JPH0977905A - Apparatus and method for recovering constituent monomers from polyethylene terephthalate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and method for recovering the constituent monomers from a waste polyethylene terephthalate(PET) in high yields whereby the percentage hydrolysis of the PET can be sufficiently increased, the constituent monomers being reaction products are recovered, and the handling of the hydrolyzate of PET can be facilitated even when the water content is low. SOLUTION: This apparatus for recovering the constituent monomers from a waste polyethylene terephthalate(PET) consists of a high-temperature high-pressure reactor 4 having a screw in its inside, a high-pressure pump which supplies a molten PET under pressure and a high-pressure pump 6 which supplies water under pressure each of which is connected to the reactor 4, a throttle valve 9 provided at the exit for products, and a means for heating the reactor 4. The method for recovering the constituent monomers from a waste PET consists of hydrolyzing the PET in the reactor 4 at a temperature equal to or higher than the melting point of the PET under a pressure equal to or higher than the saturated vapor pressure of water at this temperature, transferring the hydrolyzate with the screw under continuous agitation and discharging the reaction product from the reactor through the valve 9 and recovering the product.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for recovering raw material monomers from polyethylene terephthalate, and more specifically, to terephthalic acid and ethylene glycol corresponding to the raw material monomers for PET from waste polyethylene terephthalate (hereinafter referred to as PET). Belongs to the technical field relating to an apparatus and method for recovering slag, and in a broad sense, to the chemical recycling technical field of PET.

[0002]

2. Description of the Related Art In recent years, the growing problem of plastic waste has become serious. Conventionally, plastic waste has been disposed of by landfill, but it will become more difficult to secure a landfill site in the future, and therefore a method for effectively utilizing plastic waste by recycling is being sought.

The methods of recycling plastic waste are roughly classified into (A) material recycling in which the form of the material is changed by physical treatment for reuse, and (B) thermal recycling in which thermal energy generated by incineration is used. , (C) There are three methods of chemical recycling to recover fuel oil and raw material monomers by chemical treatment.

Of these, the method (A) has a lower purity than the original product plastic because impurities are easily mixed in, and the strength and heat resistance are also reduced, so that its use is limited. There is a drawback that it will be. There are still problems with the method (B). That is, it has been pointed out that since the plastic has a high calorie when burned, the incinerator is damaged due to a high incineration temperature and adhesion of molten plastic to the furnace wall surface.

On the other hand, chemical recycling, in particular, a method of recovering raw material monomers as a product by chemically decomposing a plastic may be performed in a closed system, and the added value of recycled products is high. Can be said to be the most ideal recycling method.

PE by such a chemical recycling method
PET is a technology that chemically decomposes T to obtain recycled products.
A recycling method is known in which the raw material monomer or oligomer is recovered by solvolysis.

For example, a method has been reported in which PET is decomposed by a solvolysis reaction using alcohol, and terephthalic acid (or its derivative dimethyl terephthalate) as a raw material monomer of PET and ethylene glycol are recovered as products. There is.

Explaining this example of the method in more detail, US Pat. No. 3,403,115 shows a method in which solvolysis of PET is carried out using methanol to recover dimethyl terephthalate as a product. However, this method does not recover ethylene glycol. U.S. Patent Publication 3776
No. 945 shows a method in which PET is subjected to solvolysis with methanol in the presence of an acid catalyst to obtain dimethyl terephthalate and ethylene glycol as products. US Patent Publications 3037050, 3321510, 3488298, 5051528 and the like show a method of recovering a raw material monomer as a product by solvolysis of PET with methanol.
Although each of these methods has its own characteristics,
The basic principle is the same.

