WO2018048629A1

WO2018048629A1 - Multi-stage adiabatic oxidative coupling of methane

Info

Publication number: WO2018048629A1
Application number: PCT/US2017/048255
Authority: WO
Inventors: Wugeng Liang; Vidya Sagar Reddy SARSANI; David West; Istvan Lengyel
Original assignee: Sabic Global Technologies, B.V.
Priority date: 2016-09-06
Filing date: 2017-08-23
Publication date: 2018-03-15

Abstract

A multi-stage method for producing olefins, wherein each stage comprises introducing a reactant mixture to an adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the reactant mixture comprises CH₄ and 0₂ and is characterized by an inlet temperature; allowing the reactant mixture to contact the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; recovering the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and optionally cooling the product mixture, wherein each stage is characterized by a narrow temperature rise, wherein the narrow temperature rise in each stage is a difference between the outlet temperature for that particular stage and the inlet temperature for that particular stage, and wherein the narrow temperature rise is from 100°C to 300°C.

Description

MULTI-STAGE ADIABATIC OXIDATIVE COUPLING OF METHANE TECHNICAL FIELD

[0001] The present disclosure relates to methods of producing olefins, more specifically methods of producing olefins by oxidative coupling of methane.

BACKGROUND

[0002] Hydrocarbons, and specifically olefins such as ethylene, are typically building blocks used to produce a wide range of products, for example, break-resistant containers and packaging materials. Currently, for industrial scale applications, ethylene is produced by heating natural gas condensates and petroleum distillates, which include ethane and higher hydrocarbons, and the produced ethylene is separated from a product mixture by using gas separation processes.

[0003] Oxidative coupling of the methane (OCM) has been the target of intense scientific and commercial interest for more than thirty years due to the tremendous potential of such technology to reduce costs, energy, and environmental emissions in the production of ethylene (C₂H₄). As an overall reaction, in the OCM, CH₄ and O₂ react exothermically over a catalyst to form C₂H₄, water (H₂O) and heat.

[0004] Ethylene can be produced by OCM as represented by Equations (I) and (II):

[0005] Oxidative conversion of methane to ethylene is exothermic. Excess heat produced from these reactions (Equations (I) and (II)) can push conversion of methane to carbon monoxide and carbon dioxide rather than the desired C₂ hydrocarbon product (e.g., ethylene):

The excess heat from the reactions in Equations (III) and (IV) further exasperate this situation, thereby substantially reducing the selectivity of ethylene production when compared with carbon monoxide and carbon dioxide production.

[0006] Additionally, while the overall OCM is exothermic, catalysts are used to overcome the endothermic nature of the C-H bond breakage. The endothermic nature of the bond breakage is due to the chemical stability of methane, which is a chemically stable molecule due to the presence of its four strong tetrahedral C-H bonds (435 kJ/mol). When catalysts are used in the OCM, the exothermic reaction can lead to a large increase in catalyst bed temperature and uncontrolled heat excursions that can lead to catalyst deactivation and a further decrease in ethylene selectivity. Furthermore, the produced ethylene is highly reactive and can form unwanted and thermodynamically favored deep oxidation products. [0007] Generally, in the OCM, CH₄ is first oxidatively converted into ethane (C₂H₆), and then into C₂H₄. CH₄ is activated heterogeneously on a catalyst surface, forming methyl free radicals (e.g., CH₃·), which then couple in a gas phase to form C₂H₆. C₂H₆ subsequently undergoes dehydrogenation to form C₂H₄. An overall yield of desired C₂ hydrocarbons is reduced by non-selective reactions of methyl radicals with oxygen on the catalyst surface and/or in the gas phase, which produce (undesirable) carbon monoxide and carbon dioxide. Some of the best reported OCM outcomes encompass a ~20% conversion of methane and ~80% selectivity to desired C₂ hydrocarbons.

[0008] There have been attempts to control the exothermic reaction of the OCM by using alternating layers of selective OCM catalysts; through the use of fluidized bed reactors; and/or by using steam as a diluent. However, these solutions are costly and inefficient. Thus, there is an ongoing need for the development of OCM processes.

BRIEF SUMMARY

[0009] Disclosed herein is a method for producing olefins comprising (a) introducing a first reactant mixture to a first reactor comprising a first oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄) and oxygen (O₂), and wherein the first reactant mixture is characterized by a first inlet temperature; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the first OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins; (c) recovering at least a portion of the first product mixture from the first reactor, wherein the first product mixture is characterized by a first outlet temperature, and wherein the first outlet temperature is greater than the first inlet temperature; (d) cooling the first product mixture from the first outlet temperature to a second inlet temperature; (e) introducing a second reactant mixture to a second reactor comprising a second OCM catalyst composition, wherein the second reactant mixture comprises at least a portion of the first product mixture and O₂, wherein the second reactant mixture is characterized by the second inlet temperature, and wherein the first inlet temperature and the second inlet temperature are the same or different; (f) allowing at least a portion of the second reactant mixture to contact at least a portion of the second OCM catalyst composition and react via an OCM reaction to form a second product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the second product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the second product mixture is greater than an amount of olefins in the first product mixture; (g) recovering at least a portion of the second product mixture from the second reactor, wherein the second product mixture is characterized by a second outlet temperature, wherein the second outlet temperature is greater than the second inlet temperature, and wherein the first outlet temperature and the second outlet temperature are the same or different; (h) optionally cooling the second product mixture to form a cooled second product mixture; and (i) recovering at least a portion of the olefins from the second product mixture and/or the cooled second product mixture.

[0010] Also disclosed herein is a method for producing olefins comprising (a) introducing a first reactant mixture to a first adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄), oxygen (O₂) and steam, wherein the first reactant mixture is characterized by an inlet temperature of from about 600^oC to about 700^oC, and wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag); wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins; (c) recovering at least a portion of the first product mixture from the first adiabatic reactor, wherein the first product mixture is characterized by an outlet temperature of from about 750^oC to about 850^oC; (d) cooling the first product mixture from the outlet temperature to the inlet temperature; (e) introducing an intermediate reactant mixture to an intermediate adiabatic reactor comprising the OCM catalyst composition, wherein the intermediate reactant mixture comprises at least a portion of the first product mixture, O₂ and steam, wherein the intermediate reactant mixture is characterized by the inlet temperature; (f) allowing at least a portion of the intermediate reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form an intermediate product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the intermediate product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the intermediate product mixture is greater than an amount of olefins in the first product mixture; (g) recovering at least a portion of the intermediate product mixture from the intermediate adiabatic reactor, wherein the intermediate product mixture is characterized by the outlet temperature; (h) cooling the intermediate product mixture from the outlet temperature to the inlet temperature; (i) introducing a terminal reactant mixture to a terminal adiabatic reactor comprising the OCM catalyst composition, wherein the terminal reactant mixture comprises at least a portion of the intermediate product mixture, O₂ and steam, wherein the terminal reactant mixture is characterized by the inlet temperature; (j) allowing at least a portion of the terminal reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a terminal product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the terminal product mixture is less than an amount of unreacted methane in the intermediate product mixture, and wherein an amount of olefins in the terminal product mixture is greater than an amount of olefins in the intermediate product mixture; (k) recovering at least a portion of the terminal product mixture from the terminal adiabatic reactor, wherein the terminal product mixture is characterized by the outlet temperature; (l) cooling the terminal product mixture to form a cooled terminal product mixture; and (m) recovering at least a portion of the olefins from the cooled terminal product mixture.

[0011] Further disclosed herein is a multi-stage method for producing olefins, wherein each stage comprises (i) introducing a reactant mixture to an adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture, wherein each stage is characterized by a narrow temperature rise, wherein the narrow temperature rise in each stage is a difference between the outlet temperature for that particular stage and the inlet temperature for that particular stage, and wherein the narrow temperature rise is from about 100^oC to about 300^oC.

[0012] Further disclosed herein is a multi-stage method for producing olefins, wherein each stage comprises (i) introducing a reactant mixture to an adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture, wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag), and wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] For a detailed description of the preferred aspects of the disclosed methods, reference will now be made to the accompanying drawing in which:

[0014] Figure 1 displays a schematic of an olefin production system employing multi-stage adiabatic oxidative coupling of methane (OCM);

[0015] Figure 2 displays a graph of methane conversion as a function temperature for an OCM reaction for different catalysts;

[0016] Figure 3 displays a graph of oxygen conversion as a function temperature for an OCM reaction for different catalysts; and [0017] Figure 4 displays a graph of C₂₊ selectivity as a function temperature for an OCM reaction for different catalysts.

