Solvent-based recycling method for polyolefin

Abstract

1. A solvent based recycle process for recycling waste polymeric material, comprising the steps of: obtaining a waste polymeric material comprising at least one polyolefin, the waste polymeric material comprising at least one polyolefin; contacting the waste polymeric material with at least one dissolving solvent to produce a slurry stream of polymer solution and undissolved solids; screening the slurry stream to produce undissolved solids and a polymer solution stream; vapor-liquid separation of the polymer solution stream into a polymer-lean vapor stream and a polymer-rich condensate stream; and recovering at least one polyolefin from the polymer-rich condensate stream, wherein the at least one dissolving solvent has a boiling point temperature of 70° C. or greater at 1 bar.

Description

Technical Field

[0001] The present invention generally relates to a solvent-based recycling method for polyolefins. More specifically, the present invention relates to a solvent-based recycling method for polyolefins that produces virgin-like polymers, has low requirements for high-load equipment in the process facilities, and can preferably be implemented in a continuous manner.

Background Art

[0002] The problems of treating accumulated waste plastics and the corresponding environmental issues have been widely noticed by the public and scholars. Therefore, in addition to the concept of preventing all plastic wastes, especially preventing the outflow of plastic wastes into the environment, the recycling of waste plastic materials has also become an important theme. Waste plastics can be converted into resources for new plastic products. Therefore, the recycling and reuse of waste plastic materials can achieve both environmental and economic benefits.

[0003] In the mid-1990s, in some countries in Europe, more differentiated waste collection systems (recycling management systems, circular economy laws) were introduced, enabling more targeted collection and separation of plastic materials from other wastes. Therefore, by separating polymer types more or less efficiently, the polymer types are finally concentrated after treatment, and secondary plastic material pieces that can be recycled more easily can be obtained. The construction of appropriate waste collection systems and, in particular, the establishment of appropriate waste separation infrastructure have been carried out in the past few decades to create sources and markets for secondary petrochemical raw materials. In parallel, several plastic recycling methods have been developed and particularly improved with the main goal of improving the achievable product quality of recyclable polymer materials.

[0004] The various generally known methods of plastic recycling include mechanical methods (material recycling), advanced physical or solvent-based (solution) methods, and chemical methods (feedstock recycling, thermochemistry such as pyrolysis and gasification, solvolysis). Among these methods, mechanical recycling and chemical recycling are the most widely implemented.

[0005] The EU's public collection and pre-sorting system reached a plastic recycling rate of 76 [wt% (Ger)] in 2018. However, regarding advanced mechanical recycling methods, the direct recycling rate of plastic materials was at a low level (for example, 12 [%] in Germany in 2018). Today, advanced mechanical recycling includes separation processes such as shredders, vibration, rotary sieves, advanced sorting methods supported by spectroscopy [e.g., NIR / VIS], and cleaning operations to reduce organic matter, biological substances, and partial malodorous pollutants generated from the surface of recyclable plastic materials. Also, polymer types are concentrated to achieve more homogeneous polymer recycled flakes. As a result, a secondary solid stream rich in plastic types, especially rich in polyolefins (PO content > 85 wt%; < wt 95%), such as polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), and / or polystyrene (PS), is obtained. These separated solid streams are then processed (extruded) into granules and processed into specific materials for conversion into products. However, the achievable product quality remains relatively low and cannot achieve both food contact applications and high-performance applications. Therefore, today, products such as flower pots, paint buckets, or shampoo bottles are common as mechanically recycled materials.

[0006] In particular, the implementation of improved and better sorting methods (e.g., colored flake sorting) affects both the concentration increase within a specific polymer type piece and the secondary washing operation, and it is desirable to more efficiently reduce harmful contaminants, etc., or improve the product quality of the final secondary polymer raw material. The latter includes additional expenditures related to complex process design, wastewater treatment, exhaust gas treatment, drying of intermediate products, etc., while reducing emissions as much as possible and combined with an increase in total energy consumption.

[0007] However, there remains the problem that it is difficult to directly remanufacture mechanical polymer recycling into high-quality end uses due to waste components such as multi-layer materials, films, or mixed flexible film waste materials. Furthermore, it is possible to find important reasons for the low predictability and controllability of the homogeneity of polymer type material mixtures, especially regarding the polymerization technologies (defining material properties such as polymer density, average molecular weight, molecular weight distribution, molecular structure, crosslinking degree, etc.) and compounding technologies (additives, filler concentration, and ultimately multiple pigment compositions) that have been historically applied. All these quality-related factors remain within the mechanically processed bulk solid mixture and cannot be covered by mechanical separation and the applied purification methods, and at best interact on the surface of the recyclable polymer material mixture.

[0008] A further approach to overcome the low quality in advanced mechanical polymer recycling is to blend the mechanically recycled polymer product with virgin polymer to achieve an acceptable and marketable quality for end uses (non-food), whereby the achievable content of the mechanically recycled polymer material remains at a low level (a few [wt%]), especially for high-quality / high-performance end uses.

[0009] The second plastic recycling route that has emerged is chemical recycling or feedstock recycling involving solvolysis and thermochemical (pyrochemical) treatment. In 2018, the technology share of chemical plastic recycling was less than 2% in total. According to technology forecasts, the share of thermochemical recycling should increase significantly from less than 2% (in 2018) to 13% by 2030. However, chemical plastic recycling offers a promising opportunity to recover pre-sorted and pre-treated solid plastic waste materials to obtain feedstock for the petrochemical industry, which can be processed back into plastics as well as chemical products and fuels. To decompose the polymer structure of plastic solid mixtures and break down shorter hydrocarbons to monomeric components, heat, catalysts, and solvents need to be applied. Depending on the specific technology, the approach of chemical recycling has a very high tolerance for mixed plastic pieces and impurities and can thus mainly handle contaminated polymer material mixtures and secondary polymer feedstocks. Nevertheless, cross-contamination between polyolefin-based material mixtures and heteroatom polymers (N / O / S, halogens) should preferably be avoided.

