CN118201750A

CN118201750A - Method and apparatus for preparing and treating a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process

Info

Publication number: CN118201750A
Application number: CN202280074092.0A
Authority: CN
Inventors: A·克里斯特尔; K·斯豪夫
Original assignee: Polymetrix AG
Current assignee: Polymetrix AG
Priority date: 2021-11-12
Filing date: 2022-11-08
Publication date: 2024-06-14

Abstract

The invention relates to a method for producing a polyester solid mixture by adding together a proportion of recycled polyester material and a proportion of polyester material from a polyester production process, wherein the proportion of recycled polyester material in the polyester solid mixture is 10-90% and has a b-value (BR) and the proportion of polyester material from the polyester production process in the polyester solid mixture is 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.

Description

Method and apparatus for preparing and treating a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process

Background

For ecological reasons, recycling of polyesters such as PET is becoming increasingly important. One variation involves mixing recycled polyester material with polyester prepolymer pellets from a polyester manufacturing process to obtain a high quality product. Preferably, the recycled polyester is introduced into the polyester manufacturing process for this purpose.

WO 00/77071A1 describes two options in which recycled polyesters can be introduced into the polyester production process.

In a first option, the pre-cleaned recycled polyester material is extruded and pelletized to obtain recycled polyester pellets, which are then mixed with polyester prepolymer pellets from a polyester manufacturing process and subjected together to a solid phase polycondensation treatment.

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

In both cases, the cleaning of the recycled polyester is performed with one or more of the following steps:

removing surface impurities in the solid phase, for example by means of a washing process;

-removing impurities in the solid phase by heat treatment, for example by a drying process;

Removing impurities in the melt phase, for example by applying a vacuum in the degassing chamber or using a purge gas;

-removing impurities in the solid phase by heat treatment in a solid phase polycondensation step.

Removal of surface impurities reduces the content of volatile, semi-volatile and non-volatile impurities. However, this is limited to impurities present on the surface or mixed with the recycled polyester. Impurities in the polyester, such as absorbed impurities or additives, are not affected.

During the heat treatment prior to extrusion, most of the volatile impurities can be removed. However, only small amounts of semi-volatile impurities are removed under generally limited process conditions. Longer residence times and higher process temperatures can increase the removal of semi-volatile impurities in this step. However, this will have adverse consequences (discoloration, formation of decomposition products, undesired viscosity increase) for the subsequent process steps and the quality of the recovered polyester.

During extrusion, residual surface impurities, absorbed impurities and impurities present as individual particles are homogeneously mixed with the recovered polyester melt. At the same time, regenerated impurities are produced. These regenerated impurities include degradation products of the impurities and degradation products of the recycled polyester, wherein degradation of the polyester is often accelerated (catalyzed) by the impurities present.

WO 00/77071A1 describes the possibility of using a degassing chamber. However, the widespread use of such equipment to remove large amounts of semi-volatile impurities will have very adverse consequences on the quality of the recovered polyester (discoloration, formation of decomposition products). In addition, the problem of the formation of degradation products cannot be solved.

From the above, it is clear that impurities from the recovered polyester are introduced into the solid phase polycondensation step at the end of the process chain. However, WO 00/77071A1 only relates to standard techniques for carrying out solid phase polycondensation. However, due to the significantly higher contamination of impurities, the mixture of freshly prepared polyester (the so-called "virgin" material) with recycled polyester is not continuously processed in conventional solid phase polycondensation apparatus for the longer operating time required.

EP-3 865 529a1 describes the possibility of removing volatile and partially volatile impurities which enter the gas phase and can be removed by a cleaning process gas.

However, a further disadvantage is caused by impurities remaining in the melt. These impurities include solid impurities and colored, yellowing impurities that are carried substantially by or formed from recycled polyester material. Although the prior art performs surface cleaning of recycled polyester material during the washing process, residues of impurities may still adhere to the surface. In addition, residues of the washing chemicals used in the washing process may adhere to the surface. Such impurities are generally less thermally stable than the polyester material and, at the temperature of the polyester melt, result in colored degradation products that cause the recycled polyester material to turn yellow.

At the same time, the recycled polyester material may contain additives that are less thermally stable, or foreign plastics may be incorporated into the polyester melt, which also leads to yellowing.

The use of the procedure proposed in EP-3 865 529A1 does not satisfactorily remove the solid impurities mentioned above. The problem of yellowing of the above-mentioned materials is not solved in this prior art either.

Disclosure of Invention

The problem underlying the present invention is to overcome the disadvantages of the prior art discussed herein and to provide an improved method and apparatus for preparing and handling a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process.

According to the invention, the present problem is solved by a method according to claim 1.

More specifically, the present invention relates to a process for preparing and treating a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process comprising the steps of:

-providing recycled polyester material in the form of a melt and subjecting the melt to a first purge by removing solid impurities using melt filtration;

-mixing, preferably in a first particle forming apparatus, the recycled polyester material in melt form with the polyester prepolymer in melt form from the polyester manufacturing process and subsequently preparing a solid mixture;

-treating the solid mixture with a process gas counter-current or cross-current to the flow direction of the mixture in a reactor for the heat treatment of bulk material;

characterized in that at least a first period of time after the start of the process, at least one further step for purifying the melt by removing solid impurities to obtain a purer recovered polyester material is performed before preparing the solid mixture.

The method is characterized in particular by the fact that: the substances introduced into the process from the recovered polyester material can be reliably removed before heat treatment, such as solid phase condensation. This makes it possible to reliably and continuously process a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process.

Bulk materials are any form of free flowing solid particles such as granules, flakes, pellets, powders or agglomerates.

According to the invention, the bulk material is a polycondensate, i.e. a polyester in solid form.

Polyesters are obtained from their monomers by polycondensation. A polymer of a polymer type may be obtained from the same main monomer. A polymer of the polymer type may also be obtained from several main monomers. The individual monomers may be arranged alternately, randomly or in blocks. Other monomers, so-called comonomers, may also be used in limited amounts.

The monomer may be obtained from fossil fuels such as crude oil, natural gas or coal, or from renewable feedstocks. Monomers can also be obtained from existing polymers, in particular recovered polymers, by depolymerization or pyrolysis.

Polycondensates are obtained by polycondensation reactions with elimination of low molecular weight reaction products. Polycondensation may be carried out directly between the monomers. Polycondensation can also be carried out via the intermediate product and then converted by transesterification, wherein transesterification can again be carried out by elimination of the low molecular weight reaction product or by ring opening polymerization. The polycondensates obtained in this way are linear in nature, although small amounts of branching may occur.

Suitable polymers according to the invention are polyesters comprising polyhydroxyalkanoates, polylactides or copolymers thereof.

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

Typically, a linear or cyclic diol component and an aromatic or heterocyclic dicarboxylic acid component are used. Instead of dicarboxylic acids, the corresponding diesters, usually dimethyl esters, can also be used. Furthermore, the reaction product of a dicarboxylic acid with two diols, which is present in particular in the form of the structure HO-R ¹-OOC-R²-COO-R¹ -OH, can be used partly or completely instead of the dicarboxylic acid. An example thereof is the preparation of polyethylene terephthalate using bis (2-hydroxyethyl) terephthalate.

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

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

One example is a polyhydroxyalkanoate having the general structure H- [ O-C (R) H- (CH ₂)_n-CO]_x -OH), wherein R is typically hydrogen or an aliphatic hydrocarbon having 1 to 15 carbon atoms, and n is 1 to 10. Examples are poly-4-hydroxybutyrate and poly-3-hydroxyvalerate.

Another example is a polylactide having the general structure H- [ O-C (R) H-CO ] _x -OH, where R is typically a methyl group or an aliphatic hydrocarbon having 1 to 15 carbon atoms.

Another example is polyglycolic acid having the general structure H- [ O-CH ₂-CO]_x -OH.

Polyesters are also polymers prepared by ring opening polymerization of heterocyclic monomers having one ester group, such as polycaprolactone prepared from caprolactone, or polymers prepared by ring opening polymerization of heterocyclic monomers having at least two ester groups, such as polylactide prepared from lactide.

The most common polylactides are polylactic acids having the structure H- [ O-C (CH ₃)H-CO]_x -OH. Due to the chirality of lactic acid, various forms of polylactic acid exist. Homopolymers are poly-L-lactide (PLLA) which is typically prepared from L, L-lactide, and poly-D-lactide (PDLA) which is typically prepared from D, D-lactide. Copolymers such as poly- (L-lactide-co-D, L-lactide) contain small amounts of lactide units which differ in chirality from the main monomer.

Polyesters can also be prepared by biosynthesis with the aid of microorganisms or in plant cells, from which they are obtained by disintegration of the cells.

Suitable polyesters may be homopolymers. Although referred to as homopolymers, a small fraction of the comonomer is still formed during the manufacturing process. For example, the formation of diethylene glycol from ethylene glycol is known to occur in the preparation of polyethylene terephthalate. However, many suitable polyesters are copolymers containing a proportion of comonomer. The comonomers may be incorporated as part of the monomer during the polyester manufacturing process, or they may be formed as part of the manufacturing process, typically resulting in a random distribution in the final polyester. The comonomers can also be introduced as blocks, prepared from different monomers, resulting in so-called block copolymers.

Suitable polyesters may be polymer blends, which may contain any number and amount of different types of polyesters. A small amount of one polyester may act as a nucleating agent in the other polyester, thereby increasing their crystallization rate.

Certain polyester mixtures can form interacted crystalline structures having a crystallization behavior different from that of the individual components. An example thereof is a mixture of PDLA and PLLA, which forms a stereocomplex crystal structure with increased crystallinity.

After polymerization, each polymer chain has a chain terminating group that typically has functionality of at least one of its monomers. For example, the polyester chain may have one or more hydroxyl and/or carboxyl end groups. Such end groups may be modified by so-called capping agents or by degradation reactions. Although not specifically mentioned in the above general structure, suitable polyesters may have such modified end groups.

Additives may be added to the polyester. Suitable additives include catalysts, colorants and pigments, UV blockers, processing aids, stabilizers, impact modifiers, foaming agents of chemical and physical nature, fillers, nucleating agents, flame retardants, plasticizers, particles to improve barrier or mechanical properties, reinforcements such as spheres or fibers, and reactive materials such as oxygen absorbers, acetaldehyde absorbers or substances to increase molecular weight.

