JP2003113125A - Method for producing monomer from polyester - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a monomer from a polyester, with which an incinerator is slightly damaged even if a distillation residue is incinerated and the recovery of a monomer is not inhibited even if the distillation residue is returned to a decomposition process again. SOLUTION: In this method for producing a monomer from a polyester, which comprises a decomposition process for reacting the polyester with a reaction solvent and recovering a monomer mixture by distillation and distillation process for separating the monomer mixture into components and with which the polyester is monomerized in a high-temperature and high-pressure reaction solvent, the method for producing the monomer from the polyester comprises a filtration process for filtering the distillation residue of the decomposition process and/or the distillation residue of the distillation process to remove inorganic substances.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to the recycling of polyesters, and more particularly to a method for producing monomers for recovering monomers from polyesters.

[0002]

2. Description of the Related Art In recent years, in the recycling of polyester, attempts have been made to depolymerize the polyester, once convert it into a monomer, and then polymerize it again. This is because the method called material recycling, in which foreign substances are removed from the discarded resin and reused as is, considering that the quality of the recycled product is not very good, the resin is chemically converted, returned to the raw material, and purified. Chemical recycling for re-synthesis has been carried out. In this chemical recycling, the system becomes complicated and the cost of recycling is high when viewed only once, but a recycled product having excellent physical properties can be obtained.

A typical chemical recycling method for polyester products such as polyethylene terephthalate (PET) bottles is DuPont's methanolysis method using high-temperature methanol vapor (European Patent No. 1).
0 484 963 A2, U.S. Pat. No. 3,907,868). In this method, high-temperature methanol vapor is blown from the bottom of molten PET to depolymerize PET, and the monomers ethylene glycol (EG) and dimethyl terephthalate (DMT) are reacted with methanol added as a reaction reagent and reaction solvent. It can be collected from the upper part of the vessel. The feature of this method is that the reaction is completed in one step and no special control is required, so that high efficiency can be obtained under certain conditions.

In addition, a method of depolymerizing PET using EG to once convert it into bis-2-hydroxyethyl terephthalate (BHET), and then esterifying this with methanol to obtain EG and DMT. (US Pat. No. 3,257,333). Further, a methanolysis method using methanol in a supercritical state can be mentioned (US Pat. No. 3,148,208, JP-A-9-249597). This method
Depolymerization is performed by bringing molten PET into contact with methanol in a supercritical state at 239 ° C. and 79 atm or higher.

Recently, as disclosed in Japanese Patent Application Laid-Open No. 2000-218167 filed by the applicants of the present application, PET is used.
And dimethyl terephthalate (DMT) are mixed and dissolved, and methanol in a supercritical state is allowed to act to depolymerize PET to form a monomer compound into DMT and EG. A catalyst for depolymerization of PET. Is proposed. Furthermore, Japanese Patent Application Laid-Open No. 2000-727 applied for by the applicant of the present application
As disclosed in Japanese Patent Publication No. 20, a PET in a homogeneous phase composed of PET, DMT, and methanol is thermally depolymerized under pressure so that methanol can exist in a liquid phase, so that further methanol is added during the progress of the depolymerization. A method of monomerizing PET to be added is known.

[0006]

Thus, when the polyester product is monomerized with methanol, ethylene glycol, water or the like, a distillation residue is produced in the reaction vessel or the distillation column of the recovered monomer mixture. The distillation residue is treated by incineration, or a part of it is returned to the decomposition step and depolymerized again to recover the monomer remaining in the residue. However, this distillation residue contains a large amount of inorganic substances such as metal catalysts added to the production of polyester, and in the incineration process, there is a problem that the inorganic substances damage the incinerator and shorten the life of the incinerator. Further, when a part is returned to the decomposition step again, there is a problem that the inorganic substances accumulate in the distillation column in the subsequent distillation step and cause a reaction that inhibits the recovery of the monomer in the distillation column.

Therefore, the present invention provides a method for producing a monomer from polyester, which is less likely to damage the incinerator even if the distillation residue is incinerated and does not hinder the recovery of the monomer even if the distillation residue is returned to the decomposition step again. .

