JP2007009150A - Method for producing polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for continuously producing a polyester by reusing a glycol generated in the production process of the polyester, capable of producing a high quality polyester economically and stably by controlling the esterification reaction by a simple method. <P>SOLUTION: This method for continuously producing the polyester by mixing an aromatic dicarboxylic acid with the glycol in a slurry-preparation vessel to make slurry, feeding the slurry into an esterification reaction vessel to perform the esterification reaction, feeding the obtained low molecular weight polyester to a polycondensation reaction vessel to polycondensate, fractionating and removing a low boiling fraction consisting mainly of water from the glycol distilled off from the polyester production process by a distillation column installed in the polyester production process and returning the glycol to the slurry preparation vessel for circulating/reusing is provided by circulating a part of a residual material taken out from the bottom part of the distillation column to the distillation column. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a polyester capable of economically and stably producing a high-quality polyester in a continuous polyester production method in which glycol generated in the production process of polyester is reused.

  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 direct esterification method, polyester is produced by preparing an aromatic dicarboxylic acid and glycol in a slurry preparation tank and supplying the slurry to an esterification reaction tank to carry out an esterification reaction. 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 the low boiling fraction of the distillate from the esterification reaction tank and circulating it to the slurry preparation tank (see Patent Document 1), and the low boiling fraction of ethylene glycol taken out from the esterification reaction tank Rectified and removed and supplied to an ethylene glycol storage tank, and a part of this is used as a circulating liquid for a wet condenser provided in the polycondensation reaction tank to supply the condensate to the ethylene glycol storage tank, and the ethylene glycol retained in the ethylene glycol storage tank. A method of reusing the mixture for slurry preparation (see Patent Document 2), condensing the distillate generated from the polycondensation reaction tank with a wet condenser, and sending it to a distillation column provided in the esterification reaction tank. After removing the water, the slurry is returned to the slurry preparation tank and reused (see Patent Document 3). The distillate generated in the polycondensation reaction tank is continuously simply distilled, and this continuous A method in which the liquid extracted from the bottom of the distillation can is sent to a batch-type single distillation can and subjected to simple distillation, and the distilled liquid excluding the first distillation portion is used as a part of the condensation liquid for the polycondensation reaction gas (Patent Document) 4), a part of the esterification reaction tank distillate and the polycondensation reaction tank distillate rectify and remove the low boiling fraction, and the remaining part of the polycondensation reaction tank distillate is the low boiling fraction. And the high boiling fraction is removed and recycled to the slurry preparation (see Patent Document 5). The distillate taken out from the reaction vessel in the second stage of the esterification reaction is directly purified without distillation purification. A method of reusing as a part or the whole amount (see Patent Document 6), a method of refining a distillate from a polycondensation reaction tank as a part of a raw material glycol by rectifying and removing a low boiling fraction by flash distillation. (See Patent Document 7).
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

  Among the above-mentioned techniques, the methods disclosed in Patent Documents 2 and 3 have a good balance between quality and economy, that is, cost performance. However, the method causes clogging of a transfer line of recovered glycol, for example. There have been problems regarding stable operation over a long period of time. In addition, with the worldwide increase in production of polyester, construction of polyester manufacturing technology with even better cost performance is desired.

  In addition, the glycol recovered by the above method includes a case where the 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.

Also disclosed is a method of controlling the total composition of raw materials and recovered liquid supplied to the reaction system by measuring the amount of water in the glycol recovered in the polyester manufacturing process so as to be within a predetermined range. (See Patent Document 8). In this patent document, for example, it is disclosed that the amount of water and the amount of diethylene glycol in the recovered glycol can be measured quickly and accurately by a near-infrared analyzer.
JP-A-10-182802

  On the other hand, in the production of polyethylene terephthalate, in order to stabilize the production process, the ratio of carboxyl end groups to hydroxyl end groups of the low polymer, which is an intermediate obtained by esterification reaction (hereinafter referred to as “end group ratio”). ) Is important.

  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 and 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 9 to 12).
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 13 to 15).
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 16 and 17).
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 the polyester formation reaction is controlled so as to be constant depending on the slurry concentration supplied to the esterification reaction.

