JP5072818B2 - Method for decomposing polylactic acid, and method for treating organic matter containing polylactic acid - Google Patents

Description

  The present invention relates to a method for decomposing polylactic acid, which can easily and efficiently obtain high-purity lactic acid from polylactic acid. Furthermore, this invention relates to the processing method of the organic substance containing polylactic acid using the said decomposition | disassembly method.

  Polylactic acid has biodegradability, and various uses are being developed as the next generation plastic. A product made from polylactic acid can be decomposed by microorganisms existing in the natural environment or in compost, so that even if it is mixed with readily decomposable organic matter, it can be used for biological treatment as it is. There is an advantage.

  However, it has been found that polylactic acid is easily decomposed in an aerobic atmosphere, but is hardly decomposed in an anaerobic atmosphere (see Patent Document 1). Therefore, if polylactic acid is used as it is for methane fermentation in which an anaerobic atmosphere is essential, there is a disadvantage that the treatment takes a long time.

  Therefore, a method for solubilizing polylactic acid under conditions of about 50 to 60 ° C. by mixing polylactic acid with waste water after methane fermentation before subjecting polylactic acid to methane fermentation has been proposed (patent document). 2). However, this method has a problem that the amount of lactic acid finally produced is small and polylactic acid cannot be solubilized efficiently yet, so that the processing efficiency of polylactic acid cannot be improved and efficient energy recovery cannot be achieved. There is.

  If lactic acid can be recovered after treating polylactic acid, it will be possible to recycle resources by providing raw materials for producing polylactic acid, which will contribute to global environmental conservation and energy saving. Therefore, establishment of a technique for recovering lactic acid from polylactic acid is also strongly desired in the industry.

  However, in the polylactic acid solubilization method described above, although polylactic acid is reduced in molecular weight, a part of the polylactic acid remains as a polymer or oligomer without being decomposed into lactic acid, so that lactic acid can be recovered with high recovery efficiency. There is a problem that it cannot be obtained.

Against the background of such conventional techniques, development of a technique for efficiently degrading polylactic acid to obtain lactic acid and a technique for efficiently recovering energy by decomposing polylactic acid are eagerly desired.
JP 2005-206735 A JP 2005-232336 A

  An object of the present invention is to provide a method for easily and efficiently decomposing organic acid containing polylactic acid into highly pure lactic acid. Furthermore, an object of the present invention is to provide a method for efficiently treating an organic substance containing polylactic acid using the method for decomposing lactic acid.

  The present inventors have conducted extensive studies to solve the above problems, and surprisingly, polylactic acid is converted into lactic acid by treating an organic substance containing polylactic acid in a gas atmosphere containing a specific amine compound. It was found that it can be efficiently decomposed and high-purity lactic acid can be recovered with high yield. The present invention has been completed by further studies based on such knowledge.

That is, this invention provides the decomposition | disassembly method of polylactic acid hung up below, and the processing method of the organic substance containing polylactic acid.
Item 1. A method for decomposing polylactic acid, comprising a step of treating an organic substance containing polylactic acid in a gas atmosphere containing a compound represented by formula (I).

[In the formula (I), R ₁ , R ₂ and R ₃ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ]
Item 2. Item 2. The decomposition method according to Item 1, wherein in general formula (I), R ₁ , R ₂ and R ₃ are the same or different and each is a hydrogen atom, a methyl group or an ethyl group.
Item 3. Item 3. The decomposition method according to Item 1 or 2, wherein the organic substance is treated in a gas atmosphere of the compound represented by the general formula (I) under a temperature condition of 40 ° C or higher.
Item 4. A method for treating an organic substance containing polylactic acid, comprising the following steps (a) and (b):
(a) a step of decomposing polylactic acid by treating an organic substance containing polylactic acid in a gas atmosphere containing a compound represented by general formula (I); and

[In the formula (I), R ₁ , R ₂ and R ₃ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ]
(b) A step of methane fermentation of the decomposition product obtained in step (a).

