Note: Descriptions are shown in the official language in which they were submitted.
14636M-DW 1
METHOD FOR PURIFYING RECLAIMED POLYETHYLENE
FIELD OF THE INVENTION
The present invention generally relates to a method for purifying contaminated
polymers
through the use of a pressurized solvent and solid media. More specifically,
this invention relates
to a method for purifying recycled polymers, such as post-consumer and post-
industrial recycled
plastics, to produce a colorless or clear, odor free, virgin-like polymer. It
is particularly useful for
the purification of polyethylene.
BACKGROUND OF THE INVENTION
Polymers, especially synthetic plastics, are ubiquitous in daily life due to
their relatively
low production costs and good balance of material properties. Synthetic
plastics are used in a
wide variety of applications, such as packaging, automotive components,
medical devices, and
consumer goods. To meet the high demand of these applications, tens of
billions of pounds of
synthetic plastics are produced globally on an annual basis. The overwhelming
majority of
synthetic plastics are produced from increasingly scarce fossil sources, such
as petroleum and
natural gas. Additionally, the manufacturing of synthetic plastics from fossil
sources produces
CO2 as a by-product.
The ubiquitous use of synthetic plastics has consequently resulted in millions
of tons of
plastic waste being generated every year. While the majority of plastic waste
is landfilled via
municipal solid waste programs, a significant portion of plastic waste is
found in the environment
as litter, which is unsightly and potentially harmful to ecosystems. Plastic
waste is often washed
into river systems and ultimately out to sea.
Plastics recycling has emerged as one solution to mitigate the issues
associated with the
wide-spread usage of plastics. Recovering and re-using plastics diverts waste
from landfills and
reduces the demand for virgin plastics made from fossil-based resources, which
consequently
reduces greenhouse gas emissions. In developed regions, such as the United
States and the
European Union, rates of plastics recycling are increasing due to greater
awareness by consumers,
businesses, and industrial manufacturing operations. The majority of recycled
materials, including
plastics, are mixed into a single stream which is collected and processed by a
material recovery
facility (MRF). At the MRF, materials are sorted, washed, and packaged for
resale. Plastics can
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be sorted into individual materials, such as high-density polyethylene (HDPE)
or poly(ethylene
terephthalate) (PET), or mixed streams of other common plastics, such as
polypropylene (PP), low-
density polyethylene (LDPE), poly(vinyl chloride) (PVC), polystyrene (PS),
polycarbonate (PC),
and polyamides (PA). The single or mixed streams can then be further sorted,
washed, and
reprocessed into a pellet that is suitable for re-use in plastics processing,
for example blow and
injection molding.
Though recycled plastics are sorted into predominately uniform streams and are
washed
with aqueous and/or caustic solutions, the final reprocessed pellet often
remains highly
contaminated with unwanted waste impurities, such as spoiled food residue and
residual perfume
components. In addition, recycled plastic pellets, except for those from
recycled beverage
containers, are darkly colored due to the mixture of dyes and pigments
commonly used to colorize
plastic articles. While there are some applications that are insensitive to
color and contamination
(for example black plastic paint containers and concealed automotive
components), the majority
of applications require non-colored pellets. The need for high quality,
"virgin-like" recycled resin
is especially important for food and drug contact applications, such as food
packaging. In addition
to being contaminated with impurities and mixed colorants, many recycled resin
products are often
heterogeneous in chemical composition and may contain a significant amount of
polymeric
contamination, such as recycled polypropylene contamination in polyethylene
and vice versa.
Mechanical recycling, also known as secondary recycling, is the process of
converting
recycled plastic waste into a re-usable form for subsequent manufacturing. A
more detailed review
of mechanical recycling and other plastics recovery processes are described in
S.M. Al-Salem, P.
Lettieri, J. Baeyens, "Recycling and recovery routes of plastic solid waste
(PSW): A review",
Waste Management, Volume 29, Issue 10, October 2009, Pages 2625-2643, ISSN
0956-053X.
While advances in mechanical recycling technology have improved the quality of
recycled
polymers to some degree, there are fundamental limitations of mechanical
decontamination
approaches, such as the physical entrapment of pigments within a polymer
matrix. Thus, even with
the improvements in mechanical recycling technology, the dark color and high
levels of chemical
contamination in currently available recycled plastic waste prevents broader
usage of recycled
resins by the plastics industry.
To overcome the fundamental limitations of mechanical recycling, there have
been many
methods developed to purify contaminated polymers via chemical approaches, or
chemical
recycling. Most of these methods use solvents to decontaminate and purify
polymers. The use of
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solvents enables the extraction of impurities and the dissolution of polymers,
which further enables
alternative separation technologies.
For example, U.S. Patent No. 7,935,736 describes a method for recycling
polyester from
polyester-containing waste using a solvent to dissolve the polyester prior to
cleaning. The '736
patent also describes the need to use a precipitant to recover the polyester
from the solvent.
In another example, U.S. Patent No. 6,555,588 describes a method to produce a
polypropylene blend from a plastic mixture comprised of other polymers. The
'588 patent
describes the extraction of contaminants from a polymer at a temperature below
the dissolution
temperature of the polymer in the selected solvent, such as hexane, for a
specified residence period.
The '588 patent further describes increasing the temperature of the solvent
(or a second solvent) to
dissolve the polymer prior to filtration. The '588 patent yet further
describes the use of shearing
or flow to precipitate polypropylene from solution. The polypropylene blend
described in the '588
patent contained polyethylene contamination up to 5.6 wt%.
In another example, European Patent Application No. 849,312 (translated from
German to
English) describes a process to obtain purified polyolefins from a polyolefin-
containing plastic
mixture or a polyolefin-containing waste. 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 between 90 C and the boiling point of the
hydrocarbon solvent.
The '312 patent application further describes contacting a hot polyolefin
solution with bleaching
clay and/or activated carbon to remove foreign components from the solution.
The '312 patent yet
further describes cooling the solution to temperatures below 70 C to
crystallize the polyolefin and
then removing adhering solvent by heating the polyolefin above the melting
point of the polyolefin,
or evaporating the adhering solvent in a vacuum or passing a gas stream
through the polyolefin
precipitate, and/or extraction of the solvent with an alcohol or ketone that
boils below the melting
point of the polyolefin.
In another example, U.S. Patent No. 5,198,471 describes a method for
separating polymers
from a physically commingled solid mixture (for example waste plastics)
containing a plurality of
polymers using a solvent at a first lower temperature to form a first single
phase solution and a
remaining solid component. The '471 patent further describes heating the
solvent to higher
temperatures to dissolve additional polymers that were not solubilized at the
first lower
temperature. The '471 patent describes filtration of insoluble polymer
components.
In another example, U.S. Patent No. 5,233,021 describes a method of extracting
pure
polymeric components from a multi-component structure (for example waste
carpeting) by
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dissolving each component at an appropriate temperature and pressure in a
supercritical fluid and
then varying the temperature and/or pressure to extract particular components
in sequence.
