Plastic processing using subcritical / supercritical fluids

Abstract

A process for recycling hard-to-recycle plastics such as, for example, polyvinyl chloride (PVC) and / or mixed plastic streams is provided. The plastics can be industrial water plastics or mixed municipal waste plastics in which PVC is present. In the present disclosure, a depolymerizing process using a subcritical or supercritical fluid of an alcohol, such a methanol, is employed to convert the PVC into a controllable mixture of organic products, e.g., C2-C4 compounds.

Description

41512PCT_Specification PLASTIC PROCESSING USING SUBCRITICAL / SUPERCRITICAL FLUIDS CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims benefit of priority to U.S. Provisional Application Serial No. 63 / 591,955 filed October 20, 2023, the entire contents of which each are incorporated herein by reference. BACKGROUND

[0002] The present disclosure relates to the recycling of plastics, and more particularly to a process for recycling hard-to-recycle plastics such as, for example, polyvinyl chloride (PVC) and / or mixed plastic streams.

[0003] Nearly 32 million tons of mixed plastics waste are sent to U.S. landfills annually. There are several reasons for this, but it is mainly attributed to lack of robust markets, inability for recycled plastic to achieve proper specifications for product containment or preservation, and consumer knowledge and actions.

[0004] Supercritical fluids (SCFs) have been used in recycling hard-to-recycle plastics such as, for example, PVC or PVC mixed with other plastics. Notably, SCFs have been investigated for a range of applications related to polymer degradation and depolymerization. Depending upon the polymer, solvent, and processing conditions, a range of depolymerization or degradation mechanisms are possible. Polymers with backbone linkages that are susceptible to solvolysis, such as polyesters, polyamides, and polycarbonates, are particularly amenable to depolymerization to well defined products in SCFs.

[0005] Depolymerization of polyesters with supercritical water (scH2O), supercritical methanol (scMeOH), and supercritical ethanol (scEtOH) has been reported. A pilot-scale process for the depolymerization of polyethylene terephthalate (PET) in bottles with scMeOH is one example.

[0006] Large-scale treatment of PET with scEtOH has not been reported, but depolymerization of lignin with scEtOH on large scales has been investigated. SCFs have also been found to be effective for debromination of flame-retardant additives in plastics.

[0007] For polyolefins and related polymers with all-carbon backbones, treatment with SCFs often leads to mixtures of products, especially with highly oxidizing scH2O. For example, polyethylene (PE) has been degraded into mixtures of alkenes and alkenes through scH2O treatment. Poly(vinyl alcohol) (PVA) exposed to scH2O in the presence of sodium hydroxide has been reported to form mixtures of C2-C18carboxylic acids. Treatment of polystyrene (PS) with scMeOH at temperatures (340-420°C) and pressures (10-30 MPa) well above the critical point (TC = 240°C, PC = 8.1 MPa) was found to result in a mixture of styrene, ethylbenzene, toluene, and other derivatives. Degradation of epoxy, phenolic, and polyether ether ketone (PEEK) resins with scH2O and scMeOH has also been found to result in mixtures of products.

[0008] The situation with PVC is more complex. While a significant portion of PVC-containing materials can be collected for mechanical recycling, the presence of PVC in mixed plastic waste streams can lead to processing difficulties. Direct pyrolysis of PVC results in the formation of chlorinated oil mixtures that need to be dechlorinated prior to further use. PVC typically decomposes upon heating before depolymerization is observed, so strategies involving catalytic dichlorination of PVC are more common.

[0009] Supercritical H2O treatments have been investigated for the conversion of a range of plastics to either oil mixtures intended for conversion to fuel. Currently, the use of SCFs for handling PVC waste has focused on degradation to gas / oil mixtures. However, these efforts have not focused on optimizing selectivity of the process to produce discrete products from complex mixtures to enable plastic conversion into chemical feedstocks. Improving reaction selectivity by adding catalysts and / or sacrificial reagents have only been applied to superheated steam conditions however, no efforts have been made to translate this approach to SCFs conditions.SUMMARY

[0010] The present disclosure provides a process for recycling hard-to-recycle plastics such as, for example, PVC and / or mixed plastic streams. The plastics can be industrial water plastics or mixed municipal waste plastics in which PVC is present. In embodiments of the present disclosure, a depolymerizing process using a subcritical or a supercritical fluid of an alcohol is employed to convert the PVC into a controllable mixture of organic products, e.g., C2-C4 compounds.

