Platinum group metal-free zeolite catalyst for upcycling plastic waste to aromatics

Abstract

A highly active and selective PGM-free solid catalyst comprising nickel and a zeolite, e.g., ZSM-5, for upcycling of plastic waste, such as high-density polyethylene, to yield valuable aromatic-containing products is disclosed.

Description

Attorney Docket No.: JHU-44212.601PLATINUM GROUP METAL-FREE ZEOLITE CATALYST FOR UPCYCLING PLASTIC WASTE TO AROMATICSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U. S. Provisional Application No. 63 / 778,464, filed March 27, 2025, the contents of which are incorporated herein by reference in its entirety.BACKGROUND

[0002] Polymers are irreplaceable in the global economy, with a myriad of uses in packaging, construction, transportation, electronics, and health-care industries. Many of these applications rely on plastics as inexpensive disposable materials, which are nonetheless often precisely constructed to confer desired properties essential for the targeted function. Their massive-scale manufacture, single-use function, long lifetimes, slow decomposition rates, and disruption of sensitive ecosystems, however, have created a crisis of plastics waste.

[0003] In light of both the large drain on global resources and the massive amount of waste material generated, plastics represent a tremendous and as-yet-untapped domestic resource for the production of chemicals and new materials. Efficient technologies for extracting this value from discarded polymers would be equivalent to recovering about 3.5 billion barrels of oil each year and could create entirely new industries. Currently, most of the stored energy in plastics is irreversibly lost into landfills that are overflowing throughout our planet. While physical recycling is desirable and widespread in many areas for a wide range of materials, it is most effective for recovering glass, paper, and metals such as aluminum. Recycling, to date, has not been able to efficiently and cleanly recoup the inherent value in plastics, especially low-density polyethylene (plastic bags), polypropylene, and polystyrene. The syntheses of many virgin plastics are currently less expensive than creating quality recycled materials, because plastics are made on a large scale in centralized plants, from inexpensive monomers such as ethylene, in processes that are tightly integrated into commodity chemical production. As a result, many plastics are just burned as fuel or inefficiently reprocessed to manufacture lower-value materials (known as downcycling), resulting in minimal economic incentives for waste recovery, sorting, and processing.

[0004] Chemical upcycling, an emerging alternative to the classical recycling approach, would use plastic waste as a feedstock for the synthesis of value-added chemicals and materials.Attorney Docket No.: JHU-44212.601Disadvantageously, most plastic collected today is not deemed suitable for upcycling due, in part, to the variability of the incoming plastic stream. The sources of the variability include the mixing of different types of plastics, the degree of degradation associated with reprocessing plastics, and the presence of low molecular weight compounds.

[0005] That said, chemical recycling with conversion into valuable liquid fuels or chemical feedstocks has been an attractive option. The available processes (typically thermo pyrolysis), however, suffer from low energy efficiency (> 500 °C) and lack of product control. Kunwar et al., 2016; Jia et al.. 2016. Zeolites / molecular sieves are widely used catalysts in the thermo pyrolysis of plastics, but present challenges in wide product distribution and coke deposition during pyrolysis process. Serrano et al., 2012; Achilias et al., 2007; Wong et al., 2016; Zhang et al., 2019. Platinum Group Metal (PGM) catalysts are known in the art. however the cost and scarcity of the PGMs has led many to seek viable PGM-free alternatives.

[0006] There is a continuing need for the development of improved PGM-free catalysts for upcycling plastic waste into value-added hydrocarbon liquids.SUMMARY

[0007] In some aspects, a catalyst comprising nickel and a zeolite is disclosed.

[0008] In some other aspects, a catalyst comprising nickel and a zeolite is disclosed, wherein the catalyst comprises a nickel loading of between about 0.05 wt% nickel to about 1.0 wt% of nickel.

[0009] In still other aspects, a catalyst comprising nickel and a zeolite is disclosed, wherein the catalyst, wherein the catalyst is substantially free of platinum group metals (PGM) selected from Ru, Rh, Pt, Pd. Ir, and Os.

[0010] In another aspect, a process for converting plastic waste into one or more aromatic compounds is disclosed, the process comprising:(a) providing a metal-exchanged zeolite catalyst;(b) contacting vaporized plastic waste, the metal-exchanged zeolite catalyst, and a stream of hydrogen and / or inert gas in a reactor; and(c) collecting the one or more aromatic compounds.

