JP2000219728A - Production of polyethylene terephthalate resin for bottle from recovered pet bottle by solid-phase polymerization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily obtain a resin which can be molded again into bottles by subjecting pellets of recovered polyethylene terephthalate bottles to solid-phase polymerization in a continuous solid-phase polymerization vessel of an air-circulating vertical hopper type for a specified pellet dwell time at a specified polymerization vessel temperature at a specified amount of N2 gas blown in and a specified N2 gas purity to give a resin having a specified intrinsic viscosity. SOLUTION: The dwell time of pellets in the continuous solid-phase polymerization vessel is 4-10 hr; the temperature inside the polymerization vessel is increased from a pellet introduction port to a pellet discharge port in a simple manner in the range of 200-220 deg.C so that equations I and II are satisfied; the amount of an N2 gas blown in is 1.0-2.0 Nm3/hr/kg-pellet; and the N2 gas purity is 99-99.99%. Thus, a resin having an intrinsic viscosity of 0.7 or higher is obtained. In the formulas, T0 and TRT are the temperatures of the pellet introduction port and the pellet discharge port, respectively; and TRT/4 and TRT/2 are the temperatures of the positions at which the pellet dwell times are 1/4 and 1/2, respectively, of the total dwell time.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a recycled polyethylene terephthalate resin (hereinafter referred to as "PET resin") for producing a polyethylene terephthalate resin having a high degree of polymerization by solid-phase polymerization using a recovered PET bottle (a bottle made of polyethylene terephthalate resin) as a raw material. ). In particular, it relates to a method for producing a high-quality recycled PET resin that can be used again for molding a bottle.

[0002]

2. Description of the Related Art Bottles made of PET resin are superior in mechanical strength, transparency, gas barrier properties, etc. as compared with other resin containers, and also have higher mechanical strength and lighter weight than glass containers. It is widely used as a food and drink container and the like.

However, PET resin bottles are bulky and are not easily weathered. Therefore, disposal after use causes a serious pollution problem. On the other hand, incinerating used bottles is also not preferable in terms of increasing the burden on the incinerator and effective use of resources.
It is desirable to reuse the resin. In particular, in recent years, PET
With the increase in the amount of bottles used and the enforcement of the “Container and Packaging Recycling Law”, there is a strong social demand for the collection and reuse of PET bottles. Above all, in order to form complete recycling, it is most preferable to reuse for bottles.

[0004] In order to reuse the recovered bottle, the intrinsic viscosity value corresponding to the molecular weight is reduced in the melt extrusion step in bottle molding. Must be raised to a value suitable for melt molding and recovered.

Conventionally, many studies have been made on the solid-state polymerization of a new PET resin, which is called a virgin PET resin, in terms of equipment, process, reaction conditions, and the like. Is coming. That is,
The process of solid-state polymerization of pelletized PET resin under predetermined conditions using a hot-air circulation type vertical hopper-type continuous solid-state polymerization tank is adopted as the most influential method.

However, little consideration has been given to the solid-state polymerization of recovered PET resin. For a long time, Japanese Unexamined Patent Publication No.
It has been proposed to carry out solid-state polymerization of ET in a rotary kiln, but handling of fine powder is difficult, and at present, it is considered to be industrially difficult to employ.

On the other hand, in Japanese Patent Application Laid-Open No. 6-184291,
There is a proposal for solid-state polymerization after the recovery bottle is made into flakes. However, there are difficulties in handling the flake material and stability in the solid state polymerization step and the melt extrusion step in bottle molding, and the operability cannot be said to be good.

Further, Japanese Patent Application Laid-Open No. Hei 7-316919 discloses a method in which a polymerization catalyst dissolved in glycol is added to a recovered PET resin to form pellets, and the pellets are subjected to solid-state polymerization. In this method, there are unstable factors such as decomposition of PET by glycol and uniform mixing of the catalyst.

As described above, the study of solid-state polymerization for reusing the recovered PET resin is still insufficient at present.
At present, the equipment and conditions for the new PET resin are diverted without clear grounds, and it is desired to establish a suitable operation process unique to the recovered PET resin.

