METHOD FOR SELECTING AND SEPARATING POLYMERS FROM URBAN AND / OR INDUSTRIAL PLASTIC WASTE

Abstract

The present invention relates to a method for selecting and separating polymers from urban and / or industrial plastic waste to obtain plastic materials for recycling, comprising a first step of supplying a polymer mixture composed of polymer flakes with dimensions between 6 and 100 mm; a step of identifying, by means of near-infrared (NIR) spectroscopy, the white and colored plastic material flakes and the black plastic material flakes and subsequent separation between them; several consecutive steps of identifying, by means of NIR spectroscopy, the different types of polymers in the white and colored plastic material and subsequent separation of said types of polymers.

Description

METHOD FOR SELECTION AND SEPARATION OF POLYMERS FROM URBAN AND / OR INDUSTRIAL PLASTIC WASTE i Rbn / n / zznza / YiAi DESCRIPTION The present invention relates to a method for selecting and separating polymers from urban and / or industrial plastic waste to obtain plastic materials for recycling. Plastic disposal is a major environmental problem, given the vast amount of plastic waste produced both domestically and industrially, especially in industrialized countries. Although most plastic currently ends up in landfills or is simply discarded into the environment at the end of its useful life, some technologies and processes exist today that attempt to address the problem of plastic disposal. Various approaches and technologies are used to tackle the issue, such as combustion, remelting plastic to produce new objects, and biodegradation, if the plastic is biodegradable. However, it is known that only a relatively small portion of the plastic currently produced is biodegradable. Each of the approaches mentioned entails a loss of value in the product obtained after transformation compared to the value of the original plastic. This is evident in the case of combustion, given that in this technology the plastic is used simply as fuel, and also in the case of biodegradation, given that the product obtained from biodegradation is used in applications with low economic value, for example, as a soil amendment in agriculture or, after further transformations, as a solid fuel. Similarly, in the case of remelting plastic for the production of objects, there is a loss of value, since the object obtained from recycled plastic is used in an application that has a lower value than the original product. None of the technologies mentioned are capable of recovering the original value of the plastic, since it is obviously not possible to transform recycled plastic into virgin plastic. Therefore, a significant amount of virgin plastic is lost each year, necessitating the production of new plastic to replace the plastic discarded in the environment, which constitutes the vast majority, and the plastic transformed into other products for applications different from those of the original plastic. Furthermore, the production of new plastic negatively impacts the availability of fossil resources, which are the raw materials used in plastic production. In recent years, techniques for differentiating plastic materials from waste have been developed, evolving to obtain reusable materials and thus reduce the production of virgin material. However, normal separation techniques do not achieve a high percentage of purity of the selected polymer, which is therefore highly contaminated by other types of polymers and can only be used for the production of low-quality articles. In this context, the technical purpose of the present invention is to provide a method for the mechanical separation of polymers from a mixture of polymers from commercial and / or industrial plastic waste capable of differentiating the different materials and separating them, obtaining high purity recycled material. Therefore, a selection and separation method capable of separating the selected polymer with high precision would be desirable, so that fractions of separated material with high purity are obtained, differentiated both by type and color of material. A selection and separation method capable of operating continuously, without interruption, to process a large amount of material would also be desirable. In particular, an object of the present invention is to provide a separation method capable of obtaining a separated fraction of polymeric material with a purity greater than 95% so that it can be used for the production of high-level articles, replacing part or all of the virgin material. Another object of the present invention is to provide a separation method capable of selecting and separating different types of plastic material also based on color, in order to obtain a single-material, single-color product that can be directly reused in the plastics industry. Another object of the present invention is to provide a method for polymer separation capable of selecting and separating polymers of different types even when the plastic material is black, in order to obtain high-purity material fractions even in this type of material. Another object of the present invention is to provide a method for polymer separation capable of operating continuously to select and separate a large quantity of material. The objects and advantages of the invention mentioned above, which will be made evident in the following description, are achieved by a method in accordance with claim 1. In particular, these objects are obtained by a method for the selection and mechanical separation of at least two polymers from a mixture of polymers derived from commercial and / or industrial plastic waste, comprising the steps of: i. provide a mixture of polymers from commercial and / or industrial plastic waste consisting of polymer flakes with dimensions between 6 and 100 mm; Identifying colored and white plastic material flakes by means of near-infrared (NIR) spectroscopy and separating a fraction (F1) rich in said colored and white plastic material flakes from a fraction (F2) rich in black plastic material flakes by suitable separation means; iii. identifying