Process of photoreforming of plastics using metal-based catalysts

Abstract

A photochemical process for converting plastics into hydrogen gas, gaseous C 1-6 hydrocarbons, and hydrocarbons greater than 6 carbons using light absorbing metal-based catalysts on a solid support under ambient conditions is disclosed.

Description

PROCESS OF PHOTOREFORMING OF PLASTICS USING METAL-BASEDCATALYSTSFIELD OF INVENTION

[0001] The present invention relates to processes for photoreforming plastic waste in the presence of light absorbing metal-based catalysts on a solid support to decompose plastic waste and produce hydrogen gas, gaseous C1-6 hydrocarbons, and hydrocarbons greater than 6 carbons.BACKGROUND OF INVENTION

[0002] Plastic waste is an environmental concern. Diversion of plastic waste from landfills is hindered by challenges in recycling plastic waste. Thermoplastics such as polyvinylchloride, polystyrene, and polyurethane make up nearly 20% of all plastics used. However, these high-use thermoplastics are not recycled due to the resulting emission of dangerous substances and low cost-effectiveness because of low densities and high viscosities. Mixed plastic waste is also difficult to recycle due to unwanted products generated during traditional recycling processes.

[0003] Mechanical recycling dominates current recycling practices due to its low cost and technological requirements. Plastic waste from municipal outputs generally contain unsorted mixed plastic types, which need to be separated before recycling.Separation of these plastic wastes is incredibly difficult. Generally, mechanical recycling occurs via the following steps: 1 ) washing to remove bio-organic materials such as food waste and paper, 2) shredding / grinding of plastic into smaller more manageable pieces, followed by 3) melting and recasting of the polymer, often with virgin material to tune properties such as rigidity and strength, into new products. However, this process ishampered by end-product degradation compared to the virgin polymer. Furthermore, chemical degradation under the heat and mechanical stress characteristic of mechanical recycling means that mechanically recycled plastic is generally not considered food-safe. Thus, the lifetime of recycled plastics via mechanical methods is limited due to harsh grinding, heating, and extrusion steps. As well, plastic composites are often unsuitable for recycling as they produce immiscible end-products with inconsistent mechanical properties. Mechanical recycling is also limited to thermoplastic waste feedstocks, which are pliable and can be reformed with heat; the other category is thermoset plastic, which only bums when heated, making them unsuitable for mechanical recycling.

[0004] Chemical recycling, or the breakdown of waste feedstock into smaller functional components, is an alternative to traditional mechanical recycling that forgoes many of its downsides. Of the chemical recycling methods, pyrolysis, which is the thermally induced breakdown of long chains into smaller parts in the absence of oxygen, is the simplest. The process’s simplicity, cost effectiveness, and disregard for sorted over unsorted waste make it an attractive option for liquid fuel generation from plastic wastes, with some reports claiming 80% conversion by weight from plastic into liquid oil, with the rest being char or gaseous products such as small molecular weight (MW) hydrocarbons (HCs) and hydrogen. However, like many thermal processes, pyrolysis suffers from large energy demands and safety concerns associated with maintaining the high temperatures needed for the reaction, where some processes demand over 800°C to prevent the formation of unwanted products. These processesare highly energy-and-carbon-emission-intensive, and the high temperatures required can only be sustained by the combustion of fossil fuels.

[0005] Similarly, gasification is the breakdown of feedstock through heating, the difference being the addition of an oxidizer. The process generally produces syngas, which is a mixture of carbon monoxide and hydrogen, and methanol, which are less valuable than unoxidized HCs.

[0006] Chemolysis is the breakdown of wastes using various reagents to essentially reverse the polymerization process. The process is limited to specific polymers, such as polycaprolactones, nylons, and polyethylene terephthalate. Chemolysis has the benefit of creating food-safe plastics identical to the virgin material but comes at the cost of needing more reagents (eg. water or glycol), which creates additional monetary and logistical expenses. Thus, plastics from chemolysis are often more expensive than their virgin counterparts, making the process not economically viable with current technologies.

[0007] Photoreformation, or the use of light to break waste material into smaller parts, are being researched for waste plastic degradation. Past studies on plastic reformation using light generally employed transition metal oxide catalysts to improve photo-generated electron conductivity and / or light absorption. For example, CdS / CdOx quantum dot systems have been investigated by llekert, T. et al. Energy Environ Sci 2018, 11 (10), 2853-2857 for photoreforming of polylactic acid (PLA), polyethylene terephthalate (PET), and polyurethane (Pll) but were hindered by catalyst toxicity and high cost.

