NL2035483B1

NL2035483B1 - A process for recycling a polyolefin containing waste material stream and an apparatus suitable therefor

Info

Publication number: NL2035483B1
Application number: NL2035483A
Authority: NL
Inventors: Franciscus Zirkzee Hendricus; Catharikus Jaspers Blandikus
Original assignee: Spex Tech B V
Priority date: 2023-07-26
Filing date: 2023-07-26
Publication date: 2025-02-10
Also published as: WO2025021980A1; EP4555012A1

Abstract

The invention provides a process for recycling a polyolefin containing waste material stream comprising inorganic components and/or non-polyolefin polymers, comprising the steps of: 5 a. Raising the temperature of the waste material stream above the melting temperature of the polyolefin(s) contained therein, to create a molten waste material stream; b. Separating solid components from the molten waste material stream; c. Adding solvent to the molten waste material stream, to create a slurry comprising a polyolefin solution and undissolved components, 10 d. Separating the undissolved components from the polyolefin solution, and e. lsolating the polyolefin from the polyolefin solution. Moreover, an apparatus for use in the process of the present invention is provided.

Description

P36379NLO0/MKO

Title: A process for recycling a polyolefin containing waste material stream and an apparatus suitable therefor

Technical Field

The present invention relates to a process for recycling a polyolefin containing waste material stream and an apparatus suitable therefor. More in particular, the invention relates to a solvent based recycling process of polyolefins containing waste streams. In addition, the present invention discloses dissolution apparatus that can separate inorganic materials, such as metals, and also other components, such as high melting polyesters from the polyolefin matrix.

Background

The challenge of the disposal of accumulated waste plastics and corresponding environmental issues have received widespread attention from the public and academician.

Therefore, besides the concepts of the prevention of plastic waste in general and the prevention of leakage of plastic waste into the environment in particular, recycling of waste plastics material has become an important topic. Waste plastics can be turned into resources for new plastic products, hereinafter recyclates. Hence, environmental and economic aspects can be combined in recycling and reusing waste plastics material.

Mid of the 90-ies, several European countries have implemented a more differentiating waste collection system (Recycling Management System, Circular Economy Law), which actually allows a more target orientated collection and separation of plastic materials from other waste materials. Thus, a more or less efficient separation of polymer types from each other can be managed to achieve, after the treatment, finally polymer types enriched and thus more easily recyclable secondary plastic material fractions. The build-up of a suitable waste collection system and especially the set-up of a suitable waste separation infrastructure took place within the last decades to generate a secondary petrochemical raw material source resp. market. Parallel, several plastic recycling processes have been developed resp. in particular improved, primary with the target to increase the achievable product quality of the recyclable polymer materials.

There are different methods of plastic recycling commonly known including mechanical [material recycling], advanced physical or solvent based [solution] and chemical processing [(feedstock recycling, thermochemical such as pyrolysis or gasification, solvolysis]. Among these methods, mechanical recycling and chemical recycling are the most widely practiced.

Although EU-public collection and pre-sorting systems reached plastic collection rates up to 76 [wt% (Ger)] in 2018, the direct plastic material recycling rates have been on a lower level for mechanical advanced recycling processes (e.g. 12 [%] for Germany in 2018, and 30 [%] in 2030 for the Netherlands). Today, advanced mechanical recycling includes separation steps such as shredding, vibrating, rotary sieving, advanced sorting methods supported by spectrometric methods [e.g. NIR/VIS] and wash operations to reduce organic, biologic and partly odorous contaminants primary from the surface of the recyclable plastic material, as well as achieving a polymer type enriched and more homogeneous polymer recycle fraction.

Thereby, plastic type-enriched resp. especially polyolefin-enriched secondary mass streams (> 85; < 95 [wt%] PO-content) can be obtained such as for example Polypropylene (PP),

High-Density-Polyethylene (HDPE), Low-Density-Polyethylene (LDPE), Polyethylene-

Terephthalate (PET) and/or Polystyrene (PS). Following, these separated mass streams will be processed to granules (extrusion) and material specific into products converted.