New P for solid phase polymerization process of recovered PET resin
One of the reasons that the ET resin cannot be diverted as it is is that the quality of pellets (referred to as raw material prepolymer or prepolymer) subjected to solid phase polymerization is different. That is, the quality of the recovered resin is deteriorated due to the thermal decomposition in the melt extrusion process in bottle molding and the melt extrusion process of the recovered bottle resin for pelletization. That is,
Not only is the intrinsic viscosity reduced, but also the number of terminal carboxyl groups and aldehydes is increased, and the color tone is deteriorated. An increase in the terminal carboxyl group results in a decrease in the polymerization rate, and the solid state polymerization conditions will be different from the new PET resin. In addition, it is necessary to apply milder conditions compared to the new resin so that the deterioration does not progress further during the long-term solid phase polymerization. When the use is for bottles, the quality requirements are particularly severe, and sufficient consideration must be given to setting the solid-state polymerization conditions.

[0011] In the case of the recovered PET resin, consideration must be given to the production cost more than the new resin. Of course, bottle collection has the significance of pollution control, but in order to promote the use of recycled PET resin, it is necessary to satisfy not only the above quality but also the cost requirement. Cost is an important factor in expanding the use of recycled PET resin, as is the case with the development of general new markets. Therefore, a thorough study for the purpose of cost reduction is required from a new viewpoint different from the new PET resin, such as equipment, process, and operating conditions. In particular, with regard to equipment and processes, it is not appropriate to easily divert the new resin as it is, and it is necessary to pursue cost reduction by adopting an optimal process for the recovered PET resin. Further, in the case of the recovered PET resin, the product quality is sensitive to the manufacturing conditions, the range of the optimum manufacturing conditions is narrow, and the product quality is easy to fluctuate. Therefore, the process stability is much larger than that of the new PET resin. Consideration is needed.

As described above, solid-phase polymerization of recovered PET resin is an important theme. In particular, although there is much room for improvement as an industrial process, there are still many technical problems. Is currently lacking.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and uses a recovered PET bottle (a bottle made of polyethylene terephthalate resin) as a raw material to produce a high-polymerized recycled PET resin by solid-state polymerization. The present invention provides a low-cost and stable production method for producing a. In particular, the present invention provides a method for producing a recycled PET resin that can easily produce a high-quality resin that can be used again for molding a bottle.

[0014]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a high-quality recycled PET resin can be obtained by performing solid-phase polymerization under the following specific conditions. I found something.

According to the present invention, the intrinsic viscosity of a solvent of an equal weight mixture of phenol and tetrachloroethane is 0.1.
In a method of producing 7 or more polyethylene terephthalate (PET) resins by solid-state polymerization using a recovered PET bottle as a raw material, a hot-air circulating vertical hopper type continuous solid-state polymerization tank is used for molding the recovered PET bottle into pellets. In performing the solid-state polymerization in, the residence time of the pellets in the continuous solid-state polymerization tank is 4 to 10 hours, and the temperature inside the continuous solid-state polymerization tank is 200 to 220 ° C.
Within the range, a monotonic increase from the pellet inlet to the pellet outlet is obtained, and the following formulas (1) and (2) are satisfied.
2.0 Nm ³ / hr, and a nitrogen gas purity of 99% or more and less than 99.999%.

[0016] _{0.3 ≦ (T RT / 4 -T} o) / (T RT -T o) ≦ 0.8 (1) 0.6 ≦ (T RT / 2 -T o) / (T RT -T _o ) ≦ 0.95 (2) where, T _o : temperature at the pellet inlet of the continuous solid-state polymerization tank, T _RT : temperature at the pellet outlet of the continuous solid-state polymerization tank, T _{RT / 4} : pellet retention Elapsed time is 1 of total residence time
/ 4, _{TRT / 2} : The residence time of the pellets is 1 of the total residence time.
/ 2 temperature.

According to the present invention, in the solid-state polymerization step for producing a recycled PET resin, a new PET resin (Virgin P
It has been found that much lower purity nitrogen gas can be used than in the solid-state polymerization process for producing ET resin). In particular,
Good results were obtained only in a specific narrow range of the nitrogen gas blowing rate.

In a general solid-state polymerization step of PET resin, the purity of nitrogen gas used is at least 99.9.
99% is required, and the larger the amount of nitrogen gas blown, the faster the polymerization rate and the less coloring, and it is naturally considered that the same applies to recycled PET resin.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.

In the present invention, PE used for solid-state polymerization
As the T resin, that is, as the prepolymer, a pellet-shaped resin having an intrinsic viscosity of 0.60 to 0.72 obtained by reshaping a recovery bottle is used.

The term "recovery bottle" refers to a bottle once used as a container and then collected from a distribution or consumption route, but also includes a bottle that is not used but is collected as waste without being used. The collection bottle is mainly a beverage container, but may be used for other purposes.

