Method for producing polyester

Abstract

To provide a method for producing a polyester, by which the polyester having a good color tone, etc., and a high quality can be produced in an early stage without causing a problem of the contamination of foreign matters, when the operation of a polyester production plant is stopped and then restarted.SOLUTION: A method for producing a polyester by reacting dicarboxylic acids and diols in a polyester production plant, the method comprising producing a polyester having an intrinsic viscosity of 0.600 to 0. 800dL / g for 1.0 hours or more before stopping the operation of the polyester production plant.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyester, and more particularly to a method for quickly producing high-quality polyester with good color tone when the polyester production plant is shut down and then restarted. [Background technology]

[0002] Polyesters, such as polyethylene terephthalate and polybutylene phthalate, are crystalline thermoplastic resins with excellent mechanical and chemical properties. Among these, polybutylene terephthalate is an engineering plastic with excellent electrical properties, chemical resistance, moldability, and colorability. Taking advantage of these characteristics, polybutylene terephthalate is widely used as a material in the electrical and electronics fields, automotive fields, and high-performance films.

[0003] Polyesters are industrially produced using batch or continuous processes. In industrial polyester production, periodic maintenance, such as equipment inspection and cleaning, is performed to ensure safe production. To perform this periodic maintenance, the polyester production plant must be shut down. After the maintenance is completed, the polyester production plant is restarted (started up) to resume polyester production. When restarting this polyester production plant, the polyester produced must achieve a quality equivalent to that before shutdown as soon as possible. This quality equivalent to that before shutdown means that the resin is free of foreign matter and has a good color tone. Examples of foreign matter that may be mixed into the resin include carbonized deposits larger than 0.3 mm that precipitate inside or on the walls of the equipment when sublimates or crosslinked products of the raw materials generated in the polyester production plant before shutdown undergo high-temperature thermal history during the polyester production process, causing crosslinking or carbonization reactions.

[0004] Conventionally, when a polyester production plant is restarted, in order to quickly achieve a quality equivalent to that before the shutdown, polymerization tanks and the like in the polyester production plant are cleaned during maintenance. As a method for cleaning a polyester production plant, a method is known in which the inside of a polymerization tank of a polyester melt polymerization apparatus is cleaned using a cleaning composition in which phosphoric acid is added to a mixed glycol of polyalkylene glycol and alkylene glycol (Patent Document 1).Also known is a method for cleaning an esterification reaction tank, a polycondensation reaction tank, etc. using an aqueous solution of an acid whose acid dissociation constant in water or whose first acid dissociation constant in water is 0.9 or more and less than 4 (Patent Document 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 11-80342 [Patent Document 2] Japanese Patent Application Laid-Open No. 2017-95620 Summary of the Invention [Problem to be solved by the invention]

[0006] However, even if the cleaning methods disclosed in Patent Documents 1 and 2 are adopted, after the polyester production plant is restarted, it is not possible to quickly achieve the same quality as the polyester before the shutdown, i.e., to eliminate the problem of contamination with foreign matter described above and to achieve good color tone and the like that are the same as before the shutdown, and the effects are not satisfactory. After the polyester production plant is restarted, the polyester cannot be extracted as a product resin until the quality of the produced polyester stabilizes and reaches a level equivalent to that before the shutdown. Therefore, after the polyester production plant is restarted, it is desirable to produce polyester of a quality equivalent to that before the shutdown as soon as possible.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a polyester production method that is free from the problem of foreign matter contamination when a polyester production plant is restarted after being shut down, and that is capable of quickly producing high-quality polyester with good color tone and the like. [Means for solving the problem]

[0008] As a result of extensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned problems can be solved by producing a polyester having a low intrinsic viscosity for a predetermined period of time or more prior to shutting down the operation of a polyester production plant, and have thus completed the present invention. That is, the present invention relates to the following inventions.

[0009] [1] A method for producing a polyester by reacting a dicarboxylic acid component with a diol component in a polyester production plant, the method comprising producing a polyester having an intrinsic viscosity of 0.600 to 0.800 dL / g for 1.0 hour or more prior to shutting down the polyester production plant.

[0010] [2] The method for producing a polyester according to [1], wherein the dicarboxylic acid component is terephthalic acid, the diol component is an alkylene diol, and the polyester is a polyalkylene terephthalate.

[0011] [3] The method for producing a polyester according to [2], wherein the alkylene diol is 1,4-butanediol and the polyalkylene terephthalate is polybutylene terephthalate.

[0012] [4] The method for producing a polyester according to [2] or [3], wherein the terephthalic acid is produced using naphtha produced from biological resources as a raw material, terephthalic acid produced using recycled naphtha produced from waste resin as a raw material, or terephthalic acid produced by depolymerization of polyester.

[0013] [5] The method for producing a polyester according to [3] or [4], wherein the 1,4-butanediol is 1,4-butanediol produced using naphtha produced from biological resources as a raw material, 1,4-butanediol produced using recycled naphtha produced from waste resin as a raw material, 1,4-butanediol produced by direct fermentation of sugar, 1,4-butanediol produced by hydrogen reduction of succinic acid or a succinic acid derivative produced using biological resources, or 1,4-butanediol produced by depolymerization of polyester. [Effects of the Invention]

[0014] According to the polyester production method of the present invention, high-quality polyester with good color tone and the like can be produced quickly without the problem of contamination with foreign matter when the polyester production plant is restarted after being shut down. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following describes in detail an embodiment of the present invention. However, the description of the constituent elements described below is an example of an embodiment of the present invention, and the present invention is not limited to the following description as long as it does not go beyond the gist of the present invention. In this specification, when the expression "to" is used, it is intended to be used as an expression that includes the numerical values ​​or physical property values ​​before and after it. In the present invention, the "main component" of a dicarboxylic acid component refers to a component that accounts for 50 mol % or more of the dicarboxylic acid component. The same applies to the "main component" of a diol component.

[0016] The method for producing a polyester of the present invention is a method for producing a polyester by reacting a dicarboxylic acid component with a diol component in a polyester production plant, and is characterized in that a polyester having an intrinsic viscosity of 0.600 to 0.800 dL / g is produced for 1.0 hour or more before shutting down the polyester production plant.

[0017] [Steps 1~4] One embodiment of the present invention is a method for producing a polyester, which includes the following steps 1 to 4, and is carried out in this order.

