Method for recycling post-consumer plastic material

Abstract

A method for recycling a vinyl chloride polymer material comprising an initial level of one or more additive compounds comprises: providing an aqueous acid composition comprising one or more alcohols and one or more acids; contacting the vinyl chloride polymer material with a volume of the acid composition to cause extraction of the one or more additive compounds from the vinyl chloride polymer material wherein the acid composition forms a two-phase system with the vinyl chloride polymer material, the two-phase system comprising a solid phase and a liquid phase, the solid phase comprises a purified vinyl chloride polymer material and the liquid phase comprises the alcohol, water, the acid and the extracted one or more additive compounds; and separating the solid phase comprising the purified vinyl chloride polymer material from the liquid phase comprising the extracted one or more additive compounds.

Description

Technical Field

[0001] The present invention relates to a method for recycling a vinyl chloride polymer material that contains an initial level of one or more heavy metals.

[0002] The present invention also relates to a method for recycling a vinyl chloride polymer material that contains an initial level of one or more additive organic compounds. Background Art

[0003] Vinyl chloride polymers are widely used in the manufacture of both a wide range of rigid and flexible products, such as window frames, flooring and roofing materials, pipes, and cable insulation. Vinyl chloride polymers can be obtained from the polymerization of vinyl chloride and are well-known for their tolerance to a range of chemicals (such as acids, bases). The properties of vinyl chloride-based polymers can be adjusted by compounding (i.e., blending) the polymer with additives to improve its mechanical and physical properties and expand its potential applications. 1、2 A wide variety of organic and inorganic additives are available for blending with vinyl chloride-based polymers at different concentrations, with the aim of adjusting material properties such as color, plasticity, abrasion resistance, flame retardancy, etc. for the intended use of the vinyl chloride polymer.

[0004] Typically, about 12% of PVC additives are flame retardants, such as non-halogenated phosphates and chlorinated paraffins. 3 Antimony trioxide (ATO) is typically used in combination with organic flame retardants. 4 Other inorganic flame retardants include metal hydroxides of aluminum or magnesium or aluminum trihydroxide.

[0005] To improve the thermal stability properties of vinyl chloride-based polymer products, thermal stabilizers or heat stabilizers are added. Typically, they account for 0.2% - 5% of PVC additives. Typical thermal stabilizers include mixed metal C8 - C18 aliphatic carboxylates that contain one or a combination of barium, calcium, cadmium, and zinc; organotin compounds; lead salts and soaps; calcium- or zinc-based fatty acid salts; organic thermal stabilizers, such as alkyl phosphites / aryl phosphites, epoxides, β-diketones, aminocrotonates, azacyclic compounds, organic sulfur compounds (i.e., ester thiols), hindered phenols, and polyols (pentaerythritol). Thus, thermal stabilizers typically contain heavy metal compounds.

[0006] Plasticizers can account for 15%-50% of the PVC formulation. By changing the type and amount of plasticizer, the PVC compound properties can be customized to meet the requirements imposed by the intended application or use. An increased plasticizer concentration increases flexibility, reduces tensile strength, and decreases hardness. For example, rigid PVC is mainly unplasticized, while flexible PVC contains added plasticizers to increase the flexibility of the plastic. Typical plasticizers used in PVC include phthalate-based esters, phosphate-based esters, and polyfunctional fatty acid esters.

[0007] Commercially available vinyl chloride polymers or products incorporating such polymers can therefore contain varying concentrations of a variety of organic compounds.

[0008] Due to its thermoplastic properties, PVC has many applications in industry and is a suitable material for recycling at end-of-life. However, the plastics collected are usually a mixture of different types of materials, even if they can be sorted by type of plastic material (e.g., PE, PET, PVC, etc.). Vinyl chloride polymers, for example, are typically a mixture of rigid, semi-rigid, and flexible materials. Alternatively, soft vinyl chloride polymers are collected as a mixture of materials with different softness levels.

[0009] However, the presence of additives (such as the organic and metal-containing additives discussed above) inhibits the primary or secondary recycling of vinyl chloride polymers as high-quality products, either because traditional initiatives enforce content below a certain level or because the cumulative concentration of certain additives deteriorates the properties of the plastic material.

[0010] In addition, the resources of some metals present in plastic additives are becoming increasingly scarce. For example, the European Commission has listed antimony as a critical raw material due to the increasing industrial demand and supply risks of antimony. During the period 2012-2016, China supplied 74% of the global antimony production. 6 In the EU, antimony is mainly used in flame retardants (43%), followed by lead-acid batteries (32%), lead alloys (14%), and to a lesser extent in plastic catalysts and stabilizers (6%) and glass and ceramics (5%). Although the plastics industry is a major user, antimony is currently only recycled on an industrial scale from spent lead-acid batteries, and due to its dispersion, recycling activities in the plastics industry remain limited. 7 Therefore, new ways are needed to recycle and recover antimony from secondary sources. 8

[0011] Laboratory-scale methods for recovering antimony from waste plastics focus on decomposing, pyrolyzing, or incinerating the waste plastics and recovering antimony or antimony trioxide from the resulting gases or residues. 8 ​These methods require the destruction of the polymers that form the plastic material in order to allow the recovery of antimony. In addition, antimony is commonly found dispersed in products derived from the recycling of waste plastics, in fly ash and bottom ash from waste incineration, and in landfills.

[0012] Accordingly, there is a need for a method by which elements such as antimony can be recovered from waste plastic materials with a high recovery rate.

[0013] Zhan et al. 11 disclosed a hydrothermal extraction method by which 87% of Sb can be recovered as SbS3 3- from ABS, and 90% of Br can be recovered as Br - from ABS. The method is carried out at 220 °C in a solution of 20 g L -1 NaOH and 50 g L - 1 Na2S at a L / S of 10 for 2 h. After extraction, the structure of the ABS is almost unchanged and suitable for further recycling. Although the Sb recovery rate is high, the method requires hydrothermal reaction conditions, i.e., it is carried out at elevated temperature and pressure. However, when such hydrothermal conditions are applied to PVC, dechlorination and hydrothermal carbonization will occur, resulting in polymer degradation and making the polymer unsuitable for further recycling.

[0014] EP 1817366 discloses a method for recovering heavy metal compounds (Pb and Cd) from vinyl chloride polymers. The method includes dissolving the vinyl chloride polymer in a solvent and treating the solution with an additive that can adsorb Pb and Cd compounds or form complexes with Pb and Cd compounds. However, the method disclosed in EP 1817366 involves dissolving the vinyl chloride polymer in a solvent, which has the risk of changing the polymer properties upon repeated use. The separation of the dissolved, purified polymer from the solvent is a complex and energy-intensive process, which may be further complicated by the presence of organic and inorganic additives contained in the vinyl chloride polymer. These additives need to be separated from the polymer and the solvent separately to allow repeated use.

[0015] Accordingly, there is a need for an economically attractive method for recycling vinyl chloride polymer materials, which makes it possible to remove additive compounds, especially heavy metal-containing additives and / or additive organic compounds, present in the vinyl chloride polymer material, and to recover vinyl chloride at a recovery rate that allows the method of interest to be scaled up to an industrial scale. There is also a need for a method that is energetically favorable and does not require the use of high temperature and pressure. Summary of the Invention

[0016] Accordingly, the present invention seeks to provide an economically and energetically attractive method for recycling vinyl chloride polymer materials at industrially interesting recovery rates, which method does not require the use of high temperatures and pressures.

[0017] According to the present invention, this is achieved by a method showing the technical features of the first claim.

[0018] Accordingly, the present invention relates to a method for recycling a vinyl chloride polymer material, which vinyl chloride polymer material contains an initial level of one or more additive compounds, preferably wherein the one or more additive compounds are selected from the group consisting of heavy metals and organic compounds. The method comprises:

[0019] (i). providing an aqueous acid composition comprising one or more alcohols and one or more acids,

[0020] (ii). contacting the vinyl chloride polymer material with a volume of the acid composition to effect extraction of the one or more additive compounds from the vinyl chloride polymer, wherein the acid composition is arranged to form a two-phase system with the vinyl chloride polymer material, the two-phase system comprising a solid phase and a liquid phase, the solid phase comprising the purified vinyl chloride polymer material, and the liquid phase comprising the alcohol, water, the acid, and the extracted one or more additive compounds,

[0021] (iii). separating the purified vinyl chloride polymer material from the liquid phase comprising the extracted one or more additive compounds.

[0022] The inventors of the present invention have surprisingly found that the method of the present invention allows extraction of most of the heavy metals present in vinyl chloride polymer plastic materials, in particular antimony (Sb), tin (Sn), zinc (Zn), lead (Pb), cobalt (Co), chromium (Cr), cadmium (Cd), and also magnesium (Mg), calcium (Ca), sodium (Na), potassium (K), aluminum (Al), barium (Ba), and phosphorus (P), and mixtures of any of these, advantageously without dissolving the vinyl chloride polymer. Depending on the nature of the metal, higher or lower extraction efficiencies can be achieved. High extraction efficiencies for Sb, Sn, S have been observed. Acceptable extraction efficiencies for Al, Ca, Cr, Mg, P, Pb, Si, Zn have been observed.

