JP2006272561A - Method for treating waste plastics - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating waste plastics which separates chlorine-containing plastics from the waste plastics by a relatively inexpensive method and can improve the reduction of the chlorine content of the waste plastics. <P>SOLUTION: In the method for treating the waste plastics for separating/recovering chlorine-free plastics from the waste plastics containing the chlorine-containing plastics, the waste plastics are separated into high-specific gravity plastics and low-specific gravity plastics by specific gravity difference, the low-specific gravity plastics are heated at a prescribed temperature to fragment the chlorine-containing plastics, and the fragmented chlorine-containing plastics are separated/removed to recover the chlorine-free plastics. The separation by a specific gravity difference is preferably carried out by a wet centrifugal separation method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a waste plastic treatment method for separating chlorine-containing plastic from waste plastic such as general waste and industrial waste and recovering non-chlorine-containing plastic.

  Plastic waste, generally called waste plastic, contains a plurality of types of plastic. In addition to polyethylene (PE), polypropylene (PP), polystyrene (PS), polyethylene terephthalate (PET), PVC (polychlorinated). Also included are chlorine-containing plastics such as vinyl) and PVDC (polyvinylidene chloride) (hereinafter, PVC and / or PVDC are referred to as “chlorine-containing plastics”). When such mixed waste plastic is reused, for example, as a furnace fuel or a reducing material for iron sources, the generation of chlorine-containing gas becomes a problem, and therefore, a process for separating chlorine-containing plastic from waste plastic is performed. ing.

  In order to remove the chlorine component from the waste plastic, a method of heating the waste plastic is also known (see, for example, Patent Document 1). Waste plastic is heated and melted using an extruder, a melting tank or the like and thermally decomposed to recover the chlorine component as hydrogen chloride gas, thereby obtaining a plastic having a low chlorine concentration. However, even when such a treatment is performed, it is effective to separate the chlorine-containing plastic from the waste plastic in advance and heat the waste plastic having a high chlorine concentration (see, for example, Patent Document 2). .

  Various treatment methods exist for separating chlorine-containing plastic from mixed waste plastic, but as a treatment method for accurately separating chlorine-containing plastic from mixed waste plastic at a relatively low cost, the waste plastic is agitated to generate frictional heat. The mixture waste plastic is heated by the frictional heat so that the non-chlorine-containing plastic is melted and granulated, and the chlorine-containing plastic is not melted. There is known a method of separating mixed waste plastic that is sieved to those having a predetermined particle diameter or more and that performs shape difference separation after granulation (see, for example, Patent Document 3).

  Further, a specific gravity difference sorting method is known as a method with higher separation accuracy of chlorine-containing plastics (see, for example, Patent Document 4). The specific gravity difference sorting method focuses on the fact that the specific gravity of chlorine-containing plastics is larger than that of non-chlorine-containing plastics such as PE, PP, PS, etc., and separates mixed waste plastics into high specific gravity and low specific gravity by specific gravity difference. This is a method of removing the high specific gravity as a chlorine-containing plastic and recovering the low specific gravity as a non-chlorine-containing plastic.

  Specific gravity difference selection methods include liquid cyclones, wet vertical separators (separators that float low specific gravity and settle high specific gravity), wet processing methods such as wet centrifugation, and no liquid. There is a processing method by a dry method, and separation processing of waste plastics by a wet centrifugal method is said to have particularly high separation accuracy. The wet centrifugation method is performed as follows.

The waste plastic dispersed in the medium liquid is charged into the rotating cylinder where water or the medium liquid whose specific gravity is adjusted stays. In the rotating drum, plastic pieces having a large specific gravity gather near the inner wall of the rotating drum, and plastic pieces having a small specific gravity gather on the inner side of the rotating drum. Then, by removing the two separated plastics from the respective outlets, the charged waste plastic is separated into a high specific gravity component made of chlorine-containing plastic and a low specific gravity component made of non-chlorine-containing plastic. The
Japanese Patent Laid-Open No. 10-110931 Japanese Patent No. 3303693 JP 2004-358964 A JP-A-9-85120

  For example, when chlorine-containing plastic is separated and removed from waste plastic having a chlorine concentration of about 2 mass% to obtain non-chlorine-containing plastic, the chlorine concentration of non-chlorine-containing plastic is set to 0. Although it can be reduced to about 8 mass%, when the chlorine-containing plastic is removed as a high specific gravity using a wet centrifugal method, the chlorine concentration of the non-chlorine-containing plastic can be reduced to about 0.6 mass%.