DETAILED DESCRIPTION

[0018] Disclosed herein are methods for producing olefins comprising (a) introducing a first reactant mixture to a first reactor comprising a first oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄) and oxygen (O₂), and wherein the first reactant mixture is characterized by a first inlet temperature; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the first OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins; (c) recovering at least a portion of the first product mixture from the first reactor, wherein the first product mixture is characterized by a first outlet temperature, and wherein the first outlet temperature is greater than the first inlet temperature; (d) cooling the first product mixture from the first outlet temperature to a second inlet temperature; (e) introducing a second reactant mixture to a second reactor comprising a second OCM catalyst composition, wherein the second reactant mixture comprises at least a portion of the first product mixture and O₂, wherein the second reactant mixture is characterized by the second inlet temperature, and wherein the first inlet temperature and the second inlet temperature are the same or different; (f) allowing at least a portion of the second reactant mixture to contact at least a portion of the second OCM catalyst composition and react via an OCM reaction to form a second product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the second product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the second product mixture is greater than an amount of olefins in the first product mixture; (g) recovering at least a portion of the second product mixture from the second reactor, wherein the second product mixture is characterized by a second outlet temperature, wherein the second outlet temperature is greater than the second inlet temperature, and wherein the first outlet temperature and the second outlet temperature are the same or different; (h) optionally cooling the second product mixture to form a cooled second product mixture; and (i) recovering at least a portion of the olefins from the second product mixture and/or the cooled second product mixture. Producing olefins can be a multi-stage process, wherein a first stage comprises steps (a) through (d), wherein a second stage comprises steps (e) through (h), and wherein the multi- stage process further comprises one or more additional stages downstream of the first stage and/or the second stage, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi- stage process.

[0019] Other than in the operating examples or where otherwise indicated, all numbers or expressions referring to quantities of ingredients, reaction conditions, and the like, used in the specification and claims are to be understood as modified in all instances by the term“about.” Various numerical ranges are disclosed herein. Because these ranges are continuous, they include every value between the minimum and maximum values. The endpoints of all ranges reciting the same characteristic or component are independently combinable and inclusive of the recited endpoint. Unless expressly indicated otherwise, the various numerical ranges specified in this application are approximations. The endpoints of all ranges directed to the same component or property are inclusive of the endpoint and independently combinable. The term“from more than 0 to an amount” means that the named component is present in some amount more than 0, and up to and including the higher named amount.

[0020] The terms“a,”“an,” and“the” do not denote a limitation of quantity, but rather denote the presence of at least one of the referenced item. As used herein the singular forms“a,”“an,” and“the” include plural referents.

[0021] As used herein,“combinations thereof” is inclusive of one or more of the recited elements, optionally together with a like element not recited, e.g., inclusive of a combination of one or more of the named components, optionally with one or more other components not specifically named that have essentially the same function. As used herein, the term“combination” is inclusive of blends, mixtures, alloys, reaction products, and the like.

[0022] Reference throughout the specification to“an aspect,”“another aspect,”“other aspects,”“some aspects,” and so forth, means that a particular element (e.g., feature, structure, property, and/or characteristic) described in connection with the aspect is included in at least an aspect described herein, and may or may not be present in other aspects. In addition, it is to be understood that the described element(s) can be combined in any suitable manner in the various aspects.

[0023] As used herein, the terms“inhibiting” or“reducing” or“preventing” or“avoiding” or any variation of these terms, include any measurable decrease or complete inhibition to achieve a desired result.

[0024] As used herein, the term“effective,” means adequate to accomplish a desired, expected, or intended result.

[0025] As used herein, the terms“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“include” and“includes”) or“containing” (and any form of containing, such as“contain” and“contains”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0026] Unless defined otherwise, technical and scientific terms used herein have the same meaning as is commonly understood by one of skill in the art.

[0027] Compounds are described herein using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash (“-”) that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, -CHO is attached through the carbon of the carbonyl group. [0028] A method for producing olefins can comprise multiple stages (e.g., as part of a multi-stage process), wherein each individual stage can comprise an oxidative coupling of methane (OCM) reactor, wherein each individual stage can be repeated as necessary to achieve a target methane conversion for the overall multi-stage process. For purposes of the disclosure herein a stage of a process can be defined as a single pass conversion through a single catalyst bed. A multi-stage process generally comprises a plurality of individual stages, wherein each individual stage comprises a single pass conversion through a single catalyst bed. While the current disclosure will be discussed in detail in the context of a single stage comprising a single reactor comprising a single catalyst bed, it should be understood that any suitable stage/reactor/catalyst bed configurations can be used. For example, two or more stages of a multi-stage process can be housed in one or more reactors. As will be appreciated by one of skill in the art, and with the help of this disclosure, multiple stages can be housed within a single reaction vessel, for example a vessel comprising two or more catalyst beds in series. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, multiple vessels can be part of a single stage, for example two or more vessels in parallel, wherein a reactant mixture is distributed between and introduced to the two or more vessels in parallel. While the current disclosure will be discussed in detail in the context of a multi-stage process comprising 2 stages, it should be understood that any suitable number of stages can be used, such as for example, 2 stages, 3 stages, 4 stages, 5 stages, 6 stages, 7 stages, 8 stages, 9 stages, 10 stages, or more stages. Such multi-stage processes may be implemented via a corresponding plurality of reactors in series, as is described herein.

[0029] In an aspect, a method for producing olefins can comprise a first stage and a second stage, wherein the first stage comprises a first reactor (e.g., first OCM reactor), and wherein the second stage comprises a second reactor (e.g., second OCM reactor), and wherein the first reactor and the second reactor are in series, with the second reactor downstream of the first reactor.

[0030] A method for producing olefins can comprise introducing a first reactant mixture to a first reactor comprising a first oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄) and oxygen (O₂), and wherein the first reactant mixture is characterized by a first inlet temperature; and allowing at least a portion of the first reactant mixture to contact at least a portion of the first OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins.

[0031] In an aspect, the OCM reactor (e.g., the first reactor, the second reactor) can be an adiabatic reactor. The OCM reactors can be fixed bed reactors, such as axial flow reactors, or radial flow reactors. As will be appreciated by one of skill in the art, and with the help of this disclosure, certain fixed bed reactors, such as radial flow reactors, can decrease a reactor pressure drop, which may in turn increase a desired selectivity. [0032] In some aspects, an OCM reactor (e.g., the first reactor, the second reactor) can comprise an OCM catalyst composition (e.g., a first OCM catalyst composition, a second OCM catalyst composition, etc.). In such aspects, the OCM catalyst composition can comprise basic oxides; mixtures of basic oxides; redox elements; redox elements with basic properties; mixtures of redox elements with basic properties; mixtures of redox elements with basic properties promoted with alkali and/or alkaline earth metals; rare earth metal oxides; mixtures of rare earth metal oxides; mixtures of rare earth metal oxides promoted by alkali and/or alkaline earth metals; manganese; manganese compounds; lanthanum; lanthanum compounds; sodium; sodium compounds; cesium; cesium compounds; calcium; calcium compounds; and the like; or combinations thereof.

[0033] In an aspect, the OCM reactor can comprise an OCM catalyst composition comprising one or more oxides; wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof; and wherein the OCM catalyst composition catalyzes the OCM reaction (e.g., the catalyst catalyzes an oxidative coupling or conversion of CH₄ to olefins). In some aspects, the one or more oxides can be doped with silver (Ag). For purposes of the disclosure herein the term“doped” refers to a physical bond and/or a chemical bond (e.g., a covalent bond) that is established between the one or more oxides and Ag. For example, Ag (e.g., Ag nanoparticles, microparticles, nanowires, etc.) can be retained onto the one or more oxides by electrostatic interactions, or other physical and/or chemical interactions.

[0034] Nonlimiting examples of the one or more oxides suitable for use in the present disclosure include

[0035] The Ag can comprise Ag nanoparticles, wherein the Ag nanoparticles can be characterized by an average size of from about 1 nm to about 500 nm, alternatively from about 2 nm to about 250 nm, alternatively from about 2.5 nm to about 100 nm, alternatively from about 5 nm to about 25 nm, or alternatively from about 10 nm to about 20 nm.

[0036] The Ag can comprise Ag microparticles, wherein the Ag microparticles can be characterized by an average size of from about 0.5 microns to about 50 microns, alternatively from about 0.5 microns to about 1.25 microns, alternatively from about 1 micron to about 25 microns, or alternatively from about 5 microns to about 10 microns.

[0037] The Ag can comprise Ag nanowires, wherein the Ag nanowires can be characterized by an average diameter of from about 1 nm to about 500 nm, alternatively from about 2 nm to about 100 nm, alternatively from about 2.5 nm to about 50 nm, or alternatively from about 25 nm to about 50 nm; and by an average length of from about 0.05 microns to about 50 microns, alternatively from about 1 micron to about 25 microns, alternatively from about 2 micron to about 50 microns, or alternatively from about 5 microns to about 10 microns.

[0038] In an aspect, the first OCM catalyst composition can comprise an OCM catalyst effective to achieve an oxygen conversion of from about 90% to 100%, alternatively from about 95% to 99.99%, or alternatively from about 98% to 99.9%, in the first reactor over a first temperature increase, wherein the first temperature increase is a difference between the first outlet temperature and the first inlet temperature. Without wishing to be limited by theory, Ag promotion of the OCM catalyst increases catalyst activity and allows the OCM catalyst to reach the same oxygen conversion at a lower temperature. Further, without wishing to be limited by theory, Ag promotion of the OCM catalyst can shift the entire temperature profile of an OCM reaction towards lower temperatures, by increasing catalyst activity and facilitating reaching the same conversion (e.g., oxygen conversion, methane conversion, etc.) at lower temperatures.