  According to the polylactic acid decomposition method of the present invention, lactic acid can be obtained from polylactic acid in a high yield by treating an organic substance containing polylactic acid in a gas atmosphere containing a specific amine compound. In particular, the liquid decomposition product obtained by the polylactic acid decomposition method of the present invention contains almost no lactic acid oligomer or lactic acid amidated with the amine compound, and contains high-purity lactic acid. Therefore, it is useful for recycling as a raw material for producing polylactic acid. Furthermore, according to the decomposition method of the present invention, polylactic acid is decomposed by treating mechanical parts and electronic parts in which polylactic acid is bonded with a metal (rare metal, etc.) or solids not decomposed by the method of the present invention. Thus, the metal can be easily recovered as a solid after being made liquid.

  In addition, according to the polylactic acid decomposition method of the present invention, polylactic acid can be efficiently converted into lactic acid suitable for biological treatment (particularly methane fermentation treatment). Useful. In particular, when organic waste is contained in a garbage bag manufactured from polylactic acid, etc., for treatment objects that are difficult to separate and recover only lactic acid decomposed and produced by the method of the present invention, By subjecting the decomposition product obtained by the method of the present invention to methane fermentation treatment, it is possible to convert from organic matter containing polylactic acid to methane gas with high efficiency in the end, so the amount of energy recovered from polylactic acid as biogas, Compared to conventional methane fermentation treatment technology, it can be dramatically increased.

  Further, when agricultural multi-film containing polylactic acid is decomposed and composted in the soil after use, it is treated in the soil after the polylactic acid is completely or partially decomposed by the method of the present invention in advance. As a result, the decomposition / composting rate in the soil can be significantly accelerated.

Hereinafter, the present invention will be described in detail.
1. Decomposition of polylactic acid In the decomposition method of the present invention, an organic substance containing polylactic acid is a treatment target.

  The polylactic acid contained in the organic substance to be treated in the present invention is a polymer having lactic acid as a main constituent unit of the polymer. In the present invention, the type of polylactic acid is not particularly limited. For example, lactic acid homopolymers such as poly L-lactic acid and poly D-lactic acid; at least one of L-lactic acid and D-lactic acid, alanine, and glycolic acid And lactic acid copolymers with at least one of glycolide, glycine, ε-caprolactone, glycol, polyethylene glycol, polypropylene glycol, polyvinyl alcohol, saccharides and polyhydric alcohols; poly D, L-lactic acid and the like.

  In the present invention, the organic matter to be treated may contain one kind of the polylactic acid alone, or may contain two or more kinds of the polylactic acid in combination.

  Furthermore, the polylactic acid contained in the organic matter to be treated may be a resin composition containing components other than polylactic acid. In the case of using a resin composition containing polylactic acid and other components, the blending ratio of polylactic acid in the resin composition is not particularly limited. For example, polylactic acid is 5 per total amount of the resin composition. -99 weight%, Preferably it is 20-99 weight%, More preferably, 50-99 weight% is mentioned. Further, an additive for efficiently mixing polylactic acid and other resin composition, or an additive for improving the physical properties of a mixture of polylactic acid itself and other resin composition may be included. . Although the ratio is not particularly limited, for example, it is desirable that the additive is about 10% or less per the total amount of the resin composition.

  In the present invention, the form of polylactic acid to be treated is not particularly limited. For example, various types of polylactic acid such as powder, film, non-woven fabric, sheet, plate, foam, and injection-molded product can be targeted. In carrying out the method of the present invention, the polylactic acid in the form of a film, non-woven fabric, sheet, plate, foam, injection-molded product, etc., before pulverization or cutting in order to make it into powder or small piece shape You may use for a process.

  In the present invention, the organic substance to be treated may be composed only of polylactic acid, or may be a mixture of polylactic acid and other organic substances. In the latter case, specific examples of organic substances to be treated include, for example, straw, raw garbage, dried garbage, food factory waste, sewage sludge, livestock waste (livestock excreta, straw, sawdust, etc. And a mixture of an organic substance such as a mixture) and polylactic acid. In particular, organic matter containing garbage and polylactic acid is suitable as a treatment target in the present invention. According to the present invention, there is an advantage that raw garbage can be collected and collected in a garbage bag manufactured from polylactic acid, and can be directly subjected to a decomposition method without separating the garbage and the garbage bag. .

  In the present invention, when a mixture of polylactic acid and other organic substances is to be treated, other organic substances are decomposed to a degree that facilitates biological treatment along with the decomposition of polylactic acid. The total cost required for this process can also be reduced.

  In the present invention, the treatment of the organic substance is performed in a gas atmosphere containing a compound represented by the following general formula (I) (hereinafter sometimes simply referred to as “amine compound”).

