Horizontal recycling method for selectively recovering pet and PVC from composite plastic waste

Abstract

[Problem] To provide a horizontal recycling method in which PVC and PET are selectively recovered as materials, without being pyrolyzed, from a composite plastic waste. [Solution] A horizontal recycling method in which PVC and PET are selectively recovered as materials, without being pyrolyzed, from composite plastic waste containing a composite plastic 3P-based plastic and plastic other than 3P-based plastic, the method for the horizontal recycling of composite plastic waste being characterized by: heating, using a glycol-type solvent that is a solvent for the solvolysis of the plastic other than the 3P-based plastic, the plastic other than the 3P-based plastic to a temperature region T1 that softens the PVC and PET without dissolving the PVC and PET; carrying out a gravity separation into a light-weight fraction containing the PA and PU in the composite plastic waste and a middle-weight fraction containing the PVC and PET in the plastic other than the 3P-based plastic; settling and fractionating the plastic in the middle-weight fraction; and then cooling the PVC and PET with a glycol-type solvent into a temperature region T2 that is 100°C or lower and separating the PVC and PET without change without dissolving the PVC and PET.

Description

Horizontal recycling method for selectively recovering PET and PVC from composite plastic waste

[0001] The present invention is a horizontal recycling (reuse) method that separates and recovers materials from composite plastics (including films laminated with metals, etc.), including household plastic waste containing a mixture of various plastics, without pyrolysis, particularly from plastics other than the 3P type, such as PVC and PET, which are considered general-purpose plastics. This method is based on the current situation where material separation is difficult.

[0002] There are internationally agreed priorities for the disposal of plastic waste, and when considering plastics, including switching to alternatives, which is particularly important, the top priority should be given to reducing plastic (reduce), as shown in Figure 1. This is followed by horizontal recycling (reuse), in which the same item is used repeatedly, as with metals, and then material recycling, in which new products are created. If these are not possible, thermal recovery, controlled landfilling, and simple incineration should be considered in that order. This is because approximately 30% of plastic waste worldwide is not treated in this way, flowing into the natural environment and contributing to marine pollution.

[0003] The biggest problem with plastic waste disposal is that unless it is pre-sorted before processing, it is difficult to recover it as a material suitable for chemical recycling, especially horizontal recycling. Plastic waste is complex and diverse, and it is currently difficult to separate and recover plastics of the same type before processing, except for PET. Therefore, in order to reduce plastics, conversion to plant-based alternatives and biodegradable plastics has been proposed. However, due to significant cost barriers, this has only been implemented to a limited extent. Therefore, unless pre-sorted collection is performed, like with PET, chemical recycling or horizontal recycling is difficult, and we have no choice but to rely on the plastic recycling methods described below. In other words, while the Plastic Recycling Law divides plastic waste into three types: thermal recycling, in which it is used as fuel; material recycling, in which it is reused as materials; and chemical recycling, in which it is regenerated into chemical raw materials and used, approximately 70% of plastic collected in 2021 was thermally recycled, including simple incineration.Even now, with the revision of the Containers and Packaging Recycling Law in July 2020, which has led to widespread separated collection, material recycling still accounts for only 21%, and chemical recycling is said to be just 4%.For this reason, with the enforcement of the Plastic Resource Circulation Promotion Act (New Plastic Law) on April 1, 2022, it is recommended to promote horizontal recycling, in which plastic is collected and reused as a material.

[0004] However, because 3P thermoplastics, including PP, PE, and PS, can be separated by gravity or by dissolution (Patent Documents 1 and 2), 3P plastics are currently used as raw materials for oil production, but only PET is sorted, identified, and recovered for material recycling, and chemical recycling and horizontal recycling of unsorted plastics are currently difficult. Furthermore, a method for sorting crushed plastic mixtures using electrostatics has been proposed (Non-Patent Document 1), but because it is a dry sorting technology, it has the problem of being unable to separate composite plastic waste in which metal and plastic are layered.

[0005] The reasons why effective recycling, including chemical recycling of plastic waste, has not progressed are, first, the difficulty of separating and recovering plastics. Second, although pyrolysis recovery methods have been proposed for plastics other than 3P, PA and PU generate HCN, which acts as a catalyst poison, while PVC generates inorganic and organic chlorine, which corrodes the equipment and causes deterioration in quality, and PET is accompanied by the deposition of terephthalate, which causes blockage of equipment piping and leads to quality deterioration.

