JP2007099663A - Separating and recovering method of waste of polylactic acid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for recovering lactic acid from a waste of a polylactic acid while separating the lactic acid by a prescribed range of optical purity. <P>SOLUTION: The lactic acid having the prescribed optical purity can be separated and recovered by heating a mixed waste of the two or more polylactic acids having different melting points to a high temperature of from about 110°C to about 200°C together with moisture in a high-temperature treatment apparatus 21, and recovering the reaction liquid at the prescribed time intervals of from about 10 min to about 24 hr while carrying out the heat treatment at a temperature of about 110°C to about 200°C after the initial treatment for about 1 hr or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and an apparatus for carrying out separation while separating the optical purity of lactic acid recovered from polylactic acid waste into predetermined ranges.

  Polylactic acid, which is one of the plastics, can be produced from plants such as corn and sweet potatoes as raw materials, and is decomposed by the action of microorganisms in nature, so-called environmentally friendly biodegradable plastics Are known. The demand for such biodegradable plastics continues to increase, and it is considered that the demand will increase further in the future. However, when biodegradable plastics are decomposed by microorganisms in the soil, considerable time is required.

  On the other hand, in recent years, from the viewpoint of consideration for the environment, research for promoting recycling of many products including general-purpose plastics has become active. As for polylactic acid, although it has been recognized that it has good degradability when it is disposed of, it has not been sufficiently studied from the viewpoint of recycling. For example, Japanese Patent Laid-Open No. 5-178777 discloses a method in which polylactic acid is hydrolyzed by heating and pressing at 100 ° C. or higher and 0.1 megapascal or higher in the presence of moisture. A method of monomerizing by treating lactic acid in the presence of moisture at about 200 ° C. to about 350 ° C. for about 5 minutes to about 60 minutes is disclosed. Japanese Patent Application Laid-Open No. 2003-313283 discloses a method of reducing the molecular weight by treating polylactic acid in the presence of moisture at 180 ° C. to 250 ° C. for 1 minute to 20 minutes.

Japanese Patent Application Laid-Open No. 5-178777 JP 2003-3000927 A JP 2003-313283 A

  In lactic acid which is a unit of polylactic acid, there are optically different isomers of D type and L type. Lactic acid produced from plants is generally L-type. Considering that the quality of polylactic acid is kept constant, it is preferable to use lactic acid as a raw material having a certain optical purity (however, this means that lactic acid having an optical purity close to 100% is always used). This means that if the optical purity is within a predetermined range (for example, about 60% to 70%), the predetermined quality can be maintained). In view of the prior art from this point of view, evaluation of the L / D ratio and yield of substances obtained after recovery is insufficient, so further research and development are required for practical application. .

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method and an apparatus for separating the optical purity of lactic acid recovered from polylactic acid waste for each predetermined range. is there.

As a result of intensive studies, the present inventors have found a phenomenon in which the melting point of polylactic acid changes depending on the optical purity of lactic acid, which is a monomer used in producing polylactic acid, rather than the molecular weight. By applying it, it succeeded in separating the optical purity of lactic acid recovered from the waste containing polylactic acid for each predetermined range, and basically completed the present invention.
Thus, the method for separating and recovering lactic acid which is a monomer according to the first invention for achieving the above object is a waste containing polylactic acid, which is a mixed waste having two or more different melting points of polylactic acid. With water, the reaction temperature is about 110 ° C. to about 200 ° C. at a high temperature for about 1 hour or more, and then heat treatment is performed at a temperature of about 110 ° C. to about 200 ° C. for about 10 minutes to about 24 The reaction solution is collected for each predetermined time segment of time.

  Polylactic acid has a different melting point depending on the optical purity of lactic acid, which is a monomer as a base. That is, as the optical purity of lactic acid decreases, the melting point of polylactic acid also decreases. For this reason, in a waste containing a plurality of types of polylactic acid, at least two different melting points of polylactic acid exist depending on the optical purity of lactic acid constituting each polylactic acid. By treating these wastes in a relatively low temperature region of about 110 ° C. to about 200 ° C., lactic acid having a low optical purity is collected in the reaction solution in order.

