A process and a plant for recovering polyamides from mixed materials such as scrap materials and waste

Abstract

There is provided a process for recovering polyamides (1) from a mixed material or waste (10) containing polyamide material (1) and non-polyamide solid material (2), comprising the steps of dissolving said polyamide material and separating the solution of polyamide material (1) from the non-polyamide solid material (2) present in said mixed material or waste, characterized in that it further comprises the steps of: preparing a solution obtained by mixing methanol (4) and salt (5) inside a dissolution vessel (A) provided with means for stirring said solution; adjusting the temperature of said solution to a value lower than the boiling point of methanol, preferably to a value in the range of 50° C to 70°C, more preferably between 56°C and 65°C; adding to said heated solution an amount of said mixed material or waste (10) containing polyamide material (1); bringing said polyamides (1) into solution so as to obtain a solution¬ dispersion (7) containing the polyamide material (1) and a non-polyamide solid portion (2); separating said solution-dispersion (7) from said non-polyamide solid materials (2), and recovering the polyamide material (1) from said solution-dispersion (7).

Description

[0001] A PROCESS AND A PLANT FOR RECOVERING POLYAMIDES FROM MIXED MATERIALS SUCH AS SCRAP MATERIALS AND WASTE

[0002] ***

[0003] The present invention relates to a process and a plant for recovering polyamides from mixed materials such as scrap materials and waste. In greater detail, the invention concerns a process and a plant for dissolving said polyamides in a solution in order to be able to separate them from non-polyamide materials.

[0004] At present, there are known techniques for recovering polyamides from mixed scrap materials, for example materials containing polyamides and other polymers or in general containing polluting materials. One type of approach to the recovery of polyamides is based on the depolymerization of polyamide into the monomers making it up.

[0005] However, this technique implies on the one hand that the polyamide then needs to be repolymerized from the monomers, while on the other hand it has been verified that the monomer or oligomers of the starting polymer of always show a high degree of impurities and must thus be purified.

[0006] There are also known techniques for recovering polyamides which envisage the use of solvents that bring the polyamide into solution, but not the non-polyamide materials, which are separated from the solution. The polyamide material is then recovered from the solution, for example by evaporation of the solvent.

[0007] The use of solvents such as propylene glycol, alkene carbonates and dimethyl sulfoxide (DMSO) for this purpose is known.

[0008] One disadvantage tied to the use of these solvents to recover polyamide materials is tied to both the high process temperatures required to bring said materials into solution, and to the reduction in the viscosity of the solution in order to make it more easily filtrable. The recovery of the known solvents also entails high-temperature processes, due to the high boiling points of the solvents. Furthermore, a treatment at high temperatures leads to a partial degradation of the polyamide polymer.

[0009] JP2009286867 discloses a method for recovering polyamide material from mixed materials in which use is made of saturated solutions of aliphatic alcohols C1-C4 with CaCh, with the addition of water. The amount of polyamide material soluble in a saturated MeOH / CaC mixture appears to be about 0.5% by weight (Example 4).

[0010] The need thus arises to solve the problem highlighted above and provide a process for recovering polyamides from mixed materials that may be implemented on an industrial scale and gives acceptable yields also in terms of energy, i.e. by using low process temperatures, is simple to carry out and may be implemented on an industrial scale in a continuous process.

[0011] This aim is achieved by means of the present invention, which relates to a process for recovering polyamides according to the independent claims 1 and 8 and a plant defined in the independent claim 17.

[0012] Preferred technical solutions are disclosed in the respective dependent claims.

[0013] In a first embodiment, the present invention regards a process for recovering polyamides from a mixed material or waste containing polyamide material and non-polyamide solid material, comprising the steps of dissolving said polyamide material and separating the solution of polyamides from the solids present in said scrap materials or waste, characterized in that it comprises the steps of: a) preparing a eutectic solution obtained by mixing at least methanol and at least one salt inside a dissolution vessel; preferably, with the exclusion of the following salts: Ca(NO3)2, e.g. Ca(NO3)2'4H2O, NaSCN, Cal2, e.g. Cal2'4H2O, and calcium salicylate; b) adjusting the temperature of said solution to a value lower than the boiling point of methanol, preferably to a value in the range of 45°C to 75°C, preferably between 50°C and 70°C, more preferably between 55°C and 65°C; c) adding to said heated solution an amount of said mixed material or waste containing polyamide material; d) bringing said polyamides into solution so as to obtain a solution-dispersion of the polyamide material and a non-polyamide solid portion; e) separating said solution-dispersion from said non-polyamide solid materials and f) recovering the polyamide material from said solution-dispersion.

[0014] Preferably, step f) comprises: precipitating the polyamide material present in said solution-dispersion, separating the methanol and obtaining a paste containing the salt, solid polyamide material and residual methanol; and recovering the polyamide material (1) present in the said paste (8).