[0011] Other aspects, features and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.Attorney Docket No.: JHU-44212.601BRIEF DESCRIPTION OF THE FIGURES

[0012] FIG. 1. An embodiment of the x wt% Ni-ZSM5 Catalyst Synthesis Scheme.

[0013] FIG. 2. An illustration of carbon-based mass yield (%) as a function of x wt% Ni-ZSM5, compared to 0.05 wt% Ir-ZSM5, after catalytic hydrocracking of HDPE at 650°C. Cl = 1 carbon hydrocarbon (HC); C2 = 2 carbon HC; C3 = 3 carbon HC.

[0014] FIG. 3. An illustration of selectivity (%) (■) of carbon-based compounds and reaction time (hours) (A) as a function of x wt% Ni-ZSM5, compared to 0.05 wt% Ir-ZSM5, after catalytic hydrocracking of HDPE at 650°C.

[0015] FIG. 4: An schematic of the tubular plug-flow reactor (PFR) system used in the Example described herein.DETAILED DESCRIPTION OF THE DISCLOSURE

[0016] Although the claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are within the scope of this disclosure as well. Various structural and parameter changes may be made without departing from the scope of this disclosure.Definitions

[0017] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0018] ‘ ‘About” and “approximately” are used to provide flexibility to a numerical range endpoint by providing that a given value may be “slightly above” or “slightly below” the endpoint without affecting the desired result, for example, + / - 5%.

[0019] The phrase “in one embodiment” or “in some embodiments” as used herein does not necessarily refer to the same embodiment, though it may. Furthermore, the phrase “in anotherAttorney Docket No.: JHU-44212.601embodiment” as used herein does not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention.

[0020] The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of’ and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.

[0021] For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

[0022] As used herein, a “system” refers to a plurality of real and / or abstract elements operating together for a common purpose. In some embodiments, a “system” is an integrated assemblage of hardware and / or software elements. In some embodiments, each component of the system interacts with one or more other elements and / or is related to one or more other elements. In some embodiments, a system refers to a combination of components and software for controlling and directing methods.

[0023] As used herein, the terms “aromatics” or “aromatic compound” are used to refer to a hydrocarbon compound or compounds comprising one or more aromatic groups such as, for example, single aromatic ring systems (e.g., benzyl, phenyl, etc.) and fused polycyclic aromatic ring systems (e.g. naphthyl, 1,2,3,4-tetrahydronaphthyl, etc.). Examples of aromatic compounds include, but are not limited to, benzene, toluene, indane, indene, 2-ethyl toluene, 3-ethyl toluene, 4-ethyl toluene, trimethyl benzene (e.g.. 1, 3, 5-trimethyl benzene, 1, 2, 4-trimethyl benzene, 1.2,3-trimethyl benzene, etc.), ethylbenzene, styrene, cumene, methylbenzene, propylbenzene, xylenes (e.g., p-xylene, m-xylene, o-xylene, etc.), naphthalene, methyl-naphthalene (e.g., 1-methyl naphthalene, anthracene, 9.10-dimethylanthracene, pyrene, phenanthrene, dimethyl-naphthalene (e.g., 1,5 -dimethylnaphthalene, 1,6-dimethylnaphthalene, 2,5-dimethylnaphthalene, etc.), ethylnaphthalene, hydrindene, methyl-hydrindene, and dymethyl-hydrindene. Single-ring and / or higher ring aromatics may also be produced in some embodiments.Attorney Docket No.: JHU-44212.601

[0024] The term “fluidized bed reactor” is given its conventional meaning in the art and is used to refer to reactors comprising a vessel that can contain a granular solid material (e.g., silica particles, catalyst particles, etc.), in which a fluid (e.g., a gas or a liquid) is passed through the granular solid material at velocities sufficiently high as to suspend the solid material and cause it to behave as though it were a fluid.

[0025] As used herein, the term “high density polyethylene (HDPE)” is a thermoplastic polymer produced from the monomer ethylene. HDPE has a high strength-to-density ratio and is used in the production of plastic bottles, corrosion-resistant piping, geomembranes, and plastic lumber. HDPE typically has a density ranging from about 930 kg / m3to 970 kg / m3.

[0026] As used herein, an “inert gas” includes, but is not limited to, nitrogen, helium, argon, neon, xenon, krypton, and radon.

[0027] The terms “plastics” and “polymers” are used interchangeably herein. A polymer is a carbon-based (at least 50 mass % C) material chiefly made up of repeating units and having a number average molecular weight of at least 100, typically greater than 1000 or greater than 10,000.