[0018] Step 1: A step of producing a polyester having a desired intrinsic viscosity in a polyester production plant, and then producing a polyester having an intrinsic viscosity of 0.600 to 0.800 dL / g (hereinafter referred to as "polyester A") for 1.0 hour or more before shutting down the operation of the polyester production plant, and then shutting down the operation of the polyester production plant. Step 2: After Step 1, restarting the polyester production plant to produce a polyester (hereinafter referred to as "polyester X") having a desired intrinsic viscosity and containing foreign matter. Step 3: After Step 2, a step of producing a polyester (hereinafter referred to as "Polyester Y") that has the desired intrinsic viscosity and is free of foreign matter but has poor color tone. Step 4: After Step 3, a step of producing a polyester (hereinafter referred to as "Polyester Z") having a desired intrinsic viscosity, no foreign matter mixed in, and a good color tone.

[0019] Here, the "desired intrinsic viscosity" refers to the intrinsic viscosity of the polyester required for the product, which varies depending on the application. The intrinsic viscosity of polyester will be described later. For example, the typical intrinsic viscosity of polybutylene terephthalate is usually 0.850±0.015 dL / g. The intrinsic viscosity of the polyester can be measured by the method described in the Examples section below.

[0020] Furthermore, examples of "foreign matter" include "carbonized precipitates larger than 0.3 mm," i.e., "carbonized precipitates with a maximum length greater than 0.3 mm." These carbonized precipitates are usually black or brownish in color. For example, as shown below, if there is one or more "carbonized precipitates larger than 0.3 mm," it is evaluated as "contains foreign matter." The number of carbonized precipitates larger than 0.3 mm is the number of carbonized precipitates larger than 0.3 mm contained in 200 g of polyester pellets, and may be counted using a foreign matter inspection device or visually, but from the viewpoint of detection accuracy, it is preferable to use a foreign matter inspection device. As the foreign matter inspection device, a commercially available product, for example, the pellet / powder foreign matter inspection device "PGI-IV" manufactured by Hublein Corporation, can be used. The measurement principle of this "PGI-IV" is as follows. First, 200g of pellets are photographed one by one with a CCD camera. If black or brownish foreign matter larger than 0.3mm is detected through image processing, it is classified as "foreign matter present" and the number of foreign matter is counted. By performing this sorting automatically, the number of foreign matter contained in 200g of polyester pellets, i.e., "carbonized precipitates larger than 0.3mm," can be calculated.

[0021] In this embodiment, "polyester containing foreign matter" refers to polyester in which, in the above-mentioned foreign matter inspection, for example, one or more foreign matter particles are present per 200 g of pellets, and "polyester not containing foreign matter" refers to polyester in which the number of foreign matter particles is zero (no foreign matter is contained) per 200 g of pellets.

[0022] The color tone of the produced polyester may be checked for coloration by visual observation, or the color tone b value of the Lab color system may be measured using a commercially available color difference meter, and polyesters with a b value within a predetermined range may be evaluated as not colored, and polyesters with a b value outside the predetermined range may be evaluated as colored. However, evaluation based on the b value is preferred from the viewpoint of preventing errors in judgment by workers. The b value can be measured by the method described in the Examples section below. The lower the b value, the less yellowish it is, which is preferable. From this viewpoint, the b value is preferably 2 or less. On the other hand, if the b value is too low, the yellowish color is reduced, but the blue color increases, which is not preferable. From this viewpoint, the b value is preferably −2 or more. That is, if the b value is between −2 and 2, the color tone can be judged to be good.

[0023] <Process 1> Step 1 is a step in which, after producing a polyester having a desired intrinsic viscosity in a polyester production plant, polyester A having an intrinsic viscosity of 0.600 to 0.800 dL / g is produced for 1.0 hour or more before shutting down the operation of the polyester production plant, and then the operation of the polyester production plant is shut down.

[0024] Polyester A is a low-viscosity polyester having an intrinsic viscosity of 0.600 to 0.800 dL / g. If the intrinsic viscosity of polyester A is too low, it will not be possible to pelletize it after forming it into strands, so the intrinsic viscosity of polyester A is 0.600 dL / g or more, preferably 0.610 dL / g or more, and more preferably 0.620 dL / g or more. On the other hand, if the intrinsic viscosity of polyester A is too high, the foreign matter reduction effect of polyester X in step 2 will not be fully achieved, so the intrinsic viscosity of polyester A is 0.800 dL / g or less, preferably 0.790 dL / g or less, and more preferably 0.780 dL / g or less.

[0025] In order to produce polyester A having a low intrinsic viscosity as described above after producing a polyester having a desired intrinsic viscosity, a simple and preferable method is to gradually reduce the degree of vacuum in the polycondensation reaction system of the polyester production plant while continuing polyester production. By reducing the degree of vacuum, i.e., by increasing the atmospheric pressure, the progress of the polycondensation reaction slows down, the molecular weight of the produced polyester decreases, and the intrinsic viscosity decreases.

[0026] The production time of polyester A is 1.0 hour or more, preferably 1.3 hours or more, and more preferably 1.5 hours or more, because if the production time is too short, the effect of reducing the foreign matter of polyester X in step 2 cannot be sufficiently obtained. On the other hand, if the production time of polyester A is too long, it takes time to produce polyester A before the polyester production plant stops operating, and the amount of polyester that cannot be commercialized increases, resulting in a poor production yield, so the production time is preferably 50 hours or less, more preferably 40 hours or less, and particularly preferably 30 hours or less.

[0027] In step 1, after polyester A is produced, the operation of the polyester production plant is stopped. After shutting down the polyester production plant, necessary maintenance can be carried out, and then prior to step 2, the polyester production plant can be cleaned by a known method such as solvent cleaning, water cleaning, or polyester depolymerization cleaning. In the present invention, when the operation of the polyester production plant is stopped in step 1, polyester A having a low intrinsic viscosity and a low molecular weight is produced for a predetermined period of time, thereby reducing sticky deposits and solidified materials in the polycondensation reaction tank, etc. of the polyester production plant, and improving the cleaning effect of this cleaning, thereby making it possible to reduce the inclusion of foreign matter in the polyester produced in step 2 and subsequent steps and deterioration of color tone.

[0028] <Process 2> Step 2 is a step of restarting the polyester production plant after the above step 1 to start producing polyester Y having a desired intrinsic viscosity and containing foreign matter. Polyester Y is of poor quality in terms of color tone and resin properties due to the presence of foreign matter.

[0029] <Process 3> Step 3 is a step for producing a polyester Y having a desired intrinsic viscosity and no foreign matter mixed in, but having poor color tone. Polyester Y is yellowish due to the influence of foreign matter in step 2, and its b value is usually greater than 2.

