FIELD OF INVENTION

[0001] The present invention generally relates to oxidative conversion of methane and more particularly to an integrated process of oxidative coupling of methane (OCM) and catalytic partial oxidation (CPO) of methane to produce mixtures of synthesis gas and C2 hydrocarbons. The present invention further includes compositions containing such mixtures.

BACKGROUND

[0002] With ever increasing demand of petrochemicals and constant change in the dynamics of feedstock prices there has been a need for exploring alternate sources of fuel and feedstock. Methane has the potential of being used extensively as a feedstock for the production of high value chemicals such as ethylene and chemical intermediates such as synthesis gas and olefins. Accordingly, an ongoing need exists for improved processes for the conversion of methane to C ₂ hydrocarbons and synthesis gas.

BRIEF SUMMARY

[0003] The present disclosure relates to a process of producing a mixture of synthesis gas and C ₂ hydrocarbons using an integrated process of oxidative coupling of methane and catalytic partial oxidation of methane. The oxidative coupling of methane and the catalytic partial oxidation of methane may be carried out simultaneously or sequentially.

[0004] Disclosed herein is a process for producing syngas and C ₂ hydrocarbons comprising (a) feeding an oxidative coupling of methane (OCM) reactant mixture to an OCM reaction zone, wherein the OCM reaction zone comprises an OCM catalyst, wherein the OCM reactant mixture comprises methane, oxygen, and optionally carbon dioxide, wherein at least a portion of the OCM reactant mixture reacts in the OCM reaction zone to produce an OCM product mixture, wherein a portion of the methane in the OCM reactant mixture reacts, via an OCM reaction, to produce C ₂ hydrocarbons, and wherein the OCM product mixture comprises C ₂ hydrocarbons, carbon dioxide, hydrogen (H ₂ ), carbon monoxide (CO), water, and methane, (b) feeding a catalytic partial oxidation (CPO) reactant mixture to a CPO reaction zone; wherein the CPO reaction zone comprises a CPO catalyst, wherein the CPO reactant mixture comprises at least a portion of the OCM product mixture, supplemental oxygen, and optionally supplemental carbon dioxide; wherein at least a portion of the CPO reactant mixture reacts in the CPO reaction zone to produce a CPO reaction zone product mixture, wherein a first portion of the methane in the CPO reactant mixture reacts, via a CPO reaction, to produce H ₂ and CO, wherein a second portion of the methane in the CPO reactant mixture optionally reacts, via a dry reforming reaction, to produce H ₂ and CO, wherein the CPO reaction zone product mixture comprises H ₂ , CO, C ₂ hydrocarbons, carbon dioxide, water, and methane, wherein the amount of methane in the CPO reaction zone product mixture is less than the amount of methane in the OCM product mixture, and wherein the amount of hydrogen in the CPO reaction zone product mixture is greater than the amount of hydrogen in the OCM product mixture, and (c) recovering a C ₂ hydrocarbons stream and a syngas stream from the CPO reaction zone product mixture, wherein the syngas stream comprises H ₂ and CO. [0005] Also disclosed herein is a process for producing syngas and C ₂ hydrocarbons comprising feeding a reactant mixture to an oxidative conversion reactor, wherein the reactant mixture comprises methane, oxygen, and optionally carbon dioxide, wherein at least a portion of the reactant mixture reacts in the oxidative conversion reactor to produce an oxidative conversion product mixture, wherein the oxidative conversion reactor comprises an oxidative conversion catalyst system, wherein the oxidative conversion catalyst system comprises an oxidative coupling of methane (OCM) catalyst component and a catalytic partial oxidation (CPO) catalyst component, wherein a first portion of the methane reacts in the presence of the OCM catalyst component, via an OCM reaction, to produce C ₂ hydrocarbons, wherein a second portion of the methane reacts in the presence of the CPO catalyst component, via a CPO reaction, to produce hydrogen (H ₂ ) and carbon monoxide (CO), wherein the OCM catalyst component comprises one or more metal oxides selected from the group consisting of MgO, La ₂ O ₃ , Sm ₂ O ₃ , CaO, Ce ₂ O ₃ , Sr ₁ Ce _0.9 Yb _0.1 O ₃ , and combinations thereof, wherein the CPO catalyst component comprises one or more metals selected from the group consisting of Ni, Fe, Co, Re, Ir, Rh, Ru, Pd, Pt, and combinations thereof, wherein the oxidative conversion catalyst system further comprises a metal oxide support; wherein at least a portion of the OCM catalyst component and/or at least a portion of the CPO catalyst component contact, coat, are embedded in, are supported by, and/or are distributed throughout at least a portion of the metal oxide support, wherein the metal oxide support is selected from the group consisting of Al ₂ O ₃ , TiO ₂ , La ₂ O ₃ , Sm ₂ O ₃ , Ce ₂ O ₃ , MgO, CaO, and combinations thereof, wherein the OCM catalyst component and the metal oxide support are the same or different, and wherein the oxidative conversion product mixture comprises C ₂ hydrocarbons, syngas, carbon dioxide, water, and methane; and wherein the syngas comprises H ₂ and CO.

[0006] Other objects, features and advantages of the present invention will become apparent from the following figures, detailed description, and examples. It should be understood, however, that the figures, detailed description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. Additionally, it is contemplated that changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. In further embodiments, features from specific embodiments may be combined with features from other embodiments. For example, features from one embodiment may be combined with features from any of the other embodiments. In further embodiments, additional features may be added to the specific embodiments described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] For a more complete understanding, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

[0008] FIG. 1 is a flow diagram for an integrated process of oxidative coupling of methane (OCM) and catalytic partial oxidation (CPO) of methane to produce mixtures of synthesis gas and C ₂ hydrocarbons; [0009] FIG. 2 is a flow diagram for an integrated process of oxidative coupling of methane (OCM) and catalytic partial oxidation (CPO) of methane to produce mixtures of synthesis gas and C ₂ hydrocarbons comprising distributed oxygen addition;

[0010] FIG. 3 is a flow diagram for an integrated process of oxidative coupling of methane (OCM) and catalytic partial oxidation (CPO) of methane to produce mixtures of synthesis gas and C ₂ hydrocarbons comprising distributed oxygen addition and carbon dioxide recycle;

[0011] FIG. 4 is a graphical representation of the combined productivity rate for the production of synthesis gas and C ₂ hydrocarbons produced from the processes illustrated under Examples 1-5; and

[0012] FIG. 5 is a graphical representation of the methane slip as impurity present in the product mixtures obtained from the processes illustrated under Examples 1-5.

[0013] FIG.6 is a graphical representation of methane conversion per mole of methane feed with C ₂ yields per mole of methane feed.

DETAILED DESCRIPTION OF THE INVENTION

[0014] The following includes definitions of various terms and phrases used throughout this specification.

[0015] The terms“about” or“approximately” are defined as being close to as understood by one of ordinary skill in the art. In one non-limiting embodiment the terms are defined to be within 10%, preferably, within 5%, more preferably, within 1%, and most preferably, within 0.5%.

[0016] The terms“wt.%”,“vol.%” or“mol.%” refers to a weight, volume, or molar percentage of a component, respectively, based on the total weight, the total volume, or the total moles of a composition that includes the component. In a non-limiting example, 10 moles of component in 100 moles of the composition is 10 mol.% of component.

[0017] The term“methane slip” means unconverted methane as impurity present in the mixture of synthesis gas and C2 hydrocarbons produced from oxidative conversion of methane.

[0018] The term“Oxidative Coupling of Methane” means a thermodynamically exothermic process for the production of C ₂ hydrocarbons such as ethylene and ethane from methane using a free radical coupling mechanism in presence of a metal oxide catalyst. Some amount of carbon dioxide, carbon monoxide and steam may also be generated as well.

[0019] The term“Partial Oxidation of Methane” means a thermodynamically exothermic process for the production of synthesis gas from methane in presence of oxygen and a metal based catalyst.

[0020] The term“standalone” in relation to any process means a single unit operation instead of an integrated process involving one or more process operating together or in tandem. For clarification standalone OCM process means a single operation involving oxidative coupling of methane.

[0021] The term“reformation of methane” or“methane reforming” means a thermodynamically endothermic process involving the reaction of methane with carbon dioxide and/or water to produce synthesis gas. [0022] The term“synthesis gas” or“syn gas” means a gaseous mixture comprising primarily, consisting of, or consisting essentially, of carbon monoxide and hydrogen.

[0023] The term“C ₂ hydrocarbons” means hydrocarbons having two carbon atoms and includes mixtures of ethane and ethylene.

[0024] The term“conversion” means the mole fraction of a reactant converted to a product or products.

[0025] The term“selectivity” means the percent of reactant that went to a specified product.

[0026] The use of the words“a” or“an” when used in conjunction with the term“comprising,” “including,”“containing,” or“having” in the claims or the specification may mean“one,” but it is also consistent with the meaning of“one or more,”“at least one,” and“one or more than one.”

[0027] The words“comprising” (and any form of comprising, such as“comprise” and“comprises”), “having” (and any form of having, such as“have” and“has”),“including” (and any form of including, such as“includes” and“include”) or“containing” (and any form of containing, such as“contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0028] The process of the present invention can“comprise,”“consist essentially of,” or“consist of” particular ingredients, components, compositions, steps, sequences, etc., disclosed throughout the specification.

