EA013407B1 - Separation of contaminants from polyester materials - Google Patents

Abstract

The present invention is generally directed to a process for separating and recovering post-consumer polyester from various contaminant materials. The invention can be utilized to separate post-consumer polyester from various contaminants including glass, dirt, paper, metal, glue, dye, and the like. The disclosed process includes several stages including a preparation stage, in which a portion of the contaminants can be removed from the polyester, as well as a reaction stage, in which a portion of the polyester can be saponified and contaminants can be physically separated from the polyester. In addition, during the reaction stage, certain hard-to-separate contaminants, such as aluminum and polyvinyl chloride, can react to a form more easily separable from the polyester.

Description

The present invention is generally directed to a process for separating a used by

- 3,013,407 live ether from various contaminating materials and extracting it. The invention can be used to separate a used polyester from various impurities, including glass, dirt, paper, metal, glue, dye, etc. Preferably, the disclosed method includes many stages, including a preparation stage in which part of the contaminants can be removed from the mixture containing impurities and polyester, as well as a reaction stage in which part of the polyester can be hydrolyzed, thus allowing to separate additional impurities from polyester. In particular, during the stage of the reaction by the method, impurities that are physically attached to the polyester or inside the polyester can be separated, so they will be more easily removed from the mixture during the separation stages. In addition, during the reaction step of the method, some difficult to remove contaminants such as aluminum and / or polyvinyl chloride (PVC) can react to form a mold that is more easily separated from the polyester. In some embodiments, the disclosed method can significantly reduce the total amount of wastewater produced, as well as the level of wastewater contamination during polyester recycling.

In general, polyester is defined as the product of an esterification reaction or a reaction between a polybasic organic acid and a polyol. It is believed that any known polyester or copolyester may be used in the process of the present invention. However, in one particular embodiment, the process of the present invention is directed to the use of a class of polyesters, referred to herein as polyol polyterephthalates, in which terephthalic acid serves as a polybasic organic acid.

As used herein, the term polybasic organic acid refers to any organic acid having two or more carboxyl groups (—COOH). Most polyesters are derived from dibasic acids, also called dicarboxylic acids. Polybasic acids may have a linear or cyclic structure. Examples of linear polybasic acids that can be used to produce polyesters include aliphatic dicarboxylic acids. In particular, aliphatic dicarboxylic acids having up to ten carbon atoms in their chains can be used. Such acids include adipic acid, glutaric acid, succinic acid, malonic acid, oxalic acid, pimelic acid, corky acid, azelaic acid, sebacic acid, maleic acid and fumaric acid.

Cyclic polybasic organic acids, on the other hand, include carbocyclic dicarboxylic acids. These acids include phthalic acid, isophthalic acid and terephthalic acid. In particular, terephthalic acid is used to produce polyethylene terephthalate, which is apparently the most commercially available polyester.

As described above, the polybasic organic acid can react with the polyol to form a polyester. Polyols are compounds that contain at least two hydroxyl groups. Many polyesters are synthesized with diol. Diols are usually prepared from an alkene by the total addition of two hydroxyl groups to the carbon double bond in a manner known as hydroxylation. Polyols are usually called glycols or polyhydric alcohols. Examples of polyols used to obtain polyesters include ethylene glycol, propylene glycol, butylene glycol and cyclohexanedimethanol.

For an example in the table. 1 contains a partial list of commercially available polyesters that can be recovered or recycled in accordance with the present invention. For each polyester, an appropriate polybasic organic acid and polyol are provided.

Table 1 Polyester Polybasic organic acid Diol Polyethylene terephthalate Terephthalic acid Ethylene glycol Polybutylene terephthalate Terephthalic acid Butylene glycol Copolymer polyethylene glycol Terephthalic acid Cyclohexanedimethanol and ethylene glycol Polybutylene glycol copolymer Terephthalic acid Cyclohexanedimethanol and butylene glycol Polycyclohexanedimethanol terephthalate Terephthalic acid Cyclohexanedimethanol Polyester ΡΕΝ Naphthalene dicarboxylic acid Ethylene glycol

In one particular embodiment of the disclosed invention, the recoverable polyester may be polyethylene terephthalate (PET). Much of this discussion relates to PET, although this should not be considered as limiting the invention to any extent only to the extraction and removal of contaminants from

- 3 013407

PAT.

In one embodiment, the process of the present invention may be considered as a three-step operation to remove contaminants from the polyester and may include a preparation step, a reaction step and a final step. In addition, each stage of the whole process may include one or more separate operations. In one embodiment, the preparation step may include at least a dry separation operation and at least one water separation operation, during which contaminants can be removed from the mixture containing the polyester. After the preparation stage, there may be a reaction stage in which a mixture containing polyester and impurities may be combined with an alkaline composition. The alkali can react with a portion of the polyester through the saponification reaction, and also react with various possible impurities in the mixture to decompose or otherwise convert the impurities into a form more easily detachable from the polyester. This stage of the process may also include, if required, separating and removing impurities from the mixture. The reaction step may also include various thermal reactions, which may, among other benefits, further purify the polyester substrate and improve the physical characteristics of the material obtained. The final final stage of the process may include operations to improve the quality of the product, for example, washing and sorting the product, as well as additional separation operations.

The method of the present invention may proceed continuously or may be installed as a batch system. In addition, any particular operation of the method can be carried out both continuously and periodically. Virtually any material containing polyester can be processed in accordance with the invention. In one preferred embodiment, polyester materials can be recovered from the solid waste stream, thereby alleviating many environmental and waste problems. In one particular embodiment, the method may be directed to the recovery and recycling of PET containers for food and / or beverages. Through the process of the present invention, used polyesters can be separated, recovered and reused, even when polyesters are in the form of a mixture with certain firm materials, such as polyvinyl chloride or aluminum, associated with various coatings, or with different materials, such as organic and / or inorganic compounds. Unfortunately, many of the polyesters used are currently disposed of in land graves or burned after use due to the lack of a cost-effective process that could be used to separate and extract the polyester.

Among the contaminants that can be glued or contained inside edible polyester materials and which the disclosed method can preferably remove, include various barrier materials. Barrier materials removed in accordance with the present invention may include barrier coatings that can be applied, for example, to beverage containers, to prevent carbon dioxide and / or oxygen from penetrating through the substrate. Other barrier materials that can be removed in accordance with this process may include some chemical additives to barrier materials, such as chemical absorbing materials added to polyester materials during the initial production, and / or decomposition products formed during the reaction of such additives. In one embodiment, the disclosed method can be used to remove barrier materials applied as coatings for placement between layers in multi-layer bottles.

In addition to barrier materials in the form of coatings, the process can also remove other coatings from polyester materials. For example, the method may remove applied labels, including paper and / or polymeric labels, labels obtained by screen printing, etc. The term “screen-printed labels” generally refers to inks that are directly applied to polyester containers, such as beverage containers. For example, many soft drink containers typically have epoxy-based ink labels. In the past, attempts to separate polyester from this type of label and ink were a big problem.

