JPH10287741A - Method for recovering dimethyl terephthalate from polyalkylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a chemical recycling method whereby DMT and an alkylene glycol are efficiently recovered by treating waste PET with methanol. SOLUTION: In recovering dimethyl terephthalate from a polyalkylene terephthalate polymer, dimethyl terephthalate and an alkylene glycol both formed by the depolymn. of the polymer are removed together with unreacted methanol from the reaction system while methanol is continuously introduced into the polymer in the at least partially molten state. In separately recovering dimethyl terephthalate, the alkylene glycol, and unreacted methanol, the reaction is conducted by adding an alkali metal compd. catalyst having a depolymn. activity in such an amt. that the total amt. (by g-mol) of an alkali metal contained in the catalyst is at least the same as that of a depolymn.-inhibiting substance in the reaction system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a fiber, a film,
The present invention relates to a method for recovering dimethyl terephthalate from a polymer such as a resin, and more particularly to a method for recovering dimethyl terephthalate from a polyalkylene terephthalate polymer by a depolymerization reaction using methanol.

[0002]

2. Description of the Related Art Polyalkylene terephthalate (hereinafter, referred to as polyalkylene terephthalate)
It may be abbreviated as PET. ) Is rapidly increasing its use in living related materials such as fibers, films, and resins, and in the food field such as drinking water and carbonated beverage bottles due to its excellent chemical stability in the living environment. I have.

[0003] However, a large amount of used PET or P
Unqualified products generated during the ET manufacturing stage (hereinafter referred to as waste PET)
May be abbreviated. The treatment of ()) has become a major social problem today.

[0004] As a use method of the above-mentioned waste PET, it is already converted into a low quality grade by melt molding.
So-called material recycling is being carried out. 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, in which PET is converted into fuel by a chemical treatment, is also performed. 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.

[0006] In contrast to the above two methods, waste PET
So-called chemical recycling in which PET is converted and recovered into a monomer, and the monomer is used as a raw material to produce and reuse PET by a polymerization reaction again has been studied. In this method, the compound can be basically recycled without any loss and the resource can be reused as originally intended.

Reacting the recovered waste PET with methanol, and simultaneously distilling and recovering the recovered PET as DMT and alkylene glycol is desirable from the viewpoint of protecting the global environment, and the respective resources can be effectively used. Ultimately, this leads to a reduction in collection costs.

However, when the recovered waste PET is treated with methanol by itself, the recovery rate of DMT may be relatively high or low, and the cause is not clear. In addition, there is a problem that it is difficult to assemble a process if such a difference in reactivity is left.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to establish a chemical cycle method for treating waste PET with methanol to recover DMT and alkylene glycol with high efficiency.

[0010] Another object of the present invention is to solve the problem of increasing the recovery rate of DMT.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have intensively studied the cause of the difference in the reactivity of the waste PET, and found the cause of the difference in the waste PET as the cause. Transesterification terminator, polymerization reaction terminator, oil agent, clarified that contains contamination components that are feared to adversely affect the depolymerization reaction such as dyes, further study, As a condition of the depolymerization reaction, when treating a molten PET with excess methanol vapor, an alkali metal catalyst effective for the depolymerization reaction including the PET content is used as a transesterification reaction terminator, a polymerization reaction terminator, By adding a deficiency to PET in advance so that at least one gram atom is present in the reaction system based on a reaction-inhibiting component such as a phosphorus-containing oil, the contours can be reduced. The present inventors have found that the recovery rate of DMT can be increased regardless of the presence or absence of a cation component and the difference between PET produced by the transesterification method and PET produced by the direct polymerization method, and completed the present invention. Was.

That is, the above two objects are to recover dimethyl terephthalate from a polyalkylene terephthalate polymer while continuously introducing methanol into the polymer, at least a part of which is in a molten state, while decomposing the polyalkylene terephthalate. A method for recovering dimethyl terephthalate by removing dimethyl terephthalate and alkylene glycol produced by the polymerization reaction together with unreacted methanol from the reaction system, and separating and recovering the produced dimethyl terephthalate, the alkylene glycol and the unreacted methanol, respectively. In the above, the reaction is performed by adding the alkali metal catalyst exhibiting the depolymerization reaction activity so that the total amount thereof becomes equal to or more than 1 gram atom, based on the depolymerization reaction inhibitor present in the reaction system. Alkylene terephthalate It is achieved by the method of recovering et dimethyl terephthalate.