However, similar to the '471 patent, the '021 patent only describes filtration
of undissolved
components.
In another example, U.S. Patent No. 5,739,270 describes a method and apparatus
for
continuously separating a polymer component of a plastic from contaminants and
other
components of the plastic using a co-solvent and a working fluid. The co-
solvent at least partially
dissolves the polymer and the second fluid (that is in a liquid, critical, or
supercritical state)
solubilizes components from the polymer and precipitates some of the dissolved
polymer from the
co-solvent. The '270 patent further describes the step of filtering the
thermoplastic-co-solvent
(with or without the working fluid) to remove particulate contaminants, such
as glass particles.
The known solvent-based methods to purify contaminated polymers, as described
above,
do not produce "virgin-like" polymer. In the previous methods, co-dissolution
and thus cross
contamination of other polymers often occurs. If adsorbent is used, a
filtration and/or
centrifugation step is often employed to remove the used adsorbent from
solution. In addition,
isolation processes to remove solvent, such as heating, vacuum evaporation,
and/or precipitation
using a precipitating chemical are used to produce a polymer free of residual
solvent.
Accordingly, a need still exists for an improved solvent-based method to
purify
contaminated polymers that uses a solvent that is readily and economically
removed from the
polymer, is relatively simple in terms of the number of unit operations,
produces a polymer without
a significant amount of polymeric cross contamination, produces a polymer that
is essentially
colorless, and produces a polymer that is essentially odorless.
SUMMARY OF THE INVENTION
A method for purifying a reclaimed polyethylene is provided. The method
involves:
a. Obtaining reclaimed polyethylene selected from the group consisting of post-
consumer
use polymers, post-industrial use polymers, and combinations thereof;
b. Contacting the reclaimed polyethylene at a temperature from about 80 C to
about 220 C
and at a pressure from about 150 psig (1.03 MPa) to about 15,000 psig (103.42
MPa) with
a first fluid solvent having a standard boiling point less than about 70 C, to
produce an
extracted reclaimed polyethylene;
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c. Dissolving the extracted reclaimed polyethylene in a solvent selected from
the group
consisting of the first fluid solvent, a second fluid solvent, and mixtures
thereof, at a
temperature from about 90 C to about 220 C and a pressure from about 350 psig
(2.41
MPa) to about 20,000 psig (137.90 MPa) to produce a first solution comprising
polyethylene and suspended contaminants;
d. Settling the first solution comprising polyethylene and suspended
contaminants at a
temperature from about 90 C to about 220 C and at a pressure from about 350
psig (2.41
MPa) to about 20,000 psig (137.90 MPa) to produce a second solution comprising
polyethylene and remaining contaminants;
e. Purifying the second solution at a temperature from about 90 C to about 220
C and at a
pressure from about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa) by
contacting
the second solution with solid media to produce a third solution comprising
purer
polyethylene; and
f. Separating the purer polyethylene from the third solution.
The second fluid solvent may have either the same chemical composition or a
different chemical
composition than the first fluid solvent.
In one embodiment, the polyethylene is separated from the third solution at a
temperature
from about 0 C to about 220 C and a pressure from about 0 psig (0 MPa) to
2,000 psig (13.79
MPa). In another embodiment, the reclaimed polyethylene is dissolved in the
fluid solvent, or fluid
solvent mixture, at a mass percent concentration of at least 0.5%. In yet
another embodiment, the
reclaimed polyethylene is dissolved in the fluid solvent, or fluid solvent
mixture, at a mass percent
concentration of at least 1%. In one embodiment, the reclaimed polyethylene is
dissolved in the
fluid solvent, or fluid solvent mixture, at a mass percent concentration of at
least 2%.
In one embodiment, the reclaimed polyethylene is dissolved in the fluid
solvent, or fluid
solvent mixture, at a mass percent concentration of at least 3%. In another
embodiment, the
reclaimed polyethylene is dissolved in the fluid solvent, or fluid solvent
mixture, at a mass percent
concentration of at least 4%. In yet another embodiment, the reclaimed
polyethylene is dissolved
in the fluid solvent, or fluid solvent mixture, at a mass percent
concentration of at least 5%.
In one embodiment, the reclaimed polyethylene is dissolved in the fluid
solvent, or fluid
solvent mixture, at a mass percent concentration up to 20%. In another
embodiment, the reclaimed
polyethylene is dissolved in the fluid solvent, or fluid solvent mixture, at a
mass percent
concentration up to 18%. In yet another embodiment, the reclaimed polyethylene
is dissolved in
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the fluid solvent, or fluid solvent mixture, at a mass percent concentration
up to 16%. In one
embodiment, the reclaimed polyethylene is dissolved in the fluid solvent, or
fluid solvent mixture,
at a mass percent concentration up to 14%. In another embodiment, the
reclaimed polyethylene is
dissolved in the fluid solvent, or fluid solvent mixture, at a mass percent
concentration up to 12%.
In one embodiment, the reclaimed polyethylene is post-consumer recycle derived
polyethylene. In another embodiment, the reclaimed polyethylene is a
polyethylene homopolymer
or a primarily polyethylene copolymer. In yet another embodiment, the fluid
solvent has a standard
boiling point less than about 0 C and greater than about -45 C and a standard
enthalpy change of
vaporization of less than about +25 kJ/mol.
In one embodiment, the fluid solvent is selected from the group consisting of
olefinic
hydrocarbons, aliphatic hydrocarbons, and mixtures thereof. In another
embodiment, the aliphatic
hydrocarbon is selected from the group consisting of C1-C6 aliphatic
hydrocarbons and mixtures
thereof. In yet another embodiment, the aliphatic hydrocarbons and mixtures
thereof is comprised
of primarily C4 aliphatic hydrocarbons.
In another embodiment, the fluid solvent consists essentially of C4 liquefied
petroleum gas.
In one embodiment, the fluid solvent is n-butane, butane isomers, or mixtures
thereof. In another
embodiment, the temperature in the contacting, dissolving, settling and
purification steps is from
about 110 C to about 170 C.
In one embodiment, the pressure in the contacting step is from about 1,100
psig (7.58 MPa) to
about 5,500 psig (37.92 MPa). In another embodiment, the pressure in the
contacting step is less
than about 1,100 psig (7.58 MPa). In yet another embodiment, the pressure in
the dissolving,
settling, and purification steps is greater than about 4,500 psig (31.03 MPa).
In one embodiment,
the pressure in the dissolving, settling, and purification steps is greater
than about 5,500 psig (37.92
MPa).
In one embodiment, the solid media is selected from the group consisting of
inorganic
substances, carbon-based substances, and mixtures thereof. In another
embodiment, the inorganic
substances are selected from the group consisting of oxides of silicon, oxides
of aluminum, oxides
of iron, aluminum silicates, amorphous volcanic glasses, and mixtures thereof
In yet another
embodiment, the inorganic substances are selected from the group consisting of
silica gel,
diatomite, sand, quartz, alumina, perlite, fuller's earth, bentonite, and
mixtures thereof.