For re-forming into pellets, the recovered bottle is generally formed into flakes by washing, crushing, etc., and then melt-extruded into pellets. By making it into a pellet form, the handleability in the solid-state polymerization step becomes good, and stable production is possible in operation.

The prepolymer pellet has an intrinsic viscosity of 0.60.
~ 0.72 is used. If it is less than 0.60, the solid-state polymerization takes a long time and the quality of the product pellets deteriorates. Alternatively, the desired intrinsic viscosity may not be reached even when solid phase polymerization is performed. On the other hand, 0.7
If it is greater than 2, relatively good results may be obtained without applying the present invention. The present invention relates to a prepolymer having an intrinsic viscosity of 0.60 to 0.72, which has the necessity and significance of solid-phase polymerization, and hardly obtains good results under ordinary processes and conditions.

The PET resin to be subjected to the solid phase polymerization generally contains a catalyst and contains a stabilizer such as an oxidation stabilizer. The recovered PET bottles are mainly used for beverages such as tea and soft drinks or for seasonings such as soy sauce. Therefore, as a catalyst contained in the PET resin subjected to solid-state polymerization,
Mainly germanium compounds with low toxicity. However, other catalysts may be mixed. PET for solid state polymerization
The resin may contain a modifying monomer as a copolymerized unit in the polymer chain in addition to diethylene glycol generated by a side reaction during the production of the PET resin.

As the solid phase polymerization apparatus, a hot air circulation type vertical hopper type continuous solid phase polymerization tank is used. This polymerization tank is the most excellent solid-state polymerization apparatus overall in terms of equipment and operation cost, operation stability, product pellet quality and the like.

As a means for removing and removing ethylene glycol (EG) and water from the prepolymer in order to promote the polymerization reaction and increase the intrinsic viscosity, there are vacuum decompression or hot air supply systems, but industrially, hot air systems are used. It is suitable. Nitrogen gas is used as a hot gas for this purpose, high-temperature nitrogen gas is supplied from the lower part of the polymerization tank, and discharged from the upper part to the outside of the polymerization tank. From the discharged gas, mixed impurities are removed by an appropriate means, and the gas is again circulated to the polymerization tank.

In this polymerization tank, a drying step or a crystallization step and a drying step are generally connected as a preceding step. In any case, a prepolymer sufficiently dried and low in water content is supplied to the solid-state polymerization tank to prevent hydrolysis. Further, as a post-process, a process of cooling and taking out the product pellets is connected.

The product pellets of the present invention are mainly used for bottles. Although it may be used for other purposes, it is an object of the present invention to make it possible to regenerate and use a resin from a collected bottle for a bottle with strict quality requirements, and to realize complete recycling.

In order to produce a bottle from the product pellets of the present invention, the bottle may be mixed with pellets of a new PET resin, but a bottle of good quality can be obtained by using the pellets of the product alone.

The inherent viscosity (intrinsic viscosity) of the product pellets is intended to be in the range of 0.72 to 0.85. This range is a range desired for bottle molding. According to the present invention, pellets having an intrinsic viscosity necessary for bottles can be obtained even from recovered PET resin. In addition, the present invention, the starting value and the target value of the intrinsic viscosity are within a predetermined narrow range, by applying specific limited solid-state polymerization conditions and the like, the recovered resin is also recycled for bottles in an industrial sense,
It has been found that it can be used.

PET in the solid-state polymerization tank according to the present invention
The residence time of the resin is preferably 4 to 10 hours, particularly preferably 5 to 8 hours. If the time is shorter than 4 hours, the increase in the intrinsic viscosity is insufficient. On the other hand, if the time is longer than 10 hours, not only is it economically disadvantageous, but even if the intrinsic viscosity increases, the quality deteriorates due to thermal decomposition, or Decomposition may be so severe that the intrinsic viscosity may rather decrease. The effect of thermal deterioration is greater than that of the prepolymer in the case of the new PET resin, and the suitable range of the residence time is narrowly limited.

The reaction temperature in the solid-state polymerization tank is 200 to
220 ° C., particularly preferably 203 to 217 ° C., is preferred. 200
If the temperature is lower than 220 ° C., solid phase polymerization does not proceed. In the recovered PET, the history of thermal decomposition such as the bottle forming process has already been added, and it is necessary to employ a narrow range and low temperature conditions in order to avoid further thermal deterioration.

