HRP20031060A2 - Process for separating polyester from other materials - Google Patents

Description

References related to the application

Claims filed with this application have priority over provisionally filed U.S. by patent application Serial No. 60/299273 dated June 19, 2001 entitled "Procedure for separating polyester from other materials"

Background of the invention

Polyesters are polymer materials made by esterification of polybasic organic acids with polyhydric acids. The most commonly produced and used polyester is believed to be polyethylene terephthalate (PET), which can be produced by reacting teraphthalic acid with ethylene glycol.

Today, the use of polyester is increasing in various applications. For example, polyesters are commonly used to make all types of beverage and food packaging, photographic films, X-ray films, magnetic tapes, electrical insulations, surgical aids such as synthetic arteries, fabrics and other textile products, and numerous other products. Because polyesters can be remelted and reformed, much effort has gone into recycling many polyesters after use. Previously, polyesters could be recycled, however, they had to be separated after use from other products and materials that could be found mixed or associated with polyester. Unfortunately, many problems can be encountered when trying to separate polyester from other waste material. In particular, many of the prior art processes are unable to effectively and economically recover polyester when a significant amount of contaminants are present. Many of the previously known procedures for separating polyester from other materials are limited to flotation separation and mechanical recovery procedures.

Using the flotation separation technique, polyesters are separated from other materials based on the difference in density. For example, materials containing polyester can be combined with water, in which polyester is known to sink. The less dense material, which floats in the water, can thus easily be separated from the submerged polyester. This procedure is relatively simple and very effective for separating polyester from pollution of a specific lower density. The flotation separation technique, however, cannot be used if the polyester is combined with materials that sink in water or have a density similar to that of the polyester.

For example, the polyester used is usually mixed with polyvinyl chloride (PVC) and aluminum, which do not float in water. In fact, PVC has a density very similar to that of PET and is often misidentified as PET. Both aluminum and PVC must be separated from polyester before reuse. In particular, if PET and PVC are melted together again, hydrochloric acid gases are evolved which destroy the properties of the resulting plastic material.

In the past, to separate PET from PVC using the flotation separation technique in specific gravity baths, other attempts to modify the surface of the PVC so that the PVC will float in an aerated aqueous medium. For example, in US Patent no. 5,234,110 Kobler and USA Patent no. No. 5,120,768 to Sisson shows various processes for separating the PET from the PVC layer. In these processes, the surface of the PVC layer is treated so that the surface of the PVC is more similar in adhesion to air bubbles when placed in an aqueous medium. That is why these procedures are effective, however, the PVC layer must have a large air surface in volume ratio. Consequently, the above procedures are deficient in separating PVC parts from PET when the PVC has a large internal volume.

In addition to the disadvantage of separating polyester from contaminants heavier than water, the flotation separation technique is also deficient for separating coatings that normally adhere to polyester. For example, polyester packaging is usually coated with an anti-evaporation coating, carp coating and/or printing ink.

The mechanical recovery process used here is a washing process using specific tapes and adhered layers of polyester thin layers without substantial reaction occurring between the polyester and the washing solution. For example, US Patent no. 5,286,463 and 5,366,998 both to Schwartz, Jr., both incorporated herein by reference, disclose the composition and process of removing adhesive tapes, particularly polyvinylidene halides and polyvinyl halide-based resins, from polyester thin films such as photographic film. In one embodiment, polyester films are mixed with a reducing sugar and a base to remove adhered polymer resins from the film. Acid is then added to precipitate the resin, which can then be separated from the polyester thin layer.

USA Patent no. 4,602,046 to Buser et al. shows a process for recovering polyester from scrap material such as photographic film having a polyester base and at least one layer of a macromolecular organic polymer.

Specifically, the scraped material is cut or cut into small individual pieces or layers and treated in a caustic alkaline solution so that a solid layer of at least 25% by volume and under vigorous stirring conditions. The organic polymer of the coating material is removed from the polyester layer. The polyester layer is then separated from the polymeric coating material by filtration or centrifugation, rinsing in water, and drying. The recovered polyester layer can be used as a raw material for making films, bottles or other polyester articles. The process and apparatus for recovering silver and plastic from used films are also shown in US Patent no. 4,392,889 from Grout. In this process, the used film is first passed through a bath preferably containing a hot caustic solution to precipitate the silver layer on the film. Then the film passes through a second hot caustic bath until the adhesive layer present on the film melts. Usually, the adhesive layer is made of polyvinylidene chloride, which holds the silver on the film. After the second caustic bath, the film dries and can be used.

Other methods for recovering polyester from photographic film are in US Pat. No. 3,928,253 to Thorton et al., US Patent No. 3,652,466 to Hittel et al., US Patent no. 3,647,422 to Wainer, and US Patent no. 3,873,314 to Wool et al.

As shown above, mechanical restoration processes are essentially limited to use with photographic film. In the recycling of photographic films, the silver is also recovered and makes the process economically valuable.

