WO2018025117A1

WO2018025117A1 - Selective catalyst system for oxidative dehydrogenation of alkanes

Info

Publication number: WO2018025117A1
Application number: PCT/IB2017/054472
Authority: WO
Inventors: Yuming Xie; Ihab N. ODEH
Original assignee: SABIC Global Technologies BV
Current assignee: SABIC Global Technologies BV
Priority date: 2016-08-03
Filing date: 2017-07-24
Publication date: 2018-02-08
Anticipated expiration: 2019-02-03

Abstract

Embodiments of the present invention are directed to a catalyst or a catalyst system that include two separated catalysts, one performing oxidation of hydrogen and the other performing dehydrogenation of alkanes.

Description

SELECTIVE CATALYST SYSTEM FOR OXIDATIVE DEHYDROGENATION OF

ALKANES

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/370,296 filed August 3, 2016, which is hereby incorporated by reference in its entirety.

BACKGROUND

A. Field of the Invention

[0002] The invention generally concerns a catalytic system for dehydrogenation of alkanes. In particular, the invention concerns a system that physically separates an alkane dehydrogenation catalyst from a hydrogen oxidation catalyst resulting in improved selectivity and conversion rate.

B. Description of the Related Art

[0003] Oxidative dehydrogenation research has been mainly focused on vanadium oxide based catalysts. With various supports, such as Zr0₂, Ti0₂, A1₂0₃ and Si0₂, monolayer VxOy species extract hydrogen from alkanes (Carrero et al, ACS Catalysis, 2014, 4, 3357- 80). The reactivity and selectivity of alkane dehydrogenation to alkene can depend on the dispersion of vanadium oxide and coverage of the species on the catalyst supports (Argyle et al., J. Catal, 2002, 208, 139; Khodakov et al, J. Catal, 1999, 181, 205; Steinfeldt et al, Appl. Catal. A., 2004, 272, 201). In order to improve the dehydrogenation selectivity, various technical approaches have been explored: (i) selection of catalyst supports and operation conditions (Christodoulakis et al, J. Catal, 2004, 222, 293); (ii) doping the catalysts with chromia and molybdenia to reduce surface acidity (Yang et al, J. Phys. Chem. B, 2006, 209, 43; Yang et al, J. Phys. Chem. B., 2005, 109, 8987; Dai et al, J. Catal, 2004, 221, 491; Solsona et al, Catal. Today, 2006, 117, 228); (iii) including additives such as phosphorous (P), potassium (K), calcium (Ca), nickel (Ni), niobium (Nb), magnesium (Mg), zinc (Zn), etc. (Lemonidou et al., Catal. Today, 2000, 61, 333; Pak et al, J. Catal 2002, 206, 49; Machli et al, Appl. Catal. A, 2002, 236, 23); and (iv) incorporation of vanadium oxide into hosting structures such as (a) MCM-41 (Kondratenko et al, J. Catal, 2005, 234, 131; Solsona et al, J. Catal. 2001, 203, 443; Wang et al., Catal. Lett., 2001, 72, 215; Kucherov et al., Catal. Today, 2003, 81, 297), (b) MCM-48 (Bruckner et al, Stud. Sur. Sci. Catal 2002, 142B, 1141) and (c) SBA-15 (Liu et al, Chem. Commun. 2002, 23, 2832; Liu et al., J. Catal 2004, 224, 417; Liu et al, Catal. Lett, 2003, 88, 61) - specifically excluding ethylene direct oxidation with oxygen on silver catalysts. However, none of these catalysts are commercially viable due to low selectivity (less than 80%) and low conversion (less than 65%). In addition, as the alkanes conversion increases, the selectivity to alkenes reduces rapidly. Therefore, these catalysts are unlikely to achieve high conversion with high selectivity needed for a commercial operation (Carrero et al., Catalysis, 2014, 4:3357-80).

[0004] Light alkanes are commercially converted to alkenes using two separate non- oxidative processes (Sattler et al., Chem. Rev. 2014, 114, 10613-53). One non-oxidative process is a CATOFIN® process, developed by Chicago Bridge and Iron (CB&I) Lummus, that uses alumina supported chromia catalyst to catalyze dehydrogenation of light alkanes in a series of adiabatic fixed bed reactors. A second process is called the Oleflex process developed by UOP, using Pt-Sn based catalyst in a fluidized bed reactor. Both these processes are non-oxidative dehydrogenation. The thermodynamics of alkane dehydrogenation constrains the conversion and results in coking, which mandates periodic regeneration of the catalysts.

[0005] Supported Pt catalysts are good dehydrogenation catalysts to convert alkanes to corresponding alkenes. In non-oxidative dehydrogenation of alkanes, the hydrocarbon feedstock reacts on platinum catalyst surface at 550 °C to 600 °C to produce alkenes and hydrogen, with needed thermal energy taken from the reactor due to the endothermic nature. Given that thermal transfer from the heat source to the reactor appeared to be a rate-limiting factor, one has to raise the reactor temperature for the higher conversion of alkanes to alkenes. Additionally, the dehydrogenation reaction is a reversible reaction, the hydrogen produced will push the reaction backwards. Removal of hydrogen from reactor is highly desirable. It is ideal to oxidize hydrogen to water, generating needed heat in-situ for the reaction and pushing the reaction equilibrium forward simultaneously. Meanwhile supported Pt catalysts are also highly effective oxidation catalyst, which catalyze undesirable complete oxidation of alkanes or alkenes in the presence of oxygen, yielding C0₂ and H₂0. Adding oxygen directly into the dehydrogenation reactor oxidizes the dehydrogenation catalysts, which will slow down the dehydrogenation reaction kinetics and reduce the selectivity. Preventing oxygen access to the catalyst surface becomes an immediate issue for using this type catalyst in oxidative dehydrogenation.

