Depolymerization catalyst system and method

Abstract

Catalytic compositions and methods for depolymerizing polyolefin-based feeds into useful petrochemical products are described. The composition is a complex of a zeolite catalyst component and a co-catalyst comprising an activated clay component and / or a solid base component. These catalyst systems are used together with heat to increase the rate of depolymerization reaction of a feed stream and inhibit poisoning effects of impurities that may be present in the polyolefin-based feed. This results in a shorter residence time in the depolymerization unit and a more efficient process.

Description

Technical Field

[0001] The present disclosure relates to a method for depolymerizing polyolefin-based materials using a catalyst system to form useful petrochemical products, such as olefin monomers, the catalyst system comprising a combination of a zeolite catalyst and a cocatalyst, the cocatalyst comprising an activated clay component and / or a solid base component. Background Art

[0002] The increasing living standards and urbanization have led to an increased demand for polymer products, especially polyolefin plastics. Polyolefins are often used in commercial plastic applications due to their outstanding properties and cost characteristics. For example, polyethylene (PE) has become one of the most widely used and recognized polyolefins because it is strong, extremely tough and very durable. This allows it to be highly engineered for a variety of applications. Similarly, polypropylene (PP) is mechanically strong but flexible and heat-resistant, and resistant to many chemical solvents, such as alkalis and acids. Therefore, polypropylene is ideal for a variety of end-use industries, mainly used for packaging and labeling, textiles, plastic parts and various types of reusable containers.

[0003] An adverse aspect of the demand for polyolefin plastics is the increase in waste. Post-consumer plastic waste usually ends up in landfills, about 12% is incinerated, and about 9% is diverted to recycling. In landfills, most plastics do not degrade rapidly, becoming a major source of waste that overloads landfills. Incineration is also not an ideal solution for dealing with plastic waste because it leads to the formation of carbon dioxide and other greenhouse gas emissions. Therefore, there is great interest in developing methods for recycling plastic waste to reduce the burden on landfills while being environmentally friendly.

[0004] The disadvantage of plastic waste recycling is that it is difficult to successfully produce commercially available or desirable products. Plastic waste recycling currently includes washing the materials and mechanically reprocessing them; however, the resulting pellets are still contaminated with impurities such as food residues, dyes and spices. Based on performance and appearance, these impurities make the pellets unsuitable for many uses. In addition, it is difficult to obtain a pure stream of any specific polymer, resulting in the possibility that the mixed plastic waste stream may not have the desired properties after recycling.

[0005] Recent progress has focused on converting plastic waste into useful products, such as fuel sources or commercially important raw materials. Methods have been developed that perform pyrolysis on a plastic waste stream followed by catalytic depolymerization to produce various products: gases, gasoline fractions, kerosene fractions, diesel fractions and waxes. Unfortunately, the catalysts themselves tend to be easily poisoned by other chemicals in the polyolefin waste feed, resulting in high process costs and time-consuming processes because they require a large amount of energy to completely decompose the polyolefin waste into useful product categories.

[0006] Despite progress in recycling polyolefins, there remains a need to develop a reliable method for converting polyolefin-rich waste feedstocks into useful petrochemical products. Ideally, these methods would overcome "poisoning" from other polymers and contaminants that may be present in the waste feedstock. SUMMARY OF THE INVENTION

[0007] The present disclosure provides novel compositions and methods for the pyrolytic depolymerization of polyolefin-based materials in the absence of oxygen. The compositions disclosed herein are combinations of zeolite catalyst components and cocatalysts for forming useful petrochemical products such as olefin monomers, the cocatalysts comprising activated clay components and / or solid base components. The combination of the zeolite catalyst component and the cocatalyst has a synergistic effect for increasing the rate of the depolymerization reaction while also inhibiting any poisoning effects from impurities that may be present in the feed stream or degradation products from such impurities. Specifically, the zeolite catalyst component and the cocatalyst comprising activated clay components and / or solid base components form a reliable depolymerization catalyst system. During a depolymerization process including at least two depolymerization reaction zones, the components of the depolymerization catalyst system are added to separate depolymerization reaction zones. The reaction mixture in each pyrolysis reaction zone is heated in the absence of oxygen in a process called thermal decomposition to rapidly produce useful petrochemical products.

[0008] In some embodiments, a catalyst system for depolymerizing a polymer comprises a zeolite catalyst component and a cocatalyst comprising an activated clay component, a solid base component, or a combination thereof.

[0009] In some embodiments, a method for depolymerizing a polymer comprises: a) adding a polyolefin-based feed stream and a first cocatalyst to a first pyrolysis reaction zone to form a first reaction mixture, wherein the first cocatalyst comprises an activated clay component, a solid base component, or a combination thereof; b) reacting the first reaction mixture in the absence of oxygen under first depolymerization conditions to form a first vapor product and char; c) adding the first vapor product to a first condensation zone, wherein the first vapor product is subjected to condensation conditions to form a second vapor product and a first liquid product; d) adding the first liquid product and a zeolite catalyst component to a second pyrolysis reaction zone to form a second reaction mixture; and e) reacting the second reaction mixture in the absence of oxygen under second depolymerization conditions to form a third vapor product, a second liquid product, and char, wherein the second liquid product comprises one or more olefin monomers.

[0010] In some embodiments, a depolymerization system includes: a) a pyrolysis reaction zone configured to heat a mixture of a polyolefin-based feed stream, a zeolite catalyst, and a cocatalyst to produce a vapor product and carbon, the cocatalyst comprising an activated clay component, a solid base component, or a combination thereof; and b) a condensation unit configured to condense the vapor product to produce a second vapor product and a liquid product comprising one or more olefin monomers.

[0011] In some embodiments, a depolymerization system includes: a) a first pyrolysis reactor configured to heat a mixture of a polyolefin-based feed stream and a first cocatalyst to produce a first vapor product and carbon; b) a first condensation unit configured to condense the first vapor product to produce a second vapor product and a first liquid product; c) a second pyrolysis reactor configured to heat a mixture of the first liquid product and an optional second cocatalyst to produce a second liquid product and carbon; and d) a second condensation unit configured to condense the second liquid product and the optional second vapor product to produce a third vapor product and a third liquid product comprising one or more olefin monomers.

[0012] The features and technical advantages of the present invention have been outlined rather broadly above so that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter, and these form the subject of the claims of the invention. It should be understood by those skilled in the art that the disclosed concepts and specific embodiments can be readily utilized as a basis for modifying or designing other catalyst compositions and / or methods for achieving the same purposes of the present invention. Those skilled in the art should also recognize that such equivalent constructs do not depart from the spirit and scope of the present invention as set forth in the appended claims. By the following description, the novel features that are considered characteristic of the invention, both as to its composition and method, together with further objects and advantages, will be better understood.

[0013] BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The claimed subject matter can be understood by reference to the following description when considered in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

[0015] Figure 1 is a simplified flow diagram of the disclosed method having two depolymerization reaction zones and two condensation zones in accordance with an embodiment of the present invention;

[0016] Figure 2 is a flow diagram of certain embodiments of the disclosed method having two depolymerization reaction zones and two condensation zones; and

[0017] Figure 3A superimposed graph showing the performance of a zeolite catalyst in the case of using a zeolite catalyst alone and in the case of adding a cocatalyst in the depolymerized waste plastic sample is shown.

[0018] While the disclosed methods and compositions may have various modifications and alternative forms, the drawings illustrate, by way of example, specific embodiments described in detail herein. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. Detailed Description

[0019] Exemplary embodiments of the claimed subject matter will now be disclosed. For clarity, some features of some actual implementations may not be described in this specification. It should be understood that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, such as compliance with system- and business-related constraints, which will vary from one implementation to another. Additionally, it should be understood that such development efforts, even if complex and time-consuming, would be a routine task for those of ordinary skill in the art who would benefit from this disclosure.

[0020] The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those of ordinary skill in the relevant art. A special definition of a term or phrase, i.e., a definition different from the ordinary and customary meaning understood by those of ordinary skill in the art. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning different from the broadest meaning understood by those of ordinary skill in the art, such special or express definition will be set forth explicitly in the specification in a manner that provides the special or express definition of the term or phrase. It must also be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless otherwise specified.

[0021] For example, the following discussion contains a non-exhaustive list of definitions of several specific terms used in this disclosure (other terms may be defined or elucidated in the manner of definitions elsewhere herein). These definitions are intended to clarify the meanings of the terms used herein. It is believed that the terms are used in a manner consistent with their ordinary meanings, but for clarity, the definitions are specified herein.

[0022] Definition

[0023] As used herein, "activated clay" describes a clay or clay mineral that has been chemically treated with a dilute acid (e.g., sulfuric acid) and heat treated between 100°C and 200°C, including but not limited to smectites or bentonites (which include montmorillonite, nontronite, beidellite, and saponite); aluminosilicates, sepiolite, attapulgite (palygorskite); kaolin; and other bleaching clays.

