RU2721317C1 - Purification method of regenerated polypropylene - Google Patents

Abstract

FIELD: chemistry.SUBSTANCE: invention relates to a method of cleaning contaminated polymers using a solvent under pressure and solid media. Method of purifying regenerated polypropylene involves obtaining regenerated polypropylene and bringing it into contact with a liquid solvent at high temperature and pressure to obtain extracted regenerated polypropylene. Extracted regenerated polypropylene is dissolved in a solvent at high temperature and pressure to obtain a solution containing polypropylene and suspended contaminants. After settling, the solution is cleaned at high temperature and pressure by bringing into contact with the solid medium to obtain a solution containing purer polypropylene. Then purer polypropylene is separated from solution.EFFECT: obtaining purified polypropylene substantially free from colour and odour.15 cl, 5 dwg, 1 tbl, 4 ex

Description

The present invention essentially relates to a method for purifying contaminated polymers using a solvent under pressure and solid media. In particular, the present invention relates to a method for cleaning recycled polymers, for example plastics, disposed of after domestic use and industrial use, to produce a colorless or transparent odorless polymer close to the original polymer. It is especially effective for cleaning polypropylene.

BACKGROUND OF THE INVENTION

Polymers, in particular synthetic plastics, are widely used in everyday life due to their relatively low cost and optimal combination of material properties. Synthetic plastics are used in a wide variety of applications, such as packaging materials, automotive components, medical devices and consumer products. To meet the high demand for these applications, hundreds of billions of pounds of synthetic plastics are produced annually in the world. The vast majority of synthetic plastics are made from gradually depleted fossil raw materials, such as oil and natural gas. In addition, the production of synthetic plastics from fossil raw materials leads to the formation of CO ₂ as a by-product.

As a result of the widespread use of synthetic plastics, millions of tons of plastic waste accumulate annually. Although most plastic waste is disposed of as part of municipal solid waste management programs, a large part of the plastic waste enters the environment in the form of garbage that damages the environment and is potentially harmful to ecosystems. Plastics waste is often washed into river systems and ultimately into the sea.

Plastics processing has become one of the solutions to reduce the problems associated with the widespread use of plastics. The recovery and reuse of plastics allows redirecting waste from landfills and reduces the need for source plastics produced from fossil resources, which consequently reduces greenhouse gas emissions. In developed regions, such as the United States and the European Union, plastics processing levels are increasing due to greater awareness among consumers, traders and industry. Most of the recyclable materials, including plastics, are combined into a single stream, which is collected and processed at specialized material recycling facilities (MRF). MRF sorts, rinses and packs materials for resale. Plastics can be sorted by individual materials, such as high density polyethylene (HDPE) or polyethylene terephthalate (PET), or by mixed flows of other common plastics, such as polypropylene (PP), low density polyethylene (LDPE), polyvinyl chloride (PVC), polystyrene ( PS), polycarbonate (PC) and polyamides (PA). Separate or mixed streams can then undergo further sorting, washing and re-processing into granules suitable for reuse in plastic processing, for example for blow molding and injection molding.

Despite the fact that recycled plastics are predominantly sorted by uniform flows and washed with aqueous and / or alkaline solutions, the final processed granules often retain a high level of contamination with undesirable waste impurities, such as residues of decomposed food products and residual components of aromatic substances. In addition, the pellets of recycled plastics, with the exception of recycled beverage containers, are dark in color due to the mixture of dyes and pigments widely used for dyeing plastic products. Although coloring and contamination are not important for some applications (for example, black plastic containers for paints and non-finishing automotive components), for most applications colorless granules are required. The need for high-quality “close to starting” recycled resins is especially important for applications in which the polymer is in contact with food or drugs, for example for packaging food. In addition to contaminants from impurities and a mixture of coloring substances, many processed resinous products are often heterogeneous in their chemical composition and may contain a significant amount of polymer contaminants, for example, contamination of polyethylene (PE) with secondary PP and vice versa.

Mechanical recycling, also known as recycling, is the process of converting recycled plastic waste into a reusable form for subsequent production. A more detailed overview of mechanical processing and other recovery processes is given in S.M. Al-Salem, P. Lettieri, J. Baeyens, "Recycling and recovery routes of plastic solid waste (PSW): A review", Waste Management, Volume 29, Issue 10, October 2009, Pages 2625-2643, ISSN 0956-053X . Although advances in mechanical regeneration technologies have made it possible to improve the quality of processed polymers to some extent, there are fundamental limitations to mechanical cleaning approaches, such as the physical capture of pigments in a polymer matrix. Thus, even with all the improvements in mechanical processing technologies, the dark color and high levels of chemical pollution in currently available recycled plastics prevent the wider use of recycled resins in the plastics industry.

To overcome the fundamental limitations of mechanical processing, many methods have been developed to purify contaminated polymers using chemical approaches or chemical processing. Most of these methods use solvents to remove impurities and purify polymers. The use of solvents allows extraction of impurities and dissolving polymers, which additionally makes it possible to use alternative separation technologies.

For example, US Pat. No. 7,935,736 describes a method for processing a polyester from polyester-containing waste 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.

As another example, US Pat. No. 6,555,588 describes a method for producing a polypropylene mixture from a mixture of plastics containing other polymers. The '588 patent describes the extraction of contaminants from a polymer at a temperature below the temperature of dissolution of the polymer in a selected solvent, for example, hexane, over a specific treatment period. The '588 patent further describes an increase in the temperature of the solvent (or second solvent) to dissolve the polymer before filtering. The '588 patent further describes the use of shear or flow to precipitate polypropylene from solution. The polypropylene mixture described in the '588 patent contained contaminants of polyethylene in an amount of up to 5.6 mass. %

In another example, the application for European patent No. 849,312 (translated from German into English) describes a method for producing purified polyolefins from a polyolefin-containing mixture of plastics or polyolefin-containing wastes. The '312 patent application describes the extraction of polyolefin mixtures or wastes with a hydrocarbon fraction of gasoline or diesel fuel with a boiling point above 90 ° C at temperatures from 90 ° C to the boiling point of the hydrocarbon solvent. The '312 patent application further describes the contact of a hot solution of polyolefins with bleaching clay and / or activated carbon to remove extraneous components from the solution. The '312 patent also further describes cooling the solution to temperatures below 70 ° C to crystallize the polyolefin and then remove the solvent by heating the polyolefin above the melting point of the polyolefin, or evaporating the solvent in vacuo, or by gas purging through the polyolefin precipitate and / or solvent extraction with alcohol or ketone, which is boiled at a temperature below the melting point of the polyolefin.

In another example, US Pat. No. 5,198,471 describes a method for separating polymers from a physically bonded solid mixture (e.g., plastic waste) containing multiple polymers using a solvent at a first lower temperature to form a first single-phase solution and residues of the solid component. The '471 patent further describes heating the solvent to higher temperatures to dissolve additional polymers that were not solubilized at the first lower temperature. The '471 patent describes filtering insoluble polymer components.

In another example, US Pat. No. 5,233,021 describes a method for extracting pure polymer components from a multicomponent structure (for example, carpet waste) by dissolving each component at an appropriate temperature and pressure in a supercritical fluid, followed by a change in temperature and / or pressure for sequential extraction of certain components. However, as in the '471 patent, the' 021 patent only describes filtering of undissolved components.

As another example, US Pat. No. 5,739,270 describes a method and apparatus for continuously separating a polymer component of a plastic from contaminants and other components of a plastic using a co-solvent and a working fluid. The co-solvent at least partially dissolves the polymer, and the second liquid (which is in a liquid, critical or supercritical state) solubilizes the polymer components and precipitates some of the dissolved polymers from the co-solvent. The '270 patent further describes the step of filtering a mixture of a thermoplastic and a co-solvent (in the presence or absence of a working fluid) to remove contaminants such as glass particles.

Known methods for purifying contaminated polymers using solvents, which are described above, do not allow to obtain a "similar to the original" polymer. In previously proposed methods, co-dissolution often occurs, and therefore cross-contamination with other polymers. When using an adsorbent, a filtration and / or centrifugation step is often used to remove the adsorbent from the solution. In addition, to obtain a polymer that does not contain a residual solvent, separation processes are used to remove the solvent, for example, heating, evaporation under vacuum and / or precipitation using a chemical precipitator.

Accordingly, for the purification of contaminated polymers, there is still a need for a more advanced solvent-based process that uses a solvent that is easily and economically removed from the polymer, and this method is relatively simple in terms of the number of separate operations, allows to obtain a polymer without a significant amount of mutually polluting polymers, provides a polymer that is essentially colorless, and makes it possible to recover a polymer that is substantially odorless.