[0008] Carbon nitride (CNx), carbon nanotubes (CNT), and nickel-based systems have also been shown by llekert, T. et al. J Am Chem Soc 2019, 141 (38), 15201 - 15210 to increase H2 production during plastic photoreformation. However, this system required another reagent, triethanolamine, as a consumable electron donor, which increases operation cost in large-scale implementations.

[0009] NiMo nanoparticles have been used by Gong, X et al. Appl Catal B 2022, 307, 121143 on a substrate of graphitic CNx and carbon nanotubes to dehydrogenate PET and PLA, but it hindered by high catalyst complexity and a tendency to decompose under high temperatures.

[0010] Thus, catalyst toxicity, high cost, complex process steps, catalyst complexity, stability, and commercial scalability are difficulties with photoreforming of plastic waste.SUMMARY OF THE INVENTION

[0011] According to an embodiment of the invention, a process for photoreforming plastic waste is provided. The process comprises exposing a plastic from plastic waste to a light source in the presence of a light-absorbing metal-based catalyst dispersed on a solid support.

[0012] According to an aspect of the invention, the plastic may comprise a pure olefinic plastic or a mixture of different olefinic plastics. The pure olefinic plastic may be polyethylene, polypropylene, polybutylene, polystyrene, polymethylpentene, all isomers of polyethylene, all isomers of polypropylene, all isomers of polybutylene, all isomers of polymethylpentene, co-polymers thereof, or mixtures thereof. The plastic may be in theform of film, powder, pellets, fibers, micro-particles, nano-particles, or combinations thereof. The plastic may be pelletized or shredded.

[0013] According to an aspect of the invention, the photoreforming of the plastic causes catalytic decomposition of plastic waste to separable hydrogen gas, light oligomeric fractions (gaseous C1 -6 hydrocarbons), and heavy oligomeric fractions (hydrocarbons greater than 6 carbons).

[0014] According to another aspect of the invention, the light-absorbing metalbased catalyst comprises metals, metal oxides or metal salts. The light-absorbing metal-based catalyst may comprise a single metal or semi-metallic atom. The single metal atom may be one of the metallic elements of the periodic table. The single metal atom may be Fe, Mn, Ni, Co, Zn, Ru, Pd, Ti, Ag, Pt, or Rh.

[0015] According to another aspect of the invention, the light-absorbing metalbased catalyst comprises one of the earth-abundant elements of the periodic table, or a mixture thereof. The earth-abundant elements may be selected from the group consisting of K, Na, Ca, Ba, Si, Al, Mg, O, H, F, Cl, C, Ti, Fe, Mn, Ni, Co, Cu, Zn, or a mixture thereof.

[0016] According to another aspect of the invention, the light-absorbing metalbased catalyst light-absorbing metal-based catalyst is selected from the group consisting of Ru and Fe.

[0017] According to another aspect of the invention, the photoreforming of the plastic is carried out under a light intensity ranging from about 0.5 to about 50 W / cm2. The photoreforming of the plastic may be carried out under a light intensity ranging from about 10 to about 50 W / cm2.

[0018] According to another aspect of the invention, the light is provided by sunlight, light emitting diodes, Xenon lights or by other artificial light sources. The wavelength of the light may range from ultraviolet, through the visible spectrum and into the infrared spectrum.

[0019] According to another aspect of the invention, the solid support is an insulator or semiconductor. The solid support may be a mixture or a doped form of a metal oxide, nitride, sulfide, phosphide, boride, silicide, carbide, silicon or carbon. The solid support may be a mixture of iron oxides and carbon.

[0020] According to another aspect of the invention, the reactor is a continuous stirred reactor or batch reactor.

[0021] According to another aspect of the invention, the process is free from hydrogen, water, or solvents as co-reactants.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following drawings are only for the purpose of illustrating one or more embodiments of the present invention and are not to be construed as limiting the invention. They may be used to understand the processes described herein and the results of the experimental work discussed below.

[0023] Figure 1 A is a diagram illustrating a photoreactor set-up according to an embodiment of the invention.

[0024] Figure 1 B is a graph showing mass balance of separated wax and gases, and mass change in the glass reactor over varying light intensities.

[0025] Figure 1 C is a graph showing selectivity of separated reaction product distribution of condensed wax and gases.