[0024] As used herein, "char" refers to coke, a carbon-containing solid that accumulates on the catalyst particles during pyrolysis.

[0025] As used herein, "feed stream" refers to the supply of polyolefin-based material for depolymerization. Depending on the depolymerization unit, the feed stream can be a continuously supplied material or a batch of material. The feed stream can be a pure polyolefin or can be a mixture of polyolefin and non-polyolefin components.

[0026] As used herein, "non-polyolefin component" refers to a material present in a polyolefin-based feed or waste stream that can reduce the ability of a zeolite catalyst to depolymerize the polyolefins present in that stream. Examples of non-polyolefin components include non-polyolefin polymers with high oxygen and / or nitrogen content.

[0027] As used herein, "post-consumer waste" refers to the type of waste generated by the ultimate consumer of a material stream.

[0028] As used herein, "post-industrial waste" refers to the type of waste generated during the production of a product.

[0029] As used herein, "reaction zone" refers to a chamber that is sufficiently enclosed to maintain selected operating conditions within the chamber to effect a desired reaction, such as a pyrolysis reaction zone or a condensation reaction zone. In some embodiments, each reaction zone can be a separate reactor. In some embodiments, a single vessel can contain multiple reaction zones.

[0030] As used herein, "residence time" refers to the time required to depolymerize a batch of polymer waste in a depolymerization unit.

[0031] As used herein, "thermal decomposition" refers to a pyrolytic depolymerization reaction that occurs in the absence of oxygen.

[0032] As used herein, "waste stream" is a type of feed stream that contains materials that have been discarded because they are no longer useful, including but not limited to post-consumer and post-industrial waste.

[0033] As used herein, "zeolite" refers to an aluminosilicate mineral having a microporous structure. In one aspect, zeolites can be used as catalysts for the methods disclosed herein. Zeolites can occur naturally or can be produced industrially.

[0034] As used herein, the term "depolymerization half-life" or "half-life of depolymerization" refers to the time required to achieve 50% mass loss of a sample at a specific temperature during a TGA thermal decomposition reaction. The depolymerization half-life is related to the residence time required for large-scale industrial depolymerization reactors.

[0035] It should be noted that in the present disclosure and particularly in the claims and / or paragraphs, terms such as "comprises", "comprised", "comprising", etc. may have the meanings given to them in United States patent law; for example, they may mean "includes", "included", "including", etc.; and terms such as "consisting essentially of" and "consists essentially of" have the meanings given to them in United States patent law, for example, they allow elements not expressly recited, but exclude elements found in the prior art or elements that affect the basic or novel characteristics of the present disclosure.

[0036] As used with respect to a feed stream, the term "pure" means a feed that is 100% polyolefin, but does not mean that the feed contains only one type of polyolefin. Instead, a "pure" feed stream may have a mixture of polyolefins (such as low density polyethylene, high density polyethylene, polypropylene, and combinations thereof).

[0037] With respect to materials, feed streams, or waste streams, the terms "polyolefin-based" and "polyolefin-rich" are used interchangeably to refer to a mixture that is at least 80% polyolefin.

[0038] Unless otherwise indicated, all concentrations herein are in weight percent ("wt. %").

[0039] Unless the context otherwise indicates, when used in a claim or specification in conjunction with the term "comprising", the use of the words "a" or "an" means one or more than one.

[0040] The term "about" means the stated value plus or minus a margin of measurement error, or plus or minus 10% if no measurement method is specified.

[0041] The term "or" as used in a claim is used to mean "and / or" unless expressly indicated to refer only to alternatives, or if the alternatives are mutually exclusive.

[0042] The terms "comprises", "has", "includes", and "contains" (and variations thereof) are open-ended conjunctive verbs and allow the addition of other elements when used in a claim.

[0043] The phrase "consisting of" is closed and excludes all additional elements.

[0044] The phrase "consisting essentially of" does not include additional material elements, but allows for non-material elements that do not substantially change the nature of the invention.

[0045] The phrase "substantially all" means greater than or equal to 95 wt%, greater than or equal to 99 wt%, greater than or equal to 99.5 wt%, or greater than or equal to 99.9 wt%.

[0046] The following abbreviations are used herein:

[0047]

[0048] Catalyst composition

[0049] The present disclosure provides catalytic compositions for recycling polyolefin-based materials into commercially important raw materials. In some embodiments, the catalyst composition for depolymerizing a polyolefin-based feed stream in a depolymerization unit comprises the following items or consists essentially of the following: a zeolite catalyst component and a cocatalyst, the cocatalyst comprising an activated clay component and / or a solid base component. The components of the composite catalyst system act synergistically to increase the depolymerization rate, thereby reducing the amount of time the polyolefin-based feed stream spends in the depolymerization unit. The increase in the depolymerization rate occurs even in the presence of impurities (such as non-polyolefin components) in the feed stream, which can reduce the catalytic activity of the zeolite in the absence of a cocatalyst comprising an activated clay component and / or a solid base component.

[0050] - Zeolite catalyst component

[0051] Zeolites are solid acid catalysts with an open three-dimensional crystal structure that have many pores and acidic active sites where chemical reactions, such as the thermal depolymerization of polyolefins, can occur. Depolymerization proceeds through hydrogen transfer reactions initiated by the acidic sites of the zeolite and subsequent chain scission to generate intermediate carbocations. In essence, zeolites rely on strong acidic sites to crack polyolefins. This cracking process starts on the surface of the zeolite because the polymer needs to decompose into smaller molecules due to the small size of its openings before entering the internal voids of these solids. This results in more contact between the polyolefin and the catalyst, leading to a faster depolymerization rate and a shorter residence time in the depolymerization unit.

[0052] Zeolites have many advantages for depolymerizing polyolefins, including the ability to adjust acidity and pore size to address specific feed stream characteristics. Additionally, zeolites are heterogeneous catalysts that can be easily separated from the depolymerization products or by-products and reused.

[0053] However, in the presence of non-olefin components (such as polymers having nitrogen-containing groups and / or high oxygen content) and / or their depolymerization products (such as furfural), zeolite catalysts are prone to poisoning and reduce catalytic activity. Additionally, many substrates with high oxygen and nitrogen content can form coke deposits on the zeolite, further reducing the activity of the zeolite. Even after multiple separation steps in a recycling facility, the feed stream of polyolefin waste is rarely pure, and the addition of a small amount of non-olefin components can inhibit the catalytic ability of the zeolite and reduce its depolymerization rate by up to 85%.

[0054] Any zeolite catalyst capable of catalyzing the polyolefin depolymerization reaction can be used in the composite catalyst. In some embodiments, the composite catalyst includes commercially available zeolites, including but not limited to beta zeolite (β), Socony Mobil-5 zeolite (ZSM-5), Y zeolite (Y), ultrastable Y zeolite (USY), amorphous acidic AlSiO x (such as 40) or combinations thereof. Combinations of zeolites can be used to address specific polyolefin-based feed contents or can be used to offset the costs associated with using only expensive zeolites in the composite material.

[0055] In some embodiments, the zeolite catalyst component has an SiO 2 / Al 2 O 3 molar ratio less than or equal to 200, less than or equal to 100, less than or equal to 50, less than or equal to 25, or less than or equal to 15. In some embodiments, the zeolite catalyst component has an SiO 2 / Al 2 O 3 molar ratio in the range of 200:1 to 3:1, 150:1 to 3:1, 100:1 to 3:1, 50:1 to 3:1, 25:1 to 3:1, or 15:1 to 3:1. In some embodiments, the zeolite catalyst component has an SiO 2 / Al 2 O 3 molar ratio in the range of 200:1 to 5:1, 150:1 to 5:1, 100:1 to 5:1, 50:1 to 5:1, 25:1 to 5:1, or 15:1 to 5:1. In some embodiments, the zeolite catalyst has an SiO 2 / Al 2 O 3Molar ratio. In some embodiments, the zeolite catalyst has an SiO 2 / Al 2 O 3 molar ratio in the range of 200:1 to 1:1, 150:1 to 1:1, 100:1 to 1:1, 50:1 to 1:1, 25:1 to 1:1, or 15:1 to 1:1.

[0056] - Promoter

[0057] The compositions and methods of the present invention overcome these problems by combining at least one zeolite with a promoter comprising an activated clay component and / or a solid base component, which is capable of inhibiting the poisoning effect of impurities (such as non-polyolefin components) from a polyolefin-based feed stream. The promoter maintains and / or restores the ability of the zeolite catalyst components to crack polyolefins. In addition to reducing and / or preventing the inhibition of zeolites by impurities in the polyolefin-rich feed, the promoter comprising an activated clay component and / or a solid base component unexpectedly acts synergistically with one or more zeolites to increase the depolymerization rate of the polyolefin-based feed stream to a greater extent than using zeolites alone, especially when the polyolefin-based feed contains impurities.

