And dicarboxylic acid.

  The diol used in the present invention is not particularly limited. For example, ethylene glycol, propanediol, butanediol, neopentyl glycol, hexamethylene glycol, diethylene glycol, polyethylene glycol, polypropylene glycol and the like can be mentioned.

  If necessary, alkali metal salts such as 5-sulfoisophthalic acid and 4-sulfonaphthalene-2,7-dicarboxylic acid, 2-sulfo-1,4-butanediol, 2,5-dimethyl-3-sulfo- Dicarboxylic acid or glycol containing a sulfonic acid metal salt such as 2,5-hexanediol may be used.

  In the polycondensation reaction of the present invention, a known polycondensation catalyst is used. For example, metals such as lithium, sodium, calcium, cesium, magnesium, calcium, barium, strontium, zinc, aluminum, titanium, cobalt, germanium, tin, lead, antimony, arsenic, cerium, boron, cadmium, manganese, and these metals The metal compound containing is mentioned. Among these, the use of antimony, germanium, titanium and aluminum based polycondensation catalysts is preferred.

  The polyester resin of the present invention thus obtained is not only stable in quality, but also can be expected to stabilize the solid phase polymerization process.

  The present invention will be specifically described with reference to the following examples. In addition, these Examples illustrate this invention and are not limited. Further, the intrinsic viscosity, oligomer carboxyl end group concentration, hydroxyl end group concentration and polymer carboxyl end group concentration in the following Examples were measured by the following methods.

(1) Intrinsic viscosity The sample is dissolved in 50 ml of phenol / tetrachloroethane (weight ratio 6/4). This solution was taken in a 40 ml Ubbelohde viscosity tube, and the intrinsic viscosity (IV) was calculated by measuring the number of seconds dropped in a constant temperature bath at 30 ° C.

(2) Oligomer carboxyl end group concentration The oligomer was pulverized with a handy mill (pulverizer) without exhibiting drying. A sample of 1.00 g was precisely weighed and 20 ml of pyridine was added. Several grains of zeolite were added and dissolved by boiling for 15 minutes. Immediately after boiling and refluxing, 10 ml of pure water was added and allowed to cool to room temperature. Titration with N / 10-NaOH was performed using phenolphthalein as an indicator. Do the same for the blank without the sample. When the oligomer did not dissolve in pyridine, the reaction was carried out in benzyl alcohol. AVo (eq / ton) is calculated according to the following equation.
AVo = (A−B) × 0.1 × f × 1000 / W
(A = drop constant (ml), B = blank drop constant (ml), f = factor N / 10-NaOH, W = weight of sample (g))

(3) Hydroxyl end group concentration of oligomer 9 mg of a sample was placed in a sample tube, and 0.3 ml of CDCl ₃ + HFIP-d2 (1 + 1) was added and dissolved. CDCl ₃ 0.3 ml wokuwae, saranipirizin-d5 30 Maikrol was added and mixed well, followed by centrifugation, and the soluble H-NMR spectrum was measured using a 500 MHz apparatus.

(4) Polymer acid value 15 mg of a sample was dissolved in 0.13 ml of a hexafluoroisopropanol (HFIP) / CDCl ₃ = 1/1 mixed solvent, diluted with 0.52 ml of CDCl ₃ , and further 0.2 M triethylamine solution (HFIP / CDCl ₃ 1/9) was added and 22 μl of the solution was used for quantitative determination by H-NMR measurement at 500 MHz. The quantitative value was measured three times and the average value was used.

