JP2010006962A - Method for producing polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a depolymerization reaction method by which diethylene glycol generated in a reaction process for depolymerizing polyester waste to the minimum and which is energy saving and nearly free from plant investment and to provide a method for producing a polyester having excellent quality. <P>SOLUTION: In the production method of the polyester, a bishydroxyethyl terephthalate having a molar ratio of ethyleneglycol to an acid component of 1.3 to 2.0 and/or an oligomer thereof is made to exist in a melted state in a reaction vessel having a rectification tower at an upper part thereof, the polyester waste and ethylene glycol are continuously supplied to the reaction vessel, depolymerization reaction is performed at such a temperature of 205 to 250°C that a tower top temperature of the rectification tower is lower than the boiling point of ethylene glycol without substantially distilling ethylene glycol from the rectification tower and then polycondensation reaction of the resultant reaction product is performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for producing polyester, in which polyester waste is regenerated as a polyester that saves energy and produces a small amount of by-product diethylene glycol.

  Polyesters are used for various purposes because of their useful functionality, and are used, for example, for clothing, materials, and clothing. Among them, polyethylene terephthalate is excellent in terms of versatility and practicality and is preferably used. For this reason, since polyethylene terephthalate products are increasing year by year, recycling of used polyethylene terephthalate has become an essential issue. Here, as a recycling technique, a method of depolymerizing even a raw material such as terephthalic acid and dimethylene terephthalate, and a method of depolymerizing a low polymer typified by bishydroxyethyl terephthalate are known.

  Polyester recycling technology has been studied for a long time. For example, when polyester waste is depolymerized with ethylene glycol, a method of using 1.0 to 3.0 moles of polyester waste to depolymerize ethylene glycol is known. (Patent Document 1). However, since this method uses a large amount of ethylene glycol for depolymerization, it not only increases the cost, but also generates a large amount of by-products such as diethylene glycol. The disadvantage is that the quality of the resulting polyester is inferior.

  Furthermore, bishydroxyethyl terephthalate having an equivalent ratio of glycol component to acid component of 1.3 to 2.0 and / or its low polymer is produced in a reaction vessel in a molten state, and polyester waste and ethylene glycol are continuously supplied. Is disclosed (Patent Document 2). In this method, although the amount of ethylene glycol used for depolymerization is small, the depolymerization reaction is carried out by distilling and refluxing ethylene glycol from the rectifying column attached to the upper part of the reaction vessel. Since it uses a lot of energy and it is necessary to heat ethylene glycol until it is distilled and refluxed, it takes a long time for the depolymerization reaction, and a large amount of by-products such as diethylene glycol are generated, resulting in poor polyester quality. Has the disadvantages.

  In addition, a method of esterifying terephthalic acid and ethylene glycol while depolymerizing polyester waste is also known (Patent Documents 3 and 4). However, in this method, since the esterification reaction is simultaneously performed, there is a problem that the amount of polyester waste that can be added to the reaction vessel and depolymerized is limited.

  Furthermore, as a recycling method for PET bottles that has been generated in large quantities in recent years, there is also a method for recovering bottles and obtaining bishydroxyethyl terephthalate with excellent quality by going through other stages such as depolymerization process and purification process. Known (Patent Document 5). However, although this method can surely obtain bishydroxyethyl terephthalate having excellent quality, it requires a large amount of capital investment and is not practical.

Therefore, as a result of diligent studies in order to solve the above problems, the present invention has found a method for depolymerizing polyester waste which is energy-saving and produces a small amount of by-product diethylene glycol. This method does not require a large capital investment, and can be a stable polyester production method by using bishydroxyethyl terephthalate and / or a low polymer obtained by the depolymerization method. Can be achieved.
JP-A-48-61447 (Claims) JP 60-248646 A (Claims) Japanese Patent Publication No. 46-15114 (Claims) JP-A-10-310637 (Claims) JP 2000-232701 (Claims)

  The object of the present invention is to solve the above-mentioned conventional problems, that is, to minimize the generation of diethylene glycol generated in the course of the depolymerization reaction, further to save energy and provide a depolymerization reaction with less equipment investment, An object of the present invention is to provide a production method capable of obtaining a polyester having a stable quality by using bishydroxyethyl terephthalate and / or its low polymer obtained by the depolymerization method.

  An object of the present invention described above is to provide a reaction vessel having a rectifying column at the top in a molten state of bishydroxyethyl terephthalate having a molar ratio of ethylene glycol to acid component of 1.3 to 2.0 and / or a low polymer thereof. Polyester waste and ethylene glycol are continuously supplied to the reaction vessel, and the top temperature of the rectification column is ethylene at 205 to 250 ° C. and substantially no ethylene glycol is distilled from the rectification column. This can be achieved by performing a depolymerization reaction at a temperature lower than the boiling point of glycol and then polycondensing the reactants.