[0010] Nevertheless, the abstraction of thermochemical plastic processing, especially polyolefin recycling technology, rather shows the replacement of fossil-based crude oil fractions with already fossil-based secondary polymer recycling materials by applying well-known traditional thermochemical unit operations, which need to be cost-compatible with secondary feedstock sources. Since the energy demand for endothermic C-C bond and C-H bond cleavage (cracking, decomposition) that consumes a large amount of heat remains, the total energy finally input is significantly higher compared to the processing from crude oil to virgin polymers - mainly because the cracking of short-chain molecules (e.g., naphtha from crude oil fractionation) is replaced by the decomposition of long-chain and branched polymers. Apart from that, pyrolysis that consumes excessive energy remains. Furthermore, the CO2 emissions of such methods also increase unless the required applied energy carriers can be easily switched to renewable / sustainable energy carriers.

[0011] The third plastic recycling route is advanced physical recycling or solvent-based recycling (SbR), which showed a plastic recycling market share of less than 1% in Germany in 2018. In the SbR process, the polymer is first dissolved in a suitable solvent, and then the solubility of the dissolved polymer is reduced by the addition of a non-solvent (dissolution / precipitation), and / or the polymer solidifies by preferably completely separating the solvent from the solidified polymer by thermal unit operations (evaporation, drying, etc.).

[0012] The polyolefin-SbR process is similar to conventional PO polymerization processes, whereby the solvent for the monomers (olefins) and the temporarily formed oligomers (waxes) and short-chain polymers is, for example, a purified fraction (such as kerosene), until the solubility limit is exceeded (long-chain polyolefins are formed during polymerization), and the final polyolefin forms a polyolefin-solvent slurry and precipitates (e.g., the Chevron slurry process). A special polyolefin process is the solution PO polymerization process, whereby the olefin is first dissolved in a paraffinic solvent blend, polymerized, and the final polyolefin remains in solution until the process conditions change significantly by vacuum or flash devolatilization.

[0013] The framework of the generally known solvent-based recycling method for waste plastic materials includes impurity removal, dissolution, and polymer reprecipitation / recrystallization and / or devolatilization. Specifically, one or more polymers are dissolved in one or more solvents, and then each polymer is selectively precipitated / crystallized. Ideally, the solvent can be used for selective dissolution if it can dissolve either the target polymer or all other polymers other than the target polymer.

[0014] Generally, it is desirable to produce virgin-like polymers by solvent-based recycling methods of waste plastic materials. Virgin-like is defined as being free of contamination, free of pigments, odorless, homogeneous, and having properties similar to those of freshly polymerized polymers in general. The need for high-quality, virgin-like recycled resins is particularly important in applications that come into contact with foods and pharmaceuticals, such as food packaging. In addition to being contaminated with impurities and mixed colorants, many recycled resin products are often heterogeneous in chemical composition and may contain significant amounts of polymer contamination, such as polyethylene being mixed into recycled polypropylene and vice versa.

[0015] EP3339361(A1) describes a polymer solvent-based recycling method that includes a step of contacting waste polymers with n-butane at a temperature of 110 - 170 °C and a pressure of 1,100 - 2,100 psig. This step is repeated four times. Subsequently, the residue of this step is redissolved in n-butane at 130 - 180 °C and 2,000 - 3,000 psig. Further, precipitation and removal of the undissolved polymer are carried out, and an adsorption step using a pure silica bed followed by an aluminum oxide (zeolite) bed at 130 - 180 °C, 350 - 20,000 psig is added. Then, the polymer is precipitated from the solvent.

[0016] The drawback of this method is that the pressure used during the process is high, and since the material strength of the plant needs to be fully considered, robust equipment is required, resulting in high investment costs.

[0017] DE102016015199 A1 uses an air dissolution method for the separation of industrial waste, particularly the separation of polyamides, polyethylene, and / or polypropylene. The solvent is a higher non-polar gasoline (kerosene) fraction with a boiling point temperature of 80 - 140 °C.

[0018] The disadvantage of this method is the high residual solvent content in the intermediate polymer product (up to 5% by volume). The removal of these unwanted solvents requires a complex and expensive post-treatment process using thin-film evaporators (low throughput) and dryers. Since the exhaust gas contains hydrocarbons, a large exhaust gas treatment plant is required.

Prior Art Documents

Patent Documents

[0019]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0020] Therefore, generally, the polymer solvent-based recycling methods known in the prior art, particularly the polyolefin solvent-based recycling methods, are either high-pressure methods with the disadvantage of high cost and labor, or target high-boiling solvents that cannot provide virgin-like recycled polyolefins because they cause problems after process treatment, especially from the perspective of solvent removal.

[0021] Furthermore, many of the solvent-based recycling methods of polyolefins described in the prior art are designed in a way that continuous methods are not possible. As already mentioned, one of the problems can lie in the technology of high-pressure methods. However, the technology of the supply method and separation can also potentially affect the possibility of continuously implementing the method.

[0022] Therefore, an object of the present invention is to find a solvent-based recycling method for polyolefins that enables the production of virgin-like polyolefins and has low requirements from the perspectives of material strength, staff experience, and cost.

[0023] A further object of the present invention is to provide a continuous solvent-based recycling method for polyolefins.

Means for Solving the Problems

[0024] Surprisingly, the above object is achieved by a solvent-based recycling method for recycling waste polymer materials, which comprises the steps of: obtaining a waste polymer material containing at least one polyolefin; contacting the waste polymer material with at least one dissolving solvent to produce a slurry stream of a polymer solution and undissolved solids; screening the slurry stream to produce an undissolved solid and a polymer solution stream; vapor-liquid separating the polymer solution stream into a polymer-lean vapor stream and a polymer-rich condensate stream; and recovering at least one polyolefin from the polymer-rich condensate stream, wherein the at least one dissolving solvent has a boiling point temperature of 70 °C or higher at 1 bar.

