Plastics recycling system using solvent targeted recovery and precipitation (STRAP).

Abstract

A solvent targeted recovery and precipitation (STRAP) system for recovering individual polymers from multilayer plastic film or mixed plastic waste includes a downsizing device that shreds the plastic into particles of a size and aspect ratio that allows the waste to flow; a feeder that delivers a constant flow of plastic particles without crosslinking; a dissolving vessel that selectively dissolves the individual polymer components in a solvent; a high-temperature filter that separates the dissolved polymer components from the insoluble plastic; a precipitator that precipitates the dissolved polymer components; a low-temperature filter that separates the precipitated polymer components from the solvent; and a distillation unit that purifies the regenerated solvent. The unique design of the feeder and dissolving vessel allows the system to operate in a semi-continuous manner.

Description

[Technical Field]

[0001] Federal Funding Statement This invention was made with government support under awards DE-EE0009285 and DE-SC0018409 from the U.S. Department of Energy, and awards 2033366 and 2222041 from the National Science Foundation. The government has certain rights in this invention. [Background technology]

[0002] Plastic production is increasing globally, but the infrastructure to recycle plastics is still lacking. Current mechanical recycling technologies are costly and inefficient for plastic waste. Most non-recyclable plastic waste ends up in landfills, with some recovered for energy. Some ends up in oceans and inland waters. This causes considerable damage to both the environment and human health. A large proportion of plastic packaging materials produced and used today are composite films made from multiple different layers. The combination of several layers of different materials improves the mechanical and physical properties of the film. Current strategies for recycling plastic packaging materials are based on mechanical separation to separate plastic materials by type, allowing them to be melted and pelletized. These methods are incompatible with layered composite films because their melting in bulk recombines all the layers into a mixture that does not share the same bulk properties as the original materials. Catalytic methods have been used to decompose polymeric materials into their original monomers. However, these strategies often require stoichiometric amounts of reagents, making them expensive and wasteful. Pyrolysis techniques have been proposed in which composite films are decomposed at high temperatures in the absence of oxygen to form liquid fuel precursors. However, these techniques typically result in low yields and require harsh process conditions.

[0003] To address the industry's unmet need for efficient recycling of plastic waste, a process named Solvent Targeted Recovery and Precipitation (STRAP) has been developed. The STRAP process efficiently recovers components of multilayer plastic film or mixed plastic waste using selective dissolution of individual plastic components guided by thermodynamic calculations of polymer solubility (Walker et al., Sci. Adv. 2020;6: eaba7599; Sanchez-Rivera et al., ChemSusChem 2021, 14, 4317-4329). Technical, economic, and life cycle analyses have provided evidence that STRAP has extremely low capital and operating costs, as well as lower process energy requirements than fossil-based resin production. This can help reduce the amount of plastic waste ending up in landfills or the environment and lead to a circular plastics economy. The present disclosure is directed to a system for performing the STRAP process to recover individual polymers from multilayer plastic film or mixed plastic waste. Summary of the Invention

[0004] Disclosed herein is a system for recovering individual polymers from multi-layer plastic film or mixed plastic waste. The system includes: (i) Downsizing devices that shred multi-layer plastic film or mixed plastic waste into plastic particles of a size and aspect ratio that allows them to flow; (ii) a feeder that delivers plastic particles at a constant flow without bridging; (iii) a dissolution vessel in which the plastic particles are mixed with a solvent, the solvent selectively dissolving the individual polymer components of the plastic particles; (iv) a high temperature filter to separate the solvent containing the dissolved polymeric components from the insoluble plastic particles; (v) a precipitator for precipitating the dissolved polymer component; and (vi) A cold filter to separate the precipitated polymer components from the solvent.

