JPH09208524A - Recovery of dimethyl terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable the smooth progress of a depolymerizing reaction and efficiently recover dimethyl terephthalate from a discarded polyalkylene terephthalate by adding a specific amount of a depolymerizing reactional metal lic catalyst into a reactional system and carrying out the reaction. SOLUTION: A depolymerizing reactional metallic catalyst (preferably manganese, calcium, magnesium, etc.) is added into a reactional system for depolymerizing (A) a polyalkylene terephthalate while continuously introducing (C) methanol into the component (A) at least partially kept in a molten state when recovering (B) dimethyl terephthalate from the component (A), removing the produced component (B) and (D) an alkylene glycol, together with the unreacted component (C), from a reactor and respectively separating and recovering the components (B) and (D) and the unreacted component (C) so that the total amount of a metal assuming depolymerizing reactional activities may be equal gram-atoms or more based on substances for inhibiting the depolymerizing reaction present in the reactional system. Furthermore, the component (A) is preferably produced from the component (B), especially from terephthalic acid.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to fibers, films,
The present invention relates to a method for recovering dimethyl terephthalate from a polymer of polyalkylene terephthalate such as resin by a depolymerization reaction using methanol.

[0002]

BACKGROUND OF THE INVENTION In the present invention, dimethyl terephthalate (hereinafter, abbreviated as DMT) is obtained by chemical recycling of polyalkylene terephthalate (hereinafter sometimes abbreviated as PET), which has recently been required to be used in gardens. ) Regarding the collection method. Since PET has excellent chemical stability in the living environment, its use in the fields of food-related materials such as textiles, films, resins and other living-related materials, drinking water, bottles for carbonated drinks, etc. is rapidly increasing. There is. By the way, the processing of used PET or quality-ineligible products (hereinafter sometimes abbreviated as waste PET) generated at the PET manufacturing stage has become a big social problem today.

As a method of utilizing the waste PET as described above, so-called material recycling has already been carried out, in which it is converted into a low quality grade by melt molding. Although this recycling has greatly improved the conventional "disposable" situation at the present stage from the viewpoint of resource reuse, it is difficult to finally avoid the disposal of PET.

On the other hand, so-called thermal recycling has been reported in which PET is converted into a fuel by a chemical treatment. Although this method has the advantage of using PET as a fuel, it is indirect, but inevitably the burning of PET, so that it saves PET raw materials and generates carbon dioxide, thereby saving resources and protecting the global environment. From the aspect of the problem, it has an undesired problem.

In contrast to these methods, in the case of chemical recycling, waste PET is converted and recovered into a monomer, and this monomer is used as a raw material to produce PET by a polymerization reaction again.
It is intended to be reused. With this method, basically, there is no loss, and it is possible to recycle the compound, and it is possible to reuse the resource as originally intended.

However, when these recovered PET wastes were treated with methanol by themselves, there were cases where the recovery rate of DMT was relatively high and cases where the recovery rate was low, and the cause was not clear. Moreover, if such a difference in reactivity is left, it is difficult to assemble the process.

Therefore, the inventors of the present invention have made diligent investigations into the cause of the difference in reactivity of the waste PET. One of the causes is that the waste PET has an ester exchange reaction terminator,
The presence of contamination components such as polymerization reaction terminators, oil agents, dyes, etc., which are feared to adversely affect the depolymerization reaction, and PE is another cause.
Whether T was originally produced by a so-called transesterification reaction (hereinafter sometimes abbreviated as EI method) using DMT as a raw material, or a direct polymerization reaction using terephthalic acid as a raw material (hereinafter abbreviated as direct weight method) It has been clarified that the kind of the component effective in the depolymerization reaction contained in PET and the content thereof are different depending on the production conditions.

[0008]

SUMMARY OF THE INVENTION The present invention aims to increase the recovery rate of DMT for the purpose of realizing a highly efficient chemical cycle in which waste PET is treated with methanol to recover DMT and alkylene glycol, respectively. Is the solution.

[0009]

In order to solve such a problem, the inventors of the present invention, as a condition of the depolymerization reaction, treat PET in a molten state with an excess amount of methanol vapor, so that the content of PET is reduced. It is required that the metal catalyst effective for the depolymerization reaction including the above satisfies the following formula (1) during the depolymerization reaction. By adding inadequate amount to PET in advance so that the metal catalyst is present in the reaction system in an amount of equal to or more than 1 gram atom with respect to a reaction inhibiting component such as a transesterification termination agent, a polymerization termination agent, or a phosphorus-containing oil agent. , Contamination components and EI method PET, direct weight method PET
It was found that the recovery rate of DMT can be increased irrespective of the difference between the above, and the present invention was reached.

