Methods for recycling post-consumer plastic materials

Abstract

A process for recycling vinyl chloride polymer material containing initial levels of one or more additive compounds includes the steps of providing an aqueous acid composition comprising one or more alcohols and one or more acids, contacting a quantity of the vinyl chloride polymer material with 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 comprising the purified vinyl chloride polymer material and a liquid phase comprising the alcohol, water, acid, and the extracted one or more additive compounds, and separating the solid phase comprising the purified vinyl chloride polymer material and the liquid phase comprising the extracted one or more additive compounds.

Description

[Technical Field]

[0001] The present invention relates to a process for the recycling of vinyl chloride polymer materials containing initial levels of one or more heavy metals.

[0002] The present invention also relates to a process for recycling vinyl chloride polymer materials containing an initial level of one or more added organic compounds. [Background technology]

[0003] Vinyl chloride polymers are widely used in the manufacture of a wide range of products, both rigid and flexible, including window frames, flooring, roofing, plumbing, and electrical wiring insulation. Vinyl chloride polymers are obtained by the polymerization of vinyl chloride and are well known for their resistance to a variety of chemicals, including acids and bases. The properties of vinyl chloride-based polymers can be tailored by compounding, i.e., blending the polymer with additives, to improve mechanical and physical properties and broaden their potential applications. 1,2 A wide variety of organic and inorganic additives are available that can be blended in various concentrations into vinyl chloride polymers to tailor material properties such as color, plasticity, abrasion resistance, and flame retardancy to suit the intended use of the vinyl chloride polymer.

[0004] Typically, about 12% of PVC additives are non-halogenated phosphate esters and chlorinated paraffins. 3 Antimony trioxide (ATO) is often used in synergy with organic flame retardants. 4 Other inorganic flame retardants include metal hydroxides of aluminum and magnesium, and aluminum oxide trihydrate.

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

[0006] Plasticizers can account for 15–50% of a PVC formulation. Varying the type and amount of plasticizer allows the properties of a PVC compound to be tailored to the requirements imposed by its intended application and use. Increasing the concentration of plasticizer increases flexibility, decreases tensile strength, and decreases hardness. For example, rigid PVC is primarily unplasticized, while flexible PVC contains plasticizers to increase the plastic's flexibility. Typical plasticizers used in PVC include phthalates, phosphates, and polyfunctional fatty acid esters.

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

[0008] Due to its thermoplastic properties, PVC has a wide range of applications in industry and is a suitable material for recycling at the end of its life. However, even if collected plastics can be separated by type of plastic material (e.g., PE, PET, PVC, etc.), they are usually a mixture of different types of material. For example, vinyl chloride polymers are often a mixture of hard, soft, and flexible materials. Alternatively, flexible vinyl chloride polymers are collected as a mixture of materials with different degrees of flexibility.

[0009] However, the presence of additives, such as the organic and metal-containing additives mentioned above, has hindered primary or secondary recycling of vinyl chloride polymers as high-quality products, as conventional approaches have limited their content below certain levels or concentrations of certain additives have accumulated to the point that they degrade the properties of the plastic material.

[0010] Furthermore, resources of some metals used in plastic additives are becoming scarce. For example, the European Commission has listed antimony as a critical raw material, given the growing industrial demand for it and supply risks. China supplied 74% of global antimony production between 2012 and 2016. 6 In the EU, antimony is primarily 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%). Despite the plastics industry being the main user, antimony is currently only recovered on an industrial scale from waste lead-acid batteries, and recovery activities in the plastics industry remain limited due to dispersion. 7 Therefore, new recovery and recycling routes for antimony from secondary resources are needed. 8 .

[0011] Laboratory-scale approaches to recovering antimony from waste plastics have focused on decomposing, pyrolyzing, or incinerating the waste plastics and recovering antimony and antimony trioxide from the resulting gases and residues. 8 These approaches require the destruction of the polymers that make up the plastic material to allow for the recovery of antimony. Furthermore, antimony is commonly found dispersed in products obtained from the recycling of waste plastics, in waste incineration fly ash and bottom ash, and in landfills.

[0012] Therefore, there is a need for a process that can recover elements such as antimony from waste plastic materials with high recovery rates.

[0013] Zhan et al. 1187% of the Sb in ABS is converted to SbS3 3- 90% of Br is Br - They disclose a hydrothermal extraction process that allows the recovery of ABS as a soluble form of PVC. The process is carried out in a solution of 20 g / L NaOH and 50 g / L Na2S at 220 °C and an L / S ratio of 10 for 2 hours. After extraction, the structure of the ABS remains almost unchanged, making it suitable for further recycling. Although the recovery rate of Sb is high, the process requires hydrothermal reaction conditions, i.e., under high temperature and pressure. However, applying such hydrothermal conditions to PVC leads to dechlorination and hydrothermal carbonization, which leads to the degradation of the polymer, making it unsuitable for further recycling.

[0014] EP 1 817 366 A1 discloses a process for recovering heavy metal compounds (Pb and Cd) from vinyl chloride polymers. This process involves dissolving the vinyl chloride polymer in a solvent and treating the solution with an additive capable of adsorbing or complexing with Pb and Cd compounds. However, the process disclosed in EP 1 817 366 A1 dissolves the vinyl chloride polymer in the solvent, which carries the risk of altering the polymer's properties upon reuse. Separation of the dissolved and purified polymer from the solvent is a complex and energy-intensive process, which can be further complicated by the presence of organic and inorganic additives contained in the vinyl chloride polymer. These additives must be separated from the polymer and solvent, respectively, to enable reuse. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] European Patent Application Publication No. 1817366 Summary of the Invention [Problem to be solved by the invention]

[0016] Therefore, there is a need for an economically attractive process for recycling vinyl chloride polymer materials that removes additive compounds present in the vinyl chloride polymer material, in particular additives containing heavy metals and / or additive organic compounds, from the vinyl chloride polymer plastic material and allows for the recovery of vinyl chloride at recovery rates that are interesting for scaling up the process to an industrial scale. There is also a need for a process that is energetically favorable and does not require the use of high temperatures and pressures.

[0017] The present invention therefore aims to provide an economically and energetically attractive process for recycling vinyl chloride polymer materials at industrially interesting recovery rates, without requiring the use of high temperatures and pressures. [Means for solving the problem]

[0018] This is achieved according to the invention by a process showing the technical features of the first claim.

[0019] The present invention therefore relates to a process for recycling vinyl chloride polymer materials containing initial levels of one or more additive compounds, preferably the one or more additive compounds are selected from the group consisting of heavy metals and organic compounds, the process comprising the following steps: (i) providing an aqueous acid composition comprising one or more alcohols and one or more acids; (ii) contacting the vinyl chloride polymer material with a volume of an acid composition to effect extraction of one or more additive compounds from the vinyl chloride polymer, the acid composition being adjusted to form a two-phase system with the vinyl chloride polymer material, the solid phase comprising the purified vinyl chloride polymer material, and a liquid phase comprising alcohol, water, acid, and the extracted one or more additive compounds; (iii) separating the purified vinyl chloride polymer material from a liquid phase containing the extracted one or more additive compounds; Includes.

[0020] The inventors have surprisingly discovered that the process of the present invention advantageously extracts most of the heavy metals present in vinyl chloride polymer plastic materials, 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), phosphorus (P), and mixtures of any of these, without the need to dissolve the vinyl chloride polymer. Depending on the nature of the metals, extraction efficiencies can be high or low. High extraction efficiencies have been observed for Sb, Sn, and S. Acceptable extraction efficiencies have been observed for Al, Ca, Cr, Mg, P, Pb, Si, and Zn.

[0021] Furthermore, significantly higher extraction rates can be achieved for at least some of the above metals compared to prior art processes. While not being bound by this theory, the inventors speculate that the presence of alcohol in the acid composition improves the acid's ability to penetrate the polymer matrix, improving access to inorganic additives embedded therein, without the need to dissolve the polymer material. The inventors also speculate that the higher extraction rates may be due to the lower pH caused by the presence of alcohol in the aqueous acid solution compared to the same acid concentration in water. It is believed that this increased accessibility and reduced acid concentration result in improved extraction of heavy metals by the strong acid and alcohol acid composition.

