Dissolving method and dissolving equipment for solvent-based recycling of polyolefins

Abstract

1. A dissolving facility for dissolving polyolefins from waste polyolefin material in a solvent to produce a polyolefin solution slurry for a continuous polyolefin recycling process, the polyolefin solution slurry comprising a polyolefin solution and undissolved residue, the dissolving facility comprising at least one feeder selected from the list consisting of a dry feeder, a wet feeder, a melt feeder, and a solution feeder, at least one dissolving facility, the at least one dissolving facility having at least one first inlet for introducing the waste polyolefin material, fluidly connected to an outlet of the at least one feeder, the at least one dissolving facility having at least one second inlet for introducing the solvent, the at least one dissolving facility having at least one outlet for removing the polyolefin solution slurry, the dissolving facility comprising a vessel including an agitator.

Description

[Technical field]

[0001] The present invention relates generally to a solvent-based recycling process for polyolefins. More specifically, the present invention discloses a dissolving equipment and a dissolving method for use in a solvent-based recycling process for polyolefins. [Background technology]

[0002] The task of processing accumulated waste plastics and the corresponding environmental problems have attracted widespread attention from the public and academics. Therefore, in addition to the concept of preventing plastic waste in general, and preventing plastic waste from entering the environment in particular, recycling waste plastic materials has also become an important topic. Waste plastics can be turned into resources for new plastic products. Therefore, recycling and reuse of waste plastic materials can achieve both environmental and economic benefits.

[0003] In the mid-90s, more differentiated waste collection systems (recycling management systems, circular economy laws) were introduced in several European countries, which in practice allowed a more targeted recovery and separation of plastic materials from other waste. Thus, a more or less efficient separation of polymer types from each other finally results in concentrated and therefore more easily recyclable secondary plastic material pieces after processing. The creation of suitable waste collection systems and especially the development of suitable waste separation infrastructures has taken place in recent decades in order to generate sources and markets for secondary petrochemical feedstocks. In parallel with this, several plastic recycling methods have been developed and especially improved, with the main goal of increasing the achievable product quality of recyclable polymer materials.

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

[0005] Although the EU's public collection and pre-sorting system reached a plastic recovery rate of 76% by weight (Ger) in 2018, advanced mechanical recycling methods have a low level of direct plastic material recycling (e.g., 12% in Germany in 2018). Today, advanced mechanical recycling includes separation steps such as shredders, vibrations, rotary sieves, advanced sorting methods supported by spectroscopy [e.g., NIR / VIS], and washing operations to reduce organic, biological, and partially malodorous pollutants from the surface of recyclable plastic materials, and also to achieve a more homogeneous polymer recycling fraction, enriched in polymer types. This results in a secondary solid stream (PO content >85%; <95%) that is especially rich in polyolefins, e.g., rich in plastic types, e.g., polypropylene (PP), high-density polyethylene (HDPE), low-density polyethylene (LDPE), polyethylene terephthalate (PET) and / or polystyrene (PS). These separated solid streams are then processed into specific materials that are then processed (extruded) into granules and transformed into products. Nevertheless, the achievable product quality remains relatively low and does not allow for both food contact and high performance applications, so that today mechanically recycled materials are typically products such as flower pots, paint buckets or shampoo bottles.

[0006] In particular, the implementation of improved and better sorting methods (e.g. color flake sorting) is desirable, affecting both the enrichment within a particular polymer type fraction and the secondary washing operations, in order to more efficiently reduce harmful pollutants etc. and to improve the product quality of the final secondary polymer feedstock. The latter, while keeping emissions as low as possible, involves additional expenditures on complex process design, waste water treatment, exhaust gas treatment, drying of intermediate products etc., coupled with an increase in total energy consumption.

[0007] However, due to waste material components such as multilayer materials and films, or mixed flexible film waste, the challenge of directly remanufacturing mechanical polymer recycling into high-quality end uses remains. Furthermore, important reasons can be found in the low predictable and controllable homogeneity of polymer-type material mixtures, especially with regard to historically applied polymerization techniques (defining material properties such as polymer density, average molecular weight, molecular weight distribution, molecular structure, degree of crosslinking, etc.) and historically applied compounding techniques (additives, filler concentrations, and finally multiple pigment compositions). All these quality factors remain inside the mechanically processed bulk solid mixture, cannot be covered by mechanical fractionation and applied purification methods, and in the best case interact at 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 mechanical polymer recycle with virgin polymers to achieve acceptable and marketable quality for end uses (non-food), so that the workable content of mechanically recycled polymeric material remains at low levels (a few [wt %]), especially for high quality / performance end uses.

[0009] The second most emerging plastic recycling route is chemical or feedstock recycling, which involves solvolysis and thermochemical processing. 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 by 2030, from less than 2% (2018) to 13%. However, 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 again into plastics as well as chemical products and fuels. Heat and / or solvents must be applied to break down the polymeric structures of plastic solid mixtures and the shorter hydrocarbons down to their monomeric components. Depending on the specific technology, chemical recycling approaches have a very high tolerance to mixed plastic fractions and impurities and can therefore mainly handle contaminated polymer material mixtures and secondary polymer feedstocks. Nonetheless, cross-contamination of polyolefin-based feedstock mixtures with heteroatom polymers (N / O / S, halogens) should preferably be avoided.

