Method and apparatus for processing incoherent plastics

Abstract

An apparatus and a method for processing incoherent plastics are disclosed, in which the material is introduced inside a container where the material is subjected to radio frequency waves, with a pressure inside the container that is lower than ambient pressure, for example lower than 1.4 x 104 absolute Pascal, so that the combination of vacuum and radio frequency determines the extraction of undesired substances, like humidity, contaminants, odorous substances, etc.

Description

Method and apparatus for processing incoherent plasticsBackground of the invention

[0001] The invention relates to a method and an apparatus for processing incoherent plastics, i.e. in the form of granules and / or microgranules and / or pellets and / or powder and / or flakes or the like, in particular for dehumidifying and / or decontaminating and / or deodorizing and / or upgrading of incoherent plastics.

[0002] Specifically, but not exclusively, the invention may be usefully applied to treating incoherent plastics obtained from recycling (PCR), in particular material containing polyethylene terephthalate from recycling.

[0003] Mixing virgin plastics with plastics obtained from recycling (PCR) is known. In the food packaging industry, using these mixtures involves special attention to the presence of contaminants. Various methods are known for decontaminating undesired substances - in particular benzene, toluene, limonene, acetaldehyde and other NIAS (“non- intentionally added substances”) - of plastics to be used in the food packaging industry.

[0004] Processes are also known that use scavengers to remove acetaldehyde, especially in the case of recycled material, with the resulting risk of an undesired increase in the concentration of scavengers.

[0005] Further, it must be emphasized that the presence of a given contaminant may be critical for food use not only in function of the percentage quantity in the material but also because of the ability of the contaminant to spread through the foodstuff. In this regard, it has been found that, for given plastics consisting of a mixture of recycled and virgin material, the ability to spread contaminants contained in the plastics increases in general with the increase in the percentage of recycled material compared with virgin material.

[0006] The prior art comprises using vacuum techniques for extracting and removing undesired substances from incoherent plastics.

[0007] Patent publication US 6,154,980 shows a dryer for granular or powder material with a plurality of hoppers rotating between positions of material filling and heating, material vacuum drying and material unloading.

[0008] Patent publication US 2021 / 276224 Al shows a process for drying granular polymer material that is dehumidified by a first flow of gas at a first temperature comprised between 100°C and 150°C, heated to a second temperature that is higher than the first temperature and dried to the second temperature by applying a set vacuum level.

[0009] Patent publication US 2018 / 264684 Al shows an apparatus for drying granular resin comprising a heating chamber, a vacuum chamber below the heating chamber, a retaining hopper below the vacuum chamber, a fan for supplying heated air through the heating chamber, a conduit for introducing dry purging air into the vacuum chamber and a conduit for introducing dry ventilating air into the retaining hopper.

[0010] Patent publication US 2023 / 251035 Al shows an apparatus for drying resin in granules comprising a first and a second drying chamber, a source of heated air, a first vacuum source for selectively generating a first vacuum in the first and in the second drying chamber, and a second vacuum source for selectively generating a second vacuum in the first and in the second drying chamber for aspirating the resin granules.Summary of the invention

[0011] One object of the invention is to make available a solution, which is alternative to those of the prior art, for extracting and removing undesired substances (for example, humidity, contaminants, odorous substances, etc) from incoherent plastics by using a vacuum process.

[0012] One object of the invention is to propose a solution that is suitable for improving the extraction of undesired substances from incoherent plastics.

[0013] One advantage is to permit the extraction of undesired substances from polymer granules by maintaining an even temperature of the granule so as to reduce the thermal gradient between the surface and the heart of the granule.

[0014] One advantage is to homogenize the humidity of the polymer granule so as to reduce the humidity gradient between the surface and the heart of the granule.

[0015] One advantage is to permit the extraction of undesired substances from a mass of incoherent plastics so as to maintain stable and uniform conditions (in particular, temperature and humidity) of the processed material.

[0016] Other advantages are reducing energy consumption and / or distributing evenly the heating energy in the mass of the processed material and / or increasing productivity and / or decreasing the duration of the extraction process.

[0017] Such objects and advantages, and still others, are achieved by an apparatus and / or a method according to one or more of the claims set out below.

[0018] In one embodiment, a treatment method comprises the steps of introducing incoherent plastics inside a container, generating a vacuum inside the container, in particular a vacuum lower than 1.4 x 104absolute Pascal, and generating radio frequencywaves on the material in the container, so that the combination of vacuum and radio frequency determines the extraction of undesired substances, like humidity, contaminants, and odorous substances.

