JP2003300933A - Method for removing minute particle from depolymerized solution of polyethylene terephthalate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for inexpensively and simply removing minute particles having 0.1-500 μm average particle size and included in a depolymerized solution of a polyethylene terephthalate with suppressing loss of a process liquid and without generating a large amount of waste. <P>SOLUTION: The polyethylene terephthalate is depolymerized with ethylene glycol to obtain an ethylene glycol solution of bis(2-hydroxyethyl) terephthalate which is passed through a column filled with metal powder. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for removing fine particles contained in a solution obtained by depolymerizing polyethylene terephthalate with ethylene glycol.

[0002]

2. Description of the Related Art As one of the methods for producing polyethylene terephthalate, it has been obtained by collecting used polyethylene terephthalate molded articles, particularly PET bottles, as described in JP-A-2000-169623. A method is known in which crude terephthalate (chips or flakes) is used as a raw material to obtain high-purity bis (2-hydroxyethyl) terephthalate, which is polycondensed in the presence of a polymerization catalyst to produce polyethylene terephthalate. In this method, a used polyethylene terephthalate molded product is pulverized, depolymerized with ethylene glycol, purified to obtain high-purity bis (2-hydroxyethyl) terephthalate, and then polycondensed again to form polyethylene terephthalate and ethylene glycol. It is a thing.

However, in the above depolymerization solution, for example, copper phthalocyanine pigment particles used as a colorant for PET bottles used in molded articles, titanium oxide as a matting agent, and other additives ( For example, fine particles of silica, carbon black, etc.) are contained.
In addition, activated carbon is generally used for the removal of the colorant and the like, but a part thereof may be mixed in the solution after the treatment. If the above-mentioned fine particles including such activated carbon are mixed in the depolymerization solution, in the subsequent steps, it may cause clogging of piping, etc., or may cause abrasion of pollution sources and equipment by adhering to equipment. Furthermore, it may be deposited on the heat transfer surface to cause heat transfer failure.

According to the results of studies by the present inventors, particles of pigments and activated carbon are in a wide particle size distribution range of about 0.1 μm to 500 μm, for example, a cartridge filter having a pore size of about 1 μm, a ceramic filter, a bag filter, etc. However, it is difficult to completely remove these particles from the depolymerization solution. On the other hand, a membrane filter with a pore size of about 0.1 μm or a pre-coated filter using diatomaceous earth is effective for removing particles, but the membrane filter is expensive and cannot be regenerated even when replacement is necessary due to clogging. There is a problem. Also,
In the precoat filter, there is a large loss due to the depolymerization solution being absorbed by the precoat material, and switching of the precoat filter, discharge and removal of the precoat filter material layer,
Since each operation of washing, pre-coating and liquid passing is required, workability is poor, and further there is a problem that a large amount of waste is discharged.

[0005]

DISCLOSURE OF THE INVENTION An object of the present invention is to produce polyethylene terephthalate in a depolymerization solution at a low cost and simply without minimizing the loss of the depolymerization solution and generating a large amount of waste. Average particle size included in 0.1μ
It is to provide a method of removing fine particles of m to 500 μm.

Another object of the present invention is to provide a filtration method having a relatively high filtration rate and a long filtration life in removing the fine particles contained in the depolymerization solution of polyethylene terephthalate by filtration.

Further objects and advantages of the present invention will be apparent from the following description.

[0008]

According to the present invention, the above objects and advantages of the present invention are to provide an ethylene glycol solution of bis (2-hydroxyethyl) terephthalate obtained by depolymerizing polyethylene terephthalate with ethylene glycol. A method for removing fine particles from a polyethylene terephthalate depolymerization solution, which comprises passing through a column filled with metal powder to remove fine particles having an average particle size of 0.1 to 500 μm contained in the solution. To be done.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to specific examples. In the present invention, first, for example, a used polyethylene terephthalate molded article, particularly a crushed product of PET bottles (flakes or pellets) is depolymerized by the reaction with excess ethylene glycol in the presence of a known catalyst, and a crude bis A mixed solution of (2-hydroxyethyl) terephthalate and ethylene glycol is prepared. This depolymerization is described, for example, in JP-A 2000-169.
It can be performed by the method described in Japanese Laid-Open Patent Publication No. 623. The weight ratio of bis (2-hydroxyethyl) terephthalate and ethylene glycol may be 1: 1 to 1: 9, preferably 1: 2 to 1: 6. Next, the temperature of this mixed solution is set to a temperature at which bis (2-hydroxyethyl) terephthalate and its oligomer do not precipitate,
Moreover, the average particle diameter contained in the mixed solution is 0.1 μm to 50 μm.
The temperature is maintained at a temperature at which fine particles of 0 μm such as pigment and activated carbon can be separated by filtration, and the filtration operation is performed under such temperature conditions. Specifically, it is preferably in the range of 30 ° C to 100 ° C, and more preferably in the range of 60 ° C to 90 ° C. When this temperature is lower than 30 ° C., bis (2-hydroxyethyl) terephthalate and its oligomer are likely to be precipitated, and therefore, they may be removed from the solution together with the fine particles by filtration. Further, since the viscosity of ethylene glycol is increased, the workability of filtration is reduced. On the other hand, when the temperature is higher than 100 ° C., the solubility of the fine particles in ethylene glycol increases, so that the fine particles migrate into the filtrate and are difficult to be removed.
In addition, the evaporation rate of ethylene glycol increases, which is not preferable in terms of work.