Mechanical recovery processes, which are very good for removing emulsion-type coatings found on photographic films, are generally not satisfactory for removing other types of polyester coatings. For example, many of these processes are not acceptable for effective removal of some anti-evaporation coatings and printing inks applied to polyesters.

Other contaminants generally cannot be removed from polyester using flotation separation techniques and mechanical recovery processes as described above if organic and inorganic compounds have entered. These contaminants include, for example, gasoline, kerosene, motor oil, toluene, pesticides, and other compounds that are absorbed onto polyesters when they come into contact with them. If these introduced organic and inorganic compounds are not actually removed from the polyester material during recycling, the recycled polyesters cannot be used as food or beverage packaging.

Due to the aforementioned disadvantages of the prior art processes, a large amount of recyclable polyester is discarded and abandoned in the fields or burned. Unfortunately, not only is polyester not reused, but polyester materials open up the problem of waste management and disposal.

Today, the focus of polyester recovery from waste leads to changes from the mechanical washing process to the chemical conversion of polyester into usable chemical components. For example, and US Patent no. 5,958,987, 6,147,129, and 6,197,838, all to Schwartz, Jr., which are incorporated herein by reference, a process for recycling polyesters wherein the proportion of polyesters reduced to their original chemical reactants is shown. The processes include the steps of combining the polyester materials with the alkaline composition to form the mixture. The mixture is heated to a temperature sufficient to convert the polyester surface into an alkaline salt of polybasic acid and polyol.

The patents described above represent a major advance in the art. The process of the presented invention is aimed at improving the polyester recycling process.

Summary of the invention

In general, the process of the presented invention is focused on the process of separating the polyester substrate from various contaminants and pollution. For example, the process of the present invention can be used to release various contaminants from the polyester substrate to which the contaminants are attached, i.e., both adhered and released contaminants.

Additionally, the process of the presented invention can enable the separation of polyester from other contaminants that may be mixed with polyester in a lot of waste; aluminum and polyvinyl chloride, for example.

The process of the present invention generally involves mixing polyester-containing materials with an acrylic mixture in the form of a thick mixture. The thick mixture can then be mixed in a powerful mixer that can not only really and evenly coat the materials with the alkaline mixture, but also provide enough energy to promote a reaction between the material and the alkaline mixture that can allow the polyester to be separated from various contaminants and contaminants. For example, a thick mixture can be mixed in a powerful shredder. In one embodiment, the mixer may be operated at a Froude number greater than about 4.2 to promote the reaction. Specifically, the mixer can operate at a Froude number greater than about 6.6. In one embodiment, the mixer may operate at a Froude number greater than about 9.5.

In general, the alkaline mixture can be a metal hydroxide solution. For example, the metal hydroxide may be sodium hydroxide, calcium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, or a mixture thereof. In one embodiment, the alkaline mixture can be only sodium hydroxide and water. For example, the alkaline mixture can be sodium hydroxide and water in a ratio of 1:1.

The alkaline mixture can be combined with the polyester materials in an amount so as to saponify the polyester as little as possible and further promote the separation of the polyester from all contaminants and impurities. For example, the alkaline mixture can be combined with the polyester material in an amount of less than 101 by weight of the polyester material. More specifically, the alkaline mixture can be combined with the polyester material in a stoichiometric amount sufficient to react with less than about 20% polyester. More precisely, the alkaline mixture can be combined with the polyester material in a stoichiometric amount sufficient to react with about 10% polyester.

The development of the reaction can significantly extract the metal hydroxide in the mixer. For example, the metal hydroxide remaining in the slurry after mixing and reaction may generally be less than about 1% by weight of the slurry. More specifically, the remaining metal hydroxide in the slurry after mixing and development of the reaction may generally be less than about 0.05% by weight of the slurry. More specifically, the remaining metal hydroxide in the slurry after mixing and reaction may generally be less than about 0.1% by weight of the slurry.

Optionally, the thick mixture can be heated after the reaction in the mixer and really finished. For example, the slurry can be heated to a first temperature, all, for example, a temperature between about 120°C and about 170°C, dry the slurry to produce a dry product, and then heat to a second temperature, all, for example a temperature between around 200°C and around 240°C, which can further degrade contaminants and make separation from the polyester substrate easier.

In one embodiment, the polyester-containing materials may include contaminants that are bound to the polyester substrate, any contaminants that have entered the polyester, or contaminants that adhere to the surface of the polyester. In this embodiment, the alkaline mixture can react with the materials during mixing and cause saponification of the polyester portion which can release contaminants from the surface of the polyester substrate.

Alternatively, the polyester-containing materials may include impurities or contaminants that are mixed with the polyester, not necessarily firmly attached to the polyester, such as polyvinyl chloride or aluminum materials, for example. In this embodiment, the alkaline mixture can react with the contaminant and then cause it to change to a form that is much easier to separate from the polyester. For example, polyvinyl chloride can be dechlorinated with an alkaline solution to a form that can be easily separated from the polyester substrate.