In the general formula (I), R ₁ , R ₂ and R ₃ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. Specific examples of the alkyl group having 1 to 5 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, isopentyl group, A neopentyl group is exemplified. Among these, from the viewpoint of further increasing the decomposition efficiency of polylactic acid into lactic acid, R ₁ , R ₂ and R ₃ are preferably the same or different and are a hydrogen atom, a methyl group, an ethyl group, a propyl group, or More preferably, R ₁ , R ₂ and R ₃ are the same or different and each is a hydrogen atom, a methyl group or an ethyl group. From the viewpoint of increasing the decomposition efficiency of polylactic acid to lactic acid, preferred specific examples of the amine compound include ammonia, monomethylamine, dimethylamine, trimethylamine, monoethylamine, diethylamine, and trimethylamine. These amine compounds may be used individually by 1 type, and may be used in combination of 2 or more type.

  In the present invention, the gas atmosphere containing an amine compound means an atmosphere in which the amine compound is vaporized and exists as a gas, and the treatment of the organic substance in the gas atmosphere of the amine compound is performed by vaporizing the amine compound. It is carried out by exposing the organic matter to the atmosphere.

The gas concentration of the amine compound in the gas atmosphere of the amine compound may be appropriately set according to the amount of organic matter to be treated, the type of amine compound, the treatment time, etc., but usually 0.1 to 100 volumes at normal pressure. %, Preferably 1 to 100% by volume, more preferably 10 to 100% by volume.
With such an amine compound gas concentration, the decomposition rate of polylactic acid can be increased and efficient decomposition can be achieved.

  In the decomposition method of the present invention, the ratio of the amine compound applied to the organic substance containing polylactic acid is determined based on the concentration of the amine compound and the amount of organic substance containing polylactic acid to be treated. In order to enable efficient degradation of polylactic acid, for example, the gas weight of the amine compound is 0.01 to 10 parts by weight, preferably 0.1 to 10 parts by weight, more preferably, per 1 part by weight of polylactic acid contained in the organic matter. It is desirable to satisfy the ratio of 1 to 10 Shirou.

  Moreover, in the decomposition | disassembly method of this invention, since polylactic acid is hydrolyzed and converted into lactic acid, it is required for water to coexist. In the present invention, since polylactic acid is decomposed by contact with an amine compound gas, it is desirable that the water used for hydrolysis exists in the state of water vapor. In the present invention, the water used for the hydrolysis may be supplied as water vapor to the amine compound gas atmosphere, but liquid water is present in the amine compound gas atmosphere, Water may be allowed to evaporate. If liquid water is present in this way, even if water vapor in the gas atmosphere is used for hydrolysis of polylactic acid, liquid water evaporates in the gas atmosphere, so that it is used for hydrolysis in the gas atmosphere. It becomes possible to supply water as water vapor. In the case where liquid water is present in the gas atmosphere of the amine compound, it is desirable to adjust the organic material to be treated so that the liquid water does not prevent contact with the amine compound gas. Specifically, (i) in a gas atmosphere of the amine compound, the liquid water and the organic substance are accommodated in different compartments so that they do not come into direct contact with each other; (ii) in the amine compound gas atmosphere, at least of the organic substance An organic substance and liquid water are mixed so that a part is exposed to the gas atmosphere of the amine compound; or (iii) liquid water is added in such a manner that the reaction temperature is increased and the water vapor pressure is increased. The method of making it exist is illustrated.

  If water is added excessively to the gas atmosphere containing the amine compound, the contact efficiency between polylactic acid and water improves, and the degradation rate of polylactic acid increases, but the decomposed and produced lactic acid dissolves in the excess water, The lactic acid concentration of the resulting degradation product will decrease.

On the other hand, when at least one of R ₁ , R ₂ and R ₃ of the amine compound is a hydrogen atom, the amine compound is amidated with a terminal carboxyl group of polylactic acid to generate water. Therefore, polylactic acid can be decomposed using this water, and it is possible to coexist polylactic acid and water without supplying water. However, it is preferable to supply water to a gas atmosphere containing an amine compound because there is no by-product of the amide compound and it can be decomposed into lactic acid with higher purity.

