JP2006101876A - Method for producing lactic acid and apparatus for lactic acid production - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a polylactic acid having a desired molecular weight in high efficiency in a short time and an apparatus for producing lactic acid having high concentration in high efficiency. <P>SOLUTION: The method for the production of a polylactic acid comprises the fermentation of vegetable starch and lactobacillus and the dehydrative polycondensation of the produced lactic acid to synthesize the polylactic acid. The polylactic acid production method contains a fermentation and concentration step to pass a DC current through a mixture containing the vegetable starch, the lactobacillus and the lactic acid in a fermentation tank having at least one pair of electrodes, a diaphragm and a concentration part separated by the diaphragm and placed at the cathode side of the electrodes and transfer and store the lactic acid to the concentration part by electro-osmosis, and a polymerization step to perform the thermal dehydrative polycondensation of the lactic acid to form the polylactic acid in a polymerization tank charged with the lactic acid stored in the concentration part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing polylactic acid, which is a biodegradable plastic, and a lactic acid production apparatus.

  Biodegradable plastics perform as well as normal plastics during use, and are quickly degraded by microorganisms in the natural environment (for example, in the soil) after use. It is a plastic that becomes water and carbon dioxide, and is currently attracting attention due to waste issues.

Various products have been announced as biodegradable plastics.
For example, polylactic acid obtained by dehydration polymerization of lactic acid obtained by fermenting starch such as corn and potato with lactic acid bacteria is used for agricultural multi-films and compost bags.

  Polylactic acid is obtained by dehydrating polycondensation of lactic acid. Conventionally, it is known that lactic acid can be obtained by lactic acid fermentation when lactic acid bacteria are allowed to act on plant starch. However, according to the conventional method, the pH of the reaction solution is lowered during the fermentation process and the activity of lactic acid bacteria is often inhibited, and it is difficult to efficiently obtain a high concentration of lactic acid. The pH drop of the reaction solution is presumed to be caused by the fact that the lactic acid produced by the fermentation remains in the fermenter when the plant starch and lactic acid bacteria are allowed to act.

  In addition, polylactic acid is added by adding an appropriate amount of a catalyst (for example, a mixture of equal amounts of ruthenium oxide and titanium oxide) to concentrated lactic acid, and heating while stirring to cause dehydration condensation polymerization of lactic acid. It is known to be obtained. At this time, it is necessary to discharge the water generated in the dehydration condensation polymerization reaction to the outside of the system, and conventionally, a method of evaporating water under reduced pressure is used as a method of discharging such water (for example, Patent Document 1). reference.).

  However, according to the method of evaporating water under reduced pressure, the viscosity of the polymer increases as the polymerization reaction proceeds, so that there is a disadvantage that the water dissociation rate becomes slow and the dehydration cannot be performed efficiently.

JP 2003-335850 A

  The present invention has been made in view of the above, and a method for producing polylactic acid capable of obtaining polylactic acid having a desired molecular weight in high efficiency and in a short time, and lactic acid from which high concentration lactic acid can be obtained with high efficiency An object is to provide a manufacturing apparatus.

In order to achieve the above object, the method for producing polylactic acid according to the present invention produces polylactic acid by fermenting plant starch and lactic acid bacteria to produce lactic acid, and dehydrating condensation polymerization of the lactic acid to synthesize polylactic acid. A fermentor provided with at least a pair of electrodes, partition walls and the partition walls, and the concentration section provided on the cathode side of the electrodes, and the plant starch and the Fermentation concentration step of transferring and storing the lactic acid to the concentration part by electroosmosis through a direct current through a mixture containing lactic acid bacteria and the lactic acid,
And a polymerization step of synthesizing polylactic acid by heating and dehydrating and condensing the lactic acid in a polymerization tank to which the lactic acid stored in the concentrating unit is supplied.

  According to the method for producing polylactic acid of the present invention (hereinafter sometimes referred to as “the production method of the present invention”), in the lactic acid production process used for the production of polylactic acid, an electroosmotic action is used to make a fermenter. The lactic acid inside can be separated from unfermented lactic acid bacteria and plant starch. Therefore, the lactic acid concentration in the mixture directly related to the production of lactic acid in the fermenter can be kept low, and the pH drop of the mixture can be suppressed. Thereby, according to the manufacturing method of this invention, high concentration lactic acid can be obtained and the polylactic acid which has a desired molecular weight can be efficiently manufactured by using this. The “electroosmosis” refers to the movement of an electrically neutral solvent by a potential difference through a porous substance such as a membrane.

  Further, according to the manufacturing method of the present invention, in an electric dehydration tank, which has at least a pair of electrodes, a partition, and a dehydration part partitioned by the partition, and the dehydration part is provided on the cathode side of the electrode In the polymerization step, an electric dehydration step may be included in which water in the lactic acid polymer is transferred to the dehydration unit by electroosmosis through a direct current through the lactic acid polymer subjected to dehydration condensation polymerization.

  According to the production method of the present invention, in the electric dehydration step, water contained in the lactic acid polymer (polylactic acid) subjected to dehydration condensation polymerization in the polymerization step can be moved to the dehydration part by electroosmosis. Thereby, even if it is the state which superposition | polymerization of the lactic acid polymer advanced and the viscosity became high, it can dehydrate efficiently. In the present specification, the “lactic acid polymer” means the stage before reaching the polylactic acid having the target molecular weight in the production method and each apparatus of the present invention, that is, an oligomer of lactic acid and a polycrystal that has not yet reached the desired molecular weight. It means lactic acid, and the lactic acid polymer includes a state in which moisture generated in the dehydration condensation polymerization reaction of lactic acid is included.

  In the production method of the present invention, corn starch can be suitably used as the vegetable starch.

  The lactic acid production apparatus of the present invention has at least a pair of electrodes, a partition wall, and a concentration section partitioned by the partition wall, and the fermentation section provided on the cathode side of the electrode, a vegetable starch, Raw material introduction means for introducing lactic acid bacteria into the fermenter, and direct current is passed through a mixture of lactic acid obtained by fermenting the plant starch and the lactic acid bacteria in the fermenter, the plant starch, and the lactic acid bacteria. The lactic acid is moved to the concentration part by electroosmosis.

