process

Abstract

Process The present invention relates to a process for recycling of polymers, and in particular of polyvinyl chloride (PVC) polymers, the process comprising: a) providing a solution comprising a polymer dissolved in a solvent mixture comprising water, a polar aprotic organic solvent (PAOS) and an organic phase separation agent (PSA), b) removing at least some of the PSA from the solution to cause precipitation of the polymer and provide a slurry of polymer particles in a liquid phase comprising water and the PAOS, c) performing a solid-liquid separation on the slurry to separate the majority of the PAOS and water present in the slurry, to provide polymer particles comprising residual PAOS and water, and d) treating the polymer particles comprising residual PAOS and water to remove the residual PAOS and water and recovering the polymer particles.

Description

[0001] Process

[0002] The present invention relates to a process for recycling of polymers, and in particular of polyvinyl chloride (PVC) polymers.

[0003] The recycling and reuse of polyvinyl chloride (PVC), as with other polymers, is highly desirable, and has been widely researched. A particular issue with PVC recycling is that PVC is commonly mixed with high levels of additives, including mineral fillers, thermal stabilisers and plasticisers. Further, a number of the additives used historically have been subsequently subject to restrictions on their use. For example, thermal stabilisers based on lead and cadmium, and plasticisers such as di (2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP) and benzyl butyl phthalate (BBP), which were historically used are now subject to restrictions on their use in “new” PVC but also their presence in recycled PVC.

[0004] One known commercial process for recycling of PVC was the VinyLoop® technology operated in Ferrara, Italy between 2002 and 2018. In this process PVC to be recycled is dissolved in a suitable solvent, and then reprecipitated.

[0005] US 7056956 describes a process for recycling a plastic (i.e. a polymer) which comprises dissolution and precipitation of the plastic. This patent describes the use of a “phase separating agent” in addition to the solvent for the plastic, which phase separating agent improves the dissolution of the plastic in the solvent. During precipitation the phase separating agent is removed, along with the solvent, to form precipitated plastic. US 7056956 exemplifies use of methyl ethyl ketone as the solvent, n-hexane as the phase separating agent and PVC as the plastic, and uses steam and liquid water to heat and cause vaporisation of the phase separating agent and solvent.

[0006] WO 2009 / 037316 relates to a similar process. This document exemplifies use of methyl ethyl ketone as the solvent, iso-hexane as the phase separating agent and PVC as the plastic, and uses steam and liquid water to heat and cause vaporisation of the phase separating agent and solvent (referred to in this document as a “polar aprotic organic solvent” or “PAOS”). This document further teaches the addition of an alcohol, such as isopropanol, to the system. This document discusses that sufficient steam and water must be introduced to remove substantially all of the phase separating agent (PSA) and solvent (PAOS). Whilst the above processes are effective for dissolution and precipitation of the plastic, specifically PVC, they suffer from requiring a significant quantity of steam and hot liquid water which must be introduced to remove all of the PSA and solvent / PAOS.

[0007] Further, whilst the solution obtained after dissolution of the polymer in the solvent may be filtered or similarly treated to separate insolubles, many polymer materials, particularly PVC materials, comprise plasticisers and / or other liquid additives which are also soluble in the solvent. These additives are then reprecipitated with the polymer and hence remain in the recovered polymer material. A number of such additives used historically have been subsequently subject to restrictions on their use. For example, plasticisers such as di (2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP) and benzyl butyl phthalate (BBP), which were historically used in PVC are now subject to restrictions on their use in “new” PVC but also their presence in recycled PVC. Thus, it is also desirable to separate such additives in any recycling process.

[0008] We have now found a process which is both more efficient from an energy use perspective, and also effective at separating the polymer from plasticisers and other soluble liquid additives.

[0009] Thus, in a first aspect, there is provided a process comprising:

[0010] (a) providing a solution comprising a polymer dissolved in a solvent mixture comprising water, a polar aprotic organic solvent (PAOS) and an organic phase separation agent (PSA),

[0011] (b) removing at least some of the PSA from the solution to cause precipitation of the polymer and provide a slurry of polymer particles in a liquid phase comprising water and the PAOS,

[0012] (c) performing a solid-liquid separation on the slurry to separate the majority of the PAOS and water present in the slurry, to provide polymer particles comprising residual PAOS and water, and

[0013] (d) treating the polymer particles comprising residual PAOS and water to remove the residual PAOS and water and recovering the polymer particles.

[0014] The present invention relates generally to recycling of polymers. In particular, the solution of polymer in step (a) is typically obtained by dissolving a polymer to be recycled, or a composition or mixture comprising a polymer to be recycled, in the solvent mixture. The polymer to be recycled may initially be mixed with or comprise insoluble components, the nature of which will depend on the previous application of the polymer. Examples can include, for example, fibres and fillers. In such cases the solution obtained by dissolving the polymer in the solvent mixture may be filtered to remove insoluble components prior to step (a) of the present invention. Such dissolution and filtration may be performed by any conventional techniques. (An example of the dissolution and filtration of a PVC cable scrap comprising fillers is described in WO 2009 / 037316 for example.)