[0058] Activated clay

[0059] For the purposes of the present invention, activated clay is understood to mean clay that has undergone a thermal or chemical activation process. In some embodiments, the clay is activated by treatment with dilute sulfuric acid and drying at a temperature in the range of 100 °C to 200 °C. Activated clay is also understood as "pickled clay". Clay (without undergoing an activation process) includes one or more of the following non-limiting examples of clay minerals (phyllosilicates): attapulgite (palygorskite), albite, aluminosilicate, beidellite, bentonite, chlorite, fuller's earth, gibbsite, goethite, halloysite, lithium montmorillonite, hematite, α-hematite, illite, kaolinite, kaolin, meta-halloysite, mica (including muscovite 2-M1 and / or illite-1M), montmorillonite, nontronite, pyrite, quartz, talc, steatite, zinc montmorillonite, sepiolite, smectite, vermiculite, and other similar components. In some embodiments, the activated clay is a mixture of several activated clays with different characteristics, or a mixture of an activated clay and one or more non-activated clays.

[0060] In some embodiments, the chemical composition of the activated clay has an Al 2 O 3 content greater than 10 wt% in the range of 10 wt% to 50 wt% or 15 wt% to 30 wt%. In some embodiments, the activated clay has an Fe content greater than 5 wt% in the range of 1 wt% to 60 wt%, 3 wt% to 20 wt%, or 5 wt% to 20 wt%.2 O 3 Content. In some embodiments, the activated clay contains other components, such as SiO 2 、Na 2 O to K 2 O.

[0061] The activated clay cocatalyst in the composite catalyst of the present invention is an inorganic material with acidic properties. Zeolites rely on strong acidic sites to initiate the depolymerization of polyolefins. Therefore, acidic cocatalyst compounds can be used as cocatalysts without affecting the initiation method of zeolites.

[0062] The amount of the activated clay cocatalyst in the composite catalyst will depend on the content of the polyolefin feed, as well as the type and amount of non-polyolefin components (if any) in the feed stream. In some embodiments, the total amount of the activated clay cocatalyst ranges from 10 wt% to 90 wt% or 20 wt% to 60 wt% of the composite catalyst, and the balance is the total amount of zeolite and solid base (if any). Alternatively, the total amount of the activated clay cocatalyst ranges from 40 wt% to about 75 wt% of the composite catalyst. Alternatively, the total amount of the activated clay cocatalyst ranges from 70 wt% to 90 wt% of the composite catalyst. Alternatively, the total amount of the activated clay cocatalyst ranges from 50 wt% to 75 wt% of the composite catalyst.

[0063] Solid base

[0064] In some embodiments, the solid base component is: a layered double hydroxide composition; an activated carbon composition; or a combination thereof.

[0065] In some embodiments, the solid base component is: a layered double hydroxide composition; an MR composition, where M is an alkali metal, alkaline earth metal, transition metal, post-transition metal, metalloid, or a combination thereof, and R is an oxide, hydroxide, carbonate, sulfate, sulfide, nitrate, nitride, phosphate, phosphite, halide, or a combination thereof; an activated carbon composition; or a combination thereof.

[0066] In some embodiments, the layered double hydroxide is hydrotalcite, quintinite, fougèrite, woodwardite, cualstibite, glaucocerinite, wermlandite, hydrocalumite, or a combination thereof. In some embodiments, the layered double hydroxide is hydrotalcite.

[0067] In some embodiments, the MR composition is Ca(OH)2 , Mg(OH) 2 , Ba(OH) 2 , Sr(OH) 2 , CaO, Al 2 O 3 or combinations thereof. In some embodiments, the MR composition is Ca(OH) 2 or combinations thereof. In some embodiments, the solid base cocatalyst is a metal oxide or a metal hydroxide. Any known metal oxide or metal hydroxide can be used, including those containing metals of Groups 2 to 8 and 11 to 16, as well as the lanthanide and actinide elements. Exemplary solid inorganic cocatalysts include Ca(OH) 2 , Mg(OH) 2 , Ba(OH) 2 , Sr(OH) 2 , NaOH, KOH, CaO and Al 2 O 3 . Any combination of solid base cocatalysts can be used. In some embodiments, the composite catalyst has both Al 2 O 3 and Ca(OH) 2 .

[0068] The solid base component can be a silicate, aluminosilicate, carbonate, phosphate, oxide or hydroxide. Zeolites rely on strong acidic sites to initiate the depolymerization of polyolefins. However, unexpectedly, it has been found that basic cocatalyst compounds can also be used without neutralizing the acidic sites of the zeolite or affecting its ability to crack polyolefins.

[0069] The amount of solid base cocatalyst in the composite catalyst will depend on the content of the polyolefin feed, as well as the type of non-polyolefin components (if any) and their amounts in the feed stream. In some embodiments, the total amount of solid base cocatalyst ranges from 10 wt% to 90 wt% or 20 wt% to 60 wt% of the composite catalyst, with the remainder being the total amount of zeolite and activated clay (if any). Alternatively, the total amount of solid base cocatalyst ranges from 40 wt% to about 75 wt% of the composite catalyst. Alternatively, the total amount of solid base cocatalyst ranges from 70 wt% to 90 wt% of the composite catalyst. Alternatively, the total amount of solid base cocatalyst ranges from 50 wt% to 75 wt% of the composite catalyst.

[0070] Depolymerization method

[0071] In some embodiments of the present disclosure, the composite catalyst is a combination of a zeolite catalyst and an activated clay cocatalyst, a solid base cocatalyst, or a combination thereof, wherein the zeolite catalyst is in the range of 25 wt% to 50 wt% of the composite catalyst. The zeolite catalyst can be one or more ZSM-5 zeolites, one or more β zeolites, one or more Y zeolites, one or more ultrastable Y zeolites, or a combination thereof. In some embodiments, the zeolite catalyst is one or more ultrastable Y zeolites.

[0072] The composite catalyst described in the present invention can be used for the thermal degradation or depolymerization of any amount of a feed stream comprising a material having a single polyolefin component or a mixture of polyolefin components. Any polyolefin can be present in the feed stream, including but not limited to polyethylene (high density and low density), polypropylene, ethylene-propylene copolymer, polybutene-1, polyisobutene, and copolymers thereof. Additionally, the feed stream is not limited to any particular form, so films, foams, textiles, or other shaped materials can be treated by the method. The polyolefin can be obtained from waste streams, including post-consumer waste streams, post-industrial waste streams, or a combination thereof.

[0073] In some embodiments, the feed stream further comprises one or more non-polyolefin components that reduce the catalytic activity of the zeolite. Alternatively, the feed stream can further comprise one or more non-polyolefin components that produce degradation products that reduce the catalytic activity of the zeolite. While many chemicals fall into this category, non-polyolefin polymers are most likely to be present in polyolefin-based feed streams, particularly when the feed stream is a waste stream. In particular, non-polyolefin polymers having a nitrogen or high oxygen content, such as polyaramides, acrylates, nylons, polyurethanes, celluloses, and polyethylene polymers, can be present in the feed stream. These polymers are commonly found in waste sites and are difficult to completely separate from polyolefins. Many of these polymers degrade into problematic products that can reduce the catalytic ability of the zeolite, such as furfural, caprolactam, various amines, phenols, and esters. Alternatively, non-polyolefin components, such as nitrogen-containing pigments, can be present in polyolefin-based waste streams and can reduce the catalytic activity of the zeolite.

[0074] In some embodiments, a method for depolymerizing a polymer includes: a) adding a polyolefin-based feed stream and a first cocatalyst to a first pyrolysis reaction zone to form a first reaction mixture, wherein the first cocatalyst comprises an activated clay component, a solid base component, or a combination thereof; b) reacting the first reaction mixture in the absence of oxygen under first depolymerization conditions to form a first vapor product and a first liquid product containing carbon; c) adding the first vapor product to a first condensation zone, wherein the first vapor product is subjected to condensation conditions to form a second vapor product and a second liquid product; d) adding the second liquid product and a zeolite catalyst component to a second pyrolysis reaction zone to form a second reaction mixture; and e) reacting the second reaction mixture in the absence of oxygen under second depolymerization conditions to form a third vapor product and a third liquid product containing carbon, wherein the third liquid product comprises one or more olefin monomers.

[0075] In further embodiments of the method for depolymerizing a polymer, the polyolefin feed stream comprises polyethylene, polypropylene, or a combination thereof. In some embodiments, the polyolefin feed stream comprises from 0 wt% to 20 wt%, from 0 wt% to 15 wt%, from 0 wt% to 10 wt%, or from 0 wt% to 5 wt% impurities, wherein the weight percentages are based on the total weight of the polyolefin feed stream. In some embodiments, the impurities include one or more members of the group consisting of polyethylene terephthalate, polystyrene, water, chlorine, or combinations thereof.

[0076] In some embodiments, the method for depolymerizing a polymer further comprises: adding a second cocatalyst to the second pyrolysis reaction zone, wherein the second cocatalyst comprises an activated clay component, a solid base component, or a combination thereof, and the second cocatalyst composition is different from the first cocatalyst composition.

