Solid-liquid extraction of lead from PVC

Abstract

The invention is directed to a method for reducing the lead content of a lead-containing polyvinyl chloride (PVC) based material. In particular, the present invention is directed to a solid-liquid extraction method for reducing a lead content of a lead-containing polyvinyl chloride (PVC) based material.

Description

[0001]Title: Solid-liquid extraction of lead from PVC BACKGROUND 1. TECHNICAL FIELD The invention is directed to a method for reducing the lead content of a lead-containing polyvinyl chloride (PVC) based material. In particular, the present invention is directed to a solid-liquid extraction method for reducing the lead content of a lead-containing polyvinyl chloride (PVC) based material. 2. RELATED ART It is essential to add stabilisers (commonly named stabiliser one- packs) to PVC during processing to avoid PVC degradation. PVC is thermally unstable because of the presence of defects; these defects that are e.g. tertiary chlorine or allylic chlorine atoms are initiation sites for degradation. In the past, lead-based stabilisers were added to PVC in Europe; lead was used to i.a. give thermal stability to the PVC and to protect PVC from photo- degradation. However, as is well known, lead is a toxic element that may affect human health and environment. Following a voluntary commitment of the Vinyl industry, lead-based stabilisers are no longer used by the PVC industry since 2015 in Europe. These stabilisers are therefore not present in new articles. However, lead can be present in post-consumer PVC recyclate coming from old PVC products. In view thereof, Commission Regulation (EU) 2023 / 923 was issued on 3 May 2023 and restricts lead content in PVC and its compounds to 0.1 wt% (=1000 ppm). This restriction does not apply until May 2033 to recycled PVC based on rigid formulations provided their lead content is below 1.5 wt% of the recovered rigid PVC. The 0.1 wt% limit shall not apply to PVC articles containing recovered flexible PVC until May 2025. To comply with the new regulations, the content of lead in Recycled PVC (R-PVC) based on post-consumer waste will have to be reduced in the coming years. It is desired to a method to reduce lead content to guarantee R-PVC fulfills the regulations in place. Several of such attempts have been made. One example is described in WO2006 / 05907. Herein, a process for the purification of PVC comprising e.g. lead is described. This process comprises dissolving PVC in a solvent and treating this solution with an additive that forms a complex with the lead. Another example is disclosed in US4071479. Herein a process is described wherein PVC resin is dissolved in a solvent and an acid is added thereto to flocculate suspended particulate additives. A non-solvent is added to precipitate essentially pure PVC resin. Further examples are described by Tsunekawa et al. (Separation and Purification Technology 89 (2012), 94-97) and Tsunekawa et al. (Journal of Hazardous Materials 191 (2011) 388-392). Disadvantageously, these methods are cumbersome as these require dissolving PVC, are energy consuming and specific extraction of lead is not possible on industrial scale. GENERAL DISCLOSURE It is therefore an object of the present invention to provide a method that overcomes at least part of the above-mentioned drawbacks. In particular, the method according to the present invention provides a simple and effective method to reduce the lead content from PVC based materials. In addition, the method may be suitable to be applied on larger scale. The present inventors surprisingly found that this objective is achieved by a solid-liquid extraction approach. Particularly, the present inventors found that incubating a mixture comprising a lead-containing PVC based material and an extraction solvent (e.g. an acid) advantageously allows for selective and effective lead extraction. There is provided that a liquid extraction method for reducing the lead content of a lead-containing polyvinyl chloride (PVC) based material, wherein the method comprises an extraction cycle comprising - providing a mixture comprising the lead-containing PVC based material and an extraction solvent; - heating the mixture to obtain a lead-reduced PVC based material and a lead-rich fraction; wherein the extraction solvent has a Hildebrand solubility parameter at 25°C and 1 atm in the range of 14 – 48 MPa1 / 2. The above method may further comprise separating the lead- reduced PVC based material and the lead-rich fraction, preferably by filtration and / or centrifugation. In the above method(s), the mixture may be heated for a period of at least 1 minutes, preferably at least 15 minutes, more preferably at least 30 minutes, even more preferably at least 60 minutes, more preferably at least 90 minutes, most preferably at least 120 minutes. In the above method(s), the mixture may be heated at a temperature of at least 20 °C, preferably at least 50 °C, more preferably at least 60 °C, even more preferably at least 85 °C, most preferably in the range of 85 – 120 °C. In the above method(s), the extraction solvent may have a Hildebrand solubility parameter in the range of 17 to 26, preferably in the range of 18 to 25, more preferably in the range of 19 to 24 and / or the extraction solvent may comprise at least one of an acid, anhydride of the acid and an aquesous solution of the acid, preferably wherein the acid is selected from the group consisting of acetic acid, acetic anhydride, levulinic acid, citric acid, nitric acid, formic acid, oxalic acid, methane sulfonic acid, hydrochloric acid, p-Toluenesulfonic acid (PTSA), Ethylenediaminetetraacetic acid (EDTA) and combinations thereof, more preferably the extraction solvent comprises acetic acid. The above method(s) further comprise pretreating the lead- containing PVC based material, preferably wherein the pretreating comprises reducing the size of the lead-containing PVC based material, more preferably wherein the method further comprises pulverizing, cutting, crushing and / or grinding of the lead-containing PVC based material. In the above method(s), the extraction cycle may be performed two or more times, such as 2 – 4 times, preferably 2 – 3 times, more preferably 2 times. In the above method(s), the lead-containing PVC based material may typically have a lead content above 1000 ppm, preferably above 4000 ppm, more preferably in the range of 6000 – 10000 ppm. In the above, method(s), the lead-reduced PVC based material may have a lead content below 1000 ppm. In the above method(s) may further comprise washing the lead- reduced PVC based material, preferably by rinsing, more preferably by rinsing with water and / or the extraction solvent. In the above method(s), at least 80 wt%, preferably at least 85 wt%, more preferably at least 90 wt%, even more preferably at least 95 wt%, preferably at least 98 wt%, more preferably at least 99 wt% of the lead- containing PVC based material remains solid. In the above method(s), the lead-reduced PVC based material may remain solid during the method. In the above method(s), the lead-containing PVC based material may comprise post-consumer PVC. In the above method(s), the lead-containing PVC based material may comprise rigid PVC and / or flexible PVC. In the above method(s), at least a first and a second extraction cycle may be performed consecutively, wherein the lead-rich fraction from the second extraction cycle may be used as extraction solvent for the first extraction cycle and preferably wherein the lead-reduced PVC based material from the first extraction cycle is as lead-containing PVC based material for the second extraction cycle. In the above method(s), the method also reduces cadmium content of a polyvinyl chloride (PVC) based material. There is provided that a method for producing the lead-reduced lead-containing polyvinyl chloride (PVC) based material, may comprise - providing a mixture comprising a lead-containing PVC based material and an extraction solvent; - heating the mixture to obtain a lead-reduced PVC based material and a lead-rich fraction; wherein the extraction solvent has a Hildebrand solubility parameter at 25°C and 1 atm in the range of 14 – 48 MPa1 / 2. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 illustrates the lead extraction efficiency on post-consumer PVC after one extraction with acetic acid for 120 minutes with varying sieve fractions and temperatures. Figure 2 illustrates the lead extraction efficiency after one and two extractions of post-consumer PVC incubated with various extraction solvents for 120 minutes at 90°C. DESCRIPTION OF EXEMPLARY EMBODIMENTS Some embodiments are directed to a solid-liquid extraction method for reducing the lead content of a lead-containing polyvinyl chloride (PVC) based material (herein also referred to as lead-containing material). The method comprises an extraction cycle comprising providing a mixture comprising the lead-containing material and an extraction solvent. The method, in particular the extraction cycle, further comprises heating the mixture to obtain a lead-reduced based material (herein also referred to as lead-reduced material) and a lead-rich fraction. The heating may include an incubating. The reducing of the lead is preferably but not limited to the depleting of almost or all lead from the material. Advantageously, the present method is energetically and environmentally favorable, it does not require any additional chemicals other than an extraction solvent and is economically friendly. The lead-containing material generally comprises a PVC matrix. The lead-containing material may be based on a flexible and / or rigid PVC formulation (herein also referred to as flexible or rigid PVC). These terms are known in the art. Generally, flexible PVC is used to refer to PVC formulations that contain plasticizers, while rigid PVC has little to no plasticizers. Due to the more additives that are typically present in flexible PVC, it may be preferred that the lead-containing material comprises rigid PVC. Nonetheless, it may be appreciated that some embodiments may be suitably applied to both flexible and rigid PVC. Lead-reduced PVC using the rigid PVC can be mechanically recycled (i) as PVC is not degraded or discoloured by the extraction process (which might be the case with other processes such as dissolution or solvent based approach) and (ii) the output material has the same morphology as the input material (e.g., micronized PVC) which is easily ‘processable.’ The lead-containing material typically has a lead content above 1000 ppm, such that it is required by the issued regulation that the lead content is reduced. Typically, the lead-containing material has a lead content above 4000 ppm or 5000 ppm, such in the range of 6000 – 10000 ppm. It may be appreciated that generally the lead-containing material comprises post-consumer PVC, for instance post-consumer PVC waste. The lead-containing material may further comprise a variety of stabilizers, such as e.g. Ca / Zn, Ba / Zn, lubricants such as oxidized polyethylene, stearic acid, fillers such as calcium carbonate, plasticizers such as phthalates, trimellitates and / or pigments. The of the lead-containing PVC material typically depends on the type of waste, for instance cable, pipe or (window) profile waste. The lead-containing material may be provided in any size and any form, such as powder, pellets, chips and / or flakes. For instance having a median particle size (d50) in the range between 1-5 mm, such as 1-3 mm, or 1-2 mm. In some cases, the lead-containing material may be provided in a smaller form, such as having a median particle size (d50) of less than 1 mm, such as less than 800 µm, or less than 500 µm or even less than 350 µm. It was found that the solid-liquid extraction method works particularly well, with good efficiency, if the lead-containing material particle size is small. Accordingly, the method further preferably comprises pretreating the lead- containing PVC material, preferably wherein the pretreating comprises reducing the size of the lead-containing material. Most preferably, the median particle size (d50) of the lead-containing PVC based material is below 400 µm, more preferably below 350 µm, more preferably below 150 µm, even more preferably below 100 µm, such as below 80 µm, most preferably below 63 µm. Accordingly, the method preferably further comprises pulverizing, cutting, crushing and / or grinding said lead-containing PVC based material. In order to prevent overheating of the lead-containing material during reducing its size, it may be appreciated that the material is cooled. Solid-liquid extraction is known in the art as a separation method in which a component is extracted from a solid matrix using an extraction solvent (also referred to as solvent). Herein, it refers to the extraction of at least a part of the lead from a PVC matrix of the lead-containing material by using an extraction solvent, which typically comprises an acid. Accordingly, none to only a little of the lead-containing material and / or lead-reduced material may dissolve. Generally, at least 80 wt%, such as at least 85%, preferably at least 90 wt%, or even at least 95 wt%, preferably at least 98 wt%, more preferably at least 99 wt% of the lead-containing PVC based material and / or the lead-reduced PVC based remain solid during the method. By extraction of the lead from the lead-containing PVC based material, the lead content is reduced. Generally, the extraction solvent requires a high permeability in the solid matrix and good reactivity with the to be extracted component, so that it can penetrate into the solid matrix and then react with the component. The permeability of the solvent in the polymer matrix depends on i.a. the solubility and diffusion of the solvent in the polymer matrix. This may be quantified by P=DxS wherein P is Permeability, D is Diffusion, S is Solubility. It is known in the art to use a Hildebrand solubility parameter to predict the solubility or compatibility between polymers and solvents. Hildebrand solubility parameter is an empirically determined number that provides a numerical estimate to the degree of interaction between materials and is a good indication of compatibility, particularly for material such as polymers. The Hildebrand solubility parameter (δ) is herein defined by equation (1) at 25°C and 1 atm and expressed in MPa1 / 2. భ^^ = ^^∆^^௩ − ^^^^^ / ^^^మ (1) wherein ΔHv: enthalpy of vaporization in J · mol-1at a temperature of 298 K and pressure of 101 325 Pa (one hundred and one thousand and three hundred and twenty-five) R: the gas constant in J·mol-1·K-1V : molar volume in mol·m-3T: temperature below solvent boiling point in K Herein V is determined according to equation (2) ^^ = ெఘ (2)wherein M: molar in g· mol-1of the solvent molecule ρ: is the density of the solvent molecule in g·m-3at a temperature of 298 K and pressure of 101325 Pa. For the purpose