[0029] The present disclosure relates to an integrated process of oxidative coupling of methane (OCM) and catalytic partial oxidation (CPO) of methane to produce a mixture of C ₂ hydrocarbons and synthesis gas (i.e., syngas) comprising carbon monoxide (CO) and hydrogen (H ₂ ). Referring to Fig. 1, a reaction zone 120 is configured to effectuate (e.g., having suitable catalysts and reaction conditions) the oxidative coupling of methane (OCM) reaction and the catalytic partial oxidation (CPO) reaction of methane. Reaction zone 120 also can be referred to as an oxidative conversion zone comprising an oxidative conversion catalyst system. The reaction zone 120 can comprise one or more oxidative conversion reactors, and the oxidative conversion catalyst system can comprise an OCM catalyst component further comprising one or more OCM catalysts and a CPO catalyst component further comprising one or more CPO catalysts. Within the reaction zone 120 a reactant mixture comprising methane, oxygen, and optionally carbon dioxide is contacted with the oxidative conversion catalyst system (e.g., an OCM catalyst component and a CPO catalyst component) under reaction conditions suitable to produce an oxidative conversion product mixture (e.g., stream 109) comprising C ₂ hydrocarbons (e.g., ethane and ethylene), syngas (i.e., carbon monoxide (CO) and hydrogen (H ₂ )), carbon dioxide, water, and methane. The OCM and CPO reactions may be carried out simultaneously (e.g., in a common reaction zone having comingled OCM and CPO catalysts) or sequentially (e.g., an upstream OCM reaction zone comprising an OCM catalyst feeding a downstream CPO reaction zone comprising a CPO catalyst), as described in more detail herein. [0030] Within the reaction zone 120, the OCM catalyst component and the CPO catalyst component may be physically blended, mixed or commingled together, for example as a uniform or homogeneous mixture or blend of one or more OCM catalysts with one or more CPO catalysts. Additionally or alternatively, an OCM catalyst component (e.g., an OCM catalytic metal of the type described herein) and a CPO catalyst component (e.g., a CPO catalytic metal of the type described herein) may be combined on a common structural support (e.g., an inert support) to yield a dual function OCM/CPO catalyst. A homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts and/or a dual function OCM/CPO catalyst may be contained within a common reactor vessel, for example within one or more catalyst beds housed within the common reactor vessel. Alternatively, a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts and/or a dual function OCM/CPO catalyst may be distributed across a plurality of reactor vessels, for example two or more reactor vessels in parallel.

[0031] In addition to or as an alternative to (i) a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts within reaction zone 120 and/or (ii) a dual function OCM/CPO catalyst within reaction zone 120, the OCM catalyst component may be contained in one or more zones that are separate and distinct from one or more zones comprising the CPO catalyst component. For example, the reaction zone 120 may have one or more OCM reaction zones 105 comprising one or more OCM catalysts and one or more CPO reaction zones 110 comprising one or more CPO catalysts. The one or more OCM reaction zones 105 and the one or more CPO reaction zones 110 may be contained within a common reactor vessel, for example one or more OCM catalyst beds upstream from one or more CPO catalyst beds within the common reactor vessel. Alternatively, the one or more OCM reaction zones 105 and the one or more CPO reaction zones 110 may be contained is separate reactor vessel, for example one or more OCM catalyst beds in a reactor vessel that is upstream from a reactor vessel comprising one or more CPO catalyst beds.

[0032] For illustrative purposes, Figures 1-3 each show a reaction zone 120 comprising an upstream OCM reaction zone 105 (comprising an OCM catalyst) and a downstream CPO reaction zone 110 (comprising a CPO catalyst). It should be understood that reaction zone 120 of Figures 1-3 may be implemented within a common reactor vessel (e.g., a OCM catalyst bed upstream from a CPO catalyst bed in a common reactor vessel) and/or implemented in separate reactor vessels (e.g., an OCM catalyst disposed within a first OCM reactor vessel upstream from a CPO catalyst disposed within a separate, second CPO reactor vessel). Figures 1-3 also show stream 106 flowing from upstream OCM reaction zone 105 to downstream CPO reaction zone 110. It should be understood that stream 106 represents the flow of an effluent composition from the OCM reaction zone 105 as a feed to the CPO reaction zone 110 regardless of the specific reactor configuration utilized in reaction zone 120. For example, within a common reactor vessel, stream 106 represents the flow of an effluent composition from an upstream OCM catalyst bed as feed to a downstream CPO catalyst bed with the common reactor vessel, and the upstream OCM catalyst bed may be positioned adjacent to or positioned a distance apart from the downstream CPO catalyst bed. For example, with separate reactor vessels, stream 106 represents flow of an effluent stream exiting the upstream OCM reactor vessel and flowing as feed to a downstream CPO reactor vessel, and the upstream OCM reactor vessel may be positioned adjacent to or positioned a distance apart from the downstream CPO reactor vessel.

[0033] With reference to Figures 1-3, an integrated process for the production of C2 hydrocarbons and syngas is shown including the steps of a) conducting the oxidative coupling of methane (OCM) in presence of a first catalyst component in an oxidative coupling reaction zone, and forming an OCM product stream comprising a mixture of C ₂ hydrocarbons, hydrogen, carbon monoxide, methane, carbon dioxide, and water (e.g., steam); and subsequently b) introducing at least a portion of the OCM product stream, in presence of oxygen, into a catalytic partial oxidative (CPO) reaction zone containing a second catalyst component and conducting the partial oxidation of methane and forming a CPO product stream comprising a mixture of hydrogen, carbon monoxide, C ₂ hydrocarbons, carbon dioxide, water, and methane. A syngas product stream and a C2 hydrocarbons product stream can be further separated and recovered from the CPO product stream.

[0034] The ratio of mole fraction of synthesis gas to C ₂ hydrocarbons present in the oxidative conversion product mixture (e.g., stream 109) ranges from 25 to 32, alternatively 26 to 30, or alternatively from 27 to 29. The oxidative conversion product mixture (e.g., stream 109) may further include carbon dioxide, water (e.g., steam) and some amount of unconverted methane as slip. The oxidative conversion product mixture (e.g., stream 109) can have a ratio of H ₂ /CO ranging from 1.9:1 to 2.2:1, alternatively a ratio ranging from 1.95:1 to 2.15:1, or alternatively a ratio ranging from 1.97:1 to 2.12:1. The oxidative conversion product mixture (e.g., stream 109) can have a methane concentration (e.g., methane slip concentration) in a range of from about 0.1 mol% to about 6 mol%, alternatively from about 0.1 mol% to about 5 mol%, alternatively about 0.1 mol% to about 4 mol%, alternatively about 0.1 mol% to about 3 mol%, alternatively about 0.1 mol% to about 2 mol%, alternatively about 0.1 mol% to about 1 mol%, or alternatively from about 2 mol% to about 4 mol%, based upon the total moles in the oxidative conversion product mixture. At such low concentration of methane as slip, the oxidative conversion product mixture (e.g., stream 109) or further product streams recovered therefrom (e.g., syngas stream 112) can be further used for downstream production of high value chemicals such as methanol, FT liquids, DME without additional methane removal steps. In general, it has been observed that a standalone OCM process, a standalone partial oxidation process, or a standalone methane reformation processes has a large amount of methane as slip which makes the direct utilization of synthesis gas or other products difficult for further downstream applications (absent additional costly methane removal steps).

[0035] The synthesis gas and C ₂ hydrocarbons are produced in reaction zone 120 (e.g., present in the oxidative conversion product mixture (e.g., stream 109)) at a combined productivity rate ranging from about 1.3 ton to about 1.9 ton per ton of methane feed to reaction zone 120, alternatively from about 1.35 ton to about 1.8 ton per ton of methane feed to reaction zone 120, alternatively from about 1.4 ton to about 1.8 ton per ton of methane feed to reaction zone 120, or alternatively from about 1.5 ton to about 1.7 ton per ton of methane feed to reaction zone 120. At such high productivity rate, the overall process economics are excellent. In general OCM process or partial oxidation process are capital intensive in nature, and hence any invention or technical advancement which demonstrates improved productivity rate by leveraging both the processes, will be useful to the efforts currently seen in the petrochemical industry for alternate feedstock and processing techniques. Although synthesis gas is the primary product formed from the process of the present invention, the amount of C ₂ hydrocarbons produced is comparable to standalone OCM processes dedicated for the production of C ₂ hydrocarbons. Particularly, the synthesis gas are produced in reaction zone 120 (e.g., present in the oxidative conversion product mixture (e.g., stream 109)) at a productivity rate ranging from 1.35 ton to 1.55 ton per ton of methane feed to reaction zone 120, alternatively from 1.4 to 1.5 ton per ton of methane feed to the reaction zone 120, and the C ₂ hydrocarbons are produced in reaction zone 120 (e.g., present in the oxidative conversion product mixture (e.g., stream 109)) at a productivity rate ranging from about 0.13 ton to about 0.15 ton per ton of methane feed to reaction zone 120, alternatively from about 0.14 ton to about 0.148 ton per ton of methane feed to reaction zone 120. The overall productivity rate of C ₂ hydrocarbons is comparable to standalone OCM processes thus indicating that the extent of C ₂ hydrocarbons conversion to CO _x products via catalytic partial oxidation (e.g., in the CPO reaction zone (110)) is substantially regulated.