[0077] In some embodiments of the method for depolymerizing a polymer, the first cocatalyst comprises a solid base component. In some embodiments of the method for depolymerizing a polymer, the first cocatalyst comprises an activated clay component. In some embodiments of the method for depolymerizing a polymer, the second cocatalyst comprises a solid base component. In some embodiments of the method for depolymerizing a polymer, the second cocatalyst comprises an activated clay component. In some embodiments of the method for depolymerizing a polymer, the first cocatalyst comprises a solid base component and the second cocatalyst comprises an activated clay cocatalyst. In some embodiments of the method for depolymerizing a polymer, the first cocatalyst comprises an activated clay cocatalyst and the second cocatalyst comprises a solid base component.

[0078] In some embodiments of the method for depolymerizing a polymer, the method further comprises: adding the second vapor product to the second condensation zone.

[0079] In some embodiments of the method for depolymerizing a polymer, the first depolymerization conditions include a temperature in the range of 250 °C to 600 °C, 400 °C to 600 °C, 425 °C to 550 °C or 450 °C to 500 °C, a pressure in the range of 100 kPa to 1,000 kPa, 100 kPa to 700 kPa, 150 kPa to 600 kPa or 200 kPa to 500 kPa, or a combination thereof.

[0080] In some embodiments of the method for depolymerizing a polymer, the second depolymerization conditions include a temperature in the range of 250 °C to 600 °C, 250 °C to 450 °C, 275 °C to 425 °C or 300 °C to 400 °C, a pressure in the range of 100 kPa to 1,000 kPa, 100 kPa to 700 kPa, 150 kPa to 600 kPa or 200 kPa to 500 kPa, or a combination thereof.

[0081] In some embodiments of the method for depolymerizing a polymer, the first condensation conditions include a temperature in the range of 20 °C to 250 °C, 30 °C to 200 °C or 40 °C to 150 °C, a pressure in the range of 100 kPa to 200 kPa, 110 kPa to 190 kPa or 120 kPa to 180 kPa, or a combination thereof.

[0082] In some embodiments of the method for depolymerizing a polymer, the second condensation conditions independently include a temperature in the range of 20 °C to 100 °C, 30 °C to 90 °C or 40 °C to 80 °C, a pressure in the range of 30 kPa to 200 kPa, 50 kPa to 170 kPa or 70 kPa to 130 kPa, or a combination thereof.

[0083] Certain embodiments

[0084] In some embodiments, due to the residence time required to completely depolymerize the feed stream, the polyolefin-based feed stream can be processed batchwise in the depolymerization unit. The estimated residence time for each batch will be in the range of 30 minutes to 300 minutes, 40 minutes to 200 minutes or 50 minutes to 100 minutes, depending on the design of the depolymerization system.

[0085] In some embodiments, the method operates in a continuous mode. Waste plastic material 201 is fed into a first depolymerization reactor 211. Steps are taken to prevent the introduction of an oxygen-containing atmosphere into the system. The barrier to the oxygen-containing atmosphere can be obtained in different ways, such as but not limited to a nitrogen filling system, a vacuum system connected to the extruder barrel, or a combination thereof. In some embodiments, the plastic waste mixture 201 is loaded into the feed system of the depolymerization reactor 201 through one hopper or two or more parallel hoppers, and the oxygen present in the atmosphere of the plastic waste material is substantially eliminated inside the hopper.

[0086] The method according to the present disclosure is very flexible and can feed a wide range of plastic waste compositions that are heterogeneous mixtures such as waste plastic materials, where polyolefins are the most abundant components, but for which additional sorting steps are no longer economical. In some embodiments, the plastic waste mixture contains an amount of polyethylene, polypropylene, or a combination thereof that is greater than or equal to 70 wt%, greater than or equal to 80 wt%, or greater than or equal to 90 wt%.

[0087] In some embodiments, the waste plastic material undergoes a pretreatment stage in which the waste plastic material is melted by heating and possibly mixed with an additive that can be a basic material. By the melting pretreatment, an inhomogeneous mixture of different types of waste plastics can be transformed into a large amount of homogeneous plastic composite material. The heating temperature in the pretreatment stage is appropriately set to a temperature according to the type and content of the plastics contained in the waste plastic material, so as to inhibit the pyrolysis of the plastic material to be treated. Such temperatures are generally in the range of 100°C to 300°C, and preferably 150°C to 250°C.

[0088] At a temperature close to 300°C or higher, the elimination of HC1 from the PVC resin that may be present occurs. If the waste plastic material is mixed with a basic material during the melting / kneading pretreatment, the gas forming HC1 can be removed via an exhaust system and continuously neutralized or trapped. To perform the melting operation, an ordinary kneader, an extruder with a screw, etc. are applicable. In some embodiments, the extruder melts the plastic waste 201 and brings it to a high temperature such as but not limited to 250°C to 350°C, and injects it into the first depolymerization reactor 211. The extruder can receive the plastic waste cut into small pieces into a feed hopper, convey the material flow in the melting section, and heat the polymer by the combined action of mixing energy and heat supplied by the barrel heater. Any extrusion system can be applied, such as a single-screw extruder, a twin-screw extruder, a twin-screw extruder with a gear pump, or a combination of the above.

[0089] Additives may optionally be incorporated into the melt in order to reduce the corrosiveness of the received plastic scrap or to improve the conversion process in the reaction section. During extrusion, one or more degassing steps may be foreseen to remove residual moisture present in the product. Before feeding into the first depolymerization reactor 211, the melt stream may be filtered by mechanical means in order to remove solid impurities present in the plastic waste. Several types of melt filtration units may be applied depending on the amount and particle size of the solid impurities. In some embodiments, a self-cleaning melt filter may operate for an extended period of time (several days) without manual intervention to replace the filter element.

[0090] In some embodiments, the melt filter is based on a circular perforated plate as the melt filter element, which has holes generated by laser or by machining, where solids accumulate. The accumulation of impurities may increase the pressure difference across the melt filter. In order to perform on-line cleaning of the filter element, a rotating scraper removes the accumulated impurities and directs them to a discharge port, which is opened for a short time to purge the process contamination material.

[0091] This cycle may be repeated several times (up to several days of operating time) without manual intervention and without stopping production for the time required to replace the filter element. Another alternative for a self-cleaning melt filter is based on the application of a continuously filtering metal belt through which the polymer stream passes. Impurities accumulate on the metal filter, resulting in an increase in pressure. Therefore, the blocked part of the filter belt is pushed out of the polymer channel area and then a clean part is inserted. The process is automatic and allows operation for a long time (up to several days) without manual intervention and without stopping production for the time required to replace the filter element.

[0092] In some embodiments, a method for depolymerizing 200 waste plastic materials and producing pyrolysis products includes: feeding 201 a polyolefin-rich waste and a first cocatalyst composition 203 into a feed system in an oxygen-free atmosphere, the feed system including a screw extruder, a mixer, or other components for heating the mixture to the melting temperature of the plastic material to produce a molten plastic feed stream 201. The first cocatalyst composition 203 includes a solid base, activated clay, or a combination thereof.

[0093] In some embodiments, the first cocatalyst composition 203 includes an activated clay component that is one or more members selected from the group consisting of montmorillonite, zinc montmorillonite, nontronite, lithium montmorillonite, beidellite, saponite, bentonite, or a combination thereof, or is bentonite containing Na-montmorillonite, Ca-montmorillonite, or a combination thereof.

[0094] In some embodiments, the first cocatalyst composition 203 comprises a solid base component that is one or more members selected from the group consisting of: a) a layered double hydroxide composition; and b) an activated carbon composition. In some embodiments, the first cocatalyst composition 203 comprises a solid base component that is one or more members selected from the group consisting of: a) a layered double hydroxide composition; b) an MR composition, where M is an alkali metal, alkaline earth metal, transition metal, post-transition metal, metalloid, or a combination thereof, and R is an oxide, hydroxide, carbonate, sulfate, sulfide, nitrate, nitride, phosphate, phosphite, halide, or a combination thereof; and c) an activated carbon composition. In some embodiments, the layered double hydroxide is hydrotalcite, quintinite, fougèrite, woodwardite, cualstibite, glaucocerinite, wermlandite, hydrocalumite, or a combination thereof, or is hydrotalcite. In some embodiments, the MR composition is Ca(OH) 2 , Mg(OH) 2 , Ba(OH) 2 , Sr(OH) 2 , CaO, Al 2 O 3 or a combination thereof, or is Ca(OH) 2 or a combination thereof.

[0095] The amount of the first cocatalyst 203 used in the method of the present invention may be limited by the requirements of the depolymerization unit. The first cocatalyst 203 is a solid that contributes to the dead volume in the unit during the depolymerization reaction. The lower the dead volume, the more polymer that can be depolymerized. In some depolymerization units, the amount of the first cocatalyst is in the range of 0.1 wt% to 20 wt%, 0.2 wt% to 15 wt%, 0.5 wt% to 10 wt%, or 1.0 wt% to 8 wt%, where the weight percentage is based on the total weight of the waste plastic 201 and the first cocatalyst component 203 fed to the first depolymerization reactor 211.

