JP2002155011A - Method for recovering terephthalic acid from pulverized product of recovered polyethylene threphthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for recovering terephthalic acid from a pulverized product of a recovered polyethylene terephthalate by which the recovery ratio of the terephthalic acid is high and the treating time is short. SOLUTION: This method for recovering the terephthalic acid from a produced terephthalate comprises a reactional degradation step of reacting and degrading the pulverized product of the recovered polyethylene terephthalate in the presence of an alkali in an equimolar amount or an excess of the polyethylene terephthalate into the terephthalate and ethylene glycol in a solvent. the reactional degradation step includes many stages of two or more stages.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for recovering terephthalic acid as a raw material from waste of polyethylene terephthalate (hereinafter abbreviated as PET) used for containers of soft drinks and the like.

[0002]

2. Description of the Related Art Various methods for decomposing PET and recovering a monomer as a raw material have been proposed. Typical examples thereof include a methanolysis method in which PET is depolymerized with methanol in a gas phase or a liquid phase to form dimethyl terephthalate, and PET is depolymerized with ethylene glycol (hereinafter, abbreviated as EG) to form a reaction intermediate. And a transesterification method in which the produced bishydroxyethyl terephthalate is converted to dimethyl terephthalate with methanol.

However, in the methanolysis method,
Since the reaction temperature is as low as about 177 ° C., the reaction needs to be performed for a long time. In addition, in the glycolysis method described above, it is similarly difficult to decompose to a complete monomer in addition to the fact that the reaction needs to be performed for a long time. Further, a part of the produced bishydroxyethyl terephthalate is dissolved in EG, so that the separation is complicated and the yield is not good. In the transesterification method described above, it is difficult to separate both the produced EG and methanol, and the separation of dimethyl terephthalate and methanol dissolved in methanol.

[0004] In order to solve this kind of problem, PET is hydrolyzed with an aqueous alkali solution, the resulting metal terephthalate is neutralized with an acid, and a hydrolysis method in which terephthalic acid is precipitated, or in EG. A method described in JP-A-9-286744 in which alkali decomposition is performed has been proposed.

[0005]

However, the method of hydrolysis or the method described in the official gazette is not a satisfactory method in terms of the recovery of terephthalic acid. There is a problem that it takes time.

Accordingly, an object of the present invention is to provide a method for recovering terephthalic acid from pulverized recovered polyethylene terephthalate, which has a high recovery rate of terephthalic acid and a short processing time.

[0007]

The present invention which has solved the above-mentioned problems is as follows. <Invention according to claim 1> The method includes the step of reacting and decomposing the recovered pulverized polyethylene terephthalate into a terephthalate and ethylene glycol in a solvent in the presence of an equimolar amount of polyethylene terephthalate or an excess of alkali to form A method for recovering terephthalic acid from a terephthalic acid salt obtained, wherein the reactive decomposition step is performed in two or more stages.

(Effects) The pulverized recovered PET is obtained by pulverizing a soft drink container or the like. However, the time required for the reaction and decomposition of the soft drink container or the like varies depending on the site. For example, 150 g of recovered PET pulverized product is put in 500 g of EG, and after heating to 172 to 173 ° C., 90 g of sodium carbonate is charged and stirred at a stirring speed of 300 rpm for 25 minutes.
The amount (remaining amount) of the crushed product is as shown in Table 1 depending on the location of the part.

[0009]

[Table 1]

Therefore, in order to completely decompose the recovered PET pulverized product composed of various parts, it is necessary to take sufficient time to completely decompose the slowest part of the reaction decomposition. In other words, for a site where the reaction decomposition is fast, the processing is continued for the site where the reaction decomposition is the slowest even after the completion of the reaction decomposition, so that the processing efficiency deteriorates.

However, according to the first aspect of the present invention, since the number of reaction decomposition steps is two or more, a step for adjusting the reaction decomposition time of the recovered pulverized PET product can be provided. Therefore, processing efficiency can be improved.

<Invention according to claim 2> A preheating step of preheating for 5 minutes or more at a temperature of 100 ° C. or higher and a temperature at which the pulverized product does not substantially start reactive decomposition, A method of heating the reaction decomposition at a temperature not lower than the temperature at which the reaction decomposition is initiated and not higher than the boiling point of the solvent.

<Invention according to claim 3> Ethylene glycol is used as a solvent, and preheating is performed for 100 hours.
The method for recovering terephthalic acid from the recovered polyethylene terephthalate pulverized product according to claim 2, wherein the decomposition and heating are performed at 130 to 180 ° C.