[0039] The first reactant mixture can comprise a hydrocarbon or mixtures of hydrocarbons, and oxygen. In some aspects, the hydrocarbon or mixtures of hydrocarbons can comprise natural gas (e.g., CH₄), liquefied petroleum gas comprising C₂-C₅ hydrocarbons, C₆₊ heavy hydrocarbons (e.g., C₆ to C₂₄ hydrocarbons such as diesel fuel, jet fuel, gasoline, tars, kerosene, etc.), oxygenated hydrocarbons, biodiesel, alcohols, dimethyl ether, and the like, or combinations thereof. In an aspect, the reactant mixture can comprise CH₄ and O₂. As will be appreciated by one of skill in the art, and with the help of this disclosure, methane (or a hydrocarbon or mixtures of hydrocarbons) is introduced into a multi-stage process in the first stage into the OCM reactor (e.g., a first reactor); the OCM reactant mixture for subsequent stages (e.g., a second stage) will utilize the unreacted methane and any other hydrocarbons present that were recovered from the first stage (after passing through any other processes that are part of the first stage). In some aspects, some methane (or a hydrocarbon or mixtures of hydrocarbons) could be optionally added to reactant mixtures in stages other than the first stage (e.g., fresh hydrocarbon feed at one or more stages subsequent to a first stage), to supplement a recovered unreacted methane, if necessary.

[0040] The O₂ used in the first reactant mixture and/or in any subsequent stages in any OCM reactor (e.g., a second reactor), can be oxygen gas (which may be obtained via a membrane separation process), technical oxygen (which may contain some air), air, oxygen enriched air, and the like, or combinations thereof.

[0041] The first reactant mixture can further comprise a diluent. A diluent can also be introduced in any subsequent stages in any OCM reactor (e.g., a second OCM reactor). The diluent is inert with respect to the OCM reaction, e.g., the diluent does not participate in the OCM reaction. In an aspect, the diluent can comprise water, nitrogen, inert gases, and the like, or combinations thereof. In an aspect, the diluent can be present in the OCM reactant mixture (e.g., first reactant mixture, second reactant mixture) in an amount of from about 0.5% to about 80%, alternatively from about 5% to about 50%, or alternatively from about 10% to about 30%, based on the total volume of the OCM reactant mixture.

[0042] In an aspect, the diluent comprises steam. Steam can be present in the first reactant mixture in an amount of from about 5% to about 70%, alternatively from about 10% to about 60%, or alternatively from about 15% to about 50%, based on the total volume of the first reactant mixture.

[_0043] The first reactant mixture can be characterized by a first inlet temperature of from about 550^oC to about 800^oC, alternatively from about 575^oC to about 750^oC, or alternatively from about 600^oC to about 700^oC.

[0044] In an aspect, a method for producing olefins can comprise recovering at least a portion of the first product mixture from the first reactor, wherein the first product mixture is characterized by a first outlet temperature, and wherein the first outlet temperature is greater than the first inlet temperature. The first product mixture can comprise olefins, water, CO, CO₂, and unreacted methane.

[0045] The first outlet temperature can be from about 700^oC to about 950^oC, alternatively from about 750^oC to about 925^oC, or alternatively from about 800^oC to about 900^oC. The first temperature increase (i.e., the difference between the first outlet temperature and the first inlet temperature) can be from about 100^oC to about 300^oC, alternatively from about 100^oC to about 275^oC, or alternatively from about 100^oC to about 250^oC. For purposes of the disclosure herein, the first temperature increase can be referred to as a“narrow temperature rise,” or a“narrow temperature increase.” Further, for purposes of the disclosure herein, the term“narrow temperature rise” refers to a temperature increase of less than about 300^oC.

[0046] In some aspects, the first reactor can be cooled to provide for a first product mixture having the first outlet temperature. As will be appreciated by one of skill in the art, and with the help of this disclosure, the OCM reaction is highly exothermic, and even if the reactor is cooled to some extent, the overall temperature can still increase; however, cooling the reactor can control how much the overall temperature increases.

[0047] In an aspect, a method for producing olefins can comprise cooling the first product mixture from the first outlet temperature to a second inlet temperature. In some aspects, the second inlet temperature and the first inlet temperature can be the same or different. The second inlet temperature can be from about 550^oC to about 800^oC, alternatively from about 575^oC to about 750^oC, or alternatively from about 600^oC to about 700^oC.

[0048] A step of cooling the first product mixture can occur in a first heat exchanger. In some aspects, the first heat exchanger can heat a methane feed stream to the first inlet temperature, and wherein the first reactant mixture comprises at least a portion of the heated methane feed stream. In other aspects, the first heat exchanger can heat the first reactant mixture.

[0049] In other aspects, the first heat exchanger can heat a stream in a process other than olefin production by OCM, such as an ethylbenzene feed stream, a stream in a dehydrogenation reaction (e.g., a stream in a propane to propylene conversion), and the like, or combinations thereof. Stated conversely, any suitable process stream may be used in the first heat exchanger to cool the first product mixture, including cooling water, steam generation (e.g., electricity cogeneration), etc. That is, the first heat exchanger can heat any suitable stream, whether in an OCM process or in a process other than an OCM process. As an example, a heated ethylbenzene feed stream (recovered from the first heat exchanger) can be fed to an ethylbenzene dehydrogenation reactor to produce styrene. The ethylbenzene dehydrogenation is generally run at elevated reaction temperatures, wherein the feed for this reaction needs to be heated to 620^oC to 650^oC. By integrating a multi-stage OCM with ethylbenzene dehydrogenation, a super-heat steam furnace can be avoided for heating an ethylbenzene feed stream, and the overall cost of styrene production can be reduced.

[0050] In an aspect, a method for producing olefins can comprise a second stage, wherein the second stage comprises a second reactor (e.g., OCM reactor) in series with and downstream from the first reactor. In such aspect, a method for producing olefins can comprise introducing a second reactant mixture to a second reactor comprising a second OCM catalyst composition, wherein the second reactant mixture comprises at least a portion of the first product mixture and O₂, wherein the second reactant mixture is characterized by the second inlet temperature, and wherein the first inlet temperature and the second inlet temperature are the same or different; allowing at least a portion of the second reactant mixture to contact at least a portion of the second OCM catalyst composition and react via an OCM reaction to form a second product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the second product mixture is less than an amount of unreacted methane in the first product mixture, with the proviso that no fresh or supplemental methane is added to the second stage to desirably produce an increase in a methane concentration, and wherein an amount of olefins in the second product mixture is greater than an amount of olefins in the first product mixture, with the proviso that no olefins are separated or recovered from the first product mixture to desirably produce a decrease in an olefin concentration; recovering at least a portion of the second product mixture from the second reactor, wherein the second product mixture is characterized by a second outlet temperature, wherein the second outlet temperature is greater than the second inlet temperature, and wherein the first outlet temperature and the second outlet temperature are the same or different; optionally cooling the second product mixture to form a cooled second product mixture, wherein the cooled second product mixture can be characterized by a temperature that is about the same as the first inlet temperature and/or the second inlet temperature; and recovering at least a portion of the olefins from the second product mixture and/or the cooled second product mixture. For purposes of the disclosure herein, all descriptions related to the first stage (such as descriptions of first reactor (e.g., OCM reactor), first OCM catalyst composition, first reactant mixture (e.g., OCM reactant mixture), first product mixture (e.g., OCM product mixture), first heat exchanger, first inlet temperature, first outlet temperature, first temperature increase, etc.) can be applied to the corresponding components of the second (such as descriptions of second reactor (e.g., OCM reactor), second OCM catalyst composition, second reactant mixture (e.g., OCM reactant mixture), second product mixture (e.g., OCM product mixture), second heat exchanger, second inlet temperature, second outlet temperature, second temperature increase, etc., respectively), unless otherwise specified herein.

[0051] In an aspect, the method for producing olefins as disclosed herein can further comprise minimizing deep oxidation of methane to carbon monoxide (CO) and/or carbon dioxide (CO₂), wherein the second product mixture can comprise less than about 15 mol%, alternatively less than about 10 mol%, or alternatively less than about 5 mol% carbon monoxide (CO) and/or carbon dioxide (CO₂).

[0052] As will be appreciated by one of skill in the art, and with the help of this disclosure, in some instances, the methane reacting in the second stage in the second reactor is primarily methane that was introduced to the first reactor, that didn’t react in the first reactor, and that was subsequently recovered as unreacted methane (as part of the first product mixture), with the proviso that no fresh or supplemental methane was added to the second stage to desirably produce an increase in a methane concentration. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, when fresh methane is introduced to the second stage, an amount of unreacted methane recovered from the second stage (as part of the second product mixture) minus the amount of fresh methane introduced to the second stage is less than the amount of unreacted methane that was recovered from the first stage (as part of the first product mixture) and was subsequently introduced to the second stage. In some aspects, a method for producing olefins can further comprise introducing additional CH₄ to the second reactor.

