Oxidative coupling of methane methods and systems

Abstract

The present disclosure provides natural gas and petrochemical processing systems including oxidative coupling of methane reactor systems that integrate process inputs and outputs to cooperatively utilize different inputs and outputs of the various systems in the production of higher hydrocarbons from natural gas and other hydrocarbon feedstocks.

Claims

1. An oxidative coupling of methane (OCM) method to generate hydrocarbon compounds containing at least two carbon atoms (C.sub.2+ compounds), the method comprising: (a) injecting oxygen (O.sub.2), methane (CH.sub.4), and ethane (C.sub.2H.sub.6) into an adiabatic OCM reactor, wherein the adiabatic OCM reactor comprises an adiabatic OCM reaction section comprising an OCM catalyst bed for facilitating an OCM reaction and an adiabatic post-bed cracking (PBC) section for facilitating conversion of C.sub.2H.sub.6 to ethylene (C.sub.2H.sub.4) with the aid of heat liberated by the OCM reaction, and wherein the C.sub.2H.sub.6 has a concentration of at least 3 mol % at an inlet of the adiabatic OCM reactor and wherein the concentration of C.sub.2H.sub.6 at the inlet of the adiabatic OCM reactor is maintained within +/−0.2 mol %; (b) with the aid of the OCM catalyst in the adiabatic OCM reaction section, performing an OCM reaction to convert the CH.sub.4 into C.sub.2+ compounds as part of a product stream; (c) in the adiabatic PBC section of the adiabatic OCM reactor and with the aid of heat liberated by the OCM reaction, converting C.sub.2H.sub.6 in the product stream into C.sub.2H.sub.4 as part of an OCM effluent; (d) separating the OCM effluent to produce at least an ethane stream and a stream enriched in C.sub.2H.sub.4; (e) recycling a portion of the ethane stream to an inlet of the adiabatic OCM reaction section; and (f) recycling a portion of the ethane stream to the adiabatic PBC section, wherein the method has a carbon efficiency of at least 60%.

2. The method of claim 1, wherein the concentration of C.sub.2H.sub.6 at an inlet of the OCM catalyst bed is at least 3.5 mol %.

3. The method of claim 1, wherein at least a portion of the C.sub.2H.sub.6 is injected into the adiabatic OCM reactor separately from the CH.sub.4.

4. The method of claim 1, further comprising increasing or decreasing an amount of CH.sub.4 injected in (a) to maintain the concentration of C.sub.2H.sub.6 during the injecting.

5. The method of claim 1, wherein the concentration of C.sub.2H.sub.6 at the inlet of the OCM reactor is from 3 mol % to 6 mol %.

6. The method of claim 1, wherein the carbon efficiency is from 60% to 85%.

7. The method of claim 1, wherein at least a portion of the C.sub.2H.sub.6 injected into the adiabatic OCM reactor is injected into a sulfur removal unit prior to being injected into the adiabatic OCM reactor.

8. The method of claim 1, wherein the methane injected into the adiabatic OCM reactor is provided by a methanated stream comprising methane produced by a methanation reactor.

9. The method of claim 8, wherein a natural gas stream comprising methane is combined with the OCM effluent prior to separating the OCM effluent.

10. An oxidative coupling of methane (OCM) method to generate hydrocarbon compounds containing at least two carbon atoms (C.sub.2+ compounds), the method comprising: (a) injecting oxygen (O.sub.2), methane (CH.sub.4), and ethane (C.sub.2H.sub.6) into an adiabatic OCM reactor, wherein the adiabatic OCM reactor comprises an OCM reaction section comprising an OCM catalyst bed for facilitating an OCM reaction and an adiabatic post-bed cracking (PBC) section for facilitating conversion of C.sub.2H.sub.6 to ethylene with the aid of heat liberated by the OCM reaction, and wherein the C.sub.2H.sub.6 has a concentration of at least 3 mol % within the OCM catalyst bed and wherein a concentration of C.sub.2H.sub.6 at an inlet of the adiabatic OCM reactor is maintained within +/−0.2 mol %; and (b) with the aid of the OCM catalyst bed in the OCM reaction section, performing an OCM reaction to convert CH.sub.4 into C.sub.2+ compounds as part of a product stream; (c) in the adiabatic PBC section of the adiabatic OCM reactor and with the aid of heat liberated by the OCM reaction, converting C.sub.2H.sub.6 in the product stream into ethylene (C.sub.2H.sub.4) as part of an OCM effluent; (d) separating the OCM effluent to produce at least an ethane stream and a stream enriched in C.sub.2H.sub.4; (e) recycling a portion of the ethane stream to the OCM reaction section; and (f) recycling a portion of the ethane stream to the adiabatic PBC section, wherein the method has a carbon efficiency of at least 60%.

11. The method of claim 10, wherein at least a portion of the C.sub.2H.sub.6 is injected into the adiabatic OCM reactor separately from the CH.sub.4.

12. The method of claim 10, further comprising increasing or decreasing an amount of CH.sub.4 injected in (a) to maintain the concentration of C.sub.2H.sub.6 at the inlet of the adiabatic OCM reactor.

13. The method of claim 10, wherein the concentration of C.sub.2H.sub.6 at the inlet of the adiabatic OCM reactor is from 3 mol % to 6 mol %.

14. The method of claim 10, wherein the carbon efficiency is from 60% to 85%.

15. The method of claim 10, wherein at least a portion of the C.sub.2H.sub.6 injected into the adiabatic OCM reactor is injected into a sulfur removal unit prior to being injected into the adiabatic OCM reactor.

16. The method of claim 10, wherein at least a portion of the methane injected into the adiabatic OCM reactor is provided by a methanated stream comprising methane produced by a methanation reactor.

17. The method of claim 16, wherein a natural gas stream comprising methane is combined with the OCM effluent prior to separating the OCM effluent.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings or figures (also referred to herein as “FIG.” and “FIGS.”), of which:

(2) FIG. 1A is a schematic illustration of an oxidative coupling of methane (OCM) process;

(3) FIG. 1B is a schematic illustration of an oxidative coupling of methane (OCM) process with separate addition of ethane;

(4) FIG. 1C shows a block flow diagram of an OCM process that includes ethane conversion, separations and methanation;

(5) FIG. 1D shows a process block flow diagram with feeds and products;

(6) FIG. 1E shows a process block flow diagram with carbon utilization;

(7) FIG. 2 is a schematic illustration of addition of ethane to an OCM reactor;

(8) FIG. 3 is a schematic illustration of a methanol production process;

(9) FIG. 4 is a schematic illustration of OCM integrated with a methanol production process;

(10) FIG. 5 is a schematic illustration of a petrochemical complex with a methanol production process and a cracker;

(11) FIG. 6 is a schematic illustration of the integration of OCM with a methanol production process and a cracker;

(12) FIG. 7 is a schematic illustration of the integration of OCM with a methanol production process and a cracker;

(13) FIG. 8 is a schematic illustration of the integration of OCM with a methanol production process and a cracker;

(14) FIG. 9 is a schematic illustration of a chloralkali process;

(15) FIG. 10 is a schematic illustration of OCM integrated with a chloralkali process;

(16) FIG. 11 is a schematic illustration of an ethylene dichloride (EDC) and vinylchloride monomer (VCM) production process;

(17) FIG. 12 is a schematic illustration of an EDC/VCM process integrated with a chloralkali process;

(18) FIG. 13 is a schematic illustration of OCM integrated with an EDC/VCM process and a chloralkali process;

(19) FIG. 14 shows an example of a process integrating OCM with a diaphragm-type chloralkali process;

(20) FIG. 15 shows a material and energy balance for the process shown in FIG. 14;

(21) FIG. 16 is a schematic illustration of OCM integrated with an ammonia process;

(22) FIG. 17 shows a schematic illustration of OCM integrated with a methanol-to-propylene (MTP) process.

(23) FIG. 18 shows a schematic illustration of an OCM process integrated with an MTP process.

(24) FIG. 19 shows a schematic illustration of an OCM process and an ETL process integrated with a liquid natural gas (LNG) process.

(25) FIG. 20 shows a schematic illustration of OCM and ETL processes integrated with an LNG process for polymer production.

(26) FIG. 21 shows a schematic illustration of an OCM process integrated with an oxalic acid/oxalate production process.

(27) FIG. 22 shows a schematic illustration of an OCM process integrated with an ethylene glycol production process.

(28) FIG. 23 shows a schematic illustration of an OCM process integrated with a metathesis-based propylene production process.

(29) FIG. 24 shows a schematic illustration of an OCM process integrated with a metathesis-based propylene production process with polypropylene production.

(30) FIG. 25A shows a schematic illustration of an OCM process integrated with a metathesis-based propylene production process having a C.sub.2 splitter.

(31) FIG. 25B shows a shows a schematic illustration of an OCM process integrated with a metathesis-based propylene production process without a C.sub.2 splitter.

DETAILED DESCRIPTION

(32) While various embodiments of the invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions may occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed.

(33) The term “higher hydrocarbon,” as used herein, generally refers to a higher molecular weight and/or higher chain hydrocarbon. A higher hydrocarbon can have a higher molecular weight and/or carbon content that is higher or larger relative to starting material in a given process (e.g., OCM or ETL). A higher hydrocarbon can be a higher molecular weight and/or chain hydrocarbon product that is generated in an OCM or ETL process. For example, ethylene is a higher hydrocarbon product relative to methane in an OCM process. As another example, a C.sub.3+ hydrocarbon is a higher hydrocarbon relative to ethylene in an ETL process. As another example, a C.sub.5+ hydrocarbon is a higher hydrocarbon relative to ethylene in an ETL process. In some cases, a higher hydrocarbon is a higher molecular weight hydrocarbon.

(34) The term “OCM process,” as used herein, generally refers to a process that employs or substantially employs an oxidative coupling of methane (OCM) reaction. An OCM reaction can include the oxidation of methane to a higher hydrocarbon and water, and involves an exothermic reaction. In an OCM reaction, methane can be partially oxidized and coupled to form one or more C.sub.2+ compounds, such as ethylene. In an example, an OCM reaction is 2CH.sub.4+O.sub.2.fwdarw.C.sub.2H.sub.4+2H.sub.2O. An OCM reaction can yield C.sub.2+ compounds. An OCM reaction can be facilitated by a catalyst, such as a heterogeneous catalyst. Additional by-products of OCM reactions can include CO, CO.sub.2, H.sub.2, as well as hydrocarbons, such as, for example, ethane, propane, propene, butane, butene, and the like.

(35) The term “non-OCM process,” as used herein, generally refers to a process that does not employ or substantially employ an oxidative coupling of methane reaction. Examples of processes that may be non-OCM processes include non-OCM hydrocarbon processes, such as, for example, non-OCM processes employed in hydrocarbon processing in oil refineries, a natural gas liquids separations processes, steam cracking of ethane, steam cracking or naphtha, Fischer-Tropsch processes, and the like.

(36) The terms “C.sub.2+” and “C.sub.2+ compound,” as used herein, generally refer to a compound comprising two or more carbon atoms. For example, C.sub.2+ compounds include, without limitation, alkanes, alkenes, alkynes and aromatics containing two or more carbon atoms. C.sub.2+compounds can include aldehydes, ketones, esters and carboxylic acids. Examples of C.sub.2+ compounds include ethane, ethene, acetylene, propane, propene, butane, and butene.

(37) The term “non-C.sub.2+ impurities,” as used herein, generally refers to material that does not include C.sub.2+ compounds. Examples of non-C.sub.2+ impurities, which may be found in certain OCM reaction product streams, include nitrogen (N.sub.2), oxygen (O.sub.2), water (H.sub.2O), argon (Ar), hydrogen (H.sub.2) carbon monoxide (CO), carbon dioxide (CO.sub.2) and methane (CH.sub.4).