[0005] Preferably, the downsizing device of the system shreds the multi-layer plastic film or mixed plastic waste into plastic particles having a size of about 1 mm to 6 mm and an aspect ratio of about 1 to 1.5. The feeding device is a live bottom hopper containing a reservoir with negative angle walls forming a base wider than the top, and one or more variable pitch screws whose pitch increases along the flow of the plastic particles. The dissolution vessel is a conical reactor, as shown in Figures 4A and 4B, that includes baffles attached to the interior walls to promote mixing. Referring now to Figure 4B, in a preferred configuration of the dissolution vessel, the outlet diameters D1 and D2 are equal (although this is not required). The ratio of D1 to the particle size of the incoming feedstock is preferably ≥ 15, and α (the angle between the cross section of the outlet and the vessel side wall) is between 45 and 90 degrees (see Figure 4B). In some cases, the dissolved polymer component is precipitated in the precipitator by reducing the temperature of the solvent containing the dissolved polymer component. In some cases, the dissolved polymer component is precipitated in the precipitator by adding an antisolvent.

[0006] The system further includes a first solvent recovery unit following the hot filter that recovers solvent from the insoluble plastic particles separated from the hot filter, and a second solvent recovery unit following the cold filter that recovers solvent from the precipitated polymer component separated from the cold filter. The system further includes an extruder that extrudes the polymer component to produce recycled plastic resin pellets and follows a second solvent recovery unit that removes residual solvent from the polymer component. The system may further include a thermal management system that controls the temperature of the solvent entering the dissolution vessel, the dissolution vessel, the hot filter, the precipitator, and the first and second solvent recovery units.

[0007] The system may further include a distillation unit to purify the recovered solvent for reuse. To recover a second polymer component from the multilayer plastic film or mixed plastic waste, the system may further include a sequential subsystem including a second dissolution vessel, a second high-temperature filter, a second precipitator, and a second low-temperature filter, where the insoluble plastic particles are sent to the second dissolution vessel to mix with a second solvent, which selectively dissolves the second polymer component. The system may also include one or more parallel subsystems that sequentially recover one or more polymer components from the multilayer plastic film or mixed plastic waste. In a preferred version of the method, there is a subsystem for each distinct type of plastic in the film to be recycled. The objects and advantages of the present disclosure will become more fully apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of a system disclosed herein for recovering individual plastic resins from multi-layer plastic film or mixed plastic waste. [Figure 2] FIG. 1 is an exploded perspective view of a live bottom hopper with negative angle walls (wider at the bottom than at the top) and a variable pitch screw. [Figure 3] Test results for the live-bottom hopper depicted in Figure 2, operated at different speeds (RPM), are shown. The mass of plastic processed by the live-bottom hopper was plotted against the time the live-bottom hopper was operated at different speeds (Panels A-E). The mass flow rate was calculated from each plot in Panels A-E and plotted against the operating speed as shown in Panel F. [Figure 4] 4A and 4B show an exemplary jacketed dissolution vessel configuration that can be used in the present method and system: Figure 4A is a perspective cutaway view of the vessel; [Figure 5]4C is a graph depicting dissolution times for extraction of certain resins from multi-part polymer films using the dissolution vessel shown in FIGS. 4A and 4B under optimized conditions. [Figure 6] 1 shows the construction of a high-temperature centrifugal filter. Such a filter can be used to separate molten plastic from solid resin. [Figure 7] The results of testing the centrifugal filter (time vs. wet plastic mass) shown in Figure 6 by adding a mixture of 750 g of shredded dry plastic and 10 L (approximately 10 kg) of water are shown. The test was repeated eight times. [Figure 8] 1 shows the mass of plastic processed by an actuated ball valve auger over time. [Figure 9] 1 shows a fully detailed process flow diagram of an exemplary system for recovering polyethylene (PE) from mixed plastic waste. DETAILED DESCRIPTION OF THE INVENTION

[0009] definition As used herein, the term "about" refers to ±10% of the referenced variable. Numerical ranges used herein are intended to include all numbers and subsets of numbers contained within the range, whether or not specifically disclosed. Furthermore, these numerical ranges should be construed as providing support for claims directed to any number or subset of numbers within that range. For example, a disclosure of 1 to 10 should be construed as supporting ranges such as 2 to 8, 3 to 7, 5 to 6, 1 to 9, 3.6 to 4.6, 3.5 to 9.9, etc. As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise.

