A process for recycling polyolefin-containing waste streams, and suitable equipment for the same.

Abstract

This invention provides a process for recycling polyolefin-containing waste streams and suitable equipment for this process. [Solution] The present invention provides a process for recycling a polyolefin-containing waste stream containing inorganic components and / or non-polyolefin polymers, comprising the following steps: a. raising the temperature of the waste stream above the melting temperature of the polyolefin(s) contained therein to form a molten waste stream; b. separating solid components from the molten waste stream; c. adding a solvent to the molten waste stream to form a slurry containing a polyolefin solution and undissolved components; d. separating undissolved components from the polyolefin solution; and e. isolating polyolefins from the polyolefin solution; wherein step b is carried out using a melt filter, step c is carried out so that a dynamic viscosity of the slurry in the range of 4200 Pa·s to 10 Pa·s is achieved, the undissolved components are separated from the slurry by filtration in step d using one or more filtration units, and step e is carried out by precipitation of the polyolefins. Furthermore, apparatus used in the process of the present invention is provided.

Description

Technical Field

[0001] The present invention relates to a process for recycling polyolefin-containing waste streams and an apparatus suitable therefor. More particularly, the present invention relates to a solvent-based recycling process for polyolefin-containing waste streams. Further, the present invention discloses a dissolving apparatus capable of separating other components such as inorganic materials such as metals and high melting point polyesters from a polyolefin matrix.

Background Art

[0002] The problem of disposal of accumulated waste plastics and the corresponding environmental problems have been widely noticed by the general public and researchers. Therefore, in addition to the general concept of prevention of waste plastics and particularly prevention of leakage of waste plastics into the environment, recycling of waste plastic materials has become an important issue. Waste plastics can be converted into resources for new plastic products (hereinafter referred to as recyclates). Therefore, recycling and reuse of waste plastic materials have both environmental and economic aspects.

[0003] In the mid-1990s, several European countries realized a more finely sorted waste collection system (Recycling Management System, Circular Economy Law) that enables more targeted recovery and separation of plastic materials from other wastes. Thus, a somewhat more efficient separation of polymer types from each other can be managed so that, after treatment, a finally concentrated polymer type is obtained and thus a secondary plastic material fraction that can be recycled more easily is obtained. The construction of an appropriate waste collection system and particularly the setup of an appropriate waste separation infrastructure have been carried out within the past few decades, and a resource market for secondary petrochemical raw materials has emerged. In parallel, several plastic recycling processes have been developed and particularly improved, with the goal of first enhancing the achievable product quality of recyclable polymer materials.

[0004] There are various commonly known methods of plastic recycling, including mechanical [material recycling], advanced physical or solvent-based [solution] and chemical treatments (including feedstock recycling, thermochemical, e.g., pyrolysis or gasification, solvolysis). Of these methods, mechanical and chemical recycling are the most widely implemented. In European public collection and pre-sorting systems, the plastic recovery rate reached 76% by weight (Ger) in 2018, but the direct plastic material recycling rate is low compared to advanced mechanical recycling processes (e.g., 12% in Germany in 2018 and 30% in the Netherlands by 2030). Currently, advanced mechanical recycling includes advanced sorting methods [e.g., NIR / VIS] assisted by separation processes, e.g., crushing, vibration, rotary sieving, and spectroscopic methods, as well as cleaning operations to reduce mainly organic, biological, and partially odorous contaminants from the surface of recyclable plastic materials, and the achievement of concentrated polymer types and more homogeneous polymer recycling fractions. This is achieved by concentrating each plastic type, particularly polyolefins. A concentrated secondary material stream (>85; <95 [wt%] PO content), such as polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET), and / or polystyrene (PS), is obtained. These separated material streams are then processed into granules (extruded) and materials specific to the products to be converted. Nevertheless, the achievable product quality remains relatively low, unsuitable for both food contact and high-performance applications, and thus products such as vases, paint buckets, or shampoo bottles are representative of the materials currently mechanically recycled. Particularly improved and more efficient sorting methods (e.g., sorting of color flakes) should improve the product quality of the final secondary polymer raw material by affecting both higher concentrations within specific polymer type fractions and secondary washing operations to more efficiently reduce interfering contaminants, respectively. The latter further includes expenditures on drying intermediate products, which are linked to complex process design, wastewater treatment, exhaust gas treatment, and increased total energy consumption, while maintaining emissions as low as possible.

