METHOD AND APPARATUS FOR THE PRODUCTION AND PROCESSING OF A MIXTURE OF RECYCLED POLYESTER MATERIAL AND A POLYESTER PREPOLYMER FROM A POLYESTER MANUFACTURING PROCESS

Description

[0001] For environmental reasons, the recycling of polyesters such as PET has become increasingly important. One approach involves blending recycled polyester material with polyester prepolymer granules from a polyester manufacturing process to obtain a high-quality product. Preferably, recycled polyester is introduced into a polyester manufacturing process for this purpose.

[0002] WO 00 / 77071 A1 describes two ways in which recycled polyester can be incorporated into a polyester manufacturing process.

[0003] In the first option, pre-cleaned, recycled polyester material is extruded and granulated to obtain recycled polyester granules, which are subsequently mixed with polyester prepolymer granules from a polyester manufacturing process and together subjected to solid-phase polycondensation treatment.

[0004] In the second option, pre-cleaned, recycled polyester material is extruded to obtain a recycled polyester melt, which is subsequently mixed with a polyester prepolymer melt from a polyester manufacturing process, granulated together and subjected to solid-phase polycondensation treatment.

[0005] In both cases, the cleaning of the recycled polyester takes place in one or more of the following steps: Removal of surface contaminants in the solid phase, for example by means of a washing process; removal of contaminants by thermal treatment in the solid phase, for example by a drying process; removal of contaminants in the melt phase, for example by applying a vacuum or by means of a purge gas in a degassing chamber; removal of contaminants by thermal treatment in the solid phase in a solid-phase polycondensation step.

[0006] Removing surface contaminants reduces the levels of volatile, semi-volatile, and non-volatile impurities. However, this is limited to contaminants present on the surface or mixed with the recycled polyester. Contaminants within the polyester, such as absorbed contaminants or additives, are not affected.

[0007] A large proportion of volatile impurities can be removed during thermal treatment prior to extrusion. However, under the typically limited process conditions, only a small amount of semi-volatile impurities are removed. The removal of semi-volatile impurities in this step could be increased by longer residence times and higher process temperatures. However, this would have adverse consequences for subsequent process steps and the quality of the recycled polyester (discoloration, formation of byproducts, and an undesirable increase in viscosity).

[0008] During extrusion, residual surface contaminants, absorbed contaminants, and contaminants present as separate particles are homogeneously mixed with the recycled polyester melt. Simultaneously, regenerated contaminants are formed. These regenerated contaminants comprise degradation products of contaminants as well as degradation products of the recycled polyester, with the degradation of the polyester often being accelerated (catalyzed) by the contaminants present.

[0009] WO 00 / 77071 A1 describes the possibility of using a degassing chamber. However, widespread use of such devices to remove larger quantities of semi-volatile impurities would have highly detrimental consequences for the quality of the recycled polyester (discoloration, formation of degradation products). Furthermore, the problem of degradation product formation would not be solved.

[0010] The aforementioned context makes it clear that impurities from recycled polyester are introduced into the solid-state polycondensation step at the end of the process chain. Nevertheless, WO 00 / 77071 A1 only refers to standard technology for carrying out solid-state polycondensation. However, due to the significantly higher impurity levels, a mixture of newly manufactured polyester (so-called "virgin" material) with recycled polyester cannot be processed continuously over the required extended operating period in a conventional solid-state polycondensation plant.

[0011] EP-3 865 529 A1 describes a method for removing volatile and semi-volatile impurities that pass into the gas phase and can be removed by cleaning the process gas.

[0012] However, further disadvantages arise from impurities that remain in the melt. These include solid impurities and coloring, yellowing impurities, which are essentially introduced with or formed from the recycled polyester material. Despite the surface cleaning of the recycled polyester material in a washing process, as performed in the prior art, residues of impurities can remain on the surface. Additionally, residues of washing chemicals used in the washing process can also remain on the surface. Such impurities usually have lower thermal stability than the polyester material and, at the temperatures in a polyester melt, lead to coloring degradation products that cause the recycled polyester material to yellow.At the same time, the recycled polyester material may contain less thermally stable additives, or foreign plastics may be introduced into the polyester melt, which also lead to yellowing.

[0013] The solid impurities described above cannot be satisfactorily removed using the method proposed in EP-3 865 529 A1. The problem of yellowing of the material mentioned above is also not solved in this prior art. Another method is known from EP1084171A1.

[0014] The object of the present invention was to overcome the disadvantages of the prior art discussed herein and to provide an improved method and an improved apparatus for the production and processing of a mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process.

[0015] The present problem is solved according to the invention by a method according to claim 1.

[0016] In detail, the present invention relates to a method for producing and processing a mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process, comprising the following steps: Provision of a recycled polyester material in the form of a melt and initial purification of the melt by removing solid impurities by melt filtration; mixing of the recycled polyester material in the form of a melt with a polyester prepolymer in the form of a melt from a polyester manufacturing process and subsequent production of a solid mixture, preferably in a first particle forming device; treatment of this solid mixture in a reactor for the thermal treatment of bulk materials with a process gas in countercurrent or crosscurrent flow to the direction of flow of the mixture; wherein, at least for an initial period after the start of the process, before the production of the solid mixture, at least one additional step is carried out to purify the melt by removing solid impurities, resulting in a purer recycled polyester material. The process according to the invention is characterized in that the additional step for purifying the melt of the recycled polyester material is carried out by melt filtration through a melt filter whose openings have an average size that is larger than the average size of the openings of the melt filter used in the first purification step.

[0017] This process is particularly distinguished by the fact that substances introduced into the process via the recycled polyester material can be reliably removed before thermal treatment, such as solid-state condensation. This enables reliable and continuous processing of a mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process.

[0018] Bulk materials are any form of free-flowing, solid particles, such as grains, flakes, granules, powders or agglomerates.

[0019] According to the invention, the bulk materials are polycondensates, namely polyester in the form of a solid.

[0020] Polyesters are produced from their monomers via polycondensation. Polymers of the same type can be formed from the same main monomers. Polymers of the same type can also be formed from multiple main monomers. The individual monomers can be arranged alternately, randomly, or in blocks. A limited amount of additional monomers, known as comonomers, can also be used.

[0021] Monomers can be obtained from fossil fuels such as petroleum, natural gas, or coal, or from renewable raw materials. Monomers can also be obtained from existing polymers, especially recycled polymers, through depolymerization or pyrolysis.

[0022] Polycondensates are obtained through a polycondensation reaction with the elimination of a low-molecular-weight reaction product. This polycondensation can occur directly between the monomers. Alternatively, it can proceed via an intermediate step, followed by transesterification. Transesterification itself can also occur with the elimination of a low-molecular-weight reaction product or via ring-opening polymerization. The resulting polycondensate is essentially linear, although a small number of branches may be present.

[0023] Suitable polymers according to the invention are polyesters including polyhydroxyalkanoates, polylactides or their copolymers.

[0024] Polyesters are polymers that are usually obtained by polycondensation from a diol component with the general structure HO-R 1< -OH and a dicarboxylic acid component with the general structure HOOC-R 2< -COOH, where R 1< and R 2< are usually aliphatic hydrocarbons with 1 to 15 carbon atoms, aromatic hydrocarbons with 1 to 3 aromatic rings, cyclic hydrocarbons with 4 to 10 carbon atoms or heterocyclic hydrocarbons with 1 to 3 oxygen atoms and 3 to 10 carbon atoms.

[0025] Typically, linear or cyclic diol components and aromatic or heterocyclic dicarboxylic acid components are used. Instead of the dicarboxylic acid, its corresponding diester, usually dimethyl ester, can also be used. Furthermore, instead of the dicarboxylic acid, the reaction product of a dicarboxylic acid with two diols can be used, in particular in the form of the structure HO-R1-OOC-R2-COO-R1-OH. An example of this is the use of bis(2-hydroxyethyl) terephthalate for the production of polyethylene terephthalate.

[0026] Typical examples of polyesters are polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene furanoate (PEF), polytrimethylene furanoate (PTF), polybutylene succinate (PBS) and polyethylene naphthalate (PEN), which are used either as homopolymers or as copolymers.

[0027] Polyesters are also polymers with repeating ester groups with the general structure H-[OR-CO] x -OH, where R is usually an aliphatic hydrocarbon with 1 to 15 carbon atoms, an aromatic hydrocarbon with 1 to 3 aromatic rings, a cyclic hydrocarbon with 4 to 10 carbon atoms, or a heterocyclic hydrocarbon with 1 to 3 oxygen or nitrogen atoms and 3 to 10 carbon atoms.

[0028] An example is polyhydroxyalkanoates with the general structure H-[OC(R)H-(CH₂)n-CO]x-OH, where R is usually a hydrogen or an aliphatic hydrocarbon with 1 to 15 carbon atoms and n is 1 to 10. Examples are poly-4-hydroxybutyrate and poly-3-hydroxyvalerate.

[0029] Another example is polylactides with the general structure H-[OC(R)H-CO] x -OH, where R is usually a methyl group or an aliphatic hydrocarbon with 1 to 15 carbon atoms.

[0030] Another example is polyglycolic acid with the general structure H-[O-CH 2 -CO] x -OH.

[0031] Polyesters are also polymers that are produced by ring-opening polymerization from heterocyclic monomers with one ester group, such as polycaprolactone from caprolactone, or by ring-opening polymerization from heterocyclic monomers with at least two ester groups, such as polylactide from lactide.

[0032] The most common polylactide is polylactic acid with the structure H-[OC(CH3)H-CO]x-OH. Due to the chirality of lactic acid, various forms of polylactic acid exist. Homopolymers include poly-L-lactide (PLLA), which is usually produced from L,L-lactide, and poly-D-lactide (PDLA), which is usually produced from D,D-lactide. Copolymers such as poly-(L-lactide-co-D,L-lactide) contain small amounts of lactide units with a chirality that differs from that of the main monomer.

[0033] Polyesters can also be produced by biosynthesis using microorganisms or in plant cells, from which they are obtained by dissecting the cell.