A non-limiting exemplary list of barrier materials (both coatings and chemical components contained in the entire polyester substrate) and non-barrier coating materials that can be removed from the polyester in accordance with the present invention may include, for example, saran, nylon, polyvinylidene chloride , acrylics, epoxy-based polymers, acetaldehyde cleaners, ethyl vinyl alcohol (for example, EUON film), etc.

The method of the present invention is also effective in removing organic and / or inorganic compounds that have been incorporated which could be absorbed by polyester materials. Such compounds, for example, may include toluene, gasoline, used motor oil, paint, pesticide residues and other volatile compounds. Such compounds can often be absorbed by polyester with simple contact with them. For example, polyester containers for food and beverages are often misused by consumers after food or beverages have been consumed. In particular, containers are often used to store various organic and / or non

- 4 013407 compounds and solvents. When trying to recycle such polyesters, it is necessary to substantially remove all absorbed organic and inorganic compounds so that the polyester can be used again as a container for beverages or food.

Preferably, regardless of the impurities present, the method of the present invention may include a first preparation step, which involves removing some of the contaminants through one or more physical separation processes after the reaction step, which, in one embodiment, contacts the mixture containing polyester with an alkaline composition, mixing the alkaline composition and the mixture containing polyester so that the solid materials in the mixture are substantially and uniformly coated with this mixture. The position and partial polyether saponification occurred, the materials were heated in one process or in a multi-stage process to a temperature sufficient to complete the saponification reaction, if necessary, and also so that, among other advantages, the physical properties of the polyester were maintained or improved, and then the mixture containing polyester, through various possible separation operations, including, for example, washing materials with a liquid, such as water.

An extraction method will now be described in accordance with one embodiment of the invention using one preferred example of the process shown in FIG. 1. As shown in FIG. 1, the disclosed method can be conveniently considered by dividing it into three stages, i.e. stage of preparation, the stage of the reaction and the final stage. However, it should be understood that this particular separation is done for the sake of convenience of the description of this embodiment and is not considered a requirement of the disclosed process.

Cooking stage

Before separating from contamination in accordance with the present invention, contaminated polyester materials may, if required, be crushed or milled in the form of flakes, for example, in a sorting operation by size. For the purposes of this description, the term polyester particle refers to polyester materials that have been ground or ground to smaller particles. The transformation of materials into scales can be carried out to facilitate use. It should be understood that in the method according to the present invention, different sizes and shapes of the material can be used, and no one size or shape is required. For example, in one embodiment, the polyester may be in a discrete form, for example, finely crushed or granulated. Examples of particle sizes after grinding may include, for example, particles ranging in size from about 1 to about 15 mm. In one embodiment, the particles may have a size of from about 0.125 to about 0.75 inches. The exact shape of the particles is not important to the present invention.

In one particular embodiment, the polyester may be milled or pulverized when the mixture containing the polyester is dry. Without relying on any particular theory, it is believed that grinding materials when they are dry can improve the separation of some contaminants from polyester substrates. For example, it is believed that when processing multilayer bottles in accordance with the disclosed method, dry grinding may facilitate the separation of the layers and the removal of coating materials located between the polyester layers in the multilayer bottles.

After any crushing or grinding of the polyester substrate, the dry blend containing the polyester and contaminants may be subjected to one or more operations to remove contaminants heavier than the polyester. For example, in accordance with one embodiment, the mixture may be subjected to an elutriation process specifically designed to remove heavy contaminants, and in particular metallic contaminants. Brushing is simply a process for separating heavier materials from lighter materials through the use of directional gas or liquid flow. Pouring was used in the past in many processes, including recycling, to remove lighter contaminants from polyester. For example, elutriation operations are known in all recycling processes to remove lighter label materials, such as paper, from the mixture. Additionally, the elutriation operations can be used at various preferred points in the process of the present invention to remove very fine particles from the mixture.

In accordance with one embodiment of the present invention, after any desired grinding or grinding of materials, a otmuchivanie process may be used to remove contaminants from the mixture that are heavier than recoverable polymeric materials. More specifically, if in the past, it was known that lighter impurities were removed from the polyester mixture through the elutriation process, in accordance with this particular embodiment of the present invention, the lighter flow can be separated from the mixture containing the polyester, and heavier contaminants such as metal, stone, dirt, etc. can be removed from the mixture as a heavier stream discharged from the otmuchivania apparatus. In accordance with this particular separation operation, the elimination flow rate may be higher than the flow rate used in previously known processes for separating lighter materials from a stream containing polyester in order to separate heavier contaminants from the mixture containing polyester. For example, in one embodiment, a flow rate (for example, air), ranging from about 3,600 cubic feet / min (kfm) to about 4,600 kfm, can be used in the wigging process at the rate of flow of solid matter

- 5,013,407 rials from about 2,500 lb / h (in / h) to about 3,500 in / h to separate heavier solids from the mixture containing polyester. In one embodiment, the incoming flow of solids may be about 3000 inches / hour.

Again, as shown in FIG. 1, at some point during the preparation stage, for example, after an otmuchivaniya process to remove heavy impurities, a mixture containing impurities and polyester can be loaded into a dry-cleaning tank. In particular, the mixture of materials loaded into the cleaning tank will contain at least some used polymer and the mixture will be dry. That is, the mixture is not in suspension. A dry mix of materials however should not be too dry. For example, the mixture should not be pretreated to remove all moisture from the mixture, and it can be loaded into a tank at atmospheric humidity.

A dry cleaning tank may include a cleaning chamber into which the dry mix is loaded. In one preferred embodiment, such a chamber may be surrounded at least partially by a mesh with a preferred aperture size. For some embodiments, it may be preferable for the majority of the individual polyester particles to be loaded into the dry cleaning tank to be larger than the size of the opening in the mesh material of the cleaning tank in order to facilitate the processing of the mixture. Sorting materials before loading them into the dry cleaning tank can also help to ensure that at least some of the contaminants will have a size that allows them to pass through the screen, although many of the contaminants can break down inside the dry cleaning tank, as described below.

In one embodiment, the chamber may include a number of blades distributed along the longitudinal axis of the chamber. Materials after loading into the tank can be rotated or twisted around the axis of the chamber, for example, due to the rotational action of the blades. In particular, the movement of materials may be sufficient to fluidize the dry mixture. For example, the blades can rotate at a speed greater than about 20 m / s to fluidize the loaded mixture. In one embodiment, the blades can rotate at a higher speed than about 2000 revolutions / min. In one embodiment, the speed of the ends of the blades can be from about 40 to about 100 m / s, for example, about 50 m / s. In another embodiment, the end speed of the blades may be from about 60 to about 80 m / s.

In addition to fluidizing the mixture, the rotation of the mixture caused by the rotating blades may also contribute to a dynamic impact between the materials in the mixture and with the walls of the chamber. Collision of materials contained in the mixture with the walls of the chamber can lead to the destruction of contaminants in the mixture and, in particular, to the destruction of contaminants to such an extent that individual particles can become smaller than the size of the holes in the surrounding wall. In addition, such dynamic collisions can facilitate physical separation from embedded or otherwise bonded contaminants from polyester. In a collision between suitably small soils (smaller than the size of the holes in the mesh wall) and the mesh, the contaminants can pass through the surrounding mesh, and the polyester can remain in the chamber. The rotation of the blades can also facilitate the flow of air through the chamber and the movement of materials from one end of the chamber to the other.