[0008]

DISCLOSURE OF THE INVENTION The present invention provides a reaction solvent of high temperature and high pressure, which comprises a decomposition step of reacting a polyester with a reaction solvent to distill and recover a monomer mixture, and a distillation step of separating the monomer mixture into components. In the method for producing a monomer from a polyester in which a polyester is made into a monomer, a distillation step of filtering the distillation residue of the decomposition step and / or the distillation residue of the distillation step to remove inorganic substances is included. A method for manufacturing the same is provided.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The polyester resin to which the present invention is applied is not particularly limited. PCT), polyethylene naphthalate (PE
N), polybutylene naphthalate (PBN), polycarbonate (PC), and other waste products. The most typical application example is the recycling of PET bottles. Other,
A PET film typified by a photographic film, a PET tape typified by a magnetic tape, a PET fiber used as a polyester fiber, a PET sheet used for a cup, a tray, a transparent packaging, or the like can be processed.

The decomposition step used in the present invention is not particularly limited, but the polyester resin is reacted with a reaction solvent such as methanol, ethanol, ethylene glycol or water in a supercritical state or a subsupercritical state to give a carboxylic acid. A method for obtaining dimethyl or diethyl carboxylate and a dihydroxy compound (dihydric alcohol) can be preferably used. The weight ratio of the polyester to the reaction solvent varies depending on the reaction temperature, contact efficiency, etc., but is usually 1:
It is in the range of (0.3 to 10), preferably in the range of 1: (3 to 7). From the viewpoint of high reactivity, it is preferable to react in a supercritical state or a subcritical state. For example, polyethylene terephthalate (PET) is added to methanol in a supercritical state or a subcritical state (preferably at a reaction temperature of 220 to 2).
Ethylene glycol (EG) and dimethyl terephthalate (DMT) can be recovered as a monomer mixture in methanol by reacting with methanol at 50 ° C., under pressure where methanol can exist in the liquid phase. These monomer mixtures are distilled and separated into each component. The obtained DMT
Can be hydrolyzed to high-purity terephthalic acid (PTA) in another step.

The reaction temperature and the reaction pressure of the depolymerization reaction differ depending on the type of the target polyalkylene terephthalate, the presence and type of the depolymerization catalyst, the reaction time and the like. If the reaction temperature or reaction pressure is too low, the reaction may be insufficient. If the reaction temperature is too high, heat deterioration of the polyester may occur. Depolymerization of polyalkylene terephthalate generally includes, for example, 250 to 400 ° C. and a pressure of 1 to 30 MPa, but preferable conditions for depolymerizing PET with supercritical methanol are 250 to 300 ° C.
Is 6 to 25 MPa, and preferable conditions for depolymerizing PET with subcritical methanol are 220 to 250 ° C. and the pressure is under saturated vapor pressure.

As disclosed in JP-A-11-100336, a method of using a decomposition product of solvolysis of polyester as a solvent for polyester resin waste when the polyester resin waste is solvolyzed to form a monomer. Can also be adopted. For example, when the polyester raw material is PET, it is preferable to recycle the monomer as a decomposition product as a solvent. That is, PET is DM
From the viewpoint of handling, it is preferable to dissolve it in T or EG and introduce it as a low-viscosity solution.

The distillation step used in the present invention is a step for separating the monomer mixture obtained in the decomposition step into its components. The separation into the components includes the case where the components are simply separated into the high-boiling component and the low-boiling components, and is not limited to the case where the constituent components are strictly separated. Therefore, the distillation process of the present invention broadly means a process of distilling.

The distillation residue to be filtered in the present invention is the distillation residue of the decomposition step and / or the distillation step. Distillation residues include, for example, unreacted polyester, thermal decomposition products of polyester, oligomers, polymerized products of monomers, paper pieces, organic substances such as additives added during molding of polyester, and a polymerization catalyst used in the production of polyester, The depolymerization catalyst used for decomposing polyester and inorganic substances such as sand are included. Among them, unreacted polyester, thermal decomposition product of polyester, oligomer, polymer of monomer, additives and the like added at the time of molding of polyester are liquid at 102 ° C. or higher, and other components are solid, It can be separated by filtration. The polymerization catalyst used in the production of polyester includes lithium, sodium, calcium, magnesium, potassium, manganese, cobalt, antimony,
Examples include aluminum, zinc, germanium, and strontium. As the depolymerization catalyst used for decomposing the polyester, titanium, zinc, manganese, tin, cobalt, lead, cadmium, magnesium, which is added as necessary, as described in JP-A-2000-218167. Calcium, weak acid salt of cerium, alkoxide,
Mention may be made of catalysts comprising metal compounds selected from oxides, chlorides, sulphides, sulphates, phosphates and mixtures thereof.