[0010] Nevertheless, the abstraction of thermochemical plastics processing, especially polyolefin recycling technology, rather indicates 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-adapted to secondary feedstock sources. The final total energy input is significantly higher compared to crude oil to virgin polymer processing, since the energy demand for the heat-intensive endothermic C-C and C-H bond cleavage (cracking, decomposition) remains - mainly the cracking of short-chain molecules (e.g. naphtha from crude oil fractionation) is replaced by the cracking of long-chain and branched polymers. Apart from that, the excessively energy-intensive pyrolysis remains. Moreover, the CO2 emissions of such methods are also high, unless the required applied energy carriers can be easily switched to renewable / sustainable energy carriers.

[0011] The third plastics recycling route is advanced physical or solvent-based recycling (SbR), which represented a plastics recycling market share of less than 1% in Germany in 2018. In the SbR process, the polymer is first dissolved in a suitable solvent, after which solidification of the polymer occurs either by reducing the solubility of the dissolved polymer by the addition of a non-solvent (dissolution / precipitation) and / or by thermal unit operations (evaporation, drying, etc.) to preferably completely separate the solvent from the solidified polymer.

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

[0013] The commonly known framework of solvent-based recycling methods for waste plastic materials includes removing impurities, dissolving, and re-precipitating / recrystallizing and / or devolatilizing the polymers. 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 other than the target polymer.

[0014] It is generally desired to produce virgin-like polymers by solvent-based recycling methods of waste plastic materials, defined as uncontaminated, pigment-free, odorless, homogeneous, and generally having properties similar to those of freshly polymerized polymers. The need for high-quality virgin-like recycled resins is particularly important in food and pharmaceutical contact applications 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 mixed into recycled polypropylene and vice versa.

[0015] The key to an efficient solvent-based polyolefin recycling process is the dissolution step, where the polymer is dissolved in a solvent. To achieve a homogeneous composition of the stream leaving the dissolution section, a high homogeneity of the solution is advantageous. This is necessary to keep the quality of the recycled polyolefin constant. Furthermore, it is desirable that the time needed to dissolve the polymer to the required homogeneity is also as short as possible. In particular, it is required to have an economical process in terms of both CAPEX and OPEX.

[0016] Among the various design criteria that must be considered in the design of a mixing device for the dissolution of waste polyolefins in a solvent-based polyolefin recycling process, mixing in the mixing vessel is very challenging. First, the viscosity of the components in the mixing vessel is relatively high. In general, the viscosity depends on the polyolefin recycling process, the polyolefin (average molecular weight) being recycled, and the corresponding conditions (pressure and temperature) used in the vessel for dissolution. An exemplary viscosity can be on the order of 0.1 Pa·s.

[0017] It is usually necessary to produce a completely solubilized polyolefin solution, especially with a view to the subsequent separation steps. To achieve this, the design of the mixing vessel usually aims for maximum homogeneity of the components.

[0018] Additionally, heat control is necessary to ensure optimal and rapid dissolution. Mixing patterns within the mixing vessel that improve homogeneity usually improve heat convection and, therefore, control.

[0019] Therefore, there is a general need in the field of solvent-based polyolefin recycling for a mixing device that is optimized in terms of homogeneity of the components in the mixing vessel, improved heat control, improved phase control, reduced dissolution time, and specific control of the mixing pattern.

[0020] CA 2376488 A1 discloses a solvent-based method for separating various polyolefins (polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE)) using two solvents, namely n-hexane and mineral spirits. The starting materials are contacted with the solvent at an elevated temperature of around 140°C. Undissolved solids are then removed from the solution in one or more steps using filtration, centrifugation or other mechanical separation methods. After removal of the undissolved solids, the solution consists mainly of the solvent and dissolved polyolefins. Each polyolefin is precipitated one after the other from the solution using crystallization under simultaneous shear action. This separates each polymer type while retaining wax, polymer chain fragments and various additives in solution. For the dissolving step, a mixing nozzle is disclosed. For mixing, no other means are explicitly disclosed. Therefore, no further improvement in mixing time and homogeneity can be obtained from the disclosure of CA 2376488 A1. [Prior art documents] [Patent documents]

[0021] [Patent Document 1] Canadian Patent Application Publication No. 2376488 A1 Summary of the Invention [Problem to be solved by the invention]

[0022] It is therefore an object of the present invention to provide a dissolution apparatus and a dissolution method for a solvent-based recycling process of polyolefins, which allows shorter dissolution times and improved homogeneity of the polyolefin solution. [Means for solving the problem]

[0023] Surprisingly, it has been found that said object is achieved by a dissolving installation for dissolving polyolefins from waste polyolefin material in a solvent to obtain a polyolefin solution slurry for a continuous polyolefin recycling process, said polyolefin solution slurry comprising a polyolefin solution and undissolved residues, said dissolving installation comprising at least one feeder selected from the list consisting of a dry feeder, a wet feeder, a melt feeder and a solution feeder, at least one dissolving installation, said at least one dissolving installation having at least one first inlet for introducing waste polyolefin material fluidly connected to an outlet of the at least one feeder, said at least one dissolving installation having at least one second inlet for introducing a solvent, said at least one dissolving installation having at least one outlet for removing the polyolefin solution slurry, said dissolving installation comprising a vessel comprising an agitator.

[0024] More surprisingly, it has been found that said object is achieved by a dissolution process for dissolving polyolefins from waste polyolefin material in a solvent to obtain a polyolefin solution slurry for a continuous polyolefin recycling process, said polyolefin solution slurry comprising a polyolefin solution and an undissolved residue, said dissolution process comprising the steps of: supplying a waste polyolefin material; and dissolving polyolefins from the waste polyolefin material in a solvent using a dissolving installation according to the present invention.

