WO2025120154A1

WO2025120154A1 - Process for purifying pvc

Info

Publication number: WO2025120154A1
Application number: PCT/EP2024/085069
Authority: WO
Inventors: Eric Romers; Corentin Dubois; Loris PANARISI; Florent MINETTE; Jean-Christophe Lepers; Jean-Philippe Dumont
Original assignee: Inovyn Europe Ltd
Current assignee: Inovyn Europe Ltd
Priority date: 2023-12-07
Filing date: 2024-12-06
Publication date: 2025-06-12
Anticipated expiration: 2026-06-07

Abstract

The present invention relates to a process for providing a puriﬁed polyvinyl chloride (PVC) polymer, and in particular with eﬃcient removal of plasticiser additives. In particular, there is provided a process for obtaining puriﬁed PVC polymer solids, the process comprising: (i) Providing a PVC composition, said PVC composition comprising PVC resin and one of more plasticisers, and said composition being provided in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7, (ii) Contacting the PVC composition with a solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble to form a slurry, said slurry comprising PVC polymer solids and dissolved plasticiser, and (iii) Separating the PVC polymer solids to obtain puriﬁed PVC polymer solids.

Description

Process

The present invention relates to a process for providing a purified polyvinyl chloride (PVC) polymer, and in particular with efficient removal of plasticiser additives.

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 such as lead and cadmium, and plasticisers such as di (2-ethylhexyl) phthalate (DEHP), dibutyl phthalate (DBP), diisobutyl phthalate (DIBP) 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.

One known commercial process for recycling of PVC was the VinyLoop® technology operated in Ferrara / Italy between 2002 and 2018. Operations were stopped in 2018, however, as the technology was not developed to remove phthalate plasticisers to meet the requirements EU REACH legislation. (In particular, the sum of DEHP, DBP, DIBP and BBP must be below lOOOppm to meet the REACH requirements.)

It is known that phthalates and other plasticisers can be removed by solid-liquid extraction by contacting solid PVC particles with a solvent in which the plasticisers is soluble but the PVC is not. WO 2022/243042, for example, discloses the use of an alcohol as solvent and transesterification to remove phthalates from a PVC filler, optionally in the presence of a co-solvent. A similar process is described also in WO 2022/243043 which uses a solvent comprising at least one chemical molecule of the ester, ether, ketal or acetal type and of a defined formula.

Other processes, such as that described in US 4038219, involve the dissolution of both PVC and plasticisers, and then the selective precipitation of the PVC.

A problem associated with many of the previous studies is that the extraction tests are often performed on "model" or relatively simple mixtures of PVC and plasticisers. In practise, PVC is often contaminated with other impurities and/or of a particle size and shape which are not amenable to extraction of the plasticisers to low levels.

It has now been found that efficient extraction of plasticisers from PVC can be performed by extraction using a suitable solvent by ensuring that the PVC particles are relatively small and also of relatively uniform shape. Thus, in a first aspect, there is provided a process for obtaining purified PVC polymer solids, the process comprising:

(i) Providing a PVC composition, said PVC composition comprising PVC resin and one or more plasticisers, and said composition being provided in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7,

(ii) Contacting the PVC composition with a solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble to form a slurry, said slurry comprising PVC polymer solids and dissolved plasticiser, and

(iii) Separating the PVC polymer solids to obtain purified PVC polymer solids.

The present invention relates to a process for obtaining purified PVC polymer solids.

In the art, and as used herein, a pure PVC is generally referred to as "PVC resin". Typically PVC resins are not used in their pure form, however, but mixed with a variety of additives. These additives, as well as the (base) PVC resin, are generally selected based on the application for which the PVC is to be used, but common additives include plasticisers, mineral fillers and thermal stabilisers. The formulated mixture of PVC resin and additives is typically referred to as a "PVC compound" or "PVC composition". In the present invention we use the term "PVC composition" to refer to such a mixture of PVC resin and additives, but where the additives include one or more plasticisers. (For example, and although the specific values vary with the intended application, a typical PVC composition for a flexible application (such as artificial leather, cable or flooring applications) may have 20-50% plasticisers (all or some of which may be phthalates) as well as significant quantities of other additives, such as fillers, in addition to the PVC resin component.)

