Polylactide manufacturing apparatus and method for manufacturing polylactide

1. An apparatus for manufacturing polylactide which includes the steps of preparing lactide through oligomerization of lactic acid and depolymerization of the resulting oligomers, effecting ring-opening polymerization of the lactide, and removing unreacted lactide from the resulting polymers, the apparatus comprising an exhausting gas treatment device for reducing pressure in the step of removing unreacted lactide,

wherein the exhausting gas treatment device includes:

a boiler for generating water vapor;

a pressure-reducing section having a stage including an ejector driven with the water vapor, a condenser connected downstream of the ejector, and a hot well tank connected to the condenser; and

a main condenser and a main hot well tank connected to the main condenser, the main condenser and the main hot well tank being disposed on a pipe line through which a gas of the unreacted lactide is suctioned into the pressure-reducing section, and

wherein the gas of the unreacted lactide is washed away in the main condenser with the use of a liquid collected in the main hot well tank.

2. An apparatus for manufacturing polylactide which includes the steps of preparing lactide through oligomerization of lactic acid and depolymerization of the resulting oligomers, effecting ring-opening polymerization of the lactide, and removing unreacted lactide from the resulting polymers, the apparatus comprising an exhausting gas treatment device for reducing pressure in the step of removing unreacted lactide,

wherein the exhausting gas treatment device includes:

a boiler for generating water vapor;

a pressure-reducing section having a stage including an ejector driven with the water vapor, a condenser connected downstream of the ejector, and a hot well tank connected to the condenser; and

a main condenser and a main hot well tank connected to the main condenser, the main condenser and the main hot well tank being disposed on a pipe line through which a gas of the unreacted lactide is suctioned into the pressure-reducing section, and

wherein the gas of the unreacted lactide is washed away in the main condenser with the use of a liquid containing lactic acid as a main component, the liquid having been collected in the main hot well tank.

3. The apparatus for manufacturing polylactide according to claim 1 , wherein the exhausting gas treatment device further includes a vacuum pump for reducing a pressure in the pressure-reducing section.

4. The apparatus for manufacturing polylactide according to claim 1 , wherein the exhausting gas treatment device further includes a water tank and pipe lines through which water in the water tank is supplied to the main hot well tank via the hot well tank.

5. The apparatus for manufacturing polylactide according to claim 4 ,

wherein each of the main hot well tank and the hot well tank includes a device that directly or indirectly measures a concentration of lactic acid, and

wherein, when a measured concentration of lactic acid has exceeded a predetermined value, a lactic acid solution of a lower concentration is caused to flow from the hot well tank to the main hot well tank or water is caused to flow from the water tank to the hot well tank, so that the concentration of lactic acid is controlled.

6. The apparatus for manufacturing polylactide according to claim 2 , wherein the exhausting gas treatment device further includes a vacuum pump for reducing a pressure in the pressure-reducing section.

7. The apparatus for manufacturing polylactide according to claim 2 , wherein the exhausting gas treatment device further includes a water tank and pipe lines through which water in the water tank is supplied to the main hot well tank via the hot well tank.

8. An apparatus for manufacturing polylactide which includes the steps of preparing lactide through oligomerization of lactic acid and depolymerization of the resulting oligomers, effecting ring-opening polymerization of the lactide, and removing unreacted lactide from the resulting polymers, the apparatus comprising an exhausting gas treatment device for reducing pressure in the step of removing unreacted lactide,

wherein the exhausting gas treatment device includes:

a boiler for generating water vapor;

a pressure-reducing section having multiple stages connected in series, the multiple stages each including an ejector driven with the water vapor, a condenser connected downstream of the ejector, and a hot well tank connected to the condenser; and

a main condenser and a main hot well tank connected to the main condenser, the main condenser and the main hot well tank being disposed on a pipe line through which a gas of the unreacted lactide is suctioned into the pressure-reducing section, and

wherein the gas of the unreacted lactide is washed away in the main condenser with the use of a liquid containing lactic acid as a main component, the liquid having been collected in the main hot well tank.

9. The apparatus for manufacturing polylactide according to claim 8 , wherein the exhausting gas treatment device further includes a water tank and pipe lines through which water in the water tank is sequentially supplied, via the multiple hot well tanks, to the main hot well tank.

10. A apparatus for manufacturing polylactide which includes the steps of preparing lactide through oligomerization of lactic acid and depolymerization of the resulting oligomers, effecting ring-opening polymerization of the lactide, and removing unreacted lactide from the resulting polymers, the apparatus comprising an exhausting gas treatment device for reducing pressure in the step of removing unreacted lactide,

wherein the exhausting gas treatment device includes:

a boiler for generating water vapor;

a pressure-reducing section having multiple stages connected in series, the multiple stages each including an ejector driven with the water vapor, a condenser connected downstream of the ejector, and a hot well tank connected to the condenser; and

a main condenser and a main hot well tank connected to the main condenser, the main condenser and the main hot well tank being disposed on a pipe line through which a gas of the unreacted lactide is suctioned into the pressure-reducing section, and

wherein the gas of the unreacted lactide is washed away in the main condenser with the use of a liquid collected in the main hot well tank.

11. The apparatus for manufacturing polylactide according to claim 8 , wherein the exhausting gas treatment device further includes a vacuum pump for reducing a pressure in the pressure-reducing section.

12. The apparatus for manufacturing polylactide according to claim 10 , wherein the exhausting gas treatment device further includes a vacuum pump for reducing a pressure in the pressure-reducing section.

13. The apparatus for manufacturing polylactide according to claim 10 , wherein the exhausting gas treatment device further includes a water tank and pipe lines through which water in the water tank is sequentially supplied, via the multiple hot well tanks, to the main hot well tank.

14. The apparatus for manufacturing polylactide according to claim 13 ,

wherein each of the main hot well tank and the multiple hot well tanks includes a device that directly or indirectly measures a concentration of lactic acid, and

wherein, when a concentration of lactic acid measured in one of the hot well tanks has exceeded a predetermined value, water or a lactic acid solution of a lower concentration is caused to flow to the relevant hot well tank from the water tank or a hot well tank that is located immediately after the relevant hot well tank, so that the concentration of lactic acid is controlled.

15. A method for manufacturing polylactide, comprising the steps of preparing lactide through oligomerization of lactic acid and depolymerization of the resulting oligomers, effecting ring-opening polymerization of the lactide, and removing unreacted lactide from the resulting polymers, the method including an exhausting gas treatment method for reducing pressure in the step of removing unreacted lactide,

wherein the exhausting gas treatment method includes the steps of:

generating water vapor;

driving an ejector with the generated water vapor so as to suction a gas of the unreacted lactide;

washing away the gas of the unreacted lactide in a main condenser with the use of a liquid containing lactic acid as a main component that has been collected in a main hot well tank, using the suction of the ejector; and

mixing the gas of the unreacted lactide suctioned by the ejector with the water vapor, guiding the mixture into a condenser connected downstream of the ejector, and guiding the lactic acid collected in the condenser into a hot well tank.

16. The method for manufacturing polylactide according to claim 15 , wherein the gas of the unreacted lactide that has passed through the ejector is suctioned by means of a vacuum pump.

17. The method for manufacturing polylactide according to claim 15 , wherein the step of mixing the gas of the unreacted lactide suctioned by the ejector with the water vapor, guiding the mixture into the condenser connected downstream of the ejector, and guiding the lactic acid collected in the condenser into the hot well tank is performed a plurality of times in series.