[0028] The term “plastic waste,” as used herein, includes at least one of the major thermoplastic resins such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and mixtures thereof. It should be appreciated that the plastic waste can include terrestrial plastic waste, for example as collected by recycling facilities, or marine plastic waste, for example, floating marine plastic waste or plastic waste collected from the bottom of a body of water. Methods of collection of marine plastic waste are known in the art.

[0029] The term “plug flow reactor,” also known as tubular reactors or continuous tubular reactors, is used to refer to reactors wherein reactants continuously flow through a tube or pipe as if they were a "plug" of fluid, with no back-mixing between different portions of the fluid, and products exit the reactor. The reactor contents are not continuously stirred but instead as the plug of fluid flows through the tube or pipe, reactants are converted to products. The interior surface of the reactor comprises catalytically active surfaces and the chemical reaction occurs within the tube or pipe of the plug-flow reactor.Attorney Docket No.: JHU-44212.601

[0030] As used herein, “substantially free” corresponds to less than 0.01 wt%, preferably less than about 0.001 wt%, more preferably less than about 0.0001 wt%, and even more preferably less than about 0.00001 wt%.

[0031] The term “yield” is used herein to refer to the amount of a product flowing out of a reactor divided by the amount of reactant flowing into the reactor, usually expressed as a percentage or fraction. Yields are often calculated on a mass basis or on the basis of a particular feed component. Mass yield is the mass of a particular product divided by the weight of feed used to prepare that product. For example, if 500 grams of polymer is fed to a reactor and 45 grams of benzene is produced, the mass yield of benzene would be 45 / 500=9% benzene.

[0032] Broadly, the presently disclosed subject matter provides a highly active and selective PGM-free solid catalyst comprising nickel (Ni) and a zeolite, e.g., ZSM-5, for upcycling of plastic waste to yield valuable hydrocarbon products including, but not limited to, aromatic compounds. In some embodiments, the valuable hydrocarbon products obtained include benzene, toluene and xylenes (BTX).

[0033] As used herein, a “zeolite” is a hydrated aluminosilicate mineral made from interlinked tetrahedra of alumina (AlO4) and silica (SiO4). Zeolites are characterized by having crystalline aluminosilicate three-dimensional structures arising from a framework of [SiO4]4-and [AlO4]5-coordination polyhedra linked through their comers. Zeolites can have many different crystalline structures, in part because they have open pores (sometimes referred to as cavities or channels) in a very regular arrangement and roughly the same size as smal l molecules. Zeolites generally have utility as catalysts for a variety of chemical reactions.

[0034] Synthetic zeolites have been designed for specific purposes, including as petroleum catalysts. Representative zeolites suitable for use as catalysts include, but are not limited to, chabazite, erionite, faujasite, ferrierite, mordenite, offretite, TEA-mordenite, clinoptilolite, phillipsite, analcime, heulandite, natrolite, stilbite, zeolite A, zeolite beta, zeolite boron beta, zeolite L, zeolite X, zeolite Y, zeolite ZK-5, Breck-6, HZSM-5, ITQ-1, ITQ-21, MCM-22, MCM-36, MCM-39. MCM-41, MCM-48, PSH-3, SUZ-4, EU-1, SAPO-5, SAPO-11, SAPO-34, (S)AIPO-31, SSZ-23, SSZ-32. TUD-1. VPI-5, ZSM-4. ZSM-5. ZSM-8, ZSM-11, ZSM-12.ZSM-20, ZSM-21, ZSM-22, ZSM-23, ZSM-34, ZSM-35, ZSM-38, ZSM-48, ZSM-50, and ZSM-57. In particular embodiments of the presently disclosed subject matter the zeolite is ZSM-5, which is a Mordenite Framework Inverted (MFI) type zeolite. The well-known zeolite ZSM-5Attorney Docket No.: JHU-44212.601is an aluminosilicate zeolite belonging to the pentasil family of zeolites having the chemical formula is NanAlnSi96-nO192·16H2O (0<n<27).

[0035] Zeolite catalysts, e.g., ZSM-5, generally comprise one or more acidic sites. In general, the zeolite can be ion exchanged with a desired cation to replace alkali metals present in the zeolite as prepared, thus obtaining more acid sites. The preferred proton source is ammonium chloride / nitrate as opposed to acids, such as hydrochloric acid, sulfuric acid and nitric acid. Ion exchange is suitably accomplished by conventional contact of the zeolite with an aqueous solution of the proton source.