[0022] Advantageously, the pH of the aqueous acid composition and / or the liquid phase is in the range of from −0.0001 to −2.5, advantageously from −0.001 to −2.5, advantageously from −0.01 to −2.5, advantageously from −0.1 to −2.0, advantageously from −0.1 to −1.5.

[0023] This improved extraction can be achieved at temperatures significantly lower than those employed in prior art processes. In addition, the present invention does not require the process to be carried out at elevated pressures above atmospheric pressure. This energy attractiveness, combined with the high recovery rates, highlights the economic attractiveness of the process for use on an industrial scale.

[0024] The inventors have further surprisingly discovered that, despite the presence of metals capable of catalyzing the reaction of acids with alcohols, the formation of such undesired reaction products is not observed. In particular, the formation of alkyl halides and alkyl chlorides is not observed. This is an advantage, since these compounds are often flammable, toxic, and carcinogenic.

[0025] The present inventors have also discovered that when vinyl chloride polymers are contacted with an acid composition, a large proportion of the organic additive compounds are co-extracted. The extracted organic additive compounds are typically additives contained in vinyl chloride polymers, particularly plasticizers and heat stabilizers. Extraction of these organic additive compounds from vinyl chloride polymers is important when the purified vinyl chloride polymer is intended for reuse, particularly when the vinyl chloride polymer is intended for reuse in applications other than the primary use from which it was subjected to the process of the present invention. Extraction of the organic additive compounds minimizes the risk of the purified vinyl chloride polymer undesirably interfering with the intended properties of the material with which it is mixed or incorporated. When the purified vinyl chloride polymer obtained by the process of the present invention is blended with virgin vinyl chloride polymer (virgin vinyl chloride polymer), additives necessary to achieve the desired properties can be added, while minimizing the risk of residual additives in the purified vinyl chloride polymer causing undesirable accumulation or adversely affecting the properties of the blend.

[0026] Advantageously, contacting the vinyl chloride polymer material with an acid composition can result in the purification, e.g., extraction, of additional compounds, such as fillers, present in the vinyl chloride polymer material. Extraction of other filler materials, such as colorants, softeners, reinforcing materials, or other fillers, e.g., calcium oxide, can be beneficial, especially when the purified vinyl chloride polymer obtained from the process of the present invention is to be further used in a subsequent compounding process.

[0027] Advantageously, the process of the present invention can be carried out at a relatively low temperature that does not affect the composition and structure of the vinyl chloride polymer or the organic additives present therein, while simultaneously achieving metal removal. Therefore, the purified vinyl chloride polymer obtained by the process of the present invention is suitable for recycling and reuse in an economically and ecologically efficient manner. This low-temperature process offers the advantage of minimizing the risk of degradation of the organic additives extracted or removed from the vinyl chloride polymer. Meanwhile, the extracted one or more additive compounds, i.e., heavy metals and organic compounds, can also be recovered from the acid composition using appropriate procedures.

[0028] Furthermore, this low-temperature process minimizes the risk of dechlorination and hydrothermal carbonization of vinyl polymer materials, i.e., the risk of vinyl chloride polymer degradation, and the purified vinyl chloride polymer that can be recovered from the process of the present invention is suitable for recycling and blending or blending with other recycled or virgin vinyl chloride polymers for further use. Furthermore, it has been observed that the thermogravimetric analysis and differential scanning calorimetry properties of the purified vinyl chloride polymer are similar to those of the polymers subjected to the process of the present invention. Also, the HCN and chlorine compositions of the purified vinyl chloride polymer are similar to those of the polymers subjected to the process of the present invention.

[0029] It will be apparent to those skilled in the art that the vinyl chloride polymer material may be subjected to the process of the present invention once, or multiple times, until the desired level of removal of certain or all additives, including heavy metals and organic compounds, is achieved.

[0030] In a next step, the purified vinyl chloride polymer material is separated from the liquid phase containing the extracted organic additive compounds and one or more heavy metals, after which the individual metals can be recovered from the liquid phase using appropriate techniques for recovering each metal, and the organic additive compounds can also be recovered using appropriate separation techniques. After removal of the organic additive compounds from the liquid phase, an aqueous alcohol phase remains containing one or more heavy metals. The one or more heavy metals can be recovered by separating the alcohol from the aqueous phase, for example, by evaporating the alcohol, followed by recovery of the one or more heavy metals using appropriate techniques known to those skilled in the art.

[0031] According to one embodiment of the present invention, the acid composition contains at least 5% by volume, preferably at least 7.5% by volume, and more preferably at least 8% by volume of alcohol relative to the acid composition. Within these ranges, optimal penetration of the alcohol-containing acid composition into the polymeric material can be achieved, and desired extraction of organic additive compounds, such as plasticizers, contained in the polymeric material can be achieved.

[0032] According to one embodiment of the present invention, the acid composition comprises a volumetric proportion of alcohol of at least 40% by volume, preferably at least 50% by volume, more preferably at least 60% by volume, in order to ensure that the efficiency of extraction of one or more heavy metals from the vinyl polymer material is maintained at a level of interest for industrial applications and to minimize the risk of polymer degradation if the acid concentration becomes too high.

[0033] Various alcohols are suitable for use in the process of the present invention. Suitable alcohols include one or more alcohols from the group consisting of monohydroxy alcohols, dihydroxy alcohols, or polyhydroxy alcohols. According to embodiments of the present invention, the alcohol may be a C1-C8 alkanol or a C1-C5 alkanol, although branched alcohols may also be used. According to embodiments of the present invention, suitable dialcohols include ethylene glycol, propylene glycol, and the like. Ethanol is a particularly preferred monoalcohol due to its low boiling point compared to water, facilitating removal of the alcohol phase and recovery of the metal(s) from the acid aqueous phase. Furthermore, ethanol has a favorable viscosity, which facilitates mixing and filtration. Higher alcohols may have higher viscosities.

[0034] According to one embodiment of the present invention, contacting the vinyl chloride polymer material with the acid composition to effect 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 at least 40°C, and most preferably at least 50°C. In particular, contacting the vinyl chloride polymer material with the acid composition to effect extraction of at least one heavy metal from the vinyl chloride polymer is carried out at a temperature of 20-100°C, preferably at least 30-90°C, more preferably at least 40-90°C, and most preferably at least 50-85°C. The inventors have observed that the accessibility of the vinyl polymer material is optimal at a temperature equal to or greater than its glass transition temperature, Tg. A maximum temperature of 100°C allows the process to be carried out at atmospheric pressure, avoiding the use of a pressurized reactor.

[0035] Various acids, particularly strong acids, can be used in the process of the present invention. The acid preferably comprises one or more strong inorganic acids having a pKa value of at most -2 in water, preferably selected from hydrochloric acid (HCl), H2SO4, HBr, and HI. The acid can also comprise one or more strong organic acids having a pKa value of at most -1.9 in water, preferably selected from p-toluenesulfonic acid and methanesulfonic acid. The acid can further comprise one or more organic acids selected from oxalic acid, methanoic acid, acetic acid, and citric acid. It will be apparent that the acid can comprise a mixture of two or more of the aforementioned acids. In a preferred embodiment of the present invention, the acid comprises HCl. In a further preferred embodiment of the present invention, the acid is a non-oxidizing acid. Selecting a non-oxidizing acid helps minimize the risk of oxidation of organic additive compounds present in the liquid. It will be apparent to those skilled in the art that other non-oxidizing acids, as well as mixtures of two or more acids, can also be used.

[0036] The concentration of the acid, preferably HCl, in the acid composition may vary within certain limits, but is preferably at least 1 M (molar ratio) 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, and most preferably 3.5-5.5 M. It has been observed that the effect of alcohol on the reaction between the metal to be extracted and the acid varies depending on the acid concentration. At concentrations below 2 M, the efficiency of extraction with HCl becomes unattractive for scaling up to industrially interesting levels, and even at 12 M, the efficiency of extraction decreases. These conditions have been confirmed particularly in the extraction of Sb and Sn. If the extraction of other metals, such as Zn or Pb, is envisioned, lower acid concentrations, such as less than 0.5 M or less than 0.25 M, and especially less than 0.1 M, may be sufficient.