Nevertheless, the achievable product quality remains relatively poor and does not allow both food contact and high performance applications and thus products such as flower pots, paint buckets or shampoo bottles are typically for the mechanically recycled materials today.

Especially improved and better performing sorting methods (e.g. colouring flake sorting) should effect both higher concentrations within the specific polymer type fraction and secondary wash operations to reduce more efficiently disturbing contaminants resp. to increase the product quality of the final secondary polymer raw material. Latter includes additionally expenditures concerning a complex process design, waste water treatment, exhaust gas treatment and intermediate product drying coupled with an increased total energy consumption, while keeping emissions as low as feasible.

However, the challenges to remanufacture directly mechanical polymer recyclates into high- quality end applications remain, caused by waste components such as multi-layer materials resp. films or mixed flexible film waste materials. Further, important reason can be found in the less predictable and controllable homogeneity of the polymer type material mixture concerning especially historically applied polymerization technology (differences in material properties such as polymer density, average molecular weight, molecular weight distribution, molecular structure, cross-linking level) and historically applied compounding technology (additive-, filler concentrations and finally multiple pigment compositions). All these quality concerning factors remain inside the mechanically processed bulk mass mixture and cannot be covered by mechanical sorting and applied purification methods, which interact in best case onto the surface of the recyclable polymer material mixture.

A further approach to overcome the lower quality in advanced mechanical polymer recycling can be found in blending mechanical polymer recyclates with virgin polymers, finally to achieve a tolerable, marketable quality for the end application (non-food), whereby the implementable content of mechanically recycled polymer materials stays on a lower level (several [wt%]), especially for high-quality/high performance end applications.

The second arising plastic recycling route is chemical or feedstock recycling, concerning solvolysis and thermochemical processing. In 2018 the technology share rate of chemical plastic recycling was less than 2 [%] in total. A technology prognosis indicates, that the thermochemical recycling share rate should significantly increase from less than 2 [%] (2018) up to 13 [%] until 2030. Chemical plastic recycling provides a promising opportunity to recover pre-sorted and pretreated solid plastic waste to obtain feedstock for the petrochemical industry, which can be processed to plastics again, as well as to chemical commodities and fuels. To degrade the polymeric structure of the plastic solid mixture to shorter hydrocarbons up to monomeric building blocks, heat, and solvents have to be applied. Depending on the specific technology, chemical recycling approaches have much higher tolerances towards mixed plastic fractions and impurities and thus are principally capable to deal with contaminated and polymer material mixtures resp. secondary polymeric raw materials. Cross- contaminations of polyolefin material mixtures with heteroatomic polymers (N/O/S, Halogen) should be preferably avoided.

Nevertheless, abstraction of especially thermochemical plastic processing, especially polyolefin recycling technologies illustrates rather the substitution of fossil based crude oil fractions to already fossil based secondary polymer recyclate materials by applying well known traditional thermochemical unit operations, which have to be adapted costly to the secondary feedstock source. The specific energy demand remain, concerning the heat- intensive endothermic C-C resp. C-H bonding breakages (cracking, degradation), so that finally the total energy input is significantly higher in comparison to crude oil to virgin polymer processing - principally the degradation of a short chain molecule (e.g. Naphtha within crude oil fractionation) will be replaced by cracking long chain and branched polymers.

Independently, the extravagant and energy-consuming thermal degradation remains.

Furthermore, the CO2-emissions of such processes are also higher as long as the necessary applied energy carrier could not easily switched to renewable/sustainable energy carriers.

The third plastic recycling route is advanced physical or Solvent based Recycling (SbR). In

SbR-processing the polymer will be initially dissolved in an appropriate solvent and following, either the solubility of the dissolved polymer will be decreased by the addition of a non- solvent (dissolution/precipitation) and/or a solidification of the polymer will be caused by the preferably complete separation of the solvent from the solidified polymer by thermal unit operations {evaporation, drying etc.).