[0015] The eutectic solution of step a) is advantageously a deep eutectic solvent adapted to solubilize the polyamides 1 at temperatures lower than the ones necessary when traditional solvents are used in common purification processes. Preferably, in the eutectic solution prepared in step a) of the said process, the concentration of the salt suitable for forming a deep eutectic solvent is between 50 and 350 g, preferably between 80 and 300 g, more preferably between 120 and 260 g, for example 130, or 140, or 150, or 160, or 170, or 180, 190, or 200, 210, or 220, or 230, or 240, or 250 g, per litre of methanol. The eutectic solution thus forms a deep eutectic solvent (DES). In step a) of the process, the preferred solution comprises methanol and a calcium salt; it preferably comprises methanol and at least one water-soluble calcium salt, and more preferably it comprises methanol and at least one calcium chloride, for example CaCh, in the amounts specified above, ranging between 50 to 350 g, preferably between 80 and 300 g, more preferably between 120 and 260 g, for example 130, or 140, or 150, or 160, or 170, or 180, 190, or 200, 210, or 220, or 230, or 240, or 250 g, per litre of methanol so as to form a deep eutectic solvent (DES). The methanol used may have various degrees of purity and can be selected from the various types of methanol existing on the market, without necessarily having to be pure methanol.

[0016] Advantageously, in step c) of said process, an amount by weight of said mixed material containing polyamide material is added to the heated solution, obtained from step b) of the process, in an amount of 5% to 25%, preferably from 7% to 15% by weight, more preferably at least 10% by weight of polyamide materials, i.e. of polyamides, relative to the weight of the solution. Preferably, the step of precipitating the polyamide material present in said solution-dispersion is carried out by distilling at least a part of said methanol from said solution-dispersion until precipitating said polyamides and obtaining a paste containing the salt used, preferably a soluble calcium salt such as, for example, a calcium chloride, the polyamides and residual methanol. Advantageously, this step takes place after step d) of said process.

[0017] In an aspect that is alternative or additional to distillation, for the purpose of precipitating the aforesaid dissolved polyamide material, the process comprises a step of cooling the solution-dispersion containing polyamide material and salt in order to precipitate said polyamide material and obtain a "paste” containing the salt and the solid polyamide material.

[0018] Preferably, said paste obtained after the step of distilling the methanol, or after the step of cooling the solutiondispersion containing polyamide material and salt, is filtered to separate the methanol from the solids.

[0019] In another preferred aspect, a solvent (that is to say, a washing liquid) for said salt is added to said paste in order to bring said salt into solution and remove it from said polyamide material. Said polyamide material is subsequently isolated and is preferably filtered and washed to recover the pure polyamide.

[0020] Preferably, said step f), before the precipitation of the polyamide material present in said solution-dispersion, comprises a step of adding a calibrated amount of water to said solution-dispersion. This addition has the aim of at least partially eliminating said salt and / or washing said polyamide material.

[0021] The process of the first embodiment of the present invention takes place in a batch mode and enables the recovery not only of the polyamide material (i.e. the polyamide or polyamides), but also of the substances and solvents used in the process for recovering said polyamide material.

[0022] Consequently, the process is highly economical and environmentally friendly thanks to the recovery of all the substances used during the recovery of the polyamide material and the subsequent reuse of such substances to recover polyamides from another subsequent processing batch.

[0023] In a second embodiment, the present invention relates to a continuous process for recovering polyamides from mixed material containing polyamide material and non-polyamide solid material, comprising the steps of dissolving said polyamide material and separating the solution of polyamides from the solids present in said mixed materials, characterized in that it further comprises the steps of: a) preparing a eutectic solution obtained by mixing at least methanol and at least one salt inside a dissolution vessel, with the exclusion of the following salts: Ca(NO3)2'4H2O, NaSCN, Cal2'4H2O and calcium salicylate; b) adjusting the temperature of said solution to a value lower than the boiling point of methanol, preferably to a value in the range of 50°C to 70°C, more preferably between 56°C and 65°C; c) adding to said heated solution an amount of said mixed material containing polyamide material; d) bringing at least part of said polyamide material into solution so as to obtain a solution-dispersion of polyamide material and a non-polyamide solid portion, e) taking a part of said solution-dispersion present in the vessel, f) feeding to said vessel (A) an amount of solution to replace said solution-dispersion removed in step e); and g) recovering said polyamide material from said solution-dispersion.

[0024] Preferably, step g) comprises: precipitating the polyamide material present in said solution-dispersion, separating the methanol and obtaining a paste containing the salt, solid polyamide material and residual methanol; and recovering the polyamide material present in said paste.

[0025] Preferably, in the solution prepared in step a) of said process, the concentration of salt is in the range of 120 to 260 g per litre of methanol.

[0026] In step a) of the process, the preferred solution comprises methanol and a calcium salt, preferably methanol and CaCI2.

[0027] In step c) of the process, the material to be treated is added to the solution heated to the preset temperature obtained in step b) of the process, without any constraints as to the particular ratios between the amount of polyamide material and the amount of eutectic solution, that is, without any particular proportional ratios between the material to be recycled, containing the polyamide material, and the deep eutectic solution.

[0028] In step e) of the process, a part of the solution-dispersion, obtained in step d) of the process, is taken with a preset speed (l / s) so as to send it into the methanol extraction vessel in order to carry out a continuous recovery process. Preferably, in the process of the second embodiment of the present invention, the step of precipitating the polyamide material present in said solution-dispersion is carried out by distilling at least part of said methanol from said solution-dispersion until precipitating said polyamides and obtaining a paste containing the salt, solid polyamides and residual methanol. Advantageously, this step takes place after step d) of said process.