[0025] The advantages of the method of the present invention are that the solvent-based recycling method can be carried out at a lower pressure than that shown in the prior art, while maintaining the ability to easily and economically remove the solvent from the final polymer. Furthermore, since the recycled solvent can be reintroduced into the solvent-based recycling method, energy and material requirements, as well as costs, are further reduced. Furthermore, since the number of unit operations used in this method is small, the maintenance effort and the possibility of downtime are reduced. Furthermore, the method of the present invention can separate more than one polymer during recycling. Finally, the produced polymer is free of significant amounts of polymer cross-contamination, is essentially colorless, and is essentially odorless (i.e., virgin-like).

Brief Description of the Drawings

[0026]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Embodiments for Carrying Out the Invention

[0027] <Definition> As used herein, the expressions "volatile" or "volatile compound" should be understood as compounds having a significantly lower molecular weight compared to the polyolefin separated by the method of the present invention. Such compounds are usually present in gaseous form when exposed to a flash separator. Generally, volatile compounds are mixtures of volatile hydrocarbons. Preferably, the mixture of volatile hydrocarbons contains at least one solvent.

[0028] "Flash separator" has been known in the prior art for decades (also known as a low-pressure separator). As is well known in the art, a liquid feed is sent to a flash vessel operated under reduced pressure. Thereby, a part of the liquid phase evaporates and can be taken out from the low-pressure separator as an overhead stream (or vapor stream). Then, the remaining part in the liquid phase is taken out from the flash vessel as a bottom stream or liquid stream. The operation of the low-pressure separator under conditions where both a gas phase and a liquid phase are present in the flash vessel explains this situation.

[0029] As used herein, "gravity separator" or "liquid-liquid separator" includes a container capable of separating a two-phase (i.e., liquid / liquid) system. The liquid phase having a lower relative density (polymer lean stream) is withdrawn from the upper end of the container, while the liquid phase having a higher relative density (in this case, polymer rich stream) is withdrawn from the lower end of the container.

[0030] The method of the present invention is a solvent-based recycling method for recycling waste polymer materials (1), wherein the waste polymer materials (1) contain at least one polyolefin (2), and the method comprises the following steps: a) obtaining a waste polymer material (1) containing at least one polyolefin (2); b) contacting the waste polymer material (1) with at least one dissolving solvent (3) to produce a slurry stream (4) of a polymer solution (5) and undissolved solids (6); c) screening the slurry stream (4) to produce an undissolved solids (6) and a polymer solution (5) stream; d) vapor-liquid separating the polymer solution (5) stream into a polymer-lean vapor stream (9) and a polymer-rich condensate stream (10); e) recovering at least one polyolefin (2) from the polymer-rich condensate stream (10) and wherein the at least one dissolving solvent (3) has a boiling temperature of 70 °C or higher at 1 bar.

[0031] The waste polymer material (1) may include various plastics such as polyethylene (PE) or polypropylene (PP), particularly high-density polyethylene (HDPE), low-density polyethylene (LDPE) or linear low-density polyethylene (LLDPE), poly(ethylene terephthalate) (PET), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), polyurethane (PUR) and polyamide (PA). Preferably, the waste polymer material (1) has a polyolefin content of more than 75% by weight, more preferably more than 80% by weight, and most preferably more than 85% by weight. The waste polymer material (1) may further contain common additives such as antioxidants, food residues, residual flavor components, dyes and pigments, and waste impurities such as components that are generally inevitably introduced into plastic waste materials during production and use. In addition to contamination, many recycled resin products often have a heterogeneous chemical composition and may contain a large amount of polymer contamination such as PE contamination in recycled PP or vice versa.

[0032] The polyolefin (2) recycled by the method of the present invention can be a mixture of polyolefins such as polypropylene or polyethylene. However, preferably, the polyolefin (2) contains a single polyolefin and preferably consists of a single polyolefin. Most preferably, the polyolefin (2) contains polypropylene and preferably consists of polypropylene. In the latter case, it should be understood that the polyethylene residue can be redissolved using the same dissolving solvent (3) at an elevated temperature and an increased residence time and separated according to the present invention.

[0033] Generally, the dissolution solvent (3) must be able to dissolve polyolefin, especially polyolefin (2). Therefore, the dissolution solvent (3) is preferably a non-polar solvent or a mixture thereof. Therefore, the solvent is preferably a hydrocarbon or a mixture of hydrocarbons. More preferably, the dissolution solvent (3) is a paraffinic solvent or a mixture of paraffinic solvents due to the paraffinicity of the polyolefin ("Similia similibus solventum"). Aromatic hydrocarbon solvents can be considered because they are known for their good solvent properties. Nevertheless, the drawback of aromatic hydrocarbons is that they promote the dissolution of polystyrene. On the other hand, for example, n-alkanes are known not to dissolve polystyrene. Most importantly, the solvent does not dissolve polar polymers such as PET, PVC, PA, PC, PUR, etc., or bio-based fractions such as cellulose or lignin. Furthermore, the boiling point of the dissolution solvent (3) at 1 bar pressure must be 70 °C or higher. Therefore, preferably, the dissolution solvent is selected from the list of low-boiling solvents and high-boiling solvents, or mixtures thereof. Low-boiling solvents include n-alkanes such as toluene and xylene, as well as aromatic hydrocarbons. The advantage of low-boiling solvents is that they can be separated from the dissolved polyolefin by evaporation. High-boiling solvents include paraffinic light oil or vacuum light oil. Such solvents have the drawback that they are difficult to remove from the product. Therefore, preferably, the dissolution solvent (3) is selected from n-alkanes or mixtures thereof having a boiling point exceeding 70 °C at a pressure of 1 bar, preferably 150 °C or lower, more preferably 140 °C or lower, even more preferably 100 °C or lower, and most preferably 90 °C or lower. Most preferably, the dissolution solvent (3) is selected from the group consisting of n-heptane, n-octane, n-nonane, and n-decane, or mixtures thereof. Step a) of obtaining the waste polymer material (1) includes a step of preparing the waste polymer material (1) from general waste, which includes washing the waste with an aqueous solution and / or a caustic solution to remove unnecessary substances from the waste polymer (see FIGS. 2-5). Further, in step a), the size of the waste polymer pieces is preferably reduced, preferably by cutting, milling and shearing, or a mixture thereof.