Metal catalyst (gram atom) -reaction inhibiting component (gram atom) ≧ 0 (1) That is, according to the method of the present invention, when recovering DMT from waste PET, in order to improve the recovery rate, In the formula (1), it is effective to add the catalyst so that the metal catalyst concentration is as high as possible.

Against this background, these recovered waste P
Reacting ET with methanol and simultaneously distilling and recovering it as DMT and alkylene glycol is desirable from the viewpoint of protecting the global environment, and each resource can be effectively used, and the recovery cost is ultimately increased. Lead to a decline.

According to the present invention, in so-called chemical recycling of waste PET, at the time of depolymerization reaction of waste PET using methanol, the ester exchange reaction terminator, polymerization reaction terminator, oil agent, dye, etc. contained in the waste PET are decomposed. For contamination components that are feared to adversely affect the polymerization reaction, the recovery rate of DMT and alkylene glycol is maintained by maintaining the odor of the catalyst having depolymerization activity equal to or more than the equivalent gram atom of those contamination components. It is intended to raise

To explain the present invention, waste PET usually means wastes such as resins and film fibers whose main component is polyester. These waste PET are added in the production stage thereof, such as a transesterification termination agent such as a phosphorus compound, a polymerization termination agent, and in the case of a film, a lubricant such as silica or alumina, or a fiber. In many cases, an oil agent such as phosphorus is included.

Further, the composition of the minor component differs depending on whether PET is produced from terephthalic acid or DMT. Some of these various contained components suppress the reaction as a contamination component with respect to the depolymerization reaction. Among oil agents, for example, phosphorus compounds are a prominent example.

The depolymerization catalyst to be added in the present invention is added in an amount of equal to or more than an equivalent gram atom with respect to the contamination component which causes a decrease in the depolymerization reaction, in order to satisfy the condition of the above formula (1). It is necessary.

As the alcohol to be added in the present invention, methanol is most preferable from the viewpoint of handling, economy, and recovery of DMT from waste PET.

If the amount of alcohol used is too small, the progress of the depolymerization reaction will be insufficient, and the vaporization of the produced DMT and alkylene glycol with alcohol will be insufficient. If the amount is too large, problems such as an increase in alcohol preheating energy and blow-through of alcohol vapor in the reactor occur. Taking these points into consideration, the amount of alcohol used is about 1 to 10 times, preferably about 2 to 5 times the amount of waste PET treated.

If the reaction temperature of the depolymerization reaction is too low, the reaction will be insufficient, the DMT produced will be insufficient, and the evaporation of the alkylene glycol and alcohol will be insufficient, and if it is too high, thermal degradation of the unreacted PET will occur. From this point, a suitable reaction temperature is 200 to 300 ° C.

If the reaction pressure of the depolymerization reaction is too low, the reaction will be insufficient, and if it is too high, the entrained distillation of the product with alcohol will be hindered. From this point, the reaction pressure is selected from 1 to 10 kg / cm ² G, preferably from ^{2 to} 8 kg / cm ² G.

As a catalyst for the depolymerization reaction, a compound used as a transesterification reaction catalyst or a polymerization reaction catalyst in the production of polyalkylene terephthalate is generally effective, but a compound containing manganese, calcium and magnesium is particularly effective. .

[0021]

The contents of the present invention will be described in detail with reference to the following examples.

[Experiment 1] A transesterification (EI) method PET10 was placed in an autoclave equipped with a stirrer and having an internal volume of 500 ml.
0 g was charged, melted at 280 ° C., and methanol vapor superheated to 260 ° C. was blown into the melt at a rate of 320 g per hour while blowing at a rate of 320 g per hour under the conditions of 280 ° C. and 5.0 kg / cm ² G ,
The reaction was performed for 2 hours. The EI method PET used contained 85 ppm of manganese and 54 ppm of phosphorus, which corresponded to 0.16 mg atom and 0.17 mg atom, respectively. After the reaction was completed, 32.7 g of the residue in the kettle and the fraction containing methanol were cooled to 40 ° C. and filtered to obtain a filtrate 62.
3 g, and 54.1 g of a precipitated cake after drying were obtained. When each sample was analyzed by a gas chromatography method, the DMT content obtained was the result shown in Table 1. The DMT recovery rate with respect to the charged PET was 60.0%.