(38) The term “small scale,” as used herein, generally refers to a system that generates less than or equal to about 250 kilotons per annum (KTA) of a given product, such as an olefin (e.g., ethylene).

(39) The term “world scale,” as used herein, generally refers to a system that generates greater than about 250 KTA of a given product, such as an olefin (e.g., ethylene). In some examples, a world scale olefin system generates at least about 1000, 1100, 1200, 1300, 1400, 1500, or 1600 KTA of an olefin.

(40) The term “item of value,” as used herein, generally refers to money, credit, a good or commodity (e.g., hydrocarbon). An item of value can be traded for another item of value.

(41) The term “carbon efficiency,” as used herein, generally refers to the ratio of the number of moles of carbon present in all process input streams (in some cases including all hydrocarbon feedstocks, such as, e.g., natural gas and ethane and fuel streams) to the number of moles of carbon present in all commercially (or industrially) usable or marketable products of the process. Such products can include hydrocarbons that can be employed for various downstream uses, such as petrochemical or for use as commodity chemicals. Such products can exclude CO and CO.sub.2. The products of the process can be marketable products, such as C.sub.2+ hydrocarbon products containing at least about 99% C.sub.2+ hydrocarbons and all sales gas or pipeline gas products containing at least about 90% methane. Process input streams can include input streams providing power for the operation of the process, such as with the aid of a turbine (e.g., steam turbine). In some cases, power for the operation of the process can be provided by heat liberated by an OCM reaction.

(42) The term “nitrogen efficiency,” as used herein, generally refers to the ratio of the number of moles of nitrogen present in all process input streams (in some cases including all nitrogen feedstocks, such as, e.g., air or purified nitrogen) to the number of moles of nitrogen present in all commercially (or industrially) usable or marketable products of the process. Such products can include ammonia and other nitrogen products that can be employed for various downstream uses, such as petrochemical use, agricultural use, or for use as commodity chemicals. Such products can exclude nitrogen oxides (NOx), such as NO and NO.sub.2. The products of the process can be marketable products, such as ammonia and derivatives thereof containing at least about 90% or 99% ammonia or ammonia derivatives. Process input streams can include input streams providing power for the operation of the process, such as with the aid of a turbine (e.g., steam turbine). In some cases, power for the operation of the process can be provided by heat liberated by a reaction, such as an OCM reaction.

(43) The term “C.sub.2+ selectivity,” as used herein, generally refers to the percentage of the moles of methane that are converted into C.sub.2+ compounds.

(44) The term “specific oxygen consumption,” as used herein, generally refers to the mass (or weight) of oxygen consumed by a process divided by the mass of C.sub.2+ compounds produced by the process.

(45) The term “specific CO.sub.2 emission,” as used herein, generally refers to the mass of CO.sub.2 emitted from the process divided by the mass of C.sub.2+ compounds produced by the process.

(46) OCM Processes

(47) In an OCM process, methane (CH.sub.4) reacts with an oxidizing agent over a catalyst bed to generate C.sub.2+ compounds. For example, methane can react with oxygen over a suitable catalyst to generate ethylene, e.g., 2 CH.sub.4+O.sub.2.fwdarw.C.sub.2H.sub.4+2 H.sub.2O (See, e.g., Zhang, Q., Journal of Natural Gas Chem., 12:81, 2003; Olah, G. “Hydrocarbon Chemistry”, Ed. 2, John Wiley & Sons (2003)). This reaction is exothermic (ΔH=−280 kJ/mol) and has typically been shown to occur at very high temperatures (e.g., >450° C. or >700° C.). Non-selective reactions that can occur include (a) CH.sub.4+2O.sub.2.fwdarw.CO.sub.2+2 H.sub.2O and (b) CH.sub.4+½ O.sub.2.fwdarw.CO+2 H.sub.2. These non-selective reactions are also exothermic, with reaction heats of −891 kJ/mol and −36 kJ/mol respectively. The conversion of methane to CO.sub.x products is undesirable due to both heat management and carbon efficiency concerns.

(48) Experimental evidence suggests that free radical chemistry is involved. (Lunsford, J. Chem. Soc., Chem. Comm., 1991; H. Lunsford, Angew. Chem., Int. Ed. Engl., 34:970, 1995). In the reaction, methane (CH.sub.4) is activated on the catalyst surface, forming methyl radicals which then couple on the surface or in the gas phase to form ethane (C.sub.2H.sub.6), followed by dehydrogenation to ethylene (C.sub.2H.sub.4). The OCM reaction pathway can have a heterogeneous/homogeneous mechanism, which involves free radical chemistry. Experimental evidence has shown that an oxygen active site on the catalyst activates the methane, removes a single hydrogen atom and creates a methyl radical. Methyl radicals react in the gas phase to produce ethane, which is either oxidative or non-oxidatively dehydrogenated to ethylene. The main reactions in this pathway can be as follows: (a) CH.sub.4+O.sup.−.fwdarw.CH.sub.3*+OH.sup.−; (b) 2 CH.sub.3*.fwdarw.C.sub.2H.sub.6; (c) C.sub.2H.sub.6+O.sup.−.fwdarw.C.sub.2H.sub.4+H.sub.2O. In some cases, to improve the reaction yield, ethane can be introduced downstream of the OCM catalyst bed and thermally dehydrogenated via the following reaction: C.sub.2H.sub.6.fwdarw.C.sub.2H.sub.4+H.sub.2. This reaction is endothermic (ΔH=144 kJ/mol), which can utilize the exothermic reaction heat produced during methane conversion. Combining these two reactions in one vessel can increase thermal efficiency while simplifying the process.

(49) Several catalysts have shown activity for OCM, including various forms of iron oxide, V.sub.2O.sub.5, MoO.sub.3, Co.sub.3O.sub.4, Pt—Rh, Li/ZrO.sub.2, Ag—Au, Au/Co.sub.3O.sub.4, Co/Mn, CeO.sub.2, MgO, La.sub.2O.sub.3, Mn.sub.3O.sub.4, Na.sub.2WO.sub.4, MnO, ZnO, and combinations thereof, on various supports. A number of doping elements have also proven to be useful in combination with the above catalysts.

(50) Since the OCM reaction was first reported over thirty years ago, it has been the target of intense scientific and commercial interest, but the fundamental limitations of the conventional approach to C—H bond activation appear to limit the yield of this attractive reaction under practical operating conditions. Specifically, numerous publications from industrial and academic labs have consistently demonstrated characteristic performance of high selectivity at low conversion of methane, or low selectivity at high conversion (J. A. Labinger, Cat. Lett., 1:371, 1988). Limited by this conversion/selectivity threshold, no OCM catalyst has been able to exceed 20-25% combined C.sub.2 yield (i.e., ethane and ethylene), and more importantly, all such reported yields required extremely high reactor inlet temperatures (>800° C.). Novel catalysts and processes have been described for use in performing OCM in the production of ethylene from methane at substantially more practicable temperatures, pressures and catalyst activities. These are described in U.S. patent application Ser. Nos. 13/115,082, 13/479,767, 13/689,611, 13/689,514, 13/901,319, 14/212,435, and 14/701,963, the full disclosures of each of which are incorporated herein by reference in its entirety for all purposes.

(51) An OCM reactor can include a catalyst that facilitates an OCM process. The catalyst may include a compound including at least one of an alkali metal, an alkaline earth metal, a transition metal, and a rare-earth metal. The catalyst may be in the form of a honeycomb, packed bed, or fluidized bed. In some embodiments, at least a portion of the OCM catalyst in at least a portion of the OCM reactor can include one or more OCM catalysts and/or nanostructure-based OCM catalyst compositions, forms and formulations. Examples of OCM reactors, separations for OCM, and OCM process designs are described in U.S. patent application Ser. Nos. 13/739,954, 13/900,898, 13/936,783, 14/553,795, and 14/592,688, the full disclosures of each of which are incorporated herein by reference in its entirety for all purposes. An OCM reactor can be adiabatic or substantially adiabatic (including, for example, a post-bed cracking unit). An OCM reactor can be isothermal or substantially isothermal.

(52) With reference to FIG. 1A, natural gas 100 and ethane 102 can enter the process through a de-sulfurization module 104, which can flow into a process gas compression module 106 where water can be removed. OCM product gas can be added to the process gas compression module 106 as well. A process gas cleanup module 108 can remove carbon dioxide (CO.sub.2), some or all which can be taken to a methanation module 110. Following cleanup, the process gas can flow into a first separations module 112 that removes C.sub.2+ compounds from the process gas stream. The remaining process gas can flow to the methanation module 110 and/or a fired heater (e.g., to heat incoming OCM gas streams 114). The C.sub.2+ compounds can be fractionated in a second separations module 116 to produce ethylene (C.sub.2H.sub.4) 118, C.sub.3 compounds 120, and C.sub.4+ compounds 122 for example. The second separations module 116 can produce an ethane (C.sub.2H.sub.6) stream 126 that is returned to the OCM reactor 128. At the OCM reactor 128, oxygen 130 can be reacted with methane from the methanation module 132. Outside boundary limits (OSBL) systems include a steam system, a boiler feed water system and a cooling water system.

(53) The OCM reactor can perform the OCM reaction and post-bed cracking (PBC), as described in U.S. patent application Ser. No. 14/553,795, which is incorporated herein by reference in its entirety. With reference to FIG. 2, the OCM reactor 200 can have an OCM reaction section 202 and a PBC section 204. Methane 206 (e.g., natural gas) and oxygen 208 can be injected (via a mixer) in to the OCM reaction region (which comprises an OCM catalyst). The OCM reaction is exothermic and the heat of reaction can be used to crack additional ethane 210 that can be injected into the PBC region 204. In some cases, yet more ethane 212 is also injected into the OCM reaction region 202 and/or the methane feed is supplemented with ethane or other C.sub.2+ alkanes (e.g., propane or butane). The OCM reactor produces an OCM effluent 214.

(54) The relative amounts of supplemental ethane 210 and 212 can be varied to achieve a range of product outcomes from the system. In some cases, no ethane is injected into the OCM reaction region 202 (referred to herein as Case-1). Another case presented herein has 3.5 mol % ethane injected into the OCM region (referred to herein as Case-2). Some process design results are presented in Table 1.

(55) TABLE-US-00001 TABLE 1 Examples of various amounts of ethane in OCM feed Case-1 Case-2 Natural gas consumed (MMSCFD) 15.5 16 Ethane consumed (MMSCFD) 2.2 8.3 [Ethane] at inlet (mol %) 0.07 3.5 [Ethylene] at outlet (mol %) 3.6 4.9 C.sub.2 products (kTa) 85 115 C.sub.3 products (kTa) 10.3 21.1 C.sub.4+ products (kTa) 2.7 2.5 O.sub.2 consumed (ton/ton ethylene) 2.2 1.8 CO.sub.2 produced from OCM (ton/ton ethylene) 0.9 0.7 CO.sub.2 produced from fired heater (ton/ton ethylene) 0.6 0.4

(56) In some cases, the amount of hydrogen (H.sub.2) exiting the OCM reactor is relatively higher for cases having relatively more ethane injection (e.g., 8% H.sub.2 for Case-1 and about H.sub.2 10% for Case-2). The amount of ethane that can be injected can be limited by the desired temperature exiting the OCM reaction region 202 or the OCM reactor 214.

(57) In some cases, the process equipment is sized to accommodate a range of amounts of additional ethane such that the process is flexible. For example, more ethane can be injected into the process when the price of ethane is relatively cheap in comparison to the price of natural gas (e.g., low frac spread).

(58) The ethane can be mixed with the natural gas and recycled to the OCM unit (as shown in FIG. 1A). In some cases, with reference to FIG. 1B, the ethane 134 can go straight to the OCM reactor, optionally through a separate de-sulfurization module 136. Injection of ethane through a separate de-sulfurization module can reduce the load in the recycle loop of the process and/or give additional production capacity keeping the same recirculation rate. The purge gas from the process can be used for fuel gas to the fired heater or sales gas.