[0005] However, the challenge of directly remanufacturing mechanically recycled polymers for high-quality end-use remains, posed by waste components such as multilayer material films or mixed flexible film waste. Furthermore, a significant reason can be found in the unpredictable and uncontrollable homogeneity of polymer-type material mixtures, particularly related to the historically applied polymerization techniques (differences in material properties such as polymer density, average molecular weight, molecular weight distribution, molecular structure, and crosslinking level) and the historically applied formulation techniques (additives, filler concentrations, and ultimately multiple pigment compositions). All of these quality-related factors remain within the mechanically processed bulk material mixture and, at best, interact on the surface of the recyclable polymer material mixture, cannot be covered by mechanical sorting and applied purification methods.

[0006] A further approach to overcome the low quality in advanced mechanical polymer recycling may be found in blending mechanical polymer recycles with non-virgin polymers to ultimately achieve market-ready quality acceptable for end-use (non-food), thereby keeping the feasible content of mechanically recycled polymer material at low levels (several [weight %]), especially for high-quality / high-performance end-uses.

[0007] The emerging second plastic recycling pathway is chemical or feedstock recycling, involving solvolysis and thermochemical treatment. In 2018, the total technological share of chemical plastic recycling was less than 2%. Technological forecasts indicate that the thermochemical recycling share will significantly increase from less than 2% (2018) to 13% by 2030. Chemical plastic recycling offers a promising opportunity to recover pre-sorted and pre-treated solid plastic waste and obtain feedstock for the petrochemical industry, which can be processed back into plastics, as well as chemical articles and fuels. Heat and solvents must be applied to decompose the polymer structure of plastic solid mixtures into shorter hydrocarbons down to monomer constituent units. Depending on the specific technology, the chemical recycling approach has a fairly high tolerance for mixed plastic fractions and impurities, and can therefore deal with contaminated mixtures and polymer material mixtures, secondary polymer feedstocks. Cross-contamination of heteroaromatic polymers (N / O / S, halogens) and polyolefin material mixtures is preferable and should be avoided.

[0008] Nevertheless, the replacement of fossil-based crude oil fractions with already fossil-based secondary polymer recyclable materials is exemplified, to be precise, by applying known conventional thermochemical unit operations, which must be adapted to secondary supply raw material sources, albeit at a cost, particularly from the abstraction of thermochemical plastic processing, especially polyolefin recycling technology. Regarding heat-intensive endothermic CC, CH bond cleavage (cracking, decomposition), there is still a certain energy demand, and as a result, the total energy input is ultimately significantly higher compared to processing non-recycled polymers with respect to crude oil - mainly the decomposition of short-chain molecules (e.g., naphtha in crude oil fractions) is replaced by cracking long-chain and branched-chain polymers. Independently, enormous and energy-consuming pyrolysis still remains. Furthermore, the CO2 emissions of such processes are also high unless the required energy carriers applied can be easily switched to renewable / sustainable energy carriers. A third plastic recycling pathway is advanced physical or solvent-based recycling (SbR). In the SbR treatment, 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 solvent is preferably completely separated from the solidified polymer by a thermal unit operation (evaporation, drying, etc.), thereby causing the polymer to solidify.

[0009] The polyolefin-SbR treatment exhibits similarities to conventional PO polymerization processes, where the solvent for monomers (olefins), transiently formed oligomers (waxes), and short-chain polymers is, for example, petroleum refined fractions (e.g., kerosene), until the solubility limit is exceeded (long-chain polyolefins are formed during polymerization) and the final polyolefin precipitates to form a polyolefin solvent slurry (e.g., Chevron slurry process). An exceptional polyolefin process is a solution PO polymerization process, where the olefin is initially dissolved in a paraffinic solvent blend, and the finished polymerized polyolefin remains soluble until process conditions are significantly altered by vacuum flash defoliation.

[0010] The framework of a generally known solvent-based recycling process for waste plastics includes the removal of impurities, dissolution of polymers, and 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, a solvent can be used for selective dissolution if it can dissolve either the target polymer or all other polymers except the target polymer.

