WO2022079468A1

WO2022079468A1 - Method and system for deodorizing post-consumer and post- commercial recycled plastic resins

Info

Publication number: WO2022079468A1
Application number: PCT/IB2020/059610
Authority: WO
Inventors: Fabrice Laberge; Laurent GIÉRULA
Original assignee: Emballages Transcontinental Flexipak Inc. / Transcontinental Packaging Flexipak Inc.
Priority date: 2020-10-13
Filing date: 2020-10-13
Publication date: 2022-04-21

Abstract

There is provided a system and method for deodorizing of post-consumer/post- commercial or post-industrial recycled plastic material. The system is adapted for deodorizing a recycled plastic material before said recycled plastic material is melted and extruded into recycled pellets, the system comprising an ozone generator adapted to generate a flow of ozone-rich gas and being fluidly connected to a drying vessel, a holding tank or one or more conduits between said drying vessel and holding tank. There is also provided a method for deodorizing the recycled plastic material after said recycled plastic material is melted or after it is extruded into recycled pellets by contacting the recycled plastic material with ozone-rich gas.

Description

METHOD AND SYSTEM FOR DEODORIZING POST-CONSUMER AND POSTCOMMERCIAL RECYCLED PLASTIC RESINS

FIELD

[0001] This technology relates to post-consumer or post-commercial recycled plastics. Such plastics are recycled into post-consumer and post commercial resins, known under the abbreviation “PCR”. More specifically this technology relates a method and system for deodorizing of plastic substances within a PCR recycling system. The method and system are suitable for use in a context of recycling of soiled plastic products, such as products recycled by consumers after their use or products recycled by industrial users.

BACKGROUND

[0002] Post consumer plastics resins such as shrink wraps, bags, or cosmetic, food and beverage packaging are increasingly sorted and recycled back into plastic pelletized resins and new plastic products rather than disposed of in landfills or incinerated. These feedstocks destined for recycling into pelletized resins (know as Post-consumer or Postcommercial resins, abbreviated as “PCR”) can be of various sources and various compositions, hardness, colour, thickness, etc. Common examples of feedstocks are cosmetic containers, food and beverage containers, redemption bags used in machines for crushing aluminum cans being redeemed for example at grocery stores, bags used for collecting fruits such as cranberry or grape harvests, etc. Similarly, post-industrial process plastics such as waste plastics, end of rolls, misprinted products, injection molding scraps, leftover bags or containers can also be sorted, cleaned and recycled into plastic resin pelletsfor reuse as feed material within a circular plastics economy.

[0003] Recycling systems and operations commonly involve receiving postconsumer, post-commercial or post-industrial plastic material feedstocks arriving at a recycling plant, sorting, shredding or grinding, washing, drying, melting and pelletizing into PCRs. The resulting PCRs pellets can then be sold and reused as raw materials or additives for the manufacturing of new products such as bags, containers, automotive parts, furniture, fabrics or various film blown, extruded or injection molded products. [0004] Using post-consumer, post-commercial or post-industrial plastics is of course good for the environment since these plastics can be melted into recycled plastic resin that can then be repurposed into new products without adding to landfills. The quality and purity of the recycled plastic feedstocks will ditacte their potential use in the making of new plastic products. One common issue with PCR is that from a feed source of various coloured material, the recycled pellets can blend into a gray colour thereby limiting their potential usage. One of the only ways to prevent this are sorting operations wherein the feedstock materials are presorted according to colour.

[0005] Another common issue is that despite vigourous washing, recycled PCR pellets often retain deleterious odours caused by the lingering presence of contaminants or pollutants. This limits their repurposing in making new products such as bags or food containers and diminishes the value of the recycled plastic material.

[0006] Thus, one drawback of PCR is that despite extensive washing or deodorizing treatments many PCR products retain stubborn odours or pathogens caused by contamination by biological or chemical substances. Also, when the feedstocks of post-consumer, post-commercial or post-industrial are plastic pouches or containers, these may retain stubborn odours caused by their contents such as food, beverages, soaps, etc., migrating into the plastic walls of the containers during handling and prolonged storage. Furthermore, even during recycling operations some pathogens, odour causing substances or substrates can become co-mingled or encapsulated in the plastic resins such as during melting and pelletizing within the recycling operations. Despite conventional sorting, washing, grinding and filtration and despite re-melting of the plastic feedstocks and degassing before or during PCR pellet production, some pathogens or some odours such as those caused by volatile organic compounds (VOC’s) remain present in the manufactured pellets and these odours are eventually released again upon remelting of the pellets when making finished products or remain perceptible by release of the odours by the finished products themselves.