(59) The concentration of ethane in the feed to the OCM reactor can be any suitable value, including about 0.0 mol %, about 0.25 mol %, about 0.5 mol %, about 0.75 mol %, about 1.0 mol %, about 1.25 mol %, about 1.5 mol %, about 1.75 mol %, about 2.0 mol %, about 2.25 mol %, about 2.5 mol %, about 2.75 mol %, about 3.0 mol %, about 3.25 mol %, about 3.5 mol %, about 3.75 mol %, about 4.0 mol %, about 4.25 mol %, about 4.5 mol %, about 4.75 mol %, about 5.0 mol %, about 5.25 mol %, about 5.5 mol %, about 5.75 mol %, about 6.0 mol %, or more. In some cases, the concentration of ethane in the feed to the OCM reactor is at least about 0.0 mol %, at least about 0.25 mol %, at least about 0.5 mol %, at least about 0.75 mol %, at least about 1.0 mol %, at least about 1.25 mol %, at least about 1.5 mol %, at least about 1.75 mol %, at least about 2.0 mol %, at least about 2.25 mol %, at least about 2.5 mol %, at least about 2.75 mol %, at least about 3.0 mol %, at least about 3.25 mol %, at least about 3.5 mol %, at least about 3.75 mol %, at least about 4.0 mol %, at least about 4.25 mol %, at least about 4.5 mol %, at least about 4.75 mol %, at least about 5.0 mol %, at least about 5.25 mol %, at least about 5.5 mol %, at least about 5.75 mol %, at least about 6.0 mol %, or more. In some cases, the concentration of ethane in the feed to the OCM reactor is at most about 0.0 mol %, at most about 0.25 mol %, at most about 0.5 mol %, at most about 0.75 mol %, at most about 1.0 mol %, at most about 1.25 mol %, at most about 1.5 mol %, at most about 1.75 mol %, at most about 2.0 mol %, at most about 2.25 mol %, at most about 2.5 mol %, at most about 2.75 mol %, at most about 3.0 mol %, at most about 3.25 mol %, at most about 3.5 mol %, at most about 3.75 mol %, at most about 4.0 mol %, at most about 4.25 mol %, at most about 4.5 mol %, at most about 4.75 mol %, at most about 5.0 mol %, at most about 5.25 mol %, at most about 5.5 mol %, at most about 5.75 mol %, or at most about 6.0 mol %.

(60) The systems and methods of the present disclosure can be carbon-efficient and/or energy-efficient. In some cases, the systems or methods of the present disclosure have a carbon efficiency of at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, or at least about 90%. In some cases, a system of the present disclosure or method for use thereof has a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system of at least about 0.4, at least about 0.50, at least about 0.55, at least about 0.60, at least about 0.65, at least about 0.70, at least about 0.75, at least about 0.80, at least about 0.85, at least about 0.90, or at least about 0.95.

(61) In some cases, the systems or methods of the present disclosure have a carbon efficiency of between about 50% and about 85%, between about 55% and about 80%, between about 60% and about 80%, between about 65% and about 85%, between about 65% and about 80%, or between about 70% and about 80%. In some cases, a system of the present disclosure or method for use thereof has a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system of between about 0.50 and about 0.85, between about 0.55 and about 0.80, between about 0.60 and about 0.80, between about 0.65 and about 0.85, between about 0.65 and about 0.80, or between about 0.70 and about 0.80.

(62) In some instances, the carbon efficiency is at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85% or at least about 90%. In some instances, the carbon efficiency is between about 50% and about 85%, between about 55% and about 80%, between about 60% and about 80%, between about 65% and about 85%, between about 65% and about 80%, or between about 70% and about 80%. In some instances, a system of the present disclosure or method for use thereof has a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system of at least about 0.60, at least about 0.65, at least about 0.70, at least about 0.75, at least about 0.80, at least about 0.85 or at least about 0.90. In some instances, a system of the present disclosure or method for use thereof has a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system of between about 0.50 and about 0.85, between about 0.55 and about 0.80, between about 0.60 and about 0.80, between about 0.65 and about 0.85, between about 0.65 and about 0.80, or between about 0.70 and about 0.80.

(63) In some cases, the systems and methods combine OCM reaction, post-bed cracking (PBC), separations and methanation. The separations can include oligomerization of ethylene to C.sub.3+ compounds, which are more easily separated as described in PCT Patent Application No. PCT/US2015/010525, which is incorporated herein by reference in its entirety. Additional details of OCM reactor and process design can be found in PCT Patent Application No. PCT/US2014/057465 and PCT Patent Application No. PCT/US2015/010688, each of which are incorporated herein by reference in their entirety.

(64) In an aspect, provided herein is a method for performing oxidative coupling of methane (OCM). The method can comprise (a) reacting oxygen (O.sub.2) with methane (CH.sub.4) to form heat, ethylene (C.sub.2H.sub.4) and optionally ethane (C.sub.2H.sub.6), hydrogen (H.sub.2), carbon monoxide (CO) or carbon dioxide (CO.sub.2); (b) reacting the heat produced in (a) with ethane (C.sub.2H.sub.6) to form ethylene (C.sub.2H.sub.4) and hydrogen (H.sub.2); (c) performing at least one of (i) enriching the ethylene (C.sub.2H.sub.4) produced in (a) and (b) or (ii) oligomerizing the ethylene (C.sub.2H.sub.4) produced in (a) and (b) to produce C.sub.3+ compounds and enriching the C.sub.3+ compounds; and (d) reacting the hydrogen (H.sub.2) produced in (a) and (b) with carbon monoxide (CO) and/or carbon dioxide (CO.sub.2) to form methane (CH.sub.4).

(65) In another aspect, provided herein is a system for performing oxidative coupling of methane (OCM). The system comprises an OCM reactor that reacts oxygen (O.sub.2) with methane (CH.sub.4) to form heat, ethylene (C.sub.2H.sub.4) and optionally ethane (C.sub.2H.sub.6), hydrogen (H.sub.2), carbon monoxide (CO) or carbon dioxide (CO.sub.2). The system further comprises a cracking vessel in fluid communication with the OCM reactor, which cracking vessel reacts the heat produced in the OCM reactor with ethane (C.sub.2H.sub.6) to form ethylene (C.sub.2H.sub.4) and hydrogen (H.sub.2). The system further comprises a separations module in fluid communication with the cracking vessel, which separation module (i) enriches the ethylene (C.sub.2H.sub.4) produced in the OCM reactor and the cracking vessel or (ii) oligomerizes the ethylene (C.sub.2H.sub.4) produced in the OCM reactor and the cracking vessel to produce C.sub.3+ compounds and enriches the C.sub.3+ compounds. The system further comprises a methanation reactor in fluid communication with the separations module, which methanation reactor reacts the hydrogen (H.sub.2) produced in the OCM reactor and the cracking vessel with carbon monoxide (CO) and/or carbon dioxide (CO.sub.2) to form methane (CH.sub.4).

(66) In some cases, the ethane (C.sub.2H.sub.6) that is cracked in the cracking vessel was produced in the OCM reactor. In some instances, at least some of the ethane (C.sub.2H.sub.6) that is cracked is in addition to the ethane (C.sub.2H.sub.6) that was produced in the OCM reactor. In some cases, the OCM reactor produces ethane (C.sub.2H.sub.6), hydrogen (H.sub.2), carbon monoxide (CO) and carbon dioxide (CO.sub.2). In some cases, the carbon monoxide (CO) and carbon dioxide (CO.sub.2) produced in the OCM reactor is methanated. The separations module can separate ethylene (C.sub.2H.sub.4) or C.sub.3+ compounds from methane (CH.sub.4), ethane (C.sub.2H.sub.6), hydrogen (H.sub.2), carbon monoxide (CO) or carbon dioxide (CO.sub.2). In some instances, the cracking vessel is a portion of the OCM reactor.

(67) The methane formed in the methanation reactor can be returned to the OCM reactor or sold as sales gas. In some embodiments, the OCM reactor has an OCM catalyst. In some embodiments, the methanation reactor has a methanation catalyst. In some embodiments, the separations module comprises an ethylene-to-liquids (ETL) reactor comprising an oligomerization catalyst. At least some of the heat produced in the OCM reactor can be converted to power.

(68) In another aspect, described herein is a method for producing C.sub.2+ compounds from methane (CH.sub.4). The method can comprise: (a) performing an oxidative coupling of methane (OCM) reaction which converts methane (CH.sub.4) and oxygen (O.sub.2) into ethylene (C.sub.2H.sub.4) and optionally ethane (C.sub.2H.sub.6); (b) optionally oligomerizing the ethylene (C.sub.2H.sub.4) to produce C.sub.3+ compounds; and (c) isolating the C.sub.2+ compounds, wherein the C.sub.2+ compounds comprise the ethylene (C.sub.2H.sub.4), the ethane (C.sub.2H.sub.6) and/or the C.sub.3+ compounds, where the method has a carbon efficiency of at least about 50%. In some cases, the isolated the C.sub.2+ compounds are not pure. In some cases, the isolated the C.sub.2+ compounds comprise methane, CO, H.sub.2, CO.sub.2 and/or water.

(69) In some cases, the systems or methods of the present disclosure consume less than about 150, less than about 140, less than about 130, less than about 120, less than about 110, less than about 100, less than about 95, less than about 90, less than about 85, less than about 80, less than about 75, less than about 70, less than about 65, less than about 60, less than about 55, or less than about 50 million British Thermal Units (MMBtu) of energy per ton of ethylene (C.sub.2H.sub.4) or C.sub.3+ compounds enriched. In some cases, the amount of energy consumed by the system includes the energy content of the feedstock used to make the ethylene (C.sub.2H.sub.4) or C.sub.3+ compounds.

(70) In some cases, the systems or methods of the present disclosure have consume between about 65 and about 100, between about 70 and about 110, between about 75 and about 120, between about 85 and about 130, between about 40 and about 80, or between about 50 and about 80 MMBtu of energy per ton of ethylene (C.sub.2H.sub.4) or C.sub.3+ compounds enriched. In some cases, the amount of energy consumed by the system includes the energy content of the feedstock used to make the ethylene (C.sub.2H.sub.4) or C.sub.3+ compounds.

(71) In some embodiments, the systems or methods of the present disclosure have a specific oxygen consumption of about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 1.7, about 1.8, about 1.9, about 2.0, about 2.1, about 2.2, about 2.3, about 2.4, about 2.5, about 2.6 about 2.7, about 2.8, about 2.9, about 3, about 3.2, about 3.4, about 3.6, about 3.8, or about 4.0.

(72) In some embodiments, the systems or methods of the present disclosure have a specific oxygen consumption of between about 1.2 and about 2.7, between about 1.5 and about 2.5, between about 1.7 and about 2.3 or between about 1.9 and about 2.1.

(73) In some embodiments, the systems or methods of the present disclosure have a specific CO.sub.2 emission of about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, about 1.1, about 1.2, about 1.3, about 1.4, about 1.5, about 1.6, about 2.0, about 2.2, about 2.4, about 2.6, about 2.8, about 3.0, about 3.2, about 3.4, or about 3.6.

(74) In some embodiments, the systems or methods of the present disclosure have a specific CO.sub.2 emission of between about 0.5 and about 1.7, between about 0.7 and about 1.4, between about 0.8 and about 1.3 or between about 0.9 and about 1.1.

(75) In some embodiments, the systems or methods of the present disclosure produces C.sub.2+ products, and the C.sub.2+ products comprise at least about 2.5%, at least about 2.5%, at least about 5%, at least about 7.5%, at least about 10%, at least about 12.5% or at least about 15% C.sub.3+ hydrocarbons.

(76) In some embodiments, the systems or methods of the present disclosure produces C.sub.2 products and C.sub.3+ products, and the ratio of the C.sub.2 products to the C.sub.3+ products is about 20, about 15, about 10, about 8, about 6 or about 5.

