Catalytic oxidation depolymerization method and catalyst

Abstract

Catalytic compositions and methods of use for depolymerizing polyolefin-based waste to useful petrochemical products are described. The catalytic composition is a mixed metal oxide having the same or higher conversion compared to non-catalytic pyrolysis. The mixed metal oxide catalysts and polyolefin-based materials are heated in the presence of oxygen to form a product comprising one or more olefin monomers.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is filed under the Patent Cooperation Treaty and claims the benefit of priority to U.S. Provisional Patent Application No. 63 / 400,816, filed on August 25, 2022, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present disclosure relates to methods of depolymerizing polyolefin-based materials using metal oxide and / or metal carbonate mixtures to form useful petrochemical products, such as olefin monomers. Background Art

[0004] The improvement of living standards and the intensification of urbanization have led to an increase in demand for polymer products, especially polyolefin plastics. Polyolefins are often used in commercial plastic applications due to their outstanding performance 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 tolerates 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.

[0005] The downside to the demand for polyolefin plastics is the increase in waste. Post-consumer plastic waste typically ends up in landfills, with about 12% being incinerated and about 9% being diverted to recycling. In landfills, most plastics do not degrade quickly, becoming a major source of waste that overloads landfills. Incineration is also not an ideal solution for dealing with plastic waste, as it leads to the formation of carbon dioxide and other greenhouse gas emissions. Therefore, there is a great interest in developing methods for recycling plastic waste that reduce the burden on landfills while being environmentally friendly.

[0006] A disadvantage of recycling plastic waste is that it is difficult to successfully produce commercially usable or desired products. Plastic waste recycling currently involves washing the material and mechanically reprocessing it; however, the resulting pellets are still contaminated with impurities such as food residues, dyes and fragrances. These impurities make the pellets unsuitable for many uses based on performance and appearance.

[0007] Recent advances have focused on converting plastic waste into usable products, such as fuel sources or commercially important raw materials. Methods have been developed to pyrolyze plastic waste streams followed by catalytic depolymerization to generate a variety of products: gases, gasoline fractions, kerosene fractions, diesel fractions, and waxes.

[0008] Lowering the depolymerization temperature and / or reducing the depolymerization time while generating an attractive liquid composition are two key drivers for waste plastic thermal decomposition catalysts. Acidic aluminosilicate catalysts with proprietary additives show good activity but produce branched paraffins and olefins that are less attractive as steam cracking feedstocks than linear isomers.

[0009] Despite the progress made in recycling polymers, there is still a need to develop a robust process for converting plastics into useful petrochemical products, such as maximizing the recovery of olefin monomers. It is also desirable to reduce the time and / or temperature required for depolymerization of polyolefin-based waste to produce a product containing a desired amount of one or more olefin monomers. Summary of the invention

[0010] The present disclosure provides novel catalyst compositions and methods for thermal depolymerization of polyolefin-based materials in the presence of oxygen and optionally using mixed metal oxide catalysts. The presently disclosed catalyst compositions are mixtures of catalyst components that have a synergistic effect that increases the rate of the depolymerization reaction at reduced temperatures.

[0011] In some embodiments, the catalyst compositions disclosed herein comprise a mixed metal oxide, M 1 Molecules containing barium titanate, strontium, lanthanum, iron, molybdenum, manganese, bismuth, yttrium or scandium, x is M 1 The number of molecules. 2 Molecules containing strontium, lanthanum, copper, barium, manganese or magnesium, y is M 2 The number of molecules of mixed metal oxides. 1 The numerator and y M 2 The number of oxygen molecules that balance the charge of the molecule is represented by the subscript z. 1 With M 2 different.

[0012] In some embodiments, the method disclosed herein includes adding a polyolefin-based feed stream and a reaction medium comprising nitrogen and oxygen to a first pyrolysis reaction zone to form a first reaction mixture. The first reaction mixture forms a first depolymerization product under depolymerization conditions, wherein the first depolymerization product comprises one or more olefin monomers of a first content. The first depolymerization product is produced from the first pyrolysis reaction zone. In some embodiments, the method further includes adding a first catalyst as described herein to the pyrolysis reaction zone, wherein the reaction mixture is reacted to further form a first deactivated catalyst. The first deactivated catalyst is discharged from the pyrolysis reaction zone and separated from the first depolymerization product. In other embodiments, the method further includes adding the first deactivated catalyst to the first oxidation reaction zone. The first deactivated catalyst is reacted with oxygen under oxidation conditions to form a first reoxidation catalyst and a first solid discharge. The first reoxidation catalyst is added to the first reaction zone. In some embodiments, the method further includes one or more additional depolymerization reaction zones, wherein the product of the upstream depolymerization reaction zone is the feed of the downstream depolymerization reaction zone. Each additional depolymerization reaction zone may optionally have a corresponding oxidation reaction zone to reoxidize the deactivated catalyst back to the associated depolymerization reaction zone.

[0013] In some embodiments, the depolymerization system includes a pyrolysis reaction zone to heat a mixture of polyolefin-based waste, nitrogen, oxygen, and optionally a first catalyst composition as disclosed herein to form a first depolymerization product and optionally a deactivated catalyst, wherein the first product comprises a first content of one or more olefin monomers. Other embodiments may include one or more additional pyrolysis reaction zones to further treat the first depolymerization product with additional catalysts to produce a second depolymerization product and a deactivated catalyst. Alternatively, or in combination with one or more additional pyrolysis reaction zones, other embodiments may include one or more oxidation reaction zones to reoxidize the deactivated catalyst and send it back to one or more pyrolysis reaction zones.

[0014] The features and technical advantages of the present invention have been outlined quite extensively above so that the following detailed description of the invention may be better understood. Other features and advantages of the present invention will be described below, and these features and advantages constitute the subject matter of the claims of the present invention. It will be appreciated by those skilled in the art that the disclosed concepts and specific embodiments may be easily used as a basis for modifying or designing other catalyst compositions and / or methods to achieve the same purposes of the present invention. It will also be appreciated by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the present invention as set forth in the appended claims. Through the following description, we may better understand the novel features that are considered to be characteristic of the present invention, whether with respect to its compositions or methods, together with further objects and advantages.

[0015] BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The claimed subject matter may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements, and in which:

[0017] Figure 1 is a simplified flow diagram of a disclosed process having one depolymerization reaction zone according to an embodiment of the present invention;

[0018] Figure 2 is a simplified flow diagram of a disclosed process having one depolymerization reaction zone and one oxidation reaction zone according to an embodiment of the present invention;

[0019] Figure 3 is a simplified flow diagram of a disclosed process having two depolymerization reaction zones according to an embodiment of the present invention;

[0020] Figure 4 and Figure 5 is an alternative simplified flow diagram of the disclosed process having two depolymerization reaction zones and one oxidation reaction zone according to an embodiment of the present invention; and

[0021] Figure 6 is a simplified flow diagram of a disclosed process having two depolymerization reaction zones and two oxidation reaction zones in accordance with an embodiment of the present invention.