[0034] Suitable polyesters can be homopolymers. Despite the term homopolymer, a small proportion of comonomers can form during the manufacturing process. For example, the formation of diethylene glycol from ethylene glycol is known to occur during the production of polyethylene terephthalate. However, many suitable polyesters are copolymers that contain a certain proportion of comonomers. The comonomers can be introduced into the polyester manufacturing process as part of the monomers, or they can form during the manufacturing process, typically resulting in a random distribution in the final polyester. The comonomers can also be incorporated as blocks made from different monomers, resulting in so-called block copolymers.

[0035] Suitable polyesters can be polymer mixtures containing any number and quantity of different polyester types. A small amount of one polyester can act as a nucleating agent in other polyesters, thereby increasing their crystallization rate.

[0036] Specific polyester mixtures can form interacting crystal structures with crystallization behavior that differs from that of the individual components. An example of this is a mixture of PDLA and PLLA, which forms a stereocomplex crystal structure with increased crystallinity.

[0037] After polymerization, every polymer chain has chain-terminating groups, typically possessing the functionality of at least one of its monomers. For example, a polyester chain can have one or more hydroxyl and / or carboxyl end groups. Such end groups can be modified by an end-capping reagent or by a degradation reaction. Although not specifically mentioned in the general structures above, suitable polyesters can possess such modified end groups.

[0038] Additives can be added to polyester. Suitable additives include, for example, catalysts, dyes and pigments, UV blockers, processing aids, stabilizers, impact modifiers, chemical and physical blowing agents, fillers, nucleating agents, flame retardants, plasticizers, particles that improve barrier or mechanical properties, reinforcing elements such as spheres or fibers, and reactive substances such as oxygen absorbers, acetaldehyde absorbers, or substances that increase molecular weight.

[0039] The polyester can be virgin or recycled. Virgin polyester is defined as polyester manufactured from its monomers, which can originate from petroleum-based sources, bio-based renewable resources, or from the depolymerization of polyester articles or waste. Monomers can also include dimers and lower oligomers with a chain length of up to nine polyester repeat units. Polyester is not considered virgin if it falls under the definition of recycled.

[0040] Recyclates are defined as reprocessed polyesters from manufacturing and processing (post-industrial) or polyesters collected and reprocessed after consumer use (post-consumer). A polyester recyclate used according to the invention preferably still has a chain length of at least 10 (preferably 20, particularly 30 or 40) repeat units of the polyester. Recycled polyesters can preferably consist of consumer waste, for example, used polyester articles. Typical examples of such articles are polyester bottles, polyester trays, or polyester fibers. Depending on their size and properties, the polyester articles must be ground and / or compacted to obtain suitable particle sizes and bulk densities for further processing. Suitable bulk densities are between 100 and 800 kg / m³, particularly between 200 and 500 kg / m³.Suitable particle sizes range from 1 to 50 mm, particularly from 2 to 25 mm. Depending on their degree of contamination, recycled polyesters must be cleaned before further processing. This can include process steps such as washing, sorting, or separating. Furthermore, recycled polyesters can be separated from volatile impurities and water by thermal treatment in a gas stream and / or at reduced pressure.

[0041] The present invention relates to the processing of a mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process.

[0042] According to the invention, polyester prepolymer from a polyester manufacturing process is provided in the form of a melt in a first reactor or a series of reactors, wherein the reactor in which the polyester prepolymer ultimately used as the starting material of the process according to the invention is produced is then referred to as the first reactor. Polyester manufacturing processes and suitable reactors for this purpose are sufficiently known in the prior art (e.g. Scheirs / Long (eds.), Modern Polyesters, Wiley 2003, II.2.4, pp. 89-98).

[0043] Continuous polyester manufacturing processes are preferred for the present invention. According to the present invention, suitable polyester manufacturing processes are designed such that a polyester prepolymer melt is produced by melt-phase polymerization. The melt-phase polymerization includes a process step in which the suitable viscosity for further processing is achieved. This can be carried out, for example, in a melt-phase reactor. Once the suitable viscosity is reached, the polyester melt is fed to one or more granulators via suitable melt lines.

[0044] Optionally, the polyester prepolymer melt can be filtered in a melt filter. The term melt filter includes screen changers and static filters or filter cartridges.

[0045] According to the invention, recycled polyester material is provided in the form of a melt in a second reactor, preferably an extruder.

[0046] A melt of recycled polyester is typically produced by extrusion. Alternatively, simple melting reactors can be used. The recycled polyester melt can optionally be subjected to further pressure build-up using a melt pump and / or separation of volatile impurities using a slurry gas or vacuum.

[0047] According to a preferred embodiment of the present invention, the melt of recycled polyesters is subjected to separation of solid impurities by melt filtration before being mixed with a polyester prepolymer in the form of a melt from a polyester manufacturing process. The first filter unit used for this purpose is arranged downstream of the second reactor. In other words, the melt of recycled polyesters is fed from the second reactor into the first filter unit via a feed line (melt line).

[0048] Preferably, the recycled polyester melt is filtered through a first filter unit, for example a sieve, with openings comparable to or smaller than those in the filter unit, for example a sieve, used for filtering the melt in the polyester manufacturing process.

[0049] The filter units used according to the invention have a multitude of openings through which the melt can pass, while the solids are retained. The openings can be round, square, or irregularly shaped. Round openings are predominantly found in lock plates. Here, the hole diameter indicates the size of the opening. Square or irregularly shaped openings are predominantly found in woven sieves. In simple sieve fabrics, the mesh size indicates the size of the opening. In sieve fabrics with a complex structure, such as twill weaves, a nominal opening size results from the size of the retained particles.

[0050] Melt filters are typically operated with several sieves with different sized openings, known as sieve packs. The openings in the finest sieve are the determining factor. However, especially with sieves, but also with lock plates, shifts, enlargements, or wear can occur, leading to slightly different opening sizes. Therefore, the average opening size is determined as the mean value across all openings.

[0051] The recycled melt is conveyed from the first filter unit through a melt line to a first melt valve, which serves as a connecting unit, and there it is combined and mixed with a melt of polyester prepolymer from a polyester manufacturing process. The melt line could, for example, be a suitable pipe fitting.

[0052] The molten mixture is then conveyed in a common melt line to a unit for producing a solid mixture, preferably a first particle forming device, particularly preferably a granulator (for example, an underwater granulation plant (UWG) or an underwater strand granulation plant (USG)), and granulated there. The first particle forming device can also consist of a plurality of particle forming devices operated in parallel.

[0053] According to a preferred embodiment of the present invention, the melt mixture can be mixed in a mixing unit before entering the unit for the production of a solid mixture. Any mixing unit suitable for mixing melts can be used for this purpose. For example, a mixing unit with a static mixer can be used.

[0054] According to the invention, a solid mixture is understood to be a mixture of particles, in particular granules, of different compositions, wherein in the present case a mixture of virgin PET particles and rPET particles may be present. However, it may also be particles or granules which were produced by mixing a recycled melt and a melt of polyester prepolymer from a polyester manufacturing process and subsequent particle forming, in particular granulation, of this mixed melt.

[0055] The first melt valve is located between the process step in which the melt reaches the appropriate viscosity for further processing (e.g., in a melt polycondensation unit or an extruder) and a unit for producing a solid mixture, preferably a granulator. The first melt valve can be located before or after optional filtration in the polyester manufacturing process.

[0056] Preferably according to the invention, the supply line (melt line) for recycled polyester melt can be shut off by means of the first melt valve.

[0057] According to the invention, preferably a second melt valve is arranged in the feed line (melt line) for recycled polyester melt upstream of the first melt valve, which also allows the feed line (melt line) for recycled polyester melt to be shut off. In this case, the second melt valve is connected to the first filter unit via a first section of the melt line and to the first melt valve via a second section of the melt line.

[0058] For continuous operation of the plant, an additional cleaning step is required. Continuous operation of the plant is defined here as operation of the plant without interruption over a longer period (e.g., 1-4 weeks, preferably 1-12 months, particularly preferably more than 1 year), during which the melts are passed through the melting area of ​​the plant without interruption.

[0059] During start-up and continuous operation of the plant, impurities are introduced into the system by the recycled polyester material, negatively impacting the quality of the final product. These product impurities are also known as black specs. To reliably remove these impurities during continuous operation, the melt must undergo an additional purification step before the production of the solid mixture. This step removes the solid impurities responsible for the formation of black specs, resulting in a purer recycled polyester material.

[0060] According to the present invention, the additional step of purifying the melt of the recycled polyester material by melt filtration takes place in a second, additional filter unit. In principle, all types of filter units can be used. These include batch filters, such as candle filters. Continuous filter units, in which an uninterrupted melt flow is ensured, are preferred. This includes continuously purifying (such as laser filters) and batch purifying filter units (such as piston filters), although batch filter units are susceptible to surge contamination.

[0061] According to the invention, preferred filters are selected from the following group: A rigid perforated plate or a rigid sieve with continuous cleaning from the melt flow. A rigid perforated plate or a rigid sieve with timed cleaning from the melt flow. A movable perforated plate or a movable sieve with continuous feeding into the melt flow. A movable perforated plate or a movable sieve with timed feeding into the melt flow, wherein the time rate is less than 5 minutes.

[0062] Such filters are known (e.g. Scheirs, Polymer recycling, Wiley 1st ed. 1998, 101-117).

[0063] According to the invention, the second melt filter has openings with an average size that is larger than the average size of the openings of the first melt filter used in the first cleaning process. By using a coarser second melt filter, the need for frequent cleaning and the associated interruption of plant operation is avoided, as such a second melt filter is significantly less prone to clogging.

[0064] According to a preferred embodiment of the present invention, the first filter unit can have openings with a size in the range of 10–75 µm, preferably 30–60 µm, and particularly preferably 35–45 µm, while the second filter unit can have openings with a size in the range of 10–300 µm, preferably 20–100 µm, preferably 40–75 µm, and particularly preferably 50–60 µm. The openings of the second filter unit must always be larger than the openings of the first filter unit.

[0065] In a further embodiment of the present invention, in which the polyester prepolymer melt is filtered in a melt filter, this filtration takes place in a third filter unit before the polyester prepolymer melt enters the first melt valve. In this embodiment, the third filter unit preferably has openings with a size in the range of 10–75 µm, more preferably 30–60 µm, and particularly preferably 35–45 µm, and most preferably corresponds to the size of the openings of the first filter unit.