[0006] Publication No. US2023 / 0174736 Publication No. WO2014 / 098229 NEWS RELEASE (Management No. 2430) "Mitsubishi Electric and Daisan begin operation of advanced plastic sorting demonstration machine" September 11, 2024 Mitsubishi Electric Corporation

[0007] The representative general-purpose plastics that are mass-produced and consumed are commonly referred to as the "five major general-purpose plastics," which include PVC, PE, PS, and PP, plus PET. Of these, the 3P plastics PE, PS, and PP are separated and used as oil-recycling materials. Therefore, horizontal recycling, including chemical recycling, that enables the reuse of plastics other than the 3Ps, especially the general-purpose plastics PVC and PET, without subjecting them to problematic pyrolysis, is desired. Therefore, the objective of this invention is to separate and recover (horizontally recycle) plastics other than the 3Ps from plastic waste, including various plastics, in a reusable state without pyrolysis (horizontal recycling).

[0008] The present inventors have observed that pre-sorting composite plastic waste, which contains various plastics, metals, and reinforcing fibers, is difficult (even when waste is sorted into containers and packaging, combustible waste, and non-combustible waste, only the containers and packaging are recycled for materials, while the combustible waste is thermally recycled, contributing to global warming through CO2 emissions, and the non-combustible waste is crushed and used as burial material, resulting in marine pollution). Given this, while it is now possible to separate 3P plastics from non-3P plastics, the difficulty of manually separating and recovering the remaining non-3P plastics highlights the importance of recovering PVC and PET from general-purpose plastics through horizontal recycling. From this perspective, the present inventors have conducted extensive research and found that the use of glycol-based solvents for solvolysis of non-3P plastics not only enables separation of 3P plastics from non-3P plastics, but also enables the recovery of at least PVC and PET from non-3P plastics without thermal decomposition or dissolution (horizontal recycling). That is, for example, when a glycol-based solvent is heated to 180 to 200°C, not only do 3P plastics not melt but float to the surface, making it easy to separate them from plastics other than 3P, but plastics other than 3P can be separated by specific gravity with PA and PU as a light weight category and PVC and PET as a medium weight category, and it has been found that the settled and separated PVC and PET can be separated in a form that can be reused as is (horizontal recycling) by cooling, preferably rapidly cooling, in the glycol-based solvent from 180 to 200°C to 100°C or lower.The present invention was made based on the above findings and is a horizontal recycling method for selectively recovering non-3P plastics, particularly PVC and PET, from composite plastic waste without pyrolysis. This horizontal recycling method for composite plastic waste involves using a glycol-based solvent, which is a solvent for solvolysis of non-3P plastics, to heat the plastics to a temperature T1 at which the PVC and PET do not melt, for example, 180 to 200°C, and separating the plastics into a light weight fraction containing PA and PU from the non-3P plastics, and a medium weight fraction containing PVC and PET from the non-3P plastics, and cooling the settled medium weight fraction to a temperature range T2 of 100°C or less with the glycol-based solvent to separate the PVC and PET without dissolving them.

[0009] This invention allows PVC and PET, which would otherwise be unreusable without pre-sorting, to be separated from composite plastics and recovered as reusable materials (horizontal recycling) without pyrolysis. This breakthrough method addresses the current situation where unsorted household plastic waste must be incinerated or landfilled, which is a hazard to the environment, and thus contributes to solving the problems of global warming and marine litter. Furthermore, while electrostatic sorting techniques cannot separate metals and laminated films, which require incineration, this invention can be applied to a wide range of composite plastic waste, including laminated films. Composite plastic waste may contain 3P plastics in addition to PVC and PET. By using glycol-based solvents, which are solvolyzing agents for non-3P plastics, these 3P plastics do not dissolve in the solvent and are easily separated from the non-3P plastics, allowing them to float, facilitating separation. Furthermore, non-3P plastics separated from 3P plastics may contain PA and PU (average specific gravity below 1.2) in addition to PVC and PET (average specific gravity around 1.4). However, using glycol-based solvents allows for separation of the lightweight PA and PU from the medium-weight PVC and PET by specific gravity. Furthermore, composite plastics, such as pharmaceutical packaging or aluminum pouches made of metal and plastic bonded together, can only be incinerated without sorting. However, using glycol-based solvents allows for separation of the metal and plastic, enabling separate collection. Furthermore, using glycol-based solvents allows for separation of the matrix resin and reinforcing fiber in FRP composites, enabling separate collection. In other words, composite plastic waste, including household plastic waste, includes a variety of plastic products, such as 3P thermoplastics, non-3P thermoplastics, thermosetting plastics, and composites with metal or reinforcing fiber. However, PVC and PET, which are included in the "five major general-purpose plastics," can be collected in a reusable state without prior sorting or thermal decomposition.Furthermore, since 3P plastics can be recycled into oil while PA and PU can be recycled as materials, this is a significant solution to the plastic recycling problem, which has traditionally been limited to incineration or landfill disposal of composite plastic waste. In particular, given the current major challenge of reducing CO2 emissions, recycling plastics without thermal recycling is of great significance. Furthermore, the present invention is also highly effective in eliminating marine pollution caused by unmanageable plastic waste. Furthermore, since the glycol-based solvent used as a separating agent does not require the thermal decomposition of PA, PU, ​​PET, and PVC plastics for recovery, there is no need for the pollution caused by thermal decomposition, making it possible to realize a green recycling project.