(Functions and Effects of Claims 2 and 3) Claim 2
The present invention according to (3) and (3), wherein a preheating step of preheating for 5 minutes or more at a temperature of 100 ° C. or higher and a temperature not higher than a temperature at which the pulverized product does not substantially start the reactive decomposition, A reaction decomposition heating step in which the reaction decomposition heating is performed at a temperature not lower than the starting temperature and not higher than the boiling point of the solvent.
At 0 ° C, decomposition heating is performed at 130 to 180 ° C. However, if preheating is performed before heating by reaction decomposition as described above, the amorphous portion of the recovered PET pulverized product is crystallized and reaction decomposition occurs. It will be in an easy state. Therefore, the reaction decomposition time is generally uniform, and the processing efficiency in the reaction decomposition heating stage is improved.

<Invention according to claim 4> Recovery of terephthalic acid from the recovered polyethylene terephthalate pulverized product according to claim 2 or 3, further comprising a step of removing foreign matters having a specific gravity smaller than that of the solvent before the step of heating. Method.

(Function and Effect) Generally, the recovered PET pulverized product contains foreign substances such as polypropylene (hereinafter abbreviated as PP) and polyethylene (hereinafter abbreviated as PE). These foreign substances are melted by heating, making it difficult to remove them. On the other hand, if they are not removed, these foreign substances solidify with cooling after heating, which may cause damage to equipment in a later step. However, the present invention according to claim 4 has a specific gravity lower than that of a solvent such as EG or water before the step of heating, and has a property of floating in such a solvent.
Since there is a step of removing foreign substances such as P and PE (see Table 2; PET has a higher specific gravity than a solvent and has a property of sinking in such a solvent), there is no fear of the above. In particular, when EG is used as the solvent, the difference in specific gravity becomes large, so that the removal becomes easy.

[0017]

[Table 2]

<Invention according to claim 5> As a reaction decomposition device at the last stage of the reaction decomposition step, a portion corresponding to the tapered portion is provided in a cylinder having a main body portion and a tapered portion located at the tip of the main body portion. Using a horizontal reactive decomposition apparatus equipped with a tapered screw conveyor, supplying the recovered polyethylene terephthalate pulverized product, the solvent and the alkali into the horizontal reactive decomposition apparatus, and heating the decomposition product mainly in the main body while decomposing and heating. 5. The method for recovering terephthalic acid from a ground polyethylene terephthalate product according to any one of claims 1 to 4, wherein the reaction product is decomposed into terephthalate and ethylene glycol, and a reaction decomposition slurry is squeezed out from the tapered portion.

(Function and Effect) Since the reaction decomposition slurry is squeezed out from the tapered portion, the process proceeds to the next step with a small content of the solvent. Therefore, the burden on the next step is reduced. In addition, since the squeezing is performed in the horizontal reaction and decomposition apparatus continuously with the reaction and decomposition, the number of equipment components can be reduced.

<Invention according to claim 6> As the alkali,
While using sodium carbonate, the mass ratio of the recovered polyethylene terephthalate ground product and ethylene glycol at the time of preheating and decomposition heating was 1: 0.8 to 1.
The method for recovering terephthalic acid from the recovered polyethylene terephthalate pulverized product according to claim 3, wherein the ratio is 2, and 1: 2.0 to 2.5.

(Effects) When sodium carbonate is used as an alkali, the recovered pulverized PET product is decomposed by reaction with sodium terephthalate and EG.
Sodium terephthalate has a property of absorbing EG. On the other hand, as described above, since the recovered PET crushed product has various reaction decomposition rates, sodium terephthalate generated from the site where reaction decomposition is fast absorbs EG until the site where reaction decomposition is slow decomposes. And EG usage increases accordingly.

However, in the present invention according to claim 6, the amount of EG absorbed by sodium terephthalate is reduced because preheating is carried out to make the reaction and decomposition time of the recovered PET pulverized product uniform. Therefore, the recovered PET pulverized product and EG during the preheating and the reaction decomposition heating and the EG (the amount of the EG during the reaction decomposition heating is not the addition amount in the reaction decomposition heating stage but the amount of the EG added in the preheating stage. Mass ratio with the amount of EG added in the decomposition heating stage) is 1: 0.8 to 1.2, and 1: 2.0 to
Since it is 2.5, the amount of EG used is reduced as a whole.

[0023]

Embodiments of the present invention will be described below with reference to the drawings. The present invention is characterized in that, in a solvent, a recovered PET pulverized product is decomposed into terephthalate and EG in a solvent in the presence of an equimolar amount of PET or an excess of alkali, and the reaction decomposition step is performed in two or more stages. In the description of the present embodiment, first, a case where the reaction decomposition step is one stage (basic mode) will be described.
When there are two or more stages (Embodiments according to the present invention)
Will be described.

Further, in the present invention, as the solvent,
Water, EG, propylene glycol (PG), silicon oil, and the like can be used. In the basic mode and the embodiment according to the present invention, the case where EG is used will be described.