(77) In some embodiments, the systems or methods of the present disclosure produces C.sub.2 products and C.sub.3+ products, and the ratio of the C.sub.2 products to the C.sub.3+ products is between about 5 and about 20, between about 6 and about 10, or between about 8 and about 10.

(78) In another aspect, provided herein is a method for producing C.sub.2+ compounds from methane (CH.sub.4), the method comprising: (a) performing an oxidative coupling of methane (OCM) reaction which converts methane (CH.sub.4) and oxygen (O.sub.2) into ethylene (C.sub.2H.sub.4) and optionally ethane (C.sub.2H.sub.6); (b) optionally oligomerizing the ethylene (C.sub.2H.sub.6) to produce C.sub.3+ compounds; and (c) isolating the C.sub.2+ compounds, wherein the C.sub.2+ compounds comprise the ethylene (C.sub.2H.sub.4), the ethane (C.sub.2H.sub.6) and/or the C.sub.3+ compounds, where the method consumes less than about 100 MMBtu of energy per ton of the C.sub.2+ compounds isolated. In some cases, the amount of energy consumed by the system includes the energy content of the feedstock used to make the isolated C.sub.2+ compounds. In some cases, the isolated the C.sub.2+ compounds are not pure. In some cases, the isolated the C.sub.2+ compounds comprise methane, CO, Hz, CO.sub.2 and/or water.

(79) In some cases, the method consumes less than about 150, less than about 140, less than about 130, less than about 120, less than about 110, less than about 100, less than about 95, less than about 90, less than about 85, less than about 80, less than about 75, less than about 70, less than about 65, less than about 60, less than about 55, or less than about 50 MMBtu of energy per ton of C.sub.2+ compounds isolated. In some cases, the method consumes between about 65 and about 100, between about 70 and about 110, between about 75 and about 120, between about 85 and about 130, between about 40 and about 80, or between about 50 and about 80 MMBtu of energy per ton of C.sub.2+ compounds isolated.

(80) In another aspect, provided herein is a method for producing C.sub.2+ compounds from methane (CH.sub.4), the method comprising performing an oxidative coupling of methane (OCM) reaction using an OCM catalyst at a set of reaction conditions to convert a quantity of methane (CH.sub.4) into ethylene (C.sub.2H.sub.4) at a carbon efficiency, where the OCM catalyst has a C.sub.2+ selectivity at the set of reaction conditions that is less than the carbon efficiency at the set of reaction conditions. The set of reaction conditions can include a temperature, a pressure, a methane to oxygen ratio and a gas hourly space velocity (GHSV).

(81) In another aspect, provided herein is a method for producing C.sub.2+ compounds from methane (CH.sub.4), the method comprising: (a) performing an oxidative coupling of methane (OCM) reaction using an OCM catalyst at a set of reaction conditions to convert a quantity of methane (CH.sub.4) into ethylene (C.sub.2H.sub.4) and ethane (C.sub.2H.sub.6); and (b) cracking the ethane (C.sub.2H.sub.6) to produce additional ethylene (C.sub.2H.sub.4), where the combined carbon efficiency of (a) and (b) is greater than the C.sub.2+ selectivity of the OCM catalyst at the set of reaction conditions. The set of reaction conditions can include a temperature, a pressure, a methane to oxygen ratio and a gas hourly space velocity (GHSV).

(82) In some instances, the C.sub.2+ selectivity is at most about 70%, at most about 65%, at most about 60%, at most about 55%, at most about 50%, at most about 45%, at most about 40%, or at most about 35%. In some instances, the C.sub.2+ selectivity is at least about 70%, at least about 65%, at least about 60%, at least about 55%, at least about 50%, at least about 45%, at least about 40%, or at least about 35%.

(83) In another aspect, provided herein is a method for producing C.sub.2+ compounds, the method comprising: (a) providing a first feedstock comprising methane (CH.sub.4) and optionally a first amount of ethane (C.sub.2H.sub.6); (b) performing an OCM reaction on the first feedstock to produce an OCM product comprising a first amount of ethylene (C.sub.2H.sub.4); (c) combining the OCM product with a second feedstock comprising a second amount of ethane (C.sub.2H.sub.6) to produce a third feedstock; and (d) cracking the third feedstock to produce a second amount of ethylene (C.sub.2H.sub.4), where the second amount of ethylene includes ethylene produced in (b) and (d).

(84) In some cases, the fraction of the second amount of ethylene (C.sub.2H.sub.4) that is derived from the first or the second amounts of ethane (C.sub.2H.sub.6) is at least about 1%, at least about 3%, at least about 5%, at least about 7%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, or at least about 55%.

(85) In some cases, the combined moles of the first amount and second amount of ethane (C.sub.2H.sub.6) divided by the combined moles of the first feedstock and the second feedstock is about 1%, about 3%, about 5%, about 7%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, or about 60%.

(86) In some cases, the combined moles of the first amount and second amount of ethane (C.sub.2H.sub.6) divided by the combined moles of the first feedstock and the second feedstock is between about 1% and about 50%, between about 1% and about 40%, between about 1% and about 30%, between about 1% and about 20%, between about 1% and about 15%, between about 1% and about 10%, or between about 10% and about 50%.

(87) In some cases, the first feedstock is natural gas. In some cases, the first feedstock is natural gas supplemented with the first amount of ethane (C.sub.2H.sub.6). In some cases, the first feedstock is natural gas having passed through a separations system to substantially remove the hydrocarbons other than methane.

(88) In some cases, the molar percent of ethane (C.sub.2H.sub.6) in methane (CH.sub.4) in the first feedstock is about 1%, about 3%, about 5%, about 7%, about 10%, about 15% or about 20%.

(89) In some cases, some or all of a methane-containing feed stream (e.g., natural gas) can be processed in a separation system prior to being directed into an OCM reactor. Directing a methane-containing feed stream into an OCM reactor via a separation system or subsystem rather than into an OCM reactor directly can provide advantages, including but not limited to increasing the carbon efficiency of the process, optimizing the OCM process for methane processing, and optimizing the post-bed cracking (PBC) process for ethane processing. Such a configuration can result in higher back-end sizing for the system; however, in some cases (e.g., when using high pressure pipeline natural gas as a feedstock, high recycle ratio), the back-end sizing increase can be reduced or moderated. The separation system or subsystem can comprise a variety of operations including any discussed in the present disclosure, such as CO.sub.2 removal via an amine system, caustic wash, dryers, de-methanizers, de-ethanizers, and C.sub.2 splitters. In some cases, all of the methane and ethane in the methane-containing feed stream (e.g., natural gas) passes through a separations system or separations subsystem prior to passing through an OCM reactor. Some or all of the ethane from the feed stream can be directed from the separation system or subsystem into the inlet of an OCM reactor or into a post-bed cracking (PBC) unit.

(90) In some configurations, an OCM system can be operated in a cycle, with at least some of the products from one unit or subsystem being processed or reacted in the next unit or subsystem (see, e.g., FIG. 1C). For example, oxygen (O.sub.2) 3201 and methane (CH.sub.4) feed 3202 can be provided to an OCM reactor 3203, which produces an OCM product stream 3204 comprising ethane (C.sub.2H.sub.6), ethylene (C.sub.2H.sub.4), carbon monoxide (CO) and/or carbon dioxide (CO.sub.2), and heat. The OCM product stream can then be fed into an ethane conversion subsystem 3205 (e.g., a cracking vessel or an ethane cracker) in fluid communication with the OCM reactor. The ethane conversion subsystem can also receive an additional C.sub.2H.sub.6 stream 3206. The ethane conversion subsystem can convert C.sub.2H.sub.6 (e.g., crack C.sub.2H.sub.6 to C.sub.2H.sub.4) with the aid of the heat liberated by the OCM reaction; this heat can also be used to crack the C.sub.2H.sub.6 in the additional C.sub.2H.sub.6 stream. A C.sub.2H.sub.4 product stream 3207 can then be directed from the ethane conversion subsystem into a separations module 3208 in fluid communication with the ethane conversion subsystem. The separations module can enrich products such as C.sub.2H.sub.4 in the product stream. The separations module can also oligomerize C.sub.2H.sub.4 to form compounds comprising three or more carbon atoms (C.sub.3+ compounds). An enriched product stream 3209 enriched in C.sub.2H.sub.4 and/or C.sub.3+ compounds can be recovered from the separations module. A lights stream 3210 comprising components such as hydrogen (H.sub.2) (e.g., hydrogen generated from the cracking of C.sub.2H.sub.6) and CO and/or CO.sub.2 can be recovered from the separations module and directed into a methanation reactor 3211 in fluid communication with the separations module. The methanation reactor can react H.sub.2 with CO and/or CO.sub.2 to form a methanated stream 3212 comprising CH.sub.4. The methanated stream can then be directed into the OCM reactor to provide additional methane for the OCM process. In some cases, energy generated in the methane conversion section in the form of high pressure steam, high temperature steam, heat, electricity, heat transferred via gas-gas heat exchanger, heat transferred via gas-liquid heat exchanger, or other forms, can be used to provide all of the energy and power required to run the entire plant or system. In some cases, a cyclical system or process can operate with a carbon efficiency such as those discussed in this disclosure. For example, such a system or process can operate with a carbon efficiency of at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, or at least about 90%. In some cases, such a system or process can operate with a carbon efficiency of between about 50% and about 85%, between about 55% and about 80%, between about 60% and about 80%, between about 65% and about 85%, between about 65% and about 80%, or between about 70% and about 80%. In some cases, such a system or process (or method) can operate such that a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system is at least about 0.50, at least about 0.55, at least about 0.60, at least about 0.65, at least about 0.70, at least about 0.75, at least about 0.80, at least about 0.85, or at least about 0.90. In some cases, such a system or process can operate such that a ratio of all carbon atoms output from the system as hydrocarbons to all carbon atoms input to the system is between about 0.50 and about 0.85, between about 0.55 and about 0.80, between about 0.60 and about 0.80, between about 0.65 and about 0.85, between about 0.65 and about 0.80, or between about 0.70 and about 0.80.

(91) FIG. 1D and FIG. 1E show an exemplary process comprising an OCM unit 3301, a process gas compressor 3302, a process gas cleanup unit 3303, a cryogenic separations unit 3304, a fractionation unit 3305, a methanation unit 3306, and a sulfur-removal unit 3307. An oxygen stream 3311 is fed into the OCM unit, along with a C.sub.1 recycle stream 3314 from the methanation unit and a C.sub.2 recycle stream 3315 from the fractionation unit. A natural gas stream 3312 and an ethane stream 3313 are fed into the sulfur removal unit. Output from the OCM unit and the sulfur removal unit are directed into the process gas compressor, and then into the process gas cleanup unit, which removes a CO.sub.2 stream 3319. The remaining product stream is directed into the cryogenic separations unit, where light components including H.sub.2 and CO or CO.sub.2 are directed into the methanation unit, and the remaining product stream, including ethylene and other C.sub.2+ compounds, is directed into the fractionation unit. The fractionation unit separates an ethylene stream 3316 and a C.sub.3+ compound stream 3317 comprising C.sub.3 compounds, C.sub.4 compounds, and C.sub.5+ compounds, as well as the C.sub.2 recycle 3315 which is directed back to the OCM unit. The methanation unit converts the light components into methane, a first portion of which is recycled 3314 to the OCM unit and a second portion of which is output as sales gas 3318. The operating flow rates for the input streams are as follows: 20.3 MT/h of oxygen 3311, 16.0 MT/h of natural gas 3312, and 2.9 MT/h of ethane 3313. The operating flow rates for the output streams are as follows: 9.0 MT/h of ethylene 3316, 1.4 MT/h of C.sub.3+ compounds 3317, 4.3 MT/h of sales gas 3318, and 8.2 MT/h of CO.sub.2 3319. The corresponding carbon content of the input streams are 972 kmol/h of carbon in the natural gas stream 3312, and 194 kmol/h of carbon in the ethane stream 3313. The corresponding carbon content of the output streams are 642 kmol/h of carbon in the ethylene stream 3316, 96 kmol/h of carbon in the C.sub.3+ compounds stream 3317, 247 kmol/h of carbon in the sales gas stream 3318, and 181 kmol/h of carbon in the CO.sub.2 stream 3319. Therefore, the amount of carbon input to the system is 1166 kmol/h, and the amount of carbon output from the system in hydrocarbon products (e.g., excluding CO.sub.2) is 985 kmol/h, for a resulting carbon efficiency of 84.5%.

