Method and system for the elimination of odours in recycled plastics

Abstract

The invention relates to a method and system for the elimination of odours in recycled plastic materials, which comprises the steps of: separating and conditioning the plastic; shredding the plastic by means of a bladed shredded, which reduces the plastic into powder-sized particles; chemically washing with a surfactant, which is carried out in a stirring tank; rinsing the plastic material to eliminate dirt and the chemicals used, which is carried out in a rinsing reactor; mechanically drying the clean material in a dryer; and deodorising the plastic, wherein volatile organic compounds (VOCs) are removed from the clean, dry material by means of steam distillation, deodorisation being performed in a steam distillation column, the VOC-free plastic exiting through the bottom part of the column.

Claims

1. A system for eliminating odors in recycled plastic materials comprising: a plant for separation by identification wherein a plastic material with volatile organic compounds enters; a shredder for reducing a size of the plastic material to provide a shredded material; a washing tank, for chemically washing the shredded material with surfactant to provide a washed material; a rinsing tank, for rinsing the washed material to provide a rinsed material; a mechanical dryer, for drying the rinsed material to provide a dry material; and a deodorizing module (MD) comprising: a distillation column through which the dry material enters, wherein the volatile organic compounds of the plastic material are removed by means of steam distillation, and through which volatile organic compound- and odor-free plastic exits; a droplet separator that receives organic product removed by the means of steam distillation; an isothermal tank that receives a liquid fraction obtained from the droplet separator; a separator that receives a portion of an organic phase from the isothermal tank; and a steam boiler that supplies steam to the distillation column; and that receives a steam fraction from the droplet separator and an aqueous phase from the isothermal tank.

2. The system for the elimination of odors in recycled plastic materials, according to claim 1, wherein the shredder is a bladed shredder or a cryogenic mill.

3. The system for the elimination of odors in recycled plastic materials, according to claim 1, wherein the washing tank is a stirred tank.

4. The system for the elimination of odors in recycled plastic materials, according to claim 1, wherein the separator is a distillation column, a hydrophobic membrane or a combination thereof.

5. A method for eliminating odors in recycled plastic materials using the system of claim 1, the method comprising: a) separating the plastic material by means of the plant for separation by identification; b) shredding the plastic material in the shredder to provide the shredded material; c) chemically washing the shredded material with the surfactant in the washing tank; d) rinsing the plastic material to eliminate dirt and chemicals used in chemical washing in the rinsing tank to provide the rinsed materials; e) drying the rinsed material in the mechanical dryer to provide the dry material; and f) deodorizing the dry material wherein: the plastic material is introduced through an upper part of the distillation column, steam from the steam boiler is supplied to the distillation column through a bottom lateral part of the distillation column, the plastic material falls by the effect of gravity along the distillation column, the plastic material comes into contact with the steam, the volatile organic components are removed from the plastic material by means of distillation, there is an outlet for organic product, which comprises water steam and volatile organic components, through an upper lateral part of the distillation column, and the volatile organic compound- and odor-free plastic exits through a bottom part of the distillation column.

6. The method according to claim 5, wherein the plastic material is selected from polyethylene, polypropylene, and polyester.

7. The method according to claim 5, wherein the identification is performed by means of near infrared spectroscopy, mid-infrared spectroscopy, infrared thermography, laser-induced breakdown spectroscopy, or X-ray fluorescence.

8. The method according to claim 5, wherein the surfactant is cationic, anionic, or neutral.

9. The method according to claim 5, wherein the rinsing is with water.

10. The method according to claim 5, wherein the drying is performed mechanically at room temperature.

11. The method according to claim 5, wherein, while deodorizing, the organic product that exits through the upper lateral part of the distillation column is channeled to a droplet separator, and wherein, in the droplet separator, there is a separation of the organic product into a steam fraction and a liquid fraction.

12. The method according to claim 11, wherein the steam fraction feeds the steam boiler.

13. The method according to claim 11, wherein the liquid fraction feeds an isothermal tank wherein the liquid fraction is separated by decanting into an aqueous phase and an organic phase comprising organic compounds and dissolved water.

14. The method according to claim 13, wherein the aqueous phase feeds the steam boiler.

15. The method according to claim 13, wherein the organic phase feeds a separator wherein a part of water is separated from a remaining portion of the organic compounds.

Description

(1) Finally, it should be noted that, throughout the description and claims, the term comprises and its variants are not intended to exclude other technical features or additional elements. Furthermore, 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:

(2) FIG. 1 is a schematic diagram of the different elements of the method for carrying out the elimination of odours in recycled plastic materials.

DETAILED DESCRIPTION OF AN EMBODIMENT

(3) The method for the elimination of odours in recycled plastic materials comprises the following steps: a) separating the recycled plastic material (P-VOCs) by means of identification in a plant for separation by identification (1); b) shredding the plastic in a shredder (2); c) chemically washing the shredded plastic with surfactant in a stirred tank (3); d) rinsing the plastic material to eliminate dirt and the chemicals used in chemical washing in a rinsing tank (4); e) drying the rinsed material in a mechanical dryer (5); f) deodorising the dry plastic material wherein: the plastic material is introduced through the upper part (61) of a distillation column (6); steam inlet (V), coming from a boiler (9), through the bottom lateral part (64) of the distillation column (6); the plastic material falls by the effect of gravity along the distillation column (6), the plastic material comes into contact with the steam (V) and the organic components are removed from the plastic material by means of distillation; there is an outlet for organic product (PO), which comprises water steam and organic components VOCs, through the upper lateral part (63) of the distillation column (6); and the VOC-free plastic (PL) exits through the bottom part (62) of the distillation column (6).