[0025] <Definition> The expression "volatile" or "volatile compounds" used herein should be understood as compounds that have a significantly lower molecular weight compared to the polyolefins separated by the method of the present invention. Such compounds are usually present in gaseous form when exposed to the flash separator. In general, the volatile compounds are mixtures of volatile hydrocarbons. Preferably, the mixture of volatile hydrocarbons includes at least one solvent. [Brief description of the drawings]

[0026] [Figure 1] FIG. 1 illustrates one embodiment of the present invention implemented in a batch mode including a dry feed system. [Diagram 2] FIG. 2 illustrates one embodiment of the present invention implemented in a batch mode including a wet feed system. [Diagram 3] FIG. 3 illustrates one embodiment of the present invention implemented in a continuous mode including a melt feeder. [Figure 4] FIG. 4 shows one embodiment of the present invention implemented in a continuous mode including a solution feeder. [Diagram 5] FIG. 5 illustrates one embodiment of the present invention implemented in a continuous mode including a dry feed system. [Figure 6] FIG. 6 illustrates one embodiment of the present invention implemented in a continuous mode involving a wet feeder. [Figure 7] FIG. 7 shows a preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] [Dissolution process] The method of the present invention will be described with reference to Figures 1 to 6. It should be noted that the basic concept of the method of the present invention is dissolving at least one waste polyolefin in a solvent.

[0028] The lysis method of the present invention generally comprises two steps: a) a feeding step of waste polyolefin material (1) to step b) a dissolving step in which polyolefin (2) is contacted at the latest with a solvent (3) to obtain a polyolefin solution slurry (4) comprising polyolefin (2) dissolved in the solvent (3) and undissolved residues from the waste polyolefin material (1). Optionally, the dissolving step may comprise a homogenization step c).

[0029] [Waste polyolefin materials] The waste polyolefin material is usually provided in a comminuted form, having already undergone some prior steps for pre-sorting and washing, as well as extraction. Such a process usually involves the preparation of waste polyolefin material (1) from municipal waste, which includes washing the waste with aqueous and / or caustic solutions to remove unwanted materials from the polyolefin containing waste. Furthermore, the size of the waste-containing polymer pieces is preferably reduced in advance, preferably by cutting, grinding and shearing, or by mixing thereof. Thus, the waste polyolefin material (1) is provided in a comminuted form, preferably in the form of flakes, preferably having a maximum diameter of 4 cm or less, more preferably 3 cm or less, typically 0.5 cm or more. The waste polyolefin material (1) is essentially free of any waste on the surface of the polyolefin flakes. Thus, the method of the present invention is essentially directed to the dissolution of waste polyolefin flakes.

[0030] [Polyolefin] The waste polyolefin material (1) may include various plastics such as polyethylene (PE) or polypropylene (PP), in particular 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 polyolefin 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, based on the total weight of the waste polyolefin material (1). The waste polyolefin material (1) may further include waste impurities such as common additives such as antioxidants, food residues, residual flavoring ingredients, dyes and pigments, as well as ingredients that are generally inevitably introduced into plastic waste materials by production and use. In addition to contamination, many recycled resin products are often heterogeneous in chemical composition and may contain a significant amount of polymer contamination, such as PE contamination in recycled PP and vice versa.

[0031] The polyolefin (2) recycled by the process of the present invention may be a mixture of polyolefins such as polypropylene or polyethylene. However, preferably, the polyolefin (2) is composed of a single polyolefin. Most preferably, the polyolefin (2) comprises polypropylene, preferably consists of polypropylene. It should be understood that in the latter case, the polyethylene residues can be dissolved again at elevated temperature and increased residence time using the same dissolution solvent (3) and separated according to the present invention.

[0032] [solvent] In general, the solvent (3) must be able to dissolve polyolefins, in particular polyolefin (2). Thus, preferably, the solvent (3) is a non-polar solvent or a mixture thereof. Thus, preferably, the solvent is a hydrocarbon or a mixture of hydrocarbons. More preferably, the solvent (3) is a paraffinic solvent or a mixture of paraffinic solvents due to the paraffinic nature ('Similia similibus solventum') of polyolefins. Aromatic hydrocarbon solvents may be considered, since they are known for their good solvent properties. However, a drawback of aromatic hydrocarbons is that they promote the dissolution of polystyrene. On the other hand, it is known that for example n-alkanes do not dissolve polystyrene. Most importantly, it is desirable that the solvent does not dissolve polar polymers such as PET, PVC, PA, PC, PUR, or bio-based fractions such as cellulose or lignin. Even more preferably, the boiling point of the solvent (3) at 1 bar pressure is higher than 70°C. Thus, preferably, the solvent is selected from the list of low boiling point solvents and high boiling point solvents or mixtures thereof. Low boiling point solvents include for example n-alkanes and aromatic hydrocarbons, such as toluene and xylene. The advantage of low boiling solvents is that they can be separated from the dissolved polyolefin by evaporation. High boiling solvents include paraffinic or vacuum diesel. Such solvents have the disadvantage that they are difficult to remove from the product. Aromatic solvents, on the other hand, may cause odor problems due to the residual amounts remaining after separation and may also cause problems when intended for applications requiring food approval. Thus, preferably, the solvent (3) is selected from n-alkanes or mixtures thereof having a boiling point at 1 bar pressure of more than 70° C., preferably not more than 150° C., more preferably not more than 140° C., even more preferably not more than 100° C., and most preferably not more than 90° C. Most preferably, the solvent (3) is selected from the group consisting of n-heptane, n-octane, n-nonane, and n-decane, or mixtures thereof.