[0022] Although the disclosed methods and compositions are susceptible to various modifications and alternative forms, the accompanying drawings illustrate specific embodiments described in detail herein by way of example. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the specific forms disclosed, but rather, the invention is intended to cover all modifications, equivalents and substitutions falling within the spirit and scope of the invention as defined by the appended claims. DETAILED DESCRIPTION

[0023] Illustrative embodiments of the subject matter claimed below will now be disclosed. For the sake of 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 implementation, many implementation-specific decisions must be made to achieve the developer's specific goals, such as complying with system and business-related constraints, which will vary from implementation to implementation. In addition, it should be understood that such development efforts, even if complex and time-consuming, are routine tasks for those of ordinary skill in the art who benefit from this disclosure.

[0024] The words and phrases used herein should be understood and interpreted as having a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. A special definition of a term or phrase, i.e., a definition that is different from the ordinary and customary meaning as understood by those skilled in the art, is a special definition of a term or phrase by those skilled in the art. To the extent that a term or phrase is intended to have a special meaning, i.e., a meaning that is different from the broadest meaning as understood by those skilled in the art, such special or clear definition will be expressly set forth in the specification in a definitional manner that provides a special or clear definition for the term or phrase.

[0025] 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 clarified in the manner defined elsewhere herein). These definitions are intended to clarify the meaning 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 here.

[0026] definition

[0027] As used herein, "aerogel" refers to a lightweight, highly porous solid material of extremely low density that is made by removing the liquid component from a traditional gel and replacing the liquid component in the traditional gel with a gas so that the resulting solid is the same size as the original solid.

[0028] As used herein, "char" refers to coke, a carbonaceous solid that accumulates on catalyst particles during the pyrolysis process.

[0029] As used herein, "feed stream" refers to a supply of polyolefin-based material for depolymerization. Depending on the depolymerization unit, the feed stream can be a continuous supply of material or a batch of material. The feed stream can be pure polyolefin or can be a mixture of polyolefin and non-polyolefin components.

[0030] As used herein, "free liquid" refers to a composition in which the liquid can be readily separated from the solid portion of the composition at standard temperature (-20°C) and pressure (101 kPa).

[0031] As used herein, "non-polyolefin components" refers to materials present in a polyolefin-based feed or waste stream that can reduce the ability of the zeolite to catalyze the depolymerization of polyolefins present in the stream. Examples of non-polyolefin components include non-polyolefin polymers having high oxygen and / or nitrogen content.

[0032] As used herein, "post-consumer waste" refers to the type of waste generated by the final consumer of a material stream.

[0033] As used herein, "post-industrial waste" refers to the type of waste generated during the production of products.

[0034] As used herein, "reaction zone" refers to a sufficiently enclosed chamber that is capable of maintaining selected operating conditions within the chamber to produce a desired reaction, such as a pyrolysis reaction zone or an oxidation reaction zone. In some embodiments, each reaction zone can be a separate reactor. In some embodiments, a single vessel can contain multiple reaction zones.

[0035] As used herein, "residence time" refers to the time required to depolymerize a batch of polymer waste in a depolymerization unit.

[0036] As used herein, "pyrolysis" refers to a thermal depolymerization reaction that occurs in the absence of oxygen.

[0037] As used herein, a "waste stream" is a type of feed stream that contains materials that are discarded because they are no longer useful, including but not limited to post-consumer and post-industrial waste.

[0038] As used herein, the term "depolymerization half time" or "half time of depolymerization" refers to the time required to achieve 50% mass loss of a sample at a specific temperature during a TGA thermolysis reaction. The depolymerization half time is related to the residence time required for large-scale industrial depolymerization reactors.

[0039] The term "pure" used with respect to a feed stream refers to 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.

[0040] With respect to a material, feed stream, or waste stream, the terms "polyolefin-based" and "polyolefin-rich" are used interchangeably to refer to a mixture that is at least 80% polyolefin.

[0041] Unless otherwise indicated, all concentrations herein are weight percent ("wt. %").

[0042] Unless the context indicates otherwise, the use of the words "a" or "an" when used in conjunction with the term "comprising" in the claims or the specification means one or more than one.

[0043] The term "about" means the stated value plus or minus a margin for measurement error, or plus or minus 10% if no measurement method is specified.

[0044] The term "or" as used in the claims is intended to mean "and / or" unless explicitly indicated to refer to only alternatives or if the alternatives are mutually exclusive.

[0045] The terms "comprise," "have," "include," and "contain" (and their variations) are open-ended linking verbs and allow for the addition of other elements when used in a claim.

[0046] The phrase "consisting of" is closed and excludes all additional elements.

[0047] The phrase "consisting essentially of" excludes additional material elements, but permits the inclusion of non-material elements that do not substantially change the nature of the invention.

[0048] 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%.

[0049] This article uses the following abbreviations:

[0050]

[0051] Catalyst composition

[0052] In some embodiments, a catalyst composition for depolymerizing a polymer comprises a mixed metal oxide in:

[0053] M 1 Molecules containing barium titanate, strontium, lanthanum, iron, molybdenum, manganese, bismuth, yttrium or scandium;

[0054] x is M 1 The number of molecules;

[0055] M 2 molecules containing strontium, lanthanum, copper, barium, manganese, or magnesium;

[0056] y is M 2 The number of molecules;

[0057] z is the mixed metal oxide used to 1 The numerator and y M 2 The number of oxygen molecules that balance the charge of the molecule; and

[0058] M 1 With M 2 different.

[0059] In some embodiments, M 1 and M 2 Defined by one or more of the following:

[0060] a)M 1 is barium titanate, and M 2 for lanthanum;

[0061] b)M 1 is lanthanum, and M 2 for strontium;

[0062] c)M 1 for iron, and M 2 For copper;

[0063] d) M 1 is molybdenum, and M 2 For barium;

[0064] e)M 1 for manganese, and M 2 for lanthanum;

[0065] f)M 1 is barium titanate, and M 2 for strontium;

[0066] g)M 1 is molybdenum, and M 2 For manganese;

[0067] h)M 1 is bismuth, and M 2 for iron;

[0068] i)M 1 is molybdenum, and M 2 for strontium;

[0069] j)M 1 for strontium, and M 2 for lanthanum;

[0070] k)M 1 is lanthanum, and M 2 For magnesium;

[0071] l)M 1 for neodymium, and M 2 For calcium;

[0072] m)M 1 for Scandium, and M 2 is barium; and

[0073] n)M 1 for yttrium, and M 2 For barium.