  Compared with bishydroxyethyl terephthalate and / or its low polymer obtained by the conventional depolymerization method, the quality of bishydroxyethyl terephthalate and / or its low polymer is good, and its bishydroxyethyl terephthalate and / or its low polymer The color tone and the quality represented by the diethylene glycol content of the polyester obtained by carrying out the polycondensation reaction using are excellent, and energy is saved.

  The present invention is described in detail below. The polyester waste depolymerization method according to the present invention can depolymerize polyester waste mainly composed of ethylene terephthalate. The polyester waste may be ethylene terephthalate as a main component, and polyester waste such as propylene terephthalate or butylene terephthalate may be contained within a range that does not impair the purpose. The form of the polyester waste may be not only polyester chip waste, film waste, and yarn waste, but also any of those used as products. The mixing ratio of these scraps needs to be changed as appropriate while confirming the stability of the quality of the polyester obtained by the polycondensation reaction after the depolymerization reaction, but basically there is no problem even if they are mixed and depolymerized. However, in order to stabilize the quality of the obtained polyester, it is preferable to use a single polyester scrap. The term “single” used here refers to the case of reusing film scraps. It is optimal to use film scraps of the same composition, but it is substantially difficult to mix several types of film scraps. May be used.

  The depolymerization method according to the present invention comprises a reaction vessel in which a bishydroxyethyl terephthalate having a molar ratio of ethylene glycol to an acid component (ethylene glycol / acid component) of 1.3 to 2.0 and / or a low polymer thereof are previously melted. It is necessary to be present. If this molten bishydroxyethyl terephthalate and / or its low polymer is not present in the reaction vessel in advance, the depolymerization reaction rate will be extremely slow, and the amount of ethylene glycol used in the depolymerization reaction will be Several times more than is required. Furthermore, it is not preferable from the viewpoint of energy saving. The molar ratio of ethylene glycol to the acid component (ethylene glycol / acid component) is preferably 1.3 to 1.8, more preferably 1.4 to 1.6. When the molar ratio is lower than 1.3, the depolymerization reaction is slowed down, so that it takes a long time to complete, and the bishydroxyethyl terephthalate and / or its low polymer are easily colored yellowish. Furthermore, since the efficiency of the depolymerization reaction is deteriorated, the consumption of polyester waste is extremely slow, which is not preferable. If the molar ratio is higher than 2.0, the depolymerization reaction proceeds smoothly, but a large amount of diethylene glycol, which is a by-product, is generated, and the quality of the polyester obtained in the subsequent polycondensation reaction is deteriorated, which is not preferable. . Use of ethylene glycol is not preferable from the viewpoint of cost. The amount (A) of bishydroxyethyl terephthalate and / or its low polymer existing in the reaction vessel in the molten state in advance is the ratio of the amount of polyester waste to be added and the amount of ethylene glycol (B) combined, It is preferable that A: B = 4: 6 to 6: 4. When the ratio of A is less than 4, it takes time for the depolymerization reaction, and the resulting bishydroxyethyl terephthalate and / or its low polymer is liable to be colored yellowish. If the ratio of A is more than 6, the depolymerization reaction proceeds smoothly, but it is not preferable because diethylene glycol as a by-product is generated, and the capacity of the reaction vessel is limited, so the consumption of polyester waste is reduced. It is not preferable.

  The polyester waste depolymerization method according to the present invention requires that polyester waste and ethylene glycol be continuously supplied. If the bishydroxyethyl terephthalate and / or its low polymer existing in the molten state are solidified at once when put into the reaction vessel all at once, the depolymerization reaction will not proceed, and the stirrer will be heavily loaded. There is also a risk of destroying. Note that “continuous” as used in the present application may be pseudo continuous, that is, the polyester waste and ethylene glycol to be charged may be divided into at least about 5 times and charged into the reaction vessel.

  Although it is preferable to start the charging at substantially the same time, there is no particular limitation as long as there is no problem in the depolymerization reaction, there is no need to start feeding at the same time and it is not necessary to end the feeding at the same time.

