Patent Description:
The present invention falls within the processes of eliminating odours in plastics, and specifically relates to a process that uses water steam to clean plastics from domestic and industrial waste.

The objective of the invention is to eliminate pollutants, and with them, volatile organic compounds (VOCs) that impart a foul odour to recycled plastics. This process is based on the removal of VOCs by means of steam distillation. This invention applies to plastics of varied nature, such as polyethylene (PE), polypropylene (PP), polyester (PET), etc. from plastic waste, whether of industrial or domestic origin.

It is known that the demand for plastic packaging is increasing and with it the volume of plastic in landfills. While plastic waste from industries can be treated by means of mechanical recycling, obtaining a reusable high-quality material as polymeric raw material, domestic plastic waste has a high content of food remains and cleaning products that are absorbed into the polymeric matrix, becoming pollutants and causing a foul odour. These odoriferous substances are volatile organic compounds that currently cannot be eliminated by means of conventional washing, which limits the reuse thereof as raw material for products for exterior use.

Currently, conventional mechanical recycling consists of a selective classification of plastic waste based on the nature of the polymer, washing with water, to which reagents such as soda, surfactants and oxidants can be added, and finally it goes through a mechanical drying step prior to the extrusion step wherein the recycled pellets are obtained. There are various additives that can be added during the extrusion step in order to encapsulate or remove the VOCs contained in the polymeric matrix, but which have not been shown to be effective in the elimination of odour.

In this sense, some documents related to this concept are known, such as patent <CIT>, which relates to a process for washing plastic material based on a high-speed stirring tank, which then passes through an extruder wherein the plastic is melted and purified water is added, which forms an azeotrope with the mixture of melted plastic. The azeotrope is discharged together with the volatiles of the plastic and the water steam through the vacuum outlet of the extruder, so that the intensity of the polymer's odour is reduced.

The invention <CIT> is also known which relates to a method for reducing odours by means of ionising rays in an atmosphere that is not necessarily inert.

The invention <CIT> relates to a washing process in which the polyolefins are washed with hot water containing dissolved oxygen for the elimination of odours in the plastic.

The invention <CIT> relates to a washing process to eliminate odours in plastic waste. The process consists of the steps of cutting the plastic waste; washing with neutral surfactant and subsequent rinsing; washing with sodium hydroxide and subsequent rinsing; degradation of the plastic particles by means of hyphae fungi and subsequent rinsing and drying; (v) grinding the plastic particles to powder size; mixing the plastic powder with a sodium hydroxide solution and subsequent rinsing; extrusion of the powder material to obtain the pellets.

The invention <CIT> relates to a process for decontaminating recycled polyethylene terephthalate (RPET) by subjecting same to steam distillation to remove the contaminants which have diffused into the RPET matrix, but not disclosing a deodorizing the dry plastic material in the way described in the present patent application.

The invention <CIT> relates to a process for treating polyolefin granules in a treatment vessel and directed to collect the organic volatile compounds from a polymer during its manufacturing process, wherein the steps of said process, for example the step of deodorizing the dry plastic material, and the complexity of installations differs from what is disclosed in the present patent application.

Taking into account the existing background in this field of the art, processes that are based on the elimination of odours by means of steam distillation are not known. By means of this process of eliminating odours in plastics from domestic and industrial waste, it is possible to resolve the problems of conventional washing and to increase the reuse of said plastics as raw material for products for subsequent use.

As has been mentioned above, due to the continuous increase in the use of plastic products, the generation of this waste has become a global problem in today's society, so that the recycling and subsequent use thereof as a raw material is required if plastic in landfills is to be reduced. At the same time, using plastic as a raw material enables reducing production costs in the industries of the sector, in addition to increasing the added value of the product, since awareness about caring for the environment and with it the demand for recycled products in the market is increasing.

The object of the present invention is to increase the quality of recycled plastics after the elimination of odours by means of the removal of the volatile organic compounds with water steam. These organic compounds are found both inside the polymeric matrix and on the surface of the plastic. The solution that is described in detail below is based on the fact that removal with steam favours the internal diffusion of volatile compounds due to the working temperature, as well as lowers the boiling point of volatile organic compounds as they are immiscible with water and, therefore, favours the evaporation thereof from the surface of the polymer towards the gaseous phase and consequent elimination.

For this, the method requires a system or equipment that comprises means for selecting and shredding the material, among which a separation system and a bladed shredder stand out; washing means, among which a washing tank, a rinsing tank and a dryer stand out; and a deodorising module, which consists of a system for the elimination of the volatile organic compounds contained in the plastic and the recovery of the same.

This deodorising module is a hermetically closed circuit that enables temperature control and heat recovery. Within this system there is a column wherein the plastic to be deodorised is inserted, in which the plastic moves against the flow with the steam that enters through the base of the column and exits through the head. At this point it must be taken into account that the boiling point of volatile organic compounds is always below the boiling point of water and therefore, working at atmospheric pressure, it is enough to feed the module with steam at <NUM> degrees. In the event of working above atmospheric pressure, the boiling point of the water increases and with it the temperature of the system, but work must always be carried out below the plastic degradation temperature. As for the flow rate, it depends on the dimensions of the reactor; therefore, this invention is not limited to a range of flow rates.