  The lactic acid production apparatus of the present invention can separate lactic acid in the fermenter from unfermented lactic acid bacteria and plant starch using electroosmosis by passing a direct current through the mixture in the fermenter. Therefore, the lactic acid concentration in the mixture directly related to the production of lactic acid in the fermenter can be kept low, and the pH drop of the mixture can be suppressed. Thereby, according to the lactic acid manufacturing apparatus of this invention, high concentration lactic acid can be manufactured efficiently. Moreover, the lactic acid manufacturing apparatus of this invention can comprise the anode of the said electrode in mesh shape.

  The lactic acid production apparatus of the present invention includes a discharge pipe that discharges lactic acid moved to the concentrating unit, a lactic acid storage tank that is supplied with the lactic acid discharged from the discharge pipe and stores the lactic acid, and the lactic acid storage tank The lactic acid in the lactic acid storage tank and discharge means for discharging the lactic acid in the lactic acid storage tank to the outside can be provided.

  The lactic acid production apparatus of the present invention can increase the concentration of lactic acid by circulating the concentration unit of the fermenter and the lactic acid storage tank through the discharge pipe and the supply pipe.

  The polylactic acid production apparatus of the present invention comprises a lactic acid introduction means for introducing lactic acid, a polymerization means for heating and dehydrating condensation polymerization of lactic acid introduced from the lactic acid introduction means, and at least a pair of electrodes, partition walls, and the partition walls. An electrodehydration means having a dehydration part partitioned and the dehydration part provided on the cathode side of the electrode, and the electric dehydration means is a lactic acid polymer subjected to dehydration condensation polymerization in the polymerization means The water in the lactic acid polymer is moved to the dehydrating part by electroosmosis through a direct current, and dehydrated.

  According to the polylactic acid production apparatus of the present invention, water contained in lactic acid (polylactic acid) subjected to dehydration condensation polymerization in a polymerization tank can be moved to a dehydration part by electroosmosis. Thereby, even if the polymerization of polylactic acid progresses and the viscosity becomes high, dehydration can be performed efficiently, and polylactic acid having a desired molecular weight can be produced with high efficiency and in a short time.

  The polylactic acid production apparatus of the present invention further includes a raw material introduction means for introducing plant starch and lactic acid bacteria, and a fermenter, and the fermenter is partitioned by at least a pair of electrodes, partition walls, and the partition walls. And a fermentation concentrating means equipped with a concentrating part provided on the cathode side of the electrode, the fermenting concentration means fermenting the plant starch and lactic acid bacteria introduced from the raw material introducing means in the fermenter The lactic acid obtained is transferred to the concentration unit by electroosmosis through direct current through direct current, the lactic acid is stored in the concentration unit, and the lactic acid stored in the concentration unit is supplied to the polymerization means. it can.

  The polylactic acid production apparatus of the present invention can supply a high concentration of lactic acid to the polymerization tank by further comprising a fermentation concentration means. Moreover, a lactic acid production | generation process and a polylactic acid polymerization process can be performed continuously, and polylactic acid can be manufactured efficiently.

  The polylactic acid production apparatus of the present invention is configured such that the fermentation concentration means is supplied with a discharge pipe for discharging the lactic acid stored in the concentration unit, and the lactic acid discharged from the discharger and stores the lactic acid. A storage tank, a supply pipe that supplies the lactic acid in the lactic acid storage tank to the concentrating unit, and a supply means that supplies the lactic acid in the lactic acid storage tank to the polymerization means.

  The polylactic acid production apparatus of the present invention can further increase the concentration of lactic acid by circulating the concentration unit of the fermenter and the lactic acid storage tank through the discharge pipe and the supply pipe. Moreover, the lactic acid manufacturing apparatus of this invention may comprise the anode of the said electrode in mesh shape.

  In the polylactic acid production apparatus of the present invention, the polymerization means has an opening at both ends, the hollow base to which the lactic acid is supplied from one opening, the interior of the hollow base, and from the one opening A rod-shaped rotating body having a spiral groove whose groove width becomes narrower toward the other opening, and a heating means for heating the inside of the hollow base, and rotating the rod-shaped rotating body to rotate the lactic acid. It can comprise so that it may compress by heating-pressing toward the said other opening part from said one opening part. The rod-shaped rotating body may have a spiral groove whose groove width becomes narrower from the one opening to the other opening.

  According to the polylactic acid production apparatus of the present invention, when the rod-like rotating body is rotated, lactic acid is heated from the lactic acid supply side provided on one side of the hollow base toward the other pressure outlet side according to the spiral groove. While being pumped, it can be compressed under a desired pressure. Thereby, lactic acid can be heated efficiently and dehydration condensation polymerization can be performed.

  The internal structure of the hollow substrate can be configured in any shape such as circular, elliptical, rectangular, rectangular, etc., but the cross section is from the point that the pressure applied to lactic acid is uniform by the rod-shaped rotating body rotating inside the substrate. A circular shape is preferred. In addition, the spiral groove can be provided from one end of the rod-shaped rotating body toward the other end so that the helical pitch (groove width) gradually narrows from the lactic acid supply side to the outlet side when the spiral groove is embedded in the hollow base body, Pumping plant material. Therefore, it is preferable that the rod-shaped rotating body is a rod-shaped body having a substantially circular cross section from the viewpoint that uniform compression can be performed efficiently.

  In the polylactic acid production apparatus of the present invention, the electric dehydration means is provided adjacent to the hollow body through which the lactic acid is inserted and the hollow body so as to reversely rotate with the insertion direction of the lactic acid as a rotation axis. And a plurality of arranged rotating blades.

  The polylactic acid production apparatus of the present invention has a structure that rotates by receiving fluid pressure due to the flow of a fluid passing through the inside of a hollow body through a rotating blade, that is, a lactic acid polymer (polylactic acid) polymerized in a polymerization tank (for example, flow direction). A blade-shaped stator that is twisted so as to rotate under the force of the above is desirable, and continuous stirring can be performed without connecting a drive unit. The rotating blades can be provided so that a plurality of adjacent blades rotate reversely with each other with the fluid insertion direction as a rotation axis (that is, alternately rotate in the reverse direction), so by stirring the lactic acid polymer, Water can be easily separated by electroosmosis. As a result, the dehydrating apparatus can be reduced in size without deteriorating the dehydrating efficiency. You may comprise a rotary blade so that it may rotate with the motor and magnetic force which were connected with the power supply. Further, the internal structure of the hollow body is configured so that a lactic acid polymer or the like can be inserted, and the cross section can be configured in an arbitrary shape such as a circular shape, an elliptical shape, a rectangular shape, a rectangular shape, and a hollow body having a circular cross section is particularly preferable. .