The average particle size contained in the depolymerization solution of polyethylene terephthalate according to the present invention is 0.1 μm to 500 μm.
It is preferable to remove fine particles of μm by a clarification filtration method. Generally, the clarification filtration method has a solid content of about 1,0.
It is applied to the case of not more than 00 ppm, and industrially about several tens of ppm. The amount of the insoluble fine particles present in the solution after the depolymerization reaction is in the form of the raw material polyethylene terephthalate (for example, bottle, film,
Depending on the sheet or fiber, etc., but generally 5
It is about 100 ppm, and a clarification filtration method can be applied. The concentration of the insoluble fine particles can be controlled to a lower concentration by setting the ratio of the PET bottle, PET film, etc. in the waste material as a raw material to a predetermined value. On the other hand, regarding the concentration of the activated carbon used for removing the colorant, etc., when the activated carbon is taken out of the solution to regenerate the activated carbon or when the activated carbon is newly replenished,
Although the concentration becomes about ppm, it decreases thereafter as the depolymerization solution moves, and becomes stable at a concentration of about 5-10 ppm. Therefore, if the concentration of the insoluble fine particles such as the colorant is controlled to a comparatively low value, even if the concentration of activated carbon is several tens of p
Since it is about pm, the clarification filtration method can be industrially applied.

The solvent used in the present invention is ethylene glycol having a relatively high viscosity, and the particles to be removed also include fine particles having a particle size of about 0.1 μm, and are therefore usually used as a filter medium. Anthracite,
Sand, glass beads, garnet, etc. are not suitable because the porosity is small, the filtration rate is low, and the filtration life is short. The filter medium used in the present invention is most preferably a metal powder used in a spin pack for spinning synthetic fibers. As a result of earnest research, the present inventor has found that the use of metal powder as a filter medium has the following advantages.

(1) Metal powder is made of stainless steel (SU
Since it is a S) -based metal, it has sufficient corrosion resistance against ethylene glycol at a temperature of 30 to 100 ° C. Also,
Since the reduction due to wear is small, the replenishment amount is small. (2) Since the metal powder has a high porosity, it can be processed at a large flow rate with a low filtration pressure and has a long filtration life. (3) When the metal powder has an irregular porous structure, single layer filling is possible, and washing, refilling, or classification filling of the filter medium is unnecessary. (4) The undiluted solution may be supplied to the filtration tower filled with the metal powder either by dropping it from the upper part of the packed bed, by flowing it from the lower part to the upper part, or by supplying it from both upper and lower parts and extracting it from the central part. May be.

The metal powder used in the present invention preferably has a particle size of 10 to 400 mesh and a porosity of 60 to 80%. The relationship between the height (L) and the diameter (D) at which the metal powder is filled is L /
The range of D = 0.5 to 5 is good, and more preferably L / D =
1-4, and more preferably L / D = 1.5-3.
Furthermore, the superficial velocity in permeation filtration is 30 m / h or less,
Further, it is preferably 10 to 20 m / h.

[0014]

EXAMPLES The following examples are given to illustrate the more specific aspects of the present invention. Needless to say, the present invention is not limited to this. The properties in the examples were measured by the following methods. (1) Superficial tower speed The liquid passing speed is divided by the cross-sectional area of the packed tower, and the unit is m / hr.
Represented by.

Example 1 75 kg of about 8 mm x 8 mm polyethylene terephthalate flakes prepared from a mixture of 10% by weight colored PET bottle containing blue phthalocyanine pigment and 90% by weight uncolored PET bottle, ethylene glycol 4
20 kg and 280 g of sodium hydroxide crystals were placed in an autoclave and the pressure was 0.15 MPa while stirring.
The reaction was carried out at a temperature of 218 ° C. for 2 hours to depolymerize polyethylene terephthalate, which was then cooled to 85 ° C. to obtain a yellow-green depolymerized solution.