After removal of one or more plasticisers from the PVC composition in the present invention there may be left a pure or substantially pure PVC resin, but more typically there will be left a mixture of PVC resin and at least some additives other than plasticisers which were present in the original PVC composition. To distinguish such from a "PVC composition" in the present invention we will use the term "PVC polymer" to refer to the product obtained after removal of plasticisers from the PVC composition. As noted, this may in theory be a PVC resin (if no additives are present in the PVC composition other than plasticisers and all plasticisers are removed), but more usually the "PVC polymer" obtained will be a mixture comprising PVC resin and additives other than plasticisers.

More specifically, in the process of the present invention, the PVC composition is contacted with a solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble, and the PVC composition to be contacted with the solvent is provided in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7.

The particles are, thus, both relatively small and also of uniform shape.

Without wishing to be bound by theory it is believed that the relatively small particle size and uniform shape enables the solvent to extract plasticisers efficiently from throughout the particles of the PVC composition, allowing PVC polymer solids with low levels of residual plasticisers to be efficiently obtained.

Typically the PVC composition is in the form of particles having a D50 of at least 50 microns, such as at least 100 microns. The D50 is preferably less than 500 microns, with a D50 in the range of from 250 to 450 microns being most preferred.

It is also preferred that few, if any, very large particles are present. Typically, the D90 is less than 800 microns and/or the D95 is less than 1000 microns.

As used herein D50, D90 and D95 refer to the points on the particle size distribution curve below which 50%, 90% and 95% respectively by number of the particles are found. Particle size distribution may be determined by a suitable measuring device or sieves, for example according to ASTM D1921- 18 "Standard Test Methods for Particle Size (Sieve Analysis) of Plastic Materials".

In terms of sphericity, the sphericity of a particle is a measure of how closely the shape of the particle resembles that of a perfect sphere. For the purposes of the present invention, the sphericity is defined as the median aspect ratio ("S50 aspect ratio"), where the aspect ratio of a particle is the ratio of the minimum FERET diameter (d^Fmin) to the maximum FERET diameter (d^Fmax). A FERET diameter is a measure of the distance between two parallel tangents located on opposite sides of a cross-section of a particle. For a sphere the value is 1 since the diameter is the same in all orientations. For a non-spherical particle/cross-section the FERET diameter varies with the orientation of the tangents. The maximum FERET diameter is the largest possible measurement and the minimum FERET diameter is the smallest possible measurement. This is illustrated for an example particle shape in Figure 1.

The sphericity in the present invention is defined as the median or S50 aspect ratio, and is the value obtained by plotting a cumulative curve of number of particles versus aspect ratio, and determining the aspect ratio of the median particle. The sphericity may be determined from particle cross-sections by analysis of an image, such as a photo, of a representative selection of the particles, for example 200 to 1000 particles, using commercially available software.

Usually, the measurement of the particle shape and calculation of the sphericity are performed by commercially available analysers designed for such purposes. These may include taking images and using suitable software or using techniques such as laser diffraction for the analysis. An example of a suitable system would include the Sympatec QICPIC analyser and its associated software.

The PVC composition is preferably in the form of particles having a sphericity of at least 0.72, such as at least 0.75 or at least 0.80. The sphericity is generally less than 1 (rather than 1), for example in the range 0.75 to 0.95.

PVC composition particles of the required D50 and sphericity are suitably, and preferably, formed by precipitation of the PVC composition from a solution in a solvent or mixture of solvents capable of dissolving the PVC resin and plasticisers. Examples of suitable solvents include hydrocarbons, such as ketones, and in particular methyl ethyl ketone.

A preferred solution comprises a mixture of solvents, such as a mixture of a ketone, an alcohol and an alkane, for example a mixture of methyl ethyl ketone (MEK) with hexane and isopropanol. A particularly preferred solution comprises between 2% and 8% by weight of alcohol, preferably isopropanol, between 13% and 17% of alkane, preferably isohexane, between 4% and 6% of water, and the remainder (namely between 69% and 79% by weight) being a ketone, preferably methyl ethyl ketone.

In a preferred embodiment, precipitation can be obtained by injection of steam into the solution of the PVC to precipitate the PVC and remove the solvent. For example, in the preferred mixture of solvents the alkane may be removed via stripping, the ketone via azeotropic evaporation (ketone/water) and the isopropanol via evaporation. The removal of the solvent gives rise to the precipitation of the PVC resin and plasticisers.

(For avoidance of doubt, other additives present in the original PVC composition of step (i) which were soluble may also be precipitated in this step.)

The solids can then be recovered from the remaining solution, for example by filtration, and drying, to provide the PVC composition for step (i) of the present invention.

