BR112019012857B1 - METHOD FOR THE PURIFICATION OF RECOVERED POLYPROPYLENE - Google Patents

Abstract

A method for purifying recovered polypropylene is provided. The method involves obtaining recovered polypropylene, contacting it with a first fluid solvent to produce an extracted recovered polypropylene, and then dissolving the extracted recovered polypropylene in a solvent to produce a first solution comprising polypropylene and suspended contaminants. The first solution is decanted to produce a second solution comprising polypropylene and remaining contaminants. The second solution is purified by contacting the second solution with solid medium to produce a third solution comprising purer polypropylene. Finally, the purest polypropylene is separated from the third solution.

Description

FIELD OF THE INVENTION

[0001] The present invention generally relates to a method for purifying contaminated polymers using a pressurized solvent and a solid medium. More specifically, this invention relates to a method for purifying recycled polymers, such as post-consumer and post-industrial recycled plastics, to produce a colorless or transparent, odor-free, virgin resin. This is particularly useful for purifying polypropylene.

BACKGROUND OF THE INVENTION

[0002] Polymers, especially synthetic plastics, are ubiquitous in daily life due to their relatively low production costs and good balance of material properties. Synthetic plastics are used in a wide variety of applications, such as packaging, automotive components, medical devices, and consumer products. To meet the high demands of these applications, tens of billions of pounds of synthetic plastics are produced around the world annually. The overwhelming majority of synthetic plastics are produced from increasingly scarce fossil sources, such as oil and natural gas. Additionally, manufacturing synthetic plastics from fossil sources produces CO2 as a by-product.

[0003] The constant use of synthetic plastics has consequently resulted in millions of tons of plastic waste being produced each year. Although most plastic waste is disposed of through municipal solid waste programs, a significant portion of plastic waste is found in the environment as litter, which is unsightly and potentially harmful to ecosystems. Plastic waste is often washed away in river systems and eventually ends up in the sea.

[0004] The recycling of plastics has emerged as a solution to mitigate the problems associated with the widespread use of plastic. The recovery and reuse of plastics diverts waste from landfills and reduces the demand for virgin plastics produced from fossil resources, which in turn reduces greenhouse gas emissions. In developed regions such as the United States and the European Union, plastics recycling rates are increasing due to increased awareness by consumers, commercial establishments, industrial and manufacturing operations. Most recycled materials, including plastics, are mixed into a single stream that is collected and processed at a material recovery facility (MRF). At MRF, materials are sorted, washed and packaged for resale. Plastics can be classified into single materials such as high density polyethylene (HDPE) or poly(ethylene terephthalate) (PET), or mixed streams of other common plastics such as polypropylene (PP), low density polyethylene (LDPE), poly(vinyl chloride) (PVC), polystyrene (PS), polycarbonate (PC), and polyamides (PA). The single or mixed streams can then be further sorted and reprocessed as a pellet which is suitable for reuse in plastics processing, for example by injection and blow molding.

[0005] Although recycled plastics are sorted into predominantly uniform streams and are washed with aqueous and/or caustic solutions, the final reprocessed pellet often remains highly contaminated by unwanted residual impurities such as spoiled food residue and perfume residual residue. In addition, recycled plastic pellets, other than those from recycled beverage containers, have a color stench due to the mixture of dyes and pigments commonly used to color plastic articles. While there are some applications that are insensitive to color and contamination (for example, black plastic paint containers and hidden automotive components), most applications require colorless pellets. The need for a high quality "virgin" recycled resin is especially important for food and drug contact applications such as food packaging. In addition to being contaminated by impurities and mixed dyes, many recycled resin products often have a heterogeneous chemical composition and can contain a significant amount of polymeric contamination, such as polyethylene (PE) contamination in recycled PP and vice versa.

[0006] Mechanical recycling, also known as secondary recycling, is the process of converting recycled plastic waste into a reusable form for subsequent manufacturing. A more detailed analysis of mechanical recycling and other plastics recovery processes is described in S.M. Al-Salem, P. Lettieri, J. Baeyens, "Recycling and recovery routes of plastic solid waste (PSW): A review", Waste Management , Volume 29, Number 10, October 2009, Pages 2625 to 2643, ISSN 0956-053X. While advances in mechanical recycling technology have improved the quality of recycled polymers to some degree, there are fundamental limitations of mechanical decontamination approaches, such as the physical entrapment of pigments in a polymeric matrix. As such, even with improvements in mechanical recycling technology, the dark color and high levels of chemical contamination in currently available recycled plastic waste impedes the wider use of recycled resins by the plastics industry.

[0007] To overcome the fundamental limitations of mechanical recycling, many methods have been developed to purify contaminated polymers through chemical approaches or chemical recycling. Most of these methods use solvents to decontaminate and purify the polymers. The use of solvents allows the extraction of impurities and the dissolution of polymers, which allows even more alternative separation technologies.

[0008] For example, US Patent No. 7,935,736 describes a method for recycling polyester from polyester-containing waste by using a solvent to dissolve the polyester before cleaning. The '736 patent also describes the need to use a precipitant to recover the polyester from the solvent.

[0009] In another example, US patent No. 6,555,588 describes a method for producing a polypropylene blend from a plastic blend comprising other polymers. The '588 patent describes extracting contaminants from a polymer at a temperature below the dissolution temperature of the polymer in the selected solvent, such as hexane, for a specified hold period. The '588 patent further describes raising the temperature of the solvent (or a second solvent) to dissolve the polymer prior to filtration. The '588 patent also further describes the use of shear or flow to precipitate polypropylene from solution. The polypropylene blend described in the '588 patent contained polyethylene contamination of up to 5.6% by weight.

[0010] In another example, European patent application No. 849,312 (translated from German into English) describes a process for obtaining purified polyolefins from a polyolefin-containing plastic mixture or a polyolefin-containing waste. The '312 patent application describes the extraction of blends or rejects of polyolefin with a hydrocarbon fraction of diesel or gasoline fuel having a boiling point above 90°C at temperatures between 90°C and the boiling point of the solvent of hydrocarbon. The '312 patent application further describes contacting a hot polyolefin solution with bleaching clay and/or activated carbon to remove foreign components from the solution. The '312 patent also further describes cooling the solution to temperatures below 70°C to crystallize the polyolefin and then removing the adhesion solvent by heating the polyolefin above the melting point of the polyolefin or evaporating the adhesion solvent. in vacuo or by passing a stream of gas through the polyolefin precipitate and/or solvent extraction with an alcohol or ketone that boils below the melting point of the polyolefin.

[0011] In another example, US Patent No. 5,198,471 describes a method for separating polymers from a physically mixed solid mixture (e.g. plastic waste) containing a plurality of polymers with the use of a solvent at a first temperature more low to form a first single-phase solution and a remaining solid component. The '471 patent further describes heating the solvent to higher temperatures to dissolve additional polymers that were not solubilized at the lower first temperature. The '471 patent describes the filtration of insoluble polymeric components.

[0012] In another example, US patent No. 5,233,021 describes a method of extracting pure polymeric components from a multicomponent structure (for example, carpet waste) by dissolving each component at a temperature and a adequate pressure in a supercritical fluid and/or temperature and/or pressure variation to extract specific components in sequence. However, similar to the '471 patent, the '021 patent only describes the filtration of undissolved components.

[0013] In another example, US Patent No. 5,739,270 describes a method and apparatus for continuously separating a polymeric component of a plastic from contaminants and other components of the plastic using a working fluid and a co-solvent. The co-solvent at least partially dissolves the polymer and the second fluid (which is in a liquid, critical, supercritical state) solubilizes the polymer components and precipitates a part of the dissolved polymer from the co-solvent. The '270 patent further describes the step of filtering the thermoplastic cosolvent (with or without the working fluid) to remove particulate contaminants, such as glass particles.

[0014] Known solvent-based methods for purifying contaminated polymers, as described above, do not produce a "virgin" polymer. In the above methods, co-dissolution and therefore cross-contamination of other polymers often occurs. If adsorbent is used, a centrifugation and/or filtration step is often employed to remove the used adsorbent from the solution. In addition, isolation processes to remove solvent, such as heating, vacuum evaporation, and/or precipitation using a precipitation chemical, are used to produce a polymer free of residual solvent.

[0015] Consequently, there is still a need for an improved solvent-based method designed to purify contaminated polymers that uses a solvent that is readily and economically removed from the polymer, is relatively simple in terms of the number of unit operations, produces a polymer without a significant amount of polymeric cross-contamination, produce a polymer that is essentially colorless, and produce a polymer that is essentially odorless.