[0011] Generally, it is desirable to produce virgin-like polymers through solvent-based recycling processes for waste plastics. "Virgin-like" is defined as being free of contaminants, pigments, and odors, being homogeneous, and having properties similar to newly polymerized polymers. The need for high-quality, virgin-like recycled resins is particularly important for food and pharmaceutical contact applications, such as food packaging. In addition to being contaminated with impurities and mixed colorants, many recycled resin products often have heterogeneous chemical compositions and can contain significant polymer contamination, such as polyethylene contamination in recycled polypropylene and vice versa.

[0012] The key to an efficient solvent-based polyolefin recycling process is the dissolution step. In this step, the polymer is dissolved in a solvent. Good homogeneity of the solution is advantageous in achieving a uniform composition of the stream, leaving a dissolution section. This is necessary to ensure a consistent quality of recycled polyolefin. Furthermore, it is desirable that the time required to dissolve the polymer to the required homogeneity be as short as possible. In particular, this needs to be an economical process in terms of both CAPEX and OPEX.

[0013] In solvent-based polyolefin recycling processes, among the various design criteria that must be considered when designing mixing equipment for dissolving waste polyolefins, mixing within the mixing vessel is particularly challenging. Firstly, the viscosity of the components within the mixing vessel is relatively high. Typically, viscosity varies depending on the polyolefin recycling process, the polyolefin being recycled (average molecular weight), its concentration (m%), and the corresponding conditions (pressure and temperature) used in the vessel for dissolution. The typical viscosity of a polyolefin solution can be around 4000-20 Pa·s, but can be reduced to approximately 0.1 Pa·s.

[0014] Typically, especially considering subsequent separation steps, it is necessary to produce a completely solubilized polyolefin solution. To achieve this, the design of the mixing vessel aims for maximum homogeneity of the components.

[0015] Furthermore, heat control is necessary to ensure optimal and rapid dissolution. Each mixing pattern within the mixing vessel, which improves uniformity, also typically leads to better thermal convection and thus better control.

[0016] Therefore, a mixing apparatus optimized to ensure uniformity of components in the mixing vessel is generally required in the field of solvent-based polyolefin recycling. This apparatus improves thermal control, phase control, and dissolution time, and allows for specific control of the mixing pattern.

[0017] CA2376488A1 discloses a solvent-based process for separating polyolefins (polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), and linear low-density polyethylene (LLDPE)) using two solvents, namely n-hexane and petroleum. The starting materials are brought into contact with the solvent at a high temperature, i.e., approximately 140°C. Subsequently, undissolved solids are removed from the solution in one or more steps using filtration, centrifugation, or other mechanical separation methods. After the removal of undissolved solids, the solution consists mainly of the solvent and dissolved polyolefins. Each polyolefin is precipitated sequentially from the solution using crystallization under simultaneous shear action. As a result, each polymer type is separated, and waxes, polymer chain fragments, and different additives are maintained in a dissolved state. For the dissolution step, a mixing nozzle is disclosed. Other means for mixing are not explicitly disclosed. Therefore, it is not possible to derive further improvements in mixing time and uniformity from the disclosure of CA2376488A1.

[0018] U.S. Patent Application Publication No. 20180171094A1 discloses a solvent-based process for purifying reclaimed polypropylene. A method for purifying reclaimed polypropylene is provided. The method comprises obtaining reclaimed polypropylene, contacting it with a first fluid solvent to produce extracted reclaimed polypropylene, then dissolving the extracted reclaimed polypropylene in the solvent to produce a first solution containing polypropylene and suspended contaminants. The first solution is allowed to settle to produce a second solution containing polypropylene and residual contaminants. The second solution is purified by contacting it with a solid medium to produce a third solution containing purer polypropylene. Finally, the purer polypropylene is separated from the third solution.

[0019] International Publication No. 2022029318A1 discloses a method for reducing a plastic material containing at least one target polymer, particularly a method for crushing; a method for removing dust from the reduced plastic material containing at least one target polymer, integrated with a solvent-type method including an extraction step; and a method for recycling a plastic material containing at least one thermoplastic target polymer, comprising an integrated step of adding a functional solid or liquid additive to a solution containing the thermoplastic target polymer. Furthermore, a method for removing additives and / or impurities from a fluid form containing the thermoplastic target polymer while simultaneously being processed in an extruder is described.