SUMMARY OF THE INVENTION

A method for purifying regenerated polypropylene is proposed. The method includes:

a. Obtaining a regenerated polypropylene selected from the group consisting of polymers after domestic use, polymers after industrial use, and combinations thereof;

b. Bringing the regenerated polypropylene into contact at a temperature of from about 80 ° C to about 220 ° C and at a pressure of from about 150 psi inch (1.03 MPa) to about 15,000 psi an inch (103.42 MPa) with a first liquid solvent with a standard boiling point of less than about 70 ° C, to obtain extracted regenerated polypropylene;

c. Dissolving the extracted regenerated polypropylene in a solvent selected from the group consisting of a first liquid solvent, a second liquid solvent, and mixtures thereof, at a temperature of from about 90 ° C. to about 220 ° C. and a pressure of about 350 psig. inch (2.41 MPa) to about 20,000 psi inch (137.90 MPa), to obtain a first solution containing polypropylene and suspended contaminants;

d. Settling the first solution containing polypropylene and suspended contaminants at a temperature of from about 90 ° C to about 220 ° C and under a pressure of about 350 psi inch (2.41 MPa) to about 20,000 psi inch (137.90 MPa) to obtain a second solution containing polypropylene and the remaining contaminants;

e. Purification of the second solution at a temperature of from about 90 ° C to about 220 ° C and at a pressure of about 350 psig. inch (2.41 MPa) to about 20,000 psi inch (137.90 MPa) by contacting the second solution with a solid medium, to obtain a third solution containing more pure polypropylene; and

f. Separating cleaner polypropylene from a third solution.

The second liquid solvent may have either the same chemical composition as the first liquid solvent, or a different chemical composition.

In one embodiment, the polypropylene is separated from the third solution at a temperature of from about 0 ° C to about 220 ° C and a pressure of from about 0 psi. inch hut (0 MPa) to about 2000 psi. inch hut (13.79 MPa). In another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 0.5%. In yet another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 1%. In one embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 2%.

In one embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 3%. In another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 4%. In yet another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percent concentration of at least 5%.

In one embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percent concentration of up to 20%. In another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of up to 18%. In yet another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of up to 16%. In one embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percent concentration of up to 14%. In another embodiment, the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of up to 12%.

In one embodiment, the regenerated polypropylene is a polypropylene obtained from regeneration after domestic use. In another embodiment, the regenerated polypropylene is a homopolymer of polypropylene or mainly a copolymer of polypropylene. In yet another embodiment, the liquid solvent has a standard boiling point of less than about 0 ° C and more than about -45 ° C, and a standard change in enthalpy during evaporation of less than about +25 kJ / mol.

In one embodiment, the liquid solvent is selected from the group consisting of olefinic hydrocarbons, aliphatic hydrocarbons, and mixtures thereof. In one embodiment, the aliphatic hydrocarbon is selected from the group consisting of C ₁ -C ₆ aliphatic hydrocarbons and mixtures thereof. In another embodiment, aliphatic hydrocarbons and mixtures thereof mainly consist of C ₄ aliphatic hydrocarbons.

In one embodiment, the liquid solvent consists essentially of C ₄ liquefied petroleum gas. In one embodiment, the liquid solvent is n-butane, butane isomers, or mixtures thereof. In another embodiment, the temperature in the steps of contacting, dissolving, settling and cleaning is from about 110 ° C to about 170 ° C.

In one embodiment, the pressure in the contacting step is from about 1100 psi. inch (7.58 MPa) to about 2100 psi inch (14.48 MPa). In another embodiment, the pressure in the contacting step is less than about 1100 psi. inch (7.58 MPa). In another embodiment, the pressure in the dissolution, sedimentation and purification steps is greater than about 1,100 psi. inch (7.58 MPa). In one embodiment, the pressure in the dissolution, sedimentation, and purification steps is greater than about 2,100 psi. inch (14.48 MPa).

In one embodiment, the solid medium is selected from the group consisting of inorganic compounds, carbon-containing compounds, and mixtures thereof. In another embodiment, the inorganic compounds are selected from the group consisting of silicon oxides, aluminum oxides, iron oxides, aluminosilicates, amorphous volcanic glasses, and mixtures thereof. In yet another embodiment, the inorganic compounds are selected from the group consisting of silica gel, diatomite, sand, quartz, alumina, perlite, fuller earth, bentonite, and mixtures thereof.

In one embodiment, the carbon-containing compounds are selected from the group consisting of anthracite coal, carbon black, coke, activated carbon, cellulose, and mixtures thereof. In another embodiment, the contacting of the solution of polypropylene with a solid medium is carried out in a compacted layer of the specified solid medium. In one embodiment, the length of the densified layer is more than 20 cm.

Additional features of the invention will be apparent to those skilled in the art after reviewing the following detailed description in conjunction with the examples.

BRIEF DESCRIPTION OF THE DRAWINGS

In FIG. 1 is a flowchart showing the main steps of one embodiment of the present invention.

In FIG. Figure 2 shows a calibration curve for calculating the polyethylene content in polypropylene using enthalpy values from measurements using differential scanning calorimetry (DSC).

In FIG. 3 shows a diagram of the experimental setup used in the extraction step of Examples 2 and 3.

In FIG. 3B is a diagram of an experimental setup used in the dissolution and precipitation steps of Examples 2 and 3.

In FIG. 4 is a photograph of illustrative examples.

DETAILED DESCRIPTION OF THE INVENTION

I. Definitions

As used herein, the term “regenerated polymer” refers to a polymer used for pre-existing purposes and then reconstituted for further processing.

As used herein, the term “regenerated polypropylene” (RPP) refers to polypropylene used for pre-existing purposes and then restored for further processing.

The term "after domestic use" in the context of this document refers to the source of the material that comes after the end user has used the material in a consumer product or product.

The term “post-consumer regeneration” (PCR) as used herein refers to material obtained after the consumer has used and disposed of the material by sending it to the waste stream.

The term "after industrial use" in the context of this document refers to the source of material that is formed in the production process of a product or product.

As used herein, the term “liquid solvent” refers to a substance that can exist in a liquid state under given conditions of temperature and pressure. In some embodiments, the liquid solvent may be a predominantly uniform chemical composition of one molecule or isomer, while in other embodiments, the liquid solvent may be a mixture of several different molecular compositions or isomers. In addition, in some embodiments of the present invention, the term "liquid solvent" may also apply to substances that are at a point near, or above the critical temperature and critical pressure (critical point) of such a substance. Those skilled in the art are well aware that substances above the critical point of such a substance are known as “supercritical fluids” that do not have the characteristic physical properties of a fluid (for example, density).

As used herein, the term “dissolved” means at least partially incorporating a solute (polymer or non-polymer) into the solvent at the molecular level. In addition, the thermodynamic stability of a solution with a dissolved substance / solvent can be described by the following equation 1:

Equation 1

where ΔG _mix denotes the change in Gibbs free energy when mixing the dissolved substance with the solvent, ΔH _mix denotes the change in enthalpy when mixing, T is the absolute temperature, and ΔS _mix denotes entropy when mixing. To maintain a stable solution of the solute in the solvent, the Gibbs free energy must be negative and at a minimum. Thus, in the present invention, any combination of solute and solvent can be used that minimizes the negative Gibbs free energy at appropriate temperature and pressure readings.

The term “standard boiling point” as used herein refers to the boiling point at an absolute pressure of exactly 100 kPa (1 bar, 14.5 absolute psi, 0.9869 atm), in accordance with the rules of the International Union of Theoretical and Applied Chemistry (IUPAC).

As used herein, the term “standard change in enthalpy by evaporation” refers to the change in enthalpy that is required to convert a certain amount of a substance from a liquid to a gaseous state at a standard boiling point of the substance.

As used herein, the term “polypropylene solution” refers to a solution of polypropylene dissolved in a solvent. The polypropylene solution may contain an undissolved substance, and therefore, the polypropylene solution can also be a "suspension" of undissolved substance suspended in a solution of polypropylene dissolved in a solvent.

As used herein, the terms “sedimentation” and “sedimentation” 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 particles.

As used herein, the term “suspended contaminants” refers to extraneous or undesirable components present in the bulk of a heterogeneous mixture.

As used herein, the term “solid medium” refers to a substance that, under the conditions of use, exists in a solid state. The solid medium may be crystalline, semi-crystalline or amorphous. The solid medium can be granular and can be supplied in granules of various shapes (for example, spheres, cylinders, balls, etc.). In the case of a granular solid medium, the particle size and particle size distribution of the solid medium can be determined by the mesh size of the sieve used to sort the granular medium. An example of standard mesh size designations can be found in ASTM E11, entitled Standard Specification for Metal-Woven Test Screen Sieve and Test Screen. The solid medium may also be a non-woven fiber mat or woven fabric.

As used herein, the term “cleaner polypropylene solution” refers to a polypropylene solution with less contaminants than the same polypropylene solution prior to the purification step.

The term "extraction", in the context of this document, refers to a method for transferring a solute from a liquid phase (or solid matrix) across a phase boundary to a separate immiscible liquid phase. The driving force (forces) for extraction is described in the theory of separation.

