Method and apparatus for processing incoherent plastics

Abstract

A method and apparatus for processing incoherent plastics are described, wherein the incoherent plastics are introduced into a vacuum container where a first extraction of acetaldehyde present in the plastics occurs and is then transferred to an extraction hopper where the plastics are passed through by a process gas and where a second extraction of residual acetaldehyde still present in the plastics occurs, and wherein at least one operating parameter of the process is feedback-controlled based on an acetaldehyde content detected in a gas at the outlet of the vacuum container and / or the extraction hopper.

Description

Method and apparatus for processing incoherent plasticsBackground of the invention

[0001] The invention concerns a method and apparatus for processing incoherent plastics, namely in the form of granules and / or microgranules and / or pellets and / or powder and / or flakes or the like. The invention may serve, in particular, to reduce the acetaldehyde content in recycled plastics.

[0002] Specifically, but not exclusively, the invention may be usefully applied in fields involving the transformation of incoherent plastics (polymer granules), such as injection moulding, extrusion, thermoforming, calendering, etc.

[0003] In the plastics processing industry, it may be necessary to limit, reduce, eliminate, or correct the acetaldehyde content of the finished product. This occurs, for example, in the food packaging field or in the production of preforms used for the production of beverage bottles.

[0004] Furthermore, the market increasingly requires the recovery of plastics. It is well known, particularly in the food packaging field, that finished products are made with recycled polymer granules — for example, polyethylene terephthalate (PET) — mixed in varying percentages with virgin resin. The recycled plastics are typically selected and processed through plasticization and pelletization. However, the use of recycled granules does not guarantee consistent characteristics of the plastics exiting an extrusion and / or regrading line.

[0005] The acetaldehyde present in the PET melting process remains trapped in the matrix of the cooled granule, which causes acetaldehyde to be released into the finished product, i.e., the packaging (for example, a plastic container), resulting in organoleptic alterations to the packaged substance.

[0006] Patent publication EP 4205933 Al describes a method for processing incoherent plastics which provides for controlling a parameter indicative of the moisture content of a process gas entering a container containing the incoherent plastics based on signals provided by olfactory sensor means which detect a value indicative of the acetaldehyde content in the process gas exiting the container, in particular by decreasing the moisture content of the process gas entering the container if the olfactory sensor means detect an increase in the acetaldehyde content in the process gas exiting the container.

[0007] A drawback of the prior art is that R PET (recycled PET) granule production systems do not allow for effective reduction of acetaldehyde content in the plastics of thefinished product.

[0008] Known methods for acetaldehyde reduction require the use of lengthy and energy-intensive thermal processes. Treatment times for large production can even exceed ten hours, with a high volume of plastics used and considerably demanding processes. For example, a plant currently capable of processing 2000 kg / h of plastics operates with a plastics residence time of ten hours in a treatment volume of approximately 24,000 dm3and with a process fluid flow rate exceeding 5000 m3 / h.Summary of the Invention

[0009] An object of the invention is to provide a method and apparatus for the reduction and / or elimination of aldehydes, particularly acetaldehyde, from incoherent plastics, particularly recycled PET and / or R PET.

[0010] An advantage is that it allows for a high reduction of aldehydes with relatively low energy consumption.

[0011] An advantage is that it allows incoherent plastics obtained from non-chemical recycling to be made economically competitive with virgin plastics and / or plastics obtained from chemical recycling.

[0012] An advantage is that it reduces treatment time and / or reduces the size of the treatment plant.

[0013] According to one aspect of the invention, a method for reducing an aldehyde content in incoherent plastics comprises the step of generating a vacuum in a container containing the incoherent plastics, the step of detecting an aldehyde content in a gas from the incoherent plastics during or after said step of generating a vacuum, and the step of controlling at least one operating parameter based on the detected aldehyde content. “Vacuum” means a pressure less than atmospheric pressure.

[0014] The vacuum container may be installed online at the exit of an extrusion and pelletization line, from which the incoherent plastics can be removed while hot (and at least partially crystallized) and then fed directly into the container. This allows for a reduction in treatment time by activating the aldehyde extraction process early, as the plastics are already at a temperature suitable for promoting aldehyde extraction.

[0015] The vacuum container may be installed offline, in which case the method may include a preheating step for the incoherent plastics before their introduction into the container.

[0016] The method in question may be controlled to reduce the residual acetaldehydelevel in a mass of R PET pellets to less than 1 ppm.

[0017] The method involves a vacuum step, i.e., a step in which the substance (aldehyde, particularly acetaldehyde) is extracted using vacuum, possibly combined with a flushing step, i.e., a step in which the substance (aldehyde, particularly acetaldehyde) is extracted using a flow of process gas (drying and / or dehumidification gas). The method may include controlling one or more operating parameters (related to vacuum and / or related to the flow of process gas) based on a detected value of the substance content.

[0018] The substance (aldehyde) content may be detected by olfactory sensor means (electronic nose) arranged to detect the substance (aldehyde, particularly acetaldehyde) content in the gas exiting from a suction line connected to the vacuum container, i.e., a suction line where an actuator (vacuum pump) operates, generating vacuum in the container.

[0019] The method involves feedback control of at least one operating parameter (e.g., the vacuum level in the container) based on the detected substance content, in particular based on signals provided by the olfactory sensor means.

[0020] The boiling point of acetaldehyde is approximately 20.2 °C (68.4 °F) at standard atmospheric pressure (1 atm). At 100 mbar absolute (i.e., a vacuum of -900 mbar) referred to atmospheric pressure, the boiling point of acetaldehyde drops to approximately -11.7 °C. This significant reduction from the standard boiling point promotes the rapid diffusion and evaporation of acetaldehyde and thus its extraction.

[0021] The use of vacuum, particularly when combined with the use of a process gas flow before or after the vacuum stage, has been found to reduce energy consumption for the same result, where the result is the achievement of a certain residual value of the substance (acetaldehyde) in the incoherent plastics (e.g., a residual acetaldehyde value below the 1 ppm limit).