Example 1
Ethylene glycol and terephthalic acid were continuously supplied to the slurry preparation tank so that the molar ratio was 1.7. The glycol temperature was controlled so that the slurry had a slurry adjustment tank of 90 ± 2 ° C. The temperature control of the slurry preparation tank continuously monitors the slurry preparation tank temperature and the glycol temperature supplied to the preparation tank, while continuously changing the glycol addition temperature using a heat exchanger by a feedback circuit, and preparing the slurry The tank was also provided with a temperature adjustment function, and the slurry temperature in the slurry preparation tank was controlled to be constant.
The slurry and antimony trioxide were continuously supplied to the ester reaction tank, and the first esterification reaction was continuously performed at 255 ° C. Subsequently, the second esterification reaction was performed at 260 ° C. in the second esterification reaction tank, and further supplied to the third esterification reaction can, and reacted at 260 ° C. with an average residence time of 0.5 hours to obtain an oligomer. . The variation rate of the slurry flow rate was controlled within ± 1.5% of the set value. The slurry flow rate was adjusted by changing the rotation speed of the liquid feed pump using a rotary piston flow meter. The molar ratio of ethylene glycol and terephthalic acid was controlled within ± 0.25%. The molar ratio was adjusted by measuring the amount of terephthalic acid in the slurry using a near-infrared spectrophotometer and adjusting the amount of ethylene glycol supplied to the slurry preparation tank. The temperature of the first esterification reaction tank was controlled within ± 1.3%. Moreover, the fluctuation | variation of the liquid level of the 1st esterification reaction tank was less than +/- 0.2%. The pressure in the esterification reaction tank was controlled by controlling the pressure at the top of the distillation column for recovering ethylene glycol. While the oligomer is continuously supplied to the polycondensation reaction tank, a bypass line is provided in the transfer line, and the carboxyl end group concentration and the hydroxyl end group concentration of the oligomer are set to wavelengths using a near-infrared spectrophotometer installed in the bypass line. The amount of ethylene glycol automatically calculated by the feedback circuit so that the amount of carboxyl end group concentration of the oligomer supplied to the polycondensation reaction step is constant based on the measured value alternately at 1444 and 2030 nm The esterification reaction was controlled by adding it to the esterification reaction tank. The ethylene glycol was obtained using a novel ethylene glycol. The glycol was supplied after adjusting to 175 ± 2 ° C.

The flow of ethylene glycol in the polyester production process is shown in FIG.
The new ethylene glycol and recovered ethylene glycol supplied to the slurry blending tank 2 are in a mass ratio of 0.4: 0.6.

  The distillate distilling from the first esterification reaction tank 3 is the distillate distilling from the second esterification reaction tank 4 and the polycondensation reaction tanks 6 to 8 into the bubble-bell type distillation column 9 having 15 stages. Is supplied to a bubble-bell type distillation column 10 having 15 stages and removes low-boiling fractions mainly composed of water. Since the distillate distilled from the three polycondensation reaction tanks 6 to 8 is generated in a reduced pressure system, it is condensed by a wet condenser installed in each reaction tank and supplied to the ethylene glycol condensate storage tanks 16 to 18. It is supplied to the distillation column 10 later. The feed liquid is supplied with heat for distillation by the heat exchanger 22. At this time, in order to suppress the temperature rise of the ethylene glycol liquid sprayed on the wet condenser, it is cooled by the coolers 19 to 21 and supplied to the wet condenser. Although this condensate is carried out by self-circulation of the condensate itself condensed in each wet condenser, new ethylene glycol may be supplied as necessary. In addition, the condensate was separated into solids by a metal mesh installed in the ethylene glycol condensate storage tanks 16 to 18 and supplied to the distillation column 10. In both distillation towers, a part of the residue discharged from the bottom was circulated to the middle part of each distillation tower. The temperature of the circulating liquid was stable at around 168 ° C. The clogging of the liquid feed line of the residual liquid (recovered ethylene glycol in this example) discharged from the bottom of the distillation column by the circulation did not occur. When the circulation was stopped, precipitation of the solid content contained in the recovered ethylene glycol occurred, and the liquid feeding line was sometimes clogged. Both distillation columns were controlled so that the temperature detected by the temperature detector installed in the seventh stage was 106 ± 2 ° C. The obtained residue is supplied to the ethylene glycol reservoir 15. The water content in the obtained recovered ethylene glycol was controlled to 3 ± 0.5% by mass. In addition, about the distillate from the esterification reaction tanks 3-5, since the heat required for distillation is enough for the heat quantity which distillate itself has, heating is not necessary. The top pressures of the distillation columns 9 and 10 were controlled within 100 kPa ± 2% (gauge pressure). The pressure was controlled by a pressure regulating valve installed in the distillation tower vent pipe.

Subsequently, the polycondensation reaction was continuously performed in a polycondensation reaction tank under reduced pressure. The produced polymer was extracted in the form of a strand and cut into a pellet after cooling with water. Pellets were continuously produced by the above method, and representative samples with different times were collected. The intrinsic viscosity, oligomer acid value, and polymer acid value of the sample were measured. The average value and standard deviation (s) between the samples are shown in Table 1. All the measured values were good and stable, and a polyester with small quality fluctuation was obtained.
The values shown in Table 1 are the evaluation results of 50 samples (for 25 days) sampled every 12 hours. Moreover, the standard deviation (s) was calculated | required by the following formula.
Standard deviation (s) = {(measured value−average value) ² sum / number of samples (50)} ^1/2

(Comparative Example 1)
In Example 1, it is the same method as Example 1 except having changed so that only the carboxyl terminal group may be measured with a near-infrared spectrophotometer and the amount of ethylene glycol added to a 2nd esterification reaction tank may be controlled. Obtained polyester. The results are shown in Table 1. Polyester quality variation increased.

