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

Abstract

Providing a horizontal recycling method that selectively recovers PVC and PET as raw materials from composite plastic waste without thermal decomposition. [Solution] This is a horizontal recycling method for composite plastic waste characterized by using a glycol-based solvent, which is a solvent for solvolysis of plastics other than 3P-based plastics, heating the plastics other than 3P-based plastics to a temperature range T1 in which they soften without dissolving PVC and PET, separating them by specific gravity into a lightweight portion containing PA and PU in the composite plastic waste and a medium-weight portion containing PVC and PET in the plastics other than 3P-based plastics, separating the medium-weight portion of the plastic by sedimentation, and then cooling the PVC and PET to a temperature range T2 of 100°C or less with a glycol-based solvent to separate them without dissolving PVC and PET.

Description

Technical Field

[0001] The present invention relates to a horizontal recycling (reuse) method for sorting and recovering, as raw materials, from composite plastics (including laminated films with metals and the like) containing domestic plastic waste in which various plastics are mixed, under the current situation where sorting of raw materials is difficult, in particular, PVC and PET which are general-purpose plastics among plastics other than 3P-based plastics, without subjecting them to thermal decomposition.

Background Art

[0002] There is an internationally agreed priority order for the treatment of plastic waste. For plastics, considering the switch to alternatives that require special consideration, as shown in Figure 1, the highest priority is given to plastic reduction (reduce), followed by horizontal recycling (reuse) in which the same item is used repeatedly in the same manner as metals, then recycling (material recycling) to create new products. If these cannot be implemented, consideration should be given in the order of heat recovery (thermal recycling), controlled landfill, and simple incineration. This is because approximately 30% of plastic waste worldwide is not treated in such a controlled manner, leaks into the natural environment, and leads to marine pollution.

[0003] The biggest problem in plastic waste treatment is that, unless pre-sorting is done before treatment, chemical recycling, especially recovery as a material for horizontal recycling, is difficult. In other words, plastic waste is complex and diverse, and sorting and pre-collecting identical types of plastic before treatment is currently difficult except for PET. Therefore, currently, the shift towards reduction, such as converting plastics to plant-based alternatives and biodegradable plastics, has been proposed. However, this is largely hindered by cost and remains limited. Consequently, chemical recycling or horizontal recycling is difficult unless pre-sorting and collection is done, as is the case with PET, and we are forced to rely on the following plastic recycling methods. In other words, plastic recycling laws are divided into thermal recycling, where plastic waste is used as fuel; material recycling, where it is reused as a material; and chemical recycling, where it is recycled into chemical raw materials for use. However, in 2021, approximately 70% of the plastic collected was used for thermal recycling, including simple incineration. Even now, with the expansion of separate collection following the amendment of the "Container and Packaging Recycling Law" in July 2020, material recycling accounts for only 21%, and chemical recycling is said to be a mere 4%. Therefore, with the enforcement of the "Plastic Resource Recycling Promotion Law" on April 1, 2022, it is recommended to promote horizontal recycling, which involves collecting plastic as a material and reusing it.

[0004] However, currently, 3P-type thermoplastics, including PP, PE, and PS, can be separated from non-3P plastics by specific gravity or dissolution (Patent Documents 1 and 2), and 3P-type plastics are being used as raw materials for oil conversion. However, among other plastics, only PET is being collected and recycled through sorting and identification, and chemical recycling and horizontal recycling of other plastics that are not sorted remain difficult. Furthermore, a method for sorting crushed plastic mixtures using electrostatics has been proposed (Non-Patent Document 1), but since it is a dry sorting technology, it has the problem that it cannot separate composite plastic waste in which metals and plastics are laminated.

[0005] In other words, the reasons why effective recycling, including the chemical recycling of plastic waste, is not progressing are, firstly, the difficulty of separate collection. Secondly, although pyrolysis recovery methods have been proposed for plastics other than 3P, PA and PU generate HCN, which is a catalyst poison, while PVC generates inorganic and organic chlorine compounds, leading to equipment corrosion and quality deterioration, and PET is accompanied by terephthalate precipitation, causing quality deterioration along with blockage of equipment piping. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] US2023 / 0174736 publication [Patent Document 2] WO2014 / 098229 publication [Non-Patent Document 1] NEWS RELEASE (Management No. 2430) "Mitsubishi Electric and Daisan Begin Operation of Advanced Plastic Sorting Demonstration Machine" September 11, 2024 Mitsubishi Electric Corporation [Overview of the project] [Problems that the invention aims to solve]