[0023] In addition, compared to existing technology methods, significantly higher extraction rates can be achieved for at least a portion of the metals listed above. Without wishing to be bound by theory, the inventors of the present invention hypothesize that the presence of the alcohol in the acid composition improves the ability of the acid to penetrate the polymer matrix and improves the accessibility of the inorganic additives embedded therein, without dissolving the polymeric material. The inventors of the present invention also hypothesize that the higher extraction rate can be attributed to the pH reduction caused by the presence of the alcohol in the acidic aqueous solution, when compared to the same acid concentration in water. Due to this improved accessibility and reduced acid concentration, improved heavy metal extraction can be achieved with an acid composition of a strong acid and an alcohol.

[0024] Advantageously, the pH of the aqueous acid composition and / or the liquid phase ranges between -0.0001 and -2.5, advantageously between -0.001 and -2.5, advantageously between -0.01 and -2.5, advantageously between -0.1 and -2.0, advantageously between -0.1 and -1.5.

[0025] This improved extraction can be achieved at temperatures significantly lower than those used in existing technology methods. In addition, the present invention does not require the method to be carried out at elevated pressures above atmospheric pressure. This energetic attractiveness combined with the high recovery rate highlights the economic attractiveness of this method for use on an industrial scale.

[0026] The inventors of the present invention have further surprisingly found that, despite the presence of metals that could otherwise catalyze the reaction between the acid and the alcohol, the formation of such unwanted reaction products has not been observed. In particular, the formation of alkyl halides or alkyl chlorides has not been observed. This is an advantage because these compounds are generally flammable, toxic, and carcinogenic.

[0027] The inventors of the present invention have also found that when a vinyl chloride polymer is brought into contact with the acid composition, most of the organic additive compounds are co-extracted. These extracted organic additive compounds are typically the additives contained in the vinyl chloride polymer, including plasticizers and heat stabilizers. The extraction of these organic additive compounds from the vinyl chloride polymer is important when envisioning the reuse of the purified vinyl chloride polymer, especially when envisioning reuse in other applications in addition to the one application from which the vinyl chloride polymer subjected to the method of the present invention originated. The extraction of the organic additive compounds minimizes the risk that the purified vinyl chloride polymer will interfere in an undesired manner with the intended properties of the materials with which it is mixed or incorporated. When the purified vinyl chloride polymer obtained from the method of the present invention is mixed with the original vinyl chloride polymer, any additives required to achieve the desired properties can be added, while minimizing the risk that any additives remaining in the purified vinyl chloride polymer will cause unwanted accumulation or adversely affect the properties of the mixture.

[0028] Advantageously, contacting the vinyl chloride polymer material with the acid composition can result in the purification, e.g., extraction, of additional additive compounds present in the vinyl chloride polymer material such as filler materials. The extraction of other filler materials (e.g., colorants, plasticizers, reinforcing materials, or other fillers such as calcium oxide) can be beneficial, especially if the purified vinyl chloride polymer obtained from the process of the present invention is further used in a subsequent compounding process.

[0029] Advantageously, the process of the present invention can be carried out at a relatively low temperature which does not affect the composition and structure of the vinyl chloride polymer or any organic additives present therein while achieving metal removal. The purified vinyl chloride polymer produced by the process of the present invention is thus suitable for recycling and reuse in an economically and ecologically efficient manner. The advantage presented by this low-temperature process is that the risk of degradation of the organic additives extracted or removed from the vinyl chloride polymer is minimal. On the other hand, appropriate procedures can also be used to recover the extracted one or more additive compounds, i.e., heavy metals and organic compounds, from the acid composition.

[0030] Furthermore, due to this low-temperature process, the risk of dechlorination and hydrothermal carbonization of the vinyl chloride polymer material (i.e., the risk of decomposition of the vinyl chloride polymer) can be minimized, and the purified vinyl chloride polymer that can be recovered from the process of the present invention is suitable for recycling and for mixing or compounding with other recycled or virgin vinyl chloride polymers for further use. In addition, it has been observed that the thermogravimetric analysis and differential scanning calorimetry characteristics of the purified vinyl chloride polymer are similar to those of the polymer subjected to the process of the present invention. Moreover, the HCN and chlorine composition of the purified vinyl chloride polymer is similar to those of the polymer subjected to the process of the present invention.

[0031] It should be clear to the person skilled in the art that the vinyl chloride polymer material can be subjected to the process of the present invention one or several times until a desired level of removal of certain or all additives (including heavy metals and organic compounds) has been obtained.

[0032] In a further step, after the purified vinyl chloride polymer material has been separated from the liquid phase containing the extracted organic additive compounds and one or more heavy metals, appropriate techniques for recovering each of these individual metals can be used to recover the metals from the liquid phase, and appropriate separation techniques can also be used to recover the organic additive compounds. After the organic additive compounds have been removed from the liquid phase, an aqueous alcohol phase containing one or more heavy metals remains. The one or more heavy metals can be recovered by separating the alcohol from the aqueous phase, e.g., by evaporating the alcohol and subsequently using appropriate techniques well known to the person skilled in the art to recover the one or more heavy metals.

[0033] According to an embodiment of the present invention, the acid composition comprises an alcohol, and the volume ratio of the alcohol to the acid composition is at least 5 vol.%, preferably at least 7.5 vol.%, more preferably at least 8 vol.%. Within these ranges, optimal penetration of the acid composition (containing the alcohol) into the polymer material and the desired extraction of the organic additive compounds (such as plasticizers) contained in the polymer material can be achieved.

[0034] According to an embodiment of the present invention, the acid composition comprises an alcohol in a volume ratio of at least 40 vol.%, preferably at least 50 vol.%, more preferably at least 60 vol.%, to ensure that the efficiency of extracting one or more heavy metals from the vinyl chloride polymer material can be maintained at a level of interest in industrial applications and to minimize the risk of polymer degradation when the acid concentration rises too high.

[0035] A variety of alcohols are suitable for use in the method of the present invention. Suitable alcohols include one or more alcohols from the group of mono-, di- or poly-hydroxide alcohols. According to an embodiment of the present invention, the alcohol can be a C1-C8 alkanol or a C1-C5 alkanol, although branched-chain alcohols can also be used. According to an embodiment of the present invention, suitable diols include ethylene glycol, propylene glycol, etc. Ethanol is a particularly preferred monohydric alcohol because, compared with water, it has a low boiling temperature, which will help remove the alcohol phase and recover one or more metals from the acid-water phase. In addition, ethanol has a favorable viscosity, which helps with mixing and filtration. Higher alcohols may have higher viscosities.

[0036] According to an embodiment of the present invention, contacting the vinyl chloride polymer material with the acid composition to cause the extraction of at least one heavy metal from the vinyl chloride polymer is carried out at a temperature of at least 20 °C, preferably at least 30 °C, more preferably 40 °C or higher, most preferably 50 °C or higher. In particular, contacting the vinyl chloride polymer material with the acid composition to cause the extraction of at least one heavy metal from the vinyl chloride polymer is carried out at a temperature between 20 °C and 100 °C, preferably between 30 °C and 90 °C, more preferably between 40 °C and 90 °C, most preferably between 50 °C and 85 °C. The inventors of the present invention have observed that the accessibility of the vinyl chloride polymer material is optimal at a temperature equal to or higher than its glass transition temperature Tg. Using a maximum temperature of 100 °C allows the method to be carried out at atmospheric pressure and thus avoids the use of a pressurized reactor.

[0037] In the method of the present invention, a variety of acids can be used, especially strong acids. The acid preferably includes one or more strong inorganic acids having a pKa value of at most -2 in water, preferably strong inorganic acids selected from hydrochloric acid HCl, H2SO4, HBr, HI. The acid can also include one or more strong organic acids having a pKa value of at most -1.9 in water, preferably selected from p-toluenesulfonic acid, methanesulfonic acid. The acid can further comprise one or more organic acids selected from oxalic acid, formic acid, acetic acid, citric acid. It should be clear that the acid can include a mixture of two or more of the above acids. In a preferred embodiment of the present invention, the acid includes HCl. In a further preferred embodiment of the present invention, the acid is a non-oxidizing acid. The selection of non-oxidizing acid helps to minimize the risk of oxidizing the organic additive compounds present in the liquid. Those skilled in the art should be clear that other non-oxidizing acids and mixtures of two or more acids can also be used.

[0038] The concentration of the acid (preferably HCl) in the acid composition can vary within a certain range, but is preferably at least 1 M (molar concentration) and at most 12 M, preferably at least 2 M and at most 10 M, more preferably at least 2 M and at most 8 M, most preferably 3.5 - 5.5 M. It has been observed that the effect of alcohol on the reaction of the acid with the metal to be extracted varies with the acid concentration. At concentrations below 2 M, the extraction efficiency achieved with HCl becomes unattractive for scaling up to industrially interesting levels, and at 12 M, the extraction efficiency also decreases. These conditions particularly support the extraction of Sb and Sn. If other metals such as Zn and Pb are envisaged for extraction, lower acid concentrations (e.g., below 0.5 M or below 0.25 M, especially below 0.1 M) may be sufficient.

