JP5457625B2 - Recycling method of polylactic acid resin - Google Patents

Description

The present invention relates to a method for significantly shortening the hydrolysis treatment time in a method for regenerating lactic acid by hydrolyzing a polylactic acid resin.

  One of the surprising abilities given to microorganisms in nature is the ability to hydrolyze macromolecular organic compounds. Microorganisms can carry out this reaction in a completely natural environment at normal temperature and pressure, breaking down the organic chain and reducing the molecular weight. This method has been acquired and improved by microorganisms over a long time of hundreds of millions of years, and this method is usually referred to as an “enzymatic hydrolysis method”.

  At present, it is difficult to imitate the hydrolysis method using this enzyme even if we gather all the power of intelligence. A degradation product by this “enzymatic hydrolysis method”, that is, a result of degradation by microorganisms, becomes a useful component for all other organisms, and is a basic element that is absorbed and organized as it is.

  Although it is difficult for humans to imitate the enzymatic hydrolysis method at this stage, there is one method for obtaining the same result by using a method other than the enzymatic hydrolysis method. The method is a “hydrolysis method using physical energy”. This method is similar to the phenomenon of decomposition by hot water that originally blows from the inside of the earth to the bottom of thousands of meters deep sea. According to this method, the reaction proceeds with both the temperature and pressure far exceeding the criticality of water (375 ° C., 220 atm). As a result of the reaction, hydrolysis of organic compounds and metals were included. Many substances (compounds) can be decomposed and the constituents of the substances can be eluted.

  Hydrolysis is possible even when such a high pressure and high temperature state is brought to a more realistic state (a state closer to room temperature). In particular, organic matter gradually hydrolyzes over time when it exceeds 100 ° C. and 1 atmosphere. The result of such “hydrolysis using physical energy” is equivalent to the result of “enzymatic hydrolysis” performed by microorganisms. As a method for decomposing a biodegradable plastic using this principle, for example, Patent Document 1 discloses a method using supercritical hydrothermal treatment, and Patent Document 2 discloses a method using subcritical hot water. It has been introduced.

Not limited to examples of reactions in supercritical and subcritical states, generally, substances undergo phase transition under the influence of partial pressure ratio under high pressure even at relatively low temperatures. However, in the case of organic substances, if the temperature is higher than the saturated water vapor pressure, carbonization occurs, and if the temperature is lower than the saturated water vapor pressure, there may be dangers such as liquefaction mixing of solvents, etc. In order to effectively use the “method”, it is difficult to set processing conditions including temperature and pressure.
That is, when supercritical and subcritical fluids are used for processing, a processing apparatus capable of generating and maintaining the extremely high temperature and pressure conditions is required. In general, an apparatus for maintaining a high temperature and high pressure state is difficult to manufacture as the volume increases, and the manufacturing cost increases dramatically. Therefore, it is difficult to apply the apparatus to a large-scale industrial facility. Furthermore, since the extremely high decomposition ability of supercritical and subcritical hot water extends not only to the organic substance to be treated but also to the treatment vessel itself, it is necessary to use an expensive material for the apparatus in order to prevent decomposition.

  Therefore, as a method for solving the above problems, a method of regenerating lactic acid biodegradable plastic by controlling the temperature and pressure of the hydrolysis treatment atmosphere under saturated water vapor pressure (see Patent Document 3) was realized. In short, this method is a method of hydrolyzing waste containing a lactic acid-based biodegradable plastic in a heating mode and a cooling mode. Here, in the heating mode, water of about 20% of the total weight of the object to be processed is added, and the object to be processed and water containing a biodegradable plastic made from lactic acid under a saturated water vapor pressure of about 140 ° C. Is a process in which biodegradable plastics are hydrolyzed to form a lactic acid aqueous solution, and the cooling mode is generated while the temperature and pressure are controlled by a computer and the hydrolysis of the workpiece is progressed. This is a process for extracting lactic acid and the like.