[0074] In some embodiments, the mixed metal oxide is the reaction product of a solid state process performed on an oxide of a first metal M1 and a carbonate of a second metal M2. The oxide of the first metal and the carbonate of the second metal are mixed and ground at a temperature ranging from 15°C to 30°C or from 20°C to 25°C to form a uniform powder. In some embodiments, the powder is ground sufficiently to have a particle size of less than or equal to 1 mm, or in a range of 1 μm to 400 μm. In some embodiments, the mixing of the M1 The oxide and the M 2 The carbonates are substantially completely reacted during calcination. The powder is then calcined at a temperature for a sufficient period of time to form a mixed metal oxide, which is a 1 The oxide and the M 2 In some embodiments, the calcination is performed at a temperature of 600° C. or more for 5.5 hours or more, at a temperature of 700° C. or more for 4.5 hours or more, or at a temperature of 800° C. or more for 3.5 hours or more.

[0075] In some embodiments, the mixed metal oxide is formed by a solid state process, wherein M 1 and M 2 Defined by one or more of the following:

[0076] a)M 1 is barium titanate, and M 2 for lanthanum;

[0077] b)M 1 for Lanthanum, and M 2 for strontium;

[0078] c)M 1 is molybdenum, and M 2 For barium;

[0079] d) M 1 for manganese, and M 2 for lanthanum;

[0080] e)M 1 is barium titanate, and M 2 for strontium;

[0081] f)M 1 is molybdenum, and M 2 For manganese;

[0082] g)M 1 is molybdenum, and M 2 for strontium;

[0083] h)M 1 for strontium, and M 2 for lanthanum;

[0084] i)M 1 is lanthanum, and M 2 For magnesium;

[0085] j)M 1 for neodymium, and M 2 For calcium;

[0086] k)M1 for Scandium, and M 2 is barium; and

[0087] l)M 1 for yttrium, and M 2 For barium.

[0088] In some embodiments, the mixed metal oxide is formed by a solid state process, wherein M 1 and M 2 Defined by one or more of the following:

[0089] a)M 1 is barium titanate, and M 2 for lanthanum;

[0090] b)M 1 is lanthanum, and M 2 for strontium;

[0091] c)M 1 for strontium, and M 2 is lanthanum; and

[0092] d) M 1 is molybdenum, and M 2 For barium.

[0093] In some embodiments, the solid-state process is performed on a mixture of SrO and La2(CO3)3, a mixture of La2O3 and SrCO3, or a combination thereof.

[0094] In some embodiments, the mixed metal oxide is formed in the solid state process. 1 is lanthanum, M 2 is strontium, and M 1 Oxide and M 2 The molar ratio of the carbonate is in the range of 7:10 to 9:5.

[0095] In some embodiments, the mixed metal oxide is formed in the solid state process. 1 is strontium, M 2 is lanthanum, and M 1 Oxide and M 2 The molar ratio of the carbonate is in the range of 2:3 to 1:3.

[0096] In some embodiments, the mixed metal oxide is formed in the solid state process. 1 is barium titanate, M 2 is lanthanum, and M 1 Oxide and M 2 The molar ratio of the carbonate is in the range of 2:3 to 3:2.

[0097] In some embodiments, the mixed metal oxide is formed in a solid state process. 1 Molybdenum, M 2 is barium, and M 1 Oxide and M 2 The molar ratio of the carbonate is in the range of 2:3 to 3:2.

[0098] In some embodiments, the mixed metal oxide is a reaction product of a citrate solution process in which a first metal M 1 Nitrates and second metals M 2 nitrate. 1 and M 2 nitrate, water and citric acid are mixed to form a solution, wherein the amount of citric acid is greater than or equal to M in moles. 1 and M 2 In some embodiments, the mixing is carried out at a temperature range of 15°C to 30°C or 20°C to 25°C. In a temperature range of 15°C to 30°C or 20°C to 25°C, the oxide of the first metal and the carbonate of the second metal are mixed and ground to form a uniform powder. Then, the solution is evaporated at a first temperature for a first time long enough to evaporate the free liquid, thereby forming a gel. In some embodiments, the evaporation is carried out at a temperature greater than or equal to 80°C for greater than or equal to 12 hours. Then, the gel is decomposed at a second temperature for a second time long enough to decompose the gel, thereby forming an aerogel. In some embodiments, the decomposition is carried out at a temperature greater than or equal to 150°C for greater than or equal to 1 hour. The aerogel is then ground into a powder. In some embodiments, the aerogel is fully ground to produce a powder with a particle size less than or equal to 1 mm or in a range of 1 μm to 400 μm. The powder is then calcined at a certain temperature for a time long enough to form a mixed metal oxide, which is the M 1 The oxide and the M 2 In some embodiments, the calcination is performed at a temperature of 600° C. or more for 5.5 hours or more, at a temperature of 700° C. or more for 4.5 hours or more, or at a temperature of 800° C. or more for 3.5 hours or more.

[0099] In some embodiments, the citrate solution process is performed on a mixture of iron and copper nitrates, a mixture of bismuth and iron nitrates, or a combination thereof.

[0100] In some embodiments, the mixed metal oxide is formed in the citrate solution process. 1 For iron, M 2 is copper, and M1 Nitrate and M 2 The molar ratio of nitrate is in the range of 2:3 to 3:2.

[0101] In some embodiments, the mixed metal oxide is formed in the citrate solution process. 1 Bismuth, M 2 is iron, and M 1 Nitrate and M 2 The molar ratio of nitrate is in the range of 2:3 to 3:2.

[0102] Depolymerization method

[0103] In some embodiments, the depolymerization method includes adding a feed stream based on polyolefin and a reaction medium comprising nitrogen and oxygen to the first pyrolysis reaction zone to form a first reaction mixture. The first reaction mixture is reacted under depolymerization conditions to form a first depolymerization product. The first depolymerization product is discharged from the first pyrolysis reaction zone. The first depolymerization product comprises one or more olefin monomers of the first content. In some embodiments, the feed stream based on polyolefin comprises post-consumer recyclate, post-industrial recyclate, or a combination thereof. In some embodiments, the feed stream based on polyolefin comprises one or more high-density polyethylene, one or more polypropylene, or a combination thereof. In some embodiments, the depolymerization conditions comprise a temperature in the range of 250°C to 450°C, 280°C to 420°C, or 280°C to 350°C; a pressure in the range of 0.5 barg (50 kPa) to 3.5 barg (350 kPa) or 1.0 barg (100 kPa) to 3.0 barg (300 kPa); and a reaction medium comprising nitrogen and up to 20 vol% oxygen, up to 10 vol% oxygen, up to 8 vol% oxygen, or up to 5 vol% oxygen, based on the total volume of nitrogen and oxygen; or a combination thereof.

