WO2019236983A1

WO2019236983A1 - Method for conversion of methane to ethylene

Info

Publication number: WO2019236983A1
Application number: PCT/US2019/036022
Authority: WO
Inventors: Aghaddin Mamedov; Balamurali Nair; Zheng Liu; Kuang Yao Brian PENG; Michael E. Huckman
Original assignee: Sabic Global Technologies B.V.
Priority date: 2018-06-08
Filing date: 2019-06-07
Publication date: 2019-12-12

Abstract

A method for the conversion of methane to ethylene involves converting by pyrolysis or partial oxidation a methane-containing feed (16) (20) to an acetylene-containing product stream (30) (32). The acetylene-containing product stream (30) (32) is combined with a hydrogenating feed (28) comprising ethane, H2, and water. The acetylene-containing product stream (30) (32) is thermally hydrogenated in the absence of catalyst to form a hydrogenated product stream (34). The hydrogenated product stream (34) is separated into a first separated stream (38) containing residual acetylene, ethylene, ethane, and hydrogen gas and a second separated stream (50) containing methane, CO₂and CO. The first and second separated streams (38) (50) are then further processed by contacting the residual acetylene of the first separated stream (38) with a hydrogenation catalyst in a catalytic hydrogenation reaction to form ethylene (42) (48) and/or combining the second separated stream (50) with steam (58) to convert by both steam reforming and carbon dioxide reforming of methane to form a syngas mixture (60) comprising carbon monoxide and hydrogen gas.

Description

METHOD FOR CONVERSION OF METHANE TO ETHYLENE

TECHNICAL FIELD

[0001] The invention relates to processes for the conversion of methane to ethylene.

BACKGROUND

[0002] Conversion of methane to acetylene by thermal pyrolysis or partial oxidation using combustion is well known. Such process has been described in U.S. Patent Nos. 5,789,644 and 5,824,834. The process involves the combustion of a portion of the methane to produce heat that is then used for high temperature pyrolysis or partial oxidation of methane to acetylene. The reaction is represented by Equations (1) and (2) below:

2CH₄ + 3.50₂ CO2 + CO + 4H₂0 DH = -157 kcal/mole (1)

2CH₄ C2H2 + 3H₂ DH = 45 kcal/mole (2)

The total products are C2H2, CO, ¾, H2O, and CO2. The product distribution depends on the CH₄/02 ratio.

[0003] Ethylene is typically used to produce a wide range of products. For industrial scale applications, ethylene is typically produced by heating natural gas condensates and petroleum distillates, which include ethane and higher hydrocarbons, and the produced ethylene is separated from the product mixture using gas separation processes.

[0004] Ethylene can also be produced by the thermal hydrogenation of acetylene. A unique method wherein methane is converted to ethylene through the intermediate production of acetylene through thermal pyrolysis or partial oxidation of methane has been described in Applicant’s previous U.S. Patent No. 8,013,196, which is incorporated herein by reference in its entirety for all purposes. In such reaction, a residual amount of acetylene may be present in the final ethylene product stream after hydrogenation. Ethylene containing more than 1-2% acetylene, however, typically cannot be used in any chemical synthesis or polymerization reactions because of its tendency to deactivate the polymerization catalyst. Thus, its presence in the ethylene product stream after hydrogenation of acetylene constitutes a problem.

[0005] Furthermore, the conversion of methane to acetylene produces byproducts of ¾, CO, and CO2, which mixes with the unreacted methane. ¾ and CO produced in the process could be used for syngas conversion reactions to form valuable products, such as for conversion to methanol and olefins by the Fischer-Tropsch reactions, thereby improving the economics of the process. In the conversion of methane to acetylene, however, unconverted methane remains present with ¾ and CO in the gas mixture. Methane present in syngas mixtures at concentrations of more than 2.5% cannot be used in such reactions. As a result, the unreacted methane, along with ¾ and CO, is typically recycled back to the combustion zone for the pyrolysis or partial oxidation reactions instead of being used to form more valuable products. Accordingly, improvements are needed to take into account the above-described shortcomings to both increase ethylene production and to take into account the utilization of byproducts and unreacted methane from the process.