[0007] A known apparatus uses a hot flush gas chamber to treat and deodorize PCR pellets obtained after a conventional recycling process. The principle at play being that heat and residence time in the hot flush gas (hot stream of air) chamber will cause a gradual degassing of the pellets and achieve some deodorization. One drawback is that these known systems use heat chambers with long pellet residence times, with or without vaccum and with or without prior treatement steps in order to extract odour causing species and molecules by further degassing. These systems are generally energy consuming and expensive. Further degassing is also known to be performed on melted recycled material before pelletizing. However odours trapped within the melt are difficult to fully extract. Thus, even after pelletizing, such degassed pellets can retain deleterious odours.

[0008] In another field of technology, ozone is known to have disinfecting and deodorizing functions and is used, for example, to sanitize municipal drinking waters. Another known use of ozone is as a strong oxidizing agent in chemical paper pulp processing. See for example, European Patent EP 3 008 240 entitled : “Method for treating chemical pulps by treatment with ozone in the presence of magnesium ions”. Another know use is to remove mold in ventilation systems. However, heretofore ozone has not been known for use in plastic recycling, let alone for deodorizing PCR material.

SUMMARY

[0009] It is an object of the present technology to ameliorate at least some of the inconveniences present in the prior art. One or more embodiments of the present technology may provide and/or broaden the scope of approaches to and/or methods of achieving the aims and objects of the present technology.

[0010] Inventors of the present technology have found that ozone gas may be efficiently used to deodorize recycled plastics, especially when used immediately before pelletizing within a recycling process. Ozone gas can also be used after or during pelletizing. The technology is efficient in that it uses little additional energy within a recycling process and is efficient at deodorizing recycled plastic particles having stubborn odours.

[0011] Thus, one or more embodiments of the present technology are directed to a method and a system for odour control of recycled plastic substances.

[0012] In an embodiment the present technology provides a system for deodorizing a recycled plastic material before said recycled plastic material is melted and extruded into recycled pellets, the system comprising an ozone generator adapted to generate a flow of ozone-rich gas and being fluidly connected to a drying vessel, a holding tank and/or one or more conduits between said drying vessel and holding tank. Preferably, the ozone-rich gas is present at a concentration of about 1 to about 6 wt% of the flow of ozone-rich gas and most preferably about 1 to about 3 wt%.

[0013] In another embodiment, the present technology provides a system for deodorizing a recycled plastic material after the plastic material is melted and/or after the plastic material is extruded into solid recycled pellets, the system comprising an ozone generator adapted to generate a flow of ozone-rich gas and being fluidly connected to an melter/extruder and/or to a pellet storage tank. Still preferably, the ozone-rich gas is present at a concentration of about 1 to about 6wt% and most preferably about 1 to about 3wt% of the flow of ozone -rich gas.

[0014] The present technology also provides a method for deodorizing a recycled plastic material before said recycled plastic material is melted and extruded into recycled pellets, the method comprising the steps of: a) shredding the recycled plastic material; b) washing the shredded recycled plastic material; c) drying the washed and shredded recycled plastic material; d) subjecting said dried, washed and shredded recycled plastic material to an ozone-rich atmosphere thereby deodorizing said material prior to melting.

[0015] In another embodiment, the present technology also provides a method for deodorizing a recycled plastic material during melting or extrusion or after said recycled plastic material is melted and/or extruded into recycled pellets, the method comprising the steps of: a) subjecting said recycled plastic material to an ozone-rich atmosphere thereby deodorizing said material during at least one of the steps of: i) melting said recycled plastic material; ii) extruding said recycled plastic material and; iii) storage of recycled pellets.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For a better understanding of the present technology, as well as other aspects and further features thereof, reference is made to the following description which is to be used in conjunction with the accompanying drawings, where:

[0017] Figure 1 depicts a schematic diagram of a sytem in accordance with one or more non-limiting embodiments of the present technology.