SUMMARY OF THE INVENTION

[0016] A method for purifying recovered polypropylene is provided. The method involves: a. obtaining recovered polypropylene selected from the group consisting of polymers for post-consumer use, polymers for post-industrial use and combinations thereof; B. bringing the recovered polypropylene at a temperature of about 80°C to about 220°C and a pressure of about 150 psig (1.03 MPa) to about 15,000 psig (103.42 MPa) in contact with a first fluid solvent having a standard boiling point of less than about 70°C, to produce an extracted recovered polypropylene; w. dissolving the extracted recovered polypropylene in a solvent selected from the group consisting of a first fluid solvent, a second fluid solvent and mixtures thereof, at a temperature of about 90°C to about 220°C and a pressure of about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa) to produce a first solution comprising polypropylene and suspended contaminants; d. decanting the first solution comprising polypropylene and suspended contaminants at a temperature of about 90°C to about 220°C and a pressure of about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa ) to produce a second solution comprising polypropylene and remaining contaminants; w. purifying the second solution at a temperature from about 90°C to about 220°C and a pressure from about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa), placing the second solution contacting the solid medium to produce a third solution comprising a purer polypropylene; and f. separate the purest polypropylene from the third solution.

[0017] The second solvent fluid has the same chemical composition or a different chemical composition as the first solvent fluid.

[0018] In one embodiment, the polypropylene is separated from the third solution at a temperature of about 0°C to about 220°C and a pressure of about 0 psig (0 MPa) to 2,000 psig (13.79 MPa) . In another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, to a weight percent concentration of at least 0.5%. In yet another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, to a weight percent concentration of at least 1%. In one embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, to a mass percent concentration of at least 2%.

[0019] In one embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a weight percent concentration of at least 3%. In another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a weight percent concentration of at least 4%. In yet another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, to a mass percent concentration of at least 5%.

[0020] In one embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a weight percent concentration of up to 20%. In another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a mass percent concentration of up to 18%. In yet another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a mass percent concentration of up to 16%. In one embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a mass percent concentration of up to 14%. In another embodiment, the recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a mass percent concentration of up to 12%.

[0021] In one embodiment, the recovered polypropylene is a polypropylene derived from post-consumer recycling. In another embodiment, the recovered polypropylene is a homopolymer of polypropylene or a copolymer primarily of polypropylene. In yet another embodiment, the fluid solvent has a standard boiling point of less than about 0°C and greater than about -45°C and a standard enthalpy change of vaporization of less than about +25 kJ/mol.

[0022] In one embodiment, the fluid solvent is selected from the group consisting of olefinic hydrocarbons, aliphatic hydrocarbons and mixtures thereof. In another embodiment, the aliphatic hydrocarbon is selected from the group consisting of C1-C6 aliphatic hydrocarbons and mixtures thereof. In yet another embodiment, the aliphatic hydrocarbons and mixtures thereof are comprised primarily of C4 aliphatic hydrocarbons.

[0023] In another embodiment, the fluid solvent consists essentially of C4 liquefied petroleum gas. In one embodiment, the eluting solvent is n-butane, butane isomers or mixtures thereof. In another embodiment, the temperature in the contacting, dissolving, decanting and purifying steps is from about 110°C to about 170°C.

[0024] In one embodiment, the pressure at the contact stage is from about 1,100 psig (7.58 MPa) to about 2,100 psig (14.48 MPa). In another embodiment, the pressure at the contact stage is less than about 1100 psig (7.58 MPa). In yet another embodiment, the pressure in the dissolving, decanting and purifying steps is greater than about 1100 psig (7.58 MPa). In one embodiment, the pressure in the dissolution, decantation and purification steps is greater than about 2100 psig (14.48 MPa).

[0025] In one embodiment, the solid medium is selected from the group consisting of inorganic substances, carbon-based substances and mixtures thereof. In another embodiment, the inorganic substances are selected from the group consisting of silicon oxides, aluminum oxides, iron oxides, aluminum silicates, amorphous volcanic glasses and mixtures thereof. In yet another embodiment, the inorganic substances are selected from the group consisting of silica gel, diatomite, sand, quartz, alumina, perlite, Fuller's earth, bentonite, and mixtures thereof.

[0026] In one embodiment, the carbon-based substances are selected from the group consisting of anthracite coal, carbon black, coke, activated carbon, cellulose, and mixtures thereof. In another embodiment, contact of the polypropylene solution with said solid medium is carried out in a bed filled with said solid medium. In yet another embodiment, the stuffed bed is longer than 20 cm.

[0027] Additional features of the invention may become apparent to those skilled in the art from a review of the following detailed description, taken in conjunction with the examples.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a block flowchart showing the main steps of an embodiment of the present invention.

[0029] Figure 2 is a calibration curve for calculating the polyethylene content in polypropylene using enthalpy values from differential scanning calorimeter (DSC) measurements.

[0030] Figure 3A is a schematic of the experimental apparatus used in the extraction step of Examples 2 and 3.

[0031] Figure 3B is a schematic of the experimental apparatus used in the dissolution and sedimentation steps of Examples 2 and 3.

[0032] Figure 4 is a photograph of the exemplary samples.

DETAILED DESCRIPTION OF THE INVENTION I. Definitions

[0033] For use in the present invention, the term "recovered polymer" refers to a polymer used for one purpose and then recovered for further processing.

[0034] As used herein, the term "recovered polypropylene" (rPP) refers to a polypropylene polymer used for a former purpose and then recovered for further processing.

[0035] For use in the present invention, the term "post-consumer" refers to a source of material that originates after the end consumer has used the material of a consumer good, or product.

[0036] As used herein, the term "post-consumer recycle" (PCR) refers to a material that is produced after the end consumer has used the material and has disposed of the material in a discard current.

[0037] For use in the present invention, the term "post-industrial" refers to a source of a material that originates during the manufacture of a commodity or product.

[0038] For use in the present invention, the term "fluid solvent" refers to a substance that can exist in a liquid state under specified conditions of temperature and pressure. In some embodiments, the fluid solvent may be an essentially homogeneous chemical composition of one molecule or isomer, while in other embodiments, the fluid solvent may be a mixture of several different molecular compositions or isomers. Additionally, in some embodiments of the present invention, the term "fluid solvent" may also apply to substances that are at, near, or above the critical temperature and critical pressure (critical point) of that substance. It is well known to those skilled in the art that substances above the critical point of substance are known as "supercritical fluids" which do not have the typical physical properties (ie, density) of a liquid.

[0039] For use in the present invention, the term "dissolved" means at least partial incorporation of a solute (polymeric or non-polymeric) in a solvent, at the molecular level. Additionally, the thermodynamic stability of the solvent/solute solution can be described by the following equation 1: Equation 1 where ΔGmix is the Gibbs free energy change of mixing a solute with a solvent, ΔHmix is the enthalpy change of the mixture, T is the absolute temperature, and ΔSmix is the entropy of the mixture. To maintain a stable solution of a solute in a solvent, the Gibbs free energy must be negative and at a minimum. Therefore, any solute and solvent combination that minimizes negative Gibbs free energy at appropriate temperatures and pressures can be used for the present invention.

[0040] For use in the present invention, the term "standard boiling point" refers to the boiling temperature at an absolute pressure of exactly 100 kPa (1 bar, 14.5 psia, 0.9869 ATM) as established by the Federal International Institute of Pure and Applied Chemistry (IUPAC).

[0041] For use in the present invention, the term "standard enthalpy change of vaporization" refers to the enthalpy change required to transform a given amount of a substance from a liquid to a vapor at the standard boiling point of the substance.

[0042] As used herein, the term "polypropylene solution" refers to a solution of polypropylene dissolved in a solvent. The polypropylene solution may contain undissolved matter and therefore the polypropylene solution may also be a "slurry" of undissolved matter suspended in a solution of polypropylene dissolved in a solvent.

[0043] For use in the present invention, the terms "settling" and "settling" refer to the tendency of particles within a suspension to separate from a liquid in response to a force (typically a gravitational force) acting on the particles.

[0044] For use in the present invention, the term "suspended contaminants" refers to unwanted or undesirable constituents that are present throughout the volume of the medium of a heterogeneous mixture.

[0045] As used herein, the term "solid medium" refers to a substance that exists in a solid state under the conditions of use. The solid medium can be crystalline, semi-crystalline or amorphous. The solid medium can be granular and can be provided in different formats (ie spheres, cylinders, pellets, etc.). If the solid medium is granular, the particle size and particle size distribution of the solid medium can be defined by the screen size used to classify the granular medium. An example of standard weave size designations can be found in the American Society for Testing and Materials (ASTM) ASTM E11 "Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves" . The solid medium can also be a fibrous non-woven web, or a woven textile material.