Here, “polylactic acid” is a kind of biodegradable plastic having a unit of lactic acid (CH ₃ CH (OH) COOH) and a plurality of lactic acids connected to have a high molecular weight. Lactic acid as a material for producing polylactic acid can be produced from plants (for example, corn, bonito, sugar cane, beet, sweet potato, etc.). In order to produce polylactic acid, lactic acid is generally cyclized into lactide, which is ring-opened and polymerized to form polylactic acid. it can.

Two types of optical isomers, L-type and D-type, are known for lactic acid as a simple substance constituting polylactic acid. The present invention relates to polylactic acid produced by using any of L-type and D-type lactic acid as a unit, polylactic acid containing L-type and D-type in any ratio, or a mixture of poly-L-lactic acid and poly-D-lactic acid. It can implement also to the polylactic acid stereocomplex polymer which becomes. According to the present invention, from a mixed waste containing a plurality of types of polylactic acid having different melting points (that is, optical purity of lactic acid as a monomer), a predetermined range (for example, about 70% to about 80%, about 80% to about About 90%, and about 90% to about 100%), the optical purity of lactic acid, which is a monomer, can be recovered while being sorted.
"Monomer" does not necessarily mean that all polylactic acid is completely converted to monomer, but that the original mixed waste becomes monomer at an appropriate ratio (for example, 50% or more). I mean.
“Waste” refers to various discarded plastics (for example, polyethylene (PE), polypropylene (PP), polystyrene (PS)) in addition to polylactic acid that has been used for a predetermined purpose and discarded as waste. , Polyvinyl chloride (PVC), polyethylene terephthalate (PET), various metals (iron, aluminum, copper, silver, lead, cobalt, manganese, alloys thereof), wood, paper, various natural fibers (cotton, hemp, (Silk) and so on.

“Under high temperature” means a temperature at which the mixed waste of polylactic acid is dissolved and reacted to recover lactic acid as a monomer. Specifically, the temperature is about 110 ° C. to about 200 ° C., preferably about 120 ° C. ° C to about 180 ° C. Below about 110 ° C., the lactic acid mixed waste reacts, making it difficult to depolymerize. When the temperature exceeds about 200 ° C., not only is it difficult to separate and collect, but thermal decomposition of lactic acid itself may occur.
The reaction temperature is a factor necessary for separating and recovering lactic acid according to the optical purity. If the reaction temperature is too low, it may take too much time to separate and collect lactic acid, and lactic acid with high optical purity may not be sufficiently recovered. On the other hand, if the reaction temperature is too high, lactic acid having low optical purity to high lactic acid are recovered at a time without being sufficiently separated by time. In the present invention, a temperature of about 110 ° C. to about 200 ° C. is used to achieve such an object. Among these temperature ranges, depending on the optical purity and separation accuracy of the lactic acid constituting the waste containing polylactic acid as a raw material, further appropriate temperature ranges (for example, about 110 ° C. to about 130 ° C., about 130 ° C. To about 150 ° C., about 150 ° C. to about 170 ° C., about 170 ° C. to about 200 ° C.).

The “initial treatment” time can be appropriately changed in about 1 hour or more depending on the optical purity of lactic acid constituting the polylactic acid and the reaction temperature. For example, when the temperature is about 140 ° C., the initial treatment is performed for about 3 hours, and when the temperature is about 120 ° C., the initial treatment is performed for about 6 hours. Thereafter, the reaction solution is collected at predetermined time intervals. be able to.
The “predetermined time segment” can be appropriately set according to the reaction temperature and the optical purity of lactic acid constituting the polylactic acid according to a region in which the range of the optical purity of lactic acid recovered as a monomer is accommodated. The time segment can be, for example, about 10 minutes, about 20 minutes, about 30 minutes, about 40 minutes, about 50 minutes, about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, about 6 hours, It can be set to about 12 hours, about 24 hours, etc., or can be set in finer time units. The time segment can be set at regular intervals (for example, a regular segment every approximately 20 minutes after the initial reaction) or can be changed as appropriate (for example, approximately every 10 minutes after the initial process). It may be collected 6 times, and then divided every about 20 minutes).