of determining the Hildebrand solubility parameter according to equation (1), it is assumed that T is the temperature below the boiling point of the extraction solvent under the stated conditions, the vapor is an ideal gas and ΔHvis preferably determined experimentally by calorimetry (or from the temperature dependence of the vapor pressure). This approach corresponds to definition A. It may be appreciated that in case the extraction solvent comprises a mixture, for instance of citric acid and water, that the Hildebrand parameter is determined according to the volumetric ratio of the mixture. For those extraction solvents for which the enthalpy of vaporization could not be found (either because never determined empirically or because the material decomposes before the boiling point), the Hildebrand solubility parameter may be determined by another definition. For example, the cohesive energy of substances is predicted with some group additivity methods based on their molecule structure as described by R.F. Fedors (Pol. Eng. Sci., 1974, Vol. 14, N°2, 147-154); this second approach corresponds to definition B. Materials with similar solubility parameters are likely to be compatible. The Hildebrand solubility (δ(SI)) of PVC is approximately 20.7 MPa1 / 2, as estimated according to definition A. Accordingly, the extraction solvent used in some embodiments has Hildebrand solubility parameter (or HSP) in the range 14 to 48 MPa1 / 2more preferably in the range of 17 to 26 MPa1 / 2, more preferably 18 to 25 MPa1 / 2, most preferably in the range of 19 to 24 MPa1 / 2. The extraction solvent of the present application may satisfy the above numerical range of the Hildebrand solubility parameter in at least one definition (e.g., the definition A or the definiton B) or multiple definitions (e.g., both of the definitions A and B)). Additionally, the solvent has a good reactivity with the to be extracted component. Without wishing to be bound by theory, the lead may be extracted by a salt metathesis reaction that forms a coordination complex of lead with the extraction solvent. Accordingly, it is preferred that the solvent may form a stable complex and is soluble in the liquid phase. A further aspect to consider may be the size of the coordination complex. Namely, a smaller coordination complex may more easily diffuse out of the PVC matrix. The extraction solvent may therefore preferably have a molecular weight of at most 200 g / mol, preferably at most 150 g / mol, more preferably at most 100 g / mol. It is preferred that the extraction solvent comprises an acid, anhydride of the acid, and / or an aqueous solution of the acid. The acid is preferably selected from the group consisting of acetic acid (HSP by the definition A: 20.7), acetic anhydride (HSP by definition A: 21.1), levulinic acid (HSP by definition B: 24.2), citric acid (HSP by def. B: 31.3), nitric acid (HSP by def. B: 28.4), formic acid (HSP by def. A: 24.7), oxalic acid (HSP by def. B: 28.9), methane sulfonic acid (HSP by def. B: 27.0), hydrochloric acid (HSP by def. B: 24.8), p-Toluenesulfonic acid (PTSA) (HSP by def. B: 25.1), Ethylenediaminetetraacetic acid (EDTA) (HSP by def. B: 20.9) and combinations thereof, preferably selected from the group consisting of acetic acid, acetic anhydride, levulinic acid, nitric acid and any combination thereof. It was found that particularly good results were obtained when the extraction solvent comprises or is acetic acid. The extraction solvent may be an acid alone or a combination of an acid and another solvent (e.g., water). The concentration of the acid may be 1-100% by weight, preferably 10-99% by weight. As an example, the extraction solvent may be a 95-99% by weight aqueous solution of acetic acid. As an example, the extraction solvent may be a 5-40% by weight aqueous solution of nitric acid. As an example, the extraction solvent may be a 95-99% by weight aqueous solution of levulinic acid acid. It may be appreciated the extraction solvent may be provided in an essentially pure form, such as having a purity level above 95%, or above 98%. This is particularly advantageous if the extraction solvent is liquid at room temperature (approximately 20 °C). Nonetheless, it may be appreciated that the extraction solvent may be diluted in e.g. water, such that the mixture comprises the lead-containing material, the extraction solvent and water. In case the extraction solvent, such as the acid, is solid at room temperature, it may in that case be dissolved in water or in another solvent. Typically the mixture is heated for a time sufficient for the extraction solvent to penetrate the PVC matrix, react with the lead and diffuse out of the PVC matrix. Accordingly, the mixture is preferably heated for a period of at least 1 minutes, preferably at least 15 minutes, more preferably at least 30 minutes, even more preferably at least 60 minutes, even more preferably at least 90 minutes, most preferably at least 120 minutes. The mixture may be