(92) Reaction heat (e.g., OCM reaction heat) can be used to supply some, most, or all of the energy used to operate systems and perform processes of the present disclosure. In some examples, reaction heat can be used to supply at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% of energy for operating systems and performing processes of the present disclosure. For example, the reaction heat can be used to supply at least about 80% or 90% of all of the energy for operating systems or processes of the present disclosure. This can provide for an efficient, substantially self-contained system with reduced or even minimum external energy input.

(93) Integration of OCM Processes with Other Chemical Processes

(94) There exists an infrastructure for chemical production throughout the world. This infrastructure is deployed on virtually every continent, addresses wide ranging industries, and employs a wide variety of different implementations of similar or widely differing technologies.

(95) The present disclosure provides systems and methods for integrating OCM systems and methods with various chemical processes, such as methanol (MeOH) production, chlorine (Cl.sub.2) and sodium hydroxide (NaOH) production (e.g., chloralkali process), vinylchloride monomer (VCM) production, ammonia (NH.sub.3) production, processes having syngas (e.g., mixtures of hydrogen (H.sub.2) and carbon monoxide (CO) in any proportion), or olefin derivative production.

(96) As will be appreciated, the capital costs associated with each of the facility types described above can run from tens of millions to hundreds of millions of dollars each. Additionally, there are inputs and outputs, of these facilities, in terms of both energy and materials, which have additional costs associated with them, both financial and otherwise that may be further optimized in terms of cost and efficiency. Further, because different facilities tend to be optimized for the particularities (e.g., products, processing conditions) of the market in which they exist, they tend to be operated in an inflexible manner, in some cases without the flexibility or option to optimize for their given market. The present inventors have recognized surprising synergies when integrating OCM with the aforementioned chemical processes which can result in improved economics and/or operational flexibility.

(97) In some cases, the OCM processes described herein are integrated with an olefin oligomerization process, such as an ethylene-to-liquids (“ETL”) process as described in U.S. patent Ser. Nos. 14/099,614, and 14/591,850, the full disclosures of each of which are incorporated herein by reference in its entirety for all purposes.

(98) In some instances, the OCM process can be sized to fit the needs of an ethylene derivatives plant. Such a synergy can liberate the derivatives producer from being a merchant buyer of ethylene, allowing the producer more ethylene cost and supply certainty. Examples of ethylene derivatives include polyethylene, including low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and high-density polyethylene (HDPE). Additional ethylene derivatives include ethylbenzene, styrene, acetic acid, vinylacetate monomer, ethylene dichloride, vinylchloride monomer, ethylene oxide and alpha olefins.

(99) Integration of OCM Processes with Methanol Processes

(100) The OCM processes can be integrated with methanol production processes to realize unexpected synergies potentially including, but not limited to (a) additional methanol capacity with minimal or no modification to the methanol plant and (b) additional ethylene capacity with low investment and environmental footprint.

(101) FIG. 3 shows an example of a block flow diagram of a methanol plant (e.g., a traditional methanol process, recognizing that alternate embodiments are allowed and details have been emitted for clarity). As shown, natural gas 300 can be used for feed and fuel for the process. The feed 302 (e.g., natural gas providing the carbon atoms for the methanol product) can have sulfur-containing compounds removed in a de-sulfurization module 304 before being fed into a steam methane reformer (SMR, entire gray shaded unit) 306. The SMR can also accept natural gas as fuel 308 (e.g., natural gas providing energy for the methanol plant), which does not necessarily have to be de-sulfurized. The effluent of the steam methane reformer is syngas, which can have heat recovered in a heat recovery module 310 and compressed in a compression module 312. Compressed syngas can be feed into the synthesis module 314 where conversion to methanol occurs. One suitable methanol synthesis module can have a catalyst that is a mixture of copper, zinc, and alumina, and operates at a pressure between about 50 and about 100 atmospheres and a temperature of about 250° C. The production of syngas produces 3 moles of H.sub.2 per mol of CH.sub.4, while the stoichiometry of methanol formation from syngas consumes only 2 moles of H.sub.2. Thus, excess H.sub.2 (and un-reacted CH.sub.4) can be purged 316 from the synthesis module and separated in a gas separation module 318 (e.g., a pressure swing adsorber). The separation module can produce additional fuel 320 for the SMR and a H.sub.2 co-product 322. The methanol product 324 can be enriched (e.g., by a distillation module 326). In some cases, the excess H.sub.2 is used as fuel (not shown).

(102) A combined process that integrates OCM with methanol production is shown in FIG. 4, where like numerals represent like elements. The OCM portion of the combined process can accept the de-sulfurized natural gas feedstock 414 and include an OCM reaction module 400, a process gas compression module 402, a CO.sub.2 removal module (e.g., process gas cleanup) 404, a drying module 406 and a separations module (e.g., a cryogenic de-methanizer) 408. In some cases, the separation module produces the C.sub.2+ compounds 410. The C.sub.2+ compounds can be further refined, and/or sent to a cracker (e.g., to the separation section of a cracker). Note that the OCM process does not require a methanation module. The OCM reaction can produce high-pressure super-heated (HPSH) steam 412 that can be used in the process and/or to produce power using a steam turbine.

(103) Continuing with FIG. 4, the OCM portion of the process can produce a stream of methane that was not converted to C.sub.2+ compounds 416 in the OCM reaction. This stream 416 can have H.sub.2 and CO in addition to methane and can be used as the feed to the methanol production process (e.g., at the SMR) and/or as fuel to the process (dashed line) 418. The stream of CO.sub.2 420 from the OCM process can also be used in the methanol synthesis module 314 to produce one mole of methanol and one mole of water from one mole of CO.sub.2 and 3 moles of H.sub.2. The water co-product can be removed in the distillation module 326.

(104) The combined OCM-methanol process has considerable economic and environmental benefits. In some cases, CO.sub.2 from OCM 420 can be used to re-balance the make-up gas to the synthesis module and convert some or all of the excess H.sub.2 to methanol (e.g., the flow-rate of stream 322 can be zero or very small in comparison to the flow rate without OCM integration). Furthermore, the reformer 306 capacity can be automatically increased due to the “pre-formed” nature of the OCM de-methanizer overhead 416 stream (e.g., already contains some H.sub.2 and CO). This can be useful for replacing a mixed feed coil. In some instances, the only cost associated with the production of extra methanol due to OCM integration is the loss in value of the H.sub.2 co-product 322 in situations where that stream is actually monetized or monetizable. Such integration schemes can result in improved efficiency of an existing methanol system, for example by using excess H.sub.2 by reacting it with CO.sub.2 produced from an OCM unit to produce a more valuable methanol product. Depending on the capacity of the OCM process, an integrated OCM-methanol system can be pushed to a low emission, high carbon efficiency process.

(105) When retrofitting an existing methanol plant, the OCM process can be sized to the desired amount of extra methanol production. From the OCM perspective, building an OCM process to be integrated with a methanol plant can require significantly less capital than building a stand-alone OCM process, e.g., due to reducing or eliminating the need for fractionation and methanation equipment. The OCM process can also use the utilities of the existing methanol plants, such as steam. In some cases, the combined process produces zero or a minimal amount of NO.sub.x and SO.sub.x compounds.

(106) The combined OCM-methanol process can be about 100% carbon efficient (e.g., with reference to FIG. 4, all of the carbon atoms input to the process 300 end up in the methanol 324 or the C.sub.2+ compounds 410). In some cases, the combined process is less than 100% carbon efficient, e.g., greater than or equal to about 99%, greater than or equal to about 98%, greater than or equal to about 97%, greater than or equal to about 96%, greater than or equal to about 95%, greater than or equal to about 93%, greater than or equal to about 90%, greater than or equal to about 85%, greater than or equal to about 80%, or greater than or equal to about 75% carbon efficient.

(107) In some cases, with reference to FIG. 5, methanol plants 500 are located in proximity to crackers 502 and/or other processes 504 that use natural gas (e.g., within 1, 5, 10, 20, 50, 100, 200 miles or more). In some cases, these processes share a piping infrastructure and/or can access a piping infrastructure for transporting natural gas, ethylene, hydrogen and other chemicals. These processes can convert the natural gas 506 into a combination of methanol 508, hydrogen 510, ethylene 512, and other products 514. OCM can be integrated with any combination of these processes (e.g., 500, 502 and 504) in a number of ways as shown in FIG. 6, FIG. 7 and FIG. 8.

(108) FIG. 6 shows a “minimum revamp case” where an OCM process 600 accepts natural gas 506 and provides CO.sub.2 602 to a methanol process 500 and crude ethylene 604 to a cracker 502. The ethylene can be refined to a finished product (e.g., polymer grade ethylene) 512 using the fractionation capacity of the cracker. In this case, the OCM process can be sized to accept an amount of natural gas that is substantially equivalent to the methanol plant natural gas input (e.g., about 60 to 70 MMSCFD). This OCM capacity can result in about 25-30 kTa additional ethylene and about 15% to 20% additional methanol produced. In some cases, for the minimum revamp case, the only capital investment is for the OCM unit 600 and in some cases mixed feed coil replacement in the SMR.

(109) FIG. 7 shows a “medium revamp case” where an OCM process 700 accepts natural gas 506 and provides CO.sub.2 702 to a methanol process 500 and crude ethylene 704 to a cracker 502. In this case, the OCM process can be sized to accept an amount of natural gas that is substantially equivalent to the methanol plant natural gas input 706 and cracker fuel input 708 (e.g., about 140 to 150 MMSCFD). This OCM capacity can result in about 60-80 kTa additional ethylene and about 30% to 40% additional methanol produced. In some cases, for the medium revamp case, capital investment is needed for the OCM unit 700 and methanol debottlenecking (e.g., reformer, syngas compressor, synthesis module and topping column).

(110) FIG. 8 shows a “maximum efficiency revamp case” where the size of the OCM process is not constrained. For example, all of the natural gas entering an entire petrochemical complex can be skimmed. An OCM process 800 accepts natural gas 506 and provides CO.sub.2 802 to a new methanol synthesis module 804. In some cases, the new methanol synthesis module 804 accepts H.sub.2 806 from various sources including an existing methanol process 500 and/or a cracker 502. The new methanol synthesis module 804 can provide crude methanol 808 to the existing methanol process for refining to a methanol product 508. As in the other revamp scenarios, crude ethylene 810 can be refined in a cracker 502. In some cases, the OCM results in about 150-200 kTa additional ethylene, the integration results in about 60% to 70% additional methanol produced. In some cases, for the maximum efficiency revamp case, capital investment is needed for the OCM unit, a new methanol synthesis module (fed with the excess H.sub.2 across the entire complex and CO.sub.2 from OCM) and in some cases debottlenecking of methanol distillation. The various revamp cases are not mutually exclusive and can be designed as successive project phases. In addition, larger capacity plants can be combined with larger methanol production plants.

