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HYDROTHERMAL TREATMENT OF MATERIALS

20250354072 ยท 2025-11-20

    Inventors

    Cpc classification

    International classification

    Abstract

    The present invention is directed to methods for converting feedstock comprising synthetic polymers into a product, comprising: generating a melt stream comprising the synthetic polymers under heat and pressure, and generating heated and pressurised water independently of the melt stream; injecting the heated and pressurised water from apertures of an injection device into the melt stream to form a reaction mixture, wherein the apertures are located internally of the melt stream; using a mixing device to separate and then combine components of the reaction mixture facilitating further mixing of the water and the melt stream, wherein the mixing device comprises two adjacent lattice modules in communication and each rotated at an angle relative to the other; and further treating the reaction mixture at a reaction temperature and pressure to thereby provide the product, as well as apparatus for conducting such methods.

    Claims

    1. A method for converting feedstock comprising synthetic polymers into a product, comprising: generating a melt stream comprising the synthetic polymers under heat and pressure, and generating heated and pressurised water independently of the melt stream; injecting the heated and pressurised water from apertures of an injection device into the melt stream to form a reaction mixture, wherein the apertures are located internally of the melt stream; using a mixing device to separate and then combine components of the reaction mixture facilitating further mixing of the water and the melt stream, wherein the mixing device comprises two adjacent lattice modules in communication and each rotated at an angle relative to the other; and further treating the reaction mixture at a reaction temperature and pressure to thereby provide the product.

    2. (canceled)

    3. The method of claim 1, wherein the water is supercritical immediately prior to the injecting into the melt stream.

    4. The method of claim 1, wherein the heated and pressurised water is injected across; (i) a full or partial cross section of the melt stream; or (ii) multiple cross sections of the melt stream, wherein at least two of the multiple cross sections are oriented at different angles relative to each other.

    5-6. (canceled)

    7. The method of claim 1, wherein the injection device comprises two injection pipes each spanning either a full or partial cross section of the melt stream, and oriented at: (i) different angles within the melt stream relative to each other; or (ii) perpendicular to each other, or, within 5, within 10, within 20, within 30, or within 40, of perpendicular.

    8. (canceled)

    9. The method of claim 7, wherein either or both injection pipes comprise a sparge pipe.

    10-11. (canceled)

    12. The method of claim 1, wherein the mixing device comprises a first lattice module rotated between 20-and 90, 40-and 90, 60-and 90, or 80-and 90 relative to a second adjacent lattice module.

    13. The method of claim 1, wherein the mixing device comprises a first lattice module rotated perpendicular or substantially perpendicular relative to a second adjacent lattice module.

    14. The method of claim 12, wherein the first and/or second lattice modules comprise a sequential series of adjacently positioned lattice sheets, wherein each individual lattice sheet of the series is rotated less than: 50, 40, 30, 20, 10 or 5; relative to other adjacent lattice sheet(s) within the series, or is not rotated relative other adjacent lattice sheet(s) within the series.

    15. The method of claim 14, wherein the series comprises 2, 3, 4, 5, 6 or more individual lattice sheets rotated less than 50, 40, 30, 20, 10 or 5 relative adjacent lattice sheet(s), or not rotated relative to adjacent lattice sheet(s).

    16. (canceled)

    17. The method of claim 14, wherein the adjacently positioned lattice sheets are in direct contact or separated by spacer component(s).

    18-27. (canceled)

    28. The method of claim 1, wherein the melt stream comprises: polyethylene (PE), Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Polypropylene (PP), Polyester, Poly(ethylene terephthalate) (PET), poly(lactic acid) (PLA), Poly(vinyl chloride) (PVC), Polystyrene (PS), Polyamide, Nylon, Nylon 6, Nylon 66, Acrylonitrile-Butadiene-Styrene (ABS), Poly(Ethylene vinyl alcohol) (E/VAL), Poly(Melamine formaldehyde) (MF), Poly(Phenol-formaldehyde) (PF), Epoxies, Polyacetal, (Acetal), Polyacrylates (Acrylic), Polyacrylonitrile (PAN), Polyamide-imide (PAI), Polyaryletherketone (PAEK), Polybutadiene (PBD), Polybutylene (PB), Polycarbonate (PC), Polydicyclopentadiene (PDCP), Polyketone (PK), polycondensate, Polyetheretherketone (PEEK), Polyetherimide (PEI), Polyethersulfone (PES), Polyethylenechlorinates (PEC), Polyimide (PI), Polymethylpentene (PMP), Poly(phenylene Oxide) (PPO), Polyphenylene Sulfide (PPS), Polyphthalamide (PTA), Polysulfone (PSU), Polyurethane (PU), Poly(vinylidene chloride) (PVDC), Poly(tetrafluoroethylene) (PTFE), Poly(fluoroxy alkane) (PFA), Poly(siloxanes), silicone, thermoplastic, plastic, or mixtures thereof.

    29. The method of claim 1, wherein during the treatment, the water and the melt stream combined comprises: (i) at least at least 30 wt %, at least 35 wt %, at least 40 wt %, at least 45 wt %, at least 50 wt %, at least 60 wt %, at least 70 wt %, at least 80 wt %, at least 90 wt %, at least 95 wt %, or at least 98 wt % of the polymeric material; or at least at least 30 wt %, a minimum of 40 wt % of the polymeric material and up to 60 wt % of the water.

    30. (canceled)

    31. The method of claim 1, wherein prior to injecting the heated and pressurised water, the melt stream is at a temperature of between 200 C. and 350 C. and at a pressure of between 100 bar and 300 bar, or at a temperature of between 250 C. and 300 C. and at a pressure of between 230 bar and 280 bar.

    32. The method of claim 1, wherein the melt stream comprising the synthetic polymers under heat and pressure is generated using an extruder.

    33. The method of claim 1, wherein: (i) the water is at a temperature of between 300 C. and 700 C. and a pressure of 100 to 300 bar immediately prior to the injecting into the melt stream; or (ii) the water is supercritical and at a temperature of between 500 C. and 700 C. and at a pressure of 221 to 300 bar; or (iii) the water is supercritical and at a temperature of between 600 C. and 700 C. and at a pressure of 221 to 300 bar; immediately prior to the injecting into the melt stream.

    34. The method of claim 1, wherein the reaction mixture enters and/or exits the mixing device: (i) at a temperature of between 200 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature of between 300 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature of between 350 C. and 550 C. and at a pressure of 100 to 300 bar, or at a temperature of between 400 C. and 500 C. and at a pressure of 100 to 300 bar; and/or (ii) at a flow rate of above 2,000 kg/hr, less than 15,000 kg/hr, or between 2,000 kg/hr and 15,000 kg/hr; and/or (iii) a viscosity of above 100 Pa.Math.s, less than 1,000 Pa.Math.s, or between 100 Pa.Math.s to 1,000 Pa.Math.s.

    35. The method of claim 1, comprising further heating of the reaction mixture after it exits the mixing device, wherein the further heating is conducted using an indirect heater located downstream of the mixing device and prior to a pressure let down device.

    36. (canceled)

    37. The method of claim 1, wherein said further treating the reaction mixture at a reaction temperature and pressure is: at a temperature of between 300 C. and 500 C. and at a pressure of between 100 bar and 350 bar, at a temperature of between 373 C. and 500 C. and at a pressure of between 220 bar and 350 bar, at a temperature of between 400 C. and 500 C. and at a pressure of between 220 bar and 350 bar, or at a temperature of between 420 C. and 480 C. and at a pressure of between 220 bar and 300 bar.

    38. The method of claim 1, wherein the method is performed under conditions of continuous flow.

    39. (canceled)

    40. The method of claim 1, wherein the injecting of the heated and pressurised water from apertures of the injection device into the melt stream is conducted while the melt stream is at a flow rate of between 1,000 kg/hr and 15,000 kg/hr and/or a viscosity of between 10 Pa.Math.s and 1,000 Pa.Math.s, a flow rate of between 3,000 kg/hr and 12,000 kg/hr and/or a viscosity of between 100 Pa.Math.s and 1,000 Pa.Math.s, a flow rate of between 5,000 kg/hr and 10,000 kg/hr, and/or a viscosity of between 400 Pa.Math.s and 800 Pa.Math.s.

    41-62. (canceled)

    Description

    BRIEF DESCRIPTION OF THE FIGURES

    [0086] Preferred embodiments of the present invention will now be described by way of example only, with reference to the accompanying figures wherein:

    [0087] FIG. 1 shows a pipe mixer design (iteration 1) in accordance with an embodiment of the invention;

    [0088] FIG. 2 shows a pipe mixer design (iteration 1 with two mixer elements) in accordance with an embodiment of the invention;

    [0089] FIG. 3 shows a pipe mixer design (iteration 1 with four mixer elements) in accordance with an embodiment of the invention;

    [0090] FIG. 4 shows a pipe mixer design (iteration 2 showing position of bars) in accordance with an embodiment of the invention;

    [0091] FIG. 5 shows a pipe mixer design (iteration 2 with two mixer elements) in accordance with an embodiment of the invention;

    [0092] FIG. 6 shows a pipe mixer design (iteration 2 with four mixer elements) in accordance with an embodiment of the invention;

    [0093] FIG. 7 shows the mixing performance of pipe mixer design (iteration 1), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0094] FIG. 8 shows the mixing performance of pipe mixer design (iteration 1 with two mixer elements), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0095] FIG. 9 shows the mixing performance of pipe mixer design (iteration 1 with four mixer elements), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0096] FIG. 10 shows the mixing performance of pipe mixer design (iteration 2), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0097] FIG. 11 shows the mixing performance of pipe mixer design (iteration 2 with two mixer elements), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0098] FIG. 12 shows the mixing performance of pipe mixer design (iteration 2 with four mixer elements), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0099] FIG. 13 shows the mixing performance of pipe mixer design (iteration 2 with four mixer elements), indicating volume fraction distribution in pipe mixer, along and across the pipe;

    [0100] FIG. 14 is a graph depicting volume uniformity of the volume fraction of molten plastic along pipe mixer;

    [0101] FIG. 15 is a bar chart depicting volume uniformity of the volume fraction of molten plastic in Threshold 9;

    [0102] FIG. 16 shows supercritical water temperature distribution in pipe mixer (iteration 2 with two mixer elements) along and across the pipe;

    [0103] FIG. 17 shows molten plastic temperature distribution in pipe mixer (iteration 2 with two mixer elements) along and across the pipe;

    [0104] FIG. 18 is a graph depicting volume average temperature of supercritical water and molten plastic along the pipe;

    [0105] FIG. 19 shows a pressure drop profile of a pipe mixer (iteration 1);

    [0106] FIG. 20 shows a pressure drop profile of a pipe mixer (iteration 1 with two mixer elements);

    [0107] FIG. 21 shows a pressure drop profile of a pipe mixer (iteration 1 with four mixer elements);

    [0108] FIG. 21 shows a pressure drop profile of a pipe mixer (iteration 2);

    [0109] FIG. 22 shows a pressure drop profile of a pipe mixer (iteration 2 with two mixer elements);

    [0110] FIG. 23 shows a pressure drop profile of a pipe mixer (iteration 2 with four mixer elements); and

    [0111] FIG. 24 is a graph showing pressure values of the different geometries;

    [0112] FIG. 25 shows an injection device according to embodiments of the present invention;

    [0113] FIG. 26 shows a lattice module of a mixing device according to embodiments of the present invention; and

    [0114] FIG. 27 shows a mixing device according to embodiments of the present invention.