incubated at a temperature in the range between room temperature and 150 °C. Preferably, the temperature is at least 20 °C, preferably at least 50 °C, more preferably at least 60 °C, more preferably at least 85 °C. Typically, a higher temperature allows for more mobility of the PVC polymer chains in the lead-containing material. The higher mobility generally allows for a more efficient extraction of the lead. Accordingly, it is preferred that the temperature is above the glass transition temperature of PVC (approximately 85 °C). At too high temperature PVC may undergo some thermal degradation and fusion, which is typically not preferred. Accordingly, the temperature is preferably in the range between 85 – 120 °C, such as in the range between 90 – 110 °C. The temperature may be optimised with each extraction agent. For example, elevating the temperature above the boiling point of the extraction agent is not appropriate. It may be appreciated that the optimal extraction efficiency may depend on one or more of the factors, such as the optimal time and / or temperature which may depend on one or more factors such as size of the lead-containing material, type extraction solvent, and / or optional impurities. For instance, if a smaller size of the lead-containing material is used, the temperature and time may be shorter than when a larger size of the lead-containing material is used. Similarly, the porosity of the lead-containing PVC based material may affect the extraction efficiency and may at least partly determine the optimal incubation time and / or temperature. A more porous material may allow for easier penetration of the extraction solvent into the PVC matrix and thus may allow for easier extraction of the lead. In that case, lower temperatures and / or shorter times may be sufficient. Typically, it is preferable to agitate the mixture during the incubation. This agitation allows for a higher extraction efficiency. This agitation may be by any means known in the art, such as stirring the mixture, or placing the mixture on a shaker platform. After incubation, the lead-reduced PVC based material and the lead-rich fraction may be separated. The lead-rich fraction typically comprises the lead-based coordination complex and the extraction solvent. As at least the majority of the lead-reduced PVC based material is typically solid and the lead-rich fraction is typically liquid, the separation may suitably be performed by any suitable solid-liquid separation such as filtration and / or centrifugation. The lead-reduced PVC based material may still comprise some residual extraction solvent and / or lead components. Accordingly, it may be preferred that the method comprises washing the lead-reduced material, preferably by rinsing, such as by rinsing with water and / or the extraction solvent. It may be appreciated that typically the lead-reduced PVC is further washed and / or rinsed at the filtration stage. In such cases, in particular for multiple rinsing cycles, the filtrate may additionally or alternatively be employed for washing. The lead-reduced material may further be dried. The lead-reduced has a lead content below 1000 ppm. Advantageously, this meets the REACH regulation set by the European union, wherein lead is identified on the candidate list as a substance of very high concern for authorization and therefore should be below 1000 ppm. Further, it may be noted that the method, in particular the extraction cycle, may be performed multiple times, such as two or more times, such as 2 – 4 times, preferably 2 – 3 times, most preferably twice, preferably in a row (e.g. consecutively). For instance, the lead-reduced material may be suitably provided in a mixture with an extraction solvent and incubated in accordance with the above-mentioned. In other words, the lead-reduced material may be used as a starting material. By performing the extraction cycle more than once, such as at least twice, more lead may be extracted. Applying multiple extractions allows reaching the desirable lead threshold more easily, especially if the threshold is not yet met after one extraction. Accordingly, in case multiple extraction cycles are performed, it may be appreciated that the method further comprises providing a further mixture comprising the lead-reduced PVC based material and a further extraction solvent and incubating this further mixture to obtain a further lead-reduced PVC based material and a further lead-rich fraction. Thus, for such cases the lead-reduced PVC based material obtained from a first extraction cycle is used as the starting material (i.e. as the lead-containing PVC based material) in a second extraction cycle and so forth. The further extraction solvent is typically independently selected from suitable extraction solvents (as defined above), most preferably the further extraction solvent is acetic acid. It may be appreciated that in case two or more extraction cycles are employed, that the lead-rich fraction may be used as an