Further, it is necessary to strictly control not only the absolute value of the reaction temperature but also the temperature distribution in the polymerization tank. First, it is assumed that the temperature rises monotonously from near the pellet inlet to near the outlet of the solid-state polymerization tank. A monotonous increase in temperature is most favorable for an increase in intrinsic viscosity.
It is a condition with little coloring and it is easy to control the temperature.

Next, it is necessary that the temperature distribution in the polymerization tank satisfies the following two equations.

0.3 ≦ (T _{RT / 4} −T _o ) / (T _RT −T _o ) ≦ 0.8 (1) 0.6 ≦ (T _{RT / 2} −T _o ) / (T _RT −T _o ) ≦ 0.95 (2) Preferably, 0.4 ≦ (T _{RT / 4} −T _o ) / (T _RT −T _o ) ≦ 0.7 (3) 0.7 ≦ (T _{RT / 2} − T _o ) / (T _RT −T _o ) ≦ 0.9 (4) where T _o : temperature of the pellet inlet of the continuous solid-state polymerization tank, T _RT : temperature of pellet outlet of the continuous solid-state polymerization tank In other words, the temperature at the time when the total retention time (Retention Time) has elapsed, _{TRT / 4} : the elapsed time of the pellet residence time is 1 of the total residence time.
/ 4, _{TRT / 2} : The residence time of the pellets is 1 of the total residence time.
/ 2 temperature.

If the value of (T _{RT / 4} -T _o ) / (T _RT -T _o ) or (T _RT -2 -T _o ) / (T _RT -T _o ) is smaller than the scope of the present invention, Insufficient viscosity increase, or
Even if the intrinsic viscosity increases, the value fluctuates and the hue deteriorates. On the other hand, when the value of (T _{RT / 4} -T _o ) / (T _RT -T _o ) or (T _RT -2 -T _o ) / (T _RT -T _o ) is larger than the range of the present invention, the intrinsic viscosity is increased. Coloring is observed even if the temperature rises. The elapsed time of the pellets in the tank can be calculated and determined from the volume, the production amount, and the position in the tank of the solid-state polymerization tank. For example, the pellet inlet is 0 hour, and the outlet corresponds to the polymerization tank residence time, that is, the polymerization time.

In the recovered PET resin, it is necessary to prevent decomposition as much as possible in comparison with the new PET resin. It has been found that, for the first time, the use of these temperature conditions makes it possible to shorten the polymerization time and prevent the deterioration of the product pellets, and also to achieve the stabilization of the product intrinsic viscosity. The temperature in the polymerization tank can be controlled by adjusting the supply conditions of the hot air gas, that is, by adjusting the supply method (batch or division), the supply position, the gas temperature, the gas flow rate, and the like. Also, of course, in the solid-state polymerization tank of the present invention, the pellet inlet is at the upper part of the layer and the outlet is at the lower part of the layer.

In the present invention, the supply source of the circulating gas is 99% or more and less than 99.999%, preferably 9% or less.
9.9 to 99.99% of new nitrogen gas is used. The nitrogen gas is produced by a cryogenic separation method, a membrane separation method, an adsorption separation method or the like.

According to the present invention, it has been found that, in the solid-state polymerization of the recovered PET resin, if the conditions of the present invention are satisfied, a high-quality product can be obtained even if the purity of nitrogen is reduced. In fact, in the solid-state polymerization of the new PET resin, nitrogen gas having a purity of 99.9999% or more is used. This is because the presence of oxygen as an impurity in the nitrogen gas causes an oxidative decomposition reaction during the solid-phase polymerization, so that it was common sense to use high-purity nitrogen gas. The reason why inexpensive and low-purity nitrogen gas can be used may be due to the delicate correlation with acetaldehyde and the like generated from the recovered PET resin, but the true reason is not clear.

If the purity of the nitrogen gas is 99% or less, the degradation reaction proceeds too, so that good quality product pellets cannot be obtained. On the other hand, use of a purity of 99.999% or more is not preferable because the product quality is not particularly improved and the cost of nitrogen gas increases.

Nitrogen gas discharged from the upper part of the tank while coming into contact with the pellets while passing through the solid-state polymerization tank is released from ethylene glycol (EG), water, acetaldehyde and PET oligomers, and fine particles of the pellets, which are released during the solid-state polymerization reaction. When the exhausted nitrogen gas is recirculated and used because it contains debris and the like, the impurities and contaminants have an adverse effect, so that removal and purification are required. For example, solid state polymerization is an equilibrium reaction,
When ethylene glycol or water is present, the progress of the reaction is suppressed.