  When this method is used, the treatment time is somewhat longer than the method using a supercritical fluid as described in Patent Documents 1 and 2 and the treatment in a subcritical state, but the regulation is severe. Compared to supercritical processing and subcritical processing, it is much easier to maintain and has better maintainability during processing without requiring special equipment and equipment to form expensive supercritical and subcritical states. This makes it possible to realize a system that is extremely practical in terms of practicality, enabling anyone and anyone to safely operate a large-scale processing device.

Although it is desirable to perform the hydrolysis treatment under conditions of as low temperature and low pressure as possible, it is not always preferable to require a long treatment time. It is desirable to shorten the hydrolysis time.
Patent Publication 11-292777 JP2003-313283A Japanese Patent Application No. 2006-60529

  The problem to be solved is that in the method described in Patent Document 3, the waste containing the lactic acid biodegradable plastic is hydrolyzed by the heating mode and the cooling mode, and the temperature is industrially practical.・ Although a method for regenerating lactic acid-based biodegradable plastics under pressure conditions has been realized, there remains a problem that the hydrolysis process requires a slightly longer time than supercritical processing or subcritical processing. It is that it was.

  The present invention has a purpose of shortening the hydrolysis time at a temperature close to normal temperature, and as a pretreatment prior to the hydrolysis treatment, the polylactic acid resin is once changed from an amorphous state to a crystalline state by heating, and then hydrolyzed. Realized by processing.

Examples of the present invention are shown below. The present invention hydrolyzes a polylactic acid resin that has been pretreated and then changed from an amorphous state to a crystalline state by heating under a saturated water vapor pressure prior to the hydrolysis treatment of an object to be treated containing the polylactic acid resin. The processing is performed. As a result of the pretreatment, the hydrolysis reaction is promoted, and the polylactic acid resin can be decomposed into lactic acid even under a relatively low saturated water vapor pressure near a pretreatment temperature of 100 ° C. In addition, the time required for complete decomposition of the polylactic acid resin under the same temperature condition is greatly reduced.

In the present invention, the pretreatment, the polylactic acid resin in an environment without added water, a process of crystallizing the polylactic acid by heating the crystallization temperature of the polylactic acid as a guide, hydrolysis treatment, the polylactic acid In this process, the resin is hydrolyzed as an object to be processed.

  FIG. 1 shows an embodiment of an apparatus used for the hydrolysis treatment according to the present invention. In FIG. 1, the apparatus for performing the hydrolysis treatment is composed of a combination of a processing chamber 1, an extraction pipe 2, a cooling tower 3, and a circulation pump 4. The processing chamber 1 is a kettle that heats a workpiece to be processed and performs a hydrolysis treatment. The outer wall of the processing chamber 1 is equipped with a heater 5, and the extraction pipe is disposed between the processing chamber 1 and the cooling tower 3. 2 are connected.

  The extraction pipe 2 is a circulation pipe that connects between the lower steam return port 6 of the processing chamber 1 and the upper steam outlet 7, and the cooling tower 3 is connected in the pipe, and the circulation pump 4 is It is connected in the pipe line on the upstream side of the cooling tower 3. Further, the processing chamber 1 has an input port 8 and a discharge port 9 for the object to be processed, in which the object to be processed input into the processing chamber 1 is agitated while rotating about the vertical axis. Equipped with a stirring blade 10.

  The cooling tower 3 is a heat exchanger that cools the gas (steam) in the extraction pipe 2, and the circulation pump 4 forcibly blows the water vapor in the processing chamber 1 to the cooling tower 3 after hydrolysis of the object to be processed. To do. The cooling tower 3 includes a drain 11, in which the extracted crude lactic acid aqueous solution that is a hydrolysis component in steam is stored, and the crude lactic acid aqueous solution stored in the cooling tower 3 is used as an extract. It is collected in the container V1. Further, the crude lactic acid aqueous solution once evaporated after being hydrolyzed in the chamber 1 and dissolved in water is recovered in the container V2 by opening the drain 11 '.