  Moreover, it is preferable to connect a power supply to said rotary blade and to function as an anode of the electrode in the said electrical dehydration means. Thereby, with stirring of the rotary blade, water mixed in the lactic acid polymer easily comes into contact with the anode, and dehydration can be performed with higher efficiency.

  As plant starch used in the lactic acid production apparatus and polylactic acid production apparatus of the present invention, corn starch can be suitably used. Any plant starch can be used in the present invention, but corn starch is preferably used from the viewpoints of work efficiency, availability, quality of polylactic acid obtained, and the like.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the polylactic acid which can obtain the polylactic acid which has a desired molecular weight highly efficiently in a short time, and the lactic acid manufacturing apparatus which can obtain high concentration lactic acid with high efficiency can be provided. .
In addition, by using the polylactic acid production method, lactic acid production apparatus, and polylactic acid production apparatus of the present invention, it is possible to carry out continuously from the production of lactic acid to the polymerization of polylactic acid, and downsizing of the equipment. It is also possible to reduce the price, simplify the operation, and reduce the manufacturing cost.

  Embodiments of the present invention will be described below with reference to the drawings. In the following, the case where corn starch is used as the vegetable starch will be mainly described, but the present invention is not limited to these embodiments.

  The method for producing polylactic acid according to the present invention is roughly divided into a fermentation and concentration step in which corn starch and lactic acid bacteria are fermented to produce and concentrate lactic acid, and a polymerization step in which the obtained lactic acid is polymerized. Hereinafter, the case where the lactic acid production apparatus and the polylactic acid production apparatus of the present invention are used in each step will be described as an example.

<Fermentation concentration process>
The lactic acid production apparatus of the present invention will be described with reference to FIGS. FIG. 1 is a schematic view conceptually showing the structure of the lactic acid production apparatus of the present invention. As shown in FIG. 1, the lactic acid production apparatus 10 of the present invention includes a mixing device 20, a fermentation tank 30, and a lactic acid storage tank 50. The lactic acid production apparatus 10 ferments a mixture containing corn starch and lactic acid bacteria mixed in the mixing apparatus 20 in a fermenter 30 to produce lactic acid, separates the produced lactic acid from other mixtures, and a lactic acid storage tank 50. By circulating and concentrating between the two, a high concentration of lactic acid is obtained.

  The mixing device 20 is not particularly limited, and is a device provided with known mixing means such as a stirrer. In addition to corn starch and lactic acid bacteria, such a mixing device 20 is supplied with water and other additives such as enzymes. At this time, the mixing ratio (mass ratio x: y) of corn starch (x) and lactic acid bacteria (y) in the mixture is preferably 1,000: 0.1 to 1,000: 10, and 1,000: 0.5. More preferably, ˜1,000: 5. Moreover, you may comprise a corn starch so that it may mix with lactic acid bacteria, after adding a saccharification process etc. previously. Examples of the additive include sodium chloride, calcium carbonate, and various enzymes. Under the present circumstances, as content of the said calcium carbonate, about 0.5-1 mass% is preferable with respect to a mixture. The mixing apparatus 20 mixes the supplied corn starch and the like to form a mixture, and introduces the mixture into the fermenter 30.

  The fermenter 30 includes at least a pair of electrodes including an anode 32 and a cathode 34, and these electrodes are connected to a power source (not shown). Further, the inside of the fermenter 30 is partitioned by a partition wall 36 so as to separate the anode 32 and the cathode 34, and a concentration unit 38 is provided on the side where the cathode 34 is provided with the partition wall 36 as a boundary. A fermentation unit 40 is provided on the side where the anode 32 is provided. The mixture supplied from the mixing device 20 is introduced into the fermentation unit 40. Moreover, as a material which comprises the fermenter 30, there is no limitation in particular, However, Titanium (Ti) is preferable from a viewpoint of rust prevention.

  The anode 32 and the cathode 34 are preferably made of a noble metal such as platinum (Pt), and it is preferable to use a material obtained by plating platinum on titanium (Ti) or a material obtained by attaching ruthenium to this surface. it can. The electrode can be obtained, for example, by rolling and attaching platinum (Pt) to a titanium (Ti) plate, electroplating ruthenium (Ru), and firing this in an oxygen atmosphere. The electrode can also be obtained by electroplating platinum on a titanium plate and firing in an oxygen atmosphere. The firing temperature is preferably about 650 to 700 ° C.

  The anode 32 and the cathode 34 are connected to a power source (not shown), and a direct current can be passed through the mixture in the fermentation unit 40 by supplying a current from the power source. In this way, when a direct current is passed through the mixture in the fermentation unit 40, the lactic acid or water, which is a liquid, is moved in the direction from the anode 32 side to the cathode 34 side (arrow A in FIG. 1) by electroosmosis. Can do.

  The partition wall 36 may have any structure as long as the liquid (lactic acid) in the mixture can pass therethrough and can suppress the passage of a solid material such as a coast starch, for example, a mesh shape. Can do. Moreover, as a material which comprises the partition 36, if it has a certain amount tolerance with respect to lactic acid etc., it can use without a restriction | limiting especially, However, Titanium (Ti) is preferable from a viewpoint of rust resistance. Further, as will be described later, the partition wall 36 itself may be formed of a metal constituting the anode 32, and the partition wall 36 itself may be used as the anode 32. In this case, the space separated from the concentration part 38 by the partition wall 36 becomes the fermentation part. Furthermore, a polyimide film or the like can be used as appropriate.

  The concentrating part 38 is formed by partitioning the fermenter 30 with a partition wall 36 and is provided on the side where the cathode 34 is provided. The concentrating part 38 stores lactic acid that has passed through the partition wall 36 by electroosmosis. Hereinafter, the lactic acid that has passed through the partition wall 36 and has moved to the concentration section is referred to as “high-concentration lactic acid”. In addition, one end of the discharge pipe 42 and one end of the supply pipe 44 are connected to the concentrating unit 38 so that high-concentration lactic acid can be circulated between the lactic acid storage tank 50.