SUMMARY

[0006] A method for the conversion of methane to ethylene involves converting by pyrolysis or partial oxidation a methane-containing feed to an acetylene-containing product stream. The acetylene-containing product stream is combined with a hydrogenating feed comprising ethane (C₂H₆), hydrogen gas (¾), and water and acetylene of the acetylene-containing product stream is thermally hydrogenated in the absence of catalyst to form a hydrogenated product stream. The hydrogenated product stream is separated into a first separated stream containing residual acetylene (C2H2), ethylene (C2H4), ethane (C2H6), and hydrogen gas and a second separated stream containing methane (CH₄), carbon dioxide (CO2) and carbon monoxide (CO). At least one of steps A and B is performed, wherein A is contacting the residual acetylene of the first separated stream with a hydrogenation catalyst in a catalytic hydrogenation reaction to form ethylene. And B is combining the second separated stream with steam to convert by both steam reforming and carbon dioxide reforming of methane to form a syngas mixture comprising carbon monoxide and hydrogen gas.

[0007] In particular embodiments step A is performed and in other embodiments step B is performed. And in still other embodiments both steps A and B are performed.

[0008] In certain instances, the hydrogenated product stream is separated into a third separated stream containing ethane, hydrogen gas, and water, at least a portion of the third separated stream is recycled to form at least a portion of the hydrogenating feed.

[0009] In various embodiments the following may be true: The hydrogenating feed may provide a tb/acetylene molar ratio of from 9 or more. Step B may be performed in certain instances wherein the syngas mixture contains less than 3 wt.% methane. The hydrogenated product stream may contain from 3 wt% or less of residual acetylene. The pyrolysis or partial oxidation of the methane-containing feed may be carried out at temperature of from 1000 °C to 3000 °C. The acetylene-containing product stream may be quenched to a temperature of from 500 °C to 950 °C prior to thermal hydrogenation. The hydrogenated product stream may be cryogenically cooled to facilitate separating the hydrogenated product stream. And heat for the steam reforming and carbon dioxide reforming of methane may be provided by at least one of the steam and the combustion of at least a portion of the carbon dioxide (CO2) and the carbon monoxide (CO) of the second separated stream.

[0010] In another method for the conversion of methane to ethylene, a methane-containing feed is converted to an acetylene-containing product stream by pyrolysis or partial oxidation at a reaction temperature of from 1000 °C to 3000 °C. The acetylene-containing product stream is quenched to a temperature of from 500 °C to 950 °C. The quenched acetylene-containing product stream is combined with a hydrogenating feed comprising ethane (C2H6), hydrogen gas (H2), and water. The acetylene of the quenched acetylene-containing product stream is thermally hydrogenated in the absence of catalyst to form a hydrogenated product stream containing less than 3 wt.% of residual acetylene. The hydrogenated product stream is separated into a first separated stream containing the residual acetylene (C2H2), ethylene (C2H4), ethane (C2H6), and hydrogen gas and a second separated stream containing methane (CH₄), carbon dioxide (CO2) and carbon monoxide (CO). At least one of steps A and B is performed, where A is contacting the residual acetylene of the first separated stream with a hydrogenation catalyst in a catalytic hydrogenation reaction to form ethylene. And B is combining the second separated stream with steam to convert by both steam reforming and carbon dioxide reforming of methane to form a syngas mixture comprising carbon monoxide and hydrogen gas.

[0011] In particular embodiments step A is performed and in other embodiments step B is performed. And in still other embodiments both steps A and B are performed.

[0012] In certain instances, the hydrogenated product stream is separated into a third separated stream containing ethane, hydrogen gas, and water, at least a portion of the third separated stream being recycled to form at least a portion of the hydrogenating feed.