[0020] European Patent No. 4074483A1 relates to a solvent-based recycling process for polyolefins, and discloses a dissolution apparatus and process used in a solvent-based recycling process for polyolefins.

[0021] The above patent disclosure does not mention how cellulose-containing materials, metals, and high-melting-point polymers are separated from polyolefin waste with the intention of recovering these materials for reuse in new / alternative applications. The reuse of these materials would generate additional economic value and improve circularity.

[0022] German Patent Application Publication No. 4414750A1 relates to a process and apparatus for clearing a viscose-based polymer molten material that may contain paper particles. The impurities are separated from the polymer molten material by centrifugation.

[0023] German Patent No. 1918183C2 relates to a method for separating the components of a product containing at least two types of plastic substances or plastic and metallic substances. The product is heated to a softening temperature, centrifuged at that temperature, and the plastic substances are disposed of.

[0024] In the disclosure of the prior art, it is suggested that the separation of a plastic stream mixed with metal and cellulose can be carried out using a centrifuge in the process configuration. However, when using a centrifuge at high temperature and high pressure, since a volatile flammable solvent is used, combined with the dissolution of the polymer, serious safety problems will occur. Summary of the Invention Problems to be Solved by the Invention

[0025] The present invention aims to overcome the above problems. More particularly, the present invention aims to improve the solvent-based recycling process of polyolefin, thereby producing a product with a reduced impurity content. There are many technologies available for recovering polyolefin, but the inventors have found that isolation by precipitation from a solvent functions best under the condition that impurities are removed in various steps. Means for Solving the Problems

[0026] Therefore, a process for recycling a polyolefin-containing waste stream containing inorganic components and / or non-polyolefin polymers, comprising: a. raising the temperature of the waste stream to a temperature exceeding the melting temperature of the polyolefin(s) contained therein; b. separating the solid components from the molten waste stream; c. adding a solvent to the molten waste stream to form a slurry containing a polyolefin solution and undissolved components; d. separating the undissolved components from the polyolefin solution; and e. isolating olefin from the polyolefin solution; comprising: step b is carried out with a melt filter, step c is carried out such that the dynamic viscosity of the slurry in the range of 4200 to 10 Pa·s is achieved, The insoluble components are separated from the slurry by filtration in step d using one or more filtration devices. There is provided a process in which step e is carried out by precipitating the polyolefin.

[0027] Furthermore, there is provided an apparatus used in the process of the present invention.

Brief Description of the Drawings

[0028] [Figure 1-3] It is a schematic diagram of different embodiments of the present invention, in which a waste stream containing polyolefin is supplied to an extruder and subjected to a heating / melting process. Downstream of the extruder, a melt filtration module is inserted and unmelted material is separated from the polymer melt. The embodiment illustrates different paths in which a suitable solvent is introduced into the polymer melt that is later subjected to a filtration step.

Embodiments for Carrying out the Invention

[0029] Surprisingly, the object of the present invention is achieved by the dissolution process according to the claims and by the dissolution process and apparatus according to the claims in which polyolefin is dissolved from a polyolefin-containing waste stream into a solvent to form a polyolefin solution slurry containing a polyolefin solution and undissolved residues. The dissolution apparatus preferably includes at least one extruder equipped with a melt filtration unit capable of separating unmelted species with a diameter > 100 μm from the polyolefin-containing waste stream. After dissolution, the second filtration system separates unmelted and undissolved species from the polymer phase in at least one filtration unit, preferably the series of units being at a level of 100 μm to submicron. The final product is isolated from the solvent by precipitation. The process of the present invention includes melt filtration and filtration of the slurry, and foreign matter contamination is significantly avoided. Color particles are usually in the range of 3 - 300 nm and tend to be small, so the use of filtration is not proposed, and this success is particularly unexpected.

[0030] The process of this invention will be explained with reference to Figures 1-3. Please note that the basic concept of the process of this invention is to dissolve at least one type of waste polyolefin in a solvent.