In the present invention, the nitrogen gas is purified by passing the discharged nitrogen gas through a water flow scrubber. Ethylene glycol, acetaldehyde, etc. are absorbed and removed by contact with a water stream. Conventionally, solid phase polymerization of new PET resin pellets uses an EG scrubber that uses ethylene glycol as an absorbing solution. However, since ethylene glycol that has absorbed impurities is reused, a process for purifying and circulating ethylene glycol is required. Met. Therefore, except for a specific factory having an ethylene glycol refining facility, extra costs are required for process construction and operation management, which has caused a cost increase. The present invention has succeeded in purifying nitrogen gas discharged by a water flow scrubber without using an EG scrubber as a result of intensive studies on the device specifications and operating conditions. Furthermore, in the case of recovered PET resin,
It has been found that the refining effect of the stream scrubber shows a rather good tendency compared to the EG scrubber. It is assumed that the content and amount of the impurities to be mixed and the absorbent are related.

The water flow scrubber of the present invention has a multi-stage structure having a plurality of absorption water supply sections so as to be able to supply absorption water having different temperatures, and is provided in a lower supply section which comes into contact with nitrogen gas discharged from the polymerization tank first. Supplies relatively high-temperature water, and low-temperature water to the upper-stage supply section which comes into contact later. With this method, the supply of low-temperature water can be reduced, and utility costs are reduced.

The nitrogen gas temperature at the upper outlet of the scrubber is:
The temperature is set at 6 to 15 ° C, preferably 7 to 13 ° C. The lower the temperature, the more impurities such as EG are removed and reduced.
Even if it is less than the above, the effect of increasing the solid-state polymerization rate is not large, and the cooling cost is increased, which is not preferable. On the other hand, 15
Above ° C, the effect of removing impurities is insufficient, and the polymerization rate and product pellet quality are reduced.

The nitrogen gas purified by passing through a water flow scrubber is then subjected to water removal through an adsorption layer having a silica gel layer and a molecular sieve layer. First, most of the water is removed by a silica gel layer, and then highly dehydrated by a molecular sieve layer. Combination of the composite adsorbent layer and the above-mentioned water scrubber allows ethylene glycol,
The object of the present invention can be achieved by efficiently removing water, acetaldehyde and the like at low cost. Note that the composite adsorption layer of the present invention can maintain its effect for a long time,
It is used as a moisture absorber consisting of a plurality of the units, and alternately performs adsorption and desorption regeneration cycles.

Next, the purified nitrogen gas is heated to a solid-state polymerization temperature to be supplied to a solid-state polymerization tank to generate hot air gas.

The supply of hot blast gas to the solid state polymerization tank is 1.0
２．０2.0 Nm ³ / resin kg · hr, preferably 1.2〜
It is carried out at 1.8 Nm ³ / kg of resin · hr. 1.0 Nm ³ /
If the resin is not more than kg · hr, the effect of accelerating solid phase polymerization is insufficient. On the other hand, at 2.0 Nm ³ / kg / hr or more of the recovered PET resin, unlike the new PET resin, the solid-state polymerization rate tends to be rather lowered, and the quality of the product pellet is slightly deteriorated. It is considered that the recovery history of the recovered PET resin is long, and the amount of the active catalyst is reduced, or it is also considered to be the influence of the separated material from the recovered PET resin and the quality characteristics of the circulating nitrogen in the present invention, but the reason is not clear. .

The nitrogen circulating in the solid-state polymerization tank and the nitrogen gas purification system is partially discharged to the outside of the solid-state polymerization system and reduced during the circulation. Secure the supply amount to the tank. The newly supplied nitrogen gas has a purity of 99 to 99.999% as described above.

[0049]

Next, the present invention will be described in detail with reference to examples. In the examples, the intrinsic viscosity was measured at a temperature of 30 ° C. using an equal weight mixture of phenol and tetrachloroethane as a solvent, and expressed in units of dl / g. The hue of the product pellet is
Good, slightly colored, slightly colored and colored large. FIG. 1 shows a typical example of the solid-state polymerization process in the present invention, and FIG. 2 shows a typical example of a preferable temperature distribution range in the solid-state polymerization tank.

