Patent Application
20210324170
The present invention generally relates to a method of producing a purer plastic from a first plastic. More specifically, the first plastic is subjected to bulk purification or surface and bulk purifications, wherein the total contamination present in the first plastic is reduced. The resulting purer plastic is sufficiently purer to allow for use in demanding applications.
Synthetic plastics are ubiquitous in daily life due to their relatively low production costs and good balance of material properties. They 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, hundreds of millions of tons 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 causes the emission of greenhouse gases (GHG), primarily CO2, in the atmosphere.
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. Also, plastic waste is leaked into the environment, e.g. washed into river systems and ultimately out to sea.
Plastics recycling has emerged as one solution to mitigate the issues associated with the poor management of the end-of-life of plastics. Recovering and re-using plastics diverts waste from landfills and reduces the demand for virgin plastics made from fossil sources, which consequently reduces GHG emissions. In developed regions of the world, 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, and due to regulatory frameworks. The majority of recycled materials, including plastics (other than films), 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 (e.g. in bales) for resale. Plastics can be sorted into individual materials, such as single streams of high-density polyethylene (HDPE) and 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 polyamide (PA)). The single or mixed streams can then be further sorted, washed, and reprocessed at a plastics recovery facility (PRF) into pellets that are suitable for re-use in plastics processing, e.g., extrusion blow molding, profile extrusion, injection molding, and film making.
However, the utilization of these recycled plastics is currently limited due to contamination, which renders the plastics less valuable compared to virgin plastics. A key to increasing the recycle rates and lowering the CO2 emissions and plastics pollution is to reduce the contamination to a level allowing broader utilization across more end markets, especially those involving demanding applications.
Films are a special case of recycled plastics and are predominately polyolefin in composition. Films offer unique challenges for recycling that have yet to be resolved. The recycled film supply stream can be split into two general categories: 1) pre-consumer recycle film, which includes both in-plant scrap/edge-trim that can be re-used in the same process that generated it and post-industrial recycle (PIR) film, which is film generated by internal plant waste that is not used in the same process that produced it; 2) post-consumer recycle (PCR) film including post-commercial recycle film, which is film that has been used in commerce but not directly by at-home consumers (e.g. back-of-store shrink wrap, pallet wrap, wholesale bags, furniture wrap, agricultural film, etc.) and post-household recycled film, which is film that has been used in commerce directly by at-home consumers (e.g. retail bags, retail food packaging, overwraps for diapers and hygiene products, trash bags, etc.). Post-industrial film waste for use in recycling is collected on a plant-by-plant basis for controlled end markets and may or may not involve (or require) significant cleaning steps before recycling. Post-commercial film is collected at the point of sale and transported to various PRFs specializing in film for various cleaning operations and eventual distribution to an end market. In the US, post-household film is primarily collected in store take-back programs where the end consumer returns the film to a collection bin at a local store. Film-based PRFs collect the film waste and deliver it to end markets after sortation and cleaning. The utilization of film recycled materials is quite limited due to contamination. The contamination of films is higher than other forms due to the high surface area to volume ratio which allows greater opportunity for external contamination. Currently, most film-based recycled plastics are down-cycled into markets that are not circular and are of limited size such as plastics lumber. As the collection of film-based waste grows, the need for end markets beyond plastics lumber is essential. Ideally, film-based waste will eventually discover a second life in film-based applications, thus ensuring ongoing circularity.
The end markets cannot grow unless contamination is greatly reduced. Considering the high volume of film that is used in demanding end markets, it is important that recycled plastics coming from these markets re-enter the same end markets to support circularity. As such, the ability to remove even greater levels of contaminants is critical to achieving circularity and reducing CO2 emissions and plastics pollution. Plastics pollution is even more problematic for film considering the tremendous surface area per use and the mobility of the waste in the environment by both air and water.
While contamination is problematic for all end market applications, demanding markets have even stricter requirements especially on certain chemical contaminants. The relevant chemical contaminants are grouped into various chemical classes depending on the chemical structure of the contaminants. Non-limiting examples of these chemical classes of contaminants are heavy metals, pesticides, dioxins, furans, polychlorinated biphenyls (PCBs), phthalates, polycyclic aromatic hydrocarbons (PAHs), organotins, bisphenols, isothiazolins, glyphosphate, alkyl phenols, alkylphenol ethoxylates, aromatic amines, and flame retardants. In addition, the target levels of these contaminants can be extremely low. For instance, the target levels may be on the order of parts per million (ppm), parts per billion (ppb), and parts per trillion (ppt), wherein the initial contaminated plastic may contain levels 1,000 times the targeted levels. Net, a 1,000× reduction in chemical contamination is often required.
Mechanical recycling, also known as secondary recycling, is a 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. et al., Waste Management, 29(10) (2009), 2625-2643. Mechanical recycling of rigid plastics typically involves some form of surface washing followed by drying and melt densification. The melt densification step typically includes melt filtration and devolatilization. For film-based materials, there are dry and wet processes. In the dry process, a controlled film stream is typically shredded, dried, and then melt extruded into the final form. Melt filtration and devolatilization are typically part of the extrusion step. In wet processes, a controlled film stream is typically shredded, washed in an aqueous solution/solutions, dried, and then melt extruded into the final form. Melt filtration and devolatilization are typically part of the extrusion step. The above methods are generally acceptable at removing intentional surface contamination such as paper labels and unintentional surface contamination such as dirt but are poor at removing bulk contaminants.
U.S. Pat. No. 10,022,725 discloses a mechanical recycling method for cleaning linear low-density polyethylene (LLDPE)/LDPE film for use in recycling. The patent further discloses the steps of shredding, a first water washing step, a second size reduction step involving wet grinding, a friction washing step or steps where hot water is used in at least one step, a drying or multiple drying steps, and a compaction step. The method is likely to be quite effective at removing some surface contamination that is loosely bound but will be ineffective at removing bulk contamination due to extremely low solubility of the bulk contaminants in the aqueous washing media and/or limited diffusivity of the bulk contaminants within the plastic.
U.S. Pat. No. 9,616,595 discloses a mechanical recycling method for de-inking surface-printed plastic films. The patent further discloses steps of grinding, ink removal steps, general washing, recovery of the cleaning solution, recovering pigments, and drying. The ink removal step involves the use of an aqueous cleaning fluid with high pH and selective cleaning agents, such as dodecyl sulfate, and high turbulence. The method claims ability to remove surface printed ink, which potentially contributes to chemical contamination following heating in the recycling process. The process will have limited ability to remove bulk contaminants due to limited solubility of the bulk contaminants in the aqueous washing media and/or limited diffusivity of the bulk contaminants within the plastic.
To overcome the fundamental limitations of mechanical recycling, there have been many methods developed to purify contaminated plastics. Most of these methods use solvents to decontaminate and purify plastics. U.S. Pat. No. 7,935,736 discloses a method for recycling polyester from plastic waste using a solvent to dissolve the polyester prior to cleaning. This patent also discloses the need to use a precipitant to recover the polyester from the solvent.
U.S. Pat. No. 6,555,588 discloses a method to produce a polypropylene blend from a plastic mixture comprising other polymers. This patent discloses 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 time. The starting material is a porous pellet and the extraction conditions are below the melting temperature to enable conveyance in the process. This patent further discloses increasing the temperature of the solvent (or a second solvent) to dissolve the polymer prior to filtration. Further, the patent discloses the use of shear flow to precipitate polypropylene from solution. The polypropylene blend described in the patent contained up to 5.6 wt. % polyethylene contamination.
European Patent Application No. 849,312 discloses a process to obtain purer polyolefins from a polyolefin-containing plastic mixture or a polyolefin-containing waste. The patent application discloses 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 patent application further discloses contacting a hot polyolefin solution with bleaching clay and/or activated carbon to remove foreign components from the solution. Also, the patent application discloses cooling the solution to temperatures below 70° C. to crystallize the polyolefin and then removing adhering solvent by heating the polyolefin above its melting point, 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.
U.S. Pat. No. 5,198,471 discloses 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 patent further discloses heating the solvent to higher temperatures to dissolve additional polymers that were not solubilized at the first lower temperature. Finally, the patent discloses filtration of insoluble polymer components.
U.S. Pat. No. 5,233,021 discloses a method of extracting pure polymeric components from a multi-component structure (for example, waste carpeting) by 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 U.S. Pat. No. 5,198,471, this patent only discloses filtration of undissolved components.
U.S. Pat. No. 5,739,270 discloses 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 patent further discloses the step of filtering the thermoplastic co-solvent (with or without the working fluid) to remove particulate contaminants, such as glass particles.
U.S. Pat. No. 5,368,796 discloses a method for surface cleaning polyethylene films. The patent further discloses the steps of shredding, a first surface washing step (involving a boiling solvent at a temperature below the melting temperature of the polyethylene and at or near ambient pressure, while applying vigorous mechanical agitation for 30 min to rub the ink off), a second surface washing step (involving fresh solvent below the melting temperature of the polyethylene, while applying vigorous mechanical agitation for 30 min), a third surface washing step (involving the solvent below the melting temperature of the polyethylene, while applying vigorous mechanical agitation for 30 to 60 min, and devolatilization), and melt densification. Optionally, the method may include a water washing step prior to treatment with solvent to remove surface dirt. The patent further discloses that the solvent washing accomplishes extraction wherein the solvent does not dissolve the polymer. However, a small amount of wax, typically <1 wt. % may be removed. The solvent washing and extraction steps are further disclosed as occurring at the boiling point of the solvent, which is selected to be below the softening point of the polyethylene to avoid agglomeration. The above method is focused on the removal of surface printed inks and is silent on the removal of bulk permeable contaminants such as those described previously.
U.S. Patent Application No. 2009/0178693 discloses a method for purifying a plastic. The patent application further discloses a multi-step process involving granulation to form plastic chips, surface washing with supercritical CO2, surface washing and extraction with a high boiling solvent or mixture of solvents (such as limonene and ethylene lactate), a final surface washing with supercritical CO2 to remove the high boiling solvent on the surface, and devolatilization. Further disclosed is that the plastic chip feed material is stirred with the solvent and the shape of the chip is maintained. Also, it is disclosed that the recovered material remains as chips, which implies the process is completed at temperatures below the plastic's primary melting point.
U.S. Pat. No. 9,834,621 discloses a method for purifying polypropylene. The patent further discloses contacting the reclaimed polypropylene at a temperature from about 80° C. to about 280° C. and at a pressure from about 10 atm to about 544 atm with a first fluid solvent having a standard boiling point less than about 70° C., to produce an extracted reclaimed polypropylene; dissolving the extracted reclaimed polypropylene 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 280° C. and a pressure from about 14 atm to about 544 atm to produce a first solution comprising polypropylene, at least one dissolved contaminant, and at least one suspended contaminant; settling the first solution comprising polypropylene, at least one dissolved contaminants, and at least one suspended contaminant at a temperature from about 90° C. to about 280° C. and at a pressure from about 14 atm to about 544 atm to produce a second solution comprising polypropylene, at least one dissolved contaminant, and less of the at least one suspended contaminant; filtering the second solution at a temperature from about 90° C. to about 280° C. and at a pressure from about 14 atm to about 544 atm to produce a third solution comprising purer polypropylene, at least one dissolved contaminant, and even less of the at least one suspended contaminant; and separating the purer polypropylene from the third solution; and where the second fluid solvent has the same chemical composition or a different chemical composition as the first fluid solvent. The above method is highly suitable for removing contamination. However, the ability to dissolve, settle, and filter plastics is quite difficult and may not be feasible or practical for plastics with high molecular weight (MW), such as those used in films and blow molded containers. In addition, the above method is silent on removing surface contamination prior to extraction and dissolution, thus increasing the burden on such disclosed processes, especially filtration.