[0036] Zeolite catalysts can be loaded or doped with Group VIII (old IUPAC) metals to facilitate secondary functions, such as dehydrogenation / hydrogenation or hydrogenolysis, in addition to the basic cracking reaction. Representative Group VIII metals include iron, osmium, cobalt, nickel, platinum, palladium, silver, gold, rhodium, ruthenium, and iridium. An embodiment of iridium doping is disclosed in U. S. Patent Application No. 17 / 998,836, filed on November 15, 2022 in the name of Chao WANG et al. and entitled “Efficient and Selective Conversion of High-Density Polyethylene into Valuable Hydrocarbons,” which is hereby incorporated by reference herein in its entirety (hereinafter the '836 application). In the ‘836 application, the catalyst comprises iridium and an HZSM-5 zeolite with an iridium loading of between about 0.05 wt% iridium to about 1.0 wt% of iridium.

[0037] In a first aspect, a catalyst that is substantially PGM-free and comprises, consists of. or consists essentially of zeolite and the Group VIII metal nickel (hereinafter a nickel-exchanged zeolite) is described.

[0038] The nickel ions can be added to the zeolite by known methods in the art including incipient wetness impregnation; wet impregnation; deposition methods including physical, chemical, vapor and atomic deposition means; ion-exchanging; and other synthetic means well known in the art. The nickel ions may be in the form of readily available compounds such as the metal salts with counter-anions such as nitrates, acetates, halides, oxy-halides, sulfates, nitrides, sulfides and the like.

[0039] Accordingly, in some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of x wt% Ni, wherein x is between about 0.05 wt% nickel to about 5.0 wt% of nickel, including 0.05, 0.1, 0.15, 0.20, 0.25, 0.3, 0.4, 0.5, 0.6, 0.7. 0.8, 0.9, 1, 2. 3, 4, and 5 wt% nickel, and any values therebetween. In certain embodiments, the nickel-exchanged zeoliteAttorney Docket No.: JHU-44212.601catalyst comprises a nickel loading of between about 0.05 wt% and about 0.5 wt%, including about 0.05, 0.1, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, and 0.50 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.05 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.1 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.15 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.2 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.25 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.3 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.35 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.4 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.45 wt% nickel. In some embodiments, the nickel-exchanged zeolite catalyst comprises a nickel loading of about 0.5 wt% nickel.

[0040] In some embodiments, the nickel bonds with one or more oxygen atoms in a lattice comprising the zeolite, e.g., ZSM-5. In some embodiments, the nickel-exchanged zeolite catalyst comprises ZSM-5. In some embodiments, the zeolite in the nickel-exchanged zeolite catalyst comprises, consists of, or consists essentially of ZSM-5.

[0041] In some embodiments, the nickel-exchanged zeolite further comprises at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Au, Ag, Re, Mo, and W. In some embodiments, the nickel-exchanged zeolite is substantially free of the PGM metals Ru. Rh, Pt. Pd, Ir, and Os.

[0042] In some embodiments, the nickel-exchanged zeolite catalyst is regenerated after use for further catalytic reactions. In some embodiments, the nickel-exchanged zeolite catalyst material is washed and dried to separate generated coke and any remaining recondensed heavy olefin products from the zeolite. Thereafter, the dried nickel-exchanged zeolite catalyst can be regenerated through calcination in air and reused.

[0043] In a second aspect, the nickel-containing catalyst disclosed herein can be used in a hydrocracking process. As used herein, the term “hydrocracking” is generally referred to as a two-stage process that combines catalytic cracking, e.g., the breaking of long-chain hydrocarbons into shorter ones, and hydrogenation. Heavier feedstocks are cracked in theAttorney Docket No.: JHU-44212.601presence of hydrogen to produce more desirable products including, but not limited to, aromatic compounds, gasoline (petrol), jet fuel, diesel fuel, naphtha, and liquefied petroleum gas (LPG). The process typically employs high pressure, high temperature, a catalyst, and hydrogen.

[0044] Accordingly, in some embodiments, the nickel-exchanged zeolite catalyst disclosed herein can be used in a process for converting plastic waste into one or more aromatic compounds, the process comprising: (a) providing a nickel-exchanged zeolite catalyst; (b) contacting vaporized plastic waste, the metal-exchanged zeolite catalyst, and a stream of hydrogen and / or inert gas in a reactor; and (c) collecting the one or more aromatic compounds produced as a result of the catalysis.