[0030] <Step 4> Step 4 is a step for producing a polyester Z having a desired intrinsic viscosity, being free from foreign matter, and having a good color tone.

[0031] The color tone b value of the polyester Z is, as described above, 2 or less and −2 or more.

[0032] In order to form polyester Z into strands and then cut and pelletize them, the intrinsic viscosity must be 0.650 dL / g or more, particularly 0.660 dL / g or more, and especially 0.670 dL / g or more. However, in order to effectively obtain the effect of producing polyester A having a low intrinsic viscosity in step 1 of the present invention, it is preferable that the intrinsic viscosity of the polyester to be produced in the present invention, i.e., the desired intrinsic viscosity, is greater than 0.800 dL / g. Therefore, when Polyester Z is used in compounds or injection molding, the intrinsic viscosity of Polyester Z is preferably greater than 0.800 dL / g and not greater than 1.300 dL / g. If the intrinsic viscosity is low, the effects of the present invention cannot be effectively achieved, and the mechanical strength of the molded product may be insufficient. If the intrinsic viscosity exceeds 1.300 dL / g, the melt viscosity becomes high, which tends to deteriorate the flowability and moldability. The intrinsic viscosity of Polyester Z is more preferably greater than 0.800 dL / g and not greater than 1.260 dL / g, and even more preferably greater than 0.800 dL / g and not greater than 1.200 dL / g.

[0033] When the polyester Z is used for extrusion of a film, sheet, or filament, the intrinsic viscosity of the polyester Z is usually preferably 1.000 to 1.600 dL / g, more preferably 1.030 to 1.500 dL / g, even more preferably 1.050 to 1.550 dL / g, particularly preferably 1.100 to 1.500 dL / g, and especially preferably 1.150 to 1.350 dL / g. If the intrinsic viscosity is less than 1.000 dL / g, the extrusion moldability tends to deteriorate, resulting in drawdown of the resin and molding defects, resulting in insufficient mechanical strength of extrusion-molded products such as films, or the melt viscosity tends to be low and the fluidity tends to be too high, resulting in poor extrusion moldability. On the other hand, if the intrinsic viscosity exceeds 1.600 dL / g, the melt viscosity tends to be high, resulting in poor fluidity and poor extrusion moldability. The intrinsic viscosity of this polyester Z is usually equal to the intrinsic viscosity of the polyester produced in step 1 before producing polyester A.

[0034] [Polyester manufacturing method] The polyester of the present invention can be produced by esterifying or transesterifying a dicarboxylic acid component and a diol component in the presence of an esterification catalyst or a transesterification catalyst. Hereinafter, the method for producing a polyester of the present invention will be described, focusing mainly on a method for producing polybutylene terephthalate (hereinafter sometimes abbreviated as "PBT") as a polyester using terephthalic acid as the dicarboxylic acid component and 1,4-butanediol (hereinafter sometimes abbreviated as "BDO") as the diol component. However, according to the method for producing a polyester of the present invention, it is also possible to produce polyesters other than PBT, such as polyethylene terephthalate (hereinafter sometimes abbreviated as "PET"), using a diol component other than 1,4-butanediol, in the same manner as the method described below.

[0035] Hereinafter, the polyester produced by the polyester production method of the present invention may be referred to as "the polyester of the present invention", and the PBT produced by the polyester production method of the present invention may be referred to as "the PBT of the present invention".

[0036] PBT refers to a polymer having a structure in which a dicarboxylic acid component and a diol component are ester-bonded, with the dicarboxylic acid component comprising a terephthalic acid component as the main component, i.e., 50 mol% or more, and the diol component comprising a BDO component as the main component, i.e., 50 mol% or more. The proportion of the terephthalic acid component in all dicarboxylic acid components is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 95 mol% or more. The proportion of BDO in all diol components is preferably 70 mol% or more, more preferably 80 mol% or more, and even more preferably 95 mol% or more. If the terephthalic acid component or BDO is less than 50 mol%, the crystallization rate of the PBT decreases, resulting in poor moldability.

[0037] The production method for producing the PBT of the present invention may be either continuous or batchwise, but the continuous method is preferred.

[0038] The PBT of the present invention can be produced by a conventional method, for example, by mixing a dicarboxylic acid component mainly composed of terephthalic acid and a diol component mainly composed of BDO in a predetermined ratio under stirring to form a raw material slurry, then heating the raw material slurry under normal or reduced pressure to cause an esterification reaction to form a polyester oligomer, and then gradually reducing the pressure of the resulting oligomer while heating it to cause a melt polycondensation reaction to obtain PBT. As described above, the method for producing the PBT of the present invention is not limited, but an example thereof includes a production method via the following esterification reaction step and polycondensation reaction step.

[0039] The terephthalic acid used as a raw material is not limited to terephthalic acid produced using fossil fuel as a raw material, but may also be terephthalic acid produced using naphtha produced from biological resources as a raw material, terephthalic acid produced using recycled naphtha produced from waste resin as a raw material, or terephthalic acid produced by depolymerization of polyester, for example, chemically recycled terephthalic acid produced by depolymerization of waste polyester such as waste polyethylene terephthalate or waste polybutylene terephthalate, or a mixture of two or more of these. As the waste polyester to be subjected to depolymerization, the polyester A in the above-mentioned step 1, the polyester X in the step 2, and the polyester Y in the step 3 can also be used.

[0040] Furthermore, the BDO is not limited to BDO produced using fossil fuels as a raw material, but may also be BDO produced using naphtha produced from biological resources as a raw material, BDO produced using recycled naphtha produced from waste resin as a raw material, BDO produced by direct fermentation of sugar, BDO produced by hydrogen reduction of succinic acid or a succinic acid derivative produced using biological resources, chemically recycled BDO produced by depolymerization of polyester, or a mixture of two or more of these. Examples of the succinic acid derivative include succinic anhydride and succinic acid esters such as dialkyl succinates (more specifically, dialkyl succinates having an alkyl group with 1 to 4 carbon atoms, preferably 1 to 3, more preferably 1 to 2, and most preferably a methyl group with 1 carbon atom). Chemically recycled BDO includes BDO produced by depolymerizing polybutylene terephthalate. The polyester to be depolymerized may be polyester A in step 1, polyester X in step 2, or polyester Y in step 3.

