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JP5280656B2 - Depolymerization method of polylactic acid - Google Patents

Depolymerization method of polylactic acid Download PDF

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JP5280656B2
JP5280656B2 JP2007197628A JP2007197628A JP5280656B2 JP 5280656 B2 JP5280656 B2 JP 5280656B2 JP 2007197628 A JP2007197628 A JP 2007197628A JP 2007197628 A JP2007197628 A JP 2007197628A JP 5280656 B2 JP5280656 B2 JP 5280656B2
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polylactic acid
zinc
depolymerization
methanol
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JP2009029757A (en
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健一 石原
実 中島
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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C08J11/16—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with inorganic material
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J2367/00—Characterised by the use of polyesters obtained by reactions forming a carboxylic ester link in the main chain; Derivatives of such polymers
    • C08J2367/04—Polyesters derived from hydroxy carboxylic acids, e.g. lactones
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/62—Plastics recycling; Rubber recycling

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Description

本発明は、亜鉛化合物の触媒存在下、メタノールを用いてアルコール分解することによるポリ乳酸を解重合する方法に関する。   The present invention relates to a method for depolymerizing polylactic acid by alcoholysis using methanol in the presence of a zinc compound catalyst.

ポリ乳酸は、従来から、環境への負荷が少ない生分解性プラスチックの代表としてよく知られてきた。近年、循環型社会構築気運が高まり、プラスチック原料が化石資源からバイオマス資源へ転換する動きがあり、デンプンなど植物が原料となるポリ乳酸が大きな注目を集めている。このポリ乳酸は、その物性として透明性に優れ、成形加工の多様性があり、安全性も高いため、農林水産用資材、土木・建築資材、食品包装・容器又は日用品用途などでの各方面での使用が期待されている。   Conventionally, polylactic acid has been well known as a representative of biodegradable plastics that have a low environmental impact. In recent years, the trend of building a recycling-oriented society has increased, and plastic raw materials have been moved from fossil resources to biomass resources, and polylactic acid made from plants such as starch has attracted much attention. This polylactic acid is excellent in transparency as its physical properties, has a variety of molding processes, and is highly safe. The use of is expected.

しかしながら、上記のような使用の増大に伴って大量に発生する、使用済みポリ乳酸、及びポリ乳酸製造段階で発生する品質不適格品（以下、これらをポリ乳酸回収物と略称することがある。）については、ポリ乳酸部位は生分解性を有するものの分解までに長時間を要する。またポリ乳酸以外の部位は生分解性を有さないことが多くそのまま自然界に残り、今後大きな社会問題となることが予想される。上記の問題に対して、ポリ乳酸回収物を元の原料に変換・回収し、この原料から再度重合反応等によってポリ乳酸ポリマーを製造し再利用する、いわゆるケミカルリサイクルが有効である。この方法は、基本的にロスの無い、化合物の資源再使用が可能な方法であり、資源の再利用が可能となる。   However, used polylactic acid generated in large quantities with the increase in use as described above, and non-qualified products generated in the polylactic acid production stage (hereinafter, these may be abbreviated as polylactic acid recovered materials). ), The polylactic acid moiety is biodegradable but takes a long time to decompose. In addition, parts other than polylactic acid often do not have biodegradability and remain in the natural world, which is expected to become a major social problem in the future. In order to solve the above problems, so-called chemical recycling is effective, in which a polylactic acid recovery product is converted and recovered to an original raw material, and a polylactic acid polymer is produced from the raw material again by a polymerization reaction or the like and reused. This method is basically a loss-free method that enables resource reuse of compounds, and enables resource reuse.