[0046] As used herein, the term "purer polypropylene solution" refers to a polypropylene solution having fewer contaminants compared to the same polypropylene solution prior to a purification step.

[0047] For use in the present invention, the term "extraction" refers to the practice of transferring a solute species from a liquid phase (or solid matrix) along a phase boundary to a separate immiscible liquid phase. The driving force(s) of extraction is(are) described by partition theory.

[0048] For use in the present invention, the term "extracted" refers to a material that has less solute species relative to the same material prior to an extraction step. For use in the present invention, the term "extracted recovered polypropylene" refers to a recovered polypropylene having less solute species relative to the same recovered polypropylene prior to an extraction step.

[0049] For use in the present invention, the term "virgin" means essentially free of contaminant, free of pigment, free of odor, homogeneous, and similar in properties to virgin polymers.

[0050] For use in the present invention, the term "primarily polypropylene copolymer" refers to a copolymer containing more than 70 mol% propylene repeating units.

[0051] As used herein, any reference to international units of pressure (eg MPa) refers to gauge pressure.

II. method for purifying contaminated polypropylene

[0052] Surprisingly, it has been found that certain fluid solvents which, in a preferred embodiment, have temperature and pressure dependent solubility for polymers, when used in a relatively simple process can be used to purify contaminated polymers, especially recovered or recycled polymers, to a quality close to that of virgin material. This process, exemplified in Figure 1, comprises 1) obtaining a recovered polymer (step a in Figure 1), followed by 2) extracting the polypropylene with a fluid solvent at an extraction temperature (TE) and an extraction pressure (PE ) (step b in Figure 1), followed by 3) dissolving the polypropylene in a fluid solvent at a dissolution temperature (TD) and a dissolution pressure (PD) (step c in Figure 1), followed by 4) sedimentation of the polymer solution at a dissolving temperature (TD) and a dissolving pressure (PD) (step d in Figure 1), followed by 5) bringing the dissolved polypropylene solution into contact with a solid medium at a dissolving temperature (TD) and at a dissolving pressure (PD) (step e in Figure 1), followed by the separation of the polypropylene from the fluid solvent (step e in Figure 1).

[0053] In one embodiment of the present invention, purified polypropylene, which can be obtained from post-consumer waste streams, is essentially free of contaminants, free of pigments, free of odors, homogeneous and similar in terms of properties , to virgin polypropylene. Furthermore, in a preferred embodiment, the physical properties of the fluid solvent of the present invention may allow for more energy efficient methods for separating the fluid solvent from purified polypropylene.

recovered polypropylene

[0054] In one embodiment of the present invention, a method for purifying recovered polypropylene includes obtaining recovered polypropylene. For purposes of the present invention, recovered polypropylene is obtained from post-consumer, post-industrial, post-commercial and/or other special waste streams. For example, post-consumer waste polypropylene can be derived from separate collection recycling streams, where end consumers place used polymers from packaging and products into a designated bin for collection by a garbage truck or recycler. Post-consumer waste polymers can also be derived from in-store "takeback" programs, where the consumer brings waste polymers into a store and places the waste polymers in a designated collection bin. An example of post-industrial waste polymer could be waste polymers produced during the manufacture or shipment of a product or good that are collected as waste material by the manufacturer (i.e., trimmings, off-spec material, scrap from match). An example of waste polymer from a special waste stream could be waste polymers derived from recycling electronic waste, also known as electronic waste ("ewaste"). Another example of waste polymer might be a special waste stream of waste polymers derived from automobile recycling. Another example of waste polymer could be a special waste stream of waste polymers derived from recycling used carpets and textiles.

[0055] For the purposes of the present invention, recovered polypropylene is a homogeneous composition of an individual polymer, or a mixture of several different polypropylene compositions. Non-limiting examples of polypropylene compositions are homopolymers of polypropylene, copolymers of propylene and ethylene (including "impact" and "clarified random" copolymers), copolymers of propylene and alpha-olefins, polypropylene rubbers and other dissolvable polypropylene compositions that may become apparent to those skilled in the art.

[0056] The recovered polypropylene may also contain various pigments, colorants, processing aids, stabilizing additives, fillers and other performance additives that were added to the polymer during polymerization or conversion of the original polymer to the final form of an article. Non-limiting examples of pigments are organic pigments such as copper phthalocyanine, inorganic pigments such as titanium dioxide, and other pigments which may be apparent to those skilled in the art. A non-limiting example of an organic dye is basic yellow 51. Non-limiting examples of processing aids are antistatic agents such as glycerol monostearate and glidants such as erucamide. A non-limiting example of a stabilizing additive is octadecyl-3-(3,5-di-tert.butyl-4-hydroxyphenyl)-propionate. Non-limiting examples of filler materials are calcium carbonate, talc and glass fibers.

Solvent

[0057] The fluid solvent of the present invention has a standard boiling point of less than about 70°C. Pressurization maintains solvents, which have standard boiling points below the operating temperature range of the present invention, in a state in which there is little or no solvent vapor. In one embodiment, the fluid solvent having a standard boiling point less than about 70°C is selected from the group consisting of carbon dioxide, ketones, alcohols, ethers, esters, alkenes, alkanes and mixtures thereof. Non-limiting examples of fluid solvents with standard boiling points below about 70°C are carbon dioxide, acetone, methanol, dimethyl ether, diethyl ether, methyl ethyl ether, tetrahydrofuran, methyl acetate, ethylene, propylene, 1 - butene, 2-butene, isobutylene, 1-pentene, 2-pentene, branched isomers of pentene, 1-hexene, 2-hexene, methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, neopentane, n-hexane, iso-hexane isomers and other substances that may be apparent to those skilled in the art.

[0058] The selection of fluid solvent to be used will dictate the temperature and pressure ranges used to perform the steps of the present invention. An analysis of the phase behavior of the polymer in solvents of the type described by the present invention is provided in the following reference: McHugh et al. (1999) Chem. Rev. 99:565 to 602.

Extraction

[0059] In one embodiment of the present invention, a method for purifying polypropylene includes contacting the recovered polypropylene with a fluid solvent at a temperature and pressure at which the polymer is essentially insoluble in the fluid solvent. Without being bound by theory, applicants believe that the temperature and pressure dependent solubility can be controlled in such a way as to prevent the fluid solvent from fully solubilizing the polymer, however the fluid solvent may diffuse into the solvent and draw out any extractable contamination. . Extractable contamination can be from residual processing aids added to the polymer, residual product formulations that came into contact with the polymer, such as perfumes and flavors, colorants, and any other materials that may have been intentionally added or inadvertently incorporated into the polymer, by for example, during manure collection and subsequent accumulation with other waste materials.

[0060] In one embodiment, controlled extraction can be performed by setting the temperature of the polymer/solvent fluid and then controlling the pressure below a pressure, or range of pressures, at which the polymer dissolves in the solvent fluid. In one embodiment, controlled extraction is performed by setting the pressure of the polymer/solvent system and then controlling the temperature below a temperature, or range of temperatures, where the polymer dissolves in the fluid solvent. Temperature and pressure controlled extraction of the polymer with a fluid solvent utilizes a suitable pressure vessel and can be configured in a way that allows continuous extraction of the polymer with the fluid solvent. In one embodiment of the present invention, the pressure vessel can be a liquid-liquid extraction column where the molten polymer is pumped to one end of the extraction column and the fluid is pumped to the same or opposite end of the extraction column. extraction. In another embodiment, the fluid containing the extracted contamination is removed from the process. In another embodiment, the fluid containing the extracted contamination is purified, recovered, and recycled for use in the extraction step, or another step in the process. In one embodiment of the present invention, the extraction can be performed as a batch method, whereby the recovered polypropylene is fixed in a pressure vessel and the fluid solvent is continuously pumped through the fixed polymeric phase. The extraction time and amount of fluid solvent used will depend on the desired purity of the final purest polymer and the amount of extractable contamination in the starting recovered polypropylene. In another embodiment, the fluid containing the extracted contamination is brought into contact with a solid medium in a separate step, as described in the "Purification" section below. In another embodiment, a method for purifying recovered polypropylene includes contacting the recovered polypropylene with a fluid solvent at a temperature and pressure at which the polymer is molten and in a liquid state. In another embodiment, the recovered polypropylene is brought into contact with the fluid solvent at a temperature and pressure at which the polymer is in a solid state.

[0061] In one embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with a fluid solvent at a temperature and pressure at which the polypropylene remains essentially undissolved. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with n-butane at a temperature of from about 80°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with n-butane at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with n-butane at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with n-butane at a pressure from about 150 psig (1.03 MPa) to about 3000 psig (20.68 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with n-butane at a pressure from about 1000 psig (6.89 MPa) to about 2750 psig (18.96 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with n-butane at a pressure from about 1500 psig (10.34 MPa) to about 2500 psig (17.24 MPa).