Detailed description of preferred achievements

The presented invention is generally aimed at the regeneration and separation of polyester from various contaminants and pollution. For example, during the process of the present invention, various contaminants can be released from the polyester substrate by all coating agents including vapor barriers, inks, and carp coatings as well as other contaminants that have entered the outer surface of the polyester substrate, such as various volatile organic and inorganic contaminants. During the process, the polyester can be partly saponified, but the larger part remains in the form of a polymer, and the contaminants can be physically released from the polyester substrate.

The process is also aimed at separating and regenerating polyester when it is mixed with other types of contaminants such as polyvinyl chloride and aluminum, for example. During the process, contaminants can be converted into a form that is much easier to separate from the polyester substrate.

Here, polyester is used in the sense that it is defined by esterification or is the product of the reaction between a polybasic organic acid and a polyol. It is believed that all known polyesters or copolyesters can be used in the process of the present invention. The process of the present invention is particularly directed to the class of polyesters referred to herein as polyterephthalates, in which terephthalic acid can serve as a polybasic organic acid.

The term polybasic organic acid is used here for all organic acids that have two or more carboxyl groups (-COOH). Most polyesters are derived from dibasic acids or, in other words, from dicarboxylic acids. Polybasic acids can have a linear or cyclic conformation. Examples of linear polybasic acids that can be used to make polyesters include aliphatic dicarboxylic acids. The fine aliphatic dicarboxylic acids used have up to ten carbon atoms in their chain. These acids include adipic acid, glutaric acid, succinic acid, malonic acid, oxalic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, maleic acid and fumaric acid.

Cyclic polybasic organic acids, on the one hand, include carbocyclic dicarboxylic acids. These acids are known as phthalic acid, isophthalic acid, and terephthalic acid. Specifically, terephthalic acid is used to make polyethylene terephthalate, which of course is the most commonly commercially available polyester.

As described above, a polybasic organic acid is combined with a polyol to produce a polyester. Polyols are compounds that contain at least two hydroxyl groups. Many polyesters are synthesized using polyols such that they contain two hydroxy groups, referred to as diols. Diols are commonly produced from alkenes with the net addition of two hydroxy groups to the carbon double bond by a method known as hydroxylation. Polyols are commonly referred to as glycols and polyhydric alcohols. Examples of polyols used to make polyesters include ethylene glycol, propylene glycol, butylene glycol, and cyclohexane dimethanol.

By way of example, the following table contains a non-exhaustive list of commercially available polyesters that can be regenerated and recycled in accordance with the present invention. For each polyester, the corresponding polybasic organic acid and polyol are provided.

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In general, the process of the present invention involves first combining polyester-containing materials with a certain amount of alkaline solution in the form of a thick mixture in a mixer. The selected mixer is one that not only provides a substantially replenished likewise coated polyester material with an alkaline solution, but can also provide excess energy for the saponification of the polyester portion, or in other words, for hydrolysis. During saponification, various coating agents may adhere to the polyester and/or other contaminants that may be loaded onto the surface of the polyester and may be released from the polyester. The energy provided by the mixer can also promote a reaction between the alkaline solution and other contaminants that can be mixed with the polyester in a thick mixture, such as polyvinyl chloride or aluminum, for example, so that the contaminants can be converted into another form, which can be more easily separated from the polyester substrate. After the reaction inside the mixer, the thick mixture can then be heated, usually in a two-stage heating process.

The process of the presented invention can run continuously or can be arranged to be a batch system. Virtually any polyester-containing material can be treated with the present invention including, but not limited to, for example, beverage and food packaging, photographic and X-ray films, reproduction tapes, insulating material, textile fibers and other products. Polyester materials that are regenerated from solid waste are preferred, thus reducing numerous environmental and disposal problems. The presented invention is particularly focused on the recycling of food and beverage packaging made of PET. During the process of the present invention, polyesters can be separated, regenerated and reused after they have been discarded, even when we find polyesters mixed with polyvinyl chloride or aluminum, held on different layers, or entered into different organic and inorganic compounds. Such materials are usually landfilled in fields or incinerated after use due to the lack of an economical process that will recover the polyester.

Prior to bonding with the alkaline mixture, polyester-containing materials may, if required, be cut or ground to size. To enable handling for the purpose of treatment, the amount of material is determined. Generally speaking, the larger the amount of material and the smaller the surface to volume ratio, the less saponification of the polyester that will occur later in the process. Consequently, smaller dimensions should be avoided and the size of the material should be left as large as necessary. However, it should be understood that all different sizes and shapes of materials can be used in the process of the present invention and no single size or shape is required.

Before being joined with an alkaline mixture, the polyester-containing materials can be immersed in water or another liquid in such a way as to separate the less dense or lighter materials from the heavier polyester-containing materials. More specifically, polyester is known to sink in water while paper products and other polymers, such as polyolefins, float in water. Thus, lighter materials can be easily separated from heavier materials when in contact with the liquid. The mentioned materials are subjected to the separation of sinking/floating in the first stage, and in connection with the alkaline mixture, not only to reduce the amount of material, but also to clean the surface of the material before the further process.