[0066] According to the invention, the additional step for cleaning the melt of the recycled polyester material by means of melt filtration in an additional second filter unit is to be carried out before the production of the solid mixture, i.e. before the melt mixture is introduced into the unit for the production of a solid mixture, preferably a granulator.

[0067] According to a preferred embodiment of the present invention, the additional step of purifying the melt of the recycled polyester material by melt filtration is carried out before the step of mixing the recycled polyester material in the form of a melt with the polyester prepolymer in the form of a melt from a polyester manufacturing process. For this purpose, a melt filter as described above is provided as a second filter unit at a position located after the first filter unit and before the first melt valve. In other words, a second filter unit is arranged in the melt line that connects the first filter unit to the first melt valve. In this way, the melt of the recycled polyester material is additionally purified before it comes into contact with the polyester prepolymer melt.

[0068] Optionally, a second melt valve as described above can be arranged between the first filter unit and the second filter unit.

[0069] Optionally, a second melting valve as described above can also be arranged before the first filter unit and after the second reactor.

[0070] In both cases, it is possible for polyester prepolymer melt from a polyester manufacturing process to flow in reverse through a filter unit. The melt filter must be selected accordingly. It may be necessary to temporarily remove screens or perforated plates from the filter unit.

[0071] According to a further preferred embodiment of the present invention, the additional step for purifying the melt of the recycled polyester material by means of melt filtration is carried out after the step of mixing the recycled polyester material in the form of a melt with the polyester prepolymer in the form of a melt from a polyester manufacturing process.

[0072] For this purpose, a melt filter as described above is provided as a second filter unit at a position located between the first melt valve and the unit for producing a solid mixture. In other words, a second filter unit is arranged in the melt line that connects the first melt valve to the unit for producing a solid mixture. In this way, the entire previously prepared melt mixture is additionally purified.

[0073] Optionally, in this embodiment, a second melt valve as described above can be arranged between the first filter unit and the first melt valve.

[0074] According to a further embodiment of the present invention, an additional step for purifying the melt by removing solid impurities and obtaining a purer recycled polyester material can be carried out by flushing the melt line that connects the first filter unit and the first melt valve. During normal operation, recycled polyester material in the form of a melt is fed into the production of the solid mixture through this melt line by being directed from the first filter unit to the first melt valve.

[0075] To remove solid impurities that accumulate in this melt line before or during plant operation, a section of the melt line connecting the first and second melt valves can be purged with the polyester prepolymer melt. For this purpose, polyester prepolymer melt from the first reactor is fed into this melt line through the first melt valve. The polyester prepolymer melt is then fed through the second melt valve into a second particle forming device. There, a solid is produced from this melt, with the entrained, deposited impurities being discharged.

[0076] The second particle forming device, preferably a granulator, can be of the same design as the first unit described above for producing a solid. However, this is not mandatory.

[0077] The second particle forming device is connected to the second melting valve.

[0078] According to this embodiment, the first melting valve and the second melting valve are designed to be switchable, so that In a first switching arrangement, polyester prepolymer in the form of a melt from a polyester manufacturing process, carrying deposited impurities from at least the section of the melt line between the first melt valve and the second melt valve, is guided through the first melt valve and the second melt valve into a second particle forming device; in a second switching arrangement, polyester prepolymer in the form of a melt from a polyester manufacturing process is guided through the first melt valve to the unit for producing a solid mixture, and melt of recycled polyester material from the first filter unit is guided through the second melt valve and the first melt valve to the unit for producing a solid mixture.and, if necessary, in a third switching arrangement, polyester prepolymer in the form of a melt from a polyester manufacturing process is directed through the first melt valve to the unit for producing a solid mixture, and melt of recycled polyester material from the first filter unit is directed through the second melt valve to the second particle forming device.

[0079] Such switchable melt valves are known (see e.g. EP 0 962 299 A1).

[0080] In the first switching arrangement, the first melt valve is set such that the polyester prepolymer melt coming from the first reactor is no longer directed exclusively to the (first) unit for the production of a solid, but at least partially into the section of the melt line that connects the second melt valve and the first melt valve. Under normal operating conditions, recycled polyester melt is directed through this melt line in the reverse flow direction to reach the first melt valve and subsequently the (first) unit for the production of a solid. In this process, the recycled polyester melt picks up impurities deposited in this melt line and introduces them into the final product. This is prevented by the purging process according to the invention.The polyester prepolymer melt passed through this section of the melt line picks up impurities deposited in this melt line during its passage.

[0081] The contaminated polyester prepolymer melt is not used for product manufacturing, but is fed to a second particle forming device.

[0082] In the first switching arrangement, the second melt valve is therefore set such that contaminated polyester prepolymer melt coming from the first reactor through the section of the melt line between the first and second melt valve is not directed to the second reactor, but to the second particle forming device.

[0083] This second particle forming device is connected to the second melt valve. The connection is preferably realized via an additional melt line.

[0084] In the second particle forming device, the contaminated polyester prepolymer melt is solidified, preferably granulated. The resulting solid is removed from the system. Optionally, this solid can be recycled as recycled polyester at a later time.

[0085] The second switching configuration of the first and second melt valves represents the switching state during normal operation. Molten recycled polyester material is fed from the first reactor through the first filter unit into the second melt valve and from there through the (now cleaned) section of the melt line back into the first melt valve. In the second switching configuration, the second melt valve is therefore set so that molten recycled polyester material cannot enter the second particle forming unit. Conversely, in the second switching configuration, the first melt valve is set so that molten recycled polyester material is fed into the (first) unit for solid production.The inflow of polyester prepolymer melt into the section of the melt line between the first and second melt valve is prevented by directing the melt into the first melt valve at a sufficiently high pressure using recycled polyester material.

[0086] The third switching configuration of the first and second melt valves represents the switching state in an additional, optional cleaning step. This additional, optional cleaning step serves to remove solid impurities that may be deposited in the section of the melt line between the first filter unit and the second melt valve. Molten recycled polyester material is fed from the second reactor through the first filter unit into the second melt valve and from there into the second particle forming device. In the third switching configuration, the second melt valve is therefore set such that molten recycled polyester material cannot enter the first melt valve.In the third switching arrangement, the first melt valve is preferably set such that polyester prepolymer melt cannot enter the second melt valve, but is guided through the first melt valve to the unit for producing a solid mixture.

[0087] In the third switching arrangement, melt of recycled polyester that does not meet the desired specifications can also be removed from the system. This could be start-up material that exhibits, in particular, excessively low viscosity and strong yellowing, or material that, due to impurities, falls outside the desired specifications for critical quality parameters (such as viscosity or color). This material is fed, analogously to the next unit for the production of a solid, preferably to a second particle forming device, where it is solidified as described above and optionally returned to the second reactor.

[0088] A fourth optional switching arrangement of the first and second melt valves represents the switching state for changing from the first to the second switching state. In this configuration, the melt valves are set such that both polyester prepolymer melt from the first reactor (through the first melt valve) and recycled polyester melt from the second reactor (through the first filter unit) are directed via the second melt valve into the second particle forming device. The melt flow through the section of the melt line between the first and second melt valves is determined by the pressure at which the different melts are conveyed through the system. In this arrangement, the pressure of the polyester prepolymer melt is higher than the pressure of the recycled polyester melt.

[0089] Another embodiment of the present invention provides that the second particle forming device is a device for underwater granulation and the second melt valve is simultaneously the start-up valve of the underwater granulation.

[0090] According to an alternative embodiment of the present invention, the purging of the melt line can also be carried out exclusively with the melt of the recycled polyester material. For this purpose, it is advantageous to arrange the second melt valve as close as possible to the first melt valve. In a preferred embodiment, the second melt valve is integrated directly into the first melt valve. The section of the melt line connecting the first melt valve to the second melt valve is thus kept as short as possible, so that purging of this section is no longer necessary.

[0091] According to this alternative embodiment, the first melting valve and the second melting valve are designed to be switchable, so that The first switching arrangement provided in the embodiment described above is no longer preferred and is preferably omitted; in a second switching arrangement, polyester prepolymer in the form of a melt from a polyester manufacturing process is directed through the first melt valve to the unit for producing a solid mixture, and melt of recycled polyester material from the first filter unit is directed through the second melt valve and the first melt valve to the unit for producing a solid mixture; in a third switching arrangement, polyester prepolymer in the form of a melt from a polyester manufacturing process is directed through the first melt valve to the unit for producing a solid mixture, and melt of recycled polyester material from the first filter unit is directed through the second melt valve into the second particle forming device.and in a fourth switching arrangement, polyester prepolymer in the form of a melt from a polyester manufacturing process is directed through the first melt valve to the unit for producing a solid mixture, and melt of recycled polyester material from the first filter unit is directed through the second melt valve into the second particle forming device and simultaneously through the second melt valve and the first melt valve to the unit for producing a solid mixture.

[0092] The components used in both alternative embodiments, which have the same name, are fundamentally identical in structure.

[0093] In this alternative embodiment, the third switching arrangement involves flushing the section of the melt line between the first filter unit and the second melt valve exclusively with the melt of the recycled polyester material. A first switching arrangement, in which a section of the melt line between the first and second melt valves would be flushed with polyester prepolymer in the form of a melt from a polyester manufacturing process, is preferably omitted in this alternative embodiment.

[0094] To minimize the problem of potential impurity buildup in the section of the melt line connecting the first and second melt valves, this section is kept as short as possible in this alternative embodiment. According to a preferred embodiment, a first melt valve is provided into which the second melt valve is integrated. Such melt valves are known. For example, such a first melt valve can be designed such that the melt lines from the first and second reactors (optionally containing filter units) open into the first melt valve and are combined there. A branch line leading to a drain valve is arranged in close proximity to this point of convergence.This drain valve represents the second melt valve and regulates the flow of the melt of recycled polyester material into the second particle forming device.

[0095] In the second switching arrangement described above, the second melt valve is therefore set such that melt of recycled polyester material cannot enter the second particle forming device. In the second switching arrangement, the first melt valve is set accordingly, so that both polyester prepolymer in the form of a melt from a polyester manufacturing process and melt of recycled polyester material enter the first melt valve, are combined there, and are directed to the unit for producing a solid mixture. This is the operating mode of the system for producing the desired solid mixture. The inflow of polyester prepolymer melt into the section of the melt line between the first and second melt valves is prevented by directing the melt of recycled polyester material into the first melt valve at a sufficiently high pressure.