    DETAILED DESCRIPTION

    [0115] The following detailed description conveys exemplary embodiments of the present invention in sufficient detail to enable those of ordinary skill in the art to practice the present invention. Features or limitations of the various embodiments described do not necessarily limit other embodiments of the present invention, or the present invention as a whole. Hence, the following detailed description does not limit the scope of the present invention, which is defined only by the claims.

    [0116] It will be appreciated by persons of ordinary skill in the art that numerous variations and/or modifications can be made to the present invention as disclosed in the specific embodiments without departing from the spirit or scope of the present invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

    [0117] The present invention addresses at least one of the difficulties associated with the application of existing hydrothermal systems to the treatment polymeric feedstock material, and in particular to the treatment of viscous polymeric feedstock materials under elevated temperature and pressure.

    [0118] Firstly, a number of existing technologies adopt a system whereby independently heated and pressurised aqueous solvents such as water (e.g. supercritical water) is injected into a melt stream of polymeric feedstock from an injection device or a series of injection devices external to the melt stream (for example, a halo injection manifold surrounding the melt stream having injection points at various positions around the circumference of a pipe). To facilitate improved access of the heated and pressurised aqueous solvent to the polymeric feedstock melt stream, the present invention provides a system facilitating the injection of heated/pressurised water from a device submerged within the melt stream itself. This injection shroud of heated/pressurised water can be applied across a partial or full cross section of the melt stream. The arrangement of an injection device within/across the main flow path ensures the melt stream flows around the injection points thereby allowing the heated/pressurised water to be applied instantaneously across all or a portion of the melt stream of polymeric material. This feature of the present invention, whether taken alone or used in combination with other feature(s) described herein, can be used to improve the hydrothermal treatment of polymeric feedstock material, and in particular the hydrothermal treatment of viscous polymeric feedstock material.

    [0119] Secondly, commercially available mixing devices adopted in current hydrothermal treatment settings often encounter difficulties in facilitating the effective mixing of heated/pressurised water with melt streams of polymeric feedstock material, particularly viscous melt streams such as those containing plastics. To address this issue, the present invention provides a mixing device capable of separating and folding a viscous melt stream of polymeric feedstock and water as it passes through the device, while providing flow paths that are wide enough to minimise blockage risk. The design is particularly advantageous for low velocity mixing of highly viscous fluids. This feature of the present invention, whether taken alone or used in combination with other feature(s) described herein, can be used to improve the hydrothermal treatment of polymeric feedstock material, and in particular the hydrothermal treatment of viscous polymeric feedstock material.

    [0120] Without limitation, the injection and mixing devices of the present invention may provide a number of advantages by, for example, increasing the surface area of polymeric material melt streams available for mixing with water thereby facilitating the generation of a homogenous reaction mixture of water and polymeric material in a shorter time period, and allowing longer residence times to be adopted to thereby reduce pressure drop across the reactor apparatus.

    Polymeric Material Feedstock

    [0121] The methods and devices of the present invention are provided for the hydrothermal conversion of polymeric material feedstock into various products.

    [0122] Non-limiting examples of polymeric materials suitable for use in the methods and devices of the present invention include prepolymers, oligomers, homopolymers, copolymers, terpolymers, graft polymers, plastic, end of life plastic, waste plastic, elastomeric material, rubber materials, and mixtures may be included in the feedstock and subjected to cracking in the reactor. Other non-limiting examples include Polyethylene (PE), Low Density Polyethylene (LDPE), High Density Polyethylene (HDPE), Polypropylene (PP), Polyester, Poly(ethylene terephthalate) (PET), poly(lactic acid) PLA, Poly(vinyl chloride) (PVC), Polystyrene (PS), Polyamide, Nylon, Nylon 6, Nylon 6,6, Acrylonitrile-Butadiene-Styrene (ABS), Poly(Ethylene vinyl alcohol) (E/VAL), Poly(Melamine formaldehyde) (MF), Poly(Phenol-formaldehyde) (PF), Epoxies, Polyacetal, (Acetal), Polyacrylates (Acrylic), Polyacrylonitrile (PAN), Polyamide-imide (PAI), Polyaryletherketone (PAEK), Polybutadiene (PBD), Polybutylene (PB), Polycarbonate (PC), Polydicyclopentadiene (PDCP), Polyketone (PK), polycondensate, Polyetheretherketone (PEEK), Polyetherimide (PEI), Polyethersulfone (PES), Polyethylenechlorinates (PEC), Polyimide, (PI), Polymethyl pentene (PMP), Poly(phenylene Oxide) (PPO), Polyphenylene Sulfide (PPS), Polyphthalamide (PTA), Polysulfone (PSU), Polyurethane (PU), Poly(vinylidene chloride) (PVDC), Poly(tetrafluoroethylene) PTFE, Poly(fluoroxy alkane) (PFA), Poly(siloxanes), silicones, thermoplastics, thermosetting polymers, natural rubbers, tyre rubbers, ethylene propylene diene monomer rubbers EPDM, chloroprene rubbers, acrylonitrile butadiene (nitrile) rubbers, polyacrylate rubbers, Ethylene Acrylic rubbers, Styrene-butadiene rubbers, Polyester urethane rubbers, Polyether urethane rubbers, Fluorosilicone rubbers, silicone rubbers, and copolymers, synthetic polymeric materials, naturally-occurring polymeric materials with carbon-carbon backbones, plastics, and mixtures thereof.

    [0123] Without limitation, the polymeric material may comprise a low content of elements other than carbon, hydrogen and oxygen. For example, the polymeric material may contain less than about 5 wt % nitrogen, less than about 1 wt % nitrogen, less than about 0.5 wt % nitrogen, less than about 0.1 wt % nitrogen, or less than about 0.01 wt % nitrogen, as a percentage of total polymeric material weight.

    [0124] Additionally or alternatively, the polymeric material may comprise less than about 5 wt % total halogens, less than about 1 wt % total halogens, less than about 0.5 wt % total halogens, less than about 0.1 wt % total halogens, less than about 0.05 wt % total halogens, or less than about 0.01% total halogens, as a percentage of total polymeric material weight.

    [0125] Additionally or alternatively, the polymeric material may comprise a molar ratio of hydrogen to carbon (H/C) that is as high. For example, the H/C molar ratio may be greater than 2.15, greater than 2.0, greater than 1.8, greater than 1.6, greater than 14, greater than 1.2, greater than 1.0, or greater than 0.8.

    [0126] The polymeric material may comprise, for example, plastics. The polymeric material may be unsuitable for physical recycling methods. The polymeric material may be suitable currently only for landfill or for incineration. The polymeric material may be End of Life Plastics (ELP). The polymeric material (e.g. plastic) may be contaminated with non-plastic materials including, but not limited to, and one or more of food waste, soil, agricultural residues, metals, putrescible material, paper, cardboard, plant and animal matter, fabric or fabric fibres.

    [0127] In some embodiments, the polymeric material may be in the form of mixed or sorted waste plastics and in some cases may be contaminated with organic and inorganic impurities. The waste plastic material may require some pre-processing before being processed according to the methods of the present invention. For example, the waste plastic may require sieving or screening to remove abrasive particles.

    [0128] Without limiting the mode of action polymers treated according to the methods of the present invention may be cracked to liquids having lower boiling and melting points and/or they may directly or indirectly act as sources of hydrogen which is then incorporated into the product liquids.

    [0129] In various embodiments of the present invention, the polymeric material may be processed prior to being combined with an independently generated heated and pressurised aqueous solvent comprising or consisting of water. Processing of the polymeric material in this manner may assist in mixing the aqueous solvent and the polymeric material.

    [0130] For example, the polymeric feedstock material may be processed to form a melt stream prior to the injection of the heated and pressurised aqueous solvent. While there is no particular limitation on the means used to provide the melt stream, examples include treatment of the polymeric material in a melt tank and/or treatment in an extruder, under elevated temperature and optionally elevated pressure, sufficient to provide a melt stream of the polymeric material. In some embodiments the melt stream is provided only by use of an extruder, whereas in other embodiments an extruder can be used in combination with other device(s) (e.g. prior treatment in a melt tank followed by treatment in the extruder). In still other embodiments, a melt tank or other device is used without using an extruder.

    [0131] Taking the example of an extruder, the skilled person will recognise that any suitable extruder may be used, non-limiting examples of which include single screw extruders, multi-screw extruders (e.g. twin-screw extruders), intermeshing screw extruders, radial extruders, and roll-type extrusion presses. The multi-screw extruders may be counter-rotating or co-rotating. The extruder may comprise kneading disk/s and/or other screw element/s for mixing or dispersing the melt. Suitable extruders typically may be from about 1 metre to about 50 metres in length and may be specifically designed for processing of waste plastic with a plastic compacting feature, with the pressure raising occurring as either a single extruder step or multi extruder steps, with or without extruder venting. By way of non-limiting example, the energy needed by the extruder to heat the polymeric material can be provided by friction and/or shearing of the material in the extruder, and/or by heating elements. The extruder may comprise one or multiple series of heating zones. The extruder may be fitted with a die to facilitate the generation of back-pressure.