  The amount of water supplied to the gas atmosphere containing the amine compound is more than the amount required for hydrolysis of polylactic acid, taking into account the lactic acid purity of the target decomposition product, the decomposition rate of polylactic acid, etc. Desirably, for example, the amount of water is 0 to 1000 parts by weight, preferably 25 to 1000 parts by weight, more preferably 100 to 1000 parts by weight, per 100 parts by weight of polylactic acid contained in the organic substance to be treated. The

  Although it does not restrict | limit as temperature conditions at the time of processing in the atmosphere containing an amine compound with respect to the organic substance containing the said polylactic acid as long as an amine compound can be maintained in gaseous state, Usually, 40 degreeC or more, Preferably it is 50-220. ° C, more preferably 60 to 100 ° C. When the organic material decomposed by the decomposition method of the present invention is further subjected to methane fermentation, methane gas generated by methane fermentation is used for maintaining the temperature in the atmosphere of the amine compound rather than using heavy oil or the like. It is desirable to use cogeneration means (gas engine, fuel cell, etc.) to obtain heat and electric power to maintain the temperature of the atmosphere.

  The treatment time of the amine compound in the gas atmosphere varies depending on the type and concentration of the amine compound to be used and the type and amount of polylactic acid to be treated and cannot be uniformly defined, but is usually 0.1 to 48 hours, preferably Is 1 to 12 hours, more preferably 1 to 2 hours.

  In the decomposition method of the present invention, the atmosphere containing the amine compound is produced by a known means. Specifically, a method of filling ammonia gas in a state where an organic substance containing polylactic acid is placed in a sealable tank; ammonia in a state where an organic substance containing polylactic acid is placed in a tank capable of inflow and outflow of gas Examples thereof include a method of continuously or intermittently performing gas inflow and outflow.

  In the decomposition method of the present invention, when the treatment is carried out in a state where water is supplied, the amine compound acts as a catalyst and does not undergo chemical change by itself. It can also be used.

  As a result of the treatment, the decomposed polylactic acid becomes lactic acid and exhibits a liquid state. By recovering the liquid generated after the treatment, a decomposition product containing lactic acid is obtained. If the amount of water added is adjusted so as not to add more water than necessary, the decomposition product becomes a 100% lactic acid solution, and the amine compound gas does not dissolve in the lactic acid solution, so the amine compound dissolved from the lactic acid solution Can be omitted. On the other hand, when water is added excessively to improve the decomposition rate, the resulting decomposition product is an aqueous lactic acid solution in which the amine compound is dissolved. The amine compound can be recovered by adding an alkali to the lactic acid aqueous solution or heating. In addition, in order to use the obtained lactic acid aqueous solution as a raw material for polylactic acid synthesis, when the lactic acid aqueous solution may contain an amine compound, or when it is desirable that the lactic acid aqueous solution contains an amine compound, A lactic acid aqueous solution in which an amine compound is dissolved can be used as it is.

  By treating in this way, polylactic acid is efficiently decomposed and converted to lactic acid. In the degradation product recovered as a liquid after the treatment, the degradation product of polylactic acid contains almost no lactic acid oligomer or low molecular weight polylactic acid, and contains lactic acid with high purity. Conventionally, it has been found that when polylactic acid is alkali-decomposed using an amine compound, lactic acid amide is by-produced in addition to lactic acid. According to the present invention, lactic acid is produced without producing such lactic acid amide. And the recovery efficiency of lactic acid is extremely high.

  The lactic acid contained in the degradation product thus obtained can also be recycled as a synthetic raw material for polylactic acid. In particular, when the content of polylactic acid in the organic matter to be treated is high, the recovered degradation product has a high purity of lactic acid and a low concentration of other compounds. It is preferably used as a raw material for the synthesis of polylactic acid.

  In addition, since the lactic acid thus obtained is a substance that is easily biodegradable, it may be subjected to biological treatment such as methane fermentation treatment and activated sludge treatment. In particular, when the organic matter to be treated contains a relatively large amount of organic matter other than polylactic acid, the recovered degradation products contain both lactic acid and other organic matter degradation products. It may be desirable to subject to further degradation.

  Since the decomposition method of the present invention can convert polylactic acid into highly pure lactic acid as described above, it can also be carried out as a method for producing lactic acid.