(111) Integration of OCM Processes with Chloralkali Processes

(112) With reference to FIG. 9, the chloralkali process 900 is an industrial process for the electrolysis of sodium chloride (NaCl) 902 to produce chlorine gas (Cl.sub.2) 904 and sodium hydroxide (NaOH) 906. The process is typically conducted with an aqueous solution of sodium chloride (NaCl) (e.g., the process uses water 908) and produces a hydrogen (H.sub.2) 910 co-product. Other chloride compounds can be used, such as lithium chloride (LiCl), potassium chloride (KCl), calcium chloride (CaCl.sub.2), and magnesium chloride (MgCl.sub.2), and hydrates thereof. The chloralkali process consumes a considerable amount of electrical power 912. There are three chloralkali methods currently used in industry, referred to as membrane plants, diaphragm plants, and mercury plants. New electrochemical cells and processes are being developed that, for example, use a metal chloride intermediate, such as described in U.S. patent application Ser. Nos. 12/989,785, 12/721,545, 12/375,632, and 12/541,055, each of which is incorporated herein by reference in its entirety. Each type of chloralkali process can be integrated with OCM to realize surprising synergies described herein.

(113) FIG. 10 shows a schematic illustration of an OCM process 1000 integrated with a chloralkali process 900. The OCM process, consumes oxygen (O.sub.2) 1002 and methane 1004 (e.g., natural gas) and produces C.sub.2+ compounds such as ethylene 1006. The OCM process can accept H.sub.2 910 from the chloralkali process (e.g., at the methanation module 110 as shown in FIG. 1A) for conversion of CO and/or CO.sub.2 to additional methane for recycle to the OCM reactor. The OCM process is exothermic and the heat of reaction can be converted to electricity 912 (e.g., cogeneration) for use in the chloralkali process.

(114) Integration of OCM Processes with EDC and/or VCM Process

(115) The present disclosure recognizes certain unexpected synergies that can be achieved by integrating OCM with the production of vinylchloride monomer (VCM) and/or ethylene dichloride (EDC) (e.g., EDC/VCM process). This is because the EDC/VCM process uses ethylene as a feedstock, but does not require polymer-grade ethylene. Therefore, the OCM process does not require significant capital and operating expense associated with purifying ethylene.

(116) With reference to FIG. 11, the ethylene 1100 can be provided by OCM (not shown). The ethylene can be about 99.99%, about 99.95%, about 99.9%, about 99.5%, about 99%, about 97%, about 95%, about 93%, about 90%, about 85%, about 80%, about 75%, or about 70% pure on a mass basis. In some cases, the ethylene is less than about 99.99%, less than about 99.95%, less than about 99.9%, less than about 99.5%, less than about 99%, less than about 97%, less than about 95%, less than about 93%, less than about 90%, less than about 85%, less than about 80%, less than about 75%, or less than about 70% pure on a mass basis. In some cases, the ethylene is greater than about 70%, greater than about 75%, greater than about 80%, greater than about 85%, greater than about 90%, greater than about 93%, greater than about 95%, greater than about 97%, greater than about 99%, greater than about 99.5%, greater than about 99.9%, greater than about 99.95%, or greater than about 99.99% pure on a mass basis.

(117) Continuing with FIG. 11, the ethylene 1100 can be added to a direct chlorination reactor 1102 and/or an oxy-chlorination reactor 1104. The direct chlorination reactor 1102 uses chlorine gas (Cl.sub.2) 1106 as a reactant and the oxy-chlorination reactor 1104 uses oxygen (O.sub.2) 1108 and hydrochloric acid (HCl) 1110 as reactants. The HCl can be produced in the process and recycled to the oxy-chlorination reactor 1104. A first separations module 1112 can be used to enrich an EDC product 1114. A portion of the EDC can be cracked in a furnace 1116 using, for example, energy derived from natural gas 1118 and/or H.sub.2 1120. The cracked EDC can be separated in a second separations module 1122 to provide a VCM product stream 1124 and HCl 1126, which can be recycled 1110 to the oxy-chlorination reactor 1104.

(118) Some chloralkali process are integrated with the production of vinylchloride monomer (VCM) and/or ethylene dichloride (EDC). As shown in FIG. 12, some of the Cl.sub.2 904 produced by the chloralkali process 900 can be used in the EDC/VCM process 1200 (e.g., in the direct chlorination reactor 1102). Also, some or all of the H.sub.2 910 produced by the chloralkali process 900 can be used in the EDC/VCM process 1200 (e.g., as fuel 1120 for the EDC cracking furnace 1116). Additional fuel for the EDC cracking furnace can be derived from natural gas 1118. The process consumes ethylene 1100 and some of the products of the combined chloralkali and EDC/VCM process include EDC product 1114, VCM 1124 and HCl 1126.

(119) In some instances, as shown in FIG. 13, OCM can be integrated with both an EDC/VCM process and a chloralkali process. In this case, the chloralkali process 900 provides H.sub.2 1300 to the OCM process, the OCM process provides electrical power 1302 to the chloralkali process, and the OCM process provides ethylene 1304 to the EDC/VCM process 1200.

(120) In some cases, a modified chloralkali process is integrated with a modified EDC production process in which Cl.sub.2 is not produced as an intermediate. Instead, a metal chloride solution can be produced (e.g., CuCl.sub.2) as the intermediate, for example as described in U.S. patent application Ser. No. 14/446,791, which is incorporated herein by reference in its entirety. OCM can also be integrated with these facilities as described herein.

(121) The processes of the present disclosure can take advantage of the synergies made possible by OCM integration to chloralkali, EDC, or VCM producing units. An OCM unit can be a good fit between inputs and outputs of the two processes; OCM can produce ethylene and power, which can be the main inputs to chloralkali, EDC, or VCM processes. Chloralkali processes can produce hydrogen as a main co-product, which can be utilized in an OCM unit (rather than being combusted or vented) to reduce or eliminate CO.sub.2 emissions and push carbon efficiency towards or up to 100%. EDC processes can operate with non-polymer-grade ethylene (alkanes are inert in EDC processes), so the separations unit of an OCM unit can produce chemical grade ethylene, which can result in a reduced capital expenditure (capex). Additionally, typical EDC scale can match small scale OCM implementations.

(122) FIG. 14 shows an example of a process integrating OCM with a diaphragm-type chloralkali process. The production capacity of the chloralkali process is at least about 300,000 tons per year (300 kTa) of chlorine. The production capacity of the OCM process is at least about 100,000 tons per year (100 kTa) of ethylene. Co-generation with the OCM process can produce about 100-120 ton/hr of steam and about 80-120 MW of power.

(123) Salt 1401 and water 1402 are fed to a brine saturation unit 1403, and purified brine 1404 is then fed into an electrolysis unit 1405. The electrolysis of purified brine in the chloralkali process uses power 1414 (e.g., up to about 2970 kWh per ton of Cl.sub.2 produced); at least a portion of this power can be provided 1415 from co-generation with the OCM process (e.g., about 80-120 MW). A chlorine product stream can be subjected to treatment and liquefaction 1406 before being output as chlorine product 1407 (e.g., at least about 300 kTa). A hydrogen stream can be subjected to cooling and oxygen removal 1408 before further use; hydrogen 1409 (e.g., at least about 8400 kTa or at least about 950 kg/hr) can be directed into a methanation unit in the OCM process, for example. A caustic soda product stream 1411 (e.g., 50% caustic soda) can be produced (e.g., about 338.4 kTa) after concentration and cooling 1410. A reclaimed salt stream 1416 can be recycled to the brine saturation unit. The cooling process can use steam 1412 (e.g., up to about 610 kWh per ton of Cl.sub.2), at least a portion of which can be provided 1413 from co-generation 1430 with the OCM process (e.g., about 100-120 ton/hr). It is assumed that 1 ton of steam is 250 kWh at 19 bar. The processes are integrated with respect to electrical power, hydrogen and steam. Natural gas 1420 and ethane 1421 can be fed into an OCM reactor 1422 with other reagents and reacted in an OCM process. Post-bed cracking 1423 can be employed to produce additional ethylene. CO.sub.2 can be removed in a CO.sub.2 removal unit 1424 and fed into a methanation unit 1425. The OCM product stream can be further processed in a drying unit 1426, a de-methanizer unit 1427, and a C.sub.2 hydrogenation unit 1428, producing an ethylene stream 1429.

(124) FIG. 15 shows a material and energy balance for the process shown in FIG. 14. All of the electrolytic hydrogen is used in the OCM unit 1501. The OCM process provides a portion of the steam 1502 used by the electrolysis unit 1503 (e.g., chloralkali process). The electrolysis unit produces at least about 300 kTa of chlorine 1504 and at least about 338.4 kTa of caustic soda 1505, as well as at least about 950 kg/hr of hydrogen 1506 which is fed into the OCM unit. The chloralkali process receives about 80-120 MW of power 1507 from the OCM process, and additional power 1508 of at least about 104 MW from other sources. The chloralkali process also receives salt 1513 and water 1514. The OCM unit produces at least about 100 kTa ethylene 1509 (e.g., at least about 0.3 tons of ethylene per ton of Cl.sub.2 produced by the chloralkali process), as well as at least about 85 ton/hr steam (e.g., up to about 610 kWh per ton of Cl.sub.2) which is fed into the electrolysis unit. The OCM unit consumes about 40-50 MMSCFD of natural gas 1510, about 15-18 MMSCFD of oxygen 1511, and about 6-9 MMSCFD of ethane 1512.

(125) Integration of OCM Processes with an Ammonia Process

(126) The present disclosure provides techniques that can advantageously employ certain unexpected synergies that can be achieved by integrating OCM with the production of ammonia (NH.sub.3). In some cases, an existing ammonia process is retrofitted with an OCM process. These synergies can include increasing the capacity of a reforming portion of an ammonia process, in some cases without modification of the steam methane reformer and/or secondary reformer. In some cases, such a reforming capacity expansion can be achieved without over-burdening other unit operations leading up to the ammonia synthesis module (e.g., the “synloop”). Therefore, the addition of an OCM process to an ammonia production process can be performed without the significant capital and operating expense that can be associated with purifying ethylene.

(127) With reference to FIG. 16, an ammonia process can comprise a steam methane reformer 1600, a secondary reformer 1602, a heat recovery module 1604, a water-gas shift conversion unit 1606, a CO.sub.2 separation module 1608, a methanation reactor 1610, a syngas compressor 1612 and an ammonia synthesis and separation module 1614. The ammonia synthesis module can be an implementation of the Haber-Bosch catalytic process.

(128) Following the ammonia process, the steam methane reformer 1600 can accept natural gas (e.g., as feedstock) 1616 and combine it with steam 1618. The feedstock can enter the tubeside of the SMR, for example at a temperature of about 500° C. A large amount of heat can be supplied to the tubes of the SMR, for example via combustion of natural gas fuel 1620 in the radiation section of the SMR, in order to heat up the reacting feed (e.g., to a temperature from about 740 to about 800° C.) and sustain an endothermic reforming reaction that produces syngas (e.g., via the reaction CH.sub.4+H.sub.2O←.fwdarw.CO+3H.sub.2, which heat of reaction can also be supplied by the natural gas fuel 1620). Because reforming is an equilibrium reaction, a certain portion of the methane may not be converted to syngas in the SMR (e.g., about 8-15%). The SMR effluent can be directed to a secondary reformer 1602 where air 1622 is added to reduce the methane (CH.sub.4) concentration to about 0.3-1.2%, such as via a combination of combustion and reforming reactions. At this point, the temperature of the stream can be as high as about 900-1000° C.; a heat recovery module 1604 can be used to lower the temperature and recover energy, such as via generation of high pressure superheated steam. The cooled product then can then be directed to a water-gas shift reactor 1606 to produce more hydrogen (e.g., via the reaction CO+H.sub.2O.fwdarw.←CO.sub.2+H.sub.2). At this point, the ratio of H.sub.2 to N.sub.2 can be about 3, which can match the reaction stoichiometry for ammonia production. CO.sub.2 can then be removed 1624 in a separation module 1608, leaving about 5-50 ppm CO.sub.2 and about 0.1-0.4% CO. CO.sub.2 and CO can be strong poisons to ammonia synthesis catalysts, so residual amounts of CO.sub.2 and CO can be converted to methane (which is inert in the ammonia synthesis reaction) in a methanation reactor 1610. A syngas compressor 1612 and an ammonia synthesis and separation module 1614 can be used to complete the process and produce ammonia 1626. Note that for clarity, various streams and units, such as ammonia purification, may not have been shown or described.

