Method for recycling polyvinyl chloride products

This invention relates to a method for recycling polyvinyl chloride (PVC) products, such that the polyvinyl chloride polymer from these products can be used for producing new polyvinyl chloride products.

Although polyvinyl chloride is a thermoplastic polymer, recycling of polyvinyl chloride products is problematic. This is mainly due to the additives and impurities that PVC products comprise. Most polyvinyl chloride products - and certainly those made of soft PVC - comprise plasticizers. Phthalates are known plasticizers. Some types of phthalates that were used in the past as plasticizers in PVC have now even been banned. Furthermore, polyvinyl chloride products can comprise, inter alia, fillers (e.g. CaCCh), colorants and heavy metals.

The composition of PVC products is strongly dependent on their application. This makes recycling of end-of-life PVC products particularly difficult.

The production of new PVC products requires polyvinyl chloride polymer containing the accompanying desired additive substances that are specific to the intended application of the new PVC product.

The object of the invention is to provide a better and widely applicable method for recycling polyvinyl chloride products so that the polyvinyl chloride polymer from these products can be used for producing new polyvinyl chloride products.

The invention relates to a method for recycling polyvinyl chloride (PVC) products. The method is characterized in that the method comprises the step of treating the polyvinyl chloride products to be recycled in an ionic liquid.

The method according to the invention has the advantage that separation of the polyvinyl chloride from the additives (such as plasticizers) and contaminants can be achieved in an efficient manner. This allows the polyvinyl chloride to be reused for a wide range of applications.

A preferred embodiment is characterized in that the polyvinyl chloride products to be recycled are particles. Preferably, 50% by volume of the particles are smaller than 1 millimeter. More preferably, 90% by volume of the particles are smaller than 1 millimeter. The particle size of the polyvinyl chloride products to be recycled can be measured by laser diffraction. This embodiment has the advantage that the method can be carried out more rapidly because migration of components from the PVC to the ionic liquid can take place more quickly.

A preferred embodiment is characterized in that treatment of the polyvinyl chloride products to be recycled in the ionic liquid takes place at elevated temperature, preferably at a temperature higher than 100°C, more preferably at a temperature higher than 150°C, more preferably at a temperature higher than 200°C. These embodiments allow optimization of the method in that treatment of the products to be recycled takes place more quickly.

A preferred embodiment is characterized in that the treatment in an ionic liquid is an extraction treatment, wherein substances are extracted by the ionic liquid from the polyvinyl chloride products to be recycled. This embodiment allows additives (e.g. plasticizers, e.g. phthalates) to be efficiently removed from the polyvinyl chloride products to be recycled so that after separation of the remaining polyvinyl chloride, this polyvinyl chloride can be used for the production of a wide range of new polyvinyl chloride products.

In the extraction treatment, plasticizers (e.g. phthalates) and/or polar components and/or acrylate resins and/or organic components and/or humus and/or auxiliaries and/or impurities (e.g. heavy metals) are preferably extracted from the polyvinyl chloride products. A preferred embodiment is characterized in that the method comprises the step wherein the polyvinyl chloride recyclate is separated from the ionic liquid, preferably by a filtration process. After separation of the polyvinyl chloride recyclate, it can be used for the production of a wide range of new polyvinyl chloride products.

Preferably, the polyvinyl chloride recyclate is washed after separation from the ionic liquid. This allows polyvinyl chloride of even higher purity to be obtained.

A preferred embodiment is characterized in that the method comprises the step wherein at least part - and preferably all - of the extracted substances (and preferably at least plasticizers, e.g. phthalates) is removed from the ionic liquid. Preferably, at least part of the extracted substances (and preferably at least plasticizers, e.g. phthalates) is removed from the ionic liquid by means of a temperature increase in the ionic liquid, more preferably by means of a distillation process.

This embodiment has the advantage that the ionic liquid can be reused when the method is carried out again with new polyvinyl chloride products to be recycled, e.g. in a closed circuit. This allows the method to be carried out in a more cost-effective manner.

A preferred embodiment is characterized in that heavy metals are extracted by the ionic liquid from the polyvinyl chloride products to be recycled, wherein the method comprises the step in which the extracted heavy metals are removed from the ionic liquid, preferably by means of precipitation (e.g. by means of reducing the metal ions, preferably by means of an electrochemical process or by means of adjustment of the acidity) or by means of electrodeposition. This embodiment has the advantage that the ionic liquid can be reused when the method is carried out again with new polyvinyl chloride products to be recycled, e.g. in a closed circuit. This allows the method to be carried out in a more cost- effective manner.