[0007] The most common general-purpose plastics produced and consumed in large quantities are commonly referred to as the "five major general-purpose plastics," which include PVC, PE, PS, PP, and PET. Of these, PE, PS, and PP, which are 3P-type plastics, are separated and used as oil-based materials. Therefore, there is a need for horizontal recycling, including chemical recycling, that enables the reuse of plastics other than 3P-type plastics, especially general-purpose plastics such as PVC and PET, without subjecting them to problematic thermal decomposition. Accordingly, the present invention aims to separate and collect (horizontally recycle) plastics other than 3P-type plastics from plastic waste, including various types of plastics, in a reusable state without thermal decomposition. [Means for solving the problem]

[0008] The inventors of this invention have observed that, in the case of composite plastic waste containing various plastics, metals, and reinforcing fibers, pre-sorting before processing is difficult (even if separated into containers and packaging, combustible waste, and non-combustible waste, only the containers and packaging are materially recycled, combustible waste is used for thermal recycling, leading to the problem of global warming due to CO2 emissions, and non-combustible waste is crushed and used as landfill material, leading to the problem of marine pollution). Considering that it is currently possible to separate 3P plastics from non-3P plastics, and that it is difficult to manually separate and collect the remaining non-3P plastics, the inventors understand how important it is to recover PVC and PET contained in general-purpose plastics through horizontal recycling. As a result of diligent research from this perspective, the inventors have found that by using a glycol-based solvent as the solvent for solvoresis of non-3P plastics, it is not only possible to separate 3P plastics from non-3P plastics, but at least PVC and PET can be recovered from non-3P plastics without thermal decomposition and without dissolution (horizontal recycling). In other words, we found that when a glycol-based solvent is heated to 180-200°C, 3P-based plastics do not melt but float, making them easy to separate from plastics other than 3P-based plastics. Furthermore, the plastics other than 3P-based plastics can be separated by specific gravity, with PA and PU being the lightweight category and PVC and PET being the medium-weight category. Moreover, when the PVC and PET separated by sedimentation are cooled in a glycol-based solvent from 180-200°C to 100°C or lower, preferably in a temperature range of 50°C to 100°C, and preferably rapidly cooled, the PVC and PET can be separated (horizontally recycled) in a form that can be reused as is. The present invention is based on the above findings and is a horizontal recycling method for selectively recovering plastics other than 3P-type plastics, particularly PVC and PET, from composite plastic waste without thermal decomposition. The method is characterized by using a glycol-based solvent, which is a solvent for solvolysis of plastics other than 3P-type plastics, heating to a temperature T1, for example, 180-200°C, which does not melt PVC and PET, separating the plastics into a lightweight portion containing PA and PU and a medium-weight portion containing PVC and PET, and then cooling the settling medium-weight portion to a temperature range T2 of 100°C or less with a glycol-based solvent to separate the PVC and PET without dissolving them. [Effects of the Invention]

[0009] In this invention, PVC and PET, which could not be reused without prior sorting before processing, can be separated and collected (horizontally recycled) as reusable materials without prior separation from composite plastics and without thermal decomposition. Currently, household plastic waste that cannot be sorted has no choice but to be incinerated or landfilled, which causes pollution, so this is a groundbreaking method to solve the problems of global warming and marine debris. Furthermore, while sorting technology using static electricity cannot separate metals and laminated films, leaving them with no choice but to be incinerated, this invention can be applied to a wide range of composite plastic waste, including laminated films. Although composite plastic waste may contain 3P-type plastics in addition to PVC and PET, these 3P-type plastics do not dissolve in glycol-based solvents, which are solubilizing agents for plastics other than 3P-type plastics. Therefore, they can be easily separated from other plastics and float to the surface, making sorting easy. Furthermore, while non-3P plastics separated from 3P plastics may contain PA and PU (average specific gravity of 1.2 or less) in addition to PVC and PET (average specific gravity of around 1.4), the specific gravity separation of the lightweight PA and PU from the medium-weight PVC and PET can be achieved in a glycol-based solvent, allowing for their separation. Furthermore, composite plastics include pharmaceutical packaging or aluminum pouches made by laminating metal and plastic. While these previously could only be incinerated unless separated, the use of glycol-based solvents allows for the separation of metal and plastic, enabling separate collection. Similarly, for FRP (fiber-reinforced plastic) composites with reinforcing fibers, the use of glycol-based solvents allows for the separation of the matrix resin from the reinforcing fibers, enabling separate collection. Therefore, composite plastic waste, including household plastic waste, encompasses a wide variety of plastic products, such as 3P-type thermoplastics, non-3P-type thermoplastics, thermosetting plastics, and composite plastics with metals or reinforced fibers. However, PVC and PET, which are included in the "five major general-purpose plastics," can be recovered in a reusable state without prior sorting or thermal decomposition. Furthermore, 3P-type plastics can be utilized as oil, while PA and PU can be recycled as materials. This significantly solves the problem of plastic recycling, which previously had to be disposed of only through incineration or landfill. In particular, given the major challenge of CO2 reduction today, the significance of recycling plastics without using thermal recycling is great, and the present invention also has a significant effect in eliminating marine pollution caused by unmanageable plastic waste. Moreover, because glycol-based solvents are used as separating agents, PA, PU, ​​PET, and PVC plastics are not recovered by thermal decomposition, there are no pollution problems associated with thermal decomposition recovery, and a green recycling project can be realized. [Brief explanation of the drawing]

