JP2013185152A - Method for depolymerizing polyester using metal oxide as catalyst and method for recovering polyester raw material using the depolymerization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for depolymerizing a polyester which can easily and rapidly perform depolymerization at low cost using a convenient ordinary heating device.SOLUTION: A method for depolymerizing a polyester is characterized in that polyester-containing moldings or scraps are heated to reflux by ordinary heating in the presence of an alkylene glycol in which one or more kinds of metal oxide powders selected from lead dioxide, trilead tetroxide, manganese dioxide and lanthanum oxide are dispersed.

Description

  The present invention relates to a method for depolymerizing polyester and a method for recovering a polyester raw material using the depolymerization method.

  Polyesters typified by polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”) have excellent chemical stability and are used in fibers, films, sheets, beverage bottles, and the like. Yes.

  In recent years, the disposal method of waste such as polyester has become a problem, and various methods for collecting and reusing the waste have been studied. As one of them, waste such as polyester is depolymerized. Therefore, chemical recycling has been studied in which polyester is converted into a monomer and recovered, and then the polyester is used as a raw material to produce a polyester such as PET again by a polymerization reaction. This chemical recycling can separate impurities, and the quality as a raw material is not so different from that of virgin products derived from crude oil. Therefore, this chemical recycling is expected as a means for realizing resource reuse.

  Broadly speaking, there are three methods for depolymerizing polyester monomers, namely, hydrolysis using water as a solvent, alcoholysis using alcohol as a solvent, and glycolysis using glycol as a solvent.

  Examples of the hydrolysis method include a method in which a PET melt is reacted with water vapor and then reacted with ammonium hydroxide to be decomposed into terephthalic acid and ethylene glycol (hereinafter sometimes abbreviated as “EG”). (Patent Document 1). This method has the advantage that it is not necessary to use glycol or alcohol for the reaction, and the above reaction is carried out under high pressure conditions, so that there is a disadvantage that a special apparatus having a pressure resistance is required. Moreover, in order to produce | generate the obtained terephthalic acid, the process which melt | dissolves as an alkali salt with an alkali, removes the filterable impurity, and returns to a terephthalic acid with an acid again is required. In other words, although it can be decomposed, the purification method is costly.

  The alcoholysis method is a method of depolymerizing polyester by heating in an alcohol solvent (adding a catalyst as necessary), for example (Patent Documents 2 and 3). This method has an advantage that, for example, when PET is depolymerized using methanol as a solvent, dimethyl terephthalate, which is a useful and easy-to-handle monomer, is produced directly by the depolymerization reaction, and the depolymerization reaction is relatively fast. However, since the alcohol used as a solvent has a low boiling point and requires pressurization to proceed with the reaction (for example, reaction in supercritical or subcritical methanol), a special apparatus with a high pressure resistance is required. There is a drawback.

  The glycolysis method is a method in which polyester is depolymerized by heating in an excess of an alkylene glycol solvent together with a catalyst such as sodium carbonate to produce saturated dibasic acid bis (hydroxyalkyl) terephthalate and ethylene glycol (Patent Literature). 4, Patent Document 5). For example, when ethylene glycol is used as the solvent, bis (hydroxyethyl) terephthalate (hereinafter sometimes abbreviated as BHET) is produced by the depolymerization reaction, and methanol is added in the presence of a transesterification catalyst. Dimethyl terephthalate can be recovered by transesterification.

  This glycolysis method can be reacted at normal pressure. However, since the reaction time is relatively long (for example, about 4 hours according to the embodiment of Patent Document 4), the operating rate cannot be increased. Further, there is a drawback that the solvent glycol is deteriorated by being heated for a long time.

  Patent Document 6 is a method for producing disodium terephthalate by depolymerizing PET in an ethylene glycol solvent containing sodium hydroxide and water. According to this depolymerization method, depolymerization can be performed in a shorter time (about 15 minutes to 1 hour) than the above-mentioned glycolysis method. For example, in the example of Patent Document 6, about 1 hour at around 180 ° C. It is described that disodium terephthalate was obtained by depolymerizing PET by heating and stirring.

