Method for the selection and separation of polymers derived from municipal and / or industrial plastic waste

Abstract

The present invention relates to a method for the selection and separation of polymers originating from municipal and / or industrial plastic waste to obtain plastic materials for recycling, comprising several successive steps: a first step of providing a polymer mixture consisting of polymer flakes with dimensions in the range of 6 to 100 mm; a step of identifying flakes of colored and white plastic material and flakes of black plastic material by near-infrared (NIR) spectroscopy and subsequently separating them from each other; a step of identifying different types of polymers from the colored and white plastic material by NIR spectroscopy and subsequently separating said polymer types.

Description

[Technical Field]

[0001] explanation The present invention relates to a method for the selection and separation of polymers derived from municipal and / or industrial waste to obtain plastic materials for recycling. [Background technology]

[0002] Considering the large amount of plastic waste generated at both the domestic and industrial levels, especially in developed countries, the disposal of plastics constitutes a significant environmental issue. Currently, the majority of plastics are primarily landfilled or disposed of directly in the environment at the end of their lifespan, but today several technologies and processes exist that attempt to solve the problem of plastic disposal. Various approaches and technologies are used to address this problem, including combustion, remelting of plastics to produce new objects, and biodegradation (if the plastic is biodegradable). However, only a relatively small amount of the plastics currently produced is known to be biodegradable.

[0003] Both of the above approaches necessarily involve a loss of value in the products obtained after transformation compared to the value of the original plastics, which is evident in the case of combustion, when it is taken into account that in this technology the plastics are simply used as fuel, and in the case of biodegradation, when it is taken into account that the products obtained from biodegradation are used for applications with low economic value (for example, as soil conditioners in agriculture or as solid fuels after further transformation). Even when plastics are remelted to manufacture objects, a loss of value occurs because the objects obtained from the recycled plastic are used in applications that have a lower value than the original product. None of the above technologies are able to convert recycled plastic into virgin plastic, and therefore cannot recover the original value of the plastic.

[0004] Thus, a significant loss of virgin plastic occurs each year, and new plastic must be produced to replace it, much of which is discarded in the environment and converted into other products for uses different from the original plastic. Furthermore, the production of new plastic has a negative impact on the availability of fossil resources, the raw materials used to produce plastics. In recent years, techniques for separating plastic materials derived from waste have been developed and evolved to obtain reusable materials and thus reduce the production of virgin materials. However, conventional separation techniques are unable to increase the purity of the selected polymer, and therefore the selected polymer is highly contaminated with other types of polymers and can only be used to produce low-quality products. Summary of the Invention [Problem to be solved by the invention]

[0005] The technical problem of the present invention is therefore to provide a method for the mechanical separation of polymers from polymer mixtures originating from commercial and / or industrial plastic waste, which allows for differential separation of different materials and allows for obtaining recycled material of high purity. [Means for solving the problem]

[0006] Therefore, a selection and separation method is desired that can separate selected polymers with high precision and obtain high purity fractions of separated material that are differentiated in both material type and color. Additionally, a selection and separation method that can process large amounts of material in continuous operation without interruption is desirable. Specifically, one object of the present invention is to provide a separation method that can result in a separated fraction of polymeric material with a purity of 95% or greater that can be used to partially or totally replace virgin material and to manufacture high-grade products.

[0007] Another object of the present invention is to provide a separation method that allows selecting and separating different types of plastic materials also according to color in order to obtain single-material, single-color products that can be directly reused in the plastics industry. A further object of the present invention is to provide a method for separating polymers that is capable of selecting and separating different types of polymers even when the plastic material is black, and that is capable of obtaining high purity material fractions even in this type of material. A further object of the present invention is to provide a method for separating polymers that can be operated continuously to select and separate large amounts of material.