In FIG. 1, a solid-state polymerization tank 1 is a hot-air circulation type vertical hopper type continuous solid-state polymerization tank. The pellets sufficiently dried from the crystallization / drying tank 2 are introduced into the pellet inlet 8.
Supply more continuously. The pellets that have been sequentially moved downward in the solid-state polymerization tank are discharged to the pellet cooling tank 3 through the pellet outlet 9. The solid-phase polymerization tank 1 has a plurality of temperature detectors 12a, 12b, 12c, 12d, etc., for detecting the temperature at each position.

Hot air nitrogen gas is supplied from the lower gas inlet 10 into the solid-state polymerization tank, and flows upward in a countercurrent to the falling pellets to perform solid-state polymerization. Discharge. The discharged nitrogen gas is supplied to the absorption water supply unit 13.
It is introduced into the lower part of the water flow scrubber 4 having a and 13b, purified by contact with the aqueous phase, and discharged from the gas outlet 14 at the upper part of the water flow scrubber. Then, silica gel layer 1
The water is supplied to the dehumidifier 5 having the molecular sieve layer 5 and the molecular sieve layer 16 to remove water. Subsequently, the nitrogen gas is heated by the heater 6 to generate hot air gas. When passing through these routes, a part of the nitrogen gas is discharged to the outside of the solid-state polymerization system and the amount of the gas is reduced. Therefore, the nitrogen gas is newly supplied from the nitrogen gas supply source 7. Next, hot-air nitrogen gas is supplied to the solid-state polymerization tank from the gas inlet 10 below the solid-state polymerization tank to form a gas circulation system.

In FIG. 2, curves 1 and 2 are examples showing the upper and lower limits of the temperature distribution of the present invention, respectively. In order to exhibit the effect of the present invention, T _{RT / 4} (1 /
It is necessary that _{T.sub.RT / 2} (temperature at one-half residence elapsed time) and _{T.sub.RT / 2} (temperature at one-half residence elapsed time) be within the range of the arrow lines at both ends.

Example 1 A bottle used for soft drink was collected, washed, crushed,
After drying, it is re-melted and molded using a melt extruder and a pelletizer, having an intrinsic viscosity of 0.67, a diameter of about 3 mm, and a length of 4 mm.
Was obtained and supplied to the solid-phase polymerization system shown in FIG. Regarding the conditions in the solid-state polymerization tank 1, the residence time (RT) of the pellet is 6
Time, the temperature near the pellet inlet (T _o ) was 205 ° C., the temperature near the pellet outlet (T _RT ) was 215 ° C., TRT _{/ 4} in the tank temperature distribution was 210.5 ° C., and T _{RT / 2} was 213.5. ℃ i.e. _{(T RT / 4 -T o)} / (T RT -T o) 0.55,
(T _{RT / 2} −T _o ) / (T _RT −T _o ) was set to 0.85, and the hot air nitrogen gas flow rate was set to 1.5 Nm ³ / kg of resin · hr. Next, the nitrogen gas discharged from the gas outlet at the top of the tank was supplied to the water flow scrubber 4. Absorbed water at 30 ° C. and 4 ° C. was supplied into the scrubber from the lower supply part and the upper supply part, respectively, and the gas temperature at the scrubber outlet was set at 8 ° C.
Nitrogen gas before the gas inlet of the scrubber contained 110 ppm of ethylene glycol and acetaldehyde 3 as impurities.
Although it contained 2 ppm, it decreased to 5 ppm of ethylene glycol and 1 ppm of acetaldehyde after the gas outlet. This refining effect is not inferior to EG scrubber,
Rather good. Subsequently, the purity of 9 was obtained from the nitrogen gas supply source.
After supplying 9.99% of new nitrogen gas and passing through a dehumidifier 5 having a silica gel layer and a molecular sieve layer, the mixture was heated by a heater 6 and circulated and supplied to the solid phase polymerization tank 1. The intrinsic viscosity of the product pellets discharged from the cooling tank 3 was stable at 0.77, and the hue was good. When a bottle for soft drinks was produced using the pellets of the present recycled PET resin, there was no particular problem in the molding process, and a bottle of good quality was obtained.

[0054]

[Table 1] Examples 2 and 3 and Comparative Examples 1 and 2 Solid phase polymerization was carried out in the same manner as in Example 1 except that the temperature distribution in the solid phase polymerization tank was changed, and the results are shown in Table 1. In Example 2 of the present invention, there was no particular problem except for slight coloring, and Example 3 except for a slight change in intrinsic viscosity. On the other hand, in Comparative Example 1, which is outside the scope of the present invention, the coloring was large, and in Comparative Example 2, the increase in the intrinsic viscosity was small, and it was recognized that the intrinsic viscosity slightly fluctuated.