  By performing the depolymerization reaction temperature at 205 to 250 ° C., the depolymerization reaction proceeds efficiently. Preferably it is 215-245 degreeC. More preferably, the depolymerization reaction is performed at 215 ° C. to 225 ° C. during continuous supply of the polyester waste and ethylene glycol, and the temperature is raised to 235 to 245 ° C. after the supply is completed, and the depolymerization reaction is performed. If it is lower than 205 ° C., the heat energy is insufficient and it takes time for the depolymerization reaction, and the resulting bishydroxyethyl terephthalate and / or its low polymer is liable to be colored yellowish. If it is higher than 250 ° C., more heat energy is applied than necessary, and thus the resulting bishydroxyethyl terephthalate and / or its low polymer is liable to be colored yellowish. Further, diethylene glycol as a by-product is likely to be generated. It is not preferable.

  A feature of the depolymerization method of polyester waste according to the present invention is that the depolymerization reaction is carried out without substantially distilling ethylene glycol from the rectifying column attached to the upper part of the reaction vessel, and further without refluxing. is there. In the known technology so far, ethylene glycol is distilled from the upper part of the rectifying column, and the depolymerization reaction is performed by refluxing the ethylene glycol and refluxing it in the reaction system. is there. The depolymerization reaction proceeds while incorporating ethylene glycol into the polyester molecular chain. The reaction stage incorporated in the molecular chain is an endothermic reaction, and thermal energy is used for the depolymerization reaction. At this time, ethylene glycol vapor is used for the depolymerization reaction without reaching the rectification column, and the depolymerization reaction proceeds. Thereafter, as the depolymerization reaction of the polyester waste proceeds and the degree of polymerization decreases, free ethylene glycol begins to increase, and ethylene glycol evaporates and reaches the top of the rectifying column. The ethylene glycol vapor reaching the top of the rectification column is cooled by a condenser and liquefied. When this liquefied ethylene glycol is refluxed, energy loss increases, which is not preferable. Furthermore, since heat energy and time are spent so much that steam is generated up to the top of the rectifying column, diethylene glycol as a by-product is easily generated, which is not preferable.

  The completion of the depolymerization reaction is judged by a thermometer installed at the top of the rectification column. In order not to allow ethylene glycol to be distilled off from the top of the rectifying column during the depolymerization reaction, the thermometer temperature always shows a boiling point of ethylene glycol, for example, a temperature lower than 197.6 ° C. at normal pressure. Preferably, the depolymerization reaction is terminated after 10 to 30 minutes from the time when the thermometer at the top of the column reaches 160 ° C., in order to minimize the amount of diethylene glycol produced as a by-product. is there. In other words, by terminating the depolymerization reaction at a temperature lower than the boiling point of ethylene glycol (197.6 ° C.), ethylene glycol is not evaporated to the top of the rectifying column, and is most efficient in terms of energy. . The column top temperature of the rectifying column is preferably 155 ° C, more preferably 150 ° C.

  Alternatively, the completion of the depolymerization reaction can also be determined by a thermometer installed in the middle stage of the rectification column. By terminating after 10 to 30 minutes from the time when the middle stage temperature reaches 180 ° C., the amount of diethylene glycol, which is a byproduct, can be minimized. In other words, by terminating the depolymerization reaction at a temperature lower than the boiling point of ethylene glycol (197.6 ° C.), it is not necessary for the ethylene glycol to evaporate to the top of the rectifying column, and it is most efficient in terms of energy. .

  The reaction pressure of the depolymerization reaction may be normal pressure or pressurization as long as the temperature at the top of the rectifying column falls within the boiling point of ethylene glycol. Of course, the depolymerization reaction may be carried out while reducing the pressure, but it is preferably carried out at normal pressure from the viewpoint of not using extra energy and equipment for pressurization / depressurization. An inert gas such as nitrogen is required for pressurization, and a decompression device is required for decompression.

  It is preferable that the molar ratio (ethylene glycol / polyester waste) of polyester waste and ethylene glycol continuously supplied to the reaction vessel is 0.3 to 1.0. The molar ratio is preferably 0.3 to 0.7, more preferably 0.4 to 0.6. If the molar ratio is less than 0.3, the depolymerization reaction is slowed, so that it takes time to finish, and bishydroxyethyl terephthalate and / or its low polymer is colored yellowish. Furthermore, since efficiency also worsens, since consumption of polyester waste becomes slow, it is not preferable. When the molar ratio is larger than 1.0, the depolymerization reaction proceeds smoothly, but a large amount of by-product diethylene glycol is generated, which is not preferable because the quality of the polyester obtained by the polycondensation reaction is deteriorated. Moreover, it is not preferable from the viewpoint of cost to use a large amount of ethylene glycol.