[0033] [Undissolved residue] The undissolved residue can generally be an undissolved solid residue or a liquid residue. Most commonly, the undissolved liquid residue is another polymer that is not soluble in the conditions and solvent selected for the method. The undissolved solid is either a non-polymeric solid, such as a pigment or an additive, that is not soluble in the dissolution solvent (3), or a polymer. Such a polymer is either a polar polymer that is not soluble in the solvent used, or a non-polar polymer that is not soluble under the conditions used in the dissolution step.

[0034] [Supply process a)] The waste polyolefin material (1) is fed in a feeding step a) to the dissolving step b). The feeding step a) can be either a batch or continuous operation of the process. The reason is the pressurized dissolving in step b) (see below), which does not allow a feeding step to feed the polyolefin during the dissolving operation. That is, dry feeding or wet feeding leads to a batch operation. On the other hand, melt feeding and solution feeding can be used in a process carried out continuously. These four feeding steps are therefore detailed below.

[0035] a) Dry supply (Figure 1) The process of dry feeding involves the direct feeding of polyolefin flakes in solid form to the solvent in the dissolution step b). Usually, the solid polyolefin flakes are purged following the feeding step a) to vent oxygen components or other gaseous substances contained in the solid material. The higher the operating pressure in the dissolution step b), the more vents are required. A typical setup used for solid dry feeding is "lockhoppers", which can also be used in pressurized vessels. A drawback can be that the vessels used for dissolution require level indication to inhibit the solvent from entering the lockhopper structure when the polyolefin flakes are introduced. Furthermore, gases can be carried into the dissolution step b) with the solid polyolefin flakes, requiring subsequent removal.

[0036] It is advisable to feed a hot solvent having a temperature higher than the final dissolution temperature separately to the dissolution step b) in order to heat the solid polyolefin flake feed. Dry feeding leads to longer dissolution times. Efficient mixing is necessary to ensure distribution of material and heat in the homogenizer and constant quality at the outlet, respectively. Moreover, efficient mixing reduces the residence time required to solubilize the polyolefin in the solvent, which has a positive effect on the plant OPEX (operating expenses) and CAPEX (capital expenses). In the preferred case of the pressurized dissolution step b), the dry feeding has to be done batchwise.

[0037] b) Wet supply (Figure 2) Feeding the solid polyolefin flakes by wet feeding means that the polyolefin flakes are mixed beforehand with a part of the solvent. Preferably, the solvent is the same as that used for dissolution. The density difference between the solid polyolefin and the solvent may result in the need for an extra mixing step under atmospheric conditions preceding step b). Furthermore, in this case, the flake size of the polyolefin feed must be within a narrow range to allow the subsequent pumping of the slurry. The oxygen component is preferably purged before the solid polyolefin flakes are added to the solvent. The slurry feeding can be carried out, for example, using a specific slurry pump. The dissolution step b) can be carried out without a gas phase. However, the same problems as in the case of the dry feeding step arise, that is, the appropriate mixing is necessary to finally solubilize the polyolefin (2), which increases the energy required. The hot solvent is fed separately to the dissolution step b) at a temperature higher than the final dissolution temperature, heating the slurry feed. In the preferred case of the pressurized dissolution step b), the wet feeding must be carried out batchwise.

[0038] c) Melt supply (Fig. 3) In the melt feed step, the solid polyolefin flakes are melted before being fed to the melting step b). The temperature of the molten polyolefin feed is preferably at or above the melting temperature in step b). More preferably, the temperature of the molten polyolefin feed is higher than the temperature in step b), since the melting is preferably performed in an extruder where temperatures of up to 200° C. or higher are applied. The molten polyolefin feed can be introduced without a gas phase into step b), i.e. into the dissolution vessel completely filled with solvent and molten polyolefin. The advantage of such a setup is that the molten polyolefin mixes faster with the solvent and dissolves faster in the solvent, compared to dry or wet feeding. The mixing is still demanding, since the viscosity difference between the melt and the solvent is still large. Therefore, efficient mixing is required, since poor mixing can lead to an uneven temperature distribution in the solution, which can affect the polymeric material, especially when the temperature of the polyolefin reaches relatively high values ​​(i.e. 250° C. for polypropylene). The hot solvent is fed separately to the melting step b) at a temperature higher than the final melting temperature, heating the slurry feed. The melt feed can be pressurized to match the pressure in the dissolving step, so that the melt feed can be carried out in a continuous manner. The embodiment as shown in FIG. 3 is the most preferred embodiment of the invention for melt feed. If the required homogeneity of the polyolefin solution slurry (4) at the outlet of the dissolving device (6) is not achieved, two options can be used to increase the homogeneity. The first option involves changing the dimensions of the dissolving device, preferably the dimensions of the vessel and / or the agitator, and optionally increasing the residence time. The second option involves the use of more than two batch dissolving devices, placed upstream of the inlet of the final dissolving device, in an embodiment comparable to the embodiment as shown in FIG. 6 as part of a wet feed system.