  However, when trying to improve the separation accuracy of chlorine-containing plastics and obtain waste plastics with a lower chlorine concentration, there is a problem that there is a limit to lowering the chlorine concentration even when the wet centrifugation method is used. There is.

  When using the wet centrifuge method, the waste plastic to be processed is crushed more finely and then added by means such as reducing the amount of processing once, optimizing the medium liquid, adding an antifoaming agent to the medium liquid, etc. Although the separation accuracy can be improved to a certain extent, there is a concern that it is difficult to industrially implement recycling of waste plastic due to an increase in processing cost. On the other hand, since it is difficult to separate a chlorine-containing plastic and a non-chlorine-containing plastic having similar specific gravity like PVC and PET, there is a limit in improving separation accuracy in principle.

  Therefore, the object of the present invention is to solve such problems of the prior art, accurately separate chlorine-containing plastic from waste plastic by a relatively low cost method, and lower the chlorine concentration of waste plastic more than before. An object of the present invention is to provide a method for treating waste plastic.

The features of the present invention for solving such problems are as follows.
(1) A waste plastic treatment method for separating and recovering non-chlorine-containing plastic from waste plastic containing chlorine-containing plastic, wherein the waste plastic is separated into high specific gravity plastic and low specific gravity plastic by a specific gravity difference, and the low specific gravity A method for treating waste plastic, comprising: refining chlorine-containing plastic by heating the plastic to a predetermined temperature; and separating and removing the refined chlorine-containing plastic to recover non-chlorine-containing plastic.
(2) The method for treating waste plastic according to (1), wherein the separation based on the difference in specific gravity is a wet centrifugation method.
(3) After the process of heating the low specific gravity plastic while stirring, the low specific gravity plastic subjected to the heating and stirring process is screened, and the content on the screen separated by the screening process is made of non-chlorine-containing plastic. The waste plastic treatment method according to (1) or (2), wherein:
(4) The low specific gravity plastic is heated to a predetermined temperature to granulate at least a part of the non-chlorine-containing plastic to obtain a granulated product, according to any one of (1) to (3) Waste plastic processing method.
(5) The method for treating waste plastic according to any one of (1) to (4), wherein the chlorine-containing plastic is polyvinyl chloride and / or polyvinylidene chloride.

  According to the present invention, waste plastic can be separated into non-chlorine-containing plastic and chlorine-containing plastic at a relatively low cost and with high accuracy. Therefore, the chlorine concentration of the plastic obtained by removing the chlorine-containing plastic from the mixed waste plastic can be reduced more than before.

  The present inventors examined a processing method for separating and removing chlorine-containing plastic from waste plastic and recovering waste plastic having a lower chlorine concentration than conventional ones.

  First, the wet centrifugation method was examined. The biggest cause of the decrease in separation accuracy in the wet centrifuge method is that waste plastics are contaminated with food residues, etc. due to waste, and changes in the specific gravity of media liquid due to contaminants and generation of bubbles It is thought that. However, if the waste plastic contamination state before processing by the wet centrifuge method is at a certain level, changing the crushing conditions of the waste plastic when the centrifuge is charged, reducing the amount of processing once, Even if the defoamer to be added is optimized, the percentage of chlorine concentration in the waste plastic separated as light specific gravity is small within the range of actual operating conditions, and it is difficult to obtain an effect commensurate with the increase in cost. there were. As another method, it is possible to reduce the chlorine concentration of the remaining waste plastic itself by removing the non-chlorine-containing plastic having a specific gravity close to that of the chlorine-containing plastic simultaneously with the chlorine-containing plastic. This is not a desirable method because the yield of the contained plastic is reduced. In other words, when separating with specific gravity by wet centrifugation, it is difficult to separate chlorine-containing plastics and non-chlorine-containing plastics with similar specific gravity. However, in order not to reduce the yield of non-chlorine-containing plastics, some chlorine is contained. The reality is that it is necessary to allow plastics to be mixed into non-chlorine containing plastics. Although it is desirable from the point of effective use of waste plastics to separate and remove only chlorine-containing plastics as much as possible to increase the yield of non-chlorine-containing plastics, contaminated waste plastics are separated with high precision by wet centrifugation. It is difficult.