[0039] In the method of the present invention, a vinyl chloride polymer material is mixed with a certain volume of an acid composition comprising water, an acid, and an alcohol to cause the extraction of at least one heavy metal from the vinyl chloride polymer. A two-phase system is formed by a solid phase comprising the vinyl chloride polymer material and a liquid phase comprising water, the acid, the alcohol, and the extracted one or more heavy metals and one or more extracted organic additive compounds. According to an embodiment of the present invention, the vinyl chloride polymer material can be mixed with the acid composition at a weight ratio of the solid polymer material to the acid composition ranging from 1:100 to 1:1, preferably from 1:50 to 1:2, preferably from 1:25 to 1:2, more preferably from 1:10 to 1:2, which is defined as the mass of the vinyl chloride polymer material relative to the total mass of the acid and the vinyl chloride polymer compound. In this way, the amounts of the acid and the alcohol used for extracting at least one heavy metal can be balanced with the amount of the polymer material to be treated, and high extraction efficiency can be achieved while limiting the amounts of the alcohol and the acid used. An excessively high vinyl chloride polymer compound loading may increase the apparent viscosity and / or impede the processing and / or separation (such as filtration) steps.

[0040] Advantageously, step (ii) does not include any substantial dissolution of the vinyl chloride polymer in the acid composition and / or the liquid phase. The aqueous acid composition, and in particular the acid in the acid composition, is advantageously a poor solvent for the vinyl chloride polymer. Advantageously, based on the weight of the vinyl chloride polymer contained in the initial vinyl chloride polymer material, at least 80% by weight, advantageously at least 85% by weight, advantageously at least 90% by weight of the vinyl chloride polymer is recovered in the solid phase. Advantageously, after leaching at 80 °C for 5 hours with continuous stirring, the aqueous acid composition is capable of dissolving no more than 8 g of vinyl chloride polymer / litre of aqueous acid composition, advantageously no more than 6 g of vinyl chloride polymer / litre of aqueous acid composition, advantageously no more than 4 g of vinyl chloride polymer / litre of aqueous acid composition. Any observed weight loss is generally not due to the dissolution of the polymer material itself, but to the leaching or dissolution of inorganic and / or organic additives contained in the vinyl chloride polymer material.

[0041] According to an embodiment of the invention, the vinyl chloride polymer material can be suspended in the acid composition. The suspension can be provided by vortexing, mixing, stirring, shaking or any other suitable suspension method known in the art. Preferably, the fluid and the vinyl chloride polymer compound are suspended (contacted) in a stirred batch reactor. Alternatively or additionally, a continuous system can be employed, in which the PVC particles are suspended. It should be understood that other types of reactors (such as fluidized bed reactors) suitable for mixing the acid composition and the vinyl chloride polymer compound phase can also be applicable.

[0042] The vinyl chloride polymer material in various forms or shapes (such as in the form of particles, flakes, sheets, slices or parts) can be brought into contact with a certain volume of the acid composition. The vinyl chloride polymer material can have a variety of sizes, for example, sizes selected in the range of 100 μm to 10 mm, preferably 100 μm to 40 mm, more preferably in the range of 500 μm to 10 mm, most preferably in the range of 1 mm to 5 mm. In other words, the polymer material used in the method of the invention can contain particles with a maximum size within the above range. The size of the particles can be determined by any suitable method known to the person skilled in the art, such as by using scanning electron microscopy (SEM) and image analysis or laser diffraction or sieving according to ISO standard 1624.

[0043] In an embodiment of the invention, the acid composition is brought into contact with the vinyl chloride polymer material at a certain temperature for a certain time to reduce the amount of heavy metals (especially antimony) by at least 50%, preferably at least 60%, more preferably at least 75%, most preferably at least 90%.

[0044] According to a further embodiment of the present invention, a purified vinyl chloride polymer is mixed with the original vinyl chloride polymer to obtain a secondary vinyl chloride polymer.

[0045] In a further aspect, the present invention relates to a purified vinyl chloride polymer material, such as obtained or obtainable by the methods disclosed herein, as listed in the appended claims. The present invention also relates to a secondary vinyl chloride polymer composition comprising the original vinyl chloride polymer and a purified vinyl chloride polymer obtained or obtainable by the methods disclosed herein, as listed in the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 Shows the leaching rates of Al and Sb as a function of reaction time in 1M HCl at 250 °C and at L / S = 10.

[0047] Figure 2A Shows the leaching rates of Al and Sb (bottom) as a function of HCl concentration at 150 °C for 2 h and at L / S = 10.

[0048] Figure 2B Shows the Eh-pH diagram of 0.03M Sb in the presence of different concentrations of Cl - The points in the figure are the average pH and Eh values measured in the solution after leaching in 1M (squares), 2M (circles), 4M (triangles) and 6M (diamonds) HCl solutions at 150 °C.

[0049] Figure 3 Shows the leaching rates of Al and Sb at 50 °C and 80 °C for 2 h at L / S = 10 in aqueous and ethanol HCl solutions of different concentrations.

[0050] Figure 4 Shows the DSC and TGA curves of the original PVC sample and the residue obtained after leaching in 4M ethanol HCl solution at 80 °C for 5 h.

[0051] Figure 5 Shows the XRD diffraction pattern of the precipitate. In-situ XRD was performed while heating the sample to different temperatures. The red question marks indicate diffraction peaks that cannot be assigned to known mineral phases in the ICDD powder diffraction database.

[0052] Figure 6 Shows the X-ray diffraction pattern of the obtained precipitate. All observed diffraction peaks can be assigned to the Sb4Cl2O5 mineral phase (space group P21 / c ( β = 97.20°)).

[0053] Figure 7AThe SEM image of the untreated PVC material is shown. Figure 7B The SEM image of the PVC material leached in ethanol 4M HCl at 80 °C for 4 h is shown. Figure 7C It shows Figure 7A The EDX image of Al of the PVC material of Figure 7D It shows Figure 7B The EDX image of Al of the PVC material of Figure 7E It shows Figure 7A The EDX image of Sb of the PVC material of Figure 7F It shows Figure 7B The EDX image of Sb of the PVC material of ; The strong coloring of Sb in the EDX picture is mainly due to background noise rather than the actual presence of Sb. Figure 7G It shows Figure 7A The EDX image of Si of the PVC material of Figure 7H It shows Figure 7B The EDX image of Si of the PVC material of

[0054] Figure 8 The TGA-DSC analysis of the PVC starting material is shown.

[0055] Figure 9 The Gibbs free energy of the reaction Sb2O5 + 3HCl → 2SbCl3 + 3H2O is shown, as modeled by HSC Chemistry8 software.

[0056] Figure 10 The DSC and TGA curves of the original cryogenically milled PVC sample and the residue obtained after leaching in 4M ethanol HCl solution at 80 °C for 4 h are shown.

[0057] Figure 11 The variation of the leaching rates of Al and Sb with the reaction temperature in 1M HCl aqueous solution or 4M HCl aqueous solution at L / S = 10 for 2 h is shown. Detailed implementation

[0058] The terms used to describe the specific embodiments of the present invention are not intended to limit the present invention. Unless the context clearly indicates otherwise, as used herein, the singular forms "a", "an" and "the" are intended to also include the plural forms. The term "and / or" includes any and all combinations of one or more of the related listed items. It should be understood that the terms "comprises" and / or "comprising" specify the presence of the stated features, but do not preclude the presence or addition of one or more other features. It should be further understood that, unless otherwise stated, when a specific step of a method is referred to as subsequent to another step, it can directly follow the said another step, or one or more intermediate steps can be carried out before carrying out this specific step. Similarly, it should be understood that when describing a connection between structures or components, unless otherwise stated, such a connection can be established directly or through intermediate structures or components.

[0059] In the case where one claim refers to another claim, this may indicate a synergistic advantage achieved by combining their respective features. However, the mere fact that certain measures are recited in different claims does not indicate that the combination of these measures cannot be used advantageously otherwise. Embodiments of the present invention can thus include all working combinations of the claims, where, unless the context clearly excludes it, each claim can in principle refer to any one of the foregoing claims. For the purposes of clear and concise description, features are described herein as part of the same or separate embodiments, however, the scope of the present invention should be understood.

[0060] Vinyl chloride polymer materials that have been subjected to the method of the present invention can be referred to as purified vinyl chloride polymers, extracted vinyl chloride polymers or recycled vinyl chloride polymers, or any other equivalent wording. Purified vinyl chloride polymer materials that have been subjected to the method of the present invention can contain reduced levels of organic additive compounds and / or metal ions relative to the vinyl chloride polymer materials to be subjected to the method of the present invention.

[0061] It should be understood that the method described herein for recycling vinyl chloride polymer compounds can be particularly useful for recycling post-consumer PVC products. Thus, the vinyl chloride polymer compounds are preferably provided by particulate post-consumer PVC products.

[0062] Advantageously, the present invention can be adapted to reduce the levels of a wide range of additives currently used in vinyl chloride polymer blends, such as heat stabilizers, plasticizers, softeners, reinforcing materials, colorants, and any other additives containing heavy metal ions, particularly antimony (Sb), tin (Sn), zinc (Zn), lead (Pb), cobalt (Co), chromium (Cr), cadmium (Cd), as well as magnesium (Mg), calcium (Ca), sodium (Na), potassium (K), aluminum (Al), barium (Ba), and phosphorus (P), and mixtures of any of these.

[0063] The main metals contained in currently used stabilizers are lead (Pb), barium (Ba), calcium (Ca), cadmium (Cd), zinc (Zn), and tin (Sn). Although the use of cadmium stabilizers is currently restricted, products containing such stabilizers are still in use and can be purified according to the present invention to allow for the recycling of vinyl chloride polymer materials. Heat stabilizers for vinyl chloride polymers can be classified as Pb stabilizers, Ba-Zn stabilizers, Ca-Zn stabilizers, and Sn stabilizers. Pb stabilizers, Ba-Zn stabilizers, and Ca-Zn stabilizers can be used as metal soaps such as stearates. Sn stabilizers are typically used as organotin (dialkyltin compounds). In addition to metal soaps, Pb stabilizers can alternatively or additionally be used as basic sulfates, basic carbonates, or basic phosphate compounds. In a preferred embodiment, the heavy metals in the heavy metal compounds are selected from the group consisting of lead, cadmium, zinc, tin, barium, calcium, or mixtures of any of these.