In one embodiment, the carbon-based substances are selected from the group
consisting of
anthracite coal, carbon black, coke, activated carbon, cellulose, and mixtures
thereof. In another
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embodiment, the contacting of the polyethylene solution with said solid media
is done in a packed
bed of said solid media. In yet another embodiment, the packed bed is greater
than 20 cm in length.
In accordance with an aspect, there is provided a method for purifying
reclaimed
polyethylene comprising:
a. Obtaining the reclaimed polyethylene wherein said reclaimed polyethylene is
selected
from the group consisting of post-consumer use polymers, post-industrial use
polymers,
and combinations thereof;
b. Contacting the reclaimed polyethylene at a temperature from about 80 C to
about 220 C
and at a pressure from about 150 psig (1.03 MPa) to about 15,000 psig (103.42
MPa)
with a first fluid solvent having a standard boiling point less than about 70
C, wherein
the polyethylene is essentially insoluble in the fluid solvent, to produce an
extracted
reclaimed polyethylene;
c. Dissolving the extracted reclaimed polyethylene in a solvent selected from
the group
consisting of the first fluid solvent, a second fluid solvent, and mixtures
thereof, at a
temperature from about 90 C to about 220 C and a pressure from about 350 psig
(2.41
MPa) to about 20,000 psig (137.90 MPa) to produce a first solution comprising
polyethylene and suspended contaminants;
d. Settling said first solution comprising polyethylene and suspended
contaminants at a
temperature from about 90 C to about 220 C and at a pressure from about 350
psig (2.41
MPa) to about 20,000 psig (137.90 MPa) to produce a second solution comprising
polyethylene and remaining contaminants;
e. Purifying said second solution at a temperature from about 90 C to about
220 C and at a
pressure from about 350 psig (2.41 MPa) to about 20,000 psig (137.90 MPa) by
contacting said second solution with solid media to produce a third solution
comprising
purer polyethylene; wherein the solid media is selected from the group
consisting of
inorganic substances, carbon-based substances, and mixtures thereof, and
recycled glass;
the inorganic substances being selected from the group consisting of oxides of
silicon,
oxides of aluminum, oxides of iron, aluminum silicates, magnesium silicates,
amorphous
volcanic glasses, silica, silica gel, diatomite, sand, quartz, reclaimed
glass, alumina,
perlite, fuller's earth, bentonite, and mixtures thereof; and the carbon-based
substances
being selected from the group consisting of anthracite coal, carbon black,
coke, activated
carbon, cellulose, and mixtures thereof; and
f. Separating said purer polyethylene from said third solution;
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wherein said second fluid solvent has the same chemical composition or a
different chemical
composition as the first fluid solvent.
Additional features of the invention may become apparent to those skilled in
the art from a
review of the following detailed description, taken in conjunction with the
examples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block flow diagram showing the major steps of one embodiment of
the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
I. Definitions
As used herein, the term "reclaimed polymer" refers to a polymer used for a
previous
purpose and then recovered for further processing.
As used herein, the term "reclaimed polyethylene" refers to a polyethylene
polymer used
for a previous purpose and then recovered for further processing.
As used herein, the term "post-consumer" refers to a source of material that
originates after
the end consumer has used the material in a consumer good or product.
As used herein, the term "post-consumer recycle" (PCR) refers to a material
that is
produced after the end consumer has used the material and has disposed of the
material in a waste
stream.
As used herein, the term "post-industrial" refers to a source of a material
that originates
during the manufacture of a good or product.
As used herein, the term "fluid solvent" refers to a substance that may exist
in the liquid
state under specified conditions of temperature and pressure. In some
embodiments the fluid
solvent may be a predominantly homogenous chemical composition of one molecule
or isomer,
while in other embodiments, the fluid solvent may be a mixture of several
different molecular
compositions or isomers. Further, in some embodiments of the present
invention, the term "fluid
solvent" may also apply to substances that are at, near, or above the critical
temperature and critical
pressure (critical point) of that substance. It is well known to those having
ordinary skill in the art
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that substances above the critical point of that substance are known as
"supercritical fluids" which
do not have the typical physical properties (i.e. density) of a liquid.
As used herein, the term "dissolved" means at least partial incorporation of a
solute
(polymeric or non-polymeric) in a solvent at the molecular level. Further, the
thermodynamic
stability of the solute/solvent solution can be described by the following
equation 1:
Equation 1
AG,ni, =H?fl¨ T
where AGõiiõ is the Gibbs free energy change of mixing of a solute with a
solvent, AHmix is
the enthalpy change of mixing, T is the absolute temperature, and ASõ,,õ is
the entropy of mixing.
To maintain a stable solution of a solute in a solvent, the Gibbs free energy
must be negative and
at a minimum. Thus, any combination of solute and solvent that minimize a
negative Gibbs free
energy at appropriate temperatures and pressures can be used for the present
invention.
As used herein, the term "standard boiling point" refers to the boiling
temperature at an
absolute pressure of exactly 100 kPa (1 bar, 14.5 psia, 0.9869 atm) as
established by the
International Union of Pure and Applied Chemistry (IUPAC).
As used herein, the term "standard enthalpy change of vaporization" refers to
the enthalpy
change required to transform a specified quantity of a substance from a liquid
into a vapor at the
standard boiling point of the substance.
As used herein, the term "polyethylene solution" refers to a solution of
polyethylene
dissolved in a solvent. The polyethylene solution may contain undissolved
matter and thus the
polyethylene solution may also be a "slurry" of undissolved matter suspended
in a solution of
polyethylene dissolved in a solvent.
As used herein, the terms "sedimentation" and "settling" refer to the tendency
of particles
within a suspension to separate from a liquid in response to a force
(typically a gravitational force)
acting upon the particles.
As used herein, the term "suspended contaminants" refers to unwanted or
undesired
constituents that are present throughout the bulk of medium of a heterogeneous
mixture.
As used herein, the term "solid media" refers to a substance that exists in
the solid state
under the conditions of use. The solid media may be crystalline, semi-
crystalline, or amorphous.
The solid media may be granular and may be supplied in different shapes (i.e.
spheres, cylinders,
pellets, etc.). If the solid media is granular, the particle size and particle
size distribution of solid
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media may be defined by the mesh size used to classify the granular media. An
example of
standard mesh size designations can be found in the American Society for
Testing and Material
(ASTM) standard ASTM Ell "Standard Specification for Woven Wire Test Sieve
Cloth and Test
Sieves." The solid media may also be a non-woven fibrous mat or a woven
textile.
As used herein, the term "purer polyethylene solution" refers to a
polyethylene solution
having fewer contaminants relative to the same polyethylene solution prior to
a purification step.
As used herein, the term "extraction" refers to the practice of transferring a
solute species
from a liquid phase (or solid matrix) across a phase boundary to a separate
immiscible liquid phase.
The driving force(s) for extraction are described by partition theory.