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 obtained spectrum is used to measure A method for analyzing the physical properties of the resin and controlling the reaction conditions during the production process based on the analysis data is disclosed (see Patent Document 18). In the patent document, the method is provided at the bottom of the polycondensation tank in the polyester 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. The issues are linked. 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 technology for stabilizing the quality of polyester disclosed in these Patent Documents 9 to 18, no consideration is given to the influence of the use of recovered glycol that greatly affects the production cost and quality of the polyester.

  An object of the present invention is to provide a method for economically and stably producing a high-quality polyester in a continuous polyester production method in which glycol generated in the production process of polyester is reused.

In order to solve the above-mentioned problems, intensive studies were made and the present invention was completed.
That is, in the present invention, an aromatic dicarboxylic acid and a glycol are mixed in a slurry mixing tank to form a slurry, the slurry is supplied to an esterification reaction tank to perform an esterification reaction, and the resulting polyester low polymer is continued. In the method for continuously producing polyester by supplying it to a polycondensation reaction tank and polycondensing, the main component is water by a distillation column provided in the polyester production process with glycol distilled from the polyester production process. A method for producing a polyester, characterized in that in the method of removing low-boiling fractions and returning them to a slurry preparation tank and recirculating them, a part of the residue extracted from the bottom of the distillation column is circulated to the distillation column. It is.
In this case, it is preferable to control the liquid temperature of the residue taken out from the bottom of the distillation column to 160 to 175 ° C.
In this case, it is preferable to adjust the amount of water in the distillation residue by controlling the temperature of the middle stage of the distillation column.
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, 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, a part of the residue extracted from the bottom of the distillation column for treating the distillate from the second esterification reaction tank onward is supplied to the esterification reaction tank on and after the second esterification reaction tank. Is preferred.
In this case, it is preferable that the slurry temperature be controlled within ± 4 ° C. of the set value and quantitatively supplied to the esterification reaction tank.

  The polyester production method of the present invention has an advantage that the production cost of the polyester can be reduced because the glycol generated in the production process of the polyester is reused. In addition, improvements have been made to prevent clogging of the recovered glycol feed line, and it has the feature that production can be continued stably over a long period of time. Furthermore, since the equipment cost of the distillation tower which collect | recovers this glycol and the running cost in this distillation can be reduced, it can lead to the significant reduction of the manufacturing cost of polyester. In addition, the quality of the polyester obtained by a very simple reaction control method of controlling the amount of water in the recovered glycol and the temperature of the slurry composed of the aromatic dicarboxylic acid and glycol supplied to the esterification reaction tank to a specific range, In particular, it has the characteristics that the fluctuation of the carboxyl end group can be suppressed and a uniform quality polyester can be produced stably. That is, it has the advantage that it is a polyester manufacturing method having extremely high cost performance.

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

  In the polyester production method of the present invention, an aromatic dicarboxylic acid and glycol are mixed in a slurry preparation tank to form a slurry, and the slurry is supplied to an esterification reaction tank to perform an esterification reaction, and the resulting polyester low polymer Is then supplied to a polycondensation reaction tank and subjected to polycondensation to continuously produce polyester.

  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 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. It is important to recycle the residue (hereinafter sometimes referred to as recovered glycol). This measure can reduce the production cost of the polyester.

  In the present invention, in the glycol recovery method, it is important to circulate a part of the residue extracted from the bottom of the distillation column to the distillation column (hereinafter referred to as distillation column liquid circulation method). By carrying out the method, occurrence of clogging of the liquid feed line corresponding to the residue is suppressed, and long-term stable production becomes possible. The glycol distilled in the polyester production process contains solids that are hardly soluble or insoluble in glycols made of polyester oligomers and the like due to entrainment of droplets. As a matter of course, the solid content is contained in the distillation column residue and recycled to the polyester production process in the distillation. Therefore, when polyester is continuously produced over a long period of time, in the liquid feed line for the residue, the solid content in the residue or the solid content precipitated in the liquid feed line There has been a problem that stable operation may be difficult due to a decrease in liquid feeding property and clogging of the line, and improvement has been desired. The present invention solves this problem by the above-mentioned extremely simple method. The reason why the above-mentioned problem is solved by the implementation of the distillation column liquid circulation method is not clear, but increases the liquid flow rate and flow rate of the residual liquid, maintains the liquid temperature, suppresses the temperature fluctuation, and extends the residence of the residual liquid in the distillation column. It is inferred that this is caused by the suppression of precipitation of solids due to the sum of a plurality of factors such as the structural change of solids due to. Here, it is speculated that the structural change takes into account the effects of both chemical change and physical change. In other words, chemical changes include improved solubility in glycol and reduced crystallinity due to lower molecular weight due to glycolysis of oligomers in solid content, and physical changes include changes in crystallinity of solid content. Conceivable. Moreover, the implementation of the distillation column liquid circulation method leads to improvement of fractionation accuracy in addition to suppression of line clogging.