[0011] The process of the present disclosure can be used for selective depolymerization of plastic materials, such as PVC, which are difficult to depolymerize by thermal methods in pure and model mixed waste streams with other plastics. In some embodiments, scEtOH or mixtures of scEtOH and scH2O are employed to achieve depolymerization of PVC into useful products. A combination of synchrotron X-ray techniques (WAXS, SAXS, XPCS, and IXS) can be coherently utilized to probe in-situ structures and dynamics of the clusters and polymer chains during depolymerization. These experimental results can be used to validate models for molecular dynamics (MD) simulation and chemical kinetics simulation. In addition, the present disclosure can be used to correlate among the clustering structures, polymer structures, and subcritical or supercritical fluid reaction mechanisms using simultaneous synchrotron X-ray scattering and infrared (IR) experiments. By combining theoretical / computational and experimental methods, optimize subcritical or supercritical fluid-based depolymerization can be obtained, leading to the development of a new pathway for scale-up.

[0012] In one aspect of the present disclosure, a process for recycling plastics is provided. The plastics can be industrial water plastics or mixed municipal waste plastics. In one embodiment, the process includes depolymerizing a waste plastic stream including at least PVC in a reactor at a temperature below a decomposition temperature of PVC and in the presence of a subcritical fluid or supercritical fluid, both these fluids comprising an alcohol. The depolymerization process converts the PVC into a non-halogen-containing compound such as, for example, C2-C4compounds, which can be recovered in the reactor that performs the depolymerization process and / or downstream from the reactor. In one embodiment, a supercritical fluid of an alcohol is employed. In another embodiment, a subcritical fluid of an alcohol is employed.

[0013] High temperature treatment of PVC leads to dehydrochlorination and other undesirable reactions. By performing the depolymerization of PVC below the decomposition temperature of PVC, the chloride displaces and enables depolymerization of the polymers at the reactor temperature.

[0014] In some embodiments of the present disclosure, the alcohol has from 1 to 8 carbon atoms. This includes methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, and / or octanol. The alcohol can be a straight chain alcohol or a branched alcohol. In some embodiments of the present disclosure, the alcohol is ethanol. The use of such alcohols, preferably, ethanol, allows for the depolymerization of PVC to a controllable mixture of organic compounds.

[0015] In some embodiments of the present disclosure, the depolymerizing is performed in the presence of a reactive clay, an aluminosilicate (including a zeolite), a base that neutralizes hydrochloric acid formation, or any combination thereof. The use of such additives can improve the selectivity of conversion to non-halogenated low molecular weight products.

[0016] In some embodiments of the present disclosure, the subcritical or supercritical fluid further comprises water. A subcritical or supercritical fluid of an alcohol and water will allow for optimization of the depolymerization process for mixtures of waste plastics that include PVC.

[0017] In some embodiments of the present disclosure, the subcritical or supercritical fluid has a ratio of water to alcohol from about 1:1 to about 10:1, more preferably about 1:1 to about 5:1, and even more preferably from about 1:1 to 4:1.

[0018] In some embodiments of the present disclosure in which water is present in the subcritical or supercritical fluid, the depolymerizing is also performed in the presence of a reactive clay, analuminosilicate (including a zeolite), a base that neutralizes hydrochloric acid formation, or any combination thereof. As stated above, the use of such additive can improve the selectivity of conversion to non-halogenated low molecular weight products.

[0019] In some embodiments of the present disclosure, the depolymerizing is performed at a pressure from about 0.1 atmospheres to about 100 atmospheres.

[0020] In some embodiments of the present disclosure, the decomposition temperature is from about 500°C or greater, and the depolymerization temperature is from about 200°C to less than 500°C.

[0021] In some embodiments of the present disclosure, the depolymerization process of the present disclosure produces a non-halogen-containing product having from 2 to 12, more preferably from 2 to 8, even more preferably from 2 to 6 carbon atoms, and most preferably from 2 to 4 carbon atoms. The non-halogen-containing product can include a polymer.