Polyolefin-SbR-processing show similarities to traditional PO-polymerization processes, whereby the solvent for the monomers (olefins) and temporary formed oligomers (waxes) and short chain polymers is for example a refinery fraction (e.g. kerosene) until the solubility limits will be exceeded (long chain polyolefins are formed during polymerization) and the final polyolefin precipitates forming a polyolefin-solvent slurry (e.g. Chevron slurry process). An extraordinary polyolefin process is the solution PO-polymerisation process, whereby the olefin is initially dissolved in a paraffinic solvent blend, polymerized and the finalized polyolefin will stay in solution until the process conditions will significantly change by depressurization resp. flash devolatilization.

The framework of commonly known waste plastics material solvent based recycling processes includes the removal of impurities, dissolution, and reprecipitation/recrystallization and/or devolatilization of the polymer. Specifically, the one or more polymer is dissolved in one or more solvent, and subsequently, each polymer is selectively precipitated/crystallized.

Ideally, if a solvent can dissolve either the target polymer or all the other polymers except the target polymer, it can be used for selective dissolution.

It is generally a desire to produce virgin-like polymers by waste plastics material solvent based recycling processes, whereas virgin-like is defined as contaminant-free, pigment-free,

Odour-free, homogeneous and generally similar in properties to freshly polymerized polymers. The need for high quality, virgin-like recycled resins is especially important for food and drug 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 a significant amount of polymeric contamination, such as polyethylene contamination in recycled polypropylene and vice versa.

Key for an efficient solvent based polyolefin recycling process is the dissolution step. In this step, the polymer is solved in the solvent. A good homogeneity of the solution is advantageous to achieve a uniform composition of the stream leaving the dissolution section.

This is needed to ensure a constant quality of the recycled polyolefin. Furthermore, the time needed to dissolve the polymer up to the homogeneity required is also desirably as low as possible. In particular, this is required to have an economical process both in terms of CAPEX and OPEX.

Among different design criteria that have to be considered for the design of a mixing device for the dissolution of the waste polyolefin in a solvent based polyolefin recycling process, the mixing inside of a mixing vessel is very challenging. First of all, the viscosity of the components inside the mixing vessel is relatively high. Typically, the viscosity depends on the polyolefin recycling process, the polyolefin recycled (average molecular weight) and the corresponding conditions used in the vessel for dissolution (pressure and temperature).

Exemplary viscosities of can be around 0.1 Pa:s.

Typically, itis needed to produce a fully solubilized polyolefin solution in particular in view of the subsequent separating steps. To achieve this, design of the mixing vessel is typically aiming at maximum homogeneity of components.

Furthermore, control of heat is needed to ensure an optimal and fast dissolution. Respective mixing patterns in the mixing vessel leading to improved homogeneity usually also lead to better heat convection and, thus, control.

Therefore, mixing devices optimized in view of homogeneity of components in the mixing vessel, improved heat control, improved phase control, shortened dissolution times, and specific control of the mixing patterns are generally needed in the field of solvent based polyolefin recycling.

CA 2376488 A1 discloses a solvent-based process to separate different polyolefins (polypropylene (PP), high density polyethylene (HDPE), low density polyethylene (LDPE) and linear low density polyethylene (LLDPE)) using two solvent, i.e. n-hexane and petroleum spirit. The starting material is contacted with the solvent at elevated temperatures, i.e. around 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 the dissolved polyolefins.

Each polyolefin is precipitated one after the other from the solution using crystallization under simultaneous shearing action. Thereby, each polymer type is separated and waxes, polymer chain fragments and different additives are kept in solution. For the dissolution step, a mixing nozzle is disclosed. No other means are explicitly disclosed about the mixing. Hence, from the disclosure of CA 2376488 A1 no further improvement of the mixing time and homogeneity can be derived.