Surprisingly, the dry cleaning operation can physically separate polyester from adhering contaminants, including embedded contaminants, as well as destroy many fragile contaminants without substantial destruction of the polyester. For example, although coating materials, such as paper label materials, or coatings that form a vapor barrier, and embedded materials, such as embedded glass and dirt, may become detachable from the polyester substrate during the dry cleaning operation, the polyester flakes themselves may remain the same size and shape as they were originally loaded into the container. In addition, although contaminants can be separated from the polyester and pass through the surrounding mesh, the polyester can remain inside the chamber for cleaning. Even in those embodiments in which the polyester includes smaller polyester flakes than the mesh openings, the bulk of very small polyester particles may remain as a suspension in the cleaning chamber and will not be lost along with the contaminants during the separation process.

If you do not associate yourself with any particular theory, it is believed that due to the centrifugal forces acting on the suspension, the materials in the mixture can be separated, while more dense materials and in particular such contaminants as glass, metals, paper, etc. that is, light materials, and in particular very fine polyester particles, can move to the outer sides of the mass, can be weighed closer to the center of the chamber. Therefore, glass-like materials and fibrous materials can break down and pass through the mesh at the outer edges of the mass, and elastomeric materials, such as PET, can remain in the mass. In general, even PET particles smaller than the hole in the grid can remain with the main rotating mass, and a very small amount of very small particles will pass through the grid and the dry cleaning operation can produce a high polyester yield.

The dry cleaning operation can be particularly effective when removing glass from a mixture that includes both glass and polyester. Glass has often been considered one of the most difficult materials to separate from used polyester during the recycling process of polyester, and glass can be detrimental to the process if it is not completely removed. Glass that is not removed

- 6 013407 during the recycling process, can not only cause serious damage to processing equipment during the recycling process, but it can also cause the destruction of materials formed from recycled polyester. For example, glass that is not removed during the recycling process may become embedded in the polyester during the subsequent material production process (for example, in the manufacture of beverage containers) and may cause the destruction of materials formed from polyester, for example, due to the formation of holes in polyester products.

In accordance with one embodiment of the present process, approximately more than 97% of the glass in the mixture containing both glass and polyester can be removed from the mixture during the disclosed dry cleaning operation. In one embodiment, more than about 98% of the glass in the mixture can be removed. In another embodiment, more than about 99% of the glass may be removed during the dry cleaning operation.

During the preparation stage, for example, either before or after the dry cleaning operation, the mixture may be further processed in accordance with one or more additional dry separation operations. For example, in one embodiment, the mixture may be subjected to an otmuchivaniya operation to remove light contaminants from the mixture. For example, the air flow through the otmuchivania apparatus can reach from about 1500 kfm to about 3000 kfm with a flow of solid materials to about 3000 inches / hour, and at least some of the lighter contaminants can be removed from the mixture. Other dry separation operations that may likely be introduced at one or more points of the preparation stage may include any separation operations commonly known in the art, such as, for example, sieving operations using vibrating sieves to separate larger or smaller impurities. than polyester, depending on the mesh size of the sieve and the size of the polyester particles.

During the preparation stage, the mixture may also undergo one or more water separation operations. For example, in the embodiment shown in FIG. 1, the intensive washing operation may follow the dry cleaning operation and the washing off operation. Preferably, due to the previous separation operation (s), so that a possible subsequent water separation operation, for example, an intensive washing operation, may indicate lower levels of contamination in the washing water, and therefore less wastewater treatment may be required by this method. In particular, since many contaminating materials and impurities can be removed by the dry separation operations described above, problems encountered earlier when using water separation methods, such as, for example, curing separated coating materials or the need for costly water treatment, can be less complicated in the method of extraction of the polyester according to the present invention.

For example, after a dry cleaning operation with additional or no additional separation operations, such as, for example, washing off, the wash water may show a decrease in the need for chemical oxygen by at least about 15% compared to the demand for the wash water directly used for contaminated polyester materials. Similarly, by using at least a dry cleaning operation before washing with water, the total level of dissolved solids in the wash water can be reduced by about 30%, and the level of oil and grease can be reduced by about 15%.

The intensive washing step may include adding water to the mixture and exposing the materials contained in the water mixture to a high shear force to facilitate the removal of some contaminants, such as oligomers, and other organic and inorganic compositions from the surface of the polyester. In general, high shear flushing may include flushing, in which the turbulence of the flushing water during operation is higher than with standard flushing, but low enough to prevent excessive damage to the flakes and / or the formation of very small particles. For example, high shear flushing in accordance with the present invention may include flushing in which the flushing rotors rotate at the speed of the ends of the blades from about 500 to about 1000 feet per second (fvs). Such high shear washers are commercially available in this field of technology from manufacturers such as KedMas, Gogesha or B @ B.

In accordance with another water separation operation suitable for use in the disclosed method, materials containing polyester can be immersed in water so that less dense or lighter materials can be separated from heavier materials, and specifically from polyester. In particular, it is known that polyester sinks in water, and other polymers, such as polyolefins, and paper products float in water. Thus, lighter materials can be easily separated from heavier materials when they come into contact with a suitable amount of water. By subjecting the materials to the separation phase as it sinks / floats and removes some of the contaminants from the mixture, it is possible not only to reduce the amount of materials being processed in the mixture, but also to facilitate the cleaning of the materials before further processing.

When applying a mixture containing impurities and polyester to a sink / float type tank, it may be preferable to introduce the mixture below the surface level of the liquid in some embodiments. it

- 7 013407 can eliminate the effect of surface tension of water in the tank on the materials contained in the mixture, and facilitate the immersion of more dense materials.

In order to further improve the disclosed method, and in particular to reduce the amount of water used in the process, the preparation step of the method may also include a recirculation tank for recycling water used, for example, in an intensive washing apparatus and / or in a sinking / floating tank. Therefore, any water used in the water operations of the preparation stage, as well as any water removed from the materials during any drying operations at any stage of the process, can be recycled through the recirculation tank. In addition, the recirculation tank may include, if required, a blender, to keep any polyester very fine particles transferred to the recirculation tank as a suspension, and thus facilitate the re-entry of these polyester very small particles back into the main process stream to remove contaminants.

Other water separation operations that can likely be used in the preparation stage of the process may include, for example, using one or more hydrocyclone separators, as is generally known in the art. For example, one hydrocyclone, two hydrocyclones or several hydrocyclones can be used sequentially to separate contaminants from a mixture containing polyester.

After the water treatment operations, for example, at the stage of intensive washing and sinking / flooding separation, the mixture containing polyester and the remaining impurities may be dried and possibly subjected to additional dry separation operations before it is combined with alkaline material during the reaction stage . This drying operation may, for example, occur at temperatures not higher than about 160 ° C. For example, in one embodiment, drying may occur at a temperature of from about 130 to about 160 ° C., and generally may be carried out by any method known in the art.