After being sorted by size and subjected to sinking/flotation separation, if required, the polyester-containing materials can be combined and mixed with an alkaline mixture to form a slurry, or mixture. Pre-freezing, the alkaline solution can be combined with materials that coat the surface of the material. In some applications, the surface of the material may resist uniform coating due to interaction with surface tension. In this case, the alkaline solution tends to "bead up" on the surface of the material. The process of the present invention, however, as described below, can overcome this problem.

In accordance with the present invention, it has been discovered that the improvement of the mixing process can be used when not only the coating of the polyester materials with the alkaline solution is complete and uniform, but in addition it can provide enough mixing energy for the saponification process outside the surface of the polyester to take place inside the mixer. For example, a mixer as described in US Patent Nos. 4,320,979 to Lučka and 4,189,242 to Lučka is incorporated herein in its entirety by reference, in addition, it can be used to coat polyester materials and saponify the smallest portion of polyester with an alkaline solution. The alkaline mixture selected for mixing with the materials is preferably sodium hydroxide, which is known as caustic soda. . Other metal hydroxides and alkalis can also be used. Such compounds include calcium hydroxide, magnesium hydroxide, potassium hydroxide, lithium hydroxide or mixtures thereof. If required, alkaline compounds can be added to polyester materials in solution. For example, and in one embodiment, a metal hydroxide, such as sodium hydroxide, can be mixed with water in a ratio of about 1:1 to form an alkaline mixture.

The amount of alkaline mixture added to materials containing polyester will depend on the type and amount of soiling and contaminants present in the material. In general, the alkaline mixture should be added only in an amount sufficient to separate the contamination from the polyester, so that saponification of the polyester is minimized. In most applications, the alkaline mixture is added to the materials in a stoichiometric amount sufficient to react with about 50% of the polyester. For example, the alkaline mixture may be added in an amount sufficient to react with less than about 20% of the polyester.

In particular, the alkaline mixture can be added in an amount sufficient to react with about less than 15% polyester.

More specifically, the alkaline mixture can also be added to an amount to react with less than about 10% polyester.

One of the advantages of the presented invention is the ability of the mixer to coat the polyester material without wetting agents. In the past, a surfactant or wetting agent was often used to facilitate mixing of the alkaline mixture with the polyester materials. Due to the provision of mixing in the present invention, the use of a wetting agent is no longer necessary.

In one embodiment of the presented invention, a reactor in the form of a mixer can be used. In one particular embodiment, a shredding mixer can be used. For example, a comminution mixer such as that available from the Lödige Company, the Littleford Day Company, or other known companies may be used. In one particular embodiment, a mixer such as the Littleford Day KM-4200 mixer can be used. This particular mixer is available from Littleford Day Company of Florence, Kentucky. Apart from that, the shredding mixer, however, should be seen as different or powerful mixers that can be used. It should also be noted that this process can take place as a continuous process or as a batch process. An amount of the basic or chopped polyester material can be added to the mixer after any required pretreatment process has been performed, such as, for example, the flotation separation process as previously discussed. The alkaline mixture can then be added to the mixer with the polyester material. For example, an alkaline solution of 50% NaOH and 50% water can be added to the mixer in an amount of about 20% by weight of the polyester-containing material, and preferably in an amount of less than about 10% by weight of the polyester-containing material.

The mixer can be operated to provide sufficient energy to mix substantially equal coated polyester materials with the alkaline mixture and promote saponification of the outer surface of the polyester material by drawing most of the alkaline reactant into the mixer. In general, mixers normally operate at the presented rotation speed, specifically in a certain case and adapted to a certain process. Therefore, to maintain equivalent energy input when different mixers are used, dimensionless Fr (Froude number) values are introduced, instead of rotation speed. Fr is a dimensionless number that describes the ratio of inertial force to gravitational force. The Froude number can be described by the following formula:

Fr= V2/(gL)

where Fr is the Froude number, V is the velocity, g is the gravitational acceleration, and L is the characteristic length.

In one embodiment of the presented invention, the mixer can operate at a Froude number greater than about 4.2, especially greater than 6.6, and especially greater than about 9.5. Certain, above-mentioned values, for the mixer of the presented invention not only mixes the thick mixture but also provides enough energy for the thick mixture to carry out the reaction of the alkaline mixture with the polyester. In fact, stirring can be continued until all of the alkaline mixture has been extracted. For example, the mixer may be operated such that the residual (unreacted) metal hydroxide present exiting the mixer may be less than about 1% by weight of the slurry. Certain residual metal hydroxide exiting the mixer may be less than about 0.5% by mass. More specifically, the remaining metal hydroxide may be less than about 0.1% by weight of the slurry.