  One end of a circulation pipe 46 is connected to the fermentation unit 40 of the fermenter 30. In addition, the other end of the circulation pipe 46 is connected to the mixing device 20, and is configured so that corn starch (starch), lactic acid bacteria, and the like that have not contributed to the reaction in the fermentation unit 40 can be supplied to the mixing device 20 and reused. ing. Further, the fermentation unit 40 is provided with a discharge port (not shown) so that fermentation residues such as corn starch after fermentation can be discharged outside the measure. In the present embodiment, the mixture is circulated between the mixing device 20 and the fermentation unit 40. However, the circulation manner is arbitrary.

  The lactic acid storage tank 50 is configured so that the high-concentration lactic acid fermented and separated in the fermenter 30 is supplied and the high-concentration lactic acid can be stored. In addition, one end of the discharge pipe 42 and one end of the supply pipe 44 are connected to the lactic acid storage tank 50 so that high-concentration lactic acid can be circulated between the concentration section 38 of the fermentation tank 30. In this way, more concentrated lactic acid can be obtained by circulating high-concentration lactic acid between the concentration unit 38 and the lactic acid storage tank 50. In the present embodiment, the high-concentration lactic acid is circulated between the concentrating unit 38 and the lactic acid storage tank 50. However, such a circulation mode is arbitrary.

  A lactic acid discharge pipe 52 is connected to the lactic acid storage tank 50 so that high-concentration lactic acid stored in the lactic acid storage tank 50 can be discharged out of the apparatus.

  The flow of lactic acid production in the lactic acid production apparatus of the present invention will be described. First, lactic acid bacteria, corn starch, water, and the like are introduced into the fermentation unit 40 of the fermenter 30 after being supplied to the mixing device 20 and mixed. In the fermentation part 40, the temperature is maintained at about 40 ° C. and the pH of the mixture is maintained at about 5 to 6, and fermentation takes place over several hours. Under the present circumstances, the mixture in the fermentation part 40 is circulated between the mixing apparatuses 20 at 10 mass% per minute, for example.

  When the mixture is fermented in the fermentation unit 40, a direct current is passed to the mixture by the anode 32 and the cathode 34. The direct current voltage at this time is preferably 1.0 to 4.0 V, more preferably 1.2 to 3.0 V, from the viewpoint of preventing lactic acid bacteria activity inhibition by free hydrochloric acid ions or the like generated by the electrode. Then, the lactic acid produced | generated by fermentation moves to an electric current direction (direction of the arrow A of FIG. 1) by electroosmosis, passes through the partition wall 36, and is stored in the concentration part 38. FIG. At this time, water also moves to the concentrating unit 38, but lactic acid is concentrated because the moving speed of lactic acid is faster. Further, when a certain amount of fermentation residue is accumulated in the fermentation unit 40, the fermentation residue is discharged from an outlet not shown.

  The high-concentration lactic acid stored in the concentration unit 38 is circulated between the lactic acid storage tank 50 and further concentrated, and then high-concentration lactic acid can be obtained from the lactic acid discharge pipe 52. The circulation of high-concentration lactic acid may be provided with a concentration sensor so that lactic acid is discharged when the concentration exceeds a certain level, or the lactic acid is discharged after being circulated for a certain time. .

  Next, the specific aspect of the fermenter used for the lactic acid manufacturing apparatus of this invention is demonstrated using FIG. 2 and 3. FIG. FIG. 2 is a cross-sectional view for explaining a specific mode of the fermenter according to the present invention, and FIG. 3 is an explanatory diagram for explaining a specific mode of the fermenter according to the present invention.

  As shown in FIG. 2, the fermenter in this invention can be formed in a cylinder shape. Moreover, as shown in FIG. 3, a cylindrical cathode 62 is provided inside the cylindrical fermenter 60 along the inner wall, and further, a cylindrical anode partition 64 having a mesh structure is provided inside thereof. Is provided. 2 and 3, the space surrounded by the cathode 62 and the anode partition 64 is the concentration unit 66, and the space surrounded only by the anode partition is the fermentation unit 68.

  The cylindrical fermenter 60 is further provided with a raw material supply port 70 and a circulating liquid supply port 72. The raw material supply port 70 communicates with the fermentation unit 68 and is configured so that the raw material (mixture) can be introduced into the fermentation unit 68. Moreover, the mixture in the fermentation part 68 is discharged | emitted from the raw material discharge port 74 in a fixed ratio, and is returned to the mixing apparatus 20 in FIG. Thereby, the corn starch etc. which did not contribute to reaction within the fermentation part 68 can be reused by mixing in a mixture. The circulating liquid supply port 72 is provided for circulating high-concentration lactic acid between the lactic acid storage tank 50 and the concentrating unit 66 in FIG. 1, and the high-concentration lactic acid supplied from the circulating liquid supply port 72 is Along with lactic acid newly transferred from the concentrating unit 66 to the concentrating unit 66 from the fermenting unit 68, the lactic acid discharge port 76 sends the lactic acid to the lactic acid storage tank 50 in FIG.

  In the cylindrical fermenter 60, lactic acid produced by fermentation of corn starch and lactic acid bacteria in the fermentation section 68 in the cylindrical anode partition 64 is supplied with a direct current from the cathode 62 and the anode partition 64 to the mixture containing them. , Moving from the fermentation unit 68 toward the concentration unit 66. Thereby, lactic acid can be separated from the mixture. Thus, by constituting the fermenter in a cylindrical shape, lactic acid can be separated and concentrated efficiently.

  Moreover, in the above, although it was set as the aspect which uses only one fermenter, this invention is not limited to this structure, The thing which connected several fermenters may be used.