[0064] Contact a fluid acid composition with a vinyl chloride polymer compound at a certain temperature for a certain time, the time and temperature being sufficient to reduce the amount of heavy metals in the vinyl chloride polymer from an initial level to a predefined desired purification level. Preferably, the acid composition and the vinyl chloride polymer material are contacted at a certain temperature for a certain time to reduce the amount of heavy metals in the vinyl chloride polymer from the initial level by at least 50%, preferably at least 60%, more preferably at least 75%, most preferably at least 80%, particularly at least 90%, more particularly at least 95%, or even at least 99.9%. Any known method in the art can be used to determine the heavy metal content in the vinyl chloride polymer compound. In particular, XRF or acid digestion can be used, followed by ICP-MS and / or ICP-OES. Advantageously, the processing parameters of the method, such as contact time, temperature, nature of the acid, loading, and their combinations, can be selected to result in the formation of a purified vinyl chloride polymer in which the level of the heavy metal additive compound is less than 1 wt.%, preferably less than 0.5 wt.%, more preferably less than 0.1% (based on the mass of the heavy metal additive compound relative to the total dry mass of the vinyl chloride polymer material, as determined by ICP-OES).

[0065] Waste vinyl chloride polymer materials are generally available in a wide variety of shapes, depending on their original use. To achieve efficient extraction from the intact polymer material down to the internal parts of the material, vinyl chloride polymer materials in the form of particles, flakes, fragments or sheets can be brought into contact with a certain volume of an acid composition. These particles, flakes, fragments or sheets should on the one hand be large enough to allow efficient separation of the solids and should be small enough to allow the acid composition phase to penetrate into the majority of the solid polymer.

[0066] Methods for comminuting plastics to smaller particle sizes include, but are not limited to, milling, grinding and cryogenic milling / grinding. It should be understood that the size reduction can be carried out by any suitable size reduction method known to the person skilled in the art, for example in the field of size reduction methods for plastic recycling, such as size reduction methods according to common practice for PVC recycling. Furthermore, granulating the vinyl chloride polymer compound can be beneficial during the remixing process using a purified vinyl chloride polymer compound as starting material. It should be understood that small amounts (e.g. up to 10% by mass) or amounts of particles smaller and / or larger than the specified range typically present after a common granulation process can also be processed. Good results have been obtained with particles having a size in the specified range, for example in the range from about 100 μm to 40 mm, more preferably in the range from 500 μm to 10 mm and most preferably in the range from 1 mm to 5 mm. Purification tests have shown near-complete heavy metal extraction, with contact times between 5 minutes and 8 hours, such as 2 hours or even 1 hour. It should be understood that the method can be carried out using different contact times, different contact temperatures, different particle sizes and / or combinations thereof, depending on the desired level of purification.

[0067] Although additional extraction steps can be considered to remove the remaining additives and one or more heavy metals - in other words, although the vinyl chloride polymer material can be subjected to the method of the invention several times - the invention is capable of reducing the level of heavy metal compounds in the purified vinyl chloride polymer (particles) to a level that allows the use (e.g. reuse) of the formed vinyl chloride polymer during the remixing process.

[0068] The purified vinyl chloride polymer will generally have a shape conforming to the shape of the vinyl chloride polymer subjected to the method of the invention. For example, the purified vinyl chloride polymer can be in the form of particles, flakes, sheets, pieces or parts or any other convenient shape.

[0069] A preferred strong acid for use in the process of the present invention is an aqueous solution of HCl, which can be particularly useful in a process for purifying vinyl chloride polymer compounds, where at least one heavy metal compound is antimony (Sb), due to the possible formation of soluble SbCl3 or ionic antimony chloride complexes. Coloring on the surface of the purified vinyl chloride polymer (so-called red discoloration) can indicate residual heavy metal additive compounds (such as salts) or other additives. It should be understood that the coloring does not necessarily indicate poor extraction performance or poor product quality, as the coloring may be visible at very low tolerable (e.g., trace) levels of heavy metal additive compounds. On the other hand, in fact, for a process aimed at reducing the Pb level in vinyl chloride polymer compounds, the absence of coloring, such as the formation of a colorless (e.g., white) vinyl chloride polymer (granules), can indicate successful heavy metal removal (reduction).

[0070] In an embodiment of the present invention, one or more alcohols, preferably ethanol, can be reused. Before reuse, any compounds contained in the one or more alcohols, such as organic compounds and / or heavy metals, can be removed from the one or more alcohols.

[0071] In other embodiments, the acid composition can be reused. In other words, after separating the purified vinyl chloride polymer compound from the acid phase, the acid phase can be reused to purify another volume of vinyl chloride polymer compound containing heavy metal compounds. Preferably, the acid composition is reused as long as the extraction efficiency results in a treated vinyl chloride polymer having an acceptable reduced level of at least one heavy metal (e.g., Sb). The desired target for vinyl chloride polymer, especially PVC compounding, limits the use of Sb to a maximum level of 0.1 wt.%. Preferably, the level of heavy metal (e.g., Sb) in the purified vinyl chloride polymer does not exceed 0.3 wt.%. Optionally, the vinyl chloride polymer compound material can be prepared by blending (e.g., mixing) a suitable amount of the original or otherwise recycled vinyl chloride polymer with the purified vinyl chloride polymer particles obtained from the present invention. In such processes, higher levels (e.g., double or quadruple) of some heavy metals can be acceptable depending on the amount of the original vinyl chloride polymer blended with the purified vinyl chloride polymer.

[0072] In some embodiments, the method of the present invention additionally includes a washing step, in which the separated and purified vinyl chloride polymer is contacted with a washing liquid to wash the residual acid phase (such as a liquid acid phase) from the vinyl chloride polymer. Washing the purified vinyl chloride polymer can remove the residual amount of acid adhering thereto, for example, adhering to the outer surface of the purified vinyl chloride polymer compound. Thus, washing can also wash (such as remove) residual heavy metal additive compounds from the purified vinyl chloride polymer compound. It should be understood that the washing can be carried out at a temperature range similar to that used during the extraction step of contacting the vinyl chloride polymer material with a certain volume of acid composition. Therefore, the washing is preferably carried out at a temperature between 20 °C and 85 °C.

[0073] The purified vinyl chloride polymer compound recovered from the method of the present invention (which has been contacted with an aqueous acid composition) can be washed with at least a first washing liquid. The washing liquid is preferably selected to have a strong interaction with heavy metals to ensure that any metal remaining on the surface of the purified vinyl chloride polymer is removed. The washing liquid preferably has a low affinity for the vinyl chloride polymer, especially low solubility. The washing liquid should not cause precipitation of heavy metals or the acid of the aqueous acid composition.

[0074] The first washing liquid can be selected from the group consisting of water and aqueous solutions of acids. However, a particularly suitable first washing liquid comprises an aqueous acid composition that contains one or more alcohols and one or more acids, and this aqueous acid composition is used to cause the extraction of one or more additive compounds from the vinyl chloride polymer material, because this will ensure better removal of any extracted aqueous acid composition remaining on the purified vinyl chloride polymer.

[0075] The washing step can be repeated several times. Thus, the same washing liquid, such as the first washing liquid, can be used, but the second washing step and any further washing steps can also be carried out with water. Good washing performance has been obtained with an aqueous washing solution, especially water itself.

[0076] It should be understood that the first washing liquid used for washing preferably has a low initial level of dissolved heavy metal additive compounds, at least low enough to achieve the dissolution of the heavy metals contained in the acid phase adhering to the purified vinyl chloride polymer compound (particles). Preferably, the first washing liquid can be reused until the washing performance deteriorates, for example, until the washed vinyl chloride polymer contains less than 0.1 wt.% of heavy metal additive compounds, such as Sb compounds.

[0077] It should be understood that the purification method for purifying vinyl chloride polymer compounds described herein can be particularly useful for the recycling of post-consumer PVC products. Therefore, the vinyl chloride polymer compounds are preferably provided by particulate post-consumer PVC products. Such products include, but are not limited to, window frames, pipes, roofing and / or flooring materials, and flexible PVC products.

[0078] According to a further aspect, the present invention relates to the use of an acid composition for reducing the level of one or more heavy metals in a heavy metal salt-stabilized PVC material (such as in a post-consumer PVC material).

[0079] According to a further aspect, the present invention relates to vinyl chloride polymers, in particular vinyl chloride polymer particles, obtainable by the purification method according to the present invention. Advantageously, the level of heavy metal compounds in the purified vinyl chloride polymer (particles) is reduced to a level that allows the use (such as reuse) of the formed vinyl chloride polymer during the compounding process. Preferably, the level of heavy metals in the purified vinyl chloride polymer does not exceed 0.1 wt.%. More preferably, the heavy metal level does not exceed 0.01 wt.%. In the absence of purification, the vinyl chloride polymer compounds can contain significant levels of heavy metal additive compounds. For example, PVC can contain up to approximately 10 wt% of heavy metal heat stabilizers. If lead stearate is used, this corresponds to a Pb loading of about 3 wt% in the compound.

