Patent Application
20250215329
The present invention relates to a method for producing a hydrocarbon product from mixed polymer waste comprising 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, as well as to a system for producing a hydrocarbon product from mixed polymer waste. The present invention also relates to a method for recycling mixed polymer waste comprising a pre-treatment to remove polymer comprising heteroatoms as well as to a system for recycling mixed polymer waste. The mixed polymer waste used as feedstock in the present invention is, e.g. plastic waste and/or post consumer plastic waste (PCW).
Polyethylene and polypropylene constitute almost 50% of the overall plastics production in the European Union, and of this 40% is used for packaging. European waste directives state that by the end of 2025, 65% of all packaging waste should be recycled. However, there are no recycling solutions commercially available for multi-layer flexible packaging film, which inherently comprises a variety of different polymer types.
Chemical recycling transforms polymer waste back to virgin materials. For example, pure polyethylene and polypropylene can be recycled by pyrolysis. The recycling process produces a range of different hydrocarbon products, e.g. waxes, hydrocarbon oils, naphtha, and other light gases. Some of these products are suitable for entry into the refinery and/or petrochemical value chain to ultimately become ethylene or propylene for production of further polyethylene or polypropylene respectively.
Multilayer flexible film used for food packaging, a common type of post consumer plastic waste, is much more challenging to recycle than monomaterial polyethylene or polypropylene because it contains a mixture of different polymers including heteroatom-containing polymers such as polyethylene terephthalate (PET) and polyamide (PA). Polymers like PET and PA cause significant problems during pyrolysis due to the formation of hazardous or corrosive degradation products, which decrease the product quality and damage equipment in the recycling plant. This problem is exacerbated with multilayer flexible films because they also tend to comprise heteroatom-containing additives, e.g. plasticisers, dyes, UV or light stabilisers etc. Like PET and PA, these additives tend to form problematic degradation products during pyrolysis. Moreover, given the huge variety of different additives used in multilayer flexible film packaging it is difficult to predict, and control, the degradation products that will be produced.
As a result, the majority of commercial plastic recycling plants only accept post-consumer plastic waste (PCW) which contains low levels of PET and PA. For PA, this is often as low as <1 wt %, and for PET it is typically <2 wt %. These requirements mean that multi-layer flexible packaging film usually cannot be recycled in such plants or it can only be accepted after mechanical sorting, which takes considerable time and energy, and achieves only modest levels of separation.
The prior art in the area of plastic recycling has focused on handling PVC, rather than heteroatom-containing polymers. U.S. Pat. No. 5,608,136, for example, discloses a method for thermal pyrolysis of waste plastic to produce high quality fuel oil, wherein a pre-treatment step is optionally carried out in an extruder. U.S. Pat. No. 5,608,136 recognises that in the conditions of the extruder, which are typically 200 to 400° C., elimination of HCl from PVC occurs, and needs to be handled. It is suggested that this can be done by introducing an alkaline agent to react with the HCl.
Viewed from a first aspect the present invention provides a method for producing a hydrocarbon product from mixed polymer waste, wherein said mixed polymer waste comprises 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, based on the total weight of the mixed polymer waste, comprising:
Viewed from a further aspect the present invention provides a system for producing a hydrocarbon product from mixed polymer waste, preferably according to a method as hereinbefore described, comprising:
Viewed from a further aspect the present invention provides a method for recycling mixed polymer waste comprising a pre-treatment to remove polymer comprising heteroatoms, wherein said pre-treatment comprises a method as hereinbefore defined.
Viewed from a further aspect the present invention provides a system for recycling mixed polymer waste, comprising:
As used herein the term “hydrocarbon product” refers to a blend or mixture of hydrocarbons. The hydrocarbons solely comprise C and H atoms.
As used herein the term “mixed polymer waste” refers to waste material that comprises a mixture of different types or classes of polymer. For example, mixed polymer waste might comprise a mixture of polyethylene, and polyethylene terephthalate or a mixture of polyethylene, polyethylene terephthalate and polyamide.
As used herein the term “post consumer plastic waste” refers to mixed polymer waste produced by an end consumer. A typical example of post consumer plastic waste is packaging.
As used herein the term “plastic waste” refers to waste comprising one or more polymers and additives.
As used herein the term “polyolefin” refers to polymers with a saturated C—C backbone and which consist of C and H atoms.
As used herein the term “polymer” refers to one or more polymers.
As used herein the term “polymer comprising heteroatoms” refers to one or more polymers which contain N, O, P and/or S atoms. Polyvinyl chloride is not a polymer comprising such heteroatoms.
As used herein the term “non-oligomeric compounds comprising heteroatoms” refers to compounds such as additives which contain N, O, P and/or S atoms.
As used herein the term “polyethylene” refers to a polymer having the repeat unit —(CH2CH2)—. Preferably at least 95% wt, more preferably at least 99% wt of the repeat units in polyethylene are —(CH2CH2)—. The term encompasses low density polyethylene (LDPE), high density (HDPE) and linear low density polyethylene (LLDPE).
As used herein the term “polypropylene” refers to a polymer having the repeat unit —(CH(CH3)CH2)—. Preferably at least 95% wt, more preferably at least 99% wt of the repeat units in polypropylene are —(CH(CH3)CH2)—. The term encompasses all different forms of polypropylene, e.g. homopolymers, heterophasic and random polypropylene. All kinds of tacticity is also covered.
As used herein the term “polyethylene terephthalate” refers to a polymer having an ethylene terephthalate repeating unit (C10H8O4). This is typically formed from monoethylene glycol and terephthalic acid. Preferably at least 95% wt, more preferably at least 99% wt of the repeat units in polyethylene terephthalate are ethylene terephthalate (C10H8O4). Optionally repeat units derived from other diols (e.g. 2-methyl-1,2-propanediol, diethyleneglycol, cyclohexane dimethanol) and/or iso-terephthalic acid may also be present.
As used herein the term “polyamide” refers to a polymer having repeating units linked by amide bonds. The term encompasses aliphatic polyamides such as Nylon PA 6 and PA 66, aromatic amides (sometimes referred to as aramids) as well as polyphthalamides (e.g. PA 6T). Preferably at least 95%, and more preferably at least 99% of the bonds linking repeat units in polyamides are amides.