[0022] The method may include a preheating step of the plastics to a temperature between 90 °C and 170 °C, if the plastics are not already available at the desired temperature.

[0023] The vacuum value used for aldehyde extraction may be between -750 mbar (250 mbar absolute) and -950 mbar (50 mbar absolute).

[0024] The method may comprise, in particular, a fluidization step (which may also be performed simultaneously with the vacuum generation step) in which a flow of an auxiliary gas (air or nitrogen) is fed to an inlet of the container (in particular, an inletlocated in a lower area of the container, in particular lower than the gas outlet connected to the suction line) to pass through the plastics (in particular, R PET granules) in the container and extract the substance (acetaldehyde) present on the external surface of the R PET granules.

[0025] The method may comprise a cooling step of the processed plastics, in particular when the plastics are to be packaged “in situ” at a relatively low temperature (typically less than 100°C).

[0026] Each of the above-mentioned method steps, in particular the steps where the extraction of the substance (aldehyde) takes place, may be carried out in a respective plastics treatment container, or it is possible to provide that two, three or more of the above-mentioned method steps, in particular the steps where the extraction of the substance (aldehyde) takes place, are carried out in the same treatment container.

[0027] The extraction method may include, in particular, the step of controlling at least one operating parameter (for example, the duration of one or more method steps or the overall duration of the extraction method, the vacuum level in the container, a treatment temperature, a process gas flow, etc.) based on a value of the substance content (aldehyde, particularly acetaldehyde) present in the incoherent plastics at the inlet of the vacuum container.

[0028] In this regard, it should be noted that the incoherent plastics, to be processed with the extraction method in question, may come from a recycling and decontamination plant (for example, for R PET) that supplies plastics with a variable and unpredictable value of the acetaldehyde content (value typically ranging between 3 ppm and 40 ppm, or between 40 ppm and 60 ppm) depending on the various production conditions.

[0029] The method may comprise the step of extracting the substance (aldehyde) using a process gas flow that passes through the incoherent plastics. The process gas flow may be configured as an open circuit. Specifically, the process gas may include air drawn from the environment and released into the environment. The method may include detecting the content of the substance (aldehyde) present in the process gas (air) used to extract the aldehyde from the plastics.

[0030] It is possible to provide a process gas flow configured as a closed circuit. The closed circuit may comprise, in particular, adsorption means configured to retain the substance (aldehyde or acetaldehyde) extracted from the process gas that has passed through the plastics. The adsorption means may comprise, in particular, molecular sieves(in the form of towers or wheels).

[0031] In the presence of amorphous or semi-crystalline incoherent plastics, it is possible to envisage the use of an extraction hopper equipped with mixing means configured to mix the plastics. The mixing means may comprise, in particular, a rotor with a rotation axis (vertical) and radial elements (spokes, blades, etc.). The mixing means serves to keep the plastics in motion in order to avoid sticking phenomena and allow proper crystallization of the amorphous or semi-crystalline material.

[0032] According to one aspect of the invention, it is possible to envisage the use of a fluidized bed system where the incoherent plastics are processed upstream of the container under vacuum. The fluidized bed system comprises a conveyor bed on which the incoherent plastics are kept in continuous motion by means of a flow that produces a sort of floating of the plastics above the conveyor bed itself. The conveyor bed may comprise, in particular, a horizontal plane and / or a plane slightly inclined toward the outlet. The fluidized bed system is configured to generate a continuous movement of the incoherent plastics from one inlet to the other.

[0033] The fluidized bed system is configured so that the movement of the incoherent plastics from an inlet to an outlet of the fluidized bed system has a predominantly horizontal component of the motion of the material particles (for example, unlike a hopper where the material is not fluidized and is moved by gravity and the predominantly vertical component of the motion of the particles).

[0034] The fluidized bed system may be arranged in a process line, in particular, downstream of an extrusion or pelletizing device and / or upstream of the vacuum vessel. The use of a fluidized bed system arranged before the vacuum vessel and / or after the extrusion or pelletizing device has several advantages. First, it reduces the treatment duration (experimental tests have shown a reduction from 6 hours without a fluidized bed to approximately 3.5 hours with a fluidized bed, for the same acetaldehyde extraction). Furthermore, it reduces the risk of granule sticking, allowing the processed material to have lower crystallinity, which favors acetaldehyde extraction. It has also been observed that the continuous and massive movement of the incoherent material in the fluidized bed ensures that the entire surface of each particle of incoherent material is hit by essentially the same amount of gas, thus also facilitating acetaldehyde extraction. Fluidized bed treatment also reduces the saturation of the treatment environment.

[0035] It has also been observed that treatment in a fluidized bed using a heatedfluidization gas (specifically, a fluidization gas at a temperature equal to or higher than the temperature of the incoherent plastics at the inlet to the fluidized bed or at the outlet from the extrusion or pelletization device) allows the incoherent plastics to exit the fluidized bed in a condition that promotes aldehyde extraction in the subsequent stages of the extraction process. It has also been seen that the use of a heated gas in the fluidized bed ensures a nearly constant extraction of the aldehyde even in the subsequent steps of the extraction process when the absolute aldehyde content has decreased.

[0036] According to one aspect of the invention, a method for reducing the content of at least one substance, particularly an aldehyde, present in incoherent plastics comprises the steps of processing incoherent plastics in a processing device, transferring the incoherent plastics from the processing device to a container such that the container receives the incoherent plastics at a temperature above room temperature, and generating a vacuum in the container. The processing device may comprise, in particular, an extrusion or pelletization device and / or a fluidized bed system.