[0096] Care should be taken not to introduce an oxygen-containing atmosphere into the system. Barriers to potential oxygen-containing atmospheres can be obtained in different ways, such as a nitrogen or vacuum system connected to the extruder barrel. Feed the molten plastic feed stream into the first depolymerization reactor 211, which is a continuous stirred tank reactor operating at a temperature in the range of 250 °C to 600 °C, 400 °C to 600 °C, 425 °C to 550 °C or 450 °C to 500 °C and at a pressure in the range of 100 kPa to 1,000 kPa, 100 kPa to 700 kPa, 150 kPa to 600 kPa or 200 kPa to 500 kPa. Depolymerization occurs in this continuous stirred tank reactor to form a first gaseous effluent and a first liquid effluent.

[0097] In some embodiments, the first depolymerization reactor 211 has a cylindrical section with a circular bottom, which has a mixer 227 mounted on the vertical axis of the reactor 211. The mixer is equipped with a gear motor that allows the blades of the mixer to rotate in order to maintain the system in a stirred state. The design of the mixer and the power of the motor can vary according to the reactor content, volume and shape. However, as a non-limiting example, the mixer 227 operates with a power input in the range of 0.2 kW / m 3 to 4 kW / m 3 、0.25 kW / m 3 to 2 kW / m 3 or 0.3 kW / m 3 to 1.5 kW / m 3 of the range.

[0098] The first depolymerization reactor 211 is a continuous stirred tank reactor and includes any equipment associated with the reactor, such as heat exchangers, control valves, temperature and pressure gauges, pumps, compressors, etc.

[0099] The first liquid effluent is removed from the first depolymerization reactor 211 via the stream 215 to the first bottom pump 217. At least a portion of the first liquid effluent is conducted through the conduit 223 to the carbon treatment unit. The remainder of the stream 215 is conducted as a stream 219 to the heater 221 and then returned to the first depolymerization reactor 211 as a heat input medium. In other embodiments (not shown), the liquid slurry portion recycled to the reactor is withdrawn from a point on the reactor different from the point where the liquid slurry portion sent to the carbon treatment is withdrawn. In some embodiments, the liquid slurry is first fed into a special vessel (not shown) equipped with lower and upper outlet points. The liquid portion 233 directed to the carbon treatment is withdrawn in concentrated form from the lower outlet point, while the liquid portion 219 to be recycled to the reactor 211 is withdrawn from the upper outlet point.

[0100] In some embodiments, the heat exchanger 221 heats the feed stream 219 by heat transfer caused by a molten salt stream heated to a temperature in the range of 300 °C to 570 °C. The feed circuit (not shown) of the molten salt is constructed in a manner to prevent molten salt leakage. The molten salt is molten solar salt, which is preferably composed of a mixture of sodium nitrate and potassium nitrate, and even more preferably in a weight ratio in the range of 2:3 to 3:2. The solar salt in turn receives heat from a dedicated furnace, which can be electric or fed with fuel. In the latter case, a portion of the recycled oil of the stream 285 from the condenser vessel 271 can be used to feed the furnace. Alternatively or in combination, heat can be generated by the combustion of gaseous or liquid hydrocarbons.

[0101] In some embodiments, rather than through the external heat exchanger 221, the heat associated with the molten salt is transferred to the depolymerization reactor by circulating the molten salt through a jacket surrounding the entire reactor and / or by feeding it to the following external heat exchanger.

[0102] The depolymerization process occurring within the reactor produces molecules with shorter chain lengths and lower boiling points. This continuously operating chain-breaking mechanism, especially near the reactor wall, produces an increasingly smaller fraction of gaseous molecules at the operating temperature and pressure.

[0103] This first gaseous effluent from the first depolymerization reactor 211 is conducted via the stream 213 to the first condenser vessel 231, from which a second gaseous stream 233 and a second liquid stream 235 are generated and withdrawn. In some embodiments of this method for depolymerizing polymers, the first condensation conditions include a temperature in the range of 20 °C to 250 °C, 30 °C to 200 °C or 40 °C to 150 °C and a pressure in the range of 100 kPa to 200 kPa, 110 kPa to 190 kPa or 120 kPa to 180 kPa or a combination thereof.

[0104] In some embodiments, the second gaseous stream 233 is sent to a second condenser vessel 271 operating at a temperature lower than that of the first condenser vessel 231. At least a portion of the second liquid stream 235 is sent to a second bottom pump 237 and is fed, together with the zeolite catalyst component 207 and an optional second cocatalyst composition 209, as a stream 245 to the second depolymerization reactor 251.

[0105] The zeolite catalyst component is one or more members selected from the group consisting of: ZSM-5 zeolite, beta zeolite, Y zeolite and ultrastable Y zeolite, or is one or more ultrastable Y zeolites.

[0106] The amount of zeolite catalyst component 207 used in the method of the present invention may be limited by the requirements of the depolymerization unit. The zeolite catalyst component 207 is a solid, which contributes to the dead volume in the unit during the depolymerization reaction. The lower the dead volume, the more polymer that can be depolymerized. In some depolymerization units, the amount of zeolite catalyst component 207 is in the range of 0.1 wt% to 20 wt%, 0.2 wt% to 15 wt%, 0.5 wt% to 10 wt% or 1.0 wt% to 8 wt%, where the weight percentage is based on the total weight of the feed stream 245, zeolite catalyst component 207 and second cocatalyst component 209 fed to the first depolymerization reactor 251.

[0107] The second cocatalyst composition 209 comprises a solid base, activated clay or a combination thereof.

[0108] In some embodiments, the second cocatalyst composition 209 comprises an activated clay component, which is one or more members selected from the group consisting of montmorillonite, zinc montmorillonite, nontronite, lithium montmorillonite, beidellite, saponite, bentonite or a combination thereof, or is bentonite comprising Na-montmorillonite, Ca-montmorillonite or a combination thereof.

[0109] In some embodiments, the second cocatalyst composition 209 comprises a solid base component, which is one or more members selected from the group consisting of: a) layered double hydroxide compositions; and b) activated carbon compositions. In some embodiments, the second cocatalyst composition 209 comprises a solid base component, which is one or more members selected from the group consisting of: a) layered double hydroxide compositions; b) MR compositions, where M is an alkali metal, alkaline earth metal, transition metal, post-transition metal, metalloid or a combination thereof, and R is an oxide, hydroxide, carbonate, sulfate, sulfide, nitrate, nitride, phosphate, phosphite, halide or a combination thereof; and c) activated carbon compositions. In some embodiments, the layered double hydroxide is hydrotalcite, quintinite, fougèrite, woodwardite, cualstibite, glaucocerinite, wermlandite, hydrocalumite or a combination thereof, or is hydrotalcite. In some embodiments, the MR composition is Ca(OH) 2 、Mg(OH) 2 、Ba(OH) 2 、Sr(OH) 2 、CaO、Al 2 O 3or combinations thereof, or Ca(OH) 2 or combinations thereof.

[0110] The amount of the second cocatalyst 209 used in the method of the present invention may be limited by the requirements of the depolymerization unit. The second cocatalyst 209 is a solid, which contributes to the dead volume in the unit during the depolymerization reaction. The lower the dead volume, the more polymer can be depolymerized. In some depolymerization units, the amount of the second cocatalyst is in the range of 0.1 wt% to 20 wt%, 0.2 wt% to 15 wt%, 0.5 wt% to 10 wt% or 1.0 wt% to 8 wt%, where the weight percentage is based on the total weight of the stream 245, the zeolite catalyst component 207 and the second cocatalyst component 209 fed to the first depolymerization reactor 251.

[0111] In some embodiments, the first cocatalyst component 203 is a solid base and the second cocatalyst component 209 is activated clay. In some embodiments, the first cocatalyst component 203 is activated clay and the second cocatalyst component 209 is a solid base.

[0112] In some embodiments, the second depolymerization reactor 251 is a continuous stirred tank reactor operating at a temperature in the range of 250 °C to 600 °C, 250 °C to 450 °C, 275 °C to 425 °C or 300 °C to 400 °C and at a pressure in the range of 100 kPa to 1,000 kPa, 100 kPa to 700 kPa, 150 kPa to 600 kPa or 200 kPa to 500 kPa, in which depolymerization occurs to form a gaseous effluent and a liquid effluent. The remainder of the stream 235 (if any) is sent to the first reflux pump 239 and then through the cooler 241 and returned to the first condenser 231 as a gas scrubbing medium.

[0113] In some embodiments, the first depolymerization reactor 251 has a cylindrical section with a circular bottom, which has a mixer 267 mounted on the vertical axis of the reactor 251, and the mixer is equipped with a gear motor that allows the blades of the mixer to rotate so as to keep the system in a stirred state. The design of the mixer and the power of the motor can vary according to the reactor content, volume and shape. However, as a non-limiting example, the mixer 227 operates with a power input in the range of 0.2 kW / m 3 to 4 kW / m 3 、0.25 kW / m 3 to 2 kW / m 3 or 0.3 kW / m 3 to 1.5 kW / m 3 of the power input.