  The supply time of the polyester waste and ethylene glycol continuously supplied to the reaction vessel is preferably 0.4 to 0.8, more preferably 0.5 to 0.7, when the depolymerization scheduled time is 1. It is. If the ratio is less than 0.4, the bishydroxyethyl terephthalate and / or its low polymer existing in the molten state are likely to solidify, and the depolymerization reaction is difficult to proceed, and the agitator is overloaded and installed. There is also a risk of destroying. When the ratio is larger than 0.8, the depolymerization reaction proceeds smoothly, but diethylene glycol, which is a by-product, is easily generated, which is not preferable.

  In the depolymerization reaction, a known depolymerization catalyst such as an alkali metal, an alkaline earth metal, a compound such as zinc, cobalt, or manganese may be used.

  Furthermore, in this application, the polyester composition excellent in the quality can be obtained by carrying out polycondensation reaction using the bishydroxyethyl terephthalate and / or its low polymer obtained by the said depolymerization method.

  Since bishydroxyethyl terephthalate and / or its low polymer obtained by depolymerizing polyester waste are recycled, the polyester finally obtained has a thermal history. For this reason, there has been a problem that the polymer obtained after the polycondensation reaction becomes yellowish. However, the coloration of the polyester is not limited to the polyester obtained by the depolymerization reaction and the subsequent polycondensation reaction, but an ester reaction or ester from a carboxylic acid such as terephthalic acid or dimethyl diterephthalate and a diol typified by ethylene glycol or the like. The same applies to polyesters obtained by polycondensation reaction using bishydroxyethyl terephthalate and / or its low polymer obtained from the exchange reaction. The present application has found that a polyester composition excellent in quality can be obtained by polycondensation reaction of bishydroxyethyl terephthalate and / or its low polymer obtained by the above depolymerization method.

  Coloring of polyester and deterioration of heat resistance are caused by a side reaction of polyester as clearly shown in a saturated polyester resin handbook (Nikkan Kogyo Shimbun, first edition, P.178-198). In the side reaction of this polyester, carbonyl oxygen is activated by a metal catalyst, and β hydrogen is extracted, thereby generating a vinyl end group component and an aldehyde component. By forming a polyene by this vinyl end group, the polymer is colored yellow, and since an aldehyde component is generated, the main chain ester bond is cleaved, so that the polymer has poor heat resistance. In particular, when a titanium compound is used as a polycondensation catalyst, since the side reaction due to heat is strongly activated, a large amount of vinyl end group components and aldehyde components are generated, resulting in a yellow colored polymer having poor heat resistance. The phosphorus compound plays a role of regulating the activity of the polycondensation catalyst by appropriately interacting with the polycondensation catalyst. However, in the conventional method in which the phosphorus compound is added before the start of the polycondensation reaction, it is inevitable to reduce the polycondensation activity as well as the side reaction activity of the polycondensation catalyst. However, according to the present invention, it is possible to keep only the side reaction activity extremely small while sufficiently maintaining the polycondensation activity of the polycondensation catalyst.

  Further, the present inventors have examined the coloring mechanism of the polyester in detail. As a result, the polycondensation reaction of the polyester is substantially completed in the β-hydrogen abstraction of the polyester and the reaction generated by the vinyl end group component and the aldehyde component. It was found that it occurred in large quantities immediately afterwards, and thereafter, a reaction in which a vinyl end group component was formed into polyene proceeded, and it was difficult to suppress even by addition of a phosphorus compound.

  Therefore, by adding a phosphorus compound not after the polycondensation reaction of the polyester is substantially completed but before the polycondensation reaction is substantially completed, the extraction of β hydrogen and the vinyl end groups that occur immediately after the completion of the polycondensation reaction are achieved. It has been found that the production of components and aldehyde components can be specifically suppressed. This cannot be achieved by the conventional phosphorus compound or the addition method of the phosphorus compound.

  In the present invention, the phosphorus compound is added at a stage of 85% or more and less than 99% of the IV setting value of the polyester. More preferably, it is between 90% and 97.5%, and particularly preferably between 92% and 96%. When the addition of the phosphorus compound is 99% or more of the point at which the polycondensation reaction is completed, it is the same as that added after the polycondensation of the polyester is substantially completed due to the dispersion time of the phosphorus compound, etc. Therefore, it becomes impossible to discharge stably and the chip shape becomes non-uniform, which may cause changes in physical properties and equipment troubles in the subsequent drying process or melting process, which is not preferable. If it is less than 85%, the polycondensation reaction is delayed, and the polymer color tone is deteriorated. The IV value of the polyester at the time when the phosphorus compound is added may be directly sampled and subjected to IV measurement by the method described later, but may be calculated from the torque load applied to the stirring blade of the reaction vessel.