[0026] Figure 2 contains photographs of white and yellowish wax collected after HDPE photo-reforming according to an embodiment of the invention.

[0027] Figure 3A shows light intensity-dependent reaction product generation of photoreforming HDPE enabled by a single atom Fe catalyst using an iron oxide-carbon support.

[0028] Figure 3B is a graph showing the durability of the single atom Fe catalyst using an iron oxide-carbon support in a single-wall glass reactor or a vacuum -separated double-wall quartz reactor.

[0029] Figure 4 shows the energy efficiency of the polymer photoreforming process of the present invention in a single-wall glass reactor or a vacuum-separated double-wall quartz reactor, over a single atom Fe catalyst using an iron oxide-carbon support.

[0030] Figure 5A shows light intensity-dependent reaction product generation of photoreforming HDPE enabled by a single atom Ru catalyst using an iron oxide-carbon support.

[0031] Figure 5B shows relative production rates of wax from HDPE enabled by a single atom Ru catalyst using a carbon support over varying conditions.

[0032] Figure 6 is a graph showing the reaction product distribution of hydrogen, hydrocarbons, and solids from HDPE enabled by a single atom Ru catalyst using a carbon support over irradiation time.DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention provides a non-toxic, simple and low-cost process for catalytic decomposition of plastic waste to hydrogen gas, light oligomeric fractions(Ci-6 hydrocarbons), and heavy oligomeric fractions (hydrocarbons greater than 6 carbons). A light-absorbing metal-based catalyst dispersed on a solid support and a light energy source are used under ambient conditions to decompose plastic waste into heavy oligomeric fractions with hydrocarbons greater than 6 carbons, gaseous C1-6 hydrocarbons and hydrogen. In the use of the present invention, the complex and high- cost prior art methods can be avoided by the use of a low-cost, non-toxic, metal-based catalyst in the presence of light to decompose plastic waste to produce hydrocarbons greater than 6 carbons, gaseous Ci -6 hydrocarbons and hydrogen. The photo-reforming process requires no co-reactants, hydrogen, water, or solvents thereby avoiding additional costs or environmental pollution.

[0034] The selectivity of wax or the gas can be flexibly tuned, during which >99% selectivity to wax or >95% selectivity to gaseous products can be achieved by controlling the reaction conditions and compositions of the catalyst.

[0035] The photoreforming process described herein can also be more efficient than comparable chemical recycling methods, as the metal-based catalysts deconstruct waste plastics directly into gas or solid wax under renewable light, without the need of co-reactants or solvents. Additionally, photoreforming using metal-based catalysts requires no additional energy other than from a light source. As well, no additional solvents or feedstocks are required other than the described plastic wastes. In addition, the waxes are purified and separated from the catalyst bed via spontaneously photoinduced evaporation. This recycling provides advantages in terms of efficiency, scalability, availability, and cost. In addition, the selectivity of this photocatalytic process is exceptionally high and flexibly tunable compared to prior thermal processes. Thesecharacteristics combined with the low cost and environmental footprint of the earth- abundant heterogeneous catalysts increase plastic recycling’s energy efficiency, lower process and product cost, and minimize environmental impact.

[0036] In the process of the present invention, plastic from plastic waste is photo reformed by exposing the plastic to a light source in the presence of a light-absorbing metal-based catalyst dispersed on a solid support resulting in the decomposition of plastic waste, and production of hydrocarbons greater than 6 carbons, gaseous hydrocarbons and hydrogen. The metal-based catalyst can absorb light (from a certain light source), convert the light into charge carriers (such as electrons) and heat, and use the charge carriers and heat to trigger the cleavage of chemical bonds in waste plastics.

[0037] The light-absorbing metal-based catalysts include but are not limited to metals, metal oxides, and metal salts (e.g. nitrates, sulphates, chlorides, carbonates). In some embodiments, the metal-based catalyst is a single metal or semi-metallic atom, In further embodiments, the single metal or semi-metallic atom is one of the metallic or semi-metallic elements of the periodic table. In further embodiments, the single metal or semi-metallic atom is Fe, Mn, Ni, Co, Zn, Ru, Pd, Ti, Ag, Pt, Rh.