  Patent Document 7 is a method of generating disodium terephthalate by performing depolymerization by irradiating a microwave to PET in a sodium hydroxide and ethylene glycol solvent. This depolymerization method makes it possible to perform depolymerization in a shorter time (1-2 minutes) than the above-mentioned Patent Document 6 by using a microwave as a heating source. Disodium terephthalate is obtained by depolymerizing PET by irradiating with waves for 2 minutes and heating and stirring.

  Patent Document 8 is a method of generating bis (hydroxyalkyl) terephthalate and ethylene glycol by performing depolymerization by irradiating PET with microwaves in a fine powder of titanium oxide and an ethylene glycol and / or propylene glycol solvent. This depolymerization method enables depolymerization by using titanium oxide as a catalyst and using microwaves as a heating source. For example, in the example of Patent Document 8, the microwaves are irradiated for 30 minutes and heated and stirred. It has succeeded in depolymerizing PET to obtain BHET. It is also described that the reaction does not proceed at all by normal heating of a heating medium or the like instead of microwave heating. However, in the method of Patent Document 8, it is necessary to use a titanium oxide fine powder having a low bulk density. Since such a titanium oxide fine powder is relatively expensive, it can be said that it is sufficient in terms of cost. Absent. Moreover, since the particle size is small, separation and removal of the titanium oxide fine powder after the reaction (separation and purification of the raw material monomer) may be complicated.

  In order to generalize the microwave glycolysis method of PET using relatively expensive fine powdered titanium oxide in Patent Document 8, screening experiments were conducted on relatively inexpensive metal oxides, and lead dioxide, lanthanum oxide, manganese dioxide, Patent Document 9 revealed that trilead oxide and iron (III) oxide have high catalytic activity.

  Special table 2003-527363 gazette   Japanese Patent Laid-Open No. 11-100300   JP 2003-300916 A   JP 2002-167468 A   JP 2004-300115 A   JP-A-11-302208   Japanese Patent No. 4680266   Japanese Patent No. 4531855   Patent pending

  As described above, the hydrolysis method and alcoholysis method, which are conventionally known depolymerization methods of polyester, require a special apparatus that can withstand reaction conditions under high temperature or high pressure conditions. On the other hand, the glycolysis method has a problem that the reaction time is relatively long although it can be reacted at normal pressure. Also, for example, although a method of performing microwave heating using titanium oxide fine powder or lead dioxide and ethylene glycol solvent has been proposed, it is satisfactory in terms of catalyst cost and ease of separation and purification of raw material monomers. I couldn't say it was going. The object of the present invention is to solve the problems in such conventional polyester depolymerization methods.

  That is, an object of the present invention is to provide a polyester depolymerization method that can be carried out easily and quickly at normal pressure and at low cost using a simple normal heating apparatus. Furthermore, it aims at providing the recovery method of the polyester raw material with few impurities using such a depolymerization method.

  In order to solve the above problems, the polyester depolymerization method of the present invention uses one or two or more metal oxide powders selected from lead dioxide, trilead tetroxide, manganese dioxide, and lanthanum oxide as a reaction catalyst. In the presence of alkylene glycol in which metal oxide powder is dispersed, a molded product or waste containing polyester is irradiated with microwaves. As said alkylene glycol, ethylene glycol or propylene glycol is preferable. Moreover, as a molded article or waste containing the polyester, for example, a molded article or waste containing polyethylene terephthalate is suitable.

  The polyester raw material recovery method of the present invention includes a step of immersing a molded product or waste containing polyester in alkylene glycol in which a specific type of metal oxide powder is dispersed, and microwave irradiation according to the above depolymerization method. And a step of generating a bis (hydroxyalkyl) ester of alkylene glycol and a saturated dibasic acid by depolymerizing the polyester. Moreover, the alkylene glycol produced | generated by the depolymerization reaction can also be reused in addition to the solvent of this depolymerization reaction.

  The normal heat depolymerization method of the present invention does not require the high-temperature pressurization device required in the conventional hydrolysis method and alcoholysis method, and the microwave heating device or the domestic microwave oven in Patent Documents 8 and 9. There is no need for special equipment. For this reason, it becomes easy to reduce the volume of waste such as collected PET bottles in the region and to make it into a monomer, and it can be transported to a polyester factory and reused.

