MXPA99008270A - Method for recycling pet flakes and pet product produced according to said method - Google Patents

Abstract

The invention relates to a method for recycling polyethylene terephtalate (PET) flakes, characterized in that the flakes are extruded and granulated under vacuum, after which the granulate is aftercondensed in a solid phase under vacuum. Extrusion is preferably carried out in differentiated vent zones and aftercondensation of the solid phase is dependent on temperature, vacuum and time spent in a tumble dryer. Said dryer ensures the even and careful mixing and constant viscosity of the PET product. Said method is used in particular for making PET beverage bottles.

Description

PROCEDURE FOR OBTAINING A RECYCLING OF POLYETHYLENE TERTHTALATE FROM SHEETS, AS WELL AS THE PRODUCT OF POLYETHYLENE TERHETHYLATE PRODUCED BY MEANS OF ESE - PROCEDURE DESCRIPTION OF THE INVENTION The invention relates to a process for obtaining recycled polyethylene terephthalate ( PET) from flakes. PET products have multiple applications, for example as beverage bottles, films and special fibers, medical devices, especially syringes for medical use. It has been tried to lead this completely in the circulation of the material, but until now it has not been possible, since a residual contamination in the product can not be completely excluded. The existing methods in the market only allow the use of recycled PET in fields of application with lower quality requirements. To meet higher quality requirements, a mixture of proportionally smaller amounts of recycled PET is allowed with proportionally larger amounts of non-recycled PET materials in the production of PET bottles. It is also known to produce bottles in three layers, the inner layer being formed in a non-recycled product blowing process and the average carrier layer consisting of a PET recycle.