"First Basic Mode" FIGS. 1 to 4 and 6 show a first basic mode. In this embodiment, the recovered PET pulverized product is used as a raw material. This crushed product is
The meaning includes cutting, breaking, or crushing of PET waste such as a PET bottle. Preferably 2-8m
It is a pulverized product of about m square.

(Reaction Decomposition Step) First, in the present embodiment, the recovered PET pulverized product is subjected to reaction decomposition, and this reaction decomposition is performed using a screw-press type horizontal reaction decomposition apparatus whose detailed example is shown in FIG. be able to. This horizontal reaction and decomposition apparatus is provided with a screw conveyor 2 having a tapered portion corresponding to the tapered portion 1B in a cylindrical body 1 having a main body portion 1A and a tapered portion 1B located at the tip of the main body portion 1A. In this horizontal reaction and decomposition apparatus, a recovered PET pulverized product,
An alkali equivalent or an excess of PET equimolar or excess and EG are charged, and the recovered PET pulverized product is decomposed into terephthalate and EG mainly at normal pressure in the main body 1A, and the reaction-decomposed slurry is formed into a tapered portion 1B. It is squeezed out from.

The base of the main body 1A has a charging port 3 for charging the recovered PET pulverized product and alkali, and the rotary shaft of the screw conveyor 2 has a charging port 4 for charging EG. The cylindrical body 1 is provided with a jacket on the periphery, and the jacket has an inlet 5 and an outlet 6 for the heat medium.
Is provided.

When the recovered PET pulverized product and the alkali are supplied from the charging port 3 and the EG is supplied from the charging port 4, the screw conveyor 2 mainly stirs the recovered PET pulverized product, the alkali and the EG in the main body 1A. It is sent to the tip side, and the recovered PET ground product is continuously decomposed into terephthalate and EG.

Further, the generated reaction decomposition slurry is squeezed out from the tapered portion 1B. Therefore, it is a process of only sending forward uniformly without back mixing.

Further, the tapered portion 1B and the tip of the screw conveyor 2 are tapered to form a squeezing means.
The addition amount of EG can be reduced, and the filtration efficiency per time in the next filtration step (solid-liquid separation step) is increased. By the way, the amount of EG in the generated reaction decomposition slurry is about 70% by mass when the throttle means is not provided, and is about 30% by mass when the throttle means is provided.

As the alkali to be added, sodium carbonate is mainly used, and sodium hydroxide,
Those containing an alkali metal hydroxide such as potassium hydroxide can be used. When sodium hydroxide is contained, the reaction is more efficiently decomposed. When sodium carbonate is used, carbon dioxide gas is generated at the same time as the start of the reaction decomposition, so that the supply of an inert gas (for example, nitrogen gas) becomes unnecessary. Sodium carbonate is economical because its cost is about half that of sodium hydroxide.

The generated carbon dioxide gas is discharged from the gas passage 7 to the outside of the system. A switching valve is installed in the gas passage 7 to discharge carbon dioxide gas and inert gas (for example, nitrogen gas).
It can be switched with the supply.

If the alkali is brought into contact with the recovered PET pulverized product beforehand by a method such as direct spraying before the start of the reaction decomposition, the reaction start time is reduced to 1/5 to 1/8 as compared with the case where EG coexists. Can be shortened. As the reaction decomposition temperature,
For example, the temperature can be set to 130 to 180 ° C.

(Solid-liquid separation / dissolution / impurity removal step) The reaction-decomposition slurry containing terephthalate and EG produced in the reaction decomposition step is subjected to a solid-liquid separation / dissolution / impurity removal machine by a pump or a transport pipe. For example, it is sent to a horizontal belt type vacuum filtration / melting machine 102 shown in detail in FIG. 3 (the horizontal belt type vacuum filtration machine 102 in FIG. 1 is schematically shown). The horizontal belt type vacuum filtration dissolver 102 separates EG from the reaction decomposition slurry in the filtration section.
Although a detailed method of the separation will be described below, the separation may be performed by a separator such as a centrifuge.

The EG in the reaction decomposition slurry is sucked into a filtrate tank 71 by a vacuum pump 61, and the EG collected in the filtrate tank 71 is passed through the transport pipe 12 by a pump 42.
Collect in filtrate tank 81. The crude EG collected in the filtrate tank 81
At an appropriate time, the liquid is passed to the purification tower 110 by the pump 43 through the transport pipe 13 to remove impurities. The removal of the impurities can be performed by a distillation operation or membrane separation.

The EG from which impurities have been removed is transported to the transport pipe 14.
And collected in a filtrate tank 82. The EG collected in the filtrate tank 82 is transferred to the transport pipe 30 by the pump 52 at an appropriate time.
Through to the screw press type horizontal reactive cracker,
Reused as a solvent material for reaction decomposition.

The crude EG from which impurities have not been removed can be reused as a solvent raw material for the reaction decomposition as long as it does not affect the purity of terephthalic acid. A part of the purified EG can be extracted from the system and used as a raw material for PET synthesis.