In the past, the saponification reaction occurred after heating the mixture in a heater or in a dryer. Heating prior to the reaction, however, may cause some of the alkaline solution to evaporate and thus additional alkaline compounds may be required to ensure an adequate level of reaction. Additionally, the alkaline compound may become anhydrous during the heating process. Thus, very dry reaction conditions with little oxygen are preferred. The present invention avoids these problems by adding a limiting amount of caustic to the heater and/or dryer.

The next advantage of the presented invention is the increase in the efficiency of the reaction process. For example, in one embodiment of the present invention, 10% by weight of 50% hydroxide, water solution can be added to the mixer with the appropriately prepared PET material. After sufficient mixing at a Froude number of approximately 6.6, about 13% of the PET can react with the caustic in the mixer. The use of the mixer of the present invention can not only substantially extract the alkaline mixture within the mixer, but also require a smaller amount of the alkaline mixture for the process due to the complete coating of the material during mixing. A lower amount of alkaline mixture required for the process can mean not only less alkaline compound required in the process, but also less water required in the process.

The saponification reaction can convert the polyester into a polyol and acid salt. For example, when polyethylene terephthalate is reacted with sodium hydroxide, the polyester involved in the reaction can be converted to ethylene glycol and sodium terephthalate. It is believed that due to complete mixing such as complete coating of the alkaline materials in the polyester materials in the mixer, the salts formed may form a layer on the polyester materials exiting the mixer. For example, in one achievement where the outer surface of PET is saponified in a mixer with a sodium hydroxide solution, it is believed that the reaction product with sodium terephthalate can coat the remaining PET. Unexpectedly, it was found that such a layer formed around the polyester parts can serve as a protection for the polyester during subsequent processes. For example, coated salt can protect polyester from oxidation due to high temperature conditions in later processes. Due to other advantages, it can be ensured that a polyester product is obtained with less discoloration than in the past.

After leaving the mixer, the thick mixture can be heated. When heated, the thick mixture is preferably heated so that it is not in contact with an open flame. Heating the mixture can dry the polyester and remaining contaminants and can cause loss, degrade the dried contaminants into a form that is more easily separated to facilitate the final separation of the contaminants from the polyester product.

The actual temperature at which the thick mixture can be heated can depend on a number of factors. In general, heating may comprise more than one heating phase. The preferred heating sequence in this case involves heating to a temperature of 120-170°C to dry the polyester, followed by heating, after drying, to a temperature of 200-240°C in an environment that is essentially free of water.

Accessories and apparatus used during the process of the present invention may vary. Until then, good results will be obtained when the saponified thick mixture is heated in a rotary dryer. To ensure two phases of the heating process, the dryer can first be heated to a lower temperature for the desired period and then the temperature can be raised to a higher level. Alternatively, the thick mixture exiting the mixer can first be heated in a dryer, such as a ConAir dryer, before being transferred to a higher temperature dryer. The rotary dryer can be heated with an electric element, heating oil or with a fossil fuel heater. An example of a suitable indirect heating dryer used in the process of the present invention is a Rotary Calciner manufactured by the Rennebrug Division of Heyl&Patterson, Inc. It is believed, however, that a thermal processor with a multidisk or an oven that will function equally well. Of course, many equivalent devices are available that can be used in the process of the present invention.

Although not required, the thick mixture can be heated in an oxygen-reduced environment. As used herein, oxygen depletion refers to an environment where oxygen is present below 19% by volume. Keeping the oxygen level low during the heating phase prevents polyester degradation and protects it from uncontrolled combustion. In one embodiment, the mixture can be heated in an inert atmosphere, such as in the presence of a layer of nitrogen. If required, the mixture can be heated under reduced pressure, which corresponds to a lower oxygen level.

As described above, the process of the present invention is specifically directed to the separation of polyester from polyvinyl chloride, aluminum, coatings adhering to the polyester, and inorganic and organic compounds that have entered. The particular stage involved in the separation of each of the above contaminants in accordance with the process of the present invention will now be discussed.

When polyvinyl chloride is present in the materials, during the process of the present invention the polyvinyl chloride can be converted into a water-floating and heat-resistant form. It is believed that when polyvinyl chloride is mixed with an alkaline mixture and energy is added to the mixer, the alkaline mixture can cause polyvinyl chloride to dechlorinate, resulting in dark colored materials that float in water and have a higher melting point than chlorinated PVC. Consequently, when polyvinyl chloride is present in the materials, an alkaline mixture can be added in excess to further dechlorinate the polyvinyl chloride or, in other words, to convert the polyvinyl chloride into a form that can be separated from the polyester. However, even if not all of the PVC has been combined with the alkaline mixture and chlorinated during the process of the present invention, when the mixture is heated to the above temperatures, PVC that is not dechlorinated comes out of the mixer and can be separated and easily separated from the polyester.

In one embodiment, after the materials containing polyvinyl chloride and polyester are mixed with an alkaline mixture and heated, in order to separate the now dechlorinated polyvinyl chloride from the polyester, the materials can be washed with water.