[0080] The present invention is described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. The provided examples are not intended to be limiting in any way. The described amounts, weights and ratios, temperatures and contact times disclosed in the above specification and the following examples can be rounded and should not be construed in a limiting manner. The usual ranges of uncertainty apply.

[0081] Examples

[0082] Materials and Methods

[0083] Materials

[0084] Commercially available antimony-containing flexible PVC sheet samples were cut into uniform thin slices of 1 cm × 1 cm and cryogenically ground to <4 mm by immersing the material in liquid nitrogen, and then processed with a Fritsch Pulverisette cutting mill equipped with a 4 mm sieve.

[0085] Hydrochloric acid (37 wt.% HCl in water) and n-hexane ( ≥98.0%) was purchased from Merck KGaA (Darmstadt, Germany), ethanol (anhydrous) and 2-propanol (technical grade, ≥98%) were purchased from VWR Chemicals (Fontenay-sous-Bois, France), and sodium chloride (99.5%) was purchased from Fisher Scientific Chemicals (Loughborough, UK). All chemicals were used as received without any further purification.

[0086] Leaching optimization experiments

[0087] Pressure leaching above 100 °C was carried out in a General Acid Digestion Reactor vessel 4744 from Parr Instrument Company. A PVC sample (2 g) was introduced into the acid digestion vessel together with 20 mL of aqueous hydrochloric acid. The reaction vessel was sealed and heated in an oven at the set reaction temperature for the selected reaction time. Next, the vessel was removed from the oven and cooled to room temperature, after which the reactor was opened and the reduction potential and pH of the reaction mixture were measured. Solid-liquid separation was carried out by vacuum filtration using a 0.45 μm mixed cellulose ester membrane filter from Whatman. The separated purified PVC was washed to remove the remaining reagents, and the wash water was collected separately. To ensure the absence of solids in the leachate for ICP-OES analysis, the leachate was filtered again using a 0.45 μm polyamide syringe filter from Macherey-Nagel, and the filtrate was diluted with 5 vol% nitric acid for preservation. The purified PVC was dried at 40 °C and subsequently analyzed by X-ray fluorescence (XRF). All experiments were carried out in duplicate.

[0088] For leaching in aqueous solution at temperatures below 100 °C, a 2 g PVC sample was placed in a PTFE container with 20 mL of aqueous hydrochloric acid. All experiments were carried out in duplicate. The PTFE container was sealed and then shaken at 225 rpm for 2 h at the set reaction temperature in a water bath. After termination of the leaching process, the container was removed from the water bath and cooled to room temperature. Subsequently, the solid and liquid fractions were recovered following the same procedure as described above for the aqueous pressure leaching experiment.

[0089] For the leaching process with an organic acid composition, the experiments were carried out in a round-bottom flask equipped with a reflux condenser to prevent solvent evaporation. During these experiments, an ethanol-hydrochloric acid solution was used as the acid composition, where 37 wt.% (12 M) aqueous HCl was diluted with pure ethanol to obtain the desired HCl concentration. The reaction mixture in the flask was heated in a water bath at the required reaction temperature for 2 h. After the leaching process, the round-bottom flask was cooled to room temperature, after which the reduction potential and pH of the liquid phase were measured. After the leaching process, the solid precipitate was separated by using a 0.45 μm polyamide syringe filter from Merck Millipore. Subsequently, the residue from the chemically leached PVC was dried at 40 °C. Since the ICP-OES analysis of the liquid fraction was carried out with aqueous standards, the ethanol present in the leachate needed to be removed by rotary evaporation. Once the ethanol was removed from the sample, the leachate was diluted to 20 mL with ultrapure water. Subsequently, 5 vol% nitric acid was added for preservation. The solid residue was dried at 40 °C and analyzed by XRF.

[0090] Antimony recovery optimization

[0091] Larger-scale leaching experiments were carried out in a 1 L round-bottom flask placed in a heating mantle and equipped with a reflux condenser. The flask was filled with 50 g of PVC sample (1×1 cm flakes) and 500 mL of 4 M HCl ethanol solution. The reaction mixture was heated to 80 °C for 5 h. After cooling to room temperature and filtration, the recovered leach solution was divided into two equal-volume identical fractions (235 mL); FR1 and FR2.

[0092] Ethanol was removed from FR1 by rotary evaporation (130 mbar, 55 °C). While FR2 was not treated by evaporation. Subsequently, at room temperature and under constant stirring by a magnetic stir bar, MilliQ water was gradually added to known volumes of FR1 and FR2 by means of a graduated burette. The pH of the solution was measured after each water addition step. Water was added until the formation of a precipitate could be observed, after which the solution was stirred for an additional 1 h. Next, the slurry obtained for FR1 was filtered through a 0.45 μm mixed cellulose ester membrane filter (Whatman) to recover the precipitate, while for the FR2 solution, the solid was recovered by centrifugation (5 min, 3500 rpm). The solid residue was dried at 40 °C in a nitrogen atmosphere until a constant mass was obtained. The liquid fraction obtained was analyzed by ICP-OES, and the solid residue was analyzed by XRD and ICP-OES after acid digestion.

[0093] Process validation experiments

[0094] Place the cryogenically milled PVC sample (50 g) into a 1 L round-bottom flask and add 500 mL of 4 M HCl ethanol solution thereto. The flask is equipped with a condenser and heated to 80 °C by a heating mantle and allowed to react for 4 h under gentle stirring (150 rpm). After cooling to room temperature, the reaction mixture is filtered through a Whatman cellulose filter to remove the solid purified PVC. The purified PVC is washed on the filter with additional ethanol, which is added to the collected filtrate. The purified PVC is dried at 50 °C and then analyzed by TGA-DSC, DART-MS, and ICP-OES (after acid digestion). Ethanol is removed from the filtrate by rotary evaporation (150 mbar, 55 °C). Subsequently, the aqueous acid composition is washed twice with 50 mL of n-hexane in a separatory funnel. The n-hexane solution is collected for DART-MS analysis and the aqueous fraction is collected in a flask. The oil layer adhering to the separatory funnel is washed off with 2-propanol and collected for DART-MS analysis. A known volume of MilliQ water is gradually added to the washed aqueous leach solution under constant stirring until a precipitate is observed. Thereafter, an additional 100 mL of MilliQ water is added and stirred for an additional 1 h. The precipitate is filtered off through a Whatman membrane filter (0.45 μm) and the filtrate is collected for ICP-OES analysis. The precipitate is dried at 50 °C and then analyzed by XRD, XRF, and ICP-OES (after acid digestion). All experiments are carried out in duplicate.

[0095] Analysis methods

[0096] ICP-OES analysis was performed using a PerkinElmer Avio 500 optical emission spectrometer with prepfast. Before ICP-OES analysis, the aqueous samples were stabilized with 5 vol% HNO3. Solid samples were subjected to acid digestion followed by ICP-OES analysis, where the samples were dissolved in HNO3 / H2O2 / HCl solution and microwave digested at 250 °C for 180 min under high pressure.

[0097] X-ray fluorescence (XRF) analysis of solid samples was performed using a Thermo Scientific Niton XL3t GOLDD+ handheld XRF analyzer.

[0098] For thermogravimetric and differential scanning calorimetric analysis of PVC samples, a NETZSCH STA 449F3 Jupiter simultaneous thermal analyzer was used.

[0099] X-ray diffraction (XRD) was performed using a PANalytical Empyrean diffractometer (Co anode) to determine the crystal phase composition of the obtained precipitate. Qualitative analysis of the diffraction patterns was carried out using HighScore Plus software.

[0100] DART-MS measurements were performed by Thermo Scientific TM Q Exactive. DART was used with helium at an operating temperature of 450 °C to qualitatively analyze the additives present in the PVC sample as well as in the organic liquid phase. Measurements were carried out in positive and negative ion modes, where liquid samples were picked up with a glass capillary, while solid PVC samples were held in front of the DART using tweezers.

[0101] The presence of organic additives was measured and quantified by GC MS. Measurements were carried out on a Trace DSQ GC MS (Thermo Fisher Scientific) equipped with a VF1701 30 m; 0.25 mm 0.25 μm column. The helium flow rate was set to 1 ml / min. The injection volume was 1 μl, the split ratio was 1:50, and the syringe temperature was 250 °C. The oven program was set to: at 20 °C min -1 , 60 °C to 280 °C. Hold for 5 min, at 20 °C / min to 320 °C, and hold again for 5 min. At a scan rate of 1000, the mass range was set to 50 - 650 amu. D4 dibutyl phthalate was incorporated into the sample as an internal standard.

[0102] SEM analysis was performed on cryo-milled PVC samples and purified PVC after leaching through the FEI NOVA NANOSEM 450 platform equipped with a BRUKER QUANTAX 200 SDD detector for EDX analysis. Before electron microscopy, the samples were embedded in Epofix resin, polished, and coated with Pt.

[0103] Thermodynamic modeling was carried out using HSC Chemistry 8 software.

[0104] Characterization of starting materials

[0105] The PVC starting materials were extensively characterized to obtain an accurate understanding of their composition. The average concentrations of inorganic elements were determined by ICP - OES analysis on 5 sub - samples of the PVC materials studied. The inorganic elements with the highest concentrations were antimony (3.8 wt.%) and aluminum (3.3 wt.%). Therefore, these two elements will be subsequently tracked to allow comparison of their leaching efficiencies. Antimony is usually present in plastics as antimony trioxide (ATO) (Sb2O3), while the presence of aluminum can be attributed to its presence as aluminum trihydroxide (ATH) (Al(OH)3), which is a commonly used filler material in plastics.