  The amount of water in the case of reacting polylactic acid with water is about 1 part by mass to about 100 parts by mass, preferably about 1 part by mass to about 80 parts by mass, about 1 part by mass with respect to 1 part by mass of polylactic acid. To about 60 parts by weight, more preferably from about 1 part by weight to about 40 parts by weight, more preferably from about 1 part by weight to about 20 parts by weight, and even more preferably from about 1 part by weight to about 10 parts by weight.

In the method for regenerating polylactic acid according to the second invention, a mixed waste having two or more different melting points of polylactic acid is mixed with water at a high reaction temperature of about 110 ° C. to about 200 ° C. for about 1 hour. An initial treatment step for performing the above heat treatment, followed by a separation and recovery step for collecting the reaction solution at predetermined time intervals of about 10 minutes to about 24 hours while performing heat treatment at a temperature of about 110 ° C. to about 200 ° C., and Of the recovered lactic acid, the lactic acid of a category lower than the predetermined optical purity is mixed with lactic acid having an optical purity of about 90% or more to adjust the lactic acid with the predetermined optical purity, and then the polylactic acid is passed through the optical purity adjustment step. It is characterized by recovering lactic acid from regenerated lactic acid.
In the above invention, a measurement step for measuring the optical purity of lactic acid in each section obtained in the separation and recovery step may be provided between the separation and recovery step and the optical purity adjustment step.

  FIG. 1 shows a comparison between the prior art (A) and the method (B) of the present invention regarding a method for recovering and recycling two types of polylactic acid wastes with optical purity of 100% and 60%. . In the conventional method, the mixed waste containing two types of polylactic acid is collectively treated at a constant temperature (for example, 200 ° C.), thereby converting polylactic acid into a monomer and recovering lactic acid. In this method, lactic acid having a certain optical purity (for example, 80%) as a whole is recovered.

With respect to the collected lactic acid, polylactic acid can be regenerated as lactic acid having an optical purity of 90%, for example, by adding lactic acid produced from biomass (optical purity 100%). However, a product made of polylactic acid is not necessarily required to have an optical purity of about 90%, and it is conceivable that it can withstand use even with an optical purity lower than that. Therefore, in the present invention, as shown in FIG. 1 (B), the mixed waste containing polylactic acid is separated and recovered in accordance with the optical purity (difference in melting point) of lactic acid, which is a monomer, using a high-temperature and high-pressure water reaction. .
In the present invention, since the temperature condition is set so as not to change the optical purity of lactic acid, the possibility of changing the optical purity of lactic acid in the polylactic acid waste is reduced. In this separation / recovery step, the polylactic acid composed of lactic acid having low optical purity is sequentially monomerized and recovered in the reaction solution.

  Next, if necessary, the optical purity of the obtained lactic acid is measured (measurement step). If the optical purity is high (for example, in the case of lactic acid (100%) in the upper part of the figure), the polylactic acid is used as it is. Can be played. On the other hand, when the optical purity of lactic acid is low (for example, in the case of lactic acid (60%) in the lower part of the figure), lactic acid having an optical purity of about 90% or more (for example, produced from biomass) ) To adjust to a predetermined optical purity (for example, 80%) (optical purity adjustment step), and then regenerated as polylactic acid.