Dechlorinated polyvinyl chloride can float and can easily separate from the submerged polyester. Likewise, it was found that treated polyvinyl chloride with an alkaline mixture in the manner described above causes the entry of air and bubbles of other gases that tend to adhere to the surface of polyvinyl chloride, which make the polyvinyl chloride float more. Consequently, when polyvinyl chloride is separated from polyester in a liquid, gas bubbles, such as air, can be added to the liquid to enhance the efficiency of the separation. Of course, other separation techniques based on density differences between polyester and dechlorinated polyvinyl chloride can also be incorporated into the process.

In addition to reducing the density, the process of the presented invention also leads to a darkening of the polyvinyl chloride color and an increase in the melting point. Consequently, in another embodiment, the dechlorinated polyvinyl chloride can be separated from the polyester by visual inspection. Furthermore, in another embodiment, the mixture containing polyester and dechlorinated polyvinyl chloride can be heated to melt the polyester. The heated mixture can then be put into the extruder. Since dechlorinated polyvinyl chloride has a much higher melting point than polyester, dechlorinated polyvinyl chloride can be screened off before entering the extruder. In this embodiment, the polyvinyl chloride should be fully dechlorinated to prevent any chlorine that will be released when the polyester is heated.

In addition, polyvinyl chloride, polyester collected from solid waste is also commonly mixed with pieces of aluminum. Aluminum can come, for example, from bottle caps attached to polyester packaging or from incomplete separation of plastic and aluminum cans found in the waste. Aluminum, like polyvinyl chloride, cannot be easily separated from polyester using the tonjen e/plutan e separation technique.

When it comes into contact with an alkaline mixture and energy is provided, such as in the mixer of the present invention, the aluminum can be converted into an alkali aluminum salt, which is usually water soluble. Thus, in one embodiment, an amount of alkaline mixture can be added to a material containing polyester and aluminum in a sufficient amount to completely convert the aluminum into an aluminum salt. A liquid, such as water, can then be added to the mixture to dissolve the aluminum salt and separate it from the polyester.

In accordance with the presented invention, however, it was determined that due to the separation of aluminum from polyester, it is not necessary for the complete conversion of aluminum into an aluminum salt. Instead, it was found that some of the aluminum reacting with the alkaline mixture could cause all the aluminum pieces to become brittle. After adding energy, the polyester and aluminum containing materials can be washed with a liquid such as water, preferably under pressure, which causes the aluminum to break into small pieces. Small pieces can be separated from the polyester by passing the water mixture through a coarse sieve that has openings large enough to collect the larger pieces of polyester while allowing the smaller pieces of aluminum to pass through.

Consequently, when aluminum is present in polyester-containing materials, an alkaline mixture should be added to the materials in an amount sufficient to react with at least a portion of the aluminum, in an amount sufficient to make the aluminum brittle. Of course, the amount will depend on the amount and size of the piece of aluminum present in the materials.

In addition, the separation of aluminum and PVC from polyester, by the process of the presented invention, which is also capable of removing various coatings that adhere to the polyester. In particular, the process of the presented invention is capable of removing coatings that are barriers to evaporation. Evaporation barrier coatings are commonly used on beverage packaging to prevent the carbon dioxide contained in the carbonated beverage from escaping and/or to prevent oxygen from entering when the liquid it contains can spoil in the presence of oxygen. Evaporation barrier coatings can be made of saran, polyvinylidene chloride, or acrylic. A printed label, on the other hand, generally refers to a printing ink that is directly applied to polyester packaging, such as beverage packaging. For example, on most packaging for soft drinks, there is usually a label printed with color on the basis of epoxy resin. In the past, many problems were encountered in trying to separate polyester from these coatings and printing inks.

Therefore, removing the above-described coatings from polyester materials in accordance with the presented invention, the polyester is combined with an alkaline mixture in an amount sufficient for saponification outside the surface of the polyester and sufficient mixing to stimulate the saponification reaction. Any coating adhering to the polyester is removed when the outer surface of the polyester is saponified. Once separated from the polyester, the coating degrades further as the material is heated. Specifically, the solvents and liquids containing the coatings then become volatile and leave relatively little contamination. When the materials are later washed with water, the remaining insoluble contaminants can be separated from the larger pieces of polyester by using sieves of appropriate sizes to pass the contaminants through and prevent the passage of polyester.

In addition to various coatings, the process of the presented invention is also effective for removing organic and inorganic compounds that can be absorbed from polyester materials. These compounds may include, for example, toluene, gasoline, used motor oils, paint smears, pesticide residues, and other volatile compounds. Compounds can be absorbed onto polyester when in contact with it. For example, consumers often abuse polyester packaging for defense and beverages after consumption. Specifically, packaging is sometimes used for various organic and inorganic compounds and solvents. When trying to recycle these polyesters, it is necessary to remove virtually all absorbed organic and inorganic compounds so that the polyester can be reused as food and beverage packaging.