The polyester may be virgin or recycled. The virgin polyester material is a polyester prepared from monomers thereof, wherein the monomers may be derived from petroleum-based sources, biologically renewable feedstocks or depolymerization of polyester articles or waste, wherein the monomers may also include dimers and lower oligomers having a chain length of up to 9 polyester repeat units. If the polyester meets the definition of recyclate, it is not considered the original material.

Recycled polyester from manufacturing and handling operations (post-industrial) or polyester collected and recycled after consumer use (post-consumer) is referred to as recycle. The chain length of the polyester recyclate to be used according to the invention is preferably still at least 10 (preferably 20, in particular 30 or 40) polyester repeat units. The recycled polyester may preferably consist of consumer waste, such as used polyester articles. Typical examples of such articles are polyester bottles, polyester trays or polyester fibers. Depending on their size and composition, the polyester articles must be ground and/or compacted in order to obtain the proper particle size and bulk weight for further processing. Suitable bulk weights are from 100 to 800kg/m ³, in particular from 200 to 500kg/m ³. Suitable particle sizes are from 1 to 50mm, in particular from 2 to 25mm. Depending on their contamination level, the recycled polyesters have to be cleaned before further treatment. This may include process steps such as washing, sorting or separation. Furthermore, the recovered polyester may be separated from volatile impurities and water by means of heat treatment in a gas stream and/or under reduced pressure.

The present invention relates to the treatment of a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process.

According to the invention, the polyester prepolymer is provided in melt form from a polyester manufacturing process in a first reactor or series of reactors, wherein the reactor in which the polyester prepolymer finally used as starting material for the process according to the invention is prepared is referred to as the first reactor. Polyester production processes and suitable reactors for this purpose are well known in the prior art (e.g. Scheirs/Long, eds., modern polyesters (Modern Polyesters), wiley 2003, II.2.4, pages 89-98).

For the purposes of the present invention, a continuous polyester production process is preferred. According to the invention, a suitable polyester production process is designed such that a polyester prepolymer melt is produced by means of melt phase polymerization. Melt phase polymerization involves a process step in which a suitable viscosity for further processing is achieved. This can be done, for example, in a melt phase reactor. Once the proper viscosity is achieved, the polyester melt is fed through a suitable melt line to one or more pelletizers.

Optionally, the polyester prepolymer melt may be filtered in a melt filter. The term melt filter includes screen changers and static or cartridge filters.

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

The melt of the recovered polyester is typically prepared by extrusion. Alternatively, however, a simple melt reactor may be used. The recovered polyester melt may optionally be subjected to further pressure build-up by means of a melt pump and/or separation of volatile impurities by means of entrained gas or vacuum.

According to a preferred embodiment of the invention, the melt of the recovered polyester is subjected to separation of solid impurities by means of melt filtration before being mixed with the polyester prepolymer in the form of a melt from the polyester manufacturing process. The first filter unit for this is located downstream of the second reactor. In other words, the melt of the recovered polyester from the second reactor is fed into the first filter unit through a feed line (melt line).

Preferably, the recovered polyester melt is filtered through a first filter unit, such as a screen, having openings comparable to or smaller than the openings of the filter unit, such as a screen, for filtering the melt during the polyester production process.

The filter unit used according to the invention has a large number of openings through which the melt can pass while the solids are retained. The openings may be circular, angular or irregularly shaped. The circular opening is mainly present in the locking plate. Here, the hole diameter means the size of the opening. Angular or irregularly shaped openings are primarily present in woven screens. In a simple woven screen, the mesh size represents the size of the openings. In screen fabrics with complex structures such as the netherlands, the nominal opening size is derived from the size of the retained particles.

Melt filters are usually operated with several screens with openings of different sizes, so-called screen packs. The openings of the finest screen are decisive. Especially for screens, but also for locking plates, displacement, expansion or wear may occur, resulting in slightly different hole sizes. For this reason, the average opening size is determined as an average value of the entire opening.

The recovered melt is fed from the first filter unit through a melt line to a first melt valve, which serves as a connecting unit, where it is combined and mixed with the melt of the polyester prepolymer from the polyester manufacturing process. For example, the melt lines may be corresponding pipe connections.

The melt mixture is then fed in a common melt line to a unit for producing a solid mixture, preferably in a first particle forming apparatus, particularly preferably in a granulator, such as an underwater pelletizing Unit (UWG) or an underwater strand pelletizing Unit (USG), where it is pelletized.

The first particle forming apparatus may also be a plurality of particle forming apparatuses operating in parallel.

According to a preferred embodiment of the invention, the melt mixture may be mixed in a mixing unit to prepare a solid mixture before entering the unit. For this purpose, any mixing unit suitable for mixing melts may be used. For example, a mixing unit with a static mixer may be used.

According to the invention, a mixture of solids is understood to be a mixture of particles of different composition, in particular granules, wherein a mixture of virgin PET particles and rPET particles may be present. However, it may also be a pellet or a granule prepared by mixing the recovered melt with a melt of a polyester prepolymer from a polyester manufacturing process and then granulating the mixed melt into a form, particularly a granule.

The first melt valve is located between the process step in which the appropriate melt viscosity for further processing is achieved (e.g. in a melt polycondensation unit or extruder) and a unit, preferably a granulator, for preparing the solid mixture. The first melt valve may be located before or after optional filtration during the polyester manufacturing process.

According to the invention, the supply line (melt line) for the recycled polyester melt can preferably be shut off by a first melt valve.

According to the invention, the second melt valve is preferably arranged in the feed line (melt line) for the recovered polyester melt upstream of the first melt valve, which also causes the feed line (melt line) for the recovered 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.

For continuous operation of the device, additional cleaning steps must be performed. Continuous operation of the device is understood here to mean that the device is operated without interruption for a longer period of time (for example 1 to 4 weeks, preferably 1 to 12 months, particularly preferably more than 1 year), in which the melt passes through the melting zone of the device without intermediate interruption.

During start-up and continuous operation of the plant, the recycled polyester material introduces impurities into the plant, which have a negative impact on the quality of the final product. These product impurities are also known as black spots (black specs).

In order to reliably remove these impurities during continuous operation, the melt must be subjected to an additional purification step prior to preparing the solid mixture in order to remove the solid impurities that cause the formation of black spots, while obtaining a purer recycled polyester material.

According to a preferred embodiment of the invention, the further step of purifying the melt of the recovered polyester material by means of melt filtration is performed in a further second filter unit. In principle, all types of filter units can be used. These include discontinuously operating filters, such as cartridge filters. Wherein a continuously operated filter unit ensuring uninterrupted melt flow is preferred. This includes continuous cleaning of filter units (such as laser filters) and discontinuous cleaning of filter units (such as piston filters), where discontinuous filter units pose a risk of surge contamination.

Preferred filters according to the invention are selected from the following:

-a rigid perforated plate or rigid screen, which continuously cleans the melt stream;

-a rigid perforated plate or rigid screen, which pulse cleans the melt stream;

-a movable perforated plate or a movable screen, which is continuously fed into the melt stream;

-a movable die plate or a movable screen pulsed into the melt stream, wherein the pulse rate is less than 5 minutes.

Such filters are well known (e.g., scheirs, polymer recovery (Polymer recycling), wiley 1 st edition 1998, 101-117).

According to the invention, the second melt filter preferably has openings with an average size that is larger than the average size of the openings of the first melt filter used during the first cleaning. The use of a coarser second melt filter avoids the need for frequent cleaning and the necessity of interrupting the operation of the apparatus, as such a second melt filter is obviously less prone to clogging.

According to a preferred embodiment of the invention, the first filter unit may have openings in the size range 10-75 μm, preferably 30-60 μm, and more preferably 35-45 μm, while the second filter unit may have openings in the size range 10-300 μm, preferably 20-100 μm, preferably 40-75 μm, and more preferably 50-60 μm. In this case, the opening of the second filter unit must always be thicker than the opening of the first filter unit.

In the case of another embodiment of the invention, wherein the filtration of the polyester prepolymer melt is carried out in a melt filter, the filtration is carried out 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, preferably 30-60 μm, and more preferably 35-45 μm, and particularly preferably corresponds to the size of the openings of the first filter unit.

According to the invention, the further step of purifying the melt of the recovered polyester material by means of melt filtration in a further second filter unit must be carried out before the preparation of the solid mixture, i.e. before the introduction of the melt mixture into the unit for preparing the solid mixture, preferably the granulator.

According to a preferred embodiment of the invention, the further step of purging the melt of the recycled polyester material by melt filtration is performed before the step of mixing the recycled polyester material in melt form with the polyester prepolymer in melt form from the polyester manufacturing process. For this purpose, a melt filter as described above is provided as a second filter unit at a position downstream of the first filter unit and upstream of the first melt valve. In other words, the second filter unit is arranged in a melt line connecting the first filter unit to the first melt valve. In this way, the melt of recycled polyester material is additionally purged prior to being contacted with the polyester prepolymer melt.

Optionally, the second melt valve described above may be arranged between the first filter unit and the second filter unit.

Also optionally, the second melt valve described above may be disposed upstream of the first filter unit and downstream of the second reactor.

In both cases, the polyester prepolymer melt from the polyester manufacturing process may flow through the filter unit in opposite directions. The melt filter must be selected accordingly. It may be necessary to temporarily remove the screen or perforated plate from the filter unit.

According to another preferred embodiment of the invention, the step of mixing the recovered polyester material in melt form with the polyester prepolymer in melt form from the polyester manufacturing process is followed by an additional step of purifying the melt of the recovered polyester material by melt filtration.

For this purpose, a melt filter as described above is provided as a second filter unit at a position between the first melt valve and the unit for preparing the solid mixture. In other words, the second filter unit is arranged in a melt line connecting the first melt valve to the unit for preparing the solid mixture. In this way, the entire melt mixture prepared beforehand is additionally purified.

Optionally, in this embodiment, the second melt valve described above may be disposed between the first filter unit and the first melt valve.

According to another embodiment of the invention, the further step of purging the melt by removing solid impurities to obtain a purer recycled polyester material may be performed by purging a melt line connecting the first filter unit and the first melt valve. Through which, during normal operation, recycled polyester material in melt form is fed into the preparation of the solid mixture by directing the melt from the first filter unit to the first melt valve.