For filtration for obtaining unreacted polyester, thermal decomposition products of polyester, oligomers, polymerization products of monomers, etc. from the distillation residue of the present invention, a filtration device using a metal nonwoven fabric filter having a filtration accuracy of 5 μm or less, etc. Is used. There is no particular limitation on the type of device for filtration, and
A line filter having a filtration accuracy of μm or less or a polymer filter having the above filtration accuracy may be used.

Since the solid content obtained by the filtration step contains a polymerization catalyst and a depolymerization catalyst, it can be reused as each catalyst if it is subjected to a treatment such as acid washing. The filtrate is
Since it contains unreacted polyester and oligomer, it is used again in the decomposition step and can contribute to the improvement of the recovery rate of the monomer. Further, since the filtrate has the metal catalyst and the like removed, it does not damage the incinerator and can be safely incinerated.

A particularly preferred example of the present invention is that P is used in the decomposition step.
This is a case where ET is reacted with supercritical or subcritical methanol. When using methanol in the supercritical state or subcritical state, it is generally unnecessary to use the depolymerization catalyst, and therefore the distillation residue does not contain the depolymerization catalyst. Therefore, the solid content separated by filtration does not contain the depolymerization catalyst but mainly contains the polymerization catalyst. Therefore, by measuring the total weight of the solid content and calculating the content rate of the polymerization catalyst component by instrumental analysis such as atomic absorption spectrometry or ICP emission spectrometry, it can be used again as a polymerization catalyst without further purification.

FIG. 1 shows one form of the constitution of the monomerization step according to the present invention. Here, PET is taken as an example of polyester, and the case where PET is dissolved with DMT and charged into a reaction container will be described, but the present invention is not limited to such an embodiment.

PET flakes for recycling the raw material are stored in the storage hopper 201. The PET flakes are supplied from the hopper 201 to the melting tank 202.
DMT which is a decomposition product of the above is supplied through a line 220 upstream of the melting tank 202. Although it is not necessary to supply DMT in this way, dissolving PET in DMT has the effect of promoting the reaction by DMT, and the thermal efficiency is also improved by using hot DMT that has just been produced. Furthermore, it has been found that the generated EG can be added to the melter 202, if necessary, and thereby the reaction efficiency is improved (Japanese Patent Application Laid-Open No. 20-29200).
No. 00-72720).

The molten PET mixture is pressurized by the pump 204, heated by the heating device 203, and sent to the decomposition reactor 210. At the same time, a chemical reaction stoichiometrically excess methanol is pumped 227 from the methanol tank 225.
Then, the pressure is increased by the heating device, the heating device 226 heats the heating device 226, and the heating device 226 feeds the decomposition reactor 210. Here, instead of the heated methanol, it is also possible to use methanol vapor that is produced in the process of purifying and separating EG. Then, the decomposition reactor 210
In, PET is depolymerized. The decomposition reactor 2
10 is preferably maintained in a supercritical state or a subcritical state of methanol, and is in a liquid phase (supercritical phase) when methanol is in a supercritical state, or in a gas phase when methanol is in a subcritical state, and melts. The PET mixture is in the liquid phase. When the reaction proceeds in such a two-phase system, the decomposition reactor 2
It is preferable to arrange the filler at 10. The mixture of methanol and monomers (DMT, EG, BHET, PTA, etc.) is taken out of the decomposition reactor 210. In addition, impurities such as metal compounds that have not been dissolved in methanol and residues such as undecomposed polyester can be taken out from the outlet 211 at the bottom of the decomposition reactor 210.

The mixture of methanol and monomer taken out of the reactor is separated into a low boiling point component rich in EG and a high boiling point component rich in DMT in the separation column 230. The low boiling components are separated into high-purity EG and methanol in the EG purification tower 240. EG can be used to make PET resin and methanol can be used to depolymerize. The high boiling point G component is further divided into a high boiling point impurity component, a low boiling point component containing methanol and the like, and a high purity DMT in the DMT purification tower 250. The high-boiling-point impurity component is taken out from the outlet 251 at the bottom of the DMT purification tower. The low boiling point component taken out from the top of the DMT purification tower is supplied to the EG purification tower 240. As described above, a part of the purified DMT is passed through the line 220 and used for melting the PET flakes. Further, the purified DMT is temporarily stored in the storage tank 260, and is DMI derived from IPA which is a copolymer of PET in the separation tank 261 (DMI is an abbreviation of dimethyl isoterephthalate, which is an isomer of DMT.). Is removed, and DMT is hydrolyzed in the hydrolysis separation reactor 265 to obtain high-purity terephthalic acid (PTA). After that, the generated PTA
After being crystallized in the crystallization tank 267, the dryer 2
Dried by 70. PTA is stored in storage hopper 270 and can be used to make PET.