A preferred embodiment is characterized in that at least part of the extracted substances is removed from the ionic liquid by means of adding water, wherein the at least part of the extracted substances passes into the water, followed by phase separation and removal of the water with the extracted substances in it. Preferably, the extracted substances that pass into water comprise one or more of salts (e.g. sodium chloride), water-soluble pigments or biomass (e.g. sugars and proteins).

This embodiment has the advantage that the ionic liquid can be reused when the method is carried out again with new polyvinyl chloride products to be recycled, e.g. in a closed circuit. This allows the method to be carried out in a more cost-effective manner.

A preferred embodiment is characterized in that the ionic liquid is used in a closed circuit, so that after removal of the extracted substances from the ionic liquid, this ionic liquid can be reused for treatment of polyvinyl chloride products to be recycled such as in any embodiment of the method according to the invention.

This embodiment means that the required amount of ionic liquid can be limited, in view of the fact that the ionic liquid is recycled in a closed circuit so as to be reused in one of the following embodiments of the method according to the invention.

A preferred embodiment is characterized in that, in the step of treating the polyvinyl chloride products to be recycled in the ionic liquid, the polyvinyl chloride of the polyvinyl chloride products to be recycled is substantially extracted or dissolved in the ionic liquid.

This embodiment has the advantage that - by selection of a suitable ionic liquid and processing conditions - the polyvinyl chloride is taken up in the ionic liquid, while additives are not taken up therein. After separation of the ionic liquid from the additives and separation of the polyvinyl chloride from the ionic liquid, the polyvinyl chloride can be used for the production of a wide range of new polyvinyl chloride products.

A preferred embodiment is characterized in that the polyvinyl chloride of the polyvinyl chloride products to be recycled is substantially extracted or dissolved in the ionic liquid at a temperature lower than the temperature at which dehydrochlorination of the polyvinyl chloride occurs in the ionic liquid used, more preferably at a temperature that is at least 10°C, and more preferably at least 20°C, lower than the temperature at which dehydrochlorination of the polyvinyl chloride occurs in the ionic liquid used.

These embodiments have the advantage that the polyvinyl chloride can be extracted or dissolved in the ionic liquid without the occurrence of dehydrochlorination of the polyvinyl chloride. This allows the polyvinyl chloride to then be recovered in order to produce new polyvinyl chloride products.

Preferably, after the substantial extraction or dissolution of the polyvinyl chloride in the ionic liquid, the method comprises the step of adding a solvent, wherein the ionic liquid dissolves in the solvent, wherein the polyvinyl chloride precipitates, so that the polyvinyl chloride can be separated.

Such embodiments have the advantage that the polyvinyl chloride can be separated and reused for producing new polyvinyl chloride products.

For example, formic acid or water can be used as a solvent in such embodiments.

Separation of precipitated polyvinyl chloride can be carried out by means of centrifugation or another suitable separation technique.

It is possible that in embodiments wherein the polyvinyl chloride of the polyvinyl chloride products to be recycled is substantially extracted or dissolved in the ionic liquid, additives (such as e.g. plasticizers) may also be dissolved from the polyvinyl chloride products in the ionic liquid. However, the polyvinyl chloride can then be separately precipitated from the ionic liquid by adding a suitable solvent to the ionic liquid.

A preferred embodiment is characterized in that the ionic liquid comprises or is a mixture of an ionic liquid A and an ionic liquid B; wherein in the method, the polyvinyl chloride of the polyvinyl chloride products to be recycled is substantially dissolved in the ionic liquid A or extracted therein; and wherein substances (e.g. additives such as e.g. plasticizers) from the polyvinyl products to be recycled are extracted or dissolved in the ionic liquid B.

Preferably, after treatment of the polyvinyl chloride products to be recycled in the ionic liquid, the method comprises the step of separation of the ionic liquid A from the ionic liquid B, for example by means of controlling the temperature.

This preferred embodiment has the advantage that the two ionic liquids are separated. The polyvinyl chloride can then be obtained from the ionic liquid A and used for the production of new polyvinyl chloride products. The ionic liquid A can then be reused. Ionic liquid B can be purified by removal of the extracted substances dissolved therein and reused.