  The present invention uses the above-mentioned apparatus to perform a hydrolysis treatment using a treatment object containing a polylactic acid resin, for example, a waste material containing a lactic acid biodegradable plastic as a treatment object. The most important thing in waste recycling is to minimize the energy (cost) required for recycling. In the regeneration treatment of lactic acid-based biodegradable plastics according to the present invention, how to minimize the treatment temperature, treatment pressure, and treatment time is an important issue.

In the present invention, the polylactic acid is crystallized as a pretreatment and then subjected to a hydrolysis treatment to achieve a reduction in treatment time. It has been clarified that by crystallization of polylactic acid in an amorphous state, hydrolysis treatment can be performed in a shorter time than those not crystallized under the same temperature condition (for example, 140 ° C.). FIG. 2 is a diagram showing a decomposition mechanism of organic substances by hydrolysis. In FIG. 2, hydrolysis refers to breaking a bond by allowing water ions (H ⁺ and OH ⁻ ) to act between oxygen and other atoms (for example, carbon C) of the organic substance bonded thereto.

That is, a phenomenon in which electrons move between “C” and “O” and are unevenly distributed, so-called polarization occurs, and water ions “H ⁺ ” and “OH ⁻ ” are attracted and electrically coupled therewith. However, the energy of each electron and atom is closely related, and temperature and pressure directly act as excitation energy for this electron and atom. Accordingly, the reaction rate of the hydrolysis reaction varies depending on the temperature and pressure applied to the reaction at this time.

  For example, lactic acid, which is a raw material for polylactic acid, is sublimated into a gas within a certain temperature range, melted into a liquid, or evaporated into a gas. However, melting itself is a reaction accompanied by decomposition. When lactic acid decomposes, it is not pure lactic acid and is difficult to be a raw material for polylactic acid. Here, it is possible to pass through this delicate reaction region by controlling the temperature and pressure of the atmosphere.

  Here, by controlling the temperature and pressure, the polylactic acid resin is hydrolyzed into a lactic acid oligomer. This lactic acid oligomer sublimes even at a relatively low temperature under high pressure, and once it becomes a gas, this gas is water-soluble, so it dissolves in a large amount in hot water under high pressure. This makes it possible to recover a large amount of lactic acid as a solution. In the present invention, in controlling the temperature and pressure in the processing chamber 1 in the hydrolysis treatment, the water vapor pressure shown in FIG. 3 is increased along the saturated water vapor pressure curve in the temperature / pressure range and the reaction is completed. Sometimes the temperature is lowered.

  By the way, when one-component gas-liquid phases coexist at a certain temperature and pressure, the state in which the vapor forming the gas phase reaches saturation is called saturated vapor, and the pressure at that time is the saturated vapor pressure. . Around the liquid of a substance, when the partial pressure of the substance is equal to the vapor pressure of the liquid, the liquid is in a vapor-liquid equilibrium state. When the temperature is lowered, the vapor condenses into a liquid. Conversely, when the temperature is raised, the liquid is vaporized (turns to vapor). Also, the same equilibrium is maintained between the solid phase and the gas phase, and this transition is called sublimation.

  Based on this theory, the present invention controls the water vapor pressure as the partial pressure in the processing chamber 1 along the saturated water vapor pressure curve in the hydrolysis treatment after the pretreatment. At this time, since the partial pressure ratio of lactic acid is very low, the water vapor pressure is dominant. In the temperature / pressure range of steam containing lactic acid-based biodegradable plastics, carbonization occurs if the temperature is slightly higher than the saturated water vapor pressure, and if it is low, there is a risk of liquefaction of the solvent. In the present invention, the temperature and pressure of the atmosphere in the processing chamber are passed through a delicate reaction region by computer control.

  FIG. 4 shows the configuration of a system that monitors the progress of the hydrolysis reaction that proceeds in the processing chamber. In the central monitoring room 12, a computer is installed as a hydrolysis control device 13. From the computer, the heater 5 is turned on, the stirring blade 10 is driven, the processing time is set, the valve opening / closing control of the piping, the circulation pump 4 is turned on. Including the drive control and the like, and the control of all the control and setting information necessary for the pretreatment and hydrolysis treatment to proceed in the treatment chamber 1. In addition to monitoring the progress of the hydrolysis reaction and the state of the produced crude lactic acid and the state of the extract obtained from the cooling tower 3, the monitor 14 has a function of sampling them. ing.