    [0132] Processing of the polymeric material in advance of combining it with the aqueous solvent may additionally or alternatively comprise physical methods, non-limiting examples of which include grinding, chipping, pelletisation, granulisation, flaking, powdering, shredding, milling (e.g. vibratory ball milling), compression/expansion, agitation, density separation, washing, air classification, filtering, drying and/or pulse-electric field (PEF) treatment. The polymeric material may, for example, be pre-treated using shredders, screens and/or sieves, magnetic and eddy current separators to remove metals, dry cleaning techniques and/or optical, infra-red, or ultraviolet and induction sorting to remove, for example, poly(vinyl chloride) and other chlorinated or halogenated polymers and metal. Additionally or alternatively, wet processes may be used (i.e. involving washing with water or another solvent) or dry processes including the use of air separators to remove glass, magnetic and/or eddy current separators to remove metals, dry or wet cleaning to remove food waste and paper, plastic drying using waste heat and/or optical, infra-red, or ultraviolet sorting to remove e.g. poly(vinyl chloride) and other chlorinated or halogenated polymers. Other types of polymeric materials that are unsuitable for particular aspects of the invention may also be removed by sorting technologies known in the art. Non-limiting examples of polymers that may be removed are polyethylene terephthalate (PET) and polyamides. Additionally or alternatively, the polymeric material may be treated using physio-chemical methods, non-limiting examples of which include pyrolysis, steam explosion, ammonia fibre explosion (AFEX), ammonia recycle percolation (ARP), and/or carbon-dioxide explosion. For example, steam explosion involves exposing the polymeric material to high pressure steam in a contained environment before the resulting product is explosively discharged to an atmospheric pressure. Pre-treatment with steam explosion may additionally involve agitation of the polymeric material. Additionally or alternatively, the polymeric material may be treated using chemical methods, non-limiting examples of which include ozonolysis, acid hydrolysis (e.g. dilute acid hydrolysis using H.sub.2SO.sub.4 and/or HCl), alkaline hydrolysis (e.g. dilute alkaline hydrolysis using sodium, potassium, calcium and/or ammonium hydroxides), and/or oxidative treatments.

    [0133] Any device used to process the polymeric material feedstock prior to combining it with the aqueous solvent may itself be fitted with a suitable feeder device (e.g. a hopper, compactor, cutter compactor) for application of the polymeric material to/into the device.

    Aqueous Solvent

    [0134] An aqueous solvent used in the methods and devices of the present invention may to comprise in excess of 70%, 80%, 90%, 95% 96%, 97%, 98%, or 99% v/v of water (i.e. as a percentage of the total volume of the aqueous solvent), or alternatively may consist of 100% water with or without insubstantial impurities.

    [0135] The solvent may comprise or consist of one or more aqueous alcohol(s). Non-limiting examples of suitable alcohols include methanol, ethanol, isopropyl alcohol, isobutyl alcohol, pentyl alcohol, hexanol, iso-hexanol, and any combination thereof. By way of non-limiting example only, the aqueous solvent may less than 5%, 10%, 15%, 20% or less than 25% v/v (i.e. as a percentage of the total volume of the aqueous solvent).

    [0136] In some embodiments, water used in aqueous solvents of the present invention may be recycled from the product of feedstock comprising polymeric material previously treated by the method. For example, a portion of the water present following treatment of a given reaction mixture may be taken off as a side stream and recycled into the aqueous solvent prior to combining it with the polymeric material.

    Combining Polymeric Material Feedstock with Aqueous Solvent

    [0137] The methods and devices of the present invention facilitate combining an independently generated flow of aqueous solvent (e.g. water) with polymeric material feedstock (e.g. extrudate comprising or consisting of polymeric material).

    [0138] An independently generated flow of aqueous solvent will be understood to require that at all or at least a portion of the aqueous solvent is heated and optionally pressurised separately from the polymeric material feedstock. The aqueous solvent may be heated and/or pressurised using any suitable means.

    [0139] While no particular limitation exists as to the particular type or category of device, or the means of combining the polymeric material and aqueous solvent, certain embodiments of the present invention provide for the injection of heated and pressurised aqueous solvent from a device submerged within the melt stream.

    [0140] By way of non-limiting example, FIG. 25 shows an injection device according to the present invention. Reactor apparatus vessel (1) facilitates the flow of polymeric feedstock melt stream in a given direction (2) such that it surrounds and passes injection pipes (3) and (4). Injection pipes (3) and (4) each contain apertures (5) for injection of heated and pressurised aqueous solvent (in this case the example uses water) into the melt stream as it flows along the vessel (1) around pipes (3) and (4). The arrangement allows the water to be injected from the apertures (5) while they are submerged within the melt stream itself, rather than injecting water through the surface of the melt stream from an external position. While the pipes (3) and (4) are shown to be oriented substantially perpendicular to each other, the skilled addressee will understand that different orientations may be used to achieve the beneficial mixing observed. Similarly, while multiple pipes (3) and (4) are shown to each span a full cross section of the vessel (1), it is possible to achieve the beneficial mixing observed using a single pipe or additional pipes in excess of two, which may fully or partially span cross section(s) of the vessel (1).

    [0141] In general, the arrangement depicted in FIG. 25 provides for beneficial mixing of the heated and pressurised aqueous solvent (in this case the example again uses water) and the melt stream of polymeric material by virtue of increasing the surface area of melt stream available for contact with the water and allowing its introduction across a partial or complete internal cross section of the melt stream, rather than only to the external surface of the melt stream. The injecting devices of the present invention may thus provide benefits including, but not limited to, improved heat transfer (heated and pressurised water contacts much more surface area of the polymeric material melt stream) and/or the avoidance of two-phase flow and early cracking of lower temperature polymers, meaning oil products can be formed earlier resulting in lower system pressure drop (less energy input required) and higher cracking rates/reaction efficiency.

    [0142] The reactor apparatuses of the present invention may provide multiple injection devices within a given vessel and/or multiple vessels containing the single or multiple injection device(s). The injection device(s) may contain any suitable number of apertures capable of injecting heated and pressurised aqueous solvents (e.g. water), a characteristic that will be determined at least in part by the size of the vessels within which they are located.

    [0143] In some embodiments, the heated and pressurised aqueous solvent (e.g. water) is supercritical at the point of combining with the melt stream as it passes through the apertures of the injection device.

    [0144] In some embodiments, one or more of the injection devices comprise a sparge pipe.

    [0145] The aqueous solvent may be in a subcritical state or a supercritical state prior to and at the time of contacting the polymeric material. In some embodiments, the aqueous solvent is water or steam (e.g. supercritical water, superheated steam, or subcritical water).

    [0146] Contacting a supercritical aqueous solvent with the polymeric material may, in some cases, initiate a supercritical to subcritical phase change in the aqueous solvent (i.e. bring it into a subcritical state as the temperature and/or pressure of the solvent falls below its critical point). The phase change may trigger a large release of energy which in turn may enhance mixing of the aqueous solvent with the polymeric material.

    [0147] Alternatively, contacting a supercritical aqueous solvent with the extruded polymeric material may not initiate a supercritical to subcritical phase change in the aqueous solvent.

    [0148] Additionally or alternatively, aqueous solvent (e.g. water), in subcritical or supercritical state, may be applied to the polymeric material at or in proximity to the exit point of a device used to generate a melt stream of the polymeric material (e.g. an extruder) and/or at multiple injection points along a length of a vessel connected to another component in a reactor including, for example, a mixing device or a reaction zone.

    [0149] In addition to a stage of initially combining the aqueous solvent and polymeric material, the methods and devices of the present invention may comprise additional stage(s) to facilitate increased mixing of these components. While no particular limitation exists as to the particular type or category of mixing device, or the means of the mixing process, certain embodiments of the present invention provide for the separation of the polymeric material melt stream with heated/pressurised water into individual streams, and their recombination in a folding process facilitating enhanced mixing of the two elements.

    [0150] By way of non-limiting example, FIG. 26 shows a lattice module (1) of a mixing device according to the present invention. The lattice module shown includes a sequential series of four adjacently positioned lattice sheets (2), (3), (4), and (5). However, any number of lattice sheet(s) may be included, including a single lattice sheet, or 2, 3, 5, 6 or more lattice sheets for example. The lattice sheets (2), (3), (4), and (5) are shown to be oriented in a manner that one sheet is not rotated in relation to other adjacent sheets. While this arrangement is preferred it is permitted also to rotate individual lattice sheets of the series relative to one another and still achieve the beneficial mixing observed. Individual lattice units (6) within the sheets are depicted as square-shaped, however there is no particular limitation and other shapes can be adopted. Melt stream may flow through lattice module (1) in a given direction (7).

    [0151] Turning to FIG. 27, individual lattice modules (2), (3), (4), (5), (6), (7), (8), (9) can be combined in a sequential manner to form a mixing device (1) of the present invention. Although multiple modules are shown, the skilled person will recognise that the mixing device (1) may contain more or fewer modules (e.g. 2, 3, 4, 5, 6, 7 9, 10 or more than 10 modules). As shown, each of lattice modules (2), (3), (4), (5), (6), (7), (8), (9) is in communication with adjacent lattice module(s), and each is rotated at an angle of approximately 90 (i.e. approximately perpendicular) relative to adjacent lattice module(s). The skilled person will recognise that a given lattice module can be rotated at an alternative angle such as, for example, an angle between 20-90, 40-90, 60-90, or 80-90 relative to an adjacent lattice module. Polymeric material melt stream and heated/pressurised aqueous solvent (e.g. water) flows through the mixing device (1) in a given direction (10), the mixture separating and recombining in a folding pattern as it passes through individual lattice modules (2), (3), (4), (5), (6), (7), (8), (9).

    [0152] Without limitation, the mixer devices of the present invention may provide any one or more of the following advantages: a wide flow path to avoid blockage, thermal expansion (e.g. room temperature to more than 500 C. in operation) whilst withstanding elevated operating pressures (e.g. up to 300 bar), a limited pressure drop, an ability to mix a dense, viscous slow moving polymeric material melt stream (e.g. plastic) with a high velocity, low density aqueous solvent such as water (e.g. supercritical water).

    Heating and Pressurisation of Reaction Components

    [0153] Reaction components such as aqueous solvent, polymeric material and other additives may be heated and pressurised using known means in the art.

    [0154] For example, pressurisation within a reactor may be generated via pump(s) and/or an extruder used to thereby pressurise material(s) being fed into the reactor. Pressure within the apparatus can be maintained using valve systems and the like, and can be monitored using standard means known in the art.

    [0155] Reaction components can be heated prior to and/or within the reactor itself. For example, prior to mixing the aqueous solvent may be heated using a boiler heated by, for example, gas (natural gas or process gas), an electric heater, or a combination hereof. Non-limiting examples of suitable boilers include coil boilers and fluid bed boilers, along with ant other suitable design of industrial boiler. The heating method utilised may be direct or indirect.

    [0156] Additionally or alternatively, the polymeric material may be heated using any one or more of an extruder, indirect heating devices including those utilising a heating medium of oil, water, steam, or gas, or direct heating devices using electric heating elements.