[0029] In one advantageous aspect, said process also comprises, in the place of or in addition to the vacuum distillation of the solvent, preferably methanol (MeOH), a step of cooling said solution-dispersion, containing polyamide material and salt, in order to precipitate said polyamide material and obtain a paste containing the salt and the solid polyamide material.

[0030] In a preferred aspect of the continuous process, said solution-dispersion is cooled to a temperature of between 20°C and 30°C.

[0031] Preferably, said paste, obtained after the step of distilling the methanol or the cooling step, is filtered to separate said solution of the solid polyamide material. Preferably, said filtered solution is brought into said dissolution vessel and fed back into the processing cycle.

[0032] In another preferred aspect, a solvent (or a washing liquid) for said salt is added to said paste in order to bring said salt into solution and remove it from said polyamide material.

[0033] The process further comprises steps of filtering and washing said polyamide material.

[0034] Preferably, said step g), before the precipitation of the polyamide material present in said solution-dispersion, comprises a step of adding a calibrated amount of water to said solution-dispersion. This addition has the aim of at least partially eliminating said salt and / or washing said polyamide material.

[0035] The process of the second embodiment of the present invention has the advantage of taking place continuously, i.e. the process does not have any stops or processing times that can interrupt the cycle, except in the loading and unloading phases, which can in any case be resolved by calibrating or designing a suitable system for feeding the dissolution vessel.

[0036] The salt used in the process of the various embodiments of the present invention includes at least one salt suitable for forming a deep eutectic solvent with methanol, with the exclusion of the salts Ca (NOs^ ^FW, NaSCN, Cal 2 • 4H2O, and calcium salicylate. These salts can possibly be present if in combination with CaCh, where CaC is preferably present in a greater amount than the other salts. Preferably, the salt is CaCh

[0037] In the embodiments of the present invention, the solvent, i.e. the washing liquid, for the salt, preferably CaCk, is selected from water, methanol, ethanol and mixtures thereof.

[0038] In the present invention, the term "polyamide material” or "polyamide” refers to a polymer chosen from nylon 6 and nylon 6,6.

[0039] The present invention further relates to a plant for recovering polyamides from mixed material or waste that contains polyamide material and non-polyamide solid material as defined in the process of the present invention. The plant comprises a dissolution vessel for dissolving the polyamide material in a solution defined in step a) of said process, a methanol extraction vessel, a storage vessel for the methanol and the salt, a pressure filter for separating the polyamides and the washing liquid containing the salt in dissolved form, and a vessel for recovering the washing liquid from the pressure filter.

[0040] Advantageously, the pressure filter and, preferably, also the methanol extraction vessel, are provided with a pump to create a negative pressure environment inside said pressure filter and / or said methanol separation vessel in order to favour the operation of said plant components.

[0041] Furthermore, the plant of the present invention includes means for heating the methanol and salt solution. In particular, the dissolution vessel is preferably provided with stirring means and heating means for stirring and heating the eutectic solution contained therein.

[0042] The mixed material or waste, containing polyamide material and non-polyamide solid material, is dissolved in a eutectic solution (DES) of methanol and salt, preferably CaCk, prepared in said dissolution vessel.

[0043] In the methanol extraction vessel, the recovery of methanol takes place by distillation and extraction from the solution obtained after the dissolution of polyamide material. This operation is advantageously carried out using a vacuum pump that creates a negative pressure environment inside said vessel. The extracted methanol is transferred into the storage vessel for methanol and salt.

[0044] In said storage vessel, the concentration of the salt is adjusted by adding salt, preferably CaCk, to the methanol so that it is preferably in the range of 120 to 260 grams per litre of methanol.

[0045] The separation from the liquid phase of methanol, still present, takes place in the pressure filter using pumps which induce a negative pressure in the environment inside the pressure filter. Furthermore, the washing liquid for removing the salt is added into the pressure filter. The washing liquid can be any solvent able to bring into solution the salt used in the solution to recover the polyamide material. Preferably, the washing liquid is selected from water, methanol, ethanol and a combination thereof.

[0046] Preferably, the washing liquid is transferred to the vessel for recovering the washing liquid, where said liquid undergoes an operation selected from distillation, extraction, and evaporation or a combination thereof in order to recover the salt and the washing liquid. In one embodiment of the invention, the salt can also be recovered by osmosis, separating the salt from the solvent.

[0047] The salt recovered is conveyed into the storage vessel for methanol and salt so as to be reused for the preparation of a solution for dissolving the polyamide material. The washing liquid, on the other hand, is transferred into the storage vessel for washing liquid so as to be used in the subsequent recovery cycle.

[0048] Preferably, in the aforesaid plant, before the precipitation of the polyamide material present in said solutiondispersion, a step of adding a calibrated amount of water to said solution-dispersion is carried out. This addition has the aim of at least partially eliminating said salt and / or washing said polyamide material.

[0049] The plant of the present invention can be used operating in cycles in accordance with the batch process of the present invention, wherein the ratio between the mixed material or waste containing polyamide material and nonpolyamide solid material, is predetermined, i.e. falls within a predetermined range.

