Method for separating polyolefins using solution separation

Abstract

The present invention relates to a method for separating polyolefins using solution separation and, more specifically, to a method for separating polyolefins, which can separate each polyolefin, particularly high-density polyethylene and homopolypropylene, from a polyolefin complex with high purity by using solution separation using an aliphatic hydrocarbon with a relatively low boiling point as a solvent, and can reduce the cost required for the process.

Description

Method for sorting polyolefins using solution separation

[0001] The present invention relates to a method for separating polyolefins using solution separation, and more specifically, to a method for separating polyolefins, which can separate each polyolefin, particularly high-density polyethylene and homopolypropylene, from a polyolefin complex with high purity by using solution separation using an aliphatic hydrocarbon having a relatively low boiling point as a solvent, and which can reduce the cost required for the process.

[0002] Polyolefins, a type of plastic, include polyethylene and polypropylene, and these polymers exist in various types due to their diverse molecular weights, densities, chain structures, and polymerization unit types. Crystalline polyolefins are generally characterized by their stability in organic solvents. However, technologies are being developed to dissolve crystalline polyolefins using specific solvents and conditions, separating and sorting them by type, and obtaining them. These technologies are being used to recycle high-purity, high-value-added plastics.

[0003] Traditional polyolefin recycling methods involve physical separation and sorting, such as handpicking, tribo-electrostatic separation, gravity separation, and flotation. However, physical recycling of mixed waste plastics often results in polymer-polymer incompatibility, reduced purity, discoloration, and decomposition, resulting in reduced physical properties. Even after separation and sorting, plastics are traded at relatively lower prices than pure plastic products.

[0004] In contrast, separating mixed waste plastics using selective dissolution can separate high-purity recycled plastics compared to physical separation and sorting. However, the process for separating and sorting various types of plastics requires the use of a variety of solvents due to differences in solubility of each plastic component. This requires adjusting process parameters based on the type of plastic, resulting in significant investment costs and significant difficulties in commercialization.

[0005] Traditionally, solvents primarily used for the selective dissolution of polyolefins have been aromatic compounds, such as xylene and toluene. These highly toxic compounds incur high costs for their use and disposal. Even trace amounts left untreated can pose serious environmental and human health risks. Therefore, the need for alternative solvents is urgent. Furthermore, separating polyolefins using the aforementioned aromatic solvents requires high temperatures, resulting in significant energy consumption and limitations in separating as many types of polyolefins as possible.

[0006] The purpose of the present invention is to provide a method for separating polyolefins, which can separate each polyolefin, particularly high-density polyethylene and homopolypropylene, from a polyolefin complex with high purity by using solution separation using an aliphatic hydrocarbon having a relatively low boiling point as a solvent, and which can reduce the cost required for the process.

[0007] The present invention relates to a method for separating and obtaining high-density polyethylene (HDPE) and homo-polypropylene (Homo PP) from a polyolefin complex containing at least one polyolefin, comprising the steps of: (1) treating the polyolefin complex with a solvent to obtain a solid phase containing high-density polyethylene and homo-polypropylene; and (2) treating the solid phase obtained in step (1) with a solvent to obtain a liquid phase containing high-density polyethylene and a solid phase containing homo-polypropylene; wherein the solvents in steps (1) and (2) are different from each other and each independently contains a saturated or unsaturated aliphatic hydrocarbon having 5 to 8 carbon atoms.

[0008] In one embodiment, the polyolefin composite further comprises a polyolefin selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), homo-polypropylene (Homo PP), random polypropylene (Random PP), block polypropylene (Block PP), terpolymer polypropylene (Ter PP), ethylene / propylene copolymer, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, polyolefin elastomer (POE), or combinations thereof.

[0009] In one specific example, each of the obtained high-density polyethylene and homopolypropylene comprises 30 wt% or less of a comonomer or 30 wt% or less of another polyolefin composite component.

[0010] In one specific embodiment, the polyolefin composite is derived from a household recycled plastic, an industrial recycled plastic, or a combination thereof, wherein the household recycled plastic or the industrial recycled plastic comprises a polymer selected from the group consisting of polyamide, polyester, polyvinyl chloride, polystyrene, ethylene vinyl alcohol, ethylene vinyl acetate, polyurethane, polyacrylate, polycarbonate, or a combination thereof; or a contaminant selected from the group consisting of metal, paper, dye, pigment, organic matter, inorganic matter, or a combination thereof.