For example, in accordance with the embodiment shown in FIG. 1, before the stage of the reaction, the mixture can be dried and then subjected to a color separation operation. The use of a color separation operation prior to the reaction step of the method turned out to be useful in some embodiments of the present invention, since this operation can serve as an essentially different purification step in the process, removing various impurities from the mixture and thereby »The mixture at the stage of the reaction. Contaminants that may be removed from the mixture prior to the stage of carrying out the reaction through a color separation operation may include, for example, metals and colored polymeric components, such as polyester materials dyed with titanium dioxide.

In general, dyed polyester materials and, in particular, white polyester materials dyed with titanium dioxide cannot be efficiently recycled, as they are considered to be contaminants of the desired clear product stream. It is therefore useful to remove such materials from the recycle stream. This has proven difficult in the past, however, since during the recirculation process itself, the supplied transparent polyester materials may crystallize and appear white, therefore it is difficult to get rid of white contaminants such as polyester / T1O ₂ materials. In accordance with the process just disclosed, such materials can be separated from the stream before the stage of carrying out the reaction and thus before possible crystallization of recycled polyesters.

In general, any color separation method commonly known in the art can be used in the disclosed invention. For example, visual inspection or automated optical sorting and separation methods can be used. Examples of commercially available equipment for optical color separation may include equipment manufactured by companies such as 8KC, 8a ake and M88.

Other separation operations that may be used in the present invention, for example, during the reaction stage of the process to remove as much contamination as possible before the reaction stage, may include, for example, water separation processes, such as additional otmuchivaniya methods, additional washing operations , additional sorting operations and / or use of operations specifically designed to remove metals from the stream.

Methods for removing metals suitable for use in the present invention may include the use of magnetic separators, such as drum magnets, waterfall magnets, whirling current machines, or any other suitable magnetic metal detectors and separators, such as commercially available from WiiChid Madieisk , From from № \\ 1op. Kaikak, USA or 8 @ 8 Jäsusyyed StN from Germany. Such devices can use any type of magnets (for example, iron-based permanent magnets, rare earth magnets, electromagnets) of any suitable design to remove at least some of the metallic contaminants contained in the mixture.

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Stage of the reaction

During the reaction step of the disclosed process, a portion of the polyester in the mixture may be hydrated by reacting the polyester with an alkaline compound. In particular, the stage of carrying out the reaction according to the method may include one or more mixers, at least one of which may be a high-energy mixer. In addition, the stage of the reaction may possibly include additional operations for carrying out the reaction, such as a high-temperature thermal curing operation.

For example, in accordance with the embodiment shown in FIG. 1, the reaction step of the method may include a first low-energy mixing operation, in which a mixture containing polyester and contaminants may be combined with an alkaline composition before being supplied to a high-energy mixing operation, in which part of the polyester may be saponified. After the high-energy mixing operation, the mixture can be dried and fed to the heat-curing operation, for example, using a kiln, in which, among other advantages, the saponification reaction can be completed if necessary. In addition, during the thermal curing operation, secondary materials can also react with the alkaline composition, and the physical properties of the polyester can be maintained and / or improved.

The step of carrying out the reaction according to the method can probably involve one or more processes for extracting the reaction by-products. For example, in PET saponification, the reacted polyester material can be converted to metal terephthalate and ethylene glycol. If required, the metal terephthalate obtained in this way can be dissolved in water and the water can be acidified, which causes precipitation of terephthalic acid. Terephthalic acid can be filtered and recovered as a by-product of the disclosed process, if required. Similarly, the polyol that was formed during the reaction of the process may either remain as a liquid in the mixture for subsequent removal, or may directly evaporate if the reaction proceeds under conditions that facilitate the evaporation of the polyol. The polyol can then be extracted, if required, for example, using a condenser.

The alkaline compound selected for mixing with materials may be in one preferred embodiment sodium hydroxide, commonly known as caustic soda. In addition to or instead of sodium hydroxide, other metal hydroxides and alkalis can be used wherever possible. For example, suitable compounds may include calcium hydroxide, magnesium hydroxide, potassium hydroxide, lithium hydroxide, or mixtures thereof. When used in solution, the metal hydroxide can be combined with water before mixing with materials containing polyester. For example, in one embodiment, the metal hydroxide can be mixed with water in a ratio of about 1: 1.

In general, the reaction step of the present invention includes a high-energy mixing step, during which a mixture containing impurities and polyester can be combined with a selected amount of alkaline solution to form a slurry. The amount of alkaline composition added to materials containing polyester will generally depend on the type and amount of impurities and impurities present inside the materials. In general, the alkaline composition should be added only in an amount sufficient to separate the impurities from the polyester in such a way as to minimize the saponification of the polyester. In most applications, the alkaline composition can be added to materials in a stoichiometric amount sufficient to react with about 50% polyester. Preferably, the alkaline composition is added in an amount sufficient to react with less than 10% polyester and most preferably with about 3% polyester.

In the embodiment shown in FIG. 1, the suspension can be obtained in the first low-energy mixer, but this is not a requirement of the invention. In other embodiments, the slurry may be prepared directly in a high-energy mixer, and a low-energy mixer may not be introduced. It is possible to add a surfactant or wetting agent to the mixture and to the alkaline composition when preparing the suspension. The addition of a surfactant can make it easier to mix the alkaline composition with the materials, helping to reduce the amount of alkaline composition that you want to add. The surfactant must be alkali resistant and may not be ionic or anionic in nature. An example of a suitable surfactant is ETNAE-3, a non-ionic surfactant supplied by E11yuh. 1ps from Steyuishe, 8th SotNie.

In those embodiments where one or more low-energy mixers are used to obtain a suspension, some low-energy reactions may also occur in the mixer. For example, when using a low-energy mixing operation, a mixer can probably be used with the parameters of the operation (for example, adding a small amount of heat energy by heating the mixer) to facilitate the reaction of the alkaline composition with some contaminants in the mixture, and in one particular embodiment, react with with aluminum. However, in those embodiments where additional energy is added to the mixture in a low-energy mixer to activate the reaction between the contaminants and the alkaline composition, the total amount of energy

- 9 013407 added to the mixture at this point in the process, should be no more than what is sufficient to activate the saponification reaction between the polyester and the alkaline composition. For example, in one embodiment, a low-energy mixer may operate at an internal temperature of from about 90 to about 110 ° C to promote the reaction between the aluminum contained in the mixture and the alkaline composition without activating the saponification reaction between the polyester contained in the mixture and the alkaline composition.

It turned out that under low-energy conditions, such as conditions that may be desirable to be created in a low-energy mixer, the alkaline composition can react with aluminum in a mixture to form, for example, an alkali aluminum salt, which can be soluble in suspension water. Thus, in some embodiments of the present invention, a low-energy mixer can be used before any saponification of the polyester contained in the mixture to obtain a suspension and effectively coat the solid materials of the mixture with an alkaline composition, as well as to activate the reaction of the alkaline composition with various impurities contained in the mixture.

It is possible to include a rinsing or rinsing operation in the process after the low-energy mixer, for example, to remove any reaction products formed in the low-energy mixer. For example, in embodiments where aluminum reacts with an alkaline composition in a low-energy mixer to form an alkaline aluminum salt, the mixture can be washed to remove at least part of the salt before additional steps in the reaction step of the process.