US 20180171094 A1 discloses a solvent based process for purifying reclaimed

Polypropylene. A method for purifying a reclaimed polypropylene is provided. The method involves obtaining reclaimed polypropylene, contacting it with a first fluid solvent to produce an extracted reclaimed polypropylene then dissolving the extracted reclaimed polypropylene in a solvent to produce a first solution comprising polypropylene and suspended contaminants. The first solution is settled to produce a second solution comprising polypropylene and remaining contaminants. The second solution is purified by contacting the second solution with solid media to produce a third solution comprising purer polypropylene.

Finally, the purer polypropylene is separated from the third solution.

WO 2022029318 A1 describes a method for downsizing, in particular shredding, plastic material comprising at least one target polymer, and removing dust from said downsized plastic material comprising at least one target polymer, integrated with a method for solvent- based, including an extraction step, recycling a plastic material comprising at least one thermoplastic target polymer with an integrated step of addition of functional solid or liquid auxiliaries to the solution comprising the thermoplastic target polymer. Further a method for removing additives and/or impurities from a fluidized form comprising a thermoplastic target polymer while being processed in an extruder is described

EP 4074483A1 relates to solvent based recycling processes of polyolefins, and discloses dissolution apparatuses and processes used for in solvent based recycling processes of polyolefins

In the above mentioned patent disclosures no mention is made how to separate cellulosic containing materials, metals and high melting polymers from the polyolefin waste materials, with the intention of retrieving these materials for re-use in new/other applications. The re-use of these materials will generate additional economic value and improve the circularity.

DE 4414750 A1 relates to a process and an apparatus for clearing viscose based polymer melts possibly contaminated with paper. The impurities being segregated from the polymer melt by centrifuging

DE 1918183 C2 relates to a method for separating the components of a product containing at least two plastic substances or a plastic and a metal substance. The Product is heated to a softening temperature and centrifuged at that temperature, where the plastic substance is disposed.

Prior art disclosures suggests that separation of plastic streams contaminated with metals and cellulose can be conducted using a centrifuge unit it the process configuration. However utilizing a centrifuge at high temperatures and pressures, combined with polymer dissolution, will generate serious safety concerns since volatile flammable solvents are used.

The present invention aims to overcome the above problems.

Summary of the Invention

Accordingly, a process is provided for recycling a polyolefin containing waste material stream comprising inorganic components and/or non-polyolefin polymers, comprising the steps of: a. Raising the temperature of the waste material stream above the melting temperature of the polyolefin(s) contained therein, to create a molten waste material stream; b. Separating solid components from the molten waste material stream; c. Adding solvent to the molten waste material stream, to create a slurry comprising a polyolefin solution and undissolved components, d. Separating the undissolved components from the polyolefin solution, and e. Isolating the polyolefin from the polyolefin solution.

Moreover, an apparatus for use in the process of the present invention is provided.

Brief description of the Drawings

Figs 1-3 are schematic representations of different embodiments of the invention wherein a waste stream containing polyolefins is fed to an extruder and undergoes a heating/melting process. Downstream of the extruder a melt filtration module is inserted where unmolten materials will be separated from the polymer melt. The embodiments illustrate different routes for a suitable solvent to be introduced into the polymer melt , whereupon it undergoes a filtration step.

Detailed description of the Invention

It has been surprisingly found that the object of the present invention is achieved by the claimed dissolution process and apparatus for dissolving from a polyolefin containing waste stream a polyolefin in a solvent yielding a polyolefin solution slurry, the polyolefin solution slurry comprising a polyolefin solution and undissolved residues. The dissolution apparatus preferably comprises at least one extruder equipped with a melt filtration unit, which is able to separate unmolten species with a diameter > 100 um from the polyolefin containing waste stream. After dissolution a second filtration system will separate unmolten and undissolved species from the polymer phase in at least one filtration unit, but preferably a series of units from 100 um to sub-micron level.

The process of the present invention will be illustrated on the basis of Figures 1-3. It should be noted that the basic concept of the process of the present invention is the dissolution of at least one waste polyolefin in a solvent.

The dissolution process of the present invention generally comprises two stages. In the first stage the polyolefin containing waste stream is fed into an extruder, preferably a single or double screw containing extruder, wherein a molten waste material stream is produced. The extruder preferably contains a melt filtration module, which removes unmolten species.