[0041] <Dicarboxylic acid component> The dicarboxylic acid component other than terephthalic acid to be subjected to the esterification reaction is not particularly limited, and examples thereof include aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, 4,4'-diphenyldicarboxylic acid, 4,4'-diphenyletherdicarboxylic acid, 4,4'-benzophenonedicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, 4,4'-diphenylsulfonedicarboxylic acid, and 2,6-naphthalenedicarboxylic acid; alicyclic dicarboxylic acids such as 1,2-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid; and aliphatic dicarboxylic acids such as malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, and sebacic acid. These dicarboxylic acid components other than terephthalic acid may be used alone or in combination of two or more.

[0042] These dicarboxylic acid components may also be made from naphtha produced from petroleum, from naphtha produced from biological resources, or from those obtained by depolymerization of polyester.

[0043] From the viewpoint of more effectively obtaining the effects of the present invention, the proportion of terephthalic acid in all dicarboxylic acid components is 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 95 mol% or more, and may be 100 mol%.

[0044] When a dicarboxylic acid derivative is used as the dicarboxylic acid component to produce PBT by transesterification, examples of the terephthalic acid derivative include esters of terephthalic acid such as dimethyl terephthalate, and ester-forming derivatives such as terephthalic acid halides. Examples of dicarboxylic acid derivatives other than terephthalic acid include the above-mentioned esters of dicarboxylic acids other than terephthalic acid, and ester-forming derivatives such as dicarboxylic acid halides.

[0045] <Diol ingredient> The diol component other than BDO to be subjected to the esterification reaction is not particularly limited, and examples thereof include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-butanediol, 1,3-butanediol, 1,5-pentanediol, neopentyl glycol, 1,6-hexanediol, 1,8-octanediol, and dibutylene glycol; alicyclic diols such as 1,2-cyclohexanediol, 1,4-cyclohexanediol, 1,1-cyclohexanedimethylol, and 1,4-cyclohexanedimethylol; polyalkylene glycols such as xylylene glycol, polyethylene glycol, polytrimethylene glycol, and polytetramethylene ether glycol; and aromatic diols such as 4,4'-dihydroxybiphenyl, 2,2-bis(4-hydroxyphenyl)propane, and bis(4-hydroxyphenyl)sulfone. These diol components other than BDO may be used alone or in combination of two or more.

[0046] These diol components may also be made from naphtha produced from petroleum, from naphtha produced from biological resources, or from the depolymerization of polyester. Alternatively, they may be made from sugar fermentation.

[0047] From the viewpoint of more effectively obtaining the effects of the present invention, the proportion of BDO in the total diol components is 50 mol% or more, preferably 70 mol% or more, more preferably 80 mol% or more, even more preferably 95 mol% or more, and may be 100 mol%.

[0048] By using a diol component other than the above-mentioned BDO, for example, an alkylene diol such as ethylene glycol, as the diol component, a polyalkylene terephthalate such as PET can be produced.

[0049] <Other Monomers> In producing the PBT of the present invention, one or more copolymerization components may be used, such as hydroxycarboxylic acids such as lactic acid, glycolic acid, m-hydroxybenzoic acid, p-hydroxybenzoic acid, 6-hydroxy-2-naphthalenecarboxylic acid, and p-β-hydroxyethoxybenzoic acid; alkoxycarboxylic acids; monofunctional components such as stearyl alcohol, benzyl alcohol, stearic acid, benzoic acid, t-butylbenzoic acid, and benzoylbenzoic acid; and trifunctional or higher polyfunctional components such as tricarballylic acid, trimellitic acid, trimesic acid, pyromelic acid, gallic acid, trimethylolethane, trimethylolpropane, glycerol, and pentaerythritol.

[0050] <Esterification reaction> An example of a process for esterifying a dicarboxylic acid component mainly composed of terephthalic acid with a diol component mainly composed of BDO to produce an oligomer is a method of producing an oligomer by carrying out the esterification reaction using a single esterification reaction tank or a multistage reaction apparatus in which multiple esterification reaction tanks are connected in series, with or without a catalyst, under normal or reduced pressure, while removing water produced in the reaction and excess diol component from the system, until the esterification reaction rate (the proportion of carboxyl groups in the raw dicarboxylic acid component that have reacted with the diol component to undergo esterification) typically reaches 90% or more. Typically, the temperature of the esterification reaction is about 210 to 230°C, the pressure is about 10 to 133 kPa, and the residence time in the reaction tank, which corresponds to the reaction time, is about 1 to 4 hours.

[0051] <Polycondensation reaction step> An example of the polycondensation reaction step is a method in which a single melt polycondensation tank or a multistage reaction apparatus in which a plurality of melt polycondensation tanks are connected in series, for example, a first-stage reactor is a complete mixing type reactor equipped with stirring blades, and second-stage and third-stage reactors are horizontal plug flow type reactors equipped with stirring blades, is used, and the diol produced is distilled out of the system while heating under reduced pressure in the presence of a catalyst. Typically, the polycondensation reaction is carried out at a temperature of 210 to 280°C, preferably about 220 to 250°C, under reduced pressure of 27 kPa or less, preferably 13 kPa or less. A single or multiple reaction vessel may be used, but in order to prevent coloration and deterioration and to suppress an increase in terminal groups such as vinyl groups, it is advisable to carry out the reaction in at least one reaction vessel under high vacuum of typically 1.3 kPa or less, preferably 0.3 kPa or less. In the process for producing the low intrinsic viscosity polyester A described above, the intrinsic viscosity of the produced polyester A can be reduced by lowering the degree of vacuum in the polycondensation reaction to, for example, about 0.30 to 0.60 kPa.

[0052] The PBT obtained by the polycondensation reaction is usually withdrawn in the form of a strand or sheet from a withdrawal port provided at the bottom of the polycondensation reaction tank, and then cut with a cutter while or after water cooling to form granular bodies such as pellets or chips (for example, lengths of about 3 to 10 mm). Alternatively, the molten resin is released from the polycondensation reaction tank through a pipe into cold water adjusted to a predetermined temperature, and then cut with a cutter to form spheres (diameters of about 2 to 10 mm).

[0053] <Polycondensation catalyst> When polycondensing the oligomer obtained by the esterification reaction of the diol component and the dicarboxylic acid component, a titanium compound and preferably a compound of a metal of Group 2A of the Periodic Table are usually used as catalysts. These catalyst components may be used in the esterification reaction and then directly subjected to the polycondensation reaction, or they may not be used in the esterification reaction, or only the titanium catalyst may be used, with the remaining catalyst components added at the polycondensation stage. Furthermore, a portion of the catalyst amount ultimately used may be used in the esterification reaction, and then appropriately added as the polycondensation reaction proceeds. In any case, in the present invention, titanium and preferably a metal from Group 2A of the Periodic Table are inevitably contained in the PBT finally obtained, and the amounts thereof will be described later.

