JP5229268B2 - Polylactic acid synthesis apparatus and method - Google Patents

Description

  The present invention relates to a method and apparatus for synthesizing polylactic acid, and more particularly to a method and apparatus for obtaining lactide by condensing and condensing lactic acid and then depolymerizing it.

  Polylactic acid is an aliphatic polyester made from lactic acid. One method of synthesizing polylactic acid is to condense lactic acid to reduce the water content and then condense to produce a lactic acid oligomer, and then add a catalyst such as tin octylate to depolymerize it once. There is a method in which a cyclic dimer (lactide) is produced by the above-mentioned method and, if necessary, purification by crystallization is performed, and then a catalyst such as tin octylate is added to the lactide to perform ring-opening polymerization.

  In the concentration step, about 10 to 15% of water (hereinafter referred to as free water) may be contained as an impurity in lactic acid, which is a monomer, and this free water is removed to facilitate esterification between the monomers. To be implemented. In this concentration step, moisture is removed by heating at 120 to 250 ° C. and, if necessary, reduced pressure using a vacuum pump or the like.

  In the condensation step, water produced by the esterification reaction between the monomers is vaporized and removed by heating at 120 to 250 ° C. and a reduced pressure environment such as a vacuum pump, preferably under a reduced pressure of 10 Torr or less. The reduced pressure here is different from that in the concentration step and is an essential condition for progressing the esterification reaction. By this condensation step, a lactic acid condensate (hereinafter referred to as oligomer) is produced from the monomer.

  The oligomer produced in the condensation step is sent to the depolymerization step, and is heated with 120 to 250 ° C. and under a reduced pressure environment such as a vacuum pump, preferably under a reduced pressure environment of 100 Torr or less, with a depolymerization catalyst such as tin octylate. Contact produces lactide (lactic acid cyclic dimer). The produced lactide is usually a gas in the environment in the depolymerization process and is usually recovered by cooling and condensation before being sent to the purification process.

  Since lactic acid is a molecule with chirality, there are enantiomers of L-lactic acid and D-lactic acid. Therefore, the lactide that is a cyclic dimer includes L-lactide that is a cyclic dimer of L-lactic acid, D-lactide that is a cyclic dimer of D-lactic acid, and a cyclic dimer of L-lactic acid and D-lactic acid. There are optical isomers such as mesolactide which is a monomer. Since lactic acid that exists abundantly in nature is L-lactic acid, L-lactide is often used for polylactic acid synthesis. In the purification step, L-lactide, D-lactide and meso-lactide are separated by methods such as solvent extraction and recrystallization.

  In the depolymerization step, the lactic acid oligomer after producing lactide is discharged as a residue. In many cases, the residue has a molecular weight increased by a ring-opening polymerization reaction, which is an equilibrium reaction of a depolymerization reaction, and a viscosity increases accordingly. This residue contains a catalyst, but in the case of a solid catalyst such as antimony oxide, it can be removed by filtration or the like (Patent Document 1).

JP 7-503490 gazette

  In Patent Document 1 described above, in the case of a liquid catalyst such as tin octylate, it cannot be separated by filtration or the like. Moreover, the depolymerization residue from which the catalyst has not been removed needs to be treated as industrial waste containing heavy metals, which increases the environmental load.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a method and an apparatus for efficiently removing a liquid catalyst present in a depolymerization residue.

  As a result of intensive studies on the above-mentioned problems in order to achieve the above object, the present inventors have found the following polylactic acid production method and apparatus.

That is, the present invention includes the following:
(1) a step of condensing lactic acid;
Depolymerizing the lactic acid condensate in the presence of a liquid catalyst to produce a lactic acid cyclic dimer;
Vaporizing and separating the produced lactic acid cyclic dimer;
Condensing and purifying the vaporized lactic acid cyclic dimer; and ring-opening polymerization of the purified lactic acid cyclic dimer;
A method for synthesizing polylactic acid containing
Removing the depolymerization residue;
Hydrolyzing the lactic acid condensate contained in the removed depolymerization residue; and, after hydrolysis, adding an alkaline earth metal hydroxide to the depolymerization residue to remove the liquid catalyst;
The method for synthesizing the polylactic acid, comprising:

(2) Lactic acid condensing equipment for condensing lactic acid;
A depolymerizer for depolymerizing a lactic acid condensate in the presence of a liquid catalyst to produce a lactic acid cyclic dimer;
A distillation column for vaporizing and separating the produced lactic acid cyclic dimer;
A condenser for condensing the vaporized lactic acid cyclic dimer;
A purification device for purifying the condensed lactic acid cyclic dimer; and a ring-opening polymerization device for ring-opening polymerization of the purified lactic acid cyclic dimer;
A polylactic acid synthesis apparatus comprising:
A depolymerization residue decomposition apparatus for removing the depolymerization residue and hydrolyzing the lactic acid condensate contained in the depolymerization residue; and after hydrolysis, an alkaline earth metal hydroxide is added to the depolymerization residue to form a liquid catalyst. A catalyst separation device for cracking and precipitation; and a catalyst removal device for removing the deposited liquid catalyst;
The polylactic acid synthesis apparatus comprising:

(3) A method for removing a liquid catalyst from a mixture of a lactic acid condensate and a liquid catalyst,
Hydrolyzing the lactic acid condensate;
After hydrolysis, adding alkaline earth metal hydroxide to remove the liquid catalyst;
A method for removing the liquid catalyst comprising:

  FIG. 1 shows a schematic diagram thereof. Lactic acid is supplied from the lactic acid supply device 1 and water is removed in the lactic acid concentration device 3 to become concentrated lactic acid. Concentrated lactic acid is supplied to the lactic acid condensing apparatus 7 through the concentrated lactic acid buffer tank 5, and becomes an oligomer (lactic acid condensate) by the condensation reaction. The oligomer is sent to the depolymerization apparatus 11 through the oligomer buffer tank 9, and after adding a catalyst such as tin octylate, it is converted into crude lactide by the depolymerization reaction and separated from the oligomer by the distillation column 12, and then the lower column 13 of the distillation column. Is condensed and recovered. The recovered crude lactide is sent to the purifier 15 to become purified lactide (L-lactide). The purified lactide is supplied to the ring-opening polymerization apparatus 17 and becomes polylactic acid by the ring-opening polymerization reaction.