by NIR spectroscopy the flakes of a polymer P1 from said fraction (F1) rich in colored and white plastic material flakes separated in step ii, and separating a fraction (F3) rich in polymer P1 flakes from said fraction (F1) rich in colored and white plastic material flakes by suitable separation means, obtaining a fraction (F4) poor in polymer P1 flakes; iv. identify by NIR spectroscopy the polymer flakes other than P1 from the fraction (F3) rich in polymer flakes P1 separated in step i¡¡ and separate a fraction (F5) rich in polymer flakes other than P1 from said fraction (F3) rich in polymer flakes P1 by suitable separation means; v. identify by NIR spectroscopy the flakes of a polymer P2 from said fraction (F4) poor in polymer P1 flakes separated in step iiii and from said fraction (F5) rich in flakes of polymers other than PI separated in step iv, and separate a fraction (F6) rich in polymer P2 flakes from said fraction (F1) rich in flakes of colored and white plastic material by suitable separation means, obtaining a fraction (F7) poor in polymer P2 flakes; vi. Identify by NIR spectroscopy the non-P2 polymer flakes from the P2 polymer flake-rich fraction (F6) separated in step vy; separate a non-P2 polymer flake-rich fraction (F8) from said P2 polymer flake-rich fraction (F6) by suitable separation means. Preferably, the method described above also includes the following steps: vi. identify by mid-infrared spectroscopy (MIR) the flakes of a P3 polymer from said (F2) flake-rich fraction of black plastic material separated in step ii, and separate a P3 polymer flake-rich fraction (F9) from said (F2) flake-rich fraction of black plastic material by suitable separation means, obtaining a P3 polymer flake-poor fraction (F10); viii. identify by MIR spectroscopy the non-P3 polymer flakes from the P3 polymer flake-rich fraction (F9) separated in step vii and separate a non-P3 polymer flake-rich fraction (F11) from said P3 polymer flake-rich fraction (F9) by suitable separation means; ix. Identifying by MIR spectroscopy the P4 polymer flakes from said fraction (F10) poor in P3 polymer flakes separated in step vii and from said fraction (F11) rich in flakes of polymers other than P3 separated in step viii, and separating a fraction (F12) of P4 polymer flakes from said fraction (F2) rich in flakes of black plastic material by suitable separation means, obtaining a fraction (F13) poor in P4 polymer flakes; x. Identify by MIR spectroscopy the non-P4 polymer flakes from the P4 polymer flake-rich fraction (F12) separated in step ix and separate a non-P4 polymer flake-rich fraction (F14) from said P4 polymer flake-rich fraction (F12) by suitable separation means. This provides a method capable of also separating black polymers, which are normally difficult to identify and separate given their color that prevents correct reading with NIR spectroscopy. i Rbn / n / zznza / YiAi Preferably, the method according to the present invention comprises a step of separating and removing any metallic material, both ferrous and non-ferrous, from the plastic material flakes before performing the identification and separation of step ii. In this way, the plastic material is cleaned of other foreign materials that can reduce the final purity of the polymer, causing damage to machinery such as, for example, the extruders used to recycle the plastic after the selection and separation described above. Preferably, the method according to the present invention comprises a step of shredding commercial and / or industrial plastic waste to obtain said material in flakes with dimensions ranging from 6 to 100 mm. In this way, the plastic material is prepared to allow a correct and efficient selection and separation of the different components in order to obtain a separated polymeric material with a purity greater than 95% so that it can be used directly in the recycling of the plastic material. Preferably, the method according to the present invention comprises the steps of: x¡. identify by NIR spectroscopy the flakes of a polymer P5 from said fraction (F7) poor in polymer P2 flakes separated in step v, and from said fraction (F8) rich in flakes of a polymer other than P2 separated in step vi, and separate a fraction (F15) rich in polymer P5 flakes from said fractions (F7) and (F8), obtaining a fraction (F16) poor in polymer P5 flakes; xii. Identify by NIR spectroscopy the non-P5 polymer flakes from the P5 polymer flake-rich fraction (F15) separated in step xii and separate a non-P5 polymer-rich fraction (F17) from said P5 polymer flake-rich fraction by suitable separation means. In this way, a method is provided that is capable of separating more than two polymers from the mixture of polymers from commercial and / or industrial plastic waste. Preferably, the method according to the present invention comprises an additional step of identifying by UV / VIS spectroscopy the color of the polymer flakes separated in the steps described above, and separating a fraction rich in uniformly colored flakes of said polymers by suitable separation means. This process yields monomaterial polymer fractions with uniform color that can be used directly in plastic material recycling processes, also for the production of high-quality objects. Preferably, the method according to the present invention comprises an additional step of identifying, by means of NIR spectroscopy, flakes of one of said polymers P1 or P2 or P5 based on the melt flow index of the polymer and separating a phase rich in said polymer by means of suitable separation means. This provides a process capable of separating HDPE (high-density polyethylene) from LDPE (low-density polyethylene). i βπη / η / ζζηζα / γίΛΐ Preferably, the method according to the present invention comprises an additional step of washing the polymer flakes P1 and P2, if necessary polymer P3 and P4 and if necessary polymer P5, after the steps of identifying and separating a phase rich in said polymer described above. This results in a final product free of impurities and dirt, so that it can be used directly in subsequent material recycling steps without