[0006] There remains a need for additional catalytic systems for oxidative dehydrogenation of alkanes. SUMMARY

[0007] A solution to the aforementioned problems associated with the selectivity and conversion problems with current methods and systems for alkane dehydrogenation reactions has been designed and described herein. The solution resides in compartmentalizing aspects of the dehydrogenation reaction by physically separating the alkane dehydrogenation catalyst from the hydrogen oxidation catalyst. In particular, the catalyst system is a mixture of catalysts in a catalyst bed or reactor where the catalysts are not physically bound to each other (see, for example FIGS. 1 and 2). Aspects of the invention lead to a catalyst system for dehydrogenating a hydrocarbon and oxidizing the hydrogen produced from the dehydrogenation reaction. The system provides for the selective flow of reactants and products in a manner that enhances the selectivity and conversion rates of the alkane dehydrogenation reaction and reduces non-beneficial side reactions. The system can include an embedded dehydrogenation catalyst that is positioned in the proximity of a hydrogen oxidation catalyst in a way in which the hydrogen oxidation catalyst can be regenerated or maintained while reducing the oxidation of the dehydrogenated alkane. In certain aspects, the dehydrogenation catalyst is embedded in a porous support matrix that is permeable to reactants such as hydrogen and hydrocarbons. The hydrogen oxidation catalyst is provided in a configuration where a hydrogen product is oxidized to water.

[0008] Described herein is a catalytic system for oxidative dehydrogenation of alkanes. Certain embodiments of the present invention are directed to a catalyst system can include two catalysts - a non-oxidative dehydrogenation catalyst and a redox-metal oxide containing hydrogen oxidation catalyst. A core-shell structure or other catalyst embedded structures can provide a mechanism to streamline gas molecule transport. In a core-shell structure, the catalyst is encapsulated in a porous alumina having a controlled porosity that allows transport of the reactant alkanes and products (hydrogen and alkenes). The second catalyst is a selective hydrogen oxidation catalyst, cerium oxide or ceria doped zirconia in a nanosize crystal form.

[0009] Oxygen storage materials such as cerium oxide, ceria stabilized zirconia (CSZ) can react with hydrogen in the absence of noble metal or alloyed catalyst at a temperature where dehydrogenation of alkanes operates, typically at 450 to 550 °C. Under such conditions, hydrogen reduces cerium oxide or cerium oxide in CSZ to form water and to release heat. As the reaction proceeds, the Ce0₂ becomes Ce₂0₃, which needs to be replenished with oxygen for future reaction. When oxygen (0₂) becomes available, the reduced Ce₂03 can be oxidized by 0₂ to become Ce0₂, then the next cycle of hydrogen oxidation can operate.

[0010] The second catalyst can be designed to be in a gas pathway or near the pore opening of the shell. In some case, the second catalyst acts like a membrane to filter off or consume most oxygen. The oxygen can be consumed by the effluent hydrogen from the core-shell catalyst at the dehydrogenation reaction operating temperature.

[0011] Certain embodiments are directed to a catalyst system for dehydrogenating a hydrocarbon and oxidizing hydrogen. A system can include (a) a non-oxidative dehydrogenation catalyst having a porous support matrix and a catalytically active metal or metal oxide impregnated within, encompassed by, or encapsulated by the porous support matrix, and (b) a redox-metal oxide containing hydrogen oxidation catalyst that is capable of oxidizing hydrogen to water with oxygen atoms from the metal oxide lattice, generating heat; and re-oxidizing the deficient oxygen anion vacancy by molecular oxygen from the feed or other source. The porous support matrix can be permeable to hydrogen and hydrocarbons, and the catalytically active metal or metal oxide is capable of catalyzing a non-oxidative dehydrogenation of hydrocarbon reaction. The non-oxidative dehydrogenation catalyst can be positioned proximate to the redox-metal oxide containing hydrogen oxidation catalyst such that hydrogen produced from the non-oxidative dehydrogenation catalyst is capable of being oxidized by the oxygen anions from the metal oxide lattice of the hydrogen oxidation catalyst.

[0012] In certain aspects, the non-oxidative dehydrogenation catalyst can have a core/shell or yolk/shell structure such that the core or yolk is the catalytically active metal or metal oxide and the shell is the porous support matrix. In a further aspect, the non-oxidative dehydrogenation catalyst can be impregnated within the porous support matrix. The non- oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst can in certain aspects form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst.

[0013] In certain aspects, the non-oxidative dehydrogenation catalyst can form a first catalytic layer or bed, and the hydrogen oxidation catalyst can form a second catalytic layer or bed. The first and second layers or beds can be proximate to one another such that hydrogen produced in the first layer or bed is capable of flowing into and being oxidized by the second layer or bed.

[0014] The porous support matrix can include alumina (AI₂O₃), silica (Si0₂), titania (Ti0₂), zirconia (Zr0₂), germania (Ge0₂), tin oxide (Sn0₂), gallium oxide (Ga₂03), zinc oxide (ZnO), hafnium oxide (Hf0₂), ytterbium oxide (Y₂O₃), lanthanide oxide (La₂03), or combinations thereof. In certain aspects, the catalytically active metal or metal oxide impregnated within or encompassed by the porous support matrix comprises noble metals including platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), gold (Au) and silver (Ag) and alloys thereof. The noble metals can be alloyed with other transition metals. By way of example, zinc (Zn), tin (Sn), or copper (Cu) can be used as additives to form an alloy. In a further aspect, the redox-metal oxide containing hydrogen oxidation catalyst can include cerium oxide (Ce0₂), ceria stabilized zirconia (CSZ), vanadium oxide, chromium oxide, manganese oxide, iron oxide, molybdenum oxide, tungsten oxide, or combinations thereof. The non-oxidative dehydrogenation catalyst and/or the redox-metal oxide containing hydrogen oxidation catalyst can each be nano- or micro-particulate material. The redox- metal oxide containing hydrogen oxidation catalyst can be coated with a material permeable to oxygen and having reduced permeability to hydrocarbons relative to oxygen. In certain aspects, the coating is a silica, silica-alumina composite, or titania coating. In some embodiments, the dehydrogenation catalyst can have a Pt-Sn alloy metal nanostructure core and a porous alumina oxide shell. The hydrogen oxidation catalyst can be a Ce/Zr oxide catalyst.