[0036] The overall conversion of methane in reaction zone 120 is greater than about 80% to about 100 % per mole of methane feed to reaction zone 120, alternatively, in a range of from about 80% to about 99% per mole of methane feed to reaction zone 120, alternatively, in a range of from about 85% to about 99% per mole of methane feed to reaction zone 120, alternatively in a range of from about 88% to about 95% per mole of methane feed to reaction zone 120, or alternatively in a range of from about 90% to about 92% per mole of methane feed to reaction zone 120. Overall methane conversion across reaction zone 120 may be calculated using the formula (I) below:

[0037] At such high conversion of methane, the extent of unconverted methane as slip is minimized and the overall productivity rate is also improved. Based on the teachings of existing literature, it may have been expected that at such high methane conversion the yield of C ₂ hydrocarbons would have been less than 10% per mole of methane feed with substantial amount of C ₂ hydrocarbons converted to CO _x products through non-selective conversion.

[0038] The overall C ₂ hydrocarbon yield in reaction zone 120 is in a range from about 15% to about 20%, alternatively in a range of from about 16% to about 18% based on the moles of methane feed to the reaction zone 120. The yield of C ₂ hydrocarbons may be calculated using the formula (II) as shown below:

While the selectivity of C2 hydrocarbons produced in reaction zone 120 may be lower than what a standalone OCM process would achieve, the high methane conversion achieved from the present inventive process, makes the overall yield of C ₂ hydrocarbons extremely favorable. In embodiments of the present invention the C ₂ hydrocarbons yield is in a range of from about 15% to about 20% per mole of methane feed to the reaction zone 120 with an overall methane conversion greater than about 80% to about 100% per mole of methane feed to the reaction zone 120.

[0039] The oxidative conversion product mixture (e.g., stream 109) may be introduced to a separation zone 115 for separating the constituents of the oxidative conversion product mixture and thereafter recovering one or more product streams such as a carbon dioxide stream 111, a syngas stream 112 (e.g., CO and H ₂ ), C ₂ hydrocarbon stream 113 (e.g., ethane and ethylene), and water stream 114. Separation zone 115 may comprise any separation equipment suitable to separate and recover one or more components from the oxidative conversion product mixture, for example one or more fractionators, distillation columns, cryogenic separators (e.g., cryogenic distillation), absorbers (e.g., pressure swing absorbers), membrane separators, etc. The separation of carbon dioxide to yield CO ₂ stream 111 may be effected through the use of any of the commonly employed techniques including CO ₂ removal by amine (e.g., monoethanolamine) absorption (e.g., amine scrubbing), pressure swing adsorption (PSA), temperature swing adsorption, gas separation membranes (e.g., porous inorganic membranes, palladium membranes, polymeric membranes, zeolites, etc.), cryogenic separation, and the like, or combinations thereof. In an aspect, CO ₂ is removed from the oxidative conversion product mixture via amine absorption to yield CO ₂ stream 111. The oxidative conversion product mixture stream 109 is at a temperature lower than the temperature of the stream 108. The lowering of temperature is due to endothermic reformation reactions of methane with carbon dioxide and methane. In embodiments of the present invention the temperature of the product mixture (109) ranges from 850 ºC to 920 ºC, alternatively from 850 ºC to 910 ºC, or alternatively from 870 ºC to 900 ºC.

[0040] In an aspect, the syngas stream (e.g., stream 112) recovered from the oxidative conversion product mixture comprises methane in an amount of from about 0.1 mol% to about 6 mol%, alternatively from about 0.1 mol% to about 5 mol%, alternatively about 0.1 mol% to about 4 mol%, alternatively about 0.1 mol% to about 3 mol%, alternatively about 0.1 mol% to about 2 mol%, or alternatively about 0.1 mol% to about 1 mol%. In an aspect, the syngas stream (e.g., stream 112) recovered from the oxidative conversion product mixture has a ratio of H ₂ /CO in a ratio ranging from 1.9:1 to 2.2:1, alternatively in a ratio ranging from 1.95:1 to 2.15:1, or alternatively in a ratio ranging from 1.97:1 to 2.12:1. Thus, the syngas (e.g., stream 112) produced in accordance with the present invention, has a beneficial stoichiometric mix of hydrogen (H ₂ ) and carbon monoxide (CO) required for downstream application with minimal amount of additional purification or processing adjustments

[0041] Referring to Figs. 1– 3, a reactant mixture comprising methane, oxygen, and optionally carbon dioxide can be preheated in preheat zone 100, and the preheated reaction mixture is fed via stream 104 to reaction zone 120, wherein at least a portion of the preheated reactant mixture reacts in the oxidative conversion zone comprising an oxidative conversion catalyst system to produce an oxidative conversion product mixture as described herein. Methane, oxygen, and optionally carbon dioxide can be combined upstream of the preheat zone 103 and introduced to preheat zone 103 as a combined stream. Alternatively, as shown in Fig.1, the methane can be fed to preheat zone 100 via stream 101, the oxygen can be fed to preheat zone via a separate stream 102/103, optional carbon dioxide can be fed to preheat zone via a separate stream (e.g., like stream 111 in Fig. 3), and the methane, oxygen, optional carbon dioxide may be combined and heated within preheat zone 100 and fed via stream 104 to reaction zone 104. In an aspect, the reaction mixture is preheated to at least 400 ºC, prior to being fed via stream 104 to reaction zone 120.

[0042] In an aspect, the reaction mixture fed via stream 104 is a gaseous mixture. In addition to methane, oxygen, and optional carbon dioxide, the reaction mixture can comprise ethane, propane, butane, pentane, or combinations thereof. The O ₂ used in the reactant mixture 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. The oxygen may be obtained, for example, via membrane separation. In an aspect, the reaction mixture fed via stream 104 comprises hydrocarbons, and the hydrocarbons comprise equal to or greater than about 90% methane, alternatively, equal to or greater than about 95% methane, alternatively equal to or greater than about 99% methane, based on the total moles of hydrocarbons in the reactant mixture. In an aspect, the stream 101 comprises natural gas and stream 102 comprises oxygen. In an aspect, stream 104 consists essentially of, or consists of, methane, oxygen, and optionally carbon dioxide at a temperature of equal or greater than about 400 ºC.

[0043] Referring to process 100 of Fig. 1, the reaction zone 120 can comprise OCM reaction zone 105 upstream of CPO reaction zone 110, wherein a preheated oxidative coupling of methane (OCM) reactant mixture is fed via stream 104 to the OCM reaction zone 105; wherein the OCM reaction zone 105 comprises an OCM catalyst; wherein the OCM reactant mixture comprises methane, oxygen, and optionally carbon dioxide; wherein at least a portion of the OCM reactant mixture reacts in the OCM reaction zone 105 to produce an OCM product mixture represented by stream 106; wherein a portion of the methane in the OCM reactant mixture reacts, via an OCM reaction, to produce C ₂ hydrocarbons; and wherein the OCM product mixture comprises C ₂ hydrocarbons, carbon dioxide, hydrogen (H ₂ ), carbon monoxide (CO), water, and methane. A catalytic partial oxidation (CPO) reactant mixture is fed to the CPO reaction zone 110; wherein the CPO reaction zone comprises a CPO catalyst; wherein the CPO reactant mixture comprises at least a portion of the OCM product mixture as represented by stream 106, optionally supplemental carbon dioxide (supplemental indicating that an amount of carbon dioxide is initially (but not necessarily) present in the reactant mixture fed via stream 104 to the OCM reaction zone 105); wherein at least a portion of the CPO reactant mixture reacts in the CPO reaction zone to produce a CPO reaction zone product mixture recovered via stream 109; wherein a first portion of the methane in the CPO reactant mixture reacts, via a CPO reaction, to produce H ₂ and CO; wherein a second portion of the methane in the CPO reactant mixture optionally reacts, via a dry reforming reaction, to produce H ₂ and CO; wherein the CPO reaction zone product mixture comprises H ₂ , CO, C ₂ hydrocarbons, carbon dioxide, water, and methane; wherein the amount of methane in the CPO reaction zone product mixture is less than the amount of methane in the OCM product mixture; and wherein the amount of hydrogen in the CPO reaction zone product mixture is greater than the amount of hydrogen in the OCM product mixture. A C ₂ hydrocarbons stream (113) and a syngas stream (112) are recovered in separation zone 115 from the CPO reaction zone product mixture stream 109, wherein the syngas stream comprises H ₂ and CO. A water stream 114 and a carbon dioxide stream 111 are recovered from separation zone 115, and all or a portion of the carbon dioxide stream 111 may optionally be recycled (referred to herein as optional carbon dioxide recycle), for example (A) recycled to the reactant mixture fed via stream 104 (e.g., via recycle of all or a portion of carbon dioxide stream 111 to preheat zone 100 as shown in Fig.3); (B) recycled and fed to the reaction zone 120 at one or more locations downstream of the location where stream 104 is fed to the reaction zone 120 (e.g., via recycle of all or a portion of carbon dioxide stream 111 to reaction zone 120 via stream 122 as shown in Fig. 3, which may be referred to as supplemental carbon dioxide when carbon dioxide is present in the reactant mixture fed via stream 104 to reaction zone 120); or both (A) and (B), which is referred to herein as distributed or staged carbon dioxide recycle.