As used herein, the term "extracted" refers to a material having fewer solute
species relative
to the same material prior to an extraction step. As used herein, the term
"extracted reclaimed
polyethylene" refers to a reclaimed polyethylene having fewer solute species
relative to the same
reclaimed polyethylene prior to an extraction step.
As used herein, the term "virgin-like" means essentially contaminant-free,
pigment-free,
odor-free, homogenous, and similar in properties to virgin polymers.
As used herein, the term "primarily polyethylene copolymer" refers a copolymer
with
greater than 70 mol% of ethylene repeating units.
As used herein, any reference to international units of pressure (e.g. MPa)
refers to gauge
pressure.
II. Method for Purifying Contaminated Polyethylene
Surprisingly, it has been found that certain fluid solvents, which in a
preferred embodiment
exhibit temperature and pressure-dependent solubility for polymers, when used
in a relatively
simple process can be used to purify contaminated polyethylene, especially
reclaimed or recycled
polyethylene, to a near virgin-like quality. This process, exemplified in FIG.
1, comprises 1)
obtaining a reclaimed polyethylene (step a in FIG. 1), followed by 2)
extracting the polyethylene
with a fluid solvent at an extraction temperature (TE) and at an extraction
pressure (PE) (step b in
FIG. 1), followed by 3) dissolution of the polyethylene in a fluid solvent at
a dissolution
temperature (TD) and at a dissolution pressure (PD) (step c in FIG. 1),
followed by 4) sedimentation
of the polymer solution at a dissolution temperature (TD) and at a dissolution
pressure (PD) (step d
in FIG. 1), followed by 5) contacting the dissolved polyethylene solution with
solid media at a
dissolution temperature (TD) and at a dissolution pressure (PD) (step e in
FIG. 1), followed by
separation of the polyethylene from the fluid solvent (step fin FIG. 1).
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In one embodiment of the present invention, the purified polyethylene, which
may be
sourced from post-consumer waste streams, is essentially contaminant-free,
pigment-free, odor-
free, homogenous, and similar in properties to virgin polymers. Furthermore,
in a preferred
embodiment, the physical properties of the fluid solvent of the present
invention may enable more
energy efficient methods for separation of the fluid solvent from the purified
polyethylene.
Reclaimed Polyethylene
In one embodiment of the present invention, a method for purifying reclaimed
polyethylene
includes obtaining reclaimed polyethylene. For the purposes of the present
invention, the
reclaimed polyethylene is sourced from post-consumer, post-industrial, post-
commercial, and/or
other special waste streams. For example, post-consumer waste polyethylene can
be derived from
curbside recycle streams where end-consumers place used polymers from packages
and products
into a designated bin for collection by a waste hauler or recycler. Post-
consumer waste polymers
can also be derived from in-store "take-back" programs where the consumer
brings waste polymers
into a store and places the waste polymers in a designated collection bin. An
example of post-
industrial waste polymers can be waste polymers produced during the
manufacture or shipment of
a good or product that are collected as unusable material by the manufacturer
(i.e. trim scraps, out
of specification material, start up scrap). An example of waste polymers from
a special waste
stream can be waste polymers derived from the recycling of electronic waste,
also known as "e-
waste." Another example of waste polymers from a special waste stream can be
waste polymers
derived from the recycling of automobiles. Another example of waste polymers
from a special
waste stream can be waste polymers derived from the recycling of used
carpeting and textiles.
For the purposes of the present invention, the reclaimed polyethylene is a
homogenous
composition of an individual polymer or a mixture of several different
polyethylene compositions.
Non-limiting examples of polyethylene compositions are homopolymers and
copolymers of
ethylene, such as high density polyethylene (HDPE), low density polyethylene
(LDPE), linear low
density polyethylene (LLDPE), copolymers of ethylene and alpha-olefins, and
other dissolvable
polyethylene polymers that may be apparent to those having ordinary skill in
the art.
The reclaimed polyethylene may also contain various pigments, dyes, process
aides,
stabilizing additives, fillers, and other performance additives that were
added to the polymer during
polymerization or conversion of the original polymer to the final form of an
article. Non-limiting
examples of pigments are organic pigments, such as copper phthalocyanine,
inorganic pigments,
such as titanium dioxide, and other pigments that may be apparent to those
having ordinary skill
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in the art. A non-limiting example of an organic dye is Basic Yellow 51. Non-
limiting examples
of process aides are antistatic agents, such as glycerol monostearate and slip-
promoting agents,
such as erucamide. A non-limiting example of a stabilizing additive is
octadecy1-3-(3,5-di-
tert.buty1-4-hydroxypheny1)-propionate. Non-limiting examples of fillers are
calcium carbonate,
talc, and glass fibers.
Solvent
The fluid solvent of the present invention has a standard boiling point less
than about 70 C.
Pressurization maintains solvents, which have standard boiling points below
the operating
temperature range of the present invention, in a state in which there is
little or no solvent vapor. In
one embodiment, the fluid solvent with a standard boiling point less than
about 70 C is selected
from the group consisting of carbon dioxide, ketones, alcohols, ethers,
esters, alkenes, alkanes, and
mixtures thereof. Non-limiting examples of fluid solvents with standard boing
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-hexane, isomers of isohexane,
and other
substances that may be apparent to those having ordinary skill in the alt.
The selection of the fluid solvent used will dictate the temperature and
pressure ranges used
to perform the steps of the present invention. A review of polymer phase
behavior in solvents of
the kind described by the present invention is provided in the following
reference: McHugh et at.
(1999) Chem. Rev. 99:565-602.
Extraction
In one embodiment of the present invention, a method for purifying
polyethylene includes
contacting reclaimed polyethylene with a fluid solvent at a temperature and at
a pressure wherein
the polymer is essentially insoluble in the fluid solvent. Although not
wishing to be bound by any
theory, applicants believe that the temperature and pressure-dependent
solubility can be controlled
in such a way to prevent the fluid solvent from fully solubilizing the
polymer, however, the fluid
solvent can diffuse into the polymer and extract any extractable
contamination. The extractable
contamination may be residual processing aides added to the polymer, residual
product
formulations which contacted the polymer, such as perfumes and flavors, dyes,
and any other
extractable material that may have been intentionally added or unintentionally
became
Date Re9ue/Date Received 2020-10-01
14636M-DW 13
incorporated into the polymer, for example, during waste collection and
subsequent accumulation
with other waste materials.