  In the present invention, pretreatment is performed prior to the hydrolysis treatment as an object to be treated containing the polylactic acid resin using the above apparatus, and then the heating mode and the cooling mode of the hydrolysis treatment are sequentially performed. A procedure for regenerating the raw material of the lactic acid-based biodegradable plastic with the waste containing the lactic acid-based biodegradable plastic as an object to be processed using the above apparatus will be described with reference to FIG. 1 using the flowchart of FIG.

  First, an object to be processed made of waste containing lactic acid-based biodegradable plastic is put into the processing chamber 1 (Step S1), the inlet 8 is closed, and the pretreatment takes about 30 minutes or more. Heat to a temperature near the crystallization point of the polylactic acid resin (step S2). Then, it transfers to a hydrolysis process and 20% of water of the to-be-processed object total weight is thrown in in the processing chamber 1 (step S3). The inlet 8 is closed, a timer is set and the heater 5 is energized (step S4), and the heating mode is started while heating the inside of the processing chamber 1 to about 100 ° C. to 150 ° C. In the heating mode, the pressure in the processing chamber 1 is maintained at the saturated water vapor pressure at the heating temperature of the hydrolysis treatment set within the range of 100 ° C to 150 ° C. Further, the stirring blade 10 is rotationally driven about once every fixed interval (for example, 2 seconds) to stir the raw material in the processing chamber 1.

  In this state, the object to be processed is exposed to an atmosphere of saturated water vapor generated in the processing chamber 1 while heating for a certain time, and the hydrolysis reaction proceeds. Depending on the heating mode, the hydrolysis reaction of the lactic acid-based biodegradable plastic proceeds to produce crude lactic acid and its vapor together with water vapor, and the vapor fills the processing chamber 1. After elapse of a predetermined time, the heater 5 is turned off to complete the heating mode (step S5).

  The time required for the hydrolysis treatment of the workpiece is usually 5 to 8 hours, although it depends on the volume of the workpiece and the processing chamber 1. That is, when heated in a sealed processing chamber 1 at a temperature in the range of about 100 ° C. to 150 ° C., biodegradation in the object to be processed within a few hours under the saturated water vapor pressure at the set temperature. The functional plastic can be hydrolyzed.

  In the hydrolysis treatment, with the inside of the treatment chamber 1 sealed, the temperature is raised to the treatment temperature together with the charged water, and the hydrolysis of the object to be treated proceeds under the saturated water vapor pressure at that temperature. When the set time has elapsed, a buzzer will notify you. In addition, even before the set time, when a processing condition abnormality (temperature abnormality, pressure abnormality) occurs, a buzzer can also notify.

  When the hydrolysis processing time set by the timer has elapsed, the heating is terminated and the chamber is cooled as it is (step S6). When the cooling is completed, the saturated lactic acid aqueous solution dropped and staying in the lower part of the processing chamber 1 is recovered.

  At the end of the treatment, an aqueous solution of crude lactic acid and other solids (such as aggregate mixed with polylactic acid) are collected in the treatment chamber 1 in a completely separated form.

When it is confirmed that the temperature and pressure in the processing chamber 1 have sufficiently decreased (at least 100 ° C. and 1 atmosphere or less), the lactic acid aqueous solution in the processing chamber 1 is recovered in the container V2 by opening the drain 11 ′. The solid product is recovered from the discharge port 9 (step S9). The crude lactic acid aqueous solution recovered in the containers V1 and V2 becomes the raw material of the biodegradable plastic product again, and the solid product recovered from the processing chamber 1 is recycled again or discarded depending on the material. The
In this example, the heater is used to directly heat the processing chamber together with water. However, if the system becomes large, heated steam is generated using a separately prepared boiler or the like and processed. It is more efficient to put it in the chamber. Further, depending on the installation location of the treatment facility, heat obtained by burning gas, oil, or the like instead of electricity can be used. In the future, by constructing a system that uses a fuel cell, it will be possible to construct a high-energy-efficient treatment device that uses both electrical energy and waste heat produced from the fuel cell.