[0045] In some embodiments, before the plastic is introduced into the reactor, it can be shredded or otherwise reduced to a particulate state. A variety of size reduction processes are known in the art including, but not limited to, a shredder, a chopper, a grinding apparatus or combinations thereof, which can be employed in a sequential, parallel, or tandem manner. In some embodiments, the plastic can first be subjected to a coarse shredding, chopping, or crashing operation. The coarsely shredded or chopped plastic can subsequently be grounded, pulverized, or further crashed to yield the fine particles required for the hydrocracking process. In some embodiments, the plastic is processed into pellets, for example as disclosed in co-pending U. S. Provisional Patent Application filed on March 27, 2025 in the name of Chao WANG, Ronaldo PANGESTU HADI. Han ZONG, and Noah ZECHER-FREEMAN, and entitled “Continuous Catalytic System for Upcycling Plastic Waste in Aromatics,” which is hereby incorporated by reference herein in its entirety. Briefly, a method of converting plastic waste to plastic pellets comprises: introducing plastic waste into a first shredder to obtain plastic flakes; washing and rinsing the plastic flakes at least once; separating the washed / rinsed plastic flakes from wastewater; optionally treating the wastewater for reuse in the method; drying the washed / rinsed plastic flakes; melting the dried plastic flakes in a vacuum or inert atmosphere to produce a plastic aggregate material; shredding the plastic aggregate material in a second shredder to produce plastic pellets; and optionally screening the plastic pellets to obtain a desired size of same.

[0046] Additional pretreatment steps can be incorporated into the recycling process, if desired, such as flotation, washing, drying, separation, or the like. Non-polymeric materials such as metals, glass, wood, paper, cloth and the like can be removed from this separation process. TheAttorney Docket No.: JHU-44212.601separation process can be accomplished using conventional means, such as a magnetic separation device, or a classification device separating according to density, such as a shaking table or a flotation tank. The separation process can be earned out before or after the size reduction step.

[0047] In some embodiments, prior to contact with the nickel-exchanged zeolite catalyst, the plastic waste is vaporized at a temperature from about 400°C to about 500°C, including about 400°C, about 410°C, about 420°C. about 430°C, about 440°C. about 450°C, about 460°C, about 470°C, about 480°C, about 490°C, and about 500°C. In some embodiments, the plastic waste is packed in a reactor, e.g., a first zone of a plug-flow reactor, using an inert material just as quartz wool, or some equivalent thereof that is inert and non-combustible.

[0048] In some embodiments, once vaporized, the plastic waste vapor is introduced into a reactor, e.g., a second zone of a plug-flow reactor, comprising the nickel-exchanged zeolite catalyst described herein, with a stream of hydrogen and / or inert gas to initiate hydrocracking to produce aromatic compounds. The hydrocracking process is conducted at a temperature from about 600°C to about 700°C, including about 600°C, about 610°C, about 620°C. about 630°C, about 640°C, about 650°C, about 660°C, about 670°C, about 680°C, about 690°C, and about 700°C. In some embodiments, the temperature is from about 640°C to about 660°C. In some embodiments, the hydrocracking process is effectuated for a time of about 0.1 to about 100 seconds. In some embodiments, the hydrocracking process is effectuated at pressure of about 0-45 psig. In some embodiments, the aromatic compounds produced include, but are not limited to, benzene, toluene, and xylenes. In some embodiments, the hydrogen and / or inert gas comprises about 1-10 wt% H2 in inert gas. In some embodiments, the hydrogen and / or inert gas comprises about 5 wt% H2 in inert gas.

[0049] In some embodiments, the process further comprises collecting the one or more aromatic compounds in a gas / liquid separation unit. In some embodiments, the gas / liquid separation unit further comprises a heat exchanger network. In some embodiments, the heat released from gas / liquid separation unit is captured by the heat exchanger network and used as heat for other parts of the system to lower the overall external energy requirements. In some embodiments, the process further comprise capturing residual hydrogen and / or inert gas and returning it to an inlet for the reuse in the process.