[0010] As used herein, the term "or" is an inclusive "or" operator and is equivalent to the term "and / or," unless the context clearly dictates otherwise. The elements and method steps described herein, whether explicitly stated or not, can be used in any combination unless otherwise specified or unless the contrary is clearly suggested by the context in which the referenced combination is made. All combinations of method steps used herein can be performed in any order unless otherwise specified or unless the contrary is clearly suggested by the context in which the referenced combination is made.

[0011] The systems disclosed herein may comprise, consist of, or consist essentially of the various steps and apparatus disclosed herein. It is understood that the disclosure is not limited to the particular elements and method steps shown and described herein, but encompasses modifications thereof as fall within the scope of the claims.

[0012] System Components Disclosed herein is a system for recovering individual polymers from multi-layer plastic film or mixed plastic waste. The system is capable of recycling a wide variety of plastics from a variety of sources, such as flexible plastic film, multi-layer plastic packaging waste, post-consumer plastic waste, industrial plastic waste, and municipal solid waste. Referring to Figure 1, the system comprises: (i) a downsizing device that shreds plastic waste to produce plastic particles of a size and aspect ratio that make them flowable and easily dissolvable; (ii) a feeding device that delivers plastic particles to the dissolving vessel at a constant flow without bridging; (iii) a dissolving vessel for effectively mixing the incoming plastic particles with one or more solvents and discharging the undissolved plastic particles and solvent (which now contains dissolved polymer components from the incoming feedstock); (iv) a first filter (preferably a hot or insulated filter) for separating the insoluble plastic from the solvent containing the dissolved polymeric components; (v) a precipitator for precipitating the dissolved polymeric components; (vi) a second filter (preferably a cold or hot filter) to separate the precipitated polymer component from the solvent; (vii) a solvent recovery unit for recovering solvent from wet plastics; and (viii) An extruder that produces large quantities of recycled plastic resin pellets and removes traces of solvent remaining in the process from the recovered resin.

[0013] The downsizing device is typically a shredder that shreds plastic waste and produces plastic particles of a specific desired size and aspect ratio. Preferably, the incoming feedstock is size-reduced to produce a flowable product. Size reduction, by its very nature, increases the surface area, thereby producing a product that is more easily dissolved. The preferred range for the size of the plastic particles is about 2 mm to 6 mm. The preferred range for the aspect ratio of the plastic particles is about 1 to 1.5. The step of producing flowable plastic particles is essential for continuous operation of the system. Furthermore, the smaller size and preferred aspect ratio facilitate faster dissolution of the plastic particles in the solvent and more uniform processing.

[0014] A feeder following the downsizing device constantly delivers plastic particles to the dissolution vessel. In a preferred embodiment, the feeder is a twin-screw live-bottom hopper, as shown in FIG. 2. Other live-bottom hoppers with different configurations may be used; the hopper shown in FIG. 2 is merely a preferred configuration. Compared to traditional live-bottom hoppers, which have a reservoir with a narrower base than the top, the live-bottom hopper shown herein has a reservoir with negative-angle walls that form a wider base than the top. The live-bottom hopper preferably includes a pair of variable-pitch screws whose pitch increases along the flow of the plastic particles. Extensive testing has found that the combination of negative-angle walls with variable-pitch screws increases the height of plastic particles that can be fed into the hopper without bridging of the incoming feedstock. Bridging of the incoming feedstock is a problem with prior art devices. Shredded plastics tend to be sticky and clump together. Bridging of material as it moves through the process causes delays and inefficiencies because the bridges must be removed to ensure a uniform supply of feedstock to the system.

[0015] The live-bottom hopper shown in Figure 2 was tested at different speeds and showed a good linear correlation between operating time and the mass of plastic processed. See Figure 3, panels A–E. Each panel shows a different speed at which the hopper was operated: 3A = 0.9 rpm, 3B = 2.7 rpm, 3C = 5.4 rpm, 3D = 8.1 rpm, and 3E = 10.8 rpm. At each tested speed, the mass of product delivered was linear with respect to time. The mass flow rate was then calculated from the tests at each operating speed and plotted against the corresponding operating speed (Figure 3, panel F). The good linear correlation between operating speed and mass flow rate indicated that the performance of the live-bottom hopper was consistent and controllable when operated at various speeds.