[0037] In the process of the present invention, a vinyl chloride polymer material is mixed with a volume of an acid composition containing water, acid, and alcohol to cause extraction of at least one heavy metal from the vinyl chloride polymer. A two-phase system is formed: a solid phase containing the vinyl chloride polymer material and a liquid phase containing water, acid, alcohol, and the extracted heavy metal(s) and organic additive compound(s). According to an embodiment of the present invention, the vinyl chloride polymer material can be mixed with the acid composition at a mass ratio of the solid polymer material to the acid composition ranging from 1:100 to 1:1, preferably 1:50 to 1:2, preferably 1:25 to 1:2, and more preferably 1:10 to 1:2, defined as the mass of the vinyl chloride polymer material relative to the total mass of the acid and vinyl chloride polymer compound. In this way, the amount of acid and alcohol used to extract at least one heavy metal can be balanced relative to the amount of polymer material to be treated, achieving high extraction efficiency while limiting the amount of alcohol and acid used. Addition of too much vinyl chloride polymer compound may increase the apparent viscosity and / or interfere with processing and / or separation, such as filtration steps.

[0038] Advantageously, in step (ii), the vinyl chloride polymer does not substantially dissolve in the acid composition and / or the liquid phase. The aqueous acid composition, particularly the acid in the acid composition, is advantageously a poor solvent for the vinyl chloride polymer. Advantageously, at least 80% by weight of the vinyl chloride polymer is recovered in the solid phase, advantageously at least 85% by weight, advantageously at least 90% by weight, based on the weight of vinyl chloride polymer contained in the initial vinyl chloride polymer material. Advantageously, the aqueous acid composition, after leaching for 5 hours at 80°C under continuous stirring, is capable of dissolving no more than 8 g of vinyl chloride polymer per liter of aqueous acid composition, advantageously no more than 6 g of vinyl chloride polymer per liter of aqueous acid composition, advantageously no more than 4 g of vinyl chloride polymer per liter of aqueous acid composition. Any observed mass loss is usually not due to dissolution of such polymeric material, but rather due to leaching or dissolution of inorganic and / or organic additives contained in the vinyl chloride polymer material.

[0039] According to an embodiment of the present invention, the vinyl chloride polymer material may be suspended in the acid composition. Suspension may be achieved 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 may be employed in which the PVC granules are suspended. It will be appreciated that other types of reactors suitable for mixing the acid composition and the vinyl chloride polymer compound phase, such as a fluidized bed reactor, may also be employed.

[0040] The vinyl chloride polymer material can be contacted with a quantity of the acid composition in a variety of forms or shapes, such as particles, flakes, sheets, pieces, or parts. The vinyl chloride polymer material can have a variety of dimensions, such as a size selected from the range of 100 μm to 10 mm, preferably 100 μm to 40 mm, more preferably 500 μm to 10 mm, and most preferably 1 mm to 5 mm. In other words, the polymer material used in the method of the present invention can comprise particles whose maximum dimensions are within the aforementioned ranges. The particle size can be determined using any suitable method known to those skilled in the art, such as scanning electron microscopy (SEM) and image analysis, laser diffraction, or sieving according to ISO Standard 1624.

[0041] In one embodiment of the present invention, the acid composition and vinyl chloride polymer material are contacted for a time and at a temperature that reduces the amount of heavy metals, particularly antimony, by at least 50%, preferably at least 60%, more preferably at least 75%, and most preferably at least 90%.

[0042] According to a further embodiment of the present invention, purified vinyl chloride polymer is mixed with virgin chloride polymer to obtain a secondary vinyl chloride polymer.

[0043] In a further aspect, the present invention relates to purified vinyl chloride polymer materials obtained or obtainable from the processes of the present disclosure, as set forth in the appended claims. The present invention also relates to secondary vinyl chloride polymer compositions comprising virgin vinyl chloride polymer and purified vinyl chloride polymer obtained or obtainable according to the processes of the present disclosure, as set forth in the appended claims. [Brief explanation of the drawings]

[0044] [Figure 1] FIG. 1 shows the leaching rates of Al and Sb as a function of reaction time in 1M HCl at 250° C. and L / S=10. [Figure 2A] Figure 2A shows the leaching rates of Al and Sb as a function of HCl concentration at 150°C for 2 hours with L / S=10 (bottom). [Figure 2B] Figure 2B shows the Eh-pH diagram for 0.03 M Sb in the presence of varying concentrations of Cl at 150 °C. The points in the diagram represent the average pH and Eh measured in solution after leaching at 150 °C in 1 M (squares), 2 M (circles), 4 M (triangles), and 6 M (diamonds) HCl solutions. [Figure 3] FIG. 3 shows the leaching rates of Al and Sb at 50° C. and 80° C. in aqueous and ethanolic HCl solutions of different concentrations for 2 hours at L / S=10. [Figure 4] FIG. 4 shows the DSC and TGA curves of the original PVC sample and the residue obtained after leaching in a 4 M ethanolic HCl solution at 80° C. for 5 hours. [Figure 5] Figure 5 shows the XRD diffractogram of the precipitate. In-situ XRD was performed while the sample was heated to various temperatures. The (red) question marks indicate diffraction peaks that could not be assigned to known mineral phases in the ICDD powder diffraction database. [Figure 6]Figure 6 shows the X-ray diffractogram of the precipitate obtained. All observed diffraction peaks can be assigned to the Sb4Cl2O5 mineral phase (space group P21 / c (a = 6.24 Å, b = 5.11 Å, c = 13.53 Å, β = 97.20°)). [Figure 7A] FIG. 7A is an SEM image of the untreated PVC material. [Figure 7B] FIG. 7B is an SEM image of PVC material leached in ethanolic 4M HCl at 80° C. for 4 hours. [Figure 7C] FIG. 7C is an EDX image of Al in the PVC material of FIG. 7A. [Figure 7D] FIG. 7D is an EDX image of Al in the PVC material of FIG. 7B. [Figure 7E] FIG. 7E is an EDX image of Sb in the PVC material of FIG. 7A. [Figure 7F] Figure 7F is an EDX image of Sb in the PVC material of Figure 7B. The strong coloration of Sb in the EDX image is primarily due to background noise and not the actual presence of Sb. [Figure 7G] FIG. 7G is an EDX image of Si of the PVC material of FIG. 7A. [Figure 7H] FIG. 7H is an EDX image of Si of the PVC material of FIG. 7B. [Figure 8] FIG. 8 shows a TGA-DSC analysis of the PVC starting material. [Figure 9] FIG. 9 shows the Gibbs free energy of the reaction Sb2O5 + 3HCl → 2SbCl3 + 3H2O, as modeled with HSC Chemistry 8 software. [Figure 10] FIG. 10 shows the DSC and TGA curves of the original cryo-ground PVC sample and the residue obtained after leaching in a 4M ethanolic HCl solution at 80° C. for 4 hours. [Figure 11] FIG. 11 shows the leaching rates of Al and Sb as a function of reaction temperature when reacted in 1M HCl or 4M HCl aqueous solution at L / S=10 for 2 hours. DETAILED DESCRIPTION OF THE INVENTION

[0045] The terms used to describe particular embodiments of the present invention are not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" in the foreign language specification and claims of this application include the plural forms unless the context clearly dictates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of the stated features but do not exclude the presence or addition of one or more other features. Furthermore, when a particular step of a method is referred to as following another step, it will be understood that the other step may follow directly, or one or more intermediate steps may be performed before the particular step is performed, unless otherwise specified. Similarly, when a connection between structures or components is described, it will be understood that the connection may be established directly or through intermediate structures or components, unless otherwise specified.

[0046] When a claim refers to another claim, this may indicate a synergistic advantage achieved by a combination of the respective features. However, the mere fact that certain measures are recited in mutually different claims does not mean that the combination of these measures cannot be advantageously utilized. Thus, the present embodiments may include all practical combinations of the claims, and each claim may in principle refer to any preceding claim unless clearly excluded by the context. For clarity and conciseness, features may be described herein as part of the same or separate embodiments, but the scope of the present invention will be understood.

[0047] The vinyl chloride polymer material subjected to the process of the present invention may be referred to as purified vinyl chloride polymer, extracted vinyl chloride polymer, recycled vinyl chloride polymer, or any other equivalent term. The purified vinyl chloride polymer material subjected to the process of the present invention may contain reduced amounts of organic additive compounds and / or metal ions compared to the vinyl chloride polymer material subjected to the process of the present invention.