  Lactide is produced from the oligomer in the depolymerizer by a depolymerization reaction, but at the same time, the molecular weight of the oligomer is increased by a ring-opening polymerization reaction which is an equilibrium reaction. The oligomer having an increased molecular weight has an increased viscosity and the dispersibility of the catalyst is decreased, so that the reaction rate of the depolymerization reaction is decreased and the yield of lactide is decreased. Therefore, oligomers with an increased molecular weight including catalyst are discharged as residues from the depolymerization apparatus, and moisture is added using the depolymerization residue decomposition apparatus 28 to hydrolyze the oligomers with an increased molecular weight to produce lactic acid. Steam, moisture-containing lactic acid or the like can be used for the hydrolysis of the oligomer. The residue obtained by hydrolyzing the oligomer is sent to the catalyst separation device 30, and an alkaline earth metal hydroxide such as calcium hydroxide is added. For example, when the catalyst is tin octylate and the alkaline earth metal hydroxide is calcium hydroxide, the catalyst is decomposed into calcium octylate and tin oxide, and the calcium octylate and tin oxide are insoluble in water. Settling. In addition, lactic acid contained in the residue becomes calcium lactate. The precipitated calcium octylate and tin oxide are separated from the depolymerization residue solution by filtration or the like in the catalyst removal device 31 and then discarded. On the other hand, after water and calcium lactate are separated by distillation or the like, water can be recycled or discarded, and calcium lactate can be reused as fertilizer.

  According to the present invention, after hydrolyzing the lactic acid oligomer contained in the residue discharged from the depolymerization apparatus using the depolymerization residue decomposition apparatus, the catalyst is decomposed and precipitated using the catalyst separation apparatus, and the catalyst removal apparatus Since the lactic acid oligomers contained in the depolymerization residue can be recovered as alkaline earth metal milk oxide, the raw material utilization rate is high, and the amount of waste discharged is stable. It is possible to provide a method for polylactic acid synthesis capable of producing polylactic acid and an apparatus for polylactic acid synthesis using the method.

It is the schematic which shows one Embodiment of the apparatus regarding the polylactic acid synthesis | combination of this invention. It is the schematic which shows one Embodiment of the apparatus regarding the polylactic acid synthesis | combination of this invention. It is the schematic which shows one Embodiment of the apparatus regarding the polylactic acid synthesis | combination of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings and tables. The apparatus for synthesizing this polylactic acid is from the upstream side of the reaction path from the lactic acid supply device 1, the liquid feed pump 2, the lactic acid concentration device 3, the liquid feed pump 4, the concentrated lactic acid buffer tank 5, the liquid feed pump 6, the lactic acid condensation device 7, and the liquid. Feed pump 8, oligomer buffer tank 9, liquid feed pump 10, depolymerization device 11, distillation tower 12, distillation tower lower stage 13, liquid feed pump 14, lactide purification device 15, liquid feed pump 16, ring-opening polymerization device 17 The depolymerization residue decomposition device 28, the catalyst separation device 30, and the catalyst removal device 31 are arranged in this order from the depolymerization residue discharge port of the depolymerization device 11.

  The polylactic acid production apparatus of the present invention is a concentrated lactic acid by evaporating water contained in lactic acid in a lactic acid concentrating device, and condensing the concentrated lactic acid in a lactic acid condensing device to produce oligomers, and depolymerizing the obtained oligomers In this method, lactide is generated by depolymerization under reduced pressure, and then purified lactide is subjected to ring-opening polymerization to produce polylactic acid.

  Water contained in lactic acid is preferably removed by heating as much as possible and evaporating.

  In the lactic acid condensation apparatus, the lactic acid is heated under reduced pressure to generate an oligomer. In the present invention, an oligomer is a concept including a lactic acid polymer having a molecular weight of about 50,000 from a dimer of lactic acid. The molecular weight of the oligomer obtained by the lactic acid condensation reaction is usually 150 to 10,000 in terms of average molecular weight. , Preferably 500 to 5,000.

  The lactic acid condensation reaction is usually performed at a pressure of 100 Torr or less, desirably 10 Torr or less, more preferably 1 Torr or less, and usually 160 to 220 ° C., preferably 170 to 200 ° C. By shortening the heating time as much as possible, thermal decomposition of lactic acid and oligomer can be suppressed.

  Regarding the lactic acid condensation reaction, a catalyst for the lactic acid condensation reaction may be added as necessary. As the catalyst, a conventionally known catalyst can be used. For example, an organic tin-based catalyst (for example, tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate) , Α-tin naphthoate, β-naphthoate tin, tin octylate, etc.) and powdered tin.

  The depolymerization reaction is performed in the presence of a liquid catalyst. The liquid catalyst used in the present invention means a catalyst that is liquid under reaction conditions. For example, a catalyst comprising a metal compound selected from Group IVA of the periodic table can be used.

  Examples of those belonging to Group IVA include organotin catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin distearate, tin dioleate, α-tin naphthoate, β-naphthoate tin, octylic acid). Tin, etc.).

  Among these, it is preferable to use tin octylate.

  These catalysts are used in an amount of 0.01 to 20% by weight, preferably 0.05 to 15% by weight, more preferably about 0.1 to 10% by weight, based on the oligomer.

  The depolymerization apparatus has at least a reactor, an oligomer supply port, a lactide discharge port, and a residue discharge port. A normal thermometer is also installed. The reactor is not particularly limited, and a vertical reactor, a horizontal reactor, or a tank reactor can be used. As the stirring blade, a paddle blade, a turbine blade, an anchor blade, a double motion blade, a helical ribbon blade, or the like can be used.