[0034] Step b) of bringing the waste polymer material (1) into contact with at least one dissolving solvent (3) is preferably a dissolving step (see FIG. 2). Thus, preferably, the polyolefin (2) is dissolved in the dissolving solvent (3) (see FIGS. 2-5). On the other hand, the resulting slurry (4) may still contain undissolved solids (6) in addition to the polymer solution (5). Such solids can be either the dissolving solvent (3) or non-polymer solids such as pigments or additives that do not dissolve in the polymer. Such polymers can be either polar polymers that are insoluble in the solvents used or non-polar polymers that are insoluble under the conditions used in the dissolving step. Preferably, the dissolved polymer in the polymer solution (5) is the polyolefin (2).

[0035] Contact step b) can be carried out in a state where only the polyolefin to be targeted is dissolved by the dissolution solvent (3). Such a configuration is particularly applicable when the target polyolefin dissolves at a lower temperature than all other polyolefins present in the waste polymer material (1). In another embodiment of step b), the conditions are selected such that even two or more polyolefins, i.e., polymer A and polymer B, are dissolved. In such a case, the subsequent liquid-liquid separation step is beneficial for separating the solubilized polymers from each other (see below). Mainly, polypropylene can be dissolved from a polyethylene / polypropylene mixture using a non-polar solvent having Hansen solubility parameters similar to / approximating the solubility parameter of polypropylene. The said conditions are preferably selected to exhibit a temperature in the range of 100 to 300 °C, more preferably 110 to 290 °C, and most preferably 120 to 280 °C. Preferably, the pressure used in step b) is in the range of 5 to 50 bar, preferably 7 to 45 bar, and most preferably 10 to 40 bar.

[0036] The waste polymer material (1) can be brought into contact with the dissolution solvent (3) either in a solid or molten state. Preferably, the waste polymer material (3) is melted, enabling rapid and complete mixing of both the polymer material and the dissolution solvent (3), i.e., shortening the time required to completely dissolve the polymer material (see Figure 6). Generally, shortening the time required for dissolving the polymer material supports the implementation of the dissolution step in a continuous manner. To further shorten the time required to dissolve the polyolefin (2), preferably, the slurry of the waste polymer material (1) and the dissolution solvent (3) is stirred. Preferably, the dissolution step b) is carried out within 1 hour.

[0037] In step c), the undissolved solids (6) are preferably removed from the polymer solution (5) by solid-liquid separation (see FIGS. 2 to 5). Preferably, step c) can be selected from hot filtration, discharge on a screw conveyor, centrifugation, filtration, and solid / liquid extraction, or a mixture thereof. The undissolved solids (6) can be collected and dissolved in another step to recover other polymer fractions contained therein. Step c) may be a series of solid-liquid separations of the stream.

[0038] Also, even more preferably, in step c), other unwanted substances still soluble in the polymer solution (2) are also screened out of the polymer solution (2). Such substances include additives, colorants, antioxidants, odors, and mixtures thereof. Most preferably, the screening step is carried out by desorption of the unwanted materials. Preferably, the desorption method is carried out with the aid of a sorption aid to which the unwanted substances adsorb or are absorbed. The sorption aid may also bind the unwanted substances by size exclusion, ion exclusion, ion exchange, or other mechanisms. Further, pigments and other materials commonly found in waste polymer materials may be polar compounds and may preferentially interact with the sorption aid, so it may be at least slightly polar. Polar-polar interactions are particularly advantageous when a non-polar solvent such as an alkane is used as the solvent in the dissolution step.

[0039] The storage aid is preferably selected from the group consisting of inorganic substances, carbon-based substances, and mixtures thereof. Non-limiting examples of inorganic substances are silicon oxide (silica), silica gel, aluminum oxide (alumina), iron oxide, aluminum silicate, magnesium silicate, amorphous volcanic glass, recycled glass, sand, quartz, diatomaceous earth, zeolite, perlite, clay, fuller's earth, bentonite clay, metal-organic framework (MOF), covalent organic framework (COF), and zeolitic imidazolate framework (ZIF). Non-limiting examples of carbon-based substances are anthracite, carbon black, coke, and activated carbon. In one embodiment of the present invention, the inorganic substance is selected from the group consisting of silicon oxide (silica), silica gel, aluminum oxide (alumina), iron oxide, aluminum silicate, magnesium silicate, amorphous volcanic glass, recycled glass, sand, quartz, diatomaceous earth, zeolite, perlite, clay, fuller's earth, bentonite clay, metal-organic framework (MOF), covalent organic framework (COF), zeolitic imidazolate framework (ZIF), and mixtures thereof. In another embodiment of the present invention, the inorganic substance is selected from the group consisting of silicon oxide (silica), silica gel, aluminum oxide (alumina), amorphous volcanic glass, recycled glass, sand, quartz, diatomaceous earth, zeolite, clay, fuller's earth, bentonite clay, and mixtures thereof. In yet another embodiment of the present invention, the carbon-based substance is selected from the group consisting of anthracite, carbon black, coke, activated carbon, and mixtures thereof.