[0019] A processing apparatus may comprise, in particular, at least one container for incoherent plastics, means for generating a vacuum inside the container, and means for generating radio frequency waves inside the container. The means for generating waves may comprise, in particular, at least one electrode connected to a source of radio frequency. The electrode may be arranged, in particular, inside the container and immersed in (and at least partly or completely surrounded by) the material. The means for generating waves may comprise, in particular, two or more electrodes.

[0020] The radio frequency waves may be controlled, in particular, so as to obtain a state of isothermal.

[0021] The radio frequency waves may have, in particular, a frequency comprised between 300 KHz and 300 GHz, more in particular a frequency comprised between 1 MHz and 1 GHz, or comprised between 1 MHz and 100 MHz, or comprised between 10 MHz and 100 MHz, or comprised between 1 MHz and 50 MHz, or comprised between 10 MHz and 50 MHz, or comprised between 300 KHz and 200 MHz, or comprised between 300 KHz and 100 MHz, or comprised between 300 KHz and 50 MHz.

[0022] In one practical non-limiting embodiment, a generator has been used that is configurable selectively at 13.56 MHz or 27.12 MHz, although it is however possible to use other frequencies.

[0023] It has been established that the combination of vacuum and radio frequency waves enables the effect of evaporation and extraction of certain substances present in the incoherent plastics to be increased considerably. This effect is particularly effective for plastics in the form of pelletized granules and / or granules containing at least partially PCR (Post-Consumer Recycled) material.

[0024] The radio frequency waves enable a controlled temperature to be maintained stably and homogenously in the mass of the processed material inside the container, guaranteeing a process of extraction of undesired substances in a relatively reduced processing time, thus increasing the efficiency of the process, in particular the efficiency for the same container size.

[0025] Heating incoherent plastics, by controlling the radio frequency waves, enables the temperature of the granules of material to be modified rapidly and effectively, so as toexploit with maximum efficiency the action, exerted mainly by vacuum, of migration of the substances that have to be extracted from the heart to the surface of the granule.

[0026] It is further possible to modulate the vacuum inside the container so as to increase the efficiency of migration of the undesired substances from the heart to the surface of the granule in relation to the temperature of the granule.

[0027] The radio frequency waves may be generated, in particular, making use of at least one electrode (or two electrodes, or more than two electrodes) in contact with the material in the container. The electrode is connected to a radio frequency generator whose power and / or frequency may be regulated (in particular by electronic and programmable control means).

[0028] The radio frequency generator may be feedback adjusted based on signals sent by sensor means configured to detect at least one process feature, for example a content of a substance extracted from the material and measured in a gas aspired by means for generating a vacuum in the container. This substance may comprise, in particular, humidity and / or a contaminant and / or an odorous substance, so that the sensor means may comprise humidity sensor means and / or detecting means for detecting a given contaminant and / or odour sensor means.

[0029] Each electrode may be in the form of bar. Each bar may extend in length with a vertically arranged longitudinal axis. The electrodes may be, in particular, parallel to one another.

[0030] Each electrode may be in the form of a cylinder. In particular, it is possible to arrange two or more cylinders (in contact with the incoherent plastics) arranged inside one another, in particular coaxially (for example, coaxially with respect to an axis of the container). The arrangement of cylinders inside one another (in particular, at a reciprocal distance so as to form a gap between two adjacent cylinders, where each gap is occupied by incoherent plastics) enables a radio frequency field to be generated. The number of cylinders (one, two, three, four, five or more than five) may be chosen, in particular, as a function of the geometry and / or the dimensions of the container.

[0031] The building material of the electrodes may comprise, in particular, at least one metal material like, for example, copper, aluminum, brass, special alloys, or also a combination of the aforesaid materials.

[0032] At least one electrode, or also each electrode, may comprise, or may be provided with, or may be associated operationally with, at least one temperature sensor,configured in particular to detect a surface temperature of the electrode. This temperature sensor may comprise, in particular, an optic fiber sensor or other type of sensor so configured as not to be affected by the action of the electromagnetic field generated by the radio frequency generator.

[0033] The length of each electrode (in the form of a bar or in the form of a cylinder, in particular of two or more cylinders inside one another) may be chosen in function of the geometry of the container. The length of each electrode chosen as a function of the type of the processed material (for example in function of the type or chemical composition of the incoherent plastics).

