US-12616767-B2 - Device and method for recycling post-consumer plastic waste shredded to flakes and washed

US12616767B2US 12616767 B2US12616767 B2US 12616767B2US-12616767-B2

Abstract

The device for recycling flakes from shredded and washed post-consumer plastic waste comprises—seen in the processing direction of the plastic waste—a pre-treatment unit ( 2 ) for drying and homogenising the flakes from shredded and washed post-consumer plastic waste, a melting extruder ( 3 ) for melting the plastic waste dried and homogenized in the pre-treatment unit ( 2 ), a degassing extruder ( 5 ) having a connection ( 5 a ) to a vacuum source for degassing the plastic melt, a granulating device ( 6 ) for granulating the plastic melt, and an odour removal unit ( 8 ) to subject the granules an odour removal. The odour removal unit ( 8 ) has a process gas feed ( 10 ) and a gas discharge ( 11 ) for discharging an exhaust gas stream, wherein the process gas feed ( 10 ) of the odour removal unit ( 8 ) is connected to an ozone source ( 12 ) or an ozone generating device ( 13 ), whereby the odour removal unit ( 8 ) may be supplied with process gas enriched with ozone.

Inventors

Jacqueline GUGGENBERGER

Assignees

STARLINGER & CO GESELLSCHAFT M.B.H.

Dates

Publication Date: 20260505
Application Date: 20230122
Priority Date: 20220202

Claims (15)

1 . A device for recycling flakes from shredded and washed post-consumer plastic waste, comprising: a pre-treatment unit for drying and homogenising the flakes from shredded and washed post-consumer plastic waste, a melting extruder arranged downstream of the pre-treatment unit for melting the plastic waste dried and homogenized in the pre-treatment unit, a degassing extruder arranged downstream of the melting extruder and having a connection to a vacuum source for degassing the plastic melt, optionally a melt filter arranged between the melting extruder and the degassing extruder for removing foreign matter from the plastic melt, a granulating device arranged downstream of the degassing extruder for granulating the plastic melt, an odour removal unit arranged downstream of the granulating device for subjecting the granules to odour removal, and optionally a drying device arranged between the granulating device and the odour removal unit for drying the granules, characterised in that the odour removal unit has a process gas feed and a gas discharge for discharging an exhaust gas stream, wherein the process gas feed of the odour removal unit is connected to an ozone source or an ozone generating device, whereby the odour removal unit may be supplied with process gas enriched with ozone.
2 . A device according to claim 1 , further comprising an in-line measuring device for measuring the ozone concentration of the exhaust gas stream from the odour removal unit.
3 . A device according to claim 1 , further comprising an adjustment device for adjusting the amount of ozone, which is supplied to the odour removal unit, in dependency on the ozone concentration of the exhaust gas stream from the odour removal unit.
4 . A device according to claim 1 , further comprising at least one apparatus for the at least partial depletion of ozone contained in the exhaust gas stream, wherein the apparatus is configured to deplete ozone preferably for the thermal or catalytic treatment of the exhaust gas stream or for irradiating the exhaust gas stream using electromagnetic waves.
5 . A device according to claim 1 , wherein the process gas to be enriched with ozone is air.
6 . A device according to claim 1 , wherein the ozone concentration in the enriched process gas is at least 0.1 ppm.
7 . A device according to claim 6 , wherein the ozone concentration in the enriched process gas is in a range between 10 ppm and 100 ppm.
8 . A method for recycling flakes from shredded and washed post-consumer plastic waste, comprising: drying and homogenising the flakes from shredded and washed post-consumer plastic waste in a gas stream, in particular a hot gas stream, melting the dried and homogenized plastic waste into a plastic melt, optionally filtering out foreign matter from the plastic melt, degassing the plastic melt, granulating the plastic melt, optionally drying the granules, removing odour from the granules by way of a process gas stream, characterised by enriching the process gas stream used for removing odour from the granules with ozone or providing the process gas stream as a gas enriched with ozone.
9 . A method according to claim 8 , wherein the amount of ozone, which is supplied to the granules when removing the odour from the granules, is adjusted in dependency on the ozone concentration of the process gas upon removal following the odour removal treatment of the granules.
10 . A method according to claim 9 , wherein the ozone concentration of the process gas upon removal following the odour removal treatment of the granules is detected by way of in-line measurements and that the adjustment of the amount of ozone supplied to the granules when removing the odour from the granules is carried out in dependency on the ozone concentration measured.
11 . A method according to claim 8 , wherein the ozone contained in the removed process gas is depleted at least in part, wherein the depletion of ozone is preferably done by way of thermal or catalytic treatment of the process gas removed.
12 . A method according to claim 8 , wherein the ozone contained in the removed process gas is depleted at least in part, wherein the depletion of ozone is done by way of irradiation of the removed process gas using electromagnetic waves, wherein the electromagnetic waves are preferably UV light having a wavelength of at least 254 nm.
13 . A method according to claim 8 , wherein the process gas to be enriched with ozone is air.
14 . A method according to claim 8 , wherein the ozone concentration in the enriched process gas is at least 0.1 ppm.
15 . A method according to claim 14 , wherein the ozone concentration in the enriched process gas is in a range between 10 ppm and 100 ppm.