[0011] In one specific example, the polyolefin composite is in any one form selected from the group consisting of flakes, granules, pellets, chips, beads, powder and other masses obtained by compressing, crushing, washing and processing household recycled plastics, industrial recycled plastics or a combination thereof.

[0012] In one specific example, the solvent treatment in step (1) is performed under temperature conditions of 70°C to 110°C and pressure conditions of 3 to 9 Bar.

[0013] In one specific example, the solvent treatment in step (1) is performed one or more times.

[0014] In one specific example, the solvent treatment result in step (1) is subjected to solid-liquid separation to obtain a solid phase including high-density polyethylene and homopolypropylene.

[0015] In one specific example, the solvent treatment in step (2) is performed under temperature conditions of 80°C to 130°C and pressure conditions of 5 to 12 Bar.

[0016] In one specific example, the solvent treatment in step (2) is performed one or more times.

[0017] In one specific example, the solvent treatment result in step (2) is subjected to solid-liquid separation to obtain a liquid phase including high-density polyethylene and a solid phase including homopolypropylene.

[0018] In one specific example, the method further comprises the step of (3) treating the solid phase obtained in step (2) with a solvent to obtain a liquid phase containing homopolypropylene.

[0019] In one specific example, the solvent treatment in step (3) is performed under temperature conditions of 100°C to 150°C and pressure conditions of 7 to 15 Bar.

[0020] In one specific example, the solvent treatment in step (3) is performed one or more times.

[0021] In one specific example, the solvent treatment result in step (3) is subjected to solid-liquid separation to obtain a liquid phase containing homopolypropylene.

[0022] In one specific example, for the liquid phase containing the high-density polyethylene obtained in step (2) or the liquid phase containing the homopolypropylene obtained in step (3), a solid phase may be obtained through solid-liquid separation after performing a subsequent process of additional separation or purification treatment, or the solid phase may be obtained through solid-liquid separation without performing a subsequent process.

[0023] In one specific example, the saturated or unsaturated aliphatic hydrocarbon having 5 to 8 carbon atoms has a boiling point of 60 to 110°C.

[0024] In one specific example, the solvent of step (1) comprises a saturated or unsaturated aliphatic cyclic hydrocarbon having 5 to 8 carbon atoms.

[0025] In one specific embodiment, the saturated or unsaturated aliphatic cyclic hydrocarbon having 5 to 8 carbon atoms is selected from the group consisting of alkylcyclopentane, cyclohexane, cyclohexene, alkylcyclohexane having 5 to 8 carbon atoms, and combinations thereof.

[0026] In one specific example, the solvent of step (2) comprises a saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms.

[0027] In one embodiment, the saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms is selected from the group consisting of hexane, hexene, hexyne, heptane, heptene, heptyne, mono- or di-alkylhexane having 5 to 8 carbon atoms, mono- or di-alkylheptane having 5 to 8 carbon atoms, and combinations thereof.

[0028] In one specific example, the solvent of step (3) comprises a saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms.

[0029] In one embodiment, the saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms is selected from the group consisting of hexane, hexene, hexyne, heptane, heptene, heptyne, mono- or di-alkylhexane having 5 to 8 carbon atoms, mono- or di-alkylheptane having 5 to 8 carbon atoms, and combinations thereof.

[0030] According to the present invention, since high-purity polyolefin can be separated using an aliphatic hydrocarbon that is low in harm to the human body and easy to recycle as a solvent, the process is advantageous in terms of economic feasibility and stability, and since most of the waste plastics from living and industrial fields containing polyolefin can be used as feedstock, the range of application is wide.

[0031] Figure 1 schematically illustrates a polyolefin selection process according to one specific example of the present invention.

[0032] Hereinafter, the present invention will be described in more detail.

[0033] A method for separating and obtaining high-density polyethylene (HDPE) and homo-polypropylene (Homo PP) from a polyolefin composite containing at least one polyolefin of the present invention comprises the steps of: (1) treating the polyolefin composite with a solvent to obtain a solid phase containing high-density polyethylene and homo-polypropylene; and (2) treating the solid phase obtained in step (1) with a solvent to obtain a liquid phase containing high-density polyethylene and a solid phase containing homo-polypropylene; wherein the solvents in steps (1) and (2) are different from each other and each independently contains a saturated or unsaturated aliphatic hydrocarbon having 5 to 8 carbon atoms.