[0037] The substance present in the incoherent plastics and whose content is reduced may include, in particular, an aldehyde (e.g., acetaldehyde), although it is possible to foresee that such a substance may include other substances or groups of substances, such as moisture, total organic carbon (TOC), one or more volatile organic compounds (VOC), benzene, limonene, methane, etc.Brief description of the drawings

[0038] The invention may be better understood and implemented with reference to the attached drawings, which illustrate an exemplary and non-limiting embodiment thereof, in which:Figure 1 is a vertical elevation diagram of a first example of an apparatus in accordance with the present invention;Figure 2 is a vertical elevation diagram of a second example of an apparatus in accordance with the present invention;Figure 3 is a vertical elevation diagram of a third example of an apparatus in accordance with the present invention.Detailed Description

[0039] The three examples of treatment apparatus illustrated in the above-mentioned figures are described below.Example 1

[0040] The first example of a treatment apparatus for reducing the acetaldehyde content present in incoherent plastics (Figure 1) comprises an extrusion or pelletizing device 1 configured for the extrusion or pelletizing of plastics. The extrusion or pelletizing device 1 may be used, in particular, for the extrusion or pelletization of plastics containing at least a percentage of recycled consumer plastics (PCR plastics). The extrusion or pelletizing device 1 may be used, in particular (as in this example), for the extrusion or pelletization of R PET.

[0041] The extrusion or pelletizing device 1 is configured so that the incoherent plastics exiting the extrusion or pelletizing device 1 have a desired degree of crystallinity (for example, greater than 10%, or greater than 15%, in particular between 15% and 25%).

[0042] In particular, the desired degree of crystallinity should be high enough to ensure the substantial absence of sticking phenomena, caused by the excessive presence of an amorphous step, during a subsequent heat treatment, as will be explained later in the description.

[0043] The extrusion or pelletizing device 1 is configured so that the incoherent plastics at the output of the extrusion or pelletizing device 1 has a desired temperature, in particular a temperature between 90 °C and 170 °C, or between 100 °C and 170 °C, or between 120 °C and 170 °C, or higher than 90 °C, or higher than 100 °C, or higher than 120 °C.

[0044] The treatment apparatus shown in Figure 1 comprises a first storage container 2 that receives the incoherent plastics exiting the extrusion or pelletization device 1 and acts as a storage tank for the plastics.

[0045] The first storage container 2 is equipped with a temperature sensor T for measuring the temperature of the incoherent plastics contained in the first storage container 2. The first storage container 2 is equipped with a level sensor L for measuring the level reached by the incoherent plastics contained in the first storage container 2.

[0046] The first storage container 2 is equipped with a lower outlet for the extraction of the plastics and a closing device 3 configured to open and close the lower outlet upon command of actuator means controlled by control means (electronic and programmable) with which the treatment apparatus is equipped. The control means may include, in particular, a PLC. The control method of the treatment apparatus is governed by control software.

[0047] The treatment apparatus comprises a vacuum container 4 configured to receivethe plastics exiting from the first accumulation container 2. The treatment apparatus comprises actuator means 5 (e.g., a vacuum pump) configured to generate a vacuum inside the vacuum container 4 via a gas outlet line. The gas outlet line is connected to a gas outlet of the vacuum container 4, which is located in an upper area of the vacuum container 4. The actuator means 5 for generating the vacuum is controlled in such a way as to allow adjustment of the degree of vacuum generated inside the vacuum container 4. The actuator means 5 may include, in particular, a vacuum pump controlled by a variable speed drive (e.g., an inverter).

[0048] The treatment apparatus comprises a substance sensor S configured to detect the content of at least one aldehyde in a gas exiting the vacuum container 4. The substance sensor S is arranged in the gas outlet line where the actuator means 5 operates. In particular, the substance sensor S is arranged downstream of the actuator means 5 to generate the vacuum. The substance sensor S may comprise, in particular, an olfactory sensor (electronic nose). The substance sensor S may be configured, in particular, to detect the content of acetaldehyde. The substance sensor may be configured, in particular, to detect the content of other substances, in addition to an aldehyde (acetaldehyde), for example to detect the content of total organic carbon (TOC) and / or the content of one or more volatile organic compounds (VOC) and / or the content of total volatile organic carbon (TVOC).

[0049] The vacuum container 4 is equipped with a temperature sensor T for measuring the temperature of the plastics contained in the vacuum container 4. The vacuum container 4 is equipped with a level sensor L for measuring the level reached by the plastics contained in the vacuum container 4. The vacuum container 4 is equipped with a pressure sensor P for measuring the pressure inside the vacuum container 4.

[0050] The treatment apparatus comprises a fluidization device 6 operatively associated with the vacuum container 4. The fluidization device 6 comprises a gas inlet line for the introduction of an auxiliary gas (for example, air or nitrogen) inside the vacuum container 4. The gas inlet line introduces the auxiliary gas into a lower area of the vacuum container 4 so as to generate an upward current of gas that passes through most of the volume of the vacuum container 4. The gas inlet line is connected to a gas inlet of the vacuum container 4 located below the gas outlet of the vacuum container 4 connected to the gas outlet line.

[0051] The fluidization device 6 is configured so that the auxiliary gas has a specificdewpoint value (for example, a value between -80 °C and 0 °C). The fluidization device 6 may include, in particular, a heater H configured to heat the auxiliary gas to a desired temperature (for example, a temperature between 120 °C and 200 °C).

[0052] During operation of the treatment apparatus, while the vacuum container 4 is maintained at a vacuum, it is possible to activate the fluidization device 6 so as to generate a flow of auxiliary gas in the plastics inside the vacuum container 4, thus increasing the extraction capacity of the substance(s) to be extracted (acetaldehyde).

[0053] The auxiliary gas flow also improves the descent of the plastics inside the vacuum container 4, particularly to prevent the formation of bridges, holes, lumps, deposits, etc.

[0054] The combined action of the vacuum and the auxiliary gas flow improves the evacuation of acetaldehyde. The combined action of the vacuum and the auxiliary gas flow promotes the migration of acetaldehyde from the polymer matrix of the granule to the surface of the granule (in fact, the plastics are observed to ooze). It has been found that the acetaldehyde extraction capacity is greater the lower the degree of crystallinity of the plastics at the inlet of the vacuum container 4. It has been found that a degree of crystallinity of the plastics at the outlet of the extrusion or pelletizing device 1 of between 15% and 25% (in the case of R PET) can represent a valid compromise to balance the conflicting needs of obtaining a high extraction of acetaldehyde and of ensuring appropriate handling of the incoherent (granular) plastics.