[0104] In some embodiments, the method further comprises adding a first catalyst to the pyrolysis reaction zone. The first reaction mixture further comprising the first catalyst is reacted under depolymerization conditions to further form a first deactivated catalyst. The first deactivated catalyst is discharged from the pyrolysis reaction zone and separated from the first depolymerization product. The first catalyst is selected from the catalysts described herein.

[0105] In some embodiments, the method further includes adding the first deactivated catalyst to the first oxidation reaction zone. The first deactivated catalyst is reacted with oxygen under oxidation conditions to form a first reoxidation catalyst and a first solid discharge. The first reoxidation catalyst is added to the first depolymerization reaction zone. In some embodiments, the oxidation conditions include a temperature in the range of 500°C to 800°C; a pressure in the range of 0.5 barg (50 kPa) to 3.5 barg (350 kPa); and a reaction medium comprising nitrogen and oxygen, wherein the content of oxygen is greater than or equal to 5 vol%, or in the range of 6 vol% to 50 vol% or 7 vol% to 21 vol%, based on the total volume of nitrogen and oxygen.

[0106] In some embodiments, the method further includes adding the first depolymerization product and a reaction medium comprising nitrogen and oxygen to a second pyrolysis reaction zone to form a second reaction mixture. The second reaction mixture is reacted under depolymerization conditions to form a second depolymerization product. The second depolymerization product is discharged from the second pyrolysis reaction zone. The second depolymerization product comprises a second content of one or more olefin monomers, and the second content is greater than the first content of one or more olefin monomers in the first depolymerization product. In some embodiments, the depolymerization conditions include a temperature in the range of 250°C to 450°C, 280°C to 420°C, or 280°C to 350°C; a pressure in the range of 0.5barg (50kPa) to 3.5barg (350kPa) or 1.0barg (100kPa) to 3.0barg (300kPa); and a reaction medium, the reaction medium comprising nitrogen and up to 20vol% oxygen, up to 10vol% oxygen, up to 8vol% oxygen, or up to 5vol% oxygen based on the total volume of nitrogen and oxygen; or a combination thereof.

[0107] In some embodiments, the method further comprises adding a second catalyst to the pyrolysis reaction zone. The second reaction mixture further comprising the second catalyst is reacted under depolymerization conditions to further form a second deactivated catalyst. The second deactivated catalyst is discharged from the pyrolysis reaction zone and separated from the second depolymerization product. The second catalyst is selected from the catalysts described herein and may be the same or different from the first catalyst.

[0108] In some embodiments, the method further includes adding the second deactivated catalyst to the second oxidation reaction zone. The second deactivated catalyst is reacted with oxygen under oxidation conditions to form a second reoxidation catalyst and a second solid discharge. The second reoxidation catalyst is added to the second depolymerization reaction zone. In some embodiments, the oxidation conditions include a temperature in the range of 500°C to 800°C; a pressure in the range of 0.5 barg (50 kPa) to 3.5 barg (350 kPa); and a reaction medium comprising nitrogen and oxygen, wherein the content of oxygen is greater than or equal to 5 vol%, or in the range of 6 vol% to 50 vol% or 7 vol% to 21 vol%, based on the total volume of nitrogen and oxygen.

[0109] Single-stage pyrolysis can be achieved by co-feeding waste plastics with controlled amounts of oxygen and a catalyst. Figure 1 One embodiment is shown comprising a single pyrolysis reaction zone 10. A polyolefin-based feed stream 1, optionally a catalyst 11, and a reaction medium 12 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are fed to the pyrolysis reaction zone 10 where the mixture is subjected to depolymerization conditions as described herein to produce pyrolysis products 15 and optionally a deactivated catalyst 16.

[0110] Single stage pyrolysis can be achieved by co-feeding the waste plastic with an oxidation catalyst and reoxidizing the spent catalyst / char with air in a separate reactor or reaction zone. It is contemplated that this can be accomplished using a fluid catalytic cracking ("FCC") type unit. Figure 2 An embodiment is shown that includes a single pyrolysis reaction zone 10 and a single oxidation reaction zone 20. A polyolefin-based feed stream 1, a catalyst 11, and a reaction medium 12 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are fed to the pyrolysis reaction zone 10 where the mixture is subjected to depolymerization conditions as described herein to produce pyrolysis products 15 and a deactivated catalyst 16.

[0111] The deactivated catalyst 16 is withdrawn from the pyrolysis reaction zone 10 and fed along with air and / or oxygen 18 to an oxidation reaction zone 20 where the mixture is subjected to oxidation conditions to produce a reoxidation catalyst 25 and char 26. The reoxidation catalyst 25 is added to the first pyrolysis reaction zone 10.

[0112] Dual-stage pyrolysis is achieved when a thermal cracking, optionally catalytic cracking step is followed by another thermal cracking, optionally oxidative catalytic cracking step. Figure 3An embodiment is shown comprising a first pyrolysis reaction zone 10 and a second pyrolysis reaction zone 30 in series. A polyolefin-based feed stream 1, optionally a first catalyst 11, and a first reaction medium 12 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to the pyrolysis reaction zone 10 where the mixture is subjected to first depolymerization conditions as described herein to produce pyrolysis products 15 and optionally a first deactivated catalyst 16.

[0113] The first pyrolysis product 15, optionally a second catalyst 31, and a second reaction medium 32 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to a pyrolysis reaction zone 30, in which the mixture is subjected to the second depolymerization conditions described herein to produce a pyrolysis product 15 and optionally a second deactivated catalyst 16.

[0114] The first catalyst 11 and the second catalyst 31, the first reaction medium 12 and the second reaction medium 32, and / or the first depolymerization conditions and the second depolymerization conditions may each independently be the same or different.

[0115] Figure 4 An embodiment is shown that includes a first pyrolysis reaction zone 10 and a second pyrolysis reaction zone 30 in series, wherein the deactivated catalyst 16 from the first pyrolysis reaction zone 10 is reoxidized in an oxidation zone 20. A polyolefin-based feed stream 1, a first catalyst 11, and a first reaction medium 12 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to the pyrolysis reaction zone 10, where the mixture is subjected to first depolymerization conditions as described herein to produce pyrolysis products 15 and a first deactivated catalyst 16.

[0116] The first pyrolysis product 15, optionally a second catalyst 31 and a second reaction medium 32 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to a pyrolysis reaction zone 30, in which the mixture is subjected to the second depolymerization conditions described herein to produce a pyrolysis product 35 and optionally a second deactivated catalyst 36.

