JP2007100011A - Production method and production apparatus for polyester - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer such as polylactic acid of high quality through the production of a cyclic condensate such as a lactide being reduced in optical isomerization and heat degradation. <P>SOLUTION: This production method for a polyester comprises a step of the ring-opening polymerization of a cyclic dimer formed by the transformation, through depolymerization, of a fused condensate of a hydroxycarboxylic acid in the presence of a polymerization catalyst in a reactor. The depolymerization is carried out by supplying continuously the fused condensate, while measuring a retained amount of the fused condensate in the reactor and forming thin layers of the condensate using external force. A production apparatus for the polyester is also disclosed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polymer synthesis method and apparatus for synthesizing a polymer from a molten polymer raw material.

  In general, in the synthesis of a polymer, as the temperature history becomes longer, the raw material or the polymer may partially be thermally decomposed, which may cause a problem of quality degradation of the final polymer. In addition, when an asymmetric carbon is present in the raw material molecule among the polymers, a part of the optical isomerization occurs with the temperature history, and quality degradation of the final polymer may be a problem.

  Polylactic acid, which is one of polymers synthesized by a ring-opening polymerization reaction, is a polyester made from lactic acid, which is one of hydroxycarboxylic acids, as a raw material. One method of synthesizing polylactic acid from lactic acid is to condense lactic acid to form oligomers, and then add a catalyst such as tin 2-ethylhexanoate or antimony oxide to cause a depolymerization reaction under reduced pressure. There is a method. There is a method in which lactide (a dimer of lactic acid) as a cyclic condensate is produced by this method, and a catalyst such as tin octylate is added to lactide to perform ring-opening polymerization. Even in this case, there is a possibility of thermal decomposition due to the thermal history of each step. For example, polyglycol synthesized by converting glycolic acid into glycolide, which is a cyclic dimer, and ring-opening polymerization thereof. The same applies to polymers of other hydroxycarboxylic acids, such as acids. Incorporation of pyrolyzate is undesirable because it can cause deterioration of physical properties such as product polymer coloring.

  In the case of polylactic acid, an asymmetric carbon is further contained in the lactic acid molecule serving as the polymer skeleton, and therefore, a part of the optical isomerization (D-lactic acid) may occur through the enolization reaction due to the thermal history of the depolymerization process. (FIG. 1). In polylactic acid, homopolymers usually using L-lactic acid as a raw material are often synthesized. This is because, when part of the lactic acid skeleton that constitutes polylactic acid is optically isomerized, the crystallinity of the polymer is lowered according to the amount, so that the polymer physical properties are deteriorated such as lowering of melting point and lowering of hydrolysis resistance. It is.

  For this reason, in the invention described in Patent Document 1, depolymerization is performed by bringing an oligomer and a catalyst into contact in a tank-type reaction tank under a reduced pressure environment. The crude lactide produced thereby is separated by distillation using the difference in boiling point, and a purification step is installed to increase the purity of LL-lactide by separating the mesolactide (lactide made of L-lactic acid and D-lactic acid) by distillation. Other purification methods include melt crystallization using a difference in melting point and solvent crystallization using a difference in solubility in a solvent. However, in any method, the thermal decomposition product and meso lactide generated are removed in the purification step, and a part of LL-lactide is lost. For this reason, the yield of a raw material falls, it has contributed to the price increase of a product polymer, and development of the technique which suppresses the thermal decomposition and optical isomerization in a depolymerization process is required. In the invention described in Patent Document 2, a thin film evaporator is applied to the reaction tank in order to terminate the depolymerization reaction in a short time and suppress optical isomerization. However, in the present invention, the relationship between the time of depolymerization reaction and optical isomerization is not specified, and it is described how to use a thin film evaporation apparatus from the viewpoint of suppressing optical isomerization. It has not been. For this reason, suppression of optical isomerization during depolymerization has been difficult.

Japanese Patent No. 3258324 Japanese Patent Laid-Open No. 10-168077

  The subject of this invention is providing the polyester synthesis method and apparatus which can synthesize | combine a high quality polymer with a high yield, when synthesize | combining a polymer from the raw material of a molten state.

As a result of intensive studies to solve the above-mentioned problems, the present inventors converted the condensate melt of hydroxycarboxylic acid into a cyclic dimer by depolymerization in the presence of a polymerization catalyst in the reaction vessel, A process for producing a polyester comprising the step of ring-opening polymerization of the polyester,
The amount of residence of the condensate melt in the reaction vessel is measured, and the condensate melt is continuously supplied on the basis thereof, and the condensate melt is thinned and depolymerized using an external force. It came to invent the manufacturing method of polyester to make.