[0022] In some embodiments of the present disclosure, the non-halogen-containing product comprises at least poly(ethyl vinyl ether).

[0023] In some embodiments of the present disclosure, the process further includes monitoring the depolymerizing for polymeric cluster formation. This will allow for an understanding how the cluster structures and dynamics of the subcritical or supercritical fluid affects the swelling and reactivity of PVC, and other plastics and their mixtures.

[0024] In some embodiments of the present disclosure, the monitoring includes at least one of synchrotron wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), inelastic X-ray scattering (IXS) and molecular dynamics (MD) simulation.

[0025] In some embodiments of the present disclosure, the monitoring can further include infrared (IR) spectroscopy.

[0026] In some embodiments of the present disclosure, the process further includes separating and recovering reaction products (e.g., the C2-C4 compounds mentioned above) formed from the depolymerizing of the recyclable plastic.

[0027] In some embodiments of the present disclosure, the separating includes an isothermal pressure drop after the depolymerizing of the recyclable plastic or adding a clay-based emulsion to a product formed by the depolymerizing.

[0028] In some embodiments of the present disclosure, the recovering includes a fractionation process.

[0029] In another aspect of the present disclosure, a recycling plant is provided. In one embodiment, the recycling plant includes a reactor configured to perform a depolymerization reaction at a temperature below a decomposition temperature of a recyclable plastic stream including at least PVC. In some embodiments, the depolymerization reaction is performed in the presence of a subcritical or supercritical fluid comprising an alcohol.

[0030] In the recycling plant, any embodiments mentioned above for the recycling process can be implemented.

[0031] Although the depolymerization process of the present disclosure utilizing a subcritical or a supercritical fluid comprising an alcohol, similar results can be obtained utilizing subcritical water.

[0032] These and other aspect of the present disclosure will be described in greater detail herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is a graph showing size-exclusion chromatography for PVC, an isolated solid after 1 hour in water, and an isolated sample after 1 hour in an ethanol (ETOH)-water mixture.

[0034] FIGS. 2A-2B are infrared spectroscopy after 1 hour treatment at 250°C (FIG. 2A), and 3 hour treatment at 250°C (FIG. 2B).

[0035] FIGS. 3A-3B are 1H NMR analysis of soluble PVC after 1 hour treatment at 250°C (FIG. 3A), and after 3 hour treatment at 250°C (FIG. 3B) DETAILED DESCRIPTION

[0036] The present disclosure will now be described in greater detail by referring to the following discussion and drawings that accompany the present disclosure. In the following description, numerous specific details are set forth, such as particular structures, components, materials, dimensions, processing steps and techniques, in order to provide an understanding of the various embodiments of the present disclosure. However, it will be appreciated by one of ordinary skill in the art that the various embodiments of the present disclosure may be practiced without these specific details. As used throughout the present disclosure, the term “about” generally indicates no more than ±10 %, ±5 %, ±2 %, ±1 % or ±0.5 % from a number. When a range is expressed in the present disclosure as being from one number to another number (e.g., 20 to 40), the present disclose contemplates any numerical value that is within the range (i.e., 22, 24, 26, 28.5, 31, 33.5, 35, 37.7, 39 or 40) or any in amount that is bounded by any of the two values that can be present within the range (e.g., 28.5-35).

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and / or“comprising”, when used in this disclosure, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0038] The present disclosure addresses hard-to recycle plastics such as, for example, PVC, which have not been successfully recycled by the traditional processes, as well several aspects of mixed plastic streams. More specifically, the present disclosure relates to recycling of high- volume commodity plastic streams using scalable depolymerization process in inexpensive supercritical solvents.

[0039] The scalable depolymerization process of the present disclosure can be applied to difficult-to-treat plastics, such as, for example, pure PVC or PVC mixed with other plastics. One reason for selecting PVC for the supercritical depolymerization pathway is that of the nearly 5 million tons of PVC waste per year, approximately 80% goes to landfills and it is not suitable for pyrolysis (or any thermal processing) due the generation of chlorinated by-products. Currently, the use of supercritical fluids (SCFs) for handling PVC waste has focused on degradation to gas / oil mixtures. However, these efforts have not focused on developing pathways to produce discrete products from complex mixtures to enable plastic conversion into chemical feedstock.