  Next, a method of performing shape difference separation after granulation was examined. The method of shape difference separation after granulation uses the melt granulation method, which is a plastic granulation technique. The waste plastic is agitated to generate frictional heat, and the temperature of the waste plastic is raised by the frictional heat. The non-chlorine-containing plastic is melted and granulated, and the granulation process is performed in a state where the chlorine-containing plastic is not melted, and the processed product produced in the granulation process is separated into a granulated product and a non-granulated product. By doing so, the chlorine-containing plastic is separated as a non-granulated product. In this method, it is difficult to accurately control the temperature during granulation due to the temperature rise accuracy of the granulator, and the chlorine-containing plastic is entangled in the softened non-chlorine-containing plastic. Since the surface may be granulated by adhering chlorine-containing plastic to the surface, it is simple and low-cost, but the separation accuracy is lowered as compared with the wet centrifugation method. However, since it is a technology for separating using the difference in softening and melting temperature of plastic, it is considered that separation is possible when the softening and melting temperature is different even for plastics with similar specific gravity.

  Based on the above findings, a processing method for separating waste plastics by combining a separation method based on a difference in specific gravity and a separation method based on a difference in softening and melting temperature was examined. Then, first, separation by specific gravity difference is performed, and after removing the main chlorine-containing plastic as heavy specific gravity, the plastic separated as light specific gravity is heated to a predetermined temperature to separate the softened and melted plastic, The present invention was completed by finding that plastics such as PVC and PET having similar specific gravity can be accurately separated, and that plastics with lower chlorination than before can be obtained.

  In addition, the inventors further examined the method of performing the shape difference separation after granulation, and when the temperature at which the waste plastic is heated is increased to such an extent that the non-chlorine-containing plastic is melted to produce a granular material or a lump, It has been found that the chlorine-containing plastic may adhere to or be encased in the granular material or lump, and the separation accuracy is slightly reduced. On the other hand, since chlorine-containing plastics become brittle and refine even when heated at a temperature lower than the temperature at which melting of non-chlorine-containing plastics begins, separation by shape even when non-chlorine-containing plastics are not granulated Was found to be possible. Therefore, it is a particularly desirable method to separate a refined chlorine-containing plastic and a non-chlorine-containing plastic by heating the specific gravity-separated low-density plastic to a predetermined temperature and embrittlement of the chlorine-containing plastic. It is.

  By heating to a predetermined temperature, the chlorine-containing plastic becomes brittle, while the non-chlorine-containing plastic does not become brittle. In order to refine the embrittled chlorine-containing plastic, it is desirable to perform a stirring process using a stirrer having rotating blades. It is also possible to provide a pulverization step using a crusher, a pulverizer or the like. When the low specific gravity plastic is subjected to a thermal stirring treatment, it is efficient because the chlorine-containing plastic can be heated to become brittle and refined in one step. Non-chlorine-containing plastics with a low melting point (for example, PE type) may be melted and granulated by heating, and those with a high melting point (for example, PP or PET type) keep the original form (such as fluff) before heating. In any case, in any case, non-chlorine-containing plastics will not be refined even if they are heated, or in some cases further stirred, depending on the particle size. By separating, chlorine-containing plastic and non-chlorine-containing plastic can be separated with higher accuracy. Fine and non-fine can be easily separated by using a sieve or the like.

  FIG. 1 is an explanatory view of a method for treating waste plastic. An embodiment of the present invention will be described with reference to FIG.

  In FIG. 1, reference numeral 100 denotes a mixed waste plastic containing chlorine-containing plastic, which is a collected waste, and the mixed waste plastic crushed into a size of about 10 to 50 mm square in the crushing step 11 is a specific gravity difference sorting step 12. Sent to. In the specific gravity difference selection step 12, a wet centrifugal separator shown in FIG. 2 described later is used, and a high specific gravity 103 having a specific gravity higher than that of PVC and a low specific gravity 102 lower than the specific gravity of PVC by performing a sorting process based on the specific gravity difference. Process to divide. Among the bisected plastics, the high specific gravity 103 is a high chlorine concentration plastic, and the low specific gravity 102 is mainly a non-chlorine-containing plastic such as PE, PP and PS. In order not to reduce the yield of the non-chlorine-containing plastic, the separation is performed under such a condition that the low specific gravity 102 contains the chlorine-containing plastic to some extent.

