Method and Installation for the Treatment of Olfactorily Contaminated Plastics

Abstract

A method and a system to increase the material utilization options of plastics with olfactory effective build-ups, such that they do not need to be disposed of, involving a pre-treatment, an oxidizing agent treatment and a conditioning to generate an end substrate that can be used as a raw material for the production of plate-type materials, molded parts, packaging and films within the scope of extrusion or injection molding methods or as an additive for other products.

Claims

1: A method of treating plastic materials that are contaminated with olfactory-active residues that adhere to the plastic materials, the method comprising the steps of: a) pre-treating a raw substrate that is made up of the plastic materials and has a defined fragment size, to obtain an intermediate substrate; b) treating the intermediate substrate with an oxidizing agent for a period of time that is a reaction holding time, to obtain a moist substrate; wherein the reaction holding time begins as soon as the oxidizing agent is added to the intermediate substrate; wherein, during the reaction holding time, the oxidizing agent modifies and/or decomposes the olfactory-active residues, such that the olfactory-active residues are no longer present when the reaction holding time is ended; wherein an amount and/or a concentration of the oxidizing agent are adjusted to achieve a modification and/or decomposition of the olfactory-active residues in the reaction holding time; wherein the amount and/or concentration of the oxidizing agent is adjustable to a specific composition of the intermediate substrate; and wherein the moist substrate substantially retains desired properties of the plastic materials; and c) conditioning the moist substrate to obtain a dry substrate that has a desired moisture content.

2: The method of claim 1, wherein the step of pre-treating the raw substrate includes a step of: d) fragmenting the raw substrate.

3: The method of claim 2, wherein the raw substrate is composed of fragments having a maximum edge length of up to 30 mm.

4: The method of claim 3, wherein the maximum edge length is between 5 and 8 mm.

5: The method of claim 1, wherein the step of pre-treating the raw substrate includes a step of: a1) providing at least one cleaning step, wherein the cleaning step includes a dry mechanical cleaning, a cold wash, or a hot wash, or any combination thereof.

6: The method of claim 1, wherein the step of pre-treating the raw substrate includes a step of: a2) fermenting the raw substrate.

7: The method of claim 5, a3) mixing the raw substrate with water to obtain a mash.

8: The method of claim 6, wherein water obtained from a subsequent method step is added to the mash.

9: The method of claim 6, wherein the step of fermenting includes a step of: a4) capturing high-energy gases for subsequent use in thermal energy recovery.

10: The method of claim 6, wherein a moisture content of the mash prior to fermentation is between 5 and 15% and the moisture content of the intermediate substrate after fermentation is between 15 and 30%.

11: The method of claim 9, wherein the moisture content prior to fermentation is between 8 and 12%.

12: The method of claim 9, wherein the moisture content on the intermediate substrate is between 15 and 20%.

13: The method of claim 1, wherein hydrogen peroxide is used as the oxidizing agent.

14: The method of claim 13, wherein the hydrogen peroxide has a concentration between 9 and 60%.

15: The method of claim 14, wherein the hydrogen peroxide has a concentration between 35 and 40%.

16: The method of claim 14, wherein the hydrogen peroxide has a concentration of 40%.

17: The method of claim 1, wherein the step of applying an oxidizing agent includes the steps of: b1) adding a defined amount of the oxidizing agent, b2) determining the reaction holding time it takes to modify and/or decompose the olfactory-active residues to a pre-specified value, b3) adjusting the defined amount of the oxidizing agent in order to obtain a specified reaction holding time.

18: The method of claim 17, wherein the specified reaction holding time is between 20 and 40 minutes.

19: The method of claim 18, wherein the specified reaction holding time is between 30 and 35 minutes.

20: The method of claim 1, the step b) including a step of: b4) subjecting the moist substrate to ultraviolet radiation.

21: The method of claim 1, the step b) including a step of: b5) monitoring the moist substrate with sensors during the reaction holding time to detect a break-down value of the olfactory-active residues.

22: The method of claim 19, the step b) including a step of: b6) adapting treatment intensity when an actual break-down value deviates from a specified break-down value.

23: The method of claim 1, wherein step c) includes a step of: c1) drying the dry substrate as needed to obtain a target moisture of between 0 and 5%.