  As described above, in the embodiment, the example in which the pretreatment of the object to be processed including the polylactic acid resin is performed in the treatment chamber 1 for the hydrolysis treatment is described. However, the pretreatment is not necessarily performed in the treatment chamber for the hydrolysis treatment. There is no need. A special processing chamber for pretreatment is prepared. As shown in FIG. 6, after pretreatment of an object to be processed in the processing chamber 15 for pretreatment, the crystal taken out from the processing chamber 15 for pretreatment is taken out. Alternatively, the hydrolyzed polylactic acid resin can be introduced into the treatment chamber 1 for hydrolysis treatment, and the hydrolysis treatment can be performed in the treatment chamber 1 for hydrolysis treatment.

  The benefit of specially preparing the pretreatment chamber 15 is that, for example, the pretreatment chamber 15 is installed in a place where polylactic acid resin waste is generated, for example, at a convenience store, a restaurant, etc. Pretreatment from the treatment chambers 15, 15,... Installed in the places where the polylactic acid resin waste scattered in various places is reduced by pretreatment at the place of occurrence. The polylactic acid resin is recovered in the central processing facility, and the processing efficiency can be increased by performing the hydrolysis treatment at once in the large-scale hydrolysis processing chamber 1 installed in the central processing facility.

(Experimental example)
In order to confirm the hydrolysis effect according to the present invention, the following experiment was conducted. In the experiment, a polylactic acid molded product (unitika polylactic acid molded product (Teramac (registered trademark)) was used as a sample. Prior to the experiment, the sample was immersed in hot water for 8 hours, and the sample was immersed in 200 ° C. air. A test was conducted as to whether or not the sample was allowed to stand for 130 hours at a temperature of 2.6 ° C. and decomposed, but the sample was not decomposed under any conditions.

  FIG. 7 shows a relationship between the temperature of a polylactic acid resin molded product (trade name Terramac (registered trademark) manufactured by Unitika) used as a sample and DSC (energy absorption amount). According to FIG. 7, it was found that the glass transition point of the sample was 67.64 ° C., crystallization occurred at 100.36 ° C., and it melted at 167.54 ° C. From this fact, there is no problem even if the temperature of the pretreatment is slightly higher than the melting point. Based on such fact, it is substantially 170 ° C. or lower, and at least a crystallization point of 100 ° C. or higher is required. Judged that there was. It was easily estimated that the higher the treatment temperature when performing the pretreatment, the faster the crystallization rate, and the subsequent hydrolysis reaction would be accelerated. There is no reason to think that it is advantageous to perform the treatment at a high temperature since the effect of the pretreatment can be confirmed sufficiently by the treatment for about 30 minutes even at ° C.

  When the melting point of the sample exceeds 167 ° C., the polylactic acid resin becomes liquefied, so that the object to be treated is collected in the pretreatment chamber 15 as shown in FIG. When the hydrolysis treatment is performed in the treatment chamber 1 for the decomposition treatment, the handling of the processed material becomes troublesome, and therefore the practical pretreatment temperature range is set to a crystallization point (in this example, about 100 ° C.). ) To a melting point (167.54 ° C. in this example) or lower and the temperature at which the object to be processed maintains a crystalline state (about 150 ° C.) as an upper limit is considered to be practical. The setting of the pretreatment temperature range of 100 ° C. to 150 ° C. is an example in the case of this sample (Teramac) and is not common to all polylactic acid products. However, since the sample is not of a special structure, it is presumed that there is no significant difference from this sample even with other polylactic acid resin molded products. Therefore, the pretreatment temperature of 100 ° C. to 150 ° C. is It is considered that this can be applied as it is as a pretreatment temperature for general polylactic acid resin molded products.