[0040] In a preferred embodiment of the solution, the polymer solution (5) is then fed to a liquid-liquid separation step c'') into a polymer-lean stream (7) and a polymer-rich stream (8). Under specific temperature and pressure conditions, the polymer solution may phase-separate into two different liquid phases, one being a liquid phase where the dissolved polymer is "lean" and the other being a liquid phase where the dissolved polymer is "rich". The phase separation occurs at the lower critical solution temperature (LCST), also known as the "cloud point" (see Figure 1). This phase separation phenomenon has been well-known in the art for many years.Details regarding phase separation can be found, for example, in de Loos et al., "Liquid-Liquid Phase Separation in Linear Low Density Polyicular Solvent Systems", Fluid Phase Equilibria 117 (1996), 40-47, Irani et al., "Lower Critical Solution Temperature Behavior of Ethylene Propylene Copolymers in Multicomponent Systems", Journal of Applied Polymer Science, Vol. 31, 1879-1899 (1986), Chan et al., "Fluid-Liquid Transitions of Poly(ethylene-co-octene-1) in Supercritical Ethylene Solutions", Ind. Eng. Chem. Res. 2000, 39, 4370-4375, Nagy et al., "High pressure phase equilibria in the system linear low density polyethylene+isohexane: Experimental results and modelling", J. of Supercritical Fluids 40 (2007), 125-133, "Handbook of Polymer Synthesis, Characterization, and Processing", First Edition, authors Enrique Saldivar-Guerra, Eduardo Vivaldo-Lima, published by John Wiley & Sons in 2013, particularly Volume 15, pages 317-334, as well as in the references cited in these documents.

[0041] An increase in temperature or a decrease in pressure at the cloud point leads to further phase separation. In other words, phase separation is promoted by higher temperature and / or lower pressure. The cloud point is partially determined by pressure, temperature, solution composition, and the solvent used in the polymerization.

[0042] Referring to FIG. 1, the separation principle of the two polymers in the L / L separation process will be described below. In this figure, the phase diagram of the two polymers (A) and (B) is shown in a simplified manner, and the function defining the boundary of the V-L-L region is assumed to be the same for both polymers. Therefore, under conditions exceeding this function, the polymer and the solvent exist without generating a further vapor phase. Nevertheless, this condensation region can be divided again into a single-phase region and an L-L region, and the mixture exists in two liquid phases, one liquid phase mainly containing the polymer and the other liquid phase mainly containing the solvent. Both regions are separated from each other by the lower critical solution temperature (LCST), which is a pressure-dependent function. When both polymers (A) and (B) are present in the polymer solution, it exists in another region, that is, between the LCST of (B) and the LCST of (A). In this region, polymer (A) remains solubilized in the liquid phase, and polymer (B) has already been separated. Therefore, in such a system, polymer (B) can be separated with a polymer-rich stream, while polymer (A) can be separated with a polymer-lean stream. Subsequently, the polymer-lean stream can be fed again into the L / L separation process (see FIG. 4). As can be seen from the schematic diagram of FIG. 1, by adjusting the pressure (decreasing when starting from the single-phase region) or the temperature (increasing when starting from the single-phase region), the region between the LCST functions can be reached. However, the pressure should not be lowered until the V-L-L region is reached.

[0043] When adopting step c'') (see FIGS. 3 and 4), the polymer-rich streams (8, 8 1、(82) is introduced into step d) (d1 and d2 in Fig. 4). The liquid-liquid separation in step c'') is preferably carried out at a temperature of 120 to 250 °C and a pressure of 10 to 100 bar. Generally, step c'') can be used to separate the polymer from the liquid phase. Thus, in step b), if only one polyolefin is dissolved in the polymer solution, step c'') can be carried out, but due to the subsequent steps d) and e) of the method of the present invention, it is not necessary to carry out. However, if two or more polyolefins are dissolved in the polymer solution in step b), step c'') can be used to separate the polymer solution in that the polymer-rich stream carries one polyolefin and the polymer-rich stream carries the other polyolefin. In this case, each of these streams is subjected to the subsequent steps d) and e) of the method of the present invention. When the polymer solution contains more than two polyolefins, the conditions of the first liquid-liquid separation step of step c'') are preferably selected such that one polyolefin is in the polymer-rich stream and the other two polyolefins are in the polymer-lean stream. The polymer-lean stream is again subjected to the second liquid-liquid separation step of step c''), and the remaining two polymers are separated from each other (see Fig. 4). Thus, when two or more polymers are dissolved in the polymer solution (5), step c'') can be a series of liquid-liquid separation steps.

[0044] In an even more preferred embodiment of the present invention including the above step c''), another step c') is carried out following step c) and preceding step c'') (see Fig. 3). In this step, the polymer solution (5) taken out from step c) is homogenized again.

[0045] Accordingly, the polymer solution (5) is preferably stirred in the tank. Therein, the mixture is maintained under conditions ensuring that the polyolefin (2) is completely dissolved in the solvent (3). Preferably, the conditions are selected in the same way as the conditions of step b). Furthermore, it is ensured that there is no gas phase in the system, i.e., in the tank. Thus, the stream leaving step c’) is a one-phase stream. The conditions are preferably selected to exhibit a temperature of 100 to 300 °C, more preferably 110 to 290 °C, and most preferably 120 to 280 °C. Preferably, the pressure used in step b) ranges from 5 to 50 bar, preferably 7 to 45 bar, and most preferably 10 to 40 bar. Preferably, step c’) is carried out to provide a polymer solution (5) stream at a temperature of 120 to 250 °C and a pressure of 10 to 100 bar. By step c’), a homogenized polymer solution (5’) is obtained, which is then fed to the liquid-liquid separation step c’’).