(129) In an ammonia process, the extent of reaction in the secondary reformer 1602 can be limited by the amount of air 1622, as the nitrogen (N.sub.2) from this air stream can be the source of N.sub.2 for the production of ammonia. However, integrating and/or retrofitting an ammonia process with an OCM process can obviate this limitation, along with providing additional benefits, including those discussed herein.

(130) With reference to FIG. 16, the OCM process can comprise an air separation unit (ASU) 1628, an OCM reactor 1630, a heat recovery module 1632, a compression module 1634, a CO.sub.2 removal unit 1636, a dryer module 1638, a de-methanizer module 1640, and a fractionation module 1642. Following the OCM process, the ASU can separate air into a nitrogen stream 1644, which can be fed to the ammonia process to provide a source of clean N.sub.2 reactant (e.g., not having oxygenated compounds such as CO or CO.sub.2). In some cases, other processes (e.g., separations) can be used to provide air and nitrogen. For example, a pressure swing adsorption (PSA) unit can be used to provide O.sub.2 and N.sub.2. The ammonia synthesis module 1614 can operates at about 80 to 200 bar pressure. The nitrogen stream 1644 can be compressed to operating pressure in an auxiliary compressor 1646 or in the syngas compressor of the ammonia process 1612. The oxygen (O.sub.2) 1648 produced by the ASU 1628 can be supplied to both the OCM reactor 1630 and the secondary reformer of the ammonia process 1602 (e.g., offsetting or supplementing O.sub.2 from air 1622). Continuing with the OCM process, the oxygen can be reacted with methane 1650 (e.g., from natural gas) to produce ethylene. Pressure can increase, and heat, CO.sub.2 and water can be recovered in a series of units (e.g., 1632, 1634, 1636 and 1638 in any order). In some cases, CO.sub.2 from the ammonia process 1624 and/or OCM process 1652 can be used in processes including but not limited to methanol, chloralkali, urea, and combinations thereof. The overhead stream 1654 from the de-methanizer 1640 can comprise un-converted methane from the OCM process which can be used to supplement and/or offset natural gas to the SMR of the ammonia process 1600. Since this overhead stream 1654 can have H.sub.2 (e.g., about 10%) and CO (e.g., about 1.5%), the stream is already partially reformed. The bottoms from the de-methanizer 1640 can be sent to the fractionation module 1642 to produce ethylene product 1656.

(131) Integrating and/or retrofitting an ammonia process with an OCM process can result in additional H.sub.2 and/or NH.sub.3 produced (e.g., at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, or at least about 40% additional H.sub.2 and/or NH.sub.3 compared to an ammonia process without OCM). This capacity expansion can emerge from any combination of a number of effects, such as: (a) the OCM process can supply the ammonia process with some partially reformed material (i.e., about 10% H.sub.2 and about 1.5% CO in the de-methanizer overhead 1654); (b) in contrast to natural gas, the de-methanizer overhead 1654 can lack “superior hydrocarbons” (e.g., C.sub.2+ alkanes), therefore the temperature threshold at which coking may occur can be higher and accordingly the SMR inlet temperature can be raised (e.g., raised from about 500° C. to about 550° C. or about 600° C.), allowing the heat supplied in the SMR radiation section to go toward the heat of reaction rather than providing a temperature increase, and thus increasing the syngas production performed by the SMR unit itself; and/or (c) supplying clean nitrogen (N.sub.2) 1644 can break the stoichiometric limit of air 1622 as the sole nitrogen source, this coupled with O.sub.2 supplementation 1658 can allow relatively more reforming to be carried out in the secondary reformer 1602, allowing a higher amount of CH.sub.4 slippage from the SMR (e.g., about 15-25% rather than 8-15% of un-converted methane).

(132) In some cases, the process units between reforming and ammonia synthesis do not need to be de-bottlenecked or capacity expanded because, while extra H.sub.2 is produced, the N.sub.2 enters the process after these steps (i.e., at 1644 rather than with the air 1622), so the total process flow is relatively unchanged.

(133) In some cases, the ammonia synloop 1614 requires expansion in a revamp, however this is a relatively low capital item in comparison to the rest of the ammonia process units and such revamp results in increased ammonia product 1626.

(134) The systems and methods of the present disclosure can be nitrogen-efficient and/or energy-efficient. In some cases, the systems or methods of the present disclosure have a nitrogen efficiency of at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, or at least about 90%. In some cases, a system of the present disclosure or method for use thereof has a ratio of all nitrogen atoms output from the system as nitrogen products to all nitrogen atoms input to the system of at least about 0.4, at least about 0.50, at least about 0.55, at least about 0.60, at least about 0.65, at least about 0.70, at least about 0.75, at least about 0.80, at least about 0.85, at least about 0.90, or at least about 0.95.

(135) In some cases, the systems or methods of the present disclosure have a nitrogen efficiency of between about 50% and about 85%, between about 55% and about 80%, between about 60% and about 80%, between about 65% and about 85%, between about 65% and about 80%, or between about 70% and about 80%. In some cases, a system of the present disclosure or method for use thereof has a ratio of all nitrogen atoms output from the system as nitrogen products to all nitrogen atoms input to the system of between about 0.50 and about 0.85, between about 0.55 and about 0.80, between about 0.60 and about 0.80, between about 0.65 and about 0.85, between about 0.65 and about 0.80, or between about 0.70 and about 0.80.

(136) In some instances, the nitrogen efficiency is at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85% or at least about 90%. In some instances, the nitrogen efficiency is between about 50% and about 85%, between about 55% and about 80%, between about 60% and about 80%, between about 65% and about 85%, between about 65% and about 80%, or between about 70% and about 80%. In some instances, a system of the present disclosure or method for use thereof has a ratio of all nitrogen atoms output from the system as nitrogen products to all nitrogen atoms input to the system of at least about 0.60, at least about 0.65, at least about 0.70, at least about 0.75, at least about 0.80, at least about 0.85 or at least about 0.90. In some instances, a system of the present disclosure or method for use thereof has a ratio of all nitrogen atoms output from the system as nitrogen products to all nitrogen atoms input to the system of between about 0.50 and about 0.85, between about 0.55 and about 0.80, between about 0.60 and about 0.80, between about 0.65 and about 0.85, between about 0.65 and about 0.80, or between about 0.70 and about 0.80.

(137) Integration of OCM Processes with a Methanol to Propylene (MTP) Process

(138) FIG. 17 shows an exemplary OCM process for integration with a methanol to propylene (MTP) process. Natural gas 1701 and oxygen 1702 are fed into an OCM reactor 1703. High pressure superheated (HPSH) steam 1704 is produced from the OCM unit. The OCM product stream is fed into a post-bed cracking unit 1705, and then into a CO.sub.2 removal unit 1706. Recovered CO.sub.2 is directed for use in a balanced syngas stream 1707. The OCM product stream is further directed through a drying unit 1708 and a de-methanizer unit 1709. C.sub.2+ compounds 1710 are recovered from the de-methanizer, while unconverted methane and other light components including H.sub.2 and CO 1711 can be directed to a reformer (e.g., a steam methane reformer) 1712 and 1713. The components are then added to the balanced syngas stream.

(139) FIG. 18 shows an exemplary integration scheme for an OCM process and an MTP process. Natural gas and oxygen are fed into an OCM unit 1801 with a post-bed cracking region. The OCM product stream is then processed in a CO.sub.2 removal unit 1802, a drying unit 1803, and a de-methanizer unit 1804. In parallel, a methane stream (e.g., natural gas) is fed into a syngas unit 1810, along with a methane stream from the de-methanizer unit. The syngas stream is fed into a methanol synthesis unit 1811, along with CO.sub.2 from the CO.sub.2 removal unit. Methanol from the methanol synthesis unit is then fed into a methanol-to-propylene synthesis unit 1812, and the MTP product stream is fed into a recovery unit 1813. The C.sub.2+ product stream from the de-methanizer unit is also fed into the recovery unit. An ethylene stream 1814, a propylene stream 1815, and a C.sub.4+ compounds stream 1816 are recovered from the recovery unit.

(140) Integration of OCM Processes with a Liquid Natural Gas (LNG) Process

(141) OCM and/or ETL processes can be integrated with liquid natural gas (LNG) processes.

(142) For example, an LNG process can be integrated with OCM and ETL processes for fuel production. Such a process can convert methane, ethane, and optionally propane into fuel such as high-octane gasoline. Capital expenditure (CapEx) can be reduced due to synergies and overlap in needed equipment, such as product separations equipment. A fuel product, such as gasoline, can be mixed with condensate from the LNG process or separated via a dedicated column.

(143) FIG. 19 shows an integration of OCM and ETL processes with an LNG process for fuel production. A feed gas preparation system 1900 (e.g., of a gas processing plant) receives gas into its inlet gas facilities 1901. The stream is then directed into a gas treating unit 1902 with a solvent regeneration unit 1903, from which CO.sub.2 and H.sub.2S 1904 are recovered. The stream is then directed into a dehydration unit 1905 with a regeneration unit 1906, from which water 1907 is recovered. The stream is then directed to a liquid petroleum gas (LPG) extraction unit 1908, from which condensate is recovered and sent to storage 1909 (e.g., LPG/C.sub.5+ storage) and offloading 1910 for transportation (e.g., on ships). Dry gas from the LPG extraction unit is directed to an LNG liquefaction unit 1911, from which LNG product is directed to storage 1912 and offloading 1913 for transportation (e.g., on ships). At least a portion of the dry gas and C.sub.2 from the LPG extraction unit can be directed to an OCM unit 1914. The OCM product stream can be directed to an ETL unit 1915, with fuel products (e.g., high octane gasoline) mixed with condensate from the LNG process or separated via a dedicated column. Light products and unreacted methane, for example, can be directed back into the gas treatment unit.

(144) LNG processes can also be integrated with OCM processes for polymer production. For example, methane and ethane can be converted to a polymer (e.g., polyethylene). Capital expenditure (CapEx) can be reduced due to synergies and overlap in needed equipment, such as product separations equipment. The value of the polymer produced can be used to pay for the OCM processes, the polymerization process, and to offset the cost of an LNG process, for example.

(145) FIG. 20 shows an integration of an OCM process with an LNG process for polymer production. C.sub.2 compounds from the LPG extraction unit are directed to a C.sub.2 splitter 2001. Ethylene from the C.sub.2 splitter is directed into a polyethylene unit 2002, while ethane from the C.sub.2 splitter is directed to the OCM unit.

(146) Integration of OCM Processes with an Oxalic Acid/Oxalate Process

(147) An OCM process can be integrated with production of oxalic acid, oxalates, or derivatives thereof. For example, CO.sub.2 produced in an OCM process can be directed to a reactor (e.g., an electrochemical reactor) for use in oxalic acid or oxalate production. Clean CO.sub.2 from OCM can be converted to oxalate or oxalic acid, and optionally further to derivatives including glycolic acid, ethylene glycol, diglycolic acid, nitriloacetic acid, glyoxylic acid, and acetic acid.

(148) FIG. 21 shows an exemplary schematic for integration of OCM with oxalic acid or oxalate production. Methane (e.g., natural gas) 2101 and oxygen 2102 are directed into an OCM unit 2103. CO.sub.2 2104 from the OCM unit and hydrogen 2105 are directed into a reactor (e.g., electrocatalytic/electrochemical reductive coupling of CO.sub.2 reactor) to produce oxalic acid and/or oxalates 2107. The oxalic acid and/or oxalates can be directed into a hydrogenation reactor 2108 to produce other derivative products 2109.