FIG. 8 is a graph of infrared spectroscopic analysis (IR) before hydrolysis of a sample, and FIG. 9 is a graph of infrared spectroscopic analysis (IR) before hydrolysis after heat treatment. In either case, the vertical scale is infrared transmittance (%), and the horizontal scale is wave number (cm ⁻¹ ). From the waveform of FIG. 8, it is determined that the sample is polylactic acid resin, and the hydrolyzed sample is determined to be lactic acid from the waveform of FIG.

  The said sample was put into the beaker in the air exposure state, and it hydrolyzed in the pressure vessel (The high pressure steam sterilizer IT-2322 by Alp Co., Ltd.) without pretreatment. The result is shown in FIG. Experimental examples 1 to 6 in FIG. 10 are results of the hydrolysis treatment performed under the conditions of the heating temperature of the hydrolysis treatment of 100 ° C. to 130 ° C. and the pressure of 1 atm to 2.7 atm. Since the polylactic acid resin exhibits a strong acidity pH by being decomposed into lactic acid, the progress of the hydrolysis reaction was detected by using a pH judgment litmus paper and visually identifying the color.

  According to the results of the experiment, it was found that the higher the temperature and the higher the pressure, the faster the progress of the hydrolysis treatment. The upper limit of the heating temperature of the hydrolysis treatment is 130 ° C. because the upper limit of the heating temperature of the pressure vessel used in the experiment was 130 ° C.

  In Experimental Examples 7 to 12 in FIG. 11, the pretreatment was performed under conditions of a pretreatment heating temperature of 130 ° C., a pressure of 2.6 atm, and a pretreatment time of 8 hours, and then a hydrolysis treatment heating temperature of 100 ° C. to 130 ° C. The result of the experiment which hydrolyzed under the conditions of ° C. and pressure of 1 atm to 2.7 atm is shown. According to these experimental results, it can be seen that hydrolysis of the sample started immediately after the start of the hydrolysis treatment. From this, it can be said that high temperature and high pressure are not necessary as pretreatment prior to the hydrolysis treatment of the sample, and that the pretreatment temperature in this experiment is substantially 130 ° C.

  FIG. 12 shows a comparative example 1 in which a pellet of polylactic acid resin was used as a sample, and the sample was hydrolyzed without pretreatment, and the pretreatment was performed at a heating temperature of 120 ° C. for 30 minutes to 4 hours. It is a figure which shows the comparison with Experimental Examples 13-16 which performed the hydrolysis process afterwards. The hydrolysis treatment was carried out under the heating temperature of the hydrolysis treatment at 130 ° C. and the water vapor pressure of 2.7 atm for both Comparative Example 1 and Experimental Examples 13-16. According to the results of the experiment, in Comparative Example 1, it took about 4 hours to start hydrolysis of the polylactic acid pellets, whereas in Examples 13 to 16 in which the pretreatment was performed, the pretreatment time was long and short. Regardless, it was found that hydrolysis of the polylactic acid pellets started in 3 hours at the latest. Therefore, as the pretreatment, as can be seen from the results of FIG. 12, it was found that the pretreatment heating temperature was 120 ° C. or more and the pretreatment time was 30 minutes.

  Next, the pretreatment temperature was set to 120 ° C. and 130 ° C. respectively, the pretreatment time was changed to 30 minutes, 1 hour, 2 hours, and 4 hours. About Experimental Examples 17-20 which performed the hydrolysis process on the conditions of water vapor pressure 2.7 atm, and the comparative example 2 which performed the hydrolysis process on the same conditions without pre-processing, the time required by decomposition | disassembly melting was measured. . The experimental results are shown in FIG. As is apparent from FIG. 13, the experimental result required 12 hours to complete the decomposition and melting in Comparative Example 2 where no pretreatment was performed, whereas in Experimental Examples 17 to 20, the experimental result was approximately 7 to 9 hours. Decomposition and melting of the sample was completed. Even if the pretreatment temperature is 120 ° C. or 130 ° C., it can be judged that there is no great difference and it is not always necessary to spend a long time for the pretreatment time. It can be seen that 120 ° C. and 30 minutes are sufficient.