[0031] The dissolution process of this invention generally comprises two steps. In the first step, a polyolefin-containing waste stream is fed into an extruder, preferably a single-screw or twin-screw extruder, to produce a molten waste stream. The extruder preferably includes a melt filtration module for removing unmelted species. Preferably, unmelted species with a size >100 μm are removed. The second step, (2), is a dissolution step in which the molten waste stream is brought into contact with a suitable solvent. This can be achieved using a static mixer, an extruder, a dissolution vessel, or a combination thereof. This forms a slurry containing the polyolefin solution and unmelted components. This is subjected to a single or series of filtration steps to remove unmelted and unmelted particles down to submicron size, providing a polyolefin slurry, from which the polyolefin can be isolated by precipitation.

[0032] Waste polyolefin materials Waste polyolefin-containing materials are typically supplied in a pulverized state and have already undergone pre-sorting and washing, and even several prior steps of pre-sorting. Such steps generally involve preparing a polyolefin-containing waste stream from general waste, which includes washing the waste with water and / or a caustic alkali solution to remove unwanted substances from the polyolefin containing the waste. Furthermore, the size of the polymer pieces containing the waste is preferably reduced beforehand, preferably by cutting, pulverizing, and shearing, or by mixing thereof. The polyolefin-containing waste stream may be supplied in a pulverized state, preferably in flake form, preferably having a maximum diameter of 3 cm or less, more preferably 2 cm or less, and most preferably 1 cm or less. The polyolefin-containing waste stream preferably contains no waste at all on the surface of the polyolefin flakes. Therefore, the process of the present invention preferably relates to the dissolution of waste polyolefin flakes that are essentially clean from contaminants therein.

[0033] Polyolefins Polyolefin-containing waste streams may contain different 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), metallocene-based polyethylene (m-PE), polyethylene terephthalate (PET), polypropylene (PP), polyvinyl chloride (PVC), polystyrene (PS), polycarbonate (PC), ethylene-vinyl alcohol (EVOH), polyurethane (PUR), and polyamide (PA). Preferably, polyolefin-containing waste streams have a polyolefin content of more than 75% by weight, more preferably more than 80% by weight, and most preferably more than 85% by weight, based on the total weight of the polyolefin-containing waste stream. Polyolefin-containing waste streams may further contain waste impurities, such as common additives like antioxidants, food residues, residual fragrance components, dyes and pigments, and components that are generally inevitably introduced into plastic waste through manufacture and use. In addition to contamination, many recyclable waste streams may contain bio-based fractions such as cellulose or lignin. Furthermore, recyclable waste streams may contain metals of considerable economic value, such as iron, copper, and aluminum.

[0034] solvent Generally, a solvent must be able to dissolve polyolefins without dissolving polymers other than polyolefins. Ideally, the solvent is a non-polar solvent or a mixture thereof. For example, the solvent is a hydrocarbon or a mixture of hydrocarbons. Aromatic hydrocarbon solvents are known for their good solvent properties and can therefore be considered. Nevertheless, a disadvantage of aromatic hydrocarbons is that they increase the solubility of polystyrene. On the other hand, n-alkanes, for example, are known not to dissolve polystyrene. Most importantly, the solvent should not dissolve polar polymers such as PET, PVC, PA, PC, PUR, or bio-based fractions such as cellulose or lignin. Furthermore, preferably, the boiling point of the solvent at a pressure of 1 bar exceeds 60°C. Most appropriately, the solvent is selected from a list of low-boiling point solvents and high-boiling point solvents or mixtures thereof. Low-boiling point solvents include n-alkanes and aromatic hydrocarbons, such as toluene and xylene. An advantage of low-boiling point solvents is that they can be separated from the dissolved polyolefin by evaporation. High-boiling point solvents include paraffinic diesel or vacuum diesel. Such solvents have the disadvantage that they are difficult to remove from the product. On the other hand, aromatic solvents may cause odor problems due to residual contents after separation, or problems when intended for applications requiring food approval. Therefore, preferably, the solvent is selected from n-alkanes or mixtures thereof having a boiling point at a pressure of 1 bar above 60°C, preferably below 150°C, more preferably below 140°C, even more preferably below 100°C, and most preferably below 90°C.

[0035] undissolved residue Undissolved residues can generally be undissolved solid or liquid residues. Most commonly, undissolved residues are other polymers that are small enough to pass through the melt filtration module and are insoluble under the conditions and solvents selected in the process. Undissolved solids can be nonpolymeric solids that are insoluble in the solvent or polymer used for dissolution, such as pigments, cellulosic materials, metals, or additives. Such polymers can be either polar polymers insoluble in the solvent used, or nonpolar polymers insoluble under the conditions used in the dissolution process.