[0034] In the past, solvents used in the separation of polyolefin solutions were mainly aromatic hydrocarbons (such as xylene and toluene) that are highly harmful to the human body, or aliphatic hydrocarbons that have high boiling points and are difficult to recycle. However, in the case of saturated or unsaturated aliphatic hydrocarbons having 5 to 8 carbon atoms applied to this technology, since their boiling points are relatively low, they can be separated at low temperatures compared to the conventional technology, which reduces energy consumption and allows for the separation of as many types of plastics as possible, and the sorting method is also environmentally friendly and simple. In cases where the carbon number and boiling point are lower than those of the solvent of the present invention, the cloud point (pressure) for the polyolefin increases, making the process operation conditions (dissolution and separation) very harsh (for example, the temperature conditions are similar, but the pressure conditions increase significantly), and in cases where the carbon number and boiling point are higher than those of the solvent of the present invention, it may be disadvantageous in terms of solvent recycling.

[0035] The above polyolefin composite may further include a polyolefin selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), homo-polypropylene (Homo PP), random polypropylene (Random PP), block polypropylene (Block PP), terpolymer polypropylene (Ter PP), ethylene / propylene copolymer, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, polyolefin elastomer (POE), or combinations thereof. In addition, the polyolefin composite may contain a small amount of other plastics, organic matter, inorganic matter, or foreign substances in addition to PE and PP.

[0036] Each of the high-density polyethylene and homo-polypropylene obtained above may comprise 30 wt% or less of a comonomer or 30 wt% or less of another polyolefin composite component (i.e., a polyolefin composite component other than the high-density polyethylene and homo-polypropylene). For example, the content of the comonomer and other polyolefin composite component may be 0.001 wt% or more, 0.1 wt% or more, 1 wt% or more, 3 wt% or more, or 5 wt% or less, 30 wt% or less, 28 wt% or less, 25 wt% or less, 22 wt% or less, or 20 wt% or less, for example, 0.001 to 30 wt%, 0.1 to 28 wt%, or 1 to 25 wt%.

[0037] The polyolefin composite may be derived from post-consumer recycled plastic, post-industrial recycled plastic, or a combination thereof, and the post-consumer recycled plastic or industrial recycled plastic may include a polymer selected from the group consisting of polyamide, polyester, polyvinyl chloride, polystyrene, ethylene vinyl alcohol, ethylene vinyl acetate, polyurethane, polyacrylate, polycarbonate, or a combination thereof; or a contaminant selected from the group consisting of metal, paper, dye, pigment, organic matter, inorganic matter, or a combination thereof. The polyolefin composite may be in any one form selected from the group consisting of flakes, granules, pellets, chips, beads, powder, and other masses obtained by compressing, crushing, washing, and processing the post-consumer recycled plastic, the post-industrial recycled plastic, or a combination thereof. In addition, in the case of the present invention, since most of the waste plastics from living and industrial fields containing polyolefins can be used as feedstock, the scope of application is wide, and by using a polyolefin complex that can be easily obtained through physical separation and sorting from the waste plastics, only polyolefins, for example, high-purity high-density polyethylene (HDPE) and homopolypropylene (Homo PP), can be separated and obtained therefrom.

[0038] In one specific example, the polyolefin composite may be a product that has been primarily separated and sorted from household recycled plastics or industrial recycled plastics by a recycling company (e.g., a material recovery facility (MRF) in the United States), and the separated and sorted product may be supplied in the form of a compressed product (Bale), flakes, granules, pellets, mass, etc., and may be processed into a form suitable for use in the present invention (e.g., a more finely divided piece form) through subsequent processing, such as crushing, washing, or melting, as needed.

[0039] In the above steps (1) and (2), high-density polyethylene, homopolypropylene, and other polyolefins are selected by taking advantage of the differences in the types of polyolefins that dissolve in the solvent depending on the temperature. In the above steps, under specific temperature and pressure conditions, the polyolefins exist in a liquid phase that dissolves in the solvent or in a solid phase that does not dissolve in the solvent, and in each step, the liquid phase and the solid phase are separated.

[0040] The purpose of step (1) is to separate low-crystallization and low-molecular-weight components from a polyolefin complex to obtain a solid phase including high-density polyethylene and homo-polypropylene and a liquid phase including other components, and the purpose of step (2) is to separate high-crystallization and high-melting-point (Tm, Melting temperature) components after step (1) to obtain a liquid phase including high-density polyethylene and a solid phase including homo-polypropylene.