[0062] In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with propane at a temperature of about 80°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with propane at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with propane at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with propane at a pressure of about 200 psig (1.38 MPa) to about 8,000 psig (55.16 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with propane at a pressure of about 1000 psig (6.89 MPa) to about 6000 psig (41.37 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene with propane at a pressure of about 2000 psig (13.79 MPa) to about 4000 psig (27.58 MPa).

Dissolution

[0063] In one embodiment of the present invention, a method for purifying recovered polypropylene includes dissolving the recovered polypropylene in a fluid solvent at a temperature and pressure at which the polymer is dissolved in the fluid solvent. Without being bound by theory, Applicants believe that temperature and pressure can be controlled to allow for thermodynamically favorable dissolution of the recovered polymer in a fluid solvent. In addition, temperature and pressure can be controlled to allow dissolution of a specific polymer or polymer blend without dissolving other polymers or polymer blends. This controllable dissolution allows the separation of polymers from polymer mixtures.

[0064] In one embodiment of the present invention, a method for purifying polymers includes dissolving the contaminated recovered polypropylene in a solvent that does not dissolve the contaminants under the same conditions of temperature and pressure. Contaminants can include pigments, fillers, dirt, and other polymers. These contaminants are released from the recovered polypropylene after dissolution and then removed from the polymer solution through a subsequent solid-liquid separation step.

[0065] In one embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in a fluid solvent at a temperature and pressure at which the polypropylene is dissolved in the fluid solvent. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane at a temperature of from about 90°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane at a pressure of about 350 psig (2.41 MPa) to about 4,000 psig (27.57 MPa). In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane at a pressure of from about 1000 psig (6.89 MPa) to about 3500 psig (24.13 MPa). In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane at a pressure of about 2000 psig (13.79 MPa) to about 3000 psig (20.68 MPa). In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane to a weight percent concentration of at least 0.5%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 1%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 2%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 3%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 4%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 5%. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in n-butane to a weight percent concentration of up to 20%. In another embodiment, the polypropylene is dissolved at a weight percent concentration of up to 18%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 16%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 14%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 12%.

[0066] In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane at a temperature of about 90°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane at a pressure of about 2000 psig (13.79 MPa) to about 8000 psig (55.16 MPa). In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane at a pressure of about 3000 psig (20.68 MPa) to about 6000 psig (41.37 MPa). In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane at a pressure of about 3500 psig (24.13 MPa) to about 5000 psig (34.47 MPa). In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane to a weight percent concentration of at least 0.5%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 1%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 2%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 3%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 4%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 5%. In another embodiment, a method for purifying recovered polypropylene includes dissolving the polypropylene in propane to a mass percent concentration of up to 20%. In another embodiment, the polypropylene is dissolved at a weight percent concentration of up to 18%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 16%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 14%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 12%.

Sedimentation

[0067] In one embodiment of the present invention, a method for purifying polypropylene includes separating undissolved contaminants from the polypropylene solution through a settling step (also known as settling) at a temperature and pressure at which the polymer remains dissolved in the fluid solvent. In one embodiment, the settling step causes the undissolved contaminants to be subjected to a force that uniformly moves the undissolved contaminants in the direction of the force. Typically, the applied settling force is gravity, but it can also be centrifugal, centripetal, or some other force. The amount of force applied and the length of settling time will depend on several parameters, including, but not limited to: particle size of the contaminating particles, densities of the contaminating particles, density of the fluid or solution, and viscosity of the fluid or solution. The following equation (equation 2) is a relationship between the aforementioned parameters and the decantation velocity, which is a measure of the contaminant sedimentation rate: Equation 2 where v is the settling velocity, Pp is the density of the contaminating particle, p? is the density of the fluid or solution, g is the acceleration due to the applied force (typically gravity), r is the radius of the contaminating particle, and g is the dynamic viscosity of the fluid or solution. Some of the main parameters that determine the viscosity of the solution are: the chemical composition of the solvent fluid, the molecular weight of the polymer dissolved in the solvent fluid, the concentration of polymer dissolved in the solvent fluid, the temperature of the solvent fluid solution, and the pressure of the solution. fluid solvent.

[0068] In one embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/fluid solvent solution at a temperature and pressure at which the polypropylene remains dissolved in the fluid solvent. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/n-butane solution at a temperature of from about 90°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/n-butane solution at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/n-butane solution at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/n-butane solution at a pressure of about 350 psig (2.41 MPa) to about 4,000 psig (27.57 MPa ). In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/n-butane solution at a pressure of about 1000 psig (6.89 MPa) to about 3500 psig (24.13 MPa ). In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/n-butane solution at a pressure of about 2000 psig (13.79 MPa) to about 3000 psig (20.68 MPa ). In another embodiment, a method for purifying recovered polypropylene includes decanting the contaminants from a polypropylene/n-butane solution in which the polypropylene is dissolved to a weight percent concentration of at least 0.5%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 1%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 2%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 3%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 4%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 5%. In another embodiment, a method for purifying recovered polypropylene includes decanting the contaminants from a polypropylene/n-butane solution in which the polypropylene is dissolved at a weight percent concentration of up to 20%. In another embodiment, the polypropylene is dissolved at a weight percent concentration of up to 18%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 16%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 14%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 12%.

[0069] In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution at a temperature of about 90°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution at a pressure of from about 2000 psig (13.79 MPa) to about 8000 psig (55.16 MPa). In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution at a pressure of about 3000 psig (20.68 MPa) to about 6000 psig (41.37 MPa). In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution at a pressure of from about 3500 psig (24.13 MPa) to about 5000 psig (34.47 MPa). In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution in which the polypropylene is dissolved to a mass percent concentration of at least 0.5%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 1%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 2%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 3%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 4%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 5%. In another embodiment, a method for purifying recovered polypropylene includes decanting contaminants from a polypropylene/propane solution in which the polypropylene is dissolved at a weight percent concentration of up to 20%. In another embodiment, the polypropylene is dissolved at a weight percent concentration of up to 18%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 16%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 14%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 12%.

Purification

[0070] In one embodiment of the present invention, a method for purifying polypropylene includes contacting a contaminated polymer solution with a solid medium at a temperature and pressure at which the polymer remains dissolved in the fluid solvent. The solid medium of the present invention is any solid material that removes at least part of the contamination from a recovered polypropylene solution dissolved in the fluid solvent of the present invention. While not wishing to be bound by any theory, applicants believe that the solid medium removes contamination through a variety of mechanisms. Non-limiting examples of possible mechanisms include adsorption, absorption, size exclusion, ion exclusion, ion exchange, and other mechanisms that may be apparent to those skilled in the art. Furthermore, pigments and other contaminants commonly found in recovered polypropylene can be polar compounds and can preferably interact with the solid medium, which can also be at least slightly polar. Polar-polar interactions are especially favorable when non-polar solvents, such as alkanes, are used as the fluid solvent.

[0071] In one embodiment of the present invention, the solid medium is selected from the group consisting of inorganic substances, carbon-based substances or mixtures thereof. Useful examples of inorganic substances include silicon oxides, aluminum oxides, iron oxides, aluminum silicates, magnesium silicates, amorphous volcanic glasses, silica, silica gel, diatomite, sand, quartz, reclaimed glass, alumina, perlite, earth Fuller's, bentonite and mixtures thereof. Useful examples of carbon-based substances include anthracite coal, carbon black, coke, activated carbon, cellulose and mixtures thereof. In another embodiment of the present invention, the solid medium is recycled glass.

[0072] In one embodiment of the present invention, the solid medium is contacted with the polymer in a container for a specified amount of time, while the solid medium is stirred. In another embodiment, the solid medium is removed from the purer polymer solution through a solid-liquid separation step. Non-limiting examples of solid-liquid separation steps include filtration, decantation, centrifugation and precipitation. In another embodiment of the present invention, the contaminated polymer solution is passed through a stationary bed of solid medium. In another embodiment of the present invention, the height or length of the stationary bed of the solid medium is greater than 5 cm. In another embodiment of the present invention, the height or length of the stationary bed of the solid medium is greater than 10 cm. In another embodiment of the present invention, the height or length of the stationary bed of the solid medium is greater than 20 cm. In another embodiment of the present invention, the solid medium is replaced as needed to maintain a desired polymer purity. In yet another embodiment, the solid medium is regenerated and reused in the purification step. In another embodiment, the solid medium is regenerated by fluidizing the solid medium during a backwash step.