(Comparative Example 2)
In Example 1, polyester was obtained by the same method as Example 1 except that the control of the slurry temperature supplied to the first esterification reaction tank was canceled. The slurry temperature was 84 ± 10 ° C. The results are shown in Table 1. Polyester quality variation increased.

(Comparative Example 3)
In Example 1, polyester was obtained in the same manner as in Example 1 except that ethylene glycol for adjusting the oligomer carboxyl end group concentration to be supplied to the second esterification reaction tank was added at a constant flow rate. The results are shown in Table 1. Polyester quality variation increased.

(Comparative Example 4)
In Example 1, except that the number of shelves of the distillation columns 9 and 10 is set to 7 and the position of the temperature detector is changed to the fourth space, and the temperature is controlled to be 106 ± 5 ° C. A polyester was obtained in the same manner as in Example 1. The water content in the recovered ethylene glycol was 3 ± 2.2% by mass. The results are shown in Table 1. Polyester quality variation increased.

(Comparative Example 5)
In Comparative Example 1, a polyester was obtained in the same manner as in Example 1 except that ethylene glycol for adjusting the oligomer carboxyl end group concentration supplied to the second esterification reaction tank was added at a constant flow rate. The results are shown in Table 1. The quality variation of the polyester further increased as compared with Comparative Example 1.

(Comparative Example 6)
In Comparative Example 2 , a polyester was obtained in the same manner as in Example 1 except that ethylene glycol for adjusting the oligomer carboxyl end group concentration supplied to the second esterification reaction tank was added at a constant flow rate. The results are shown in Table 1. The quality variation of the polyester further increased as compared with Comparative Example 2 .

(Example 2)
Example 1 is the same as Example 1 except that the number of shelves of the distillation column 10 is set to 9 and the residue discharged from the bottom of the distillation column 10 is supplied to the center of the distillation column 9. Polyester was obtained by the method. The flow of ethylene glycol in the polyester production process is shown in FIG. The temperature of the space of the fifth-stage distillation column 10 was controlled at 1 0 6 ± 2 ℃. The results are shown in Table 1. As in Example 1, the quality fluctuation of the polyester was suppressed.

(Example 3)
In the method of Example 2 , it changes so that some ethylene glycol discharged | emitted from the tower bottom part of the distillation tower 10 may be used as ethylene glycol supplied to a 2nd esterification reaction tank for oligomer carboxyl terminal group density | concentration adjustment. Except for the above, polyester was obtained in the same manner as in Example 1. The flow of ethylene glycol in the polyester production process is shown in FIG. The results are shown in Table 1. Polyester quality fluctuations were slightly higher than in Example 2, but were suppressed at a high level.

(Examples 4 to 6)
The polyester resins obtained in Examples 1 to 3 were supplied to a solid phase polymerization reaction tank, and a solid phase polymerization reaction was carried out for 6 hours in a state where the pressure in the tank was controlled at 67 Pa under reduced pressure and 240 ° C. Five batch reactions were performed in the same manner, and after completion of the reaction, the resin of each batch was sampled and the intrinsic viscosity was measured. Moreover, the yarn for tire cord was spun using the obtained solid phase polycondensation polyester. The results are shown in Table 2. In all the examples, the quality fluctuation of the polyester was suppressed, the number of yarn breakage during spinning was small, and the spinning operability was excellent.

(Comparative Examples 7 to 12 )
Except for using the polyester resins obtained in Comparative Examples 1 to 6, respectively, 5 batches of solid phase polymerization were performed according to Example 4 , and the resin was sampled. Moreover, the yarn for tire cord was spun using the obtained solid phase polycondensation polyester. The results are shown in Table 2. In all of the comparative examples, the quality variation of the polyester was larger than in the examples, the number of yarn breakage during spinning was large, and the spinning operability was inferior.