[0053] In an aspect, a method for producing olefins can be a multi-stage process, wherein the multi-stage process further comprises one or more additional stages downstream of the first stage and/or the second stage (with each successive downstream stage having a corresponding OCM reactor in series with and downstream of an immediately preceding stage/reactor), as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process. In an aspect, the multi-stage process can have from 2 to about 8 stages, alternatively from 3 to about 8 stages, alternatively from 3 to about 6 stages, or alternatively from 4 to about 6 stages. Each additional stage can comprise (i) introducing a reactant mixture to a reactor comprising an OCM catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture. In some aspects, the reactant mixture can comprise at least a portion of an upstream product mixture recovered from an upstream reactor. In other aspects, the reactant mixture can further comprise at least a portion of a downstream product mixture recovered from a downstream reactor. For purposes of the disclosure herein, all descriptions related to the first stage (such as descriptions of first reactor (e.g., OCM reactor), first OCM catalyst composition, first reactant mixture (e.g., OCM reactant mixture), first product mixture (e.g., OCM product mixture), first heat exchanger, first inlet temperature, first outlet temperature, first temperature increase, etc.) can be applied to the corresponding components of any subsequent stage (such as descriptions of reactor (e.g., OCM reactor), OCM catalyst composition, reactant mixture (e.g., OCM reactant mixture), product mixture (e.g., OCM product mixture), heat exchanger, inlet temperature, outlet temperature, temperature increase, etc., respectively), unless otherwise specified herein.

[0054] In an aspect, an overall yield to C₂₊ hydrocarbons in a multi-stage process as disclosed herein can be from about 15% to about 50%, alternatively from about 20% to about 45%, or alternatively from about 30% to about 40%.

[0055] In an aspect, a methane conversion in a multi-stage process (e.g., an overall methane conversion) can be from about 15% to about 100%, alternatively from about 25% to about 95%, or alternatively from about 40% to about 90%. Generally, a conversion of a reagent or reactant refers to the percentage (usually mol%) of reagent that reacted to both undesired and desired products, based on the total amount (e.g., moles) of reagent present before any reaction took place. For example, the methane conversion in a multi-stage process can be calculated by using equation (1):

w^herein of moles of methane that was introduced to

o t m lti stage process

t^{he multi-stage process; and}

M of moles of methane that was recovered from the multi-stage process.

[0056] In an aspect, an oxygen conversion in a multi-stage process (e.g., an overall oxygen conversion) can be from about 90% to about 100%, alternatively from about 95% to 99.99%, or alternatively from about 98% to 99.9%. For example, the oxygen conversion in a multi-stage process can be calculated by using equation (2):

wherein of moles of oxygen that was introduced to the

multi-stage process; and of moles of oxygen that was

recovered from the multi-stage process.

[0057] In an aspect, an overall selectivity to C₂₊ hydrocarbons in a multi-stage process as disclosed herein can be from about 50% to about 99%, alternatively from about 60% to 95%, or alternatively from about 70% to 90%). Generally, a selectivity to a desired product or products refers to how much desired product was formed divided by the total products formed, both desired and undesired. For purposes of the disclosure herein, the selectivity to a desired product is a % selectivity based on moles converted into the desired product. Further, for purposes of the disclosure herein, a C_X selectivity (e.g., C₂₊ selectivity, C₂ selectivity, etc.) can be calculated by dividing a number of moles of carbon (C) from CH₄ that were converted into the desired product (e.g.,

by the total number of moles of C from CH₄ that were converted (e.g.,

of moles of C from CH₄ that were converted into C₂H₄;

of moles of C from CH₄ that were converted into of moles of C from

that were converted into of moles of C from CH₄ that were converted into C₃H₆;

of moles of C from CH₄ that were converted into

of moles of C from CH₄ that were converted into C₄ hydrocarbons

of moles of C from CH₄ that were converted into

of moles of C from CH₄ that were converted into CO; etc.

[0058] A C₂₊ selectivity (e.g., selectivity to C₂₊ hydrocarbons) refers to how much

and C₄s (if no products higher than C₄ are produced) were formed divided by the total products formed, including For example, the C₂₊ selectivity can be

calculated by using equation (3):

[0059] As will be appreciated by one of skill in the art, and with the help of this disclosure, if a specific product and/or hydrocarbon product having x number of carbon atoms is not produced in a certain OCM reaction/process, then the corresponding C_Cx is 0, and the term is simply removed from selectivity calculations.

[0060] In an aspect, a method for producing ethylene can comprise (a) introducing a first reactant mixture to a first adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CFL_t), oxygen (0₂) and steam, wherein the first reactant mixture is characterized by an inlet temperature of from about 600^oC to about 700^oC, and wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag); wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and ethylene; (c) recovering at least a portion of the first product mixture from the first adiabatic reactor, wherein the first product mixture is characterized by an outlet temperature of from about 750^oC to about 850^oC; (d) cooling the first product mixture from the outlet temperature to the inlet temperature; (e) introducing an intermediate reactant mixture to an intermediate adiabatic reactor comprising the OCM catalyst composition, wherein the intermediate reactant mixture comprises at least a portion of the first product mixture, O₂ and steam, wherein the intermediate reactant mixture is characterized by the inlet temperature; (f) allowing at least a portion of the intermediate reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form an intermediate product mixture comprising unreacted methane and ethylene, wherein an amount of unreacted methane in the intermediate product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of ethylene in the intermediate product mixture is greater than an amount of ethylene in the first product mixture; (g) recovering at least a portion of the intermediate product mixture from the intermediate adiabatic reactor, wherein the intermediate product mixture is characterized by the outlet temperature; (h) cooling the intermediate product mixture from the outlet temperature to the inlet temperature; (i) introducing a terminal reactant mixture to a terminal adiabatic reactor comprising the OCM catalyst composition, wherein the terminal reactant mixture comprises at least a portion of the intermediate product mixture, O₂ and steam, wherein the terminal reactant mixture is characterized by the inlet temperature; (j) allowing at least a portion of the terminal reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a terminal product mixture comprising unreacted methane and ethylene, wherein an amount of unreacted methane in the terminal product mixture is less than an amount of unreacted methane in the intermediate product mixture, and wherein an amount of ethylene in the terminal product mixture is greater than an amount of ethylene in the intermediate product mixture; (k) recovering at least a portion of the terminal product mixture from the terminal adiabatic reactor, wherein the terminal product mixture is characterized by the outlet temperature; (l) cooling the terminal product mixture to form a cooled terminal product mixture; and (m) recovering at least a portion of the ethylene from the cooled terminal product mixture. In such aspect, producing ethylene can be a multi-stage process, wherein the multi-stage process comprises (1) a first stage comprising steps (a) through (d); (2) two or more intermediate stages, as necessary to achieve a target methane conversion and/or a target C₂ selectivity for the overall multi-stage process, wherein each intermediate stage comprises steps (e) through (h); and (3) a terminal stage comprising steps (i) through (m). The two or more intermediate stages comprise two or more intermediate adiabatic reactors, respectively. In an aspect, at least a portion of the intermediate product mixture can be recycled to the intermediate adiabatic reactor as the intermediate reactant mixture, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process.

[0061] Referring to Figure 1, an olefin production system 100 is disclosed. The olefin production system 100 generally comprises the following components in fluid communication and arranged in series as shown in the figure: a first adiabatic reactor 10; a first heat exchanger 15; a first intermediate adiabatic reactor 20; a second heat exchanger 25; a second intermediate adiabatic reactor 30; a third heat exchanger 35; a terminal adiabatic reactor 40; and a fourth heat exchanger 45. As will be appreciated by one of skill in the art, and with the help of this disclosure, olefin production system components can be in fluid communication with each other through any suitable conduits (e.g., pipes, streams, etc.). For purposes of the disclosure herein, all descriptions related to any stage of a multi-stage process (such as descriptions of OCM reactors, OCM reactant mixtures, OCM product mixtures, heat exchangers, etc.) previously disclosed herein can be applied to the corresponding components of Figure 1 (such as descriptions of OCM reactors, adiabatic reactors, OCM reactant mixtures, OCM product mixtures, heat exchangers, etc., respectively), and vice-versa, unless otherwise specified herein. Further, as will be appreciated by one of skill in the art, and with the help of this disclosure, while the olefin production system 100 disclosed in Figure 1 comprises a four-stage process, it should be understood that an olefin production system, such as the olefin production system 100, can comprise any suitable number of stages, such as for example, 2 stages, 3 stages, 4 stages, 5 stages, 6 stages, 7 stages, 8 stages, 9 stages, 10 stages, or more stages.