The present invention also provides a reaction vessel, a means for supplying a melt of a condensate of hydroxycarboxylic acid to the reaction vessel, a means for supplying a polymerization catalyst to the reaction vessel, and thereby contacting the catalyst in the reaction vessel. An apparatus for producing a polyester by converting it into a cyclic dimer by depolymerization by means of ring-opening polymerization,
Provided is a polyester production apparatus characterized by having a thin-film evaporation apparatus provided with an apparatus for measuring the residence amount of the condensate melt, thereby thinning and depolymerizing the condensate melt. It is.

  According to the present invention, a high quality polymer can be synthesized in a high yield.

  The depolymerization step for converting the condensate melt of lactic acid into lactide includes a depolymerization reaction for producing lactide from the condensate melt and its reverse chemical reaction, and an evaporation reaction for the produced lactide.

  It has been found that the depolymerization reaction is accelerated in proportion to the 4/3 power of the concentration of the catalyst added, and is accelerated by increasing this, while the optical isomerization reaction shown in FIG. 1 is similarly accelerated. In addition, a method for lowering the depolymerization temperature is not desirable because the depolymerization reaction itself is slowed together with the optical isomerization reaction and the operation efficiency of the process is lowered. Therefore, continuous supply of the condensate melt, continuous discharge of the produced crude lactide, addition / dispersion of the catalyst before depolymerization to the continuously supplied condensate melt, and constant retention of the condensate melt in the reaction vessel. By at least one, the catalyst concentration in the condensate melt is made constant. At the same time, the height or depth of the liquid of the condensate melt is decreased to increase the interfacial area with the gas phase, and the evaporation of the produced lactide is accelerated (retention is proportional to the liquid power 1/2) It has been found that the heat history time in the depolymerization process is shortened by increasing the time), and the number of optical isomerization reactions is reduced. And it discovered that thermal decomposition could also be reduced by the method of the present invention.

  One embodiment of the present invention is a method for producing a polyester by converting a condensate melt of hydroxycarboxylic acid into a cyclic dimer by depolymerization by contact with a catalyst, and subjecting this to a ring-opening polymerization. In this method, the condensate melt can be continuously fed into the reaction vessel in a reduced pressure environment while measuring the amount of residence, and depolymerized by thinning using an external force.

  Another embodiment is a method for producing a polyester by converting a condensate melt of hydroxycarboxylic acid into a cyclic dimer by depolymerization by contact with a catalyst, and subjecting this to ring-opening polymerization. According to this method, after the catalyst is added to and dispersed in the condensate melt, it can be continuously supplied into the reaction vessel in a reduced pressure environment, and thinned using an external force for depolymerization.

  In another embodiment, a condensate melt of hydroxycarboxylic acid is continuously supplied to a reduced pressure environment, and is converted into a cyclic dimer by depolymerization by thinning using an external force, and this is subjected to ring-opening polymerization. This is a method for producing polyester. According to this method, polyester synthesis including at least one of gravity and centrifugal force as an external force used for the thinning can be performed.

  Another embodiment is an apparatus for producing a polyester by converting a condensate melt of hydroxycarboxylic acid into a cyclic dimer by depolymerization by contact with a catalyst, and subjecting this to ring-opening polymerization. According to this apparatus, the thinning and depolymerization of the condensate melt can be performed by a thin film evaporation apparatus provided with a residence amount measuring device. As the thin film evaporator, a horizontal centrifugal thin film evaporator is particularly preferable.

  Another embodiment is an apparatus for producing a polyester by converting a condensate melt of hydroxycarboxylic acid into a cyclic dimer by depolymerization by contact with a catalyst, and subjecting this to ring-opening polymerization. After adding and dispersing the catalyst in the condensate melt in advance, the catalyst can be flowed down along the outer surface of the structure installed in a reduced pressure environment, whereby thinning and depolymerization can be performed.

  The polymer synthesis method and apparatus of the present invention are suitably used for polymerizing a polymer produced by a ring-opening polymerization reaction. About the polymer produced | generated by ring-opening polymerization reaction, it uses suitably for the polymer raw material of a cyclic condensate, especially the polymer synthesize | combined by the ring-opening polymerization reaction of a cyclic dimer, especially polyester. For example, polylactic acid, a copolymer containing lactic acid as a main component, a polyglycolic acid, a copolymer containing glycolic acid as a main component, a homopolymer of hydroxycarboxylic acid, and a copolymer containing these.