Accordingly, the setting of the liquid temperature of the residual portion and the temperature range, the storage capacity of the residual portion at the bottom of the distillation column, the return position of the circulating liquid, the circulation amount, etc. are important. The conditions are not limited, but the following method is preferred. For example, the return position of the circulating liquid is preferably the uppermost portion of the storage portion of the residue from the middle stage of the distillation column to the bottom of the distillation column. Although it is preferable to return to the middle stage of the distillation column in terms of improving the distillation accuracy, it is disadvantageous in terms of temperature control. It is determined as appropriate in the balance between the two. The pump used for circulation may be either a reverse type or a non-reverse type, but the reverse type is preferred. The storage amount is preferably maintained at 25 to 70% by mass with respect to the circulation amount. The circulation amount is preferably 30 to 75% by mass of the residual amount.
In addition, regarding the control of the liquid level of the distillation column, for example, it is conceivable to control the flow rate of glycol added to the distillation column in addition to glycol distilled from the esterification reaction tank. As the glycol to be added to the distillation column, any of a novel glycol, a glycol generated and recovered in the polymerization step, a glycol distilled from another distillation column, and a glycol recovered from another system may be used. It is not necessary to directly control the flow rate of glycol added to the distillation column, even if the flow rate is indirectly regulated within a certain range by controlling the glycol storage tank and the liquid level and temperature of the previous process. Good. It is also conceivable to control the liquid level by the amount extracted from the distillation column. In this case, the extraction amount is preferably within a range in which the storage amount is kept at 25 to 70% by mass with respect to the circulation amount and the circulation amount is kept at 30 to 75% by mass as described above. It is not necessary to directly control the flow rate of the extraction amount, and the flow rate may be indirectly regulated within a certain range depending on the process into which the extracted liquid flows or the liquid level and temperature in the subsequent process.
The circulating fluid temperature is more preferably 160 to 180 ° C. 164-173 degreeC is more preferable, and 168-175 degreeC is further more preferable. It is preferable to add a temperature adjusting function to the circulation line for maintaining the temperature and controlling the temperature. When the temperature is lower than 160 ° C., the line clogging frequency increases. On the contrary, when it exceeds 180 degreeC, it leads to the increase in energy loss and becomes economically disadvantageous. Moreover, it leads to the fall of distillation accuracy.

  In the present invention, the number and capacity of distillation columns are not limited. For example, the entire amount of the distillate distilled from the polyester production process may be treated in a lump with one conventionally known distillation column, but at least two distillation columns are provided to provide the first esterification reaction. It is preferable to fractionate the glycol distilled from the tank and the glycol distilled after the second esterification reaction 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, the distillate glycol from the first esterification reaction tank and the glycol distillate after the second esterification reaction tank are separated and fractionated in separate distillation towers to give a total amount of distillate. The cost performance can be improved as compared with the methods disclosed in Patent Documents 11 and 12 for fractional distillation using a distillation column. In other words, by dividing the distillation column, the performance and size can be set according to the amount of glycol and water generated in each reactor, leading to a reduction in the total capital investment of the distillation column and the running cost of fractional distillation. Economically advantageous. It is also advantageous in terms of stabilizing the quality of the recovered glycol. The number of the distillation tower is not limited, but two is preferable. Three or more groups may be used.

  In the case of fractional distillation in two or more distillation towers of the present invention, the distillate glycol from the first esterification reaction tank is obtained by distilling and removing the low-boiling fraction mainly composed of water into the slurry preparation tank. It is preferable to recycle and reuse (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 a distillation that distills the distillate glycol of the first esterification reaction tank from the residue obtained by fractionating and removing the low-boiling fraction mainly composed of water. The method of supplying to the tower and re-distilling together with the residual distillate glycol 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 in the case of the distillation control method, 8 to 18 stages are preferable. 9 to 15 stages are more preferable. In the case of the moisture adjustment method, 25 to 40 stages are preferable. 22 to 38 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 reaction tank from the column may have a lower number of stages.