[0034] The solid particle material that is processed may comprise, in particular, plastics in pelletized granules. The processed plastics may comprise one or more polymers included in the following set: polyethylene terephthalate (PET), polyamide (PA), acrylonitrile-butadiene-styrene (ABS), polyphenylene sulphide (PPS), polystyrene (PS), polyvinyl chloride (PVC), polysulphone (PSU), polymethylmethacrylate (PMMA), polyolefins in general. Further, the processed plastics may comprise, in particular, at least one percentage of post-consumer recycled plastics (PCR).

[0035] Each electrode may be controlled (by programmable electronic control means comprising, for example, a central processing unit, a programmable logic controller, a microprocessor, etc) with a set point value of the power supplied to the electrode. Each electrode may be controlled by a maximum set point value, that must not be exceeded, of a temperature of a surface of the electrode. Each electrode may be controlled by a set point value of the temperature of the surface of the electrode.

[0036] Controlling each electrode enables a desired transfer of the radio frequency energy to the polymer resin solid particles to be obtained. The power may be supplied to the electrode continuously, or in pulse trains to avoid local overheating and / or plasticization of the material.

[0037] It is possible to provide, in particular, for most or the entire length of each electrode (in the form of a bar or in the form of a cylinder or in yet another form) to be immersed in (and at least partly or completely surrounded by) the material to improve the heating efficacy of the material with the power emitted by the radio frequency. The number of electrodes (bars, cylinders or still other types) may be chosen based on the volume of material that has to be processed and in which the electrodes are immersed.

[0038] The arrangement, the number and the shape of the electrodes may be chosen, inparticular, so as to reduce the dead zones, i.e. the zones of the process volume (i.e. the internal volume of the container of the material) not affected by the radio frequency, and at the same time so as to avoid excessive overlapping of the radiation emitted by the electrodes, to avoid accumulation of energy with the risk of degradation of the material.

[0039] In general, the number of electrodes for emitting the radio frequency may depend on the cross section of the container (diameter of the hopper) where the extraction process by vacuum radio frequency occurs, to ensure homogenous distribution of the energy supplied by the radio frequency waves.

[0040] The combined action of radio frequency and vacuum enables, compared with another type of heating, energy consumption to be reduced, and the efficiency to be increased of extracting undesired product (humidity, contaminant, odorous substance, etc) from the polymer granule.

[0041] The radio frequency generator may be controlled, in particular, on the basis of the chemical-physical features of the processed material. For example, in the case of PET, it is possible to generate waves with radiofrequency comprised between 1 MHz and 100 MHz, or comprised between 10 MHz and 50 MHz, for example equal to 27.12 MHz.

[0042] The radio frequency generator may be controlled, in particular, based on a filling factor of the container, i.e. a ratio between the volume actually occupied by the material in the container during the process (volume that may be controlled with control means of known type) and the maximum total value available inside the container to contain the material.

[0043] It has been established that the heating efficiency of the radio frequency in the heart of the granule increases if the granule is preheated to take the granule to a temperature greater than ambient temperature, for example if a PET granule has reached a temperature greater than 70 °C.

[0044] In one embodiment, a dehumidification method comprises a stage upstream, in which the material in particles is preheated in an upstream container (up to a set temperature) by a flow of process gas, and a main stage, in which the material, after it has been taken from the upstream container and then been introduced into a main container in a vacuum (at a pressure lower than an ambient pressure), is heated by radio frequency waves.

[0045] The aforesaid two-stage method (with vacuum radio frequency following processing with process gas) may be used, in particular, for recycled polymer material(PCR plastics) or for other material that could suffer high temperature processing for a long period.

[0046] The aforesaid two-stage method with radio frequency heating in a vacuum in the second stage may be used, in particular, to process the material at a relatively low temperature in the stage upstream (in particular, with a process gas at a temperature lower than the degradation temperature of the polymer, for example lower than 65 °C for polyolefins and lower than 120-140 °C for polyethylene terephthalate), obtaining a lower level of extraction, and using the radio frequency waves in combination with the vacuum in the subsequent stage to obtained more intense heating as far as the heart of the plastic granule.

[0047] It is possible to provide one embodiment of a two-stage method that comprises a stage upstream, in which the plastics are subjected to pelletization treatment (by extrusion) to obtain plastics in granular form, and a main stage, in which the material in granules supplied from the stage upstream (at a temperature greater than ambient temperature) is removed and introduced into a main container in a vacuum (at a pressure lower than an ambient pressure) and is heated here by radio frequency waves. In practice, the material in granules leaving a pelletization stage is supplied, with transfer in line, entering an extraction stage with radio frequency and vacuum, which enables a thermal residue to be exploited that is present in the granules exiting the pelletization stage to improve the efficiency of the stage with vacuum and radio frequency. This two-stage method (extraction stage through radio frequency and vacuum following a pelletization stage) may be used, in particular, for recycled polymer material (PCR plastics) or for another material that could be subjected to high temperature treatment for a long period.