In one embodiment, the controlled extraction may be accomplished by fixing the
temperature of the polymer/fluid solvent system and then controlling the
pressure below a pressure,
or pressure range, where the polymer dissolves in the fluid solvent. In
another embodiment, the
controlled extraction is accomplished by fixing the pressure of the
polymer/solvent system and
then controlling the temperature below a temperature, or temperature range
where the polymer
dissolves in the fluid solvent. The temperature and pressure-controlled
extraction of the polymer
with a fluid solvent uses a suitable pressure vessel and may be configured in
a way that allows for
continuous extraction of the polymer with the fluid solvent. In one embodiment
of the present
invention, the pressure vessel may be a continuous liquid-liquid extraction
column where molten
polymer is pumped into one end of the extraction column and the fluid solvent
is pumped into the
same or the opposite end of the extraction column. In another embodiment, the
fluid containing
extracted contamination is removed from the process. In another embodiment,
the fluid containing
extracted contamination is purified, recovered, and recycled for use in the
extraction step or a
different step in the process. In one embodiment of the present invention, the
extraction may be
performed as a batch method, wherein the reclaimed polyethylene is fixed in a
pressure vessel and
the fluid solvent is continuously pumped through the fixed polymer phase. The
extraction time or
the amount of fluid solvent used will depend on the desired purity of the
final purer polymer and
the amount of extractable contamination in the starting reclaimed
polyethylene. In another
embodiment, the fluid containing extracted contamination is contacted with
solid media in a
separate step as described in the "Purification" section below. In another
embodiment, a method
for purifying reclaimed polyethylene includes contacting reclaimed
polyethylene with a fluid
solvent at a temperature and at a pressure wherein the polymer is molten and
in the liquid state. In
another embodiment, the reclaimed polyethylene is contacted with the fluid
solvent at a
temperature and at a pressure wherein the polymer is in the solid state.
In one embodiment, a method for purifying reclaimed polyethylene includes
contacting
polyethylene with a fluid solvent at a temperature and a pressure wherein the
polyethylene remains
essentially undissolved. In another embodiment, a method for purifying
reclaimed polyethylene
includes contacting polyethylene with n-butane at a temperature from about 80
C to about 220 C.
In another embodiment, a method for purifying reclaimed polyethylene includes
contacting
polyethylene with n-butane at a temperature from about 100 C to about 200 C.
In another
embodiment, a method for purifying reclaimed polyethylene includes contacting
polyethylene with
Date Re9ue/Date Received 2020-10-01
14636M-DW 14
n-butane at a temperature from about 130 C to about 180 C. In another
embodiment, a method
for purifying reclaimed polyethylene includes contacting polyethylene with n-
butane at a pressure
from about 150 psig (1.03 MPa) to about 6,500 psig (44.82 MPa). In another
embodiment, a
method for purifying reclaimed polyethylene includes contacting polyethylene
with n-butane at a
pressure from about 3,000 psig (20.68 MPa) to about 6,000 psig (41.37 MPa). In
another
embodiment, a method for purifying reclaimed polyethylene includes contacting
polyethylene with
n-butane at a pressure from about 4,500 psig (31.03 MPa) to about 5,500 psig
(37.92 MPa).
In another embodiment, a method for purifying reclaimed polyethylene includes
contacting
polyethylene with propane at a temperature from about 80 C to about 220 C. In
another
embodiment, a method for purifying reclaimed polyethylene includes contacting
polyethylene with
propane at a temperature from about 100 C to about 200 C. In another
embodiment, a method for
purifying reclaimed polyethylene includes contacting polyethylene with propane
at a temperature
from about 130 C to about 180 C. In another embodiment, a method for purifying
reclaimed
polyethylene includes contacting polyethylene with propane at a pressure from
about 1,000 psig
(6.89 MPa) to about 15,000 psig (103.42 MPa). In another embodiment, a method
for purifying
reclaimed polyethylene includes contacting polyethylene with propane at a
pressure from about
2,000 psig (13.79 MPa) to about 10,000 psig (68.95 MPa). In another
embodiment, a method for
purifying reclaimed polyethylene includes contacting polyethylene with propane
at a pressure from
about 5,000 psig (34.47 MPa) to about 9,000 psig (62.05 MPa).
Dissolution
In one embodiment of the present invention, a method for purifying reclaimed
polyethylene
includes dissolving the reclaimed polyethylene in a fluid solvent at a
temperature and at a pressure
wherein the polymer is dissolved in the fluid solvent. Although not wishing to
be bound by any
theory, applicants believe that the temperature and pressure can be controlled
in such a way to
enable thermodynamically favorable dissolution of the reclaimed polymer in a
fluid solvent.
Furthermore, the temperature and pressure can be controlled in such a way to
enable dissolution of
a particular polymer or polymer mixture while not dissolving other polymers or
polymer mixtures.
This controllable dissolution enables the separation of polymers from polymer
mixtures.
In one embodiment of the present invention, a method for purifying polymers
includes
dissolving contaminated reclaimed polyethylene in a solvent that does not
dissolve the
contaminants under the same conditions of temperature and pressure. The
contaminants may
include pigments, fillers, dirt, and other polymers. These contaminants are
released from the
Date Re9ue/Date Received 2020-10-01
14636M-DW 15
reclaimed polyethylene upon dissolution and then removed from the polymer
solution via a
subsequent solid-liquid separation step.
In one embodiment of the present invention, a method for purifying reclaimed
polyethylene
includes dissolving polyethylene in a fluid solvent at a temperature and at a
pressure wherein the
polyethylene is dissolved in the fluid solvent. In another embodiment, a
method for purifying
reclaimed polyethylene includes dissolving polyethylene in n-butane at a
temperature from about
90 C to about 220 C. In another embodiment, a method for purifying reclaimed
polyethylene
includes dissolving polyethylene in n-butane at a temperature from about 100 C
to about 200 C.
In another embodiment, a method for purifying reclaimed polyethylene includes
dissolving
polyethylene in n-butane at a temperature from about 130 C to about 180 C. In
another
embodiment, a method for purifying reclaimed polyethylene includes dissolving
polyethylene in
n-butane at a pressure from about 1,000 psig (6.89 MPa) to about 12,000 psig
(82.74 MPa). In
another embodiment, a method for purifying reclaimed polyethylene includes
dissolving
polyethylene in n-butane at a pressure from about 2,000 psig (13.79 MPa) to
about 10,000 psig
(68.95 MPa). In another embodiment, a method for purifying reclaimed
polyethylene includes
dissolving polyethylene in n-butane at a pressure from about 4,000 psig (27.58
MPa) to about 6,000
psig (41.37 MPa). In another embodiment, a method for purifying reclaimed
polyethylene includes
dissolving polyethylene in n-butane at a mass percent concentration of at
least 0.5%. In another
embodiment, the polyethylene is dissolved at a mass percent concentration of
at least 1%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration of at least 2%.
In another embodiment, the polyethylene is dissolved at a mass percent
concentration of at least
3%. In another embodiment, the polyethylene is dissolved at a mass percent
concentration of at
least 4%. In another embodiment, the polyethylene is dissolved at a mass
percent concentration of
at least 5%. In another embodiment, a method for purifying reclaimed
polyethylene includes
dissolving polyethylene in n-butane at a mass percent concentration up to 20%.
In another
embodiment, the polyethylene is dissolved at a mass percent concentration up
to 18%. In another
embodiment, the polyethylene is dissolved at a mass percent concentration up
to 16%. In another
embodiment, the polyethylene is dissolved at a mass percent concentration up
to 14%. In another
embodiment, the polyethylene is dissolved at a mass percent concentration up
to 12%.