Preferably unmolten species of size >100 um are removed. The second stage, (2), is a dissolution stage, in which the molten waste material stream is brought into contact with a suitable solvent. This may be achieved with a static mixer, an extruder, a dissolution vessel or combinations thereof. This creates a slurry comprising a polyolefin solution and undissolved components. This may be subjected to a single or series of filtration steps, which removes unmolten and undissolved particulates to sub-micron size and provides a polyolefin slurry from which the polyolefin may be isolated.

Waste polyolefin material

The waste polyolefin containing material is typically provided in a ground form, being subject already to several preceding steps for pre-sorting and washing, even extracting. Such steps are generally steps of preparing the polyolefin containing waste material stream from general waste, including washing the waste with aqueous and/or caustic solutions to remove unwanted material from the polyolefin comprising waste. Furthermore, the size of the pieces of polymer comprising waste is preferably reduced beforehand, preferably by cutting, milling, and shearing, or mixtures thereof. The polyolefin containing waste material stream may for instance be provided in ground form, preferably in the form of flakes, preferably having a largest diameter of not greater than 3 cm, more preferably not greater than 2 cm, and most preferably not greater than 1 cm. The polyolefin containing waste material stream is preferably free of any waste on the surface of the polyolefin flakes. Thus, the process of the present invention is preferably directed to the dissolution of waste polyolefin flakes being essentially clean but from the contaminants within.

Polyolefin

The polyolefin containing waste material stream, can contain different 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), metallocene based Polyethylene (m-PE), Polyethylene terephthalate (PET), polypropylene (PP), poly(vinyl chloride) (PVC), polystyrene (PS), polycarbonate (PC)

Ethylene-vinyl alcohol (EVOH), polyurethanes (PUR) and polyamides (PA). Preferably, polyolefin containing waste material stream has a polyolefin content of higher than 75 wt®%, more preferably of higher than 80 wt% and most preferably higher than 85 wt% of the total weight of the polyolefin containing waste material stream. The polyolefin containing waste material stream further can comprise waste impurities, such as common additives, such as antioxidants, food residues, residual perfume components, dyes and pigments, and generally components inevitably introduced in plastic waste material by production and usage. In addition to contaminations, many recycled waste streams can contain bio-based fractions such as cellulose or lignin. In addition to contaminations, recycled waste streams can contain metals, which represent a significant economic value, such as iron, copper, aluminium.

Solvent

Generally, the solvent must be able to solve polyolefins, without dissolving polymers other than the polyolefin. Suitably, the solvent is a non-polar solvent or a mixture thereof. For example, the solvent may be a hydrocarbon or a mixture of hydrocarbons. Aromatic hydrocarbon solvents are known for good solvent properties and can therefore be considered.

Nevertheless, a drawback of aromatic hydrocarbons lies in enhanced dissolution of polystyrene. On the other hand, e.g. n-alkanes are known as not dissolving 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 at 1 bar pressure of the solvent is higher than 60 °C. More suitably, the solvent is selected from the list of low boiling solvents and high boiling solvents or mixtures thereof. Low boiling solvents comprise n-alkanes and aromatic hydrocarbons, such as toluene and xylene. The advantage of low boiling solvents is that they can be separated from dissolved polyolefins via evaporation. High-boiling solvents comprise paraffinic gas oil or vacuum gas oil. Such solvents have the disadvantage that they are difficult to be removed from the product.

Aromatic solvents on the other hand may cause odour problems due to the residual content after separation or may cause problems when targeting applications where food approval is required. Therefore, preferably, the solvent is selected from n-alkanes or mixtures thereof having a boiling point at 1 bar pressure of more than 60 °C and 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 980 °C.