[0038] The light-absorbing metal-based catalysts may include one of the earth- abundant elements of the periodic table, or a mixture thereof. In some embodiments, the earth abundant heterogeneous catalyst is K, Na, Ca, Ba, Si, Al, Mg, O, H, F, Cl, C, Ti, Fe, Mn, Ni, Co, Cu, Zn, or a mixture thereof. Additionally, these materials can be functionalized with single metal atoms or metal nanoparticles or doped with non-metals. In certain embodiments, the metal-based catalyst comprises a main group andtransition group metal elements. In some embodiments, the metal-based catalyst is iron, copper, manganese, silicon, aluminum, or oxygen.

[0039] The solid support may be an insulator or semiconductor. In some embodiments, the solid support may be mixture or a doped form of a metal oxide, nitride, sulfide, phosphide, boride, silicide, carbide, silicon or carbon. In some embodiments, the solid support may be a carbon, crystalline or amorphous, or a doped form thereof exemplified by a carbon nitride.

[0040] The metal-based catalyst is prepared by dispersing single atoms of the selected metal-based catalyst on the solid support. The catalyst bearing solid support is used in a reactor into which a plastic is introduced. Plastic from the plastic waste may be in the form of film, powder, pellets, fibers, micro-particles, nano-particles, or combinations thereof. Preferably, the plastic is pelletized or shredded. The plastic may have low, medium, or high molecular weight. The plastic may be a pure olefinic plastic or a mixture of different olefinic plastics. Examples of suitable olefinic plastics include, but are not limited to polyethylene and all isomers thereof, polypropylene and all isomers thereof, polybutylene and all isomers thereof, polystyrene, polymethylpentene and all isomers thereof, co-polymers thereof, or mixtures thereof. Co-polymers may include the co-polymerization of poly-a-olefins and addition of plasticizers and other additives.

[0041] The mass ratio between the metal-based catalyst and the plastic can be 1 :1 to 1 :1000.

[0042] The surface of the solid support is irradiated with light. The light energy can be from artificial and / or natural sources, such as solar light, a Xenon light source,light emitting diode (LED) light source, or other artificial light source. The light source may be located within or outside of the reactor. The light source may be single, multiple, or continuous wavelengths ranging from the ultraviolet to infrared. In some embodiments, the light intensity ranges from about 5 suns (or 5 kW / m2) to about 10,000 suns (or 10,000 kW / m2). In further embodiments, the light intensity is below 2000 suns (or 2000 kW / m2). In further embodiments, the light intensity is below 100 suns (or 100 kW / m2). In some embodiments, the light intensity may also range from about 0.5 to about 50 W cm2, or from about 10 to about 50 W cm2.

[0043] The intensity of the light may be adjusted by optical or electronic means, such as by the use of lenses, or by adjusting the power to the xenon, LED, or other artificial lighting used. The surface of the solid support is irradiated with an appropriate intensity of light so that the reaction can start. The surface of the solid support should be irradiated for sufficient time so that the desired reaction product mixture is achieved.Optionally, additional heating may be utilized to kickstart the melting of plastic to ensure greater enabler / reactant contact and increase rate of reaction.

[0044] The gaseous and solid products produced by the process of the present invention can be readily identified and separated by conventional means to separate hydrogen gas, light oligomeric fractions (gaseous C1-6 hydrocarbons), and heavy oligomeric fractions (hydrocarbons greater than 6 carbons), which can be collected and purified by standard methods.

[0045] Use of light energy together with the use of one or more metal-based catalysts can catalyze the decomposition of polymers into hydrogen gas and valuablemonomers and oligomers at lower temperatures than those required in the prior art, with consequent lower energy consumption.

[0046] Artificial lighting used in the process of the present invention may be powered by renewable energy. In one embodiment, LEDs operate 24-7. In another embodiment, LEDs may be combined intermittently with solar irradiation during nondaylight hours. Thus, the process can be driven using solar light during daylight hours and LEDs during non-daylight hours to allow the process to run continuously.Compared to traditional thermal strategies, using solar energy, or artificial light generated from renewable energy, to trigger reformation of plastics can break the thermodynamic limitation and access the reactions at milder conditions, as well as to mitigate greenhouse gas emissions.

[0047] The process of the present invention may be carried out at ambient temperatures, such as temperatures as low as 20 degrees Celsius, although the rate of production of hydrogen may increase as temperatures in the reactor are increased, Notwithstanding this, the use of light and metal-based catalyst permits the generation of hydrogen at temperatures substantially lower than those of the prior art.

[0048] The process of the present invention may be carried out in a continuous stirred reactor, batch reactor or flow process at pressures from about ambient pressure to 30 psi, or at other pressures within the skill and knowledge of a person skilled in the art.