A recycling method has also been disclosed in which PET is solvolytically decomposed with glycols other than methanol to recover raw material monomers or oligomers. For example, US Pat. No. 3,222,299 discloses a method of solvolyzing a terephthalic acid type polyester with glycol to obtain a diglycol ester of terephthalic acid. U.S. Pat. No. 3,907,868 shows a method of solvating PET with ethylene glycol first and then with methanol in the presence of a catalyst to obtain dimethyl terephthalate and ethylene glycol. In addition, a method has been reported in which an amine, an alkoxide, a metal acetate, or the like is used as a catalyst to lower the molecular weight of PET with propylene glycol to obtain an oligomer as a product (Ind.Eng.Chem.Re.
s., 26 , 194 (1987)).

In addition to the alcohol solvolysis method described above, a technique relating to a hydrolysis method has also been reported. For example, U.S. Pat. No. 4,542,239 discloses that PE with high temperature water using an acid such as sulfuric acid or an alkali such as ammonium hydroxide as a catalyst.
A method of hydrolyzing T is shown. US Patent Publication 46
In the case of No. 05762, PET is also used at 100 ° C or less by an acid catalyst.
The method of hydrolyzing In addition, Japanese Patent Publication
No. 8 and Japanese Patent Laid-Open No. 6-72922 disclose that P under high temperature and high pressure.
Techniques for removing impurities from products obtained by hydrolyzing ET are described. Furthermore, Kamal et al. Reported a method for hydrolyzing PET using a twin-screw extruder (ANTEC. Pp.
2896-2900 (1994)).

[0011]

With respect to the above-mentioned alcohol solvolysis method of PET, it has been reported that the plant for practical use is in operation. However, the high cost of using a large amount of alcohol as a reagent, the danger associated with the flammability of alcohol, and the high cost of requiring a catalyst still remain problems.

The hydrolysis method of PET has the potential to solve these problems at once. That is, the high cost and flammability of reagents such as those in the alcohol solvolysis method can be avoided, and if water in a high temperature and high pressure state is used, the water itself (hydrogen ion and hydroxide ion accompanying ionization of water) functions as a catalyst. Therefore, it is not necessary to add a catalyst. Nevertheless, the hydrolysis method of PET has not been put to practical use. One reason is that terephthalic acid, which is a hydrolysis reaction product, is solid at room temperature and atmospheric pressure, and its solubility in water at room temperature and atmospheric pressure is extremely low, resulting in poor fluidity and easy handling. It is said that.

In view of such circumstances, the water content (the ratio of water contained in PET and water, the water content per unit mass, or the water content) for the purpose of improving the fluidity of the hydrolysis reaction product and facilitating its handling. However, in this case, the amount of water per unit mass is high, so that a large amount of energy is consumed to heat the water, resulting in a high heating cost. That is, increase the moisture content,
The higher the amount of water per unit mass, the easier the handling of the hydrolysis reaction product, but PET and water
There is a disadvantage in that much energy is consumed for heating to the high temperature necessary for the hydrolysis of T, which is disadvantageous in terms of cost.

Therefore, a twin-screw extruder has been used as a means for facilitating the handling of the hydrolysis reaction product without increasing the water content. That is, PET using a twin-screw extruder
The hydrolysis method of was proposed by Kamal et al. However, in this method, it is not possible to operate under the optimum conditions for the hydrolysis reaction due to the restriction on the equipment such as the twin-screw extruder used. Since high pressure cannot be achieved, there is a problem that a sufficient hydrolysis rate cannot be obtained, and it has not been put to practical use.

The present invention has been made in view of such circumstances, and an object thereof is to solve the problems of the conventional technique of recovering the raw material monomer from PET by the hydrolysis method and to increase the water content. And a device for recovering a raw material monomer from PET that makes it possible to easily handle a hydrolysis reaction product, obtains a sufficient hydrolysis rate, and recovers a raw material monomer at a high rate. Compared with a recovery method, that is, a method of hydrolyzing PET using a twin-screw extruder, the recovery rate of the raw material monomer is high and the recovery rate of the raw material monomer can be increased, and It is intended to provide a recovery method.

[0016]

In order to achieve the above object, the present invention provides an apparatus and a method for recovering a raw material monomer from PET (polyethylene terephthalate) having the following constitution.