  Further, after pretreatment at a treatment temperature of 130 ° C., hydrolysis treatment was performed at a treatment temperature of 130 ° C. or higher. The experimental results are shown below. In the experiment, sample 1 (polylactic acid molded product with pretreatment (Teramac (registered trademark)), sample 2 (polylactic acid molded product with no pretreatment (terramac (registered trademark)), sample 3 (polylactic acid molded product) Each sample (about 1 g sample) was individually placed in a pressure vessel (Hyperglaster TEM-V1000N, manufactured by Pressure Glass Co., Ltd.) and used as Experimental Examples 21-25. The decomposition temperature (water vapor pressure at that time) is 130 ° C. (2.7 atm), 135 ° C. (3.1 atm), 140 ° C. (3.6 atm), 145 ° C. (4.1 atm), 150 ° C. (4.7 atm), respectively. The hydrolysis start time of the polylactic acid resin was measured for each of the experimental examples, and the experimental results are shown in Fig. 14. From the results of Fig. 14, hydrolysis of sample 1 that had been pretreated was performed. The start time was remarkably advanced, and it was found that the hydrolysis reaction started instantly at a hydrolysis temperature of 150 ° C., but the hydrolysis treatment can be completed in 1 hour at 135 ° C. to 140 ° C. In terms of level, it is judged that it is sufficient to set the hydrolysis temperature in the range of 135 ° C. to 140 ° C. In any of the experimental examples, the hydrolysis is performed after about 20 to 30 minutes after the start of hydrolysis. The decomposition reaction was finished.

(Consideration of results)
Based on the above results, the pretreatment is carried out by heating the polylactic acid resin from the amorphous state by heating the polylactic acid resin at a temperature at or below the crystallization temperature of the polylactic acid resin up to a temperature below the melting point of the polylactic acid resin, or at a temperature above the crystallization temperature. a process for changing the state, to the normal case, it is possible that a process of heating at a temperature in the range of 100 ℃ ~167 ℃. In addition, as a heating mode of the hydrolysis treatment following the pretreatment, a sufficient amount of water is added to fill the inside of the treatment chamber with the saturated water vapor pressure, and the saturated water vapor pressure at a temperature in the range of about 100 ° C. to 150 ° C. Under the condition, a polylactic acid resin and moisture can be reacted to generate an aqueous lactic acid solution.

  Furthermore, pretreatment of the polylactic acid resin has a great significance not only in promoting the hydrolysis treatment reaction in the post-process but also in plastic separation. That is, since the pretreated polylactic acid resin is significantly brittle, it can be pulverized between a pair of rollers. Most other synthetic resins can only be deformed and cannot be crushed even if they are crushed between rollers. Therefore, once the synthetic resin waste is heated at a temperature of 100 ° C. to 130 ° C. and then the treated product is passed between rollers, the polylactic acid resin becomes powder and is separated from other synthetic resins in particle size. This suggests that only the polylactic acid resin thus obtained can be taken out and hydrolyzed.

  According to the present invention, prior to the hydrolysis treatment, by performing a pretreatment simply by heating to a temperature exceeding 100 ° C., the subsequent hydrolysis treatment time is greatly shortened, and this is a raw material for polylactic acid resin. Lactic acid and lactic acid aqueous solution can be recovered. Therefore, according to the present invention, by realizing the complete chemical recycling of polylactic acid resin, the problem of waste disposal and the problem of effective use of resources are solved, which is a particularly preferable closed cycle of resources. A system can be realized.