[0040] The present disclosure provides a new approach of depolymerization of plastic materials in subcritical or supercritical fluids, provides new processes, methods and tools based on synchrotron X-ray techniques and molecular dimension (MD) simulations, and develops a pathway for reaction product separation and process scale-up.

[0041] The present disclosure uses advanced depolarization chemistry in subcritical or supercritical fluids to achieve both selectivity of conversion of the recycled plastics by tuning temperature / pressure conditions and utilizing reactive additives such as, for example, clay, and / or aluminosilicates (including zeolites) and / or a base that neutralize hydrochloric acid formation. The present disclosure also provides for the valorization of mixed polymers anddepolymerization molecules by developing methods of polymer fractionation and recovery of valuable products in the reactor and / or downstream, via the use of a clay based emulsion. The present disclosure can be used to provide a comprehensive understanding of the molecular-level structural and dynamical transformations in subcritical or supercritical fluid-based polymer recycling to control / optimize reaction rates. The present disclosure can also be used to provide a better understanding of the flickering cluster process to control the subcritical or supercritical fluid-based reaction, and the present disclosure can be used to develop a roadmap for scalability of the subcritical or supercritical fluid-based depolymerization.

[0042] In one aspect of the present disclosure, a process for recycling plastics is provided. The process of the present disclosure can be used to recycle industrial water plastics or mixed municipal waste plastics. Exemplary plastics that can be recycled by the process of the present disclosure include, but are not limited to, polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), polyvinyl chloride (PVC), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), mixed or composite plastics, or any combination (including all) of these plastics. Preferably, the process of the present disclosure can be used to recycle PVC, mixed or composite plastics, or a recycling stream of PVC and mixed or composite plastics.

[0043] Plastics that contain PET include, for example, water bottles, plastic trays, soda bottles, and / or food containers. Plastics that contain HDPE include, for example, shampoo bottles, cleaning product bottles and / or milk containers. Plastics that contain PVC include, for example, pipes, toys, and / or window frames. Plastics that contain LDPE include, for example, plastic bags, cling wrap and / or squeeze bottles. Plastics that contain PP include, for example, yogurt containers, cream containers, butter containers and / or ready-meal trays. Plastics that contain PS include, for example, cups, plates, egg cartons and / or meat trays.

[0044] The process of present disclosure is especially preferred for use in recycling difficult to recycle plastics such as, for example, PVC, mixed or composite plastics, or a combinationthereof (i.e., a plastic stream containing PVS and the mixed or composite plastics). In a most preferred embodiment, the process of the present disclosure is used to recycle PVC.

[0045] In one embodiment, the process of the present disclosure includes depolymerizing a waste plastic stream including at least PVC in a reactor at a temperature below a decomposition temperature of PVC and in the presence of a subcritical or supercritical fluid comprising an alcohol. In another embodiment, the depolymerization can be performed in the presence of subcritical water. In any of these embodiments, the depolymerization process of the present disclosure converts the PVC into a non-halogen-containing compound such as, for example, C2- C4compounds (including polymers), which can be recovered in the reactor that performs the depolymerization process and / or downstream from the reactor.

[0046] In the present disclosure, high temperature treatment of PVC is avoided since it leads to dehydrochlorination and other undesirable reactions. By performing the depolymerization of PVC below the decomposition temperature of PVC, the chloride displaces and enables depolymerization of the polymers at the reactor temperature.

[0047] In a preferred embodiment, reactive processing of PVC with ethanol under subcritical or supercritical conditions can be tunable to allow partial / full conversion to poly(ethyl vinyl ether) (PEVE) while minimizing formation of polyacetylene units resulting from dehydrochlorination. Prior studies of scH2O degradation of PVC have shown that substitution to vinyl alcohol repeating units is favored over elimination at temperatures below 400°C. Treatment of PVC with supercritical or subcritical EtOH, which can be done at lower temperatures (Tc (EtOH) = 241°C) than scH2O, can favor the nucleophilic reaction of ethanol with PVC to form ethyl vinyl ether (EVE) repeating units. Because poly(vinyl ethers) can undergo depolymerization at accessible temperatures (T < 320°C, but 130°C, and 110°C in blends, have been reported), this strategy will enable depolymerization of PVC to non-halogenated molecules including EVE, acetaldehyde, acetic acid, and ethyl acetate, with the products depending upon the extent of oxidation during processing. Many common PVC additives (e.g., phthalates) can also be extracted and / or separated by treatment with these subcritical or supercritical fluids.