[0096] In the third switching arrangement described above, the second melt valve is adjusted such that molten recycled polyester material cannot enter the first melt valve. In this third switching arrangement, the first melt valve is preferably adjusted such that polyester prepolymer melt cannot enter the second melt valve, but is instead directed through the first melt valve to the unit for producing a solid mixture. In this switching arrangement, the molten recycled polyester material is directed through the second melt valve into the second particle forming device. There, any deposits carried from the melt line coming from the second reactor are solidified along with the molten recycled polyester material and optionally returned to the second reactor.The polyester prepolymer in the form of a melt from a polyester manufacturing process is guided through the first melt valve to the unit for producing a solid mixture.

[0097] In the fourth switching arrangement described above, unlike the third switching arrangement, the first melt valve is set so that it is not blocked from the influence of molten recycled polyester material. Thus, a portion of the molten recycled polyester material enters the first melt valve and subsequently the unit for producing a solid mixture, while another portion of the molten recycled polyester material is directed through the second melt valve into the second particle forming device. The ratio of the amounts of molten recycled polyester material that pass through the two different pathways can be controlled by appropriately adjusting the first and second melt valves.In this switching arrangement, which represents a transitional operating state of the plant, partial removal of deposits from the corresponding melt line is achieved while the desired solid mixture is being produced. The melt flow through the section of the melt line between the first and second melt valves is determined by the pressure at which the different melts are conveyed through the plant. In this arrangement, the pressure of the polyester prepolymer melt is lower than the pressure of the recycled polyester melt.

[0098] In the embodiments according to the invention with an additional step for cleaning the melt of the recycled polyester material by rinsing a section of the melt line either between the second and first melt valve or between the first filter unit and the second melt valve, a further step for cleaning the melt of the recycled polyester material by means of melt filtration can preferably be carried out.

[0099] As described above, a second filter unit with a melt filter is used for this purpose, the openings of which have an average size larger than the average size of the openings of the melt filter used in the first cleaning process. Reference is made to the preceding description of the second filter unit.

[0100] In these embodiments according to the invention, the further purification step by melt filtration is carried out after the step of mixing the recycled polyester material in the form of a melt with the polyester prepolymer in the form of a melt from a polyester manufacturing process. In other words, the second filter unit is provided at a position located between the first melt valve and the unit for producing a solid mixture.

[0101] A further disadvantage of the process according to WO 00 / 77071 A1 arises from the frequently varying quality of the recycled input material. Excessive amounts of impurities, some of which are present in clusters, often cannot be detected by analytical methods. Quality defects are usually only apparent after granulation or sometimes only in the final product. This can result in large quantities of substandard production batches, in which not only the recycled polyester but also the polyester prepolymer from the manufacturing process becomes unusable.

[0102] According to a further preferred embodiment of the invention, a quality parameter is therefore measured in the melt line for recycled polyester melt.

[0103] The measured quality parameter can be used to automatically remove the recycled polyester melt from the system when a critical value is reached, as described above for the third switching arrangement.

[0104] The measured quality parameter can alternatively be used to make adjustments in the polyester manufacturing process based on the measured parameter, or to automatically adjust process parameters via a control system. Particularly preferred is the measurement of a color value and the adjustment or control of dye addition in the polyester manufacturing process.

[0105] Alternatively, the measuring point can also be located after the first melting valve.

[0106] Key quality parameters include color and viscosity. Both can be measured in-line or online. In-line viscosity measurement is performed, for example, using instruments that measure the torsional force of a probe within the melt. Another method involves measuring the pressure drop in a defined gap through which the melt flows, with the measured melt remaining in the process or being returned to it. Online viscosity measurement is performed, for example, by measuring the pressure drop in a defined gap through which a portion of the melt flows, with the measured melt then being removed from the process. In all cases, viscosity is calculated based on comparative measurements of a mechanical quantity.

[0107] For example, in-line measurement of color is carried out using a light source on one side of the melting line and a light-sensitive sensor on the other side of the melting line, whereby a color value can be calculated from the amount of light absorbed at different wavelengths.

[0108] Online color measurement is performed, for example, using a light source on one side of a test strip produced from the melt and a light-sensitive sensor on the other side. A color value can then be calculated from the amount of light absorbed at different wavelengths. The light source and sensor can be connected to the actual measuring point via fiber optics.

[0109] Optionally, melt pumps can be used in melt lines to overcome pressure losses in the melt lines, melt filters, and particle forming devices. Melt pumps typically have a predetermined flow direction and must be arranged to prevent reverse melt flow. Preferred installation locations are after the first reactor or after the second melt filter, after the second reactor or after the first melt filter, or after the third melt filter. However, placement in the melt line between the first and second melt valves should be avoided if, according to the invention, reverse flow through this section of the melt line is required.

[0110] Throttle valves can also be used optionally to adjust or regulate the pressure conditions according to the required flow direction and quantity.

[0111] According to a preferred embodiment of the present invention, the solid-state polycondensation step is dimensioned such that both the substantially full capacity of the polyester prepolymer manufacturing process and the substantially full quantity of the installed capacity of recycled material can be processed. In particular, during a subsequent conversion of a polyester manufacturing plant, the overall plant capacity can be increased by removing the solid-state polycondensation step after the installation of a recycled material feed device.

[0112] The mixture of recycled polyester and polyester prepolymer from a polyester manufacturing process can comprise any desired mixing ratio. According to the invention, the ratio of recycled material to prepolymer is preferably in the range of 10% to 90% to 90% to 10%, more preferably from 20% to 80% to 80% to 20%, even more preferably from 25% to 75% to 75% to 25%, and particularly preferably 50% to 50%.

[0113] A limiting factor here is that a plant for the production of polyester prepolymer is designed to a certain size and its capacity cannot be reduced arbitrarily. A preferred embodiment of the present invention therefore provides a mixture of recycled polyester and polyester prepolymer from a polyester manufacturing process with a maximum recycled content of 50%. The minimum recycled content of the mixture results from the economic viability of the additional process step of blending, which typically necessitates a recycled content of at least 10%, and in particular at least 15%.

[0114] An additional problem may be that, due to its history, the recycled polyester has an insufficient blue coloration, which is commercially desirable for the product to be manufactured according to the invention.

[0115] The color of a material is characterized by its b* value. The b* value is defined in the CIELAB color space, where the b* axis lies between blue and yellow (see Römpp Lexikon Lacke und Druckfarben, Thieme 1998, "CIE"). A positive b* value corresponds to a yellow color, and a negative b* value corresponds to a blue color. According to the invention, the b* values ​​are preferably measured using a colorimeter, for example, a Konica Minolta CM3500d, with a D65 lamp in reflection mode. For comparative b* value measurements, all samples must be in the same state; e.g., the same particle type (granules, powder, or molded parts), the same shape (round or cylindrical granules or thickness of molded parts), and the same state of crystallinity (amorphous or crystalline).For measuring absolute values, according to the invention, all samples are preferably converted into granules weighing 10–30 mg per granule and crystallized (20 min / 175°C or comparable conditions) to obtain crystalline granules. To assess whether a molded body has a b* value < 0, a measurement can also be taken directly on the molded body. For improved measurability, the molded body can be ground, preferably using a sieve with an opening in the range of 0.5–1 mm. Grinding must be carried out under cooling to prevent discoloration.

[0116] According to the invention, it has been shown that the desired blue coloration of the product to be manufactured, as described above, can be achieved by adding a coloring additive with a negative b* value to the polyester prepolymer.

[0117] According to a preferred embodiment of the invention, the proportion of recycled polyester material in the solid mixture comprises 10-90% and has a b* value (BR), and the proportion of polyester prepolymer from a polyester manufacturing process in the solid mixture comprises 90-10% and has a b* value (BN), and wherein the resulting solid mixture has a b* value (BM) and BM < 0, BN < 0 and BR > BN.

[0118] According to the invention, it is preferred that BN < -3, preferably < -5, and even more preferably < -8.

[0119] It is further preferred according to the invention that the proportion of recycled polyester material comprises >20%, preferably >25% and particularly preferably >40%, based on the total polyester solid mixture.

[0120] It has been shown that the coloring additive with a negative b* value can be added to the polyester prepolymer melt without additional contamination, since a monomer of the prepolymer melt, preferably ethylene glycol, can act as an additive carrier. Conversely, the coloring additive with a negative b* value can only be added to the recycled polyester material using a specific additive carrier, which leads to additional contamination of the material. Additive carriers are substances used to facilitate the incorporation of coloring additives during the extrusion of rPET flakes or in the preform manufacturing process.Additive carriers include, for example, high-boiling mineral oils or other organic substances, usually in liquid form at room temperature, which do not decompose at the processing temperatures of PET, typically 260–310°C, do not cause bubble formation, and do not result in undesirable side reactions. Such additive carriers remain as components in the rPET material during the recycling of PET articles and can lead to undesirable accumulation during repeated recycling cycles.

[0121] According to a preferred embodiment of the invention, a coloring additive with a negative b* value is added to the polyester prepolymer from a polyester manufacturing process before it is combined with the recycled polyester material, wherein the coloring additive is added to the polyester prepolymer from a polyester manufacturing process without prior dilution or as part of an additive mixture which further comprises a monomer of the polyester, and no coloring additive with a negative b* value is added to the recycled polyester material before it is combined with the polyester prepolymer from a polyester manufacturing process.

[0122] According to the invention, it is preferred that the coloring additive is dissolved or suspended in the monomer of the polyester.

[0123] According to the invention, this concept can also be applied independently of the additional purification of the melt described above by removing solid impurities, resulting in a purer recycled polyester material.

[0124] The present invention thus also relates to a method for producing a polyester solid mixture by combining a proportion of recycled polyester material and a proportion of polyester material from a polyester manufacturing process, wherein the proportion of recycled polyester material in the polyester solid mixture comprises 10-90% and has a b* value (BR), and the proportion of polyester material from a polyester manufacturing process in the polyester solid mixture comprises 90-10% and has a b* value (BN), and wherein the resulting polyester solid mixture has a b* value (BM), characterized in that BM < 0, BN < 0 and BR > BN.