[0016] The dissolution vessel receives plastic particles from a feeder and mixes them with a solvent that selectively dissolves the individual polymer components of the mixed plastics. The solvent is typically an incubator solvent heated to a specific temperature before entering the dissolution vessel. The temperature of the dissolution vessel is also controlled for rapid dissolution of the single polymer components within the feedstock. In a preferred embodiment, the dissolution vessel has the structure shown in Figures 4A and 4B. The dissolution vessel includes an impeller to mix the materials and baffles attached to the interior wall to promote vigorous and thorough mixing. Actuated ball valves at the inlet and outlet of the dissolution vessel allow for remote automatic control. The dissolution vessel may further include a nitrogen purge (or vessel purge, if necessary) to perform dissolution under pressure. The dissolution vessel is operated in a batch mode. Generally speaking, the dissolution step tends to be the rate-limiting step of the system. Rapid dissolution and discharge can be achieved by optimizing parameters such as the plastic-to-solvent ratio, mixing speed, dissolution time, temperature, and pressure within the dissolution vessel, allowing the system to operate in a semi-continuous mode. That is, the incoming feedstock can be processed batchwise in the dissolution step while the remaining steps occur continuously. In this manner, the overall process is largely continuous by optimizing the rate at which the dissolution chamber is operated relative to the additional downstream processing steps. In Figure 5, the yield of dissolution of a single target plastic polymer component under the conditions specified above is shown. It can be seen that complete dissolution is achieved after 20 seconds.

[0017] The plastic-solvent mixture from the dissolution vessel enters a hot filter, which separates the insoluble plastic from the solvent solution containing the dissolved polymer components. A hot filter (or insulated filter) is a device configured to receive the plastic-solvent mixture from the dissolution vessel. The filter is temperature-controlled and generally operates at an elevated temperature. It is sized and configured to separate the remaining solid phase from the liquid phase. Any type of filter capable of achieving this purpose is contemplated as useful herein. An exemplary hot filter is the centrifugal filter shown in FIG. 6. The plastic-solvent mixture from the dissolution vessel enters the centrifugal filter from the left in FIG. 6 and is sent to a section with a rotating paddle that forces the plastic-solvent mixture through a mesh cylinder. The liquid phase passes through the mesh and proceeds to an outer outlet channel (labeled "insulated plastic solution outlet" in FIG. 6). The solid phase is retained by the mesh and sent through an inner central channel to another outlet channel, labeled "insulated insoluble plastic outlet" on the right of FIG. 6.

[0018] It should be noted that incoming plastics contain various types of inks and pigments. It is necessary to produce recycled resins that minimize any retained inks or pigments to the extent possible. Currently, these inks and pigments fall into three general categories: (i) those that dissolve in the same selected solvent as the specific resin and do not precipitate at room temperature. These inks and pigments pass through the filter along with the dissolved plastic solution. Because they do not precipitate at room temperature, the precipitated resin does not contain these inks and pigments; (ii) those that dissolve in the same selected solvent as the specific resin and precipitate with (and become mixed into) the resin at room temperature. These inks and pigments pass through the filter along with the dissolved resin. To remove these impurities in the resin, the mixture must go through another STRAP cycle, this time using a different solvent that selectively dissolves the inks and pigments; and (iii) micron-sized particles that do not dissolve in the selected solvent and are separated from the target resin using a 1-400 μm filter (depending on the actual size of the pigment particles). After each run, some impurities remain in the recycled solvent. However, because these impurities are present only in minute concentrations, the solvent solution requires only occasional cleaning by distillation.

[0019] Figure 7 shows the test results of the centrifugal filter shown in Figure 6 receiving a mixture of 750 g of shredded dry plastic and 10 L (approximately 10 kg) of water. The results showed that after filtration, the mass of the plastic increased by approximately 30% due to water uptake. This experiment shows that a significant amount of solvent (roughly 30% by mass of the incoming dry plastic) remains in the solid phase after filtration. Therefore, a recovery unit is required to recover the solvent from the wet plastic. The recovered solvent can be recycled back into the system, reducing the total solvent consumption of the process.