[0039] In order to prevent further degradation of the polyolefin feed during the melt feeding step, the polyolefin flakes, preferably comprising polyethylene and / or polypropylene, more preferably polypropylene, can be stabilized before or during the melting step as follows, based on the total weight of the polyolefin flake composition: (a) the addition of 0 to 3500 ppm, more preferably 100 to 3000 ppm, even more preferably 1000 to 2500 ppm, of a phenolic antioxidant; and / or (b) the addition of 0 to 3500 ppm, more preferably 100 to 3500 ppm, even more preferably 1000 to 3300 ppm of an organic phosphite stabilizer; and / or (c) the addition of 0 to 6000 ppm, preferably 100 to 5000 ppm, and even more preferably 1000 to 4000 ppm, of a sulfur-containing stabilizer; and / or (d) The addition of 0 to 2500 ppm, preferably 50 to 2500 ppm, and even more preferably 100 to 2000 ppm of an acid scavenger (e.g., calcium stearate or hydrotalcite).

[0040] d) Solution supply (Figure 4) The solution feed is carried out similarly to the melt feed. However, the molten polyolefin feed, i.e. the feed from the extruder, is further mixed with at least a portion of the solvent, which is already heated. The polyolefin concentration after mixing is preferably the final concentration required in the dissolution step b). In this case, only the homogeneity of the solution is improved in the dissolution step b). Preferably, a separate feed of hot solvent to the dissolution step b) is not required. The advantage of the solution feed is that the viscosity difference between the molten polyolefin feed and the polyolefin solution in the dissolution step b) is even lower than in the melt feed, which further reduces the energy required in step b). The solution feed can be pressurized to match the pressure of the dissolution step, so that it can be carried out continuously.

[0041] [Dissolution step b)] Step b) is a dissolution step, whereby the waste polyolefin material (1) is contacted with at least one solvent (3). Thus, in step b), the polyolefin (2) is dissolved in the dissolution solvent (3). Meanwhile, the resulting polyolefin solution slurry (4) may still contain undissolved residues besides the polyolefin solution. It is to be noted that separation of said undissolved residues is carried out downstream of step b) of the present invention.

[0042] Step b) may be carried out with only a single target polyolefin dissolved in the dissolution solvent (3). Such an arrangement is particularly applicable when the target polyolefin dissolves at a lower temperature than all other polyolefins present in the waste polyolefin material (1). In another embodiment of step b), conditions are selected such that even two or more polyolefins are dissolved, i.e. polyolefin A and polyolefin B. In such cases, a subsequent liquid-liquid separation step is beneficial to separate the solubilized polyolefins from each other (see below). Mainly polypropylene may be dissolved from the polyethylene / polypropylene mixture using a non-polar solvent having a similar / approximate Hansen solubility parameter to that of polypropylene. Preferably, conditions are selected to exhibit temperatures between 100-350°C, more preferably 100-300°C, even more preferably 110-290°C, most preferably 120-280°C. Preferably, the pressure used in step b) is in the range of from 5 to 100 bar, more preferably from 5 to 50 bar, even more preferably from 7 to 45 bar, most preferably from 10 to 40 bar.

[0043] The dissolution process of the invention can be carried out batchwise or continuously. Preferably, the dissolution process of the invention is carried out continuously. In that case, the feeding step a) must support continuous operation at pressurized dissolution. This is especially true for melt feeding and solution feeding. However, continuous operation is also possible with dry feeding and wet feeding, as shown in Figures 5 and 6 and as described below.

[0044] FIG. 5 shows a process that includes a dry feed to two batch dissolution steps b), instead of only one. In each dissolution step, a hot solvent (3) is introduced and the solid polyolefin flakes are dissolved in the solvent. However, the resulting polyolefin solution slurry (4) is fed to a homogenization step c), where both slurries are mixed and homogenized. From this homogenization step c), the resulting polyolefin solution slurry (4) can be continuously removed and fed to a downstream process. The operating times of the two dissolution steps are not identical and overlap. Thus, if the first dissolution step needs to be fed batchwise with solid polyolefin flakes, the other dissolution step can still feed the homogenization step c). The homogenization step c) thus acts as a reservoir in addition to homogenizing the received stream. It should be noted that more than two dissolution steps b) can be used in parallel, reducing the risk of dry running of the homogenization step c) and interruption of the continuous process. However, too many dissolution steps b) only increase the cost without further reliability contribution. Therefore, the preferred range of parallel dissolution steps b) is 2-4, most preferably there are two dissolution steps b) in parallel. Generally, the feed to the parallel dissolution step b) is carried out at low pressure, preferably atmospheric pressure, and the pressure is increased after the feed is finished to dissolve the solid polyolefin flakes. Ideally and preferably, the transfer between the parallel dissolution step b) and the homogenization step c) is carried out using gravity. It should also be noted that the homogenization step c) can use equipment with smaller dimensions than the equipment used in the parallel dissolution step b). In the most preferred embodiment, the homogenization step c) can even be omitted completely. However, the requirement of such an embodiment is that the homogeneity and polyolefin concentration of the polyolefin solution slurry produced by the parallel dissolution step b) are approximately the same.

[0045] Figure 6 shows a method including wet feeding to two parallel dissolution steps b) instead of only one dissolution step b). The additional setup is identical to the additional device used in the embodiment of Figure 5. Thus, the parallel dissolution steps b) are fed to a homogenization step c), thereby generating a continuous flow of polyolefin solution slurry (4). Preferably, the temperature of the solvent (3) fed to the wet step of the wet feeding step is lower than the temperature of the solvent (3) fed to the parallel dissolution step b).