[0008] These and other objects and advantages of the present invention that will become apparent from the following description are achieved by the method set forth in claim 1. Specifically, the object is to provide a method for mechanically selecting and separating at least two polymers from a polymer mixture derived from commercial and / or industrial plastic waste, comprising the following steps: i. providing a mixture of polymers derived from commercial and / or industrial plastic waste, the mixture consisting of polymer flakes having dimensions in the range of 6 to 100 mm; ii. identifying the flakes of colored and white plastic material by near-infrared (NIR) spectroscopy and separating the fraction (F1) enriched in flakes of colored and white plastic material from the fraction (F2) enriched in flakes of black plastic material by suitable separation means; iii. identifying the flakes of polymer P1 from the fraction (F1) rich in flakes of colored and white plastic material separated in step ii by NIR spectroscopy, and separating the fraction (F3) rich in flakes of polymer P1 from the fraction (F1) rich in flakes of colored and white plastic material by suitable separation means to obtain a fraction (F4) poor in flakes of polymer P1; iv. identifying flakes of polymers different from P1 from the fraction (F3) enriched in flakes of polymer P1 separated in step iii by NIR spectroscopy, and separating a fraction (F5) enriched in flakes of polymers different from P1 from the fraction (F3) enriched in flakes of polymer P1 by an appropriate separation means; v. identifying the flakes of polymer P2 from the fraction (F4) poor in flakes of polymer P1 separated in step iii and the fraction (F5) rich in flakes of a polymer different from P1 separated in step iv by NIR spectroscopy, and separating the fraction (F6) rich in flakes of polymer P2 from the fraction (F1) rich in flakes of colored and white plastic materials by suitable separation means to obtain a fraction (F7) poor in flakes of polymer P2; vi. Identifying flakes of a polymer different from P2 from the fraction (F6) enriched in flakes of polymer P2 separated in step v by NIR spectroscopy, and separating a fraction (F8) enriched in flakes of a polymer different from P2 from the fraction (F6) enriched in flakes of polymer P2 by an appropriate separation means. This is achieved by a method comprising:

[0009] Preferably, the method comprises the following steps: vii. identifying the flakes of polymer P3 from the fraction (F2) rich in flakes of black plastic material separated in step ii by mid-infrared (MIR) spectroscopy, and separating the fraction (F9) rich in flakes of polymer P3 from the fraction (F2) rich in flakes of black plastic material by suitable separation means to obtain a fraction (F10) poor in flakes of polymer P3; viii. Identifying flakes of polymers other than P3 from the fraction (F9) enriched in flakes of polymer P3 separated in step vii by MIR spectroscopy, and separating a fraction (F11) enriched in flakes of polymers other than P3 from the fraction (F9) enriched in flakes of polymer P3 by an appropriate separation means; ix. identifying the flakes of polymer P4 from the fraction (F10) poor in flakes of polymer P3 separated in step vii and the fraction (F11) rich in flakes of a polymer different from P3 separated in step viii by MIR spectroscopy, and separating the fraction (F12) of flakes of polymer P4 from the fraction (F2) rich in flakes of black plastic material by suitable separation means to obtain a fraction (F13) poor in flakes of polymer P4; x. Identifying flakes of polymers other than P4 from the fraction (F12) enriched in flakes of polymer P4 separated in step ix by MIR spectroscopy, and separating a fraction (F14) enriched in flakes of polymers other than P4 from the fraction (F12) enriched in flakes of polymer P4 by an appropriate separation means. Further includes: In this way, a method is provided that can separate even black polymers that are normally difficult to identify and separate due to their color preventing accurate readings in NIR spectroscopy.

[0010] Preferably, the method according to the invention includes the step of separating and removing metallic materials, both ferrous and non-ferrous, from the flakes of plastic material prior to the identification and separation of step ii. In this way, the plastic material is freed of other foreign matter that could reduce the final polymer purity and cause damage to machinery, such as extruders, used to recycle the plastics after the above selection and separation. Preferably, the method according to the invention comprises a step of crushing commercial and / or industrial plastic waste to obtain said flake material having a size in the range of 6 to 100 mm. In this way, a plastic material is prepared that allows for accurate and effective selection and separation of the various components to obtain separated polymeric materials with a purity of 95% or more that can be used directly for recycling of the plastic material.