The present invention relates to a method for producing a hydrocarbon product from mixed polymer waste, wherein said mixed polymer waste comprises 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, based on the total weight of the mixed polymer waste, comprising:
The method of the present invention can advantageously be used in a recycling process as a pre-treatment step, prior to pyrolysis, for ultimately converting the mixed polymer waste into a form that can re-enter the refinery value chain. Typically, the mixed polymer waste is plastic waste. The mixed polymer waste is preferably post consumer plastic waste (PCW). One of the main advantages of the method of the present invention is that the mixed polymer waste may contain relatively high levels of heteroatom-containing polymers as well as non-polymeric heteroatom-containing compounds, such as additives, e.g. up to 50 wt %. This is many orders of magnitude more than commercial recycling plants currently in operation, and avoids the need to mechanically separate different classes of polymer. This is because the method of the invention degrades the heteroatom-containing polymer, and if present, the heteroatom-containing non-oligomeric compounds such as additives, and the degradation products can be removed from the reaction mixture before pyrolysis is carried out. Optionally the degradation products can be recovered. Optionally the degradation products are useful chemicals, e.g. monomers and/or monomer derivatives. Recovery of the degradation products is particularly advantageous in such cases. At the same time, the method of the invention advantageously causes initial cracking of the polyolefins and produces a more homogeneous, and less viscous, melt thereby facilitating its processing to the pyrolysis reactor and the pyrolysis reaction itself.
The method of the present invention is predominantly based on a chemical degradation reaction, specifically hydrolysis, of the heteroatom-containing polymer, and optionally compounds such as additives. This is preferable over thermal degradation of these polymers and compounds because it is controlled, and gives rise to known degradation compounds, which can be removed from the polymer melt before the melt enters the pyrolysis reactor. This avoids the formation of corrosive or harmful substances such as acids and cyanides. Moreover, the improved purity and homogeneity of the hydrocarbon product for the pyrolysis reaction means that a significantly improved product, in terms of purity and homogeneity, is obtained from the pyrolysis reaction. The pyrolysis reaction is conducted at elevated temperatures and otherwise gives rise to a complex mixture of heteroatom-containing products that is impossible to fully comprehend and control. The method of the present invention reduces or avoids the need for complicated, and expensive, purification steps that are not normally, or currently, available at hydrotreatment facilities to clean up the post-pyrolysis reaction product, and allows for improved process control.
The mixed polymer waste processed in the method of the present invention is preferably plastic waste, and more preferably post consumer plastic waste.
The mixed polymer waste that is processed in the method of the present invention is predominantly polyolefin. Thus the major component of the mixed polymer waste should be polyolefin. In preferred methods of the present invention, the mixed polymer waste comprises 50-99 wt % polyolefins, more preferably 65-98 wt % polyolefins, and yet more preferably 70-95 wt % polyolefins, based on the total weight of the mixed polymer waste composition.
In a preferred method of the invention, the polyolefins present in the mixed polymer waste are selected from polyethylene (e.g. LDPE, HDPE, LLDPE), polypropylene, polystyrene and mixtures thereof. In some preferred methods of the invention the polyolefins present in the mixed polymer waste comprise, or consist of, polyethylenes. In other preferred methods of the invention the polyolefins present in the mixed polymer waste comprise, or consist of, polypropylenes. Preferably the mixed polymer waste comprises less than 10 wt %, more preferably 0-10 wt %, still more preferably 0-5 wt % and yet more preferably 0-2 wt % polyvinyl chloride.
In preferred methods of the invention the mixed polymer waste comprises 1-50 wt %, more preferably 2-35 wt % and yet more preferably 5-30 wt % polymer comprising heteroatoms, based on the total weight of the mixed polymer waste composition. This is highly advantageous as it avoids the need to try to mechanically separate different polymer classes prior to carrying out the method of the invention. Mechanical separation is commonplace in recycling operations currently in use but achieves only modest levels of separation.
The heteroatoms present in the heteroatom-containing polymer are preferably selected from N, O, S, and P, and more preferably N, O and S. More preferably the polymer comprising heteroatoms comprise N and/or O atoms.
In preferred methods of the present invention the mixed polymer waste further comprises non-oligomeric compounds comprising heteroatoms, i.e. the mixed polymer waste comprises a mixture of non-polymeric compounds and polymers, both comprising heteroatoms. Whilst the method of the present invention advantageously removes non-polymeric heteroatom-containing compounds, it is particularly beneficial for removal of heteroatom-containing polymers. This is because the polymers tend to contain higher amounts of heteroatoms than the non-polymeric compounds, and also because the polymers tend to be present in mixed polymer waste in higher amounts. This is because such polymers are a key component of multi-layered packaging film.
When the mixed polymer waste comprises non-polymeric compounds comprising heteroatoms, the non-polymeric compounds are preferably additives, and more preferably additives selected from antioxidants, acid scavengers, slip agents, anti-block agents, processing aids, fillers, extenders, pigments, nucleation agents, lubricants, antistatic agents, UV stabilisers, anti-fogging agents, flame retardants, and mixtures thereof. Representative examples of heteroatom-containing additives that may be present in mixed polymer waste include tris(2,4-di-tert-butylphenyl) phosphite, bis(2,4-di-tert-butylphenyl) pentaerythritol diphosphate, octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate, pentaerythritol Tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate), 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, α-tocopherol (Vitamin E), calcium stearate, zinc stearate, hydrotalcite, synthetic, cis-13-docosenoamide, oleamide, LUDOX® CL colloidal silica, magnesium silicate monohydrate, titanium (IV) oxide, limestone, magnesium silicate monohydrate, 1,3:2,4-bis(3,4-dimethylobenzylideno) sorbitol, 1,2,3-trideoxy-4,6:5,7-bis-O-((4-propylphenyl)methylene)-nonitol, glyceryl monostearate, 2,2′-iminobis-, N—C12-18-alkyl derivatives, and mixtures thereof.
In the methods of the present invention, the polymer comprising heteroatoms comprises repeating units, derived from monomers, which contain heteroatoms. Preferred heteroatom-containing polymers are those having repeating units joined by amide bonds, ester bonds, carbamate bonds, carbonate bonds, or mixtures thereof. In the conditions of the present invention, these bonds are preferably hydrolytically degraded and the heteroatom-containing polymer is degraded to degradation products that can be removed from the polymer melt.