In another embodiment, a method for purifying reclaimed polyethylene includes
dissolving
polyethylene in propane at a temperature from about 90 C to about 220 C. In
another embodiment,
a method for purifying reclaimed polyethylene includes dissolving polyethylene
in propane at a
temperature from about 100 C to about 200 C. In another embodiment, a method
for purifying
Date Re9ue/Date Received 2020-10-01
14636M-DW 16
reclaimed polyethylene includes dissolving polyethylene in propane at a
temperature from about
130 C to about 180 C. In another embodiment, a method for purifying reclaimed
polyethylene
includes dissolving polyethylene in propane at a pressure from about 3,000
psig (20.68 MPa) to
about 20,000 psig (137.90 MPa). In another embodiment, a method for purifying
reclaimed
polyethylene includes dissolving polyethylene in propane at a pressure from
about 5,000 psig
(34.47 MPa) to about 15,000 psig (103.42 MPa). In another embodiment, a method
for purifying
reclaimed polyethylene includes dissolving polyethylene in propane at a
pressure from about 8,000
psig (55.16 MPa) to about 11,000 psig (75.84 MPa). In another embodiment, a
method for
purifying reclaimed polyethylene includes dissolving polyethylene in propane
at a mass percent
concentration of at least 0.5%. In another embodiment, the polyethylene is
dissolved at a mass
percent concentration of at least 1%. In another embodiment, the polyethylene
is dissolved at a
mass percent concentration of at least 2%. In another embodiment, the
polyethylene is dissolved
at a mass percent concentration of at least 3%. In another embodiment, the
polyethylene is
dissolved at a mass percent concentration of at least 4%. In another
embodiment, the polyethylene
is dissolved at a mass percent concentration of at least 5%. In another
embodiment, a method for
purifying reclaimed polyethylene includes dissolving polyethylene in propane
at a mass percent
concentration up to 20%. In another embodiment, the polyethylene is dissolved
at a mass percent
concentration up to 18%. In another embodiment, the polyethylene is dissolved
at a mass percent
concentration up to 16%. In another embodiment, the polyethylene is dissolved
at a mass percent
concentration up to 14%. In another embodiment, the polyethylene is dissolved
at a mass percent
concentration up to 12%.
Sedimentation
In one embodiment of the present invention, a method for purifying
polyethylene includes
separating the undissolved contaminants from the polyethylene solution via a
sedimentation (also
known as settling) step at a temperature and at a pressure wherein the polymer
remains dissolved
in the fluid solvent. In one embodiment, the settling step causes the
undissolved contaminants to
experience a force that uniformly moves the undissolved contaminants in the
direction of the force.
Typically the applied settling force is gravity, but can also be a
centrifugal, centripetal, or some
other force. The amount of applied force and duration of settling time will
depend upon several
parameters, including, but not limited to: particle size of the contaminant
particles, contaminant
particle densities, density of the fluid or solution, and the viscosity of the
fluid or solution. The
Date Re9ue/Date Received 2020-10-01
14636M-DW 17
following equation (equation 2) is a relationship between the aforementioned
parameters and the
settling velocity, which is a measure of the contaminant sedimentation rate:
Equation 2
= 2(pp ¨ pf)9r2
v ______________________________
917
where v is the settling velocity, pp is the density of the contaminant
particle, pf is the
density of the fluid or solution, g is the acceleration due to the applied
force (typically gravity), r
is the radius of the contaminant particle and n is the dynamic viscosity of
the fluid or solution.
Some of the key parameters that determine the solution viscosity are: the
chemical composition
of the fluid solvent, the molecular weight of the polymer dissolved in the
fluid solvent, the
concentration of dissolved polymer in the fluid solvent, the temperature of
the fluid solvent
solution, and the pressure of the fluid solvent solution.
In one embodiment, a method for purifying reclaimed polyethylene includes
settling
contaminants from a polyethylene/fluid solvent solution at a temperature and
at a pressure wherein
the polyethylene remains dissolved in the fluid solvent. In another
embodiment, a method for
purifying reclaimed polyethylene includes settling contaminants from a
polyethylene/n-butane
solution at a temperature from about 90 C to about 220 C. In another
embodiment, a method for
purifying reclaimed polyethylene includes settling contaminants from a
polyethylene/n-butane
solution at a temperature from about 100 C to about 200 C. In another
embodiment, a method for
purifying reclaimed polyethylene includes settling contaminants from a
polyethylene/n-butane
solution at a temperature from about 130 C to about 180 C. In another
embodiment, a method for
purifying reclaimed polyethylene includes settling contaminants from a
polyethylene/n-butane
solution at a pressure from about 1,000 psig (6.89 MPa) to about 12,000 psig
(82.74 MPa). In
another embodiment, a method for purifying reclaimed polyethylene includes
settling
contaminants from a poly ethy lene/n-butane solution at a pressure about 2,000
psig (13.79 MPa) to
about 10,000 psig (68.95 MPa). In another embodiment, a method for purifying
reclaimed
polyethylene includes settling contaminants from a polyethylene/n-butane
solution at a pressure
from about 4,000 psig (27.58 MPa) to about 6,000 psig (41.37 MPa). In another
embodiment, a
method for purifying reclaimed polyethylene includes settling contaminants
from a
polyethylene/n-butane solution wherein the polyethylene is dissolved at a mass
percent
concentration of at least 0.5%. In another embodiment, the polyethylene is
dissolved at a mass
Date Re9ue/Date Received 2020-10-01
14636M-DW 18
percent concentration of at least 1%. In another embodiment, the polyethylene
is dissolved at a
mass percent concentration of at least 2%. In another embodiment, the
polyethylene is dissolved
at a mass percent concentration of at least 3%. In another embodiment, the
polyethylene is
dissolved at a mass percent concentration of at least 4%. In another
embodiment, the polyethylene
is dissolved at a mass percent concentration of at least 5%. In another
embodiment, a method for
purifying reclaimed polyethylene includes settling contaminants from a
polyethylene/n-butane
solution where in the polyethylene is dissolved at a mass percent
concentration up to 20%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration up to 18%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration up to 16%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration up to 14%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration up to 12%.
In another embodiment, a method for purifying reclaimed polyethylene includes
settling
contaminants from a polyethylene/propane solution at a temperature from about
90 C to about
220 C. In another embodiment, a method for purifying reclaimed polyethylene
includes settling
contaminants from a polyethylene/propane solution with at a temperature from
about 100 C to
about 200 C. In another embodiment, a method for purifying reclaimed
polyethylene includes
settling contaminants from a polyethylene/propane solution at a temperature
from about 130 C to
about 180 C. In another embodiment, a method for purifying reclaimed
polyethylene includes
settling contaminants from a polyethylene/propane solution at a pressure from
about 3,000 psig
(20.68 MPa) to about 20,000 psig (137.90 MPa). In another embodiment, a method
for purifying
reclaimed polyethylene includes settling contaminants from a
polyethylene/propane solution at a
pressure from about 5,000 psig (34.47 MPa) to about 15,000 psig (103.42 MPa).