  The decomposition method of the present invention can be performed by an apparatus including a tank (hereinafter, sometimes referred to as a decomposition tank) that can adjust and maintain the above processing conditions. Hereinafter, an aspect of an apparatus for performing the decomposition method of the present invention will be described with reference to FIG. A decomposition tank 10 for treating the organic substance 1 containing polylactic acid in a gas atmosphere containing an amine compound, an organic substance supply means for supplying the organic substance 1 containing polylactic acid into the decomposition tank 10, and an amine compound gas 5 Is provided with an amine compound gas supply means (not shown in FIG. 1) for supplying the gas into the decomposition tank. In FIG. 1, the organic substance supply means is provided with a transport part 2 for transporting the organic substance 1 and a charging part 3 for charging the organic substance 1 into the decomposition tank. In addition, since the removable gas barrier unit 4 is provided between the input unit 3 and the decomposition tank 10, it is possible to input an organic substance when the gas barrier unit 4 is not installed, and when the gas barrier unit 4 is installed. It is possible to seal the inside of the decomposition tank. The decomposition tank 10 is preferably configured so that the inside of the tank can be sealed during the treatment. Further, as described above, since the decomposed product of polylactic acid is in a liquid state, in order to easily recover the decomposed product, a solid-liquid separation filter 6 is provided at the bottom of the decomposition tank 10 to provide a liquid decomposed product 7. May be configured to be discharged from the lactic acid discharge port 9 outside the decomposition tank. Moreover, as shown in FIG. 1, by installing the lactic acid discharge port 9 above the bottom of the decomposition tank 10 and below the upper surface of the decomposition tank 10, the liquid decomposition product 7 in the decomposition tank 10 Since it accumulates to the same height as the lactic acid discharge port 9 and exerts a barrier function against the gas 5 containing the amine compound, the gas 5 containing the amine compound in the decomposition tank flows out from the bottom through the lactic acid discharge port 9. This can also be prevented. In addition, as shown in FIG. 1, a contaminant removal means 11 for removing solid contaminants contained in the degradation product 7 is provided between the solid-liquid separation filter 6 and the lactic acid discharge port 9. May be. The contaminants removed by the contaminant removal unit 11 are discharged from the contaminant discharge port 8, and the lactic acid from which the contaminants have been removed by the contaminant removal unit 11 is discharged from the lactic acid discharge port 9.

  Hereinafter, as a method for biologically treating the degradation product obtained by the degradation method of the present invention, a method for treating an organic substance containing polylactic acid will be described by taking a methane fermentation treatment method as a specific example.

2. Methane fermentation treatment In order to subject the decomposition product obtained by the above-described decomposition method to methane fermentation treatment, methane fermentation may be carried out under conventionally known conditions using conventionally known methane fermentation bacteria and methane fermentation tanks. In the methane fermentation treatment, the decomposition product obtained by the decomposition method of the present invention is decomposed into methane and carbon dioxide.

  The temperature condition at the time of methane fermentation of the methane fermentation treatment can be appropriately set from a wide temperature range depending on the type of methane fermentation bacteria used, and is not particularly limited, but generally about 20 to 60 ° C, For example, a so-called medium temperature of about 35 ° C. or a so-called high temperature of about 55 ° C. may be used. When the nitrogen content contained in the decomposition product obtained by the above-described decomposition method is small, an intermediate temperature of about 35 ° C., in which methane fermentation is less susceptible to ammonia inhibition, is preferable. On the other hand, when the nitrogen content contained in the decomposition product obtained by the above decomposition method is large, a high temperature of about 55 ° C. is preferable from the viewpoint of increasing the methane fermentation rate.

  The methane fermentation treatment time in the methane fermentation treatment varies depending on the type and amount of the decomposition product obtained by the above decomposition method, the type of methane fermentation bacteria used, the fermentation temperature, the fermentation form, and the like, and cannot be defined uniformly. However, it is usually 14 to 30 days, preferably 10 to 20 days, and more preferably 10 to 14 days.

  In the methane fermentation treatment, the type of methane fermentation is not particularly limited. Any known type used in methane fermentation such as a batch type, a fixed bed type, and a UASB (Upflow Anaerobic Sludge Bed) type may be used. Moreover, you may implement by supplying the decomposition product obtained by said decomposition method, and extracting the methane fermentation processed material in a methane fermentation tank continuously or intermittently. When supply of the decomposition product and extraction of the methane fermentation treatment product are performed continuously or intermittently, the supply rate of the decomposition product and the extraction rate of the methane fermentation treatment product are the average residence time of the decomposition product in the methane fermentation tank. May be set as appropriate so as to be the fermentation treatment time.