[0073] In one embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/fluid solvent solution with a solid medium at a temperature and pressure at which the polypropylene remains dissolved in the fluid solvent. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/n-butane solution with a solid medium at a temperature of from about 90°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/n-butane solution with a solid medium at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/n-butane solution with a solid medium at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/n-butane solution with a solid medium at a pressure of about 350 psig (2.41 MPa) to about 4,000 psig (27 MPa). .57 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/n-butane solution with a solid medium at a pressure of about 1000 psig (6.89 MPa) to about 3500 psig (24 .13 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/n-butane solution with a solid medium at a pressure of about 2000 psig (13.79 MPa) to about 3000 psig (20 .68 MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/n-butane solution with a solid medium in which the polypropylene is dissolved at a mass percent concentration of at least 0.5%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 1%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 2%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 3%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 4%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 5%. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/n-butane solution with a solid medium in which the polypropylene is dissolved at a mass percent concentration of at least 20%. In another embodiment, the polypropylene is dissolved at a weight percent concentration of up to 18%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 16%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 14%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 12%.

[0074] In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/propane solution with a solid medium at a temperature of from about 90°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/propane solution with a solid medium at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/propane solution with a solid medium at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/propane solution with a solid medium at a pressure of about 2000 psig (13.79 MPa) to about 8000 psig (55.16 MPa). MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/propane solution with a solid medium at a pressure of about 3000 psig (20.68 MPa) to about 6000 psig (41.37 MPa). MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/propane solution with a solid medium at a pressure of about 3500 psig (24.13 MPa) to about 5000 psig (34.47 MPa). MPa). In another embodiment, a method for purifying recovered polypropylene includes contacting the polypropylene/propane solution with a solid medium in which the polypropylene is dissolved at a mass percent concentration of at least 0.5%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 1%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 2%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 3%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 4%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of at least 5%. In another embodiment, a method for purifying recovered polypropylene includes contacting a polypropylene/propane solution with a solid medium in which the polypropylene is dissolved at a mass percent concentration of up to 20%. In another embodiment, the polypropylene is dissolved at a weight percent concentration of up to 18%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 16%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 14%. In another embodiment, the polypropylene is dissolved in a weight percent concentration of up to 12%.

Separation

[0075] In one embodiment of the present invention, a method for purifying recovered polypropylene includes separating the purer polymer from the fluid solvent at a temperature and pressure at which the polymer precipitates out of solution and is no longer dissolved in the fluid solvent . In another embodiment, precipitation of the purest polymer from the fluid solvent is fluid obtained by reducing the pressure at a fixed temperature. In another embodiment, precipitation of the purest polymer from the fluid solvent is fluid obtained by reducing the temperature at a fixed pressure. In another embodiment, precipitation of the purest polymer from the fluid solvent is fluid obtained by increasing the temperature at a fixed pressure. In another embodiment, precipitation of the purest polymer from the fluid solvent is achieved by reducing the temperature and pressure. The solvent can be partially or completely converted from the liquid phase to the vapor phase by controlling temperature and pressure. In another embodiment, the precipitated polymer is separated from the eluted solvent without completely converting the eluted solvent into a 100% vapor phase by controlling the temperature and pressure of the solvent during the separation step. Separation of the purest precipitated polymer is carried out by any liquid-liquid or liquid-solid separation method. Non-limiting examples of liquid-liquid or liquid-solid separations include filtration, decantation, centrifugation and precipitation.

[0076] In one embodiment, a method for purifying recovered polypropylene includes separating polypropylene from a polypropylene/fluid solvent solution at a temperature and pressure at which polypropylene precipitates from solution. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/n-butane solution at a temperature of from about 0°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/n-butane solution at a temperature of from about 100°C to about 200°C. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/n-butane solution at a temperature of from about 130°C to about 180°C. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/n-butane solution at a pressure of about 0 psig (0 MPa) to about 2000 psig (13.79 MPa). In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/n-butane solution at a pressure of about 50 psig (0.34 MPa) to about 1500 psig (10.34 MPa ). In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/n-butane solution at a pressure of about 75 psig (0.52 MPa) to about 1,000 psig (6.89 MPa ).

[0077] In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/propane solution at a temperature of about -42°C to about 220°C. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/propane solution at a temperature of from about 0°C to about 150°C. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/propane solution at a temperature of from about 50°C to about 130°C. In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/propane solution at a pressure of from about 0 psig (0 MPa) to about 6,000 psig (41.37 MPa). In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/propane solution at a pressure of from about 50 psig (0.34 MPa) to about 3000 psig (20.68 MPa). In another embodiment, a method for purifying recovered polypropylene includes separating the polypropylene from a polypropylene/propane solution at a pressure of from about 75 psig (0.52 MPa) to about 1000 psig (6.89 MPa).

III. test methods

[0078] The test methods described here are used to measure the effectiveness of various methods for purifying polymers. Specifically, the described methods demonstrate the effectiveness of a given purification method in improving color and translucency/clarity (i.e., bringing the color and opacity of recovered polypropylene closer to that of an uncolored virgin polymer), reducing or eliminating elemental contamination (i.e., remove heavy metals), reduce or eliminate non-combustible contamination (i.e., inorganic fillers), reduce or eliminate volatile compounds (especially volatile compounds that contribute to the unpleasant odor of recovered polypropylene), and reduce or eliminate polymeric contamination (ie, polyethylene contamination on polypropylene).

Color and opacity measurement:

[0079] The color and opacity/translucency of a polymer are important parameters that determine whether a polymer can obtain the desired visual aesthetics of an article produced from the polymer or not. Recovered polypropylene, especially post-consumer derived recovered polypropylene, is typically dark in color and opaque due to residual pigments and filler and other types of contamination. Thus, color and opacity measurements are important parameters in determining the effectiveness of a method for purifying polymers.

[0080] Prior to color measurement, samples of powders or polymer pellets were compression molded into square test specimens 30 mm wide x 30 mm long x 1 mm thick (with rounded corners). Powder samples were first densified at room temperature (about 20 to 23°C) by cold pressing the powder into a sheet using clean, never-used aluminum foil as a contact release layer between the powders. stainless steel printing rollers. Approximately 0.85 g of cold pressed powder or pellets were then pressed into test samples on a Carver model C press (Carver, Inc., Wabash, IN 46992-0554 USA) preheated to 200°C using if aluminum plates, unused aluminum foil release layers and a stainless steel wedge with a cavity that corresponds to the dimensions of the mentioned square test samples. Samples were heated for 5 minutes before pressure was applied. After 5 minutes, the press was then compressed with at least 2 tons (1.81 metric tons) of hydraulic pressure for at least 5 seconds and then released. The molding stack was then removed and placed between two flat metal thick heatsinks for cooling. The aluminum foil contact release layers were then peeled off the sample and discarded. The coating around the sample on at least one side was peeled back to the edge of the mold, and then the sample was pushed through the mold. Each test sample was visually evaluated for bubble/void defects and only samples without defects in the color measurement area (0.7 in (17.78 mm) minimum diameter) were used for the color measurement.

[0081] The color of each sample was characterized using the International Commission on Illumination (CIE) three-dimensional color space L*, a*, b*. The L* dimension is a measure of the luminosity of a sample, with L*=0 corresponding to the darkest black sample and L*=100 corresponding to the brightest white sample. The a* dimension is a measure of the red or green color of a sample with positive a* values corresponding to the red color and negative a* values corresponding to the green color. The b* dimension is a measure of the blue or yellow color of a sample with positive b* values corresponding to the yellow color and negative b* values corresponding to the blue color. The L*a*b* values of each 30 mm wide x 1 mm long x 1 mm thick square test specimen were measured with a HunterLab model LabScan XE spectrophotometer (Hunter Associates Laboratory, Inc, Reston, VA 20190 -5280, USA). The spectrophotometer was configured with D65 as the standard illuminant, an observer angle of 10°, a view area diameter of 1.75 in (44.45 mm), and a port diameter of 0.7 in (17.78 mm). ).

[0082] The opacity of each sample, which is a measure of how much light passes through the sample (i.e., a measure of the translucency of the sample), was determined using the aforementioned HunterLab spectrophotometer using the contrast ratio opacity mode . Two measurements were taken to determine the opacity of each sample. One to measure the brightness value of the sample supported with a white background, Ybackgroundwhite, and one to measure the brightness value of the sample supported with a black background, Ybackgroundblack. Opacity was then calculated from the gloss values using the following equation 3: Equation 3

Elementary analysis:

[0083] Many sources of recovered polypropylene have unacceptably high concentrations of heavy metal contamination. The presence of heavy metals, for example lead, mercury, cadmium and chromium, may preclude the use of recovered polypropylene in certain applications, such as food or drug contact applications, or medical device applications. Therefore, measurement of heavy metal concentration is important when determining the effectiveness of a method for purifying polymers.