In preferred methods of the present invention, the polymer comprising heteroatoms are polymers selected from polyethylene terephthalate (PET), polyamide (PA), polyurethane (PU), biopolymers (e.g. polylactic acid, polyhydroxyalkanoates), cellulose, poly(ethylene-co-vinyl acetate) (EVA), poly(vinyl alcohol-co-ethylene) (EVOH), polycarbonate, poly(acrylonitrile-co-butadiene-co-styrene) (ABS), poly(styrene-co-acrylonitrile) (SAN), polymethylmethacrylate (PMMA) and mixtures thereof. Preferably the polymer comprising heteroatoms are polymers selected from polyethylene terephthalate (PET), polyamide (PA), polyurethane (PU), biopolymers (e.g. polylactic acid, polyhydroxyalkanoates and mixtures thereof). Another possible biopolymer comprising heteroatoms is polyethylene furanoate (PEF). Still more preferably the polymer comprising heteroatoms are polymers selected from polyethylene terephthalate (PET), polyamide (PA), and mixtures thereof. In some preferred methods of the invention mixtures of PET and PA are preferred. The polymers may be virgin material or may be, e.g. plastic waste or post consumer plastic waste (PCW).
In preferred methods of the present invention, the mixed polymer waste is washed (e.g. with water) prior to step (i) of the method herein described. Preferably the mixed polymer waste is also treated to remove materials that might damage the processing equipment (e.g. metal, stones, glass etc) prior to step (i) of the method herein described. Washing and separation to remove bulk contaminants may be carried out using conventional equipment. Advantageously, the mixed polymer waste does not need to undergo mechanical separation into different polymer types prior to step (i) of the method described herein. Advantageously, the mixed polymer waste does not need to undergo extensive drying to remove water prior to step (i).
The mixed polymer waste is preferably in the form of pellets or flakes. In preferred methods of the present invention, the mixed polymer waste is shredded or cut prior to entry into the method of the present invention. Conventional equipment may be used.
In preferred methods of the present invention, the mixed polymer waste is HDPE monomaterial, artificial turf (PE), flexible intermediate bulk containers (FIBC, PE/PP), or multi-layered film. In particularly preferred methods of the invention, the mixed polymer waste is multi-layered packaging film. Preferably the multi-layered film is shredded or cut into flakes for entry into the method of the present invention. Thus a preferred method of the invention comprises a prior step of shredding or cutting the mixed polymer waste into flakes. Preferably the flakes have an average dimension of 3-8 mm, more preferably 3-5 mm.
In the method of the present invention the mixed polymer waste is fed into an extruder. During its time in the extruder, two key processes occur. First the polyolefin present in the mixed polymer waste undergoes cracking to produce a hydrocarbon product in the form of a melt. Second the heteroatom-containing compounds, i.e. polymer and optionally non-polymeric compounds such as additives, present in the mixed polymer waste undergo degradation to produce degradation products that can be removed from the hydrocarbon melt.
In some preferred methods of the present invention, the mixed polymer waste is mixed with water prior to feeding said mixed polymer waste to the extruder. The water may be in the form of a liquid or gas (i.e. steam). The water is a chemical in the method of the invention since it drives the hydrolysis reaction that degrades the heteroatom-containing polymer and optionally non-polymeric compounds containing heteroatoms such as additives. Preferably the water is provided as an alkaline or acidic solution, and more preferably an alkaline solution. Mixing of the mixed polymer waste with an acid or alkali promotes the degradation of the heteroatom-containing compounds, i.e. polymer, and if present, non-polymeric compounds such as additives, by chemical degradation, rather than thermal degradation. As mentioned above, this gives rise to stable degradation products that can then be removed from the hydrocarbon product.
In other preferred methods of the invention, the mixed polymer waste is not mixed with water prior to feeding said mixed polymer waste to the extruder. These methods are preferred when the mixed polymer waste already contains sufficient water for the hydrolysis reaction.
In other preferred methods of the invention, water is optionally added to the mixed polymer waste in the extruder. The water may be in the form of a liquid or gas (i.e. steam). In these methods, the mixed polymer waste is fed into the extruder, and water is added separately. Preferably the water is an alkaline solution.
In more preferred methods of the invention, the chemicals added to the mixed polymer waste are an alkali metal salt and/or an alkaline earth metal salt. Examples of preferred salts are alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal oxides, alkaline earth metal oxides, alkali metal carbonates, alkaline earth metal carbonates or mixtures thereof. Alkali metal carbonates, alkaline earth metal carbonates or mixtures thereof are particularly preferred. These may be added in the form of an alkaline solution. Alternatively, e.g. when there is sufficient water in the mixed polymer waste, they may be added as solids.
In some preferred methods of the present invention the chemicals added to the mixed polymer waste are an alkaline solution. Preferably the alkaline solution is selected from ammonia solutions, and solutions of alkali metal or alkaline earth metal hydroxides, alkali metal or alkaline earth metal oxides, alkali metal or alkaline earth metal carbonates or mixtures thereof.
In other preferred methods of the present invention, the chemicals added to the mixed polymer waste are solid alkali metal salts and/or alkaline earth metal salts.
In preferred methods of the present invention, the mixture of water and mixed polymer waste comprises 5-15 wt % water, more preferably 5-12 wt % water and still more preferably 8-12 wt % water, based on the total weight of the mixture. It will be appreciated that the amount of water in the mixture may vary slightly at the inlet of the extruder and in the extruder itself. These values preferably represent the amount of water present in the mixture of water and mixed polymer waste in the extruder, where degradation occurs. The presence of higher amounts of water (e.g. >5 wt %) has been found to be particularly useful when the heteroatom-containing compound is PET.
In preferred methods of the present invention, the mixture of water, alkali metal salt and/or alkaline earth metal salt, and mixed polymer waste is thoroughly mixed prior to feeding it into the extruder. This helps to ensure efficient removal of the heteroatom-containing compounds therein, particularly heteroatom-containing polymers, and optionally compounds such as additives. In preferred methods of the invention, the mixture of water, alkali metal salt and/or alkaline earth metal salt, and mixed polymer waste is all fed into the extruder, i.e. no water is removed prior to entry into the extruder.