24: The method of claim 23, wherein the target moisture is between 2 and 3%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The present invention is described with reference to the accompanying drawing.

[0062] FIG. 1 is a flow chart that illustrates the method according to the invention of treating olfactorily contaminated plastic materials.

DETAILED DESCRIPTION OF THE INVENTION

[0063] The present invention will now be described more fully in detail with reference to the accompanying drawing. This invention should not, however, be construed as limited to the embodiments set forth herein; rather, the drawing is provided so that this disclosure will be complete and will fully convey the scope of the invention to those skilled in the art.

[0064] FIG. 1 illustrates the steps of a multi-stage process 1 for the treatment of olfactorily contaminated plastic materials 10, referred to hereinafter simply as the plastic materials 10. In general, organic residues such as fats, proteins, and fungi or fungal spores, can adhere to plastic materials of any kind, and this is particularly the case with plastic packaging of foodstuffs. These residues eventually cause unpleasant odors and make these materials unacceptable for use in other products that use recycled plastic materials. The removal of organic residues is therefore required before a subsequent use.

[0065] The method 1 shown in FIG. 1 is a multi-step process that produces a final substrate 17 from the plastic materials 10 that have been cleaned to the extent that they are now suitable for many different uses 18 in subsequently manufactured products. The process parameters of method 1 are adaptable to the type of plastics in the plastic materials 10 and to the olfactory-active residues that adhere to those plastic materials 10. Pre-sorting is not a required step of method 1, but does significantly increase the economic efficiency of the method 1.

[0066] Referring now to FIG. 1, the first step is comminuting or fragmenting the plastic materials 10, to obtain a so-called ‘raw substrate’ made up of pieces of solid material that are relatively uniform in size, which increases the effectiveness and the process reliability of the subsequent method steps. The equipment for comminution depends on the type of the plastic materials 10. For example, larger pieces of plastics are reduced in size in a hammer mill, whereas plastic film is shredded in a carding drum.

[0067] The comminution 2 is followed by a cleaning step 3. For this purpose, the raw substrate 11 is subjected to a dry-mechanical cleaning 3. Coarse contaminants are released from the raw substrate 11, for example via a screen rotor, without the use of a cleaning fluid. The raw substrate 11 is then subjected to fermentation in step 5. For this purpose, the coarsely cleaned raw substrate 11 is filled into a treatment tank and mixed with water to make a mash 4. In the mashing step 4, the moisture content of the raw substrate 11 is increased to between 8 and 12%. The mashing step 4 improves the accessibility of the olfactory-active residues, as well as the raw substrate 11 during the fermentation process 5. Also, raising the water content allows the raw substrate 11 to be transported more easily to different processing stations, because the mash can be pumped. Process water 20 that is won as a by-product in a subsequent processing step may be used to make the mash 4.

[0068] The fermentation process is a dry fermentation. The raw substrate 11 is pumped into a bioreactor that is constructed as a plug flow fermenter and fermented. At this stage, the substrate is now referred to as an ‘intermediate substrate’ 14. Dry fermentation in a plug flow fermenter is a particularly suitable process for partially breaking down the residues, because the dryness of hydrophobic plastic materials, as well as the presence of extremely burdensome substances, does not significantly reduce the efficiency of the method 1. In addition, the decomposition of anaerobic microbials may be integrated as a continuous process into the method 1. The raw substrate 11 may contain mineral components and/or organic acids and for this reason, the plug flow fermenter is constructed of wear-resistant and corrosion-resistant materials. After fermentation 5, the intermediate substrate 14 has a moisture content of between 15 and 20%.

[0069] FIG. 1 illustrates that an energy-containing gas 19, for example, methane, that is released during fermentation 5 is captured and supplied to a thermal recovery plant 21 to produce electrical and/or thermal energy. Electrical energy produced by a generator is used for the power the equipment for implementing the method 1. The heat energy released during the combustion of the energy-containing gas 19 is fed to the plug flow fermenter and used to maintain constant optimal fermentation temperatures. Any excess thermal energy is used in a subsequent conditioning step 8.