[0048] The reactor employed in the present disclosure includes any reactor that can be used in the recycling of plastics and that can generate and / or maintain a subcritical or supercritical fluid environment. The reactor employed includes a chamber to house the plastics needing to be recycled and at least one inlet port to allow an alcohol to be introduced in the chamber. Other inlet ports can also be present. At least one of the other inlet ports can allow water to be introduced into the chamber. In some embodiments, a mixture of an alcohol and water can be introduced though a single inlet port. The reactor can also include a vacuum port that allows for evacuation of the chamber and the formation of a supercritical fluid (SCF) of an alcohol or SCF of a mixture of an alcohol and water. The term “supercritical fluid or SCF” is used throughout the present disclosure to a substance at a given temperature and pressure above its critical point, where distinct liquid and gas phases do not exist, but below the pressure required to compress it into a solid. For example, a SCF of methanol exists at critical temperature of about 512°C, a critical pressure of about 79.9 atmospheres and at a critical density of 0.272. In another example, a SCF of ethanol exists at critical temperature of about 514°C, a critical pressure of about 60.6 atmospheres and at a critical density of 0.276. The term “subcritical fluid” is used throughout the present disclosure to denote a fluid / liquid that is below the critical point of the substance.

[0049] The reactor that can be employed also includes a means, such as a conveyor belt, for introducing the plastic(s) that need(s) to be recycled into the chamber of the reactor, and a means, such as the same conveyor belt, for removing the recycled, i.e., depolymerized, material from the chamber of the reactor. The reactor further includes a heating device / element that can be used to heat the chamber. It is noted that in some embodiments, the SFC is formed outside of the reactor chamber and the SCF is then introduced into the reactor chamber through one of the inlet ports. In such an embodiment, the heating device / element and the evacuation used in forming the SCF is performed outside of the chamber of the reactor. In such an embodiment, the SCF can be formed in a SFC chamber that is connected to one of the inlet ports of the reactor.

[0050] In some embodiments of the present disclosure, the alcohol that is used in providing the subcritical or supercritical fluid has from 1 to 8 carbon atoms. Suitable alcohols that can beemployed in the present disclosure thus include ethanol, methanol, propanol, butanol, pentanol, hexanol, heptanol, and / or octanol. The alcohol can be a straight chain alcohol or a branched alcohol. The alcohol that is employed in the present disclosure is preferably an unsubstituted alcohol. In some embodiments, a single alcohol is employed. In other embodiments, a mixture of at least two different C1-C8 alcohols can be used. In a preferred embodiment of the present disclosure the alcohol is ethanol and thus a subcritical or supercritical fluid of ethanol is used in the recycling process of the present disclosure.

[0051] In some embodiments of the present disclosure, the alcohol-containing subcritical or supercritical fluid further comprises water. That is, a mixture of an alcohol and water can be used. In one preferred embodiment, the subcritical or supercritical fluid is a mixture of ethanol and water. In embodiments in which water is employed, the subcritical or supercritical fluid has a ratio of water to alcohol from about 1:1 to about 10:1, more preferably about 1:1 to about 5:1, and even more preferably from about 1:1 to 4:1. A subcritical or supercritical fluid of an alcohol and water will allow for optimization of the depolymerization process for mixtures of waste plastics that include PVC.

[0052] In some embodiments of the present disclosure, the depolymerizing is also performed in the presence of a reactive clay, an aluminosilicate (including a zeolite), a base that neutralizes hydrochloric acid formation, or any combination thereof. Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. These ‘additive’ materials can be added to the chamber of the reactor anytime during the depolymerization process. Typically, these additive materials are added to the chamber of the reactor prior to the initiation of the depolymerization process.