[0011] Preferably, the method according to the invention comprises the following steps: xi. Identifying the flakes of polymer P5 from the fraction (F7) poor in flakes of polymer P2 separated in step v and the fraction (F8) rich in flakes of a polymer different from P2 separated in step vi by NIR spectroscopy, and separating the fraction (F15) rich in flakes of polymer P5 from the fractions (F7) and (F8) to obtain a fraction (F16) poor in flakes of polymer P5; xii. Identifying flakes of a polymer different from P5 from the fraction (F15) enriched in flakes of polymer P5 separated in step xi by NIR spectroscopy, and separating a fraction (F17) enriched in a polymer different from P5 from the fraction enriched in flakes of polymer P5 by an appropriate separation means. Includes. In this way, a method is provided that allows for the separation of three or more polymers from a polymer mixture derived from commercial and / or industrial plastic waste.

[0012] Preferably, the method according to the present invention further comprises the step of identifying the color of the polymer flakes separated in the previous step by UV / VIS spectroscopy and isolating a fraction enriched in polymer flakes of the same color by suitable separation means. In this way, a homogeneous polymer fraction of the same color is obtained which can be used directly in the recycling process of plastic materials and can also be used to manufacture high-quality products. Preferably, the method according to the invention further comprises the step of identifying the flakes of one of said polymers P1 or P2 or P5 based on the melt flow index of said polymer by NIR spectroscopy and isolating the polymer-rich phase by suitable separation means. In this way, a method is provided by which HDPE (high density polyethylene) can be separated from LDPE (low density polyethylene).

[0013] Preferably, the method according to the invention further comprises, after the step of identifying and separating the aforementioned polymer-rich phase, a step of washing the flakes of polymers P1 and P2, optionally also the flakes of polymers P3 and P4, and optionally also the flakes of polymer P5. In this way, an impurity-free and uncontaminated final product is obtained that can be used directly in subsequent material recycling steps without altering the quality of the polymer and, consequently, the products manufactured with it. Preferably, in the method according to the present invention, in the step of identifying and separating, the reading unit is 1 to 20 kg / cm 2 The material to be identified and separated has a surface distribution in the range of This ensures accurate positioning of the flakes when they are identified by NIR or MIR spectroscopy to obtain isolated polymeric material with a purity of 95% or greater.

[0014] Preferably, the method according to the invention provides for the separation of the polymer by means of a jet of compressed air. In this way, high workflow and optimal separation of the selected polymers is possible. According to the present invention, polymers P3 and P4 can be of equivalent or different chemical type to polymers P1 and P2 selected and separated in the previous steps, 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. DETAILED DESCRIPTION OF THE INVENTION

[0015] The method according to the present invention will now be described in its preferred, non-limiting embodiments. The method according to the invention can be carried out using machines already used in industry, such as belt conveyors, feed hoppers, etc., as will be described below. The method according to the invention can be applied to the selection and separation of various polymers, such as, for example, polypropylene (PP), polystyrene (PS), polyethylene (PE), high-density and low-density polyethylene (HDPE, LDPE), polyethylene terephthalate (PET), polyvinyl chloride (PVC), acrylonitrile-butadiene-styrene (ABS), etc. The method according to the present invention is implemented in a process of mechanical selection and separation of polymers, as described below. Specifically, the separation process of three different polymers from a polymer mixture is described.