[0046] Thus, in the dissolution method, the feeding step a) comprises at least one step selected from the list of dry feeding, wet feeding, melt feeding and solution feeding.

[0047] Preferably, when the dissolution process of the invention is carried out continuously, the feeding step a) comprises at least one step selected from the list of dry feeding, wet feeding, melt feeding and solution feeding.

[0048] Since dry feeding and wet feeding in continuous mode are relatively complicated and difficult to control, when the dissolution process of the present invention is carried out in continuous mode, more preferably the feeding step a) comprises at least one feeding step selected from the list of melt feeding and solution feeding.

[0049] Most preferably, the feeding step a) comprises only a solution feeding step, which, as explained above, can provide the lowest viscosity difference in the dissolving step b), thereby minimizing the time required for complete homogenization and solubilization.

[0050] Most preferably, the melting method of the present invention is carried out using the melting equipment of the present invention described below.

[0051] [Melting equipment according to the present invention] The dissolution installation according to the invention for dissolving at least one polyolefin (2) from waste polyolefin material (1) in a solvent (3) comprises at least one feed device (5) and at least one dissolution device (6). Optionally, the dissolution device according to the invention further comprises a homogenization device (7).

[0052] [Feeding device] Possible feeding devices are parallel to the feeding steps already described above, therefore they will be described accordingly.

[0053] [Dry supply device (Fig. 1)] Preferably, the dry feed system includes one or more lock hoppers that feed into a line connected to the dissolver. In order to be able to feed into the line, the line should not be pressurized. Thus, the dry feed system cannot feed into a pressurized dissolver, resulting in a batch-type operation.

[0054] [Wet supply device (Fig. 2)] Preferably, the wet feeder comprises one or more lock hoppers which feed into a line connected to the wetter (8). The wetter (8) is preferably a vessel, more preferably a vessel equipped with an agitator. The wetter may be implemented as described below for the dissolver. The outlet of the wetter is preferably connected to a pump (9) which is capable of pressurizing the slurry from the wetter before it enters the dissolver. For the same reasons as the dry feeder, the wet feeder cannot also feed into a pressurized dissolver, resulting in a batch operation.

[0055] [Melting supply device (Fig. 3)] The melt feed system preferably includes an extruder (10) fluidly connected to the melt system. Such a setup can be operated continuously. In a more preferred case, the melt feed system includes a melt filter for filtering solids from the polyolefin melt.

[0056] [Solution supply device (Figure 4)] The solution feeder comprises the same equipment as the melt feeder. However, in addition, the melt stream is fed to a mixer (11) to which the solvent (3) can also be fed. Preferably, the mixer (11) is a static mixer or a dynamic mixer. Most preferably, the mixer is a static mixer. As with the melt feeder, such a setup can be operated continuously. In a more preferred case, the solution feeder also comprises a melt filter for filtering solids from the polyolefin melt.

[0057] [Dissolving device] Preferably, the dissolution device (6) comprises at least one first inlet for introducing the solvent (3), at least one second inlet for introducing the waste polyolefin material (1), at least one outlet for removing the polyolefin solution slurry (4), and a mixer (see FIG. 7).

[0058] The mixer and the vessel are configured to achieve the most efficient mixing pattern, which allows the polyolefin (2) to be rapidly and completely dissolved and homogenized in the solvent (3). Preferably, the mixing pattern includes an upward flow along the axis of the agitator to the top of the vessel and a downward flow along the vessel wall. Similarly, a back-mixing pattern including a downward flow along the axis of the agitator and an upward flow along the vessel wall is also contemplated.

[0059] Such behavior is supported by the presence of baffles in the vessel. Preferably, 2 to 12 baffles are included in the vessel. More preferably, 4 to 11 baffles are included in the vessel, even more preferably, 6 to 9 baffles are included in the vessel. Most preferably, the vessel contains 8 baffles. Preferably, the baffles are attached to the top and bottom of the vessel, at a distance from the vessel wall and directed inwards, preferably towards the axis of the stirrer. The width b of the baffles is preferably in the range of 1 / 4 to 1 / 24 of the vessel diameter T, more preferably 1 / 6 to 1 / 18 of T, most preferably 1 / 12 of T. Furthermore, the distance a between the baffles and the vessel wall is preferably 1 / 80 to 1 / 40 of the vessel diameter T, more preferably 1 / 70 to 1 / 50 of T, most preferably 1 / 60 of T.

[0060] The shape of the container is preferably cylindrical. More preferably, the top and / or bottom of the container is a korbbogen shape. A korbbogen shape is a torispherical head, also called a semi-elliptical head, defined according to DIN 28013. The inner radius of the head is 80% of the cylindrical outer diameter of the container (r1=0.8×T). The radius of the knuckles is (r2=0.154×T).

[0061] Preferably, the height / diameter ratio (H / T) of the vessel is in the range of 1-3, preferably 1.5-2.5, and most preferably the ratio H / T is 2.

[0062] When the feeding of the vessel is carried out by melt feeding or solution feeding, preferably the feed point is at the bottom of the vessel and the discharge point of the vessel is at the top.

[0063] The agitator includes an axis that is parallel to the axis of symmetry of the vessel. Additionally, the agitator includes at least one impeller that extends from the axis toward the vessel wall at an angle of more than 10°. Preferably, the impellers extend in two opposite directions.