The terephthalate salt separated and recovered from the EG continuously moves to the dissolving section of the horizontal belt type vacuum filtration dissolving machine 102, and is dissolved by warm water sprayed from above. Examples of the warm water include terephthalate salts 3 to
Five times that of about 80 ° C. can be used, producing an aqueous solution of terephthalate. Instead of this warm water, it is also possible to use washing water in an adsorption tower described later, waste water in a solid-liquid separation / washing step, and condensed water obtained by cooling evaporated water in a concentration / crystallization / glauberin separation step.

The aqueous solution of terephthalate is supplied to a vacuum pump 6
1 sucks into the aqueous solution separation tank 72. The sucked aqueous solution is sent by the pump 51 through the transport pipe 18 to the next soluble impurity removing step.

At the downstream end of the filter cloth 96 provided in the horizontal belt type vacuum filtration dissolving machine 102, a scraper 98 is arranged so as to oppose to remove insoluble impurities.

(Impurity Removal Step) The aqueous solution of terephthalate is transported by the pump 51 through the transport pipe 18 to remove impurities, for example, the activated carbon packed column 10 for rigid cylindrical adsorption.
The solution is preferably passed through 4 at a rate of 5 to 10 mm / m ² · min. This makes it possible to remove soluble impurities mixed in the terephthalate aqueous solution. After the passage, the activated carbon is washed with warm water. The washing wastewater can be returned to the horizontal belt type vacuum filtration dissolver 102 as regenerated washing water through the transport pipe 16 and reused. In order to remove pulverized coal, it is preferable to backwash granular coal or granulated coal with pure water. The removal of impurities in this step can also be performed by using an ion-exchange resin together, adsorbing with the ion-exchange resin, or membrane separation.

(Neutralization / Precipitation Step) The aqueous solution of terephthalate from which impurities have been removed is neutralized with an acid to pH 2 in a neutralization tank 114.
Neutralize to ~ 4. As the acid to be added, mineral acids such as sulfuric acid, hydrochloric acid, phosphoric acid, and nitric acid can be used.
Preference is given to using sulfuric acid.

In the neutralization tank 114, it is necessary to uniformly stir and mix the acid to ensure the neutralization reaction. The terephthalic acid slurry generated by the neutralization reaction is collected in a precipitation tank 105 composed of a rigid cylindrical stirring tank. This deposition tank 105
Is provided with a jacket 91 through which a heat medium 92 passes.

In the neutralization tank 114, when an acid is added, a neutralization reaction occurs instantaneously, and fine crystals of terephthalic acid are generated. The aggregate of these fine crystals contains unreacted acid inside. I will be wrapped up. Then, the acid entrapped in the inside is leached from the inside in the precipitation tank 105, and the neutralization reaction is caused again with a delay. This means that p
H preparation and terephthalic acid generation.

In order to prevent such a situation, FIG.
As shown in FIG.
Simultaneously with the stirring by the ultrasonic generator 114B attached
Thus, it is preferable to cause micro vibrations caused by ultrasonic waves in the terephthalic acid slurry. As a result, inclusion of acid by the terephthalic acid microcrystals can be prevented, and the pH can be adjusted well, so that the generation of terephthalic acid can be improved.

The capacity of the neutralization tank 114 may be smaller than that of the precipitation tank 105, and may be about 1/50 to 1/500.

In the neutralization tank 114, a stirrer 114A
While stirring, the acid (sulfuric acid) is supplied into the stirring shaft, and the shaft 1 of the stirring blade 114C communicating with the inside of the stirring shaft.
The solution is jetted through 14D into a terephthalate aqueous solution (terephthalic acid slurry). Thereby, the effect of stirring and mixing becomes high. As a result, the effect of preventing the inclusion of acid by the terephthalic acid microcrystals is greater than when the acid (sulfuric acid) is simply supplied from the upper part of the neutralization tank 114, and the crystal particle size of terephthalic acid is made uniform.

The terephthalic acid slurry collected in the precipitation tank 105 is stirred in the precipitation tank. As a result, the crystal grain size of terephthalic acid becomes uniform and the crystal size grows.

In the precipitation tank 105, stirring is performed while maintaining a heating state at 50 to 95 ° C., for example, about 85 ° C., and crystals that have grown uniformly are extracted from the bottom by the pump 45. As a result, the particle size distribution of the terephthalic acid crystal particles in the slurry containing terephthalic acid and the alkali salt is made uniform (see FIG. 5; (A) shows normal temperature, and (B) shows heating). Table 3 shows the filtration speed in the solid-liquid separation process.
Grow like.

[0050]

[Table 3]

(Solid-Liquid Separation / Washing Step) The terephthalic acid precipitation slurry generated in the neutralization / precipitation step is sent to a solid-liquid separator, for example, a horizontal belt vacuum filter 106 by the pump 45 through the transport pipe 17. .

