WO2010132325A1

WO2010132325A1 - An integrated process to produce hydrocarbons from natural gas containing carbon dioxide

Info

Publication number: WO2010132325A1
Application number: PCT/US2010/034174
Authority: WO
Inventors: Jose Luis Bravo; Howard Lam Ho Fong; Richard Dale Swain
Original assignee: Shell Oil Company; Shell Internationale Research Maatschappij B.V.
Priority date: 2009-05-12
Filing date: 2010-05-10
Publication date: 2010-11-18

Abstract

A process for producing higher hydrocarbons from methane which contains carbon dioxide which comprises: (a) contacting methane, with a halogen, preferably bromine, under process conditions sufficient to produce a monohalomethane, preferably monobromomethane, which contains unreacted carbon dioxide, (b) reacting the monohalomethane in the presence of a coupling catalyst to produce higher hydrocarbons which contain carbon dioxide, and (c) separating carbon dioxide from the higher hydrocarbons.

Description

AN INTEGRATED PROCESS TO PRODUCE HYDROCARBONS FROM NATURAL GAS CONTAINING CARBON DIOXIDE

Field of the Invention This invention relates to an improved process for the production of hydrocarbons by bromination of methane. More particularly, the invention relates to such a process wherein the feed is natural gas which contains significant amounts of carbon dioxide. Background of the Invention

There are trillions of cubic feet of natural gas reserves in the world that contain over 10% by volume of carbon dioxide. Very little of this gas is commercially monetized because the separation of carbon dioxide from methane by distillation is prohibitively expensive. Amine scrubbing is a well-proven commercial process for removing carbon dioxide from methane. However, since the "spent" amine must be regenerated by stripping the carbon dioxide away from the amine, the capital cost and energy consumption go up in proportion to the carbon dioxide content of the gas. Another drawback of carbon dioxide removal via amine scrubbing is that carbon dioxide is recovered at relatively low pressures. Carbon dioxide gas recompression will likely be required prior to sub-surface re-injection of the carbon dioxide and this is both capital and energy intensive. Other methods for carbon dioxide/methane separation, such as the use of membranes, suffer from similar drawbacks. Typically, natural gas fields containing in excess of 10 to 15% carbon dioxide are considered economically less attractive or unattractive. After carbon dioxide removal, the methane would still have to be converted to a transportable product, such as LNG via liquefaction or GTL (Gas to Liquids) via Fischer-Tropsch chemistry . It can be seen that it would be advantageous to provide a process concept wherein undesirable natural gas containing relatively high levels of carbon dioxide can be used without requiring any of the above-described methods to separate the carbon dioxide from the natural gas. The present invention provides such a process which also utilizes the methane to produce value-added hydrocarbons .

In US2008/0269534, a method of synthesizing hydrocarbons from smaller hydrocarbons is described. The method includes the steps of hydrocarbon halogenation, simultaneous oligomerization and hydrogen halide neutralization, and product recovery, with a metal-oxygen cataloreactant used to facilitate carbon-carbon coupling. Treatment with air or oxygen liberates halogen and regenerates the cataloreactant. Methane is the preferred smaller hydrocarbon. Mixed feedstocks such as raw natural gas may be used in the process but there is no suggestion of the use of a high carbon dioxide content natural gas and the problems associated with it. Summary of the Invention

The present invention provides a process for producing higher hydrocarbons, including both aromatic and non-aromatic hydrocarbons from methane which contains carbon dioxide which comprises : (a) contacting methane which contains carbon dioxide with a halogen, preferably bromine, under process conditions sufficient to produce a monohalomethane, preferably monobromomethane, which contains unreacted carbon dioxide, hydrogen bromide, and, optionally, polyhalomethanes, (b) reacting the monohalomethane in the presence of a coupling catalyst to produce higher hydrocarbons which contain carbon dioxide, and (c) separating carbon dioxide from the higher hydrocarbons .

Another embodiment of this invention comprises:

(a) contacting methane which contains carbon dioxide with a halogen, preferably bromine, under process conditions sufficient to produce a monohalomethane, preferably monobromomethane, which contains unreacted carbon dioxide, hydrogen bromide, and, optionally, polyhalomethanes,

(b) separating carbon dioxide from the other components, and

(c) reacting the monohalomethane in the presence of a coupling catalyst to produce higher hydrocarbons.