[0048] It will be appreciated that the methods described herein for recycling vinyl chloride polymer compounds may be particularly useful for recycling post-consumer PVC products. Accordingly, the vinyl chloride polymer compounds are preferably obtained from granular post-consumer PVC products.

[0049] Advantageously, the present invention can be applied to reduce the levels of a wide range of additives currently used in the formulation of vinyl chloride polymers, such as heat stabilizers, plasticizers, softeners, reinforcing materials, colorants, 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), phosphorus (P), and any other additives, including mixtures of any of these.

[0050] The main metals contained in stabilizers currently in use 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 enable the recycling of vinyl chloride polymer materials. Thermal stabilizers for vinyl chloride polymers can be classified into 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 sulfate, basic carbonate, or basic phosphate compounds. In a preferred embodiment, the heavy metal in the heavy metal compound is selected from the group consisting of lead, cadmium, zinc, tin, barium, calcium, or any mixture thereof.

[0051] The fluid acid composition and the vinyl chloride polymer compound are contacted for a time and at a temperature sufficient to reduce the amount of heavy metals in the vinyl chloride polymer from its initial level to a predetermined desired purification level. Preferably, the acid composition and the vinyl chloride polymer material are contacted for a time and at a temperature sufficient to reduce the amount of heavy metals in the vinyl chloride polymer by at least 50%, preferably at least 60%, more preferably at least 75%, most preferably at least 80%, particularly at least 90%, even more particularly at least 95%, and even at least 99.9% from its initial level. Any method known in the art can be used to measure the heavy metal content in the vinyl chloride polymer compound. In particular, XRF or acid digestion followed by ICP-MS and / or ICP-OES can be used. Advantageously, the process parameters such as contact time, temperature, nature of the acid, amount added, and combinations thereof can be selected to result in the formation of purified vinyl chloride polymer, wherein the level of heavy metal-added compounds is less than 1% by weight, preferably less than 0.5% by weight, more preferably less than 0.1% by weight (based on the weight of heavy metal-added compounds relative to the total dry weight of the vinyl chloride polymer material as determined by ICP-OES).

[0052] Waste vinyl polymer materials are usually available in a wide variety of forms depending on their intended use. To efficiently extract the entire polymer material down to its interior, the vinyl chloride polymer material can be contacted with a certain amount of acid composition in the form of particles, flakes, scraps, or sheets. The particles, flakes, scraps, or sheets must, on the one hand, be large enough to allow efficient separation of the solids, and, on the other hand, be small enough to allow the acid composition phase to penetrate most of the solid polymer.

[0053] Methods for reducing plastics to smaller particle sizes include, but are not limited to, grinding, milling, and freeze-grinding / milling. It will be understood that size reduction can be performed by any suitable size reduction method known to those skilled in the art, for example, any suitable size reduction method known in the field of size reduction methods for plastic recycling, such as a size reduction method according to common practices for PVC recycling. Furthermore, granulating vinyl chloride polymer compounds can be beneficial in reformulation processes that use purified vinyl chloride polymer compounds as starting materials. It will be understood that small amounts (e.g., up to 10% by weight) of particles smaller and / or larger than the specified range, or amounts typically present after typical granulation processes, can also be processed. Good results have been obtained with granules having a size within a specific range, for example, approximately 100 μm to 40 mm, more preferably 500 μm to 10 mm, and most preferably 1 mm to 5 mm. Purification tests have shown that contact times of 5 minutes to 8 hours, e.g., 2 hours, or even 1 hour, result in near complete extraction of heavy metals. It will be appreciated that the process can be carried out using different contact times, different contact temperatures, different granule sizes, and / or combinations thereof, depending on the level of purification desired.

[0054] Although additional extraction steps can be considered to remove residues of additives and one or more heavy metals, in other words, the vinyl chloride polymer material can be subjected to the process of the present invention several times, the present invention can reduce the level of heavy metal compounds in the purified vinyl chloride polymer (particles) to a level where the vinyl chloride polymer formed can be used, e.g., reused, in a compounding process.

[0055] The purified vinyl chloride polymer will generally have a shape that is compatible with the shape of the vinyl chloride polymer that is to be subjected to the process of the present invention; for example, the purified vinyl chloride polymer may be in the form of particles, flakes, sheets, pieces or parts, or any other convenient shape.

[0056] A preferred strong acid for use in the method of the present invention is an aqueous solution of HCl, which may be particularly useful in the purification process of vinyl chloride polymer compounds in which at least one heavy metal compound is antimony (Sb) due to the potential formation of soluble SbCl or ionic antimony chloride complexes. Discoloration (so-called pinking) on ​​the surface of the purified vinyl chloride polymer may indicate the presence of residual heavy metal additive compounds, such as salts or other additives. It will be appreciated that coloration does not necessarily indicate poor extraction performance or poor product quality, since coloration may be visible even at very low, acceptable, e.g., trace levels of heavy metal additive compounds. On the other hand, the absence of coloration, e.g., the formation of colorless (e.g., white) vinyl chloride polymer (granules), may indicate successful removal (reduction) of heavy metals in a process aimed at substantially reducing Pb levels in vinyl chloride polymer compounds.

[0057] In one embodiment of the present invention, the alcohol(s), preferably ethanol, can be recycled, and before recycling, compounds such as organic compounds and / or heavy metals contained in the alcohol(s) can be removed from the alcohol(s).

[0058] In another embodiment, the acid composition may be recycled. In other words, after separating the purified vinyl chloride polymer compound from the acid phase, the acid phase may be recycled to purify additional amounts of vinyl chloride polymer compound containing heavy metal compounds. Preferably, the acid composition is recycled as long as the extraction efficiency results in a treated vinyl chloride polymer having an acceptable reduction level of at least one heavy metal, e.g., Sb. A desirable goal for vinyl chloride polymer, particularly PVC compounding, is to limit the use of Sb to a maximum level of 0.1% by weight. Preferably, the level of heavy metals, e.g., Sb, in the purified vinyl chloride polymer does not exceed 0.3% by weight. Optionally, in some cases, a vinyl chloride polymer composite material can be prepared by blending, e.g., mixing, an appropriate amount of virgin or otherwise recovered vinyl chloride polymer with the purified vinyl chloride polymer particles obtained from the present invention. In such a process, higher levels of some heavy metals (e.g., two or four times higher) may be tolerated, depending on the amount of virgin vinyl chloride polymer blended with the purified vinyl chloride polymer.

[0059] In some embodiments, the process of the present invention further comprises a washing step in which the separated, purified vinyl chloride polymer is contacted with a washing solution to wash the residual acid phase (e.g., liquid acid phase) from the vinyl chloride polymer. Washing the purified vinyl chloride polymer can, for example, remove residual acid adhering to the outer surface of the purified vinyl chloride polymer compound. Thus, washing can also wash (e.g., remove) residual heavy metal-added compounds from the purified vinyl chloride polymer compound. It will be appreciated that washing can be carried out at a temperature range similar to that used in the extraction step in which the vinyl chloride polymer material is contacted with a certain amount of an acid composition. Thus, washing is preferably carried out at a temperature range of 20°C to 85°C.

[0060] The purified vinyl chloride polymer compound recovered by the process of the present invention after contact with the aqueous acid composition can be washed with at least a first washing solution. The washing solution is preferably selected to have a strong interaction with heavy metals to ensure that any metals remaining on the surface of the purified vinyl chloride polymer are removed. The washing solution preferably has a low affinity, particularly low solubility, for the vinyl chloride polymer. The washing solution should not cause precipitation of heavy metals or the acid of the aqueous acid composition.

[0061] The first wash liquid can be selected from the group consisting of water, an aqueous solution of an acid, etc. However, a particularly suitable first wash liquid comprises an aqueous acid composition containing one or more alcohols and one or more acids used to cause extraction of one or more added compounds from the vinyl chloride polymer material, as this can more reliably remove the extracted aqueous acid composition remaining on the purified vinyl chloride polymer.

[0062] The cleaning process may be repeated several times. In this case, the same cleaning solution, for example, the first cleaning solution, may be used, but water may be used in subsequent cleaning steps. Good cleaning performance has been achieved by using an aqueous cleaning solution, especially water itself.