[0117] The deactivated catalyst 16 is withdrawn from the pyrolysis reaction zone 10 and fed to an oxidation reaction zone 20 along with air and / or oxygen 18 where the mixture is subjected to oxidation conditions to produce a reoxidation catalyst 25 and char 26. The reoxidation catalyst 25 is added to the second pyrolysis reaction zone 10.

[0118] The first catalyst 11 and the second catalyst 31, the first reaction medium 12 and the second reaction medium 32, and / or the first depolymerization conditions and the second depolymerization conditions may each independently be the same or different.

[0119] Figure 5 An embodiment is shown that comprises a first pyrolysis reaction zone 10 and a second pyrolysis reaction zone 30 in series, wherein the deactivated catalyst 36 from the second pyrolysis reaction zone 30 is reoxidized in an oxidation zone 40. A polyolefin-based feed stream 1, optionally a first catalyst 11, and a first reaction medium 12 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to the pyrolysis reaction zone 10, wherein the mixture is subjected to the first depolymerization conditions described herein to produce a pyrolysis product 15 and optionally a first deactivated catalyst 16.

[0120] The first pyrolysis product 15, the second catalyst 31 and a second reaction medium 32 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to a pyrolysis reaction zone 30, in which the mixture is subjected to the second depolymerization conditions described herein to produce a pyrolysis product 35 and a deactivated catalyst 36.

[0121] The deactivated catalyst 36 is withdrawn from the second pyrolysis reaction zone 30 and fed to an oxidation reaction zone 40 along with air and / or oxygen 38 where the mixture is subjected to oxidation conditions to produce a reoxidation catalyst 45 and char 46. The reoxidation catalyst 45 is added to the second pyrolysis reaction zone 30.

[0122] The first catalyst 11 and the second catalyst 31, the first reaction medium 12 and the second reaction medium 32, and / or the first depolymerization conditions and the second depolymerization conditions may each independently be the same or different.

[0123] Figure 6 An embodiment is shown that includes a first pyrolysis reaction zone 10 and a second pyrolysis reaction zone 30 in series, wherein the deactivated catalyst 16 discharged from the first pyrolysis reaction zone 10 is reoxidized in a first oxidation zone 20, and the deactivated catalyst 36 discharged from the second pyrolysis reaction zone 30 is reoxidized in a second oxidation zone 40. A polyolefin-based feed stream 1, a first catalyst 11, and a first reaction medium 12 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to the pyrolysis reaction zone 10, in which the mixture is subjected to the first depolymerization conditions described herein to produce a pyrolysis product 15 and a deactivated catalyst 16.

[0124] The first pyrolysis product 15, the second catalyst 31 and a second reaction medium 32 comprising nitrogen and up to 5 vol% oxygen (based on the total volume of nitrogen and oxygen) are added to a pyrolysis reaction zone 30, in which the mixture is subjected to the second depolymerization conditions described herein to produce a pyrolysis product 35 and a deactivated catalyst 36.

[0125] The deactivated catalyst 16 is withdrawn from the pyrolysis reaction zone 10 and fed along with air and / or oxygen 18 to an oxidation reaction zone 20 where the mixture is subjected to oxidation conditions to produce a reoxidation catalyst 25 and char 26. The reoxidation catalyst 25 is added to the first pyrolysis reaction zone 10.

[0126] The deactivated catalyst 36 is withdrawn from the second pyrolysis reaction zone 30 and fed to an oxidation reaction zone 40 along with air and / or oxygen 38 where the mixture is subjected to oxidation conditions to produce a reoxidation catalyst 45 and char 46. The reoxidation catalyst 45 is added to the second pyrolysis reaction zone 30.

[0127] The first catalyst 11 and the second catalyst 31, the first reaction medium 12 and the second reaction medium 32, the first depolymerization conditions and the second depolymerization conditions and / or the first oxidation conditions and the second oxidation conditions may each independently be the same or different.

[0128] Depolymerization method

[0129] In some embodiments, the depolymerization system includes a first pyrolysis reaction zone to heat a mixture of polyolefin-based waste, nitrogen, oxygen, and optionally a first catalyst composition to form a first product and optionally a first deactivated catalyst, wherein the first product comprises a first content of one or more olefin monomers.

[0130] In some embodiments, the depolymerization system further comprises a first oxidation reaction zone, wherein the first deactivated catalyst from the first pyrolysis reaction zone is reacted with oxygen to produce a reoxidized catalyst, which is sent to the first pyrolysis reaction zone.

[0131] In some embodiments, the depolymerization system includes a second pyrolysis reaction zone to heat the mixture of the first depolymerization product, nitrogen, oxygen, and optionally a second catalyst to form a second depolymerization product and optionally a second deactivated catalyst, wherein the second product comprises a second content of one or more olefin monomers, and the second content is greater than the first content.

[0132] In some embodiments, the depolymerization system includes a second oxidation reaction zone, wherein the second deactivated catalyst from the second pyrolysis reaction zone is reacted with oxygen to produce a reoxidized catalyst, which is sent to the second pyrolysis reaction zone.

[0133] Certain embodiments

[0134] In a first group of embodiments, the catalyst composition for depolymerizing a polymer comprises a mixed metal oxide in:

[0135] M 1 Molecules containing barium titanate, strontium, lanthanum, iron, molybdenum, manganese, bismuth, yttrium or scandium;

[0136] x is M 1 The number of molecules;

[0137] M 2 molecules containing strontium, lanthanum, copper, barium, manganese, or magnesium;

[0138] y is M 2 The number of molecules;

[0139] z is the mixed metal oxide used to 1 The numerator and y M 2 The number of oxygen molecules that balance the charge of the molecule; and

[0140] M 1 With M 2 different.

[0141] In a second group of embodiments, the mixed metal oxide comprises 1 and M 2 Defined by one or more of the following:

[0142] a)M 1 is barium titanate, and M 2 for lanthanum;

[0143] b)M 1 is lanthanum, and M 2 for strontium;

[0144] c)M 1 for iron, and M 2 For copper;

[0145] d) M 1 is molybdenum, and M 2 For barium;

[0146] e)M 1 for manganese, and M 2 for lanthanum;

[0147] f)M 1is barium titanate, and M 2 for strontium;

[0148] g)M 1 is molybdenum, and M 2 For manganese;

[0149] h)M 1 is bismuth, and M 2 for iron;

[0150] i)M 1 is molybdenum, and M 2 for strontium;

[0151] j)M 1 for strontium, and M 2 for lanthanum;

[0152] k)M 1 is lanthanum, and M 2 For magnesium;

[0153] l)M 1 for neodymium, and M 2 For calcium;

[0154] m)M 1 for Scandium, and M 2 is barium; and

[0155] n)M 1 for yttrium, and M 2 For barium.