In the present invention, when recovering dimethyl terephthalate from the polyalkylene terephthalate polymer, at least a part thereof is subjected to a depolymerization reaction of the polyalkylene terephthalate while continuously introducing methanol into the polymer in a molten state. It is necessary to remove the generated dimethyl terephthalate and alkylene glycol from the reaction system together with unreacted methanol. By employing such a method, the effect of improving the rate of the depolymerization reaction can be obtained. Alcohol introduced into the reaction system in the present invention is D
From the viewpoint of MT recovery, methanol must be used.

Further, after the above-mentioned removal, the produced dimethyl terephthalate, the alkylene glycol and the unreacted methanol are separately recovered, whereby each monomer and unreacted methanol can be reused. However, at that time, as a method for the separation and recovery, in the case of dimethyl terephthalate, methods such as distillation and centrifugation can be mentioned, and in the case of unreacted methanol and ethylene glycol, distillation can be mentioned. it can.

The amount of the alkali metal catalyst to be added in the present invention is set to be equal to or more than 1 gram atom based on the contamination component which causes a decrease in the depolymerization reaction so as to satisfy the condition of the following formula (1). It is necessary to add.
By adding such an amount, waste PET can be reduced to D
When recovering MT, the concentration of the alkali metal catalyst is increased and the recovery rate can be improved.

[0016]

## EQU1 ## Metal catalyst (gram atom) -reaction inhibiting component (gram atom) ≧ 0 (I)

In the present invention, waste PET refers to waste such as resin and film fiber containing polyester as a main component, and the waste PET includes phosphorus-based compounds and the like added during the production stage. Transesterification terminator,
In many cases, the film contains a polymerization reaction terminator, a lubricant such as silica or alumina in the case of a film, and an oil agent such as a phosphorus-based material in the case of a fiber.

Further, the constitution of the trace components such as a transesterification catalyst and a polymerization catalyst differs depending on whether PET is produced from terephthalic acid or dimethyl terephthalate. These various components suppress the reaction as a contamination component with respect to the depolymerization reaction. For example, an oil agent containing a phosphorus compound as a main component is a remarkable example.

On the other hand, if the amount of the alcohol is too small, the progress of the depolymerization reaction becomes insufficient, and the entrainment of the produced DMT and alkylene glycol with the alcohol becomes insufficient. On the other hand, if the amount is too large, problems such as an increase in energy for alcohol preheating and blowing of alcohol vapor in the reactor occur. Considering these points, the amount of alcohol used is preferably 1 to 10 times based on the processing weight of waste PET, and 2 to 5 times.
It is particularly preferable that the ratio is about twice.

If the reaction temperature for performing the depolymerization reaction is too low, the reaction becomes insufficient.
And the accompanying evaporation of the alkylene glycol with the alcohol becomes insufficient, and if it is too high, thermal degradation of the unreacted PET is liable to be caused. Therefore, the temperature of the depolymerization reaction is in the range of 200 to 300 ° C. Is preferred.

Further, if the reaction pressure of the depolymerization reaction is too low, the reaction becomes insufficient, and if it is too high, entrainment of the product with alcohol is inhibited. 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 the catalyst contained in the alkali metal compound catalyst exhibiting depolymerization reaction activity, a compound containing at least one alkali metal selected from the group consisting of lithium, sodium and potassium can be preferably used. The metal compounds may be used alone or in combination.

[0023]

EXAMPLES The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited by these examples.

Each value in the examples was measured by the following method.

(1) Quantitative analysis of phosphorus: 0.2 ml of a sample was added with 3 ml of sulfuric acid, heated on a hot plate to dissolve and carbonize the sample, cooled, and then cooled with 5 ml of nitric acid and 5 ml of perchloric acid.
The mixture is heated again, and after the sample is completely decomposed, it is cooled.

5 ml of the sample solution obtained by the above operation is taken, diluted with pure water to 40 ml, and a 1.5% ammonium molybdate solution is used as a standard sample in an ultraviolet-visible spectrophotometer (an ultraviolet-visible spectrophotometer manufactured by Shimadzu Corporation). Total UV-16
The quantitative analysis of phosphorus was performed according to A).

(2) DMT recovery rate (%) Based on the theoretical amount of DMT constituting PET before depolymerization, DMT contained in the reaction system after actual depolymerization was Quantified by chromatography,
The recovery rate was determined.