The term "extracted", in the context of this document, refers to a material having a lower amount of solute compared with the same material before the extraction stage. The term "extracted regenerated polypropylene", as used herein, refers to regenerated polypropylene having a lower amount of solute than the same regenerated polypropylene before the extraction step.

As used herein, the term “similar to the starting material” means substantially free of contaminants, free of pigments, odorless, uniform and similar in properties to the starting polymers.

As used herein, the term “substantially polypropylene copolymer” refers to a copolymer containing more than 70 mol% of repeating propylene units.

In this document, any reference to international pressure units (e.g. MPa) refers to gauge pressure.

II. The method of purification of contaminated polypropylene

It was unexpectedly discovered that some liquid solvents, which in a preferred embodiment exhibit temperature and pressure-dependent solubility of the polymers, when used in a relatively simple method, can be used to purify contaminated polymers, in particular reduced or recycled polymers, to almost similar initial quality. This method, an example of which is shown in FIG. 1 includes 1) obtaining regenerated polypropylene (stage a in FIG. 1), followed by 2) extraction of polypropylene with a liquid solvent at an extraction temperature (T _E ) and at an extraction pressure (P _E ) (stage b in FIG. 1), s followed by 3) dissolving the polypropylene in a liquid solvent at a dissolution temperature (T _D ) and at a dissolution pressure (P _D ) (step c in FIG. 1), followed by 4) settling the polypropylene solution at a dissolution temperature (T _D ) and a dissolution pressure ( P _D) (step d in FIG. 1), followed by 5) driving the extensible contact ora dissolved solid polypropylene with dissolution medium at a temperature (T _D) and a pressure of dissolution (P _D) (step e in FIG. 1), followed by separation of the polypropylene from the solvent liquid (step f in FIG. 1).

In one embodiment of the present invention, purified polypropylene, the source of which may be waste streams after domestic use, is substantially free of contaminants, pigments, odorless, uniform and similar in properties to the starting polypropylene. In addition, in a preferred embodiment, the physical properties of the liquid solvent of the present invention can provide more energy-efficient methods for separating the liquid solvent from purified polypropylene.

Regenerated Polypropylene

In one embodiment of the present invention, a method for purifying regenerated polypropylene comprises the preparation of regenerated polypropylene. For the purposes of the present invention, the source of regenerated polypropylene is waste streams after domestic use, after industrial use, after commercial use and / or other specific waste streams. For example, polypropylene waste after domestic use can be obtained from recycled street waste streams, where end consumers place used polymers from packaging and other products in designated containers for collection by garbage trucks or recycling companies. After household use, polymer waste can also be obtained from packaging retailers in stores, with consumers bringing the polymer waste to the store and placing the polymer waste in specially designated collection containers. An example of polymer waste after industrial use can be polymer waste that is generated during the production or shipment of a product or product and which is collected by the manufacturer as a material not to be used (for example, edging, non-conforming material, waste after pretreatment). An example of spent polymers from a specific waste stream may be the waste of polymers obtained from the processing of electronic waste, also called electronic scrap. Another example of polymer wastes from a specific waste stream may be polymer wastes obtained after the disposal of automobiles. Another example of polymer wastes from a specific waste stream may be polymer wastes obtained after processing used carpet and textiles.

For the purposes of the present invention, regenerated polypropylene is a homogeneous single polymer composition or a mixture of several different polypropylene compositions. Non-limiting examples of polypropylene compositions include propylene homopolymers, propylene-ethylene copolymers (including “impact resistant” and “statistical clarified” copolymers), propylene-alpha olefin copolymers, polypropylene rubbers and other soluble polypropylene compositions that may be apparent to those skilled in the art. in this area.

Regenerated polypropylene may also contain various pigments, dyes, processing aids, stabilizing additives, fillers and other processing aids that are introduced into the polymer during polymerization or the transformation of the starting polymer into the final shape of the product. Non-limiting examples of pigments are organic pigments, such as copper phthalocyanine, inorganic pigments, such as titanium dioxide, and other pigments that 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 friction-reducing substances, 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 fillers are calcium carbonate, talc and fiberglass.

Solvent

The liquid solvent of the present invention has a standard boiling point of less than about 70 ° C. The increase in pressure allows the solvent with standard boiling points to be kept below the operating temperature range of the present invention in a state in which slight evaporation of the solvent or complete absence of evaporation is observed. In one embodiment, the liquid solvent with a standard boiling point of 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 liquid solvents with standard boiling points less than about 70 ° C are carbon dioxide, acetone, methanol, dimethyl ether, diethyl ether, ethyl methyl 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-hexene, isohexane isomers and other substances that may be apparent to those skilled in the art.

The choice of the liquid solvent used will determine the temperature and pressure ranges used to carry out the steps of the present invention. The following is a link to a review of polymer phase behavior in solvents similar to those described in the present invention: McHugh et al. (1999) Chem. Rev. 99: 565-602.

Extraction

In one embodiment of the present invention, a method for purifying polypropylene comprises contacting the regenerated polypropylene with a liquid solvent at temperatures and pressures such that the polymer is substantially insoluble in the liquid solvent. Without reference to any theory, applicants believe that temperature and pressure-dependent solubility can be controlled in such a way as to prevent complete solubilization of the polymer with a liquid solvent, while the liquid solvent can diffuse into the polymer to extract any extractable contaminants from it. Extracted contaminants may include residual processing aids added to the polymer, residual components of the product that came into contact with the polymer, such as perfumes and flavors, dyes, and any other extracted material that could have been specially added or accidentally incorporated into the polymer, for example, the process of waste collection and their subsequent accumulation together with other waste materials.

In one embodiment, controlled extraction may be carried out by fixing the temperature in the polymer / liquid solvent system, followed by lowering the pressure below the level or pressure range at which the polymer dissolves in the liquid solvent. In another embodiment, controlled extraction is carried out by fixing the pressure in the polymer / solvent system, followed by lowering the temperature below a level or temperature range at which the polymer is dissolved in a liquid solvent. For the extraction of the polymer with a liquid solvent at a controlled temperature and pressure, a suitable high-pressure apparatus is used, which can be made in such a way as to enable continuous extraction of the polymer with a liquid solvent. In one embodiment of the present invention, the high-pressure apparatus may be an extraction column for continuous extraction from a liquid phase, a molten polymer being supplied from one end of such an extraction column, and a liquid solvent being supplied from the same or opposite end of the extraction column. In another embodiment, the process involves the removal of liquid containing extracted contaminants. In another embodiment, the liquid containing the extracted contaminants is cleaned, regenerated, and returned for use in the extraction step or other process step. In one embodiment of the present invention, the extraction can be carried out in a batch manner in which the regenerated polypropylene is fixed in a high-pressure apparatus and a liquid solvent is continuously fed through the phase of the fixed polymer. The time of extraction or the amount of liquid solvent used will depend on the desired purity of the final cleaner polymer and the amount of contaminants to be extracted in the initial regenerated polypropylene. In another embodiment, the liquid containing the extracted contaminants is contacted with the solid medium in a separate step, as described below in the "Cleaning" section. In another embodiment, the method of purification of regenerated polypropylene comprises contacting the regenerated polypropylene with a liquid solvent at such temperature and pressure that the polymer is in a molten and liquid state. In another embodiment, the regenerated polypropylene is contacted with a liquid solvent at such temperature and pressure that the polymer is in a solid state.

In one embodiment, the method of purifying regenerated polypropylene involves contacting the polypropylene with a liquid solvent at such temperature and pressure that the polypropylene remains substantially undissolved. In another embodiment, a method for purifying regenerated polypropylene comprises contacting the polypropylene with n-butane at a temperature of from about 80 ° C to about 220 ° C. In another embodiment, the method of purification of regenerated polypropylene comprises contacting the polypropylene with n-butane at a temperature of from about 100 ° C to about 200 ° C. In another embodiment, the method of purification of regenerated polypropylene comprises contacting the polypropylene with n-butane at a temperature of from about 130 ° C to about 180 ° C. In another embodiment, a method of purifying regenerated polypropylene involves contacting the polypropylene with n-butane at a pressure of about 150 psi. inch (1.03 MPa) to about 3,000 psi inch (20.68 MPa). In another embodiment, a method of purifying regenerated polypropylene involves contacting the polypropylene with n-butane at a pressure of about 1000 psi. inch (6.89 MPa) to about 2750 psi inch (18.96 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting the polypropylene with n-butane at a pressure of about 1,500 psi. inch (10.34 MPa) to about 2,500 psi inch (17.24 MPa).

