KR100880465B1 - Method for solid-state polymerization of waste polyester and apparatus therefor - Google Patents

Abstract

The present invention relates to a solid phase polymerization method and apparatus for waste polyester flakes, wherein after the flakes are loaded in the solid phase polymerization reactor by size, different reaction temperatures are applied according to the size of the flakes, but the smaller the flake size, the lower the reaction temperature. According to this, the molecular weight deviation of the flakes according to the particle size after the solid phase polymerization is minimized to obtain a uniformity of the molecular weight quality of the recycled pellets.

Description

Method for solid-state polymerization of waste polyester flakes and apparatus therefor}             

1 is a cross-sectional view of a cylindrical solid state polymerization reactor according to an embodiment of the present invention,

FIG. 2 shows the shape of a screen installed in the device of FIG. 1, in which FIG. 2A shows an upper screen, FIG. 2B shows an intermediate screen, and FIG. 2C shows a lower screen.

* Explanation of symbols for main parts of the drawings

10: solid state polymerization reactor

S1, S2, S3: Screen

H1, H2, H3, H4: heating means

11,12,13,14: reaction part

The present invention is a method of reusing PET molded from polyethylene terephthalate (hereinafter referred to as 'PET'), and the waste PET container is cut into flakes, followed by solid state polymerization and re-extrusion. The present invention relates to a device capable of reducing molecular weight differences by grain size of flakes after solid state polymerization in a method of reusing pelletizing.

PET is widely used as a fiber, a beverage container, a film, a tire cord. Among them, PET consumption as a material of a container such as a beverage bottle is increasing very rapidly. Recently, with increasing interest in environmental issues, various methods of reusing used waste PET containers have been developed. One of the most attention among the methods, the waste PET container is finely cut into scrap (flake) flakes (solid), solid-phase polymerization, re-extruded pellets and reused.

In this method, the flakes are obtained by cutting waste containers, so that the size and properties of each grain, for example, the density and the elongated state of the material, are not uniform, and the non-uniformity of these sizes and physical properties is the same under which the flakes are subsequently subjected to solid phase polymerization. In the polymerization conditions of the will cause a difference in the polymerization rate. As a result, the flakes after the completion of the solid-state polymerization, the molecular weight difference is noticeable by granules, the use of such materials will not be able to avoid the occurrence of defective products.

Therefore, in view of the above-mentioned problems of the prior art as described above, it is a technical problem to provide a recycled pellet having a uniform molecular weight from a waste PET container.

In the study for solving the above problems, the inventors of the present invention suggest that the solid phase polymerization rate is larger as the surface area relative to the volume of the grains, so that the byproducts in the grains are easily diffused during the polymerization and the solid phase polymerization rate is faster. In view of the high speed and high molecular weight after solid phase polymerization, flakes are classified by size before solid phase polymerization, and granules of similar size are placed at similar sites in the solid phase polymerization reactor during solid phase polymerization, By operating differently, it was confirmed that the difference between the grains of the final molecular weight after the solid phase polymerization and the uniformity of the molecular weight quality of the regenerated pellets was confirmed to complete the present invention.

Therefore, according to the present invention, in the solid phase polymerization method of the flakes obtained by cutting and / or crushing the waste PET container, the flakes are loaded into the solid phase polymerization reactor by size, and different reaction temperatures are applied according to the size of the flakes. The smaller the size, the lower the reaction temperature, there is provided a solid phase polymerization method of the waste PET flakes.

In addition, according to the present invention, as one of the preferred solid phase polymerization reactor of the waste PET flakes for implementing the above method, one or more screens for horizontally dividing the inside of the cylindrical reactor, and each reaction unit divided into screens at different temperatures Provided is a solid phase polymerization apparatus for waste PET flakes, comprising heating means for heating the furnace.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

1 to 2 schematically illustrate a cylindrical solid phase polymerization reactor according to one embodiment of the present invention. The solid-state polymerization reactor shown is an example of having four reaction sections 11, 12, 13, 14 divided by three screens S1, S2, S3, but two reactions by one screen if desired. It may be made into the division divided into parts, and may have a plurality of reaction parts divided by two or more, More preferably, two to five screens. When dividing the solid state polymerization reactor into two or more screens, it should be noted that each screen should have a different mesh size so that the particle size of the flakes charged to each reaction section is different.