[0050] In one embodiment, the plant can be used according to a continuous process in which said ratio between the polyamide material and eutectic solution is not fixed, but the concentration of the salt (CaCh) relative to one litre of methanol in the methanol and salt solution to be used to recover the polyamides is fixed.

[0051] In the context of the present invention, the term "pressure filter” is understood as any type of filtering system.

[0052] The features and advantages of the invention are clarified below by the detailed description of preferred embodiments of the invention, with reference to the appended drawings, in which:

[0053] Fig. 1 shows a diagram for carrying out the process of the present invention by operating in a batch mode.

[0054] Fig. 2 shows a diagram for carrying out the process of the present invention by operating in a continuous mode.

[0055] Fig. 3 is a graph showing the quantity of polyamides recovered by the process of the present invention in relation to time.

[0056] With reference to Figure 1 , the polyamides of the recovery process according to the invention are generically denoted by the number 1.

[0057] The invention comprises a new process for recovering polyamides (1) from a material (10). The material (10) is a mixed material, such as, for example, post-consumer fabric products or ropes, or fishing nets, airbag cushions for the automotive industry made of polyamides coated with other polymers, fabric floor coverings, packaging films or sheets, or a scrap from the industrial production of said products. Therefore, the material (10) comprises polyamide material, that is to say, polyamides (1) and non-polyamide solid material.

[0058] The non-polyamide solid material (2) comprises materials of varying nature, depending on the original use for which the material (10) was intended before use. For example, the non-polyamide solid material (2) can comprise fabrics containing fibres of varying nature, e.g. carbon fibres, polyolefin fibres, polyester fibres, elastomeric fibres, natural fibres or fibres of other materials, woven with the fibres of polyamides (1) to produce, for example, work clothes or garments such as gowns or overalls, etc.

[0059] The material (10) may comprise non-polyamide solid material (2) of another nature, tied to the use of the material (10). In this regard, the ropes used for fishing nets can contain residues of sand or mollusc shells clinging to the net.

[0060] The non-polyamide solid material (2) may also be a coating film or a waterproofing agent. For example, the non- polyamide solid material (2) can include silicone resins used to waterproof the fabric of inflatable airbag cushions, made of polyamide (1).

[0061] Example 1 : Batch process for recovering polyamide

[0062] The recovery process of the present invention preferably comprises a preliminary step of reducing the size of the material (10). Reducing the size has the advantage of making the material (10) more easily processable. For example, if the material (10) is a fabric, reducing it to smaller sizes can be achieved with cutting or unravelling operations.

[0063] In the process, the polyamides (1) preferably comprise a polymer selected from nylon 6 and nylon 6,6. This type of polymer, which is the one most widely used in the applications described previously, is effectively recovered by means of the process according to the invention.

[0064] The solvent used in the process of the present invention is a deep eutectic solvent (DES). Typically, a deep eutectic solvent forms when a solvent binds to a solute, for example a salt, by means of hydrogen bonds. Therefore, the function of a deep eutectic solvent is only that of bringing the liquefied solute into contact with the solid material to be dissolved, which, in the case of the present invention, is the solid polyamide. If the latter establishes with the solute of the deep eutectic solvent "stronger” hydrogen bonds than those between the solvent and the solute in the deep eutectic solvent, the solute will proceed to interact with the polyamide, modifying it. In the case of polyamides, the modification produces a decrease in the forces of attraction between the macromolecules of the polyamide, so the latter is dissolved.

[0065] In this regard, in the batch process schematically shown in Figure 1 , a solution (6) is prepared by mixing at least methanol (4) and at least one salt (5) in the dissolution vessel (A), i.e. a vessel where the at least partial dissolution of polyamide material (1) takes place. Methanol (4) is a polar, protic solvent, in a liquid state at room temperature, with a low boiling point. Therefore, the use thereof is advantageous, as it makes the temperatures required to produce a deep eutectic solvent capable of solubilising the polyamides (1) also low.

[0066] The salt (5) is a salt suitable for causing the formation of the deep eutectic solvent with the methanol (4). Preferably, the solution (6) comprises methanol and CaCk, wherein the concentration of CaC is in the range of 120 to 260 grams per litre of methanol.

[0067] The dissolution vessel (A) is provided with stirring means (not shown) to ensure the stirring of the methanol and CaCl2 solution, and heating means (not shown) to maintain said solution at a temperature preferably between 56°C and 65°C.

[0068] The mixed material (10), containing a polyamide material (i.e. polyamides) (1) and a non-polyamide solid material (2), is subsequently added into the dissolution vessel (A) in a quantity of 10% by weight relative to the amount, for example in kg, of the prepared and heated methanol and CaCh solution (6).

[0069] Following the dissolution of said polyamide material present in the mixed material (10) in the dissolution vessel A, a solution-dispersion (7) is obtained containing methanol, salt (CaCh) and the polyamide material (1) (i.e. polyamides) that had been added to said dissolution vessel (A) and was dissolved in the solvent (DES). This solution-dispersion (7) is transferred into the methanol extraction vessel (B), whereas the non-polyamide solid part (2) is eliminated.