In another embodiment, a method for purifying regenerated polypropylene comprises contacting the polypropylene with propane at a temperature of from about 80 ° C to about 220 ° C. In another embodiment, the method of purification of regenerated polypropylene comprises contacting the polypropylene with propane at a temperature of from about 100 ° C to about 200 ° C. In another embodiment, the method of purification of regenerated polypropylene comprises contacting the polypropylene with propane at a temperature of from about 130 ° C to about 180 ° C. In another embodiment, a method for purifying regenerated polypropylene involves contacting the polypropylene with propane at a pressure of about 200 psi. inch (1.38 MPa) to about 8,000 psi inch (55.16 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting the polypropylene with propane at a pressure of about 1000 psi. inch (6.89 MPa) to about 6,000 psi inch (41.37 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting the polypropylene with propane at a pressure of about 2000 psi. inch (13.79 MPa) to about 4,000 psi inch (27.58 MPa).

Dissolution

In one embodiment of the present invention, a method for purifying regenerated polypropylene comprises dissolving the regenerated polypropylene in a liquid solvent at such temperature and pressure that the polymer dissolves in the liquid solvent. Without being bound by any theory, applicants believe that temperature and pressure can be controlled in such a way as to provide thermodynamically favorable dissolution of the regenerated polymer in a liquid solvent. In addition, temperature and pressure can be controlled in such a way as to ensure the dissolution of a particular polymer or mixture of polymers, preventing the dissolution of other polymers or mixtures of polymers. Such controlled dissolution allows the separation of polymers from polymer blends.

In one embodiment of the present invention, a method for purifying polymers comprises dissolving a contaminated regenerated polypropylene in a solvent which does not dissolve contaminants under the same temperature and pressure conditions. Contaminants may include pigments, fillers, dirt, and other polymers. Such contaminants are released from the regenerated polypropylene upon dissolution, and then removed from the polymer solution in the subsequent separation stage of the solid and liquid phases.

In one embodiment, a method for purifying regenerated polypropylene comprises dissolving the polypropylene in a liquid solvent at temperatures and pressures such that the polypropylene dissolves in the liquid solvent. In another embodiment, a method for purifying regenerated polypropylene comprises 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 regenerated polypropylene comprises 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 regenerated polypropylene involves 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 regenerated polypropylene involves dissolving the polypropylene with n-butane at a pressure of about 350 psi. inch (2.41 MPa) to about 4,000 psi inch (27.57 MPa). In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene with n-butane at a pressure of about 1000 psi. inch (6.89 MPa) to about 3,500 psi inch (24.13 MPa). In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene with n-butane at a pressure of about 2000 psi. inch (13.79 MPa) to about 3,000 psi inch (20.68 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises dissolving the polypropylene in n-butane at a weight percent concentration of at least 0.5%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 1%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 2%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 3%. In another embodiment, polypropylene is dissolved at a weight percent concentration of at least 4%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 5%. In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in n-butane at a weight percent concentration of up to 20%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 18%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 16%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 14%. In another embodiment, polypropylene is dissolved at a weight percent concentration of up to 12%.

In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a temperature of from about 90 ° C to about 220 ° C. In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a temperature of from about 100 ° C to about 200 ° C. In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a temperature of from about 130 ° C to about 180 ° C. In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a pressure of about 2000 psi. inch (13.79 MPa) to about 8,000 psi inch (55.16 MPa). In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a pressure of about 3,000 psi. inch (20.68 MPa) to about 6,000 psi inch (41.37 MPa). In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a pressure of about 3,500 psi. inch (24.13 MPa) to about 5,000 psi inch (34.47 MPa). In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a weight percent concentration of at least 0.5%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 1%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 2%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 3%. In another embodiment, polypropylene is dissolved at a weight percent concentration of at least 4%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 5%. In another embodiment, a method for purifying regenerated polypropylene involves dissolving the polypropylene in propane at a mass percentage of up to 20%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 18%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 16%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 14%. In another embodiment, polypropylene is dissolved at a weight percent concentration of up to 12%.

Precipitation

In one embodiment of the present invention, a method for purifying regenerated polypropylene involves separating undissolved contaminants from the polypropylene solution by a precipitation step (also known as settling) at a temperature and pressure at which the polymer remains dissolved in the liquid solvent. In one embodiment, the deposition step causes the undissolved contaminants to experience a force that uniformly moves the undissolved contaminants in the direction of the force. A commonly used clamping force is a gravitational force, but may also be a centrifugal, centripetal, or some other force. The amount of applied force and the duration of the deposition time will depend on several parameters, including, without limitation: particle size of the pollutant particles, density of the pollutant particles, density of the fluid or solution, and viscosity of the fluid or solution. The following equation (equation 2) is the ratio between the above parameters and the deposition rate, which is a measure of the deposition rate of contaminants:

Equation 2

where ν is the deposition rate, ρ _p is the density of the polluting particle, ρ _ƒ is the density of the fluid or solution, g is the acceleration in eliminating the applied force (usually by gravity), r is the radius of the polluting particle, and η is dynamic viscosity of a fluid or solution. Some of the key parameters that determine the viscosity of a solution are: the chemical composition of the liquid solvent, the molecular weight of the polymer dissolved in the liquid solvent, the concentration of the dissolved polymer in the liquid solvent, the temperature of the liquid solvent solution, and the pressure of the liquid solvent solution.

In one embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / liquid solvent solution at a temperature and pressure at which the polypropylene remains dissolved in the liquid solvent. In another embodiment, a method for purifying regenerated polypropylene involves the deposition of 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 regenerated polypropylene comprises depositing contaminants from a polypropylene / n-butane solution at a temperature of from about 100 ° C to about 200 ° C. In another embodiment, the method of purification of regenerated polypropylene involves the deposition of contaminants from a solution of polypropylene / n-butane at a temperature of from about 130 ° C to about 180 ° C. In another embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / n-butane solution at a pressure of about 350 psi. inch (2.41 MPa) to about 4,000 psi inch (27.57 MPa). In another embodiment, a method for purifying regenerated polypropylene involves the deposition of contaminants from a polypropylene / n-butane solution at a pressure of about 1000 psi. inch (6.89 MPa) to about 3,500 psi inch (24.13 MPa). In another embodiment, a method for purifying regenerated polypropylene involves depositing contaminants from a polypropylene / n-butane solution at a pressure of about 2000 psi. inch (13.79 MPa) to about 3,000 psi inch (20.68 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / n-butane solution, the polypropylene being dissolved at a mass percentage of at least 0.5%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 1%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 2%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 3%. In another embodiment, polypropylene is dissolved at a weight percent concentration of at least 4%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 5%. In another embodiment, a method for purifying regenerated polypropylene involves the deposition of contaminants from a polypropylene / n-butane solution, the polypropylene being dissolved at a mass percentage of up to 20%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 18%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 16%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 14%. In another embodiment, polypropylene is dissolved at a weight percent concentration of up to 12%.

In another embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / propane solution at a temperature of from about 90 ° C to about 220 ° C. In another embodiment, a method for purifying regenerated polypropylene comprises depositing 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 regenerated polypropylene comprises depositing 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 regenerated polypropylene comprises depositing contaminants from a polypropylene / propane solution at a pressure of about 2000 psi. inch (13.79 MPa) to about 8,000 psi inch (55.16 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / propane solution at a pressure of about 3000 psi. inch (20.68 MPa) to about 6,000 psi inch (41.37 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / propane solution at a pressure of about 3,500 psi. inch (24.13 MPa) to about 5,000 psi inch (34.47 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises depositing contaminants from a polypropylene / propane solution, the polypropylene being dissolved at a mass percentage of at least 0.5%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 1%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 2%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 3%. In another embodiment, polypropylene is dissolved at a weight percent concentration of at least 4%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 5%. In another embodiment, a method for purifying regenerated polypropylene involves the deposition of contaminants from a polypropylene / propane solution, the polypropylene being dissolved at a mass percent concentration of up to 20%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 18%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 16%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 14%. In another embodiment, polypropylene is dissolved at a weight percent concentration of up to 12%.

Cleaning

In one embodiment of the present invention, a method for purifying polypropylene comprises contacting a solution of a contaminated polymer with a solid medium at temperatures and pressures such that the polymer remains dissolved in the liquid solvent. A solid medium in the present invention is any solid material that removes at least some contaminants from a solution of regenerated polypropylene dissolved in a liquid solvent of the present invention. Without being tied to any theory, applicants believe that a solid medium removes contaminants through various 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. In addition, pigments and other contaminants that are typically present in regenerated polypropylene can be polar compounds and can preferably react with a solid medium, which can also be at least slightly polar. Interactions between polar components can be especially effective if non-polar solvents, such as alkanes, are used as the liquid solvent.