In preferred methods of the present invention, the extruder is operated at unconventionally high temperatures. It has been found this yields the highest quality hydrocarbon products (e.g. lowest wt % heteroatom-containing compounds in the product). Preferably the extruder is at a temperature of at least 300° C., preferably 300-400° C., still more preferably 350-395° C. and yet more preferably 370-390° C. A further advantage of operating the extruder at such a high temperature is that the temperature of the hydrocarbon product that exits the extruder is also high, and the amount of further heating it needs to enter the pyrolysis reactor is significantly reduced.
In the methods of the present invention, the extruder may be operated at a pressure of up to 400 bar, and more preferably 0 to 200 bar. Whilst in some preferred methods of the invention, no pressure is applied in the extruder, in other preferred methods, a pressure of 50-200 bar is used.
In preferred methods of the invention the residence time of the mixed polymer waste in said extruder is 0.1 to 20 minutes, preferably 0.5-15 minutes, more preferably 0.5 to 10 minutes, still more preferably 1 to 7 minutes and yet more preferably 1.5 to 5 minutes. The short residence time in the extruder is beneficial since it means large volumes of mixed polymer waste can be pre-treated in any given time period. At the same time, the polyolefin present in the mixed polymer waste is at least partially cracked. Preferably the average molecular weight and viscosity of the hydrocarbon product is reduced, and the MFR2 of the hydrocarbon product is increased compared to the polyolefin present in the mixed waste starting material. The method of the invention represents a fast, and efficient, mechanism for preparing ideal feedstock for pyrolysis from mixed polymer waste, that otherwise could not undergo pyrolysis.
The residence time in the extruder is dependent on the scale (e.g. length and diameter) and screw design of the extruder as well as the RPM at which it is operated. In preferred methods of the invention, the RPM is set to ensure the afore-mentioned residence times are satisfied for the particular extruder in use. For a single screw extruder, with a diameter of 25 mm, a length/diameter ratio of 25, the RPM is preferably 10-200, more preferably 10-100 and still more preferably 15-60 RPM, e.g. about 20 RPM. The skilled person can readily identify equivalent RPMs for extruders of different scale and/or screw design to ensure the residence time requirements are satisfied.
In preferred methods of the present invention, different polymers comprising heteroatoms are simultaneously degraded in the extruder. Optionally non-polymeric compounds such as additives are also simultaneously degraded in the extruder. Thus preferably the polymers and optionally non-polymeric compounds such as additives, both comprising heteroatoms, are all degraded in a single pass through the extruder. This is highly advantageous as it means that a single pass through the extruder simultaneously deals with the majority of the different heteroatom-containing compounds, i.e. polymer and non-polymeric, present in mixed plastic waste. It is clearly much more time, energy and cost efficient compared to processes wherein each contaminant type is dealt with separately. In a particularly preferred method of the invention, a mixture of heteroatom-containing polymers is simultaneously degraded in the extruder. Still more preferably a mixed polymer waste comprising PET and PA as heteroatom-containing polymers is simultaneously degraded in the extruder.
In the methods of the invention the extruder may be a commercially available extruder. The extruder may have a twin screw or a single screw. Generally, single screw extruders are preferred.
Preferably the screw diameter is in the range 14 mm-125 mm. Preferably the length/diameter ratio is 15-60, and is configured with single-stage or two-stage screws. The screw(s) may be a standard screw, a barrier screw, or a screw equipped with elements such as metering zones, mixing elements, kneading zones and back flow elements. The screw(s) and barrel may be conically shaped or standard cylinder-shaped with equal diameter. Optionally the barrel may be equipped with inlets for additional of chemicals (e.g. alkali metal salt and/or alkaline earth metal salt) and/or steam, such as in a mixing zone or feeding zone.
In some preferred methods of the invention, the barrel comprises a devolatilization outlet. This allows degradation products in the form of volatiles to escape from the extruder. Alternatively degradation products in the form of volatiles may escape through the extruder die. Optionally the extruder may be operated with a vacuum at its exit, in order to encourage volatile degradation products to escape through the extruder die. Thus in some preferred methods of the invention, the degradation products derived from the polymer comprising heteroatoms, and optionally from non-polymeric compounds comprising heteroatoms, are removed in the form of volatiles and via a devolatization outlet of the extruder or through the extruder die.
In other preferred methods of the invention, the extruder is connected to a downstream devolatilization unit. In such methods, the volatiles produced by degradation of heteroatom-containing compounds, i.e. polymer and optionally non-polymeric compounds such as additives, remain in the hydrocarbon product that exits the extruder, and is fed to a devolatilization unit (e.g. a degasser unit). Thus in other preferred methods of the invention, the degradation products derived from the polymer comprising heteroatoms, and optionally from non-polymeric compounds comprising heteroatoms, are removed in the form of volatiles and via a devolatization unit. Preferably the devolatization unit is connected to the extruder exit, or if present, a melt filter.
In further preferred methods of the invention, the hydrocarbon product collected or exited from the extruder is passed through a melt filter. When a melt filter is present, the extruder is preferably operated under pressure, as discussed above. Preferably the melt filter is directly connected to the outlet of the extruder. Preferably the melt filter removes the solid degradation products (e.g. salts) produced in the extruder from the heteroatom-containing compounds. Thus in some preferred methods of the invention, the degradation products derived from the polymer comprising heteroatoms, and optionally from non-polymeric compounds comprising heteroatoms, are removed in the form of solids and via a melt filter. Preferably the melt filter is directly connected to the extruder exit.
In preferred methods of the present invention, the solid degradation products produced in the extruder from the heteroatom-containing compounds are collected. Optionally these products are recycled.
Preferably the melt filter also removes other solid contaminants present in the mixed polymer waste, e.g. metal, wood, fibres etc. Small amounts of solid contaminants sometimes remain in the mixed polymer waste due to deficiencies in the clean-up processes carried out prior to the method of the present invention. Preferably these solid contaminants are removed in the melt filter, and do not enter the pyrolysis reactor.