[0018] Figure 2 depicts a schematic diagram of a sub-system of the system of Figure 1 also in accordance with one or more non-limiting embodiments of the present technology.

DETAILED DESCRIPTION

[0019] The description and conditional language recited herein are principally intended to aid the reader in understanding the principles of the present technology and not to limit its scope to such specifically described embodiements and conditions. It will be appreciated that those skilled in the art may devise various arrangements which, although not explicitly described or shown herein, nonetheless embody the principles of the present technology and are included within its spirit and scope.

[0020] Furthermore, as an aid to understanding, the following description may describe relatively simplified implementations of the present technology. As persons skilled in the art would understand, various implementations of the present technology may be of a greater complexity.

[0021] In some cases, what are believed to be helpful examples of modifications to the present technology may also be set forth. This is done merely as an aid to understanding, and, again, not to define the scope or set forth the bounds of the present technology. These modifications are not an exhaustive list, and a person skilled in the art may make other modifications while nonetheless remaining within the scope of the present technology. Further, where no examples of modifications have been set forth, it should not be interpreted that no modifications are possible and/or that what is described is the sole manner of implementing that element of the present technology.

[0022] Moreover, all statements herein reciting principles, aspects, and implementations of the present technology, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof, whether they are currently known or developed in the future. Thus, for example, it will be appreciated by those skilled in the art that any block diagrams, pictorials or flowcharts herein represent conceptual views of illustrative systems embodying the principles of the present technology. Also, when used herein, the term “about” is to refer to numerical values plus or minus approximately 10% of the numerical value referred to.

[0023] In the context of the present specification, “ozone” refers to O3.

[0024] Ozone (O3) is created when diatomic oxygen (O2) is exposed to a high energy electrical field or ultraviolet (UV) light. Exposure to these forms of of energy causes a portion of the diatomic oxygen molecules to split into individual oxygen atoms. These free oxygen atoms quikcly recombine with diatomic oxygen molecules to form ozone.

[0025] It is known that ozone molecules are unstable and after a certain amount of time decompose back to diatomic oxygen molecules.

[0026] Some industrial ozone generators use UV light at about 185 nanometer wavelength applied to a feed of air or oxygen (higher concentration than air). This is similar to the how the ozone layer in the earth atmosphere is made.

[0027] However, most industrial ozone generators operate by exposing a feed of air, oxygen enriched air or pure oxygen to a corona discharge of electricity which is a high-voltage discharge of electricity between an electrode and a dielectric substance through the dielectric gap which is the space between the electrode and the dielectric substance. This creates a broad and steady corona discharge within a cell.

[0028] The amount and concentration of ozone created with ozone generators are function of multiple parameters such as oxygen concentration of the feed gas, flowrate of feed gas, energy usage and size of the ozone generators, and residence time in the corona chamber. Corona discharge can produce moderate-to-high concentrations of ozone (typically about 1 to about 6% by weight from clean, dry air and up to about 15% weight from concentrated or pure oxygen) over broad ranges of output flows. Oxygen concentration and flow rate of the feed gas impact the ozone output of the reactor. Generally, ozone concentration can be increased by increasing the oxygen concentration of the feed gas or by diminishing the flow rate of air through the corona discharge chamber.. Indeed, reducing the feed gas flow rate through the generator increases ozone concentration by increasing the residence time of oxygen molecules present in the corona discharge chamber. Such parameters are known to the skilled artisan.

[0029] In an embodiment of the present technology, a corona discharge ozone generator such as Model CFS-7 form SUEZ Treatment Solutions Inc. is used with an input of ambient air and generates an output gas flow of air containing more than about 1% by weight and preferably about 6 % or more by weight and most preferably about 3% or more by weight of output gas flow.

[0030] In other embodiments, an ozone generator uses a feed gas of oxygen- enriched air or a feed gas of pure oxygen. In such case, the output gas flow contains more than about 6% by weight of ozone by weight of output gas flow and preferably about 10% by weight of ozone by weight of output gas flow.