To remove solid impurities deposited in the melt line prior to or during operation of the apparatus, a section of the melt line connecting the first melt valve and the second melt valve may be flushed with a polyester prepolymer melt. For this purpose, a polyester prepolymer melt is fed from the first reactor through a first melt valve into the melt line. The polyester prepolymer melt is then fed through a second melt valve into a second particle forming apparatus. There, solids are produced from the melt, in which entrained precipitated impurities are discharged.

The second particle forming apparatus, particularly preferably a granulator, may have the same design as the first unit for preparing solids described above. However, this is not mandatory.

The second particle forming apparatus is connected to a second melt valve.

According to this embodiment, the first melt valve and the second melt valve are designed to be switchable such that

In a first switching arrangement, polyester prepolymer in melt form from the polyester manufacturing process passes through a first melt valve and a second melt valve into a second particle forming apparatus, entraining deposited impurities from at least a section of a melt line between the first melt valve and the second melt valve,

In a second switching arrangement, the polyester prepolymer in melt form from the polyester manufacturing process passes through a first melt valve to a unit for preparing a solid mixture, and the melt of the recovered polyester material from the first filter unit passes through a second melt valve and a first melt valve to a unit for preparing a solid mixture, and

In a third switching arrangement, if necessary, the polyester prepolymer in melt form from the polyester manufacturing process is fed through a first melt valve into a unit for preparing a solid mixture, and the melt of recycled polyester material from the first filter unit is fed through a second melt valve into a second particle forming apparatus.

Switchable melt valves of this kind are known (see, for example, EP 0 962 A1).

In the first switching arrangement, the first melt valve is set in such a way that the polyester prepolymer melt from the first reactor is no longer guided only to the (first) unit for producing solids, but at least partly into the section of the melt line connecting the second melt valve and the first melt valve. During normal operation, the recovered polyester melt is fed through the melt line in the opposite direction of flow to reach the first melt valve and then to the (first) unit for preparing solids. Here, the recovered polyester melt absorbs impurities deposited in the melt line and introduces them into the final product. This is prevented by the purging process according to the invention. The polyester prepolymer melt passing through this section of the melt line absorbs impurities deposited in the melt line as it passes through.

The polyester prepolymer melt contaminated in this way is not used for product manufacture but is fed into the second particle forming apparatus.

In the first switching arrangement, the second melt valve is thus set in such a way that the contaminated polyester prepolymer melt from the first reactor, which passes through the section of the melt line between the first melt valve and the second melt valve, is not guided to the second reactor, but to the second particle forming apparatus.

The second particle forming apparatus is connected to a second melt valve. The connection is preferably effected via a further melt line.

In the second particle forming apparatus, the contaminated polyester prepolymer melt is solidified, preferably pelletized. The resulting solid material was removed from the apparatus. Optionally, the solid material obtained in this way can be returned as recycled polyester at a later stage.

The second switching arrangement of the first and second melt valves represents a switching state in normal operation. The melt of the recovered polyester material is fed from the first reactor through a first filter unit into a second melt valve and from there through a (now clean) section of the melt line into the first melt valve. In the second switching arrangement, the second melt valve is thus set in such a way that the melt of the recycled polyester material cannot enter the second particle forming apparatus. In the second switching arrangement, the first melt valve is set accordingly in such a way that the melt of the recovered polyester material is led into the (first) unit for preparing the solid. By directing the melt of the recycled polyester material into the first melt valve at a sufficiently high pressure, the polyester prepolymer melt is prevented from flowing into the section of the melt line between the first and second melt valves.

The third switching arrangement of the first and second melt valves represents the switching state in a further optional cleaning step. This further 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. The melt of recovered 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 apparatus. In the third switching arrangement, the second melt valve is thus set in such a way that the melt of the recovered polyester material cannot enter the first melt valve. In the third switching arrangement, the first melt valve is preferably set accordingly in such a way that the polyester prepolymer melt cannot enter the second melt valve, but is guided through the first melt valve to the unit for producing the solid mixture.

In a third switching arrangement, the melt-recovered polyester that does not meet the desired specifications may also be discharged from the apparatus. This may be especially a starting material with too low a viscosity and too strong a yellow color, or a material exceeding the desired specifications for critical quality parameters (such as viscosity or color) due to impurities. The material is similarly fed to another unit for preparing solids, preferably to a second particle forming apparatus, where the material is solidified as described above and optionally returned to the second reactor.

The optional fourth switching arrangement of the first melt valve and the second melt valve represents a switching state for switching from the first switching state to the second switching state. The melt valves are set in such a way that both the polyester prepolymer melt from the first reactor (through the first melt valve) and the recovered polyester material melt from the second reactor (through the first filter unit) are fed via the second melt valve into the second particle forming apparatus. The melt flow through the section of the melt line between the first melt valve and the second melt valve is determined by the pressure at which the different melts are fed through the device. In this arrangement, the pressure of the polyester prepolymer melt is greater than the pressure of the melt of recycled polyester material.

Another embodiment of the invention provides that the second particle forming apparatus is an apparatus for underwater pelletizing and that the second melt valve is simultaneously an activated valve for underwater pelletizing.

According to an alternative embodiment of the invention, purging of the melt line may also be performed with only the melt of 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. Thus, the section of the melt line connecting the first melt valve to the second melt valve is kept as short as possible, so that purging of this section is no longer necessary.

According to this alternative embodiment, the first melt valve and the second melt valve are designed to be switchable such that

The first switching arrangement provided in the above-described embodiments is no longer preferred, and is preferably omitted,

In a second switching arrangement, the polyester prepolymer in melt form from the polyester manufacturing process passes through a first melt valve to a unit for preparing a solid mixture, and the melt of recovered polyester material from the first filter unit passes through a second melt valve and the first melt valve to a unit for preparing a solid mixture,

In a third switching arrangement, the polyester prepolymer in melt form from the polyester manufacturing process passes through a first melt valve to a unit for preparing a solid mixture, and the melt of recovered polyester material from the first filter unit passes through a second melt valve into a second particle forming apparatus, and

In a fourth switching arrangement, the polyester prepolymer in melt form from the polyester manufacturing process passes through the first melt valve to the unit for preparing the solid mixture, and the melt of the recovered polyester material from the first filter unit passes through the second melt valve into the second particle forming apparatus and simultaneously passes through the second melt valve and the first melt valve to the unit for preparing the solid mixture.

Components having the same name are used in both alternative embodiments to be substantially identical.

In this alternative embodiment, in the third switching arrangement, the section of the melt line between the first filter unit and the second melt valve is purged with only the melt of recycled polyester material. In this alternative embodiment, it is preferred not to provide a first switching arrangement in which the section of the melt line between the first melt valve and the second melt valve is to be purged with polyester prepolymer in melt form from the polyester manufacturing process.

In order to minimize the problem of any impurity accumulation in the section of the melt line connecting the first melt valve to the second melt valve, this section is kept as short as possible in this alternative embodiment. According to a preferred embodiment, a first melt valve is provided in which the second melt valve is integrated. Such melt valves are known. For example, such a first melt valve can be designed in such a way that melt lines from the first reactor and the second reactor (possibly with filter units arranged therein) flow into the first melt valve and collect there in the actual first melt valve. A branch line to the discharge valve is arranged immediately upstream of the melt line junction. The discharge valve represents a second melt valve and regulates the flow of the melt of recycled polyester material into the second particle forming apparatus.

In the second switching arrangement described above, the second melt valve is thus set in such a way that the melt of the recycled polyester material cannot enter the second particle forming apparatus. In the second switching arrangement, the first melt valve is set accordingly in such a way that both the polyester prepolymer in melt form from the polyester manufacturing process and the melt of the recycled polyester material enter the first melt valve, where they are combined and fed into the unit for preparing the solid mixture. This is the mode of operation of the apparatus for preparing the desired solid mixture. By directing the melt of the recycled polyester material into the first melt valve at a sufficiently high pressure, the polyester prepolymer melt is prevented from flowing into the section of the melt line between the first and second melt valves.

On the other hand, in the third switching arrangement described above, the second melt valve is thus set in such a way that the melt of the recovered polyester material cannot enter the first melt valve. In the third switching arrangement, the first melt valve is preferably set accordingly in such a way that the polyester prepolymer melt cannot enter the second melt valve, but is fed through the first melt valve into the unit for producing the solid mixture. In this switching arrangement, the melt of recycled polyester material is fed into the second particle forming apparatus through the second melt valve. There, entrained deposits from the melt line of the second reactor are solidified with the melt of recycled polyester material and optionally fed back into the second reactor. The polyester prepolymer in melt form from the polyester manufacturing process is fed through a first melt valve into a unit for preparing a solid mixture.

In the fourth switching arrangement described above, the first melt valve is set in such a way that its inflow to the melt of the recycled polyester material is not blocked, contrary to the third switching arrangement. Thus, a portion of the melt of the recycled polyester material enters the first melt valve and then enters the unit for preparing the solid mixture, while another portion of the melt of the recycled polyester material is fed through the second melt valve into the second particle forming apparatus. The ratio of the melt amounts of recycled polyester material passing through two different pipe paths can be controlled by adjusting the first melt valve and the second melt valve accordingly. In this switching arrangement, which represents a transitional state of operation of the device, it is thus achieved that the deposit in the respective melt line is removed from the device part at the same time as the desired solid mixture is prepared. The melt flow through the section of the melt line between the first melt valve and the second melt valve is determined by the pressure at which the various melts are fed through the device. In this arrangement, the pressure of the polyester prepolymer melt is lower than the pressure of the melt of recycled polyester material.

In an embodiment according to the invention with the further step of cleaning the melt of the recovered polyester material by purging a section of the melt line between the second melt valve and the first melt valve or between the first filter unit and the second melt valve, preferably a further step of cleaning the melt of the recovered polyester material by means of melt filtration may also be performed.

As mentioned above, for this purpose a second filter unit is used which has a melt filter with openings having an average size which is larger than the average size of the openings of the melt filter used in the first cleaning process. Reference is made to the description of the second filter unit above.

In these embodiments according to the invention, the step of mixing the recovered polyester material in melt form with the polyester prepolymer in melt form from the polyester manufacturing process is followed by another purging step by melt filtration. In other words, the second filter unit is provided at a position between the first melt valve and the unit for preparing the solid mixture.

Another disadvantage of the process according to WO 00/77071A1 is that the quality of the recovered input material often varies. Excess impurities, some of which are present in the clusters, are often undetectable by analytical measurements. Quality defects are usually only apparent after granulation or sometimes only in the final product. This can result in large quantities of poor quality production batches in which not only the recycled polyester but also the polyester prepolymer from the manufacturing process becomes unusable.