In an embodiment, the hydrogen bromide is removed from the monohalomethane prior to the coupling reaction. In another embodiment, the hydrogen bromide is removed from the monohalomethane after the coupling reaction.

The present invention also provides a novel process for separating carbon dioxide from contaminated natural gas by halogenating, preferably brominating, the methane and then separating the carbon dioxide from the halogenated methane. Brief Description of the Drawing

Fig. 1 is a flow diagram illustrating one embodiment of the process of the present invention.

Fig. 2 is a flow diagram illustrating another embodiment of the process of the present invention. Detailed Description of the Invention

This invention provides a novel process to reactively separate methane from carbon dioxide in high carbon dioxide content natural gas via halogenation, especially bromination, of the contained methane. The resultant methylbromides may then be directly converted to value-added hydrocarbons such as benzene, toluene and/or xylene (BTX) aromatics, C2/C3 lower olefins, hydrocarbon fuel and LPG. As used herein the term "higher hydrocarbons" means hydrocarbons having 2 or more carbon atoms including, but not limited to, ethylene, propylene, benzene, toluene, and xylenes.

The present invention provides an improved process for the production of higher hydrocarbons including aromatic compounds and, optionally, ethylene and/or propylene, from methane which contain significant amounts of carbon dioxide. Preferably, the source of the methane is natural gas which contains more than 20 mole%, more preferably more than 10 mole%, carbon dioxide. Other alkanes, such as ethane, propane, butane, and pentane, may be mixed in with the methane. First, methane containing carbon dioxide is halogenated by reacting it with a halogen, preferably bromine. The monohalomethane, preferably monobromomethane, which is produced thereby contains unreacted carbon dioxide and byproduct hydrogen bromide and usually excess methane. The carbon dioxide may be separated from the monohalomethane. The hydrogen bromide may also be separated from the monohalomethane . The monohalomethane, either containing carbon dioxide and/or hydrogen bromide or being relatively carbon dioxide- and/or hydrogen bromide-free, may be contacted with a suitable coupling catalyst which causes the monohalomethane to react with itself to produce the desired product higher molecular weight hydrocarbons. A small amount of methane may also be produced.

Any byproduct hydrogen bromide remaining in the higher hydrocarbons after the coupling reaction may be separated from the higher hydrocarbons at this point. Any carbon dioxide remaining in the higher hydrocarbons after the coupling reaction may be separated from the higher hydrocarbons at this point. Carbon dioxide and methane may be separated together from the higher hydrocarbons. This carbon dioxide stream containing some amount of methane may then be optionally re-injected to sub-surface natural gas reservoirs .

Any C₂-₄ alkanes, or any portion thereof, produced in this process may be recycled to the bromination step, cracked in an alkane cracking system to produce ethylene and/or propylene, or hydrotreated to produce LPG.

In another embodiment of this invention, carbon dioxide and methane may be separated from the monohalomethane after the halogenation step. The byproduct hydrogen bromide may also be separated from the monohalomethane at this point. This carbon dioxide stream containing some amount of methane may then be optionally re-injected to sub-surface natural gas reservoirs. The monohalomethane together with hydrogen bromide (if it has not been removed) may then be sent to the coupling step as described above.

In this invention, a novel method is advanced to separate carbon dioxide from methane and concomitantly convert the methane to higher hydrocarbons. This is achieved by halogenating, preferably brominating, the methane in the feed to halomethane, preferably bromomethane, which is then coupled to produce higher hydrocarbons. Carbon dioxide is an inert in both of these reactions. The primary advantages are : 1) Monobromomethane has a boiling point similar to that of butane. Once methane is converted to mono or polybromomethane, separation from carbon dioxide by distillation becomes relatively easy. Similarly, once monobromomethane is coupled to produce the desired product higher hydrocarbons, these components have significantly higher boiling points than carbon dioxide, making the separation of carbon dioxide relatively easy. 2) Bromination, and optionally, the coupling reaction, may be carried out essentially at natural gas incoming (high) pressures. Hence, carbon dioxide-rich gas can be recovered at high pressures for ease of re-injection into sub-surface natural gas reservoirs.