  The methane fermentation treatment product obtained by the methane fermentation treatment may be subjected to water treatment such as activated sludge treatment as it is or after the solid-liquid separation. The method of solid-liquid separation is not particularly limited, and known methods such as precipitation separation, membrane separation, and centrifugation can be employed. The solid-liquid separation may be performed for all methane fermentation processed products, or a part thereof.

  Moreover, the solid content containing fraction (sludge) which isolate | separated the methane fermentation processed material into solid and liquid can return a part or all to a methane fermentation tank, and can also use for a methane fermentation process again. By this operation, the solid content is further thoroughly decomposed, so that the amount of waste solid content can be further reduced and the amount of methane gas generated can be increased. In addition, methane bacteria are returned to the system. The merit of improving the stability of is also obtained. However, if the return ratio is increased, the solid content concentration in the methane fermenter will increase, which may be disadvantageous in terms of stirring and pumping in the methane fermenter. It is good to decide the return amount.

  In the methane fermentation treatment, the solid content is accumulated in the methane fermentation tank as the methane fermentation progresses. Therefore, the solid content is usually extracted appropriately as sludge. The extracted sludge is treated by various methods. For example, as it is, it is returned to farmland as liquid fertilizer, processed after dehydration and converted into farmland, dehydrated and discarded, incinerated after dehydration, discarded after dehydration and drying, incinerated after dehydration and drying, etc. . In addition, low-temperature waste heat can be effectively used for drying, and when methane gas is used in a gas engine, a micro gas turbine, a boiler, or the like, the waste heat can be used for drying. In some cases, the dehydrated filtrate can be discharged as it is, depending on the water quality and drainage standards. If not, it may be subjected to water treatment again. Since the methane fermentation treatment is performed in an anaerobic atmosphere, if the water treatment is a treatment performed in an aerobic atmosphere such as activated sludge treatment, even if it is polylactic acid or its decomposition product that was not decomposed by methane fermentation, It may be decomposed by water treatment such as activated sludge treatment. This is preferable because the amount of sludge to be discarded is reduced.

  EXAMPLES Hereinafter, although an Example etc. are given and this invention is demonstrated, this invention is not limited to these Examples.

Example 1 Decomposition treatment of polylactic acid with ammonia gas Into a 2.5 mL sealed container, 1 g of polylactic acid (in which a polylactic acid produced by Nature Works was molded into a sheet) and 0.25 g of water were placed. Ammonia gas (ammonia 0.1 mmol; 100% by volume) was charged and allowed to stand at 70 ° C. for 10 hours (note that the pressure in the sealed container is normal pressure). Thereafter, no polylactic acid remained in the container, and all was converted to 1.25 g of a liquid decomposition product. In addition, the production rate of lactic acid in this decomposition treatment (lactic acid production rate from the start of the decomposition treatment to 10 hours later) was 13,888 μg / sec-L. In addition, the production | generation rate of lactic acid was computed according to the following formula.

  The composition of the obtained liquid decomposition product was analyzed by ion chromatography using DX-300 manufactured by Dionex. As a result, a single peak of lactic acid was obtained, and its concentration was 2.38 mg / L. (See FIG. 2). Since the specific gravity of lactic acid is 1.2, it is clear that the obtained liquid decomposition product is about 100% by weight of lactic acid and contains only 1% by weight or less of water. In addition, the presence of amidated lactic acid was not observed in the liquid decomposition product.

  From the above results, it was revealed that polylactic acid was hydrolyzed to lactic acid by ammonia gas. In addition, since the obtained liquid decomposition product was almost 100% pure lactic acid, it was also confirmed that hydrolysis using ammonia gas did not by-produce lactic acid oligomers or lactic acid amide compounds. . Moreover, under this condition, since almost no water remained in the obtained liquid decomposition product, it was considered that almost all of the water added at the start of the treatment was used for hydrolysis of polylactic acid.

Example 2 Decomposition treatment of polylactic acid with various amine compound gases The above procedure was performed except that the same amount of another amine compound (shown in Table 1) was used instead of ammonia gas, and the treatment time was 6 hours. Polylactic acid was decomposed under the same conditions as in Example 1. Table 1 shows the results of calculating the production rate of lactic acid in this decomposition treatment (lactic acid production rate after 6 hours from the start of the decomposition treatment) in the same manner as in Example 1.

