JP4804115B2 - Method for separating mixed plastics - Google Patents

Description

  The present invention relates to the separation of plastics composed of composite materials, and in particular, light plastics such as polypropylene and / or polyethylene contained in PET bottle waste in general and industrial waste for reuse, and polyester plastics such as polyethylene terephthalate. The present invention relates to a method for separating mixed plastics by specific gravity separation.

  In order to protect resources, recyclable resources are collected from waste, treated appropriately, and reused, that is, recycling is an extremely important issue in modern society. In particular, plastics are made from petroleum, which is a finite resource, as a main raw material, and are prone to many environmental problems when treated as waste, so recycling is very important. Waste plastics, including PET bottles, which have been relatively sorted and collected, have a large percentage of closure of those used as containers for food, cosmetics, detergents, and the like. In these PET bottles, polypropylene and / or polyethylene, which are light plastics, are used for the cap portion, and polyethylene and polystyrene are often used for labels and the like. In recycling, it is necessary to sort these plastics efficiently and with high precision, and there is a demand for a technology that can achieve both separation precision and a recovery rate in the course of recycling activities.

As a method of separating a composite material of plastic into a single material, a method of separating by specific gravity selection using a gas flow (for example, see Patent Document 1) is known, but the purity of the plastic separated in gas is 60 to 70. It is difficult to recycle as a virgin material. In addition, as a method for separating plastic having a specific gravity of more than 1.0 and plastic having a density of less than 1.0 , a method of putting plastic into an open water tank and separating it into a settling and floating one (see, for example, Patent Documents 2 and 3). Then, when polystyrene and polyester having a specific gravity exceeding 1.0 are mixed, it is difficult to separate them.

  In addition, the waste plastic water slurry is supplied to the center of the sorting device filled with a cylindrical liquid with drainage ports at the top and bottom, and the low specific gravity plastic is fed from the upper discharge port by the upward and downward flow while swirling by the swirl flow. A method of recovering high specific gravity plastic from the lower discharge port (see, for example, Patent Document 4) has also been proposed, but since there is a downward flow of liquid components, the purity of the high specific gravity plastic mainly exceeds 99% due to the liquid flow. In reality, it is difficult to increase the flow rate, and since it is in the low flow rate range, there is a problem that a very large facility is required for large-scale processing. In addition to these, there has also been proposed a method (for example, see Patent Document 5) in which a liquid specific gravity separator having a liquid cyclone shape separates waste plastic water slurry into a single material plastic. However, these facilities generally have a small processable amount and cannot handle a large amount of processing, so if the processing amount increases, it is necessary to install a multi-sequence separation device, which is economical. There is also a drawback of not.

Japanese Patent Laid-Open No. 6-63941 (Claims) Japanese Patent Laid-Open No. 48-1000076 (Claims) JP-A-4-326955 (Claims) JP-A-9-150417 (Claims) JP 2000-288422 A (Claims)

  The present invention has been made against the background of the problems of the prior art as described above, and its purpose is mainly directed to PET bottle scraps composed of polypropylene and / or polyethylene, polystyrene, and polyester, and a high-purity polyester component. A method of separating waste plastics that can be separated and collected at a high recovery rate, and at the same time, separates polypropylene and / or polyethylene containing almost no polyester component and polyester component, and can be processed on a large scale while maintaining separation performance. It is in.

