METHOD FOR DECONTAMINATING RECYCLED PLASTIC

Abstract

The invention relates to a method for decontaminating recycled plastic materials, which comprises the steps of selecting, grinding, washing, rinsing, drying and decontaminating, wherein decontaminating is carried out by means of the steps of extracting and rinsing, and extracting is carried out using a water-soluble solvent having a boiling point greater than 180° C. at atmospheric pressure.

Claims

1. A method for decontaminating recycled plastic comprising the following steps of: a. Separating and grinding of the plastic; b. Washing, rinsing and drying; and c. Decontaminating; i. Extracting with a water-soluble solvent having a boiling point greater than 180° C.; and ii. Rinsing at room temperature; wherein a parallel water recovery method and a parallel solvent recovery method are included, which enables the recirculation and reuse thereof, making the method more sustainable.

2. The method for decontaminating recycled plastic according to claim 1, wherein the separation step can be carried out by means of identification techniques such as NIR, MIR, infrared thermography, LIBS or X-ray fluorescence.

3. The method for decontaminating recycled plastic according to claim 1, wherein the grinding is carried out by means of a bladed grinder, a cryogenic mill or grinder, to reduce the size of the material to flake or powder.

4. The method for decontaminating recycled plastic according to claim 1, wherein the washing step is performed with an anionic, cationic or neutral surfactant.

5. The method for decontaminating recycled plastic according to claim 1, wherein in the washing step oxidising agents can be used to remove surface impurities.

6. The method for decontaminating recycled plastic according to claim 1, wherein the drying step is mechanically performed.

7. The method for decontaminating recycled plastic according to claim 1, wherein the solvent used for extraction is polyethylene glycol.

8. The method for decontaminating recycled plastic according to claim 1, wherein the solvent used for extraction is polypropylene glycol.

9. The method for decontaminating recycled plastic according to claim 1, wherein the solvent used for extraction is dimethylsulfoxide.

10. The method for decontaminating recycled plastic according to claim 1, wherein a centrifugation is carried out before and after the rinsing step in the decontamination, before rinsing to remove solvent and after rinsing to dry the material.

11. The method for decontaminating recycled plastic according to claim 1, wherein the water recovery is carried out by means of ultrafiltration and flocculation-decanting.

12. The method for decontaminating recycled plastic according to claim 1, wherein the water recovery is carried out by means of crystallisation and flocculation-decanting.

13. The method for decontaminating recycled plastic according to claim 1, wherein the solvent recovery is carried out by means of an ultrafiltration membrane and subsequent filtering.

14. The method for decontaminating recycled plastic according to claim 1, wherein the decontamination step is carried out independently from the recycling process, so that an inlet input of the decontamination step can be plastic recycled by means of other methods.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0039] In order to complete the description and to make the features of the invention more readily understandable, a FIGURE is presented wherein the following is represented by way of illustration and not limitation:

[0040] FIG. 1 is a schematic diagram of the different elements of the method for carrying out the decontamination in recycled plastic materials. It shows the three modules of the method: the separation and grinding module, the washing, rinsing and drying module, and the decontamination module, with the pieces of equipment that make each step up and the inlet and outlet streams in each of them.

DETAILED DESCRIPTION OF AN EMBODIMENT

[0041] The method for removing contaminants in recycled plastic materials comprises the following steps:

1. Selecting and grinding

[0042] The fraction of plastic material from landfill or from the domestic recycled plastic container (p1) is fed to the separation system (101). Once separated (p2), the bags, films, bottles and other containers that arrive at the plant are introduced into a bladed grinder (102) that reduces the particle size as much as required (p3).

2. Washing, rinsing and drying

[0043] The shredded plastic stream (p3) enters the washing tank (103), and comes out through the stream p4, which is fed to the rinsing tank (104) to remove chemicals used in the wash and remaining dirt. Once the dirt and chemical substances have been removed, a clean material (p5) is obtained that must be mechanically dried in the dryer (105) before being decontaminated.

3. Decontaminating

[0044] The stream of partially clean and dry plastic but still containing unwanted contaminants (p6) is fed to the decontamination module. The stream p6 enters the extractor (106) and after extracting the contaminants, it comes out through the stream p7. The extraction must be carried out with a water-soluble solvent having a high boiling point, greater than 180° C. at atmospheric pressure, and working at high temperatures (taking care not to reach the degradation temperature of the plastic itself). In a preferred embodiment, the solvent used was polyethylene glycol (PEG). The stream p7 passes through a centrifuge (107) in order to remove the largest proportion of solvent from the plastic and the already dry stream of solvent p8 passes to a water rinsing step in the second rinsing tank (108). The rinsed plastic comes out through the stream p9, which goes through another centrifugation step in the second centrifuge (110) in order to remove the moisture. The stream p10 comes out from this second centrifuge (110), where the completely decontaminated plastic is obtained.

[0045] The water recovery and solvent recovery systems are parallel to this plastic decontaminating system, so that they can be recirculated and reused, making the method more sustainable.

[0046] The water recovery system starts with the stream s3 coming out of the second rinsing tank (108) and the stream s4 coming out of the second centrifuge (110). The stream s3 contains mostly water along with residual solvent that remained in the plastic, and the stream s4 contains runoff from the plastic after centrifugation at (110) which mostly consists of water and residual solvent. The streams s3 and s4 enter the ultrafiltration membrane (109) which separates the solvent from the water and the contaminants. After separation in the ultrafiltration membrane (109), the solvent is separated into the stream s5 on the one hand and the water with the contaminants in s6 on the other hand. The water is separated from the contaminants in the flocculation-decanting module (111) obtaining a recirculation water in the current s8 that is introduced again in the decontamination module in the second rinsing tank (108). The flocculation-decanting module (111) also comes out of the stream s7, which contains the contaminants.

[0047] The solvent recovery system starts with the currents s1 and s2, composed of the solvent and the contaminants that have been extracted from the extractor (106) and the centrifuge (107). The streams s1 and s2 are introduced into a second ultrafiltration membrane (113) such that contaminants are removed through the stream s12 and the solvent comes out through s11. Finally, stream s11, together with stream s5 that comes from water recovery, may contain solids in suspension and must pass through a filter (112), from which the stream s9 with the retained solids and the stream s10, which is the clean solvent that is recirculated to the extractor (106) come out.

[0048] In a preferred embodiment, the decontaminating system acts as a module that is entirely independent from the recycling process and its input is the recycled pellets, i.e., it is a system for improving the quality of the product already recycled by other companies.