[0031] The flowrate of ozone rich gas exiting the ozone generator is preferably set at about 260 to about 500 grams of ozone per hour.

[0032] Referring to Figure 1, there is shown a schematic view of an embodiment of the system (10) of the present technology. Plastic feedstock material that may be soiled and may contain odours is fed by a worker or machine to an input ramp (20) generally constituted of an upwardly inclined movable rubber belt power driven by rollers under the belt (not shown). Input ramp (20) having fixed side walls to retain the feedstock material on the rubber belt (not shown). The rubber belt transfers the feedstock material into a hopper (not shown) funnelling the material into shredder (30) where it is shredded in small pieces. In one embodiment, the feedstock material consists of large polyethelyne bags. When shredded, such material is ripped into shreds or flakes. [0033] The shredded material is then sent by another belt to a cascade of three washing stations (40, 50, 60) where the material is progressively washed with water and agitated. The washing stations remove containments, foreign objects and soilage on the shredded material and also remove fines by skimming. The cleaning water operates in a closed loop provided with filtration and purification means and top-up water as necessary.

[0034] After exiting the last washing station, excess water is removed by a mechanical dryer or other similar means and the excess water is recycled (not shown). The clean but still wet or damp material is sent to an electric heater with adaptive heat system (dryer) which can be adjusted to the input material (70) where the material is dried with hot air from an electric heater at a temperature of about 85°C to about 90°C. The essentially dried material in the form of dried shreds, flakes or particles exits dryer (70) via a forced air conduit (120), shown in Figure 2, fluidly linked and leading to a material holding tank (90). Holding tank (90) is a closed tank where the flakes or particles of material reside before entering into a melting vessel and pelletizer (100) where the material is melted and extruded as output recycled PCR pellets (110).

[0035] The installation of the ozone generator will now be described in further detail by reference to Figure 2. A corona discharge ozone generator (130), shown in Figure 2, generates a gaseous output stream that is operatively connected to the forced air conduit (120) and/or dryer (70) and/or the holding tank (90) by means of one or more tubes (140, 150, 160). Tubes (140, 150, 160) are placed, sized and configured to carry a flow of ozone -rich gas so as to optimize contact with all of the flakes or particles of material. The ozone-rich gas is provided with sufficient output concentration of ozone, preferably about 1 to 6%wt and most preferably about 1 to 3%wt of ozone in the ozonerich gas and sufficient flowrate to effectively contact essentially all of the material. The residence time of the material within holding tank (90) is also sufficiently long to allow sufficient contact of the ozone -rich gas with the flakes or particles of material. It is suitable to introduce the ozone-rich gas to the flakes or particles in or when exiting the dryer since the ozone-rich atmosphere thus created will follow the path of the material to the holding tank by entrainment of the fluid gas flow, thus optimizing the deodorizing effect of the ozone-rich gas by optimizing contact time. The deodorizing effect is caused by the highly oxidative effect of the ozone molecule or odour-causing species present on or within the flakes or particles of material. [0036] Thus, it has been found that subjecting these recycled materials to ozone rich gas exposure within an enclosed vessel, during, before or after drying, preferably during drying and preferably in a holding tank after drying, allows for effective deodorizing of the material. This is especially efficient in that the ozone gas is made to contact the flakes or particles of material having maximal surface area being in contact with the ozone -rich gas as opposed to contacting the ozone-rich gas with recycled plastic pellets.

[0037] In practice, after ozone-rich gas treatment followed by melting and pelletizing, the pelletized PCR material generally do not require further deodorizing or degassing as per prior art systems. Essentially such further treatments as per prior art systems is no longer required since deleterious odours are no longer entrapped within the pellets during pelletizing. This is advantageous for later use of the pellets as raw materials or additives in the fabrication of other plastic resin products since the pellets or finished products retain essentially no perceptible deleterious odours. In a comparative test, the flakes and pellets treated as per the present technology retained a fresh and clean odour in comparison to the same material without the ozone treatement of the present technology.