  Further, in the conventional glycolysis reaction or the like, it took a long time to depolymerize the polyester, but in the depolymerization method of the present invention, the reaction time of the depolymerization is remarkably shortened, for example, about 100 minutes in about 20 minutes to 1 hour. It is possible to perform depolymerization at a reaction rate close to%, and it is possible to quickly and efficiently perform depolymerization of a molded product or waste containing polyester.

  In addition, the metal oxide powder used in the depolymerization method of the present invention is, for example, about 1/8 to 1/40 of the titanium oxide fine powder used in Patent Document 8, and is inexpensive. Is advantageous. In addition, since the metal oxide powder used in the depolymerization of the present invention does not need to have a very small particle size, it is easier to handle than the titanium oxide fine powder of Patent Document 8, and is separated and removed after the depolymerization reaction ( Separation and purification of raw material monomers is also easy.

  In the depolymerization method of the present invention, for example, an ester compound of a saturated dibasic acid having an alcohol residue used as a reaction solvent is obtained. Such a compound can be further used as a raw material for producing a polyester after being transesterified with methanol or the like and converted to dimethyl terephthalate or the like.

  Furthermore, since the depolymerization method of the present invention normally uses heating, the irradiation time is short even when the polyester or the like is heated, so that the alkylene glycol produced by the depolymerization is less likely to deteriorate and the alkylene glycol has a high purity. Can be recovered.

  The embodiment of the molded product or waste containing the polyester that is the subject of the depolymerization method of the present invention is not particularly limited, as long as it is produced and recovered by known general means. Hereinafter, the matter regarding the molded article or waste containing polyester is demonstrated one by one.

(polyester)
The “polyester” that is the object of the depolymerization method of the present invention is a polyester obtained by polymerizing a saturated dibasic acid and an alkylene glycol (for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, etc.). Saturated dibasic acid and alkylene glycol can be recovered by depolymerizing these polyesters.

(Alkylene glycol)
Examples of the alkylene glycol constituting the polyester, that is, recoverable according to the present invention include, for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4. -Butanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexanediol, 1,4-benzene Examples include diols.

(Saturated dibasic acid)
Examples of the saturated dibasic acid constituting the polyester, that is, recoverable according to the present invention include, for example, terephthalic acid, phthalic acid (ortho), isophthalic acid, dibromoisophthalic acid, sodium sulfoisophthalate, phenylenedioxydicarboxylic acid, Aromatics such as 4,4'-diphenyldicarboxylic acid, 4,4'-diphenylether dicarboxylic acid, 4,4'-diphenylketone dicarboxylic acid, 4,4'-diphenoxyethanedicarboxylic acid, trimellitic acid, pyromellitic acid Dicarboxylic acid is mentioned. Examples of other dicarboxylic acids include alicyclic dicarboxylic acids such as hexahydroterephthalic acid and hexahydroisophthalic acid, and succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and undecadicarboxylic acid. Acids and aliphatic dicarboxylic acids such as dodecadicarboxylic acid are also mentioned as the saturated dibasic acid.

(Molded products, waste)
In the industrial use of the depolymerization method and the monomer recovery method of the present invention, it is assumed that molded articles containing polyester or wastes are targeted. In particular, the molded product may be a molded product composed only of polyester, or a molded product containing polyester and other components (known and commonly used additives such as colorants). Moreover, the cloth and clothing containing polyester may be sufficient.

  In particular, the waste means not only the waste generated after using the molded product but also the residue, defective product, etc. generated during the manufacturing of the molded product. For example, used PET bottles, cups, strings, packaging containers, or the like, or burrs, spools when molding these, sheets after cutting the cup after vacuum forming, and the like can be mentioned.

<Reaction solvent>
In the depolymerization method of the present invention, depolymerization is performed in the presence of alkylene glycol in which a metal oxide is dispersed. Hereinafter, the alkylene glycol and metal oxide used in the depolymerization reaction will be sequentially described.