A particularly preferred process for the precipitation to prepare PVC composition particles of the required D50 and sphericity is the process for recovery of a polymer described in WO 2009/037316. In particular, the process preferably comprises injection of steam, and optionally liquid water (which itself may be in the form of an aqueous phase containing solvent, such as a ketone, recovered from an earlier precipitation step), into a solution of PVC resin and plasticisers. As described in WO 2009/037316, the solution comprises a polar aprotic organic solvent (PAOS) that has an azeotrope with water (such as the herein preferred ketone), a polar organic compound that is miscible with the PAOS and immiscible with water and that acts as a phase separation agent (PSA)(such as the herein preferred alkane), and an alcohol. As described in this document the boiling point of the PSA is below that of the water/PAOS azeotrope. The amount of steam injected is selected to give rise to the substantial removal of the PSA via stripping and that of the PAOS via azeotropic evaporation, whilst the total amount of water is such as to give rise to the precipitation of the polymer. In preferred embodiments the PVC composition provided in step (i) is relatively "pure" of components other than those typically found in a PVC composition i.e. other than PVC resin, the one or more plasticisers and other PVC additives which were originally added to the PVC composition for its intended use.

Contrary to the position described in WO 2009/037316, however, it is preferred to use one or more dispersing agents during the precipitation, and preferably to use both a primary dispersing agent and a secondary dispersing agent. WO 2009/037316 notes that the process therein obtains good results without use of dispersing agents. However, we have found that the addition of dispersing agents can provide particles which are particularly suitable for efficient plasticiser extraction according to the present invention.

The use of dispersing agents is known in the art. In general the dispersing agent or agents can be added at any suitable time. It is generally preferred that as at least one dispersing agent is present when the precipitation starts. Typical dispersing agents includes surfactants, such as bentonite, polyvinyl alcohol, gelatin, cellulose esters or ethers and water-soluble (co) polymers. The one or more dispersing agents, when used, are typically used in an amount generally greater than or equal to 0.01%, preferably greater than or equal to 0.1% by weight relative to the weight of PVC. The amount of dispersing agent is generally less than or equal to 5%, or less than or equal to 2%, or less than 1% by weight relative to the weight of PVC. It is preferred that at least one partially hydrolysed polyvinyl alcohol is used as a dispersing agent.

It is most preferred that at least two dispersing agents are used, the two being referred to a primary dispersing agent and a secondary dispersing agent respectively. In this case the dispersing agents are advantageously chosen from cellulose ethers and polyvinyl alcohols. Most preferably both the primary and second dispersing agents are polyvinyl alcohols but having differing levels of hydrolysis. In particular, the primary dispersing agent may be a partially hydrolysed polyvinyl alcohol which is at least 65% hydrolysed, such as at least 70% hydrolysed. The primary dispersing agent may be less than or equal to 90%, such as less than or equal to 80% hydrolysed. It is preferably from 65% to 90% hydrolysed, and more preferably from 70 to 80% hydrolysed. The second dispersing agent may be a partially hydrolysed polyvinyl alcohol with of hydrolysis than the primary dispersing agent, such as being less than or equal to 60% hydrolysed, such as less than or equal to 55% hydrolysed. The secondary dispersing agent is preferably from 25 to 55%, such as from 30 to 50% hydrolysed.

The PVC composition used in step (i) may have been, and preferably has been, obtained after treatment of an initial mixture comprising a PVC composition 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 components such as metals, polyolefins and other polymers, or any other foreign contaminant prior to step (i) of the present invention.

The removal of components other than those typically found in a PVC composition may be performed prior to any steps taken to provide the PVC composition particles of the required D50 and sphericity, such as prior to the precipitation process described above. Alternatively, or additionally, removal of components other than those typically found in a PVC composition may be performed during such processing, for example after dissolution but before precipitation. This latter option is particularly preferred for components which are not soluble in the solvent(s) used for dissolution, which can then be removed by filtration, centrifuge or other solids separation step prior to precipitation. The components which may be present at this stage generally depend on the source of the initial mixture comprising the PVC composition and also what treatment/separations have been performed prior to the dissolution, but can include, for example, other polymers, rubber seals, pieces of glass, concrete, wood and copper wire.

The initial mixture comprising a PVC composition, prior to any treatment or precipitation steps, 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 a PVC composition 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 composition may therefore be or be derived from waste window profiles. Another common use of PVC is in wire and cable applications. Thus, the PVC composition 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 composition include membranes, tarpaulins, textiles and other coated fabrics, PVC flooring, vinyl wallpaper, flexible hoses and numerous automotive applications. By using a PVC composition previously used for a particular application, generally speaking the PVC resin and additives in the composition will be of a consistent and similar type. This can assist in the purification. Most usefully, however, this means that the resulting purified PVC polymer will also then be generally suitable for reuse in the same application or in other specific applications which require similar PVC properties.