As a result of intensive studies in view of the above-described conventional technology, the present inventors are a method of recovering a plastic having a specific gravity from waste plastic that has been crushed in advance, and include the following steps (a) to (c): High-purity polyester and polypropylene and / or polypropylene from plastic bottle waste containing polypropylene and / or polypropylene, polystyrene, and polyester by using a separation method of waste plastic characterized by separating using a separation device The method of sorting at a high recovery rate has been completed.
(A) It has a supply port for crushed waste plastic and water, mixes the crushed waste plastic in the stirring tank with water to form a water slurry, separates bubbles adhering to the waste plastic, A step (b) for transporting the waste plastic water slurry to the step (b), a lower cone type cylindrical stirring tank having a lower cone part angle of 40 degrees or less, and a storage tank provided thereunder via a connecting pipe; For an apparatus having a transportation facility for taking out the internal packing to the outside, the waste plastic water slurry of step (a) is placed in the lower cone type cylindrical stirring tank so that a swirling flow is generated in the lower cone type cylindrical stirring tank. The water slurry is supplied from the water slurry supply port installed in the tangential direction of the straight body portion, and the water in the water slurry is caused by the rising speed of 7 to 40 mm / second while the water swirls inside the lower cone type cylindrical stirring tank. The specific gravity plastic is put together with water from the overflow port installed at the upper part of the lower cone type cylindrical stirring tank so that the height from the water slurry supply port is 0.5 to 5.0 times the diameter of the lower cone type cylindrical stirring tank. At the same time of discharging, the process of discharging the high specific gravity plastic in the water slurry from the lower part of the storage tank through the lower cone type cylindrical stirring tank using a transport facility, and further separating the discharged high specific gravity plastic and water with a dehydrator (C) The separated water slurry of the low specific gravity plastic is supplied to the centrifuge, the components having a higher specific gravity than water are discharged as solids, the components having a lower specific gravity than water are discharged together with the water, and further discharged. The process of separating plastic and water with a dehydrator

  By using the waste plastic separation method using the separation apparatus described above, high purity polyester and polypropylene and / or polypropylene can be recovered from polypropylene bottles and / or polypropylene, polystyrene, and PET bottle waste containing polyester with high recovery rate. It can be separated and is extremely useful.

  Hereinafter, the embodiment of the present invention will be described in detail with reference to the drawings when the waste plastic is a bottle (pet bottle) mainly made of polyethylene terephthalate. Although this is a preferred embodiment of the present invention, the present invention is not limited to the case where the waste plastic is a plastic bottle or the same equipment as in FIG.

  Waste PET bottles 1 made of polypropylene and / or polypropylene 1a, polystyrene 1b and polyester 1c previously crushed by a crusher or the like are mixed from the waste PET bottle inlet 5 and water 2 is mixed from the water supply port 7 respectively. 4 is input. Next, while mixing by No. 1 stirrer 6, it becomes a uniform water slurry, and bubbles adhering to the surface of the waste PET bottle are removed. At this time, the concentration of the waste PET bottle in the water slurry can be arbitrarily selected by adjusting the supply amount, but if the water slurry concentration becomes high, uniform mixing becomes difficult, and bubbles adhering to the surface of the waste PET bottle small piece In order to achieve the purpose of removing the content, it is preferably 10% by weight or less. Further, the size of the waste PET bottle crushing is not particularly limited, but is preferably about 8 mm to 20 mm, because the crushing surface increases and the crushing surface is entangled with fluffing. Furthermore, stirring is sufficient to achieve the purpose of removing bubbles, and it is sufficient if the water slurry can be mixed uniformly. As stirring blades, all commonly used stirring blades such as paddle blades and turbine blades are used. it can.