(4) Taking into account the steps of the method, and as seen in FIG. 1, the system for the elimination of odours in recycled plastic materials comprises the following equipment: a plant for separation by identification (1) wherein the plastic with VOCs (P-VOCs) enters; a shredder (2) of the bladed or cryogenic mill type, for reducing the plastic material; a stirred tank (3) for chemical washing, for washing the shredded material with surfactant; a rinsing tank (4), for rinsing the washed material; a mechanical dryer (5), for drying the rinsed material; and a deodorising module (MD) comprising: a distillation column (6) through which the dry material enters, wherein the organic components of the plastic material are removed by means of steam distillation (V), and through which the VOC- and odour-free plastic (PL) exits; a droplet separator (7) that receives the organic product (PO) removed by means of steam distillation; an isothermal tank (8) that receives a liquid fraction (FL) obtained from the droplet separator (7); a separator (10) that receives a portion of organic product (PO') from the isothermal tank (8); and a steam boiler (9) that supplies steam (V) to the distillation column (6); and that receives a steam fraction (FV) from the droplet separator (7) and an aqueous phase (FA) from the isothermal tank (8).

(5) Further describing each step, and in turn, further describing FIG. 1, the method and the system required to carry out the method comprises:

(6) Step 1. Separation of the recycled plastic

(7) The fraction of plastic material coming from landfills or from the domestic recycled plastic container (P-VOCs), wherein the plastic with VOCs is selected from polyethylenePE; polypropylenePP; and polyesterPET, is introduced into a system or plant for separation by identification (1), wherein the material is identified by means of near infrared spectroscopyNIR; mid-infrared spectroscopMIR; infrared thermography IR; laser-induced breakdown spectroscopyLIBS; or X-ray fluorescence.

(8) Step 2: Shredding

(9) Once separated, the bags, films, bottles and other containers that arrive at the plant are introduced into a shredder (2) wherein the size of the plastic particles is reduced. Shredder (2) that can be a bladed-type shredder if the plastic is to be processed in flake form; or it can be of the cryogenic mill type if wanting to work with or reduce the particle size to less than 1 mm.

(10) Step 3: Chemical washing

(11) The stream of cut plastic enters the washing tank (3), wherein a washing with surfactant is performed to eliminate dirt from the plastic material which is adhered to the surface. Both anionic and cationic or neutral surfactants can be used. The washing is performed in a stirred tank-type reactor.

(12) Step 4: Rinsing

(13) The plastic material is rinsed to eliminate dirt and the chemicals used. To do this, the product that comes out of the chemical washing enters a rinsing tank (4) to eliminate the chemicals used in the chemical washing and the remaining dirt, wherein said rinsing product is water.

(14) Step 5: Drying

(15) Once the dirt and the chemical compounds have been eliminated after rinsing, a clean material is obtained that is mechanically dried by means of centrifugation, pressure or compressed air in a mechanical dryer (5). Drying is at room temperature and in a closed system. In this drying step, the moisture contained is eliminated as much as possible, although it is not required that it be totally eliminated.

(16) Step 6: Deodorising

(17) The stream of clean and dry plastic product, but with an odour, is introduced into a deodorising module (MD) comprising, among others, a distillation column (6).

(18) Said plastic with odour, and with variable size depending on the shredding, although preferably of powder size, enters the head (61) of the steam distillation column and the clean product, i.e., the VOC- and odour-free plastic (PL) and odours exits from the bottom part (62) of the column. These plastic particles fall by the effect of gravity and are subjected to the contact of the steam. It is not an object of the present invention, but inside the column there may be plates or other devices that prevent direct fall and that cause the particles to fall more slowly, therefore prolonging the time of exposure to the steam.

(19) The steam (V) enters through the bottom lateral part (64) of the column and exits through the upper lateral part (63) of the same. This steam (V) entering through the bottom lateral part (64) is fed by a steam boiler (9) adjacent to the column (6).

(20) The stream of steam that exits through the upper part (after having been in contact with the odorous plastic) contains a mixture of water steam and organic compounds, i.e., it is a mixture of organic product (PO). By means of a conduit, this mixture is introduced into a droplet separator (7). After the droplet separator (7), the steam fraction (FV) exits through one side and the liquid fraction (FL) through the other.

(21) The steam fraction (FV) is made up of water and is recirculated to the steam boiler (9).

(22) The liquid fraction (FL) is a condensed product that is made up of the organic phase together with the water dissolved therein. This condensed product is channelled to an isothermal tank (8) wherein the organic phase (FO) is separated from the aqueous phase (FA) by decanting, without the need for filters.

(23) The stream of the aqueous phase (FA) is made up of condensed water that is re-introduced into the steam boiler (9), optimising the performance of the system.

(24) The stream of the organic phase (FO) contains organic compounds and water in solution. This stream is channelled to a separator (10) that separates the water (FO-2) from the rest of the organic compounds (FO-1)

(25) As mentioned above, apart from obtaining a clean product that is a VOC- and odour-free plastic (PL) that is reusable for other uses (main objective of the present invention); an organic product (PO) is finally generated that is also reusable, wherein there is water (FO-2) that can be used externally for other uses, also being able to be reused in order to be recirculated to the boiler (9); and wherein there are organic remains (FO-1) essentially made up of essential oils that can be marketed, or that can even be reused as fuel for steam generation.