    [0157] Following the stage of aqueous solvent combination with the polymeric material, the reaction mixture so formed may be brought to and/or maintained at a reaction temperature or range of reaction temperatures using an indirect heater to provide heat energy to the reaction mixture by means of superheated steam or supercritical water from a process boiler. The steam may be produced readily from the combustion of process gas and the temperature of the incoming steam may be controlled, to thereby avoiding thereby avoiding excessive metal temperatures that would cause excessive charring of the plastic mixture. By using the steam that is ultimately fed into the process the pressure drop across the elements of each heater can be minimised and any internal tube leak would represent a small flow of steam into the process.

    [0158] In some embodiments additional heating of the reaction mixture, for example, prior to, during or after entry of the mixture into the mixer device, may be achieved by means of electrical heating elements, and/or by a fluid heat exchanger and/or by a fluidized bed of, for example, ilmenite heated by combustion of calorific gas. In some embodiments, the heating elements are not circumferential. In some embodiments such calorific gas may comprise process gases and vapours formed by the depolymerization of polymeric material.

    [0159] There is no particular limitation regarding the specific location of heating elements used in the methods and devices of the present invention, or the stage(s) at which they are used. Without limitation, the heating elements can be employed at any one or more of the following: separately heating the polymeric material and/or aqueous solvent prior to combining them into a reaction mixture; heating the reaction mixture as it approaches a mixing device, and/or within a mixing device, and/or as it exits a mixing device; heating the reaction mixture in a vessel or tank located between two mixing devices; or heating the reaction mixture in a vessel or tank located downstream relative to a mixing device and leading to a reactor exit point (e.g. a pressure let down device).

    Reaction Parameters

    [0160] The present invention facilitates the hydrothermal conversion of polymeric materials into products using aqueous solvents under elevated temperature and pressure. Provided herein are methods and devices for converting polymeric materials into products, at least by virtue of facilitating more thorough mixing of aqueous solvents and the polymeric materials. This in turn enhances key chemical interactions required for depolymerisation of the polymeric material and the generation of products. For example, the cracking rate (i.e. depolymerisation) of the polymeric material feedstock may be significantly enhanced due to the thorough mixing of the polymeric material and aqueous solvent, providing increased product yields (e.g. naphtha) without increasing energy requirements. This advantageous effect may arise from a higher cracking efficiency than currently known methods.

    [0161] The skilled person will acknowledge that the methods and devices for improving the mixing of polymeric material and aqueous solvents have broad applicability and capable of incorporation into a wide range of hydrothermal conversion processes. Hence, the reaction exemplary reaction process discussed below in the current section will be understood to be non-limiting and provided by way of example only.

    [0162] In a first stage of the exemplary reaction process, polymeric material feedstock and aqueous solvent may be heated and/or pressurised independently of one another, and then combined together in a process that enhances mixing between the two entities.

    [0163] In some embodiments of the present invention, the polymeric material may be provided in a melt stream for subsequent combination with an aqueous solvent. When forming the melt stream of polymeric material prior to combining with the aqueous solvent, the polymeric material may be heated to temperature/s sufficient for the material to melt and flow. For example, the polymeric material may be heated to more than 50 C., to more than 75 C., to more than 100 C., to more than 150 C., to more than 200 C., to more than 250 C., to more than 300 C., more than 350 C., or to more than 400 C. Accordingly, the polymeric material may be heated for example, to between about: 200 C. and 300 C., 250 C. and 350 C., 275 C. and 375 C., 300 C. and 400 C., 50 C. and 350 C., 50 C. and 300 C., 50 C. and 200 C., 50 C. and 150 C., 80 C. and 300 C., 80 C. and 200 C., or 80 C. and 150 C. The melt stream may thus also contact the aqueous solvent and/or exit a device within which it has been generated (e.g. a melt tank or extruder) at any of these temperatures or ranges of temperatures.

    [0164] Additionally or alternatively, the polymeric material may be pressurised, for example, to between 50 bar and 400 bar, 100 bar and 350 bar, 150 bar and 350 bar, 150 bar and 300 bar, 150 and 250 bar, 200 bar and 350 bar, or 200 bar and 300 bar. The melt flow may thus also contact the aqueous solvent and/or exit a device within which it has been generated (e.g. a melt tank or extruder) at any of these pressure ranges.

    [0165] In some embodiments, the polymeric material may be heated to a temperature of between 200 C. and 300 C. and pressurised to between 100 bar and 350 bar. In these embodiments, the melt flow may thus also contact the aqueous solvent and/or exit a device within which it has been generated (e.g. a melt tank or extruder) within these temperature and pressure ranges.

    [0166] In some embodiments, a melt stream of polymeric material may contact the aqueous solvent and/or exit the device in which it was generated (e.g. melt tank and/or extruder) at a temperature of between about 150 C. and about 400 C. and a pressure of between about 200 bar and 350 bar; at a temperature of between about 250 C. and about 350 C. and a pressure of between about 250 bar and 350 bar; or at a temperature of between about 220 C. and about 280 C. and a pressure of between about 200 bar and 350 bar.

    [0167] In other embodiments, immediately prior injection of the water into the melt stream, the melt stream is at a flow rate of between 1,000 kg/hr and 15,000 kg/hr and/or a viscosity of between 10 Pa.Math.s and 1,000 Pa.Math.s, a flow rate of between 3,000 kg/hr and 12,000 kg/hr and/or a viscosity of between 100 Pa.Math.s and 1,000 Pa.Math.s, a flow rate of between 5,000 kg/hr and 10,000 kg/hr, and/or a viscosity of between 400 Pa.Math.s and 800 Pa.Math.s.

    [0168] In some embodiments, the melt stream of polymeric material (e.g. plastic melt stream) may be processed at an amount of up to 1000 kg/hour, up to 2000 kg/hour or up to 3000 kg/hour.

    [0169] The residence time of the polymeric feedstock in a device used to provide the melt stream of polymeric material (e.g. a melt tank and/or extruder) may be, for example, about 30 seconds to about 20 minutes, about 2 minutes to about 6 minutes, or about 3 minutes to about 5 minutes.

    [0170] In some embodiments of the present invention, aqueous solvent comprising or consisting of water is provided for subsequent combination with the polymeric material (e.g. a melt stream of the polymeric material). The aqueous solvent may be provided in a supercritical state. Alternatively, it may be provided in a subcritical state.

    [0171] By way of non-limiting example only, the aqueous solvent may be provided at a temperature of between about: 375 C. and 800 C., 375 C. and 600 C., 375 C. and 550 C., 375 C. and 500 C., 375 C. and 450 C., 500 C. and 700 C., or between 600 C. and 700 C. The aqueous solvent may thus be provided at any of these temperature ranges at the time of contacting the polymeric material (e.g. an extruded melt stream of the polymeric material).

    [0172] Additionally or alternatively, the aqueous solvent may be provided at a temperature of between about: 50 bar and 400 bar, 100 bar and 350 bar, 150 bar and 350 bar, 150 bar and 300 bar, 150 and 250 bar, 200 bar and 350 bar, or 200 bar and 300 bar. The aqueous solvent may thus be provided at any of these pressure ranges at the time of contacting the polymeric material (e.g. an extruded melt stream of the polymeric material).

    [0173] In some embodiments, the aqueous solvent may be provided at a temperature of between about 400 C. and 700 C. a pressure of between about 220 bar and 350 bar; at a temperature of between about 375 C. and about 550 C. and a pressure of between about 220 bar and 350 bar; or at a temperature of between about 375 C. and about 500 C. and a pressure of between about 220 bar and 350 bar. The aqueous solvent may thus be provided at any of these temperature and pressure ranges at the time of contacting the polymeric material (e.g. an extruded melt stream of the polymeric material).

    [0174] In some embodiments, the aqueous solvent may be provided at a viscosity of between 110.sup.5 Pa.Math.s and 1 Pa.Math.s, between 110.sup.5 Pa.Math.s and 0.5 Pa.Math.s, between 110.sup.5 Pa.Math.s and 0.1 Pa.Math.s, between 110.sup.5 Pa.Math.s and-0.05 Pa.Math.s, or between 110.sup.5 Pa.Math.s and 0.01 Pa.Math.s, immediately prior to its injection into the melt stream.

    [0175] In some embodiments, the aqueous solvent may be processed in an amount of up to 1000 kg/hour, up to 2000 kg/hour, up to 3000 kg/hour, up to 4000 kg/hour or up to 5000 kg/hour.

    [0176] Combination of the polymeric material and the aqueous solvent may provide a reaction mixture for further treatment. Without limitation and again by way of non-limiting example, the reaction mixture may comprise at least: 40 wt %, 50 wt %, 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt %, or 98 wt %; of the polymeric material (i.e. as a percentage of the total weight of the reaction mixture). Accordingly, the reaction mixture may additionally comprise less than: 2 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt %, 50 wt %, or 60 wt %; of the aqueous solvent (i.e. as a percentage of the total weight of the reaction mixture).

    [0177] In some embodiments, the reaction mixture comprises between: 40 wt % and 90 wt %, 40 wt % and 80 wt %, 40 wt % and 70 wt %, 40 wt % and 60 wt %, 40 wt % and 50 wt %, 50 wt % and 90 wt %, 50 wt % and 80 wt %, 50 wt % and 70 wt %, 50 wt % and 60 wt %, 60 wt % and 90 wt %, 60 wt % and 80 wt %, or 60 wt % and 70 wt %; of the polymeric material (i.e. as a percentage of the total weight of the reaction mixture). Accordingly, the reaction mixture may additionally comprise between: 10 wt % and 60 wt %, 10 wt % and 40 wt %, 20 wt % and 40 wt %, or 30 wt % and 40 wt %; of the aqueous solvent (as a proportion of the total weight of feedstock and/or reaction mixture).

    [0178] In some embodiments feedstock polymeric material fed into the extruder and/or the reaction mixture comprises at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% polyethylene by weight on a dry basis (db).

    [0179] In some embodiments feedstock polymeric material fed into the extruder and/or the reaction mixture comprises at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% polypropylene by weight on a dry basis (db).

    [0180] In some embodiments feedstock polymeric material fed into the extruder and/or the reaction mixture comprises at least 30%, at least 40%, at least 50%, 60%, at least 70%, at least 80%, or at least 90% polystyrene by weight on a dry basis (db).

    [0181] By way of non-limiting example, polymeric materials suitable for the methods of the present invention may have a melt mass-flow rate (MFR) of between 0.05 grams to 20 grams per 10 minutes, or 0.1 gram to 10 grams per 10 minutes, or 0.01 grams to 5 grams per 10 minutes as measured according to ISO 1133-1-2011 PlasticsDetermination of the Melt Mass-Flow Rate (MFR).