<Polymerization process>
Next, the polylactic acid production apparatus of the present invention will be described with reference to FIGS. FIG. 4 is a schematic view conceptually showing the structure of the polylactic acid production apparatus of the present invention. As shown in FIG. 4, the polylactic acid production apparatus 80 of the present invention includes a mixing apparatus 82, a polymerization tank 90, and an electric dehydration tank 100. The polylactic acid production apparatus 80 mixes the catalyst together with lactic acid in the mixing apparatus 82, heats the mixture in the polymerization tank 90 to perform dehydration condensation polymerization, and further dehydrates the electrodehydration tank 100 by electroosmotic action, Desired polylactic acid can be obtained. In the polylactic acid production apparatus 80 of the present invention, a polymerization tank 90 and an electric dehydration tank 100 are connected by a circulation pipe 116, and have a desired molecular weight by repeating polymerization and drying for a predetermined number of times and time. Polylactic acid can be obtained.

  The mixing device 82 is not particularly limited, and is a device provided with known mixing means such as a stirrer. The mixing device 82 is supplied with lactic acid and a catalyst. At this time, the mixing ratio (mass ratio q: w) of lactic acid (q) and catalyst (w) in the mixture is preferably 100: 1 to 100: 10, and more preferably 100: 3 to 100: 5. The catalyst is not particularly limited as long as it is a catalyst used for dehydration condensation polymerization of lactic acid. For example, a mixture of ruthenium oxide and titanium oxide at a mass ratio of 50% by mass is preferable. The weight average volume particle size of the catalyst is preferably about 0.1 to 1 μm. The mixing device 82 mixes the supplied lactic acid and the catalyst into a mixture, and introduces the mixture into the polymerization tank 90.

  The polymerization tank 90 performs dehydration condensation polymerization by heating a mixture of lactic acid and a catalyst supplied from the mixing device 82. In the polymerization tank 90, lactic acid can be converted into polylactic acid having a desired molecular weight through a two-stage lactic acid polymerization process. The first lactic acid polymerization step is a step of synthesizing an oligomer from lactic acid, and the heating temperature at this time is preferably about 110 to 160 ° C, more preferably about 130 to 150 ° C. The second lactic acid polymerization step is a step of synthesizing polylactic acid having a desired molecular weight by linking oligomers, and the heating temperature at that time is about 110 to 140 ° C, and about 115 to 120 ° C. Further preferred.

  In addition, the polymerization tank 90 preferably proceeds with the polymerization reaction by heating lactic acid while stirring using a stirring means in order to improve the polymerization efficiency as described later.

  In the polymerization tank 90, a lactic acid polymer discharge pipe 92 for supplying the electric dehydration tank 100 with a lactic acid polymer (including oligomers and polylactic acid that does not reach the desired molecular weight) heated for a certain period of time and dehydrated and polymerized. Is provided.

  The electric dehydration tank 100 includes at least a pair of electrodes including an anode 102 and a cathode 104, and these electrodes are connected to a power source (not shown). Further, the inside of the electric dehydration tank 100 is partitioned by a partition wall 106 so as to separate the anode 102 and the cathode 104, and a dehydration unit 108 is provided on the side where the cathode 104 is provided with the partition wall 106 as a boundary. In addition, a portion to be dehydrated 110 is provided on the side where the anode 102 is provided. The mixture supplied from the polymerization tank 90 is introduced into the portion to be dehydrated 110.

  The anode 102 and the cathode 104 are preferably made of a noble metal such as platinum (Pt), and a material obtained by plating platinum on titanium (Ti) or a material obtained by attaching ruthenium to this surface is preferably used. it can. The anode 102 and the cathode 104 are connected to a power supply (not shown), and a direct current can be passed through the lactic acid polymer in the portion to be dehydrated 110 by supplying a current from the power supply. In this way, when a direct current is passed through the lactic acid polymer in the portion to be dehydrated 110, water contained in the lactic acid polymer is directed from the anode 102 side to the cathode 104 side (arrow B in FIG. 4) by electroosmosis. ).

  The partition wall 106 may have any structure as long as it can pass water in the mixture and can suppress the passage of a solid material such as polylactic acid. For example, the partition wall 106 may have a mesh shape. Moreover, as a material which comprises the partition 36, if it has a certain amount of tolerance with respect to lactic acid etc., it can use without a restriction | limiting in particular. Alternatively, the partition wall 106 itself may be formed of a metal constituting the anode 102, and the partition wall 36 itself may be used as the anode 102. In this case, the space separated from the dewatering unit 108 by the partition wall 106 is the dewatered unit. Furthermore, a polyimide film or the like can be used as appropriate.

  The dehydrating unit 108 is formed by partitioning the inside of the electric dehydration tank 100 with a partition wall 106 and is provided on the side of the electric dehydration tank 100 where the cathode 104 is provided. A glycerin supply pipe 112 and a glycerin discharge pipe 114 are connected to the dehydration unit 108, and the glycerin circulates in the dehydration unit 108. The moisture that has moved from the dehydration unit 110 to the dehydration unit 108 is absorbed by anhydrous glycerin and discharged from the dehydration unit 108 as hydrous glycerin. The water-containing glycerin discharged from the dehydration unit 108 is reused as anhydrous glycerin after the water is removed by a known means such as vacuum distillation.

  One end of a circulation pipe 116 is connected to the portion to be dehydrated 110 of the electric dehydration tank 100. Further, the other end of the circulation pipe 116 is connected to the polymerization tank 90 and is configured to circulate between the polymerization tank 90 and the electric dehydration tank 100 until the polylactic acid in the dewatered part 110 reaches a desired molecular weight. Yes. Furthermore, the dehydrating part 110 is provided with a discharge port (not shown) so that polylactic acid having a desired molecular weight can be discharged out of the measure. The discharge port may be provided in the polymerization tank. The material constituting the polymerization tank 90 and the electric dehydration tank 100 is not particularly limited, but titanium (Ti) is preferable from the viewpoint of rust prevention.

  The flow of polylactic acid production in the polylactic acid production apparatus of the present invention will be described. First, lactic acid and a catalyst are supplied to the mixing device 82 and mixed, and then introduced into the portion to be dehydrated 110 of the electric dehydration tank 100. The lactic acid introduced into the portion to be dehydrated 110 is subjected to dehydration condensation polymerization in the polymerization tank 90 and then dehydrated in the electric dehydration tank 100, and the desired polylactic acid is obtained by repeating such a process a desired number of times or for a predetermined time. It is done. The number and time of repeating such steps can be appropriately set in consideration of the molecular weight of the target polylactic acid. At this time, the polymerization tank 90 and the electric dehydration tank 100 are circulated at, for example, 10% by mass per minute.