[0049] To demonstrate / determine the utility of the process of the present invention in reforming plastics, plastic HDPE pellets were exposed to a light source inthe present of a light-absorbing metal-based catalyst dispersed on a solid support in a reactor, as described in more detail in the following examples.Light Absorbing Metal Catalyst & Plastic

[0050] Fe nanochain powder catalyst used for the reactions was prepared using a scalable wet chemistry process. NaBH4 solution was added dropwise into FeCI3 solution, followed by filtration, KOH surface passivation, and drying of generated black iron precipitate. The obtained black iron nanochains, 100 nm to >3 microns in length, consisted of self-assembled Fe@Fe3O4 core-shell nanoparticles of 30—200 nm in diameter.

[0051] High-density polyethylene (HDPE) pellets (Baystar HDPE 5502 STCC 2821142) were used for all reactions.Gas Characterization

[0052] Preliminary product gases were characterized using gas- chromatography / mass-spectrometry (GCMS) or gas-chromatography / thermal conductivity detector (GC-TCD).

[0053] Gaseous CO, CO2 and hydrocarbons (C1 -C6) were analyzed using either GCMS or GC-TCD. The GCMS setup contained an Agilent 7890B GC-MS eguipped with five capillary columns (DB-FFAP, 123-3212, 15 m x 0.320 mm x 0.25 mm; HP- PLOT Q PT, 19091 P-QO3PT, 15 m x 0.320 mm x 20 mm; HP-PLOT Molesieve, 19091 P-MS4E, 30 m x 0.320 mm x 12 mm; 160-2625-5, FST 0.15 mm x 5 m; 160- 2615-5, FST 0.18 mm x 5 m) using 5.0 purity He carrier gas, or a SRI 8610C (columns: HAYESEP-D and MS13X). The GC-TCD setup contained an Agilent (columns: Agilent113-3133 and J&W 113-3133) GC equipped with a TCD and methanizer / flame ionization detector (FID) using a 5.0 purity Ar carrier gas.

[0054] Hydrogen gas was characterized by GC-TCD. The GC-TCD setup contained an Agilent (columns: Agilent 113-3133 and J&W 113-3133) GC equipped with a TCD and methanizer / flame ionization detector (FID) using a 5.0 purity Ar carrier gas. Solid Characterization

[0055] Molecular weight distributions of the virgin HDPE and the hydrocarbon products were analyzed on a Malvern Viscotek high-temperature gel permeation chromatograph module 350A system equipped with one guard column, three analytical columns, and a refractive index (Rl) detector. Samples were dissolved in 1 ,2,4- trichlorobenzene (TCB) containing c / / -te / t-butylhydroxytoluene (BHT, 0.5 g / L) by stirring for at least 20 min at 140°C. Elution was achieved using TCB (with BHT) at 140 °C and 1.0 mL min-1. The molecular weight response was calibrated with monomodal polystyrene (PS) standards with narrow dispersity.Reactor

[0056] Testing of the catalysts was carried out in a laboratory scale reactor, which may have a stainless steel reactor body with one or more quartz glass windows disposed on its circumference, and valves controlling the inflow and outflow of gas to and from the reactor body. The quartz glass windows in the reactor allowed light, which could be solar, or LED or Xenon lighting, simulating solar light, to irradiate the catalyst on a solid support upon which the plastic mixture is dispersed within the reactor and to promote the decomposition of plastic and generation of reaction products in the reactor.The reactor may be heated by way of, for example, a heating cartridge located inside or outside the reactor body.

[0057] Either solar power, magnified by the use of optical lenses, Xenon lighting, or four combined or separated LED lights (UV, blue, green and red) were used as the light source for the reaction. Manually varying the power to the Xenon or LED lights yielded varying light intensities. Adjustment could further vary the diameter of the light spot using focusing lenses for example, light intensities to achieve the intensities used.

[0058] The laboratory reactor could be connected to a temperature thermocouple and pressure gauge. In one embodiment, the reactor may be used with a Perfect LightTM solar simulator 300WXe lamp. A NewportTM power meter with an 18 mm detector spot diameter could be used to determine the irradiation intensity.