[0016] The process described below selects polyethylene (PE), polystyrene (PS) and polypropylene (PP) from a polymer mixture derived from plastic waste. Said polymers have been arbitrarily selected to allow a better understanding of the separation method according to the invention and therefore should not be considered as limiting the method. Mixtures of polymers resulting from commercial and / or industrial plastic waste, preferably mixtures of polymers from which non-polymeric organic or inorganic materials have already been removed, are processed by crushing the material to produce particles having approximate dimensions in the range of 6 to 100 mm or about 6 to 100 mm. 2 The resulting material is fed to a grinder capable of obtaining flakes of plastic material having a surface in the range of 15 to 80 mm. Preferably, the size of the flakes of ground material is between 15 and 80 mm in order to obtain flakes that are easy to select and separate by suitable selection and separation means, as described below.

[0017] A suitable conveyor belt transports the plastic material flakes to a device that uses neodymium magnets to remove ferrous metals present in the polymer mixture, and then the flakes are transported to a second device where eddy currents are used to remove non-ferrous metals present in the polymer mixture. The substantially metal-free polymer mixture is then applied to a conveyor belt such that the surface distribution of the material is 1 to 20 kg / cm 2 within the range of 3 to 10 kg / cm 2The flakes are deposited on a conveyor belt so that they are within the range of 0.01 mm. In this way, the flakes are optimally distributed to avoid overlapping flakes that would invalidate subsequent selection by the optical instrument. The distribution of material can be defined as the surface distribution per reading unit. The material thus distributed is sent to a selection device where flakes of colored or white plastic material are identified from flakes of black plastic material by near infrared (NIR) spectroscopy.

[0018] According to the present invention, the term "colored" denotes a material that absorbs all incident electromagnetic radiation in the visible range except for radiation having a wavelength related to the color mentioned. According to the present invention, the term "white (or colorless)" denotes a material that is able to reflect all incident electromagnetic radiation in the visible range. According to the present invention, the term "black" refers to an object that absorbs all incident electromagnetic radiation in the visible range without reflecting it. Black corresponds to the visual impression experienced when no visible light reaches the eye.

[0019] As known in the art, NIR (near infrared) spectroscopy is a spectroscopic absorption method using electromagnetic radiation in the near infrared spectrum, ie, electromagnetic radiation having wavelengths within the range of 780 nm to 2500 nm. Using near-infrared spectroscopy, materials of different properties can be selected based on the selective absorption of infrared radiation by different plastic materials. Thus, the first device can select colored or white plastic materials by near-infrared spectroscopy, since the black pigments present in the plastic material absorb infrared light, making the material "invisible" to the optical selector. The plastic materials thus selected are separated by a jet of compressed air which strikes the selected materials (i.e., materials identified by NIR spectroscopy) and pushes them onto another conveyor belt. Depending on the settings of the machine, the jet of compressed air may also strike the non-selected materials, i.e., materials not identified by NIR spectroscopy.

[0020] The remaining plastic material is then transferred by gravity to another conveyor belt. This separation procedure is used for all selection and separation steps described below. Other separation methods and procedures not specifically described herein may also be used in accordance with the present invention. After separation by a jet of compressed air, two fractions of different plastic materials will be present: a fraction F1 enriched in flakes of colored and white plastic material and a fraction F2 enriched in flakes of black plastic material. The fraction F1, rich in flakes of colored and white plastic material, is then sent to a selection device where the PE flakes are recognized by NIR spectroscopy and separated by a jet of compressed air to form a PE flake-rich fraction F3, as well as a PE flake-poor fraction F4.

[0021] The PE flake-rich fraction F3 is sent back to the selector, where NIR spectroscopy is used to identify flakes of polymers other than PE. The flakes are separated with a jet of compressed air to form fraction F5, which is enriched in flakes of polymers other than PE. The remaining PE flakes have a purity of 95% or more with respect to PE. The PP flake-poor fraction F4 and the fraction enriched in flakes of polymers other than PE, F5, are sent together on one conveyor belt to a selector where the PP flakes are identified by NIR spectroscopy and separated by a jet of compressed air to form a PP flake-rich fraction F6, as well as a PP flake-poor fraction F7. The PP flake-rich fraction F6 is again sent to a selector where flakes of polymers other than PP are identified by NIR spectroscopy. The flakes are separated with a jet of compressed air to form fraction F8, which is enriched in flakes of polymers other than PP. The remaining PP flakes have a purity of 95% or more with respect to PP.