In summary, the solvent-based methods to purify contaminated plastics, as described above, do not address the issue of removing both surface and bulk contaminants from plastics sufficiently and efficiently to enable utilization in demanding applications, particularly in films and rigid applications involving high 1\4W plastics. Accordingly, there is a need for a method that: 1) produces a purer plastic, i.e., plastic without a significant amount of contamination that would allow use of it in demanding applications; 2) is relatively simple in terms of the number of unit operations; and 3) can be used in high MW plastics, such as those sourced from film and rigid applications.
In embodiments of the present invention, a method to extract contaminates from a first plastic to produce a purer plastic is provided that comprises providing a first plastic comprising individual contaminants, each individual contaminant having a concentration; extracting said individual contaminates from said first plastic at a temperature and a pressure, using an extraction solvent, in extraction stages, to produce a purer plastic comprising individual contaminates, each having a concentration; wherein said extraction is liquid/liquid wherein said temperature is above the primary melting point of the first plastic; wherein said first plastic individual contaminants comprise at least one of alkyl phenols, bisphenols, dioxins, PCBs, and phthalates; wherein each individual contaminate concentration in said purer plastic is reduced compared to each individual contaminate concentration in said first plastic; and wherein the average of said reductions of said concentrations of said first plastic contaminants to said purer plastic contaminants is at least about 55% or LOQ.
As used herein, the term “plastic” refers to polymer, such as polyethylene (PE), PP, PET, LLDPE, LDPE, HDPE, polyethylene co-polymers, ethyl vinyl acetate copolymer (EVA), ethyl vinyl alcohol copolymer (EVOH), ethylene acrylic acid copolymer (EAA), PS, PC, PVC, PET, SBS, PA, etc., or mixtures thereof. Such polymers are characterized by high molecular weight, which generally determines melt processability and solid-state mechanical properties. For the purposes of the present invention, the terms “polymer” and “plastic” are used interchangeably, and the term “MW” refers to the weight-average molecular weight of the polymer.
As used herein, the term “reclaimed plastic” refers to re-grind, post-industrial, post-commercial, or post-household plastic of various forms including film, fiber, non-woven, and rigid packaging.
As used herein, the term “recycled plastic” refers to reclaimed plastic converted to a form that is used in making products and packaging either in blends with virgin plastic or by itself. The recycled plastic may be purer than the reclaimed plastic or may be identical except in form.
As used herein, the term “Pre-Consumer Plastic” refers to plastic waste that has not met its intended end purpose and has not been used in commerce or used by end consumers. Pre-Consumer Plastic has two subcategories of reclaim including 1) Internal Scrap/regrind and 2) Post-Industrial. Internal scrap/regrind is different from Post-Industrial in that Post-Industrial is not re-usable in the same process in which it was produced. Recycle resulting from Post-Industrial reclaim is referred to as Post-Industrial Recycle or PIR.
As used herein, the term “Post-Consumer Plastic” refers to plastic reclaim that has met its intended end purpose and has been used in commerce. Post-Consumer Plastic has two subcategories of reclaim including 1) Post-Commercial Plastic and 2). Post-Household Plastic. Post-commercial plastics includes plastics that have been used in commerce and have met their desired purpose. Examples include back of store reclaim and wholesale bags. Post-household plastics include plastics that have been used in homes of retail consumers. Examples include front of store plastics, retail bags, retail packaging, etc. Recycle resulting from Post-Consumer Plastic reclaim is referred to as Post-Consumer Recycle or PCR.
As used herein, the term “first plastic” refers to the plastic which is fed into the purification process and has a level of contamination that may include both surface and bulk contamination. Non-limiting examples of first plastic are reclaimed film and reclaimed HDPE bottles.
As used herein, the term “purer plastic” refers to the plastic which is produced by the purification process from a first plastic. The purer plastic has a level of contamination that is generally lower than that of the first plastic.
As used herein, the term “1st Life plastic” refers to a virgin plastic that has not been utilized in its polymer form for any purpose.
As used herein, the term “contaminant” refers to any undesirable material contained on or within the plastic. The term “chemical contaminant” refers to any undesirable chemical species on the surface of the plastic or within the bulk of the plastic and comprises the molecular or elemental composition of the contaminant. The terms may be used interchangeably depending upon the intent. For example, paper contamination comprises cellulose. Net, cellulose would be one chemical contaminant within the paper contaminant. As used herein, the term “contamination” refers to the sum of all contaminants and the term “chemical contamination” refers to the sum of all chemical contaminants. The chemical contaminants are grouped in classes, which include chemical contaminants that have similar chemical structure. For example, As, Hg, and Cr are chemical contaminants in the “heavy metals” classification. Each contaminant may have different chemical attributes, such as solubility and diffusivity in the plastic, and target levels depending upon concentration and end use market.
As used herein, the term “surface contaminant” refers to a contaminant that is on the surface of the plastic. Similarly, the term “surface chemical contaminant” refers to the molecular or elemental composition of the surface contaminant. The surface contaminant may be attached to the surface of the plastic either loosely through physical attraction forces, or more strongly through polar or other forces. In general, a surface contaminant will have less than about 80% of its surface area embedded in the plastic.
As used herein, the term “bulk contaminant” refers to a contaminant that is in the bulk of the plastic. Similarly, the term “bulk chemical contaminant” refers to the molecular or elemental composition of the bulk contaminant. In general, a bulk contaminant will have more than about 80% of its surface area embedded in the plastic.
As used herein, the term “surface contamination” and “surface chemical contamination” refers to the sum of all surface contaminants and all surface chemical contaminants, respectively.
As used herein, the term “bulk contamination” and “bulk chemical contamination” refers to the sum of all bulk contaminants and all bulk chemical contaminants, respectively.
As used herein, the term “total contamination” refers to the sum of the surface contamination and bulk contamination and the sum of all the surface chemical contamination and bulk chemical contamination, respectively.
As used herein, the term “permeable contaminant” refers to a chemical contaminant that is both soluble and diffusible in the plastic. Non-limiting examples of permeable contaminants are formaldehyde, bisphenol A, and naphthalene.
As used herein, the term “impermeable contaminant” refers to a chemical contaminant that is either insoluble or non-diffusible in the plastic. Non-limiting examples of impermeable contaminants are heavy metals and gel particles composed of cross-linked or ultra-high molecular weight plastic (too large to diffuse).
As used herein, the term “permeable contamination” is the sum of all permeable contaminants and the term “impermeable contamination” is the sum of all impermeable contaminants. The sum of all permeable and impermeable contamination is the “chemical contamination” if described in molecular or elemental terms or just simply “the contamination” if described in general terms (such as cellulose vs paper).
As used herein, the term “intentional contaminant” refers to a contaminant that is intentionally added by the supply chain for a specific purpose to benefit the producer, retailer, or consumer, but may not be desired in the recycled plastic. Examples include print, paper labels, adhesives for labels, pigments (such as TiO2), process additives (such as antioxidant (AO)), etc., that are necessary for marketing, branding, processability, and/or end use performance. As used herein, the term “intentional chemical contaminant” refers to an intentional contaminant described by its chemical composition. As used herein, the term “intentional contamination” refers to the sum of all intentional contaminants and the term “intentional chemical contamination” refers to the intentional contamination described by its chemical composition.
As used herein, the term “unintentional contaminant” refers to any contaminant not intentionally added. Examples include dirt and cross-contamination that is not intentionally added by the producer, retailer, or consumer. As used herein, the term “unintentional chemical contaminant” refers to an unintentional contaminant described by its chemical composition. As used herein, the term “unintentional contamination” refers to the sum of all unintentional contaminants and the term “unintentional chemical contamination” refers to the unintentional contamination described by its chemical composition.
As used herein, the term “densified” refers to a state of plastic in which the bulk density of the plastic is higher than the bulk density of the original/pre-densified plastic and the original surface of the plastic is reduced and/or rendered inaccessible to wetting fluids. The process of producing a densified material is referred to as densification.
As used herein, the term “melt densification” refers to densification done near, at, or above the primary melting point of the plastic. Non-limiting methods of melt densification include melt extrusion and agglomeration with equipment, such as the Herbold HV series plastcompactor.
As used herein, the term “primary melting point” refers to the peak melting point (highest endothermic peak on a zero-slope baseline) of the plastic as measured using Differential Scanning calorimetry (DSC). For the purposes of the present invention, the terms “primary melting point”, “melting point”, “melting temperature”, and “primary melting temperature” are used interchangeably. For amorphous materials and/or materials lacking a distinct melting point, the defining temperature will be the approximate softening point of the material, which may be best characterized by the glass transition temperature. Those skilled in the art will understand the appropriateness of the criteria for non-semi-crystalline materials.
As used herein, the term “hexane” refers to a blend of hexane isomers, such as normal hexane (at least 45 vol %, and typically, about 53 vol %), iso hexane (2-methylpentane, 3-methylpentane, and 2,3-dimethylbutane), and neo hexane (2,2-dimethylbutane).
As used herein, the term “limit of quantification” or “LOQ” refers to the lower detection limit for a given chemical contaminant as determined by the analytical methods disclosed in section IX. The LOQ is a function of the methods used and may vary from test method to test method. The LOQ used herein is specific to the method listed in section IX.
As used herein, the term “ppm” refers to parts per million, “ppb” refers to parts per billion, and “pptr” refers to parts per trillion.
Plastics are predominately free of contamination (virgin plastics) when first produced at resin suppliers, such as Dow, Nova, ExxonMobil, etc. However, during the plastic's lifecycle (from production through distribution, consumer utilization, and eventual recycling) contamination is introduced either intentionally or unintentionally.
Non-limiting examples of intentional contamination include surface print, paper labels, adhesives for labels, pigments (such as TiO2), process additives (such as antioxidant (AO)), etc., that are necessary for marketing, branding, processability, and/or end use performance. Non-limiting examples of unintentional contamination are dirt, cross-contamination, certain heavy metals, pesticides, dioxins, furans, PCBs, etc. Also, unintentional contamination can be produced from reactions involving intentional contaminants, such as the oxidation of paper labels to dioxins, degradation of adhesives or print binders, etc. Most of the latter occurs during melt densification methods used during the recycling process. Further, oxidation of the plastic during melt processing steps, such as those used for original package or product creation and/or latter recycling, will produce unintentional contamination, such as gels. In addition, unintentional contamination may result from interaction with products. For example, packaging materials that contain cleaning mixtures (e.g. limonene, surfactants, etc.), food (e.g. various organics), etc., will potentially become contaminated with such products. Finally, unintentional contamination can enter the plastic during production, e.g. contamination of a plastic with reaction by-products, unreacted monomers, etc.