[0064] In such a case, the impeller diameter is preferably in the range of 0.5 to 0.9 of the vessel diameter T, and more preferably in the range of 0.6 to 0.8 of T. Most preferably, the impeller diameter is 0.7×T.

[0065] The agitator of the dissolving device of the dissolving facility of the present invention preferably includes 1 to 8 impellers, more preferably 3 to 6 impellers, and most preferably includes 4 impellers.

[0066] The impeller is preferably of the MIG type, or of the Intermig type, or of the Paravisc type. Most preferably, the impeller is an Intermig type impeller.

[0067] The mixer of the present invention has very high axial mixing and low radial mixing and can be operated in the viscosity range of 0.03 to 10 Pa·s.

[0068] Additionally, the mixer of the present invention induces circulation up or down within the vessel and then in the opposite direction (down or up) through the vessel wall, creating minimal radial mixing and maximum axial mixing.

[0069] Preferably, the dissolution device of the present invention has a circulation time of the polyolefin solution of less than 1 minute, preferably less than 20 seconds.

[0070] The agitator is rotated preferably in the range of 20-200 rpm, more preferably 80-120 rpm, most preferably 100 rpm. If the rotation speed is too high, too much energy is consumed. If the rotation speed is too low, the time to homogenize is too long. Furthermore, the mixing efficiency decreases with the decrease of the Reynolds number, which affects the homogeneity of the mixer contents.

[0071] [Homogenization device] The homogenizer (7) may be identical to the dissolver as described above. However, the dimensions of the homogenizer may be smaller than those of the dissolver. If the mixture in the dissolver is already very homogenous, the homogenizer may simply be a vessel with a reservoir function, or even just a branched line for combining the slurry streams from the dissolver.

[0072] In general, any feeder can be combined with a dissolver as described above. Nevertheless, dry and wet feeders require batch operation.

[0073] However, as already mentioned above, the dissolution apparatus shown in Figures 5 and 6 overcomes this drawback and allows the dry and wet feed apparatus to be operated in continuous mode.

[0074] The embodiment of Figure 5 combines a dry feeder (5) with two dissolvers (6), the outlet of the dry feeder (5) being fluidly connected to at least one inlet for introducing waste polyolefin material (1) of at least two dissolvers (6), and optionally at least one outlet for removing polyolefin solution slurry (4) being fluidly connected to the inlet of a homogenizer (6).

[0075] Similarly, the embodiment of Figure 6 combines a wet feeder (5) with two dissolvers (6), but the wetter outlet of the wet feeder (5) is fluidly connected to at least one inlet for introducing waste polyolefin material (1) of at least two dissolvers (6). Furthermore, optionally, at least one outlet for removing polyolefin solution slurry (4) is fluidly connected to the inlet of the homogenizer (6).

[0076] Preferred embodiments of the present invention are those suitable for continuous mode, including those shown and described in Figures 3-6, and due to the increased complexity of continuously operable embodiments including dry and wet feeders, more preferred are melting installations including melt or solution feeders.

[0077] Most preferred is a dissolution apparatus that includes only a solution supply device.

[0078] Generally, and preferably, the wetting unit (8), dissolver (6) and homogenizer (8) are operated independently of one another so as to be completely filled with liquid and optionally solids, thereby not allowing the presence of a gas phase within the units.

[0079] The most preferred dissolution installation according to the present invention comprises one or more solution feeders (5) in fluid communication with at least one inlet of the dissolution device (6), the dissolution device (6) being equipped with an agitator, the vessel having a cylindrical shape with a Kolbogen shaped top and bottom, the ratio of height to diameter of the vessel being in the range of 1-3, the feed point being at the bottom of the vessel and the discharge point of the vessel being at the top, the agitator comprising an axis parallel to the axis of symmetry of the vessel, and four Intermig impellers, wherein the diameter of said impellers is in the range of 0.5-0.9 x vessel diameter T. [Explanation of symbols]

[0080] 1. Waste polyolefin materials 2. Polyolefins 3. Solvent 4. Polyolefin solution slurry 5 Feeding device 6 Melting equipment 7 Homogenizer 8 Wet equipment 9. Pump 10 Extruder 11 Static mixer Preferred aspects of the present specification include at least the following. [1] A dissolution facility for dissolving polyolefin (2) from waste polyolefin material (1) in a solvent (3) to produce a polyolefin solution slurry (4) for a continuous polyolefin recycling process, the polyolefin solution slurry (4) comprising a polyolefin solution and an undissolved residue, the dissolution facility comprising: - at least one feeder (5) selected from the list consisting of a dry feeder, a wet feeder, a melt feeder and a solution feeder, - at least one melting device (6) Including, the at least one dissolver (6) has at least one first inlet for introducing the waste polyolefin material (1), the first inlet being fluidly connected to an outlet of the at least one feeder (5); the at least one dissolution device (6) has at least one second inlet for introducing a solvent (3); said at least one dissolver (6) having at least one outlet for removing the polyolefin solution slurry (4); and The dissolving apparatus (6) is a dissolving facility including a vessel containing an agitator. [2] The dissolution installation according to [1], wherein the at least one supply device (5) is selected from the list consisting of a melt supply device and a solution supply device. [3] The dissolution equipment according to [1] or [2], wherein the at least one supply device (5) is a solution supply device. [4] The dissolution installation according to any one of [1] to [3], wherein the dissolution device (6) is suitable for forming a mixing pattern in the vessel, the mixing pattern including an upward flow along the axis of the agitator to an upper part of the vessel and downward flows along the walls of the vessel, or the mixing pattern including a downward flow along the axis of the agitator to a bottom of the vessel and upward flows along the walls of the vessel. [5] The dissolution equipment according to any one of [1] to [4], wherein the vessel of the dissolution device (6) includes 2 to 12 baffles. [6] The dissolution equipment according to [5], wherein the baffles are arranged at the top and bottom of the vessel at a distance from the vessel wall and facing the axis of the stirrer, the width b of the baffle is preferably in the range of 1 / 4 to 1 / 24 of the diameter T of the vessel, and the distance a between the baffle and the vessel wall is in the range of 1 / 80 to 1 / 40. [7] The dissolution equipment according to any one of [1] to [6], wherein the shape of the container is preferably cylindrical, and the top and bottom of the container are formed in a korbbogen shape. [8] The dissolution equipment according to any one of [1] to [7], wherein a height / diameter ratio (H / T) of the vessel is within a range of 1 to 3. [9] The dissolution equipment described in any one of [2] to [8], wherein the supply point is at the bottom of the container and the discharge point is at the top of the container.