The details of the horizontal belt type vacuum filter 106 will be described with reference to FIG. First, the precipitated slurry is sent onto the filter cloth 96 and moves in the horizontal direction (from left to right in this drawing). At this time, the acid and alkali salt contained in the slurry are sucked by the vacuum pump 61 into the vacuum box 97 that moves like the filter cloth 96, and collected in the filtrate tank 71A through the transport pipe 26A.

The filter cloth 96 is washed with warm water, and this washing water is once collected in the filter cloth cleaning device 27A, and thereafter, the cleaning device 27B is passed through the transport pipe 27 by the pump 50.
Collect in one. The washing water collected in the washing device 27B1 is
It is used for washing terephthalic acid obtained by removing acids and alkali salts from the slurry by suction. Further, the washing water used to wash the terephthalic acid is supplied to the vacuum box 97 by the vacuum pump 61.
And collected in the filtrate tank 72A through the transport pipe 28. The washing water collected in the filtrate tank 72A is collected by the pump 51 through the transport pipe 29 into the washing device 27B2.
It is used again as terephthalic acid washing water.

The washing water, which has washed terephthalic acid again, is sucked into the vacuum box 97 by the vacuum pump 61, and is transferred to the transport pipe 26B.
And collected in the filtrate tank 71B. The washing water collected in the filtrate tank 71B can be used for dissolving the upstream terephthalate.

Such a countercurrent washing increases the purity of terephthalic acid as shown in Table 4.

[0056]

[Table 4]

(Concentration, Crystallization, Separation of Glauber's Salt (Recovery of Alkaline Salt)) The alkali salts collected in the filtrate tanks 71A, 71B are once collected in the filtrate tank 83 through the transport pipe 20 by the pumps 42A, 42B. Then, pump 48
, The transport pipe 21 and the heater 32 for water evaporation
To supply it to the crystal can 33.

Since the crystal can 33 is decompressed by the vacuum pump 62, the water in the alkali salt slurry evaporates, and the evaporated water is cooled and condensed by the cooler 34 provided in the decompression tube 31, and solid-liquid separation is performed. -Reuse as water used in the dissolution / impurity removal process or as filter cloth and cake washing water used in the solid-liquid separation / washing process.

The crystal slurry in the crystal can 33 is supplied to the pump 4
According to 6, it is sent to the centrifuge 108 through the transport pipe 19. This centrifugal separator 108 performs solid-liquid separation into an alkali salt, EG and alkali. The separated alkali salt is sent by a belt conveyor 113 to an indirect heating dryer, for example, a paddle type rotary vacuum dryer 109 having a structure capable of circulating a heating medium through a jacket 94 and a shaft 95. In the dryer 109, high-purity alkali salts are recovered by drying under vacuum.

When sulfuric acid is used in the neutralization step,
Glauber's salt can be recovered as an alkali salt, and can be used for various applications.

At this time, the separated EG and alkali are once collected in the filtrate tank 84 through the transport pipe 23,
Further, it is mixed with the filtrate tank 81 through the transport pipe 24 by the pump 49. Subsequent processing is the same as described above.

(Drying / Pulverizing Step) On the other hand, the terephthalic acid washed by the horizontal belt type vacuum filter 106 can be circulated to the indirect heating dryer, for example, the jacket 94 and the shaft 95 by the belt conveyor 112. It is sent to a paddle type rotary vacuum dryer 107 having a structure. Since the dryer 107 is evacuated by the vacuum pump 63, terephthalic acid can be dried in a short time and without any deterioration. Thereby, highly pure terephthalic acid can be recovered. Moisture that evaporates during drying is cooled through the transport pipe 25 and then transferred to the transport pipe 2.
2 and collected in a filtrate tank 83.

The subsequent pulverization of the recovered terephthalic acid can be performed by known means.

[Second Basic Mode] FIG. 7 shows a second basic mode. This form is a vertical cylindrical stirring tank 10
1 is used to carry out a reactive decomposition. The vertical cylindrical stirring tank 101 has a heating jacket 91 on the outer wall through which a heating medium 92 flows, and has a cooling water coil 93 for temperature adjustment inside, for example, under a temperature condition of 130 ° C. to 180 ° C. and normal pressure. ,
The reaction is decomposed by stirring for about 30 to 90 minutes.

The reaction-decomposed slurry decomposed into terephthalate and EG can be directly sent to the horizontal belt type vacuum filtration dissolving machine 102 shown in FIG. After performing the operation, it can be sent to the horizontal belt type vacuum filtration dissolver 102.

The squeezing device 100 has a screw press type structure, and has a tapered screw conveyor 100A disposed in a main body. EG can be returned to the vertical cylindrical stirring tank 101 by the pump 47 from an appropriate position in the main body of the expansion device 100. Aperture device 10
By providing 0, the supply amount of EG can be reduced, and the filtration efficiency per time in the next filtration step (solid-liquid separation step) can be increased.