The apparatus for separating and recovering lactic acid according to the present invention is a high temperature of about 110 ° C. to about 200 ° C. in a state of containing mixed waste having two or more different melting points of polylactic acid and moisture therein. A high temperature processing machine and a reaction liquid take-out hole for taking out a reaction liquid inside the processing machine to the outside are provided.
As said apparatus, it can use regardless of a batch type (batch type) and a continuous type. In addition, in order to be able to treat polylactic acid-containing waste at high temperatures in a mixture of liquid water instead of steam, a high-temperature treatment machine is used as a batch type and a pressure higher than 0.1 megapascal. It is preferable to process under. In order to be able to treat a large amount of mixed waste, it is preferable to use a continuous high-temperature treatment machine.

  This apparatus is provided with a reaction vessel that is heated to a high temperature with polylactic acid or lactic acid placed inside. In addition, since it is preferable to treat polylactic acid or lactic acid at a high temperature in a state where liquid water is mixed instead of steam, the high-temperature processor can process at a high pressure higher than 0.1 megapascal. It is preferable. Moreover, in order to be able to process a large amount of polylactic acid or lactic acid, it is preferable that the high-temperature processor is a continuous type. The reaction tank is preferably provided with a stirrer for stirring the polylactic acid and water in order to promote the reaction.

An example of an apparatus for separating and recovering lactic acid according to the present invention is as follows.
FIG. 2 shows a batch-type lactic acid separation and recovery device 20. The apparatus 20 is provided with a high-temperature processor 21 for reacting polylactic acid waste with water and a heat treatment apparatus 22 for raising the internal temperature. As the heat treatment apparatus 22, for example, an apparatus for bringing a pipe through which a high-temperature substance (for example, water vapor) can be brought into contact with the mixture inside the reaction tank, an apparatus for blowing a high-temperature substance (for example, water vapor) into the high-temperature processing machine 21, or the like is used. be able to. The high-temperature processor 21 is provided with a stirrer 23 that can stir the contents. The high-temperature processor 21 is connected to a cooler 24 for cooling the gas and / or solution flowing out from the inside. The cooler 24 is provided with a return path 25 for returning the condensate to the high-temperature processor 21 and a vent path 26 for discharging.

The high-temperature processor 21 is provided with a reaction liquid outlet hole 29 for taking out an internal reaction liquid to the outside, and a pipe 19 connected to a hold tank 27 for storing the solution after the reaction process is connected to the high temperature processor 21. Has been. The take-out hole 29 is provided with a valve (not shown) that can be opened every predetermined time. The solution stored in the hold tank 27 is sent to the purification system 28.
The operation method of the apparatus 20 will be described as follows. First, at least 2 from the group consisting of the circulating liquid 17 in the process containing unreacted polylactic acid in the high-temperature processor 21, or the polylactic acid waste 16, the circulating liquid 17 in the process containing unreacted polylactic acid, and water W. A seed-containing component is introduced, and after the introduction, a heat treatment by the heat treatment apparatus 22 is performed. Then, the mixture of the waste 16 and the water W (and the circulating liquid) 17 is heated and pressurized, and is gradually decomposed into lactic acid. When an appropriate time has elapsed from the start of the reaction, the valve is opened every appropriate time, and the reaction solution is sent from the reaction solution outlet hole 29 to the hold tank 27 through the pipe 19 and then sent to the purification system 28. The circulating liquid 17 in the process is composed of the residue of the reaction tank of the monomerization process, the residue of the purification system, and the like.

  FIG. 3 shows a continuous lactic acid separation and recovery apparatus 30. The separation / recovery device 30 is provided with a high-temperature treatment device 31 for reacting the mixed waste of polylactic acid and water, and a heat treatment device 32 for raising the internal temperature of the high-temperature treatment device 31. The high-temperature processor 31 is provided with a stirrer 33 that can stir the contents and a water supply path 44 that can supply water heated by the heater 43. In addition, a melting tank 34 for pre-processing the polylactic acid waste 16 and the circulating liquid 17 in the process containing water and unreacted polylactic acid as necessary is connected to the high-temperature treatment machine 31 through a pipe 35. Has been. The melting tank 34 is provided with a stirrer 36 for stirring the contents and a heat treatment device 37 for heating the contents.