[0020] After the dissolved polymer component is separated from the insoluble plastic, it enters a precipitator that cools the solvent, thereby precipitating the dissolved polymer component. In some cases, the polymer component can be precipitated simply by changing the temperature, i.e., by lowering the temperature. In some cases, a co-solvent (i.e., anti-solvent) is added to insolubilize the dissolved polymer component. Preferably, the precipitator has a twin-screw design for high cooling efficiency and self-cleaning. The residence time and temperature of the precipitator can be optimized to achieve complete precipitation with a small footprint.

[0021] The precipitated polymer component is separated from the solvent by a cold filter (or hot / cold filter) following the precipitator. The cold filter can have a similar configuration to the hot filter, but does not necessarily have the ability to process materials at high temperatures. Again, after filtration, the precipitated polymer component may still contain a significant amount of solvent. A solvent recovery unit is needed to recover the solvent for reuse. The system typically includes (or may include) an extruder that extrudes the recycled polymer into uniformly sized pellets after the final solvent recovery unit. Extruding the precipitated polymer fraction also helps remove (by volatilization) at least a portion of any remaining solvent in the polymer.

[0022] The system may further include other components, such as solvent storage tanks, distillation units, thermal management systems, augers, etc., to support smooth, continuous, and efficient processing of complex feedstocks. The system may include one or more solvent storage tanks to store, collect, and reuse solvent. The thermal management system controls the temperature of the solvent storage tanks, dissolution vessels, hot filters, precipitators, and solvent recovery units. The distillation unit can be used to purify solvent for reuse when needed. The system may further include an auger to continuously transfer material from one component to the next. For example, Figure 8 shows test results for a 4" auger with a 4" actuated ball valve, with a mass flow rate of approximately 1.8 kg / min. As shown in Figure 8, it depicts the linear delivery of feedstock over time.

[0023] Use of the system to perform the STRAP process The Solvent Targeted Recovery and Precipitation (STRAP) process is a method for breaking down multilayer plastic film or mixed plastic waste into its constituent resins through a series of solvent washes. The general principle underlying the STRAP process is to selectively dissolve a single polymer component in a solvent system in which the target polymer component is soluble, but other polymer components are not. The solubilized polymer component is then separated from the multilayer film or mixed plastic waste by mechanical filtration and precipitated by changing the temperature and / or adding a co-solvent (i.e., antisolvent) that insolubilizes the dissolved polymer. The solvent and antisolvent are recovered and reused, and the target polymer component is recovered as a dry, pure, solid resin. This process is repeated for each of the polymer components in the multilayer film or mixed plastic waste, resulting in several isolated streams that can then be recycled. The STRAP process can be used to separate and recover polymeric components in any multilayer film or mixed plastic waste, where the polymeric components may include, but are not limited to, polyethylene (PE), ethylene vinyl alcohol (EVOH), polyethylene terephthalate (PET), polypropene (PP), polyvinyl chloride (PVC), polyamide (PA), polyethylene terephthalate glycol (PETG), polystyrene (PS), polycarbonate (PC), polyethersulfone (PES), polyoxymethylene (POM), polyetherimide (PEI), polyphenylene oxide (PPO), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), nylon, styrene maleic anhydride (SMA), and styrene acrylonitrile (SAN). Among these polymers, PE is often classified by its density and branching, and includes ultra-high molecular weight polyethylene (UHMWPE), ultra-low molecular weight polyethylene (ULMWPE or PE-WAX), high molecular weight polyethylene (HMWPE), high density polyethylene (HDPE), high density cross-linked polyethylene (HDXLPE), cross-linked polyethylene (PEX or XLPE), medium density polyethylene (MDPE), linear low density polyethylene (LLDPE), low density polyethylene (LDPE), very low density polyethylene (VLDPE), and chlorinated polyethylene (CPE). All of these types of polyethylene are included within the definition of the simple term polyethylene ("PE") as used herein.