  The polyester production method of the present invention can suppress the quality fluctuation of the obtained polyester by a highly simplified and highly economical reaction control method. Therefore, the solid phase polycondensation reaction can be stabilized by using the polyester as a prepolymer, and the spinning operability of high strength fibers can be improved by using the solid phase polycondensation polyester. In addition, the polyester production method of the present invention is characterized by excellent cost performance because the above characteristics are maintained even when applied to a production method in which glycol generated in the polyester production process is recovered and reused. Therefore, it is important to contribute to the industry.

2 is a flow chart of ethylene glycol in a polyester production process in Example 1. FIG. 2 is a flow chart of ethylene glycol in a polyester production process in Example 2. FIG. 4 is a flowchart of ethylene glycol in a polyester production process in Example 3. FIG.

Explanation of symbols

1: Metering tank 2: Slurry preparation tank 3: First esterification reaction tank 4: Second esterification reaction tank 5: Third esterification reaction tank 6: First polycondensation reaction tank 7: Second polycondensation reaction tank 8 : Third polycondensation reaction tank 9, 10: Distillation column 11-13: Wet condenser 14: Ethylene glycol storage tank 15-17: Ethylene glycol condensate storage tank 18-20: Cooler 21: Heat exchanger 22-37: Pump

Claims (11)

Aromatic dicarboxylic acid and glycol are mixed in a slurry preparation tank to form a slurry, and the slurry is quantitatively supplied to an esterification reaction tank to carry out an esterification reaction, and the resulting polyester low polymer is subsequently polycondensation reaction tank. In the method of continuously producing polyester by supplying to the polycondensation,
From the glycol distilled from the polyester manufacturing process, the low-boiling fraction mainly composed of water is removed by distillation in the distillation tower provided in the polyester manufacturing process, and the residual glycol taken out from the bottom of the distillation tower is recovered. As a circular reuse
The glycol is ethylene glycol,
In the fractionation, the middle stage temperature of the distillation column having a line for returning the residue to the slurry preparation tank as recovered glycol is controlled to 106 ± 3 ° C.,
The manufacturing method of polyester characterized by satisfying the following conditions simultaneously.
(1) In the process of preparing a slurry composed of carboxylic acid and glycol in a slurry preparation tank and continuously supplying the slurry to the esterification reaction tank, the temperature of the slurry is controlled within ± 4 ° C. of the set value to perform esterification Supply to the reaction vessel.
(2) The carboxyl end group concentration and hydroxyl end group concentration of the polyester low polymer at the end of the final esterification reaction tank are continuously detected online, and supplied to the esterification reaction step by a feedback circuit based on the detected values. The esterification reaction is controlled by changing the amount of glycol added . A low-boiling fraction comprising water as a main component by providing at least two distillation columns and separating a glycol distilled from the first esterification reaction tank and a glycol distilled after the second esterification reaction tank polyester production process according to claim 1, wherein the fractionation removing. The method for producing a polyester according to claim 1 or 2 , wherein a residue of the distilled glycol from the first esterification reaction tank is returned to the slurry preparation tank. Claims 1 to 3, wherein the returning the remainder of the distillate glycol from the second esterification reaction tank to a distillation tower for fractionating the slurry preparation tank and / or distillate glycol from the first esterification reaction tank The manufacturing method of polyester in any one of. The water content in the recovered glycol X ± 2.0 wt% (where X is a number from 2 to 3) of the polyester according to any one of claims 1 to 3, characterized in that control within Production method. The method for producing a polyester according to any one of claims 1 to 5 , wherein in the fractionation, the top pressure of the distillation column is controlled to 10 to 300 kPa. Detects the temperature of the slurry preparation tank, the temperature of claims 1-6, characterized in that the feedback glycolic temperature supplied to the slurry preparation tank controlled to be within ± 4 ° C. of setpoint The manufacturing method of polyester in any one. By performing reaction control by changing the amount of glycol added continuously after the second esterification reaction tank by a feedback circuit based on the carboxyl end group concentration and hydroxyl end group concentration detected by the above method, The method for producing a polyester according to any one of claims 1 to 7, wherein the terminal group concentration is controlled so that the standard deviation (s) is 2.5 or less. The method for producing a polyester according to any one of claims 1 to 8 , wherein the carboxyl end group concentration and the hydroxyl end group concentration of the product are detected using a near-infrared spectrophotometer. Solid phase polycondensation of the polyester of the polyester obtained by the polyester production method according to any one of claims 1 to 9, characterized in that the solid phase polycondensation. A high strength polyester fiber obtained by spinning the polyester obtained by the solid phase polycondensation method according to claim 10 .

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