  Further, the high temperature processor 31 is provided with a reaction liquid takeout hole 29 for taking out an internal reaction liquid to the outside, and a flash tank 38 for storing the solution after the reaction process and processing a vent gas and the like is connected to the pipe. 19 are connected. The take-out hole 29 is provided with a valve (not shown) that can be opened every predetermined time. A cooler 39 is connected to the flash tank 38. The cooler 39 is provided with a return path 40 for returning the condensate to the flash tank 38 again and a vent path 41 for discharging. The solution stored in the flash tank 38 is sent to the purification system 42.

  The operation method of the separation and recovery device 30 will be described as follows. First, the circulating liquid 17 in the process containing the polylactic acid waste 16 and unreacted polylactic acid, etc., if necessary, is put into the melting tank 34 and stirred by the stirrer 36 while being heated by the heat treatment device 37. To put the charged mixture into a molten state. Next, the newly heated water is continuously supplied to the high temperature processor 31 through the water supply path 44 while the molten liquid is continuously transferred from the melting tank 34 to the high temperature processor 31. In the high-temperature processor 31, the charged polylactic acid waste is decomposed into lactic acid by the operation of the heat treatment apparatus 32. When an appropriate time has elapsed from the start of the reaction, the valve is opened every appropriate time, and the reaction solution is extracted from the reaction solution outlet hole 29 through the pipe 19 to the flash tank 38 and depressurized to atmospheric pressure. At this time, a part of water, lactic acid and the like is vaporized, and the internal temperature of the reaction solution is lowered by the amount of heat of vaporization.

  By using the method and apparatus of the present invention, waste containing polylactic acid composed of lactic acid having different purity can be decomposed and recovered while sorting the optical purity of lactic acid as a monomer within a predetermined range. By applying this technology, the recycling process of polylactic acid can be effectively advanced.

Next, embodiments of the present invention will be described in detail with reference to the drawings. However, the technical scope of the present invention is not limited by the following embodiments, and various changes can be made without changing the gist thereof. It can be carried out with modification. Further, the technical scope of the present invention extends to an equivalent range.
First, the configuration and measurement parameters of the separation and recovery device will be described.

<Separation and recovery device>
FIG. 4 shows a polylactic acid waste separation and recovery apparatus 1 (hereinafter simply referred to as “apparatus 1”) used in the examples. In this apparatus 1, a temperature-controllable molten salt tank 2 (for example, TSC-B600 type manufactured by Pressure Glass Co., Ltd.) and a heat resistance / pressure resistance immersed in the molten salt tank 2 can be used. A sealed processing vessel 3 (for example, stainless steel (SUS316) batch type reaction tube (outer diameter 12.7 mm, wall thickness 1.24 mm, inner diameter 10.2 mm, length 10 cm, inner volume 8.2 mL)) And a pressure sensor 4 is provided.

A heater 6 and a rotary blade 5 are provided inside the molten salt tank 2. The liquid in the molten salt tank 2 (for example, a mixture of KNO ₃ (45%) and NaNO ₃ (55%) can be used) by rotating the rotor blade 5 with the heater 6 turned on. To obtain a uniform temperature. The heater 6 is provided with a computer (not shown), and the temperature in the molten salt tank 2 can be controlled within a predetermined range. In this processing apparatus 1, high temperature treatment of polylactic acid and moisture can be performed while controlling the inside of the molten salt tank 2 to a predetermined temperature within a range of about 120 ° C to about 300 ° C.