[0024] The multilayer plastic film may further include any number of tie layers (also known as adhesive films), such as ethylene vinyl acetate (EVA), moisture-containing bonding adhesives, and additives (such as TiO) that may be present in small amounts (typically <1% by weight of the total composition) compared to the major resin fraction. The selective solvent used in the process may be any common industrial solvent, including, but not limited to, toluene, o-xylene, p-xylene, benzene, cyclohexane, n-butanol, dimethylformamide (DMF), tetrahydrofurfuryl alcohol, dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), N-methyl-2-pyrrolidone (NMP), gamma-valerolactone (GVL), acetone, 1-propanol, isopropyl alcohol (IPA), methanol, water, furfural, acetonitrile, 1,4-dioxane, cyrene, and dihydropyran.

[0025] The key to successful implementation of the STRAP process is the ability to preselect a solvent system and temperature that can selectively dissolve a single polymer component among all the components present in the multilayer film or mixed plastic waste. A guided approach for rational solvent selection using calculations of Hansen solubility parameters (HSP), molecular dynamics (MD) simulations, and a coupled quantum chemistry and statistical mechanics approach called the Conductor-Like Screening Model of Realistic Solvents (COSMO-RS) can be used to preselect a solvent system, such as those described in Walker et al., Sci. Adv. 2020;6 and Sanchez-Rivera et al., ChemSusChem 2021, 14, 4317-4329.

[0026] The disclosed system can be used to perform the STRAP process to recover one or more polymeric components from multilayer film or mixed plastic waste. Using the system described herein, a first polymeric component is recovered using a first solvent that selectively dissolves the first polymeric component. The resulting insoluble plastic from the process is then subjected to a parallel subsystem to recover a second polymeric component using a second solvent that selectively dissolves the second polymeric component. The system can include one or more parallel subsystems that sequentially recover one or more polymeric components from the multilayer plastic film or mixed plastic waste.

[0027] The following is an exemplary STRAP process that can be performed using the system disclosed herein. The examples are not intended to limit the scope of processes that the system can perform. In the examples, temperatures and reaction times can be further optimized depending on the parameters of the system components. 1. A process for separating and recovering polymer components from multi-layer plastic films containing PE, EVOH, and PET. The process includes: (i) selectively dissolving the PE fraction in toluene at about 110°C for about 5 minutes or less and separating the solubilized fraction from the EVOH and PET by filtration; (ii) precipitating the solubilized PE by lowering the temperature of the toluene solution containing dissolved PE to about 35°C and separating the precipitated PE from the toluene by filtration; (iii) selectively dissolving the EVOH fraction in 60% DMSO-40% water (vol / vol) at about 95°C for about 5 minutes or less and separating the solubilized fraction from the remaining PET by filtration; (iv) precipitating the solubilized EVOH fraction by lowering the temperature of the aqueous DMSO solution containing dissolved EVOH to about 35°C, and separating the precipitated EVOH from the aqueous DMSO solution by filtration; and (v) The residual solid is PET.

[0028] 2. A process for separating and recovering polymer components from multilayer films containing PE, EVOH, PET, and EVA tie layers. The process includes: (i) selectively dissolving the PE and EVA fractions in toluene at about 110°C for about 5 minutes or less and separating the solubilized fraction from the EVOH and PET by filtration; (ii) precipitating the solubilized PE by lowering the temperature of the toluene solution containing dissolved PE and EVA to about 35°C, and separating the precipitated PE from the toluene solution containing EVA by filtration; (iii) precipitating the solubilized EVA by adding the antisolvent acetone and separating the precipitated EVA from toluene by filtration; (iv) selectively dissolving the EVOH fraction in 60% DMSO-40% water (vol / vol) at about 95°C for about 5 minutes or less and separating the solubilized fraction from the remaining PET by filtration; (v) precipitating the solubilized EVOH fraction by lowering the temperature of the aqueous DMSO solution containing dissolved EVOH to about 35°C, and separating the precipitated EVOH from the aqueous DMSO solvent by filtration; (vi) The residual solid is PET.