  The phosphorus compound according to the present invention may be added in several divided portions, or may be continuously added with a feeder or the like, but in the case of batch polycondensation, when adding a phosphorus compound, The phosphorus compound may be added alone, or may be added in a state dissolved or dispersed in a diol component such as ethylene glycol. However, if a diol component such as ethylene glycol is brought in and added in a large amount, depolymerization of the polyester (polyester main chain cleavage reaction) proceeds, so it is preferable to add the phosphorus compound alone.

  The phosphorus compound added in the present invention is a trivalent phosphorus compound, and refers to phosphite compounds, phosphonite compounds, phosphinite compounds, phosphine compounds, and alkyl esters or aryl esters thereof. These trivalent phosphorus compounds convert a peroxide generated by a side reaction (R—O—OH further promotes the side reaction) to alcohol (R—OH), and turn into a pentavalent phosphorus compound. This significantly suppresses the side reaction of the polyester.

  In the present invention, the phosphorus compound added between the start of pressure reduction in the polycondensation reaction vessel after the addition of the polycondensation catalyst and before the completion of the polycondensation of the polyester is in the range of 100 to 400 ° C. It is preferable that When the melting point is less than 100 ° C., the phosphorus compound is scattered when the phosphorus compound is added under reduced pressure, and a desired amount of the phosphorus compound may not be added to the polyester. The melting point of the phosphorus compound is preferably in the range of 115 to 350 ° C., and more preferably in the range of 175 to 300 ° C. so that the phosphorus compound does not scatter under reduced pressure conditions and is uniformly dispersed. The phosphorus compound according to the present invention can be dissolved or melted in the polycondensation system, and is preferably added in a capsule made of a polymer having substantially the same component as the polymer obtained in the present invention. When the phosphorus compound is added to the capsule as described above and added, the phosphorus compound can be prevented from being scattered in the polycondensation reaction vessel under reduced pressure conditions and distilling into the reduced pressure line, A desired amount of phosphorus compound can be added to the polymer. The capsule referred to in the present invention is not limited as long as the phosphorus compound is collected, and includes, for example, an injection-molded container having a lid or a stopper, or a sheet or film sealed or sewn into a bag shape. . It is more preferable that the capsules make air vents such as holes. When a phosphorus compound is added to a capsule that has been ventilated, even if it is added to the polycondensation reaction vessel under vacuum conditions, the capsule bursts due to air expansion and the phosphorus compound distills into the decompression line, or the polycondensation reaction vessel A desired amount of a phosphorus compound can be added to the polymer without adhering to the upper part or wall surface of the polymer. If the capsule is too thick, it takes longer to dissolve and melt, so it is better to make the capsule thinner. However, the capsule should be thick enough not to burst during the encapsulation / addition operation of the phosphorus compound. For this purpose, a uniform and non-uniform thickness with a thickness of 10 to 500 μm is preferable.

  Specific examples of the phosphorus compound added in the present invention include bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol-di-phosphite (melting point: 234) represented by the following formula 1. ˜240 ° C.) and tris [2-{(2,4,8,10-tetra-t-butyldibenz [d, f] [1,3,2] -dioxaphosphine- 6-yl) oxy} ethyl] amine (melting point: 190-210 ° C.), 6- [3- (3-tert-butyl-4-hydroxy-5-methyl) propoxy] -2,4 represented by formula 3 , 8,10-tetra-t-butyldibenz [d, f] [1,3,2] -dioxaphosphine (melting point: 115 ° C. to 125 ° C.), tetrakis (2,4- Di-t-butyl-5-methylphenyl) [1,1- Phenyl] -4,4'-diyl bis phosphonite (mp: 234-240 ° C.) are preferred. In these compounds, Formula 1 is ADK STAB PEP-36 (manufactured by ADEKA Corporation), Formula 2 is IRGAFOS12 (manufactured by Ciba Specialty Chemicals), Formula 3 is Sumitizer GP (manufactured by Sumitomo Chemical Co., Ltd.), and Formula 4 is ( It is available as GSY-P101) manufactured by Osaki Industrial Chemical Co., Ltd. These compounds may be used alone or in combination.

  In the present invention, the trivalent phosphorus compound added at a stage of 85% or more and less than 99% of the IV setting value of the polyester should be added so as to be 10 to 200 ppm in terms of phosphorus atoms with respect to the obtained polyester. Is preferable in order to reduce the color tone of the polyester and the coloration in the production process of the molded product on fibers, films, bottles and the like. If the addition amount is less than the above range, it does not reach the desired effect, and if the addition amount is more than the above range, the phosphorus compound is insufficiently dispersed, so that it cannot be stably discharged from the polycondensation reaction vessel. Since the chip shape is not uniform, it may cause a change in physical properties and equipment trouble in the subsequent drying process or melting process, which is not preferable. The amount of phosphorus added is preferably 12 to 150 ppm, more preferably 15 to 100 ppm.