[0015] Certain embodiments are directed to a reactor for performing a dehydrogenation of hydrocarbon reaction and an oxidation of hydrogen reaction. The reactor can include: (a) a reaction zone that includes the catalyst system of the present invention; (b) at least one inlet in fluid communication with the reaction zone capable of introducing and contacting a hydrocarbon containing feed stream with the catalyst system; and (c) at least one outlet in fluid communication with the reaction zone capable of removing a product feed stream comprising a dehydrogenated hydrocarbon and water from the reaction zone. In certain aspects, the reactor can be a continuous flow reactor selected from a fixed-bed reactor, a fluidized reactor, or a moving bed reactor. In one aspect, the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system can form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst. In another aspect, the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst of the system form first and second catalytic layers or beds, respectively. The first and second catalytic layers or beds can be positioned proximate to one another such that hydrogen produced in the first catalytic layer or bed is capable of flowing into and being oxidized by the second catalytic layer or bed. The reactor can further include a second inlet for an oxygen gas (0₂) containing feed stream that is positioned proximate to the second catalytic layer or bed such that the 0₂ containing feed stream is capable of flowing into the second catalytic layer or bed.

[0016] Certain embodiments are directed to methods for dehydrogenating a hydrocarbon and oxygenating hydrogen gas. In certain aspects the method can include: (a) contacting a hydrocarbon containing feed stream with the non-oxidative dehydrogenation catalyst of the catalyst system of the present invention under reaction conditions sufficient to produce a dehydrogenated hydrocarbon and hydrogen gas (H₂); and (b) contacting the produced H₂ with the redox-metal oxide containing hydrogen oxidation catalyst of the system under reaction conditions sufficient to produce water from the H₂ and oxygen anions from the metal oxide lattice of the hydrogen oxidation catalyst and to release heat, where steps (a) and (b) are performed in a reaction zone of a reactor. In certain aspects, the reactor can be a continuous flow reactor selected from a fixed-bed reactor, a fluidized reactor, or a moving bed reactor. In a further aspect, the hydrocarbon containing feed stream can include a C₂ to C₄ alkane that is dehydrogenated to a C₂ to C₄ alkene. In certain aspects, the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst. In another aspect, the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst of the catalyst system form first and second catalytic layers or beds, respectively, where the hydrocarbon containing feed stream contacts the first catalytic layer or bed, and the produced H₂ flows into and contacts the second catalytic layer or bed. The method can further include continuously, periodically, or intermittently contacting the hydrogen oxidation catalyst during the reaction with an oxygen-containing feed stream that is positioned proximate to the second catalytic layer or bed such that the 0₂ containing feed stream flows into the second catalytic layer or bed and substantially avoids flowing into the first catalytic layer or bed, where the oxygen containing feed stream regenerates or maintains the oxidation of the hydrogen oxidation catalyst. In certain aspects, the method can further include continuously, periodically, or intermittently contacting the hydrogen oxidation catalyst during the reaction with oxygen to regenerate or maintain the oxidation of the hydrogen oxidation catalyst. In certain aspects, the amount of oxygen can be regulated to maintain the oxidation of the hydrogen oxidation catalyst and minimize alkene oxidation. In another aspect, the reaction can be performed at a temperature of at least 400 °C, preferably 400 °C to 600 °C, more preferably 450 to 500 °C.

[0017] In an aspect of the invention, 26 embodiments are described. Embodiment 1 describes a catalyst system for dehydrogenating a hydrocarbon and oxidizing hydrogen and includes: (a) a non-oxidative dehydrogenation catalyst having a porous support matrix and a catalytically active metal or metal oxide impregnated within or encapsulated by the porous support matrix, wherein the porous support matrix is permeable to hydrogen and hydrocarbons, and the catalytically active metal or metal oxide is capable of catalyzing a non- oxidative dehydrogenation of hydrocarbon reaction; and (b) a redox-metal oxide containing hydrogen oxidation catalyst that is capable of oxidizing hydrogen to water with oxygen atoms from the metal oxide lattice and generating exotherm; and re-oxidizing the deficient oxygen anion vacancy by molecular oxygen from the feed, wherein the non-oxidative dehydrogenation catalyst is positioned proximate to the redox-metal oxide containing hydrogen oxidation catalyst such that hydrogen produced from the non-oxidative dehydrogenation catalyst is capable of being oxidized by the oxygen anions from the metal oxide lattice of the hydrogen oxidation catalyst. Embodiment 2 is the catalyst system of embodiment 1, wherein the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst are configured to operate in a temperature range of 400 °C to 600 °C. Embodiment 3 is the catalyst system of embodiment 1, wherein the non-oxidative dehydrogenation catalyst has a core/shell or yolk/shell structure such that the core or yolk is the catalytically active metal or metal oxide and the shell is the porous support matrix. Embodiment 4 is the catalyst system of embodiment 1, wherein the non-oxidative dehydrogenation catalyst is impregnated within the porous support matrix. Embodiment 5 is the catalyst system of any one of embodiments 1 to 4, wherein the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst. Embodiment 6 is the catalyst system of any one of embodiments 1 to 4, wherein the non-oxidative dehydrogenation catalyst forms a first catalytic layer or bed and the hydrogen oxidation catalyst forms a second catalytic layer or bed, wherein the first and second layers or beds are proximate to one another such that hydrogen produced in the first layer or bed is capable of flowing into and being oxidized by the second layer or bed. Embodiment 7 is the catalyst system of any one of embodiments 1 to 6, wherein the porous support matrix comprises alumina (AI2O3), silica (Si0₂), titania (Ti0₂), zirconia (Zr0₂), germania (Ge0₂), tin oxide (Sn0₂), gallium oxide (Ga₂03), zinc oxide (ZnO), hafnium oxide (Hf0₂), ytterbium oxide (Y₂0₃), lanthanide oxide (La₂0₃), or combinations thereof. Embodiment 8 is the catalyst system of embodiment 7, wherein the catalytically active metal or metal oxide impregnated within or encompassed by the porous support matrix comprises noble metals including Pt, Pd, Ir and Rh, Au and Ag and alloys among these metals, wherein additional metals including Zn, Sn, or Cu can be used as additives to form alloys. Embodiment 9 is the catalyst system of any one of embodiments 1 to 8, wherein the redox-metal oxide containing hydrogen oxidation catalyst comprises cerium oxide (Ce0₂), ceria stabilized zirconia (CSZ), vanadium oxide, chromium oxide, manganese oxide, iron oxide, molybdenum oxide and tungsten oxide. Embodiment 10 is the catalyst system of any one of embodiments 1 to 9, wherein the non- oxidative dehydrogenation catalyst and/or the redox-metal oxide containing hydrogen oxidation catalyst are each nano- or micro-particulate material. Embodiment 11 is the catalyst system of any one of embodiments 1 to 10, wherein the redox-metal oxide containing hydrogen oxidation catalyst is coated with a material permeable to oxygen and reduced permeability to hydrocarbons when compared with oxygen permeability. Embodiment 12 is the catalyst system of embodiment 11, wherein the coating is a silica, silica-alumina composite, or titania coating.