[0070] The combined pre-treatment steps of the dry mechanical cleaning 3 and the fermentation 5 are particularly useful in making the method 1 as efficient as possible. Coarse contaminants that could adversely affect the efficiency of the treatment steps 6 and 7 are removed and the olfactory-active residues are made more susceptible to the subsequent treatment steps 6 and 7. Depending on the type of contamination, the fermentation 5 may also partially break-down or modify the olfactory-active residues. The use of by-products won in the course of method 1, i.e., using captured heat for thermal energy recovery 21 and re-using the process water 20 in the mash step 4, make the method 1 particularly efficient in its use of resources and eliminates the need for processing and/or disposing of these by-products.

[0071] Following fermentation 5, the intermediate substrate 14 is treated by applying an oxidizing agent 6 to the substrate, which is now referred to as a ‘moist substrate’ 15. Hydrogen peroxide, which has a strong cytotoxic effect, is used as the oxidizing agent, at a concentration of 40%, whereby the concentration may be adapted according to the specific olfactory-active residues or type of plastic materials. The oxidizing agent 6 works to modify and/or decompose the organic residues, such as fats, proteins, fungi or fungal spores and other organic molecular groups. An optimal moisture content of the moist substrate 15 plays a significant role in the efficiency of the oxidation step 6. For example, a moist substrate 15 that is too dry counteracts a uniform treatment, with the result that extremely intense oxidation can occur locally. On the other hand, a moist substrate 15 that is too wet will inhibit oxidation.

[0072] In one embodiment, a conveyor is used to carry the intermediate substrate 14, whereby it is understood that the conveyor has to be constructed of materials that are resistant to the oxidizing agent and any organic acids that may be present in the substrate.

[0073] Prior to the step of adding the oxidizing agent 6, the intermediate substrate 14 is deposited onto the conveyor by means of a substrate output device that controls the thickness of the layer of the substrate that is deposited onto the conveyor. In a preferred embodiment, the intermediate substrate 14 is deposited across the width of the conveyor with a layer thickness of at most 50 mm. This thickness ensures that the oxidizing agent 6 penetrates through the entire layer. The moisture content of the intermediate substrate 14 is controlled to facilitate an even distribution of the substrate 14 on the conveyor and to have a viscosity that prevents the substrate from oozing or dripping from the conveyor.

[0074] Precisely controllable spray heads are fastened above the conveyor and spray the oxidizing agent 6 onto the intermediate substrate 14 across the entire width of the conveyor. Metering units are provided that allow the spray heads to precisely meter the amount of oxidizing agent 6 that is applied to the substrate 14. Additional spray heads may be provided above the conveyor along the conveying path, to apply additional amounts of the oxidizing agent. The spray heads are individually controllable, so that defined amounts of the oxidizing agent 6 are applied with a high spatial precision. As a result, the amount of the oxidizing agent applied is limited to only what is needed to modify and/or decompose the organic residues and to minimize a degradation of the characteristics of the plastic materials themselves, i.e., the elasto-mechanical properties of the final substrate 17 that is obtained at the conclusion of the method 1.

[0075] FIG. 1 illustrates that, in addition to the oxidation step 6, the moist substrate 15 is also subjected to an ultraviolet radiation treatment 7. The UV radiation intensifies the modification and/or the break-down of olfactory-active components. Ultraviolet radiation emitters are arranged above the conveyor in such a way that the moist substrate 15 is irradiated immediately after the addition of the oxidizing agent 6. The area of radiation extends over essentially the entire width of the conveyor and length of the conveying distance. The ultraviolet radiation emitters may be individually controllable, thereby allowing specific regions of the moist substrate 15 located on the conveyor to be irradiated.

[0076] A reaction holding time begins as soon as the oxidizing agent 6 is initially added to the moist substrate 15. During this reaction holding time, the moist substrate 15 reacts with the oxidizing agent 6 and, due to exothermic reactions, the process temperature rises to 60 to 80° C. This results in an increase in temperature of the liquid in the moist substrate 15 and a decomposition of thermo-sensitive substances that are contained therein. Additional oxidizing agent 6 may be added during the reaction holding time and the reaction intensified by the ultraviolet radiation treatment 7. Easily volatile organic substances diffuse out of the moist substrate 15 and are removed by a suction device. Less volatile and non-volatile organic fragments remain in the moist substrate 15 and aggregate to some extent with mineral components of the moist substrate 15.