  In the polyester according to the present invention, a titanium compound, an antimony compound, a germanium compound, an aluminum compound, or the like is used as a polycondensation catalyst. These polycondensation catalysts may be used alone or in combination, or in addition, compounds such as sodium, potassium, lithium, magnesium, calcium, zinc, cobalt and manganese may be used in combination. These polycondensation catalysts are preferably added in an amount of 1 to 1000 ppm in terms of metal atoms with respect to the resulting polyester. Among these, it is preferable to use a titanium compound as a polycondensation catalyst because generation of foreign matters is suppressed.

  When the polycondensation catalyst is a titanium compound, it is preferable to add 1 to 30 ppm in terms of titanium atom with respect to the obtained polyester. When the content is 2.5 to 15 ppm, the thermal stability and color tone of the polymer are more preferable, and more preferably 4 to 10 ppm.

  The titanium compound used as the polycondensation catalyst is preferably a titanium complex having a polycarboxylic acid and / or hydroxycarboxylic acid and / or nitrogen-containing carboxylic acid as a chelating agent from the viewpoint of thermal stability and color tone of the polymer. . Examples of chelating agents for titanium compounds include polyvalent carboxylic acids such as phthalic acid, trimellitic acid, trimesic acid, hemititic acid, pyromellitic acid, and hydroxycarboxylic acids such as lactic acid, malic acid, tartaric acid, and citric acid. As the nitrogen-containing carboxylic acid, ethylenediaminetetraacetic acid, nitrilotripropionic acid, carboxyiminodiacetic acid, carboxymethyliminodipropionic acid, diethylenetriaminopentaacetic acid, triethylenetetraminohexaacetic acid, iminodiacetic acid, iminodipropionic acid Hydroxyethyliminodiacetic acid, hydroxyethyliminodipropionic acid, methoxyethyliminodiacetic acid and the like. These titanium compounds may be used alone or in combination.

  In addition to particles such as titanium oxide, silicon oxide, calcium carbonate, silicon nitride, clay, talc, kaolin, silicon, carbon black, additives such as anti-coloring agents, stabilizers, antioxidants, etc. It may be contained within the range.

  The polycondensation step in the method for producing polyester according to the present invention is expected to have a more remarkable improvement effect in a batch system. In the case of a batch system, when a desired setting IV is reached, an inert gas is caused to flow into the reactor, the inside of the reactor is brought to normal pressure or pressure, the polycondensation reaction is stopped, and the mixture is discharged out of the reaction vessel.

Hereinafter, the present invention will be described in more detail with reference to examples. In addition, the physical-property value in an Example was measured with the following method.
(1) Intrinsic viscosity of polymer IV
Measurement was performed at 25 ° C. using orthochlorophenol as a solvent.
(2) Color tone of polymer Using a color difference meter (SM color computer model SM-T45, manufactured by Suga Test Instruments Co., Ltd.), it was measured as a Hunter value (L, b value).

      The L value and b value of the polymer sampled in half the time in terms of weight in the discharge process are used as the color tone representative of the polymer. For example, when 2 tons of polymer is discharged, the polymer at 1000 kg is sampled.

      The obtained polymer b value was judged according to the following criteria.

◎: Lower than 7.6 ○: 7.6 or higher, 10.5 or lower ×: higher than 10.5 (3) Bishydroxyethyl terephthalate and / or its low polymer and polymer diethylene glycol content Bishydroxyethyl terephthalate and / or its The low polymer and polyester were thermally decomposed with monomethanolamine, diluted with 1,6 hexanediol / methanol, neutralized with terephthalic acid, and determined from the peak area of gas chromatography.

      The amount of diethylene glycol in the resulting bishydroxyethyl terephthalate and / or its low polymer was judged according to the following criteria. In addition, the sampling method of bishydroxyethyl terephthalate and / or its low polymer is not particularly limited, but it is necessary to measure what the depolymerization reaction has been completed. You may sample from the attached sampling tube.

◎: Lower than 1.2 ○: 1.2 or higher and 1.6 or lower ×: higher than 1.6 The amount of diethylene glycol of the obtained polymer was judged according to the following criteria.