The processing container 3 can be made of, for example, stainless steel (for example, SUS316), hastelloy, or inconel (an alloy containing Ni, Cr, Mo, or the like). A lid is attached to the upper part of the processing container 3, and an appropriate temperature can be obtained with the internal space of the processing container 3 sealed. At the time of the test, a sample diluted at an arbitrary magnification is put into the processing container 3, and the upper lid is placed on the container and sealed. Thereafter, the processing container 3 and the pressure sensor 4 are connected.
After sealing the processing container 3, the processing container 3 is put into the molten salt tank 2 that has been heated to a preset temperature in advance, and this time is set to 0 minutes, and high-temperature processing is started.

<Experimental method and results>
1. Relationship between optical purity of lactic acid and melting point of polylactic acid The melting point of polylactic acid (weight average molecular weight 220,000) produced from L-lactic acid having an optical purity of 88% to 100% was evaluated. The melting point was carried out and analyzed using a differential operation calorimeter.
In the test, 0.24 g of the sample (polylactic acid) and 4.8 g of purified water were put into the processing container 3 and the mass ratio of sample: purified water was 1:20.

The processing vessel 3 was sealed, the air inside was replaced with argon, and then immersed in the molten salt bath 2 that had been heated to a predetermined temperature. After a predetermined processing time had elapsed, the processing vessel 3 was quickly removed from the molten salt bath 2, immersed in a cold water bath and quickly returned to room temperature, thereby avoiding an excessive reaction. The product after the reaction was analyzed using an HPLC organic acid analysis system (LC-10A, manufactured by Shimadzu Corporation) equipped with an ion exclusion column.
The test results are shown in FIG. As a result, it was found that as the optical purity of L-lactic acid increased from 88% to 100%, the melting point of polylactic acid also increased from 144 ° C to 186 ° C.

2. Relationship between lactic acid recovery from polylactic acid and reaction time Next, the relationship between the reaction time when polylactic acid was treated at 160 ° C. to 200 ° C. and the lactic acid recovery rate was examined. Polylactic acid having a melting point of about 175 ° C. was selected. The test was performed using a batch separation and recovery apparatus in the same manner as in 1 above. The molten salt tank 2 is set at 160 ° C., 170 ° C., 180 ° C., 190 ° C., and 200 ° C., and a processing vessel 3 in which polylactic acid (0.24 g) and purified water (4.8 g) are added thereto. Soaked. After the start of the reaction, the processing vessel 3 was taken out from the molten salt tank 2 within 5 to 180 minutes and quickly returned to room temperature, and then the product after the reaction was analyzed by an HPLC organic acid analysis system.

The test results are shown in FIG. As a result, recovery of lactic acid was observed after 60 minutes even at 160 ° C., which is lower than the melting point. It was also found that the higher the treatment temperature, the faster the time for collecting lactic acid. At any temperature, a lactic acid recovery rate of almost 100% was obtained with a reaction time of 180 minutes.
5 and 6, when polylactic acid produced from L-lactic acid having different optical purity (that is, having different melting points) coexists, the reaction temperature is around the melting point (including a temperature lower than the melting point). By controlling with, the possibility that it can be recovered while appropriately controlling the optical purity of the obtained lactic acid was shown.

3. Experiments on recovery of lactic acid from polylactic acid with different melting points (1)
Three types of polylactic acid having different molecular weight, constitutional L-lactic acid optical purity, and melting point were heat-treated with moisture, and the yield of recovered lactic acid was evaluated.
Table 1 shows the molecular weight of three types of polylactic acid, the optical purity of L-lactic acid, and the melting point. In addition, the melting point of PLA-80 was an expected value, which seemed to be between 140 ° C and 160 ° C.

  The relationship between the reaction time and the lactic acid recovery rate when each polylactic acid was treated at 140 ° C. was examined. The test was conducted in the same manner as in 1 above using a batch separation and recovery apparatus. The molten salt tank 2 was set to 140 ° C., and the processing vessel 3 charged with polylactic acid (0.24 g) and purified water (4.8 g) was immersed therein. 30 minutes to 12 hours after the start of the reaction, the processing vessel 3 was taken out from the molten salt bath 2 and quickly returned to room temperature, and then the product after the reaction was analyzed by an HPLC organic acid analysis system.