[0084] Elemental analysis was performed using inductively coupled plasma mass spectrometry (ICP-MS). Test solutions were prepared in n=2 to n=6 depending on sample availability by combining ~0.25 g of sample with 4 mL of concentrated nitric acid and 1 mL of concentrated hydrofluoric acid (HF). Samples were digested using an Ultrawave microwave digestion protocol, which consists of a 20-minute ramp to 125°C, a 10-minute ramp to 250°C, and a 20-minute hold at 250°C. Digested samples were cooled to room temperature. Digested samples were diluted to 50 ml after adding 0.25 ml of 100 ppm Ge and Rh as the internal standard. In order to evaluate the accuracy of the measurement, pre-digestion peaks were prepared by boosting with a virgin polymer. The virgin polymer-reinforced samples were weighed using the same procedure mentioned above and reinforced with the appropriate amount of each isolated element of interest, which included the following: Na, Al, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Cd, and Pb. Boosters were prepared at two different levels: a "low booster content" and a "high booster content". Each booster was prepared in triplicate. In addition to the virgin polymer booster, a control sample was also added to ensure that there were no errors during pipetting and to track recovery through the process. Control booster samples were also prepared in triplicate at two different levels and were treated in the same manner as virgin polymer and test samples. A 9 point calibration curve was made by making solutions with 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, 500 ppb containing Na, Al, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Cd, and Pb. All calibration standards were prepared by diluting pure reference standard solutions and 0.25 mL of 100 ppm Ge and Rh as the internal standard with 4 mL of concentrated nitric acid and 1 mL of concentrated HF. The prepared standards, test samples and spiked test samples were analyzed using an Agilent 8800 ICP-QQQ MS instrument, optimized according to the manufacturer's recommendations. The m/z monitored for each analyte and the collision cell gas that was used for the analysis was as follows: Na, 23 m/z, H2; Al, 27 m/z, H2; Ca, 40 m/z, H2; Ti, 48 m/z, H2; Cr, 52 m/z, He; Fe, 56 m/z, H2; Ni, 60 m/z; without gas; Cu, 65 m/z, without gas; Zn, 64 m/z, He; Cd, 112 m/z; H2; Pb, sum of 206^206, 207^207, 208 > 208 m/z, no gas; Ge, 72 m/z, all modes; Rh, 103 m/z, all modes. Ge was used as an internal standard for all elements < 103 m/z and Rh was used for all elements > 103 m/z.

Residual ash content:

[0085] Many sources of recovered polypropylene contain various fillers, for example calcium carbonate, talc and fiberglass. While useful in the original application of recovered polypropylene, these fillers alter the physical properties of a polymer in ways that may be undesirable for the next application of recovered polypropylene. Therefore, measuring the amount of filler is important when determining the effectiveness of a method for purifying polymers.

[0086] Thermogravimetric analysis (TGA) was performed to quantify the amount of non-combustible materials in the sample (sometimes called ash content). About 5 to 15 mg of sample was loaded into a platinum sample tray and heated to 700°C at a rate of 20°C/min in an atmosphere of air in a TA Instruments model Q500 TGA instrument. The sample was kept isothermal for 10 min at 700°C. The percentage of residual mass was measured at 700°C after isothermal retention.

Odor analysis:

[0087] Sensory odor analysis was performed by placing about 3 g of each sample in a 20 mL glass vial and the sample was equilibrated at room temperature for at least 30 min. After equilibration, each vial was opened and the free space was aspirated (sniffed) by a trained classifier to determine odor intensity and descriptor profile. The odor intensity was classified according to the following scale: 5 = very strong 4 = strong 3 = moderate 2 = weak to moderate 1 = weak 0 = no odor

Analysis of polymeric contamination:

[0088] Many sources of recovered polypropylene, especially recovered polypropylene originating from mixed flow sources, may contain unwanted polymeric contamination. Without being bound by theory, polymeric contamination, for example contamination of polyethylene in polypropylene, can influence the physical properties of the polymer due to the presence of heterogeneous phases and the resulting weak interfaces. Furthermore, polymeric contamination can also increase the degree of opacity of the polymer and have an influence on the color. Therefore, measuring the amount of polymeric contamination is important when determining the effectiveness of a method for purifying polymers.

[0089] Semi-crystalline polymeric contamination was evaluated using Differential Scanning Calorimetry (DSC). To measure the amount of polyethylene contamination in the polypropylene, a set of five polypropylene/polyethylene blends was prepared with 2, 4, 6, 8, and 10%, by weight, of Formolene® HB5502F HDPE (Formosa Plastics Corporation, USA) in Pro-fax 6331 polypropylene (LyondellBasell Industries Holdings, B.V.). About 5 to 15 mg of each sample was sealed in an aluminum DSC pan and analyzed with a TA Instruments model Q2000 DSC equipment with the following method: 1. Equilibrate at 30.00°C 2. Elevate to 20. 00°C/min to 200.00°C 3. Mark the end of cycle 0 4. Increase to 20.00°C/min to 30.00°C 5. Mark the end of cycle 1 6. Increase to 20, 00°C/min to 200.00°C 7. Mark the end of cycle 2 8. Increase to 20.00°C/min to 30.00°C 9. Mark the end of cycle 3 10. Increase to 5, 00°C/min to 200.00°C 11. Mark the end of cycle 4

[0090] The enthalpy of fusion for the HDPE peak around 128°C was calculated for each sample of known HDPE content using the DSC thermogram at 5.00°C/min. A linear calibration curve, shown in Figure 2, was established by plotting the enthalpy of melt versus the known concentration of HDPE (% by weight).

[0091] Samples with unknown PE content were analyzed using the same equipment and DSC method mentioned above. The PE content was calculated using the calibration curve mentioned above. The particular HDPE used to generate the calibration curve will most likely have a different degree of crystallinity than the polyethylene contamination (or polyethylene blend) that may be present in a recovered polypropylene sample. The degree of crystallinity can independently influence the measured enthalpy of fusion for polyethylene and therefore influence the resulting calculation of polyethylene content. However, the DSC test method described in the present invention is intended to serve as a relative metric to compare the effectiveness of different methods to purify polymers, and is not intended to be a quantification of polyethylene content in a polymer blend. Although the previously mentioned method described the measurement of polyethylene contamination in polypropylene, this method can be applied for the measurement of other semi-crystalline polymers using different temperature ranges and peaks and peaks in the DSC thermogram. In addition, alternative methods, such as nuclear magnetic resonance (NMR) spectroscopy, can also be used to measure the amount of semicrystalline and amorphous polymeric contamination in a sample.

EXAMPLES

[0092] The following examples further describe and demonstrate embodiments that are within the scope of the present invention. The examples are provided for illustrative purposes only and are not to be considered as limitations on the present invention, as many variations thereof are possible without departing from the spirit and scope of the invention.

Example 1

[0093] A mixed-color flake sample of post-consumer-derived recycled polypropylene was obtained from a supplier of recycled resins. Post-consumer recycled polypropylene originated from the United States and Canada. The as-received mixed color flake was homogenized by compounding in a Century/W&P ZSK30 twin screw extruder equipped with two general purpose 30mm screws each with standard mixing and conveying elements. The screw rotation speed was about 50 rpm, the feeder speed was about 20 pounds/hour (9.07 kg/hour) and the cylinder temperature was in the range of about 210°C in the die at about 150°C in the feed tube. The gray yarn exiting the extruder was cooled in a water bath at room temperature, air dried, and chopped into pellets.

[0094] The sample was characterized using the test methods disclosed herein, and the resulting data are summarized in Table 1. The purpose of this example is to show the properties of a representative post-consumer derived recycled resin prior to purification.

[0095] The pellets and the corresponding square test specimens were dark gray in color, as indicated by the L*a*b* values of the square samples. The opacity of the samples averaged around 100% opaque (i.e. no transparency). A photograph of the square test sample is shown in Figure 4 as Example 1. As shown in Figure 4, the sample was dark in color and lacked translucency.

[0096] This example serves as a representative baseline for heavy metal contamination found in post-consumer derived recycled polypropylene. When compared to other examples, heavy metal contamination was found to be much higher in post-consumer derived recycled polypropylene as received.

[0097] Samples from example 1 had ash content values that averaged 1.2117% by weight, which also serves as a baseline for the amount of non-combustible substances that are often present in recycled polypropylene post-consumer derivative.

[0098] This example also serves as a representative baseline for odor compound contamination found in post-consumer derived recycled polypropylene. Samples from Example 1 were found to have an odor intensity of 3.75 on a 5-point scale (5 being the most intense), and were described as having a "garbage", "dusty", or "sour" odor. ".