[0055] The treatment apparatus may comprise, in particular, a heating device 7 configured to heat the incoherent plastics in the vacuum container 4. The heating device 7 may comprise a radio frequency device equipped with one or more electrodes E (for example electrodes E immersed at least partly in the mass of the plastics contained in the vacuum container 4) suitable for generating radio frequency waves (in particular with a frequency between 300 KHz and 300 GHz, or 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) suitable for heating the plastics. Heating the plastics, particularly by radio frequency, allows the desired temperature to be maintained inside the vacuum container 4 and provides a supply of thermal energy that promotes the extraction of acetaldehyde during the vacuum step.

[0056] The vacuum container 4 is equipped with a lower outlet for the extraction of the plastics and a closing device 3 configured to open and close the lower outlet uponcommand of actuator means controlled by the control means (electronic and programmable) of the treatment apparatus.

[0057] The treatment apparatus includes a pressure control system 8 that is located at the plastics inlet and at the plastics outlet of the vacuum container 4 and which is configured to allow the introduction of the plastics into the vacuum container 4 and the extraction of the plastics from the vacuum container 4. The pressure control system 8 may include, in particular, a system of controlled vacuum-tight shut-off valves.

[0058] The operation of the treatment apparatus involves loading a certain quantity of plastics into the vacuum container 4 (loading step), then maintaining a desired degree of vacuum inside the vacuum container 4 (in particular, a vacuum 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) for a treatment period in which the aforementioned quantity of plastics is processed (treatment step), and then the aforementioned quantity of processed plastics is evacuated (unloading step).

[0059] The treatment apparatus in Figure 1 comprises a second storage container 2 that receives the plastics exiting the vacuum container 4 and acts as a storage tank for the plastics.

[0060] The second storage container 2 is equipped with a temperature sensor T for measuring the temperature of the plastics contained in the second storage container 2. The second storage container 2 is equipped with a level sensor L for measuring the level reached by the plastics contained in the second storage container 2. The second storage container 2 is equipped with a lower outlet for the extraction of the plastics and a closing device 3 configured to open and close the lower outlet upon command of actuator means controlled by the control means (electronic and programmable) of the treatment apparatus.

[0061] The plastics exiting the second storage container 2 may be transported to a cooling zone 9 where the plastics can be cooled. Cooling may be performed, in particular, by means of a flow of a cooling gas (for example, a flow in an open circuit). The cooling gas may comprise, in particular, dehumidified air.

[0062] The plastics exiting the second storage container 2 may be transported (before being sent to the cooling zone 9, if applicable) to an extraction hopper 10 where the plastics can be passed through by a flow of a process gas (flushing phase). The flushing step is optional.

[0063] The flushing step may be performed based on a detected acetaldehyde contentin the plastics, specifically a value detected in the plastics exiting the extrusion or pelletizing device 1. For example, the flushing step is performed if the detected acetaldehyde content in the plastics exiting the extrusion or pelletizing device 1 is greater than 15 ppm and is not performed if the aforementioned value is less than 15 ppm, or it is performed if the aforementioned value is in the range of 15 to 30 ppm and is not performed if the aforementioned value is outside the range of 15 to 30 ppm.

[0064] The process gas flow in this flushing step may be in an open circuit (not illustrated) or in a closed circuit (as in the example illustrated). The closed circuit allows for the recovery of a portion of the energy used. The closed circuit may include, as in the example shown in Figure 1, a dehumidification system 11 for dehumidifying the process gas. The dehumidification system 11 may include, in particular, molecular sieves 12 suitable for performing specific adsorption for acetaldehyde. The molecular sieves 12 may be used, in particular, in the form of adsorption towers (for example, two towers arranged in parallel and controlled with alternating adsorption and regeneration phases), or in the form of an adsorption wheel.

[0065] A heater H may be arranged to heat the process gas at the inlet of the extraction hopper 10. The extraction hopper 10 may comprise, in particular, a dehumidification hopper. The extraction hopper 10 may comprise, in particular, a diffuser 13 (e.g., a diffuser cone) arranged in the internal volume of the extraction hopper 10, in contact with the plastics, to diffuse the process gas. The plastics exiting the extraction hopper 10 may be transported to the cooling zone 9.

[0066] The extraction hopper 10 is equipped with one or more temperature sensors T, for example, a temperature sensor T for measuring the temperature of the plastics in an intermediate height zone of the extraction hopper 10 and / or a temperature sensor T for measuring the temperature of the plastics in a lower zone of the extraction hopper 10 and / or a temperature sensor T for measuring the temperature of the process gas at a gas inlet of the extraction hopper 10 and / or a temperature sensor T for measuring the temperature of the process gas at a gas outlet of the extraction hopper 10. The extraction hopper 10 is equipped with a level sensor L for measuring the level reached by the plastics contained in the extraction hopper 10.

[0067] The extraction hopper 10 is equipped with at least one substance sensor S configured to detect the content of at least one aldehyde, in particular the content of acetaldehyde. The extraction hopper 10 is equipped, in particular, with a substance sensorS arranged to detect the content of the substance present in a process gas outlet line that connects a gas outlet of the extraction hopper 10 to a gas inlet of the process gas dehumidification system 11. The extraction hopper 10 is equipped, in particular, with a substance sensor S arranged to detect the content of the substance present in a process gas inlet line that connects a gas outlet of the dehumidification system 11 to a gas inlet of the extraction hopper 10. The extraction hopper 10 is equipped, in particular, with a substance sensor S arranged to detect the content of the substance present in the plastics, for example in the plastics located near the lower plastics outlet of the extraction hopper 10.

[0068] Also for the extraction hopper 10, as well as for the vacuum container 4, each substance sensor S may include an olfactory sensor (or electronic nose). Also for the extraction hopper 10, as well as for the vacuum container 4, each substance sensor S may be configured (i.e., characterized, set, or programmed) to detect acetaldehyde content.