In preferred embodiments the PVC composition provided for step (i) of the first aspect of the present invention constitutes at least 90wt% of the total solids contacted with the solvent in step (ii), such as at least 95wt%, and more preferably at least 98wt% i.e. if there are components which are other than those typically found in a PVC composition, they are present, in the PVC composition provided for step (i), in a maximum amount of no more than 10wt%, preferably no more than 5wt% and more preferably no more than 2wt%. In preferred embodiments, there is less than lwt% metals and/or less than 1 wt% polymers other than PVC present.

As noted, the PVC composition for step (i) is typically obtained by treating an initial mixture comprising a PVC composition to remove other components.

Generally, therefore, an initial mixture comprising a PVC composition and other (non-PVC) components may be provided by selecting one or more PVC containing waste streams comprising PVC from a desired application (e.g. comprising PVC from waste wire and cable applications or PVC from waste window profiles). Especially if this has not already been done on the PVC waste containing stream or streams as provided, this initial waste mixture may then be subject to mechanical pre-sorting or other physical separation to remove at least some non-PVC components. The remaining stream may then be treated to provide the PVC composition in the form of a PVC composition in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7. This latter step is preferably done by dissolution and then precipitation of the PVC composition from a suitable solvent, as already described.

In step (ii) of the first aspect of the present invention the provided PVC composition is contacted with a solvent in which the one or more plasticisers are soluble but in which the PVC resin is insoluble to form a slurry, said slurry comprising PVC polymer solids and dissolved plasticisers.

The solvent may be any suitable solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble. Known solvents suitable for this step include, generically, CO2, alkanes, alcohols, esters and ethers. The solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble may be mixture, such as a mixture of two or more of the above. It may also be a mixture comprising a ketone, such as methyl ethyl ketone (MEK), and water. Such a solvent is particularly preferred where the PVC composition has been obtained by precipitation of the PVC composition from a solution comprising such components. The solvent used in this case may, for example, be a mixture comprising ketone and 10-25% of water, such as a mixture comprising 2-10% of alcohol (such as iso-propanol), 10-25% of water and 65-88% of ketone (preferably MEK). The solvent preferably comprises an absence or a relatively low level (e.g. less than 2.5%) of alkane. A particular advantage of this solvent is that where the PVC composition has been obtained by precipitation of the PVC composition from a solution comprising ketone and water then it is generally not necessary to separate residual ketone and/or water from the PVC composition formed in the precipitation step. So steps such as drying the precipitated PVC composition are not required.

(A difference of such a solvent compared to that which might be used in the earlier step is that the solvent for this later step will generally comprise a higher level of water and an absence or a relatively low level (e.g. less than 2.5%) of alkane. This can provide a solution in which the PVC is no longer soluble but the plasticizers are still soluble.)

Although the main advantage of the present invention arises from the particle size and shape of the PVC composition, it has also been found that particularly good results i.e. particularly high levels of plasticisers extraction from the PVC composition, can be obtained when the solvent is selected from CO2, alcohols having one to six carbon atoms, alkanes having one to six carbon atom, dialkylethers where each alkyl has 1 to 5 carbon atoms or a mixture of a dialkyl ketone and water. Particularly preferred alkanes are hexanes, and in particular n-hexane or iso-hexane, or mixtures thereof. A particularly preferred dialkylether is methyl tert-butyl ether. A particularly preferred dialkyl ketone for use with water, as already noted, is methyl ethyl ketone.

The contacting may be performed under any suitable conditions. In general, for solvents other than CO2 the solvent should be in a liquid state during the contacting (such that the extraction of plasticisers is a solid-liquid extraction method). The temperature and pressure in the contacting step should therefore generally be selected such that the solvent is in liquid state and the PVC is in the solid state. For solvents which would be gaseous at room temperature and atmospheric pressure then an elevated pressure is required.

The contacting with the solvent in a liquid state may be performed at ambient temperature, although use of an elevated temperature can improve the rate of plasticisers removal, and allow a lower contacting time. The temperature should be selected to make the extraction as efficient as possible. The temperature is preferably in the range 20°C to 120°C. There is no minimum or maximum contacting time during the extraction, although excessive contacting time generally provides no or only limited additional plasticisers removal. Typically contacting times with solvents where contacting is performed in a liquid state are less than 2 hours in practise, and preferably less than 1 hour. Preferred contacting times are 1 minute to 2 hours, such as 5 minutes to 1 hour.

