JPH11100336A - Decomposition of polyester and device for converting polyester into monomers - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decompose a polyester under conditions comprising a satisfiable reaction time, a satisfiable temperature and the like by recirculating the solvolysis products of the polyester as solvents for the polyester. SOLUTION: This method for decomposing a polyester in a high recovery by the solvolysis of the polyester comprises recirculating the solvolysis products of the polyester as solvents for the polyester. In the solvolysis, a lower alkyl alcohol such as methanol is preferably used as a solvent, and a dicarboxylic acid dialkyl ester and a dihydroxy compound such as dimethyl dicarboxylate and a dihydroxy compound are preferably successively recovered as decomposition products under vacuum and subsequently recirculated. The decomposition products are preferably recirculated in a total amount of 30-500 pts.wt. per 100 pts.wt. of the polyester.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for decomposing a polyester to promote the reaction of decomposing the polyester into a raw material and a raw material derivative when the monomer is converted into a raw material and a raw material derivative.

[0002]

2. Description of the Related Art When polyester is reused as the same kind of polyester material, there are material recycling and chemical recycling. In material recycling, polyester is softened by heat or the like, and then remolded. This recycling method has a low recycling cost when viewed only once because the process is simple. However, the physical properties such as moldability are inferior to the original material each time remolding is performed, so that the number of times of recycling is limited, or conversion to a use that can be performed with lower physical properties is inevitable. On the other hand, in chemical recycling, polyester is chemically converted, returned to a raw material state, purified, and then resynthesized. As a result, the system becomes complicated, and the recycling cost increases when viewed only once. However, since the number of times of recycling is dramatically increased and the use of the recycling destination is not limited, the added value is high.

[0003]

There are many methods for monomerizing polyester, but the reaction rate is not sufficient because of the surface reaction. Typical methods include solvolysis with methanol and hydrolysis with water.
Since the polyester does not dissolve in methanol or water, the reaction is carried out while being separated into two phases. Therefore, none of the conditions such as reaction time and temperature were satisfactory.

[0004] For example, a report by Sako et al. Of the Institute of Materials Science of the Institute of Technology shows that in the decomposition of PET in methanol, 300
A treatment at 80 ° m for 30 minutes at ℃ is required. However, in a test in which the same weight of PET was finely pulverized and the reaction vessel was divided so as not to be reassembled during melting, a 1
The present inventors have confirmed that 100% decomposition is possible in 0 to 20 minutes, and that the PET depends on the specific surface area. Therefore,
There is a need for a simple method for realizing an increase in the effective specific surface area of the reaction in an actual plant.

[0005]

In the present invention, the decomposition product of solvolysis is introduced into the reaction system together with the polyester in the decomposition of the polyester. That is, for example, in the polyester decomposition, dimethyl carboxylate and a dihydroxy compound corresponding to the decomposition product of solvolysis with methanol are introduced into the reaction system together with the polyester. Thereby, the decomposition rate can be increased. This is thought to be because the dimethyl carboxylate corresponding to the decomposition product dissolves the polyester above the melting point, thereby increasing the effective reaction area or assisting dissolution or mixing with methanol.

That is, the present invention relates to a method for decomposing a polyester by solvolyzing the polyester to form a monomer, wherein the decomposition product obtained by the solvolysis is recycled as a solvent for the polyester. is there. For example, in a preferred embodiment of the present invention, a dimethyl carboxylate and a dihydroxy compound obtained by solvolysis of a polyester with methanol are charged and mixed with a polyester melt in advance, and the polyester is solvolyzed. . The solvent used in the solvolysis is generally a polar solvent. Alcohols are preferred, lower alkyl alcohols (generally alkyl alcohols having 1 to 5 carbon atoms) are more preferred, and methanol is most preferred.

In the present invention, the decomposition product is recycled as a solvent for the polyester as described above. When a lower alkyl alcohol is used as the polar solvent, the recycled decomposition products are dialkyl carboxylate and dihydroxy compounds. When methanol is used as the polar solvent, the recycled decomposition products are dimethyl carboxylate and dihydroxy compounds. The polyester to be monomerized or decomposed in the present invention includes, for example, polyethylene butylene terephthalate (PEBT), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polycyclohexane dimethyl terephthalate (PCT), and polyethylene naphthalate (PE).
N), polybutylene naphthalate (PBN), and polycarbonate (PC). In the examples described below, the effectiveness of the present invention was established in all the tested polyesters,
The method of the present invention appears to be universal for polyesters.

In the present invention, it is preferable to collect and recycle the decomposition products while sequentially reducing the pressure. further,
According to the present invention, a high-pressure reaction vessel for reacting the solvent and the polyester that has been melted and fed, a pressure reducing means for sequentially decompressing decomposition products generated by decomposition in the high-pressure reaction vessel, and collecting the decomposition products, and An apparatus for polyester monomerization comprising a recovery means and a path for recycling the decomposition product from the recovery means to the high-pressure reactor as a solvent for the polyester is provided. In addition, as an object to be recycled, an oligomer and / or a solvent which is insufficiently decomposed may be included. According to this monomerization apparatus, a high recovery rate can be expected in a short time. Generally, a recovery tank is used as the recovery means.