As can be seen from FIG. 1, the cylindrical solid-state polymerization reactor 10 has four reaction parts 11, 12, 13, and 14 divided by three screens S1, S2, and S3. As illustrated in FIGS. 2A to 2C, the upper screen S1 has the largest mesh size (mesh size) and the lowest screen S3 has the smallest mesh size among the screens. Waste PET flakes supplied to the first reaction part 11, the second reaction part 12, the third reaction part 13, and the fourth reaction part 14 due to the separation of the screens S1, S2, and S3. In the order of) it is gradually filled with a smaller particle size. At this time, in order to facilitate the separation of the waste PET flakes, a vibration means (not shown) may be installed in the solid-state polymerization reactor (10). In such a configuration, when the flakes are injected from the top of the reactor and the vibrating means is used to vibrate the reactor, it is easy to position the flakes at different heights of the reactor by size.

In addition, the heating means (H1, H2, H3, H4) for each of the reaction parts (11, 12, 13, 14) of the solid-state polymerization apparatus, wherein each heating means can heat each reaction part at a different temperature. It is designed to be. For example, each heating means may be configured in the form of a steam jacket, an electric heater surrounding each reaction unit. It should be noted that the smaller the particle size of the flakes charged in the reaction section, the lower the solid phase reaction temperature from the heating means. The reason is that the solid phase polymerization rate is the larger the surface area relative to the volume of the flake particles, the easier the diffusion of by-products in the granules during polymerization, and the higher the solid phase polymerization rate, the smaller the flake particle size is, the faster the solid phase polymerization rate is. Since the molecular weight is obtained, in order to ensure that the flakes discharged after the solid state polymerization in each reaction part have a uniform molecular weight, the flakes having a relatively large particle size are reacted at a relatively high temperature and the flakes having a relatively small particle size have a relatively low temperature. This is because the difference in solid state polymerization rate of the flakes charged to each reaction unit must be reduced.

In general, PET solid state polymerization reactors require a temperature condition of 200-220 ℃ in common, but a vacuum device is used to remove ethylene glycol or water, which are volatile by-products generated during the polymerization reaction, out of the reactor. It can be divided into two types, a closed system or an open system circulating an inert gas (mostly nitrogen). In general, in the case of an open system, the reactants are continuously injected into the reactor at a constant injection rate and piled up toward the bottom of the reactor for a predetermined time, while the polymerized product exits the reactor at the bottom of the reactor. It is not applicable to equations, but has restrictions that apply only to batch methods.

That is, in the case of a closed system using a vacuum device, in addition to the line connected to a vacuum pump, the reactor is blocked outside from the outside, the reactor is rotated, and a vacuum is applied to react. In this case, the raw material flakes are injected from the top of the reactor in a state where the cylindrical reactor is made upright, screened by size, and then the cylindrical reactor is horizontally laid down and rotated in the circumferential direction of the cylinder. You can proceed.

Next, in the case of an open system in which an inert gas such as nitrogen is circulated and the reaction proceeds, the raw material flakes are injected from the upper part of the reactor while the cylindrical reactor is placed vertically in the height direction, and the sieve is separated by size. (screening), the reaction can proceed by circulating an inert gas such as nitrogen without changing the position of the cylindrical reactor. In this case, however, the nitrogen gas cannot be operated in a continuous system even though it is an open system, and there is a restriction in that it must be operated in a batch manner. In other words, even when using a nitrogen-type open-type reactor, the reaction is not operated continuously in which the flakes of reactants are continuously injected and the polymerized product exits, and once the reactants are vibrated at the top of the reactor. The present invention can be applied only in a batch manner in which the reaction is started after injecting and sifting and the reaction is terminated after a certain time.