[0125] According to the invention, it is preferred that BN < -3, preferably < -5, and even more preferably < -8.

[0126] It is further preferred according to the invention that the proportion of recycled polyester material comprises >20%, preferably >25% and particularly preferably >40%, based on the total polyester solid mixture.

[0127] In this process, preferably, analogous to the embodiment described above, a coloring additive with a negative b* value is added to the polyester material from a polyester manufacturing process before it is combined with the recycled polyester material, wherein the coloring additive is added to the polyester material from a polyester manufacturing process without prior dilution or as part of an additive mixture that further comprises a monomer of the polyester, and no coloring additive with a negative b* value is added to the recycled polyester material before it is combined with the polyester material from a polyester manufacturing process.

[0128] This process can be carried out as described above, with or without additional purification of the melt by removing solid impurities to obtain a purer recycled polyester material. In the variant with such additional purification, the process is carried out as described above, but with the addition of a coloring additive to the polyester prepolymer from a polyester manufacturing process. In the variant without such additional purification, the process is modified such that a coloring additive is added to the polyester prepolymer from a polyester manufacturing process, but the melt of recycled polyester material is not additionally purified. Therefore, in this variant, it is not necessary to provide a separate unit for removing solid impurities to obtain a purer recycled polyester material.The provision of a second melt valve is also not required with this variant.

[0129] The solid mixture produced according to the invention is subsequently treated in a reactor for the thermal treatment of bulk materials with a process gas in countercurrent or crosscurrent flow to the direction of the mixture. This applies to the variant with or without additional purification of the melt by removing solid impurities to obtain a purer recycled polyester material.

[0130] According to the invention, the thermal treatment can be selected from the list consisting of drying, crystallization, dealdehydization, solid-phase post-condensation, and combinations thereof. Preferably, in solid-phase post-condensation, the intrinsic viscosity of the polyester solid mixture is increased by at least 5%, more preferably by at least 7%, and most preferably by at least 10%.

[0131] Depending on the type of thermal treatment, the solid mixture must first undergo crystallization. This is well known from the prior art (see Scheirs / Long (eds.), Modern Polyesters, Wiley 2003).

[0132] The thermally treated solid mixture can then be shaped into a desired body using known forming processes. Examples include blow molding for bottle production or injection molding. Alternatively, the solid mixture (e.g., the granules) can be melted and the melt transferred into a film, followed by forming the film, or the solid mixture (e.g., the granules) can be compressed into a forming tool.

[0133] As described above, to obtain a molded part with the desired blue color, it is advantageous to add a coloring additive to the polyester prepolymer from a polyester manufacturing process to compensate for an undesirable color of the recycled polyester. Adding such a coloring additive during the molding process is unnecessary and undesirable.

[0134] Thus, the present invention also relates to a method for producing a molded body, comprising the forming of a molded body from a polyester solid mixture produced according to one of the methods described above, wherein no coloring additive with a negative b* value is added during the forming of the molded body and the molded body has a b* value (BF) where BF < 0.

[0135] According to the invention, it is preferred that BF < -2, more preferably <-3 and in particular preferably < -5.

[0136] A preferred embodiment of the invention provides that a dark blue colored molded body is produced from a solid mixture consisting of a dark blue colored polyester material and a recycled material that is at least partially produced from dark blue colored molded bodies. In this process, the addition of a blue coloring additive during the manufacturing process of the molded body can be omitted or at least significantly reduced.

[0137] For the thermal treatment of bulk materials, process gases with a low oxygen content, such as nitrogen, carbon dioxide, noble gases, steam, or mixtures of these gases, are used. Such process gases are commonly referred to as inert gases. Inert gases are particularly suitable when the bulk materials are oxygen-sensitive.

[0138] Bulk materials are classified as oxygen-sensitive if, during thermal treatment, they undergo more significant changes due to the presence of oxygen than would occur during thermal treatment without oxygen. Such changes can lead to discoloration, the formation of decomposition products, and / or a reduction in the molecular weight of the bulk material.

[0139] Despite being called an inert gas, the process gas may contain small amounts of oxygen, which may have entered the process gas through leaks or remained in the process gas due to incomplete combustion, for example.

[0140] A thermal treatment process for bulk materials refers to any process in which bulk materials are treated under the influence of a process gas for a specific residence time at a specific temperature. Residence time and temperature can be varied over a very wide range, with residence times from a few minutes to several hundred hours and temperatures between the boiling point of the process gas and the melting or decomposition temperature of the bulk material being conceivable.

[0141] Thermal treatment typically takes place in a treatment chamber that can accommodate the bulk material and the process gas. This treatment chamber is usually formed by reactors. Suitable reactors can be conical or cylindrical, with a round or square cross-section. Suitable reactors have at least one inlet and one outlet for the bulk material, as well as at least one inlet and one outlet for the process gas. The reactors can incorporate various internal components to influence the product flow and / or gas flow.

[0142] The process gas acts in such a way that organic substances from the polymer are absorbed by the process gas and carried out of the treatment room.

[0143] Preferably, the thermal treatment is carried out continuously or semi-continuously, with both the process gas and the bulk material being fed into the reactor either continuously or in individual batches smaller than the reactor volume. The process gas is guided either in cross-flow or counter-flow to the flow direction of the bulk material. A preferred embodiment provides for continuous thermal treatment in a moving bed reactor in counter-flow.

[0144] Alternatively, a discontinuous operating mode is also conceivable, in which a given quantity of bulk material is passed through a reactor by process gas.

[0145] The size of the reactors is determined by the requirements of the thermal treatment (residence time and throughput). Examples of such reactors are known from EP-2 398 598 A1.

[0146] The organic substances absorbed by the process gas include any organic substances released from the bulk material during its thermal treatment, whether in gaseous form or dissolved in the process gas. If the bulk material is a polymer, the organic substances primarily comprise residues from the polymerization process, degradation products from the polymer and its additives, as well as impurities introduced into the treatment process along with the polymers and their degradation products. These organic substances are typically hydrocarbons, and may contain foreign atoms such as nitrogen, phosphorus, sulfur, chlorine, fluorine, or metallic complexing agents.

[0147] At least a portion of the process gas is recirculated. For this purpose, process gas from the treatment chamber, preferably a reactor, is fed to the thermal treatment of a bulk material via catalytic combustion and then returned to the treatment chamber. This recirculation process with process gas purification is described in EP-3 865 529 A1.

[0148] In this process, the method for purifying a process gas from a thermal treatment process of bulk materials includes at least one step of catalytic combustion.

[0149] The contaminated process gas can undergo further process steps before catalytic combustion, such as pressure increase, a process step for the separation of solid impurities, for example by means of a cyclone separator and / or a filter, mixing with the supplied oxygen-containing gas, for example by means of a static mixer, and heating to increase the temperature to a suitable combustion temperature, for example by means of a heat exchanger for heat recovery and / or by means of a process gas heater.

[0150] If necessary, the catalyst bed can also be heated directly, for example by external heat sources or by the heat of combustion of the impurities.

[0151] After catalytic combustion, the purified process gas can undergo further process steps, such as cooling, drying, pressure increase, a process step for the separation of solid impurities, for example by means of a cyclone separator and / or a filter, heating, and mixing with additives or other process gas streams.

[0152] Adsorption steps for removing so-called catalyst poisons are known in the prior art. Catalyst poisons are mostly inorganic substances that deposit on the surface of the catalyst material, thus directly deactivating the catalyst for catalytic combustion. Common catalyst poisons include halogens, sulfur, and heavy metals. The adsorption of the catalyst poisons can occur on the adsorption material itself or on an adsorbing coating on a support material. Common adsorbing coatings include bases such as sodium hydroxide, potassium hydroxide, or calcium oxide, as well as sodium or potassium carbonates.

[0153] Such adsorption materials are also suitable for removing high-boiling organic substances or organic substances with high combustion temperatures. Incomplete combustion of such substances leads to the deactivation of the catalyst for catalytic combustion. High-boiling hydrocarbons, in particular, have a deactivating effect because incomplete combustion can lead to carbon deposits on the catalyst material or directly clog the pores of the support material on which the catalyst material is applied.

[0154] According to one embodiment of the present invention, the contaminated gas undergoes a step for the adsorption of high-boiling organic substances or organic substances with a high combustion temperature onto a solid adsorption material in a protective bed prior to catalytic combustion.

[0155] The protective bed can be designed as a surface coated with an adsorption material. Preferably, however, the protective bed consists of a solid material in bulk, which can consist entirely of an adsorption material or be coated with one. Preferably, the protective bed is located within an adsorption vessel. The process gas flows through the adsorption vessel in any direction and passes through the adsorption bed, but preferably in one direction from a specific inlet side to a specific outlet side. The inlet side can be located at the top or bottom of the adsorption vessel. If liquid substances are to be removed, a bottom inlet position is preferred, so that the gas flows through the protective bed from bottom to top.The liquid residue can be discharged from the adsorption vessel, for example, via a valve. If sublimable substances are to be removed, an inlet at the top of the adsorption vessel is preferred, allowing the gas to flow from top to bottom through the protective bed. The uppermost layer of sublimated residue can then be removed.

[0156] The protective bed material can be placed on a separating element, which allows gas to pass through but not the protective bed material, in the central part of the adsorption vessel. The separating element is typically a sieve arranged in the adsorption vessel such that all process gas must flow through the sieve and the protective bed located on it. Preferably, the sieve can be heated to prevent deposits.

[0157] The adsorption vessel may have additional openings besides those for the inlet and outlet of the process gas. Preferably, an outlet opening for the protective bed material from the adsorption vessel may be located in the lower part of the vessel, and / or an outlet opening for the protective bed material from the adsorption vessel may be located in the middle part, and / or a feed opening for fresh or recycled protective bed material may be located in the upper part of the adsorption vessel. Furthermore, inlet and outlet openings for purge gas, in particular inert gas, may be provided to remove oxygen from the protective bed material. Additionally, an opening for sampling protective bed material may be located in the middle part of the adsorption vessel.

[0158] According to an alternative embodiment, the separating element can be conical and connected to a lockable outlet opening for the protective bed material from the adsorption vessel, so that the protective bed material can be emptied from the adsorption vessel by opening the outlet opening. According to a further alternative embodiment, the complete or partial emptying of the protective bed material from the adsorption vessel can be carried out in such a way that heavily contaminated protective bed material can be separated from less contaminated protective bed material and the less contaminated protective bed material is returned to the adsorption vessel.