"Third Basic Mode" FIGS. 8 and 9 show a third basic mode. In this embodiment, similarly to the second basic embodiment, a reactive decomposition is performed using a vertical cylindrical stirring tank 101.

The reaction-decomposed slurry, which has undergone the reaction decomposition in the vertical cylindrical stirring tank 101, is transported by the pump 41 through the transport pipe 11, and the horizontal belt type vacuum filter 106A shown in FIG. (Having the same structure as the horizontal belt type vacuum filter 106 in the latter stage of the above). In the horizontal belt type vacuum filter 106, EG is removed and washing is performed with washing water.

The terephthalate salt obtained by removing the EG is charged by a cake transport belt conveyor 111 into a vertical cylindrical stirring tank 103 installed separately from the horizontal belt type vacuum filter 106A. In this vertical cylindrical stirring tank 103,
For example, hot water of about 80 ° C., which is three times the amount of terephthalate, is added to dissolve terephthalate. As the warm water, there can be used the regenerated water in the above-described system and the regenerated washing water obtained by returning the washing wastewater from the activated carbon packed column 104 for rigid cylindrical adsorption through the transport pipe 16.

The aqueous solution of the terephthalate is supplied by the pump 44 to the soluble impurity remover, for example, the activated carbon packed column 104 for rigid cylindrical adsorption through the transport pipe 15.
At this time, the aqueous solution of terephthalate is supplied to the vertical cylindrical stirring tank 1
It is preferable that insoluble impurities are removed by a check filter 99 attached to 03 or the like.

In the third basic mode, similarly to the second basic mode, the reaction-decomposed slurry decomposed into terephthalate and EG is subjected to a squeezing operation by the squeezing device 100 in advance, and then horizontally. It can be supplied to the belt-type vacuum filter 106A.

"Other Basic Forms" Terephthalate and E
As described above, it is possible to use a separator such as a centrifugal separator without using the horizontal belt type vacuum filtration dissolver 102 when separating EG from the reaction decomposition slurry with G. Further, it is possible to construct a system by appropriately combining the elements of the above embodiments.

[First Embodiment] Next, an embodiment of the present invention will be described. The present invention is characterized in that the reaction decomposition step in the basic mode described above is performed in two or more stages. First, FIG. 10 shows a first embodiment. In this embodiment, the reaction decomposition step is carried out in the vertical cylindrical stirring tank 101A at a temperature of 100 ° C. or higher and a temperature not higher than the temperature at which the recovered PET pulverized product does not substantially start the reaction decomposition, and is reserved for 5 minutes or more, preferably 20 minutes or more. The preheating step of heating is divided into the preheating step of heating and the decomposition heating step of heating at a temperature not lower than the temperature at which the recovered PET pulverized product substantially starts reaction decomposition and not higher than the boiling point of the solvent in the vertical cylindrical stirring tank 101B. Is what you do. In particular, in the present embodiment using EG as the solvent, it is preferable that the preheating is performed at 100 to 140 ° C and the decomposition heating is performed at 130 to 180 ° C. The recovered PET pulverized product starts to react and decompose at a lower temperature when the amount of water in the solvent increases, but in this embodiment using only EG without using water as the solvent, 130 to 140 Decomposition will start around ℃. Further, since the boiling point of EG is 196 ° C., if EG boils, the required amount increases, so the reaction decomposition heating is set to 180 ° C. or less. The vertical cylindrical stirring tanks 101A and 101B used in this case may have the same configuration as the vertical cylindrical stirring tank 101 used in the reaction and decomposition step of the second and third basic modes. it can. That is, the vertical cylindrical stirring tanks 101A, 101A
1B has heating jackets 91A and 91B on the outer wall through which the heat mediums 92A and 92B flow, and cooling water coils 93A and 93B for temperature adjustment inside, and is stirred under the temperature conditions and normal pressure in each stage. Is what you do.

The PET, alkali, and EG are transported by the transport pipe 9
Through the vertical cylindrical stirring tank 10 while adjusting with the valve 9A.
1A. In the present embodiment, the collected PET
The mass ratio between the pulverized product and the EG is set to be 1: 0.8 to 1.2. In the vertical cylindrical stirring tank 101A, PE
T, alkali, and EG are stirred while being preheated to form a slurry, and this slurry liquid is passed through the transport pipe 10 and adjusted by the valve 10A to form a vertical cylindrical stirring tank 101B.
To supply. In this vertical cylindrical stirring tank 101B,
Further, if necessary, in the present embodiment, the mass ratio between the recovered PET pulverized product and the EG is 1: 2.0 to 2.5.
EG is added to the mixture, and the mixture is stirred while being heated for the reaction decomposition, and the recovered PET pulverized product is decomposed into terephthalate and EG. The reaction-decomposed slurry liquid is sent to the solid-liquid separation step through the transport pipe 11 by the pump 41 while being adjusted by the valve 11A. Subsequent processing is the same as that described in the basic mode.