The test results are shown in FIG. 7 and FIG. FIG. 7 shows a graph comparing # 5000 and # 9010, and FIG. 8 shows a graph comparing # 5000 and PLA-80. As a result, it was found that polylactic acid having a lower melting point was recovered as lactic acid earlier. In any of the polylactic acids, the recovery rate of lactic acid was almost 100% with a reaction time of about 9 hours.
From this, when a plurality of polylactic acids having different melting points are mixed, by treating the reaction solution at an appropriate time while processing at a constant reaction temperature, lactic acid having a predetermined optical purity can be obtained. It was shown to be recoverable.

4). Experiments on recovery of lactic acid from polylactic acid with different melting points (2)
Two of the three types of polylactic acid used in 3 above (# 5000 and PLA-80) were heat-treated with water at 120 ° C., and the yield of recovered lactic acid was evaluated.
The test was conducted in the same manner as in 1 above using a batch separation and recovery apparatus. The molten salt tank 2 was set to 120 ° C., and the processing vessel 3 charged with polylactic acid (0.24 g) and purified water (4.8 g) was immersed therein. After the start of the reaction, the processing vessel 3 was taken out from the molten salt bath 2 within 1 hour to 72 hours (3 days) and quickly returned to room temperature, and then the product after the reaction was analyzed by an HPLC organic acid analysis system.

  The test results are shown in FIG. As a result, as in FIG. 8, it was reconfirmed that PLA-80, which is polylactic acid having a low melting point, was recovered as lactic acid earlier than # 5000. However, it was found that about 100% of PLA-80 was recovered as lactic acid in the reaction for about 1 day, while about 3 days were required for recovery of lactic acid from # 5000. Further, after about 2 days from the start of the reaction, the difference in the rate at which both polylactic acids were recovered was as large as 40% or more. Thus, in order to separate and recover lactic acid obtained from polylactic acid having different melting points based on the results of 3 and 4 above, and to keep the optical activity of the recovered lactic acid within a predetermined range, (1) heat treatment is performed at as low a temperature as possible. However, it was found that (2) when the heat treatment was performed at a high temperature, it was effective to narrow the time width for recovery.

5. Experiments on recovery of lactic acid from polylactic acid with different melting points (3)
Two types of polylactic acid (# 5000 and PLA-80) used in the above 4 were mixed and heat-treated with water at 120 ° C., and the yield and optical activity of the recovered lactic acid were evaluated.
The test was conducted in the same manner as in 1 above using a batch separation and recovery apparatus. The molten salt tank 2 was set at 140 ° C., and the processing vessel 3 charged with polylactic acid (about 0.25 g) and purified water (4.8 g) was immersed therein. After 24 hours (one day) after the start of the reaction, the processing vessel 3 was taken out from the molten salt bath 2 and quickly returned to room temperature, and then the product after the reaction was analyzed by an HPLC organic acid analysis system. Table 2 shows the mixing amount of the two types of polylactic acid, the residual resin amount, the residual resin rate, the lactic acid recovery rate, and the optical purity. This test was performed four times independently. The optical purity can be obtained by | 1-2α | when the ratio of L-lactic acid is α and the ratio of D-lactic acid is (1-α). (The optical purity of PLA-80 is | 1- 2 * 0.2 | = 60%).

The resin remaining after the reaction was subjected to a heat treatment reaction at 200 ° C. for 60 minutes. As a result, almost 100% of lactic acid was recovered. The optical purity of the lactic acid collected at this time was about 100%.
From these results, it was found that PLA-80 was recovered as lactic acid by a heat treatment reaction at 120 ° C. for 24 hours, and part of # 5000 was decomposed, but most remained as a resin. It was.