[0029] 3. A process for separating and recovering polymer components from multilayer films including PETG, PE, EVOH, and PET. The process includes: (i) selectively dissolving the PETG fraction in a mixture of 60% DMF-40% THF (vol / vol) at about 87°C for about 5 minutes or less, and separating the solubilized fraction from PE, EVOH, and PET by filtration; (ii) precipitating the solubilized PETG by adding an anti-solvent, 1-propanol, and separating the precipitated PETG from the DMF-THF solvent by filtration; (iii) selectively dissolving the PE fraction in toluene at about 110°C for about 5 minutes or less and separating the solubilized fraction from the EVOH and PET by filtration; (iv) precipitating the solubilized PE by lowering the temperature of the toluene solution containing the dissolved PE to about 35°C and separating the precipitated PE from the toluene by filtration; (v) selectively dissolving the EVOH fraction in a mixture of 60% DMSO-40% water (volume / volume) at about 95°C for about 5 minutes or less, and separating the solubilized fraction from the remaining PET by filtration; (vi) precipitating the solubilized EVOH by lowering the temperature of the aqueous DMSO solution containing the dissolved EVOH to about 35°C, and separating the precipitated EVOH from the aqueous DMSO solution by filtration; and (vii) The residual solid is PET.

[0030] 4. A process for separating and recovering PE and PP from mixed plastic waste containing PE, PP, PVC, PET and PA. The process includes: (i) selectively dissolving the PE fraction in dodecane at about 100°C for about 5 minutes or less and separating the solubilized fraction from PP, PVC, PET, and PA by filtration; (ii) precipitating the solubilized PE by lowering the temperature of the dodecane solution containing dissolved PE to about 35°C and separating the precipitated PE from the dodecane by filtration; (iii) selectively dissolving the PP fraction in toluene at about 110° C. for about 5 minutes or less, and then separating the solubilized fraction from the PVC, PET, and PA by filtration; and (iv) precipitating the solubilized PP by lowering the temperature of the toluene solution containing the dissolved PP to about 35°C, and separating the precipitated PP from the toluene by filtration.

[0031] The disclosed system can also be used to remove ink from printed plastics and, if applicable, dissolve lipids. For example, ink in a multilayer plastic film containing PE, EVOH, and PET can be removed by treating the multilayer film in 50% THF-50% DMF (volume / volume) at about 83°C for up to about 5 minutes. The PE, EVOH, and PET polymers are not dissolved in the THF-DMF solvent and can be separated from the ink-containing solvent solution by filtration. The PE, EVOH, and PET polymer components can be further recovered from the deinked plastic film by the STRAP process described above. [Example]

[0032] This example illustrates an exemplary system according to the present disclosure for recovering PE from mixed plastic waste using dodecane as a selective solvent and precipitating the dissolved PE by lowering the temperature of the solvent solution. A flow diagram of the exemplary system is shown in Figure 9. The symbols for the equipment included in Figure 9 are listed in Table 1. The temperatures and component flow rates of streams 1-20, indicated by the diamond symbols in Figure 9, are listed in Table 2. As shown in Figure 9 and Table 2, mixed plastic waste entering stream 1 is shredded to a size of approximately 4.0 mm by a shredder (M-101) and sent to a dissolver (V-201) via stream 2, which includes a live bottom hopper (M-103). The PE fraction in dodecane in the dissolver (V-201) is dissolved at approximately 90°C. Stream 3 exiting the dissolver (V-201) enters a hot filter (G-601), which separates the plastic-solvent mixture into stream 6, a dodecane solution containing dissolved PE, and stream 7, an insoluble plastic. Stream 6 enters a precipitator (M-107), which lowers the temperature of the dodecane solution to approximately 35°C to precipitate the dissolved PE. Stream 8 from the precipitator (M-107) enters a cold filter (F-602), which separates the precipitated PE from the dodecane, yielding stream 9, containing precipitated PE, and stream 18, containing the dodecane solvent. The wet plastic in each of streams 7 and 9 passes through a solvent recovery unit (V-202 and V-203, respectively) to recover dodecane by evaporation at about 100° C. The dried PE solids in stream 10 then enter an extruder (M-109) to produce recycled PE resin in stream 11.

[0033] The mass balance of the system shows that after each cycle, about 0.1 kg of solvent (corresponding to about 0.002%) and about 2.3 kg of PE (corresponding to about 0.7%) were lost. Overall, this example demonstrates that the system effectively recovers PE polymer from mixed plastic waste. The system is also effective at recovering solvent, thereby reducing solvent costs by recycling and reusing the recovered solvent.