It is recognized that different reclaimed plastic sources have different contamination and associated risks. Clearly, reclaimed plastic streams of unknown origin and lifecycle will be most abundant but also represent the highest potential for contamination. On the other side, controlled reclaimed plastic streams are available and represent lower potential risk for demanding applications. For instance, if a reclaimed plastic stream is known to be from medical or food applications, then such reclaimed plastic stream will not contain any undesirable contaminants up to the point of distribution to the consumer else these plastics would not have been approved for use in these applications. As such, contamination preventing re-use in these same applications would primarily be unintentional contamination, which must originate from external sources and enter the plastic through surface contamination. A small amount of contamination could result from reactions involving intentional contamination such as oxidation of cellulosics to dioxins during melt densification.
Pre-consumer plastic generally has the lowest level of contamination due to its known composition and controlled history. It may include intentional contamination, such as surface print and opacifiers, but because these are known and controlled, it is quite easy to find applications tolerating such known contaminants. In addition, pre-consumer plastic tends to have low amounts of unintentional contamination due to the controlled history preventing external contamination. Thus, pre-consumer plastics that were originally destined for use in demanding applications such as medical or food, will be ideal sources of reclaimed plastic for various uses with minimal cleaning/purification. The latter pre-consumer plastic in the form of film is referred to as “Approved Sourced Post-Industrial Film” (ASPIF). On the downside, the ASPIF stream is very limited in supply and does not support circularity.
Post-consumer plastics are generally more contaminated than pre-consumer plastics. The post-commercial subclass of post-consumer plastic has the next lowest level of contamination relative to pre-consumer recycle considering the somewhat controlled life cycle within the commerce supply chain. In general, post-commercial reclaim plastic will have a known and controlled level of intentional contamination, thus enabling broad utilization as reclaimed plastic. However, unintentional contamination is known to be ubiquitous and problematic with this stream, which prevents broad usage in controlled fields like medical or food. Post-commercial plastic that is sourced from controlled fields, such as medical or food, will be potentially usable back into these fields following adequate cleaning/purification. Post-commercial plastic sourced from demanding applications in the form of film is referred to as “Approved Source Post-Commercial Film” (ASPCF). To accommodate the on-going need of purer reclaimed plastic, recycle material suppliers have recently introduced post-commercial film sources with more controlled and known history. These new sources are called High-Custody sources and are primarily utilized with the post-commercial film stream. Net, High-Custody Post-Commercial film sources should have reduced level of contamination relative to general Post-Commercial film sources. On the downside, these High-Custody sources are of limited volume and are more costly.
The post-household subclass of post-consumer has the highest level of contamination considering the uncontrolled life cycle within the commerce channel. Such plastic has high levels of both intentional and unintentional contamination that is highly variable, unknown, and uncontrolled. Such plastic may include plastic sources that were originally unacceptable for use in demanding applications.
Surprisingly, plastics made purer by the present invention may allow source plastics from post-industrial (both ASPIF and uncontrolled source), post-commercial (both ASPCF and uncontrolled source), and post-household plastic to be used in the demanding areas of medical and food applications with some limitations.
For the purposes of the present invention, non-limiting examples of plastic are film, sheet, injection molded parts, blow molded parts, fiber, nonwovens, wovens, thermoformed parts, and extruded strands.
The first plastic can be a virgin plastic or a reclaimed plastic. Also, the first plastic can be a first-life plastic (has been used only once before it entered the reclaimed plastic stream), second-life plastic (has been used twice before it entered the reclaimed plastic stream), or higher-life plastic (has been used many times before it entered the reclaimed plastic stream). In embodiments of the present invention, the first plastic comprises a reclaimed plastic. In another embodiment of the present invention, the first plastic comprises a virgin plastic. In one embodiment of the present invention, the first plastic comprises film. In yet another embodiment of the present invention, the first plastic is selected from the group comprising film, injection molded part, blow molded part, nonwoven, woven, thermoformed part, extruded strand, or mixtures thereof.
In embodiments of the present invention, the first plastic comprises a regrind/edge-trim/in-plant waste plastic. In another embodiment of the present invention, the first plastic comprises a post-industrial plastic. In yet another embodiment of the present invention, the first plastic comprises a post-industrial film. In yet another embodiment of the present invention, the first plastic comprises a post-industrial non-woven. In yet another embodiment of the present invention, the post-industrial film is ASPIF. In embodiments of the present invention, the first plastic comprises a post-commercial plastic. In another embodiment of the present invention, the first plastic comprises a post-commercial film. In another embodiment of the present invention, the first plastic comprises a post-commercial non-woven. In yet another embodiment of the present invention, the post-commercial film is ASPCF. In yet another embodiment of the present invention, the first plastic comprises High-Custody post-commercial film. In embodiments of the present invention, the first plastic comprises a post-household plastic. In another embodiment of the present invention, the first plastic comprises a post-household film. In yet another embodiment of the present invention, the first plastic comprises a post-household non-woven.
In embodiments of the present invention, the first plastic comprises polystyrene, co-polystyrene, polyamides, co-polyamides, polycarbonates, thermoplastic elastomers, styrenic block copolymers, polyesters, co-polyesters, polyvinylalcohols, pvcs, and copolymers of any of the above and mixtures of any of the above. In embodiments of the present invention, the first plastic comprises polyolefins, polyolefin copolymers, and polyolefin polar copolymers. In another embodiment of the present invention, the first plastics comprises LDPE and LLDPE copolymers.
In another embodiment of the present invention, the first plastic comprises PP. In yet another embodiment of the present invention, the first plastic comprises HDPE and HDPE copolymers. In embodiments of the present invention, the first plastic comprises film, and the film comprises polyethylene and polyethylene copolymers.
The first plastic may be in many forms including but not limited to pellets, micronized pellets, ground pellets, shredded film, shredded or ground injection molded parts, shredded or ground blow molded parts, thermoformed parts, shredded nonwoven or woven, extruded strands, or agglomerated particles. In embodiments of the present invention, the first plastic comprises pellets.
Contaminants can generally be broken down into two migration categories: 1) permeable; and 2) impermeable. Contaminants that are permeable have solubility and diffusivity in the first plastic to allow migration into, through the plastic, and out of the plastic due to a chemical potential gradient. In other words, permeable contaminants and the grouping called permeable contamination are mobile. Impermeable implies that the contaminant does not have sufficient solubility and diffusivity to significantly move into, through the plastic, and out of the plastic. In other words, impermeable contamination represented by the summation of all impermeable contaminants is essentially immobile. Net, wherever impermeable contamination is first deposited, such contamination will remain in that location until physically removed, convectively transferred, or placed in contact with a different material which is permeable to the contaminant.
The chemical contaminants in the first plastic may be numerous but generally fall into one of several relevant chemical classes. Representative classes comprise pesticides, aldehydes, allergic fragrances, izioalines, alkylphenol ethoxylates, alkylphenol s, bisphenols, dioxins, dioxin-like, furans, PCBs, organotins, metals, phthalates, polyaromatic hydrocarbons (PAHs), etc. Only some of these chemical classes are routinely found in pre and post-consumer reclaim materials including pesticides, alkylphenol ethoxylates, alkylphenol s, bisphenols, dioxins, dioxin-like, furans, PCBs, metals, organotins, phthalates, and PAHs.
Using the analytical methods disclosed in section IX Methods, the LOQs of the various contaminants may differ by orders of magnitude. For example, the LOQ of a typical pesticide is about 10 ppb; the LOQ of typical alkylphenol ethoxylate is about 50 ppb; the LOQ of a typical alkylphenol is about 5 ppb; the LOQ of bisphenol-A is about 5 ppb; the LOQ of typical dioxin is about 0.2 pptr; the LOQ of a typical furan is about 0.2 pptr; the LOQ of a typical PCB is about 5 pptr; the LOQ of a typical heavy metal is about 100 ppb; the LOQ of a typical organotin is about 300 pptr; the LOQ of typical phthalate is 50 ppb; the LOQ of a typical PAH is 1 ppb.
Several films sources were broadly classified for chemical contamination including three ASPIF sources, three High-Custody Post-Commercial Film sources, three Post-Commercial film sources, and one Post-Household film source using the analytical methods disclosed in section IX Methods, as shown in TABLES 1a-1i. Note: To simplify the presentation of chemical contamination results, the concentration data is displayed in terms of LOQ instead of absolute weight fraction. For example, if the contaminant concentration is 10 ppm and the LOQ is 1 ppm, then the concentration would be 10×LOQ or just 10 displayed in the data tables.
The tested ASPIF sources were primarily absent detectable levels of chemical contaminants except for alkylphenols and heavy metals and small amounts of organotins and PAHs. The chemical contaminant results for these ASPIF sources serves as a guide for the level of chemical contamination representative of these controlled end markets and demonstrates that heavy metals, which are of low transfer risk anyway, are ubiquitous across all film sources. Hence, heavy metals were not included in ongoing analysis within this application. The tested High-Custody Post-Commercial film sources were largely free of pesticides and alkylphenol ethoxylates, but contained detectable levels of alkylphenols, bisphenol-A, dioxins/furans/PCBs, and PAHs and low levels of phthalates. The tested Post-Commercial Film sources were heavily contaminated with every class evaluated; for example, dioxins were typically as high as 40× the LOQ, but for one source, dioxins were as high as 200× the LOQ. The tested Post-Household source was the most heavily contaminated; for example, dioxins were as high as 300× the LOQ and PCBs were as high as 180× the LOQ.
From TABLES 1a-1i, representative chemical species were selected from the various classes based upon prevalence across the spectrum of reclaim sources. The selected representative chemical species within these classes include: piperonyl butoxide (representing pesticides); 4-t-octylphenolhexaethoxylate and iso-nonylphenoltriethoxylate (representing alkylphenolethoxylates); iso-nonylphenol and 4-tert-pentylphenol (representing alkylphenol s); bisphenol-A (representing phenols); 1.2.3.6.7.8-HxCDD, 1.2.3.4.6.7.8-HpCDD, and OCDD (representing dioxins); OCDF (representing furans); PCB 105 and PCB 118 (representing PCBs); monobutyltin and dibutyltin (representing organotins); dibutyl phthalate and di-2-ethylhexyl phthalate (representing phthalates); and fluoranthene and phenanthrene (representing polycyclicaromatic hydrocarbons (PAHs).
In embodiments of the present invention, said chemical contaminants in said first plastic include at least one chemical contaminant and such is selected from the group comprising pesticides, alkyl phenols, alkylphenol ethoxylates, bisphenols, dioxins, furans, PCBs, phthalates, PAHs or mixtures thereof.