The mixed waste plastic water slurry forms a swirl flow inside the tank from the waste PET bottle water slurry supply port 11 tangentially installed in the straight body of the lower cone type cylindrical stirring tank 9 by the No. 1 slurry pump 8. Supplied as The waste plastic bottle in the supplied water slurry turns while turning. 2 The polyester component, which is a high specific gravity plastic, is settled by releasing the overlapping of small pieces by the stirring effect by the stirrer 10, and falls into the high specific gravity component sedimentation tank (storage tank) 14 through the connecting pipe 13. When the angle of the lower cone of the lower cone type cylindrical stirring tank exceeds 40 degrees, the polyester component is slow to fall into the high specific gravity component settling tank 14, and the polyester piece may be blocked at the upper part of the connecting pipe. The lower cone part angle is preferably 40 degrees or less. The supplied water is more preferably 30 degrees or less, and the supplied water forms a rising flow while swirling the whole amount and is discharged from the overflow port 12. Polypropylene and / or polyethylene having a specific gravity of less than 1 is taken out from the overflow port 12 along with the flow of water without being accompanied by the polyester component due to the stirring effect. Moreover, although the specific gravity is smaller than that of polyester, the label of a PET bottle mainly composed of polystyrene 1b having a specific gravity greater than 1 has a water flow higher than the sedimentation speed by setting the rising flow of the supplied water to 7 mm / second or more. The ascending flow becomes stronger and is taken out from the overflow port 12 together with the water flow without being mixed into the polyester side. On the other hand, if the upward flow of water exceeds 40 mm / second, the polyester component begins to be mixed into the overflow port side by the water flow as in the case of polystyrene, so that the polyester recovery rate as a high specific gravity component decreases. Therefore, it is important that the upward flow of water is in the range of 7 mm / second to 40 mm / second. More preferably, the stable high separation ability can be maintained by setting the speed to 10 mm / second to 20 mm / second. Waste plastic brought into the overflow port side is precisely separated by the upward flow of water between the waste plastic bottle water slurry supply port 11 and the overflow port 12. When this distance is short, the separation time cannot be taken and the mixing ratio of the polyester component to the overflow port side increases, and when it is long, the apparatus size of the lower cone type cylindrical stirring tank increases, and the polystyrene component enters the apparatus. Since a problem such as stagnation may occur, the vertical distance between the waste PET bottle water slurry supply port 11 and the overflow port 12 must be 0.5 to 5 times the diameter of the lower cone type cylindrical stirring tank. More preferably, high separation performance can be achieved by adjusting the diameter of the lower cone type cylindrical stirring tank to 1.0 to 2 times.

  The polyester component 1c is conveyed from the high specific gravity component sedimentation tank 14 to the surface of the water by the screw conveyor 15, and is dehydrated and recovered by the No. 1 dehydrator 17 from the high specific gravity component discharge port 16. On the other hand, an aqueous slurry of polypropylene and / or polyethylene and polystyrene taken out from the overflow port 12 is supplied to the centrifuge 19 by a No. 2 slurry pump 18 and the polystyrene component 1b is recovered from the cake discharge port 20 side. At the same time, the polypropylene and / or polyethylene component 1c discharged together with water from the filtrate outlet 21 is No. 2 Dehydrated by the dehydrator 22 and collected. The machine equipment such as No. 1 and No. 2 dehydrators, No. 1 and No. 2 slurry pumps, centrifuges and the like are not particularly limited, such as type, and general-purpose machines can be used. Polyester components recovered by using this equipment can achieve a purity of 99.8% or more and a recovery rate of 99% or more. At the same time, polypropylene and / or polyethylene achieve a purity and recovery rate of 99.5% or more. In addition, waste plastic processing of several tons / hour or more is possible, and even when the processing amount is reduced, the separation ability can be prevented from being lowered by adjusting the concentration of the water slurry.

The contents of the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. The recovery rate was calculated based on the following formula.
Recovery rate = plastic weight sorted at each location x purity of the target component / target component weight in the waste plastic

[Example 1]
The waste PET bottle was crushed into a 12 mm size using the equipment shown in FIG. In the fractionation experiment, the water slurry concentration was adjusted so that the upward flow of water in the lower cone type cylindrical stirring tank was 10 mm / second, and bubbles adhering to the crushed material were removed during this time. Also shows together a distance to the overflow position with So径from the feed position of the lower cone type cylindrical stirring vessel, a result of processing when waste PET bottles 1000 kg / in device cone angle of 30 degrees to the first embodiment in the following table .

[Examples 2-3, Comparative Examples 1-3]
Examples 2 to 3 and Comparative Examples 1 to 3 were carried out by changing the value of the water upward flow and the height from the feed position to the overflow position of the lower cone type cylindrical stirring tank. Details of the results are summarized in Table 1. The comparison items are the purity and recovery rate of each fraction.

[Comparative Example 4]
Except that the cone portion angle of the lower cone type cylindrical stirring tank 45 degrees devices result of the fractionation test under the same conditions as in Example 1, a polyester is a high density component at a lower cone type cylindrical mixing chamber cone section Was blocked and could not continue the separation test.