In one embodiment of the present invention, the solid medium is selected from the group consisting of inorganic compounds, carbon-containing compounds, or mixtures thereof. Suitable examples of inorganic compounds include silicon oxides, aluminum oxides, iron oxides, aluminosilicates, magnesium silicates, amorphous volcanic glasses, silica, silica gel, diatomite, sand, quartz, regenerated glass, alumina, perlite, fuller’s earth, bentonite and mixtures thereof. Suitable examples of carbon-containing compounds include anthracite carbon, carbon black, coke, activated carbon, cellulose, and mixtures thereof. In another embodiment of the present invention, the solid medium is regenerated glass.

In one embodiment of the present invention, the solid medium is in contact with the polymer in the reactor for a predetermined period of time, while the solid medium is mixed. In another embodiment, a solid medium is removed from a solution of a purer polymer in a solid / liquid separation step. Non-limiting examples of solid and liquid phase separation steps include filtration, decantation, centrifugation, and precipitation. In another embodiment of the present invention, a contaminated polymer solution is passed through a fixed bed of a solid medium. In another embodiment of the present invention, the height or length of the fixed layer of solid medium exceeds 5 cm. In another embodiment of the present invention, the height or length of the fixed layer of solid medium exceeds 10 cm. In another embodiment of the present invention, the height or length of the fixed layer of solid medium exceeds 20 cm In another embodiment of the present invention, the solid medium is replaced as necessary to maintain the desired purity of the polymer. In yet another embodiment, the solid medium is regenerated and reused in the purification step. In another embodiment, the solid medium is regenerated, creating a fluidized bed of solid medium in the backwash stage.

In one embodiment, the method for purifying regenerated polypropylene comprises contacting the polypropylene / liquid solvent solution with a solid medium at such temperature and pressure that the polypropylene remains dissolved in the liquid solvent. In another embodiment, a method for purifying regenerated polypropylene comprises contacting a solution of polypropylene / n-butane with a solid medium at a temperature of from about 90 ° C to about 220 ° C. In another embodiment, a method for purifying regenerated polypropylene comprises contacting a solution of polypropylene / n-butane with a solid medium at a temperature of from about 100 ° C to about 200 ° C. In another embodiment, a method for purifying regenerated polypropylene comprises contacting a 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 regenerated polypropylene comprises contacting a polypropylene / n-butane solution with a solid medium at a pressure of about 350 psi. inch (2.41 MPa) to about 4,000 psi inch (27.57 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting a polypropylene / n-butane solution with a solid medium at a pressure of about 1000 psi. inch (6.89 MPa) to about 3,500 psi inch (24.13 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting a polypropylene / n-butane solution with a solid medium at a pressure of about 2000 psi. inch (13.79 MPa) to about 3,000 psi inch (20.68 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting a solution of polypropylene / n-butane with a solid medium, the polypropylene being dissolved at a mass percentage of at least 0.5%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 1%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 2%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 3%. In another embodiment, polypropylene is dissolved at a weight percent concentration of at least 4%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 5%. In another embodiment, a method for purifying regenerated polypropylene involves contacting a solution of polypropylene / n-butane with a solid medium, the polypropylene being dissolved at a mass percent concentration of up to 20%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 18%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 16%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 14%. In another embodiment, polypropylene is dissolved at a weight percent concentration of up to 12%.

In another embodiment, a method for purifying regenerated polypropylene comprises contacting a 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 regenerated polypropylene comprises contacting a 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 regenerated polypropylene comprises contacting a 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 regenerated polypropylene involves contacting a polypropylene / propane solution with a solid medium at a pressure of about 2000 psi. inch (13.79 MPa) to about 8,000 psi inch (55.16 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting a polypropylene / propane solution with a solid medium at a pressure of about 3,000 psi. inch (20.68 MPa) to about 6,000 psi inch (41.37 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting a polypropylene / propane solution with a solid medium at a pressure of about 3,500 psi. inch (24.13 MPa) to about 5,000 psi inch (34.47 MPa). In another embodiment, a method for purifying regenerated polypropylene involves contacting a polypropylene / propane solution with a solid medium, the polypropylene being dissolved at a mass percentage of at least 0.5%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 1%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 2%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 3%. In another embodiment, polypropylene is dissolved at a weight percent concentration of at least 4%. In another embodiment, polypropylene is dissolved at a mass percent concentration of at least 5%. In another embodiment, a method for purifying regenerated polypropylene involves contacting a polypropylene / propane solution with a solid medium, the polypropylene being dissolved at a mass percent concentration of up to 20%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 18%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 16%. In another embodiment, polypropylene is dissolved at a mass percent concentration of up to 14%. In another embodiment, polypropylene is dissolved at a weight percent concentration of up to 12%.

Separation

In one embodiment of the present invention, a method for purifying regenerated polypropylene involves separating a purer polymer from a liquid solvent at such temperature and pressure that the polymer precipitates from the solution and does not remain dissolved in the liquid solvent. In another embodiment, the deposition of a purer polymer from a liquid solvent is achieved by reducing pressure at a fixed temperature. In another embodiment, the deposition of a purer polymer from a liquid solvent is achieved by lowering the temperature at a fixed pressure. In another embodiment, the deposition of a purer polymer from a liquid solvent is achieved by increasing the temperature at a fixed pressure. In another embodiment, the deposition of a purer polymer from a liquid solvent is achieved by lowering both 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 liquid solvent without completely converting the 100% liquid solvent to the vapor phase by controlling the temperature and pressure of the solvent in the separation step. The precipitated cleaner polymer is separated by any method of separating the liquid phases or the solid and liquid phases. Non-limiting examples of separation of liquid phases or solid and liquid phases are filtration, decantation, centrifugation and sedimentation.

In one embodiment, a method for purifying regenerated polypropylene comprises separating polypropylene from a polypropylene / liquid solvent solution at such temperature and pressure conditions that polypropylene precipitates from the solution. In another embodiment, a method for purifying regenerated polypropylene comprises separating 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 regenerated polypropylene comprises separating 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 regenerated polypropylene comprises separating 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 regenerated polypropylene comprises separating polypropylene from a polypropylene / n-butane solution at a pressure of about 0 psig. inch (0 MPa) to about 2000 psi inch (13.79 MPa). In another embodiment, a method for purifying regenerated polypropylene involves separating polypropylene from a polypropylene / n-butane solution at a pressure of about 50 psi. inch (0.34 MPa) to about 1,500 psi inch (10.34 MPa). In another embodiment, a method for purifying regenerated polypropylene involves separating polypropylene from a polypropylene / n-butane solution at a pressure of about 75 psi. inch (0.52 MPa) to about 1000 psi inch (6.89 MPa).

In another embodiment, a method for purifying regenerated polypropylene comprises separating polypropylene from a polypropylene / propane solution at a temperature of from about -42 ° C to about 220 ° C. In another embodiment, a method for purifying regenerated polypropylene comprises separating 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 regenerated polypropylene comprises separating 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 regenerated polypropylene comprises separating polypropylene from a polypropylene / propane solution at a pressure of about 0 psig. inch (0 MPa) to about 6,000 psi inch (41.37 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises separating polypropylene from a polypropylene / propane solution at a pressure of about 50 psi. inch (0.34 MPa) to about 3,000 psi inch (20.68 MPa). In another embodiment, a method for purifying regenerated polypropylene comprises separating polypropylene from a polypropylene / propane solution at a pressure of about 75 psi. inch (0.52 MPa) to about 1000 psi inch (6.89 MPa).

III. Test methods

The test methods described herein were used to measure the effectiveness of various polymer purification methods. In particular, the described methods demonstrate the effectiveness of a certain cleaning method in improving color or light transmission / transparency (for example, achieving color and opacity of regenerated polypropylene close to the characteristics of a colorless starting polymer), reducing or removing elementary contaminants (for example, removing heavy metals) reducing or removing non-combustible contaminants (e.g., inorganic fillers), reducing or removing volatile compounds (especially volatile compounds that cause unpleasant odors of regenerated polypropylene), and reducing or removing polymer contaminants (e.g., polyethylene impurities in polypropylene).

Measuring color and opacity

The color and degree of opacity / light transmission of the polymer are important parameters that determine whether using the given polymer can achieve the desired visual aesthetic qualities of the product made from this polymer. Regenerated polypropylene, in particular polypropylene obtained by regeneration after domestic use, is usually dark in color and opaque due to the presence of residual pigments, fillers and other contaminants. Therefore, the measurement of color and opacity are important parameters to determine the effectiveness of the method of purification of polymers.