[0010] [Figure 1] This graph shows the priority order for waste plastic processing. [Figure 2] This is a schematic diagram of the equipment illustrating a specific example of the horizontal recycling method of the present invention. [Figure 3] This is a schematic diagram of the cooling method using a conveyor for horizontal recycling according to the present invention. [Figure 4](a) is a photograph showing the recovery form of PET resin and (b) PVC resin when rapidly cooled in a glycol-based solvent. [Modes for carrying out the invention]

[0011] Composite plastic waste typically includes household plastic waste containing various plastics, aluminum pouches and pharmaceutical packaging which are composite materials with metal, and composite plastics CRP and FRP reinforced with carbon fiber and glass fiber. It also includes 3P plastics represented by PP, PE, and PS, non-3P plastics including PA, PU, ​​PVC, and PET, and third components other than plastic such as metal, reinforced glass fiber, and carbon fiber. According to the present invention, horizontal recycling can be achieved by selectively recovering at least PET and chlorine-based PVC from this composite plastic waste as reusable materials without thermal decomposition. Moreover, according to the present invention, 3P plastics can be recovered as oil-based materials, while PA and PU, which are non-3P plastics, can also be recycled as materials. Furthermore, composite plastics with metals, etc., which were mainly incinerated, were difficult to separate by physical sorting such as electrostatic discharge, but it is possible to separate and recover the metals and plastics.

[0012] In this invention, a glycol-based solvent, which is a solvent for solvolysis of plastics other than 3P-based solvents, is used as the separation solvent. The glycol-based solvent includes 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. It can be used in mixture with other solvents as long as it does not hinder the horizontal recycling and recovery function of PVC and PET. For the horizontal recycling and recovery function of PVC and PET, a composition is selected that allows for the optimal heating temperature, for example, 180-200°C, to selectively separate the PVC and PET without dissolving them. Since TEG has a boiling point of 288°C, it can be used alone as a glycol-based solvent. A significant advantage of the glycol-based solvent is that it can be recovered together with the plastic, 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, due to their low specific gravity, float on the glycol-based solvent. Therefore, 3P plastics can be easily separated from composite plastic waste by flotation using glycol-based solvents.

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

[0015] Accordingly, when 3P-based plastics are separated from composite plastic waste, plastics other than 3P including PA, PU, PVC, PET and PDCC are classified as a light weight fraction, in which 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 form an upper layer, while PET with a specific gravity of 1.38 to 1.39, PVC with a specific gravity of 1.35 to 1.45, vinylidene chloride PVDC with a specific gravity of 1.69 and the like are present in a middle layer, and metal components such as aluminum are separated by specific gravity into the lowermost layer. ABS resins and the like usually contain GF and the like, and belong to the medium weight fraction resins.

[0016] Here, it is important to heat the PET, PVC and PVDC in the middle layer to a temperature at which they do not dissolve in a glycol-based solvent, preferably to 180 to 200°C, to perform specific gravity separation into a light weight fraction and a medium weight fraction. The reasons for setting the heating temperature of the glycol-based solvent to 180 to 200°C are as follows. 1. Since the glycol-based solvent (separating agent) has high permeability to composite plastics, it facilitates peeling of the composited 3P-based plastics, plastics other than 3P, and the third components such as metals and reinforcing fibers. 2. Since plastic films have a low bulk specific gravity, they melt in about 3 to 5 minutes at 180 to 200°C, reducing their viscosity. The lamination of composite plastics formed by laminating metals and plastics is separated, enabling sorting. 3. The process can be performed at a temperature of 200°C or lower that does not decompose plastics other than 3P, PA, PU, PVC and PET. 4. The moisture in the raw material can be evaporated quickly.

[0017] Figure 1 is a schematic diagram of equipment for recovering PVC and PET through horizontal recycling. The blending composition of ED, DEG and TEG as the glycol-based solvent is adjusted, and the heating temperature is set to 200°C which is below the boiling point.

[0018] Post-consumer plastics include 3P-based plastics, plastics other than 3P-based plastics, and a third component. The 3P-based plastics include PP, PE, and PS, the plastics other than 3P-based plastics include PA, PU, PET, PVC, and filler-containing ABS, and the third component includes metals such as aluminum, glass fibers, carbon fibers, and the like. In the first stage, the 3P-based plastics and the plastics other than 3P-based plastics are separated from post-consumer plastic waste using a glycol-based solvent. Then, in the second stage, the plastics other than 3P-based plastics are classified into a light weight category (average 1.0 to 1.2 or less) including PA and PU, and a medium weight category (average 1.4) including the remaining PET (specific gravity 1.38 to 1.39) and PVC (specific gravity 1.35 to 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 higher) of metals including Al (specific gravity: 2.7) and reinforcing fibers (specific gravity of glass fiber: 2.5, specific gravity of carbon fiber: 1.8), sand, and stones.