In embodiments of the present invention, the pesticides comprise piperonyl butoxide, BAC, DEET, and DDAC. In another embodiment of the present invention, the alkylphenol ethoxylates comprise iso-Nonylphenolmonoethoxylate, iso-Nonylphenoldiethoxylate, iso-Nonylphenoltriethoxylate, and iso-Nonylphenoltetraethoxylate. In yet another embodiment of the present invention, the alkyl phenols comprise iso-Nonylphenol, 4-tert-butylphenol, and 4-tert-Pentylphenol. In even yet another embodiment of the present invention, the bisphenols comprise bisphenol-A. In even yet another embodiment of the present invention, the dioxins comprise 1,2,3,6,7,8-HxCDD, 1.2.3.4.6.7.8-HpCDD, and OCDD. In even yet another embodiment of the present invention, the furans comprise OCDF. In even yet another embodiment of the present invention, the PCBs comprise PCB 77, PCB 81, PCB 126, PCB 105, PCB 114, PCB 118, PCB 123, PCB 156, and PCB 167. In event yet another embodiment of the present invention, the phthalates comprise di-2-propylheptyl phthalate, disobutyl phthalate, dibutyl phthalate, di-1-ethylhexyl phthalate, and diisononyl phthalate. In even yet another embodiment of the present invention, the PAHs comprise acenaphthene, acenaphthylene, anthracene, benzo[a]anthracene, benzo[b]fluoroanthene, benzo[e]pyrene, benzo[g.h.i]perylene, chrysene, cyclopenta[c.d]pyrene, flyoroanthene, fluorene, naphthalene, phenanthrene, and pyrene. In even yet another embodiment of the present invention, the organotins comprise monobutylin, dibutyltin, and dioctylin.
In embodiments of the present invention, the contaminants in the first plastic may comprise 4-tert-pentylphenol. In embodiments of the present invention, the contaminants in the first plastic may comprise bisphenol-A. In embodiments of the present invention, the contaminants in the first plastic may comprise OCDD. In embodiments of the present invention, the contaminants in the first plastic may comprise PCB 118. In embodiments of the present invention, the contaminants in the first plastic may comprise di-2-ethylhexyl phthalate.
In order to simplify the presentation of the purification results for objects of the present invention and associated examples, the number of chemical species presented per chemical class is limited to the aforementioned representative chemical species for each chemical class as shown in Table 2 along with the associated LOQ and the respective levels for the tested ASPIF sources. Note: Even though more in-depth and complete chemical analysis was completed for all objects of the present invention, only the representative chemicals are shown ongoing. This simplification does not impact or alter the inventive matter or conclusions reached from such. The specific chemicals selected, adequately and consistently represent the broader class with respect to purification.
In embodiments of the present invention, the concentration of each pesticide in the purer plastic is lower than its respective LOQ; wherein the first plastic has at least one detectable pesticide. In embodiments of the present invention, the concentration of bis-phenol A in the purer plastic is lower than its respective LOQ; wherein the first plastic has at least detectable bis-phenol A. In embodiments of the present invention, the concentration of each dioxin in the purer plastic is lower than its respective LOQ; wherein the first plastic has at least one detectable dioxin. In embodiments of the present invention, the concentration of each PCB in the purer plastic is lower than its respective LOQ; wherein the first plastic has at least one detectable PCB. In embodiments of the present invention, the concentration of each phthalate in the purer plastic is lower than its respective LOQ; wherein the first plastic has at least one detectable phthalate.
In embodiments of the present invention, the concentration of piperonyl butoxide in said purer plastic is less than about 10 ppb; wherein said first plastic has a concentration of piperonyl butoxide above 10 ppb; the concentration of 4-tert-Pentylphenol in said purer plastic is less than about 5 ppb; wherein said first plastic has a concentration of 4-tert-pentylphenol is above 5 ppb; the concentration of bisphenol-A in said purer plastic is less than about 5 ppb; wherein said first plastic has a concentration of bisphenol-A is above 5 ppb; the concentration of OCDD in said purer plastic is less than about 0.2 pptt; wherein said first plastic has a concentration of OCDD above 0.2 pptr; the concentration of PCB 118 in said purer plastic is less than about 10 pptr; wherein said first plastic has a concentration of PCB 118 above 10 pptr; and the concentration of di-2-ethylhexyl phthalate in said purer plastic is less than about 50 ppb; wherein said first plastic has a concentration of di-2-ethylhexyl phthalate above 50 ppb.
In general, the efficacy of a cleaning process to remove a specific chemical contaminant is determined by the removal efficiency, defined as the difference in concentration of the chemical contaminant in the first plastic and the concentration of the chemical contaminant in the purer plastic divided by the concentration of the chemical contaminant in first plastic expressed as a percentage. However, the removal efficiency is somewhat insufficient due to the inability to determine concentrations below the LOQ. For example, if a cleaning process reduces the contamination from 2×LOQ to less than the LOQ, then the removal efficiency could be anywhere between 50% and 100%, which is a significant difference. Thus, the removal efficiency is only sufficient when the first plastic and purer plastic chemical contaminant concentration are both above LOQ. For simplicity, if the purer plastic has a chemical contaminant concentration below LOQ, then removal efficiency is calculated by assuming the chemical contaminant concentration of the purer plastic is at the LOQ and the removal efficiency is considered a minimum value and designated with >. For the above example, the removal efficiency would be calculated as 100(2×LOQ−1×LOQ)/(2×LOQ)=100(2−1)/2=50%. Thus, the removal efficiency would be >50%. In certain cases, the purer plastic will have a higher level of a contaminant than the first plastic due to 1) measurement error, 2) contaminant hot spots and cold spots in the first plastic, 3) external contamination during sampling, and 4) the purification process adds contamination. In such cases, the removal efficiency is set to 0% to not bias the average results. If such occurs consistently for a given cleaning process, then such is more likely attributable to the purification process and should be more closely examined, but such was not generally the case for the cleaning processes of the present invention.
In embodiments of the present invention, the removal efficiency of the piperonyl butoxide contaminant is >55% wherein said piperonyl butoxide concentration in the first plastic is at least 10 ppb. In another embodiment of the present invention, the removal efficiency of the piperonyl butoxide contaminant is >75% wherein said piperonyl butoxide concentration in the first plastic is at least 10 ppb. In yet another embodiment of the present invention, the removal efficiency of the piperonyl butoxide contaminant is >90% wherein said piperonyl butoxide concentration in the first plastic is at least about 10 ppb.
In embodiments of the present invention, the removal efficiency of the 4-tert-pentylphenol contaminant is >55% wherein said 4-tert-pentylphenol concentration in the first plastic is at least 5 ppb. In another embodiment of the present invention, the removal efficiency of the 4-tert-pentylphenol contaminant is >70% wherein said 4-tert-pentylphenol concentration in the first plastic is at least 5 ppb.
In embodiments of the present invention, the removal efficiency of the bisphenol A contaminant is >55% wherein said bisphenol A concentration in the first plastic is at least 5 ppb. In another embodiment of the present invention, the removal efficiency of the bisphenol A contaminant is >75% wherein said bisphenol A concentration in the first plastic is at least 5 ppb. In yet another embodiment of the present invention, the removal efficiency of the bisphenol A contaminant is >90% wherein said bisphenol A concentration in the first plastic is at least 5 ppb.
In embodiments of the present invention, the removal efficiency of the OCDD contaminant is >55% wherein said OCDD concentration in the first plastic is at least about 0.2 pptr. In another embodiment of the present invention, the removal efficiency of the OCDD contaminant is >75% wherein said OCDD concentration in the first plastic is at least about 0.2 pptr. In yet another embodiment of the present invention, the removal efficiency of the OCDD contaminant is >85% wherein said OCDD concentration in the first plastic is at least about 0.2 pptr.
In embodiments of the present invention, the removal efficiency of the PCB 118 contaminant is >55% wherein said PCB 118 concentration in the first plastic is at least 10 pptr. In another embodiment of the present invention, the removal efficiency of the PCB 118 contaminant is >75% wherein said PCB 118 concentration in the first plastic is at least 10 pptr. In yet another embodiment of the present invention, the removal efficiency of the PCB 118 contaminant is >90% wherein said PCB 118 concentration in the first plastic is at least 10 pptr.
In embodiments of the present invention, the removal efficiency of the Phenanthrene contaminant is >55% wherein said Phenanthrene concentration in the first plastic is at least 1 part per billion. In another embodiment of the present invention, the removal efficiency of the Phenanthrene is >75% wherein said Phenanthrene concentration in the first plastic is at least 1 part per billion. In yet another embodiment of the present invention, the removal efficiency of the Phenanthrene contaminant is >90% wherein said Phenanthrene concentration in the first plastic is at least 1 part per billion.
In general, chemical contaminants include both permeable and impermeable chemical contaminants. Not wishing to be bound by theory, applicants believe that, with respect to polyethylene and polypropylene type reclaimed materials, contaminants such as pesticides, dioxins, furans, PCBs, phthalates, PAHs, bisphenols, alkyl phenols, and alkylphenol ethoxylates should be permeable; and contaminants, such as heavy metals should be impermeable. Organotins may be permeable or impermeable depending upon the molecular size.
Contamination can be located on the surface of the plastic or in the bulk. Contamination on the surface is most readily and easily removed by surface cleaning technologies available on the market today. If the surface contamination is permeable in the plastic, then it will become bulk contamination over time through diffusion mechanisms, thus complicating reduction and limit the effectiveness of surface cleaning technologies. If the surface contamination is impermeable in the plastic, then such contamination will not diffuse into the bulk and will be reduced by simple surface cleaning methods, such as aqueous washing. Bulk contamination of either permeable or impermeable type typically cannot be effectively removed via simple surface purification methods, such as aqueous washing. Bulk contamination of the impermeable type (also known as bulk impermeable contamination) is trapped in the bulk plastic and may be freed through mechanisms comprising melt convection, melt filtration, or dissolution/disintegration of the bulk plastic.
As discussed previously, contamination can be introduced externally throughout the lifecycle of the plastic. If the contamination is impermeable, then such contamination will largely remain on the surface during the plastic lifecycle up to the point of reclaiming. If the contamination is permeable, then over time, the contamination will migrate into the bulk plastic. Thus, absent a contamination or purification event, the contamination will remain essentially constant, but the balance of surface to bulk contamination will change with time but will approach equilibrium at long time. In general, loosely bound surface contamination such as dirt may be in the 0.01 to about 0.1 wt %; whereas the chemical contamination, especially the chemical contaminants of concern for this invention, will be ppm, ppb, or even pptrillion.
Permeable and impermeable contamination represents different challenges in various uses, such as medical or food applications. For instance, permeable contamination whether in the bulk plastic or on the surface of the plastic will have the potential to migrate to uncontaminated materials, such as a product or to human skin. Thus, if a package contains permeable contaminants, then such contaminants will have the potential to migrate into the product and render it unsuitable for various uses. However, if the contaminant is impermeable and in the bulk of the plastic, then it will have low ability to transfer to the product or to the user's skin unless the bulk plastic is disintegrated or ingested. Thus, a package could potentially use this contaminated plastic material and not risk contamination transfer to the product or transfer directly to skin. However, if the contaminant is impermeable and on the surface of the plastic, then such contamination would have the ability to transfer to the product or skin by direct contact transfer and would be unacceptable for use in these demanding applications. Surface contamination, both permeable and impermeable, can be transformed into bulk contamination through convective mechanism, such as melt mixing and melt densification. These methods exchange or eliminate surface area with bulk material. For example, if surface contaminated film is melt-densified or melt extruded into a different shape, such as a pellet, then all original surface contamination will become bulk contamination whether such is impermeable or not and such bulk contamination will be more difficult to remove with purification processes. Melt densification is common in the recycle industry. It is also common in the recycle industry to shred incoming plastics. The latter methods generally do not convert surface contamination to bulk contamination. Ideally, surface purification methods, such as surface washing, take place on the original contaminated surface such as shredded film wherein all original surface area is reachable by the surface washing fluid.