[0059] An temperature controller may be attached to a heating cartridge inserted into a copper block along with a thermocouple inserted into the reactor for measuring and controlling the temperature in the reactor.Example 1 : Photoreforming of Plastic with Single Atom Fe Catalyst

[0060] Figure 1 A is an embodiment of a lab-scale reactor set-up using a single atom Fe catalyst to photolytically drive the decomposition of plastic. ~0.1 g of Fe nanochain powder catalyst is placed in a reactor bed and four polyethylene (HDPE) pellets totaling ~0.1 g are placed on top. The reactor is purged with inert gas and sealed. Then the reactor is irradiated with 2.6-3.1 W / cm2of light from a Xe lamp for 24 hours to achieve the temperature spread of 60-80 C at the reactor top and 230-310 C at the catalyst.

[0061] Reactors were allowed to cool to room temperature before gas analysis by GCMS and GC-TCD detection methods and solid product characterization described above.

[0062] The deposition of reaction products are also illustrated in Figure 1A. The separated solid products (wax C15-C225 hydrocarbons) are condensed on the window and interior walls of the reactor. In particular, this wax product was vaporized from the light-irradiated hot catalyst bed and condensed at the cooler parts of the solar reactor with ultra-high purity, readily for physical collection.

[0063] Separated gas products such as gaseous C1-C6 hydrocarbons and hydrogen are located in the reactor.

[0064] Mixed solids such as the single atom Fe catalyst and HDPE are located in the reactor.

[0065] Temperature variations across the reactor are illustrated in Figure 1A. The image shows temperature variation across one embodiment of the invention in a stainless steel batch reactor equipped with a quartz window. Temperatures were measured using a thermocouple.Example 2: Reaction Product Mass Selectivity with Single Atom Fe Catalyst over Varying Light Intensities

[0066] To evaluate the reaction product mass selectivity based on light intensity, various light intensities were tested to determine the mass change of HDPE with a single atom Fe catalyst on a solid support over five runs in addition to the relative masses of produced gaseous C1-C6 hydrocarbons and hydrogen gas, as illustrated in Figure 1 B.

[0067] For each run, ~0.1 g of Fe nanochain powder catalyst is placed in a reactor bed and four polyethylene (HDPE) pellets totaling ~0.1 g are placed on top. The reactor is purged with inert gas and sealed. Then the reactor is irradiated with 2.6-3.1 W / cm2of light from a Xe lamp for 24 hours.

[0068] In between each run, gaseous and solid products were collected. Reactors were allowed to cool to room temperature before gas analysis by GCMS and GC-TCD detection methods and solid product characterization described above.

[0069] Am-reactor is the change in mass of contents inside the glass cup and is equal to the difference in mass before and after each reaction run after products are collected (Am-reactor = mbefore reaction - m after reaction). After collecting the reaction products from each run, more HDPE was added to the reactor bed. The light intensities used for each run were 2.6, 2.7, 2.8, 2.9 and 3.1 W / cm2Xe lamp for runs 1 through 5, respectively. Catalyst temperatures were measured by a thermocouple to be between 230-310 °C. Each run composed of irradiating the reaction bed with light from a Xe lamp for 24 hours. Error bars indicated standard derivations obtained from three separate runs.

[0070] In five successive runs, the wax (C15-C225) weight production kept steadily increasing from ~10% to ~80% of the mass of starting HDPE, with the highest wax selectivity achieved as 62-96%.

[0071] The rest of the products are gaseous Ci-Ce hydrocarbons and carbon oxides (4-37%), and hydrogen (~1 %). Figure 1 C illustrates the corresponding mass selectivity of separated products from the five reactions described in Figure 1 B, includedseparated wax C15-C225 hydrocarbons, gaseous hydrogen and gaseous C1-C6 hydrocarbons.Example 3: Colour of Regenerated Wax

[0072] Figure 2 contains photographs of examples of white and yellowish wax collected after HDPE photo-reforming for 10 minutes using the embodiment described in Example 1 . The white or yellowish colour of the wax generated according to the process of the present invention indicates higher quality wax as compared to the black and brown coloured wax produced in prior art processes. Furthermore, the wax products contain an average molecular chain of C40 (dispersity D = 1 .15) to C86 (D = 1.50), with the minimum and maximum chains as C15 and C225, respectively, which are larger than the C18-C70 (average molecular chain ~C25) wax obtained in prior art processes. Since the longer molecular chains mean less bond cleavage during the HDPE deconstruction, this indicates that the process of the present invention is more energy efficient as less energy is consumed during the recycling.Example 4: Wax Regeneration Rate with Single Atom Fe Catalyst on Iron OxideCarbon Support

