JP4872387B2 - Polyhydroxycarboxylic acid synthesis method and polyhydroxycarboxylic acid synthesis apparatus used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a reaction device or piping from occlusion by capturing process-scattered substances and also improve reaction efficiency by reusing the scattered substances. <P>SOLUTION: This synthetic method is provided by capturing the process-scattered substances containing acid condensates generated in at least one of depolymerization process or monomer removal process by using a wet type condenser using a hydroxycarboxylic acid which is a raw material, as a coolant and reusing them as the raw material. The synthetic device suitable for performing the above method is also provided. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a method for synthesizing polyhydroxycarboxylic acid and a polyhydroxycarboxylic acid synthesizer used therefor, and more particularly to a method and apparatus for synthesizing polylactic acid.

  Hereinafter, the case where lactic acid is used as the hydroxycarboxylic acid will be mainly described. Polylactic acid is an aliphatic polyester made from lactic acid. As one method of synthesizing polylactic acid, lactic acid oligomers are produced by condensing lactic acid to reduce the water content and then condensing it, and then adding a catalyst such as tin 2-ethylhexanoate to dissolve it. There is a method in which a cyclic dimer (lactide) is produced by polymerization, and after purification by crystallization as necessary, a catalyst such as tin 2-ethylhexanoate is added to the lactide to perform ring-opening polymerization. is there.

  In the concentration step, about 10 to 15% of moisture (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 depolymerization of tin 2-ethylhexanoate or the like under a reduced pressure environment such as heating at 120 to 250 ° C. and a vacuum pump, preferably under a reduced pressure environment of 100 Torr or less. Lactide (lactic acid cyclic dimer ester) is produced by contact with the catalyst. The produced lactide is usually a gas in the environment in the depolymerization process and is often recovered by cooling and condensation.

  The lactide generated in the depolymerization step is sent to the ring-opening polymerization step, and contacted with a ring-opening polymerization catalyst such as tin 2-ethylhexanoate and a polymerization initiator such as 1-dodecanol under heating at 120 to 250 ° C. Polylactic acid is produced.

  The polylactic acid produced in the ring-opening polymerization step contains unreacted monomers and a catalyst. If the unreacted monomer remains in the polymer, deterioration of the polymer properties and decomposition of the polymer may be promoted, so it is necessary to remove the unreacted monomer. Therefore, the unreacted polymer is evaporated from the polymer surface by vacuum degassing using a stirrer or the like. The evaporated unreacted polymer is cooled and recovered.

  In the depolymerization process and de-monomer process, process waste containing lactic acid condensates such as lactic acid, oligomers, and lactide contained in the exhaust is cooled and recovered using a heat exchanger. Therefore, it has become one of the causes of a decrease in raw material yield. Moreover, in the indirect heat exchanger generally used, there existed a problem that an oligomer and lactide coagulate | solidify in a heat exchanger, a piping is obstruct | occluded, and cooling performance falls. Further, there is a problem in that the solidity of the process scattered material enters the vacuum pump on the downstream side of the exhaust, the inner wall of the pump is worn and corroded, and the pump performance is lowered to lower the degree of vacuum.

  On the other hand, in the polymerization of polycondensation polyester such as polyethylene terephthalate, the ethylene glycol vapor distilled off as a by-product in the polycondensation process is recovered using a wet condenser that is directly cooled by spraying cooling ethylene glycol, There exists invention of patent document 1 etc. which reuse as a raw material. Thereby, the deposit | attachment in a condenser can be washed away and obstruction | occlusion of an exhaust system can be avoided.

JP 61-130336 A

  In the technique described in Patent Document 1 described above, since the recovered ethylene glycol vapor contains a large amount of water and terephthalic acid generated in the condensation reaction (esterification reaction), it can be reused as a raw material. I can't do it. Then, although it is necessary to distill ethylene glycol using a distillation column, there exists a problem that an installation cost and an operating cost increase.

  The present invention has been made in view of the above problems, and the object of the present invention is to reduce the degree of vacuum due to blockage of the exhaust system due to process scattered matter in the exhaust gas generated in the depolymerization step and / or the demonomer step and reduction in pump performance. At the same time, process yields are hydrolyzed with water contained in lactic acid and reused as a raw material, while at the same time increasing the concentration of lactic acid to improve polylactic acid yield and synthesis efficiency That is.