In general, surface contamination and bulk contamination are difficult to differentiate using analytical methods. Most analytical methods for permeable chemical contaminants involve solvent extraction of the contaminant from the plastic over extended periods of time >6 hours and with exposure to extreme solvent to plastic mass ratios >100:1 and then quantifying the contaminant in the solvent using methods, such as Gas Chromatography-Mass Spectrometry (GC-MS). Such analytical methods quantify contamination but do not differentiate surface from bulk contaminants. The efficiency of a purification method to remove surface contamination can be estimated from the difference in contamination before and after the surface cleaning step but such assumes bulk contamination is not significant impacted, which is likely the case for surface washing with aqueous surface washing fluids discussed in the current invention. A more accurate way to quantify surface contamination is through washing and then solvent extraction of the contaminant at various times and then extrapolating the amount of the contaminant removed at infinitesimal time, which will approximate the amount of surface contamination. However, this method is time consuming and costly especially for contaminants that are difficult to measure in general. In addition, since the balance of surface and bulk contaminants are dynamic, it is difficult to quantify without referencing an exact sampling time. A simple method for quantifying general surface contamination (not chemical surface contamination or species based chemical contaminants) is weighing the first plastic before and after the surface washing step.
In general, bulk contamination will not be appreciably removed by simple aqueous surface washing. Permeable bulk contamination can be removed by diffusion mechanisms through gradients in chemical potential. Whereas bulk impermeable contamination is essentially trapped by the bulk polymer and methods to free the trapped contaminant comprise melt convection, melt filtration, and dissolution/disintegration of the plastic.
Surface purification methods reduce surface contamination. One such method is surface washing with a surface washing fluid that is typically water based. Surface washing is ideally completed before any melt mixing or melt densification to allow effective cleaning of the original contaminated surface. The first plastic will generally be in the form of pellets, loose or compacted film, loose or compacted flexible packages, loose or compacted rigids, loose or compacted non-wovens, etc. which will be difficult to surface wash due to excessive overall size. Hence, prior to surface washing, a granulation or shredding step is preferred. For films, it is especially important to exfoliate all available film layers, such that the washing fluid can access all original surface contamination. Thus, the size reduction step prior to surface washing should not significantly decrease the surface area to volume ratio of the reclaimed source or exchange such with new surface area. In embodiments of the present invention, said surface washing of said first plastic is conducted after a shredding or granulation step. The surface washing will include significant mechanical agitation to loosen surface dirt and other contaminants to allow physical removal and transfer to the washing fluid wherein the dirt or other contaminants may or may not solubilize. As used herein, a surface washing method is any method wherein the reclaimed plastic in its original contaminated form (except for the possibility of bulk size reduction that does not eliminate more than 25% of the original surface) is contacted with an aqueous solution under mechanical agitation and then separated from the aqueous media which now contains such contamination. Such a method will in general remove the majority of loosely bound surface contamination including but not limited to dirt, wood, loosely bound paper, and some surface chemical contamination. Typical levels of loosely bound surface contamination for film based reclaimed sources are between about 0.01 and 0.1 wt %. For objects of the present invention involving a surface washed first plastic, the surface washing process will remove greater than about 80% of the loosely bound surface contamination as determined by method 2 shown in section IX.
Surface washing technologies are available extensively on the market. One representative technology is from Lindner (Lindner Washtech GmbH, Haldenfeld 4, Germany). The technology is described in detail elsewhere (https://www.lindner-washtech.com/system-solutions) but involves water washing under vigorous mechanical agitation and the potential for application of caustic to remove adhesives followed by drying and pelletization.
Another representative surface washing technology is from Herbold (Herbold Meckesheim USA, North Smithfield, R.I.). The technology is described in detail elsewhere (https://www.herbold.com/en/machines/washing-separating-drying-2/) but also involves various water washing steps under vigorous mechanical agitation followed by drying and pelletization.
Another representative technology is from Sorema (Sorema S.r.l., Anzano del Parco, Italy). The technology is described in detail elsewhere (http://sorema.it/en_US/applications/washing-line/) but involves similar aqueous operations relative to Lindner and Herbold.
Another representative surface washing technology is from Cadel called De-inking (Cadel Deinking, Alicante, Spain). The technology is described elsewhere (http://cadeldeinking.com/en/) but essentially involves the surface washing of materials using high temperature aqueous based solutions with specific surfactants, followed by water rinsing, drying, devolatilization, and pelletization. This method differs from other known methods in that it claims to remove surface printed inks. Such would be advantageous due to lowering the burden for chemical contaminant removal by the bulk purification methods of the current invention.
Three surface washing technologies of the prior art were evaluated for removal of the targeted classes of chemical contaminants (Comparative Examples 1, 2, and 3). Each of the surface washing technologies was evaluated using a different reclaimed film input with different levels of contamination. Overall, the surface washing technologies of the prior art were not able to purify the reclaimed materials sufficiently for use in controlled end markets. For the targeted contaminants, the commercial technologies were not able to reduce to levels near the LOQ despite low initial contamination of the respective reclaimed sources. In addition, the average removal efficiency for 4-tert-pentylphenol, bisphenol A, OCDD, PCB 118, di-2-ethylhexyl phthalate was less than about 55%.
The plastic coming out of the surface washing step will generally be in a similar geometric form and with similar surface area to volume ratio as the incoming reclaimed plastic. For example, if the reclaimed plastic is loose film, then after surface washing, the film will exit surface purification as a shredded film. Because such loose plastic is difficult to feed to certain bulk purification methods, it may be desirable to melt densify such plastic prior to bulk purification. A preferred method for melt densification is melt extrusion. The melt extrusion not only densifies the plastic, but it may provide the pressure necessary for the downstream bulk purifications like liquid-liquid extraction. The melt extrusion may also include optional steps, such as melt filtration, and/or devolatilization to remove large bulk contaminants and/or volatile bulk contaminants. In addition, the molten densified plastic may be further pressurized using a melt pump. The melt pump may be necessary to increase the pressure necessary for the downstream bulk purification step. Other methods of densification are known in the art including rotating disc and rotating drum densifiers, which occur at lower temperatures relative to melt based methods. In embodiments of the present invention, said melt densification comprises melt extrusion. In another embodiment of the present invention, said melt extrusion comprises melt filtration. In yet another embodiment of the present invention, said melt extrusion comprises melt devolatilization. In embodiments of the present invention, said melt densification comprises melt extrusion, melt filtration, melt devolatilization, and melt pumping.
In general, bulk contamination will not be appreciably reduced by simple aqueous surface washing. Melt filtration and melt devolatilization will have the potential to remove bulk contaminants of large geometric size and remove some volatile bulk contaminants but will be largely ineffective against most bulk contaminants especially to the required levels.
One technology available on the market to complete bulk purification is InterRema Refresher™ from EREMA (EREMA Group, Ansfelden, Austria) https://www.erema.com/en/refresher/). The technology is described in detail elsewhere but essentially consists of devolatilization of pelletized materials over extended periods of time at temperatures below the primary melting point of the plastic to remove volatile organics. Most of the chemical contaminants relevant to reclaimed materials and discussed in the prior sections are highly non-volatile with normal boiling points typically above 200 C. Hence, this type of devolatilization technology will have limited ability to remove most chemical contamination referenced in this application.
Other technologies based upon devolatilization are common. These may be stand-alone unit operations or combined with other operations including extrusion and melt filtration. Those utilizing sub-ambient pressure over a molten stream of the reclaimed plastic are common.
One bulk purification technology involving devolatilization was analyzed for purification capability. The technology involved slightly elevated temperatures but below the primary melting point of the plastic, long residence times (>about 2 hours), and continuous reflux of purified air to provide the devolatilization (as shown below in Comparative Example 4). The commercial devolatilization technology was unable to sufficiently remove the targeted contaminants. For example, the targeted contaminants were still well above LOQ. In addition, the average removal efficiency was ˜20%.
Extraction is a preferred bulk purification method. Extraction involves the use of a purification solvent to remove bulk permeable contaminants through creation of a chemical potential gradient between the first plastic and the solvent. The rate of permeable chemical contaminant removal will depend upon the diffusivity and solubility of the contaminant in the plastic under the conditions created in the process. For high molecular weight plastics, the diffusivity of large molecules indicative of chemical contaminants is quite low, especially in the solid state of the plastic. In addition, the solubility may be limited due to the high MW of the first plastic and lack of enthalpic mixing. Thus, the time required to remove permeable contaminants through diffusion mechanisms can be quite long and not conducive to economically viable processes at commercial scale. Methods to resolve these time scale limitations include 1). increased diffusivity through elevated temperature and/or plastic relaxation through solvent swelling, 2). decrease of diffusion path length through increased surface area to volume ratio of the first plastic exposed to the solvent, 3) increased convective transport of the contaminant through the plastic/solvent interface by: increased solubility of the contaminant in the solvent, increased partitioning of the contaminant within the solvent relative to the plastic; increased convection around the plastic/solvent interface, and increased solvent sink relative to plastic sink. The solubility of the bulk purification solvent in the plastic can be increased by operating the extraction at high pressures especially at, near, or above the critical pressure.
It is important for the extraction method to be scalable to large volumes at low cost. Hence, the time required for extraction should be low to allow for such scalability. In embodiments of the present invention, the total time for extraction is less than about 6 hours, preferably less than about 4 hours, more preferably less than about 2 hours, and even more preferably less than about 1 hour. If the extraction is completed in stages, then the time per stage may be less than this range but the overall time will still fall within these times.
Extractions may take place above, near, at, or below the primary melting point of the first plastic. Extraction taking place at, near, or above the primary melting point of the first plastic are called liquid-liquid extractions. Liquid-liquid extractions are termed liquid/liquid since both the first plastic and solvent are in a fluid state (not necessarily liquid since supercritical conditions may be present). Extractions taking place below the primary melting point of the first plastic are called leaching extractions. Liquid-liquid extractions have the advantages of higher temperature, which drives higher diffusivity and greater ability to manipulate the surface area exposed to the solvent compared to leaching extractions.
In embodiments of the present invention, the temperature of said bulk purification is above the primary melting point of the first plastic. In another embodiment of the present invention, the temperature of said bulk purification is above the primary melting point of the first plastic, and the pressure of the bulk purification is about atmospheric. In another embodiment of the present invention, the temperature of said bulk purification is above the primary melting point of the first plastic, and the pressure of the bulk purification is low pressure (up to about 34 atm). In another embodiment of the present invention, the temperature of said bulk purification is above the primary melting point of the first plastic, and the pressure of the bulk purification is high pressure (greater than about 34 atm). In another embodiment of the present invention, the temperature of said bulk purification is above the primary melting point of the first plastic and at or above the critical temperature of the purification solvent, and the pressure of the bulk purification is at or above the critical pressure.
The temperature may be changed during the course of the extraction process but is generally consistent within a given stage of a unit operation. The pressure may be changed to vary solubility of the solvent in the first plastic or to increase solubility of the chemical contaminant within the solvent.