[0050] In some embodiments of the second aspect, the nickel-exchanged zeolite catalyst disclosed herein can be used in a process for converting plastic waste into one or more aromaticAttorney Docket No.: JHU-44212.601compounds, the process comprising: (a) providing a nickel-exchanged zeolite catalyst; (b) vaporizing the plastic waste; (c) contacting vaporized plastic waste, the metal-exchanged zeolite catalyst, and a stream of hydrogen and / or inert gas in a reactor; and (d) collecting the one or more aromatic compounds produced as a result of the catalysis. In some embodiments, the reactor is a plug-flow reactor. In some embodiments, the plastic waste is vaporized at temperatures in a range from about 400°C to about 500°C. In some embodiments, the plastic waste is vaporized in a first zone of the reactor. In some embodiments, a second zone of the reactor comprises the metal-exchanged zeolite catalyst. In some embodiments, the metal-exchanged zeolite catalyst comprises the catalyst described herein in the first aspect. In some embodiments, the metal-exchanged zeolite catalyst comprises between about 0.05 wt% nickel to about 1.0 wt% of nickel, preferably about 0.05 wt% nickel to about 0.5 wt% of nickel. In some embodiments, the metal-exchanged zeolite catalyst comprises between about 0.05 wt% nickel to about 1.0 wt% of nickel, preferably about 0.05 wt% nickel to about 0.5 wt% of nickel, and is PGM-free. In some embodiments, the contacting is conducted at a temperature from about 600°C to about 700°C. In some embodiments, the hydrogen and / or inert gas comprises hydrogen and nitrogen, e.g., about a 5% hydrogen / 95% nitrogen mixture. In some embodiments, the one or more aromatic compounds is collected in a in a gas / liquid separation unit. In some embodiments, the one or more aromatic compounds comprise at least one of benzene, toleune, at least one xylene, or any combination thereof.

[0051] In a third aspect, a method of synthesizing a nickel-exchanged zeolite catalyst of the first aspect, said method comprising:injecting a nickel salt-containing solution into dried, calcined zeolite for time and under conditions to impregnate the zeolite with nickel;drying the nickel-impregnated zeolite; andcalcining the dried nickel-impregnated zeolite to produce the nickel-exchanged zeolite catalyst of the first aspect.

[0052] In some embodiments, the dried, calcined zeolite is obtained by stirring a calcined acidic (H+) form of zeolite at about 100°C to about 200°C under vacuum for time in a range of about 4 hr to about 10 hr. In some embodiments, the injecting is effectuated with stirring in a vacuum at about 15°C to about 30°C for time in a range of about 8 hr to about 20 hr. Following impregnation, in some embodiments, the nickel-impregnated zeolite is dried with stirring at about atmosphericAttorney Docket No.: JHU-44212.601pressure at about 100°C to about 150°C for time in a range of about 3 hr to about 10 hr. Following drying, the dried nickel-impregnated zeolite is calcined to produce the nickel-exchanged zeolite catalyst. In some embodiments, the calcination of the dried nickel-impregnated zeolite is effectuated at about 500°C to about 600°C at about atmospheric pressure for time in a range of about 3 hr to about 10 hr. It should be appreciated by the person skilled in the art that a desired amount of nickel in the nickel-exchanged zeolite catalyst, i.e., “nickel loading,” can be obtained by adjusting the concentration of nickel ions in the nickel-salt containing solution. Further, it should be appreciated that by adjusting the nickel loading: (a) reaction times for processing plastic waste to produce one or more aromatic compounds can be adjusted; (b) the selectively of the desired product, e.g., BTX, can be adjusted; and (c) the coke yield can be minimized, as understood by the person skilled in the art.

[0053] In light of the present disclosure and the general level of skill in the art, those of skill can appreciate that the following examples are intended to be exemplary only and that numerous changes, modifications, and alterations can be employed without departing from the scope of the presently disclosed subject matter. The synthetic descriptions and specific examples that follow are only intended for the purposes of illustration, and are not to be construed as limiting in any manner to make compounds of the disclosure by other methods.EXAMPLE

[0054] The commercial ammonium form of ZSM-5 with the Si / Al ratio of 11.5 was first calcined at 550°C at atmospheric pressure for 6 hours to obtain HZSM-5 as the precursor. The calcined HZSM-5 was then dried under vacuum and vigorously stirred at 150°C for 6 hours. The corresponding amount of nickel salt to make.v wt%Ni-ZSM5 was dissolved in water and injected into dried calcined ZSM-5 after the ZSM-5 powder was cooled down to room temperature. This impregnation was done under vigorous stirring in a vacuum, and at room temperature, for 12 hours. The mixture was then transferred to a drying container under vigorous stirring at 120°C and atmospheric pressure for 6 hours. The resulting solid was then calcined at 550°C at atmospheric pressure for 6 hours. The obtained catalyst was then sieved into 40 / 60 mesh before use. For the purpose of this example, Ni-ZSM-5 catalysts with five Ni loadings (0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 5 wt%) were synthesized.Attorney Docket No.: JHU-44212.601