  Next, in order to further reduce the chlorine concentration of the low specific gravity 102 obtained by separating and removing the chlorine-containing plastic from the mixed waste plastic, it is sent to the heating and stirring step 13 and heated while stirring, and then the sieving step In 14, the sieve is sieved with a sieve having a predetermined size. This sieving process separates the under-sieving portion 105 containing a large amount of chlorine-containing plastic powders and fine particles and the above-sieving portion 104 made of non-chlorine-containing plastic containing little chlorine-containing plastic. The sieve top 104 is reused as a blast furnace reducing agent, fuel, material recycled material raw material, and the like.

  In the heating and stirring step 13, a heating and stirring apparatus shown in FIG. 3 to be described later is used. This heating and stirring device has a heating and stirring tank equipped with a stirrer configured to be capable of rotating at high speed. The mixed waste plastic charged in the heating and stirring tank is stirred at a high speed to generate frictional heat. The temperature can be raised to a predetermined temperature by heat.

  Then, in the heating and stirring step 13, the mixed waste plastic that has been charged is heated to a predetermined temperature range while stirring at high speed, and stirring is continued at a predetermined temperature for a predetermined time. During this heating and stirring, the plasticizer in the chlorine-containing plastic is volatilized and the chlorine-containing plastic piece becomes brittle, and the chlorine-containing plastic piece is crushed into powder and fine particles.

  Next, the heated and stirred processed product discharged from the heating and stirring step 13 is sieved with a sieve having a predetermined size in the sieving step 14. By this sieving operation, the sieving part 105 containing a large amount of powder and fine particles of chlorine-containing plastic and the sieving part 104 made of non-chlorine-containing plastic containing little chlorine-containing plastic are divided. Since PET is not pulverized, PVC and PET, which could not be separated by the specific gravity difference sorting process, are separated, and the PET is recovered as a non-chlorine-containing plastic. The on-sieving portion 104 is directed to reuse as a blast furnace reducing agent or fuel.

  In the heating and stirring step 13, the heating and holding temperature is particularly preferably set to a temperature lower than the temperature at which the charged plastic begins to melt or the temperature at which some of the plastic starts to melt and in the vicinity thereof. . The setting of the heating and holding temperature varies depending on the type of plastic contained in the mixed waste plastic, but is preferably 140 to 165 ° C. when the chlorine-containing plastic is mainly polyvinyl chloride and / or polyvinylidene chloride. . When the heating and holding temperature is increased, non-chlorine-containing plastics such as PE, PP, and PS having a low melting point are melted to form granular materials or lumps. There is a case where it adheres to or encloses a lump, and the separation accuracy of the chlorine-containing plastic is slightly lowered. Chlorine-containing plastics that are mixed with non-chlorine-containing plastics if part of the mixed plastics is heated and held at a temperature that melts some of the plastics, but part of it becomes granular, but if the amount produced is not large Therefore, it is desirable to heat at a temperature higher than the softening temperature of PE and lower than the softening temperature of PP or PET, considering the processing efficiency.

  As described above, if the stirring of the plastic is continued, the temperature of the plastic rises to a region exceeding the range of the heating and holding temperature. The stirring is continued while performing the operation of cooling by spraying.

  Further, the heating time in the heating and stirring step 13 is the time required for the chlorine-containing plastic piece to be crushed to become a powder or fine particles, so the size and thickness of the chlorine-containing plastic contained in the mixed waste plastic Although it changes with heating holding temperature etc., when the shape is a film form, it is normally about 10 minutes-20 minutes.

  As described above, in the present invention, non-chlorine is used from waste plastic by using a wet centrifugation method suitable as a large-scale treatment method for waste plastic, and then using extremely simple means of heating and stirring treatment and sieving treatment. Mass processing for recovering the contained plastic can be efficiently performed with high accuracy.

  Next, the wet centrifugal separator will be described. FIG. 2 is a diagram showing an example of the configuration of the wet centrifugal separator used in the specific gravity difference sorting step. The wet centrifuge 20 has a truncated cone-shaped portion formed on both sides, a rotating cylinder 21 that rotates while retaining water or a medium liquid whose specific gravity is adjusted, and a slightly different speed from the rotating cylinder 21. The main part is composed of a rotating shaft to be rotated and screw conveyors 22a and 22b made of screws provided on the shaft. In the figure, reference numeral 102 denotes a low specific gravity plastic, and 103 denotes a high specific gravity plastic.