[0041] In the above step (1), the solvent treatment can be performed under temperature conditions of 70°C to 110°C and pressure conditions of 3 to 9 Bar.

[0042] (1) The solvent treatment step can be carried out under inert gas (e.g., N2gas) conditions, and can be pressurized as needed to reach appropriate pressure conditions.

[0043] (1) The temperature at which the solvent treatment is performed in step may be 70°C or higher, 75°C or higher, 80°C or higher, 85°C or higher, or 90°C or higher, or 110°C or lower, 100°C or lower, 98°C or lower, 97°C or lower, or 95°C or lower, and for example, may be 70°C to 110°C, 75°C to 98°C, or 85°C to 95°C.

[0044] (1) The pressure at which the solvent treatment is performed in step may be 3 bar or more, 3.5 bar or more, 4 bar or more, 5 bar or more, 5.5 bar or more, 6 bar or more, or 6.5 bar or more, or 9 bar or less, 8.5 bar or less, 8.0 bar or less, or 7.5 bar or less, and may be, for example, 3 to 9 bar, 3.5 to 8.5 bar, or 5 to 8 bar.

[0045] (1) The dissolution time during which the solvent treatment is performed in step may be 10 minutes or more, 15 minutes or more, 20 minutes or more, or 25 minutes or more, or 60 minutes or less, 50 minutes or less, 45 minutes or less, or 40 minutes or less, and for example, may be 10 to 60 minutes, 20 to 50 minutes, or 25 to 40 minutes.

[0046] (1) If the temperature, pressure, and dissolution time at which the solvent treatment is performed in step (1) are below the above ranges, polyolefins other than the high-density polyethylene and homo-polypropylene to be separated may not sufficiently dissolve, and thus the purity and yield of the high-density polyethylene and homo-polypropylene to be separated may decrease. If the temperature, pressure, and dissolution time exceed the above ranges, the high-density polyethylene and homo-polypropylene may be excessively dissolved, and thus the purity and yield of the separated product may decrease.

[0047] In the above step (1), the solvent treatment may be performed more than once, and for example, may be performed 1 to 2 times, 2 to 4 times, or 2 to 5 times depending on the degree of dissolution of the polyolefin according to the solvent treatment. For example, in step (1), the solvent treatment twice is performed by subjecting the polyolefin complex to a solvent treatment to obtain a first solid phase (here, a solid phase including high-density polyethylene and homopolypropylene), and then subjecting the obtained first solid phase to a solvent treatment again to obtain a second solid phase, thereby additionally dissolving the undissolved polyolefin.

[0048] In the above step (1), the solvent treatment result is subjected to solid-liquid separation to obtain a solid phase including high-density polyethylene and homo polypropylene, wherein the solid-liquid separation may be performed by a method selected from the group consisting of filtration, centrifugation, decantation, sedimentation, flash devolatilization, and combinations thereof. For example, the solid-liquid separation may be performed by filtration. The filtration may use a filter of 60 mesh to 300 mesh, wherein n mesh means that n sieves exist on one side of a square that is 1 inch wide X 1 inch long, and the total number of sieves of n mesh is n 2 In addition, the separation step can be performed under inert gas (e.g., N2gas) conditions.

[0049] In the above step (2), the solvent treatment can be performed under temperature conditions of 80°C to 130°C and pressure conditions of 5 to 12 Bar.

[0050] (2) The solvent treatment step can be carried out under inert gas (e.g., N2gas) conditions, and can be pressurized as needed to reach appropriate pressure conditions.

[0051] (2) The temperature at which the solvent treatment is performed in step may be 80°C or higher, 85°C or higher, 90°C or higher, 95°C or higher, or 100°C or higher, or 130°C or lower, 125°C or lower, 120°C or lower, 118°C or lower, or 115°C or lower, and may be, for example, 80°C to 130°C, 85°C to 125°C, or 100°C to 120°C.

[0052] (2) The pressure at which the solvent treatment is performed in step may be 5 bar or more, 5.5 bar or more, 6 bar or more, or 6.5 bar or more, or 12 bar or less, 11 bar or less, 10 bar or less, 9 bar or less, 8.5 bar or less, 8.0 bar or less, or 7.5 bar or less, for example, 5 to 12 bar, 5.5 to 10 bar, or 6 to 8 bar.