[0156] In some embodiments, the mixed metal oxide is the reaction product of a solid state process in which an oxide of a first metal M1 and an oxide of a second metal M2 are reacted. 的 The first metal oxide and the second metal carbonate are mixed and ground at a temperature ranging from 15°C to 30°C or 20°C to 25°C to form a uniform powder. In some embodiments, the powder is ground sufficiently to have a particle size of less than or equal to 1 mm, or in a range of 1 μm to 400 μm. In some embodiments, the mixture is mixed to form a uniform powder. 1 The oxide and the M 2 The carbonates are substantially completely reacted during calcination. The powder is then calcined at a temperature for a sufficient period of time to form a mixed metal oxide, which is a 1 The oxide and the M 2 In some embodiments, the calcination is performed at a temperature of 600° C. or more for 5.5 hours or more, at a temperature of 700° C. or more for 4.5 hours or more, or at a temperature of 800° C. or more for 3.5 hours or more.

[0157] In a third group of embodiments, the mixed metal oxide comprises 1 and M 2 Defined by one or more of the following:

[0158] a)M 1 is barium titanate, and M 2 for lanthanum;

[0159] b)M 1 is lanthanum, and M 2 for strontium;

[0160] c)M 1 is molybdenum, and M 2 For barium;

[0161] d) M 1 for manganese, and M 2 for lanthanum;

[0162] e)M 1 is barium titanate, and M 2 for strontium;

[0163] f)M 1 is molybdenum, and M 2 For manganese;

[0164] g)M 1 is molybdenum, and M 2 for strontium;

[0165] h)M 1 for strontium, and M 2 for lanthanum;

[0166] i)M 1 is lanthanum, and M 2 For magnesium;

[0167] j)M 1 for neodymium, and M 2 For calcium;

[0168] k)M 1 for Scandium, and M 2 is barium; and

[0169] l)M 1 for yttrium, and M 2 For barium.

[0170] In a fourth group of embodiments, the mixed metal oxide comprises 1 and M 2 Defined by one or more of the following:

[0171] a)M 1 is barium titanate, and M 2 for lanthanum;

[0172] b)M 1 is lanthanum, and M 2 for strontium;

[0173] c)M 1 for strontium, and M 2 is lanthanum; and

[0174] d) M 1 is molybdenum, and M 2 For barium.

[0175] In some embodiments, the mixed metal oxide of the first, second, third or fourth group of embodiments is formed by a solid state process comprising:

[0176] a) Obtain M 1 Oxide and M 2 of carbonates;

[0177] b) In some embodiments, mixing and grinding selected molar ratios of M 1 Oxide and M 2 of carbonate to form a homogeneous powder:

[0178] i) mixing and grinding at a temperature ranging from 15°C to 30°C or from 20°C to 25°C;

[0179] ii) the powder has a particle size less than or equal to 1 mm, or in the range of 1 μm to 400 μm; and

[0180] iii) Mixing M 1 Oxide and M 2 The carbonates are substantially completely reacted during calcination. The powder is then calcined at a temperature for a sufficient period of time to form a mixed metal oxide, which is a 1 The oxide and the M 2 a reaction product of a carbonate; and

[0181] c) in some embodiments, calcining the powder at a temperature and for a time sufficient to form a mixed metal oxide, the mixed metal oxide being the M 1 The oxide and the M 2 The reaction products of carbonates are:

[0182] i) calcining at a temperature greater than or equal to 600° C. for greater than or equal to 5.5 hours;

[0183] ii) calcining at a temperature greater than or equal to 700° C. for greater than or equal to 4.5 hours; or

[0184] iii) calcining at a temperature greater than or equal to 800° C. for greater than or equal to 3.5 hours.

[0185] In some embodiments, the mixed metal oxide of the first, second, third or fourth group of embodiments is formed by a citrate solution process comprising:

[0186] a) Obtain M 1 Nitrate and M 2 of nitrates;

[0187] b) In some embodiments, the temperature of M is within the range of 15°C to 30°C or 20°C to 25°C. 1 Nitrate, M 2 The nitrate, water and citric acid are mixed to form a solution, the amount of citric acid being greater than or equal to M in moles. 1 and M 2 The amount of

[0188] c) evaporating the solution at a first temperature for a first time sufficient to evaporate free liquid to form a gel, in some embodiments, evaporating at a temperature of 60° C. or greater for 24 hours or greater, or at a temperature in the range of 80° C. to 100° C. for 12 hours or greater;

[0189] d) decomposing the gel at a second temperature for a second time sufficient to form an aerogel, in some embodiments, at a temperature of 140° C. or greater for 2 hours or greater, or at a temperature in the range of 150° C. to 180° C. for 1 hour or greater;

[0190] e) grinding the aerogel to form a powder, in some embodiments, thereby forming a powder having a particle size less than or equal to 1 mm, or in a range of 1 μm to 400 μm; and

[0191] f) in some embodiments, calcining the mixture at a temperature and for a time sufficient to form the mixed metal oxide according to one or more of the following;

[0192] i) calcining at a temperature greater than or equal to 600° C. for greater than or equal to 5.5 hours;

[0193] ii) calcining at a temperature greater than or equal to 700° C. for greater than or equal to 4.5 hours; or

[0194] iii) calcining at a temperature greater than or equal to 800° C. for greater than or equal to 3.5 hours.

[0195] Catalyst compositions disclosed herein and methods for depolymerizing polyolefin-based feed streams using this catalyst composition are illustrated in the following examples. These examples are included to illustrate the 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. It will be appreciated by those skilled in the art that many changes may be made to the disclosed specific embodiments without departing from the spirit and scope disclosed herein, and still obtaining the same or similar results. The following examples should not be construed as limiting or defining the scope of the appended claims.

[0196] Example

[0197] The following examples are included to illustrate preferred embodiments of the present invention. It will be appreciated by those skilled in the art that the techniques disclosed in the following examples represent techniques that the inventors have found to work well in the practice of the present invention and therefore can be considered to constitute preferred modes for its practice. However, in accordance with the present invention, it will be appreciated by those skilled in the art that many changes may be made to the disclosed specific embodiments without departing from the spirit and scope of the present invention and still obtaining the same or similar results.

[0198] raw material

[0199] The raw materials used herein are shown in Table 1 below.