Before measuring color indicators, compression molding of samples of polymer powders or granules is carried out to obtain square test samples (with rounded corners) with dimensions of 30 mm width × 30 mm length × 1 mm thickness. The powder samples are first compacted at room temperature (about 20-23 ° C) by cold pressing the powder into a sheet between stainless steel pressure plates using a clean, previously unused aluminum foil as a separation layer. Then, about 0.85 g of powder after cold pressing or granules is pressed into test samples using a Carver Press Model C (Carver, Inc., Wobash, Indiana, IN 46992-0554, USA), preheated to 200 ° C, using aluminum pressure plates, using previously unused aluminum foil as a spacer layer and stainless steel gaskets with a cavity corresponding to the above sizes of square test specimens. Before applying pressure, the samples are heated for 5 minutes. After 5 minutes, the press is turned on with a hydraulic pressure of at least 2 tons (1.81 metric tons) for at least 5 seconds, after which the pressure is removed. The molded stack is then removed and placed between two thick flat metal heat sink devices for cooling. After that, the separation layers of aluminum foil are separated from the sample and disposed of. The extruding around the sample to the edge of the mold is separated on at least one side, and then the sample is removed from the mold. Each test specimen is visually inspected for defects in the form of voids / bubbles, and only samples are used to measure color indices in which there are no any defects.

The color of each sample was described using indicators of the three-dimensional color space L *, a *, b * from the International Commission on Lighting (CIE). The parameter L * is a measure of the lightness of the sample, while L * = 0 corresponds to the darkest black sample, and L * = 100 corresponds to the lightest white sample. The parameter a * is a measure of the color of the red or green color of the sample, while positive values of a * correspond to red, and negative values of a * correspond to green. The b * parameter is a measure of the color of the blue or yellow color of the sample, with positive values of b * corresponding to yellow, and negative values of b * corresponding to blue. The L * a * b * values of each square test specimen measuring 30 mm width × 30 mm length × 1 mm thickness were measured using a HunterLab spectrophotometer of the LabScan XE model (Hunter Associates Laboratory, Inc., Reston, Virginia, VA 20190- 5280, USA). The spectrophotometer was designed to use the D65 as a standard illuminator, with an observer angle of 10 °, a field of view diameter of 1.75 inches (44.45 mm) and a port diameter of 0.7 inches (17.78 mm).

The degree of opacity of each sample, which is a measure of the amount of light passing through the sample (i.e., the measure of light transmission of the sample), was determined using the HunterLab spectrophotometer mentioned above in the opaque mode with a contrast ratio. To determine the degree of opacity of each sample, two measurements were performed. One for measuring the brightness value of a sample with a white background, Y _{white. background} , and one for measuring the brightness of the sample with a black background, Y _{black. background} . Then, the degree of opacity was calculated from the brightness values using the following equation 3:

Equation 3

Elemental analysis

Many sources of regenerated polypropylene are characterized by unacceptably high concentrations of contaminants of heavy metals. The presence of heavy metals, such as lead, mercury, cadmium, and chromium, may limit the use of regenerated polypropylene in certain applications, for example, applications where there is contact with food or medicine, or in applications related to medical devices. Therefore, the measurement of the concentration of heavy metals is important to determine the effectiveness of the method of purification of polymers.

Elemental analysis is performed using inductively coupled plasma mass spectrometry (ICP-MS). Test solutions were prepared in an amount of n = 2 to n = 6 depending on the availability of the sample, mixing ~ 0.25 g of the sample with 4 ml of concentrated nitric acid and 1 ml of concentrated hydrofluoric acid (HF). Samples were degassed using the Ultrawave microwave digestion protocol, which provided a linear temperature change of up to 125 ° C for 20 minutes, a linear temperature change of up to 250 ° C for 10 minutes, and aging at 250 ° C for 20 minutes. Decomposed samples were cooled to room temperature. Decomposed samples were diluted to 50 ml after adding 0.25 ml of 100 ppm Ge and Rh as an internal standard. To evaluate the accuracy of the measurements, standards were prepared before decomposition by adding additives to the starting polymer. Samples of the additive-containing starting polymer were weighed in accordance with the above procedure and the required amount of standard of each individual element of interest was added, which included the following: Na, Al, Ca, Ti, Cr, Fe, Ni, Cu, Zn, Cd and Pb. Standards were prepared for two different levels: “low additive level” and “high additive level”. Each standard was prepared in triplicate. In addition to introducing additives into the starting polymer, a control additive was also added to make sure that there were no errors in sampling with a pipette and to monitor recovery during the process. Samples with control additives were also prepared in triplicate with two different levels and they were processed in the same way as samples of the additive containing the starting polymer and test samples. To construct the calibration curve, 9 points were used, which were obtained by preparing solutions of 0.05, 0.1, 0.5, 1, 5, 10, 50, 100, and 500 ppm containing Na, Al, Ca, Ti, Cr Fe, Ni, Cu, Zn, Cd and Pb. All calibration standards were prepared by diluting pure standard reference solutions and 0.25 ml of 100 ppm Ge and Rh as an internal standard with 4 ml of concentrated nitric acid and 1 ml of concentrated HF. The prepared standards, test samples and test samples with additives were analyzed using an Agilent 8800 ICP-QQQMS, optimized in accordance with the manufacturer's recommendations. The following are the tracked m / z values for each element analyzed and the collision cell gas used for the analysis: Na, 23 m / z, H ₂ ; Al, 27 m / z, H ₂ ; Ca, 40 m / z, H ₂ ; Ti, 48 m / z, H ₂ ; Cr, 52 m / z, He; Fe, 56 m / z, H ₂ ; Ni, 60 m / z; without gas; Cu, 65 m / z, without gas; Zn, 64 m / z, He; Cd, 112 m / z; H ₂ ; Pb, sum 206≥206, 207≥207, 208≥208 m / z, without 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

Many sources of regenerated polypropylene contain various fillers, for example calcium carbonate, talc and fiberglass. Despite their useful functional properties for the initial uses of regenerated polypropylene, such fillers alter the physical properties of the polymer in a way that may not be desirable for subsequent use of regenerated polypropylene. Therefore, measuring the amount of fillers is important to determine the effectiveness of the polymer purification process.

To quantify non-combustible materials in a sample (also sometimes referred to as ash), measurements were made using thermogravimetric analysis (TGA). About 5-15 mg of the sample was loaded into a platinum sample crucible and heated to 700 ° C at a rate of 20 ° C / min in air atmosphere in a TA Instruments model Q500 TGA. The sample was kept in isothermal conditions for 10 min at 700 ° C. The percentage residual mass was measured at 700 ° C after isothermal aging.

Odor analysis

An organoleptic odor analysis was carried out by placing about 3 g of each sample in a 20 ml glass vial and keeping the sample at room temperature for at least 30 minutes to balance. After balancing, each bottle was opened, and a qualified appraiser inhaled the upper air sample (inhalation through the nose) to determine the intensity of the smell and the profile of its description. Odor intensity was evaluated in accordance with the following scale:

5 = very strong

4 = strong

3 = moderate

2 = mild to moderate

1 = weak

0 = no smell

Analysis of polymer contaminants

Many sources of regenerated polypropylene, in particular regenerated polypropylene obtained from mixed sources, may contain undesired polymeric contaminants. Without reference to any theory, it is generally accepted that polymer contaminants, for example, contaminants of polyethylene in polypropylene, can affect the physical properties of the polymer due to the presence of heterogeneous phases and resulting from fragile interactions. Moreover, polymeric contaminants can also increase the degree of opacity of the polymer and affect the color. Therefore, measuring the amount of polymer contaminants is important to determine the effectiveness of the polymer purification process.

Semi-crystalline polymer contaminants were evaluated using differential scanning calorimetry (DSC). To measure the amount of contaminants of polyethylene in polypropylene, a set of five polypropylene / polyethylene mixtures containing 2, 4, 6, 8, and 10 masses was prepared. % HDPE Formolene® HB5502F (Formosa Plastics Corporation, USA) in polypropylene Pro-fax 6331 (LyondellBasell Industries Holdings, B.V.). About 5-15 mg of each sample was sealed in an aluminum crucible for DSC and analyzed using a TA Instruments model Q2000 DSC using the method described below.

1. Balancing at 30.00 ° C

2. A linear change in temperature at a rate of 20.00 ° C / min to 200.00 ° C

3. End of cycle 0 mark.

4. A linear change in temperature at a rate of 20.00 ° C / min to 30.00 ° C

5. End of cycle 1 mark

6. A linear change in temperature at a rate of 20.00 ° C / min to 200.00 ° C

7. End of cycle 2 mark

8. A linear change in temperature at a rate of 20.00 ° C / min to 30.00 ° C

9. End of cycle 3 mark

10. A linear change in temperature at a rate of 5.00 ° C / min to 200.00 ° C

11. End of cycle 4

The melting enthalpy for the HDPE peak at a temperature of about 128 ° C was calculated for each sample with a known HDPE content from a DSC thermogram of 5.00 ° C / min. The linear calibration curve shown in FIG. 2, were built by plotting the enthalpy of melting depending on the known concentration of HDPE (wt.%).