REF .: 31126 If a PET product must meet the requirement to be produced exclusively from recycling, it must be ensured that the recycling is almost completely free of azetaldehyde or pptrf (mg / kg). Thus, under laboratory conditions, the flakes obtained from PET products are contaminated, for example 1,1-trichloroethane, toluene, chlorobenzene, phenylcyanohexane and benzophenone. During recycling, these contaminants must be eliminated or reduced completely. DE 40 34 459 Al discloses a process according to the main idea of claim 1. This relates to the preparation of polyester waste subjected to heat treatment. To prepare the waste for recovery in the production of highly valuable PET synthetic materials, they are crushed, washed, sorted and post-condensed. The crushed comprises polyester waste with different molar masses and refining grades. The grinding is melted and the filtrate solidified and granulated, the granulate in the solid phase is subjected to a post-condensation, in which the molar mass of the solid phase condensate increases against the starting mass of the granulate. The condensed granulate is conveyed to an extruder and, together with the original raw material, is extruded in the form of films, injected molten material or in skeins. The condensation of the solid phase is carried out in a rotary dryer with a sub-pressure of 0.1 bar for a period of approximately twelve hours at 200-250 ° C. The essence of the described procedure consists in achieving the reuse of polyester waste of different productions, where the usual losses of the mechanical and optical properties can be recovered to a large extent by means of post-condensation. The cleaning of the polyester waste is carried out by means of filtering the contaminants with a particle size of up to 5 to 10 μm, as well as by means of post-condensation of solids under vacuum. In this way, however, the preparation does not go so far that the new PET product can be produced from the PET recycling without the addition of an original raw material. The recycling of PET is therefore not suitable to be used as a single starting material for the production of a product that comes into direct contact with food. From US-A-3 804 411 a method for obtaining PET recycle from flakes is known, wherein the flakes are extruded and granulated and finally a post-condensation of solids under vacuum is carried out. From US-A-5 597 891 a method for reducing the azetaldehyde content of the starting product for PET products is known. There the separation is carried out by means of inert gas dosing in a twin-screw extruder with three degassing zones. The task of the invention is a process for obtaining a PET recycling from flakes, which makes it possible to produce from starting flakes with impurities a starting product almost free of azetaldehyde or ppm (mg / kg), for PET products. -. The invention proposes a method for obtaining a PET recycle from flakes with the features of claim 1. The process according to the invention is divided into two stages: first the flakes are extruded under vacuum, whereby at this stage of the process, the main parts of the volatile by-products such as azetaldehyde and oligomers are removed under vacuum. The extrusion and the granulation is carried out as a first stage of the process, in order to achieve that the extruded product has a clearly defined shape and size, as well as a product in which a constant viscosity can be adjusted. In the next step of the process, post-condensation of solid under vacuum almost completely reduces the residual contamination, so that the directly obtained recycled product directly represents the starting product for new PET products. Therefore it is not necessary to prepare the new PET product from the recycled product and an additional original raw material. The recycling of PET is therefore suitable as the only starting material for the preparation of a product which comes into direct contact with food.In the process according to the invention, the step of the separation process is provided in the production of the granulate from the flakes and the subsequent treatment of the granulate. For this, an inert gas, for example nitrogen and / or water vapor, is injected under a homogenous distribution, in order to obtain a greater surface area in the process, whereby the by-products / pollutants are distributed better and can therefore be eliminated. optimal way. According to the invention, the leaflets are extruded and granulated in a worm screw extruder, especially in a twin screw extruder, with differentiated degassing zones. Three degasification zones are provided. The vacuum is produced in the first two degassing zones by injecting annular pumps to -fluid in the cycle and in the third zone by means of a piston pump station. This ensures that a particularly low pressure predominates in the last degassing zone. The post-condensation of the solid is carried out below the melting point of the granulate, in particular at a temperature of 220 to 250 ° C. The pressure during post-condensation of the solid should be in the range between 0.1 and 0.01 mbar. The post-condensation of solids is carried out especially for a period of ten to twelve hours. According to a special embodiment of the invention, it is provided that the post-condensation of the solid of the granulate is carried out in a rotating drum, in particular of the wobble type. The number of revolutions of the drum is in particular 1 to 5 per minute, especially 2. This guarantees a careful and uniform mixing of the granulate and a predetermined constant viscosity, which has a decisive significance for obtaining the desired parameters of the PET product . __ The field of application of the procedure according to "the invention is the recycling of bottles for beverages made of PET that as a suitable raw material are recycled in one hundred percent in the cycle of production of plastic bottles, for example you can also think that this cycle refers to the production of films and plastic fibers of good quality as well as devices for use in medicine consisting of PET In relation to the recycling of ppm-free materials and azetaldehyde in bottles for beverages made of PET, it is presented the procedure to recycle the bottles in the following way: After the corresponding circulation, the PET bottles are cleaned, the bottles are pressed, sorted, washed with different peripheral treatments and milled, forming the milled product, the so-called flakes, the base starting materials for the process according to the invention The flakes are extruded, peeled and granulated in the extruder with a specific configuration of the worm, with differentiated degassing zones and corresponding vacuum application in a predetermined temperature range. During this process step, the main part of the volatile by-products is eliminated. The residual contamination remaining in the product is completely reduced by means of the post-condensation and separation process. Depending on the temperature, vacuum, time and separation the granulate reaches its parameters required for the production of PET bottles in a rotary dryer, with corresponding accessories that guarantees a careful and uniform mixing as well as a constant viscosity. In the only appended figure a block diagram of the process according to the invention is shown in relation to the recycling of PET flakes described, where, in relation to the case of concrete application of the recycling of PET bottles, the steps of the procedure from the depuration of the PET bottles after the corresponding circulation to the recycling of the P ET leaflets obtained from these bottles.The purified PET bottles are sent loose or pressed in the form of balls. to a pre-wash, then the separation between the clear PET parts and the green ones is carried out. A metal detector removes metal parts. Then the PET bottles are milled and the flakes are obtained. These are washed and separated, also separating at this stage of the procedure the metal pieces that eventually exist. By means of the previous washing and the washing process itself, an essential part of the contaminants is removed, so that only those that actually adhere to the material are driven to the subsequent recycling process. The washed flakes are conducted to the special extruder with a melt filter. It is an extruder with a double worm screw, which operates at the number of revolutions of the spirals from 1350 to 1450 min. "1 The diameter of the worm screws is, for example, 100 mm, three zones are provided in the extruder. of degassing, the first two zones are connected to two annular pumps for fluids while in the last degassing zone there is a piston pumping station The mass obtained through the extruder is heated to a temperature of for example 280 ° C An inert gas is injected (separation) as nitrogen and / or water vapor under a homogeneous distribution. The granulate leaving the extruder is subjected to a post-condensation of solids and a separation process. The viscosity of the PET material returns to its value. This is necessary to be able to blow-form new bottles from the recycled PET product, which is only possible in a narrow viscosity range. The treatment of the granulate is carried out in a rotary dryer discontinuously. The quantity of PET to be treated is mixed in the rotary dryer for a certain period of time, in particular ten to twelve hours. Working in this batch system has the advantage that PET bottles from different manufacturers can be recycled, which have different viscosities, so that the mixing of the PET granules remains also ensures that the viscosity can be adjusted to a defined value. The profitability of the post-condensation process of solids in the batch system is obtained due to the size of the system. For example, the drum has a capacity of up to 44 m3. The post-condensation of solids is carried out in a temperature range of 220 to 250 ° C, thus at a sufficient distance from the melting point of the granulate. The drum rotates slowly, for example twice per minute. A pressure of 0.1 to 0.01 bar predominates in the drum. After the post-condensation of solids, quality control of the recycled PET flakes is carried out. Tests with contaminated flakes, in which the concentration of contaminants (toluene, chlorobenzene, phenylcyclohexane and benzophenone) was up to 1000 mg / kg, showed that the final post-condensate product was almost free of ppm (mg / kg) or azetaldehydes .

Claims (8)

1. CLAIMS 1.- Procedure to obtain a recycling of polyethylene terephthalate -PET-, from flakes by means of extrusion, granulation and subsequent post-condensation of the solid of the vacuum granulate and separation by means of the injection under a homogeneous distribution of Inert gas, such as nitrogen and / or water vapor, the process is characterized in that the extrusion is carried out under vacuum and separation by means of a screw extruder, especially a twin screw extruder, with three zones of Differentiated degassing, vacuum is produced in the first two degassing zones by means of annular pumps for fluids and in the third zone by means of a piston pumping station.
2. 2. Method according to claim 1, characterized in that the post-condensation of solids is carried out below the melting point of the granulate at a temperature of 220 to 250 ° C.
3. 3. Method according to claim 1 or 2, characterized in that the post-condensation is carried out at a pressure of 0.1 to 0.01 mbar.
4. 4. Method according to one of claims 1 to 3, characterized in that the post-condensation of solids is carried out for 10 to 12 hours.
5. 5. Method according to one of claims 1 to 4, characterized in that the post-condensation of solids of the granulate is carried out in a rotary drum.
6. 6. Method according to claim 5, characterized in that the post-condensation of solids of the granulate is carried out in a rotary dryer.
7. 7. Method according to one of claims 1 to 6, characterized in that the number of revolutions per minute of the drum is from 1 to 5, especially 2.
8. 8. - Process according to one of claims 1 to 7, characterized in that the flakes are obtained from bottles for beverages made of PET.