After any possible low-energy mixing operation, materials can be fed into one or more high-energy mixers. As mentioned above, in those embodiments in which a low-energy mixer is not used to produce a suspension, this suspension can be obtained in the highest-energy mixer. Moreover, the alkaline composition can be added to the mixture in a high-energy mixer not only in those embodiments where the suspension is formed in a high-energy mixer, but also when washing a suspension containing alkali, to remove contaminants before flowing it into a high-energy mixer or to replace the alkaline composition that reacted with contaminants in a low-energy mixer, regardless of whether it was flushed or not.

The high energy mixer used is one that can provide not only a substantially complete and even coating of polyester materials with an alkaline composition, if required, but can also transfer enough energy to cause saponification of part of the polyester or, in other words, hydrolysis, without the need to add large quantities ( or in some embodiments any amount of heat into the mixer. For example, mixers such as those described in U.S. Pat. No. 4,320,979 to Bieck and Bicke No. 4,189,242, which are here considered essentially with reference to them, can be used in a high-energy blending operation to activate saponification of at least part of the polyester with an alkaline solution .

In one embodiment of the present invention, the high-energy mixer may operate with a Froude number greater than about 4.2, in particular, greater than 6.6, and more preferably greater than about 9.5. In particular, at the above speeds, the mixer of the present invention not only mixes the slurry, but also gives it enough energy to cause the alkaline composition to react with the polyester. In one embodiment, the high-energy mixing can be continued until substantially all of the alkaline composition is consumed. For example, a high-energy mixer may operate in such a way that the remaining (unreacted) metal hydroxide coming out of the mixer may be less than about 1% by weight of the suspension. In particular, the remaining metal hydroxide leaving the mixer may be less than about 0.5 wt.% Moreover, the remaining metal hydroxide may be less than about 0.1 wt.% By weight of the suspension, for example, less than about 0.05 wt.% .

During saponification, various coatings can peel off the polyester, which can adhere to the polyester, and / or other contaminants that can be applied to the surface of the polyester. The energy provided by the mixer can also activate the reaction between the alkaline solution and other contaminants that may be in suspension, such as, for example, polyvinyl chloride or aluminum. By reacting these types of materials with an alkaline composition, the impurities can be converted into another form, which is more easily separated from the polyester substrate.

In addition, it is also believed that due to the completeness of the mixing, as well as the essentially even alkali coating supplied to the polyester materials in the high-energy mixer, the salt that is the product of the reaction can form a coating on the polyester materials that are removed from the mixer. For example, if the outer surface of PET flakes is saponified in a high-energy mixer with a composition of sodium hydroxide, then it is believed that the reaction product disodium terephthalate can cover the remaining PET. Moreover, it is believed that this coating formed around the polyester particle can serve as protection for the polyester during subsequent processing operations. For example, a salt coating can protect the polyester from oxidation due to the high temperature conditions that occur later in the heat curing operation. Among other benefits is my

- 10 013407 zhet to provide a polyester product with less discoloration than the products obtained in the past.

In some embodiments, after the reaction in one or more high-energy mixers, the mixture can be dried and supplied to the final stage, or it is possible to flow directly from the high-energy mixer to the final stage. In particular, in those embodiments where the recycled polyester product obtained by the process is not intended to be used as a food product, additional reaction steps, and in particular the heat-cure operation, discussed below, may be unnecessary. In those embodiments where a food grade product is required, the method, however, may include at least one thermal curing step.

After the reaction is carried out in a high-energy mixer, the suspension can be dried and in some embodiments supplied to the heat-curing operation. For example, the mixture may first be dried by heating to a temperature of from about 150 to about 160 ° C, followed by additional heating to a heat-curing temperature, which may contribute to the additional reaction of the materials. The actual temperature to which the mixture is heated during the heat curing operation may depend on a number of factors. In general, the mixture should be heated to the highest possible temperature, but without melting the polyester. For example, PET has a melting point of 250 to about 270 ° C. Therefore, when substantial amounts of PET are contained within the materials, the mixture should be heated to a temperature of approximately below 270 ° C during the heat-curing operation. In most applications, the temperature can range from about 100 to about 270 ° C.

In general, a heat-curing operation can be carried out under conditions in which at least substantially no water is present, in an environment of dry air. However, although a dry air environment may be preferred in some embodiments, for example, due to cost considerations, an inert atmosphere of gases such as nitrogen, argon, carbon dioxide, or the like, such as a nitrogen blanket, can also be effectively used. . If desired, the mixture can also be heated at reduced pressures, which correspond to lower oxygen levels. The term "at least substantially no water" means that the amount of water present in the medium is less than the amount that leads to degradation of the polyester during heating. This amount is usually not more than 80 ppm (dew point -40 ° E), preferably not more than about 10 ppm, more preferably not more than about 5 ppm (dew point -80 ° E). There is no theoretical minimum for water content, since the amount of water in the medium can be as low as 1 ppm or even less.

Also in one embodiment, the mixture may preferably be heated in an oxygen-depleted environment. The term oxygen depleted, as used herein, refers to a medium in which oxygen is present in an amount below about 19% by volume. In combination with a dry atmosphere, maintaining lower oxygen levels during the heat-curing phase can also eliminate significant damage or discoloration of the polyester and can also further prevent uncontrolled ignition. If desired, the mixture can also be heated at reduced pressures, which correspond to lower oxygen levels. In addition, during heating, the suspension can generally be heated indirectly so that it does not come into contact with an open flame.

An oxygen-depleted environment is not a requirement of the invention, however, in other embodiments, it may be preferable to heat the mixture in an oxygen-enriched environment, i.e. in an environment containing oxygen in an amount greater than about 19% by volume.

The equipment and apparatus used during the heat curing operation of the present invention may vary. For example, in one embodiment, the heat curing operation may be carried out in a rotary kiln. The rotary kiln can be heated by an electric element or heated by oil burners or burners on fossil fuels. One example of a suitable indirectly fired kiln for use in the process of the present invention is a K.O1satt furnace, supplied by Keppeigigd Όίνίδίοη οί Neu1 @ Rayegop, 1ps. However, in other embodiments, multidisk thermal processors or furnaces may be used. Of course, other similar devices are commercially available, for example, infrared thermal processors, microwave heaters, etc., which may possibly be used in the processes of the present invention.

In one embodiment, the calcining furnace may first be heated to a lower temperature for a predetermined period of time to dry the materials removed from the high-energy mixer, and then the temperature may be raised to a higher level. Alternatively, the slurry coming out of the high-energy mixer may first be heated in a drying apparatus, such as, for example, a CopAi dryer, before it is fed into the kiln for a more high-temperature thermal curing operation. In another embodiment, the calcining furnace can be used to relatively quickly raise the temperature of the mixture to a predetermined level, and the hot materials can then be sent to a larger drying apparatus of the column type or any other system for solid materials, where they can be maintained at a given temperature for a given time.

- 11 013407 th time interval.