That is, the apparatus for recovering raw material monomers from PET according to the present invention has a screw inside a cylindrical container having an inlet for PET and water, and PET and water are continuously fed by rotation of the screw. A high-temperature and high-pressure reaction container that is transferred while stirring and is reacted under high temperature and high pressure, and discharges the reaction product to the outside of the cylindrical container through a discharge port of the reaction product and a throttle valve connected to the discharge port, A means for heating the high-temperature and high-pressure reaction vessel, a high-pressure pump connected to the water inlet through which water is supplied under pressure into the high-temperature high-pressure reaction vessel, and a pipe connected to the PET inlet through the high-temperature high-pressure reaction vessel. It is an apparatus for recovering a raw material monomer from PET, which has a high-pressure pump for supplying PET in a molten state under high temperature and high pressure to a reaction container.

The method for recovering the raw material monomer from PET according to the present invention comprises supplying molten PET under high temperature and high pressure into a high temperature and high pressure reaction vessel, and supplying water under pressure.
T and water are reacted at a temperature above the melting point of PET and at a pressure above the saturated steam pressure at that temperature to cause a hydrolysis reaction of PET and transfer while continuously stirring by rotation of the screw in the high temperature high pressure reaction vessel. Then, the reaction product containing terephthalic acid and ethylene glycol, which are the raw material monomers for PET, is discharged to the outside of the high temperature and high pressure reaction vessel through the outlet of the reaction product and the throttle valve connected to the outlet, and recovered. Is a method for recovering a raw material monomer from PET.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The apparatus for recovering raw material monomers from PET according to the present invention can be manufactured, for example, as follows. An inlet for PET and water is provided near one end of the cylindrical container, an outlet for the reaction product is provided at the other end, and a throttle valve is connected to the outlet. This tubular container is installed horizontally, a screw is inserted into the tubular container, and the screw shaft is connected to a rotating means such as a motor outside the tubular container. Then, an external heating means is attached to the cylindrical container to form a high temperature and high pressure reaction container. To this reaction vessel, a high-pressure pump A for supplying water under pressure is connected to the water inlet, while a high-pressure pump B for supplying PET in a molten state under high temperature and high pressure is connected to the PE.
A pipe is connected to the inlet of T to form a raw material monomer recovery device from PET.

According to such a recovery apparatus, the raw material monomer can be recovered from PET, for example, as follows. While the screw is rotated, water is continuously supplied to the high-temperature high-pressure reaction vessel under pressure by the high-pressure pump A and PET is melted under high-temperature high-pressure reaction by the high-pressure pump B while external heating is performed. The high temperature and high pressure reaction vessel is heated by means. Then, PET and water are continuously transferred in the high temperature and high pressure reaction vessel while being stirred by the rotation of the screw, and at the same time, they are reacted under high temperature and high pressure, and a reaction product containing terephthalic acid and ethylene glycol, which are the raw material monomers of PET. And the reaction products are discharged one after another to the outside of the high temperature and high pressure reaction container through the outlet of the reaction product and the throttle valve connected to the outlet,
And it is collected.

Here, the reaction product is transferred, discharged and collected by the rotation of the screw, so that the water content may be low, and therefore the reaction product may be transferred, discharged and discharged without increasing the water content. The handling of collection can be easily performed. Further, unlike the twin-screw extruder, the high-temperature and high-pressure reaction vessel as described above has few restrictions on the apparatus, and therefore, the inside of the reaction vessel can be set to a sufficient high-temperature and high-pressure condition, particularly a necessary high-pressure condition. The hydrolysis rate can be increased as compared with the case of the waste PET hydrolysis method using a twin-screw extruder, and as a result, the recovery rate of the raw material monomer can be increased.

The method for recovering the raw material monomer from PET according to the present invention is a method for recovering the raw material monomer from PET by using the above-described apparatus for recovering the raw material monomer from PET. The inside of the reaction vessel is heated to a temperature not lower than the melting point of PET and to a pressure not lower than the saturated steam pressure at that temperature, and PET and water are reacted at this temperature and pressure to cause a hydrolysis reaction of PET. is there.