[0159] The protective bed can be selected in such a way that it chemically binds substances from the process gas, or that it physically deposits substances from the process gas.

[0160] The inlet temperature of the process gas into the adsorption vessel can cover a wide range. However, it must be high enough to ensure any necessary chemical reactions and low enough to allow sufficient deposition of physically binding substances.

[0161] In particular, the temperature is adjusted such that high-boiling substances condense and can be absorbed by the adsorption material. If the process gas contains water, the temperature is selected to prevent condensation of water in the protective bed. For the treatment of thermoplastic polycondensates, whether virgin or recycled, the preferred temperature is in the range of 100 to 250°C, more preferably above 120°C, and particularly preferably below 170°C, and especially preferably from 120°C to 170°C.

[0162] To control the temperature, the process gas can be heated or, more commonly, cooled using heat exchangers. Cooling is preferably carried out in double-jacketed tubes or shell-and-tube heat exchangers to prevent deposits of condensing substances.

[0163] The contact time of the process gas in the protective bed ranges from one-tenth of a second to several minutes. Contact times in the range of 2 to 20 seconds are preferred.

[0164] The cross-sectional area of ​​the protective bed is selected such that a linear velocity of the process gas, or a conduit velocity (operating volume flow / protective bed packing cross-section in the direction of gas flow), is achieved in a range of approximately 0.05 to 3 m / s, resulting in a pressure drop of 10 mbar to 200 mbar, particularly 20 mbar to 100 mbar. The thickness of the protective bed should be constant across its entire cross-section and be in a ratio of 10:1 to 1:10 to the diameter of the protective bed packing.

[0165] In particular, the adsorption material is selected such that high-boiling substances are removed from the process gas, with at least a reduction to below 20%, preferably to below 10% of their initial value in the process gas.

[0166] Examples of adsorption materials that can be used include zeolites, silica gels, activated carbon, activated aluminum oxide and aluminum dioxide.

[0167] The present invention further relates to a device for producing and processing a mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process, comprising a first reactor for providing polyester prepolymer from a polyester manufacturing process in the form of a melt; a second reactor for providing recycled polyester material in the form of a melt; a first filter unit for purifying the melt of recycled polyester material, which is arranged downstream of the second reactor; a unit for producing a solid mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process, preferably a first particle forming device;wherein a first melt valve is arranged between the first reactor and the unit for producing the solid mixture, and a melt line and optionally a second melt valve are arranged between the first filter unit and the first melt valve, the second being connected to the first filter unit via a first section of the melt line and to the first melt valve via a second section of the melt line; a reactor for the thermal treatment of the solid mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process with a process gas which can be supplied to the solid mixture in countercurrent or crosscurrent flow to the direction of flow of the mixture; characterized in that a second filter unit is provided for removing solid impurities while obtaining a purer recycled polyester material, wherein the second filter unit is a melt filter whose openings have an average size larger than the average size of the openings of the melt filter used in the first filter unit, and the second filter unit is provided at a position selected from the group consisting of a position between the first melt valve and the unit for producing a solid mixture, and a position after the first filter unit and before the first melt valve, and optionally a second particle forming device is provided, wherein the second particle forming device is connected to the second melt valve, and wherein the first melt valve and the second melt valve are configured to be switchable.so that in a first switching arrangement in the first melting valve all melt lines are released and in the second melting valve the section of the melt line coming from the first filter unit is blocked and the section of the melt line leading to the first melting valve as well as the melt line leading to the second particle forming device are released, in a second switching arrangement in the first melting valve all melt lines are released and in the second melting valve the section of the melt line coming from the first filter unit as well as the section of the melt line leading to the first melting valve are released and the melt line leading to the second particle forming device is blocked,In a third switching arrangement, the melt line coming from the first reactor and the line leading to the unit for producing a solid mixture are opened in the first melt valve, and the section of the melt line leading to the second melt valve is blocked; in the second melt valve, the section of the melt line leading to the first melt valve is blocked, and the section of the melt line coming from the first filter unit and the melt line leading to the second particle forming device are opened; in a fourth switching arrangement, all melt lines are opened in both the first and second melt valves.

[0168] According to the invention, conventional systems for the thermal treatment of bulk material can be converted into a device according to the invention, in which one of the methods according to the invention can be carried out.

[0169] The present invention therefore also relates to a method for converting a plant for the production and thermal treatment of a bulk virgin material, preferably for the production and post-condensation of virgin polyester granulate, into a plant for the production and thermal treatment of polyester granulate comprising at least partially recycled material, which comprises at least partially regranulated polyester recycled material. wherein the plant comprises: a first reactor for providing polyester prepolymer from a polyester manufacturing process in the form of a melt; a unit for producing a solid, preferably a first particle forming device; a reactor for thermally treating the solid made of recycled polyester material and a polyester prepolymer from a polyester manufacturing process with a process gas, which can be supplied to the solid mixture in countercurrent or crosscurrent flow to the direction of flow of the mixture; wherein the plant is additionally equipped with: a second reactor for providing recycled polyester material in the form of a melt; a first filter unit for purifying the melt of recycled polyester material,which is arranged downstream of the second reactor; a first melt valve between the first reactor and the unit for producing the solid mixture; optionally a second melt valve between the first filter unit and the first melt valve, which is connected to the first filter unit via a first section of the melt line and to the first melt valve via a second section of the melt line; a second filter unit for removing solid impurities to obtain a purer recycled polyester material, wherein the second filter unit is a melt filter having an average size of openings larger than the average size of the openings of the melt filter used in the first filter unit, and the second filter unit is provided at a positionselected from the group consisting of a position between the first melt valve and the unit for producing a solid mixture, and a position after the first filter unit and before the first melt valve, and optionally a further unit for producing a solid, preferably a second particle forming device, which is connected to the second melt valve, wherein the first melt valve and the second melt valve are switchable, such that in a first switching arrangement in the first melt valve all melt lines are released and in the second melt valve the section of the melt line coming from the first filter unit is blocked and the section of the melt line leading to the first melt valve as well as the melt line leading to the second particle forming device are released,In a second switching arrangement, all melt lines are released in the first melt valve, and in the second melt valve, the section of the melt line coming from the first filter unit and the section of the melt line leading to the first melt valve are released, and the melt line leading to the second particle forming device is blocked; in a third switching arrangement, the melt line coming from the first reactor and the line leading to the unit for producing a solid mixture are released in the first melt valve, and the section of the melt line leading to the second melt valve is blocked; and in the second melt valve, the section of the melt line leading to the first melt valve is blocked, and the section of the melt line coming from the first filter unit and the melt line leading to the second particle forming device are released.In a fourth switching arrangement, all melt lines are opened in the first melting valve and the second melting valve.

[0170] The present invention is explained in more detail below with reference to non-limiting examples and drawings. These show: Fig. 1 a schematic view of a system according to the invention according to a first embodiment. Fig. 2 a schematic view of a system according to the invention according to a second embodiment. Fig. 3 a schematic view of a system according to the invention according to a third embodiment. Fig. 4 a schematic view of a system according to the invention according to a fourth embodiment. Fig. 5 a schematic view of a system according to the invention according to a fifth embodiment. Fig. 6 a schematic view of a system according to the invention according to a sixth embodiment. Fig. 7 a schematic view of a system according to the invention according to a seventh embodiment. Fig. 8 a schematic view of a system according to the invention according to an eighth embodiment.

[0171] In the figures, the same reference symbols denote the same components.

[0172] In Fig. 1Figure 1 shows a schematic view of a system according to the invention in a first embodiment.

[0173] In a first reactor 1, a slurry is prepared from terephthalic acid (TPA) and ethylene glycol (EG) and subsequently subjected to esterification, prepolymerization, and melt polycondensation in a finisher. A prepolymer melt of virgin PET (vPET) leaves the first reactor 1 and enters a first melt valve 1a.

[0174] Recycled PET (rPET, preferably PET flakes) is fed into a second reactor 2, preferably an extruder, where it is melted and extruded. The rPET melt is introduced into a first filter unit 3 (melt filter) and purified of solid impurities. The purified rPET melt is then conveyed via a melt line 3a to the first melt valve 1a and combined there with the prepolymer melt of virgin PET. A second melt valve 3b can preferably be arranged in the rPET melt line 3a to prevent the introduction of contaminated or low-quality rPET melt. The second melt valve 3b is connected to the first filter unit 3 via a first section 3a1 of the melt line 3a and to the first melt valve 1a via a second section 3a2 of the melt line 3a.In addition, at least one unit for measuring a quality parameter can be arranged in the melt line 3a for the rPET melt.

[0175] The melt mixture combined in the first melting valve 1a is then mixed in an optional mixing unit 4, here a static mixer, and subsequently granulated in a unit for the production of a solid 6, here a granulator (preferably an underwater granulator or underwater strand granulator), optionally dried, and brought to a desired degree of crystallinity in a crystallizer 7. The partially crystalline PET granule mixture is heated in a preheater 8 to a temperature required for the SSP reaction and subjected to an SSP reaction in the reactor 9 for thermal treatment. The finished PET mixture leaves the reactor 9 with the desired intrinsic viscosity and can optionally be cooled, transported, and / or stored and subsequently processed further.

[0176] The facility according to Fig. 1The system is characterized by the fact that a second filter unit 5 is arranged between the mixing unit 4 and the unit for producing a solid 6. In the second filter unit 5, solid impurities are removed, resulting in a purer recycled polyester material. The second filter unit 5 comprises a melt filter whose openings have an average size that is larger than the average size of the openings of the melt filter used in the first filter unit 3.

[0177] In Fig. 2 Figure 1 shows a schematic view of a system according to the invention in a second embodiment. The system according to Fig. 2 differs from the system according to Fig. 1The second filter unit 5 is arranged between the second melt valve 3b and the first melt valve 1a. Additionally, a third filter unit 10 is arranged between the first reactor and the first melt valve.