[Second Embodiment] Next, FIG. 11 shows a second embodiment. FIG. 11 corresponds to the preheating step and the reactive decomposition step in FIG. This embodiment is different from the vertical cylindrical stirring tank 10 in the first embodiment.
Instead of 1B, a screw press type horizontal reactive decomposition apparatus used in the reactive decomposition step in the first basic mode is used. The configuration of this reactive decomposition apparatus is the first
In the same manner as in the basic mode, the slurry liquid obtained by preheating and stirring PET, alkali, and EG is supplied to a valve 10A.
While adjusting at, the EG is injected into the input port 3 through the transport pipe 10 and, if necessary, the EG is input into the input port 4.
Mainly in the main body 1A, the recovered pulverized PET is continuously decomposed into terephthalate and EG. The reaction-decomposed slurry liquid is squeezed out from the tapered portion 1B and sent to the solid-liquid separation step. Subsequent processing is the same as that described in the basic mode.

[Third Embodiment] Further, FIG.
The third embodiment has been described. In this embodiment, there are a plurality of vertical cylindrical stirring tanks 101A in the first embodiment, and in this embodiment, there are three, 101A1, 101A2, and 101A3. Generally, the stage of preheating for crystallizing the recovered PET pulverized product requires more time than the stage of decomposition heating for reacting and decomposing the recovered PET pulverized product. Therefore, if preheating is performed in parallel in a plurality of vertical cylindrical stirring tanks as in the present embodiment, the vertical cylindrical stirring tank 101B
Can also be continuously performed.

The PET, alkali, and EG are transported by the transport pipe 9
And supplied to the vertical cylindrical stirring tanks 101A1-3 while adjusting with the valves 9A1-3. This vertical cylindrical stirring tank 10
In 1A1 to 3A, PET, alkali, and EG are stirred while being preheated to form a slurry. The slurry liquid is supplied to the vertical cylindrical stirring tank 101B through the transport pipe 10 while being adjusted by the valves 10A1 to 10A1. I do. The processing after the vertical cylindrical stirring tank 101B is the same as that in the first embodiment.

[Other Embodiments] In addition to the above, a step of removing foreign matters floating on the EG such as PP and PE having a lower specific gravity than the solvent can be provided before the heating step.

[0079]

(Example) EG12 was placed in a vertical cylindrical stirring tank having a heating jacket of 150 mmφ × 200 mmH on the outer wall.
After the temperature was raised to 150 ° C., 600 g of collected ground PET of 6 to 8 mm square and sodium carbonate 360
and stirred for 10 minutes (preheating step). Next, the slurry obtained by this stirring was supplied to a vertical cylindrical stirring tank having the same shape as the vertical cylindrical stirring tank in the preheating stage. Then, 600 g of EG was added, the temperature was raised to 180 ° C., and the mixture was stirred for 10 minutes (reaction decomposition heating step).

The solid terephthalate was separated from the slurry after the reaction decomposition and dissolved in water. As a result, the residual unreacted PET was 0 g, and the conversion was 100%.

Comparative Example EG1 was placed in a vertical cylindrical stirring tank having a heating jacket of 150 mmφ × 200 mmH on the outer wall.
After filling 800 g and raising the temperature to 180 ° C., 6 to 8 mm
600 g of pulverized PET collected with horns and sodium carbonate 36
And then stirred for 30 minutes.

The terephthalate salt as a solid content was separated from the slurry after the reaction decomposition and dissolved in water. As a result, the residual unreacted PET was 22 g, and the conversion was 96.3%.

From the above, the provision of the preheating step of preheating increases the recovery rate of terephthalic acid,
It was found that the processing time was shortened.

[0084]

As described above, according to the method for recovering terephthalic acid from the recovered pulverized polyethylene terephthalate according to the present invention, the recovery rate of terephthalic acid is high and the processing time is short.

[Brief description of the drawings]

FIG. 1 is a flow sheet of the entire first basic mode.

FIG. 2 is a conceptual diagram of a horizontal reactor.

FIG. 3 is a conceptual diagram of a horizontal belt type vacuum filtration and melting machine.

FIG. 4 is a schematic diagram of a configuration example of a neutralization tank.

FIG. 5 is a particle size distribution graph of terephthalic acid depending on whether or not heating is performed in a neutralization step.

FIG. 6 is a schematic diagram of a horizontal belt type vacuum filter.

FIG. 7 is a flow sheet of the entire second basic mode.

FIG. 8 is a flow sheet of the entire third basic mode.

FIG. 9 is a schematic diagram of a horizontal belt type vacuum filter used in a solid-liquid separation step at a preceding stage in the third basic mode.