[0015] The present invention may be applied to any suitable polymer. A number of suitable polymers are described, for example, in WO 2009 / 037316, and include polymers of ethylene (PE) or of propylene (PP), polymers derived from styrene monomers, acrylic monomers and halogenated ethylenically unsaturated monomers or copolymers of ethylene and vinyl alcohol (EVOH) or vinyl acetate (EVA, EBA, etc.). Preferably, however, the present invention is directed to recycling of PVC, and the polymer is therefore a PVC polymer, or to polymers which have a solubility parameter close to that of PVC (such as PMMA (polymethyl methacrylate), PVA (polyvinyl alcohol) and PUR (polyurethane)). The term "close" is understood to define solubility parameters (expressed in MPa1 / 2) that do not generally differ from one another by more than around 1.8.

[0016] Preferably the polymer is PVC. The PVC may be a homopolymer or a copolymer, for example with vinyl acetate or an alkyl (meth)acrylate as comonomer.

[0017] The present invention is based on the surprising finding that the polymer initially present in the solution of step (a) can be largely or completely precipitated by removal of the phase separating agent (PSA) even if the majority of the PAOS is still present.

[0018] Without wishing to be bound by theory, the solvent mixture for the dissolution comprises water, the PAOS and the PSA. The polymer is soluble in the PAOS “alone”, but its solubility is decreased by the presence of water. Thus, at significant levels of water (above about 10wt%) in a mixture which comprises just the water and PAOS, the polymer is largely insoluble. In contrast, in the presence of the PSA, the water content in the organic phase is reduced, and hence in a solvent mixture comprising PAOS, PSA and water the solubility of the polymer is increased. Thus, in an initial solvent mixture comprising PAOS, PSA and water the polymer is soluble. When the PSA is removed from this mixture the polymer is caused to precipitate.

[0019] Preferably the removal of the PSA is achieved by addition of further water, either by addition of liquid water or steam or a combination thereof. Addition of water at least partially via addition of steam is preferred. This has the dual advantage of providing heat for stripping of the PSA but also increasing the water content of the remaining solution / liquid phase, which assists in further precipitation of the polymer material.

[0020] Typically, the solvent mixture in step (a), which is usually the solvent mixture used to dissolve the polymer in an earlier step, comprises less than 10% by weight, and preferably less than 6% by weight of water. The major component of the solvent mixture is PAOS typically found in a weight ratio, relative to the PSA of 4: 1 to 8: 1. The solvent mixture may, and preferably does, also comprise an alcohol, such as described in WO 2009 / 037316.

[0021] Preferred PAOS, PSA and, where present, alcohol, are as described in US 7056956 and WO 2009 / 037316 already noted. As noted in WO 2009 / 037316 in particular, suitably: the PAOS is a compound which forms an azeotrope with water; the PSA is an apolar organic compound that is miscible with the PAOS and immiscible with water; the boiling point of the PSA is below that of the water / PAOS azeotrope.

[0022] Preferred PAOS’s include, dimethyl sulphoxide (DMSO), tetrahydrofuran (THF) and substituted tetrahydrofurans, such as 2-methyltetrahydrofuran (2Me-THF) and ketones. Particularly preferred are ketones, such as diethylketone (DEK) or, most preferably, methylethylketone (MEK).

[0023] Preferred PSA’s are alkanes having 5 to 7 carbons atoms, more preferably hexanes, such as n-hexane and iso-hexane, and with iso-hexane being most preferred.

[0024] Preferred alcohols are tert-butyl alcohol (2-methyl-2-propanol) and iso-propanol, with iso-propanol being most preferred.

[0025] A preferred solvent mixture for the solution of step (a) is a mixture of a ketone (as the PAOS), an alkane (as the PSA), an alcohol and water, for example a mixture of methyl ethyl ketone (MEK) with hexane, iso-propanol and water. A particularly solvent mixture in the solution of step (a) comprises, and preferably consists essentially of, between 2% and 8% by weight of alcohol, preferably iso-propanol, between 13% and 17% by weight of alkane, preferably iso-hexane, between 3% and 6% by weight of water, and between 69% and 82% by weight of a ketone, preferably methyl ethyl ketone.

[0026] The solution of step (a) is typically, and preferably, a solution obtained by an earlier step of dissolution of the polymer in the solvent mixture. The solution may have been treated, after dissolution of the polymer, to separate the solution from insoluble components of the initial polymer material to be recycled. It may also have been treated to remove heavy metals, if present, for example using chelating agents.

[0027] The concentration of polymer in the solution of step (a) is typically at least 5wt%, such as 5 to 20wt%. Concentrations in the range 8 to 14wt%, are preferred.