  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, it is preferable to prevent clogging of the liquid feed line of the distillation residue due to the solid analysis by the distillation column liquid circulation method described above.

  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 recovered glycol storage tank and reused. In this case, the volume of the lower part of the distillation column may be increased, and the amount supplied to the recovered glycol storage tank may be adjusted by storing in this part. Moreover, you may supply to a slurry preparation tank directly, without collect | recovering collection | recovery glycol.

    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 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 ± 1.8% by mass (where X represents a number of 2 or more and 3 or less) is more preferable, and within X ± 1.5% 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 carrying out by this method, it is possible to balance the effect on the esterification reaction due to the amount of water and the recovery cost. Furthermore, the fluidity of the slurry consisting of carboxylic acid and glycol is improved by the moisture in the recovered glycol, leading to stabilization of the esterification reaction, and as a result, the effect of leading to stabilization of the quality of the polyester is manifested. Is done. 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. That is, when the set value exceeds 3% by mass, the effect of improving the fluidity of the slurry is saturated, the esterification reaction becomes unstable, and the characteristic fluctuation of the polyester oligomer increases, resulting in the carboxyl of the final polyester. It is not preferable because quality fluctuations such as end group concentration and color tone increase. Conversely, if the set value is less than 2% by mass, the recovery cost increases and the fluidity of the slurry deteriorates, which is not preferable. In addition, when the variation range exceeds ± 2% by mass, the esterification reaction becomes unstable and the characteristic variation of the polyester oligomer increases, resulting in a large quality variation such as the carboxyl end group concentration and color tone of the final polyester. Therefore, it is not preferable.

  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 taken out from the bottom of the distillation column is controlled by controlling the top temperature. In order to achieve this, it is necessary to control the temperature in a very narrow range. On the other hand, for example, when the temperature is controlled at the temperature at the bottom of the column disclosed in Patent Document 10, the temperature at the top of the column is determined and the amount of ethylene glycol in the low-boiling fraction mainly composed of water taken out from the column top. Fluctuation 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 110 ° 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 taken 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. Also good.

  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 present invention, a part of the residue taken out from the bottom of the distillation column for treating the distillate from the reaction tank after the second esterification reaction tank of the above method is used as the esterification reaction tank after the second esterification reaction tank. It is preferable to supply to. For example, Patent Document 18 discloses a method of supplying a distillation residue from a first esterification reaction tank to a second esterification reaction tank. However, in the present invention, the method is used. Leads to a problem that the esterification reaction fluctuates greatly when the amount of water contained in the residual liquid is large. On the other hand, the amount of water in the distillation residue of the distillate distilled from the second esterification reaction tank onward is from the amount of water in the distillation residue of the distillate distilled from the first esterification reaction tank. Therefore, the above problem can be suppressed. In addition, since the residual portion has a higher temperature of the residual portion, the temperature difference from the temperature in the esterification reaction tank is reduced, so that the effect of further suppressing the fluctuation of the esterification reaction is added.

  In the present invention, the amount of water in the recovered glycol may be controlled by measuring the amount of water in the glycol recovered by the above method online and changing the distillation tower temperature by a feedback circuit based on the variation in the amount of water. The method for measuring the moisture content is not limited, but it is preferable to quantify using a near-infrared spectrophotometer.

  When carried out by the method of quantifying using the near-infrared spectrophotometer, for example, the detector of the near-infrared spectrophotometer at the bottom of the distillation column or the recovered glycol feed line from the bottom of the distillation column to the slurry preparation tank Is installed to measure the amount of water in the recovered glycol online and feed back the measured value to the temperature setting value of the distillation column (hereinafter referred to as distillation control method). In addition, the water content in the recovered glycol is adjusted to 1% by mass or less, and the water content in the recovered glycol is adjusted by adding water to the recovered glycol while continuously measuring the water content using a near infrared spectrophotometer. (Hereinafter referred to as a moisture adjustment method). The moisture content can be adjusted at any place until the recovered glycol is supplied to the slurry preparation tank. Further, the adjustment method is not limited. For example, a water adjustment tank is provided in the supply line of the recovered glycol to the slurry preparation tank, a detector of a near infrared spectrophotometer is installed in the water adjustment tank, and the amount of water in the recovered glycol is measured online. The method of adjusting the quantity of the water added so that a measured value may become the said moisture content range is mentioned. The latter method is disadvantageous economically because it is necessary to improve the performance of the above-described distillation column, and the former method is more preferable.