[0010] 1 is a graph showing the priority order in waste plastic processing. 2 is a schematic diagram of equipment showing a specific example of the horizontal recycling method of the present invention. 3 is a schematic diagram of a cooling method using a conveyor for horizontal recycling of the present invention. 4 is a photograph showing the recovery form of (a) PET resin when quenched in a glycol-based solvent, and (b) PVC resin.

[0011] Representative examples of composite plastic waste include household plastic waste containing various plastics, aluminum pouches and pharmaceutical packaging composites with metals, and carbon and glass fiber-reinforced composite plastics (CRP and FRP). These include 3P plastics (typically PP, PE, and PS), non-3P plastics (such as PA, PU, ​​PVC, and PET), and third components (metals, reinforced glass fiber, and carbon fiber). This invention enables horizontal recycling, selectively recovering at least PET and chlorinated PVC as reusable materials from these composite plastic wastes without pyrolysis. Furthermore, this invention recovers 3P plastics as oil-recycling materials, while also recycling non-3P plastics (PA and PU) as materials. Furthermore, composite plastics with metals, which have traditionally been incinerated, have been difficult to separate using physical separation techniques such as electrostatic separation, but this invention allows for the separation and recovery of metals and plastics.

[0012] In this invention, glycol-based solvents, which are used for the solvolysis of plastics other than 3Ps, are used as separation solvents. Glycol-based solvents include one or more of the following: EG (ethylene glycol) with a specific gravity of 1.115 and a boiling point of 197.3°C; DEG (diethylene glycol) with a specific gravity of 1.12 and a boiling point of 244.3°C; and TEG (triethylene glycol) with a specific gravity of 1.124 and a boiling point of 285°C. These solvents can be mixed with other solvents as long as they do not interfere with the horizontal recycling of PVC and PET. For horizontal recycling of PVC and PET, a composition is selected that allows for optimal heating temperatures for selective separation, e.g., 180-200°C, without dissolving the PVC and PET to be selectively separated. TEG has a boiling point of 288°C, so it can be used alone as a glycol-based solvent. A significant advantage of glycol-based solvents is that they can be recovered with plastics, separated by distillation, and reused.

[0013] 3P plastics include PP, PE, and PS. PP has a specific gravity (g / cm3) of 0.9-0.91 and a melting point of 180°C, PE has a specific gravity of 0.94-0.96 and a melting point of 130°C, and PS has a specific gravity of 1.04-1.07 and a melting point of 230°C. They do not dissolve in glycol-based solvents and, because of their light specific gravity, float on glycol-based solvents. Therefore, 3P plastics can be easily separated from composite plastic waste by floating them using glycol-based solvents.

[0014] Plastics other than the 3P type include thermoplastic resins that are soluble or compatible with the glycol-based solvents, and in terms of specific gravity, the lightweight category includes PA with a specific gravity of 1.01, PC with a specific gravity of 1.2, and PU with a specific gravity of 1.2, while the medium weight category includes PET with a specific gravity of 1.38 to 1.39, PVC with a specific gravity of 1.35 to 1.45, and vinylidene chloride PVDC with a specific gravity of 1.69. ABS usually contains reinforcing fibers and has a specific gravity of about 1.4.