[0028] The dissolution may have been performed at an elevated pressure. Where this is the case then the solution obtained in step (a) may also be at elevated pressure, such as from 200 to 500 kPag (2 to 5 barg).

[0029] In step (b) of the present invention at least some of the PSA is removed from the solution to cause precipitation of the polymer and provide a slurry of polymer particles in a liquid phase comprising water and the PAOS.

[0030] Where the solution is initially at elevated pressure, removal of the PSA may be achieved, at least in part, by reducing the pressure of the solution. Removal of the PSA may be obtained by heating of the solution, for example by injection of hot water or steam. It is most preferred that step (b) includes the addition of further water (i.e. further to that already present), in the form of either liquid water or steam, or both. (This may be done in addition to a pressure reduction.) As already noted this has the dual advantage of providing heat for stripping of the PSA but also increasing the water content of the remaining slurry, which assists in further precipitation of the polymer material.

[0031] Optionally a dispersing agent, such as a partially hydrolysed polyvinyl acetate (PVA), may be present during this step, either by addition during this step, or by addition to the solution of step (a) prior to this step.

[0032] In step (b) the majority of the PSA should be removed from the solution as provided in step (a). Typically, at least 80% by weight of the PSA which is present in the solution provided in step (a) should be removed in this step, preferably at least 90% by weight, such as 95-100% by weight.

[0033] In contrast, whilst some PAOS may be removed, generally the majority of the PAOS should not be removed in this step. Thus, typically the slurry obtained in step (b) comprises at least 70% by weight of the PAOS which was in the solution provided in step (a), preferably at least 80% by weight, such as at least 90% by weight. In one embodiment, the slurry obtained in step (b) and treated in step (c) comprises less than 20%, preferably less than 10%, of the PSA which was present in the solution of step (a) and at least 80% of the PAOS which was in the solution of step (a).

[0034] In absolute terms, the slurry liquid phase obtained in step (b), including additional water where added, typically comprises at least 10wt% water, such as 10-40wt% water, for example 10-25wt% water. The slurry liquid phase preferably comprises at least 55%, such as at least 65% by weight of PAOS. In preferred embodiments, where an alcohol is also present, the slurry liquid phase preferably comprises 2% and 10% by weight of alcohol, preferably iso-propanol, between 10% and 40%, such as between 10% and 25%, by weight of water, and between 55% and 85%, such as between 65% and 88%, by weight of PAOS, preferably a ketone, and more preferably methyl ethyl ketone. Residual amounts of the PSA may be present, but the concentration of PSA is generally less than 2.5wt%, such as in the range 0 to 2.5wt%, and more preferably 0 to 1.5wt%.

[0035] For avoidance of doubt it should be noted that the slurry liquid phase obtained may in fact comprise two phases, one being an aqueous phase and the other being an organic phase.

[0036] The above numbers relate to the total liquids present, and more generally, unless clearly otherwise the case, reference to the slurry liquid phase as used herein refers to the total liquids present.

[0037] The removal of PS A in step (b) causes precipitation of the polymer and provides a slurry of polymer particles in a liquid phase comprising the water and the PAOS, and typically also comprising an alcohol.

[0038] The precipitated polymer is in the form of polymer particles containing residual PAOS and water. In particular, typically the polymer particles comprise absorbed PAOS and water, and may be considered as solvent “swollen”.

[0039] In known processes, steam and / or water addition is performed to remove all solvent and leave particles in an aqueous phase. In the present invention, and in particular in step (c) of the present invention, the slurry is instead treated at this stage by performing a solidliquid separation on the slurry. The solid-liquid separation separates the majority of the PAOS and water present in the slurry, to provide polymer particles comprising residual PAOS and water. (For avoidance of doubt, although we will describe the separation and subsequent treatment in relation to separation of PAOS and water as a liquid phase and also to residual PAOS and water associated with the solid particles, there may also be present alcohol in both (i.e. alcohol in the liquid phase separated and “residual alcohol” with the polymer particles) if alcohol is present in the solvent mixture used, and there may also be traces of the PSA in both if this is not completely removed in step (b).)

[0040] In embodiments the solid-liquid separation separates the majority of the PAOS and water but sufficient of the slurry liquid phase is retained such that the polymer particles comprising residual PAOS and water provided after the solid-liquid separation are still in the form of a concentrated slurry. The concentrated slurry may have a solids concentration, for example, of at least 40wt%, such as at least 50wt% solids by weight of the slurry.

[0041] In other embodiments the solid-liquid separation separates the vast majority of the PAOS and water, such as at least 90% by weight, preferably at least 95% by weight of the PAOS and water initially present in the slurry liquid phase. In particular, sufficient PAOS and water are removed in the solid-liquid separation such that the polymer particles comprising residual PAOS and water provided after the solid-liquid separation are in solids form. (They may be considered as “wet” in the sense that there is residual PAOS and water absorbed in or on the particles, but the polymer particles are no longer in sufficient liquid to form a slurry).