[0054] (Example of titanium compound) Specific examples of titanium compounds used as catalysts include inorganic titanium compounds such as titanium oxide and titanium tetrachloride, titanium alcoholates such as tetramethyl titanate, tetraisopropyl titanate and tetrabutyl titanate, titanium phenolates such as tetraphenyl titanate, etc. These may be used alone or in combination of two or more. Of these, tetraalkyl titanates are preferred, and among these, tetrabutyl titanate is preferred.

[0055] (titanium catalyst amount) The content of the titanium catalyst in the PBT of the present invention is preferably 5 to 100 ppm by mass of titanium atoms relative to the PBT. This amount is more preferably 10 ppm or more, even more preferably 20 ppm or more, and most preferably 25 ppm or more. This amount is more preferably 90 ppm or less, even more preferably 80 ppm or less, particularly preferably 70 ppm or less, especially preferably 60 ppm or less, and most preferably 50 ppm or less. If the titanium content is too high, the color tone, hydrolysis resistance, and solution haze will deteriorate, and the number of fish eyes will increase in the resulting molded product.If the titanium content is too low, the polymerization property will deteriorate.

[0056] (Example of group 2A metal compounds) Specific examples of the Group 2A metal compound of the periodic table used as a catalyst include various compounds of beryllium, magnesium, calcium, strontium, and barium. From the viewpoints of ease of handling and availability, and catalytic effect, magnesium compounds and / or calcium compounds are preferred, and magnesium compounds, which have excellent catalytic effect, are particularly preferred. Specific examples of magnesium compounds include magnesium acetate, magnesium hydroxide, magnesium carbonate, magnesium oxide, magnesium alkoxide, magnesium hydrogen phosphate, and the like. Specific examples of calcium compounds include calcium acetate, calcium hydroxide, calcium carbonate, calcium oxide, calcium alkoxide, and calcium hydrogen phosphate. These Group 2A metal compounds of the periodic table may be used alone or in combination of two or more. Of these, magnesium acetate is preferred.

[0057] (Group 2A metal catalyst amount) The content of the Group 2A metal catalyst in the polyester of the present invention is not particularly limited, but is preferably 3 to 50 ppm by mass relative to the PBT as Group 2A metal atoms. This amount is more preferably 5 ppm or more, and even more preferably 10 ppm or more. This amount is more preferably 40 ppm or less, even more preferably 30 ppm or less, particularly preferably 20 ppm or less, and most preferably 15 ppm or less. If the content of the Group 2A metal is too high, color tone and hydrolysis resistance will deteriorate, while if it is too low, polymerization will deteriorate. When an acetate of a metal of Group 2A of the Periodic Table is used, the amount of the metal of Group 2A of the Periodic Table in the PBT is preferably 15 ppm or less, since the acetic acid source enters the reaction system.

[0058] (M / Ti ratio) The molar ratio of titanium atoms to Group 2A metal atoms of the periodic table (Group 2A metal atoms of the periodic table / titanium) contained in the PBT of the present invention is usually 0.01 to 100, preferably 0.1 to 10, more preferably 0.3 to 3, and even more preferably 0.3 to 1.5.

[0059] (Metal analysis method) The content of metals such as titanium atoms in PBT can be measured using methods such as atomic emission, atomic absorption, and ICP emission after recovering the metals in the PBT using methods such as wet ashing.

[0060] (Other catalysts) In producing the PBT of the present invention, in addition to the titanium compound and the compound of a metal of Group 2A of the Periodic Table, reaction aids such as antimony compounds such as antimony trioxide, germanium compounds such as germanium dioxide and germanium tetroxide, manganese compounds, zinc compounds, zirconium compounds, cobalt compounds, phosphorus compounds such as orthophosphoric acid, phosphorous acid, hypophosphorous acid, polyphosphoric acid, esters or metal salts thereof, sodium hydroxide, sodium benzoate, etc. may be used.

[0061] <Compound> The polyester of the present invention can be made into a compound product by adding various additives or compounding materials as required during or after the polyester production stage. [Example]

[0062] The present invention will be explained in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0063] [Raw materials] Terephthalic acid was produced by mixing paraxylene with acetic acid and a catalyst and then blowing air into the mixture under high temperature and pressure conditions. The petroleum-derived 1,4-butanediol used was a product of Mitsubishi Chemical Corporation. The biomass-derived 1,4-butanediol used was 1,4-butanediol produced by Zhejiang Boju New Materials Co., Ltd., which was produced by hydrogenating dimethyl succinate.

[0064] [Measurement and evaluation method] <Intrinsic viscosity> Using a fully automatic viscosity measuring device (model DT553, capillary type) manufactured by Sentec Co., Ltd., the following procedure was followed. Using a mixed solution with a mass ratio of 1 / 1 of phenol and 1,1,2,2-tetrachloroethane as the solvent, at 30 °C, the dropping seconds of a PBT sample solution with a concentration of 1.0 g / dL and the solvent alone were measured, and calculated from the following formula. Intrinsic viscosity (dL / g) = ((1 + 4KHη3)0.5 - 1) / (2KHC) (However, η3 = η / η0 - 1, where η is the dropping seconds of the sample solution, η0 is the dropping seconds of the solvent, C is the PBT concentration (g / dL) of the sample solution, and KH is Huggins' constant. KH = 0.33 was adopted.)

[0065] <Measurement method for carbonized deposits larger than 0.3 mm> Using "PGI-IV" manufactured by Hubrain Co., Ltd., carbonized deposits larger than 0.3 mm were measured. First, after removing the fine powder and moisture contained in the PBT to be measured with an air gun, 200 g of PBT pellets were obtained, and using "PGI-IV" manufactured by Hubrain Co., Ltd., the number of deposits larger than 0.3 mm was measured.

[0066] <Time when the number of carbonized deposits larger than 0.3 mm became zero> The time when the number of carbonized deposits larger than 0.3 mm became zero was determined as the first time when, after the restart of the polyester manufacturing plant, the obtained PBT pellets were sampled every 2 hours and no carbonized deposits larger than 0.3 mm were continuously detected for 4 times (8 hours).

[0067] <Color tone of PBT> The color tone of PBT was evaluated in the Lab color system using a color difference meter "Z-300A type" manufactured by Nippon Denshoku Industries Co., Ltd. The lower the b value, the less yellowish and more preferable. However, when the b value is lower than -2.0, although the yellowish tint is less, the bluish tint increases and the color tone is not preferable.