Where CO2 is used as the solvent, then the contacting is preferably performed using supercritical CO₂. The temperature and pressure in the contacting step are therefore generally selected such that the CO₂ is in the supercritical state and the PVC is in the solid state. Supercritical CO2 generally requires a temperature of at least about 31°C, and a pressure of at least about 7380 kPa (73.8 bar).

The temperature for the contacting step when using supercritical CO₂ is preferably at least 35°C. The temperature is preferably less than 120°C, preferably less than 80°C, and most preferably in the range 40°C to 80°C.

The pressure may be any pressure suitable to maintain the CO₂ in a supercritical state. It is preferably at least 7500 kPa, and more preferably at least 10 MPa. There is no particular restriction on the maximum pressure, but generally providing equipment to handle very high pressures is expensive and unnecessary. Hence the pressure is preferably less than 60 MPa, such as less than 40 MPa or less than 30 MPa. Pressures in the range 10 MPa to 20 MPa are most preferred, and more preferably less than but preferably takes place at an elevated temperature as this can improve the rate of plasticisers removal, and allow a lower contacting time. The temperature should be selected to make the extraction as efficient as possible. The temperature is preferably in the range 30°C to 120°C.

There is no minimum or maximum contacting time during the extraction using CO₂, although again excessive contacting times generally provide no or only limited additional plasticisers removal. Contacting time when CO2 is used as the solvent may typically be at least 2 minutes. Typically contacting times where contacting is performed with CO2 in a supercritical state are less than 4 hours in practise, and preferably 3 hours or less. Preferred contacting times are 30 minutes to 2 hours.

Contacting of the PVC composition with the solvent may take place in any suitable vessel. This could include a tank, such as a stirred tank, or a column, such as a trayed or staged column.

Contacting of the PVC composition with the solvent may be performed as batch reaction/process, but is preferably performed as a continuous reaction/process.

In step (iii) of the first aspect of the present invention the PVC polymer solids are separated (from the slurry/dissolved plasticisers) to obtain purified PVC polymer solids. The separation may be by any suitable method for separating solids from a liquid, such as decanting, settling, centrifugation or filtration. The purified PVC polymer solids may be washed if required, for example with water and optionally stripped (at atmospheric pressure or under vacuum) to remove any residual solvent. The purified PVC polymer solids may be dried, for example after a washing step as noted. In other embodiments however, with a solvent which is a gas at room temperature and pressure, such as CO2, the purified PVC polymer solids may be separated from residual solvent simply by allowing vaporisation of the solvent.

The solvent comprising dissolved plasticisers, after separation of the purified PVC polymer solids, may be treated to precipitate and separate the plasticisers so that the solvent 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.

A further advantage of the process of the present invention is that additives other than plasticisers can also be removed from the PVC composition on contact with the solvent in which the one or more plasticisers are soluble, and in particular where said other additives are also soluble in the solvent.

Particular examples of other additives which can be present and which can be removed by the process and solvents of the present invention include medium chain chlorinated paraffins ("MCCP"), short chain chlorinated paraffins ("SCCP") and bisphenol A. Medium and/or short chain chlorinated paraffins, for example, can be added to PVC products as flame retardants and softening agents, whilst bisphenol-A can be added as an antioxidant. Thus, such components can also be present in the PVC composition of the present invention. It has been found that such compounds are generally also soluble in the solvent used for removing plasticisers, and hence are also effectively and efficiently removed by the process of the present invention.

As already noted, the PVC composition particles provided in step (i) are preferably formed by precipitation of the PVC composition from a solvent or mixture of solvents capable of dissolving the PVC resin and plasticisers, and also after treatment of an initial mixture comprising the PVC composition to remove other components, such as metals, polyolefins and other polymers and/or other impurities.

In a preferred embodiment of the first aspect of the present invention, the PVC composition of step (i) is provided by a particular series of steps, and in particular by: a. providing a mixture comprising a PVC composition and non-PVC components, said PVC composition comprising PVC resin and one of more plasticisers, b. Contacting the mixture with a first solvent in which the PVC resin and one or more plasticisers are soluble to form a solution comprising dissolved PVC resin, dissolved plasticiser(s) and insoluble non-PVC components, c. Separating the insoluble non-PVC components from the solution, d. Precipitating the PVC resin and at least some of the dissolved plasticiser from the solution to form a PVC composition, said PVC composition being in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7, and e. Providing the PVC composition as the PVC composition of step (i).