In particularly preferred methods of the invention, the hydrocarbon product collected or exited from the extruder is passed through a melt filter and then to a devolatilization unit (e.g. a degasser unit). In the devolatilization unit, volatile products produced in the extruder from the heteroatom-containing compounds are preferably collected. These include heteroatom-containing gases as well as low molecular weight hydrocarbons. Preferably these gases are collected and condensed to liquid or solid form. Optionally, these products are separately recycled.
Thus in some preferred methods of the invention, the degradation products derived from the polymer comprising heteroatoms, and optionally from non-polymeric compounds comprising heteroatoms, are removed via a melt filter and/or a devolatization unit. Preferably the melt filter is directly connected to the extruder exit. Preferably the devolatisation unit is directly connected to the extruder exit, or if present, the melt filter.
In particularly preferred methods of the invention, the degradation products are recovered and optionally recycled. Preferably the degradation products comprise monomers derived from heteroatom-containing polymers.
In some preferred methods of the invention, the hydrocarbon product is collected from the extruder, or if present, the melt filter or devolatilization unit. Optionally, the hydrocarbon product is processed, e.g. to form pellets.
In further preferred methods of the invention, the hydrocarbon product from the method of the invention is then fed to a pyrolysis unit. The method of the invention is advantageous because the quality of this hydrocarbon product as a pyrolysis feedstock is significantly improved compared to the mixed polymer waste. For example, it is much more homogeneous, and it contains far fewer heteroatom-containing compounds that cause damage to pyrolysis equipment and lead to production of hazardous and corrosive substances. As a result, the pyrolysis reaction carried out after the process of the present invention is also much improved.
In preferred methods of the present invention the hydrocarbon product produced is suitable for pyrolysis.
In preferred methods of the present invention the hydrocarbon product comprises 0-5 wt %, more preferably 0-3 wt %, still more preferably 0-2 wt % and yet more preferably 0-1 wt % polyethylene terephthalate (PET), based on the total weight of the hydrocarbon product. Preferably the amount of PET present in the hydrocarbon product is assessed as described in the examples herein.
In a further preferred methods of the invention, the hydrocarbon product comprises 0-5 wt %, more preferably 0-3 wt %, still more preferably 0-2 wt % and yet more preferably 0-1 wt % polyamide (PA), based on the total weight of the hydrocarbon product. Preferably the amount of PA present in the hydrocarbon product is assessed as described in the examples herein.
In a further preferred method of the invention the hydrocarbon product comprises 0-10 wt %, more preferably 0-8 wt %, still more preferably 0-4 wt % and yet more preferably 0-2 wt % compounds comprising heteroatoms, based on the total weight of the hydrocarbon product. Preferably the total amount of compounds comprising heteroatoms present in the hydrocarbon product is assessed by HCNSO ultimate analysis for elemental composition.
As described above, in the method of the present invention, the polyolefins present in the mixed polymer waste undergo cracking in the extruder. This is advantageous for a variety of reasons, including that the hydrocarbon product is easier to feed to a pyrolysis unit, and is an improved feedstock for a pyrolysis unit. Aside from containing fewer compounds comprising heteroatoms, the hydrocarbon product is much more homogeneous than the mixed polymer waste, which leads to better thermal conduction and heat transfer in the pyrolysis unit.
Preferably the hydrocarbon product has a lower weight average molecular weight than the mixed polymer waste. Preferably the weight average molecular weight of the hydrocarbon product is 1-95%, more preferably 1-85% and still more preferably 1-50% of the weight average molecular weight of the mixed polymer waste. The decreased weight average molecular weight of the hydrocarbon product is evidence that cracking occurs in the extruder.
When the mixed polymer waste predominantly comprises LLDPE, the hydrocarbon product has a weight average molecular weight of 5000-100000 g/mol, more preferably 5000-50000 g/mol and still more preferably 5000-32000 g/mol.
When the mixed polymer waste predominantly comprises LDPE, the hydrocarbon product has a weight average molecular weight of 5000-65000 g/mol, more preferably 5000-58000 g/mol and still more preferably 5000-35000 g/mol.
When the mixed polymer waste predominantly comprises HDPE, the hydrocarbon product has a weight average molecular weight of 5000-190000 g/mol, more preferably 5000-135000 g/mol and still more preferably 5000-60000 g/mol.
When the mixed polymer waste predominantly comprises PP, the hydrocarbon product has a weight average molecular weight of 5000-130000 g/mol, more preferably 5000-90000 g/mol and still more preferably 5000-50000 g/mol.
Another advantage of the method of the invention is that the viscosity of the hydrocarbon product is lower than that of the mixed polymer waste. This is beneficial as it makes it much easier to feed the hydrocarbon product into the pyrolysis unit, i.e. the processing of the hydrocarbon product is facilitated. Preferably the hydrocarbon product has a lower complex viscosity, Eta (0.5) than the mixed polymer waste. Preferably the hydrocarbon product has a lower complex viscosity, Eta (200) than the mixed polymer waste.
Preferably the hydrocarbon product has a complex viscosity η*, Eta (0.5) of 0.05-75%, more preferably 0.05-10% and still more preferably 0.05-1% of the complex viscosity, Eta (0.5) of the mixed polymer waste.
Preferably the hydrocarbon product has a complex viscosity η*, Eta (200) of 0.01-60%, more preferably 0.05-10% and still more preferably 0.05-1% of the complex viscosity, Eta (200) of the mixed polymer waste.
When the mixed polymer waste predominantly comprises LLDPE, preferably the hydrocarbon product has a complex viscosity, Eta (0.5) of 2-1500 Pa*s, more preferably 2-200 Pa*s and still more preferably 2-20 Pa*s.
When the mixed polymer waste predominantly comprises LLDPE, preferably the hydrocarbon product has a complex viscosity, Eta (200) of 1-330 Pa*s, more preferably 1-50 Pa*s and still more preferably 1-5 Pa*s.
Preferably the hydrocarbon product has a higher MFR2 than said mixed polymer waste. Preferably the hydrocarbon product has a MFR2 which is at least 150%, more preferably 150-100,000% and still more preferably 500-30,000% of the MFR2 of the mixed polymer waste.
When the mixed polymer waste predominantly comprises LLDPE, preferably the hydrocarbon product has a MFR2 of at least 1 g/10 min, more preferably 1-800 g/10 min, still more preferably 100-800 g/10 min and yet more preferably 200-800 g/10 min.