altering the quality of the polymer and, consequently, without altering the quality of the products manufactured with these polymers. Preferably, the method according to the present invention provides that in said identification and separation steps the material to be identified and separated has a surface distribution ranging from 1 to 20 kg / cm2 per reading unit. This ensures the correct positioning of the flakes when they are subjected to identification by NIR spectroscopy or MIR spectroscopy to obtain a separated polymeric material with a purity greater than 95%. Preferably, the method according to the present invention provides for the separation of the polymers by means of compressed air jets. This makes it possible to have a high workflow and optimal separation of the selected polymer. According to the present invention, polymers P3 and P4 can be of the same or different chemical type as polymers P1 and P2, selected and separated in the steps described above. In other words, polymers P3 and P4 can be the same polymers P1 and P2, but selected and separated from a mixture of black polymer flakes. The method in accordance with the present invention will be described below in a preferred, non-limiting embodiment thereof. The method in accordance with the present invention can be implemented by using machinery already used in the industry, for example, conveyor belts, loading hoppers, etc., as will be described below. The method according to the present invention can be applied for the selection and separation of various polymers such as, for example, polypropylene (PP), polystyrene (PS), polyethylene (PE), high and low density polyethylene (HDPE, LDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS) or others. The method according to the present invention is implemented in a process for the mechanical selection and separation of polymers, as described below. In particular, a process for separating three different polymers from a polymer mixture will be described. The process described below refers to the selection of polyethylene (PE), polystyrene (PS) and polypropylene (PP) from a mixture of polymers derived from plastic waste. These polymers are arbitrarily selected to allow a better understanding of the separation method according to the present invention, and therefore cannot be considered limiting or reducing of said method. i βπη / η / ζζηζα / γίΛΐ A mixture of polymers from commercial and / or industrial plastic waste, preferably already cleaned of any organic or non-polymeric inorganic material, is fed into a grinder capable of grinding the material to obtain plastic flakes with approximate dimensions ranging from 6 to 100 mm or with a surface area ranging from approximately 6 to 100 mm². Preferably, the dimensions of the ground flakes are between 15 and 80 mm, in order to obtain a flake that is easy to select and separate using suitable sorting and separation means, as described below. Using suitable conveyor belts, the plastic flakes are transported to a device where any ferrous metal present in the polymer mixture is removed using neodymium magnets. The flakes are then transported to a second device where any non-ferrous metal present in the polymer mixture is removed using eddy currents. The substantially metal-free polymer mixture is then deposited onto a conveyor belt to achieve a surface distribution of the material on the belt ranging from 1 to 20 kg / cm², preferably between 3 and 10 kg / cm². This ensures optimal flaking distribution, preventing any overlap that would invalidate subsequent selection using optical instruments. This material distribution can be defined as the surface distribution per reading unit. The material thus distributed is sent to a sorting device where, by means of near-infrared (NIR) spectroscopy, the colored or white plastic material flakes are identified from the black plastic material flakes. In accordance with the present invention, the term color indicates a material that absorbs all electromagnetic radiations incident in the visible field with the exception of radiations with wavelengths relative to the color referred to. In accordance with the present invention, the term white (or achromatic color) indicates a material capable of reflecting all electromagnetic radiations that fall within the visible field. According to the present invention, the term "black" indicates an object that absorbs all electromagnetic radiation incident on the visible spectrum without reflecting it. Black corresponds to the visual impression experienced when no visible light reaches the eye. As is known in the field, NIR (near infrared) spectroscopy is a spectroscopic absorption technique that uses electromagnetic radiation in the near infrared spectrum, that is, with a wavelength ranging from 780 nm to 2500 nm. With NIR spectroscopy, materials of different natures can be selected based on the selective absorption of infrared radiation by the different plastic materials. Thus, the first device is able to select the colored or white plastic material thanks to NIR spectroscopy, since the black pigments present in the plastic material absorb infrared rays, making the material invisible to the optical selector. i Rbn / n / zznza / YiAi The selected plastic material is separated by jets of compressed air that strike the selected material—that is, the material identified by NIR spectroscopy—projecting it onto a separate conveyor belt. Depending on the device configuration, the jets of compressed air may also strike the unselected material—that is, the material not identified by NIR spectroscopy. The remaining plastic material is transferred by gravity to another conveyor belt. This separation procedure will be used for all the selection and separation steps described below. In accordance with the present invention, other separation methods and procedures, not explicitly described herein, may also be used. After the separation obtained thanks to the compressed air jets, there will be two fractions of different plastic material, a fraction F1 rich in flakes of colored and white plastic material, and a fraction F2 rich in flakes