[0022] In order to select and separate different types of polymers also from the fraction rich in black plastic material flakes selected and separated in one of the previous steps, fraction F2 is sent to a selection device, where PE flakes are identified from fraction F2 of black plastic material flakes by MIR spectroscopy. As known in the art, MIR (mid-infrared radiation) spectroscopy is a spectroscopic absorption method using electromagnetic radiation in the mid-infrared spectrum, ie, electromagnetic radiation having wavelengths in the range of 2.5 μm to 25 μm. After selection and separation of PE from fraction F2, fraction F9 enriched in black PE flakes and corresponding fraction F10 depleted in black PE flakes are obtained.

[0023] The fraction F9 enriched in black PE flakes is sent again to a selection device where flakes of polymers other than PE are identified by MIR spectroscopy. The flakes are separated with a jet of compressed air to form fraction F11 enriched in flakes of polymers other than PE. The remaining black PE flakes have a purity of 95% or more with respect to PE. The fraction F10, which is depleted in black PE flakes, and the fraction F11, which is enriched in black flakes of polymers other than PE, are sent together on a conveyor belt to a selector, where the black PP flakes are identified by MIR spectroscopy and separated by a jet of compressed air to form a fraction F12, which is enriched in black PP flakes, and a fraction F13, which is depleted in black PP flakes. The fraction F12 enriched in black PP flakes is again sent to a selector where flakes of polymers other than PP are identified by MIR. The flakes are separated with a jet of compressed air to form a fraction F14 enriched in flakes of polymers other than PP. The remaining PP black polymer flakes have a purity of 95% or more with respect to PP.

[0024] To separate further types of polymers from the polymer mixture derived from plastic waste, the aforementioned fractions F7 and F8 are sent together on a conveyor belt to a selector, where PS flakes are identified by NIR spectroscopy. The flakes are separated by a jet of compressed air to form a PS flake-rich fraction F15, as well as a PS flake-poor fraction F16. The PS flake-rich fraction F15 is again sent to a selection device where flakes of polymers other than PS are identified by NIR spectroscopy. The flakes are separated with a jet of compressed air to form fraction F17, which is enriched in flakes of polymers other than PS. The remaining PS flakes have a purity of 95% or more with respect to PS.

[0025] The previously selected and separated polyethylene flakes (both colored and white flakes and black flakes) can be further selected and separated by a further separation step based on NIR or MIR spectroscopy. In fact, it is widely known that differences in the average length (average molecular weight) of PE polymer chains affect the NIR or MIR spectrum of the polymer. Therefore, by a further NIR-based or MIR-based selection step, PE flakes with higher molecular weights (PE flakes qualitatively characterized by a lower melt flow index) can be selected and separated from PE flakes with lower molecular weights (PE flakes qualitatively characterized by a higher melt flow index). Specifically, PE flakes are selected by NIR or MIR spectroscopy as previously described and separated by a jet of compressed air.

[0026] The flakes previously selected and separated according to the type of component polymer are then sent to a suitable crushing device to further reduce the size, resulting in flakes of material having dimensions suitable for immediate use in plastic extrusion equipment. These flakes are also sent to a suitable washing device where they are washed with water, and optionally with a specific product, to remove any remaining dirt or dust of polymeric material that may have formed in the above selection and separation steps. The previously separated, crushed and washed coloured and white flakes of PE (both HDPE and LDPE), PP and PS are conveyed to a continuous sorting and separation unit where they are selected according to their specific colour by UV / VIS spectroscopy and separated by a jet of compressed air. As known in the art, UV / VIS (ultraviolet / visible) spectroscopy is a spectroscopic absorption method using electromagnetic radiation in the ultraviolet / visible spectrum, i.e., electromagnetic radiation having wavelengths within the range of 400 nm to 700 nm. The method of the present invention allows for the selection and separation of an unlimited number of different polymers, and therefore can be applied to mixtures containing more than three polymers as described above without compromising the selection and separation efficiency.