  The measuring device and the measurement wavelength in the case of online measurement by quantifying using the near infrared spectrophotometer are not limited.

  A measuring instrument will not be specifically limited if it is a near-infrared spectrophotometer which can measure continuously on-line. For example, commercial products such as NIRS Systems (Nireco), BRAN LUEBBE, and near infrared on-line analyzers manufactured by Yokogawa Electric may be used, or a systemized device for this purpose can be manufactured. May correspond.

  The measurement wavelength is not limited. It is preferable to use a glycol sample with a known water content and to investigate and measure the wavelength with high sensitivity and little disturbance, and to prepare and measure a calibration curve. For example, it is preferable to use a wavelength of 1922 nm. Moreover, you may calculate from the analytical curve which combined the some wavelength.

  In the present invention, in the process of preparing a slurry consisting of carboxylic acid and glycol of the production method as described above in a slurry preparation tank and continuously supplying the slurry to the esterification reaction tank, the temperature of the slurry is adjusted to a set value ±. It is preferable to feed the esterification reaction tank in a fixed amount by controlling it within 4 ° C. 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., even if the water content in the recovered glycol is controlled within the range of the present invention, the fluctuation of the progress of the esterification reaction becomes large, and the polyester oligomer (hereinafter sometimes simply referred to as oligomer) This is not preferable because the concentration of the carboxyl end groups of the polyester increases, which leads to the progress of the subsequent polycondensation reaction and the quality of the final product polyester such as color tone and transparency. 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, the recovered glycol generated in the polyester production process is used as 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.

  In the present invention, the slurry supplied to the esterification reaction tank is premised on a fixed supply. That is, it is preferable to control the supply amount of the slurry to the esterification reaction tank within a set value ± 3%. Within ± 2.5% is more preferred, and within ± 2.0% is even more preferred. The lower limit is most preferably ± 0% with no variation, but is preferably ± 0.3%, more preferably ± 0.5% from the viewpoint of cost performance. When the fluctuation of the supply amount exceeds the set value ± 3%, the effect of the present invention may not be sufficiently exhibited.

  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.

  Moreover, in this invention, the effect of this invention can be expressed stably by suppressing the fluctuation | variation of the conditions of the 1st esterification reaction tank which supplies a slurry.

  For example, the molar ratio of carboxylic acid to glycol in the slurry also affects the esterification reaction, so that 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.

  Further, since the esterification reaction is affected by the temperature, pressure and residence time of the first esterification tank (in the limited polyester production line, the liquid level of the reaction tank), the factor is controlled within the set condition range. It is preferable. For example, the temperature is preferably within a set value ± 3%, and more preferably within ± 2%. On the other hand, the lower limit is most preferably ± 0% with no variation, but from the viewpoint of cost performance, ± 0.2% is preferable, and ± 0.5% is more preferable. Further, the pressure is preferably within a set value ± 4%, more preferably within ± 3%. Within ± 2.5% is more preferable. On the other hand, the lower limit is most preferably ± 0% with no variation, but from the viewpoint of cost performance, ± 0.2% is preferable, and ± 0.5% is more preferable. The liquid level is preferably within a set value ± 0.2%, and more preferably within ± 0.1%. On the other hand, the lower limit is most preferably ± 0%, which is unchanged, but from the viewpoint of cost performance, ± 0.02% is preferable, and ± 0.05% is more preferable. The liquid level can be controlled by setting the slurry flow rate control within the above range.

  In the present invention, by carrying out the above-described control for homogenizing the reaction, the concentration of the carboxyl end group of the polyester oligomer at the outlet of the final esterification reaction tank, which greatly affects the quality of the subsequent polycondensation reaction and final polyester, can be achieved. Although the fluctuation is suppressed and the quality of the polyester can be stabilized, in the production method as described above, the carboxyl terminal group concentration of the polyester oligomer at the outlet of the final esterification reaction tank is measured, and the feedback due to the fluctuation of the carboxyl end group concentration. By controlling the reaction by changing the amount of glycol added after the second esterification reaction tank by the circuit, the variation in the carboxyl end group concentration of the oligomer can be further reduced.

  The average value of the carboxyl end group concentration of the oligomer 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 the 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, the method for detecting the carboxyl end group concentration in the oligomer is not limited. You may carry out by the intermittent evaluation method by the evaluation by regular sampling, for example, install the detector which can measure the carboxyl end group concentration such as a near infrared spectrophotometer on-line continuously at the outlet of the final esterification reaction tank. Online measurement may be performed by a continuous evaluation method.