of black plastic material. The F1 fraction, rich in colored and white plastic flakes, is then sent to a sorting unit where, using NIR spectroscopy, the PE flakes are identified and separated by compressed air jets, forming an F3 fraction rich in PE flakes. Similarly, an F4 fraction poor in PE flakes is formed. The F3 fraction, rich in PE flakes, is sent back to a sorting unit where NIR spectroscopy identifies flakes of polymers other than PE. These flakes are separated using compressed air jets, forming an F5 fraction rich in flakes of polymers other than PE. The remaining PE flakes will have a purity, in terms of PE, of 95% or higher. The F4 fraction, low in PP flakes, and the F5 fraction, rich in flakes of polymers other than PE, are placed together on a single conveyor belt and sent to a sorting unit where, using NIR spectroscopy, the PP flakes are identified and separated by jets of compressed air, so that a PP-rich F6 fraction is formed. Similarly, a PP-poor F7 fraction is formed. The F6 fraction, rich in PP flakes, is sent back to a sorting unit where NIR spectroscopy identifies flakes of polymers other than PP. These flakes are separated using compressed air jets, forming an F8 fraction rich in flakes of polymers other than PP. The remaining PP flakes will have a purity, in terms of PP, of 95% or higher. To select and separate different types of polymers also from the flake-rich fraction of black plastic material, selected and separated in one of the steps described above, the F2 fraction is sent to a selection apparatus where the PE flakes of the F2 fraction of black plastic material are identified by MIR spectroscopy. As is known in the art, MIR (mid-infrared radiation) spectroscopy is a spectroscopic absorption technique that uses electromagnetic radiation in the mid-infrared spectrum, specifically with a wavelength ranging from 2.5 pm to 25 pm. i Rbn / n / zznzu / YiAi After the selection and separation of PE from fraction F2, a fraction F9 rich in black PE flakes and a corresponding fraction F10 poor in black PE flakes are obtained. The F9 fraction, rich in black PE flakes, is sent back to a sorting unit where MIR spectroscopy identifies flakes of polymers other than PE. These flakes are separated using compressed air jets, forming an F11 fraction rich in flakes of polymers other than PE. The remaining black PE flakes will have a purity, in terms of PE, of 95% or higher. The F10 fraction, which is low in black PE flakes, and the F11 fraction, which is high in black flakes of polymers other than PE, are placed together on the same conveyor belt and sent to a sorting unit. There, using MIR spectroscopy, the black PP flakes are identified and separated by compressed air jets, forming an F12 fraction rich in black PP flakes. Similarly, an F13 fraction, which is low in black PP flakes, is formed. The F12 fraction, rich in black PP flakes, is sent back to a sorting unit where MIR is used to identify polymer flakes other than black PP. These flakes are separated using compressed air jets, forming an F14 fraction rich in polymer flakes other than PP. The remaining black PP polymer flakes will have a purity, in terms of PP, of 95% or higher. To separate another type of polymer from the mixture of polymers derived from plastic waste, the F7 and F8 fractions described above are placed together on a single conveyor belt and sent to a sorting unit where PS flakes are identified using NIR spectroscopy. These flakes are then separated using jets of compressed air, resulting in a PS-rich F15 fraction. Similarly, a PS-poor F16 fraction is formed. The F15 fraction, rich in PS flakes, is sent back to a sorting unit where NIR spectroscopy identifies flakes of polymers other than PS. These flakes are separated using compressed air jets, forming an F17 fraction rich in flakes of polymers other than PS. The remaining PS flakes will have a purity, in terms of PS, of 95% or higher. The previously selected and separated polyethylene flakes, both colored and white as well as black, can be further selected and separated by an additional separation step based on NIR or MIR spectroscopy. It is widely known that the varying average chain lengths of PE polymers (average molecular weight) affect the polymer's NIR or MIR spectrum. Therefore, by means of an additional selection step based on NIR or MIR, it is possible to select and separate the higher molecular weight PE flakes (qualitatively characterized by a lower melt flow index) from the lower molecular weight PE flakes (qualitatively characterized by a higher melt flow index). In particular, PE flakes are selected by NIR or MIR spectroscopy and separated by compressed air jets as described above. i βπη / η / ζζηζα / γίΛΐ The flakes, previously selected and separated according to the type of polymer they are made of, are then sent to a suitable grinding machine to further reduce their size, thus obtaining flakes of material that have a size that can be used immediately in plastic extrusion equipment. These flakes are also sent to a suitable washing unit, where they are washed with water, and if necessary with specific products, to remove dirt residue or eliminate any polymeric material dust that may have formed in the selection and separation steps described above. The colored and white flakes of PE (both HDPE and LDPE), PP and PS, previously separated, ground and washed, are transported to a successive selection and separation apparatus where, using UV / VIS spectroscopy, they are selected according to the specific color and separated by jets of compressed air. As is known in the field, UV / VIS (ultraviolet / visible) spectroscopy is a spectroscopic absorption technique that uses electromagnetic radiation in the ultraviolet / visible spectrum, that is, with a wavelength ranging from 400 nm to 700 nm. With a method such as that described in the present invention, it is possible to select and separate an indefinite number of different polymers. Therefore, the method can be applied to mixtures comprising more than three polymers, as described above, without reducing the efficiency of the selection and separation.