    [0182] In a second stage of the exemplary reaction process, a reaction mixture formed by combining the polymeric material and aqueous solvent comprising or consisting of water is fed into a mixer device of the present invention. Following combination of the polymeric material and aqueous solvent, the reaction mixture so formed may optionally be heated or alternatively cooled prior to entering the mixing device (see section above titled Combining polymeric material feedstock with aqueous solvent for suitable mixing devices).

    [0183] In some embodiments, the reaction mixture enters and/or exits the mixing device at a temperature between 200 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature between 300 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature between 350 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature of between 400 C. and 500 C. and at a pressure of 100 to 300 bar, at a temperature between 373 C. and 550 C. and at a pressure of 221 bar to 350 bar, at a temperature between 300 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature between 350 C. and 550 C. and at a pressure of 100 to 300 bar, at a temperature of between 400 C. and 500 C. and at a pressure of 100 to 300 bar.

    [0184] In some embodiments, the flow rate of the reaction mixture after exiting the mixing device exceeds the flow rate of the reaction mixture prior to entering the mixing device. Additionally or alternatively, the viscosity of the reaction mixture after exiting the mixing device exceeds the viscosity of the reaction mixture prior to entering the mixing device.

    [0185] In some embodiments, the reaction mixture enters and/or exits the mixing device at a flow rate of 2,000 kg/hr to 15,000 kg/hr and/or a viscosity of 0.01 to 10 Pa.Math.s. The flow rate may be less than 15,000 kg/hr. The flow rate may be between 2,000 kg/hr and 15,000 kg/hr, between 3,000 kg/hr and 15,000 kg/hr, between 4,000 kg/hr and 15,000 kg/hr, between 5,000 kg/hr and 15,000 kg/hr, between 6,000 kg/hr and 15,000 kg/hr, between 8,000 kg/hr and 15,000 kg/hr, between 2,000 kg/hr and 10,000 kg/hr, between 3,000 kg/hr and 10,000 kg/hr, between 4,000 kg/hr and 10,000 kg/hr, between 5,000 kg/hr and 10,000 kg/hr, between 6,000 kg/hr and 10,000 kg/hr, or between 8,000 kg/hr and 10,000 kg/hr. The viscosity of the reaction mixture as it enters and/or exits the mixing device may be between 0.01 Pa.Math.s and 100 Pa.Math.s, between 0.1 Pa.Math.s and 100 Pa.Math.s, between 1 Pa.Math.s and 100 Pa.Math.s, between 0.01 Pa.Math.s and 50 Pa.Math.s, between 0.1 Pa.Math.s and 50 Pa.Math.s, between 1 Pa.Math.s and 50 Pa.Math.s, between 0.01 Pa.Math.s and 10 Pa.Math.s, between 0.1 Pa.Math.s and 10 Pa.Math.s, between 1 Pa.Math.s and 10 Pa.Math.s, less than 800 Pa.Math.s, less than 700 Pa.Math.s, less than 600 Pa.Math.s, less than 500 Pa.Math.s, less than 400 Pa.Math.s, less than 300 Pa.Math.s, less than 200 Pa.Math.s, less than 100 Pa.Math.s, less than 80 Pa.Math.s, less than 60 Pa.Math.s, less than 40 Pa.Math.s, less than 20 Pa.Math.s, less than 10 Pa.Math.s, less than 5 Pa.Math.s, less than 4 Pa.Math.s, less than 3 Pa.Math.s, less than 4 Pa.Math.s, less than 1 Pa.Math.s, less than 0.5 Pa.Math.s, less than 0.1 Pa.Math.s, or less than 0.01 Pa.Math.s.

    [0186] In a third stage of the exemplary reaction process, reaction mixture having exited the mixing device may continue to be treated for a time period to maximise the formation and yield of product. In some embodiments, the reaction mixture continues to flow through a vessel of a reactor apparatus and may optionally be heated for example, by a heater (e.g. an indirect heater or similar-see section above titled Heating and pressurisation of reaction components).

    [0187] In some embodiments, a reaction mixture formed by mixing the polymeric material and aqueous solvent may be treated at a minimum reaction temperature and pressure, or a range or reaction temperatures and pressures, over a time period prior to cooling and depressurisation. For example, the reaction mixture may be treated at temperature(s) of above 374 C. and pressure(s) of above 20 bar; temperature(s) of above 374 C. and pressure(s) above 40 bar; temperature(s) of above 374 C. and pressure(s) of above 60 bar; temperature(s) of above 374 C. and pressure(s) of above 80 bar; temperature(s) of above 374 C. and pressure(s) of above 100 bar; temperature(s) of above 374 C. and pressure(s) of above 120 bar; temperature(s) of above 374 C. and pressure(s) of above 140 bar; temperature(s) of above 374 C. and pressure(s) of above 160 bar; temperature(s) of above 374 C. and pressure(s) of above 180 bar: temperature(s) of above 374 C. and pressure(s) of above 200 bar; temperature(s) of above 374 C. and pressure(s) of above 221 bar; temperature(s) of above 374 C. and pressure(s) of above 240 bar; temperature(s) of above 374 C. and pressure(s) of above 260 bar: temperature(s) of above 374 C. and pressure(s) of above 280 bar; temperature(s) of above 374 C. and pressure(s) of above 300 bar; temperature(s) of above 374 C. and pressure(s) of above 350 bar; temperature(s) of above 400 C. and pressure(s) of above 20 bar; temperature(s) of above 400 C. and pressure(s) above 40 bar; temperature(s) of above 400 C. and pressure(s) of above 60 bar; temperature(s) of above 400 C. and pressure(s) of above 80 bar; temperature(s) of above 400 C. and pressure(s) of above 100 bar; temperature(s) of above 400 C. and pressure(s) of above 120 bar; temperature(s) of above 400 C. and pressure(s) of above 140 bar; temperature(s) of above 400 C. and pressure(s) of above 160 bar; temperature(s) of above 400 C. and pressure(s) of above 180 bar: temperature(s) of above 400 C. and pressure(s) of above 200 bar; temperature(s) of above 400 C. and pressure(s) of above 221 bar; temperature(s) of above 400 C. and pressure(s) of above 240 bar; temperature(s) of above 400 C. and pressure(s) of above 260 bar; temperature(s) of above 400 C. and pressure(s) of above 280 bar; temperature(s) of above 400 C. and pressure(s) of above 300 bar; temperature(s) of above 400 C. and pressure(s) of above 350 bar temperature(s) of above 374 C. and pressure(s) of above 221 bar; temperature(s) of above 375 C. and pressure(s) of above 225 bar; temperature(s) of between 370 C. and 550 C. and pressure(s) of between 20 bar and 400 bar; temperature(s) of between 374 C. and 500 C. and pressure(s) of between 221 bar and 400 bar; temperature(s) of between 374 C. and 550 C. and pressure(s) of between 221 bar and 400 bar; temperature(s) of between 375 C. and 550 C. and pressure(s) of between 221 bar and 400 bar; temperature(s) of between 375 C. and 550 C. and pressure(s) of between 221 bar and 400 bar; and temperature(s) of between 400 C. and 550 C. and pressure(s) of between 100 bar and 300 bar. For example, the reaction mixture may be treated at a temperature between 370 C. and 500 C., between 370 C. and 480 C., between 374 C. and 500 C., between 380 C. and 500 C., between 380 C. and 450 C., between 400 C. and 480 C., or between 440 C. and 480 C.; and the pressure may be more than 100 bar, more than 221 bar, or between 221 bar and 250 bar. For example, the reaction mixture may be treated at a temperature greater than about: 350 C., 360 C., 370 C., 380 C., 390 C., 400 C., 410 C., 420 C., 430 C., 440 C., 450 C., 460 C., 470 C., or 480 C., and a pressure that is greater than about: 180 bar, 200 bar, 221 bar, 240 bar, 260 bar, 280 bar, 300 bar, or 320 bar.

    [0188] In some embodiments, the reaction mixture during the third stage of the exemplary reaction process has a flow rate of 2,000 kg/hr to 15,000 kg/hr and/or a viscosity of 0.01 to 10 Pa.Math.s. The flow rate may be less than 15,000 kg/hr. The flow rate may be between 2,000 kg/hr and 15,000 kg/hr, between 3,000 kg/hr and 15,000 kg/hr, between 4,000 kg/hr and 15,000 kg/hr, between 5,000 kg/hr and 15,000 kg/hr, between 6,000 kg/hr and 15,000 kg/hr, between 8,000 kg/hr and 15,000 kg/hr, between 2,000 kg/hr and 10,000 kg/hr, between 3,000 kg/hr and 10,000 kg/hr, between 4,000 kg/hr and 10,000 kg/hr, between 5,000 kg/hr and 10,000 kg/hr, between 6,000 kg/hr and 10,000 kg/hr, or between 8,000 kg/hr and 10,000 kg/hr. The viscosity of the reaction mixture as it enters and/or exits the mixing device may be between 0.01 Pas and 100 Pa.Math.s, between 0.1 Pa.Math.s and 100 Pa.Math.s, between 1 Pa.Math.s and 100 Pa.Math.s, between 0.01 Pas and 50 Pa.Math.s, between 0.1 Pa.Math.s and 50 Pa.Math.s, between 1 Pa.Math.s and 50 Pa.Math.s, between 0.01 Pa.Math.s and 10 Pa.Math.s, between 0.1 Pa.Math.s and 10 Pa.Math.s, between 1 Pa.Math.s and 10 Pa.Math.s, less than 800 Pa.Math.s, less than 700 Pa.Math.s, less than 600 Pa.Math.s, less than 500 Pa.Math.s, less than 400 Pa.Math.s, less than 300 Pa.Math.s, less than 200 Pa.Math.s, less than 100 Pa.Math.s, less than 80 Pa.Math.s, less than 60 Pa.Math.s, less than 40 Pa.Math.s, less than 20 Pa.Math.s, less than 10 Pa.Math.s, less than 5 Pa.Math.s, less than 4 Pa.Math.s, less than 3 Pa.Math.s, less than 4 Pa.Math.s, less than 1 Pa.Math.s, less than 0.5 Pa.Math.s, less than 0.1 Pa.Math.s, or less than 0.01 Pa.Math.s.

    [0189] A reaction mixture formed upon the combination of aqueous solvent and polymeric feedstock as described herein may be treated for a specified retention time. The specific time period may depend on a number of different factors including, for example, the type of polymeric material under treatment and the relative proportions or types of components in the reaction mixture (e.g. the proportion of aqueous solvent, additive catalyst(s), and/or any other additional component/s), and/or the type of apparatus in which the methods are performed. These and other factors may be varied in order to optimise a given method so as to maximise the yield of certain products and/or reduce the processing time. Preferably, the retention time is sufficient to convert or substantially all of the polymeric material used as a feedstock into product.