Description

The invention relates to a device and a method for recycling flakes from shredded and washed post-consumer plastic waste. Re-using plastic materials plays a crucial role in terms of a sustainable recycling economy. To make this possible, it is necessary to remove odour-intensive and infectious contaminants from post-consumer plastic waste in particular. When using recycled plastic as food packaging, particularly high purity requirements are placed on the recycled plastic. It must also be ensured that taste, odour and consistency of the foodstuff are not affected in any way by their packaging obtained from recycled goods. Recycling of post-consumer plastic waste is usually realized by shredding the waste into flakes/chopped material in a first step and then feeding it into a washing process. The washing process is preferably realized in a hot wash with the addition of caustic soda or other washing additives to clean the surface. If a certain amount of colour purity for any further use is required, optical pre-sorting of the post-consumer plastic waste is recommended before it is shredded, if necessary, also in combination with sorting following the washing process. The flakes thus produced can then be extruded into regranulates. These regranulates are subsequently aerated using hot air for a shorter period of time (hours to days) or using ambient air for a longer period of time (days to weeks) to reduce the odour of the regranulates. In order to make a decisive contribution to a positive eco-balance, the processing of plastic waste and its upgrading to as-new products must be as energy-saving as possible, conserve resources and the environment, and be cost-effective compared to the production of virgin material. With conventional degassing systems, the decontamination of post-consumer waste is particularly energy- and time-intensive, as the contaminated pellets are exposed to a stream of hot air for several hours or remain under vacuum. From the publication EP 2507022 B1, there have been known a method and a facility for the decontamination of plastic waste, in which flakes are extruded into pellets and the pellets thus obtained are subjected to odour reduction, by blowing hot air through an odour removal unit in which the pellets dwell. The object of the present invention is to provide an efficient and, at the same time, environmentally friendly process for the recycling of post-consumer waste, which can provide odourless regranulate. Ideally, the present invention can improve the cleaning efficiency in the recycling of post-consumer plastics to such an extent that the recycling provides food-grade regranulate. From the document CN 108641398 there has been known to wash plastic bottles in a special washing solution and to enrich with ozone in a mixer up to 180-220° C. Then, the plastic may be granulated. The document CA 601047 describes the treatment of PET staple fibres and the PET film with ozone at room temperature to enable printing thereon. It has been shown that the PET material thereby remains flexible and robust, wherein a bleach effect has been observed, though. Ozone treatment was carried out in a mixture of water vapour and ozone. In tests there has been shown that treating the PET material at a temperature of 180-230° C. did not have any negative effects on the material. In the case of even higher temperatures, however, the ozone will disintegrate into oxygen. In the document EP 0602505 there is described an ozone forming UV light radiator for treating liquids to reduce noxious substances. Document EP 3705252 A1 describes a method for producing a plastic material from plastic waste. This method comprises selecting industrial or post-consumer plastic waste, grinding the waste, treating the waste to reduce the odour generated by waste, treating the waste for reducing the microbial load, tempering the waste in water, regranulating the waste and dehumidifying the granules. In order to reduce odour and to reduce the microbial load, there may be used ozonisation, which will not be explained in greater detail. This known method is disadvantageous in that the treatment for reducing odour and microbial load is only performed on the ground waste. It is, however, known that in particular apolar compounds will migrate into the plastic material, see e.g. Resources, Conservation & Recycling 161 (2020), “Development and application of an analytical method to quantify odour removal in plastic waste recycling processes”. During regranulation as well as during further processing of regranulate, impurities can be released, which in turn constitute an odour nuisance and therefore prevent the regranulate from being used for higher-value applications, in particular to produce packaging for foodstuffs. Therefore, there is still a need for an efficient and at the same time environmentally friendly process for the treatment of post-consumer waste, which can provide odourless regranulate, as well as for devices to carry