Thus, according to another preferred embodiment of the invention, the quality parameter is measured in the melt line of the recovered polyester melt.

As described above for the third switching arrangement, when the critical value is reached, the measured quality parameter can be used to automatically drain the recovered polyester melt from the apparatus.

Alternatively, the measured quality parameter may be used for setting in the polyester manufacturing process based on the measured parameter or for automatically adjusting the process parameter by means of a control system. Measurement of color values and adjustment or control of colorant addition during polyester production are particularly preferred.

Alternatively, the measuring point may also be located after the first melt valve.

The quality parameters include in particular color and viscosity. Both can be measured on-line (in-line) or on-line (on-line). For example, the viscosity is measured on-line (in-line) using a measuring device that measures the torsional force of a measuring probe in the melt. Also for example, the viscosity is measured on-line (in-line) by measuring the pressure drop in a defined measuring gap through which the melt flows, wherein the measured melt remains in the process or is fed back into the process. An on-line measurement of viscosity is performed, for example, by measuring the pressure drop in a defined measurement gap through which a portion of the fluid flows, wherein the measured melt is removed from the process. In all cases, the viscosity is calculated by measuring a mechanical variable on the basis of comparative measurements.

On-line (in-line) measurement of color is performed, for example, using a light source on one side of the melt line and a light sensitive sensor on the other side of the melt line, wherein the color values can be calculated using the amounts of light absorbed at the different wavelengths.

On-line measurement of color is performed, for example, by means of a light source on one side and a light-sensitive sensor on the other side of a test strip prepared from the melt, wherein the color values can be calculated using the amounts of light absorbed at the different wavelengths. The light source and the sensor may be connected to the actual measuring point via a light guide.

Optionally, a melt pump may be used in the melt line to overcome pressure losses in the melt line, melt filter, and particle forming equipment. The melt pump generally has a predetermined flow direction and must be arranged in such a way that no melt flow occurs in the opposite direction. The preferred installation location is 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, wherein according to the invention an arrangement in the melt line between the first melt valve and the second melt valve should be avoided if the flow through this section of the melt line takes place in the opposite direction.

The throttle valve may also be used as an option to adjust or regulate the pressure ratio depending on the desired flow direction and amount.

According to a preferred embodiment of the invention, the solid phase polycondensation step is sized so that substantially the full capacity of the polyester prepolymer production process and substantially the full equipment capacity (INSTALLED CAPACITY) of the recycle can be treated. In particular, in the case of subsequent retrofitting of the polyester production plant, the total plant capacity can be increased by expanding the solid phase polycondensation after installation of the recycle feed unit.

The mixture of recycled polyester and polyester prepolymer from the polyester manufacturing process may comprise any desired mixing ratio. According to the invention, the ratio of recovery to prepolymer preferably ranges from 10% to 90% to 10%, more preferably from 20% to 80% to 20%, even more preferably from 25% to 75% to 25%, and particularly preferably from 50% to 50%.

The limiting factor here is that the apparatus for preparing the polyester prepolymer is designed to have a certain size and cannot arbitrarily reduce its yield. Accordingly, a preferred embodiment of the present invention provides a mixture of recycled polyester and polyester prepolymer from a polyester manufacturing process having a maximum recycle content of 50%. The minimum recovery content of the mixture results from the economics of the additional process steps of the mixing, which generally requires a recovery content of at least 10%, in particular at least 15%.

A further problem may be that the recycled polyester has insufficient blue coloration due to its previous history, which is commercially desirable for the product made according to the present invention.

The color of the material is characterized by the b-value. It is known that in the CIELAB color space, the b-value defines the position of the b-axis between blue and yellow (seeLexikon Lacke und Druckfarben, thieme 1998, "CIE"). Positive b corresponds to yellow coloration and negative b corresponds to blue coloration. According to the invention, the b-value is preferably measured in reflection mode by means of a colorimeter, such as a Konica-Minolta CM3500D, using a D65 lamp. To measure the comparison b-value, all samples must be in the same state; for example, the same particle type (pellet, powder or shaped body), the same shape (thickness of round or cylindrical pellets or shaped body) and the same crystallinity state (amorphous or crystalline). For the measurement of the absolute value, it is preferable to convert all samples into pellets having a weight of 10 to 30mg per pellet and crystallize (20 min/175 ℃ C. Or equivalent conditions) to obtain crystallized pellets. In order to evaluate whether the shaped body has a b value <0, the measurement can also be carried out directly on the shaped body. For better measurability, a screen abrasive compact having openings of 0.5 to 1mm may be preferably used. Grinding must be carried out with cooling to prevent discoloration due to grinding.

According to the present invention, it has been shown that by adding a coloring additive having a negative b-value to the process chain used to prepare the polyester prepolymer, as described above, the desired blue coloring of the product to be manufactured can be achieved.

The process chain for preparing the polyester prepolymer includes the steps of preparing a monomer mixture, esterifying the monomer, prepolymerizing in a finishing tool, and melt phase polymerizing. Before the melt phase polymerization is completed, a coloring additive must be added. The additive may be added in one of the preceding process steps of the process chain or in a pipeline connecting the process steps.

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

According to the invention, BN < -3 is preferred, with < -5 being preferred, and < -8 being even more preferred.

It is further preferred according to the invention that the proportion of polyester material recovered is > 20%, preferably > 25% and particularly preferably > 40% relative to the total polyester solids mixture.

In one embodiment according to the present invention, the desired slightly negative BM value can be achieved by mixing the recycled polyester material with a polyester prepolymer of sufficient blue color to compensate for yellowing of the recycled polyester material (i.e. BR higher than 0). Preferably, the indirect color compensation also compensates for yellowing of the heat treatment steps to which the mixture is exposed during preparation and treatment.

In another embodiment according to the present invention, a significantly negative BM value can be achieved by mixing the recycled polyester material with a strong blue polyester prepolymer and still having an excess of blue toner to compensate for the yellowing of the recycled polyester material (i.e. BR higher than 0).

Optical brighteners can be added to compensate for any grey hues produced by the color compensation.

It has been shown that coloring additives with negative b-values can be added to the process chain for preparing polyester prepolymers without further contamination or affecting the product specifications (in particular molecular weight), since the monomers used for preparing the prepolymer melt, preferably ethylene glycol, can act as additive carriers or no color additive carrier at all is required.

As mentioned above, it is difficult to prepare a solid mixture having the desired b-value (BM) of BM <0 from recycled polyester material and polyester prepolymer from the polyester manufacturing process, because recycled polyester material typically has a b-value (BR) of BR > 0 due to impurities. The positive b-value due to yellowing must be compensated by a colorant having a negative b-value.

However, coloring additives having negative b-values may only be added to the recycled polyester material using a specific additive carrier. Additive carriers are substances that act as carrier materials to facilitate the introduction of coloring additives during extrusion of the rPET sheet or during preform fabrication. The addition of the colorant requires that the colorant be provided as a suspension in a liquid additive carrier. The additive carrier must meet various requirements. It must be stable at sufficient temperature to withstand the process steps used to prepare the solid mixture described above without decomposing. It must be liquid at the processing temperature of the polyester and miscible with the polyester in order to achieve the most uniform possible distribution of the colorant in the polyester, and finally, it must not affect the molecular weight of the polyester, otherwise it will affect the quality or specification of the solid mixture.

Thus, in the prior art, substances such as high boiling mineral oils or other organic substances are used which are normally liquid at room temperature, do not decompose at the processing temperatures of PET, typically 260-310 ℃, do not lead to the formation of bubbles, and do not lead to any undesired side reactions.

Colorants suspended in a color additive carrier are typically added to recycled polyester materials or solid mixtures, i.e., substances that exhibit undesirable color deviations.

Wherever the color additive carrier with suspended colorant is added, it then remains in the product, which leads to additional material contamination. Such additive carriers remain as a component in the rPET material, particularly when recycling PET articles, and lead to undesirable accumulation during repeated recycling cycles.

This problem leads to the behavior that in the manufacture of polyester bulk products such as PET bottles, colorants suspended in the color additive carrier are only very reluctant, if at all, to be added to the process cycle.

This problem is solved by the above-described invention. It has been found that colorants can be added to the process chain used to prepare the polyester prepolymer, i.e., prior to prepolymer or polymer formation, without the need for a color additive carrier that would cause contamination of the polyester stream. In the case where, depending on the colorant used, a color additive carrier has to be used, it has been found according to the invention that monomers of the polyester to be prepared can be used as carrier.

In the case of the preparation of polyethylene terephthalate (PET), monomeric ethylene glycol is preferably used as carrier. The monomer is then incorporated into a polyester to give the desired quality or gauge polyester. If a colorant suspended in a monomer is added to a polyester prepolymer or polyester, the monomer will react with the polyester prepolymer or polyester and change its quality or gauge.

The present invention thus solves the above-described contamination problem by not adding colorants to the recycled polyester material or the solid mixture or the final product, which would require the use of color additive carriers that would contaminate or affect the product specifications (such as molecular weight). Instead, colorants are added to the reaction mixture to prepare fresh polyester material. The addition of the colorant to the process chain for preparing fresh polyester prepolymer is also not a clear variant, since on the one hand it requires the colorant to be added to the components which do not require correction of any color value, as opposed to the yellowing recyclates), and on the other hand the colorant added to the process chain remains in the reaction system for a longer period of time (several hours are required for further conversion of the entire polyester prepolymer prepared) and yields the correspondingly colored product in this period of time. According to the invention, it was found that this is not only tolerable in the current process, but can even lead to the desired result.

According to a preferred embodiment of the invention, therefore, in the process chain for preparing the polyester prepolymer, a coloring additive having a negative b-value is added to the polyester prepolymer from the polyester manufacturing process prior to combining with the recycled polyester material, wherein the coloring additive is added to the polyester prepolymer from the polyester manufacturing process without prior dilution or as part of an additive mixture further comprising monomers of the polyester, and the coloring additive having a negative b-value is not added to the recycled polyester material prior to combining with the polyester prepolymer from the polyester manufacturing process.

According to the invention, the coloring additive is preferably dissolved or suspended in the monomer of the polyester.

According to the invention, the concept can also be used independently of the above-mentioned further purification of the melt by removing solid impurities to obtain a purer recycled polyester material.

The invention therefore also relates to a process for preparing a polyester solid mixture by adding together 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 is 10-90% and has a b-value (BR), the proportion of polyester material from a polyester manufacturing process in the polyester solid mixture is 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.