  The method and apparatus of the present invention are particularly preferably used for the synthesis of polylactic acid by ring-opening polymerization of lactide and polyglycolic acid by ring-opening polymerization of glycolide. Here, lactide used as a raw material for polylactic acid means a cyclic ester produced by dehydrating two molecules of water from two molecules of lactic acid, and polylactic acid means a polymer mainly composed of lactic acid, Poly L-lactic acid homopolymer, poly D-lactic acid homopolymer, poly L / D-lactic acid copolymer, and other ester bond-forming components such as hydroxy carboxylic acid, lactones, dicarboxylic acid and diol Copolymerized polylactic acid obtained by copolymerizing and the like, and those in which additives are mixed as secondary components are included.

  Glycolide means a cyclic ester produced by dehydrating two molecules of water from two molecules of glycolic acid, polyglycolic acid means a polymer mainly composed of glycolic acid, and other ester bond-forming components For example, hydroxycarboxylic acids, lactones, copolymerized polyglycolic acid obtained by copolymerizing dicarboxylic acid and diol, and those obtained by mixing additives as secondary components are included. Examples of hydroxycarboxylic acids other than lactic acid and glycolic acid include hydroxybutylcarboxylic acid and hydroxybenzoic acid, examples of lactones include butyrolactone and caprolactone, and examples of dicarboxylic acids include aliphatic dicarboxylic acids having 4 to 20 carbon atoms. There are aromatic dicarboxylic acids such as acid, phthalic acid, isophthalic acid, terephthalic acid and naphthalenedicarboxylic acid.

  Examples of the diol include aliphatic diols having 2 to 20 carbon atoms. Polyalkylene ether oligomers and polymers such as polyethylene glycol, polypropylene glycol, and polybutylene ether are also used as copolymerization components.

  Similarly, oligomers and polymers of polyalkylene carbonate are also used as copolymerization components. Examples of additives include antioxidants, stabilizers, ultraviolet absorbers, pigments, colorants, inorganic particles, various fillers, mold release agents, plasticizers, and the like. The addition ratio of these copolymerization components and additives is arbitrary, but the main component is lactic acid or derived from lactic acid, and the copolymerization components and additives are preferably 50% by weight or less, particularly preferably 30% or less.

  The polymer synthesis method and apparatus of the present invention are for converting a condensate of a raw material into a cyclic condensate that is an intermediate raw material in a molten state. The molten condensate is continuously supplied and heated. The depolymerization is performed by bringing the catalyst into contact with the catalyst and placing it in a reduced pressure environment. A raw material means the monomer used as the frame | skeleton structural element of the polymer to superpose | polymerize. In the case of polylactic acid, it is lactic acid, and in the case of polyglycolic acid, it is glycolic acid. The raw material condensate is an aggregate of low molecular weight polymers in which the raw material molecules themselves are ester-linked in a plurality of linear forms by a condensation reaction, and is hereinafter referred to as an oligomer.

  The oligomer usually includes a low molecular weight polymer having a polymerization degree of 1 or more and a plurality of polymerization degrees. A cyclic condensate is a low molecular weight polymer in which a plurality of raw material molecules are ester-linked in a cyclic manner, and is an intermediate raw material for ring-opening polymerization. In the case of polylactic acid and polyglycolic acid, they are lactide and glycolide, which are cyclic dimers, respectively. In the present specification, the reaction liquid includes all melted products and products circulated in the synthesis process, such as molten oligomer, a mixture of oligomer and catalyst, a mixture of oligomer, catalyst, and cyclic condensate.

  In the present invention, continuously synthesizing has a meaning usually used in the technical field. Therefore, when the time period for supplying raw materials and the like and discharging the products and reaction liquids overlap at least partially, or when supplying raw materials etc. continuously and discharging the products and reaction liquids continuously Is included.

  In order for the oligomer to be in a molten state, the heating temperature needs to be higher than the melting point of the oligomer. Although melting | fusing point changes with the polymerization degree distribution of an oligomer, the kind of raw material monomer, a compounding rate, etc., it is 100-250 degreeC normally, Preferably it is 180-220 degreeC.

  As a catalyst for the polymerization reaction, those skilled in the art can appropriately select a suitable catalyst depending on the polymer to be synthesized. For example, as a catalyst used for depolymerization of an oligomer of lactic acid or glycolic acid, a conventionally known catalyst for ring-opening polymerization of polylactic acid or polyglycolic acid can be used. For example, periodic groups IA, IVA, IVB A catalyst containing at least one metal or metal compound selected from the group consisting of Group VA and Group VA can be used.