  Separation of plastic by this apparatus is performed as follows. An amount of medium liquid that allows a space to be formed in the upper portion of the rotating drum 21 is retained and rotated, and a waste plastic crushed product dispersed in the medium liquid is charged from the waste plastic charging pipe 23. In the rotary cylinder 21, among the plastic pieces inserted from the waste plastic charging tube 23 into the central portion of the rotary cylinder 21, those having a specific gravity smaller than the medium liquid float up and have a specific gravity larger than the medium liquid. Settles. At this time, the settling of the plastic having a specific gravity larger than that of the medium liquid is promoted by the action of the centrifugal force generated as the rotating drum 21 rotates. The plastic piece having a high specific gravity (high specific gravity) gathers in the vicinity of the inner wall of the rotary drum 21, and the plastic piece having a low specific gravity (low specific gravity) is near the liquid surface of the medium liquid (on the center side of the rotary drum 21). get together. The high specific gravity portion 103 is scraped out by the screw conveyor 22a having a large diameter, discharged from the high specific gravity portion outlet 24, and processed as a chlorine-containing plastic portion. The low specific gravity 102 is scraped out by a screw conveyor 22b having a small diameter, discharged from the low specific gravity outlet 25, and recovered as non-chlorine-containing plastic.

  FIG. 3 is a diagram showing an example of a heating and stirring device used in the heating and stirring step and a sieving device used in the sieving step. In FIG. 3, 30 is a heating and stirring device, and 40 is a sieving device.

  Reference numeral 31 denotes a heating and stirring tank of a heating and stirring apparatus that is charged with mixed waste plastic and heated while stirring, and generates frictional heat by rotating a stirrer 32 provided at the bottom thereof at high speed. Reference numeral 100 denotes the charged waste plastic.

  A temperature measuring device 33 for measuring the temperature of the waste plastic being stirred is provided at the side of the heating and stirring tank 31, and a watering device 34 is provided at the top. The watering device 34 is provided for cooling to suppress an excessive rise in the temperature of the waste plastic heated by the frictional heat and for cooling after the heating and stirring process is completed. Operates and stops in response to an instruction signal. The set value of the heating and holding temperature is input to the watering control device 35, and when the measured value of the temperature measuring device 33 reaches the set value, the control valve 38 is opened for a very short time. A small amount of water is sprayed, and the temperature of the waste plastic in the tank is kept near the set value. In addition, when a predetermined heating and stirring time has elapsed, sufficient water spraying is performed for a predetermined time and cooling is performed. In the figure, reference numeral 36 denotes a cooling water supply pipe provided with a watering nozzle 37 at an end in the tank.

  The sieving device 40 is a device that removes powdered substances and fine particles generated by pulverizing the chlorine-containing plastic by sieving the processed product heated and stirred as described above with a sieve having a predetermined opening. The on-sieving portion 104 having a predetermined diameter or more that has been sieved by the sieving device 40 is recovered as a non-chlorine-containing plastic. Further, the under-sieving portion 105 having a diameter less than the predetermined diameter is treated as a chlorine-containing plastic.

  As described above, by sieving with a sieve with a predetermined opening, it is separated into non-chlorine-containing plastics and chlorine-containing plastics, but the waste plastic after heating and stirring treatment contains more chlorine as the diameter decreases. Therefore, the opening size of the sieve that determines the lower limit of the diameter to be recovered as reusable plastic is based on past results, taking into account the properties of the waste plastic to be processed and the transfer conditions of the melt granulator. Determined. In the sieving step, a sieve having an opening of 1 to 3 mm is usually used.

  The heating and stirring device 30 shown in FIG. 3 is provided for the purpose of heating waste plastic to make the chlorine-containing plastic brittle and crushing the chlorine-containing plastic. Accordingly, the heating and stirring device 30 is not limited to the vertical tank shown in FIG. 5 provided with a stirrer, for example, a rotating cylindrical body configured to be capable of heating and stirring is pulverized having a selected shape and specific gravity. A device such as a ball mill in which a medium is charged may be used, and a device configured to pulverize a brittle chlorine-containing plastic.

  Further, the heating / stirring device 30 may be a device other than the one that uses only the frictional heat of stirring as shown in FIG. In particular, in an apparatus that does not perform a high-speed stirring operation, for example, an indirect heating type apparatus using steam or the like, an apparatus for heating by blowing hot air, or the like can be used.

  Next, examples of the present invention will be described.