[0044] Referring to process 200 of Fig.2, process 200 is similar to process 100 except that oxygen is added to the reaction zone 120 in two or more separate locations, which may be referred to herein as distributed or staged oxygen addition. As shown in Fig.2, oxygen is added to reaction zone 120 at a first location where the reactant mixture is introduced via stream 104 and supplemental oxygen is added to reaction zone 120 at one or more additional locations (e.g., a second location corresponding to stream 107) that is downstream from the first location. Referring to process 200 of Fig.2, the reaction zone 120 can comprise OCM reaction zone 105 upstream of CPO reaction zone 110, wherein a preheated oxidative coupling of methane (OCM) reactant mixture is fed via stream 104 to the OCM reaction zone 105; wherein the OCM reaction zone 105 comprises an OCM catalyst; wherein the OCM reactant mixture comprises methane, oxygen, and optionally carbon dioxide; wherein at least a portion of the OCM reactant mixture reacts in the OCM reaction zone 105 to produce an OCM product mixture represented by stream 106; wherein a portion of the methane in the OCM reactant mixture reacts, via an OCM reaction, to produce C ₂ hydrocarbons; and wherein the OCM product mixture comprises C ₂ hydrocarbons, carbon dioxide, hydrogen (H ₂ ), carbon monoxide (CO), water, and methane. A catalytic partial oxidation (CPO) reactant mixture is fed via stream 108 to the CPO reaction zone 110; wherein the CPO reaction zone comprises a CPO catalyst; wherein the CPO reactant mixture comprises at least a portion of the OCM product mixture as represented by stream 106, supplemental oxygen as represented by stream 107, and optionally supplemental carbon dioxide (supplemental indicating that an amount of carbon dioxide is initially (but not necessarily) present in the reactant mixture fed via stream 104 to the OCM reaction zone 105); wherein at least a portion of the CPO reactant mixture reacts in the CPO reaction zone to produce a CPO reaction zone product mixture recovered via stream 109; wherein a first portion of the methane in the CPO reactant mixture reacts, via a CPO reaction, to produce H ₂ and CO; wherein a second portion of the methane in the CPO reactant mixture optionally reacts, via a dry reforming reaction, to produce H ₂ and CO; wherein the CPO reaction zone product mixture comprises H ₂ , CO, C ₂ hydrocarbons, carbon dioxide, water, and methane; wherein the amount of methane in the CPO reaction zone product mixture is less than the amount of methane in the OCM product mixture; and wherein the amount of hydrogen in the CPO reaction zone product mixture is greater than the amount of hydrogen in the OCM product mixture. A C ₂ hydrocarbons stream (113) and a syngas stream (112) are recovered in separation zone 115 from the CPO reaction zone product mixture stream 109, wherein the syngas stream comprises H ₂ and CO. A water stream 114 and a carbon dioxide stream 111 are recovered from separation zone 115, and all or a portion of the carbon dioxide stream 111 may optionally be recycled (e.g., as described with reference to Fig.3).

[0045] Referring to process 300 of Fig. 3, process 300 is similar to process 200 except that carbon dioxide is recycled and added at one or more locations to the reaction zone 120. Distributed carbon dioxide recycle refers to adding recycled carbon dioxide at two or more locations to the reaction zone 120. As shown in Fig.3, carbon dioxide stream 111 is (A) recycled and fed to reaction zone 120 at a first location corresponding to where the reactant mixture is introduced via stream 104 (e.g., via recycle of all or a portion of carbon dioxide stream 111 to preheat zone 100 as shown in Fig. 3); (B) recycled and fed to the reaction zone 120 at one or more locations downstream of the location where stream 104 is fed to the reaction zone 120 (e.g., via recycle of all or a portion of carbon dioxide stream 111 to reaction zone 120 via stream 122 as shown in Fig. 3, which may be referred to as supplemental carbon dioxide when carbon dioxide is present in the reactant mixture fed via stream 104 to reaction zone 120); or both (A) and (B), which is referred to herein as distributed carbon dioxide recycle. Referring to process 300 of Fig. 3, the reaction zone 120 can comprise OCM reaction zone 105 upstream of CPO reaction zone 110, wherein a preheated oxidative coupling of methane (OCM) reactant mixture is fed via stream 104 to the OCM reaction zone 105; wherein the OCM reaction zone 105 comprises an OCM catalyst; wherein the OCM reactant mixture comprises methane, oxygen, and recycled carbon dioxide via stream 111; wherein at least a portion of the OCM reactant mixture reacts in the OCM reaction zone 105 to produce an OCM product mixture represented by stream 106; wherein a portion of the methane in the OCM reactant mixture reacts, via an OCM reaction, to produce C2 hydrocarbons; and wherein the OCM product mixture comprises C ₂ hydrocarbons, carbon dioxide, hydrogen (H ₂ ), carbon monoxide (CO), water, and methane. A catalytic partial oxidation (CPO) reactant mixture is fed via stream 108 to the CPO reaction zone 110; wherein the CPO reaction zone comprises a CPO catalyst; wherein the CPO reactant mixture comprises at least a portion of the OCM product mixture as represented by stream 106, supplemental oxygen as represented by stream 107, and optionally supplemental carbon dioxide via stream 122; wherein at least a portion of the CPO reactant mixture reacts in the CPO reaction zone to produce a CPO reaction zone product mixture recovered via stream 109; wherein a first portion of the methane in the CPO reactant mixture reacts, via a CPO reaction, to produce H ₂ and CO; wherein a second portion of the methane in the CPO reactant mixture optionally reacts, via a dry reforming reaction, to produce H ₂ and CO; wherein the CPO reaction zone product mixture comprises H ₂ , CO, C ₂ hydrocarbons, carbon dioxide, water, and methane; wherein the amount of methane in the CPO reaction zone product mixture is less than the amount of methane in the OCM product mixture; and wherein the amount of hydrogen in the CPO reaction zone product mixture is greater than the amount of hydrogen in the OCM product mixture. A C ₂ hydrocarbons stream (113) and a syngas stream (112) are recovered in separation zone 115 from the CPO reaction zone product mixture stream 109, wherein the syngas stream comprises H ₂ and CO. A water stream 114 and a carbon dioxide stream 111 are recovered from separation zone 115, and all or a portion of the carbon dioxide stream 111 is recycled as described above.