According to the invention, the outlet 21 of the decomposition reactor
1 and / or the distillation residue from the outlet 251 of the DMT purification column can be filtered, and preferably the filtrate can be introduced into the separation column 230 to increase the monomer yield.

[0023]

EXAMPLES The present invention will be described below based on examples.
The present invention is not limited to this. Examples 1 to 3 and Comparative Example 1 DMT50 was added to 100 parts by weight of PET in a decomposition reaction container.
After reacting the reaction raw material solution added with parts by weight with 500 parts by weight of supercritical methanol at 300 ° C. and 150 atm,
Purified to obtain DMT and EG. Through this series of operations, a total of 5 parts by weight of the decomposition residue and the distillation residue were recovered. 1 of this collection
The temperature was maintained at 70 ° C., and filtration was performed using a metal nonwoven fabric filter having a filtration accuracy of 3 μm. The metal removal rate at this time is shown below.

[0024]

[Table 1]

Example 4 The filtrate recovered during the filtration using the filter having the filtration accuracy of 3 μm was charged again in the decomposition reaction container,
Supercritical methanol 500 at 300 ° C and 150 atm
As a result of reacting with 1 part by weight, 95% of DMT could be recovered.

[0026]

As described above, according to the present invention, the incinerator is less likely to be damaged during incineration, and even if the distillation residue is returned to the decomposition step again, the inorganic substances are not accumulated in the distillation step, which is a problem. In the distillation process, the reaction that hinders the monomer recovery is not caused. Particularly preferably, when PET is reacted with methanol in a supercritical or subcritical state to produce a monomer from PET, a depolymerization catalyst is not used. Therefore, the inorganic substance removed by filtration is used as a polyester polymerization catalyst. Can be reused.

[Brief description of drawings]

FIG. 1 shows a schematic diagram of a monomerization process according to the present invention.

[Explanation of symbols]

201 Storage hopper 202 melting tank 203 heating device 204 pump 210 Decomposition reactor 211 outlet 220 DMT supply line 225 Methanol tank 226 heating device 227 pump 230 separation tower 240 EG purification tower 250 DMT purification tower 251 outlet 260 storage tank 261 separation tank 265 Water separation reactor 267 Crystallization tank 270 dryer 271 storage hopper

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C07C 31/20 C07C 31/20 A 67/03 67/03 67/54 67/54 69/80 69/80 A C08J 11/14 C08J 11/14 11/22 ZAB 11/22 ZAB // C08L 67:00 C08L 67:00 (72) Inventor Fumitoshi Yano 1-1-1 Wadazaki-cho, Hyogo-ku, Hyogo Prefecture Mitsubishi Heavy Industry Co., Ltd.Kobe Shipyard (72) Inventor Yuichi Kondo 1-1-1, Wadasaki-cho, Hyogo-ku, Kobe-shi, Hyogo Prefecture 6-22 No. 6 Hiroshima Research Center, Mitsubishi Heavy Industries, Ltd. (72) Inventor Setsuo Omoto 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima City, Hiroshima Prefecture F-Term (Reference) 4 Hiroshima Research Center, Mitsubishi Heavy Industries, Ltd. 4 D066 AB10 BB14 4D076 AA12 AA16 BB05 FA04 FA18 FA31 HA03 4F301 AA25 CA09 CA23 4H006 AA02 AC48 AC91 AD11 AD17 BB14 BC15 BD33 BD52 BD60 BJ50 FE11 FG24

Claims (3)

[Claims] 1. A method for converting a polyester into a monomer into a monomer in a reaction solvent, comprising a decomposition step of reacting the polyester with a reaction solvent to distill and recover the monomer mixture, and a distillation step of separating the monomer mixture into components. A method for producing a monomer from polyester, which comprises a filtration step of removing the inorganic residue by filtering the distillation residue of the decomposition step and / or the distillation residue of the distillation step. 2. The method for producing a monomer from polyester according to claim 1, wherein the filtered material from which the inorganic substances have been removed in the filtering step is introduced into the decomposition step. 3. The method for producing a monomer from polyester according to claim 2, wherein in the decomposition step, the polyester is polyethylene terephthalate and the reaction solvent is supercritical or subcritical methanol.