  As a result of intensive studies on the above-mentioned problems in order to achieve the above object, the present inventors have found a method and an apparatus for producing polyhydroxycarboxylic acid, particularly lactic acid, which will be explained. That is, in the present invention, the captured and recovered process scattered matter is hydrolyzed using free water contained in a raw material hydroxycarboxylic acid such as lactic acid to return to the original raw material hydroxycarboxylic acid, and reused as a raw material. The present invention relates to a method for producing a polyhydroxycarboxylic acid, which can improve the efficiency of the synthesis process and reduce the cost. Furthermore, the present invention relates to a polyhydroxycarboxylic acid synthesis apparatus including a raw material supply system, a condensation apparatus, a depolymerization apparatus, a purification apparatus, a ring-opening polymerization apparatus, and a demonomer apparatus, and an exhaust system above the depolymerization apparatus and the demonomer apparatus. At least one wet condenser is provided, and the lactic acid cooled in the wet condenser is sprayed or contacted to wash away and remove the process scattered matter contained in the exhaust to prevent clogging of the synthesizer piping and the like.

  According to the present invention, it is possible to prevent the exhaust system from being blocked by the process scattered matter in the exhaust gas generated in the depolymerization process and / or the demonomer process, and the vacuum degree from being lowered due to the pump performance deterioration. Furthermore, the yield of a polyhydroxycarboxylic acid such as polylactic acid and the efficiency of synthesis can be improved by decomposing process waste and reusing it as a raw material.

  As shown in FIG. 1, the typical synthesis process of the present invention concentrates a raw material hydroxycarboxylic acid containing free water in a concentrating device 2, performs condensation polymerization in a condensation polymerization device 3, and then in a depolymerization device 4. After depolymerization and purification, ring-opening polymerization is performed in the ring-opening polymerization apparatus 8 to obtain polyhydroxycarboxylic acid, which is demonomerized in the demonomer apparatus 9 to obtain the target polyhydroxycarboxylic acid. In this synthesis process (condensation reaction, depolymerization, purification, ring-opening polymerization, de-monomer, etc.), process scatters such as hydroxycarboxylic acid monomers and oligomers scatter in the system and adhere to the tube wall and the like. The present invention captures the scattered matter by bringing the gas containing the scattered matter in the depolymerization step and / or the demonomer step in which the oligomer easily scatters into contact with the cooling liquid containing the raw material monomer and free water. In particular, by hydrolyzing the oligomers contained in the scattered matter with the above-mentioned free water and returning it to the raw material monomer, it is possible to reuse the scattered matter that had to be discarded in the past as a raw material, thereby improving the synthesis efficiency. Can do.

  The details will be described below with reference to FIG. Lactic acid is supplied from the lactic acid supply device 1, and moisture is removed in the lactic acid concentration device 2 to form concentrated lactic acid. The concentrated lactic acid is supplied to the lactic acid condensing apparatus 3 and becomes an oligomer (lactic acid condensate) by the condensation reaction. The oligomer is sent to the depolymerization apparatus 4 and becomes lactide by the depolymerization reaction. The lactide is sent to the lactide cooler 6 through the reflux device 5 and separated from moisture, unreacted substances, etc., and then sent to the purification device 7 for purification. The purified lactide is sent to the ring-opening polymerization apparatus 8, and becomes polylactic acid by the ring-opening polymerization reaction. The polylactic acid is sent to the demonomer unit 9 where water, unreacted monomers and the like are removed.

  The wet condenser is installed in at least one of the exhaust system downstream of the lactide cooler and the exhaust system downstream of the demonomer unit. When the wet condenser 10 is provided in the exhaust system downstream of the lactide cooler, the process scattered matter in the exhaust is dissolved and collected by circulating the lactic acid cooled in the condenser. In the case where the wet condenser 11 is provided in the exhaust system downstream of the demonomer apparatus, the process scattered matter in the exhaust is dissolved and collected by circulating lactic acid cooled in the condenser. An indirect heat exchanger may be installed on the exhaust downstream side of the wet condensers 10 and 11. A part of the lactic acid raw material is supplied to the scattered matter collecting tanks 21 and 22 through the pipe 31 and used as the scattered matter capturing liquid of the wet capacitors 10 and 11.