[0042] Preferably, in either embodiment, the “residual PAOS and water” comprises less than 10% by weight, preferably less than 5% by weight relative to the amount of PAOS and water initially present in the slurry liquid phase.

[0043] This solid-liquid separation may be performed by any known solid-liquid separation means for separating solids (in this case the polymer particles or a concentrated slurry thereof) from a liquid phase. Examples include settling, centrifuging (spinning), filtering, etc. One preferred solid-liquid separation comprises filtering. This may be any conventional filter, including, for example, a rotary pressure filter, Nutsche filter, Candle filter, etc. A further preferred solid-liquid separation comprises centrifuging by use of a centrifuge, such as a decanter centrifuge. Examples of suitable decanter centrifuges are those produced by Tomoe Engineering Co. Limited, Andritz Separation and GEA.

[0044] For avoidance of doubt, by “solid-liquid separation” is meant a process in which the solids are separated from a liquid phase whilst keeping the liquid phase in a liquid form. Thus, the PAOS and water separated in the solid-liquid separation are separated in a liquid form. Nevertheless, depending on the solid-liquid separation technique used and / or how it is applied there may be obtained a single liquid phase product or two or more separate liquid phase products from this step e.g. an aqueous phase product and an organic phase product. (A decanter centrifuge, for example, can be operated to separate two or more liquid phases of differing densities.)

[0045] In step (d) of the present invention the separated polymer particles are treated to remove the residual PAOS and water, and thereby to recover the polymer particles. Whether the solid-liquid separation provides polymer particles which are still in the form of a concentrated slurry or provides polymer particles which are in solids form, it is generally preferred that the polymer particles are mixed with water prior to step (d) of the present invention, to provide a slurry comprising polymer particles in an aqueous phase. The obtained slurry preferably has a solids concentration of at least 20wt%, such as 20- 35wt%. In one preferred embodiment this may be performed using a portion of the water which is initially separated in this step (c). This could be, for example, using an aqueous phase obtained where such a phase is separated directly by the solid-liquids separation or could be after separation of water from a liquid stream comprising both water and PAOS where such is initially obtained. For example, the PAOS and water are generally immiscible, so water / an aqueous phase could be separated by allowing the two phases to separate, such as in a decanter.

[0046] Typically the polymer particles will be heated, optionally using steam or hot water, to remove the residual PAOS and to provide a slurry of the polymer particles in water (with reduced level, and preferably the substantial absence of PAOS). The particles can then be separated from the water, again using any suitable separation means for separating a solid from a liquid phase, such as those already described, and then dried to remove residual water.

[0047] In embodiments, the polymer particles with residual PAOS and water may be first washed with a solvent wash stream. In one embodiment a “clean” mixture comprising the PAOS and water may be used as a solvent wash stream. In particular, the PAOS and water initially present may comprise small amounts of PSA or, as will be discussed below, plasticisers and / or other soluble liquid additives, and it may be desirable to wash with a “clean” solvent stream to separate these first. Several wash steps may be performed if desired. The obtained, “washed” particles can then be treated, for example heated with steam or hot water to remove any organic components of the solvent wash stream or streams and leave polymer particles in water which can be separated and dried as already described.

[0048] As already noted, the solid-liquid separation of step (c) of the present invention results in one or more liquid phase products comprising the majority of the PAOS and water which was present in the slurry. In preferred embodiments it is desirable to recover and recycle / reuse at least the PAOS.

[0049] Where there is obtained from step (c) a single liquid phase product comprising PAOS and water the liquid product is preferably treated to recover the PAOS or a mixture comprising PAOS and water but with a lower level of water. In this regard, the PAOS and water are generally immiscible and hence, if left to settle, form two phases, comprising an aqueous phase and an organic (PAOS) phase. Thus, the PAOS may be separated from the aqueous phase by decantation or similar. The separated PAOS may, if desired, be treated to further purify, for example by distillation or by drying to remove residual water.

[0050] Where there is obtained from step (c) two or more liquid phase products, then PAOS may be recovered from any products which comprise PAOS. Similar techniques to those noted above can be applied. For example, for liquid phase products which comprise PAOS and water they can be left to settle, and the PAOS may be separated from the aqueous phase by decantation or similar. Any product from such steps, or any products which are already essentially or largely PAOS as recovered, may, if desired, be treated to further purify, for example by distillation or drying as already noted.

[0051] However obtained, recovered PAOS can be used for dissolution of further polymer to form a further solution for step (a). All or part could also be used as part of a washing solvent stream in step (d) where this step is performed.