  Examples of those belonging to the group IVA include organotin-based catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate, tin α-naphthoate). , Β-naphthoic acid tin, 2-ethylhexanoic acid tin, etc.), and powdered tin. Examples of those belonging to Group IA include alkali metal hydroxides (for example, sodium hydroxide, potassium hydroxide, lithium hydroxide), alkali metal and weak acid salts (for example, sodium lactate, sodium acetate, sodium carbonate). Sodium octylate, sodium stearate, potassium lactate, potassium acetate, potassium carbonate, potassium octylate, etc.), alkali metal alkoxides (eg sodium methoxide, potassium methoxide, sodium ethoxide, potassium ethoxide, etc.) Can be mentioned. Examples of those belonging to Group IVB include titanium compounds such as tetrapropyl titanate and zirconium compounds such as zirconium isopropoxide. Examples of those belonging to Group VA include antimony compounds such as antimony trioxide. Among these, an organotin catalyst or a tin compound is particularly preferable from the viewpoint of activity.

  If the catalyst is a liquid or powdered solid, it is added to the molten oligomer by a catalyst addition apparatus usually used in the technical field, and then the mixed liquid is continuously supplied to the depolymerization apparatus, and the residual liquid after depolymerization is removed. It is added directly to the continuous discharge method and the depolymerizer. Alternatively, any method in which the molten oligomer that has been continuously supplied is brought into contact with each other in the depolymerization apparatus is possible. However, since the catalyst can depolymerize the molten oligomer for a predetermined life (period having catalytic activity), the latter method is taken, and the residual liquid is discharged at a stage where the catalytic activity has decreased, and a new one is taken. The method of adding a catalyst is efficient. In addition, when the catalyst is solid, there is a method in which the catalyst is supported on at least a part of the surface in contact with the molten oligomer in the equipment or structure in the depolymerization apparatus. While this method eliminates the need for a catalyst addition device, the actual contact area with the melted oligomer is reduced compared to the above method, resulting in a slow depolymerization reaction. There are disadvantages such as the need to maintain the structure.

  In the present invention, as shown in FIG. 2 (a), the centrifugal thin film evaporator forms a liquid film by applying the liquid to be concentrated supplied into the apparatus to the inner surface of the apparatus casing by centrifugal force, Evaporation is promoted by heating from the outer surface of the device casing. Centrifugal force is applied to the liquid to be concentrated through a rotating blade and a rotor with blades installed in a fixed device casing. This method has the advantages that the equipment scale can be made compact, and the liquid film thickness can be controlled by controlling the gap width between the blade and the casing and the rotation of the blade. In addition, as a device for thinning and evaporating the concentrated liquid by flowing along the outer surface of the structure installed in a reduced pressure environment, the concentrated liquid is applied to the outer surface of the structure such as a tube group or a plate group from above. Evaporation is promoted by pouring and forming a liquid film along the outer shape (horizontal pipe descending film evaporator [FIG. 2 (b)] or vertical long pipe descending film evaporator [FIG. 2 (c). )]). About structures, such as a tube group and a board group, when it has a heat source in the inside, a liquid film can be heated. This method has an advantage that a thin film can be formed by the flow of a liquid film accompanying gravity without using power.

  Furthermore, as a device having both the characteristics of a centrifugal thin film evaporator and a falling film evaporator, the liquid to be concentrated is poured from above along the inner surface of the structure, and a rotor with blades installed inside the structure is rotated. There is a stirring film type evaporator (FIG. 2D) that scrapes a liquid film having a predetermined thickness or more with a blade and promotes evaporation by heating from the outer surface of the structure. This method has the advantage that the liquid film thickness can be controlled by the gap width between the blade and the casing while the thin film is formed by the flow of the liquid film accompanying gravity without using power. Any of these apparatuses can be applied to the continuous depolymerization apparatus for molten oligomers in the present invention. Among these, in the case of an apparatus that forms a flow liquid film along the outer surface of the structure by gravity, it is necessary to add and disperse the catalyst in advance because the catalyst cannot be added and dispersed in the middle of the flow. Further, it is desirable to continuously discharge the flow reaching the lower end of the apparatus so as not to stay in the apparatus. This is due to the fact that the flow reaching the lower end of the apparatus contains a high concentration of catalyst, and its remaining may increase optical isomerization.

  On the other hand, in the horizontal centrifugal thin film evaporator [FIG. 2 (a)], the catalyst can be retained in the apparatus, and the catalyst can be dispersed in the molten oligomer by the operation of the rotor and blades. Therefore, even if the molten oligomer is continuously supplied from one end of the apparatus, if the amount corresponds to the discharge amount of the cyclic dimer vapor, the retention amount can be kept constant, so it is not always necessary to continuously discharge from the other end. . When the retention amount increases due to the decrease in the efficiency of the depolymerization reaction due to the decrease in the catalyst activity or the accumulation of residues after depolymerization of the molten oligomer, the liquid in the apparatus is intermittently discharged and a new catalyst is added to the apparatus. Then you can resume driving.