  In the present invention, as the wet capacitor, one or more shelves are provided, and a liquid film is generated by circulating and flowing raw lactic acid as a cooling liquid from above, and the process is dispersed by contacting exhaust with the liquid film. A shelf type that dissolves and collects substances, a shower nozzle that is provided with a shower nozzle above, sprays raw lactic acid as a cooling liquid, and contacts and discharges the process scattered matters by contacting the droplets with exhaust, There are a combination of a shelf type and a shower type, and the shelf type is arranged at the top and the shower type is arranged at the bottom, and any of them may be used. FIG. 2 is a schematic diagram of a shelf type wet capacitor, FIG. 3 is a schematic diagram of a shower type wet capacitor, and FIG. 4 is a schematic diagram of a wet capacitor in which a shelf type and a shower type are combined. In the figure, 23 is a wet condenser body, 24 is a gas inlet pipe, 25 is a non-condensable gas discharge pipe, 26 is a lactic acid supply pipe, 27 is a condensate discharge pipe, 28 is a lactic acid supply nozzle, 29 is a shelf, 30 is a lactic acid shower nozzle.

  In the present invention, as a wet capacitor, one or a plurality of shelves are provided, and a raw material lactic acid is circulated and flowed down as a cooling liquid from above to generate a liquid film, and exhaust gas is brought into contact with this liquid film to process scattered matter. There is a shelf type that dissolves and collects, a shower nozzle that is provided with a shower nozzle above, sprays raw lactic acid as a cooling liquid, and contacts and discharges process splashes by contacting the droplets with exhaust. However, either one may be used.

  This method has the following advantages. Compared to conventionally used indirect heat exchangers, there is an advantage that process scattered matters are not solidified and blocked in the heat exchanger. This is because, in the heat exchanger, the process scattered matter made of lactide, oligomer, etc. is washed away with raw material lactic acid and hydrolyzed with water contained in the lactic acid, so that the scattered material returns to the raw material lactic acid and becomes liquid. In addition, since the water contained in lactic acid is consumed by hydrolysis, the lactic acid used for cooling is concentrated, and by reusing it, the time required for the concentration process can be shortened and energy can be saved. There is also an advantage in terms of improvement. Moreover, unlike the case of polyester polymerization described in Patent Document 1, lactic acid used for cooling is concentrated, so that it is not necessary to separate it from water in a distillation column. As a result, facility costs and operating costs are reduced.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings. The apparatus for synthesizing this polylactic acid is, from the upstream side of the reaction path, lactic acid supply device 1, lactic acid concentration device 2, lactic acid condensation device 3, depolymerization device 4, reflux device 5, lactide cooler 6, purification device 7, ring-opening polymerization device. 8. Arranged in the order of the demonomer unit 9.

  The polylactic acid production apparatus of the present invention is obtained by evaporating moisture contained in lactic acid in the lactic acid concentrating apparatus 2 to form concentrated lactic acid, and condensing the concentrated lactic acid in the lactic acid condensing apparatus 3 to generate a lactic acid oligomer, and the obtained lactic acid oligomer Is depolymerized under reduced pressure in the depolymerizer 4, and then purified by a purifier to obtain lactide. The obtained lactide is subjected to ring-opening polymerization under reduced pressure in the ring-opening polymerizer 8, and then the demonomer unit 9. The product is produced by removing unreacted materials and the like.

  Water contained in lactic acid is preferably removed by heating as much as possible and evaporating. In the lactic acid condensation apparatus 3, lactic acid oligomer is produced by heating lactic acid under reduced pressure. In the present invention, the lactic acid oligomer is a concept including a lactic acid polymer having a molecular weight of about 50,000 from a dimer of lactic acid, but the molecular weight of the lactic acid oligomer obtained by the lactic acid condensation reaction is usually 500 to 500 in terms of average molecular weight. It is 10,000, preferably 1,000 to 5,000.

  The lactic acid condensation reaction is usually carried out at a pressure of 100 Torr or less, desirably 10 Torr or less, more preferably 1 Torr or less, and usually 100 to 220 ° C., preferably 130 to 200 ° C. By shortening the heating time as much as possible, thermal decomposition of lactic acid and lactic acid 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, conventionally known ones can be used.For example, organotin catalysts such as tin lactate, tin tartrate, tin dicaprylate, tin dilaurate, tin dipalmitate, tin distearate, tin dioleate, Examples thereof include tin α-naphthoate, tin β-naphthoate, tin octylate, and powdered tin.