[0069] Each substance sensor S may be configured, in particular, to detect other substances in addition to an aldehyde (acetaldehyde), for example, to detect the total organic carbon (TOC) content and / or the content of one or more volatile organic compounds (VOC) and / or the total volatile organic carbon (TVOC) content.

[0070] The aforementioned radio frequency heating step and the aforementioned flushing step are optional. The aforementioned radio frequency heating step and the aforementioned flushing step may be performed alternatively to each other. The aforementioned radio frequency heating step and the aforementioned flushing step may be performed in combination with each other or may both be omitted.

[0071] The first example of a treatment apparatus allows for continuous operation at the inlet and outlet, i.e., with a continuous flow of incoherent plastics at the inlet of the apparatus and a continuous flow of incoherent plastics at the outlet of the apparatus, and for batch operation at least in the intermediate vacuum phase, i.e., with a batch of intermediate plastics processed in the vacuum container, while still ensuring an adequate treatment time for each individual phase of the aldehyde extraction process.Example 2

[0072] The second example of a treatment apparatus for reducing the acetaldehyde content (Figure 2) presents some elements similar to those of the first example. For simplicity and clarity of explanation, the similar elements of different embodiments have been indicated with the same numbering.

[0073] The treatment apparatus shown in Figure 2 includes a storage system 14 (e.g.,at least one silo) for storing incoherent plastics.

[0074] In general, the incoherent plastics in this case comprise polymer granules with a relatively high degree of crystallinity. For this reason, it is envisaged to process the plastics before introducing it into a vacuum container 4. In particular, the incoherent plastics are processed in an extraction hopper 10. In particular, the process to which the incoherent plastics are subjected inside the extraction hopper 10 includes heating with a heated process gas (hot air).

[0075] The incoherent plastics are removed from the storage system 14 and fed to the extraction hopper 10. A vacuum transport system 15 (or other type of transport system) may be provided to transport the plastics from the storage system 14 to the extraction hopper 10.

[0076] In the extraction hopper 10, a flow of process gas (e.g., hot and / or dehumidified air) passes through the plastics. The process gas flow may be in an open or closed circuit.

[0077] In the example shown in Figure 2, the process gas flow is in a closed circuit. The closed circuit may include a dehumidification system 11. The dehumidification system 11 may include molecular sieves specifically designed to perform acetaldehyde adsorption. Molecular sieves may be used, in particular, in the form of adsorption towers (for example, two towers arranged in parallel and controlled with alternating adsorption and regeneration phases) or in the form of an adsorption wheel. A heater H may be installed to heat the process gas at the inlet of the extraction hopper 10.

[0078] The extraction hopper 10 may comprise, in particular, a dehumidification hopper. The extraction hopper 10 may comprise, in particular, a diffuser 13 (e.g., a diffuser cone) arranged in the internal volume of the extraction hopper 10, in contact with the plastics, to diffuse the process gas.

[0079] The plastics exiting the extraction hopper 10 are transported to a container system comprising at least three containers arranged in series with each other in a manner similar to the treatment apparatus of figure 1, i.e. a first accumulation container 2, a vacuum container 4 downstream of the first accumulation container 2 and a second accumulation container 2 downstream of the vacuum container 4. The container system in series arranged downstream of the extraction hopper 10 of Figure 2 is substantially similar to that described with reference to Figure 1 (arranged upstream of the extraction hopper 10).

[0080] The extraction hopper 10 is equipped with one or more temperature sensors T, for example a temperature sensor T for measuring the temperature of the plastics in an intermediate height zone of the extraction hopper 10 and / or a temperature sensor T for measuring the temperature of the plastics in a lower zone of the extraction hopper 10 and / or a temperature sensor T for measuring the temperature of the process gas at a gas inlet of the extraction hopper 10 and / or a temperature sensor T for measuring the temperature of the process gas at a gas outlet of the extraction hopper 10. The extraction hopper 10 is equipped with a level sensor for measuring the level reached by the plastics contained in the extraction hopper 10.

[0081] The extraction hopper 10 is equipped with at least one substance sensor S configured to detect a content of at least one aldehyde, in particular an acetaldehyde content. The extraction hopper 10 is provided, in particular, with a substance sensor S arranged to detect the content of the substance present in a process gas outlet line that connects a gas outlet of the extraction hopper 10 to a gas inlet of the process gas dehumidification system 11. The extraction hopper 10 is provided, in particular, with a substance sensor S arranged to detect the content of the substance present in a process gas inlet line that connects a gas outlet of the dehumidification system 11 to a gas inlet of the extraction hopper 10. The extraction hopper 10 may be provided, in particular, with a substance sensor S arranged to detect the content of the substance present in the plastics, for example in the plastics located near the lower plastics outlet of the extraction hopper 10.

[0082] Also for the vacuum container 4 and the extraction hopper 10 of the processing apparatus of Figure 2, as well as for the vacuum container 4 and the extraction hopper 10 of the processing apparatus of Figure 1, each substance sensor may comprise, in particular, an olfactory sensor (or electronic nose). Each substance S sensor may be specifically configured (i.e., characterized, set, or programmed) to detect acetaldehyde content. Each substance S sensor may be specifically configured to detect substances other than aldehyde (acetaldehyde), for example, total organic carbon (TOC) content and / or one or more volatile organic compounds (VOC) content and / or total volatile organic carbon (TVOC) content.

[0083] The operation of the treatment apparatus of Figure 2 involves the incoherent plastics being taken from the storage system 14 and introduced into the extraction hopper 10 where it is processed with a process gas (hot, dehumidified air), for example processgas at a temperature above 90 °C, or between 90 °C and 170 °C, or above 100 °C, or between 100 °C and 170 °C, or above 120 °C, or between 120 °C and 170 °C.