Undissolved residues

The undissolved residues generally can be undissolved solid or liquid residues. Most commonly, the undissolved liquid residues are other polymers, sufficient small in particle size to pass the melt filtration module, and not soluble at the conditions and in the solvent chosen in the process. Undissolved solids can either be non-polymeric solids, such as pigments, cellulosic material, metals or additives not soluble in the dissolving solvent or polymers. Such polymers can be either polar polymers, which are not solvable in the used solvent, or non- polar polymers, which are not solvable under the conditions used in the dissolution step.

Melt feeding and melt filtration

In the melt feeding step, the polyolefin containing waste material stream, preferably in the form of flakes, are molten before being fed to the dissolution stage. The temperature of the molten waste material stream is preferably at the dissolution temperature in the second stage or higher. More preferably, the temperature of the molten waste material stream is 20-60 °C higher than the melting temperatures of the polyolefins contained therein, but below the melting temperatures of the non-polyolefin components therein, such as high melting polyesters. The temperature may therefore be in the range of 110 to 300°C, preferably 150 to 250°C. The melting preferably is carried out in an single or double screw equipped extruder, more preferably, in which temperatures in the range of 180-245 °C are applied. Continuous melt filters, supplied by Maag, Pall, etc, are suitable for separation of materials with up to 16% by weight contamination and are guaranteed to remain in use for long periods without changing the filter. In general, melt filters are capable of processing a wide range of polymers (e.g. LDPE, LLDPE, HDPE, PP, PS, ABS, PC / ABS, TPE, TPU, POM). All solid or elastomer foreign particles such as paper, wood, aluminium, copper, rubber, silicone, or high-melting polymer composites may be efficiently removed. Melt filters can in principle be used in any extrusion line — either single or twin-screw and irrespective of the type of pelletizing system or other downstream unit. In this particular embodiment efficient removal of PET, aluminium and copper from the molten waste material stream has been demonstrated utilizing filters internals with a pore size of 500 um down to 100 um without compromising on capacity.

Solvent introduction and polymer dissolution

The molten waste material stream, after the melt filtration unit, can be introduced to the second stage, with introduction of solvent and subsequent dissolution of the polyolefin to create a slurry comprising a polyolefin solution and undissolved components. It is important to consider the following aspects: (1) There will be a high difference in viscosity between the polymer melt and the solvent, the mixing will be demanding. Efficient mixing is therefore still needed since bad mixing might cause uneven temperature distribution in the solution that could affect the polymeric material, especially when the temperature of the polyolefin reaches relatively high values, i.e. 250 °C for polypropylene. (2) Melt feeding can be performed in a continuous manner, as the melt feed can be pressurized to match the pressure in the dissolution step, without involving a gaseous phase, i.e. into a 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 also dissolves faster in the solvent in comparison to the dry or wet feeding.

It may be advantageous that hot solvent is fed separately to the dissolution at a higher temperature than the final dissolution temperature to heat up the slurry feed. Melt feeding can be and preferably is performed in a continuous manner, as the melt feed can be pressurized to match the pressure in the dissolution step. Preferably, melt feeding is performed in a continuous manner, as the melt feed can be pressurized to match the pressure in the dissolution step. Suitable temperatures after melt filtration will generally be above 200 °C, where the dissolution temperature is expected to be in the range of 130-150 °C.

Solvent may be introduced at one point or at several point. For instance, solvent may be introduced to create a slurry with a dynamic viscosity in the range of 4200 Pa s to 1500 Pa s.

To this additional solvent may be added, to reduce the dynamic viscosity to the range of 100

Pasto10Pas.

The process may be carried out with different configurations of apparatus. Three configurations are preferred which are described in greater detail hereafter.