In embodiments wherein, in the step of treating the polyvinyl chloride products to be recycled in the ionic liquid, the polyvinyl chloride of the polyvinyl chloride products to be recycled is substantially extracted or dissolved in the ionic liquid, the ionic liquid preferably comprises one or more of l-butyl-3 -methyl imidazolium tetrafluorob orate ([BMIM][BF4]), l-butyl-3 -methyl imidazolium hexafluorophosphate ([BMIM][PF6]), 2,4-bis(2-hydroxypropyl)-l, 1,3,3-tetramethyl guanidinium tetrafluorob orate ([TMGHPO2][BF4]), or tetramethyl guanidinelactate (TMGL).

These ionic liquids are highly effective for dissolving polyvinyl chloride.

A preferred embodiment is characterized in that the ionic liquid comprises an organic cation; and an organic or an inorganic anion. Preferably, the organic cation comprises a phosphorus or a nitrogen atom.

Such ionic liquids are highly suitable for use in the method according to the invention.

A preferred embodiment of the invention is characterized in that the ionic liquid is selected from the following classes: an ammonium ionic liquid, a phosphonium ionic liquid, an imidazolium ionic liquid, a pyridinium ionic liquid, a pyrrolidinium ionic liquid.

Such ionic liquids are highly suitable for use in the method according to the invention.

A preferred embodiment is characterized in that the ionic liquid is selected from 1-octyl- 3-methylimidazolium tetrafluoroborate ([C8mim][BF4]), l-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), or triethylammonium hydrogen sulfate ([HNEt3][HSO4]).

Such ionic liquids are highly suitable for the removal of phthalate plasticizers from the polyvinyl chloride products to be recycled. Phthalate plasticizers are the most important group of additives that must be removed from the polyvinyl chloride products to be recycled.

A preferred embodiment of the method of the invention is characterized in that the anion of the ionic liquid is selected from one or more of MeSOf (methyl sulfonate anion), FSI (bis(fhiorosulfonyl)imide), N(CN)2- (dicyanamide anion), alkylOSCh', HSOF, NOS’, benzene sulfonate anion, vinyl sulfonate anion, tosylate anion, propane disulfonate anion.

These anions have the advantage for use in the invention in that they function as dehydrochlorination inhibitors in the ionic liquid used. This allows the breakdown of polyvinyl chloride - for example when it is dissolved or extracted in the ionic liquid - to be prevented. In this manner, a maximum amount of polyvinyl chloride can be recycled for use in the production of new polyvinyl chloride products.

An advantageous method is characterized in that the cation of the ionic liquid is selected from one or more of TOMP (trioctylmethylphosphonium), TBMA (methyltributylammonium), TOMA (methyltrioctylammonium), and TOAH (trioctylammonium). These cations have the advantage of being inexpensive and readily available. Furthermore, they have the advantage that in combination with a suitable anion, polyvinyl chloride can be dissolved in the ionic liquid at a temperature lower than the temperature at which dehydrochlorination of polyvinyl chloride occurs.

A preferred embodiment of the method is characterized in that the ionic liquid is selected from one or more of

TOMP (trioctylmethylphosphonium) as cation and MeSOf (methyl sulfonate anion) as anion,

TBMA (methyltributylammonium) as cation and MeSOf (methyl sulfonate anion) as anion,

TOMA (methyltrioctylammonium) as cation and MeSOf (methyl sulfonate anion) as anion,

TOMA (methyltrioctylammonium) as cation and NOs' as anion,

TOAH (tri octyl ammonium) as cation and MeSOf (methyl sulfonate anion) as anion, TOAH (trioctylammonium) as cation and tosylate anion as anion,

TOAH (trioctylammonium) as cation and benzene sulfonate anion as anion.

These ionic liquids have the advantage of being readily available and inexpensive. Furthermore, polyvinyl chloride can be dissolved therein at temperatures lower than the dehydrochlorination temperature of polyvinyl chloride in the treatment of polyvinyl chloride products with these ionic liquids.

It has also been found that after dissolution of polyvinyl chloride in these ionic liquids, the polyvinyl chloride can be precipitated from the ionic liquid by adding a solvent to the ionic liquid in which the polyvinyl chloride is dissolved. For example, formic acid or water can be used as solvent.