[0062] In an aspect, a method for producing olefins can comprise four stages (e.g., four-stage process as represented in the configuration of Figure 1), for example (i) a first stage comprising (a1) introducing a first reactant mixture 11 to a first adiabatic reactor 10 comprising an oxidative coupling of methane (OCM) catalyst composition 10a, wherein the first reactant mixture 11 comprises methane (CH₄), oxygen (O₂) and steam, and wherein the first reactant mixture 11 is characterized by an inlet temperature of from about 600^oC to about 700^oC, (b1) allowing at least a portion of the first reactant mixture 11 to contact at least a portion of the OCM catalyst composition 10a and react via an OCM reaction to form a first product mixture 12 comprising unreacted methane and ethylene, (c1) recovering at least a portion of the first product mixture 12 from the first adiabatic reactor 10, wherein the first product mixture 12 is characterized by an outlet temperature of from about 750^oC to about 850^oC, and (d1) cooling via the first heat exchanger 15 the first product mixture 12 from the outlet temperature to the inlet temperature to produce a cooled first product mixture 13; (ii) a second stage comprising (a2) introducing a first intermediate reactant mixture 21 to a first intermediate adiabatic reactor 20 comprising the OCM catalyst composition 20a, wherein the first intermediate reactant mixture 21 comprises at least a portion of the cooled first product mixture 13, O₂21a, and steam, wherein the first intermediate reactant mixture 21 is characterized by the inlet temperature, (b2) allowing at least a portion of the first intermediate reactant mixture 21 to contact at least a portion of the OCM catalyst composition 20a and react via an OCM reaction to form a first intermediate product mixture 22 comprising unreacted methane and ethylene, wherein an amount of unreacted methane in the first intermediate product mixture 22 is less than an amount of unreacted methane in the first product mixture 12, and wherein an amount of ethylene in the first intermediate product mixture 22 is greater than an amount of ethylene in the first product mixture 12, (c2) recovering at least a portion of the first intermediate product mixture 22 from the first intermediate adiabatic reactor 20, wherein the first intermediate product mixture 22 is characterized by the outlet temperature, and (d2) cooling via the second heat exchanger 25 the first intermediate product mixture 22 from the outlet temperature to the inlet temperature to form a cooled first intermediate product mixture 23; (iii) a third stage comprising (a3) introducing a second intermediate reactant mixture 31 to a second intermediate adiabatic reactor 30 comprising the OCM catalyst composition 30a, wherein the second intermediate reactant mixture 31 comprises at least a portion of the cooled first intermediate product mixture 23, O₂31a, and steam, wherein the second intermediate reactant mixture 31 is characterized by the inlet temperature, (b3) allowing at least a portion of the second intermediate reactant mixture 31 to contact at least a portion of the OCM catalyst composition 30a and react via an OCM reaction to form a second intermediate product mixture 32 comprising unreacted methane and ethylene, wherein an amount of unreacted methane in the second intermediate product mixture 32 is less than an amount of unreacted methane in the first intermediate product mixture 22, and wherein an amount of ethylene in the second intermediate product mixture 32 is greater than an amount of ethylene in the first intermediate product mixture 22, (c3) recovering at least a portion of the second intermediate product mixture 32 from the second intermediate adiabatic reactor 30, wherein the second intermediate product mixture 32 is characterized by the outlet temperature, and (d3) cooling via the third heat exchanger 35 the second intermediate product mixture 32 from the outlet temperature to the inlet temperature to form a cooled second intermediate product mixture 33; and (iv) a fourth stage comprising (a4) introducing a terminal reactant mixture 41 to a terminal adiabatic reactor 40 comprising the OCM catalyst composition 40a, wherein the terminal reactant mixture 41 comprises at least a portion of the cooled second intermediate product mixture 33, O₂41a, and steam, wherein the terminal reactant mixture 41 is characterized by the inlet temperature, (b4) allowing at least a portion of the terminal reactant mixture 41 to contact at least a portion of the OCM catalyst composition 40a and react via an OCM reaction to form a terminal product mixture 42 comprising unreacted methane and ethylene, wherein an amount of unreacted methane in the terminal product mixture 42 is less than an amount of unreacted methane in the second intermediate product mixture 32, and wherein an amount of ethylene in the terminal product mixture 42 is greater than an amount of ethylene in the second intermediate product mixture 32, (c4) recovering at least a portion of the terminal product mixture 42 from the terminal adiabatic reactor 40, wherein the terminal product mixture 42 is characterized by the outlet temperature, and (d4) cooling via the fourth heat exchanger 45 the terminal product mixture 42 to form a cooled terminal product mixture 43. The method comprises recovering at least a portion of the ethylene from the cooled terminal product mixture 43. The first product mixture 12 can be cooled to produce the cooled first product mixture 13 in the first heat exchanger 15 by heating stream 16 to produce heated stream 17. The first intermediate product mixture 22 can be cooled to produce the cooled first intermediate product mixture 23 in the second heat exchanger 25 by heating stream 26 to produce heated stream 27. The second intermediate product mixture 32 can be cooled to produce the cooled second intermediate product mixture 33 in the third heat exchanger 35 by heating stream 36 to produce heated stream 37. The terminal product mixture 42 can be cooled to produce the cooled terminal product mixture 43 in the fourth heat exchanger 45 by heating stream 46 to produce heated stream 47. In some aspects, the first adiabatic reactor 10; the first intermediate adiabatic reactor 20; the second intermediate adiabatic reactor 30; and the terminal adiabatic reactor 40 can be radial flow reactors.

[_0063] An overall yield, overall methane conversion, overall oxygen conversion, overall selectivity to C₂₊ hydrocarbons, etc. can be calculated across the olefin production system 100 of Figure 1. Selectivities and conversions can generally be calculated for multi-stage processes by using equations (1), (2) and (3), via a mass balance of reactants introduced in any stage (e.g., initial stage, intermediate stage(s), terminal stage) and products and/or unreacted reagents recovered from any stage (e.g., initial stage, intermediate stage(s), terminal stage). For the multi-stage process conducted with the olefin production system 100 of Figure 1, a methane conversion rate, for example, would account for methane introduced in the initial stage and for unconverted methane recovered from the terminal stage. For example, an overall methane conversion across the olefin in multi stage process ^{production system 100 can be calculated by using equation (1), wherein} M

number of moles of methane that was introduced to the olefin production system 100 via the first reactant out multi stage process

m^{ixture 11; and wherein}

o es of moles of methane that was recovered from the olefin production system 100 via the cooled terminal product mixture 43. As yet another example, an overall oxygen conversion across the olefin production system 100 can be calculated by using equation (2), ^wherein of moles of oxygen that was introduced to the olefin

production system 100 via the first reactant mixture 11, O₂ 21a, O₂ 31a, and O₂ 41a; and wherein of moles of oxygen that was recovered from the olefin production

system 100 via the cooled terminal product mixture 43. As still yet another example, an overall C₂₊ selectivity can be calculated by using equation (3), e.g., accounting for how much C₂₊ hydrocarbons were recovered from the olefin production system 100 via the cooled terminal product mixture 43 divided by the total products present in the cooled terminal product mixture 43, including C₂₊ hydrocarbons, CO₂ and CO. An overall yield can be calculated as the multiplication product of overall methane conversion with the overall C₂₊ selectivity. [0064] In an aspect, a method for producing olefins as disclosed herein can advantageously display improvements in one or more method characteristics when compared to an otherwise similar method that does not use multiple adiabatic reactors with a narrow temperature rise in each reactor. The use of adiabatic reactors can result in a lower the cost of the reactors.

[0065] In an aspect, a temperature rise in each reactor can be advantageously controlled by controlling the O₂ supply to each reactor, that is by controlling the methane to O₂ ratio for each reactor. With the use of multiple adiabatic reactors, O₂ is distributed to each reactor, so that the O₂ supply in each reactor is lower, thereby resulting in a higher methane to O₂ ratio, and a lower temperature rise.

[0066] In an aspect, a multi-stage process for producing olefins as disclosed herein can advantageously allow for controlling the temperature rise in each stage to a narrow range. With the narrow temperature rise, a higher C₂₊ selectivity can be obtained, when comparing to a C₂₊ selectivity that can be obtained with other reactor designs which have higher temperature rise, e.g., reactor designs that do not use multiple adiabatic reactors with a narrow temperature rise in each reactor as disclosed herein.

[0067] In an aspect, with a controlled narrow temperature rise, the rate of catalyst deactivation can be advantageously reduced significantly, so that a high performance (e.g., high selectivity) catalyst which tends to deactivate at high temperatures can be used in such reactor designs. Further, the use of a high selectivity catalyst can allow for the production of less deep oxidation products (CO and CO₂) (as compared to the production of deep oxidation products with the use of lower selectivity catalysts), therefore, the temperature rise will be easier to control, which will benefit the catalyst stability and reaction performance.

[0068] The method for producing olefins as disclosed herein can advantageously allow for using the reaction heat generated for heating any suitable process stream via external heat exchange. In some aspects, an external heat exchanger can be used to capture the reaction heat and to heat a feed for the OCM process, and as such the high cost of a furnace for heating the feed can be saved. The method for producing olefins as disclosed herein can advantageously employ a steam diluent for the feed to have a better control of the temperature rise in each stage.

[0069] In an aspect, a method for producing olefins as disclosed herein can advantageously mix oxygen into the reactant mixture at a low temperature to reduce the occurrence gas phase reactions (as opposed to reactions on a catalyst surface).

[0070] In an aspect, a method for producing olefins as disclosed herein can advantageously employ inlet temperatures in each stage that enable the OCM catalyst to display increased selectivity. The outlet temperatures in each stage can advantageously allow for the OCM catalyst to remain stable, active and have increased selectivity. Additional advantages of the methods for the production of olefins as disclosed herein can be apparent to one of skill in the art viewing this disclosure. EXAMPLES

[0071] The subject matter having been generally described, the following examples are given as particular embodiments of the disclosure and to demonstrate the practice and advantages thereof. It is understood that the examples are given by way of illustration and are not intended to limit the specification of the claims to follow in any manner.