  The lactic acid condensation apparatus has at least a reactor, a concentrated lactic acid supply port, and a lactic acid oligomer discharge port. The reactor may be vertical or horizontal.

  As a heating method in the reactor, a method usually used in this technical field can be used. For example, a heating medium jacket is provided 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.

  The depolymerization apparatus 4 is provided with a decompression device, and usually depolymerization reaction of lactic acid oligomer by heating at 120 to 250 ° C., preferably 170 to 200 ° C. in a reduced pressure environment of 100 Torr or less, preferably 10 Torr or less. To implement. Lactide is generated as a gas by the depolymerization reaction. In the present invention, lactide is a cyclic ester produced by dehydrating two molecules of water from two molecules of lactic acid.

  The depolymerization apparatus 4 has at least a reactor, a lactic acid oligomer supply port, and a lactide 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 usually used in this technical field can be used. For example, a heating medium jacket is provided 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.

  In the depolymerization reaction, a catalyst for the depolymerization reaction may be added 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 Group IA, Group IIIA, Group IVA, Group IIB and Group 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, and aluminum chloride.

  Examples of those belonging to the group IVA include organotin-based catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin distearate, tin dioleate, α-naphthoic acid tin, β-naphthoic acid 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 the catalyst used is 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 lactic acid oligomer.

  The vapor containing lactide generated in the depolymerization apparatus 4 is discharged out of the depolymerization apparatus and supplied to the lactide cooler. Here, the lactide is cooled, condensed and recovered, and then transferred to a purification apparatus.

  For the lactide cooler, 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 to prevent lactide from contacting with a water-containing refrigerant and causing hydrolysis to produce an acid. When the acid is generated, the progress of the ring-opening polymerization reaction is hindered as an acid catalyst, and there is a possibility of causing corrosion of a material such as a cooler. When using a refrigerant inert to lactide, such as nitrogen gas, it is not limited to the above. In that case, it is necessary to sufficiently dry the refrigerant to reduce moisture.

  The lactide discharged from the purification device 7 is transferred to the ring-opening polymerization device 8. 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 8 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 arranged 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 usually used in this technical field can be used. For example, a heating medium jacket is provided 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.

  In the ring-opening polymerization reaction, a catalyst for the depolymerization reaction may be added 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 Group IA, Group IIIA, Group IVA, Group IIB and Group 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, and aluminum chloride.

  Examples of those belonging to the group IVA include organotin-based catalysts (for example, tin lactate, tin tartrate, tin dicaprylate, tin distearate, tin dioleate, α-naphthoic acid tin, β-naphthoic acid 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 a depolymerization reaction may be added as necessary for the purpose of adjusting the molecular weight. As the polymerization initiator, alcohols such as 1-dodecanol can be used.

  The polylactic acid produced in the ring-opening polymerizer 8 is sent to a demonomer apparatus. The demonomer apparatus creates a negative pressure environment while maintaining a molten state, and removes unreacted lactide and the like.

  A depressurization apparatus is installed in the demonomer apparatus 9 and is heated at a temperature of usually 120 to 250 ° C., preferably 180 to 200 ° C. and higher than the ring-opening polymerizer under a reduced pressure environment of 100 Torr or less, preferably 1 Torr or less. By doing so, the de-monomer from polylactic acid is implemented.

  The demonomer apparatus has at least a reactor, a polylactic acid supply port, and a polylactic acid discharge port. A normal thermometer is also installed. The reactor is not particularly limited, and various reactors such as a twin-screw extruder, a single-screw extruder, or a four-screw extruder horizontal reactor 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.

  The wet capacitors 10 and 11 are used in at least one of an exhaust system downstream of the depolymerization apparatus 9 or an exhaust system downstream of the demonomer apparatus 9. Exhaust gas discharged from the depolymerization device and / or the demonomer device is introduced into the wet condenser, and lactic acid cooled by a cooler is circulated to dissolve and collect process scattered matters contained in the exhaust gas.