[0068] <Time when PBT with good color tone was obtained> The time when PBT with a good color tone was obtained was determined as the time when the b value became 2 or less after sampling the obtained PBT pellets every two hours after the number of carbonized precipitates larger than 0.3 mm became zero.

[0069] Example 1 In this example, the terephthalic acid and 1,4-butanediol used were both derived from petroleum. Polybutylene terephthalate was continuously produced using a polybutylene terephthalate production apparatus comprising an esterification reaction tank, a vertical polycondensation reaction tank, a horizontal polycondensation reaction tank, a polymer filter, a die head, a cooling tank and a chip cutter. Using the above-mentioned polybutylene terephthalate production equipment, a slurry of terephthalic acid and 1,4-butanediol and a solution of tetrabutoxytitanium and 1,4-butanediol were fed so that the titanium concentration in the resulting polybutylene terephthalate was 40 ppm by mass, and an esterification reaction was carried out to obtain an esterification reaction liquid. A solution of magnesium acetate and 1,4-butanediol was fed to the resulting esterification reaction liquid so that the magnesium concentration in the resulting polybutylene terephthalate was 10 ppm by mass, and a polycondensation reaction was carried out under a high vacuum of 0.15 kPa to obtain a polycondensation reaction liquid. The resulting polycondensation reaction liquid was passed through a polymer filter, and polybutylene terephthalate was obtained at a rate of 3,000 kg per hour. The resulting polybutylene terephthalate was stranded using a die head, cooled in a cooling tank, and then pelletized using a chip cutter. The resulting polybutylene terephthalate pellets had an intrinsic viscosity of 0.848 to 0.854 dL / g and a color b value of 0.3 to 0.6.

[0070] The degree of vacuum in the polycondensation reaction was then gradually reduced over two hours, i.e., the pressure in the system was increased to 0.56 kPa, yielding a polycondensation reaction solution A. The resulting polycondensation reaction solution A was passed through a polymer filter to yield polybutylene terephthalate A at a rate of 3,000 kg per hour. The resulting polybutylene terephthalate A was formed into strands using a die head, cooled in a cooling tank, and then pelleted with a chip cutter to yield polybutylene terephthalate A pellets A. The resulting polybutylene terephthalate A pellets A had an ultimate intrinsic viscosity of 0.635 dL / g. Furthermore, 200 g of the resulting polybutylene terephthalate A pellets A contained zero carbonized precipitates. The operating conditions were maintained, and polybutylene terephthalate A with an intrinsic viscosity of 0.635 dL / g was produced for two hours, after which the operation of the polybutylene terephthalate production plant was shut down. In addition, when the degree of vacuum was gradually reduced over 0.5 hours during the polycondensation reaction, the intrinsic viscosity of the produced polybutylene terephthalate was 0.800 dL / g or less when the pressure reached 0.20 kPa. Therefore, the time required to produce polyester A with an intrinsic viscosity of 0.635 to 0.800 dL / g was estimated to be 2.4 hours.

[0071] After the operation of the polybutylene terephthalate production plant was stopped, the inside of the plant was washed with triethylene glycol. After the above-mentioned cleaning, the polybutylene terephthalate production plant was restarted, and a slurry of terephthalic acid and 1,4-butanediol and a solution of tetrabutoxytitanium and 1,4-butanediol were again supplied so that the titanium concentration in the resulting polybutylene terephthalate was 40 ppm by mass, and an esterification reaction was carried out to obtain an esterification reaction liquid W. A solution of magnesium acetate and 1,4-butanediol was supplied to the obtained esterification reaction liquid W so that the magnesium concentration in the resulting polybutylene terephthalate W was 10 ppm by mass, and a polycondensation reaction was carried out at 0.70 kPa to obtain a polycondensation reaction liquid W. The obtained polycondensation reaction liquid W was passed through a polymer filter to obtain polybutylene terephthalate W. Because polybutylene terephthalate W had a low viscosity, it was extracted into a container.

[0072] The degree of vacuum during the polycondensation reaction was then gradually increased to 0.15 kPa to obtain a polycondensation reaction solution X. The obtained polycondensation reaction solution X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4,000 kg per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.845 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 11 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and pellets were sampled every two hours.

[0073] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, pellets were sampled every two hours. 28 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets was zero. The intrinsic viscosity of the obtained polybutylene terephthalate was 0.850 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4,000 kg per hour × 28 hours = 112,000 kg = 112 tons.

[0074] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 32 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.3 and a good color tone.

[0075] <Example 2> The same procedure as in Example 1 was repeated, except that the ultimate intrinsic viscosity of polybutylene terephthalate A was changed to 0.694 dL / g instead of 0.635 dL / g, and the production time for polybutylene terephthalate A with an intrinsic viscosity of 0.694 dL / g was changed to 6 hours instead of 2 hours. In this example, polybutylene terephthalate A with an intrinsic viscosity of 0.694 to 0.800 dL / g was produced over 6.3 hours.

[0076] Thereafter, the degree of vacuum during the polycondensation reaction was gradually increased in the same manner as in Example 1, to obtain a polycondensation reaction liquid X. The obtained polycondensation reaction liquid X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4,000 kg per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.848 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 12 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and the pellets were sampled every two hours.

[0077] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, pellets were sampled every two hours. 20 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets became zero, and the intrinsic viscosity was 0.850 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4,000 kg per hour × 20 hours = 80,000 kg = 80 tons.

[0078] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 24 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.5 and a good color tone.

[0079] Example 3 The same procedure as in Example 1 was carried out, except that the ultimate intrinsic viscosity of polybutylene terephthalate A was changed to 0.742 dL / g instead of 0.635 dL / g in Example 1. In this example, polybutylene terephthalate A having an intrinsic viscosity of 0.742 to 0.800 dL / g was produced in 2.4 hours.

[0080] Thereafter, the degree of vacuum during the polycondensation reaction was gradually increased in the same manner as in Example 1, to obtain a polycondensation reaction liquid X. The obtained polycondensation reaction liquid X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4,000 kg per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.852 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 14 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and pellets were sampled every two hours.

[0081] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, pellets were sampled every two hours. 36 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets became zero, and the intrinsic viscosity was 0.852 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4,000 kg per hour × 36 hours = 144,000 kg = 144 tons.

[0082] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 40 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.6 and a good color tone.