[0114] The first depolymerization reactor 251 is a continuous stirred tank reactor and includes any equipment associated with the reactor, such as heat exchangers, control valves, temperature and pressure gauges, pumps, compressors, etc.

[0115] A third gaseous effluent stream 253 is withdrawn from the second depolymerization reactor 251 and fed to a second condensation unit 271, from which a fourth gaseous stream 273 and a fourth liquid stream 275 are generated and withdrawn. In some embodiments, the second condensation conditions independently include a temperature in the range of 20°C to 100°C, 30°C to 90°C or 40°C to 80°C, a pressure in the range of 30 kPa to 200 kPa, 50 kPa to 170 kPa or 70 kPa to 130 kPa, or a combination thereof.

[0116] In some embodiments, at least a portion of the third liquid effluent 255 is recycled as stream 265 to the first depolymerization reactor 211. The portion of the third liquid effluent 255 that exceeds stream 265 is directed to a third bottom pump 257, where the discharge of the third bottom pump 257 is directed to a heater 261 and then returned to the first depolymerization reactor 211 as a heat input medium via stream 259, to the carbon treatment unit via stream 263, or a combination thereof.

[0117] In some embodiments, the heat exchanger 261 heats stream 259 by heat transfer caused by a molten salt stream heated to a temperature in the range of 300°C to 570°C. The feed circuit of the molten salt (not shown) is constructed in a manner to prevent molten salt leakage. The molten salt is molten solar salt, which preferably consists of a mixture of sodium nitrate and potassium nitrate, and even more preferably is in a weight ratio in the range of 2:3 to 3:2. The solar salt in turn receives heat from a dedicated furnace, which can be electric or fed with fuel. In the latter case, a portion of the recovered oil from stream 285 from the condenser vessel 271 can be used to feed the furnace. Alternatively or in combination, heat can be generated by the combustion of gaseous or liquid hydrocarbons.

[0118] At least a portion of the fourth liquid stream 275 is sent to a fourth bottom pump 283, which is used to discharge the pyrolysis product from the depolymerization treatment unit 200. In some embodiments, the remainder (if any) of stream 275 is sent to a first reflux pump 277 and then passed through a cooler 281 and returned to the second condenser vessel 271 as a gas scrubbing medium.

[0119] In some embodiments, the amounts of the first cocatalyst, the second cocatalyst, and the zeolite catalyst component are each independently in the range of 0.1 wt% to 20 wt%, 0.2 wt% to 15 wt%, 0.5 wt% to 10 wt%, or 1.0 wt% to 8 wt%, where the weight percentages are based on the total weight of the waste plastic stream 201, the first cocatalyst component 203, the second cocatalyst component 209, and the zeolite catalyst component 207 used in the method 200. In some embodiments, the composite catalyst system comprises the first cocatalyst 203 and the zeolite catalyst component 207. In some embodiments, the composite catalyst system comprises the second cocatalyst 209 and the zeolite catalyst component 207.

[0120] Depending on the type of depolymerization unit, optional additives such as sand can be added to the polyolefin-based feed stream and the composite catalyst mixture. Some of these optional additives may contribute to the dead volume of the depolymerization unit, further limiting the amount of the composite catalyst. For example, a screw kiln depolymerization reactor uses sand as a heat conductor, which limits the amount of dead volume available for the composite catalyst.

[0121] The composite catalysts disclosed by the present invention and methods for depolymerizing polyolefin-based feed streams using them are illustrated with reference to the following examples. These examples are included to illustrate embodiments of the appended claims. However, these are merely exemplary, and the present invention can be widely applied to any combination of polyolefin-based feeds and composite catalysts with and without non-polyolefin components. Those skilled in the art should understand that many changes can be made to the specific embodiments disclosed herein without departing from the spirit and scope of the disclosure, and still obtain the same or similar results. The following examples should not be construed as limiting or defining the scope of the appended claims.

[0122] Examples

[0123] The following examples are included to illustrate embodiments of the present invention. Those skilled in the art should understand that the techniques disclosed in the following examples represent techniques that the inventors have found to function well in the practice of the present invention and thus can be considered to constitute a preferred mode of its practice. However, those skilled in the art should understand that, in accordance with the present invention, many changes can be made to the specific embodiments disclosed without departing from the spirit and scope of the present invention, and still obtain the same or similar results.

[0124] Raw materials

[0125] In Examples 1 to 76, polyolefin-based feeds containing impurities ("PBF1" and "PBF2") were used to evaluate the depolymerization performance of certain zeolite catalysts, activated clays, solid bases, or combinations thereof. The polyolefin-based feed "PBF1" consists of a mixture of approximately equal amounts of: post-consumer recyclate containing polyethylene and polypropylene in a 1:1 ratio, and a non-polyolefin component with 5 wt% ash, 0.9 wt% water, 0.8 wt% polystyrene, 0.3 wt% polyethylene terephthalate, and 0.3 wt% chlorine, where all weight percentages are based on the total weight of PBF1. The polyolefin-based feed "PBF2" consists of a mixture of approximately equal amounts of: post-consumer recyclate containing polyethylene and polypropylene in a 1:1 ratio, and a non-polyolefin component with 7 wt% ash, 1 wt% water, 0.5 wt% polystyrene, 4 wt% polyethylene terephthalate, and 0.3 wt% chlorine, where all weight percentages are based on the total weight of PBF2.

[0126] The zeolite catalysts used herein are shown in Table 1 below. The SiO 2 / Al 2 O 3 molar ratio ("SAR") is shown for each catalyst.

[0127] Table 1

[0128]

[0129]

[0130] The cocatalysts used herein are shown in Table 2 below.

[0131] Table 2

[0132]

[0133]

[0134] 1 has active Lewis and acid sites

[0135] Experimental procedure

[0136] Unless otherwise stated, the depolymerization unit is a thermogravimetric analysis (TGA) instrument. For the TGA thermal decomposition reaction, a homogeneous sample is heated to the depolymerization temperature of 400 °C at 10 K / min under nitrogen in a Mettler Toledo TGA / DSC 3+ (Mettler Toledo, Columbus, Ohio) and held for 1 hour. The depolymerization half-life at a specific temperature, defined as the time required to reach 50% mass loss, is directly recorded if the value is less than 60 minutes or determined as t 1 / 2 = 0.693 / k, where k is the first-order rate constant, which is determined graphically using the Ln(C 0 / C) versus time plot.

[0137] The depolymerization half-life is related to the residence time required in the large-scale depolymerization unit. The shorter the half-life, the shorter the residence time of a batch of polymer feed in the depolymerization unit and the faster the depolymerization rate k.

[0138] Samples are prepared by melt compounding with a composite catalyst in a HAAK MiniCTW compounder at 200 °C and 200 RPM for 5 minutes. Each composition and its depolymerization half-life are shown in Tables 3 to 9.

[0139] Examples 1 to 4

[0140] Table 3 summarizes the results of Examples 1 to 4. Examples 1 to 4 were each performed with 5 g of PBF1 sample. Example 1 provides baseline data for the depolymerization of PBF1 without a zeolite catalyst, a solid base cocatalyst, or an activated clay cocatalyst. Example 2 shows that when only activated clay is added, t 1 / 2 increases by 79% relative to Example 1. Example 3 shows that when only the solid base is added to the reactor, t 1 / 2 increases by 34% relative to Example 1. Example 4 shows that when the solid base and activated clay are added to the reactor, t 1 / 2 increases by 34% relative to Example 1.

[0141] Without wishing to be bound by any particular theory, it is believed that compared to Example 2, Example 4 shows a 25% reduction in t 1 / 2 because the addition of the solid base cocatalyst to the reactor provides a poisoning mitigation effect, enabling the catalysis of the reaction with the weak acid activated clay cocatalyst in the reactor.

[0142] Table 3

[0143]

[0144] Examples 5 to 12

[0145] Table 4 summarizes the results of Examples 5 to 12. Examples 5 to 12 were each performed with a 5 g PBF1 sample. Example 5 provides baseline data for the depolymerization of PBF1 in a reactor with only a beta zeolite catalyst. Example 6 shows that when only a solid base was added to the reactor, t 1 / 2 was reduced by 23% relative to Example 5. Example 7 shows that when only activated clay was added to the reactor, t 1 / 2 was reduced by 25% relative to Example 5. Examples 8 to 10 show that adding both a solid base and activated clay to the reactor, along with the zeolite catalyst, reduced t 1 / 2 time compared to adding either a solid base (Example 6) or activated clay (Example 7) and the zeolite catalyst.

[0146] Without wishing to be bound by any particular theory, it is believed that Examples 11 and 12 did not perform as well as Examples 8 to 10 because the beta zeolites in Examples 11 and 12 had a significantly higher silicon to alumina molar ratio (“SAR”).