Examples 4 to 5 and Comparative Examples 3 to 4 The residence time in the solid-state polymerization tank was changed, and
/ 2 residence elapsed time has changed, but T _o , T _{RT / 4} , T
_{RT / 2} and T _RT remain unchanged, ie (T _{RT / 4} −T _o ) /
Solid-state polymerization was carried out in the same manner as in Example 1 except that the values of (T _RT -T _o ) and (T _RT -2 -T _o ) / (T _RT -T _o ) were not changed. . In Example 4 where the residence time was 4.5 hours, the intrinsic viscosity of the product pellet was 0.74, and the hue was good. In Example 5 for 9 hours, the product intrinsic viscosity was 0.7
9, indicating that the hue was slightly colored. In Comparative Example 3 for 3 hours, the intrinsic viscosity was as low as 0.71.
In Comparative Example 4 for 11 hours, the intrinsic viscosity was 0.79, but the coloring was large.

Examples 6-7 and Comparative Examples 5-6 The upper and lower temperatures in the solid state polymerization tank were changed,
_{RT / 4} and T _{RT / 2} were changed, but (T _{RT / 4} −T _o ) / (T
_RT -T _o) and _{(T RT / 2 -T o)} / (T RT value of -T _o) without changing, and was subjected to solid phase polymerization in the other conditions similarly as in Example 1. In Example 6 in which the temperature near the pellet inlet was 202 ° C and the temperature near the outlet was 215 ° C, the product intrinsic viscosity was 0.74 and the hue was good. The temperature near the inlet is 2
In Example 7 in which the temperature near the outlet was 218 ° C. at 05 ° C.,
The intrinsic viscosity was 0.78, and the color was slightly colored. Temperature near inlet 195 ° C, temperature near outlet 215 ° C
In Comparative Example 5, the intrinsic viscosity was as low as 0.71. The temperature near the inlet was 205 ° C and the temperature near the outlet was 2 ° C.
In Comparative Example 6 at 25 ° C., the intrinsic viscosity was 0.79, but the coloring was large.

Examples 8 to 9 and Comparative Example 7 Solid-state polymerization was carried out in the same manner as in Example 1 except that the purity of the new nitrogen gas as a supply source of the circulating gas was changed. In Example 8 having a purity of 99%, the intrinsic viscosity of the product was 0.75, which was a degree of slight coloring. 99.9 purity
%, The intrinsic viscosity was 0.76 and the hue was good. Comparative Example 7 having a purity of 98%
In this case, the intrinsic viscosity was 0.69 and the coloring was large.

Examples 10 to 11 and Comparative Examples 8 to 9 Solid state polymerization was carried out in the same manner as in Example 1 except that the amount of hot air gas circulated to the solid state polymerization tank was changed. In Example 10 in which the gas supply amount is 1.1 Nm ³ / resin kg · hr,
The product intrinsic viscosity was 0.75 and the hue was good.
In Example 11, in which the gas supply amount was 1.9 Nm ³ / kg of resin · hr, the intrinsic viscosity was 0.77, and the color was slightly colored. Gas supply rate is 0.7 Nm ³ / resin k
In Comparative Example 8 where g · hr, the intrinsic viscosity was 0.73, and the polymerization rate was considerably inferior to Example 1. Further, in Comparative Example 9 in which the gas supply amount was 2.5 Nm ³ / kg of resin · hr, the intrinsic viscosity was 0.76, which was slightly colored.

Examples 12 and 13 and Reference Example 1 Example 1 was repeated except that the gas temperature at the outlet of the water stream scrubber was changed.
Solid state polymerization was carried out in the same manner as described above. Outlet gas temperature is 6.5
In Example 12 at a temperature of ° C., the concentration of ethylene glycol in the gas after the gas outlet was 5 ppm, the concentration of acetaldehyde was 1 ppm, the intrinsic viscosity of the product was 0.77, and the hue was good. In Example 13 in which the outlet gas temperature was 14 ° C., the concentration of ethylene glycol in the gas after the gas outlet was 14 ppm, the concentration of acetaldehyde was 2 ppm, the intrinsic viscosity was 0.75, and the pellets were slightly colored. Was. In Reference Example 1 in which the outlet gas temperature was 20 ° C., the concentration of ethylene glycol in the gas after the gas outlet was 20 ppm, the concentration of acetaldehyde was 4 ppm, the intrinsic viscosity was 0.73, and the coloring was large.