Under such temperature and pressure, P
Since ET is in a molten state and water is in a liquid state, it is extremely easy for the hydrolysis reaction of PET to proceed with water, the hydrolysis rate becomes high, and the recovery rate of the raw material monomer can be increased. In addition, since the reaction product is transferred by the rotation of the screw, discharged and collected, as described above,
The reaction products can be easily handled without increasing the water content.

As can be seen from the above, according to the present invention, when hydrolyzing PET and recovering the raw material monomer as the reaction product, the hydrolysis reaction product can be easily handled without increasing the water content. Can be
Moreover, a sufficient hydrolysis rate can be obtained, and the raw material monomer can be recovered at a high rate. That is, as compared with the case of the PET hydrolysis method using a twin-screw extruder, the hydrolysis rate is high and the recovery rate of the raw material monomer can be increased.

The details will be described below.

PET is a polyester resin synthesized by dehydration condensation polymerization (that is, esterification) of terephthalic acid as a raw material monomer and ethylene glycol. PET having such a chemical bond mode undergoes a reverse reaction of an esterification reaction, that is, a hydrolysis reaction with high temperature and high pressure water, and is decomposed into terephthalic acid and ethylene glycol which are raw material monomers. This is because, under high temperature and high pressure, the hydrolysis reaction rate is significantly increased, and in addition, the ionic product of water is significantly increased, and the concentrations of hydrogen ion and hydroxide ion are increased accordingly. This is because the hydrolysis reaction is promoted.

The present inventor conducted an experiment on the hydrolysis reaction of PET, and in order to increase the hydrolysis rate of PET, and thus the recovery rate of the raw material monomer, at a temperature above the melting point of PET (245 ° C.) and It was found that it is necessary to carry out the hydrolysis reaction at a pressure equal to or higher than the saturated steam pressure of water at the temperature. That is, at temperatures below the melting point of PET, PE
Since T is in a non-molten state, it is difficult for the hydrolysis reaction to proceed,
Even if the temperature is equal to or higher than the melting point of PET, at a pressure lower than the saturated steam pressure at that temperature, water is a gas (steam),
In order to confirm that the hydrolysis reaction does not substantially proceed and to increase the recovery rate of the raw material monomer, it is necessary to set the temperature to the melting point of PET or higher and the saturated steam pressure at the temperature or higher. I confirmed that there is.

On the other hand, in order to efficiently proceed the reaction from the viewpoint of cost, it is necessary to make the mass of water added per unit mass of PET as low as possible. This is because the energy required for heating water can be reduced. But,
There are the following problems. That is, the terephthalic acid in the raw material monomer contained in the hydrolysis reaction product is a solid at room temperature and atmospheric pressure, and has a very low solubility in water. Does not dissolve. Therefore, the lower the mass fraction of water, the higher the proportion of solid terephthalic acid, which reduces the fluidity of the reaction product. This is a fatal problem of clogging of pipes and valves in the system where the reaction is continuously carried out in an ordinary tubular or tank type reactor and the reaction products are continuously taken out. Wake up.

To avoid this, Kamal et al. Applied a twin-screw extruder to the hydrolysis of PET. In this case, the inside of the barrel of the twin-screw extruder was in a sufficiently high pressure state (that is, above the melting point of PET). Since it cannot be maintained at a pressure equal to or higher than the saturated steam pressure at the temperature), the recovery rate of the raw material monomer is low.