  As a heating method in the reactor, a method generally used in this technical field can be used. For example, a heating medium jacket is installed on the outer periphery of the reactor, and the reaction liquid is heated by heat transfer through the reactor wall surface. There is a method, or a method of heating by heat transfer through a heating medium inside the rotating shaft of the stirring blade, and these may be used alone or in combination.

  The depolymerizer is equipped with a decompressor, and the oligomer is depolymerized by heating at a pressure of usually 100 Torr or less, preferably 10 Torr or less, usually 120 to 250 ° C., preferably 120 to 200 ° C. To do. Lactide is generated as a gas by the depolymerization reaction. In the present invention, lactide refers to a cyclic ester produced by dehydrating two molecules of water from two molecules of lactic acid.

  The vapor containing lactide generated in the depolymerization apparatus is discharged out of the depolymerization apparatus and introduced into the distillation column. By appropriately controlling the temperature of the refrigerant, lactide vapor is allowed to pass through, and the oligomer is condensed and liquefied and then refluxed. A liquid containing an oligomer separated from lactide may have a reduced molecular weight due to a depolymerization reaction. The molecular weight in this case is preferably a weight average molecular weight of less than 500, particularly preferably less than 1000. In order to improve the yield of lactide, it is desirable to condense again to improve the molecular weight. Therefore, it is desirable that the liquid containing the low molecular weight oligomer is condensed again in the lactic acid condensation apparatus. Examples of the apparatus for returning the oligomer include a lactic acid concentrating device, a concentrated lactic acid buffer tank, a lactic acid condensing device, an oligomer buffer tank, and a depolymerization device inlet. Further, the distillation column may be multi-staged in order to reflux after the oligomer is separated according to the molecular weight. In this case, the low molecular weight oligomer should be returned to at least one of the lactic acid concentrator, concentrated lactic acid buffer tank, and lactic acid condensation device, and the high molecular weight oligomer should be returned to at least one of the lactic acid condensation device, lactic acid oligomer buffer tank, and depolymerization device inlet. Is desirable. The lactide passing through here is transferred to the lower stage of the distillation column.

  For the distillation column, a surface condenser in which the vapor and the refrigerant are in indirect contact with each other through a metal tube is desirable. This is because lactide and oligomer are decomposed to produce an acid when they come 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 distillation column. When the refrigerant is inert to lactide and oligomer, it is not limited to the above. In that case, it is necessary to sufficiently dry the refrigerant to reduce moisture.

  The vapor containing the oligomer liquefied in the distillation column and the separated lactide is supplied to the lower stage of the distillation column. Here, the lactide is cooled, condensed and recovered, and then transferred to a lactide purification apparatus.

  For the lower stage of the distillation column, a surface condenser in which the vapor and the refrigerant are in indirect contact with each other through a metal tube is desirable. This is because when lactide comes into direct contact with a refrigerant containing water, it decomposes to produce an acid. This hinders the progress of the ring-opening polymerization reaction as an acid catalyst and may cause corrosion of the material such as the lower stage of the distillation column. In the case where a refrigerant inert to lactide is used, it is not limited to the above, but in that case, it is necessary to sufficiently dry the refrigerant to reduce moisture.

  The lactide purification apparatus separates and purifies the desired lactide, mainly L-lactide and other impurities. The purification method is not particularly limited, and solvent extraction or melt crystallization can be used.

  The lactide purification apparatus has at least a reactor, a crude lactide supply port, a purified lactide discharge port, and a waste liquid discharge port. A normal thermometer is also installed.

  The lactide discharged from the lactide purification apparatus is transferred to a ring-opening polymerization apparatus.

  In the ring-opening polymerization apparatus, the ring-opening polymerization reaction of lactide is carried out by heating at 120 to 250 ° C., preferably 120 to 200 ° C. in an inert gas atmosphere. Polylactic acid is produced by the ring-opening polymerization reaction.

  The ring-opening polymerization apparatus has at least a reactor, a lactide supply port, and a polylactic acid discharge port. A normal thermometer is also installed. The reactor is not particularly limited, and a vertical reactor, a horizontal reactor, or a tank reactor can be used, and two or more reactors may be connected in series. As the stirring blade, a paddle blade, a turbine blade, an anchor blade, a double motion blade, a helical ribbon blade, or the like can be used.

  As a heating method in the reactor, a method generally used in this technical field can be used. For example, a heating medium jacket is installed on the outer periphery of the reactor, and the reaction liquid is heated by heat transfer through the reactor wall surface. There are a method and a method of heating by heat transfer through a heat transfer tube (coil) inside the reactor, and these may be used alone or in combination.

  As the catalyst for the ring-opening polymerization reaction, the same catalyst as that for the depolymerization reaction may be used as necessary. A conventionally known catalyst can be used as the catalyst, for example, a catalyst made of a metal or a metal compound selected from the group consisting of groups IA, IIIA, IVA, IIB and VA of the periodic table is used. it can.

  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 IIIA include aluminum ethoxide, aluminum isopropoxide, alumina, aluminum chloride and the like.

  Examples of those belonging to Group IVA include organotin catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin distearate, tin dioleate, α-tin naphthoate, β-naphthoate tin, octylic acid). In addition to tin, etc., powder tin, tin oxide, tin halide and the like can be mentioned.

  Examples of those belonging to Group IIB include zinc powder, zinc halide, zinc oxide, and organic zinc compounds.

  Examples of those belonging to Group IVB include titanium compounds such as tetrapropyl titanate and zirconium compounds such as zirconium isopropoxide.

  Among these, it is preferable to use a tin compound such as tin octylate or an antimony compound such as antimony trioxide.

  The amount of these catalysts used is about 1 to 2000 ppm, preferably 5 to 1500 ppm, and more preferably about 10 to 1000 ppm with respect to lactide.

  In the ring-opening polymerization reaction, a polymerization initiator for the ring-opening polymerization reaction may be added as necessary for the purpose of adjusting the molecular weight or the like. As the polymerization initiator, a substance having a hydroxyl group such as alcohols such as 1-dodecanol can be used.