[0013] In various embodiments the following may be true: The hydrogenating feed may provide a tb/acetylene molar ratio of from 9 or more. Step B may be performed in certain instances wherein the syngas mixture contains less than 3 wt.% methane. The hydrogenated product stream may contain from 3 wt% or less of residual acetylene. The pyrolysis or partial oxidation of the methane-containing feed may be carried out at temperature of from 1000 °C to 3000 °C. The acetylene-containing product stream may be quenched to a temperature of from 500 °C to 950 °C prior to thermal hydrogenation. The hydrogenated product stream may be cryogenically cooled to facilitate separating the hydrogenated product stream. And heat for the steam reforming and carbon dioxide reforming of methane may be provided by at least one of the steam and the combustion of at least a portion of the carbon dioxide (CO2) and the carbon monoxide (CO) of the second separated stream. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] For a more complete understanding of the embodiments described herein, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying figure, in which:

[0015] FIG. 1 is a schematic representation of a system for carrying out the processes used in the conversion of methane to ethylene and syngas.

DETAILED DESCRIPTION

[0016] Referring to FIG. 1, a system 10 is shown for carrying out the processes described herein. The system 10 includes a reactor or unit 12 having four different zones. The first zone 14 constitutes a combustion zone wherein a feed 16 of a methane-containing gas, such as natural gas, and oxygen gas (0₂) are introduced and combusted to generate heat. Heat generated in the combustion zone 14 is used for the heat for thermal pyrolysis or partial oxidation of methane, which may herein be collectively referred to as“cracking,” in second zone 18. A further methane-containing gas feed 20 may be introduced together or separately into the cracking zone 18, in certain embodiments. The products produced in cracking zone 18 are rapidly quenched by introducing them into a quenching zone 22. A separate coolant 24 may be introduced into the zone 22 for this purpose. Finally, the quenched products are introduced into a thermal hydrogenation zone 26. In the hydrogenation zone 26, a recycle stream 28 containing ethane (C₂H₆), hydrogen gas (¾), and water are introduced. The recycle stream 28 provides the hydrogen necessary for the hydrogenation of acetylene to form ethylene.

[0017] Formation of acetylene in the cracking zone 18 may utilize the so-called two-stage pyrolysis process scheme developed by Hoechst AG. The CH4/O2 molar ratio from the feed streams 16 and 20 may vary and the final products produced, such as ethylene (C2H4) and syngas (i.e., ¾ and CO), will vary depending on this ratio. In certain embodiments the total CH4/O2 molar ratio may range from 2:3 to 2:5. The CH4/O2 molar ratio in feed 16 may be that which provides complete combustion, with or without excess oxygen, while the CH4/O2 molar ratio in the feed 20 to the cracking zone may be less than stoichiometric for complete combustion of the methane feed. In certain instances, the feed 20 may contain little or no oxygen. In still other embodiments, the CH4/O2 molar ratio in feed stream 16 may be less than required for complete combustion with only a portion of the methane of feed stream 16 being combusted to provide the heat necessary for cracking of the remaining methane feed. In such cases, no additional feed from feed stream 20 may be supplied, as all the methane for combustion and pyrolysis is supplied through feed stream 16.

[0018] Although the feed streams 16 and 20 are shown as a combined feed (CH4 + O2), the methane and oxygen may be fed separately to each zone 14 and 18 of the unit 12. The methane- containing feed in many cases will constitute natural gas. The oxygen gas may be a pure or enriched oxygen gas or air. The methane-containing feed, as well as the oxygen feed, may be preheated of from 200 °C to 800 °C, more particularly from 400 °C to 700 °C, prior to introduction into the reactor 12. Other components may also be introduced with the feeds 16 and 20, such as steam used to protect the reactor wall from the high temperatures within the reactor 12.

[0019] In the combustion zone 14 the temperature typically ranges from 1000 °C to 3000 °C. The methane from feed 20 is quickly mixed with effluents from the combustion zone 14 in cracking zone 18 to form acetylene. The temperature within the cracking zone 18 may range from 1000 °C to 3000 °C, more particularly from 1000 °C to 2500 °C, and still more particularly from 1300 °C or 1400 °C to 1600 °C. The residence time in the cracking section 18 may range from 3 ms to 30 ms, more particularly from 5 ms to 10 ms. The pressure of the cracking zone may range from 0.05 to 0.5 MPa, more particularly from 0.05 MPa to 0.2 MPa.