[0106] DART - MS analysis of the starting materials qualitatively revealed the presence of the following organic additives in the PVC materials: Phosflex (bis(2 - ethylhexyl)phenyl phosphate), dioctyl phthalate, and diethyl phthalate, along with SbCl3OH, FeCl3, FeCl4, and some other trace compounds of unknown composition (m / z 372 and 451).

[0107] Detailed analysis by GC - MS confirmed the presence of bis(2 - ethylhexyl)phenyl phosphate (7188 μg g -1 )(also known under the trade name Phosflex ) and diisononyl phthalate (26364 μg g -1 ). In addition, the antioxidant butylated hydroxytoluene (5893 μg g -1 ) was also detected.

[0108] Table 1 : Elemental composition of PVC, average of 5 samples measured by ICP - OES.

[0109]

[0110]

[0111] The N, C, H, and S contents of the analyzed material were 0.20 wt%, 42.84 wt%, 6.37 wt%, and 0.23 wt% respectively. Finally, the chlorine content was 22 wt%. Comparison between the H:C molar ratios of fresh PVC and treated PVC provides an indicative measure of its dechlorination rate. Respectively, for pure PVC, H:C = 1.5 and for its polyol or polyene dechlorination products, H:C = 2 or 1. The H:C molar ratio of the starting materials studied was equal to 1.8.

[0112] Measurements of the thermal behavior of the studied PVC samples in air by TGA-DSC showed a glass transition temperature of 58.2 °C, and decomposition in air started at about 200 °C and proceeded very rapidly at 272 °C( Figure 8 ). At 513 °C, a strong exothermic peak was observed, indicating pyrolysis of the organic material.

[0113] Aqueous chloride leaching

[0114] Pilot experiments carried out by the inventors of the present invention have shown that inorganic additives can be leached from waste PVC in a closed reactor in 1 M HCl at 250 °C for 24 h. Under such conditions, PVC is dechlorinated, while for a shorter reaction time of 2 h, less dechlorination occurs and a similar inorganic element extraction yield is obtained. These reaction conditions were chosen as the starting point of this study. A fixed liquid-to-solid ratio (L / S) of 10 was chosen. According to reaction equation (1), the HCl leaching of Sb2O3 usually occurs via the formation of soluble SbCl3. This reaction is thermodynamically favorable above about 130 °C( Figure 9 ), and according to the Eh-pH diagram, the formation of SbCl3 requires a high chloride ion concentration and a very low pH. Therefore, when increasing the chloride ion concentration or temperature, the stability of SbCl3 in solution extends to higher pH:

[0115] Sb2O3 + 3HCl → 2SbCl3 + 3H2O (1).

[0116] First, the effect of leaching time at 250 °C was studied. Figure 1 It is shown that the Al leaching rate increases with time, while the Sb leaching rate reaches a maximum at 2 h and then decreases at 4 h of leaching. This decrease can be explained by the instability of the antimony chloride complex under the selected reaction conditions (1 M HCl), where SbCl3 hydrolyzes with water to precipitate as antimony oxychloride, as shown by Chae et al. (2020). After increasing the reaction time at 250 °C, the dechlorination of the PVC polymer increases as the H:C molar ratio decreases from 1.8 (starting material) to 1.06 ± 0.01 after 2 h of reaction. Similarly, the chlorine concentration drops to 6.9 wt.% ± 0.1 wt.%. Plastic embrittlement and blackening were also observed. However, at shorter reaction times of 0.5 h and 1 h, less dechlorination occurs, as the H:C molar ratios of the residues are 1.56 ± 0.02 and 1.43 ± 0.00, respectively, and the chlorine concentrations are 30 wt.% ± 4 wt.% and 31 wt.% ± 2 wt.%.

[0117] Figure 1 Shows the variation of the leaching rates of Al and Sb with reaction time at 250 °C in 1 M HCl and at L / S = 10.

[0118] Since the aim is to avoid PVC dechlorination, a reaction temperature of 250 °C is not suitable. Therefore, a higher HCl concentration is applied at a lower temperature to achieve effective antimony extraction. A moderate reaction temperature of 150 °C was chosen to study the effect of HCl concentration.

[0119] Increasing the HCl concentration has a positive effect on the antimony leaching rate ( Figure 2A ). Thermodynamic modeling shows that when the chloride ion concentration increases from 1 M to 6 M, the stable region of SbCl3 at 150 °C expands to higher pH values ( Figure 2B ). In addition, increasing the HCl concentration shifts the solution pH to lower values, allowing the formation of stable SbCl3. The latter pH effect is as important as the chloride ion concentration, as in a control experiment at 200 °C for 2 h and at L / S = 10, when 4 M HCl (pH = -0.74 ± 0.2) was replaced by a 1 M HCl + 3 M NaCl solution (pH = -0.52 ± 0.7), respectively, the Sb leaching rate decreased sharply from 68% ± 14% to 12% ± 1%. When the HCl concentration was increased to 4 M, a significant increase in the antimony extraction yield was observed, while a further increase in the HCl concentration to 6 M only caused a slight additional increase in the extraction yield.

[0120] In addition, in 1 M HCl and 4 M HCl, at L / S = 10, for a reaction time of 2 h, the effect of the reaction temperature was tested in the range of 50 °C - 250 °C below and above the normal boiling point of water ( Figure 10 ). In 1 M HCl, the extraction rates of Al and Sb increased with temperature, but at 250 °C for 2 h, the maximum extraction rate of Sb was still limited to 38% ± 11%, and the maximum extraction rate of Al was still limited to 50% ± 2%. In 4 M HCl, the antimony leaching rate did not increase significantly above 150 °C, while the aluminum leaching rate increased to a maximum of 79.6% ± 0.4% at 250 °C. The mass loss of PVC after the reaction was determined and showed a sharp increase starting from 225 °C (i.e., 14 wt% ± 3 wt% at 225 °C and 45 wt% ± 4 wt% at 250 °C), indicating decomposition. Therefore, for the aqueous HCl leaching of antimony from PVC, the mildest conditions for an optimal antimony extraction rate of 66% ± 2% are 4 M HCl, L / S = 10, under hydrothermal conditions at 150 °C for 2 h. Under these conditions, no visually observable decomposition of the plastic occurred.

[0121] In the case of the hydrothermal leaching system studied above, the requirement to conduct the reaction at elevated temperatures and under autogenous pressure poses potential engineering and economic challenges for further scale-up.

[0122] In another experiment and referring to Figure 3, the ethanol-HCl leaching system was tested at 50 °C and 80 °C in 2 M HCl, 4 M HCl, and 6 M HCl, and was compared to the aqueous leaching system described above. It should be noted that the HCl solutions were prepared by diluting 12 M aqueous HCl with ethanol. Thus, the ethanol:water ratio in the 6 M HCl solution was 1:1, while for 4 M HCl, the ethanol:water ratio was 2:1. The ethanol system caused a significant increase in the antimony extraction rate at both test temperatures. The pH of the compositions measured after leaching in ethanol solutions was on average approximately 0.4 lower than that of the aqueous solutions with the same HCl concentration.

[0123] When the temperature was increased from 50 °C to 80 °C, the antimony extraction rate achieved by ethanol-HCl leaching increased sharply. However, at 80 °C, more antimony was extracted in the 4 M ethanol-HCl solution compared to the 6 M ethanol-HCl solution. One possible explanation is that the effect of ethanol on the chloride activity decreased at the increased HCl concentration. It is worth noting that aluminum did not show an increase in the leaching rate when switching from the HCl aqueous solution to the ethanol-HCl solution. Thus, the antimony leaching selectivity was improved relative to aluminum and was optimal in the 4 M ethanol-HCl solution at L / S = 10, 80 °C for 2 h.

[0124] The purified PVC obtained after leaching retained its original shape and color, but was observed to be less flexible. The residue was analyzed and its composition was compared to that of the original sample. The chlorine content of the PVC decreased slightly from 22 wt.% in the original sample to 18 wt.% - 21 wt.% in the residue, and the H:C ratio decreased from 1.8 to 1.3 - 1.7, respectively. No clear trend in the chlorine content and H:C ratio of the residue with respect to the reaction temperature or the HCl concentration in the glycolic acid composition was observed, and the values obtained did not indicate that PVC degradation occurred.

[0125] Antimony Recovery Process Optimization

[0126] Based on the above findings, larger-scale experiments were carried out in which two different antimony recovery routes were tested after leaching.

[0127] An extraction experiment was carried out, where 50 g of PVC was continuously extracted for 5 h in 500 mL of the ethanol 4M HCl solution obtained as indicated above at 80 °C. After the reaction, the pH and ORP (Ag / AgCl) of the acid composition were measured to be -0.89 mV and 439 mV, respectively. The plastic residue after extraction was recovered, and a mass loss of 5.3 wt% was recorded. The elemental composition of the residue shown in Table 2 indicates that approximately 67% of antimony and significant amounts of phosphorus (64%), sulfur (28%), tin (56%), and zinc (33%) were removed. Small amounts of Ca, Cr, Mg, and Na were removed, while the extraction percentages of Al, K, Pb, and Si were very low and negligible. The solid residue had a chlorine concentration of 19 wt.% and an H:C molar ratio of 1.5, indicating that no significant decomposition of PVC occurred. This was confirmed by comparing the thermogravimetric and calorimetric behavior of the purified PVC with that of the original PVC sample, which were similar( Figure 4 ).