[0053] The reactive clay can be used for enhanced subcritical or supercritical fluids assisted conversion of PVC. The reactive clay can be used as bulk or it can be present on a metal support. Reactive clays are prone to large volume changes (swelling and shrinking) that are directly related to water content. Illustrative examples of reactive clays that can be used in the present disclosure include, but are not limited to, bentonite. The reactive clay can be used inamounts that are effective in improving the selectivity of the conversion mentioned above. In one example, the reactive clay can be used in an amount from about 0.5 weight percent to about 25.0 weight percent; other amounts that are below or above the aforementioned range can also be employed.

[0054] When an aluminosilicate (including a zeolite) is used, it can be used alone or typically in combination with one of the bases listed below, e.g., CaO. The aluminosilicate (including zeolite) can be used in an amount from about 0.5 weight percent to about 25.0 weight percent, other amounts that are below or above the aforementioned range can also be employed. The aluminosilicate (including zeolite) can be used for increasing the yield of low molecular weight products in subcritical or supercritical fluids, while assisting their downstream separation. The aluminosilicate (including zeolite) can be used bulk or it can be present on a metal support.

[0055] The base that neutralizes hydrochloric acid (HCl) formation can include, for example, an oxide such as calcium oxide, aluminum oxide, silicon oxide, iron oxide and / or magnesium oxide. In one example, the base can be used in an amount from about 0.5 weight percent to about 25.0 weight percent, other amounts that are below or above the aforementioned range can also be employed. The oxide bases can be used to provide a high degree of chlorine conversion into inorganic chlorides, while addressing any toxicity issue of chlorinated organics.

[0056] In some embodiments of the present disclosure, the depolymerizing is performed at a pressure from about 0.1 atmospheres to about 100 atmospheres, with a pressure of from about 0.5 atmospheres to about 75 atmospheres being more preferred, and with a pressure of from about 1 atmosphere to about 50 atmospheres being more preferred.

[0057] In some embodiments of the present disclosure, the decomposition temperature of the plastic, i.e., PVC, is from about 500°C or greater, with a decomposition temperature from about 525°C to 1200°C being more preferred, and with a decomposition temperature from about 550°C to 1000°C being even more preferred. The depolymerizing is thus performed at a temperature that is below the decomposition of PVC. Typically, the depolymerization is performed at atemperature (i.e., the depolymerization temperature) from about 200°C to less than 500°C, with a temperature from about 250°C to 450°C being even more preferred. The depolymerization is typically performed for a time period of from about 1 hour to about 5 hours; although shorter and longer depolymerization times can be employed.

[0058] In some embodiments of the present disclosure, the depolymerizing produces a non- halogen-containing product (compound or polymer) having from 2 to 12, more preferably from 2 to 8, even more preferably from 2 to 6 carbon atoms, and most preferably from 2 to 4 carbon atoms. In some embodiments of the present disclosure, the non-halogen-containing product comprises at least poly(ethyl vinyl ether).

[0059] In some embodiments of the present disclosure, the process further includes monitoring the depolymerizing for polymeric cluster formation. In some embodiments, the monitoring includes at least one of synchrotron wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), inelastic X-ray scattering (IXS) and molecular dynamics (MD) simulation. In some embodiments, a combination of these monitoring techniques can be employed. These monitoring techniques can be used to determine the structure(s) of the cluster(s) that can be formed as well as the dynamics of that cluster formation. The flickering cluster processes in subcritical fluids and supercritical fluids can significantly affect the depolymerization of PVC and other plastics. Thus, the above monitoring techniques can be used to establish comprehensive correlation between the structure, dynamics and other reaction products that could be critical for maximizing C2-C4 product selectivity.

[0060] The WAXS, SAXS, XPCS, and IXS include apparatuses that are well known to those skilled in the art. These apparatuses can be used in conjunction with the reactor in which depolymerization takes place and can be used to take measurements anytime during the depolymerization process. Monitoring can occur continuously throughout the entire depolymerization process or it can be performed at selective times during the depolymerization process. A baseline can be established by taking a measurement prior to performing the depolymerization process.