  The temperature in the polymerization tank 90 is different between the first lactic acid polymerization step and the second lactic acid polymerization step. At this time, the temperature in the polymerization tank 90 can be switched according to a predetermined number of times and time. In the present invention, it is preferable to pass a step of evaporating water in lactic acid at about 110 to 120 ° C. before performing the first lactic acid polymerization step.

  In the electric dehydration tank 100, a direct current is passed to the lactic acid polymer by the anode 102 and the cathode 104. The DC voltage at this time is preferably about 3.0 to 6.0 V, more preferably 4.0 to 5.0 V. Then, the water generated by the polymerization reaction of lactic acid moves in the current direction (in the direction of arrow B in FIG. 4) due to electroosmosis, passes through the partition wall 106 and moves to the dehydrating unit 108. Moreover, the polylactic acid synthesize | combined to the desired molecular weight can be obtained by circulating between the polymerization tank 90 and an electric dehydration tank for the desired frequency | count or time.

  Next, specific modes of the polymerization tank and the electric dehydration tank used in the polylactic acid production apparatus of the present invention will be described with reference to FIG. FIG. 5 is a cross-sectional view for explaining specific embodiments of the polymerization tank and the electric dehydration tank in the present invention.

  As shown in FIG. 5, the cylindrical polymerization tank 120 has a hollow cylinder (hollow substrate) 124 provided with a lactic acid supply unit 122, and from one side where the lactic acid supply unit 122 is provided to the other side (that is, And a screw (rod-like rotating body) 126 having a spiral groove toward the screw tip side, and the other side (screw tip side) of the cylinder 124 where the lactic acid supply unit 122 is not provided is provided with lactic acid weight. A coalescence outlet 128 is provided so that the lactic acid polymer polymerized from the lactic acid polymer outlet 128 can be transferred while heating and stirring the lactic acid by rotating the screw 126. The lactic acid polymer discharged from the lactic acid polymer outlet 128 is introduced into the electric dehydration tank 150. A motor (driving means) 130 is provided on the side of the screw 126 where the lactic acid supply unit 122 is provided, and the screw 126 is connected to the motor 130 via a reduction gear having a driving gear and a driven gear (not shown). It can be rotated by receiving power from a power source (not shown).

  As the screw 126 rotates in the cylinder, the supplied lactic acid undergoes dehydration condensation polymerization at a temperature corresponding to the first and second lactic acid polymerization processes. An electric heater 132 for heating the inside through the cylinder wall is provided outside the cylinder 124 so as to cover the periphery of the cylinder so that the inside of the cylinder can be uniformly heated.

  The cylindrical polymerization tank 120 is provided with a lactic acid polymer inlet 134 into which the lactic acid polymer dehydrated in the electric dehydration tank 150 is introduced, and polylactic acid can be circulated between the electric dehydration tank 150. It is configured as follows.

  In FIG. 5, the electric dehydration tank 150 is communicated with the cylindrical polymerization tank 120 through a pipe connected to the lactic acid polymer outlet 128. As shown in FIG. 5, the electric dehydration tank 150 is provided inside a cylindrical body 156 having a lactic acid polymer supply port 152 at one end and a dehydrated discharge port 154 at the other end. The cylindrical cylindrical polyimide film 158 and the twisted blades are adjacent to the inside of the cylindrical polyimide film 158 so as to alternately rotate in reverse directions about the axis parallel to the insertion direction (arrow direction C in FIG. 4). And a static mixer 160 arranged in three stages, so that the lactic acid polymer supplied from the lactic acid polymer supply port 152 is inserted in reverse and sequentially reversely kneaded for dehydration. It has become. The wall surface of the cylindrical body 156 is made of titanium (Ti).

  The cylindrical polyimide film 158 provided inside the cylindrical body 156 has a fine mesh structure, and allows only water to permeate through the lactic acid polymer and water. The inside of the cylindrical body 156 has a cylindrical polyimide film 158 as a boundary, and the inside of the cylindrical polyimide film serves as a portion to be dehydrated 162, and a dewatering portion 164 is formed outside the cylindrical polyimide film 158.

  In addition, the wall surface of the cylindrical body 156 is provided with a glycerin supply port 166 for supplying anhydrous glycerin to the dehydration unit 164 and a glycerin discharge port 165 for discharging water-containing glycerin inside the dehydration unit. Glycerin is configured to circulate in the portion 164.

  In the electric dehydration tank 150, a static power supply (not shown) is connected to the static mixer 160 and the wall surface of the cylindrical body 156. The static mixer 160 constitutes an anode electrode, and the cylindrical body 156 constitutes a cathode electrode. is doing. For this reason, when an electric current is passed through the mixture introduced from the cylindrical polymerization tank 120, the water dissociated from the lactic acid polymer moves in the direction from the inside to the outside of the cylindrical body 156 due to the electroosmotic action. The moisture moved from the inside to the outside of the cylindrical body 156 passes through the cylindrical polyimide film 158 and moves to the dehydrating unit 164. Anhydrous glycerin is supplied to the dehydration unit 164, and moisture that has permeated through the tubular polyimide film 158 is absorbed by the anhydrous glycerin and becomes hydrous glycerin and is discharged outside the electric dehydration tank 150. The water-containing glycerin discharged to the outside of the electric dehydration tank 150 is removed from the system by an appropriate means such as vacuum distillation, and is supplied again from the glycerin supply port 166 as anhydrous glycerin.

  For example, as shown in FIG. 6, the static mixer 160 serving as an anode electrode of the electric dehydration tank 150 is plated with platinum (Pt) on titanium (Ti) and further has a plated plate on which ruthenium (Ru) is attached. The twisted blades 160a to 160c that are left-handed or right-handed (for example, twisted at 90 °) have a configuration in which three stages are adjacent to each other. The static mixer 160 receives fluid pressure in the direction of arrow C when the lactic acid polymer passes through the inside of the cylindrical body 156 and rotates according to the direction of twisting. By providing the static mixer 160 having such a configuration in the electric dehydration tank 150, the water in the lactic acid polymer can easily come into contact with the anode, and the electroosmotic action can be efficiently exhibited. Efficiency can be increased.