[0200] Table 1

[0201] Composition describe source Metal oxides Purity ≥99.5% Sigma Aldrich, St. Louis, MO Metal carbonates Purity ≥99.5% Sigma Aldrich, St. Louis, MO Metal Nitrates Purity ≥99.5% Sigma Aldrich, St. Louis, MO High-density polyethylene (HDPE) <![CDATA[Hostalen TM ACP9 255]]> LyondellBasell, Houston, TX Polypropylene (PP) <h2 style=";text-align:left;direction:ltr"><![CDATA[Moplen <h2 style=";text-align:left;direction:ltr"> TM <h2 style=";text-align:left;direction:ltr"> HP522H<h2 style=";text-align:left;direction:ltr"> LyondellBasell, Houston, TX

[0202] Synthesis of metal oxides

[0203] - Solid-state synthesis of mixed metal oxides

[0204] Prepare 2.5 g of mixed metal oxide and carbonate samples with oxide / carbonate molar equivalents varying from 1:2 to 2:1. Place appropriate masses of oxide and carbonate in a stainless steel vial equipped with a ball pestle and pulverize in a Wig-L-Bug. TM The mixed metal oxide samples were mixed in a grinder / shaker (purchased from Thermo Fisher Scientific, Richardson, TX) for 15 minutes. The mixed sample was then removed and calcined in a ceramic evaporating dish. In some cases, grinding / shaking caused the mixture to stick to the inner wall of the vial, requiring the use of a spatula to scrape the material out. The mixed metal oxide sample was calcined at 800°C for 3.5 hours and transferred to a sample bottle after cooling.

[0205] -Synthesis of mixed metal oxides using citrate solution

[0206] Mixed metal oxides of the specified nominal composition were prepared by evaporating aqueous solutions of the corresponding nitrates and citric acid in an equimolar amount to the metal in air at 80°C for 12 h, followed by decomposition in an oven at 150°C for 1 h. The resulting aerogels were ground and the resulting powders were calcined at 600°C or 800°C for 4 h. The resulting materials were ground again and used as depolymerization catalysts: Fe2CoO4 [Example 43], Fe2MnO4 [Example 27], Fe2CuO4 [Example 5], La2MoO6 [Example 44], SrMoO4 ​​[Example 28].

[0207] TGA depolymerization kinetics test

[0208] A homogenous mixed sample of approximately 5 g of polyolefin-based feed, the desired amount of catalyst and optional additives was prepared by melt compounding in a HAAK MiniCTW compounder at 200°C and 200 rpm for 5 minutes. The resulting extrudate was heated to the specified depolymerization temperature at a rate of 10°C / min in a nitrogen or air atmosphere and held for 1 hour in a MettlerToledo TGA / DSC 3+ (available from Mettler Toledo, Columbus, OH). TGA testing was performed by placing the sample at a depolymerization temperature of 400°C for 1 hour in a nitrogen atmosphere or at a depolymerization temperature of 300°C for 1 hour in an air atmosphere (approximately 78 vol% nitrogen and approximately 21 vol% oxygen). The weight loss of the polyolefin-based feed sample (conversion to lower molecular weight components) during the 1-hour isothermal test was used to quantify the depolymerization efficiency.

[0209] At 400°C N2 The mixed oxides were compounded and tested by TGA using a 1:1 mixture of HDPE and PP under 240°C purge and 300°C air (about 78 vol% nitrogen and about 21 vol% oxygen). Baseline experiments showed that changing the replacement gas from N2 Switching to air can achieve similar levels of weight loss (conversion to lower molecular weight components) within 1 hour while allowing a reduction in the hold temperature.

[0210] In the N2 experiments, the kinetics roughly followed a first-order rate dependence, so the half-weightlessness time (t 1 / 2 ) to quantify the effect of the catalyst on the rate, where t 1 / 2 is the time (in minutes) required for half the weight of the sample to be converted. The data in Table 2 were examined and no significant rate increase was found according to the TGA method.

[0211] Table 2 shows the properties of certain commercially available metal oxides and mixed metal oxides produced by the solid state process and the citrate solution process. Each first catalyst component comprises a Group 2 alkaline earth metal oxide, a Group 2 alkaline earth metal carbonate, or a combination thereof. Each second catalyst component comprises a Group 3 metal oxide, a Group 3 metal carbonate, or a combination thereof.

[0212] For TGA tests conducted in air, the conversion of the material within 1 hour was used to quantify the depolymerization efficiency at a specific temperature of 300°C when significant deviations of the rate versus time from first order kinetics were observed.

[0213] Examples 1-55 in Table 2 show the conversion of HDPE / PP (1:1) feed using certain metal oxides and mixed metal oxides synthesized by solid state or citrate solution methods. Example 19 shows the pyrolysis conversion without the use of a catalyst, which is used as a benchmark for mixed metal oxides. Table 2 is sorted by the last column, reflecting the conversion of HDPE / PP (1:1) feed at 300°C for 1 hour with a catalyst. The conversions of Examples 1-18 are all equal to or better than Example 19, even if the conversions are the same, the composition of the depolymerization products is expected to be different.

[0214] Table 2

[0215]

[0216]

[0217]

[0218] *M 1 Oxide: M 2 Carbonate or M 1 Nitrate: M 2 Nitrates

[0219] The depolymerization half-life is related to the required residence time in a 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.

[0220] Quartz tube depolymerization test

[0221] In each experiment, 5 g of polyolefin-based feed and optionally catalyst (5 wt%) were placed in a quartz pyrolysis tube and heated in a furnace at a rate of 10°C / min to a set temperature of 700°C. The tube was purged from the bottom with a nitrogen stream or a nitrogen stream containing 5 vol% oxygen at a flow rate of 15 sccm. The condensable products were collected in a Hickman trap cooled with dry CO2. When the first sign of liquid collection was observed, the temperature of the reaction mixture was measured with a thermocouple located at the bottom of the pyrolysis tube.

[0222] The quartz tube depolymerization experiments of HDPE:PP (1:1) blends confirmed the use of 5% LaSrOx mixed metal oxides. O2 / N2 The beneficial effect of the purge gas, which is based on the reduction of the depolymerization onset temperature, is shown in Table 3. The composition and boiling point characteristics of the light yellow non-waxy depolymerization liquid produced during the catalytic and non-catalytic depolymerization in the presence of O2 are similar to those in the presence of N2. 2氛围下不使用催化剂时产生的热解液非常相似 , which confirms the mechanism of the process.

[0223] Table 3

[0224]

[0225]

[0226] For the sake of brevity, only certain ranges are explicitly disclosed herein. However, in addition to the ranges listed, any lower limit can be combined with any upper limit to list a range that is not explicitly listed, and the range from any lower limit can be combined with any other lower limit to list a range that is not explicitly listed, and similarly, the range from any upper limit can be combined with any other upper limit to list a range that is not explicitly listed. Additionally, even if not explicitly stated, each point or single value between its endpoints is also included in the range. Therefore, each point or single value can be combined as its own lower limit or upper limit with any other point or single value or any other lower limit or upper limit to list a range that is not explicitly listed.