[0023]

[Table 1]

[Experiment 2] The same operation as in Experiment 1 was carried out except that 0.1 g of manganese acetate (Mn (CH ₃ COO) ₂ .4H ₂ O) was added as a depolymerization catalyst. PE at this time
The manganese concentration in T was 310 ppm, 0.56 mg atom. Table 2 shows the results. The DMT recovery rate with respect to the charged PET was 82.5%.

[0025]

[Table 2]

[Experiments 3 to 4] T which is a typical phosphorus-based oil agent
-5800 (Matsumoto Yushi Co., Ltd.) and SF-333 (Matsumoto Yushi Co., Ltd.) were added in the same manner as in Experiment 2 except that 1 g each was added, and the results shown in Table 3 were obtained.

[0027]

[Table 3]

[Experiments 5 to 8] The same operations as in Experiments 3 to 4 were performed except that the addition amount of manganese acetate was as shown in Table 4. The results are shown in Table 4.

[0029]

[Table 4]

[Experiments 9 to 10] The same operations as in Experiments 5 to 8 were performed, except that manganese acetate was changed to 0.5 g of calcium acetate (Ca (CH ₃ COO) ₂ .H ₂ O). Table 5 shows the results.

[0031]

[Table 5]

[0032] [Experiment 11-12] manganese acetate and magnesium acetate _{(Mg (CH 3 COO) 2} · 4H2O) 0.
The same operations as in Experiments 5 to 8 were performed except that the amount was changed to 5 g.
Table 6 shows the results.

[0033]

[Table 6]

[Experiment 13] EI as a raw material for the depolymerization reaction
The same operation as in Experiment 1 was performed except that direct weight PET was used in place of method PET. The results were as shown in Table 7. In addition, 2 pp of manganese was used in the direct weight PET used.
m, phosphorus 32ppm, which is 0.00 each
It corresponded to 4 mg atom and 0.10 mg atom.

[0035]

[Table 7]

[Experiments 14 to 17] The same operation as in Experiment 9 was performed except that 1 g of each oil agent was added and the amount of manganese acetate added was as shown in Table 6. Table 8 shows the results.

[0037]

[Table 8]

[0038]

EFFECTS OF THE INVENTION In chemical recycling of discarded polyalkylene terephthalate (PET), when depolymerizing PET using methanol, a transesterification reaction terminator, a polymerization reaction terminator, an oil agent, which impairs the depolymerization activity, Regardless of the presence of a dye or the like (hereinafter referred to as a contamination component), the depolymerization reaction can be smoothly proceeded by adjusting the concentration of the metal catalyst exhibiting the depolymerization activity to be equal to or more than the gram atom of the contamination component. , Waste P
It has become possible to efficiently collect DMT and the like from ET.

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Claims (8)

[Claims] 1. A method for recovering dimethyl terephthalate from polyalkylene terephthalate, which comprises depolymerizing polyalkylene terephthalate while continuously introducing methanol into polyalkylene terephthalate, at least a part of which is in a molten state. In the method for recovering dimethyl terephthalate, which comprises removing dimethyl terephthalate and alkylene glycol together with unreacted methanol from the reactor, and separately collecting the produced dimethyl terephthalate, the alkylene glycol and the unreacted methanol, The depolymerization reaction inhibitor is present in the reaction system, the reaction is carried out by adding a depolymerization reaction metal catalyst so that the total amount of the metal exhibiting the depolymerization reaction activity is equal to or more than an equivalent gram atom. From polyalkylene terephthalate Method for recovery of dimethyl terephthalate. 2. The method for recovering dimethyl terephthalate according to claim 1, wherein the polyalkylene terephthalate is produced from dimethyl terephthalate. 3. The method for recovering dimethyl terephthalate according to claim 1, wherein the polyalkylene terephthalate is produced from terephthalic acid. 4. The method for recovering dimethyl terephthalate according to claim 1, wherein the depolymerization reaction inhibitor is an ester exchange reaction terminator, a polymerization reaction terminator and / or an oil agent. 5. The amount of methanol used for the depolymerization reaction is 1 to polyalkylene terephthalate polymer.
The method for recovering dimethyl terephthalate according to claim 1, wherein the amount is 10 times by weight. 6. A depolymerization reaction temperature of 200 ° C. to 30
The method for recovering dimethyl terephthalate according to claim 1, wherein the range of 0 ° C is selected. 7. The method for recovering dimethyl terephthalate according to claim 1, wherein the depolymerization reaction pressure is 1 kg / cm ² G to 10 kg / cm ² G. 8. The method for recovering dimethyl terephthalate according to claim 1, wherein the depolymerization reaction catalyst is at least one metal selected from the group consisting of manganese, calcium and magnesium.