[0020] The acetylene-containing product stream 30 produced from the cracking zone 18 will typically contain acetylene, ethylene, ¾, CO2, CO, H2O, and unreacted methane. On a water- free basis the CO2 content of the acetylene-containing product stream will typically range from 20 vol.% to 30 vol.%. The H2/CO molar ratio of this product stream will typically range from 1:1 to 2:1. In addition to the formation of ethylene from the produced acetylene, by the utilization of the CO2 and CO to produce additional useful products, as is described in more detail further on, the carbon efficiency of the process is greatly increased and leads to better overall economics.

[0021] The acetylene-containing product stream 30 from cracking zone 18 is rapidly quenched in the quenching zone 22 of unit 12. This rapid cooling eliminates or reduces decomposition of the acetylene to coke and also cools the acetylene-containing product stream 30 to a temperature to facilitate thermal hydrogenation. The coolant 24 for quenching zone 22 may include heavy oil, such as those heavy oils from petroleum refining. Other coolants 24 may include water and natural gas. The coolants 24 are introduced at a temperature and quantity sufficient to rapidly cool the acetylene-containing product stream from cracking zone 18 to a temperature of from 500 °C to 950 °C, more particularly from 500 °C to 650 °C, and still more particularly from 600 °C to 650 °C.

[0022] In the hydrogenation zone 26, the quenched acetylene-containing product stream 32 is combined with ethane, hydrogen gas, and water from the hydrogenating feed 28. The hydrogenating feed 28 supplies the necessary hydrogen for hydrogenation in hydrogenation zone 26. In other embodiments, additional ethane and/or hydrogen gas may be added and introduced in hydrogenation zone 26 from other sources in lieu of or in addition to the hydrogenating feed stream 28, which constitutes a recycle stream described in more detail later on, to form the hydrogenating feed, such as during startup operations. The ethane of the hydrogenating feed 28 is present in an amount to provide an ethane/acetylene molar ratio of from 5:1 to 0.2: 1, more particularly from 5:1 to 4:1, and still more particularly from 4:4 to 4:2. The ethane added to the hydrogenation zone creates additional ethylene as well as more hydrogen for the hydrogenation reaction with acetylene. The molecular hydrogen gas of the hydrogenating feed is present in an amount to provide a Fb/acetylene molar ratio of from 8 or more, more particularly from 8 to 4, and still more particularly from 8 to 5.

[0023] In the thermal hydrogenation step, the hydrogenation is carried out in a gas phase without the use or presence of any hydrogenating catalyst. The residence or contact time in the hydrogenation zone 26 can range from 0.05 to 1 second, more particularly from 0.1 to 0.6 seconds. The pressure within the hydrogenation zone 26 may range from 0.05 MPa to 0.5 MPa. Operating temperatures during hydrogenation may range from 500 °C to 950 °C, more particularly from 700 °C to 950 °C, and still more particularly from 800 °C to 900 °C, 910 °C, 920 °C, 930 °C, 940 °C, or 950 °C.

[0024] The products removed in the hydrogenating zone 26 constitute a hydrogenated product stream 34. The hydrogenated product stream 34 will typically contain from 6 vol.% to 15 vol.% ethylene, from 1 vol.% to 3 vol.% of residual or unconverted acetylene, from 20 vol.% to 30 vol.% CO2, from 5 vol.% to 10 vol.% ethane, from 20 vol.% to 30 vol. % CO, from 35 vol.% to 70 vol.% Fb, and from 10 vol.% to 20 vol.% H2O. On a weight basis, the residual acetylene content of the hydrogenated product stream 34 may be from 3 wt.% or less, more typically from 1 wt.% to 2 wt. % in the product stream. As previously discussed, the ethylene product with such amounts of acetylene (e.g., from 1 wt.% to 2 wt.%) cannot be used in any chemical synthesis or polymerization reactions. While the process described in U.S. Patent No. 8,013,196 merely recycled the unconverted acetylene after hydrogenation, here the residual or unconverted acetylene is further processed to form additional ethylene, as is described in more detail further on.