In a further preferred embodiment of the first aspect, the precipitated PVC composition is separated from the solution before provision as the PVC composition of step (i), in which case the PVC composition of step (i) is provided by the following series of steps: a. providing a mixture comprising a PVC composition and non-PVC components, said PVC composition comprising PVC resin and one of more plasticisers, b. Contacting the mixture with a first solvent in which the PVC resin and one or more plasticisers are soluble to form a solution comprising dissolved PVC resin, dissolved plasticiser(s) and insoluble non-PVC components, c. Separating the insoluble non-PVC components from the solution, d. Precipitating the dissolved PVC resin and at least some of the dissolved plasticiser from the solution, e. Separating the precipitated solids from the solution to form a PVC composition, said composition being in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7, and f. Providing the PVC composition as the PVC composition of step (i).

Further, in a second aspect, the present invention provides a process for obtaining purified PVC polymer solids, the process comprising: a. providing a mixture comprising a PVC composition and non-PVC components, said PVC composition comprising PVC resin and one of more plasticisers, b. Contacting the mixture with a first solvent in which the PVC resin and one or more plasticisers are soluble to form a solution comprising dissolved PVC resin, dissolved plasticiser(s) and insoluble non-PVC components, c. Separating the insoluble non-PVC components from the solution, d. Contacting the PVC composition with a solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble to form a slurry, said slurry comprising PVC polymer solids and dissolved plasticiser, and e. Separating the PVC polymer solids to obtain purified PVC polymer solids.

In an embodiment of the second aspect, the present invention provides a process for obtaining purified PVC polymer solids, the process comprising: a. providing a mixture comprising a PVC composition and non-PVC components, said PVC composition comprising PVC resin and one of more plasticisers, b. Contacting the mixture with a first solvent in which the PVC resin and one or more plasticisers are soluble to form a solution comprising dissolved PVC resin, dissolved plasticiser(s) and insoluble non-PVC components, c. Separating the insoluble non-PVC components from the solution, d. Precipitating the dissolved PVC resin and at least some of the dissolved plasticiser in the solution , e. Separating the precipitated solids from the solution to form a PVC composition comprising the polymer resin and one or more plasticisers, f. Contacting the PVC composition with a solvent in which the one or more plasticisers are soluble but the PVC resin is insoluble to form a slurry, said slurry comprising PVC polymer solids and dissolved plasticiser, and g. Separating the PVC polymer solids to obtain purified PVC polymer solids.

The mixture comprising a PVC composition and non-PVC components in these preferred embodiments of the first aspect and in the second aspect may generally be as already described for the initial mixture comprising a PVC composition and other (non-PVC) components prior to any treatment or precipitation steps. Alternatively, it may be a mixture comprising a PVC composition and non-PVC components obtained after some initial treatment, for example mechanical pre-sorting or other physical separation to remove at least some non-PVC components. Either way, it may comprise a PVC composition recycled from any suitable source, but preferably is obtained by recycling of PVC previously used for a particular application.

Typically, the PVC composition present in this mixture is in a form which has a D50 of more than 600 microns, usually significantly more, and/or a sphericity of less than 0.3. The PVC composition in this mixture, and typically the mixture as a whole, is usually 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 composition 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.

The non-PVC components may, for example, comprise one or more of more of metals, such as aluminium, polyolefins, polymers other than PVC or polyolefins and/or fillers, such as natural or synthetic fibres. In preferred embodiments, the mixture comprising a PVC composition provided in step (a) comprises one or more of: a. 5wt% or more of metals, such as aluminium, b. 5wt% or more of polyolefins, c. 5wt% or more of polymers other than PVC or polyolefins, d. 5wt% of more of fillers, such as natural or synthetic fibres,

At least some of the non-PVC components, and preferably the substantial majority, should be insoluble in the solvent, and hence will form the insoluble non-PVC components in the solution.

Suitable and preferred solvents for use for the first solvent are as already described. I particular, a mixture of solvents, such as a mixture of a ketone, an alcohol and an alkane, for example a mixture of methyl ethyl ketone (MEK) with hexane and isopropanol, is preferred.

The separation of the insoluble non-PVC components from the solution may be performed by any suitable method for separating solids from a liquid, such as settling, centrifugation or filtration.