[0036] Melt supply and melt filtration In the melting feed process, preferably a flake-shaped polyolefin-containing waste stream is melted before being fed to the dissolution stage. The temperature of the molten waste stream is preferably above the dissolution temperature in the second stage. More preferably, the temperature of the molten waste stream is 20 to 60°C higher than the melting temperature of the polyolefin contained therein, but below the melting temperature of the non-polyolefin components contained therein, such as high-melting-point polyester. Therefore, the temperature may be in the range of 110 to 300°C, preferably 150 to 250°C. Melting is preferably carried out in an extruder equipped with a single-screw or twin-screw machine, and a temperature in the range of 180 to 245°C is applied. Continuous melt filters supplied by Maag, Pall, etc., are suitable for separating materials containing up to 16% by weight of contaminants and are guaranteed to maintain their usable condition for extended periods without filter replacement. In general, melt filters can process a wide range of polymers (e.g., LDPE, LLDPE, HDPE, PP, PS, ABS, PC / ABS, TPE, TPU, POM). All solid or elastomeric foreign particles, such as paper, wood, aluminum, copper, rubber, silicone, or high-melting-point polymer compositions, can be efficiently removed. In principle, melt filters can be used regardless of the type of extrusion line—single-screw or twin-screw and pelletizing system—or other downstream units. In this particular embodiment, efficient removal of PET, aluminum, and copper from molten waste streams has been demonstrated using internal filters with pore sizes ranging from 500 μm to 100 μm without compromising performance.

[0037] Introduction of solvent and dissolution of polymer The molten waste stream after the melt filtration unit is introduced into a second stage, which involves the introduction of a solvent and the subsequent dissolution of polyolefin, to form a slurry containing the polyolefin solution and undissolved components. It is important to consider the following aspects: (1) There is a large difference in viscosity between the polymer molten material and the solvent, making mixing difficult. Therefore, efficient mixing is still required. Insufficient mixing may result in an uneven temperature distribution in the solution, which can affect the polymer material, especially when the temperature of the polyolefin reaches relatively high values, i.e., 250°C for polypropylene. (2) The melt feed can be carried out in a continuous manner, as the melt feed can be pressurized to match the pressure in the dissolution process, without including a gas phase, i.e., in a dissolution vessel completely filled with solvent and molten polyolefin. The advantage of such a process is that, compared to dry or wet feed, the molten polyolefin mixes rapidly with the solvent and dissolves rapidly in the solvent.

[0038] It may be advantageous to heat the slurry feed material by supplying a separate hot solvent for dissolution at a temperature higher than the final dissolution temperature. Since the molten feed material can be pressurized to match the pressure in the dissolution process, molten feed can and preferably be carried out in a continuous manner. Preferably, since the molten feed material can be pressurized to match the pressure in the dissolution process, molten feed is carried out in a continuous manner. The appropriate temperature after molten filtration is generally expected to be above 200°C, and the dissolution temperature is expected to be in the range of 130-150°C.

[0039] The solvent can be introduced at one point or several points. For example, the solvent can be introduced to form a slurry having a dynamic viscosity in the range of 4200 to 1500 Pa·s. Additional solvent can then be added to reduce the dynamic viscosity to the range of 100 to 10 Pa·s. The concept of dynamic viscosity, sometimes called absolute viscosity, is known to those skilled in the art. General measurement methods are used.

[0040] This process may be carried out with apparatus in different configurations. Three configurations, described in detail below, are preferred.