Inner diameter 102.3 mm, height 1,000 mm
The column of SUS304 of No. 2 was attached with a warm water jacket at 85 ° C., and metal powder having a porosity of 70% with 50 to 100 mesh was filled at a height of 204 mm to set L / D = 2.
Filtration was performed while changing the flow rate in advance, and the limit value of the flow rate at which a clear liquid was obtained was determined to be 120 liter / h. The above depolymerization solution was continuously supplied while maintaining a liquid layer having a height of 150 mm on the upper part of the filter material, and the filtrate was extracted from a plurality of nozzles having a metal mesh of 150 mesh for stopping metal powder at the tip. The superficial velocity at this time is 14.59.
It was m / h. Yellow-green depolymerization solution 495 kg (44
3 liters) was filtered over 3.69 hours to give a yellow filtrate.

In order to evaluate the effect of the filtration, 100 ml of the depolymerization solution was filtered through a membrane filter having a pore size of 0.1 μm, the obtained solid content was washed with water and dried, and the mass of the solid content was measured. When the concentration of pigment fine particles and other insoluble particles removed by filtration was determined,
It was 63 ppm. On the other hand, the concentration of pigment fine particles and other insoluble particles contained in the filtrate of the depolymerization solution was 1.3 ppm as determined by the same measurement.

Next, the yellow filtrate obtained by the filtration using the metal powder was treated with an inner diameter of 500 mm and a height of 1,50.
A 0 mm column was packed with activated carbon and the temperature of the activated carbon was 85
The filtrate was decolorized by supplying it to the column while adjusting the temperature so as to be ℃. The filtrate was passed through a column newly filled with metal powder at a flow rate of 120 liter / h in the same manner as above to remove the activated carbon fine particles contained in the filtrate. The concentration of activated carbon fine particles contained in the filtrate was 47 ppm before filtration, but decreased to 0.6 ppm after filtration.

Comparative Example 1 In the same manner as in Example 1, a solution prepared by depolymerizing polyethylene terephthalate with ethylene glycol was prepared, and silica sand having an average particle size of 40 to 60 mesh and a porosity of 47% was used as L / D.
When the depolymerization solution was passed through a column packed so as to be = 2 at a flow rate of 120 liters / hour, fine particles were mixed in the filtrate, and most of the fine particles were removed from the depolymerization solution as the stock solution. I couldn't. In order to remove fine particles and obtain a clear filtrate, it was necessary to set the flow rate to 35 liter / h (superficial velocity 4.26 m / h) or less.

Comparative Example 2 In the same manner as in Example 1, a solution prepared by depolymerizing polyethylene terephthalate with ethylene glycol was prepared, and glass beads having an average particle diameter of 0.2 to 0.3 mm and a porosity of 39% were L / D. When the depolymerization solution was passed through a column packed so as to be = 2 at a flow rate of 120 liters / hour, fine particles were mixed in the filtrate, and most of the fine particles were removed from the depolymerization solution as the stock solution. I couldn't. To remove fine particles and obtain a clear filtrate, the flow rate is 17 liter / h.
(Superficial velocity 2.07 m / h) It was necessary to make it below.

FIG. 1 shows the relationship between the porosity of the filter medium and the superficial velocity capable of removing fine particles in the solution. In the recycling process, the superficial velocity that can be adopted is 8 to 30 m in view of the total work time, work throughput, etc.
/ H, preferably 10 to 20 m / h. As is clear from FIG. 1, according to the filter medium of the present invention, a superficial velocity of 14.59 m / h can be obtained with a porosity of 70%, and fine particles can be removed from the depolymerization solution at a rate that can be sufficiently adopted in the process. confirmed.

[0022]

As described above, according to the method of removing fine particles from the polyethylene terephthalate depolymerization solution of the present invention, the fine particles can be removed from the depolymerization solution at a rate that can be sufficiently adopted in the recycling process. You can Further, it is possible to remove the fine particles contained in the depolymerization solution of polyethylene terephthalate inexpensively and easily without minimizing the loss of the process fluid and generating a large amount of waste.

[Brief description of drawings]

FIG. 1 shows the relationship between the porosity of a filter medium and the superficial velocity capable of removing fine particles in a solution.

Claims (6)

[Claims] 1. An ethylene glycol solution of bis (2-hydroxyethyl) terephthalate obtained by depolymerizing polyethylene terephthalate with ethylene glycol is passed through a column filled with metal powder to obtain an average content of the solution. A method for removing fine particles from a polyethylene terephthalate depolymerization solution, which comprises removing fine particles having a particle size of 0.1 to 500 μm. 2. The metal powder has a particle size of 10 to 400.
A mesh and having a porosity of 60-80%.
The method described in. 3. The method according to claim 1, wherein the metal powder is made of SUS and has an amorphous porous structure. 4. The method according to claim 1, wherein the temperature of the solution is 30 to 100 ° C. 5. The method according to claim 1, wherein the metal powder is packed so that the packing height with respect to the diameter of the column is 0.5 to 5. 6. The superficial velocity in permeation filtration is 8 to 30 m.
/ H, The method according to any one of claims 1 to 5.