[0063] It will be appreciated that the first wash liquid used to perform the washing preferably has a low initial level of dissolved heavy metal additive compounds, at least low enough to dissolve the heavy metals contained in the acid phase adhering to the purified vinyl chloride polymer compound (granules). Preferably, the first wash liquid can be reused until its washing performance deteriorates, for example, until the washed vinyl chloride polymer contains less than 0.1 wt. % heavy metal additive compounds, such as Sb compounds.

[0064] It will be appreciated that the purification process described herein for purifying vinyl chloride polymer compounds can be particularly useful for recycling post-consumer PVC products. Thus, the vinyl chloride polymer compounds are preferably derived from granular post-consumer PVC products, including, but not limited to, window frames, piping, roofing and / or flooring, and flexible PVC products.

[0065] 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 PVC materials stabilized with heavy metal salts, such as post-consumer PVC materials.

[0066] In a further aspect, the present invention relates to vinyl chloride polymers, particularly 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 for use, e.g., reuse, in compounding processes of the formed vinyl chloride polymer. Preferably, the heavy metal level in the purified vinyl chloride polymer does not exceed 0.1% by weight. More preferably, the heavy metal level does not exceed 0.01% by weight. In the absence of purification, vinyl chloride polymer compounds may contain significant levels of heavy metal additive compounds. For example, PVC may contain up to about 10% by weight of heavy metal heat stabilizer. If lead stearate is used, this corresponds to a Pb loading of about 3% by weight in the compound.

[0067] The present invention will now be described more fully with reference to the accompanying examples, which illustrate embodiments of the present invention. The examples provided are not intended to be limiting in any way. The amounts, masses and ratios, temperatures and contact times set forth in the above description and in the following examples may be rounded and should not be construed as limiting. Normal uncertainty ranges apply. [Example]

[0068] Materials and Methods <Material> Commercially available antimony-containing flexible PVC sheet samples were cut into uniform flakes of 1 cm × 1 cm and the material was cryo-ground to less than 4 mm by immersion in liquid nitrogen before being processed in a Fritsch Pulverisette cutting mill equipped with a 4 mm sieve.

[0069] Hydrochloric acid (37% by weight HCl in water) and n-hexane (SupraSolv®, ≥98.0%) were purchased from Merck KGaA (Darmstadt, Germany), ethanol (absolute) 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 reagents were used as received without further purification.

[0070] <Leaching optimization test> Pressure leaching at temperatures above 100°C was performed using a Parr Instrument Company general-purpose acid digestion reactor 4744. A PVC sample (2 g) was introduced into the acid digestion reactor along with 20 mL of aqueous hydrochloric acid. The reactor was sealed and heated in an oven at the desired reaction temperature for the desired reaction time. The reactor was then removed from the oven and cooled to room temperature. The reactor was then opened and the reduction potential and pH of the reaction mixture were measured. Solid-liquid separation was performed by vacuum filtration using a 0.45 μm mixed cellulose ester membrane filter (Whatman). The purified PVC was washed to remove residual reagents, and the wash water was collected separately. To confirm the absence of solids in the leachate for ICP-OES analysis, the leachate was filtered again using a 0.45 μm polyamide syringe filter (Macherey-Nagel). The filtrate was diluted with 5% nitric acid by volume and stored. The purified PVC was dried at 40°C and then analyzed by X-ray fluorescence (XRF). All experiments were performed in duplicate.

[0071] For leaching tests in aqueous solutions below 100°C, 2 g of PVC sample was placed in a PTFE container with 20 mL of aqueous hydrochloric acid. All tests were performed in duplicate. The PTFE container was sealed and shaken horizontally at 225 rpm for 2 hours in a water bath at the set reaction temperature. After the leaching process was completed, the container was removed from the water bath and allowed to cool to room temperature. The solid and liquid fractions were then collected following the same procedure as described above for the aqueous pressure leaching test.

[0072] The leaching process using the organic acid composition was tested in a round-bottom flask equipped with a reflux condenser to prevent solvent evaporation. In this test, an ethanolic hydrochloric acid solution was used as the acid composition. A 37% by weight (12 M) HCl solution was diluted with pure ethanol to the desired HCl concentration. The reaction mixture in the flask was heated in a water bath at the required reaction temperature for 2 hours. After the leaching process, the round-bottom flask was cooled to room temperature, and then the reduction potential and pH of the liquid phase were measured. After the leaching process, the solid precipitate was separated using a 0.45 μm polyamide syringe filter manufactured by Macherey-Nagel. The residue from the PVC after chemical leaching was then dried at 40°C. Because ICP-OES analysis of the liquid fraction was performed using aqueous standards, the ethanol contained in the leachate had to be removed using a rotary evaporator. After removing the ethanol from the sample, the leachate was diluted to 20 mL with ultrapure water. Five percent by volume of nitric acid was then added for storage. The solid residue was dried at 40°C and analyzed by XRF.

[0073] <Optimization of antimony recovery> Large-scale leaching tests were performed in a 1 L round-bottom flask placed in a heating mantle and equipped with a reflux condenser. The flask was charged with 50 g of PVC sample (1 x 1 cm flakes) and 500 mL of 4 M ethanolic HCl. The reaction mixture was heated at 80 °C for 5 h. After cooling to room temperature and filtration, the collected leachate was divided into two fractions (FR1 and FR2) of equal volume (235 mL).

[0074] Ethanol was removed from FR1 by rotary evaporation (130 mbar, 55°C). FR2, on the other hand, was not subjected to evaporation. Then, MilliQ water was added stepwise to known amounts of FR1 and FR2 using a graduated burette at room temperature under constant stirring with a magnetic stir bar. The pH of the solution was measured after each water addition step. Water was added until a precipitate formed, after which the solution was stirred for an additional hour. The resulting slurry from FR1 was then filtered through a 0.45 μm mixed cellulose ester membrane filter (Whatman) to recover the precipitate, while the solid from the FR2 solution was recovered by centrifugation (5 min, 3500 rpm). The solid residue was dried at 40°C under a nitrogen atmosphere until a constant mass was obtained. The resulting liquid fraction was analyzed by ICP-OES, and the solid residue was analyzed by XRD and ICP-OES after acid digestion.

[0075] <Process Verification Test> A cryo-ground PVC sample (50 g) was placed in a 1 L round-bottom flask and 500 mL of 4 M HCl ethanol solution was added. The flask was fitted with a condenser and heated to 80 °C using a heating mantle. The reaction was allowed to proceed for 4 hours with gentle stirring (150 rpm). After cooling to room temperature, the reaction mixture was filtered through a Whatmann cellulose filter to remove the solid purified PVC. The purified PVC was washed on the filter with additional ethanol added to the collected filtrate. The purified PVC was dried at 50 °C and then analyzed by TGA-DSC, DART-MS, and ICP-OES (after acid digestion). The ethanol was removed from the filtrate using a rotary evaporator (150 mbar, 55 °C). The aqueous acid composition was then washed twice with 50 mL of n-hexane using a separatory funnel. The n-hexane solution was collected for DART-MS analysis, and the aqueous fraction was collected in a flask. The oily layer adhering to the separatory funnel was washed with 2-propanol and collected for DART-MS analysis. A certain amount of MilliQ water was added stepwise to the washed aqueous leachate solution under constant stirring until a precipitate was observed. An additional 100 mL of MilliQ water was then added and stirred for an additional hour. The precipitate was filtered through a Whatmann membrane filter (0.45 μm), and the filtrate was collected for ICP-OES analysis. The precipitate was dried at 50°C and then analyzed by XRD, XRF, and ICP-OES (after acid digestion). All experiments were performed in duplicate.

[0076] <Analysis method> A PerkinElmer Avio 500 optical emission spectrometer (with prepfast) was used for ICP-OES analysis. Aqueous samples were stabilized with 5% HNO3 by volume before ICP-OES analysis. Solid samples were subjected to acid digestion prior to ICP-OES analysis. The samples were dissolved in a HNO3 / H2O2 / HCl solution and microwave digested at 250 °C under high pressure for 180 min.

[0077] X-ray fluorescence (XRF) analysis of solid samples was performed on a Thermo Scientific Niton XL3t GOLDD+ handheld XRF analyzer.

[0078] A NETZSCH STA 449 F3 Jupiter simultaneous thermal analyzer was used for thermogravimetric and differential scanning calorimetry analysis of the PVC samples.