extraction solvent for the previous extraction cycle. For a final cycle, a fresh extraction solvent may be used. In other words, the extraction solvent used in a first extraction cycle may be the lead-rich fraction from a second cycle and so forth. This advantageously allows saving solvents. Thus, in such a preferred method at least a first and a second extraction cycle are performed consecutively and the lead-rich fraction from the second extraction cycle is used as extraction solvent for the first extraction cycle. For a more efficient method it may be preferred that the lead-reduced PVC based material from the first extraction cycle is used as the lead-containing PVC based material for the second extraction cycle and so forth. The methods according to some embodiments may allow for extraction efficiencies of at least 60%, such as at least 80% or even above 90%. The methods according to the above embodiments may also work for extracting cadmium from the PVC based material. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. The present invention may further be illustrated by the following non-limiting examples. In the examples, the lead and cadmium extraction efficiencies havecalculated in the following way:(^^^^ [ ] [ ]^^^^^^ ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^ [%] = ை ppm − ^^^^ ^^^^^^ )^^ ^ ோ^^^^^^ை^ [ppm]where PbOr: Original lead content before extraction PbRes: Residual lead content after extraction process (^^^^ [p ] [ ]^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^^^^^ [%] = ை^ pm − ^^^^ோ^^ ^^^^^^ )^^^^ை^ [ppm]where CdOr: Original cadmium content before extraction CdRes: Residual cadmium content after extraction process Example 1: single extraction with acetic acid Lead-containing PVC based material comprising post-consumer PVC was grinded to a size <150 The grinded lead-containing material was mixed with acetic acid (99% purity) as extraction solvent and incubated for 120 minutes at a temperature of 90 °C, while stirring. The Hildebrand solubility parameter of the extraction solvent is 20.7 MPa1 / 2(for instance, based on Source: CRC Handbook of Solubility Parameters and other cohesion parameters, 2nd edition A.F.M Barton, Ch. 8 Table 1)(according to definition A). The mixture was filtered and rinsed with water. A lead extraction efficiency of 90% was obtained, as illustrated in Figure 1. Example 2: single extraction with acetic acid at various sizes and temperatures A first lead-containing PVC based material comprising post- consumer PVC was grinded to a size of approximately 350 µm. This post- consumer PVC was sieved in different fractions, i.e; < 63 µm, <125 µm and <350 µm. The three fractions of the grinded lead-containing material were mixed with acetic acid (99% purity) as extraction solvent and incubated for 120 minutes at a temperature of 69°C or 90 °C, while stirring. The Hildebrand solubility parameter of the extraction solvent is 20.7 MPa1 / 2(based on the same source as indicated above). All mixtures were filtered and rinsed with water. The results are illustrated in Figure 1. Example 3: double extraction with acetic acid Lead-containing PVC based material obtained from artificially made sheets, was grinded to a size <400 µm. The grinded lead-containing material was mixed with acetic acid (99% purity) as extraction solvent and incubated for 60 minutes at a temperature of 110 °C, while stirring. The Hildebrand solubility parameter of the extraction solvent is 20.7 MPa1 / 2(based on the same source as indicated above). The mixture was filtered optionally rinsed with water. The extraction process was repeated a second time: the residue from the first filtration was mixed with acetic acid (99% purity) and incubated for 60 minutes at a temperature of 110 °C, while stirring. A lead extraction efficiency between 75% and 85% was obtained. These results are obtained on artificially made samples. It should be noted that extraction efficiencies are typically roughly 10% higher when tests are based on post-consumer PVC samples than on artificially produced samples. Example 4: comparison of extraction solvents Lead-containing PVC based material comprising post-consumer PVC was grinded to a size <350 µm. The grinded lead-containing material was mixed with nitric acid (26%), nitric acid (13%), acetic anhydride (>99% purity), levulinic acid (98% purity) or acetic acid (99%-100% purity) as extraction solvent and incubated for 120 minutes at a temperature of 90°C, while stirring. The Hildebrand solubility parameters of the extraction solvents nitric acid, acetic anhydride, levulinic acid and acetic acid are 28.4 MPa1 / 2(def. B), 21.1 MPa1 / 2(def. A), 24.2 MPa1 / 2(def. B) and 20.7 MPa1 / 2(def. A), respectively. The Hildebrand solubility parameters of nitric acid 26% solution in water is 40.8 MPa1 / 2(def. B), and nitric acid 13% solution in water is 43.0 MPa1 / 2(def. B). These solubility parameters were estimated based on equations (1) and (2) where possible (def. A); if not, these were