[0015] As a result, when 3P plastics are separated from composite plastic waste, plastics other than the 3P, including PA, PU, ​​PVC, PET, and PDCC, form the upper layer as light-weight categories, with PA with a specific gravity of 1.01, PC with a specific gravity of 1.2, and PU with a specific gravity of 1.2, while the middle layer contains PET with a specific gravity of 1.38 to 1.39, PVC with a specific gravity of 1.35 to 1.45, and vinylidene chloride (PVDC) with a specific gravity of 1.69, with aluminum and other metal components in the bottom layer, separated by specific gravity. ABS resins and the like usually contain GF and belong to the medium-weight category of resins.

[0016] The key here is to heat the PET, PVC, and PVDC middle layers to a temperature at which they do not dissolve in the glycol-based solvent, preferably 180-200°C, to separate them into a lightweight and a medium-weight fraction. The reasons for using a glycol-based solvent at a heating temperature of 180-200°C are as follows: 1. Glycol-based solvents (separating agents) have high permeability to composite plastics, making it easy to peel the composite 3P plastics, non-3P plastics, and the third component, metal and reinforcing fiber. 2. Because plastic films have a low bulk density, they melt in about 3-5 minutes at 180-200°C, reducing their viscosity. The composite plastic layers formed by laminating metal and plastic are separated and can be separated. 3. Plastics other than 3P, PA, PU, ​​PVC, and PET can be processed at temperatures below 200°C, which does not decompose them. 4. Moisture in the raw materials can be evaporated quickly.

[0017] Figure 1 shows a schematic diagram of a facility for recovering PVC and PET by horizontal recycling. The composition of the glycol solvent, ED, DEG, and TEG, is adjusted and the heating temperature is set to 200°C, below the boiling point.

[0018] Household plastics consist of 3P plastics, non-3P plastics, and third components. 3P plastics include PP, PE, and PS, while non-3P plastics include PA, PU, ​​PET, PVC, and filled ABS. Third components include metals such as aluminum, glass fiber, and carbon fiber. In the first stage, 3P plastics are separated from non-3P plastics using a glycol-based solvent. In the second stage, non-3P plastics are separated into a light weight category (average 1.0-1.2) including PA and PU, and a medium weight category (average 1.4) including other PET (specific gravity 1.38-1.39) and PVC (specific gravity 1.35-1.45).

[0019] The medium weight category includes thermosetting plastics (epoxy resin 1.6 to 2.0), composite plastics (average specific gravity 1.4 or more) made of metal containing Al (specific gravity: 2.7) and reinforcing fiber (specific gravity of glass fiber: 2.5, specific gravity of carbon fiber: 1.8), sand, and stone.

[0020] Finally, as shown in FIG. 4, PVC and PET are recovered as raw materials and separated from thermosetting plastics, metals, and composite plastics.

[0021] Household plastic waste is fed from a flexible container bag through an inlet 120 into a dissolution tank 100 containing a glycol-based solvent, which is TEG or a mixture of ED, DEG, and TEG, heated to 200°C. As the water evaporates, it is collected in a condenser 102 and recovered in a receiving tank 110.

[0022] The 3P plastics do not dissolve in the glycol-based solvent in the separation tank 101, so they melt and float to the top of the solvent. They are separated from the glycol-based solvent and recovered in the recovery tank 103, where they are separated into the solvent and the 3P plastics. The 3P components are sent to a thermal decomposition device, converted into oil, and recovered. The solvent is preferably sent to a vacuum machine and recovered.

[0023] After separating the 3P plastics, plastics other than the 3P remain in the glycol-based solvent, but lightweight plastics such as PA and PU have a specific gravity of 1.2 or less, so they form an upper layer in the glycol-based solvent.In contrast, PET, PVC, and ABS resins containing glass fiber have a specific gravity of around 1.4, so they form a middle layer in the glycol-based solvent.

[0024] The bottom of separation tank 101 is inclined, and the inclined portion is maintained at approximately 100°C with hot water, and is discharged into quenching layer 112 via withdrawal valve 105. Therefore, plastics other than 3P are gravity separated by the glycol-based solvent at 180°C to 200°C into a light-weight PA (nylon) and PU (urethane) phase and a medium-weight PVC and PET phase, but they settle in the glycol-based solvent together with metal components and thermosetting resin components to form a lower layer of the glycol solvent.