[0079] To determine the crystalline phase composition of the resulting precipitates, X-ray diffraction (XRD) was performed using a PANalytical Empyrean diffractometer (Co anode). Qualitative analysis of the diffractograms was performed using HighScore Plus software.

[0080] DART-MS measurements were performed on a Thermo Scientific™ Q Exactive. The DART was operated at 450°C using helium gas to assay for additives present in the PVC sample and the organic liquid phase. Measurements were performed in positive and negative ion modes; the liquid sample was collected with a glass capillary, and the solid PVC sample was held in front of the DART with tweezers.

[0081] The presence of organic additives was measured and quantified by GCMS. Measurements were performed using 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 injector temperature was set to 250 °C, and 1 μL was injected with a split ratio of 1:50. The oven program was set to heat from 60 °C to 280 °C at 20 °C / min, hold for 5 min, then heat to 320 °C at 20 °C / min, and hold for 5 min again. The mass range was set to 50–650 amu, and the scan rate was set to 1000. D4 di-n-butyl phthalate was added to the samples as an internal standard.

[0082] SEM analysis of the cryo-ground PVC samples and the purified PVC after leaching was performed using an FEI NOVA NANOSEM 450 platform equipped with a BRUKER QUANTAX 200 SDD detector for EDX analysis. Prior to electron microscopy, the samples were embedded in Epofix resin, polished, and Pt-coated.

[0083] Thermodynamic modeling was performed using HSC Chemistry 8 software.

[0084] <Characterization of starting materials> The PVC starting material was extensively characterized to gain precise insight into its composition. The average concentrations of inorganic elements were determined by ICP-OES analysis of five subsamples of the PVC material examined. The inorganic elements with the highest concentrations were antimony (3.8% by mass) and aluminum (3.3% by mass). Therefore, these two elements were followed up to allow for comparison of their leaching efficiencies. While antimony is commonly present in plastics as antimony trioxide (ATO) (Sb2O3), the presence of aluminum is attributed to its presence as aluminum trihydroxide (ATH) (Al(OH)3), a filler material commonly used in plastics.

[0085] DART-MS analysis of the starting material allowed qualitative deducing the presence of the following organic additives in the PVC material: Phosflex 362® (2-ethylhexyl diphenyl phosphate), dioctyl phthalate, diethyl phthalate, as well as SbCl3OH, FeCl3, FeCl4, and other trace compounds of unknown composition (m / z 372 and 451).

[0086] Further analysis by GC-MS confirmed the presence of 2-ethylhexyl diphenyl phosphate (7188 μg / g), also known as Phosflex 362®, and diisononyl phthalate (26364 μg / g). Additionally, the antioxidant butylated hydroxytoluene (5893 μg / g) was detected.

[0087] [Table 1]

[0088] The N, C, H, and S contents of the material were analyzed to be 0.20%, 42.84%, 6.37%, and 0.23% by weight, respectively. Finally, the chloride content was 22% by weight. Comparing the H:C molar ratio of the PVC before and after treatment provided an indication of its dichlorination rate, with H:C = 1.5 for pure PVC and 2 or 1 for its polyol or polyene dechlorinated products, respectively. The H:C molar ratio of the starting material investigated was 1.8.

[0089] The thermal behavior of the investigated PVC sample in air was measured by TGA-DSC, which showed that the glass transition temperature was 58.2°C, and decomposition in air began at approximately 200°C and proceeded very rapidly at 272°C (Figure 8). A strong exothermic peak was observed at 513°C, suggesting thermal decomposition of organic matter.

[0090] <Aqueous chloride leaching> Exploratory studies by the present inventors have shown that leaching of inorganic additives from waste PVC is possible in a closed reactor in 1 M HCl at 250 °C for 24 hours. Under these conditions, PVC was dechlorinated, but a shorter reaction time of 2 hours resulted in less dechlorination and comparable extraction yields of inorganic elements. These reaction conditions served as the starting point for this study. A fixed liquid-to-solid ratio (L / S) of 10 was selected. HCl leaching of SbO generally occurs via the formation of soluble SbCl according to reaction equation (1). This reaction is thermodynamically favorable at temperatures above approximately 130 °C (Figure 9), and the formation of SbCl requires high chloride concentrations and a very low pH, according to the Eh-pH diagram. Therefore, the stability of SbCl in solution extends to higher pH levels by increasing the chloride concentration or temperature. Sb2O3 + 3HCl → 2SbCl3 + 3H2O (1)

[0091] First, we investigated the effect of leaching time at 250 °C. As shown in Figure 1, the leaching rate of Al increased with time, while the leaching rate of Sb reached a maximum at 2 h and then decreased after 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), which led to the hydrolysis of SbCl3 in water and precipitation as antimony oxychloride, as shown by Chae et al. (2020). Increasing the reaction time at 250 °C accelerated the dechlorination of PVC polymer, as the H:C molar ratio decreased from 1.8 (starting material) to 1.06 ± 0.01 after 2 h of reaction. Similarly, the chloride concentration decreased to 6.9 ± 0.1 wt%. We also observed that the plastic became brittle and darkened. Nevertheless, at short reaction times of 0.5 and 1 h, dechlorination did not occur significantly, as the H:C molar ratios of the residues were 1.56 ± 0.02 and 1.43 ± 0.00, and chloride concentrations were 30 ± 4 and 31 ± 2 wt%, respectively.

[0092] Figure 1 shows the leaching rates of Al and Sb as a function of reaction time in 1 M HCl, L / S = 10,250 °C.

[0093] Since the aim was to avoid dechlorination of PVC, a reaction temperature of 250 °C was inappropriate. Therefore, to achieve efficient antimony extraction, a higher HCl concentration was applied at a lower temperature. A moderate reaction temperature of 150 °C was chosen to investigate the effect of HCl concentration.

[0094] Increasing the HCl concentration had a positive effect on the antimony leaching rate (Figure 2A). Thermodynamic modeling showed that increasing the chloride concentration from 1 to 6 M expanded the stability region of SbCl3 at 150 °C to higher pH values ​​(Figure 2B). Furthermore, increasing the HCl concentration shifted the solution pH to lower values, allowing the formation of stable SbCl3. The latter pH effect was just as important as the chloride concentration. In a control experiment at 200 °C for 2 h with L / S = 10, the Sb leaching rate significantly decreased from 68 ± 14% to 12 ± 1% when 4 M HCl (pH = -0.74 ± 0.2) was replaced with a 1 M HCl + 3 M NaCl solution (pH = -0.52 ± 0.7), respectively. A significant increase in antimony extraction was observed when the HCl concentration was increased to 4 M, but further increase to 6 M only slightly increased the extraction yield.

[0095] Furthermore, the effects of reaction temperatures below and above the normal boiling point of water in the range of 50°C to 250°C were examined for 1M and 4M HCl solutions with L / S = 10 and a 2-hour reaction time (Figure 10). With 1M HCl, the extraction of Al and Sb increased with temperature, but the maximum extraction rates were only 38±11% for Sb and 50±2% for Al at 250°C for 2 hours. With 4M HCl, the leaching rate of antimony did not increase significantly above 150°C, but the leaching rate of aluminum increased to a maximum of 79.6±0.4% at 250°C. The mass loss of the PVC after the reaction was measured and showed a sharp increase from 225°C (i.e., 14±3% by mass at 225°C and 45±4% by mass at 250°C), indicating decomposition. Therefore, the mildest conditions for aqueous HCl leaching of antimony from PVC, resulting in an optimum antimony extraction rate of 66±2%, were hydrothermal conditions of 4 M HCl, L / S=10, 150°C, and 2 h, which did not result in any visible degradation of the plastic.

[0096] The hydrothermal leaching systems tested above require reactions at elevated temperatures and self-generated pressures, which may pose engineering and economic challenges to further scale-up.

[0097] In a separate study, ethanolic HCl leaching systems were tested at 50°C and 80°C with 2, 4, and 6M HCl, respectively, and compared to the aqueous leaching systems described above, as shown in Figure 3. Note that the HCl solutions were prepared by diluting 12M aqueous HCl with ethanol. Thus, the ethanol:water ratio for the 6M HCl solution was 1:1, while for the 4M HCl solution it was 2:1. These ethanol systems significantly increased antimony extraction at both test temperatures. The measured pH of the post-leaching compositions was, on average, approximately 0.4 lower for the ethanolic solutions compared to the aqueous solutions with the same HCl concentrations.