[Reference Example] In an autoclave with a stirrer having an inner volume of 500 ml, 100 g of transesterification PET was used.
Was melted at 280 ° C., and methanol vapor superheated to 260 ° C. was blown at a rate of 320 g per hour from a blowing nozzle dipped in the melt at 280 ° C. and 5.0 kg / cm ² G under the conditions of 5.0 kg / cm ² G. The reaction was performed for 2 hours. The transesterification PE method used
T contains 54 ppm of phosphorus, which is 0.1 ppm.
Equivalent to 7 milligram atoms. After the completion of the reaction,
7 g, a fraction containing methanol was cooled to 40 ° C., and filtered to obtain 623 g of a filtrate and 54.1 g of a dried cake. The DMT recovery with respect to the charged PET was 60.0%, and is shown in Table 1 together with the results in which the number of phosphorus milligram atoms was described.

Example 1 The same operation was performed as in the reference example except that 0.5 g of lithium carbonate (Li ₂ CO ₃ ) was added as a depolymerization catalyst. At this time, the lithium concentration in PET was 941 ppm and 13.55 milligram atoms. Table 2 shows the results. The DMT recovery rate for the charged PET was 81.6%. Table 1 shows the results.

Example 2 In Example 1, 0.5 g of sodium carbonate (Na ₂ CO ₃ ) was used instead of lithium carbonate.
The same operation was performed except that was used. Table 1 shows the results.

Example 3 The same operation was performed as in Example 1, except that 0.5 g of potassium carbonate (K ₂ CO ₃ ) was used instead of lithium carbonate. Table 1 shows the results.

[0032]

[Table 1]

[Comparative Example 1] The same operation as in Reference Example was carried out except that 1 g of T-500 (manufactured by Matsumoto Yushi Co., Ltd.) as a phosphorus-based oil agent was added, and the results in Table 2 were obtained. .

[Comparative Example 2] The same operation as in Reference Example was carried out except that 1 g of SF-333 (manufactured by Matsumoto Yushi Co., Ltd.) as a phosphorus-based oil agent was added, and the results in Table 2 were obtained. .

Example 4 The same operation as in Comparative Example 1 was carried out except that 1.0 g of lithium carbonate (Li ₂ CO ₃ ) was added, and the results shown in Table 2 were obtained.

Example 5 The same operation as in Comparative Example 2 was carried out except that 1.0 g of lithium carbonate (Li ₂ CO ₃ ) was added, and the results shown in Table 2 were obtained.

[0037]

[Table 2]

[0038]

According to the method of the present invention, in the chemical recycling of discarded polyalkylene terephthalate (PET), a transesterification reaction terminator that impairs the depolymerization activity when depolymerizing PET with methanol. Regardless of the presence of a polymerization reaction terminator, an oil agent, a dye, and the like (hereinafter, referred to as a contamination component), the depolymerization reaction can proceed smoothly, and DMT and the like can be efficiently recovered from waste PET.

Claims (8)

[Claims] When recovering dimethyl terephthalate from a polyalkylene terephthalate polymer, terephthalic acid generated by a depolymerization reaction of the polyalkylene terephthalate while continuously introducing methanol into the polymer in at least a part of a molten state. In the method for recovering dimethyl terephthalate, wherein dimethyl and alkylene glycol are removed from the reaction system together with unreacted methanol, and the generated dimethyl terephthalate, the alkylene glycol and the unreacted methanol are separated and recovered, respectively. Based on the depolymerization reaction inhibitor
A method for recovering dimethyl terephthalate from polyalkylene terephthalate, wherein the reaction is performed by adding the alkali metal contained in the alkali metal compound catalyst exhibiting depolymerization reaction activity so that the total amount becomes equal to or more than 1 gram atom. . 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 inhibiting substance is a transesterification reaction terminator, a polymerization reaction terminator and / or an oil agent. 5. The method for recovering dimethyl terephthalate according to claim 1, wherein the amount of methanol used in the depolymerization reaction is in the range of 1 to 10 times based on the weight of the polyalkylene terephthalate polymer. 6. The method for recovering dimethyl terephthalate according to claim 1, wherein the depolymerization reaction temperature is in the range of 200 to 300 ° C. 7. A depolymerization reaction pressure of 1 to 10 kg / cm ²
The method for recovering dimethyl terephthalate according to claim 1, wherein G is within the range of G. 8. An alkali metal catalyst comprising at least one selected from the group consisting of lithium, sodium and potassium.
The method for recovering dimethyl terephthalate according to claim 1, wherein a compound containing a kind of alkali metal is used.