例えば、ポリ乳酸をケミカルリサイクルする方法の一つとして、ポリ乳酸回収物を熱分解してラクチドを回収する方法がある。ポリ乳酸製品をスクリュー式押出機内において水及び触媒の存在下、２００〜４００℃に加熱してラクチドを回収する方法が提案されている（例えば特許文献１参照。）。また、高分子量のポリ乳酸（重量平均分子量：５０００〜３０万）をスズ又はスズ化合物からなる触媒の存在下、ポリ乳酸回収物の溶融温度以上の温度（１７０℃〜３００℃）に加熱すると共に、前記温度におけるラクチドの蒸気圧以下の圧力に減圧して、生成したラクチドを留去して回収する方法が提案されている（例えば特許文献２参照。）。   For example, as one method of chemically recycling polylactic acid, there is a method of recovering lactide by thermally decomposing a polylactic acid recovery product. A method for recovering lactide by heating a polylactic acid product to 200 to 400 ° C. in the presence of water and a catalyst in a screw extruder has been proposed (see, for example, Patent Document 1). In addition, while heating high molecular weight polylactic acid (weight average molecular weight: 5000 to 300,000) in the presence of a catalyst composed of tin or a tin compound, the polylactic acid is heated to a temperature (170 ° C. to 300 ° C.) higher than the melting temperature of the polylactic acid recovery product. A method has been proposed in which the pressure is reduced to a pressure equal to or lower than the vapor pressure of lactide at the above temperature, and the produced lactide is distilled off and recovered (see, for example, Patent Document 2).

しかしながら、いずれの方法も高温条件下熱分解反応を実施するため、ポリ乳酸の光学純度が低下し、ポリ乳酸回収物に含まれる異素材の熱分解を回避することができず、最終的には、ポリ乳酸の品質低下を招くという問題がある。その他のポリ乳酸のケミカルリサイクル方法として、塩基触媒下、１価のアルコールを用いて加溶媒分解する方法が提案されている（例えば特許文献３参照。）。しかしながら、該方法も塩基触媒を使用するため、取扱い安全上問題が生じる。   However, since both methods carry out a thermal decomposition reaction under high temperature conditions, the optical purity of polylactic acid decreases, and thermal decomposition of foreign materials contained in the polylactic acid recovery product cannot be avoided. There is a problem that the quality of polylactic acid is lowered. As another chemical recycling method for polylactic acid, a method of solvolysis using a monovalent alcohol under a base catalyst has been proposed (for example, see Patent Document 3). However, since this method also uses a base catalyst, there is a problem in handling safety.

特開平０７−３０９８６３号公報Japanese Patent Application Laid-Open No. 07-309863 特開平０９−７７９０４号公報JP 09-77904 A 特開２００４−２５０４１４号公報JP 2004-250414 A

本発明の目的は、従来技術が有していた問題点を解決し、ポリ乳酸の品質低下を防止し、取扱い容易な触媒を使用するポリ乳酸を解重合する方法を提供することにある。   An object of the present invention is to solve the problems of the prior art and to provide a method for depolymerizing polylactic acid using a catalyst that prevents the deterioration of the quality of polylactic acid and is easy to handle.

本発明者らは上記従来技術に鑑み、鋭意検討を行った結果、本発明を完成するに至った。すなわち本発明は、安息香酸亜鉛及び／又は炭酸亜鉛からなる亜鉛化合物の触媒存在下、メタノールを用いて６０〜１００℃でポリ乳酸をアルコール分解するポリ乳酸の解重合方法である。 As a result of intensive studies in view of the above-described prior art, the present inventors have completed the present invention. That is, the present invention is a polylactic acid depolymerization method in which polylactic acid is alcoholically decomposed at 60 to 100 ° C. using methanol in the presence of a zinc compound catalyst comprising zinc benzoate and / or zinc carbonate.

本発明の方法によれば、メタノールを用いてポリ乳酸を解重合する場合、特定の亜鉛化合物の触媒を用いることで、品質の良好な乳酸メチルを製造することが可能である。また、そのような亜鉛化合物の触媒を使用するため、触媒の取扱いも容易となる。   According to the method of the present invention, when polylactic acid is depolymerized using methanol, it is possible to produce methyl lactate with good quality by using a catalyst of a specific zinc compound. Further, since such a zinc compound catalyst is used, handling of the catalyst becomes easy.