[0046] In additional process configurations of Figs. 1– 3, as an alternative to reaction zone 120 comprising a distinct OCM reaction zone 105 that is separate and upstream from a distinct CPO reaction zone 110, the OCM and CPO reactions may be carried out simultaneously (e.g., in a common reaction zone having comingled OCM and CPO catalysts). For example the reaction zone 120 of Figs. 1– 3 can comprise (i) a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts; (ii) a dual function OCM/CPO catalyst; or (iii) both (i) and (ii), as described in more detail herein. Within the reaction zone 120 of Figs. 1– 3, the OCM catalyst component and the CPO catalyst component may be physically blended, mixed or commingled together, for example as a uniform or homogeneous mixture or blend of one or more OCM catalysts with one or more CPO catalysts. Additionally or alternatively, an OCM catalyst component (e.g., an OCM catalytic metal of the type described herein) and a CPO catalyst component (e.g., a CPO catalytic metal of the type described herein) may be combined on a common structural support (e.g., an inert support) to yield a dual function OCM/CPO catalyst. Reaction zone 120 of Figures 1– 3 can comprise a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts and/or a dual function OCM/CPO catalyst contained within a common reactor vessel, for example within one or more catalyst beds housed within the common reactor vessel. For example, reaction zone 120 of Fig. 1 can comprise a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts and/or a dual function OCM/CPO catalyst contained within a common reactor vessel, wherein reaction zone 120 further comprises carbon dioxide recycle (e.g., recycle of stream 111); distributed carbon dioxide recycle (e.g., recycle of carbon dioxide via stream 111 and supplemental carbon dioxide via stream 122 as shown in Fig. 3); distributed oxygen addition (e.g., oxygen addition via stream 103 and supplemental oxygen addition via stream 107 in Fig. 2); or both distributed carbon dioxide recycle (e.g., recycle of carbon dioxide via stream 111 and supplemental carbon dioxide via stream 122 as shown in Fig. 3) and distributed oxygen addition (e.g., oxygen addition via stream 103 and supplemental oxygen addition via stream 107 in Fig. 3). Alternatively, reaction zone 120 of Figures 1– 3 can comprise a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts and/or a dual function OCM/CPO catalyst distributed across a plurality of reactor vessels, for example two or more reactor vessels in parallel. For example, reaction zone 120 of Figure 1 can comprise a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts and/or a dual function OCM/CPO catalyst distributed across a plurality of reactor vessels, e.g., two or more reactor vessels in parallel, wherein reaction zone 120 further comprises carbon dioxide recycle (e.g., recycle of stream 111); distributed carbon dioxide recycle (e.g., recycle of carbon dioxide via stream 111 and supplemental carbon dioxide via stream 122 as shown in Fig. 3); distributed oxygen addition (e.g., oxygen addition via stream 103 and supplemental oxygen addition via stream 107 in Fig. 2); or both distributed carbon dioxide recycle (e.g., recycle of carbon dioxide via stream 111 and supplemental carbon dioxide via stream 122 as shown in Fig. 3) and distributed oxygen addition (e.g., oxygen addition via stream 103 and supplemental oxygen addition via stream 107 in Fig. 3). A process for producing syngas and C ₂ hydrocarbons can comprise feeding a reactant mixture to a reaction zone 120 comprising a oxidative conversion reactor; wherein the reactant mixture is fed to the oxidative conversion reactor at a first location and comprises methane, oxygen, and optionally carbon dioxide; wherein at least a portion of the reactant mixture reacts in the oxidative conversion reactor to produce an oxidative conversion product mixture; wherein the oxidative conversion reactor comprises an oxidative conversion catalyst system; wherein the oxidative conversion catalyst system comprises an oxidative coupling of methane (OCM) catalyst component and a catalytic partial oxidation (CPO) catalyst component; wherein a first portion of the methane reacts in the presence of the OCM catalyst component, via an OCM reaction, to produce C ₂ hydrocarbons; wherein a second portion of the methane reacts in the presence of the CPO catalyst component, via a CPO reaction, to produce hydrogen (H ₂ ) and carbon monoxide (CO); wherein the oxidative conversion product mixture comprises C ₂ hydrocarbons, syngas, carbon dioxide, water, and methane; wherein the syngas comprises H ₂ and CO; and wherein, optionally, oxygen, carbon dioxide or both are added to the oxidative conversion reactor at a second location that is downstream from the first location. A process for producing syngas and C ₂ hydrocarbons can comprise feeding a reactant mixture to a reaction zone 120 comprising a oxidative conversion reactor; wherein the oxidative conversion reactor comprises (i) a homogeneous mixture of one or more OCM catalysts with one or more CPO catalysts; (ii) a dual function OCM/CPO catalyst; or (iii) both (i) and (ii); wherein the reactant mixture is fed to the oxidative conversion reactor at a first location and comprises methane, oxygen, and optionally carbon dioxide; wherein at least a portion of the reactant mixture reacts in the oxidative conversion reactor to produce an oxidative conversion product mixture; wherein the oxidative conversion reactor comprises an oxidative conversion catalyst system; wherein the oxidative conversion catalyst system comprises an oxidative coupling of methane (OCM) catalyst component and a catalytic partial oxidation (CPO) catalyst component; wherein a first portion of the methane reacts in the presence of the OCM catalyst component, via an OCM reaction, to produce C ₂ hydrocarbons; wherein a second portion of the methane reacts in the presence of the CPO catalyst component, via a CPO reaction, to produce hydrogen (H ₂ ) and carbon monoxide (CO); wherein the oxidative conversion product mixture comprises C ₂ hydrocarbons, syngas, carbon dioxide, water, and methane; wherein the syngas comprises H ₂ and CO; and wherein, optionally, oxygen, carbon dioxide or both are added to the oxidative conversion reactor at a second location that is downstream from the first location. In such embodiments where the OCM and CPO reactions can be carried out simultaneously (e.g., in a common reaction zone having comingled OCM and CPO catalysts), a C ₂ hydrocarbons stream, a syngas stream, a carbon dioxide stream, and a water stream can be recovered from the oxidative conversion product mixture; wherein the C ₂ hydrocarbons stream comprises ethylene and ethane; wherein the syngas stream comprises methane in an amount of from about 0.1 mol% to about 6 mol%; wherein the syngas stream is characterized by a H ₂ /CO molar ratio of from about 1.9 to about 2.2; and wherein at least a portion of the carbon dioxide stream is optionally recycled to the oxidative conversion reactor. In such embodiments where the OCM and CPO reactions can be carried out simultaneously (e.g., in a common reaction zone having comingled OCM and CPO catalysts), the overall methane conversion is from about 80% to about 99%, based on the moles of methane fed to the oxidative conversion reactor; wherein the overall productivity rate is from about 1.3 tons to about 1.9 tons of C ₂ hydrocarbons and syngas produced per ton of methane fed to the oxidative conversion reactor; and wherein the overall C ₂ hydrocarbons yield is from about 15% to about 20%, based on the moles of methane fed to the oxidative conversion reactor.

[0047] In embodiments, oxidative coupling of methane is conducted in the OCM reaction zone (105). The oxidative coupling of methane is a highly exothermic process, and is utilized for generating C ₂ hydrocarbons from feed mixture comprising methane and oxygen (104). In some embodiments of the present invention, the feed mixture may be preheated in a preheating zone (100). The methane stream (101) and oxygen stream (103) may be injected into the preheating zone (100) so as to adiabatically preheat the feed mixture to at least 400 ºC. The preheating helps in activating the otherwise inert hydrocarbons including methane, to help undergo the oxidative coupling effectively during the OCM process. Preheating of the feed mixture (104) also reduces the need of applying excess heat in the OCM reaction zone (105) during the OCM process and thereby ensuring better heat management and prevents catalyst degradation.

[0048] The feed mixture comprising methane and oxygen can be introduced into the OCM reaction zone at a methane to oxygen ratio in a range from 4:1 to 16:1, alternatively in a range from 5:1 to 7.5:1. In an aspect, the ratio of methane to oxygen in the feed mixture of stream 104 is 7.4:1. The ratio of the methane and oxygen in the feed is beneficial to determine the productivity rate and conversion of methane. At low ratio of methane to oxygen, over oxidation and low selectivity of C ₂ hydrocarbons occurs which reduces product yield of C ₂ hydrocarbons. At high methane to oxygen ratio, the overall methane conversion is low leading to large amount of methane as slip in recovered products. The feed mixture can additionally contain carbon dioxide. The carbon dioxide, when present in the feed, helps in reducing the flammability of the methane and oxygen feed.

[0049] The OCM reaction zone (105) can comprise any suitable reactor vessel, for example a continuous flow reactor which may include one of more of fixed bed reactor such as axial flow reactors and radial flow reactor, a stacked bed reactor, a fluidized bed reactor, or an ebullating bed reactor.

[0050] The feed mixture 104 can be introduced into the OCM reaction zone (105) at a flow rate of at least about 8000 kmol/hr for methane and at least about 1080 kmol/hr for oxygen. The hourly space velocity (GHSV, hr-1) for injecting the feed mixture (104) in the OCM zone (105) can be in the range from about 24,000 hr-1 to about 1,800,000 hr-1 with a catalyst contact time in the ranging from about 2- 150 ms. The OCM reaction zone (105) can be maintained at a temperature from about 800 ºC to about 1100 ºC, alternatively at a temperature from about 810 ºC to about 1050 ºC, or alternatively at a temperature from about 820 ºC to about 1010 ºC. The operating temperature inside the OCM reaction zone (105) can be optimized to maximize productivity. At lower operating temperature the heat required to activate methane for oxidative coupling may not be sufficient to ensure the desired level of productivity. At high temperature the reaction rate is thermodynamically unfavorable and the OCM reaction may slow down owing to the exothermic nature of the process. Further at high temperature, heat management challenges and catalyst deactivation may occur. The pressure condition maintained inside the OCM reaction zone can range from about 5 barg to about 11 barg, alternatively the pressure can be maintained from about 6 barg to about 10 barg, or alternatively the pressure can be maintained from about 7 barg to about 9 barg.

[0051] The OCM catalyst component used in the OCM reaction zone is a metal oxide based catalyst which functions as an OCM reaction catalyst. The catalyst aids optimum selectivity and yield of C ₂ hydrocarbons while ensuring the high temperature catalyst stability inside the OCM reaction zone. The OCM catalyst component for the purpose of oxidative coupling of methane includes one or more metal oxides selected from the group consisting of , and combinations thereof; wherein a is 1.0; wherein b is from about 0.1 to about 3.0; wherein c is from about 0.01 to about 1.0; and wherein x balances the oxidation states. In an embodiment, the OCM catalyst component is Sr ₁ -Ce _0.9 -Yb _0.1 O _3. The OCM catalyst component can be prepared by any of the known methods of preparation described in the art involving the steps of co-precipitation of the metal oxides to form a precursor mixture using weak basic solutions such as ammonium bicarbonate and subsequently calcining such precursor mixture at high temperature to obtain the catalyst.

[ _0052] The OCM process produces the OCM product mixture (106) comprising C ₂ hydrocarbons and some portions of carbon dioxide, carbon monoxide and steam. The OCM process may be represented by the reaction schemes below:

[0053] The temperature of the OCM product mixture is at least 900 ºC and in some embodiments at least 1000 ºC. The temperature of the OCM reaction zone (105) is adapted to ensure high methane conversion with substantially all of the oxygen present in the feed stream being consumed. In an aspect, oxygen conversion in the OCM reaction zone is at least 99.5 % per mole of oxygen present in the feed mixture (104), alternatively oxygen conversion is at least 99.6% per mole of oxygen present in the feed mixture (104). Such high oxygen conversion can result in the OCM product mixture (106) having depleted levels of oxygen which is insufficient for further oxidative conversion of methane, and supplemental oxygen may be added upstream of the CPO reaction zone as described herein.