[0052] This slurry liquid phase may, as described further below, also comprise plasticisers and / or other soluble liquid additives which were present in the original polymer. During the solid-liquid separation these additives are separated with the liquid phase, and in particular with the organic (PAOS) phase. The PAOS may be treated to separate the plasticisers so that the PAOS can be recycled and reused in the present invention. Typically the separated plasticisers may comprise phthalate plasticisers but also other non-phthalate plasticisers. The separated plasticisers may be purified, e.g. by hydrogenation, so that they can be reused as plasticisers under EU REACH or similar regulations in other jurisdictions and / or other applications. As already noted, a particular advantage of the present invention is that it is more efficient from an energy use perspective, and in particular compared to the previously operated processes. As also already noted, in the previously operated processes it was necessary to provide sufficient steam and liquid water to remove not just the PSA present in the solution but also the PAOS. The latter, of course, not only typically having a higher boiling point (either per se or as an azeotrope with water) than the PSA, but also formed the major part by weight of the solution.

[0053] In the present invention the process requires a much lower “energy input”. In particular, to remove the PSA in step (b) of the present invention clearly requires much less energy input than removing all of the PSA and all of the PAOS (in the form of an azeotrope, so also a lot of water is both added and removed to remove the PAOS). The present invention does contemplate also providing some energy in other steps, but typically the energy requirements are much lower than savings made by not having to remove the PAOS using steam and liquid water. For example, the amount of energy, for example in the form of liquid water or steam, required to separate residual PAOS and water from the polymer particles in step (d) is much less than required compared to the previously operated process i.e. much less than the energy saved in step (b) by not having to remove all PAOS in that step. Similarly, the amount of energy required for treatment and recovery of PAOS separated in step (c) to make this suitable for recycle is generally relatively low because the PAOS can be readily separated from the majority of the water before it needs to be treated.

[0054] Where the removal of the PSA from the solution of step (b) comprises injection of steam into the solution then the amount of steam required for this is much less than required for the removal of the PSA and PAOS as noted above. In terms of the actual amount of steam required for this step, this generally depends on the amount of PS A it is necessary to remove. This can itself be dependent on the initial polymer mixture to be subject to recycling, and in particular on the amount of solvent necessary to dissolve the polymer.

[0055] Typically, however, where the removal of the PSA from the solution of step (b) comprises injection of steam into the solution, the amount of steam injected is less than 2 kg steam per kg of polymer present, such as less than 1.5 kg steam per kg of polymer present. In embodiments, the amount of steam injected is less than 1 kg steam per kg of polymer present. (This is particularly the case where the polymer is a PVC polymer and the PSA is an alkane having 5 to 7 carbons atoms, for example.)

[0056] Further, whilst dependent on the amounts of PSA and PAOS in the respective steps, most preferably, the total amount of steam for the removal of PSA from the solution in step (b) and treating the polymer particles to remove the residual PAOS and water in step (d) (i.e. the total for the steps in which evaporation of organic solvents by steam injection may be implemented) is less than or equal to 5 kg steam per kg of polymer, such as less than or equal to 4 kg steam per kg of polymer, or even less than or equal to 3 kg steam per kg of polymer. (This is particularly the case where the polymer is a PVC polymer, the PSA is an alkane having 5 to 7 carbons atoms and the PAOS is a ketone, for example.)

[0057] Thus, the present invention is much less energy intensive.

[0058] The recovered polymer particles from step (d) of the present invention are, in terms of particle size and shape, generally the same or similar to that obtained by the known process. Typically, the particles are relatively uniform in size. Typically the D50 may be from 100 to 250 pm, and the particles may have a SPAN ((D90-D10) / D50)) of less than 1. (D10, D50 and D90 may be measured by known methods, such as ASTM D1921-18.)

[0059] However, the particles can differ in composition of those obtained from the known process.

[0060] In particular, a yet further advantage of the present invention arises where the polymer to be recycled comprises plasticisers and / or other soluble liquid additives. For example, flexible PVC generally comprises significant quantities of plasticisers. Rigid PVC generally does not comprise plasticisers but may comprise other soluble liquid additives, such as stabilisers, phosphite ester or soybean oil.

[0061] As already noted, any insoluble components present in the initial polymer material to be recycled are generally separated before the solution of step (a) is provided. Plasticisers and / or other soluble liquid additives may nevertheless be present as dissolved species in the solution of step (a). In the present invention removal of at least some of the PSA from the solution in step (b) causes precipitation of the polymer to provide a slurry of polymer particles, water and the PAOS. It has been found that in this step a portion of the plasticisers and other soluble liquid additives stay dissolved in the slurry liquid phase. Thus, a portion of the plasticisers and other soluble liquid additives initially present are found in the liquid phase product or products separated in the solid-liquid separation of step (c) of the present invention.

[0062] Thus, the present invention also effectively and efficiently separates the polymer particles from at least a portion of plasticisers and / or other soluble liquid additives which are present.