[0046] If the polymer-lean stream (7) from step c’’) mainly contains the solvent, it can be reintroduced into the contacting step b) after purification of the solvent (see Figures 3 and 4). The purification of the solvent preferably includes the removal of molecules of lower and higher molecular weight than the solvent molecules. If only one polymer is dissolved in the polymer solution (5) and one liquid-liquid separation step is employed in step c’’), the polymer-lean stream (7) mainly contains the solvent. However, if two or more polymers are dissolved in the polymer solution, the polymer-lean stream (7) is the polymer-lean stream of the last liquid-liquid separation step of step c’’) because the polymer-lean stream of the preceding liquid-liquid separation step still contains polymers.

[0047] Recycling the polymer-lean stream to the contacting step b) has the advantage of reducing the energy and materials consumed, resulting in an economically and environmentally favorable method.

[0048] The gas-liquid separation step d) of separating the polymer-rich stream (8) into a polymer-lean vapor stream (9) and a polymer-rich condensate stream (10) is preferably carried out as a flash separation step (see Figures 2 to 5). Preferably, step d) is carried out under conditions that evaporate the volatile compounds in the polymer-rich stream (8) from the condensate phase mainly containing the polymer. The temperature used in step d) is preferably 100 to 400 °C, more preferably 130 to 300 °C, and most preferably 170 to 250 °C. Also preferably, the pressure used in step d) is preferably 1 to 15 bar, more preferably 1 to 5 bar, and most preferably 1 to 3 bar. When step d) is the only flash separation step in the process, the pressure conditions can be selected with a vacuum condition as the lower limit. Accordingly, the polymer-rich condensate stream (10) exiting step d) is cooled to 150 to 250 °C, preferably 170 to 230 °C, and most preferably 190 to 210 °C. Most preferably, step d) is preferably carried out at a temperature of 170 to 250 °C and a pressure of 1 to 3 barg.

[0049] After purification, the polymer-lean vapor stream (9) can be reintroduced into the contacting step b) after adjusting the temperature and pressure to meet the dissolution requirements occurring in step b) (see Figures 2 to 5).

[0050] Step d) can be repeated a plurality of times, preferably up to 3 times continuously. Thus, in such a setting, the polymer-rich vapor phase (8) exiting the first step d) is fed again to the second flash separation step d’), thereby generating a second polymer-rich vapor phase (8’), which can in turn be fed to a third flash separation step d’’). The flash separation steps d) to d’’) each generate a polymer-rich condensate stream (10), which can be further processed together or separately. When step d) is carried out continuously a plurality of times, the pressure is decreased step by step and the temperature is increased step by step. Thus, the preferred levels described for the temperature and pressure of step d) preferably determine the temperature and pressure used in steps d), d’) and d’’). If the liquid-liquid separation step c’’) is employed before step d), the pressure may already be less than 10 bar before entering step d). Thus, it is necessary to change the conditions of step d) respectively. That is, either increasing the pressure of the polymer-rich stream in step c’’) or increasing the temperature in step d).

[0051] The step e) of recovering the polymer from the polymer-rich condensate stream (10), each polymer-rich condensate stream (10) to (102), or a combination of the polymer-rich condensate streams (10) to (102) is preferably carried out in an extruder (see FIGS. 2 to 5). Even more preferably, step e) is carried out in a devolatilization extruder. More preferably, the extruder has a rear degassing means under atmospheric conditions and a front degassing dome under vacuum conditions. Most preferably, the extruder utilizes the injection of water between the degassing domes.

[0052] Thus, in the preferred embodiment according to FIG. 2, a solvent-based recycling method for recycling a waste polymer material (1) containing at least one polyolefin (2) comprises the following steps: a) obtaining a waste polymer material (1) containing at least one polyolefin (2); b) contacting the waste polymer material (1) with at least one dissolving solvent (3), preferably at a pressure of 10 to 40 bar and a temperature of 120 to 280 °C, to produce a slurry stream (4) of a polymer solution (5) and undissolved solids (6); c) screening the slurry stream (4), preferably by solid-liquid separation and / or desorption, to obtain an undissolved solids (6) and a polymer solution (5) stream; d) vapor-liquid separating the polymer solution (5) stream, preferably at a temperature of 170 to 250 °C and a pressure of 1 to 3 barg, into a polymer-lean vapor stream (9) and a polymer-rich condensate stream (10); e) recovering at least one polyolefin (2) from the polymer-rich condensate stream (10); comprising.

[0053] Furthermore, in a preferred embodiment according to Figure 3, a solvent-based recycling method for recycling a waste polymer material (1) containing at least one polyolefin (2) comprises the following steps: a) obtaining a waste polymer material (1) containing at least one polyolefin (2); b) contacting the waste polymer material (1) with at least one dissolving solvent (3), preferably at a pressure of 10 to 40 bar and a temperature of 120 to 280 °C, to produce a slurry stream (4) of a polymer solution (5) and undissolved solids (6); c) screening the slurry stream (4), preferably by solid-liquid separation and / or desorption, to obtain an undissolved solids (6) and a polymer solution (5) stream; c’) homogenizing the polymer solution (5), preferably at a pressure of 10 to 40 bar and a temperature of 120 to 280 °C, to obtain a homogenized polymer solution (5’); c’’) liquid-liquid separating the homogenized polymer solution stream (5’), preferably at a temperature of 120 to 250 °C and a pressure of 10 to 100 bar, into a polymer-lean stream (7) and a polymer-rich stream (8), and preferably returning the polymer-lean stream to step b); d) Separating the polymer-rich stream (8) into a polymer-lean vapor stream (9) and a polymer-rich condensed stream (10), preferably at a temperature of 170 to 250 °C and a pressure of 1 to 3 barg; e) Recovering at least one polyolefin (2) from the polymer-rich condensed stream (10); comprises.