[0061] In some embodiments of the present disclosure, the monitoring can further include infrared (IR) spectroscopy. In such embodiments, IR can be used in in conjunction with at least one of WAXS, SAXS, XPCS, IXS and MD simulation. IR monitoring can be obtained utilizing any well-known IR apparatus. The IR can be in communication with the chamber of the reactor and can be used to take measurements anytime during the depolymerization process. IR monitoring can occur continuously throughout the entire depolymerization process or it can be performed at selective times during the depolymerization process. A baseline can be established by taking an IR measurement prior to performing the depolymerization process.

[0062] In embodiments of the present disclosure, a combination of in-situ IXS and IR can be used to correlate clustering structures of polymer chains with a potential reaction mechanism.

[0063] In embodiments of the present disclosure, a fundamental understanding of solvent / solvent and solvent / solute clustering structures can be correlated to reaction mechanisms via a combination of in-situ IR and WAXS / SAXS techniques.

[0064] In embodiments of the present disclosure, fine tuning of reaction selectivity towards low molecular weight dechlorinated products can be achieved by correlating time-resolved in-situ X- ray and IR results in the subcritical fluids and supercritical fluids of the present disclosure.

[0065] In some embodiments of the present disclosure, the process further includes separating and recovering reaction products formed from the depolymerizing of the recyclable plastic. In some embodiments, the separating can occur inside the reactor chamber. In other embodiments, the separating of the reaction products typically takes place downstream from the chamber in which the depolymerization occurs. In such embodiments, the reaction products can be transferred downstream to a separation zone that includes one or more separation devices.

[0066] In some embodiments of the present disclosure, the separating includes an isothermal pressure drop after the depolymerizing of the recyclable plastic in the subcritical fluids andsupercritical fluids. In some embodiments of the present disclosure, the separating includes adding a clay-based emulsion to a product formed by the depolymerizing. Clay-emulsions can be formed by adding a reactive clay as defined above to any well-known emulsifying agent or mixture of emulsifying agents. In such an embodiment, achieving a low interfacial viscosity of the emulsion can result in formation of a continuous product bank, and formation of this bank early in the flow process could maximize the overall efficiency of the recovery process.

[0067] In some embodiments of the present disclosure, the recovering includes a fractionation process. Fraction is a separation process in which a certain quantity of a mixture (of gasses, solids, liquids, etc.) is divided during a phase transition, into a number of smaller quantities (fractions) in which the composition varies according to a gradient. Fractions are collected based on differences in a specific property of the individual components. A common trait in fractionations is the need to find an optimum between the amount of fractions collected and the desired purity in each fraction. Fractionation makes it possible to isolate more than two components in a mixture in a single run. This property sets it apart from other separation techniques.

[0068] In another aspect of the present disclosure, a recycling plant is provided. In one embodiment, the recycling plant includes a reactor configured to perform a depolymerization reaction at a temperature below a decomposition temperature of a recyclable plastic stream including at least PVC. In some embodiments, the depolymerization reaction is performed in the presence of a subcritical or supercritical fluid comprising an alcohol. That is, the depolymerization can be performed using a subcritical fluid comprising an alcohol or a supercritical fluid comprising an alcohol.

[0069] In the recycling plant, any embodiments mentioned above for the recycling process can be implemented.

[0070] The reactor in which depolymerization takes place can be used with other types of recycling reactors that are present in plastic recycling plants and can be used in conjunction with one or more separating / product recovering devices.

[0071] All plastics to be recycled can be treated, i.e., washed, prior to introducing them into the reactor. The recycling plant can include one or more recovery devices / units located downstream of the reactor in which recycling occurs.

[0072] As mentioned above, the depolymerization reaction of the present disclosure can also be performed in the presence of subcritical water. EXAMPLE

[0073] Depolymerization experiments were carried out in aqueous solutions under subcritical (P=3~4 MPa) conditions to approach low-temperature depolymerization strategies while minimizing flammability of solvent mixtures. Commercially available PVC was mixed with either water or a 4:1 v / v water / ethanol mixture (0.2 g / mL) and heated to 250°C for 1 hr. Treatment of PVC with scH2O has previously been shown to lead to complete dechlorination with formation of aromatic degradation products between 300 and 370°C in 1 hr. Size-exclusion chromatography (SEC) of the solid remaining after processing shows a slight decrease in molecular weight occurred (See, for example, FIG. 1), but more effective depolymerization is expected at the higher temperatures and pressures, where the effects of the aforementioned short- range and long-range clusters become significant.