When the mixed polymer waste predominantly comprises LDPE, preferably the hydrocarbon product has a MFR2 of at least 1 g/10 min, more preferably 1-800 g/10 min, still more preferably 100-800 g/10 min and yet more preferably 200-800 g/10 min.
When the mixed polymer waste predominantly comprises HDPE, preferably the hydrocarbon product has a MFR2 of at least 1 g/10 min, more preferably 1-800 g/10 min, still more preferably 100-800 g/10 min and yet more preferably 200-800 g/10 min.
When the mixed polymer waste predominantly comprises PP, preferably the hydrocarbon product has a MFR2 of at least 1 g/10 min, more preferably 3-800 g/10 min, still more preferably 150-800 g/10 min and yet more preferably 200-800 g/10 min.
Preferably the hydrocarbon product is substantially free of cross linking.
Preferred methods of the present invention further comprise pyrolysis of the hydrocarbon product. Pyrolysis may be carried out according to conventional techniques which are well known in the art.
The pyrolysis reaction produces hydrocarbons, e.g. waxes, oils, naphtha, pyrolysis oils, that can enter the refinery value chain.
The present invention also relates to a system for producing a hydrocarbon product from mixed polymer waste, preferably according to a method as hereinbefore described, comprising:
an extruder for conversion of mixed polymer waste comprising 50-99.5 wt % polyolefins and 0.5-50 wt % polymer comprising heteroatoms, and chemicals, preferably alkali metal salt and/or alkaline earth metal salt, into a mixture of hydrocarbon product and degradation products derived from the polymer comprising heteroatoms;
In preferred systems of the present invention, the outlet of the extruder from which the mixture of hydrocarbon product and degradation products is extruded is directly connected to the inlet of the melt filter unit.
In further preferred systems of the present invention, the outlet of the melt filter unit is directly connected to the inlet of the degassing unit.
Optionally the system comprises a mixing tank for mixing the mixed polymer waste and chemicals, preferably alkali metal salt and/or alkaline earth metal salt. Preferably the mixing tank is connected to the inlet of the extruder so the resulting mixture can be fed to the extruder. Alternatively, the mixing tank may be connected to an inlet of the extruder barrel so the chemicals may be added separately to the mixed polymer waste in the extruder. At least when an alkali metal salt and/or alkaline earth metal salt is employed, it is believed that some degradation of polymer comprising heteroatoms and/or non-polymeric compounds comprising heteroatoms may occur during this mixing. However, to achieve high levels of removal of polymer comprising heteroatoms and non-polymeric compounds comprising heteroatoms, it was found to be necessary to extrude the mixture according to the process hereinbefore described.
Optionally the system further comprises one or more holding tanks for storage of mixed polymer waste and chemicals.
Optionally the system further comprises a pump and delivery device. The pump repressurizes and transports the hydrocarbon product, in the form of a melt, to a delivery device. Preferably the delivery device delivers or transports the hydrocarbon product into a pyrolysis reactor unit.
Optionally the system further comprises a heating unit in between the degassing unit and the pump. This heating unit preferably heats the hydrocarbon product to 450-500° C. prior to entry to the pyrolysis unit.
The present invention also relates to a method for recycling mixed polymer waste comprising a pre-treatment to remove polymer comprising heteroatoms, wherein said pre-treatment comprises a method as hereinbefore defined. Preferred methods further comprise pyrolysis of the hydrocarbon product to produce hydrocarbons suitable for entry into the refinery value chain, e.g. waxes, oils and/or naphthas.
Preferred features of the method hereinbefore described are also preferred features of the method for recycling mixed polymer waste.
The present invention also relates to a system for recycling mixed polymer waste, comprising:
The invention will now be described using the following non-limiting examples and Figures, wherein:
The following materials listed in Table 1 were prepared and mixed to simulate post-consumer waste (PCW) comprising PET and PA from multilayer film packaging.
As a reference, a PE/PA-6 multilayer film with 34 wt % PA was included in some experiments, marked “MF”. The film was shredded and diluted with LLDPE to reach 5% PA in the feed.
Virgin LLDPE (Q1018N, Total) was mixed with pure extrusion grade PA-6 (B40LN, BASF, 5-15 wt %) and/or PET (RAMA-PET N180, 5-15 wt %) to simulate typical and extreme PCW compositions. Sodium hydroxide (NaOH, Sigma-Aldrich) and/or calcium hydroxide (Ca(OH)2, Sigma-Aldrich) was dissolved in distilled water (5-12 wt %) and stirred into the polymer blends in various concentrations (0.5-2 wt %). The homogeneous blends were extruded immediately after preparation.
Samples comprising LDPE and/or PP were prepared in an analogous manner.
Unless otherwise stated, the materials were extruded in a GA25-25D single screw extruder in the temperature range 350 to 380° C. The RPM range was 20 to 200 revolutions per minute (RPM), corresponding to a residence time of 4.0-4.7 minutes to 0.5-0.8 minutes, respectively (see Table 2 below). The conversion of RPM to residence time was measured by determining the amount of time it takes for a sample to pass through the extruder at different RPM levels. The extrudate samples were collected at stable operating conditions and were cooled to room temperature for analysis.
A number of experiments were also conducted to compare the performance of the above-mentioned GA25-25D extruder, with a screw designed for optimal venting out of the extruder die, to screw designed for optimal mixing. Both arrangements employed the same extruder, but with different screws. The second arrangement, herein referred to as “screw 2” is the GA-25D extruder with a mixing screw in place. It has a D of 25 mm and several mixing elements.
During extrusion, the degradation products that are volatiles (e.g. CO2, H2O, ethylene glycol, low MW hydrocarbons) are removed through the extruder (there is a slight vacuum at the end of the extruder). The salts formed (e.g. sodium/calcium benzoate, sodium/calcium terephthalate, sodium/calcium carbonate) were extruded with the homogeneous blend and subsequently removed from the blend in a melt filter.
The samples were prepared for analysis by cutting and milling the samples to granulates approximately 5-10 mm size. The sample granulates were hot pressed to films of 0.1 mm thickness with a hot press (M-4411 Collin 200P hydraulic press) using a copper mould with Teflon sheets. At least 2 parallels were pressed of each sample.