The precipitation of the PVC resin and at least some of the dissolved plasticiser from the solution is also generally performed by the steps already described, and in particular as described in WO 2009/037316.

The separation of the precipitated solids from the solution to form a second PVC composition may again take place by any suitable method for separating solids from a liquid, such as settling, centrifugation or filtration.

The PVC composition obtained may be washed if required, for example with water, and optionally stripped, to remove any residual first solvent. The PVC composition may be dried, preferably after a washing step as noted. The subsequent separation and contacting steps of the second aspect may also be as generally described already for the first aspect.

The present invention may be illustrated by the following examples.

Examples

A. Preparation of PVC composition with required D50 and sphericity

45 kg of a mixture comprising a PVC composition derived from cable scrap, and comprising with 47.6% PVC resin, 28.7% plasticizers (including a significant proportion of phthalates), and 23.7% fillers was dissolved in 180 kg of solvent comprising 15% isohexane, 4% isopropanol, 5% water and 76% MEK, with stirring and heating at 100°C, and under a pressure of 300 kPa.

The solution thus obtained was filtered to remove insoluble impurities, and then subjected to a flash evaporation by reducing the pressure to 100 kPa.

Partially hydrolysed polyvinyl alcohol (72% hydrolysed) was added as a dispersing agent. Water and steam in a ratio of 3:1 were then introduced until the isohexane had completely evaporated, followed by further water and steam in a sufficient amount to bring about the phase inversion of the medium. Injection of steam continued until the precipitation medium reached 100°C.

The solids obtained were removed by filtration and dried. The obtained PVC composition was in the form of particles with a D50 of 400 microns and a sphericity of 0.80. (S50 aspect ratio as defined in the description.) The composition was approximately the same as the initial PVC composition i.e. 47.6% PVC resin, 28.7% plasticizers and 23.7% fillers.

The PVC composition was analysed for individual phthalate components, as well as for bisphenol A, and short and medium chain chlorinated paraffins. The results are shown in Table 1.

Table 1

B. Runs 1-5 - Purification of PVC composition using iso-hexane and MTBE

The PVC composition produced in part A above was contacted with either iso-hexane or MTBE as solvent as described below. In each case 25g of the PVC composition was mixed with 200g of the solvent. The contacting is performed for a defined contact time and at a temperature as shown below, following which the solids are separated from the solvent (slurry) by filtration. In a number of the tests the contacting is repeated using fresh solvent, again as indicated below.

After the final contacting step, the solvent (from all contacting steps where more than one) is collected and distilled to recover the solvent and to separate plasticisers from the solvent. In addition, the recovered PVC polymer solids are also analysed for residual plasticisers. The results are shown in Table 2.

Table 2

rt = room temperature nd = not determined

* - below detection limit

These results show that iso-hexane, and particularly MTBE, are efficient at removing the plasticisers from the PVC composition. They also show that the treatment with MTBE can also remove medium and short chain chlorinated paraffins.

C. Run 6 - Purification of PVC composition using a mixture comprising MEK and water

The PVC composition produced in part A above was contacted a solvent comprising 83% MEK, 10.4% water, 4.1% iso-propanol and 2.5% iso-hexane.

In each case 10 g of the PVC composition was contacted with 80g of the solvent. The contacting was performed for 10 minutes at 55°C, and was repeated 4 times.

As with Runs 1-5, the solvent from all contacting steps is collected and distilled to recover the solvent and to separate plasticisers from the solvent. In addition, the recovered PVC polymer solids are also analysed for residual plasticisers.

The extraction rate for the plasticisers was approximately 100%.

The residual concentrations of the various phthalate species, bisphenol A and chlorinated paraffins were measured for the PVC. The results are shown in Table 3.

Table 3

* - below detection limit

These results show that the solvent comprising MEK and water is efficient at removing the plasticisers from the PVC composition, and also MCCP, SCCP and bisphenol A additives. D. Runs 7-9 - Purification of PVC composition using CO2

The PVC composition produced in part A above was contacted with supercritical CO2 as solvent. (Instead of using iso-hexane, MTBE or MEK and water.)

In each case 25g of the PVC composition was placed in a contacting vessel and contacted with liquid CO2 at temperatures and pressures as detailed below. In particular, liquid CO2 is continuously passed to the contacting vessel, with a corresponding flow of liquid CO2 removed from the contacting vessel. The removed CO2 stream is passed to a separation vessel where it is depressurised, leading to vaporisation of the CO2 and collection of the plasticisers. The vaporised CO2 is recovered and condensed such that it can be recycled to the contacting vessel.