Claims

1. A method for the selection and mechanical separation of at least two polymers from a polymer mixture derived from commercial and / or industrial plastic waste, said method comprising the steps of: i. providing a polymer mixture from commercial and / or industrial plastic waste consisting of flakes of said polymers ranging in size from 6 to 100 mm; ii. identifying colored and white plastic material flakes by near-infrared (NIR) spectroscopy and separating a fraction (F1) rich in said colored and white plastic material flakes from a fraction (F2) rich in black plastic material flakes by suitable separation means; iii.identifying by NIR spectroscopy the flakes of a polymer P1 from said fraction (F1) rich in flakes of colored and white plastic material separated in step ii, and separating a fraction (F3) rich in flakes of polymer P1 from said fraction (F1) rich in flakes of colored and white plastic material by suitable separation means, so that a fraction (F4) poor in flakes of polymer P1 is obtained; iv. identifying by NIR spectroscopy the flakes of polymer other than P1 from the fraction (F3) rich in flakes of polymer P1 separated in step iii and separating a fraction (F5) rich in flakes of polymers other than P1 from said fraction (F3) rich in flakes of polymer P1 by suitable separation means; v.identifying by NIR spectroscopy the flakes of a polymer P2 in said fraction (F4) poor in polymer P1 flakes separated in step iii and in said fraction (F5) rich in flakes of polymers other than P1 separated in step iv, and separating a fraction (F6) rich in polymer P2 flakes from said fraction (F1) rich in flakes of colored and white plastic material by suitable separation means, so that a fraction (F7) poor in polymer P2 flakes is obtained; vi. identifying by NIR spectroscopy the flakes of polymers other than P2 in the fraction (F6) rich in polymer P2 flakes separated in step vy; separating a fraction (F8) rich in flakes of polymers other than P2 from said fraction (F6) rich in polymer P2 flakes by suitable separation means.