  The lactic acid polymer dehydrated in the electric dehydration tank 150 is circulated between the cylindrical polymerization tank 120 and the electric dehydration tank 150 until a desired molecular weight such as a desired number of times or time is reached. The lactic acid polymer dehydrated in the electric dehydration tank 150 is discharged from the dehydrated discharge port 154 and is again introduced into the cylindrical polymerization tank 120.

  Thus, the lactic acid polymer circulated between the cylindrical polymerization tank 120 and the electric dehydration tank 150 for a predetermined number of times or time so as to have a desired molecular weight is the cylindrical polymerization tank 120 as polylactic acid having a desired molecular weight. Are discharged from the polylactic acid outlet 136. As described above, when the polylactic acid polymerization apparatus of the present invention is used, polylactic acid having a desired molecular weight can be produced with low energy and about half the time as compared with the case of using the conventional vacuum dehydration method. Synthesis of polylactic acid having a desired molecular weight can be performed in a short time and with low energy, and polylactic acid having a sufficient molecular weight can be obtained with high efficiency and in a short time.

  Thus, according to the polylactic acid production apparatus of the present invention, it is possible to continuously carry out everything from the production of lactic acid to the polymerization of polylactic acid, making the equipment smaller, lowering the cost, and simplifying the operation. Further, the manufacturing cost can be reduced. In the above, only one polymerization tank and one electric dehydration tank are used. However, the present invention is not limited to this configuration, and a plurality of polymerization tanks and electric dehydration tanks are connected. May be.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to this.

[Example 1]
1. Production of lactic acid Lactic acid was produced according to the following procedure using a lactic acid production apparatus having a cylindrical fermenter shown in FIGS.

(1) Preparation of raw material suspension Corn starch (30 parts by mass), sodium chloride (0.5 parts by mass), and water (69.5 parts by mass) were stirred at 150 rpm for 5 minutes using a mixing device, A raw material suspension was prepared.

(2) Preparation of liquefied starch The raw material suspension obtained from the above was steamed at 95 ° C for 15 minutes to prepare gelatinized starch. The obtained gelatinized starch (99.4 parts by mass), calcium carbonate (0.5 parts by mass), and starch liquefying enzyme (trade name: Kokugen T, manufactured by Daiwa Kasei Co., Ltd.) (0.1 parts by mass) After adjusting pH with acetic acid (pH = 6-7), the mixture was stirred at 30 rpm for 10 minutes at a temperature of 90 ° C. with a mixing apparatus. The resulting mixture was left for a further 60 minutes at a temperature of 90 ° C. and a pH of 6-7 to prepare a liquefied starch.

(3) Preparation of saccharified starch After cooling the liquefied starch (99.9 parts by mass) obtained above to 70 ° C. or less, starch debranching enzyme (trade name: Christase PL, manufactured by Daiwa Kasei Co., Ltd.) (0.1 parts by mass) was added, and the pH was adjusted with acetic acid (pH = 5 to 6), followed by stirring at 50 rpm for 10 minutes with a mixing apparatus at a temperature of 65 ° C. The resulting mixture was allowed to stand for a further 60 minutes at a temperature of 65 ° C. and a pH of 5-6 to prepare saccharified starch.

(4) Production of lactic acid After the saccharified starch (99.9 parts by mass) obtained above was cooled to 45 ° C. or less, lactic acid bacteria (0.1 parts by mass) were added, and the mixing apparatus A was used at 150 rpm for 10 minutes. The mixture was stirred at a temperature of 45 ° C. At this time, the pH of the mixture was 5-6.

  The resulting mixture was introduced into the fermentor shown in FIGS. Fermentation was carried out through direct current, and 20% by mass of lactic acid was obtained. Under the present circumstances, fermentation conditions were temperature: 40 degreeC, pH: 5-6, reaction time 240 minutes, and electroosmosis voltage: DC2.4V. Moreover, the mixture was circulated between the fermenter and the mixing apparatus A at 10 mass% per minute.

<Evaluation>
Above 1. Of 1 g of lactic acid bacteria to 1 kg of saccharified starch obtained under the same conditions as above, and the relationship between the voltage applied between the electroosmotic electrodes at 40 ° C. and the concentration of lactic acid produced using the same fermentor as in Example 1 Was measured. At this time, the electroosmosis voltage was measured as 0 V, 1.2 V, 2.4 V, and 3.6 V, respectively. The results are shown in FIG.
FIG. 7 is a graph showing the relationship between the lactic acid concentration and the electroosmotic voltage. As can be seen from FIG. 7, when no current was passed between the electrodes (0 V), the lactic acid concentration did not become 5.6% by mass or more, but when the electroosmosis voltage was changed to 1.2 V, After 8 hours, the concentration was improved to 16.3% by mass. Furthermore, when the electroosmotic pressure was changed to 2.4 V, the lactic acid concentration after 8 hours was improved to 24.5% by mass. On the other hand, when the electroosmosis voltage was changed to 3.6 V, the concentration of lactic acid obtained was about 14% by mass. As a result, it is understood that the electroosmotic voltage is preferably between 1.2 and 3.0V.

2. Synthesis of Polylactic Acid Lactic acid was produced according to the following procedure using a lactic acid production apparatus having a cylindrical polymerization tank and an electric dehydration tank shown in FIG.

(1) Drying step 99.5 parts by mass of lactic acid having a concentration of 20% obtained from the above and 0.5 parts by mass of a catalyst (a mixture of ruthenium oxide and titanium oxide at a mass ratio of 50% by mass) are mixed. For 10 minutes at 150 rpm. At this time, the pH of the mixture was about 3.5 to 4, and the temperature was 90 ° C. The resulting mixture was then evaporated to dryness at 110-120 ° C. for 0.5 hour. At this time, the concentration of lactic acid was approximately 60% by mass.

(2) Polymerization / Dehydration Step The mixture of the obtained lactic acid and catalyst was circulated between the polymerization tank and the electric dehydration tank at 10% by mass per minute using the polymerization tank and the electric dehydration tank shown in FIG. Polymerization and dehydration were performed for 240 minutes. At this time, in the electric dehydration tank, dehydration was performed by passing a direct current through the polylactic acid at an electroosmotic voltage of 4.8 V between the electrodes. The temperature of the polymerization tank was 140 to 145 ° C. for the first 90 minutes, and 115 to 120 ° C. for the remaining 150 minutes. It was 120,000 when the weight average molecular weight of the obtained polylactic acid was measured by DSC.