[0084] In this example, the process gas from the extraction hopper 10 is in a closed circuit. Even in the case of an open circuit, the operation of the treatment apparatus requires the plastics to be taken from the storage system 14 and introduced into the extraction hopper 10 where, in this case, the plastics are heated with a process gas (hot air), for example to a temperature above 90 °C, or between 90 °C and 170 °C, or above 100 °C, or between 100 °C and 170 °C, or above 120 °C, or between 120 °C and 170 °C. In the case of an open circuit, it is not necessary to provide a monitoring system controlled by a substance sensor S as in the example in Figure 2 with a closed circuit.

[0085] In this first process stage, which takes place in the extraction hopper 10, the plastics (with high crystallinity) are heated and passed through by a flow of process gas to obtain an initial extraction of aldehydes (particularly acetaldehyde), both in the case of a closed and open circuit.

[0086] The duration of the process (at a temperature above 90 °C, or 100 °C, or 120 °C, as mentioned) may be between 2 and 4 hours. Process control may include a preset duration (particularly in the case of an open circuit). Process control may include feedback control of at least one process parameter (e.g., flow rate and / or temperature of the process gas) based on real-time detection of the acetaldehyde content in the process gas by the substance sensor S (particularly in the case of a closed circuit). Process control may include termination of the process upon reaching a specific limit value, detected in real time, of the acetaldehyde content in the process gas and / or the plastics (particularly in the case of a closed circuit).

[0087] After treatment in the extraction hopper 10, the plastics (at a relatively high temperature, particularly above 90°C) pass into the vacuum stage inside the vacuum container 4, for example, using the same methods described for the treatment apparatus in Figure 1.

[0088] The extraction hopper 10 (both in the example in Figure 1 and in the example in Figure 2) may include, in particular, mixing means (not illustrated) configured to mix the plastics, particularly useful in the presence of incoherent amorphous or semi -crystalline plastics. Mixing devices may include, in particular, a rotor with a rotation axis (especially a vertical rotation axis) and radial elements (spokes, blades, etc.). Mixing devices serve to prevent sticking and allow proper crystallization of the amorphous or semi-crystallinematerial.

[0089] The second example of a treatment apparatus also allows for continuous operation at the inlet and outlet, i.e., with a continuous flow of incoherent plastics at the inlet of the apparatus and a continuous flow of incoherent plastics at the outlet of the apparatus, and for batch operation at least in the intermediate vacuum phase, i.e., with a batch of intermediate plastics processed in the vacuum container, while still ensuring an adequate treatment time for each individual phase of the aldehyde extraction process. Example 3

[0090] The third example of a treatment apparatus for reducing the acetaldehyde content in incoherent plastics (Figure 3) features some elements similar to those of the first example. For simplicity and clarity of explanation, similar elements from different embodiments have been indicated with the same numbering.

[0091] The processing apparatus comprises an extrusion or pelletizing device 1 configured for the extrusion or pelletization of plastics. The extrusion or pelletizing device 1 may be used, in particular, for the extrusion or pelletization of plastics containing at least a percentage of recycled consumer plastics (PCR plastics). The extrusion or pelletizing device 1 may be used, in particular (as in this example), for the extrusion or pelletization of R PET.

[0092] The extrusion or pelletizing device 1 is configured so that the incoherent plastics at the output of the extrusion or pelletizing device 1 has a desired degree of crystallinity (for example, greater than 10%, or greater than 15%, in particular between 15% and 25%). In particular, the desired degree of crystallinity should be the minimum degree that guarantees the substantial absence of sticking phenomena, caused by the excessive presence of an amorphous phase, during the subsequent heat treatment in a fluidized bed.

[0093] The extrusion or pelletizing device 1 is configured so that the incoherent plastics exiting the extrusion or pelletizing device 1 has a desired temperature, in particular a temperature between 90°C and 170°C, or between 100°C and 170°C, or between 120°C and 170°C, or higher than 90°C, or higher than 100°C, or higher than 120°C.

[0094] The treatment apparatus comprises a fluidized bed system 16 that receives the incoherent plastics exiting from the extrusion or pelletizing device 1 to subject the plastics to fluidization by passing a flow of a gas (e.g. air) through the incoherent material. The fluidized bed system 16 also acts as a storage tank for the plastics.

[0095] The fluidized bed system 16 comprises a container with an inlet for the incoherent plastics and an outlet for the incoherent plastics. The fluidized bed system 16 comprises an actuator 17 (e.g., a fan) configured to generate the flow of the fluidizing gas.

[0096] The fluidized bed system 16 comprises a conveyor plane on which the incoherent plastics are moved from the inlet to the outlet. It is possible to provide a conveyor plane that is permeable to the fluidizing gas and impermeable to the incoherent plastics. The conveyor plane may comprise, in particular, a horizontal plane and / or a plane slightly inclined towards the outlet. The fluidized bed system 16 may comprise, in particular, an upper screen that is permeable to the fluidizing gas and impermeable to the incoherent plastics to facilitate the exit of the fluidizing gas without dispersing the incoherent plastics.

[0097] The evacuation of aldehyde (acetaldehyde) is significantly increased if the fluidized bed system 16 uses a fluidizing gas at a temperature equal to or higher than the temperature of the incoherent plastics at the inlet to the fluidized bed system 16 (or at the outlet of the extrusion or pelletizing device 1).

[0098] The fluidizing gas velocity of the fluidized bed system 16, i.e., the speed at which the gas passes through the fluidized bed, may be, in particular, greater than 0.2 m / sec, or greater than 0.5 m / sec. The fluidizing gas velocity is set as a function of the dimensions of the fluidized bed system 16 (length, width, and thickness of the fluidized bed). Generally, there is an upper limit to the fluidizing gas velocity beyond which adequate transport of the incoherent plastics is not ensured (for example, it is necessary to prevent the incoherent plastics from being transported in flight outside the fluidized bed).

[0099] Experimentally, it has been shown that the extraction capacity of acetaldehyde from the surface of the granules, by heating all the granules in the fluidized bed to a temperature greater than 100 °C and maintaining a uniformly distributed temperature throughout the entire mass of the plastics processed thanks to the fluidized bed, is capable of reducing the acetaldehyde content from an initial value of approximately 10-15 ppm (at the inlet of the fluidized bed system 16) to a value of approximately 2 ppm after approximately 2 or 3 hours of treatment (at the outlet of the fluidized bed system 16).