[0054] Furthermore, in a preferred embodiment according to Figure 3, a solvent-based recycling method for recycling a waste polymer material (1) containing at least one polyolefin (2) comprises the following steps: a) Obtaining a waste polymer (1) containing at least two polyolefins (2); b) Contacting the waste polymer material (1) with at least one dissolving solvent (3), preferably at a pressure of 10 to 40 bar and a temperature of 120 to 280 °C, to produce a slurry stream (4) of a polymer solution (5) and undissolved solids (6); c) Screening the slurry stream (4), preferably by solid-liquid separation and / or desorption, to obtain an undissolved solids (6) and a polymer solution (5) stream; c’) Optionally, homogenizing the polymer solution (5), preferably at a pressure of 10 to 40 bar and a temperature of 120 to 280 °C, to obtain a homogenized polymer solution (5’); c’’1) Separating the homogenized polymer solution stream (5’) or the polymer solution stream (5) into a polymer-lean stream (71) containing a first polyolefin (21) and a polymer-rich stream (81) containing a second polyolefin (22), preferably at a temperature of 120 to 250 °C and a pressure of 10 to 100 bar, and preferably returning the polymer-lean stream to step b); c’’2) Separating the polymer-lean stream (71) into a second polymer-lean stream (72) and a second polymer-rich stream (82) containing a second polyolefin (22), preferably at a temperature of 120 to 250 °C and a pressure of 10 to 100 bar, and preferably returning the second polymer-lean stream (72) to step b); Step d1): Separating the polymer-rich stream (81) into a polymer-lean vapor stream (91) and a polymer-rich condensed stream (101) at a temperature preferably between 170 and 250 °C and a pressure of 1 to 3 barg, and preferably returning the polymer-lean vapor stream (91) to step b); Step d2): Separating the second polymer-rich stream (82) into a second polymer-lean vapor stream (92) and a second polymer-rich condensed stream (102) at a temperature preferably between 170 and 250 °C and a pressure of 1 to 3 barg, and preferably returning the second polymer-lean vapor stream (92) to step b); Step e1): Recovering the second polyolefin (22) from the polymer-rich condensed stream (101); Step e2): Recovering the first polyolefin (21) from the polymer-rich condensed stream (102); It includes the following steps.

[0055] This specific embodiment has the advantage that two polymers can be dissolved simultaneously in the method, so they can be separated by a single continuous method, improving the economic efficiency of the method.

[0056] Preferably, the method of the present invention includes a pretreatment step a') following step a) of obtaining the waste polymer material (1), and a step b) of bringing the waste polymer material (1) into contact with the dissolving solvent (3) (see Figure 5). Such a pretreatment step can include an extraction step and / or a melting step. Preferably, the pretreatment step a') includes a melting step. In a particularly preferred embodiment of the present invention, the pretreatment step a') includes a first extraction step, a subsequent melting step, and optionally another second extraction step following the melting step.

[0057] When the pretreatment step a') includes an extraction step, the waste polymer material (1) is brought into contact with an extraction solvent (3e) to remove unnecessary substances present in the waste polymer material (1). Therefore, the extraction solvent (3e) preferably has the same boiling point as the dissolution solvent (3) at a pressure of 1 bar. More preferably, the extraction solvent (3e) is identical to the dissolution solvent (3). Generally, the conditions selected in step a') are milder than those in step b), where milder defines lower temperature and lower pressure. Generally, the conditions of step a') are selected such that they do not dissolve the target polyolefin but only other components.

[0058] When the pretreatment step a') includes a melting step, the waste polymer material (1) is fed into an extruder where the polymer is first melted (see Figure 6). Subsequently, and preferably, the polymer melt is fed into a melt pump to increase the pressure within the melt. High pressure within the melt has the advantage of enhancing the ability to separate solid particles and impurities of the material through melt sieves. Furthermore, the supply of the polymer material to the subsequent separation step is ensured.

[0059] When the pretreatment step a') includes a melting step, the extraction solvent (3e) is preferably mixed with the molten polymer within a mixing device downstream of the melt pump. This promotes rapid mixing of the extraction solvent (3e) and the molten polymer. The final concentration of the extraction solvent (3e) in the mixture of the molten polymer and the extraction solvent (3e) is preferably 1.0 - 95 wt%. Preferably, the mixing device is a static mixer or a dynamic mixer, more preferably a static mixer having the advantage of low maintenance costs (see Figure 6).

[0060] During the mixing of the extraction solvent (3e) and the molten polymer, a homogeneous polymer mixture can be produced. In such a case, it is advantageous if the extraction solvent (3e) is identical to the dissolution solvent (3) used in the dissolution step b). Such a setting has the advantage that the dissolution time in the dissolution step b) is significantly shortened. Furthermore, this method can be implemented in a continuous manner.

[0061] When the extraction solvent (3e) is removed from the polymer melt again, this step can be regarded as a second extraction step following the melting step.

[0062] The addition of the extraction solvent (3e) can be carried out in a single step or multiple steps. Multiple steps can further promote extraction and dissolution. The temperature and pressure used in step a') are preferably 150 - 250 °C and 50 - 150 bar.

[0063] The main advantage of the step of melting the polymer is that the melt can preferably be filtered, and thus impurities not in the molten state can be removed before step b). Furthermore, when an additional degassing dome is used, such a setting brings the possibility of degassing gas components such as water and volatile substances. Another advantage is that the melt bulk density is relatively high compared to the solid polymer. This improves fluidity and makes it easier to supply the polymer to the contacting step b). Furthermore, this method can be carried out in a continuous mode and can be simplified by eliminating the extraction step. Finally, when the extraction step is removed from the method, the required solvent cycle is only once, which not only further reduces the complexity of the method but also reduces the consumption of the required materials and energy.