  The depolymerization residue discharged from the depolymerization apparatus is transferred to the depolymerization residue decomposition apparatus.

  In the depolymerization residue decomposing apparatus, the hydrolysis reaction of the lactic acid oligomer contained in the depolymerization residue is performed by heating at 100 to 250 ° C., preferably 120 to 200 ° C. in an inert gas atmosphere. The hydrolysis reaction produces lactic acid or low molecular weight oligomers.

  The depolymerization residue decomposition apparatus has at least a reactor, a depolymerization residue supply port, and a depolymerization residue discharge port. A normal thermometer is also installed. The reactor is not particularly limited, and a vertical reactor, a horizontal reactor, or a tank reactor can be used. As the stirring blade, a paddle blade, a turbine blade, an anchor blade, a double motion blade, a helical ribbon blade, or the like can be used.

  As a heating method in the reactor, a method generally used in this technical field can be used. For example, a heating medium jacket is installed on the outer periphery of the reactor, and the reaction liquid is heated by heat transfer through the reactor wall surface. There is a method, or a method of heating by heat transfer through a heating medium inside the rotating shaft of the stirring blade, and these may be used alone or in combination.

  In the depolymerization residue decomposing apparatus, it is desirable to maintain the melted state of the depolymerization residue in order to improve the mixability of the depolymerization residue. For this purpose, it is necessary to maintain the temperature of the depolymerization residue at about 130 to 200 ° C. There is. On the other hand, since the boiling point of lactic acid at atmospheric pressure is about 120 ° C., a pressure vessel such as an autoclave is used as a reaction vessel, and the depolymerization residue is kept in a molten state by hydrolysis under pressure conditions. Decomposition can proceed. Alternatively, the depolymerization residue can be solidified, pulverized into powder, and then hydrolyzed.

  The decomposed depolymerization residue discharged from the depolymerization residue decomposition apparatus is transferred to the catalyst separation apparatus.

  In the catalyst separation apparatus, the decomposition reaction of the catalyst contained in the depolymerization residue is carried out by adding alkaline earth metal hydroxide at 0 to 250 ° C., preferably 5 to 130 ° C. in an inert gas atmosphere. A metal oxide contained in the catalyst component is generated by the decomposition reaction.

  The catalyst separation device has at least a reactor, a depolymerization residue supply port, and a depolymerization residue discharge port. A normal thermometer is also installed. And an alkaline-earth metal supply port is provided. The reactor is not particularly limited, and a vertical reactor, a horizontal reactor, or a tank reactor can be used. As the stirring blade, a paddle blade, a turbine blade, an anchor blade, a double motion blade, a helical ribbon blade, or the like can be used.

  As a heating method in the reactor, a method generally used in this technical field can be used. For example, a heating medium jacket is installed on the outer periphery of the reactor, and the reaction liquid is heated by heat transfer through the reactor wall surface. There is a method, or a method of heating by heat transfer through a heating medium inside the rotating shaft of the stirring blade, and these may be used alone or in combination.

  Any alkaline earth metal hydroxide may be used as long as it can separate the catalyst components, but calcium hydroxide and magnesium hydroxide are particularly desirable.

  The depolymerization residue discharged from the catalyst separation device is transferred to the catalyst removal device.

  The catalyst removal device has at least a removal device, a depolymerization residue supply port, and a depolymerization residue discharge port. A normal thermometer is also installed. The removal device is not particularly limited, and a filtration separation device, a sedimentation separation device, a centrifugal separation device, or the like can be used.

  The depolymerization residue discharged from the catalyst removing device is transferred to the water separation device, and the water is removed. The removed water is refluxed to a depolymerization residue decomposition apparatus or the like, but may be discarded. The depolymerized residue from which water has been removed is an alkaline earth metal lactate, but can be used as a fertilizer. Further, the catalyst removed by the catalyst removing device is discarded.

  In one embodiment of the present invention, polylactic acid is produced using a polylactic acid apparatus having the apparatus configuration shown in FIG.

  In the lactic acid concentrating device 3, water contained in lactic acid is evaporated by heating. Heating is performed at 120 to 150 ° C. under a nitrogen gas flow.

  In the lactic acid concentration reaction, water and lactic acid are generated as gas. These gases enter the reflux unit 18, lactic acid is removed from the gas, and refluxed to the lactic acid concentrator 3.

  The concentrated lactic acid produced by the lactic acid concentrating device 3 is sent to the lactic acid condensing device 7 through the concentrated lactic acid buffer tank 5.

  The lactic acid condensing device 7 advances the condensation reaction of lactic acid and evaporates the water generated therewith. The reaction is performed at a temperature of 120 to 250 ° C. under reduced pressure to 10 torr or less. In the lactic acid condensation reaction, moisture, lactic acid, low molecular weight oligomers, and lactide generated by the decomposition thereof are generated as gases. These move from the lactic acid condensation device 7 toward the decompression device 23. These gases enter the reflux device 21, lactic acid, low-molecular oligomers, and lactide are removed from the gas, and are refluxed to the lactic acid condensation apparatus 7.

  The oligomer produced by the lactic acid condensation device 7 is sent to the depolymerization device 11.

  The depolymerization apparatus 11 advances the depolymerization reaction of the oligomer. The reaction is carried out by reducing the pressure to 10 torr or less and bringing the lactic acid oligomer into contact with tin octylate as a depolymerization catalyst at a temperature of 120 to 250 ° C. The gaseous lactide generated by this reaction is sent to the reflux condenser 12.

  In the reflux condenser 12, the gaseous lactide is cooled to liquefy impurities such as oligomers contained in the lactide, and the gaseous lactide is sent to the lactide condenser 13. Many liquids containing oligomers separated from lactide have a reduced molecular weight due to the depolymerization reaction. In order to improve the yield of lactide, it is desirable to improve the molecular weight by again condensing oligomers having a low molecular weight, so that the liquid containing the low molecular weight oligomer separated from the lactide is refluxed to the lactic acid condensation apparatus 7.