[0100] The treatment apparatus of this third example may comprise, in particular, the same elements already described with reference to the first example, in which the fluidized bed system 16 is arranged, along the process line, downstream of the extrusion or pelletization device 1 and upstream of the first accumulation container 2.

[0101] It is possible to provide for the process step that takes place in the extraction hopper 10 to be omitted since this process step could be made superfluous by the fact that, thanks to the process step that takes place in the fluidized bed system 16, the incoherent plastics at the exit of the process step that takes place in the vacuum container 4 could already be sufficiently clean.

[0102] The fluidized bed system 16 may be controlled so that the transit time of the incoherent plastics from the inlet to the outlet of the fluidization vessel is between 30 and 60 minutes. The duration of the vacuum phase in the vacuum vessel 4 may be between 60 and 90 minutes. The duration of the final washing phase in the extraction hopper 10 may be between 60 and 120 minutes. Therefore, in this third example, the total treatment duration may be between 2.5 hours and 4.5 hours.

[0103] The action of the fluidizing gas (with buoyancy and continuous transport of the incoherent plastics with a predominantly horizontal transport direction), in addition to reducing the saturation of the treatment environment, allows for a drastic reduction in treatment time. Furthermore, the action of the fluidizing gas allows for a relatively low crystallinity of the incoherent plastics (a lower degree of crystallinity than examples 1 and 2 without a fluidized bed), since the fluidized bed keeps the plastics in constant motion and therefore reduces the risk of sticking. The lower crystallinity promotes aldehyde extraction. The fluidized bed, by keeping the incoherent plastics in constant motion, reduces contact between the granules (for example, compared to treatment in a hopper) and therefore allows essentially the entire surface of each individual granule to be covered by essentially the same amount of fluidizing gas (air), thus promoting aldehyde extraction.

[0104] The use of a fluidizing gas heated to an appropriate temperature in the fluidized bed (specifically, a temperature of at least 100 °C or a temperature equal to or higher than the temperature of the incoherent plastics at the inlet to the fluidized bed) allows for highly effective aldehyde extraction. Specifically, it maintains a nearly constant aldehyde extraction rate even when the residual aldehyde content is less than 4 ppm.

[0105] The third treatment apparatus also allows for continuous operation at the inlet and outlet, i.e., with a continuous flow of incoherent plastics at the inlet of the apparatus and a continuous flow of incoherent plastics at the outlet of the apparatus, and for batch operation at least in the intermediate vacuum phase, i.e., with a batch of intermediate plastics processed in the vacuum container, while still ensuring an adequate treatment time for each individual phase of the aldehyde extraction process.

Claims

CLAIMS1. Method for reducing a content of at least one aldehyde in incoherent plastics, said method comprising the steps of: generating a vacuum in a container (4) containing said incoherent plastics, detecting a content of said at least one aldehyde in a gas coming from said incoherent plastics during or after said step of generating a vacuum, and controlling at least one operating parameter based on said detected content.

2. Method according to claim 1, wherein said at least one controlled operating parameter comprises a value of said vacuum.

3. Method according to claim 2, wherein said value of said vacuum is maintained within a range between -750 mbar and -950 mbar.

4. Method according to any one of the preceding claims, wherein said at least one controlled operating parameter comprises at least one operating parameter of a heater (H) arranged to heat said incoherent plastics before said step of generating a vacuum; said incoherent plastics being, in particular, heated to a temperature higher than 90 °C, or between 90 °C and 170 °C before said step of generating a vacuum.

5. Method according to any one of the preceding claims, comprising the step of generating a flow of a process gas passing through said incoherent plastics before said step of generating a vacuum and / or after said step of generating a vacuum, said at least one controlled operating parameter being selected from the following group of parameters: a flow rate of said process gas, a temperature of said process gas, a time during which said process gas passes through said incoherent plastics.

6. Method according to claim 5, wherein said detecting step comprises detecting a content of said at least one aldehyde present in said process gas which has passed through said incoherent plastics.

7. Method according to claim 5 or 6, wherein said flow of a process gas is a flow of gas passing through said incoherent plastics in an extraction hopper (10) disposed upstream of said container (4) and / or in an extraction hopper (10) arranged downstream of said container (4).

8. Method according to claim 7, wherein said at least one controlled operating parameter comprises a residence time of said incoherent plastics in said extraction hopper (10) during which said process gas passes through said incoherent plastics.

9. Method according to any one of the preceding claims, wherein said controllingcomprises a feedback regulation.

10. Method according to any one of the preceding claims, wherein said at least one operating parameter is controlled such that said gas coming from said incoherent plastics during or after said step of generating a vacuum has a content of said at least one aldehyde which is lower than a predetermined value, in particular an acetaldehyde value lower than 1 ppm.

11. Method according to any one of the preceding claims, comprising the step of measuring at least an initial value of a content of said at least one aldehyde present in said incoherent plastics before said step of generating a vacuum, and the step of setting at least one operating parameter based on said at least initial measured value.

12. Method for reducing a content of at least one substance, in particular an aldehyde, present in incoherent plastics, in particular according to any one of the preceding claims, said method comprising the steps of introducing incoherent plastics into a container (4) and generating a vacuum in said container (4) which contains said incoherent plastics, said incoherent plastics being introduced into said container (4) at a temperature higher than ambient temperature or higher than 90 °C.

13. Method for reducing a content of at least one substance, in particular an aldehyde, present in incoherent plastics, in particular according to any one of the preceding claims, said method comprising the steps of in-line connecting a container (4) to an extrusion or pelletizing device (1) so that said container (4) receives incoherent plastics coming from said extrusion or pelletizing device (1) at a temperature higher than ambient temperature or higher than 90 °C, and generating a vacuum in said container (4) which contains said incoherent plastics.