The heat curing operation of the disclosed method can provide many useful functions. For example, during a heat-curing operation, by-products such as ethylene glycol formed during the saponification reaction during high-energy mixing in a high-energy mixer, or in a heat-curing operation, can be evaporated from the stream. The evaporated materials can then be collected, for example, in a condenser and directed to a suitable treatment operation, for example, if required, to a water treatment operation for their extraction. In addition, during the heat-curing operation, any remaining unreacted alkali that has passed from the high-energy mixing operation can react either with polyester or with other chemically active contaminants in the mixture.

The remaining organic and / or inorganic compounds that can be absorbed by the polyester can be removed from the polymer product during the heat curing operation. In particular, any remaining volatile organic and inorganic compounds can be substantially removed during the heat-curing stage not only from polyester, but also, depending on the properties of the compound, completely from the stream by means of exhaust gases. By ensuring the removal of substantially all trapped organic and inorganic compounds, a “food grade” polyester can be extracted, which can be used in an unlimited manner. In addition, heating the mixture can cause the destruction of the free dried contaminants to a more easily separable form in order to facilitate the final separation of these contaminants from the polyester product.

The heat curing operation can also improve the physical characteristics of the polyester in the blend. In particular, the thermal solidification operation is believed to increase the transparency and intrinsic viscosity of the polyester product. For this purpose, the heating stage in a dry atmosphere can be carried out for a period of time sufficient to increase the intrinsic viscosity of the polyester. For example, in accordance with one embodiment of the process just disclosed, the intrinsic viscosity of the polyester in the feed stream may increase from about 0.76 bb / d to about 0.82 bb / d. For example, the intrinsic viscosity of the feed materials may be increased by about 5-10% in accordance with one embodiment of the disclosed present invention. The minimum time depends, for example, on the water content in the medium and can be as short as 5-10 minutes.

After the physical separation of the impurities from the polyester has been carried out, such impurities, such as the now separated coating materials and / or trapped materials, can be further degraded when they are processed in subsequent operations. For example, solvents and liquids contained in coatings or removed from polyester during a heat-curing operation can be evaporated and possibly removed from the kiln and re-trapped in a condenser, similar to the ethylene glycol product trapping process described above. Remaining in the mixture may be some pollution of a relatively smaller size. When the mixture is then subjected to additional separation operations, for example, in the final stage of the process, the remaining insoluble contaminants can be separated from larger polyester particles, for example, using a sieve of a suitable size, which allows the passage of contaminants, but does not pass the polyester.

During the reaction stage of the method, in addition to the saponification of part of the polyester, some difficult to remove contaminants, usually found in used polyester, can be converted into a form that can be more easily separated from the mixture. In particular, during the reaction step of the method, impurities such as polyvinyl chloride, polylactonic acid (PLC) and aluminum can be converted into forms that can be more easily separated from the polyester.

When polyvinyl chloride and / or polylactic acid is present inside the materials, the materials can be converted into a form that is more easily separated from the mixture. For example, in accordance with one embodiment, at least a portion of the PVC can be made into a form that is darker and thus separable from the mixture through color-sorted methods. In some embodiments, PVC contamination can be converted to a form that floats in water. In other embodiments, PVC may react to form a mold that exhibits enhanced heat resistance. Moreover, combinations of these characteristics can manifest themselves reacted PVC. In general, the specific reactions of PVC with an alkaline composition may depend on the special characteristics of the PVC impurities contained in the mixture. However, whatever the specific initial characteristics of the contaminating PVC, it is believed that when the mixture is mixed with the alkaline composition and when the corresponding energy is supplied, PVC can react to form a form that is more easily separated from the polyester contained in the mixture. Therefore, when the polyvinyl chloride is present in the materials, it is preferable to add a certain amount of alkaline composition to the suspension, sufficient to react with the polyvinyl chloride or, in other words, to transform the polyvinyl chloride into a form that is separable from the polyester.

However, if PVC does not react with the alkaline composition in a high-energy mixer and / or during heat curing, then it is possible to remove PVC from the mixture by heating

- 12 013407 mixture to a temperature that is above the melting point of PVC, but below the melting point of the polyester contained in the mixture, while PVC can be melted and then removed from the mixture, for example, using a sieve or other suitable separation method during the reaction stage, or perhaps during the final stage of the process. PLC can be removed from the mix in accordance with similar processes as described above for PVC. In particular, any changes in the process, for example, changes in the amount of alkaline composition, changes in processing conditions (for example, temperature, etc.), which may differ from those described above for PVC, are well known to ordinary specialists in the field and therefore not will be described here in detail.

In addition to polyvinyl chloride, polyester collected from the solid waste stream can usually also be mixed with aluminum particles, as mentioned above. Aluminum may occur, for example, from bottle caps used in polyester beverage containers or due to the imperfect separation of used plastic and aluminum cans found in the waste. Aluminum, like polyvinyl chloride, cannot be easily separated from polyester using standard separation methods such as sinking / flooding separation operations.

Upon contact with the alkaline composition and providing suitable energy to any or all low energy mixers, high energy mixers and / or heat curing operations, aluminum can be converted to an alkaline aluminum salt, which is generally soluble in water. Thus, in one embodiment, the amount of alkaline composition that can be added to materials containing polyester and aluminum is sufficient to completely convert aluminum to an aluminum salt. After the reaction, a stream of, for example, water can then be added to the mixture to dissolve the aluminum salt and separate it from the polyester.

In accordance with one embodiment of the present invention, not all aluminum contained in the stream entering the reaction step must be converted to an aluminum salt. Instead, only a portion of the aluminum can be converted by the alkaline composition to an aluminum salt. In particular, it was found that after the reaction of a part of aluminum with an alkaline composition, the remaining aluminum particles may become brittle. In accordance with this embodiment, materials containing polyester mixed with the remaining aluminum can then be mixed under shear conditions and the remaining brittle aluminum can break into small particles. The fine particles can then be separated from the polyester, for example, by means of a suitable separation operation, for example, by a simple screening process using a sieve of a size sufficient to trap the larger polyester particles and to pass smaller, shattered aluminum particles.

Therefore, when aluminum is present inside materials containing polyester, the alkaline composition may be added to the materials in an amount sufficient to react with at least part of the aluminum and sufficient for the remaining aluminum to be brittle. Of course, the actual amount of alkaline composition to be added may depend not only on the amount of aluminum present in the materials, but also on the size (eg, thickness) of the aluminum particles.

Additional operations that may be included in the reaction step may include, for example, additional heating operations, for example, to keep the mixture at a suitable temperature for a period of time to further increase the intrinsic viscosity of the polyester product. For example, after a heat-curing operation at a high temperature, for example, in a kiln, the mixture can be kept in one or more kilns at a given temperature for a period of time to ensure food-grade polyester, further improve the physical characteristics of the product, remove additional volatile contaminants and / or remove additional nonvolatile contaminants, such as, for example, paper fibers, by convection of heat and / or heat radiation in a kiln. In such an embodiment, any suitable oven may be used, including an infrared oven.

Final stage

The specific operations included in the final stage of the disclosed process may generally vary depending on the particular contaminants and / or impurities in the starting compositions. In addition, and depending on the specific impurities found in the starting material, the invention can not only effectively extract polyester from a variety of contaminants and / or impurities, but also can extract specific contaminants found in the waste stream as byproducts of the process. For example, polyolefins removed from a stream by sinking / flooding type operations can be dried and removed.