◎: Lower than 1.9 ○: 1.9 or higher, 2.3 or lower ×: higher than 2.3 (4) Content of titanium element, phosphorus element, antimony element, etc. in polymer X-ray fluorescence elemental analyzer ( It was obtained by HORIBA, Ltd., MESA-500W type.

Example 1
In a depolymerization reaction vessel equipped with a rectifying column, a polyester waste feeder, and a stirrer, bishydroxyethyl terephthalate having a molar ratio of 1.5 and / or 2000 kg of its low polymer was present at 220 ° C. under a nitrogen atmosphere at normal pressure. Keep it. Thereto, 2000 kg of polyester waste having a molar ratio of ethylene glycol / polyester waste of 0.5 and 325 kg of ethylene glycol are continuously supplied over 3 hours. After the supply is completed, the temperature of the reaction vessel is raised to 240 ° C. over 30 minutes, and is kept at 240 ° C. after the temperature rise. After the tower top temperature of the rectifying column reached 160 ° C., the depolymerization reaction was completed in 20 minutes to obtain bishydroxyethyl terephthalate and / or its low polymer. At this time, ethylene glycol did not reach the top of the rectifying column. The depolymerization reaction process was 4 hours and 20 minutes. The obtained bishydroxyethyl terephthalate and / or its low polymer was sampled, and the amount of diethylene glycol was measured and found to be 1.2% by weight.

  This bishydroxyethyl terephthalate and / or its low polymer was transferred to a polycondensation reaction vessel through a filter (nominal opening 40 μm), and 110 g of phosphoric acid (55 ppm as the phosphoric acid concentration in the resulting polyester) was added. Thereafter, the mixture was stirred for 6 minutes. Thereafter, 600 g of antimony trioxide (300 ppm as the concentration of antimony trioxide in the obtained polyester), 340 g of cobalt acetate (170 ppm as the concentration of cobalt acetate in the obtained polyester), and 6 kg of titanium oxide (oxidation in the obtained polyester) are added. 0.3% for titanium). Thereafter, while stirring the low polymer at 30 rpm, the reaction temperature was gradually raised from 240 ° C. to 290 ° C., and the pressure was lowered to 40 Pa. When a predetermined stirring torque was reached, the reaction system was purged with nitrogen and returned to normal pressure to stop the polycondensation reaction. After cooling in the form of a strand and cooling, cutting was performed immediately to obtain polymer pellets. The time from the start of decompression to the arrival of the predetermined stirring torque was 2 hours and 55 minutes. The obtained polyester had a polymer L value of 60, a polymer b value of 8.5, and diethylene glycol of 1.9% by weight.

Examples 2-18
Molar ratio of the low polymer existing in the molten state, depolymerization reaction temperature, tower top temperature of the rectification tower, time after reaching the tower top temperature of the rectification tower, mole ratio of polyester waste / ethylene glycol, polyester waste / Ethylene glycol was charged under the same conditions as in Example 1 except that the method of adding polyester, the type of polyester waste, the polycondensation catalyst and the phosphorus compound were changed as shown in Table 1. As shown in Table 1, the polyester obtained by bishydroxyethyl terephthalate and / or its low polymer having excellent quality and then obtained by polycondensation reaction was excellent in quality.

Example 19
The excellent quality bishydroxyethyl terephthalate and / or its low polymer obtained by the method described in Example 1 was transferred to a polycondensation reaction vessel through a filter (nominal opening 40 μm), and 5 ppm in terms of titanium atom. 166 g of a corresponding citrate chelate titanium compound is added, 340 g of cobalt acetate (170 ppm as the concentration of cobalt acetate in the resulting polyester), and 6 kg of titanium oxide (0.3% of titanium oxide in the resulting polyester) are added. Thereafter, while stirring the low polymer at 30 rpm, the reaction temperature was gradually raised from 240 ° C. to 290 ° C., and the pressure was lowered to 40 Pa. When 95% of the predetermined stirring torque (IV set value) is reached (2 hours and 45 minutes from the start of decompression), the equivalent of 250 ppm (25 ppm in terms of phosphorus atoms) from the top of the reaction can with respect to the polymer Bis (2,6-di-tert-butyl-4-methylphenyl) pentaerythritol-di-phosphite (manufactured by ADKA, ADK STAB PEP-36, melting point 236 ° C., polyethylene terephthalate in advance by injection molding to a thickness of 200 μm Then, 500 g of a container having an internal volume of 500 cm ^{3 and} a container formed on its lid (packed in a container and a lid having a weight of 30 g) were added. Thereafter, the reaction is continued, and when the predetermined stirring torque is reached, the reaction system is purged with nitrogen and returned to normal pressure to stop the polycondensation reaction, discharged into a strand, cooled, and immediately cut to remove polymer pellets. Obtained. The time from the start of decompression to the arrival of the predetermined stirring torque was 2 hours and 55 minutes. The obtained polyester had a polymer L value of 58, a polymer b value of 9.2, and diethylene glycol of 1.9% by weight, and was excellent in quality.