In another
embodiment, a method for purifying reclaimed polyethylene includes settling
contaminants from
a polyethylene/propane solution with at a pressure from about 8,000 psig
(55.16 MPa) to about
11,000 psig (75.84 MPa). In another embodiment, a method for purifying
reclaimed polyethylene
includes settling contaminants from a polyethylene/propane solution wherein
the polyethylene is
dissolved at a mass percent concentration of at least 0.5%. In another
embodiment, the
polyethylene is dissolved at a mass percent concentration of at least 1%. In
another embodiment,
the polyethylene is dissolved at a mass percent concentration of at least 2%.
In another
embodiment, the polyethylene is dissolved at a mass percent concentration of
at least 3%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration of at least 4%.
In another embodiment, the polyethylene is dissolved at a mass percent
concentration of at least
5%. In another embodiment, a method for purifying reclaimed polyethylene
includes settling
Date Re9ue/Date Received 2020-10-01
14636M-DW 19
contaminants from a polyethylene/propane solution where in the polyethylene is
dissolved at a
mass percent concentration up to 20%. In another embodiment, the polyethylene
is dissolved at a
mass percent concentration up to 18%. In another embodiment, the polyethylene
is dissolved at a
mass percent concentration up to 16%. In another embodiment, the polyethylene
is dissolved at a
mass percent concentration up to 14%. In another embodiment, the polyethylene
is dissolved at a
mass percent concentration up to 12%.
Purification
In one embodiment of the present invention, a method for purifying
polyethylene includes
contacting a contaminated polymer solution with solid media at a temperature
and at a pressure
wherein the polymer remains dissolved in the fluid solvent. The solid media of
the present
invention is any solid material that removes at least some of the
contamination from a solution of
reclaimed polyethylene dissolved in the fluid solvent of the present
invention. Although not
wishing to be bound by any theory, the applicants believe that the solid media
removes
contamination by a variety of mechanisms. Non-limiting examples of possible
mechanisms
include adsorption, absorption, size exclusion, ion exclusion, ion exchange,
and other mechanisms
that may be apparent to those having ordinary skill in the art. Furthermore,
the pigments and other
contaminants commonly found in reclaimed polyethylene may be polar compounds
and may
preferentially interact with the solid media, which may also be at least
slightly polar. The polar-
polar interactions are especially favorable when non-polar solvents, such as
alkanes, are used as
the fluid solvent.
In one embodiment of the present invention, the solid media is selected from
the group
consisting of inorganic substances, carbon-based substances, or mixtures
thereof. Useful examples
of inorganic substances include oxides of silicon, oxides of aluminum, oxides
of iron, aluminum
silicates, magnesium silicates, amorphous volcanic glasses, silica, silica
gel, diatomite, sand,
quartz, reclaimed glass, alumina, perlite, fuller's earth, bentonite, and
mixtures thereof. Useful
examples of carbon-based substances include anthracite coal, carbon black,
coke, activated carbon,
cellulose, and mixtures thereof. In another embodiment of the present
invention, the solid media
is recycled glass.
In one embodiment of the present invention, the solid media is contacted with
the polymer
in a vessel for a specified amount of time while the solid media is agitated.
In another embodiment,
the solid media is removed from the purer polymer solution via a solid-liquid
separation step. Non-
limiting examples of solid-liquid separation steps include filtration,
decantation, centrifugation,
Date Re9ue/Date Received 2020-10-01
14636M-DW 20
and settling. In another embodiment of the present invention, the contaminated
polymer solution
is passed through a stationary bed of solid media. In another embodiment of
the present invention,
the height or length of the stationary bed of solid media is greater than 5
cm. In another
embodiment of the present invention, the height or length of the stationary
bed of solid media is
greater than 10 cm. In another embodiment of the present invention, the height
or length of the
stationary bed of solid media is greater than 20 cm. In another embodiment of
the present
invention, the solid media is replaced as needed to maintain a desired purity
of polymer. In yet
another embodiment, the solid media is regenerated and re-used in the
purification step. In another
embodiment, the solid media is regenerated by fluidizing the solid media
during a backwashing
step.
In one embodiment, a method for purifying reclaimed polyethylene includes
contacting a
polyethylene/fluid solvent solution with solid media at a temperature and a
pressure wherein the
polyethylene remains dissolved in the fluid solvent. In another embodiment, a
method for
purifying reclaimed polyethylene includes contacting a polyethylene/n-butane
solution with solid
media at a temperature from about 90 C to about 220 C. In another embodiment,
a method for
purifying reclaimed polyethylene includes contacting a polyethylene/n-butane
solution with solid
media at a temperature from about 100 C to about 200 C. In another embodiment,
a method for
purifying reclaimed polyethylene includes contacting a polyethylene/n-butane
solution with solid
media at a temperature from about 130 C to about 180 C. In another embodiment,
a method for
purifying reclaimed polyethylene includes contacting a polyethylene/n-butane
solution with solid
media at a pressure from about 1,000 psig (6.89 MPa) to about 12,000 psig
(82.74 MPa). In another
embodiment, a method for purifying reclaimed polyethylene includes contacting
a polyethylene/n-
butane solution with solid media at a pressure from about 2,000 psig (13.79
MPa) to about 10,000
psig (68.95 MPa). In another embodiment, a method for purifying reclaimed
polyethylene includes
contacting a polyethylene/n-butane solution with solid media at a pressure
from about 4,000 psig
(27.58 MPa) to about 6,000 psig (41.37 MPa). In another embodiment, a method
for purifying
reclaimed polyethylene includes contacting a polyethylene/n-butane solution
with solid media
wherein the polyethylene is dissolved at a mass percent concentration of at
least 0.5%. In another
embodiment, the polyethylene is dissolved at a mass percent concentration of
at least 1%. In
another embodiment, the polyethylene is dissolved at a mass percent
concentration of at least 2%.
In another embodiment, the polyethylene is dissolved at a mass percent
concentration of at least
3%. In another embodiment, the polyethylene is dissolved at a mass percent
concentration of at
least 4%. In another embodiment, the polyethylene is dissolved at a mass
percent concentration of
Date Re9ue/Date Received 2020-10-01
14636M-DW 21
at least 5%. In another embodiment, a method for purifying reclaimed
polyethylene includes
contacting a poly ethylene/n-butane solution with solid media wherein the
polyethylene is dissolved
at a mass percent concentration up to 20%. In another embodiment, the
polyethylene is dissolved
at a mass percent concentration up to 18%. In another embodiment, the
polyethylene is dissolved
at a mass percent concentration up to 16%. In another embodiment, the
polyethylene is dissolved
at a mass percent concentration up to 14%. In another embodiment, the
polyethylene is dissolved
at a mass percent concentration up to 12%.