[0074] These conditions will be investigated, resulting in new knowledge connecting molecular dynamics and reaction pathways. In addition to 4:1 v / v water / ethanol mixture, ethanolysis of PVC under subcritical (240°C) and supercritical (250°C) conditions in pure ethanol were compared. After heating the supernatant of each sample was analyzed.

[0075] Ion chromatography of samples heated for 3 hours shows that samples treated under supercritical conditions had a 6× higher concentration of chloride than those treated at subcritical temperatures.

[0076] Infrared spectroscopy (see, for example, FIGS. 2A-2B) shows a significant decrease in the peak arising from the C-Cl stretch (612 cm-1) after 3 hours (See, FIG. 2B) and the appearance of soluble alkene products (1650 cm-1, 3015 cm-1) at both 1 hour (See, FIG. 2A) and 3 hours (See FIG. 2B).

[0077] 1H NMR analysis of the supernatant show peaks corresponding to soluble PVC after 1 hour at 250°C (See, for example, FIG. 3A), which are substantially diminished after 3 hours (See, for example, FIG. 3B). These results provide evidence that supercritical ethanolysis can be used to degrade PVC.

[0078] While the present disclosure has been particularly shown and described with respect to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present disclosure. It is therefore intended that the present disclosure not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.

Claims

CLAIMS What is claimed is:

1. A process for recycling plastics, the process comprising: depolymerizing a waste plastic stream comprising at least polyvinyl chloride (PVC) in a reactor at a temperature below a decomposition temperature of PVC and in the presence of a subcritical or supercritical fluid comprising an alcohol.

2. The process of Claim 1, wherein the alcohol has from 1 to 8 carbon atoms.

3. The process of Claim 2, wherein the alcohol is ethanol.

4. The process of Claim 1, wherein the depolymerizing is performed in the presence of a reactive clay, an aluminosilicate, a base that neutralizes hydrochloric acid formation, or any combination thereof.

5. The process of Claim 1, wherein the subcritical or supercritical fluid further comprises water.

6. The process of Claim 5, wherein the subcritical or supercritical fluid comprises ethanol and water.

7. The process of Claim 5, wherein the subcritical or supercritical fluid has a ratio of water to alcohol from about 1:1 to about 10:

1.

8. The process of Claim 5, wherein the depolymerizing is performed in the presence of a reactive clay, an aluminosilicate, a base that neutralizes hydrochloric acid formation, or any combination thereof.

9. The process of Claim 1, wherein the depolymerizing is performed at a pressure from about 0.1 atmospheres to about 100 atmospheres.

10. The process of Claim 1, wherein the decomposition temperature is from about 500°C or greater, and the temperature of the depolymerizing is from about 200°C to less than 500°C.

11. The process of Claim 1, wherein the depolymerizing produces a non-halogen-containing product having from 2 to 12 carbon atoms.

12. The process of Claim 1, wherein the depolymerizing produces a non-halogen-containing product having from 2 to 4 carbon atoms.

13. The process of Claim 11, wherein the non-halogen-containing product comprises at least poly(ethyl vinyl ether).

14. The process of Claim 1, further comprising monitoring the depolymerizing for polymeric cluster formation.

15. The process of Claim 14, wherein the monitoring comprises at least one of synchrotron wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), X-ray photon correlation spectroscopy (XPCS), inelastic X-ray scattering (IXS) and molecular dynamics (MD) simulation.

16. The process of Claim 15, wherein the monitoring further comprises infrared (IR) spectroscopy.

17. The process of Claim 1, further comprising separating and recovering reaction products formed from the depolymerizing.

18. The process of Claim 17, wherein the separating comprises an isothermal pressure drop after the depolymerizing or adding a clay-based emulsion to a product formed by the depolymerizing.

19. The process of Claim 17, wherein the recovering comprises a fractionation process.

20. A recycling plant comprising: a reactor configured to perform a depolymerization reaction at a temperature below a decomposition temperature of a recyclable plastic stream comprising at least PVC, wherein the depolymerization reaction is performed in the presence a subcritical or supercritical fluid comprising an alcohol.

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