[0053] (2) The dissolution time during which the solvent treatment is performed in step may be 10 minutes or more, 15 minutes or more, 20 minutes or more, or 25 minutes or more, or 60 minutes or less, 50 minutes or less, 45 minutes or less, or 40 minutes or less, and for example, may be 10 to 60 minutes, 20 to 50 minutes, or 25 to 40 minutes.

[0054] (2) If the temperature, pressure, and dissolution time at which the solvent treatment is performed in step (2) are below the above range, the high-density polyethylene to be separated may not be sufficiently dissolved, and thus the purity and yield of the high-density polyethylene and homo-polypropylene to be separated may decrease. If the temperature, pressure, and dissolution time exceed the above range, the homo-polypropylene may be excessively dissolved, and thus the purity and yield of the separated product may decrease.

[0055] In the above step (2), the solvent treatment may be performed more than once, and for example, may be performed 1 to 2 times, 2 to 4 times, or 2 to 5 times depending on the degree of dissolution of the polyolefin according to the solvent treatment. For example, in step (2), the two solvent treatments may be performed by performing a solvent treatment on the solid phase obtained in step (1) to obtain a first solid phase (here, a solid phase including homopolypropylene), and then performing a solvent treatment again on the obtained first solid phase to obtain a second solid phase, thereby additionally dissolving undissolved high-density polyethylene.

[0056] In the above step (2), the solvent treatment result is subjected to solid-liquid separation to obtain a liquid phase containing high-density polyethylene and a solid phase containing homopolypropylene, and the solid-liquid separation can be performed in the same manner as in the above-described step (1).

[0057] The method of the present invention may further include a step (3) of treating the solid phase obtained in step (2) with a solvent to obtain a liquid phase containing homo-polypropylene. Figure 1 schematically illustrates a polyolefin sorting process according to one specific example of the present invention, wherein the solid phase obtained in step (2) may be treated with a solvent to separate homo-polypropylene and impurities, etc. The method of the present invention may include such an additional step as needed, which is arbitrarily referred to as step (n). As in Figure 1, solvent treatment and separation may be additionally performed in step (n) after step (2).

[0058] In the above step (3), the solvent treatment can be performed under temperature conditions of 100°C to 150°C and pressure conditions of 7 to 15 Bar.

[0059] (3) The solvent treatment step can be carried out under inert gas (e.g., N2gas) conditions, and can be pressurized as needed to reach appropriate pressure conditions.

[0060] (3) The temperature at which the solvent treatment is performed in step may be 100°C or higher, 105°C or higher, 110°C or higher, 115°C or higher, or 120°C or higher, or 150°C or lower, 145°C or lower, 140°C or lower, 138°C or lower, or 135°C or lower, and may be, for example, 100°C to 150°C, 105°C to 145°C, or 110°C to 140°C.

[0061] (3) The pressure at which the solvent treatment is performed in step may be 7 bar or more, 7.5 bar or more, 8 bar or more, 8.5 bar or more, 9 bar or more, or 9.5 bar or more, and may be 15 bar or less, 14 bar or less, 13 bar or less, or 12 bar or less, for example, 7 to 15 bar, 8 to 14 bar, or 9 to 12 bar.

[0062] (3) The dissolution time during which the solvent treatment is performed in step may be 10 minutes or more, 15 minutes or more, 20 minutes or more, or 25 minutes or more, or 60 minutes or less, 50 minutes or less, 45 minutes or less, or 40 minutes or less, and for example, may be 10 to 60 minutes, 20 to 50 minutes, or 25 to 40 minutes.

[0063] (3) If the temperature, pressure, and dissolution time at which the solvent treatment is performed in step (3) are below the above range, the homo polypropylene to be separated may not be sufficiently dissolved, and thus the purity and yield of the homo polypropylene may decrease. If the temperature, pressure, and dissolution time exceed the above range, it is difficult to expect additional effects.

[0064] In the above step (3), the solvent treatment may be performed more than once, and for example, may be performed 1 to 2 times, 2 to 4 times, or 2 to 5 times depending on the degree of dissolution of the polyolefin according to the solvent treatment. For example, in step (3), the solvent treatment twice is performed by performing a solvent treatment on the solid phase obtained in step (2) to obtain a first solid phase (here, a solid phase remaining after homo polypropylene is separated due to dissolution), and then performing a solvent treatment again on the obtained first solid phase to obtain a second solid phase, thereby additionally dissolving undissolved homo polypropylene.