[0054] For example, supplemental oxygen can be provided via a cold oxygen stream (107) added to the OCM product mixture (106) to form an oxygen rich OCM product mixture (108) having oxygen concentrations sufficient to conduct partial oxidation. Oxygen is added at a concentration ranging from 10% to 30%, alternatively from 15% to 25% or alternatively from 20% to 23% per mole of the OCM product mixture. The concentration of oxygen added should be sufficient to ensure that the methane present in the OCM product mixture (106) is partially oxidized in the CPO reaction zone 110. At high concentrations of oxygen, the C ₂ hydrocarbons will be oxidized to CO _x products. At low oxygen concentration, the methane conversion will be low leading to more of reformation reaction and high levels of methane slip in the resultant product mixtures.

[0055] The oxygen rich OCM product mixture (108) is introduced into a CPO reaction zone (110) containing the CPO catalyst component. Partial oxidation of methane over a catalyst bed is described as a catalytic partial oxidation process and is an exothermic process. The catalytic partial oxidation process is primarily used for the production of synthesis gas and is regarded as an alternate to the wet (e.g., steam) and/or dry reformation of methane. The heat generated from the oxidative coupling of methane is used effectively in the catalytic partial oxidation process. This helps in the overall heat management of the entire reactor system and helps limiting the extent of non-selective methane conversion reactions during the catalytic partial oxidation process to CO _x products instead of synthesis gas. The overall reaction scheme for the catalytic partial oxidative process is as shown below:

[0056] Portions of the C ₂ hydrocarbons present in the oxygen rich OCM product mixture (108) may also undergo some conversion with some of the ethane undergoing oxy-dehydrogenation to ethylene and some portion to synthesis gas and other CO _x products by the following reactions:

The conversion of C ₂ hydrocarbons to CO _x products, reduces the overall yield of C ₂ hydrocarbons and hence any such conversions should be mitigated as much as possible by moderating the oxygen concentration added to the OCM product mixture (106) and by the appropriate choice of the CPO catalyst component for conducting the partial oxidation.

[0057] Methane in the oxygen rich OCM product mixture (108) may additionally undergo reformation in presence of carbon dioxide and steam, and thus CPO reaction zone 110 may also be referred to as a reforming and partial oxidation zone. Reformation (i.e., reforming) reactions are endothermic in nature and help balance the heat generated from the exothermic partial oxidation process and contribute to the overall heat management process. Methane reformation reactions include a) wet reforming where methane reacts with water (e.g., steam) to form synthesis gas and b) dry reforming where methane reacts with carbon dioxide to form synthesis gas, as shown by the following reforming reactions:

[0058] The oxygen rich OCM product mixture (108) is at a temperature of at least 870 ºC but not greater than 950 ºC, when injected inside the CPO reaction zone (110). The temperature of the stream (108) is lower than that of the stream (106) due to the addition of the relatively colder oxygen stream (107). The stream (108) is introduced inside the CPO reaction zone (110) at a flow rate of at least about 260000 kg/hr and at a hourly space velocity (GHSV, hr-1) ranging from about 360,000 h-1 to about 36,000,000 h-1 with a catalyst contact time of about 0.1-10 ms. The CPO reaction zone (110) is maintained at a temperature ranges of from about 600 ºC to about 1000 ºC, alternatively at a temperature of from about 750 ºC to about 980 ºC, or alternatively at a temperature of from about 800 ºC to about 950 ºC. The effective utilization of heat from the OCM process allows the CPO reaction zone (110) to be operated at a relatively lower temperature than that of the OCM reaction zone (105). The pressure in CPO reaction zone 110 can be maintained at ranges from about 2 barg to about 10 barg, alternatively the pressure is maintained at from about 3 barg to about 9 barg, or alternatively the pressure is maintained at from about 4 barg to about 6 barg. The pressure inside the CPO reaction zone (110) is maintained at a lower pressure than that corresponding to the OCM reaction zone (105). It has been observed that in catalytic partial oxidation of methane, with increase in pressure, the ratio of H ₂ /CO present in the synthesis gas decreases which is generally not desirable for methanol production from synthesis gas. In addition, with increase in pressure, coke deposition on the partial oxidation catalyst increases, resulting in catalyst deactivation.

[0059] The CPO catalyst component for the purpose of catalytic partial oxidation of methane includes one or more metals selected from the group consisting of Ni, Co, Fe, Re, Ir, Rh, Ru, Pd, Pt and combinations thereof. In some embodiments of the present invention, the CPO catalyst component includes one or more metal oxide catalyst supports selected from the group consisting of Al ₂ O ₃ , TiO ₂ , La ₂ O ₃ , Sm ₂ O ₃ , Ce ₂ O ₃ , MgO, CaO and combinations thereof, wherein the one or more metals contacts, coats, is embedded in, is support by, and/or is distributed throughout at least a portion of the metal oxide support. In an aspect, the CPO catalyst component is 3% Ni on La ₂ O ₃ support. In general it has been observed that, Nickel (Ni) based catalyst provide high methane conversion with excellent selectivity for CO and H ₂ .

[0060] In embodiments of the present invention, the CPO catalyst component can be prepared by a process involving co-precipitation of precursor metal salts in presence of a weak base such as ammonium hydroxide followed by calcination and sieving.

[0061] In an aspect, the oxidative conversion catalyst system comprises an OCM catalyst component, a CPO catalyst component, and a metal oxide support, wherein the OCM catalyst component comprises one or more metal oxides selected from the group consisting of MgO, La ₂ O ₃ , Sm ₂ O ₃ , CaO, Ce ₂ O ₃ , Sr ₁ Ce _0.9 Yb _0.1 O ₃ , and combinations thereof; wherein the CPO catalyst component comprises one or more metals selected from the group consisting of Ni, Fe, Co, Re, Ir, Rh, Ru, Pd, Pt, and combinations thereof; wherein at least a portion of the OCM catalyst component and/or at least a portion of the CPO catalyst component contact, coat, are embedded in, are supported by, and/or are distributed throughout at least a portion of the metal oxide support; wherein the metal oxide support is selected from the group consisting of Al ₂ O ₃ , TiO ₂ , La ₂ O ₃ , Sm ₂ O ₃ , Ce ₂ O ₃ , MgO, CaO, and combinations thereof; wherein the OCM catalyst component and the metal oxide support are the same or different.

[0062] In an aspect, the oxidative conversion catalyst system comprises a homogenous mixture of an OCM catalyst component comprising one or more metal oxides selected from the group consisting of MgO, La ₂ O ₃ , Sm ₂ O ₃ , CaO, Ce ₂ O ₃ , Sr _a Ce _b Yb _c O _x , and combinations thereof; wherein a is 1.0; wherein b is from about 0.1 to about 3.0; wherein c is from about 0.01 to about 1.0; and wherein x balances the oxidation states; and a CPO catalyst component comprising one or more metals selected from the group consisting of Ni, Co, Fe, Re, Ir, Rh, Ru, Pd, Pt and combinations thereof.

[0063] In an aspect, the oxidative conversion catalyst system comprises dual function OCM/CPO catalyst comprising an OCM catalyst component and an CPO catalyst component supported via a common metal oxide support, wherein the OCM catalyst component comprises one or more metal oxides selected from the group consisting of MgO, La ₂ O ₃ , Sm ₂ O ₃ , CaO, Ce ₂ O ₃ , Sr _a Ce _b Yb _c O _x , and combinations thereof; wherein a is 1.0; wherein b is from about 0.1 to about 3.0; wherein c is from about 0.01 to about 1.0; and wherein x balances the oxidation states; wherein the CPO catalyst component comprises one or more metals selected from the group consisting of Ni, Co, Fe, Re, Ir, Rh, Ru, Pd, Pt and combinations thereof; and wherein at least a portion of the OCM catalyst component and at least a portion of the CPO catalyst component contact, coat, are embedded in, are supported by, and/or are distributed throughout at least a portion of the metal oxide support; wherein the metal oxide support is selected from the group consisting of Al ₂ O ₃ , TiO ₂ , La ₂ O ₃ , Sm ₂ O ₃ , Ce ₂ O ₃ , MgO, CaO, and combinations thereof; wherein the OCM catalyst component and the metal oxide support are the same or different. In an aspect, the oxidative conversion catalyst system comprises dual function OCM/CPO catalyst comprising an OCM catalyst component and an CPO catalyst component supported via a common metal oxide support, wherein the OCM catalyst component comprises Sr ₁ Ce _0.9 Yb _0.1 O ₃ and the CPO catalyst component comprises Ni on La ₂ O ₃ support.

[0064] A process has been discovered for producing mixtures of synthesis gas and C2 hydrocarbons with unseen benefits of high methane conversion with excellent C2 hydrocarbons yield, low methane slip as impurity, high productivity rate and reduced carbon dioxide emissions. By leveraging oxidative coupling of methane as the lead methane conversion reaction, the high preheating feed temperature for partial oxidation is avoided and the heat of reaction is effectively managed so as to ensure that the product mixtures of synthesis gas and C2 hydrocarbons are produced at high productivity with excellent methane conversion.

[0065] The invention further includes a composition comprising mixtures of synthesis gas and C2 hydrocarbons having low methane concentration as slip, thereby avoiding the cost associated with additional purification or recycling steps for further downstream application.