  Hereinafter, embodiments of a method and an apparatus for a depolymerization reaction will be described. All of the embodiments described below relate to the depolymerization step in a series of steps shown in FIG. 3 for synthesizing a polymer from raw material monomers. 4 includes a raw material monomer concentration step, a concentrate condensation step, an oligomer depolymerization step, a cyclic condensate purification step, a ring-opening polymerization step, a residual monomer treatment separation step, and a polymer drying step. The These may be omitted depending on the properties of the polymer and the necessity of the process, or other steps may be added during the process. The residual monomer treatment step can be selected from methods such as desorption / removal of the monomer under a reduced pressure environment and solid phase polymerization at a temperature below the melting point.

  In one embodiment of the present invention, a centrifugal thin film evaporator is used as the depolymerizer. The centrifugal thin film evaporator is depressurized by a vacuum pump installed via a cyclic condensate condenser and an impurity condenser, and a catalyst is intermittently added. The molten oligomer obtained by the concentration and condensation of the raw material monomers is continuously fed into the centrifugal thin film evaporator. The residence amount of the molten oligomer in the apparatus is measured by a residence amount measuring device, and the supply amount is adjusted so as to be constant. A liquid catalyst is added in the centrifugal thin film evaporator, and the molten oligomer and the liquid catalyst are mixed by the rotation of the rotor blades and pressed against the inner surface of the device casing by centrifugal force, and the liquid film follows the shape of the inner surface. Form. The outer surface of the apparatus casing is heated with a heating medium or the like, whereby the liquid film is heated, and the evaporation of the cyclic condensate generated by contact with the catalyst is promoted. The vapor containing the cyclic condensate is discharged out of the centrifugal thin film evaporator and supplied to the cyclic condensate condenser.

  Here, the cyclic condensate is condensed and recovered and transferred to the purification step. Vapor exiting the cyclic condensate condenser enters the impurity condenser where it is liquefied. Condensed impurities are usually discarded. The gas exiting the impurity condenser is discharged out of the system via a vacuum pump.

  For centrifugal thin film evaporators, the above method is a method of applying centrifugal force by rotating the blades in a fixed device casing, and the blades are usually plate-like ones parallel to the rotating shaft and are installed radially from the rotating shaft. There are many cases. In addition, there may be used a screw-like product obtained by twisting the wing. The centrifugal thin film evaporator may be any one whose rotation axis is horizontal to the ground, vertical, or an intermediate angle. Further, a liquid level meter using a liquid head, a dielectric constant of a molten oligomer, a differential pressure, or the like can be applied to the retention amount measuring device.

  Regarding the addition of the catalyst, when the weight of the substance discharged out of the centrifugal thin film evaporator decreases or when the retention amount increases with time, it is considered that the catalyst activity has decreased. Then, once the internal reaction liquid is discharged from the apparatus drain, a predetermined amount of molten oligomer and catalyst are added and mixed, the apparatus operation is resumed, and continuous supply of molten oligomer and continuous discharge of cyclic condensate vapor are started. . When the solid catalyst is installed on the inner surface of the casing or the like, the catalyst supply operation / device is not required.

  As for the cyclic condensate condenser and the impurity condenser, a surface condenser in which the above-mentioned refrigerant indirectly contacts with a metal tube is desirable. This is because the cyclic condensate decomposes to produce an acid when it comes into direct contact with a refrigerant containing water. This hinders the progress of the ring-opening polymerization reaction as an acid catalyst and may cause corrosion of a material such as a condenser. The impurity condensate may contain an optical isomer component having a low melting point, which also generates an acid when contacted with water, which may similarly cause corrosion. In the case of using a refrigerant inert to the cyclic condensate, it is not limited to the above, but in that case, it is necessary to sufficiently dry the refrigerant to reduce moisture.

  In another embodiment of the present invention, a stirring film evaporator is used as the depolymerization device. The inside of the stirring membrane evaporator is depressurized by a vacuum pump installed via a cyclic condensate condenser and an impurity condenser, and the catalyst is intermittently added. A liquid catalyst is added to the molten oligomer obtained by the concentration and condensation of the raw material monomers. The added catalyst is dispersed in the molten oligomer by a dispersing device. And the molten oligomer which disperse | distributed the catalyst is continuously supplied from the stirring film | membrane type evaporator upper part, and flows down along the inner surface of a casing. In the agitated membrane evaporator, the excess thickness portion of the liquid film is removed by a rotary blade, and the production and evaporation of the cyclic condensate by heat transfer from the outer surface of the device casing heated by a heating medium or the like is promoted.