3) The monobromomethane can be directly converted into value-added higher hydrocarbons .

The hydrocarbon feed may be comprised of methane containing carbon dioxide and one or more other low molecular weight alkanes. These other low molecular weight alkanes include ethane and propane, as well as butane and pentane. The preferred feed is natural gas which is comprised of methane and often contains smaller amounts of ethane, propane and other hydrocarbons. The most preferred feed is methane. Carbon dioxide contaminated natural gas may comprise from about 0.5 to about 60% carbon dioxide by mole. However, the process of the present invention is most advantageous when the contaminated natural gas comprises from about 20 to about 50% carbon dioxide by mole. In a preferred embodiment, the coupling reaction may be carried out such that the production of aromatic hydrocarbons, specifically BTX, is maximized. The production of aromatic hydrocarbons may be achieved by the use of a suitable coupling catalyst under suitable operating conditions. In another preferred embodiment, the coupling reaction may be carried out such that other higher hydrocarbons are produced in significant amounts, i.e., such that the production of lower olefins, specifically ethylene and propylene, is maximized. Representative halogens include bromine and chlorine.

It is also contemplated that fluorine and iodine may be used but not necessarily with equivalent results. Some of the problems associated with fluorine possibly may be addressed by using dilute streams of fluorine. It is expected that more vigorous reaction conditions will be required for alkyl fluorides to couple and form higher molecular weight hydrocarbons. Similarly, problems associated with iodine (such as the endothermic nature of some iodine reactions) may likely be addressed by carrying out the halogenation and/or coupling reactions at higher temperatures and/or pressures. The use of bromine or chlorine is preferred and the use of bromine is most preferred. While the foregoing and following description may only refer to bromine, bromination and/or bromomethanes, the description is applicable to the use of other halogens and halomethanes as well.

Bromination of methane containing carbon dioxide (methane will be used in the following description but other alkanes may be present as discussed above) may be carried out in an open pipe, a fixed bed reactor, a tube-and-shell reactor or another suitable reactor, preferably at a temperature and pressure where the bromination products and reactants are gases. Fast mixing between bromine and methane is preferred to help prevent over-bromination and coking.

For example, the reaction pressure may be from about 100 to about 6000 kPa and the temperature may be from about 150 to about 600°C, more preferably from about 350 to about 575°C and even more preferably from about 425 to about 550°C. Higher temperatures tend to favor coke formation and lower temperatures require larger reactors. Methane bromination may be initiated using heat or light with thermal means being preferred.

A halogenation catalyst may also be used. In an embodiment, the reactor may contain a halogenation catalyst such as a zeolite, amorphous alumino-silicate, acidic zirconia, tungensteastes, solid phosphoric acids, metal oxides, mixed metal oxides, metal halides, mixed metal halides (the metal in such cases being for example nickel, copper, cerium, cobalt, etc.) and/or other catalysts as described in U.S. Patent Nos. 3,935,289 and 4,971,664, each of which is herein incorporated by reference in its entirety. Specific catalysts include a metal bromide (for example, sodium bromide, potassium bromide, copper bromide, nickel bromide, magnesium bromide and calcium bromide), a metal oxide (for example, silicon dioxide, zirconium dioxide and aluminum trioxide) or metal (for example, platinum, palladium, ruthenium, iridium, or rhodium) to help generate the desired brominated methane.

The bromination reaction product comprises monobromomethane, HBr and also small amounts of dibromomethane and tribromomethane, as well as unreacted carbon dioxide and excess methane. Generally, the polybromomethanes are separated from the other products for optional recycle to the bromination reactor. The other reaction products boil at lower temperatures and may form the light ends stream in a distillation procedure. In one embodiment, the entire light ends stream is sent to the coupling reaction without further separation. Carbon dioxide, methane, and hydrogen bromide do not interfere with the coupling reaction of monobromomethane to higher hydrocarbons, and may actually be desirable for product selectivity by lowering the partial pressure of the feed monobromomethane .