A liquid-liquid extraction may take place in stages and be combined with additional liquid-liquid extraction processes. In addition, liquid-liquid processes may be combined with leaching processes in various stages to form a given purification process. In one embodiment of the present invention, the number of liquid-liquid stages is more than one. In another embodiment of the present invention, the number of leaching stages is more than one. In yet another embodiment of the present invention, the number of liquid-liquid stages is one or more and the number of leaching stages is one or more.
The liquid-liquid extraction will comprise a heavy phase (also called raffinate phase) and a light phase (also called extract phase) where the two phases are immiscible. In a preferred execution, the light phase will be represented by a bulk purification solvent-rich/plastic-poor phase. The heavy liquid phase will be represented by a plastic-rich/bulk purification solvent-poor phase. Thus, the liquid-liquid solvent should solubilize into the plastic to form a miscible bulk purification solvent/plastic heavy phase (<about 25 wt % solvent). In addition, the plastic should slightly solubilize (<25 wt % first plastic) into the liquid-liquid solvent to form a miscible plastic/liquid-liquid solvent light phase. The heavy and light phases will be immiscible. In the heavy phase, the contaminants will diffuse much more rapidly compared to the inherent first plastic due to the relaxed state of the first plastic due to slight swelling/slight miscibility of the solvent in the first plastic. In addition, the contaminants will be convectively transported closer to the surface due to the mixing in the liquid state. Ideally, the surface area between the heavy and light phases will be maximized due to a combination of distributive and dispersive mixing within the process. The maximal content of surface area between the heavy and light phases is more easily achieved when the rheological properties and interfacial properties of the heavy and light phases are more closely matched. This will generally be better achieved when the liquid-liquid solvent and first plastic are more similar and when the plastic dissolves into solvent such is the case for alkanes and other non-polar solvents when using polyolefin first plastics. The latter benefit is potentially offset by the decreased partitioning of the contaminants in such a non-polar solvent compared to the first plastic. Counter-current and co-current liquid-liquid extraction equipment and methods are well known to those skilled in the art. Such equipment is designed to effectively distribute and disperse the light and heavy phases assuming the rheological properties are within a matched range.
In embodiments of the present invention, said bulk purification comprises a liquid-liquid extraction; and said bulk purification solvent comprises a liquid-liquid extraction solvent. In another embodiment of the present invention, said liquid-liquid extraction comprises multiple extraction steps or stages.
In embodiments of the present invention, less than about 25% of said first plastic is dissolved in said liquid-liquid extraction solvent at said temperature of said liquid-liquid extraction and said pressure of said liquid-liquid extraction. In another embodiment of the present invention, less than about 10% of said first polymer is dissolved in said liquid-liquid extraction solvent at said temperature of said liquid-liquid extraction and said pressure of said liquid-liquid extraction solvent. In yet another embodiment of the present invention, less than about 5% of said first polymer is dissolved in said liquid-liquid extraction solvent at said temperature of said liquid-liquid extraction and said pressure of said liquid-liquid extraction.
In embodiments of the present invention, a two-phase system is formed in said liquid-liquid extraction solvent comprising a phase rich in the first plastic and a phase rich in the liquid-liquid extraction solvent; and said phase rich in the first polymer comprises at least about 5 wt. % of said liquid-liquid extraction solvent at said temperature of said liquid-liquid extraction and said pressure of said liquid-liquid extraction. In another embodiment of the present invention, a two-phase system is formed in said liquid-liquid extraction comprising a phase rich in the first polymer and a phase rich in the liquid-liquid extraction solvent; and said phase rich in the first polymer comprises at least about 1 wt. % of said liquid-liquid extraction solvent at said temperature of said liquid-liquid extraction and said pressure of said liquid-liquid extraction. In yet another embodiment of the present invention, a two-phase system is formed in said liquid-liquid extraction comprising a phase rich in the first polymer and a phase rich in the liquid-liquid extraction solvent; and said phase rich in the first polymer comprises at least about 0.5 wt. % of said liquid-liquid extraction solvent at said temperature of said liquid-liquid extraction and said pressure of said liquid-liquid extraction.
In embodiments of the present invention, wherein the number of stages is 1 to about 50. In another embodiment of the present invention, wherein the number of stages is 5.
While not wishing to be bound by theory, the theoretical maximum contaminant removal capacity for an extraction process is based upon the thermodynamic equilibrium/partitioning of the chemical contaminants between the first plastic and solvent at the temperature and pressure of the process. Thermodynamic equilibrium may not be achieved due to kinetic limitations in the extraction process. This is true for the complete extraction process and is also true for each extraction stage. A higher solvent to first plastic mass ratio will drive both thermodynamics and kinetics in favor of purification at the expense of greater solvent consumption and greater extraction process size, which equals greater cost. Thus, a balance must be found between these important design and operational variables for the targeted chemical contaminant removal efficiency. In general, the applicants have found that the overall fresh or renewed solvent to first plastic mass ratio is preferably above ˜about 5:1, more preferably above ˜about 10:1, more preferably above ˜about 15:1, even more preferably above ˜about 20:1, and most preferably above ˜about 30:1 but less than about 100:1. If the extraction is completed in progressive or sequential stages, then the solvent to first plastic ratio per stage may be lower than this stated range, but the total solvent used to the total first plastic represented by the sum of solvent used in all stages should be within this range. In addition, the contaminated solvent from any stage may be used “as-is” as the solvent for another stage. Contaminated solvent at any point in the process may be renewed through known methods of distillation, filtration, ion-exchange, etc or combinations.
A means for increasing the effective mass transfer is through indirectly applying energy to the first plastic such as but not limited to vibrational in the form of ultrasonic energy and/or microwave.
The solvent is critical in many aspects. In general, the solvent should have a reasonably low boiling point to allow for removal from the first plastic and allow renewal/purification of the solvent using distillation. Higher boiling solvents may be used but solvent regeneration and first polymer devolatilization once purified become more problematic. Preferably, the solvent has a normal boiling point of <200 C, more preferably <120 C, and most preferably <90 C.
The solvent may be hydrocarbons. The solvent may be straight chain hydrocarbons or branched hydrocarbons. The solvents may be aliphatic or aromatic. The hydrocarbons may be alkanes.
In embodiments of the present invention, said extraction solvent is selected from the group comprising hydrocarbons. In another embodiment of the present invention, said extraction solvent is selected from the group comprising aliphatic hydrocarbons. In even another embodiment of the present invention, said extraction solvent is selected from the group comprising aromatic hydrocarbons. In even yet another embodiment of the present invention, said extraction solvent is selected from the group comprising alkanes.
In embodiments of the present invention, said extraction solvent is selected from the group comprising methane, ethane, propane, normal butane, isobutane, normal pentane, isopentane, neopentane, hexanes (normal hexane, isohexane, and neohexene), heptanes, octanes, or mixtures thereof. In another embodiment of the present invention, said bulk purification solvent comprises critical or supercritical ethane. In yet another embodiment of the present invention, said bulk purification solvent comprises critical or supercritical butane. In even yet another embodiment of the present invention, said bulk purification solvent comprises supercritical pentane. In embodiments of the present invention, said bulk purification solvent comprises critical or supercritical hexane.
The solvents may be oxygenated. Non-limiting examples of oxygenated compounds are alcohols, esters, ethers, aldehydes, ketones, etc. Specific non-limiting examples include but are not limited to dimethyl ether (DME), diethyl ether, MEK, ethyl acetate, THF, acetone, and methanol. Polar solvents such as methylene chloride may be used. The solvent may be CO2. The solvent may be CO2 at critical or supercritical conditions. The CO2 may be blended with other solvents including water to tailorize solubility. The solubility of CO2 in polymers and the solubility of contaminants within CO2 can be extensively varied based upon the temperature and pressure of the CO2. Thus, CO2 can be used to pull out different contaminants at different times based upon pulsing the process pressure over a range of pressure.
In embodiments of the present invention, said extraction solvent is selected from the group comprising dimethyl ether (DME), diethyl ether, MEK, ethyl acetate, THF, acetone, methanol, and CO2. In another embodiment of the present invention, said extraction solvent comprises di-methyl ether. In yet another embodiment of the present invention, said extraction solvent comprises critical or super critical di-methyl ether. In event yet another embodiment of the present invention, said extraction solvent comprises ethyl-acetate. In even yet another embodiment of the present invention, said extraction solvent comprises THF. In even yet another embodiment of the present invention, said extraction solvent comprises CO2. In even yet another embodiment of the present invention, said extraction solvent comprises critical or supercritical CO2.
Solvents may be used as blends that are tailored to remove specific contaminants. In addition, different solvents or solvent blends may be used during the different stages of each extraction or each extraction type. The specific solvent selected will be influenced by the desired type of extraction process.
Following the bulk purification involving extraction, the plastic may be devolatilized to produce a purer plastic. The contaminated solvent will contain a small amount of dissolved purer plastic, the extracted contaminants, and the pure extraction solvent. There are many ways to recover the purer polymer and bulk purification solvent independent of the extracted contaminants.
In general, up to about 25 wt % of the first plastic may dissolve into the extraction solvent, which complicates recovery of the solvent and first plastic. In particular, low molecular weight waxes that are inherent to most first plastics are particularly prone to solubilization into the extracting solvent. These may become problematic in distillation-based recovery of the purified solvent due to deposition of the waxes on process equipment. Methods are known to reduce this tendency. One such method is to lower the temperature of the contaminated solvent to below the cloud point to precipitate the polymer or wax phase followed by filtration. Unlike the first plastic, the residual plastic or waxes resulting plastic from the precipitation from the contaminated solvent may contain significant chemical contaminants and may not be usable in various areas.
Distillation of the contaminated bulk purification solvent may be used to regenerate the solvent for re-use in the various extraction operations. However, distillation may not be preferred due to the high solvent volume utilized in the present invention. In addition, because the chemical contaminants of interest in this invention are extremely low in concentration, the concentration of these chemical contaminants in the contaminated solvent may be correspondingly low or even lower (ppb and pptr). Thus, a preferred method to purify the contaminated solvent is through direct removal of the contaminants without having to completely volatilize the contaminated solvent. Such methods include ion exchange, adsorption/absorption methods, etc. Examples include passing the contaminated solvent through a bed of activated carbon or alumina. This method can be used alone or in combination with distillation to achieve the right level of purification at the right energy consumption. In embodiments of the present invention, the contaminated extraction solvent is renewed through adsorption/absorption methods and may potentially include distillation either continuously or at various time points when required.
The purer plastic may contain small amounts of the solvent in either physically adsorbed or bulk absorbed form. The concentration of the solvent in the purer plastic may be reduced by devolatilization techniques. In embodiments of the present invention, said purer plastic is devolatilized to a content of <1 wt % solvent in the first plastic.