[0048] As said previously, it has been found that heating polymer granules with radio frequency in a vacuum enables extracting the undesired substance (humidity, contaminant odorous substance) from the granule to be significantly speeded up if the granule is already at a high temperature (in particular, by a pre-heating step performed in a container upstream of the main container where heating with radio frequency in a vacuum occurs). Extraction efficacy thus becomes greater than heating with process gas.

[0049] It has also been found that the extraction of undesired substances by heating with radio frequency in a vacuum is effective, particularly when the incoherent material to be processed has a high degree of humidity, i.e. extraction with radio frequency in a vacuum can be more effective than extraction with a process gas when the polymer granulehas a high degree of humidity.

[0050] In one embodiment, an extraction method comprises a main stage, in which the material in particles is heated in a container by radio frequency waves in a vacuum, and a stage downstream, in which the already at least partially processed material, taken from the main container and introduced into a downstream container, is processed further (to extract at least one undesired substance) by a flow of process gas inside the downstream container.

[0051] The aforesaid two-stage extraction method (with radio frequency heating in a vacuum upstream followed by a stage with process gas downstream) may be used, in particular, to dehumidify polymer material that has high humidity.

[0052] It is thus possible to provide at least two embodiments of two-stage extraction methods: a first embodiment in which a stage with radio frequency in a vacuum precedes a stage with a flow of process gas; and a second embodiment in which a stage with radio frequency in a vacuum follows a stage with a flow of process gas.

[0053] Both for the first embodiment, and for the second embodiment, a reduction (comprised between 30% and 50%) of the processing time of extraction from the polymer resin compared with single-stage processes has been established.

[0054] It is also possible to provide at least one embodiment of a method with three stages, in which a stage with radio frequency in a vacuum follows a stage upstream with a flow of process gas and precedes a stage downstream with a flow of process gas.

[0055] It is possible to arrange, in particular, a handling device for handling the material in the container in a vacuum, for example by a stirrer that remixes the material in the process volume and / or by a recirculating system that takes a part of the material from an outlet from the container and returns the material to an inlet of the container. Handling the material in the container enables uniform spreading of the energy to be promoted, improving the efficacy of heating and extraction.

[0056] The handling device enables the efficiency of the processing to be increased in particular in the case of a batch type process, which is particularly indicated, especially for materials that require, owing to the chemical, physical and mechanical features thereof, to be subjected to moderate temperature gradients or to be processed with reduced volumes of material to limit the thrust of the mass of the material onto the discharge port of the container.Brief description of the drawings

[0057] The invention can be understood and implemented with reference to theattached drawings that illustrate some embodiments thereof by way of non-limiting example, in which:Figure 1 is a drawing in a vertical elevation of an embodiment of a processing apparatus for the extraction of at least one undesired substance from incoherent plastics that is devised in accordance with the present invention;Figure 2 is a diagram of a part of the apparatus of Figure 1.Detailed description

[0058] With reference to the aforementioned figures, an apparatus for processing incoherent plastics has been indicated with 1.

[0059] The apparatus 1 comprises at least one container 2 (for example, a hopper) configured to contain incoherent plastics. The container 2 may comprise, in particular, an upper inlet for introducing the incoherent plastics and a lower outlet for releasing the incoherent plastics.

[0060] The apparatus 1 comprises means for generating a vacuum inside the container 2. The means for generating a vacuum may comprise, in particular, an expulsion conduit 3 connected to an outlet of the container 2 and a vacuum pump 4 arranged in the expulsion conduit 3 to aspirate air from the container 2.

[0061] The apparatus 1 comprises a radio frequency device configured to subject the incoherent plastics inside the container 2 to radio frequency waves. The radio frequency device may comprise, in particular, one, two, three or more electrodes 5 (for example, in the form of one or more bars and / or one or more cylinders inside one another) arranged inside the container 2 and connected to a radio frequency generator 6 arranged outside the container 2. Each electrode 5 may be arranged in the container 2 so as to be able to be in contact with the incoherent plastics contained therein.