  As described above, the glycol used for adjusting the carboxyl terminal group concentration of the oligomer may be recovered glycol or the distillation column residue extracted from the bottom of the distillation column, but the preparation effect is more stable when using the new glycol. This is preferable.

  In the present invention, it is preferable that the standard deviation (s) of the carboxyl terminal group of the obtained polyester is 1.2 or less. 1.1 or less is more preferable, and 1.0 or less is more preferable.

  Specific examples of the polyester according to the present invention include polyethylene terephthalate, polytetramethylene terephthalate, polycyclohexylene dimethylene terephthalate, polyethylene-2,6-naphthalene dicarboxylate, polyethylene-1,2-bis (2-chlorophonoxy) ) 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. Of 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, for example, solid phase polycondensation is performed using the obtained polyester, and further polycondensation of the polyester is advanced to increase the degree of polymerization. Stabilization of the solid phase polycondensation step for obtaining polyester can also be linked. Therefore, the polyester obtained in the present invention is particularly preferably applied to the production of a prepolymer for a solid phase polycondensation polyester used for high-strength fibers.

  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 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) 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 temperature in the slurry preparation tank was 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 oligomer was continuously fed to the polycondensation reaction tank. 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. Moreover, the temperature and pressure fluctuations of the first esterification reaction tank were 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. The oligomer is sampled every 2 hours to measure the carboxyl end group concentration of the oligomer, and the feedback circuit automatically adjusts the amount of carboxyl end group concentration of the oligomer supplied to the polycondensation reaction process based on the measured value. The esterification reaction was controlled by adding a calculated amount of ethylene glycol to the second esterification reactor. The ethylene glycol was adjusted to 175 ± 2 ° C. and supplied using a part of the residue extracted from the bottom of the distillation column for distilling the distillate distilled after the second esterification reaction vessel described later.

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 distilled from the first esterification reaction tank 3 is added to a bubble-bell type distillation tower 9 having 15 stages, a second esterification reaction tank 4, a third esterification reaction tank 5, and a polycondensation reaction tank 6. The fractions distilled from ˜8 are supplied to the bubble-bell type distillation column 10 having 9 stages, and the low-boiling fraction is mainly removed from 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 taken out 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) taken out from the bottom of the distillation column by the circulation did not occur. The distillation column 9 was 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. Further, the temperature of the fifth column space was controlled at 126 ± 2 ° C. in the distillation column 10, and the obtained residue was supplied to the middle column of the distillation column 9. Further, as described above, a part of the residue was supplied to the second esterification reaction tank. The water content in the obtained residue was 0.5 ± 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 pressure at the top of the distillation column was 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. Table 1 shows the average value, fluctuation range, and standard deviation (s) between the samples. All the measured values were good and stable, and a polyester with small quality fluctuation was obtained. In addition, stable production was possible for a long time.
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, the circulation line to the distillation column of the residue extracted from the bottom of the distillation column provided in the distillation columns 9 and 10 is removed, the circulation is stopped, and the entire amount of the residue is sent to each supply destination. A polyester was obtained in the same manner as in Example 1 except that The flow of ethylene glycol in the polyester production process of this comparative example is shown in FIG. In the case of carrying out in this comparative example, in the residual liquid feed line extracted from the bottom of the distillation column, clogging of the line due to solid analysis sometimes occurred, and stable production could not be performed for a long time.

(Comparative Example 2)
Comparative Example 1 is the same as Comparative Example 1 except that the number of shelves of the distillation column 9 is set to 7 and the position of the temperature detector is changed to the fourth stage space and the temperature is controlled at 106 ± 5 ° C. A polyester was obtained in the same manner as above. The water content in the recovered ethylene glycol was 3 ± 2.2% by mass. The results are shown in Table 1. In the case of carrying out by the method of this comparative example, the quality fluctuation of the polyester increased in addition to the problem of the comparative example 1.

(Comparative Example 3)
In Comparative Example 2, polyester was obtained in the same manner as in Comparative Example 2, except that the control of the slurry temperature supplied to the first esterification reaction tank was canceled. The slurry temperature was 90 ± 10 ° C. The results are shown in Table 1. In the case of carrying out in this comparative example, the quality fluctuation of the polyester was larger than in Comparative Example 2.