[0073] Figure 3A shows that the light intensity-dependent behavior of HDPE over a single atom Fe catalyst using a mixture of iron oxides and carbon as support was evaluated over various light intensities. Photoreforming of HDPE was conducted over a single atom Fe catalyst on an iron oxide-carbon support. Single atom Fe catalyst was placed in a reactor bed and covered in HDPE plastic and allowed to react a set amount of time under Xe lamp irradiation. Prior to irradiation, the reactor was vacuumed of all air. Samples were irradiated for 24 hours under light intensities of 0.5 to 3.1 W / cm2. Forhigher light intensities of 3.9 and 4.8 W / cm2, the single atom Fe catalyst and iron oxidecarbon support were irradiated for 40 and 10 minutes, respectively.

[0074] These results demonstrated that single atom Fe catalyst on an iron oxidecarbon support result in greater wax generation at higher light intensities.Example 5: Durability of Single Atom Fe Catalyst on Iron Oxide-Carbon Support

[0075] Figure 3B shows a durability test of a single-atom Fe catalyst on an iron oxide-carbon support, using an uninsulated single-wall glass reactor or an insulated vacuum -separated double-wall quartz reactor (bar at the top of the graph). The same reactor set up as in Fig 1 B was used, with the exception of replacing the glass cup ("glass reactor") with an insulated vacuum -separated double-wall quartz cup for the test labelled "vacuum reactor". Using the single-atom iron catalyst on an iron oxide-carbon support, around 100% HDPE conversion could be achieved in only 10 minutes under 4.8 W / cm2 light intensity in the insulated reactor, yielding >90% wax and <10% C1 -C6 gases and hydrogen. At lower light intensities using the uninsulated glass cup reactor, similar wax and gas regeneration should take around 24 hours. The results demonstrate that an insulated reactor is more efficient at HDPE conversion.Example 6: Energy Efficiency of Reactor Type

[0076] Figure 4 shows the distribution of energy from light in one embodiment of the invention using a heat-conductive and uninsulated single-walled glass reactor or an insulated double-walled vacuum reactor described in Fig 3B. The results show that the energy efficiency of the polymer photo-reforming process is exceptionally high to a maximum of 14% if the reaction proceeds continuously, or 8% for batch-mode operations.Example 7: Photoreforming of Plastic with Single Atom Ru Catalyst on CarbonSupport

[0077] Figure 5A shows light intensity-dependent reaction product generation of photoreforming HDPE enabled by 0.1 g of a single atom Ru catalyst (1 % Ru by mass) dispersed on a carbon support. The single-atom Ru catalyst on a carbon support is placed in a reactor bed and 0.1 g HDPE pellets are placed on top. The reactor is purged with inert gas and sealed. Then the reactor is irradiated with 2.1 -5.1 W / cm2light intensity using simulated sunlight.

[0078] Reactors were allowed to cool to room temperature before gas analysis by GCMS and GC-TCD detection methods and solid product characterization described above.

[0079] When tuning the light intensity under reaction periods of 10 min to 36 hours, the weight of hydrogen and hydrocarbon products kept steadily increasing from ~1 % to ~99% of the mass of starting HDPE, with the highest selectivity of non-gaseous products achieved as ~85%. The rest of the products are gaseous hydrocarbons, hydrogen and trace amount of carbon oxides.Example 8: Wax Regeneration Rate of HDPE

[0080] To confirm the utility of the photoresponsivity of HDPE and the single atom Ru catalyst on a carbon support, control experiments were conducting over various conditions. Figure 5B shows the mass wax product generated from the photoreforming of HDPE as compared to “dark” conditions with and without the single atom Ru catalyst enabler over varying temperatures.

[0081] Control experiments indicated that the catalyst under thermal heating yielded products at least 10 times lower than that under light. Without the catalyst or HDPE, no product could be obtained. In addition, when the HDPE was placed under the catalyst so that the HDPE could not be illuminated directly under light intensity below 3.1 W / cm2, no products were detected. These results confirm the light intensitydependent behavior of HDPE over a single atom Ru catalyst using a carbon support.Example 9: Single Atom Ru Catalyst on Iron Oxide-Carbon Support

[0082] Figure 6 is a graph showing the reaction product distribution of hydrogen, hydrocarbons, and solids from HDPE enabled by a single atom Ru catalyst using a mixed carbon-iron oxide support over irradiation time. HDPE photo-reforming in a compact reactor and the mass balance under ~8 W / cm2light intensity. The gas products were extracted for quantification every two hours during the reaction using the gas product characterization methods described above.