[0227] Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and modifications can be made here without departing from the spirit and scope of the present invention as defined by the appended claims. In addition, the scope of the present application is not intended to be limited to the specific embodiments of the process, machine, film structure, composition, means, method and / or step described in the specification. As will be readily understood by those of ordinary skill in the art from the disclosure of the present invention, according to the present invention, the process, machine, film structure, composition, device, method and / or step of the layer that currently exists or will be developed later to perform the functions substantially the same as the corresponding embodiments described herein or to achieve substantially the same results can be used. Therefore, the appended claims are intended to include such processes, machines, film structures, composition, means, method and / or steps of the layer within their scope.

Claims

1. A catalyst composition for depolymerizing a polymer, the composition comprising a mixed metal oxide Mx1My2Oz, wherein: M 1 Molecules containing barium titanate, strontium, lanthanum, iron, molybdenum, manganese, bismuth, yttrium or scandium; x is M 1 The number of molecules; M 2 molecules containing strontium, lanthanum, copper, barium, manganese, or magnesium; y is M 2 The number of molecules; z is the number of M in the mixed metal oxide used to 1 Numerator and y M 2 The number of oxygen molecules that balance the charge of the molecule; and M 1 With M 2 different.

2. The catalyst composition of claim 1, wherein the mixed metal oxide is formed by: a) Obtain M 1 Oxide and M 2 of carbonates; b) mixing and grinding the M 1 The oxide and the M 2 of carbonate to form a uniform powder; and c) calcining the powder at a temperature and for a time sufficient to form the mixed metal oxide as the M 1 The oxide and the M 2 The carbonate reaction product.

3. The catalyst composition according to claim 2, wherein the powder is ground sufficiently to have a particle size of less than or equal to 1 mm.

4. The catalyst composition according to claim 2, wherein the calcination is carried out at a temperature greater than or equal to 800°C for greater than or equal to 3.5 hours.

5. The catalyst composition of claim 1, wherein the mixed metal oxide is formed by: a) Obtain M 1 Nitrate and M 2 of nitrates; b) the M 1 of nitrate, the M 2 nitrate, water and citric acid are mixed to form a solution, wherein the amount of citric acid is greater than or equal to M in moles. 1 and M 2 The amount, c) evaporating the solution at a first temperature for a first time sufficient to evaporate free liquid, thereby forming a gel; d) decomposing the gel at a second temperature for a second time sufficient to form an aerogel; e) grinding the aerogel to form a powder; and f) calcining the mixture at a temperature and for a time sufficient to form the mixed metal oxide.

6. The catalyst composition according to claim 5, wherein the powder is ground sufficiently to have a particle size of less than or equal to 1 mm.

7. The catalyst composition according to claim 5, wherein the evaporation is performed at a temperature greater than or equal to 80°C for greater than or equal to 12 hours.

8. The catalyst composition of claim 5, wherein the decomposition is performed at a temperature greater than or equal to 150°C for greater than or equal to 1 hour.

9. The catalyst composition of claim 5, wherein the calcination is performed at a temperature greater than or equal to 800°C for greater than or equal to 4.0 hours.

10. A method comprising: a) adding a polyolefin-based feed stream and a reaction medium comprising nitrogen and oxygen to a first pyrolysis reaction zone to form a first reaction mixture; b) reacting the first reaction mixture under depolymerization conditions to form a first depolymerization product, wherein the first depolymerization product comprises a first content of one or more olefin monomers; as well as c) discharging the first depolymerization product from the first pyrolysis reaction zone.

11. The method according to claim 10, further comprising: a) adding the first catalyst according to claim 1 to the first pyrolysis reaction zone, wherein the reaction mixture is further reacted to form a first deactivated catalyst; as well as b) discharging the first deactivated catalyst from the pyrolysis reaction zone.

12. The process of claim 10, wherein the depolymerization conditions comprise a temperature in the range of 250°C to 450°C, a pressure in the range of 0.5 barg (50 kPa) to 3.5 barg (350 kPa), and a reaction medium comprising nitrogen and up to 20 vol% oxygen, based on the total volume of nitrogen and oxygen, or a combination thereof.

13. A process according to claim 12, wherein the temperature is in the range of 280°C to 350°C, the pressure is in the range of 1.0 barg (100 kPa) to 3.0 barg (300 kPa), and the reaction medium comprises nitrogen and up to 10 vol% oxygen, based on the total volume of nitrogen and oxygen.

14. The method according to claim 11, further comprising: a) adding the first deactivated catalyst to a first oxidation reaction zone; b) reacting the first deactivated catalyst with oxygen under oxidizing conditions to form a first reoxidation catalyst and a first solid effluent; as well as b) adding the first reoxidation catalyst to the first reaction zone.

15. The method according to claim 10, further comprising: a) adding the first depolymerization product and a reaction medium comprising nitrogen and oxygen to a second pyrolysis reaction zone to form a second reaction mixture; b) reacting the second reaction mixture under depolymerization conditions to form a second depolymerization product, wherein the second depolymerization product comprises a second amount of one or more olefin monomers, and the second amount is greater than the first amount; and c) discharging the second depolymerization product from the second pyrolysis reaction zone.

16. The method according to claim 15, further comprising: a) adding a second catalyst according to claim 1 to the pyrolysis reaction zone, wherein the reaction mixture is further reacted to form a first deactivated catalyst; as well as b) discharging the first deactivated catalyst from the pyrolysis reaction zone.

17. The method according to claim 16, further comprising: a) adding the second deactivated catalyst to a second oxidation reaction zone; b) reacting the second deactivated catalyst with oxygen under oxidizing conditions to form a second reoxidation catalyst and a second solid effluent; b) adding the second reoxidation catalyst to the second reaction zone.

18. A depolymerization system comprising a first pyrolysis reaction zone to heat a mixture of polyolefin-based waste, nitrogen, oxygen, and optionally a first catalyst composition to form a first product and optionally a first deactivated catalyst, wherein the first product comprises a first content of one or more olefin monomers.

19. The depolymerization system of claim 18, further comprising a first oxidation reaction zone, wherein the first deactivated catalyst from the first pyrolysis reaction zone is reacted with oxygen to produce a reoxidized catalyst, which is sent to the first pyrolysis reaction zone.

20. The depolymerization system of claim 18, further comprising a second pyrolysis reaction zone to heat a mixture of the first product, nitrogen, oxygen, and an optional second catalyst to form a second product and an optional second deactivated catalyst, wherein the second product comprises a second content of one or more olefin monomers, and the second content is greater than the first content.

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