[0038] However, in some embodiments of the present invention, the present technology of subjecting the recycled material to an ozone-rich air stream can also or alternatively be used upon melting, extrusion and storage of the extruded PCR pellets. In one embodiment, extruded PCR pellets are stored in tank (170) as illustrated in Figure 2. A vaccum can be applied to tank (170) to create an air gap which is filled with an ozonerich gas stream. This is either done batchwise on as a continuous flow of ozone-rich gas. This permits continued deodorizing of the recycled PCR pellets during storage.

[0039] The present technology thus enables improving of odour control of PCR material while minimizing additional energy usage, within a broader recycling process.

[0040] The system 10 can also comprise inter alia an ozone generator communicatively coupled with dryer (70) or other units of system (10) so as to regulate the flow rate of ozone-rich gas as a function of the quantity or flowrate of feedstock material being handled by system 10 or to regulate other parameters. The implementation of such communication devices is well known to the person skilled in the art and can involve sensors, communications network either wired or wireless, controllers, actuators, servers and databases.

[0041] The apparatus and methods described herein can be used with various types of feedstock material, including post-industrial plastic materials, without departing from the present invention.

[0042] Modifications and improvements to the above-described implementations of the present technology may become apparent to those skilled in the art. The foregoing description is intended to be exemplary rather than limiting.

Claims

CLAIMS What is claimed is:

1. A system for deodorizing a recycled plastic material before or during the time said recycled plastic material is melted and extruded into recycled pellets, the system comprising an ozone generator adapted to generate a flow of ozone -rich gas and being fluidly connected to a drying vessel, a holding tank or one or more conduits between said drying vessel and holding tank, or to the vessel and conduits for melting and extrusion.

2. A system for deodorizing a recycled plastic material after said recycled plastic material is melted and extruded into recycled pellets, the system comprising an ozone generator adapted to generate a flow of ozone -rich gas and being fluidly connected to a storage vessel for said pellets.

3. The system of claims 1 or 2 wherein the ozone-rich gas is present at a concentration of about 1 to about 10% by weight of the flow of ozone-rich gas, preferably about 6t% by weight and most preferably about 3 % by weight.

4. The system of claim 3 wherein the ozone -rich gas can be set to a flowrate of ozone-rich gas of about 260 to about 500 grams of ozone per hour.

5. A method for deodorizing a recycled plastic material before said recycled plastic material is melted and extruded into recycled pellets, the method comprising the steps of: a) shredding the recycled plastic material; b) washing the shredded recycled plastic material; c) drying the washed and shredded recycled plastic material; d) subjecting said dried, washed and shredded recycled plastic material to an ozone -rich atmosphere thereby deodorizing said material.

6. A method for deodorizing a recycled plastic material before or during said recycled plastic material is melted and extruded into recycled pellets, the method comprising the steps of: a) shredding the recycled plastic material; b) washing the shredded recycled plastic material; c) drying the washed and shredded recycled plastic material; d) subjecting said dried, washed and shredded recycled plastic material to an ozone -rich atmosphere thereby deodorizing said material. e) melting and extruding into pellets said material of step d) and subjecting said material to an ozone-rich atmosphere thereby further deodorizing said material and thereby generating deodorized pellets.

7. A method for deodorizing a recycled plastic material during the melting and extrusion of said recycled plastic into recycled pellets, the method comprising the steps of: a) shredding the recycled plastic material; b) washing the shredded recycled plastic material; c) drying the washed and shredded recycled plastic material; d) melting and extruding said material of step c) and subjecting said material to an ozone-rich atmosphere thereby deodorizing said material thereby generating deodorized pellets.

8. A method for deodorizing a recycled plastic material after said recycled plastic material is melted and extruded into recycled pellets, the method comprising the steps of: a) transferring said deodorized pellets to one or more storage tanks; and b) subjecting said pellets to an ozone-rich atmosphere within said storage tank(s).

9. The method of any one of claims 5 to 8 wherein the ozone-rich atmosphere contains a concentration of about 1 to about 10% by weight of ozone based on the weight of the flow of ozone-rich atmosphere, preferably about 6t% by weight and most preferably about 3 % by weight.

10. The method of claim 9 the flowrate of ozone in the ozone-rich atmosphere is about 260 to about 500 grams of ozone per hour.