[0062] The apparatus 1 may comprise, in particular, an outlet device W for controlling the outflow of the incoherent material from the container 2. The outlet device W may comprise, in particular, a shutter member or another type of control member for controlling the outlet of the material. The outlet device W is controlled by (electronic and programmable) control means CPU of the apparatus 1.

[0063] The apparatus 1 may comprise, in particular, one or more vacuum seal valves V1-V5 and one or more buffer volumes R1-R2 for managing the vacuum in the container 2. The apparatus 1 may comprise, in particular, a vacuum seal valve VI at the inlet of the container 2. The apparatus 1 may comprise, in particular, a vacuum seal valve V2 arrangeddownstream of the container 2. The apparatus 1 may comprise, in particular, a buffer volume R1 arranged upstream of the container 2. The buffer volume R1 may comprise, in particular, a vacuum seal valve V3 to connect the buffer volume R1 to the outside environment. The apparatus 1 may comprise, in particular, a vacuum seal valve V4 arranged upstream of the buffer volume Rl. The apparatus 1 may comprise, in particular, a buffer volume R2 arranged downstream of the container 2, in particular arranged downstream of the vacuum seal valve V2. The apparatus 1 may comprise, in particular, a vacuum seal valve V5 arranged downstream of the buffer volume R2. The buffer volume R2 may comprise, in particular, a vacuum seal valve to connect the buffer volume R2 to the outside environment.

[0064] The apparatus 1 may comprise, in particular, at least one upstream container 7 (for example, a hopper) configured to contain incoherent plastics and to perform preprocessing of the material. The upstream container 7 comprises and inlet IN to introduce the incoherent plastics into the apparatus 1.

[0065] The upstream container 7 may be configured, in particular, to introduce the incoherent plastics from the top and to release the incoherent plastics from the bottom.

[0066] The apparatus 1 may comprise, in particular, means for generating a flow of a process gas that is able to pass through the incoherent plastics in the upstream container 7 (for example, from the bottom to the top). This means for generating a flow may comprise, in particular, a blower or a fan 8 arranged in a supply conduit of the process gas, and a heater 9 to heat the process gas supplied to the upstream container 7.

[0067] The apparatus 1 may comprise, in particular, transfer means 10 for transferring the incoherent plastics from the upstream container 7 to the container 2. This transfer means 10 may comprise, in particular, pneumatic conveying means, or mechanical conveying means (belt, vibrating, bucket, slide conveying means, etc), or conveying means of still yet another type, in general conveying means suitable for conveying loose material.

[0068] The apparatus 1 may comprise, in particular, a downstream container 11 (for example, a hopper) configured to contain incoherent plastics and to perform postprocessing of the material. The downstream container 11 comprises an outlet OUT for extracting the incoherent plastics from the apparatus 1.

[0069] The downstream container 11 may be configured, in particular, to introduce the incoherent plastics from the top and to release the incoherent plastics from the bottom.

[0070] The apparatus 1 may comprise, in particular, means for generating a flow of aprocess gas that is able to pass through the incoherent plastics in the downstream container 11 (for example, from the bottom to the top).

[0071] This means for generating a flow may comprise, in particular, a dehumidifying device 12 configured to dehumidify the process gas that circulates in a supply circuit and is provided with means (blower or fan) for circulating the process gas in the supply circuit.

[0072] The supply circuit may comprise, in particular, a closed circuit that takes the used process gas from the downstream container 11 and returns the (in particular dehumidified) process gas to the downstream container 11. The dehumidifying device 12 may comprise, in particular, an air dehumidifier, for example of the adsorption type, of mechanical-refrigerating type, or of yet another type. It is possible to provide, to substitute the dehumidifying device 12, a handling device for handling the process gas (without the humidity extraction function).

[0073] The apparatus 1 may comprise, in particular, transfer means for transferring the incoherent plastics from the container 2 to the downstream container 11. This transfer means may comprise, in particular, pneumatic conveying means, or mechanical conveying means (belt, vibrating, bucket, slide conveying means, etc), or conveying means of still yet another type that is suitable for conveying loose material.

[0074] The apparatus 1 may comprise, in particular, temperature sensor means T1 for measuring a temperature in the container 2. The apparatus 1 may comprise, in particular, pressure sensor means P for measuring a pressure in the container 2.