In another embodiment, carbon dioxide and methane may be separated by distillation from the lower boiling monobromomethane and hydrogen bromide prior to the coupling reaction. Separation of carbon dioxide and methane from the monobromomethane and from the polybromides may be accomplished by high pressure distillation with the light fraction being the carbon dioxide and residual methane, the middle cut being the monobromomethane, and the heavy cut the polybromides . Hydrogen bromide may be recovered either in the light fraction or the middle fraction. The monobromomethane stream goes to coupling, the carbon dioxide is purged at high pressure from the system as the overhead and the polybromides go to reproportionation for recycle. This scheme can be designed to cut and purge large amounts of carbon dioxide at high pressure with the concomitant loss of unreacted methane or to purge only a part of the carbon dioxide allowing the rest to go on with separation after coupling. This distillation may have a deliberate feed heat recovery system so the heat may be available for both reactions and the distillation may take place at a lower temperature. Conceivably the feed to distillation may be cooled by heating the feed to the bromination or coupling reaction .

If desired, the HBr may also be removed from the monobromomethane prior to coupling by distillation or water absorption but this is not necessary. The presence of large concentrations of the polybrominated species in the feed to the coupling reactor may decrease bromine efficiency and result in an undesirable increase in coke formation. In many applications, such as the production of aromatics, light olefins or higher non- aromatic hydrocarbons, it is desirable to feed only monobromomethane to the coupling reactor to improve the conversion to the final higher molecular weight hydrocarbon products. In an embodiment of the invention, a separation step is added after the halogenation reactor in which the monobromomethane is separated from the other bromomethanes . The di- and tribromomethane species may be recycled to the bromination reactor. One separation method is described in U.S. Published Patent Application No. 2007/02388909, which is herein incorporated by reference in its entirety. Preferably, the separation is carried out by distillation. The di- and tribromomethanes are higher boiling than the monobromomethane, unreacted methane and HBr, which is also made by the bromination reaction:

CH₄ + Br₂ → CH₃Br + HBr

In a preferred embodiment, the polybromomethanes may be recycled to the halogenation reaction and preferably reproportionated to convert them to monobromomethane. The polybromomethanes contain two or more bromine atoms per molecule. Reproportionation may be accomplished according to U.S. Published Patent Application 2007/0238909 which is herein incorporated by reference in its entirety. Reactive reproportionation is accomplished by allowing the methane feedstock and any recycled alkanes to react with the polybrominated methane species from the halogenation reactor, preferably in the substantial absence of molecular halogen. Reproportionation may be carried out in a separate reactor or in a region of the halogenation reactor. The bromination and coupling reactions may be carried out in separate reactors or the process may be carried out in an integrated reactor, for example, in a zone reactor as described in U.S. Patent No. 6,525,230 which is herein incorporated by reference in its entirety. In this case, halogenation of methane may occur within one zone of the reactor and may be followed by a coupling step in which the liberated hydrobromic acid may be adsorbed within the material that catalyzes condensation of the halogenated hydrocarbon. Hydrocarbon coupling may take place within this zone of the reactor and may yield the product higher molecular weight hydrocarbons including aromatic hydrocarbons. It is preferred that separate reactors be used for bromination and coupling because operating conditions may be optimized for the individual steps and this allows for the possibility of removing polybrominated-methane before the coupling step.

Coupling of monobromomethane may be carried out in a fixed bed, fluidized bed or other suitable reactor. The temperature may range from about 150 to about 600°C, preferably from about 300 to about 550°C, most preferably from about 350 to about 475°C, and the pressure may range from about 10 to about 6000 kPa absolute, preferably about 100 to about 4500 kPa absolute. In general, a relatively long residence time favors conversion of reactants to products as well as product selectivity to higher hydrocarbons such as BTX, while a short residence time means higher throughput and possibly improved economics. It is possible to change product selectivity by changing the catalyst, altering the reaction temperature, pressure and/or altering the residence time in the reactor. Low molecular weight alkanes may also exit the coupling reactor. These low molecular weight alkanes may be comprised of ethane and propane but may also include methane and a small amount of C₄_₅ alkanes and smaller amounts of alkenes. Some of these may be recycled to the bromination reactor but preferably the low molecular weight alkanes may be directed to a cracking step to produce ethylene and/or propylene or may be hydrotreated and liquefied to produce a LPG.