[0098] Antimony extraction by ethanolic HCl leaching increased dramatically when the temperature was increased from 50 to 80°C. However, at 80°C, more antimony was extracted from 4 M ethanolic HCl than from 6 M ethanolic HCl. One possible explanation is that the effect of ethanol on chloride activity decreases with increasing HCl concentration. Notably, switching from aqueous HCl to ethanolic HCl did not increase the leaching rate of aluminum. Thus, the leaching selectivity of antimony relative to aluminum improved and was optimal at 4 M ethanolic HCl, L / S = 10, 80°C, and 2 h.

[0099] The purified PVC obtained after leaching maintained its original shape and color, but was observed to be less flexible. The residue was analyzed, and its composition was compared with that of the original sample. The chloride content of the PVC slightly decreased from 22% by mass in the original sample to 18-21% by mass in the residue, and the H:C ratio decreased from 1.8 to 1.3-1.7. No clear trends were observed in the changes in the chloride content and H:C ratio of the residue as a function of reaction temperature or HCl concentration in the ethanolic acid composition, and the values ​​obtained did not indicate that degradation of the PVC had occurred.

[0100] <Optimization of antimony recovery process> Based on the above findings, a larger scale trial was carried out to test two different routes for recovering antimony after leaching.

[0101] In the leaching experiment, 50 g of PVC was leached in 500 mL of the ethanolic 4 M HCl solution prepared as described above at 80 °C for 5 h. After the reaction, the pH and ORP (Ag / AgCl) of the acid composition were measured and found to be -0.89 and 439 mV, respectively. The plastic residue after leaching was recovered and a mass loss of 5.3% by mass was recorded. The elemental composition of the residue is shown in Table 2. Approximately 67% of the antimony was removed, along with significant amounts of phosphorus (64%), sulfur (28%), tin (56%), and zinc (33%). Trace amounts of Ca, Cr, Mg, and Na were removed, while the extraction yields of Al, K, Pb, and Si were very low or negligible. The chloride concentration of the solid residue was 19% by mass, and the H:C molar ratio was 1.5, indicating that no significant degradation of the PVC had occurred. This was confirmed by comparing the thermogravimetric and calorimetric behavior of the purified PVC with the original PVC sample, which was similar (Figure 4).

[0102] [Table 2]

[0103] The resulting infusion was observed to be cloudy and was separated into two fractions, FR1 and FR2.

[0104] In FR1, after the ethanol was removed by evaporation, the solution turned yellowish in color and an oil phase was observed above the aqueous phase. This suggests that organic additives, such as plasticizers, may be co-extracted during the ethanolic HCl leaching process. The ethanolic HCl leaching process increases the penetration of the acidic composition into the polymer matrix, increasing its accessibility to embedded inorganic additives, such as antimony trioxide.

[0105] The distilled FR1 (pH = -1.46) and non-distilled FR2 (pH = -1.14) were then treated by slowly adding water to precipitate antimony oxychloride by hydrolysis of SbCl3 according to the following equations (2) and (3): SbCl3 + H2O → SbOCl + HCl (2) 4SbOCl+H2O→Sb4O5Cl2+2HCl (3) When water was added and the pH of the solution was measured, a precipitate was formed when the pH reached 0.06 for FR1 and 0.50 for FR2. water :V FR1 Precipitation occurred at approximately a 7:1 addition, and the pH remained stable over time.

[0106] The precipitate was filtered and dried at 40° C. The recovered precipitate was enriched in antimony (50% by mass) and also contained tin (0.18% by mass) as the main metal impurity (Table 3).

[0107] [Table 3]

[0108] The recoveries from solution were high for S (84%), Sn (94%), and Sb (92%), and ranged from 11 to 40% for the other elements examined, suggesting significant coprecipitation. However, due to the low concentrations of the other elements in the leachate, their final concentrations in the precipitate remained quite low. Nevertheless, further purification is required to make the antimony product suitable for commercial use.

[0109] X-ray diffraction of the resulting FR1 precipitate showed the presence of Sb2O3 (valentinite), but also another major phase that could not be assigned to known crystalline phases in the ICDD powder diffraction database in the X'Pert PANalytical High Score Plus software. To gain further insight into the phase composition, the sample was heated and an XRD diffractogram was obtained (Figure 5).

[0110] A phase change occurred at approximately 225 °C, forming SbOCl as the temperature increased. Therefore, it can be assumed that the unknown phase contained antimony and chloride. Furthermore, the material contained a significant amount of phosphorus (40% by mass), suggesting the presence of Phosflex 362® (2-ethylhexyl diphenyl phosphate) or its derivatives. The decomposition temperature of the former is approximately 240 °C, which may be consistent with the phase change observed upon heating in the temperature range of 225 °C to 250 °C (Figure 5).

[0111] Also, the presence of phthalate additives could not be ruled out. Antimony is known to form numerous organic complexes, including with phthalate and phosphate molecules. It is advantageous to remove organic material from the leachate prior to antimony precipitation to increase the purity of the precipitate and allow for identification of the organic additive compounds.

[0112] In FR2, which still contained ethanol, when water was added, the pH changed and the precipitate that formed tended to redissolve when the solution was left standing for a long time. Therefore, it was necessary to add a significant amount of water (i.e., V water :V FR2 = 6.2:1, which means that ethanol is not removed, so V FR2 >>V FR1 ). The resulting precipitate was difficult to recover by filtration, so it was centrifuged and the supernatant liquid was removed. After drying, the recovered FR2 precipitate exhibited an oily appearance. Therefore, to remove any oily fraction that may have been present due to the co-extraction of organic additives during the ethanolic HCl leaching, the material was washed with n-hexane. This washing step removed most of the solid residue fraction, indicating that antimony precipitation by adding water to FR2 was not successful.

[0113] <Process verification> Based on the above findings, we experimentally tested a process that considered (i) the need to pulverize PVC samples to increase the antimony extraction yield, and (ii) the need to remove co-extracted organic additives from the acid composition prior to antimony recovery to avoid interference and contamination during antimony precipitation. In the leaching process, 50 g of cryo-ground PVC (<4 mm) was leached in an ethanolic 4 M HCl solution at L / S = 10 at 80 °C for 4 h. Subsequent steps involved filtration and distillation of the filtrate to remove the ethanol. The resulting aqueous phase was then washed with n-hexane in a glass separatory funnel. After removing the liquid phase from the separatory funnel, a brown oily phase adhered to the glass wall and was recovered by washing with 2-propanol. Finally, antimony was recovered from the purified aqueous leachate by precipitation with water.

[0114] DART-MS analysis was performed on the PVC before and after leaching, as well as on the resulting n-hexane and 2-propanol liquid fractions (Table 4). All materials contained organic additives, such as dioctyl phthalate and diethyl phthalate, but Phosflex 362® was not observed in the 2-propanol solution. Based on GC-MS measurements, 76 ± 9% of 2-ethylhexyldiphenylphosphate and 71 ± 3% of di-n-octylphenylphosphate were removed during the ethanolic HCl leaching. On the other hand, the extraction efficiencies of butylated hydroxytoluene and 9-octadecanamide were low, at 15% and 30%, respectively. The extraction efficiency of diisononyl phthalate was 51%. After leaching, the ethanol was evaporated, and the remaining aqueous solution was washed with hexane to remove any co-extracted organic additives. Furthermore, potential decomposition products of the organic additives were observed in the purified PVC. Although DART-MS is not a quantitative analytical method, it indicated that the n-hexane wash fraction removed the organic additives from the aqueous HCl fraction.

[0115] Subsequent hydrolysis of antimony in washed aqueous HCl (WAS) resulted in a 5:1 V:V ratio reaching a pH of 0.231. water :V WASA precipitate was obtained by adding 100 ml of HCl. 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). The presence of an amorphous phase was also observed, which was quantified by Rietveld analysis of the X-ray diffraction pattern to be 25.3 mass% of the total composition. Chemical analysis of the precipitate showed high purity (Table 5).

[0116] Co-extraction of organic additives from PVC occurred during the ethanolic HCl leaching. These co-extracted organic compounds need to be removed from solution prior to antimony precipitation by hydrolysis to obtain the pure product.