[10] The dissolution equipment according to any one of [1] to [9], wherein the agitator includes at least one impeller having a diameter in the range of 0.5 to 0.9 times the diameter T of the vessel.

[11] A dissolution method for dissolving polyolefins (2) from waste polyolefin material (1) in a solvent (3) to produce a polyolefin solution slurry (4) for a continuous polyolefin recycling process, the polyolefin solution slurry comprising a polyolefin solution and undissolved residue, the dissolution method comprising the steps of: a) providing a waste polyolefin material (1); b) A step of dissolving polyolefin (2) from the waste polyolefin material (1) in a solvent (3) using a dissolving device according to any one of [1] to

[10] . The dissolution method comprising:

[12] The dissolution method according to

[11] , which is a continuous method.

[13] The method for dissolving according to

[11] or

[12] , wherein step a) is selected from the list consisting of dry feeding, wet feeding, melt feeding, solution feeding, and mixtures thereof.

[14] The dissolving method according to any one of

[11] to

[13] , wherein step a) is a solution supplying step.

[15] The dissolution method according to any one of

[11] to

[14] , wherein step b) is carried out at a temperature of 110 to 350° C. and a pressure of 7 to 100 bar.

Claims

1. A dissolving facility for dissolving polyolefins (2) from waste polyolefin materials (1) in a solvent (3) to produce a polyolefin solution slurry (4) for a continuous polyolefin recycling process, the polyolefin solution slurry (4) comprising a polyolefin solution and undissolved residue, the dissolving facility comprising: at least one feed device (5) selected from the list consisting of a melt feed device and a solution feed device, at least one dissolution device (6) Including, said at least one dissolver (6) having at least one first inlet for introducing the waste polyolefin material (1), said first inlet being fluidly connected to an outlet of said at least one feeder (5); said at least one dissolution device (6) having at least one second inlet for introducing a solvent (3); said at least one dissolver (6) having at least one outlet for removing the polyolefin solution slurry (4); and The dissolution equipment (6) includes a vessel containing an agitator.

2. The dissolution installation according to claim 1, wherein said at least one supply device (5) is a solution supply device.

3. 2. The dissolution installation according to claim 1, wherein the dissolution device (6) is suitable for forming a mixing pattern in the vessel, the mixing pattern comprising an upward flow along the axis of the stirrer to the top of the vessel and a downward flow along the wall of the vessel, or the mixing pattern comprising a downward flow along the axis of the stirrer to the bottom of the vessel and an upward flow along the wall of the vessel.

4. The melting installation according to claim 1, wherein the vessel of the melting device (6) comprises 2 to 12 baffles.

5. 5. The dissolution equipment according to claim 4, wherein the baffles are arranged at the top and bottom of the vessel at a distance from the vessel wall and facing the axis of the stirrer, the width b of the baffle is in the range of 1 / 4 to 1 / 24 of the diameter T of the vessel, and the distance a between the baffle and the vessel wall is in the range of 1 / 80 to 1 / 40.

6. 2. The melting equipment of claim 1, wherein the vessel is cylindrical in shape and the top and bottom of the vessel are formed in a korbbogen shape.

7. The melting equipment according to claim 1, wherein the height / diameter ratio (H / T) of the vessel is in the range of 1-3.

8. 2. The melting facility of claim 1, wherein the feed point is at the bottom of the vessel and the discharge point is at the top of the vessel.

9. The dissolution equipment according to claim 1, wherein the agitator includes at least one impeller having a diameter in the range of 0.5 to 0.9 times the diameter T of the vessel.

10. A dissolution process for dissolving polyolefins (2) from waste polyolefin material (1) in a solvent (3) to produce a polyolefin solution slurry (4) for a continuous polyolefin recycling process, the polyolefin solution slurry comprising a polyolefin solution and undissolved residue, the dissolution process comprising the steps of: a) feeding waste polyolefin material (1) using at least one feeding device selected from the list consisting of a melt feeding device and a solution feeding device; b) dissolving polyolefin (2) from waste polyolefin material (1) in a solvent (3) using the dissolving device according to claim 1. The dissolution method comprising:

11. The dissolution process of claim 10 which is a continuous process.

12. The method of claim 10, wherein step a) is a solution supplying step.

13. The dissolution process according to claim 10, wherein step b) is carried out at a temperature of from 110 to 350° C. and a pressure of from 7 to 100 bar.

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