According to the invention, the organic and inorganic compounds that can be absorbed onto the polyester are released from the polymer during the saponification process. More precisely, all volatile organic and inorganic compounds are actually removed during the heating phase in the dryer. Less volatile compounds and compounds that slowly diffuse from the polyester, on the one hand, are removed by first saponification from the outer edge of the polyester in the mixer and then any remaining organic or inorganic compounds are evaporated in the appropriate heating phase. By removing all incoming organic and inorganic compounds, a "food grade" polyester is obtained, which can be used indefinitely.

In accordance with the presented invention, organic and inorganic compounds that have entered can be absorbed into the polyester and can be released from the polymer during the saponification process. In particular, volatile organic and inorganic compounds are significantly removed during the heating phase, so in the dryer. A smaller amount of volatile compounds and compounds diffused from the polyester, on the other hand, were first removed by saponification from the outer surface of the polyester in the mixer and then by evaporation of any remaining organic and inorganic compounds in the later heating phase. By substantially removing all incoming organic and inorganic compounds, the "food grade" polyesters are restored when they can be used in an unlimited way.

Briefly, regardless of the contaminants present, the process of the present invention includes contact materials containing polyester with an alkaline mixture, mixing the alkaline mixture and polyester coating materials together with such materials which are substantially uniformly coated with the composition and partially saponified polyester, heated materials in a one- or two-step process at a temperature sufficient to chemically convert them into forms that are more easily separated, and then wash the heated materials with a liquid such as water. During washing, contaminants floating in the water can be separated from the polyester. In the same way, the water mixture can pass through the sieve in such a way as to separate smaller sized impurities from the polyester.

In addition to washing the heated material with water only, in another embodiment, the heated materials may be washed according to a conventional mechanical regeneration process as discussed above. For example, after heating, the polyester coating materials can be mixed with a hot aqueous solution containing a surfactant or a hot aqueous solution containing an alkaline mixture and washed. If required, the mixture can be heated with stirring during the washing phase. Washing the material can generally clean the polyester and can dissolve and can separate some of the contaminants.

During the process, part of the polyester that has been saponified is converted into a polyol and into an acid salt. For example, when PET is saponified with sodium hydroxide, PET is converted to ethylene glycol and disodium terephthalate. The polyol formed during the process remains as a liquid in the mixture or has evaporated if the above mixture is heated to the boiling point of the polyol.

The resulting acid salts or metal salts, such as disodium terephthalate, may dissolve in water when materials are washed in water. If required, the metal salts can be regenerated later from the wash water. For example, if the salt of the acid is terephthalate, the wash water is filtered to remove any undissolved dirt and contaminant. Next, the wash water can be acidified causing the terephthalic acid to precipitate. In order to acidify the solution, a mineral acid such as hydrochloric acid, phosphoric acid or sulfuric acid or an organic acid such as acetic acid, carbonic acid can be added to the solution. When the terephthalic acid precipitates, the terephthalic acid can be filtered, washed and dried, the residue is a relatively pure product.

These and other modifications and variations of the presented invention can be practiced by experts, without deviating from the spirit and purpose of the presented invention, which is shown in more detail in the patent claims.

In addition, it should be understood that aspects of the various embodiments may be modified in whole or in part. Further, those skilled in the art will appreciate that the above descriptions are exemplary only, and are not intended to limit the invention by the further descriptions in the claims.

Claims (44)