Samples with unknown PE content were analyzed using the above equipment and the DSC method. The PE content was calculated using the above calibration curve. HDPE of a certain brand, used to construct the calibration curve, is most likely to have a different degree of crystallinity compared to polyethylene contaminants (or polyethylene mixtures) that may be present in the sample of regenerated polypropylene. The degree of crystallinity can independently affect the measured enthalpy of melting of polyethylene and, thus, affect the final calculations of the polyethylene content. Nevertheless, the DSC test method described in this document is intended to serve as a relative measure to compare the effectiveness of various methods of purification of polymers and is not intended to accurately quantify the content of polyethylene in the polymer mixture. Despite the fact that the above method describes the measurement of contaminants of polyethylene in polypropylene, this method can be used to measure other semi-crystalline polymers using different temperature ranges and peaks in the DSC thermogram. In addition, alternative methods, such as nuclear magnetic resonance (NMR), can also be used to measure the amount of semi-crystalline and amorphous polymer contaminants in a sample.

EXAMPLES

The following examples further describe and demonstrate embodiments that are within the scope of the present invention. These examples are for illustrative purposes only and should not be construed as limitations of the present invention, since numerous variations are possible within the spirit and scope of the invention.

Example 1

A sample of recycled polypropylene chips of mixed colors after domestic use was obtained from a supplier of recycled resins. Regenerated polypropylene after domestic use came from the USA and Canada. The obtained mixed color chips were homogenized by extrusion using a Century / W & P ZSK30 twin-screw extruder with two 30 mm general purpose screws, each with standard mixing and feeding elements. The screw rotational speed was about 50 rpm, the feed rate was about 20 pounds / hour (9.07 kg / hour), and the cylinder temperature ranged from about 210 ° C at the head to about 150 ° C at the feed hole. The gray core leaving the extruder was cooled in a water bath at room temperature, air dried and cut into granules.

Samples were analyzed using the test methods disclosed herein, and the data obtained are summarized in table 1. The purpose of this example is to demonstrate the properties of a representative recycled resin after domestic use before cleaning.

The granules and corresponding square test specimens were dark gray in color, as follows from the L * a * b * values for the square test specimens. The degree of opacity of the samples averaged about 100% opacity (i.e. lack of light transmission). A photograph of a square test sample is shown in FIG. 4 as an example 1. As shown in FIG. 4, the sample was dark in color and was opaque.

This example serves as a representative baseline of heavy metal contaminants found in regenerated polypropylene coming from domestic use. When compared with other samples, the contaminants of heavy metals were much higher in the resulting regenerated polypropylene after domestic use.

The ash values in the samples of example 1 averaged about 1.2117 mass. %, which also served as an indicator of the initial level for the amount of non-combustible substances that are often present in regenerated polypropylene after household use.

The present example also serves as a representative baseline of contaminants with odorous substances found in regenerated polypropylene coming from domestic use. It was found that the samples from example 1 are characterized by an odor intensity of 3.75 on a 5-point scale (5 corresponds to the highest intensity), and according to the descriptions they had a “sloppy”, “dusty” or “sour” smell.

The present example also serves as a representative baseline of polyethylene contaminants found in regenerated polypropylene coming from domestic use. The polyethylene content in the samples of example 1 averaged about 5.5 mass. %

Example 2

A sample of recycled polypropylene chips of mixed colors after domestic use, described in Example 1, was processed using the experimental setup shown in FIG. 3A and FIG. 3B, in accordance with the procedure described below:

1. 286 g of mixed color crumbs were loaded into a Parr Instrument Company Model 4552M apparatus with a 7.57-liter autoclave equipped with an overhead mechanical stirrer.

2. Then the autoclave was completely filled with n-butane and brought to an internal liquid temperature of 140 ° C. and a fluid pressure of 900 psi (6.21 MPa).

3. The material in the autoclave was then extracted using the experimental configuration shown in FIG. 3A and the following procedure:

a. The content of the system was stirred for 10 min at 140 ° C and 900 psi (6.21 MPa).

b. After stirring, the system was allowed to stand for 10 minutes at 140 ° C. and 900 psi (6.21 MPa).

c. One vessel of n-butane was washed in an autoclave into a flask to collect samples at 140 ° C and 900 psi (6.21 MPa).

d. The extraction procedure described above was repeated four more times.

e. Material collected for all extraction cycles was designated as "fraction 1".

4. The material remaining in the autoclave after extraction was then dissolved in n-butane using the experimental configuration shown in FIG. 3B followed by the procedure:

a. The system pressure was balanced to 1800 psi (12.41 MPa).

b. The content of the system was stirred for 10 min at 140 ° C and 1800 psi (12.41 MPa).

c. Then the stirring was stopped and the solution was defended for 30 minutes at 140 ° C and 1800 psi (6.21 MPa).

d. After the settling step, the solution was removed from the autoclave by displacement with nitrogen under pressure (previously equilibrated to 140 ° C. and 1800 psi). The solution exiting the autoclave through an immersion tube was then passed through two heat-treated columns with a solid medium. Each column had an inner diameter of 0.68 inches (1.73 cm) and a length of about 9.5 inches (24.13 cm). The first column contained about 21 g of fuller earth in 8-16 mesh (Jaxon Filtration, JF 752-8 / 16, USA), which was pre-mixed in a glass with about 21 g of fuller earth in 30-60 mesh (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 previously mixed in a beaker with about 21 g of alumina (activated alumina, Selexsorb CDX, 7 × 14, BASF, USA). In a liquid stream leaving the lower part of the second high-pressure apparatus, pressure was released by feeding through an expansion valve into an Erlenmeyer flask with a side outlet. After depressurizing the liquid stream into an Erlenmeyer flask, solvent vapors were discharged through a side outlet, and all liquids / solids were collected in the flask. Each fraction contained about 30 g of material and was sequentially labeled starting with "fraction 2". Fractions were collected until no release of material into the flask was already observed.

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 residual sample.

Data for a sample of fraction 3 collected in accordance with the procedure disclosed herein are shown in table 1.

The solid particles isolated in fraction 3 in this example were white. After the white solid particles from fraction 3 were compression molded to obtain square test samples, these samples were colorless and transparent and in appearance resembled the original polypropylene. A photograph of a square test sample obtained from fraction 3 is shown in FIG. 4 as an example 2. As a reference, the starting polypropylene is shown in FIG. 4 as an example 4. As shown in FIG. 4, the sample was transparent and comparable in color and light transmission with the original polypropylene. L * a * b * values indicate that the square test samples were essentially colorless and showed a significant improvement in color characteristics compared to the square test samples from example 1 (i.e. polypropylene in the form in which it was obtained after household use). The L * values for square samples for testing from fraction 3 of Example 2 averaged 80.44, which was significantly better compared to the L * values of square samples for testing from Example 1, which averaged 39.76. The opacity of the square samples for testing from fraction 3 of Example 2 averaged 10.30% of the opacity (i.e., the light transmittance is approximately 90%), which was also much better than the opacity of the square samples for testing from Example 1, which in averaged about 100% opacity.

The concentration of heavy metal contaminants in samples from fraction 3 of example 2 was also much more favorable compared to samples from example 1. For example, the concentration of sodium in samples from fraction 3 of example 2 averaged only 4100 ppm, while the concentration of sodium in the samples of example 1 averaged 136,000 ppm (decrease of about 97%). The concentrations of all other measured elements in all cases decreased by 77-100% for samples from fraction 3 of example 2 compared with samples from example 1.

The ash values in the samples from fraction 3 of Example 2 averaged about 0.3874% by weight, which was significantly lower than the ash values for the samples from Example 1, which averaged about 1.2117% by weight.

It was found that the samples from fraction 3 of example 2 differ in odor intensity of 0.5 points on a 5-point scale (5 corresponds to the highest intensity), which was significantly better compared to the odor intensity of samples from example 1, where the odor intensity was 3.75 point. Despite the low odor intensity, samples from fraction 2 of Example 2 were described as having a “plastic” odor, similar to the original polypropylene.

The polyethylene content in the samples from fraction 3 of Example 2 averaged about 1.1% by weight, which was better compared to the polyethylene content in the samples from Example 1, which averaged about 5.5% by weight.

Example 3

A sample of recycled polypropylene chips of mixed colors after domestic use, described in Example 1, was processed using the experimental setup shown in FIG. 3A and FIG. 3B, in accordance with the procedure described below:

6. 173 g of mixed color chips were loaded into a Parr Instrument Company Model 4552 M apparatus with a 7.57 liter autoclave equipped with an overhead mechanical stirrer.

7. Then the autoclave was completely filled with n-butane and brought to an internal liquid temperature of 140 ° C and a fluid pressure of 900 psi (6.21 MPa).

8. The material in the autoclave was then extracted using the experimental configuration shown in FIG. 3A and the following procedure:

f. The content of the system was stirred for 10 min at 140 ° C and 900 psi (6.21 MPa).

g. After stirring, the system was allowed to stand for 10 minutes at 140 ° C. and 900 psi (6.21 MPa).

h. One vessel of n-butane was washed in an autoclave into a flask to collect samples at 140 ° C and 900 psi (6.21 MPa).

i. The extraction procedure described above was repeated four more times.

j. Samples collected for each extraction cycle were sequentially labeled “fraction 1” to “fraction 5”.