  The rotation of the wing can be stopped if necessary. In this case, it substantially functions as a falling film evaporator. The vapor containing the cyclic condensate is discharged out of the stirred membrane evaporator and supplied to the cyclic condensate condenser. Here, the cyclic condensate is condensed and recovered and transferred to the purification step. Vapor exiting the cyclic condensate condenser enters the impurity condenser where it is liquefied. Condensed impurities are usually discarded. The gas exiting the impurity condenser is discharged out of the system via a vacuum pump.

  As for the stirring film type evaporator, it is desirable that the rotation axis is perpendicular to the ground from the viewpoint of homogenizing the flow of the reaction liquid on the inner surface of the casing. Various falling film evaporators can be applied instead of the stirring film evaporator. Various things, such as a shape and the installation angle with respect to the ground, can be considered. In order to homogenize the flow of the reaction liquid, a contrivance is made so that the flow of the molten oligomer spreads along the outer surface of the structure, that is, the evaporation surface. For example, it is desirable to employ a method in which a plurality of molten oligomer supply ports are installed along the outer surface of the structure.

  Regarding the addition / dispersion of the catalyst, it is desirable to continuously supply the molten oligomer to the molten oligomer, and to mix it using a static mixer or the like before being supplied to the evaporator. This is because if the depolymerization is performed in a non-homogeneous state, the optical isomerization increases locally in the high concentration catalyst region, whereas the depolymerization reaction may be delayed in the low concentration region. The reaction liquid flowing down the evaporation surface is discharged from the apparatus drain. Since there is a high concentration of catalyst that still has activity in the effluent, it can be recycled back to the molten oligomer supply system without being discarded. When the solid catalyst is installed on the inner surface of the casing or the like, the catalyst supply operation / device is not required. For cyclic condensate condensers and impurity condensers, surface condensers are also desirable.

  The present invention will be described in more detail with reference to the following examples, but the scope of the present invention is not limited thereto.

Example 1
FIG. 4 shows an embodiment of a depolymerization step of a lactic acid oligomer in which a centrifugal thin film evaporator is applied to a continuous depolymerization device as an embodiment of a continuous depolymerization step in the polymer synthesizer of the present invention. In this embodiment, the oligomer supply tank 1, the catalyst supply tank 2, the continuous depolymerization device 3, the drain recovery tank 4, the lactide condenser 5, the lactide recovery tank 6, the impurity condenser 7, the impurity recovery tank 8, the vacuum pump 9, Lactide is synthesized by an apparatus including a liquid feed pump 10 to 15, valves 16 to 26, and a liquid level gauge 36. For the lactide condenser 5 and the impurity condenser 7 of the present embodiment, a plurality of stages are prepared as necessary, and either a series or parallel installation is possible. Moreover, it is omissible as needed about the oligomer supply tank 1, the liquid feeding pumps 10-15, and the valves 16-26.

  The valve 16 is opened and the liquid feed pump 10 is operated to continuously supply the molten oligomer from the oligomer supply tank 1 to the continuous depolymerization apparatus 3. The continuous depolymerization apparatus 3 is supplied with the catalyst from the catalyst supply tank 2 as necessary by opening the valve 17 and operating the liquid feed pump 11. In the continuous depolymerization apparatus 3, the inner blade 29 rotates, whereby the molten oligomer and the catalyst are mixed, and the mixed liquid receives centrifugal force and is pressed against the inner surface of the casing 30 to form a liquid film. The molten oligomer residence amount in the continuous depolymerization apparatus 3 is measured by the liquid level gauge 36, and the liquid feed pump 10 is adjusted so as to be constant. A thermocouple 27 is installed in the liquid film portion, and the liquid film temperature can be measured. The output of the thermocouple 27 is sent to the temperature controller 28. The outer surface of the casing 30 is heated by a heat medium jacket 33 having a heat medium heating device 32 under the control of the temperature controller 28 so that the mixed liquid temperature becomes 200 ° C. The lactide generated by depolymerization of the molten oligomer upon contact with the catalyst upon evaporation is evaporated from the liquid film. When the valves 22 to 26 are opened, the steam is discharged from the steam exhaust port 34.