Claims

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

2. Follow these steps: vii. identifying the flakes of polymer P3 from the fraction (F2) rich in flakes of black plastic material separated in step ii by mid-infrared (MIR) spectroscopy, and separating the fraction (F9) rich in flakes of polymer P3 from the fraction (F2) rich in flakes of black plastic material by a suitable separation means to obtain a fraction (F10) poor in flakes of polymer P3; viii. Identifying flakes of polymers other than P3 from the fraction (F9) enriched in flakes of polymer P3 separated in step vii by MIR spectroscopy, and separating the fraction (F11) enriched in flakes of polymers other than P3 from the fraction (F9) enriched in flakes of polymer P3 by an appropriate separation means; ix. Identifying the flakes of polymer P4 from the fraction (F10) depleted in flakes of polymer P3 separated in step vii and the fraction (F11) enriched in flakes of a polymer different from P3 separated in step viii by MIR spectroscopy, and separating the fraction (F12) of flakes of polymer P4 from the fraction (F2) enriched in flakes of black plastic material by suitable separation means to obtain a fraction (F13) depleted in flakes of polymer P4; x. Identifying flakes of polymers other than P4 from the fraction (F12) enriched in flakes of polymer P4 separated in step ix by MIR spectroscopy, and separating a fraction (F14) enriched in flakes of polymers other than P4 from the fraction (F12) enriched in flakes of polymer P4 by an appropriate separation means. The method of claim 1 further comprising:

3. 3. A method according to claim 1 or 2, characterized in that it includes the step of separating and removing metallic materials, both ferrous and non-ferrous, from the flakes of plastic material before carrying out the identification and separation of step ii.

4. Commercial and / or industrial plastic waste is crushed to have a size within the range of 6 to 100 mm.

4. The method of claim 1, further comprising obtaining the flake material.

5. Follow these steps: xi. Identifying the flakes of polymer P5 from the fraction (F7) poor in flakes of polymer P2 separated in step v and the fraction (F8) rich in flakes of a polymer different from P2 separated in step vi by NIR spectroscopy, and separating the fraction (F15) rich in flakes of polymer P5 from the fractions (F7) and (F8) to obtain a fraction (F16) poor in flakes of polymer P5; xii. The method of claim 1, further comprising the step of identifying flakes of a polymer different from P5 from the fraction (F15) enriched in flakes of polymer P5 separated in step xi by NIR spectroscopy, and separating a fraction (F17) enriched in a polymer different from P5 from the fraction enriched in flakes of polymer P5 by an appropriate separation means.

6. 6. The method according to claim 1 or claim 5, further comprising the step of identifying the color of the separated polymer flakes by UV / VIS spectroscopy and isolating a fraction enriched in polymer flakes of the same color by an appropriate separation means.

7. 7. The method according to any one of claims 1 to 6, further comprising the step of identifying the flakes of one of the polymers P1 or P2 or P5 according to the average molecular weight of said polymer by NIR spectroscopy and isolating the polymer-rich phase by suitable separation means.

8. 2. The method of claim 1, further comprising a step of flake washing of polymers P1 and P2 after the step of identifying and separating the polymer-rich phase.

9. The method of claim 2, further comprising the step of washing the flakes of polymers P1, P2, P3 and P4 after the step of identifying and separating the polymer-rich phase.

10. The method of claim 6, further comprising the step of washing the flakes of polymers P1, P2, P3, P4 and P5 after the step of identifying and separating the polymer-rich phase.

11. 11. The method according to claim 1, wherein the polymer is separated by a jet of compressed air.