[0128] Table 2: Elemental composition measured by ICP - OES after digestion and derived extraction yields of purified PVC after leaching for 5 h in 4M HCl ethanol acid composition at 80 °C (average of duplicate experiments).

[0129] Element <![CDATA[Concentration (mg kg -1 )]]> Extraction rate (%) Al 29000±5700 15±16 Ca 144±13 20±7 Cr 136±1 17.8±0.1 K 160±170 11±95 Mg 64±30 37±29 Na 1001±93 22±7 P 426±15 64±1 Pb 710±0.0 0.7±0.8 S 407±5 28±1 Sb 13400±3700 67±9 Si 1570±520 13±28 Sn 252±12 56±2 Zn 250±14 33±4

[0130] The obtained leachate solution was observed to be turbid. The leachate solution was divided into two fractions: FR1 and FR2.

[0131] For FR1, ethanol was removed by evaporation, at which point the color of the solution turned light yellow, and an oil phase was observed on top of the aqueous phase. This indicates that possible organic additives such as plasticizers were co - extracted during the ethanol HCl extraction. Ethanol HCl extraction allows an increase in the penetration of the acid composition into the polymer matrix and increases the accessibility of embedded inorganic additives such as antimony trioxide.

[0132] Subsequently, distilled FR1 (pH = - 1.46) and undistilled FR2 (pH = - 1.14) were treated by gradually adding water, aiming to perform the hydrolysis of SbCl3 to precipitate antimony oxychloride according to the following equations (2) and (3).

[0133] SbCl3 + H2O → SbOCl + HCl (2)

[0134] 4SbOCl + H2O → Sb4O5Cl2 + 2HCl (3)

[0135] After adding water, the pH of the solution was measured, and a precipitate formed when the pH of FR1 reached 0.06 and the pH of FR2 reached 0.50. For distilled FR1, at approximately 7:1 V水 : V FR1 Precipitation occurred upon addition and the pH remained stable over time.

[0136] The precipitate was filtered out and dried at 40 °C. The recovered precipitate was rich in antimony (50 wt%) and also contained 0.18 wt% tin as the main metal impurity (Table 3).

[0137] Table 3 : Elemental composition measured by ICP-OES after digestion of the obtained precipitate. The recovery was calculated based on the elemental concentrations in the starting solution FR1 and in the solution after removal of the precipitate (average of duplicate experiments).

[0138] Element <![CDATA[Concentration (mg kg -1 )]]> Recovery rate (%) Al 76±90 20±34 Ca 26±9 / Cr <5 23±35 K 125±160 / Mg <10 14±51 Na <10 11±35 P 4400±140 40±8 Pb 113±24 27±29 S 468±32 84±9 Sb 568000±95000 92±1 Si 118±54 / Sn 1800±0.0 94±1 Zn <10 19±33

[0139] The recoveries of S (84%), Sn (94%) and Sb (92%) from the solution were high, and the recoveries of the other studied elements from the solution were in the range of 11% - 40%, indicating significant coprecipitation. However, given the low concentrations of the other elements in the leachate, their final concentrations in the precipitate were still quite low. However, further purification of the antimony product is required to make it suitable for commercial use.

[0140] X-ray diffraction of the obtained FR1 precipitate showed the presence of Sb2O3 (valentinite), but there was also another major phase that could not be assigned to a known crystal phase in the ICDD powder diffraction database of the X'Pert PANalytical High Score Plus software. XRD diffractograms were taken after heating the sample to gain further insight into the phase composition ( Figure 5 ).

[0141] A phase change occurred at about 225 °C, where SbOCl was formed at increasing temperature. Therefore, it can be speculated that the unknown phase contains antimony and chlorine. In addition, the material contained a significant amount of phosphorus (40 wt%), indicating the presence of Phosflex (bis(2-ethylhexyl) phosphate) or its derivatives. The former has a decomposition temperature of about 240 °C, which could match the phase change observed upon heating in the temperature range of 225 °C - 250 °C ( Figure 5 ).

[0142] In addition, the presence of phthalate additives cannot be excluded. Antimony is known to form a large number of organic complexes, including those with phthalate and phosphate molecules. It is advantageous to remove organic matter from the leachate before antimony precipitation to improve the purity of the precipitate and allow identification of the organic additive compounds.

[0143] For FR2 that still contains ethanol, after adding water, when the solution is left standing over time, the pH changes and the formed precipitate tends to redissolve. Therefore, a relatively large amount of water needs to be added (i.e., 6.2:1 V 水 :V FR2 where V FR2 >>V FR1 , as the ethanol has not been removed). The formed precipitate is difficult to recover by filtration, so centrifugation is applied to deposit the precipitate and remove the supernatant. After drying, the precipitate recovered from FR2 has an oily appearance. Therefore, the material is washed with n-hexane to remove the oily fraction, which may be present due to the co-extraction of organic additives during ethanol HCl leaching. This washing step removes most of the solid residue fraction, indicating that antimony precipitation by adding water to FR2 is not successful.

[0144] Process Validation

[0145] Based on the above findings, the process was experimentally tested, considering (i) the need to have a fine-grained PVC sample to increase the antimony extraction yield, and (ii) the need to remove the co-extracted organic additives from the acid composition before antimony recovery to avoid interference and contamination during antimony precipitation. During the leaching step, 50 g of cryogenically ground PVC (<4 mm) was leached in a 4 M HCl solution in ethanol at 80 °C with L / S = 10 for 4 h. The subsequent steps involved filtering and distilling the filtrate to remove ethanol. Next, the obtained aqueous phase was washed with n-hexane in a glass separatory funnel. After removing the liquid phase from the separatory funnel, the brown oily phase adhered to the glass wall and was collected by rinsing with 2-propanol. Finally, antimony was recovered from the purified aqueous leachate by precipitation via water addition.

[0146] DART-MS analysis was performed on the PVC before and after leaching and on the obtained n-hexane and 2-propanol liquid fractions (Table 4). All materials contained organic additives such as dioctyl phthalate and diethyl phthalate, while no Phosflex was observed in 2-propanol. Based on GC-MS measurements, during ethanol HCl leaching, 76% ± 9% of bis(2-ethylhexyl) phenyl phosphate and 71% ± 3% of dinonyl phenyl phosphate were removed. While the extraction efficiencies of butylated hydroxytoluene and 9-octadecanamide were lower, at 15% and 30% respectively. The extraction efficiency of diisononyl phthalate was 51%. After leaching, ethanol was distilled off and the remaining aqueous solution was washed with hexane to remove the co-extracted organic additives. In addition, possible decomposition products of organic additives were observed in the purified PVC. Although DART-MS is not a quantitative analysis method, it shows that the washing fraction of n-hexane removed the organic additives from the aqueous HCl fraction.

[0147] At 5:1 V 水 :V WAS Upon addition (to reach pH = 0.231), subsequent hydrolysis of antimony in the washed HCl aqueous solution (WAS) produced a precipitate. The mass of the dried precipitate was 2.138 g. The X-ray diffraction pattern of the obtained precipitate showed only diffraction peaks of the Sb4Cl2O5 phase ( Figure 6 ). In addition, the presence of an amorphous phase was observed and could be quantified by Rietveld analysis of the XRD diffraction pattern as 25.3 wt.% of the total composition. Chemical analysis of the precipitate showed high purity (Table 5).

[0148] During ethanol HCl leaching, co-extraction of organic additives in PVC occurred. These co-extracted organic compounds needed to be removed from the solution before antimony precipitation by hydrolysis to obtain a pure product.

[0149] Table 4 : Additives observed by DART-MS measurement in the PVC starting material and purified PVC and in the n-hexane and 2-propanol wash fractions.

[0150]

[0151] Table 5 : Elemental composition of the obtained precipitate. Most of the reported elements were measured by ICP-OES after digestion, while Cl was measured by ion chromatography. The recovery was calculated based on the elemental concentrations in the rich leaching solution and in the solution after removal of the precipitate.

[0152]

[0153]

[0154] Chemical analysis showed the presence of 768000 mg kg -1 Sb and 100000 mg kg -1 Cl, as well as trace impurities Al (28.5 mg kg -1 ), P (240 mg kg -1 ), Pb (440 mg kg -1 ), Si (150 mg kg -1 ), and Sn (44 mg kg -1 ). The precipitate also contained 0.8 wt.% carbon and thus carbon could be considered the main impurity. The elements Ca, Cr, K, Mg, Na, S, or Zn were not present in the precipitate. The total recovery of antimony (mainly as Sb4Cl2O5) from the PVC starting material was 80 wt.%.

[0155] TGA-DSC analysis of the purified PVC gave a temperature profile similar to that of the starting material ( Figure 11 ), and the molar H:C ratio was equal to 1.7, indicating that the PVC did not decompose during leaching. However, when comparing the SEM-EDX analysis of the starting material with the leached PVC, it was shown that by leaching with 4M HCl ethanol solution, small antimony-containing particles were removed, while larger aluminum-containing particles and medium-sized silicon-containing particles were not removed ( Figures 7A - 7H - The top figures on each page ( Figure 7A 、 7C 、7E、7G) were obtained from untreated PVC material, and the bottom figures on each page ( Figure 7B 、 7D 、7F、7H) were obtained from PVC material leached in ethanol 4M HCl at 80 °C for 4 h).