In embodiments of the present invention, said temperature of said liquid-liquid extraction is between about the primary melting point of the first plastic and about 300° C.; and said pressure of said liquid-liquid extraction is between about atmospheric pressure and about 1,000 atm. In another embodiment of the present invention, said temperature of said liquid-liquid extraction is between about 150° C. and about 250° C.; and said pressure of said liquid-liquid extraction is between about atmospheric pressure and about 1,000 atm. In even yet another embodiment of the present invention, said temperature of said liquid-liquid extraction is between about 150° C. and about 250° C.; and said pressure of said liquid-liquid extraction is between about 14 atm and about 340 atm. In even yet another embodiment of the present invention, said temperature of said liquid-liquid extraction is between about 150° C. and about 240° C.; and said pressure of said liquid-liquid extraction is between about 34 atm and about 68 atm. In even yet another embodiment of the present invention, said temperature of said liquid-liquid extraction is about 235° C.; and said pressure of said liquid-liquid extraction is about 41 atm. In even yet another embodiment of the present invention, said temperature of said liquid-liquid extraction is about 235° C.; said pressure of said liquid-liquid extraction is about 41 atm; and said liquid-liquid extraction solvent comprises hexanes.
The removal efficiency of liquid-liquid was established to be significantly more effective than the existing surface washing methods. For example (Example 1 and Table 8), liquid-liquid extraction with hexane removed most targeted contaminants to below LOQ and the average removal efficiency for 4-tert-pentylphenol, bisphenol A, OCDD, PCB 118, di-2-ethylhexyl phthalate was greater than about 70%.
In an embodiment of the present invention, said liquid-liquid extraction conducted at about 235 C and about 41 atm with a liquid-liquid extraction solvent comprising hexane; wherein the hexane to first plastic mass ratio is about 55:1 and the total extraction time within the liquid-liquid state is about 65 minutes; wherein the average removal efficiency for 4-tert-pentylphenol, bisphenol A, OCDD, PCB 118, di-2-ethylhexyl phthalate is greater than about 70%.
In an embodiment of the present invention, said temperature of said liquid-liquid extraction is about 170° C.; said pressure of said liquid-liquid extraction is about 129 atm and said liquid-liquid extraction solvent comprises di-methyl-ether. In yet another embodiment of the present invention, said liquid-liquid extraction is conducted at about 170° C.; wherein said liquid-liquid extraction takes place at a liquid-liquid extraction solvent to first plastic ratio of about 107:1 and the total extraction time is about 65 minutes; wherein said pressure of said liquid-liquid extraction is about 129 atm and said liquid-liquid extraction solvent of said liquid-liquid extraction comprises supercritical di-methyl-ether. In even yet another embodiment of the present invention (Example 2 Table 9), said liquid-liquid extraction involves 5 stages conducted at about 170° C. and about 41 atm with an liquid-liquid extraction solvent comprising di-methyl-ether with a di-methyl-ether to first plastic mass fed ratio of about 22.7, 21.9, 21.0, 20.8, and 20.8 at stages 1 through 5 respectively and an average extraction time per stage of about 13 minutes for a total di-methyl-ether to first plastic mass ratio of about 107:1 for a total extraction time of about 65 minutes; wherein the average removal efficiency for 4-tert-pentylphenol, bisphenol A, OCDD, PCB 118, di-2-ethylhexyl phthalate is about 66.8%.
In embodiments of the present invention, wherein said liquid-liquid extraction solvent is CO2. In embodiments of the present invention, said liquid-liquid extraction is conducted in a stirred tank; wherein said stirred tank may be in stages.
In general, the combination of surface purification methods with bulk purification methods provide synergistic benefits to the overall removal of contamination. Surface purification methods will effectively remove surface contamination both impermeable and permeable including chemical contaminants and chemical contaminant precursors. Thus, the surface purification lowers the burden on the bulk purification and allows such to be more effective. If a first plastic is heavily contaminated with surface contamination, then such contamination is preferably removed first by a surface purification method and then followed by a bulk purification method. Once the surface purification method removes the surface contamination, the bulk purification method will remove the remaining bulk permeable contamination. The only contamination not significantly removed by this two-step approach is bulk impermeable contamination such as heavy metals that were intentionally added during original plastic part production. Also, organotins will be difficult to remove due to the large size and hence low permeability in the first plastic. The latter may still be removed with extensive bulk purification.
Preferred methods of surface washing have already been discussed in the surface purification section. An even more preferred method of surface washing is the de-inking method also described in the surface purification method (Comparative Example 3). This method not only removes surface contamination such as dirt but also removes surface printed inks. The method is also quite effective at removing paper labels, which are chemical contaminant precursors. In this method, first plastic with the original surface area exposed is fed to a multi-step aqueous washing process where the surface contamination including surface printed inks, dirt, grit, paper, adhesives, etc. are removed. The resulting material is then dried. The dried material may be further densified into pellets using extrusion including devolatilization and melt filtration. For the purposes of this invention, a de-inking method is any surface washing method wherein said method removes surface print sufficient to produce less than about a 10% difference in the dE between the de-inked and the unprinted first plastic (dE measured using Method 3 in Section IX).
For nomenclature purposes, the contaminated plastic that is fed to the surface purification method will be termed the first plastic. The resulting surface purified plastic will be termed the second plastic. The second plastic will be fed to the bulk purification process and will be purified to the purer plastic. The surface purification method may involve multiple surface purification processes. The bulk purification method may involve multiple bulk purification processes of various types. The removal efficiency for the combined surface and bulk purification methods will be calculated from the first plastic concentration and the associated purer plastic.
In embodiments of the present invention, a method to produce a purer plastic from a first plastic is presented; wherein said first plastic has a concentration of contaminants; wherein said purer plastic has a concentration of contaminants; wherein said contaminants of said first plastic comprise at least one of the following chemical classes; dioxins, PCBs, phthalates, bisphenols, and alkyl phenols; wherein said method comprises 1) a surface washing method to remove surface contamination followed by 2) a liquid-liquid extraction conducted at a temperature and a pressure, and using an extraction solvent; wherein said method reduces said concentration of contaminants in said first plastic to said concentration of contaminants in said purer plastic; and wherein the average of said reductions of said concentrations of contaminants from said first plastic to said purer plastic is at least about 55% or LOQ.
In embodiments of the present invention, said extraction takes place after a surface washing. In another embodiment of the present invention, said extraction takes place after a surface washing wherein the first plastic is not densified prior to surface washing. In yet another embodiment of the present invention, said extraction takes place after a surface washing; wherein the first plastic is not densified prior to surface washing; wherein the second plastic may be densified prior to the extraction process.
The purer plastic produced from the first plastic will have a lower level of contamination relative to the first plastic. The purer plastic from the bulk purification step may be further processed to produce a pellet or other end use material. If a pellet is desired, then such step could involve melt extrusion followed by pelletization. The melt extrusion may optionally include a melt filtration step and/or a devolatilization step. The melt extrusion may include additional ingredients to the purer plastic, such as AO, slip agents, anti-block agents, TiO2, colorants, etc. In embodiments of the present invention, wherein said purer plastic has a concentration of said liquid-liquid extraction solvent of less than about 1 wt %.
A first plastic material, consisting of High-Custody Post-Commercial Film #1, was fed into a commercially available purification process. The cleaning process consisted of shredding, various water washing steps, drying, and melt densification. The shredding homogenized the material while reducing its fundamental size. The aqueous water washing should have effectively removed surface contamination. However, the ability of this process to remove bulk permeable contamination should be minimal due to the low solubility of the chemical contaminants in the water. A small amount of volatile bulk contamination should be removed during drying and melt densification, but overall, the bulk contamination should be largely unaffected. Also, the high-custody post-commercial film source used as the first plastic had limited chemical contamination as demonstrated by the low levels of pesticides, dioxins, and phthalates. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods. After purification, the purer plastic contained a slightly reduced level of chemical contamination as shown in Table 3. The removal of the five selected species were as follows: For 4-tert-pentylphenol, the removal efficiency was 0%. For bisphenol A, the removal efficiency was 94%. For OCDD, the removal efficiency was 78%. For the PCB 118, the removal efficiency was 68%. For the di-2-ethylhexyl phthalate, the removal efficiency was 22%. The average removal efficiency for the five targeted species was about 52%.
A first plastic material, consisting of High-Custody Post-Commercial Film #2, was fed into a surface purification process available on the market to produce a purer plastic. The cleaning process consisted of shredding, aqueous hot water washing, drying, and melt densification. As was the case with Water Wash Process #1, this process should remove surface contamination but be limited in ability to remove bulk permeable contamination. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods, as shown in Table 4. The high-custody film source, first plastic, had limited chemical contamination as demonstrated by the low levels of dioxins, PCBs, phthalates, and PAHs. The purer plastic contained a mixture of increased and slightly decreased levels of chemical contamination. The increase in certain chemical contaminants were likely due to cross-contamination from other more heavily contaminated feed streams and/or variability in the contamination level of the current feed. The removal of the five selected species were as follows: For 4-tert-pentylphenol, the removal efficiency was 0%. For bisphenol A, the removal efficiency was 96%. For OCDD, the removal efficiency was 0%. For the PCB 118, the removal efficiency was 68%. For the di-2-ethylhexyl phthalate, the removal efficiency was 0%. The average removal efficiency for the five targeted species was about 14%.
A first plastic material, consisting of Post-Commercial Film #1, was fed into a purification process available on the market from Cadel called De-inking (http://cadeldeinking.com/en/) to produce a purer plastic. The process consisted of shredding, aqueous de-inking, water washing/rinsing, and drying. From the patent art, the de-inking step involves elevated temperatures, elevated pH, and surfactants. The various washing steps should effectively remove surface contamination. In addition, small amounts of bulk permeable contamination will be removed due to the elevated temperatures, which will increase the diffusivity, and the potential increase in solubility of the contaminants in the water due to the surfactant/pH combination. However, the bulk extraction was expected to be low. The incoming first plastic was determined to have 0.125 wt % loosely bound surface contamination compared to about 0.02 wt % for the purer plastic in the form of shreds. Therefore, this cleaning process removed greater than 80% of the incoming loosely bound surface contamination. After cleaning but prior to analyzing the first plastic for chemical contamination, the shreds were melt densified using a single screw extruder at 190 C to produce pellets. The pellets were ground to a mass average diameter of 300 to 500 microns. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods, as shown in Table 5. The first plastic contained a moderate level of chemical contamination indicative of post-commercial film lacking a high custody lifecycle. For example, the incoming dioxins like OCDD were 40× the LOQ, which is higher than the previously described high-custody sources of COMPARATIVE EXAMPLES 1, 2, and 5. In addition, this particular source has a high level of paper contamination, which has the potential to form additional chemical contamination once re-melted for densification/pelletization. This particular source was especially high in alkylphenols (˜1,000× the LOQ) further indicating the level of chemical contamination within this recycle source. This first plastic was composed of shredded film with significant portions being melted together into clumps of plastic. Hence, the effectiveness of surface washing techniques with this source will be somewhat inhibited due to the lack of access to the complete contaminated surfaces. After the deinking process, the purer plastic contained a reduced level of chemical contamination. The removal of the five selected species were as follows: For 4-tert-pentylphenol, the removal efficiency was 71%. For bisphenol A, the removal efficiency was 0%. For OCDD, the removal efficiency was 60%. For the PCB 118, the removal efficiency was 0%. For the di-2-ethylhexyl phthalate, the removal efficiency was 22%. The average removal efficiency for the five targeted species was about 31%.