    [0190] In certain embodiments, the retention time is less than about 60 minutes, 45 minutes, 30 minutes, 25 minutes, 20 minutes, 15 minutes, 10 minutes or less than about 5 minutes. In certain embodiments, the retention time is more than about 60 minutes, 45 minutes, 30 minutes, 25 minutes, 20 minutes, 15 minutes, 10 minutes or more than about 5 minutes. In other embodiments, the retention time is between about 1 minute and about 60 minutes. In additional embodiments, the retention time is between about 5 minutes and about 45 minutes, between about 5 minutes and about 35 minutes, between about 10 minutes and about 35 minutes, or between about 15 minutes and about 30 minutes. In further embodiments, the retention time is between about 20 minutes and about 30 minutes.

    [0191] The optimal retention time for a given set of reaction conditions as described herein may be readily determined by the skilled addressee by preparing and running a series of reactions that differ only by the retention time, and analysing the yield and/or quality of upgraded product generated.

    [0192] The average residence or retention time may be determined or measured or constrained by the flow rate of the polymeric material melt stream and/or the aqueous solvent.

    [0193] In some embodiments the retention time is about 30 seconds, about 1 minute, about 2 minutes, about 5 minutes, between 5 minutes and 10 minutes, between 10 minutes and 20 minutes, between 20 minutes and 30 minutes, between 30 minutes and 40 minutes, greater than 40 minutes, or less than about 60 minutes.

    [0194] In a fourth stage of the exemplary reaction process, a product stream generated from the reaction mixture can be depressurised and cooled, and optionally separated, refined and/or otherwise processed into individual product components.

    [0195] In some embodiments, depressurisation and cooling can be achieved using flash depressurization at the reaction temperature. The flash depressurization may constitute a form of heat recovery, wherein the heat energy released during depressurization may be used to fractionate the product into at least two different boiling ranges using, for example, a distillation column directly connected to the flash depressurization unit.

    [0196] In some embodiments the reaction mixture may be flash depressurized from a temperature of at least 350 C., 375 C., 400 C., 410 C., 420 C., 430 C., 440 C., 450 C. or at least 460 C. and a pressure of at least 200 bar, 221 bar, 222 bar, 240 bar, 260 bar, 280 bar, 300 bar to a pressure of less than 25 bar, 20 bar, 15 bar, 10 bar, 8 bar, 6 bar, 4 bar, 2 bar, 1.5 bar, 1.2 bar absolute. The flash depressurization may, for example, be regulated by means of one or more valves. The depressurized stream may be directed into a depressurization and fractionation vessel or vessels where the stream is fractionated into at least three boiling range fractions plus a gas and/or vapour stream. A part of the energy in the process stream fluids may thereby be used to fractionate the product stream into product fractions e.g. gas/vapour, naphtha, middle distillate or gas oil, heavy gas oil, heavy wax residue.

    [0197] In some embodiments the depressurization-fractionation apparatus may comprise a flash vessel and two or more condensers in series. In the case where two condensers are used, the first condenser may be employed to condense distillates boiling in the range approximately 200 C. to 400 C. AEBP, or 450 C. or 500 C. AEBP, the second condenser may be employed to condense distillates boiling in the range approximately 20 C. to 200 C. AEBP, and fractions boiling above about 400 C. or 450 C. or 500 C. AEBP may be retained in the bottom of the flash vessel and periodically or continually drained to storage vessels. Water may be separated from the output of the second condenser by means of decantation, the water being more dense than and immiscible with the liquid products.

    [0198] In some embodiments, the depressurization-fractionation apparatus may comprise a flash vessel and a fractionating column in series. The vessel comprising fractionation column may act also as the flash vessel (i.e. the fractionating column is itself a flash vessel). The fractionating column may be used to separate product fractions into at least three boiling ranges. The boiling ranges may be, for example, about 20 C. to about 200 C. AEBP, about 200 C. to about 360 C. AEBP, about 360 C. to about 400 C. AEBP, about 360 C. to about 450 C. AEBP, or 360 C. to about 500 C. AEBP. Gases and vapours not condensed by the primary condenser may be directed to a boiler and/or a flare for combustion. Water may be separated from the lowest boiling liquid fraction (e.g. the fraction boiling from about 20 C. to about 200 C. AEBP) or other liquid fractions by means of a separator. The separator may, for example, be a gravity plate separator, an API-separator, an electrostatic separator. Alternatively or additionally the separator may be an enhanced gravity separator e.g. a centrifuge, a decanter centrifuge, or a hydrocyclone. Fractions boiling above about 500 C. AEBP may be retained in the bottom of the flash vessel and periodically or continually drained to storage vessels.

    [0199] In certain embodiments steam or superheated steam or supercritical water may be additionally introduced into the depressurization vessel in order to facilitate fractionation of the liquid products.

    [0200] The processes of heating/pressurisation and cooling/de-pressurisation and fractionation can be performed in a continuous flow system (see section below entitled Continuous flow).

    [0201] The fractionating column may contain distillation trays for the separation of condensed liquid product.

    [0202] The fractionating column may fractionate the product stream into different boiling ranges. As referred to herein, boiling points will be taken to mean atmospheric equivalent boiling points (AEBP) unless otherwise stated. For example, the fractionating column may separate the product stream by boiling range into a naphtha fraction boiling between about 70 C. and about 210 C. AEBP and a distillate gas oil fraction boiling between about 210 C. and about 360 C. AEPB and a heavy gas oil fraction boiling between about 360 C. to about 400 C. AEBP, about 360 C. to about 450 C. AEBP, or 360 C. to about 500 C. AEBP. The gas oil and heavy gas oil fractions may be wholly or partly waxy solids at 25 C. Gases and vapours not condensing in the column may pass to a condenser which may condense a low boiling oil (naphtha fraction). The naphtha fraction and any other condensed fractions may be wholly or partly recirculated into the fractionating column. The gases and vapours passing the condenser may be directed to the boiler whereupon the gases may be combusted producing the supercritical aqueous solvent, optionally with the addition of an additional fuel gas such as natural gas. The combustion may recover energy from the gas and can destroy any compounds of environmental concern in the combustion process. Optionally, some or all of the gases and vapours may be directed to a flare. The flare may be an enclosed flare.

    [0203] In some embodiments, a non-distillable part of the product stream (heavy wax residue), having a boiling point of e.g. >500 C. may be continuously or intermittently removed from the bottom of the depressurisation vessel (located at the bottom of the fractionating column).

    [0204] It will be evident to those skilled in the art that the fractionating column may be operated in a manner known in the field to provide desired boiling ranges for the product fractions.

    [0205] In some embodiments the non-distilled residue from the flash vessel and/or the fractionating column may be optionally distilled in a vacuum distillation unit to provide a vacuum gas oil fraction and a heavy residue. The boiling range of the VGO fraction may be e.g. 360 C. to 650 C. AEBP.

    [0206] In some embodiments of the present invention the lower part of the flash column can be a demister. Without any particular limitation, the mixture entering the flash column after being pressure reduced from very high pressure to near atmospheric pressure may predominantly be in the gaseous phase with liquid droplets of high boiling hydrocarbons comprising an aerosol. The design of the lowest section of the flash column is therefore to act as a demister separating the high boiling hydrocarbon droplets from the gaseous mixture.

    [0207] On entry into the column the product gas stream may be forced by a baffle plate to make a sharp turn, whilst the gas turns, the momentum of the droplets mean that they impact on the baffle plate where they coalesce and flow downwards as a liquid in to bottom of the flash column.

    [0208] The flash column base may have a diameter sufficiently large to ensure a very low upward velocity within that section of the column. The diameter at the base of the column may be selected so that the largest droplets that are carried by the gaseous phase are about 50 microns or about 40 microns or about 30 microns or about 20 microns or about 10 microns or about 5 microns in diameter. Droplets larger than about this diameter may not be transported upwards and fall into the liquid residue at the base of the column.

    Continuous Flow

    [0209] The methods and devices of the present invention are well suited to processing reaction mixtures under conditions of continuous flow.

    [0210] Performing the process of the invention under conditions of continuous flow may provide a number of advantageous effects. For example, continuous flow may facilitate the accelerated implementation and/or removal of heat and/or pressure applied to a reaction mixture. This may assist in achieving the desired rates of mass and heat transfer, heating/cooling and/or pressurisation/de-pressurisation. Continuous flow may also allow the retention time to be tightly controlled. Without limitation to a particular mode of action, it is postulated that the increased speed of heating/cooling and/or pressurisation/de-pressurisation facilitated by continuous flow conditions along with the capacity to tightly regulate retention time assists in preventing the occurrence of undesirable side-reactions (e.g. re-polymerisation, char formation) as the reaction mixture heats/pressurises and/or cools/de-pressurises. Continuous flow is also believed to enhance reactions responsible for converting polymeric materials into hydrocarbon products by virtue of generating mixing and shear forces believed to aid in emulsification.

    [0211] Accordingly, the methods of the present invention are performed under conditions of continuous flow. As used herein, the term continuous flow refers to a process wherein: [0212] (i) reaction mixture precursors (e.g. polymeric material melt streams, aqueous solvent) are maintained in a stream of continuous movement into the reactor apparatus; [0213] (ii) reaction mixtures are maintained in a stream of continuous movement through the reactor apparatus; and [0214] (iii) product stream/s are maintained in a stream of continuous movement out of the reactor apparatus

    [0215] Accordingly, in a continuous flow system the reaction mixture is maintained in a stream of continuous movement along the length (or partial length) of a given surface of reactor apparatus from the point of entry into the reactor to the point of exiting the reactor.

    [0216] Continuous flow conditions as contemplated herein imply no particular limitation regarding flow velocity of a reaction mixture provided that it is maintained in a stream of continuous movement.

    [0217] Continuous flow conditions may be facilitated, for example, by performing the methods of the invention in a suitable reactor apparatus. A suitable reactor apparatus will generally comprise heating/cooling, pressurising/de-pressuring and reaction components in which a continuous stream of reaction mixture is maintained.

    [0218] The use of a suitable flow velocity (under conditions of continuous flow) may be advantageous in preventing scale-formation along the length of a particular surface that the reaction mixture moves along (e.g. vessel walls of a reactor apparatus) and/or generating an effective mixing regime for efficient heat transfer into and within the reaction mixture.