(149) Integration of OCM Processes with an Ethylene Glycol Process

(150) An OCM process can be integrated with production of ethylene glycol. For example, ethylene produced in an OCM process can be directed to a reactor (e.g., an oxidation reactor) for use in ethylene oxide production. Ethylene oxide can then be converted further to derivatives including ethylene glycol.

(151) FIG. 22 shows an exemplary schematic for integration of OCM with ethylene glycol production. Methane (e.g., natural gas) 2201 and oxygen 2202 are directed into an OCM unit 2203 to produce ethylene 2204. The ethylene and oxygen 2205 (e.g., air or pure oxygen) are directed into an oxidation reactor 2206, which produces ethylene oxide 2207. The ethylene oxide is then directed into a hydration reactor 2208 to produce ethylene glycol 2209.

(152) Integration of OCM Processes with a Propylene Process

(153) OCM processes can be integrated with processes for the production of propylene, such as metathesis processes. Metathesis units can convert butene-2 and ethylene into propylene. The propylene produced can be of polymer grade and used as a feedstock to produce polypropylene.

(154) The metathesis reaction can utilize an ethylene feed and a C.sub.4 olefinic feed to produce propylene via a disproportionation reaction. In the absence of a C.sub.4 feed, ethylene can be dimerized to produce the C.sub.4 olefins used for metathesis. The C.sub.4 olefin can be a butene-2 rich stream where the butene-2 content can be greater than about 90%, greater than about 93%, greater than about 95%, greater than about 97% or greater than about 99%. An OCM module can provide ethylene (e.g., polymer grade) to a dimerization unit, and/or to a metathesis unit. The metathesis reactor may contain a section for isomerization of butene-1 to butene-2. The product from the metathesis unit can contain predominantly propylene (and varying amounts of unreacted ethylene and butenes), along with some heavy C.sub.5+ components. Conventional metathesis units can include C.sub.2 separation, C.sub.3 separation and a de-oiler (C.sub.5+ removal). A metathesis unit integrated with an OCM system can have a common separations and purification system where the product stream from the metathesis unit is routed to the C.sub.2 separations section of the OCM module (de-ethanizer). The de-ethanizer overhead can be sent to the C.sub.2 splitter to generate polymer grade ethylene and an ethane product. The ethane product can be recycled to the OCM reactor. A part of the ethylene produced can be sent to the dimerization reactor and the remaining ethylene is sent to the metathesis unit. The de-ethanizer bottoms stream can be sent to a de-propanizer, followed by a C.sub.3 splitter to produce (polymer grade) propylene. The de-propanizer bottoms can be sent to a de-butanizer or a de-pentanizer to recover a C.sub.4 raffinate. In some embodiments, the butene rich stream from dimerization reactor can be isomerized in a reactive distillation section to convert butene-1 to butene-2 and separate the butene-2 for the metathesis reactor.

(155) In some embodiments, the C.sub.4 rich stream can be sourced from a refinery or a steam cracker. The refinery or steam cracker C.sub.4 stream can be sufficient to provide for the metathesis unit with no dimerization required. In some cases, the C.sub.4 stream can be mixed with the C.sub.4 stream from the dimerization reactor. In either case (i.e., dimerization alone, dimerization plus off gas recovery or only off gas processing), the C.sub.4 processing can also include either a selective hydrogenation unit (SHU) to hydrogenate any C.sub.4 dienes to olefins, or a butadiene recovery unit or a total hydrogenation unit to hydrogenate the remaining C.sub.4s after butene-2 has been utilized. In some cases, the final product is a C.sub.4 LPG/C.sub.4 raffinate containing butanes, and unreacted butenes.

(156) The integrations described herein (e.g., OCM+metathesis+ polypropylene) can yield many advantages from a process and economic standpoint. The combined system can have a common separations and recovery system, a common refrigeration system, and take advantage of an integrated site with respect to utilities and off-sites. Additionally, the OCM system can generate excess steam for the entire system.

(157) Additionally, ethylene from an OCM process can be supplied as a co-monomer for polypropylene production (e.g., 8-15% ethylene co-monomer). A separations section of an OCM process can handle the recycle streams from a metathesis unit and a polypropylene unit in addition to the separations for the OCM process itself.

(158) For example, FIG. 23 shows an exemplary schematic for integration of OCM with metathesis for propylene production. An OCM unit 2300 with an OCM reactor 2301 and a separations section 2302 receives a methane stream 2303 (e.g., natural gas) and produces an ethylene product stream 2304 (e.g., polymer-grade ethylene). A portion of the ethylene stream can be directed into a dimerization reactor 2305 to produce C.sub.4 products, which can then be separated in a C.sub.4 separation unit 2306. Butene-2 2307 from the C.sub.4 separation unit can be directed into a metathesis reactor 2308 along with ethylene from the OCM unit. The metathesis product stream can be directed to a C.sub.2 separation unit 2309, with C.sub.2 compounds being sent as a recycle stream to the OCM unit separations section. C.sub.3+ compounds can be directed from the C.sub.2 separations unit to a C.sub.3 separations unit 2310. Propylene 2311 can be recovered from the C.sub.3 separations unit, with C.sub.4+ compounds directed to the C.sub.4 separation unit.

(159) Propylene can be further processed into polypropylene. For example, FIG. 24 shows the propylene 2311 being directed, along with ethylene co-monomer 2401 from the OCM unit, into a polypropylene unit 2402 to produce polypropylene 2403.

(160) Metathesis can be conducted as a vapor phase equilibrium reaction. Metathesis can achieve n-butene conversion of about 72% single pass and about 90%-95% overall conversion. The reaction can be conducted at isothermal or nearly isothermal conditions, and can be energy neutral. The presence of iso-butene can lead to more side reactions producing 2,3-dimethylbutene and isoamylene.

(161) In some cases, the recovery systems are integrated. For example, with reference to FIG. 25A, a case is shown having a C.sub.2 splitter 2500 that produces enriched ethylene 2501 for the metathesis unit 2502 and/or the dimerization unit 2504. In some cases, the enriched ethylene is polymer-grade ethylene (which can also be used as a co-monomer in the production of polypropylene). In some instances, the C.sub.2 splitter 2500 is not operated at conditions that result in polymer-grade ethylene. The enriched ethylene stream can be about 60%, about 70%, about 80%, about 90%, about 95%, or about 99% ethylene by mass. In some cases, the enriched ethylene stream is at least about 60%, at least about 70%, at least about 80%, at least about 90%, at least about 95%, or at least about 99% ethylene by mass.

(162) Continuing with FIG. 25A, reactants 2506 (i.e., methane and O.sub.2) can be fed into an OCM reactor 2508 having a catalyst bed 2509 and an ethane conversion section 2510. The OCM reactor can produce an OCM effluent 2511 that goes to a de-methanizer 2512. In some cases, there are additional units in the OCM process that are not shown, such as compressors, CO.sub.2 removal units, drying units, desulfurization units, quenchers and heat exchangers. The de-methanizer overhead 2513 can contain C.sub.1 compounds and go to a methanation unit 2514 for conversion into methane and recycle to the OCM reactor 2508. As used herein, the terms “overhead” and “bottoms” do not limit the portion or section of the separation column from which the stream emerges (e.g., in some cases, the “bottoms” can come out of the middle or top of the separation column).

(163) The de-methanizer bottoms 2515 can include C.sub.2+ compounds and continue into a fractionation train including a de-ethanizer 2516, a de-propanizer 2517 and a de-butanizer 2518. The de-ethanizer overhead 2519 can contain C.sub.2 compounds and go to a hydrogenation unit 2520, which hydrogenation unit can (selectively) hydrogenate acetylene. As described herein, the C.sub.2 compounds can be separated into an enriched ethylene stream (i.e., using the C.sub.2 splitter 2500), or not separated as shown in FIG. 25B.

(164) The de-ethanizer bottoms 2521 can contain C.sub.3+ compounds and be taken to the de-propanizer 2517. The de-propanizer overhead 2522 can contain C.sub.3 compounds that can be split in a C.sub.3 splitter 2523 into propane 2524 and propylene 2525. In some cases, the propylene is polymer-grade. In some cases, the propylene is used to make polypropylene (optionally with an ethylene co-monomer, such as derived from the present process, i.e., from the C.sub.2 splitter 2500). In some embodiments, the propylene 2525 is about 85%, about 90%, about 95%, about 99%, about 99.5%, about 99.9%, or about 99.95% pure. In some instances, the propylene 2525 is at least about 85%, at least about 90%, at least about 95%, at least about 99%, at least about 99.5%, at least about 99.9%, or at least about 99.95% pure.

(165) The de-propanizer bottoms 2526 can contain C.sub.4+ compounds and be directed to a de-butanizer 2518. The de-butanizer can produce a bottoms stream 2527 that includes C.sub.5+ compounds and an overhead stream 2528 comprising C.sub.4 compounds, which C.sub.4 compounds can be sent to a C.sub.4 splitter 2529. The C.sub.4 splitter can produce a plurality of streams (i.e., 2530, 2531 and 2532) including a stream enriched in butene-2 2532. In some embodiments, the butene-2 2532 is about 85%, about 90%, about 95%, about 99%, about 99.5%, about 99.9%, or about 99.95% pure. In some instances, the butene-2 2532 is at least about 85%, at least about 90%, at least about 95%, at least about 99%, at least about 99.5%, at least about 99.9%, or at least about 99.95% pure. The butene-2 2532 can go to the metathesis unit 2502.

(166) Additional butene-2 2533 can be produced from the dimerization module 2504 (i.e., from ethylene). The additional butene-2 2533 can be used directly in the metathesis reactor 2502 in some cases. However, as shown here, the additional butene-2 can be recycled to the fractionation train (e.g., to the de-ethanizer 2516) to enrich the concentration of butene-2 prior to metathesis.

(167) The metathesis unit can produce a propylene stream 2534 that can be utilized directly or enriched (e.g., to polymer grade propylene) by recycling the dilute propylene stream 2534 to the fractionation train (e.g., to the de-ethanizer 2516).

(168) The process can produce a number of additional streams that can be utilized directly or recycled in the process, such as an ethane stream 2535 coming from the C.sub.2 splitter that can be recycled to the catalyst bed 2509 and/or ethane conversion section 2510 of the OCM reactor 2508.

(169) In some cases, the C.sub.2 compounds are not split into enriched ethylene or enriched ethane streams. With reference to FIG. 25B, the de-ethanizer overhead 2519 can be used in the metathesis module 2502, in the dimerization module 2504, and/or can be recycled to the OCM reactor 2508 directly (e.g., without first being separated in a C.sub.2 splitter). In some cases, the C.sub.2 stream 2519 can go through a hydrogenation unit 2520 (e.g., that hydrogenates acetylene) to produce a hydrogenated C.sub.2 stream 2540, which hydrogenated C.sub.2 stream 2540 can be used in the metathesis module 2502, in the dimerization module 2504. In some embodiments, the hydrogenated C.sub.2 stream 2540 can contain about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 90%, or about 95% compounds other than ethylene. In some cases, the hydrogenated C.sub.2 stream 2540 can contain at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, or at least about 95% compounds other than ethylene.

(170) It should be understood from the foregoing that, while particular implementations have been illustrated and described, various modifications can be made thereto and are contemplated herein. It is also not intended that the invention be limited by the specific examples provided within the specification. While the invention has been described with reference to the aforementioned specification, the descriptions and illustrations of the preferable embodiments herein are not meant to be construed in a limiting sense. Furthermore, it shall be understood that all aspects of the invention are not limited to the specific depictions, configurations or relative proportions set forth herein which depend upon a variety of conditions and variables. Various modifications in form and detail of the embodiments of the invention will be apparent to a person skilled in the art. It is therefore contemplated that the invention shall also cover any such modifications, variations and equivalents. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.