[0065] In the above step (3), the solvent treatment result is subjected to solid-liquid separation to obtain a liquid phase containing homopolypropylene.

[0066] For the liquid phase containing the high-density polyethylene obtained in step (2) or the liquid phase containing the homopolypropylene obtained in step (3), a solid phase can be obtained through solid-liquid separation after performing a subsequent process of additional separation or purification treatment, or the solid phase can be obtained through solid-liquid separation without performing a subsequent process. The solid-liquid separation can be performed in the same manner as in step (1) described above.

[0067] The saturated or unsaturated aliphatic hydrocarbon having 5 to 8 carbon atoms used in the method of the present invention may have a boiling point of 60 to 110°C, and the carbon atoms may be 5 to 8, 5 to 7, or 6 to 7, and the boiling point may be 60 to 110°C, 60 to 105°C, 62.5 to 105°C, or 65 to 105°C.

[0068] In one specific example, the solvent of step (1) may include a saturated or unsaturated aliphatic cyclic hydrocarbon having 5 to 8 carbon atoms, for example, the saturated or unsaturated aliphatic cyclic hydrocarbon having 5 to 8 carbon atoms may be selected from the group consisting of alkylcyclopentane, cyclohexane, cyclohexene, alkylcyclohexane having 5 to 8 carbon atoms, and combinations thereof. In one specific example, the solvent of step (1) may be methylcyclohexane, cyclohexane, cyclohexene, methylcyclopentane, ethylcyclopentane, or the like.

[0069] In one specific example, the solvent of step (2) may include a saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms, for example, the saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms may be selected from the group consisting of hexane, hexene, hexyne, heptane, heptene, heptine, mono- or di-alkylhexane having 5 to 8 carbon atoms, mono- or di-alkylheptane having 5 to 8 carbon atoms, and combinations thereof. In one specific example, the solvent of step (2) may be n-hexane, 2-methyl-hexane, 1-hexene, 1-hexyne, n-heptane, 1-heptene, 1-heptyne, 2-methyl-hexene, 3-methyl-hexane, 2,2-dimethyl-heptane, 2-methyl-heptane, 2-methyl-heptene, 3-methyl-heptane, etc.

[0070] In one specific example, the solvent of step (3) may include a saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms, for example, the saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms may be selected from the group consisting of hexane, hexene, hexyne, heptane, heptene, heptine, mono- or di-alkylhexane having 5 to 8 carbon atoms, mono- or di-alkylheptane having 5 to 8 carbon atoms, and combinations thereof. In one specific example, the solvent of step (3) may be n-hexane, 2-methyl-hexane, 1-hexene, 1-hexyne, n-heptane, 1-heptene, 1-heptyne, 2-methyl-hexene, 3-methyl-hexane, 2,2-dimethyl-heptane, 2-methyl-heptane, 2-methyl-heptene, 3-methyl-heptane, etc.

[0071] The purity of the separated high-density polyethylene and homo-polypropylene can be 95% or higher, for example, 96% or higher, 97% or higher, 98% or higher, or 99% or higher. The separated high-density polyethylene and homo-polypropylene can be used as environmentally friendly recycled plastic products as high-purity recycled polyolefins with a purity of 95% or higher.

[0072]

[0073] Hereinafter, the present invention will be described in more detail through examples, but these are only for the purpose of explaining the present invention, and the scope of the present invention is not limited in any way by the examples.

[0074] [Example]

[0075] Manufacturing Example: Manufacturing and Preparation of Model Feed of Polyolefin Composites

[0076] A model feed of a polyolefin composite to be used in the polyolefin sorting method of an embodiment of the present invention was prepared with the component contents described below.

[0077]

[0078]

[0079] The above model feed is composed of a composition similar to a polyolefin composite obtained from a specific waste plastic separation / sorting company, and this example does not limit the composition of the composite.

[0080]

[0081] Examples and Comparative Examples

[0082] Polyolefin selection was performed by setting the solvent and conditions of the examples and comparative examples as shown in Table 1 below.