In this method, preferably, similar to the embodiments described above, in the process chain for preparing the polyester prepolymer, a coloring additive having a negative b-value is added to the polyester material from the polyester manufacturing process prior to combining with the recycled polyester material, wherein the coloring additive is added to the polyester material from the polyester manufacturing process without prior dilution or as part of an additive mixture further comprising monomers of the polyester, and the coloring additive having a negative b-value is not added to the recycled polyester material prior to combining with the polyester material from the polyester manufacturing process.

The process may be carried out as described above with or without further purification of the melt by removal of solid impurities to obtain a purer recovered polyester material. In a variant with this further purge, the process proceeds as described above, but with the addition of a coloring additive to the process chain for preparing the polyester prepolymer. In a variant without such additional purging, the process is carried out in an improved manner such that the coloring additive is added to the process chain for preparing the polyester prepolymer, but the melt of the recovered polyester material is not otherwise purged. Thus, in this variant, there is no need to provide a further unit for removing solid impurities while obtaining a purer recovered ester material. This variant also does not require the provision of a second melt valve.

The solid mixture produced according to the invention is then treated with a process gas counter-current or cross-current to the flow direction of the mixture in a reactor for the heat treatment of bulk materials. This applies to variants with or without further purification of the melt by removal of solid impurities to obtain purer recycled polyester material.

According to the invention, the heat treatment may be selected from drying, crystallization, dealdehyding, solid phase post-condensation and combinations thereof. According to the invention, the intrinsic viscosity of the polyester solid mixture is preferably increased by at least 5%, preferably by at least 7% and particularly preferably by at least 10% during the solid phase post-condensation.

Depending on the type of heat treatment, the solid mixture must first undergo crystallization. This is well known in the art (see Scheirs/Long, incorporated by reference), modern polyesters (Modern Polyesters), wiley 2003).

The solid mixture subjected to the heat treatment may then be shaped into a desired shape using known shaping methods. Examples include blow extrusion processes or injection molding processes for preparing bottles. It is also possible to melt the solid mixture (e.g. pellets) and transfer the melt into the film, followed by re-forming the film, or by pressing the solid mixture (e.g. pellets) in a forming tool.

As mentioned above, in order to obtain shaped articles having the desired blue color, it is advantageous to add a coloring additive to the process chain used to prepare the polyester prepolymer in order to compensate for the undesired color of the polyester recycle. For the reasons described above, the addition of such coloring additives during the forming process is not necessary or desirable.

The invention therefore also relates to a process for preparing a shaped article comprising forming a shaped article from a polyester solid mixture prepared according to one of the above processes, wherein no coloring additive having a negative b-value is added during the formation of the shaped article, and the shaped article has a b-value (BF), wherein BF < 0.

According to the present invention, BF < -2 is preferred, more preferred is < -3, and particularly preferred is < -5.

According to a preferred embodiment of the present invention there is provided a deep blue shaped article prepared from a mixture of solids consisting of a deep blue polyester material and a recycle which is at least partially prepared from the deep blue shaped article. The addition of blue colouring additives during the manufacture of the shaped article can be omitted or at least greatly reduced.

Process gases with a low oxygen content, such as nitrogen, carbon dioxide, inert gases, water vapor or mixtures of these gases, are used for the heat treatment of bulk materials. Such process gases are commonly referred to as inert gases. In particular when the bulk material is an oxygen sensitive bulk material, an inert gas is used.

If the bulk material changes more during the heat treatment due to the action of oxygen than in the case of heat treatment without oxygen, the bulk material is referred to as an oxygen sensitive bulk material. Such changes may, for example, lead to discoloration, formation of degradation products and/or a reduction in the molecular weight of the bulk material.

Although the term inert gas, the process gas may contain small amounts of oxygen, which may permeate the process gas, for example, due to leakage, or may remain in the process gas due to incomplete combustion.

The heat treatment process of the bulk material is any process in which the bulk material is treated for a residence time at a temperature under the influence of a process gas. The residence time and temperature can vary within wide limits, wherein residence times of a few minutes to a few hundred hours and temperatures between the boiling temperature of the process gas and the melting or decomposition temperature of the bulk material are conceivable.

The heat treatment is typically performed in a process chamber that may contain bulk material and process gases. The corresponding process chamber is typically formed by a reactor. Suitable reactors may be conical or cylindrical with a circular or rectangular cross section. Suitable reactors have at least one inlet opening and one outlet opening for the bulk material, and at least one inlet opening and one outlet opening for the process gas. The reactor may have various internal elements for influencing the product stream and/or the gas stream.

The action of the process gas causes the organic material from the polymer to be absorbed by the process gas and exhausted from the process chamber.

Preferably, the heat treatment is performed continuously or semi-continuously, wherein both the process gas and the bulk material are fed into the reactor continuously or in separate batches smaller than the reactor volume. The process gas is fed in cross-current or counter-current to the flow direction of the bulk material. The preferred embodiment provides a continuous heat treatment in countercurrent in a moving bed reactor.

Alternatively, a discontinuous mode of operation is also conceivable, in which the process gas flows through a given amount of bulk material in the reactor.

The size of the reactor is determined by the requirements of the heat treatment (residence time and throughput). Examples of corresponding reactors are known from EP-2 39998A 1.

Organic substances that are absorbed by the process gas include any organic substances that are released from the bulk material during the heat treatment of the bulk material and that are present in gaseous form or dissolved in the process gas. If the bulk material is a polymer, the organic material mainly comprises residues from the polymerization process, decomposition products from the polymer and additives contained in the polymer, as well as impurities introduced into the process together with the polymer and their decomposition products. The organic material is typically a hydrocarbon, which may contain foreign atoms such as nitrogen, phosphorus, sulfur, chlorine, fluorine, or metal complexing agents.

At least a portion of the process gas is recycled. For this purpose, the process gas is fed from a treatment chamber, preferably a reactor, for the heat treatment of the bulk material to catalytic combustion, and is then returned to the treatment chamber. Such a cyclic process with purification of the process gas is described in EP-3 865 529a 1.

Here, the process for cleaning the process gas from the heat treatment process of the bulk material comprises at least one catalytic combustion step.

The contaminated process gas may undergo further process steps prior to catalytic combustion, such as an increase in pressure, a process step for separating solid impurities, for example by means of cyclones and/or filters, mixing with the supplied oxygen-containing gas, for example by means of static mixers, and heating to increase the temperature to a suitable combustion temperature, for example by means of heat exchangers for heat recovery and/or by means of process gas heaters.

The catalyst bed may also be heated directly, for example by an external heat source or by the heat of combustion of the impurities, if desired.

After catalytic combustion, the cleaned process gas may be subjected to further process steps such as cooling, drying, increasing pressure, process steps for separating solid impurities, e.g. by means of cyclones and/or filters, heating, and mixing with additives or other process gas streams.

Adsorption steps for removing so-called catalyst poisons are known in the prior art. Catalyst poisons are generally known as inorganic substances deposited on the surface of the catalyst material and thus lead to a direct deactivation of the catalyst for catalytic combustion. Common catalyst poisons are halogens, sulfur and heavy metals. The catalyst poison may be adsorbed on the adsorbent material or on an adsorbent coating on the support material. Common sorbent coatings are bases such as sodium hydroxide, potassium hydroxide or calcium oxide, and sodium carbonate or potassium carbonate.

Such adsorbent materials are also suitable for removing high boiling point organic materials or organic materials having a high combustion temperature. In the case of incomplete combustion, this material leads to deactivation of the catalyst used for catalytic combustion. High boiling hydrocarbons are particularly deactivated because they can lead to carbon deposition on the catalyst material in the event of incomplete combustion or directly plug the pores of the support material to which the catalyst material is applied.

According to one embodiment of the invention, the contaminated gas is subjected to a step of adsorbing high boiling point organic substances or organic substances having a high combustion temperature onto a solid adsorption material in a guard bed prior to catalytic combustion.

The guard bed may be designed as a surface coated with an adsorbent material. Preferably, however, the guard bed consists of a solid material in loose form, which may consist entirely of the adsorbent material or may be coated with the adsorbent material. The guard bed is preferably located in the adsorption vessel. The process gas flows through the adsorption vessel and through the adsorption bed in any direction, but preferably flows through the adsorption vessel and through the adsorption bed in any direction from the particular inlet side to the particular outlet side. The inlet side may be located at the top or bottom of the canister. If liquid material is to be removed, it is preferable to arrange the inlet side at the bottom of the adsorption tank so that the gas flows through the guard bed from bottom to top. For example, the liquid residue may be directed out of the canister through a valve. If sublimable substances are to be removed, an arrangement on the inlet side of the top of the adsorption vessel is preferred such that the gas flows through the guard bed from top to bottom. The top layer with sublimated residues can then be removed.

The guard bed material may be placed on a separation element in the central portion of the adsorption vessel that allows gas but does not allow the guard bed material to pass through. The separation element is typically a screen which is arranged in the adsorption vessel in such a way that all the process gas has to flow through the screen and the guard bed located thereon. Preferably, the screen may be heated to prevent deposits.

The adsorption vessel may have further openings in addition to the openings for the inlet and outlet of the process gas. Preferably, the outlet opening for guard bed material from the adsorption vessel may be arranged in the lower part of the adsorption vessel and/or the outlet opening for guard bed material from the adsorption vessel may be arranged in the middle part and/or the supply opening for fresh or returned guard bed material may be arranged in the upper part of the adsorption vessel. Furthermore, inlet and outlet openings for a purge gas, in particular an inert gas, may be provided in order to remove oxygen from the guard bed material. Furthermore, an opening for sampling the guard bed material may be arranged in the central portion of the adsorption vessel.

According to an alternative embodiment, the separation element may be conical and connected to a lockable outlet opening for guard bed material from the adsorption vessel, such that the guard bed material may be emptied from the adsorption vessel by opening the outlet opening.

According to another alternative embodiment, the complete or partial evacuation of the guard bed material from the adsorption vessel may be performed in such a way that the heavily contaminated guard bed material may be separated from the less contaminated guard bed material and the less contaminated guard bed material returned to the adsorption vessel.

The guard bed may be selected in such a way that it chemically binds the material from the process gas or that it physically accumulates the material from the process gas.

The inlet temperature of the process gas into the canister can cover a wide range. However, it must be high enough to ensure any necessary chemical reactions, and low enough to allow sufficient accumulation of the substances to be physically bound.