  The discharged steam is supplied to the lactide condenser 5. Here, the lactide is cooled to a temperature close to a melting point of 95 to 98 ° C., condensed, and flows down to the lactide recovery tank 6 to be recovered. Then, the valve 19 is opened, the liquid feed pump 13 is operated, and the lactide is transferred to the purification process. The The vapor exiting the lactide condenser 5 enters the impurity condenser 7, and the impurities are cooled to a temperature close to the melting point of meso lactide at 53 ° C., condensed and recovered in the impurity recovery tank 8. The impurity condensate is discharged out of the system by opening the valve 20 and operating the liquid feed pump 14. The gas exiting the impurity condenser 7 is discharged out of the system via the vacuum pump 9. If the weight of the substance discharged out of the continuous depolymerization apparatus 3 decreases, it is considered that the catalytic activity has decreased. After the liquid feed pump 10 is stopped once, the valve 18 is opened and the liquid feed pump 12 is used. The internal reaction liquid is discharged from the apparatus drain port 35 to the drain recovery tank 4.

  The drain liquid is discharged out of the system by opening the valve 21 and operating the liquid feed pump 15. Thereafter, the feed pump 10 is operated to start supplying the molten oligomer, and the valve 17 is opened, the feed pump 11 is operated to add a predetermined amount of catalyst, and the apparatus operation is restarted.

Crude lactide was synthesized by the apparatus shown in Example 1. The oligomer used in this experiment had a number average molecular weight of 630. When the oligomer detention time in the continuous depolymerization unit 3 is 5 h, the liquid film thickness is 5 cm, and the catalyst (tin 2-ethylhexanoate) concentration is 0.7 kg / m ³ , the increase in the optical isomerization rate in the depolymerization step is 1%. Here, the oligomer residence time is the same as the flow rate of the molten oligomer and the flow rate of the condensate of the steam discharged from the steam exhaust port 34, and the flow rate of the melted oligomer when the liquid film thickness is stabilized / It was defined by the amount of molten oligomer residence. Further, the coloration of polylactic acid ring-opening polymerized with the present lactide is 2.5 in b value, and it is considered that the influence of thermal decomposition during depolymerization is small.

(Example 2)
FIG. 5 shows an example of a depolymerization step of a lactic acid oligomer in which a stirring film evaporator is applied to a continuous depolymerization device as an example of the continuous depolymerization step in the polymer synthesizer of the present invention. In this embodiment, the oligomer supply tank 1, the catalyst supply tank 2, the continuous depolymerization device 3, the drain recovery tank 4, the lactide condenser 5, the lactide recovery tank 6, the impurity condenser 7, the impurity recovery tank 8, the vacuum pump 9, Lactide is synthesized by an apparatus including a liquid feed pump 10 to 15, valves 16 to 26, and a static mixer 37. For the lactide condenser 5 and the impurity condenser 7 of the present embodiment, a plurality of stages are prepared as necessary, and either a series or parallel installation is possible. Moreover, it is omissible as needed about the oligomer supply tank 1, the liquid feeding pumps 10-15, and the valves 16-26.

  The valve 16 is opened and the liquid feed pump 10 is operated to continuously supply the molten oligomer from the oligomer supply tank 1 to the continuous depolymerization apparatus 3. Before the molten oligomer reaches the continuous depolymerization apparatus 3, the valve 17 is opened and the liquid feed pump 11 is operated from the catalyst supply tank 2 to supply the catalyst, and the molten oligomer is dispersed in the molten oligomer by the static mixer 37. In the continuous depolymerization apparatus 3, a mixed solution of molten oligomer and catalyst is poured along the inner surface of the casing 30 from above. The blade 29 of the continuous depolymerization apparatus 3 rotates, and the excessive thickness portion of the liquid film of the mixed liquid is removed to form a liquid film having a uniform thickness. A thermocouple 27 is installed in the liquid film portion, and the liquid film temperature can be measured. The output of the thermocouple 27 is sent to the temperature controller 28.

  The outer surface of the casing 30 is heated by a heat medium jacket 33 having a heat medium heating device 32 under the control of the temperature controller 28 so that the mixed liquid temperature becomes 200 ° C. The lactide generated by the depolymerization of the molten oligomer under the above heating evaporates from the liquid film. When the valves 22 to 26 are opened, the steam is discharged from the steam exhaust port 34. The discharged steam is supplied to the lactide condenser 5. Here, the lactide is cooled to a temperature close to a melting point of 95 to 98 ° C., condensed, and flows down to the lactide recovery tank 6 to be recovered. Then, the valve 19 is opened, the liquid feed pump 13 is operated, and the lactide is transferred to the purification process. The The vapor exiting the lactide condenser 5 enters the impurity condenser 7, and the impurities are cooled to a temperature close to the melting point of meso lactide at 53 ° C., condensed and recovered in the impurity recovery tank 8. The impurity condensate is discharged out of the system by opening the valve 20 and operating the liquid feed pump 14. The gas exiting the impurity condenser 7 is discharged out of the system via the vacuum pump 9.