[0075] The apparatus 1 may comprise, in particular, temperature sensor means T2 for measuring a temperature in the expulsion conduit 3. The apparatus 1 may comprise, in particular, substance sensor means G arranged in the expulsion conduit 3 of the gas that is aspired by the container 2 placed in a vacuum (as in this embodiment) and / or arranged in the container 2. The substance sensor means G is configured to measure a content (as a percentage) of at least one undesired substance (for example, humidity, one or more contaminants, one or more odorous substances, etc) that it is desired to extract from the processed material. The substance sensor means G may comprise, in particular, humidity sensor means and / or contaminant sensor means (for example sensor means of gas chromatographic type) and / or odour sensor means (for example an electronic nose).

[0076] The apparatus 1 may comprise, in particular, weight sensor means LC arranged for measuring a weight of the container 2. The weight sensor means LC may comprise, in particular, one or more load cells. The weight sensor means LC enable a weight differenceof the container 2 to be determined between an extraction start step and an extraction end step. In a batch type process, this difference in weight may be correlated with a quantity of extracted substances.

[0077] The apparatus 1 may comprise, in particular, level sensor means K arranged for measuring a level of incoherent material present in the container 2. The level sensor means K may be, for example, of radar type, or of capacitive type, or of another suitable type for measuring the level of solid incoherent material inside a receptacle. The level sensor means K may be configured, in particular, for continuously measuring the level of material in the container 2. The level sensor means K may comprise, in particular, one or more reference rods arranged vertically in the containing volume of the material in the container 2 (for example, fitted to an upper wall of the container 2) and sensor means configured to read remotely (for example, with a radar system or another type of system) the level of material along the extent of each reference rod, in particular through at least one transparent window extending vertically on a side wall of the container 2. The level sensor means K may be configured, in particular, so as not to interfere with the electromagnetic field generated by the radio frequency electrodes, without altering the field or falsifying the detection because of the action of the field. It is possible for the level sensor means K to comprise, in particular, in addition to or in replacement of level sensor means with continuous measuring, level sensor means with discrete measuring, for example comprising two or more material presence sensors arranged in the container 2 and spaced apart from one another in a vertical direction. In a batch type process, the level sensor means K may be used, in particular, to determine a quantity or a volume of processed material in the container 2 to ensure that the volume of material that is discharged from the upstream container 7 may be received by the container 2. In particular, the level sensor means K may be used to determine a difference in the level of material in the container 2 between two operating steps of a work cycle, for example an initial step of loading and a final step of extracting the material.

[0078] The apparatus 1 may comprise, in particular, humidity sensor means arranged for measuring humidity content in the material in the container 2 and / or in the gas evacuated from the container 2 to generate the vacuum.

[0079] It is possible to correlate the difference in weight of the processed material (determined by the weight sensor means LC) and the quantity of humidity removed from the material (determined by the humidity sensor means) to ascertain the quantity ofcontaminant substances or odorous substances actually removed.

[0080] A method is now disclosed for processing incoherent plastics that, in particular, may be actuated using the apparatus 1.

[0081] The method comprises the step of subjecting the incoherent plastics to radio frequency waves inside a container 2 inside which process pressure lower than ambient pressure is present.

[0082] The radio frequency waves may be generated, in particular, by at least one electrode 5 in contact with the material in the container 2.

[0083] The method may comprise, in particular, the step of feedback regulation of the process pressure and / or the radio frequency waves based on an undesired substance content detected in the container 2 or detected in a gas that is aspirated and exits the container 2 to generate the process pressure.

[0084] The method may comprise, in particular, the steps of regulating the radio frequency waves to maintain a constant temperature and feedback regulate the process pressure based on an undesired substance content detected in the container 2 or in a gas that is aspirated to generate the process pressure (for example, by increasing the vacuum intensity in the container 2 if the detected content of the undesired substance is greater than a determined threshold value and decreasing the vacuum intensity in the container 2 if the detected content of the undesired substance is less than a given threshold value).

[0085] The method may comprise, in particular, the steps of adjusting the process pressure to maintain a constant pressure in the container 2 and feedback regulate the radio frequency waves based on an undesired substance content detected in the container 2 or in a gas that is aspirated to generate the process pressure (for example, by increasing the intensity of the radio frequency waves of the detected content if the undesired substance is greater than a determined threshold value and decreasing the intensity of the radio frequency waves if the detected content of the undesired substance is less than a given threshold value).

[0086] The method may comprise, in particular, the step of controlling a process time, during which the material is processed in the container 2, based on an undesired substance content detected in the container 2 or in a gas that is aspirated to generate the process pressure.