In one embodiment, the final stage of the process may include at least one washing or washing operation, one color screening operation to remove discolored impurities from the mixture, and at least one freezing operation to remove very small particles and any remaining light impurities. from the product.

It is possible that in addition to simply washing the materials with water or instead of them, the materials may be washed with a cleaning solution. For example, a mixture containing polyester and any remaining impurities may be mixed with a hot aqueous solution containing surfactant

- 13 013407 substance, or with a hot aqueous solution containing alkaline material, and washed. If desired, the mixture can be heated by stirring or by high-intensity washing, such as described above in the preparation step. Washing the materials can clean the polyester by directly separating the polyester from the contaminants and can also dissolve and / or break up some of the contaminants.

During the final stage, the acid salt or metal salt obtained in the saponification reaction may be dissolved in the wash water. If desired, the metal salt can then be removed from the wash water to remove or as a by-product of the process. For example, if the acid salt is terephthalate, the wash water may first be filtered to remove any undissolved impurities and contaminants. Then the wash water may be acidified to cause precipitation of terephthalic acid. To acidify the solution, a mineral acid, such as hydrochloric acid, phosphoric acid or sulfuric acid, or an organic acid, such as acetic or carboxylic acid, can be added to the solution. After precipitation of terephthalic acid, it can be filtered, washed and dried to obtain a relatively pure product.

To separate some contaminants, such as some polyvinyl chloride reaction products, from the polyester, the mixture can be combined with a liquid such as water during the final stage. When placed in water, the polyester will sink, and dechlorinated polyvinyl chloride may float. In addition, it turned out that the treatment of polyvinyl chloride with an alkaline composition in the manner described above can improve the adhesion of trapped air and other gas bubbles to the surface of the polyvinyl chloride reaction product, which makes it even more buoyant. Therefore, when the mixture is in a liquid (for example, in water), gas bubbles, such as air bubbles, can forcefully move through the liquid and increase the separation efficiency. Of course, other methods of separation can probably be introduced into the process, based on the difference in the specific weights of polyester and dechlorinated polyvinyl chloride.

As described above, the reaction of PVC with an alkaline composition can also darken the color of polyvinyl chloride and increase its melting point. Consequently, in another embodiment, the polyvinyl chloride reaction product can be separated from the polyester during the final stage by sorting by color, such as described above in the preparation stage. Other contaminants can be separated from the mixture through the sorting operation by color also during the final stage. For example, in some embodiments, the injected polyester product may include some barrier materials, such as acetaldehyde cleaning barrier materials in reacted or unreacted form. In accordance with the present invention, such contaminants may become discolored during the process just opened, for example, during the thermal curing operations of the present invention. During the sorting operation by color during the final stage, such contaminants and, in particular, contaminants that can change their color during the reaction stage of the process can be removed from the mixture.

In one embodiment, the final step may include neutralizing any remaining alkaline material by adding a suitable acid to the mixture, such as an inorganic acid, including, for example, hydrochloric acid, phosphoric acid and / or sulfuric acid, or an organic acid, such as acetic acid and / or carboxylic acid. After neutralizing any remaining base by adding an acidic solution, the mixture can be dried before any dry separation operations.

During the final stage, the remaining metallic impurities can be removed from the mixture in a metal removal operation. One embodiment of a high quality metal removal operation suitable for use in the present invention is shown in FIG. 2. As can be seen in FIG. 2, in accordance with this particular embodiment, the metal removal operation may include a plurality of metal detectors in series or parallel to form a battery from separate metal removal devices to ensure more complete removal of metallic contaminants than is provided in metal separation operations known in the past.

It should be understood that, although this particular metal separation operation is presented here as an operation occurring during the final stage of the disclosed process, an equivalent operation can probably be introduced into this process somewhere, for example, during the preparation stage. In addition, many operations for the removal of high-quality metal, as described here, can be included in the method of extraction of the polyester in various relevant stages of the method.

In one embodiment, the method may include many batteries from two or more devices for removing metals in one processing step. In accordance with this embodiment, the entire mixture stream can be divided among two or more batteries from metal removal devices to create many smaller input streams to each device battery. For example, one processing step in a polyester extraction process may include one, two, or even more batteries from devices. For example, a high-quality metal removal operation can include anywhere from one to 10, 20, 30, and even more batteries, each of which contains two or more detection devices and

- 14 013407 removal of metals.

FIG. 2 shows one battery of devices in accordance with one embodiment of the invention. As can be seen, in accordance with this particular embodiment, the battery includes five devices for detecting and removing metals, but it should be understood that this specific number is not a requirement of the invention. In other embodiments, the device battery may include an additional number or possibly a smaller number of individual devices. For example, a device battery may include as few as two devices and an infinitely greater number of individual devices inserted into the battery. Although practically speaking, there may generally be economic considerations in determining the preferred number of individual devices included in the battery, as well as the total number of batteries introduced into the processing step of the process.

All incoming flow introduced into the battery is processed in the first unit 1 for the detection of metals. When detecting a metal in the incoming stream, a part of the stream, including the detected metal, is separated and removed from the stream, as a rejected stream 10. The “Clean” or suitable stream 7 and the rejected stream 10 discharged from unit 1 to detect the metal are then fed to additional blocks 2, 5 for metal detection. In block 2 for the detection of metal, the process of detection and separation is repeated, while the rejected stream 11 (which contains the detected metal) is fed to block 5 for detecting metal, and a suitable stream 8 is fed to another block 3 of detection and separation and then to final block 4 for metal detection. Each rejected stream 12, 13 from the metal detection units 3 and 4 is fed into the recycle stream 6, and the final suitable stream 18 continues to flow into the entire process. In block 5 for the detection and removal of metals, a suitable stream 20 is fed back into the recycled stream 6 and the rejected stream 14 is removed from the process as waste containing metal.

In addition to recycling rejected streams 10, 11, 12, 13 and a suitable stream 20 back through the method by means of recycled stream 6, the individual metal detectors contained in the battery can be tuned to increased sensitivity when the stream passes through the process, as shown by the side arrow. For example, blocks 2, 3, and 4 for metal detection may have increased sensitivity in comparison with each other, as well as in comparison with block 1 for metal detection. Moreover, the sensitivity of unit 5 for metal detection may be higher than the sensitivity of unit 1 for metal detection.

In the entire process of the present invention, which includes a high-quality metal removal operation, essentially all of the metal contained in the incoming process stream can be removed from the polyester product stream.

In general, the final stage of the operation may also include one or more otmuchivaniya operations to remove any remaining light contaminants, such as any remaining paper or paper fibers or any very polymer particles.

Other separation operations that may be used in the final stage, as well as between operations in the preparation stage and / or the reaction stage, may include physical separation operations, such as were described above in relation to the preparation stage, as well as any other suitable separation operations, commonly known in the art, such as, for example, using one or more operations to remove large particles to remove glass, and / or using hydrocyclones. For example, in one embodiment, two hydrocyclones can be used in which materials can be pumped into the first hydrocyclone to remove high specific gravity contaminants such as glass and / or metal, and then fed into the second tank and pumped into the second hydrocyclone to remove contaminants lower specific gravity, such as, for example, paper and / or polyolefins.