FIG. 10 is a flow sheet until a terephthalate of the first embodiment is produced.

FIG. 11 is a flow sheet until a terephthalate of the second embodiment is produced.

FIG. 12 is a flow sheet until a terephthalate of the third embodiment is produced.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylindrical body, 1A ... Main body part, 1B ... Tapered part, 2,100A
... screw conveyor, 3, 4 ... inlet, 5 ... heat medium inlet, 6 ... heat medium outlet, 7 ... gas passage, 9-25, 2
6A, 26B, 27-30: transport tube, 9A, 9A1
3, 10A, 10A1-3, 11A ... valve, 27A ... filter cloth cleaning device, 27B1, 27B2 ... cleaning device, 31 ... decompression tube, 32 ... heater, 33 ... crystal can, 34 ... cooler, 4
1, 42, 42A, 42B, 43 to 52 ... pump, 61
~ 63 ... vacuum pump, 71, 71A, 71B, 72A,
81 to 84: filtrate tank, 72: aqueous solution separation tank, 91, 91
A, 91B, 94 ... jacket, 92, 92A, 92B
... heat medium, 93, 93A, 93B ... cooling water coil, 95
... shaft, 96 ... filter cloth, 97 ... vacuum box, 98 ... scraper, 99 ... check filter, 100 ... drawing device,
101, 101A, 101A1-3, 101B, 103
... vertical cylindrical stirring tank, 102 ... horizontal belt type vacuum filtration and dissolution machine, 104 ... activated carbon packed column for rigid cylindrical adsorption, 105
... Precipitation tank, 106, 106A ... Horizontal belt type vacuum filter, 107,109 ... Paddle type rotary vacuum dryer, 108
... Centrifuge, 110 ... Purification tower, 111-113 ... Belt conveyor, 114 ... Neutralization tank, 114A ... Agitator, 11
4B: ultrasonic generator, 114C: stirring blade, 114D
... shaft of stirring blade.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Nobuyuki Funakoshi 2--17-15 Tsukushima, Chuo-ku, Tokyo Tsukishima Machinery Co., Ltd. (72) Inventor Kazuho Tanaka 2--17-15 Tsukushima, Chuo-ku, Tokyo Tsukishima Machine F term in reference (reference) 4H006 AA02 AC46 AC47 AC91 BB14 BC10 BC31 BC35 BD10 BD60 BD81 BE10 BE12 BJ50 BS30 BS70

Claims (6)

[Claims] 1. A process for decomposing a recovered polyethylene terephthalate pulverized product into a terephthalate and ethylene glycol in a solvent in the presence of an equimolar amount of polyethylene terephthalate or an excess of an alkali to produce terephthalic acid A method for recovering terephthalic acid from a salt, wherein the step of reacting and decomposing is performed in two or more stages is a method for recovering terephthalic acid from a ground polyethylene terephthalate product. 2. A preheating step of preheating for 5 minutes or more at a temperature of 100 ° C. or higher and not higher than a temperature at which the pulverized product does not substantially start reactive decomposition, and a temperature at which the pulverized product substantially starts reactive decomposition. The method for recovering terephthalic acid from the recovered pulverized polyethylene terephthalate product according to claim 1, further comprising a step of heating the reaction decomposition at a temperature not lower than the boiling point of the solvent. 3. The method for recovering terephthalic acid from a ground polyethylene terephthalate product according to claim 2, wherein ethylene glycol is used as a solvent, and preheating is performed at 100 to 140 ° C. and decomposition heating is performed at 130 to 180 ° C. . 4. The method according to claim 2, further comprising the step of removing foreign matters having a specific gravity smaller than that of the solvent before the step of heating.
A method for recovering terephthalic acid from a ground polyethylene terephthalate product as described in the above. 5. A screw-conveyor having a tapered portion corresponding to the tapered portion inside a cylinder having a main body and a tapered portion located at the tip of the main body portion, as a reactive decomposition device at the final stage of the reactive cracking step. Using a horizontal reaction and decomposition apparatus provided, a recovered polyethylene terephthalate pulverized product, a solvent and an alkali are supplied into the horizontal reaction and decomposition apparatus, and the pulverized product is terephthalate and ethylene mainly in the main body while being decomposed and heated. The method for recovering terephthalic acid from a pulverized recovered polyethylene terephthalate product according to any one of claims 1 to 4, wherein the reaction-decomposed slurry is squeezed from the tapered portion by reacting with glycerol. 6. A method in which sodium carbonate is used as an alkali, and the mass ratio of the recovered polyethylene terephthalate pulverized product and ethylene glycol during preheating and decomposition heating is determined by
The method for recovering terephthalic acid from a ground polyethylene terephthalate product according to claim 3, wherein the ratio is 1: 0.8 to 1.2 and 1: 2.0 to 2.5.