Gel Permeation Chromatography was carried out according to ISO16014-1, -2, -4, 2012 using a GPC-IR5 MCT from Polymer Char equipped with an IR5 MCT Infrared detector. The polymer samples were dissolved in trichlorobenzene (TCB) at 160° C. for 1-4 hours (0.25-1.8 mg/mL). The columns 1 PL gel Guard and 4 PL gel 20 μm MIXED-A were heated to 150° C. Two parallels were used.
GPC was used for determination of:
Complex viscosity, η*, is a measure of the total resistance to flow as a function of angular frequency. η* was measured according to ISO6721-10:2015 using an RDA II W-4408 instrument. The samples were compression moulded into plates with dimensions 1.5 mm thickness and 30 mm diameter. The preheat time was 200 s to reach 300° C. The test conditions were 300° C.; frequency range 0.1-300 rad/sec; scraping off gap 1.25 mm; measuring gap 1.20 mm; plate geometry Plate-Plate; plate diameter 25 mm.
The method is used to determine values of the following dynamic rheological properties:
Where eta (0.5): Complex viscosity at frequency 0.5 rad/sec and eta (200): Complex viscosity at frequency 200 rad/sec are reported herein.
Gas Chromatography with Mass Spectrometric Detector, GC-MS
Selected pure virgin grades, LLDPE, LDPE and PP, were extruded in a GA25-25D single screw extruder at 300, 350, 370 and 380° C. using 20 or 60 revolutions per minute (RPM), corresponding to a residence time of approximately 1.4-1.8 and 4.0-4.7 minutes. The extrudate samples were collected after obtaining steady state conditions and cooled in room temperature. (800 g/10 min at 2.16 kg is set as value whenever the melt flow rate is too high for correct measurement (normally over 700). MFR2 was used to measure the viscosity of the melt after extrusion. Each of LLDPE and PP was investigated more closely with dynamic rheology to measure complex viscosity at different shear rates at 300° C. The polymer molecular weight and distribution were analysed by GPC. The results are shown in Table 3 and in
Comparison of the results for LLDPE with the standard screw and screw 2 show that employing a screw designed for mixing reduces the molecular weight and viscosity to higher levels. The MFR2 was, in fact, too high to measure.
HDPE was also degraded similarly to LLDPE and LDPE.
This experiment demonstrates the baseline degradation, referred to as pre-cracking, of virgin LDPE, LLDPE and PP upon extrusion in the range 300-380° C. and 20-60 RPM.
Table 4 below lists common additives present in PE and PP typically used for packaging. These additives, and their degradation products, are well known and can be identified by HPLC, GC-MS and GC-FID.
Table 5 below lists the additives that were identified in the PP, LLDPE and HDPE grades employed before and after extrusion (LDPE was not included because it did not contain any additives). Extrusion was carried out at 380° C. and 20 RPM, with or without alkaline solution. The effect of pre-mixing the polymer with an alkaline solution (1 wt % NaOH, 1 wt % Ca(OH)2, 5 wt % H2O) was studied. The additives and their degradation products were detected by HPLC and GC-MS as described above. ND means not detected.
The results show that the process of the invention effectively degrades the heteroatom containing additives commonly present in PP, LLDPE and HDPE. Specifically, in PP and HDPE Arvin 2 and Arvin 4, which are the hydrolysis products of AO-168 were detected. Residual AO-168, A-1010 and A-1076 were not detected in polymers, which underwent extrusion in the presence of alkaline solution.
Virgin LLDPE (Q1018N, Total) was mixed with pure extrusion grade PA-6 (B40LN, BASF, 5-15 wt %) and PET (RAMA-PET N180, 5-15 wt %) to simulate PCW compositions. Three sample compositions were prepared: 1) 5% PA-6 and 5% PET in PE; 2) 10% of PET and 10% PA in PE, and; 3) 15% PA and 15% PET in PE. Sodium hydroxide (NaOH, Sigma-Aldrich) and calcium hydroxide (Ca(OH)2, Sigma-Aldrich) was added to the 3 samples: 1) 1.5% NaOH and 1% Ca(OH)2; 2) 3 wt % NaOH+2% Ca(OH)2, and 3) 4.5% NaOH+3% Ca(OH)2. Distilled water was added to the mixture and kept constant at 12 wt %. The homogeneous blends were extruded immediately after preparation in a GA25-25D single screw extruder at 370° C. and 20 revolutions per minute (RPM), corresponding to a residence time of approximately 4.0-4.7 minutes. The extrudate samples were collected after obtaining steady state conditions and cooled in room temperature. The volatised side products exiting the extruder with the polymer melt were vented out, and hence separated from the polymer.
The samples were prepared for analysis as described above. FTIR spectra were recorded using the acquisition method, and then analysed, as described above. MFR2 was measured at standard conditions (190° C.) using 0.5 mm die as described above. Selected samples were investigated more closely with dynamic rheology to measure complex viscosity at different shear rates at 300° C. The results are shown in Table 6 below and in
The results demonstrate the efficient, concurrent, removal of PA-6 and PET from feedstock comprising 5%, 10% and 15 wt % of both PET and PA-6 in LLDPE (i.e. up to 30% wt compounds containing heteroatoms). Specifically, the results show 68-87% concurrent removal of PA and PET from feed containing up to 30 wt % heteroatom-containing polymer after extrusion at 370° C. and 20 RPM in aqueous alkaline conditions. This test feedstock contains significantly more heteroatom-containing polymers that conventional PCW feedstock. It is surprising that the process is able to remove so much PET and PA, even from feedstock containing a total of 30 wt % PET and PA. The result for the feedstock comprising 15 wt % PET and PA-6 shows that the hydrocarbon product emerging from the extruder contains 1.9 wt % PET and 2.4 wt % PA, which is less than the amount of PET and PA typically present in PCW that can be recycled. Thus the process provides a highly efficient method to remove heteroatom-containing polymers from highly contaminated PCW prior to further processing to achieve recycling.
The MFR2 results indicate that the viscosities of the hydrocarbon product produced in the process is higher than, or comparable to baseline degradation of LLDPE (˜111 vs. 100) at these conditions.