A preferred embodiment is characterized in that treatment of the polyvinyl chloride products to be recycled in the ionic liquid is carried out with a first ionic liquid according to any embodiment of the method according to the invention. This preferred embodiment further comprises the step wherein the polyvinyl chloride products to be recycled are treated in a second ionic liquid according to any embodiment of the method according to the invention. The first ionic liquid has a different chemical composition in this case from the second ionic liquid.

Through suitable selection of the first ionic liquid and the second ionic liquid, this embodiment allows the polyvinyl chloride products to be recycled to be optimally purified. By suitable selection of the first ionic liquid and the second ionic liquid, a first portion of additives can be extracted in the first ionic liquid, while a second portion of additives can be extracted in the second ionic liquid.

A preferred embodiment is characterized in that the ionic liquid is a mixture of at least a first ionic liquid and a second ionic liquid, wherein the first ionic liquid has a different chemical composition from the second ionic liquid.

Through suitable selection of the first ionic liquid and the second ionic liquid, this embodiment allows the polyvinyl chloride products to be recycled to be optimally purified. By suitable selection of the first ionic liquid and the second ionic liquid, a first portion of additives can be extracted in the first ionic liquid, while a second portion of additives can be extracted in the second ionic liquid. After the treatment with the mixture of these ionic liquids, a phase separation of the two ionic liquids can be carried out, for example by controlling the temperature, followed by removal of the extracted substances from the two ionic liquids, after which both of these ionic liquids can be reused.

A preferred embodiment is characterized in that the method comprises the step wherein extraction of the polyvinyl chloride products to be recycled is carried out in supercritical carbon dioxide; preferably wherein in this step, organic substances, preferably plasticizers, more preferably phthalates, are extracted by the supercritical carbon dioxide from the polyvinyl chloride products to be recycled.

This embodiment makes it possible, with the aid of the supercritical carbon dioxide, to extract organic substances, for example phthalate plasticizers, from the polyvinyl chloride to be recycled. Other additives in the polyvinyl chloride products to be recycled can be recycled using the ionic liquid from the polyvinyl chloride to be recycled. By suitably selecting the ionic liquid, one can therefore achieve optimum purification of the polyvinyl chloride to be recycled: the additives and other substances in the polyvinyl chloride that cannot be removed - or are difficult to remove or cannot be completely removed - by the treatment with supercritical carbon dioxide can be removed using the ionic liquid.

In the embodiment wherein the method comprises the step in which extraction of the polyvinyl chloride products to be recycled is carried out in supercritical carbon dioxide, in the step of treating the polyvinyl chloride products to be recycled in the ionic liquid, heavy metals and/or pigments are preferably extracted using the ionic liquid from the polyvinyl chloride products to be recycled. Extraction with supercritical carbon dioxide is not suitable for removing heavy metals and pigments (primarily inorganic pigments) from polyvinyl chloride. These substances can be removed from the polyvinyl chloride by suitably selecting the ionic liquid. This embodiment therefore allows optimum purification of the polyvinyl chloride products to be recycled to be achieved.

In a preferred embodiment wherein extraction of the polyvinyl chloride products to be recycled is carried out in supercritical carbon dioxide, this step is carried out after the step of treating the polyvinyl chloride products to be recycled in the ionic liquid.

This embodiment makes it possible to work with a smaller amount of supercritical carbon dioxide or to reduce the duration of effect of the supercritical carbon dioxide. The treatment with the ionic liquid has already removed substances from the polyvinyl chloride, which facilitates migration of substances to be extracted through the supercritical carbon dioxide and allows the extraction with supercritical carbon dioxide to be carried out more easily.

In a preferred embodiment wherein extraction of the polyvinyl chloride products to be recycled is carried out in supercritical carbon dioxide, this step is carried out before the step of treating the polyvinyl chloride products to be recycled in the ionic liquid. This embodiment has the advantage that, in the treatment with supercritical carbon dioxide, substances (e.g. phthalate plasticizers) are already removed from the polyvinyl chloride, which gives the polyvinyl chloride a more open structure. This facilitates the effect of the ionic liquid, thus allowing it to better and more quickly extract substances from the polyvinyl chloride.