  The gaseous lactide is cooled and condensed in the lower stage 13 of the distillation column, and then sent to the lactide purification device 15. The gas containing a large amount of water vapor separated from lactide enters the condenser 24, and lactic acid, low-molecular oligomers, and lactide are removed from the gas and refluxed to the lower stage 13 of the distillation column.

  The vapor not condensed in the condenser 24 enters the impurity cooler 25 where it is condensed and liquefied. The liquefied impurities are usually discarded. The gas that has not been condensed by the impurity cooler 25 is discharged out of the system through the decompression device 26.

  The lactide purification apparatus 15 separates and purifies the target lactide, mainly L-lactide and other impurities. The purification method is not particularly limited, and solvent extraction or melt crystallization can be used. For example, in the melt crystallization method, the molten crude lactide is cooled to at least the freezing point of the lactide, and the melt is partially crystallized to form a solid crystal phase with few impurities and a liquid phase with many impurities, After separating the liquid phase and the liquid phase, the crystalline phase is perspired to melt and remove impurities.

  The lactide purification apparatus has at least a reactor, a crude lactide supply port, a purified lactide discharge port, and a waste liquid discharge port. A normal thermometer is also installed.

  The lactide discharged from the lactide purification device 15 is transferred to the ring-opening polymerization device 17.

  The ring-opening polymerization apparatus 17 advances the ring-opening polymerization reaction of lactide. The reaction is carried out by reducing the pressure to 10 torr or less and contacting lactide with a ring-opening polymerization catalyst such as antimony trioxide and tin octylate and a polymerization initiator such as 1-dodecanol at a temperature of 120 to 250 ° C. When the concentration of the polymerization initiator was 700 ppm, the polylactic acid had a weight average molecular weight of about 200,000.

  In the depolymerization residue decomposition apparatus 28, the depolymerization residue discharged | emitted from the depolymerization apparatus 11 is hydrolyzed. Hydrolysis is performed by adding steam to the depolymerization residue at a temperature of 120 to 250 ° C. under pressure. The depolymerization residue decomposed into lactic acid or a low molecular weight oligomer by this reaction is sent to the catalyst separation device 30 through the buffer tank 29.

  The catalyst separation device 30 decomposes and separates the catalyst (tin octylate) contained in the depolymerization residue discharged from the depolymerization residue decomposition device 28. The decomposition of the catalyst is performed by adding calcium hydroxide to the depolymerization residue at a temperature of 0 to 200 ° C. in an inert gas atmosphere. By this reaction, tin octylate, which is a catalyst, is decomposed into calcium octylate and tin oxide, which precipitate because they are insoluble in water and lactic acid. The depolymerization residue obtained by decomposing the catalyst component is sent to the catalyst removing device 31.

  The catalyst removing device 31 removes the decomposing and decomposed catalyst components (calcium octylate and tin oxide) discharged from the catalyst separation device 30. Removal of the catalyst component is performed using a filtration device. The depolymerization residue from which the catalyst component has been removed is sent to the water separator 32, where the water is separated, and then secondarily used or discarded as calcium lactate.

  In another embodiment of the present invention, polylactic acid is produced using a polylactic acid apparatus having the apparatus configuration shown in FIG.

  In the lactic acid concentrating device 3, water contained in lactic acid is evaporated by heating. Heating is performed at 120 to 150 ° C. under a nitrogen gas flow.

  In the lactic acid concentration reaction, water and lactic acid are generated as gas. These gases enter the reflux unit 18, lactic acid is removed from the gas, and refluxed to the lactic acid concentrator 3.

  The concentrated lactic acid produced by the lactic acid concentrating device 3 is sent to the lactic acid condensing device 7 through the concentrated lactic acid buffer tank 5.

  The lactic acid condensing device 7 advances the condensation reaction of lactic acid and evaporates the water generated therewith. The reaction is performed at a temperature of 120 to 250 ° C. under reduced pressure to 10 torr or less. In the lactic acid condensation reaction, moisture, lactic acid, low molecular weight oligomers, and lactide generated by the decomposition thereof are generated as gases. These move from the lactic acid condensation device 7 toward the decompression device 23. These gases enter the reflux device 21, lactic acid, low-molecular oligomers, and lactide are removed from the gas, and are refluxed to the lactic acid condensation apparatus 7.

  The oligomer produced by the lactic acid condensation device 7 is sent to the depolymerization device 11.

  The depolymerization apparatus 11 advances the depolymerization reaction of the oligomer. The reaction is carried out by reducing the pressure to 10 torr or less and bringing the lactic acid oligomer into contact with tin octylate as a depolymerization catalyst at a temperature of 120 to 250 ° C. The gaseous lactide generated by this reaction is sent to the reflux condenser 12.

  In the reflux condenser 12, the gaseous lactide is cooled to liquefy impurities such as oligomers contained in the lactide, and the gaseous lactide is sent to the lactide condenser 13. Many liquids containing oligomers separated from lactide have a reduced molecular weight due to the depolymerization reaction. In order to improve the yield of lactide, it is desirable to improve the molecular weight by again condensing oligomers having a low molecular weight, so that the liquid containing the low molecular weight oligomer separated from the lactide is refluxed to the lactic acid condensation apparatus 7.

  The gaseous lactide is cooled and condensed in the lower stage 13 of the distillation column, and then sent to the lactide purification device 15. The gas containing a large amount of water vapor separated from lactide enters the condenser 24, and lactic acid, low-molecular oligomers, and lactide are removed from the gas and refluxed to the lower stage 13 of the distillation column.

  The vapor not condensed in the condenser 24 enters the impurity cooler 25 where it is condensed and liquefied. The liquefied impurities are usually discarded. The gas that has not been condensed by the impurity cooler 25 is discharged out of the system through the decompression device 26.

  The lactide purification apparatus 15 separates and purifies the target lactide, mainly L-lactide and other impurities. The purification method is not particularly limited, and solvent extraction or melt crystallization can be used. For example, in the melt crystallization method, the molten crude lactide is cooled to at least the freezing point of the lactide, and the melt is partially crystallized to form a solid crystal phase with few impurities and a liquid phase with many impurities, After separating the liquid phase and the liquid phase, the crystalline phase is perspired to melt and remove impurities.