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

[0021] Post-consumer plastic waste is charged from a flexible container bag through a charging port 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. Since moisture evaporates, it is collected by a aggregator 102 and recovered in a receiving tank 110.

[0022] Since the 3P-based plastics are insoluble in the glycol-based solvent in the separation tank 101, they melt and float on the solvent. They are fractionated, separated together with the glycol-based solvent, recovered in a recovery tank 103, and separated into the solvent and the 3P plastics. The 3P components are sent to a pyrolysis apparatus, and recovered after being converted into oil. The solvent is preferably sent to a vacuum machine for recovery.

[0023] When 3P plastics are separated, plastics other than 3P remain in the glycol-based solvent. Lighter components such as PA and PU have a specific gravity of 1.2 or less, so they form the upper layer in the glycol-based solvent. In contrast, PET, PVC, and ABS resin containing glass fibers have a specific gravity of around 1.4, so they form the middle layer in the glycol-based solvent.

[0024] The bottom of the separation tank 101 is sloped, and the sloped section is maintained at around 100°C with hot water, which is then discharged to the rapid cooling layer 112 via the extraction valve 105. As a result, plastics other than 3P are separated by specific gravity using a glycol-based solvent at 180°C to 200°C into a lightweight PA (nylon) and PU (urethane) phase and a medium-weight PVC and PET phase. However, along with metal components and thermosetting resin components, they settle in the glycol-based solvent, forming a lower layer of the glycol solvent.

[0025] Therefore, the upper layer is left intact, and the lower layer is removed and discharged to the rapid cooling layer 112 outside the system via valve 105. The separation agent is temporarily received in the separation agent receiving tank 111, sent by pump 109, cooled by water recovered in the condenser 102, and returned to the rapid cooling layer 112.

[0026] The remaining crystalline solvent and the upper layers of PA and PU are extracted and collected in the separation tank 104 to recover the lightweight components PA and PU. The solvent is recovered by distillation in the separation agent heating layer 107, which is heated by an electric heater 108, and the separation agent is returned to the dissolution tank 101 by pump 109. A portion of the separation agent heated in the separation agent heater is used to heat the dissolution tank 101. The recovered PA and PU components are used as material.

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

[0028] In Figure 2, the materials are removed from the dissolution tank system and cooled in the rapid cooling layer 112. However, as shown in Figure 3, the middle and bottom layers of PET, PVC, and fiber-reinforced ABS resin are removed from the system along with the metal in the dissolution tank 101, sent upwards by the conveyor 202, rapidly cooled by spraying 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 to cool to below 100°C, allowing for specific gravity separation.

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

[0030] 100... Plastic separation equipment 101...Separation tank 102...Aggregator 103···3P Recovery Tank 202... Conveyor 203...Heavy liquid receiving tank

Claims

1. A horizontal recycling method for composite plastic waste comprising 3P plastics including at least PE, PP, and PS and non-3P plastics including at least PA, PU, ​​PVC, and PET, wherein PVC and PET are selectively recovered from non-3P plastics without thermal decomposition, characterized in that a glycol-based solvent, which is a solvent for solvolysis of non-3P plastics, is used, and the PVC and PET are heated to a separation temperature range T1 in which they are softened without dissolving, separating them by specific gravity into a lightweight portion containing PA and PU in the composite plastic waste and a medium-weight portion containing PVC and PET in the non-3P plastics, and then the PVC and PET of the medium-weight portion are cooled to a cooling temperature range T2 of 100°C or less with a glycol-based solvent to horizontally recycle the PVC and PET as raw materials.

2. A method for recycling composite plastics according to claim 1, wherein, when separating the plastics other than 3P in the composite plastic into a lightweight portion containing PA and PU and a medium-weight portion containing PET and PVC by specific gravity, a glycol-based solvent, which is a solvent for solvorization (solbolysis) of the plastics other than 3P, is used to separate and recover the 3P plastics from the plastics other than 3P.

3. A method for recycling a composite plastic according to claim 1, wherein the plastics other than the 3P type in the composite plastic are separated by specific gravity into a lightweight portion containing PA and PU and a medium-weight portion containing PET and PVC, the lightweight portion containing PA and PU is separated together with a glycol-based solvent, and the lightweight portion containing PA and PU is separated from the glycol-based solvent and recycled as a material.

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

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

6. The recycling method for 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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