At the end of the contacting the pressure in the contacting vessel is released, causing vaporisation of the CO2 therein to leave purified PVC solids. The collected solids ("recovered plasticisers") in the separation vessel are also weighed. The results are shown in Table 4

Table 4

These results show that CO2 is efficient at removing the plasticisers from the PVC composition. Runs 10 and 11 - Purification of PVC composition using CO?

Runs 10 and 11 further exemplify the use of supercritical CO₂ as solvent.

The PVC composition used in these Examples was derived from a different application and comprised 77% PVC resin, 10% plasticizers and 12% fillers. It was dissolved in a solvent and subsequently precipitated in an equivalent manner to that described above to provide a PVC composition in the form of particles with a D50 of 378 microns and a sphericity of 0.89. (S50 aspect ratio as defined in the description.)

The composition of the precipitated particles was approximately the same as the initial PVC composition. This composition was contacted with supercritical CO₂ as solvent as described for Runs 7-9 but under the conditions detailed in Table 5 below.

Table s

These results further show that CO2 is efficient at removing the plasticisers from the PVC composition. In particular, these results show that efficient removal can be obtained at relatively low temperatures and pressures.

Claims

1. A process for obtaining purified PVC polymer solids, the process comprising:

(i) Providing a PVC composition, said PVC composition comprising PVC resin and one of more plasticisers, and said composition being provided in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7,

(iii) Separating the PVC polymer solids to obtain purified PVC polymer solids.

2. A process according to claim 1 wherein the PVC composition is in the form of particles having a D50 from 200 to 400 microns.

3. A process according to claim 1 or claim 2 wherein the PVC composition is in the form of particles having a sphericity of at least 0.8.

4. A process according to any one of the preceding claims wherein the PVC composition provided for step (i) constitutes at least 90wt% of the total solids contacted with the solvent in step (ii), such as at least 95wt%, and more preferably at least 98wt%

5. A process according to any one of the preceding claims wherein the PVC composition provided for step (i) comprises at least 90wt% PVC polymer and plasticisers, such as at least 95wt% PVC polymer and plasticisers.

6. A process according to claim 4 or claim 5 wherein there is less than lwt% metals and/or less than 1 wt% polymers other than PVC present.

7. A process according to any one of the preceding claims wherein the solvent is selected from CO2, alkanes, alcohols, esters and ethers.

8. A process according to any one of the preceding claims wherein the solvent is selected from CO2, alcohols having one to six carbon atoms, alkanes having one to six carbon atoms, dialkylethers where each alkyl has 1 to 5 carbon atoms or a mixture of a dialkyl ketone and water.

9. A process according to any one of the preceding claims wherein the solvent is methyl tertbutyl ether.

10. A process according to any one of claims 1 to 8 wherein the solvent is a mixture comprising a ketone, such as methyl ethyl ketone (MEK), and water.

11. A process according to any one of the preceding claims wherein the PVC composition of step (i) is provided by the steps of: a. providing a mixture comprising a PVC composition, said PVC composition comprising PVC polymer and one of more plasticisers, b. Contacting the mixture with a solvent in which the PVC resin and one or more plasticisers are soluble to form a solution comprising dissolved PVC resin, dissolved plasticiser(s) and insoluble non-PVC components, c. Separating the insoluble non-PVC components from the solution, d. Precipitating the PVC resin to form a PVC composition, said PVC composition being in the form of particles with a D50 of less than 600 microns and a sphericity of at least 0.7, and e. Providing the PVC composition as the PVC composition of step (i).

12. A process according to claim 11 wherein the mixture comprising a PVC composition is in a form which has a D50 of more than 600 microns and/or a sphericity of less than 0.3.

13. A process according to claim 11 or claim 12 wherein the mixture comprising a PVC composition is in the form of lumps, strips, flakes or chips, for example obtained by grinding, shredding, cutting or chopping of larger forms of product, and having an average particle size in the range of 5 to 80mm.

14. A process according to any one of claims 11 to 13 wherein the mixture comprising a PVC composition comprises one or more of: a. 5wt% or more of metals, such as aluminium, b. 5wt% or more of polyolefins, c. 5wt% or more of polymers other than PVC or polyolefins, d. 5wt% of more of fillers, such as natural or synthetic fibres, at least some of which are insoluble in the first solvent and form the insoluble non-PVC components.

15. A process according to any of claims 11 to 14 wherein the first solvent comprises methyl ethyl ketone (MEK), preferably in a mixture with hexane and isopropanol.