9. The material remaining in the autoclave after extraction was then dissolved in n-butane using the experimental configuration shown in FIG. 3B followed by the procedure:

e. The system pressure was balanced to 1800 psi (12.41 MPa).

f. The content of the system was stirred for 10 min at 140 ° C and 1800 psi (12.41 MPa).

g. Then the stirring was stopped and the solution was defended for 60 min at 140 ° C and 1800 psi (6.21 MPa).

h. After the settling step, the solution was removed from the autoclave by displacement with n-butane under pressure (previously equilibrated to 140 ° C and 1800 psi). The solution exiting the autoclave through an immersion tube was then passed through two heat-treated columns with a solid medium. Each column had an inner diameter of 0.68 inches (1.73 cm) and a length of about 9.5 inches (24.13 cm). In this example, both columns were empty and did not contain any solid supports. In a liquid stream leaving the lower part of the second high-pressure apparatus, pressure was released by feeding through an expansion valve into an Erlenmeyer flask with a side outlet. After depressurizing the liquid stream into an Erlenmeyer flask, solvent vapors were discharged through a side outlet, and all liquids / solids were collected in the flask. Each fraction contained about 30 g of material and was sequentially labeled starting with "fraction 6". Fractions were collected until no release of material into the flask was already observed.

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 residual sample.

Data for a sample of fraction 6 collected in accordance with the procedure disclosed herein are shown in table 1.

The solids recovered in fractions 6 in this example were nearly white to yellow in color. After the solid particles from almost white to yellow from fraction 6 were compression molded to obtain square test samples, these samples were yellow in appearance. A photograph of a square test sample is shown in FIG. 4 as an example 3. As shown in FIG. 4, the color and transparency of the samples from example 3 were improved compared to the samples from example 1, but were not comparable with the original polypropylene shown in FIG. 4 as an example 4. Even without the stage of contact with the solid support, the L * a * b * values demonstrate that the square test samples from fraction 6 of Example 3 had slightly improved color characteristics compared to the samples of Example 1 (that is, polypropylene in the form in which it was obtained after domestic use). The L * values for square test samples from fraction 6 of Example 3 averaged 72.41, which was significantly better than the L * values of square test samples from Example 1, which averaged 39.76. The opacity for square test samples from fraction 6 of Example 3 averaged 35.25% opacity, which was better than the opacity of square test specimens from Example 1, which averaged about 100% opacity.

The concentration of heavy metal contaminants in samples from fraction 6 of example 3 was also much more favorable compared to samples from example 1. For example, the concentration of sodium in samples from fraction 6 of example 3 averaged only 16,400 ppm, while the concentration of sodium in samples from Example 1, the average was 136,000 ppm (a decrease of about 88%). The concentrations of all other measured elements in all cases decreased by 82-100% for samples from fraction 6 of example 3 in comparison with the samples of example 1.

The ash values in the samples from fraction 6 of Example 3 averaged about 0.2292% of the mass, which was significantly lower than the ash values for the samples from Example 1, which averaged about 1.2117% of the mass.

It was found that the samples from fraction 6 of Example 3 were characterized by an odor intensity of 0.5 points on a 5-point scale (5 corresponds to the highest intensity), which was significantly better than the odor intensity of the samples from Example 1, where the odor intensity was 3, 75 points. Despite the low odor intensity, samples from fraction 6 of Example 3 were described as having a “plastic” odor, similar to the original polypropylene.

The polyethylene content in the samples from fraction 6 of Example 3 averaged about 1.0% by weight, which was much better compared to the polyethylene content in the samples from Example 1, which averaged about 5.5% by weight.

Example 4 - Comparative samples of the source polypropylene

For all comparative samples of the “initial PP”, Pro-fax 6331 polypropylene (LyondellBasell Industries Holdings, BV) was used. The granules of the original PP were transformed into square test specimens in accordance with the method described herein. The values of L * a * b * for samples made from the initial PP were on average 85.13 ± 0.18, -0.71 ± 0.01, and 2.27 ± 0.02, respectively. The average opacity of the square test specimens was 7.56 ± 0.21% opacity. This example is a comparison of the amount of heavy metal contaminants in a representative sample of the starting polypropylene. Samples of the original polypropylene had ash values, which averaged about 0.3031% of the mass. The granules of the initial PP had a smell intensity of 0.5 points on a 5-point scale (5 corresponds to the highest intensity) and, according to the descriptions, had a smell similar to “plastic”. No polyethylene was found in the sample of the starting propylene.

Each document referred to in the present description, including cross-references or a related patent or patent application, is incorporated herein in its entirety by reference, unless explicitly excluded or otherwise limited. Mention of any document does not constitute recognition that it constitutes prior art with respect to any invention described or claimed herein, or that it alone, or in any combination with any other reference or references, represents, proposes or describes any such invention. In addition, if any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated herein by reference, the meaning or definition assigned to this term in this document takes precedence.

Although specific embodiments of the present invention are shown and described herein, those skilled in the art will appreciate that various other changes and modifications are acceptable without departing from the spirit and scope of the invention. Thus, it is intended that the appended claims cover all of these changes and modifications within the scope of the present invention.

Claims (22)

1. The method of purification of regenerated polypropylene, including: a) obtaining regenerated polypropylene, said polypropylene being selected from the group consisting of polymers after domestic use, polymers after industrial use, and combinations thereof; b) contacting the regenerated polypropylene at a temperature of from 80 ° C to 220 ° C and at a pressure of 150 psi. inch (1.03 MPa) to 15,000 psi an inch (103.42 MPa) with a first liquid solvent with a standard boiling point of less than 70 ° C, to obtain extracted regenerated polypropylene; c) dissolving the extracted regenerated polypropylene in a solvent selected from the group consisting of a first liquid solvent, a second liquid solvent, and mixtures thereof, at a temperature of from 90 ° C to 220 ° C and a pressure of 350 psi. inch (2.41 MPa) to 20,000 psi inch (137.90 MPa), to obtain a first solution containing polypropylene and suspended contaminants; d) settling said first solution containing polypropylene and suspended contaminants at a temperature of from 90 ° C to 220 ° C and under a pressure of 350 psi. inch (2.41 MPa) to 20,000 psi inch (137.90 MPa) to obtain a second solution containing polypropylene and the remaining contaminants; e) cleaning said second solution at a temperature of from 90 ° C to 220 ° C and at a pressure of 350 psig. inch (2.41 MPa) to 20,000 psi an inch (137.90 MPa) by contacting said second solution with a solid medium to obtain a third solution containing more pure polypropylene; and f) separating said cleaner polypropylene from said third solution; wherein said second liquid solvent has the same chemical composition as the first liquid solvent, or a different chemical composition. 2. The method according to p. 1, in which the specified polypropylene is separated from the specified third solution at a temperature of from 0 ° C to 220 ° C and a pressure of from 0 psi. inch hut (0 MPa) up to 2000 psi inch hut (13.79 MPa). 3. The method according to p. 1, characterized in that the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage concentration of at least 0.5%. 4. The method according to p. 1, characterized in that the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 2%. 5. The method according to p. 1, characterized in that the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of at least 5%. 6. The method according to p. 1, characterized in that the regenerated polypropylene is dissolved in a liquid solvent or in a mixture of a liquid solvent at a mass percentage of up to 20%. 7. The method according to claim 1, wherein said regenerated polypropylene is dissolved in a liquid solvent or in a mixture of liquid solvents at a mass percentage of up to 12%. 8. The method according to p. 1, characterized in that the regenerated polypropylene is a polypropylene obtained by regeneration after domestic use. 9. The method according to p. 1, characterized in that the regenerated polypropylene is a homopolymer of polypropylene or a copolymer of polypropylene containing more than 70 mol% of repeating units of propylene. 10. The method according to p. 1, characterized in that said liquid solvent has a standard boiling point of less than 0 ° C and more than -45 ° C and a standard change in enthalpy during evaporation of less than +25 kJ / mol. 11. The method according to p. 1, characterized in that said liquid solvent is selected from the group consisting of olefinic hydrocarbons, aliphatic hydrocarbons and mixtures thereof. 12. The method according to p. 11, characterized in that said aliphatic hydrocarbon is selected from the group consisting of C ₁ -C ₆ aliphatic hydrocarbons and mixtures thereof. 13. The method according to p. 11, characterized in that the said liquid solvent is n-butane, butane isomers or mixtures thereof. 14. The method according to p. 1, characterized in that the temperature at the stages of contact, dissolution, precipitation and purification is from 110 ° C to 170 ° C. 15. The method according to p. 1, characterized in that the specified pressure at the stage of bringing into contact is from 1100 psi. inch hut (7.58 MPa) up to 2100 psi inch hut (14.48 MPa).

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