A preferred embodiment of the method according to the invention is characterized in that the polyvinyl chloride of the polyvinyl chloride products to be recycled, after treatment of the polyvinyl chloride products to be recycled in an ionic liquid, is separated. This polyvinyl chloride can then be used in the production of new polyvinyl chloride products, wherein suitable additives (such as suitable environmentally friendly plasticizers in the desired amounts) can be added.

Figure 1 describes an example of implementing the method according to the invention.

Figure 1 shows a first reaction vessel 1 that contains an ionic liquid 2. Examples of ionic liquids that can be used include: l-octyl-3-methylimidazolium tetrafluoroborate ([C8mim][BF4]), l-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]) or triethylammonium hydrogen sulfate ([HNEt3][HSO4]).

Polyvinyl chloride product to be recycled 3 is added and ground into fine particles. This polyvinyl chloride product to be recycled can comprise one or more of production waste or post-consumer waste. If the polyvinyl chloride product comprises or is composed of post-consumer waste, this may be of widely varying composition, primarily with respect to the additives, filler substances and impurities in the polyvinyl chloride.

Extraction takes place in reaction vessel 1, wherein the ionic liquid 2 extracts plasticizers (e.g. phthalates) and a wide range of additives and impurities (such as heavy metals) are removed from the polyvinyl chloride products to be recycled. Via a line 3, the entire mixture is fed to a filter 4, where the polyvinyl chloride is separated. This polyvinyl chloride 5 is free of plasticizers, additives and impurities and can be used for the production of new polyvinyl chloride products. The ionic liquid - with the substances extracted therein - is fed into a second reaction vessel 6. By means of distillation, plasticizers 7 (e.g. phthalates) and other substances are separated in this reaction vessel from the ionic liquid via line 6.

The ionic liquid is then fed into a third reaction vessel 8, wherein the heavy metals are precipitated using electrodeposition and evacuated via drain 9.

The ionic liquid is then fed back via line 10 to the first reaction vessel 1. The method of the invention is carried out in this manner, wherein the ionic liquid is used in a closed circuit.

Table I: Test results for dissolution of polyvinyl chloride in selected ionic liquids

Table I shows the test results for tests of dissolution of polyvinyl chloride in seven different ionic liquids. “T diss (°C)” indicates the temperature at which the polyvinyl chloride could be dissolved in the ionic liquid. “T DHCL (°C)” indicates the temperature at which dehydrochlorination of polyvinyl chloride occurs when polyvinyl chloride comes into contact with the respective ionic liquid. Polyvinyl chloride therefore dissolves in each of these seven ionic liquids without the occurrence of dehydrochlorination of the polyvinyl chloride.

Using these seven ionic liquids, tests were conducted at 100°C in order to determine whether common additives used in polyvinyl chloride products also dissolve in the ionic liquid. The additives tested were COPO (a polyvinyl-polyacetate copolymer), DOTP (dioctyl terephthalate), DINCH (di(isononyl)cyclohexane-l,2-dicarboxylate) and DINP (diisononyl phthalate).

Each of the above-mentioned plasticizers could be dissolved in the ionic liquids of test numbers 1, 5 and 7 (see Table I) at 100°C. In the ionic liquid of test number 4 (see Table I), COPO, DOTP and DINP could be dissolved at 100°C, but not DINCH. In test numbers 2, 3 and 6 (see Table I), none of the plasticizers tested could be dissolved.

It was also tested whether aluminum sulfate, frequently used in polyvinyl chloride products as a filler, could be dissolved in the seven ionic liquids of Table I. This was not the case. This aluminum sulfate can therefore easily be separated from thoroughly dissolved polyvinyl chloride.

Even in the event that both polyvinyl chloride and some or all additives of the polyvinyl chloride products can be dissolved in the ionic liquid used, it is possible to isolate the polyvinyl chloride by adding a suitable solvent (e.g. formic acid). This causes the polyvinyl chloride to precipitate, while additives remain in solution. The precipitated polyvinyl chloride can then be separated, for example by centrifugation. This polyvinyl chloride can then - after adding suitable and desired additives - be used in the production of new polyvinyl chloride products.

In a similar manner, additives can be removed from the ionic liquid using a suitable solvent.

It is possible to recover the ionic liquids and reuse them.

The present invention is by no means limited to the embodiments described above; rather, similar methods can be carried out according to different variants without departing from the scope of the present invention.