The steam that exits through the head of the column after having been in contact with the recycled plastic and containing VOCs passes through a droplet separator that eliminates the organic phase content. The droplet separator is a unit independent from the distillation column and the condensation of organic compounds takes place therein, i.e., the organic compounds are trapped in the droplet separator by condensation while the clean, aqueous phase remains in the form of steam.

The steam portion that remains clean is returned to the steam boiler directly and the liquid portion containing water and VOCs is taken to an isothermal tank, wherein the aqueous phase is separated from the organic portion by decanting. The aqueous phase is fed back to the boiler, thus closing the water circuit.

The organic phase is fed to a separator wherein water dissolved in the organic phase is obtained through one side and the organic compounds are obtained through the other. This separator can be a distillation column wherein the water evaporates, separating it from the organic compounds; a hydrophobic membrane wherein only organic compounds pass through the membrane or separation by means of membrane by molecular size, which is possible if the size of the organic molecules differs significantly from the size of the water molecule; or equivalent devices or a combination thereof. In any case, the waste water can be used to re-feed the boiler, or for any other use.

It has been observed that, in addition, other advantages are achieved, and, generally, this organic phase is composed of essential oils that can be marketed, since they have a high value in the industry, such as limonene or pinene. If these oils are not to be marketed, the organic phase can be reused as fuel for steam generation.

In any case, the development of the process for eliminating VOCs that cause foul odour in recycled domestic plastic is carried out within a mechanical recycling process. It is implemented directly after the washing line or after extrusion and pelletising, as the last treatment, wherein the steps described below are envisaged:.

It is possible that the deodorising module is independent from the recycling process. In this case, the deodorising system acts as a module that is totally independent from the recycling process and its input into the process is the recycled pellets, i.e., it is a system for improving the quality of the product already recycled by other companies.

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:
<FIG> is a schematic diagram of the different elements of the method for carrying out the elimination of odours in recycled plastic materials.

The method for the elimination of odours in recycled plastic materials comprises the following steps:.

Taking into account the steps of the method, and as seen in <FIG>, the system for the elimination of odours in recycled plastic materials comprises the following equipment:.

Further describing each step, and in turn, further describing <FIG>, the method and the system required to carry out the method comprises:.

Said plastic with odour, and with variable size depending on the shredding, although preferably of powder size, enters the head (<NUM>) 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 (<NUM>) 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.

The steam (V) enters through the bottom lateral part (<NUM>) of the column and exits through the upper lateral part (<NUM>) of the same. This steam (V) entering through the bottom lateral part (<NUM>) is fed by a steam boiler (<NUM>) adjacent to the column (<NUM>).

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 (<NUM>). After the droplet separator (<NUM>), the steam fraction (FV) exits through one side and the liquid fraction (FL) through the other.

The steam fraction (FV) is made up of water and is recirculated to the steam boiler (<NUM>).

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 (<NUM>) wherein the organic phase (FO) is separated from the aqueous phase (FA) by decanting, without the need for filters.

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

The stream of the organic phase (FO) contains organic compounds and water in solution. This stream is channelled to a separator (<NUM>) that separates the water (FO-<NUM>) from the rest of the organic compounds (FO-<NUM>).

Claim 1:
A method for the elimination of odours in recycled plastic materials comprising the following steps:
a) separating the recycled plastic material (P-VOCs) by means of identification in a plant for separation by identification (<NUM>);
b) shredding the plastic in a shredder (<NUM>) and reducing the size of the plastic particles;
c) chemically washing the shredded plastic with surfactant in a washing tank (<NUM>);
d) rinsing the plastic material to eliminate dirt and the chemicals used in chemical washing in a rinsing tank (<NUM>);
e) drying the rinsed material in a mechanical dryer (<NUM>);
f) deodorising the dry plastic material wherein:
- the plastic material is introduced through the upper part (<NUM>) of a distillation column (<NUM>);
- steam inlet (V), coming from a boiler (<NUM>), through the bottom lateral part (<NUM>) of the distillation column (<NUM>);
- the plastic material falls by the effect of gravity along the distillation column (<NUM>), 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 (<NUM>) of the distillation column (<NUM>); and
- the VOC-free plastic (PL) exits through the bottom part (<NUM>) of the distillation column (<NUM>)
wherein while deodorising, the organic product (PO) that exits through the upper part of the column (<NUM>) is channeled to a droplet separator (<NUM>), and wherein in the droplet separator (<NUM>) there is a separation of the product into a steam fraction (FV) and a liquid fraction (FL), and
wherein the liquid fraction (FL) feeds an isothermal tank (<NUM>) wherein the liquid fraction (FL) is separated by decanting into an aqueous phase (FA) and an organic phase (FO) comprising organic compounds and dissolved water.