[0083] Example 4 The same procedure as in Example 1 was repeated, except that the ultimate intrinsic viscosity of polybutylene terephthalate A was changed to 0.643 dL / g instead of 0.635 dL / g, and the production time for polybutylene terephthalate A with an intrinsic viscosity of 0.643 dL / g was changed to 1.0 hour instead of 2 hours. In this example, polybutylene terephthalate A with an intrinsic viscosity of 0.643 to 0.800 dL / g was produced in 1.4 hours.

[0084] Thereafter, the degree of vacuum during the polycondensation reaction was gradually increased in the same manner as in Example 1, to obtain a polycondensation reaction liquid X. The obtained polycondensation reaction liquid X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4,000 kg per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.848 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 13 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and the pellets were sampled every two hours.

[0085] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, pellets were sampled every two hours. 32 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets became zero, and the intrinsic viscosity was 0.850 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4,000 kg per hour × 32 hours = 128,000 kg = 128 tons.

[0086] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 36 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.5 and a good color tone.

[0087] <Comparative Example 1> The same procedure as in Example 1 was carried out, except that the ultimate intrinsic viscosity of polybutylene terephthalate A was changed to 0.553 dL / g instead of 0.635 dL / g. The obtained polybutylene terephthalate A was formed into strands by a die head, and then cooled in a cooling tank. An attempt was made to obtain pellets using a chip cutter, but cutting was not possible, and operation was not possible.

[0088] <Comparative Example 2> In Example 1, Polyester A was not produced before the shutdown of the polybutylene terephthalate production plant, and production of polybutylene terephthalate with an intrinsic viscosity of 0.848 to 0.854 dL / g was continued. Finally, polybutylene terephthalate with an intrinsic viscosity of 0.854 dL / g was produced for 2 hours, and then the plant operation was shut down. Thereafter, cleaning was carried out in the same manner as in Example 1, and the plant was then restarted. Production of polybutylene terephthalate was resumed in the same manner as in Example 1, and low-viscosity polybutylene terephthalate W was extracted into a container.

[0089] Thereafter, the degree of vacuum during the polycondensation reaction was gradually increased in the same manner as in Example 1, to obtain a polycondensation reaction liquid X. The obtained polycondensation reaction liquid X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4,000 kg per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.848 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 38 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and the pellets were sampled every two hours.

[0090] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, pellets were sampled every two hours. 200 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets became zero, and the intrinsic viscosity was 0.844 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4,000 kg per hour × 200 hours = 800,000 kg = 800 tons.

[0091] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 204 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.5 and a good color tone.

[0092] <Comparative Example 3> The same procedure as in Example 1 was repeated, except that the ultimate intrinsic viscosity of polybutylene terephthalate A was changed to 0.646 dL / g instead of 0.635 dL / g, and the production time for polybutylene terephthalate A with an intrinsic viscosity of 0.646 dL / g was changed to 0.3 hours instead of 2 hours. In this example, polybutylene terephthalate A with an intrinsic viscosity of 0.646 to 0.800 dL / g was produced in 0.7 hours.

[0093] Thereafter, the degree of vacuum during the polycondensation reaction was gradually increased in the same manner as in Example 1, to obtain a polycondensation reaction liquid X. The obtained polycondensation reaction liquid X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4,000 kg per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.848 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 15 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and the pellets were sampled every two hours.

[0094] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, the pellets were sampled every two hours. 64 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm in 200 g of pellets became zero, and the intrinsic viscosity was 0.850 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4,000 kg per hour × 64 hours = 256,000 kg = 256 tons.

[0095] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 68 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.6 and a good color tone.

[0096] In Examples 1 to 4 and Comparative Examples 1 to 3, the attained intrinsic viscosity of polybutylene terephthalate A (PBT A), the production amount of polybutylene terephthalate X (PBT X), and the time required after the production of polybutylene terephthalate Y (PBT Y) to obtain polybutylene terephthalate Z (PBT Z) having no carbonized precipitates larger than 0.3 mm in 200 g of pellets and having a good color tone are summarized in Table 1. Table 1 shows that when polybutylene terephthalate A has a predetermined intrinsic viscosity and is produced for a predetermined production time, the amount of polybutylene terephthalate X having one or more carbonized precipitates larger than 0.3 mm is reduced, and the time required to obtain polybutylene terephthalate Z having a good color tone and containing zero carbonized precipitates larger than 0.3 mm in 200 g of pellets is shortened.

[0097] [Table 1]

[0098] <Example 5> In this example, petroleum-derived terephthalic acid was used as the terephthalic acid, and biomass-derived 1,4-butanediol was used for all 1,4-butanediol. Polybutylene terephthalate was continuously produced using a polybutylene terephthalate production apparatus comprising an esterification reaction tank, a vertical polycondensation reaction tank, a horizontal polycondensation reaction tank, a polymer filter, a die head, a cooling tank and a chip cutter. Using the above-mentioned polybutylene terephthalate production equipment, a slurry of terephthalic acid and 1,4-butanediol produced from petroleum, and a solution of tetrabutoxytitanium and 1,4-butanediol were fed so that the titanium concentration in the resulting polybutylene terephthalate was 40 ppm by mass, and an esterification reaction was carried out to obtain an esterification reaction liquid. A solution of magnesium acetate and 1,4-butanediol was fed to the resulting esterification reaction liquid so that the magnesium concentration in the resulting polybutylene terephthalate was 10 ppm by mass, and a polycondensation reaction was carried out under a high vacuum of 0.15 kPa to obtain a polycondensation reaction liquid. The resulting polycondensation reaction liquid was passed through a polymer filter, and polybutylene terephthalate was obtained at a rate of 3 parts by mass per hour. The resulting polybutylene terephthalate was stranded using a die head, cooled in a cooling tank, and then pelletized using a chip cutter. The resulting polybutylene terephthalate pellets had an intrinsic viscosity of 0.848 to 0.857 dL / g and a color b value of 0.3 to 0.8.

[0099] The degree of vacuum in the polycondensation reaction was then gradually reduced over two hours, i.e., the pressure in the system was increased to 0.56 kPa, yielding a polycondensation reaction solution A. The resulting polycondensation reaction solution A was passed through a polymer filter to yield polybutylene terephthalate A at a rate of 3 parts by mass per hour. The resulting polybutylene terephthalate A was formed into strands using a die head, cooled in a cooling tank, and then pelleted with a tip cutter to obtain polybutylene terephthalate A pellets A. The resulting polybutylene terephthalate A pellets A had an ultimate intrinsic viscosity of 0.633 dL / g. Furthermore, 200 g of the resulting polybutylene terephthalate A pellets A contained zero carbonized precipitates. The operating conditions were maintained, and polybutylene terephthalate A with an intrinsic viscosity of 0.633 dL / g was produced for two hours, after which the operation of the polybutylene terephthalate production plant was shut down. During the polycondensation reaction, when the degree of vacuum was gradually reduced over 0.5 hours and the pressure reached 0.20 kPa, the intrinsic viscosity of the produced polybutylene terephthalate was 0.800 dL / g or less, and therefore the time required to produce polyester A with an intrinsic viscosity of 0.635 to 0.800 dL / g was estimated to be 3 hours.