本発明において、ポリ乳酸とは主成分がポリ乳酸であり、ポリ乳酸回収物全体の６０重量％以上含むものが好ましく、より好ましくは８０重量％以上である。ポリ乳酸については、ポリＬ−乳酸、ポリＤ−乳酸、ラセミ体のポリ乳酸、ラセミ体以外のポリＬ−乳酸とポリＤ−乳酸の混合物、ポリ乳酸ステレオコンプレックスポリマーなど各種ポリ乳酸に適用できる。   In the present invention, the main component of polylactic acid is polylactic acid, and preferably contains 60% by weight or more, more preferably 80% by weight or more of the whole polylactic acid recovered product. The polylactic acid can be applied to various polylactic acids such as poly-L-lactic acid, poly-D-lactic acid, racemic polylactic acid, a mixture of non-racemic poly-L-lactic acid and poly-D-lactic acid, and polylactic acid stereocomplex polymer.

また、本発明の解重合方法には、各種ポリ乳酸と他の異素材との混合物にも適用可能である。さらに本発明の方法においては、ポリ乳酸は一般に水洗浄及び粗粉砕などの前処理を施し、解重合反応に適した形状にしてから解重合工程に投入することが好ましい。この前処理の操作の際に水に極めて易溶な異素材も取り除くことができるので好ましい。また、この前処理を行う前及び／又は前処理を行った後で、簡易的な機械的又は物理的手段によって可能な限りポリ乳酸回収物から異素材を取り除くことが好ましい。例えば目視で異素材と判別できるものを取り除く方法、又は磁石を用いて磁石に吸い付けられる金属類を取り除くなどの方法である。更に本発明の解重合方法によって得られる乳酸メチルとは、２種類の光学異性体（Ｌ−乳酸メチルとＤ−乳酸メチル）が存在する。   The depolymerization method of the present invention can also be applied to a mixture of various polylactic acids and other different materials. Further, in the method of the present invention, it is preferable that the polylactic acid is generally subjected to pretreatment such as washing with water and coarse pulverization to form a shape suitable for the depolymerization reaction, and then charged into the depolymerization step. This pretreatment is preferable because foreign materials that are very easily soluble in water can be removed. Further, before the pretreatment and / or after the pretreatment, it is preferable to remove foreign materials from the polylactic acid recovered material as much as possible by simple mechanical or physical means. For example, there are a method of removing a material that can be visually discriminated from a different material, or a method of removing a metal attracted to the magnet using a magnet. Further, methyl lactate obtained by the depolymerization method of the present invention includes two types of optical isomers (L-methyl lactate and D-methyl lactate).

本発明のポリ乳酸の解重合方法については、ポリ乳酸回収物の性状に特に限定されることはなく、そのポリ乳酸回収物の性状等によって、任意に解重合反応時間、用いるメタノールの量、後述の亜鉛化合物触媒の量等をそれぞれ独自に調整することができる。また、後述する範囲内で解重合温度、亜鉛化合物触媒の種類を調整することができる。また、解重合反応は回分式又は連続式いずれも採用可能である。   The polylactic acid depolymerization method of the present invention is not particularly limited to the properties of the polylactic acid recovery product. Depending on the properties of the polylactic acid recovery product, etc., the depolymerization reaction time, the amount of methanol used, The amount of the zinc compound catalyst can be adjusted independently. Further, the depolymerization temperature and the type of zinc compound catalyst can be adjusted within the ranges described below. The depolymerization reaction can be either batchwise or continuous.