In particular, the temperature is set in such a way that high boilers condense and can be absorbed by the adsorption material. If the process gas comprises water, the temperature is selected in such a way that no condensation of water takes place in the guard bed. For the treatment of the thermoplastic polycondensates in the form of the starting materials or in the form of recyclates, the preferred temperature ranges from 100 to 250 ℃, more preferably above 120 ℃ and particularly preferably below 170 ℃, particularly preferably from 120 to 170 ℃.

To regulate the temperature, a heat exchanger may be used to heat or generally cool the process gas. The cooling is preferably carried out in a double-tube or tube bundle heat exchanger in order to avoid deposits of condensed material.

The contact time of the process gas on the guard bed is from one tenth of a second to a few minutes. The contact time is preferably 2 to 20 seconds.

The cross-sectional area of the guard bed is selected in such a way that the linear or apparent velocity of the process gas (operating volumetric flow rate/guard bed packing cross-section in the direction of gas flow) results in a range of about 0.05 to 3m/s with a pressure loss of 10 mbar to 200 mbar, in particular 20 mbar to 100 mbar. The layer thickness of the guard bed should be constant over its entire cross section and the ratio to the diameter of the guard bed packing should be from 10:1 to 1:10.

In particular, the adsorption material is selected in such a way that high boilers are removed from the process gas, wherein they should be reduced at least to below 20%, preferably to below 10% of their initial value in the process gas.

Examples of adsorbent materials that can be used are zeolites, silica gel, activated carbon, activated alumina and alumina dioxide.

The invention also relates to a device for preparing and treating a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process, comprising

-A first reactor for providing polyester prepolymer in melt form from a polyester manufacturing process;

-a second reactor for providing recycled polyester material in melt form;

-a first filter unit for cleaning the melt of the recycled polyester material, arranged downstream of the second reactor;

-a unit for preparing a solid mixture of recycled polyester material and 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 preparing 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 melt line 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 heat treating a solid mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process with a process gas which can be fed to the solid mixture in countercurrent or cross-current to the flow direction of the mixture;

Characterized in that a further unit for removing solid impurities to obtain a purer recycled polyester material is provided, selected from the group consisting of a second filter unit, a second particle forming apparatus and a combination thereof, wherein a melt filter having an average size of openings larger than the average size of openings of the melt filter used in the first filter unit is used as the second 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 preparing the solid mixture, and a position after the first filter unit and before the first melt valve, and

Wherein the second particle forming apparatus is connected to a second melt valve, wherein the first melt valve and the second melt valve are designed to be switchable such that

In the first switching arrangement, all melt lines are unblocked in the first melt valve, and in the second melt valve the section of the melt line from the first filter unit is blocked, the section of the melt line to the first melt valve and the melt line to the second particle forming apparatus are unblocked,

In the second switching arrangement, all melt lines are unblocked in the first melt valve, and in the second melt valve the sections of the melt lines from the first filter unit and the sections of the melt lines to the first melt valve are unblocked, and the melt lines to the second particle forming apparatus are blocked,

In a third switching arrangement, the melt line from the first reactor and the line to the unit for preparing the solid mixture are unblocked in the first melt valve, the section of the melt line to the second melt valve is blocked, and the section of the melt line to the first melt valve is blocked in the second melt valve, the section of the melt line from the first filter unit and the melt line to the second particle forming apparatus are unblocked,

In a fourth switching arrangement, all melt lines in the first and second melt valves are unblocked.

According to the invention, a conventional device for the heat 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.

The invention therefore also relates to a method for retrofitting an apparatus for producing and heat-treating a bulk starting material, preferably for producing and post-condensing polyester pellet starting material, to an apparatus for producing and heat-treating polyester pellets comprising an at least partially recycled material comprising an at least partially re-pelletized polyester recycle,

Wherein the device comprises:

-a unit for preparing a solid, preferably a first particle forming device;

-a reactor for heat treating the solid material from the recycled polyester material and the polyester prepolymer from the polyester manufacturing process with a process gas, which may be fed to the solid material mixture in countercurrent or cross-current to the flow direction of the mixture;

Characterized in that the device is additionally equipped with:

-a second reactor for providing recycled polyester material in melt form;

-a first melt valve between the first reactor and the unit for preparing the solid mixture;

-optionally, a second melt valve between the first filter unit and the first melt valve, 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 further unit for removing solid impurities to obtain a purer recycled polyester material, selected from a second filter unit, a second particle forming device and combinations thereof, wherein the second filter unit is a melt filter having an average size of openings larger than the average size of openings of melt filters used in the first filter unit, and the second filter unit is provided at a position selected from a position between the first melt valve and the unit for preparing the solid mixture, and a position after the first filter unit and before the first melt valve, and

Wherein the second particle forming apparatus is connected to a second melt valve, the first melt valve and the second melt valve being designed to be switchable such that

In the second switching arrangement, all melt lines are unblocked in the first melt valve, and in the second melt valve the sections of the melt lines from the first filter unit and the melt lines to the first melt valve are unblocked, and the melt lines to the second particle forming apparatus are blocked,

Drawings

The invention is explained in more detail below with reference to non-limiting examples and the accompanying drawings. The following are shown:

fig. 1 is a schematic view of an apparatus according to a first embodiment of the invention.

Fig. 2 is a schematic view of an apparatus according to a second embodiment of the invention.

Fig. 3 is a schematic view of an apparatus according to a third embodiment of the invention.

Fig. 4 is a schematic view of an apparatus according to a fourth embodiment of the invention.

Fig. 5 is a schematic view of an apparatus according to a fifth embodiment of the invention.

Fig. 6 is a schematic view of an apparatus according to a sixth embodiment of the invention.

Fig. 7 is a schematic view of an apparatus according to a seventh embodiment of the invention.

Fig. 8 is a schematic view of an apparatus according to an eighth embodiment of the invention.

In the drawings, like reference numerals refer to like components.

Detailed Description

Fig. 1 shows a schematic view of an apparatus according to a first embodiment of the invention.

In the first reactor 1, a slurry is prepared from the corresponding monomers, in the case of PET, the monomers terephthalic acid (TPA) and Ethylene Glycol (EG), and then subjected to esterification, prepolymerization and melt polymer condensation in a finishing tool. The prepolymer melt, for example virgin PET (vPET), leaves the first reactor 1 and reaches the first melt valve 1a. The polyester production process may also be carried out in a series of reactors, in which case the reactor for producing the polyester prepolymer which is ultimately used as starting material for the process according to the invention is referred to as first reactor 1. Polyester production processes and suitable reactors for this purpose are sufficiently known from the prior art (for example from Scheirs/Long, modern polyesters (Modern Polyesters), wiley 2003, II.2.4, pages 89 to 98).

In one embodiment of adding the coloring additive, the coloring additive may be introduced into the reactor 1, or into any of these reactors if the polyester manufacturing process is performed in a series of reactors.

The polyester recycle, preferably PET recycle (rPET, preferably PET flakes), is introduced into a second reactor 2, preferably an extruder, where it is melted and extruded. The melt of polyester recyclate, preferably rPET, is fed into a first filter unit 3 (melt filter) where the solid impurities are cleaned. The purged polyester recycle melt, preferably rPET melt, is then fed via melt line 3a to a first melt valve 1a where it is combined with the prepolymer melt of the polyester prepolymer, preferably "virgin" PET. The second melt valve 3b may preferably be arranged in the melt line 3a for the melt of the polyester recyclate, preferably the rPET melt, in order to prevent the introduction of contaminated or low quality polyester recyclate melt, preferably the 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 3 a. In addition, at least one unit for measuring quality parameters may be arranged in the melt line 3a for the melt of the polyester recyclate, preferably the rPET melt.

The melt mixture combined in the first melt valve 1a is then mixed in an optional mixing unit 4, in which case the mixing unit 4 is a static mixer, and then granulated in a unit 6 for preparing solids, in which case the unit 6 is a granulator (preferably an underwater granulator or an underwater strand granulator), dried if necessary, and brought to the desired crystallinity in a crystallizer 7. The partially crystalline polyester pellet mixture, preferably PET pellet mixture, is heated in a preheater 8 to the temperature required for the SSP reaction and subjected to the SSP reaction in a reactor 9 for heat treatment. The final polyester mixture, preferably a PET mixture, leaves the reactor 9 at the desired intrinsic viscosity and may optionally be cooled, transported and/or stored and then further processed.

The device according to fig. 1 is characterized in that a second filter unit 5 is arranged between the mixing unit 4 and the unit 6 for preparing the solid material. In the second filter unit 5, solid impurities are removed while obtaining a purer recycled polyester material. The second filter unit 5 comprises a melt filter with an average size of openings larger than the average size of openings of the melt filters used in the first filter unit 3.

Fig. 2 shows a schematic view of an apparatus according to a second embodiment of the invention. The device according to fig. 2 differs from the device according to fig. 1 in that a second filter unit 5 is arranged between the second melt valve 3b and the first melt valve 1 a. In addition, a third filter unit 10 is arranged between the first reactor and the first melt valve.

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

The device according to fig. 3 has switchable melt valves 1a, 3b and can be operated in various switching arrangements as described above. In a first switching arrangement, the polyester prepolymer melt can pass from the first reactor 1 through an optionally arranged third filter unit 10, through a first melt valve 1a, a second section 3a2 of a melt line 3a and a second melt valve 3b into a second particle forming apparatus 5' to prepare a solid. In the second switching arrangement, the polyester recyclate melt can pass from the second reactor 2 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 preparing solids. In a third switching arrangement, the polyester recyclate melt may pass from the second reactor 2 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 apparatus 5' to prepare solids.

Fig. 4 shows a schematic view of an apparatus according to a fourth embodiment of the invention. The device according to fig. 4 differs from the device according to fig. 3 in that a second filter unit 5 is additionally arranged between the mixing unit 4 and the unit 6 for preparing solids. The optional third filter unit 10 is omitted here.