(Alkylene glycol)
As the alkylene glycol used as the reaction solvent in the depolymerization method of the present invention, the alkylene glycols mentioned as the above-mentioned polyester monomers can be used, but the same as the alkylene glycol constituting the polyester to be depolymerized. Or different. For example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 3-methyl-1,5-pentanediol, 1,6- Examples include hexanediol, 1,9-nonanediol, neopentyl glycol, polytetramethylene glycol, 1,4-cyclohexanediol, and 1,4-benzenediol. Of these, ethylene glycol or propylene glycol is preferable because it is inexpensive and has a low viscosity. These alkylene glycols may be used alone or in combination of two or more.

(Metal oxide powder)
The metal oxide powder used in the present invention is one or more selected from lead dioxide, lanthanum oxide, manganese dioxide, and trilead tetroxide. Of these, lead dioxide and trilead tetraoxide are preferable because of their high activity. The average particle diameter of the metal oxide powder used in the present invention is usually 100 μm or less, preferably 50 μm to 50 nm, more preferably 10 μm to 100 nm.

  In addition, the said metal oxide powder used by this invention is cheap with the price about 1/8-1/40 with respect to the titanium oxide fine powder used by patent document 8, for example, and is advantageous in terms of cost. It is. Further, the titanium oxide fine powder used in Patent Document 8 generally cannot exhibit a sufficient catalytic activity unless the particle size is 20 nm or less, whereas the metal oxide powder used in the present invention is 100 μm. Sufficient catalytic activity is exhibited even with the following particle sizes. For this reason, the metal oxide powder used in the present invention is easier to handle than the titanium oxide fine powder of Patent Document 8, and separation and removal after the depolymerization reaction (separation and purification of the raw material monomer) are also easy.

<Depolymerization method>
The polyester depolymerization method of the present invention generally comprises a step of preparing a reaction solvent, a step of immersing the polyester in the reaction solvent, a step of proceeding the depolymerization reaction using normal heating, and the like.
The polyester depolymerization method will be described below step by step.

(Optional process: Washing, grinding, etc.)
When the recovered polyester waste is targeted, before being subjected to the depolymerization method of the present invention, these wastes are washed to remove dirt adhering to the waste, such as contents and soil. It is desirable.

  In addition, since the depolymerization reaction in the present invention has a high reaction rate, the recovered polyester waste or the like can be used for the depolymerization reaction with a relatively large section, but the reaction proceeds more efficiently. The pulverization may be performed using a known pulverization method.

  Furthermore, if necessary, the components of different plastics such as caps and labels that are lighter than polyester may be separated and removed using a known method such as specific gravity separation.

  As described above, even if the cap, label, foreign matter, etc. are not completely removed, the depolymerization reaction of the present invention is not affected at all. Therefore, separation, washing, and pulverization are performed carefully as in the current chemical recycling method. There is no need to do it.

(Step 1: Preparation of reaction solvent)
In the depolymerization method of the present invention, first, a metal oxide powder as a reaction catalyst is added to and dispersed in alkylene glycol to prepare a reaction solvent. These metal oxide powders are preferably added little by little while stirring the alkylene glycol. The addition amount of the metal oxide powder to the alkylene glycol is usually 0.1 to 20 parts by weight, preferably 0.5 to 10 parts by weight, particularly preferably 1.0 to 7 parts by weight, based on 100 parts by weight of the polyester. It is a range.

(Process 2: Immersion of polyester)
Next, the polyester is immersed in the reaction solvent prepared in Step 1. In this case, the weight ratio of the reaction solvent to the polyester is about 1 to 50: 1, preferably about 1 to 15: 1, particularly preferably about 1 to 3: 1.

(Process 3: Depolymerization reaction by normal heating)
After the above preparation is completed, the reaction solvent / polyester mixture is heated. The reaction format may be either batch type or continuous type. These mixtures can be made of commonly used glass or metal containers.

  The time for the depolymerization reaction is not particularly limited, and can be appropriately adjusted according to the reaction solvent (alkylene glycol, metal oxide) to be used and the type and amount of the object to be subjected to the depolymerization reaction. Is usually carried out in the range of 5 minutes to 10 hours, preferably 10 minutes to 1 hour, particularly preferably 15 minutes to 45 minutes.