[0100] After the operation of the polybutylene terephthalate production plant was stopped, the inside of the plant was washed with triethylene glycol. After the above-mentioned cleaning, the polybutylene terephthalate production plant was restarted, and a slurry of terephthalic acid and 1,4-butanediol and a solution of tetrabutoxytitanium and 1,4-butanediol were again supplied so that the titanium concentration in the resulting polybutylene terephthalate was 40 ppm by mass, and an esterification reaction was carried out to obtain an esterification reaction liquid W. A solution of magnesium acetate and 1,4-butanediol was supplied to the obtained esterification reaction liquid W so that the magnesium concentration in the resulting polybutylene terephthalate W was 10 ppm by mass, and a polycondensation reaction was carried out at 0.70 kPa to obtain a polycondensation reaction liquid W. The obtained polycondensation reaction liquid W was passed through a polymer filter to obtain polybutylene terephthalate W. Because polybutylene terephthalate W had a low viscosity, it was extracted into a container.

[0101] The degree of vacuum during the polycondensation reaction was then gradually increased to 0.15 kPa to obtain a polycondensation reaction solution X. The obtained polycondensation reaction solution X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4 parts by mass per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.843 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 11 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and the pellets were sampled every two hours.

[0102] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, pellets were sampled every two hours. 24 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets became zero. The intrinsic viscosity of the obtained polybutylene terephthalate was 0.852 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4 parts by mass per hour × 24 hours = 96 parts by mass.

[0103] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 28 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.3 and a good color tone.

[0104] <Comparative Example 4> In Example 5, Polyester A was not produced before the shutdown of the polybutylene terephthalate production plant, and production of polybutylene terephthalate with an intrinsic viscosity of 0.848 to 0.857 dL / g was continued. Finally, polybutylene terephthalate with an intrinsic viscosity of 0.854 dL / g was produced for 2 hours, and then the plant operation was shut down. Thereafter, cleaning was carried out in the same manner as in Example 5, and the plant was then restarted, and production of polybutylene terephthalate was resumed in the same manner as in Example 5, and low-viscosity polybutylene terephthalate W was extracted into a container.

[0105] Thereafter, the degree of vacuum during the polycondensation reaction was gradually increased in the same manner as in Example 5, to obtain a polycondensation reaction liquid X. The obtained polycondensation reaction liquid X was passed through a polymer filter to obtain polybutylene terephthalate X at a rate of 4 parts by mass per hour. The obtained polybutylene terephthalate X was formed into strands using a die head, cooled in a cooling tank, and then pellets X of polybutylene terephthalate X were obtained using a chip cutter. The intrinsic viscosity of the obtained polybutylene terephthalate X pellets X was 0.845 dL / g. Furthermore, 200 g of the obtained polybutylene terephthalate X pellets X contained 42 carbonized precipitates larger than 0.3 mm. The time when the obtained polybutylene terephthalate X began to pass through the die head was defined as time 0. The operating conditions were maintained, and the pellets were sampled every two hours.

[0106] While maintaining the operating conditions under which polybutylene terephthalate X was obtained, the pellets were sampled every two hours. 220 hours after the production of polybutylene terephthalate X, the number of carbonized precipitates larger than 0.3 mm contained in 200 g of pellets became zero, and the intrinsic viscosity was 0.844 dL / g, indicating that polybutylene terephthalate Y was obtained. The production amount of polybutylene terephthalate X was 4 parts by mass per hour × 220 hours = 880 parts by mass.

[0107] While maintaining the operating conditions under which polybutylene terephthalate Y was obtained, the pellets were sampled every two hours. 224 hours after the production of polybutylene terephthalate X, 200 g of pellets contained zero carbonized precipitates larger than 0.3 mm, and polybutylene terephthalate Z was obtained, which had a b value of 0.4 and a good color tone.

[0108] In Example 5 and Comparative Example 4, the achieved intrinsic viscosity of polybutylene terephthalate A (PBT A), the production amount of polybutylene terephthalate X (PBT X), and the time required after the production of polybutylene terephthalate Y (PBT Y) to obtain polybutylene terephthalate Z (PBT Z) having no carbonized precipitates larger than 0.3 mm in 200 g of pellets and having a good color tone are summarized in Table 2. Table 2 shows that even when 1,4-butanediol derived from biomass resources is used, when polybutylene terephthalate A has a predetermined intrinsic viscosity and is produced for a predetermined production time, the amount of polybutylene terephthalate X having one or more carbonized precipitates larger than 0.3 mm is reduced, and the time required to obtain polybutylene terephthalate Z having a good color tone and containing zero carbonized precipitates larger than 0.3 mm in 200 g of pellets is shortened.

[0109] [Table 2]

Claims

1. A method for producing a polyester by reacting a dicarboxylic acid component with a diol component in a polyester production plant, The method for producing polyester comprises producing a polyester having an intrinsic viscosity of 0.600 to 0.800 dL / g for 1.0 hour or more prior to shutting down the polyester production plant.

2. 2. The method for producing a polyester according to claim 1, wherein the dicarboxylic acid component is terephthalic acid, the diol component is an alkylene diol, and the polyester is a polyalkylene terephthalate.

3. 3. The method for producing a polyester according to claim 2, wherein the alkylene diol is 1,4-butanediol and the polyalkylene terephthalate is polybutylene terephthalate.

4. 3. The method for producing a polyester according to claim 2, wherein the terephthalic acid is produced using naphtha produced from biological resources as a raw material, terephthalic acid produced using recycled naphtha produced from waste resin as a raw material, or terephthalic acid produced by depolymerization of a polyester.

5. 5. The method for producing a polyester according to claim 3, wherein the 1,4-butanediol is 1,4-butanediol produced using naphtha produced from biological resources as a raw material, 1,4-butanediol produced using recycled naphtha produced from waste resin as a raw material, 1,4-butanediol produced by direct fermentation of sugar, 1,4-butanediol produced by hydrogen reduction of succinic acid or a succinic acid derivative produced using biological resources, or 1,4-butanediol produced by depolymerization of a polyester.

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