[0178] In Fig. 3 Figure 1 shows a schematic view of a system according to the invention in a third embodiment. The system according to Fig. 3 differs from the system according to Fig. 1 In that, instead of a second filter unit 5, a second particle forming device 5' for producing a solid is provided as a further unit for removing solid impurities while obtaining a purer recycled polyester material. The second particle forming device 5' for producing a solid is here a granulator (preferably an underwater granulator or underwater strand granulator) which is connected to the second melt valve 3b.

[0179] The facility according to Fig. 3The unit features switchable melt valves 1a and 3b and can be operated in various switching configurations as described above. In a first switching configuration, polyester prepolymer melt from the first reactor 1 can pass through an optional third filter unit 10, the first melt valve 1a, the second section 3a2 of the melt line 3a, and the second melt valve 3b into the second particle forming device 5' for the production of a solid. In a second switching configuration, polyester recyclate melt from the second reactor 2 can pass through the first filter unit 3, the first section 3a1 of the melt line 3a, the second melt valve 3b, the second section 3a2 of the melt line 3a, and the first melt valve 1a into the unit 6 for the production of a solid.In a third switching arrangement, polyester recyclate melt from the second reactor 2 can pass through the first filter unit 3, the first section 3a1 of the melt line 3a and the second melt valve 3b into the second particle forming device 5' for the production of a solid.

[0180] In Fig. 4 Figure 1 shows a schematic view of a system according to the invention, specifically a fourth embodiment. The system according to Fig. 4 differs from the system according to Fig. 3 in that a second filter unit 5 is additionally arranged between the mixing unit 4 and the unit for producing a solid 6. The optional third filter unit 10 is omitted here.

[0181] In Fig. 5 Figure 1 shows a schematic view of a system according to the invention, specifically a fifth embodiment. The system according to Fig. 5 differs from the system according to Fig. 3The second melt valve 3b is arranged in close proximity to the first melt valve. When the melt line from the first filter unit 3 and the melt line to the second particle forming device 5' are opened in the second melt valve 3b, melt from recycled PET can be directed through the first filter unit 3 and the melt line 3a into the second particle forming device 5' for the production of a solid. In this process, the melt from recycled PET carries impurities from the entire piping system 3a1 between the second reactor 2 and the second melt valve 3b out of the system. Purging the very short melt line 3a2 between the first melt valve 1a and the second melt valve 3b with prepolymer melt made from virgin PET (vPET) is not necessary.Particularly preferred for this embodiment is a piston valve for shutting off the melt of PET recyclate, wherein the shut-off piston, in the closed state, displaces a large part of the volume of the melt line between the second melt valve 3b and the point in the first melt valve 1a where the melt streams are combined.

[0182] In Fig. 6 Figure 1 shows a schematic view of a plant according to a fifth embodiment of the invention. In a first reactor 1, a slurry is prepared from terephthalic acid (TPA) and ethylene glycol (EG) and subsequently subjected to esterification, prepolymerization, and melt polycondensation in a finisher. A prepolymer melt of virgin PET (vPET) leaves the first reactor 1 and enters a first melt valve 1a.

[0183] Recycled PET (rPET, preferably PET flakes) is fed into a second reactor 2, preferably an extruder, where it is melted and extruded. Optionally, the rPET melt is introduced into a first filter unit (melt filter, not shown) and purified of solid impurities. The rPET melt is then conveyed via a melt line 3a to the first melt valve 1a and combined there with the prepolymer melt of virgin PET. A second melt valve (not shown) can optionally be arranged in the rPET melt line 3a to prevent the introduction of contaminated or low-quality rPET melt. Furthermore, at least one unit for measuring a quality parameter can be arranged in the rPET melt line 3a.

[0184] The melt mixture combined in the first melting valve 1a is then mixed in an optional mixing unit (not shown) and subsequently granulated in a unit for the production of a solid 6, here a granulator (preferably an underwater granulator or underwater strand granulator) and, if necessary, dried.

[0185] Optionally, the rPET melt can be purified of solid impurities in a second filter unit (melt filter, not shown). Likewise, the vPET melt can optionally be purified of solid impurities in a second filter unit (melt filter, not shown).

[0186] The PET granule mixture is optionally brought to a desired degree of crystallinity in a crystallizer (not shown). The partially crystalline PET granule mixture is optionally heated in a preheater (not shown) to a temperature required for thermal treatment and then subjected to thermal treatment in reactor 9. The thermal treatment includes processes for the removal of volatile components and processes for an SSP reaction. The finished PET mixture leaves reactor 9 with the desired intrinsic viscosity and purity and can optionally be cooled, transported, and / or stored and subsequently processed further.

[0187] The facility according to Fig. 6This method can be used when a molded body with a b* value (BF) < 0 is required. A coloring additive with a negative b* value is preferably added to the polyester prepolymer in the first reactor 1 or at any point in a first series of reactors. No further addition of a coloring additive with a negative b* value is carried out in the system. The solid mixture produced in the unit for manufacturing a solid 6 is then fed to the first reactor 9 for thermal treatment and to a further reactor 11 for thermal treatment, where it is, for example, dried. Subsequently, the PET solid mixture is formed into a desired molded body in a unit 12 for manufacturing a molded body. The molded body is typically produced by melting the PET solid mixture.

[0188] In Fig. 7Figure 1 shows a schematic view of a system according to the invention, specifically a sixth embodiment. The system according to Figure 2... Fig. 7 differs from the system according to Fig. 6 The polyester recyclate melt exiting the second reactor 2 enters a granulator 6' (another unit for producing a solid mixture) and is combined with the virgin PET granules from granulator 6. The first melt valve 1a and the melt line 3a are omitted. The remaining steps are identical.

[0189] In Fig. 8 Figure 1 shows a schematic view of a system according to the invention, specifically a seventh embodiment. The system according to Fig. 8 differs from the system according to Fig. 7in that the polyester recyclate converted into a solid in granulator 6' is first processed in a third reactor 13 for thermal treatment, here a solid phase post-condensation (SSP) or dealdehydization, before it is combined with the vPET which has also already been subjected to thermal treatment in reactor 9. Example 1

[0190] In a conventional polyethylene terephthalate (PET) production plant, a slurry was prepared from terephthalic acid (TPA) and ethylene glycol (EG). This slurry was then subjected to esterification, prepolymerization, and melt-phase polymerization in a finisher. A blue coloring additive in ethylene glycol was added, resulting in a b* value of -4.1 for the polyester prepolymer melt. To measure the b* value, the melt was granulated and crystallized.

[0191] A polyester recyclate melt with a b* value of +0.2 was produced from washed PET bottle waste in an extruder. No coloring additive was added to the polyester recyclate melt. To measure the b* value, the melt was granulated and crystallized.

[0192] Both melts were subjected to melt filtration to remove solid impurities. Sieves with a 60 µm mesh size were used.

[0193] The two product streams are continuously blended into a PET solid mixture in proportion to their production output (130 t / d of polyester prepolymer and 30 t / d of recycled polyester) and processed into cylindrical, amorphous PET prepolymer granules (granule weight approx. 18 mg) by underwater strand granulation. The granules were subjected to crystallization in a fluidized bed reactor, preheating to the SSP reaction temperature under inert gas in a roof-mounted heat exchanger, and solid-phase treatment via solid-phase polycondensation (SSP). The vPET granules exhibited an IV of 0.62 dl / g before SSP and an IV of 0.82 dl / g after SSP.

[0194] The PET solid mixture was treated in a continuously operated fixed-bed reactor in countercurrent flow with nitrogen at 204°C for 12 hours.

[0195] The PET solid mixture treated in this way had a b* value of -2.8.

[0196] The PET solid mixture was processed into preforms for beverage bottles. No additional coloring additive was added to the PET solid mixture. The preforms still exhibited a slight blue hue. Measured in the milled state, the b* value was -0.3.

[0197] In this example, the addition of the coloring additive during vPET production not only compensated for the initial yellowing of the rPET, but also the yellowing that occurred during thermal treatment and preform production. Clearer, almost colorless preforms could be produced without the need for an additional coloring additive during preform production.

[0198] By further increasing the amount of coloring additive in the polyester prepolymer, a PET solid mixture appearing blue was produced. This could then be processed into blue-appearing preforms without the need for any further coloring additives during preform production. Comparison example 1

[0199] A PET solid mixture was produced from 8t / h vPET and 2t / h rPET in a device according to Figure 6 Compared to the production of pure vPET, the addition of a solution of a blue-coloring additive in ethylene glycol to the vPET manufacturing process was increased by 10%. Preforms were produced by injection molding, whereby a blue-coloring additive had to be added in a liquid additive carrier to produce preforms with a bluish appearance. Example 2

[0200] Comparative Example 1 was repeated, increasing the addition of the blue-coloring additive solution in ethylene glycol to the vPET manufacturing process by a further 3% (i.e., to plus 13%). The result was a PET solid mixture with a b* value of -3.2. This PET solid mixture could be processed into preforms with a bluish appearance without further addition of a blue-coloring additive to the injection molding process. Comparison example 2

[0201] A PET solid mixture was produced from 8.7 t / h vPET and 1.7 t / h rPET in a device according to Figure 3 The vPET melt was purified of solids using a candle filter 10 with a nominal screen opening of 56 µm. The rPET melt was purified of solids using a piston filter 3 (screen changer with backflushing) with a nominal screen opening of 56 µm.

[0202] First, the melt valves 1a, 3b were adjusted such that the vPET melt was fed in the main stream to two parallel strand pelletizing units 6 and the rPET melt was fed in the secondary stream to a separate strand pelletizing unit 5'.

[0203] After a start-up phase of one day, the melt valves were adjusted so that the rPET melt was fed to the vPET melt and the mixture was fed to the two parallel granulators 6 in the main stream.

[0204] Samples of amorphous granules were taken from all granulators every two hours. The average amount of black specks in the range of 100–500 µm per kilogram was calculated over 12 hours. The values ​​from the two granulators operating in parallel in the main stream were averaged. Example 2 black specs in quantity per kg vPET rPET mixture Starting 1.6 14 n / a 0-12 hours after switching (1.6) (47) 9 >48 hours after switching (1.6) (19) 4.3

[0205] The values ​​in parentheses are calculated values ​​assuming that the black spec number in the vPET has not changed after startup.

[0206] Additionally, it was observed that black specks larger than 500 µm were found in some samples during the first 12 hours after switching to the melt valves. Such contaminants were not present before switching the melt valves. Irregularly shaped black specks are sized as the diameter of a circle of the same area.