<Monomer recovery method>
In the present invention, when the polyester is depolymerized, bis (hydroxyalkyl) esters of alkylene glycol and saturated dibasic acid can be produced and recovered, and the obtained alkylene glycol and saturated dibasic acid can be recycled as a raw material for polyester. Can be used.

<Recovery of alkylene glycol>
When an alkylene glycol different from the constituent components of the polyester is used as a reaction solvent in the depolymerization method of the present invention, the alkylene glycol produced by the depolymerization and the reaction solvent are once mixed, but separated by a known distillation / concentration method, It can be recovered.

  On the other hand, when the alkylene glycol produced by the depolymerization reaction and the reaction solvent are of the same type, they can be reused as the reaction solvent in the depolymerization step without separation.

<Recovery of bis (hydroxyalkyl) ester of saturated dibasic acid>
The bis (hydroxyalkyl) ester of a saturated dibasic acid obtained by the depolymerization method of the present invention varies depending on the type of reaction solvent. For example, when PET is depolymerized using ethylene glycol as a reaction solvent, BHET is generated as a monomer, and when PET is depolymerized using propylene glycol as a reaction solvent, bis (hydroxyalkyl) terephthalate is mainly generated as a monomer. It can be recovered.

  The bis (hydroxyalkyl) ester of the saturated dibasic acid thus obtained can be recovered as a dimethyl ester of a saturated dibasic acid by further transesterification with methanol.

<Recovery and removal of metal oxide>
Further, unlike the finely powdered titanium oxide in Patent Document 8, the average particle size is as large as 5 to 10 μm and can be easily removed by filtration. In some cases, the recovered metal oxide can be reused. When discarding, it is necessary to carefully dispose of lead as industrial waste in accordance with regulations.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not restrict | limited to these Examples at all.

  In a 100 ml three-necked flask, 10 g (161 mmol) of ethylene glycol was added, and 0.060 g (0.25 mmol) of lead dioxide powder having an average particle size of 5 to 10 μm was gradually added and dispersed. Next, 0.96 g (5.0 mmol) of PET was added, a reflux condenser and a thermometer were attached, and the mixture was heated to reflux for 20 minutes. After cooling, the product was dissolved using 40 ml of acetone, and unreacted PET and lead dioxide were separated by filtration. Next, acetone was distilled off under reduced pressure. Furthermore, it distilled off under reduced pressure using the Kugelrohr distillation apparatus, and obtained 3.0g of unreacted ethylene glycol. As a residue, 1.24 g (yield 98%) of BHET as a white solid was obtained. Moreover, since no unreacted PET was collected at all, the reaction rate was 99% or more. The results are shown in Table 1. The structure was identified from the results of IR measurement and NMR measurement.

  PET depolymerization and monomer recovery were carried out in the same manner as in Example 1 except that the reaction catalyst was changed from lead dioxide powder to trilead tetraoxide powder having an average particle size of 1 to 3 μm. The results are shown in Table 1.

  PET depolymerization and monomer recovery were carried out in the same manner as in Example 1 except that the reaction catalyst was changed from lead dioxide powder to manganese dioxide powder having an average particle size of 3 to 5 μm. The results are shown in Table 1.

  PET depolymerization and monomer recovery were carried out in the same manner as in Example 1 except that the reaction catalyst was changed from lead dioxide powder to lanthanum oxide powder having an average particle size of 3 to 5 μm. The results are shown in Table 1.

[Comparative Example 1]
In a 100 ml three-necked flask, 10 g (161 mmol) of ethylene glycol was added, and 0.040 g (0.25 mmol) of titanium oxide powder having an average particle diameter of 7 nm was added and dispersed. Next, 0.96 g (5.0 mmol) of PET was added, a reflux condenser and a thermometer were attached, and the mixture was heated to reflux for 20 minutes. After cooling, the product was dissolved using 40 ml of acetone, and unreacted PET and titanium oxide were separated by filtration. Next, acetone was distilled off under reduced pressure. Further, unreacted ethylene glycol was distilled off using a Kugelrohr distillation apparatus. As a residue, BHET was obtained as a white solid (0.089 g, yield 7%). In addition, 0.86 g of unreacted PET was recovered. The results are shown in Table 1.