    Additional Reagents and Catalysts

    [0219] Optionally, additional (i.e. supplementary) reagent/s and/or catalyst/s may be added to the process.

    [0220] In some embodiments the supplementary reagent/s and/or catalyst/s may be solid at room temperature, and may be mixed with the polymeric feedstock prior to the polymeric material entering an extruder. In some embodiments the additive may be solid at room temperature and may be mixed with the polymeric feedstock within an extruder by means of a suitable port.

    [0221] In some embodiments the supplementary catalysts may be a solid calcium salt chosen from calcium oxide, calcium hydroxide, calcium carbonate, calcium bicarbonate. In some embodiments the supplementary catalysts may be a solid base chosen from sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, lithium hydroxide, lithium carbonate, magnesium oxide, magnesium hydroxide, barium oxide and barium hydroxide.

    [0222] Without limitation to a mode of action, the additive may react with organic halides or with halogen-containing species, e.g. hydrogen chloride, to form inorganic halides. The inorganic halides may be removed as solids by blowdown in the hydrothermal reactors.

    [0223] Without limitation to a mode of action, the additive may accelerate the decomposition of compounds such as terephthalic acid (TPA) and/or benzoic acid (BA), formed from the decomposition or depolymerization of poly(ethylene terephthalate) present in the polymeric feedstock. The TPA and BPA may be decomposed to other aromatic compounds including but not limited to benzene, toluene, benzophenone and benzaldehyde. The additive may be removed as solid by blowdown, the form of the additive may have changed by chemical reaction prior to said removal.

    [0224] In some embodiments the supplementary reagent/s and/or catalyst/s may be added in liquid form (e.g. as aqueous solutions). The liquids may be added under pressure using a high pressure dosing pump or similar means. The liquid may be added at any stage of the process prior to the depressurization step. The liquid may be added to the extruder, between the extruder and the supercritical aqueous fluid addition point(s), after the supercritical aqueous fluid addition point(s) but before the additional heating stages if present, or before any of the reactor vessels, or before the depressurization stage.

    [0225] In some embodiments of the present invention, base may be included in the polymeric material melt stream/extrudate, aqueous solvent stream and/or reaction mixture. There is no particular restriction on the type or form of base that may be used or the point/s in the process that it may be introduced. By way of non-limiting example, the base may be introduced, for example, as a solid co-feed to the extruder with the polymeric material and/or as a liquid form at any point after the extrusion stage (e.g. to the extrudate/melt stream, to the aqueous solvent stream, and/or directly to the reaction mixture). In a continuous or semi-continuous version of the process of the invention, at least some base may be added prior to the final reactor leg.

    [0226] Non limiting examples of bases suitable for this purpose are carbonates, hydroxides, hydrogen carbonates, oxides of Group I and Group II metals and materials containing significant quantities thereof (e.g. black liquor, white liquor, green liquor, red mud, limestone, calcite).

    [0227] A reaction mixture for use in accordance with the methods of the present invention may comprise catalysts which may enhance the formation of desired products.

    [0228] The catalysts may be intrinsic catalysts which are derived from other components of the reaction mixture itself (e.g. from the polymeric material, aqueous solvent, any other reaction mixture component), will be understood to be generated in situ during the treatment of the reaction mixture in accordance with the methods of the present invention, and/or are derived from the mixer materials and walls of a reactor apparatus within which the reaction mixture is treated. For example, the catalysts may be hydronium/hydroxide ions of water in the reaction mixture, compound/s in the polymeric material and/or transition/noble metals from the reactor vessel walls. Waste plastic polymers treated according to the methods of the present invention may have contaminants with catalytic activity.

    [0229] Additionally or alternatively, the catalysts may be supplementary catalysts which are not derived from other components of the reaction mixture itself, are not generated in situ during the treatment of the reaction mixture in accordance with the methods of the present invention, and are not derived from the materials of construction or the walls of a reactor apparatus within which the reaction mixture is treated. Rather, the supplementary catalysts are separately added to the reaction mixture as a discrete/stand-alone component, and are thus additional to intrinsic catalysts present in the reaction mixture.

    [0230] Although the addition of supplementary catalysts may be advantageous in certain circumstances, the skilled addressee will recognise that the methods of the invention may be performed without using them.

    [0231] A supplementary catalyst as contemplated herein may be any catalyst that enhances the formation of the desired hydrocarbon products such as fuels and chemicals from polymeric material feedstocks using the methods of the invention, non-limiting examples of which include base catalysts, acid catalysts, alkali metal hydroxide catalysts, transition metal hydroxide catalysts, alkali metal formate catalysts, transition metal formate catalysts, reactive carboxylic acid catalysts, transition metal catalysts, sulphide catalysts, noble metal catalysts, water-gas-shift catalysts, metals supported on nitrogen doped carbon materials, and combinations thereof.

    [0232] Without being limited to theory, supplementary base catalysts may play a multiple role in that they may enhance product formation and also control pH, which may be advantageous for reducing corrosion rates in reactor metal components, and may promote the precipitation of halogens contained in the feedstock as metal halides that are insoluble or sparingly soluble in supercritical water. Upon cooling and depressurisation the metal halides can re-dissolve in the water phase. This action is advantageous because the halogens, in particular chlorine, may effectively be removed from the gas phase and/or from the oil phase. Chlorines are undesirable in gas and oil phases because they may ultimately form dioxins and other environmental pollutants if incompletely combusted in a subsequent process.

    [0233] In some embodiments, supplementary catalysts known in the art to promote water-gas shift (WGS) reactions may be included in the reaction mixture to promote hydrogen transfer from water to oil products. Any WGS catalysts or hydrogen transfer catalysts known in the art may be utilised. Without limitation the catalysts may be in the form of a finely dispersed solid added to the extruder feed. Additionally or alternatively, they may be in the form of a fixed bed. Additionally or alternatively, they may be homogenous when present in a reaction stream (e.g. aqueous solvent, polymeric material extrudate, and/or reaction mixture) under subcritical conditions and/or supercritical conditions.

    [0234] Without being bound by theory, the addition of WGS and/or hydrogen transfer catalysts may increase the degree of saturation of hydrocarbons in the product. This may be desirable as the cetane number of middle distillates in the product may increase and the proportion of n-paraffins in the wax fractions in the product may also increase, making the waxes valuable by virtue of their high purity and sharp and discrete melting point ranges.

    [0235] In some embodiments of the invention solid metal catalysts are contacted with the reaction stream.

    [0236] In some embodiments the solid metal catalysts are fixed metal surfaces within the reactor vessels. The solid metal catalysts may be, for example, wires, meshes, foils, and shapes known in the art such as Raschig rings.

    [0237] In some embodiments the solid metal catalysts comprise nickel. In some embodiments the nickel is in a formal zero oxidation state. The nickel may be present as an alloy with other metals e.g. as stainless steel 310 or 316.

    [0238] Without being bound by theory, the nickel may facilitate the transfer of hydrogen from the aqueous solvent to the depolymerization products of the polymeric feed.

    [0239] It will be appreciated by persons of ordinary skill in the art that numerous variations and/or modifications can be made to the present invention as disclosed in the specific embodiments without departing from the spirit or scope of the present invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.

    EXAMPLES

    [0240] The present invention will now be described with reference to specific Examples, which should not be construed as in any way limiting.

    Example One: Computational Fluid Dynamics (CFD) of Pipe Mixer

    (i) Methods

    [0241] A Computational Fluid Dynamics (CFD) characterisation exercise was carried out for a Molten Plastic/Supercritical Water (SCW) mixing process. The characterisation exercise has the intention of comparing several design options for this mixing process through the creation of a series of CFD models, assessing the mixing performance of each option and heat transfer performance to determine a preferred option to take forward to further development.

    [0242] The geometry options assessed were: [0243] 1. Iteration 16 inch pipe with four radial 10 mm diameter SCW inlets in a single plane [0244] 2. Iteration 1 with two static mixer elements [0245] 3. Iteration 1 with four static mixer elements [0246] 4. Iteration 26-inch pipe with four 10 mm diameter SCW inlets in two planes 50 mm apart and triangular bars just upstream of the SCW inlets [0247] 5. Iteration 2 with two mixer elements [0248] 6. Iteration 2 with four mixer elements

    [0249] The geometry for the model was built within the CFD software (Siemens STAR-CCM+) using the in-built 3D CAD package. The geometrical representations of the pipe mixer within the simulation domain were built based on mixer sketches and STEP 3D CAD geometry imports. Between each iteration and associated designs, similar dimensions remain the same e.g. pipe diameter. Geometrical representations of the pipe mixer in the simulation domain are shown in FIGS. 1-6.

    [0250] A qualitative mesh selection approach was used, in which the cell size is reduced until geometric features within the simulation domain look well defined, this was achieved at a cell base size of 5 mm. In instances where the geometry is complicated i.e. static mixers, the mesh was refined to a smaller Base size of 3 mm and minimum size of 1.5 mm. On average the simulations carried an approximate cell count of one million cells.

    [0251] In defining the physics used within the simulation domain the following operating conditions were taken into account:

    a. Boundary Conditions [0252] Molten plastic inlet: [0253] Mass flow rate: 2782 kg/h [0254] Temperature: 350 C. [0255] Supercritical water inlet: [0256] Mass flow rate across four inlets: 1762 kg/h [0257] Temperature: 500 C. [0258] Pipe walls [0259] Adiabatic

    B. Physical Properties

    [0260] the physical properties are temperature dependent as described in the extract from the Mixer datasheet in Table 1 below.

    TABLE-US-00001 TABLE 1 Plastics properties 16 Temperature C. 325 350 375 400 425 450 17 Shear rate 1/s 10 10 10 10 10 10 18 Viscosity Pa .Math. s 331 270 224 189 161 139 19 Density kg/m.sup.3 665 670 655 640 625 610 20 Enthalpy kJ/kg 1019 1109 1201 1295 1391 1486 Supercritical steam/water properties @300 bar 21 Temperature C. 350 375 400 425 450 500 22 Viscosity Pa .Math. s 7.55E05 6.45E05 4.39E05 3.19E05 3.09E05 0.000032 23 Density kg/m.sup.3 644 556 357 169 148 115 24 Enthalpy kJ/kg 1609 1792 2153 2612 2821 3085 [0261] Additionally, thermal conductivity variation with temperature were as shown in Table 2 and 3.