[0025] The hydrogenated product stream 34 is delivered to one or more separation units 36. The separation unit 36 may contain more than one separation devices along with associated heat transfer equipment and coolant streams and cooling equipment to cool the product stream 34 and separate the product stream into its various components. In some embodiments, different quenching or cooling steps may occur, with certain components being cryogenically cooled to facilitate separation.

[0026] As can be seen in FIG. 1, the separation unit 36 separates the hydrogenated product stream into separated stream 28. Stream 28 constitutes unreacted ethane, Fb, and water from the hydrogenation stream 34. The stream 28 is used as a recycle stream to provide hydrogen for the gas phase thermal hydrogenation reaction of hydrogenation zone 26 of reactor unit 12, as well as additional ethane for forming ethylene, as previously described.

[0027] A further separated stream 38 from separator unit 36 contains the residual or unconverted acetylene, ethylene, ethane, and ¾. This is delivered to a tail-end gas phase catalytic hydrogenation reactor unit 40 under conditions suitable for the catalytic gas-phase hydrogenation of acetylene to convert the residual acetylene to ethylene. The reactor unit 40 contains a hydrogenation catalyst to facilitate the gas phase hydrogenation. Suitable hydrogenation catalysts include nickel, palladium, and platinum metal catalysts. Examples, include Pd/AhO , or Pd/AkCb containing Ag or Zn in amount of from 2 wt.% to 3 wt.%

[0028] The reaction is typically carried out at a temperature of from 70 °C to 120 °C and a pressure of from atmospheric to 2.5 MPa. A Pb/acetylene molar ratio of from 40:1 or higher is typically used, more particularly from 40: 1 to 50:1, to carry out the tail-end catalytic hydrogenation reaction. If necessary, additional ¾ from external sources may be delivered to the reactor 40 to provide the necessary amount of hydrogen to facilitate the hydrogenation reaction.

[0029] The acetylene content of the separated stream 38 is typically from 1.5 wt. % to 2 wt.%. The reduced amount of acetylene in stream 38 makes it possible to utilize a catalyst in hydrogenation unit 40. Higher acetylene content results in fast catalyst deactivation from the oligomerization of acetylene to form green oil.

[0030] Products from the reactor 40 are removed as tail-end product stream 42. The product stream 42 contains ethylene, as well as unreacted ethane and hydrogen. The acetylene content of the product stream 42 will typically be from 0.05 wt.% or less, more typically from 0.01 wt.% or less, with zero or only trace amounts of acetylene being present in many cases. The stream 42 is delivered to separation unit 44 where ethane and hydrogen gas are separated as stream 46. The ethane and hydrogen stream 46 can be combined with stream 28 as part of the recycle to hydrogenation zone 26 of unit 12 or is recycled to the tail-end hydrogenation reactor unit 40.

[0031] Ethylene product stream 48 from separation unit 44 with acetylene now removed or eliminated can be stored or delivered elsewhere for use in chemical synthesis and polymerization reactions where the presence of even low levels of acetylene would make the ethylene product unusable in such reactions.

[0032] An additional separated stream 50 is removed from separator unit 36. The stream 50 is composed of unreacted methane from reactor unit 12, as well CO2, and CO. The methane content of the removed separated stream may range from 10 mol% to 20 mol %. As described earlier, syngas (i.e., ¾ and CO) can be converted to methanol and olefins by the Fischer- Tropsch reaction. Where methane is present in the syngas in concentrations of more than 2.5 mol%, however, the syngas cannot be used in such reactions.