[0041] Figure 1 shows a first embodiment in which a polyolefin-containing waste stream (1) is fed into an extruder (5) and subjected to a heating / melting process, thereby forming a molten waste stream containing polymer molten material. Downstream of the extruder (5), a melt filtration module is inserted, where unmelted material (2), such as metals and high-melting-point polymers, is separated from the molten waste stream. This module preferably includes a molten material pressure-controlled scraper system that removes contaminants from the surface of a rotating screen disk into a discharge screw system. In this embodiment, a gear pump (6) is preferably used to maintain the relevant pressure. A suitable solvent (3) is introduced into the polymer molten material by a homogenization device (7), and further solvent addition is carried out in a dissolution vessel (8). The polymer is completely dissolved and undergoes a further process as filtration using one or more filtration units (9), where very fine particles containing, for example, metals, inorganic components, and high-melting-point polymers are separated. The embodiment shown in Figure 1 illustrates a preferred embodiment in which a static mixer (7a) is used as the homogenization device (7), and (part of) the solvent (3) is introduced. The solvent (3) can be preheated. Typically, it is introduced into the homogenization device (7) at a pressure higher than the pressure of the melt flow. The solvent-containing melt flow is transferred to the dissolution vessel (8). Additional solvent can be introduced into the dissolution vessel (8). The dissolution vessel (8) is operated appropriately at a temperature in the range of 130-150°C and a corresponding pressure of 7-20 bar(g). Preferably, the dissolution vessel (8) takes the form of a continuous stirred tank reactor. The ratio of solvent additions between the homogenization device (7) and the dissolution vessel (8) can be changed. Typically, the ratio of polymer to solvent is in the range of 1-30% by weight.

[0042] Figure 2 shows a second embodiment similar to the first embodiment, in which a polyolefin-containing waste stream (1) is fed into an extruder (5) and subjected to a heating / melting process, thereby forming a molten waste stream containing a polymer molten material. The homogenization device (7) in this embodiment is a second extruder (7b). The extruder (7b) preferably has a twin-screw design and a screw design including precise transport and mixing modules. The barrel design of the extruder is equipped with a solvent inlet so that the molten material is sealed and the injection of solvent (3) (or part thereof) is introduced. The solvent (3) may be preheated. Typically, it is injected into the extruder at a pressure higher than the pressure of the melt flow. To maintain sufficient back pressure after the introduction of the solvent, the extruder (7b) is equipped with a diverter valve (not shown).

[0043] The embodiment shown in Figure 3 is similar to the first embodiment, except that this embodiment does not include a dissolution vessel as a homogenization device (7), which is a device (7c) on which the dissolution process can be carried out and completed. Therefore, the device (7c) comprises a well-designed tube having a plurality of solvent injection posts and housing a plurality of static mixers inside. A gear pump (6) may be used to maintain the associated pressure.

[0044] In the design of homogenization devices, particularly those using static mixers, it is recommended that fouling should be given special consideration due to the presence of undissolved and / or unmelted particles in the polymer slurry.

[0045] Polymer filtration Upon completion of the dissolution process, the slurry containing the polyolefin solution and undissolved components is transferred to one or more filtration units (9). The slurry may contain undissolved solids having a particle size in the range of approximately 100 to 0.1 μm. The undissolved solids may be nonpolymeric solids that are not soluble in the dissolution solvent (3), such as pigments, cellulosic materials, metals or additives, or non-polyolefin polymers that are not soluble in the solvent used. A single unit may be used, but preferably a series of units are used. Preferably, it or each filtration unit includes a regeneration module for the operation. Preferably, it or each filtration unit is designed to operate in a safe mode and is designed to match the operating pressure and temperature in conjunction with the flammable solvent. Preferably, one to three sets of filtration units are used to separate, for example, particles of 100 to 20 μm, 20 to 1 μm, and less than 1 μm. This preferred configuration allows for the efficient separation of high-melting-point polymers and metals having particle sizes in the range of 100–20 μm, as well as other contaminants / additives having particle sizes in the range of 20 submicrons. The filtration element may be a candle, a filter disc, or the filter housing may contain an essentially inorganic filter aid that selectively removes impurities from the polymer slurry (4). Preferably, it or each filtration unit operates in batch or continuous mode at 150–200°C. It may be advantageous to add a decolorizing agent that can absorb or neutralize small impurities. It may also be advantageous to include centrifugation to remove impurities.

[0046] Polymer isolation Polyolefins are isolated by precipitation. By selecting the above process steps, precipitation (e.g., by crystallization) can be carried out without contamination. The solvent can then be removed by filtration (under vacuum). For example, any remaining solvent can be removed during the granulation of the precipitated polyolefin. During granulation, it may also be advantageous to add common additives such as stabilizers to the polyolefin.

[0047] The process for recycling polyolefin-containing waste streams containing inorganic components and / or non-polyolefin polymers, as described in this application, is considered novel and can be carried out in apparatus with different configurations. The apparatus configurations shown in Figures 1-3 are also considered novel.