Preferred coupling catalysts for use in the present invention are described in U.S. Patent Application No. 2007/0238909 and U.S. Patent No. 7,244,867, each of which is herein incorporated by reference in its entirety. A metal-oxygen cataloreactant may also be used to facilitate the coupling reaction. The term "metal-oxygen cataloreactant" is used herein to a cataloreactant material containing both metal and oxygen. Such cataloreactants are described in detail in U.S. Published Patent Application Nos. 2005/0038310 and 2005/0171393 which are herein incorporated by reference in their entirety. Examples of metal-oxygen cataloreactants given therein include zeolites, doped zeolites, metal oxides, metal oxide-impregnated zeolites and mixtures thereof. Nonlimiting examples of dopants include alkaline earth metals, such as calcium, magnesium, manganese and barium and their oxides and/or hydroxides.

Hydrogen bromide may also be produced along with monobromomethane in the bromination reactor. The hydrogen bromide may be carried over to the coupling reactor or, if desired, may be separated before coupling. The products of the coupling reaction may include Cε-s hydrocarbons especially BTX, C2-5 alkanes and likely some alkenes, Cg₊ hydrocarbons and hydrogen bromide.

The coupling reaction product containing higher hydrocarbons, carbon dioxide, methane and hydrogen bromide may be sent to an absorption column wherein the hydrogen bromide may be absorbed in water using a packed column or other contacting device. Input water in the product stream may be contacted either in co-current or countercurrent flow with countercurrent flow preferred for its improved efficiency. One method for removing the hydrogen bromide from the higher molecular weight hydrocarbon reaction product is described in U.S. Patent No. 7,244,867 which is herein incorporated by reference in its entirety. HBr present in the C₂-₅ alkanes and alkenes stream or the product stream from the bromination reactor may also be removed therefrom by this method. In an embodiment, the hydrogen bromide is recovered by displacement as a gas from its aqueous solution in the presence of an electrolyte that shares a common ion or an ion that has a higher hydration energy than hydrogen bromide. Also aqueous solutions of metal bromides such as calcium bromide, magnesium bromide, sodium bromide, potassium bromide, etc. may be used as extractive agents.

In another embodiment, catalytic halogen generation is carried out by reacting hydrogen bromide and molecular oxygen over a suitable catalyst. The oxygen source may be air, pure oxygen or enriched air. A number of materials have been identified as halogen generation catalysts. It is possible to use oxides, halides, and/or oxyhalides of one or more metals, such as magnesium, calcium, barium, chromium, manganese, iron, cobalt, nickel, copper, zinc, etc. After the HBr is separated from the hydrocarbon products, it may be reacted to produce bromine for recycle to the bromination step. Catalysts and methods for regeneration of the bromine are described in detail in U.S. Published Application

2007/0238909 which is herein incorporated by reference in its entirety. Recovery of bromine is also described therein.

After hydrogen bromide removal as described above, carbon dioxide and methane may be separated from the remaining product higher hydrocarbons. Separation of carbon dioxide and methane from the higher hydrocarbons after coupling may also be accomplished by distillation as described above. This scheme may increase the volumetric rates through coupling resulting in possibly larger reactors. The overhead stream which is rich in carbon dioxide and lean in methane may be optionally re-compressed for subsurface re-injection. Heat from the conversion of methane to higher hydrocarbons, including heat generated in the generation of bromine, may be used in the process to supply energy required in alkane cracking, heating the feed streams for the bromination, reproportionation and/or coupling reactions and for heat required in any of the fractionation operations. At least part of the energy released in the conversion of hydrogen bromide to bromine may be recovered and utilized in steps (a) - (c) or any combination thereof and optionally in upstream (including but not limited to gas feedstock processing) and/or downstream processing (including, but not limited to light olefin and BTX conversion and purification, disproportion reactions, aromatic Cg₊ hydrocarbon reproportionation reactions, isomerization reactions, and conversion of ethylene and propylene and BTX to downstream products) . One embodiment of the invention is illustrated in Figure 1. Methane gas (120) containing 50% by volume of carbon dioxide is contacted with bromine (110) in the bromination reactor (100) . The bromine to methane molar ratio may preferably be from about 0.7 to about 1.0. The stream exiting the bromination reactor (100) contains carbon dioxide, unreacted methane, monobromomethane, polybromomethanes and hydrogen bromide (HBr) . In the polybromide separator (200), the other components are distilled away (250) and polybromomethanes are recovered and recycled to the bromination reactor (100) in line (150) where they are reproportionated with feed methane to form more monobromomethane .