[0018] Embodiment 13 is a reactor for performing a dehydrogenation of hydrocarbon reaction and an oxidation of hydrogen reaction, the reactor comprising: (a) a reaction zone comprising the catalyst system of any one of embodiments 1 to 12; (b) at least one inlet in fluid communication with the reaction zone capable of introducing and contacting a hydrocarbon containing feed stream with the catalyst system; and (c) at least one outlet in fluid communication with the reaction zone capable of removing a product feed stream comprising a dehydrogenated hydrocarbon and water from the reaction zone. Embodiment 14 is the reactor of embodiment 13, wherein the reactor is a continuous flow reactor selected from a fixed-bed reactor, a fluidized reactor, or a moving bed reactor. Embodiment 15 is the reactor of any one of embodiments 13 to 14, wherein the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst. Embodiment 16 is the reactor of any one of embodiments 13 to 14, wherein the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst of the catalyst system form first and second catalytic layers or beds, respectively, wherein the first and second catalytic layers or beds are positioned proximate to one another such that hydrogen produced in the first catalytic layer or bed is capable of flowing into and being oxidized by the second catalytic layer or bed. Embodiment 17 is the reactor of embodiment 16, further comprising a second inlet for an oxygen gas (0₂) containing feed stream that is positioned proximate to the second catalytic layer or bed such that the 0₂ containing feed stream is capable of flowing into the second catalytic layer or bed.

[0019] Embodiment 18 is a method for dehydrogenating a hydrocarbon and oxygenating hydrogen gas, the method includes: (a) contacting a hydrocarbon containing feed stream with the non-oxidative dehydrogenation catalyst of the catalyst system of any one of embodiments 1 to 12 under reaction conditions sufficient to produce a dehydrogenated hydrocarbon and hydrogen gas (H₂); and (b) contacting the produced H₂ with the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system under reaction conditions sufficient to produce water from the H₂ and the oxygen anions from the metal oxide lattice of the hydrogen oxidation catalyst and to release exotherm, wherein steps (a) and (b) are performed in a reaction zone of a reactor. Embodiment 19 is the method of embodiment 18, wherein the reactor is a continuous flow reactor selected from a fixed-bed reactor, a fluidized reactor, or a moving bed reactor. Embodiment 20 is the method of any one of embodiments 18 to 19, wherein the hydrocarbon containing feed stream comprises a C₂ to C₄ alkane that is dehydrogenated to a C₂ to C₄ alkene. Embodiment 21 is the method of any one of embodiments 18 to 20, wherein the non-oxidative dehydrogenation catalyst and the redox- metal oxide containing hydrogen oxidation catalyst of the catalyst system form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst. Embodiment 22 is the method of any one of embodiments 18 to 20, wherein the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst of the catalyst system form first and second catalytic layers or beds, respectively, wherein the hydrocarbon containing feed stream contacts the first catalytic layer or bed and the produced H₂ flows into and contacts the second catalytic layer or bed. Embodiment 23 is the method of embodiment 22, further comprising continuously, periodically, or intermittently contacting the hydrogen oxidation catalyst during the reaction with an oxygen-containing feed stream that is positioned proximate to the second catalytic layer or bed such that the 0₂ containing feed stream is capable of flowing into the second catalytic layer or bed and substantially avoids flowing into the first catalytic layer or bed, wherein the oxygen containing feed stream regenerates or maintains the oxidation of the hydrogen oxidation catalyst. Embodiment 24 is the method of any one of embodiments 18 to 22, further comprising continuously, periodically, or intermittently contacting the hydrogen oxidation catalyst during the reaction with oxygen to regenerate or maintain the oxidation of the hydrogen oxidation catalyst. Embodiment 25 is the method of any one of embodiments 23 to 24, wherein the amount of oxygen is regulated to maintain the oxidation of the hydrogen oxidation catalyst and minimize alkene oxidation. Embodiment 26 is the method of any one of embodiments 18 to 25, wherein the reaction is performed at a temperature of at least 400 °C, preferably 400 °C to 600 °C, more preferably 450 to 500 °C.