[0063] It can be noted that where the initial polymer comprises plasticisers and / or other soluble liquid additives then residual quantities of the plasticisers and / or other soluble liquid additives may be found in the residual PAOS and water of the separated polymer particles. Typically, the polymer particles comprising residual PAOS and water which are separated in step (c), before any subsequent treatment if performed, comprise less than 60% weight, such as less than 50% by weight or less than 40% by weight, of any plasticisers and / or soluble liquid additives which were present in the solution of step (a).

[0064] The amounts of plasticisers and / or other soluble liquid additives in the separated polymer particles are generally much lower than those initially present in the polymer being recycled, and may be acceptable. In cases where complete or further removal of plasticisers and / or other soluble liquid additives is desired then the polymer particles may be subjected to a washing step or steps as already noted to remove further plasticisers and / or soluble liquid additives.

[0065] This is a further significant advantage of the present invention. In particular, in the previously operated processes, the removal of the PAOS resulted in precipitation also of any plasticisers and / or other soluble liquid additives, and hence did not separate these additives. Additional steps would therefore need to be applied in such processes, whereas the present invention “inherently” separates significant quantities of these additives from the polymer.

[0066] As noted previously, the present invention is preferably applied to a PVC polymer. The following paragraphs apply to such embodiments, and in particular to the preparation of the solution of step (a).

[0067] In such embodiments the PVC may comprise PVC recycled from any suitable source. It may, for example, comprise PVC which has been physically separated from household or industrial waste. Preferably the PVC is obtained by recycling of PVC previously used for a particular application. For example, PVC is commonly used for window frames and profiles, and the PVC may therefore be or be derived from waste PVC window profiles. Another common use of PVC is in wire and cable applications. Thus, the PVC may be waste wire and cable or derived from waste wire and cable, for example by separating the PVC from the metal wire. Other sources of the PVC include membranes, tarpaulins, textiles and other coated fabrics, PVC flooring, vinyl wallpaper, flexible hoses and numerous automotive applications.

[0068] By using a PVC previously used for a particular application, generally speaking the PVC and any additives present will be of a consistent and similar type. Most usefully, however, this means that the resulting purified PVC polymer particles will also then be generally suitable for reuse in the same application or in other specific applications which require similar PVC properties.

[0069] Typically, the PVC prior to the dissolution in the solvent mixture is in the form of lumps, strips, flakes or chips, for example obtained by grinding, shredding, cutting or chopping of larger forms of product. An example would be, for example, cut window profiles or PVC cable. The PVC in this mixture, and typically the mixture as a whole, more usually has an average particle size in the range of several millimetres to tens of millimetres, for example 5 to 80mm, with particle sizes of 5 to 25mm most usual.

[0070] Non-PVC components, which as defined herein refers to components which are other than those typically found in a PVC composition, may be present. Non-PVC components may, for example, comprise polyolefins and polymers other than PVC or polyolefins. These may be present, for example, because the PVC was used in an application with another polymer or may be present as “contaminants” from the PVC collection and sorting process.

[0071] In preferred embodiments the PVC is relatively “pure” of components other than those typically found in a PVC composition i.e. other than PVC resin and PVC additives which were originally added to the PVC resin for its intended use. The PVC polymer prior to dissolution may have been, and preferably has been, obtained after treatment of an initial mixture comprising the PVC and other components, for example a mixed polymer stream or a stream comprising PVC and metals, such as copper, obtained from wire and cable scrap, to remove such components or any other foreign contaminant.

[0072] The dissolution of the PVC in the solvent mixture (to provide a solution for step (a) of the present invention) may be performed at any suitable temperature and pressure. Typically an elevated temperature, such as a temperature in the range 90 to 120°C is preferred. Whilst ambient pressure can be used, elevated pressure is generally used at temperatures above the boiling point of the solvent mixture. Typically stirring is applied to assist in the dissolution step.

[0073] The present invention may be illustrated by the following Examples: Comparative Example A

[0074] This Comparative Example describes the recycling of a cushion vinyl flooring waste according to methods known in the prior art. The flooring waste is composed of 42.1% of PVC polymer resin, 21.8% of liquid additives, including phthalate plasticizers, and 36.1% of solid additives or insoluble components, including mineral fillers, metal stabilizers and glass fibers.

[0075] 600g of the flooring waste is dissolved in 2.5 kg of solvent composed of 76.2% of methyl ethyl ketone (MEK) as PAOS, 4.4% of water, 15.3% of iso-hexane, as PSA, and 4.1% of iso-propanol. The dissolution is carried out at 100°C and 3 barg during 30 minutes under agitation. The PVC solution obtained is mixed with a chelating agent in order to improve extraction of insoluble components, and the insoluble components then separated from the PVC solution by combining filtration using a Nutsche filter and centrifugation at 2000 G and 55°C during 225 seconds.