EXAMPLE 1

[_0072] A Mn-Na₂WO₄/SiO₂ catalyst (catalyst #1) was prepared as follows. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mn(NO₃)₂·4H₂O (1.73 g) was dissolved in deionized water (18.6 mL), and then added dropwise onto the silica gel. The resulting manganese impregnated silica material was dried overnight. Na₂WO₄·4H₂O (1.13 g) was dissolved in deionized water (18.6 mL), and the solution obtained was added onto the dried manganese silica material above. The resulting material obtained was dried overnight at 125°C, and then calcined at 800°C for 6 hours under airflow to obtain the Mn-Na₂WO₄/SiO₂ catalyst.

[0073] Oxidative coupling of methane (OCM) reactions were conducted as follows. A mixture of methane and oxygen along with an internal standard, an inert gas (neon) were fed to a quartz reactor with an internal diameter (I.D.) of 4 mm heated by a traditional clamshell furnace. A catalyst (e.g., catalyst bed) loading was 100 mg, and a total flow rate of reactants was 33.3 cc/min. The reactor was first heated to a desired temperature under an inert gas flow and then a desired gas mixture was fed to the reactor. With catalyst #1, a methane to O₂ ratio of 16 was used. Methane conversion, oxygen conversion and C₂₊ selectivity were calculated as described previously herein.

[0074] Single stage. With catalyst #1, under CH₄/O₂ = 16, the following results (Table 1) were obtained at 750^oC with 300 mg catalyst loading and 76.7 sccm total flowrate.

[0075] Multi-stage. In a multi-stage process, the local O₂ concentration is reduced, so that the C₂₊ selectivity would be improved. The multi-stage performance was estimated based on experimental data published by Choudary et al., J. Chem. Soc., Chem. Commun., 1989, 1526; which is incorporated by reference herein in its entirety, and which is shown in Table 2. The better performance of Mn-Na₂WO₄/SiO₂ catalyst (catalyst #1) as compared to the performance of the catalyst used by Choudary et al. was also taken into account in the estimation. [0076] With each stage having CH₄/O₂ = 16, to achieve a total CH₄/O₂ = 4.0, 4 stage reactors were needed. The estimated performance is shown in Table 2.

Table 2. Estimated performance for 4 stage operation with a total CH₄/O₂ = 4.0

[0077] The performance of a system employing CH₄/O₂ = 4 without staged operation was also obtained experimentally with catalyst #1, and the resulting data is displayed in Table 3.

Table 3. Single stage results under CH₄/O₂ = 4.0

[0078] The data in Tables 2 and 3 indicate that the staged operation (e.g., multi-stage operation) shows better performance, which can be due to the lowered local O₂ concentration due to the staged system as discussed above.

[0079] With the higher selectivity obtained with staged operation, much less heat was produced in each stage of the four stage operation when compared to the single stage operation in Table 3. Therefore, a lower temperature rise was observed for each reactor in the staged operation, which would result in better selectivity and a much lower rate of catalyst deactivation. EXAMPLE 2

[0080] A 1.0 % Ag-Mn-Na₂WO₄/SiO₂ catalyst (catalyst #2) was prepared as follows. Silica gel (18.6 g, Davisil® Grade 646) was used after drying overnight. Mn(NO₃)₂·4H₂O (1.73 g) was dissolved in deionized water (18.6 mL), and then added dropwise onto the silica gel and the material obtained was dried at 125°C overnight. AgNO₃ (0.32 g) was dissolved in deionized water (18.6 mL), and the solution obtained was added dropwise onto the dried manganese silica gel and the material obtained was dried at 125°C overnight. Na₂WO₄·4H₂O (1.13 g) was dissolved in deionized water (18.6 mL), and the solution obtained was added onto the dried manganese silica material above. The resultant material obtained was dried at 125°C overnight and calcined at 800^oC for 6 hours under airflow to produce catalyst #2.

[0081] Oxidative coupling of methane (OCM) reactions were conducted as described in Example 1 by using catalyst #1 and catalyst #2 at a methane to oxygen molar ratio of 7.4. Methane conversion, oxygen conversion and C₂₊ selectivity were calculated as described previously herein.

[0082] Silver promoted Mn-Na₂WO₄/SiO₂ catalyst (Ag-Mn-Na₂WO₄/SiO₂, catalyst #2) could lower the inlet temperature (T_in). A relatively low outlet temperature (T_out) could be achieved with a low T_in, such that catalyst deactivation could be prevented. The low T_in performance could be achieved by using Ag-Mn-Na₂WO₄/SiO₂ catalyst. The performances of Ag-Mn-Na₂WO₄/SiO₂ catalyst (catalyst #2) and unpromoted Mn-Na₂WO₄/SiO₂ catalyst (catalyst #1) are shown in Figures 2 to 4. For Ag-Mn-Na₂WO₄/SiO₂ catalyst (catalyst #2), much higher conversions were obtained than for Mn-Na₂WO₄/SiO₂ catalyst (catalyst #1). For example, at 700^oC, methane conversion for Mn-Na₂WO₄/SiO₂ catalyst (catalyst #1) was 4.8%, whereas, the methane conversion obtained for Ag-Mn-Na₂WO₄/SiO₂ catalyst (catalyst #2) was 12.8%. With the Ag promoted catalyst, the reaction temperature T_in could be lowered.

[0083] For OCM reactions, generally, the C₂₊ selectivity should be lower at lower reaction temperatures, as described in Sinev et al., J. Natural Gas Chemistry, 18 (2009), 273; which is attached by reference herein in its entirety. However, Ag promoted catalysts show different results. The C₂₊ selectivities obtained for catalysts #1 and #2 are displayed in Figure 4. A higher C₂₊ selectivity was obtained with Ag-Mn-Na₂WO₄/SiO₂ catalyst (catalyst #2) than with the unpromoted catalyst #1. Such results could make it possible for a lower T_in operation without losing performance. Another advantageous feature of catalyst #2 shown in Figure 4 is that the selectivity does not change much with the increase of reaction temperature from 675^oC to 800^oC. Catalyst #2 retained its high selectivity in this temperature range, and this temperature range could be used as the temperature range between T_in and T_out, such that the best performance could be achieved in each stage of the adiabatic operation.

[0084] With the Ag-Mn-Na₂WO₄/SiO₂ catalyst and adiabatic operation with a controlled temperature rise in each stage, high process performance could be achieved. Due to the controlled temperature rise, the catalyst deactivation could be prevented. Therefore, the current disclosure provides a practical process for high performance OCM.

[0085] For the purpose of any U.S. national stage filing from this application, all publications and patents mentioned in this disclosure are incorporated herein by reference in their entireties, for the purpose of describing and disclosing the constructs and methodologies described in those publications, which might be used in connection with the methods of this disclosure. Any publications and patents discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention.

[0086] In any application before the United States Patent and Trademark Office, the Abstract of this application is provided for the purpose of satisfying the requirements of 37 C.F.R. § 1.72 and the purpose stated in 37 C.F.R. § 1.72(b)“to enable the United States Patent and Trademark Office and the public generally to determine quickly from a cursory inspection the nature and gist of the technical disclosure.” Therefore, the Abstract of this application is not intended to be used to construe the scope of the claims or to limit the scope of the subject matter that is disclosed herein. Moreover, any headings that can be employed herein are also not intended to be used to construe the scope of the claims or to limit the scope of the subject matter that is disclosed herein. Any use of the past tense to describe an example otherwise indicated as constructive or prophetic is not intended to reflect that the constructive or prophetic example has actually been carried out.

[0087] The present disclosure is further illustrated by the following examples, which are not to be construed in any way as imposing limitations upon the scope thereof. On the contrary, it is to be clearly understood that resort can be had to various other aspects, embodiments, modifications, and equivalents thereof which, after reading the description herein, can be suggest to one of ordinary skill in the art without departing from the spirit of the present invention or the scope of the appended claims.

ADDITIONAL DISCLOSURE

[0088] A first aspect, which is a method for producing olefins comprising (a) introducing a first reactant mixture to a first reactor comprising a first oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄) and oxygen (O₂), and wherein the first reactant mixture is characterized by a first inlet temperature; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the first OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins; (c) recovering at least a portion of the first product mixture from the first reactor, wherein the first product mixture is characterized by a first outlet temperature, and wherein the first outlet temperature is greater than the first inlet temperature; (d) cooling the first product mixture from the first outlet temperature to a second inlet temperature; (e) introducing a second reactant mixture to a second reactor comprising a second OCM catalyst composition, wherein the second reactant mixture comprises at least a portion of the first product mixture and O₂, wherein the second reactant mixture is characterized by the second inlet temperature, and wherein the first inlet temperature and the second inlet temperature are the same or different; (f) allowing at least a portion of the second reactant mixture to contact at least a portion of the second OCM catalyst composition and react via an OCM reaction to form a second product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the second product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the second product mixture is greater than an amount of olefins in the first product mixture; (g) recovering at least a portion of the second product mixture from the second reactor, wherein the second product mixture is characterized by a second outlet temperature, wherein the second outlet temperature is greater than the second inlet temperature, and wherein the first outlet temperature and the second outlet temperature are the same or different; (h) optionally cooling the second product mixture to form a cooled second product mixture; and (i) recovering at least a portion of the olefins from the second product mixture and/or the cooled second product mixture.