それらの方法の中で本発明の解重合方法のより現実的な実施態様は、前記ポリ乳酸をメタノールと有機カルボン酸亜鉛及び／又は炭酸亜鉛からなる亜鉛化合物の触媒共存下、６０〜１００℃の温度下でアルコール分解することが必要である。必要に応じて前記温度におけるメタノールの蒸気圧以上の圧力条件にして、ポリ乳酸を解重合する方法である。解重合反応において、解重合反応温度は６０℃〜１００℃であることが必要である。解重合反応温度が１００℃より高くするためには、反応時の圧力をより高く維持する必要があり、高圧仕様の設備を必要とする。一方、解重合反応温度が６０℃より低いと、解重合反応速度が非常に遅くなる。解重合時の圧力については、前記解重合反応温度におけるメタノールの蒸気圧以上の圧力条件に設定されることが好ましい。圧力は常圧条件にすることが最も好ましい。   Among these methods, a more realistic embodiment of the depolymerization method of the present invention is that the polylactic acid is heated at a temperature of 60 to 100 ° C. in the presence of a catalyst of a zinc compound comprising methanol and an organic zinc carboxylate and / or zinc carbonate. It is necessary to decompose alcohol under temperature. In this method, polylactic acid is depolymerized under a pressure condition equal to or higher than the vapor pressure of methanol at the above temperature as necessary. In the depolymerization reaction, the depolymerization reaction temperature needs to be 60 ° C to 100 ° C. In order to make the depolymerization reaction temperature higher than 100 ° C., it is necessary to maintain a higher pressure during the reaction, and high-pressure equipment is required. On the other hand, when the depolymerization reaction temperature is lower than 60 ° C., the depolymerization reaction rate becomes very slow. About the pressure at the time of depolymerization, it is preferable to set it as pressure conditions more than the vapor pressure of methanol in the said depolymerization reaction temperature. Most preferably, the pressure is atmospheric pressure.

解重合反応時間については、解重合反応温度、反応圧力、ポリ乳酸回収物の性状、使用するメタノールの量、亜鉛化合物触媒の種類、亜鉛化合物触媒の量等により任意に設定することが可能である。メタノールの使用量は、ポリ乳酸に対し０．５〜５．０重量倍であることが好ましい。メタノールの使用量が０．５重量倍より少なくなると、ポリ乳酸がメタノールと充分に混合できず、ポリ乳酸の解重合反応速度が非常に遅くなる。一方、メタノールの使用量が５．０重量倍より多くなると、その分加熱するエネルギーの使用量が多くなり、経済的な観点から好ましくない。   The depolymerization reaction time can be arbitrarily set depending on the depolymerization reaction temperature, reaction pressure, the properties of the polylactic acid recovered product, the amount of methanol used, the type of zinc compound catalyst, the amount of zinc compound catalyst, and the like. . The amount of methanol used is preferably 0.5 to 5.0 times the weight of polylactic acid. If the amount of methanol used is less than 0.5 times by weight, polylactic acid cannot be sufficiently mixed with methanol, and the depolymerization reaction rate of polylactic acid becomes very slow. On the other hand, if the amount of methanol used exceeds 5.0 times by weight, the amount of energy used for heating increases, which is not preferable from an economical viewpoint.

また使用する触媒については、有機カルボン酸亜鉛及び／又は炭酸亜鉛からなる亜鉛化合物であることが必要である。更にその中でも、酢酸亜鉛及び／又は安息香酸亜鉛であることが好ましい。更に反応装置については、連続式或いは回分式いずれも適用可能である。   Moreover, about the catalyst to be used, it is necessary to be a zinc compound which consists of organic carboxylate and / or zinc carbonate. Among them, zinc acetate and / or zinc benzoate are preferable. Further, as the reaction apparatus, either a continuous type or a batch type can be applied.