[0033] In the present invention, methane and CO2 can be converted to syngas in a bi-reforming process wherein methane and water and methane and CO2 are converted to H2 and CO in parallel steam-methane reforming (SMR) and carbon dioxide or dry reforming of methane (DRM) processes according to Equations (3) and (4) below:

CH₄ + H2O 3H₂ + CO DH = 50 kcal/mole (3)

CH₄ + C0₂ 2CO + 2H₂ DH = 60 kcal/mole (4)

[0034] Accordingly, all or a portion of the separated stream 50 is delivered as stream 52 to a bi-reforming reactor 54 containing a methane reforming catalyst under conditions to facilitate methane reforming according to Equations 3 and 4 above. The reaction may be carried out at a temperature of from 800 °C to 950 °C with heat being supplied to facilitate the reaction. The reactor 54 may be a tubular reactor located in a furnace for burning fuel for heating reactor tubes containing a reforming catalyst through which the reactants pass. In certain instances, the fuel used for heating in the bi-reforming reactor may be supplied by burning a portion 56 of the separated stream 50. Suitable reforming catalysts may include nickel-based catalyst, such as N1/AI2O3, which may contain promoters, such as Ba, Cd, and K.

[0035] As shown in FIG. 1, water or steam 58 is introduced into the reactor 54 along with stream 52 to facilitate steam methane reforming. Heat for the reforming reactions can also be supplied by the steam 58 introduced into the reactor 54. Additionally, a portion of the methane- containing stream 50 (e.g., stream 56) may also be burned to facilitate formation of or heating of the steam 58.

[0036] The syngas (i.e., H2 + CO) produced in the reforming reactor 54 is removed as syngas product stream 60. The syngas stream 60 contains from 3 wt.% or less methane, more particularly from 2 wt.%, 1.5 wt.%, or 1 wt.% or less methane so that it can be used in other reactions, such as the synthesis of methanol or other Fischer-Tropsch reactions.

[0037] As can be seen, the process and system described maximizes the production of ethylene and syngas and makes full use of the byproducts produced that would otherwise contaminate or inhibit the use of ethylene and syngas products for use in other reactions, such as the polymerization of ethylene and methanol and Fischer-Tropsch synthesis of syngas. [0038] The following examples serve to further illustrate various embodiments and applications.

EXAMPLES

EXAMPLE 1

[0039] Methane-containing feed of natural gas and oxygen gas was combusted and used in pyrolysis that was carried out in a pilot scale reactor at high temperature ranging from 1200 °C to 2000 °C to form an acetylene and ethylene mixture. The reaction conditions and product conversion and yield are presented in Table 1 below.

Table 1

EXAMPLE 2

[0040] Non-catalytic gas-phase thermal hydrogenation of acetylene was carried out in a 4 mm ID quartz reactor at 900 °C. The acetylene-containing mixture contained 8 vol.% C2H2, 8 vol.% C2H6, 60 vol.% H2, 15 vol. % CO, and 7 vol.% CO2, with the addition of water in an amount of 0.06 cc/min and a contact time of 0.4 seconds. The results obtained are presented in Table 2 below.

Table 2

EXAMPLE 3

[0041] A gas composition containing 37.7 vol.% ¾, 21.3 vol.% CO2, 15.4 vol.% CH₄, and 25.7 vol.% CO at a flow rate of 100 cc/min was mixed with 0.024 ml/min of H2O at room temperature and fed to a fixed bed quartz reactor containing 2 ml of nickel-based catalyst (l5%Ni-5%Ba/Al₂0₃). The reactor was heated by electric furnace to 850 °C. The reactor output had the composition (vol.%) presented in Table 3 below.