Reference Examples 2 and 3 Solid phase polymerization was carried out in the same manner as in Example 1 except that the constitution of the adsorption layer of the moisture absorber was changed. In Reference Example 2 in which only the silica gel layer was used as the adsorption layer, the product intrinsic viscosity was 0.72, and the polymerization rate was considerably inferior to Example 1. Further, in Reference Example 3 in which only the molecular sieve was used as the adsorption layer, a tendency that the increase in the intrinsic viscosity became small with the elapse of the operation time was recognized.

[0061]

According to the present invention, using a polyester resin from a recovery bottle, industrially, low cost and stable,
High intrinsic viscosity pellets for bottles can be obtained, and PET resin for bottles can be recycled.

[Brief description of the drawings]

FIG. 1 is a model diagram showing a configuration example of a solid-state polymerization system of the present invention.

FIG. 2 is a diagram showing an example of a suitable temperature distribution range in the solid-state polymerization tank of the present invention.

[Explanation of symbols]

1: solid-state polymerization tank, 2: crystallization / drying tank, 3: cooling tank,
4: water flow scrubber, 5: dehumidifier, 6: heater, 7: nitrogen gas supply source

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Yasuyuki Nagatsuna 304 Hishie, Higashi-Osaka-shi, Osaka F-term (reference) 4J029 AA03 AB04 AC01 AD01 AE01 BA03 CB06A KD01 KD02 KD09 KD17 KE12 KJ03

Claims (5)

[Claims] 1. A polyethylene terephthalate (PET) resin having an intrinsic viscosity of 0.7 or more when an equal weight mixture of phenol and tetrachloroethane is used as a solvent,
In a method of manufacturing a T bottle as a raw material by solid phase polymerization, using a recovered PET bottle formed into a pellet,
In performing the solid-phase polymerization in a hot-air circulation type vertical hopper type continuous solid-state polymerization tank, the residence time of the pellet in the continuous solid-state polymerization tank is 4-1.
0 hours, and the temperature inside the continuous solid-state polymerization tank monotonically increases from the pellet inlet to the pellet outlet within the range of 200 to 220 ° C., and satisfies the following formulas (1) and (2). And the nitrogen gas blowing rate is 1.0 kg / kg pellet.
A ~2.0Nm ³ / hr, and wherein the nitrogen gas purity is less than 99.999% 99% or more, a manufacturing method of recycled polyethylene terephthalate resin. 0.3 ≦ (T _{RT / 4} −T _o ) / (T _RT −T _o ) ≦ 0.8 (1) 0.6 ≦ (T _{RT / 2} −T _o ) / (T _RT −T _o ) ≦ 0.95 (2) where, T _o : temperature of the pellet inlet of the continuous solid-state polymerization tank, T _RT : temperature of the pellet outlet of the continuous solid-state polymerization tank, T _{RT / 4} : residence time of the pellets , One of the total residence time
/ 4, _{TRT / 2} : The residence time of the pellets is 1 of the total residence time.
/ 2 temperature. 2. The nitrogen gas discharged from the continuous solid-state polymerization tank is passed through a water flow scrubber and an adsorption and absorption tank, and then heated and circulated and supplied to the continuous solid-state polymerization tank. 2. The method for producing a recycled polyethylene terephthalate resin according to item 1. 3. The water-flow type scrubber is a multi-stage water-flow scrubber having absorption water supply units having different temperatures, wherein the temperature of the nitrogen gas at the discharge port is 6 to 15 ° C. A method for producing the recycled polyethylene terephthalate resin according to the above. 4. A pellet formed from a recovered PET bottle is a resin having an intrinsic viscosity of 0.60 to 0.72, and the obtained recycled polyethylene terephthalate resin has an intrinsic viscosity of 0.72 to 0.85. The method for producing a recycled polyethylene terephthalate resin according to claim 1, wherein the resin is a bottle resin. 5. The method according to claim 1, wherein the temperature distribution in the continuous solid-state polymerization tank satisfies the following expressions (3) to (4).
A method for producing the recycled polyethylene terephthalate resin according to the above. 0.4 ≦ (T _{RT / 4} −T _o ) / (T _RT −T _o ) ≦ 0.7 (3) 0.7 ≦ (T _{RT / 2} −T _o ) / (T _RT −T _o ) ≦ 0.9 (4)