Examples 20-28
The same conditions as in Example 19 were followed except that the polycondensation catalyst, the phosphorus compound to be added, the addition amount of the phosphorus compound, and the addition timing of the phosphorus compound were changed as shown in Table 1. As shown in Table 1, the polyester was excellent in quality.

Comparative Examples 1-5, 7, 8, 10
The molar ratio of the low polymer present in the molten state, the depolymerization reaction temperature, the tower top temperature, the presence or absence of ethylene glycol distillation from the tower top, the polyester waste / ethylene glycol mole ratio, It implemented on the same conditions as Example 1 except having changed the polycondensation reaction catalyst and the phosphorus compound as Table 2. FIG. As shown in Table 2, since it was bishydroxyethyl terephthalate and / or its low polymer inferior in quality, the polyester obtained by the polycondensation reaction thereafter had poor quality.

Comparative Example 6
The reaction was carried out under the same conditions as in Example 1 except that the depolymerization reaction temperature was changed as shown in Table 2. As shown in Table 2, bishydroxyethyl terephthalate and / or its low polymer were excellent in quality, but the polyester obtained by the polycondensation reaction thereafter had poor color tone.

Comparative Example 9
The polyester waste / ethylene glycol supply method was charged all at once into the reaction vessel. However, the bishydroxyethyl terephthalate and / or its low polymer that had previously existed in the reaction vessel solidified, and the stirrer was overloaded. The polymerization reaction was stopped.

Comparative Example 11
A depolymerization reaction and a subsequent polycondensation reaction were performed by the method described in Comparative Example 1 except for the timing of addition of the phosphorus compound. The addition timing of the phosphorus compound is that after the polyester reaches the target IV, the valve of the distilling tube is closed and the inside of the polycondensation reactor is kept in a reduced pressure state, and the phosphorus compound is added and stirred for 10 minutes, and then mixed. Thereafter, discharging was performed. The quality of bishydroxyethyl terephthalate and / or its low polymer obtained by the depolymerization reaction was poor, and then the polyester obtained was poor.

Comparative Example 12
The depolymerization reaction and the subsequent polycondensation reaction were carried out by the method described in Comparative Example 3 except for the timing of adding the phosphorus compound. The quality of bishydroxyethyl terephthalate and / or its low polymer obtained by the depolymerization reaction was poor and the addition timing of the phosphorus compound was carried out as shown in Table 2. However, the polycondensation catalyst was deactivated and the target IV was achieved. Did not reach.

Comparative Example 13
A depolymerization reaction and a subsequent polycondensation reaction were performed by the method described in Comparative Example 4 except for the addition amount of the phosphorus compound. The quality of the bishydroxyethyl terephthalate and / or its low polymer obtained by the depolymerization reaction was poor, the dispersibility of the phosphorus compound added in the subsequent polycondensation reaction in the polyester was insufficient, and the discharge was not possible.

Claims (5)

  Bishydroxyethyl terephthalate having a molar ratio of ethylene glycol to acid component of 1.3 to 2.0 and / or a low polymer thereof in a molten state is present in a reaction vessel having a rectifying column at the top, and polyester is contained in the reaction vessel. Scrap and ethylene glycol are continuously supplied, and the top temperature of the rectifying column is lower than the boiling point of ethylene glycol at 205 to 250 ° C. and without substantially distilling ethylene glycol from the rectifying column. A method for producing a polyester, comprising performing a depolymerization reaction and then polycondensing the reaction product.   The method for producing a polyester according to claim 1, wherein the molar ratio (ethylene glycol / polyester waste) of the polyester waste and ethylene glycol continuously supplied to the reaction vessel is 0.3 to 1.0.   The method for producing a polyester according to claim 1 or 2, wherein the depolymerization reaction is completed in 10 to 30 minutes from the time when the top temperature of the rectifying column reaches 160 ° C.   The method for producing a polyester according to any one of claims 1 to 3, wherein a titanium compound is used as a catalyst for the polycondensation reaction.   The polyester according to any one of claims 1 to 4, wherein a trivalent phosphorus compound of 10 to 200 ppm in terms of phosphorus is added at a time of 85 to 99% with respect to the target IV of the obtained polymer. Manufacturing method.