Table 3

[0042] As can be seen from Examples 1 and 2, the H2/CO ratio of syngas produced from methane combustion pyrolysis is less than 2 and is not suitable for methanol synthesis. But integrated methane steam reforming of a gas mixture, as shown by Example 3, produces syngas with a suitable H2/CO ratio required for methanol synthesis with significantly reduced methane content. [0043] While the invention has been shown in some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes and modifications without departing from the scope of the invention based on experimental data or other optimizations considering the overall economics of the process. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims

CLAIMS We claim:

1. A method for the conversion of methane to ethylene comprising: converting by pyrolysis or partial oxidation a methane-containing feed to an acetylene- containing product stream; combining the acetylene-containing product stream with a hydrogenating feed comprising ethane (C₂H₆), hydrogen gas (¾), and water and thermally hydrogenating acetylene of the acetylene-containing product stream in the absence of catalyst to form a hydrogenated product stream; separating the hydrogenated product stream into a first separated stream containing residual acetylene (C₂H₂), ethylene (C₂H₄), ethane (C₂H₆), and hydrogen gas and a second separated stream containing methane (CH₄), carbon dioxide (CO₂) and carbon monoxide (CO); and

at least one of A and B wherein:

A is contacting the residual acetylene of the first separated stream with a hydrogenation catalyst in a catalytic hydrogenation reaction to form ethylene; and

B is combining the second separated stream with steam to convert by both steam reforming and carbon dioxide reforming of methane to form a syngas mixture comprising carbon monoxide and hydrogen gas.

2. The method of claim 1, wherein:

A is performed.

3. The method of claim 1, wherein:

B is performed.

4. The method of claim 1, wherein: both A and B are performed.

5. The method of claim 1, further comprising: separating the hydrogenated product stream into a third separated stream containing ethane, hydrogen gas, and water, at least a portion of the third separated stream being recycled to form at least a portion of the hydrogenating feed.

6. The method of claim 1, wherein: the hydrogenating feed provides a th/acetylene molar ratio of from 9 or more.

7. The method of claim 1, wherein:

B is performed and wherein the syngas mixture contains less than 3 wt.% methane.

8. The method of claim 1, wherein: the hydrogenated product stream contains from 3 wt% or less of residual acetylene.

9. The method of claim 1, wherein: the pyrolysis or partial oxidation of the methane-containing feed is carried out at temperature of from 1000 °C to 3000 °C.

10. The method of claim 1, wherein: the acetylene-containing product stream is quenched to a temperature of from 500 °C to 950 °C prior to thermal hydrogenation.

11. The method of claim 1, wherein: the hydrogenated product stream is cryogenically cooled to facilitate separating the hydrogenated product stream.

12. The method of claim 1, wherein: heat for the steam reforming and carbon dioxide reforming of methane is provided by at least one of the steam and the combustion of at least a portion of the carbon dioxide (CO2) and the carbon monoxide (CO) of the second separated stream.

13. A method for the conversion of methane to ethylene comprising: converting by pyrolysis or partial oxidation at a reaction temperature of from 1000 °C to 3000 °C a methane-containing feed to an acetylene-containing product stream; quenching the acetylene-containing product stream to a temperature of from 500 °C to

950 °C; combining the quenched acetylene-containing product stream with a hydrogenating feed comprising ethane (C₂H₆), hydrogen gas (¾), and water and thermally hydrogenating acetylene of the quenched acetylene-containing product stream in the absence of catalyst to form a hydrogenated product stream containing less than 3 wt.% of residual acetylene; separating the hydrogenated product stream into a first separated stream containing the residual acetylene (C₂H₂), ethylene (C₂H₄), ethane (C₂H₆), and hydrogen gas and a second separated stream containing methane (CH₄), carbon dioxide (CO₂) and carbon monoxide (CO); and

at least one of A and B wherein:

14. The method of claim 13, wherein:

A is performed.

15. The method of claim 13, wherein:

B is performed.

16. The method of claim 13, wherein: both A and B are performed.

17. The method of claim 13, further comprising: separating the hydrogenated product stream into a third separated stream containing ethane, hydrogen gas, and water, at least a portion of the third separated stream being recycled to form at least a portion of the hydrogenating feed.

18. The method of claim 13, wherein: the hydrogenating feed provides a tb/acetylene molar ratio of from 9 or more.

19. The method of claim 13, wherein:

20. The method of claim 13, wherein: heat for the steam reforming and carbon dioxide reforming of methane is provided by at least one of the steam and the combustion of at least a portion of the carbon dioxide (CO2) and the carbon monoxide (CO) of the second separated stream.