Explanation of symbols

[0064] 1: Waste polymer material 1a: Molten waste polymer material 2: Polyolefin 3: Dissolving solvent 3e: Extraction solvent 4: Slurry of undissolved solids and polymer solution 5: Polymer solution 6: Undissolved solids 7: Polymer-lean stream (produced in the liquid-liquid separation step) 8: Polymer-rich stream (produced in the liquid-liquid separation step) 9: Polymer-lean vapor stream (produced in the gas-liquid separation step) 10: Polymer-rich condensate stream (produced in the gas-liquid separation step) a): Step of obtaining the waste polymer material (1) a'): Step of pretreating waste polymer material (1) b): Step of dissolving polyolefin (1) c): Step of screening polymer solution c'): Step of homogenizing polymer solution c''): Step of liquid-liquid separating polyolefin from polymer solution (5) d): Step of vapor-liquid separating polymer from solvent of either polymer solution (5) or polymer-rich stream (8) e): Step of recovering polyolefin (2)

[0065] Since steps c'') and d) may occur continuously multiple times, they can be represented as c''1 or d2, but it should be understood that the index indicates the order of continuous processing of the steps (i.e., 1 → first, 2 → second). The same applies to the stream (stream) following the plurality of steps and the steps following it downstream (i.e., e2). The initial disclosure of this specification includes at least the following aspects. [1] A solvent-based recycling method for recycling waste polymer material (1), wherein the waste polymer material (1) contains at least one polyolefin (2), and the method comprises the following steps: a) Obtaining a waste polymer material (1) containing at least one polyolefin (2); b) Contacting the waste polymer material (1) with at least one dissolving solvent (3) to generate a slurry stream (4) of a polymer solution (5) and undissolved solids (6); c) Screening the slurry stream (4) to generate an undissolved solids (6) and a polymer solution (5) stream; d) Vapor-liquid separating the polymer solution (5) stream into a polymer-lean vapor stream (9) and a polymer-rich condensate stream (10); e) Recovering at least one polyolefin (2) from the polymer-rich condensate stream (10); The method, wherein the at least one dissolving solvent (3) has a boiling point temperature of 70 °C or higher at 1 bar. [2] The method further comprises, following step c) and preceding step d), the following step: C'') Liquid-liquid separating the polymer solution (5) stream into a polymer-lean stream (7) and a polymer-rich stream (8), and the polymer-rich stream (8) is supplied to step d). The solvent-based recycling method according to [1] above. [3] The solvent-based recycling method according to [2] above, wherein step c) comprises a solid-liquid separation step of separating undissolved solids (6) from the polymer solution (5). [4] Further comprising a homogenization step c') of receiving the polymer solution (5) and obtaining a homogenized polymer solution (5'), which is carried out following step c) and preceding step c''), and the homogenized polymer solution (5') is supplied to step c''). The solvent-based recycling method according to any one of [1] to [4] above. [5] The method further comprises, following step a) and preceding step b), the following step: a') Extracting the waste polymer material (1) with at least one extraction solvent (3e), or melting the waste polymer material (1) The solvent-based recycling method according to any one of [1] to [4] above. [6] The solvent-based recycling method according to [5] above, wherein step a') melts the waste polymer material (1) to generate a molten waste material (1a). [7] The solvent-based recycling method according to [6], wherein in step a'), the molten waste material (1a) is mixed with the dissolution solvent (3) in the mixing device. [8] Step c'') is carried out at least twice, and the polymer lean stream (7 1 ) of the first step c'' 1 ) is supplied to the second step C'' 2 ) The solvent-based recycling method according to any one of [2] to [7] above. [9] Step d) is carried out at least twice, and the polymer-rich condensate stream (10) of the first step d') is supplied to the second step d''), and the solvent-based recycling method according to any one of [1] to [8] above.

Claims

1. A solvent-based recycling method for recycling waste polymer material (1), wherein the waste polymer material (1) contains at least one polyolefin (2), and the method comprises the following steps: a) obtaining a waste polymer material (1) containing at least one polyolefin (2); b) contacting the waste polymer material (1) with at least one dissolving solvent (3) to produce a slurry stream (4) of a polymer solution (5) and undissolved solids (6); c) screening the slurry stream (4) to produce undissolved solids (6) and a polymer solution (5) stream; d) vapor-liquid separating the polymer solution (5) stream into a polymer-lean vapor stream (9) and a polymer-rich condensate stream (10), purifying the polymer-lean vapor stream (9), adjusting the temperature and pressure, and then reintroducing it into step b); e) recovering at least one polyolefin (2) from the polymer-rich condensate stream (10). The method includes the steps, wherein the at least one dissolving solvent (3) has a boiling point temperature of 70 °C or higher at 1 bar, and further includes the following step, which is carried out subsequent to step c) and prior to step d): C'') liquid-liquid separating the polymer solution (5) stream into a polymer-lean stream (7) and a polymer-rich stream (8), supplying the polymer-rich stream (8) to step d), and recycling the polymer-lean stream (7) to step b).

2. The solvent-based recycling method according to claim 1, wherein step c) includes a step of solid-liquid separating undissolved solids (6) from the polymer solution (5).

3. The solvent-based recycling method according to claim 1, further including a homogenization step c') that receives the polymer solution (5), subsequent to step c) and prior to step c''), to obtain a homogenized polymer solution (5'), and the homogenized polymer solution (5') is supplied to step c'').

4. The method further includes the following step subsequent to step a) and prior to step b): a') extracting the waste polymer material (1) with at least one extraction solvent (3e), or melting the waste polymer material (1). The solvent-based recycling method according to claim 1.

5. The solvent-based recycling method according to claim 4, wherein step a') melts the waste polymer material (1) to produce a molten waste material (1a).

6. The solvent-based recycling method according to claim 5, wherein in step a'), the molten waste material (1a) is mixed with the dissolving solvent (3) in a mixing device.

7. The engineering c'') is carried out at least twice, and the first engineering c'' １ ) of the polymer lean stream (7 １ ) is supplied to the second process C'' ２ ) The solvent-based recycling method according to claim 1.

8. The solvent-based recycling method according to claim 1, wherein step d) is carried out at least twice, and the polymer-rich condensate stream (10) of the first step d') is supplied to the second step d'').

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