[0099] This example also serves as a representative baseline for polyethylene contamination found in post-consumer derived recycled polypropylene. Samples from Example 1 had polyethylene contents averaging about 5.5% by weight.

Example 2

[0100] The mixed color flake sample of post-consumer derived recycled polypropylene, described in Example 1, was processed using the experimental apparatus shown in Figure 3A and Figure 3B and the following procedure: 1. 286 g of flake of mixed color were placed in a 7.57 liter Parr Instrument Company Model 4552M autoclave equipped with an overhead mechanical stirrer. 2. The autoclave was then completely filled with n-butane and equilibrated to an internal fluid temperature of 140°C and a hydrostatic pressure of 900 psig (6.21 MPa). 3. The material in the autoclave was then extracted using the experimental setup shown in Figure 3A and the following procedure: a. The system was shaken for 10 min at 140°C and 900 psig (6.21 MPa). B. After stirring, the system sat for 10 minutes at 140°C and 900 psig (6.21 MPa). w. One canister volume of n-butane was flushed through the autoclave into a sample collection bottle at 140°C and 900 psig (6.21 MPa). d. The above extraction procedure was repeated four more times. It is. The material collected for all extraction cycles was labeled "Fraction 1". 4. The material remaining in the autoclave after extraction was then dissolved in n-butane using the experimental setup shown in Figure 3B and the following procedure: a. The system pressure was balanced to 1800 psig (12.41 MPa). B. The system was shaken for 10 min at 140°C and 1800 psig (12.41 MPa). w. Stirring was then stopped and the solution was allowed to stand for 30 min at 140°C and 1800 psig (6.21 MPa). d. After decantation, the solution was removed from the autoclave by displacement with pressurized nitrogen (pre-equilibrated at 140°C and 1800 psig). The solution exiting the autoclave through a dip tube was then passed through two electrically traced solid medium columns. Each column had an inside diameter (ID) of 0.68 in (1.73 cm) and a length of about 9.5 in (24.13 cm). The first column contained about 21 g of 8 to 16 mesh Fuller's earth (Jaxon Filtration, JF 752-8/16, USA) which was premixed in a beaker with about 21 g of 30 mesh Fuller's earth to 60 (Jaxon Filtration, JF 752-3060, USA). The second column contained about 21 g of silica gel (Silicycle Ultra Pure Silica Gels, SiliaFlash GE60, Parc-Technologies, USA) which was premixed in a beaker with about 21 g of aluminum oxide (activated alumina, Selexsorb CDX, 7x14, BASF, USA). The fluid stream leaving the bottom of the second pressure vessel was depressurized through an expansion valve into a sidearm Erlenmeyer flask. After the flow of fluid in the Erlenmeyer flask was depressurized, the solvent vapor was vented through the side arm port and all liquid/solids were collected as fractions in the flask. Each fraction contained approximately 30 g of material and was labeled sequentially starting with "Fraction 2". Fractions were collected until no further elution of material was observed in the flask. 5. After all samples were collected, the autoclave was equilibrated to atmospheric pressure and room temperature. All residual material in the autoclave was then collected as a sample residue.

[0101] The sample data of fraction 3 collected according to the procedure disclosed herein are summarized in Table 1.

[0102] The isolated solids in fraction 3 of this example were white in color. When the white solids from fraction 3 were compression molded into square test specimens, the specimens were nearly colorless and transparent, and similar in appearance to virgin polypropylene. A photograph of the square test sample produced in fraction 3 is shown in Figure 4 as Example 2. As a reference, virgin polypropylene is shown in Figure 4 as Example 4. As shown in Figure 4, the sample was transparent and comparable in terms of in color and translucency, to virgin polypropylene. The L*a*b* values showed that the square test samples were essentially colorless, and showed a dramatic improvement in color over the square test samples of Example 1 (i.e. post-consumer derived polypropylene such as received). The L* values for the square test samples from Fraction 3 of Example 2 averaged 80.44, which was greatly improved compared to the L* values for the square test samples from Example 1, which were at the mean of 80.44. average of 39.76. The opacity of the square test swatches from fraction 3 of Example 2, which averaged 10.30% opacity (i.e. about 90% translucent), was also greatly improved when compared to the opacity values for the swatches. test squares from Example 1, which averaged about 100% opacity.

[0103] The concentration of heavy metal contamination for samples from fraction 3 of Example 2 was also greatly improved when compared to samples from Example 1. For example, the sodium concentration in samples from fraction 3 of Example 2 was averaged just 4,100 ppb, while the sodium concentration in the Example 1 samples averaged 136,000 ppb (a reduction of about 97%). The concentrations of all other elements measured were all reduced by more than 77 to 100% of the Example 2 fraction 3 samples, relative to the Example 1 samples.

[0104] The samples from fraction 3 of Example 2 showed ash content values that averaged about 03874% by weight, which was significantly lower than the ash content values for the samples from Example 1 , which averaged about 1.2117% by weight.

[0105] The samples from fraction 3 of Example 2 were considered to have an odor intensity of 0.5 on a 5-point scale (5 being the most intense), which was greatly improved compared to the odor intensity of the samples from Example 1, which had an odor intensity of 3.75. Although low in terms of odor intensity, samples from fraction 2 of Example 2 were reported to have a "plastic" odor similar to virgin polypropylene.

[0106] The samples from fraction 3 of Example 2 had average polyethylene content values of about 1.1% by weight, which was greatly improved when compared to the polyethylene content of the samples from Example 1, which was in the average of about 5.5% by weight.

Example 3

[0107] The mixed color flake sample of post-consumer derived recycled polypropylene, described in Example 1, was processed using the experimental apparatus shown in Figure 3A and Figure 3B and the following procedure: 6. 173 g of flake of mixed color were placed in a 7.57 liter Parr Instrument Company Model 4552M autoclave equipped with an overhead mechanical stirrer. 7. The autoclave was then filled completely with n-butane and equilibrated to an internal fluid temperature of 140°C and a hydrostatic pressure of 900 psig (6.21 MPa). 8. The material in the autoclave was then extracted using the experimental setup shown in Figure 3A and the following procedure: f. The system was shaken for 10 min at 140°C and 900 psig (6.21 MPa). g. After stirring, the system sat for 10 minutes at 140°C and 900 psig (6.21 MPa). H. One canister volume of n-butane was flushed through the autoclave into a sample collection bottle at 140°C and 900 psig (6.21 MPa). i. The above extraction procedure was repeated four more times. j. Samples collected for each extraction cycle were sequentially identified as "fraction 1" to "fraction 5". 9. The material remaining in the autoclave after extraction was then dissolved in n-butane using the experimental setup shown in Figure 3B and the following procedure: e. The system pressure was balanced to 1800 psig (12.41 MPa). f. The system was shaken for 10 min at 140°C and 1800 psig (12.41 MPa). g. Stirring was then stopped and the solution was allowed to stand for 60 min at 140°C and 1800 psig (6.21 MPa). H. After decantation, the solution was removed from the autoclave by displacement with pressurized butane (pre-equilibrated at 140°C and 1,800 psig). The solution exiting the autoclave through a dip tube was then passed through two electrically traced solid medium columns. Each column had an inside diameter (ID) of 0.68 in (1.73 cm) and a length of about 9.5 in (24.13 cm). In this example, both columns were empty and did not contain any solid media. The fluid stream leaving the bottom of the second pressure vessel was depressurized through an expansion valve into a sidearm Erlenmeyer flask. After the flow of fluid in the Erlenmeyer flask was depressurized, the solvent vapor was vented through the side arm port and all liquid/solids were collected as fractions in the flask. Each fraction contained about 30 g of material and was sequentially labeled starting with "Fraction 6". Fractions were collected until no further elution of material was observed in the flask. 10. After all samples were collected, the autoclave was equilibrated to atmospheric pressure and room temperature. All residual material in the autoclave was then collected as a sample residue.

[0108] The sample data of fraction 6 collected according to the procedure disclosed herein are summarized in Table 1.

[0109] The isolated solids in fraction 6 of this example were off-white to yellow in color. When the off-white to yellow solids from fraction 6 were compression molded into square test specimens, the specimens had a yellow appearance. A photograph of the square test sample is shown in Figure 4 as Example 3. As shown in Figure 4, the color and translucency of the Samples from Example 3 were improved over the samples from Example 1, but were not comparable to the virgin polypropylene shown in the Figure 4 as Example 4. Even without the solid media contact step, the L*a*b* values show that the square test samples from fraction 6 of Example 3 were improved in color compared to the samples of Example 1 (i.e., post-consumer derived polypropylene, as received). The L* values for the square test samples from Fraction 6 from Example 3 averaged 72.41, which was improved compared to the L* values for the square test samples from Example 1, which were on the average from 39.76. The opacity for the square test swatches from Fraction 6 from Example 3, which averaged 35.25% opacity, was also improved when compared to the opacity values for the square test swatches from Example 1, which were on average of about 100% opacity.