[0066] Without being bound by any specific theory, the balance between methane conversion and C ₂ hydrocarbons yield may be achieved through a combination of catalyst employed, oxygen concentration added to the OCM product mixture (106) and appropriate reactor conditions, as employed in the inventive process of the present invention.

[0067] In embodiments where carbon dioxide stream 111 is recycled to the preheating zone 100 (e.g., as shown in Fig. 3), the flammability of the oxygen rich feed mixture (104) is lowered and the emission of carbon dioxide generated from both the oxidative coupling and partial oxidative processes is suppressed. Lowering of flammability of feed mixture is beneficial in OCM and partial oxidation process particularly as the oxygen rich feed mixture is subjected to high temperature exothermic conditions. The increased carbon dioxide concentration may allow for more endothermic dry reformation of methane which further helps in the heat management of the present inventive process. The reduced emission of carbon dioxide as greenhouse gas is another advantage of employing this particular embodiment of the present invention, making the overall process environmentally friendly and savings in capital expenditures required for carbon dioxide sequestration. Further, the use of CO ₂ as an oxidant will reduce the consumption of expensive oxygen per mole of converted methane when compared with the oxidative coupling of methane using oxygen as the sole source of oxidant.

[0068] As part of the disclosure of the present invention, specific examples are included below. The examples are for illustrative purposes only and are not intended to limit the invention. Those of ordinary skill in the art will readily recognize parameters that can be changed or modified to yield essentially the same results.

EXAMPLES

[0069] The present invention will be described in greater detail by way of specific examples. The following examples are offered for illustrative purposes only, and are not intended to limit the invention in any manner. Those of skill in the art will readily recognize a variety of noncritical parameters which can be changed or modified to yield essentially the same results.

[0070] Examples 1 and 2 describe two specific embodiments of the present invention with Examples 3-5 functioning as comparative examples to illustrate the merits of the specific inventive features of the present invention. The inventive embodiments of Example 1 and Example 2 demonstrate the production of synthesis gas and C ₂ hydrocarbons with at least one or more attribute of high productivity rate, low methane slip, high methane conversion and excellent C ₂ hydrocarbons yield.

Example 1

Oxidative coupling of methane followed by partial oxidation in presence of oxygen added through an oxygen feed stream

[0071] Purpose: Example 1 demonstrates the production of a mixture of synthesis gas and C ₂ hydrocarbons using Oxidative Coupling of Methane (OCM) followed by Partial Oxidation of Methane. The present Example further demonstrates the production of synthesis gas and C ₂ hydrocarbons having excellent methane conversion with desirable C ₂ selectivity and reduced methane concentration as slip in the recovered synthesis gas.

[0072] Materials: A fixed bed reactor was used for conducting the OCM and Partial Oxidation. The fixed bed reactor in the OCM reaction zone was loaded with metal oxide catalyst having a composition represented by the formula Sr ₁ -Ce _0.9 -Yb _0.1 O ₃ . For the CPO reaction zone, a metal catalyst comprising Nickel (Ni) on Lanthanum oxide (La ₂ O ₃ ) support was used.

[0073] Process/Procedure: The following process for producing a mixture of synthesis gas and C ₂ hydrocarbons was practiced for the purpose of this example. An OCM product mixture comprising a mixture of C ₂ hydrocarbons, H ₂ , CO, methane, carbon dioxide, and steam was formed in the presence of the first catalyst component, functioning as an oxidative coupling catalyst, in an OCM reaction zone. Subsequently, the OCM product mixture, in presence of oxygen, was fed into the CPO reaction zone containing the second catalyst component to form the mixture of synthesis gas and C ₂ hydrocarbons.

[0074] More particularly, referring to Fig. 2 the process for producing a mixture of C ₂ hydrocarbons and synthesis gas included the steps of preheating a feed stream comprising methane (101) and oxygen (103) present in a ratio of 7.5:1, in a preheating zone (100) and formed a preheated feed stream (104). The preheated feed stream (104) was thereafter injected into the OCM reaction zone (105) containing the first catalyst component and formed an OCM product mixture (106) comprising a mixture of C ₂ hydrocarbons, hydrogen, carbon monoxide, methane, carbon dioxide, and steam. Subsequently, the OCM product mixture (106) in presence of oxygen supplied by the oxygen stream (107) was passed to the CPO reaction zone (110) containing the second catalyst component and formed the product mixture (109) comprising synthesis gas, C ₂ hydrocarbons, carbon dioxide and steam. The product mixture (109) was passed to a gas separation zone (115) and product streams of synthesis gas (112), C ₂ hydrocarbons or Olefin stream (113), carbon dioxide (112) and steam (114) were recovered.

Operating Parameters: The operating conditions maintained for producing the mixture of synthesis gas and C ₂ hydrocarbons for the purpose of this Example is as given in the table below. [0075] The temperature in both the oxidative coupling and CPO reaction zones were maintained near their optimum operating range, although the OCM reaction zone temperature was slightly over 1000 °C. The feed injected into the preheating feed zone (100) was heated to 400 °C to achieve an optimum temperature for activating the methane, prior to oxidative coupling of methane. Inside the OCM reaction zone (105) there was an adiabatic temperature rise, which increased the temperature of the OCM product mixture (106) to 1023 °C. The temperature of the stream (108) formed from the mixing of OCM product mixture (106) with the cold oxygen stream (107) measured to be at 931 °C. The temperature of the product mixture stream (109) dropped to 900 °C at the outlet of the CPO reaction zone (110). The pressure condition inside the OCM reaction zone was maintained at 8 barg while that inside the partial oxidation zone was kept at 5 barg. The feed rate of methane and oxygen injected into the preheating zone was kept at 8000 kmol/hr and 1081.21 kmol/hr respectively. [0076] The OCM product mixture (106) had depleted oxygen levels, which was replenished by the addition of the cold oxygen stream (107) and was subsequently passed to the partial oxidation zone (110). The depleted O ₂ levels indicated high consumption of O ₂ during the oxidative coupling process.

[0077] Results: The product mixtures obtained were analyzed and the results are tabulated as below:

Table 4: Mole fraction (%) data of product mixture components

[0078] Using the data from Table 4, specific ratios indicating productivity and selectivity of the product mixtures is calculated as reported below:

[0079] Discussion: The results from the data under Table 4 and Table 5 were analyzed in detail and the key learnings from the analysis are summarized under Table 6:

Table 6: Key characteristic parameters of Example 1

[0080] Example 1 as an embodiment of the present invention demonstrated the merits of employing the present invention for the production of synthesis gas and C2 hydrocarbons. The combined productivity rate for the production of synthesis gas and C2 hydrocarbons is reported at 1.58 tons per ton of methane feed injected. More particularly, the productivity rate of synthesis gas produced measured 1.44 ton per ton of methane feed and that of C2 hydrocarbons measured 0.14 ton per ton of methane feed. The process conditions and the catalyst used in the CPO reaction zone was such that the C2 hydrocarbons present in the OCM product mixture underwent only minimum conversion to COx products. The overall methane conversion was reported at 91.4% with a C2 hydrocarbons yield of 15.53%. Further, it is reported that the recovered synthesis gas stream (112) has a methane slip of 3.73%, which is acceptable for further downstream industrial use. At such low methane concentration as slip, the recovered synthesis gas may be used directly for further downstream industrial processes without any additional steps of purification leading to savings in operation and capital expenses. It may also be appreciated that although methane conversion using the process of Example 1 was higher than 90%, the yield of C2 hydrocarbons was not adversely compromised as may have been expected.

Example 2

Oxidative coupling of methane followed by partial oxidation of methane and recycling of recovered CO ₂

[ _0081] Purpose: Example 2 demonstrates the production of a mixture of synthesis gas and C ₂ hydrocarbons using Oxidative Coupling of Methane (OCM) followed by Partial Oxidation of Methane using additional oxygen stream added to the OCM product mixture and recycling the recovered carbon dioxide to the preheating zone. The present Example also demonstrates improved product yields while mitigating feed mixture flammability, methane slip and Green House Gas emissions.

[0082] Materials: The materials used were same as that described under Example 1.

[0083] Process/Procedure: Referring to Fig. 3, the procedure followed was same as described under Example 1 with the additional step of recycling the recovered carbon dioxide product stream (111) to the preheating zone (100).

[0084] Operating parameters: Operating parameters were kept same as that described under Example 1, except that the temperature in both oxidative coupling and partial oxidation zone was maintained at their optimum operating range of 800°C to 1000 °C. The temperature of the OCM product mixture (106) measured 994 °C. The temperature of the OCM product mixture (106) with the addition of the cold oxygen stream (107) measured 891 °C and the temperature of the product mixture stream (109) at the outlet of the partial oxidation zone measured 877 °C. The pressure condition inside the OCM reaction zone was maintained at 8 barg while that inside the CPO reaction zone was maintained at 5 barg. The OCM product mixture (106) had depleted oxygen levels, which was replenished by the addition of the oxygen stream (107) and subsequently passed to the CPO reaction zone (110).