[0083] First, a 3L pressure vessel was prepared and purged with N2 gas. Then, 2L of solvent was added and stirred, and the temperature was raised to the set temperature (N2 gas was pressurized as necessary). After reaching the set temperature, 3 wt% (based on solvent) of the model feed of the polyolefin composite was added and stirred for the set dissolution time. After stirring was completed, the liquid phase and the solid phase were separated using a filter (60-300 mesh). The filtration was performed while maintaining the corresponding dissolution conditions (temperature / pressure).

[0084] The liquid phase was obtained by precipitating under room temperature / normal pressure conditions, removing the solvent, and drying, and the solid phase was obtained by drying immediately. The obtained liquid phase and solid phase were weighed and analyzed, and the results are shown in Table 2. The process flow of the example of the present invention is as follows.

[0085]

[0086] - Feed (polyolefin model feed) input → solvent treatment in step (1) → solid phase containing high-density polyethylene and homo polypropylene obtained → feed input (solid phase in step (1)) → solvent treatment in step (2) → liquid phase containing high-density polyethylene and solid phase containing homo polypropylene obtained → solvent removal and drying of liquid phase containing high-density polyethylene → solid phase containing homo polypropylene dried → analysis

[0087]

[0088] [Table 1]

[0089]

[0090]

[0091] - Separation yield (%)

[0092] ① (1) Step

[0093] Solid phase: [Solid phase yield (g) / Model feed (g)] x 100

[0094] Liquid phase: [Liquid phase yield (g) / Model feed (g)] x 100

[0095] ② (2) Step

[0096] Solid phase: [Solid phase yield (g) / Solid phase of step (1) (g)] x 100

[0097] Liquid phase: [Liquid phase yield (g) / Solid phase (g) of step (1)] x 100

[0098]

[0099] - Analysis: DSC, FT-IR, GPC-IR (additional analysis such as NMR, NIR, CRYSTAF, etc. as needed)

[0100] - Purity measurement: Based on the analysis results, the content of high-density polyethylene (HDPE) and homo polypropylene (Homo PP) contained in the liquid phase containing high-density polyethylene and the solid phase containing homo polypropylene is calculated (wt%).

[0101]

[0102] [Table 2]

[0103]

[0104]

[0105] As confirmed from the results in Table 2 above, in the examples of the present invention treated with two or more solvents containing saturated or unsaturated aliphatic hydrocarbons having 5 to 8 carbon atoms, high-density polyethylene and homopolypropylene with a purity of 95% or higher could be separated. In addition, in the examples of the present invention, since aliphatic hydrocarbons, which are low in human hazard and easy to recycle, were used as solvents, it can be seen that the process is advantageous in terms of economic feasibility and stability.

[0106] However, in Comparative Example 1 using a solvent containing an aromatic hydrocarbon, or in Comparative Examples 2 and 3 using an aliphatic hydrocarbon as a single solvent, it was found that the purity of high-density polyethylene and homo-polypropylene was significantly lower than in the examples. In addition, when a solvent containing an aromatic hydrocarbon was used, as in Comparative Example 1, it was found that it was difficult to secure the economic feasibility and stability of the process because it was highly harmful to the human body and difficult to recycle. Additionally, as in Comparative Examples 4 to 6, even when the same solvent as in the examples was used but the operating condition ranges, such as temperature and pressure, were different, it was confirmed that the purity of high-density polyethylene and homo-polypropylene was lower than in the examples.

[0107] The final separation yield may vary depending on the model feed used. The model feed used in this example has a high PE content. If a feed with a high PP content is used, the yield of Homo PP may be higher than that of HDPE.

Claims

1. A method for obtaining high-density polyethylene (HDPE) and homo polypropylene (Homo PP) by separating them from a polyolefin complex containing at least one polyolefin, (1) a step of treating the polyolefin complex with a solvent to obtain a solid phase including high-density polyethylene and homopolypropylene; and (2) a step of treating the solid phase obtained in the above step (1) with a solvent to obtain a liquid phase including high-density polyethylene and a solid phase including homo polypropylene; A method wherein the solvents in steps (1) and (2) are different from each other and each independently contains a saturated or unsaturated aliphatic hydrocarbon having 5 to 8 carbon atoms.

2. A method according to claim 1, wherein the polyolefin composite further comprises a polyolefin selected from the group consisting of low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), high-density polyethylene (HDPE), homo-polypropylene (Homo PP), random polypropylene (Random PP), block polypropylene (Block PP), terpolymer polypropylene (Ter PP), ethylene / propylene copolymer, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, polyolefin elastomer (POE), or a combination thereof.