estimated according to definition B. The mixture was filtered. The extraction process was repeated a second time: the residue from the first filtration was mixed with the same extraction solvent and incubated for 120 minutes at a temperature of 90°C, while stirring. The results are illustrated in Figure 2. Lead extraction efficiencies are varying between 40% and 75% after the first extraction and between 50% and 90% after the second extraction. Example 5: single extraction with acetic acid – Cd extraction Lead- and cadmium-containing PVC based material comprising micronized post-consumer PVC (particle size < 1000 µm) was taken as starting material. The micronized post-consumer PVC was mixed with acetic acid (99% purity) as extraction solvent and heated for 120 minutes at a temperature of 110 °C, while stirring. The Hildebrand solubility parameter of the extraction solvent is 20.7 MPa1 / 2(according to the same source as indicated above). The mixture was filtered and rinsed with water. Two different post- consumer samples with the same size have been tested with an original lead content varying between 6000 ppm and 13000 ppm and a cadmium content between 40 ppm and 200 ppm. Lead and cadmium extraction efficiencies after a single extraction were 84% and 74%, respectively. Example 6: double extraction with acetic acid – extraction on flexible PVC Lead-containing PVC based rigid and flexible material obtained from artificially made sheets, was grinded to a size <400 µm. The grinded lead-containing material was mixed with acetic acid (99% purity) as extraction solvent and heated for 120 minutes at a temperature of 90 °C, while stirring. The Hildebrand solubility parameter of the extraction solvent is 20.7 MPa1 / 2(see above). The mixture was only filtered. The extraction process was repeated a second time: the residue from the first filtration was mixed with acetic acid (99% purity) and incubated for 120 minutes at a temperature of 90 °C, while stirring. Lead extraction efficiencies after a double extraction on the rigid and flexible samples were 74% and 84%, respectively. Extraction efficiencies are typically roughly 10% higher when tests are based on flexible samples than on rigid samples. Example 7: single extraction with Sulfonic Acid (MSA) or citric acid Lead-containing PVC based material comprising post-consumer PVC was grinded. After grinding, the sieve fraction <63 μm was collected and mixed either with methane sulfonic acid (≥99% purity) or with citric acid (50 % w / v solution of citric acid in water) as solvent and incubated for 120 minutes at a temperature of 90 °C, while stirring. The Hildebrand solubility parameters of the methane sulfonic acid and of the citric acid (50%w / v) are 27.0 MPa1 / 2and 38.3 MPa1 / 2, respectively (according to definition B). The mixture was filtered, rinsed with water and further dried. A lead extraction efficiency of 45-50% was obtained with both extraction agents. Example 8: single extraction with formic acid and oxalic acid Lead-containing PVC based material comprising micronized post- consumer PVC (particle size < 630 µm, as received from recycler) was taken as starting material. The micronized post-consumer PVC was mixed either with formic acid (>96% purity) or with oxalic acid (purity >99.5%)(55% w / v solution of oxalic acid in water) as extraction solvent and heated for 120 minutes at a temperature of 110 °C, while stirring. The Hildebrand solubility parameters of the formic acid and oxalic acid (55% w / v) are 24.7 MPa1 / 2(HSP acc. def. A) and 36.2 MPa1 / 2(HSP acc. def. B), respectively. The mixture was filtered, rinsed with water and further dried. Lead extraction efficiency after a single extraction was 40% and 15% with formic acid and oxalic acid, respectively. Example 9: single extraction with mixtures of acetic acid and water Lead-containing PVC based material comprising micronized post- consumer PVC (particle size < 630 µm, as received from recycler) was taken as starting material. The micronized post-consumer PVC was mixed with different ratios of acetic acid and water as extraction solvent and heated for 120 minutes at a temperature of °C, while stirring. The following percentages of water in acetic acid were tested: 0%v / v, 3%v / v, 7%v / v, 10%v / v, 20 %v / v, 50%v / v, 75%v / v and 90%v / v. The Hildebrand solubility parameters of the various water / acetic acid mixtures vary from 20.7 MPa1 / 2when no water is added to 45.2 MPa1 / 2for a 90% / 10%v / v water / acetic acid ratio (according to definition A). As in previous examples, the mixture was filtered, rinsed with water and further dried. Lead extraction efficiency after a single extraction decreased from 88% (no water addition), to 80% for 10%v / v water addition, to 70% for 20%v / v water addition and further down to 50% for 50%v / v water addition. Increasing the water ratio from 50%v / v to 90%v / v did not further reduce the efficiency: the lead extraction efficiency was maintained at a level of 50%.