  Furthermore, as shown in Table 2, lactic acid (0.62 g) with an optical purity of 98.0% was mixed with lactic acid (0.15 g) obtained with an optical purity of 67.3%. When the optical purity was measured, the optical purity was 92% and could be adjusted to an optical purity of 90% or more.

  As described above, according to the present embodiment, in the waste mixed with polylactic acid having different melting points, the lactic acid is recovered by collecting lactic acid every predetermined time while performing an appropriate heat treatment together with moisture. The purity can be separated for each predetermined range. By applying this technology, the recycling process of polylactic acid can be effectively advanced.

It is a figure which shows the outline | summary of the isolation | separation collection process of a polylactic acid waste. (A) shows the present flow chart, and (B) shows the flow chart of the present invention. 1 is a diagram illustrating a batch-type lactic acid separation and recovery apparatus according to the present invention. 1 is a drawing illustrating a continuous lactic acid separation and recovery apparatus according to the present invention. It is a figure which shows the outline | summary of the batch-type separation and collection apparatus of lactic acid in this embodiment. It is a graph which shows the relationship between the ratio of L-lactic acid and melting | fusing point of polylactic acid. It is a graph which shows the relationship between reaction time and lactic acid recovery. It is a graph which shows the relationship between reaction time and lactic acid recovery. It is a graph which shows the relationship between reaction time and lactic acid recovery. It is a graph which shows the relationship between reaction time and lactic acid recovery.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Separation-and-recovery apparatus 2 ... Molten salt tank 3 ... Processing container 4 ... Pressure sensor 5 ... Rotor blade 6 ... Heater 16 ... Polylactic acid waste 17 ... Process Circulating fluid 19, 35 ... Pipes 20, 30 ... Separation and recovery devices 21, 31 ... High-temperature treatment machines 22, 32, 37 ... Heat treatment devices 23, 33, 36 ... Stirrers 24, 39 ... Coolers 25, 40 ... return paths 26, 41 ... discharge vent path 27 ... hold tanks 28, 42 ... purification system 29 ... reaction liquid takeout hole W ... water 34 ... -Melting tank 38 ... Flash tank 43 ... Heater 44 ... Water supply path

Claims (5)

Initial treatment of waste containing polylactic acid having two or more different polylactic acid melting points with moisture at a reaction temperature of about 110 ° C. to about 200 ° C. for about 1 hour or more And then recovering the reaction solution at predetermined time intervals of about 10 minutes to about 24 hours while performing heat treatment at a temperature of about 110 ° C. to about 200 ° C. Collection method. Heat treatment for about 1 hour or more at a high temperature of about 110 ° C. to about 200 ° C. with a mixture of wastes containing polylactic acid and having two or more different melting points of polylactic acid together with moisture An initial treatment step, a separation / recovery step for recovering the reaction solution at predetermined time intervals of about 10 minutes to about 24 hours while performing heat treatment at a temperature of about 110 ° C. to about 200 ° C., and recovered lactic acid Among these, lactic acid in a section lower than the predetermined optical purity is collected through a step of adjusting the optical purity by adjusting lactic acid having a predetermined optical purity by mixing lactic acid having an optical purity of about 90% or more. A method for separating and recovering lactic acid. A high-temperature treatment machine that has a high temperature of about 110 ° C. to about 200 ° C. in a state of containing mixed waste having two or more different melting points of polylactic acid and moisture therein, and a reaction liquid inside the treatment machine And a reaction liquid take-out hole for taking out the product to the outside. 4. The separation and recovery device is a continuous type capable of setting a pressure higher than 0.1 megapascal in a state where polylactic acid and liquid water are mixed. Lactic acid separation and recovery equipment. The separation and recovery apparatus is a batch type apparatus capable of setting a pressure higher than 0.1 megapascal in a state where polylactic acid and liquid water are mixed. Lactic acid separation and recovery equipment.

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