[0055] For the experiment, a tubular plug-flow reactor (PFR) system, as illustrated generally in FIG. 4, equipped with a single step gas-liquid separator was operated at atmospheric pressure at temperatures 450°C and 650°C for the first zone (Zl) and the second zone (Z2), respectively. Plastic (200 mg) was introduced in the first zone, where it was vaporized, and flown at 10 seem with 5% H₂ / He gas to the second zone containing 100 mg x wt% Ni-ZSM5 catalyst and then gasliquid separation was effectuated. As shown in FIG. 4, the plastic in the first zone is sandwiched by quartz wool, or the equivalent thereof and the catalyst in the second zone is sandwiched by quartz wool, or the equivalent thereof. The gas product was analyzed in situ using gas chromatography (GC) and the liquid product was analyzed by GC ex situ. Prior to the experiment, the whole system was purged with a carrier gas without applying temperature until there was no remaining oxygen remaining, as confirmed using GC. Thereafter, a fast ramping of temperature, e.g., 100°C / min, was used for both zones. In this experiment, the ramping temperature was applied consecutively starting with the second zone followed by the first zone after the second zone achieved its target. To calculate yields, the liquid product was collected by rinsing the parts of the PFR from after the catalyst location until before the GC inlet, including the PFR reactor tube, gasliquid separator, and connections therebetween, using analytical grade ethanol. The spent catalyst was regenerated by flowing air at about 550°C for 1 hour. In all performance tests, more than 95% of HDPE can be converted into hydrocarbon products. FIG. 2 shows that 0.05 wt% Ir-ZSM5 had the greatest yield of BTX at 68 %, but 0.05 wt% Ni-ZSM5 had a yield of BTX of 58.0 %. Given the high availability and low cost of nickel relative to iridium, the results were promising. FIG. 3 illustrates the variety loading of Ni-ZSM5 start from 0.05 to 5wt%. As shown in FIG. 2, higher Ni loading leads to longer reaction time indicating lower activity. Further, higher Ni loading leads to a higher coke yield, indicating less selectivity to the desired product (BTX). In addition, higher Ni loading leads to lower recovered liquid and gas mass. The remaining yield is the solid wax. Notably, there is no 99.98% selectivity - that is just recovered mass percentage.Attorney Docket No.: JHU-44212.601REFERENCESAchilias, D. S., Roupakias, C., Megalokonomos, P., Lappas, A. A. and Antonakou, E. V.Chemical recycling of plastic wastes made from polyethylene (LDPE and HDPE) and polypropylene (PP). J Hazard Mater 149, 536-542 (2007).Jia, X. Q., Qin, C., Friedberger, T., Guan, Z. B. and Huang, Z. Efficient and selective degradation of polyethylenes into liquid fuels and waxes under mild conditions. Sci Adv 2 (2016).Kunwar, B., Cheng, H. N., Chandrashekaran, S. R. and Sharma, B. K. Plastics to fuel: a review. Renew Sust Energ Rev 54, 421-428 (2016).Serrano, D. P., Aguado, J. and Escola, J. M. Developing Advanced Catalysts for the Conversion of Polyolefinic Waste Plastics into Fuels and Chemicals. Acs Catal 2, 1924-1941 (2012).Wong, S., Ngadi, N., Abdullah, T. A. T. and Inuwa, I. M. Catalytic Cracking of LDPE Dissolved in Benzene Using Nickel-Impregnated Zeolites. Ind Eng Chem Res 55, 2543-2555 (2016).Zhang, Z. et al. Recovering waste plastics using shape-selective nano-scale reactors as catalysts. Nat Sustain 2, 39-42 (2019).

Claims

Attorney Docket No.: JHU-44212.601CLAIMSWhat is claimed is:

1. A catalyst comprising nickel and a zeolite.

2. The catalyst of claim 1, wherein the catalyst comprises a nickel loading of between about 0.05 wt% nickel to about 1.0 wt% of nickel, preferably about 0.05 wt% nickel to about 0.5 wt% of nickel.

3. The catalyst of claims 1 or 2, wherein the zeolite comprises ZSM-5.

4. The catalyst of any of claims 1-3, wherein the catalyst is substantially free of platinum group metals (PGM) selected from Ru, Rh, Pt, Pd, Ir, and Os.