[0020] Other embodiments of the invention are discussed throughout this application. Any embodiment discussed with respect to one aspect of the invention applies to other aspects of the invention as well and vice versa. Each embodiment described herein is understood to be embodiments of the invention that are applicable to other aspects of the invention. It is contemplated that any embodiment discussed herein can be implemented with respect to any method or composition of the invention, and vice versa. Furthermore, compositions and kits of the invention can be used to achieve methods of the invention. [0021] The following includes definitions of various terms and phrases used throughout this specification.

[0022] The terms "about" or "approximately" are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment, the terms are defined to be within 10%, preferably within 5%, more preferably within 1%, and most preferably within 0.5%.

[0023] The terms "wt.%", "vol.%", or "mol.%" refers to a weight percentage of a component, a volume percentage of a component, or molar percentage of a component, respectively, based on the total weight, the total volume of material, or total moles, that includes the component. In a non-limiting example, 10 grams of component in 100 grams of the material is 10 wt.% of component.

[0024] The term "substantially" and its variations are defined to include ranges within 10%, within 5%, within 1%, or within 0.5%. [0025] The terms "inhibiting" or "reducing" or "preventing" or "avoiding" or any variation of these terms, when used in the claims and/or the specification includes any measurable decrease or complete inhibition to achieve a desired result.

[0026] The term "effective," as that term is used in the specification and/or claims, means adequate to accomplish a desired, expected, or intended result.

[0027] The use of the words "a" or "an" when used in conjunction with any of the terms "comprising," "including," "containing," or "having" in the claims, or the specification, may mean "one," but it is also consistent with the meaning of "one or more," "at least one," and "one or more than one." [0028] The words "comprising" (and any form of comprising, such as "comprise" and "comprises"), "having" (and any form of having, such as "have" and "has"), "including" (and any form of including, such as "includes" and "include") or "containing" (and any form of containing, such as "contains" and "contain") are inclusive or open-ended and do not exclude additional, unrecited elements or method steps. [0029] The catalyst systems of the present invention can "comprise," "consist essentially of," or "consist of particular ingredients, components, compositions, etc. disclosed throughout the specification. With respect to the transitional phase "consisting essentially of," in one non-limiting aspect, a basic and novel characteristic of the catalysts of the present invention are their abilities to catalyze oxidative dehydrogenation of alkanes. [0030] Other objects, features and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

DESCRIPTION OF THE DRAWINGS

[0031] The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of the specification embodiments presented herein. [0032] FIG. 1 is an illustration of a core-shell catalytic system of the present invention of a mixture of catalysts physically separated. In certain embodiments, the dehydrogenation catalyst can be encapsulated with a porous alumina with a controlled porosity that allows the reactant alkanes and products (hydrogen and alkenes) transport. The second catalyst can be a selective hydrogen oxidation catalyst, cerium oxide or ceria doped zirconia in a nano size crystal form. The second catalyst can be designed to be on the gas pathway or nearby the pore opening of the shell.

[0033] FIG. 2 is an illustration of a catalyst bed catalytic system of the present invention with a mixture of catalysts physically separated. In certain embodiments, the oxygen storage materials can be arranged in a segment of catalyst bed, where oxygen can be selectively delivered so the hydrogen oxidation can be continuously operated without any cycling.

DESCRIPTION

[0034] A solution to the some of the problems associated with oxidative dehydrogenation of alkanes has been discovered. The solution is premised on a catalyst system that includes two separated catalysts, one performing oxidation of hydrogen and the other performing dehydrogenation of alkanes. catalytic system. In the current system for oxidative dehydrogenation of alkanes, the hydrogen formed during dehydrogenation can react with oxygen to form water and release heat, which can be used for the endothermic dehydrogenation of alkanes. Removal of H₂ through an oxidation reaction can drive the dehydrogenation reaction to higher conversions.

[0035] Non-oxidative Dehydrogenation Catalysts. In certain aspects, the non-oxidative dehydrogenation catalyst needs to limit oxygen access. A core-shell structure or other embedded structure can provide a mechanism to streamline transport of gas. For example in a core-shell structure, the catalyst can be encapsulated within a porous alumina with a controlled porosity that allows transport of the reactant alkanes and products (hydrogen and alkenes).

[0036] Hydrogen oxidation catalysts. The hydrogen oxidation catalysts can be selective hydrogen oxidation catalysts. The hydrogen oxidation catalysts can be oxygen storage materials that oxidize hydrogen at a temperature of greater than 400 °C. Oxygen storage materials such as cerium oxide, ceria stabilized zirconia (CSZ) can react with hydrogen in the absence of the noble metal catalyst at a temperature where dehydrogenation of alkanes operates, typically at 450 °C to 550 °C, 475 °C to 525 °C or any value there between. Under such conditions, hydrogen reduces cerium oxide or cerium oxide in CSZ to form water and to release heat. As the reaction proceeds, the Ce0₂ becomes Ce₂0₃, which needs to be replenished with oxygen for future reaction. When oxygen becomes available, the reduced Ce₂0₃ will pick up the oxygen to become Ce0₂, then the next cycle of hydrogen oxidation can operate. The dehydrogenation catalysts can be configured as doped noble metal catalyst in core-shell forms. The selective hydrogen oxidation catalyst can include cerium oxide or ceria doped zirconia. These catalysts can be in the form of a crystalline nanoparticle. The hydrogen oxidation catalyst can be designed to be on the gas pathway or near the pore opening of the shell. In some case, the hydrogen oxidation catalyst acts like a membrane to filter off oxygen or consumes most of the oxygen using the hydrogen effluent from the core- shell catalyst at the dehydrogenation reaction operating temperature.