The light-end stream (250) from polybromide separator (200), which contains carbon dioxide, methane, monobromomethane and HBr, is sent to the coupling reactor (400) wherein monobromomethane is converted to higher hydrocarbons. By changing the catalyst used and operating conditions, the composition of the higher hydrocarbon products may be somewhat tailored. For example, C₆₊ aromatics may be targeted. Alternatively, C₄₊ hydrocarbons or C₂/C₃ olefins may be targeted. Lower alkanes co-produced may be optionally liquefied to LPG or cracked to produce more lower olefins. The product stream (350) from coupling reactor (400) may first be processed to remove HBr in hydrobromide recovery section (500) . An illustrative recovery method is water scrubbing. The product hydrocarbon stream containing a small amount of methane, C₂-C₅ hydrocarbons and C₆₊ hydrocarbons, and a fairly large amount of carbon dioxide is then separated in product recovery section (600). Carbon dioxide, methane and optionally ethane are sent to re-injection compression section (300) through line (450) . The heavier hydrocarbons are then further purified and processed into desired product fractions in product finishing section (700) .

The HBr from hydrobromide recovery section (500) may be regenerated into bromine in the bromine regenerator (800) using air or oxygen. The recovered bromine may be recycled for use in bromination reactor (100) . Water is generated in bromine regenerator (800) . It may be cleaned of residual bromides in water purification section (900) before discharge or downstream use. Spent air exiting bromine regenerator (800) may be cleaned up in air purification section (1000) before discharge into the atmosphere.

In the description given above, carbon dioxide and unconverted methane from bromination reactor (100) and generated in coupling section (400) are recovered in product recovery section (600) . In another variation, shown in Figure 2, carbon dioxide and methane may be recovered in the polybromide separator section (200) and only monobromomethane and hydrogen bromide are sent to the coupling reactor (400) . In this variation, the volume of gas sent to section (400) will be reduced. In this scenario, carbon dioxide/methane will be optionally sent to the reinjection compression section (300). In the description given above, the methane- lean carbon dioxide is recovered for sub-surface reinjection to achieve a desirable low carbon dioxide footprint. Other options exist. One such option is to combust the residual methane with oxygen to recover energy for utilities and to recover the carbon dioxide stream for enhanced oil recovery applications .

EXAMPLE 1

Referring to Figure 1, 1,000 moles/hr of high-carbon dioxide content natural gas containing 500 moles/hr of methane and carbon dioxide, respectively, are fed to the bromination section (100) via stream (120) . Bromine feed rate is 400 moles/hr and is fed via stream (110) . Bromination (100) is carried out at 525⁰C and 3000 kPa. At the polybromide separation section (200), 150 moles/hr of polybromomethanes are recycled to section (100) via stream (150) to be reproportionated with unreacted methane to produce more monobromomethane . Stream (250) feeding the coupling section (400) contains 500 moles/hr of carbon dioxide, 400 moles/hr of hydrogen bromide, 100 moles/hr of methane, and 400 moles/hr of monobromomethane.

Coupling section (400) is operated at 425⁰C and 2500 kPa. The conversion of monobromomethane is essentially 100%. Stream (350) exiting coupling reactor (400) contains 500 moles/hr of carbon dioxide, 800 moles/hr of HBr, 110 moles/hr of methane, and approximately 200 moles/hr each of C₅₊ and C₄_ hydrocarbons (carbon basis), respectively.