  The mixed liquid reaching the bottom of the continuous depolymerization apparatus 3 opens the valve 18 and discharges the internal reaction liquid from the apparatus drain port 35 to the drain recovery tank 4 using the liquid feed pump 12. The drain liquid opens the valve 21 and operates the liquid feed pump 15 to be discharged out of the system or returned to the catalyst supply tank 2 as necessary and supplied to the molten lactide.

Crude lactide was synthesized by the apparatus shown in Example 2. The same oligomer as used in Example 1 was used. When the oligomer detention time in the continuous depolymerization apparatus 3 is 5 h, the liquid film thickness is 5 cm, and the catalyst (tin ethyl 2-ethylhexanoate) concentration is 0.7 kg / m ³ , the increase in the optical isomerization rate in the depolymerization step, The coloring of polylactic acid ring-opening polymerized using this lactide was almost the same as in Example 1.

(Comparative example)
Using the same oligomer as in Example 1, batch depolymerization was performed in a conventional tank reactor. The depolymerization time was 10 hours, the initial liquid surface height was 80 cm, and the initial catalyst concentration was 5 kg / m ³ . As a result, regarding the produced lactide, the increase in the optical isomerization rate in the depolymerization step was 9%, and the coloration of the polylactic acid ring-opening polymerized using this lactide was 4.4 in b value.

  From the above, it has been clarified that a high-quality polymer such as polylactic acid can be obtained by obtaining a cyclic condensate such as lactide with little optical isomerization and thermal decomposition by the method of the present invention.

It is a figure explaining the optical isomerization reaction of lactic acid made into object by this invention. It is sectional drawing which shows the evaporation apparatus which can be used with the continuous depolymerization apparatus of this invention. It is a flowchart which shows the whole process of the polymer synthesizer using this invention. It is a schematic diagram which shows one Example of the continuous depolymerization apparatus of this invention. It is a schematic diagram which shows another Example of the continuous depolymerization apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Oligomer supply tank, 2 ... Catalyst supply tank, 3 ... Continuous depolymerization apparatus, 4 ... Drain collection tank, 5 ... Lactide condenser, 6 ... Lactide collection tank, 7 ... Impurity condenser, 8 ... Impurity collection tank, 9 DESCRIPTION OF SYMBOLS ... Vacuum pump, 10-15 ... Liquid feed pump, 16-26 ... Valve, 27 ... Thermocouple, 28 ... Temperature controller, 29 ... Blade, 30 ... Casing, 31 ... Heat-medium circulation pump, 32 ... Heat-medium heating device 33 ... Heat medium jacket, 34 ... Steam exhaust port, 35 ... Device drain port, 36 ... Liquid level gauge, 37 ... Static mixer.

Claims (6)

A process for producing a polyester comprising a step of converting a condensate melt of hydroxycarboxylic acid into a cyclic dimer by depolymerization in the presence of a polymerization catalyst in a reaction vessel, and ring-opening polymerization thereof,
The amount of residence of the condensate melt in the reaction vessel is measured, and the condensate melt is continuously supplied on the basis thereof, and the condensate melt is thinned and depolymerized using an external force. A method for producing polyester.   The polymerization catalyst is added to and dispersed in the condensate melt, and then continuously supplied to the reaction tank, and the condensate melt is thinned and depolymerized using an external force. The manufacturing method of polyester of description.   The method for producing a polyester according to claim 1 or 2, wherein the external force used for thinning the condensate melt includes gravity and / or centrifugal force. A reaction vessel, a means for supplying a condensate melt of hydroxycarboxylic acid to the reaction vessel, a means for supplying a polymerization catalyst to the reaction vessel, and thereby a ring is formed by depolymerization by contact with the catalyst in the reaction vessel. An apparatus for producing a polyester by converting it into a dimer and subjecting it to ring-opening polymerization,
A polyester production apparatus comprising a thin-film evaporation apparatus provided with a device for measuring the residence amount of the condensate melt, thereby thinning and depolymerizing the condensate melt.   The polyester manufacturing apparatus according to claim 4, wherein the thin film evaporator is a horizontal centrifugal thin film evaporator.   A device for adding and dispersing a catalyst to the condensate melt, and a device for thinning the liquid by flowing down along the surface of the structure, thereby performing depolymerization of the condensate melt. The polyester manufacturing apparatus according to claim 4, wherein

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