Fig. 5 shows a schematic view of an apparatus according to a fifth embodiment of the invention. The device according to fig. 5 differs from the device according to fig. 3 in that the second melt valve 3b is arranged directly next to the first melt valve. If the melt line from the first filter unit 3 and the melt line to the second particle forming apparatus 5 'are unblocked in the second melt valve 3b, the melt prepared from the polyester recycle, preferably the PET recycle, can be fed through the first filter unit 3 and the melt line 3a into the second particle forming apparatus 5' to prepare a solid. Here, the melt of the polyester recyclate, preferably PET recyclate, brings impurities out of the device from the entire line system 3a1 between the second reactor 2 and the second melt valve 3 b. The very short melt line 3a2 between the first melt valve 1a and the second melt valve 3b need not be purged with polyester prepolymer melt, preferably virgin PET (vPET). Particularly preferred for this embodiment is a piston valve for cutting off the melt of polyester recyclate, preferably PET recyclate, wherein the cutting piston in the closed state displaces a large part of the volume of the melt line between the point in the second melt valve 3b and the first melt valve 1a where the melt streams merge.

Fig. 6 shows a schematic view of an apparatus according to a fifth embodiment of the invention. In the first reactor 1, a slurry is prepared from the corresponding monomers, in the case of PET, the monomers terephthalic acid (TPA) and Ethylene Glycol (EG), and then subjected to esterification, prepolymerization and melt polymer condensation in a finishing tool. The prepolymer melt, for example "virgin" PET (vPET), leaves the first reactor 1 and reaches the first melt valve 1a.

The polyester production process may also be carried out in a series of reactors, in which case the reactor for producing the polyester prepolymer which is ultimately used as starting material for the process according to the invention is referred to as first reactor 1. Polyester production processes and suitable reactors for this purpose are sufficiently known from the prior art (for example from Scheirs/Long, modern polyesters (Modern Polyesters), wiley 2003, II.2.4, pages 89 to 98).

The polyester recycle, preferably PET recycle (rPET, preferably PET flakes), is introduced into a second reactor 2, preferably an extruder, where it is melted and extruded. Optionally, the melt of the polyester recycle, preferably rPET, is fed to a first filter unit (melt filter, not shown) where the solid impurities are cleaned. The polyester recycle melt, preferably rPET melt, is then fed via melt line 3a to a first melt valve 1a where it is combined with the polyester prepolymer melt, preferably the melt of "virgin" PET. A second melt valve (not shown) may optionally be arranged in the melt line 3a for the polyester recycle melt, preferably the rPET melt, in order to prevent the introduction of contaminated or low quality polyester recycle melt, preferably the rPET melt. In addition, at least one unit for measuring quality parameters may be arranged in the melt line 3a for the polyester recyclate melt, preferably the rPET melt.

The melt mixture combined in the first melt valve 1a is then mixed in an optional mixing unit (not shown) and then granulated in a unit 6 for preparing solids, in which case the unit 6 is a granulator (preferably an underwater granulator or an underwater strand granulator), if desired dried.

Optionally, the melt of the polyester recycle, preferably rPET, may be cleaned of solid impurities in a second filter unit (melt filter, not shown). Also optionally, the melt of the polyester prepolymer, preferably vPET, may be cleaned of solid impurities in a second filter unit (melt filter, not shown).

The polyester pellet mixture, preferably the PET pellet mixture, optionally reaches a desired crystallinity in a crystallizer (not shown). The partially crystalline polyester pellet mixture, preferably the PET pellet mixture, is optionally heated in a preheater (not shown) to a temperature required for heat treatment and subjected to heat treatment in reactor 9. The heat treatment includes a process of removing volatile components and a process of SSP reaction. The final polyester mixture, preferably a PET mixture, leaves the reactor 9 at the desired intrinsic viscosity and purity, and may optionally be cooled, transported and/or stored, and then further processed.

If it is desired to provide a shaped body with a b-value (BF), where BF < 0, the device according to fig. 6 may be used. Here, it is preferred to add a coloring additive having a negative b-x value to the reaction mixture to prepare the polyester prepolymer in the first reactor 1 or at any point in the first series of reactors. No coloring additive with negative b-value was added to the device. The solid mixture prepared in the unit 6 for preparing solids is then fed to a first reactor 9 for heat treatment and to a further reactor 11 for heat treatment, where it is subjected to, for example, drying. The polyester solid mixture, preferably the PET solid mixture, is then formed into the desired shaped article in unit 12 for preparing the shaped article. Shaped articles are generally prepared by melting a polyester solid mixture, preferably a PET solid mixture.

Fig. 7 shows a schematic view of an apparatus according to a sixth embodiment of the invention. The apparatus according to fig. 7 differs from the apparatus according to fig. 6 in that the polyester recyclate melt leaving the second reactor 2 enters the granulator 6' (another unit for preparing a solid mixture) and is combined with polyester prepolymer pellets, preferably virgin PET pellets, from the granulator 6. The first melt valve 1a and the melt line 3a are omitted. The remaining steps are identical.

Fig. 8 shows a schematic view of an apparatus according to a seventh embodiment of the invention. The apparatus according to fig. 8 differs from the apparatus according to fig. 7 in that the polyester recovery converted to solid in the granulator 6' is first subjected to a heat treatment in a third reactor 13, in this case solid phase post-condensation (SSP) or dealdehyding, and then combined with vPET which has been subjected to a heat treatment in the reactor 9.

Example 1

In a conventional apparatus for preparing polyethylene terephthalate (PET), a slurry is prepared from terephthalic acid (TPA) and Ethylene Glycol (EG). The slurry is then subjected to the steps of esterification, prepolymerization and melt phase polymerization in a finishing tool. Before the polymerization is completed, a blue coloring additive in ethylene glycol is added in the esterification step, with the result that the b-value of the polyester prepolymer melt is finally-4.1. To measure b, the melt was granulated and crystallized.

A polyester recycle melt having a b value of +0.2 was prepared from the washed PET bottle waste in an extruder. No coloring additives are added to the polyester recycle melt. The melt was granulated and crystallized to measure the b value.

The two melts were subjected to melt filtration to remove solid impurities. A screen having a mesh size of 60 μm was used.

The two product streams were continuously mixed in proportion to their production outputs (130 t/d polyester prepolymer and 30t/d polyester recycle) to form a PET solid mixture and processed by underwater strand pelletization into cylindrical, amorphous PET prepolymer pellets (pellet weight about 18 mg). The pellets were subjected to crystallization in a fluidized bed apparatus, preheated to SSP reaction temperature in an overhead heat exchanger under inert gas, and subjected to solid phase treatment by solid phase polycondensation (SSP), wherein vPET pellets had an IV of 0.62dl/g before SSP and an IV of 0.82dl/g after SSP. The PET solid mixture was treated with nitrogen in countercurrent in a continuously operated fixed bed reactor at 204℃for 12 hours.

The b-value of the PET solid mixture treated in this way was-2.8.

The PET solid mixture is processed into a preform for a beverage bottle. No additional coloring additives were added to the PET solid mixture. The preform continued to have a slight blue hue. The measured b-value in the ground state is-0.3.

In this example, the addition of the coloring additive during vPET preparation not only compensates for the initial yellowing of rPET, but also compensates for the yellowing that occurs during heat treatment and preform preparation. During preform preparation, a more transparent, nearly colorless preform can be prepared without the use of another coloring additive.

If the amount of coloring additive added to the process chain for preparing the polyester prepolymer is further increased, a PET solid mixture exhibiting a blue color is prepared. This in turn can be processed into a preform having a blue appearance without the use of another coloring additive during preform preparation.

Comparative example 1

A PET solid mixture was prepared from 8t/h vPET and 2t/hr PET in an apparatus as shown in FIG. 6. The addition of a solution of blue coloring additive in ethylene glycol to vPET preparation was increased by 10% compared to the pure vPET preparation. The preform is prepared by injection molding, wherein a blue coloring additive must be added to the liquid additive carrier to prepare a preform having a bluish appearance.

Example 2

Comparative example 1 was repeated with an additional 3% (i.e., up to +13%) increase in the addition of the blue coloring additive to the solution in ethylene glycol during vPET manufacturing. This resulted in a PET solid mixture with b-3.2. The PET solid mixture can be processed into a preform having a bluish appearance without the need to add a blue coloring additive to the injection forming process.

Comparative example 2

A PET solid mixture was prepared from 8.7t/h vPET and 1.7t/h rPET in an apparatus as shown in FIG. 3. The vPET melt was purged of solids using a cartridge filter 10 having a nominal mesh size of 56 μm. Solids in the rPET melt were removed by a piston filter 3 (screen changer with backwash) with nominal mesh size of 56 μm.

First, the melt valves 1a, 3b are adjusted in such a way that vPET melt in the main stream is fed into the two strand granulation units 6 arranged in parallel, and rPET melt in the side stream is fed into the individual strand granulation units 5'.

After a start-up phase of the day, the melt valve is adjusted so that the rPET melt is fed into vPET melt and the mixture is fed into two parallel granulators 6 in the main stream.

Samples of amorphous pellets were taken every two hours from all the granulator. Average values were taken over 12 hours and the average amount of black spots was calculated to be 100-500 μm per kg. The values of two granulators operating in parallel in the main stream are averaged.

The values in brackets are calculated values assuming that the number of black dots in vPET does not change after start-up.

In addition, it was observed that black spots with a size greater than 500 μm were found in some of the samples 12 hours before switching. Such impurities are not present prior to switching of the melt valve. The size of the irregularly shaped black dots is designated as the diameter of a circle of equal area.

Because of this mode of operation, the preparation of a good quality vPET/rPET solid mixture can be achieved only after 2 days. An inferior PET of almost 500 tons was produced.

Example 3

Comparative example 2 was repeated, wherein after start-up the melt valves 1a, 3b were set in such a way that vPET melt was fed to the individual strand pelletizing units 5' for two days. After switching the melt valves 1a, 3b to prepare vPET/rPET mixture, a product with a black spot content of < 5 was obtained directly, wherein this value was even further reduced to 3.9 after 72 hours.

This mode of operation makes it possible to prepare a good quality vPET/rPET solid mixture immediately after switching the melt valves 1a and 3 b. An inferior rPET of about 80 tons was produced.

Example 4

The apparatus shown in fig. 3 is supplemented directly upstream of the valve 1a with a further melt filter 5 for combining the rPET and vPET melts. This is a continuously operated laser filter with a perforated plate with openings of 100-120 μm. Comparative example 2 was repeated, in which after start-up the melt valves 1a, 3b were adjusted in such a way that vPET/rPET mixtures were prepared directly. The product having a black spot content of < 5 is obtained directly, wherein the value is further reduced to 2.7 after 72 hours.

This mode of operation makes it possible to prepare a good quality vPET/rPET solid mixture immediately after switching the melt valves 1a, 3 b. No inferior product was produced.