[0207] Using this procedure, it took two days to produce a good-quality vPET / rPET solid mixture. Almost 500 tons of substandard PET were produced. Example 3

[0208] Comparative example 2 was repeated, with the melt valves 1a and 3b being adjusted after start-up such that vPET melt was fed to the separate strand granulation unit 5' for two days. After switching the melt valves 1a and 3b to produce the vPET / rPET mixture, a product with a black spec content <5 was obtained directly, with the value having decreased further to 3.9 after 72 hours.

[0209] This operating procedure enabled the immediate production of a high-quality vPET / rPET solid mixture after switching the melting valves 1a and 3b. Approximately 80 tons of low-quality rPET were produced. Example 4

[0210] The facility according to Fig. 3The system was supplemented by an additional melt filter 5 directly upstream of valve 1a for combining the rPET and vPET melts. This was a continuously operated laser filter with a perforated plate with openings in the range of 100–120 µm. Comparative example 2 was repeated, with the melt valves 1a and 3b being adjusted after start-up to directly produce a vPET / rPET mixture. A product with a black spec content of <5 was obtained immediately, and this value had decreased further to 2.7 after 72 hours.

[0211] This procedure enabled the production of a high-quality vPET / rPET solid mixture immediately after switching melt valves 1a and 3b. No inferior product was produced.

Claims

1. A process for producing and processing a blend of recycled polyester material and a polyester prepolymer from a polyester manufacturing process, comprising the steps of: - Provision of a recycled polyester material in the form of a melt and initial purification of the melt by removing solid impurities using melt filtration; - Mixing of the recycled polyester material in the form of a melt with a polyester prepolymer in the form of a melt from a polyester manufacturing process and subsequent production of a solid mixture, preferably in a first particle forming device (6); - Treatment of this solid mixture in a reactor (7, 8, 9, 11) for the thermal treatment of bulk material with a process gas in counterflow or crossflow to the flow direction of the mixture; wherein at least for a first period after the start of the process, prior to the production of the solid mixture, at least one additional step is carried out to purify the melt by removing solid impurities to obtain a purer recycled polyester material, characterized in that the additional step of purifying the melt of the recycled polyester material by means of melt filtration is carried out by a melt filter (5) whose openings have an average size which is larger than the average size of the openings of the melt filter used in the first purification.

2. The process according to claim 1, characterized in that the additional step of purifying the melt of the recycled polyester material by means of melt filtration is carried out before the step of mixing the recycled polyester material in the form of a melt with the polyester prepolymer in the form of a melt from a polyester manufacturing process.

3. The process according to claim 1, characterized in that the additional step of purifying the melt of the recycled polyester material by means of melt filtration is carried out after the step of mixing the recycled polyester material in the form of a melt with the polyester prepolymer in the form of a melt from a polyester manufacturing process.

4. The process according to claim 1, characterized in that an additional step of purifying the melt of the recycled polyester material is achieved by introducing the polyester prepolymer in the form of a melt from a polyester manufacturing process or the recycled polyester material in the form of a melt, in each case with entrainment of deposited impurities from at least one section (3a1, 3a2) of the melt line (3a), into a second particle forming device (5') and the production of the solid material with discharge of entrained deposited impurities in the further unit.

5. A process according to any one of the preceding claims, characterized in that the proportion of recycled polyester material in the solid mixture comprises 10 - 90% and has a b* value (BR), and the proportion of polyester prepolymer from a polyester manufacturing process in the solid mixture comprises 90 - 10% and has a b* value (BN), and wherein the resulting solid mixture has a b* value (BM) and BM < 0, BN < 0 and BR > BN.

6. The process according to claim 5, characterized in that a coloring additive having a negative b* value is added to the polyester prepolymer from a polyester manufacturing process prior to combining with the recycled polyester material, the coloring additive being added to the polyester prepolymer from a polyester manufacturing process without prior dilution or as part of an additive mixture, further comprising a monomer of the polyester, and no coloring additive having a negative b* value is added to the recycled polyester material prior to combining with the polyester prepolymer from a polyester manufacturing process.

7. A device for producing and processing a mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process, comprising - a first reactor (1) for providing polyester prepolymer from a polyester manufacturing process in the form of a melt; - a second reactor (2) for providing recycled polyester material in the form of a melt; - a first filter unit (3) for cleaning the melt of recycled polyester material, which is arranged downstream of the second reactor; - a unit (6) for producing a solid mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process, preferably a first particle forming device; wherein a first melt valve (1a) is arranged between the first reactor (1) and the unit (6) for producing the solid mixture, and a melt line (3a) and optionally a second melt valve (3b) which is connected to the first filter unit (3) via a first section (3a1) of the melt line (3a) and to the first melt valve (1a) via a second section (3a2) of the melt line (3a) are arranged between the first filter unit (3) and the first melt valve (1a),; - a reactor (7, 8, 9, 11) for the thermal treatment of the solid mixture of recycled polyester material and a polyester prepolymer from a polyester manufacturing process with a process gas which can be fed to the solid mixture in countercurrent or crosscurrent to the flow direction of the mixture; characterized in that a second filter unit (5) is provided for removing solid impurities for obtaining a purer recycled polyester material, wherein the second filter unit (5) used is a melt filter whose openings have an average size which is larger than the average size of the openings of the melt filter used in the first filter unit (3), and the second filter unit (5) is provided at a position selected from the group consisting of a position between the first melt valve (1a) and the unit (6) for producing a solid mixture and a position after the first filter unit (3) and before and the first melt valve (1a), and optionally a second particle forming device (5') is provided, the second particle forming device (5') being connected to the second melt valve (3b), wherein the first melt valve (1a) and the second melt valve (3b) are designed to be switchable, such that in a first switching arrangement in the first melt valve (1a) all melt lines are released, and in the second melt valve (3b) the section (3a1) of the melt line (3a) coming from the first filter unit (3) is blocked and the section (3a2) of the melt line (3a) leading to the first melt valve (1a) and the melt line leading to the second particle forming device (5') are released, in a second switching arrangement, all melt lines in the first melt valve (1a) are released, and in the second melt valve (3b) the section (3a1) of the melt line (3a) coming from the first filter unit (3) and the section (3a2) of the melt line (3a) leading to the first melt valve (1a) are released and the melt line leading to the second particle forming device (5') is blocked, in a third switching arrangement, in the first melt valve (1a), the melt line coming from the first reactor (1) and the line leading to the unit (6) for producing a solid mixture are unblocked and the section (3a2) of the melt line (3) leading to the second melt valve (3b) is blocked, and in the second melt valve (3b) the section (3a2) of the melt line (3a) leading to the first melt valve (1a) is blocked and the section (3a1) of the melt line (3a) coming from the first filter unit (3) and the melt line leading to the second particle forming device (5') are unblocked, in a fourth switching arrangement in the first melt valve (1a) and the second melt valve (3b), all melt lines are released.

8. Process for retrofitting a plant for the production and thermal treatment of a bulk virgin material, preferably for the production and post-condensation of polyester granulate virgin material, into a plant for the production and thermal treatment of a polyester granulate comprising at least partially recycled material, which comprises at least partially regranulated polyester recyclate, wherein the system comprises: - a first reactor (1) for providing polyester prepolymer from a polyester manufacturing process in the form of a melt; - a unit (6) for producing a solid, preferably a first particle forming device; - a reactor (7, 8, 9, 11) for the thermal treatment of the solid material consisting of recycled polyester material and a polyester prepolymer from a polyester manufacturing process with a process gas which can be fed to the solid material mixture in counterflow or crossflow to the flow direction of the mixture; characterized in that the system is additionally equipped with: - a second reactor (2) for providing recycled polyester material in the form of a melt; - a first filter unit (3) for cleaning the melt of recycled polyester material, which is arranged downstream of the second reactor (2); - a first melt valve (1a) between the first reactor (1) and the unit (6) for producing the solid mixture; - optionally a second melt valve (3b) between the first filter unit (3) and the first melt valve (1a), which is connected to the first filter unit (3) via a first section (3a1) of the melt line (3a) and to the first melt valve (1a) via a second section (3a2) of the melt line (3a); - a second filter unit (5) for removing solid impurities for obtaining a purer recycled polyester material, wherein the second filter unit (5) is a melt filter whose openings have an average size which is larger than the average size of the openings of the melt filter used in the first filter unit (3), and the second filter unit (5) is provided at a position selected from the group consisting of a position between the first melt valve (1a) and the unit (6) for producing a solid mixture, and a position after the first filter unit (3) and before the first melt valve (1a), and - optionally a further unit (5') for producing a solid, preferably a second particle forming device, which is connected to the second melt valve (3b), the first melt valve (1a) and the second melt valve (3b) being designed to be switchable so that in a first switching arrangement in the first melt valve (1a) all melt lines are released, and in the second melt valve (3b) the section (3a1) of the melt line (3a) coming from the first filter unit (3) is blocked and the section (3a2) of the melt line (3a) leading to the first melt valve (1a) and the melt line leading to the second particle forming device (5') are released, in a second switching arrangement, in the first melt valve (1a) all melt lines are released, and in the second melt valve (3b) the section (3a1) of the melt line (3a) coming from the first filter unit (3) and the section (3a2) of the melt line (3a) leading to the first melt valve (1a) are released and the melt line leading to the second particle forming device (5') is blocked, in a third switching arrangement, in the first melt valve (1a) the melt line coming from the first reactor (1) and the line leading to the unit (6) for producing a solid mixture are unblocked and the section (3a2) of the melt line (3) leading to the second melt valve (3b) is blocked, and in the second melt valve (3b) the section (3a2) of the melt line (3a) leading to the first melt valve (1a) is blocked and the section (3a1) of the melt line (3a) coming from the first filter unit (3) and the melt line leading to the second particle forming device (5') are unblocked, in a fourth switching arrangement in the first melt valve (1a) and the second melt valve (3b), all melt lines are released.

9. A process of manufacturing a molded article comprising the steps of: Preparation of a polyester solid mixture by a process according to any one of claims 1 to 6, and molding a molded body from the polyester solid mixture, wherein no coloring additive with a negative b* value is added during the molding of the molded body and the molded body has a b* value (BF), wherein BF < 0.