    TABLE-US-00002 TABLE 2 Plastics Properties Temperature (deg C.) 350 375 400 425 450 Thermal conductivity 0.138 0.1355 0.133 0.1305 0.128 (W/m .Math. K)

    TABLE-US-00003 TABLE 3 SCW @ 300 bar Temperature (deg C.) 350 375 400 425 450 Thermal conductivity 0.49597 0.43807 0.33204 0.17582 0.13616 (W/m .Math. K)

    [0262] The physical properties provided in Tables 2 and 3 were then described by means of Polynomial equations within the software from which the solver would determine each of the physical properties based on temperature as the solution progressed. The polynomial equations were valid within the prescribed temperature range i.e. 350 to 500 C.; molten plastic inlet temperature to SCW inlet temperature.

    C. Physics Models

    [0263] Below is a summary of the key physics models utilised in generating the simulations: [0264] Three dimensionalthe simulation domain/vessel is 3-dimensional. [0265] TurbulentThe flow regime associated with the SCW. [0266] Reynolds-Averaged Navier-Stokes (RANS)Governs the transport of the mean flow quantities. Automatically selected with the selection of the Turbulent flow regime. [0267] K-Epsilon TurbulenceThe K-Epsilon turbulence model is a two-equation model that solves transport equations for the Turbulent Kinetic Energy and the Turbulent Dissipation Rate in order to determine the Turbulent Eddy Viscosity. It is the most widely used model for industrial applications. [0268] Realizable K-Epsilon Two-LayerThe Realizable Two-Layer K-Epsilon models offer the most mesh flexibility. They can be used with the same meshes as the high Reynolds number versions. They give good results on fine meshes and also produce the least inaccuracies for intermediate meshes. The model is automatically selected with the K-Epsilon Turbulence Model. [0269] Two-Layer All y+ Wall TreatmentThis model is used in predicting the flow of fluid across walls and the transition into the bulk fluid in the domain and it is automatically selected with the selection of the K-Epsilon Turbulence Model. [0270] Exact Wall DistanceThe Exact Wall Distance model makes an exact projection calculation in real space, which is based on a triangulation of the surface mesh [1]. This is more accurate as opposed to an estimation. The model is automatically selected with the selection of the K-Epsilon Turbulence Model. [0271] Segregated Fluid TemperatureThe simulations had a focus on temperature. The model allows for the simulation to solve the total energy with temperature as the solved variable [1]. [0272] Cell Quality RemediationThe Cell Quality Remediation model helps to mitigate the negative effects of individual low-quality mesh cells, minimising their effect on solution quality. [0273] GravityGravity affects the flow pattern of the fluid. [0274] Multiphase Segregated FlowAllows for phases to be defined with their own velocity, energy, and other variables, and their own physical properties. Individual phases are defined along with the interactions between them. [0275] Polynomial DensityThis allows the phases density to be described by means of polynomial equations in temperature. [0276] Eulerian MultiphaseThis affects the selection of phases that are present in the simulation domain. It allows for the presence of the molten plastic liquid and SCW water gas phases within the simulation domain. [0277] Phase Coupled EnergyAllows for the use of energy related functionality and resolution within the simulation domain.

    (ii) Results & Discussion

    [0278] The results of interest are: [0279] Mixing performance [0280] Temperature profile distribution [0281] Pressure drop profile

    [0282] To carry out analysis of the above, the use of Planes, for qualitative analysis, and Thresholds, for quantitative analysis, was employed. Thresholds are used to specify a volume within the simulation domain. In this instance the Thresholds were used to specify sections of the pipe mixer along its length.

    [0283] Each Threshold has a length of one pipe diameter i.e. 132 mm. The following arrangement was adapted-Thresholds 0, 2, 4, 6 and 8, with Thresholds 1, 3, 5, 7 and 9 sitting in between them in chronological order. The midpoint of Threshold 0 is the plane in which the SCW inlets exist.

    [0284] From a qualitative point of view, the main plane section used to show variables is a plane section at a 45 angle along the length the pipe. It cuts through two of the SCW inlets. Additionally, cross-section planes across the pipe mixer start at the SCW inlets with planes sitting 132 mm apart i.e. 1 diameter.

    A. Mixing Performance

    [0285] Mixing performance was measured qualitatively by visualising the volume fraction of the fluids on planes and quantitatively by a property automatically generated by the simulation called Volume Uniformity. Volume Uniformity is a measure of how uniformly distributed a property is within a pre-defined volume. The scale of uniformity ranges from 0, for a property that is completely unevenly distributed throughout the pre-defined volume, to 1, for a property that is perfectly distributed throughout the volume.

    [0286] Volume fraction distribution along and across each a pipe mixer design is shown in FIGS. 7-12. It is important to note that the colour scale bar each of FIGS. 7-12 specifies what each colour means. For example, FIG. 7 shows Volume fraction of SCW and the scale ranges from 0 to 1 against the colours. Anywhere shown with a red colour reflects a volume fraction of SCW of 1 meaning that area is entire SCW. Since the domain is only molten plastic and SCW, blue means entirely molten plastic.

    [0287] Quantitatively, volume uniformity of the volume fraction of the fluids was used to analyse the mixing performance in the different iterations of pipe design. The volume uniformity was monitored in the thresholds and is shown in FIG. 13.

    [0288] The results for all geometry iterations, show the majority of the mixing occurs in the area around the supercritical water (SCW) inlets. This is to be expected as the SCW comes in at a velocity of approximately 15 m/s and penetrates through to mix with the molten plastic. Further mixing occurs as the fluids traverse down the pipe mixer.

    [0289] It is interesting to note that the iterations with mixers achieve higher volume uniformity compared to those that do not. The highest being the two iterations with 4 static mixer elements as shown in FIG. 14 (Bar chart of volume uniformity of volume fraction of molten plastic in Threshold 9).

    B. Temperature Distribution Profile

    [0290] The simulation recognised the Molten Plastic and SCW as two segregated fluids. The segregated fluids therefore have segregated temperatures associated with them. FIGS. 15 and 16 show temperatures of the two fluids separately within the domain. That is to say whatever amount of a fluid that exists in an area is at the temperature shown in the respective figure. With regards to temperature analysis, there was a focus on Iteration 2 with 2 mixer elements. Heat transfer between the two fluids is, amongst other things, primarily associated with how well mixed the two fluids are within the domain. Since fluid mixing analysis was carried out on all designs, a focus on one design for temperature analysis was deemed sufficient. Heat transfer between the two fluids was initiated when the SCW is introduced into the domain, and the FIGS. 15 and 16 therefore show temperature profiles from the SCW inlets and downstream of this point.

    [0291] Since the two fluids within the domain are treated separately, the expectation is the SCW temperature decreases whilst that of Molten plastic increases. FIG. 17 shows that as expected, the temperature profiles trend towards each other along the pipe mixer length with a settling temperature approximately between 43 and 420 C.

    C. Pressure Drop

    [0292] The pressure drop profile along the pipe mixer is assessed qualitatively on the plane along the pipe, the planes showing the differential pressure between the inlet and outlet. Quantitatively, using the pipe and mixer geometry, the model calculates the pressure drop through the system.

    [0293] The mixer geometry used within the simulation domain was a scaled 2 inch version CAD drawing of the mixer elements (supplied by the manufacturer of the mixer) to fit the 6 inch pipe. This was used as the 6 inch CAD drawing was not available at the time the work was undertaken. A subsequent comparison with the actual 6-inch drawing showed that the flow channeling elements of the mixer elements stay the same in the scaled geometry, but the elements modelled were slightly thicker. As a consequence, the pressure drop calculated is higher than experienced on the real mixer.

    [0294] For the purpose of reporting the pressure drop it was assumed that the reactor pressure is kept constant and the upstream pressure delivered by the plastic pump will vary. FIGS. 18-23 show the downstream reactor pressure is reported as zero, thus the figures show pressure drop as opposed to system pressure.

    [0295] FIG. 24 summarises pressure drop across the various mixer types. The iterations with 4 mixers showed the highest amount of pressure drop. This shows the mixers contribute a significant amount of resistance to fluid flow within the pipe. The version of each of the iterations that has two mixers has a pressure drop of approximately 5 to 6 bar more that the version that does not. This implies each mixer element, for the given fluids, mass flow rates and geometry, contributes roughly 2.5 to 3 bar of pressure drop.

    [0296] Additionally, the two geometry iterations have a difference in pressure drop of approximately 1 bar. This implies, for the given fluids, mass flow rates and geometry, the two bars that sit just upstream of the SCW inlets contribute approximately 1bar of pressure drop.

    (iii) Conclusions

    [0297] From the mixing it was observed that mixing starts upon SCW entry. This was expected as the turbulent SCW streams meet the molten plastic stream at high velocity which induces turbulence and mixing.

    [0298] The geometry iterations that do not have mixer elements included performed the worst. Of these two, Iteration 2 with triangular bars produced better mixing performance. This may be because the bars themselves induce turbulence and also give SCW the opportunity to penetrate to the middle of the pipe.

    [0299] Of the geometry options with mixer elements included, the geometry options with four mixer elements produce the best results (at threshold 9). The mixing performance between all cases with mixer elements included is similar (0.98-0.99 volume uniformity of volume fraction of molten plastic).

    [0300] The fastest rate of mixing (within the first 3 Thresholds), was observed in the Iteration 2 geometries that have mixers.

    [0301] The plots of temperature distribution are separated into two, temperature of SCW and Molten plastic along the pipe. This is because the simulation recognised the two as segregated fluids that interact with each other. SCW comes in at 500 C. and molten plastic at 350 C., the expectation is therefore for the SCW water to cool whilst the molten plastic gets hotter as the segregated fluids mix and interact. Looking at the Iteration 2-2 Mixers geometry configuration, the temperature of the two fluids trend towards each other along the length of the pipe and seemingly set between 42 and 430 C. before leaving the simulation domain.

    [0302] With regard to pressure drop, the comparative results were as expected, more resistance in the pipe equates to higher pressure drop. The variability of waste plastic properties combined with the use of a scaled mixer means that the following results are indicative only:

    [0303] In the model: [0304] Introduction of bars immediately upstream of the SCW inlets introduced a pressure drop of approximately 1bar [0305] Each mixer element introduced a pressure drop of approximately 2.5 bar (so 4 mixers added is approximately 10 bar)

    [0306] Ultimately the results (mixing, temperature, pressure drop) should be considered on a comparative basis. There was no validation exercise carried out to go with the simulation work. These models though, are based on well-established and proven physics models so they should provide reasonably accurate results even without external validation.

    [0307] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms in particular features of any one of the various described examples may be provided in any combination in any of the other described examples. Various modifications and alterations to this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention. It should be understood that this invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein and that such examples and embodiments are presented by way of example only with the scope of the invention intended to be limited only by the claims set forth herein as follows.