  The temperature of the cooled lactic acid is 0 to 100 ° C, preferably about 10 to 30 ° C. As shown in FIGS. 2 to 4, as the wet capacitor, one or more shelves are provided, and a liquid film is generated by circulating and flowing down lactic acid as a cooling liquid from above, and exhaust is brought into contact with the liquid film. A shelf type that dissolves and collects process scattered matter by providing a shower nozzle above, spraying lactic acid as a cooling liquid, and contacting the exhaust with this droplet dissolves and collects the process scattered matter There is a shower type or the like, and any of them may be used.

  In addition, since the water vapor | steam generate | occur | produced in the depolymerization process and / or the monomer removal process is contained in exhaust_gas | exhaustion, the indirect heat exchanger for condensing and collecting water vapor | steam can also be arrange | positioned in the front stage of a wet condenser. The wet capacitor may be applied to an exhaust system in a crystallization process, a drying process, and a solid phase degassing process performed after the demonomer process.

  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]
In the lactic acid concentrating device 2, 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 device 14, lactic acid is removed from the gas, and refluxed to the lactic acid concentrator 2. The concentrated lactic acid produced by the lactic acid concentrating device 2 is sent to the lactic acid condensing device 3.

  In the lactic acid condensing apparatus 3, the condensation reaction of lactic acid is advanced, and the water | moisture content generated in connection with this is evaporated. 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, a low molecular weight lactic acid oligomer and lactide generated by the decomposition thereof are generated as a gas. These move from the lactic acid condensation device 5 toward the decompression device 8. These gases enter the reflux device 6, lactic acid, low molecular weight lactic acid oligomers, and lactide are removed from the gas and are refluxed to the lactic acid condensing apparatus 5.

  The lactic acid oligomer produced by the lactic acid condensation device 3 is sent to the depolymerization device 4. In the depolymerization apparatus 4, the depolymerization reaction of the lactic acid oligomer proceeds. The reaction is carried out by reducing the pressure to 10 torr or less and bringing the lactic acid oligomer into contact with a depolymerization catalyst such as antimony trioxide or tin octylate at a temperature of 120 to 250 ° C. The gaseous lactide generated by this reaction is cooled and condensed in the lactide cooler 6 and then sent to the purifier 7.

  The lactide purified by the purification device 7 is sent to the ring-opening polymerization device 8. In the ring-opening polymerization apparatus 8, the ring-opening polymerization reaction of lactide proceeds. 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. The polylactic acid produced by this reaction is sent to the demonomer apparatus 9.

  The monomer removal apparatus 9 creates a negative pressure environment while maintaining a molten state, and removes unreacted lactide and the like contained in polylactic acid. The reaction is performed under a reduced pressure to 10 torr or less and at a temperature of 120 to 250 ° C. and higher than that of the ring-opening polymerization apparatus.

  The wet condenser 10 is used for an exhaust system downstream of the depolymerization apparatus, and the wet condenser 11 is used for an exhaust system downstream of the demonomer 9. Exhaust gas discharged from the depolymerizer is introduced into the wet condenser 10, and lactic acid cooled by the cooler 19 is circulated to dissolve and collect process scattered matters contained in the exhaust gas. The temperature of the cooled lactic acid is 0 to 100 ° C, preferably about 10 to 30 ° C.

  Exhaust gas discharged from the demonomer unit 9 is introduced into the wet condenser 11, and lactic acid cooled by the cooler 20 is circulated to dissolve and collect process scattered matters contained in the exhaust gas.

  Lactic acid is sent from the lactic acid supply device 1 to the recovery tanks 21 and 22 for use as a cooling medium for the wet capacitors 10 and 11 via the lactic acid concentration device 2 and the pipe 31. The branched lactic acid is supplied to the recovery tanks 21 and 22 via the pipes 32 and 33, respectively. Since unconcentrated lactic acid is supplied to the wet condenser here, lactic acid is also heated and concentrated when used for trapping and collecting scattered matter, and as a result, energy consumption in the concentrator 2 is reduced. Can do.