[0089] A second aspect, which is the method of the first aspect, wherein producing olefins is a multi- stage process, wherein a first stage comprises steps (a) through (d), wherein a second stage comprises steps (e) through (h), and wherein the multi-stage process further comprises one or more additional stages downstream of the first stage and/or the second stage, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process.

[0090] A third aspect, which is the method of the second aspect, wherein each additional stage comprises (i) introducing a reactant mixture to a reactor comprising an OCM catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture.

[0091] A fourth aspect, which is the method of the third aspect, wherein the reactant mixture comprises at least a portion of an upstream product mixture recovered from an upstream reactor.

[0092] A fifth aspect, which is the method of any one of the first through the fourth aspects, wherein the reactant mixture comprises at least a portion of a downstream product mixture recovered from a downstream reactor.

[0093] A sixth aspect, which is the method of the second aspect, wherein the multi-stage process has from 3 to about 8 stages. [0094] A seventh aspect, which is the method of any one of the first through the sixth aspects, wherein the first OCM catalyst composition and/or the second OCM catalyst composition comprise an OCM catalyst effective to achieve an oxygen conversion of from about 90% to 100% in the first reactor over a first temperature increase and/or in the second reactor over a second temperature increase, respectively, wherein the first temperature increase is a difference between the first outlet temperature and the first inlet temperature, wherein the second temperature increase is a difference between the second outlet temperature and the second inlet temperature, and wherein the first temperature increase and the second temperature increase are the same or different.

[0095] An eighth aspect, which is the method of the seventh aspect, wherein the first temperature increase and/or the second temperature increase are from about 100^oC to about 300^oC.

[0096] A ninth aspect, which is the method of any one of the first through the eighth aspects, wherein the first OCM catalyst composition and/or the second OCM catalyst composition comprise one or more oxides doped with silver (Ag); and wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof.

[0097] A tenth aspect, which is the method of any one of the first through the ninth aspects, wherein the first OCM catalyst composition and/or the second OCM catalyst composition comprise one or more oxides, wherein the one or more oxides comprises

[0098] An eleventh aspect, which is the method of the tenth aspect, wherein the one or more oxides are doped with silver.

[0099] A twelfth aspect, which is the method of any one of the first through the eleventh aspects, wherein the first inlet temperature and/or the second inlet temperature are from about 550^oC to about 800^oC.

[00100] A thirteenth aspect, which is the method of any one of the first through the twelfth aspects, wherein the first outlet temperature and/or the second outlet temperature are from about 700^oC to about 950^oC.

[00101] A fourteenth aspect, which is the method of any one of the first through the thirteenth aspects, wherein the step (d) of cooling the first product mixture occurs in a first heat exchanger.

[00102] A fifteenth aspect, which is the method of the fourteenth aspect, wherein the first heat exchanger heats a methane feed stream to the first inlet temperature, and wherein the first reactant mixture comprises at least a portion of the heated methane feed stream [00103] A sixteenth aspect, which is the method of any one of the first through the fifteenth aspects, wherein the first heat exchanger heats a stream in a process other than olefin production by OCM, an ethylbenzene feed stream, a stream in a dehydrogenation reaction, a stream in a propane to propylene conversion, or combinations thereof.

[00104] A seventeenth aspect, which is the method of any one of the first through the sixteenth aspects, wherein the first reactor and/or the second reactor are adiabatic reactors.

[00105] An eighteenth aspect, which is the method of any one of the first through the seventeenth aspects, wherein the first reactor and/or the second reactor are fixed bed reactors, axial flow reactors, or radial flow reactors.

[00106] A nineteenth aspect, which is the method of any one of the first through the eighteenth aspects, wherein the first reactor and/or the second reactor are cooled to provide for a first product mixture having the first outlet temperature and/or a second product mixture having the second outlet temperature, respectively.

[00107] A twentieth aspect, which is the method of any one of the first through the nineteenth aspects, wherein the first reactant mixture and/or the second reactant mixture further comprise steam.

[00108] A twenty-first aspect, which is the method of any one of the first through the twentieth aspects, wherein an overall yield is from about 15% to about 50%.

[00109] A twenty-second aspect, which is the method of any one of the first through the twenty-first aspects, wherein an overall methane conversion is from about 15% to 100%.

[00110] A twenty-third aspect, which is the method of any one of the first through the twenty-second aspects, wherein an overall oxygen conversion is from about 90% to 100%.

[00111] A twenty-fourth aspect, which is the method of any one of the first through the twenty-third aspects, wherein an overall C₂₊ selectivity is from about 50% to about 99%.

[00112] A twenty-fifth aspect, which is the method of any one of the first through the twenty-fourth aspects, wherein the second product mixture comprises less than about 15 mol% carbon monoxide (CO) and/or carbon dioxide (CO₂).

[00113] A twenty-sixth aspect, which is the method of any one of the first through the twenty-fifth aspects, wherein the step (h) of optionally cooling the second product mixture occurs in a second heat exchanger, wherein the second heat exchanger heats a methane feed stream to the first inlet temperature, and wherein the first reactant mixture comprises at least a portion of the heated methane feed stream.

[00114] A twenty-seventh aspect, which is the method of the twentieth aspect, wherein steam is present in the first reactant mixture and/or the second reactant mixture in an amount of from about 5% to about 70%, based on the total volume of the first reactant mixture and/or the second reactant mixture, respectively. [00115] A twenty-eighth aspect, which is the method of any one of the first through the twenty-seventh aspects further comprising introducing additional CH₄ to the second reactor.

[00116] A twenty-ninth aspect, which is a method for producing olefins comprising (a) introducing a first reactant mixture to a first adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄), oxygen (O₂) and steam, wherein the first reactant mixture is characterized by an inlet temperature of from about 600^oC to about 700^oC, and wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag); wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins; (c) recovering at least a portion of the first product mixture from the first adiabatic reactor, wherein the first product mixture is characterized by an outlet temperature of from about 750^oC to about 850^oC; (d) cooling the first product mixture from the outlet temperature to the inlet temperature; (e) introducing an intermediate reactant mixture to an intermediate adiabatic reactor comprising the OCM catalyst composition, wherein the intermediate reactant mixture comprises at least a portion of the first product mixture, O₂ and steam, wherein the intermediate reactant mixture is characterized by the inlet temperature; (f) allowing at least a portion of the intermediate reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form an intermediate product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the intermediate product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the intermediate product mixture is greater than an amount of olefins in the first product mixture; (g) recovering at least a portion of the intermediate product mixture from the intermediate adiabatic reactor, wherein the intermediate product mixture is characterized by the outlet temperature; (h) cooling the intermediate product mixture from the outlet temperature to the inlet temperature; (i) introducing a terminal reactant mixture to a terminal adiabatic reactor comprising the OCM catalyst composition, wherein the terminal reactant mixture comprises at least a portion of the intermediate product mixture, O₂ and steam, wherein the terminal reactant mixture is characterized by the inlet temperature; (j) allowing at least a portion of the terminal reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a terminal product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the terminal product mixture is less than an amount of unreacted methane in the intermediate product mixture, and wherein an amount of olefins in the terminal product mixture is greater than an amount of olefins in the intermediate product mixture; (k) recovering at least a portion of the terminal product mixture from the terminal adiabatic reactor, wherein the terminal product mixture is characterized by the outlet temperature; (l) cooling the terminal product mixture to form a cooled terminal product mixture; and (m) recovering at least a portion of the olefins from the cooled terminal product mixture.

[00117] A thirtieth aspect, which is the method of the twenty-ninth aspect, wherein producing olefins is a multi-stage process, wherein the multi-stage process comprises (1) a first stage comprising steps (a) through (d); (2) two or more intermediate stages, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process, wherein each intermediate stage comprises steps (e) through (h); and (3) a terminal stage comprising steps (i) through (m).

[00118] A thirty-first aspect, which is the method of the thirtieth aspect, wherein the two or more intermediate stages comprise two or more intermediate adiabatic reactors, respectively.

[00119] A thirty-second aspect, which is the method of any one of the twenty-ninth through the thirty- first aspects, wherein at least a portion of the intermediate product mixture is recycled to the intermediate adiabatic reactor as the intermediate reactant mixture, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process.

[00120] A thirty-third aspect, which is a multi-stage method for producing olefins, wherein each stage comprises (i) introducing a reactant mixture to an adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture, wherein each stage is characterized by a narrow temperature rise, wherein the narrow temperature rise in each stage is a difference between the outlet temperature for that particular stage and the inlet temperature for that particular stage, and wherein the narrow temperature rise is from about 100^oC to about 300^oC.

[00121] A thirty-fourth aspect, which is the multi-stage method of the thirty-third aspect, wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag), and wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof.