Features and other advantages of the present invention as described above will become more apparent from the following examples. However, the present invention is not limited to the following examples.

Example 1

As shown in FIG. 1, the solid-state polymerization is divided into four reaction parts by three screens (upper screen: horizontal × vertical 5 × 5 mm, middle screen: horizontal × vertical 3 × 3 mm, lower screen: horizontal × vertical 1 × 1 mm). 1 kg of waste PET flakes were added to the reactor, followed by sieving, and the reaction parts were solid-phase polymerized at different temperatures for 5 hours. At this time, the solid phase polymerization method used a vacuum closed system. The flake particle size and the temperature of the reaction part charged in each reaction part are shown in Table 1. In addition, the intrinsic viscosity (IV) of the flakes before and after solid phase polymerization was measured. The results are also shown in Table 1.

Reaction part Filling Flakes Particle Size (mm) Reaction part temperature (℃) Flake IV Maximum IV Deviation by Region Solid state polymerization After solid state polymerization First reaction part 11 5 or more 208 0.70 0.79 0.03 Second reaction part 12 3 to 5 205 0.71 0.81 Third reaction part 13 1 to 3 202 0.70 0.82 Fourth reaction part 14 1 or less 200 0.69 0.80

Example 2

The waste PET flakes were solid-phase polymerized under the same conditions as in Example 1 except that the nitrogen cycle was applied instead of the vacuum closed system as the solid phase polymerization.

The particle size of the flakes charged to each reaction part and the temperature of the reaction part, the intrinsic viscosity (IV) of the flakes before and after the solid phase polymerization are shown in Table 2.

Reaction part Filling Flakes Particle Size (mm) Reaction part temperature (℃) Flake IV Maximum IV Deviation by Region Solid state polymerization After solid state polymerization First reaction part 11 5 or more 208 0.70 0.80 0.03 Second reaction part 12 3 to 5 205 0.71 0.81 Third reaction part 13 1 to 3 202 0.70 0.81 Fourth reaction part 14 1 or less 200 0.69 0.83

[Comparative Example]

1 kg of the recycled PET flakes used in Example 1 were subjected to solid phase polymerization at 205 ° C. for 5 hours without the step of screening according to the conventional method. After completion of the solid phase polymerization, the screened solidified polymerized flakes were classified by size to measure the IV of the PET flakes for each size as shown in Table 3.

Filling Flakes Particle Size (mm) Reactor temperature (℃) Flake IV Maximum IV Deviation by Region Solid state polymerization After solid state polymerization 5 or more 205 0.70 0.78 0.08 3 to 5 0.71 0.81 1 to 3 0.70 0.84 1 or less 0.69 0.86

As can be clearly seen from the results of the above embodiment, the flakes are classified by size before solid phase polymerization, and the flakes having similar sizes during solid phase polymerization are placed at similar sites in the solid phase polymerization reactor, and then the temperature conditions are different for each site of the reactor. In operation, the molecular weight deviation of the flakes according to the particle size after the solid phase polymerization is minimized to obtain uniformity of molecular weight quality of the recycled pellets.

Claims (3)

In the method for solid-phase polymerization of flakes obtained by cutting and / or crushing waste PET containers, the flakes are loaded in a solid-phase polymerization reactor, and then different reaction temperatures are applied for each flake size. A solid phase polymerization method of waste polyester flakes, characterized by lowering the temperature. An apparatus for solid-phase polymerization of flakes obtained by cutting and / or crushing waste PET containers, the apparatus comprising: one or more screens for horizontally dividing the inside of a cylindrical reactor, and for heating each reaction section divided into screens at different temperatures. Solid-state polymerization apparatus of the waste polyester flakes characterized by comprising a heating means. The solid phase polymerization apparatus of the waste polyester flakes according to claim 2, wherein the number of screens for dividing the inside of the cylindrical reactor horizontally is 2 to 5, and the screens have a smaller mesh size from the top to the bottom of the reactor.

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