<Evaluation>
Regarding the polymerization / dehydration step of lactic acid, 2. (Initial lactic acid temperature: 60% by mass, electroosmotic voltage 4.8V, end point polylactic acid mass molecular weight: 120,000, using polymerization tank and electric dehydration tank shown in FIG. 5) And a method by a conventional vacuum dehydration method described in JP-A No. 2003-335850 (initial lactic acid concentration: 60 mass%, vacuum degree of vacuum: 0.08 (MPa), endpoint polylactic acid weight average molecular weight: 120,000) A comparison was made. The results are shown in FIG. FIG. 8 is a graph showing the relationship between the polymerization temperature and the polymerization time for the polymerization reaction of polylactic acid.

  As can be seen from FIG. 8, when polymerization / dehydration is performed by the method according to the present invention using an electroosmotic dehydration tank, the time (T1 ′) required for the first lactic acid polymerization step is approximately 20 minutes, Since the time (T2 ′) required for the second lactic acid polymerization step was about 160 minutes, polylactic acid having a weight average molecular weight of 120,000 could be obtained in about 240 minutes including the drying and evaporation step. .

  On the other hand, when polymerization and dehydration are performed using a conventional method using a vacuum dehydration method, the time (T1) required for the first lactic acid polymerization step is approximately 30 minutes, which is necessary for the second lactic acid polymerization step. Since the time (T2) was about 390 minutes, it took 480 minutes to obtain polylactic acid having a weight average molecular weight of 120,000 including the drying and evaporation step. For this reason, the polymerization time of the present invention using an electroosmotic dehydration tank at the heart of the present invention is approximately half the time compared to the case of using a conventional vacuum dehydration method, and polylactic acid having a desired molecular weight is obtained. I was able to.

  Further, as can be seen from FIG. 8, when the method of the present invention is used, the polymerization temperature required for the first lactic acid polymerization step (T1 ′) is 137 ° C., and the polymerization required for the second lactic acid polymerization step (T2 ′). Since the temperature was 118 ° C., the polymerization temperature required for the first lactic acid polymerization step (T1) was 145 ° C., and the polymerization temperature required for the second lactic acid polymerization step (T2) was 123 ° C. It can be seen that the polymerization temperature can be lowered by about 4 to 6% as compared with the case of using the reduced pressure dehydration method.

It is the schematic which shows notionally the structure of the lactic acid manufacturing apparatus of this invention. It is sectional drawing for demonstrating the specific aspect of the fermenter in this invention. It is explanatory drawing for demonstrating the specific aspect of the fermenter in this invention. It is the schematic which shows notionally the structure of the polylactic acid manufacturing apparatus of this invention. It is sectional drawing for demonstrating the specific aspect of the superposition | polymerization tank and electric dehydration tank in this invention. It is a perspective view which shows the structural example of the static mixer used for an electric dehydration tank. It is a graph which shows the relationship between lactic acid concentration and electroosmosis voltage. It is a graph which shows the relationship between superposition | polymerization temperature and superposition | polymerization time about the polymerization reaction of polylactic acid.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Lactic acid production apparatus 20 Mixing apparatus 30 Fermenter 32 Anode 34 Cathode 36 Partition wall 38 Concentration part 42 Discharge pipe 44 Supply pipe 46 Circulation pipe 50 Lactic acid storage tank 52 Lactic acid discharge pipe 80 Polylactic acid production apparatus 82 Mixing apparatus 90 Polymerization tank 92 Lactic acid weight Combined discharge pipe 100 Electric dehydration tank 102 Anode 104 Cathode 106 Partition wall 108 Dehydration part 110 Dehydrated part 112 Glycerin supply pipe 114 Glycerin discharge pipe 116 Circulation pipe 120 Cylindrical polymerization tank 122 Lactic acid supply part 124 Cylinder 126 Screw 128 Lactic acid polymer outlet 134 Lactic acid polymer inlet 136 Polylactic acid outlet 150 Electric dehydration tank 152 Lactic acid polymer supply port 156 Cylindrical body 158 Cylindrical polyimide film 160 Static mixer 162 Dehydrated part 164 Dehydrated part

Claims (6)

A method for producing polylactic acid comprising fermenting plant starch and lactic acid bacteria to produce lactic acid, and dehydrating condensation polymerization of the lactic acid to synthesize polylactic acid,
The plant starch, the lactic acid bacteria, and the lactic acid are contained in a fermenter that has at least a pair of electrodes, a partition, and a concentration unit partitioned by the partition, and the concentration unit is provided on the cathode side of the electrode. A fermentation concentration step in which the lactic acid is transferred to the concentration part by electroosmosis through a direct current through a mixture containing
A polymerization step of synthesizing polylactic acid by heating and dehydrating condensation polymerization of the lactic acid in a polymerization tank to which the lactic acid stored in the concentration unit is supplied;
A process for producing polylactic acid, comprising:   The method for producing polylactic acid according to claim 1, wherein the vegetable starch is corn starch. A fermenter having at least a pair of electrodes, partition walls and a concentration section partitioned by the partition walls, and the concentration section provided on the cathode side of the electrodes;
Raw material introduction means for introducing plant starch and lactic acid bacteria into the fermentor;
The lactic acid obtained by fermenting the plant starch and the lactic acid bacteria in the fermenter, the plant starch and the lactic acid bacteria through a direct current, and transferring the lactic acid to the concentrating part by electroosmosis. Lactic acid production apparatus characterized by the above.   A discharge pipe for discharging the lactic acid moved to the concentration unit, a lactic acid storage tank for supplying the lactic acid discharged from the discharge pipe and storing the lactic acid, and lactic acid in the lactic acid storage tank for the concentration unit The lactic acid production apparatus according to claim 3, further comprising: a supply pipe to be supplied; and discharge means for discharging the lactic acid in the lactic acid storage tank to the outside.   The lactic acid production apparatus according to claim 3 or 4, wherein the plant starch is corn starch.   The lactic acid production apparatus according to any one of claims 3 to 5, wherein the anode of the electrode has a mesh shape.

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