[0070] The extraction of the methanol (4) takes place in the methanol extraction vessel (B). This operation is carried out by precipitating the polyamide material (1) present in the solution-dispersion (7), separating the methanol (4) and obtaining a paste (8) containing the salt (5), solid polyamide material (1) and residual methanol. As will be clearer below, the polyamide material (1) is then recovered from the paste (8).

[0071] In one embodiment, the extraction of the methanol (4) can be carried out by distilling the methanol (4) from the solution-dispersion (7), which can be favoured by using pumps (not shown) which generate negative internal pressure in said vessel (B).

[0072] As mentioned, at the end of this operation a product generally in the form of a paste (8) is obtained, containing the precipitated polyamide (1), the salt (CaCh) (5) and a residue of methanol (4). The methanol (4) coming from said distillation is transferred into the storage vessel (C) for the methanol and salt adjacent to the dissolution vessel (A) where salt (CaC ) (5) will be added in order to maintain a desired salt concentration of between 120 and 260 grams per litre of methanol (4) in the solution (mixture) (6) in said storage vessel (C).

[0073] The storage vessel (C) can be provided with heating means to maintain the temperature of the solution containing methanol and salt recovered during the process at the desired temperature, for example in a range of between 56°C and 65°C.

[0074] The paste (8) obtained in the methanol extraction vessel (B) is transferred into the pressure filter (pf), where the methanol still present is separated from the solid phase by means of pumps which induce a negative pressure in the internal environment of the pressure filter (pf), thereby favouring the evaporation and recovery of the methanol (4).

[0075] Subsequently, inside the pressure filter (pf), the washing liquid (9) is added to remove the salt (5), in particular CaCl2. It is possible to carry out several washing cycles. The number of washing cycles and volumes of washing liquid depend on the type of washing liquid (9).

[0076] At the end of said washing, the polyamide material (1) remains inside the pressure filter (pf) and it will be removed to allow the pressure filter (pf) to operate for the next cycle.

[0077] The washing liquid, containing the salt (5) in dissolved form, is transferred from the pressure filter (pf) to the vessel for recovering the washing liquid (D), where it is extracted and / or evaporated and recovered in the storage vessel for the washing liquid (E).

[0078] The salt (preferably CaCh) (5) is recovered from the vessel for recovering the washing liquid (D) so as then to be added in a suitable quantity to the methanol recovered in the storage vessel (C) for the methanol and salt.

[0079] The cycle is repeated for every load of material for recovery / separation. The productivity is dependent on the complete dissolution of the material loaded into the dissolution vessel (A). The production times are also conditioned by the other processing treatments, such as the separation and recovery of the methanol (4) and the washing liquid (9).

[0080] In a variant embodiment, before proceeding with the precipitation of the polyamide material (1) present in the solution-dispersion (7), for example by distilling the methanol (4), a step of adding a calibrated amount of water to the solution-dispersion (7) is carried out. This addition has the aim of at least partially eliminating the salt (5) and / or washing the polyamide material (1).

[0081] For example, in order to carry out this separation, in a situation in which the proportions are the following: polyamide material 10 (by weight), methanol 100 (by volume), and salt 15 (by weight), an amount of water between 30 and 50 (by volume), preferably between 35 and 45 (by volume), and in particular substantially equal to about 40 (by volume) is used.

[0082] The process then continues with the extraction of the methanol (4), as described above.

[0083] The process described with reference to Figure 1 may also be carried out by means of a suitable modification of the steps following the dissolution of polyamide material 1. In particular, the solution-dispersion (7) obtained in the dissolution vessel (A), containing methanol (4), salt (preferably CaCh) (5) and dissolved polyamides (1) and having a temperature of between 56°C and 65°C, is introduced into the methanol extraction vessel B, where the temperature is lowered, thus causing the polyamides (nylon 6 and nylon 6,6) (1) in the solution to precipitate. The solution-dispersion (7) thus obtained is transferred into the pressure filter (pf), where it will then be washed with methanol (washing liquid) (9) in order to further lower the solubility of said solution-dispersion (7). In this manner, the concentration of the salt (CaCh) (5) will be diluted, which will produce a further precipitation of the polyamides (nylon 6 and nylon 6,6) (1). The polyamides (1) thus separated remain on the filter of the pressure filter (pf) and the methanol (washing liquid) (9) used to wash the pressure filter (pf) is separated and fed directly back into the dissolution vessel (A).

[0084] According to one aspect, the salt (5) (in particular CaC ) that is used to form the eutectic mixture DES (6) is added to the washing methanol (9), used to wash the pressure filter and then recovered, in order to exploit the exothermic reaction resulting from the addition and make the process even more efficient from an energy and environmental viewpoint.

[0085] The polyamides (1) accumulated in the pressure filter are washed with water (washing liquid) (9) to recover the salt (CaCh). The washing water (9), containing a methanol residue and salt (CaCh), is transferred from the pressure filter to the vessel (D) for recovering the washing liquid, where it is distilled to separate the salt (CaCh) (5). The polyamides (1) collected by the filter of the pressure filter (pf) are dried and prepared for subsequent processing.