Claims

1. A process for preparing and treating a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process comprising the steps of:

-providing recycled polyester material in the form of a melt and initially purging the melt by removing solid impurities using melt filtration;

-mixing, preferably in a first particle forming apparatus (6), the recovered polyester material in melt form with polyester prepolymer in melt form from a polyester manufacturing process and subsequently preparing a solid mixture;

-treating the solid mixture with a process gas counter-current or cross-current to the flow direction of the mixture in a reactor (7, 8, 9, 11) for the heat treatment of bulk material;

Characterized in that at least a first period of time after the start of the process, at least one further step for purifying the melt by removing solid impurities to obtain a purer recovered polyester material is performed before the preparation of the solid mixture.

2. The method according to claim 1, characterized in that the further step of purifying the melt of the recycled polyester material is performed by means of melt filtration.

3. A method according to claim 2, characterized in that the further step of purifying the melt of the recycled polyester material is performed by means of a melt filter (3), the average size of the openings of the melt filter (3) being larger than the average size of the openings of the melt filter used in the first purification.

4. A method according to claim 3, characterized in that a further step of purging the melt of the recycled polyester material by means of melt filtration is performed before the step of mixing the recycled polyester material in melt form with the polyester prepolymer in melt form from the polyester manufacturing process.

5. A method according to claim 3, characterized in that after the step of mixing the recovered polyester material in the melt form with the polyester prepolymer in the melt form from the polyester manufacturing process, a further step of purifying the melt of the recovered polyester material by means of melt filtration is performed.

6. A method according to claim 1, characterized in that the further step of purifying the melt of the recovered polyester material is effected by introducing the polyester prepolymer in melt form from the polyester manufacturing process or the recovered polyester material in melt form, entraining in each case deposited impurities from at least one section (3 a1, 3a 2) of the melt line (3 a) into a second particle forming apparatus (5') and discharging the entrained deposited impurities in another unit to prepare a solid material.

7. The method according to claim 6, characterized in that the further step for purifying the melt of the recycled polyester material is performed by means of melt filtration, wherein a melt filter (5) is used for the further purification step, the average size of the openings of which is larger than the average size of the openings of the melt filter (3) used in the first purification, and wherein the further purification step by means of melt filtration is performed after the step of mixing the recycled polyester material in the melt form with the polyester prepolymer in the melt form from the polyester manufacturing process.

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

9. The method of claim 8, wherein a coloring additive having a negative b-value is added to the polyester prepolymer from the polyester manufacturing process prior to combining with the recycled polyester material, the coloring additive is added to the polyester prepolymer from the polyester manufacturing process without prior dilution or as part of an additive mixture further comprising monomers of the polyester, and a coloring additive having a negative b-value is not added to the recycled polyester material prior to combining with the polyester prepolymer from the polyester manufacturing process.

10. An apparatus for preparing and processing a mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process comprising

-A first reactor (1) for providing polyester prepolymer in melt form from a polyester manufacturing process;

-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 the recycled polyester material, arranged downstream of the second reactor;

-a unit (6), preferably a first particle forming device, for preparing a solid mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process;

Wherein a first melt valve (1 a) is arranged between the first reactor (1) and a unit (6) for preparing a solid mixture, and a melt line (3 a) and optionally a second melt valve (3 b) is arranged between the first filter unit (3) and the first melt valve (1 a), which is connected to the first filter unit (3) via a first section (3 a 1) of the melt line (3 a) and to the first melt valve (1 a) via a second section (3 a 2) of the melt line (3 a);

-a reactor (7, 8, 9, 11) for heat treating a solid mixture of recycled polyester material and polyester prepolymer from a polyester manufacturing process with a process gas, which process gas can be fed to the solid mixture in countercurrent or cross-current to the flow direction of the mixture;

Characterized in that a further unit (5, 5') for removing solid impurities to obtain a purer recycled polyester material is provided, selected from the group consisting of a second filter unit (5), a second particle forming device and combinations thereof,

Wherein a melt filter having an average size of openings larger than that of a melt filter used in the first filter unit (3) is used as the second filter unit (5), and the second filter unit (5) is provided at a position selected from a position between the first melt valve (1 a) and a unit (6) for preparing a solid mixture, and a position after the first filter unit (3) and before the first melt valve (1 a), and

Wherein the second particle forming device (5') is connected to the second melt valve (3 b), wherein the first melt valve (1 a) and the second melt valve (3 b) are designed to be switchable such that

In a first switching arrangement, all melt lines in the first melt valve (1 a) are unblocked, and in the second melt valve (3 b), a section (3 a 1) of the melt line (3 a) from the first filter unit (3) is blocked, a section (3 a 2) of the melt line (3 a) leading to the first melt valve (1 a) and a melt line leading to the second particle forming apparatus (5') are unblocked,

In a second switching arrangement, all melt lines in the first melt valve (1 a) are unblocked, and in the second melt valve (3 b) the section (3 a 1) of the melt line (3 a) from the first filter unit (3) and the section (3 a 2) of the melt line (3 a) leading to the first melt valve (1 a) are unblocked, and the melt line leading to the second particle forming apparatus (5') is blocked,

In a third switching arrangement, in the first melt valve (1 a), the melt line from the first reactor (1) and the line leading to the unit (6) for preparing the solid mixture are unblocked, the section (3 a 2) of the melt line (3) leading to the second melt valve (3 b) is blocked, and in the second melt valve (3 b), the section (3 a 2) of the melt line (3 a) leading to the first melt valve (1 a) is blocked, and the section (3 a 1) of the melt line (3 a) 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, all melt lines in the first melt valve (1 a) and the second melt valve (3 b) are unblocked.

11. A process for retrofitting a device for preparing and heat treating a bulk starting material, preferably for preparing and post-condensing polyester pellet starting material, to a device for preparing and heat treating polyester pellets comprising an at least partially recycled material comprising an at least partially re-pelletized polyester recycle,

Wherein the apparatus comprises:

-a unit (6) for preparing a solid, preferably a first particle forming device;

-a reactor (7, 8, 9, 11) for heat-treating the recovered polyester material and the solid material of the polyester prepolymer from the polyester manufacturing process with a process gas, which can be fed to the solid material mixture in countercurrent or cross-current to the flow direction of the mixture;

Characterized in that the device is additionally equipped with:

-a first filter unit (3) for cleaning the melt of the recycled polyester material, arranged downstream of the second reactor (2);

-a first melt valve (1 a) between the first reactor (1) and a unit (6) for preparing the solid mixture;

-optionally, a second melt valve (3 b) between the first filter unit (3) and the first melt valve (1 a), connected to the first filter unit (3) via a first section (3 a 1) of the melt line (3 a) and to the first melt valve (1 a) via a second section (3 a 2) of the melt line (3 a);

-a further unit (5, 5 ') for removing solid impurities to obtain a purer recycled polyester material, selected from a second filter unit (5), a further unit (5') for preparing solids, preferably a second particle forming apparatus, and combinations thereof, wherein a melt filter is used as the second filter unit (5), the average size of the openings of 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 a position between the first melt valve (1 a) and the unit (6) for preparing a solid mixture, and a position after the first filter unit (3) and before the first melt valve (1 a), and

12. A process for preparing a polyester solid mixture by adding together 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 is 10-90% and has a b-value (BR), the proportion of polyester material from a polyester manufacturing process in the polyester solid mixture is 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.

13. The method according to claim 12, wherein a coloring additive having a negative b-value is added to a process chain for preparing the polyester prepolymer from a polyester manufacturing process prior to combining 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 further comprising monomers of the polyester, and wherein a coloring additive having a negative b-value is not added to the recycled polyester material prior to combining with the polyester material from a polyester manufacturing process.

14. The method according to claim 12 or 13, wherein the polyester is polyethylene terephthalate and the monomer of the polyester is ethylene glycol.

15. The method according to any one of claims 12 to 14, characterized in that BN < -3, preferably < -5, and even more preferably < -8.

16. The method according to any one of claims 12 to 15, characterized in that the polyester solid mixture prepared is treated with a process gas counter-current or cross-current to the flow direction of the mixture in a reactor (7, 8, 9, 11) for the heat treatment of bulk material.

17. The method according to any one of claims 12 to 16, wherein the preparation and processing of the mixture of recycled polyester material and polyester prepolymer from the polyester manufacturing process comprises the steps of:

wherein at least a first period of time after the start of the process, before preparing the solid mixture, at least one further step is performed to purge the melt by removing solid impurities to obtain a purer recovered polyester material.

18. The method according to claim 17, characterized in that the further step of purifying the melt of the recycled polyester material is performed by means of melt filtration.

19. The method according to claim 18, characterized in that the further step of purifying the melt of the recycled polyester material is performed by means of a melt filter (3), the average size of the openings of the melt filter (3) being larger than the average size of the openings of the melt filter used in the first purification.

20. The method according to claim 19, characterized in that a further step of purging the melt of the recycled polyester material by means of melt filtration is performed before the step of mixing the recycled polyester material in melt form with the polyester prepolymer in melt form from the polyester manufacturing process.

21. The method according to claim 20, characterized in that after the step of mixing the recovered polyester material in the melt form with the polyester prepolymer in the melt form from the polyester manufacturing process, a further step of purging the melt of the recovered polyester material by means of melt filtration is performed.

22. A method according to claim 17, characterized in that the further step of purifying the melt of the recovered polyester material is effected by introducing the polyester prepolymer in melt form from the polyester manufacturing process or the recovered polyester material in melt form, entraining in each case deposited impurities from at least one section (3 a1, 3a 2) of the melt line (3 a) into the second particle forming apparatus (5') and discharging the entrained deposited impurities in another unit to prepare a solid material.

23. The method according to claim 22, characterized in that the further step for purifying the melt of the recycled polyester material is performed by means of melt filtration, wherein a melt filter (5) is used for the further purification step, the average size of the openings of which is larger than the average size of the openings of the melt filter (3) used in the first purification step, and wherein the further purification step by means of melt filtration is performed after the step of mixing the recycled polyester material in the melt form with the polyester prepolymer in the melt form from the polyester manufacturing process.

24. A process for preparing a shaped article comprising forming a shaped article from the polyester solid mixture prepared according to any one of claims 12 to 23, wherein no coloring additive having a negative b-value is added during the formation of the shaped article, and the shaped article has a b-value (BF), wherein BF < 0.