2. A method according to claim 1, further comprising the steps of: vii. identifying by mid-infrared (MIR) spectroscopy the P3 polymer flakes from said black plastic material flake-rich fraction (F2) separated in step ii, and separating a P3 polymer flake-rich fraction (F9) from said black plastic material flake-rich fraction (F2) by suitable separation means, so as to obtain a P3 polymer flake-poor fraction (F10); viii. identifying by MIR spectroscopy the non-P3 polymer flakes from the P3 polymer flake-rich fraction (F9) separated in step vii and separating a non-P3 polymer flake-rich fraction (F11) from said P3 polymer flake-rich fraction (F9) by suitable separation means; i Rbn / n / zznza / YiAi ix.Identifying by MIR spectroscopy the flakes of a P4 polymer from said fraction (F10) poor in P3 polymer flakes separated in step vii and from said fraction (F11) rich in flakes of polymers other than P3 separated in step viii, and separating a fraction (F12) of P4 polymer flakes from said fraction (F2) rich in flakes of black plastic material by suitable separation means, so that a fraction (F13) poor in P4 polymer flakes is obtained; x. Identifying by MIR spectroscopy the flakes of polymers other than P4 from the fraction (F12) rich in P4 polymer flakes separated in step ix and separating a fraction (F14) rich in flakes of polymers other than P4 from said fraction (F12) rich in P4 polymer flakes by suitable separation means.

3. Method in accordance with one or more of the preceding claims, characterized in that it comprises a step of separating and removing any metallic material, both ferrous and non-ferrous, from said plastic material flakes before performing the identification and separation of step ii.

4. A method in accordance with one or more of the preceding claims, characterized in that it comprises a step of shredding commercial and / or industrial plastic waste to obtain said material in flakes with dimensions ranging from 6 to 100 mm.

5. A method according to claim 1, further comprising the steps of: xi. identifying by NIR spectroscopy the flakes of a polymer P5 from said fraction (F7) poor in polymer P2 flakes separated in step v, and from said fraction (F8) rich in polymer flakes other than P2 separated in step vi, and separating a fraction (F15) rich in polymer P5 flakes from said fractions (F7) and (F8), obtaining a fraction (F16) poor in polymer P5 flakes; xii. identifying by NIR spectroscopy the flakes of polymers other than P5 from the fraction (F15) rich in polymer P5 flakes separated in step xi and separating a fraction (F17) rich in polymers other than P5 from said fraction rich in polymer P5 flakes by suitable separation means.

6. Method according to claim 1 or claim 5, characterized in that it comprises an additional step of identifying by UV / VIS spectroscopy the color of the flakes of the polymers separated in said claims 1 and 5, and of separating a fraction rich in uniformly colored flakes of said polymers by suitable separation means.

7. A method according to one or more of the preceding claims, characterized in that it comprises an additional step of identifying, by means of NIR spectroscopy, the flakes of one of said polymers P1 or P2 or P5 according to the average molecular weight of the polymer and separating a phase rich in said polymer by means of suitable separation means.

8. Method according to claim 1 and / or 2 and / or 6, characterized in that it comprises an additional step of washing said polymer flakes P1 and P2, optionally polymer P3 and P4 and Rbn / n / zznza / YiAi optionally polymer P5, after the step of identifying and separating a phase rich in said polymer.

9. Method in accordance with one or more of the preceding claims, characterized in that said separation of the polymers is carried out by means of jets of compressed air.