[0087] The radio frequency waves may be controlled, in particular, with a frequency comprised between 300 KHz and 300 GHz. The radio frequency waves may be controlled,in particular, at a frequency comprised between 1 MHz and 1 GHz, or between 10 MHz and 100 MHz, or between 1 MHz and 50 MHz, or between 10 MHz and 50 MHz, or between 1 MHz and 100 MHz, or between 300 KHz and 200 MHz, or between 300 KHz and 100 MHz, or between 300 KHz and 50 MHz.

[0088] The radio frequency waves may be controlled, in particular, so as to maintain a desired value of a temperature measured inside the container 2. The desired value may be, in particular, greater than 60 °C, or greater than 70 °C, or greater than 80 °C. The desired value may be, in particular, lower than 150 °C, or lower than 140 °C, or lower than 130 °C.

[0089] The process pressure in the container 2 may be controlled, in particular, so as to be lower than 7.5 x 104absolute Pascal, or lower than 5 x 104absolute Pascal, or lower than 2.5 x 104absolute Pascal, or lower than 1.4 x 104absolute Pascal. The process pressure in the container 2 may be controlled, in particular, so as to be greater than 2 x 103absolute Pascal.

[0090] The process time, during which the material is processed in the container 2, may be, in particular, comprised between 15 and 150 minutes, or comprised between 30 and 150 minutes, or comprised between 60 and 150 minutes, or comprised between 15 and 120 minutes, or comprised between 30 and 120 minutes, or comprised between 60 and 120 minutes.

[0091] It is possible, in particular, for the incoherent plastics to be introduced inside the container 2 at a material temperature that is higher than an ambient temperature, in particular at a material temperature that is higher than 50 °C, or greater than 60 °C, or greater than 70 °C.

[0092] The incoherent plastics may comprise, in particular, post-consumer recycled plastics in the form of pelletized granules.

[0093] Using the vacuum in combination with the radio frequency is particularly effective for dehumidifying and / or decontaminating and / or deodorizing and / or upgrading plastics in the form of pelletized granules (modelling by extrusion). The granules may be processed on the line directly after extrusion or subsequently after cooling. The process with vacuum and radio frequency enables, in particular, contaminant residues that may be still present in the pelletized granules to be reduced with significant efficacy and great efficiency. The process with vacuum and radio frequency is actuatable and effective with relatively reduced energy consumption and environmental impact. The process with vacuum and radio frequency may be used to process non-food grade granules so as toobtain food-grade granules. The process with vacuum and radio frequency enables, in particular, food-grade granules to be obtained from granules with a recycled concentration greater than 10% by weight.

[0094] It has been found that the combination of vacuum and radio frequency promotes the migration of undesired substances (in particular, high-boiling substances) from the heart of the granule to the surface, also at relatively low process temperatures. The process with vacuum and radio frequency permits effective extraction even at relatively low temperatures of the material. The process with vacuum and radio frequency reduces, or substantially eliminates, the phenomenon of oxidation and / or thermal degradation of the plastics. Owing to the combination of vacuum and radio frequency, the vacuum may be maintained continuously and the energy consumption used to generate the vacuum may be relatively reduced. The process in question reduces processing time drastically.

[0095] It has been further found that the control of the radio frequency (in particular, the control of the power supplied to the radio frequency generator) based on temperature signals advantageously enables the process of extracting undesired substances to be accelerated for the same degree of vacuum used. As has been seen, it is possible to feedback control the degree of vacuum and / or the power of radio frequency based on the measurement of the composition of the mixture (air with humidity and / or contaminants and / or odorous substances and / or other undesired substances) that is aspired to generate the negative process pressure. Further, also the processing time may be controlled based on the measurement of the composition of the mixture extracted to generate the vacuum. Processing may be stopped, in particular, when a given threshold value is reached of the content of a given substance that it is desired to extract (for example, to obtain a foodgrade polymer to be recycled, more processing time will be necessary).

[0096] As said, if the undesired substance to be extracted is water, it is possible, by analyzing the humidity of the mixture extracted to generate the vacuum, to ascertain when the material being processed has reached a desired degree of dehumidification, for example a suitable degree for a subsequent moulding process.

[0097] As has been seen, it is possible for the main stage of the process (vacuum stage with radio frequency) to be preceded by a process stage upstream and be followed by a process stage downstream. The stage upstream may comprise preheating of the material with a process gas at a set temperature and a given flowrate. The stage upstream maycomprise, in other embodiments that are not shown, a process of producing (in particular, by extrusion) the plastic granule (in particular, from at least partially recycled plastics), connected directly on the line to the main stage (with radio frequency and vacuum), which enables a preceding heat treatment to be exploited to process a granule that is already at a temperature. The stage downstream of the main stage (with radio frequency and vacuum) may be used, in particular, in order for the plastic granules to be available at a desired degree of temperature and / or dehumidification, for example a degree of temperature and dehumidification that is suitable for a subsequent transformation process.