5. The catalyst of any of claims 1-4, further comprising at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Cu, Au, Ag, Re, Mo, and W.

6. A process for converting plastic waste into one or more aromatic compounds, the process comprising:(a) providing a metal-exchanged zeolite catalyst;(b) contacting vaporized plastic waste, the metal-exchanged zeolite catalyst, and a stream of hydrogen and / or inert gas in a reactor; and(c) collecting the one or more aromatic compounds.

7. The process of claim 6, wherein the reactor is a plug-flow reactor.

8. The process of claims 6 or 7, wherein the plastic waste comprises a thermoplastic resin.

9. The process of claim 8, wherein the thermoplastic resin is selected from the group consisting of high-density polyethylene (HDPE), low-density polyethylene (LDPE),Attorney Docket No.: JHU-44212.601polypropylene (PP), polystyrene (PS), polyvinyl chloride (PVC), polyethylene terephthalate (PET), and mixtures thereof.

10. The process of any of claims 6-9, further comprising vaporizing the plastic waste at temperatures in a range from about 400°C to about 500°C.

11. The process of claim 10, wherein the plastic waste is vaporized in a first zone of the reactor.

12. The process of any of claims 6-11, wherein a second zone of the reactor comprises the metal-exchanged zeolite catalyst.

13. The process of any of claims 6-12, wherein the metal-exchanged zeolite catalyst comprises nickel.

14. The process of any of claims 6-13, wherein the metal-exchanged zeolite catalyst comprises a zeolite selected from the group consisting of clinoptilolite, chabazite, phillipsite, mordenite, analcime, heulandite, natrolite, and stilbite.

15. The process of any of claims 6-13, wherein the metal-exchanged zeolite catalyst comprises a zeolite selected from the group consisting of ZSM-5, SSZ-13, and mordenite.

16. The process of any of claims 6-13, wherein the metal-exchanged zeolite catalyst comprises ZSM-5.

17. The process of any of claims 6-16, wherein the metal-exchanged zeolite catalyst comprises between about 0.05 wt% nickel to about 1.0 wt% of nickel, preferably about 0.05 wt% nickel to about 0.5 wt% of nickel.

18. The process of any of claims 6-17, wherein the metal-exchanged zeolite catalyst is substantially free of platinum group metals (PGM) selected from Ru, Rh, Pt, Pd, Ir, and Os.Attomey Docket No.: JHU-44212.60119. The process of any of claims 6-18, wherein the metal-exchanged zeolite catalyst further comprises at least one transition metal selected from the group consisting of Ti, V, Cr, Mn, Fe. Co, Cu, Au, Ag, Re, Mo, and W.

20. The process of any of claims 6-19, wherein the contacting is conducted at a temperature from about 600°C to about 700°C.

21. The process of any of claims 6-20, wherein the contacting is earned out for a time period from about 0. sec to about 10 sec.22.. The process of any of claims 6-21, wherein the hydrogen and / or inert gas comprises about a 5% hydrogen / 95% nitrogen mixture.

23. The process of any of claims 6-22, further comprising collecting the one or more aromatic compounds in a gas / liquid separation unit.

24. The process of claim 23, wherein the gas / liquid separation unit further comprises a heat exchanger network.

25. The process of claim 24, wherein heat released from gas / liquid separation unit is captured by the heat exchanger network and used to heat an inlet stream of hydrogen gas.

26. The process of any of claims 6-25, further comprising capturing residual hydrogen and / or inert gas and returning it to the process.

27. The process of any of claims 6-26, wherein the one or more aromatic compounds are selected from the group consisting of benzene, toluene, indane, indene, 2-ethyl toluene, 3-ethyl toluene, 4-ethyl toluene, 1, 3, 5-trimethyl benzene, 1,2, 4- trimethyl benzene, 1,2,3-trimethyl benzene, ethylbenzene, styrene, cumene, methylbenzene, propylbenzene, xylenes, naphthalene, 1-methyl naphthalene, anthracene, 9.10-dimethylanthracene, pyrene, phenanthrene, 1,5-Attorney Docket No.: JHU-44212.601dimethylnaphthalene, 1,6-dimethylnaphthalene, 2,5-dimethylnaphthalene, ethyl-naphthalene, hydrindene, methyl-hydrindene, and dimethyl-hydrindene, and any combination thereof.

28. The process of any of claims 6-26, wherein the one or more aromatic compounds comprise at least one of benzene, toleune, at least one xylene, or any combination thereof.

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