In the product recovery section (600), carbon dioxide is recovered with methane, and optionally part or all of the C₂. The stream (450) to the re-injection compression section (300) contains approximately 500 moles/hr of carbon dioxide and 110 moles/hr of methane. The carbon dioxide stream which contains about 20% of the methane in the feed is optionally compressed in section (300) to 3000 kPa or higher and reinjected to the sub-surface.

800 moles/hr of hydrogen bromide are sent to the bromine regeneration section (800). Bromine regeneration is operated at 35O⁰C and 200 kPa. Air, or optionally enriched air or oxygen, used for bromine regeneration in section (800) contains about 250 moles/hr of oxygen. About 25% molar excess oxygen is needed to regenerate the hydrogen bromide to bromine. Conversion and selectivity of HBr to bromine are both essentially 100%. 400 moles/hr of bromine and water are generated in section (800) . Bromine is separated from water and spent air in section (900) and is recycled to section (100) after drying. Water and spent air are discharged after appropriate purification to reduce residual bromine/bromide to acceptable levels.

Overall, the process uses 400 moles/hr of methane in high-CO2 natural gas (50% molar CO2) to produce approximately 390 moles of C2₊ hydrocarbons (carbon basis) . The CO2 stream to be optionally re-injected contains approximately 18% molar methane .

Claims

C L A I M S

1. A process for producing higher hydrocarbons from methane which contains carbon dioxide which comprises: (a) contacting methane which contains carbon dioxide with a halogen, preferably bromine, under process conditions sufficient to produce a monohalomethane, preferably monobromomethane, which contains unreacted carbon dioxide, hydrogen bromide, and, optionally, polyhalomethanes, (b) reacting the monohalomethane in the presence of a coupling catalyst to produce higher hydrocarbons which contain carbon dioxide, and

(c) separating carbon dioxide from the higher hydrocarbons .

2. The process of claim 1 wherein the carbon dioxide content of the methane feed in step (a) is at least 10% by mole .

3. The process of claim 1 wherein at least 30% of the methane in the carbon dioxide-containing feed is halogenated in step (a) .

4. The process of claim 1 wherein the pressure in steps (a) and (b) is at least 500 kPa.

5. The process of claim 1 wherein the amount of benzene, toluene and xylenes in the higher hydrocarbons exiting step (b) is at least 15% by mole on a carbon basis.

6. The process of claim 1 wherein the C₂-₄ content of the higher hydrocarbons exiting step (b) is at least 15% by mole on a carbon basis.

7. The process of claim 1 wherein polyhalomethanes are formed in step (a) and are separated from the monohalomethane prior to step (b) and recycled to step (a) .

8. The process of claim 1 wherein the carbon dioxide recovered in step (c) is re-injected to sub-surface after optional compression.

9. A process for separating carbon dioxide from methane containing carbon dioxide by halogenating, preferably brominating, the methane, to produce halomethanes, and separating the carbon dioxide from the halomethanes.

10. A process for producing higher hydrocarbons from methane which contains carbon dioxide which comprises:

(a) contacting methane, which contains carbon dioxide, with a halogen, preferably bromine, under process conditions sufficient to produce a monohalomethane, preferably monobromomethane, which contains unreacted carbon dioxide, hydrogen bromide, and, optionally, polyhalomethanes,

(b) separating carbon dioxide from the other components, and

11. The process of claim 10 wherein the carbon dioxide content of the methane feed in step (a) is at least 10% by mole .

12. The process of claim 10 wherein at least 30% of the methane in the carbon dioxide-containing feed is halogenated in step (a) .

13. The process of claim 10 wherein the pressure in steps (a) and (b) is at least 500 kPa.

14. The process of claim 10 wherein the amount of benzene, toluene and xylenes in the higher hydrocarbons exiting step (c) is at least 15% by mole on a carbon basis.

15. The process of claim 10 wherein the C2-4 content of the higher hydrocarbons exiting step (c) is at least 15% by mole on a carbon basis.

16. The process of claim 10 wherein polyhalomethanes are formed in step (a) and are separated from the monohalomethane prior to step (b) or step (c) and recycled to step (a) .

17. The process of claim 10 wherein the carbon dioxide recovered in step (b) is re-injected to sub-surface after optional compression.