[0156] Abbreviations

[0157] EDX: Energy Dispersive X-Ray.

[0158] DSC: Differential Scanning Calorimetry.

[0159] TGA: Thermogravimetric Analysis.

[0160] ICP-OES: Inductively Coupled Plasma Optical Emission Spectroscopy.

[0161] ICP-MS: Inductively Coupled Plasma Mass Spectrometry.

[0162] XRD: X-Ray Diffraction.

[0163] XRF: X-Ray Fluorescence.

[0164] DART-MS: Direct Analysis in Real Time Mass Spectrometry. DART-MS utilizes an ion source that generates electronically or vibrationally excited species that ionize ambient or dopant molecules from gases such as helium, argon, or nitrogen. Ions produced from ambient or dopant molecules undergo ion-molecule reactions with sample molecules to produce analyte ions. Analytes with low ionization energy can be directly ionized. Depending on the potential applied to the exit electrode, the DART ionization process can produce positive or negative ions.

[0165] GC MS: Gas Chromatography Mass Spectrometry.

[0166] SEM: Scanning Electron Microscopy.

[0167] References

[0168] 1. J.N. Hahladakis, C.A. Velis, R. Weber, E. Iacovidou and P. Purnell, “An overview of chemical additives present in plastics: Migration, release, fate and environmental impact during their use, disposal and recycling”, J Hazard Mater, 2018, 344, 179 - 199.

[0169] 2. S. Ugduler, K.M. Van Geem, M. Roosen, E.I.P. Delbeke and S. De Meester, “Challenges and opportunities of solvent - based additive extraction methods for plastic recycling”, Waste Manag, 2020, 104, 148 - 182.

[0170] 3. R. Babinsky, “PVC additives: a global review”, Plastics Additives & Compounding, 2006, DOI: 10.1016 / S1464 - 391X(06)70526 - 8, 38 - 40.

[0171] 4. A. Sevenster, “VinylPlus, the new European PVC industry’s voluntary programme toward sustainability”, J Mater Cycles Waste Manag, 2012, 14, 281 - 285.

[0172] 5. M. Filella, P. Hennebert, G. Okkenhaug and A. Turner, J Hazard, “Occurrence and fate of antimony in plastics”, Mater, 2020, 390, 121764.

[0173] 6. European Commission, Study on the EU's list of Critical Raw Materials - Final Report, 2020.

[0174] 7. European Commission, Study on the EU's list of Critical Raw Materials (2020) - Critical Raw Materials Factsheets, 2020, DOI: 10.2873 / 631546.

[0175] 8. D. Dupont, S. Arnout, P. T. Jones and K. Binnemans, “Antimony Recovery from End-of-Life Products and Industrial Process Residues: A Critical Review”, Journal of Sustainable Metallurgy, 2016, 2, 79 - 103.

[0176] 9. A. Alassali, C. Picuno, H. Samara, S. Diedler, S. Fiore and K. Kuchta, “Antimony Mining from PET Bottles and E-Waste Plastic Fractions”, Sustainability, 2019, 11(15), DOI: 10.3390 / su11154021.

[0177] 10. S. Tostar, E. Stenvall, A. Boldizar and M. R. S. Foreman, “Antimony leaching in plastics from waste electrical and electronic equipment (WEEE) with various acids and gamma irradiation”, Waste Management, 2013, 33, 1478 - 1482.

[0178] 11.L.Zhan,X.Zhao,Z.Ahmad and Z.Xu,“Leaching behavior of Sb and Brfrom E-waste flame retardant plastics”,Chemosphere,2020,245,125684.

Claims

1. A method for recycling a vinyl chloride polymer material, the vinyl chloride polymer material comprising an initial level of one or more additive compounds, preferably wherein the one or more additive compounds are selected from the group consisting of heavy metals and organic compounds, the method comprising: (i). Provide an aqueous acid composition comprising one or more alcohols and one or more acids. (ii). Contact the vinyl chloride polymer material with a certain volume of the acid composition to cause extraction of the one or more additive compounds from the vinyl chloride polymer material, wherein the acid composition and the vinyl chloride polymer material form a two-phase system, the two-phase system comprising a solid phase and a liquid phase, the solid phase comprising the purified vinyl chloride polymer material, and the liquid phase comprising the alcohol, water, the acid, and the extracted one or more additive compounds. (iii). Separate the solid phase comprising the purified vinyl chloride polymer material from the liquid phase comprising the extracted one or more additive compounds.

2. The method according to the preceding claim, wherein, The acid composition comprises the alcohol, and the volume ratio of the alcohol to the acid composition is at least 5 vol.%, preferably at least 7.5 vol.%, more preferably at least 8 vol.%.

3. The method according to claim 1 or 2, wherein, The acid composition comprises the alcohol in a volume ratio of at least 40 vol.%, preferably at least 50 vol.%, more preferably at least 60 vol.% based on the total volume of the acid composition.

4. The method according to any one of the preceding claims, wherein, The alcohol is selected from the group of mono-, di-, or poly-hydroxide alcohols.

5. The method according to claim 4, wherein, The alcohol is a C1-C8 alkanol, preferably a C1-C5 alkanol, more preferably ethanol.

6. The method according to any one of the preceding claims, wherein, Contacting the vinyl chloride polymer material with the volume of the acid composition to cause extraction of the one or more additive compounds from the vinyl chloride polymer is carried out at a temperature of at least 20°C, preferably at least 30°C, more preferably 40°C or higher, most preferably 50°C or higher, more preferably between 20°C and 100°C, most preferably between 30°C and 90°C, especially between 40°C and 90°C or between 50°C and 85°C.

7. The method according to any one of the preceding claims, wherein, The acid comprises one or more strong inorganic acids having a pKa value of at most -2 in water, preferably strong inorganic acids selected from hydrochloric acid (HCl), H2SO4, HBr, HI; or one or more strong organic acids having a pKa value of at most -1.9 in water, preferably selected from p-toluenesulfonic acid, methanesulfonic acid; one or more organic acids selected from oxalic acid, formic acid, acetic acid, citric acid; and mixtures of two or more of the above acids, preferably HCl.

8. The method according to any one of the preceding claims, wherein, The acid is preferably an aqueous solution of the acid that is at least 1M and at most 12M, preferably at least 2M and at most 10M, more preferably at least 2M and at most 8M, most preferably between 3.5M and 5.5M.

9. The method according to any one of the preceding claims, wherein, Mix the solid vinyl chloride polymer material with the acid composition at a mass ratio of the solid vinyl chloride polymer material to the acid composition in the range of 1:100 to 1:2, preferably between 1:50 and 1:2, more preferably between 1:25 and 1:

2.

10. The method according to any one of the preceding claims, wherein, The one or more additive compounds comprise one or more heavy metals, wherein the one or more heavy metals are selected from the group consisting of antimony, tin, zinc, lead, cobalt, cadmium, aluminum, calcium, sodium, barium, or mixtures of any one of these.

11. The method according to any one of the preceding claims, wherein, Contact the vinyl chloride polymer material in the form of particles, flakes or sheets having a size selected in the range of 100 μm to 40 mm, more preferably in the range of 500 μm to 10 mm, and most preferably in the range of 1 mm to 5 mm with a certain volume of the acid composition.

12. The method according to any one of the preceding claims, wherein, Contact the acid composition with the vinyl chloride polymer material at a certain temperature for a certain time to reduce the amount of these heavy metals, especially antimony, by at least 50%, preferably at least 60%, more preferably at least 75%, and most preferably at least 90%.

13. The method according to any one of the preceding claims, the method further comprising: Subject the purified and separated vinyl chloride polymer to a washing step using a washing liquid, preferably an acid, a base or water, for the purpose of washing the remaining acid and / or heavy metals from the purified vinyl chloride polymer.

14. The method according to any one of the preceding claims, wherein, The vinyl chloride polymer is provided by granular post-consumer PVC.

15. The method according to any one of the preceding claims, wherein, Repeat steps (i)-(iii) one or several times.

16. The method according to any one of the preceding claims, wherein, Remove / evaporate the alcohol from the liquid phase to form an acidic liquid phase, and the method further includes contacting the acidic liquid phase with a non-polar solvent to extract at least a portion of these organic compounds.

17. The method according to claim 16, wherein, The non-polar solvent is hexane.

18. The method according to any one of the preceding claims, the method further comprising:Mix the purified vinyl chloride polymer with the original vinyl chloride polymer to obtain a secondary vinyl chloride polymer.

19. A purified vinyl chloride polymer material obtained from the method according to any one of claims 1-17, wherein, The purified vinyl chloride polymer material includes a mass ratio of heavy metal additive compounds to the total dry mass of the purified vinyl chloride polymer that is less than 1 wt.%, preferably less than 0.5 wt.%, and more preferably less than 0.1 wt.%, as determined by ICP-OES.

20. A purified vinyl chloride polymer material obtained from the method according to any one of claims 1-17, wherein, The purified vinyl chloride polymer material includes a mass ratio of Sb that is 0.3 wt.% or less, preferably 0.1 wt.% or less, to the total dry mass of the purified vinyl chloride polymer material, as determined by ICP-OES.

21. A secondary vinyl chloride polymer composition, the secondary vinyl chloride polymer composition comprising an original vinyl chloride polymer and a purified vinyl chloride polymer obtained from the method according to any one of claims 1-17 or a purified vinyl chloride polymer material according to claim 19 or 20.

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