As shown in Examples 1 to 3 and Comparative Examples 1 to 3, polypropylene and / or polypropylene, polystyrene, and polyester can be obtained by using the waste plastic separation method using the separation apparatus described above. High-purity polyester and polypropylene and / or polypropylene can be separated from the plastic bottle scraps contained at a high recovery rate. Therefore, recycling of each plastic can be carried out efficiently and is extremely useful.

It is the schematic which showed the one aspect | mode of implementation of the process (a) in this invention.

DESCRIPTION OF SYMBOLS 1 ... Waste PET bottle 1a ... Polypropylene and / or polyethylene component 1b ... Polystyrene component 1c ... Polyester component 2 ... Water 3 ... Drainage 4 ... Mixing tank 5 ... Waste plastic bottle input Mouth 6 ... No. 1 Stirrer 7 ... Water supply port 8 ... No. 1 Slurry pump 9... Lower cone type cylindrical stirring tank 10. 2 Stirrer 11 ... Waste PET bottle water slurry supply port 12 ... Overflow port 13 ... Connecting pipe 14 ... High specific gravity component sedimentation tank 15 ... Screw conveyor 16 ... High specific gravity component discharge port 17 ... No. 1 Dehydrator 18 ... No. 2 Slurry pump 19 ... Centrifuge 20 ... Cake outlet 21 ... Filtrate outlet 22 ... No. 2 dehydrator

Claims (5)

A method for recovering a plastic having a specific gravity from waste plastic that has been crushed in advance, wherein the plastic is separated using a sorting apparatus having the following steps (a) to (c).
(A) It has a supply port for crushed waste plastic and water, mixes the crushed waste plastic in the stirring tank with water to form a water slurry, separates bubbles adhering to the waste plastic, A step (b) for transporting the waste plastic water slurry to the step (b), a lower cone type cylindrical stirring tank having a lower cone part angle of 40 degrees or less, and a storage tank provided thereunder via a connecting pipe; For an apparatus having a transportation facility for taking out the internal packing to the outside, the waste plastic water slurry of step (a) is placed in the lower cone type cylindrical stirring tank so that a swirling flow is generated in the lower cone type cylindrical stirring tank. The water slurry is supplied from the water slurry supply port installed in the tangential direction of the straight body portion, and the water in the water slurry is caused by the rising speed of 7 to 40 mm / second while the water swirls inside the lower cone type cylindrical stirring tank. The specific gravity plastic is put together with water from the overflow port installed at the upper part of the lower cone type cylindrical stirring tank so that the height from the water slurry supply port is 0.5 to 5.0 times the diameter of the lower cone type cylindrical stirring tank. At the same time of discharging, the process of discharging the high specific gravity plastic in the water slurry from the lower part of the storage tank through the lower cone type cylindrical stirring tank using a transport facility, and further separating the discharged high specific gravity plastic and water with a dehydrator (C) The separated water slurry of the low specific gravity plastic is supplied to the centrifuge, the components having a higher specific gravity than water are discharged as solids, the components having a lower specific gravity than water are discharged together with the water, and further discharged. The process of separating plastic and water with a dehydrator   2. The method for separating waste plastics according to claim 1, wherein the rising speed of the flow of water rising while swirling inside the cylindrical stirring tank in the step (b) is 10 mm / second to 20 mm / second.   In the lower cone type cylindrical stirring tank in the step (b), the vertical distance from the waste plastic water slurry supply port to the overflow port is in the range of 1.0 to 2.0 times the diameter of the lower cone type cylindrical stirring tank. The method for separating waste plastics according to claim 1.   2. The method for separating waste plastic according to claim 1, wherein the waste plastic crushed in advance is a bottle mainly composed of polyethylene terephthalate. The method for separating plastic waste according to claim 1, wherein the lower cone portion angle in the lower cone type cylindrical stirring tank in step (b) is 30 degrees or less.

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