In another embodiment, a method for purifying reclaimed polyethylene includes
contacting
a polyethylene/propane solution with solid media at a temperature from about
90 C to about 220 C.
In another embodiment, a method for purifying reclaimed polyethylene includes
contacting a
polyethylene/propane solution with solid media at a temperature from about 100
C to about 200 C.
In another embodiment, a method for purifying reclaimed polyethylene includes
contacting a
polyethylene/propane solution with solid media at a temperature from about 130
C to about 180 C.
In another embodiment, a method for purifying reclaimed polyethylene includes
contacting a
polyethylene/propane solution with solid media at a pressure from about 3,000
psig (20.68 MPa)
to about 20,000 psig (137.90 MPa). In another embodiment, a method for
purifying reclaimed
polyethylene includes contacting a polyethylene/propane solution with solid
media at a pressure
from about 5,000 psig (34.47 MPa) to about 15,000 psig (103.42 MPa). In
another embodiment,
a method for purifying reclaimed polyethylene includes contacting a
polyethylene/propane
solution with solid media at a pressure from about 8,000 psig (55.16 MPa) to
about 11,000 psig
(75.84 MPa). In another embodiment, a method for purifying reclaimed
polyethylene includes
contacting a polyethylene/propane solution with solid media wherein the
polyethylene is dissolved
at a mass percent concentration of at least 0.5%. In another embodiment, the
polyethylene is
dissolved at a mass percent concentration of at least 1%. In another
embodiment, the polyethylene
is dissolved at a mass percent concentration of at least 2%. In another
embodiment, the
polyethylene is dissolved at a mass percent concentration of at least 3%. In
another embodiment,
the polyethylene is dissolved at a mass percent concentration of at least 4%.
In another
embodiment, the polyethylene is dissolved at a mass percent concentration of
at least 5%. In
another embodiment, a method for purifying reclaimed polyethylene includes
contacting a
polyethylene/propane solution with solid media wherein the polyethylene is
dissolved at a mass
percent concentration up to 20%. In another embodiment, the polyethylene is
dissolved at a mass
percent concentration up to 18%. In another embodiment, the polyethylene is
dissolved at a mass
percent concentration up to 16%. In another embodiment, the polyethylene is
dissolved at a mass
Date Re9ue/Date Received 2020-10-01
14636M-DW 22
percent concentration up to 14%. In another embodiment, the polyethylene is
dissolved at a mass
percent concentration up to 12%.
Separation
In one embodiment of the present invention, a method for purifying reclaimed
polyethylene
includes separating the purer polymer from the fluid solvent at a temperature
and at a pressure
wherein the polymer precipitates from solution and is no longer dissolved in
the fluid solvent. In
another embodiment, the precipitation of the purer polymer from the fluid
solvent is accomplished
by reducing the pressure at a fixed temperature. In another embodiment, the
precipitation of the
purer polymer from the fluid solvent is accomplished by reducing the
temperature at a fixed
pressure. In another embodiment, the precipitation of the purer polymer from
the fluid solvent is
accomplished by increasing the temperature at a fixed pressure. In another
embodiment, the
precipitation of the purer polymer from the fluid solvent is accomplished by
reducing both the
temperature and pressure. The solvent can be partially or completely converted
from the liquid to
the vapor phase by controlling the temperature and pressure. In another
embodiment, the
precipitated polymer is separated from the fluid solvent without completely
converting the fluid
solvent into a 100% vapor phase by controlling the temperature and pressure of
the solvent during
the separation step. The separation of the precipitated purer polymer is
accomplished by any
method of liquid-liquid or liquid-solid separation. Non-limiting examples of
liquid-liquid or
liquid-solid separations include filtration, decantation, centrifugation, and
settling.
In one embodiment, a method for purifying reclaimed polyethylene includes
separating
polyethylene from a polyethylene/fluid solvent solution at a temperature and a
pressure wherein
the polyethylene precipitates from solution. In another embodiment, a method
for purifying
reclaimed polyethylene includes separating polyethylene from a polyethylene/n-
butane solution at
a temperature from about 0 C to about 220 C. In another embodiment, a method
for purifying
reclaimed polyethylene includes separating polyethylene from a polyethylene/n-
butane solution at
a temperature from about 50 C to about 175 C. In another embodiment, a method
for purifying
reclaimed polyethylene includes separating polyethylene from a polyethylene/n-
butane solution at
a temperature from about 100 C to about 160 C. In another embodiment, a method
for purifying
reclaimed polyethylene includes separating polyethylene from a polyethylene/n-
butane solution at
a pressure from about 0 psig (0 MPa) to about 4,000 psig (27.58 MPa). In
another embodiment, a
method for purifying reclaimed polyethylene includes separating polyethylene
from a
polyethylene/n-butane solution at a pressure from about 50 psig (0.34 MPa) to
about 2,000 psig
Date Re9ue/Date Received 2020-10-01
14636M-DW 23
(13.79 MPa). In another embodiment, a method for purifying reclaimed
polyethylene includes
separating polyethylene from a polyethylene/n-butane solution at a pressure
from about 75 psig
(0.52 MPa) to about 1,000 psig (6.89 MPa).
In another embodiment, a method for purifying reclaimed polyethylene includes
separating
polyethylene from a polyethylene/propane solution at a temperature from about -
42 C to about
220 C. In another embodiment, a method for purifying reclaimed polyethylene
includes separating
polyethylene from a polyethylene/propane solution at a temperature from about
0 C to about
150 C. In another embodiment, a method for purifying reclaimed polyethylene
includes separating
polyethylene from a polyethylene/propane solution at a temperature from about
50 C to about
130 C. In another embodiment, a method for purifying reclaimed polyethylene
includes separating
polyethylene from a polyethylene/propane solution at a pressure from about 0
psig (0 MPa) to
about 15,000 psig (103.42 MPa). In another embodiment, a method for purifying
reclaimed
polyethylene includes separating polyethylene from a polyethylene/propane
solution at a pressure
from about 50 psig (0.34 MPa) to about 5,000 psig (34.48 MPa). In another
embodiment, a method
for purifying reclaimed polyethylene includes separating polyethylene from a
polyethylene/propane solution at a pressure from about 75 psig (0.52 MPa) to
about 1,000 psig
(6.89 MPa).
The citation of any document is not an admission that it is prior art with
respect to any
invention disclosed or claimed herein or that it alone, or in any combination
with any other
reference or references, teaches, suggest or discloses any such invention.
Further, to the extent
that any meaning or definition of a term in this document conflicts with any
meaning or definition
of the same term in a document cited herein, the meaning or definition
assigned to that term in this
document shall govern.
While particular embodiments of the present invention have been illustrated
and described,
it would be obvious to those skilled in the art that various other changes and
modification can be
made without departing from the spirit and scope of the invention. It is
therefore intended to cover
in the appended claims all such changes and modification that are within the
scope of the present
invention.
Date Re9ue/Date Received 2020-10-01