Claims

Claims 1. Solid-liquid extraction method for reducing the lead content of a lead-containing polyvinyl chloride (PVC) based material, wherein said method comprises an extraction cycle comprising - providing a mixture comprising said lead-containing PVC based material and an extraction solvent; - heating said mixture to obtain a lead-reduced PVC based material and a lead-rich fraction; wherein said extraction solvent has a Hildebrand solubility parameter at 25°C and 1 atm in the range of 14 – 48 MPa1 / 2.

2. Method according to the previous claim, further comprising separating said lead-reduced PVC based material and said lead-rich fraction, preferably by filtration and / or centrifugation.

3. Method according to any of the previous claims, wherein said mixture is heated for a period of at least 1 minutes, preferably at least 15 minutes, more preferably at least 30 minutes, even more preferably at least 60 minutes, more preferably at least 90 minutes, most preferably at least 120 minutes.

4. Method according to any of the previous claims, wherein said mixture is heated at a temperature of at least 20 °C, preferably at least 50 °C, more preferably at least 60 °C, even more preferably at least 85 °C, most preferably in the range of 85 – 120 °C.

5. Method according to any of the previous claims, wherein said extraction solvent has a Hildebrand solubility parameter in the range of 17 to 26, preferably in the range of 18 to 25, more preferably in the range of 19 to 24 and / or wherein the extraction solvent comprises an acid and / oranhydride, preferably wherein the extraction solvent comprises at least one of an acid, anhydride of the acid, and an aqueous solution of the acid, the acid being selected from the group consisting of acetic acid, acetic anhydride, levulinic acid, citric acid, nitric acid, formic acid, oxalic acid, methane sulfonic acid, hydrochloric acid, p-Toluenesulfonic acid (PTSA), Ethylenediaminetetraacetic acid (EDTA) and combinations thereof, more preferably the extraction solvent comprises acetic acid.

6. Method according to any of the previous claims, further comprising pretreating the lead-containing PVC based material, preferably wherein said pretreating comprises reducing the size of the lead-containing PVC based material, more preferably wherein said method further comprises pulverizing, cutting, crushing and / or grinding of said lead-containing PVC based material.

7. Method according to any of the previous claims, wherein said extraction cycle is performed two or more times, such as 2 – 4 times, preferably 2 – 3 times, more preferably 2 times.

8. Method according to any of the previous claims, wherein the lead- containing PVC based material has typically a lead content above 1000 ppm, preferably above 4000 ppm, more preferably in the range of 6000 – 10000 ppm.

9. Method according to any of the previous claims, wherein the lead- reduced PVC based material has a lead content below 1000 ppm.

10. Method according to any of the previous claims, further comprising washing the lead-reduced PVC based material, preferably by rinsing, more preferably by rinsing with water and / or the extraction solvent.

11. Method according to any of the previous claims, wherein at least 80 wt%, preferably at least 85 wt%, more preferably at least 90 wt%, evenmore preferably at least 95 wt%, preferably at least 98 wt%, more preferably at least 99 wt% of said lead-containing PVC based material remains solid.

12. Method according to any of the previous claims, wherein said lead- reduced PVC based material remains solid during the method.

13. Method according to any of the previous claims, wherein said lead- containing PVC based material comprises post-consumer PVC.

14. Method according to any of the previous claims, wherein the lead- containing PVC based material comprises rigid PVC and / or flexible PVC.

15. Method according to any of the previous claims, wherein at least a first and a second extraction cycle are performed consecutively, wherein the lead-rich fraction from said second extraction cycle is used as extraction solvent for said first extraction cycle and preferably wherein the lead-reduced PVC based material from said first extraction cycle is used as lead-containing PVC based material for said second extraction cycle.

16. Method according to any of the previous claims, wherein the method also reduces cadmium content of a (PVC) based material.

17. Method for producing the lead-reduced lead-containing polyvinyl chloride (PVC) based material, comprising - providing a mixture comprising a lead-containing PVC based material and an extraction solvent; - heating said mixture to obtain a lead-reduced PVC based material and a lead-rich fraction; wherein said extraction solvent has a Hildebrand solubility parameter at 25°C and 1 atm in the range of 14 – 48 MPa1 / 2.

Images