[0025] Therefore, the upper layer is left, and the lower layer is extracted and discharged to a quenching tank 112 outside the system through a valve 105. The separating agent is temporarily received in a separating agent receiving tank 111, sent by a pump 109, and cooled by recovering water in a condenser 102, and returned to the quenching tank 112.

[0026] The remaining glycol-based solvent and the upper layer PA and PU are extracted and recovered in a separation tank 104, and the light components PA and PU are recovered. The solvent is recovered by distillation in a separating agent heating tank 107 heated by an electric heater 108, and the separating agent is returned to the dissolving tank 101 by a pump 109. A part of the separating agent heated by the separating agent heater is used to heat the dissolving tank 101. The recovered PA and PU components are used as material ingredients.

[0027] In the quenching layer 112, the PET, PVC, and fiber-containing ABS resin in the middle and bottom layers in a glycol-based solvent at 180 to 200°C are cooled together with the metal to 50 to 100°C, and the PET and PVC are horizontally recycled so that they can be used as raw materials as they are, as shown in Figure 4.

[0028] In Figure 2, the resin is removed from the dissolution tank system and cooled in the quenching tank 112, but as shown in Figure 3, the PET, PVC, and fiber-containing ABS resin in the middle and bottom layers are removed from the dissolution tank 101 system together with the metal, sent upward on a conveyor 202, and quenched by being sprayed with a glycol-based solvent at room temperature, and then introduced into a heavy liquid receiving phase 203 of a glycol-based solvent (heavy liquid) at 70°C, where it is cooled to 100°C or less and subjected to gravity separation.

[0029] Figures 4(a) and (b) show the state of PVC and PET resins after they have been held at 190-200°C for 5 minutes and then rapidly cooled. As shown in Figures 4(a) and (b), the PVC and PET recovered from composite plastic waste do not dissolve, and after cooling, the PET and PVC resin pieces can be individually extracted and reused as they are.

[0030] 100: Plastic separation equipment 101: Separation tank 102: Coagulator 103: 3P recovery tank 202: Conveyor 203: Heavy liquid receiving tank

Claims

1. A horizontal recycling method for selectively recovering, without pyrolyzing, PVC and PET among plastics other than 3P plastics from composite plastic waste containing at least 3P plastics including PE, PP, and PS and plastics other than 3P plastics including at least PA, PU, PVC, and PET, which uses a glycol-based solvent that is a solvent for solvolysis of plastics other than 3P plastics, heats to a separation temperature range T1 at which PVC and PET are not dissolved but softened, and separates by specific gravity into a lightweight fraction containing PA and PU in the composite plastic waste and a medium-weight fraction containing PVC and PET in plastics other than 3P plastics, and then cools the PVC and PET in the medium-weight fraction to a cooling temperature range T2 of 100°C or lower with the glycol-based solvent to horizontally recycle PVC and PET as materials. A recycling method for composite plastic waste, characterized by this.

2. When separating the plastics other than 3P plastics in the composite plastics into a lightweight fraction containing PA and PU and a medium-weight fraction containing PET and PVC by specific gravity, the recycling method for composite plastics according to claim 1, which uses a glycol-based solvent that is a solvent for solvolysis of the plastics other than 3P plastics, separates the 3P plastics from the plastics other than 3P plastics, and recovers them.

3. After separating the plastics other than 3P plastics in the composite plastics into a lightweight fraction containing PA and PU and a medium-weight fraction containing PET and PVC by specific gravity, the lightweight fraction containing PA and PU is separated and taken together with the glycol-based solvent, and the lightweight fraction containing PA and PU is recycled as a material after separating from the glycol-based solvent. The recycling method for composite plastics according to claim 1.

4. The recycling method for composite plastic waste according to claim 1, wherein the composite plastic waste includes composite plastics with a metal as a third component and / or composite plastics with reinforcing fibers, and separates the plastics from the metal and the reinforcing fibers in the separation temperature range T1 of the glycol-based solvent.

5. The glycol-based solvent is a solvent for solvolysis of plastics other than 3P plastics, which is other than 3P-based solvents, and contains one or more selected from the group consisting of ethylene glycol, diethylene glycol, and triethylene glycol, does not dissolve 3P plastics, and can dissolve plastics other than 3P plastics. The method for recycling composite plastic waste according to claim 1.

6. The method for recycling composite plastic waste according to claim 1, wherein the separation temperature T1 is in the range of 180 to 200 °C.

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