  Waste plastic collected by local governments and used for containers and packaging whose chlorine content is about 1.5% is separated and removed to obtain waste plastic with a low chlorine concentration. went. The main non-chlorine-containing plastic contained in the waste plastic was PE.

  The treatment for separating the chlorine-containing plastic was performed as follows. A container-packaged plastic bale product was loosened with a crusher and then crushed with a crusher to obtain a screen passing material of about 10 to 50 mm.

  The crushed material was charged into a wet centrifuge having the same configuration as that shown in FIG. 2, and a specific gravity difference sorting process for separating the crushed material into a high specific gravity component and a low specific gravity component was performed. Water was used as the medium liquid for dispersing the plastic crushed material. The ratio of the low specific gravity recovered as non-chlorine-containing plastic by this treatment was 72 mass% with respect to the charged crushed material, and the chlorine content was 0.6 mass%. The proportion of the high specific gravity was 28 mass%, and the chlorine content was 3.8 mass%.

  Next, the low specific gravity was charged into the heating and stirring apparatus shown in FIG. 3, and the temperature was increased by rotating the stirrer at high speed. And the heating holding temperature was set to 160 degreeC, and it stirred for 20 minutes, performing temperature control by a watering control apparatus. After elapse of a predetermined time, water was sprayed to cool and take out. When the state of the heated and stirred processed product was observed, a part of the processed product was granular.

  The heated and stirred processed product discharged from the heating and stirring device is sieved with a sieve having a mesh opening of 2.3 mm, so that it is smaller than the predetermined particle size (under sieve) and larger than the predetermined particle size (on sieve). divided. The proportion of the sieve top recovered as non-chlorine-containing plastic by this treatment was 80 mass% with respect to the low specific gravity charged in the heating and stirring device, and the chlorine content was 0.2 mass%. Moreover, the ratio of under-sieving was 20 mass%, and the chlorine content was 2.2 mass%.

  As described above, after the specific gravity separation by the wet centrifugal separator, the heating and stirring treatment and the sieving treatment were performed. As a result, the chlorine content of the plastic recovered as a non-chlorine-containing plastic was reduced to 0.2 mass%, and the recovery was performed. The rate was about 57 mass%.

It is explanatory drawing of one Embodiment which concerns on the waste plastic processing method of this invention. It is a figure which shows an example which concerns on the structure of the wet centrifuge used in a specific gravity difference selection process. It is a figure which shows an example of the apparatus used by a heating stirring process and a sieving process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Crushing process 12 Specific gravity difference selection process 13 Heating and stirring process 14 Sieving process 20 Wet centrifuge 21 Rotating drum 22a Screw conveyor 22b Screw conveyor 23 Waste plastic charging pipe 24 High specific gravity outlet 25 Low specific gravity outlet 30 Heating and stirring apparatus DESCRIPTION OF SYMBOLS 31 Heating stirrer 32 Stirrer 33 Temperature measuring device 34 Sprinkling device 35 Sprinkling control device 36 Cooling water supply pipe 37 Sprinkling nozzle 38 Control valve 40 Sieving device 100 Mixed waste plastic 102 Low specific gravity 103 High specific gravity 104 Sifting top 105 Lower part

Claims (5)

  A waste plastic treatment method for separating and recovering non-chlorine-containing plastic from waste plastic containing chlorine-containing plastic, wherein the waste plastic is separated into a high specific gravity plastic and a low specific gravity plastic by a specific gravity difference, and the low specific gravity plastic is predetermined. A method for treating waste plastic, characterized in that the chlorine-containing plastic is refined by heating to a temperature of 1, and the refined chlorine-containing plastic is separated and removed to recover non-chlorine-containing plastic.   2. The method for treating waste plastic according to claim 1, wherein the separation based on the difference in specific gravity is a wet centrifugation method.   After the low specific gravity plastic is heated while being stirred, the low specific gravity plastic that has been heated and stirred is sieved, and the fraction on the sieve separated by the sieving treatment is recovered as non-chlorine-containing plastic. The method for treating waste plastic according to claim 1 or 2, characterized in that:   The waste plastic according to any one of claims 1 to 3, wherein the low specific gravity plastic is heated to a predetermined temperature to granulate at least a part of the non-chlorine-containing plastic. Processing method.   The method for treating waste plastic according to any one of claims 1 to 4, wherein the chlorine-containing plastic is polyvinyl chloride and / or polyvinylidene chloride.

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