[00122] A thirty-fifth aspect, which is a multi-stage method for producing olefins, wherein each stage comprises (i) introducing a reactant mixture to an adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture, wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag), and wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof.

[00123] A thirty-sixth aspect, which is the multi-stage method of the thirty-fifth aspect, wherein a difference between the outlet temperature and the inlet temperature for a particular stage is from about 100^oC to about 300^oC.

[00124] While aspects of the disclosure have been shown and described, modifications thereof can be made without departing from the spirit and teachings of the invention. The aspects and examples described herein are exemplary only, and are not intended to be limiting. Many variations and modifications of the invention disclosed herein are possible and are within the scope of the invention.

[00125] Accordingly, the scope of protection is not limited by the description set out above but is only limited by the claims which follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated into the specification as an aspect of the present invention. Thus, the claims are a further description and are an addition to the detailed description of the present invention. The disclosures of all patents, patent applications, and publications cited herein are hereby incorporated by reference.

Claims

CLAIMS What is claimed is:

1. A method for producing olefins comprising:

(a) introducing a first reactant mixture to a first reactor comprising a first oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄) and oxygen (O₂), and wherein the first reactant mixture is characterized by a first inlet temperature; (b) allowing at least a portion of the first reactant mixture to contact at least a portion of the first OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins;

(c) recovering at least a portion of the first product mixture from the first reactor, wherein the first product mixture is characterized by a first outlet temperature, and wherein the first outlet temperature is greater than the first inlet temperature;

(d) cooling the first product mixture from the first outlet temperature to a second inlet temperature; (e) introducing a second reactant mixture to a second reactor comprising a second OCM catalyst composition, wherein the second reactant mixture comprises at least a portion of the first product mixture and O₂, wherein the second reactant mixture is characterized by the second inlet temperature, and wherein the first inlet temperature and the second inlet temperature are the same or different;

(f) allowing at least a portion of the second reactant mixture to contact at least a portion of the second OCM catalyst composition and react via an OCM reaction to form a second product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the second product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the second product mixture is greater than an amount of olefins in the first product mixture;

(g) recovering at least a portion of the second product mixture from the second reactor, wherein the second product mixture is characterized by a second outlet temperature, wherein the second outlet temperature is greater than the second inlet temperature, and wherein the first outlet temperature and the second outlet temperature are the same or different;

(h) optionally cooling the second product mixture to form a cooled second product mixture; and (i) recovering at least a portion of the olefins from the second product mixture and/or the cooled second product mixture.

2. The method of claim 1, wherein producing olefins is a multi-stage process, wherein a first stage comprises steps (a) through (d), wherein a second stage comprises steps (e) through (h), and wherein the multi-stage process further comprises one or more additional stages downstream of the first stage and/or the second stage, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process.

3. The method of claim 2, wherein each additional stage comprises (i) introducing a reactant mixture to a reactor comprising an OCM catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture.

4. The process of claim 3, wherein the reactant mixture comprises at least a portion of an upstream product mixture recovered from an upstream reactor.

5. The method of any one of claims 1-4, wherein the reactant mixture comprises at least a portion of a downstream product mixture recovered from a downstream reactor.

6. The method of claim 2, wherein the multi-stage process has from 3 to about 8 stages.

7. The method of any one of claims 1-6, wherein the first OCM catalyst composition and/or the second OCM catalyst composition comprise an OCM catalyst effective to achieve an oxygen conversion of from about 90% to 100% in the first reactor over a first temperature increase and/or in the second reactor over a second temperature increase, respectively, wherein the first temperature increase is a difference between the first outlet temperature and the first inlet temperature, wherein the second temperature increase is a difference between the second outlet temperature and the second inlet temperature, and wherein the first temperature increase and the second temperature increase are the same or different.

8. The method of claim 7, wherein the first temperature increase and/or the second temperature increase are from about 100^oC to about 300^oC.

9. The method of any one of claims 1-8, wherein the first OCM catalyst composition and/or the second OCM catalyst composition comprise one or more oxides doped with silver (Ag); and wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof.

10. The method of any one of claims 1-9, wherein the first OCM catalyst composition and/or the second OCM catalyst composition comprise one or more oxides, wherein the one or more oxides comprises CeO₂,

Sr/Mn-Na₂WO₄, or combinations thereof.

11. The method of any one of claims 1-10, wherein the first inlet temperature and/or the second inlet temperature are from about 550^oC to about 800^oC.

12. The method of any one of claims 1-11, wherein the first outlet temperature and/or the second outlet temperature are from about 700^oC to about 950^oC.

13. The method of any one of claims 1-12, wherein the step (d) of cooling the first product mixture occurs in a first heat exchanger.

14. The method of claim 13, wherein the first heat exchanger heats a methane feed stream to the first inlet temperature, and wherein the first reactant mixture comprises at least a portion of the heated methane feed stream.

15. The method of any one of claims 1-14, wherein the first heat exchanger heats a stream in a process other than olefin production by OCM, an ethylbenzene feed stream, a stream in a dehydrogenation reaction, a stream in a propane to propylene conversion, or combinations thereof.

16. The method of any one of claims 1-15, wherein the first reactor and/or the second reactor are adiabatic reactors.

17. The method of any one of claims 1-16, wherein the step (h) of optionally cooling the second product mixture occurs in a second heat exchanger, wherein the second heat exchanger heats a methane feed stream to the first inlet temperature, and wherein the first reactant mixture comprises at least a portion of the heated methane feed stream.

18. A method for producing olefins comprising:

(a) introducing a first reactant mixture to a first adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the first reactant mixture comprises methane (CH₄), oxygen (O₂) and steam, wherein the first reactant mixture is characterized by an inlet temperature of from about 600^oC to about 700^oC, and wherein the OCM catalyst composition comprises one or more oxides doped with silver (Ag); wherein the one or more oxides comprises a single metal oxide, mixtures of single metal oxides, a mixed metal oxide, mixtures of mixed metal oxides, or combinations thereof;

(b) allowing at least a portion of the first reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a first product mixture comprising unreacted methane and olefins;

(c) recovering at least a portion of the first product mixture from the first adiabatic reactor, wherein the first product mixture is characterized by an outlet temperature of from about 750^oC to about 850^oC; (d) cooling the first product mixture from the outlet temperature to the inlet temperature; (e) introducing an intermediate reactant mixture to an intermediate adiabatic reactor comprising the OCM catalyst composition, wherein the intermediate reactant mixture comprises at least a portion of the first product mixture, O₂ and steam, wherein the intermediate reactant mixture is characterized by the inlet temperature;

(f) allowing at least a portion of the intermediate reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form an intermediate product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the intermediate product mixture is less than an amount of unreacted methane in the first product mixture, and wherein an amount of olefins in the intermediate product mixture is greater than an amount of olefins in the first product mixture;

(g) recovering at least a portion of the intermediate product mixture from the intermediate adiabatic reactor, wherein the intermediate product mixture is characterized by the outlet temperature;

(h) cooling the intermediate product mixture from the outlet temperature to the inlet temperature;

(i) introducing a terminal reactant mixture to a terminal adiabatic reactor comprising the OCM catalyst composition, wherein the terminal reactant mixture comprises at least a portion of the intermediate product mixture, O₂ and steam, wherein the terminal reactant mixture is characterized by the inlet temperature;

(j) allowing at least a portion of the terminal reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a terminal product mixture comprising unreacted methane and olefins, wherein an amount of unreacted methane in the terminal product mixture is less than an amount of unreacted methane in the intermediate product mixture, and wherein an amount of olefins in the terminal product mixture is greater than an amount of olefins in the intermediate product mixture;

(k) recovering at least a portion of the terminal product mixture from the terminal adiabatic reactor, wherein the terminal product mixture is characterized by the outlet temperature;

(l) cooling the terminal product mixture to form a cooled terminal product mixture; and

(m) recovering at least a portion of the olefins from the cooled terminal product mixture.

19. The method of claim 18, wherein producing olefins is a multi-stage process, wherein the multi-stage process comprises (1) a first stage comprising steps (a) through (d); (2) two or more intermediate stages, as necessary to achieve a target methane conversion and/or a target C₂₊ selectivity for the overall multi-stage process, wherein each intermediate stage comprises steps (e) through (h); and (3) a terminal stage comprising steps (i) through (m).

20. A multi-stage method for producing olefins, wherein each stage comprises (i) introducing a reactant mixture to an adiabatic reactor comprising an oxidative coupling of methane (OCM) catalyst composition, wherein the reactant mixture comprises CH₄ and O₂, and wherein the reactant mixture is characterized by an inlet temperature; (ii) allowing at least a portion of the reactant mixture to contact at least a portion of the OCM catalyst composition and react via an OCM reaction to form a product mixture comprising unreacted methane and olefins; (iii) recovering at least a portion of the product mixture from the reactor, wherein the product mixture is characterized by an outlet temperature, and wherein the outlet temperature is greater than the inlet temperature; and (iv) optionally cooling the product mixture,

wherein each stage is characterized by a narrow temperature rise, wherein the narrow temperature rise in each stage is a difference between the outlet temperature for that particular stage and the inlet temperature for that particular stage, and wherein the narrow temperature rise is from about 100^oC to about 300^oC.