[0083] The results show that using the single-atom Ru catalyst on a mixed carbon-iron oxide support, around 95% HDPE conversion could be achieved in 10 hours under ~8 W / cm2light intensity with a compact batch-reactor design, which was realized either though increased amount of catalyst, or the reduced volume of the reaction chamber. Products included 12% gaseous hydrogen, ~42% gaseous hydrocarbons, and 40% solid carbon or char.

[0084] While the embodiments of the present disclosure have been described in detail, it is to be understood that, unless otherwise specified, the present disclosure is not limited to particular materials, reaction materials, processes, or the like, as such can vary. It is also to be understood that the terminology used herein is for purposes ofdescribing particular embodiments only, and is not intended to be limiting. It is also possible in the present disclosure that steps can be executed in different sequences where this is logically possible.

Claims

CLAIMS1 . A process for photoreforming plastic waste, the process comprising exposing a plastic from plastic waste to a light source in the presence of a light-absorbing metal-based catalyst dispersed on a solid support.

2. The process of claim 1 , wherein the plastic comprises a pure olefinic plastic or a mixture of different olefinic plastics.

3. The process of claim 2, wherein the pure olefinic plastic is polyethylene, polypropylene, polybutylene, polystyrene, polymethylpentene, all isomers of polyethylene, all isomers of polypropylene, all isomers of polybutylene, all isomers of polymethylpentene, co-polymers thereof, or mixtures thereof.

4. The process according to any one of claims 1 - 3, wherein the plastic is in the form of film, powder, pellets, fibers, micro-particles, nano-particles, or combinations thereof.

5. The process according to any one of claims 1 - 3, wherein the plastic is pelletized or shredded.

6. The process of any one of claims 1 - 3 wherein the photoreforming of the plastic causes catalytic decomposition of plastic waste to separable hydrogen gas, light oligomeric fractions (gaseous C1-6 hydrocarbons), and heavy oligomeric fractions (hydrocarbons greater than 6 carbons).

7. The process of any of one of claims 1 - 3, wherein the light-absorbing metalbased catalyst comprises metals, metal oxides or metal salts.

8. The process of any of one of claims 1 - 3, wherein the light-absorbing metalbased catalyst comprises a single metal or semi-metallic atom.

9. The process of any of clam 8, wherein the single metal atom is one of the metallic elements of the periodic table.

10. The process of any of clam 8, wherein the single metal atom is Fe, Mn, Ni, Co, Zn, Ru, Pd, Ti, Ag, Pt, or Rh.11 . The process of any of one of claims 1 - 3, wherein the light-absorbing metalbased catalyst comprises one of the earth-abundant elements of the periodic table, or a mixture thereof.

12. The process of claim 11 , wherein the earth-abundant elements is selected from the group consisting of K, Na, Ca, Ba, Si, Al, Mg, 0, H, F, Cl, C, Ti, Fe, Mn, Ni, Co, Cu, Zn, or a mixture thereof.

13. The process of any one of claims 1 - 3, wherein the light-absorbing metal-based catalyst is selected from the group consisting of Ru and Fe.

14. The process of any one of claims 1 - 3, wherein the photoreforming of the plastic is carried out under a light intensity ranging from about 0.5 to about 50 W / cm215. The process of any one of claims 1 - 3, wherein the photoreforming of the plastic is carried out under a light intensity ranging from about 10 to about 50 W / cm2.

16. The process of any one of claims 1 - 3, wherein the light is provided by sunlight, light emitting diodes, Xenon lights or by other artificial light sources.

17. The process of any one of claims 1 - 3, wherein the wavelength of the light ranges from ultraviolet, through the visible spectrum and into the infrared spectrum.

18. The process of any one of claims 1 - 3, wherein the solid support is an insulator or semiconductor.

19. The process of any one of claims 1 - 3, wherein the solid support is a mixture or a doped form of a metal oxide, nitride, sulfide, phosphide, boride, silicide, carbide, silicon or carbon.

20. The process of claim 1 , wherein the solid support is a mixture of iron oxides and carbon.21 . The process according to claim 1 , wherein the reactor is a continuous stirred reactor or batch reactor.

22. The process according to claim 1 , wherein the process is free from hydrogen, water, or solvents as co-reactants.