The sample preparation and analysis procedure were as described above and in Experiment 1. The experiments were carried out at temperatures in the range 350-370° C., and at 20-200 RPM, using the recipes and conditions set out in Table 6. The results are shown in Table 7, and
The results show that the PET and PA are degraded and removed during extrusion wherein the mixed polymer waste has a residence time in the extruder between 0.5-4.7 min. The removal of PET and PA in PE is significantly more efficient at 20 RPM (residence time 4.0-4.7 min) than at 200 RPM (residence time 0.5-0.8 min) and 100 RPM (residence time 1.0-1.2 min). This is consistently the case regardless of the PET/PA content, the alkaline mix and the water content. Whilst alkaline hydrolysis of PA appears to be slower than for PET, both PA and PET can be concurrently removed from PCW. MFR2 increases with decreasing RPM, but is affected by the wt % PET and PA present when compared to baseline LLDPE degradation.
This experiment also included some multilayer film (MF) to compare the results for a real film versus the feedstock specifically prepared for development purposes. The results appear to be comparable.
The sample preparation and analysis procedure were as described above and in Experiment 1. The experiments were carried out at temperatures of 350, 370 and 380° C. using 60 and 20 revolutions per minute (RPM), corresponding to a residence time of 1.4-1.8 minutes and 4.0-4.7 minutes respectively, using the recipes and conditions set out in Table 8. The results are shown in Table 8 and in
The results show that concurrent removal of mixed PA and PET is efficient at 20 RPM in the temperature 350-380° C. range. MFR2 is significantly lower at 60 RPM vs. 20 RPM.
The sample preparation and analysis procedure were as described above and in Experiment 1. The experiments were carried out using the recipes and conditions set out in Table 9. In this experiment model waste is represented both as blended PA-6 and LLDPE pellets and multilayer film (MF) flakes for comparison with a more realistic feed. The results are shown in Table 9 and in
Corresponding to examples 2 and 3, the results indicate that PA-6 is removed more efficiently at 20 RPM vs. 60 RPM in the range 350-380° C. Small variations are observed across the chemical recipes and temperature range. The results suggest that residence time (RPM) is the most significant factor in determining the efficiency of PA-6 removal.
The sample preparation and analysis procedure were as described above and in Experiment 1. The experiments were carried out using the recipes and conditions set out in Tables 11.1 and 11.2. Tables 11.1 and 11.2 also show the results achieved.
The results in these tables show that PET is more efficiently removed using a higher amount of (e.g. 8%) water as opposed to a lower amount (e.g. 5%) water. This suggests that aqueous hydrolysis is generally preferable. Without wishing to be bound by theory, it is thought that using higher % wts of water promotes hydrolytic degradation over thermal degradation. This is desirable as hydrolytic degradation gives rise to degradation products that can be removed from the extrudate. Moreover, at least some of the degradation products are in the form of monomers that can be recovered and recycled.
Some purified extrudates were selected for complex viscosity measurements. The following data provide further insight in viscosity of a relevant product stream vs. the baseline degradation.
Table 12 lists complex viscosities measured at 0.5 and 200 rad/s of selected samples from experiment 1-5; PET/PE, PA/PE and one PET/PA/PE.
The results demonstrate that the complex viscosity of the extruded hydrocarbon product is in the range of the baseline degradation of LLDPE in the process window 350-380° C. and 20-60 RPM.
The sample preparation was conducted as described in Experiment 1 and is summarised in Table 13 below. The homogeneous blends were extruded immediately after preparation in a GA25-25D single screw extruder at 380° C. and 20 revolutions per minute (RPM), corresponding to a residence time of approximately 3.5-4 minutes. The polymer melt samples was collected after obtaining steady state conditions and cooled in room temperature.
Two extrusion trials with a duration of 4-5-hours were conducted with 2 different water compositions to collect enough of the condensable side product for analyses. The degradation product was separated from the polymer stream in a buffer tank (“hopper tank”) as a volatile product in, immediately after being collected from the extruder using a slight vacuum. The volatile product exiting the extruder die and polymer melt was condensed and collected during extrusion. Some of the product was condensed in the condenser, rather than in the round flask further downstream, indicating higher boiling point. This was also collected and analysed separately (sample PA-26). The condensable products were analysed by HPLC, which was calibrated for specific substances expected from PA-6, PA-6.6 and PET. The results are summarised in Table 13 below.
The sample preparation was conducted as described in Experiment 1 as summarised below in Table 14 below. Two extrusion trials were conducted with different compositions of the chemical package. The homogeneous blends were extruded immediately after preparation in a GA25-25D single screw extruder at 350° C. and 20 and 60 revolutions per minute (RPM). The extrudate samples were collected after obtaining steady state conditions and cooled at room temperature. HPLC measurements were carried out to identify compounds in the polymer melt after extrusion of 5% PET in LLDPE model waste with NaOH and NaOH/Ca(OH)2/H2O. The method identifies sodium or calcium benzoate or terephthalate. (The method cannot distinguish between terephthalate and benzoate, or whether the associated cation is sodium or calcium).
Sodium and/or calcium benzoate/terephthalate side products were identified by HPLC analysis in the extruded PE/PET material. These are the expected products from alkaline hydrolysis of PET. PET-4 contained 60 ppm sodium benzoate/terephthalate. PET-7 contained 40 ppm of sodium and/or calcium benzoate/terephthalate. (Due to overlapping peaks in the chromatogram, the contribution from the individual substances could not be determined).
This example demonstrates that the method can be carried out in a twin screw extruder. It is beneficial due to its mixing abilities for incompatible elements in the feed.
The sample preparation of 5% PET/PE and chemicals was carried out by the method explained for example 1. The feed rate of the model waste to the extruder was 1 kg/h using a hopper with a screw feeder. The twin screw extruder was set to its minimum 120 RPM which corresponds to 50 sec residence time. This is the lowest RPM possible. The feedstock was extruded at 370° C. and 380° C.
The twin screw extruder has screw diameter of 18 mm and l/d=60 and operates in co-rotating configuration.
Table 15 and
| Number | Date | Country | Kind |
|---|---|---|---|
| 501736 | Mar 2022 | LU | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2023/057444 | 3/23/2023 | WO |