A first plastic material, consisting of Post-Household Film #1, was fed into the surface purification process of COMPARATIVE EXAMPLE 3A to produce a purer plastic. The incoming first plastic was determined to have 0.047 wt % loosely bound surface contamination compared to about 0.003 wt % for the purer plastic. Therefore, this cleaning process removed greater than 80% of the incoming loosely bound surface contamination. Prior to analyzing for chemical contamination, the shreds of Post-Household Film #1 were melt densified using an extruder and pelletized. The pelletized material was ground to a mass average particle size of 300 to 500 microns. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods, as shown in Table 5. The first plastic contained an extremely high level of chemical contamination including significant dirt. For example, the pesticide piperonylbutoxide was ˜7× the LOQ; alkylphenol ethoxylates were ˜1,000× the LOQ; dioxins and phthalates were ˜300× the LOQ. The purer plastic contained a reduced level of chemical contamination. Note: The difference in removal efficacy between COMPARATIVE EXAMPLES 3A AND 3B despite using identical cleaning processes were likely due to 1). differences in the surface area exposed for the cleaning process, 2). the differences in the distribution of the chemical contaminants on the surface and within the bulk, and 3). inherent variability in the chemical contaminants within a sample and variability in the measurement technique. The removal of the five selected species were as follows: For 4-tert-pentylphenol, the removal efficiency was 38%. For bisphenol A, the removal efficiency was 92%. For OCDD, the removal efficiency was 21%. For the PCB 118, the removal efficiency was 0%. For the di-2-ethylhexyl phthalate, the removal efficiency was 73%. The average removal efficiency for the five targeted species was about 45%.
A first plastic material, consisting of High Custody Post-Commercial Film #3, was fed into a de-odorization technology. The process consisted of exposing the pelletized feed material to moderate temperatures and continuous air flushing. As such, this cleaning technique primarily removes volatile surface and bulk contamination. However, most of the chemical contaminants of relevance to controlled end markets are highly non-volatile. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods, as shown in Table 6. The high-custody film source #3 had limited chemical contamination as demonstrated by the low levels of dioxins, PCBs, phthalates, and PAHs. The purer plastic contained a slightly reduced level of chemical contamination. The removal of the five selected species were as follows: For 4-tert-pentylphenol, the removal efficiency was 88%. For bisphenol A, the removal efficiency was 96%. For OCDD, the removal efficiency was 20%. For the PCB 118, the removal efficiency was 0%. For the di-2-ethylhexyl phthalate, the removal efficiency was 0%. The average removal efficiency for the five targeted species was about 41%.
In general, the established methods for purifying/cleaning films and other plastic waste including water washing, de-inking, and devolatilization are currently not able to sufficiently remove chemical contaminants, especially in sources that are high-custody. Even with high-custody sources, the chemical contamination is still present and not removed completely, which might limit end use for certain customers. Net, there is an unmet need for a cleaning technology that is capable of more completely removing chemical contamination sufficient for highly contaminated sources and for any market desiring purer recycled materials.
A first plastic material, consisting of Post-Commercial Film #2 in the form of pellets, was fed into a lab-scale batch Liquid/Liquid extraction process. The first plastic was in the form of 4 mm spherical pellets for a surface area to volume ratio of −1.5 mm-1. The first plastic was subjected to a bulk purification step of liquid-liquid extraction as follows (at Phasex Corporation, 125 Flagship Drive, North Andover, Mass.). A 7 L autoclave was loaded with about 280 g of pellets of the first plastic; Then, the autoclave was vacuumed and purged with N2 three times, and it was heated to achieve an internal temperature of about ˜235° C. and pressure of about 41 atm; Then, ˜3,100 g of hexane (Hexanes ACS; Catalog #: 35900ACS; >98.5% Hexane isomers and methyl cyclopentane; Pharmco by Greenfield Global, Inc.; Brookfield, Conn.) was added to the autoclave. At those conditions, the hexane is at critical conditions (critical temperature of normal hexane is 235° C. and pressure is 31 atm). After the autoclave reached the temperature and pressure mentioned above, mechanical stirring started at about 680 rpm and lasted for about 10 minutes. At those conditions, the polyethylene of the first plastic and hexane formed a two-phase system, a light phase (extract) with low concentration of polyethylene in hexane and a heavy phase (raffinate) with high concentration of polyethylene in hexane. Then, the stirring stopped for about 10 min, the raffinate phase settled, the extract phase floated at the top, and a flow of hexane of ˜3,100 grams of fresh hexane was added to the reactor in such a manner to remove the hexane from stage 1 of the liquid-liquid extraction. This step was repeated 4 more times, and the material remaining after the 5 extraction steps in the autoclave (i.e., the raffinate phase) was collected, devolatilized, and solidified to produce the purer plastic. The overall ratio of hexane to first plastic mass was 55:1 and the total extraction time was around 100 minutes but only ˜65 minutes were in an optimal mass transfer state of stirring. In a commercial liquid-liquid countercurrent continuous extractor, the relevant time scale would be ˜65 minutes. Hence, the true extraction time was closer to about 65 minutes. The purer plastic after devolatilization had a mass of ˜230 g for a total extracted mass of ˜50 grams (18 wt %), which included both first plastic contaminants and dissolved first plastic. The above process was used to simulate a continuous and large-scale liquid-liquid extraction, as it is well known in the art. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods, as shown in Table 7. Prior to analyzing the purer plastic, it was ground to a mass average particle size of ˜1 mm. The first plastic contained a moderate level of chemical contamination. For example, the pesticide piperonylbutoxide was ˜12× the LOQ; the alkylphenol iso-nonylphenol was ˜170× the LOQ, bisphenol-A was ˜320× the LOQ; OCDD was ˜17× the LOQ; PCB 118 was ˜30× the LOQ, and PAHs were 50 to 100× the LOQ. The purer plastic contained a significantly reduced level of chemical contamination as shown in Table 10. The vast majority of chemical contaminants were extensively removed. Pesticides, alkylphenol ethoxylates, bisphenol-A and most dioxins/furans, and PCBs, were removed below the LOQ. Even when not reduced below LOQ, most were significantly reduced. At least one contaminant from the classes of pesticides, alkylphenol ethoxylates, bisphenol-A, dioxins, PCBs, phthalates, and PAHs, was removed at an efficiency >99%. For the contaminant 4-tert-pentylphenol, the removal efficiency was 72%. For the contaminant bis-phenol A, the removal efficiency was 99.7%. For the contaminant OCDD, the removal efficiency was 88%. For the PCB 118, the removal efficiency was 88%. For the di-2-ethylhexyl phthalate, the removal efficiency was not calculated due to external contamination during sampling. However, the similar phthalate dibutyl phthalate was removed >89%. The minimum removal capacity for the contaminants, 4-tert-pentylphenol, bis-phenol A, OCDD, PCB 118, and di-2-ethylhexyl phthalate was 72%. Only organotins were not significantly removed by the extraction due to low diffusivity in the molten PE and availability on in the initial bulk first plastic. If a high-custody film source had been used, then complete removal of most if not all chemical contaminants would have likely been achieved.
The removal of the five selected species were as follows: For 4-tert-pentylphenol, the removal efficiency was 72%. For bisphenol A, the removal efficiency was 99.7%. For OCDD, the removal efficiency was 88%. For the PCB 118, the removal efficiency was 88%. For the di-2-ethylhexyl phthalate, the removal efficiency was 0%. The average removal efficiency for the five targeted species was >about 70%.
Post-Household Film #1 was shredded, melt densified to pellets using a single screw extruder, and then ground to a particle size of −1 mm. The resulting ground material was the first plastic. Thus, the first plastic had a surface area to volume ratio of 6 mm-1. The first plastic was subjected to a bulk purification step of liquid-liquid extraction as follows (at Phasex Corporation, 125 Flagship Drive, North Andover, Mass.). A 7 L autoclave was loaded with about 152 g of pellets of the first plastic. Then, the autoclave was vacuumed and purged with N2 three times, and it was heated to achieve an internal temperature of about 170° C. and pressure of about 129 atm. 3,500 grams of DME was added. After the autoclave reached the temperature and pressure mentioned above, mechanical stirring started at about 680 rpm and lasted for about 10 minutes. At those conditions, the polyethylene of the first plastic and DME formed a two-phase system, a light phase (extract) with low concentration of polyethylene in DME and a heavy phase (raffinate) with high concentration of polyethylene in DME. Then, the stirring stopped for about 10 min, the raffinate phase settled, the extract phase floated at the top, and a flow of DME of about 3,300 grams of DME was added to remove the contaminated DME from stage 1. The stirring was initiated and allowed to continue for 10 minutes. These stages were repeated for a total of 5 times. Thus, the total solvent used was about 17 kg for a solvent to first plastic ratio of about 111:1 and the total reaction time was ˜65 minutes similar to the liquid-liquid hexanes example. The residual from the contaminated solvent was ˜3.5 grams and the purer plastic had a mass of ˜148.5 g. The material remaining after the 5 extraction steps in the autoclave (i.e., the raffinate phase) was collected, devolatilized, and solidified to produce the purer plastic. The first plastic and purer plastic were analyzed for the classes of chemical contaminants typically present in recycled materials by GALAB Laboratories GmbH (Am Schleusengraben 7, 21029 Hamburg, Germany) using the methods disclosed in section IX Methods, as shown in Table 8. Prior to analyzing the purer plastic, it was ground to a mass average particle size of ˜1 mm.
At least one contaminant from the classes of pesticides, alkylphenol ethoxylates, bisphenol-A, dioxins, PCBs, phthalates, and PAHs, was removed at an efficiency 97.8%. For the contaminant 4-tert-pentylphenol, the removal efficiency was 55%. For the contaminant bisphenol A, the removal efficiency was 97.6%. For the contaminants OCDD, the removal efficiency was 87.7%. For the PCB 118, the removal efficiency was 97.6%. For the di-2-ethylhexyl phthalate, the removal efficiency was about 0%. The average removal capacity for the contaminants, 4-tert-pentylphenol, bis-phenol A, OCDD, PCB 118, and di-2-ethylhexyl phthalate was about 67%.
A method to produce a purer plastic from reclaimed film; wherein the reclaimed film has a mass average surface area to volume ratio greater than about 40 mm-1 is fed into a surface washing step, comprising an aqueous surface washing step while applying vigorous mechanical agitation for a time of ˜30 min wherein the loosely bound surface contamination is removed at greater than about 80%; wherein said surface washed plastic is fed to a melt extruder which delivers the molten and high pressure first plastic to an extraction method involving a continuous counter-current liquid-liquid extractor operating a temperature of about 235 C and a pressure of about 41 atm; wherein said extraction uses a liquid-liquid extraction solvent; wherein said liquid-liquid extraction solvent is hexanes; wherein the mass ratio of hexanes to surface washed plastic is greater than about 30:1; wherein said extraction method involves an extraction time; wherein said extraction time is less than about 1 hour; wherein the average removal capacity for the contaminants, 4-tert-pentylphenol, bis-phenol A, OCDD, PCB 118, and di-2-ethylhexyl phthalate is greater than about 55%.
The foregoing description is given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications within the scope of the invention may be apparent to those having ordinary skill in the art.
The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”
Every document cited herein, comprising any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. 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, suggests 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 incorporated by reference, 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 modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
| Number | Date | Country | |
|---|---|---|---|
| 63010078 | Apr 2020 | US |