[0086] The final washing of the pressure filter (pf) can be carried out with water, methanol, or ethanol or with a mixture thereof.

[0087] In general, in order to recover and reuse the salt (5) used in the solution-dispersion (7) for recovering polyamides, one may proceed by distillation (to extract the various solvents used for washing the polyamides) or by osmosis, to separate the salt from the solvents.

[0088] Example 2: Continuous process for recovering polyamide

[0089] The process of the present invention can be carried out continuously. This type of process is exemplified in Figure 2 of the present invention. The continuous process includes a step of preparing a solution (6) by mixing methanol and salt (preferably CaCh) and a step of heating said solution (6) in the dissolution vessel (A). These steps of the continuous process take place in the same manner as described with reference to Figure 1 . The dissolution vessel (A) is loaded with the mixed material (10), containing polyamide material (1) and non-polyamide solid material (2), without having to consider the proportional ratios between said material and said solution. A given amount of the solution-dispersion (7) obtained in said dissolution vessel (A) and containing methanol (4), salt (CaCh) (5) and the polyamide material (1) added to said dissolution vessel (A) is taken from the dissolution vessel (A) itself. The amount taken from the solution-dispersion (7) is transferred into the methanol extraction vessel (B). In general, after introducing the mixed material into the dissolution vessel, one waits a few minutes while keeping the solution and the material under stirring before taking a portion of the solution containing dissolved polyamide materials.

[0090] Subsequently, with the aim of maintaining the continuous process (Figure 2), an amount of solution (6) of methanol (4) and salt (5) is transferred from the recovery / storage vessel (C) for the methanol (4) and salt (CaCh) (5) into the dissolution vessel (A), so that said amount substantially corresponds to the amount of solution-dispersion (7) taken from the dissolution vessel (A) and transferred into the methanol extraction vessel (B). The fresh solution added will dissolve other polyamide material.

[0091] Irrespective of whether one waits for a suitable period of time to favour an accumulation of dissolved polyamides or immediately begins to take solution from the dissolution vessel, the extraction of the methanol (4) from the solution-dispersion (7) takes place in the extraction vessel (B). This operation is carried out by precipitating the polyamide material (1) present in the solution dispersion (7), separating the methanol (4) and obtaining a paste (8) containing the salt (5), solid polyamide material (1) and residual methanol. The polyamide material (1) is then recovered from the paste (8).

[0092] In one embodiment, the methanol (4) is extracted by distillation and / or evaporation; the extracted methanol (4) is conveyed back into the recovery / storage vessel (C) using one or more pumps (not shown) which generate a reduced pressure in said extraction vessel (B).

[0093] As mentioned, at the end of the extraction of methanol, there remains a solid in the form of a paste (8), containing the salt (preferably CaCh), solid polyamides and residual methanol; the paste is conveyed from the methanol extraction vessel (B) to the pressure filter (pf) in order to be further concentrated through a further extraction of the solvent methanol (4), similarly to what occurs in the batch process described with reference to Figure 1.

[0094] The material remaining inside the pressure filter (pf) undergoes washing through cycles whose number is tied to the type of washing liquid used. Consequently, the number of washing cycles and the volumes of washing liquid depend on the type of washing liquid used. The washing liquid (9) is transferred from the pressure filter (pf) into the vessel (D) for recovering the washing liquid, where the separation of the salt (CaCh) (5) from the washing liquid (9) takes place by evaporation and / or distillation under negative pressure. The separated salt (5) is transferred into the storage tank for the methanol and salt (C). The extracted washing liquid (9) is transferred into the storage vessel for the washing liquid (E). The polyamide (1) is recovered in solid form from the pressure filter (pf).

[0095] In the continuous process shown in Figure 2, the recovered methanol (4) and the recovered salt (5) are collected in the storage vessel (B) in order to be reintroduced into the dissolution vessel (A).

[0096] Advantageously, this continuous process allows the amount of solution (6) to be used in the first step of dissolution (in the dissolution vessel A) to be a function solely of the rate of solubilization of the polyamides (1) and not of the ratio existing between the salt (5) - solvent (4) - polyamide (1). This aspect translates into a rationalization of the process, with a reduction in consumption and in the operating costs of the distillation and / or evaporation, as the lot to be distilled and / or evaporated will always be smaller compared to the batch process.

[0097] In a variant embodiment, before proceeding with the precipitation of the polyamide material (1) present in the solution-dispersion (7), for example by distilling the methanol (4), a step of adding a calibrated amount of water to the solution-dispersion (7) is carried out. This addition has the aim of at least partially eliminating the salt (5) and / or washing the polyamide material (1).

[0098] For example, in order to carry out this separation, in a situation in which the proportions are the following: polyamide material 10 (by weight), methanol 100 (by volume), and salt 15 (by weight), an amount of water between 30 and 50 (by volume), preferably between 35 and 45 (by volume), and in particular substantially equal to about 40 (by volume) is used.

[0099] The process then continues with the extraction of the methanol (4), as described above.

[0100] The continuous process described above with reference to Figure 2 can be carried out continuously using a step of cooling the solution to favour the precipitation of the solids.