1. The process of releasing contaminants from the polyester substrate, characterized by the fact that it contains: combined materials containing contaminated polyester with an alkaline mixture to form a thick solution; and mixing said thick solution with a high powered mixer, wherein said mixer actually coats said materials with said alkaline mixture and provides sufficient energy to said materials to saponify the outer surface of said polyester and cause said contaminants to be released from said polyester into said thick mixture. 2. The method of claim 1, further comprising heating said thick mixture to a first temperature to produce a dry product comprising a polyester substrate mixed with dry contaminants, wherein said first temperature is below the melting point of the polyester substrate. 3. The method of claim 2, characterized in that said thick mixture is heated to a first temperature of between about 120°C and about 170°C. 4. The method from claim 2, characterized in that it further comprises heating the said dry product to a second temperature higher than the said first temperature, where the second temperature is below the melting point of the said polyester substrate. 5. The method of claim 4, characterized in that said second temperature is between about 200°C and about 240°C. 6. The method of claim 1, characterized in that it further comprises the separation of said polyester from said contaminants. 7. The method of claim 1, characterized in that said contaminants include contaminants that entered said polyester substrate. 8. The method of claim 1, characterized in that said contaminants include coatings applied to the surface of said polyester substrate. 9. The process of claim 1, wherein said alkaline mixture is a combination of said materials in a stoichiometric amount sufficient to react with less than about 20% polyester. 10. The method of claim 1, wherein said alkaline mixture is combined with said materials in a stoichiometric amount sufficient to react with at least about 10% of said polyester. 11. The method of claim 1, characterized in that said alkaline mixture is combined with said materials in an amount less than about 10% of the weight of said materials. 12. The method of claim 1, characterized in that said alkaline mixture comprises metal hydroxide. 13. The method of claim 12, characterized in that said metal hydroxide is selected from the group containing sodium hydroxide, calcium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, or a mixture thereof. 14. The method of claim 13, characterized in that said alkaline mixture contains mainly sodium hydroxide and water. 15. The method of claim 14, characterized in that said alkaline mixture contains sodium hydroxide and water in a ratio of 1:1. 16. The method of claim 12, characterized in that said metal hydroxide in said thick mixture after mixing is less than about 1% of said thick mixture. 17. The method of claim 12, characterized in that said remaining metal hydroxide in the thick mixture after said mixing is less than about 0.5% of the mass of said thick mixture. 18. The method of claim 1, characterized in that said mixer operates at a Froude number greater than about 4.2. 19. The method of claim 1, characterized in that said mixer operates at a Froude number greater than about 6.6. 20. The method of claim 1, characterized in that the powerful mixer is a shredding mixer. 21. A method for releasing contaminants from a polyester substrate characterized by comprising: combining materials containing contaminated polyester with an alkaline mixture in an amount of less than about 10% by weight of said materials to form a thick mixture, said alkaline mixture comprising at least one metal hydroxide in a stoichiometric amount sufficient to react with less than about 20% of the polyester; and mixing said thick mixture in a high-powered mixer, wherein said high-powered mixer substantially coats said materials with an alkaline mixture and provides sufficient energy to said materials to accelerate the saponification reaction between said metal hydroxide and said polyester, such that said contaminants are released from said polyester in said reaction , where the remaining metal hydroxide in the specified thick mixture following the specified reaction is less than about 0.5% of the mass of the specified thick mixture; heating the thick mixture to a first temperature to produce a dry product comprising a polyester substrate mixed with dry contaminants, where said first temperature is below the melting point of said polyester substrate; and heating the dry product to a second temperature higher than said first temperature, where said second temperature is below the melting point of said polyester substrate. 22. The method of claim 21, characterized in that said thick mixture is heated to a first temperature that is between about 120°C and about 170°C. 23. The method of claim 21, wherein said second temperature is between about 220°F and about 240°F. 24. The method of claim 21, characterized in that said contaminants include contaminants entered into said polyester substrate. 25. The method of claim 21, characterized in that said contaminants include coatings applied to the surface of said polyester substrate. 26. The method of claim 21, characterized in that said alkaline mixture contains mainly sodium hydroxide and water. 27. The method of claim 21, characterized in that said residual metal hydroxide in said thick mixture followed by said reaction is less than about 0.1% of the mass of the thick mixture. 28. The method of claim 21, characterized in that said mixer operates at a Froude number of about 6.6. 29. The method of claim 21, characterized in that said mixer operates at a Froude number greater than about 9.5. 30. The method of claim 21, characterized in that said powerful mixer is a shredding mixer. 31. A process for separating polyester from polyvinyl chloride characterized in that it includes: combining materials containing polyester and polyvinyl chloride with an alkaline mixture comprising at least a metal hydroxide to form a thick mixture; and mixing said thick mixture in a high-powered mixer, wherein said mixer essentially coats said materials with an alkaline mixture and provides sufficient energy to said materials to dechlorinate at least a portion of said polyvinyl chloride to convert the polyvinyl chloride into a form that can be separated from said polyester. 32. The method of claim 31, characterized in that said alkaline mixture is combined with said materials in an amount not less than 10% of the amount of said materials. 33. The method of claim 31, characterized in that said metal hydroxide is selected from the group containing sodium hydroxide, calcium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, or a mixture of the above. 34. The method of claim 31, characterized in that said alkaline mixture contains mainly sodium hydroxide and water. 35. The method from claim 31, characterized in that said mixer operates at a Froude number greater than 4.2. 36. The method of claim 31, characterized in that said mixer operates at a Froud number greater than about 6.6. 37. The method of claim 31, characterized in that said high-power mixer is a shredding mixer. 38. A process for separating polyester from aluminum, characterized in that it includes: joining materials containing polyester and aluminum with an alkaline mixture of at least one metal hydroxide in the form of a thick mixture; and mixing said thick mixture in a high-powered mixer, wherein said high-powered mixer actually coats said material with an alkaline mixture and feeds said material excess energy so that said materials react with at least a portion of said aluminum to convert said aluminum into a separable form of the specified polyester. 39. The method of claim 38, characterized in that said alkaline mixture is combined with said materials in an amount not less than about 10% of the mass of said materials. 40. The method of claim 38, characterized in that said metal hydroxide is selected from the group containing sodium hydroxide, calcium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, or a mixture thereof. 41. The method of claim 38, characterized in that said alkaline mixture contains mainly sodium hydroxide and water. 42. The method of claim 38, characterized in that said mixer operates at a Froude number greater than about 4.2. 43. The method of claim 38, characterized in that said mixer operates at a Froude number greater than about 6.6. 44. The method of claim 38, characterized in that said high-power mixer is a shredding mixer.