[0076] The obtained clarified PVC solution, comprising the dissolved PVC polymer resin and also dissolved plasticizer components of the original flooring waste, is then transferred to a precipitation vessel along with a partially hydrolyzed polyvinyl alcohol (72% hydrolyzed) as dispersing agent.

[0077] 1.2 kg of an aqueous phase, composed of water saturated with MEK, and 1 kg of demineralized water are added in the vessel. The initial temperature is 40-45°C. The operating pressure is reduced to 600 mbar(a), inducing a first partial removal of the isohexane by flash. Steam is then injected to heat the mixture and cause evaporation of the organic solvent. Precipitation of PVC polymer grains is observed when the temperature reaches 51 °C and steam injection is continued until all the organic solvent is evaporated and precipitated PVC polymer grains are obtained in suspension in water. The stripping of the organic solvent requires a total of 1.5 kg of steam, corresponding to 5.9 kg of steam per kg of the PVC polymer resin.

[0078] During the stripping PVC grains are precipitated together with the plasticizers initially in the flooring application. The PVC grains are separated from the water and dried. The total content of plasticizers in the PVC grains is 34,2% in weight i.e. corresponding to all the plasticisers original present.

[0079] Example 1

[0080] The initial stages of the process of Comparative Example 1 are repeated to obtain the clarified PVC solution comprising the PVC polymer resin and plasticizer components of the original flooring waste dissolved in the solvent.

[0081] This solution is then transferred to a precipitation vessel along with a partially hydrolyzed polyvinyl alcohol (72% hydrolyzed) as dispersing agent and 1.2 kg of an aqueous phase, composed of water saturated with MEK is added.

[0082] The initial temperature is 40-45°C. The operating pressure is reduced to 600 mbar(a), inducing a first partial removal of the iso-hexane by flash. Sufficient team is then injected to heat the mixture to 55°C. At this temperature, the residual content of iso-hexane in the organic phase is around 2%, corresponding to a removal of approximately 99% of the initial iso-hexane solvent by flash and steam stripping. The required steam consumption to reach this temperature is around 280 g, corresponding to 1.1 kg of steam per kg of the PVC polymer resin.

[0083] There is obtained a suspension of PVC polymer grains in a mixture of two phases: an aqueous phase and an organic phase. The aqueous phase comprises predominantly water saturated with MEK, but also some iso-propanol. The organic phase comprises predominantly MEK, but also comprises iso-hexane, iso-propanol and water. The organic phase also contains a portion of the plasticizers initially present in the flooring waste, solubilized in the organic phase.

[0084] The suspension is centrifuged at 2000 G during 225 seconds, resulting in three distinct phases - an aqueous phase, an organic phase and an intermediate phase comprising the PVC polymer grains, swollen by residual presence of solvent. The organic phase and a part of the aqueous phase are separated by decantation and the intermediate phase mixed with the remaining aqueous phase to obtain PVC polymer grains in a slurry in the aqueous phase.

[0085] The slurry is agitated and pressure is reduced at 600 mbar(a). Steam is injected to evaporate residual MEK and any other remaining organic components of the solvent. The required steam consumption will depend on the amount of aqueous phase in the vessel, but about 850g steam is required in this Example, leading to an overall steam consumption of 1.13 kg of steam, corresponding to approximately 4.5 kg of steam per kg of the PVC polymer resin. This is a reduction of total steam consumption compared to the Comparative Example.

[0086] The PVC polymer grains are separated from the water and dried in an oven at 80°C during 6 hours. The total content of plasticizers in the PVC polymer grains obtained is 18.47% in weight showing that 46% of the plasticizers initially in the flooring waste are separated from the PVC in this Example.

[0087] The final PVC polymer grains have a D10 of l31 pm, D50 of 173 pm and D90 of 237 pm.

[0088] Example 2

[0089] Example 1 is repeated except that the PVC polymer grains obtained after centrifugation and decantation of the organic phase and part of the aqueous phase are, prior to steam stripping, contacted with an organic solvent to remove further plasticisers. More specifically the organic solvent is composed of 83% MEK, 10.7% water, 4.3% isopropanol and 2% iso-hexane, and is obtained from the organic phase separated by the decantation after treatment to remove plasticisers. Contacting is performed 3 times for 10 minutes each time and at 55°C, with the weight ratio solvent / PVC for each of the 3 steps around 7.

[0090] The obtained PVC polymer grains are mixed with a portion of the aqueous phase to form a slurry which is then reduced in pressure and steam is injected to evaporate residual MEK and any other remaining organic components of the solvent as in Example 1. However, by performing the additional solvent contacting steps the residual content of plasticizers in the PVC polymer grains is reduced to below 1% in weight.

[0091] Example 3

[0092] Example 3 is largely the same as Example 2 except as indicated herein. In this Example the initial feedstock used is a cable waste, composed of 28.4% of PVC polymer resin, 18.6% of liquid additives, including phthalate plasticizers and among others DEHP, and 53% of insoluble components, including rubber, polyolefins, mineral fillers such as CaCO3 and metal stabilizers such as Pb.