[0101] According to this embodiment, the solution of methanol and salt (preferably CaCh) (6) is initially prepared and said solution is heated in the dissolution vessel (A). The subsequent cooling step is carried out in a manner analogous to what was described with reference to Figure 1 and carried out in the continuous process.

[0102] In other words, after the dissolution vessel (A) has been loaded with the mixed material (10), containing polyamide material (1) and non-polyamide solid material (2), without taking account of the ratio between said material and said solution, and a preset amount of the solution-dispersion (7) obtained in said dissolution vessel (A) has been taken, the methanol-polymer-salt (CaCh) solution is transferred into the pressure filter (pf) and is cooled to a temperature of between 20°C and 30°C to precipitate the polyamide material. Through the cooling process, a part of the polyamides contained in said solution will be intercepted by the pressure filter (pf), whereas the cooled solution will be transferred into the dissolution vessel (A).

[0103] The material thus remaining inside the pressure filter (pf) undergoes the extraction operation by evaporation of the methanol (4) it still contains, as was previously described with reference to the batch process, i.e. by evaporation and the associated recovery using pumps which induce a reduced pressure in the environment inside the pressure filter (pf).

[0104] Subsequently, the material remaining inside the pressure filter (pf) undergoes the washing operation through washing cycles, like in the continuous process, and one proceeds with the subsequent steps described for the continuous process to recover the polyamide (1) in solid form.

[0105] Figure 3 shows a graph regarding the percentage of nylon 6 and nylon 6, 6 recovered according to the process of the present invention (by dissolution in DES) in relation to time. From Figure 3 it may be deduced that the process of the present invention enables a nearly total recovery of nylon in a short period of time.

[0106] The process according to the present invention achieves important advantages.

[0107] In fact, the use of deep eutectic solvents (DES) enables the process to be carried out at lower temperatures than the ones required in traditional purification processes, with considerable energy savings.

[0108] Furthermore, the lower temperatures make it possible to reduce the viscosity of the solutions and mixtures during the process, as well as to prevent a thermal degradation of the polymer to be recovered.

[0109] Another advantage of the process is tied to the fact that the solution of methanol and salt (preferably CaCI2) used enables a total recovery of the substances employed, thus ensuring that the process is environmentally friendly.

[0110] In fact, the process of the present invention enables the separation of the polyamide material by dilution of the solution containing CaC and said polyamide material, a dilution obtainable by adding a solvent, preferably methanol. In this manner, one alters the ability of the system to solubilize the polyamide material by extraction from the system in equilibrium of CaCh, which is responsible for the formation of the bonds with the polyamide that enable the solubilization thereof. In particular, said operation makes it possible to lower the viscosity of the paste formed between the solvent-salt-polyamide material and to continue with the subsequent processing step, with separation and filtration.

[0111] The environmental advantage is also tied to the fact that, by means of this process, one prevents the waste containing this type of polymer from being released into the environment. In fact, the waste making up the material (10) cannot be easily disposed of in a waste-to-energy plant, since the energy balance of their combustion is negative. Therefore, if they are not recovered through recycling processes, they are released into the environment. The recovery process, moreover, makes it possible to obtain nylon powders which are particularly suitable for being used in rotational moulding processes. Therefore, the process according to the invention enables the recovery of nylon from scraps and the simultaneous production of powders for rotational moulding in a single process.

[0112] Finally, the process has the advantage of enabling the recovery and purification of nylon to be achieved by means of a process that is simple to carry out, since it takes place using known, easily implementable purification techniques.

[0113] The invention is susceptible of variants falling within the scope of the inventive concept defined by the claims.

[0114] Within that scope, all the details may be replaced by equivalent elements and the materials, shapes and sizes may be any whatsoever.

Claims

CLAIMS1. A process for recovering polyamides (1) from a mixed material or waste (10) containing polyamide material (1) and non-polyamide solid material (2), comprising the steps of dissolving said polyamide material and separating the solution of polyamide material (1) from the non-polyamide solid material (2) present in said mixed material or waste, characterized in that it further comprises the steps of: a) preparing a eutectic solution (6) obtained by mixing methanol (4) and a salt (5) inside a vessel (A), with the exclusion of the following salts: Ca(NO3)2'4H2O, NaSCN, Cal2'4H2O and calcium salicylate; b) adjusting the temperature of said solution (6) to a value lower than the boiling point of methanol (4), preferably to a value in the range of 50°C to 70°C, more preferably between 56°C and 65°C; c) adding to said heated eutectic solution (6) an amount of said mixed material (10) containing polyamide material (1); d) bringing said polyamides into solution so as to obtain a solution of polyamide material (1) and a non- polyamide solid portion (2); e) separating said solution-dispersion (7) from said non-polyamide solid materials (2); and f) recovering the polyamide material (1) from said solution-dispersion (7) wherein step f) comprises: precipitating the polyamide material (1) present in said solution-dispersion (7), separating the methanol (4) and obtaining a paste (8) containing the salt (5), solid polyamide material (1) and residual methanol; and recovering the polyamide material (1) present in said paste (8).

2. The process according to claim 1 , wherein in step a) said salt is calcium chloride CaC and the concentration of the salt (5) in the solution (6) is in the range of 120 to 260 grams per litre of methanol (4), and characterized in that in step c) said mixed material (10) is added to aid solution (6) in an amount of 10% by weight per litre of said solution (6) prepared in step a) of the process.