以下、実施例により本発明の内容を更に具体的に説明するが、本発明はこれにより何ら限定を受けるものではない。尚実施例及び比較例において「部」と称しているものは重量部を表す。
（１）乳酸メチルの測定方法（ｗｔ％）
ポリ乳酸を解重合して得られる乳酸メチルは、ガスクロマトグラフ（カラム：ジーエルサイエンス株式会社製 Ｉｎｅｒｔ Ｃａｐ（φ０．５３ｍｍ×Ｌ１５ｍ））によって測定し、乳酸メチルの割合を求めた。
（２）乳酸メチルの光学純度測定方法（％）高速液体クロマトグラフ（カラム：住友化学ＯＡ−２５００Ｌ （φ４．６ｍｍ×Ｌ２５ｃｍ）、溶離液：ｎ−ヘキサン／エタノール＝９５／５）によって測定し、Ｌ−乳酸メチル、Ｄ−乳酸メチルの割合を求めた。 Hereinafter, the content of the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto. In addition, what is called "part" in an Example and a comparative example represents a weight part.
(1) Methyl lactate measurement method (wt%)
Methyl lactate obtained by depolymerizing polylactic acid was measured by a gas chromatograph (column: Inert Cap (φ0.53 mm × L15 m) manufactured by GL Sciences Inc.) to determine the ratio of methyl lactate.
(2) Optical purity measurement method for methyl lactate (%) Measured by high performance liquid chromatograph (column: Sumitomo Chemical OA-2500L (φ4.6 mm × L25 cm), eluent: n-hexane / ethanol = 95/5) The ratios of L-methyl lactate and D-methyl lactate were determined.

〔参考例１〕
ポリ乳酸（Ｌ体＝９３．１％、分子量：１２９，０００、ラクティＴＭ９０１０（株式会社島津製作所製））１００部、酢酸亜鉛３．８部、メタノール１００部を攪拌翼及び冷却管付き反応器に投入し、攪拌翼を５００ｒｐｍで攪拌下徐々に加温し温度を上げ、常圧条件下、リフラックス状態で維持した。固体状のポリ乳酸は徐々に溶解し、反応液がリフラックス状態になってからから３時間で得られた反応生成物を分析したところ、乳酸メチルの収率は６５ｍｏｌ％であり、そのうちＬ−乳酸の割合は９３．０重量％であった。 [ Reference Example 1]
100 parts of polylactic acid (L-form = 93.1%, molecular weight: 129,000, Lacty TM 9010 (manufactured by Shimadzu Corporation)), 3.8 parts of zinc acetate, and 100 parts of methanol were added to a reactor equipped with a stirring blade and a cooling tube. The stirring blade was gradually heated under stirring at 500 rpm to raise the temperature, and maintained in a reflux state under normal pressure conditions. The solid polylactic acid dissolved gradually, and the reaction product obtained in 3 hours after the reaction solution became refluxed was analyzed. As a result, the yield of methyl lactate was 65 mol%, of which L- The proportion of lactic acid was 93.0% by weight.

〔参考例２〕
参考例１において、反応時間を６時間に変更し、同様の操作を行った。その結果、得られた反応生成物を分析したところ、乳酸メチルの収率は８６ｍｏｌ％であり、そのうちＬ−乳酸の割合は９２．８重量％であった。 [ Reference Example 2]
In Reference Example 1, the reaction time was changed to 6 hours, and the same operation was performed. As a result, when the obtained reaction product was analyzed, the yield of methyl lactate was 86 mol%, and the proportion of L-lactic acid was 92.8 wt%.

〔参考例３〕
参考例１において、メタノールを２００部に変更し、同様の操作を行った。その結果、得られた反応生成物を分析したところ、乳酸メチルの収率は８８ｍｏｌ％であり、そのうちＬ−乳酸の割合は９３．１重量％であった。 [ Reference Example 3]
In Reference Example 1, methanol was changed to 200 parts, and the same operation was performed. As a result, when the obtained reaction product was analyzed, the yield of methyl lactate was 88 mol%, and the ratio of L-lactic acid was 93.1% by weight.