[0093] 750g of the cable waste is dissolved in 2.5 kg of solvent composed of 76.2% of MEK, 4.4% of water, 15.3% of iso-hexane and 4.1% of iso-propanol at 100°C and 3 barg during 30 minutes under agitation. The PVC containing solution obtained is mixed with a chelating agent in order extract heavy metals and insoluble components, which are separated from the solution by combining filtration using a Nutsche filter and centrifugation as previously.

[0094] Partially hydrolyzed polyvinyl alcohol and 1.2 kg of aqueous phase are added and the pressure reduced and steam injected until the temperature reaches 55°C. The required steam consumption to reach this temperature is around 220 g. The required steam consumption to reach this temperature is around 300 g, corresponding to 1.0 kg of steam per kg of the PVC polymer resin.

[0095] The PVC polymer grains obtained after decantation are contacted 3 times at 55°C with an organic solvent as before except that the solvent / PVC ratio is 5.

[0096] The obtained PVC polymer grains are mixed with a portion of the aqueous phase to form a slurry which is then reduced in pressure and steam is injected to evaporate residual MEK and any other remaining organic components of the solvent as in Examples 1 and 2. 860g steam is required in this step, corresponding to approximately 4.0 kg of steam per kg of the PVC polymer resin.

[0097] The total residual content of plasticizers in the PVC grains obtained was 2.85% by weight. (Further reduction could be obtained by increasing the number of contacting steps or increasing the solvent-to-PVC ratio if required.)

Claims

Claims1. A process compri sing :(a) providing a solution comprising a polymer dissolved in a solvent mixture comprising water, a polar aprotic organic solvent (PAOS) and an organic phase separation agent (PSA),(b) removing at least some of the PSA from the solution to cause precipitation of the polymer and provide a slurry of polymer particles in a liquid phase comprising water and the PAOS,(c) performing a solid-liquid separation on the slurry to separate the majority of the PAOS and water present in the slurry, to provide polymer particles comprising residual PAOS and water, and(d) treating the polymer particles comprising residual PAOS and water to remove the residual PAOS and water and recovering the polymer particles.

2. A process according to claim 1 wherein the slurry obtained in step (b) and treated in step (c) comprises less than 20% of the PSA which was present in the solution of step (a) and at least 80% of the PAOS which was in the solution of step (a).

3. A process according to claim 1 or claim 2 wherein the polymer is a PVC polymer.

4. A process according to any one of the preceding claims wherein the solvent mixture in step (a) comprises less than 10% by weight, and preferably less than 6% by weight of water.

5. A process according to any one of the preceding claims wherein the PAOS is a ketone, and most preferably, methylethylketone (MEK).

6. A process according to any one of the preceding claims wherein the PSA is an alkane having 5 to 7 carbons atoms, with iso-hexane being most preferred.

7. A process according to any one of the preceding claims wherein the solution further comprises an alcohol, and most preferably isopropanol.

8. A process according to any one of the preceding claims wherein the solvent mixture in the solution of step (a) comprises between 2% and 8% by weight of alcohol, preferably iso-propanol, between 13% and 17% of alkane, preferably isohexane, between 3% and 6% of water, and between 69% and 82% of ketone, preferably methyl ethyl ketone.

9. A process according to any one of the preceding claims wherein in step (b) at least some of the removal of the PSA is achieved by addition of further water (i.e. further to that already present), in the form of either liquid water or steam, or both.

10. A process according to any one of the preceding claims wherein the slurry liquid phase obtained in step (b) comprises at least 10wt% water, such as 10-25wt% water.

11. A process according to claim 10 wherein the slurry liquid phase comprises 2% and 10% by weight of alcohol, preferably iso-propanol, between 10% and 25% by weight of water, and between 65% and 88% by weight of PAOS, preferably a ketone, and more preferably methyl ethyl ketone.

12. A process according to any one of the preceding claims wherein the separation of step (c) comprises use of a filter, such as a rotary pressure filter, Nutsche filter, Candle filter, etc. and / or a centrifuge, such as a decanter centrifuge.

13. A process according to any one of the preceding claims wherein the solvent mixture comprising the PAOS and water which is obtained in step (c) is treated to recover the PAOS or a mixture comprising PAOS and water but with a lower level of water, and all or part of this separated PAOS stream is recycled.

14. A process according to claim 13 wherein the solution in step (a) also comprises plasticisers and / or other soluble liquid additives which were present in the original polymer, at least a portion of which are separated with the PAOS separated in step (c), and the separated PAOS is treated to remove these before recycle.

15. A process according to any one of the preceding claims wherein the removal of the PSA from the solution of step (b) comprises injection of steam into the solution, the amount of steam injected is less than 1.5 kg steam per kg of polymer present.