Therefore, in the present invention, P as described above is used.
An apparatus and method for recovering raw material monomers from ET have been developed and invented. In this recovery device, the reaction product is forcibly transferred by the screw in the high-temperature high-pressure reaction vessel instead of the piston flow of the normal tubular reactor, so that the water content does not increase (PET ratio is At the highest, the problem of clogging caused by terephthalic acid contained in the hydrolysis reaction product can be avoided. In addition, a reaction temperature sufficiently high in the high temperature and high pressure reaction vessel (a temperature required to accelerate the hydrolysis reaction) by means of heating the vessel.
At the same time, it is possible to supply water and PET, which are raw materials, into the container by a high-pressure pump, and to adjust the opening of a throttle valve connected to the outlet of the reaction product. The inside can be maintained at a sufficiently high reaction pressure (the pressure required to accelerate the hydrolysis reaction), and therefore the hydrolysis rate is higher than in the case of the PET hydrolysis method using a twin-screw extruder. As a result, the recovery rate of the raw material monomer can be increased.

A throttle valve is connected to the outlet of the reaction product so that the inside of the high temperature and high pressure reaction vessel can maintain the back pressure necessary for the hydrolysis reaction by adjusting the opening of the throttle valve. In addition, the reaction product can be discharged and collected.

In the present invention, the number of screws is not particularly limited, and may be one (uniaxial) or 2
It is possible to make two or more axes in which two or more are provided in parallel.

[0033]

FIG. 1 shows the apparatus used in the examples of the present invention.
In FIG. 1, reference numeral 4 is a high temperature and high pressure reaction vessel, and the sectional shape of the reaction vessel 4 is shown in FIG. The reaction vessel 4 is a long tubular body having such a cross-sectional shape, and has two screws (not shown) in parallel (two axes) inside the reaction vessel 4, and the screw axis is outside the vessel 4. It is connected to the installed motor. Further, a throttle valve 9 is provided at the outlet of the reaction product of the reaction container 4. Using such an apparatus, the raw material monomer was recovered from PET in the following manner.

PET is supplied to the feeder 1, heated and melted by the heater 2, pressurized by the high pressure pump 3, and supplied to the high temperature and high pressure reaction container 4. On the other hand, water is pressurized from a water tank 5 by a high-pressure pump 6, and sent to a heat exchanger 8 via a check valve 7 if necessary, and heated here to be high-temperature high-pressure water, which is supplied to a high-temperature high-pressure reaction vessel 4. To do. Here, the inside of the reaction vessel 4 is PE by an external heating means (not shown).
The temperature is maintained at a temperature T ₁ above the melting point (245 ° C.) of T, and at the same time, a pressure P ₁ above the saturated steam pressure at the temperature T ₁ .
The screw is rotated by the motor.

Then, the PET and water supplied to the reaction vessel 4 are heated by the screw while being stirred.
It reacts at T ₁ and pressure P ₁ to form a reaction product containing terephthalic acid and ethylene glycol, which are raw material monomers for PET, and is transferred toward the throttle valve 9 by a screw, and the reaction product is the throttle valve. It is discharged from the pipe 10 via 9 and collected.

In this example, terephthalic acid and ethylene glycol were separated from the reaction product as follows. That is, the reaction product was discharged from the pipe 10 into the water in the collector 11 and cooled. Then, the solid terephthalic acid that has settled at the bottom of the collector 11 is taken out by means 12
Was taken out, washed and dried by a dry washing operation, and collected as a recycled product. On the other hand, the aqueous solution in which ethylene glycol was dissolved was sent from the outflow hole 13 through the filter 14 to the distillation column 15, where ethylene glycol was separated from water and recovered as a regenerated product.

As a result, without increasing the moisture content (PET
Even if the ratio of
The raw material monomer recovery processing operation from PET could be continuously performed, and the raw material monomer could be recovered at a high rate. That is, the recovery rate of the raw material monomers could be significantly improved as compared with the case of the PET hydrolysis method using a twin-screw extruder.

Regarding typical operating conditions as an example of the present invention, the feed mass ratio of PET to water = 1: 1, the hydrolysis reaction temperature T ₁ = 300 ° C., the hydrolysis reaction pressure P ₁ = 10 MPa,
The condition is that the average residence time in the high-temperature and high-pressure reaction vessel (time from the time of supplying PET and water to the time of discharging the reaction product) = 30 minutes. The saturated water vapor pressure at T ₁ = 300 ° C is
Since it is 8.6 MPa, the above-mentioned P ₁ has a higher pressure than this.