[0117] [Table 4]

[0118] [Table 5]

[0119] Chemical analysis indicated the presence of 768,000 mg / kg Sb and 100,000 mg / kg Cl, with trace impurities of Al (28.5 mg / kg), P (240 mg / kg), Pb (440 mg / kg), Si (150 mg / kg), and Sn (44 mg / kg). The precipitate also contained 0.8% carbon by mass, which is believed to be the major impurity. The precipitate contained no Ca, Cr, K, Mg, Na, S, or Zn. Overall recovery of antimony (primarily as Sb4Cl2O5) from the PVC starting material was 80% by mass.

[0120] TGA-DSC analysis of the purified PVC showed a similar temperature profile to that of the starting material (Figure 11), with a molar H:C ratio of 1.7, indicating that the PVC did not decompose during leaching. Meanwhile, SEM-EDX analysis of the starting and leached PVC showed that small antimony-containing particles were removed, whereas larger aluminum-containing particles and medium-sized silicon-containing particles were not removed by leaching with 4M ethanolic HCl (Figures 7A–7H—the top panels (Figures 7A, 7C, 7E, and 7G) are from untreated PVC material, while the bottom panels (Figures 7B, 7D, 7F, and 7H) are from PVC material leached in 4M ethanolic HCl at 80°C for 4 hours).

[0121] Abbreviation EDX: Energy dispersive X-ray analysis. DSC: Differential scanning calorimetry. TGA: Thermogravimetric analysis. ICP-OES: Inductively Coupled Plasma Optical Emission Spectroscopy. ICP-MS: Inductively coupled plasma mass spectrometry. XRD: X-ray diffraction. XRF: X-ray fluorescence analysis. DART-MS: Direct Analysis by Real-Time Mass Spectrometry. DART-MS utilizes an ion source that generates electronically or vibrationally excited species from gases such as helium, argon, or nitrogen, which ionize atmospheric or dopant molecules. The ions generated from the atmospheric or dopant molecules undergo ion-molecule reactions with sample molecules to produce analyte ions. Analytes with low ionization energies can also be directly ionized. The DART ionization process can produce positive or negative ions, depending on the potential applied to the exit electrode. GC MS: Gas chromatography mass spectrometry. SEM: scanning electron microscope.

[0122] (References) 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. 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. 3.R. Babinsky, “PVC additives: a global review”, Plastics Additives & Compounding, 2006, DOI: 10.1016 / S1464-391X(06)70526-8, 38-40. 4.A. Sevenster, “VinylPlus, the new European PVC industry’s voluntary programme toward sustainability”, J Mater Cycles Waste Manag, 2012, 14, 281- 285. 5.M. Filella, P. Hennebert, G. Okkenhaug and A. Turner, J Hazard, “Occurrence and fate of antimony in plastics”, Mater, 2020, 390, 121764. 6.European Commission, Study on the EU's list of Critical Raw Materials - Final Report, 2020. 7.European Commission, Study on the EU's list of Critical Raw Materials (2020) - Critical Raw Materials Factsheets, 2020, DOI: 10.2873 / 631546. 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. 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. 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. 11.L. Zhan, X. Zhao, Z. Ahmad and Z. Xu, “Leaching behavior of Sb and Br from E-waste flame retardant plastics”, Chemosphere, 2020, 245, 125684.

Claims

1. 1. A method for recycling vinyl chloride polymer material containing initial levels of one or more additive compounds, preferably wherein said one or more additive compounds are selected from the group consisting of heavy metals and organic compounds, comprising the steps of: (i) providing an aqueous acid composition comprising one or more alcohols and one or more acids; (ii) contacting a vinyl chloride polymer material with a volume of said acid composition to cause extraction of said one or more additive compounds from said vinyl chloride polymer material, said acid composition forming a two-phase system with said vinyl chloride polymer material, said two-phase system comprising a solid phase comprising purified vinyl chloride polymer material and a liquid phase comprising said alcohol, water, said acid, and the extracted one or more additive compounds; (iii) separating a solid phase containing the purified vinyl chloride polymer material from a liquid phase containing the extracted one or more additive compounds; A method comprising:

2. 2. The method of claim 1, wherein the acid composition comprises at least 5% by volume, preferably at least 7.5% by volume, more preferably at least 8% by volume alcohol to acid composition.

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

4. 4. The method according to any one of claims 1 to 3, wherein the alcohol is selected from the group of monohydroxy alcohols, dihydroxy alcohols, or polyhydroxide alcohols.

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

6. 6. A process according to any one of claims 1 to 5, wherein contacting the vinyl chloride polymer material with the volume of acid composition to effect extraction of the one or more added 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 more, most preferably 50°C or more, more preferably from 20 to 100°C, most preferably from 30 to 90°C, in particular from 40 to 90°C or from 50 to 85°C.

7. The acid is one or more strong inorganic acids having a pKa value of at most −2 in water, preferably hydrochloric acid (HCl), H ２ SO ４ , HBr, HI; or one or more strong organic acids having a pKa value of at most -1.9 in water, preferably p-toluenesulfonic acid, methanesulfonic acid; one or more organic acids selected from oxalic acid, methanoic acid, acetic acid, citric acid; and mixtures of one or more of the aforementioned acids, preferably comprising an acid selected from the group consisting of: oxalic acid, methanoic acid, acetic acid, citric acid;

8. 8. The method according to any one of claims 1 to 7, wherein the acid is an aqueous solution of acid, preferably at least 1 M 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 to 5.5 M.

9. 9. A method according to any one of claims 1 to 8, wherein the solid vinyl chloride polymer material is mixed with the acid composition in a mass ratio of solid vinyl chloride polymer material to acid composition between 1:100 and 1:2, preferably between 1:50 and 1:2, more preferably between 1:25 and 1:

2.

10. 10. The method of any one of claims 1 to 9, wherein the one or more additive compounds comprise one or more heavy metals, and the one or more heavy metals are selected from the group consisting of antimony, tin, zinc, lead, cobalt, cadmium, aluminum, calcium, sodium, zinc, tin, barium, or a mixture of any thereof.

11. 11. A method according to any one of the preceding claims, wherein the vinyl chloride polymer material is contacted with the volume of the acid composition in the form of particles, flakes or sheets having dimensions 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.

12. 12. A method according to any one of claims 1 to 11, wherein the acid composition and vinyl chloride polymer material are contacted for a time and at a temperature which reduces the amount of heavy metals, in particular antimony, by at least 50%, preferably at least 60%, more preferably at least 75%, and most preferably at least 90%.

13. 13. The method according to any one of claims 1 to 12, further comprising subjecting 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 residual acid and / or heavy metals from the purified vinyl chloride polymer.

14. The method of any one of claims 1 to 13, wherein the vinyl chloride polymer is derived from granular post-consumer PVC.

15. The method according to any one of claims 1 to 14, wherein steps (i) to (iii) are repeated once or several times.

16. 16. The method of any one of claims 1 to 15, further comprising removing / evaporating the alcohol from the liquid phase to form an acid liquid phase, and contacting the acid liquid phase with a non-polar solvent to extract at least a portion of the organic compounds.

17. 17. The method of claim 16, wherein the non-polar solvent is hexane.

18. 18. The method of any one of claims 1 to 17, further comprising blending the purified vinyl chloride polymer with virgin chloride polymer to obtain a secondary vinyl chloride polymer.

19. 18. A purified vinyl chloride polymer material obtainable by the method of any one of claims 1 to 17, wherein said purified vinyl chloride polymer material contains less than 1%, preferably less than 0.5%, more preferably less than 0.1%, by weight of heavy metal additive compounds relative to the total dry weight of the purified vinyl chloride polymer, as determined by ICP-OES.

20. 18. A purified vinyl chloride polymer material obtainable by the method of any one of claims 1 to 17, wherein the purified vinyl chloride polymer material contains no more than 0.3 wt. %, preferably no more than 0.1 wt. % Sb, based on the total dry weight of the purified vinyl chloride polymer material, as determined by ICP-OES.

21. 21. A secondary vinyl chloride polymer composition comprising a virgin vinyl chloride polymer and a purified vinyl chloride polymer obtainable by the method of any one of claims 1 to 17, or a purified vinyl chloride polymer material according to claim 19 or 20.

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