[0034]

Table 1

[0035]

Table 2

Claims

1. 1. A system for recovering individual polymers from multi-layer plastic film or mixed plastic waste, comprising: (i) a downsizing device that shreds the multilayer plastic film or the mixed plastic waste into plastic particles having a size and aspect ratio that allows them to flow; (ii) a feeder that delivers said plastic particles at a constant flow without crosslinking; (iii) a dissolution vessel in which the plastic particles are mixed with a solvent, the solvent selectively dissolving the individual polymer components of the plastic particles; (iv) a first filter for separating the solvent containing the dissolved polymeric components from insoluble plastic particles; (v) a precipitator for precipitating the dissolved polymer component; and (vi) a second filter that separates the precipitated polymer component from the solvent.

2. 2. The system of claim 1, wherein the downsizing device shreds the multi-layer plastic film or the mixed plastic waste into plastic particles having a size of about 2 mm to 6 mm.

3. 10. The system of claim 1, wherein the downsizing device shreds the multi-layer plastic film or the mixed plastic waste into plastic particles having an aspect ratio of about 1 to 1.

5.

4. 2. The system of claim 1, wherein the feeding device is a live bottom hopper including a reservoir having negative angle walls forming a base that is wider than the top, and one or more variable pitch screws whose pitch increases along the flow of the plastic particles.

5. 10. The system of claim 1, wherein the dissolution vessel is a conical reactor having a sidewall, an outlet having a diameter, and a cross-section of the outlet, wherein a ratio of particle size of the incoming feedstock to the outlet diameter is greater than about 15, and wherein the cross-section of the outlet and the sidewall of the dissolution vessel define an angle of about 45 degrees to about 90 degrees.

6. 10. The system of claim 1, wherein the dissolution vessel includes baffles attached to an interior wall to promote mixing.

7. 10. The system of claim 1, wherein a high temperature centrifugal filter is used to separate the insoluble polymer and dye from the solution.

8. The system of claim 1 , wherein the dye present in the multilayer plastic film or the mixed plastic waste is not dissolved in the solvent.

9. The system of claim 1 , wherein the dissolved polymer component is precipitated in the precipitator by reducing the temperature of the solvent containing the dissolved polymer component.

10. 10. The system of claim 1, wherein the pigments present in the multilayer plastic film or the mixed plastic waste are dissolved in the solvent but do not precipitate at room temperature.

11. 10. The system of claim 1, wherein the dye present in the multilayer plastic film or the mixed plastic waste is dissolved in the selected solvent and precipitated at room temperature along with the individual polymer components.

12. The system of claim 1 , wherein the dissolved polymer component is precipitated in the precipitator by the addition of an antisolvent.

13. 10. The system of claim 1, further comprising a distillation unit for purifying the recovered solvent for reuse.

14. 10. The system of claim 1, further comprising a first solvent recovery unit following the hot filter that recovers the solvent from the insoluble plastic particles separated from the hot filter, and a second solvent recovery unit following the cold filter that recovers the solvent from the precipitated polymer component separated from the cold filter.

15. 15. The system of claim 14, further comprising an extruder following the second solvent recovery unit that extrudes the polymer component to produce recycled plastic resin pellets and removes solvent from the polymer component.

16. 15. The system of claim 14, further comprising a thermal management system that controls the temperature of the solvent entering the dissolution vessel, the dissolution vessel, the high temperature filter, the precipitator, and the first and second solvent recovery units.

17. 15. The system of claim 14, further comprising a sequential subsystem including a second dissolution vessel, a second hot filter, a second precipitator, and a second cold filter, wherein the insoluble plastic particles are conveyed to the second dissolution vessel to mix with a second solvent, and the second solvent selectively dissolves the second polymer component.

18. 10. The system of claim 1, further comprising a sequential subsystem including a second dissolution vessel, a second hot filter, a second precipitator, and a second cold filter, wherein the insoluble plastic particles are conveyed to the second dissolution vessel to mix with a second solvent, the second solvent selectively dissolving a second polymer component.

19. 20. The system of claim 18, further comprising a distillation unit for purifying the recovered solvent for reuse.

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