When using an ordinary tubular or tank type reactor,
When the water content is increased to facilitate the handling of the reaction product and prevent clogging of the piping, etc., the PET / water feed mass ratio is about 1:10. Moisture content under typical operating conditions as an example is 1/10
Very low. Also from this, according to the present invention, it is not necessary to increase the water content, the reaction product is easy to handle even if the water content is low (the PET ratio is high), and the pipes and the like are not blocked. It can be seen that the operation can be continuously performed without any occurrence.

Although the external heating type heater is used as the heating means for the PET in the above embodiment, an internal heating type heater or a heating means other than the heater may be used. The supply position of the high-temperature high-pressure water to the high-temperature high-pressure reaction container 4 is located farther from the throttle valve 9 than the supply position of the molten PET, but the reverse is also possible. The bottom of the collector 11 is formed in a conical shape, but this is for facilitating the accumulation of precipitated solid terephthalic acid and for facilitating its removal. It is desirable to select the shape in consideration of this point. It is desirable that the collector 11 be equipped with a cooling means for keeping the water temperature constant. It is desirable that the filter 14 be equipped with a backwash means for preventing clogging.

[0041]

According to the present invention, PET is hydrolyzed,
When recovering the raw material monomer as the reaction product,
It is not necessary to increase the water content, and even if the water content is low (PET
Even if the ratio is high), the reaction product can be easily handled, the operation of recovering the raw material monomer can be continuously performed without causing the clogging of the piping, etc., and a sufficient hydrolysis rate can be obtained. Thus, the raw material monomer can be recovered at a high rate. That is, as compared with the case of the PET hydrolysis method using a twin-screw extruder, the hydrolysis rate is high and the recovery rate of the raw material monomer can be increased.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus for recovering raw material monomers from polyethylene terephthalate according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a cross-sectional shape of a high-temperature and high-pressure reaction container in a device for recovering raw material monomers from polyethylene terephthalate according to an example of the present invention.

[Explanation of symbols]

1--Feeder, 2--Heater, 3--High pressure pump, 4--High temperature and high pressure reaction vessel, 5--Water tank, 6--High pressure pump, 7--Check valve, 8--Heat exchanger, 9 --Throttle valve, 10--tube, 11--collector, 12--extraction means, 13--outflow hole, 14--filter, 15--distillation column.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C08L 67:02

Claims (2)

[Claims] 1. A screw is provided inside a tubular container having an inlet for introducing polyethylene terephthalate and water, and the polyethylene terephthalate and water are transferred while being continuously stirred by the rotation of the screw, and the reaction is performed under high temperature and high pressure. A high temperature and high pressure reaction container for discharging the reaction product to the outside of the cylindrical container through the outlet of the reaction product and a throttle valve connected to the outlet, a means for heating the high temperature and high pressure reaction container, and A high-pressure pump, which is connected to the inlet of water and supplies water under pressure to the high-temperature and high-pressure reaction vessel, and a tube which is connected to the inlet of the polyethylene terephthalate, which is high-temperature and high-pressure in the molten state of polyethylene terephthalate. A device for recovering raw material monomers from polyethylene terephthalate, comprising: 2. Polyethylene terephthalate in a molten state is supplied into a high temperature and high pressure reaction vessel under high temperature and high pressure and water is supplied under pressure, and polyethylene terephthalate and water are saturated at a temperature not lower than the melting point of polyethylene terephthalate and at that temperature. The reaction is carried out at a pressure higher than the water vapor pressure to hydrolyze polyethylene terephthalate, and the polyethylene terephthalate is transferred while being continuously stirred by the rotation of the screw in the high-temperature high-pressure reaction vessel. A method for recovering a raw material monomer from polyethylene terephthalate, which comprises discharging the reaction product containing the reaction product out of a high-temperature high-pressure reaction container through a discharge port of the reaction product and a throttle valve connected to the discharge port to recover the reaction product.