[0009]

Embodiments of the present invention will be described below. These embodiments specifically explain the concept of the present invention, and the technical scope of the present invention is not limited by these embodiments. Embodiment of the invention (Part 1) FIG. 1 illustrates a process according to an embodiment of the decomposition process of the polyester according to the present invention. In the figure, a polyester 1 is melted in a melter 4 via a hopper 2 and a feeder 3 and supplied to a reactor 5. On the other hand, methanol / catalyst 6 is added to some decomposition products 7, which are heated by heater 8 and sent to reactor 5, where they undergo solvolysis in the reactor, and the decomposition products A part 10 at a branch 9
Is recovered, and the other part is methanol / catalyst 6 as described above.
And is recycled to the reactor 5. Reference numeral 11 denotes a branch path on the methanol injection side. The amount of the decomposition products to be recycled is preferably 30 to 500 parts by weight based on 100 parts by weight of the polyester.

That is, the process is a process of recirculating a part of the decomposition product to the reaction vessel 5 without separating the entire decomposition product. According to this treatment process, the dimethyl carboxylate and the dihydroxy compound corresponding to the decomposition product can be easily introduced into the reactor 5 and the heat loss can be minimized. As described above, in the present embodiment, in order to obtain a desired effect, the polyester is melted and supplied to the reactor, and methanol and a catalyst are heated and supplied to the reactor, and the polyester is solvolyzed with methanol. The decomposition product dimethyl carboxylate and a part of the dihydroxy compound are recycled to the reactor to solvolyze the polyester.

Embodiment 2 of the Invention FIG. 3 shows a process using a monomerization apparatus according to another embodiment of the present invention. In this process, PET 101 is put into a hopper 102 as polyester, and fed into a high-pressure reaction vessel 105 by a high-pressure pump 104 through a melter 103. As a result, PET is decomposed into monomers by methanol fed through another route. The decomposition products are reduced in pressure through the pressure reducing valve 106. 2 atm to 1
By setting the pressure to 0 atm, the oligomer that is insufficiently decomposed is condensed in the crude oligomer tank 108. Further, the gas component is further decompressed to form dimethyl terephthalate (DM
T) condenses in the crude DMT tank 109. Further, by lowering the temperature of the remaining gas to 80 ° C. in the condenser 112, ethylene glycol (EG) is condensed in the crude EG tank 110. Further, the remaining methanol is condensed in the crude methanol tank 111 by lowering the temperature to room temperature in the condenser 112. The above oligomer, DM
T, EG, and methanol are partially circulated through the high-pressure pump 104 and the heater 107 in the same manner as in the first embodiment.

As described above, in the apparatus for monomerizing polyester according to the present embodiment, the decomposition products generated by decomposition in the high-pressure reaction vessel are sequentially reduced in pressure by the pressure reducing means.
A path is provided such that the decomposition products are recovered by a plurality of recovery means, and the decomposition products are recycled from the plurality of recovery means to the high-pressure reaction vessel as a polyester solvent. In addition, as described in this embodiment, not only decomposition products but also poorly decomposed oligomers and / or solvents such as methanol can be circulated. According to this device, a high recovery rate can be expected in a short time.

[0013]

Embodiment 1 Embodiment 1 is an embodiment corresponding to the above-described embodiment (part 1) described with reference to FIG. In this example, the reaction was performed using the autoclave shown in FIG. 2 as the reactor 5 in FIG. A reaction mixture 13 of a polyester, a catalyst, methanol, dimethyl carboxylate, and a dihydroxy compound was placed in an autoclave 14, sealed, and the inside was replaced with nitrogen. Then it was heated in a tin bath 15. A comparison was made between the case where the corresponding dimethyl carboxylate and the corresponding dihydroxy compound, which were twice the molar ratio when the polyester was completely solvolyzed, were put together with the polyester in the autoclave, and where they were not put. In each case described above, experiments were performed at two different reaction temperatures. When the reaction temperature was in the subcritical region of methanol, zinc acetate was added to the catalyst. When the reaction temperature was in the supercritical region of methanol, the pressure was controlled without adding a catalyst. The above was tested for six types of polyester. Table 1 shows the results. Details of the conditions and results are shown below.

The decomposition rate was calculated as the methanol-insoluble solid remaining after the reaction as an undecomposed product. When 95% or more is decomposed, the product is analyzed by gas chromatography, liquid chromatography, or mass spectrometry, and is decomposed into the corresponding dimethyl carboxylate and dihydroxy compound, and by-products are detected in each analysis. It was confirmed that the peak was less than 10%.