(Example 2)
In Example 1, the detection terminal of the near-infrared spectrophotometer was installed in the extraction line of the residue from the bottom of the distillation column 9, and the water content in the recovered ethylene glycol was measured at a wavelength of 1922 nm. The amount of water in the recovered ethylene glycol is 3 ± by controlling the temperature by feeding back to the temperature detected by the temperature detector installed in the seventh stage of the distillation column so that the amount of water becomes constant based on A polyester was obtained in the same manner as in Example 1 except that the amount was controlled so as to be 0.5% by mass. The results are shown in Table 1. When carried out in this example, the quality fluctuation of the polyester was further reduced as compared with the case carried out in Example 1.

(Example 3)
In Example 1, a bypass line was provided in the transfer line of the polyester oligomer from the third esterification reaction tank 5 to the first polycondensation reaction tank, and the oligomer was measured using a near-infrared spectrophotometer installed in the bypass line. The carboxyl end group concentration is measured at a wavelength of 1444 nm, and 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 A polyester was obtained in the same manner as in Example 1 except that the esterification reaction was controlled by adding to the second esterification reaction tank. The results are shown in Table 1. When carried out in this example, the quality fluctuation of the polyester was further reduced as compared with the case carried out in Example 1.

(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. The polyesters obtained in any of the examples were uniform in quality, had few yarn breaks, and had good spinning operation stability.

(Comparative Examples 3 and 4)
Except for using the polyester resins obtained in Comparative Examples 2 and 3, respectively, 5 batches of solid phase polymerization were performed according to Examples 4 to 6, 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. Since the polyester resins obtained in these comparative examples were inferior in quality uniformity as compared with the polyesters obtained in Examples 1 to 3, the number of yarn breaks was large and the spinning operation stability was inferior.

  The polyester production method of the present invention has an advantage that the production cost of the polyester can be reduced because the glycol generated in the production process of the polyester is reused. In addition, improvements have been made to prevent clogging of the recovered glycol feed line, and it has the feature that production can be continued stably over a long period of time. Furthermore, since the equipment cost of the distillation tower which collect | recovers this glycol and the running cost in this distillation can be reduced, it can lead to the significant reduction of the manufacturing cost of polyester. In addition, the quality of the polyester obtained by a very simple reaction control method of controlling the amount of water in the recovered glycol and the temperature of the slurry composed of the aromatic dicarboxylic acid and glycol supplied to the esterification reaction tank to a specific range, In particular, it has the characteristics that the fluctuation of the carboxyl end group can be suppressed and a uniform quality polyester can be produced stably. That is, it has the advantage that it is a polyester manufacturing method having extremely high cost performance. 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. 3 is a flowchart of ethylene glycol in a polyester production process in Comparative Example 1. 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 (7)

  Aromatic dicarboxylic acid and glycol are mixed in a slurry mixing tank to form a slurry. The slurry is supplied to an esterification reaction tank to carry out an esterification reaction, and the resulting polyester low polymer is subsequently added to a polycondensation reaction tank. In the method for continuously producing polyester by feeding and polycondensation, the low-boiling fraction containing water as a main component is separated by a distillation column provided in the polyester production process using glycol distilled from the polyester production process. A method for producing a polyester, characterized in that, in the method of distilling off and returning to a slurry preparation tank, a part of the residue extracted from the bottom of the distillation column is circulated to the distillation column.   The method for producing a polyester according to claim 1, wherein the liquid temperature of the residue taken out from the bottom of the distillation column is controlled at 160 to 175 ° C.   The method for producing a polyester according to claim 1 or 2, wherein the water content in the distillation residue is adjusted by controlling the temperature of the middle stage of the distillation column.   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 The method for producing a polyester according to claim 1, wherein the fraction is removed by fractional distillation.   The production of the polyester according to any one of claims 1 to 4, wherein the water content in the recovered glycol is controlled within X ± 2.0 mass% (where X represents a number of 2 or more and 3 or less). Method.   A part of the residue extracted from the bottom of the distillation column for treating the distillate from the second esterification reaction tank onward is supplied to the esterification reaction tank on and after the second esterification reaction tank. A process for producing the polyester according to 4 or 5.   The method for producing a polyester according to any one of claims 1 to 6, wherein the temperature of the slurry is controlled within ± 4 ° C of a set value and quantitatively supplied to the esterification reaction tank.

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