[0037] In one embodiment of the present invention, the Ce0₂ or ceria stabilized zirconia in the absence of noble and/or precious metals can be directly used as a catalyst for hydrogen oxidation in a net reducing environment such as an alkane dehydrogenation gas flow. The produced hydrogen reacts with lattice oxygen to form water and heat. As the oxygen is being consumed, the oxygen gas can be fed in with the dehydrogenation reactant flow so the reduced Ce0₂ can be re-oxidized for hydrogen oxidation (See, FIG. 2).

[0038] The oxygen storage materials can be highly divided nanocrystal Ce0₂, or ceria stabilized zirconia, or transitional metal oxides that have similar redox function as Ce0₂. To prevent the noble and/or precious metal from direct contact with the oxygen storage materials, which causes hydrocarbon total oxidation, one can coat the oxygen storage materials with silica, silica-alumina composite, or titania. In certain aspects, the oxygen storage material has a surface coating.

[0039] In another embodiment of the present invention, the oxygen storage materials can be arranged in a segment of a catalyst bed, where oxygen can be selectively delivered so the hydrogen oxidation can be continuously operated without any cycling.

[0040] The combination of two catalysts can be simultaneously used in a dehydrogenation reactor. In certain aspects, the reactor can be a fluidized bed or fixed bed form. The oxygen can be fed in as mixture in reactant flow continuously or intermittently and/or added at multiple entry points.

[0041] The catalyst system of the present invention can be contacted with feedstock under suitable conditions to facilitate a dehydrogenation reaction. For example, propane can be used as a feedstock to produce propylene and zso-butane can be used as a feedstock to produce zso-butylene. Non-limiting examples of feedstock materials include aliphatic compounds containing about 2 or up to 30 carbon atoms per molecule, or greater than, equal to, or between any two of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and 30. The feedstocks suitable for use with the catalyst system of the present invention can include paraffinic hydrocarbons having about 2 or more and about 20 or less carbon atoms or greater than, equal to, or between any two of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. In another embodiment, the feedstocks contain paraffinic hydrocarbons having about 3 or more and about 12 or less carbon atoms, or 3 to 6, or 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 carbon atoms. In one embodiment, the feedstocks boil at a temperature of about 400 °C or less at atmospheric pressure. In another embodiment, the feedstocks boil at a temperature of about 250 °C or less at atmospheric pressure.

[0042] Certain aspects are directed to a process to dehydrogenate hydrocarbons for use as feed for commercial chemical manufacture. Feedstocks having about 3 up to 5 carbon atoms can be dehydrogenated into olefinic feedstocks for the subsequent production of polyethylene, polypropylene, polybutylene, polyisobutlyene, or other chemical compositions that are commonly sold in solid or liquid forms.

[0043] The feedstocks can be processed through the catalytic processes described herein neat or can be combined with recycled portions of the product stream from the dehydrogenation process. Similarly, combinations of the above-described feedstock can be directed to the catalytic processes of the present invention, and the products subsequently fractionated to individual product pools. The catalytic processes of the present invention can also be operated in "blocked out" mode where only one feedstock is processed through the system at any one time. [0044] The dehydrogenation process described herein optionally begins with preheating a hydrocarbon feedstock. The feedstock can be preheated in feed/reactor effluent heat exchangers prior to entering a furnace or contacting other high temperature waste heat as a means for final preheating to a targeted catalytic reaction zone inlet temperature. Suitable final preheating means include, for example, waste heat from other refinery processes such as a fluid catalytic cracking unit, a fluidized or delayed coking unit, a catalytic hydrocracker, a crude distillation unit, a catalytic reforming unit, and/or hydrotreating units found in conventional petroleum refineries. [0045] The reaction zone can include one or more fixed bed reactors containing the same or different catalysts, a moving bed reactor, or a fluidized bed reactor. The feedstock can be contacted with the catalyst bed in one or more of an upward, downward, or radial flow fashion. The reactants may be in the liquid phase, mixed liquid and vapor phase, or the vapor phase.

[0046] In embodiments where a fixed bed reactor is employed, a dehydrogenation reaction zone can contain one or at least two fixed bed reactors. Fixed bed reactors in accordance with the subject innovation can also contain a plurality of catalyst beds. The plurality of catalyst beds in a single fixed bed reactor can also contain the same or different catalysts. [0047] In certain aspects, inter-stage heating can be employed, consisting of heat transfer devices between fixed bed reactors or between catalyst beds in the same reactor shell. Heat sources can include conventional process heaters such as one or more process furnaces or can include internally produced heat. Heating requirements can also be met from heating sources available from other process units. [0048] The dehydrogenation reaction zone effluent can be generally cooled and the effluent stream can be directed to a separator device such as a stripper tower where light hydrocarbons formed during the reaction step can be removed and directed to more appropriate hydrocarbon pools.

[0049] The separated liquid effluent product can conveyed to downstream processing facilities. The olefin product optionally can be directed to a polymerization facility or to an isomerization process for isomerization and thereafter directed to an ether facility for conversion, in the presence of an alkanol, to an ether. Where at least a portion of the olefin from the process described herein can be an z^'so-olefin, the stream can be sent directly to an ether facility or to a polymerization facility. Prior to direction to an ether facility, the product stream can be purified by removing unconverted paraffinic hydrocarbon from the product. This unconverted product can be recycled back to the reaction zone or further manipulated in other process units. The olefin product can be directed to an alkylation process for reaction with z^'so-paraffin to form higher octane, lower volatility gasoline blending components. The olefin product can be directed to a chemical manufacture process for conversion to other commodity chemical products or process streams. Methods for integration of the process described herein with other conventional refinery or chemical plant processes or products are known to those skilled in the art. [0050] The catalyst system described herein can be used at a pressure to facilitate catalytic dehydrogenation processes. In one embodiment, the pressure during catalytic dehydrogenation is about 0, 2, 20 psia (0 to 1.4 MPa) or more to about 20, 300, 500 psia (1.4 MPa, 2.0 MPa, 3.45 MPa) or less. Excessively high reaction pressures increase energy and equipment costs and provide diminishing marginal benefits.