One or two methods of vibrating screening can also be used at various points in the entire process, for example, for separating contaminating materials removed from the top of the tank with the process water for sinking / flooding type separation, for removing contaminants in the form of powder after the heat-curing operation and after the washing operation with a shearing force in the preparation stage and / or in the final stage, or after the final washing and drying operation in the final stage.

In one embodiment, heavy contaminants can be removed from the mixture at any suitable point in the process by using a lock operation. For example, immediately before or after water separation operations in the preparation stage or immediately before or after any water separation operations in the final stage, it may be useful in some embodiments of the process to include a lock operation to remove some heavy contaminants from the mixture.

The processing method of the disclosed invention can provide a number of important advantages. For example, it can clean and / or remove impurities from polyester. Indeed, the polyester can be purified and / or impurities can be removed from it to a degree that is sufficient to meet the various established requirements and, in particular, a polyester food-grade product can be obtained. Of course, it should be recognized that a given level of cleaning or removal of impurities may depend on the intended use of the polyester. In particular, the method can provide

- 15 013407 recycled polyester product having improved properties, for example, high purity, good color and even improved intrinsic viscosity. Moreover, the disclosed method can provide these products with a suitable yield and at a lower cost of preparation, since, for example, it does not require the "re-polymerization" of monomers as opposed to typical depolymerization processes.

These and other modifications and changes of the present invention may be made by those of ordinary skill in the art without departing from the spirit and scope of the present invention, which is more specifically described in the appended claims. In addition, it should be understood that aspects of different incarnations can be interchanged both in general and in particular. Moreover, the average experts in this field will appreciate that the preceding description is only an example and is not intended to limit the invention, further described in the claims.

Claims (19)

CLAIM 1. A method for separating contaminants from a polyester, comprising providing a blend comprising contaminants and polyester; removal of a part of the impurities from the mixture during the elutriation operation, in which heavier impurities than polyester are removed from the mixture during the elutriation operation; combining the mixture with an alkaline composition in a stoichiometric amount sufficient for the reaction to take up to about 50% polyester; and saponification of only part of the polyester in accordance with the saponification reaction between the alkaline composition and the polyester. 2. The method according to claim 1, in which the alkaline composition is an aqueous composition, wherein the mixture is combined with the alkaline composition to form a suspension. 3. The method according to claim 2, also comprising mixing the suspension in a high-energy mixer, in which said mixing gives enough energy to said suspension to activate the saponification reaction between the polyester and the alkaline composition, and in which saponification occurs in the high-energy mixer in accordance with the saponification reaction, in which any heat added to the suspension in a high-energy mixer is insufficient for independently activating the saponification reaction of the polyester with an alkaline composition. 4. The method according to claim 1, also comprising heating the mixture to a temperature that is not higher than the melting point of the polyester in the heat-curing operation, in which the mixture is heated in an environment that includes a water content of less than about 80 ppm. 5. A method of separating impurities from a polyester, including providing a blend including impurities and polyester, the contaminants containing colored polyester; conducting with the mixture of the operation of sorting by color, and at least part of the impurities of the dyed polyester is removed from the mixture during the operation of sorting by color; compounding the mixture with an alkaline composition in a stoichiometric amount sufficient for the reaction to take up to about 50% polyester, the mixture and the alkaline composition being combined after the sorting operation by color; and saponification of only part of the polyester in accordance with the saponification reaction between the alkaline composition and the polyester. 6. The method according to claim 5, in which the alkaline composition is an aqueous composition, wherein the mixture is combined with the alkaline composition to form a suspension. 7. The method according to claim 6, also comprising mixing the suspension in a high-energy mixer, in which said mixing gives enough energy to said suspension to activate the saponification reaction between the polyester and the alkaline composition, and in which saponification occurs in the high-energy mixer in accordance with the saponification reaction, however, any heat added to the suspension in a high-energy mixer is not sufficient to independently activate the polyamide saponification reaction with an alkaline composition. 8. The method according to claim 5, also comprising heating the mixture to a temperature that is not higher than the melting temperature of the polyester in the heat-curing operation, in which the mixture is heated in an environment containing less than about 80 ppm of water. 9. The method according to claim 5, also comprising conducting with the mixture a second screening operation according to color after the saponification reaction. 10. A method of separating impurities from a polyester, comprising providing a mixture comprising impurities and polyester, in which impurities include aluminum; compound mixture with an alkaline composition in a stoichiometric amount sufficient for the reaction to take up to about 50% polyester, and the mixture and the alkaline composition are combined in - 16 013407 low-energy mixer for the formation of suspensions; conducting the reaction of the alkaline composition with at least a portion of the aluminum while the mixture is in a low-energy mixer; mixing the suspension in a high-energy mixer, in which the specified high-energy mixing provides enough energy to the specified suspension to activate the saponification reaction between the polyester and the alkaline composition; and saponification of only part of the polyester in the high-energy mixer in accordance with the saponification reaction, in which any heat added to the suspension in the high-energy mixer is insufficient for independently activating the polyamide saponification reaction with an alkaline composition. 11. The method according to claim 10, also comprising heating the mixture to a temperature that is not higher than the melting temperature of the polyester in the heat-curing operation, in which the mixture is heated in an environment containing less than about 80 ppm of water. 12. The method of claim 10, also comprising washing the suspension after reacting at least a portion of the aluminum and adding an additional alkaline composition to the suspension before the saponification reaction in a high-energy mixer. 13. A method of separating impurities from a polyester, comprising providing a mixture comprising impurities and polyester in which the impurities include a metal; removing at least part of the metal contamination from the mixture in the operation of detecting and removing at least one metal, where the operation of detecting and removing at least one metal includes at least one battery of metal detectors, each battery including two or more metal detectors connected sequentially, in parallel or in combination; combining the mixture with an alkaline composition in a stoichiometric amount sufficient for the reaction to take up to about 50% polyester; and saponification of only part of the polyester in accordance with the saponification reaction between the alkaline composition and the polyester. 14. The method according to claim 13, wherein the alkaline composition is an aqueous composition, wherein the mixture is combined with the alkaline composition to form a suspension. 15. The method of claim 14, also comprising mixing the suspension in a high-energy mixer, wherein said mixing reports additional energy to said suspension to activate the saponification reaction between the polyester and the alkaline composition, and saponification occurs in the high-energy mixer according to the saponification reaction, in which any heat added to the suspension is insufficient to independently activate the saponification reaction of the polyester with an alkaline composition. 16. The method according to claim 13, also comprising heating the mixture to a temperature that is not greater than the melting point of the polyester. 17. The method of claim 13, wherein the operation of detecting and removing at least one metal comprises forming a suitable stream and a reject stream for each metal detector, the method also comprising recycling at least one reject stream through the metal detection and removal operation. 18. The method according to item 13, in which at least one battery of metal detectors includes at least two metal detectors connected in series, where successively connected metal detectors show increased sensitivity to the metal as it moves from one detector to another. 19. The method according to claim 5, wherein the impurities of the dyed polyester include components colored with titanium dioxide. - 17 013407