  Furthermore, when the treatment time was extended to 10 hours and the polylactic acid decomposition treatment was continued, as in Example 1, no polylactic acid remained in the container, and all the liquid decomposition product 1.25 g It was converted to.

  Further, when the liquid decomposition product obtained in this decomposition treatment was analyzed, almost 100% by weight was lactic acid, water was 1% by weight or less, and lactic acid amidation product was not contained.

  From the above results, other amine compound gases can be decomposed from polylactic acid to lactic acid in the same manner as ammonia gas, and alkylamines can convert polylactic acid to high-purity lactic acid. Indicated.

Comparative Example 1 Alkali Decomposition Treatment of Polylactic Acid with Ammonia Water <Comparative Example: Alkaline Hydrolysis>
10 g of polylactic acid was added to 10 ml of water, pH was adjusted to 8.5, 9.5, or 10.5 with a 25 vol% aqueous ammonia solution as an initial setting value, and a decomposition treatment was started at 70 ° C. Since the lactic acid is produced with the decomposition of the polylactic acid and the pH of the reaction solution is lowered, a 25 vol% aqueous ammonia solution was appropriately added so that the pH was always kept at the initial set value. Further, during the decomposition treatment, the concentration of lactic acid produced over time was measured.

  Table 2 shows the cumulative amount of ammonia added when the concentration of lactic acid in the reaction solution reached 0, 1, 5, and 10 g / l under each condition.

  While the concentration of lactic acid in the reaction solution was changed from 0 g / l to 5 g / l under each condition, the ratio of increase in the cumulative amount of added ammonia to the increase in lactic acid concentration was almost constant. That is, when the lactic acid concentration is between 0 g / l and 5 g / l, a proportional relationship is recognized between the lactic acid concentration and the cumulative amount of added ammonia. This is presumably because ammonia was used to suppress the decrease in pH due to the produced lactic acid.

  On the other hand, when the concentration of lactic acid in the reaction solution is changed from 5 g / l to 10 g / l under each condition, the ratio of increase in the cumulative amount of added ammonia to the increase in lactic acid concentration is clearly improved. This indicates that the lactic acid produced was amidated while the concentration of lactic acid was changed from 5 g / l to 10 g / l, and ammonia was also used as a substrate for the amidated product.

  The lactic acid production rates under the above conditions were 1.2 μg / sec-L (pH initial setting value 8.5), 15 μg / sec-L (pH initial setting value 9.5), 109 μg, respectively. / L-L (initial setting value of pH 10.5), which is much lower than that in Example 1 above. In addition, the production | generation rate of lactic acid was computed according to the following formula.

It is a figure which shows an example of a structure of the apparatus for performing the decomposition | disassembly method of this invention. It is a figure which shows the result of having analyzed the liquid decomposition product obtained in Example 1. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Organic substance containing polylactic acid 2 Conveying part 3 Input part 4 Gas barrier part 5 Gas containing amine compound 6 Solid-liquid separation filter 7 Liquid decomposition product 8 Contaminant discharge port 9 Lactic acid discharge port 10 Decomposition tank 11 Contaminant removal means

Claims (4)

A method for decomposing polylactic acid, comprising a step of treating an organic substance containing polylactic acid in a gas atmosphere containing a compound represented by formula (I) and water .

[In the formula (I), R ₁ , R ₂ and R ₃ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ] The decomposition method according to claim ₁ , wherein, in the general formula (I), R ₁ , R ₂ and R ₃ are the same or different and are a hydrogen atom, a methyl group or an ethyl group. The decomposition method according to claim 1 or 2, wherein the organic substance is treated in a gas atmosphere containing a compound represented by the general formula (I) and water under a temperature condition of 40 ° C or higher. A method for treating an organic substance containing polylactic acid, comprising the following steps (a) and (b):
(a) a step of decomposing polylactic acid by treating an organic substance containing polylactic acid in a gas atmosphere containing a compound represented by general formula (I) and water ; and

[In the formula (I), R ₁ , R ₂ and R ₃ are the same or different and each represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ]
(b) A step of methane fermentation of the decomposition product obtained in step (a).

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