Figure 1 shows a first embodiment, where the polyolefin containing waste stream (1) is fed to an extruder (5) and undergoes a heating/melting process thereby creating a molten waste material stream comprising a polymer melt. Downstream of the extruder (5) a melt filtration module is inserted where unmolten materials (2), e.g., metals and high melting polymers, will be separated from the molten waste material stream. This module preferably comprises a melt pressure-controlled scraper system that removes the contamination from the surface of a rotating screen disc into a discharge screw system, In this embodiment preferably a gear pump (6) is employed to maintain the relevant pressure. A suitable solvent (3) is introduced to the polymer melt via the homogenizing device (7) and further solvent addition occurs in the dissolution vessel (8). The polymer is completely dissolved and undergoes further steps as filtration with one or more filtration units (9), where very fine particulates containing e.g., metals, inorganic components and high melting polymers will be separated. The embodiment as shown in Figure 1 illustrates a preferred embodiment, wherein a static mixer (7a) is used as homogenizing device (7), and where (part) of the solvent (3) is introduced. The solvent (3) may be preheated. Typically it is inserted into the homogenizing device (7) at higher pressure than the pressure of the melt flow. The solvent containing melt flow is transferred to the dissolution vessel (8). Additional solvent may be introduced within the dissolution vessel (8).

The dissolution vessel (8) is suitably operated at temperature in the range of 130-150 °C and corresponding pressures of 7-20 bar (g). Preferably, the dissolution vessel (8) is in the form of a continuous stirred tank reactor. The ratio of solvent addition between the homogenizing device (7) and the dissolution vessel (8) can be altered. Typically polymer to solvent ratios are in the range of 1-30 wt®%.

Figure 2 shows a second embodiment, similar to the first embodiment, but where the polyolefin containing waste stream (1) is fed to an extruder (5) and undergoes a heating/melting process thereby creating a molten waste material stream comprising a polymer melt. The homogenizing device (7) in this embodiment is a second extruder (7b). The extruder (7b) is preferably equipped with a double screw, with a screw design containing the correct transport and mixing modules. The barrel design of the extruder is equipped with solvent injection ports in such a way that the melt seal is maintained while injection of (part) of the solvent (3) is introduced. The solvent (3) may be preheated. Typically it is inserted into the extruder at higher pressure than the pressure of the melt flow. In order to maintain sufficient backpressure, after solvent introduction, the extruder (7b) may equipped with a divertor valve (not shown).

The embodiment as shown in Figure 3 is similar to the first embodiment, but without a dissolution vessel, as the homogenizing device (7), in this embodiment is a device (7c) that is able to conduct the dissolution process to completion. Device (7¢) is therefore equipped with properly designed tubing with multiple solvent injection posts and containing multiple static mixers as internal. In order to maintain the relevant pressure a gear pump (6) may be used.

It is recommended that in the design of the homogenizing devices, in particular those employing static mixers, special consideration should be given to fouling, since particles of undissolved and/or unmolten species are still present in the polymer slurry.

Polymer filtration

When the dissolution process is completed the slurry comprising a polyolefin solution and undissolved components is transferred to one or more filtration units (9). The slurry can have undissolved solids with particle size in the range of approximately 100-0.1 um. The undissolved solids can either be non-polymeric solids, such as pigments, cellulosic material, metals or additives not soluble in the dissolving solvent (3) or non-polyolefin polymers which are not solvable in the used solvent. A singly unit may be used, but preferably a series of units is used. Preferably, the or each filtration unit is equipped with a regeneration modus of operation. Preferably the or each filtration unit is designed to operate in a safe mode and is designed for the operating pressure and temperature in combination with flammable solvents.

Preferably one to three set of filtrations units are employed, for instance, to separate particulates of 100-20 um, 20-1 um and below 1 um. This preferred configuration enables efficient separation of high melting polymers and metals which have particle sizes in the range of 100-20 um, and other pollutants/additives which have particle sizes of 20-sub micron range. The filtration elements can be candles, filter discs, or the filter housing is containing a filtering aid, inorganic in nature, which selectively removes the impurities from the polymer slurry (4). Preferably the or each filtration unit operates at 150-200°C in batch or continuous mode.

The process for recycling a polyolefin containing waste material stream comprising inorganic components and/or non-polyolefin polymers as described in this application is believed to be new, which may be carried out in an apparatus of different configuration. The configuration of the apparatus in Figures 1-3 are also believed to be new.