  The circulation of lactic acid is performed until its concentration rises to an arbitrary value, and then returned to the lactic acid supply device 1 or the lactic acid concentration device 2 to be reused as a raw material. The concentration is desirably 98% or less, preferably 95% or less, from the viewpoint of reducing poor circulation due to an increase in viscosity. In addition, since the water vapor | steam generate | occur | produced in the depolymerization process and the de-monomer process is contained in exhaust_gas | exhaustion, you may arrange | position the indirect heat exchanger for condensing and collecting water vapor | steam in the front | former stage of a wet condenser. When polylactic acid was synthesized following the depolymerization step and the demonomer step, the raw material yield was 65%.

(Comparative example)
When polylactic acid was synthesized with a polylactic acid synthesizer using a conventional indirect heat exchanger in the exhaust system, the raw material yield was 60%. When using an indirect heat exchanger, it is not possible to capture, recover and reuse the scattered matter from the reactor or demonomer unit. Compared to lower.

It is the schematic which shows one Embodiment of the apparatus regarding the polylactic acid synthesis | combination of this invention. Schematic which shows the 1st structural example of the wet capacitor | condenser in the polylactic acid synthesis apparatus of this invention. Schematic which shows the 2nd structural example of the wet capacitor | condenser in the polylactic acid synthesis apparatus of this invention. Schematic which shows the 3rd structural example of the wet capacitor | condenser in the polylactic acid synthesis apparatus of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Lactic acid supply apparatus, 2 ... Lactic acid concentration apparatus, 3 ... Lactic acid condensation apparatus, 4 ... Depolymerization apparatus, 5 ... Refluxer, 6 ... Lactide cooler, 7 ... Purification apparatus, 8 ... Ring-opening polymerization apparatus, 9 ... Desorption Monomer unit, 10, 11 ... wet condenser, 12 ... decompression device, 13 ... decompression device, 14 ... reflux, 15 ... decompression device, 16 ... indirect heat exchanger, 17 ... indirect heat exchanger, 18 ... indirect heat exchanger , 23 ... wet condenser body, 24 ... gas inlet pipe, 25 ... non-condensable gas discharge pipe, 26 ... lactic acid supply pipe, 27 ... condensate discharge pipe, 28 ... lactic acid supply nozzle, 29 ... shelf, 30 ... lactic acid shower nozzle.

Claims (6)

After concentrating the raw material hydroxycarboxylic acid with a concentrating device, performing condensation polymerization in a condensation polymerization device, performing depolymerization with a depolymerization device, purifying the product, and performing opening polymerization with a ring-opening polymerization device, process debris containing condensate of the acid generated at least one depolymerization step and demonomer step in polyhydroxycarboxylic acid synthesis demonomer with de monomer unit, as a raw material, a hydroxy carboxylic acid containing water A step of contacting the refrigerant with the condensate using a wet condenser provided in an exhaust system of the depolymerization step or demonomer step as a refrigerant to hydrolyze the condensate and return it to a raw material hydroxycarboxylic acid. A method for synthesizing polyhydroxycarboxylic acid. The method for synthesizing a polyhydroxycarboxylic acid according to claim 1 , wherein the hydroxycarboxylic acid produced by hydrolysis is reused as a raw material for the synthesis of polyhydroxycarboxylic acid. 2. The method for synthesizing a polyhydroxycarboxylic acid according to claim 1 , wherein the hydroxycarboxylic acid is lactic acid. The method for synthesizing a polyhydroxycarboxylic acid according to claim 1 , wherein the hydroxycarboxylic acid is glycolic acid. Concentration device for concentrating the raw material hydroxycarboxylic acid, condensation polymerization device for condensation polymerization of the hydroxycarboxylic acid, depolymerization device for depolymerizing the condensate obtained by the condensation device, and generation device for purifying the product A ring-opening polymerization apparatus for ring-opening polymerization of the produced polymer, a demonomer apparatus for demonomerization from the obtained polymer, and a wet system provided in at least one of the exhaust system of the depolymerization apparatus and the demonomer apparatus The wet-type capacitor has a capacitor , and the process uses a hydroxycarboxylic acid containing moisture as a raw material as a refrigerant, and includes a process product containing a hydroxycarboxylic acid condensate generated in the exhaust system of the depolymerization unit or demonomer unit. Is brought into contact with the refrigerant and hydrolyzed to return to the raw material hydroxycarboxylic acid . 6. The apparatus for synthesizing polyhydroxycarboxylic acid according to claim 5 , wherein the captured scattered matter is reused as a raw material for synthesizing polyhydroxycarboxylic acid.

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