〔参考例４〕
参考例１において、酢酸亜鉛を７．６部に変更し、同様の操作を行った。その結果、得られた反応生成物を分析したところ、乳酸メチルの収率は７９ｍｏｌ％であり、そのうちＬ−乳酸の割合は９２．８重量％であった。 [ Reference Example 4]
In Reference Example 1, zinc acetate was changed to 7.6 parts, and the same operation was performed. As a result, when the obtained reaction product was analyzed, the yield of methyl lactate was 79 mol%, and the proportion of L-lactic acid was 92.8 wt%.

〔実施例５〕
参考例１において、亜鉛化合物を安息香酸亜鉛３．８部に変更し、同様の操作を行った。その結果、得られた反応生成物を分析したところ、乳酸メチルの収率は５１．２ｍｏｌ％であり、そのうちＬ−乳酸の割合は９３．０重量％であった。 Example 5
In Reference Example 1, the zinc compound was changed to 3.8 parts of zinc benzoate, and the same operation was performed. As a result, when the obtained reaction product was analyzed, the yield of methyl lactate was 51.2 mol%, and the proportion of L-lactic acid was 93.0 wt%.

〔比較例１〕
参考例１において、酢酸亜鉛を添加せずに、同様の操作を行った。その結果、固体状のポリ乳酸はそのままの形状で残り、得られた反応生成物を分析したが、乳酸メチルの生成は確認できなかった。 [Comparative Example 1]
In Reference Example 1, the same operation was performed without adding zinc acetate. As a result, solid polylactic acid remained as it was, and the obtained reaction product was analyzed, but formation of methyl lactate could not be confirmed.

〔比較例２〕
参考例１において、反応温度を５０℃として、同様の操作を行った。その結果、固体状のポリ乳酸の大部分はそのままの形状で残り、得られた反応生成物を分析したところ、乳酸メチルの収率は３ｍｏｌ％であった。 [Comparative Example 2]
In Reference Example 1, the same operation was performed at a reaction temperature of 50 ° C. As a result, most of the solid polylactic acid remained as it was, and when the obtained reaction product was analyzed, the yield of methyl lactate was 3 mol%.

本発明により、ポリ乳酸を解重合する際、ポリ乳酸の品質低下を防止し、また、取扱い容易な触媒を使用する方法で実施することができるため、その工業的な意義は大きい。   According to the present invention, when polylactic acid is depolymerized, the degradation of the quality of polylactic acid can be prevented and the method using an easy-to-handle catalyst can be carried out.

Claims (4)

安息香酸亜鉛及び／又は炭酸亜鉛からなる亜鉛化合物の触媒存在下、メタノールを用いて６０〜１００℃でポリ乳酸をアルコール分解するポリ乳酸の解重合方法。 A method for depolymerizing polylactic acid, comprising subjecting polylactic acid to alcohol decomposition at 60 to 100 ° C. using methanol in the presence of a catalyst of a zinc compound comprising zinc benzoate and / or zinc carbonate. 亜鉛化合物が安息香酸亜鉛である請求項１記載のポリ乳酸の解重合方法。 The method for depolymerizing polylactic acid according to claim 1, wherein the zinc compound is zinc benzoate . メタノールの使用量がポリ乳酸に対して０．５〜５．０重量倍であることを特徴とする請求項１または２記載のポリ乳酸の解重合方法。The method for depolymerizing polylactic acid according to claim 1 or 2, wherein the amount of methanol used is 0.5 to 5.0 times by weight of polylactic acid. 亜鉛化合物の使用量がポリ乳酸１００部に対して３．８〜７．６部であることを特徴とする請求項１〜３のいずれか１項記載のポリ乳酸の解重合方法。 The method for depolymerizing polylactic acid according to any one of claims 1 to 3, wherein the amount of zinc compound used is 3.8 to 7.6 parts per 100 parts of polylactic acid.
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