Claims

CONCLUSIONS

1. A process for recycling a polyolefin-containing waste material stream containing inorganic components and/or non-polyolefin polymers, consisting of the steps of:

a. increasing the temperature of the waste material stream above the melting temperature of the polyolefin(s) present therein, to create a molten waste material stream;

Db. the separation of solid components from the molten waste material stream;

C. adding solvent to the molten waste material stream to create a slurry consisting of a polyolefin solution and undissolved components,

d. separating the undissolved components from the polyolefin solution, and e. isolating the polyolefin from the polyolefin solution.

2. The process of claim 1, wherein the temperature in step a is increased using a melting device equipped with a melting filter.

3. The process of claim 2, wherein the melting apparatus may be a single-screw or twin-screw extruder.

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

5. The process of any one of claims 1 to 4, wherein the solids are separated from the molten waste stream by filtration.

6. The process of any one of claims 1 to 5, wherein step c is carried out in a homogenisation apparatus.

7. The process of any one of claims 1 to 6, wherein the solvent is selected from non-polar aliphatic solvents or mixtures, or aromatic hydrocarbons, or mixtures of aromatic and aliphatic solvents.

8. The process according to any one of claims 1 to 7, wherein the dynamic viscosity of the slurry is between 4200 Pa s and 1500 Pa s.

9. The process of any one of claims 1 to 10, wherein an additional solvent is added to the slurry of step c to reduce the dynamic viscosity to 100 Pa s to 10 Pa s.

10. The process of claim 9, wherein a solution vessel is used which operates at a temperature between 150-200 °C and a pressure between 10-20 bar(g), preferably under a nitrogen atmosphere.

11. The process of claim 9 or 10, wherein the additional solvent or the mixed solvent is the same as used for preparing the slurry.

12. The process of any one of claims 1 to 11, wherein the undissolved components of the slurry are separated by filtration.

13. The process of any of claims 12, wherein one or more filtration units are used.

14. The process of claim 13, wherein the or each filtration unit operates at 150-200°C in batch or continuous mode.

15. The process of claim 12 or 13, wherein a set of filtration units is used to remove the undissolved constituents in successive modules from 100 µm to less than 1 µm.

16. An apparatus for recycling a polyolefin-containing waste stream containing inorganic components and/or non-polyolefin polymers as claimed in any one of claims 1 to 17, comprising: - a melting apparatus with internal or external filtration module (5); - a homogenising apparatus (7); - optionally a dissolution vessel (8), and - at least one filtration unit (9).

17. The apparatus of claim 16, wherein the melting apparatus (5) is a single- or twin-screw extruder.

18. The apparatus of any of claims 18-17, wherein the filtration module of the melting apparatus (5) is equipped with a melt pressure controlled scraper system for removing contamination from the surface of a rotating screen disc in a discharge screw system.

19. The apparatus of any of claims 16-18, further comprising a pump (6).

20. The apparatus of any one of claims 16 to 19, wherein the homogenizing apparatus (7) is a homogenizer (7a) equipped with a solvent injection port and comprising at least one internal mixing element, preferably a mixing element consisting of interlocking and crossing rods disposed at an angle to the axis of the flow direction.

21. The apparatus of any of claims 18 to 19, wherein the homogenizing apparatus (7) is a twin-screw extruder (7b) having a solvent injection port and a distribution valve.

22. The apparatus of any of claims 16 to 19, wherein the homogenizing device (7) is a homogenizer (7c) equipped with two or more solvent injection ports and comprising two or more internal mixing elements, preferably a mixing element consisting of interlocking and crossing rods disposed at an angle to the axis of the flow direction.

23. The apparatus of any of claims 18 to 22, wherein the solution vessel (8) is a continuous stirred tank reactor.

24. The apparatus of any of claims 18 to 23, wherein a set of filtration units (9) is used to separate particles of 100-20 µm, 20-1 µm and less than 1 µm.

25. Recycled polyolefin prepared according to the process of any one of claims 1 to 15 and/or produced in the apparatus of any one of claims 16 to 24.