[0085] Results: The product mixtures were analyzed as discussed under Example 1 and is tabulated as below:

[0086] Specific ratios were further calculated to determine product and process characteristics of the present Example. The product mixtures were analyzed as discussed under Example 1 and is tabulated as below:

[0087] Discussion: The yield/productivity of the products were calculated using the data under Table 8 and Table 9 and reported below:

[0088] Example 2 as an embodiment of the present invention demonstrated the merits of the present invention. The combined productivity rate for the production of synthesis gas and C ₂ hydrocarbons was 1.63 tons per ton of methane feed injected. More particularly, the productivity of synthesis gas produced was calculated at 1.49 ton per ton of methane feed and that of C ₂ hydrocarbons was calculated at 0.14 ton per ton of methane feed. The overall methane conversion was reported at 91.3% with a C ₂ hydrocarbons yield at 16%. Further, it was demonstrated that the recovered synthesis gas stream (112) had a methane slip of 3.8%, which is acceptable for further downstream industrial application with no additional requirement of methane separation. Further, the carbon dioxide recovered (111) was recycled back to the preheating zone to reduce the flammability of the oxygen rich feed and also to ensure reduced carbon dioxide emission. As with Example 1, the process described under Example 2 provided methane conversion without affecting the yield of C ₂ hydrocarbons.

Example 3 (Comparative Example)

Producing a mixture of C2 hydrocarbons and Synthesis gas using Oxidative Coupling of Methane followed by Methane Reformation

[0089] Purpose: Example 3 demonstrates the production of a mixture of synthesis gas and C ₂ hydrocarbons using Oxidative Coupling of Methane (OCM) followed by Reformation of Methane in the presence of carbon dioxide and water. Particularly, the purpose of this Example is to compare the inventive embodiments under Examples 1 and 2 with that of an integrated process of oxidative coupling of methane with that of methane reformation.

[0090] Materials: The materials used are same as that described under Example 1.

[0091] Process/Procedure: Referring to Fig. 1, the procedure practiced for this example was same as described under Example 1, except that there was no additional oxygen feed stream added to the OCM product mixture (106).

[0092] Operating Parameters: The operating conditions maintained for producing the mixture of synthesis gas and C ₂ hydrocarbons for the purpose of this Example is as given in the table below.

[0093] The intermediate feed stream of the OCM product mixture (106) had depleted oxygen levels as shown in the table below. However, for the purpose of this comparative example, there was no additional oxygen stream mixed with the OCM product mixture (106). The OCM product mixture (106) was subsequently passed into the zone (110) for reforming methane.

Table 12: Mole fraction (%) data of intermediate product stream components

[0094] Results: The mixture of synthesis gas and C ₂ hydrocarbons obtained from the product stream (109) and the recovered product stream of individual components of synthesis gas (112) and C ₂ hydrocarbons (113), were analyzed in detail. As most of the oxygen was consumed during the oxidative coupling of methane, the unconverted methane in the OCM product mixture underwent only reformation in presence of water and carbon dioxide. The results are tabulated as below:

[0095] Specific ratios characterizing the process practiced for the present Example is provided below:

[0096] Discussion: Using the data under Table 13 and Table 14 the key parameters are discussed as below:

[0097] The results of Example 3 as a comparative example demonstrate that although a mixture of synthesis gas and C2 hydrocarbons can be produced by the integration of an OCM reaction zone with methane reformation, the synthesis gas obtained has a large concentration of methane as slip. At such large concentration of methane, additional purification or methane separation is required for further downstream industrial production adding on to capital and operational expenditure. Further, as demonstrated the combined productivity rate for the production of synthesis gas and C ₂ hydrocarbons is at least 72% lower compared to the inventive embodiments shown under Example 1 and Example 2. More particularly, the productivity of the synthesis gas produced was reported at 0.29 ton per ton of methane feed injected and that of C2 hydrocarbons was reported at 0.14 ton per ton of methane feed injected. The overall methane conversion was reported at 33.3% with a C ₂ hydrocarbons yield of 15.51%. The recovered synthesis gas stream (112) has a methane concentration of 54.86% as slip. The overall methane concentration as slip generated in the inventive embodiments of Example 1 and Example 2 was at least 93% lower than that obtained from the process under comparative Example 3.

Example 4 (Comparative Example)

Oxidative Coupling of Methane as a single standalone process

[0098] Purpose: Example 4 demonstrates the production of a mixture of synthesis gas and C ₂ hydrocarbons using Oxidative Coupling of Methane (OCM) as a single standalone process.

[0099] Materials: The materials used were same as that described under Example 1.

[00100] Procedure: The procedure followed was identical to the process described under Example 1, pertaining to the aspect of oxidative coupling of methane. The preheated feed stream (104) was injected inside the OCM reaction zone (105) and the OCM product mixture (106) was further analyzed. The product stream (106) was passed to a separation zone were individual products were recovered.

[00101] Operating parameters: The operating parameters for oxidative coupling of methane were identical to that described for the oxidative coupling of methane under Example 1. The reaction zone outlet temperature was at 1023 °C.

[00102] Results: The oxidative coupling product stream was analyzed in detail and the results were tabulated as below:

[00103] Specific product ratios characterizing the products obtained from the comparative example was reported as below:

[00104] Discussion: The yield and productivity was calculated using the data under Table 16 and Table 17 and reported as below:

[00105] The comparative example as shown here demonstrates that although a standalone oxidative coupling of methane produces a mixture of synthesis gas and C ₂ hydrocarbons, the methane concentration present as slip in the recovered synthesis gas was very high which would limit the use of synthesis gas for further downstream industrial application. The methane concentration obtained through the inventive embodiments of Example 1 and Example 2 was at least 94% lower than what was obtained through the process of Example 4. In addition, the overall productivity rate of the combined production of synthesis gas and C ₂ hydrocarbons obtained from the inventive embodiments of Example 1 and Example 2 was at least 780% higher than that obtained from the standalone OCM process described under Example 4.

Example 5 (Comparative Example)

Partial Oxidation of Methane as a standalone process

[00106] Purpose: Example 5 demonstrates a conventional catalytic partial oxidation process of methane as a single standalone process.

[00107] Materials: The materials used for partial oxidation for the purpose of this Example are same as that described under Example 1 for the partial oxidation process.

[00108] Procedure: The process followed for partial oxidation is similar to that described under Example 1. A feed stream containing methane and oxygen was passed into a CPO reaction zone containing a partial oxidative metal catalyst. The products of the CPO reaction zone were recovered and analyzed.

[00109] Operating parameters: The operating parameters for CPO reaction zone was kept same as that described for the partial oxidative process of methane as described under Example 1. The reaction zone outlet temperature was maintained at 885 °C.

[00110] Results: The partial oxidative product stream was analyzed in detail and tabulated as below:

[00111] Discussion: The yield and productivity was calculated using the data under Table 19:

[00112] From the present comparative example, it is evident that a standalone partial oxidation process produces synthesis gas with no substantial formation of C ₂ hydrocarbons. As one of the objectives of the present invention is to coproduce both synthesis gas and C ₂ hydrocarbons, the present comparative example clearly demonstrates that the inventive embodiments of Example 1 and Example 2 meet the objectives of the current invention. Further, the overall methane conversion was lower than that achieved in the inventive embodiments of Example 1 and Example 2 resulting in a relatively higher methane concentration as slip in the recovered synthesis gas.

[00113] Summary of Results from Examples 1-5: The results of the Examples 1 and 2 with that of Comparative Examples 3, 4 and 5, are summarized below and may be appreciated further by way of Figs. 4, 5, and 6.

[00114] As can be observed from Table 21, the inventive embodiments under Example 1 and Example 2 meet the objectives of the present invention of coproducing synthesis gas and C ₂ hydrocarbons with previously unseen benefits of high productivity rate, high methane conversion and low methane concentration as slip in the recovered products. The combined productivity rate of synthesis gas and C ₂ hydrocarbons produced using the inventive embodiments of Example 1 and Example 2, is at least 260% greater than that produced from the processes used under the Examples 3 and 4. At such high productivity rate, overall operational efficiency is maximized. Further as demonstrated, for the inventive embodiments shown under Example 1 and 2, has a much lower concentration of methane as slip compared to what is produced from the processes described under Example 3, Example 4 and Example 5. At such low concentration of methane as slip the synthesis gas produced, can be used directly for downstream industrial application without further purification steps. The overall methane conversion using the inventive embodiments of Example 1 and Example 2 is at least 90% with a C ₂ hydrocarbons yield of at least 15.5%. Although it is expected that at such high methane conversion, the C ₂ yield and selectivity is usually compromised, however from Example 1 and Example 2 it is demonstrated that high methane conversion and with desirable level of C ₂ yield can be achieved using the inventive embodiments of the present invention.

[00115] The inventive embodiments under Example 1 and Example 2 further demonstrate that the overall yield of C ₂ hydrocarbons produced is comparable to that produced using the process of Example 3 and Example 4 and from such observation it may be inferred that the extent oxidative conversion of C ₂ hydrocarbons in the CPO reaction zone can be regulated even in the presence of O ₂ . Example 5 demonstrated that the use of a standalone partial oxidation process does not generate substantial amount of C ₂ hydrocarbons and hence would not meet the objective of present invention. It may be noted that the synthesis gas produced using the process under inventive embodiments has the appropriate ratio of H ₂ to CO for further downstream industrial applications including production of methanol.