[0077] The modification and/or decomposition processes taking place during the reaction holding time have a significant influence on the elasto-mechanical properties of the final substrate 17. Thus, it is necessary to actively monitor and control the reaction holding time and, in particular, to have an automated process monitoring system to monitor of the decomposition of the olfactory-active compounds.

[0078] Sensors are provided above the substrate-bearing surface of the conveyor to monitor the moist substrate 15 optically, chemically, and physically during the reaction hold time. Temperature and moisture sensors detect the air temperature and the moisture content of the moist substrate 15. The data thus obtained allows conclusions to be drawn about the chemical reaction that is ongoing. Color sensors detect the appearance of the moist substrate 15. If the moist substrate 15 deviates in certain regions optically from a predetermined specified value, additional hydrogen peroxide 6 may be applied in a targeted manner. Furthermore, the oxidation reaction may be regulated by adjusting the concentration or the amount of the oxidizing agent 6, so that the thus optimized process parameters may be taken into consideration for the subsequent treatment. This also allows the treatment process to be continuously optimized.

[0079] The ultraviolet radiation treatment 7 is applied in a targeted manner, to optimize the modification and/or the decomposition of the olfactory-active components in the moist substrate 15. The moist substrate 15 is chemically monitored during the reaction holding time by an in situ analysis of the gas evolution. If, for example, a decreasing VOC content is detected, thereby indicating that the amount of hydrogen peroxide is being used up as decomposition progresses, the radiation intensity may be increased by switching on additional ultraviolet radiation sources.

[0080] The feed rate of the conveyor provides a further control variable for adjusting the intensity or duration of the treatment. The aim is that at the end of the reaction holding time, the organic components, in particular the olfactory-active contaminants, are largely modified and/or decomposed, so that no odor-related restrictions stand in the way of subsequent recycling uses. To maintain a preferred duration of the reaction holding time 30 to 35 minutes, the conveyor is driven at a feed rate of 1 m/min.

[0081] As shown in FIG. 1, at the end of reaction holding time the treatment steps 6 and 7 are followed by a conditioning step 8 that adjusts the moisture content of the moist substrate 15 to a desired moisture content. At the end of the conditioning 8, the substrate is then referred to as a dry substrate 16. In one embodiment, the conditioning unit is a condensation dryer and the moist substrate 15 is dried to obtain a target moisture content of between 2 and 3% in the dry substrate 16, depending on the intended subsequent recycling use 18 of the final substrate 17. The target moisture is obtained by raising the temperature and/or introducing water or water vapor, as needed. The moist substrate 15 is dried at temperatures between 95 and 175° C. and any olfactory-active components are thermally stressed, thereby promoting a further modification and/or decomposition. Moreover, the elevated process temperatures mobilize organic fragments, so that they diffuse out of the moist substrate 15, thereby contributing to an additional purification of the moist substrate 15.

[0082] The dry substrate 16 is then sorted 9 after exiting the conditioning unit 8. Screens with different mesh sizes and air separators with different flow rates separate the individual fragment fractions of the treated plastic materials from one another and make it possible to separate out the mineral components. A final substrate 17 emerges from the sorting process 9. This final substrate 17 has a high degree of purity and is acceptable for recycling in a very wide variety of use options 18.

[0083] The final substrate 17 is suitable for use in extrusion or injection molding processes and and may be incorporated into a variety of final substrate uses 18, such as, panel-like material, molded parts, packaging, film, or be used as an additive, for example, as a filler. In principle, the suitability of the final substrate 17 for different the use options 18 is determined by the specified requirements for the elasto-mechanical properties of the final substrate 17. The type of plastic materials, as well as the process control of the method 1, are determinative for these properties. The concentration and/or the amount of the oxidizing agent 6 and the intensity of the ultraviolet radiation 7 are the primary process parameters that need to be individually adapted.

[0084] It is understood that the embodiments described herein are merely illustrative of the present invention. Variations in the construction of the method of treating olfactorily contaminated plastic materials and the devices used to implement the method may be contemplated by one skilled in the art without limiting the intended scope of the invention herein disclosed and as defined by the following claims.