[0147] Table 4

[0148]

[0149] Examples 13 to 23

[0150] Table 5 summarizes the results of Examples 13 to 23. Examples 13 to 23 were each performed with a 5 g PBF1 sample. Example 13 provides baseline data for the depolymerization of PBF1 in a reactor with only a ZSM-5 zeolite catalyst. Example 15 shows that when only a solid base was added to the first microreactor, t 1 / 2 was reduced by 49% relative to Example 13. Example 14 shows that when only activated clay was added to the reactor, t 1 / 2 was reduced by 31% relative to Example 13. Example 16 shows that adding both a solid base and activated clay to the reactor, along with the same ZSM-5 zeolite catalyst, reduced t 1 / 2 time compared to adding either a solid base (Example 15) or activated clay (Example 14) and the zeolite catalyst.

[0151] Without wishing to be bound by any particular theory, it is believed that Examples 17 to 23 showed a tendency to increase t 1 / 2 relative to Example 16, which is related to the increased SAR of these ZSM-5 zeolites.

[0152] Table 5

[0153]

[0154] Examples 24 to 44 and Examples 86 to 95

[0155] Table 6 summarizes the results of Examples 24 to 56 and Examples 86 to 95. Examples 24 to 56 and Examples 86 to 95 were each carried out with 5 g of PBF1 sample and demonstrated the use of 0.1 g to 0.2 g of ultrastable Y (HUSY) zeolite catalyst in the reactor. Examples 24 and 27 provided baseline data for the depolymerization of PBF1 in the first and second microreactors, where only the HUSY zeolite catalyst was present in the second microreactor. Examples 26, 29 to 56 and Examples 86 to 95 showed that, relative to Examples 24 and 27, t 1 / 2 decreases.

[0156] Without wishing to be bound by any particular theory, it is believed that the lower combined amounts of catalyst and cocatalyst in Examples 25 and 28 were insufficient to overcome the negative effects of impurities in the polyolefin-based feed. It is also believed that in the commercial continuous operation of two reactors in series, all results will be improved because the pyrolysis and removal of the char waste stream in the first reactor will result in the removal of some portion of the catalyst poisons removed from the product from the first reactor and thus from the feed to the second reactor.

[0157] Table 6

[0158]

[0159]

[0160] Examples 45 to 51

[0161] Table 7 summarizes the results of Examples 45 to 51. Examples 24 and 27 were copied from Table 6 to provide baseline data for the depolymerization of PBF1 in the first and second microreactors, where only the HUSY zeolite catalyst was present in the reactor. Examples 45 to 51 were each carried out with 5 g of PBF1 sample and demonstrated the use of 0.2 g of HUSY zeolite catalyst in the reactor and different amounts of different solid bases in the first microreactor. Since no clay component was present, Examples 45 to 47 and Examples 49 to 51 all showed a significant reduction in t 1 / 2 in terms of time.

[0162] Without wishing to be bound by any particular theory, it is believed that in Example 48, relative to Examples 24 and 27, t 1 / 2The increase in time is due to the need for a clay component as well as a specific solid base in order to achieve the desired effect. It is also believed that in commercial continuous operation of two reactors in series, all results will be improved because the pyrolysis in the first reactor and the removal of the char waste stream will result in the removal of some portion of the catalyst poisons removed from the product from the first reactor and therefore the feed to the second reactor.

[0163] Table 7

[0164]

[0165] Examples 52 to 69 and Example 96

[0166] Table 8 summarizes the results of Examples 52 to 69 and 96. Examples 52 to 69 and 96 were each performed with 5 g of PBF1 sample and demonstrated the use of 0.1 g to 0.3 g of HUSY zeolite catalyst in the reactor and different amounts of different solid bases in the reactor. When compared with the results in Table 6 (HUSY zeolite and activated clay in the reactor) and Table 7 (HUSY zeolite and solid base in the reactor), Examples 52 to 69 and 96 in Table 8 (HUSY zeolite and activated clay in the second microreactor and solid base in the reactor) showed the following trend: t was reduced more when both co-catalysts were used than when either co-catalyst was used alone. 1 / 2 time.

[0167] Examples 55, 57 and 61 show that when used in combination with two co-catalysts, the t 1 / 2 However, Example 55 (activated carbon as solid base) and Example 57 (hydrotalcite as solid base) demonstrated t values ​​of 45 minutes and 44.7 minutes, respectively. 1 / 2 Example 47 (activated carbon as solid base) and Example 48 (hydrotalcite as solid base) in Table 7 demonstrated t of 99.0 minutes and 108.3 minutes, respectively. 1 / 2 Therefore, when compared with similar types of solid bases, the addition of activated clay co-catalyst in the second microreactor reduced t 1 / 2 time, a reduction of more than 50%. Although Example 61 (halloysite as activated clay) shows a higher t 1 / 2 time, but it is believed that in commercial continuous operation of two reactors in series, the use of solid base in the first reactor and halloysite in the second reactor will result in better conversion than produced in the microreactor because the removal of the char waste stream from the first reactor will result in the removal of some portion of the catalyst poisons from the product from the first reactor and therefore the feed to the second reactor.

[0168] Table 8

[0169]

[0170]

[0171] Examples 70 to 73

[0172] Table 9 summarizes the results of Examples 70 to 73. Examples 70 to 73 were each carried out with 5 g of PBF1 sample and demonstrated the use of 0.2 g of several different Y zeolite catalysts, both activated clay and solid base, in the reactor. Similarly, when using two co-catalysts, these different Y zeolites showed performance similar to that of other zeolites used in combination with the two co-catalysts.

[0173] Table 9

[0174]

[0175] Examples 74 to 76

[0176] Table 10 summarizes the results of Examples 74 to 76. Examples 74 to 76 were carried out using a Frontier Lab tandem microreactor system (Model: Rx-3050TR) connected to an Agilent GC / MS (Models 8890 and 5977). The feed used in Examples 74 to 76 was the waste feed PBF2. The zeolite used in these examples was HUSY (CFG-1). The activated clay used in these examples was bentonite F20X. The solid base used in these examples was Ca(OH) 2 .

[0177] These examples demonstrate the value of staging the co-catalyst with a system using two pyrolysis reactors in series. The first microreactor operates at a temperature of 500 °C and a pressure of 13 psig. The second microreactor operates at a temperature of 300 °C and a pressure of 13 psig.

[0178] Example 74 shows the depolymerization conversion performance using only the zeolite catalyst in the second reactor. Example 75 shows improved depolymerization conversion performance over Example 74 achieved by adding activated clay and solid base co-catalysts in the first reactor and a zeolite catalyst in the second reactor. Example 76 shows further improved depolymerization conversion performance over Example 75 achieved by adding only the solid base co-catalyst in the first reactor and an activated clay co-catalyst and a zeolite catalyst in the second reactor.

[0179] Table 10

[0180]

[0181] Figure 3 Graphical comparisons of Examples 74 to 76 under the conditions described above and shown in Table 10 are presented. The catalytic efficiency is measured by the level of propylene trimer in the product stream, where lower propylene trimer content values are associated with higher catalyst activity levels and higher propylene trimer content values are associated with lower catalyst activity levels. In Examples 74 to 76, the propylene trimer content measurements, calculated as a percentage of the total mass spectrometry (MS) area in the first 30 minutes of operation, are shown as the y-axis values in Figure 3 . The effective catalyst life is shown by the amount of waste plastic processed per unit of zeolite catalyst. The feed weight / catalyst weight measurements in Examples 74 to 76 are shown by the x-axis values in Figure 3 .

[0182] A comparison of Example 75 with Example 74 shows that the addition of both clay and base cocatalyst improves the catalyst life and catalyst efficiency. A comparison of Example 76 with Example 75 shows that the addition of the base cocatalyst before the clay cocatalyst further improves both the catalyst life and catalyst efficiency.

[0183] Examples 77 to 84

[0184] Raw materials for Examples 77 to 84

[0185] In Examples 80 to 87, a post-consumer polyolefin-based feedstock containing impurities (“PBF3”) was used to evaluate the depolymerization performance of certain activated clays. The polyolefin-based feedstock “PBF3” consisted of a mixture of approximately 97 wt% of polypropylene and polyethylene in a 30 / 70 weight ratio (PP:PE) with the remainder containing trace amounts of other common polymers (polyethylene terephthalate, polystyrene, polyamide, and polyurethane) and inorganic contaminants.

[0186] Experimental procedures for Examples 77 to 84

[0187] Thirty (30) grams of PBF3 was loaded into a 500 mL round glass reactor having three necks equipped with a thermocouple and a nitrogen inlet. Based on the weight of PBF3, 2.5 weight percent (2.5 wt%) of the solid catalyst H-Y zeolite catalyst (CBV400, Zeolyst International) was added to the reactor for each of Examples 77 to 84. In each of Examples 78 to 84, based on the weight of PBF3, 2.5 weight percent (2.5 wt%) of the cocatalyst shown in Table 12 was also added to the reactor. Two glass condensers were connected in series to the three necks of the reactor and maintained at 110 °C and -8 °C respectively using an oil bath (Cryostat Julabo). The reactor was placed in an electrically heated system (i.e., a mantle bath). The sample was heated to a depolymerization temperature of 430 °C at 10 K / min under nitrogen and held for two hours.