[Table 1]

Note 1) Reactants PET: polyethylene terephthalate, PBT: polybutylene terephthalate, PCT: polycyclohexane dimethylene terephthalate, PEN: polyethylene naphthalate, PBN: polybutylene naphthalate, PC: polycarbonate Note 2) dimethyl dicarboxylate DMT : Dimethyl terephthalate, NDCM: 2, 6
-Dimethyl naphthalene dicarboxylate, DMC: dimethyl carbonate, DPC: diphenyl carbonate Note 3) Dihydroxy compound EG: ethylene glycol, TMG: tetramethylene glycol, CHDM: cyclohexane dimethanol, B
PA: Bisphenol A Note 4) Catalyst Zn (OAc) 2: Zinc acetate

The additives that are effective in decomposing each polyester are specific to the type of polyester. Table 2 shows effective examples.

[Table 2]

Thus, polyethylene terephthalate (PET), polybutylene terephthalate (PBT),
Polycyclohexane dimethylene terephthalate (PC
T), polyethylene naphthalate (PEN), polybutylene naphthalate (PBN), polycarbonate (P
Regarding any of C), even if the reaction temperature is in the subcritical region or the supercritical region, the two types of monomers obtained by solvolysis of methanol are mixed before the start of the reaction, as shown in Table 1. Thus, the decomposition reaction could be promoted.

Example 2 A test was conducted on the apparatus for monomerizing polyester according to the embodiment (No. 2) of the invention described with reference to FIG. PET is put into the hopper 102 and the high-pressure reactor 1
05. At this time, the high-pressure reactor 105
The temperature was controlled at 00 ° C. and 10 MPa. After treatment for a residence time of 10 minutes, the pressure was reduced to 0.3 MPa. Set the temperature in the system to about 2
By maintaining the temperature at 40 ° C., DMT, EG, and methanol remained in a gas state, and the insufficiently decomposed oligomer was liquefied. Although the temperature at this time is lower than the boiling point of DMT, it does not liquefy because it coexists with EG and methanol. The oligomer was further reacted and re-charged as a PET solvent. Further, the pressure was reduced to atmospheric pressure, and DMT was condensed by maintaining the temperature at 200 ° C. Furthermore, EG and methanol were separated by repeating the condensation. DMT and some of the methanol were recycled as solvent and reagents. The recovered DMT, EG, and methanol can be distilled and purified at a later stage. By this process, the reaction vessel 10
In spite of the short residence time of 10 minutes in 5, the DMT recovery rate was 85% and the EG recovery rate was 70%.

The monomerization of PET with methanol at 300 ° C. and 10 MPa generally requires a reaction time of 30 minutes or more. As described above, the oligomer and DMT are sequentially recovered and circulated to form PET. By using this solvent, sufficient reaction efficiency could be obtained in a reaction time of 10 minutes.

[0020]

As is clear from the above description, according to the present invention, in the decomposition of polyester, the decomposition product of solvolysis is introduced into the reaction system together with the polyester, so that the reaction time, temperature and other conditions are reduced. The present invention provides a method for decomposing a polyester, which can sufficiently satisfactorily form a monomer. Further, according to the present invention, there is provided a method for decomposing a polyester and a monomer conversion apparatus which can expect a high recovery rate in a short time by collecting and recirculating the decomposition products while sequentially reducing the pressure. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a process according to an embodiment to which the present invention is applied.

FIG. 2 is a conceptual diagram of the monomerization employed in Example 1.

FIG. 3 is a diagram showing a process according to another embodiment to which the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 polyester 4 melter 5 reactor 6 methanol / catalyst 8 heater 13 reaction mixture 14 autoclave 15 tin bath 111 PET 102 hopper 103 melter 104 high pressure pump 105 high pressure reaction vessel 106 pressure reducing valve 107 heater 108 crude oligomer tank 109 crude DMT Tank 110 Crude EG tank 111 Crude methanol tank 112 Condenser

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kikuo Okazaki 2-19-19 Shinhama, Arai-machi, Takasago-shi, Hyogo Prefecture Takahashi Engineering Co., Ltd.

Claims (6)

[Claims] 1. A method for decomposing a polyester, which comprises solvolyzing the polyester to form a monomer, wherein the decomposition product obtained by the solvolysis is recycled as a solvent for the polyester. 2. The method for decomposing a polyester according to claim 1, wherein the polyester is solvolyzed with an alcohol, and a decomposition product of the solvolysis with the alcohol is recycled as a solvent for the polyester. 3. The polyester is solvolyzed with a lower alkyl alcohol, and the dialkyl carboxylate and the dihydroxy compound, which are decomposition products of the solvolysis with the lower alkyl alcohol, are recycled as a solvent for the polyester. The method for decomposing a polyester according to claim 1. 4. The method according to claim 1, wherein the polyester is solvolyzed with methanol, and dimethyl carboxylate and a dihydroxy compound, which are decomposition products of the solvolysis with methanol, are recycled as a solvent for the polyester. A method for decomposing a polyester as described above. 5. The method for decomposing a polyester according to claim 1, wherein the decomposition products are recovered while sequentially reducing the pressure, and recycled. 6. A high-pressure reactor for reacting a solvent fed with a melted polyester, a decompression product sequentially decompressed in the high-pressure reactor, and a decompression means for collecting the decomposition products and a recovery means. And a route for recirculating the decomposition product from the recovery means to the high-pressure reactor as a solvent for the polyester.