It is a block diagram of a hydrolysis apparatus. It is a figure explaining the hydrolysis mechanism of organic substance. It is a graph which shows a saturated water vapor pressure curve. It is a block diagram of the system which implements the method of this invention. It is a figure which shows the flow of this invention method. It is a figure which shows the example which uses a process chamber properly for pre-processing and for heat processing. It is a graph which shows the relationship between the temperature of polylactic acid resin, and energy absorption. It is a graph of infrared spectroscopy (IR) before hydrolysis of a sample. It is a graph of infrared spectroscopy (IR) after hydrolysis after heat treatment of a sample. It is a figure which shows the result of the experiment which hydrolyzed the polylactic acid resin molded product without the pretreatment. It is a figure which shows the result of the experiment which hydrolyzed the polylactic acid resin molded article after performing the pretreatment. It is a figure which shows the comparison with the comparative example which performed the hydrolysis process, without performing pre-processing about the polylactic acid resin molded article, and the experiment example which performed the hydrolysis process after pre-processing. It is a figure which shows the difference of the hydrolysis completion time when changing a pre-processing condition variously and performing a hydrolysis process. It is a figure which shows the comparison of the hydrolysis start time when a polylactic acid resin molded product and the pellet which is the material perform a hydrolysis process at 130 to 150 degreeC.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Processing chamber 2 Extraction pipe 3 Cooling tower 4 Circulating pump 5 Heater 6 Steam return port 7 Steam delivery port 8 Input port 9 Outlet port 10 Stirring blade 11, 11 'Drain 12 Central monitoring room 13 Hydrolysis control device 14 Monitor 15 Pretreatment Processing chamber for
V1, V2 container

Claims (4)

A method for regenerating a polylactic acid resin, comprising pretreating prior to the hydrolysis treatment and then hydrolyzing the polylactic acid resin to regenerate it into lactic acid,
The pretreatment is a treatment in which the polylactic acid resin is put into a processing chamber, the polylactic acid resin is heated at a temperature in the range of 100 ° C. to 170 ° C., and the polylactic acid resin is changed from an amorphous state to a crystalline state.
The hydrolysis treatment consists of a heating mode and a cooling mode. After the pretreatment, a sufficient amount of water is added to fill the inside of the treatment chamber with saturated water vapor pressure in the heating mode, and the temperature is in the range of 100 ° C to 150 ° C. This is a process of producing a lactic acid aqueous solution by reacting a polylactic acid resin and moisture under the saturated water vapor pressure of the water, and the cooling mode reduces the vapor pressure along a predetermined saturated water vapor pressure curve to produce polylactic acid. A method for regenerating a polylactic acid resin, which is a process for extracting lactic acid generated with the progress of hydrolysis of the resin . An object to be treated containing a polylactic acid resin is put into a processing chamber, and as a pretreatment, the polylactic acid resin to be treated is heated in a temperature range of 100 ° C. to 170 ° C. for at least 30 minutes to make the polylactic acid resin amorphous. A step of changing from a state to a crystalline state, a step of sealing a processing chamber by supplying a sufficient amount of water to fill the processing chamber with a saturated water vapor pressure, and a processing chamber within a range of 100 ° C. to 150 ° C. The pressure in the processing chamber is kept at the saturated water vapor pressure at the heating temperature of the hydrolysis treatment of 100 ° C. to 150 ° C., and under the saturated water vapor pressure at a temperature in the range of 100 ° C. to 150 ° C. A step of reacting a polylactic acid resin with water to form a lactic acid aqueous solution, and a saturated water vapor pressure curve predetermined in a cooling mode after completion of the heating mode of the workpiece. Controlling the temperature and pressure along the line, and recovering the steps of condensed vapor in the processing chamber by lowering the vapor pressure to extract the aqueous lactic acid solution, the extracted lactic acid aqueous solution, into the processing chamber 2. A method of reclaiming polylactic acid resin according to claim 1, further comprising a step of recovering a solid such as a treatment object other than the remaining polylactic acid. After pre-processing the object to be treated containing polylactic acid resin, the object to be treated is crushed, separated from other synthetic resins that cannot be crushed simply by being deformed by crushing, and only the polylactic acid resin powdered by crushing is removed. The method for regenerating a polylactic acid resin according to claim 1, wherein the polylactic acid resin is taken out and hydrolyzed. The pretreatment is a treatment in which polylactic acid resin is put into a treatment chamber for pretreatment and heated,
2. The polylactic acid according to claim 1 , wherein the hydrolysis treatment is performed by introducing the crystallized polylactic acid resin taken out from the pretreatment chamber into the hydrolysis treatment chamber and performing the hydrolysis treatment. 3. Resin regeneration method.

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