Claims

1. A method for recycling polyolefin-containing waste streams containing inorganic components and / or non-polyolefin polymers, comprising the following steps: a. A step of raising the temperature of the waste stream above the melting temperature of the polyolefin contained therein to form a molten waste stream; b. A step of separating solid components from the molten waste stream; c. A step of adding a solvent to the molten waste stream to form a slurry containing a polyolefin solution and undissolved components; d. A step of separating the undissolved components from the polyolefin solution; and e. A step of isolating the polyolefin from the polyolefin solution; Includes, Step b is carried out using a melt filter. Step c is carried out so that a dynamic viscosity of the slurry in the range of 4200 Pa s to 10 Pa s is achieved. The insoluble components are separated from the slurry by filtration in step d using one or more filtration units. A method wherein step e is carried out by precipitating the polyolefin.

2. The method according to claim 1, wherein the temperature in step a is raised using a melting device equipped with a melt filter.

3. The method according to claim 2, wherein the melting device may be a single-screw or twin-screw extruder.

4. The method according to any one of claims 1 to 3, wherein the temperature in step a is raised to a range of 110 to 300°C, preferably 150 to 250°C, and more preferably 180 to 245°C.

5. The method according to any one of claims 1 to 4, wherein the solid component is separated from the molten waste stream by filtration, and unmelted species with a diameter >100 μm are removed from the polyolefin-containing waste stream.

6. The method according to any one of claims 1 to 5, wherein step c is carried out in a homogenization device.

7. The method according to any one of claims 1 to 6, wherein the solvent is selected from a nonpolar aliphatic solvent or a mixture thereof, or an aromatic hydrocarbon, or a mixture of an aromatic solvent and an aliphatic solvent.

8. The method according to any one of claims 1 to 7, wherein an additional solvent is added to the slurry in step c to reduce the dynamic viscosity to a range of 100 to 10 Pa s.

9. The method according to claim 8, wherein a dissolution vessel is used that operates at a temperature in the range of 150 to 200°C and a pressure in the range of 10 to 20 bar (g), preferably in a nitrogen atmosphere.

10. The method according to claim 8 or 9, wherein the additional solvent or mixed solvent is the same as the solvent used to prepare the slurry.

11. The method according to any one of claims 1 to 10, wherein the filtration unit or each filtration unit operates in a batch or continuous manner at 150 to 200°C.

12. The method according to claim 11, wherein a set of filtration units is used to remove insoluble components in the next module, ranging from 100 μm to less than 1 μm.

13. Apparatus for recycling polyolefin-containing waste streams comprising inorganic components and / or non-polyolefin polymers as described in any one of claims 1 to 12: (5) A melting device equipped with an internal or external filtration module; • Homogenization device (7); • Dissolving container (8); and • At least one filtration unit (9); Includes, An apparatus in which the melting device (5) is a single-screw or twin-screw extruder.

14. The apparatus according to claim 13, wherein the filtration module of the melting device (5) comprises a melting pressure controlled scraper system for removing contamination from the surface of the rotating screen disk into the discharge screw system.

15. The apparatus according to claim 13 or 14, further comprising a pump (6).

16. The apparatus according to any one of claims 13 to 15, wherein the homogenizing device (7) is a homogenizer (7a) having a solvent inlet and including at least one internal mixing element, a mixing element including a meshing rod and a crossing rod positioned at any angle with respect to the axis of flow direction.

17. The apparatus according to any one of claims 13 to 15, wherein the homogenization device (7) is a twin-screw extruder (7b) equipped with a solvent inlet and a diverter valve.

18. The apparatus according to any one of claims 13 to 15, wherein the homogenizing device (7) is a homogenizer (7c) comprising two or more solvent inlets and two or more internal mixing elements, preferably a mixing element comprising interlocking rods and crossing rods positioned at an angle with respect to the axis of flow direction.

19. The apparatus according to any one of claims 13 to 18, wherein the dissolution container (8) is a continuous stirring tank reactor.

20. The apparatus according to any one of claims 13 to 19, wherein the set of filtration units (9) is used to separate particles of 100 to 20 μm, 20 to 1 μm, and less than 1 μm.

Images