3. The process according to claim 1 or 2, wherein the step of precipitating the polyamide material (1) present in said solution-dispersion (7) is carried out by distilling at least part of said methanol (4) from said solution of polyamide material (1).

4. The process according to claim 1 or 2, wherein the step of precipitating the polyamide material (1) present in said solution-dispersion (7) is carried out by cooling said solution-dispersion (7) containing polyamide material (1) and salt (5).

5. The process according to claim 3 or 4, wherein said paste (8) is filtered to separate the residual methanol (4) from the solids.

6. The process according to claim 3, 4 or 5, wherein a solvent for said salt (5) is added to said paste (8) in order to bring said salt (5) into solution and remove it from said polyamide material (1).

7. The process according to claim 6, comprising the steps of filtering and washing said polyamide material (1).

8. The process according to any one of the preceding claims, wherein said step f), prior to the precipitation ofthe polyamide material (1) present in said solution-dispersion (7), comprises a step of adding a calibrated amount of water to said solution-dispersion (7) to at least partially eliminate said salt (5) and / or to wash said polyamide material (1).

9. A process for recovering polyamides (1) from mixed material (10) containing polyamide material (1) and nonpolyamide solid material (2), the process comprising the steps of dissolving said polyamide material (1) and separating the solution of polyamide material (1) from the solids present in said mixed material (10), characterized in that it further comprises the steps of: a) preparing a eutectic solution (6) obtained by mixing methanol (4) and salt (5) inside a dissolution vessel (A) with the exclusion of the following salts: Ca(NO3)2'4H2O, NaSCN, Cal2'4H2O and calcium salicylate; b) adjusting the temperature of said solution (6) to a value lower than the boiling point of methanol (4), preferably to a value in the range of 50°C to 70°C, more preferably between 56°C and 65°C; c) adding to said heated solution (6) an amount of said mixed material (10) containing polyamide material (1); d) bringing into solution at least part of said polyamide material (1) to obtain a solution-dispersion (7) containing said polyamide material (1) and a non-polyamide solid portion (2); e) taking a part of said solution-dispersion (7); f) feeding to said vessel (A) an amount of solution to replace said solution-dispersion removed in step e); and g) recovering said polyamide material (1) from said solution-dispersion (7) wherein step g) comprises: precipitating the polyamide material (1) present in said solution-dispersion (7), separating the methanol (4) and obtaining a paste (8) containing the salt (5), solid polyamide material (1) and residual methanol; and recovering the polyamide material (1) present in said paste (8).

10. The process according to claim 9, wherein said salt is calcium chloride and in step a) the concentration of the salt (5) in the solution (6) is in the range of 120 to 260 grams per litre of methanol (4).

11. The process according to claim 9 or 10, wherein the step of precipitating the polyamide material (1) present in said solution-dispersion (7) is carried out by distilling at least part of said methanol (4) from said solutiondispersion (7) obtained in step e).

12. The process according to claim 9 or 10, wherein the step of precipitating the polyamide material (1) present in said solution-dispersion (7) is carried out by cooling said solution-dispersion (7) obtained in step e).

13. The process according to claim 11 or 12, wherein said paste (8) is filtered to separate the methanol (4) from the solids.

14. The process according to any one of claims 11 to 13, wherein a washing liquid (9) is added to said paste (8) in order to bring said salt (5) into solution and remove it from said solid polyamide material (1).

15. The process according to claim 13 or 14 when dependent on claim 13, wherein said filtered methanol solutionis conveyed to said dissolution vessel (A) and fed back into the processing cycle.

16. The process according to claim 14 or 15, comprising the steps of filtering and washing said polyamide material (1).

17. The process according to claim 14 or either of claims 15-16 when dependent on claim 14, wherein said washing liquid (9) for dissolving the salt (5) is selected from water, methanol and ethanol.

18. The process according to any one of claims 9-17, wherein said step g), prior to the precipitation of the polyamide material (1) present in said solution-dispersion (7), comprises a step of adding a calibrated amount of water to said solution-dispersion (7) to at least partially eliminate said salt (5) and / or to wash said polyamide material (1).

19. A plant for recovering polyamides from mixed material (10) containing polyamide material (1) and nonpolyamide solid material (2) as defined in the process according to any one of claims 1 to 8 or in the process according to any one of claims 9 to 18, the plant comprising a dissolution vessel (A) for dissolving said polyamide material (1), a methanol extraction vessel (B), a storage vessel (C) for the methanol (4) and the salt (5), a pressure filter (pf) for separating the polyamide material (1) and a washing liquid (9), and a vessel for recovering the washing liquid (D) from the pressure filter (pf).

20. The plant according to claim 17, wherein said pressure filter (pf) and, preferably, also said methanol extraction vessel (B) are provided with means for producing a reduced pressure.

21. The plant according to claim 17 or 18, wherein said dissolution vessel (A) and / or said storage vessel (C) for the methanol (4) and the salt (5) are provided with heating means.

22. The plant according to any one of claims 17 to 19, comprising a storage vessel for the washing liquid (E).

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