EXAMPLES

[0051] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

Example 1

(Synthesis of Pt Nanoparticles)

[0052] Ethylene glycol (Sigma-Aldrich® (U.S.A.), 300 mL, 99 mass%) was added to a reaction vessel. Polyvinylpyrrolidone (Sigma-Aldrich®, 3.05 g, 99.0 mass%; average molecular weight: 40,000) and sodium hydroxide (Sigma-Aldrich®, 0.064 g, 95 mass%; as portion of a solid pellet.) was added to the ethylene glycol. The mixture was heated to 120 °C. In a separate vessel, tetrachloroplatinum hydrate dihydrochloride (Sigma-Aldrich®, 0.989 g, 65.049 mass%) was dissolved in deionized water (240 mL). The Pt solution was added dropwise to the hot glycol solution, with the rate being adjusted rate to maintain the temperature at about 110 to 120 °C. An initial yellowish color appeared when the Pt solution was added, but the color turned brown, then black after a couple of minutes. After addition was complete, the solution was kept stirring at 115 °C for 25 min, the heat discontinued, and the solution was allowed to cool to room temperature while maintaining stirring. A portion of black mixture was poured into acetone (about 4-5 x volume) to achieve a cloudy grey- brown suspension. The suspension was split into 50 mL polypropylene (PP) centrifuge tubes and centrifuged at 4,500 RPM for 3 to 5 min to separate particles and recover all the particles. The material was washed with acetone for 3 more times and air dried briefly. Absolute ethanol (40 mL) was added to make a black suspension at a concentration of about 3 mg Pt/mL. The size of nano-Pt particles was measured by transmission electron microscopy and found to be at 2-4 nm range with average about 3 nm. Prophetic Example 1

(Coating Sn0₂ on Pt particles)

[0053] The collected Pt nanoparticles from Example 1 (2.33 or 6.98 g) will be dispersed in pure ethanol (50 mL) at the Pt/Sn ratio of 1 or 3. Tin chloride dihydrate (SnCl₂ 2H₂0, 2.26 g) and concentrated HC1 (37 wt.%, 2.5 mL) will be added into the Pt dispersion under stirring. After the reaction is completed, the coated particles will be collected through centrifugation after washing with deionized (DI) water.

Prophetic Example 2

(Coating of Porous A1₂C>3 on Sn0₂ Coated Pt Particles)

[0054] Aluminum nitrate (A1(N0₃)₃, 10 g) and tetraethyl orthosilicate (2 g) will be dissolved in water (100 mL). Sn0₂ coated Pt particles from Prophetic Example 1 (1.0 g) will be added into the solution. Analytical grade urea (10 g) will be added into the solution, which will be subsequently heated to 80 °C for overnight. The coated particles will be separated from the solution by centrifugation. After washing with water for several rounds, the particles will be dispersed in a 0.1 M NH₄F/HF solution to remove the Si0₂ to obtain the porous A1₂0₃ on the Sn0₂ coated Pt particles. These particles will be dried at 120 °C.

Prophetic Example 3

(Alloying the Catalyst)

[0055] The Prophetic Example 2 core-shell catalyst can be heated up to 800 °C in 20% H₂ in N₂ for 4 hours. XRD will be used to determine if the alloy nanoparticles formed.

Prophetic Example 4

(Hydrogen Oxidation Catalyst Preparation)

[0056] Cerium nitrate hexahydrate (4.34 g) and zirconium oxynitrate hydrate (2.31 g) will be dissolved in water (50 mL). The mixed salt solution will be added dropwise into a concentrated H₄OH solution (50 mL). After the reactions are completed, the precipitated hydroxides will be washed with anhydrous ethanol for 6 times, dried and then calcined at 500 °C for 4 hours. The catalyst will be ground into fine powder.

Prophetic Example 5

(Preparation of Propane Oxidative Dehydrogenation Catalyst)

[0057] The hydrogen oxidation catalyst (Prophetic Example 4) and dehydrogenation catalyst (Prophetic Example 5) will be co-dispersed into water and then filtered. The mixed catalysts will be collected and calcined at 500 °C for 4 hours and be ready to test. Prophetic Example 6

(Dehydrogenation of Propane to Propylene)

[0058] In a proper reactor, the Prophetic Example 5 catalyst can be loaded. Mixed propane and oxygen with nitrogen dilution will be flowed through the catalyst bed at 450 °C to 550 °C. The effluent gases will be analyzed with a gas chromatograph. The conversion of propane and selectivity to propylene will be calculated from GC data.

Claims

A catalyst system for dehydrogenating a hydrocarbon and oxidizing hydrogen comprising:

(a) a non-oxidative dehydrogenation catalyst having a porous support matrix and a catalytically active metal or metal oxide impregnated within or encapsulated by the porous support matrix, wherein the porous support matrix is permeable to hydrogen and hydrocarbons, and the catalytically active metal or metal oxide is capable of catalyzing a non-oxidative dehydrogenation of hydrocarbon reaction; and

(b) a redox-metal oxide containing hydrogen oxidation catalyst that is capable of oxidizing hydrogen to water with oxygen atoms from the metal oxide lattice and generating exotherm; and re-oxidizing the deficient oxygen anion vacancy by molecular oxygen from the feed, wherein the non-oxidative dehydrogenation catalyst is positioned proximate to the redox-metal oxide containing hydrogen oxidation catalyst such that hydrogen produced from the non-oxidative dehydrogenation catalyst is capable of being oxidized by the oxygen anions from the metal oxide lattice of the hydrogen oxidation catalyst.