  The lactide purification apparatus has at least a reactor, a crude lactide supply port, a purified lactide discharge port, and a waste liquid discharge port. A normal thermometer is also installed.

  The lactide discharged from the lactide purification device 15 is transferred to the ring-opening polymerization device 17.

  The ring-opening polymerization apparatus 17 advances the ring-opening polymerization reaction of lactide. The reaction is carried out by reducing the pressure to 10 torr or less and contacting lactide with a ring-opening polymerization catalyst such as antimony trioxide and tin octylate and a polymerization initiator such as 1-dodecanol at a temperature of 120 to 250 ° C. When the concentration of the polymerization initiator was 700 ppm, the polylactic acid had a weight average molecular weight of about 200,000.

  In the depolymerization residue decomposition apparatus 28, the depolymerization residue discharged | emitted from the depolymerization apparatus 11 is hydrolyzed. Hydrolysis is performed by adding 50% lactic acid to the depolymerization residue at a temperature of 120 to 250 ° C. under pressure. The depolymerization residue decomposed into lactic acid or a low molecular weight oligomer by this reaction is sent to the catalyst separation device 30 through the buffer tank 29.

  The catalyst separation device 30 decomposes and separates the catalyst (tin octylate) contained in the depolymerization residue discharged from the depolymerization residue decomposition device 28. The decomposition of the catalyst is performed by adding calcium hydroxide to the depolymerization residue at a temperature of 0 to 200 ° C. in an inert gas atmosphere. By this reaction, tin octylate, which is a catalyst, is decomposed into calcium octylate and tin oxide, which precipitate because they are insoluble in water and lactic acid. The depolymerization residue obtained by decomposing the catalyst component is sent to the catalyst removing device 31.

  The catalyst removing device 31 removes the decomposing and decomposed catalyst components (calcium octylate and tin oxide) discharged from the catalyst separation device 30. Removal of the catalyst component is performed using a filtration device. The depolymerization residue from which the catalyst component has been removed is sent to the water separator 32, where the water is separated, and then secondarily used or discarded as calcium lactate.

  In a further embodiment of the present invention, polylactic acid is produced using a polylactic acid apparatus having the apparatus configuration shown in FIG.

  In the lactic acid concentrating device 3, water contained in lactic acid is evaporated by heating. Heating is performed at 120 to 150 ° C. under a nitrogen gas flow.

  In the lactic acid concentration reaction, water and lactic acid are generated as gas. These gases enter the reflux unit 18, lactic acid is removed from the gas, and refluxed to the lactic acid concentrator 3.

  The concentrated lactic acid produced by the lactic acid concentrating device 3 is sent to the lactic acid condensing device 7 through the concentrated lactic acid buffer tank 5.

  The lactic acid condensing device 7 advances the condensation reaction of lactic acid and evaporates the water generated therewith. The reaction is performed at a temperature of 120 to 250 ° C. under reduced pressure to 10 torr or less. In the lactic acid condensation reaction, moisture, lactic acid, low molecular weight oligomers, and lactide generated by the decomposition thereof are generated as gases. These move from the lactic acid condensation device 7 toward the decompression device 23. These gases enter the reflux device 21, lactic acid, low-molecular oligomers, and lactide are removed from the gas, and are refluxed to the lactic acid condensation apparatus 7.

  The oligomer produced by the lactic acid condensation device 7 is sent to the depolymerization device 11.

  The depolymerization apparatus 11 advances the depolymerization reaction of the oligomer. The reaction is carried out by reducing the pressure to 10 torr or less and bringing the lactic acid oligomer into contact with tin octylate as a depolymerization catalyst at a temperature of 120 to 250 ° C. The gaseous lactide generated by this reaction is sent to the reflux condenser 12.

  In the reflux condenser 12, the gaseous lactide is cooled to liquefy impurities such as oligomers contained in the lactide, and the gaseous lactide is sent to the lactide condenser 13. Many liquids containing oligomers separated from lactide have a reduced molecular weight due to the depolymerization reaction. In order to improve the yield of lactide, it is desirable to improve the molecular weight by again condensing oligomers having a low molecular weight, so that the liquid containing the low molecular weight oligomer separated from the lactide is refluxed to the lactic acid condensation apparatus 7.

  The gaseous lactide is cooled and condensed in the lower stage 13 of the distillation column, and then sent to the lactide purification device 15. The gas containing a large amount of water vapor separated from lactide enters the condenser 24, and lactic acid, low-molecular oligomers, and lactide are removed from the gas and refluxed to the lower stage 13 of the distillation column.

  The vapor not condensed in the condenser 24 enters the impurity cooler 25 where it is condensed and liquefied. The liquefied impurities are usually discarded. The gas that has not been condensed by the impurity cooler 25 is discharged out of the system through the decompression device 26.

  The lactide purification apparatus 15 separates and purifies the target lactide, mainly L-lactide and other impurities. The purification method is not particularly limited, and solvent extraction or melt crystallization can be used. For example, in the melt crystallization method, the molten crude lactide is cooled to at least the freezing point of the lactide, and the melt is partially crystallized to form a solid crystal phase with few impurities and a liquid phase with many impurities, After separating the liquid phase and the liquid phase, the crystalline phase is perspired to melt and remove impurities.

  The lactide purification apparatus has at least a reactor, a crude lactide supply port, a purified lactide discharge port, and a waste liquid discharge port. A normal thermometer is also installed.

  The lactide discharged from the lactide purification device 15 is transferred to the ring-opening polymerization device 17.

  The ring-opening polymerization apparatus 17 advances the ring-opening polymerization reaction of lactide. The reaction is carried out by reducing the pressure to 10 torr or less and contacting lactide with a ring-opening polymerization catalyst such as antimony trioxide and tin octylate and a polymerization initiator such as 1-dodecanol at a temperature of 120 to 250 ° C. When the concentration of the polymerization initiator was 700 ppm, the polylactic acid had a weight average molecular weight of about 200,000.