Claims

CLAIMS1. Method for processing incoherent plastics, wherein said plastics are subjected to radio frequency waves inside a container (2) at a process pressure lower than an ambience pressure.

2. Method according to claim 1, wherein said process pressure is feedback regulated based on a detected content of an undesired substance; said undesired substance content being detected, in particular, in said container (2) or in a gas that is aspirated to generate said process pressure.

3. Method according to claim 1 or 2, wherein said radio frequency waves are feedback regulated based on a detected content of an undesired substance; said undesired substance content being detected, in particular, in said container (2) or in a gas that is aspirated to generate said process pressure.

4. Method according to any one of the preceding claims, wherein a process time is controlled based on a detected content of an undesired substance; said undesired substance content being detected, in particular, in said container (2) or in a gas that is aspirated to generate said process pressure.

5. Method according to any one of the preceding claims, wherein said radio frequency waves have a frequency comprised between 300 KHz and 300 GHz, or a frequency comprised between 1 MHz and 1 GHz.

6. Method according to any one of the preceding claims, wherein said radio frequency waves have a frequency comprised between 10 MHz and 100 MHz, or between 1 MHz and 50 MHz, or between 10 MHz and 50 MHz, or between 1 MHz and 100 MHz.

7. Method according to any one of the preceding claims, wherein said radio frequency waves have a frequency comprised between 300 KHz and 200 MHz, or between 300 KHz and 100 MHz, or between 300 KHz and 50 MHz.

8. Method according to any one of the preceding claims, wherein said process pressure is lower than 7.5 x 104absolute Pascal, or 5 x 104absolute Pascal, or 2.5 x 104absolute Pascal, or 1.4 x 104absolute Pascal.

9. Method according to any one of the preceding claims, wherein said process pressure is greater than 2 x 103absolute Pascal.

10. Method according to any one of the preceding claims, wherein a process time, during which said plastics are processed in said container (2), is comprised between 15 and150 minutes, or is comprised between 30 and 150 minutes, or is comprised between 15 and 120 minutes, or is comprised between 30 and 120 minutes.

11. Method according to any one of the preceding claims, wherein said radio frequency waves are generated by at least one electrode (5) that is arranged inside said container (2) and is in contact with said plastics; said at least one electrode (5) being, in particular, immersed in said plastics and at least partly or completely surrounded by said plastics.

12. Method according to any one of the preceding claims, wherein said radio frequency waves are controlled so as to maintain a desired value of a temperature measured inside said container (2); said desired value being, in particular, greater than 80 °C and / or lower than 150 °C.

13. Method according to any one of the preceding claims, wherein said incoherent plastics are introduced inside said container (2) at a material temperature that is higher than an ambient temperature, in particular at a material temperature that is higher than 50, or 60, or 70 °C.

14. Method according to any one of the preceding claims, wherein said incoherent plastics comprise post-consumer recycled plastics in the form of pelletized granules.

15. Method according to any one of the preceding claims, comprising the steps of detecting at least one weight of said container (2) and at least one quantity of humidity removed from said plastics, and determining a quantity of contaminating and / or odorous substances removed from said plastics based on said detecting.

16. Apparatus for processing incoherent plastics, comprising at least one container (2) configured to contain incoherent plastics, means for generating a vacuum inside said container (2), and a radio frequency device configured to subject the incoherent plastics inside said container (2) to radio frequency waves.

17. Apparatus according to claim 16, wherein said radio frequency device comprises at least one electrode (5) connected to a radio frequency generator (6) and arranged inside said container (2) so as to be able to be in contact with the incoherent plastics contained therein.

18. Apparatus according to claim 16 or 17, comprising an upstream container (7) for incoherent plastics, means for generating a flow of a process gas that is able to pass through the incoherent plastics in said upstream container (7), and transfer means (10) for transferring the incoherent plastics from said upstream container (7) to saidcontainer (2).

19. Apparatus according to any one of claims 16 to 18, comprising a downstream container (11) for incoherent plastics, means for generating a flow of a process gas that is able to pass through the incoherent plastics in said downstream container (11), and transfer means for transferring the incoherent plastics from said container (2) to said downstream container (11).

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