14. Method for reducing a content of at least one substance, in particular an aldehyde, present in incoherent plastics, in particular according to any one of the preceding claims, said method comprising the step of generating a vacuum in a container (4) containing incoherent plastics, said container (4) being connected in-line to a fluidized bed system (16) to receive said incoherent plastics from said fluidized bed system (16) at a temperature higher than ambient temperature or higher than 90 °C.

15. Method according to claims 14 and 13, wherein said incoherent plastics are fluidized in said fluidized bed system (16) by a flow of a fluidizing gas at a temperature not lower than a temperature of said incoherent plastics exiting from said extrusion or pelletizing device (1).

16. Method according to claim 14 or 15, wherein said incoherent plastics are fluidized in said fluidized bed system (16) by a flow of a fluidizing gas at a temperature equal to or greater than 100 °C.

17. Method for reducing a content of at least one substance, in particular an aldehyde, present in incoherent plastics, in particular according to any one of the preceding claims, said method comprising the step of generating a vacuum in a container (4) containing said incoherent plastics, and the step of generating a flow of an auxiliary gas which is fed to an inlet of said container (4) and then passes through said plastics contained in said container (4) during said step of generating a vacuum; said auxiliary gas comprising, in particular, air or nitrogen.

18. Method according to claim 17, wherein said auxiliary gas is introduced into a lower zone of said container (4).

19. Method according to claim 17 or 18, wherein said auxiliary gas has a dewpoint value between -80 °C and 0 °C.

20. Method according to any one of the preceding claims, wherein said incoherent plastics are heated before said step of generating a vacuum; said incoherent plastics being heated, in particular, before being introduced into said container (4).

21. Method according to any one of the preceding claims, comprising the step of heating said incoherent plastics contained in said container (4) during said step of generating a vacuum.

22. Method according to claim 21, wherein said heating step is performed by radio frequency waves.

23. Method according to any one of the preceding claims, comprising the step of generating a flow of a process gas passing through said incoherent plastics before said step of generating a vacuum; said flow of a process gas passing through said incoherent plastics inside an extraction hopper (10) arranged upstream of said container (4).

24. Method according to any one of the preceding claims, comprising the step of generating a flow of a process gas passing through said incoherent plastics after said step of generating a vacuum; said flow of a process gas passing through said incoherent plastics inside an extraction hopper (10) arranged downstream of said container (4).

25. Method according to claim 23 or 24, wherein said flow of a process gas, after passingthrough said incoherent plastics, is passed through a dehumidification system (11) and then is returned in a closed circuit through said incoherent plastics.

26. Method according to any one of the preceding claims, wherein said at least one aldehyde comprises acetaldehyde.

27. Apparatus for reducing a content of an aldehyde present in incoherent plastics, said apparatus comprising at least one container (4) for containing the incoherent plastics, vacuum generating means configured to generate a vacuum in said container (4), at least one substance sensor (S) configured to detect a content of an aldehyde in a gas coming from said container (4) or in a gas that has processed incoherent plastics coming from said container (4), and control means, in particular electronic and programmable control means, configured to control at least one operating parameter based on said detected content.

28. Apparatus for reducing a content of at least one substance, in particular an aldehyde, present in incoherent plastics, said apparatus being made, in particular, according to claim 27, said apparatus comprising: at least one container (4) configured to contain the incoherent plastics, vacuum generating means configured to generate a vacuum in said container (4), and at least one process device configured to process plastics, said container (4) being arranged to receive in-line incoherent plastics coming from said process device at a temperature higher than ambient temperature or higher than 90 °C.

29. Apparatus according to claim 28, wherein said process device comprises an extrusion or pelletizing device (1).

30. Apparatus according to claim 28 or 29, wherein said process device comprises a fluidized bed system (16).

31. Apparatus according to claims 30 and 29, wherein said fluidized bed system (16) is arranged to receive incoherent plastics exiting from said extrusion or pelletizing device (1).

32. Apparatus according to any one of claims 27 to 31, wherein said at least one controlled operating parameter comprises a value of said vacuum, said vacuum being controlled, in particular, at a value between -750 mbar and -950 mbar.

33. Apparatus according to any one of claims 27 to 32, comprising means for heating the incoherent plastics so that the incoherent plastics in said container (4) under vacuum has a desired temperature, in particular a temperature between 90 °C and 170 °C.

34. Apparatus according to any one of claims 27 to 33, comprising flow generating means configured to generate a flow of a process gas passing through the incoherent plastics.

35. Apparatus according to claim 34, comprising an extraction hopper (10) arranged upstream or downstream of said container (4) for supplying / receiving incoherent plastics to / from said container (4), said flow of a process gas passing through the incoherent plastics contained in said extraction hopper (10); said at least substance sensor (S) being arranged, in particular, to detect a content of said at least one aldehyde in said process gas exiting said extraction hopper (10); said at least one controlled operating parameter comprising, in particular, a flow rate of said process gas and / or a temperature of said process gas and / or a residence time of the incoherent plastics in said extraction hopper (10).

36. Apparatus according to claim 35, comprising adsorption separator means, and a closed circuit configured to take said process gas from said extraction hopper (10), pass said process gas through said adsorption separator means and then return said process gas to said extraction hopper (10).

37. Apparatus according to any one of claims 27 to 36, wherein: said at least one aldehyde includes acetaldehyde; and / or said control means is configured to feedback regulate said at least one operating parameter based on said detected content; and / or said container (4) is connected in-line to an extrusion or pelletizing device (1) to receive from the latter the incoherent plastics at a temperature higher than ambient temperature or higher than 90 °C; and / or said apparatus comprises means for generating a flow of an auxiliary gas, for example air or nitrogen, which is fed to said container (4) to pass through said plastics in said container (4); said auxiliary gas being introduced, in particular, into a lower zone of said container (4); said auxiliary gas having, in particular, a dewpoint value between -80 °C and 0 °C; and / or said apparatus comprises means for heating said incoherent plastics contained in said container (4), in particular means for heating by means of radio frequency waves; and / or said apparatus comprises a first accumulation container (2) arranged upstream of said container (4) and a second accumulation container (2) arrangeddownstream of said container (4).

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