[Comparative Example 2]
PET depolymerization and monomer recovery were carried out in the same manner as in Example 1 except that the reaction catalyst was changed from titanium oxide powder to iron (III) oxide powder having an average particle diameter of 500 nm to 1 μm. The results are shown in Table 1.

As shown in Table 1 above, using a solvent in which powder of lead dioxide, trilead tetroxide, manganese dioxide, lanthanum oxide is dispersed in ethylene glycol, using a normal heating, a short reaction time of about 20 minutes under heating and refluxing It was found that polyethylene terephthalate can be efficiently depolymerized with (Examples 1 to 4). On the other hand, when titanium oxide and triiron tetroxide powders are used, polyethylene terephthalate cannot be sufficiently decomposed even if the reaction is performed under the same normal heating for 20 minutes under reflux, and the yield of BHET Was low (Comparative Examples 1-2).
result of analysis

Obtained white solid mp: 110.5-111.5 ° C
^{IR (cm -1): 3440 (} v-OH), 3065 (v Ph -), 2964 (v-CH 2 -), 2880 (v-CH 2 -), 1713 (v C = O), 1687 (v C = O), 1272 (v-CO-), 1249 (v-CO-), 1228 (σ-CH-), 1131 (v-CO-), 1110 (v-CO-), 1067 (σ-OH) ), 1016 (δ Ph−), 873 (δ Ph−)
¹ H-NMR (CDCl ₃ , 400 MHz, TMS = 0.00 ppm): δ 3.97-3.99 (4H, HOCH ₂ —), 4.48-4.50 (4H, COOCH ₂ —), 8.10 (4H, Ph-H)
¹³ C-NMR (CDCl ₃ , 400 MHz, TMS = 0.00 ppm): 61.21 (—CH ₂ —), 67.05 (—CH ₂ —), 129.71 (Ph—), 133.87 (Ph) -), 166.07 (C = O)

BHET mp of standard substance: 110.5-111.5 ° C
^{IR (cm -1): 3438 (} v-OH), 3064 (v Ph -), 2964 (v-CH 2 -), 2880 (v-CH 2 -), 1713 (v C = O), 1687 (v C = O), 1273 (v-CO-), 1249 (v-CO-), 1228 (σ-CH-), 1126 (v-CO-), 1110 (v-CO-), 1067 (σ-OH) ), 1016 (δ Ph−), 874 (δ Ph−)
¹ H-NMR (CDCl ₃ , 400 MHz, TMS: 0.00 ppm): δ 3.98-4.01 (4H, HOCH ₂ —), 4.49-4.52 (4H, COOCH ₂ —), 8.13 (4H, Ph-H)
¹³ C-NMR (CDCl ₃ , 400 MHz, TMS = 0.00 ppm): 61.29 (—CH ₂ —), 67.05 (—CH ₂ —), 129.71 (—Ph), 133.85 (— Ph), 166.05 (C = O)

Claims (5)

  A method for depolymerizing a molded article or waste containing polyester in the presence of alkylene glycol in which one or more metal oxide powders selected from lead dioxide, trilead tetroxide, lanthanum oxide and manganese dioxide are dispersed. .   The method for depolymerizing a polyester according to claim 1, wherein the alkylene glycol is ethylene glycol and / or propylene glycol.   The polyester depolymerization method according to claim 1, wherein the molded article or waste containing the polyester is a molded article or waste containing polyethylene terephthalate.   A step of impregnating a molded product or waste containing polyester in alkylene glycol in which one or more metal oxide powders selected from lead dioxide, trilead tetraoxide, lanthanum oxide, and manganese dioxide are dispersed; and A method for recovering a polyester raw material, comprising a step of producing a bis (hydroxyalkyl) ester of alkylene glycol and a saturated dibasic acid using the polyester depolymerization method according to any one of 1 to 3.   The method for recovering a polyester raw material according to claim 4, wherein the alkylene glycol produced by the depolymerization reaction is reused as a dispersion medium for the depolymerization reaction.