[0110] The concentration of heavy metal contamination for samples from fraction 6 of Example 3 was also greatly improved when compared to samples from Example 1. For example, the sodium concentration in samples from fraction 6 of Example 3 was averaged just 16,400 ppb, while the sodium concentration in the Example 1 samples averaged 136,000 ppb (a reduction of about 88%). The concentrations of all other elements measured were all reduced by more than 82 to 100% of the Example 3 fraction 6 samples relative to the Example 1 samples.

[0111] The samples from fraction 6 of Example 3 showed ash content values that averaged about 0.2292% by weight, which was significantly lower than the ash content values for the samples from Example 1, which averaged about 1.2117% by weight.

[0112] The samples from fraction 6 of Example 3 were considered to have an odor intensity of 0.5 on a 5-point scale (5 being the most intense), which was greatly improved compared to the odor intensity of the samples from Example 1, which had an odor intensity of 3.75. Although low in terms of odor intensity, samples from fraction 6 of Example 3 were reported to have a "plastic" odor similar to virgin polypropylene.

[0113] The samples from fraction 6 of Example 3 had average polyethylene content values of about 1.0% by weight, which was greatly improved when compared to the polyethylene content of the samples from Example 1, which was in the average of about 5.5% by weight.

Example 4 - Comparative samples of virgin polypropylene

[0114] Polypropylene Pro-fax 6331 (LyondellBasell Industries Holdings, BV) was used for all comparative samples of "virgin PP". Virgin PP pellets were processed into square test samples according to the method described in the present invention. L*a*b* values for samples made from virgin PP averaged 85.13 ± 0.18, -0.71 ± 0.01 and 2.27 ± 0.02, respectively. The square test samples had a mean opacity of 7.56 ± 0.21%. This example serves as a comparison to the amount of heavy metal contamination found in a representative sample of virgin polypropylene. The virgin polypropylene samples showed values of ash content with an average of about 0.3031% by weight. The virgin PP pellets had an odor intensity of 0.5 on a 5-point scale (5 being the most intense) and had an odor described as being similar to "plastic." No polyethylene was detected in the virgin propylene sample. Table 1. Color, contamination and odor removal of examples 1 to 4

[0115] Every document cited in the present invention, including any related cross-reference, patent or patent application, is hereby incorporated in full by reference unless expressly excluded or otherwise limited. Mention of any document is not an admission that it is prior art in relation to any invention shown or claimed in the present invention, nor that by itself or in any combination with any other reference or references, it teaches, suggests or describes such invention. . In addition, if there is a conflict between any meaning or definition of a term mentioned in this document and any meaning or definition of the same term in a document incorporated by reference, the meaning or definition given to that term in this document will take precedence.

[0116] While specific embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this disclosure.

Claims (32)

1. Method for purifying a recovered polypropylene, characterized in that it comprises: a. obtaining recovered polypropylene, said recovered polypropylene being selected from the group consisting of post-consumer polymers, post-industrial polymers and combinations thereof; B. bringing the recovered polypropylene at a temperature of 80 °C to 220 °C and a pressure of 150 psig (1.03 MPa) to 15,000 psig (103.42 MPa) in contact with a first fluid solvent having a boiling point standard less than 70 °C, where the polypropylene is essentially insoluble in the fluid solvent, to produce an extracted recovered polypropylene; w. dissolving the extracted recovered polypropylene in a solvent selected from the group consisting of a first fluid solvent, a second fluid solvent, and mixtures thereof, at a temperature of 90 °C to 220 °C and a pressure of 350 psig (2.41 MPa) to 20,000 psig (137.90 MPa) to produce a first solution comprising polypropylene and suspended contaminants; d. decanting the first solution comprising polypropylene and suspended contaminants at a temperature of 90°C to 220°C and a pressure of 350 psig (2.41 MPa) to 20,000 psig (137.90 MPa) to produce a second solution comprising polypropylene and remaining contaminants; It is. purifying said second solution at a temperature of 90 °C to 220 °C and a pressure of 350 psig (2.41 MPa) to 20,000 psig (137.90 MPa), placing said second solution in contact with the solid medium to produce a third solution comprising a purer polypropylene, wherein the solid medium is selected from the group consisting of inorganic substances, carbon-based substances and mixtures thereof, and recycled glass; the inorganic substances being selected from the group consisting of silicon oxides, aluminum oxides, iron oxides, aluminum silicates, magnesium silicates, amorphous volcanic glasses, silica, silica gel, diatomite, sand, quartz, alumina recovered glass , perlite, fuller's earth, bentonite and mixtures thereof; and the carbon-based substances being selected from the group consisting of anthracitic carbon, carbon black, coke, activated carbon, cellulose and mixtures thereof;; and f. separating said purest polypropylene from said third solution; wherein said second fluid solvent has the same chemical composition or a different chemical composition as the first fluid solvent. 2. Method according to claim 1, characterized in that said polypropylene is separated from said third solution at a temperature of 0 °C to 220 °C and a pressure of 0 psig (0 MPa) to 2,000 psig (13.79 MPa). 3. Method, according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in mass percentage of at least 0.5%. 4. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of at least 1%. 5. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of at least 2%. 6. Method, according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of at least 3%. 7. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of at least 4%. 8. Method, according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of at least 5%. 9. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of up to 20%. 10. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of up to 18%. 11. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of up to 16%. 12. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of up to 14%. 13. Method according to claim 1, characterized in that said recovered polypropylene is dissolved in the fluid solvent, or fluid solvent mixture, at a concentration in percentage by mass of up to 12%. 14. Method according to claim 1, characterized in that said recovered polypropylene is a polypropylene derived from post-consumer recycling. 15. Method according to claim 1, characterized in that said recovered polypropylene is a homopolymer of polypropylene or a copolymer mainly of polypropylene. 16. Method according to claim 1, characterized in that said fluid solvent has a standard boiling point less than 0 °C and greater than -45 °C and a standard enthalpy change of vaporization less than +25 kJ/mol. 17. Method according to claim 1, characterized in that said fluid solvent is selected from the group consisting of olefinic hydrocarbons, aliphatic hydrocarbons and mixtures thereof. 18. Method according to claim 17, characterized in that said aliphatic hydrocarbon is selected from the group consisting of C1-C6 aliphatic hydrocarbons and mixtures thereof. 19. Method according to claim 17, characterized in that said aliphatic hydrocarbons and mixtures thereof mainly comprise C4 aliphatic hydrocarbons. 20. Method according to claim 17, characterized in that said fluid solvent essentially consists of C4 liquefied petroleum gas. 21. Method according to claim 17, characterized in that said fluid solvent is n-butane, butane isomers or mixtures thereof. 22. Method, according to claim 1, characterized in that said temperature in the steps of contact, dissolution, decantation and purification is 110 °C to 170 °C. 23. Method, according to claim 1, characterized in that said pressure in the contact stage is 1,100 psig (7.58 MPa) to 2,100 psig (14.48 MPa). 24. Method, according to claim 1, characterized by the fact that said pressure in the contact stage is less than 1,100 psig (7.58 MPa). 25. Method, according to claim 1, characterized by the fact that said pressure in the dissolution, decantation and purification steps is greater than 1,100 psig (7.58 MPa). 26. Method, according to claim 1, characterized by the fact that said pressure in the dissolution, decantation and purification steps is greater than 2,100 psig (14.48 MPa). 27. Method according to claim 1, characterized in that said solid medium is selected from the group consisting of inorganic substances, carbon-based substances and mixtures thereof. 28. Method, according to claim 27, characterized in that said inorganic substances are selected from the group consisting of silicon oxides, aluminum oxides, iron oxides, aluminum silicates, amorphous volcanic glasses and mixtures thereof . 29. Method, according to claim 27, characterized in that said inorganic substances are selected from the group consisting of silica gel, diatomite, sand, quartz, alumina, perlite, Fuller's earth, bentonite and mixtures thereof . 30. Method, according to claim 27, characterized in that said carbon-based substances are selected from the group consisting of anthracite coal, carbon black, coke, activated carbon, cellulose and mixtures thereof. 31. Method, according to claim 1, characterized in that said contact of the polypropylene solution with said solid medium is made in a packed bed of said solid medium. 32. Method according to claim 31, characterized in that said packed bed has a length greater than 20 cm.