3. A method according to claim 1, wherein each of the obtained high-density polyethylene and homopolypropylene comprises 30 wt% or less of a comonomer or 30 wt% or less of another polyolefin composite component.

4. In paragraph 1, the polyolefin composite is derived from a household recycled plastic, an industrial recycled plastic, or a combination thereof, The above-mentioned recycled plastics from daily life or industrial recycled plastics are, A polymer selected from the group consisting of polyamide, polyester, polyvinyl chloride, polystyrene, ethylene vinyl alcohol, ethylene vinyl acetate, polyurethane, polyacrylate, polycarbonate or combinations thereof; or Containing a contaminant selected from the group consisting of metals, paper, dyes, pigments, organic matter, inorganic matter or a combination thereof; method.

5. In the fourth paragraph, the polyolefin composite is a method in which any one form selected from the group consisting of flakes, granules, pellets, chips, beads, powder and other masses obtained by compressing, crushing, washing and processing household recycled plastics, industrial recycled plastics or a combination thereof.

6. A method according to claim 1, wherein the solvent treatment in step (1) is performed under a temperature condition of 70°C to 110°C and a pressure condition of 3 to 9 Bar.

7. A method according to claim 1, wherein the solvent treatment is performed at least once in step (1).

8. A method in which the solvent treatment result in step (1) is subjected to solid-liquid separation to obtain a solid phase containing high-density polyethylene and homopolypropylene.

9. A method according to claim 1, wherein the solvent treatment in step (2) is performed under temperature conditions of 80°C to 130°C and pressure conditions of 5 to 12 Bar.

10. A method according to claim 1, wherein the solvent treatment is performed at least once in step (2).

11. A method in which the solvent treatment result in step (2) is subjected to solid-liquid separation to obtain a liquid phase containing high-density polyethylene and a solid phase containing homopolypropylene.

12. In paragraph 1, (3) A method further comprising a step of treating the solid phase obtained in step (2) with a solvent to obtain a liquid phase containing homopolypropylene.

13. A method according to claim 12, wherein the solvent treatment in step (3) is performed under a temperature condition of 100°C to 150°C and a pressure condition of 7 to 15 Bar.

14. A method according to claim 12, wherein the solvent treatment is performed at least once in step (3).

15. A method in claim 12, wherein the result of solvent treatment in step (3) is subjected to solid-liquid separation to obtain a liquid phase containing homopolypropylene.

16. In paragraph 11 or 15, A method for obtaining a solid phase through solid-liquid separation after performing a subsequent process of additional separation or purification treatment on a liquid phase containing high-density polyethylene obtained in step (2) or a liquid phase containing homo-polypropylene obtained in step (3), or obtaining a solid phase through solid-liquid separation without performing a subsequent process.

17. A method according to any one of claims 1 to 15, wherein the saturated or unsaturated aliphatic hydrocarbon having 5 to 8 carbon atoms has a boiling point of 60 to 110°C.

18. A method according to any one of claims 1 to 15, wherein the solvent in step (1) comprises a saturated or unsaturated aliphatic cyclic hydrocarbon having 5 to 8 carbon atoms.

19. A method according to claim 18, wherein the saturated or unsaturated aliphatic cyclic hydrocarbon having 5 to 8 carbon atoms is selected from the group consisting of alkylcyclopentane, cyclohexane, cyclohexene, alkylcyclohexane having 5 to 8 carbon atoms, and combinations thereof.

20. A method according to any one of claims 1 to 15, wherein the solvent in step (2) comprises a saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms.

21. A method according to claim 20, wherein the saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms is selected from the group consisting of hexane, hexene, hexyne, heptane, heptene, heptine, mono- or di-alkylhexane having 5 to 8 carbon atoms, mono- or di-alkylheptane having 5 to 8 carbon atoms, and combinations thereof.

22. A method according to any one of claims 12 to 15, wherein the solvent in step (3) comprises a saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms.

23. A method according to claim 22, wherein the saturated or unsaturated aliphatic linear or branched hydrocarbon having 5 to 8 carbon atoms is selected from the group consisting of hexane, hexene, hexyne, heptane, heptene, heptine, mono- or di-alkylhexane having 5 to 8 carbon atoms, mono- or di-alkylheptane having 5 to 8 carbon atoms, and combinations thereof.

Images