[0188] Table 12

[0189]

[0190]

[0191] Then, the pyrolysis oil, gaseous products, and solid residue remaining in the reactor were collected and measured. Table 12 summarizes the cocatalyst efficiency as the percentage reduction in solid residue normalized to the results of Example 77. It is apparent from Table 12 that the systems including the Fulcat 435, Tonsil Supreme 115FF, and M300UF cocatalysts provided the greatest reduction in residual solids.

[0192] Example 85

[0193] The following experimental procedure was carried out in a depolymerization apparatus of two reactors connected in series consisting of mechanically stirred vessels jacketed for heating. The first reactor was provided with an inlet for plastic waste from an extruder feed and an outlet for the generated gas. The gas discharged from the reactor was conveyed to a condensation unit, from which non-condensable gas and pyrolysis oil were obtained. A thermocouple was placed in the reactor to monitor and record the temperature. The oil collected from the condensation unit was fed into a second depolymerization reactor, which was also provided with an inlet for catalyst feed. The catalyst was fed into the reactor as a solid slurry by mixing it with a portion of the same oil from the condensation section.

[0194] The second reactor was also provided with an outlet line to recycle a portion of the reactor contents back to the first depolymerization reactor.

[0195] The polyolefin-based feedstock "PFB4" consists of a mixture of post-consumer PE and PP in a 2:1 weight ratio, and non-polyolefin components of 8 wt% ash, 1 wt% polystyrene, and 1 wt% nylon 6, where all weight percentages are based on the total weight of PFB4.

[0196] The PFB4 feedstock is homogenized and pelletized, and then loaded into a hopper that feeds an extruder operating at a temperature of 290 °C and continuously discharging at 4 kg / h into a depolymerization reactor. The first depolymerization reactor operates at a pressure of 4 barg and a temperature of approximately 412 °C, with an average residence time of approximately 192 minutes. The gaseous phase of the reactor is sent to a condensation unit formed by a cooling / washing tower operating at 80 °C and a partial condenser operating at 25 °C. Then, the oil stream is fed into a second vessel operating at 335 °C and 5.5 barg. The average residence time in this case is approximately 138 minutes. In this second reactor, samples of the H-USY zeolite type (CFG-1, Zeolyst International) and activated clay (Fulcat 435, BYK USA Inc.) were tested. The catalyst mixture was fed into the pyrolyzer in an amount to obtain a ratio of 6 wt% relative to the mass of the reaction phase.

[0197] Table 11

[0198]

[0199] Rx1 T(°C) = Reactor 1 - Pyrolysis temperature PFG

[0200] Rx1 p(barg) = Reactor 1 - Pyrolysis pressure

[0201] Rx1 tau(minutes) = Reactor 1 - Pyrolysis residence time

[0202] Rx2 T(°C) = Reactor 2 - Pyrolysis temperature

[0203] Rx2 p(barg) = Reactor 2 - Pyrolysis pressure

[0204] Rx2 tau(minutes) = Reactor 2 - Pyrolysis residence time

[0205] Solid (wt%) = Residue in the reactor related to the feedstock

[0206] Pyrolysis oil (wt%) = Liquid yield relative to the feedstock

[0207] Gas (wt%) = Gas yield relative to the feedstock

[0208] Table 11 summarizes the process conditions and results of Example 85, showing that the product contains: 54 wt% pyrolysis oil, 35 wt% gaseous product, and 11 wt% solid.

[0209] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to the recited ranges, any lower limit can be combined with any upper limit to recite ranges not explicitly recited, and ranges from any lower limit can be combined with any other lower limit to recite ranges not explicitly recited, and similarly, ranges from any upper limit can be combined with any other upper limit to recite ranges not explicitly recited. Additionally, even if not explicitly recited, every point or single value between the endpoints of a range is included within the range. Thus, each point or single value can be combined with any other point or single value or any other lower limit or upper limit as its own lower or upper limit to recite ranges not explicitly recited.

[0210] Although the invention has been described in detail with its advantages, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Additionally, the scope of this application is not intended to be limited to the specific embodiments of the processes, machines, components, methods, and / or steps described in the specification. As will be readily understood by those of ordinary skill in the art from the disclosure of the present invention, processes, machines, components, methods, and / or steps that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein can be utilized according to the present invention, whether currently existing or later developed. Accordingly, the appended claims are intended to include such processes, machines, components, methods, and / or steps within their scope.

Claims

1. A catalyst system for depolymerizing polymers, the catalyst system comprising: a) a zeolite catalyst component; and b) a cocatalyst, the cocatalyst comprising an activated clay component, a solid base component, or a combination thereof.

2. The catalyst system according to claim 1, wherein the zeolite catalyst component is one or more members selected from the group consisting of: ZSM-5 zeolite, β zeolite, Y zeolite, and ultrastable Y zeolite.

3. The catalyst system according to claim 1, wherein the zeolite catalyst component has an SiO 2 / Al 2 O 3 molar ratio in the range of 200:1 to 1:

1.

4. The catalyst system according to claim 1, wherein the activated clay component is one or more members selected from the group consisting of: montmorillonite, zinc montmorillonite, nontronite, lithium montmorillonite, beidellite, saponite, bentonite, or a combination thereof.

5. The catalyst system according to claim 1, wherein the solid base component is one or more members selected from the group consisting of: a) a layered double hydroxide composition; and b) an activated carbon composition.

6. The catalyst composition according to claim 5, the catalyst composition further comprising an MR composition, wherein M is an alkali metal, an alkaline earth metal, a transition metal, a post-transition metal, a metalloid, or a combination thereof, and R is an oxide, a hydroxide, a carbonate, a sulfate, a sulfide, a nitrate, a nitride, a phosphate, a phosphite, a halide, or a combination thereof.

7. A method for depolymerizing polymers, the method comprising: a) adding a polyolefin-based feed stream and a first cocatalyst to a first pyrolysis reaction zone to form a first reaction mixture, wherein the first cocatalyst comprises an activated clay component, a solid base component, or a combination thereof; b) reacting the first reaction mixture in the absence of oxygen under first depolymerization conditions to form a first vapor stream and a first liquid stream containing carbon; c) adding the first vapor stream to a first condensation zone, wherein the first vapor stream is subjected to condensation conditions to form a second vapor stream and a second liquid stream; d) adding the second liquid stream and a zeolite catalyst component to a second pyrolysis reaction zone to form a second reaction mixture; e) reacting the second reaction mixture in the absence of oxygen under second depolymerization conditions to form a third vapor stream and a third liquid stream containing carbon; and f) adding the third vapor stream to a second condensation zone, wherein the third vapor stream is subjected to condensation conditions to form a fourth vapor stream and a fourth liquid stream, wherein the second liquid product comprises one or more olefin monomers.

8. The method according to claim 7, wherein the polyolefin feed stream comprises polyethylene, polypropylene, or a combination thereof.

9. The method according to claim 7, wherein the polyolefin feed stream comprises up to 20 wt% impurities, wherein the weight percentage is based on the total weight of the polyolefin feed stream.

10. The method according to claim 9, wherein the impurities include one or more members selected from the group consisting of: polyethylene terephthalate, polystyrene, water, chlorine, or a combination thereof.

11. The method according to claim 7, the method further comprising: Add a second cocatalyst to the second pyrolysis reaction zone, wherein the second cocatalyst comprises an activated clay component, a solid base component, or a combination thereof, and the second cocatalyst composition is different from the first cocatalyst composition.

12. The method according to claim 7, wherein the first cocatalyst comprises a solid base component.

13. The method according to claim 7, wherein the first cocatalyst comprises an activated clay component.

14. The method according to claim 11, wherein the second cocatalyst comprises a solid base component.

15. The method according to claim 11, wherein the second cocatalyst comprises an activated clay component.

16. The method according to claim 7, the method further comprises: Adding the second vapor product to the second condensation zone.

17. The method according to claim 7, wherein the first depolymerization conditions include a temperature in the range of 400 °C to 600 °C, a pressure in the range of 1.0 barg (100 kPa) to 7.0 barg (700 kPa), or a combination thereof.

18. The method according to claim 7, wherein the second depolymerization conditions include a temperature in the range of 250 °C to 450 °C, a pressure in the range of 1.0 barg (100 kPa) to 7.0 barg (700 kPa), or a combination thereof.

19. The method according to claim 7, wherein the first condensation conditions include a temperature in the range of 20 °C to 250 °C, a pressure in the range of 1.0 barg (100 kPa) to 2.0 barg (200 kPa), or a combination thereof.

20. The method according to claim 7, wherein the second condensation conditions independently include a temperature in the range of 20 °C to 100 °C, a pressure in the range of 0.3 barg (30 kPa) to 2.0 barg (200 kPa), or a combination thereof.

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