  In the depolymerization residue decomposition apparatus 28, the depolymerization residue discharged | emitted from the depolymerization apparatus 11 is hydrolyzed. Hydrolysis is carried out by adding 50% lactic acid to the depolymerization residue that has been pulverized and powdered at a temperature of 100 to 120 ° C. in an inert gas atmosphere. The depolymerization residue decomposed into lactic acid or a low molecular weight oligomer by this reaction is sent to the catalyst separation device 30 through the buffer tank 29.

  The catalyst separation device 30 decomposes and separates the catalyst (tin octylate) contained in the depolymerization residue discharged from the depolymerization residue decomposition device 28. The decomposition of the catalyst is performed by adding calcium hydroxide to the depolymerization residue at a temperature of 0 to 200 ° C. in an inert gas atmosphere. By this reaction, tin octylate, which is a catalyst, is decomposed into calcium octylate and tin oxide, which precipitate because they are insoluble in water and lactic acid. The depolymerization residue obtained by decomposing the catalyst component is sent to the catalyst removing device 31.

  The catalyst removing device 31 removes the decomposing and decomposed catalyst components (calcium octylate and tin oxide) discharged from the catalyst separation device 30. Removal of the catalyst component is performed using a filtration device. The depolymerization residue from which the catalyst component has been removed is sent to the water separator 32, where the water is separated, and then secondarily used or discarded as calcium lactate.

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

[Example 1]
Polylactic acid was produced using the polylactic acid production apparatus shown in FIG. As a raw material, a lactic acid oligomer having a number average molecular weight of 630 was charged into the depolymerization apparatus 11. The reaction in the depolymerization apparatus 11 was performed at a temperature of 200 ° C. under reduced pressure to 10 torr or less. The residence time of the lactic acid oligomer in the depolymerizer 11 was 5 hours, the liquid film thickness (liquid depth) was 55 cm, and the catalyst (tin 2-ethylhexanoate) concentration was 0.7 kg / m ³ .

  Here, the oligomer residence time is equal to the supply flow rate of the melted oligomer and the condensate flow rate of the vapor discharged from the depolymerization apparatus, and the melt oligomer supply flow rate when the liquid film thickness is stabilized / melting in the oligomer depolymerization apparatus 11. The amount of oligomer retention was defined.

  The reaction in the ring-opening polymerization apparatus 17 was performed at a temperature of 200 ° C. under reduced pressure to 10 torr or less. The concentration of the polymerization initiator in the ring-opening polymerization was 700 ppm. The obtained polylactic acid had a weight average molecular weight of about 200,000.

  The reaction in the depolymerization residue decomposition apparatus 28 was performed at a temperature of 200 ° C. under pressure. The amount of steam added to the depolymerization residue was about 15 times by weight.

  The reaction in the catalyst separation device 30 was performed at a temperature of 20 ° C. in an inert gas atmosphere. The amount of calcium hydroxide added to the depolymerization residue was about 55%.

  In the catalyst removal apparatus 31, the filter component was used to remove calcium octylate and tin oxide as catalyst components. The tin concentration contained in the depolymerization residue at the catalyst removal apparatus outlet was 1 ppm or less.

  As described above, waste can be reduced by efficiently separating and removing the catalyst component from the depolymerization residue from the depolymerization apparatus that has been conventionally discarded.

[Example 2]
Polylactic acid was produced using the polylactic acid production apparatus shown in FIG. As a raw material, a lactic acid oligomer having a number average molecular weight of 630 was charged into the depolymerization apparatus 11. The reaction in the depolymerization apparatus 11 was performed at a temperature of 200 ° C. under reduced pressure to 10 torr or less. The residence time of the lactic acid oligomer in the depolymerizer 11 was 5 hours, the liquid film thickness (liquid depth) was 55 cm, and the catalyst (tin 2-ethylhexanoate) concentration was 0.7 kg / m ³ .

  Here, the oligomer residence time is equal to the supply flow rate of the melted oligomer and the condensate flow rate of the vapor discharged from the depolymerization apparatus, and the melt oligomer supply flow rate when the liquid film thickness is stabilized / melting in the oligomer depolymerization apparatus 11. The amount of oligomer retention was defined.

  The reaction in the ring-opening polymerization apparatus 17 was performed at a temperature of 200 ° C. under reduced pressure to 10 torr or less. The concentration of the polymerization initiator in the ring-opening polymerization was 700 ppm. The obtained polylactic acid had a weight average molecular weight of about 200,000.

  The reaction in the depolymerization residue decomposition apparatus 28 was performed at a temperature of 200 ° C. under pressure. The amount of 50% lactic acid added to the depolymerization residue was about 10 times by weight.

  The reaction in the catalyst separation device 30 was performed at a temperature of 20 ° C. in an inert gas atmosphere. The amount of calcium hydroxide added to the depolymerization residue was about 100%.

  In the catalyst removal apparatus 31, the calcium octylate and tin oxide which are catalyst components were removed using the precipitation tank. The tin concentration contained in the depolymerization residue at the catalyst removal apparatus outlet was 1 ppm or less.

  As described above, waste can be reduced by efficiently separating and removing the catalyst component from the depolymerization residue from the depolymerization apparatus that has been conventionally discarded.

Example 3
Polylactic acid was produced using the polylactic acid production apparatus shown in FIG. As a raw material, a lactic acid oligomer having a number average molecular weight of 630 was charged into the depolymerization apparatus 11. The reaction in the depolymerization apparatus 11 was performed at a temperature of 200 ° C. under reduced pressure to 10 torr or less. The residence time of the lactic acid oligomer in the depolymerizer 11 was 5 hours, the liquid film thickness (liquid depth) was 55 cm, and the catalyst (tin 2-ethylhexanoate) concentration was 0.7 kg / m ³ .