The catalyst system of claim 1, wherein the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst are configured to operate in a temperature range of 400 °C to 600 °C.

The catalyst system of claim 1, wherein the non-oxidative dehydrogenation catalyst has a core/shell or yolk/shell structure such that the core or yolk is the catalytically active metal or metal oxide and the shell is the porous support matrix.

The catalyst system of claim 1, wherein the non-oxidative dehydrogenation catalyst is impregnated within the porous support matrix.

The catalyst system of claim 1, wherein the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst.

The catalyst system of claim 1, wherein the non-oxidative dehydrogenation catalyst forms a first catalytic layer or bed and the hydrogen oxidation catalyst forms a second catalytic layer or bed, wherein the first and second layers or beds are proximate to one another such that hydrogen produced in the first layer or bed is capable of flowing into and being oxidized by the second layer or bed.

7. The catalyst system of claim 1, wherein the porous support matrix comprises alumina (AI2O3), silica (S1O2), titania (Ti0₂), zirconia (Zr0₂), germania (Ge0₂), tin oxide (Sn0₂), gallium oxide (Ga₂0₃), zinc oxide (ZnO), hafnium oxide (Hf0₂), ytterbium oxide (Y₂0₃), lanthanide oxide (La₂0₃), or combinations thereof.

8. The catalyst system of claim 7, wherein the catalytically active metal or metal oxide impregnated within or encompassed by the porous support matrix comprises noble metals including platinum (Pt), palladium (Pd), iridium (Ir), ruthenium (Rh), silver (Au), gold (Ag) and alloys thereof.

9. The catalyst system of claim 8, wherein the catalytically active metal is alloyed with a a transition metal, preferably tin (Sn) or zinc (Zn).

10. The catalyst system of claim 1, wherein the redox-metal oxide containing hydrogen oxidation catalyst comprises cerium oxide (Ce0₂), ceria stabilized zirconia (CSZ), vanadium oxide, chromium oxide, manganese oxide, iron oxide, molybdenum oxide and tungsten oxide.

11. The catalyst system of claim 1, wherein the non-oxidative dehydrogenation catalyst and/or the redox-metal oxide containing hydrogen oxidation catalyst are each nano- or micro-parti culate material.

12. The catalyst system of claim 1, wherein the redox-metal oxide containing hydrogen oxidation catalyst is coated with a material permeable to oxygen and reduced permeability to hydrocarbons when compared with oxygen permeability.

13. The catalyst system of claim 12, wherein the coating is a silica, silica-alumina composite, or titania coating.

14. A reactor for performing a dehydrogenation of hydrocarbon reaction and an oxidation of hydrogen reaction, the reactor comprising:

(a) a reaction zone comprising the catalyst system of claim 1;

(b) at least one inlet in fluid communication with the reaction zone capable of introducing and contacting a hydrocarbon containing feed stream with the catalyst system; and (c) at least one outlet in fluid communication with the reaction zone capable of removing a product feed stream comprising a dehydrogenated hydrocarbon and water from the reaction zone.

15. The reactor of claim 14, wherein the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst, or the non- oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst of the catalyst system form first and second catalytic layers or beds, respectively, wherein the first and second catalytic layers or beds are positioned proximate to one another such that hydrogen produced in the first catalytic layer or bed is capable of flowing into and being oxidized by the second catalytic layer or bed.

16. The reactor of claim 15, further comprising a second inlet for an oxygen gas (0₂) containing feed stream that is positioned proximate to the second catalytic layer or bed such that the 0₂ containing feed stream is capable of flowing into the second catalytic layer or bed.

17. A method for dehydrogenating a hydrocarbon and oxygenating hydrogen gas, the method comprising:

(a) contacting a hydrocarbon containing feed stream with the non-oxidative dehydrogenation catalyst of the catalyst system of claim 1, under reaction conditions sufficient to produce a dehydrogenated hydrocarbon and hydrogen gas (H₂); and

(b) contacting the produced H₂ with the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system under reaction conditions sufficient to produce water from the H₂ and the oxygen anions from the metal oxide lattice of the hydrogen oxidation catalyst and to release exotherm,

wherein steps (a) and (b) are performed in a reaction zone of a reactor at a temperature of at least 400 °C.

18. The method of claim 17, wherein the hydrocarbon containing feed stream comprises a C₂ to C₄ alkane that is dehydrogenated to a C₂ to C₄ alkene.

19. The method of claim 17, wherein the non-oxidative dehydrogenation catalyst and the redox-metal oxide containing hydrogen oxidation catalyst of the catalyst system form a mixture such that the hydrogen oxidation catalyst is positioned proximate to the porous support matrix of the non-oxidative dehydrogenation catalyst or wherein the non-oxidative dehydrogenation catalyst and the hydrogen oxidation catalyst of the catalyst system form first and second catalytic layers or beds, respectively, wherein the hydrocarbon containing feed stream contacts the first catalytic layer or bed and the produced H₂ flows into and contacts the second catalytic layer or bed.

20. The method of claim 19, further comprising continuously, periodically, or intermittently contacting the hydrogen oxidation catalyst during the reaction with an oxygen-containing feed stream that is positioned proximate to the second catalytic layer or bed such that the 0₂ containing feed stream is capable of flowing into the second catalytic layer or bed and substantially avoids flowing into the first catalytic layer or bed, wherein the oxygen containing feed stream regenerates or maintains the oxidation of the hydrogen oxidation catalyst or continuously, periodically, or intermittently contacting the hydrogen oxidation catalyst during the reaction with oxygen to regenerate or maintain the oxidation of the hydrogen oxidation catalyst and wherein the amount of oxygen is regulated to maintain the oxidation of the hydrogen oxidation catalyst and minimize alkene oxidation.