  Here, the oligomer residence time is equal to the supply flow rate of the melted oligomer and the condensate flow rate of the vapor discharged from the depolymerization apparatus, and the melt oligomer supply flow rate when the liquid film thickness is stabilized / melting in the oligomer depolymerization apparatus 11. The amount of oligomer retention was defined.

  The reaction in the ring-opening polymerization apparatus 17 was performed at a temperature of 200 ° C. under reduced pressure to 10 torr or less. The concentration of the polymerization initiator in the ring-opening polymerization was 700 ppm. The obtained polylactic acid had a weight average molecular weight of about 200,000.

  The reaction in the depolymerization residue decomposition apparatus 28 was performed at a temperature of 200 ° C. under pressure. The amount of 50% lactic acid added to the depolymerization residue was about 10 times by weight.

  The reaction in the catalyst separation device 30 was performed at a temperature of 20 ° C. in an inert gas atmosphere. The amount of calcium hydroxide added to the depolymerization residue was about 100%.

  In the catalyst removal apparatus 31, the filter component was used to remove calcium octylate and tin oxide as catalyst components. The tin concentration contained in the depolymerization residue at the catalyst removal apparatus outlet was 1 ppm or less.

  As described above, waste can be reduced by efficiently separating and removing the catalyst component from the depolymerization residue from the depolymerization apparatus that has been conventionally discarded.

[Comparative Example]
Polymerization was carried out using a lactic acid oligomer having the same number average molecular weight 630 as in Examples 1 and 2 in a conventional apparatus in which the depolymerization residue was not decomposed and the catalyst was not separated / removed. As a result, the tin content of the depolymerization residue discharged from the depolymerization apparatus was 5%.

DESCRIPTION OF SYMBOLS 1 Lactic acid supply apparatus 2 Liquid feeding pump 3 Lactic acid concentration apparatus 4 Liquid feeding pump 5 Concentrated lactic acid buffer tank 6 Liquid feeding pump 7 Lactic acid condensation apparatus 8 Liquid feeding pump 9 Oligomer buffer tank 10 Liquid feeding pump 11 Depolymerization apparatus 12 Distillation tower 13 Distillation Lower column 14 Liquid feed pump 15 Lactide purification device 16 Liquid feed pump 17 Ring-opening polymerization device 18 Refluxer 19 Cooler 20 Decompression device 21 Refluxer 22 Cooler 23 Decompression device 24 Condenser 25 Impurity cooler 26 Decompression device 27 Depolymerization Residue buffer tank 28 Depolymerization residue decomposition device 29 Buffer tank 30 Catalyst separation device 31 Catalyst removal device 32 Moisture separation device 33 Refluxer 34 Cooler 35 Water supply device

Claims (13)

Condensing lactic acid;
Depolymerizing the lactic acid condensate in the presence of a liquid catalyst to produce a lactic acid cyclic dimer;
Vaporizing and separating the produced lactic acid cyclic dimer;
Condensing and purifying the vaporized lactic acid cyclic dimer; and ring-opening polymerization of the purified lactic acid cyclic dimer;
A method for synthesizing polylactic acid containing
Removing the depolymerization residue;
Hydrolyzing the lactic acid condensate contained in the removed depolymerization residue; and, after hydrolysis, adding an alkaline earth metal hydroxide to the depolymerization residue to remove the liquid catalyst;
The method for synthesizing the polylactic acid, comprising:   The synthesis method according to claim 1, wherein hydrolysis is performed by adding water vapor to the depolymerization residue.   The synthesis method according to claim 1, wherein hydrolysis is performed by adding lactic acid containing water to the depolymerization residue.   The synthesis method according to claim 1, wherein hydrolysis of the depolymerization residue is performed under pressure.   The synthesis method according to claim 1, wherein the depolymerization residue separated from the lactic acid cyclic dimer is refluxed to the lactic acid condensation step.   2. The synthesis method according to claim 1, wherein calcium hydroxide is added to the hydrolyzed depolymerization residue, and the catalyst contained in the depolymerization residue is decomposed and precipitated.   The synthesis method according to claim 1, wherein magnesium hydroxide is added to the hydrolyzed depolymerization residue, and the catalyst contained in the depolymerization residue is decomposed and precipitated. A lactic acid condensing apparatus for condensing lactic acid;
A depolymerizer for depolymerizing a lactic acid condensate in the presence of a liquid catalyst to produce a lactic acid cyclic dimer;
A distillation column for vaporizing and separating the produced lactic acid cyclic dimer;
A condenser for condensing the vaporized lactic acid cyclic dimer;
A purification device for purifying the condensed lactic acid cyclic dimer; and a ring-opening polymerization device for ring-opening polymerization of the purified lactic acid cyclic dimer;
A polylactic acid synthesis apparatus comprising:
A depolymerization residue decomposition apparatus for removing the depolymerization residue and hydrolyzing the lactic acid condensate contained in the depolymerization residue;
A catalyst separation device for decomposing and depositing a liquid catalyst by adding an alkaline earth metal hydroxide to the depolymerization residue after hydrolysis; and a catalyst removing device for removing the deposited liquid catalyst;
The polylactic acid synthesis apparatus comprising:   9. The synthesis apparatus according to claim 8, further comprising a steam device for hydrolyzing the depolymerization residue by adding water vapor.   9. The synthesizer according to claim 8, further comprising a lactic acid and water supply device for hydrolysis by adding lactic acid containing water to the depolymerization residue.   9. The synthesis apparatus according to claim 8, further comprising a pressurizing device for performing hydrolysis of the depolymerization residue under a pressurizing condition.   9. The synthesis apparatus according to claim 8, further comprising a liquid feed pump for refluxing the depolymerization residue separated from the lactic acid cyclic dimer to the lactic acid condensation step. A method of removing a liquid catalyst from a mixture of a lactic acid condensate and a liquid catalyst,
Hydrolyzing the lactic acid condensate;
After hydrolysis, adding alkaline earth metal hydroxide to remove the liquid catalyst;
A method for removing the liquid catalyst comprising:

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